102 // bias revocation.
103 if (UseBiasedLocking) {
104 if (BiasedLockingStartupDelay > 0) {
105 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
106 task->enroll();
107 } else {
108 enable_biased_locking();
109 }
110 }
111 }
112
113
114 bool BiasedLocking::enabled() {
115 assert(UseBiasedLocking, "precondition");
116 // We check "BiasedLockingStartupDelay == 0" here to cover the
117 // possibility of calls to BiasedLocking::enabled() before
118 // BiasedLocking::init().
119 return _biased_locking_enabled || BiasedLockingStartupDelay == 0;
120 }
121
122 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
123 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
124 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
125 if (info != NULL) {
126 return info;
127 }
128
129 info = new GrowableArray<MonitorInfo*>();
130
131 // It's possible for the thread to not have any Java frames on it,
132 // i.e., if it's the main thread and it's already returned from main()
133 if (thread->has_last_Java_frame()) {
134 RegisterMap rm(thread);
135 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
136 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
137 if (monitors != NULL) {
138 int len = monitors->length();
139 // Walk monitors youngest to oldest
140 for (int i = len - 1; i >= 0; i--) {
141 MonitorInfo* mon_info = monitors->at(i);
142 if (mon_info->eliminated()) continue;
143 oop owner = mon_info->owner();
144 if (owner != NULL) {
145 info->append(mon_info);
146 }
147 }
148 }
149 }
150 }
151
152 thread->set_cached_monitor_info(info);
153 return info;
154 }
155
156 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
157 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
158 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
159 markOop mark = obj->mark();
160 if (!mark->has_bias_pattern()) {
161 if (log_is_enabled(Info, biasedlocking)) {
162 ResourceMark rm;
163 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT
164 ", mark " INTPTR_FORMAT ", type %s"
165 ", requesting thread " INTPTR_FORMAT
166 " because it's no longer biased)",
167 p2i((void *)obj), (intptr_t) mark,
168 obj->klass()->external_name(),
169 (intptr_t) requesting_thread);
170 }
171 return BiasedLocking::NOT_BIASED;
172 }
173
174 uint age = mark->age();
175 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
176 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
177
178 // Log at "info" level if not bulk, else "trace" level
179 if (!is_bulk) {
180 ResourceMark rm;
181 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
182 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
183 ", allow rebias %d, requesting thread " INTPTR_FORMAT,
184 p2i((void *)obj),
185 (intptr_t) mark,
186 obj->klass()->external_name(),
187 (intptr_t) obj->klass()->prototype_header(),
188 (allow_rebias ? 1 : 0),
189 (intptr_t) requesting_thread);
190 } else {
191 ResourceMark rm;
197 obj->klass()->external_name(),
198 (intptr_t) obj->klass()->prototype_header(),
199 (allow_rebias ? 1 : 0),
200 (intptr_t) requesting_thread);
201 }
202
203 JavaThread* biased_thread = mark->biased_locker();
204 if (biased_thread == NULL) {
205 // Object is anonymously biased. We can get here if, for
206 // example, we revoke the bias due to an identity hash code
207 // being computed for an object.
208 if (!allow_rebias) {
209 obj->set_mark(unbiased_prototype);
210 }
211 // Log at "info" level if not bulk, else "trace" level
212 if (!is_bulk) {
213 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
214 } else {
215 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
216 }
217 return BiasedLocking::BIAS_REVOKED;
218 }
219
220 // Handle case where the thread toward which the object was biased has exited
221 bool thread_is_alive = false;
222 if (requesting_thread == biased_thread) {
223 thread_is_alive = true;
224 } else {
225 ThreadsListHandle tlh;
226 thread_is_alive = tlh.includes(biased_thread);
227 }
228 if (!thread_is_alive) {
229 if (allow_rebias) {
230 obj->set_mark(biased_prototype);
231 } else {
232 obj->set_mark(unbiased_prototype);
233 }
234 // Log at "info" level if not bulk, else "trace" level
235 if (!is_bulk) {
236 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread ("
237 PTR_FORMAT ")", p2i(biased_thread));
238 } else {
239 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
240 PTR_FORMAT ")", p2i(biased_thread));
241 }
242 return BiasedLocking::BIAS_REVOKED;
243 }
244
245 // Log at "info" level if not bulk, else "trace" level
246 if (!is_bulk) {
247 log_info(biasedlocking)(" Revoked bias of object biased toward live thread ("
248 PTR_FORMAT ")", p2i(biased_thread));
249 } else {
250 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread ("
251 PTR_FORMAT ")", p2i(biased_thread));
252 }
253
254 // Thread owning bias is alive.
255 // Check to see whether it currently owns the lock and, if so,
256 // write down the needed displaced headers to the thread's stack.
257 // Otherwise, restore the object's header either to the unlocked
258 // or unbiased state.
259 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
260 BasicLock* highest_lock = NULL;
261 for (int i = 0; i < cached_monitor_info->length(); i++) {
262 MonitorInfo* mon_info = cached_monitor_info->at(i);
263 if (oopDesc::equals(mon_info->owner(), obj)) {
264 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
265 p2i((void *) mon_info->owner()),
266 p2i((void *) obj));
267 // Assume recursive case and fix up highest lock later
268 markOop mark = markOopDesc::encode((BasicLock*) NULL);
269 highest_lock = mon_info->lock();
270 highest_lock->set_displaced_header(mark);
271 } else {
272 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
273 p2i((void *) mon_info->owner()),
274 p2i((void *) obj));
275 }
276 }
277 if (highest_lock != NULL) {
278 // Fix up highest lock to contain displaced header and point
279 // object at it
280 highest_lock->set_displaced_header(unbiased_prototype);
281 // Reset object header to point to displaced mark.
282 // Must release storing the lock address for platforms without TSO
283 // ordering (e.g. ppc).
284 obj->release_set_mark(markOopDesc::encode(highest_lock));
285 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
286 // Log at "info" level if not bulk, else "trace" level
287 if (!is_bulk) {
288 log_info(biasedlocking)(" Revoked bias of currently-locked object");
289 } else {
290 log_trace(biasedlocking)(" Revoked bias of currently-locked object");
291 }
292 } else {
293 // Log at "info" level if not bulk, else "trace" level
294 if (!is_bulk) {
295 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
296 } else {
297 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
298 }
299 if (allow_rebias) {
300 obj->set_mark(biased_prototype);
301 } else {
302 // Store the unlocked value into the object's header.
303 obj->set_mark(unbiased_prototype);
304 }
305 }
306
307 // If requested, return information on which thread held the bias
308 if (biased_locker != NULL) {
309 *biased_locker = biased_thread;
310 }
311
312 return BiasedLocking::BIAS_REVOKED;
313 }
314
315
316 enum HeuristicsResult {
317 HR_NOT_BIASED = 1,
318 HR_SINGLE_REVOKE = 2,
319 HR_BULK_REBIAS = 3,
320 HR_BULK_REVOKE = 4
321 };
322
323
324 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
325 markOop mark = o->mark();
326 if (!mark->has_bias_pattern()) {
327 return HR_NOT_BIASED;
328 }
329
330 // Heuristics to attempt to throttle the number of revocations.
331 // Stages:
332 // 1. Revoke the biases of all objects in the heap of this type,
333 // but allow rebiasing of those objects if unlocked.
334 // 2. Revoke the biases of all objects in the heap of this type
335 // and don't allow rebiasing of these objects. Disable
336 // allocation of objects of that type with the bias bit set.
