Mercurial > hg > graal-jvmci-8
comparison src/share/vm/gc_implementation/concurrentMarkSweep/concurrentMarkSweepGeneration.cpp @ 0:a61af66fc99e jdk7-b24
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author | duke |
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date | Sat, 01 Dec 2007 00:00:00 +0000 |
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children | 2faf283ce688 |
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1 /* | |
2 * Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved. | |
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
4 * | |
5 * This code is free software; you can redistribute it and/or modify it | |
6 * under the terms of the GNU General Public License version 2 only, as | |
7 * published by the Free Software Foundation. | |
8 * | |
9 * This code is distributed in the hope that it will be useful, but WITHOUT | |
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
12 * version 2 for more details (a copy is included in the LICENSE file that | |
13 * accompanied this code). | |
14 * | |
15 * You should have received a copy of the GNU General Public License version | |
16 * 2 along with this work; if not, write to the Free Software Foundation, | |
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
18 * | |
19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, | |
20 * CA 95054 USA or visit www.sun.com if you need additional information or | |
21 * have any questions. | |
22 * | |
23 */ | |
24 | |
25 # include "incls/_precompiled.incl" | |
26 # include "incls/_concurrentMarkSweepGeneration.cpp.incl" | |
27 | |
28 // statics | |
29 CMSCollector* ConcurrentMarkSweepGeneration::_collector = NULL; | |
30 bool CMSCollector::_full_gc_requested = false; | |
31 | |
32 ////////////////////////////////////////////////////////////////// | |
33 // In support of CMS/VM thread synchronization | |
34 ////////////////////////////////////////////////////////////////// | |
35 // We split use of the CGC_lock into 2 "levels". | |
36 // The low-level locking is of the usual CGC_lock monitor. We introduce | |
37 // a higher level "token" (hereafter "CMS token") built on top of the | |
38 // low level monitor (hereafter "CGC lock"). | |
39 // The token-passing protocol gives priority to the VM thread. The | |
40 // CMS-lock doesn't provide any fairness guarantees, but clients | |
41 // should ensure that it is only held for very short, bounded | |
42 // durations. | |
43 // | |
44 // When either of the CMS thread or the VM thread is involved in | |
45 // collection operations during which it does not want the other | |
46 // thread to interfere, it obtains the CMS token. | |
47 // | |
48 // If either thread tries to get the token while the other has | |
49 // it, that thread waits. However, if the VM thread and CMS thread | |
50 // both want the token, then the VM thread gets priority while the | |
51 // CMS thread waits. This ensures, for instance, that the "concurrent" | |
52 // phases of the CMS thread's work do not block out the VM thread | |
53 // for long periods of time as the CMS thread continues to hog | |
54 // the token. (See bug 4616232). | |
55 // | |
56 // The baton-passing functions are, however, controlled by the | |
57 // flags _foregroundGCShouldWait and _foregroundGCIsActive, | |
58 // and here the low-level CMS lock, not the high level token, | |
59 // ensures mutual exclusion. | |
60 // | |
61 // Two important conditions that we have to satisfy: | |
62 // 1. if a thread does a low-level wait on the CMS lock, then it | |
63 // relinquishes the CMS token if it were holding that token | |
64 // when it acquired the low-level CMS lock. | |
65 // 2. any low-level notifications on the low-level lock | |
66 // should only be sent when a thread has relinquished the token. | |
67 // | |
68 // In the absence of either property, we'd have potential deadlock. | |
69 // | |
70 // We protect each of the CMS (concurrent and sequential) phases | |
71 // with the CMS _token_, not the CMS _lock_. | |
72 // | |
73 // The only code protected by CMS lock is the token acquisition code | |
74 // itself, see ConcurrentMarkSweepThread::[de]synchronize(), and the | |
75 // baton-passing code. | |
76 // | |
77 // Unfortunately, i couldn't come up with a good abstraction to factor and | |
78 // hide the naked CGC_lock manipulation in the baton-passing code | |
79 // further below. That's something we should try to do. Also, the proof | |
80 // of correctness of this 2-level locking scheme is far from obvious, | |
81 // and potentially quite slippery. We have an uneasy supsicion, for instance, | |
82 // that there may be a theoretical possibility of delay/starvation in the | |
83 // low-level lock/wait/notify scheme used for the baton-passing because of | |
84 // potential intereference with the priority scheme embodied in the | |
85 // CMS-token-passing protocol. See related comments at a CGC_lock->wait() | |
86 // invocation further below and marked with "XXX 20011219YSR". | |
87 // Indeed, as we note elsewhere, this may become yet more slippery | |
88 // in the presence of multiple CMS and/or multiple VM threads. XXX | |
89 | |
90 class CMSTokenSync: public StackObj { | |
91 private: | |
92 bool _is_cms_thread; | |
93 public: | |
94 CMSTokenSync(bool is_cms_thread): | |
95 _is_cms_thread(is_cms_thread) { | |
96 assert(is_cms_thread == Thread::current()->is_ConcurrentGC_thread(), | |
97 "Incorrect argument to constructor"); | |
98 ConcurrentMarkSweepThread::synchronize(_is_cms_thread); | |
99 } | |
100 | |
101 ~CMSTokenSync() { | |
102 assert(_is_cms_thread ? | |
103 ConcurrentMarkSweepThread::cms_thread_has_cms_token() : | |
104 ConcurrentMarkSweepThread::vm_thread_has_cms_token(), | |
105 "Incorrect state"); | |
106 ConcurrentMarkSweepThread::desynchronize(_is_cms_thread); | |
107 } | |
108 }; | |
109 | |
110 // Convenience class that does a CMSTokenSync, and then acquires | |
111 // upto three locks. | |
112 class CMSTokenSyncWithLocks: public CMSTokenSync { | |
113 private: | |
114 // Note: locks are acquired in textual declaration order | |
115 // and released in the opposite order | |
116 MutexLockerEx _locker1, _locker2, _locker3; | |
117 public: | |
118 CMSTokenSyncWithLocks(bool is_cms_thread, Mutex* mutex1, | |
119 Mutex* mutex2 = NULL, Mutex* mutex3 = NULL): | |
120 CMSTokenSync(is_cms_thread), | |
121 _locker1(mutex1, Mutex::_no_safepoint_check_flag), | |
122 _locker2(mutex2, Mutex::_no_safepoint_check_flag), | |
123 _locker3(mutex3, Mutex::_no_safepoint_check_flag) | |
124 { } | |
125 }; | |
126 | |
127 | |
128 // Wrapper class to temporarily disable icms during a foreground cms collection. | |
129 class ICMSDisabler: public StackObj { | |
130 public: | |
131 // The ctor disables icms and wakes up the thread so it notices the change; | |
132 // the dtor re-enables icms. Note that the CMSCollector methods will check | |
133 // CMSIncrementalMode. | |
134 ICMSDisabler() { CMSCollector::disable_icms(); CMSCollector::start_icms(); } | |
135 ~ICMSDisabler() { CMSCollector::enable_icms(); } | |
136 }; | |
137 | |
138 ////////////////////////////////////////////////////////////////// | |
139 // Concurrent Mark-Sweep Generation ///////////////////////////// | |
140 ////////////////////////////////////////////////////////////////// | |
141 | |
142 NOT_PRODUCT(CompactibleFreeListSpace* debug_cms_space;) | |
143 | |
144 // This struct contains per-thread things necessary to support parallel | |
145 // young-gen collection. | |
146 class CMSParGCThreadState: public CHeapObj { | |
147 public: | |
148 CFLS_LAB lab; | |
149 PromotionInfo promo; | |
150 | |
151 // Constructor. | |
152 CMSParGCThreadState(CompactibleFreeListSpace* cfls) : lab(cfls) { | |
153 promo.setSpace(cfls); | |
154 } | |
155 }; | |
156 | |
157 ConcurrentMarkSweepGeneration::ConcurrentMarkSweepGeneration( | |
158 ReservedSpace rs, size_t initial_byte_size, int level, | |
159 CardTableRS* ct, bool use_adaptive_freelists, | |
160 FreeBlockDictionary::DictionaryChoice dictionaryChoice) : | |
161 CardGeneration(rs, initial_byte_size, level, ct), | |
162 _dilatation_factor(((double)MinChunkSize)/((double)(oopDesc::header_size()))), | |
163 _debug_collection_type(Concurrent_collection_type) | |
164 { | |
165 HeapWord* bottom = (HeapWord*) _virtual_space.low(); | |
166 HeapWord* end = (HeapWord*) _virtual_space.high(); | |
167 | |
168 _direct_allocated_words = 0; | |
169 NOT_PRODUCT( | |
170 _numObjectsPromoted = 0; | |
171 _numWordsPromoted = 0; | |
172 _numObjectsAllocated = 0; | |
173 _numWordsAllocated = 0; | |
174 ) | |
175 | |
176 _cmsSpace = new CompactibleFreeListSpace(_bts, MemRegion(bottom, end), | |
177 use_adaptive_freelists, | |
178 dictionaryChoice); | |
179 NOT_PRODUCT(debug_cms_space = _cmsSpace;) | |
180 if (_cmsSpace == NULL) { | |
181 vm_exit_during_initialization( | |
182 "CompactibleFreeListSpace allocation failure"); | |
183 } | |
184 _cmsSpace->_gen = this; | |
185 | |
186 _gc_stats = new CMSGCStats(); | |
187 | |
188 // Verify the assumption that FreeChunk::_prev and OopDesc::_klass | |
189 // offsets match. The ability to tell free chunks from objects | |
190 // depends on this property. | |
191 debug_only( | |
192 FreeChunk* junk = NULL; | |
193 assert(junk->prev_addr() == (void*)(oop(junk)->klass_addr()), | |
194 "Offset of FreeChunk::_prev within FreeChunk must match" | |
195 " that of OopDesc::_klass within OopDesc"); | |
196 ) | |
197 if (ParallelGCThreads > 0) { | |
198 typedef CMSParGCThreadState* CMSParGCThreadStatePtr; | |
199 _par_gc_thread_states = | |
200 NEW_C_HEAP_ARRAY(CMSParGCThreadStatePtr, ParallelGCThreads); | |
201 if (_par_gc_thread_states == NULL) { | |
202 vm_exit_during_initialization("Could not allocate par gc structs"); | |
203 } | |
204 for (uint i = 0; i < ParallelGCThreads; i++) { | |
205 _par_gc_thread_states[i] = new CMSParGCThreadState(cmsSpace()); | |
206 if (_par_gc_thread_states[i] == NULL) { | |
207 vm_exit_during_initialization("Could not allocate par gc structs"); | |
208 } | |
209 } | |
210 } else { | |
211 _par_gc_thread_states = NULL; | |
212 } | |
213 _incremental_collection_failed = false; | |
214 // The "dilatation_factor" is the expansion that can occur on | |
215 // account of the fact that the minimum object size in the CMS | |
216 // generation may be larger than that in, say, a contiguous young | |
217 // generation. | |
218 // Ideally, in the calculation below, we'd compute the dilatation | |
219 // factor as: MinChunkSize/(promoting_gen's min object size) | |
220 // Since we do not have such a general query interface for the | |
221 // promoting generation, we'll instead just use the mimimum | |
222 // object size (which today is a header's worth of space); | |
223 // note that all arithmetic is in units of HeapWords. | |
224 assert(MinChunkSize >= oopDesc::header_size(), "just checking"); | |
225 assert(_dilatation_factor >= 1.0, "from previous assert"); | |
226 } | |
227 | |
228 void ConcurrentMarkSweepGeneration::ref_processor_init() { | |
229 assert(collector() != NULL, "no collector"); | |
230 collector()->ref_processor_init(); | |
231 } | |
232 | |
233 void CMSCollector::ref_processor_init() { | |
234 if (_ref_processor == NULL) { | |
235 // Allocate and initialize a reference processor | |
236 _ref_processor = ReferenceProcessor::create_ref_processor( | |
237 _span, // span | |
238 _cmsGen->refs_discovery_is_atomic(), // atomic_discovery | |
239 _cmsGen->refs_discovery_is_mt(), // mt_discovery | |
240 &_is_alive_closure, | |
241 ParallelGCThreads, | |
242 ParallelRefProcEnabled); | |
243 // Initialize the _ref_processor field of CMSGen | |
244 _cmsGen->set_ref_processor(_ref_processor); | |
245 | |
246 // Allocate a dummy ref processor for perm gen. | |
247 ReferenceProcessor* rp2 = new ReferenceProcessor(); | |
248 if (rp2 == NULL) { | |
249 vm_exit_during_initialization("Could not allocate ReferenceProcessor object"); | |
250 } | |
251 _permGen->set_ref_processor(rp2); | |
252 } | |
253 } | |
254 | |
255 CMSAdaptiveSizePolicy* CMSCollector::size_policy() { | |
256 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
257 assert(gch->kind() == CollectedHeap::GenCollectedHeap, | |
258 "Wrong type of heap"); | |
259 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*) | |
260 gch->gen_policy()->size_policy(); | |
261 assert(sp->is_gc_cms_adaptive_size_policy(), | |
262 "Wrong type of size policy"); | |
263 return sp; | |
264 } | |
265 | |
266 CMSGCAdaptivePolicyCounters* CMSCollector::gc_adaptive_policy_counters() { | |
267 CMSGCAdaptivePolicyCounters* results = | |
268 (CMSGCAdaptivePolicyCounters*) collector_policy()->counters(); | |
269 assert( | |
270 results->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind, | |
271 "Wrong gc policy counter kind"); | |
272 return results; | |
273 } | |
274 | |
275 | |
276 void ConcurrentMarkSweepGeneration::initialize_performance_counters() { | |
277 | |
278 const char* gen_name = "old"; | |
279 | |
280 // Generation Counters - generation 1, 1 subspace | |
281 _gen_counters = new GenerationCounters(gen_name, 1, 1, &_virtual_space); | |
282 | |
283 _space_counters = new GSpaceCounters(gen_name, 0, | |
284 _virtual_space.reserved_size(), | |
285 this, _gen_counters); | |
286 } | |
287 | |
288 CMSStats::CMSStats(ConcurrentMarkSweepGeneration* cms_gen, unsigned int alpha): | |
289 _cms_gen(cms_gen) | |
290 { | |
291 assert(alpha <= 100, "bad value"); | |
292 _saved_alpha = alpha; | |
293 | |
294 // Initialize the alphas to the bootstrap value of 100. | |
295 _gc0_alpha = _cms_alpha = 100; | |
296 | |
297 _cms_begin_time.update(); | |
298 _cms_end_time.update(); | |
299 | |
300 _gc0_duration = 0.0; | |
301 _gc0_period = 0.0; | |
302 _gc0_promoted = 0; | |
303 | |
304 _cms_duration = 0.0; | |
305 _cms_period = 0.0; | |
306 _cms_allocated = 0; | |
307 | |
308 _cms_used_at_gc0_begin = 0; | |
309 _cms_used_at_gc0_end = 0; | |
310 _allow_duty_cycle_reduction = false; | |
311 _valid_bits = 0; | |
312 _icms_duty_cycle = CMSIncrementalDutyCycle; | |
313 } | |
314 | |
315 // If promotion failure handling is on use | |
316 // the padded average size of the promotion for each | |
317 // young generation collection. | |
318 double CMSStats::time_until_cms_gen_full() const { | |
319 size_t cms_free = _cms_gen->cmsSpace()->free(); | |
320 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
321 size_t expected_promotion = gch->get_gen(0)->capacity(); | |
322 if (HandlePromotionFailure) { | |
323 expected_promotion = MIN2( | |
324 (size_t) _cms_gen->gc_stats()->avg_promoted()->padded_average(), | |
325 expected_promotion); | |
326 } | |
327 if (cms_free > expected_promotion) { | |
328 // Start a cms collection if there isn't enough space to promote | |
329 // for the next minor collection. Use the padded average as | |
330 // a safety factor. | |
331 cms_free -= expected_promotion; | |
332 | |
333 // Adjust by the safety factor. | |
334 double cms_free_dbl = (double)cms_free; | |
335 cms_free_dbl = cms_free_dbl * (100.0 - CMSIncrementalSafetyFactor) / 100.0; | |
336 | |
337 if (PrintGCDetails && Verbose) { | |
338 gclog_or_tty->print_cr("CMSStats::time_until_cms_gen_full: cms_free " | |
339 SIZE_FORMAT " expected_promotion " SIZE_FORMAT, | |
340 cms_free, expected_promotion); | |
341 gclog_or_tty->print_cr(" cms_free_dbl %f cms_consumption_rate %f", | |
342 cms_free_dbl, cms_consumption_rate() + 1.0); | |
343 } | |
344 // Add 1 in case the consumption rate goes to zero. | |
345 return cms_free_dbl / (cms_consumption_rate() + 1.0); | |
346 } | |
347 return 0.0; | |
348 } | |
349 | |
350 // Compare the duration of the cms collection to the | |
351 // time remaining before the cms generation is empty. | |
352 // Note that the time from the start of the cms collection | |
353 // to the start of the cms sweep (less than the total | |
354 // duration of the cms collection) can be used. This | |
355 // has been tried and some applications experienced | |
356 // promotion failures early in execution. This was | |
357 // possibly because the averages were not accurate | |
358 // enough at the beginning. | |
359 double CMSStats::time_until_cms_start() const { | |
360 // We add "gc0_period" to the "work" calculation | |
361 // below because this query is done (mostly) at the | |
362 // end of a scavenge, so we need to conservatively | |
363 // account for that much possible delay | |
364 // in the query so as to avoid concurrent mode failures | |
365 // due to starting the collection just a wee bit too | |
366 // late. | |
367 double work = cms_duration() + gc0_period(); | |
368 double deadline = time_until_cms_gen_full(); | |
369 if (work > deadline) { | |
370 if (Verbose && PrintGCDetails) { | |
371 gclog_or_tty->print( | |
372 " CMSCollector: collect because of anticipated promotion " | |
373 "before full %3.7f + %3.7f > %3.7f ", cms_duration(), | |
374 gc0_period(), time_until_cms_gen_full()); | |
375 } | |
376 return 0.0; | |
377 } | |
378 return work - deadline; | |
379 } | |
380 | |
381 // Return a duty cycle based on old_duty_cycle and new_duty_cycle, limiting the | |
382 // amount of change to prevent wild oscillation. | |
383 unsigned int CMSStats::icms_damped_duty_cycle(unsigned int old_duty_cycle, | |
384 unsigned int new_duty_cycle) { | |
385 assert(old_duty_cycle <= 100, "bad input value"); | |
386 assert(new_duty_cycle <= 100, "bad input value"); | |
387 | |
388 // Note: use subtraction with caution since it may underflow (values are | |
389 // unsigned). Addition is safe since we're in the range 0-100. | |
390 unsigned int damped_duty_cycle = new_duty_cycle; | |
391 if (new_duty_cycle < old_duty_cycle) { | |
392 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 5U); | |
393 if (new_duty_cycle + largest_delta < old_duty_cycle) { | |
394 damped_duty_cycle = old_duty_cycle - largest_delta; | |
395 } | |
396 } else if (new_duty_cycle > old_duty_cycle) { | |
397 const unsigned int largest_delta = MAX2(old_duty_cycle / 4, 15U); | |
398 if (new_duty_cycle > old_duty_cycle + largest_delta) { | |
399 damped_duty_cycle = MIN2(old_duty_cycle + largest_delta, 100U); | |
400 } | |
401 } | |
402 assert(damped_duty_cycle <= 100, "invalid duty cycle computed"); | |
403 | |
404 if (CMSTraceIncrementalPacing) { | |
405 gclog_or_tty->print(" [icms_damped_duty_cycle(%d,%d) = %d] ", | |
406 old_duty_cycle, new_duty_cycle, damped_duty_cycle); | |
407 } | |
408 return damped_duty_cycle; | |
409 } | |
410 | |
411 unsigned int CMSStats::icms_update_duty_cycle_impl() { | |
412 assert(CMSIncrementalPacing && valid(), | |
413 "should be handled in icms_update_duty_cycle()"); | |
414 | |
415 double cms_time_so_far = cms_timer().seconds(); | |
416 double scaled_duration = cms_duration_per_mb() * _cms_used_at_gc0_end / M; | |
417 double scaled_duration_remaining = fabsd(scaled_duration - cms_time_so_far); | |
418 | |
419 // Avoid division by 0. | |
420 double time_until_full = MAX2(time_until_cms_gen_full(), 0.01); | |
421 double duty_cycle_dbl = 100.0 * scaled_duration_remaining / time_until_full; | |
422 | |
423 unsigned int new_duty_cycle = MIN2((unsigned int)duty_cycle_dbl, 100U); | |
424 if (new_duty_cycle > _icms_duty_cycle) { | |
425 // Avoid very small duty cycles (1 or 2); 0 is allowed. | |
426 if (new_duty_cycle > 2) { | |
427 _icms_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, | |
428 new_duty_cycle); | |
429 } | |
430 } else if (_allow_duty_cycle_reduction) { | |
431 // The duty cycle is reduced only once per cms cycle (see record_cms_end()). | |
432 new_duty_cycle = icms_damped_duty_cycle(_icms_duty_cycle, new_duty_cycle); | |
433 // Respect the minimum duty cycle. | |
434 unsigned int min_duty_cycle = (unsigned int)CMSIncrementalDutyCycleMin; | |
435 _icms_duty_cycle = MAX2(new_duty_cycle, min_duty_cycle); | |
436 } | |
437 | |
438 if (PrintGCDetails || CMSTraceIncrementalPacing) { | |
439 gclog_or_tty->print(" icms_dc=%d ", _icms_duty_cycle); | |
440 } | |
441 | |
442 _allow_duty_cycle_reduction = false; | |
443 return _icms_duty_cycle; | |
444 } | |
445 | |
446 #ifndef PRODUCT | |
447 void CMSStats::print_on(outputStream *st) const { | |
448 st->print(" gc0_alpha=%d,cms_alpha=%d", _gc0_alpha, _cms_alpha); | |
449 st->print(",gc0_dur=%g,gc0_per=%g,gc0_promo=" SIZE_FORMAT, | |
450 gc0_duration(), gc0_period(), gc0_promoted()); | |
451 st->print(",cms_dur=%g,cms_dur_per_mb=%g,cms_per=%g,cms_alloc=" SIZE_FORMAT, | |
452 cms_duration(), cms_duration_per_mb(), | |
453 cms_period(), cms_allocated()); | |
454 st->print(",cms_since_beg=%g,cms_since_end=%g", | |
455 cms_time_since_begin(), cms_time_since_end()); | |
456 st->print(",cms_used_beg=" SIZE_FORMAT ",cms_used_end=" SIZE_FORMAT, | |
457 _cms_used_at_gc0_begin, _cms_used_at_gc0_end); | |
458 if (CMSIncrementalMode) { | |
459 st->print(",dc=%d", icms_duty_cycle()); | |
460 } | |
461 | |
462 if (valid()) { | |
463 st->print(",promo_rate=%g,cms_alloc_rate=%g", | |
464 promotion_rate(), cms_allocation_rate()); | |
465 st->print(",cms_consumption_rate=%g,time_until_full=%g", | |
466 cms_consumption_rate(), time_until_cms_gen_full()); | |
467 } | |
468 st->print(" "); | |
469 } | |
470 #endif // #ifndef PRODUCT | |
471 | |
472 CMSCollector::CollectorState CMSCollector::_collectorState = | |
473 CMSCollector::Idling; | |
474 bool CMSCollector::_foregroundGCIsActive = false; | |
475 bool CMSCollector::_foregroundGCShouldWait = false; | |
476 | |
477 CMSCollector::CMSCollector(ConcurrentMarkSweepGeneration* cmsGen, | |
478 ConcurrentMarkSweepGeneration* permGen, | |
479 CardTableRS* ct, | |
480 ConcurrentMarkSweepPolicy* cp): | |
481 _cmsGen(cmsGen), | |
482 _permGen(permGen), | |
483 _ct(ct), | |
484 _ref_processor(NULL), // will be set later | |
485 _conc_workers(NULL), // may be set later | |
486 _abort_preclean(false), | |
487 _start_sampling(false), | |
488 _between_prologue_and_epilogue(false), | |
489 _markBitMap(0, Mutex::leaf + 1, "CMS_markBitMap_lock"), | |
490 _perm_gen_verify_bit_map(0, -1 /* no mutex */, "No_lock"), | |
491 _modUnionTable((CardTableModRefBS::card_shift - LogHeapWordSize), | |
492 -1 /* lock-free */, "No_lock" /* dummy */), | |
493 _modUnionClosure(&_modUnionTable), | |
494 _modUnionClosurePar(&_modUnionTable), | |
495 _is_alive_closure(&_markBitMap), | |
496 _restart_addr(NULL), | |
497 _overflow_list(NULL), | |
498 _preserved_oop_stack(NULL), | |
499 _preserved_mark_stack(NULL), | |
500 _stats(cmsGen), | |
501 _eden_chunk_array(NULL), // may be set in ctor body | |
502 _eden_chunk_capacity(0), // -- ditto -- | |
503 _eden_chunk_index(0), // -- ditto -- | |
504 _survivor_plab_array(NULL), // -- ditto -- | |
505 _survivor_chunk_array(NULL), // -- ditto -- | |
506 _survivor_chunk_capacity(0), // -- ditto -- | |
507 _survivor_chunk_index(0), // -- ditto -- | |
508 _ser_pmc_preclean_ovflw(0), | |
509 _ser_pmc_remark_ovflw(0), | |
510 _par_pmc_remark_ovflw(0), | |
511 _ser_kac_ovflw(0), | |
512 _par_kac_ovflw(0), | |
513 #ifndef PRODUCT | |
514 _num_par_pushes(0), | |
515 #endif | |
516 _collection_count_start(0), | |
517 _verifying(false), | |
518 _icms_start_limit(NULL), | |
519 _icms_stop_limit(NULL), | |
520 _verification_mark_bm(0, Mutex::leaf + 1, "CMS_verification_mark_bm_lock"), | |
521 _completed_initialization(false), | |
522 _collector_policy(cp), | |
523 _unload_classes(false), | |
524 _unloaded_classes_last_cycle(false), | |
525 _sweep_estimate(CMS_SweepWeight, CMS_SweepPadding) | |
526 { | |
527 if (ExplicitGCInvokesConcurrentAndUnloadsClasses) { | |
528 ExplicitGCInvokesConcurrent = true; | |
529 } | |
530 // Now expand the span and allocate the collection support structures | |
531 // (MUT, marking bit map etc.) to cover both generations subject to | |
532 // collection. | |
533 | |
534 // First check that _permGen is adjacent to _cmsGen and above it. | |
535 assert( _cmsGen->reserved().word_size() > 0 | |
536 && _permGen->reserved().word_size() > 0, | |
537 "generations should not be of zero size"); | |
538 assert(_cmsGen->reserved().intersection(_permGen->reserved()).is_empty(), | |
539 "_cmsGen and _permGen should not overlap"); | |
540 assert(_cmsGen->reserved().end() == _permGen->reserved().start(), | |
541 "_cmsGen->end() different from _permGen->start()"); | |
542 | |
543 // For use by dirty card to oop closures. | |
544 _cmsGen->cmsSpace()->set_collector(this); | |
545 _permGen->cmsSpace()->set_collector(this); | |
546 | |
547 // Adjust my span to cover old (cms) gen and perm gen | |
548 _span = _cmsGen->reserved()._union(_permGen->reserved()); | |
549 // Initialize the span of is_alive_closure | |
550 _is_alive_closure.set_span(_span); | |
551 | |
552 // Allocate MUT and marking bit map | |
553 { | |
554 MutexLockerEx x(_markBitMap.lock(), Mutex::_no_safepoint_check_flag); | |
555 if (!_markBitMap.allocate(_span)) { | |
556 warning("Failed to allocate CMS Bit Map"); | |
557 return; | |
558 } | |
559 assert(_markBitMap.covers(_span), "_markBitMap inconsistency?"); | |
560 } | |
561 { | |
562 _modUnionTable.allocate(_span); | |
563 assert(_modUnionTable.covers(_span), "_modUnionTable inconsistency?"); | |
564 } | |
565 | |
566 if (!_markStack.allocate(CMSMarkStackSize)) { | |
567 warning("Failed to allocate CMS Marking Stack"); | |
568 return; | |
569 } | |
570 if (!_revisitStack.allocate(CMSRevisitStackSize)) { | |
571 warning("Failed to allocate CMS Revisit Stack"); | |
572 return; | |
573 } | |
574 | |
575 // Support for multi-threaded concurrent phases | |
576 if (ParallelGCThreads > 0 && CMSConcurrentMTEnabled) { | |
577 if (FLAG_IS_DEFAULT(ParallelCMSThreads)) { | |
578 // just for now | |
579 FLAG_SET_DEFAULT(ParallelCMSThreads, (ParallelGCThreads + 3)/4); | |
580 } | |
581 if (ParallelCMSThreads > 1) { | |
582 _conc_workers = new YieldingFlexibleWorkGang("Parallel CMS Threads", | |
583 ParallelCMSThreads, true); | |
584 if (_conc_workers == NULL) { | |
585 warning("GC/CMS: _conc_workers allocation failure: " | |
586 "forcing -CMSConcurrentMTEnabled"); | |
587 CMSConcurrentMTEnabled = false; | |
588 } | |
589 } else { | |
590 CMSConcurrentMTEnabled = false; | |
591 } | |
592 } | |
593 if (!CMSConcurrentMTEnabled) { | |
594 ParallelCMSThreads = 0; | |
595 } else { | |
596 // Turn off CMSCleanOnEnter optimization temporarily for | |
597 // the MT case where it's not fixed yet; see 6178663. | |
598 CMSCleanOnEnter = false; | |
599 } | |
600 assert((_conc_workers != NULL) == (ParallelCMSThreads > 1), | |
601 "Inconsistency"); | |
602 | |
603 // Parallel task queues; these are shared for the | |
604 // concurrent and stop-world phases of CMS, but | |
605 // are not shared with parallel scavenge (ParNew). | |
606 { | |
607 uint i; | |
608 uint num_queues = (uint) MAX2(ParallelGCThreads, ParallelCMSThreads); | |
609 | |
610 if ((CMSParallelRemarkEnabled || CMSConcurrentMTEnabled | |
611 || ParallelRefProcEnabled) | |
612 && num_queues > 0) { | |
613 _task_queues = new OopTaskQueueSet(num_queues); | |
614 if (_task_queues == NULL) { | |
615 warning("task_queues allocation failure."); | |
616 return; | |
617 } | |
618 _hash_seed = NEW_C_HEAP_ARRAY(int, num_queues); | |
619 if (_hash_seed == NULL) { | |
620 warning("_hash_seed array allocation failure"); | |
621 return; | |
622 } | |
623 | |
624 // XXX use a global constant instead of 64! | |
625 typedef struct OopTaskQueuePadded { | |
626 OopTaskQueue work_queue; | |
627 char pad[64 - sizeof(OopTaskQueue)]; // prevent false sharing | |
628 } OopTaskQueuePadded; | |
629 | |
630 for (i = 0; i < num_queues; i++) { | |
631 OopTaskQueuePadded *q_padded = new OopTaskQueuePadded(); | |
632 if (q_padded == NULL) { | |
633 warning("work_queue allocation failure."); | |
634 return; | |
635 } | |
636 _task_queues->register_queue(i, &q_padded->work_queue); | |
637 } | |
638 for (i = 0; i < num_queues; i++) { | |
639 _task_queues->queue(i)->initialize(); | |
640 _hash_seed[i] = 17; // copied from ParNew | |
641 } | |
642 } | |
643 } | |
644 | |
645 // "initiatingOccupancy" is the occupancy ratio at which we trigger | |
646 // a new collection cycle. Unless explicitly specified via | |
647 // CMSTriggerRatio, it is calculated by: | |
648 // Let "f" be MinHeapFreeRatio in | |
649 // | |
650 // intiatingOccupancy = 100-f + | |
651 // f * (CMSTriggerRatio/100) | |
652 // That is, if we assume the heap is at its desired maximum occupancy at the | |
653 // end of a collection, we let CMSTriggerRatio of the (purported) free | |
654 // space be allocated before initiating a new collection cycle. | |
655 if (CMSInitiatingOccupancyFraction > 0) { | |
656 _initiatingOccupancy = (double)CMSInitiatingOccupancyFraction / 100.0; | |
657 } else { | |
658 _initiatingOccupancy = ((100 - MinHeapFreeRatio) + | |
659 (double)(CMSTriggerRatio * | |
660 MinHeapFreeRatio) / 100.0) | |
661 / 100.0; | |
662 } | |
663 // Clip CMSBootstrapOccupancy between 0 and 100. | |
664 _bootstrap_occupancy = ((double)MIN2((intx)100, MAX2((intx)0, CMSBootstrapOccupancy))) | |
665 /(double)100; | |
666 | |
667 _full_gcs_since_conc_gc = 0; | |
668 | |
669 // Now tell CMS generations the identity of their collector | |
670 ConcurrentMarkSweepGeneration::set_collector(this); | |
671 | |
672 // Create & start a CMS thread for this CMS collector | |
673 _cmsThread = ConcurrentMarkSweepThread::start(this); | |
674 assert(cmsThread() != NULL, "CMS Thread should have been created"); | |
675 assert(cmsThread()->collector() == this, | |
676 "CMS Thread should refer to this gen"); | |
677 assert(CGC_lock != NULL, "Where's the CGC_lock?"); | |
678 | |
679 // Support for parallelizing young gen rescan | |
680 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
681 _young_gen = gch->prev_gen(_cmsGen); | |
682 if (gch->supports_inline_contig_alloc()) { | |
683 _top_addr = gch->top_addr(); | |
684 _end_addr = gch->end_addr(); | |
685 assert(_young_gen != NULL, "no _young_gen"); | |
686 _eden_chunk_index = 0; | |
687 _eden_chunk_capacity = (_young_gen->max_capacity()+CMSSamplingGrain)/CMSSamplingGrain; | |
688 _eden_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, _eden_chunk_capacity); | |
689 if (_eden_chunk_array == NULL) { | |
690 _eden_chunk_capacity = 0; | |
691 warning("GC/CMS: _eden_chunk_array allocation failure"); | |
692 } | |
693 } | |
694 assert(_eden_chunk_array != NULL || _eden_chunk_capacity == 0, "Error"); | |
695 | |
696 // Support for parallelizing survivor space rescan | |
697 if (CMSParallelRemarkEnabled && CMSParallelSurvivorRemarkEnabled) { | |
698 size_t max_plab_samples = MaxNewSize/((SurvivorRatio+2)*MinTLABSize); | |
699 _survivor_plab_array = NEW_C_HEAP_ARRAY(ChunkArray, ParallelGCThreads); | |
700 _survivor_chunk_array = NEW_C_HEAP_ARRAY(HeapWord*, 2*max_plab_samples); | |
701 _cursor = NEW_C_HEAP_ARRAY(size_t, ParallelGCThreads); | |
702 if (_survivor_plab_array == NULL || _survivor_chunk_array == NULL | |
703 || _cursor == NULL) { | |
704 warning("Failed to allocate survivor plab/chunk array"); | |
705 if (_survivor_plab_array != NULL) { | |
706 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array); | |
707 _survivor_plab_array = NULL; | |
708 } | |
709 if (_survivor_chunk_array != NULL) { | |
710 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array); | |
711 _survivor_chunk_array = NULL; | |
712 } | |
713 if (_cursor != NULL) { | |
714 FREE_C_HEAP_ARRAY(size_t, _cursor); | |
715 _cursor = NULL; | |
716 } | |
717 } else { | |
718 _survivor_chunk_capacity = 2*max_plab_samples; | |
719 for (uint i = 0; i < ParallelGCThreads; i++) { | |
720 HeapWord** vec = NEW_C_HEAP_ARRAY(HeapWord*, max_plab_samples); | |
721 if (vec == NULL) { | |
722 warning("Failed to allocate survivor plab array"); | |
723 for (int j = i; j > 0; j--) { | |
724 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_plab_array[j-1].array()); | |
725 } | |
726 FREE_C_HEAP_ARRAY(ChunkArray, _survivor_plab_array); | |
727 FREE_C_HEAP_ARRAY(HeapWord*, _survivor_chunk_array); | |
728 _survivor_plab_array = NULL; | |
729 _survivor_chunk_array = NULL; | |
730 _survivor_chunk_capacity = 0; | |
731 break; | |
732 } else { | |
733 ChunkArray* cur = | |
734 ::new (&_survivor_plab_array[i]) ChunkArray(vec, | |
735 max_plab_samples); | |
736 assert(cur->end() == 0, "Should be 0"); | |
737 assert(cur->array() == vec, "Should be vec"); | |
738 assert(cur->capacity() == max_plab_samples, "Error"); | |
739 } | |
740 } | |
741 } | |
742 } | |
743 assert( ( _survivor_plab_array != NULL | |
744 && _survivor_chunk_array != NULL) | |
745 || ( _survivor_chunk_capacity == 0 | |
746 && _survivor_chunk_index == 0), | |
747 "Error"); | |
748 | |
749 // Choose what strong roots should be scanned depending on verification options | |
750 // and perm gen collection mode. | |
751 if (!CMSClassUnloadingEnabled) { | |
752 // If class unloading is disabled we want to include all classes into the root set. | |
753 add_root_scanning_option(SharedHeap::SO_AllClasses); | |
754 } else { | |
755 add_root_scanning_option(SharedHeap::SO_SystemClasses); | |
756 } | |
757 | |
758 NOT_PRODUCT(_overflow_counter = CMSMarkStackOverflowInterval;) | |
759 _gc_counters = new CollectorCounters("CMS", 1); | |
760 _completed_initialization = true; | |
761 _sweep_timer.start(); // start of time | |
762 } | |
763 | |
764 const char* ConcurrentMarkSweepGeneration::name() const { | |
765 return "concurrent mark-sweep generation"; | |
766 } | |
767 void ConcurrentMarkSweepGeneration::update_counters() { | |
768 if (UsePerfData) { | |
769 _space_counters->update_all(); | |
770 _gen_counters->update_all(); | |
771 } | |
772 } | |
773 | |
774 // this is an optimized version of update_counters(). it takes the | |
775 // used value as a parameter rather than computing it. | |
776 // | |
777 void ConcurrentMarkSweepGeneration::update_counters(size_t used) { | |
778 if (UsePerfData) { | |
779 _space_counters->update_used(used); | |
780 _space_counters->update_capacity(); | |
781 _gen_counters->update_all(); | |
782 } | |
783 } | |
784 | |
785 void ConcurrentMarkSweepGeneration::print() const { | |
786 Generation::print(); | |
787 cmsSpace()->print(); | |
788 } | |
789 | |
790 #ifndef PRODUCT | |
791 void ConcurrentMarkSweepGeneration::print_statistics() { | |
792 cmsSpace()->printFLCensus(0); | |
793 } | |
794 #endif | |
795 | |
796 void ConcurrentMarkSweepGeneration::printOccupancy(const char *s) { | |
797 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
798 if (PrintGCDetails) { | |
799 if (Verbose) { | |
800 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"("SIZE_FORMAT")]", | |
801 level(), short_name(), s, used(), capacity()); | |
802 } else { | |
803 gclog_or_tty->print(" [%d %s-%s: "SIZE_FORMAT"K("SIZE_FORMAT"K)]", | |
804 level(), short_name(), s, used() / K, capacity() / K); | |
805 } | |
806 } | |
807 if (Verbose) { | |
808 gclog_or_tty->print(" "SIZE_FORMAT"("SIZE_FORMAT")", | |
809 gch->used(), gch->capacity()); | |
810 } else { | |
811 gclog_or_tty->print(" "SIZE_FORMAT"K("SIZE_FORMAT"K)", | |
812 gch->used() / K, gch->capacity() / K); | |
813 } | |
814 } | |
815 | |
816 size_t | |
817 ConcurrentMarkSweepGeneration::contiguous_available() const { | |
818 // dld proposes an improvement in precision here. If the committed | |
819 // part of the space ends in a free block we should add that to | |
820 // uncommitted size in the calculation below. Will make this | |
821 // change later, staying with the approximation below for the | |
822 // time being. -- ysr. | |
823 return MAX2(_virtual_space.uncommitted_size(), unsafe_max_alloc_nogc()); | |
824 } | |
825 | |
826 size_t | |
827 ConcurrentMarkSweepGeneration::unsafe_max_alloc_nogc() const { | |
828 return _cmsSpace->max_alloc_in_words() * HeapWordSize; | |
829 } | |
830 | |
831 size_t ConcurrentMarkSweepGeneration::max_available() const { | |
832 return free() + _virtual_space.uncommitted_size(); | |
833 } | |
834 | |
835 bool ConcurrentMarkSweepGeneration::promotion_attempt_is_safe( | |
836 size_t max_promotion_in_bytes, | |
837 bool younger_handles_promotion_failure) const { | |
838 | |
839 // This is the most conservative test. Full promotion is | |
840 // guaranteed if this is used. The multiplicative factor is to | |
841 // account for the worst case "dilatation". | |
842 double adjusted_max_promo_bytes = _dilatation_factor * max_promotion_in_bytes; | |
843 if (adjusted_max_promo_bytes > (double)max_uintx) { // larger than size_t | |
844 adjusted_max_promo_bytes = (double)max_uintx; | |
845 } | |
846 bool result = (max_contiguous_available() >= (size_t)adjusted_max_promo_bytes); | |
847 | |
848 if (younger_handles_promotion_failure && !result) { | |
849 // Full promotion is not guaranteed because fragmentation | |
850 // of the cms generation can prevent the full promotion. | |
851 result = (max_available() >= (size_t)adjusted_max_promo_bytes); | |
852 | |
853 if (!result) { | |
854 // With promotion failure handling the test for the ability | |
855 // to support the promotion does not have to be guaranteed. | |
856 // Use an average of the amount promoted. | |
857 result = max_available() >= (size_t) | |
858 gc_stats()->avg_promoted()->padded_average(); | |
859 if (PrintGC && Verbose && result) { | |
860 gclog_or_tty->print_cr( | |
861 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe" | |
862 " max_available: " SIZE_FORMAT | |
863 " avg_promoted: " SIZE_FORMAT, | |
864 max_available(), (size_t) | |
865 gc_stats()->avg_promoted()->padded_average()); | |
866 } | |
867 } else { | |
868 if (PrintGC && Verbose) { | |
869 gclog_or_tty->print_cr( | |
870 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe" | |
871 " max_available: " SIZE_FORMAT | |
872 " adj_max_promo_bytes: " SIZE_FORMAT, | |
873 max_available(), (size_t)adjusted_max_promo_bytes); | |
874 } | |
875 } | |
876 } else { | |
877 if (PrintGC && Verbose) { | |
878 gclog_or_tty->print_cr( | |
879 "\nConcurrentMarkSweepGeneration::promotion_attempt_is_safe" | |
880 " contiguous_available: " SIZE_FORMAT | |
881 " adj_max_promo_bytes: " SIZE_FORMAT, | |
882 max_contiguous_available(), (size_t)adjusted_max_promo_bytes); | |
883 } | |
884 } | |
885 return result; | |
886 } | |
887 | |
888 CompactibleSpace* | |
889 ConcurrentMarkSweepGeneration::first_compaction_space() const { | |
890 return _cmsSpace; | |
891 } | |
892 | |
893 void ConcurrentMarkSweepGeneration::reset_after_compaction() { | |
894 // Clear the promotion information. These pointers can be adjusted | |
895 // along with all the other pointers into the heap but | |
896 // compaction is expected to be a rare event with | |
897 // a heap using cms so don't do it without seeing the need. | |
898 if (ParallelGCThreads > 0) { | |
899 for (uint i = 0; i < ParallelGCThreads; i++) { | |
900 _par_gc_thread_states[i]->promo.reset(); | |
901 } | |
902 } | |
903 } | |
904 | |
905 void ConcurrentMarkSweepGeneration::space_iterate(SpaceClosure* blk, bool usedOnly) { | |
906 blk->do_space(_cmsSpace); | |
907 } | |
908 | |
909 void ConcurrentMarkSweepGeneration::compute_new_size() { | |
910 assert_locked_or_safepoint(Heap_lock); | |
911 | |
912 // If incremental collection failed, we just want to expand | |
913 // to the limit. | |
914 if (incremental_collection_failed()) { | |
915 clear_incremental_collection_failed(); | |
916 grow_to_reserved(); | |
917 return; | |
918 } | |
919 | |
920 size_t expand_bytes = 0; | |
921 double free_percentage = ((double) free()) / capacity(); | |
922 double desired_free_percentage = (double) MinHeapFreeRatio / 100; | |
923 double maximum_free_percentage = (double) MaxHeapFreeRatio / 100; | |
924 | |
925 // compute expansion delta needed for reaching desired free percentage | |
926 if (free_percentage < desired_free_percentage) { | |
927 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); | |
928 assert(desired_capacity >= capacity(), "invalid expansion size"); | |
929 expand_bytes = MAX2(desired_capacity - capacity(), MinHeapDeltaBytes); | |
930 } | |
931 if (expand_bytes > 0) { | |
932 if (PrintGCDetails && Verbose) { | |
933 size_t desired_capacity = (size_t)(used() / ((double) 1 - desired_free_percentage)); | |
934 gclog_or_tty->print_cr("\nFrom compute_new_size: "); | |
935 gclog_or_tty->print_cr(" Free fraction %f", free_percentage); | |
936 gclog_or_tty->print_cr(" Desired free fraction %f", | |
937 desired_free_percentage); | |
938 gclog_or_tty->print_cr(" Maximum free fraction %f", | |
939 maximum_free_percentage); | |
940 gclog_or_tty->print_cr(" Capactiy "SIZE_FORMAT, capacity()/1000); | |
941 gclog_or_tty->print_cr(" Desired capacity "SIZE_FORMAT, | |
942 desired_capacity/1000); | |
943 int prev_level = level() - 1; | |
944 if (prev_level >= 0) { | |
945 size_t prev_size = 0; | |
946 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
947 Generation* prev_gen = gch->_gens[prev_level]; | |
948 prev_size = prev_gen->capacity(); | |
949 gclog_or_tty->print_cr(" Younger gen size "SIZE_FORMAT, | |
950 prev_size/1000); | |
951 } | |
952 gclog_or_tty->print_cr(" unsafe_max_alloc_nogc "SIZE_FORMAT, | |
953 unsafe_max_alloc_nogc()/1000); | |
954 gclog_or_tty->print_cr(" contiguous available "SIZE_FORMAT, | |
955 contiguous_available()/1000); | |
956 gclog_or_tty->print_cr(" Expand by "SIZE_FORMAT" (bytes)", | |
957 expand_bytes); | |
958 } | |
959 // safe if expansion fails | |
960 expand(expand_bytes, 0, CMSExpansionCause::_satisfy_free_ratio); | |
961 if (PrintGCDetails && Verbose) { | |
962 gclog_or_tty->print_cr(" Expanded free fraction %f", | |
963 ((double) free()) / capacity()); | |
964 } | |
965 } | |
966 } | |
967 | |
968 Mutex* ConcurrentMarkSweepGeneration::freelistLock() const { | |
969 return cmsSpace()->freelistLock(); | |
970 } | |
971 | |
972 HeapWord* ConcurrentMarkSweepGeneration::allocate(size_t size, | |
973 bool tlab) { | |
974 CMSSynchronousYieldRequest yr; | |
975 MutexLockerEx x(freelistLock(), | |
976 Mutex::_no_safepoint_check_flag); | |
977 return have_lock_and_allocate(size, tlab); | |
978 } | |
979 | |
980 HeapWord* ConcurrentMarkSweepGeneration::have_lock_and_allocate(size_t size, | |
981 bool tlab) { | |
982 assert_lock_strong(freelistLock()); | |
983 size_t adjustedSize = CompactibleFreeListSpace::adjustObjectSize(size); | |
984 HeapWord* res = cmsSpace()->allocate(adjustedSize); | |
985 // Allocate the object live (grey) if the background collector has | |
986 // started marking. This is necessary because the marker may | |
987 // have passed this address and consequently this object will | |
988 // not otherwise be greyed and would be incorrectly swept up. | |
989 // Note that if this object contains references, the writing | |
990 // of those references will dirty the card containing this object | |
991 // allowing the object to be blackened (and its references scanned) | |
992 // either during a preclean phase or at the final checkpoint. | |
993 if (res != NULL) { | |
994 collector()->direct_allocated(res, adjustedSize); | |
995 _direct_allocated_words += adjustedSize; | |
996 // allocation counters | |
997 NOT_PRODUCT( | |
998 _numObjectsAllocated++; | |
999 _numWordsAllocated += (int)adjustedSize; | |
1000 ) | |
1001 } | |
1002 return res; | |
1003 } | |
1004 | |
1005 // In the case of direct allocation by mutators in a generation that | |
1006 // is being concurrently collected, the object must be allocated | |
1007 // live (grey) if the background collector has started marking. | |
1008 // This is necessary because the marker may | |
1009 // have passed this address and consequently this object will | |
1010 // not otherwise be greyed and would be incorrectly swept up. | |
1011 // Note that if this object contains references, the writing | |
1012 // of those references will dirty the card containing this object | |
1013 // allowing the object to be blackened (and its references scanned) | |
1014 // either during a preclean phase or at the final checkpoint. | |
1015 void CMSCollector::direct_allocated(HeapWord* start, size_t size) { | |
1016 assert(_markBitMap.covers(start, size), "Out of bounds"); | |
1017 if (_collectorState >= Marking) { | |
1018 MutexLockerEx y(_markBitMap.lock(), | |
1019 Mutex::_no_safepoint_check_flag); | |
1020 // [see comments preceding SweepClosure::do_blk() below for details] | |
1021 // 1. need to mark the object as live so it isn't collected | |
1022 // 2. need to mark the 2nd bit to indicate the object may be uninitialized | |
1023 // 3. need to mark the end of the object so sweeper can skip over it | |
1024 // if it's uninitialized when the sweeper reaches it. | |
1025 _markBitMap.mark(start); // object is live | |
1026 _markBitMap.mark(start + 1); // object is potentially uninitialized? | |
1027 _markBitMap.mark(start + size - 1); | |
1028 // mark end of object | |
1029 } | |
1030 // check that oop looks uninitialized | |
1031 assert(oop(start)->klass() == NULL, "_klass should be NULL"); | |
1032 } | |
1033 | |
1034 void CMSCollector::promoted(bool par, HeapWord* start, | |
1035 bool is_obj_array, size_t obj_size) { | |
1036 assert(_markBitMap.covers(start), "Out of bounds"); | |
1037 // See comment in direct_allocated() about when objects should | |
1038 // be allocated live. | |
1039 if (_collectorState >= Marking) { | |
1040 // we already hold the marking bit map lock, taken in | |
1041 // the prologue | |
1042 if (par) { | |
1043 _markBitMap.par_mark(start); | |
1044 } else { | |
1045 _markBitMap.mark(start); | |
1046 } | |
1047 // We don't need to mark the object as uninitialized (as | |
1048 // in direct_allocated above) because this is being done with the | |
1049 // world stopped and the object will be initialized by the | |
1050 // time the sweeper gets to look at it. | |
1051 assert(SafepointSynchronize::is_at_safepoint(), | |
1052 "expect promotion only at safepoints"); | |
1053 | |
1054 if (_collectorState < Sweeping) { | |
1055 // Mark the appropriate cards in the modUnionTable, so that | |
1056 // this object gets scanned before the sweep. If this is | |
1057 // not done, CMS generation references in the object might | |
1058 // not get marked. | |
1059 // For the case of arrays, which are otherwise precisely | |
1060 // marked, we need to dirty the entire array, not just its head. | |
1061 if (is_obj_array) { | |
1062 // The [par_]mark_range() method expects mr.end() below to | |
1063 // be aligned to the granularity of a bit's representation | |
1064 // in the heap. In the case of the MUT below, that's a | |
1065 // card size. | |
1066 MemRegion mr(start, | |
1067 (HeapWord*)round_to((intptr_t)(start + obj_size), | |
1068 CardTableModRefBS::card_size /* bytes */)); | |
1069 if (par) { | |
1070 _modUnionTable.par_mark_range(mr); | |
1071 } else { | |
1072 _modUnionTable.mark_range(mr); | |
1073 } | |
1074 } else { // not an obj array; we can just mark the head | |
1075 if (par) { | |
1076 _modUnionTable.par_mark(start); | |
1077 } else { | |
1078 _modUnionTable.mark(start); | |
1079 } | |
1080 } | |
1081 } | |
1082 } | |
1083 } | |
1084 | |
1085 static inline size_t percent_of_space(Space* space, HeapWord* addr) | |
1086 { | |
1087 size_t delta = pointer_delta(addr, space->bottom()); | |
1088 return (size_t)(delta * 100.0 / (space->capacity() / HeapWordSize)); | |
1089 } | |
1090 | |
1091 void CMSCollector::icms_update_allocation_limits() | |
1092 { | |
1093 Generation* gen0 = GenCollectedHeap::heap()->get_gen(0); | |
1094 EdenSpace* eden = gen0->as_DefNewGeneration()->eden(); | |
1095 | |
1096 const unsigned int duty_cycle = stats().icms_update_duty_cycle(); | |
1097 if (CMSTraceIncrementalPacing) { | |
1098 stats().print(); | |
1099 } | |
1100 | |
1101 assert(duty_cycle <= 100, "invalid duty cycle"); | |
1102 if (duty_cycle != 0) { | |
1103 // The duty_cycle is a percentage between 0 and 100; convert to words and | |
1104 // then compute the offset from the endpoints of the space. | |
1105 size_t free_words = eden->free() / HeapWordSize; | |
1106 double free_words_dbl = (double)free_words; | |
1107 size_t duty_cycle_words = (size_t)(free_words_dbl * duty_cycle / 100.0); | |
