107 #endif // ndef DTRACE_ENABLED
108
109 // This exists only as a workaround of dtrace bug 6254741
110 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
111 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
112 return 0;
113 }
114
115 #define NINFLATIONLOCKS 256
116 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
117
118 // global list of blocks of monitors
119 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL;
120 // global monitor free list
121 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
122 // global monitor in-use list, for moribund threads,
123 // monitors they inflated need to be scanned for deflation
124 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
125 // count of entries in gOmInUseList
126 int ObjectSynchronizer::gOmInUseCount = 0;
127
128 static volatile intptr_t gListLock = 0; // protects global monitor lists
129 static volatile int gMonitorFreeCount = 0; // # on gFreeList
130 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
131
132 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
133
134
135 // =====================> Quick functions
136
137 // The quick_* forms are special fast-path variants used to improve
138 // performance. In the simplest case, a "quick_*" implementation could
139 // simply return false, in which case the caller will perform the necessary
140 // state transitions and call the slow-path form.
141 // The fast-path is designed to handle frequently arising cases in an efficient
142 // manner and is just a degenerate "optimistic" variant of the slow-path.
143 // returns true -- to indicate the call was satisfied.
144 // returns false -- to indicate the call needs the services of the slow-path.
145 // A no-loitering ordinance is in effect for code in the quick_* family
146 // operators: safepoints or indefinite blocking (blocking that might span a
193 }
194
195 // biased locking and any other IMS exception states take the slow-path
196 return false;
197 }
198
199
200 // The LockNode emitted directly at the synchronization site would have
201 // been too big if it were to have included support for the cases of inflated
202 // recursive enter and exit, so they go here instead.
203 // Note that we can't safely call AsyncPrintJavaStack() from within
204 // quick_enter() as our thread state remains _in_Java.
205
206 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
207 BasicLock * lock) {
208 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
209 assert(Self->is_Java_thread(), "invariant");
210 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
211 NoSafepointVerifier nsv;
212 if (obj == NULL) return false; // Need to throw NPE
213 const markOop mark = obj->mark();
214
215 if (mark->has_monitor()) {
216 ObjectMonitor * const m = mark->monitor();
217 assert(oopDesc::equals((oop) m->object(), obj), "invariant");
218 Thread * const owner = (Thread *) m->_owner;
219
220 // Lock contention and Transactional Lock Elision (TLE) diagnostics
221 // and observability
222 // Case: light contention possibly amenable to TLE
223 // Case: TLE inimical operations such as nested/recursive synchronization
224
225 if (owner == Self) {
226 m->_recursions++;
227 return true;
228 }
229
230 // This Java Monitor is inflated so obj's header will never be
231 // displaced to this thread's BasicLock. Make the displaced header
232 // non-NULL so this BasicLock is not seen as recursive nor as
233 // being locked. We do this unconditionally so that this thread's
234 // BasicLock cannot be mis-interpreted by any stack walkers. For
235 // performance reasons, stack walkers generally first check for
236 // Biased Locking in the object's header, the second check is for
237 // stack-locking in the object's header, the third check is for
238 // recursive stack-locking in the displaced header in the BasicLock,
239 // and last are the inflated Java Monitor (ObjectMonitor) checks.
240 lock->set_displaced_header(markOopDesc::unused_mark());
241
242 if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
243 assert(m->_recursions == 0, "invariant");
244 assert(m->_owner == Self, "invariant");
245 return true;
246 }
247 }
248
249 // Note that we could inflate in quick_enter.
250 // This is likely a useful optimization
251 // Critically, in quick_enter() we must not:
252 // -- perform bias revocation, or
253 // -- block indefinitely, or
254 // -- reach a safepoint
255
256 return false; // revert to slow-path
257 }
258
259 // -----------------------------------------------------------------------------
260 // Fast Monitor Enter/Exit
261 // This the fast monitor enter. The interpreter and compiler use
262 // some assembly copies of this code. Make sure update those code
263 // if the following function is changed. The implementation is
264 // extremely sensitive to race condition. Be careful.
265
266 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
267 bool attempt_rebias, TRAPS) {
310 // does not own the Java Monitor.
311 ObjectMonitor * m = mark->monitor();
312 assert(((oop)(m->object()))->mark() == mark, "invariant");
313 assert(m->is_entered(THREAD), "invariant");
314 }
315 }
316 #endif
317 return;
318 }
319
320 if (mark == (markOop) lock) {
321 // If the object is stack-locked by the current thread, try to
322 // swing the displaced header from the BasicLock back to the mark.
323 assert(dhw->is_neutral(), "invariant");
324 if (object->cas_set_mark(dhw, mark) == mark) {
325 return;
326 }
327 }
328
329 // We have to take the slow-path of possible inflation and then exit.
330 inflate(THREAD, object, inflate_cause_vm_internal)->exit(true, THREAD);
331 }
332
333 // -----------------------------------------------------------------------------
334 // Interpreter/Compiler Slow Case
335 // This routine is used to handle interpreter/compiler slow case
336 // We don't need to use fast path here, because it must have been
337 // failed in the interpreter/compiler code.
338 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
339 markOop mark = obj->mark();
340 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
341
342 if (mark->is_neutral()) {
343 // Anticipate successful CAS -- the ST of the displaced mark must
344 // be visible <= the ST performed by the CAS.
345 lock->set_displaced_header(mark);
346 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
347 return;
348 }
349 // Fall through to inflate() ...
350 } else if (mark->has_locker() &&
351 THREAD->is_lock_owned((address)mark->locker())) {
352 assert(lock != mark->locker(), "must not re-lock the same lock");
353 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
354 lock->set_displaced_header(NULL);
355 return;
356 }
357
358 // The object header will never be displaced to this lock,
359 // so it does not matter what the value is, except that it
360 // must be non-zero to avoid looking like a re-entrant lock,
361 // and must not look locked either.
362 lock->set_displaced_header(markOopDesc::unused_mark());
363 inflate(THREAD, obj(), inflate_cause_monitor_enter)->enter(THREAD);
364 }
365
366 // This routine is used to handle interpreter/compiler slow case
367 // We don't need to use fast path here, because it must have
368 // failed in the interpreter/compiler code. Simply use the heavy
369 // weight monitor should be ok, unless someone find otherwise.
370 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
371 fast_exit(object, lock, THREAD);
372 }
373
374 // -----------------------------------------------------------------------------
375 // Class Loader support to workaround deadlocks on the class loader lock objects
376 // Also used by GC
377 // complete_exit()/reenter() are used to wait on a nested lock
378 // i.e. to give up an outer lock completely and then re-enter
379 // Used when holding nested locks - lock acquisition order: lock1 then lock2
380 // 1) complete_exit lock1 - saving recursion count
381 // 2) wait on lock2
382 // 3) when notified on lock2, unlock lock2
383 // 4) reenter lock1 with original recursion count
384 // 5) lock lock2
385 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
386 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
387 if (UseBiasedLocking) {
388 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
389 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
390 }
391
392 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
393
394 return monitor->complete_exit(THREAD);
395 }
396
397 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
398 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
399 if (UseBiasedLocking) {
400 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
401 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
402 }
403
404 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_vm_internal);
405
406 monitor->reenter(recursion, THREAD);
407 }
408 // -----------------------------------------------------------------------------
409 // JNI locks on java objects
410 // NOTE: must use heavy weight monitor to handle jni monitor enter
411 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
412 // the current locking is from JNI instead of Java code
413 if (UseBiasedLocking) {
414 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
415 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
416 }
417 THREAD->set_current_pending_monitor_is_from_java(false);
418 inflate(THREAD, obj(), inflate_cause_jni_enter)->enter(THREAD);
419 THREAD->set_current_pending_monitor_is_from_java(true);
420 }
421
422 // NOTE: must use heavy weight monitor to handle jni monitor exit
423 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
424 if (UseBiasedLocking) {
425 Handle h_obj(THREAD, obj);
426 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
427 obj = h_obj();
428 }
429 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
430
431 ObjectMonitor* monitor = inflate(THREAD, obj, inflate_cause_jni_exit);
432 // If this thread has locked the object, exit the monitor. Note: can't use
433 // monitor->check(CHECK); must exit even if an exception is pending.
434 if (monitor->check(THREAD)) {
435 monitor->exit(true, THREAD);
436 }
437 }
438
439 // -----------------------------------------------------------------------------
440 // Internal VM locks on java objects
441 // standard constructor, allows locking failures
442 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
443 _dolock = doLock;
444 _thread = thread;
445 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
446 _obj = obj;
447
448 if (_dolock) {
449 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
450 }
451 }
452
453 ObjectLocker::~ObjectLocker() {
454 if (_dolock) {
455 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
456 }
457 }
458
459
460 // -----------------------------------------------------------------------------
461 // Wait/Notify/NotifyAll
462 // NOTE: must use heavy weight monitor to handle wait()
463 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
464 if (UseBiasedLocking) {
465 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
466 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
467 }
468 if (millis < 0) {
469 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
470 }
471 ObjectMonitor* monitor = inflate(THREAD, obj(), inflate_cause_wait);
472
473 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
474 monitor->wait(millis, true, THREAD);
475
476 // This dummy call is in place to get around dtrace bug 6254741. Once
477 // that's fixed we can uncomment the following line, remove the call
478 // and change this function back into a "void" func.
479 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
480 return dtrace_waited_probe(monitor, obj, THREAD);
481 }
482
483 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
484 if (UseBiasedLocking) {
485 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
486 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
487 }
488 if (millis < 0) {
489 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
490 }
491 inflate(THREAD, obj(), inflate_cause_wait)->wait(millis, false, THREAD);
492 }
493
494 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
495 if (UseBiasedLocking) {
496 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
497 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
498 }
499
500 markOop mark = obj->mark();
501 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
502 return;
503 }
504 inflate(THREAD, obj(), inflate_cause_notify)->notify(THREAD);
505 }
506
507 // NOTE: see comment of notify()
508 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
509 if (UseBiasedLocking) {
510 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
511 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
512 }
513
514 markOop mark = obj->mark();
515 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
516 return;
517 }
518 inflate(THREAD, obj(), inflate_cause_notify)->notifyAll(THREAD);
519 }
520
521 // -----------------------------------------------------------------------------
522 // Hash Code handling
523 //
524 // Performance concern:
525 // OrderAccess::storestore() calls release() which at one time stored 0
526 // into the global volatile OrderAccess::dummy variable. This store was
527 // unnecessary for correctness. Many threads storing into a common location
528 // causes considerable cache migration or "sloshing" on large SMP systems.
529 // As such, I avoided using OrderAccess::storestore(). In some cases
530 // OrderAccess::fence() -- which incurs local latency on the executing
531 // processor -- is a better choice as it scales on SMP systems.
532 //
533 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
534 // a discussion of coherency costs. Note that all our current reference
535 // platforms provide strong ST-ST order, so the issue is moot on IA32,
536 // x64, and SPARC.
537 //
538 // As a general policy we use "volatile" to control compiler-based reordering
692 Handle hobj(Self, obj);
693 // Relaxing assertion for bug 6320749.
694 assert(Universe::verify_in_progress() ||
695 !SafepointSynchronize::is_at_safepoint(),
696 "biases should not be seen by VM thread here");
697 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
698 obj = hobj();
699 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
700 }
701 }
702
703 // hashCode() is a heap mutator ...
704 // Relaxing assertion for bug 6320749.
705 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
706 !SafepointSynchronize::is_at_safepoint(), "invariant");
707 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
708 Self->is_Java_thread() , "invariant");
709 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
710 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
711
712 ObjectMonitor* monitor = NULL;
713 markOop temp, test;
714 intptr_t hash;
715 markOop mark = ReadStableMark(obj);
716
717 // object should remain ineligible for biased locking
718 assert(!mark->has_bias_pattern(), "invariant");
719
720 if (mark->is_neutral()) {
721 hash = mark->hash(); // this is a normal header
722 if (hash != 0) { // if it has hash, just return it
723 return hash;
724 }
725 hash = get_next_hash(Self, obj); // allocate a new hash code
726 temp = mark->copy_set_hash(hash); // merge the hash code into header
727 // use (machine word version) atomic operation to install the hash
728 test = obj->cas_set_mark(temp, mark);
729 if (test == mark) {
730 return hash;
731 }
732 // If atomic operation failed, we must inflate the header
733 // into heavy weight monitor. We could add more code here
734 // for fast path, but it does not worth the complexity.
735 } else if (mark->has_monitor()) {
736 monitor = mark->monitor();
737 temp = monitor->header();
738 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
739 hash = temp->hash();
740 if (hash != 0) {
741 return hash;
742 }
743 // Skip to the following code to reduce code size
744 } else if (Self->is_lock_owned((address)mark->locker())) {
745 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
746 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
747 hash = temp->hash(); // by current thread, check if the displaced
748 if (hash != 0) { // header contains hash code
749 return hash;
750 }
751 // WARNING:
752 // The displaced header in the BasicLock on a thread's stack
753 // is strictly immutable. It CANNOT be changed in ANY cases.
754 // So we have to inflate the stack lock into an ObjectMonitor
755 // even if the current thread owns the lock. The BasicLock on
756 // a thread's stack can be asynchronously read by other threads
757 // during an inflate() call so any change to that stack memory
758 // may not propagate to other threads correctly.
759 }
760
761 // Inflate the monitor to set hash code
762 monitor = inflate(Self, obj, inflate_cause_hash_code);
763 // Load displaced header and check it has hash code
764 mark = monitor->header();
765 assert(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
766 hash = mark->hash();
767 if (hash == 0) {
768 hash = get_next_hash(Self, obj);
769 temp = mark->copy_set_hash(hash); // merge hash code into header
770 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
771 test = Atomic::cmpxchg(temp, monitor->header_addr(), mark);
772 if (test != mark) {
773 // The only update to the ObjectMonitor's header/dmw field
774 // is to merge in the hash code. If someone adds a new usage
775 // of the header/dmw field, please update this code.
776 hash = test->hash();
777 assert(test->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(test));
778 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
779 }
780 }
781 // We finally get the hash
782 return hash;
783 }
784
785 // Deprecated -- use FastHashCode() instead.
786
787 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
788 return FastHashCode(Thread::current(), obj());
789 }
790
791
792 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
793 Handle h_obj) {
794 if (UseBiasedLocking) {
795 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
796 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
797 }
798
799 assert(thread == JavaThread::current(), "Can only be called on current thread");
800 oop obj = h_obj();
801
802 markOop mark = ReadStableMark(obj);
803
804 // Uncontended case, header points to stack
805 if (mark->has_locker()) {
806 return thread->is_lock_owned((address)mark->locker());
807 }
808 // Contended case, header points to ObjectMonitor (tagged pointer)
809 if (mark->has_monitor()) {
810 ObjectMonitor* monitor = mark->monitor();
811 return monitor->is_entered(thread) != 0;
812 }
813 // Unlocked case, header in place
814 assert(mark->is_neutral(), "sanity check");
815 return false;
816 }
817
818 // Be aware of this method could revoke bias of the lock object.
819 // This method queries the ownership of the lock handle specified by 'h_obj'.
820 // If the current thread owns the lock, it returns owner_self. If no
821 // thread owns the lock, it returns owner_none. Otherwise, it will return
822 // owner_other.
823 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
824 (JavaThread *self, Handle h_obj) {
825 // The caller must beware this method can revoke bias, and
826 // revocation can result in a safepoint.
827 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
828 assert(self->thread_state() != _thread_blocked, "invariant");
829
830 // Possible mark states: neutral, biased, stack-locked, inflated
831
832 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
833 // CASE: biased
834 BiasedLocking::revoke_and_rebias(h_obj, false, self);
835 assert(!h_obj->mark()->has_bias_pattern(),
836 "biases should be revoked by now");
837 }
838
839 assert(self == JavaThread::current(), "Can only be called on current thread");
840 oop obj = h_obj();
841 markOop mark = ReadStableMark(obj);
842
843 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
844 if (mark->has_locker()) {
845 return self->is_lock_owned((address)mark->locker()) ?
846 owner_self : owner_other;
847 }
848
849 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
850 // The Object:ObjectMonitor relationship is stable as long as we're
851 // not at a safepoint.
