14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "oops/klass.inline.hpp"
27 #include "oops/markOop.hpp"
28 #include "runtime/basicLock.hpp"
29 #include "runtime/biasedLocking.hpp"
30 #include "runtime/task.hpp"
31 #include "runtime/vframe.hpp"
32 #include "runtime/vmThread.hpp"
33 #include "runtime/vm_operations.hpp"
34
35 static bool _biased_locking_enabled = false;
36 BiasedLockingCounters BiasedLocking::_counters;
37
38 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
39 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
40
41 static void enable_biased_locking(Klass* k) {
42 k->set_prototype_header(markOopDesc::biased_locking_prototype());
43 }
44
45 class VM_EnableBiasedLocking: public VM_Operation {
46 private:
47 bool _is_cheap_allocated;
48 public:
49 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
50 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
51 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
52 bool is_cheap_allocated() const { return _is_cheap_allocated; }
53
125 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
126 if (monitors != NULL) {
127 int len = monitors->length();
128 // Walk monitors youngest to oldest
129 for (int i = len - 1; i >= 0; i--) {
130 MonitorInfo* mon_info = monitors->at(i);
131 if (mon_info->eliminated()) continue;
132 oop owner = mon_info->owner();
133 if (owner != NULL) {
134 info->append(mon_info);
135 }
136 }
137 }
138 }
139 }
140
141 thread->set_cached_monitor_info(info);
142 return info;
143 }
144
145
146 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread) {
147 markOop mark = obj->mark();
148 if (!mark->has_bias_pattern()) {
149 if (TraceBiasedLocking) {
150 ResourceMark rm;
151 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)",
152 obj->klass()->external_name());
153 }
154 return BiasedLocking::NOT_BIASED;
155 }
156
157 uint age = mark->age();
158 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
159 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
160
161 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
162 ResourceMark rm;
163 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,
164 p2i((void *)obj), (intptr_t) mark, obj->klass()->external_name(), (intptr_t) obj->klass()->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread);
165 }
166
236 // Reset object header to point to displaced mark.
237 // Must release storing the lock address for platforms without TSO
238 // ordering (e.g. ppc).
239 obj->release_set_mark(markOopDesc::encode(highest_lock));
240 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
241 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
242 tty->print_cr(" Revoked bias of currently-locked object");
243 }
244 } else {
245 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
246 tty->print_cr(" Revoked bias of currently-unlocked object");
247 }
248 if (allow_rebias) {
249 obj->set_mark(biased_prototype);
250 } else {
251 // Store the unlocked value into the object's header.
252 obj->set_mark(unbiased_prototype);
253 }
254 }
255
256 return BiasedLocking::BIAS_REVOKED;
257 }
258
259
260 enum HeuristicsResult {
261 HR_NOT_BIASED = 1,
262 HR_SINGLE_REVOKE = 2,
263 HR_BULK_REBIAS = 3,
264 HR_BULK_REVOKE = 4
265 };
266
267
268 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
269 markOop mark = o->mark();
270 if (!mark->has_bias_pattern()) {
271 return HR_NOT_BIASED;
272 }
273
274 // Heuristics to attempt to throttle the number of revocations.
275 // Stages:
356
357 // Now walk all threads' stacks and adjust epochs of any biased
358 // and locked objects of this data type we encounter
359 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
360 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
361 for (int i = 0; i < cached_monitor_info->length(); i++) {
362 MonitorInfo* mon_info = cached_monitor_info->at(i);
363 oop owner = mon_info->owner();
364 markOop mark = owner->mark();
365 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
366 // We might have encountered this object already in the case of recursive locking
367 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
368 owner->set_mark(mark->set_bias_epoch(cur_epoch));
369 }
370 }
371 }
372 }
373
374 // At this point we're done. All we have to do is potentially
375 // adjust the header of the given object to revoke its bias.
