Mercurial > hg > graal-compiler
annotate src/share/vm/runtime/biasedLocking.cpp @ 83:d3cd40645d0d
6681646: Relocking of a scalar replaced object during deoptimization is broken
Summary: Relocking of a thread-local object during deoptimization is broken
Reviewed-by: kbr, jrose, never
author | kvn |
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date | Tue, 01 Apr 2008 16:14:18 -0700 |
parents | 7ee622712fcf |
children | 6e085831cad7 |
rev | line source |
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0 | 1 |
2 /* | |
3 * Copyright 2005-2007 Sun Microsystems, Inc. All Rights Reserved. | |
4 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | |
5 * | |
6 * This code is free software; you can redistribute it and/or modify it | |
7 * under the terms of the GNU General Public License version 2 only, as | |
8 * published by the Free Software Foundation. | |
9 * | |
10 * This code is distributed in the hope that it will be useful, but WITHOUT | |
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | |
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | |
13 * version 2 for more details (a copy is included in the LICENSE file that | |
14 * accompanied this code). | |
15 * | |
16 * You should have received a copy of the GNU General Public License version | |
17 * 2 along with this work; if not, write to the Free Software Foundation, | |
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | |
19 * | |
20 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, | |
21 * CA 95054 USA or visit www.sun.com if you need additional information or | |
22 * have any questions. | |
23 * | |
24 */ | |
25 | |
26 # include "incls/_precompiled.incl" | |
27 # include "incls/_biasedLocking.cpp.incl" | |
28 | |
29 static bool _biased_locking_enabled = false; | |
30 BiasedLockingCounters BiasedLocking::_counters; | |
31 | |
32 static GrowableArray<Handle>* _preserved_oop_stack = NULL; | |
33 static GrowableArray<markOop>* _preserved_mark_stack = NULL; | |
34 | |
35 static void enable_biased_locking(klassOop k) { | |
36 Klass::cast(k)->set_prototype_header(markOopDesc::biased_locking_prototype()); | |
37 } | |
38 | |
39 class VM_EnableBiasedLocking: public VM_Operation { | |
40 public: | |
58
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41 VM_EnableBiasedLocking() {} |
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42 VMOp_Type type() const { return VMOp_EnableBiasedLocking; } |
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43 Mode evaluation_mode() const { return _async_safepoint; } |
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44 bool is_cheap_allocated() const { return true; } |
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45 |
0 | 46 void doit() { |
47 // Iterate the system dictionary enabling biased locking for all | |
48 // currently loaded classes | |
49 SystemDictionary::classes_do(enable_biased_locking); | |
50 // Indicate that future instances should enable it as well | |
51 _biased_locking_enabled = true; | |
52 | |
53 if (TraceBiasedLocking) { | |
54 tty->print_cr("Biased locking enabled"); | |
55 } | |
56 } | |
57 | |
58 bool allow_nested_vm_operations() const { return false; } | |
59 }; | |
60 | |
61 | |
62 // One-shot PeriodicTask subclass for enabling biased locking | |
63 class EnableBiasedLockingTask : public PeriodicTask { | |
64 public: | |
65 EnableBiasedLockingTask(size_t interval_time) : PeriodicTask(interval_time) {} | |
66 | |
67 virtual void task() { | |
58
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68 // Use async VM operation to avoid blocking the Watcher thread. |
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69 // VM Thread will free C heap storage. |
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70 VM_EnableBiasedLocking *op = new VM_EnableBiasedLocking(); |
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71 VMThread::execute(op); |
0 | 72 |
73 // Reclaim our storage and disenroll ourself | |
74 delete this; | |
75 } | |
76 }; | |
77 | |
78 | |
79 void BiasedLocking::init() { | |
80 // If biased locking is enabled, schedule a task to fire a few | |
81 // seconds into the run which turns on biased locking for all | |
82 // currently loaded classes as well as future ones. This is a | |
83 // workaround for startup time regressions due to a large number of | |
84 // safepoints being taken during VM startup for bias revocation. | |
85 // Ideally we would have a lower cost for individual bias revocation | |
