Mercurial > hg > truffle
annotate src/share/vm/runtime/biasedLocking.cpp @ 374:a4b729f5b611
6716466: par compact - remove VerifyParallelOldWithMarkSweep code
Reviewed-by: jmasa
author | jcoomes |
---|---|
date | Tue, 30 Sep 2008 11:49:31 -0700 |
parents | d1605aabd0a1 |
children | 2b42b31e7928 |
rev | line source |
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0 | 1 /* |
196 | 2 * Copyright 2005-2008 Sun Microsystems, Inc. All Rights Reserved. |
0 | 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/_biasedLocking.cpp.incl" | |
27 | |
28 static bool _biased_locking_enabled = false; | |
29 BiasedLockingCounters BiasedLocking::_counters; | |
30 | |
31 static GrowableArray<Handle>* _preserved_oop_stack = NULL; | |
32 static GrowableArray<markOop>* _preserved_mark_stack = NULL; | |
33 | |
34 static void enable_biased_locking(klassOop k) { | |
35 Klass::cast(k)->set_prototype_header(markOopDesc::biased_locking_prototype()); | |
36 } | |
37 | |
38 class VM_EnableBiasedLocking: public VM_Operation { | |
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39 private: |
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40 bool _is_cheap_allocated; |
0 | 41 public: |
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42 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; } |
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43 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } |
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44 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; } |
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45 bool is_cheap_allocated() const { return _is_cheap_allocated; } |
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46 |
0 | 47 void doit() { |
48 // Iterate the system dictionary enabling biased locking for all | |
49 // currently loaded classes | |
50 SystemDictionary::classes_do(enable_biased_locking); | |
51 // Indicate that future instances should enable it as well | |
52 _biased_locking_enabled = true; | |
53 | |
54 if (TraceBiasedLocking) { | |
55 tty->print_cr("Biased locking enabled"); | |
56 } | |
57 } | |
58 | |
59 bool allow_nested_vm_operations() const { return false; } | |
60 }; | |
61 | |
62 | |
63 // One-shot PeriodicTask subclass for enabling biased locking | |
64 class EnableBiasedLockingTask : public PeriodicTask { | |
65 public: | |
66 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} | |
67 | |
68 virtual void task() { | |
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69 // Use async VM operation to avoid blocking the Watcher thread. |
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70 // VM Thread will free C heap storage. |
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71 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(true); |
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72 VMThread::execute(op); |
0 | 73 |
74 // Reclaim our storage and disenroll ourself | |
75 delete this; | |
76 } | |
77 }; | |
78 | |
79 | |
80 void BiasedLocking::init() { | |
81 // If biased locking is enabled, schedule a task to fire a few | |
82 // seconds into the run which turns on biased locking for all | |
83 // currently loaded classes as well as future ones. This is a | |
84 // workaround for startup time regressions due to a large number of | |
85 // safepoints being taken during VM startup for bias revocation. | |
86 // Ideally we would have a lower cost for individual bias revocation | |
87 // and not need a mechanism like this. | |
88 if (UseBiasedLocking) { | |
89 if (BiasedLockingStartupDelay > 0) { | |
90 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); | |
91 task->enroll(); | |
92 } else { | |
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93 VM_EnableBiasedLocking op(false); |
0 | 94 VMThread::execute(&op); |
95 } | |
96 } | |
97 } | |
98 | |
99 | |
100 bool BiasedLocking::enabled() { | |
101 return _biased_locking_enabled; | |
102 } | |
103 | |
104 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order | |
105 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { | |
106 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); | |
107 if (info != NULL) { | |
108 return info; | |
109 } | |
110 | |
111 info = new GrowableArray<MonitorInfo*>(); | |
112 | |
113 // It's possible for the thread to not have any Java frames on it, | |