1108 size_t offset_words = (free_words - duty_cycle_words) / 2; | |
1109 | |
1110 _icms_start_limit = eden->top() + offset_words; | |
1111 _icms_stop_limit = eden->end() - offset_words; | |
1112 | |
1113 // The limits may be adjusted (shifted to the right) by | |
1114 // CMSIncrementalOffset, to allow the application more mutator time after a | |
1115 // young gen gc (when all mutators were stopped) and before CMS starts and | |
1116 // takes away one or more cpus. | |
1117 if (CMSIncrementalOffset != 0) { | |
1118 double adjustment_dbl = free_words_dbl * CMSIncrementalOffset / 100.0; | |
1119 size_t adjustment = (size_t)adjustment_dbl; | |
1120 HeapWord* tmp_stop = _icms_stop_limit + adjustment; | |
1121 if (tmp_stop > _icms_stop_limit && tmp_stop < eden->end()) { | |
1122 _icms_start_limit += adjustment; | |
1123 _icms_stop_limit = tmp_stop; | |
1124 } | |
1125 } | |
1126 } | |
1127 if (duty_cycle == 0 || (_icms_start_limit == _icms_stop_limit)) { | |
1128 _icms_start_limit = _icms_stop_limit = eden->end(); | |
1129 } | |
1130 | |
1131 // Install the new start limit. | |
1132 eden->set_soft_end(_icms_start_limit); | |
1133 | |
1134 if (CMSTraceIncrementalMode) { | |
1135 gclog_or_tty->print(" icms alloc limits: " | |
1136 PTR_FORMAT "," PTR_FORMAT | |
1137 " (" SIZE_FORMAT "%%," SIZE_FORMAT "%%) ", | |
1138 _icms_start_limit, _icms_stop_limit, | |
1139 percent_of_space(eden, _icms_start_limit), | |
1140 percent_of_space(eden, _icms_stop_limit)); | |
1141 if (Verbose) { | |
1142 gclog_or_tty->print("eden: "); | |
1143 eden->print_on(gclog_or_tty); | |
1144 } | |
1145 } | |
1146 } | |
1147 | |
1148 // Any changes here should try to maintain the invariant | |
1149 // that if this method is called with _icms_start_limit | |
1150 // and _icms_stop_limit both NULL, then it should return NULL | |
1151 // and not notify the icms thread. | |
1152 HeapWord* | |
1153 CMSCollector::allocation_limit_reached(Space* space, HeapWord* top, | |
1154 size_t word_size) | |
1155 { | |
1156 // A start_limit equal to end() means the duty cycle is 0, so treat that as a | |
1157 // nop. | |
1158 if (CMSIncrementalMode && _icms_start_limit != space->end()) { | |
1159 if (top <= _icms_start_limit) { | |
1160 if (CMSTraceIncrementalMode) { | |
1161 space->print_on(gclog_or_tty); | |
1162 gclog_or_tty->stamp(); | |
1163 gclog_or_tty->print_cr(" start limit top=" PTR_FORMAT | |
1164 ", new limit=" PTR_FORMAT | |
1165 " (" SIZE_FORMAT "%%)", | |
1166 top, _icms_stop_limit, | |
1167 percent_of_space(space, _icms_stop_limit)); | |
1168 } | |
1169 ConcurrentMarkSweepThread::start_icms(); | |
1170 assert(top < _icms_stop_limit, "Tautology"); | |
1171 if (word_size < pointer_delta(_icms_stop_limit, top)) { | |
1172 return _icms_stop_limit; | |
1173 } | |
1174 | |
1175 // The allocation will cross both the _start and _stop limits, so do the | |
1176 // stop notification also and return end(). | |
1177 if (CMSTraceIncrementalMode) { | |
1178 space->print_on(gclog_or_tty); | |
1179 gclog_or_tty->stamp(); | |
1180 gclog_or_tty->print_cr(" +stop limit top=" PTR_FORMAT | |
1181 ", new limit=" PTR_FORMAT | |
1182 " (" SIZE_FORMAT "%%)", | |
1183 top, space->end(), | |
1184 percent_of_space(space, space->end())); | |
1185 } | |
1186 ConcurrentMarkSweepThread::stop_icms(); | |
1187 return space->end(); | |
1188 } | |
1189 | |
1190 if (top <= _icms_stop_limit) { | |
1191 if (CMSTraceIncrementalMode) { | |
1192 space->print_on(gclog_or_tty); | |
1193 gclog_or_tty->stamp(); | |
1194 gclog_or_tty->print_cr(" stop limit top=" PTR_FORMAT | |
1195 ", new limit=" PTR_FORMAT | |
1196 " (" SIZE_FORMAT "%%)", | |
1197 top, space->end(), | |
1198 percent_of_space(space, space->end())); | |
1199 } | |
1200 ConcurrentMarkSweepThread::stop_icms(); | |
1201 return space->end(); | |
1202 } | |
1203 | |
1204 if (CMSTraceIncrementalMode) { | |
1205 space->print_on(gclog_or_tty); | |
1206 gclog_or_tty->stamp(); | |
1207 gclog_or_tty->print_cr(" end limit top=" PTR_FORMAT | |
1208 ", new limit=" PTR_FORMAT, | |
1209 top, NULL); | |
1210 } | |
1211 } | |
1212 | |
1213 return NULL; | |
1214 } | |
1215 | |
1216 oop ConcurrentMarkSweepGeneration::promote(oop obj, size_t obj_size, oop* ref) { | |
1217 assert(obj_size == (size_t)obj->size(), "bad obj_size passed in"); | |
1218 // allocate, copy and if necessary update promoinfo -- | |
1219 // delegate to underlying space. | |
1220 assert_lock_strong(freelistLock()); | |
1221 | |
1222 #ifndef PRODUCT | |
1223 if (Universe::heap()->promotion_should_fail()) { | |
1224 return NULL; | |
1225 } | |
1226 #endif // #ifndef PRODUCT | |
1227 | |
1228 oop res = _cmsSpace->promote(obj, obj_size, ref); | |
1229 if (res == NULL) { | |
1230 // expand and retry | |
1231 size_t s = _cmsSpace->expansionSpaceRequired(obj_size); // HeapWords | |
1232 expand(s*HeapWordSize, MinHeapDeltaBytes, | |
1233 CMSExpansionCause::_satisfy_promotion); | |
1234 // Since there's currently no next generation, we don't try to promote | |
1235 // into a more senior generation. | |
1236 assert(next_gen() == NULL, "assumption, based upon which no attempt " | |
1237 "is made to pass on a possibly failing " | |
1238 "promotion to next generation"); | |
1239 res = _cmsSpace->promote(obj, obj_size, ref); | |
1240 } | |
1241 if (res != NULL) { | |
1242 // See comment in allocate() about when objects should | |
1243 // be allocated live. | |
1244 assert(obj->is_oop(), "Will dereference klass pointer below"); | |
1245 collector()->promoted(false, // Not parallel | |
1246 (HeapWord*)res, obj->is_objArray(), obj_size); | |
1247 // promotion counters | |
1248 NOT_PRODUCT( | |
1249 _numObjectsPromoted++; | |
1250 _numWordsPromoted += | |
1251 (int)(CompactibleFreeListSpace::adjustObjectSize(obj->size())); | |
1252 ) | |
1253 } | |
1254 return res; | |
1255 } | |
1256 | |
1257 | |
1258 HeapWord* | |
1259 ConcurrentMarkSweepGeneration::allocation_limit_reached(Space* space, | |
1260 HeapWord* top, | |
1261 size_t word_sz) | |
1262 { | |
1263 return collector()->allocation_limit_reached(space, top, word_sz); | |
1264 } | |
1265 | |
1266 // Things to support parallel young-gen collection. | |
1267 oop | |
1268 ConcurrentMarkSweepGeneration::par_promote(int thread_num, | |
1269 oop old, markOop m, | |
1270 size_t word_sz) { | |
1271 #ifndef PRODUCT | |
1272 if (Universe::heap()->promotion_should_fail()) { | |
1273 return NULL; | |
1274 } | |
1275 #endif // #ifndef PRODUCT | |
1276 | |
1277 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; | |
1278 PromotionInfo* promoInfo = &ps->promo; | |
1279 // if we are tracking promotions, then first ensure space for | |
1280 // promotion (including spooling space for saving header if necessary). | |
1281 // then allocate and copy, then track promoted info if needed. | |
1282 // When tracking (see PromotionInfo::track()), the mark word may | |
1283 // be displaced and in this case restoration of the mark word | |
1284 // occurs in the (oop_since_save_marks_)iterate phase. | |
1285 if (promoInfo->tracking() && !promoInfo->ensure_spooling_space()) { | |
1286 // Out of space for allocating spooling buffers; | |
1287 // try expanding and allocating spooling buffers. | |
1288 if (!expand_and_ensure_spooling_space(promoInfo)) { | |
1289 return NULL; | |
1290 } | |
1291 } | |
1292 assert(promoInfo->has_spooling_space(), "Control point invariant"); | |
1293 HeapWord* obj_ptr = ps->lab.alloc(word_sz); | |
1294 if (obj_ptr == NULL) { | |
1295 obj_ptr = expand_and_par_lab_allocate(ps, word_sz); | |
1296 if (obj_ptr == NULL) { | |
1297 return NULL; | |
1298 } | |
1299 } | |
1300 oop obj = oop(obj_ptr); | |
1301 assert(obj->klass() == NULL, "Object should be uninitialized here."); | |
1302 // Otherwise, copy the object. Here we must be careful to insert the | |
1303 // klass pointer last, since this marks the block as an allocated object. | |
1304 HeapWord* old_ptr = (HeapWord*)old; | |
1305 if (word_sz > (size_t)oopDesc::header_size()) { | |
1306 Copy::aligned_disjoint_words(old_ptr + oopDesc::header_size(), | |
1307 obj_ptr + oopDesc::header_size(), | |
1308 word_sz - oopDesc::header_size()); | |
1309 } | |
1310 // Restore the mark word copied above. | |
1311 obj->set_mark(m); | |
1312 // Now we can track the promoted object, if necessary. We take care | |
1313 // To delay the transition from uninitialized to full object | |
1314 // (i.e., insertion of klass pointer) until after, so that it | |
1315 // atomically becomes a promoted object. | |
1316 if (promoInfo->tracking()) { | |
1317 promoInfo->track((PromotedObject*)obj, old->klass()); | |
1318 } | |
1319 // Finally, install the klass pointer. | |
1320 obj->set_klass(old->klass()); | |
1321 | |
1322 assert(old->is_oop(), "Will dereference klass ptr below"); | |
1323 collector()->promoted(true, // parallel | |
1324 obj_ptr, old->is_objArray(), word_sz); | |
1325 | |
1326 NOT_PRODUCT( | |
1327 Atomic::inc(&_numObjectsPromoted); | |
1328 Atomic::add((jint)CompactibleFreeListSpace::adjustObjectSize(obj->size()), | |
1329 &_numWordsPromoted); | |
1330 ) | |
1331 | |
1332 return obj; | |
1333 } | |
1334 | |
1335 void | |
1336 ConcurrentMarkSweepGeneration:: | |
1337 par_promote_alloc_undo(int thread_num, | |
1338 HeapWord* obj, size_t word_sz) { | |
1339 // CMS does not support promotion undo. | |
1340 ShouldNotReachHere(); | |
1341 } | |
1342 | |
1343 void | |
1344 ConcurrentMarkSweepGeneration:: | |
1345 par_promote_alloc_done(int thread_num) { | |
1346 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; | |
1347 ps->lab.retire(); | |
1348 #if CFLS_LAB_REFILL_STATS | |
1349 if (thread_num == 0) { | |
1350 _cmsSpace->print_par_alloc_stats(); | |
1351 } | |
1352 #endif | |
1353 } | |
1354 | |
1355 void | |
1356 ConcurrentMarkSweepGeneration:: | |
1357 par_oop_since_save_marks_iterate_done(int thread_num) { | |
1358 CMSParGCThreadState* ps = _par_gc_thread_states[thread_num]; | |
1359 ParScanWithoutBarrierClosure* dummy_cl = NULL; | |
1360 ps->promo.promoted_oops_iterate_nv(dummy_cl); | |
1361 } | |
1362 | |
1363 // XXXPERM | |
1364 bool ConcurrentMarkSweepGeneration::should_collect(bool full, | |
1365 size_t size, | |
1366 bool tlab) | |
1367 { | |
1368 // We allow a STW collection only if a full | |
1369 // collection was requested. | |
1370 return full || should_allocate(size, tlab); // FIX ME !!! | |
1371 // This and promotion failure handling are connected at the | |
1372 // hip and should be fixed by untying them. | |
1373 } | |
1374 | |
1375 bool CMSCollector::shouldConcurrentCollect() { | |
1376 if (_full_gc_requested) { | |
1377 assert(ExplicitGCInvokesConcurrent, "Unexpected state"); | |
1378 if (Verbose && PrintGCDetails) { | |
1379 gclog_or_tty->print_cr("CMSCollector: collect because of explicit " | |
1380 " gc request"); | |
1381 } | |
1382 return true; | |
1383 } | |
1384 | |
1385 // For debugging purposes, change the type of collection. | |
1386 // If the rotation is not on the concurrent collection | |
1387 // type, don't start a concurrent collection. | |
1388 NOT_PRODUCT( | |
1389 if (RotateCMSCollectionTypes && | |
1390 (_cmsGen->debug_collection_type() != | |
1391 ConcurrentMarkSweepGeneration::Concurrent_collection_type)) { | |
1392 assert(_cmsGen->debug_collection_type() != | |
1393 ConcurrentMarkSweepGeneration::Unknown_collection_type, | |
1394 "Bad cms collection type"); | |
1395 return false; | |
1396 } | |
1397 ) | |
1398 | |
1399 FreelistLocker x(this); | |
1400 // ------------------------------------------------------------------ | |
1401 // Print out lots of information which affects the initiation of | |
1402 // a collection. | |
1403 if (PrintCMSInitiationStatistics && stats().valid()) { | |
1404 gclog_or_tty->print("CMSCollector shouldConcurrentCollect: "); | |
1405 gclog_or_tty->stamp(); | |
1406 gclog_or_tty->print_cr(""); | |
1407 stats().print_on(gclog_or_tty); | |
1408 gclog_or_tty->print_cr("time_until_cms_gen_full %3.7f", | |
1409 stats().time_until_cms_gen_full()); | |
1410 gclog_or_tty->print_cr("free="SIZE_FORMAT, _cmsGen->free()); | |
1411 gclog_or_tty->print_cr("contiguous_available="SIZE_FORMAT, | |
1412 _cmsGen->contiguous_available()); | |
1413 gclog_or_tty->print_cr("promotion_rate=%g", stats().promotion_rate()); | |
1414 gclog_or_tty->print_cr("cms_allocation_rate=%g", stats().cms_allocation_rate()); | |
1415 gclog_or_tty->print_cr("occupancy=%3.7f", _cmsGen->occupancy()); | |
1416 gclog_or_tty->print_cr("initiatingOccupancy=%3.7f", initiatingOccupancy()); | |
1417 } | |
1418 // ------------------------------------------------------------------ | |
1419 | |
1420 // If the estimated time to complete a cms collection (cms_duration()) | |
1421 // is less than the estimated time remaining until the cms generation | |
1422 // is full, start a collection. | |
1423 if (!UseCMSInitiatingOccupancyOnly) { | |
1424 if (stats().valid()) { | |
1425 if (stats().time_until_cms_start() == 0.0) { | |
1426 return true; | |
1427 } | |
1428 } else { | |
1429 // We want to conservatively collect somewhat early in order | |
1430 // to try and "bootstrap" our CMS/promotion statistics; | |
1431 // this branch will not fire after the first successful CMS | |
1432 // collection because the stats should then be valid. | |
1433 if (_cmsGen->occupancy() >= _bootstrap_occupancy) { | |
1434 if (Verbose && PrintGCDetails) { | |
1435 gclog_or_tty->print_cr( | |
1436 " CMSCollector: collect for bootstrapping statistics:" | |
1437 " occupancy = %f, boot occupancy = %f", _cmsGen->occupancy(), | |
1438 _bootstrap_occupancy); | |
1439 } | |
1440 return true; | |
1441 } | |
1442 } | |
1443 } | |
1444 | |
1445 // Otherwise, we start a collection cycle if either the perm gen or | |
1446 // old gen want a collection cycle started. Each may use | |
1447 // an appropriate criterion for making this decision. | |
1448 // XXX We need to make sure that the gen expansion | |
1449 // criterion dovetails well with this. | |
1450 if (_cmsGen->shouldConcurrentCollect(initiatingOccupancy())) { | |
1451 if (Verbose && PrintGCDetails) { | |
1452 gclog_or_tty->print_cr("CMS old gen initiated"); | |
1453 } | |
1454 return true; | |
1455 } | |
1456 | |
1457 if (cms_should_unload_classes() && | |
1458 _permGen->shouldConcurrentCollect(initiatingOccupancy())) { | |
1459 if (Verbose && PrintGCDetails) { | |
1460 gclog_or_tty->print_cr("CMS perm gen initiated"); | |
1461 } | |
1462 return true; | |
1463 } | |
1464 | |
1465 return false; | |
1466 } | |
1467 | |
1468 // Clear _expansion_cause fields of constituent generations | |
1469 void CMSCollector::clear_expansion_cause() { | |
1470 _cmsGen->clear_expansion_cause(); | |
1471 _permGen->clear_expansion_cause(); | |
1472 } | |
1473 | |
1474 bool ConcurrentMarkSweepGeneration::shouldConcurrentCollect( | |
1475 double initiatingOccupancy) { | |
1476 // We should be conservative in starting a collection cycle. To | |
1477 // start too eagerly runs the risk of collecting too often in the | |
1478 // extreme. To collect too rarely falls back on full collections, | |
1479 // which works, even if not optimum in terms of concurrent work. | |
1480 // As a work around for too eagerly collecting, use the flag | |
1481 // UseCMSInitiatingOccupancyOnly. This also has the advantage of | |
1482 // giving the user an easily understandable way of controlling the | |
1483 // collections. | |
1484 // We want to start a new collection cycle if any of the following | |
1485 // conditions hold: | |
1486 // . our current occupancy exceeds the initiating occupancy, or | |
1487 // . we recently needed to expand and have not since that expansion, | |
1488 // collected, or | |
1489 // . we are not using adaptive free lists and linear allocation is | |
1490 // going to fail, or | |
1491 // . (for old gen) incremental collection has already failed or | |
1492 // may soon fail in the near future as we may not be able to absorb | |
1493 // promotions. | |
1494 assert_lock_strong(freelistLock()); | |
1495 | |
1496 if (occupancy() > initiatingOccupancy) { | |
1497 if (PrintGCDetails && Verbose) { | |
1498 gclog_or_tty->print(" %s: collect because of occupancy %f / %f ", | |
1499 short_name(), occupancy(), initiatingOccupancy); | |
1500 } | |
1501 return true; | |
1502 } | |
1503 if (UseCMSInitiatingOccupancyOnly) { | |
1504 return false; | |
1505 } | |
1506 if (expansion_cause() == CMSExpansionCause::_satisfy_allocation) { | |
1507 if (PrintGCDetails && Verbose) { | |
1508 gclog_or_tty->print(" %s: collect because expanded for allocation ", | |
1509 short_name()); | |
1510 } | |
1511 return true; | |
1512 } | |
1513 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
1514 assert(gch->collector_policy()->is_two_generation_policy(), | |
1515 "You may want to check the correctness of the following"); | |
1516 if (gch->incremental_collection_will_fail()) { | |
1517 if (PrintGCDetails && Verbose) { | |
1518 gclog_or_tty->print(" %s: collect because incremental collection will fail ", | |
1519 short_name()); | |
1520 } | |
1521 return true; | |
1522 } | |
1523 if (!_cmsSpace->adaptive_freelists() && | |
1524 _cmsSpace->linearAllocationWouldFail()) { | |
1525 if (PrintGCDetails && Verbose) { | |
1526 gclog_or_tty->print(" %s: collect because of linAB ", | |
1527 short_name()); | |
1528 } | |
1529 return true; | |
1530 } | |
1531 return false; | |
1532 } | |
1533 | |
1534 void ConcurrentMarkSweepGeneration::collect(bool full, | |
1535 bool clear_all_soft_refs, | |
1536 size_t size, | |
1537 bool tlab) | |
1538 { | |
1539 collector()->collect(full, clear_all_soft_refs, size, tlab); | |
1540 } | |
1541 | |
1542 void CMSCollector::collect(bool full, | |
1543 bool clear_all_soft_refs, | |
1544 size_t size, | |
1545 bool tlab) | |
1546 { | |
1547 if (!UseCMSCollectionPassing && _collectorState > Idling) { | |
1548 // For debugging purposes skip the collection if the state | |
1549 // is not currently idle | |
1550 if (TraceCMSState) { | |
1551 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " skipped full:%d CMS state %d", | |
1552 Thread::current(), full, _collectorState); | |
1553 } | |
1554 return; | |
1555 } | |
1556 | |
1557 // The following "if" branch is present for defensive reasons. | |
1558 // In the current uses of this interface, it can be replaced with: | |
1559 // assert(!GC_locker.is_active(), "Can't be called otherwise"); | |
1560 // But I am not placing that assert here to allow future | |
1561 // generality in invoking this interface. | |
1562 if (GC_locker::is_active()) { | |
1563 // A consistency test for GC_locker | |
1564 assert(GC_locker::needs_gc(), "Should have been set already"); | |
1565 // Skip this foreground collection, instead | |
1566 // expanding the heap if necessary. | |
1567 // Need the free list locks for the call to free() in compute_new_size() | |
1568 compute_new_size(); | |
1569 return; | |
1570 } | |
1571 acquire_control_and_collect(full, clear_all_soft_refs); | |
1572 _full_gcs_since_conc_gc++; | |
1573 | |
1574 } | |
1575 | |
1576 void CMSCollector::request_full_gc(unsigned int full_gc_count) { | |
1577 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
1578 unsigned int gc_count = gch->total_full_collections(); | |
1579 if (gc_count == full_gc_count) { | |
1580 MutexLockerEx y(CGC_lock, Mutex::_no_safepoint_check_flag); | |
1581 _full_gc_requested = true; | |
1582 CGC_lock->notify(); // nudge CMS thread | |
1583 } | |
1584 } | |
1585 | |
1586 | |
1587 // The foreground and background collectors need to coordinate in order | |
1588 // to make sure that they do not mutually interfere with CMS collections. | |
1589 // When a background collection is active, | |
1590 // the foreground collector may need to take over (preempt) and | |
1591 // synchronously complete an ongoing collection. Depending on the | |
1592 // frequency of the background collections and the heap usage | |
1593 // of the application, this preemption can be seldom or frequent. | |
1594 // There are only certain | |
1595 // points in the background collection that the "collection-baton" | |
1596 // can be passed to the foreground collector. | |
1597 // | |
1598 // The foreground collector will wait for the baton before | |
1599 // starting any part of the collection. The foreground collector | |
1600 // will only wait at one location. | |
1601 // | |
1602 // The background collector will yield the baton before starting a new | |
1603 // phase of the collection (e.g., before initial marking, marking from roots, | |
1604 // precleaning, final re-mark, sweep etc.) This is normally done at the head | |
1605 // of the loop which switches the phases. The background collector does some | |
1606 // of the phases (initial mark, final re-mark) with the world stopped. | |
1607 // Because of locking involved in stopping the world, | |
1608 // the foreground collector should not block waiting for the background | |
1609 // collector when it is doing a stop-the-world phase. The background | |
1610 // collector will yield the baton at an additional point just before | |
1611 // it enters a stop-the-world phase. Once the world is stopped, the | |
1612 // background collector checks the phase of the collection. If the | |
1613 // phase has not changed, it proceeds with the collection. If the | |
1614 // phase has changed, it skips that phase of the collection. See | |
1615 // the comments on the use of the Heap_lock in collect_in_background(). | |
1616 // | |
1617 // Variable used in baton passing. | |
1618 // _foregroundGCIsActive - Set to true by the foreground collector when | |
1619 // it wants the baton. The foreground clears it when it has finished | |
1620 // the collection. | |
1621 // _foregroundGCShouldWait - Set to true by the background collector | |
1622 // when it is running. The foreground collector waits while | |
1623 // _foregroundGCShouldWait is true. | |
1624 // CGC_lock - monitor used to protect access to the above variables | |
1625 // and to notify the foreground and background collectors. | |
1626 // _collectorState - current state of the CMS collection. | |
1627 // | |
1628 // The foreground collector | |
1629 // acquires the CGC_lock | |
1630 // sets _foregroundGCIsActive | |
1631 // waits on the CGC_lock for _foregroundGCShouldWait to be false | |
1632 // various locks acquired in preparation for the collection | |
1633 // are released so as not to block the background collector | |
1634 // that is in the midst of a collection | |
1635 // proceeds with the collection | |
1636 // clears _foregroundGCIsActive | |
1637 // returns | |
1638 // | |
1639 // The background collector in a loop iterating on the phases of the | |
1640 // collection | |
1641 // acquires the CGC_lock | |
1642 // sets _foregroundGCShouldWait | |
1643 // if _foregroundGCIsActive is set | |
1644 // clears _foregroundGCShouldWait, notifies _CGC_lock | |
1645 // waits on _CGC_lock for _foregroundGCIsActive to become false | |
1646 // and exits the loop. | |
1647 // otherwise | |
1648 // proceed with that phase of the collection | |
1649 // if the phase is a stop-the-world phase, | |
1650 // yield the baton once more just before enqueueing | |
1651 // the stop-world CMS operation (executed by the VM thread). | |
1652 // returns after all phases of the collection are done | |
1653 // | |
1654 | |
1655 void CMSCollector::acquire_control_and_collect(bool full, | |
1656 bool clear_all_soft_refs) { | |
1657 assert(SafepointSynchronize::is_at_safepoint(), "should be at safepoint"); | |
1658 assert(!Thread::current()->is_ConcurrentGC_thread(), | |
1659 "shouldn't try to acquire control from self!"); | |
1660 | |
1661 // Start the protocol for acquiring control of the | |
1662 // collection from the background collector (aka CMS thread). | |
1663 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), | |
1664 "VM thread should have CMS token"); | |
1665 // Remember the possibly interrupted state of an ongoing | |
1666 // concurrent collection | |
1667 CollectorState first_state = _collectorState; | |
1668 | |
1669 // Signal to a possibly ongoing concurrent collection that | |
1670 // we want to do a foreground collection. | |
1671 _foregroundGCIsActive = true; | |
1672 | |
1673 // Disable incremental mode during a foreground collection. | |
1674 ICMSDisabler icms_disabler; | |
1675 | |
1676 // release locks and wait for a notify from the background collector | |
1677 // releasing the locks in only necessary for phases which | |
1678 // do yields to improve the granularity of the collection. | |
1679 assert_lock_strong(bitMapLock()); | |
1680 // We need to lock the Free list lock for the space that we are | |
1681 // currently collecting. | |
1682 assert(haveFreelistLocks(), "Must be holding free list locks"); | |
1683 bitMapLock()->unlock(); | |
1684 releaseFreelistLocks(); | |
1685 { | |
1686 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); | |
1687 if (_foregroundGCShouldWait) { | |
1688 // We are going to be waiting for action for the CMS thread; | |
1689 // it had better not be gone (for instance at shutdown)! | |
1690 assert(ConcurrentMarkSweepThread::cmst() != NULL, | |
1691 "CMS thread must be running"); | |
1692 // Wait here until the background collector gives us the go-ahead | |
1693 ConcurrentMarkSweepThread::clear_CMS_flag( | |
1694 ConcurrentMarkSweepThread::CMS_vm_has_token); // release token | |
1695 // Get a possibly blocked CMS thread going: | |
1696 // Note that we set _foregroundGCIsActive true above, | |
1697 // without protection of the CGC_lock. | |
1698 CGC_lock->notify(); | |
1699 assert(!ConcurrentMarkSweepThread::vm_thread_wants_cms_token(), | |
1700 "Possible deadlock"); | |
1701 while (_foregroundGCShouldWait) { | |
1702 // wait for notification | |
1703 CGC_lock->wait(Mutex::_no_safepoint_check_flag); | |
1704 // Possibility of delay/starvation here, since CMS token does | |
1705 // not know to give priority to VM thread? Actually, i think | |
1706 // there wouldn't be any delay/starvation, but the proof of | |
1707 // that "fact" (?) appears non-trivial. XXX 20011219YSR | |
1708 } | |
1709 ConcurrentMarkSweepThread::set_CMS_flag( | |
1710 ConcurrentMarkSweepThread::CMS_vm_has_token); | |
1711 } | |
1712 } | |
1713 // The CMS_token is already held. Get back the other locks. | |
1714 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), | |
1715 "VM thread should have CMS token"); | |
1716 getFreelistLocks(); | |
1717 bitMapLock()->lock_without_safepoint_check(); | |
1718 if (TraceCMSState) { | |
1719 gclog_or_tty->print_cr("CMS foreground collector has asked for control " | |
1720 INTPTR_FORMAT " with first state %d", Thread::current(), first_state); | |
1721 gclog_or_tty->print_cr(" gets control with state %d", _collectorState); | |
1722 } | |
1723 | |
1724 // Check if we need to do a compaction, or if not, whether | |
1725 // we need to start the mark-sweep from scratch. | |
1726 bool should_compact = false; | |
1727 bool should_start_over = false; | |
1728 decide_foreground_collection_type(clear_all_soft_refs, | |
1729 &should_compact, &should_start_over); | |
1730 | |
1731 NOT_PRODUCT( | |
1732 if (RotateCMSCollectionTypes) { | |
1733 if (_cmsGen->debug_collection_type() == | |
1734 ConcurrentMarkSweepGeneration::MSC_foreground_collection_type) { | |
1735 should_compact = true; | |
1736 } else if (_cmsGen->debug_collection_type() == | |
1737 ConcurrentMarkSweepGeneration::MS_foreground_collection_type) { | |
1738 should_compact = false; | |
1739 } | |
1740 } | |
1741 ) | |
1742 | |
1743 if (PrintGCDetails && first_state > Idling) { | |
1744 GCCause::Cause cause = GenCollectedHeap::heap()->gc_cause(); | |
1745 if (GCCause::is_user_requested_gc(cause) || | |
1746 GCCause::is_serviceability_requested_gc(cause)) { | |
1747 gclog_or_tty->print(" (concurrent mode interrupted)"); | |
1748 } else { | |
1749 gclog_or_tty->print(" (concurrent mode failure)"); | |
1750 } | |
1751 } | |
1752 | |
1753 if (should_compact) { | |
1754 // If the collection is being acquired from the background | |
1755 // collector, there may be references on the discovered | |
1756 // references lists that have NULL referents (being those | |
1757 // that were concurrently cleared by a mutator) or | |
1758 // that are no longer active (having been enqueued concurrently | |
1759 // by the mutator). | |
1760 // Scrub the list of those references because Mark-Sweep-Compact | |
1761 // code assumes referents are not NULL and that all discovered | |
1762 // Reference objects are active. | |
1763 ref_processor()->clean_up_discovered_references(); | |
1764 | |
1765 do_compaction_work(clear_all_soft_refs); | |
1766 | |
1767 // Has the GC time limit been exceeded? | |
1768 check_gc_time_limit(); | |
1769 | |
1770 } else { | |
1771 do_mark_sweep_work(clear_all_soft_refs, first_state, | |
1772 should_start_over); | |
1773 } | |
1774 // Reset the expansion cause, now that we just completed | |
1775 // a collection cycle. | |
1776 clear_expansion_cause(); | |
1777 _foregroundGCIsActive = false; | |
1778 return; | |
1779 } | |
1780 | |
1781 void CMSCollector::check_gc_time_limit() { | |
1782 | |
1783 // Ignore explicit GC's. Exiting here does not set the flag and | |
1784 // does not reset the count. Updating of the averages for system | |
1785 // GC's is still controlled by UseAdaptiveSizePolicyWithSystemGC. | |
1786 GCCause::Cause gc_cause = GenCollectedHeap::heap()->gc_cause(); | |
1787 if (GCCause::is_user_requested_gc(gc_cause) || | |
1788 GCCause::is_serviceability_requested_gc(gc_cause)) { | |
1789 return; | |
1790 } | |
1791 | |
1792 // Calculate the fraction of the CMS generation was freed during | |
1793 // the last collection. | |
1794 // Only consider the STW compacting cost for now. | |
1795 // | |
1796 // Note that the gc time limit test only works for the collections | |
1797 // of the young gen + tenured gen and not for collections of the | |
1798 // permanent gen. That is because the calculation of the space | |
1799 // freed by the collection is the free space in the young gen + | |
1800 // tenured gen. | |
1801 | |
1802 double fraction_free = | |
1803 ((double)_cmsGen->free())/((double)_cmsGen->max_capacity()); | |
1804 if ((100.0 * size_policy()->compacting_gc_cost()) > | |
1805 ((double) GCTimeLimit) && | |
1806 ((fraction_free * 100) < GCHeapFreeLimit)) { | |
1807 size_policy()->inc_gc_time_limit_count(); | |
1808 if (UseGCOverheadLimit && | |
1809 (size_policy()->gc_time_limit_count() > | |
1810 AdaptiveSizePolicyGCTimeLimitThreshold)) { | |
1811 size_policy()->set_gc_time_limit_exceeded(true); | |
1812 // Avoid consecutive OOM due to the gc time limit by resetting | |
1813 // the counter. | |
1814 size_policy()->reset_gc_time_limit_count(); | |
1815 if (PrintGCDetails) { | |
1816 gclog_or_tty->print_cr(" GC is exceeding overhead limit " | |
1817 "of %d%%", GCTimeLimit); | |
1818 } | |
1819 } else { | |
1820 if (PrintGCDetails) { | |
1821 gclog_or_tty->print_cr(" GC would exceed overhead limit " | |
1822 "of %d%%", GCTimeLimit); | |
1823 } | |
1824 } | |
1825 } else { | |
1826 size_policy()->reset_gc_time_limit_count(); | |
1827 } | |
1828 } | |
1829 | |
1830 // Resize the perm generation and the tenured generation | |
1831 // after obtaining the free list locks for the | |
1832 // two generations. | |
1833 void CMSCollector::compute_new_size() { | |
1834 assert_locked_or_safepoint(Heap_lock); | |
1835 FreelistLocker z(this); | |
1836 _permGen->compute_new_size(); | |
1837 _cmsGen->compute_new_size(); | |
1838 } | |
1839 | |
1840 // A work method used by foreground collection to determine | |
1841 // what type of collection (compacting or not, continuing or fresh) | |
1842 // it should do. | |
1843 // NOTE: the intent is to make UseCMSCompactAtFullCollection | |
1844 // and CMSCompactWhenClearAllSoftRefs the default in the future | |
1845 // and do away with the flags after a suitable period. | |
1846 void CMSCollector::decide_foreground_collection_type( | |
1847 bool clear_all_soft_refs, bool* should_compact, | |
1848 bool* should_start_over) { | |
1849 // Normally, we'll compact only if the UseCMSCompactAtFullCollection | |
1850 // flag is set, and we have either requested a System.gc() or | |
1851 // the number of full gc's since the last concurrent cycle | |
1852 // has exceeded the threshold set by CMSFullGCsBeforeCompaction, | |
1853 // or if an incremental collection has failed | |
1854 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
1855 assert(gch->collector_policy()->is_two_generation_policy(), | |
1856 "You may want to check the correctness of the following"); | |
1857 // Inform cms gen if this was due to partial collection failing. | |
1858 // The CMS gen may use this fact to determine its expansion policy. | |
1859 if (gch->incremental_collection_will_fail()) { | |
1860 assert(!_cmsGen->incremental_collection_failed(), | |
1861 "Should have been noticed, reacted to and cleared"); | |
1862 _cmsGen->set_incremental_collection_failed(); | |
1863 } | |
1864 *should_compact = | |
1865 UseCMSCompactAtFullCollection && | |
1866 ((_full_gcs_since_conc_gc >= CMSFullGCsBeforeCompaction) || | |
1867 GCCause::is_user_requested_gc(gch->gc_cause()) || | |
1868 gch->incremental_collection_will_fail()); | |
1869 *should_start_over = false; | |
1870 if (clear_all_soft_refs && !*should_compact) { | |
1871 // We are about to do a last ditch collection attempt | |
1872 // so it would normally make sense to do a compaction | |
1873 // to reclaim as much space as possible. | |
1874 if (CMSCompactWhenClearAllSoftRefs) { | |
1875 // Default: The rationale is that in this case either | |
1876 // we are past the final marking phase, in which case | |
1877 // we'd have to start over, or so little has been done | |
1878 // that there's little point in saving that work. Compaction | |
1879 // appears to be the sensible choice in either case. | |
1880 *should_compact = true; | |
1881 } else { | |
1882 // We have been asked to clear all soft refs, but not to | |
1883 // compact. Make sure that we aren't past the final checkpoint | |
1884 // phase, for that is where we process soft refs. If we are already | |
1885 // past that phase, we'll need to redo the refs discovery phase and | |
1886 // if necessary clear soft refs that weren't previously | |
1887 // cleared. We do so by remembering the phase in which | |
1888 // we came in, and if we are past the refs processing | |
1889 // phase, we'll choose to just redo the mark-sweep | |
1890 // collection from scratch. | |
1891 if (_collectorState > FinalMarking) { | |
1892 // We are past the refs processing phase; | |
1893 // start over and do a fresh synchronous CMS cycle | |
1894 _collectorState = Resetting; // skip to reset to start new cycle | |
1895 reset(false /* == !asynch */); | |
1896 *should_start_over = true; | |
1897 } // else we can continue a possibly ongoing current cycle | |
1898 } | |
1899 } | |
1900 } | |
1901 | |
1902 // A work method used by the foreground collector to do | |
1903 // a mark-sweep-compact. | |
1904 void CMSCollector::do_compaction_work(bool clear_all_soft_refs) { | |
1905 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
1906 TraceTime t("CMS:MSC ", PrintGCDetails && Verbose, true, gclog_or_tty); | |
1907 if (PrintGC && Verbose && !(GCCause::is_user_requested_gc(gch->gc_cause()))) { | |
1908 gclog_or_tty->print_cr("Compact ConcurrentMarkSweepGeneration after %d " | |
1909 "collections passed to foreground collector", _full_gcs_since_conc_gc); | |
1910 } | |
1911 | |
1912 // Sample collection interval time and reset for collection pause. | |
1913 if (UseAdaptiveSizePolicy) { | |
1914 size_policy()->msc_collection_begin(); | |
1915 } | |
1916 | |
1917 // Temporarily widen the span of the weak reference processing to | |
1918 // the entire heap. | |
1919 MemRegion new_span(GenCollectedHeap::heap()->reserved_region()); | |
1920 ReferenceProcessorSpanMutator x(ref_processor(), new_span); | |
1921 | |
1922 // Temporarily, clear the "is_alive_non_header" field of the | |
1923 // reference processor. | |
1924 ReferenceProcessorIsAliveMutator y(ref_processor(), NULL); | |
1925 | |
1926 // Temporarily make reference _processing_ single threaded (non-MT). | |
1927 ReferenceProcessorMTProcMutator z(ref_processor(), false); | |
1928 | |
1929 // Temporarily make refs discovery atomic | |
1930 ReferenceProcessorAtomicMutator w(ref_processor(), true); | |
1931 | |
1932 ref_processor()->set_enqueuing_is_done(false); | |
1933 ref_processor()->enable_discovery(); | |
1934 // If an asynchronous collection finishes, the _modUnionTable is | |
1935 // all clear. If we are assuming the collection from an asynchronous | |
1936 // collection, clear the _modUnionTable. | |
1937 assert(_collectorState != Idling || _modUnionTable.isAllClear(), | |
1938 "_modUnionTable should be clear if the baton was not passed"); | |
1939 _modUnionTable.clear_all(); | |
1940 | |
1941 // We must adjust the allocation statistics being maintained | |
1942 // in the free list space. We do so by reading and clearing | |
1943 // the sweep timer and updating the block flux rate estimates below. | |
1944 assert(_sweep_timer.is_active(), "We should never see the timer inactive"); | |
1945 _sweep_timer.stop(); | |
1946 // Note that we do not use this sample to update the _sweep_estimate. | |
1947 _cmsGen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()), | |
1948 _sweep_estimate.padded_average()); | |
1949 | |
1950 GenMarkSweep::invoke_at_safepoint(_cmsGen->level(), | |
1951 ref_processor(), clear_all_soft_refs); | |
1952 #ifdef ASSERT | |
1953 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); | |
1954 size_t free_size = cms_space->free(); | |
1955 assert(free_size == | |
1956 pointer_delta(cms_space->end(), cms_space->compaction_top()) | |
1957 * HeapWordSize, | |
1958 "All the free space should be compacted into one chunk at top"); | |
1959 assert(cms_space->dictionary()->totalChunkSize( | |
1960 debug_only(cms_space->freelistLock())) == 0 || | |
1961 cms_space->totalSizeInIndexedFreeLists() == 0, | |
1962 "All the free space should be in a single chunk"); | |
1963 size_t num = cms_space->totalCount(); | |
1964 assert((free_size == 0 && num == 0) || | |
1965 (free_size > 0 && (num == 1 || num == 2)), | |
1966 "There should be at most 2 free chunks after compaction"); | |
1967 #endif // ASSERT | |
1968 _collectorState = Resetting; | |
1969 assert(_restart_addr == NULL, | |
1970 "Should have been NULL'd before baton was passed"); | |
1971 reset(false /* == !asynch */); | |
1972 _cmsGen->reset_after_compaction(); | |
1973 | |
1974 if (verifying() && !cms_should_unload_classes()) { | |
1975 perm_gen_verify_bit_map()->clear_all(); | |
1976 } | |
1977 | |
1978 // Clear any data recorded in the PLAB chunk arrays. | |
1979 if (_survivor_plab_array != NULL) { | |
1980 reset_survivor_plab_arrays(); | |
1981 } | |
1982 | |
1983 // Adjust the per-size allocation stats for the next epoch. | |
1984 _cmsGen->cmsSpace()->endSweepFLCensus(sweepCount() /* fake */); | |
1985 // Restart the "sweep timer" for next epoch. | |
1986 _sweep_timer.reset(); | |
1987 _sweep_timer.start(); | |
1988 | |
1989 // Sample collection pause time and reset for collection interval. | |
1990 if (UseAdaptiveSizePolicy) { | |
1991 size_policy()->msc_collection_end(gch->gc_cause()); | |
1992 } | |
1993 | |
1994 // For a mark-sweep-compact, compute_new_size() will be called | |
1995 // in the heap's do_collection() method. | |
1996 } | |
1997 | |
1998 // A work method used by the foreground collector to do | |
1999 // a mark-sweep, after taking over from a possibly on-going | |
2000 // concurrent mark-sweep collection. | |
2001 void CMSCollector::do_mark_sweep_work(bool clear_all_soft_refs, | |
2002 CollectorState first_state, bool should_start_over) { | |
2003 if (PrintGC && Verbose) { | |
2004 gclog_or_tty->print_cr("Pass concurrent collection to foreground " | |
2005 "collector with count %d", | |
2006 _full_gcs_since_conc_gc); | |
2007 } | |
2008 switch (_collectorState) { | |
2009 case Idling: | |
2010 if (first_state == Idling || should_start_over) { | |
2011 // The background GC was not active, or should | |
2012 // restarted from scratch; start the cycle. | |
2013 _collectorState = InitialMarking; | |
2014 } | |
2015 // If first_state was not Idling, then a background GC | |
2016 // was in progress and has now finished. No need to do it | |
2017 // again. Leave the state as Idling. | |
2018 break; | |
2019 case Precleaning: | |
2020 // In the foreground case don't do the precleaning since | |
2021 // it is not done concurrently and there is extra work | |
2022 // required. | |
2023 _collectorState = FinalMarking; | |
2024 } | |
2025 if (PrintGCDetails && | |
2026 (_collectorState > Idling || | |
2027 !GCCause::is_user_requested_gc(GenCollectedHeap::heap()->gc_cause()))) { | |
2028 gclog_or_tty->print(" (concurrent mode failure)"); | |
2029 } | |
2030 collect_in_foreground(clear_all_soft_refs); | |
2031 | |
2032 // For a mark-sweep, compute_new_size() will be called | |
2033 // in the heap's do_collection() method. | |
2034 } | |
2035 | |
2036 | |
2037 void CMSCollector::getFreelistLocks() const { | |
2038 // Get locks for all free lists in all generations that this | |
2039 // collector is responsible for | |
2040 _cmsGen->freelistLock()->lock_without_safepoint_check(); | |
2041 _permGen->freelistLock()->lock_without_safepoint_check(); | |
2042 } | |
2043 | |
2044 void CMSCollector::releaseFreelistLocks() const { | |
2045 // Release locks for all free lists in all generations that this | |
2046 // collector is responsible for | |
2047 _cmsGen->freelistLock()->unlock(); | |
2048 _permGen->freelistLock()->unlock(); | |
2049 } | |
2050 | |
2051 bool CMSCollector::haveFreelistLocks() const { | |
2052 // Check locks for all free lists in all generations that this | |
2053 // collector is responsible for | |
2054 assert_lock_strong(_cmsGen->freelistLock()); | |
2055 assert_lock_strong(_permGen->freelistLock()); | |
2056 PRODUCT_ONLY(ShouldNotReachHere()); | |
2057 return true; | |
2058 } | |
2059 | |
2060 // A utility class that is used by the CMS collector to | |
2061 // temporarily "release" the foreground collector from its | |
2062 // usual obligation to wait for the background collector to | |
2063 // complete an ongoing phase before proceeding. | |
2064 class ReleaseForegroundGC: public StackObj { | |
2065 private: | |
2066 CMSCollector* _c; | |
2067 public: | |
2068 ReleaseForegroundGC(CMSCollector* c) : _c(c) { | |
2069 assert(_c->_foregroundGCShouldWait, "Else should not need to call"); | |
2070 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); | |
2071 // allow a potentially blocked foreground collector to proceed | |
2072 _c->_foregroundGCShouldWait = false; | |
2073 if (_c->_foregroundGCIsActive) { | |
2074 CGC_lock->notify(); | |
2075 } | |
2076 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
2077 "Possible deadlock"); | |
2078 } | |
2079 | |
2080 ~ReleaseForegroundGC() { | |
2081 assert(!_c->_foregroundGCShouldWait, "Usage protocol violation?"); | |
2082 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); | |
2083 _c->_foregroundGCShouldWait = true; | |
2084 } | |
2085 }; | |
2086 | |
2087 // There are separate collect_in_background and collect_in_foreground because of | |
2088 // the different locking requirements of the background collector and the | |
2089 // foreground collector. There was originally an attempt to share | |
2090 // one "collect" method between the background collector and the foreground | |
2091 // collector but the if-then-else required made it cleaner to have | |
2092 // separate methods. | |
2093 void CMSCollector::collect_in_background(bool clear_all_soft_refs) { | |
2094 assert(Thread::current()->is_ConcurrentGC_thread(), | |
2095 "A CMS asynchronous collection is only allowed on a CMS thread."); | |
2096 | |
2097 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
2098 { | |
2099 bool safepoint_check = Mutex::_no_safepoint_check_flag; | |
2100 MutexLockerEx hl(Heap_lock, safepoint_check); | |
2101 MutexLockerEx x(CGC_lock, safepoint_check); | |
2102 if (_foregroundGCIsActive || !UseAsyncConcMarkSweepGC) { | |
2103 // The foreground collector is active or we're | |
2104 // not using asynchronous collections. Skip this | |
2105 // background collection. | |
2106 assert(!_foregroundGCShouldWait, "Should be clear"); | |
2107 return; | |
2108 } else { | |
2109 assert(_collectorState == Idling, "Should be idling before start."); | |
2110 _collectorState = InitialMarking; | |
2111 // Reset the expansion cause, now that we are about to begin | |
2112 // a new cycle. | |
2113 clear_expansion_cause(); | |
2114 } | |
2115 _unloaded_classes_last_cycle = cms_should_unload_classes(); // ... from last cycle | |
2116 // This controls class unloading in response to an explicit gc request. | |
2117 // If ExplicitGCInvokesConcurrentAndUnloadsClasses is set, then | |
2118 // we will unload classes even if CMSClassUnloadingEnabled is not set. | |
2119 // See CR 6541037 and related CRs. | |
2120 _unload_classes = _full_gc_requested // ... for this cycle | |
2121 && ExplicitGCInvokesConcurrentAndUnloadsClasses; | |
2122 _full_gc_requested = false; // acks all outstanding full gc requests | |
2123 // Signal that we are about to start a collection | |
2124 gch->increment_total_full_collections(); // ... starting a collection cycle | |
2125 _collection_count_start = gch->total_full_collections(); | |
2126 } | |
2127 | |
2128 // Used for PrintGC | |
2129 size_t prev_used; | |
2130 if (PrintGC && Verbose) { | |
2131 prev_used = _cmsGen->used(); // XXXPERM | |
2132 } | |
2133 | |
2134 // The change of the collection state is normally done at this level; | |
2135 // the exceptions are phases that are executed while the world is | |
2136 // stopped. For those phases the change of state is done while the | |
2137 // world is stopped. For baton passing purposes this allows the | |
2138 // background collector to finish the phase and change state atomically. | |
2139 // The foreground collector cannot wait on a phase that is done | |
2140 // while the world is stopped because the foreground collector already | |
2141 // has the world stopped and would deadlock. | |
2142 while (_collectorState != Idling) { | |
2143 if (TraceCMSState) { | |
2144 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d", | |
2145 Thread::current(), _collectorState); | |
2146 } | |
2147 // The foreground collector | |
2148 // holds the Heap_lock throughout its collection. | |
2149 // holds the CMS token (but not the lock) | |
2150 // except while it is waiting for the background collector to yield. | |
2151 // | |
2152 // The foreground collector should be blocked (not for long) | |
2153 // if the background collector is about to start a phase | |
2154 // executed with world stopped. If the background | |
2155 // collector has already started such a phase, the | |
2156 // foreground collector is blocked waiting for the | |
2157 // Heap_lock. The stop-world phases (InitialMarking and FinalMarking) | |
2158 // are executed in the VM thread. | |
2159 // | |
2160 // The locking order is | |
2161 // PendingListLock (PLL) -- if applicable (FinalMarking) | |
2162 // Heap_lock (both this & PLL locked in VM_CMS_Operation::prologue()) | |
2163 // CMS token (claimed in | |
2164 // stop_world_and_do() --> | |
2165 // safepoint_synchronize() --> | |
2166 // CMSThread::synchronize()) | |
2167 | |
2168 { | |
2169 // Check if the FG collector wants us to yield. | |
2170 CMSTokenSync x(true); // is cms thread | |
2171 if (waitForForegroundGC()) { | |
2172 // We yielded to a foreground GC, nothing more to be | |
2173 // done this round. | |
2174 assert(_foregroundGCShouldWait == false, "We set it to false in " | |
2175 "waitForForegroundGC()"); | |
2176 if (TraceCMSState) { | |
2177 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT | |
2178 " exiting collection CMS state %d", | |
2179 Thread::current(), _collectorState); | |
2180 } | |
2181 return; | |
2182 } else { | |
2183 // The background collector can run but check to see if the | |
2184 // foreground collector has done a collection while the | |
2185 // background collector was waiting to get the CGC_lock | |
2186 // above. If yes, break so that _foregroundGCShouldWait | |
2187 // is cleared before returning. | |
2188 if (_collectorState == Idling) { | |
2189 break; | |
2190 } | |
2191 } | |
2192 } | |
2193 | |
2194 assert(_foregroundGCShouldWait, "Foreground collector, if active, " | |
2195 "should be waiting"); | |
2196 | |
2197 switch (_collectorState) { | |
2198 case InitialMarking: | |
2199 { | |
2200 ReleaseForegroundGC x(this); | |
2201 stats().record_cms_begin(); | |
2202 | |
2203 VM_CMS_Initial_Mark initial_mark_op(this); | |
2204 VMThread::execute(&initial_mark_op); | |
2205 } | |
2206 // The collector state may be any legal state at this point | |
2207 // since the background collector may have yielded to the | |
2208 // foreground collector. | |
2209 break; | |
2210 case Marking: | |
2211 // initial marking in checkpointRootsInitialWork has been completed | |
2212 if (markFromRoots(true)) { // we were successful | |
2213 assert(_collectorState == Precleaning, "Collector state should " | |
2214 "have changed"); | |
2215 } else { | |
2216 assert(_foregroundGCIsActive, "Internal state inconsistency"); | |
2217 } | |
2218 break; | |
2219 case Precleaning: | |
2220 if (UseAdaptiveSizePolicy) { | |
2221 size_policy()->concurrent_precleaning_begin(); | |
2222 } | |
2223 // marking from roots in markFromRoots has been completed | |
2224 preclean(); | |
2225 if (UseAdaptiveSizePolicy) { | |
2226 size_policy()->concurrent_precleaning_end(); | |
2227 } | |
2228 assert(_collectorState == AbortablePreclean || | |
2229 _collectorState == FinalMarking, | |
2230 "Collector state should have changed"); | |
2231 break; | |
2232 case AbortablePreclean: | |
2233 if (UseAdaptiveSizePolicy) { | |
2234 size_policy()->concurrent_phases_resume(); | |
2235 } | |
2236 abortable_preclean(); | |
2237 if (UseAdaptiveSizePolicy) { | |
2238 size_policy()->concurrent_precleaning_end(); | |
2239 } | |
2240 assert(_collectorState == FinalMarking, "Collector state should " | |
2241 "have changed"); | |
2242 break; | |
2243 case FinalMarking: | |
2244 { | |
2245 ReleaseForegroundGC x(this); | |
2246 | |
2247 VM_CMS_Final_Remark final_remark_op(this); | |
2248 VMThread::execute(&final_remark_op); | |
2249 } | |
2250 assert(_foregroundGCShouldWait, "block post-condition"); | |
2251 break; | |
2252 case Sweeping: | |
2253 if (UseAdaptiveSizePolicy) { | |
2254 size_policy()->concurrent_sweeping_begin(); | |
2255 } | |
2256 // final marking in checkpointRootsFinal has been completed | |
2257 sweep(true); | |
2258 assert(_collectorState == Resizing, "Collector state change " | |
2259 "to Resizing must be done under the free_list_lock"); | |
2260 _full_gcs_since_conc_gc = 0; | |
2261 | |
2262 // Stop the timers for adaptive size policy for the concurrent phases | |
2263 if (UseAdaptiveSizePolicy) { | |
2264 size_policy()->concurrent_sweeping_end(); | |
2265 size_policy()->concurrent_phases_end(gch->gc_cause(), | |
2266 gch->prev_gen(_cmsGen)->capacity(), | |
2267 _cmsGen->free()); | |
2268 } | |
2269 | |
2270 case Resizing: { | |
2271 // Sweeping has been completed... | |
2272 // At this point the background collection has completed. | |
2273 // Don't move the call to compute_new_size() down | |
2274 // into code that might be executed if the background | |
2275 // collection was preempted. | |
2276 { | |
2277 ReleaseForegroundGC x(this); // unblock FG collection | |
2278 MutexLockerEx y(Heap_lock, Mutex::_no_safepoint_check_flag); | |
2279 CMSTokenSync z(true); // not strictly needed. | |
2280 if (_collectorState == Resizing) { | |
2281 compute_new_size(); | |
2282 _collectorState = Resetting; | |
2283 } else { | |
2284 assert(_collectorState == Idling, "The state should only change" | |
2285 " because the foreground collector has finished the collection"); | |
2286 } | |
2287 } | |
2288 break; | |
2289 } | |
2290 case Resetting: | |
2291 // CMS heap resizing has been completed | |
2292 reset(true); | |
2293 assert(_collectorState == Idling, "Collector state should " | |
2294 "have changed"); | |
2295 stats().record_cms_end(); | |
2296 // Don't move the concurrent_phases_end() and compute_new_size() | |
2297 // calls to here because a preempted background collection | |
2298 // has it's state set to "Resetting". | |
2299 break; | |
2300 case Idling: | |
2301 default: | |
2302 ShouldNotReachHere(); | |
2303 break; | |
2304 } | |
2305 if (TraceCMSState) { | |
2306 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d", | |
2307 Thread::current(), _collectorState); | |
2308 } | |
2309 assert(_foregroundGCShouldWait, "block post-condition"); | |
2310 } | |
2311 | |
2312 // Should this be in gc_epilogue? | |
2313 collector_policy()->counters()->update_counters(); | |
2314 | |
2315 { | |
2316 // Clear _foregroundGCShouldWait and, in the event that the | |
2317 // foreground collector is waiting, notify it, before | |
2318 // returning. | |
2319 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); | |
2320 _foregroundGCShouldWait = false; | |
2321 if (_foregroundGCIsActive) { | |
2322 CGC_lock->notify(); | |
2323 } | |
2324 assert(!ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
2325 "Possible deadlock"); | |
2326 } | |
2327 if (TraceCMSState) { | |
2328 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT | |
2329 " exiting collection CMS state %d", | |
2330 Thread::current(), _collectorState); | |
2331 } | |
2332 if (PrintGC && Verbose) { | |
2333 _cmsGen->print_heap_change(prev_used); | |
2334 } | |
2335 } | |
2336 | |
2337 void CMSCollector::collect_in_foreground(bool clear_all_soft_refs) { | |
2338 assert(_foregroundGCIsActive && !_foregroundGCShouldWait, | |
2339 "Foreground collector should be waiting, not executing"); | |
2340 assert(Thread::current()->is_VM_thread(), "A foreground collection" | |
2341 "may only be done by the VM Thread with the world stopped"); | |
2342 assert(ConcurrentMarkSweepThread::vm_thread_has_cms_token(), | |
2343 "VM thread should have CMS token"); | |
2344 | |
2345 NOT_PRODUCT(TraceTime t("CMS:MS (foreground) ", PrintGCDetails && Verbose, | |
2346 true, gclog_or_tty);) | |
2347 if (UseAdaptiveSizePolicy) { | |
2348 size_policy()->ms_collection_begin(); | |
2349 } | |
2350 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact); | |
2351 | |
2352 HandleMark hm; // Discard invalid handles created during verification | |
2353 | |
2354 if (VerifyBeforeGC && | |
2355 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { | |
2356 Universe::verify(true); | |
2357 } | |
2358 | |
2359 bool init_mark_was_synchronous = false; // until proven otherwise | |
2360 while (_collectorState != Idling) { | |
2361 if (TraceCMSState) { | |
2362 gclog_or_tty->print_cr("Thread " INTPTR_FORMAT " in CMS state %d", | |
2363 Thread::current(), _collectorState); | |
2364 } | |
2365 switch (_collectorState) { | |
2366 case InitialMarking: | |
2367 init_mark_was_synchronous = true; // fact to be exploited in re-mark | |
2368 checkpointRootsInitial(false); | |
2369 assert(_collectorState == Marking, "Collector state should have changed" | |
2370 " within checkpointRootsInitial()"); | |
2371 break; | |
2372 case Marking: | |
2373 // initial marking in checkpointRootsInitialWork has been completed | |
2374 if (VerifyDuringGC && | |
2375 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { | |
2376 gclog_or_tty->print("Verify before initial mark: "); | |
2377 Universe::verify(true); | |
2378 } | |
2379 { | |
2380 bool res = markFromRoots(false); | |
2381 assert(res && _collectorState == FinalMarking, "Collector state should " | |
2382 "have changed"); | |
2383 break; | |
2384 } | |
2385 case FinalMarking: | |
2386 if (VerifyDuringGC && | |
2387 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { | |
2388 gclog_or_tty->print("Verify before re-mark: "); | |
2389 Universe::verify(true); | |
2390 } | |
2391 checkpointRootsFinal(false, clear_all_soft_refs, | |
2392 init_mark_was_synchronous); | |
2393 assert(_collectorState == Sweeping, "Collector state should not " | |
2394 "have changed within checkpointRootsFinal()"); | |
2395 break; | |
2396 case Sweeping: | |
2397 // final marking in checkpointRootsFinal has been completed | |
2398 if (VerifyDuringGC && | |
2399 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { | |
2400 gclog_or_tty->print("Verify before sweep: "); | |
2401 Universe::verify(true); | |
2402 } | |
2403 sweep(false); | |
2404 assert(_collectorState == Resizing, "Incorrect state"); | |
2405 break; | |
2406 case Resizing: { | |
2407 // Sweeping has been completed; the actual resize in this case | |
2408 // is done separately; nothing to be done in this state. | |
2409 _collectorState = Resetting; | |
2410 break; | |
2411 } | |
2412 case Resetting: | |
2413 // The heap has been resized. | |
2414 if (VerifyDuringGC && | |
2415 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { | |
2416 gclog_or_tty->print("Verify before reset: "); | |
2417 Universe::verify(true); | |
2418 } | |
2419 reset(false); | |
2420 assert(_collectorState == Idling, "Collector state should " | |
2421 "have changed"); | |
2422 break; | |
2423 case Precleaning: | |
2424 case AbortablePreclean: | |
2425 // Elide the preclean phase | |
2426 _collectorState = FinalMarking; | |
2427 break; | |
2428 default: | |
2429 ShouldNotReachHere(); | |
2430 } | |
2431 if (TraceCMSState) { | |
2432 gclog_or_tty->print_cr(" Thread " INTPTR_FORMAT " done - next CMS state %d", | |
2433 Thread::current(), _collectorState); | |
2434 } | |
2435 } | |
2436 | |
2437 if (UseAdaptiveSizePolicy) { | |
2438 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
2439 size_policy()->ms_collection_end(gch->gc_cause()); | |
2440 } | |
2441 | |
2442 if (VerifyAfterGC && | |
2443 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { | |
2444 Universe::verify(true); | |
2445 } | |
2446 if (TraceCMSState) { | |
2447 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT | |
2448 " exiting collection CMS state %d", | |
2449 Thread::current(), _collectorState); | |
2450 } | |
2451 } | |
2452 | |
2453 bool CMSCollector::waitForForegroundGC() { | |
2454 bool res = false; | |
2455 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
2456 "CMS thread should have CMS token"); | |
2457 // Block the foreground collector until the | |
2458 // background collectors decides whether to | |
2459 // yield. | |
2460 MutexLockerEx x(CGC_lock, Mutex::_no_safepoint_check_flag); | |
2461 _foregroundGCShouldWait = true; | |
2462 if (_foregroundGCIsActive) { | |
2463 // The background collector yields to the | |
2464 // foreground collector and returns a value | |
2465 // indicating that it has yielded. The foreground | |
2466 // collector can proceed. | |
2467 res = true; | |
2468 _foregroundGCShouldWait = false; | |
2469 ConcurrentMarkSweepThread::clear_CMS_flag( | |
2470 ConcurrentMarkSweepThread::CMS_cms_has_token); | |
2471 ConcurrentMarkSweepThread::set_CMS_flag( | |
2472 ConcurrentMarkSweepThread::CMS_cms_wants_token); | |
2473 // Get a possibly blocked foreground thread going | |
2474 CGC_lock->notify(); | |
2475 if (TraceCMSState) { | |
2476 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " waiting at CMS state %d", | |
2477 Thread::current(), _collectorState); | |
2478 } | |
2479 while (_foregroundGCIsActive) { | |
2480 CGC_lock->wait(Mutex::_no_safepoint_check_flag); | |
2481 } | |
2482 ConcurrentMarkSweepThread::set_CMS_flag( | |
2483 ConcurrentMarkSweepThread::CMS_cms_has_token); | |
2484 ConcurrentMarkSweepThread::clear_CMS_flag( | |
2485 ConcurrentMarkSweepThread::CMS_cms_wants_token); | |
2486 } | |
2487 if (TraceCMSState) { | |
2488 gclog_or_tty->print_cr("CMS Thread " INTPTR_FORMAT " continuing at CMS state %d", | |
2489 Thread::current(), _collectorState); | |
2490 } | |
2491 return res; | |
2492 } | |
2493 | |
2494 // Because of the need to lock the free lists and other structures in | |
2495 // the collector, common to all the generations that the collector is | |
2496 // collecting, we need the gc_prologues of individual CMS generations | |
2497 // delegate to their collector. It may have been simpler had the | |
2498 // current infrastructure allowed one to call a prologue on a | |
2499 // collector. In the absence of that we have the generation's | |
2500 // prologue delegate to the collector, which delegates back | |
2501 // some "local" work to a worker method in the individual generations | |
2502 // that it's responsible for collecting, while itself doing any | |
2503 // work common to all generations it's responsible for. A similar | |
2504 // comment applies to the gc_epilogue()'s. | |
2505 // The role of the varaible _between_prologue_and_epilogue is to | |
2506 // enforce the invocation protocol. | |
2507 void CMSCollector::gc_prologue(bool full) { | |
2508 // Call gc_prologue_work() for each CMSGen and PermGen that | |
2509 // we are responsible for. | |
2510 | |
2511 // The following locking discipline assumes that we are only called | |
2512 // when the world is stopped. | |
2513 assert(SafepointSynchronize::is_at_safepoint(), "world is stopped assumption"); | |
2514 | |
2515 // The CMSCollector prologue must call the gc_prologues for the | |
2516 // "generations" (including PermGen if any) that it's responsible | |
2517 // for. | |
2518 | |
2519 assert( Thread::current()->is_VM_thread() | |
2520 || ( CMSScavengeBeforeRemark | |
2521 && Thread::current()->is_ConcurrentGC_thread()), | |
2522 "Incorrect thread type for prologue execution"); | |
2523 | |
2524 if (_between_prologue_and_epilogue) { | |
2525 // We have already been invoked; this is a gc_prologue delegation | |
2526 // from yet another CMS generation that we are responsible for, just | |
2527 // ignore it since all relevant work has already been done. | |
2528 return; | |
2529 } | |
2530 | |
2531 // set a bit saying prologue has been called; cleared in epilogue | |
2532 _between_prologue_and_epilogue = true; | |
2533 // Claim locks for common data structures, then call gc_prologue_work() | |
2534 // for each CMSGen and PermGen that we are responsible for. | |
2535 | |
2536 getFreelistLocks(); // gets free list locks on constituent spaces | |
2537 bitMapLock()->lock_without_safepoint_check(); | |
2538 | |
2539 // Should call gc_prologue_work() for all cms gens we are responsible for | |
2540 bool registerClosure = _collectorState >= Marking | |
2541 && _collectorState < Sweeping; | |
2542 ModUnionClosure* muc = ParallelGCThreads > 0 ? &_modUnionClosurePar | |
2543 : &_modUnionClosure; | |
2544 _cmsGen->gc_prologue_work(full, registerClosure, muc); | |
2545 _permGen->gc_prologue_work(full, registerClosure, muc); | |
2546 | |
2547 if (!full) { | |
2548 stats().record_gc0_begin(); | |
2549 } | |
2550 } | |
2551 | |
2552 void ConcurrentMarkSweepGeneration::gc_prologue(bool full) { | |
2553 // Delegate to CMScollector which knows how to coordinate between | |
2554 // this and any other CMS generations that it is responsible for | |
2555 // collecting. | |
2556 collector()->gc_prologue(full); | |
2557 } | |
2558 | |
2559 // This is a "private" interface for use by this generation's CMSCollector. | |
2560 // Not to be called directly by any other entity (for instance, | |
2561 // GenCollectedHeap, which calls the "public" gc_prologue method above). | |
2562 void ConcurrentMarkSweepGeneration::gc_prologue_work(bool full, | |
2563 bool registerClosure, ModUnionClosure* modUnionClosure) { | |
2564 assert(!incremental_collection_failed(), "Shouldn't be set yet"); | |
2565 assert(cmsSpace()->preconsumptionDirtyCardClosure() == NULL, | |
2566 "Should be NULL"); | |
2567 if (registerClosure) { | |
2568 cmsSpace()->setPreconsumptionDirtyCardClosure(modUnionClosure); | |
2569 } | |
2570 cmsSpace()->gc_prologue(); | |
2571 // Clear stat counters | |
2572 NOT_PRODUCT( | |
2573 assert(_numObjectsPromoted == 0, "check"); | |
2574 assert(_numWordsPromoted == 0, "check"); | |
2575 if (Verbose && PrintGC) { | |
2576 gclog_or_tty->print("Allocated "SIZE_FORMAT" objects, " | |
2577 SIZE_FORMAT" bytes concurrently", | |
2578 _numObjectsAllocated, _numWordsAllocated*sizeof(HeapWord)); | |
2579 } | |
2580 _numObjectsAllocated = 0; | |
2581 _numWordsAllocated = 0; | |
2582 ) | |
2583 } | |
2584 | |
2585 void CMSCollector::gc_epilogue(bool full) { | |
2586 // The following locking discipline assumes that we are only called | |
2587 // when the world is stopped. | |
2588 assert(SafepointSynchronize::is_at_safepoint(), | |
2589 "world is stopped assumption"); | |
2590 | |
2591 // Currently the CMS epilogue (see CompactibleFreeListSpace) merely checks | |
2592 // if linear allocation blocks need to be appropriately marked to allow the | |
2593 // the blocks to be parsable. We also check here whether we need to nudge the | |
2594 // CMS collector thread to start a new cycle (if it's not already active). | |
2595 assert( Thread::current()->is_VM_thread() | |
2596 || ( CMSScavengeBeforeRemark | |
2597 && Thread::current()->is_ConcurrentGC_thread()), | |
2598 "Incorrect thread type for epilogue execution"); | |
2599 | |
2600 if (!_between_prologue_and_epilogue) { | |
2601 // We have already been invoked; this is a gc_epilogue delegation | |
2602 // from yet another CMS generation that we are responsible for, just | |
2603 // ignore it since all relevant work has already been done. | |
2604 return; | |
2605 } | |
2606 assert(haveFreelistLocks(), "must have freelist locks"); | |
2607 assert_lock_strong(bitMapLock()); | |
2608 | |
2609 _cmsGen->gc_epilogue_work(full); | |
2610 _permGen->gc_epilogue_work(full); | |
2611 | |
2612 if (_collectorState == AbortablePreclean || _collectorState == Precleaning) { | |
2613 // in case sampling was not already enabled, enable it | |
2614 _start_sampling = true; | |
2615 } | |
2616 // reset _eden_chunk_array so sampling starts afresh | |
2617 _eden_chunk_index = 0; | |
2618 | |
2619 size_t cms_used = _cmsGen->cmsSpace()->used(); | |
2620 size_t perm_used = _permGen->cmsSpace()->used(); | |
2621 | |
2622 // update performance counters - this uses a special version of | |
2623 // update_counters() that allows the utilization to be passed as a | |
2624 // parameter, avoiding multiple calls to used(). | |
2625 // | |
2626 _cmsGen->update_counters(cms_used); | |
2627 _permGen->update_counters(perm_used); | |
2628 | |
2629 if (CMSIncrementalMode) { | |
2630 icms_update_allocation_limits(); | |
2631 } | |
2632 | |
2633 bitMapLock()->unlock(); | |
2634 releaseFreelistLocks(); | |
2635 | |
2636 _between_prologue_and_epilogue = false; // ready for next cycle | |
2637 } | |
2638 | |
2639 void ConcurrentMarkSweepGeneration::gc_epilogue(bool full) { | |
2640 collector()->gc_epilogue(full); | |
2641 | |
2642 // Also reset promotion tracking in par gc thread states. | |
2643 if (ParallelGCThreads > 0) { | |
2644 for (uint i = 0; i < ParallelGCThreads; i++) { | |
2645 _par_gc_thread_states[i]->promo.stopTrackingPromotions(); | |
2646 } | |
2647 } | |
2648 } | |
2649 | |
2650 void ConcurrentMarkSweepGeneration::gc_epilogue_work(bool full) { | |
2651 assert(!incremental_collection_failed(), "Should have been cleared"); | |
2652 cmsSpace()->setPreconsumptionDirtyCardClosure(NULL); | |
2653 cmsSpace()->gc_epilogue(); | |
2654 // Print stat counters | |
2655 NOT_PRODUCT( | |
2656 assert(_numObjectsAllocated == 0, "check"); | |
2657 assert(_numWordsAllocated == 0, "check"); | |
2658 if (Verbose && PrintGC) { | |
2659 gclog_or_tty->print("Promoted "SIZE_FORMAT" objects, " | |
2660 SIZE_FORMAT" bytes", | |
2661 _numObjectsPromoted, _numWordsPromoted*sizeof(HeapWord)); | |
2662 } | |
2663 _numObjectsPromoted = 0; | |
2664 _numWordsPromoted = 0; | |
2665 ) | |
2666 | |
2667 if (PrintGC && Verbose) { | |
2668 // Call down the chain in contiguous_available needs the freelistLock | |
2669 // so print this out before releasing the freeListLock. | |
2670 gclog_or_tty->print(" Contiguous available "SIZE_FORMAT" bytes ", | |
2671 contiguous_available()); | |
2672 } | |
2673 } | |
2674 | |
2675 #ifndef PRODUCT | |
2676 bool CMSCollector::have_cms_token() { | |
2677 Thread* thr = Thread::current(); | |
2678 if (thr->is_VM_thread()) { | |
2679 return ConcurrentMarkSweepThread::vm_thread_has_cms_token(); | |
2680 } else if (thr->is_ConcurrentGC_thread()) { | |
2681 return ConcurrentMarkSweepThread::cms_thread_has_cms_token(); | |
2682 } else if (thr->is_GC_task_thread()) { | |
2683 return ConcurrentMarkSweepThread::vm_thread_has_cms_token() && | |
2684 ParGCRareEvent_lock->owned_by_self(); | |
2685 } | |
2686 return false; | |
2687 } | |
2688 #endif | |
2689 | |
2690 // Check reachability of the given heap address in CMS generation, | |
2691 // treating all other generations as roots. | |
2692 bool CMSCollector::is_cms_reachable(HeapWord* addr) { | |
2693 // We could "guarantee" below, rather than assert, but i'll | |
2694 // leave these as "asserts" so that an adventurous debugger | |
2695 // could try this in the product build provided some subset of | |
2696 // the conditions were met, provided they were intersted in the | |
2697 // results and knew that the computation below wouldn't interfere | |
2698 // with other concurrent computations mutating the structures | |
2699 // being read or written. | |
2700 assert(SafepointSynchronize::is_at_safepoint(), | |
2701 "Else mutations in object graph will make answer suspect"); | |
2702 assert(have_cms_token(), "Should hold cms token"); | |
2703 assert(haveFreelistLocks(), "must hold free list locks"); | |
2704 assert_lock_strong(bitMapLock()); | |
2705 | |
2706 // Clear the marking bit map array before starting, but, just | |
2707 // for kicks, first report if the given address is already marked | |
2708 gclog_or_tty->print_cr("Start: Address 0x%x is%s marked", addr, | |
2709 _markBitMap.isMarked(addr) ? "" : " not"); | |
2710 | |
2711 if (verify_after_remark()) { | |
2712 MutexLockerEx x(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); | |
2713 bool result = verification_mark_bm()->isMarked(addr); | |
2714 gclog_or_tty->print_cr("TransitiveMark: Address 0x%x %s marked", addr, | |
2715 result ? "IS" : "is NOT"); | |
2716 return result; | |
2717 } else { | |
2718 gclog_or_tty->print_cr("Could not compute result"); | |
2719 return false; | |
2720 } | |
2721 } | |
2722 | |
2723 //////////////////////////////////////////////////////// | |
2724 // CMS Verification Support | |
2725 //////////////////////////////////////////////////////// | |
2726 // Following the remark phase, the following invariant | |
2727 // should hold -- each object in the CMS heap which is | |
2728 // marked in markBitMap() should be marked in the verification_mark_bm(). | |
2729 | |
2730 class VerifyMarkedClosure: public BitMapClosure { | |
2731 CMSBitMap* _marks; | |
2732 bool _failed; | |
2733 | |
2734 public: | |
2735 VerifyMarkedClosure(CMSBitMap* bm): _marks(bm), _failed(false) {} | |
2736 | |
2737 void do_bit(size_t offset) { | |
2738 HeapWord* addr = _marks->offsetToHeapWord(offset); | |
2739 if (!_marks->isMarked(addr)) { | |
2740 oop(addr)->print(); | |
2741 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr); | |
2742 _failed = true; | |
2743 } | |
2744 } | |
2745 | |
2746 bool failed() { return _failed; } | |
2747 }; | |
2748 | |
2749 bool CMSCollector::verify_after_remark() { | |
2750 gclog_or_tty->print(" [Verifying CMS Marking... "); | |
2751 MutexLockerEx ml(verification_mark_bm()->lock(), Mutex::_no_safepoint_check_flag); | |
2752 static bool init = false; | |
2753 | |
2754 assert(SafepointSynchronize::is_at_safepoint(), | |
2755 "Else mutations in object graph will make answer suspect"); | |
2756 assert(have_cms_token(), | |
2757 "Else there may be mutual interference in use of " | |
2758 " verification data structures"); | |
2759 assert(_collectorState > Marking && _collectorState <= Sweeping, | |
2760 "Else marking info checked here may be obsolete"); | |
2761 assert(haveFreelistLocks(), "must hold free list locks"); | |
2762 assert_lock_strong(bitMapLock()); | |
2763 | |
2764 | |
2765 // Allocate marking bit map if not already allocated | |
2766 if (!init) { // first time | |
2767 if (!verification_mark_bm()->allocate(_span)) { | |
2768 return false; | |
2769 } | |
2770 init = true; | |
2771 } | |
2772 | |
2773 assert(verification_mark_stack()->isEmpty(), "Should be empty"); | |
2774 | |
2775 // Turn off refs discovery -- so we will be tracing through refs. | |
2776 // This is as intended, because by this time | |
2777 // GC must already have cleared any refs that need to be cleared, | |
2778 // and traced those that need to be marked; moreover, | |
2779 // the marking done here is not going to intefere in any | |
2780 // way with the marking information used by GC. | |
2781 NoRefDiscovery no_discovery(ref_processor()); | |
2782 | |
2783 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) | |
2784 | |
2785 // Clear any marks from a previous round | |
2786 verification_mark_bm()->clear_all(); | |
2787 assert(verification_mark_stack()->isEmpty(), "markStack should be empty"); | |
2788 assert(overflow_list_is_empty(), "overflow list should be empty"); | |
2789 | |
2790 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
2791 gch->ensure_parsability(false); // fill TLABs, but no need to retire them | |
2792 // Update the saved marks which may affect the root scans. | |
2793 gch->save_marks(); | |
2794 | |
2795 if (CMSRemarkVerifyVariant == 1) { | |
2796 // In this first variant of verification, we complete | |
2797 // all marking, then check if the new marks-verctor is | |
2798 // a subset of the CMS marks-vector. | |
2799 verify_after_remark_work_1(); | |
2800 } else if (CMSRemarkVerifyVariant == 2) { | |
2801 // In this second variant of verification, we flag an error | |
2802 // (i.e. an object reachable in the new marks-vector not reachable | |
2803 // in the CMS marks-vector) immediately, also indicating the | |
2804 // identify of an object (A) that references the unmarked object (B) -- | |
2805 // presumably, a mutation to A failed to be picked up by preclean/remark? | |
2806 verify_after_remark_work_2(); | |
2807 } else { | |
2808 warning("Unrecognized value %d for CMSRemarkVerifyVariant", | |
2809 CMSRemarkVerifyVariant); | |
2810 } | |
2811 gclog_or_tty->print(" done] "); | |
2812 return true; | |
2813 } | |
2814 | |
2815 void CMSCollector::verify_after_remark_work_1() { | |
2816 ResourceMark rm; | |
2817 HandleMark hm; | |
2818 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
2819 | |
2820 // Mark from roots one level into CMS | |
2821 MarkRefsIntoClosure notOlder(_span, verification_mark_bm(), true /* nmethods */); | |
2822 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. | |
2823 | |
2824 gch->gen_process_strong_roots(_cmsGen->level(), | |
2825 true, // younger gens are roots | |
2826 true, // collecting perm gen | |
2827 SharedHeap::ScanningOption(roots_scanning_options()), | |
2828 NULL, ¬Older); | |
2829 | |
2830 // Now mark from the roots | |
2831 assert(_revisitStack.isEmpty(), "Should be empty"); | |
2832 MarkFromRootsClosure markFromRootsClosure(this, _span, | |
2833 verification_mark_bm(), verification_mark_stack(), &_revisitStack, | |
2834 false /* don't yield */, true /* verifying */); | |
2835 assert(_restart_addr == NULL, "Expected pre-condition"); | |
2836 verification_mark_bm()->iterate(&markFromRootsClosure); | |
2837 while (_restart_addr != NULL) { | |
2838 // Deal with stack overflow: by restarting at the indicated | |
2839 // address. | |
2840 HeapWord* ra = _restart_addr; | |
2841 markFromRootsClosure.reset(ra); | |
2842 _restart_addr = NULL; | |
2843 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); | |
2844 } | |
2845 assert(verification_mark_stack()->isEmpty(), "Should have been drained"); | |
2846 verify_work_stacks_empty(); | |
2847 // Should reset the revisit stack above, since no class tree | |
2848 // surgery is forthcoming. | |
2849 _revisitStack.reset(); // throwing away all contents | |
2850 | |
2851 // Marking completed -- now verify that each bit marked in | |
2852 // verification_mark_bm() is also marked in markBitMap(); flag all | |
2853 // errors by printing corresponding objects. | |
2854 VerifyMarkedClosure vcl(markBitMap()); | |
2855 verification_mark_bm()->iterate(&vcl); | |
2856 if (vcl.failed()) { | |
2857 gclog_or_tty->print("Verification failed"); | |
2858 Universe::heap()->print(); | |
2859 fatal(" ... aborting"); | |
2860 } | |
2861 } | |
2862 | |
2863 void CMSCollector::verify_after_remark_work_2() { | |
2864 ResourceMark rm; | |
2865 HandleMark hm; | |
2866 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
2867 | |
2868 // Mark from roots one level into CMS | |
2869 MarkRefsIntoVerifyClosure notOlder(_span, verification_mark_bm(), | |
2870 markBitMap(), true /* nmethods */); | |
2871 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. | |
2872 gch->gen_process_strong_roots(_cmsGen->level(), | |
2873 true, // younger gens are roots | |
2874 true, // collecting perm gen | |
2875 SharedHeap::ScanningOption(roots_scanning_options()), | |
2876 NULL, ¬Older); | |
2877 | |
2878 // Now mark from the roots | |
2879 assert(_revisitStack.isEmpty(), "Should be empty"); | |
2880 MarkFromRootsVerifyClosure markFromRootsClosure(this, _span, | |
2881 verification_mark_bm(), markBitMap(), verification_mark_stack()); | |
2882 assert(_restart_addr == NULL, "Expected pre-condition"); | |
2883 verification_mark_bm()->iterate(&markFromRootsClosure); | |
2884 while (_restart_addr != NULL) { | |
2885 // Deal with stack overflow: by restarting at the indicated | |
2886 // address. | |
2887 HeapWord* ra = _restart_addr; | |
2888 markFromRootsClosure.reset(ra); | |
2889 _restart_addr = NULL; | |
2890 verification_mark_bm()->iterate(&markFromRootsClosure, ra, _span.end()); | |
2891 } | |
2892 assert(verification_mark_stack()->isEmpty(), "Should have been drained"); | |
2893 verify_work_stacks_empty(); | |
2894 // Should reset the revisit stack above, since no class tree | |
2895 // surgery is forthcoming. | |
2896 _revisitStack.reset(); // throwing away all contents | |
2897 | |
2898 // Marking completed -- now verify that each bit marked in | |
2899 // verification_mark_bm() is also marked in markBitMap(); flag all | |
2900 // errors by printing corresponding objects. | |
2901 VerifyMarkedClosure vcl(markBitMap()); | |
2902 verification_mark_bm()->iterate(&vcl); | |
2903 assert(!vcl.failed(), "Else verification above should not have succeeded"); | |
2904 } | |
2905 | |
2906 void ConcurrentMarkSweepGeneration::save_marks() { | |
2907 // delegate to CMS space | |
2908 cmsSpace()->save_marks(); | |
2909 for (uint i = 0; i < ParallelGCThreads; i++) { | |
2910 _par_gc_thread_states[i]->promo.startTrackingPromotions(); | |
2911 } | |
2912 } | |
2913 | |
2914 bool ConcurrentMarkSweepGeneration::no_allocs_since_save_marks() { | |
2915 return cmsSpace()->no_allocs_since_save_marks(); | |
2916 } | |
2917 | |
2918 #define CMS_SINCE_SAVE_MARKS_DEFN(OopClosureType, nv_suffix) \ | |
2919 \ | |
2920 void ConcurrentMarkSweepGeneration:: \ | |
2921 oop_since_save_marks_iterate##nv_suffix(OopClosureType* cl) { \ | |
2922 cl->set_generation(this); \ | |
2923 cmsSpace()->oop_since_save_marks_iterate##nv_suffix(cl); \ | |
2924 cl->reset_generation(); \ | |
2925 save_marks(); \ | |
2926 } | |
2927 | |
2928 ALL_SINCE_SAVE_MARKS_CLOSURES(CMS_SINCE_SAVE_MARKS_DEFN) | |
2929 | |
2930 void | |
2931 ConcurrentMarkSweepGeneration::object_iterate_since_last_GC(ObjectClosure* blk) | |
2932 { | |
2933 // Not currently implemented; need to do the following. -- ysr. | |
2934 // dld -- I think that is used for some sort of allocation profiler. So it | |
2935 // really means the objects allocated by the mutator since the last | |
2936 // GC. We could potentially implement this cheaply by recording only | |
2937 // the direct allocations in a side data structure. | |
2938 // | |
2939 // I think we probably ought not to be required to support these | |
2940 // iterations at any arbitrary point; I think there ought to be some | |
2941 // call to enable/disable allocation profiling in a generation/space, | |
2942 // and the iterator ought to return the objects allocated in the | |
2943 // gen/space since the enable call, or the last iterator call (which | |
2944 // will probably be at a GC.) That way, for gens like CM&S that would | |
2945 // require some extra data structure to support this, we only pay the | |
2946 // cost when it's in use... | |
2947 cmsSpace()->object_iterate_since_last_GC(blk); | |
2948 } | |
2949 | |
2950 void | |
2951 ConcurrentMarkSweepGeneration::younger_refs_iterate(OopsInGenClosure* cl) { | |
2952 cl->set_generation(this); | |
2953 younger_refs_in_space_iterate(_cmsSpace, cl); | |
2954 cl->reset_generation(); | |
2955 } | |
2956 | |
2957 void | |
2958 ConcurrentMarkSweepGeneration::oop_iterate(MemRegion mr, OopClosure* cl) { | |
2959 if (freelistLock()->owned_by_self()) { | |
2960 Generation::oop_iterate(mr, cl); | |
2961 } else { | |
2962 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); | |
2963 Generation::oop_iterate(mr, cl); | |
2964 } | |
2965 } | |
2966 | |
2967 void | |
2968 ConcurrentMarkSweepGeneration::oop_iterate(OopClosure* cl) { | |
2969 if (freelistLock()->owned_by_self()) { | |
2970 Generation::oop_iterate(cl); | |
2971 } else { | |
2972 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); | |
2973 Generation::oop_iterate(cl); | |
2974 } | |
2975 } | |
2976 | |
2977 void | |
2978 ConcurrentMarkSweepGeneration::object_iterate(ObjectClosure* cl) { | |
2979 if (freelistLock()->owned_by_self()) { | |
2980 Generation::object_iterate(cl); | |
2981 } else { | |
2982 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); | |
2983 Generation::object_iterate(cl); | |
2984 } | |
2985 } | |
2986 | |
2987 void | |
2988 ConcurrentMarkSweepGeneration::pre_adjust_pointers() { | |
2989 } | |
2990 | |
2991 void | |
2992 ConcurrentMarkSweepGeneration::post_compact() { | |
2993 } | |
2994 | |
2995 void | |
2996 ConcurrentMarkSweepGeneration::prepare_for_verify() { | |
2997 // Fix the linear allocation blocks to look like free blocks. | |
2998 | |
2999 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those | |
3000 // are not called when the heap is verified during universe initialization and | |
3001 // at vm shutdown. | |
3002 if (freelistLock()->owned_by_self()) { | |
3003 cmsSpace()->prepare_for_verify(); | |
3004 } else { | |
3005 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); | |
3006 cmsSpace()->prepare_for_verify(); | |
3007 } | |
3008 } | |
3009 | |
3010 void | |
3011 ConcurrentMarkSweepGeneration::verify(bool allow_dirty /* ignored */) { | |
3012 // Locks are normally acquired/released in gc_prologue/gc_epilogue, but those | |
3013 // are not called when the heap is verified during universe initialization and | |
3014 // at vm shutdown. | |
3015 if (freelistLock()->owned_by_self()) { | |
3016 cmsSpace()->verify(false /* ignored */); | |
3017 } else { | |
3018 MutexLockerEx fll(freelistLock(), Mutex::_no_safepoint_check_flag); | |
3019 cmsSpace()->verify(false /* ignored */); | |
3020 } | |
3021 } | |
3022 | |
3023 void CMSCollector::verify(bool allow_dirty /* ignored */) { | |
3024 _cmsGen->verify(allow_dirty); | |
3025 _permGen->verify(allow_dirty); | |
3026 } | |
3027 | |
3028 #ifndef PRODUCT | |
3029 bool CMSCollector::overflow_list_is_empty() const { | |
3030 assert(_num_par_pushes >= 0, "Inconsistency"); | |
3031 if (_overflow_list == NULL) { | |
3032 assert(_num_par_pushes == 0, "Inconsistency"); | |
3033 } | |
3034 return _overflow_list == NULL; | |
3035 } | |
3036 | |
3037 // The methods verify_work_stacks_empty() and verify_overflow_empty() | |
3038 // merely consolidate assertion checks that appear to occur together frequently. | |
3039 void CMSCollector::verify_work_stacks_empty() const { | |
3040 assert(_markStack.isEmpty(), "Marking stack should be empty"); | |
3041 assert(overflow_list_is_empty(), "Overflow list should be empty"); | |
3042 } | |
3043 | |
3044 void CMSCollector::verify_overflow_empty() const { | |
3045 assert(overflow_list_is_empty(), "Overflow list should be empty"); | |
3046 assert(no_preserved_marks(), "No preserved marks"); | |
3047 } | |
3048 #endif // PRODUCT | |
3049 | |
3050 void CMSCollector::setup_cms_unloading_and_verification_state() { | |
3051 const bool should_verify = VerifyBeforeGC || VerifyAfterGC || VerifyDuringGC | |
3052 || VerifyBeforeExit; | |
3053 const int rso = SharedHeap::SO_Symbols | SharedHeap::SO_Strings | |
3054 | SharedHeap::SO_CodeCache; | |
3055 | |
3056 if (cms_should_unload_classes()) { // Should unload classes this cycle | |
3057 remove_root_scanning_option(rso); // Shrink the root set appropriately | |
3058 set_verifying(should_verify); // Set verification state for this cycle | |
3059 return; // Nothing else needs to be done at this time | |
3060 } | |
3061 | |
3062 // Not unloading classes this cycle | |
3063 assert(!cms_should_unload_classes(), "Inconsitency!"); | |
3064 if ((!verifying() || cms_unloaded_classes_last_cycle()) && should_verify) { | |
3065 // We were not verifying, or we _were_ unloading classes in the last cycle, | |
3066 // AND some verification options are enabled this cycle; in this case, | |
3067 // we must make sure that the deadness map is allocated if not already so, | |
3068 // and cleared (if already allocated previously -- | |
3069 // CMSBitMap::sizeInBits() is used to determine if it's allocated). | |
3070 if (perm_gen_verify_bit_map()->sizeInBits() == 0) { | |
3071 if (!perm_gen_verify_bit_map()->allocate(_permGen->reserved())) { | |
3072 warning("Failed to allocate permanent generation verification CMS Bit Map;\n" | |
3073 "permanent generation verification disabled"); | |
3074 return; // Note that we leave verification disabled, so we'll retry this | |
3075 // allocation next cycle. We _could_ remember this failure | |
3076 // and skip further attempts and permanently disable verification | |
3077 // attempts if that is considered more desirable. | |
3078 } | |
3079 assert(perm_gen_verify_bit_map()->covers(_permGen->reserved()), | |
3080 "_perm_gen_ver_bit_map inconsistency?"); | |
3081 } else { | |
3082 perm_gen_verify_bit_map()->clear_all(); | |
3083 } | |
3084 // Include symbols, strings and code cache elements to prevent their resurrection. | |
3085 add_root_scanning_option(rso); | |
3086 set_verifying(true); | |
3087 } else if (verifying() && !should_verify) { | |
3088 // We were verifying, but some verification flags got disabled. | |
3089 set_verifying(false); | |
3090 // Exclude symbols, strings and code cache elements from root scanning to | |
3091 // reduce IM and RM pauses. | |
3092 remove_root_scanning_option(rso); | |
3093 } | |
3094 } | |
3095 | |
3096 | |
3097 #ifndef PRODUCT | |
3098 HeapWord* CMSCollector::block_start(const void* p) const { | |
3099 const HeapWord* addr = (HeapWord*)p; | |
3100 if (_span.contains(p)) { | |
3101 if (_cmsGen->cmsSpace()->is_in_reserved(addr)) { | |
3102 return _cmsGen->cmsSpace()->block_start(p); | |
3103 } else { | |
3104 assert(_permGen->cmsSpace()->is_in_reserved(addr), | |
3105 "Inconsistent _span?"); | |
3106 return _permGen->cmsSpace()->block_start(p); | |
3107 } | |
3108 } | |
3109 return NULL; | |
3110 } | |
3111 #endif | |
3112 | |
3113 HeapWord* | |
3114 ConcurrentMarkSweepGeneration::expand_and_allocate(size_t word_size, | |
3115 bool tlab, | |
3116 bool parallel) { | |
3117 assert(!tlab, "Can't deal with TLAB allocation"); | |
3118 MutexLockerEx x(freelistLock(), Mutex::_no_safepoint_check_flag); | |
3119 expand(word_size*HeapWordSize, MinHeapDeltaBytes, | |
3120 CMSExpansionCause::_satisfy_allocation); | |
3121 if (GCExpandToAllocateDelayMillis > 0) { | |
3122 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); | |
3123 } | |
3124 size_t adj_word_sz = CompactibleFreeListSpace::adjustObjectSize(word_size); | |
3125 if (parallel) { | |
3126 return cmsSpace()->par_allocate(adj_word_sz); | |
3127 } else { | |
3128 return cmsSpace()->allocate(adj_word_sz); | |
3129 } | |
3130 } | |
3131 | |
3132 // YSR: All of this generation expansion/shrinking stuff is an exact copy of | |
3133 // OneContigSpaceCardGeneration, which makes me wonder if we should move this | |
3134 // to CardGeneration and share it... | |
3135 void ConcurrentMarkSweepGeneration::expand(size_t bytes, size_t expand_bytes, | |
3136 CMSExpansionCause::Cause cause) | |
3137 { | |
3138 assert_locked_or_safepoint(Heap_lock); | |
3139 | |
3140 size_t aligned_bytes = ReservedSpace::page_align_size_up(bytes); | |
3141 size_t aligned_expand_bytes = ReservedSpace::page_align_size_up(expand_bytes); | |
3142 bool success = false; | |
3143 if (aligned_expand_bytes > aligned_bytes) { | |
3144 success = grow_by(aligned_expand_bytes); | |
3145 } | |
3146 if (!success) { | |
3147 success = grow_by(aligned_bytes); | |
3148 } | |
3149 if (!success) { | |
3150 size_t remaining_bytes = _virtual_space.uncommitted_size(); | |
3151 if (remaining_bytes > 0) { | |
3152 success = grow_by(remaining_bytes); | |
3153 } | |
3154 } | |
3155 if (GC_locker::is_active()) { | |
3156 if (PrintGC && Verbose) { | |
3157 gclog_or_tty->print_cr("Garbage collection disabled, expanded heap instead"); | |
3158 } | |
3159 } | |
3160 // remember why we expanded; this information is used | |
3161 // by shouldConcurrentCollect() when making decisions on whether to start | |
3162 // a new CMS cycle. | |
3163 if (success) { | |
3164 set_expansion_cause(cause); | |
3165 if (PrintGCDetails && Verbose) { | |
3166 gclog_or_tty->print_cr("Expanded CMS gen for %s", | |
3167 CMSExpansionCause::to_string(cause)); | |
3168 } | |
3169 } | |
3170 } | |
3171 | |
3172 HeapWord* ConcurrentMarkSweepGeneration::expand_and_par_lab_allocate(CMSParGCThreadState* ps, size_t word_sz) { | |
3173 HeapWord* res = NULL; | |
3174 MutexLocker x(ParGCRareEvent_lock); | |
3175 while (true) { | |
3176 // Expansion by some other thread might make alloc OK now: | |
3177 res = ps->lab.alloc(word_sz); | |
3178 if (res != NULL) return res; | |
3179 // If there's not enough expansion space available, give up. | |
3180 if (_virtual_space.uncommitted_size() < (word_sz * HeapWordSize)) { | |
3181 return NULL; | |
3182 } | |
3183 // Otherwise, we try expansion. | |
3184 expand(word_sz*HeapWordSize, MinHeapDeltaBytes, | |
3185 CMSExpansionCause::_allocate_par_lab); | |
3186 // Now go around the loop and try alloc again; | |
3187 // A competing par_promote might beat us to the expansion space, | |
3188 // so we may go around the loop again if promotion fails agaion. | |
3189 if (GCExpandToAllocateDelayMillis > 0) { | |
3190 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); | |
3191 } | |
3192 } | |
3193 } | |
3194 | |
3195 | |
3196 bool ConcurrentMarkSweepGeneration::expand_and_ensure_spooling_space( | |
3197 PromotionInfo* promo) { | |
3198 MutexLocker x(ParGCRareEvent_lock); | |
3199 size_t refill_size_bytes = promo->refillSize() * HeapWordSize; | |
3200 while (true) { | |
3201 // Expansion by some other thread might make alloc OK now: | |
3202 if (promo->ensure_spooling_space()) { | |
3203 assert(promo->has_spooling_space(), | |
3204 "Post-condition of successful ensure_spooling_space()"); | |
3205 return true; | |
3206 } | |
3207 // If there's not enough expansion space available, give up. | |
3208 if (_virtual_space.uncommitted_size() < refill_size_bytes) { | |
3209 return false; | |
3210 } | |
3211 // Otherwise, we try expansion. | |
3212 expand(refill_size_bytes, MinHeapDeltaBytes, | |
3213 CMSExpansionCause::_allocate_par_spooling_space); | |
3214 // Now go around the loop and try alloc again; | |
3215 // A competing allocation might beat us to the expansion space, | |
3216 // so we may go around the loop again if allocation fails again. | |
3217 if (GCExpandToAllocateDelayMillis > 0) { | |
3218 os::sleep(Thread::current(), GCExpandToAllocateDelayMillis, false); | |
3219 } | |
3220 } | |
3221 } | |
3222 | |
3223 | |
3224 | |
3225 void ConcurrentMarkSweepGeneration::shrink(size_t bytes) { | |
3226 assert_locked_or_safepoint(Heap_lock); | |
3227 size_t size = ReservedSpace::page_align_size_down(bytes); | |
3228 if (size > 0) { | |
3229 shrink_by(size); | |
3230 } | |
3231 } | |
3232 | |
3233 bool ConcurrentMarkSweepGeneration::grow_by(size_t bytes) { | |
3234 assert_locked_or_safepoint(Heap_lock); | |
3235 bool result = _virtual_space.expand_by(bytes); | |
3236 if (result) { | |
3237 HeapWord* old_end = _cmsSpace->end(); | |
3238 size_t new_word_size = | |
3239 heap_word_size(_virtual_space.committed_size()); | |
3240 MemRegion mr(_cmsSpace->bottom(), new_word_size); | |
3241 _bts->resize(new_word_size); // resize the block offset shared array | |
3242 Universe::heap()->barrier_set()->resize_covered_region(mr); | |
3243 // Hmmmm... why doesn't CFLS::set_end verify locking? | |
3244 // This is quite ugly; FIX ME XXX | |
3245 _cmsSpace->assert_locked(); | |
3246 _cmsSpace->set_end((HeapWord*)_virtual_space.high()); | |
3247 | |
3248 // update the space and generation capacity counters | |
3249 if (UsePerfData) { | |
3250 _space_counters->update_capacity(); | |
3251 _gen_counters->update_all(); | |
3252 } | |
3253 | |
3254 if (Verbose && PrintGC) { | |
3255 size_t new_mem_size = _virtual_space.committed_size(); | |
3256 size_t old_mem_size = new_mem_size - bytes; | |
3257 gclog_or_tty->print_cr("Expanding %s from %ldK by %ldK to %ldK", | |
3258 name(), old_mem_size/K, bytes/K, new_mem_size/K); | |
3259 } | |
3260 } | |
3261 return result; | |
3262 } | |
3263 | |
3264 bool ConcurrentMarkSweepGeneration::grow_to_reserved() { | |
3265 assert_locked_or_safepoint(Heap_lock); | |
3266 bool success = true; | |
3267 const size_t remaining_bytes = _virtual_space.uncommitted_size(); | |
3268 if (remaining_bytes > 0) { | |
3269 success = grow_by(remaining_bytes); | |
3270 DEBUG_ONLY(if (!success) warning("grow to reserved failed");) | |
3271 } | |
3272 return success; | |
3273 } | |
3274 | |
3275 void ConcurrentMarkSweepGeneration::shrink_by(size_t bytes) { | |
3276 assert_locked_or_safepoint(Heap_lock); | |
3277 assert_lock_strong(freelistLock()); | |
3278 // XXX Fix when compaction is implemented. | |
3279 warning("Shrinking of CMS not yet implemented"); | |
3280 return; | |
3281 } | |
3282 | |
3283 | |
3284 // Simple ctor/dtor wrapper for accounting & timer chores around concurrent | |
3285 // phases. | |
3286 class CMSPhaseAccounting: public StackObj { | |
3287 public: | |
3288 CMSPhaseAccounting(CMSCollector *collector, | |
3289 const char *phase, | |
3290 bool print_cr = true); | |
3291 ~CMSPhaseAccounting(); | |
3292 | |
3293 private: | |
3294 CMSCollector *_collector; | |
3295 const char *_phase; | |
3296 elapsedTimer _wallclock; | |
3297 bool _print_cr; | |
3298 | |
3299 public: | |
3300 // Not MT-safe; so do not pass around these StackObj's | |
3301 // where they may be accessed by other threads. | |
3302 jlong wallclock_millis() { | |
3303 assert(_wallclock.is_active(), "Wall clock should not stop"); | |
3304 _wallclock.stop(); // to record time | |
3305 jlong ret = _wallclock.milliseconds(); | |
3306 _wallclock.start(); // restart | |
3307 return ret; | |
3308 } | |
3309 }; | |
3310 | |
3311 CMSPhaseAccounting::CMSPhaseAccounting(CMSCollector *collector, | |
3312 const char *phase, | |
3313 bool print_cr) : | |
3314 _collector(collector), _phase(phase), _print_cr(print_cr) { | |
3315 | |
3316 if (PrintCMSStatistics != 0) { | |
3317 _collector->resetYields(); | |
3318 } | |
3319 if (PrintGCDetails && PrintGCTimeStamps) { | |
3320 gclog_or_tty->date_stamp(PrintGCDateStamps); | |
3321 gclog_or_tty->stamp(); | |