376 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread);
377 } else {
378 if (TraceBiasedLocking) {
379 ResourceMark rm;
380 tty->print_cr("* Disabling biased locking for type %s", klass->external_name());
381 }
382
383 // Disable biased locking for this data type. Not only will this
384 // cause future instances to not be biased, but existing biased
385 // instances will notice that this implicitly caused their biases
386 // to be revoked.
387 klass->set_prototype_header(markOopDesc::prototype());
388
389 // Now walk all threads' stacks and forcibly revoke the biases of
390 // any locked and biased objects of this data type we encounter.
391 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
392 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
393 for (int i = 0; i < cached_monitor_info->length(); i++) {
394 MonitorInfo* mon_info = cached_monitor_info->at(i);
395 oop owner = mon_info->owner();
396 markOop mark = owner->mark();
397 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
398 revoke_bias(owner, false, true, requesting_thread);
399 }
400 }
401 }
402
403 // Must force the bias of the passed object to be forcibly revoked
404 // as well to ensure guarantees to callers
405 revoke_bias(o, false, true, requesting_thread);
406 }
407
408 if (TraceBiasedLocking) {
409 tty->print_cr("* Ending bulk revocation");
410 }
411
412 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
413
414 if (attempt_rebias_of_object &&
415 o->mark()->has_bias_pattern() &&
416 klass->prototype_header()->has_bias_pattern()) {
417 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
418 klass->prototype_header()->bias_epoch());
419 o->set_mark(new_mark);
420 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
421 if (TraceBiasedLocking) {
422 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
423 }
424 }
425
428 "bug in bulk bias revocation");
429
430 return status_code;
431 }
432
433
434 static void clean_up_cached_monitor_info() {
435 // Walk the thread list clearing out the cached monitors
436 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
437 thr->set_cached_monitor_info(NULL);
438 }
439 }
440
441
442 class VM_RevokeBias : public VM_Operation {
443 protected:
444 Handle* _obj;
445 GrowableArray<Handle>* _objs;
446 JavaThread* _requesting_thread;
447 BiasedLocking::Condition _status_code;
448
449 public:
450 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
451 : _obj(obj)
452 , _objs(NULL)
453 , _requesting_thread(requesting_thread)
454 , _status_code(BiasedLocking::NOT_BIASED) {}
455
456 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
457 : _obj(NULL)
458 , _objs(objs)
459 , _requesting_thread(requesting_thread)
460 , _status_code(BiasedLocking::NOT_BIASED) {}
461
462 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
463
464 virtual bool doit_prologue() {
465 // Verify that there is actual work to do since the callers just
466 // give us locked object(s). If we don't find any biased objects
467 // there is nothing to do and we avoid a safepoint.
468 if (_obj != NULL) {
469 markOop mark = (*_obj)()->mark();
470 if (mark->has_bias_pattern()) {
471 return true;
472 }
473 } else {
474 for ( int i = 0 ; i < _objs->length(); i++ ) {
475 markOop mark = (_objs->at(i))()->mark();
476 if (mark->has_bias_pattern()) {
477 return true;
478 }
479 }
480 }
481 return false;
482 }
483
484 virtual void doit() {
485 if (_obj != NULL) {
486 if (TraceBiasedLocking) {
487 tty->print_cr("Revoking bias with potentially per-thread safepoint:");
488 }
489 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread);
490 clean_up_cached_monitor_info();
491 return;
492 } else {
493 if (TraceBiasedLocking) {
494 tty->print_cr("Revoking bias with global safepoint:");
495 }
496 BiasedLocking::revoke_at_safepoint(_objs);
497 }
498 }
499
500 BiasedLocking::Condition status_code() const {
501 return _status_code;
502 }
503 };
504
505
506 class VM_BulkRevokeBias : public VM_RevokeBias {
507 private:
508 bool _bulk_rebias;
509 bool _attempt_rebias_of_object;
510
511 public:
512 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
513 bool bulk_rebias,
514 bool attempt_rebias_of_object)
515 : VM_RevokeBias(obj, requesting_thread)
516 , _bulk_rebias(bulk_rebias)
517 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
518
519 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
520 virtual bool doit_prologue() { return true; }
521
522 virtual void doit() {
592 if (heuristics == HR_NOT_BIASED) {
593 return NOT_BIASED;
594 } else if (heuristics == HR_SINGLE_REVOKE) {
595 Klass *k = obj->klass();
596 markOop prototype_header = k->prototype_header();
597 if (mark->biased_locker() == THREAD &&
598 prototype_header->bias_epoch() == mark->bias_epoch()) {
599 // A thread is trying to revoke the bias of an object biased
600 // toward it, again likely due to an identity hash code
601 // computation. We can again avoid a safepoint in this case
602 // since we are only going to walk our own stack. There are no
603 // races with revocations occurring in other threads because we
604 // reach no safepoints in the revocation path.