337 Klass* k = o->klass();
338 jlong cur_time = os::javaTimeMillis();
339 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
340 int revocation_count = k->biased_lock_revocation_count();
341 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
342 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
343 (last_bulk_revocation_time != 0) &&
344 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
357 revocation_count = 0;
358 }
359
360 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
361 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
362 revocation_count = k->atomic_incr_biased_lock_revocation_count();
363 }
364
365 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
366 return HR_BULK_REVOKE;
367 }
368
369 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
370 return HR_BULK_REBIAS;
371 }
372
373 return HR_SINGLE_REVOKE;
374 }
375
376
377 static BiasedLocking::Condition bulk_revoke_or_rebias_at_safepoint(oop o,
378 bool bulk_rebias,
379 bool attempt_rebias_of_object,
380 JavaThread* requesting_thread) {
381 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
382
383 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
384 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
385 (bulk_rebias ? "rebias" : "revoke"),
386 p2i((void *) o),
387 (intptr_t) o->mark(),
388 o->klass()->external_name());
389
390 jlong cur_time = os::javaTimeMillis();
391 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
392
393
394 Klass* k_o = o->klass();
395 Klass* klass = k_o;
396
397 {
398 JavaThreadIteratorWithHandle jtiwh;
399
400 if (bulk_rebias) {
401 // Use the epoch in the klass of the object to implicitly revoke
402 // all biases of objects of this data type and force them to be
403 // reacquired. However, we also need to walk the stacks of all
404 // threads and update the headers of lightweight locked objects
405 // with biases to have the current epoch.
406
407 // If the prototype header doesn't have the bias pattern, don't
408 // try to update the epoch -- assume another VM operation came in
409 // and reset the header to the unbiased state, which will
410 // implicitly cause all existing biases to be revoked
411 if (klass->prototype_header()->has_bias_pattern()) {
412 int prev_epoch = klass->prototype_header()->bias_epoch();
413 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
415
416 // Now walk all threads' stacks and adjust epochs of any biased
417 // and locked objects of this data type we encounter
418 for (; JavaThread *thr = jtiwh.next(); ) {
419 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
420 for (int i = 0; i < cached_monitor_info->length(); i++) {
421 MonitorInfo* mon_info = cached_monitor_info->at(i);
422 oop owner = mon_info->owner();
423 markOop mark = owner->mark();
424 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
425 // We might have encountered this object already in the case of recursive locking
426 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
427 owner->set_mark(mark->set_bias_epoch(cur_epoch));
428 }
429 }
430 }
431 }
432
433 // At this point we're done. All we have to do is potentially
434 // adjust the header of the given object to revoke its bias.
435 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL);
436 } else {
437 if (log_is_enabled(Info, biasedlocking)) {
438 ResourceMark rm;
439 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
440 }
441
442 // Disable biased locking for this data type. Not only will this
443 // cause future instances to not be biased, but existing biased
444 // instances will notice that this implicitly caused their biases
445 // to be revoked.
446 klass->set_prototype_header(markOopDesc::prototype());
447
448 // Now walk all threads' stacks and forcibly revoke the biases of
449 // any locked and biased objects of this data type we encounter.
450 for (; JavaThread *thr = jtiwh.next(); ) {
451 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
452 for (int i = 0; i < cached_monitor_info->length(); i++) {
453 MonitorInfo* mon_info = cached_monitor_info->at(i);
454 oop owner = mon_info->owner();
455 markOop mark = owner->mark();
456 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
457 revoke_bias(owner, false, true, requesting_thread, NULL);
458 }
459 }
460 }
461
462 // Must force the bias of the passed object to be forcibly revoked
463 // as well to ensure guarantees to callers
464 revoke_bias(o, false, true, requesting_thread, NULL);
465 }
466 } // ThreadsListHandle is destroyed here.
467
468 log_info(biasedlocking)("* Ending bulk revocation");
469
470 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
471
472 if (attempt_rebias_of_object &&
473 o->mark()->has_bias_pattern() &&
474 klass->prototype_header()->has_bias_pattern()) {
475 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
476 klass->prototype_header()->bias_epoch());
477 o->set_mark(new_mark);
478 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
479 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
480 }
481
482 assert(!o->mark()->has_bias_pattern() ||
483 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
484 "bug in bulk bias revocation");
485
486 return status_code;
487 }
488
489
490 static void clean_up_cached_monitor_info() {
491 // Walk the thread list clearing out the cached monitors
492 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
493 thr->set_cached_monitor_info(NULL);
494 }
495 }
496
497
498 class VM_RevokeBias : public VM_Operation {
499 protected:
500 Handle* _obj;
501 GrowableArray<Handle>* _objs;
502 JavaThread* _requesting_thread;
503 BiasedLocking::Condition _status_code;
504 traceid _biased_locker_id;
505 uint64_t _safepoint_id;
506
507 public:
508 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
509 : _obj(obj)
510 , _objs(NULL)
511 , _requesting_thread(requesting_thread)
512 , _status_code(BiasedLocking::NOT_BIASED)
513 , _biased_locker_id(0)
514 , _safepoint_id(0) {}
515
516 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
517 : _obj(NULL)
518 , _objs(objs)
519 , _requesting_thread(requesting_thread)
520 , _status_code(BiasedLocking::NOT_BIASED)
521 , _biased_locker_id(0)
522 , _safepoint_id(0) {}
523
524 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
525
526 virtual bool doit_prologue() {
527 // Verify that there is actual work to do since the callers just
528 // give us locked object(s). If we don't find any biased objects
529 // there is nothing to do and we avoid a safepoint.
530 if (_obj != NULL) {
531 markOop mark = (*_obj)()->mark();
532 if (mark->has_bias_pattern()) {
533 return true;
534 }
535 } else {
536 for ( int i = 0 ; i < _objs->length(); i++ ) {
537 markOop mark = (_objs->at(i))()->mark();
538 if (mark->has_bias_pattern()) {
539 return true;
540 }
541 }
542 }
543 return false;
544 }
545
546 virtual void doit() {
547 if (_obj != NULL) {
548 log_info(biasedlocking)("Revoking bias with potentially per-thread safepoint:");
549 JavaThread* biased_locker = NULL;
550 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker);
551 if (biased_locker != NULL) {
552 _biased_locker_id = JFR_THREAD_ID(biased_locker);
553 }
554 _safepoint_id = SafepointSynchronize::safepoint_id();
555 clean_up_cached_monitor_info();
556 return;
557 } else {
558 log_info(biasedlocking)("Revoking bias with global safepoint:");
559 BiasedLocking::revoke_at_safepoint(_objs);
560 }
561 }
562
563 BiasedLocking::Condition status_code() const {
564 return _status_code;
565 }
566
567 traceid biased_locker() const {
568 return _biased_locker_id;
569 }
570
571 uint64_t safepoint_id() const {
572 return _safepoint_id;
573 }
574 };
575
576
577 class VM_BulkRevokeBias : public VM_RevokeBias {
578 private:
579 bool _bulk_rebias;
580 bool _attempt_rebias_of_object;
581
582 public:
583 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
584 bool bulk_rebias,
585 bool attempt_rebias_of_object)
586 : VM_RevokeBias(obj, requesting_thread)
587 , _bulk_rebias(bulk_rebias)
588 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
589
590 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
591 virtual bool doit_prologue() { return true; }
592
593 virtual void doit() {
594 _status_code = bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
595 _safepoint_id = SafepointSynchronize::safepoint_id();
596 clean_up_cached_monitor_info();
597 }
598
599 bool is_bulk_rebias() const {
600 return _bulk_rebias;
601 }
602 };
603
604 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) {
605 assert(event != NULL, "invariant");
606 assert(k != NULL, "invariant");
607 assert(event->should_commit(), "invariant");
608 event->set_lockClass(k);
609 event->commit();
610 }
611
612 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, VM_RevokeBias* op) {
613 assert(event != NULL, "invariant");
614 assert(k != NULL, "invariant");
615 assert(op != NULL, "invariant");
616 assert(event->should_commit(), "invariant");
617 event->set_lockClass(k);
618 event->set_safepointId(op->safepoint_id());
619 event->set_previousOwner(op->biased_locker());
620 event->commit();
621 }
622
623 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) {
624 assert(event != NULL, "invariant");
625 assert(k != NULL, "invariant");
626 assert(op != NULL, "invariant");
627 assert(event->should_commit(), "invariant");
628 event->set_revokedClass(k);
629 event->set_disableBiasing(!op->is_bulk_rebias());
630 event->set_safepointId(op->safepoint_id());
631 event->commit();
632 }
633
634 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
635 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
636
637 // We can revoke the biases of anonymously-biased objects
638 // efficiently enough that we should not cause these revocations to
639 // update the heuristics because doing so may cause unwanted bulk
640 // revocations (which are expensive) to occur.