86 // and not need a mechanism like this. | |
87 if (UseBiasedLocking) { | |
88 if (BiasedLockingStartupDelay > 0) { | |
89 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay); | |
90 task->enroll(); | |
91 } else { | |
92 VM_EnableBiasedLocking op; | |
93 VMThread::execute(&op); | |
94 } | |
95 } | |
96 } | |
97 | |
98 | |
99 bool BiasedLocking::enabled() { | |
100 return _biased_locking_enabled; | |
101 } | |
102 | |
103 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order | |
104 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) { | |
105 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info(); | |
106 if (info != NULL) { | |
107 return info; | |
108 } | |
109 | |
110 info = new GrowableArray<MonitorInfo*>(); | |
111 | |
112 // It's possible for the thread to not have any Java frames on it, | |
113 // i.e., if it's the main thread and it's already returned from main() | |
114 if (thread->has_last_Java_frame()) { | |
115 RegisterMap rm(thread); | |
116 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { | |
117 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); | |
118 if (monitors != NULL) { | |
119 int len = monitors->length(); | |
120 // Walk monitors youngest to oldest | |
121 for (int i = len - 1; i >= 0; i--) { | |
122 MonitorInfo* mon_info = monitors->at(i); | |
123 oop owner = mon_info->owner(); | |
124 if (owner != NULL) { | |
125 info->append(mon_info); | |
126 } | |
127 } | |
128 } | |
129 } | |
130 } | |
131 | |
132 thread->set_cached_monitor_info(info); | |
133 return info; | |
134 } | |
135 | |
136 | |
137 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) { | |
138 markOop mark = obj->mark(); | |
139 if (!mark->has_bias_pattern()) { | |
140 if (TraceBiasedLocking) { | |
141 ResourceMark rm; | |
142 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)", | |
143 Klass::cast(obj->klass())->external_name()); | |
144 } | |
145 return BiasedLocking::NOT_BIASED; | |
146 } | |
147 | |
148 int age = mark->age(); | |
149 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age); | |
150 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age); | |
151 | |
152 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
153 ResourceMark rm; | |
154 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, | |
155 (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); | |
156 } | |
157 | |
158 JavaThread* biased_thread = mark->biased_locker(); | |
159 if (biased_thread == NULL) { | |
160 // Object is anonymously biased. We can get here if, for | |
161 // example, we revoke the bias due to an identity hash code | |
162 // being computed for an object. | |
163 if (!allow_rebias) { | |
164 obj->set_mark(unbiased_prototype); | |
165 } | |
166 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
167 tty->print_cr(" Revoked bias of anonymously-biased object"); | |
168 } | |
169 return BiasedLocking::BIAS_REVOKED; | |
170 } | |
171 | |
172 // Handle case where the thread toward which the object was biased has exited | |
173 bool thread_is_alive = false; | |
174 if (requesting_thread == biased_thread) { | |
175 thread_is_alive = true; | |
176 } else { | |
177 for (JavaThread* cur_thread = Threads::first(); cur_thread != NULL; cur_thread = cur_thread->next()) { | |
178 if (cur_thread == biased_thread) { | |
179 thread_is_alive = true; | |
180 break; | |
181 } | |
182 } | |
183 } | |
184 if (!thread_is_alive) { | |
185 if (allow_rebias) { | |
186 obj->set_mark(biased_prototype); | |
187 } else { | |
188 obj->set_mark(unbiased_prototype); | |
189 } | |
190 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
191 tty->print_cr(" Revoked bias of object biased toward dead thread"); | |
192 } | |
193 return BiasedLocking::BIAS_REVOKED; | |
194 } | |
195 | |
196 // Thread owning bias is alive. | |
197 // Check to see whether it currently owns the lock and, if so, | |
198 // write down the needed displaced headers to the thread's stack. | |
199 // Otherwise, restore the object's header either to the unlocked | |
200 // or unbiased state. | |
201 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread); | |
202 BasicLock* highest_lock = NULL; | |
203 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
204 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
205 if (mon_info->owner() == obj) { | |
206 if (TraceBiasedLocking && Verbose) { | |
207 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")", | |
208 (intptr_t) mon_info->owner(), | |
209 (intptr_t) obj); | |
210 } | |