852 if (mark->has_monitor()) {
853 void * owner = mark->monitor()->_owner;
854 if (owner == NULL) return owner_none;
855 return (owner == self ||
856 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
857 }
858
859 // CASE: neutral
860 assert(mark->is_neutral(), "sanity check");
861 return owner_none; // it's unlocked
862 }
863
864 // FIXME: jvmti should call this
865 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
866 if (UseBiasedLocking) {
867 if (SafepointSynchronize::is_at_safepoint()) {
868 BiasedLocking::revoke_at_safepoint(h_obj);
869 } else {
870 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
871 }
872 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
873 }
874
875 oop obj = h_obj();
876 address owner = NULL;
877
878 markOop mark = ReadStableMark(obj);
879
880 // Uncontended case, header points to stack
881 if (mark->has_locker()) {
882 owner = (address) mark->locker();
883 }
884
885 // Contended case, header points to ObjectMonitor (tagged pointer)
886 else if (mark->has_monitor()) {
887 ObjectMonitor* monitor = mark->monitor();
888 assert(monitor != NULL, "monitor should be non-null");
889 owner = (address) monitor->owner();
890 }
891
892 if (owner != NULL) {
893 // owning_thread_from_monitor_owner() may also return NULL here
894 return Threads::owning_thread_from_monitor_owner(t_list, owner);
895 }
896
897 // Unlocked case, header in place
898 // Cannot have assertion since this object may have been
899 // locked by another thread when reaching here.
900 // assert(mark->is_neutral(), "sanity check");
901
902 return NULL;
903 }
904
905 // Visitors ...
906
907 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
908 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
909 while (block != NULL) {
910 assert(block->object() == CHAINMARKER, "must be a block header");
911 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
912 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
913 oop object = (oop)mid->object();
914 if (object != NULL) {
915 closure->do_monitor(mid);
916 }
917 }
918 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
919 }
920 }
921
922 // Get the next block in the block list.
923 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
924 assert(block->object() == CHAINMARKER, "must be a block header");
925 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
926 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
927 return block;
928 }
929
930 static bool monitors_used_above_threshold() {
931 if (gMonitorPopulation == 0) {
932 return false;
933 }
934 int monitors_used = gMonitorPopulation - gMonitorFreeCount;
1005 // See also: GuaranteedSafepointInterval
1006 //
1007 // The current implementation uses asynchronous VM operations.
1008
1009 static void InduceScavenge(Thread * Self, const char * Whence) {
1010 // Induce STW safepoint to trim monitors
1011 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1012 // More precisely, trigger an asynchronous STW safepoint as the number
1013 // of active monitors passes the specified threshold.
1014 // TODO: assert thread state is reasonable
1015
1016 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1017 // Induce a 'null' safepoint to scavenge monitors
1018 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1019 // to the VMthread and have a lifespan longer than that of this activation record.
1020 // The VMThread will delete the op when completed.
1021 VMThread::execute(new VM_ScavengeMonitors());
1022 }
1023 }
1024
1025 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self) {
1026 // A large MAXPRIVATE value reduces both list lock contention
1027 // and list coherency traffic, but also tends to increase the
1028 // number of objectMonitors in circulation as well as the STW
1029 // scavenge costs. As usual, we lean toward time in space-time
1030 // tradeoffs.
1031 const int MAXPRIVATE = 1024;
1032 for (;;) {
1033 ObjectMonitor * m;
1034
1035 // 1: try to allocate from the thread's local omFreeList.
1036 // Threads will attempt to allocate first from their local list, then
1037 // from the global list, and only after those attempts fail will the thread
1038 // attempt to instantiate new monitors. Thread-local free lists take
1039 // heat off the gListLock and improve allocation latency, as well as reducing
1040 // coherency traffic on the shared global list.
1041 m = Self->omFreeList;
1042 if (m != NULL) {
1043 Self->omFreeList = m->FreeNext;
1044 Self->omFreeCount--;
1045 guarantee(m->object() == NULL, "invariant");
1046 m->FreeNext = Self->omInUseList;
1047 Self->omInUseList = m;
1048 Self->omInUseCount++;
1049 return m;
1050 }
1051
1052 // 2: try to allocate from the global gFreeList
1053 // CONSIDER: use muxTry() instead of muxAcquire().
1054 // If the muxTry() fails then drop immediately into case 3.
1055 // If we're using thread-local free lists then try
1056 // to reprovision the caller's free list.
1057 if (gFreeList != NULL) {
1058 // Reprovision the thread's omFreeList.
1059 // Use bulk transfers to reduce the allocation rate and heat
1060 // on various locks.
1061 Thread::muxAcquire(&gListLock, "omAlloc(1)");
1062 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1063 gMonitorFreeCount--;
1064 ObjectMonitor * take = gFreeList;
1065 gFreeList = take->FreeNext;
1066 guarantee(take->object() == NULL, "invariant");
1067 guarantee(!take->is_busy(), "invariant");
1068 take->Recycle();
1069 omRelease(Self, take, false);
1070 }
1071 Thread::muxRelease(&gListLock);
1072 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1073 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1074
1075 const int mx = MonitorBound;
1076 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1077 // We can't safely induce a STW safepoint from omAlloc() as our thread
1078 // state may not be appropriate for such activities and callers may hold
1079 // naked oops, so instead we defer the action.
1080 InduceScavenge(Self, "omAlloc");
1081 }
1082 continue;
1083 }
1084
1085 // 3: allocate a block of new ObjectMonitors
1086 // Both the local and global free lists are empty -- resort to malloc().
1087 // In the current implementation objectMonitors are TSM - immortal.
1088 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1101
1102 // NOTE: (almost) no way to recover if allocation failed.
1103 // We might be able to induce a STW safepoint and scavenge enough
1104 // objectMonitors to permit progress.
1105 if (temp == NULL) {
1106 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1107 "Allocate ObjectMonitors");
1108 }
1109 (void)memset((void *) temp, 0, neededsize);
1110
1111 // Format the block.
1112 // initialize the linked list, each monitor points to its next
1113 // forming the single linked free list, the very first monitor
1114 // will points to next block, which forms the block list.
1115 // The trick of using the 1st element in the block as gBlockList
1116 // linkage should be reconsidered. A better implementation would
1117 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1118
1119 for (int i = 1; i < _BLOCKSIZE; i++) {
1120 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1121 }
1122
1123 // terminate the last monitor as the end of list
1124 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1125
1126 // Element [0] is reserved for global list linkage
1127 temp[0].set_object(CHAINMARKER);
1128
1129 // Consider carving out this thread's current request from the
1130 // block in hand. This avoids some lock traffic and redundant
1131 // list activity.
1132
1133 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1134 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1135 Thread::muxAcquire(&gListLock, "omAlloc(2)");
1136 gMonitorPopulation += _BLOCKSIZE-1;
1137 gMonitorFreeCount += _BLOCKSIZE-1;
1138
1139 // Add the new block to the list of extant blocks (gBlockList).
1140 // The very first objectMonitor in a block is reserved and dedicated.
1143 // There are lock-free uses of gBlockList so make sure that
1144 // the previous stores happen before we update gBlockList.
1145 OrderAccess::release_store(&gBlockList, temp);
1146
1147 // Add the new string of objectMonitors to the global free list
1148 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1149 gFreeList = temp + 1;
1150 Thread::muxRelease(&gListLock);
1151 }
1152 }
1153
1154 // Place "m" on the caller's private per-thread omFreeList.
1155 // In practice there's no need to clamp or limit the number of
1156 // monitors on a thread's omFreeList as the only time we'll call
1157 // omRelease is to return a monitor to the free list after a CAS
1158 // attempt failed. This doesn't allow unbounded #s of monitors to
1159 // accumulate on a thread's free list.
1160 //
1161 // Key constraint: all ObjectMonitors on a thread's free list and the global
1162 // free list must have their object field set to null. This prevents the
1163 // scavenger -- deflate_monitor_list() -- from reclaiming them.
1164
1165 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1166 bool fromPerThreadAlloc) {
1167 guarantee(m->header() == NULL, "invariant");
1168 guarantee(m->object() == NULL, "invariant");
1169 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1170 // Remove from omInUseList
1171 if (fromPerThreadAlloc) {
1172 ObjectMonitor* cur_mid_in_use = NULL;
1173 bool extracted = false;
1174 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1175 if (m == mid) {
1176 // extract from per-thread in-use list
1177 if (mid == Self->omInUseList) {
1178 Self->omInUseList = mid->FreeNext;
1179 } else if (cur_mid_in_use != NULL) {
1180 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1181 }
1182 extracted = true;
1183 Self->omInUseCount--;
1184 break;
1185 }
1186 }
1187 assert(extracted, "Should have extracted from in-use list");
1188 }
1189
1190 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1191 m->FreeNext = Self->omFreeList;
1192 Self->omFreeList = m;
1193 Self->omFreeCount++;
1194 }
1195
1196 // Return the monitors of a moribund thread's local free list to
1197 // the global free list. Typically a thread calls omFlush() when
1198 // it's dying. We could also consider having the VM thread steal
1199 // monitors from threads that have not run java code over a few
1200 // consecutive STW safepoints. Relatedly, we might decay
1201 // omFreeProvision at STW safepoints.
1202 //
1203 // Also return the monitors of a moribund thread's omInUseList to
1204 // a global gOmInUseList under the global list lock so these
1205 // will continue to be scanned.
1206 //
1207 // We currently call omFlush() from Threads::remove() _before the thread
1208 // has been excised from the thread list and is no longer a mutator.
1209 // This means that omFlush() cannot run concurrently with a safepoint and
1210 // interleave with the deflate_idle_monitors scavenge operator. In particular,
1211 // this ensures that the thread's monitors are scanned by a GC safepoint,
1212 // either via Thread::oops_do() (if safepoint happens before omFlush()) or via
1213 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1214 // monitors have been transferred to the global in-use list).
1215
1216 void ObjectSynchronizer::omFlush(Thread * Self) {
1217 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1218 ObjectMonitor * tail = NULL;
1219 int tally = 0;
1220 if (list != NULL) {
1221 ObjectMonitor * s;
1222 // The thread is going away, the per-thread free monitors
1223 // are freed via set_owner(NULL)
1224 // Link them to tail, which will be linked into the global free list
1225 // gFreeList below, under the gListLock
1226 for (s = list; s != NULL; s = s->FreeNext) {
1227 tally++;
1228 tail = s;
1229 guarantee(s->object() == NULL, "invariant");
1230 guarantee(!s->is_busy(), "invariant");
1231 s->set_owner(NULL); // redundant but good hygiene
1232 }
1233 guarantee(tail != NULL, "invariant");
1234 assert(Self->omFreeCount == tally, "free-count off");
1235 Self->omFreeList = NULL;
1236 Self->omFreeCount = 0;
1237 }
1238
1239 ObjectMonitor * inUseList = Self->omInUseList;
1240 ObjectMonitor * inUseTail = NULL;
1241 int inUseTally = 0;
1242 if (inUseList != NULL) {
1243 ObjectMonitor *cur_om;
1244 // The thread is going away, however the omInUseList inflated
1245 // monitors may still be in-use by other threads.
1246 // Link them to inUseTail, which will be linked into the global in-use list
1247 // gOmInUseList below, under the gListLock
1248 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1249 inUseTail = cur_om;
1250 inUseTally++;
1251 }
1252 guarantee(inUseTail != NULL, "invariant");
1253 assert(Self->omInUseCount == inUseTally, "in-use count off");
1254 Self->omInUseList = NULL;
1255 Self->omInUseCount = 0;
1256 }
1257
1258 Thread::muxAcquire(&gListLock, "omFlush");
1259 if (tail != NULL) {
1260 tail->FreeNext = gFreeList;
1261 gFreeList = list;
1262 gMonitorFreeCount += tally;
1263 }
1264
1265 if (inUseTail != NULL) {
1266 inUseTail->FreeNext = gOmInUseList;
1267 gOmInUseList = inUseList;
1268 gOmInUseCount += inUseTally;
1269 }
1270
1271 Thread::muxRelease(&gListLock);
1272
1273 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1281 }
1282 if (ls != NULL) {
1283 ls->print_cr("omFlush: jt=" INTPTR_FORMAT ", free_monitor_tally=%d"
1284 ", in_use_monitor_tally=%d" ", omFreeProvision=%d",
1285 p2i(Self), tally, inUseTally, Self->omFreeProvision);
1286 }
1287 }
1288
1289 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1290 const oop obj,
1291 ObjectSynchronizer::InflateCause cause) {
1292 assert(event != NULL, "invariant");
1293 assert(event->should_commit(), "invariant");
1294 event->set_monitorClass(obj->klass());
1295 event->set_address((uintptr_t)(void*)obj);
1296 event->set_cause((u1)cause);
1297 event->commit();
1298 }
1299
1300 // Fast path code shared by multiple functions
1301 void ObjectSynchronizer::inflate_helper(oop obj) {
1302 markOop mark = obj->mark();
1303 if (mark->has_monitor()) {
1304 assert(ObjectSynchronizer::verify_objmon_isinpool(mark->monitor()), "monitor is invalid");
1305 assert(mark->monitor()->header()->is_neutral(), "monitor must record a good object header");
1306 return;
1307 }
1308 inflate(Thread::current(), obj, inflate_cause_vm_internal);
1309 }
1310
1311 ObjectMonitor* ObjectSynchronizer::inflate(Thread * Self,
1312 oop object,
1313 const InflateCause cause) {
1314 // Inflate mutates the heap ...
1315 // Relaxing assertion for bug 6320749.
1316 assert(Universe::verify_in_progress() ||
1317 !SafepointSynchronize::is_at_safepoint(), "invariant");
1318
1319 EventJavaMonitorInflate event;
1320
1321 for (;;) {
1322 const markOop mark = object->mark();
1323 assert(!mark->has_bias_pattern(), "invariant");
1324
1325 // The mark can be in one of the following states:
1326 // * Inflated - just return
1327 // * Stack-locked - coerce it to inflated
1328 // * INFLATING - busy wait for conversion to complete
1329 // * Neutral - aggressively inflate the object.
1330 // * BIASED - Illegal. We should never see this
1331
1332 // CASE: inflated
1333 if (mark->has_monitor()) {
1334 ObjectMonitor * inf = mark->monitor();
1335 markOop dmw = inf->header();
1336 assert(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1337 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1338 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1339 return inf;
1340 }
1341
1342 // CASE: inflation in progress - inflating over a stack-lock.
1343 // Some other thread is converting from stack-locked to inflated.
1344 // Only that thread can complete inflation -- other threads must wait.
1345 // The INFLATING value is transient.
1346 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1347 // We could always eliminate polling by parking the thread on some auxiliary list.
1348 if (mark == markOopDesc::INFLATING()) {
1349 ReadStableMark(object);
1350 continue;
1351 }
1352
1353 // CASE: stack-locked
1354 // Could be stack-locked either by this thread or by some other thread.
1355 //
1356 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1357 // to install INFLATING into the mark word. We originally installed INFLATING,
1358 // allocated the objectmonitor, and then finally STed the address of the
1359 // objectmonitor into the mark. This was correct, but artificially lengthened
1360 // the interval in which INFLATED appeared in the mark, thus increasing
1361 // the odds of inflation contention.
1362 //
1363 // We now use per-thread private objectmonitor free lists.
1364 // These list are reprovisioned from the global free list outside the
1365 // critical INFLATING...ST interval. A thread can transfer
1366 // multiple objectmonitors en-mass from the global free list to its local free list.
1367 // This reduces coherency traffic and lock contention on the global free list.
1368 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1369 // before or after the CAS(INFLATING) operation.
1370 // See the comments in omAlloc().
1371
1372 LogStreamHandle(Trace, monitorinflation) lsh;
1373
1374 if (mark->has_locker()) {
1375 ObjectMonitor * m = omAlloc(Self);
1376 // Optimistically prepare the objectmonitor - anticipate successful CAS
1377 // We do this before the CAS in order to minimize the length of time
1378 // in which INFLATING appears in the mark.
1379 m->Recycle();
1380 m->_Responsible = NULL;
1381 m->_recursions = 0;
1382 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1383
1384 markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1385 if (cmp != mark) {
1386 omRelease(Self, m, true);
1387 continue; // Interference -- just retry
1388 }
1389
1390 // We've successfully installed INFLATING (0) into the mark-word.
1391 // This is the only case where 0 will appear in a mark-word.
1392 // Only the singular thread that successfully swings the mark-word
1393 // to 0 can perform (or more precisely, complete) inflation.
1394 //
1395 // Why do we CAS a 0 into the mark-word instead of just CASing the
1403 // value from the basiclock on the owner's stack to the objectMonitor, all
1404 // the while preserving the hashCode stability invariants. If the owner
1405 // decides to release the lock while the value is 0, the unlock will fail
1406 // and control will eventually pass from slow_exit() to inflate. The owner
1407 // will then spin, waiting for the 0 value to disappear. Put another way,
1408 // the 0 causes the owner to stall if the owner happens to try to
1409 // drop the lock (restoring the header from the basiclock to the object)
1410 // while inflation is in-progress. This protocol avoids races that might
1411 // would otherwise permit hashCode values to change or "flicker" for an object.