641 markOop mark = obj->mark();
642 if (mark->is_biased_anonymously() && !attempt_rebias) {
643 // We are probably trying to revoke the bias of this object due to
644 // an identity hash code computation. Try to revoke the bias
645 // without a safepoint. This is possible if we can successfully
646 // compare-and-exchange an unbiased header into the mark word of
647 // the object, meaning that no other thread has raced to acquire
648 // the bias of the object.
649 markOop biased_value = mark;
650 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
651 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
652 if (res_mark == biased_value) {
653 return BIAS_REVOKED;
654 }
655 } else if (mark->has_bias_pattern()) {
656 Klass* k = obj->klass();
657 markOop prototype_header = k->prototype_header();
658 if (!prototype_header->has_bias_pattern()) {
659 // This object has a stale bias from before the bulk revocation
660 // for this data type occurred. It's pointless to update the
661 // heuristics at this point so simply update the header with a
662 // CAS. If we fail this race, the object's bias has been revoked
663 // by another thread so we simply return and let the caller deal
664 // with it.
665 markOop biased_value = mark;
666 markOop res_mark = obj->cas_set_mark(prototype_header, mark);
667 assert(!obj->mark()->has_bias_pattern(), "even if we raced, should still be revoked");
668 return BIAS_REVOKED;
669 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
670 // The epoch of this biasing has expired indicating that the
671 // object is effectively unbiased. Depending on whether we need
672 // to rebias or revoke the bias of this object we can do it
673 // efficiently enough with a CAS that we shouldn't update the
674 // heuristics. This is normally done in the assembly code but we
675 // can reach this point due to various points in the runtime
676 // needing to revoke biases.
677 if (attempt_rebias) {
678 assert(THREAD->is_Java_thread(), "");
679 markOop biased_value = mark;
680 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
681 markOop res_mark = obj->cas_set_mark(rebiased_prototype, mark);
682 if (res_mark == biased_value) {
683 return BIAS_REVOKED_AND_REBIASED;
684 }
685 } else {
686 markOop biased_value = mark;
687 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
688 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
689 if (res_mark == biased_value) {
690 return BIAS_REVOKED;
691 }
692 }
693 }
694 }
695
696 HeuristicsResult heuristics = update_heuristics(obj(), attempt_rebias);
697 if (heuristics == HR_NOT_BIASED) {
698 return NOT_BIASED;
699 } else if (heuristics == HR_SINGLE_REVOKE) {
700 Klass *k = obj->klass();
701 markOop prototype_header = k->prototype_header();
702 if (mark->biased_locker() == THREAD &&
703 prototype_header->bias_epoch() == mark->bias_epoch()) {
704 // A thread is trying to revoke the bias of an object biased
705 // toward it, again likely due to an identity hash code
706 // computation. We can again avoid a safepoint in this case
707 // since we are only going to walk our own stack. There are no
708 // races with revocations occurring in other threads because we
709 // reach no safepoints in the revocation path.
710 // Also check the epoch because even if threads match, another thread
711 // can come in with a CAS to steal the bias of an object that has a
712 // stale epoch.
713 ResourceMark rm;
714 log_info(biasedlocking)("Revoking bias by walking my own stack:");
715 EventBiasedLockSelfRevocation event;
716 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL);
717 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
718 assert(cond == BIAS_REVOKED, "why not?");
719 if (event.should_commit()) {
720 post_self_revocation_event(&event, k);
721 }
722 return cond;
723 } else {
724 EventBiasedLockRevocation event;
725 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
726 VMThread::execute(&revoke);
727 if (event.should_commit() && revoke.status_code() != NOT_BIASED) {
728 post_revocation_event(&event, k, &revoke);
729 }
730 return revoke.status_code();
731 }
732 }
733
734 assert((heuristics == HR_BULK_REVOKE) ||
735 (heuristics == HR_BULK_REBIAS), "?");
736 EventBiasedLockClassRevocation event;
737 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
738 (heuristics == HR_BULK_REBIAS),
739 attempt_rebias);
740 VMThread::execute(&bulk_revoke);
741 if (event.should_commit()) {
742 post_class_revocation_event(&event, obj->klass(), &bulk_revoke);
743 }
744 return bulk_revoke.status_code();
745 }
746
747
748 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
749 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
750 if (objs->length() == 0) {
751 return;
752 }
753 VM_RevokeBias revoke(objs, JavaThread::current());
754 VMThread::execute(&revoke);
755 }
756
757
758 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
759 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
760 oop obj = h_obj();
761 HeuristicsResult heuristics = update_heuristics(obj, false);
762 if (heuristics == HR_SINGLE_REVOKE) {
763 revoke_bias(obj, false, false, NULL, NULL);
764 } else if ((heuristics == HR_BULK_REBIAS) ||
765 (heuristics == HR_BULK_REVOKE)) {
766 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
767 }
768 clean_up_cached_monitor_info();
769 }
770
771
772 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
773 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
774 int len = objs->length();
775 for (int i = 0; i < len; i++) {
776 oop obj = (objs->at(i))();
777 HeuristicsResult heuristics = update_heuristics(obj, false);
778 if (heuristics == HR_SINGLE_REVOKE) {
779 revoke_bias(obj, false, false, NULL, NULL);
780 } else if ((heuristics == HR_BULK_REBIAS) ||
781 (heuristics == HR_BULK_REVOKE)) {
782 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
783 }
784 }
785 clean_up_cached_monitor_info();
786 }
787
788
789 void BiasedLocking::preserve_marks() {
790 if (!UseBiasedLocking)
791 return;
792
793 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
794
795 assert(_preserved_oop_stack == NULL, "double initialization");
796 assert(_preserved_mark_stack == NULL, "double initialization");
797
798 // In order to reduce the number of mark words preserved during GC
799 // due to the presence of biased locking, we reinitialize most mark
845
846 int len = _preserved_oop_stack->length();
847 for (int i = 0; i < len; i++) {
848 Handle owner = _preserved_oop_stack->at(i);
849 markOop mark = _preserved_mark_stack->at(i);
850 owner->set_mark(mark);
851 }
852
853 delete _preserved_oop_stack;
854 _preserved_oop_stack = NULL;
855 delete _preserved_mark_stack;
856 _preserved_mark_stack = NULL;
857 }
858
859
860 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
861 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
862 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
863 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
864 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
865 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
866 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
867
868
869 // BiasedLockingCounters
870
871 int BiasedLockingCounters::slow_path_entry_count() const {
872 if (_slow_path_entry_count != 0) {
873 return _slow_path_entry_count;
874 }
875 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
876 _rebiased_lock_entry_count + _revoked_lock_entry_count +
877 _fast_path_entry_count;
878
879 return _total_entry_count - sum;
880 }
881
882 void BiasedLockingCounters::print_on(outputStream* st) const {
883 tty->print_cr("# total entries: %d", _total_entry_count);
884 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
885 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
886 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
887 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
888 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
889 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
890 }
891
892 void BiasedLockingCounters::print() const { print_on(tty); }
|
102 // bias revocation.
