1 /*
2 * Copyright (c) 1998, 2026, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "classfile/vmSymbols.hpp"
26 #include "gc/shared/collectedHeap.hpp"
27 #include "jfr/jfrEvents.hpp"
28 #include "logging/log.hpp"
29 #include "logging/logStream.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/padded.hpp"
32 #include "memory/resourceArea.hpp"
33 #include "memory/universe.hpp"
34 #include "oops/markWord.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "runtime/atomicAccess.hpp"
37 #include "runtime/basicLock.inline.hpp"
38 #include "runtime/frame.inline.hpp"
39 #include "runtime/globals.hpp"
40 #include "runtime/handles.inline.hpp"
41 #include "runtime/handshake.hpp"
42 #include "runtime/interfaceSupport.inline.hpp"
43 #include "runtime/javaThread.hpp"
44 #include "runtime/lockStack.inline.hpp"
45 #include "runtime/mutexLocker.hpp"
46 #include "runtime/objectMonitor.inline.hpp"
47 #include "runtime/objectMonitorTable.hpp"
48 #include "runtime/os.inline.hpp"
49 #include "runtime/osThread.hpp"
50 #include "runtime/safepointMechanism.inline.hpp"
51 #include "runtime/safepointVerifiers.hpp"
52 #include "runtime/sharedRuntime.hpp"
53 #include "runtime/stubRoutines.hpp"
54 #include "runtime/synchronizer.hpp"
55 #include "runtime/threads.hpp"
56 #include "runtime/timer.hpp"
57 #include "runtime/timerTrace.hpp"
58 #include "runtime/trimNativeHeap.hpp"
59 #include "runtime/vframe.hpp"
60 #include "runtime/vmThread.hpp"
61 #include "utilities/align.hpp"
62 #include "utilities/concurrentHashTable.inline.hpp"
63 #include "utilities/concurrentHashTableTasks.inline.hpp"
64 #include "utilities/dtrace.hpp"
65 #include "utilities/events.hpp"
66 #include "utilities/globalCounter.inline.hpp"
67 #include "utilities/globalDefinitions.hpp"
68 #include "utilities/linkedlist.hpp"
69 #include "utilities/preserveException.hpp"
70
71 class ObjectMonitorDeflationLogging;
72
73 void MonitorList::add(ObjectMonitor* m) {
74 ObjectMonitor* head;
75 do {
76 head = AtomicAccess::load(&_head);
77 m->set_next_om(head);
78 } while (AtomicAccess::cmpxchg(&_head, head, m) != head);
79
80 size_t count = AtomicAccess::add(&_count, 1u, memory_order_relaxed);
81 size_t old_max;
82 do {
83 old_max = AtomicAccess::load(&_max);
84 if (count <= old_max) {
85 break;
86 }
87 } while (AtomicAccess::cmpxchg(&_max, old_max, count, memory_order_relaxed) != old_max);
88 }
89
90 size_t MonitorList::count() const {
91 return AtomicAccess::load(&_count);
92 }
93
94 size_t MonitorList::max() const {
95 return AtomicAccess::load(&_max);
96 }
97
98 class ObjectMonitorDeflationSafepointer : public StackObj {
99 JavaThread* const _current;
100 ObjectMonitorDeflationLogging* const _log;
101
102 public:
103 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
104 : _current(current), _log(log) {}
105
106 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
107 };
108
109 // Walk the in-use list and unlink deflated ObjectMonitors.
110 // Returns the number of unlinked ObjectMonitors.
111 size_t MonitorList::unlink_deflated(size_t deflated_count,
112 GrowableArray<ObjectMonitor*>* unlinked_list,
113 ObjectMonitorDeflationSafepointer* safepointer) {
114 size_t unlinked_count = 0;
115 ObjectMonitor* prev = nullptr;
116 ObjectMonitor* m = AtomicAccess::load_acquire(&_head);
117
118 while (m != nullptr) {
119 if (m->is_being_async_deflated()) {
120 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
121 // modify the list once per batch. The batch starts at "m".