605 // Also check the epoch because even if threads match, another thread
606 // can come in with a CAS to steal the bias of an object that has a
607 // stale epoch.
608 ResourceMark rm;
609 if (TraceBiasedLocking) {
610 tty->print_cr("Revoking bias by walking my own stack:");
611 }
612 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD);
613 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
614 assert(cond == BIAS_REVOKED, "why not?");
615 return cond;
616 } else {
617 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
618 VMThread::execute(&revoke);
619 return revoke.status_code();
620 }
621 }
622
623 assert((heuristics == HR_BULK_REVOKE) ||
624 (heuristics == HR_BULK_REBIAS), "?");
625 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
626 (heuristics == HR_BULK_REBIAS),
627 attempt_rebias);
628 VMThread::execute(&bulk_revoke);
629 return bulk_revoke.status_code();
630 }
631
632
633 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
634 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
635 if (objs->length() == 0) {
636 return;
637 }
638 VM_RevokeBias revoke(objs, JavaThread::current());
639 VMThread::execute(&revoke);
640 }
641
642
643 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
644 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
645 oop obj = h_obj();
646 HeuristicsResult heuristics = update_heuristics(obj, false);
647 if (heuristics == HR_SINGLE_REVOKE) {
648 revoke_bias(obj, false, false, NULL);
649 } else if ((heuristics == HR_BULK_REBIAS) ||
650 (heuristics == HR_BULK_REVOKE)) {
651 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
652 }
653 clean_up_cached_monitor_info();
654 }
655
656
657 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
658 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
659 int len = objs->length();
660 for (int i = 0; i < len; i++) {
661 oop obj = (objs->at(i))();
662 HeuristicsResult heuristics = update_heuristics(obj, false);
663 if (heuristics == HR_SINGLE_REVOKE) {
664 revoke_bias(obj, false, false, NULL);
665 } else if ((heuristics == HR_BULK_REBIAS) ||
666 (heuristics == HR_BULK_REVOKE)) {
667 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
668 }
669 }
670 clean_up_cached_monitor_info();
671 }
672
673
674 void BiasedLocking::preserve_marks() {
675 if (!UseBiasedLocking)
676 return;
677
678 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
679
680 assert(_preserved_oop_stack == NULL, "double initialization");
681 assert(_preserved_mark_stack == NULL, "double initialization");
682
683 // In order to reduce the number of mark words preserved during GC
684 // due to the presence of biased locking, we reinitialize most mark
|
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "oops/klass.inline.hpp"
27 #include "oops/markOop.hpp"
28 #include "runtime/basicLock.hpp"
29 #include "runtime/biasedLocking.hpp"
30 #include "runtime/task.hpp"
31 #include "runtime/vframe.hpp"
32 #include "runtime/vmThread.hpp"
33 #include "runtime/vm_operations.hpp"
34 #include "jfr/support/jfrThreadId.hpp"
35 #include "jfr/jfrEvents.hpp"
36
37 static bool _biased_locking_enabled = false;
38 BiasedLockingCounters BiasedLocking::_counters;
39
40 static GrowableArray<Handle>* _preserved_oop_stack = NULL;
41 static GrowableArray<markOop>* _preserved_mark_stack = NULL;
42
43 static void enable_biased_locking(Klass* k) {
44 k->set_prototype_header(markOopDesc::biased_locking_prototype());
45 }
46