114 // i.e., if it's the main thread and it's already returned from main() | |
115 if (thread->has_last_Java_frame()) { | |
116 RegisterMap rm(thread); | |
117 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { | |
118 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); | |
119 if (monitors != NULL) { | |
120 int len = monitors->length(); | |
121 // Walk monitors youngest to oldest | |
122 for (int i = len - 1; i >= 0; i--) { | |
123 MonitorInfo* mon_info = monitors->at(i); | |
124 oop owner = mon_info->owner(); | |
125 if (owner != NULL) { | |
126 info->append(mon_info); | |
127 } | |
128 } | |
129 } | |
130 } | |
131 } | |
132 | |
133 thread->set_cached_monitor_info(info); | |
134 return info; | |
135 } | |
136 | |
137 | |
138 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) { | |
139 markOop mark = obj->mark(); | |
140 if (!mark->has_bias_pattern()) { | |
141 if (TraceBiasedLocking) { | |
142 ResourceMark rm; | |
143 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)", | |
144 Klass::cast(obj->klass())->external_name()); | |
145 } | |
146 return BiasedLocking::NOT_BIASED; | |
147 } | |
148 | |
149 int age = mark->age(); | |
150 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age); | |
151 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age); | |
152 | |
153 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
154 ResourceMark rm; | |
155 tty->print_cr("Revoking bias of object " INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s , prototype header " INTPTR_FORMAT " , allow rebias %d , requesting thread " INTPTR_FORMAT, | |
156 (intptr_t) obj, (intptr_t) mark, Klass::cast(obj->klass())->external_name(), (intptr_t) Klass::cast(obj->klass())->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread); | |
157 } | |
158 | |
159 JavaThread* biased_thread = mark->biased_locker(); | |
160 if (biased_thread == NULL) { | |
161 // Object is anonymously biased. We can get here if, for | |
162 // example, we revoke the bias due to an identity hash code | |
163 // being computed for an object. | |
164 if (!allow_rebias) { | |
165 obj->set_mark(unbiased_prototype); | |
166 } | |
167 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
168 tty->print_cr(" Revoked bias of anonymously-biased object"); | |
169 } | |
170 return BiasedLocking::BIAS_REVOKED; | |
171 } | |
172 | |
173 // Handle case where the thread toward which the object was biased has exited | |
174 bool thread_is_alive = false; | |
175 if (requesting_thread == biased_thread) { | |
176 thread_is_alive = true; | |
177 } else { | |
178 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) { | |
179 if (cur_thread == biased_thread) { | |
180 thread_is_alive = true; | |
181 break; | |
182 } | |
183 } | |
184 } | |
185 if (!thread_is_alive) { | |
186 if (allow_rebias) { | |
187 obj->set_mark(biased_prototype); | |
188 } else { | |
189 obj->set_mark(unbiased_prototype); | |
190 } | |
191 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
192 tty->print_cr(" Revoked bias of object biased toward dead thread"); | |
193 } | |
194 return BiasedLocking::BIAS_REVOKED; | |
195 } | |
196 | |
197 // Thread owning bias is alive. | |
198 // Check to see whether it currently owns the lock and, if so, | |
199 // write down the needed displaced headers to the thread's stack. | |
200 // Otherwise, restore the object's header either to the unlocked | |
201 // or unbiased state. | |
202 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); | |
203 BasicLock* highest_lock = NULL; | |
204 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
205 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
206 if (mon_info->owner() == obj) { | |
207 if (TraceBiasedLocking && Verbose) { | |
208 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", | |
209 (intptr_t) mon_info->owner(), | |
210 (intptr_t) obj); | |
211 } | |
212 // Assume recursive case and fix up highest lock later | |
213 markOop mark = markOopDesc::encode((BasicLock*) NULL); | |
214 highest_lock = mon_info->lock(); | |
215 highest_lock->set_displaced_header(mark); | |
216 } else { | |
217 if (TraceBiasedLocking && Verbose) { | |
218 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", | |
219 (intptr_t) mon_info->owner(), | |
220 (intptr_t) obj); | |
221 } | |
222 } | |
223 } | |