211 // Assume recursive case and fix up highest lock later | |
212 markOop mark = markOopDesc::encode((BasicLock*) NULL); | |
213 highest_lock = mon_info->lock(); | |
214 highest_lock->set_displaced_header(mark); | |
215 } else { | |
216 if (TraceBiasedLocking && Verbose) { | |
217 tty->print_cr(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")", | |
218 (intptr_t) mon_info->owner(), | |
219 (intptr_t) obj); | |
220 } | |
221 } | |
222 } | |
223 if (highest_lock != NULL) { | |
224 // Fix up highest lock to contain displaced header and point | |
225 // object at it | |
226 highest_lock->set_displaced_header(unbiased_prototype); | |
227 // Reset object header to point to displaced mark | |
228 obj->set_mark(markOopDesc::encode(highest_lock)); | |
229 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit"); | |
230 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
231 tty->print_cr(" Revoked bias of currently-locked object"); | |
232 } | |
233 } else { | |
234 if (TraceBiasedLocking && (Verbose || !is_bulk)) { | |
235 tty->print_cr(" Revoked bias of currently-unlocked object"); | |
236 } | |
237 if (allow_rebias) { | |
238 obj->set_mark(biased_prototype); | |
239 } else { | |
240 // Store the unlocked value into the object's header. | |
241 obj->set_mark(unbiased_prototype); | |
242 } | |
243 } | |
244 | |
245 return BiasedLocking::BIAS_REVOKED; | |
246 } | |
247 | |
248 | |
249 enum HeuristicsResult { | |
250 HR_NOT_BIASED = 1, | |
251 HR_SINGLE_REVOKE = 2, | |
252 HR_BULK_REBIAS = 3, | |
253 HR_BULK_REVOKE = 4 | |
254 }; | |
255 | |
256 | |
257 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) { | |
258 markOop mark = o->mark(); | |
259 if (!mark->has_bias_pattern()) { | |
260 return HR_NOT_BIASED; | |
261 } | |
262 | |
263 // Heuristics to attempt to throttle the number of revocations. | |
264 // Stages: | |
265 // 1. Revoke the biases of all objects in the heap of this type, | |
266 // but allow rebiasing of those objects if unlocked. | |
267 // 2. Revoke the biases of all objects in the heap of this type | |
268 // and don't allow rebiasing of these objects. Disable | |
269 // allocation of objects of that type with the bias bit set. | |
270 Klass* k = o->blueprint(); | |
271 jlong cur_time = os::javaTimeMillis(); | |
272 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time(); | |
273 int revocation_count = k->biased_lock_revocation_count(); | |
274 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) && | |
275 (revocation_count < BiasedLockingBulkRevokeThreshold) && | |
276 (last_bulk_revocation_time != 0) && | |
277 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) { | |
278 // This is the first revocation we've seen in a while of an | |
279 // object of this type since the last time we performed a bulk | |
280 // rebiasing operation. The application is allocating objects in | |
281 // bulk which are biased toward a thread and then handing them | |
282 // off to another thread. We can cope with this allocation | |
283 // pattern via the bulk rebiasing mechanism so we reset the | |
284 // klass's revocation count rather than allow it to increase | |
285 // monotonically. If we see the need to perform another bulk | |
286 // rebias operation later, we will, and if subsequently we see | |
287 // many more revocation operations in a short period of time we | |
288 // will completely disable biasing for this type. | |
289 k->set_biased_lock_revocation_count(0); | |
290 revocation_count = 0; | |
291 } | |
292 | |
293 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold | |
294 if (revocation_count <= BiasedLockingBulkRevokeThreshold) { | |
295 revocation_count = k->atomic_incr_biased_lock_revocation_count(); | |
296 } | |
297 | |
298 if (revocation_count == BiasedLockingBulkRevokeThreshold) { | |
299 return HR_BULK_REVOKE; | |
300 } | |
301 | |
302 if (revocation_count == BiasedLockingBulkRebiasThreshold) { | |
303 return HR_BULK_REBIAS; | |
304 } | |
305 | |
306 return HR_SINGLE_REVOKE; | |
307 } | |
308 | |
309 | |
310 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o, | |
311 bool bulk_rebias, | |
312 bool attempt_rebias_of_object, | |
313 JavaThread* requesting_thread) { | |
314 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint"); | |
315 | |
316 if (TraceBiasedLocking) { | |
317 tty->print_cr("* Beginning bulk revocation (kind == %s) because of object " | |
318 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s", | |
319 (bulk_rebias ? "rebias" : "revoke"), | |