122 size_t unlinked_batch = 0;
123 ObjectMonitor* next = m;
124 // Look for at most MonitorUnlinkBatch monitors, or the number of
125 // deflated and not unlinked monitors, whatever comes first.
126 assert(deflated_count >= unlinked_count, "Sanity: underflow");
127 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
128 do {
129 ObjectMonitor* next_next = next->next_om();
130 unlinked_batch++;
131 unlinked_list->append(next);
132 next = next_next;
133 if (unlinked_batch >= unlinked_batch_limit) {
134 // Reached the max batch, so bail out of the gathering loop.
135 break;
136 }
137 if (prev == nullptr && AtomicAccess::load(&_head) != m) {
138 // Current batch used to be at head, but it is not at head anymore.
139 // Bail out and figure out where we currently are. This avoids long
140 // walks searching for new prev during unlink under heavy list inserts.
141 break;
142 }
143 } while (next != nullptr && next->is_being_async_deflated());
144
145 // Unlink the found batch.
146 if (prev == nullptr) {
147 // The current batch is the first batch, so there is a chance that it starts at head.
148 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
149 ObjectMonitor* prev_head = AtomicAccess::cmpxchg(&_head, m, next);
150 if (prev_head != m) {
151 // Something must have updated the head. Figure out the actual prev for this batch.
152 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
153 prev = n;
154 }
155 assert(prev != nullptr, "Should have found the prev for the current batch");
156 prev->set_next_om(next);
157 }
158 } else {
159 // The current batch is preceded by another batch. This guarantees the current batch
160 // does not start at head. Unlink the entire current batch without updating the head.
161 assert(AtomicAccess::load(&_head) != m, "Sanity");
162 prev->set_next_om(next);
163 }
164
165 unlinked_count += unlinked_batch;
166 if (unlinked_count >= deflated_count) {
167 // Reached the max so bail out of the searching loop.
168 // There should be no more deflated monitors left.
169 break;
170 }
171 m = next;
172 } else {
173 prev = m;
174 m = m->next_om();
175 }
176
177 // Must check for a safepoint/handshake and honor it.
178 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
179 }
180
181 #ifdef ASSERT
182 // Invariant: the code above should unlink all deflated monitors.
183 // The code that runs after this unlinking does not expect deflated monitors.
184 // Notably, attempting to deflate the already deflated monitor would break.
185 {
186 ObjectMonitor* m = AtomicAccess::load_acquire(&_head);
187 while (m != nullptr) {
188 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
189 m = m->next_om();
190 }
191 }
192 #endif
193
194 AtomicAccess::sub(&_count, unlinked_count);
195 return unlinked_count;
196 }
197
198 MonitorList::Iterator MonitorList::iterator() const {
199 return Iterator(AtomicAccess::load_acquire(&_head));
200 }
201
202 ObjectMonitor* MonitorList::Iterator::next() {
203 ObjectMonitor* current = _current;
204 _current = current->next_om();
205 return current;
206 }
207
208 // The "core" versions of monitor enter and exit reside in this file.
209 // The interpreter and compilers contain specialized transliterated
210 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
211 // fast_lock(...) for instance. If you make changes here, make sure to modify the
212 // interpreter, and both C1 and C2 fast-path inline locking code emission.
213 //
214 // -----------------------------------------------------------------------------
215
216 #ifdef DTRACE_ENABLED
217
218 // Only bother with this argument setup if dtrace is available
219 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
220
221 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
222 char* bytes = nullptr; \
223 int len = 0; \
224 jlong jtid = SharedRuntime::get_java_tid(thread); \
225 Symbol* klassname = obj->klass()->name(); \
226 if (klassname != nullptr) { \
227 bytes = (char*)klassname->bytes(); \
228 len = klassname->utf8_length(); \
229 }
230
231 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
232 { \
233 if (DTraceMonitorProbes) { \
234 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
235 HOTSPOT_MONITOR_WAIT(jtid, \
236 (uintptr_t)(monitor), bytes, len, (millis)); \
237 } \
238 }
239
240 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
241 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
242 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
243
244 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
245 { \
246 if (DTraceMonitorProbes) { \
247 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
248 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
249 (uintptr_t)(monitor), bytes, len); \
250 } \
251 }
252
253 #else // ndef DTRACE_ENABLED
254
255 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
256 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
257
258 #endif // ndef DTRACE_ENABLED
259
260 // This exists only as a workaround of dtrace bug 6254741
261 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
262 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
263 return 0;
264 }
265
266 static constexpr size_t inflation_lock_count() {
267 return 256;
268 }
269
270 // Static storage for an array of PlatformMutex.