47 class VM_EnableBiasedLocking: public VM_Operation {
48 private:
49 bool _is_cheap_allocated;
50 public:
51 VM_EnableBiasedLocking(bool is_cheap_allocated) { _is_cheap_allocated = is_cheap_allocated; }
52 VMOp_Type type() const { return VMOp_EnableBiasedLocking; }
53 Mode evaluation_mode() const { return _is_cheap_allocated ? _async_safepoint : _safepoint; }
54 bool is_cheap_allocated() const { return _is_cheap_allocated; }
55
127 GrowableArray<MonitorInfo*> *monitors = vf->monitors();
128 if (monitors != NULL) {
129 int len = monitors->length();
130 // Walk monitors youngest to oldest
131 for (int i = len - 1; i >= 0; i--) {
132 MonitorInfo* mon_info = monitors->at(i);
133 if (mon_info->eliminated()) continue;
134 oop owner = mon_info->owner();
135 if (owner != NULL) {
136 info->append(mon_info);
137 }
138 }
139 }
140 }
141 }
142
143 thread->set_cached_monitor_info(info);
144 return info;
145 }
146
147 // After the call, *biased_locker will be set to obj->mark()->biased_locker() if biased_locker != NULL,
148 // AND it is a living thread. Otherwise it will not be updated, (i.e. the caller is responsible for initialization).
149 static BiasedLocking::Condition revoke_bias(oop obj, bool allow_rebias, bool is_bulk, JavaThread* requesting_thread, JavaThread** biased_locker) {
150 markOop mark = obj->mark();
151 if (!mark->has_bias_pattern()) {
152 if (TraceBiasedLocking) {
153 ResourceMark rm;
154 tty->print_cr(" (Skipping revocation of object of type %s because it's no longer biased)",
155 obj->klass()->external_name());
156 }
157 return BiasedLocking::NOT_BIASED;
158 }
159
160 uint age = mark->age();
161 markOop biased_prototype = markOopDesc::biased_locking_prototype()->set_age(age);
162 markOop unbiased_prototype = markOopDesc::prototype()->set_age(age);
163
164 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
165 ResourceMark rm;
166 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,
167 p2i((void *)obj), (intptr_t) mark, obj->klass()->external_name(), (intptr_t) obj->klass()->prototype_header(), (allow_rebias ? 1 : 0), (intptr_t) requesting_thread);
168 }
169
239 // Reset object header to point to displaced mark.
240 // Must release storing the lock address for platforms without TSO
241 // ordering (e.g. ppc).
242 obj->release_set_mark(markOopDesc::encode(highest_lock));
243 assert(!obj->mark()->has_bias_pattern(), "illegal mark state: stack lock used bias bit");
244 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
245 tty->print_cr(" Revoked bias of currently-locked object");
246 }
247 } else {
248 if (TraceBiasedLocking && (Verbose || !is_bulk)) {
249 tty->print_cr(" Revoked bias of currently-unlocked object");
250 }
251 if (allow_rebias) {
252 obj->set_mark(biased_prototype);
253 } else {
254 // Store the unlocked value into the object's header.
255 obj->set_mark(unbiased_prototype);
256 }
257 }
258
259 // If requested, return information on which thread held the bias
260 if (biased_locker != NULL) {
261 *biased_locker = biased_thread;
262 }
263
264 return BiasedLocking::BIAS_REVOKED;
265 }
266
267
268 enum HeuristicsResult {
269 HR_NOT_BIASED = 1,
270 HR_SINGLE_REVOKE = 2,
271 HR_BULK_REBIAS = 3,
272 HR_BULK_REVOKE = 4
273 };
274
275
276 static HeuristicsResult update_heuristics(oop o, bool allow_rebias) {
277 markOop mark = o->mark();
278 if (!mark->has_bias_pattern()) {
279 return HR_NOT_BIASED;
280 }
281
282 // Heuristics to attempt to throttle the number of revocations.