320 (intptr_t) o, (intptr_t) o->mark(), Klass::cast(o->klass())->external_name()); | |
321 } | |
322 | |
323 jlong cur_time = os::javaTimeMillis(); | |
324 o->blueprint()->set_last_biased_lock_bulk_revocation_time(cur_time); | |
325 | |
326 | |
327 klassOop k_o = o->klass(); | |
328 Klass* klass = Klass::cast(k_o); | |
329 | |
330 if (bulk_rebias) { | |
331 // Use the epoch in the klass of the object to implicitly revoke | |
332 // all biases of objects of this data type and force them to be | |
333 // reacquired. However, we also need to walk the stacks of all | |
334 // threads and update the headers of lightweight locked objects | |
335 // with biases to have the current epoch. | |
336 | |
337 // If the prototype header doesn't have the bias pattern, don't | |
338 // try to update the epoch -- assume another VM operation came in | |
339 // and reset the header to the unbiased state, which will | |
340 // implicitly cause all existing biases to be revoked | |
341 if (klass->prototype_header()->has_bias_pattern()) { | |
342 int prev_epoch = klass->prototype_header()->bias_epoch(); | |
343 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch()); | |
344 int cur_epoch = klass->prototype_header()->bias_epoch(); | |
345 | |
346 // Now walk all threads' stacks and adjust epochs of any biased | |
347 // and locked objects of this data type we encounter | |
348 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
349 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); | |
350 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
351 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
352 oop owner = mon_info->owner(); | |
353 markOop mark = owner->mark(); | |
354 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { | |
355 // We might have encountered this object already in the case of recursive locking | |
356 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment"); | |
357 owner->set_mark(mark->set_bias_epoch(cur_epoch)); | |
358 } | |
359 } | |
360 } | |
361 } | |
362 | |
363 // At this point we're done. All we have to do is potentially | |
364 // adjust the header of the given object to revoke its bias. | |
365 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread); | |
366 } else { | |
367 if (TraceBiasedLocking) { | |
368 ResourceMark rm; | |
369 tty->print_cr("* Disabling biased locking for type %s", klass->external_name()); | |
370 } | |
371 | |
372 // Disable biased locking for this data type. Not only will this | |
373 // cause future instances to not be biased, but existing biased | |
374 // instances will notice that this implicitly caused their biases | |
375 // to be revoked. | |
376 klass->set_prototype_header(markOopDesc::prototype()); | |
377 | |
378 // Now walk all threads' stacks and forcibly revoke the biases of | |
379 // any locked and biased objects of this data type we encounter. | |
380 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
381 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr); | |
382 for (int i = 0; i < cached_monitor_info->length(); i++) { | |
383 MonitorInfo* mon_info = cached_monitor_info->at(i); | |
384 oop owner = mon_info->owner(); | |
385 markOop mark = owner->mark(); | |
386 if ((owner->klass() == k_o) && mark->has_bias_pattern()) { | |
387 revoke_bias(owner, false, true, requesting_thread); | |
388 } | |
389 } | |
390 } | |
391 | |
392 // Must force the bias of the passed object to be forcibly revoked | |
393 // as well to ensure guarantees to callers | |
394 revoke_bias(o, false, true, requesting_thread); | |
395 } | |
396 | |
397 if (TraceBiasedLocking) { | |
398 tty->print_cr("* Ending bulk revocation"); | |
399 } | |
400 | |
401 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED; | |
402 | |
403 if (attempt_rebias_of_object && | |
404 o->mark()->has_bias_pattern() && | |
405 klass->prototype_header()->has_bias_pattern()) { | |
406 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(), | |
407 klass->prototype_header()->bias_epoch()); | |
408 o->set_mark(new_mark); | |
409 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED; | |
410 if (TraceBiasedLocking) { | |
411 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread); | |
412 } | |
413 } | |
414 | |
415 assert(!o->mark()->has_bias_pattern() || | |
416 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)), | |
417 "bug in bulk bias revocation"); | |
418 | |
419 return status_code; | |
420 } | |
421 | |
422 | |
423 static void clean_up_cached_monitor_info() { | |