224 if (highest_lock != NULL) { | |
225 // Fix up highest lock to contain displaced header and point | |
226 // object at it | |
227 highest_lock->set_displaced_header(unbiased_prototype); | |
228 // Reset object header to point to displaced mark | |
229 obj->set_mark(markOopDesc::encode(highest_lock)); | |
230 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit"); | |
231 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
232 tty->print_cr(" Revoked bias of currently-locked object"); | |
233 } | |
234 } else { | |
235 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
236 tty->print_cr(" Revoked bias of currently-unlocked object"); | |
237 } | |
238 if (allow_rebias) { | |
239 obj->set_mark(biased_prototype); | |
240 } else { | |
241 // Store the unlocked value into the object's header. | |
242 obj->set_mark(unbiased_prototype); | |
243 } | |
244 } | |
245 | |
246 return BiasedLocking::BIAS_REVOKED; | |
247 } | |
248 | |
249 | |
250 enum HeuristicsResult { | |
251 HR_NOT_BIASED = 1, | |
252 HR_SINGLE_REVOKE = 2, | |
253 HR_BULK_REBIAS = 3, | |
254 HR_BULK_REVOKE = 4 | |
255 }; | |
256 | |
257 | |
258 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { | |
259 markOop mark = o->mark(); | |
260 if (!mark->has_bias_pattern()) { | |
261 return HR_NOT_BIASED; | |
262 } | |
263 | |
264 // Heuristics to attempt to throttle the number of revocations. | |
265 // Stages: | |
266 // 1. Revoke the biases of all objects in the heap of this type, | |
267 // but allow rebiasing of those objects if unlocked. | |
268 // 2. Revoke the biases of all objects in the heap of this type | |
269 // and don't allow rebiasing of these objects. Disable | |
270 // allocation of objects of that type with the bias bit set. | |
271 Klass* k = o->blueprint(); | |
272 jlong cur_time = os::javaTimeMillis(); | |
273 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); | |
274 int revocation_count = k->biased_lock_revocation_count(); | |
275 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && | |
276 (revocation_count < BiasedLockingBulkRevokeThreshold) && | |
277 (last_bulk_revocation_time != 0) && | |
278 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { | |
279 // This is the first revocation we've seen in a while of an | |
280 // object of this type since the last time we performed a bulk | |
281 // rebiasing operation. The application is allocating objects in | |
282 // bulk which are biased toward a thread and then handing them | |
283 // off to another thread. We can cope with this allocation | |
284 // pattern via the bulk rebiasing mechanism so we reset the | |
285 // klass's revocation count rather than allow it to increase | |
286 // monotonically. If we see the need to perform another bulk | |
287 // rebias operation later, we will, and if subsequently we see | |
288 // many more revocation operations in a short period of time we | |
289 // will completely disable biasing for this type. | |
290 k->set_biased_lock_revocation_count(0); | |
291 revocation_count = 0; | |
292 } | |
293 | |
294 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold | |
295 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { | |
296 revocation_count = k->atomic_incr_biased_lock_revocation_count(); | |
297 } | |
298 | |
299 if (revocation_count == BiasedLockingBulkRevokeThreshold) { | |
300 return HR_BULK_REVOKE; | |
301 } | |
302 | |
303 if (revocation_count == BiasedLockingBulkRebiasThreshold) { | |
304 return HR_BULK_REBIAS; | |
305 } | |
306 | |
307 return HR_SINGLE_REVOKE; | |
308 } | |
309 | |
310 | |
311 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, | |
312 bool bulk_rebias, | |
313 bool attempt_rebias_of_object, | |
314 JavaThread* requesting_thread) { | |
315 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); | |
316 | |
317 if (TraceBiasedLocking) { | |
318 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object " | |
319 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", | |
320 (bulk_rebias ? "rebias" : "revoke"), | |
321 (intptr_t) o, (intptr_t) o->mark(), Klass::cast(o->klass())->external_name()); | |
322 } | |
323 | |
324 jlong cur_time = os::javaTimeMillis(); | |
325 o->blueprint()->set_last_biased_lock_bulk_revocation_time(cur_time); | |
326 | |
327 | |
328 klassOop k_o = o->klass(); | |
329 Klass* klass = Klass::cast(k_o); | |