1412 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1413 // 0 serves as a "BUSY" inflate-in-progress indicator.
1414
1415
1416 // fetch the displaced mark from the owner's stack.
1417 // The owner can't die or unwind past the lock while our INFLATING
1418 // object is in the mark. Furthermore the owner can't complete
1419 // an unlock on the object, either.
1420 markOop dmw = mark->displaced_mark_helper();
1421 // Catch if the object's header is not neutral (not locked and
1422 // not marked is what we care about here).
1423 assert(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1424
1425 // Setup monitor fields to proper values -- prepare the monitor
1426 m->set_header(dmw);
1427
1428 // Optimization: if the mark->locker stack address is associated
1429 // with this thread we could simply set m->_owner = Self.
1430 // Note that a thread can inflate an object
1431 // that it has stack-locked -- as might happen in wait() -- directly
1432 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1433 m->set_owner(mark->locker());
1434 m->set_object(object);
1435 // TODO-FIXME: assert BasicLock->dhw != 0.
1436
1437 // Must preserve store ordering. The monitor state must
1438 // be stable at the time of publishing the monitor address.
1439 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1440 object->release_set_mark(markOopDesc::encode(m));
1441
1442 // Hopefully the performance counters are allocated on distinct cache lines
1443 // to avoid false sharing on MP systems ...
1444 OM_PERFDATA_OP(Inflations, inc());
1445 if (log_is_enabled(Trace, monitorinflation)) {
1446 ResourceMark rm(Self);
1447 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1448 INTPTR_FORMAT ", type='%s'", p2i(object),
1449 p2i(object->mark()), object->klass()->external_name());
1450 }
1451 if (event.should_commit()) {
1452 post_monitor_inflate_event(&event, object, cause);
1453 }
1454 return m;
1455 }
1456
1457 // CASE: neutral
1458 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1459 // If we know we're inflating for entry it's better to inflate by swinging a
1460 // pre-locked objectMonitor pointer into the object header. A successful
1461 // CAS inflates the object *and* confers ownership to the inflating thread.
1462 // In the current implementation we use a 2-step mechanism where we CAS()
1463 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1464 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1465 // would be useful.
1466
1467 // Catch if the object's header is not neutral (not locked and
1468 // not marked is what we care about here).
1469 assert(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
1470 ObjectMonitor * m = omAlloc(Self);
1471 // prepare m for installation - set monitor to initial state
1472 m->Recycle();
1473 m->set_header(mark);
1474 m->set_owner(NULL);
1475 m->set_object(object);
1476 m->_recursions = 0;
1477 m->_Responsible = NULL;
1478 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1479
1480 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1481 m->set_header(NULL);
1482 m->set_object(NULL);
1483 m->Recycle();
1484 omRelease(Self, m, true);
1485 m = NULL;
1486 continue;
1487 // interference - the markword changed - just retry.
1488 // The state-transitions are one-way, so there's no chance of
1489 // live-lock -- "Inflated" is an absorbing state.
1490 }
1491
1492 // Hopefully the performance counters are allocated on distinct
1493 // cache lines to avoid false sharing on MP systems ...
1494 OM_PERFDATA_OP(Inflations, inc());
1495 if (log_is_enabled(Trace, monitorinflation)) {
1496 ResourceMark rm(Self);
1497 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1498 INTPTR_FORMAT ", type='%s'", p2i(object),
1499 p2i(object->mark()), object->klass()->external_name());
1500 }
1501 if (event.should_commit()) {
1502 post_monitor_inflate_event(&event, object, cause);
1503 }
1504 return m;
1505 }
1506 }
1507
1508
1509 // We maintain a list of in-use monitors for each thread.
1510 //
1511 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1512 // deflate_idle_monitors() scans only a global list of in-use monitors which
1513 // is populated only as a thread dies (see omFlush()).
1514 //
1515 // These operations are called at all safepoints, immediately after mutators
1516 // are stopped, but before any objects have moved. Collectively they traverse
1517 // the population of in-use monitors, deflating where possible. The scavenged
1518 // monitors are returned to the global monitor free list.
1519 //
1520 // Beware that we scavenge at *every* stop-the-world point. Having a large
1521 // number of monitors in-use could negatively impact performance. We also want
1522 // to minimize the total # of monitors in circulation, as they incur a small
1523 // footprint penalty.
1524 //
1525 // Perversely, the heap size -- and thus the STW safepoint rate --
1526 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1527 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1528 // This is an unfortunate aspect of this design.
1529
1530 // Deflate a single monitor if not in-use
1531 // Return true if deflated, false if in-use
1532 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1533 ObjectMonitor** freeHeadp,
1534 ObjectMonitor** freeTailp) {
1535 bool deflated;
1536 // Normal case ... The monitor is associated with obj.
1537 const markOop mark = obj->mark();
1538 guarantee(mark == markOopDesc::encode(mid), "should match: mark="
1539 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, p2i(mark),
1540 p2i(markOopDesc::encode(mid)));
1541 // Make sure that mark->monitor() and markOopDesc::encode() agree:
1542 guarantee(mark->monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1543 ", mid=" INTPTR_FORMAT, p2i(mark->monitor()), p2i(mid));
1544 const markOop dmw = mid->header();
1545 guarantee(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1546
1547 if (mid->is_busy()) {
1548 deflated = false;
1549 } else {
1550 // Deflate the monitor if it is no longer being used
1551 // It's idle - scavenge and return to the global free list
1552 // plain old deflation ...
1553 if (log_is_enabled(Trace, monitorinflation)) {
1554 ResourceMark rm;
1555 log_trace(monitorinflation)("deflate_monitor: "
1556 "object=" INTPTR_FORMAT ", mark="
1557 INTPTR_FORMAT ", type='%s'", p2i(obj),
1558 p2i(mark), obj->klass()->external_name());
1559 }
1560
1561 // Restore the header back to obj
1562 obj->release_set_mark(dmw);
1563 mid->clear();
1564
1565 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1566 p2i(mid->object()));
1567
1568 // Move the object to the working free list defined by freeHeadp, freeTailp
1569 if (*freeHeadp == NULL) *freeHeadp = mid;
1570 if (*freeTailp != NULL) {
1571 ObjectMonitor * prevtail = *freeTailp;
1572 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1573 prevtail->FreeNext = mid;
1574 }
1575 *freeTailp = mid;
1576 deflated = true;
1577 }
1578 return deflated;
1579 }
1580
1581 // Walk a given monitor list, and deflate idle monitors
1582 // The given list could be a per-thread list or a global list
1583 // Caller acquires gListLock as needed.
1584 //
1585 // In the case of parallel processing of thread local monitor lists,
1586 // work is done by Threads::parallel_threads_do() which ensures that
1587 // each Java thread is processed by exactly one worker thread, and
1588 // thus avoid conflicts that would arise when worker threads would
1589 // process the same monitor lists concurrently.
1590 //
1591 // See also ParallelSPCleanupTask and
1592 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1593 // Threads::parallel_java_threads_do() in thread.cpp.
1594 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1595 ObjectMonitor** freeHeadp,
1596 ObjectMonitor** freeTailp) {
1597 ObjectMonitor* mid;
1598 ObjectMonitor* next;
1599 ObjectMonitor* cur_mid_in_use = NULL;
1600 int deflated_count = 0;
1604 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1605 // if deflate_monitor succeeded,
1606 // extract from per-thread in-use list
1607 if (mid == *listHeadp) {
1608 *listHeadp = mid->FreeNext;
1609 } else if (cur_mid_in_use != NULL) {
1610 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1611 }
1612 next = mid->FreeNext;
1613 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1614 mid = next;
1615 deflated_count++;
1616 } else {
1617 cur_mid_in_use = mid;
1618 mid = mid->FreeNext;
1619 }
1620 }
1621 return deflated_count;
1622 }
1623
1624 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1625 counters->nInuse = 0; // currently associated with objects
1626 counters->nInCirculation = 0; // extant
1627 counters->nScavenged = 0; // reclaimed (global and per-thread)
1628 counters->perThreadScavenged = 0; // per-thread scavenge total
1629 counters->perThreadTimes = 0.0; // per-thread scavenge times
1630 }
1631
1632 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
1633 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1634 bool deflated = false;
1635
1636 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1637 ObjectMonitor * freeTailp = NULL;
1638 elapsedTimer timer;
1639
1640 if (log_is_enabled(Info, monitorinflation)) {
1641 timer.start();
1642 }
1643
1644 // Prevent omFlush from changing mids in Thread dtor's during deflation
1645 // And in case the vm thread is acquiring a lock during a safepoint
1646 // See e.g. 6320749
1647 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
1648
1649 // Note: the thread-local monitors lists get deflated in
1650 // a separate pass. See deflate_thread_local_monitors().
1651
1652 // For moribund threads, scan gOmInUseList
1653 int deflated_count = 0;
1666 // constant-time list splice - prepend scavenged segment to gFreeList
1667 freeTailp->FreeNext = gFreeList;
1668 gFreeList = freeHeadp;
1669 }
1670 Thread::muxRelease(&gListLock);
1671 timer.stop();
1672
1673 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1674 LogStreamHandle(Info, monitorinflation) lsh_info;
1675 LogStream * ls = NULL;
1676 if (log_is_enabled(Debug, monitorinflation)) {
1677 ls = &lsh_debug;
1678 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
1679 ls = &lsh_info;
1680 }
1681 if (ls != NULL) {
1682 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
1683 }
1684 }
1685
1686 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
1687 // Report the cumulative time for deflating each thread's idle
1688 // monitors. Note: if the work is split among more than one
1689 // worker thread, then the reported time will likely be more
1690 // than a beginning to end measurement of the phase.
1691 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->perThreadTimes, counters->perThreadScavenged);
1692
1693 gMonitorFreeCount += counters->nScavenged;
1694
1695 if (log_is_enabled(Debug, monitorinflation)) {
1696 // exit_globals()'s call to audit_and_print_stats() is done
1697 // at the Info level.
1698 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
1699 } else if (log_is_enabled(Info, monitorinflation)) {
1700 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
1701 log_info(monitorinflation)("gMonitorPopulation=%d, gOmInUseCount=%d, "
1702 "gMonitorFreeCount=%d", gMonitorPopulation,
1703 gOmInUseCount, gMonitorFreeCount);
1704 Thread::muxRelease(&gListLock);
1705 }
1706
1707 ForceMonitorScavenge = 0; // Reset
1708
1709 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
1710 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
1711
1712 GVars.stwRandom = os::random();
1713 GVars.stwCycle++;
1714 }
1715
1716 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
1717 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1718
1719 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
1720 ObjectMonitor * freeTailp = NULL;
1721 elapsedTimer timer;
1722
1723 if (log_is_enabled(Info, safepoint, cleanup) ||
1724 log_is_enabled(Info, monitorinflation)) {
1725 timer.start();
1726 }
1727
1728 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
1729
1730 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
1731
1732 // Adjust counters
1733 counters->nInCirculation += thread->omInUseCount;
1734 thread->omInUseCount -= deflated_count;
1735 counters->nScavenged += deflated_count;
1736 counters->nInuse += thread->omInUseCount;
1737 counters->perThreadScavenged += deflated_count;
1738
1907 } else {
1908 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
1909 }
1910
1911 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1912 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1913 // When exiting this log output is at the Info level. When called
1914 // at a safepoint, this log output is at the Trace level since
1915 // there can be a lot of it.
1916 log_in_use_monitor_details(ls, on_exit);
1917 }
1918
1919 ls->flush();
1920
1921 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1922 }
1923
1924 // Check a free monitor entry; log any errors.
1925 void ObjectSynchronizer::chk_free_entry(JavaThread * jt, ObjectMonitor * n,
1926 outputStream * out, int *error_cnt_p) {
1927 if (n->is_busy()) {
1928 if (jt != NULL) {
1929 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1930 ": free per-thread monitor must not be busy.", p2i(jt),
1931 p2i(n));
1932 } else {
1933 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1934 "must not be busy.", p2i(n));
1935 }
1936 *error_cnt_p = *error_cnt_p + 1;
1937 }
1938 if (n->header() != NULL) {
1939 if (jt != NULL) {
1940 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1941 ": free per-thread monitor must have NULL _header "
1942 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
1943 p2i(n->header()));
1944 } else {
1945 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1946 "must have NULL _header field: _header=" INTPTR_FORMAT,
1947 p2i(n), p2i(n->header()));
1948 }
1949 *error_cnt_p = *error_cnt_p + 1;
1950 }
1951 if (n->object() != NULL) {
1952 if (jt != NULL) {
1953 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
1954 ": free per-thread monitor must have NULL _object "
1955 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
1956 p2i(n->object()));
1957 } else {
1958 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
1959 "must have NULL _object field: _object=" INTPTR_FORMAT,
1960 p2i(n), p2i(n->object()));
1961 }
1962 *error_cnt_p = *error_cnt_p + 1;
1963 }
1964 }
1965
1966 // Check the global free list and count; log the results of the checks.
1967 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
1968 int *error_cnt_p) {
1969 int chkMonitorFreeCount = 0;
1970 for (ObjectMonitor * n = gFreeList; n != NULL; n = n->FreeNext) {
2096 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omInUseCount=%d is not "
2097 "equal to chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2098 chkOmInUseCount);
2099 *error_cnt_p = *error_cnt_p + 1;
2100 }
2101 }
2102
2103 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2104 // flags indicate why the entry is in-use, 'object' and 'object type'
2105 // indicate the associated object and its type.
2106 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2107 bool on_exit) {
2108 if (!on_exit) {
2109 // Not at VM exit so grab the global list lock.
2110 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2111 }
2112
2113 if (gOmInUseCount > 0) {
2114 out->print_cr("In-use global monitor info:");
2115 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2116 out->print_cr("%18s %s %18s %18s",
2117 "monitor", "BHL", "object", "object type");
2118 out->print_cr("================== === ================== ==================");
2119 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2120 const oop obj = (oop) n->object();
2121 const markOop mark = n->header();
2122 ResourceMark rm;
2123 out->print_cr(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(n),
2124 n->is_busy() != 0, mark->hash() != 0, n->owner() != NULL,
2125 p2i(obj), obj->klass()->external_name());
2126 }
2127 }
2128
2129 if (!on_exit) {
2130 Thread::muxRelease(&gListLock);
2131 }
2132
2133 out->print_cr("In-use per-thread monitor info:");
2134 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2135 out->print_cr("%18s %18s %s %18s %18s",
2136 "jt", "monitor", "BHL", "object", "object type");
2137 out->print_cr("================== ================== === ================== ==================");
2138 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2139 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2140 const oop obj = (oop) n->object();
2141 const markOop mark = n->header();
2142 ResourceMark rm;
2143 out->print_cr(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT
2144 " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2145 mark->hash() != 0, n->owner() != NULL, p2i(obj),
2146 obj->klass()->external_name());
2147 }
2148 }
2149
2150 out->flush();
2151 }
2152
2153 // Log counts for the global and per-thread monitor lists and return
2154 // the population count.
2155 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2156 int popCount = 0;
2157 out->print_cr("%18s %10s %10s %10s",
2158 "Global Lists:", "InUse", "Free", "Total");
2159 out->print_cr("================== ========== ========== ==========");
2160 out->print_cr("%18s %10d %10d %10d", "",
2161 gOmInUseCount, gMonitorFreeCount, gMonitorPopulation);
2162 popCount += gOmInUseCount + gMonitorFreeCount;
2163
2164 out->print_cr("%18s %10s %10s %10s",
2165 "Per-Thread Lists:", "InUse", "Free", "Provision");
2166 out->print_cr("================== ========== ========== ==========");
|
107 #endif // ndef DTRACE_ENABLED
108
109 // This exists only as a workaround of dtrace bug 6254741
110 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
111 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
112 return 0;
113 }
114
115 #define NINFLATIONLOCKS 256
116 static volatile intptr_t gInflationLocks[NINFLATIONLOCKS];
117
118 // global list of blocks of monitors
119 PaddedEnd<ObjectMonitor> * volatile ObjectSynchronizer::gBlockList = NULL;
120 // global monitor free list
121 ObjectMonitor * volatile ObjectSynchronizer::gFreeList = NULL;
122 // global monitor in-use list, for moribund threads,
123 // monitors they inflated need to be scanned for deflation
124 ObjectMonitor * volatile ObjectSynchronizer::gOmInUseList = NULL;
125 // count of entries in gOmInUseList
126 int ObjectSynchronizer::gOmInUseCount = 0;
127 bool ObjectSynchronizer::_gOmShouldDeflateIdleMonitors = false;
128 bool volatile ObjectSynchronizer::_is_cleanup_requested = false;
129
130 static volatile intptr_t gListLock = 0; // protects global monitor lists
131 static volatile int gMonitorFreeCount = 0; // # on gFreeList
132 static volatile int gMonitorPopulation = 0; // # Extant -- in circulation
133
134 #define CHAINMARKER (cast_to_oop<intptr_t>(-1))
135
136
137 // =====================> Quick functions
138
139 // The quick_* forms are special fast-path variants used to improve
140 // performance. In the simplest case, a "quick_*" implementation could
141 // simply return false, in which case the caller will perform the necessary
142 // state transitions and call the slow-path form.