424 // Walk the thread list clearing out the cached monitors | |
425 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) { | |
426 thr->set_cached_monitor_info(NULL); | |
427 } | |
428 } | |
429 | |
430 | |
431 class VM_RevokeBias : public VM_Operation { | |
432 protected: | |
433 Handle* _obj; | |
434 GrowableArray<Handle>* _objs; | |
435 JavaThread* _requesting_thread; | |
436 BiasedLocking::Condition _status_code; | |
437 | |
438 public: | |
439 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread) | |
440 : _obj(obj) | |
441 , _objs(NULL) | |
442 , _requesting_thread(requesting_thread) | |
443 , _status_code(BiasedLocking::NOT_BIASED) {} | |
444 | |
445 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread) | |
446 : _obj(NULL) | |
447 , _objs(objs) | |
448 , _requesting_thread(requesting_thread) | |
449 , _status_code(BiasedLocking::NOT_BIASED) {} | |
450 | |
451 virtual VMOp_Type type() const { return VMOp_RevokeBias; } | |
452 | |
453 virtual bool doit_prologue() { | |
454 // Verify that there is actual work to do since the callers just | |
455 // give us locked object(s). If we don't find any biased objects | |
456 // there is nothing to do and we avoid a safepoint. | |
457 if (_obj != NULL) { | |
458 markOop mark = (*_obj)()->mark(); | |
459 if (mark->has_bias_pattern()) { | |
460 return true; | |
461 } | |
462 } else { | |
463 for ( int i = 0 ; i < _objs->length(); i++ ) { | |
464 markOop mark = (_objs->at(i))()->mark(); | |
465 if (mark->has_bias_pattern()) { | |
466 return true; | |
467 } | |
468 } | |
469 } | |
470 return false; | |
471 } | |
472 | |
473 virtual void doit() { | |
474 if (_obj != NULL) { | |
475 if (TraceBiasedLocking) { | |
476 tty->print_cr("Revoking bias with potentially per-thread safepoint:"); | |
477 } | |
478 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread); | |
479 clean_up_cached_monitor_info(); | |
480 return; | |
481 } else { | |
482 if (TraceBiasedLocking) { | |
483 tty->print_cr("Revoking bias with global safepoint:"); | |
484 } | |
485 BiasedLocking::revoke_at_safepoint(_objs); | |
486 } | |
487 } | |
488 | |
489 BiasedLocking::Condition status_code() const { | |
490 return _status_code; | |
491 } | |
492 }; | |
493 | |
494 | |
495 class VM_BulkRevokeBias : public VM_RevokeBias { | |
496 private: | |
497 bool _bulk_rebias; | |
498 bool _attempt_rebias_of_object; | |
499 | |
500 public: | |
501 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread, | |
502 bool bulk_rebias, | |
503 bool attempt_rebias_of_object) | |
504 : VM_RevokeBias(obj, requesting_thread) | |
505 , _bulk_rebias(bulk_rebias) | |
506 , _attempt_rebias_of_object(attempt_rebias_of_object) {} | |
507 | |
508 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; } | |
509 virtual bool doit_prologue() { return true; } | |
510 | |
511 virtual void doit() { | |
512 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread); | |
513 clean_up_cached_monitor_info(); | |
514 } | |
515 }; | |
516 | |
517 | |
518 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) { | |
519 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); | |
520 | |
521 // We can revoke the biases of anonymously-biased objects | |
522 // efficiently enough that we should not cause these revocations to | |
523 // update the heuristics because doing so may cause unwanted bulk | |
524 // revocations (which are expensive) to occur. | |
525 markOop mark = obj->mark(); | |
526 if (mark->is_biased_anonymously() && !attempt_rebias) { | |
527 // We are probably trying to revoke the bias of this object due to | |
528 // an identity hash code computation. Try to revoke the bias | |
529 // without a safepoint. This is possible if we can successfully | |
530 // compare-and-exchange an unbiased header into the mark word of | |
531 // the object, meaning that no other thread has raced to acquire | |
532 // the bias of the object. | |
533 markOop biased_value = mark; | |
534 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); | |
535 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); | |
536 if (res_mark == biased_value) { | |
537 return BIAS_REVOKED; | |
538 } | |
539 } else if (mark->has_bias_pattern()) { | |
540 Klass* k = Klass::cast(obj->klass()); | |
541 markOop prototype_header = k->prototype_header(); | |
542 if (!prototype_header->has_bias_pattern()) { | |
543 // This object has a stale bias from before the bulk revocation | |
544 // for this data type occurred. It's pointless to update the | |