330 | |
331 if (bulk_rebias) { | |
332 // Use the epoch in the klass of the object to implicitly revoke | |
333 // all biases of objects of this data type and force them to be | |
334 // reacquired. However, we also need to walk the stacks of all | |
335 // threads and update the headers of lightweight locked objects | |
336 // with biases to have the current epoch. | |
337 | |
338 // If the prototype header doesn't have the bias pattern, don't | |
339 // try to update the epoch -- assume another VM operation came in | |
340 // and reset the header to the unbiased state, which will | |
341 // implicitly cause all existing biases to be revoked | |
342 if (klass->prototype_header()->has_bias_pattern()) { | |
343 int prev_epoch = klass->prototype_header()->bias_epoch(); | |
344 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); | |
345 int cur_epoch = klass->prototype_header()->bias_epoch(); | |
346 | |
347 // Now walk all threads' stacks and adjust epochs of any biased | |
348 // and locked objects of this data type we encounter | |
349 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
350 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); | |
351 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
352 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
353 oop owner = mon_info->owner(); | |
354 markOop mark = owner->mark(); | |
355 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { | |
356 // We might have encountered this object already in the case of recursive locking | |
357 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); | |
358 owner->set_mark(mark->set_bias_epoch(cur_epoch)); | |
359 } | |
360 } | |
361 } | |
362 } | |
363 | |
364 // At this point we're done. All we have to do is potentially | |
365 // adjust the header of the given object to revoke its bias. | |
366 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread); | |
367 } else { | |
368 if (TraceBiasedLocking) { | |
369 ResourceMark rm; | |
370 tty->print_cr("* Disabling biased locking for type %s", klass->external_name()); | |
371 } | |
372 | |
373 // Disable biased locking for this data type. Not only will this | |
374 // cause future instances to not be biased, but existing biased | |
375 // instances will notice that this implicitly caused their biases | |
376 // to be revoked. | |
377 klass->set_prototype_header(markOopDesc::prototype()); | |
378 | |
379 // Now walk all threads' stacks and forcibly revoke the biases of | |
380 // any locked and biased objects of this data type we encounter. | |
381 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
382 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); | |
383 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
384 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
385 oop owner = mon_info->owner(); | |
386 markOop mark = owner->mark(); | |
387 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { | |
388 revoke_bias(owner, false, true, requesting_thread); | |
389 } | |
390 } | |
391 } | |
392 | |
393 // Must force the bias of the passed object to be forcibly revoked | |
394 // as well to ensure guarantees to callers | |
395 revoke_bias(o, false, true, requesting_thread); | |
396 } | |
397 | |
398 if (TraceBiasedLocking) { | |
399 tty->print_cr("* Ending bulk revocation"); | |
400 } | |
401 | |
402 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; | |
403 | |
404 if (attempt_rebias_of_object && | |
405 o->mark()->has_bias_pattern() && | |
406 klass->prototype_header()->has_bias_pattern()) { | |
407 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), | |
408 klass->prototype_header()->bias_epoch()); | |
409 o->set_mark(new_mark); | |
410 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; | |
411 if (TraceBiasedLocking) { | |
412 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); | |
413 } | |
414 } | |
415 | |
416 assert(!o->mark()->has_bias_pattern() || | |
417 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), | |
418 "bug in bulk bias revocation"); | |
419 | |
420 return status_code; | |
421 } | |
422 | |
423 | |
424 static void clean_up_cached_monitor_info() { | |
425 // Walk the thread list clearing out the cached monitors | |
426 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
427 thr->set_cached_monitor_info(NULL); | |
428 } | |