143 // The fast-path is designed to handle frequently arising cases in an efficient
144 // manner and is just a degenerate "optimistic" variant of the slow-path.
145 // returns true -- to indicate the call was satisfied.
146 // returns false -- to indicate the call needs the services of the slow-path.
147 // A no-loitering ordinance is in effect for code in the quick_* family
148 // operators: safepoints or indefinite blocking (blocking that might span a
195 }
196
197 // biased locking and any other IMS exception states take the slow-path
198 return false;
199 }
200
201
202 // The LockNode emitted directly at the synchronization site would have
203 // been too big if it were to have included support for the cases of inflated
204 // recursive enter and exit, so they go here instead.
205 // Note that we can't safely call AsyncPrintJavaStack() from within
206 // quick_enter() as our thread state remains _in_Java.
207
208 bool ObjectSynchronizer::quick_enter(oop obj, Thread * Self,
209 BasicLock * lock) {
210 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
211 assert(Self->is_Java_thread(), "invariant");
212 assert(((JavaThread *) Self)->thread_state() == _thread_in_Java, "invariant");
213 NoSafepointVerifier nsv;
214 if (obj == NULL) return false; // Need to throw NPE
215
216 while (true) {
217 const markOop mark = obj->mark();
218
219 if (mark->has_monitor()) {
220 ObjectMonitorHandle omh;
221 if (!omh.save_om_ptr(obj, mark)) {
222 // Lost a race with async deflation so try again.
223 assert(AsyncDeflateIdleMonitors, "sanity check");
224 continue;
225 }
226 ObjectMonitor * const m = omh.om_ptr();
227 assert(oopDesc::equals((oop) m->object(), obj), "invariant");
228 Thread * const owner = (Thread *) m->_owner;
229
230 // Lock contention and Transactional Lock Elision (TLE) diagnostics
231 // and observability
232 // Case: light contention possibly amenable to TLE
233 // Case: TLE inimical operations such as nested/recursive synchronization
234
235 if (owner == Self) {
236 m->_recursions++;
237 return true;
238 }
239
240 // This Java Monitor is inflated so obj's header will never be
241 // displaced to this thread's BasicLock. Make the displaced header
242 // non-NULL so this BasicLock is not seen as recursive nor as
243 // being locked. We do this unconditionally so that this thread's
244 // BasicLock cannot be mis-interpreted by any stack walkers. For
245 // performance reasons, stack walkers generally first check for
246 // Biased Locking in the object's header, the second check is for
247 // stack-locking in the object's header, the third check is for
248 // recursive stack-locking in the displaced header in the BasicLock,
249 // and last are the inflated Java Monitor (ObjectMonitor) checks.
250 lock->set_displaced_header(markOopDesc::unused_mark());
251
252 if (owner == NULL && Atomic::replace_if_null(Self, &(m->_owner))) {
253 assert(m->_recursions == 0, "invariant");
254 assert(m->_owner == Self, "invariant");
255 return true;
256 }
257 }
258 break;
259 }
260
261 // Note that we could inflate in quick_enter.
262 // This is likely a useful optimization
263 // Critically, in quick_enter() we must not:
264 // -- perform bias revocation, or
265 // -- block indefinitely, or
266 // -- reach a safepoint
267
268 return false; // revert to slow-path
269 }
270
271 // -----------------------------------------------------------------------------
272 // Fast Monitor Enter/Exit
273 // This the fast monitor enter. The interpreter and compiler use
274 // some assembly copies of this code. Make sure update those code
275 // if the following function is changed. The implementation is
276 // extremely sensitive to race condition. Be careful.
277
278 void ObjectSynchronizer::fast_enter(Handle obj, BasicLock* lock,
279 bool attempt_rebias, TRAPS) {
322 // does not own the Java Monitor.
323 ObjectMonitor * m = mark->monitor();
324 assert(((oop)(m->object()))->mark() == mark, "invariant");
325 assert(m->is_entered(THREAD), "invariant");
326 }
327 }
328 #endif
329 return;
330 }
331
332 if (mark == (markOop) lock) {
333 // If the object is stack-locked by the current thread, try to
334 // swing the displaced header from the BasicLock back to the mark.
335 assert(dhw->is_neutral(), "invariant");
336 if (object->cas_set_mark(dhw, mark) == mark) {
337 return;
338 }
339 }
340
341 // We have to take the slow-path of possible inflation and then exit.
342 ObjectMonitorHandle omh;
343 inflate(&omh, THREAD, object, inflate_cause_vm_internal);
344 omh.om_ptr()->exit(true, THREAD);
345 }
346
347 // -----------------------------------------------------------------------------
348 // Interpreter/Compiler Slow Case
349 // This routine is used to handle interpreter/compiler slow case
350 // We don't need to use fast path here, because it must have been
351 // failed in the interpreter/compiler code.
352 void ObjectSynchronizer::slow_enter(Handle obj, BasicLock* lock, TRAPS) {
353 markOop mark = obj->mark();
354 assert(!mark->has_bias_pattern(), "should not see bias pattern here");
355
356 if (mark->is_neutral()) {
357 // Anticipate successful CAS -- the ST of the displaced mark must
358 // be visible <= the ST performed by the CAS.
359 lock->set_displaced_header(mark);
360 if (mark == obj()->cas_set_mark((markOop) lock, mark)) {
361 return;
362 }
363 // Fall through to inflate() ...
364 } else if (mark->has_locker() &&
365 THREAD->is_lock_owned((address)mark->locker())) {
366 assert(lock != mark->locker(), "must not re-lock the same lock");
367 assert(lock != (BasicLock*)obj->mark(), "don't relock with same BasicLock");
368 lock->set_displaced_header(NULL);
369 return;
370 }
371
372 // The object header will never be displaced to this lock,
373 // so it does not matter what the value is, except that it
374 // must be non-zero to avoid looking like a re-entrant lock,
375 // and must not look locked either.
376 lock->set_displaced_header(markOopDesc::unused_mark());
377 ObjectMonitorHandle omh;
378 inflate(&omh, THREAD, obj(), inflate_cause_monitor_enter);
379 omh.om_ptr()->enter(THREAD);
380 }
381
382 // This routine is used to handle interpreter/compiler slow case
383 // We don't need to use fast path here, because it must have
384 // failed in the interpreter/compiler code. Simply use the heavy
385 // weight monitor should be ok, unless someone find otherwise.
386 void ObjectSynchronizer::slow_exit(oop object, BasicLock* lock, TRAPS) {
387 fast_exit(object, lock, THREAD);
388 }
389
390 // -----------------------------------------------------------------------------
391 // Class Loader support to workaround deadlocks on the class loader lock objects
392 // Also used by GC
393 // complete_exit()/reenter() are used to wait on a nested lock
394 // i.e. to give up an outer lock completely and then re-enter
395 // Used when holding nested locks - lock acquisition order: lock1 then lock2
396 // 1) complete_exit lock1 - saving recursion count
397 // 2) wait on lock2
398 // 3) when notified on lock2, unlock lock2
399 // 4) reenter lock1 with original recursion count
400 // 5) lock lock2
401 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
402 intptr_t ObjectSynchronizer::complete_exit(Handle obj, TRAPS) {
403 if (UseBiasedLocking) {
404 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
405 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
406 }
407
408 ObjectMonitorHandle omh;
409 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
410 intptr_t ret_code = omh.om_ptr()->complete_exit(THREAD);
411 return ret_code;
412 }
413
414 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
415 void ObjectSynchronizer::reenter(Handle obj, intptr_t recursion, TRAPS) {
416 if (UseBiasedLocking) {
417 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
418 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
419 }
420
421 ObjectMonitorHandle omh;
422 inflate(&omh, THREAD, obj(), inflate_cause_vm_internal);
423 omh.om_ptr()->reenter(recursion, THREAD);
424 }
425 // -----------------------------------------------------------------------------
426 // JNI locks on java objects
427 // NOTE: must use heavy weight monitor to handle jni monitor enter
428 void ObjectSynchronizer::jni_enter(Handle obj, TRAPS) {
429 // the current locking is from JNI instead of Java code
430 if (UseBiasedLocking) {
431 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
432 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
433 }
434 THREAD->set_current_pending_monitor_is_from_java(false);
435 ObjectMonitorHandle omh;
436 inflate(&omh, THREAD, obj(), inflate_cause_jni_enter);
437 omh.om_ptr()->enter(THREAD);
438 THREAD->set_current_pending_monitor_is_from_java(true);
439 }
440
441 // NOTE: must use heavy weight monitor to handle jni monitor exit
442 void ObjectSynchronizer::jni_exit(oop obj, Thread* THREAD) {
443 if (UseBiasedLocking) {
444 Handle h_obj(THREAD, obj);
445 BiasedLocking::revoke_and_rebias(h_obj, false, THREAD);
446 obj = h_obj();
447 }
448 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
449
450 ObjectMonitorHandle omh;
451 inflate(&omh, THREAD, obj, inflate_cause_jni_exit);
452 ObjectMonitor * monitor = omh.om_ptr();
453 // If this thread has locked the object, exit the monitor. Note: can't use
454 // monitor->check(CHECK); must exit even if an exception is pending.
455 if (monitor->check(THREAD)) {
456 monitor->exit(true, THREAD);
457 }
458 }
459
460 // -----------------------------------------------------------------------------
461 // Internal VM locks on java objects
462 // standard constructor, allows locking failures
463 ObjectLocker::ObjectLocker(Handle obj, Thread* thread, bool doLock) {
464 _dolock = doLock;
465 _thread = thread;
466 debug_only(if (StrictSafepointChecks) _thread->check_for_valid_safepoint_state(false);)
467 _obj = obj;
468
469 if (_dolock) {
470 ObjectSynchronizer::fast_enter(_obj, &_lock, false, _thread);
471 }
472 }
473
474 ObjectLocker::~ObjectLocker() {
475 if (_dolock) {
476 ObjectSynchronizer::fast_exit(_obj(), &_lock, _thread);
477 }
478 }
479
480
481 // -----------------------------------------------------------------------------
482 // Wait/Notify/NotifyAll
483 // NOTE: must use heavy weight monitor to handle wait()
484 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
485 if (UseBiasedLocking) {
486 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
487 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
488 }
489 if (millis < 0) {
490 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
491 }
492 ObjectMonitorHandle omh;
493 inflate(&omh, THREAD, obj(), inflate_cause_wait);
494 ObjectMonitor * monitor = omh.om_ptr();
495
496 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), THREAD, millis);
497 monitor->wait(millis, true, THREAD);
498
499 // This dummy call is in place to get around dtrace bug 6254741. Once
500 // that's fixed we can uncomment the following line, remove the call
501 // and change this function back into a "void" func.
502 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
503 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
504 return ret_code;
505 }
506
507 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
508 if (UseBiasedLocking) {
509 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
510 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
511 }
512 if (millis < 0) {
513 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
514 }
515 ObjectMonitorHandle omh;
516 inflate(&omh, THREAD, obj(), inflate_cause_wait);
517 omh.om_ptr()->wait(millis, false, THREAD);
518 }
519
520 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
521 if (UseBiasedLocking) {
522 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
523 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
524 }
525
526 markOop mark = obj->mark();
527 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
528 return;
529 }
530 ObjectMonitorHandle omh;
531 inflate(&omh, THREAD, obj(), inflate_cause_notify);
532 omh.om_ptr()->notify(THREAD);
533 }
534
535 // NOTE: see comment of notify()
536 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
537 if (UseBiasedLocking) {
538 BiasedLocking::revoke_and_rebias(obj, false, THREAD);
539 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
540 }
541
542 markOop mark = obj->mark();
543 if (mark->has_locker() && THREAD->is_lock_owned((address)mark->locker())) {
544 return;
545 }
546 ObjectMonitorHandle omh;
547 inflate(&omh, THREAD, obj(), inflate_cause_notify);
548 omh.om_ptr()->notifyAll(THREAD);
549 }
550
551 // -----------------------------------------------------------------------------
552 // Hash Code handling
553 //
554 // Performance concern:
555 // OrderAccess::storestore() calls release() which at one time stored 0
556 // into the global volatile OrderAccess::dummy variable. This store was
557 // unnecessary for correctness. Many threads storing into a common location
558 // causes considerable cache migration or "sloshing" on large SMP systems.
559 // As such, I avoided using OrderAccess::storestore(). In some cases
560 // OrderAccess::fence() -- which incurs local latency on the executing
561 // processor -- is a better choice as it scales on SMP systems.
562 //
563 // See http://blogs.oracle.com/dave/entry/biased_locking_in_hotspot for
564 // a discussion of coherency costs. Note that all our current reference
565 // platforms provide strong ST-ST order, so the issue is moot on IA32,
566 // x64, and SPARC.
567 //
568 // As a general policy we use "volatile" to control compiler-based reordering
722 Handle hobj(Self, obj);
723 // Relaxing assertion for bug 6320749.
724 assert(Universe::verify_in_progress() ||
725 !SafepointSynchronize::is_at_safepoint(),
726 "biases should not be seen by VM thread here");
727 BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
728 obj = hobj();
729 assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
730 }
731 }
732
733 // hashCode() is a heap mutator ...
734 // Relaxing assertion for bug 6320749.
735 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
736 !SafepointSynchronize::is_at_safepoint(), "invariant");
737 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
738 Self->is_Java_thread() , "invariant");
739 assert(Universe::verify_in_progress() || DumpSharedSpaces ||
740 ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant");
741
742 while (true) {
743 ObjectMonitor* monitor = NULL;
744 markOop temp, test;
745 intptr_t hash;
746 markOop mark = ReadStableMark(obj);
747
748 // object should remain ineligible for biased locking
749 assert(!mark->has_bias_pattern(), "invariant");
750
751 if (mark->is_neutral()) {
752 hash = mark->hash(); // this is a normal header
753 if (hash != 0) { // if it has hash, just return it
754 return hash;
755 }
756 hash = get_next_hash(Self, obj); // allocate a new hash code
757 temp = mark->copy_set_hash(hash); // merge the hash code into header
758 // use (machine word version) atomic operation to install the hash
759 test = obj->cas_set_mark(temp, mark);
760 if (test == mark) {
761 return hash;
762 }
763 // If atomic operation failed, we must inflate the header
764 // into heavy weight monitor. We could add more code here
765 // for fast path, but it does not worth the complexity.
766 } else if (mark->has_monitor()) {
767 ObjectMonitorHandle omh;
768 if (!omh.save_om_ptr(obj, mark)) {
769 // Lost a race with async deflation so try again.
770 assert(AsyncDeflateIdleMonitors, "sanity check");
771 continue;
772 }
773 monitor = omh.om_ptr();
774 temp = monitor->header();
775 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
776 hash = temp->hash();
777 if (hash != 0) {
778 return hash;
779 }
780 // Skip to the following code to reduce code size
781 } else if (Self->is_lock_owned((address)mark->locker())) {
782 temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
783 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
784 hash = temp->hash(); // by current thread, check if the displaced
785 if (hash != 0) { // header contains hash code
786 return hash;
787 }
788 // WARNING:
789 // The displaced header in the BasicLock on a thread's stack
790 // is strictly immutable. It CANNOT be changed in ANY cases.
791 // So we have to inflate the stack lock into an ObjectMonitor
792 // even if the current thread owns the lock. The BasicLock on
793 // a thread's stack can be asynchronously read by other threads
794 // during an inflate() call so any change to that stack memory
795 // may not propagate to other threads correctly.
796 }
797
798 // Inflate the monitor to set hash code
799 ObjectMonitorHandle omh;
800 inflate(&omh, Self, obj, inflate_cause_hash_code);
801 monitor = omh.om_ptr();
802 // Load displaced header and check it has hash code
803 mark = monitor->header();
804 assert(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
805 hash = mark->hash();
806 if (hash == 0) {
807 hash = get_next_hash(Self, obj);
808 temp = mark->copy_set_hash(hash); // merge hash code into header
809 assert(temp->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(temp));
810 test = Atomic::cmpxchg(temp, monitor->header_addr(), mark);
811 if (test != mark) {
812 // The only non-deflation update to the ObjectMonitor's
813 // header/dmw field is to merge in the hash code. If someone
814 // adds a new usage of the header/dmw field, please update
815 // this code.