3322 gclog_or_tty->print_cr(": [%s-concurrent-%s-start]", | |
3323 _collector->cmsGen()->short_name(), _phase); | |
3324 } | |
3325 _collector->resetTimer(); | |
3326 _wallclock.start(); | |
3327 _collector->startTimer(); | |
3328 } | |
3329 | |
3330 CMSPhaseAccounting::~CMSPhaseAccounting() { | |
3331 assert(_wallclock.is_active(), "Wall clock should not have stopped"); | |
3332 _collector->stopTimer(); | |
3333 _wallclock.stop(); | |
3334 if (PrintGCDetails) { | |
3335 gclog_or_tty->date_stamp(PrintGCDateStamps); | |
3336 if (PrintGCTimeStamps) { | |
3337 gclog_or_tty->stamp(); | |
3338 gclog_or_tty->print(": "); | |
3339 } | |
3340 gclog_or_tty->print("[%s-concurrent-%s: %3.3f/%3.3f secs]", | |
3341 _collector->cmsGen()->short_name(), | |
3342 _phase, _collector->timerValue(), _wallclock.seconds()); | |
3343 if (_print_cr) { | |
3344 gclog_or_tty->print_cr(""); | |
3345 } | |
3346 if (PrintCMSStatistics != 0) { | |
3347 gclog_or_tty->print_cr(" (CMS-concurrent-%s yielded %d times)", _phase, | |
3348 _collector->yields()); | |
3349 } | |
3350 } | |
3351 } | |
3352 | |
3353 // CMS work | |
3354 | |
3355 // Checkpoint the roots into this generation from outside | |
3356 // this generation. [Note this initial checkpoint need only | |
3357 // be approximate -- we'll do a catch up phase subsequently.] | |
3358 void CMSCollector::checkpointRootsInitial(bool asynch) { | |
3359 assert(_collectorState == InitialMarking, "Wrong collector state"); | |
3360 check_correct_thread_executing(); | |
3361 ReferenceProcessor* rp = ref_processor(); | |
3362 SpecializationStats::clear(); | |
3363 assert(_restart_addr == NULL, "Control point invariant"); | |
3364 if (asynch) { | |
3365 // acquire locks for subsequent manipulations | |
3366 MutexLockerEx x(bitMapLock(), | |
3367 Mutex::_no_safepoint_check_flag); | |
3368 checkpointRootsInitialWork(asynch); | |
3369 rp->verify_no_references_recorded(); | |
3370 rp->enable_discovery(); // enable ("weak") refs discovery | |
3371 _collectorState = Marking; | |
3372 } else { | |
3373 // (Weak) Refs discovery: this is controlled from genCollectedHeap::do_collection | |
3374 // which recognizes if we are a CMS generation, and doesn't try to turn on | |
3375 // discovery; verify that they aren't meddling. | |
3376 assert(!rp->discovery_is_atomic(), | |
3377 "incorrect setting of discovery predicate"); | |
3378 assert(!rp->discovery_enabled(), "genCollectedHeap shouldn't control " | |
3379 "ref discovery for this generation kind"); | |
3380 // already have locks | |
3381 checkpointRootsInitialWork(asynch); | |
3382 rp->enable_discovery(); // now enable ("weak") refs discovery | |
3383 _collectorState = Marking; | |
3384 } | |
3385 SpecializationStats::print(); | |
3386 } | |
3387 | |
3388 void CMSCollector::checkpointRootsInitialWork(bool asynch) { | |
3389 assert(SafepointSynchronize::is_at_safepoint(), "world should be stopped"); | |
3390 assert(_collectorState == InitialMarking, "just checking"); | |
3391 | |
3392 // If there has not been a GC[n-1] since last GC[n] cycle completed, | |
3393 // precede our marking with a collection of all | |
3394 // younger generations to keep floating garbage to a minimum. | |
3395 // XXX: we won't do this for now -- it's an optimization to be done later. | |
3396 | |
3397 // already have locks | |
3398 assert_lock_strong(bitMapLock()); | |
3399 assert(_markBitMap.isAllClear(), "was reset at end of previous cycle"); | |
3400 | |
3401 // Setup the verification and class unloading state for this | |
3402 // CMS collection cycle. | |
3403 setup_cms_unloading_and_verification_state(); | |
3404 | |
3405 NOT_PRODUCT(TraceTime t("\ncheckpointRootsInitialWork", | |
3406 PrintGCDetails && Verbose, true, gclog_or_tty);) | |
3407 if (UseAdaptiveSizePolicy) { | |
3408 size_policy()->checkpoint_roots_initial_begin(); | |
3409 } | |
3410 | |
3411 // Reset all the PLAB chunk arrays if necessary. | |
3412 if (_survivor_plab_array != NULL && !CMSPLABRecordAlways) { | |
3413 reset_survivor_plab_arrays(); | |
3414 } | |
3415 | |
3416 ResourceMark rm; | |
3417 HandleMark hm; | |
3418 | |
3419 FalseClosure falseClosure; | |
3420 // In the case of a synchronous collection, we will elide the | |
3421 // remark step, so it's important to catch all the nmethod oops | |
3422 // in this step; hence the last argument to the constrcutor below. | |
3423 MarkRefsIntoClosure notOlder(_span, &_markBitMap, !asynch /* nmethods */); | |
3424 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
3425 | |
3426 verify_work_stacks_empty(); | |
3427 verify_overflow_empty(); | |
3428 | |
3429 gch->ensure_parsability(false); // fill TLABs, but no need to retire them | |
3430 // Update the saved marks which may affect the root scans. | |
3431 gch->save_marks(); | |
3432 | |
3433 // weak reference processing has not started yet. | |
3434 ref_processor()->set_enqueuing_is_done(false); | |
3435 | |
3436 { | |
3437 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) | |
3438 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. | |
3439 gch->gen_process_strong_roots(_cmsGen->level(), | |
3440 true, // younger gens are roots | |
3441 true, // collecting perm gen | |
3442 SharedHeap::ScanningOption(roots_scanning_options()), | |
3443 NULL, ¬Older); | |
3444 } | |
3445 | |
3446 // Clear mod-union table; it will be dirtied in the prologue of | |
3447 // CMS generation per each younger generation collection. | |
3448 | |
3449 assert(_modUnionTable.isAllClear(), | |
3450 "Was cleared in most recent final checkpoint phase" | |
3451 " or no bits are set in the gc_prologue before the start of the next " | |
3452 "subsequent marking phase."); | |
3453 | |
3454 // Temporarily disabled, since pre/post-consumption closures don't | |
3455 // care about precleaned cards | |
3456 #if 0 | |
3457 { | |
3458 MemRegion mr = MemRegion((HeapWord*)_virtual_space.low(), | |
3459 (HeapWord*)_virtual_space.high()); | |
3460 _ct->ct_bs()->preclean_dirty_cards(mr); | |
3461 } | |
3462 #endif | |
3463 | |
3464 // Save the end of the used_region of the constituent generations | |
3465 // to be used to limit the extent of sweep in each generation. | |
3466 save_sweep_limits(); | |
3467 if (UseAdaptiveSizePolicy) { | |
3468 size_policy()->checkpoint_roots_initial_end(gch->gc_cause()); | |
3469 } | |
3470 verify_overflow_empty(); | |
3471 } | |
3472 | |
3473 bool CMSCollector::markFromRoots(bool asynch) { | |
3474 // we might be tempted to assert that: | |
3475 // assert(asynch == !SafepointSynchronize::is_at_safepoint(), | |
3476 // "inconsistent argument?"); | |
3477 // However that wouldn't be right, because it's possible that | |
3478 // a safepoint is indeed in progress as a younger generation | |
3479 // stop-the-world GC happens even as we mark in this generation. | |
3480 assert(_collectorState == Marking, "inconsistent state?"); | |
3481 check_correct_thread_executing(); | |
3482 verify_overflow_empty(); | |
3483 | |
3484 bool res; | |
3485 if (asynch) { | |
3486 | |
3487 // Start the timers for adaptive size policy for the concurrent phases | |
3488 // Do it here so that the foreground MS can use the concurrent | |
3489 // timer since a foreground MS might has the sweep done concurrently | |
3490 // or STW. | |
3491 if (UseAdaptiveSizePolicy) { | |
3492 size_policy()->concurrent_marking_begin(); | |
3493 } | |
3494 | |
3495 // Weak ref discovery note: We may be discovering weak | |
3496 // refs in this generation concurrent (but interleaved) with | |
3497 // weak ref discovery by a younger generation collector. | |
3498 | |
3499 CMSTokenSyncWithLocks ts(true, bitMapLock()); | |
3500 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); | |
3501 CMSPhaseAccounting pa(this, "mark", !PrintGCDetails); | |
3502 res = markFromRootsWork(asynch); | |
3503 if (res) { | |
3504 _collectorState = Precleaning; | |
3505 } else { // We failed and a foreground collection wants to take over | |
3506 assert(_foregroundGCIsActive, "internal state inconsistency"); | |
3507 assert(_restart_addr == NULL, "foreground will restart from scratch"); | |
3508 if (PrintGCDetails) { | |
3509 gclog_or_tty->print_cr("bailing out to foreground collection"); | |
3510 } | |
3511 } | |
3512 if (UseAdaptiveSizePolicy) { | |
3513 size_policy()->concurrent_marking_end(); | |
3514 } | |
3515 } else { | |
3516 assert(SafepointSynchronize::is_at_safepoint(), | |
3517 "inconsistent with asynch == false"); | |
3518 if (UseAdaptiveSizePolicy) { | |
3519 size_policy()->ms_collection_marking_begin(); | |
3520 } | |
3521 // already have locks | |
3522 res = markFromRootsWork(asynch); | |
3523 _collectorState = FinalMarking; | |
3524 if (UseAdaptiveSizePolicy) { | |
3525 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
3526 size_policy()->ms_collection_marking_end(gch->gc_cause()); | |
3527 } | |
3528 } | |
3529 verify_overflow_empty(); | |
3530 return res; | |
3531 } | |
3532 | |
3533 bool CMSCollector::markFromRootsWork(bool asynch) { | |
3534 // iterate over marked bits in bit map, doing a full scan and mark | |
3535 // from these roots using the following algorithm: | |
3536 // . if oop is to the right of the current scan pointer, | |
3537 // mark corresponding bit (we'll process it later) | |
3538 // . else (oop is to left of current scan pointer) | |
3539 // push oop on marking stack | |
3540 // . drain the marking stack | |
3541 | |
3542 // Note that when we do a marking step we need to hold the | |
3543 // bit map lock -- recall that direct allocation (by mutators) | |
3544 // and promotion (by younger generation collectors) is also | |
3545 // marking the bit map. [the so-called allocate live policy.] | |
3546 // Because the implementation of bit map marking is not | |
3547 // robust wrt simultaneous marking of bits in the same word, | |
3548 // we need to make sure that there is no such interference | |
3549 // between concurrent such updates. | |
3550 | |
3551 // already have locks | |
3552 assert_lock_strong(bitMapLock()); | |
3553 | |
3554 // Clear the revisit stack, just in case there are any | |
3555 // obsolete contents from a short-circuited previous CMS cycle. | |
3556 _revisitStack.reset(); | |
3557 verify_work_stacks_empty(); | |
3558 verify_overflow_empty(); | |
3559 assert(_revisitStack.isEmpty(), "tabula rasa"); | |
3560 | |
3561 bool result = false; | |
3562 if (CMSConcurrentMTEnabled && ParallelCMSThreads > 0) { | |
3563 result = do_marking_mt(asynch); | |
3564 } else { | |
3565 result = do_marking_st(asynch); | |
3566 } | |
3567 return result; | |
3568 } | |
3569 | |
3570 // Forward decl | |
3571 class CMSConcMarkingTask; | |
3572 | |
3573 class CMSConcMarkingTerminator: public ParallelTaskTerminator { | |
3574 CMSCollector* _collector; | |
3575 CMSConcMarkingTask* _task; | |
3576 bool _yield; | |
3577 protected: | |
3578 virtual void yield(); | |
3579 public: | |
3580 // "n_threads" is the number of threads to be terminated. | |
3581 // "queue_set" is a set of work queues of other threads. | |
3582 // "collector" is the CMS collector associated with this task terminator. | |
3583 // "yield" indicates whether we need the gang as a whole to yield. | |
3584 CMSConcMarkingTerminator(int n_threads, TaskQueueSetSuper* queue_set, | |
3585 CMSCollector* collector, bool yield) : | |
3586 ParallelTaskTerminator(n_threads, queue_set), | |
3587 _collector(collector), | |
3588 _yield(yield) { } | |
3589 | |
3590 void set_task(CMSConcMarkingTask* task) { | |
3591 _task = task; | |
3592 } | |
3593 }; | |
3594 | |
3595 // MT Concurrent Marking Task | |
3596 class CMSConcMarkingTask: public YieldingFlexibleGangTask { | |
3597 CMSCollector* _collector; | |
3598 YieldingFlexibleWorkGang* _workers; // the whole gang | |
3599 int _n_workers; // requested/desired # workers | |
3600 bool _asynch; | |
3601 bool _result; | |
3602 CompactibleFreeListSpace* _cms_space; | |
3603 CompactibleFreeListSpace* _perm_space; | |
3604 HeapWord* _global_finger; | |
3605 | |
3606 // Exposed here for yielding support | |
3607 Mutex* const _bit_map_lock; | |
3608 | |
3609 // The per thread work queues, available here for stealing | |
3610 OopTaskQueueSet* _task_queues; | |
3611 CMSConcMarkingTerminator _term; | |
3612 | |
3613 public: | |
3614 CMSConcMarkingTask(CMSCollector* collector, | |
3615 CompactibleFreeListSpace* cms_space, | |
3616 CompactibleFreeListSpace* perm_space, | |
3617 bool asynch, int n_workers, | |
3618 YieldingFlexibleWorkGang* workers, | |
3619 OopTaskQueueSet* task_queues): | |
3620 YieldingFlexibleGangTask("Concurrent marking done multi-threaded"), | |
3621 _collector(collector), | |
3622 _cms_space(cms_space), | |
3623 _perm_space(perm_space), | |
3624 _asynch(asynch), _n_workers(n_workers), _result(true), | |
3625 _workers(workers), _task_queues(task_queues), | |
3626 _term(n_workers, task_queues, _collector, asynch), | |
3627 _bit_map_lock(collector->bitMapLock()) | |
3628 { | |
3629 assert(n_workers <= workers->total_workers(), | |
3630 "Else termination won't work correctly today"); // XXX FIX ME! | |
3631 _requested_size = n_workers; | |
3632 _term.set_task(this); | |
3633 assert(_cms_space->bottom() < _perm_space->bottom(), | |
3634 "Finger incorrectly initialized below"); | |
3635 _global_finger = _cms_space->bottom(); | |
3636 } | |
3637 | |
3638 | |
3639 OopTaskQueueSet* task_queues() { return _task_queues; } | |
3640 | |
3641 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } | |
3642 | |
3643 HeapWord** global_finger_addr() { return &_global_finger; } | |
3644 | |
3645 CMSConcMarkingTerminator* terminator() { return &_term; } | |
3646 | |
3647 void work(int i); | |
3648 | |
3649 virtual void coordinator_yield(); // stuff done by coordinator | |
3650 bool result() { return _result; } | |
3651 | |
3652 void reset(HeapWord* ra) { | |
3653 _term.reset_for_reuse(); | |
3654 } | |
3655 | |
3656 static bool get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, | |
3657 OopTaskQueue* work_q); | |
3658 | |
3659 private: | |
3660 void do_scan_and_mark(int i, CompactibleFreeListSpace* sp); | |
3661 void do_work_steal(int i); | |
3662 void bump_global_finger(HeapWord* f); | |
3663 }; | |
3664 | |
3665 void CMSConcMarkingTerminator::yield() { | |
3666 if (ConcurrentMarkSweepThread::should_yield() && | |
3667 !_collector->foregroundGCIsActive() && | |
3668 _yield) { | |
3669 _task->yield(); | |
3670 } else { | |
3671 ParallelTaskTerminator::yield(); | |
3672 } | |
3673 } | |
3674 | |
3675 //////////////////////////////////////////////////////////////// | |
3676 // Concurrent Marking Algorithm Sketch | |
3677 //////////////////////////////////////////////////////////////// | |
3678 // Until all tasks exhausted (both spaces): | |
3679 // -- claim next available chunk | |
3680 // -- bump global finger via CAS | |
3681 // -- find first object that starts in this chunk | |
3682 // and start scanning bitmap from that position | |
3683 // -- scan marked objects for oops | |
3684 // -- CAS-mark target, and if successful: | |
3685 // . if target oop is above global finger (volatile read) | |
3686 // nothing to do | |
3687 // . if target oop is in chunk and above local finger | |
3688 // then nothing to do | |
3689 // . else push on work-queue | |
3690 // -- Deal with possible overflow issues: | |
3691 // . local work-queue overflow causes stuff to be pushed on | |
3692 // global (common) overflow queue | |
3693 // . always first empty local work queue | |
3694 // . then get a batch of oops from global work queue if any | |
3695 // . then do work stealing | |
3696 // -- When all tasks claimed (both spaces) | |
3697 // and local work queue empty, | |
3698 // then in a loop do: | |
3699 // . check global overflow stack; steal a batch of oops and trace | |
3700 // . try to steal from other threads oif GOS is empty | |
3701 // . if neither is available, offer termination | |
3702 // -- Terminate and return result | |
3703 // | |
3704 void CMSConcMarkingTask::work(int i) { | |
3705 elapsedTimer _timer; | |
3706 ResourceMark rm; | |
3707 HandleMark hm; | |
3708 | |
3709 DEBUG_ONLY(_collector->verify_overflow_empty();) | |
3710 | |
3711 // Before we begin work, our work queue should be empty | |
3712 assert(work_queue(i)->size() == 0, "Expected to be empty"); | |
3713 // Scan the bitmap covering _cms_space, tracing through grey objects. | |
3714 _timer.start(); | |
3715 do_scan_and_mark(i, _cms_space); | |
3716 _timer.stop(); | |
3717 if (PrintCMSStatistics != 0) { | |
3718 gclog_or_tty->print_cr("Finished cms space scanning in %dth thread: %3.3f sec", | |
3719 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers | |
3720 } | |
3721 | |
3722 // ... do the same for the _perm_space | |
3723 _timer.reset(); | |
3724 _timer.start(); | |
3725 do_scan_and_mark(i, _perm_space); | |
3726 _timer.stop(); | |
3727 if (PrintCMSStatistics != 0) { | |
3728 gclog_or_tty->print_cr("Finished perm space scanning in %dth thread: %3.3f sec", | |
3729 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers | |
3730 } | |
3731 | |
3732 // ... do work stealing | |
3733 _timer.reset(); | |
3734 _timer.start(); | |
3735 do_work_steal(i); | |
3736 _timer.stop(); | |
3737 if (PrintCMSStatistics != 0) { | |
3738 gclog_or_tty->print_cr("Finished work stealing in %dth thread: %3.3f sec", | |
3739 i, _timer.seconds()); // XXX: need xxx/xxx type of notation, two timers | |
3740 } | |
3741 assert(_collector->_markStack.isEmpty(), "Should have been emptied"); | |
3742 assert(work_queue(i)->size() == 0, "Should have been emptied"); | |
3743 // Note that under the current task protocol, the | |
3744 // following assertion is true even of the spaces | |
3745 // expanded since the completion of the concurrent | |
3746 // marking. XXX This will likely change under a strict | |
3747 // ABORT semantics. | |
3748 assert(_global_finger > _cms_space->end() && | |
3749 _global_finger >= _perm_space->end(), | |
3750 "All tasks have been completed"); | |
3751 DEBUG_ONLY(_collector->verify_overflow_empty();) | |
3752 } | |
3753 | |
3754 void CMSConcMarkingTask::bump_global_finger(HeapWord* f) { | |
3755 HeapWord* read = _global_finger; | |
3756 HeapWord* cur = read; | |
3757 while (f > read) { | |
3758 cur = read; | |
3759 read = (HeapWord*) Atomic::cmpxchg_ptr(f, &_global_finger, cur); | |
3760 if (cur == read) { | |
3761 // our cas succeeded | |
3762 assert(_global_finger >= f, "protocol consistency"); | |
3763 break; | |
3764 } | |
3765 } | |
3766 } | |
3767 | |
3768 // This is really inefficient, and should be redone by | |
3769 // using (not yet available) block-read and -write interfaces to the | |
3770 // stack and the work_queue. XXX FIX ME !!! | |
3771 bool CMSConcMarkingTask::get_work_from_overflow_stack(CMSMarkStack* ovflw_stk, | |
3772 OopTaskQueue* work_q) { | |
3773 // Fast lock-free check | |
3774 if (ovflw_stk->length() == 0) { | |
3775 return false; | |
3776 } | |
3777 assert(work_q->size() == 0, "Shouldn't steal"); | |
3778 MutexLockerEx ml(ovflw_stk->par_lock(), | |
3779 Mutex::_no_safepoint_check_flag); | |
3780 // Grab up to 1/4 the size of the work queue | |
3781 size_t num = MIN2((size_t)work_q->max_elems()/4, | |
3782 (size_t)ParGCDesiredObjsFromOverflowList); | |
3783 num = MIN2(num, ovflw_stk->length()); | |
3784 for (int i = (int) num; i > 0; i--) { | |
3785 oop cur = ovflw_stk->pop(); | |
3786 assert(cur != NULL, "Counted wrong?"); | |
3787 work_q->push(cur); | |
3788 } | |
3789 return num > 0; | |
3790 } | |
3791 | |
3792 void CMSConcMarkingTask::do_scan_and_mark(int i, CompactibleFreeListSpace* sp) { | |
3793 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); | |
3794 int n_tasks = pst->n_tasks(); | |
3795 // We allow that there may be no tasks to do here because | |
3796 // we are restarting after a stack overflow. | |
3797 assert(pst->valid() || n_tasks == 0, "Uninitializd use?"); | |
3798 int nth_task = 0; | |
3799 | |
3800 HeapWord* start = sp->bottom(); | |
3801 size_t chunk_size = sp->marking_task_size(); | |
3802 while (!pst->is_task_claimed(/* reference */ nth_task)) { | |
3803 // Having claimed the nth task in this space, | |
3804 // compute the chunk that it corresponds to: | |
3805 MemRegion span = MemRegion(start + nth_task*chunk_size, | |
3806 start + (nth_task+1)*chunk_size); | |
3807 // Try and bump the global finger via a CAS; | |
3808 // note that we need to do the global finger bump | |
3809 // _before_ taking the intersection below, because | |
3810 // the task corresponding to that region will be | |
3811 // deemed done even if the used_region() expands | |
3812 // because of allocation -- as it almost certainly will | |
3813 // during start-up while the threads yield in the | |
3814 // closure below. | |
3815 HeapWord* finger = span.end(); | |
3816 bump_global_finger(finger); // atomically | |
3817 // There are null tasks here corresponding to chunks | |
3818 // beyond the "top" address of the space. | |
3819 span = span.intersection(sp->used_region()); | |
3820 if (!span.is_empty()) { // Non-null task | |
3821 // We want to skip the first object because | |
3822 // the protocol is to scan any object in its entirety | |
3823 // that _starts_ in this span; a fortiori, any | |
3824 // object starting in an earlier span is scanned | |
3825 // as part of an earlier claimed task. | |
3826 // Below we use the "careful" version of block_start | |
3827 // so we do not try to navigate uninitialized objects. | |
3828 HeapWord* prev_obj = sp->block_start_careful(span.start()); | |
3829 // Below we use a variant of block_size that uses the | |
3830 // Printezis bits to avoid waiting for allocated | |
3831 // objects to become initialized/parsable. | |
3832 while (prev_obj < span.start()) { | |
3833 size_t sz = sp->block_size_no_stall(prev_obj, _collector); | |
3834 if (sz > 0) { | |
3835 prev_obj += sz; | |
3836 } else { | |
3837 // In this case we may end up doing a bit of redundant | |
3838 // scanning, but that appears unavoidable, short of | |
3839 // locking the free list locks; see bug 6324141. | |
3840 break; | |
3841 } | |
3842 } | |
3843 if (prev_obj < span.end()) { | |
3844 MemRegion my_span = MemRegion(prev_obj, span.end()); | |
3845 // Do the marking work within a non-empty span -- | |
3846 // the last argument to the constructor indicates whether the | |
3847 // iteration should be incremental with periodic yields. | |
3848 Par_MarkFromRootsClosure cl(this, _collector, my_span, | |
3849 &_collector->_markBitMap, | |
3850 work_queue(i), | |
3851 &_collector->_markStack, | |
3852 &_collector->_revisitStack, | |
3853 _asynch); | |
3854 _collector->_markBitMap.iterate(&cl, my_span.start(), my_span.end()); | |
3855 } // else nothing to do for this task | |
3856 } // else nothing to do for this task | |
3857 } | |
3858 // We'd be tempted to assert here that since there are no | |
3859 // more tasks left to claim in this space, the global_finger | |
3860 // must exceed space->top() and a fortiori space->end(). However, | |
3861 // that would not quite be correct because the bumping of | |
3862 // global_finger occurs strictly after the claiming of a task, | |
3863 // so by the time we reach here the global finger may not yet | |
3864 // have been bumped up by the thread that claimed the last | |
3865 // task. | |
3866 pst->all_tasks_completed(); | |
3867 } | |
3868 | |
3869 class Par_ConcMarkingClosure: public OopClosure { | |
3870 CMSCollector* _collector; | |
3871 MemRegion _span; | |
3872 CMSBitMap* _bit_map; | |
3873 CMSMarkStack* _overflow_stack; | |
3874 CMSMarkStack* _revisit_stack; // XXXXXX Check proper use | |
3875 OopTaskQueue* _work_queue; | |
3876 | |
3877 public: | |
3878 Par_ConcMarkingClosure(CMSCollector* collector, OopTaskQueue* work_queue, | |
3879 CMSBitMap* bit_map, CMSMarkStack* overflow_stack): | |
3880 _collector(collector), | |
3881 _span(_collector->_span), | |
3882 _work_queue(work_queue), | |
3883 _bit_map(bit_map), | |
3884 _overflow_stack(overflow_stack) { } // need to initialize revisit stack etc. | |
3885 | |
3886 void do_oop(oop* p); | |
3887 void trim_queue(size_t max); | |
3888 void handle_stack_overflow(HeapWord* lost); | |
3889 }; | |
3890 | |
3891 // Grey object rescan during work stealing phase -- | |
3892 // the salient assumption here is that stolen oops must | |
3893 // always be initialized, so we do not need to check for | |
3894 // uninitialized objects before scanning here. | |
3895 void Par_ConcMarkingClosure::do_oop(oop* p) { | |
3896 oop this_oop = *p; | |
3897 assert(this_oop->is_oop_or_null(), | |
3898 "expected an oop or NULL"); | |
3899 HeapWord* addr = (HeapWord*)this_oop; | |
3900 // Check if oop points into the CMS generation | |
3901 // and is not marked | |
3902 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { | |
3903 // a white object ... | |
3904 // If we manage to "claim" the object, by being the | |
3905 // first thread to mark it, then we push it on our | |
3906 // marking stack | |
3907 if (_bit_map->par_mark(addr)) { // ... now grey | |
3908 // push on work queue (grey set) | |
3909 bool simulate_overflow = false; | |
3910 NOT_PRODUCT( | |
3911 if (CMSMarkStackOverflowALot && | |
3912 _collector->simulate_overflow()) { | |
3913 // simulate a stack overflow | |
3914 simulate_overflow = true; | |
3915 } | |
3916 ) | |
3917 if (simulate_overflow || | |
3918 !(_work_queue->push(this_oop) || _overflow_stack->par_push(this_oop))) { | |
3919 // stack overflow | |
3920 if (PrintCMSStatistics != 0) { | |
3921 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " | |
3922 SIZE_FORMAT, _overflow_stack->capacity()); | |
3923 } | |
3924 // We cannot assert that the overflow stack is full because | |
3925 // it may have been emptied since. | |
3926 assert(simulate_overflow || | |
3927 _work_queue->size() == _work_queue->max_elems(), | |
3928 "Else push should have succeeded"); | |
3929 handle_stack_overflow(addr); | |
3930 } | |
3931 } // Else, some other thread got there first | |
3932 } | |
3933 } | |
3934 | |
3935 void Par_ConcMarkingClosure::trim_queue(size_t max) { | |
3936 while (_work_queue->size() > max) { | |
3937 oop new_oop; | |
3938 if (_work_queue->pop_local(new_oop)) { | |
3939 assert(new_oop->is_oop(), "Should be an oop"); | |
3940 assert(_bit_map->isMarked((HeapWord*)new_oop), "Grey object"); | |
3941 assert(_span.contains((HeapWord*)new_oop), "Not in span"); | |
3942 assert(new_oop->is_parsable(), "Should be parsable"); | |
3943 new_oop->oop_iterate(this); // do_oop() above | |
3944 } | |
3945 } | |
3946 } | |
3947 | |
3948 // Upon stack overflow, we discard (part of) the stack, | |
3949 // remembering the least address amongst those discarded | |
3950 // in CMSCollector's _restart_address. | |
3951 void Par_ConcMarkingClosure::handle_stack_overflow(HeapWord* lost) { | |
3952 // We need to do this under a mutex to prevent other | |
3953 // workers from interfering with the expansion below. | |
3954 MutexLockerEx ml(_overflow_stack->par_lock(), | |
3955 Mutex::_no_safepoint_check_flag); | |
3956 // Remember the least grey address discarded | |
3957 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); | |
3958 _collector->lower_restart_addr(ra); | |
3959 _overflow_stack->reset(); // discard stack contents | |
3960 _overflow_stack->expand(); // expand the stack if possible | |
3961 } | |
3962 | |
3963 | |
3964 void CMSConcMarkingTask::do_work_steal(int i) { | |
3965 OopTaskQueue* work_q = work_queue(i); | |
3966 oop obj_to_scan; | |
3967 CMSBitMap* bm = &(_collector->_markBitMap); | |
3968 CMSMarkStack* ovflw = &(_collector->_markStack); | |
3969 int* seed = _collector->hash_seed(i); | |
3970 Par_ConcMarkingClosure cl(_collector, work_q, bm, ovflw); | |
3971 while (true) { | |
3972 cl.trim_queue(0); | |
3973 assert(work_q->size() == 0, "Should have been emptied above"); | |
3974 if (get_work_from_overflow_stack(ovflw, work_q)) { | |
3975 // Can't assert below because the work obtained from the | |
3976 // overflow stack may already have been stolen from us. | |
3977 // assert(work_q->size() > 0, "Work from overflow stack"); | |
3978 continue; | |
3979 } else if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { | |
3980 assert(obj_to_scan->is_oop(), "Should be an oop"); | |
3981 assert(bm->isMarked((HeapWord*)obj_to_scan), "Grey object"); | |
3982 obj_to_scan->oop_iterate(&cl); | |
3983 } else if (terminator()->offer_termination()) { | |
3984 assert(work_q->size() == 0, "Impossible!"); | |
3985 break; | |
3986 } | |
3987 } | |
3988 } | |
3989 | |
3990 // This is run by the CMS (coordinator) thread. | |
3991 void CMSConcMarkingTask::coordinator_yield() { | |
3992 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
3993 "CMS thread should hold CMS token"); | |
3994 | |
3995 // First give up the locks, then yield, then re-lock | |
3996 // We should probably use a constructor/destructor idiom to | |
3997 // do this unlock/lock or modify the MutexUnlocker class to | |
3998 // serve our purpose. XXX | |
3999 assert_lock_strong(_bit_map_lock); | |
4000 _bit_map_lock->unlock(); | |
4001 ConcurrentMarkSweepThread::desynchronize(true); | |
4002 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
4003 _collector->stopTimer(); | |
4004 if (PrintCMSStatistics != 0) { | |
4005 _collector->incrementYields(); | |
4006 } | |
4007 _collector->icms_wait(); | |
4008 | |
4009 // It is possible for whichever thread initiated the yield request | |
4010 // not to get a chance to wake up and take the bitmap lock between | |
4011 // this thread releasing it and reacquiring it. So, while the | |
4012 // should_yield() flag is on, let's sleep for a bit to give the | |
4013 // other thread a chance to wake up. The limit imposed on the number | |
4014 // of iterations is defensive, to avoid any unforseen circumstances | |
4015 // putting us into an infinite loop. Since it's always been this | |
4016 // (coordinator_yield()) method that was observed to cause the | |
4017 // problem, we are using a parameter (CMSCoordinatorYieldSleepCount) | |
4018 // which is by default non-zero. For the other seven methods that | |
4019 // also perform the yield operation, as are using a different | |
4020 // parameter (CMSYieldSleepCount) which is by default zero. This way we | |
4021 // can enable the sleeping for those methods too, if necessary. | |
4022 // See 6442774. | |
4023 // | |
4024 // We really need to reconsider the synchronization between the GC | |
4025 // thread and the yield-requesting threads in the future and we | |
4026 // should really use wait/notify, which is the recommended | |
4027 // way of doing this type of interaction. Additionally, we should | |
4028 // consolidate the eight methods that do the yield operation and they | |
4029 // are almost identical into one for better maintenability and | |
4030 // readability. See 6445193. | |
4031 // | |
4032 // Tony 2006.06.29 | |
4033 for (unsigned i = 0; i < CMSCoordinatorYieldSleepCount && | |
4034 ConcurrentMarkSweepThread::should_yield() && | |
4035 !CMSCollector::foregroundGCIsActive(); ++i) { | |
4036 os::sleep(Thread::current(), 1, false); | |
4037 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
4038 } | |
4039 | |
4040 ConcurrentMarkSweepThread::synchronize(true); | |
4041 _bit_map_lock->lock_without_safepoint_check(); | |
4042 _collector->startTimer(); | |
4043 } | |
4044 | |
4045 bool CMSCollector::do_marking_mt(bool asynch) { | |
4046 assert(ParallelCMSThreads > 0 && conc_workers() != NULL, "precondition"); | |
4047 // In the future this would be determined ergonomically, based | |
4048 // on #cpu's, # active mutator threads (and load), and mutation rate. | |
4049 int num_workers = ParallelCMSThreads; | |
4050 | |
4051 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); | |
4052 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace(); | |
4053 | |
4054 CMSConcMarkingTask tsk(this, cms_space, perm_space, | |
4055 asynch, num_workers /* number requested XXX */, | |
4056 conc_workers(), task_queues()); | |
4057 | |
4058 // Since the actual number of workers we get may be different | |
4059 // from the number we requested above, do we need to do anything different | |
4060 // below? In particular, may be we need to subclass the SequantialSubTasksDone | |
4061 // class?? XXX | |
4062 cms_space ->initialize_sequential_subtasks_for_marking(num_workers); | |
4063 perm_space->initialize_sequential_subtasks_for_marking(num_workers); | |
4064 | |
4065 // Refs discovery is already non-atomic. | |
4066 assert(!ref_processor()->discovery_is_atomic(), "Should be non-atomic"); | |
4067 // Mutate the Refs discovery so it is MT during the | |
4068 // multi-threaded marking phase. | |
4069 ReferenceProcessorMTMutator mt(ref_processor(), num_workers > 1); | |
4070 | |
4071 conc_workers()->start_task(&tsk); | |
4072 while (tsk.yielded()) { | |
4073 tsk.coordinator_yield(); | |
4074 conc_workers()->continue_task(&tsk); | |
4075 } | |
4076 // If the task was aborted, _restart_addr will be non-NULL | |
4077 assert(tsk.completed() || _restart_addr != NULL, "Inconsistency"); | |
4078 while (_restart_addr != NULL) { | |
4079 // XXX For now we do not make use of ABORTED state and have not | |
4080 // yet implemented the right abort semantics (even in the original | |
4081 // single-threaded CMS case). That needs some more investigation | |
4082 // and is deferred for now; see CR# TBF. 07252005YSR. XXX | |
4083 assert(!CMSAbortSemantics || tsk.aborted(), "Inconsistency"); | |
4084 // If _restart_addr is non-NULL, a marking stack overflow | |
4085 // occured; we need to do a fresh marking iteration from the | |
4086 // indicated restart address. | |
4087 if (_foregroundGCIsActive && asynch) { | |
4088 // We may be running into repeated stack overflows, having | |
4089 // reached the limit of the stack size, while making very | |
4090 // slow forward progress. It may be best to bail out and | |
4091 // let the foreground collector do its job. | |
4092 // Clear _restart_addr, so that foreground GC | |
4093 // works from scratch. This avoids the headache of | |
4094 // a "rescan" which would otherwise be needed because | |
4095 // of the dirty mod union table & card table. | |
4096 _restart_addr = NULL; | |
4097 return false; | |
4098 } | |
4099 // Adjust the task to restart from _restart_addr | |
4100 tsk.reset(_restart_addr); | |
4101 cms_space ->initialize_sequential_subtasks_for_marking(num_workers, | |
4102 _restart_addr); | |
4103 perm_space->initialize_sequential_subtasks_for_marking(num_workers, | |
4104 _restart_addr); | |
4105 _restart_addr = NULL; | |
4106 // Get the workers going again | |
4107 conc_workers()->start_task(&tsk); | |
4108 while (tsk.yielded()) { | |
4109 tsk.coordinator_yield(); | |
4110 conc_workers()->continue_task(&tsk); | |
4111 } | |
4112 } | |
4113 assert(tsk.completed(), "Inconsistency"); | |
4114 assert(tsk.result() == true, "Inconsistency"); | |
4115 return true; | |
4116 } | |
4117 | |
4118 bool CMSCollector::do_marking_st(bool asynch) { | |
4119 ResourceMark rm; | |
4120 HandleMark hm; | |
4121 | |
4122 MarkFromRootsClosure markFromRootsClosure(this, _span, &_markBitMap, | |
4123 &_markStack, &_revisitStack, CMSYield && asynch); | |
4124 // the last argument to iterate indicates whether the iteration | |
4125 // should be incremental with periodic yields. | |
4126 _markBitMap.iterate(&markFromRootsClosure); | |
4127 // If _restart_addr is non-NULL, a marking stack overflow | |
4128 // occured; we need to do a fresh iteration from the | |
4129 // indicated restart address. | |
4130 while (_restart_addr != NULL) { | |
4131 if (_foregroundGCIsActive && asynch) { | |
4132 // We may be running into repeated stack overflows, having | |
4133 // reached the limit of the stack size, while making very | |
4134 // slow forward progress. It may be best to bail out and | |
4135 // let the foreground collector do its job. | |
4136 // Clear _restart_addr, so that foreground GC | |
4137 // works from scratch. This avoids the headache of | |
4138 // a "rescan" which would otherwise be needed because | |
4139 // of the dirty mod union table & card table. | |
4140 _restart_addr = NULL; | |
4141 return false; // indicating failure to complete marking | |
4142 } | |
4143 // Deal with stack overflow: | |
4144 // we restart marking from _restart_addr | |
4145 HeapWord* ra = _restart_addr; | |
4146 markFromRootsClosure.reset(ra); | |
4147 _restart_addr = NULL; | |
4148 _markBitMap.iterate(&markFromRootsClosure, ra, _span.end()); | |
4149 } | |
4150 return true; | |
4151 } | |
4152 | |
4153 void CMSCollector::preclean() { | |
4154 check_correct_thread_executing(); | |
4155 assert(Thread::current()->is_ConcurrentGC_thread(), "Wrong thread"); | |
4156 verify_work_stacks_empty(); | |
4157 verify_overflow_empty(); | |
4158 _abort_preclean = false; | |
4159 if (CMSPrecleaningEnabled) { | |
4160 _eden_chunk_index = 0; | |
4161 size_t used = get_eden_used(); | |
4162 size_t capacity = get_eden_capacity(); | |
4163 // Don't start sampling unless we will get sufficiently | |
4164 // many samples. | |
4165 if (used < (capacity/(CMSScheduleRemarkSamplingRatio * 100) | |
4166 * CMSScheduleRemarkEdenPenetration)) { | |
4167 _start_sampling = true; | |
4168 } else { | |
4169 _start_sampling = false; | |
4170 } | |
4171 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); | |
4172 CMSPhaseAccounting pa(this, "preclean", !PrintGCDetails); | |
4173 preclean_work(CMSPrecleanRefLists1, CMSPrecleanSurvivors1); | |
4174 } | |
4175 CMSTokenSync x(true); // is cms thread | |
4176 if (CMSPrecleaningEnabled) { | |
4177 sample_eden(); | |
4178 _collectorState = AbortablePreclean; | |
4179 } else { | |
4180 _collectorState = FinalMarking; | |
4181 } | |
4182 verify_work_stacks_empty(); | |
4183 verify_overflow_empty(); | |
4184 } | |
4185 | |
4186 // Try and schedule the remark such that young gen | |
4187 // occupancy is CMSScheduleRemarkEdenPenetration %. | |
4188 void CMSCollector::abortable_preclean() { | |
4189 check_correct_thread_executing(); | |
4190 assert(CMSPrecleaningEnabled, "Inconsistent control state"); | |
4191 assert(_collectorState == AbortablePreclean, "Inconsistent control state"); | |
4192 | |
4193 // If Eden's current occupancy is below this threshold, | |
4194 // immediately schedule the remark; else preclean | |
4195 // past the next scavenge in an effort to | |
4196 // schedule the pause as described avove. By choosing | |
4197 // CMSScheduleRemarkEdenSizeThreshold >= max eden size | |
4198 // we will never do an actual abortable preclean cycle. | |
4199 if (get_eden_used() > CMSScheduleRemarkEdenSizeThreshold) { | |
4200 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); | |
4201 CMSPhaseAccounting pa(this, "abortable-preclean", !PrintGCDetails); | |
4202 // We need more smarts in the abortable preclean | |
4203 // loop below to deal with cases where allocation | |
4204 // in young gen is very very slow, and our precleaning | |
4205 // is running a losing race against a horde of | |
4206 // mutators intent on flooding us with CMS updates | |
4207 // (dirty cards). | |
4208 // One, admittedly dumb, strategy is to give up | |
4209 // after a certain number of abortable precleaning loops | |
4210 // or after a certain maximum time. We want to make | |
4211 // this smarter in the next iteration. | |
4212 // XXX FIX ME!!! YSR | |
4213 size_t loops = 0, workdone = 0, cumworkdone = 0, waited = 0; | |
4214 while (!(should_abort_preclean() || | |
4215 ConcurrentMarkSweepThread::should_terminate())) { | |
4216 workdone = preclean_work(CMSPrecleanRefLists2, CMSPrecleanSurvivors2); | |
4217 cumworkdone += workdone; | |
4218 loops++; | |
4219 // Voluntarily terminate abortable preclean phase if we have | |
4220 // been at it for too long. | |
4221 if ((CMSMaxAbortablePrecleanLoops != 0) && | |
4222 loops >= CMSMaxAbortablePrecleanLoops) { | |
4223 if (PrintGCDetails) { | |
4224 gclog_or_tty->print(" CMS: abort preclean due to loops "); | |
4225 } | |
4226 break; | |
4227 } | |
4228 if (pa.wallclock_millis() > CMSMaxAbortablePrecleanTime) { | |
4229 if (PrintGCDetails) { | |
4230 gclog_or_tty->print(" CMS: abort preclean due to time "); | |
4231 } | |
4232 break; | |
4233 } | |
4234 // If we are doing little work each iteration, we should | |
4235 // take a short break. | |
4236 if (workdone < CMSAbortablePrecleanMinWorkPerIteration) { | |
4237 // Sleep for some time, waiting for work to accumulate | |
4238 stopTimer(); | |
4239 cmsThread()->wait_on_cms_lock(CMSAbortablePrecleanWaitMillis); | |
4240 startTimer(); | |
4241 waited++; | |
4242 } | |
4243 } | |
4244 if (PrintCMSStatistics > 0) { | |
4245 gclog_or_tty->print(" [%d iterations, %d waits, %d cards)] ", | |
4246 loops, waited, cumworkdone); | |
4247 } | |
4248 } | |
4249 CMSTokenSync x(true); // is cms thread | |
4250 if (_collectorState != Idling) { | |
4251 assert(_collectorState == AbortablePreclean, | |
4252 "Spontaneous state transition?"); | |
4253 _collectorState = FinalMarking; | |
4254 } // Else, a foreground collection completed this CMS cycle. | |
4255 return; | |
4256 } | |
4257 | |
4258 // Respond to an Eden sampling opportunity | |
4259 void CMSCollector::sample_eden() { | |
4260 // Make sure a young gc cannot sneak in between our | |
4261 // reading and recording of a sample. | |
4262 assert(Thread::current()->is_ConcurrentGC_thread(), | |
4263 "Only the cms thread may collect Eden samples"); | |
4264 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
4265 "Should collect samples while holding CMS token"); | |
4266 if (!_start_sampling) { | |
4267 return; | |
4268 } | |
4269 if (_eden_chunk_array) { | |
4270 if (_eden_chunk_index < _eden_chunk_capacity) { | |
4271 _eden_chunk_array[_eden_chunk_index] = *_top_addr; // take sample | |
4272 assert(_eden_chunk_array[_eden_chunk_index] <= *_end_addr, | |
4273 "Unexpected state of Eden"); | |
4274 // We'd like to check that what we just sampled is an oop-start address; | |
4275 // however, we cannot do that here since the object may not yet have been | |
4276 // initialized. So we'll instead do the check when we _use_ this sample | |
4277 // later. | |
4278 if (_eden_chunk_index == 0 || | |
4279 (pointer_delta(_eden_chunk_array[_eden_chunk_index], | |
4280 _eden_chunk_array[_eden_chunk_index-1]) | |
4281 >= CMSSamplingGrain)) { | |
4282 _eden_chunk_index++; // commit sample | |
4283 } | |
4284 } | |
4285 } | |
4286 if ((_collectorState == AbortablePreclean) && !_abort_preclean) { | |
4287 size_t used = get_eden_used(); | |
4288 size_t capacity = get_eden_capacity(); | |
4289 assert(used <= capacity, "Unexpected state of Eden"); | |
4290 if (used > (capacity/100 * CMSScheduleRemarkEdenPenetration)) { | |
4291 _abort_preclean = true; | |
4292 } | |
4293 } | |
4294 } | |
4295 | |
4296 | |
4297 size_t CMSCollector::preclean_work(bool clean_refs, bool clean_survivor) { | |
4298 assert(_collectorState == Precleaning || | |
4299 _collectorState == AbortablePreclean, "incorrect state"); | |
4300 ResourceMark rm; | |
4301 HandleMark hm; | |
4302 // Do one pass of scrubbing the discovered reference lists | |
4303 // to remove any reference objects with strongly-reachable | |
4304 // referents. | |
4305 if (clean_refs) { | |
4306 ReferenceProcessor* rp = ref_processor(); | |
4307 CMSPrecleanRefsYieldClosure yield_cl(this); | |
4308 assert(rp->span().equals(_span), "Spans should be equal"); | |
4309 CMSKeepAliveClosure keep_alive(this, _span, &_markBitMap, | |
4310 &_markStack); | |
4311 CMSDrainMarkingStackClosure complete_trace(this, | |
4312 _span, &_markBitMap, &_markStack, | |
4313 &keep_alive); | |
4314 | |
4315 // We don't want this step to interfere with a young | |
4316 // collection because we don't want to take CPU | |
4317 // or memory bandwidth away from the young GC threads | |
4318 // (which may be as many as there are CPUs). | |
4319 // Note that we don't need to protect ourselves from | |
4320 // interference with mutators because they can't | |
4321 // manipulate the discovered reference lists nor affect | |
4322 // the computed reachability of the referents, the | |
4323 // only properties manipulated by the precleaning | |
4324 // of these reference lists. | |
4325 stopTimer(); | |
4326 CMSTokenSyncWithLocks x(true /* is cms thread */, | |
4327 bitMapLock()); | |
4328 startTimer(); | |
4329 sample_eden(); | |
4330 // The following will yield to allow foreground | |
4331 // collection to proceed promptly. XXX YSR: | |
4332 // The code in this method may need further | |
4333 // tweaking for better performance and some restructuring | |
4334 // for cleaner interfaces. | |
4335 rp->preclean_discovered_references( | |
4336 rp->is_alive_non_header(), &keep_alive, &complete_trace, | |
4337 &yield_cl); | |
4338 } | |
4339 | |
4340 if (clean_survivor) { // preclean the active survivor space(s) | |
4341 assert(_young_gen->kind() == Generation::DefNew || | |
4342 _young_gen->kind() == Generation::ParNew || | |
4343 _young_gen->kind() == Generation::ASParNew, | |
4344 "incorrect type for cast"); | |
4345 DefNewGeneration* dng = (DefNewGeneration*)_young_gen; | |
4346 PushAndMarkClosure pam_cl(this, _span, ref_processor(), | |
4347 &_markBitMap, &_modUnionTable, | |
4348 &_markStack, &_revisitStack, | |
4349 true /* precleaning phase */); | |
4350 stopTimer(); | |
4351 CMSTokenSyncWithLocks ts(true /* is cms thread */, | |
4352 bitMapLock()); | |
4353 startTimer(); | |
4354 unsigned int before_count = | |
4355 GenCollectedHeap::heap()->total_collections(); | |
4356 SurvivorSpacePrecleanClosure | |
4357 sss_cl(this, _span, &_markBitMap, &_markStack, | |
4358 &pam_cl, before_count, CMSYield); | |
4359 dng->from()->object_iterate_careful(&sss_cl); | |
4360 dng->to()->object_iterate_careful(&sss_cl); | |
4361 } | |
4362 MarkRefsIntoAndScanClosure | |
4363 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable, | |
4364 &_markStack, &_revisitStack, this, CMSYield, | |
4365 true /* precleaning phase */); | |
4366 // CAUTION: The following closure has persistent state that may need to | |
4367 // be reset upon a decrease in the sequence of addresses it | |
4368 // processes. | |
4369 ScanMarkedObjectsAgainCarefullyClosure | |
4370 smoac_cl(this, _span, | |
4371 &_markBitMap, &_markStack, &_revisitStack, &mrias_cl, CMSYield); | |
4372 | |
4373 // Preclean dirty cards in ModUnionTable and CardTable using | |
4374 // appropriate convergence criterion; | |
4375 // repeat CMSPrecleanIter times unless we find that | |
4376 // we are losing. | |
4377 assert(CMSPrecleanIter < 10, "CMSPrecleanIter is too large"); | |
4378 assert(CMSPrecleanNumerator < CMSPrecleanDenominator, | |
4379 "Bad convergence multiplier"); | |
4380 assert(CMSPrecleanThreshold >= 100, | |
4381 "Unreasonably low CMSPrecleanThreshold"); | |
4382 | |
4383 size_t numIter, cumNumCards, lastNumCards, curNumCards; | |
4384 for (numIter = 0, cumNumCards = lastNumCards = curNumCards = 0; | |
4385 numIter < CMSPrecleanIter; | |
4386 numIter++, lastNumCards = curNumCards, cumNumCards += curNumCards) { | |
4387 curNumCards = preclean_mod_union_table(_cmsGen, &smoac_cl); | |
4388 if (CMSPermGenPrecleaningEnabled) { | |
4389 curNumCards += preclean_mod_union_table(_permGen, &smoac_cl); | |
4390 } | |
4391 if (Verbose && PrintGCDetails) { | |
4392 gclog_or_tty->print(" (modUnionTable: %d cards)", curNumCards); | |
4393 } | |
4394 // Either there are very few dirty cards, so re-mark | |
4395 // pause will be small anyway, or our pre-cleaning isn't | |
4396 // that much faster than the rate at which cards are being | |
4397 // dirtied, so we might as well stop and re-mark since | |
4398 // precleaning won't improve our re-mark time by much. | |
4399 if (curNumCards <= CMSPrecleanThreshold || | |
4400 (numIter > 0 && | |
4401 (curNumCards * CMSPrecleanDenominator > | |
4402 lastNumCards * CMSPrecleanNumerator))) { | |
4403 numIter++; | |
4404 cumNumCards += curNumCards; | |
4405 break; | |
4406 } | |
4407 } | |
4408 curNumCards = preclean_card_table(_cmsGen, &smoac_cl); | |