271 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
272
273 static inline PlatformMutex* inflation_lock(size_t index) {
274 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
275 }
276
277 void ObjectSynchronizer::initialize() {
278 for (size_t i = 0; i < inflation_lock_count(); i++) {
279 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
280 }
281 // Start the ceiling with the estimate for one thread.
282 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
283
284 // Start the timer for deflations, so it does not trigger immediately.
285 _last_async_deflation_time_ns = os::javaTimeNanos();
286
287 ObjectSynchronizer::create_om_table();
288 }
289
290 MonitorList ObjectSynchronizer::_in_use_list;
291 // monitors_used_above_threshold() policy is as follows:
292 //
293 // The ratio of the current _in_use_list count to the ceiling is used
294 // to determine if we are above MonitorUsedDeflationThreshold and need
295 // to do an async monitor deflation cycle. The ceiling is increased by
296 // AvgMonitorsPerThreadEstimate when a thread is added to the system
297 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
298 // removed from the system.
299 //
300 // Note: If the _in_use_list max exceeds the ceiling, then
301 // monitors_used_above_threshold() will use the in_use_list max instead
302 // of the thread count derived ceiling because we have used more
303 // ObjectMonitors than the estimated average.
304 //
305 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
306 // no-progress async monitor deflation cycles in a row, then the ceiling
307 // is adjusted upwards by monitors_used_above_threshold().
308 //
309 // Start the ceiling with the estimate for one thread in initialize()
310 // which is called after cmd line options are processed.
311 static size_t _in_use_list_ceiling = 0;
312 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
313 bool volatile ObjectSynchronizer::_is_final_audit = false;
314 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
315 static uintx _no_progress_cnt = 0;
316 static bool _no_progress_skip_increment = false;
317
318 // These checks are required for wait, notify and exit to avoid inflating the monitor to
319 // find out this inline type object cannot be locked.
320 #define CHECK_THROW_NOSYNC_IMSE(obj) \
321 if ((obj)->mark().is_inline_type()) { \
322 JavaThread* THREAD = current; \
323 ResourceMark rm(THREAD); \
324 THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
325 }
326
327 #define CHECK_THROW_NOSYNC_IMSE_0(obj) \
328 if ((obj)->mark().is_inline_type()) { \
329 JavaThread* THREAD = current; \
330 ResourceMark rm(THREAD); \
331 THROW_MSG_0(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
332 }
333
334 // =====================> Quick functions
335
336 // The quick_* forms are special fast-path variants used to improve
337 // performance. In the simplest case, a "quick_*" implementation could
338 // simply return false, in which case the caller will perform the necessary
339 // state transitions and call the slow-path form.
340 // The fast-path is designed to handle frequently arising cases in an efficient
341 // manner and is just a degenerate "optimistic" variant of the slow-path.
342 // returns true -- to indicate the call was satisfied.
343 // returns false -- to indicate the call needs the services of the slow-path.
344 // A no-loitering ordinance is in effect for code in the quick_* family
345 // operators: safepoints or indefinite blocking (blocking that might span a
346 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
347 // entry.
348 //
349 // Consider: An interesting optimization is to have the JIT recognize the
350 // following common idiom:
351 // synchronized (someobj) { .... ; notify(); }
352 // That is, we find a notify() or notifyAll() call that immediately precedes
353 // the monitorexit operation. In that case the JIT could fuse the operations
354 // into a single notifyAndExit() runtime primitive.