283 // Stages:
364
365 // Now walk all threads' stacks and adjust epochs of any biased
366 // and locked objects of this data type we encounter
367 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
368 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
369 for (int i = 0; i < cached_monitor_info->length(); i++) {
370 MonitorInfo* mon_info = cached_monitor_info->at(i);
371 oop owner = mon_info->owner();
372 markOop mark = owner->mark();
373 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
374 // We might have encountered this object already in the case of recursive locking
375 assert(mark->bias_epoch() == prev_epoch || mark->bias_epoch() == cur_epoch, "error in bias epoch adjustment");
376 owner->set_mark(mark->set_bias_epoch(cur_epoch));
377 }
378 }
379 }
380 }
381
382 // At this point we're done. All we have to do is potentially
383 // adjust the header of the given object to revoke its bias.
384 revoke_bias(o, attempt_rebias_of_object && klass->prototype_header()->has_bias_pattern(), true, requesting_thread, NULL);
385 } else {
386 if (TraceBiasedLocking) {
387 ResourceMark rm;
388 tty->print_cr("* Disabling biased locking for type %s", klass->external_name());
389 }
390
391 // Disable biased locking for this data type. Not only will this
392 // cause future instances to not be biased, but existing biased
393 // instances will notice that this implicitly caused their biases
394 // to be revoked.
395 klass->set_prototype_header(markOopDesc::prototype());
396
397 // Now walk all threads' stacks and forcibly revoke the biases of
398 // any locked and biased objects of this data type we encounter.
399 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
400 GrowableArray<MonitorInfo*>* cached_monitor_info = get_or_compute_monitor_info(thr);
401 for (int i = 0; i < cached_monitor_info->length(); i++) {
402 MonitorInfo* mon_info = cached_monitor_info->at(i);
403 oop owner = mon_info->owner();
404 markOop mark = owner->mark();
405 if ((owner->klass() == k_o) && mark->has_bias_pattern()) {
406 revoke_bias(owner, false, true, requesting_thread, NULL);
407 }
408 }
409 }
410
411 // Must force the bias of the passed object to be forcibly revoked
412 // as well to ensure guarantees to callers
413 revoke_bias(o, false, true, requesting_thread, NULL);
414 }
415
416 if (TraceBiasedLocking) {
417 tty->print_cr("* Ending bulk revocation");
418 }
419
420 BiasedLocking::Condition status_code = BiasedLocking::BIAS_REVOKED;
421
422 if (attempt_rebias_of_object &&
423 o->mark()->has_bias_pattern() &&
424 klass->prototype_header()->has_bias_pattern()) {
425 markOop new_mark = markOopDesc::encode(requesting_thread, o->mark()->age(),
426 klass->prototype_header()->bias_epoch());
427 o->set_mark(new_mark);
428 status_code = BiasedLocking::BIAS_REVOKED_AND_REBIASED;
429 if (TraceBiasedLocking) {
430 tty->print_cr(" Rebiased object toward thread " INTPTR_FORMAT, (intptr_t) requesting_thread);
431 }
432 }
433
436 "bug in bulk bias revocation");
437
438 return status_code;
439 }
440
441
442 static void clean_up_cached_monitor_info() {
443 // Walk the thread list clearing out the cached monitors
444 for (JavaThread* thr = Threads::first(); thr != NULL; thr = thr->next()) {
445 thr->set_cached_monitor_info(NULL);
446 }
447 }
448
449
450 class VM_RevokeBias : public VM_Operation {
451 protected:
452 Handle* _obj;
453 GrowableArray<Handle>* _objs;
454 JavaThread* _requesting_thread;
455 BiasedLocking::Condition _status_code;
456 traceid _biased_locker_id;
457
458 public:
459 VM_RevokeBias(Handle* obj, JavaThread* requesting_thread)
460 : _obj(obj)
461 , _objs(NULL)
462 , _requesting_thread(requesting_thread)
463 , _status_code(BiasedLocking::NOT_BIASED)
464 , _biased_locker_id(0) {}
465
466 VM_RevokeBias(GrowableArray<Handle>* objs, JavaThread* requesting_thread)
467 : _obj(NULL)
468 , _objs(objs)
469 , _requesting_thread(requesting_thread)
470 , _status_code(BiasedLocking::NOT_BIASED)
471 , _biased_locker_id(0) {}
472
473 virtual VMOp_Type type() const { return VMOp_RevokeBias; }
474
475 virtual bool doit_prologue() {
476 // Verify that there is actual work to do since the callers just
477 // give us locked object(s). If we don't find any biased objects
478 // there is nothing to do and we avoid a safepoint.