429 } | |
430 | |
431 | |
432 class VM_RevokeBias : public VM_Operation { | |
433 protected: | |
434 Handle* _obj; | |
435 GrowableArray<Handle>* _objs; | |
436 JavaThread* _requesting_thread; | |
437 BiasedLocking::Condition _status_code; | |
438 | |
439 public: | |
440 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) | |
441 : _obj(obj) | |
442 , _objs(NULL) | |
443 , _requesting_thread(requesting_thread) | |
444 , _status_code(BiasedLocking::NOT_BIASED) {} | |
445 | |
446 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) | |
447 : _obj(NULL) | |
448 , _objs(objs) | |
449 , _requesting_thread(requesting_thread) | |
450 , _status_code(BiasedLocking::NOT_BIASED) {} | |
451 | |
452 virtual VMOp_Type type() const { return VMOp_RevokeBias; } | |
453 | |
454 virtual bool doit_prologue() { | |
455 // Verify that there is actual work to do since the callers just | |
456 // give us locked object(s). If we don't find any biased objects | |
457 // there is nothing to do and we avoid a safepoint. | |
458 if (_obj != NULL) { | |
459 markOop mark = (*_obj)()->mark(); | |
460 if (mark->has_bias_pattern()) { | |
461 return true; | |
462 } | |
463 } else { | |
464 for ( int i = 0 ; i < _objs->length(); i++ ) { | |
465 markOop mark = (_objs->at(i))()->mark(); | |
466 if (mark->has_bias_pattern()) { | |
467 return true; | |
468 } | |
469 } | |
470 } | |
471 return false; | |
472 } | |
473 | |
474 virtual void doit() { | |
475 if (_obj != NULL) { | |
476 if (TraceBiasedLocking) { | |
477 tty->print_cr("Revoking bias with potentially per-thread safepoint:"); | |
478 } | |
479 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread); | |
480 clean_up_cached_monitor_info(); | |
481 return; | |
482 } else { | |
483 if (TraceBiasedLocking) { | |
484 tty->print_cr("Revoking bias with global safepoint:"); | |
485 } | |
486 BiasedLocking::revoke_at_safepoint(_objs); | |
487 } | |
488 } | |
489 | |
490 BiasedLocking::Condition status_code() const { | |
491 return _status_code; | |
492 } | |
493 }; | |
494 | |
495 | |
496 class VM_BulkRevokeBias : public VM_RevokeBias { | |
497 private: | |
498 bool _bulk_rebias; | |
499 bool _attempt_rebias_of_object; | |
500 | |
501 public: | |
502 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, | |
503 bool bulk_rebias, | |
504 bool attempt_rebias_of_object) | |
505 : VM_RevokeBias(obj, requesting_thread) | |
506 , _bulk_rebias(bulk_rebias) | |
507 , _attempt_rebias_of_object(attempt_rebias_of_object) {} | |
508 | |
509 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } | |
510 virtual bool doit_prologue() { return true; } | |
511 | |
512 virtual void doit() { | |
513 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); | |
514 clean_up_cached_monitor_info(); | |
515 } | |
516 }; | |
517 | |
518 | |
519 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { | |
520 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); | |
521 | |
522 // We can revoke the biases of anonymously-biased objects | |
523 // efficiently enough that we should not cause these revocations to | |
524 // update the heuristics because doing so may cause unwanted bulk | |
525 // revocations (which are expensive) to occur. | |
526 markOop mark = obj->mark(); | |
527 if (mark->is_biased_anonymously() && !attempt_rebias) { | |
528 // We are probably trying to revoke the bias of this object due to | |
529 // an identity hash code computation. Try to revoke the bias | |
530 // without a safepoint. This is possible if we can successfully | |
531 // compare-and-exchange an unbiased header into the mark word of | |
532 // the object, meaning that no other thread has raced to acquire | |
533 // the bias of the object. | |
534 markOop biased_value = mark; | |
535 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); | |
536 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); | |
537 if (res_mark == biased_value) { | |
538 return BIAS_REVOKED; | |
539 } | |
540 } else if (mark->has_bias_pattern()) { | |
541 Klass* k = Klass::cast(obj->klass()); | |
542 markOop prototype_header = k->prototype_header(); | |
543 if (!prototype_header->has_bias_pattern()) { | |
544 // This object has a stale bias from before the bulk revocation | |
545 // for this data type occurred. It's pointless to update the | |
546 // heuristics at this point so simply update the header with a | |