355
356 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
357 assert(current->thread_state() == _thread_in_Java, "invariant");
358 NoSafepointVerifier nsv;
359 if (obj == nullptr) return false; // slow-path for invalid obj
360 assert(!obj->klass()->is_inline_klass(), "monitor op on inline type");
361 const markWord mark = obj->mark();
362
363 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
364 // Degenerate notify
365 // fast-locked by caller so by definition the implied waitset is empty.
366 return true;
367 }
368
369 if (mark.has_monitor()) {
370 ObjectMonitor* const mon = read_monitor(obj, mark);
371 if (mon == nullptr) {
372 // Racing with inflation/deflation go slow path
373 return false;
374 }
375 assert(mon->object() == oop(obj), "invariant");
376 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
377
378 if (mon->first_waiter() != nullptr) {
379 // We have one or more waiters. Since this is an inflated monitor
380 // that we own, we quickly notify them here and now, avoiding the slow-path.
381 if (all) {
382 mon->quick_notifyAll(current);
383 } else {
384 mon->quick_notify(current);
385 }
386 }
387 return true;
388 }
389
390 // other IMS exception states take the slow-path
391 return false;
392 }
393
394 // Handle notifications when synchronizing on value based classes
395 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
396 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
397 frame last_frame = locking_thread->last_frame();
398 bool bcp_was_adjusted = false;
399 // Don't decrement bcp if it points to the frame's first instruction. This happens when
400 // handle_sync_on_value_based_class() is called because of a synchronized method. There
401 // is no actual monitorenter instruction in the byte code in this case.
402 if (last_frame.is_interpreted_frame() &&
403 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
404 // adjust bcp to point back to monitorenter so that we print the correct line numbers
405 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
406 bcp_was_adjusted = true;
407 }
408
409 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
410 ResourceMark rm;
411 stringStream ss;
412 locking_thread->print_active_stack_on(&ss);
413 char* base = (char*)strstr(ss.base(), "at");
414 char* newline = (char*)strchr(ss.base(), '\n');
415 if (newline != nullptr) {
416 *newline = '\0';
417 }
418 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
419 } else {
420 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
421 ResourceMark rm;
422 Log(valuebasedclasses) vblog;
423
424 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
425 if (locking_thread->has_last_Java_frame()) {
426 LogStream info_stream(vblog.info());
427 locking_thread->print_active_stack_on(&info_stream);
428 } else {
429 vblog.info("Cannot find the last Java frame");
430 }
431
432 EventSyncOnValueBasedClass event;
433 if (event.should_commit()) {
434 event.set_valueBasedClass(obj->klass());
435 event.commit();
436 }
437 }
438
439 if (bcp_was_adjusted) {
440 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
441 }
442 }
443
444 // -----------------------------------------------------------------------------
445 // JNI locks on java objects
446 // NOTE: must use heavy weight monitor to handle jni monitor enter
447 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
448 JavaThread* THREAD = current;
449 // Top native frames in the stack will not be seen if we attempt
450 // preemption, since we start walking from the last Java anchor.
451 NoPreemptMark npm(current);
452
453 if (obj->klass()->is_value_based()) {
454 handle_sync_on_value_based_class(obj, current);
455 }
456
457 if (obj->klass()->is_inline_klass()) {
458 ResourceMark rm(THREAD);
459 stringStream ss;
460 ss.print("Cannot synchronize on an instance of value class %s",
461 obj->klass()->external_name());
462 THROW_MSG(vmSymbols::java_lang_IdentityException(), ss.as_string());
463 }
464
465 // the current locking is from JNI instead of Java code
466 current->set_current_pending_monitor_is_from_java(false);
467 // An async deflation can race after the inflate() call and before
468 // enter() can make the ObjectMonitor busy. enter() returns false if
469 // we have lost the race to async deflation and we simply try again.