816 // ObjectMonitor::install_displaced_markword_in_object()
817 // does mark the header/dmw field as part of async deflation,
818 // but that protocol cannot happen now due to the
819 // ObjectMonitorHandle above.
820 hash = test->hash();
821 assert(test->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(test));
822 assert(hash != 0, "Trivial unexpected object/monitor header usage.");
823 }
824 }
825 // We finally get the hash
826 return hash;
827 }
828 }
829
830 // Deprecated -- use FastHashCode() instead.
831
832 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
833 return FastHashCode(Thread::current(), obj());
834 }
835
836
837 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* thread,
838 Handle h_obj) {
839 if (UseBiasedLocking) {
840 BiasedLocking::revoke_and_rebias(h_obj, false, thread);
841 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
842 }
843
844 assert(thread == JavaThread::current(), "Can only be called on current thread");
845 oop obj = h_obj();
846
847 while (true) {
848 markOop mark = ReadStableMark(obj);
849
850 // Uncontended case, header points to stack
851 if (mark->has_locker()) {
852 return thread->is_lock_owned((address)mark->locker());
853 }
854 // Contended case, header points to ObjectMonitor (tagged pointer)
855 if (mark->has_monitor()) {
856 ObjectMonitorHandle omh;
857 if (!omh.save_om_ptr(obj, mark)) {
858 // Lost a race with async deflation so try again.
859 assert(AsyncDeflateIdleMonitors, "sanity check");
860 continue;
861 }
862 bool ret_code = omh.om_ptr()->is_entered(thread) != 0;
863 return ret_code;
864 }
865 // Unlocked case, header in place
866 assert(mark->is_neutral(), "sanity check");
867 return false;
868 }
869 }
870
871 // Be aware of this method could revoke bias of the lock object.
872 // This method queries the ownership of the lock handle specified by 'h_obj'.
873 // If the current thread owns the lock, it returns owner_self. If no
874 // thread owns the lock, it returns owner_none. Otherwise, it will return
875 // owner_other.
876 ObjectSynchronizer::LockOwnership ObjectSynchronizer::query_lock_ownership
877 (JavaThread *self, Handle h_obj) {
878 // The caller must beware this method can revoke bias, and
879 // revocation can result in a safepoint.
880 assert(!SafepointSynchronize::is_at_safepoint(), "invariant");
881 assert(self->thread_state() != _thread_blocked, "invariant");
882
883 // Possible mark states: neutral, biased, stack-locked, inflated
884
885 if (UseBiasedLocking && h_obj()->mark()->has_bias_pattern()) {
886 // CASE: biased
887 BiasedLocking::revoke_and_rebias(h_obj, false, self);
888 assert(!h_obj->mark()->has_bias_pattern(),
889 "biases should be revoked by now");
890 }
891
892 assert(self == JavaThread::current(), "Can only be called on current thread");
893 oop obj = h_obj();
894
895 while (true) {
896 markOop mark = ReadStableMark(obj);
897
898 // CASE: stack-locked. Mark points to a BasicLock on the owner's stack.
899 if (mark->has_locker()) {
900 return self->is_lock_owned((address)mark->locker()) ?
901 owner_self : owner_other;
902 }
903
904 // CASE: inflated. Mark (tagged pointer) points to an ObjectMonitor.
905 // The Object:ObjectMonitor relationship is stable as long as we're
906 // not at a safepoint and AsyncDeflateIdleMonitors is false.
907 if (mark->has_monitor()) {
908 ObjectMonitorHandle omh;
909 if (!omh.save_om_ptr(obj, mark)) {
910 // Lost a race with async deflation so try again.
911 assert(AsyncDeflateIdleMonitors, "sanity check");
912 continue;
913 }
914 ObjectMonitor * monitor = omh.om_ptr();
915 void * owner = monitor->_owner;
916 if (owner == NULL) return owner_none;
917 return (owner == self ||
918 self->is_lock_owned((address)owner)) ? owner_self : owner_other;
919 }
920
921 // CASE: neutral
922 assert(mark->is_neutral(), "sanity check");
923 return owner_none; // it's unlocked
924 }
925 }
926
927 // FIXME: jvmti should call this
928 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
929 if (UseBiasedLocking) {
930 if (SafepointSynchronize::is_at_safepoint()) {
931 BiasedLocking::revoke_at_safepoint(h_obj);
932 } else {
933 BiasedLocking::revoke_and_rebias(h_obj, false, JavaThread::current());
934 }
935 assert(!h_obj->mark()->has_bias_pattern(), "biases should be revoked by now");
936 }
937
938 oop obj = h_obj();
939
940 while (true) {
941 address owner = NULL;
942 markOop mark = ReadStableMark(obj);
943
944 // Uncontended case, header points to stack
945 if (mark->has_locker()) {
946 owner = (address) mark->locker();
947 }
948
949 // Contended case, header points to ObjectMonitor (tagged pointer)
950 else if (mark->has_monitor()) {
951 ObjectMonitorHandle omh;
952 if (!omh.save_om_ptr(obj, mark)) {
953 // Lost a race with async deflation so try again.
954 assert(AsyncDeflateIdleMonitors, "sanity check");
955 continue;
956 }
957 ObjectMonitor* monitor = omh.om_ptr();
958 assert(monitor != NULL, "monitor should be non-null");
959 owner = (address) monitor->owner();
960 }
961
962 if (owner != NULL) {
963 // owning_thread_from_monitor_owner() may also return NULL here
964 return Threads::owning_thread_from_monitor_owner(t_list, owner);
965 }
966
967 // Unlocked case, header in place
968 // Cannot have assertion since this object may have been
969 // locked by another thread when reaching here.
970 // assert(mark->is_neutral(), "sanity check");
971
972 return NULL;
973 }
974 }
975
976 // Visitors ...
977
978 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure) {
979 PaddedEnd<ObjectMonitor> * block = OrderAccess::load_acquire(&gBlockList);
980 while (block != NULL) {
981 assert(block->object() == CHAINMARKER, "must be a block header");
982 for (int i = _BLOCKSIZE - 1; i > 0; i--) {
983 ObjectMonitor* mid = (ObjectMonitor *)(block + i);
984 if (mid->is_active()) {
985 ObjectMonitorHandle omh(mid);
986
987 if (mid->object() == NULL ||
988 (AsyncDeflateIdleMonitors && mid->_owner == DEFLATER_MARKER)) {
989 // Only process with closure if the object is set.
990 // For async deflation, race here if monitor is not owned!
991 // The above ref_count bump (in ObjectMonitorHandle ctr)
992 // will cause subsequent async deflation to skip it.
993 // However, previous or concurrent async deflation is a race.
994 continue;
995 }
996 closure->do_monitor(mid);
997 }
998 }
999 block = (PaddedEnd<ObjectMonitor> *)block->FreeNext;
1000 }
1001 }
1002
1003 // Get the next block in the block list.
1004 static inline PaddedEnd<ObjectMonitor>* next(PaddedEnd<ObjectMonitor>* block) {
1005 assert(block->object() == CHAINMARKER, "must be a block header");
1006 block = (PaddedEnd<ObjectMonitor>*) block->FreeNext;
1007 assert(block == NULL || block->object() == CHAINMARKER, "must be a block header");
1008 return block;
1009 }
1010
1011 static bool monitors_used_above_threshold() {
1012 if (gMonitorPopulation == 0) {
1013 return false;
1014 }
1015 int monitors_used = gMonitorPopulation - gMonitorFreeCount;
1086 // See also: GuaranteedSafepointInterval
1087 //
1088 // The current implementation uses asynchronous VM operations.
1089
1090 static void InduceScavenge(Thread * Self, const char * Whence) {
1091 // Induce STW safepoint to trim monitors
1092 // Ultimately, this results in a call to deflate_idle_monitors() in the near future.
1093 // More precisely, trigger an asynchronous STW safepoint as the number
1094 // of active monitors passes the specified threshold.
1095 // TODO: assert thread state is reasonable
1096
1097 if (ForceMonitorScavenge == 0 && Atomic::xchg (1, &ForceMonitorScavenge) == 0) {
1098 // Induce a 'null' safepoint to scavenge monitors
1099 // Must VM_Operation instance be heap allocated as the op will be enqueue and posted
1100 // to the VMthread and have a lifespan longer than that of this activation record.
1101 // The VMThread will delete the op when completed.
1102 VMThread::execute(new VM_ScavengeMonitors());
1103 }
1104 }
1105
1106 ObjectMonitor* ObjectSynchronizer::omAlloc(Thread * Self,
1107 const InflateCause cause) {
1108 // A large MAXPRIVATE value reduces both list lock contention
1109 // and list coherency traffic, but also tends to increase the
1110 // number of objectMonitors in circulation as well as the STW
1111 // scavenge costs. As usual, we lean toward time in space-time
1112 // tradeoffs.
1113 const int MAXPRIVATE = 1024;
1114
1115 if (AsyncDeflateIdleMonitors) {
1116 JavaThread * jt = (JavaThread *)Self;
1117 if (jt->omShouldDeflateIdleMonitors && jt->omInUseCount > 0 &&
1118 cause != inflate_cause_vm_internal) {
1119 // Deflate any per-thread idle monitors for this JavaThread if
1120 // this is not an internal inflation. Clean up your own mess.
1121 // (Gibbs Rule 45) Otherwise, skip this cleanup.
1122 // deflate_global_idle_monitors_using_JT() is called by the ServiceThread.
1123 debug_only(jt->check_for_valid_safepoint_state(false);)
1124 ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT();
1125 }
1126 }
1127
1128 for (;;) {
1129 ObjectMonitor * m;
1130
1131 // 1: try to allocate from the thread's local omFreeList.
1132 // Threads will attempt to allocate first from their local list, then
1133 // from the global list, and only after those attempts fail will the thread
1134 // attempt to instantiate new monitors. Thread-local free lists take
1135 // heat off the gListLock and improve allocation latency, as well as reducing
1136 // coherency traffic on the shared global list.
1137 m = Self->omFreeList;
1138 if (m != NULL) {
1139 Self->omFreeList = m->FreeNext;
1140 Self->omFreeCount--;
1141 guarantee(m->object() == NULL, "invariant");
1142 m->set_allocation_state(ObjectMonitor::New);
1143 m->FreeNext = Self->omInUseList;
1144 Self->omInUseList = m;
1145 Self->omInUseCount++;
1146 return m;
1147 }
1148
1149 // 2: try to allocate from the global gFreeList
1150 // CONSIDER: use muxTry() instead of muxAcquire().
1151 // If the muxTry() fails then drop immediately into case 3.
1152 // If we're using thread-local free lists then try
1153 // to reprovision the caller's free list.
1154 if (gFreeList != NULL) {
1155 // Reprovision the thread's omFreeList.
1156 // Use bulk transfers to reduce the allocation rate and heat
1157 // on various locks.
1158 Thread::muxAcquire(&gListLock, "omAlloc(1)");
1159 for (int i = Self->omFreeProvision; --i >= 0 && gFreeList != NULL;) {
1160 gMonitorFreeCount--;
1161 ObjectMonitor * take = gFreeList;
1162 gFreeList = take->FreeNext;
1163 guarantee(take->object() == NULL, "invariant");
1164 if (AsyncDeflateIdleMonitors) {
1165 // Clear any values we allowed to linger during async deflation.
1166 take->_header = NULL;
1167 take->set_owner(NULL);
1168
1169 if (take->ref_count() < 0) {
1170 // Add back max_jint to restore the ref_count field to its
1171 // proper value.
1172 Atomic::add(max_jint, &take->_ref_count);
1173
1174 assert(take->ref_count() >= 0, "must not be negative: ref_count=%d",
1175 take->ref_count());
1176 }
1177 }
1178 guarantee(!take->is_busy(), "invariant");
1179 take->Recycle();
1180 assert(take->is_free(), "invariant");
1181 omRelease(Self, take, false);
1182 }
1183 Thread::muxRelease(&gListLock);
1184 Self->omFreeProvision += 1 + (Self->omFreeProvision/2);
1185 if (Self->omFreeProvision > MAXPRIVATE) Self->omFreeProvision = MAXPRIVATE;
1186
1187 const int mx = MonitorBound;
1188 if (mx > 0 && (gMonitorPopulation-gMonitorFreeCount) > mx) {
1189 // We can't safely induce a STW safepoint from omAlloc() as our thread
1190 // state may not be appropriate for such activities and callers may hold
1191 // naked oops, so instead we defer the action.
1192 InduceScavenge(Self, "omAlloc");
1193 }
1194 continue;
1195 }
1196
1197 // 3: allocate a block of new ObjectMonitors
1198 // Both the local and global free lists are empty -- resort to malloc().
1199 // In the current implementation objectMonitors are TSM - immortal.
1200 // Ideally, we'd write "new ObjectMonitor[_BLOCKSIZE], but we want
1213
1214 // NOTE: (almost) no way to recover if allocation failed.
1215 // We might be able to induce a STW safepoint and scavenge enough
1216 // objectMonitors to permit progress.
1217 if (temp == NULL) {
1218 vm_exit_out_of_memory(neededsize, OOM_MALLOC_ERROR,
1219 "Allocate ObjectMonitors");
1220 }
1221 (void)memset((void *) temp, 0, neededsize);
1222
1223 // Format the block.
1224 // initialize the linked list, each monitor points to its next
1225 // forming the single linked free list, the very first monitor
1226 // will points to next block, which forms the block list.
1227 // The trick of using the 1st element in the block as gBlockList
1228 // linkage should be reconsidered. A better implementation would
1229 // look like: class Block { Block * next; int N; ObjectMonitor Body [N] ; }
1230
1231 for (int i = 1; i < _BLOCKSIZE; i++) {
1232 temp[i].FreeNext = (ObjectMonitor *)&temp[i+1];
1233 assert(temp[i].is_free(), "invariant");
1234 }
1235
1236 // terminate the last monitor as the end of list
1237 temp[_BLOCKSIZE - 1].FreeNext = NULL;
1238
1239 // Element [0] is reserved for global list linkage
1240 temp[0].set_object(CHAINMARKER);
1241
1242 // Consider carving out this thread's current request from the
1243 // block in hand. This avoids some lock traffic and redundant
1244 // list activity.
1245
1246 // Acquire the gListLock to manipulate gBlockList and gFreeList.
1247 // An Oyama-Taura-Yonezawa scheme might be more efficient.
1248 Thread::muxAcquire(&gListLock, "omAlloc(2)");
1249 gMonitorPopulation += _BLOCKSIZE-1;
1250 gMonitorFreeCount += _BLOCKSIZE-1;
1251
1252 // Add the new block to the list of extant blocks (gBlockList).
1253 // The very first objectMonitor in a block is reserved and dedicated.
1256 // There are lock-free uses of gBlockList so make sure that
1257 // the previous stores happen before we update gBlockList.
1258 OrderAccess::release_store(&gBlockList, temp);
1259
1260 // Add the new string of objectMonitors to the global free list
1261 temp[_BLOCKSIZE - 1].FreeNext = gFreeList;
1262 gFreeList = temp + 1;
1263 Thread::muxRelease(&gListLock);
1264 }
1265 }
1266
1267 // Place "m" on the caller's private per-thread omFreeList.
1268 // In practice there's no need to clamp or limit the number of
1269 // monitors on a thread's omFreeList as the only time we'll call
1270 // omRelease is to return a monitor to the free list after a CAS
1271 // attempt failed. This doesn't allow unbounded #s of monitors to
1272 // accumulate on a thread's free list.
1273 //
1274 // Key constraint: all ObjectMonitors on a thread's free list and the global
1275 // free list must have their object field set to null. This prevents the
1276 // scavenger -- deflate_monitor_list() or deflate_monitor_list_using_JT()
1277 // -- from reclaiming them while we are trying to release them.