545 // heuristics at this point so simply update the header with a | |
546 // CAS. If we fail this race, the object's bias has been revoked | |
547 // by another thread so we simply return and let the caller deal | |
548 // with it. | |
549 markOop biased_value = mark; | |
550 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(prototype_header, obj->mark_addr(), mark); | |
551 assert(!(*(obj->mark_addr()))->has_bias_pattern(), "even if we raced, should still be revoked"); | |
552 return BIAS_REVOKED; | |
553 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) { | |
554 // The epoch of this biasing has expired indicating that the | |
555 // object is effectively unbiased. Depending on whether we need | |
556 // to rebias or revoke the bias of this object we can do it | |
557 // efficiently enough with a CAS that we shouldn't update the | |
558 // heuristics. This is normally done in the assembly code but we | |
559 // can reach this point due to various points in the runtime | |
560 // needing to revoke biases. | |
561 if (attempt_rebias) { | |
562 assert(THREAD->is_Java_thread(), ""); | |
563 markOop biased_value = mark; | |
564 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch()); | |
565 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(rebiased_prototype, obj->mark_addr(), mark); | |
566 if (res_mark == biased_value) { | |
567 return BIAS_REVOKED_AND_REBIASED; | |
568 } | |
569 } else { | |
570 markOop biased_value = mark; | |
571 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age()); | |
572 markOop res_mark = (markOop) Atomic::cmpxchg_ptr(unbiased_prototype, obj->mark_addr(), mark); | |
573 if (res_mark == biased_value) { | |
574 return BIAS_REVOKED; | |
575 } | |
576 } | |
577 } | |
578 } | |
579 | |
580 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias); | |
581 if (heuristics == HR_NOT_BIASED) { | |
582 return NOT_BIASED; | |
583 } else if (heuristics == HR_SINGLE_REVOKE) { | |
584 if (mark->biased_locker() == THREAD) { | |
585 // A thread is trying to revoke the bias of an object biased | |
586 // toward it, again likely due to an identity hash code | |
587 // computation. We can again avoid a safepoint in this case | |
588 // since we are only going to walk our own stack. There are no | |
589 // races with revocations occurring in other threads because we | |
590 // reach no safepoints in the revocation path. | |
591 ResourceMark rm; | |
592 if (TraceBiasedLocking) { | |
593 tty->print_cr("Revoking bias by walking my own stack:"); | |
594 } | |
595 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD); | |
596 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL); | |
597 assert(cond == BIAS_REVOKED, "why not?"); | |
598 return cond; | |
599 } else { | |
600 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD); | |
601 VMThread::execute(&revoke); | |
602 return revoke.status_code(); | |
603 } | |
604 } | |
605 | |
606 assert((heuristics == HR_BULK_REVOKE) || | |
607 (heuristics == HR_BULK_REBIAS), "?"); | |
608 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD, | |
609 (heuristics == HR_BULK_REBIAS), | |
610 attempt_rebias); | |
611 VMThread::execute(&bulk_revoke); | |
612 return bulk_revoke.status_code(); | |
613 } | |
614 | |
615 | |
616 void BiasedLocking::revoke(GrowableArray<Handle>* objs) { | |
617 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint"); | |
618 if (objs->length() == 0) { | |
619 return; | |
620 } | |
621 VM_RevokeBias revoke(objs, JavaThread::current()); | |
622 VMThread::execute(&revoke); | |
623 } | |
624 | |
625 | |
626 void BiasedLocking::revoke_at_safepoint(Handle h_obj) { | |
627 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
628 oop obj = h_obj(); | |
629 HeuristicsResult heuristics = update_heuristics(obj, false); | |
630 if (heuristics == HR_SINGLE_REVOKE) { | |
631 revoke_bias(obj, false, false, NULL); | |
632 } else if ((heuristics == HR_BULK_REBIAS) || | |
633 (heuristics == HR_BULK_REVOKE)) { | |
634 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); | |
635 } | |
636 clean_up_cached_monitor_info(); | |
637 } | |
638 | |
639 | |
640 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) { | |
641 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
642 int len = objs->length(); | |
643 for (int i = 0; i < len; i++) { | |
644 oop obj = (objs->at(i))(); | |
645 HeuristicsResult heuristics = update_heuristics(obj, false); | |
646 if (heuristics == HR_SINGLE_REVOKE) { | |
647 revoke_bias(obj, false, false, NULL); | |