4409 if (CMSPermGenPrecleaningEnabled) { | |
4410 curNumCards += preclean_card_table(_permGen, &smoac_cl); | |
4411 } | |
4412 cumNumCards += curNumCards; | |
4413 if (PrintGCDetails && PrintCMSStatistics != 0) { | |
4414 gclog_or_tty->print_cr(" (cardTable: %d cards, re-scanned %d cards, %d iterations)", | |
4415 curNumCards, cumNumCards, numIter); | |
4416 } | |
4417 return cumNumCards; // as a measure of useful work done | |
4418 } | |
4419 | |
4420 // PRECLEANING NOTES: | |
4421 // Precleaning involves: | |
4422 // . reading the bits of the modUnionTable and clearing the set bits. | |
4423 // . For the cards corresponding to the set bits, we scan the | |
4424 // objects on those cards. This means we need the free_list_lock | |
4425 // so that we can safely iterate over the CMS space when scanning | |
4426 // for oops. | |
4427 // . When we scan the objects, we'll be both reading and setting | |
4428 // marks in the marking bit map, so we'll need the marking bit map. | |
4429 // . For protecting _collector_state transitions, we take the CGC_lock. | |
4430 // Note that any races in the reading of of card table entries by the | |
4431 // CMS thread on the one hand and the clearing of those entries by the | |
4432 // VM thread or the setting of those entries by the mutator threads on the | |
4433 // other are quite benign. However, for efficiency it makes sense to keep | |
4434 // the VM thread from racing with the CMS thread while the latter is | |
4435 // dirty card info to the modUnionTable. We therefore also use the | |
4436 // CGC_lock to protect the reading of the card table and the mod union | |
4437 // table by the CM thread. | |
4438 // . We run concurrently with mutator updates, so scanning | |
4439 // needs to be done carefully -- we should not try to scan | |
4440 // potentially uninitialized objects. | |
4441 // | |
4442 // Locking strategy: While holding the CGC_lock, we scan over and | |
4443 // reset a maximal dirty range of the mod union / card tables, then lock | |
4444 // the free_list_lock and bitmap lock to do a full marking, then | |
4445 // release these locks; and repeat the cycle. This allows for a | |
4446 // certain amount of fairness in the sharing of these locks between | |
4447 // the CMS collector on the one hand, and the VM thread and the | |
4448 // mutators on the other. | |
4449 | |
4450 // NOTE: preclean_mod_union_table() and preclean_card_table() | |
4451 // further below are largely identical; if you need to modify | |
4452 // one of these methods, please check the other method too. | |
4453 | |
4454 size_t CMSCollector::preclean_mod_union_table( | |
4455 ConcurrentMarkSweepGeneration* gen, | |
4456 ScanMarkedObjectsAgainCarefullyClosure* cl) { | |
4457 verify_work_stacks_empty(); | |
4458 verify_overflow_empty(); | |
4459 | |
4460 // strategy: starting with the first card, accumulate contiguous | |
4461 // ranges of dirty cards; clear these cards, then scan the region | |
4462 // covered by these cards. | |
4463 | |
4464 // Since all of the MUT is committed ahead, we can just use | |
4465 // that, in case the generations expand while we are precleaning. | |
4466 // It might also be fine to just use the committed part of the | |
4467 // generation, but we might potentially miss cards when the | |
4468 // generation is rapidly expanding while we are in the midst | |
4469 // of precleaning. | |
4470 HeapWord* startAddr = gen->reserved().start(); | |
4471 HeapWord* endAddr = gen->reserved().end(); | |
4472 | |
4473 cl->setFreelistLock(gen->freelistLock()); // needed for yielding | |
4474 | |
4475 size_t numDirtyCards, cumNumDirtyCards; | |
4476 HeapWord *nextAddr, *lastAddr; | |
4477 for (cumNumDirtyCards = numDirtyCards = 0, | |
4478 nextAddr = lastAddr = startAddr; | |
4479 nextAddr < endAddr; | |
4480 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { | |
4481 | |
4482 ResourceMark rm; | |
4483 HandleMark hm; | |
4484 | |
4485 MemRegion dirtyRegion; | |
4486 { | |
4487 stopTimer(); | |
4488 CMSTokenSync ts(true); | |
4489 startTimer(); | |
4490 sample_eden(); | |
4491 // Get dirty region starting at nextOffset (inclusive), | |
4492 // simultaneously clearing it. | |
4493 dirtyRegion = | |
4494 _modUnionTable.getAndClearMarkedRegion(nextAddr, endAddr); | |
4495 assert(dirtyRegion.start() >= nextAddr, | |
4496 "returned region inconsistent?"); | |
4497 } | |
4498 // Remember where the next search should begin. | |
4499 // The returned region (if non-empty) is a right open interval, | |
4500 // so lastOffset is obtained from the right end of that | |
4501 // interval. | |
4502 lastAddr = dirtyRegion.end(); | |
4503 // Should do something more transparent and less hacky XXX | |
4504 numDirtyCards = | |
4505 _modUnionTable.heapWordDiffToOffsetDiff(dirtyRegion.word_size()); | |
4506 | |
4507 // We'll scan the cards in the dirty region (with periodic | |
4508 // yields for foreground GC as needed). | |
4509 if (!dirtyRegion.is_empty()) { | |
4510 assert(numDirtyCards > 0, "consistency check"); | |
4511 HeapWord* stop_point = NULL; | |
4512 { | |
4513 stopTimer(); | |
4514 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), | |
4515 bitMapLock()); | |
4516 startTimer(); | |
4517 verify_work_stacks_empty(); | |
4518 verify_overflow_empty(); | |
4519 sample_eden(); | |
4520 stop_point = | |
4521 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); | |
4522 } | |
4523 if (stop_point != NULL) { | |
4524 // The careful iteration stopped early either because it found an | |
4525 // uninitialized object, or because we were in the midst of an | |
4526 // "abortable preclean", which should now be aborted. Redirty | |
4527 // the bits corresponding to the partially-scanned or unscanned | |
4528 // cards. We'll either restart at the next block boundary or | |
4529 // abort the preclean. | |
4530 assert((CMSPermGenPrecleaningEnabled && (gen == _permGen)) || | |
4531 (_collectorState == AbortablePreclean && should_abort_preclean()), | |
4532 "Unparsable objects should only be in perm gen."); | |
4533 | |
4534 stopTimer(); | |
4535 CMSTokenSyncWithLocks ts(true, bitMapLock()); | |
4536 startTimer(); | |
4537 _modUnionTable.mark_range(MemRegion(stop_point, dirtyRegion.end())); | |
4538 if (should_abort_preclean()) { | |
4539 break; // out of preclean loop | |
4540 } else { | |
4541 // Compute the next address at which preclean should pick up; | |
4542 // might need bitMapLock in order to read P-bits. | |
4543 lastAddr = next_card_start_after_block(stop_point); | |
4544 } | |
4545 } | |
4546 } else { | |
4547 assert(lastAddr == endAddr, "consistency check"); | |
4548 assert(numDirtyCards == 0, "consistency check"); | |
4549 break; | |
4550 } | |
4551 } | |
4552 verify_work_stacks_empty(); | |
4553 verify_overflow_empty(); | |
4554 return cumNumDirtyCards; | |
4555 } | |
4556 | |
4557 // NOTE: preclean_mod_union_table() above and preclean_card_table() | |
4558 // below are largely identical; if you need to modify | |
4559 // one of these methods, please check the other method too. | |
4560 | |
4561 size_t CMSCollector::preclean_card_table(ConcurrentMarkSweepGeneration* gen, | |
4562 ScanMarkedObjectsAgainCarefullyClosure* cl) { | |
4563 // strategy: it's similar to precleamModUnionTable above, in that | |
4564 // we accumulate contiguous ranges of dirty cards, mark these cards | |
4565 // precleaned, then scan the region covered by these cards. | |
4566 HeapWord* endAddr = (HeapWord*)(gen->_virtual_space.high()); | |
4567 HeapWord* startAddr = (HeapWord*)(gen->_virtual_space.low()); | |
4568 | |
4569 cl->setFreelistLock(gen->freelistLock()); // needed for yielding | |
4570 | |
4571 size_t numDirtyCards, cumNumDirtyCards; | |
4572 HeapWord *lastAddr, *nextAddr; | |
4573 | |
4574 for (cumNumDirtyCards = numDirtyCards = 0, | |
4575 nextAddr = lastAddr = startAddr; | |
4576 nextAddr < endAddr; | |
4577 nextAddr = lastAddr, cumNumDirtyCards += numDirtyCards) { | |
4578 | |
4579 ResourceMark rm; | |
4580 HandleMark hm; | |
4581 | |
4582 MemRegion dirtyRegion; | |
4583 { | |
4584 // See comments in "Precleaning notes" above on why we | |
4585 // do this locking. XXX Could the locking overheads be | |
4586 // too high when dirty cards are sparse? [I don't think so.] | |
4587 stopTimer(); | |
4588 CMSTokenSync x(true); // is cms thread | |
4589 startTimer(); | |
4590 sample_eden(); | |
4591 // Get and clear dirty region from card table | |
4592 dirtyRegion = _ct->ct_bs()->dirty_card_range_after_preclean( | |
4593 MemRegion(nextAddr, endAddr)); | |
4594 assert(dirtyRegion.start() >= nextAddr, | |
4595 "returned region inconsistent?"); | |
4596 } | |
4597 lastAddr = dirtyRegion.end(); | |
4598 numDirtyCards = | |
4599 dirtyRegion.word_size()/CardTableModRefBS::card_size_in_words; | |
4600 | |
4601 if (!dirtyRegion.is_empty()) { | |
4602 stopTimer(); | |
4603 CMSTokenSyncWithLocks ts(true, gen->freelistLock(), bitMapLock()); | |
4604 startTimer(); | |
4605 sample_eden(); | |
4606 verify_work_stacks_empty(); | |
4607 verify_overflow_empty(); | |
4608 HeapWord* stop_point = | |
4609 gen->cmsSpace()->object_iterate_careful_m(dirtyRegion, cl); | |
4610 if (stop_point != NULL) { | |
4611 // The careful iteration stopped early because it found an | |
4612 // uninitialized object. Redirty the bits corresponding to the | |
4613 // partially-scanned or unscanned cards, and start again at the | |
4614 // next block boundary. | |
4615 assert(CMSPermGenPrecleaningEnabled || | |
4616 (_collectorState == AbortablePreclean && should_abort_preclean()), | |
4617 "Unparsable objects should only be in perm gen."); | |
4618 _ct->ct_bs()->invalidate(MemRegion(stop_point, dirtyRegion.end())); | |
4619 if (should_abort_preclean()) { | |
4620 break; // out of preclean loop | |
4621 } else { | |
4622 // Compute the next address at which preclean should pick up. | |
4623 lastAddr = next_card_start_after_block(stop_point); | |
4624 } | |
4625 } | |
4626 } else { | |
4627 break; | |
4628 } | |
4629 } | |
4630 verify_work_stacks_empty(); | |
4631 verify_overflow_empty(); | |
4632 return cumNumDirtyCards; | |
4633 } | |
4634 | |
4635 void CMSCollector::checkpointRootsFinal(bool asynch, | |
4636 bool clear_all_soft_refs, bool init_mark_was_synchronous) { | |
4637 assert(_collectorState == FinalMarking, "incorrect state transition?"); | |
4638 check_correct_thread_executing(); | |
4639 // world is stopped at this checkpoint | |
4640 assert(SafepointSynchronize::is_at_safepoint(), | |
4641 "world should be stopped"); | |
4642 verify_work_stacks_empty(); | |
4643 verify_overflow_empty(); | |
4644 | |
4645 SpecializationStats::clear(); | |
4646 if (PrintGCDetails) { | |
4647 gclog_or_tty->print("[YG occupancy: "SIZE_FORMAT" K ("SIZE_FORMAT" K)]", | |
4648 _young_gen->used() / K, | |
4649 _young_gen->capacity() / K); | |
4650 } | |
4651 if (asynch) { | |
4652 if (CMSScavengeBeforeRemark) { | |
4653 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
4654 // Temporarily set flag to false, GCH->do_collection will | |
4655 // expect it to be false and set to true | |
4656 FlagSetting fl(gch->_is_gc_active, false); | |
4657 NOT_PRODUCT(TraceTime t("Scavenge-Before-Remark", | |
4658 PrintGCDetails && Verbose, true, gclog_or_tty);) | |
4659 int level = _cmsGen->level() - 1; | |
4660 if (level >= 0) { | |
4661 gch->do_collection(true, // full (i.e. force, see below) | |
4662 false, // !clear_all_soft_refs | |
4663 0, // size | |
4664 false, // is_tlab | |
4665 level // max_level | |
4666 ); | |
4667 } | |
4668 } | |
4669 FreelistLocker x(this); | |
4670 MutexLockerEx y(bitMapLock(), | |
4671 Mutex::_no_safepoint_check_flag); | |
4672 assert(!init_mark_was_synchronous, "but that's impossible!"); | |
4673 checkpointRootsFinalWork(asynch, clear_all_soft_refs, false); | |
4674 } else { | |
4675 // already have all the locks | |
4676 checkpointRootsFinalWork(asynch, clear_all_soft_refs, | |
4677 init_mark_was_synchronous); | |
4678 } | |
4679 verify_work_stacks_empty(); | |
4680 verify_overflow_empty(); | |
4681 SpecializationStats::print(); | |
4682 } | |
4683 | |
4684 void CMSCollector::checkpointRootsFinalWork(bool asynch, | |
4685 bool clear_all_soft_refs, bool init_mark_was_synchronous) { | |
4686 | |
4687 NOT_PRODUCT(TraceTime tr("checkpointRootsFinalWork", PrintGCDetails, false, gclog_or_tty);) | |
4688 | |
4689 assert(haveFreelistLocks(), "must have free list locks"); | |
4690 assert_lock_strong(bitMapLock()); | |
4691 | |
4692 if (UseAdaptiveSizePolicy) { | |
4693 size_policy()->checkpoint_roots_final_begin(); | |
4694 } | |
4695 | |
4696 ResourceMark rm; | |
4697 HandleMark hm; | |
4698 | |
4699 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
4700 | |
4701 if (cms_should_unload_classes()) { | |
4702 CodeCache::gc_prologue(); | |
4703 } | |
4704 assert(haveFreelistLocks(), "must have free list locks"); | |
4705 assert_lock_strong(bitMapLock()); | |
4706 | |
4707 if (!init_mark_was_synchronous) { | |
4708 // We might assume that we need not fill TLAB's when | |
4709 // CMSScavengeBeforeRemark is set, because we may have just done | |
4710 // a scavenge which would have filled all TLAB's -- and besides | |
4711 // Eden would be empty. This however may not always be the case -- | |
4712 // for instance although we asked for a scavenge, it may not have | |
4713 // happened because of a JNI critical section. We probably need | |
4714 // a policy for deciding whether we can in that case wait until | |
4715 // the critical section releases and then do the remark following | |
4716 // the scavenge, and skip it here. In the absence of that policy, | |
4717 // or of an indication of whether the scavenge did indeed occur, | |
4718 // we cannot rely on TLAB's having been filled and must do | |
4719 // so here just in case a scavenge did not happen. | |
4720 gch->ensure_parsability(false); // fill TLAB's, but no need to retire them | |
4721 // Update the saved marks which may affect the root scans. | |
4722 gch->save_marks(); | |
4723 | |
4724 { | |
4725 COMPILER2_PRESENT(DerivedPointerTableDeactivate dpt_deact;) | |
4726 | |
4727 // Note on the role of the mod union table: | |
4728 // Since the marker in "markFromRoots" marks concurrently with | |
4729 // mutators, it is possible for some reachable objects not to have been | |
4730 // scanned. For instance, an only reference to an object A was | |
4731 // placed in object B after the marker scanned B. Unless B is rescanned, | |
4732 // A would be collected. Such updates to references in marked objects | |
4733 // are detected via the mod union table which is the set of all cards | |
4734 // dirtied since the first checkpoint in this GC cycle and prior to | |
4735 // the most recent young generation GC, minus those cleaned up by the | |
4736 // concurrent precleaning. | |
4737 if (CMSParallelRemarkEnabled && ParallelGCThreads > 0) { | |
4738 TraceTime t("Rescan (parallel) ", PrintGCDetails, false, gclog_or_tty); | |
4739 do_remark_parallel(); | |
4740 } else { | |
4741 TraceTime t("Rescan (non-parallel) ", PrintGCDetails, false, | |
4742 gclog_or_tty); | |
4743 do_remark_non_parallel(); | |
4744 } | |
4745 } | |
4746 } else { | |
4747 assert(!asynch, "Can't have init_mark_was_synchronous in asynch mode"); | |
4748 // The initial mark was stop-world, so there's no rescanning to | |
4749 // do; go straight on to the next step below. | |
4750 } | |
4751 verify_work_stacks_empty(); | |
4752 verify_overflow_empty(); | |
4753 | |
4754 { | |
4755 NOT_PRODUCT(TraceTime ts("refProcessingWork", PrintGCDetails, false, gclog_or_tty);) | |
4756 refProcessingWork(asynch, clear_all_soft_refs); | |
4757 } | |
4758 verify_work_stacks_empty(); | |
4759 verify_overflow_empty(); | |
4760 | |
4761 if (cms_should_unload_classes()) { | |
4762 CodeCache::gc_epilogue(); | |
4763 } | |
4764 | |
4765 // If we encountered any (marking stack / work queue) overflow | |
4766 // events during the current CMS cycle, take appropriate | |
4767 // remedial measures, where possible, so as to try and avoid | |
4768 // recurrence of that condition. | |
4769 assert(_markStack.isEmpty(), "No grey objects"); | |
4770 size_t ser_ovflw = _ser_pmc_remark_ovflw + _ser_pmc_preclean_ovflw + | |
4771 _ser_kac_ovflw; | |
4772 if (ser_ovflw > 0) { | |
4773 if (PrintCMSStatistics != 0) { | |
4774 gclog_or_tty->print_cr("Marking stack overflow (benign) " | |
4775 "(pmc_pc="SIZE_FORMAT", pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")", | |
4776 _ser_pmc_preclean_ovflw, _ser_pmc_remark_ovflw, | |
4777 _ser_kac_ovflw); | |
4778 } | |
4779 _markStack.expand(); | |
4780 _ser_pmc_remark_ovflw = 0; | |
4781 _ser_pmc_preclean_ovflw = 0; | |
4782 _ser_kac_ovflw = 0; | |
4783 } | |
4784 if (_par_pmc_remark_ovflw > 0 || _par_kac_ovflw > 0) { | |
4785 if (PrintCMSStatistics != 0) { | |
4786 gclog_or_tty->print_cr("Work queue overflow (benign) " | |
4787 "(pmc_rm="SIZE_FORMAT", kac="SIZE_FORMAT")", | |
4788 _par_pmc_remark_ovflw, _par_kac_ovflw); | |
4789 } | |
4790 _par_pmc_remark_ovflw = 0; | |
4791 _par_kac_ovflw = 0; | |
4792 } | |
4793 if (PrintCMSStatistics != 0) { | |
4794 if (_markStack._hit_limit > 0) { | |
4795 gclog_or_tty->print_cr(" (benign) Hit max stack size limit ("SIZE_FORMAT")", | |
4796 _markStack._hit_limit); | |
4797 } | |
4798 if (_markStack._failed_double > 0) { | |
4799 gclog_or_tty->print_cr(" (benign) Failed stack doubling ("SIZE_FORMAT")," | |
4800 " current capacity "SIZE_FORMAT, | |
4801 _markStack._failed_double, | |
4802 _markStack.capacity()); | |
4803 } | |
4804 } | |
4805 _markStack._hit_limit = 0; | |
4806 _markStack._failed_double = 0; | |
4807 | |
4808 if ((VerifyAfterGC || VerifyDuringGC) && | |
4809 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { | |
4810 verify_after_remark(); | |
4811 } | |
4812 | |
4813 // Change under the freelistLocks. | |
4814 _collectorState = Sweeping; | |
4815 // Call isAllClear() under bitMapLock | |
4816 assert(_modUnionTable.isAllClear(), "Should be clear by end of the" | |
4817 " final marking"); | |
4818 if (UseAdaptiveSizePolicy) { | |
4819 size_policy()->checkpoint_roots_final_end(gch->gc_cause()); | |
4820 } | |
4821 } | |
4822 | |
4823 // Parallel remark task | |
4824 class CMSParRemarkTask: public AbstractGangTask { | |
4825 CMSCollector* _collector; | |
4826 WorkGang* _workers; | |
4827 int _n_workers; | |
4828 CompactibleFreeListSpace* _cms_space; | |
4829 CompactibleFreeListSpace* _perm_space; | |
4830 | |
4831 // The per-thread work queues, available here for stealing. | |
4832 OopTaskQueueSet* _task_queues; | |
4833 ParallelTaskTerminator _term; | |
4834 | |
4835 public: | |
4836 CMSParRemarkTask(CMSCollector* collector, | |
4837 CompactibleFreeListSpace* cms_space, | |
4838 CompactibleFreeListSpace* perm_space, | |
4839 int n_workers, WorkGang* workers, | |
4840 OopTaskQueueSet* task_queues): | |
4841 AbstractGangTask("Rescan roots and grey objects in parallel"), | |
4842 _collector(collector), | |
4843 _cms_space(cms_space), _perm_space(perm_space), | |
4844 _n_workers(n_workers), | |
4845 _workers(workers), | |
4846 _task_queues(task_queues), | |
4847 _term(workers->total_workers(), task_queues) { } | |
4848 | |
4849 OopTaskQueueSet* task_queues() { return _task_queues; } | |
4850 | |
4851 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } | |
4852 | |
4853 ParallelTaskTerminator* terminator() { return &_term; } | |
4854 | |
4855 void work(int i); | |
4856 | |
4857 private: | |
4858 // Work method in support of parallel rescan ... of young gen spaces | |
4859 void do_young_space_rescan(int i, Par_MarkRefsIntoAndScanClosure* cl, | |
4860 ContiguousSpace* space, | |
4861 HeapWord** chunk_array, size_t chunk_top); | |
4862 | |
4863 // ... of dirty cards in old space | |
4864 void do_dirty_card_rescan_tasks(CompactibleFreeListSpace* sp, int i, | |
4865 Par_MarkRefsIntoAndScanClosure* cl); | |
4866 | |
4867 // ... work stealing for the above | |
4868 void do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, int* seed); | |
4869 }; | |
4870 | |
4871 void CMSParRemarkTask::work(int i) { | |
4872 elapsedTimer _timer; | |
4873 ResourceMark rm; | |
4874 HandleMark hm; | |
4875 | |
4876 // ---------- rescan from roots -------------- | |
4877 _timer.start(); | |
4878 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
4879 Par_MarkRefsIntoAndScanClosure par_mrias_cl(_collector, | |
4880 _collector->_span, _collector->ref_processor(), | |
4881 &(_collector->_markBitMap), | |
4882 work_queue(i), &(_collector->_revisitStack)); | |
4883 | |
4884 // Rescan young gen roots first since these are likely | |
4885 // coarsely partitioned and may, on that account, constitute | |
4886 // the critical path; thus, it's best to start off that | |
4887 // work first. | |
4888 // ---------- young gen roots -------------- | |
4889 { | |
4890 DefNewGeneration* dng = _collector->_young_gen->as_DefNewGeneration(); | |
4891 EdenSpace* eden_space = dng->eden(); | |
4892 ContiguousSpace* from_space = dng->from(); | |
4893 ContiguousSpace* to_space = dng->to(); | |
4894 | |
4895 HeapWord** eca = _collector->_eden_chunk_array; | |
4896 size_t ect = _collector->_eden_chunk_index; | |
4897 HeapWord** sca = _collector->_survivor_chunk_array; | |
4898 size_t sct = _collector->_survivor_chunk_index; | |
4899 | |
4900 assert(ect <= _collector->_eden_chunk_capacity, "out of bounds"); | |
4901 assert(sct <= _collector->_survivor_chunk_capacity, "out of bounds"); | |
4902 | |
4903 do_young_space_rescan(i, &par_mrias_cl, to_space, NULL, 0); | |
4904 do_young_space_rescan(i, &par_mrias_cl, from_space, sca, sct); | |
4905 do_young_space_rescan(i, &par_mrias_cl, eden_space, eca, ect); | |
4906 | |
4907 _timer.stop(); | |
4908 if (PrintCMSStatistics != 0) { | |
4909 gclog_or_tty->print_cr( | |
4910 "Finished young gen rescan work in %dth thread: %3.3f sec", | |
4911 i, _timer.seconds()); | |
4912 } | |
4913 } | |
4914 | |
4915 // ---------- remaining roots -------------- | |
4916 _timer.reset(); | |
4917 _timer.start(); | |
4918 gch->gen_process_strong_roots(_collector->_cmsGen->level(), | |
4919 false, // yg was scanned above | |
4920 true, // collecting perm gen | |
4921 SharedHeap::ScanningOption(_collector->CMSCollector::roots_scanning_options()), | |
4922 NULL, &par_mrias_cl); | |
4923 _timer.stop(); | |
4924 if (PrintCMSStatistics != 0) { | |
4925 gclog_or_tty->print_cr( | |
4926 "Finished remaining root rescan work in %dth thread: %3.3f sec", | |
4927 i, _timer.seconds()); | |
4928 } | |
4929 | |
4930 // ---------- rescan dirty cards ------------ | |
4931 _timer.reset(); | |
4932 _timer.start(); | |
4933 | |
4934 // Do the rescan tasks for each of the two spaces | |
4935 // (cms_space and perm_space) in turn. | |
4936 do_dirty_card_rescan_tasks(_cms_space, i, &par_mrias_cl); | |
4937 do_dirty_card_rescan_tasks(_perm_space, i, &par_mrias_cl); | |
4938 _timer.stop(); | |
4939 if (PrintCMSStatistics != 0) { | |
4940 gclog_or_tty->print_cr( | |
4941 "Finished dirty card rescan work in %dth thread: %3.3f sec", | |
4942 i, _timer.seconds()); | |
4943 } | |
4944 | |
4945 // ---------- steal work from other threads ... | |
4946 // ---------- ... and drain overflow list. | |
4947 _timer.reset(); | |
4948 _timer.start(); | |
4949 do_work_steal(i, &par_mrias_cl, _collector->hash_seed(i)); | |
4950 _timer.stop(); | |
4951 if (PrintCMSStatistics != 0) { | |
4952 gclog_or_tty->print_cr( | |
4953 "Finished work stealing in %dth thread: %3.3f sec", | |
4954 i, _timer.seconds()); | |
4955 } | |
4956 } | |
4957 | |
4958 void | |
4959 CMSParRemarkTask::do_young_space_rescan(int i, | |
4960 Par_MarkRefsIntoAndScanClosure* cl, ContiguousSpace* space, | |
4961 HeapWord** chunk_array, size_t chunk_top) { | |
4962 // Until all tasks completed: | |
4963 // . claim an unclaimed task | |
4964 // . compute region boundaries corresponding to task claimed | |
4965 // using chunk_array | |
4966 // . par_oop_iterate(cl) over that region | |
4967 | |
4968 ResourceMark rm; | |
4969 HandleMark hm; | |
4970 | |
4971 SequentialSubTasksDone* pst = space->par_seq_tasks(); | |
4972 assert(pst->valid(), "Uninitialized use?"); | |
4973 | |
4974 int nth_task = 0; | |
4975 int n_tasks = pst->n_tasks(); | |
4976 | |
4977 HeapWord *start, *end; | |
4978 while (!pst->is_task_claimed(/* reference */ nth_task)) { | |
4979 // We claimed task # nth_task; compute its boundaries. | |
4980 if (chunk_top == 0) { // no samples were taken | |
4981 assert(nth_task == 0 && n_tasks == 1, "Can have only 1 EdenSpace task"); | |
4982 start = space->bottom(); | |
4983 end = space->top(); | |
4984 } else if (nth_task == 0) { | |
4985 start = space->bottom(); | |
4986 end = chunk_array[nth_task]; | |
4987 } else if (nth_task < (jint)chunk_top) { | |
4988 assert(nth_task >= 1, "Control point invariant"); | |
4989 start = chunk_array[nth_task - 1]; | |
4990 end = chunk_array[nth_task]; | |
4991 } else { | |
4992 assert(nth_task == (jint)chunk_top, "Control point invariant"); | |
4993 start = chunk_array[chunk_top - 1]; | |
4994 end = space->top(); | |
4995 } | |
4996 MemRegion mr(start, end); | |
4997 // Verify that mr is in space | |
4998 assert(mr.is_empty() || space->used_region().contains(mr), | |
4999 "Should be in space"); | |
5000 // Verify that "start" is an object boundary | |
5001 assert(mr.is_empty() || oop(mr.start())->is_oop(), | |
5002 "Should be an oop"); | |
5003 space->par_oop_iterate(mr, cl); | |
5004 } | |
5005 pst->all_tasks_completed(); | |
5006 } | |
5007 | |
5008 void | |
5009 CMSParRemarkTask::do_dirty_card_rescan_tasks( | |
5010 CompactibleFreeListSpace* sp, int i, | |
5011 Par_MarkRefsIntoAndScanClosure* cl) { | |
5012 // Until all tasks completed: | |
5013 // . claim an unclaimed task | |
5014 // . compute region boundaries corresponding to task claimed | |
5015 // . transfer dirty bits ct->mut for that region | |
5016 // . apply rescanclosure to dirty mut bits for that region | |
5017 | |
5018 ResourceMark rm; | |
5019 HandleMark hm; | |
5020 | |
5021 OopTaskQueue* work_q = work_queue(i); | |
5022 ModUnionClosure modUnionClosure(&(_collector->_modUnionTable)); | |
5023 // CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! CAUTION! | |
5024 // CAUTION: This closure has state that persists across calls to | |
5025 // the work method dirty_range_iterate_clear() in that it has | |
5026 // imbedded in it a (subtype of) UpwardsObjectClosure. The | |
5027 // use of that state in the imbedded UpwardsObjectClosure instance | |
5028 // assumes that the cards are always iterated (even if in parallel | |
5029 // by several threads) in monotonically increasing order per each | |
5030 // thread. This is true of the implementation below which picks | |
5031 // card ranges (chunks) in monotonically increasing order globally | |
5032 // and, a-fortiori, in monotonically increasing order per thread | |
5033 // (the latter order being a subsequence of the former). | |
5034 // If the work code below is ever reorganized into a more chaotic | |
5035 // work-partitioning form than the current "sequential tasks" | |
5036 // paradigm, the use of that persistent state will have to be | |
5037 // revisited and modified appropriately. See also related | |
5038 // bug 4756801 work on which should examine this code to make | |
5039 // sure that the changes there do not run counter to the | |
5040 // assumptions made here and necessary for correctness and | |
5041 // efficiency. Note also that this code might yield inefficient | |
5042 // behaviour in the case of very large objects that span one or | |
5043 // more work chunks. Such objects would potentially be scanned | |
5044 // several times redundantly. Work on 4756801 should try and | |
5045 // address that performance anomaly if at all possible. XXX | |
5046 MemRegion full_span = _collector->_span; | |
5047 CMSBitMap* bm = &(_collector->_markBitMap); // shared | |
5048 CMSMarkStack* rs = &(_collector->_revisitStack); // shared | |
5049 MarkFromDirtyCardsClosure | |
5050 greyRescanClosure(_collector, full_span, // entire span of interest | |
5051 sp, bm, work_q, rs, cl); | |
5052 | |
5053 SequentialSubTasksDone* pst = sp->conc_par_seq_tasks(); | |
5054 assert(pst->valid(), "Uninitialized use?"); | |
5055 int nth_task = 0; | |
5056 const int alignment = CardTableModRefBS::card_size * BitsPerWord; | |
5057 MemRegion span = sp->used_region(); | |
5058 HeapWord* start_addr = span.start(); | |
5059 HeapWord* end_addr = (HeapWord*)round_to((intptr_t)span.end(), | |
5060 alignment); | |
5061 const size_t chunk_size = sp->rescan_task_size(); // in HeapWord units | |
5062 assert((HeapWord*)round_to((intptr_t)start_addr, alignment) == | |
5063 start_addr, "Check alignment"); | |
5064 assert((size_t)round_to((intptr_t)chunk_size, alignment) == | |
5065 chunk_size, "Check alignment"); | |
5066 | |
5067 while (!pst->is_task_claimed(/* reference */ nth_task)) { | |
5068 // Having claimed the nth_task, compute corresponding mem-region, | |
5069 // which is a-fortiori aligned correctly (i.e. at a MUT bopundary). | |
5070 // The alignment restriction ensures that we do not need any | |
5071 // synchronization with other gang-workers while setting or | |
5072 // clearing bits in thus chunk of the MUT. | |
5073 MemRegion this_span = MemRegion(start_addr + nth_task*chunk_size, | |
5074 start_addr + (nth_task+1)*chunk_size); | |
5075 // The last chunk's end might be way beyond end of the | |
5076 // used region. In that case pull back appropriately. | |
5077 if (this_span.end() > end_addr) { | |
5078 this_span.set_end(end_addr); | |
5079 assert(!this_span.is_empty(), "Program logic (calculation of n_tasks)"); | |
5080 } | |
5081 // Iterate over the dirty cards covering this chunk, marking them | |
5082 // precleaned, and setting the corresponding bits in the mod union | |
5083 // table. Since we have been careful to partition at Card and MUT-word | |
5084 // boundaries no synchronization is needed between parallel threads. | |
5085 _collector->_ct->ct_bs()->dirty_card_iterate(this_span, | |
5086 &modUnionClosure); | |
5087 | |
5088 // Having transferred these marks into the modUnionTable, | |
5089 // rescan the marked objects on the dirty cards in the modUnionTable. | |
5090 // Even if this is at a synchronous collection, the initial marking | |
5091 // may have been done during an asynchronous collection so there | |
5092 // may be dirty bits in the mod-union table. | |
5093 _collector->_modUnionTable.dirty_range_iterate_clear( | |
5094 this_span, &greyRescanClosure); | |
5095 _collector->_modUnionTable.verifyNoOneBitsInRange( | |
5096 this_span.start(), | |
5097 this_span.end()); | |
5098 } | |
5099 pst->all_tasks_completed(); // declare that i am done | |
5100 } | |
5101 | |
5102 // . see if we can share work_queues with ParNew? XXX | |
5103 void | |
5104 CMSParRemarkTask::do_work_steal(int i, Par_MarkRefsIntoAndScanClosure* cl, | |
5105 int* seed) { | |
5106 OopTaskQueue* work_q = work_queue(i); | |
5107 NOT_PRODUCT(int num_steals = 0;) | |
5108 oop obj_to_scan; | |
5109 CMSBitMap* bm = &(_collector->_markBitMap); | |
5110 size_t num_from_overflow_list = | |
5111 MIN2((size_t)work_q->max_elems()/4, | |
5112 (size_t)ParGCDesiredObjsFromOverflowList); | |
5113 | |
5114 while (true) { | |
5115 // Completely finish any left over work from (an) earlier round(s) | |
5116 cl->trim_queue(0); | |
5117 // Now check if there's any work in the overflow list | |
5118 if (_collector->par_take_from_overflow_list(num_from_overflow_list, | |
5119 work_q)) { | |
5120 // found something in global overflow list; | |
5121 // not yet ready to go stealing work from others. | |
5122 // We'd like to assert(work_q->size() != 0, ...) | |
5123 // because we just took work from the overflow list, | |
5124 // but of course we can't since all of that could have | |
5125 // been already stolen from us. | |
5126 // "He giveth and He taketh away." | |
5127 continue; | |
5128 } | |
5129 // Verify that we have no work before we resort to stealing | |
5130 assert(work_q->size() == 0, "Have work, shouldn't steal"); | |
5131 // Try to steal from other queues that have work | |
5132 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { | |
5133 NOT_PRODUCT(num_steals++;) | |
5134 assert(obj_to_scan->is_oop(), "Oops, not an oop!"); | |
5135 assert(bm->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); | |
5136 // Do scanning work | |
5137 obj_to_scan->oop_iterate(cl); | |
5138 // Loop around, finish this work, and try to steal some more | |
5139 } else if (terminator()->offer_termination()) { | |
5140 break; // nirvana from the infinite cycle | |
5141 } | |
5142 } | |
5143 NOT_PRODUCT( | |
5144 if (PrintCMSStatistics != 0) { | |
5145 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals); | |
5146 } | |
5147 ) | |
5148 assert(work_q->size() == 0 && _collector->overflow_list_is_empty(), | |
5149 "Else our work is not yet done"); | |
5150 } | |
5151 | |
5152 // Return a thread-local PLAB recording array, as appropriate. | |
5153 void* CMSCollector::get_data_recorder(int thr_num) { | |
5154 if (_survivor_plab_array != NULL && | |
5155 (CMSPLABRecordAlways || | |
5156 (_collectorState > Marking && _collectorState < FinalMarking))) { | |
5157 assert(thr_num < (int)ParallelGCThreads, "thr_num is out of bounds"); | |
5158 ChunkArray* ca = &_survivor_plab_array[thr_num]; | |
5159 ca->reset(); // clear it so that fresh data is recorded | |
5160 return (void*) ca; | |
5161 } else { | |
5162 return NULL; | |
5163 } | |
5164 } | |
5165 | |
5166 // Reset all the thread-local PLAB recording arrays | |
5167 void CMSCollector::reset_survivor_plab_arrays() { | |
5168 for (uint i = 0; i < ParallelGCThreads; i++) { | |
5169 _survivor_plab_array[i].reset(); | |
5170 } | |
5171 } | |
5172 | |
5173 // Merge the per-thread plab arrays into the global survivor chunk | |
5174 // array which will provide the partitioning of the survivor space | |
5175 // for CMS rescan. | |
5176 void CMSCollector::merge_survivor_plab_arrays(ContiguousSpace* surv) { | |
5177 assert(_survivor_plab_array != NULL, "Error"); | |
5178 assert(_survivor_chunk_array != NULL, "Error"); | |
5179 assert(_collectorState == FinalMarking, "Error"); | |
5180 for (uint j = 0; j < ParallelGCThreads; j++) { | |
5181 _cursor[j] = 0; | |
5182 } | |
5183 HeapWord* top = surv->top(); | |
5184 size_t i; | |
5185 for (i = 0; i < _survivor_chunk_capacity; i++) { // all sca entries | |
5186 HeapWord* min_val = top; // Higher than any PLAB address | |
5187 uint min_tid = 0; // position of min_val this round | |
5188 for (uint j = 0; j < ParallelGCThreads; j++) { | |
5189 ChunkArray* cur_sca = &_survivor_plab_array[j]; | |
5190 if (_cursor[j] == cur_sca->end()) { | |
5191 continue; | |
5192 } | |
5193 assert(_cursor[j] < cur_sca->end(), "ctl pt invariant"); | |
5194 HeapWord* cur_val = cur_sca->nth(_cursor[j]); | |
5195 assert(surv->used_region().contains(cur_val), "Out of bounds value"); | |
5196 if (cur_val < min_val) { | |
5197 min_tid = j; | |
5198 min_val = cur_val; | |
5199 } else { | |
5200 assert(cur_val < top, "All recorded addresses should be less"); | |
5201 } | |
5202 } | |
5203 // At this point min_val and min_tid are respectively | |
5204 // the least address in _survivor_plab_array[j]->nth(_cursor[j]) | |
5205 // and the thread (j) that witnesses that address. | |
5206 // We record this address in the _survivor_chunk_array[i] | |
5207 // and increment _cursor[min_tid] prior to the next round i. | |
5208 if (min_val == top) { | |
5209 break; | |
5210 } | |
5211 _survivor_chunk_array[i] = min_val; | |
5212 _cursor[min_tid]++; | |
5213 } | |
5214 // We are all done; record the size of the _survivor_chunk_array | |
5215 _survivor_chunk_index = i; // exclusive: [0, i) | |
5216 if (PrintCMSStatistics > 0) { | |
5217 gclog_or_tty->print(" (Survivor:" SIZE_FORMAT "chunks) ", i); | |
5218 } | |
5219 // Verify that we used up all the recorded entries | |
5220 #ifdef ASSERT | |
5221 size_t total = 0; | |
5222 for (uint j = 0; j < ParallelGCThreads; j++) { | |
5223 assert(_cursor[j] == _survivor_plab_array[j].end(), "Ctl pt invariant"); | |
5224 total += _cursor[j]; | |
5225 } | |
5226 assert(total == _survivor_chunk_index, "Ctl Pt Invariant"); | |
5227 // Check that the merged array is in sorted order | |
5228 if (total > 0) { | |
5229 for (size_t i = 0; i < total - 1; i++) { | |
5230 if (PrintCMSStatistics > 0) { | |
5231 gclog_or_tty->print(" (chunk" SIZE_FORMAT ":" INTPTR_FORMAT ") ", | |
5232 i, _survivor_chunk_array[i]); | |
5233 } | |
5234 assert(_survivor_chunk_array[i] < _survivor_chunk_array[i+1], | |
5235 "Not sorted"); | |
5236 } | |
5237 } | |
5238 #endif // ASSERT | |
5239 } | |
5240 | |
5241 // Set up the space's par_seq_tasks structure for work claiming | |
5242 // for parallel rescan of young gen. | |
5243 // See ParRescanTask where this is currently used. | |
5244 void | |
5245 CMSCollector:: | |
5246 initialize_sequential_subtasks_for_young_gen_rescan(int n_threads) { | |
5247 assert(n_threads > 0, "Unexpected n_threads argument"); | |
5248 DefNewGeneration* dng = (DefNewGeneration*)_young_gen; | |
5249 | |
5250 // Eden space | |
5251 { | |
5252 SequentialSubTasksDone* pst = dng->eden()->par_seq_tasks(); | |
5253 assert(!pst->valid(), "Clobbering existing data?"); | |
5254 // Each valid entry in [0, _eden_chunk_index) represents a task. | |
5255 size_t n_tasks = _eden_chunk_index + 1; | |
5256 assert(n_tasks == 1 || _eden_chunk_array != NULL, "Error"); | |
5257 pst->set_par_threads(n_threads); | |
5258 pst->set_n_tasks((int)n_tasks); | |
5259 } | |
5260 | |
5261 // Merge the survivor plab arrays into _survivor_chunk_array | |
5262 if (_survivor_plab_array != NULL) { | |
5263 merge_survivor_plab_arrays(dng->from()); | |
5264 } else { | |
5265 assert(_survivor_chunk_index == 0, "Error"); | |
5266 } | |
5267 | |
5268 // To space | |
5269 { | |
5270 SequentialSubTasksDone* pst = dng->to()->par_seq_tasks(); | |
5271 assert(!pst->valid(), "Clobbering existing data?"); | |
5272 pst->set_par_threads(n_threads); | |
5273 pst->set_n_tasks(1); | |
5274 assert(pst->valid(), "Error"); | |
5275 } | |
5276 | |
5277 // From space | |
5278 { | |
5279 SequentialSubTasksDone* pst = dng->from()->par_seq_tasks(); | |
5280 assert(!pst->valid(), "Clobbering existing data?"); | |
5281 size_t n_tasks = _survivor_chunk_index + 1; | |
5282 assert(n_tasks == 1 || _survivor_chunk_array != NULL, "Error"); | |
5283 pst->set_par_threads(n_threads); | |
5284 pst->set_n_tasks((int)n_tasks); | |
5285 assert(pst->valid(), "Error"); | |
5286 } | |
5287 } | |
5288 | |
5289 // Parallel version of remark | |
5290 void CMSCollector::do_remark_parallel() { | |
5291 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
5292 WorkGang* workers = gch->workers(); | |
5293 assert(workers != NULL, "Need parallel worker threads."); | |
5294 int n_workers = workers->total_workers(); | |
5295 CompactibleFreeListSpace* cms_space = _cmsGen->cmsSpace(); | |
5296 CompactibleFreeListSpace* perm_space = _permGen->cmsSpace(); | |
5297 | |
5298 CMSParRemarkTask tsk(this, | |
5299 cms_space, perm_space, | |
5300 n_workers, workers, task_queues()); | |
5301 | |
5302 // Set up for parallel process_strong_roots work. | |
5303 gch->set_par_threads(n_workers); | |
5304 gch->change_strong_roots_parity(); | |
5305 // We won't be iterating over the cards in the card table updating | |
5306 // the younger_gen cards, so we shouldn't call the following else | |
5307 // the verification code as well as subsequent younger_refs_iterate | |
5308 // code would get confused. XXX | |
5309 // gch->rem_set()->prepare_for_younger_refs_iterate(true); // parallel | |
5310 | |
5311 // The young gen rescan work will not be done as part of | |
5312 // process_strong_roots (which currently doesn't knw how to | |
5313 // parallelize such a scan), but rather will be broken up into | |
5314 // a set of parallel tasks (via the sampling that the [abortable] | |
5315 // preclean phase did of EdenSpace, plus the [two] tasks of | |
5316 // scanning the [two] survivor spaces. Further fine-grain | |
5317 // parallelization of the scanning of the survivor spaces | |
5318 // themselves, and of precleaning of the younger gen itself | |
5319 // is deferred to the future. | |
5320 initialize_sequential_subtasks_for_young_gen_rescan(n_workers); | |
5321 | |
5322 // The dirty card rescan work is broken up into a "sequence" | |
5323 // of parallel tasks (per constituent space) that are dynamically | |
5324 // claimed by the parallel threads. | |
5325 cms_space->initialize_sequential_subtasks_for_rescan(n_workers); | |
5326 perm_space->initialize_sequential_subtasks_for_rescan(n_workers); | |
5327 | |
5328 // It turns out that even when we're using 1 thread, doing the work in a | |
5329 // separate thread causes wide variance in run times. We can't help this | |
5330 // in the multi-threaded case, but we special-case n=1 here to get | |
5331 // repeatable measurements of the 1-thread overhead of the parallel code. | |
5332 if (n_workers > 1) { | |
5333 // Make refs discovery MT-safe | |
5334 ReferenceProcessorMTMutator mt(ref_processor(), true); | |
5335 workers->run_task(&tsk); | |
5336 } else { | |
5337 tsk.work(0); | |
5338 } | |
5339 gch->set_par_threads(0); // 0 ==> non-parallel. | |
5340 // restore, single-threaded for now, any preserved marks | |
5341 // as a result of work_q overflow | |
5342 restore_preserved_marks_if_any(); | |
5343 } | |
5344 | |
5345 // Non-parallel version of remark | |
5346 void CMSCollector::do_remark_non_parallel() { | |
5347 ResourceMark rm; | |
5348 HandleMark hm; | |
5349 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
5350 MarkRefsIntoAndScanClosure | |
5351 mrias_cl(_span, ref_processor(), &_markBitMap, &_modUnionTable, | |
5352 &_markStack, &_revisitStack, this, | |
5353 false /* should_yield */, false /* not precleaning */); | |
5354 MarkFromDirtyCardsClosure | |
5355 markFromDirtyCardsClosure(this, _span, | |
5356 NULL, // space is set further below | |
5357 &_markBitMap, &_markStack, &_revisitStack, | |
5358 &mrias_cl); | |
5359 { | |
5360 TraceTime t("grey object rescan", PrintGCDetails, false, gclog_or_tty); | |
5361 // Iterate over the dirty cards, marking them precleaned, and | |
5362 // setting the corresponding bits in the mod union table. | |
5363 { | |
5364 ModUnionClosure modUnionClosure(&_modUnionTable); | |
5365 _ct->ct_bs()->dirty_card_iterate( | |
5366 _cmsGen->used_region(), | |
5367 &modUnionClosure); | |
5368 _ct->ct_bs()->dirty_card_iterate( | |
5369 _permGen->used_region(), | |
5370 &modUnionClosure); | |
5371 } | |
5372 // Having transferred these marks into the modUnionTable, we just need | |
5373 // to rescan the marked objects on the dirty cards in the modUnionTable. | |
5374 // The initial marking may have been done during an asynchronous | |
5375 // collection so there may be dirty bits in the mod-union table. | |
5376 const int alignment = | |
5377 CardTableModRefBS::card_size * BitsPerWord; | |
5378 { | |
5379 // ... First handle dirty cards in CMS gen | |
5380 markFromDirtyCardsClosure.set_space(_cmsGen->cmsSpace()); | |
5381 MemRegion ur = _cmsGen->used_region(); | |
5382 HeapWord* lb = ur.start(); | |
5383 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment); | |
5384 MemRegion cms_span(lb, ub); | |
5385 _modUnionTable.dirty_range_iterate_clear(cms_span, | |
5386 &markFromDirtyCardsClosure); | |
5387 verify_work_stacks_empty(); | |
5388 if (PrintCMSStatistics != 0) { | |
5389 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in cms gen) ", | |
5390 markFromDirtyCardsClosure.num_dirty_cards()); | |
5391 } | |
5392 } | |
5393 { | |
5394 // .. and then repeat for dirty cards in perm gen | |
5395 markFromDirtyCardsClosure.set_space(_permGen->cmsSpace()); | |
5396 MemRegion ur = _permGen->used_region(); | |
5397 HeapWord* lb = ur.start(); | |
5398 HeapWord* ub = (HeapWord*)round_to((intptr_t)ur.end(), alignment); | |
5399 MemRegion perm_span(lb, ub); | |
5400 _modUnionTable.dirty_range_iterate_clear(perm_span, | |
5401 &markFromDirtyCardsClosure); | |
5402 verify_work_stacks_empty(); | |
5403 if (PrintCMSStatistics != 0) { | |
5404 gclog_or_tty->print(" (re-scanned "SIZE_FORMAT" dirty cards in perm gen) ", | |
5405 markFromDirtyCardsClosure.num_dirty_cards()); | |
5406 } | |
5407 } | |
5408 } | |
5409 if (VerifyDuringGC && | |
5410 GenCollectedHeap::heap()->total_collections() >= VerifyGCStartAt) { | |
5411 HandleMark hm; // Discard invalid handles created during verification | |
5412 Universe::verify(true); | |
5413 } | |
5414 { | |
5415 TraceTime t("root rescan", PrintGCDetails, false, gclog_or_tty); | |
5416 | |
5417 verify_work_stacks_empty(); | |
5418 | |
5419 gch->rem_set()->prepare_for_younger_refs_iterate(false); // Not parallel. | |
5420 gch->gen_process_strong_roots(_cmsGen->level(), | |
5421 true, // younger gens as roots | |
5422 true, // collecting perm gen | |
5423 SharedHeap::ScanningOption(roots_scanning_options()), | |
5424 NULL, &mrias_cl); | |
5425 } | |
5426 verify_work_stacks_empty(); | |
5427 // Restore evacuated mark words, if any, used for overflow list links | |
5428 if (!CMSOverflowEarlyRestoration) { | |
5429 restore_preserved_marks_if_any(); | |
5430 } | |
5431 verify_overflow_empty(); | |
5432 } | |
5433 | |
5434 //////////////////////////////////////////////////////// | |
5435 // Parallel Reference Processing Task Proxy Class | |
5436 //////////////////////////////////////////////////////// | |
5437 class CMSRefProcTaskProxy: public AbstractGangTask { | |
5438 typedef AbstractRefProcTaskExecutor::ProcessTask ProcessTask; | |
5439 CMSCollector* _collector; | |
5440 CMSBitMap* _mark_bit_map; | |
5441 MemRegion _span; | |
5442 OopTaskQueueSet* _task_queues; | |
5443 ParallelTaskTerminator _term; | |
5444 ProcessTask& _task; | |
5445 | |
5446 public: | |
5447 CMSRefProcTaskProxy(ProcessTask& task, | |
5448 CMSCollector* collector, | |
5449 const MemRegion& span, | |
5450 CMSBitMap* mark_bit_map, | |
5451 int total_workers, | |
5452 OopTaskQueueSet* task_queues): | |
5453 AbstractGangTask("Process referents by policy in parallel"), | |
5454 _task(task), | |
5455 _collector(collector), _span(span), _mark_bit_map(mark_bit_map), | |
5456 _task_queues(task_queues), | |
5457 _term(total_workers, task_queues) | |
5458 { } | |
5459 | |
5460 OopTaskQueueSet* task_queues() { return _task_queues; } | |
5461 | |
5462 OopTaskQueue* work_queue(int i) { return task_queues()->queue(i); } | |
5463 | |
5464 ParallelTaskTerminator* terminator() { return &_term; } | |
5465 | |
5466 void do_work_steal(int i, | |
5467 CMSParDrainMarkingStackClosure* drain, | |
5468 CMSParKeepAliveClosure* keep_alive, | |
5469 int* seed); | |
5470 | |
5471 virtual void work(int i); | |
5472 }; | |
5473 | |
5474 void CMSRefProcTaskProxy::work(int i) { | |
5475 CMSParKeepAliveClosure par_keep_alive(_collector, _span, | |
5476 _mark_bit_map, work_queue(i)); | |
5477 CMSParDrainMarkingStackClosure par_drain_stack(_collector, _span, | |
5478 _mark_bit_map, work_queue(i)); | |
5479 CMSIsAliveClosure is_alive_closure(_mark_bit_map); | |
5480 _task.work(i, is_alive_closure, par_keep_alive, par_drain_stack); | |
5481 if (_task.marks_oops_alive()) { | |
5482 do_work_steal(i, &par_drain_stack, &par_keep_alive, | |
5483 _collector->hash_seed(i)); | |
5484 } | |
5485 assert(work_queue(i)->size() == 0, "work_queue should be empty"); | |
5486 assert(_collector->_overflow_list == NULL, "non-empty _overflow_list"); | |
5487 } | |
5488 | |
5489 class CMSRefEnqueueTaskProxy: public AbstractGangTask { | |
5490 typedef AbstractRefProcTaskExecutor::EnqueueTask EnqueueTask; | |
5491 EnqueueTask& _task; | |
5492 | |
5493 public: | |
5494 CMSRefEnqueueTaskProxy(EnqueueTask& task) | |
5495 : AbstractGangTask("Enqueue reference objects in parallel"), | |
5496 _task(task) | |
5497 { } | |
5498 | |
5499 virtual void work(int i) | |
5500 { | |
5501 _task.work(i); | |
5502 } | |
5503 }; | |
5504 | |