1278
1279 void ObjectSynchronizer::omRelease(Thread * Self, ObjectMonitor * m,
1280 bool fromPerThreadAlloc) {
1281 guarantee(m->header() == NULL, "invariant");
1282 guarantee(m->object() == NULL, "invariant");
1283 guarantee(((m->is_busy()|m->_recursions) == 0), "freeing in-use monitor");
1284 m->set_allocation_state(ObjectMonitor::Free);
1285 // Remove from omInUseList
1286 if (fromPerThreadAlloc) {
1287 ObjectMonitor* cur_mid_in_use = NULL;
1288 bool extracted = false;
1289 for (ObjectMonitor* mid = Self->omInUseList; mid != NULL; cur_mid_in_use = mid, mid = mid->FreeNext) {
1290 if (m == mid) {
1291 // extract from per-thread in-use list
1292 if (mid == Self->omInUseList) {
1293 Self->omInUseList = mid->FreeNext;
1294 } else if (cur_mid_in_use != NULL) {
1295 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1296 }
1297 extracted = true;
1298 Self->omInUseCount--;
1299 break;
1300 }
1301 }
1302 assert(extracted, "Should have extracted from in-use list");
1303 }
1304
1305 // FreeNext is used for both omInUseList and omFreeList, so clear old before setting new
1306 m->FreeNext = Self->omFreeList;
1307 guarantee(m->is_free(), "invariant");
1308 Self->omFreeList = m;
1309 Self->omFreeCount++;
1310 }
1311
1312 // Return the monitors of a moribund thread's local free list to
1313 // the global free list. Typically a thread calls omFlush() when
1314 // it's dying. We could also consider having the VM thread steal
1315 // monitors from threads that have not run java code over a few
1316 // consecutive STW safepoints. Relatedly, we might decay
1317 // omFreeProvision at STW safepoints.
1318 //
1319 // Also return the monitors of a moribund thread's omInUseList to
1320 // a global gOmInUseList under the global list lock so these
1321 // will continue to be scanned.
1322 //
1323 // We currently call omFlush() from Threads::remove() _before the thread
1324 // has been excised from the thread list and is no longer a mutator.
1325 // This means that omFlush() cannot run concurrently with a safepoint and
1326 // interleave with the deflate_idle_monitors scavenge operator. In particular,
1327 // this ensures that the thread's monitors are scanned by a GC safepoint,
1328 // either via Thread::oops_do() (if safepoint happens before omFlush()) or via
1329 // ObjectSynchronizer::oops_do() (if it happens after omFlush() and the thread's
1330 // monitors have been transferred to the global in-use list).
1331 //
1332 // With AsyncDeflateIdleMonitors, deflate_global_idle_monitors_using_JT()
1333 // and deflate_per_thread_idle_monitors_using_JT() (in another thread) can
1334 // run at the same time as omFlush() so we have to be careful.
1335
1336 void ObjectSynchronizer::omFlush(Thread * Self) {
1337 ObjectMonitor * list = Self->omFreeList; // Null-terminated SLL
1338 ObjectMonitor * tail = NULL;
1339 int tally = 0;
1340 if (list != NULL) {
1341 ObjectMonitor * s;
1342 // The thread is going away, the per-thread free monitors
1343 // are freed via set_owner(NULL)
1344 // Link them to tail, which will be linked into the global free list
1345 // gFreeList below, under the gListLock
1346 for (s = list; s != NULL; s = s->FreeNext) {
1347 tally++;
1348 tail = s;
1349 guarantee(s->object() == NULL, "invariant");
1350 guarantee(!s->is_busy(), "invariant");
1351 s->set_owner(NULL); // redundant but good hygiene
1352 }
1353 guarantee(tail != NULL, "invariant");
1354 ADIM_guarantee(Self->omFreeCount == tally, "free-count off");
1355 Self->omFreeList = NULL;
1356 Self->omFreeCount = 0;
1357 }
1358
1359 ObjectMonitor * inUseList = Self->omInUseList;
1360 ObjectMonitor * inUseTail = NULL;
1361 int inUseTally = 0;
1362 if (inUseList != NULL) {
1363 ObjectMonitor *cur_om;
1364 // The thread is going away, however the omInUseList inflated
1365 // monitors may still be in-use by other threads.
1366 // Link them to inUseTail, which will be linked into the global in-use list
1367 // gOmInUseList below, under the gListLock
1368 for (cur_om = inUseList; cur_om != NULL; cur_om = cur_om->FreeNext) {
1369 inUseTail = cur_om;
1370 inUseTally++;
1371 ADIM_guarantee(cur_om->is_active(), "invariant");
1372 }
1373 guarantee(inUseTail != NULL, "invariant");
1374 ADIM_guarantee(Self->omInUseCount == inUseTally, "in-use count off");
1375 Self->omInUseList = NULL;
1376 Self->omInUseCount = 0;
1377 }
1378
1379 Thread::muxAcquire(&gListLock, "omFlush");
1380 if (tail != NULL) {
1381 tail->FreeNext = gFreeList;
1382 gFreeList = list;
1383 gMonitorFreeCount += tally;
1384 }
1385
1386 if (inUseTail != NULL) {
1387 inUseTail->FreeNext = gOmInUseList;
1388 gOmInUseList = inUseList;
1389 gOmInUseCount += inUseTally;
1390 }
1391
1392 Thread::muxRelease(&gListLock);
1393
1394 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1402 }
1403 if (ls != NULL) {
1404 ls->print_cr("omFlush: jt=" INTPTR_FORMAT ", free_monitor_tally=%d"
1405 ", in_use_monitor_tally=%d" ", omFreeProvision=%d",
1406 p2i(Self), tally, inUseTally, Self->omFreeProvision);
1407 }
1408 }
1409
1410 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1411 const oop obj,
1412 ObjectSynchronizer::InflateCause cause) {
1413 assert(event != NULL, "invariant");
1414 assert(event->should_commit(), "invariant");
1415 event->set_monitorClass(obj->klass());
1416 event->set_address((uintptr_t)(void*)obj);
1417 event->set_cause((u1)cause);
1418 event->commit();
1419 }
1420
1421 // Fast path code shared by multiple functions
1422 void ObjectSynchronizer::inflate_helper(ObjectMonitorHandle * omh_p, oop obj) {
1423 while (true) {
1424 markOop mark = obj->mark();
1425 if (mark->has_monitor()) {
1426 if (!omh_p->save_om_ptr(obj, mark)) {
1427 // Lost a race with async deflation so try again.
1428 assert(AsyncDeflateIdleMonitors, "sanity check");
1429 continue;
1430 }
1431 ObjectMonitor * monitor = omh_p->om_ptr();
1432 assert(ObjectSynchronizer::verify_objmon_isinpool(monitor), "monitor is invalid");
1433 markOop dmw = monitor->header();
1434 assert(dmw->is_neutral(), "sanity check: header=" INTPTR_FORMAT, p2i(dmw));
1435 return;
1436 }
1437 inflate(omh_p, Thread::current(), obj, inflate_cause_vm_internal);
1438 return;
1439 }
1440 }
1441
1442 void ObjectSynchronizer::inflate(ObjectMonitorHandle * omh_p, Thread * Self,
1443 oop object, const InflateCause cause) {
1444 // Inflate mutates the heap ...
1445 // Relaxing assertion for bug 6320749.
1446 assert(Universe::verify_in_progress() ||
1447 !SafepointSynchronize::is_at_safepoint(), "invariant");
1448
1449 EventJavaMonitorInflate event;
1450
1451 for (;;) {
1452 const markOop mark = object->mark();
1453 assert(!mark->has_bias_pattern(), "invariant");
1454
1455 // The mark can be in one of the following states:
1456 // * Inflated - just return
1457 // * Stack-locked - coerce it to inflated
1458 // * INFLATING - busy wait for conversion to complete
1459 // * Neutral - aggressively inflate the object.
1460 // * BIASED - Illegal. We should never see this
1461
1462 // CASE: inflated
1463 if (mark->has_monitor()) {
1464 if (!omh_p->save_om_ptr(object, mark)) {
1465 // Lost a race with async deflation so try again.
1466 assert(AsyncDeflateIdleMonitors, "sanity check");
1467 continue;
1468 }
1469 ObjectMonitor * inf = omh_p->om_ptr();
1470 markOop dmw = inf->header();
1471 assert(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1472 assert(oopDesc::equals((oop) inf->object(), object), "invariant");
1473 assert(ObjectSynchronizer::verify_objmon_isinpool(inf), "monitor is invalid");
1474 return;
1475 }
1476
1477 // CASE: inflation in progress - inflating over a stack-lock.
1478 // Some other thread is converting from stack-locked to inflated.
1479 // Only that thread can complete inflation -- other threads must wait.
1480 // The INFLATING value is transient.
1481 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1482 // We could always eliminate polling by parking the thread on some auxiliary list.
1483 if (mark == markOopDesc::INFLATING()) {
1484 ReadStableMark(object);
1485 continue;
1486 }
1487
1488 // CASE: stack-locked
1489 // Could be stack-locked either by this thread or by some other thread.
1490 //
1491 // Note that we allocate the objectmonitor speculatively, _before_ attempting
1492 // to install INFLATING into the mark word. We originally installed INFLATING,
1493 // allocated the objectmonitor, and then finally STed the address of the
1494 // objectmonitor into the mark. This was correct, but artificially lengthened
1495 // the interval in which INFLATED appeared in the mark, thus increasing
1496 // the odds of inflation contention.
1497 //
1498 // We now use per-thread private objectmonitor free lists.
1499 // These list are reprovisioned from the global free list outside the
1500 // critical INFLATING...ST interval. A thread can transfer
1501 // multiple objectmonitors en-mass from the global free list to its local free list.
1502 // This reduces coherency traffic and lock contention on the global free list.
1503 // Using such local free lists, it doesn't matter if the omAlloc() call appears
1504 // before or after the CAS(INFLATING) operation.
1505 // See the comments in omAlloc().
1506
1507 LogStreamHandle(Trace, monitorinflation) lsh;
1508
1509 if (mark->has_locker()) {
1510 ObjectMonitor * m;
1511 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1512 // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1513 // we won't stop for a potential safepoint in omAlloc.
1514 m = omAlloc(Self, cause);
1515 } else {
1516 // If AsyncDeflateIdleMonitors and not an internal inflation, then
1517 // we may stop for a safepoint in omAlloc() so protect object.
1518 Handle h_obj(Self, object);
1519 m = omAlloc(Self, cause);
1520 object = h_obj(); // Refresh object.
1521 }
1522 // Optimistically prepare the objectmonitor - anticipate successful CAS
1523 // We do this before the CAS in order to minimize the length of time
1524 // in which INFLATING appears in the mark.
1525 m->Recycle();
1526 m->_Responsible = NULL;
1527 m->_recursions = 0;
1528 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // Consider: maintain by type/class
1529
1530 markOop cmp = object->cas_set_mark(markOopDesc::INFLATING(), mark);
1531 if (cmp != mark) {
1532 omRelease(Self, m, true);
1533 continue; // Interference -- just retry
1534 }
1535
1536 // We've successfully installed INFLATING (0) into the mark-word.
1537 // This is the only case where 0 will appear in a mark-word.
1538 // Only the singular thread that successfully swings the mark-word
1539 // to 0 can perform (or more precisely, complete) inflation.
1540 //
1541 // Why do we CAS a 0 into the mark-word instead of just CASing the
1549 // value from the basiclock on the owner's stack to the objectMonitor, all
1550 // the while preserving the hashCode stability invariants. If the owner
1551 // decides to release the lock while the value is 0, the unlock will fail
1552 // and control will eventually pass from slow_exit() to inflate. The owner
1553 // will then spin, waiting for the 0 value to disappear. Put another way,
1554 // the 0 causes the owner to stall if the owner happens to try to
1555 // drop the lock (restoring the header from the basiclock to the object)
1556 // while inflation is in-progress. This protocol avoids races that might
1557 // would otherwise permit hashCode values to change or "flicker" for an object.
1558 // Critically, while object->mark is 0 mark->displaced_mark_helper() is stable.
1559 // 0 serves as a "BUSY" inflate-in-progress indicator.
1560
1561
1562 // fetch the displaced mark from the owner's stack.
1563 // The owner can't die or unwind past the lock while our INFLATING
1564 // object is in the mark. Furthermore the owner can't complete
1565 // an unlock on the object, either.
1566 markOop dmw = mark->displaced_mark_helper();
1567 // Catch if the object's header is not neutral (not locked and
1568 // not marked is what we care about here).
1569 ADIM_guarantee(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1570
1571 // Setup monitor fields to proper values -- prepare the monitor
1572 m->set_header(dmw);
1573
1574 // Optimization: if the mark->locker stack address is associated
1575 // with this thread we could simply set m->_owner = Self.
1576 // Note that a thread can inflate an object
1577 // that it has stack-locked -- as might happen in wait() -- directly
1578 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1579 m->set_owner(mark->locker());
1580 m->set_object(object);
1581 // TODO-FIXME: assert BasicLock->dhw != 0.
1582
1583 omh_p->set_om_ptr(m);
1584 assert(m->is_new(), "freshly allocated monitor must be new");
1585 m->set_allocation_state(ObjectMonitor::Old);
1586
1587 // Must preserve store ordering. The monitor state must
1588 // be stable at the time of publishing the monitor address.
1589 guarantee(object->mark() == markOopDesc::INFLATING(), "invariant");
1590 object->release_set_mark(markOopDesc::encode(m));
1591
1592 // Hopefully the performance counters are allocated on distinct cache lines
1593 // to avoid false sharing on MP systems ...
1594 OM_PERFDATA_OP(Inflations, inc());
1595 if (log_is_enabled(Trace, monitorinflation)) {
1596 ResourceMark rm(Self);
1597 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1598 INTPTR_FORMAT ", type='%s'", p2i(object),
1599 p2i(object->mark()), object->klass()->external_name());
1600 }
1601 if (event.should_commit()) {
1602 post_monitor_inflate_event(&event, object, cause);
1603 }
1604 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
1605 return;
1606 }
1607
1608 // CASE: neutral
1609 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1610 // If we know we're inflating for entry it's better to inflate by swinging a
1611 // pre-locked objectMonitor pointer into the object header. A successful
1612 // CAS inflates the object *and* confers ownership to the inflating thread.
1613 // In the current implementation we use a 2-step mechanism where we CAS()
1614 // to inflate and then CAS() again to try to swing _owner from NULL to Self.
1615 // An inflateTry() method that we could call from fast_enter() and slow_enter()
1616 // would be useful.
1617
1618 // Catch if the object's header is not neutral (not locked and
1619 // not marked is what we care about here).
1620 ADIM_guarantee(mark->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(mark));
1621 ObjectMonitor * m;
1622 if (!AsyncDeflateIdleMonitors || cause == inflate_cause_vm_internal) {
1623 // If !AsyncDeflateIdleMonitors or if an internal inflation, then
1624 // we won't stop for a potential safepoint in omAlloc.
1625 m = omAlloc(Self, cause);
1626 } else {
1627 // If AsyncDeflateIdleMonitors and not an internal inflation, then
1628 // we may stop for a safepoint in omAlloc() so protect object.
1629 Handle h_obj(Self, object);
1630 m = omAlloc(Self, cause);
1631 object = h_obj(); // Refresh object.
1632 }
1633 // prepare m for installation - set monitor to initial state
1634 m->Recycle();
1635 m->set_header(mark);
1636 m->set_owner(NULL);
1637 m->set_object(object);
1638 m->_recursions = 0;
1639 m->_Responsible = NULL;
1640 m->_SpinDuration = ObjectMonitor::Knob_SpinLimit; // consider: keep metastats by type/class
1641
1642 omh_p->set_om_ptr(m);
1643 assert(m->is_new(), "freshly allocated monitor must be new");
1644 m->set_allocation_state(ObjectMonitor::Old);
1645
1646 if (object->cas_set_mark(markOopDesc::encode(m), mark) != mark) {
1647 m->set_header(NULL);
1648 m->set_object(NULL);
1649 m->Recycle();
1650 omh_p->set_om_ptr(NULL);
1651 // omRelease() will reset the allocation state
1652 omRelease(Self, m, true);
1653 m = NULL;
1654 continue;
1655 // interference - the markword changed - just retry.
1656 // The state-transitions are one-way, so there's no chance of
1657 // live-lock -- "Inflated" is an absorbing state.
1658 }
1659
1660 // Hopefully the performance counters are allocated on distinct
1661 // cache lines to avoid false sharing on MP systems ...
1662 OM_PERFDATA_OP(Inflations, inc());
1663 if (log_is_enabled(Trace, monitorinflation)) {
1664 ResourceMark rm(Self);
1665 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1666 INTPTR_FORMAT ", type='%s'", p2i(object),
1667 p2i(object->mark()), object->klass()->external_name());
1668 }
1669 if (event.should_commit()) {
1670 post_monitor_inflate_event(&event, object, cause);
1671 }
1672 ADIM_guarantee(!m->is_free(), "inflated monitor to be returned cannot be free");
1673 return;
1674 }
1675 }
1676
1677
1678 // We maintain a list of in-use monitors for each thread.
1679 //
1680 // deflate_thread_local_monitors() scans a single thread's in-use list, while
1681 // deflate_idle_monitors() scans only a global list of in-use monitors which
1682 // is populated only as a thread dies (see omFlush()).