648 } else if ((heuristics == HR_BULK_REBIAS) || | |
649 (heuristics == HR_BULK_REVOKE)) { | |
650 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL); | |
651 } | |
652 } | |
653 clean_up_cached_monitor_info(); | |
654 } | |
655 | |
656 | |
657 void BiasedLocking::preserve_marks() { | |
658 if (!UseBiasedLocking) | |
659 return; | |
660 | |
661 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint"); | |
662 | |
663 assert(_preserved_oop_stack == NULL, "double initialization"); | |
664 assert(_preserved_mark_stack == NULL, "double initialization"); | |
665 | |
666 // In order to reduce the number of mark words preserved during GC | |
667 // due to the presence of biased locking, we reinitialize most mark | |
668 // words to the class's prototype during GC -- even those which have | |
669 // a currently valid bias owner. One important situation where we | |
670 // must not clobber a bias is when a biased object is currently | |
671 // locked. To handle this case we iterate over the currently-locked | |
672 // monitors in a prepass and, if they are biased, preserve their | |
673 // mark words here. This should be a relatively small set of objects | |
674 // especially compared to the number of objects in the heap. | |
675 _preserved_mark_stack = new (ResourceObj::C_HEAP) GrowableArray<markOop>(10, true); | |
676 _preserved_oop_stack = new (ResourceObj::C_HEAP) GrowableArray<Handle>(10, true); | |
677 | |
678 ResourceMark rm; | |
679 Thread* cur = Thread::current(); | |
680 for (JavaThread* thread = Threads::first(); thread != NULL; thread = thread->next()) { | |
681 if (thread->has_last_Java_frame()) { | |
682 RegisterMap rm(thread); | |
683 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) { | |
684 GrowableArray<MonitorInfo*> *monitors = vf->monitors(); | |
685 if (monitors != NULL) { | |
686 int len = monitors->length(); | |
687 // Walk monitors youngest to oldest | |
688 for (int i = len - 1; i >= 0; i--) { | |
689 MonitorInfo* mon_info = monitors->at(i); | |
690 oop owner = mon_info->owner(); | |
691 if (owner != NULL) { | |
692 markOop mark = owner->mark(); | |
693 if (mark->has_bias_pattern()) { | |
694 _preserved_oop_stack->push(Handle(cur, owner)); | |
695 _preserved_mark_stack->push(mark); | |
696 } | |
697 } | |
698 } | |
699 } | |
700 } | |
701 } | |
702 } | |
703 } | |
704 | |
705 | |
706 void BiasedLocking::restore_marks() { | |
707 if (!UseBiasedLocking) | |
708 return; | |
709 | |
710 assert(_preserved_oop_stack != NULL, "double free"); | |
711 assert(_preserved_mark_stack != NULL, "double free"); | |
712 | |
713 int len = _preserved_oop_stack->length(); | |
714 for (int i = 0; i < len; i++) { | |
715 Handle owner = _preserved_oop_stack->at(i); | |
716 markOop mark = _preserved_mark_stack->at(i); | |
717 owner->set_mark(mark); | |
718 } | |
719 | |
720 delete _preserved_oop_stack; | |
721 _preserved_oop_stack = NULL; | |
722 delete _preserved_mark_stack; | |
723 _preserved_mark_stack = NULL; | |
724 } | |
725 | |
726 | |
727 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); } | |
728 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); } | |
729 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); } | |
730 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); } | |
731 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); } | |
732 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); } | |
733 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); } | |
734 | |
735 | |
736 // BiasedLockingCounters | |
737 | |
738 int BiasedLockingCounters::slow_path_entry_count() { | |
739 if (_slow_path_entry_count != 0) { | |
740 return _slow_path_entry_count; | |
741 } | |
742 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count + | |
743 _rebiased_lock_entry_count + _revoked_lock_entry_count + | |
744 _fast_path_entry_count; | |
745 | |
746 return _total_entry_count - sum; | |
747 } | |
748 | |
749 void BiasedLockingCounters::print_on(outputStream* st) { | |
750 tty->print_cr("# total entries: %d", _total_entry_count); | |
751 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count); | |
752 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count); | |
753 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count); | |
754 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count); | |
755 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count); | |
756 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count()); | |
757 } |