103 if (UseBiasedLocking) {
104 if (BiasedLockingStartupDelay > 0) {
105 EnableBiasedLockingTask* task = new EnableBiasedLockingTask(BiasedLockingStartupDelay);
106 task->enroll();
107 } else {
108 enable_biased_locking();
109 }
110 }
111 }
112
113
114 bool BiasedLocking::enabled() {
115 assert(UseBiasedLocking, "precondition");
116 // We check "BiasedLockingStartupDelay == 0" here to cover the
117 // possibility of calls to BiasedLocking::enabled() before
118 // BiasedLocking::init().
119 return _biased_locking_enabled || BiasedLockingStartupDelay == 0;
120 }
121
122
123 // Returns MonitorInfos for all objects locked on this thread in youngest to oldest order
124 static GrowableArray<MonitorInfo*>* get_or_compute_monitor_info(JavaThread* thread) {
125 GrowableArray<MonitorInfo*>* info = thread->cached_monitor_info();
126 if (info != NULL) {
127 return info;
128 }
129
130 info = new GrowableArray<MonitorInfo*>();
131
132 // It's possible for the thread to not have any Java frames on it,
133 // i.e., if it's the main thread and it's already returned from main()
134 if (thread->has_last_Java_frame()) {
135 RegisterMap rm(thread);
136 for (javaVFrame* vf = thread->last_java_vframe(&rm); vf != NULL; vf = vf->java_sender()) {
137 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
138 if (monitors != NULL) {
139 int len = monitors->length();
140 // Walk monitors youngest to oldest
141 for (int i = len - 1; i >= 0; i--) {
142 MonitorInfo* mon_info = monitors->at(i);
143 if (mon_info->eliminated()) continue;
144 oop owner = mon_info->owner();
145 if (owner != NULL) {
146 info->append(mon_info);
147 }
148 }
149 }
150 }
151 }
152
153 thread->set_cached_monitor_info(info);
154 return info;
155 }
156
157
158 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
159 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
160 BiasedLocking::Condition BiasedLocking::single_revoke_at_safepoint(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
161 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
162 assert(Thread::current()->is_VM_thread(), "must be VMThread");
163
164 markOop mark = obj->mark();
165 if (!mark->has_bias_pattern()) {
166 if (log_is_enabled(Info, biasedlocking)) {
167 ResourceMark rm;
168 log_info(biasedlocking)(" (Skipping revocation of object " INTPTR_FORMAT
169 ", mark " INTPTR_FORMAT ", type %s"
170 ", requesting thread " INTPTR_FORMAT
171 " because it's no longer biased)",
172 p2i((void *)obj), (intptr_t) mark,
173 obj->klass()->external_name(),
174 (intptr_t) requesting_thread);
175 }
176 return NOT_BIASED;
177 }
178
179 uint age = mark->age();
180 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
181 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
182
183 // Log at "info" level if not bulk, else "trace" level
184 if (!is_bulk) {
185 ResourceMark rm;
186 log_info(biasedlocking)("Revoking bias of object " INTPTR_FORMAT ", mark "
187 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
188 ", allow rebias %d, requesting thread " INTPTR_FORMAT,
189 p2i((void *)obj),
190 (intptr_t) mark,
191 obj->klass()->external_name(),
192 (intptr_t) obj->klass()->prototype_header(),
193 (allow_rebias ? 1 : 0),
194 (intptr_t) requesting_thread);
195 } else {
196 ResourceMark rm;
202 obj->klass()->external_name(),
203 (intptr_t) obj->klass()->prototype_header(),
204 (allow_rebias ? 1 : 0),
205 (intptr_t) requesting_thread);
206 }
207
208 JavaThread* biased_thread = mark->biased_locker();
209 if (biased_thread == NULL) {
210 // Object is anonymously biased. We can get here if, for
211 // example, we revoke the bias due to an identity hash code
212 // being computed for an object.
213 if (!allow_rebias) {
214 obj->set_mark(unbiased_prototype);
215 }
216 // Log at "info" level if not bulk, else "trace" level
217 if (!is_bulk) {
218 log_info(biasedlocking)(" Revoked bias of anonymously-biased object");
219 } else {
220 log_trace(biasedlocking)(" Revoked bias of anonymously-biased object");
221 }
222 return BIAS_REVOKED;
223 }
224
225 // Handle case where the thread toward which the object was biased has exited
226 bool thread_is_alive = false;
227 if (requesting_thread == biased_thread) {
228 thread_is_alive = true;
229 } else {
230 ThreadsListHandle tlh;
231 thread_is_alive = tlh.includes(biased_thread);
232 }
233 if (!thread_is_alive) {
234 if (allow_rebias) {
235 obj->set_mark(biased_prototype);
236 } else {
237 obj->set_mark(unbiased_prototype);
238 }
239 // Log at "info" level if not bulk, else "trace" level
240 if (!is_bulk) {
241 log_info(biasedlocking)(" Revoked bias of object biased toward dead thread ("
242 PTR_FORMAT ")", p2i(biased_thread));
243 } else {
244 log_trace(biasedlocking)(" Revoked bias of object biased toward dead thread ("
245 PTR_FORMAT ")", p2i(biased_thread));
246 }
247 return BIAS_REVOKED;
248 }
249
250 // Log at "info" level if not bulk, else "trace" level
251 if (!is_bulk) {
252 log_info(biasedlocking)(" Revoked bias of object biased toward live thread ("
253 PTR_FORMAT ")", p2i(biased_thread));
254 } else {
255 log_trace(biasedlocking)(" Revoked bias of object biased toward live thread ("
256 PTR_FORMAT ")", p2i(biased_thread));
257 }
258
259 // Thread owning bias is alive.
260 // Check to see whether it currently owns the lock and, if so,
261 // write down the needed displaced headers to the thread's stack.
262 // Otherwise, restore the object's header either to the unlocked
263 // or unbiased state.