1683 //
1684 // These operations are called at all safepoints, immediately after mutators
1685 // are stopped, but before any objects have moved. Collectively they traverse
1686 // the population of in-use monitors, deflating where possible. The scavenged
1687 // monitors are returned to the global monitor free list.
1688 //
1689 // Beware that we scavenge at *every* stop-the-world point. Having a large
1690 // number of monitors in-use could negatively impact performance. We also want
1691 // to minimize the total # of monitors in circulation, as they incur a small
1692 // footprint penalty.
1693 //
1694 // Perversely, the heap size -- and thus the STW safepoint rate --
1695 // typically drives the scavenge rate. Large heaps can mean infrequent GC,
1696 // which in turn can mean large(r) numbers of ObjectMonitors in circulation.
1697 // This is an unfortunate aspect of this design.
1698
1699 void ObjectSynchronizer::do_safepoint_work(DeflateMonitorCounters* _counters) {
1700 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
1701
1702 // The per-thread in-use lists are handled in
1703 // ParallelSPCleanupThreadClosure::do_thread().
1704
1705 if (!AsyncDeflateIdleMonitors || is_cleanup_requested()) {
1706 // Use the older mechanism for the global in-use list or
1707 // if a special cleanup has been requested.
1708 ObjectSynchronizer::deflate_idle_monitors(_counters);
1709 return;
1710 }
1711
1712 log_debug(monitorinflation)("requesting deflation of idle monitors.");
1713 // Request deflation of global idle monitors by the ServiceThread:
1714 _gOmShouldDeflateIdleMonitors = true;
1715 MutexLockerEx ml(Service_lock, Mutex::_no_safepoint_check_flag);
1716 Service_lock->notify_all();
1717 }
1718
1719 // Deflate a single monitor if not in-use
1720 // Return true if deflated, false if in-use
1721 bool ObjectSynchronizer::deflate_monitor(ObjectMonitor* mid, oop obj,
1722 ObjectMonitor** freeHeadp,
1723 ObjectMonitor** freeTailp) {
1724 bool deflated;
1725 // Normal case ... The monitor is associated with obj.
1726 const markOop mark = obj->mark();
1727 guarantee(mark == markOopDesc::encode(mid), "should match: mark="
1728 INTPTR_FORMAT ", encoded mid=" INTPTR_FORMAT, p2i(mark),
1729 p2i(markOopDesc::encode(mid)));
1730 // Make sure that mark->monitor() and markOopDesc::encode() agree:
1731 guarantee(mark->monitor() == mid, "should match: monitor()=" INTPTR_FORMAT
1732 ", mid=" INTPTR_FORMAT, p2i(mark->monitor()), p2i(mid));
1733 const markOop dmw = mid->header();
1734 guarantee(dmw->is_neutral(), "invariant: header=" INTPTR_FORMAT, p2i(dmw));
1735
1736 if (mid->is_busy()) {
1737 deflated = false;
1738 } else {
1739 // Deflate the monitor if it is no longer being used
1740 // It's idle - scavenge and return to the global free list
1741 // plain old deflation ...
1742 if (log_is_enabled(Trace, monitorinflation)) {
1743 ResourceMark rm;
1744 log_trace(monitorinflation)("deflate_monitor: "
1745 "object=" INTPTR_FORMAT ", mark="
1746 INTPTR_FORMAT ", type='%s'", p2i(obj),
1747 p2i(mark), obj->klass()->external_name());
1748 }
1749
1750 // Restore the header back to obj
1751 obj->release_set_mark(dmw);
1752 mid->clear();
1753
1754 assert(mid->object() == NULL, "invariant: object=" INTPTR_FORMAT,
1755 p2i(mid->object()));
1756 assert(mid->is_free(), "invariant");
1757
1758 // Move the object to the working free list defined by freeHeadp, freeTailp
1759 if (*freeHeadp == NULL) *freeHeadp = mid;
1760 if (*freeTailp != NULL) {
1761 ObjectMonitor * prevtail = *freeTailp;
1762 assert(prevtail->FreeNext == NULL, "cleaned up deflated?");
1763 prevtail->FreeNext = mid;
1764 }
1765 *freeTailp = mid;
1766 deflated = true;
1767 }
1768 return deflated;
1769 }
1770
1771 // Deflate the specified ObjectMonitor if not in-use using a JavaThread.
1772 // Returns true if it was deflated and false otherwise.
1773 //
1774 // The async deflation protocol sets owner to DEFLATER_MARKER and
1775 // makes ref_count negative as signals to contending threads that
1776 // an async deflation is in progress. There are a number of checks
1777 // as part of the protocol to make sure that the calling thread has
1778 // not lost the race to a contending thread or to a thread that just
1779 // wants to use the ObjectMonitor*.
1780 //
1781 // The ObjectMonitor has been successfully async deflated when:
1782 // (owner == DEFLATER_MARKER && ref_count < 0)
1783 // Contending threads or ObjectMonitor* using threads that see those
1784 // values know to retry their operation.
1785 //
1786 bool ObjectSynchronizer::deflate_monitor_using_JT(ObjectMonitor* mid,
1787 ObjectMonitor** freeHeadp,
1788 ObjectMonitor** freeTailp) {
1789 assert(AsyncDeflateIdleMonitors, "sanity check");
1790 assert(Thread::current()->is_Java_thread(), "precondition");
1791 // A newly allocated ObjectMonitor should not be seen here so we
1792 // avoid an endless inflate/deflate cycle.
1793 assert(mid->is_old(), "must be old: allocation_state=%d",
1794 (int) mid->allocation_state());
1795
1796 if (mid->is_busy() || mid->ref_count() != 0) {
1797 // Easy checks are first - the ObjectMonitor is busy or ObjectMonitor*
1798 // is in use so no deflation.
1799 return false;
1800 }
1801
1802 if (Atomic::replace_if_null(DEFLATER_MARKER, &(mid->_owner))) {
1803 // ObjectMonitor is not owned by another thread. Our setting
1804 // owner to DEFLATER_MARKER forces any contending thread through
1805 // the slow path. This is just the first part of the async
1806 // deflation dance.
1807
1808 if (mid->_contentions != 0 || mid->_waiters != 0) {
1809 // Another thread has raced to enter the ObjectMonitor after
1810 // mid->is_busy() above or has already entered and waited on
1811 // it which makes it busy so no deflation. Restore owner to
1812 // NULL if it is still DEFLATER_MARKER.
1813 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
1814 return false;
1815 }
1816
1817 if (Atomic::cmpxchg(-max_jint, &mid->_ref_count, (jint)0) == 0) {
1818 // Make ref_count negative to force any contending threads or
1819 // ObjectMonitor* using threads to retry. This is the second
1820 // part of the async deflation dance.
1821
1822 if (mid->_owner == DEFLATER_MARKER) {
1823 // If owner is still DEFLATER_MARKER, then we have successfully
1824 // signaled any contending threads to retry. If it is not, then we
1825 // have lost the race to an entering thread and the ObjectMonitor
1826 // is now busy. This is the third and final part of the async
1827 // deflation dance.
1828 // Note: This owner check solves the ABA problem with ref_count
1829 // where another thread acquired the ObjectMonitor, finished
1830 // using it and restored the ref_count to zero.
1831
1832 // Sanity checks for the races:
1833 guarantee(mid->_contentions == 0, "must be 0: contentions=%d",
1834 mid->_contentions);
1835 guarantee(mid->_waiters == 0, "must be 0: waiters=%d", mid->_waiters);
1836 guarantee(mid->_cxq == NULL, "must be no contending threads: cxq="
1837 INTPTR_FORMAT, p2i(mid->_cxq));
1838 guarantee(mid->_EntryList == NULL,
1839 "must be no entering threads: EntryList=" INTPTR_FORMAT,
1840 p2i(mid->_EntryList));
1841
1842 const oop obj = (oop) mid->object();
1843 if (log_is_enabled(Trace, monitorinflation)) {
1844 ResourceMark rm;
1845 log_trace(monitorinflation)("deflate_monitor_using_JT: "
1846 "object=" INTPTR_FORMAT ", mark="
1847 INTPTR_FORMAT ", type='%s'",
1848 p2i(obj), p2i(obj->mark()),
1849 obj->klass()->external_name());
1850 }
1851
1852 // Install the old mark word if nobody else has already done it.
1853 mid->install_displaced_markword_in_object(obj);
1854 mid->clear_using_JT();
1855
1856 assert(mid->object() == NULL, "must be NULL: object=" INTPTR_FORMAT,
1857 p2i(mid->object()));
1858 assert(mid->is_free(), "must be free: allocation_state=%d",
1859 (int) mid->allocation_state());
1860
1861 // Move the deflated ObjectMonitor to the working free list
1862 // defined by freeHeadp and freeTailp.
1863 if (*freeHeadp == NULL) {
1864 // First one on the list.
1865 *freeHeadp = mid;
1866 }
1867 if (*freeTailp != NULL) {
1868 // We append to the list so the caller can use mid->FreeNext
1869 // to fix the linkages in its context.
1870 ObjectMonitor * prevtail = *freeTailp;
1871 // Should have been cleaned up by the caller:
1872 assert(prevtail->FreeNext == NULL, "must be NULL: FreeNext="
1873 INTPTR_FORMAT, p2i(prevtail->FreeNext));
1874 prevtail->FreeNext = mid;
1875 }
1876 *freeTailp = mid;
1877
1878 // At this point, mid->FreeNext still refers to its current
1879 // value and another ObjectMonitor's FreeNext field still
1880 // refers to this ObjectMonitor. Those linkages have to be
1881 // cleaned up by the caller who has the complete context.
1882
1883 // We leave owner == DEFLATER_MARKER and ref_count < 0
1884 // to force any racing threads to retry.
1885 return true; // Success, ObjectMonitor has been deflated.
1886 }
1887
1888 // The owner was changed from DEFLATER_MARKER so we lost the
1889 // race since the ObjectMonitor is now busy.
1890
1891 // Add back max_jint to restore the ref_count field to its
1892 // proper value (which may not be what we saw above):
1893 Atomic::add(max_jint, &mid->_ref_count);
1894
1895 assert(mid->ref_count() >= 0, "must not be negative: ref_count=%d",
1896 mid->ref_count());
1897 return false;
1898 }
1899
1900 // The ref_count was no longer 0 so we lost the race since the
1901 // ObjectMonitor is now busy or the ObjectMonitor* is now is use.
1902 // Restore owner to NULL if it is still DEFLATER_MARKER:
1903 Atomic::cmpxchg((void*)NULL, &mid->_owner, DEFLATER_MARKER);
1904 }
1905
1906 // The owner field is no longer NULL so we lost the race since the
1907 // ObjectMonitor is now busy.
1908 return false;
1909 }
1910
1911 // Walk a given monitor list, and deflate idle monitors
1912 // The given list could be a per-thread list or a global list
1913 // Caller acquires gListLock as needed.
1914 //
1915 // In the case of parallel processing of thread local monitor lists,
1916 // work is done by Threads::parallel_threads_do() which ensures that
1917 // each Java thread is processed by exactly one worker thread, and
1918 // thus avoid conflicts that would arise when worker threads would
1919 // process the same monitor lists concurrently.
1920 //
1921 // See also ParallelSPCleanupTask and
1922 // SafepointSynchronize::do_cleanup_tasks() in safepoint.cpp and
1923 // Threads::parallel_java_threads_do() in thread.cpp.
1924 int ObjectSynchronizer::deflate_monitor_list(ObjectMonitor** listHeadp,
1925 ObjectMonitor** freeHeadp,
1926 ObjectMonitor** freeTailp) {
1927 ObjectMonitor* mid;
1928 ObjectMonitor* next;
1929 ObjectMonitor* cur_mid_in_use = NULL;
1930 int deflated_count = 0;
1934 if (obj != NULL && deflate_monitor(mid, obj, freeHeadp, freeTailp)) {
1935 // if deflate_monitor succeeded,
1936 // extract from per-thread in-use list
1937 if (mid == *listHeadp) {
1938 *listHeadp = mid->FreeNext;
1939 } else if (cur_mid_in_use != NULL) {
1940 cur_mid_in_use->FreeNext = mid->FreeNext; // maintain the current thread in-use list
1941 }
1942 next = mid->FreeNext;
1943 mid->FreeNext = NULL; // This mid is current tail in the freeHeadp list
1944 mid = next;
1945 deflated_count++;
1946 } else {
1947 cur_mid_in_use = mid;
1948 mid = mid->FreeNext;
1949 }
1950 }
1951 return deflated_count;
1952 }
1953
1954 // Walk a given ObjectMonitor list and deflate idle ObjectMonitors using
1955 // a JavaThread. Returns the number of deflated ObjectMonitors. The given
1956 // list could be a per-thread in-use list or the global in-use list.
1957 // Caller acquires gListLock as appropriate. If a safepoint has started,
1958 // then we save state via savedMidInUsep and return to the caller to
1959 // honor the safepoint.
1960 //
1961 int ObjectSynchronizer::deflate_monitor_list_using_JT(ObjectMonitor** listHeadp,
1962 ObjectMonitor** freeHeadp,
1963 ObjectMonitor** freeTailp,
1964 ObjectMonitor** savedMidInUsep) {
1965 assert(AsyncDeflateIdleMonitors, "sanity check");
1966 assert(Thread::current()->is_Java_thread(), "precondition");
1967
1968 ObjectMonitor* mid;
1969 ObjectMonitor* next;
1970 ObjectMonitor* cur_mid_in_use = NULL;
1971 int deflated_count = 0;
1972
1973 if (*savedMidInUsep == NULL) {
1974 // No saved state so start at the beginning.
1975 mid = *listHeadp;
1976 } else {
1977 // We're restarting after a safepoint so restore the necessary state
1978 // before we resume.
1979 cur_mid_in_use = *savedMidInUsep;
1980 mid = cur_mid_in_use->FreeNext;
1981 }
1982 while (mid != NULL) {
1983 // Only try to deflate if there is an associated Java object and if
1984 // mid is old (is not newly allocated and is not newly freed).
1985 if (mid->object() != NULL && mid->is_old() &&
1986 deflate_monitor_using_JT(mid, freeHeadp, freeTailp)) {
1987 // Deflation succeeded so update the in-use list.
1988 if (mid == *listHeadp) {
1989 *listHeadp = mid->FreeNext;
1990 } else if (cur_mid_in_use != NULL) {
1991 // Maintain the current in-use list.
1992 cur_mid_in_use->FreeNext = mid->FreeNext;
1993 }
1994 next = mid->FreeNext;
1995 mid->FreeNext = NULL;
1996 // At this point mid is disconnected from the in-use list
1997 // and is the current tail in the freeHeadp list.
1998 mid = next;
1999 deflated_count++;
2000 } else {
2001 // mid is considered in-use if it does not have an associated
2002 // Java object or mid is not old or deflation did not succeed.
2003 // A mid->is_new() node can be seen here when it is freshly
2004 // returned by omAlloc() (and skips the deflation code path).
2005 // A mid->is_old() node can be seen here when deflation failed.
2006 // A mid->is_free() node can be seen here when a fresh node from
2007 // omAlloc() is released by omRelease() due to losing the race
2008 // in inflate().
2009
2010 cur_mid_in_use = mid;
2011 mid = mid->FreeNext;
2012
2013 if (SafepointSynchronize::is_synchronizing() &&
2014 cur_mid_in_use != *listHeadp && cur_mid_in_use->is_old()) {
2015 // If a safepoint has started and cur_mid_in_use is not the list
2016 // head and is old, then it is safe to use as saved state. Return
2017 // to the caller so gListLock can be dropped as appropriate
2018 // before blocking.
2019 *savedMidInUsep = cur_mid_in_use;
2020 return deflated_count;
2021 }
2022 }
2023 }
2024 // We finished the list without a safepoint starting so there's
2025 // no need to save state.
2026 *savedMidInUsep = NULL;
2027 return deflated_count;
2028 }
2029
2030 void ObjectSynchronizer::prepare_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2031 counters->nInuse = 0; // currently associated with objects
2032 counters->nInCirculation = 0; // extant
2033 counters->nScavenged = 0; // reclaimed (global and per-thread)
2034 counters->perThreadScavenged = 0; // per-thread scavenge total
2035 counters->perThreadTimes = 0.0; // per-thread scavenge times
2036 }
2037
2038 void ObjectSynchronizer::deflate_idle_monitors(DeflateMonitorCounters* counters) {
2039 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2040
2041 if (AsyncDeflateIdleMonitors) {
2042 // Nothing to do when global idle ObjectMonitors are deflated using
2043 // a JavaThread unless a special cleanup has been requested.