547 // CAS. If we fail this race, the object's bias has been revoked | |
548 // by another thread so we simply return and let the caller deal | |
549 // with it. | |
550 markOop biased_value = mark; | |
551 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark); | |
552 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); | |
553 return BIAS_REVOKED; | |
554 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { | |
555 // The epoch of this biasing has expired indicating that the | |
556 // object is effectively unbiased. Depending on whether we need | |
557 // to rebias or revoke the bias of this object we can do it | |
558 // efficiently enough with a CAS that we shouldn't update the | |
559 // heuristics. This is normally done in the assembly code but we | |
560 // can reach this point due to various points in the runtime | |
561 // needing to revoke biases. | |
562 if (attempt_rebias) { | |
563 assert(THREAD->is_Java_thread(), ""); | |
564 markOop biased_value = mark; | |
565 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); | |
566 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark); | |
567 if (res_mark == biased_value) { | |
568 return BIAS_REVOKED_AND_REBIASED; | |
569 } | |
570 } else { | |
571 markOop biased_value = mark; | |
572 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); | |
573 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); | |
574 if (res_mark == biased_value) { | |
575 return BIAS_REVOKED; | |
576 } | |
577 } | |
578 } | |
579 } | |
580 | |
581 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); | |
582 if (heuristics == HR_NOT_BIASED) { | |
583 return NOT_BIASED; | |
584 } else if (heuristics == HR_SINGLE_REVOKE) { | |
585 if (mark->biased_locker() == THREAD) { | |
586 // A thread is trying to revoke the bias of an object biased | |
587 // toward it, again likely due to an identity hash code | |
588 // computation. We can again avoid a safepoint in this case | |
589 // since we are only going to walk our own stack. There are no | |
590 // races with revocations occurring in other threads because we | |
591 // reach no safepoints in the revocation path. | |
592 ResourceMark rm; | |
593 if (TraceBiasedLocking) { | |
594 tty->print_cr("Revoking bias by walking my own stack:"); | |
595 } | |
596 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD); | |
597 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); | |
598 assert(cond == BIAS_REVOKED, "why not?"); | |
599 return cond; | |
600 } else { | |
601 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); | |
602 VMThread::execute(&revoke); | |
603 return revoke.status_code(); | |
604 } | |
605 } | |
606 | |
607 assert((heuristics == HR_BULK_REVOKE) || | |
608 (heuristics == HR_BULK_REBIAS), "?"); | |
609 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, | |
610 (heuristics == HR_BULK_REBIAS), | |
611 attempt_rebias); | |
612 VMThread::execute(&bulk_revoke); | |
613 return bulk_revoke.status_code(); | |
614 } | |
615 | |
616 | |
617 void BiasedLocking::revoke(GrowableArray<Handle>* objs) { | |
618 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); | |
619 if (objs->length() == 0) { | |
620 return; | |
621 } | |
622 VM_RevokeBias revoke(objs, JavaThread::current()); | |
623 VMThread::execute(&revoke); | |
624 } | |
625 | |
626 | |
627 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { | |
628 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
629 oop obj = h_obj(); | |
630 HeuristicsResult heuristics = update_heuristics(obj, false); | |
631 if (heuristics == HR_SINGLE_REVOKE) { | |
632 revoke_bias(obj, false, false, NULL); | |
633 } else if ((heuristics == HR_BULK_REBIAS) || | |
634 (heuristics == HR_BULK_REVOKE)) { | |
635 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); | |
636 } | |
637 clean_up_cached_monitor_info(); | |
638 } | |
639 | |
640 | |
641 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { | |
642 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
643 int len = objs->length(); | |
644 for (int i = 0; i < len; i++) { | |
645 oop obj = (objs->at(i))(); | |
646 HeuristicsResult heuristics = update_heuristics(obj, false); | |
647 if (heuristics == HR_SINGLE_REVOKE) { | |
648 revoke_bias(obj, false, false, NULL); | |
649 } else if ((heuristics == HR_BULK_REBIAS) || | |