264 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_thread);
265 BasicLock* highest_lock = NULL;
266 for (int i = 0; i < cached_monitor_info->length(); i++) {
267 MonitorInfo* mon_info = cached_monitor_info->at(i);
268 if (oopDesc::equals(mon_info->owner(), obj)) {
269 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
270 p2i((void *) mon_info->owner()),
271 p2i((void *) obj));
272 // Assume recursive case and fix up highest lock below
273 markOop mark = markOopDesc::encode((BasicLock*) NULL);
274 highest_lock = mon_info->lock();
275 highest_lock->set_displaced_header(mark);
276 } else {
277 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
278 p2i((void *) mon_info->owner()),
279 p2i((void *) obj));
280 }
281 }
282 if (highest_lock != NULL) {
283 // Fix up highest lock to contain displaced header and point
284 // object at it
285 highest_lock->set_displaced_header(unbiased_prototype);
286 // Reset object header to point to displaced mark.
287 // Must release store the lock address for platforms without TSO
288 // ordering (e.g. ppc).
289 obj->release_set_mark(markOopDesc::encode(highest_lock));
290 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
291 // Log at "info" level if not bulk, else "trace" level
292 if (!is_bulk) {
293 log_info(biasedlocking)(" Revoked bias of currently-locked object");
294 } else {
295 log_trace(biasedlocking)(" Revoked bias of currently-locked object");
296 }
297 } else {
298 // Log at "info" level if not bulk, else "trace" level
299 if (!is_bulk) {
300 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
301 } else {
302 log_trace(biasedlocking)(" Revoked bias of currently-unlocked object");
303 }
304 if (allow_rebias) {
305 obj->set_mark(biased_prototype);
306 } else {
307 // Store the unlocked value into the object's header.
308 obj->set_mark(unbiased_prototype);
309 }
310 }
311
312 // If requested, return information on which thread held the bias
313 if (biased_locker != NULL) {
314 *biased_locker = biased_thread;
315 }
316
317 return BIAS_REVOKED;
318 }
319
320
321 enum HeuristicsResult {
322 HR_NOT_BIASED = 1,
323 HR_SINGLE_REVOKE = 2,
324 HR_BULK_REBIAS = 3,
325 HR_BULK_REVOKE = 4
326 };
327
328
329 static HeuristicsResult update_heuristics(oop o) {
330 markOop mark = o->mark();
331 if (!mark->has_bias_pattern()) {
332 return HR_NOT_BIASED;
333 }
334
335 // Heuristics to attempt to throttle the number of revocations.
336 // Stages:
337 // 1. Revoke the biases of all objects in the heap of this type,
338 // but allow rebiasing of those objects if unlocked.
339 // 2. Revoke the biases of all objects in the heap of this type
340 // and don't allow rebiasing of these objects. Disable
341 // allocation of objects of that type with the bias bit set.
342 Klass* k = o->klass();
343 jlong cur_time = os::javaTimeMillis();
344 jlong last_bulk_revocation_time = k->last_biased_lock_bulk_revocation_time();
345 int revocation_count = k->biased_lock_revocation_count();
346 if ((revocation_count >= BiasedLockingBulkRebiasThreshold) &&
347 (revocation_count < BiasedLockingBulkRevokeThreshold) &&
348 (last_bulk_revocation_time != 0) &&
349 (cur_time - last_bulk_revocation_time >= BiasedLockingDecayTime)) {
362 revocation_count = 0;
363 }
364
365 // Make revocation count saturate just beyond BiasedLockingBulkRevokeThreshold
366 if (revocation_count <= BiasedLockingBulkRevokeThreshold) {
367 revocation_count = k->atomic_incr_biased_lock_revocation_count();
368 }
369
370 if (revocation_count == BiasedLockingBulkRevokeThreshold) {
371 return HR_BULK_REVOKE;
372 }
373
374 if (revocation_count == BiasedLockingBulkRebiasThreshold) {
375 return HR_BULK_REBIAS;
376 }
377
378 return HR_SINGLE_REVOKE;
379 }
380
381
382 BiasedLocking::Condition BiasedLocking::bulk_revoke_or_rebias_at_safepoint(oop o,
383 bool bulk_rebias,
384 bool attempt_rebias_of_object,
385 JavaThread* requesting_thread) {
386 assert(SafepointSynchronize::is_at_safepoint(), "must be done at safepoint");
387 assert(Thread::current()->is_VM_thread(), "must be VMThread");
388
389 log_info(biasedlocking)("* Beginning bulk revocation (kind == %s) because of object "
390 INTPTR_FORMAT " , mark " INTPTR_FORMAT " , type %s",
391 (bulk_rebias ? "rebias" : "revoke"),
392 p2i((void *) o),
393 (intptr_t) o->mark(),
394 o->klass()->external_name());
395
396 jlong cur_time = os::javaTimeMillis();
397 o->klass()->set_last_biased_lock_bulk_revocation_time(cur_time);
398
399 Klass* k_o = o->klass();
400 Klass* klass = k_o;
401
402 {
403 JavaThreadIteratorWithHandle jtiwh;
404
405 if (bulk_rebias) {
406 // Use the epoch in the klass of the object to implicitly revoke
407 // all biases of objects of this data type and force them to be
408 // reacquired. However, we also need to walk the stacks of all
409 // threads and update the headers of lightweight locked objects
410 // with biases to have the current epoch.
411
412 // If the prototype header doesn't have the bias pattern, don't
413 // try to update the epoch -- assume another VM operation came in
414 // and reset the header to the unbiased state, which will
415 // implicitly cause all existing biases to be revoked
416 if (klass->prototype_header()->has_bias_pattern()) {
417 int prev_epoch = klass->prototype_header()->bias_epoch();
418 klass->set_prototype_header(klass->prototype_header()->incr_bias_epoch());
420
421 // Now walk all threads' stacks and adjust epochs of any biased
422 // and locked objects of this data type we encounter
423 for (; JavaThread *thr = jtiwh.next(); ) {
424 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
425 for (int i = 0; i < cached_monitor_info->length(); i++) {
426 MonitorInfo* mon_info = cached_monitor_info->at(i);
427 oop owner = mon_info->owner();
428 markOop mark = owner->mark();
429 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
430 // We might have encountered this object already in the case of recursive locking
431 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
432 owner->set_mark(mark->set_bias_epoch(cur_epoch));
433 }
434 }
435 }
436 }
437
438 // At this point we're done. All we have to do is potentially
439 // adjust the header of the given object to revoke its bias.
440 single_revoke_at_safepoint(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL);
441 } else {
442 if (log_is_enabled(Info, biasedlocking)) {
443 ResourceMark rm;
444 log_info(biasedlocking)("* Disabling biased locking for type %s", klass->external_name());
445 }
446
447 // Disable biased locking for this data type. Not only will this
448 // cause future instances to not be biased, but existing biased
449 // instances will notice that this implicitly caused their biases
450 // to be revoked.
451 klass->set_prototype_header(markOopDesc::prototype());
452
453 // Now walk all threads' stacks and forcibly revoke the biases of
454 // any locked and biased objects of this data type we encounter.
455 for (; JavaThread *thr = jtiwh.next(); ) {
456 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
457 for (int i = 0; i < cached_monitor_info->length(); i++) {
458 MonitorInfo* mon_info = cached_monitor_info->at(i);
459 oop owner = mon_info->owner();
460 markOop mark = owner->mark();
461 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
462 single_revoke_at_safepoint(owner, false, true, requesting_thread, NULL);
463 }
464 }
465 }
466
467 // Must force the bias of the passed object to be forcibly revoked
468 // as well to ensure guarantees to callers
469 single_revoke_at_safepoint(o, false, true, requesting_thread, NULL);
470 }
471 } // ThreadsListHandle is destroyed here.