5505 CMSParKeepAliveClosure::CMSParKeepAliveClosure(CMSCollector* collector, | |
5506 MemRegion span, CMSBitMap* bit_map, OopTaskQueue* work_queue): | |
5507 _collector(collector), | |
5508 _span(span), | |
5509 _bit_map(bit_map), | |
5510 _work_queue(work_queue), | |
5511 _mark_and_push(collector, span, bit_map, work_queue), | |
5512 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4), | |
5513 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))) | |
5514 { } | |
5515 | |
5516 // . see if we can share work_queues with ParNew? XXX | |
5517 void CMSRefProcTaskProxy::do_work_steal(int i, | |
5518 CMSParDrainMarkingStackClosure* drain, | |
5519 CMSParKeepAliveClosure* keep_alive, | |
5520 int* seed) { | |
5521 OopTaskQueue* work_q = work_queue(i); | |
5522 NOT_PRODUCT(int num_steals = 0;) | |
5523 oop obj_to_scan; | |
5524 size_t num_from_overflow_list = | |
5525 MIN2((size_t)work_q->max_elems()/4, | |
5526 (size_t)ParGCDesiredObjsFromOverflowList); | |
5527 | |
5528 while (true) { | |
5529 // Completely finish any left over work from (an) earlier round(s) | |
5530 drain->trim_queue(0); | |
5531 // Now check if there's any work in the overflow list | |
5532 if (_collector->par_take_from_overflow_list(num_from_overflow_list, | |
5533 work_q)) { | |
5534 // Found something in global overflow list; | |
5535 // not yet ready to go stealing work from others. | |
5536 // We'd like to assert(work_q->size() != 0, ...) | |
5537 // because we just took work from the overflow list, | |
5538 // but of course we can't, since all of that might have | |
5539 // been already stolen from us. | |
5540 continue; | |
5541 } | |
5542 // Verify that we have no work before we resort to stealing | |
5543 assert(work_q->size() == 0, "Have work, shouldn't steal"); | |
5544 // Try to steal from other queues that have work | |
5545 if (task_queues()->steal(i, seed, /* reference */ obj_to_scan)) { | |
5546 NOT_PRODUCT(num_steals++;) | |
5547 assert(obj_to_scan->is_oop(), "Oops, not an oop!"); | |
5548 assert(_mark_bit_map->isMarked((HeapWord*)obj_to_scan), "Stole an unmarked oop?"); | |
5549 // Do scanning work | |
5550 obj_to_scan->oop_iterate(keep_alive); | |
5551 // Loop around, finish this work, and try to steal some more | |
5552 } else if (terminator()->offer_termination()) { | |
5553 break; // nirvana from the infinite cycle | |
5554 } | |
5555 } | |
5556 NOT_PRODUCT( | |
5557 if (PrintCMSStatistics != 0) { | |
5558 gclog_or_tty->print("\n\t(%d: stole %d oops)", i, num_steals); | |
5559 } | |
5560 ) | |
5561 } | |
5562 | |
5563 void CMSRefProcTaskExecutor::execute(ProcessTask& task) | |
5564 { | |
5565 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
5566 WorkGang* workers = gch->workers(); | |
5567 assert(workers != NULL, "Need parallel worker threads."); | |
5568 int n_workers = workers->total_workers(); | |
5569 CMSRefProcTaskProxy rp_task(task, &_collector, | |
5570 _collector.ref_processor()->span(), | |
5571 _collector.markBitMap(), | |
5572 n_workers, _collector.task_queues()); | |
5573 workers->run_task(&rp_task); | |
5574 } | |
5575 | |
5576 void CMSRefProcTaskExecutor::execute(EnqueueTask& task) | |
5577 { | |
5578 | |
5579 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
5580 WorkGang* workers = gch->workers(); | |
5581 assert(workers != NULL, "Need parallel worker threads."); | |
5582 CMSRefEnqueueTaskProxy enq_task(task); | |
5583 workers->run_task(&enq_task); | |
5584 } | |
5585 | |
5586 void CMSCollector::refProcessingWork(bool asynch, bool clear_all_soft_refs) { | |
5587 | |
5588 ResourceMark rm; | |
5589 HandleMark hm; | |
5590 ReferencePolicy* soft_ref_policy; | |
5591 | |
5592 assert(!ref_processor()->enqueuing_is_done(), "Enqueuing should not be complete"); | |
5593 // Process weak references. | |
5594 if (clear_all_soft_refs) { | |
5595 soft_ref_policy = new AlwaysClearPolicy(); | |
5596 } else { | |
5597 #ifdef COMPILER2 | |
5598 soft_ref_policy = new LRUMaxHeapPolicy(); | |
5599 #else | |
5600 soft_ref_policy = new LRUCurrentHeapPolicy(); | |
5601 #endif // COMPILER2 | |
5602 } | |
5603 verify_work_stacks_empty(); | |
5604 | |
5605 ReferenceProcessor* rp = ref_processor(); | |
5606 assert(rp->span().equals(_span), "Spans should be equal"); | |
5607 CMSKeepAliveClosure cmsKeepAliveClosure(this, _span, &_markBitMap, | |
5608 &_markStack); | |
5609 CMSDrainMarkingStackClosure cmsDrainMarkingStackClosure(this, | |
5610 _span, &_markBitMap, &_markStack, | |
5611 &cmsKeepAliveClosure); | |
5612 { | |
5613 TraceTime t("weak refs processing", PrintGCDetails, false, gclog_or_tty); | |
5614 if (rp->processing_is_mt()) { | |
5615 CMSRefProcTaskExecutor task_executor(*this); | |
5616 rp->process_discovered_references(soft_ref_policy, | |
5617 &_is_alive_closure, | |
5618 &cmsKeepAliveClosure, | |
5619 &cmsDrainMarkingStackClosure, | |
5620 &task_executor); | |
5621 } else { | |
5622 rp->process_discovered_references(soft_ref_policy, | |
5623 &_is_alive_closure, | |
5624 &cmsKeepAliveClosure, | |
5625 &cmsDrainMarkingStackClosure, | |
5626 NULL); | |
5627 } | |
5628 verify_work_stacks_empty(); | |
5629 } | |
5630 | |
5631 if (cms_should_unload_classes()) { | |
5632 { | |
5633 TraceTime t("class unloading", PrintGCDetails, false, gclog_or_tty); | |
5634 | |
5635 // Follow SystemDictionary roots and unload classes | |
5636 bool purged_class = SystemDictionary::do_unloading(&_is_alive_closure); | |
5637 | |
5638 // Follow CodeCache roots and unload any methods marked for unloading | |
5639 CodeCache::do_unloading(&_is_alive_closure, | |
5640 &cmsKeepAliveClosure, | |
5641 purged_class); | |
5642 | |
5643 cmsDrainMarkingStackClosure.do_void(); | |
5644 verify_work_stacks_empty(); | |
5645 | |
5646 // Update subklass/sibling/implementor links in KlassKlass descendants | |
5647 assert(!_revisitStack.isEmpty(), "revisit stack should not be empty"); | |
5648 oop k; | |
5649 while ((k = _revisitStack.pop()) != NULL) { | |
5650 ((Klass*)(oopDesc*)k)->follow_weak_klass_links( | |
5651 &_is_alive_closure, | |
5652 &cmsKeepAliveClosure); | |
5653 } | |
5654 assert(!ClassUnloading || | |
5655 (_markStack.isEmpty() && overflow_list_is_empty()), | |
5656 "Should not have found new reachable objects"); | |
5657 assert(_revisitStack.isEmpty(), "revisit stack should have been drained"); | |
5658 cmsDrainMarkingStackClosure.do_void(); | |
5659 verify_work_stacks_empty(); | |
5660 } | |
5661 | |
5662 { | |
5663 TraceTime t("scrub symbol & string tables", PrintGCDetails, false, gclog_or_tty); | |
5664 // Now clean up stale oops in SymbolTable and StringTable | |
5665 SymbolTable::unlink(&_is_alive_closure); | |
5666 StringTable::unlink(&_is_alive_closure); | |
5667 } | |
5668 } | |
5669 | |
5670 verify_work_stacks_empty(); | |
5671 // Restore any preserved marks as a result of mark stack or | |
5672 // work queue overflow | |
5673 restore_preserved_marks_if_any(); // done single-threaded for now | |
5674 | |
5675 rp->set_enqueuing_is_done(true); | |
5676 if (rp->processing_is_mt()) { | |
5677 CMSRefProcTaskExecutor task_executor(*this); | |
5678 rp->enqueue_discovered_references(&task_executor); | |
5679 } else { | |
5680 rp->enqueue_discovered_references(NULL); | |
5681 } | |
5682 rp->verify_no_references_recorded(); | |
5683 assert(!rp->discovery_enabled(), "should have been disabled"); | |
5684 | |
5685 // JVMTI object tagging is based on JNI weak refs. If any of these | |
5686 // refs were cleared then JVMTI needs to update its maps and | |
5687 // maybe post ObjectFrees to agents. | |
5688 JvmtiExport::cms_ref_processing_epilogue(); | |
5689 } | |
5690 | |
5691 #ifndef PRODUCT | |
5692 void CMSCollector::check_correct_thread_executing() { | |
5693 Thread* t = Thread::current(); | |
5694 // Only the VM thread or the CMS thread should be here. | |
5695 assert(t->is_ConcurrentGC_thread() || t->is_VM_thread(), | |
5696 "Unexpected thread type"); | |
5697 // If this is the vm thread, the foreground process | |
5698 // should not be waiting. Note that _foregroundGCIsActive is | |
5699 // true while the foreground collector is waiting. | |
5700 if (_foregroundGCShouldWait) { | |
5701 // We cannot be the VM thread | |
5702 assert(t->is_ConcurrentGC_thread(), | |
5703 "Should be CMS thread"); | |
5704 } else { | |
5705 // We can be the CMS thread only if we are in a stop-world | |
5706 // phase of CMS collection. | |
5707 if (t->is_ConcurrentGC_thread()) { | |
5708 assert(_collectorState == InitialMarking || | |
5709 _collectorState == FinalMarking, | |
5710 "Should be a stop-world phase"); | |
5711 // The CMS thread should be holding the CMS_token. | |
5712 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
5713 "Potential interference with concurrently " | |
5714 "executing VM thread"); | |
5715 } | |
5716 } | |
5717 } | |
5718 #endif | |
5719 | |
5720 void CMSCollector::sweep(bool asynch) { | |
5721 assert(_collectorState == Sweeping, "just checking"); | |
5722 check_correct_thread_executing(); | |
5723 verify_work_stacks_empty(); | |
5724 verify_overflow_empty(); | |
5725 incrementSweepCount(); | |
5726 _sweep_timer.stop(); | |
5727 _sweep_estimate.sample(_sweep_timer.seconds()); | |
5728 size_policy()->avg_cms_free_at_sweep()->sample(_cmsGen->free()); | |
5729 | |
5730 // PermGen verification support: If perm gen sweeping is disabled in | |
5731 // this cycle, we preserve the perm gen object "deadness" information | |
5732 // in the perm_gen_verify_bit_map. In order to do that we traverse | |
5733 // all blocks in perm gen and mark all dead objects. | |
5734 if (verifying() && !cms_should_unload_classes()) { | |
5735 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(), | |
5736 bitMapLock()); | |
5737 assert(perm_gen_verify_bit_map()->sizeInBits() != 0, | |
5738 "Should have already been allocated"); | |
5739 MarkDeadObjectsClosure mdo(this, _permGen->cmsSpace(), | |
5740 markBitMap(), perm_gen_verify_bit_map()); | |
5741 _permGen->cmsSpace()->blk_iterate(&mdo); | |
5742 } | |
5743 | |
5744 if (asynch) { | |
5745 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); | |
5746 CMSPhaseAccounting pa(this, "sweep", !PrintGCDetails); | |
5747 // First sweep the old gen then the perm gen | |
5748 { | |
5749 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), | |
5750 bitMapLock()); | |
5751 sweepWork(_cmsGen, asynch); | |
5752 } | |
5753 | |
5754 // Now repeat for perm gen | |
5755 if (cms_should_unload_classes()) { | |
5756 CMSTokenSyncWithLocks ts(true, _permGen->freelistLock(), | |
5757 bitMapLock()); | |
5758 sweepWork(_permGen, asynch); | |
5759 } | |
5760 | |
5761 // Update Universe::_heap_*_at_gc figures. | |
5762 // We need all the free list locks to make the abstract state | |
5763 // transition from Sweeping to Resetting. See detailed note | |
5764 // further below. | |
5765 { | |
5766 CMSTokenSyncWithLocks ts(true, _cmsGen->freelistLock(), | |
5767 _permGen->freelistLock()); | |
5768 // Update heap occupancy information which is used as | |
5769 // input to soft ref clearing policy at the next gc. | |
5770 Universe::update_heap_info_at_gc(); | |
5771 _collectorState = Resizing; | |
5772 } | |
5773 } else { | |
5774 // already have needed locks | |
5775 sweepWork(_cmsGen, asynch); | |
5776 | |
5777 if (cms_should_unload_classes()) { | |
5778 sweepWork(_permGen, asynch); | |
5779 } | |
5780 // Update heap occupancy information which is used as | |
5781 // input to soft ref clearing policy at the next gc. | |
5782 Universe::update_heap_info_at_gc(); | |
5783 _collectorState = Resizing; | |
5784 } | |
5785 verify_work_stacks_empty(); | |
5786 verify_overflow_empty(); | |
5787 | |
5788 _sweep_timer.reset(); | |
5789 _sweep_timer.start(); | |
5790 | |
5791 update_time_of_last_gc(os::javaTimeMillis()); | |
5792 | |
5793 // NOTE on abstract state transitions: | |
5794 // Mutators allocate-live and/or mark the mod-union table dirty | |
5795 // based on the state of the collection. The former is done in | |
5796 // the interval [Marking, Sweeping] and the latter in the interval | |
5797 // [Marking, Sweeping). Thus the transitions into the Marking state | |
5798 // and out of the Sweeping state must be synchronously visible | |
5799 // globally to the mutators. | |
5800 // The transition into the Marking state happens with the world | |
5801 // stopped so the mutators will globally see it. Sweeping is | |
5802 // done asynchronously by the background collector so the transition | |
5803 // from the Sweeping state to the Resizing state must be done | |
5804 // under the freelistLock (as is the check for whether to | |
5805 // allocate-live and whether to dirty the mod-union table). | |
5806 assert(_collectorState == Resizing, "Change of collector state to" | |
5807 " Resizing must be done under the freelistLocks (plural)"); | |
5808 | |
5809 // Now that sweeping has been completed, if the GCH's | |
5810 // incremental_collection_will_fail flag is set, clear it, | |
5811 // thus inviting a younger gen collection to promote into | |
5812 // this generation. If such a promotion may still fail, | |
5813 // the flag will be set again when a young collection is | |
5814 // attempted. | |
5815 // I think the incremental_collection_will_fail flag's use | |
5816 // is specific to a 2 generation collection policy, so i'll | |
5817 // assert that that's the configuration we are operating within. | |
5818 // The use of the flag can and should be generalized appropriately | |
5819 // in the future to deal with a general n-generation system. | |
5820 | |
5821 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
5822 assert(gch->collector_policy()->is_two_generation_policy(), | |
5823 "Resetting of incremental_collection_will_fail flag" | |
5824 " may be incorrect otherwise"); | |
5825 gch->clear_incremental_collection_will_fail(); | |
5826 gch->update_full_collections_completed(_collection_count_start); | |
5827 } | |
5828 | |
5829 // FIX ME!!! Looks like this belongs in CFLSpace, with | |
5830 // CMSGen merely delegating to it. | |
5831 void ConcurrentMarkSweepGeneration::setNearLargestChunk() { | |
5832 double nearLargestPercent = 0.999; | |
5833 HeapWord* minAddr = _cmsSpace->bottom(); | |
5834 HeapWord* largestAddr = | |
5835 (HeapWord*) _cmsSpace->dictionary()->findLargestDict(); | |
5836 if (largestAddr == 0) { | |
5837 // The dictionary appears to be empty. In this case | |
5838 // try to coalesce at the end of the heap. | |
5839 largestAddr = _cmsSpace->end(); | |
5840 } | |
5841 size_t largestOffset = pointer_delta(largestAddr, minAddr); | |
5842 size_t nearLargestOffset = | |
5843 (size_t)((double)largestOffset * nearLargestPercent) - MinChunkSize; | |
5844 _cmsSpace->set_nearLargestChunk(minAddr + nearLargestOffset); | |
5845 } | |
5846 | |
5847 bool ConcurrentMarkSweepGeneration::isNearLargestChunk(HeapWord* addr) { | |
5848 return addr >= _cmsSpace->nearLargestChunk(); | |
5849 } | |
5850 | |
5851 FreeChunk* ConcurrentMarkSweepGeneration::find_chunk_at_end() { | |
5852 return _cmsSpace->find_chunk_at_end(); | |
5853 } | |
5854 | |
5855 void ConcurrentMarkSweepGeneration::update_gc_stats(int current_level, | |
5856 bool full) { | |
5857 // The next lower level has been collected. Gather any statistics | |
5858 // that are of interest at this point. | |
5859 if (!full && (current_level + 1) == level()) { | |
5860 // Gather statistics on the young generation collection. | |
5861 collector()->stats().record_gc0_end(used()); | |
5862 } | |
5863 } | |
5864 | |
5865 CMSAdaptiveSizePolicy* ConcurrentMarkSweepGeneration::size_policy() { | |
5866 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
5867 assert(gch->kind() == CollectedHeap::GenCollectedHeap, | |
5868 "Wrong type of heap"); | |
5869 CMSAdaptiveSizePolicy* sp = (CMSAdaptiveSizePolicy*) | |
5870 gch->gen_policy()->size_policy(); | |
5871 assert(sp->is_gc_cms_adaptive_size_policy(), | |
5872 "Wrong type of size policy"); | |
5873 return sp; | |
5874 } | |
5875 | |
5876 void ConcurrentMarkSweepGeneration::rotate_debug_collection_type() { | |
5877 if (PrintGCDetails && Verbose) { | |
5878 gclog_or_tty->print("Rotate from %d ", _debug_collection_type); | |
5879 } | |
5880 _debug_collection_type = (CollectionTypes) (_debug_collection_type + 1); | |
5881 _debug_collection_type = | |
5882 (CollectionTypes) (_debug_collection_type % Unknown_collection_type); | |
5883 if (PrintGCDetails && Verbose) { | |
5884 gclog_or_tty->print_cr("to %d ", _debug_collection_type); | |
5885 } | |
5886 } | |
5887 | |
5888 void CMSCollector::sweepWork(ConcurrentMarkSweepGeneration* gen, | |
5889 bool asynch) { | |
5890 // We iterate over the space(s) underlying this generation, | |
5891 // checking the mark bit map to see if the bits corresponding | |
5892 // to specific blocks are marked or not. Blocks that are | |
5893 // marked are live and are not swept up. All remaining blocks | |
5894 // are swept up, with coalescing on-the-fly as we sweep up | |
5895 // contiguous free and/or garbage blocks: | |
5896 // We need to ensure that the sweeper synchronizes with allocators | |
5897 // and stop-the-world collectors. In particular, the following | |
5898 // locks are used: | |
5899 // . CMS token: if this is held, a stop the world collection cannot occur | |
5900 // . freelistLock: if this is held no allocation can occur from this | |
5901 // generation by another thread | |
5902 // . bitMapLock: if this is held, no other thread can access or update | |
5903 // | |
5904 | |
5905 // Note that we need to hold the freelistLock if we use | |
5906 // block iterate below; else the iterator might go awry if | |
5907 // a mutator (or promotion) causes block contents to change | |
5908 // (for instance if the allocator divvies up a block). | |
5909 // If we hold the free list lock, for all practical purposes | |
5910 // young generation GC's can't occur (they'll usually need to | |
5911 // promote), so we might as well prevent all young generation | |
5912 // GC's while we do a sweeping step. For the same reason, we might | |
5913 // as well take the bit map lock for the entire duration | |
5914 | |
5915 // check that we hold the requisite locks | |
5916 assert(have_cms_token(), "Should hold cms token"); | |
5917 assert( (asynch && ConcurrentMarkSweepThread::cms_thread_has_cms_token()) | |
5918 || (!asynch && ConcurrentMarkSweepThread::vm_thread_has_cms_token()), | |
5919 "Should possess CMS token to sweep"); | |
5920 assert_lock_strong(gen->freelistLock()); | |
5921 assert_lock_strong(bitMapLock()); | |
5922 | |
5923 assert(!_sweep_timer.is_active(), "Was switched off in an outer context"); | |
5924 gen->cmsSpace()->beginSweepFLCensus((float)(_sweep_timer.seconds()), | |
5925 _sweep_estimate.padded_average()); | |
5926 gen->setNearLargestChunk(); | |
5927 | |
5928 { | |
5929 SweepClosure sweepClosure(this, gen, &_markBitMap, | |
5930 CMSYield && asynch); | |
5931 gen->cmsSpace()->blk_iterate_careful(&sweepClosure); | |
5932 // We need to free-up/coalesce garbage/blocks from a | |
5933 // co-terminal free run. This is done in the SweepClosure | |
5934 // destructor; so, do not remove this scope, else the | |
5935 // end-of-sweep-census below will be off by a little bit. | |
5936 } | |
5937 gen->cmsSpace()->sweep_completed(); | |
5938 gen->cmsSpace()->endSweepFLCensus(sweepCount()); | |
5939 } | |
5940 | |
5941 // Reset CMS data structures (for now just the marking bit map) | |
5942 // preparatory for the next cycle. | |
5943 void CMSCollector::reset(bool asynch) { | |
5944 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
5945 CMSAdaptiveSizePolicy* sp = size_policy(); | |
5946 AdaptiveSizePolicyOutput(sp, gch->total_collections()); | |
5947 if (asynch) { | |
5948 CMSTokenSyncWithLocks ts(true, bitMapLock()); | |
5949 | |
5950 // If the state is not "Resetting", the foreground thread | |
5951 // has done a collection and the resetting. | |
5952 if (_collectorState != Resetting) { | |
5953 assert(_collectorState == Idling, "The state should only change" | |
5954 " because the foreground collector has finished the collection"); | |
5955 return; | |
5956 } | |
5957 | |
5958 // Clear the mark bitmap (no grey objects to start with) | |
5959 // for the next cycle. | |
5960 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); | |
5961 CMSPhaseAccounting cmspa(this, "reset", !PrintGCDetails); | |
5962 | |
5963 HeapWord* curAddr = _markBitMap.startWord(); | |
5964 while (curAddr < _markBitMap.endWord()) { | |
5965 size_t remaining = pointer_delta(_markBitMap.endWord(), curAddr); | |
5966 MemRegion chunk(curAddr, MIN2(CMSBitMapYieldQuantum, remaining)); | |
5967 _markBitMap.clear_large_range(chunk); | |
5968 if (ConcurrentMarkSweepThread::should_yield() && | |
5969 !foregroundGCIsActive() && | |
5970 CMSYield) { | |
5971 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
5972 "CMS thread should hold CMS token"); | |
5973 assert_lock_strong(bitMapLock()); | |
5974 bitMapLock()->unlock(); | |
5975 ConcurrentMarkSweepThread::desynchronize(true); | |
5976 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
5977 stopTimer(); | |
5978 if (PrintCMSStatistics != 0) { | |
5979 incrementYields(); | |
5980 } | |
5981 icms_wait(); | |
5982 | |
5983 // See the comment in coordinator_yield() | |
5984 for (unsigned i = 0; i < CMSYieldSleepCount && | |
5985 ConcurrentMarkSweepThread::should_yield() && | |
5986 !CMSCollector::foregroundGCIsActive(); ++i) { | |
5987 os::sleep(Thread::current(), 1, false); | |
5988 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
5989 } | |
5990 | |
5991 ConcurrentMarkSweepThread::synchronize(true); | |
5992 bitMapLock()->lock_without_safepoint_check(); | |
5993 startTimer(); | |
5994 } | |
5995 curAddr = chunk.end(); | |
5996 } | |
5997 _collectorState = Idling; | |
5998 } else { | |
5999 // already have the lock | |
6000 assert(_collectorState == Resetting, "just checking"); | |
6001 assert_lock_strong(bitMapLock()); | |
6002 _markBitMap.clear_all(); | |
6003 _collectorState = Idling; | |
6004 } | |
6005 | |
6006 // Stop incremental mode after a cycle completes, so that any future cycles | |
6007 // are triggered by allocation. | |
6008 stop_icms(); | |
6009 | |
6010 NOT_PRODUCT( | |
6011 if (RotateCMSCollectionTypes) { | |
6012 _cmsGen->rotate_debug_collection_type(); | |
6013 } | |
6014 ) | |
6015 } | |
6016 | |
6017 void CMSCollector::do_CMS_operation(CMS_op_type op) { | |
6018 gclog_or_tty->date_stamp(PrintGC && PrintGCDateStamps); | |
6019 TraceCPUTime tcpu(PrintGCDetails, true, gclog_or_tty); | |
6020 TraceTime t("GC", PrintGC, !PrintGCDetails, gclog_or_tty); | |
6021 TraceCollectorStats tcs(counters()); | |
6022 | |
6023 switch (op) { | |
6024 case CMS_op_checkpointRootsInitial: { | |
6025 checkpointRootsInitial(true); // asynch | |
6026 if (PrintGC) { | |
6027 _cmsGen->printOccupancy("initial-mark"); | |
6028 } | |
6029 break; | |
6030 } | |
6031 case CMS_op_checkpointRootsFinal: { | |
6032 checkpointRootsFinal(true, // asynch | |
6033 false, // !clear_all_soft_refs | |
6034 false); // !init_mark_was_synchronous | |
6035 if (PrintGC) { | |
6036 _cmsGen->printOccupancy("remark"); | |
6037 } | |
6038 break; | |
6039 } | |
6040 default: | |
6041 fatal("No such CMS_op"); | |
6042 } | |
6043 } | |
6044 | |
6045 #ifndef PRODUCT | |
6046 size_t const CMSCollector::skip_header_HeapWords() { | |
6047 return FreeChunk::header_size(); | |
6048 } | |
6049 | |
6050 // Try and collect here conditions that should hold when | |
6051 // CMS thread is exiting. The idea is that the foreground GC | |
6052 // thread should not be blocked if it wants to terminate | |
6053 // the CMS thread and yet continue to run the VM for a while | |
6054 // after that. | |
6055 void CMSCollector::verify_ok_to_terminate() const { | |
6056 assert(Thread::current()->is_ConcurrentGC_thread(), | |
6057 "should be called by CMS thread"); | |
6058 assert(!_foregroundGCShouldWait, "should be false"); | |
6059 // We could check here that all the various low-level locks | |
6060 // are not held by the CMS thread, but that is overkill; see | |
6061 // also CMSThread::verify_ok_to_terminate() where the CGC_lock | |
6062 // is checked. | |
6063 } | |
6064 #endif | |
6065 | |
6066 size_t CMSCollector::block_size_using_printezis_bits(HeapWord* addr) const { | |
6067 assert(_markBitMap.isMarked(addr) && _markBitMap.isMarked(addr + 1), | |
6068 "missing Printezis mark?"); | |
6069 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); | |
6070 size_t size = pointer_delta(nextOneAddr + 1, addr); | |
6071 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), | |
6072 "alignment problem"); | |
6073 assert(size >= 3, "Necessary for Printezis marks to work"); | |
6074 return size; | |
6075 } | |
6076 | |
6077 // A variant of the above (block_size_using_printezis_bits()) except | |
6078 // that we return 0 if the P-bits are not yet set. | |
6079 size_t CMSCollector::block_size_if_printezis_bits(HeapWord* addr) const { | |
6080 if (_markBitMap.isMarked(addr)) { | |
6081 assert(_markBitMap.isMarked(addr + 1), "Missing Printezis bit?"); | |
6082 HeapWord* nextOneAddr = _markBitMap.getNextMarkedWordAddress(addr + 2); | |
6083 size_t size = pointer_delta(nextOneAddr + 1, addr); | |
6084 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), | |
6085 "alignment problem"); | |
6086 assert(size >= 3, "Necessary for Printezis marks to work"); | |
6087 return size; | |
6088 } else { | |
6089 assert(!_markBitMap.isMarked(addr + 1), "Bit map inconsistency?"); | |
6090 return 0; | |
6091 } | |
6092 } | |
6093 | |
6094 HeapWord* CMSCollector::next_card_start_after_block(HeapWord* addr) const { | |
6095 size_t sz = 0; | |
6096 oop p = (oop)addr; | |
6097 if (p->klass() != NULL && p->is_parsable()) { | |
6098 sz = CompactibleFreeListSpace::adjustObjectSize(p->size()); | |
6099 } else { | |
6100 sz = block_size_using_printezis_bits(addr); | |
6101 } | |
6102 assert(sz > 0, "size must be nonzero"); | |
6103 HeapWord* next_block = addr + sz; | |
6104 HeapWord* next_card = (HeapWord*)round_to((uintptr_t)next_block, | |
6105 CardTableModRefBS::card_size); | |
6106 assert(round_down((uintptr_t)addr, CardTableModRefBS::card_size) < | |
6107 round_down((uintptr_t)next_card, CardTableModRefBS::card_size), | |
6108 "must be different cards"); | |
6109 return next_card; | |
6110 } | |
6111 | |
6112 | |
6113 // CMS Bit Map Wrapper ///////////////////////////////////////// | |
6114 | |
6115 // Construct a CMS bit map infrastructure, but don't create the | |
6116 // bit vector itself. That is done by a separate call CMSBitMap::allocate() | |
6117 // further below. | |
6118 CMSBitMap::CMSBitMap(int shifter, int mutex_rank, const char* mutex_name): | |
6119 _bm(NULL,0), | |
6120 _shifter(shifter), | |
6121 _lock(mutex_rank >= 0 ? new Mutex(mutex_rank, mutex_name, true) : NULL) | |
6122 { | |
6123 _bmStartWord = 0; | |
6124 _bmWordSize = 0; | |
6125 } | |
6126 | |
6127 bool CMSBitMap::allocate(MemRegion mr) { | |
6128 _bmStartWord = mr.start(); | |
6129 _bmWordSize = mr.word_size(); | |
6130 ReservedSpace brs(ReservedSpace::allocation_align_size_up( | |
6131 (_bmWordSize >> (_shifter + LogBitsPerByte)) + 1)); | |
6132 if (!brs.is_reserved()) { | |
6133 warning("CMS bit map allocation failure"); | |
6134 return false; | |
6135 } | |
6136 // For now we'll just commit all of the bit map up fromt. | |
6137 // Later on we'll try to be more parsimonious with swap. | |
6138 if (!_virtual_space.initialize(brs, brs.size())) { | |
6139 warning("CMS bit map backing store failure"); | |
6140 return false; | |
6141 } | |
6142 assert(_virtual_space.committed_size() == brs.size(), | |
6143 "didn't reserve backing store for all of CMS bit map?"); | |
6144 _bm.set_map((uintptr_t*)_virtual_space.low()); | |
6145 assert(_virtual_space.committed_size() << (_shifter + LogBitsPerByte) >= | |
6146 _bmWordSize, "inconsistency in bit map sizing"); | |
6147 _bm.set_size(_bmWordSize >> _shifter); | |
6148 | |
6149 // bm.clear(); // can we rely on getting zero'd memory? verify below | |
6150 assert(isAllClear(), | |
6151 "Expected zero'd memory from ReservedSpace constructor"); | |
6152 assert(_bm.size() == heapWordDiffToOffsetDiff(sizeInWords()), | |
6153 "consistency check"); | |
6154 return true; | |
6155 } | |
6156 | |
6157 void CMSBitMap::dirty_range_iterate_clear(MemRegion mr, MemRegionClosure* cl) { | |
6158 HeapWord *next_addr, *end_addr, *last_addr; | |
6159 assert_locked(); | |
6160 assert(covers(mr), "out-of-range error"); | |
6161 // XXX assert that start and end are appropriately aligned | |
6162 for (next_addr = mr.start(), end_addr = mr.end(); | |
6163 next_addr < end_addr; next_addr = last_addr) { | |
6164 MemRegion dirty_region = getAndClearMarkedRegion(next_addr, end_addr); | |
6165 last_addr = dirty_region.end(); | |
6166 if (!dirty_region.is_empty()) { | |
6167 cl->do_MemRegion(dirty_region); | |
6168 } else { | |
6169 assert(last_addr == end_addr, "program logic"); | |
6170 return; | |
6171 } | |
6172 } | |
6173 } | |
6174 | |
6175 #ifndef PRODUCT | |
6176 void CMSBitMap::assert_locked() const { | |
6177 CMSLockVerifier::assert_locked(lock()); | |
6178 } | |
6179 | |
6180 bool CMSBitMap::covers(MemRegion mr) const { | |
6181 // assert(_bm.map() == _virtual_space.low(), "map inconsistency"); | |
6182 assert((size_t)_bm.size() == (_bmWordSize >> _shifter), | |
6183 "size inconsistency"); | |
6184 return (mr.start() >= _bmStartWord) && | |
6185 (mr.end() <= endWord()); | |
6186 } | |
6187 | |
6188 bool CMSBitMap::covers(HeapWord* start, size_t size) const { | |
6189 return (start >= _bmStartWord && (start + size) <= endWord()); | |
6190 } | |
6191 | |
6192 void CMSBitMap::verifyNoOneBitsInRange(HeapWord* left, HeapWord* right) { | |
6193 // verify that there are no 1 bits in the interval [left, right) | |
6194 FalseBitMapClosure falseBitMapClosure; | |
6195 iterate(&falseBitMapClosure, left, right); | |
6196 } | |
6197 | |
6198 void CMSBitMap::region_invariant(MemRegion mr) | |
6199 { | |
6200 assert_locked(); | |
6201 // mr = mr.intersection(MemRegion(_bmStartWord, _bmWordSize)); | |
6202 assert(!mr.is_empty(), "unexpected empty region"); | |
6203 assert(covers(mr), "mr should be covered by bit map"); | |
6204 // convert address range into offset range | |
6205 size_t start_ofs = heapWordToOffset(mr.start()); | |
6206 // Make sure that end() is appropriately aligned | |
6207 assert(mr.end() == (HeapWord*)round_to((intptr_t)mr.end(), | |
6208 (1 << (_shifter+LogHeapWordSize))), | |
6209 "Misaligned mr.end()"); | |
6210 size_t end_ofs = heapWordToOffset(mr.end()); | |
6211 assert(end_ofs > start_ofs, "Should mark at least one bit"); | |
6212 } | |
6213 | |
6214 #endif | |
6215 | |
6216 bool CMSMarkStack::allocate(size_t size) { | |
6217 // allocate a stack of the requisite depth | |
6218 ReservedSpace rs(ReservedSpace::allocation_align_size_up( | |
6219 size * sizeof(oop))); | |
6220 if (!rs.is_reserved()) { | |
6221 warning("CMSMarkStack allocation failure"); | |
6222 return false; | |
6223 } | |
6224 if (!_virtual_space.initialize(rs, rs.size())) { | |
6225 warning("CMSMarkStack backing store failure"); | |
6226 return false; | |
6227 } | |
6228 assert(_virtual_space.committed_size() == rs.size(), | |
6229 "didn't reserve backing store for all of CMS stack?"); | |
6230 _base = (oop*)(_virtual_space.low()); | |
6231 _index = 0; | |
6232 _capacity = size; | |
6233 NOT_PRODUCT(_max_depth = 0); | |
6234 return true; | |
6235 } | |
6236 | |
6237 // XXX FIX ME !!! In the MT case we come in here holding a | |
6238 // leaf lock. For printing we need to take a further lock | |
6239 // which has lower rank. We need to recallibrate the two | |
6240 // lock-ranks involved in order to be able to rpint the | |
6241 // messages below. (Or defer the printing to the caller. | |
6242 // For now we take the expedient path of just disabling the | |
6243 // messages for the problematic case.) | |
6244 void CMSMarkStack::expand() { | |
6245 assert(_capacity <= CMSMarkStackSizeMax, "stack bigger than permitted"); | |
6246 if (_capacity == CMSMarkStackSizeMax) { | |
6247 if (_hit_limit++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) { | |
6248 // We print a warning message only once per CMS cycle. | |
6249 gclog_or_tty->print_cr(" (benign) Hit CMSMarkStack max size limit"); | |
6250 } | |
6251 return; | |
6252 } | |
6253 // Double capacity if possible | |
6254 size_t new_capacity = MIN2(_capacity*2, CMSMarkStackSizeMax); | |
6255 // Do not give up existing stack until we have managed to | |
6256 // get the double capacity that we desired. | |
6257 ReservedSpace rs(ReservedSpace::allocation_align_size_up( | |
6258 new_capacity * sizeof(oop))); | |
6259 if (rs.is_reserved()) { | |
6260 // Release the backing store associated with old stack | |
6261 _virtual_space.release(); | |
6262 // Reinitialize virtual space for new stack | |
6263 if (!_virtual_space.initialize(rs, rs.size())) { | |
6264 fatal("Not enough swap for expanded marking stack"); | |
6265 } | |
6266 _base = (oop*)(_virtual_space.low()); | |
6267 _index = 0; | |
6268 _capacity = new_capacity; | |
6269 } else if (_failed_double++ == 0 && !CMSConcurrentMTEnabled && PrintGCDetails) { | |
6270 // Failed to double capacity, continue; | |
6271 // we print a detail message only once per CMS cycle. | |
6272 gclog_or_tty->print(" (benign) Failed to expand marking stack from "SIZE_FORMAT"K to " | |
6273 SIZE_FORMAT"K", | |
6274 _capacity / K, new_capacity / K); | |
6275 } | |
6276 } | |
6277 | |
6278 | |
6279 // Closures | |
6280 // XXX: there seems to be a lot of code duplication here; | |
6281 // should refactor and consolidate common code. | |
6282 | |
6283 // This closure is used to mark refs into the CMS generation in | |
6284 // the CMS bit map. Called at the first checkpoint. This closure | |
6285 // assumes that we do not need to re-mark dirty cards; if the CMS | |
6286 // generation on which this is used is not an oldest (modulo perm gen) | |
6287 // generation then this will lose younger_gen cards! | |
6288 | |
6289 MarkRefsIntoClosure::MarkRefsIntoClosure( | |
6290 MemRegion span, CMSBitMap* bitMap, bool should_do_nmethods): | |
6291 _span(span), | |
6292 _bitMap(bitMap), | |
6293 _should_do_nmethods(should_do_nmethods) | |
6294 { | |
6295 assert(_ref_processor == NULL, "deliberately left NULL"); | |
6296 assert(_bitMap->covers(_span), "_bitMap/_span mismatch"); | |
6297 } | |
6298 | |
6299 void MarkRefsIntoClosure::do_oop(oop* p) { | |
6300 // if p points into _span, then mark corresponding bit in _markBitMap | |
6301 oop thisOop = *p; | |
6302 if (thisOop != NULL) { | |
6303 assert(thisOop->is_oop(), "expected an oop"); | |
6304 HeapWord* addr = (HeapWord*)thisOop; | |
6305 if (_span.contains(addr)) { | |
6306 // this should be made more efficient | |
6307 _bitMap->mark(addr); | |
6308 } | |
6309 } | |
6310 } | |
6311 | |
6312 // A variant of the above, used for CMS marking verification. | |
6313 MarkRefsIntoVerifyClosure::MarkRefsIntoVerifyClosure( | |
6314 MemRegion span, CMSBitMap* verification_bm, CMSBitMap* cms_bm, | |
6315 bool should_do_nmethods): | |
6316 _span(span), | |
6317 _verification_bm(verification_bm), | |
6318 _cms_bm(cms_bm), | |
6319 _should_do_nmethods(should_do_nmethods) { | |
6320 assert(_ref_processor == NULL, "deliberately left NULL"); | |
6321 assert(_verification_bm->covers(_span), "_verification_bm/_span mismatch"); | |
6322 } | |
6323 | |
6324 void MarkRefsIntoVerifyClosure::do_oop(oop* p) { | |
6325 // if p points into _span, then mark corresponding bit in _markBitMap | |
6326 oop this_oop = *p; | |
6327 if (this_oop != NULL) { | |
6328 assert(this_oop->is_oop(), "expected an oop"); | |
6329 HeapWord* addr = (HeapWord*)this_oop; | |
6330 if (_span.contains(addr)) { | |
6331 _verification_bm->mark(addr); | |
6332 if (!_cms_bm->isMarked(addr)) { | |
6333 oop(addr)->print(); | |
6334 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr); | |
6335 fatal("... aborting"); | |
6336 } | |
6337 } | |
6338 } | |
6339 } | |
6340 | |
6341 ////////////////////////////////////////////////// | |
6342 // MarkRefsIntoAndScanClosure | |
6343 ////////////////////////////////////////////////// | |
6344 | |
6345 MarkRefsIntoAndScanClosure::MarkRefsIntoAndScanClosure(MemRegion span, | |
6346 ReferenceProcessor* rp, | |
6347 CMSBitMap* bit_map, | |
6348 CMSBitMap* mod_union_table, | |
6349 CMSMarkStack* mark_stack, | |
6350 CMSMarkStack* revisit_stack, | |
6351 CMSCollector* collector, | |
6352 bool should_yield, | |
6353 bool concurrent_precleaning): | |
6354 _collector(collector), | |
6355 _span(span), | |
6356 _bit_map(bit_map), | |
6357 _mark_stack(mark_stack), | |
6358 _pushAndMarkClosure(collector, span, rp, bit_map, mod_union_table, | |
6359 mark_stack, revisit_stack, concurrent_precleaning), | |
6360 _yield(should_yield), | |
6361 _concurrent_precleaning(concurrent_precleaning), | |
6362 _freelistLock(NULL) | |
6363 { | |
6364 _ref_processor = rp; | |
6365 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); | |
6366 } | |
6367 | |
6368 // This closure is used to mark refs into the CMS generation at the | |
6369 // second (final) checkpoint, and to scan and transitively follow | |
6370 // the unmarked oops. It is also used during the concurrent precleaning | |
6371 // phase while scanning objects on dirty cards in the CMS generation. | |
6372 // The marks are made in the marking bit map and the marking stack is | |
6373 // used for keeping the (newly) grey objects during the scan. | |
6374 // The parallel version (Par_...) appears further below. | |
6375 void MarkRefsIntoAndScanClosure::do_oop(oop* p) { | |
6376 oop this_oop = *p; | |
6377 if (this_oop != NULL) { | |
6378 assert(this_oop->is_oop(), "expected an oop"); | |
6379 HeapWord* addr = (HeapWord*)this_oop; | |
6380 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); | |
6381 assert(_collector->overflow_list_is_empty(), "should be empty"); | |
6382 if (_span.contains(addr) && | |
6383 !_bit_map->isMarked(addr)) { | |
6384 // mark bit map (object is now grey) | |
6385 _bit_map->mark(addr); | |
6386 // push on marking stack (stack should be empty), and drain the | |
6387 // stack by applying this closure to the oops in the oops popped | |
6388 // from the stack (i.e. blacken the grey objects) | |
6389 bool res = _mark_stack->push(this_oop); | |
6390 assert(res, "Should have space to push on empty stack"); | |
6391 do { | |
6392 oop new_oop = _mark_stack->pop(); | |
6393 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); | |
6394 assert(new_oop->is_parsable(), "Found unparsable oop"); | |
6395 assert(_bit_map->isMarked((HeapWord*)new_oop), | |
6396 "only grey objects on this stack"); | |
6397 // iterate over the oops in this oop, marking and pushing | |
6398 // the ones in CMS heap (i.e. in _span). | |
6399 new_oop->oop_iterate(&_pushAndMarkClosure); | |
6400 // check if it's time to yield | |
6401 do_yield_check(); | |
6402 } while (!_mark_stack->isEmpty() || | |
6403 (!_concurrent_precleaning && take_from_overflow_list())); | |
6404 // if marking stack is empty, and we are not doing this | |
6405 // during precleaning, then check the overflow list | |
6406 } | |
6407 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); | |
6408 assert(_collector->overflow_list_is_empty(), | |
6409 "overflow list was drained above"); | |
6410 // We could restore evacuated mark words, if any, used for | |
6411 // overflow list links here because the overflow list is | |
6412 // provably empty here. That would reduce the maximum | |
6413 // size requirements for preserved_{oop,mark}_stack. | |
6414 // But we'll just postpone it until we are all done | |
6415 // so we can just stream through. | |
6416 if (!_concurrent_precleaning && CMSOverflowEarlyRestoration) { | |
6417 _collector->restore_preserved_marks_if_any(); | |
6418 assert(_collector->no_preserved_marks(), "No preserved marks"); | |
6419 } | |
6420 assert(!CMSOverflowEarlyRestoration || _collector->no_preserved_marks(), | |
6421 "All preserved marks should have been restored above"); | |
6422 } | |
6423 } | |
6424 | |
6425 void MarkRefsIntoAndScanClosure::do_yield_work() { | |
6426 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
6427 "CMS thread should hold CMS token"); | |
6428 assert_lock_strong(_freelistLock); | |
6429 assert_lock_strong(_bit_map->lock()); | |
6430 // relinquish the free_list_lock and bitMaplock() | |
6431 _bit_map->lock()->unlock(); | |
6432 _freelistLock->unlock(); | |
6433 ConcurrentMarkSweepThread::desynchronize(true); | |
6434 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
6435 _collector->stopTimer(); | |
6436 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); | |
6437 if (PrintCMSStatistics != 0) { | |
6438 _collector->incrementYields(); | |
6439 } | |
6440 _collector->icms_wait(); | |
6441 | |
6442 // See the comment in coordinator_yield() | |
6443 for (unsigned i = 0; i < CMSYieldSleepCount && | |
6444 ConcurrentMarkSweepThread::should_yield() && | |
6445 !CMSCollector::foregroundGCIsActive(); ++i) { | |
6446 os::sleep(Thread::current(), 1, false); | |
6447 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
6448 } | |
6449 | |
6450 ConcurrentMarkSweepThread::synchronize(true); | |
6451 _freelistLock->lock_without_safepoint_check(); | |
6452 _bit_map->lock()->lock_without_safepoint_check(); | |
6453 _collector->startTimer(); | |
6454 } | |
6455 | |
6456 /////////////////////////////////////////////////////////// | |
6457 // Par_MarkRefsIntoAndScanClosure: a parallel version of | |
6458 // MarkRefsIntoAndScanClosure | |
6459 /////////////////////////////////////////////////////////// | |
6460 Par_MarkRefsIntoAndScanClosure::Par_MarkRefsIntoAndScanClosure( | |
6461 CMSCollector* collector, MemRegion span, ReferenceProcessor* rp, | |
6462 CMSBitMap* bit_map, OopTaskQueue* work_queue, CMSMarkStack* revisit_stack): | |
6463 _span(span), | |
6464 _bit_map(bit_map), | |
6465 _work_queue(work_queue), | |
6466 _low_water_mark(MIN2((uint)(work_queue->max_elems()/4), | |
6467 (uint)(CMSWorkQueueDrainThreshold * ParallelGCThreads))), | |
6468 _par_pushAndMarkClosure(collector, span, rp, bit_map, work_queue, | |
6469 revisit_stack) | |
6470 { | |
6471 _ref_processor = rp; | |
6472 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); | |
6473 } | |
6474 | |
6475 // This closure is used to mark refs into the CMS generation at the | |
6476 // second (final) checkpoint, and to scan and transitively follow | |
6477 // the unmarked oops. The marks are made in the marking bit map and | |
6478 // the work_queue is used for keeping the (newly) grey objects during | |
6479 // the scan phase whence they are also available for stealing by parallel | |
6480 // threads. Since the marking bit map is shared, updates are | |
6481 // synchronized (via CAS). | |
6482 void Par_MarkRefsIntoAndScanClosure::do_oop(oop* p) { | |
6483 oop this_oop = *p; | |
6484 if (this_oop != NULL) { | |
6485 // Ignore mark word because this could be an already marked oop | |
6486 // that may be chained at the end of the overflow list. | |
6487 assert(this_oop->is_oop(true /* ignore mark word */), "expected an oop"); | |
6488 HeapWord* addr = (HeapWord*)this_oop; | |
6489 if (_span.contains(addr) && | |
6490 !_bit_map->isMarked(addr)) { | |
6491 // mark bit map (object will become grey): | |
6492 // It is possible for several threads to be | |
6493 // trying to "claim" this object concurrently; | |
6494 // the unique thread that succeeds in marking the | |
6495 // object first will do the subsequent push on | |
6496 // to the work queue (or overflow list). | |
6497 if (_bit_map->par_mark(addr)) { | |
6498 // push on work_queue (which may not be empty), and trim the | |
6499 // queue to an appropriate length by applying this closure to | |
6500 // the oops in the oops popped from the stack (i.e. blacken the | |
6501 // grey objects) | |
6502 bool res = _work_queue->push(this_oop); | |
6503 assert(res, "Low water mark should be less than capacity?"); | |
6504 trim_queue(_low_water_mark); | |
6505 } // Else, another thread claimed the object | |
6506 } | |
6507 } | |
6508 } | |
6509 | |
6510 // This closure is used to rescan the marked objects on the dirty cards | |
6511 // in the mod union table and the card table proper. | |
6512 size_t ScanMarkedObjectsAgainCarefullyClosure::do_object_careful_m( | |
6513 oop p, MemRegion mr) { | |
6514 | |
6515 size_t size = 0; | |
6516 HeapWord* addr = (HeapWord*)p; | |
6517 DEBUG_ONLY(_collector->verify_work_stacks_empty();) | |
6518 assert(_span.contains(addr), "we are scanning the CMS generation"); | |
6519 // check if it's time to yield | |
6520 if (do_yield_check()) { | |
6521 // We yielded for some foreground stop-world work, | |
6522 // and we have been asked to abort this ongoing preclean cycle. | |
6523 return 0; | |
6524 } | |
6525 if (_bitMap->isMarked(addr)) { | |
6526 // it's marked; is it potentially uninitialized? | |
6527 if (p->klass() != NULL) { | |
6528 if (CMSPermGenPrecleaningEnabled && !p->is_parsable()) { | |
6529 // Signal precleaning to redirty the card since | |
6530 // the klass pointer is already installed. | |
6531 assert(size == 0, "Initial value"); | |
6532 } else { | |
6533 assert(p->is_parsable(), "must be parsable."); | |
6534 // an initialized object; ignore mark word in verification below | |
6535 // since we are running concurrent with mutators | |
6536 assert(p->is_oop(true), "should be an oop"); | |
6537 if (p->is_objArray()) { | |
6538 // objArrays are precisely marked; restrict scanning | |
6539 // to dirty cards only. | |
6540 size = p->oop_iterate(_scanningClosure, mr); | |
6541 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), | |
6542 "adjustObjectSize should be the identity for array sizes, " | |
6543 "which are necessarily larger than minimum object size of " | |
6544 "two heap words"); | |
6545 } else { | |
6546 // A non-array may have been imprecisely marked; we need | |
6547 // to scan object in its entirety. | |
6548 size = CompactibleFreeListSpace::adjustObjectSize( | |
6549 p->oop_iterate(_scanningClosure)); | |
6550 } | |
6551 #ifdef DEBUG | |
6552 size_t direct_size = | |
6553 CompactibleFreeListSpace::adjustObjectSize(p->size()); | |
6554 assert(size == direct_size, "Inconsistency in size"); | |
6555 assert(size >= 3, "Necessary for Printezis marks to work"); | |
6556 if (!_bitMap->isMarked(addr+1)) { | |
6557 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size); | |
6558 } else { | |
6559 _bitMap->verifyNoOneBitsInRange(addr+2, addr+size-1); | |
6560 assert(_bitMap->isMarked(addr+size-1), | |
6561 "inconsistent Printezis mark"); | |
6562 } | |
6563 #endif // DEBUG | |
6564 } | |
6565 } else { | |
6566 // an unitialized object | |
6567 assert(_bitMap->isMarked(addr+1), "missing Printezis mark?"); | |
6568 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); | |
6569 size = pointer_delta(nextOneAddr + 1, addr); | |
6570 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), | |
6571 "alignment problem"); | |
6572 // Note that pre-cleaning needn't redirty the card. OopDesc::set_klass() | |
6573 // will dirty the card when the klass pointer is installed in the | |
6574 // object (signalling the completion of initialization). | |
6575 } | |
6576 } else { | |
6577 // Either a not yet marked object or an uninitialized object | |
6578 if (p->klass() == NULL || !p->is_parsable()) { | |
6579 // An uninitialized object, skip to the next card, since | |
6580 // we may not be able to read its P-bits yet. | |
6581 assert(size == 0, "Initial value"); | |
6582 } else { | |
6583 // An object not (yet) reached by marking: we merely need to | |
6584 // compute its size so as to go look at the next block. | |
6585 assert(p->is_oop(true), "should be an oop"); | |
6586 size = CompactibleFreeListSpace::adjustObjectSize(p->size()); | |
6587 } | |
6588 } | |
6589 DEBUG_ONLY(_collector->verify_work_stacks_empty();) | |
6590 return size; | |
6591 } | |
6592 | |