650 (heuristics == HR_BULK_REVOKE)) { | |
651 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); | |
652 } | |
653 } | |
654 clean_up_cached_monitor_info(); | |
655 } | |
656 | |
657 | |
658 void BiasedLocking::preserve_marks() { | |
659 if (!UseBiasedLocking) | |
660 return; | |
661 | |
662 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
663 | |
664 assert(_preserved_oop_stack == NULL, "double initialization"); | |
665 assert(_preserved_mark_stack == NULL, "double initialization"); | |
666 | |
667 // In order to reduce the number of mark words preserved during GC | |
668 // due to the presence of biased locking, we reinitialize most mark | |
669 // words to the class's prototype during GC -- even those which have | |
670 // a currently valid bias owner. One important situation where we | |
671 // must not clobber a bias is when a biased object is currently | |
672 // locked. To handle this case we iterate over the currently-locked | |
673 // monitors in a prepass and, if they are biased, preserve their | |
674 // mark words here. This should be a relatively small set of objects | |
675 // especially compared to the number of objects in the heap. | |
676 _preserved_mark_stack = new (ResourceObj::C_HEAP) GrowableArray<markOop>(10, true); | |
677 _preserved_oop_stack = new (ResourceObj::C_HEAP) GrowableArray<Handle>(10, true); | |
678 | |
679 ResourceMark rm; | |
680 Thread* cur = Thread::current(); | |
681 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { | |
682 if (thread->has_last_Java_frame()) { | |
683 RegisterMap rm(thread); | |
684 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { | |
685 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); | |
686 if (monitors != NULL) { | |
687 int len = monitors->length(); | |
688 // Walk monitors youngest to oldest | |
689 for (int i = len - 1; i >= 0; i--) { | |
690 MonitorInfo* mon_info = monitors->at(i); | |
691 oop owner = mon_info->owner(); | |
692 if (owner != NULL) { | |
693 markOop mark = owner->mark(); | |
694 if (mark->has_bias_pattern()) { | |
695 _preserved_oop_stack->push(Handle(cur, owner)); | |
696 _preserved_mark_stack->push(mark); | |
697 } | |
698 } | |
699 } | |
700 } | |
701 } | |
702 } | |
703 } | |
704 } | |
705 | |
706 | |
707 void BiasedLocking::restore_marks() { | |
708 if (!UseBiasedLocking) | |
709 return; | |
710 | |
711 assert(_preserved_oop_stack != NULL, "double free"); | |
712 assert(_preserved_mark_stack != NULL, "double free"); | |
713 | |
714 int len = _preserved_oop_stack->length(); | |
715 for (int i = 0; i < len; i++) { | |
716 Handle owner = _preserved_oop_stack->at(i); | |
717 markOop mark = _preserved_mark_stack->at(i); | |
718 owner->set_mark(mark); | |
719 } | |
720 | |
721 delete _preserved_oop_stack; | |
722 _preserved_oop_stack = NULL; | |
723 delete _preserved_mark_stack; | |
724 _preserved_mark_stack = NULL; | |
725 } | |
726 | |
727 | |
728 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } | |
729 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } | |
730 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } | |
731 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } | |
732 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } | |
733 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } | |
734 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } | |
735 | |
736 | |
737 // BiasedLockingCounters | |
738 | |
739 int BiasedLockingCounters::slow_path_entry_count() { | |
740 if (_slow_path_entry_count != 0) { | |
741 return _slow_path_entry_count; | |
742 } | |
743 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + | |
744 _rebiased_lock_entry_count + _revoked_lock_entry_count + | |
745 _fast_path_entry_count; | |
746 | |
747 return _total_entry_count - sum; | |
748 } | |
749 | |
750 void BiasedLockingCounters::print_on(outputStream* st) { | |
751 tty->print_cr("# total entries: %d", _total_entry_count); | |
752 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); | |
753 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); | |
754 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); | |
755 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); | |
756 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); | |
757 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); | |
758 } |