472
473 log_info(biasedlocking)("* Ending bulk revocation");
474
475 BiasedLocking::Condition status_code = BIAS_REVOKED;
476
477 if (attempt_rebias_of_object &&
478 o->mark()->has_bias_pattern() &&
479 klass->prototype_header()->has_bias_pattern()) {
480 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
481 klass->prototype_header()->bias_epoch());
482 o->set_mark(new_mark);
483 status_code = BIAS_REVOKED_AND_REBIASED;
484 log_info(biasedlocking)(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
485 }
486
487 assert(!o->mark()->has_bias_pattern() ||
488 (attempt_rebias_of_object && (o->mark()->biased_locker() == requesting_thread)),
489 "bug in bulk bias revocation");
490
491 return status_code;
492 }
493
494
495 static void clean_up_cached_monitor_info(JavaThread* thread = NULL) {
496 if (thread != NULL) {
497 thread->set_cached_monitor_info(NULL);
498 } else {
499 // Walk the thread list clearing out the cached monitors
500 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *thr = jtiwh.next(); ) {
501 thr->set_cached_monitor_info(NULL);
502 }
503 }
504 }
505
506
507 class VM_BulkRevokeBias : public VM_Operation {
508 private:
509 Handle* _obj;
510 JavaThread* _requesting_thread;
511 bool _bulk_rebias;
512 bool _attempt_rebias_of_object;
513 BiasedLocking::Condition _status_code;
514 uint64_t _safepoint_id;
515
516 public:
517 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
518 bool bulk_rebias,
519 bool attempt_rebias_of_object)
520 : _obj(obj)
521 , _requesting_thread(requesting_thread)
522 , _bulk_rebias(bulk_rebias)
523 , _attempt_rebias_of_object(attempt_rebias_of_object)
524 , _status_code(BiasedLocking::NOT_BIASED)
525 , _safepoint_id(0) {}
526
527 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
528
529 virtual void doit() {
530 _status_code = BiasedLocking::bulk_revoke_or_rebias_at_safepoint((*_obj)(), _bulk_rebias, _attempt_rebias_of_object, _requesting_thread);
531 _safepoint_id = SafepointSynchronize::safepoint_id();
532 clean_up_cached_monitor_info();
533 }
534
535 bool is_bulk_rebias() const {
536 return _bulk_rebias;
537 }
538
539 BiasedLocking::Condition status_code() const {
540 return _status_code;
541 }
542
543 uint64_t safepoint_id() const {
544 return _safepoint_id;
545 }
546 };
547
548
549 class RevokeOneBias : public ThreadClosure {
550 protected:
551 Handle _obj;
552 JavaThread* _requesting_thread;
553 JavaThread* _biased_locker;
554 BiasedLocking::Condition _status_code;
555 traceid _biased_locker_id;
556
557 public:
558 RevokeOneBias(Handle obj, JavaThread* requesting_thread, JavaThread* biased_locker)
559 : _obj(obj)
560 , _requesting_thread(requesting_thread)
561 , _biased_locker(biased_locker)
562 , _status_code(BiasedLocking::NOT_BIASED)
563 , _biased_locker_id(0) {}
564
565 void do_thread(Thread* target) {
566 assert(target == _biased_locker, "Wrong thread");
567
568 oop o = _obj();
569 markOop mark = o->mark();
570
571 if (!mark->has_bias_pattern()) {
572 return;
573 }
574
575 markOop prototype = o->klass()->prototype_header();
576 if (!prototype->has_bias_pattern()) {
577 // This object has a stale bias from before the handshake
578 // was requested. If we fail this race, the object's bias
579 // has been revoked by another thread so we simply return.
580 markOop biased_value = mark;
581 mark = o->cas_set_mark(markOopDesc::prototype()->set_age(mark->age()), mark);
582 assert(!o->mark()->has_bias_pattern(), "even if we raced, should still be revoked");
583 if (biased_value == mark) {
584 _status_code = BiasedLocking::BIAS_REVOKED;
585 }
586 return;
587 }
588
589 if (_biased_locker == mark->biased_locker()) {
590 if (mark->bias_epoch() == prototype->bias_epoch()) {
591 // Epoch is still valid. This means biaser could be currently
592 // synchronized on this object. We must walk its stack looking
593 // for monitor records associated with this object and change
594 // them to be stack locks if any are found.
595 ResourceMark rm;
596 BiasedLocking::walk_stack_and_revoke(o, _biased_locker);
597 _biased_locker->set_cached_monitor_info(NULL);
598 assert(!o->mark()->has_bias_pattern(), "invariant");
599 _biased_locker_id = JFR_THREAD_ID(_biased_locker);
600 _status_code = BiasedLocking::BIAS_REVOKED;
601 return;
602 } else {
603 markOop biased_value = mark;
604 mark = o->cas_set_mark(markOopDesc::prototype()->set_age(mark->age()), mark);
605 if (mark == biased_value || !mark->has_bias_pattern()) {
606 assert(!o->mark()->has_bias_pattern(), "should be revoked");
607 _status_code = (biased_value == mark) ? BiasedLocking::BIAS_REVOKED : BiasedLocking::NOT_BIASED;
608 return;
609 }
610 }
611 }
612
613 _status_code = BiasedLocking::NOT_REVOKED;
614 }
615
616 BiasedLocking::Condition status_code() const {
617 return _status_code;
618 }
619
620 traceid biased_locker() const {
621 return _biased_locker_id;
622 }
623 };
624
625
626 static void post_self_revocation_event(EventBiasedLockSelfRevocation* event, Klass* k) {
627 assert(event != NULL, "invariant");
628 assert(k != NULL, "invariant");
629 assert(event->should_commit(), "invariant");
630 event->set_lockClass(k);
631 event->commit();
632 }
633
634 static void post_revocation_event(EventBiasedLockRevocation* event, Klass* k, RevokeOneBias* op) {
635 assert(event != NULL, "invariant");
636 assert(k != NULL, "invariant");
637 assert(op != NULL, "invariant");
638 assert(event->should_commit(), "invariant");
639 event->set_lockClass(k);
640 event->set_safepointId(0);
641 event->set_previousOwner(op->biased_locker());
642 event->commit();
643 }
644
645 static void post_class_revocation_event(EventBiasedLockClassRevocation* event, Klass* k, VM_BulkRevokeBias* op) {
646 assert(event != NULL, "invariant");
647 assert(k != NULL, "invariant");
648 assert(op != NULL, "invariant");
649 assert(event->should_commit(), "invariant");
650 event->set_revokedClass(k);
651 event->set_disableBiasing(!op->is_bulk_rebias());
652 event->set_safepointId(op->safepoint_id());
653 event->commit();
654 }
655
656
657 BiasedLocking::Condition BiasedLocking::single_revoke_with_handshake(Handle obj, JavaThread *requester, JavaThread *biaser) {
658
659 EventBiasedLockRevocation event;
660 if (PrintBiasedLockingStatistics) {
661 Atomic::inc(handshakes_count_addr());
662 }
663 log_info(biasedlocking, handshake)("JavaThread " INTPTR_FORMAT " handshaking JavaThread "
664 INTPTR_FORMAT " to revoke object " INTPTR_FORMAT, p2i(requester),
665 p2i(biaser), p2i(obj()));
666
667 RevokeOneBias revoke(obj, requester, biaser);
668 bool executed = Handshake::execute(&revoke, biaser);
669 if (revoke.status_code() == NOT_REVOKED) {
670 return NOT_REVOKED;
671 }
672 if (executed) {
673 log_info(biasedlocking, handshake)("Handshake revocation for object " INTPTR_FORMAT " succeeded. Bias was %srevoked",
674 p2i(obj()), (revoke.status_code() == BIAS_REVOKED ? "" : "already "));
675 if (event.should_commit() && revoke.status_code() == BIAS_REVOKED) {
676 post_revocation_event(&event, obj->klass(), &revoke);
677 }
678 assert(!obj->mark()->has_bias_pattern(), "invariant");
679 return revoke.status_code();
680 } else {
681 // Thread was not alive.