479 if (_obj != NULL) {
480 markOop mark = (*_obj)()->mark();
481 if (mark->has_bias_pattern()) {
482 return true;
483 }
484 } else {
485 for ( int i = 0 ; i < _objs->length(); i++ ) {
486 markOop mark = (_objs->at(i))()->mark();
487 if (mark->has_bias_pattern()) {
488 return true;
489 }
490 }
491 }
492 return false;
493 }
494
495 virtual void doit() {
496 if (_obj != NULL) {
497 if (TraceBiasedLocking) {
498 tty->print_cr("Revoking bias with potentially per-thread safepoint:");
499 }
500 JavaThread* biased_locker = NULL;
501 _status_code = revoke_bias((*_obj)(), false, false, _requesting_thread, &biased_locker);
502 if (biased_locker != NULL) {
503 _biased_locker_id = JFR_THREAD_ID(biased_locker);
504 }
505 clean_up_cached_monitor_info();
506 return;
507 } else {
508 if (TraceBiasedLocking) {
509 tty->print_cr("Revoking bias with global safepoint:");
510 }
511 BiasedLocking::revoke_at_safepoint(_objs);
512 }
513 }
514
515 BiasedLocking::Condition status_code() const {
516 return _status_code;
517 }
518
519 traceid biased_locker() const {
520 return _biased_locker_id;
521 }
522 };
523
524
525 class VM_BulkRevokeBias : public VM_RevokeBias {
526 private:
527 bool _bulk_rebias;
528 bool _attempt_rebias_of_object;
529
530 public:
531 VM_BulkRevokeBias(Handle* obj, JavaThread* requesting_thread,
532 bool bulk_rebias,
533 bool attempt_rebias_of_object)
534 : VM_RevokeBias(obj, requesting_thread)
535 , _bulk_rebias(bulk_rebias)
536 , _attempt_rebias_of_object(attempt_rebias_of_object) {}
537
538 virtual VMOp_Type type() const { return VMOp_BulkRevokeBias; }
539 virtual bool doit_prologue() { return true; }
540
541 virtual void doit() {
611 if (heuristics == HR_NOT_BIASED) {
612 return NOT_BIASED;
613 } else if (heuristics == HR_SINGLE_REVOKE) {
614 Klass *k = obj->klass();
615 markOop prototype_header = k->prototype_header();
616 if (mark->biased_locker() == THREAD &&
617 prototype_header->bias_epoch() == mark->bias_epoch()) {
618 // A thread is trying to revoke the bias of an object biased
619 // toward it, again likely due to an identity hash code
620 // computation. We can again avoid a safepoint in this case
621 // since we are only going to walk our own stack. There are no
622 // races with revocations occurring in other threads because we
623 // reach no safepoints in the revocation path.
624 // Also check the epoch because even if threads match, another thread
625 // can come in with a CAS to steal the bias of an object that has a
626 // stale epoch.