6593 void ScanMarkedObjectsAgainCarefullyClosure::do_yield_work() { | |
6594 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
6595 "CMS thread should hold CMS token"); | |
6596 assert_lock_strong(_freelistLock); | |
6597 assert_lock_strong(_bitMap->lock()); | |
6598 // relinquish the free_list_lock and bitMaplock() | |
6599 _bitMap->lock()->unlock(); | |
6600 _freelistLock->unlock(); | |
6601 ConcurrentMarkSweepThread::desynchronize(true); | |
6602 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
6603 _collector->stopTimer(); | |
6604 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); | |
6605 if (PrintCMSStatistics != 0) { | |
6606 _collector->incrementYields(); | |
6607 } | |
6608 _collector->icms_wait(); | |
6609 | |
6610 // See the comment in coordinator_yield() | |
6611 for (unsigned i = 0; i < CMSYieldSleepCount && | |
6612 ConcurrentMarkSweepThread::should_yield() && | |
6613 !CMSCollector::foregroundGCIsActive(); ++i) { | |
6614 os::sleep(Thread::current(), 1, false); | |
6615 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
6616 } | |
6617 | |
6618 ConcurrentMarkSweepThread::synchronize(true); | |
6619 _freelistLock->lock_without_safepoint_check(); | |
6620 _bitMap->lock()->lock_without_safepoint_check(); | |
6621 _collector->startTimer(); | |
6622 } | |
6623 | |
6624 | |
6625 ////////////////////////////////////////////////////////////////// | |
6626 // SurvivorSpacePrecleanClosure | |
6627 ////////////////////////////////////////////////////////////////// | |
6628 // This (single-threaded) closure is used to preclean the oops in | |
6629 // the survivor spaces. | |
6630 size_t SurvivorSpacePrecleanClosure::do_object_careful(oop p) { | |
6631 | |
6632 HeapWord* addr = (HeapWord*)p; | |
6633 DEBUG_ONLY(_collector->verify_work_stacks_empty();) | |
6634 assert(!_span.contains(addr), "we are scanning the survivor spaces"); | |
6635 assert(p->klass() != NULL, "object should be initializd"); | |
6636 assert(p->is_parsable(), "must be parsable."); | |
6637 // an initialized object; ignore mark word in verification below | |
6638 // since we are running concurrent with mutators | |
6639 assert(p->is_oop(true), "should be an oop"); | |
6640 // Note that we do not yield while we iterate over | |
6641 // the interior oops of p, pushing the relevant ones | |
6642 // on our marking stack. | |
6643 size_t size = p->oop_iterate(_scanning_closure); | |
6644 do_yield_check(); | |
6645 // Observe that below, we do not abandon the preclean | |
6646 // phase as soon as we should; rather we empty the | |
6647 // marking stack before returning. This is to satisfy | |
6648 // some existing assertions. In general, it may be a | |
6649 // good idea to abort immediately and complete the marking | |
6650 // from the grey objects at a later time. | |
6651 while (!_mark_stack->isEmpty()) { | |
6652 oop new_oop = _mark_stack->pop(); | |
6653 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); | |
6654 assert(new_oop->is_parsable(), "Found unparsable oop"); | |
6655 assert(_bit_map->isMarked((HeapWord*)new_oop), | |
6656 "only grey objects on this stack"); | |
6657 // iterate over the oops in this oop, marking and pushing | |
6658 // the ones in CMS heap (i.e. in _span). | |
6659 new_oop->oop_iterate(_scanning_closure); | |
6660 // check if it's time to yield | |
6661 do_yield_check(); | |
6662 } | |
6663 unsigned int after_count = | |
6664 GenCollectedHeap::heap()->total_collections(); | |
6665 bool abort = (_before_count != after_count) || | |
6666 _collector->should_abort_preclean(); | |
6667 return abort ? 0 : size; | |
6668 } | |
6669 | |
6670 void SurvivorSpacePrecleanClosure::do_yield_work() { | |
6671 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
6672 "CMS thread should hold CMS token"); | |
6673 assert_lock_strong(_bit_map->lock()); | |
6674 // Relinquish the bit map lock | |
6675 _bit_map->lock()->unlock(); | |
6676 ConcurrentMarkSweepThread::desynchronize(true); | |
6677 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
6678 _collector->stopTimer(); | |
6679 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); | |
6680 if (PrintCMSStatistics != 0) { | |
6681 _collector->incrementYields(); | |
6682 } | |
6683 _collector->icms_wait(); | |
6684 | |
6685 // See the comment in coordinator_yield() | |
6686 for (unsigned i = 0; i < CMSYieldSleepCount && | |
6687 ConcurrentMarkSweepThread::should_yield() && | |
6688 !CMSCollector::foregroundGCIsActive(); ++i) { | |
6689 os::sleep(Thread::current(), 1, false); | |
6690 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
6691 } | |
6692 | |
6693 ConcurrentMarkSweepThread::synchronize(true); | |
6694 _bit_map->lock()->lock_without_safepoint_check(); | |
6695 _collector->startTimer(); | |
6696 } | |
6697 | |
6698 // This closure is used to rescan the marked objects on the dirty cards | |
6699 // in the mod union table and the card table proper. In the parallel | |
6700 // case, although the bitMap is shared, we do a single read so the | |
6701 // isMarked() query is "safe". | |
6702 bool ScanMarkedObjectsAgainClosure::do_object_bm(oop p, MemRegion mr) { | |
6703 // Ignore mark word because we are running concurrent with mutators | |
6704 assert(p->is_oop_or_null(true), "expected an oop or null"); | |
6705 HeapWord* addr = (HeapWord*)p; | |
6706 assert(_span.contains(addr), "we are scanning the CMS generation"); | |
6707 bool is_obj_array = false; | |
6708 #ifdef DEBUG | |
6709 if (!_parallel) { | |
6710 assert(_mark_stack->isEmpty(), "pre-condition (eager drainage)"); | |
6711 assert(_collector->overflow_list_is_empty(), | |
6712 "overflow list should be empty"); | |
6713 | |
6714 } | |
6715 #endif // DEBUG | |
6716 if (_bit_map->isMarked(addr)) { | |
6717 // Obj arrays are precisely marked, non-arrays are not; | |
6718 // so we scan objArrays precisely and non-arrays in their | |
6719 // entirety. | |
6720 if (p->is_objArray()) { | |
6721 is_obj_array = true; | |
6722 if (_parallel) { | |
6723 p->oop_iterate(_par_scan_closure, mr); | |
6724 } else { | |
6725 p->oop_iterate(_scan_closure, mr); | |
6726 } | |
6727 } else { | |
6728 if (_parallel) { | |
6729 p->oop_iterate(_par_scan_closure); | |
6730 } else { | |
6731 p->oop_iterate(_scan_closure); | |
6732 } | |
6733 } | |
6734 } | |
6735 #ifdef DEBUG | |
6736 if (!_parallel) { | |
6737 assert(_mark_stack->isEmpty(), "post-condition (eager drainage)"); | |
6738 assert(_collector->overflow_list_is_empty(), | |
6739 "overflow list should be empty"); | |
6740 | |
6741 } | |
6742 #endif // DEBUG | |
6743 return is_obj_array; | |
6744 } | |
6745 | |
6746 MarkFromRootsClosure::MarkFromRootsClosure(CMSCollector* collector, | |
6747 MemRegion span, | |
6748 CMSBitMap* bitMap, CMSMarkStack* markStack, | |
6749 CMSMarkStack* revisitStack, | |
6750 bool should_yield, bool verifying): | |
6751 _collector(collector), | |
6752 _span(span), | |
6753 _bitMap(bitMap), | |
6754 _mut(&collector->_modUnionTable), | |
6755 _markStack(markStack), | |
6756 _revisitStack(revisitStack), | |
6757 _yield(should_yield), | |
6758 _skipBits(0) | |
6759 { | |
6760 assert(_markStack->isEmpty(), "stack should be empty"); | |
6761 _finger = _bitMap->startWord(); | |
6762 _threshold = _finger; | |
6763 assert(_collector->_restart_addr == NULL, "Sanity check"); | |
6764 assert(_span.contains(_finger), "Out of bounds _finger?"); | |
6765 DEBUG_ONLY(_verifying = verifying;) | |
6766 } | |
6767 | |
6768 void MarkFromRootsClosure::reset(HeapWord* addr) { | |
6769 assert(_markStack->isEmpty(), "would cause duplicates on stack"); | |
6770 assert(_span.contains(addr), "Out of bounds _finger?"); | |
6771 _finger = addr; | |
6772 _threshold = (HeapWord*)round_to( | |
6773 (intptr_t)_finger, CardTableModRefBS::card_size); | |
6774 } | |
6775 | |
6776 // Should revisit to see if this should be restructured for | |
6777 // greater efficiency. | |
6778 void MarkFromRootsClosure::do_bit(size_t offset) { | |
6779 if (_skipBits > 0) { | |
6780 _skipBits--; | |
6781 return; | |
6782 } | |
6783 // convert offset into a HeapWord* | |
6784 HeapWord* addr = _bitMap->startWord() + offset; | |
6785 assert(_bitMap->endWord() && addr < _bitMap->endWord(), | |
6786 "address out of range"); | |
6787 assert(_bitMap->isMarked(addr), "tautology"); | |
6788 if (_bitMap->isMarked(addr+1)) { | |
6789 // this is an allocated but not yet initialized object | |
6790 assert(_skipBits == 0, "tautology"); | |
6791 _skipBits = 2; // skip next two marked bits ("Printezis-marks") | |
6792 oop p = oop(addr); | |
6793 if (p->klass() == NULL || !p->is_parsable()) { | |
6794 DEBUG_ONLY(if (!_verifying) {) | |
6795 // We re-dirty the cards on which this object lies and increase | |
6796 // the _threshold so that we'll come back to scan this object | |
6797 // during the preclean or remark phase. (CMSCleanOnEnter) | |
6798 if (CMSCleanOnEnter) { | |
6799 size_t sz = _collector->block_size_using_printezis_bits(addr); | |
6800 HeapWord* start_card_addr = (HeapWord*)round_down( | |
6801 (intptr_t)addr, CardTableModRefBS::card_size); | |
6802 HeapWord* end_card_addr = (HeapWord*)round_to( | |
6803 (intptr_t)(addr+sz), CardTableModRefBS::card_size); | |
6804 MemRegion redirty_range = MemRegion(start_card_addr, end_card_addr); | |
6805 assert(!redirty_range.is_empty(), "Arithmetical tautology"); | |
6806 // Bump _threshold to end_card_addr; note that | |
6807 // _threshold cannot possibly exceed end_card_addr, anyhow. | |
6808 // This prevents future clearing of the card as the scan proceeds | |
6809 // to the right. | |
6810 assert(_threshold <= end_card_addr, | |
6811 "Because we are just scanning into this object"); | |
6812 if (_threshold < end_card_addr) { | |
6813 _threshold = end_card_addr; | |
6814 } | |
6815 if (p->klass() != NULL) { | |
6816 // Redirty the range of cards... | |
6817 _mut->mark_range(redirty_range); | |
6818 } // ...else the setting of klass will dirty the card anyway. | |
6819 } | |
6820 DEBUG_ONLY(}) | |
6821 return; | |
6822 } | |
6823 } | |
6824 scanOopsInOop(addr); | |
6825 } | |
6826 | |
6827 // We take a break if we've been at this for a while, | |
6828 // so as to avoid monopolizing the locks involved. | |
6829 void MarkFromRootsClosure::do_yield_work() { | |
6830 // First give up the locks, then yield, then re-lock | |
6831 // We should probably use a constructor/destructor idiom to | |
6832 // do this unlock/lock or modify the MutexUnlocker class to | |
6833 // serve our purpose. XXX | |
6834 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
6835 "CMS thread should hold CMS token"); | |
6836 assert_lock_strong(_bitMap->lock()); | |
6837 _bitMap->lock()->unlock(); | |
6838 ConcurrentMarkSweepThread::desynchronize(true); | |
6839 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
6840 _collector->stopTimer(); | |
6841 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); | |
6842 if (PrintCMSStatistics != 0) { | |
6843 _collector->incrementYields(); | |
6844 } | |
6845 _collector->icms_wait(); | |
6846 | |
6847 // See the comment in coordinator_yield() | |
6848 for (unsigned i = 0; i < CMSYieldSleepCount && | |
6849 ConcurrentMarkSweepThread::should_yield() && | |
6850 !CMSCollector::foregroundGCIsActive(); ++i) { | |
6851 os::sleep(Thread::current(), 1, false); | |
6852 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
6853 } | |
6854 | |
6855 ConcurrentMarkSweepThread::synchronize(true); | |
6856 _bitMap->lock()->lock_without_safepoint_check(); | |
6857 _collector->startTimer(); | |
6858 } | |
6859 | |
6860 void MarkFromRootsClosure::scanOopsInOop(HeapWord* ptr) { | |
6861 assert(_bitMap->isMarked(ptr), "expected bit to be set"); | |
6862 assert(_markStack->isEmpty(), | |
6863 "should drain stack to limit stack usage"); | |
6864 // convert ptr to an oop preparatory to scanning | |
6865 oop this_oop = oop(ptr); | |
6866 // Ignore mark word in verification below, since we | |
6867 // may be running concurrent with mutators. | |
6868 assert(this_oop->is_oop(true), "should be an oop"); | |
6869 assert(_finger <= ptr, "_finger runneth ahead"); | |
6870 // advance the finger to right end of this object | |
6871 _finger = ptr + this_oop->size(); | |
6872 assert(_finger > ptr, "we just incremented it above"); | |
6873 // On large heaps, it may take us some time to get through | |
6874 // the marking phase (especially if running iCMS). During | |
6875 // this time it's possible that a lot of mutations have | |
6876 // accumulated in the card table and the mod union table -- | |
6877 // these mutation records are redundant until we have | |
6878 // actually traced into the corresponding card. | |
6879 // Here, we check whether advancing the finger would make | |
6880 // us cross into a new card, and if so clear corresponding | |
6881 // cards in the MUT (preclean them in the card-table in the | |
6882 // future). | |
6883 | |
6884 DEBUG_ONLY(if (!_verifying) {) | |
6885 // The clean-on-enter optimization is disabled by default, | |
6886 // until we fix 6178663. | |
6887 if (CMSCleanOnEnter && (_finger > _threshold)) { | |
6888 // [_threshold, _finger) represents the interval | |
6889 // of cards to be cleared in MUT (or precleaned in card table). | |
6890 // The set of cards to be cleared is all those that overlap | |
6891 // with the interval [_threshold, _finger); note that | |
6892 // _threshold is always kept card-aligned but _finger isn't | |
6893 // always card-aligned. | |
6894 HeapWord* old_threshold = _threshold; | |
6895 assert(old_threshold == (HeapWord*)round_to( | |
6896 (intptr_t)old_threshold, CardTableModRefBS::card_size), | |
6897 "_threshold should always be card-aligned"); | |
6898 _threshold = (HeapWord*)round_to( | |
6899 (intptr_t)_finger, CardTableModRefBS::card_size); | |
6900 MemRegion mr(old_threshold, _threshold); | |
6901 assert(!mr.is_empty(), "Control point invariant"); | |
6902 assert(_span.contains(mr), "Should clear within span"); | |
6903 // XXX When _finger crosses from old gen into perm gen | |
6904 // we may be doing unnecessary cleaning; do better in the | |
6905 // future by detecting that condition and clearing fewer | |
6906 // MUT/CT entries. | |
6907 _mut->clear_range(mr); | |
6908 } | |
6909 DEBUG_ONLY(}) | |
6910 | |
6911 // Note: the finger doesn't advance while we drain | |
6912 // the stack below. | |
6913 PushOrMarkClosure pushOrMarkClosure(_collector, | |
6914 _span, _bitMap, _markStack, | |
6915 _revisitStack, | |
6916 _finger, this); | |
6917 bool res = _markStack->push(this_oop); | |
6918 assert(res, "Empty non-zero size stack should have space for single push"); | |
6919 while (!_markStack->isEmpty()) { | |
6920 oop new_oop = _markStack->pop(); | |
6921 // Skip verifying header mark word below because we are | |
6922 // running concurrent with mutators. | |
6923 assert(new_oop->is_oop(true), "Oops! expected to pop an oop"); | |
6924 // now scan this oop's oops | |
6925 new_oop->oop_iterate(&pushOrMarkClosure); | |
6926 do_yield_check(); | |
6927 } | |
6928 assert(_markStack->isEmpty(), "tautology, emphasizing post-condition"); | |
6929 } | |
6930 | |
6931 Par_MarkFromRootsClosure::Par_MarkFromRootsClosure(CMSConcMarkingTask* task, | |
6932 CMSCollector* collector, MemRegion span, | |
6933 CMSBitMap* bit_map, | |
6934 OopTaskQueue* work_queue, | |
6935 CMSMarkStack* overflow_stack, | |
6936 CMSMarkStack* revisit_stack, | |
6937 bool should_yield): | |
6938 _collector(collector), | |
6939 _whole_span(collector->_span), | |
6940 _span(span), | |
6941 _bit_map(bit_map), | |
6942 _mut(&collector->_modUnionTable), | |
6943 _work_queue(work_queue), | |
6944 _overflow_stack(overflow_stack), | |
6945 _revisit_stack(revisit_stack), | |
6946 _yield(should_yield), | |
6947 _skip_bits(0), | |
6948 _task(task) | |
6949 { | |
6950 assert(_work_queue->size() == 0, "work_queue should be empty"); | |
6951 _finger = span.start(); | |
6952 _threshold = _finger; // XXX Defer clear-on-enter optimization for now | |
6953 assert(_span.contains(_finger), "Out of bounds _finger?"); | |
6954 } | |
6955 | |
6956 // Should revisit to see if this should be restructured for | |
6957 // greater efficiency. | |
6958 void Par_MarkFromRootsClosure::do_bit(size_t offset) { | |
6959 if (_skip_bits > 0) { | |
6960 _skip_bits--; | |
6961 return; | |
6962 } | |
6963 // convert offset into a HeapWord* | |
6964 HeapWord* addr = _bit_map->startWord() + offset; | |
6965 assert(_bit_map->endWord() && addr < _bit_map->endWord(), | |
6966 "address out of range"); | |
6967 assert(_bit_map->isMarked(addr), "tautology"); | |
6968 if (_bit_map->isMarked(addr+1)) { | |
6969 // this is an allocated object that might not yet be initialized | |
6970 assert(_skip_bits == 0, "tautology"); | |
6971 _skip_bits = 2; // skip next two marked bits ("Printezis-marks") | |
6972 oop p = oop(addr); | |
6973 if (p->klass() == NULL || !p->is_parsable()) { | |
6974 // in the case of Clean-on-Enter optimization, redirty card | |
6975 // and avoid clearing card by increasing the threshold. | |
6976 return; | |
6977 } | |
6978 } | |
6979 scan_oops_in_oop(addr); | |
6980 } | |
6981 | |
6982 void Par_MarkFromRootsClosure::scan_oops_in_oop(HeapWord* ptr) { | |
6983 assert(_bit_map->isMarked(ptr), "expected bit to be set"); | |
6984 // Should we assert that our work queue is empty or | |
6985 // below some drain limit? | |
6986 assert(_work_queue->size() == 0, | |
6987 "should drain stack to limit stack usage"); | |
6988 // convert ptr to an oop preparatory to scanning | |
6989 oop this_oop = oop(ptr); | |
6990 // Ignore mark word in verification below, since we | |
6991 // may be running concurrent with mutators. | |
6992 assert(this_oop->is_oop(true), "should be an oop"); | |
6993 assert(_finger <= ptr, "_finger runneth ahead"); | |
6994 // advance the finger to right end of this object | |
6995 _finger = ptr + this_oop->size(); | |
6996 assert(_finger > ptr, "we just incremented it above"); | |
6997 // On large heaps, it may take us some time to get through | |
6998 // the marking phase (especially if running iCMS). During | |
6999 // this time it's possible that a lot of mutations have | |
7000 // accumulated in the card table and the mod union table -- | |
7001 // these mutation records are redundant until we have | |
7002 // actually traced into the corresponding card. | |
7003 // Here, we check whether advancing the finger would make | |
7004 // us cross into a new card, and if so clear corresponding | |
7005 // cards in the MUT (preclean them in the card-table in the | |
7006 // future). | |
7007 | |
7008 // The clean-on-enter optimization is disabled by default, | |
7009 // until we fix 6178663. | |
7010 if (CMSCleanOnEnter && (_finger > _threshold)) { | |
7011 // [_threshold, _finger) represents the interval | |
7012 // of cards to be cleared in MUT (or precleaned in card table). | |
7013 // The set of cards to be cleared is all those that overlap | |
7014 // with the interval [_threshold, _finger); note that | |
7015 // _threshold is always kept card-aligned but _finger isn't | |
7016 // always card-aligned. | |
7017 HeapWord* old_threshold = _threshold; | |
7018 assert(old_threshold == (HeapWord*)round_to( | |
7019 (intptr_t)old_threshold, CardTableModRefBS::card_size), | |
7020 "_threshold should always be card-aligned"); | |
7021 _threshold = (HeapWord*)round_to( | |
7022 (intptr_t)_finger, CardTableModRefBS::card_size); | |
7023 MemRegion mr(old_threshold, _threshold); | |
7024 assert(!mr.is_empty(), "Control point invariant"); | |
7025 assert(_span.contains(mr), "Should clear within span"); // _whole_span ?? | |
7026 // XXX When _finger crosses from old gen into perm gen | |
7027 // we may be doing unnecessary cleaning; do better in the | |
7028 // future by detecting that condition and clearing fewer | |
7029 // MUT/CT entries. | |
7030 _mut->clear_range(mr); | |
7031 } | |
7032 | |
7033 // Note: the local finger doesn't advance while we drain | |
7034 // the stack below, but the global finger sure can and will. | |
7035 HeapWord** gfa = _task->global_finger_addr(); | |
7036 Par_PushOrMarkClosure pushOrMarkClosure(_collector, | |
7037 _span, _bit_map, | |
7038 _work_queue, | |
7039 _overflow_stack, | |
7040 _revisit_stack, | |
7041 _finger, | |
7042 gfa, this); | |
7043 bool res = _work_queue->push(this_oop); // overflow could occur here | |
7044 assert(res, "Will hold once we use workqueues"); | |
7045 while (true) { | |
7046 oop new_oop; | |
7047 if (!_work_queue->pop_local(new_oop)) { | |
7048 // We emptied our work_queue; check if there's stuff that can | |
7049 // be gotten from the overflow stack. | |
7050 if (CMSConcMarkingTask::get_work_from_overflow_stack( | |
7051 _overflow_stack, _work_queue)) { | |
7052 do_yield_check(); | |
7053 continue; | |
7054 } else { // done | |
7055 break; | |
7056 } | |
7057 } | |
7058 // Skip verifying header mark word below because we are | |
7059 // running concurrent with mutators. | |
7060 assert(new_oop->is_oop(true), "Oops! expected to pop an oop"); | |
7061 // now scan this oop's oops | |
7062 new_oop->oop_iterate(&pushOrMarkClosure); | |
7063 do_yield_check(); | |
7064 } | |
7065 assert(_work_queue->size() == 0, "tautology, emphasizing post-condition"); | |
7066 } | |
7067 | |
7068 // Yield in response to a request from VM Thread or | |
7069 // from mutators. | |
7070 void Par_MarkFromRootsClosure::do_yield_work() { | |
7071 assert(_task != NULL, "sanity"); | |
7072 _task->yield(); | |
7073 } | |
7074 | |
7075 // A variant of the above used for verifying CMS marking work. | |
7076 MarkFromRootsVerifyClosure::MarkFromRootsVerifyClosure(CMSCollector* collector, | |
7077 MemRegion span, | |
7078 CMSBitMap* verification_bm, CMSBitMap* cms_bm, | |
7079 CMSMarkStack* mark_stack): | |
7080 _collector(collector), | |
7081 _span(span), | |
7082 _verification_bm(verification_bm), | |
7083 _cms_bm(cms_bm), | |
7084 _mark_stack(mark_stack), | |
7085 _pam_verify_closure(collector, span, verification_bm, cms_bm, | |
7086 mark_stack) | |
7087 { | |
7088 assert(_mark_stack->isEmpty(), "stack should be empty"); | |
7089 _finger = _verification_bm->startWord(); | |
7090 assert(_collector->_restart_addr == NULL, "Sanity check"); | |
7091 assert(_span.contains(_finger), "Out of bounds _finger?"); | |
7092 } | |
7093 | |
7094 void MarkFromRootsVerifyClosure::reset(HeapWord* addr) { | |
7095 assert(_mark_stack->isEmpty(), "would cause duplicates on stack"); | |
7096 assert(_span.contains(addr), "Out of bounds _finger?"); | |
7097 _finger = addr; | |
7098 } | |
7099 | |
7100 // Should revisit to see if this should be restructured for | |
7101 // greater efficiency. | |
7102 void MarkFromRootsVerifyClosure::do_bit(size_t offset) { | |
7103 // convert offset into a HeapWord* | |
7104 HeapWord* addr = _verification_bm->startWord() + offset; | |
7105 assert(_verification_bm->endWord() && addr < _verification_bm->endWord(), | |
7106 "address out of range"); | |
7107 assert(_verification_bm->isMarked(addr), "tautology"); | |
7108 assert(_cms_bm->isMarked(addr), "tautology"); | |
7109 | |
7110 assert(_mark_stack->isEmpty(), | |
7111 "should drain stack to limit stack usage"); | |
7112 // convert addr to an oop preparatory to scanning | |
7113 oop this_oop = oop(addr); | |
7114 assert(this_oop->is_oop(), "should be an oop"); | |
7115 assert(_finger <= addr, "_finger runneth ahead"); | |
7116 // advance the finger to right end of this object | |
7117 _finger = addr + this_oop->size(); | |
7118 assert(_finger > addr, "we just incremented it above"); | |
7119 // Note: the finger doesn't advance while we drain | |
7120 // the stack below. | |
7121 bool res = _mark_stack->push(this_oop); | |
7122 assert(res, "Empty non-zero size stack should have space for single push"); | |
7123 while (!_mark_stack->isEmpty()) { | |
7124 oop new_oop = _mark_stack->pop(); | |
7125 assert(new_oop->is_oop(), "Oops! expected to pop an oop"); | |
7126 // now scan this oop's oops | |
7127 new_oop->oop_iterate(&_pam_verify_closure); | |
7128 } | |
7129 assert(_mark_stack->isEmpty(), "tautology, emphasizing post-condition"); | |
7130 } | |
7131 | |
7132 PushAndMarkVerifyClosure::PushAndMarkVerifyClosure( | |
7133 CMSCollector* collector, MemRegion span, | |
7134 CMSBitMap* verification_bm, CMSBitMap* cms_bm, | |
7135 CMSMarkStack* mark_stack): | |
7136 OopClosure(collector->ref_processor()), | |
7137 _collector(collector), | |
7138 _span(span), | |
7139 _verification_bm(verification_bm), | |
7140 _cms_bm(cms_bm), | |
7141 _mark_stack(mark_stack) | |
7142 { } | |
7143 | |
7144 | |
7145 // Upon stack overflow, we discard (part of) the stack, | |
7146 // remembering the least address amongst those discarded | |
7147 // in CMSCollector's _restart_address. | |
7148 void PushAndMarkVerifyClosure::handle_stack_overflow(HeapWord* lost) { | |
7149 // Remember the least grey address discarded | |
7150 HeapWord* ra = (HeapWord*)_mark_stack->least_value(lost); | |
7151 _collector->lower_restart_addr(ra); | |
7152 _mark_stack->reset(); // discard stack contents | |
7153 _mark_stack->expand(); // expand the stack if possible | |
7154 } | |
7155 | |
7156 void PushAndMarkVerifyClosure::do_oop(oop* p) { | |
7157 oop this_oop = *p; | |
7158 assert(this_oop->is_oop_or_null(), "expected an oop or NULL"); | |
7159 HeapWord* addr = (HeapWord*)this_oop; | |
7160 if (_span.contains(addr) && !_verification_bm->isMarked(addr)) { | |
7161 // Oop lies in _span and isn't yet grey or black | |
7162 _verification_bm->mark(addr); // now grey | |
7163 if (!_cms_bm->isMarked(addr)) { | |
7164 oop(addr)->print(); | |
7165 gclog_or_tty->print_cr(" ("INTPTR_FORMAT" should have been marked)", addr); | |
7166 fatal("... aborting"); | |
7167 } | |
7168 | |
7169 if (!_mark_stack->push(this_oop)) { // stack overflow | |
7170 if (PrintCMSStatistics != 0) { | |
7171 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " | |
7172 SIZE_FORMAT, _mark_stack->capacity()); | |
7173 } | |
7174 assert(_mark_stack->isFull(), "Else push should have succeeded"); | |
7175 handle_stack_overflow(addr); | |
7176 } | |
7177 // anything including and to the right of _finger | |
7178 // will be scanned as we iterate over the remainder of the | |
7179 // bit map | |
7180 } | |
7181 } | |
7182 | |
7183 PushOrMarkClosure::PushOrMarkClosure(CMSCollector* collector, | |
7184 MemRegion span, | |
7185 CMSBitMap* bitMap, CMSMarkStack* markStack, | |
7186 CMSMarkStack* revisitStack, | |
7187 HeapWord* finger, MarkFromRootsClosure* parent) : | |
7188 OopClosure(collector->ref_processor()), | |
7189 _collector(collector), | |
7190 _span(span), | |
7191 _bitMap(bitMap), | |
7192 _markStack(markStack), | |
7193 _revisitStack(revisitStack), | |
7194 _finger(finger), | |
7195 _parent(parent), | |
7196 _should_remember_klasses(collector->cms_should_unload_classes()) | |
7197 { } | |
7198 | |
7199 Par_PushOrMarkClosure::Par_PushOrMarkClosure(CMSCollector* collector, | |
7200 MemRegion span, | |
7201 CMSBitMap* bit_map, | |
7202 OopTaskQueue* work_queue, | |
7203 CMSMarkStack* overflow_stack, | |
7204 CMSMarkStack* revisit_stack, | |
7205 HeapWord* finger, | |
7206 HeapWord** global_finger_addr, | |
7207 Par_MarkFromRootsClosure* parent) : | |
7208 OopClosure(collector->ref_processor()), | |
7209 _collector(collector), | |
7210 _whole_span(collector->_span), | |
7211 _span(span), | |
7212 _bit_map(bit_map), | |
7213 _work_queue(work_queue), | |
7214 _overflow_stack(overflow_stack), | |
7215 _revisit_stack(revisit_stack), | |
7216 _finger(finger), | |
7217 _global_finger_addr(global_finger_addr), | |
7218 _parent(parent), | |
7219 _should_remember_klasses(collector->cms_should_unload_classes()) | |
7220 { } | |
7221 | |
7222 | |
7223 void CMSCollector::lower_restart_addr(HeapWord* low) { | |
7224 assert(_span.contains(low), "Out of bounds addr"); | |
7225 if (_restart_addr == NULL) { | |
7226 _restart_addr = low; | |
7227 } else { | |
7228 _restart_addr = MIN2(_restart_addr, low); | |
7229 } | |
7230 } | |
7231 | |
7232 // Upon stack overflow, we discard (part of) the stack, | |
7233 // remembering the least address amongst those discarded | |
7234 // in CMSCollector's _restart_address. | |
7235 void PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { | |
7236 // Remember the least grey address discarded | |
7237 HeapWord* ra = (HeapWord*)_markStack->least_value(lost); | |
7238 _collector->lower_restart_addr(ra); | |
7239 _markStack->reset(); // discard stack contents | |
7240 _markStack->expand(); // expand the stack if possible | |
7241 } | |
7242 | |
7243 // Upon stack overflow, we discard (part of) the stack, | |
7244 // remembering the least address amongst those discarded | |
7245 // in CMSCollector's _restart_address. | |
7246 void Par_PushOrMarkClosure::handle_stack_overflow(HeapWord* lost) { | |
7247 // We need to do this under a mutex to prevent other | |
7248 // workers from interfering with the expansion below. | |
7249 MutexLockerEx ml(_overflow_stack->par_lock(), | |
7250 Mutex::_no_safepoint_check_flag); | |
7251 // Remember the least grey address discarded | |
7252 HeapWord* ra = (HeapWord*)_overflow_stack->least_value(lost); | |
7253 _collector->lower_restart_addr(ra); | |
7254 _overflow_stack->reset(); // discard stack contents | |
7255 _overflow_stack->expand(); // expand the stack if possible | |
7256 } | |
7257 | |
7258 | |
7259 void PushOrMarkClosure::do_oop(oop* p) { | |
7260 oop thisOop = *p; | |
7261 // Ignore mark word because we are running concurrent with mutators. | |
7262 assert(thisOop->is_oop_or_null(true), "expected an oop or NULL"); | |
7263 HeapWord* addr = (HeapWord*)thisOop; | |
7264 if (_span.contains(addr) && !_bitMap->isMarked(addr)) { | |
7265 // Oop lies in _span and isn't yet grey or black | |
7266 _bitMap->mark(addr); // now grey | |
7267 if (addr < _finger) { | |
7268 // the bit map iteration has already either passed, or | |
7269 // sampled, this bit in the bit map; we'll need to | |
7270 // use the marking stack to scan this oop's oops. | |
7271 bool simulate_overflow = false; | |
7272 NOT_PRODUCT( | |
7273 if (CMSMarkStackOverflowALot && | |
7274 _collector->simulate_overflow()) { | |
7275 // simulate a stack overflow | |
7276 simulate_overflow = true; | |
7277 } | |
7278 ) | |
7279 if (simulate_overflow || !_markStack->push(thisOop)) { // stack overflow | |
7280 if (PrintCMSStatistics != 0) { | |
7281 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " | |
7282 SIZE_FORMAT, _markStack->capacity()); | |
7283 } | |
7284 assert(simulate_overflow || _markStack->isFull(), "Else push should have succeeded"); | |
7285 handle_stack_overflow(addr); | |
7286 } | |
7287 } | |
7288 // anything including and to the right of _finger | |
7289 // will be scanned as we iterate over the remainder of the | |
7290 // bit map | |
7291 do_yield_check(); | |
7292 } | |
7293 } | |
7294 | |
7295 void Par_PushOrMarkClosure::do_oop(oop* p) { | |
7296 oop this_oop = *p; | |
7297 // Ignore mark word because we are running concurrent with mutators. | |
7298 assert(this_oop->is_oop_or_null(true), "expected an oop or NULL"); | |
7299 HeapWord* addr = (HeapWord*)this_oop; | |
7300 if (_whole_span.contains(addr) && !_bit_map->isMarked(addr)) { | |
7301 // Oop lies in _span and isn't yet grey or black | |
7302 // We read the global_finger (volatile read) strictly after marking oop | |
7303 bool res = _bit_map->par_mark(addr); // now grey | |
7304 volatile HeapWord** gfa = (volatile HeapWord**)_global_finger_addr; | |
7305 // Should we push this marked oop on our stack? | |
7306 // -- if someone else marked it, nothing to do | |
7307 // -- if target oop is above global finger nothing to do | |
7308 // -- if target oop is in chunk and above local finger | |
7309 // then nothing to do | |
7310 // -- else push on work queue | |
7311 if ( !res // someone else marked it, they will deal with it | |
7312 || (addr >= *gfa) // will be scanned in a later task | |
7313 || (_span.contains(addr) && addr >= _finger)) { // later in this chunk | |
7314 return; | |
7315 } | |
7316 // the bit map iteration has already either passed, or | |
7317 // sampled, this bit in the bit map; we'll need to | |
7318 // use the marking stack to scan this oop's oops. | |
7319 bool simulate_overflow = false; | |
7320 NOT_PRODUCT( | |
7321 if (CMSMarkStackOverflowALot && | |
7322 _collector->simulate_overflow()) { | |
7323 // simulate a stack overflow | |
7324 simulate_overflow = true; | |
7325 } | |
7326 ) | |
7327 if (simulate_overflow || | |
7328 !(_work_queue->push(this_oop) || _overflow_stack->par_push(this_oop))) { | |
7329 // stack overflow | |
7330 if (PrintCMSStatistics != 0) { | |
7331 gclog_or_tty->print_cr("CMS marking stack overflow (benign) at " | |
7332 SIZE_FORMAT, _overflow_stack->capacity()); | |
7333 } | |
7334 // We cannot assert that the overflow stack is full because | |
7335 // it may have been emptied since. | |
7336 assert(simulate_overflow || | |
7337 _work_queue->size() == _work_queue->max_elems(), | |
7338 "Else push should have succeeded"); | |
7339 handle_stack_overflow(addr); | |
7340 } | |
7341 do_yield_check(); | |
7342 } | |
7343 } | |
7344 | |
7345 | |
7346 PushAndMarkClosure::PushAndMarkClosure(CMSCollector* collector, | |
7347 MemRegion span, | |
7348 ReferenceProcessor* rp, | |
7349 CMSBitMap* bit_map, | |
7350 CMSBitMap* mod_union_table, | |
7351 CMSMarkStack* mark_stack, | |
7352 CMSMarkStack* revisit_stack, | |
7353 bool concurrent_precleaning): | |
7354 OopClosure(rp), | |
7355 _collector(collector), | |
7356 _span(span), | |
7357 _bit_map(bit_map), | |
7358 _mod_union_table(mod_union_table), | |
7359 _mark_stack(mark_stack), | |
7360 _revisit_stack(revisit_stack), | |
7361 _concurrent_precleaning(concurrent_precleaning), | |
7362 _should_remember_klasses(collector->cms_should_unload_classes()) | |
7363 { | |
7364 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); | |
7365 } | |
7366 | |
7367 // Grey object rescan during pre-cleaning and second checkpoint phases -- | |
7368 // the non-parallel version (the parallel version appears further below.) | |
7369 void PushAndMarkClosure::do_oop(oop* p) { | |
7370 oop this_oop = *p; | |
7371 // Ignore mark word verification. If during concurrent precleaning | |
7372 // the object monitor may be locked. If during the checkpoint | |
7373 // phases, the object may already have been reached by a different | |
7374 // path and may be at the end of the global overflow list (so | |
7375 // the mark word may be NULL). | |
7376 assert(this_oop->is_oop_or_null(true/* ignore mark word */), | |
7377 "expected an oop or NULL"); | |
7378 HeapWord* addr = (HeapWord*)this_oop; | |
7379 // Check if oop points into the CMS generation | |
7380 // and is not marked | |
7381 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { | |
7382 // a white object ... | |
7383 _bit_map->mark(addr); // ... now grey | |
7384 // push on the marking stack (grey set) | |
7385 bool simulate_overflow = false; | |
7386 NOT_PRODUCT( | |
7387 if (CMSMarkStackOverflowALot && | |
7388 _collector->simulate_overflow()) { | |
7389 // simulate a stack overflow | |
7390 simulate_overflow = true; | |
7391 } | |
7392 ) | |
7393 if (simulate_overflow || !_mark_stack->push(this_oop)) { | |
7394 if (_concurrent_precleaning) { | |
7395 // During precleaning we can just dirty the appropriate card | |
7396 // in the mod union table, thus ensuring that the object remains | |
7397 // in the grey set and continue. Note that no one can be intefering | |
7398 // with us in this action of dirtying the mod union table, so | |
7399 // no locking is required. | |
7400 _mod_union_table->mark(addr); | |
7401 _collector->_ser_pmc_preclean_ovflw++; | |
7402 } else { | |
7403 // During the remark phase, we need to remember this oop | |
7404 // in the overflow list. | |
7405 _collector->push_on_overflow_list(this_oop); | |
7406 _collector->_ser_pmc_remark_ovflw++; | |
7407 } | |
7408 } | |
7409 } | |
7410 } | |
7411 | |
7412 Par_PushAndMarkClosure::Par_PushAndMarkClosure(CMSCollector* collector, | |
7413 MemRegion span, | |
7414 ReferenceProcessor* rp, | |
7415 CMSBitMap* bit_map, | |
7416 OopTaskQueue* work_queue, | |
7417 CMSMarkStack* revisit_stack): | |
7418 OopClosure(rp), | |
7419 _collector(collector), | |
7420 _span(span), | |
7421 _bit_map(bit_map), | |
7422 _work_queue(work_queue), | |
7423 _revisit_stack(revisit_stack), | |
7424 _should_remember_klasses(collector->cms_should_unload_classes()) | |
7425 { | |
7426 assert(_ref_processor != NULL, "_ref_processor shouldn't be NULL"); | |
7427 } | |
7428 | |
7429 // Grey object rescan during second checkpoint phase -- | |
7430 // the parallel version. | |
7431 void Par_PushAndMarkClosure::do_oop(oop* p) { | |
7432 oop this_oop = *p; | |
7433 // In the assert below, we ignore the mark word because | |
7434 // this oop may point to an already visited object that is | |
7435 // on the overflow stack (in which case the mark word has | |
7436 // been hijacked for chaining into the overflow stack -- | |
7437 // if this is the last object in the overflow stack then | |
7438 // its mark word will be NULL). Because this object may | |
7439 // have been subsequently popped off the global overflow | |
7440 // stack, and the mark word possibly restored to the prototypical | |
7441 // value, by the time we get to examined this failing assert in | |
7442 // the debugger, is_oop_or_null(false) may subsequently start | |
7443 // to hold. | |
7444 assert(this_oop->is_oop_or_null(true), | |
7445 "expected an oop or NULL"); | |
7446 HeapWord* addr = (HeapWord*)this_oop; | |
7447 // Check if oop points into the CMS generation | |
7448 // and is not marked | |
7449 if (_span.contains(addr) && !_bit_map->isMarked(addr)) { | |
7450 // a white object ... | |
7451 // If we manage to "claim" the object, by being the | |
7452 // first thread to mark it, then we push it on our | |
7453 // marking stack | |
7454 if (_bit_map->par_mark(addr)) { // ... now grey | |
7455 // push on work queue (grey set) | |
7456 bool simulate_overflow = false; | |
7457 NOT_PRODUCT( | |
7458 if (CMSMarkStackOverflowALot && | |
7459 _collector->par_simulate_overflow()) { | |
7460 // simulate a stack overflow | |
7461 simulate_overflow = true; | |
7462 } | |
7463 ) | |
7464 if (simulate_overflow || !_work_queue->push(this_oop)) { | |
7465 _collector->par_push_on_overflow_list(this_oop); | |
7466 _collector->_par_pmc_remark_ovflw++; // imprecise OK: no need to CAS | |
7467 } | |
7468 } // Else, some other thread got there first | |
7469 } | |
7470 } | |
7471 | |
7472 void PushAndMarkClosure::remember_klass(Klass* k) { | |
7473 if (!_revisit_stack->push(oop(k))) { | |
7474 fatal("Revisit stack overflowed in PushAndMarkClosure"); | |
7475 } | |
7476 } | |
7477 | |
7478 void Par_PushAndMarkClosure::remember_klass(Klass* k) { | |
7479 if (!_revisit_stack->par_push(oop(k))) { | |
7480 fatal("Revist stack overflowed in Par_PushAndMarkClosure"); | |
7481 } | |
7482 } | |
7483 | |
7484 void CMSPrecleanRefsYieldClosure::do_yield_work() { | |
7485 Mutex* bml = _collector->bitMapLock(); | |
7486 assert_lock_strong(bml); | |
7487 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
7488 "CMS thread should hold CMS token"); | |
7489 | |
7490 bml->unlock(); | |
7491 ConcurrentMarkSweepThread::desynchronize(true); | |
7492 | |
7493 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
7494 | |
7495 _collector->stopTimer(); | |
7496 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); | |
7497 if (PrintCMSStatistics != 0) { | |
7498 _collector->incrementYields(); | |
7499 } | |
7500 _collector->icms_wait(); | |
7501 | |
7502 // See the comment in coordinator_yield() | |
7503 for (unsigned i = 0; i < CMSYieldSleepCount && | |
7504 ConcurrentMarkSweepThread::should_yield() && | |
7505 !CMSCollector::foregroundGCIsActive(); ++i) { | |
7506 os::sleep(Thread::current(), 1, false); | |
7507 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
7508 } | |
7509 | |
7510 ConcurrentMarkSweepThread::synchronize(true); | |
7511 bml->lock(); | |
7512 | |
7513 _collector->startTimer(); | |
7514 } | |
7515 | |
7516 bool CMSPrecleanRefsYieldClosure::should_return() { | |
7517 if (ConcurrentMarkSweepThread::should_yield()) { | |
7518 do_yield_work(); | |
7519 } | |
7520 return _collector->foregroundGCIsActive(); | |
7521 } | |
7522 | |
7523 void MarkFromDirtyCardsClosure::do_MemRegion(MemRegion mr) { | |
7524 assert(((size_t)mr.start())%CardTableModRefBS::card_size_in_words == 0, | |
7525 "mr should be aligned to start at a card boundary"); | |
7526 // We'd like to assert: | |
7527 // assert(mr.word_size()%CardTableModRefBS::card_size_in_words == 0, | |
7528 // "mr should be a range of cards"); | |
7529 // However, that would be too strong in one case -- the last | |
7530 // partition ends at _unallocated_block which, in general, can be | |
7531 // an arbitrary boundary, not necessarily card aligned. | |
7532 if (PrintCMSStatistics != 0) { | |
7533 _num_dirty_cards += | |
7534 mr.word_size()/CardTableModRefBS::card_size_in_words; | |
7535 } | |
7536 _space->object_iterate_mem(mr, &_scan_cl); | |
7537 } | |
7538 | |
7539 SweepClosure::SweepClosure(CMSCollector* collector, | |
7540 ConcurrentMarkSweepGeneration* g, | |
7541 CMSBitMap* bitMap, bool should_yield) : | |
7542 _collector(collector), | |
7543 _g(g), | |
7544 _sp(g->cmsSpace()), | |
7545 _limit(_sp->sweep_limit()), | |
7546 _freelistLock(_sp->freelistLock()), | |
7547 _bitMap(bitMap), | |
7548 _yield(should_yield), | |
7549 _inFreeRange(false), // No free range at beginning of sweep | |
7550 _freeRangeInFreeLists(false), // No free range at beginning of sweep | |
7551 _lastFreeRangeCoalesced(false), | |
7552 _freeFinger(g->used_region().start()) | |
7553 { | |
7554 NOT_PRODUCT( | |
7555 _numObjectsFreed = 0; | |
7556 _numWordsFreed = 0; | |
7557 _numObjectsLive = 0; | |
7558 _numWordsLive = 0; | |
7559 _numObjectsAlreadyFree = 0; | |
7560 _numWordsAlreadyFree = 0; | |
7561 _last_fc = NULL; | |
7562 | |
7563 _sp->initializeIndexedFreeListArrayReturnedBytes(); | |
7564 _sp->dictionary()->initializeDictReturnedBytes(); | |
7565 ) | |
7566 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), | |
7567 "sweep _limit out of bounds"); | |
7568 if (CMSTraceSweeper) { | |
7569 gclog_or_tty->print("\n====================\nStarting new sweep\n"); | |
7570 } | |
7571 } | |
7572 | |
7573 // We need this destructor to reclaim any space at the end | |
7574 // of the space, which do_blk below may not have added back to | |
7575 // the free lists. [basically dealing with the "fringe effect"] | |
7576 SweepClosure::~SweepClosure() { | |
7577 assert_lock_strong(_freelistLock); | |
7578 // this should be treated as the end of a free run if any | |
7579 // The current free range should be returned to the free lists | |
7580 // as one coalesced chunk. | |
7581 if (inFreeRange()) { | |
7582 flushCurFreeChunk(freeFinger(), | |
7583 pointer_delta(_limit, freeFinger())); | |
7584 assert(freeFinger() < _limit, "the finger pointeth off base"); | |
7585 if (CMSTraceSweeper) { | |
7586 gclog_or_tty->print("destructor:"); | |
7587 gclog_or_tty->print("Sweep:put_free_blk 0x%x ("SIZE_FORMAT") " | |
7588 "[coalesced:"SIZE_FORMAT"]\n", | |
7589 freeFinger(), pointer_delta(_limit, freeFinger()), | |
7590 lastFreeRangeCoalesced()); | |
7591 } | |
7592 } | |
7593 NOT_PRODUCT( | |
7594 if (Verbose && PrintGC) { | |
7595 gclog_or_tty->print("Collected "SIZE_FORMAT" objects, " | |
7596 SIZE_FORMAT " bytes", | |
7597 _numObjectsFreed, _numWordsFreed*sizeof(HeapWord)); | |
7598 gclog_or_tty->print_cr("\nLive "SIZE_FORMAT" objects, " | |
7599 SIZE_FORMAT" bytes " | |
7600 "Already free "SIZE_FORMAT" objects, "SIZE_FORMAT" bytes", | |
7601 _numObjectsLive, _numWordsLive*sizeof(HeapWord), | |
7602 _numObjectsAlreadyFree, _numWordsAlreadyFree*sizeof(HeapWord)); | |
7603 size_t totalBytes = (_numWordsFreed + _numWordsLive + _numWordsAlreadyFree) * | |
7604 sizeof(HeapWord); | |
7605 gclog_or_tty->print_cr("Total sweep: "SIZE_FORMAT" bytes", totalBytes); | |
7606 | |
7607 if (PrintCMSStatistics && CMSVerifyReturnedBytes) { | |
7608 size_t indexListReturnedBytes = _sp->sumIndexedFreeListArrayReturnedBytes(); | |
7609 size_t dictReturnedBytes = _sp->dictionary()->sumDictReturnedBytes(); | |
7610 size_t returnedBytes = indexListReturnedBytes + dictReturnedBytes; | |
7611 gclog_or_tty->print("Returned "SIZE_FORMAT" bytes", returnedBytes); | |
7612 gclog_or_tty->print(" Indexed List Returned "SIZE_FORMAT" bytes", | |
7613 indexListReturnedBytes); | |
7614 gclog_or_tty->print_cr(" Dictionary Returned "SIZE_FORMAT" bytes", | |
7615 dictReturnedBytes); | |
7616 } | |
7617 } | |
7618 ) | |
7619 // Now, in debug mode, just null out the sweep_limit | |
7620 NOT_PRODUCT(_sp->clear_sweep_limit();) | |
7621 if (CMSTraceSweeper) { | |
7622 gclog_or_tty->print("end of sweep\n================\n"); | |
7623 } | |
7624 } | |
7625 | |
7626 void SweepClosure::initialize_free_range(HeapWord* freeFinger, | |
7627 bool freeRangeInFreeLists) { | |
7628 if (CMSTraceSweeper) { | |
7629 gclog_or_tty->print("---- Start free range 0x%x with free block [%d] (%d)\n", | |
7630 freeFinger, _sp->block_size(freeFinger), | |
7631 freeRangeInFreeLists); | |
7632 } | |
7633 assert(!inFreeRange(), "Trampling existing free range"); | |
7634 set_inFreeRange(true); | |
7635 set_lastFreeRangeCoalesced(false); | |
7636 | |
7637 set_freeFinger(freeFinger); | |
7638 set_freeRangeInFreeLists(freeRangeInFreeLists); | |
7639 if (CMSTestInFreeList) { | |
7640 if (freeRangeInFreeLists) { | |
7641 FreeChunk* fc = (FreeChunk*) freeFinger; | |
7642 assert(fc->isFree(), "A chunk on the free list should be free."); | |
7643 assert(fc->size() > 0, "Free range should have a size"); | |
7644 assert(_sp->verifyChunkInFreeLists(fc), "Chunk is not in free lists"); | |
7645 } | |
7646 } | |
7647 } | |
7648 | |
7649 // Note that the sweeper runs concurrently with mutators. Thus, | |
7650 // it is possible for direct allocation in this generation to happen | |
7651 // in the middle of the sweep. Note that the sweeper also coalesces | |
7652 // contiguous free blocks. Thus, unless the sweeper and the allocator | |
7653 // synchronize appropriately freshly allocated blocks may get swept up. | |
7654 // This is accomplished by the sweeper locking the free lists while | |
7655 // it is sweeping. Thus blocks that are determined to be free are | |
7656 // indeed free. There is however one additional complication: | |
7657 // blocks that have been allocated since the final checkpoint and | |
7658 // mark, will not have been marked and so would be treated as | |
7659 // unreachable and swept up. To prevent this, the allocator marks | |
7660 // the bit map when allocating during the sweep phase. This leads, | |
7661 // however, to a further complication -- objects may have been allocated | |
7662 // but not yet initialized -- in the sense that the header isn't yet | |
7663 // installed. The sweeper can not then determine the size of the block | |
7664 // in order to skip over it. To deal with this case, we use a technique | |
7665 // (due to Printezis) to encode such uninitialized block sizes in the | |
7666 // bit map. Since the bit map uses a bit per every HeapWord, but the | |
7667 // CMS generation has a minimum object size of 3 HeapWords, it follows | |
7668 // that "normal marks" won't be adjacent in the bit map (there will | |
7669 // always be at least two 0 bits between successive 1 bits). We make use | |
7670 // of these "unused" bits to represent uninitialized blocks -- the bit | |
7671 // corresponding to the start of the uninitialized object and the next | |
7672 // bit are both set. Finally, a 1 bit marks the end of the object that | |
7673 // started with the two consecutive 1 bits to indicate its potentially | |
7674 // uninitialized state. | |
7675 | |
7676 size_t SweepClosure::do_blk_careful(HeapWord* addr) { | |
7677 FreeChunk* fc = (FreeChunk*)addr; | |
7678 size_t res; | |
7679 | |