2044 if (!is_cleanup_requested()) {
2045 return;
2046 }
2047 }
2048
2049 bool deflated = false;
2050
2051 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
2052 ObjectMonitor * freeTailp = NULL;
2053 elapsedTimer timer;
2054
2055 if (log_is_enabled(Info, monitorinflation)) {
2056 timer.start();
2057 }
2058
2059 // Prevent omFlush from changing mids in Thread dtor's during deflation
2060 // And in case the vm thread is acquiring a lock during a safepoint
2061 // See e.g. 6320749
2062 Thread::muxAcquire(&gListLock, "deflate_idle_monitors");
2063
2064 // Note: the thread-local monitors lists get deflated in
2065 // a separate pass. See deflate_thread_local_monitors().
2066
2067 // For moribund threads, scan gOmInUseList
2068 int deflated_count = 0;
2081 // constant-time list splice - prepend scavenged segment to gFreeList
2082 freeTailp->FreeNext = gFreeList;
2083 gFreeList = freeHeadp;
2084 }
2085 Thread::muxRelease(&gListLock);
2086 timer.stop();
2087
2088 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2089 LogStreamHandle(Info, monitorinflation) lsh_info;
2090 LogStream * ls = NULL;
2091 if (log_is_enabled(Debug, monitorinflation)) {
2092 ls = &lsh_debug;
2093 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2094 ls = &lsh_info;
2095 }
2096 if (ls != NULL) {
2097 ls->print_cr("deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2098 }
2099 }
2100
2101 // Deflate global idle ObjectMonitors using a JavaThread.
2102 //
2103 void ObjectSynchronizer::deflate_global_idle_monitors_using_JT() {
2104 assert(AsyncDeflateIdleMonitors, "sanity check");
2105 assert(Thread::current()->is_Java_thread(), "precondition");
2106 JavaThread * self = JavaThread::current();
2107
2108 _gOmShouldDeflateIdleMonitors = false;
2109
2110 deflate_common_idle_monitors_using_JT(true /* is_global */, self);
2111 }
2112
2113 // Deflate per-thread idle ObjectMonitors using a JavaThread.
2114 //
2115 void ObjectSynchronizer::deflate_per_thread_idle_monitors_using_JT() {
2116 assert(AsyncDeflateIdleMonitors, "sanity check");
2117 assert(Thread::current()->is_Java_thread(), "precondition");
2118 JavaThread * self = JavaThread::current();
2119
2120 self->omShouldDeflateIdleMonitors = false;
2121
2122 deflate_common_idle_monitors_using_JT(false /* !is_global */, self);
2123 }
2124
2125 // Deflate global or per-thread idle ObjectMonitors using a JavaThread.
2126 //
2127 void ObjectSynchronizer::deflate_common_idle_monitors_using_JT(bool is_global, JavaThread * self) {
2128 int deflated_count = 0;
2129 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged ObjectMonitors
2130 ObjectMonitor * freeTailp = NULL;
2131 ObjectMonitor * savedMidInUsep = NULL;
2132 elapsedTimer timer;
2133
2134 if (log_is_enabled(Info, monitorinflation)) {
2135 timer.start();
2136 }
2137
2138 if (is_global) {
2139 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(1)");
2140 OM_PERFDATA_OP(MonExtant, set_value(gOmInUseCount));
2141 } else {
2142 OM_PERFDATA_OP(MonExtant, inc(self->omInUseCount));
2143 }
2144
2145 do {
2146 int local_deflated_count;
2147 if (is_global) {
2148 local_deflated_count = deflate_monitor_list_using_JT((ObjectMonitor **)&gOmInUseList, &freeHeadp, &freeTailp, &savedMidInUsep);
2149 gOmInUseCount -= local_deflated_count;
2150 } else {
2151 local_deflated_count = deflate_monitor_list_using_JT(self->omInUseList_addr(), &freeHeadp, &freeTailp, &savedMidInUsep);
2152 self->omInUseCount -= local_deflated_count;
2153 }
2154 deflated_count += local_deflated_count;
2155
2156 if (freeHeadp != NULL) {
2157 // Move the scavenged ObjectMonitors to the global free list.
2158 guarantee(freeTailp != NULL && local_deflated_count > 0, "freeTailp=" INTPTR_FORMAT ", local_deflated_count=%d", p2i(freeTailp), local_deflated_count);
2159 assert(freeTailp->FreeNext == NULL, "invariant");
2160
2161 if (!is_global) {
2162 Thread::muxAcquire(&gListLock, "deflate_per_thread_idle_monitors_using_JT(2)");
2163 }
2164 // Constant-time list splice - prepend scavenged segment to gFreeList.
2165 freeTailp->FreeNext = gFreeList;
2166 gFreeList = freeHeadp;
2167
2168 gMonitorFreeCount += local_deflated_count;
2169 OM_PERFDATA_OP(Deflations, inc(local_deflated_count));
2170 if (!is_global) {
2171 Thread::muxRelease(&gListLock);
2172 }
2173 }
2174
2175 if (savedMidInUsep != NULL) {
2176 // deflate_monitor_list_using_JT() detected a safepoint starting.
2177 if (is_global) {
2178 Thread::muxRelease(&gListLock);
2179 }
2180 timer.stop();
2181 {
2182 if (is_global) {
2183 log_debug(monitorinflation)("pausing deflation of global idle monitors for a safepoint.");
2184 } else {
2185 log_debug(monitorinflation)("jt=" INTPTR_FORMAT ": pausing deflation of per-thread idle monitors for a safepoint.", p2i(self));
2186 }
2187 assert(SafepointSynchronize::is_synchronizing(), "sanity check");
2188 ThreadBlockInVM blocker(self);
2189 }
2190 // Prepare for another loop after the safepoint.
2191 freeHeadp = NULL;
2192 freeTailp = NULL;
2193 if (log_is_enabled(Info, monitorinflation)) {
2194 timer.start();
2195 }
2196 if (is_global) {
2197 Thread::muxAcquire(&gListLock, "deflate_global_idle_monitors_using_JT(3)");
2198 }
2199 }
2200 } while (savedMidInUsep != NULL);
2201 if (is_global) {
2202 Thread::muxRelease(&gListLock);
2203 }
2204 timer.stop();
2205
2206 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2207 LogStreamHandle(Info, monitorinflation) lsh_info;
2208 LogStream * ls = NULL;
2209 if (log_is_enabled(Debug, monitorinflation)) {
2210 ls = &lsh_debug;
2211 } else if (deflated_count != 0 && log_is_enabled(Info, monitorinflation)) {
2212 ls = &lsh_info;
2213 }
2214 if (ls != NULL) {
2215 if (is_global) {
2216 ls->print_cr("async-deflating global idle monitors, %3.7f secs, %d monitors", timer.seconds(), deflated_count);
2217 } else {
2218 ls->print_cr("jt=" INTPTR_FORMAT ": async-deflating per-thread idle monitors, %3.7f secs, %d monitors", p2i(self), timer.seconds(), deflated_count);
2219 }
2220 }
2221 }
2222
2223 void ObjectSynchronizer::finish_deflate_idle_monitors(DeflateMonitorCounters* counters) {
2224 // Report the cumulative time for deflating each thread's idle
2225 // monitors. Note: if the work is split among more than one
2226 // worker thread, then the reported time will likely be more
2227 // than a beginning to end measurement of the phase.
2228 // Note: AsyncDeflateIdleMonitors only deflates per-thread idle
2229 // monitors at a safepoint when a special cleanup has been requested.
2230 log_info(safepoint, cleanup)("deflating per-thread idle monitors, %3.7f secs, monitors=%d", counters->perThreadTimes, counters->perThreadScavenged);
2231
2232 bool needs_special_cleanup = is_cleanup_requested();
2233 if (!AsyncDeflateIdleMonitors || needs_special_cleanup) {
2234 // AsyncDeflateIdleMonitors does not use these counters unless
2235 // there is a special cleanup request.
2236
2237 gMonitorFreeCount += counters->nScavenged;
2238
2239 OM_PERFDATA_OP(Deflations, inc(counters->nScavenged));
2240 OM_PERFDATA_OP(MonExtant, set_value(counters->nInCirculation));
2241 }
2242
2243 if (log_is_enabled(Debug, monitorinflation)) {
2244 // exit_globals()'s call to audit_and_print_stats() is done
2245 // at the Info level.
2246 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
2247 } else if (log_is_enabled(Info, monitorinflation)) {
2248 Thread::muxAcquire(&gListLock, "finish_deflate_idle_monitors");
2249 log_info(monitorinflation)("gMonitorPopulation=%d, gOmInUseCount=%d, "
2250 "gMonitorFreeCount=%d", gMonitorPopulation,
2251 gOmInUseCount, gMonitorFreeCount);
2252 Thread::muxRelease(&gListLock);
2253 }
2254
2255 ForceMonitorScavenge = 0; // Reset
2256 GVars.stwRandom = os::random();
2257 GVars.stwCycle++;
2258 if (needs_special_cleanup) {
2259 set_is_cleanup_requested(false); // special clean up is done
2260 }
2261 }
2262
2263 void ObjectSynchronizer::deflate_thread_local_monitors(Thread* thread, DeflateMonitorCounters* counters) {
2264 assert(SafepointSynchronize::is_at_safepoint(), "must be at safepoint");
2265
2266 if (AsyncDeflateIdleMonitors) {
2267 if (!is_cleanup_requested()) {
2268 // Mark the JavaThread for idle monitor cleanup if a special
2269 // cleanup has NOT been requested.
2270 if (thread->omInUseCount > 0) {
2271 // This JavaThread is using monitors so mark it.
2272 thread->omShouldDeflateIdleMonitors = true;
2273 }
2274 return;
2275 }
2276 }
2277
2278 ObjectMonitor * freeHeadp = NULL; // Local SLL of scavenged monitors
2279 ObjectMonitor * freeTailp = NULL;
2280 elapsedTimer timer;
2281
2282 if (log_is_enabled(Info, safepoint, cleanup) ||
2283 log_is_enabled(Info, monitorinflation)) {
2284 timer.start();
2285 }
2286
2287 int deflated_count = deflate_monitor_list(thread->omInUseList_addr(), &freeHeadp, &freeTailp);
2288
2289 Thread::muxAcquire(&gListLock, "deflate_thread_local_monitors");
2290
2291 // Adjust counters
2292 counters->nInCirculation += thread->omInUseCount;
2293 thread->omInUseCount -= deflated_count;
2294 counters->nScavenged += deflated_count;
2295 counters->nInuse += thread->omInUseCount;
2296 counters->perThreadScavenged += deflated_count;
2297
2466 } else {
2467 log_error(monitorinflation)("found monitor list errors: error_cnt=%d", error_cnt);
2468 }
2469
2470 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2471 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2472 // When exiting this log output is at the Info level. When called
2473 // at a safepoint, this log output is at the Trace level since
2474 // there can be a lot of it.
2475 log_in_use_monitor_details(ls, on_exit);
2476 }
2477
2478 ls->flush();
2479
2480 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2481 }
2482
2483 // Check a free monitor entry; log any errors.
2484 void ObjectSynchronizer::chk_free_entry(JavaThread * jt, ObjectMonitor * n,
2485 outputStream * out, int *error_cnt_p) {
2486 if ((!AsyncDeflateIdleMonitors && n->is_busy()) ||
2487 (AsyncDeflateIdleMonitors && n->is_busy_async())) {
2488 if (jt != NULL) {
2489 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2490 ": free per-thread monitor must not be busy.", p2i(jt),
2491 p2i(n));
2492 } else {
2493 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2494 "must not be busy.", p2i(n));
2495 }
2496 *error_cnt_p = *error_cnt_p + 1;
2497 }
2498 if (n->header() != NULL) {
2499 if (jt != NULL) {
2500 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2501 ": free per-thread monitor must have NULL _header "
2502 "field: _header=" INTPTR_FORMAT, p2i(jt), p2i(n),
2503 p2i(n->header()));
2504 *error_cnt_p = *error_cnt_p + 1;
2505 } else if (!AsyncDeflateIdleMonitors) {
2506 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2507 "must have NULL _header field: _header=" INTPTR_FORMAT,
2508 p2i(n), p2i(n->header()));
2509 *error_cnt_p = *error_cnt_p + 1;
2510 }
2511 }
2512 if (n->object() != NULL) {
2513 if (jt != NULL) {
2514 out->print_cr("ERROR: jt=" INTPTR_FORMAT ", monitor=" INTPTR_FORMAT
2515 ": free per-thread monitor must have NULL _object "
2516 "field: _object=" INTPTR_FORMAT, p2i(jt), p2i(n),
2517 p2i(n->object()));
2518 } else {
2519 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": free global monitor "
2520 "must have NULL _object field: _object=" INTPTR_FORMAT,
2521 p2i(n), p2i(n->object()));
2522 }
2523 *error_cnt_p = *error_cnt_p + 1;
2524 }
2525 }
2526
2527 // Check the global free list and count; log the results of the checks.
2528 void ObjectSynchronizer::chk_global_free_list_and_count(outputStream * out,
2529 int *error_cnt_p) {
2530 int chkMonitorFreeCount = 0;
2531 for (ObjectMonitor * n = gFreeList; n != NULL; n = n->FreeNext) {
2657 out->print_cr("ERROR: jt=" INTPTR_FORMAT ": omInUseCount=%d is not "
2658 "equal to chkOmInUseCount=%d", p2i(jt), jt->omInUseCount,
2659 chkOmInUseCount);
2660 *error_cnt_p = *error_cnt_p + 1;
2661 }
2662 }
2663
2664 // Log details about ObjectMonitors on the in-use lists. The 'BHL'
2665 // flags indicate why the entry is in-use, 'object' and 'object type'
2666 // indicate the associated object and its type.
2667 void ObjectSynchronizer::log_in_use_monitor_details(outputStream * out,
2668 bool on_exit) {
2669 if (!on_exit) {
2670 // Not at VM exit so grab the global list lock.
2671 Thread::muxAcquire(&gListLock, "log_in_use_monitor_details");
2672 }
2673
2674 if (gOmInUseCount > 0) {
2675 out->print_cr("In-use global monitor info:");
2676 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2677 out->print_cr("%18s %s %7s %18s %18s",
2678 "monitor", "BHL", "ref_cnt", "object", "object type");
2679 out->print_cr("================== === ======= ================== ==================");
2680 for (ObjectMonitor * n = gOmInUseList; n != NULL; n = n->FreeNext) {
2681 const oop obj = (oop) n->object();
2682 const markOop mark = n->header();
2683 ResourceMark rm;
2684 out->print_cr(INTPTR_FORMAT " %d%d%d %7d " INTPTR_FORMAT " %s",
2685 p2i(n), n->is_busy() != 0, mark->hash() != 0,
2686 n->owner() != NULL, (int)n->ref_count(), p2i(obj),
2687 obj->klass()->external_name());
2688 }
2689 }
2690
2691 if (!on_exit) {
2692 Thread::muxRelease(&gListLock);
2693 }
2694
2695 out->print_cr("In-use per-thread monitor info:");
2696 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2697 out->print_cr("%18s %18s %s %7s %18s %18s",
2698 "jt", "monitor", "BHL", "ref_cnt", "object", "object type");
2699 out->print_cr("================== ================== === ======= ================== ==================");
2700 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
2701 for (ObjectMonitor * n = jt->omInUseList; n != NULL; n = n->FreeNext) {
2702 const oop obj = (oop) n->object();
2703 const markOop mark = n->header();
2704 ResourceMark rm;
2705 out->print_cr(INTPTR_FORMAT " " INTPTR_FORMAT " %d%d%d %7d "
2706 INTPTR_FORMAT " %s", p2i(jt), p2i(n), n->is_busy() != 0,
2707 mark->hash() != 0, n->owner() != NULL, (int)n->ref_count(),
2708 p2i(obj), obj->klass()->external_name());
2709 }
2710 }
2711
2712 out->flush();
2713 }
2714
2715 // Log counts for the global and per-thread monitor lists and return
2716 // the population count.
2717 int ObjectSynchronizer::log_monitor_list_counts(outputStream * out) {
2718 int popCount = 0;
2719 out->print_cr("%18s %10s %10s %10s",
2720 "Global Lists:", "InUse", "Free", "Total");
2721 out->print_cr("================== ========== ========== ==========");
2722 out->print_cr("%18s %10d %10d %10d", "",
2723 gOmInUseCount, gMonitorFreeCount, gMonitorPopulation);
2724 popCount += gOmInUseCount + gMonitorFreeCount;
2725
2726 out->print_cr("%18s %10s %10s %10s",
2727 "Per-Thread Lists:", "InUse", "Free", "Provision");
2728 out->print_cr("================== ========== ========== ==========");
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