682 // Grab Threads_lock before manually trying to revoke bias. This avoids race with a newly
683 // created JavaThread (that happens to get the same memory address as biaser) synchronizing
684 // on this object.
685 {
686 MutexLocker ml(Threads_lock);
687 markOop mark = obj->mark();
688 // Check if somebody else was able to revoke it before biased thread exited.
689 if (!mark->has_bias_pattern()) {
690 return NOT_BIASED;
691 }
692 ThreadsListHandle tlh;
693 markOop prototype = obj->klass()->prototype_header();
694 if (!prototype->has_bias_pattern() || (!tlh.includes(biaser) && biaser == mark->biased_locker() &&
695 prototype->bias_epoch() == mark->bias_epoch())) {
696 obj->cas_set_mark(markOopDesc::prototype()->set_age(mark->age()), mark);
697 if (event.should_commit()) {
698 post_revocation_event(&event, obj->klass(), &revoke);
699 }
700 assert(!obj->mark()->has_bias_pattern(), "bias should be revoked by now");
701 return BIAS_REVOKED;
702 }
703 }
704 }
705
706 return NOT_REVOKED;
707 }
708
709
710 // Caller should have instantiated a ResourceMark object before calling this method
711 void BiasedLocking::walk_stack_and_revoke(oop obj, JavaThread* biased_locker) {
712 assert(!SafepointSynchronize::is_at_safepoint() || !ThreadLocalHandshakes,
713 "if ThreadLocalHandshakes is enabled this should always be executed outside safepoints");
714 assert(Thread::current() == biased_locker || Thread::current()->is_VM_thread(), "wrong thread");
715
716 markOop mark = obj->mark();
717 assert(mark->biased_locker() == biased_locker &&
718 obj->klass()->prototype_header()->bias_epoch() == mark->bias_epoch(), "invariant");
719
720 log_trace(biasedlocking)("%s(" INTPTR_FORMAT ") revoking object " INTPTR_FORMAT ", mark "
721 INTPTR_FORMAT ", type %s, prototype header " INTPTR_FORMAT
722 ", biaser " INTPTR_FORMAT " %s",
723 Thread::current()->is_VM_thread() ? "VMThread" : "JavaThread",
724 p2i(Thread::current()),
725 p2i(obj),
726 p2i(mark),
727 obj->klass()->external_name(),
728 p2i(obj->klass()->prototype_header()),
729 p2i(biased_locker),
730 Thread::current()->is_VM_thread() ? "" : "(walking own stack)");
731
732 markOop unbiased_prototype = markOopDesc::prototype()->set_age(obj->mark()->age());
733
734 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(biased_locker);
735 BasicLock* highest_lock = NULL;
736 for (int i = 0; i < cached_monitor_info->length(); i++) {
737 MonitorInfo* mon_info = cached_monitor_info->at(i);
738 if (oopDesc::equals(mon_info->owner(), obj)) {
739 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") == obj (" PTR_FORMAT ")",
740 p2i(mon_info->owner()),
741 p2i(obj));
742 // Assume recursive case and fix up highest lock below
743 markOop mark = markOopDesc::encode((BasicLock*) NULL);
744 highest_lock = mon_info->lock();
745 highest_lock->set_displaced_header(mark);
746 } else {
747 log_trace(biasedlocking)(" mon_info->owner (" PTR_FORMAT ") != obj (" PTR_FORMAT ")",
748 p2i(mon_info->owner()),
749 p2i(obj));
750 }
751 }
752 if (highest_lock != NULL) {
753 // Fix up highest lock to contain displaced header and point
754 // object at it
755 highest_lock->set_displaced_header(unbiased_prototype);
756 // Reset object header to point to displaced mark.
757 // Must release store the lock address for platforms without TSO
758 // ordering (e.g. ppc).
759 obj->release_set_mark(markOopDesc::encode(highest_lock));
760 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
761 log_info(biasedlocking)(" Revoked bias of currently-locked object");
762 } else {
763 log_info(biasedlocking)(" Revoked bias of currently-unlocked object");
764 // Store the unlocked value into the object's header.
765 obj->set_mark(unbiased_prototype);
766 }
767
768 assert(!obj->mark()->has_bias_pattern(), "must not be biased");
769 }
770
771
772 BiasedLocking::Condition BiasedLocking::revoke_and_rebias(Handle obj, bool attempt_rebias, TRAPS) {
773 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
774
775 while (true) {
776 // We can revoke the biases of anonymously-biased objects
777 // efficiently enough that we should not cause these revocations to
778 // update the heuristics because doing so may cause unwanted bulk
779 // revocations (which are expensive) to occur.
780 markOop mark = obj->mark();
781 if (mark->is_biased_anonymously() && !attempt_rebias) {
782 // We are probably trying to revoke the bias of this object due to
783 // an identity hash code computation. Try to revoke the bias
784 // without a safepoint. This is possible if we can successfully
785 // compare-and-exchange an unbiased header into the mark word of
786 // the object, meaning that no other thread has raced to acquire
787 // the bias of the object.
788 markOop biased_value = mark;
789 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
790 markOop res_mark = obj->cas_set_mark(unbiased_prototype, mark);
791 if (res_mark == biased_value) {
792 return BIAS_REVOKED;
793 }
794 mark = res_mark; // Refresh mark with the latest value.
795 } else if (mark->has_bias_pattern()) {
796 Klass* k = obj->klass();
797 markOop prototype_header = k->prototype_header();
798 if (!prototype_header->has_bias_pattern()) {
799 // This object has a stale bias from before the bulk revocation
800 // for this data type occurred. It's pointless to update the
801 // heuristics at this point so simply update the header with a
802 // CAS. If we fail this race, the object's bias has been revoked
803 // by another thread so we simply return and let the caller deal
804 // with it.
805 obj->cas_set_mark(prototype_header->set_age(mark->age()), mark);
806 assert(!obj->mark()->has_bias_pattern(), "even if we raced, should still be revoked");
807 return BIAS_REVOKED;
808 } else if (prototype_header->bias_epoch() != mark->bias_epoch()) {
809 // The epoch of this biasing has expired indicating that the
810 // object is effectively unbiased. Depending on whether we need
811 // to rebias or revoke the bias of this object we can do it
812 // efficiently enough with a CAS that we shouldn't update the
813 // heuristics. This is normally done in the assembly code but we
814 // can reach this point due to various points in the runtime
815 // needing to revoke biases.