627 ResourceMark rm;
628 if (TraceBiasedLocking) {
629 tty->print_cr("Revoking bias by walking my own stack:");
630 }
631 EventBiasedLockSelfRevocation event;
632 BiasedLocking::Condition cond = revoke_bias(obj(), false, false, (JavaThread*) THREAD, NULL);
633 ((JavaThread*) THREAD)->set_cached_monitor_info(NULL);
634 assert(cond == BIAS_REVOKED, "why not?");
635 if (event.should_commit()) {
636 event.set_lockClass(k);
637 event.commit();
638 }
639 return cond;
640 } else {
641 EventBiasedLockRevocation event;
642 VM_RevokeBias revoke(&obj, (JavaThread*) THREAD);
643 VMThread::execute(&revoke);
644 if (event.should_commit() && (revoke.status_code() != NOT_BIASED)) {
645 event.set_lockClass(k);
646 // Subtract 1 to match the id of events committed inside the safepoint
647 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
648 event.set_previousOwner(revoke.biased_locker());
649 event.commit();
650 }
651 return revoke.status_code();
652 }
653 }
654
655 assert((heuristics == HR_BULK_REVOKE) ||
656 (heuristics == HR_BULK_REBIAS), "?");
657 EventBiasedLockClassRevocation event;
658 VM_BulkRevokeBias bulk_revoke(&obj, (JavaThread*) THREAD,
659 (heuristics == HR_BULK_REBIAS),
660 attempt_rebias);
661 VMThread::execute(&bulk_revoke);
662 if (event.should_commit()) {
663 event.set_revokedClass(obj->klass());
664 event.set_disableBiasing((heuristics != HR_BULK_REBIAS));
665 // Subtract 1 to match the id of events committed inside the safepoint
666 event.set_safepointId(SafepointSynchronize::safepoint_counter() - 1);
667 event.commit();
668 }
669 return bulk_revoke.status_code();
670 }
671
672
673 void BiasedLocking::revoke(GrowableArray<Handle>* objs) {
674 assert(!SafepointSynchronize::is_at_safepoint(), "must not be called while at safepoint");
675 if (objs->length() == 0) {
676 return;
677 }
678 VM_RevokeBias revoke(objs, JavaThread::current());
679 VMThread::execute(&revoke);
680 }
681
682
683 void BiasedLocking::revoke_at_safepoint(Handle h_obj) {
684 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
685 oop obj = h_obj();
686 HeuristicsResult heuristics = update_heuristics(obj, false);
687 if (heuristics == HR_SINGLE_REVOKE) {
688 revoke_bias(obj, false, false, NULL, NULL);
689 } else if ((heuristics == HR_BULK_REBIAS) ||
690 (heuristics == HR_BULK_REVOKE)) {
691 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
692 }
693 clean_up_cached_monitor_info();
694 }
695
696
697 void BiasedLocking::revoke_at_safepoint(GrowableArray<Handle>* objs) {
698 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
699 int len = objs->length();
700 for (int i = 0; i < len; i++) {
701 oop obj = (objs->at(i))();
702 HeuristicsResult heuristics = update_heuristics(obj, false);
703 if (heuristics == HR_SINGLE_REVOKE) {
704 revoke_bias(obj, false, false, NULL, NULL);
705 } else if ((heuristics == HR_BULK_REBIAS) ||
706 (heuristics == HR_BULK_REVOKE)) {
707 bulk_revoke_or_rebias_at_safepoint(obj, (heuristics == HR_BULK_REBIAS), false, NULL);
708 }
709 }
710 clean_up_cached_monitor_info();
711 }
712
713
714 void BiasedLocking::preserve_marks() {
715 if (!UseBiasedLocking)
716 return;
717
718 assert(SafepointSynchronize::is_at_safepoint(), "must only be called while at safepoint");
719
720 assert(_preserved_oop_stack == NULL, "double initialization");
721 assert(_preserved_mark_stack == NULL, "double initialization");
722
723 // In order to reduce the number of mark words preserved during GC
724 // due to the presence of biased locking, we reinitialize most mark
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