7680 // check if we are done sweepinrg | |
7681 if (addr == _limit) { // we have swept up to the limit, do nothing more | |
7682 assert(_limit >= _sp->bottom() && _limit <= _sp->end(), | |
7683 "sweep _limit out of bounds"); | |
7684 // help the closure application finish | |
7685 return pointer_delta(_sp->end(), _limit); | |
7686 } | |
7687 assert(addr <= _limit, "sweep invariant"); | |
7688 | |
7689 // check if we should yield | |
7690 do_yield_check(addr); | |
7691 if (fc->isFree()) { | |
7692 // Chunk that is already free | |
7693 res = fc->size(); | |
7694 doAlreadyFreeChunk(fc); | |
7695 debug_only(_sp->verifyFreeLists()); | |
7696 assert(res == fc->size(), "Don't expect the size to change"); | |
7697 NOT_PRODUCT( | |
7698 _numObjectsAlreadyFree++; | |
7699 _numWordsAlreadyFree += res; | |
7700 ) | |
7701 NOT_PRODUCT(_last_fc = fc;) | |
7702 } else if (!_bitMap->isMarked(addr)) { | |
7703 // Chunk is fresh garbage | |
7704 res = doGarbageChunk(fc); | |
7705 debug_only(_sp->verifyFreeLists()); | |
7706 NOT_PRODUCT( | |
7707 _numObjectsFreed++; | |
7708 _numWordsFreed += res; | |
7709 ) | |
7710 } else { | |
7711 // Chunk that is alive. | |
7712 res = doLiveChunk(fc); | |
7713 debug_only(_sp->verifyFreeLists()); | |
7714 NOT_PRODUCT( | |
7715 _numObjectsLive++; | |
7716 _numWordsLive += res; | |
7717 ) | |
7718 } | |
7719 return res; | |
7720 } | |
7721 | |
7722 // For the smart allocation, record following | |
7723 // split deaths - a free chunk is removed from its free list because | |
7724 // it is being split into two or more chunks. | |
7725 // split birth - a free chunk is being added to its free list because | |
7726 // a larger free chunk has been split and resulted in this free chunk. | |
7727 // coal death - a free chunk is being removed from its free list because | |
7728 // it is being coalesced into a large free chunk. | |
7729 // coal birth - a free chunk is being added to its free list because | |
7730 // it was created when two or more free chunks where coalesced into | |
7731 // this free chunk. | |
7732 // | |
7733 // These statistics are used to determine the desired number of free | |
7734 // chunks of a given size. The desired number is chosen to be relative | |
7735 // to the end of a CMS sweep. The desired number at the end of a sweep | |
7736 // is the | |
7737 // count-at-end-of-previous-sweep (an amount that was enough) | |
7738 // - count-at-beginning-of-current-sweep (the excess) | |
7739 // + split-births (gains in this size during interval) | |
7740 // - split-deaths (demands on this size during interval) | |
7741 // where the interval is from the end of one sweep to the end of the | |
7742 // next. | |
7743 // | |
7744 // When sweeping the sweeper maintains an accumulated chunk which is | |
7745 // the chunk that is made up of chunks that have been coalesced. That | |
7746 // will be termed the left-hand chunk. A new chunk of garbage that | |
7747 // is being considered for coalescing will be referred to as the | |
7748 // right-hand chunk. | |
7749 // | |
7750 // When making a decision on whether to coalesce a right-hand chunk with | |
7751 // the current left-hand chunk, the current count vs. the desired count | |
7752 // of the left-hand chunk is considered. Also if the right-hand chunk | |
7753 // is near the large chunk at the end of the heap (see | |
7754 // ConcurrentMarkSweepGeneration::isNearLargestChunk()), then the | |
7755 // left-hand chunk is coalesced. | |
7756 // | |
7757 // When making a decision about whether to split a chunk, the desired count | |
7758 // vs. the current count of the candidate to be split is also considered. | |
7759 // If the candidate is underpopulated (currently fewer chunks than desired) | |
7760 // a chunk of an overpopulated (currently more chunks than desired) size may | |
7761 // be chosen. The "hint" associated with a free list, if non-null, points | |
7762 // to a free list which may be overpopulated. | |
7763 // | |
7764 | |
7765 void SweepClosure::doAlreadyFreeChunk(FreeChunk* fc) { | |
7766 size_t size = fc->size(); | |
7767 // Chunks that cannot be coalesced are not in the | |
7768 // free lists. | |
7769 if (CMSTestInFreeList && !fc->cantCoalesce()) { | |
7770 assert(_sp->verifyChunkInFreeLists(fc), | |
7771 "free chunk should be in free lists"); | |
7772 } | |
7773 // a chunk that is already free, should not have been | |
7774 // marked in the bit map | |
7775 HeapWord* addr = (HeapWord*) fc; | |
7776 assert(!_bitMap->isMarked(addr), "free chunk should be unmarked"); | |
7777 // Verify that the bit map has no bits marked between | |
7778 // addr and purported end of this block. | |
7779 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); | |
7780 | |
7781 // Some chunks cannot be coalesced in under any circumstances. | |
7782 // See the definition of cantCoalesce(). | |
7783 if (!fc->cantCoalesce()) { | |
7784 // This chunk can potentially be coalesced. | |
7785 if (_sp->adaptive_freelists()) { | |
7786 // All the work is done in | |
7787 doPostIsFreeOrGarbageChunk(fc, size); | |
7788 } else { // Not adaptive free lists | |
7789 // this is a free chunk that can potentially be coalesced by the sweeper; | |
7790 if (!inFreeRange()) { | |
7791 // if the next chunk is a free block that can't be coalesced | |
7792 // it doesn't make sense to remove this chunk from the free lists | |
7793 FreeChunk* nextChunk = (FreeChunk*)(addr + size); | |
7794 assert((HeapWord*)nextChunk <= _limit, "sweep invariant"); | |
7795 if ((HeapWord*)nextChunk < _limit && // there's a next chunk... | |
7796 nextChunk->isFree() && // which is free... | |
7797 nextChunk->cantCoalesce()) { // ... but cant be coalesced | |
7798 // nothing to do | |
7799 } else { | |
7800 // Potentially the start of a new free range: | |
7801 // Don't eagerly remove it from the free lists. | |
7802 // No need to remove it if it will just be put | |
7803 // back again. (Also from a pragmatic point of view | |
7804 // if it is a free block in a region that is beyond | |
7805 // any allocated blocks, an assertion will fail) | |
7806 // Remember the start of a free run. | |
7807 initialize_free_range(addr, true); | |
7808 // end - can coalesce with next chunk | |
7809 } | |
7810 } else { | |
7811 // the midst of a free range, we are coalescing | |
7812 debug_only(record_free_block_coalesced(fc);) | |
7813 if (CMSTraceSweeper) { | |
7814 gclog_or_tty->print(" -- pick up free block 0x%x (%d)\n", fc, size); | |
7815 } | |
7816 // remove it from the free lists | |
7817 _sp->removeFreeChunkFromFreeLists(fc); | |
7818 set_lastFreeRangeCoalesced(true); | |
7819 // If the chunk is being coalesced and the current free range is | |
7820 // in the free lists, remove the current free range so that it | |
7821 // will be returned to the free lists in its entirety - all | |
7822 // the coalesced pieces included. | |
7823 if (freeRangeInFreeLists()) { | |
7824 FreeChunk* ffc = (FreeChunk*) freeFinger(); | |
7825 assert(ffc->size() == pointer_delta(addr, freeFinger()), | |
7826 "Size of free range is inconsistent with chunk size."); | |
7827 if (CMSTestInFreeList) { | |
7828 assert(_sp->verifyChunkInFreeLists(ffc), | |
7829 "free range is not in free lists"); | |
7830 } | |
7831 _sp->removeFreeChunkFromFreeLists(ffc); | |
7832 set_freeRangeInFreeLists(false); | |
7833 } | |
7834 } | |
7835 } | |
7836 } else { | |
7837 // Code path common to both original and adaptive free lists. | |
7838 | |
7839 // cant coalesce with previous block; this should be treated | |
7840 // as the end of a free run if any | |
7841 if (inFreeRange()) { | |
7842 // we kicked some butt; time to pick up the garbage | |
7843 assert(freeFinger() < addr, "the finger pointeth off base"); | |
7844 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger())); | |
7845 } | |
7846 // else, nothing to do, just continue | |
7847 } | |
7848 } | |
7849 | |
7850 size_t SweepClosure::doGarbageChunk(FreeChunk* fc) { | |
7851 // This is a chunk of garbage. It is not in any free list. | |
7852 // Add it to a free list or let it possibly be coalesced into | |
7853 // a larger chunk. | |
7854 HeapWord* addr = (HeapWord*) fc; | |
7855 size_t size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); | |
7856 | |
7857 if (_sp->adaptive_freelists()) { | |
7858 // Verify that the bit map has no bits marked between | |
7859 // addr and purported end of just dead object. | |
7860 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); | |
7861 | |
7862 doPostIsFreeOrGarbageChunk(fc, size); | |
7863 } else { | |
7864 if (!inFreeRange()) { | |
7865 // start of a new free range | |
7866 assert(size > 0, "A free range should have a size"); | |
7867 initialize_free_range(addr, false); | |
7868 | |
7869 } else { | |
7870 // this will be swept up when we hit the end of the | |
7871 // free range | |
7872 if (CMSTraceSweeper) { | |
7873 gclog_or_tty->print(" -- pick up garbage 0x%x (%d) \n", fc, size); | |
7874 } | |
7875 // If the chunk is being coalesced and the current free range is | |
7876 // in the free lists, remove the current free range so that it | |
7877 // will be returned to the free lists in its entirety - all | |
7878 // the coalesced pieces included. | |
7879 if (freeRangeInFreeLists()) { | |
7880 FreeChunk* ffc = (FreeChunk*)freeFinger(); | |
7881 assert(ffc->size() == pointer_delta(addr, freeFinger()), | |
7882 "Size of free range is inconsistent with chunk size."); | |
7883 if (CMSTestInFreeList) { | |
7884 assert(_sp->verifyChunkInFreeLists(ffc), | |
7885 "free range is not in free lists"); | |
7886 } | |
7887 _sp->removeFreeChunkFromFreeLists(ffc); | |
7888 set_freeRangeInFreeLists(false); | |
7889 } | |
7890 set_lastFreeRangeCoalesced(true); | |
7891 } | |
7892 // this will be swept up when we hit the end of the free range | |
7893 | |
7894 // Verify that the bit map has no bits marked between | |
7895 // addr and purported end of just dead object. | |
7896 _bitMap->verifyNoOneBitsInRange(addr + 1, addr + size); | |
7897 } | |
7898 return size; | |
7899 } | |
7900 | |
7901 size_t SweepClosure::doLiveChunk(FreeChunk* fc) { | |
7902 HeapWord* addr = (HeapWord*) fc; | |
7903 // The sweeper has just found a live object. Return any accumulated | |
7904 // left hand chunk to the free lists. | |
7905 if (inFreeRange()) { | |
7906 if (_sp->adaptive_freelists()) { | |
7907 flushCurFreeChunk(freeFinger(), | |
7908 pointer_delta(addr, freeFinger())); | |
7909 } else { // not adaptive freelists | |
7910 set_inFreeRange(false); | |
7911 // Add the free range back to the free list if it is not already | |
7912 // there. | |
7913 if (!freeRangeInFreeLists()) { | |
7914 assert(freeFinger() < addr, "the finger pointeth off base"); | |
7915 if (CMSTraceSweeper) { | |
7916 gclog_or_tty->print("Sweep:put_free_blk 0x%x (%d) " | |
7917 "[coalesced:%d]\n", | |
7918 freeFinger(), pointer_delta(addr, freeFinger()), | |
7919 lastFreeRangeCoalesced()); | |
7920 } | |
7921 _sp->addChunkAndRepairOffsetTable(freeFinger(), | |
7922 pointer_delta(addr, freeFinger()), lastFreeRangeCoalesced()); | |
7923 } | |
7924 } | |
7925 } | |
7926 | |
7927 // Common code path for original and adaptive free lists. | |
7928 | |
7929 // this object is live: we'd normally expect this to be | |
7930 // an oop, and like to assert the following: | |
7931 // assert(oop(addr)->is_oop(), "live block should be an oop"); | |
7932 // However, as we commented above, this may be an object whose | |
7933 // header hasn't yet been initialized. | |
7934 size_t size; | |
7935 assert(_bitMap->isMarked(addr), "Tautology for this control point"); | |
7936 if (_bitMap->isMarked(addr + 1)) { | |
7937 // Determine the size from the bit map, rather than trying to | |
7938 // compute it from the object header. | |
7939 HeapWord* nextOneAddr = _bitMap->getNextMarkedWordAddress(addr + 2); | |
7940 size = pointer_delta(nextOneAddr + 1, addr); | |
7941 assert(size == CompactibleFreeListSpace::adjustObjectSize(size), | |
7942 "alignment problem"); | |
7943 | |
7944 #ifdef DEBUG | |
7945 if (oop(addr)->klass() != NULL && | |
7946 ( !_collector->cms_should_unload_classes() | |
7947 || oop(addr)->is_parsable())) { | |
7948 // Ignore mark word because we are running concurrent with mutators | |
7949 assert(oop(addr)->is_oop(true), "live block should be an oop"); | |
7950 assert(size == | |
7951 CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()), | |
7952 "P-mark and computed size do not agree"); | |
7953 } | |
7954 #endif | |
7955 | |
7956 } else { | |
7957 // This should be an initialized object that's alive. | |
7958 assert(oop(addr)->klass() != NULL && | |
7959 (!_collector->cms_should_unload_classes() | |
7960 || oop(addr)->is_parsable()), | |
7961 "Should be an initialized object"); | |
7962 // Ignore mark word because we are running concurrent with mutators | |
7963 assert(oop(addr)->is_oop(true), "live block should be an oop"); | |
7964 // Verify that the bit map has no bits marked between | |
7965 // addr and purported end of this block. | |
7966 size = CompactibleFreeListSpace::adjustObjectSize(oop(addr)->size()); | |
7967 assert(size >= 3, "Necessary for Printezis marks to work"); | |
7968 assert(!_bitMap->isMarked(addr+1), "Tautology for this control point"); | |
7969 DEBUG_ONLY(_bitMap->verifyNoOneBitsInRange(addr+2, addr+size);) | |
7970 } | |
7971 return size; | |
7972 } | |
7973 | |
7974 void SweepClosure::doPostIsFreeOrGarbageChunk(FreeChunk* fc, | |
7975 size_t chunkSize) { | |
7976 // doPostIsFreeOrGarbageChunk() should only be called in the smart allocation | |
7977 // scheme. | |
7978 bool fcInFreeLists = fc->isFree(); | |
7979 assert(_sp->adaptive_freelists(), "Should only be used in this case."); | |
7980 assert((HeapWord*)fc <= _limit, "sweep invariant"); | |
7981 if (CMSTestInFreeList && fcInFreeLists) { | |
7982 assert(_sp->verifyChunkInFreeLists(fc), | |
7983 "free chunk is not in free lists"); | |
7984 } | |
7985 | |
7986 | |
7987 if (CMSTraceSweeper) { | |
7988 gclog_or_tty->print_cr(" -- pick up another chunk at 0x%x (%d)", fc, chunkSize); | |
7989 } | |
7990 | |
7991 HeapWord* addr = (HeapWord*) fc; | |
7992 | |
7993 bool coalesce; | |
7994 size_t left = pointer_delta(addr, freeFinger()); | |
7995 size_t right = chunkSize; | |
7996 switch (FLSCoalescePolicy) { | |
7997 // numeric value forms a coalition aggressiveness metric | |
7998 case 0: { // never coalesce | |
7999 coalesce = false; | |
8000 break; | |
8001 } | |
8002 case 1: { // coalesce if left & right chunks on overpopulated lists | |
8003 coalesce = _sp->coalOverPopulated(left) && | |
8004 _sp->coalOverPopulated(right); | |
8005 break; | |
8006 } | |
8007 case 2: { // coalesce if left chunk on overpopulated list (default) | |
8008 coalesce = _sp->coalOverPopulated(left); | |
8009 break; | |
8010 } | |
8011 case 3: { // coalesce if left OR right chunk on overpopulated list | |
8012 coalesce = _sp->coalOverPopulated(left) || | |
8013 _sp->coalOverPopulated(right); | |
8014 break; | |
8015 } | |
8016 case 4: { // always coalesce | |
8017 coalesce = true; | |
8018 break; | |
8019 } | |
8020 default: | |
8021 ShouldNotReachHere(); | |
8022 } | |
8023 | |
8024 // Should the current free range be coalesced? | |
8025 // If the chunk is in a free range and either we decided to coalesce above | |
8026 // or the chunk is near the large block at the end of the heap | |
8027 // (isNearLargestChunk() returns true), then coalesce this chunk. | |
8028 bool doCoalesce = inFreeRange() && | |
8029 (coalesce || _g->isNearLargestChunk((HeapWord*)fc)); | |
8030 if (doCoalesce) { | |
8031 // Coalesce the current free range on the left with the new | |
8032 // chunk on the right. If either is on a free list, | |
8033 // it must be removed from the list and stashed in the closure. | |
8034 if (freeRangeInFreeLists()) { | |
8035 FreeChunk* ffc = (FreeChunk*)freeFinger(); | |
8036 assert(ffc->size() == pointer_delta(addr, freeFinger()), | |
8037 "Size of free range is inconsistent with chunk size."); | |
8038 if (CMSTestInFreeList) { | |
8039 assert(_sp->verifyChunkInFreeLists(ffc), | |
8040 "Chunk is not in free lists"); | |
8041 } | |
8042 _sp->coalDeath(ffc->size()); | |
8043 _sp->removeFreeChunkFromFreeLists(ffc); | |
8044 set_freeRangeInFreeLists(false); | |
8045 } | |
8046 if (fcInFreeLists) { | |
8047 _sp->coalDeath(chunkSize); | |
8048 assert(fc->size() == chunkSize, | |
8049 "The chunk has the wrong size or is not in the free lists"); | |
8050 _sp->removeFreeChunkFromFreeLists(fc); | |
8051 } | |
8052 set_lastFreeRangeCoalesced(true); | |
8053 } else { // not in a free range and/or should not coalesce | |
8054 // Return the current free range and start a new one. | |
8055 if (inFreeRange()) { | |
8056 // In a free range but cannot coalesce with the right hand chunk. | |
8057 // Put the current free range into the free lists. | |
8058 flushCurFreeChunk(freeFinger(), | |
8059 pointer_delta(addr, freeFinger())); | |
8060 } | |
8061 // Set up for new free range. Pass along whether the right hand | |
8062 // chunk is in the free lists. | |
8063 initialize_free_range((HeapWord*)fc, fcInFreeLists); | |
8064 } | |
8065 } | |
8066 void SweepClosure::flushCurFreeChunk(HeapWord* chunk, size_t size) { | |
8067 assert(inFreeRange(), "Should only be called if currently in a free range."); | |
8068 assert(size > 0, | |
8069 "A zero sized chunk cannot be added to the free lists."); | |
8070 if (!freeRangeInFreeLists()) { | |
8071 if(CMSTestInFreeList) { | |
8072 FreeChunk* fc = (FreeChunk*) chunk; | |
8073 fc->setSize(size); | |
8074 assert(!_sp->verifyChunkInFreeLists(fc), | |
8075 "chunk should not be in free lists yet"); | |
8076 } | |
8077 if (CMSTraceSweeper) { | |
8078 gclog_or_tty->print_cr(" -- add free block 0x%x (%d) to free lists", | |
8079 chunk, size); | |
8080 } | |
8081 // A new free range is going to be starting. The current | |
8082 // free range has not been added to the free lists yet or | |
8083 // was removed so add it back. | |
8084 // If the current free range was coalesced, then the death | |
8085 // of the free range was recorded. Record a birth now. | |
8086 if (lastFreeRangeCoalesced()) { | |
8087 _sp->coalBirth(size); | |
8088 } | |
8089 _sp->addChunkAndRepairOffsetTable(chunk, size, | |
8090 lastFreeRangeCoalesced()); | |
8091 } | |
8092 set_inFreeRange(false); | |
8093 set_freeRangeInFreeLists(false); | |
8094 } | |
8095 | |
8096 // We take a break if we've been at this for a while, | |
8097 // so as to avoid monopolizing the locks involved. | |
8098 void SweepClosure::do_yield_work(HeapWord* addr) { | |
8099 // Return current free chunk being used for coalescing (if any) | |
8100 // to the appropriate freelist. After yielding, the next | |
8101 // free block encountered will start a coalescing range of | |
8102 // free blocks. If the next free block is adjacent to the | |
8103 // chunk just flushed, they will need to wait for the next | |
8104 // sweep to be coalesced. | |
8105 if (inFreeRange()) { | |
8106 flushCurFreeChunk(freeFinger(), pointer_delta(addr, freeFinger())); | |
8107 } | |
8108 | |
8109 // First give up the locks, then yield, then re-lock. | |
8110 // We should probably use a constructor/destructor idiom to | |
8111 // do this unlock/lock or modify the MutexUnlocker class to | |
8112 // serve our purpose. XXX | |
8113 assert_lock_strong(_bitMap->lock()); | |
8114 assert_lock_strong(_freelistLock); | |
8115 assert(ConcurrentMarkSweepThread::cms_thread_has_cms_token(), | |
8116 "CMS thread should hold CMS token"); | |
8117 _bitMap->lock()->unlock(); | |
8118 _freelistLock->unlock(); | |
8119 ConcurrentMarkSweepThread::desynchronize(true); | |
8120 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
8121 _collector->stopTimer(); | |
8122 GCPauseTimer p(_collector->size_policy()->concurrent_timer_ptr()); | |
8123 if (PrintCMSStatistics != 0) { | |
8124 _collector->incrementYields(); | |
8125 } | |
8126 _collector->icms_wait(); | |
8127 | |
8128 // See the comment in coordinator_yield() | |
8129 for (unsigned i = 0; i < CMSYieldSleepCount && | |
8130 ConcurrentMarkSweepThread::should_yield() && | |
8131 !CMSCollector::foregroundGCIsActive(); ++i) { | |
8132 os::sleep(Thread::current(), 1, false); | |
8133 ConcurrentMarkSweepThread::acknowledge_yield_request(); | |
8134 } | |
8135 | |
8136 ConcurrentMarkSweepThread::synchronize(true); | |
8137 _freelistLock->lock(); | |
8138 _bitMap->lock()->lock_without_safepoint_check(); | |
8139 _collector->startTimer(); | |
8140 } | |
8141 | |
8142 #ifndef PRODUCT | |
8143 // This is actually very useful in a product build if it can | |
8144 // be called from the debugger. Compile it into the product | |
8145 // as needed. | |
8146 bool debug_verifyChunkInFreeLists(FreeChunk* fc) { | |
8147 return debug_cms_space->verifyChunkInFreeLists(fc); | |
8148 } | |
8149 | |
8150 void SweepClosure::record_free_block_coalesced(FreeChunk* fc) const { | |
8151 if (CMSTraceSweeper) { | |
8152 gclog_or_tty->print("Sweep:coal_free_blk 0x%x (%d)\n", fc, fc->size()); | |
8153 } | |
8154 } | |
8155 #endif | |
8156 | |
8157 // CMSIsAliveClosure | |
8158 bool CMSIsAliveClosure::do_object_b(oop obj) { | |
8159 HeapWord* addr = (HeapWord*)obj; | |
8160 return addr != NULL && | |
8161 (!_span.contains(addr) || _bit_map->isMarked(addr)); | |
8162 } | |
8163 | |
8164 // CMSKeepAliveClosure: the serial version | |
8165 void CMSKeepAliveClosure::do_oop(oop* p) { | |
8166 oop this_oop = *p; | |
8167 HeapWord* addr = (HeapWord*)this_oop; | |
8168 if (_span.contains(addr) && | |
8169 !_bit_map->isMarked(addr)) { | |
8170 _bit_map->mark(addr); | |
8171 bool simulate_overflow = false; | |
8172 NOT_PRODUCT( | |
8173 if (CMSMarkStackOverflowALot && | |
8174 _collector->simulate_overflow()) { | |
8175 // simulate a stack overflow | |
8176 simulate_overflow = true; | |
8177 } | |
8178 ) | |
8179 if (simulate_overflow || !_mark_stack->push(this_oop)) { | |
8180 _collector->push_on_overflow_list(this_oop); | |
8181 _collector->_ser_kac_ovflw++; | |
8182 } | |
8183 } | |
8184 } | |
8185 | |
8186 // CMSParKeepAliveClosure: a parallel version of the above. | |
8187 // The work queues are private to each closure (thread), | |
8188 // but (may be) available for stealing by other threads. | |
8189 void CMSParKeepAliveClosure::do_oop(oop* p) { | |
8190 oop this_oop = *p; | |
8191 HeapWord* addr = (HeapWord*)this_oop; | |
8192 if (_span.contains(addr) && | |
8193 !_bit_map->isMarked(addr)) { | |
8194 // In general, during recursive tracing, several threads | |
8195 // may be concurrently getting here; the first one to | |
8196 // "tag" it, claims it. | |
8197 if (_bit_map->par_mark(addr)) { | |
8198 bool res = _work_queue->push(this_oop); | |
8199 assert(res, "Low water mark should be much less than capacity"); | |
8200 // Do a recursive trim in the hope that this will keep | |
8201 // stack usage lower, but leave some oops for potential stealers | |
8202 trim_queue(_low_water_mark); | |
8203 } // Else, another thread got there first | |
8204 } | |
8205 } | |
8206 | |
8207 void CMSParKeepAliveClosure::trim_queue(uint max) { | |
8208 while (_work_queue->size() > max) { | |
8209 oop new_oop; | |
8210 if (_work_queue->pop_local(new_oop)) { | |
8211 assert(new_oop != NULL && new_oop->is_oop(), "Expected an oop"); | |
8212 assert(_bit_map->isMarked((HeapWord*)new_oop), | |
8213 "no white objects on this stack!"); | |
8214 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); | |
8215 // iterate over the oops in this oop, marking and pushing | |
8216 // the ones in CMS heap (i.e. in _span). | |
8217 new_oop->oop_iterate(&_mark_and_push); | |
8218 } | |
8219 } | |
8220 } | |
8221 | |
8222 void CMSInnerParMarkAndPushClosure::do_oop(oop* p) { | |
8223 oop this_oop = *p; | |
8224 HeapWord* addr = (HeapWord*)this_oop; | |
8225 if (_span.contains(addr) && | |
8226 !_bit_map->isMarked(addr)) { | |
8227 if (_bit_map->par_mark(addr)) { | |
8228 bool simulate_overflow = false; | |
8229 NOT_PRODUCT( | |
8230 if (CMSMarkStackOverflowALot && | |
8231 _collector->par_simulate_overflow()) { | |
8232 // simulate a stack overflow | |
8233 simulate_overflow = true; | |
8234 } | |
8235 ) | |
8236 if (simulate_overflow || !_work_queue->push(this_oop)) { | |
8237 _collector->par_push_on_overflow_list(this_oop); | |
8238 _collector->_par_kac_ovflw++; | |
8239 } | |
8240 } // Else another thread got there already | |
8241 } | |
8242 } | |
8243 | |
8244 ////////////////////////////////////////////////////////////////// | |
8245 // CMSExpansionCause ///////////////////////////// | |
8246 ////////////////////////////////////////////////////////////////// | |
8247 const char* CMSExpansionCause::to_string(CMSExpansionCause::Cause cause) { | |
8248 switch (cause) { | |
8249 case _no_expansion: | |
8250 return "No expansion"; | |
8251 case _satisfy_free_ratio: | |
8252 return "Free ratio"; | |
8253 case _satisfy_promotion: | |
8254 return "Satisfy promotion"; | |
8255 case _satisfy_allocation: | |
8256 return "allocation"; | |
8257 case _allocate_par_lab: | |
8258 return "Par LAB"; | |
8259 case _allocate_par_spooling_space: | |
8260 return "Par Spooling Space"; | |
8261 case _adaptive_size_policy: | |
8262 return "Ergonomics"; | |
8263 default: | |
8264 return "unknown"; | |
8265 } | |
8266 } | |
8267 | |
8268 void CMSDrainMarkingStackClosure::do_void() { | |
8269 // the max number to take from overflow list at a time | |
8270 const size_t num = _mark_stack->capacity()/4; | |
8271 while (!_mark_stack->isEmpty() || | |
8272 // if stack is empty, check the overflow list | |
8273 _collector->take_from_overflow_list(num, _mark_stack)) { | |
8274 oop this_oop = _mark_stack->pop(); | |
8275 HeapWord* addr = (HeapWord*)this_oop; | |
8276 assert(_span.contains(addr), "Should be within span"); | |
8277 assert(_bit_map->isMarked(addr), "Should be marked"); | |
8278 assert(this_oop->is_oop(), "Should be an oop"); | |
8279 this_oop->oop_iterate(_keep_alive); | |
8280 } | |
8281 } | |
8282 | |
8283 void CMSParDrainMarkingStackClosure::do_void() { | |
8284 // drain queue | |
8285 trim_queue(0); | |
8286 } | |
8287 | |
8288 // Trim our work_queue so its length is below max at return | |
8289 void CMSParDrainMarkingStackClosure::trim_queue(uint max) { | |
8290 while (_work_queue->size() > max) { | |
8291 oop new_oop; | |
8292 if (_work_queue->pop_local(new_oop)) { | |
8293 assert(new_oop->is_oop(), "Expected an oop"); | |
8294 assert(_bit_map->isMarked((HeapWord*)new_oop), | |
8295 "no white objects on this stack!"); | |
8296 assert(_span.contains((HeapWord*)new_oop), "Out of bounds oop"); | |
8297 // iterate over the oops in this oop, marking and pushing | |
8298 // the ones in CMS heap (i.e. in _span). | |
8299 new_oop->oop_iterate(&_mark_and_push); | |
8300 } | |
8301 } | |
8302 } | |
8303 | |
8304 //////////////////////////////////////////////////////////////////// | |
8305 // Support for Marking Stack Overflow list handling and related code | |
8306 //////////////////////////////////////////////////////////////////// | |
8307 // Much of the following code is similar in shape and spirit to the | |
8308 // code used in ParNewGC. We should try and share that code | |
8309 // as much as possible in the future. | |
8310 | |
8311 #ifndef PRODUCT | |
8312 // Debugging support for CMSStackOverflowALot | |
8313 | |
8314 // It's OK to call this multi-threaded; the worst thing | |
8315 // that can happen is that we'll get a bunch of closely | |
8316 // spaced simulated oveflows, but that's OK, in fact | |
8317 // probably good as it would exercise the overflow code | |
8318 // under contention. | |
8319 bool CMSCollector::simulate_overflow() { | |
8320 if (_overflow_counter-- <= 0) { // just being defensive | |
8321 _overflow_counter = CMSMarkStackOverflowInterval; | |
8322 return true; | |
8323 } else { | |
8324 return false; | |
8325 } | |
8326 } | |
8327 | |
8328 bool CMSCollector::par_simulate_overflow() { | |
8329 return simulate_overflow(); | |
8330 } | |
8331 #endif | |
8332 | |
8333 // Single-threaded | |
8334 bool CMSCollector::take_from_overflow_list(size_t num, CMSMarkStack* stack) { | |
8335 assert(stack->isEmpty(), "Expected precondition"); | |
8336 assert(stack->capacity() > num, "Shouldn't bite more than can chew"); | |
8337 size_t i = num; | |
8338 oop cur = _overflow_list; | |
8339 const markOop proto = markOopDesc::prototype(); | |
8340 NOT_PRODUCT(size_t n = 0;) | |
8341 for (oop next; i > 0 && cur != NULL; cur = next, i--) { | |
8342 next = oop(cur->mark()); | |
8343 cur->set_mark(proto); // until proven otherwise | |
8344 assert(cur->is_oop(), "Should be an oop"); | |
8345 bool res = stack->push(cur); | |
8346 assert(res, "Bit off more than can chew?"); | |
8347 NOT_PRODUCT(n++;) | |
8348 } | |
8349 _overflow_list = cur; | |
8350 #ifndef PRODUCT | |
8351 assert(_num_par_pushes >= n, "Too many pops?"); | |
8352 _num_par_pushes -=n; | |
8353 #endif | |
8354 return !stack->isEmpty(); | |
8355 } | |
8356 | |
8357 // Multi-threaded; use CAS to break off a prefix | |
8358 bool CMSCollector::par_take_from_overflow_list(size_t num, | |
8359 OopTaskQueue* work_q) { | |
8360 assert(work_q->size() == 0, "That's the current policy"); | |
8361 assert(num < work_q->max_elems(), "Can't bite more than we can chew"); | |
8362 if (_overflow_list == NULL) { | |
8363 return false; | |
8364 } | |
8365 // Grab the entire list; we'll put back a suffix | |
8366 oop prefix = (oop)Atomic::xchg_ptr(NULL, &_overflow_list); | |
8367 if (prefix == NULL) { // someone grabbed it before we did ... | |
8368 // ... we could spin for a short while, but for now we don't | |
8369 return false; | |
8370 } | |
8371 size_t i = num; | |
8372 oop cur = prefix; | |
8373 for (; i > 1 && cur->mark() != NULL; cur = oop(cur->mark()), i--); | |
8374 if (cur->mark() != NULL) { | |
8375 oop suffix_head = cur->mark(); // suffix will be put back on global list | |
8376 cur->set_mark(NULL); // break off suffix | |
8377 // Find tail of suffix so we can prepend suffix to global list | |
8378 for (cur = suffix_head; cur->mark() != NULL; cur = (oop)(cur->mark())); | |
8379 oop suffix_tail = cur; | |
8380 assert(suffix_tail != NULL && suffix_tail->mark() == NULL, | |
8381 "Tautology"); | |
8382 oop observed_overflow_list = _overflow_list; | |
8383 do { | |
8384 cur = observed_overflow_list; | |
8385 suffix_tail->set_mark(markOop(cur)); | |
8386 observed_overflow_list = | |
8387 (oop) Atomic::cmpxchg_ptr(suffix_head, &_overflow_list, cur); | |
8388 } while (cur != observed_overflow_list); | |
8389 } | |
8390 | |
8391 // Push the prefix elements on work_q | |
8392 assert(prefix != NULL, "control point invariant"); | |
8393 const markOop proto = markOopDesc::prototype(); | |
8394 oop next; | |
8395 NOT_PRODUCT(size_t n = 0;) | |
8396 for (cur = prefix; cur != NULL; cur = next) { | |
8397 next = oop(cur->mark()); | |
8398 cur->set_mark(proto); // until proven otherwise | |
8399 assert(cur->is_oop(), "Should be an oop"); | |
8400 bool res = work_q->push(cur); | |
8401 assert(res, "Bit off more than we can chew?"); | |
8402 NOT_PRODUCT(n++;) | |
8403 } | |
8404 #ifndef PRODUCT | |
8405 assert(_num_par_pushes >= n, "Too many pops?"); | |
8406 Atomic::add_ptr(-(intptr_t)n, &_num_par_pushes); | |
8407 #endif | |
8408 return true; | |
8409 } | |
8410 | |
8411 // Single-threaded | |
8412 void CMSCollector::push_on_overflow_list(oop p) { | |
8413 NOT_PRODUCT(_num_par_pushes++;) | |
8414 assert(p->is_oop(), "Not an oop"); | |
8415 preserve_mark_if_necessary(p); | |
8416 p->set_mark((markOop)_overflow_list); | |
8417 _overflow_list = p; | |
8418 } | |
8419 | |
8420 // Multi-threaded; use CAS to prepend to overflow list | |
8421 void CMSCollector::par_push_on_overflow_list(oop p) { | |
8422 NOT_PRODUCT(Atomic::inc_ptr(&_num_par_pushes);) | |
8423 assert(p->is_oop(), "Not an oop"); | |
8424 par_preserve_mark_if_necessary(p); | |
8425 oop observed_overflow_list = _overflow_list; | |
8426 oop cur_overflow_list; | |
8427 do { | |
8428 cur_overflow_list = observed_overflow_list; | |
8429 p->set_mark(markOop(cur_overflow_list)); | |
8430 observed_overflow_list = | |
8431 (oop) Atomic::cmpxchg_ptr(p, &_overflow_list, cur_overflow_list); | |
8432 } while (cur_overflow_list != observed_overflow_list); | |
8433 } | |
8434 | |
8435 // Single threaded | |
8436 // General Note on GrowableArray: pushes may silently fail | |
8437 // because we are (temporarily) out of C-heap for expanding | |
8438 // the stack. The problem is quite ubiquitous and affects | |
8439 // a lot of code in the JVM. The prudent thing for GrowableArray | |
8440 // to do (for now) is to exit with an error. However, that may | |
8441 // be too draconian in some cases because the caller may be | |
8442 // able to recover without much harm. For suych cases, we | |
8443 // should probably introduce a "soft_push" method which returns | |
8444 // an indication of success or failure with the assumption that | |
8445 // the caller may be able to recover from a failure; code in | |
8446 // the VM can then be changed, incrementally, to deal with such | |
8447 // failures where possible, thus, incrementally hardening the VM | |
8448 // in such low resource situations. | |
8449 void CMSCollector::preserve_mark_work(oop p, markOop m) { | |
8450 int PreserveMarkStackSize = 128; | |
8451 | |
8452 if (_preserved_oop_stack == NULL) { | |
8453 assert(_preserved_mark_stack == NULL, | |
8454 "bijection with preserved_oop_stack"); | |
8455 // Allocate the stacks | |
8456 _preserved_oop_stack = new (ResourceObj::C_HEAP) | |
8457 GrowableArray<oop>(PreserveMarkStackSize, true); | |
8458 _preserved_mark_stack = new (ResourceObj::C_HEAP) | |
8459 GrowableArray<markOop>(PreserveMarkStackSize, true); | |
8460 if (_preserved_oop_stack == NULL || _preserved_mark_stack == NULL) { | |
8461 vm_exit_out_of_memory(2* PreserveMarkStackSize * sizeof(oop) /* punt */, | |
8462 "Preserved Mark/Oop Stack for CMS (C-heap)"); | |
8463 } | |
8464 } | |
8465 _preserved_oop_stack->push(p); | |
8466 _preserved_mark_stack->push(m); | |
8467 assert(m == p->mark(), "Mark word changed"); | |
8468 assert(_preserved_oop_stack->length() == _preserved_mark_stack->length(), | |
8469 "bijection"); | |
8470 } | |
8471 | |
8472 // Single threaded | |
8473 void CMSCollector::preserve_mark_if_necessary(oop p) { | |
8474 markOop m = p->mark(); | |
8475 if (m->must_be_preserved(p)) { | |
8476 preserve_mark_work(p, m); | |
8477 } | |
8478 } | |
8479 | |
8480 void CMSCollector::par_preserve_mark_if_necessary(oop p) { | |
8481 markOop m = p->mark(); | |
8482 if (m->must_be_preserved(p)) { | |
8483 MutexLockerEx x(ParGCRareEvent_lock, Mutex::_no_safepoint_check_flag); | |
8484 // Even though we read the mark word without holding | |
8485 // the lock, we are assured that it will not change | |
8486 // because we "own" this oop, so no other thread can | |
8487 // be trying to push it on the overflow list; see | |
8488 // the assertion in preserve_mark_work() that checks | |
8489 // that m == p->mark(). | |
8490 preserve_mark_work(p, m); | |
8491 } | |
8492 } | |
8493 | |
8494 // We should be able to do this multi-threaded, | |
8495 // a chunk of stack being a task (this is | |
8496 // correct because each oop only ever appears | |
8497 // once in the overflow list. However, it's | |
8498 // not very easy to completely overlap this with | |
8499 // other operations, so will generally not be done | |
8500 // until all work's been completed. Because we | |
8501 // expect the preserved oop stack (set) to be small, | |
8502 // it's probably fine to do this single-threaded. | |
8503 // We can explore cleverer concurrent/overlapped/parallel | |
8504 // processing of preserved marks if we feel the | |
8505 // need for this in the future. Stack overflow should | |
8506 // be so rare in practice and, when it happens, its | |
8507 // effect on performance so great that this will | |
8508 // likely just be in the noise anyway. | |
8509 void CMSCollector::restore_preserved_marks_if_any() { | |
8510 if (_preserved_oop_stack == NULL) { | |
8511 assert(_preserved_mark_stack == NULL, | |
8512 "bijection with preserved_oop_stack"); | |
8513 return; | |
8514 } | |
8515 | |
8516 assert(SafepointSynchronize::is_at_safepoint(), | |
8517 "world should be stopped"); | |
8518 assert(Thread::current()->is_ConcurrentGC_thread() || | |
8519 Thread::current()->is_VM_thread(), | |
8520 "should be single-threaded"); | |
8521 | |
8522 int length = _preserved_oop_stack->length(); | |
8523 assert(_preserved_mark_stack->length() == length, "bijection"); | |
8524 for (int i = 0; i < length; i++) { | |
8525 oop p = _preserved_oop_stack->at(i); | |
8526 assert(p->is_oop(), "Should be an oop"); | |
8527 assert(_span.contains(p), "oop should be in _span"); | |
8528 assert(p->mark() == markOopDesc::prototype(), | |
8529 "Set when taken from overflow list"); | |
8530 markOop m = _preserved_mark_stack->at(i); | |
8531 p->set_mark(m); | |
8532 } | |
8533 _preserved_mark_stack->clear(); | |
8534 _preserved_oop_stack->clear(); | |
8535 assert(_preserved_mark_stack->is_empty() && | |
8536 _preserved_oop_stack->is_empty(), | |
8537 "stacks were cleared above"); | |
8538 } | |
8539 | |
8540 #ifndef PRODUCT | |
8541 bool CMSCollector::no_preserved_marks() const { | |
8542 return ( ( _preserved_mark_stack == NULL | |
8543 && _preserved_oop_stack == NULL) | |
8544 || ( _preserved_mark_stack->is_empty() | |
8545 && _preserved_oop_stack->is_empty())); | |
8546 } | |
8547 #endif | |
8548 | |
8549 CMSAdaptiveSizePolicy* ASConcurrentMarkSweepGeneration::cms_size_policy() const | |
8550 { | |
8551 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap(); | |
8552 CMSAdaptiveSizePolicy* size_policy = | |
8553 (CMSAdaptiveSizePolicy*) gch->gen_policy()->size_policy(); | |
8554 assert(size_policy->is_gc_cms_adaptive_size_policy(), | |
8555 "Wrong type for size policy"); | |
8556 return size_policy; | |
8557 } | |
8558 | |
8559 void ASConcurrentMarkSweepGeneration::resize(size_t cur_promo_size, | |
8560 size_t desired_promo_size) { | |
8561 if (cur_promo_size < desired_promo_size) { | |
8562 size_t expand_bytes = desired_promo_size - cur_promo_size; | |
8563 if (PrintAdaptiveSizePolicy && Verbose) { | |
8564 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize " | |
8565 "Expanding tenured generation by " SIZE_FORMAT " (bytes)", | |
8566 expand_bytes); | |
8567 } | |
8568 expand(expand_bytes, | |
8569 MinHeapDeltaBytes, | |
8570 CMSExpansionCause::_adaptive_size_policy); | |
8571 } else if (desired_promo_size < cur_promo_size) { | |
8572 size_t shrink_bytes = cur_promo_size - desired_promo_size; | |
8573 if (PrintAdaptiveSizePolicy && Verbose) { | |
8574 gclog_or_tty->print_cr(" ASConcurrentMarkSweepGeneration::resize " | |
8575 "Shrinking tenured generation by " SIZE_FORMAT " (bytes)", | |
8576 shrink_bytes); | |
8577 } | |
8578 shrink(shrink_bytes); | |
8579 } | |
8580 } | |
8581 | |
8582 CMSGCAdaptivePolicyCounters* ASConcurrentMarkSweepGeneration::gc_adaptive_policy_counters() { | |
8583 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
8584 CMSGCAdaptivePolicyCounters* counters = | |
8585 (CMSGCAdaptivePolicyCounters*) gch->collector_policy()->counters(); | |
8586 assert(counters->kind() == GCPolicyCounters::CMSGCAdaptivePolicyCountersKind, | |
8587 "Wrong kind of counters"); | |
8588 return counters; | |
8589 } | |
8590 | |
8591 | |
8592 void ASConcurrentMarkSweepGeneration::update_counters() { | |
8593 if (UsePerfData) { | |
8594 _space_counters->update_all(); | |
8595 _gen_counters->update_all(); | |
8596 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); | |
8597 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
8598 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats(); | |
8599 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind, | |
8600 "Wrong gc statistics type"); | |
8601 counters->update_counters(gc_stats_l); | |
8602 } | |
8603 } | |
8604 | |
8605 void ASConcurrentMarkSweepGeneration::update_counters(size_t used) { | |
8606 if (UsePerfData) { | |
8607 _space_counters->update_used(used); | |
8608 _space_counters->update_capacity(); | |
8609 _gen_counters->update_all(); | |
8610 | |
8611 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); | |
8612 GenCollectedHeap* gch = GenCollectedHeap::heap(); | |
8613 CMSGCStats* gc_stats_l = (CMSGCStats*) gc_stats(); | |
8614 assert(gc_stats_l->kind() == GCStats::CMSGCStatsKind, | |
8615 "Wrong gc statistics type"); | |
8616 counters->update_counters(gc_stats_l); | |
8617 } | |
8618 } | |
8619 | |
8620 // The desired expansion delta is computed so that: | |
8621 // . desired free percentage or greater is used | |
8622 void ASConcurrentMarkSweepGeneration::compute_new_size() { | |
8623 assert_locked_or_safepoint(Heap_lock); | |
8624 | |
8625 GenCollectedHeap* gch = (GenCollectedHeap*) GenCollectedHeap::heap(); | |
8626 | |
8627 // If incremental collection failed, we just want to expand | |
8628 // to the limit. | |
8629 if (incremental_collection_failed()) { | |
8630 clear_incremental_collection_failed(); | |
8631 grow_to_reserved(); | |
8632 return; | |
8633 } | |
8634 | |
8635 assert(UseAdaptiveSizePolicy, "Should be using adaptive sizing"); | |
8636 | |
8637 assert(gch->kind() == CollectedHeap::GenCollectedHeap, | |
8638 "Wrong type of heap"); | |
8639 int prev_level = level() - 1; | |
8640 assert(prev_level >= 0, "The cms generation is the lowest generation"); | |
8641 Generation* prev_gen = gch->get_gen(prev_level); | |
8642 assert(prev_gen->kind() == Generation::ASParNew, | |
8643 "Wrong type of young generation"); | |
8644 ParNewGeneration* younger_gen = (ParNewGeneration*) prev_gen; | |
8645 size_t cur_eden = younger_gen->eden()->capacity(); | |
8646 CMSAdaptiveSizePolicy* size_policy = cms_size_policy(); | |
8647 size_t cur_promo = free(); | |
8648 size_policy->compute_tenured_generation_free_space(cur_promo, | |
8649 max_available(), | |
8650 cur_eden); | |
8651 resize(cur_promo, size_policy->promo_size()); | |
8652 | |
8653 // Record the new size of the space in the cms generation | |
8654 // that is available for promotions. This is temporary. | |
8655 // It should be the desired promo size. | |
8656 size_policy->avg_cms_promo()->sample(free()); | |
8657 size_policy->avg_old_live()->sample(used()); | |
8658 | |
8659 if (UsePerfData) { | |
8660 CMSGCAdaptivePolicyCounters* counters = gc_adaptive_policy_counters(); | |
8661 counters->update_cms_capacity_counter(capacity()); | |
8662 } | |
8663 } | |
8664 | |
8665 void ASConcurrentMarkSweepGeneration::shrink_by(size_t desired_bytes) { | |
8666 assert_locked_or_safepoint(Heap_lock); | |
8667 assert_lock_strong(freelistLock()); | |
8668 HeapWord* old_end = _cmsSpace->end(); | |
8669 HeapWord* unallocated_start = _cmsSpace->unallocated_block(); | |
8670 assert(old_end >= unallocated_start, "Miscalculation of unallocated_start"); | |
8671 FreeChunk* chunk_at_end = find_chunk_at_end(); | |
8672 if (chunk_at_end == NULL) { | |
8673 // No room to shrink | |
8674 if (PrintGCDetails && Verbose) { | |
8675 gclog_or_tty->print_cr("No room to shrink: old_end " | |
8676 PTR_FORMAT " unallocated_start " PTR_FORMAT | |
8677 " chunk_at_end " PTR_FORMAT, | |
8678 old_end, unallocated_start, chunk_at_end); | |
8679 } | |
8680 return; | |
8681 } else { | |
8682 | |
8683 // Find the chunk at the end of the space and determine | |
8684 // how much it can be shrunk. | |
8685 size_t shrinkable_size_in_bytes = chunk_at_end->size(); | |
8686 size_t aligned_shrinkable_size_in_bytes = | |
8687 align_size_down(shrinkable_size_in_bytes, os::vm_page_size()); | |
8688 assert(unallocated_start <= chunk_at_end->end(), | |
8689 "Inconsistent chunk at end of space"); | |
8690 size_t bytes = MIN2(desired_bytes, aligned_shrinkable_size_in_bytes); | |
8691 size_t word_size_before = heap_word_size(_virtual_space.committed_size()); | |
8692 | |
8693 // Shrink the underlying space | |
8694 _virtual_space.shrink_by(bytes); | |
8695 if (PrintGCDetails && Verbose) { | |
8696 gclog_or_tty->print_cr("ConcurrentMarkSweepGeneration::shrink_by:" | |
8697 " desired_bytes " SIZE_FORMAT | |
8698 " shrinkable_size_in_bytes " SIZE_FORMAT | |
8699 " aligned_shrinkable_size_in_bytes " SIZE_FORMAT | |
8700 " bytes " SIZE_FORMAT, | |
8701 desired_bytes, shrinkable_size_in_bytes, | |
8702 aligned_shrinkable_size_in_bytes, bytes); | |
8703 gclog_or_tty->print_cr(" old_end " SIZE_FORMAT | |
8704 " unallocated_start " SIZE_FORMAT, | |
8705 old_end, unallocated_start); | |
8706 } | |
8707 | |
8708 // If the space did shrink (shrinking is not guaranteed), | |
8709 // shrink the chunk at the end by the appropriate amount. | |
8710 if (((HeapWord*)_virtual_space.high()) < old_end) { | |
8711 size_t new_word_size = | |
8712 heap_word_size(_virtual_space.committed_size()); | |
8713 | |
8714 // Have to remove the chunk from the dictionary because it is changing | |
8715 // size and might be someplace elsewhere in the dictionary. | |
8716 | |
8717 // Get the chunk at end, shrink it, and put it | |
8718 // back. | |
8719 _cmsSpace->removeChunkFromDictionary(chunk_at_end); | |
8720 size_t word_size_change = word_size_before - new_word_size; | |
8721 size_t chunk_at_end_old_size = chunk_at_end->size(); | |
8722 assert(chunk_at_end_old_size >= word_size_change, | |
8723 "Shrink is too large"); | |
8724 chunk_at_end->setSize(chunk_at_end_old_size - | |
8725 word_size_change); | |
8726 _cmsSpace->freed((HeapWord*) chunk_at_end->end(), | |
8727 word_size_change); | |
8728 | |
8729 _cmsSpace->returnChunkToDictionary(chunk_at_end); | |
8730 | |
8731 MemRegion mr(_cmsSpace->bottom(), new_word_size); | |
8732 _bts->resize(new_word_size); // resize the block offset shared array | |
8733 Universe::heap()->barrier_set()->resize_covered_region(mr); | |
8734 _cmsSpace->assert_locked(); | |
8735 _cmsSpace->set_end((HeapWord*)_virtual_space.high()); | |
8736 | |
8737 NOT_PRODUCT(_cmsSpace->dictionary()->verify()); | |
8738 | |
8739 // update the space and generation capacity counters | |
8740 if (UsePerfData) { | |
8741 _space_counters->update_capacity(); | |
8742 _gen_counters->update_all(); | |
8743 } | |
8744 | |
8745 if (Verbose && PrintGCDetails) { | |
8746 size_t new_mem_size = _virtual_space.committed_size(); | |
8747 size_t old_mem_size = new_mem_size + bytes; | |
8748 gclog_or_tty->print_cr("Shrinking %s from %ldK by %ldK to %ldK", | |
8749 name(), old_mem_size/K, bytes/K, new_mem_size/K); | |
8750 } | |
8751 } | |
8752 | |
8753 assert(_cmsSpace->unallocated_block() <= _cmsSpace->end(), | |
8754 "Inconsistency at end of space"); | |
8755 assert(chunk_at_end->end() == _cmsSpace->end(), | |
8756 "Shrinking is inconsistent"); | |
8757 return; | |
8758 } | |
8759 } | |
8760 | |
8761 // Transfer some number of overflown objects to usual marking | |
8762 // stack. Return true if some objects were transferred. | |
8763 bool MarkRefsIntoAndScanClosure::take_from_overflow_list() { | |
8764 size_t num = MIN2((size_t)_mark_stack->capacity()/4, | |
8765 (size_t)ParGCDesiredObjsFromOverflowList); | |
8766 | |
8767 bool res = _collector->take_from_overflow_list(num, _mark_stack); | |
8768 assert(_collector->overflow_list_is_empty() || res, | |
8769 "If list is not empty, we should have taken something"); | |
8770 assert(!res || !_mark_stack->isEmpty(), | |
8771 "If we took something, it should now be on our stack"); | |
8772 return res; | |
8773 } | |
8774 | |
8775 size_t MarkDeadObjectsClosure::do_blk(HeapWord* addr) { | |
8776 size_t res = _sp->block_size_no_stall(addr, _collector); | |
8777 assert(res != 0, "Should always be able to compute a size"); | |
8778 if (_sp->block_is_obj(addr)) { | |
8779 if (_live_bit_map->isMarked(addr)) { | |
8780 // It can't have been dead in a previous cycle | |
8781 guarantee(!_dead_bit_map->isMarked(addr), "No resurrection!"); | |
8782 } else { | |
8783 _dead_bit_map->mark(addr); // mark the dead object | |
8784 } | |
8785 } | |
8786 return res; | |
8787 } |