816 markOop res_mark;
817 if (attempt_rebias) {
818 assert(THREAD->is_Java_thread(), "");
819 markOop biased_value = mark;
820 markOop rebiased_prototype = markOopDesc::encode((JavaThread*) THREAD, mark->age(), prototype_header->bias_epoch());
821 res_mark = obj->cas_set_mark(rebiased_prototype, mark);
822 if (res_mark == biased_value) {
823 return BIAS_REVOKED_AND_REBIASED;
824 }
825 } else {
826 markOop biased_value = mark;
827 markOop unbiased_prototype = markOopDesc::prototype()->set_age(mark->age());
828 res_mark = obj->cas_set_mark(unbiased_prototype, mark);
829 if (res_mark == biased_value) {
830 return BIAS_REVOKED;
831 }
832 }
833 mark = res_mark; // Refresh mark with the latest value.
834 }
835 }
836
837 HeuristicsResult heuristics = update_heuristics(obj());
838 if (heuristics == HR_NOT_BIASED) {
839 return NOT_BIASED;
840 } else if (heuristics == HR_SINGLE_REVOKE) {
841 JavaThread *blt = mark->biased_locker();
842 assert(blt != NULL, "invariant");
843 if (blt == THREAD) {
844 // A thread is trying to revoke the bias of an object biased
845 // toward it, again likely due to an identity hash code
846 // computation. We can again avoid a safepoint/handshake in this case
847 // since we are only going to walk our own stack. There are no
848 // races with revocations occurring in other threads because we
849 // reach no safepoints in the revocation path.
850 EventBiasedLockSelfRevocation event;
851 ResourceMark rm;
852 walk_stack_and_revoke(obj(), blt);
853 blt->set_cached_monitor_info(NULL);
854 assert(!obj->mark()->has_bias_pattern(), "invariant");
855 if (event.should_commit()) {
856 post_self_revocation_event(&event, obj->klass());
857 }
858 return BIAS_REVOKED;
859 } else {
860 BiasedLocking::Condition cond = single_revoke_with_handshake(obj, (JavaThread*)THREAD, blt);
861 if (cond != NOT_REVOKED) {
862 return cond;
863 }
864 }
865 } else {
866 assert((heuristics == HR_BULK_REVOKE) ||
867 (heuristics == HR_BULK_REBIAS), "?");
868 EventBiasedLockClassRevocation event;
869 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*)THREAD,
870 (heuristics == HR_BULK_REBIAS),
871 attempt_rebias);
872 VMThread::execute(&bulk_revoke);
873 if (event.should_commit()) {
874 post_class_revocation_event(&event, obj->klass(), &bulk_revoke);
875 }
876 return bulk_revoke.status_code();
877 }
878 }
879 }
880
881 // All objects in objs should be locked by biaser
882 void BiasedLocking::revoke(GrowableArray<Handle>* objs, JavaThread *biaser) {
883 bool clean_my_cache = false;
884 for (int i = 0; i < objs->length(); i++) {
885 oop obj = (objs->at(i))();
886 markOop mark = obj->mark();
887 if (mark->has_bias_pattern()) {
888 walk_stack_and_revoke(obj, biaser);
889 clean_my_cache = true;
890 }
891 }
892 if (clean_my_cache) {
893 clean_up_cached_monitor_info(biaser);
894 }
895 }
896
897
898 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
899 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
900 oop obj = h_obj();
901 HeuristicsResult heuristics = update_heuristics(obj);
902 if (heuristics == HR_SINGLE_REVOKE) {
903 JavaThread* biased_locker = NULL;
904 single_revoke_at_safepoint(obj, false, false, NULL, &biased_locker);
905 if (biased_locker) {
906 clean_up_cached_monitor_info(biased_locker);
907 }
908 } else if ((heuristics == HR_BULK_REBIAS) ||
909 (heuristics == HR_BULK_REVOKE)) {
910 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
911 clean_up_cached_monitor_info();
912 }
913 }
914
915
916 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
917 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
918 int len = objs->length();
919 for (int i = 0; i < len; i++) {
920 oop obj = (objs->at(i))();
921 HeuristicsResult heuristics = update_heuristics(obj);
922 if (heuristics == HR_SINGLE_REVOKE) {
923 single_revoke_at_safepoint(obj, false, false, NULL, NULL);
924 } else if ((heuristics == HR_BULK_REBIAS) ||
925 (heuristics == HR_BULK_REVOKE)) {
926 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
927 }
928 }
929 clean_up_cached_monitor_info();
930 }
931
932
933 void BiasedLocking::preserve_marks() {
934 if (!UseBiasedLocking)
935 return;
936
937 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
938
939 assert(_preserved_oop_stack == NULL, "double initialization");
940 assert(_preserved_mark_stack == NULL, "double initialization");
941
942 // In order to reduce the number of mark words preserved during GC
943 // due to the presence of biased locking, we reinitialize most mark
989
990 int len = _preserved_oop_stack->length();
991 for (int i = 0; i < len; i++) {
992 Handle owner = _preserved_oop_stack->at(i);
993 markOop mark = _preserved_mark_stack->at(i);
994 owner->set_mark(mark);
995 }
996
997 delete _preserved_oop_stack;
998 _preserved_oop_stack = NULL;
999 delete _preserved_mark_stack;
1000 _preserved_mark_stack = NULL;
1001 }
1002
1003
1004 int* BiasedLocking::total_entry_count_addr() { return _counters.total_entry_count_addr(); }
1005 int* BiasedLocking::biased_lock_entry_count_addr() { return _counters.biased_lock_entry_count_addr(); }
1006 int* BiasedLocking::anonymously_biased_lock_entry_count_addr() { return _counters.anonymously_biased_lock_entry_count_addr(); }
1007 int* BiasedLocking::rebiased_lock_entry_count_addr() { return _counters.rebiased_lock_entry_count_addr(); }
1008 int* BiasedLocking::revoked_lock_entry_count_addr() { return _counters.revoked_lock_entry_count_addr(); }
1009 int* BiasedLocking::handshakes_count_addr() { return _counters.handshakes_count_addr(); }
1010 int* BiasedLocking::fast_path_entry_count_addr() { return _counters.fast_path_entry_count_addr(); }
1011 int* BiasedLocking::slow_path_entry_count_addr() { return _counters.slow_path_entry_count_addr(); }
1012
1013
1014 // BiasedLockingCounters
1015
1016 int BiasedLockingCounters::slow_path_entry_count() const {
1017 if (_slow_path_entry_count != 0) {
1018 return _slow_path_entry_count;
1019 }
1020 int sum = _biased_lock_entry_count + _anonymously_biased_lock_entry_count +
1021 _rebiased_lock_entry_count + _revoked_lock_entry_count +
1022 _fast_path_entry_count;
1023
1024 return _total_entry_count - sum;
1025 }
1026
1027 void BiasedLockingCounters::print_on(outputStream* st) const {
1028 tty->print_cr("# total entries: %d", _total_entry_count);
1029 tty->print_cr("# biased lock entries: %d", _biased_lock_entry_count);
1030 tty->print_cr("# anonymously biased lock entries: %d", _anonymously_biased_lock_entry_count);
1031 tty->print_cr("# rebiased lock entries: %d", _rebiased_lock_entry_count);
1032 tty->print_cr("# revoked lock entries: %d", _revoked_lock_entry_count);
1033 tty->print_cr("# handshakes entries: %d", _handshakes_count);
1034 tty->print_cr("# fast path lock entries: %d", _fast_path_entry_count);
1035 tty->print_cr("# slow path lock entries: %d", slow_path_entry_count());
1036 }
1037
1038 void BiasedLockingCounters::print() const { print_on(tty); }
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