470 while (true) {
471 BasicLock lock;
472 if (ObjectSynchronizer::inflate_and_enter(obj(), &lock, inflate_cause_jni_enter, current, current) != nullptr) {
473 break;
474 }
475 }
476 current->set_current_pending_monitor_is_from_java(true);
477 }
478
479 // NOTE: must use heavy weight monitor to handle jni monitor exit
480 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
481 JavaThread* current = THREAD;
482 CHECK_THROW_NOSYNC_IMSE(obj);
483
484 ObjectMonitor* monitor;
485 monitor = ObjectSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
486 // If this thread has locked the object, exit the monitor. We
487 // intentionally do not use CHECK on check_owner because we must exit the
488 // monitor even if an exception was already pending.
489 if (monitor->check_owner(THREAD)) {
490 monitor->exit(current);
491 }
492 }
493
494 // -----------------------------------------------------------------------------
495 // Internal VM locks on java objects
496 // standard constructor, allows locking failures
497 ObjectLocker::ObjectLocker(Handle obj, TRAPS) : _thread(THREAD), _obj(obj),
498 _npm(_thread, _thread->at_preemptable_init() /* ignore_mark */), _skip_exit(false) {
499 assert(!_thread->preempting(), "");
500
501 _thread->check_for_valid_safepoint_state();
502
503 if (_obj() != nullptr) {
504 ObjectSynchronizer::enter(_obj, &_lock, _thread);
505
506 if (_thread->preempting()) {
507 // If preemption was cancelled we acquired the monitor after freezing
508 // the frames. Redoing the vm call later in thaw will require us to
509 // release it since the call should look like the original one. We
510 // do it in ~ObjectLocker to reduce the window of time we hold the
511 // monitor since we can't do anything useful with it now, and would
512 // otherwise just force other vthreads to preempt in case they try
513 // to acquire this monitor.
514 _skip_exit = !_thread->preemption_cancelled();
515 ObjectSynchronizer::read_monitor(_obj())->set_object_strong();
516 _thread->set_pending_preempted_exception();
517
518 }
519 }
520 }
521
522 ObjectLocker::~ObjectLocker() {
523 if (_obj() != nullptr && !_skip_exit) {
524 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
525 }
526 }
527
528 void ObjectLocker::wait_uninterruptibly(TRAPS) {
529 ObjectSynchronizer::waitUninterruptibly(_obj, 0, _thread);
530 if (_thread->preempting()) {
531 _skip_exit = true;
532 ObjectSynchronizer::read_monitor(_obj())->set_object_strong();
533 _thread->set_pending_preempted_exception();
534 }
535 }
536
537 // -----------------------------------------------------------------------------
538 // Wait/Notify/NotifyAll
539 // NOTE: must use heavy weight monitor to handle wait()
540
541 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
542 JavaThread* current = THREAD;
543 CHECK_THROW_NOSYNC_IMSE_0(obj);
544 if (millis < 0) {
545 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
546 }
547
548 ObjectMonitor* monitor;
549 monitor = ObjectSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
550
551 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
552 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
553
554 // This dummy call is in place to get around dtrace bug 6254741. Once
555 // that's fixed we can uncomment the following line, remove the call
556 // and change this function back into a "void" func.
557 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
558 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
559 return ret_code;
560 }
561
562 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
563 assert(millis >= 0, "timeout value is negative");
564
565 ObjectMonitor* monitor;
566 monitor = ObjectSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
567 monitor->wait(millis, false, THREAD);
568 }
569
570
571 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
572 JavaThread* current = THREAD;
573 CHECK_THROW_NOSYNC_IMSE(obj);
574
575 markWord mark = obj->mark();
576 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
577 // Not inflated so there can't be any waiters to notify.
578 return;
579 }
580 ObjectMonitor* monitor = ObjectSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
581 monitor->notify(CHECK);
582 }
583
584 // NOTE: see comment of notify()
585 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
586 JavaThread* current = THREAD;
587 CHECK_THROW_NOSYNC_IMSE(obj);
588
589 markWord mark = obj->mark();
590 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
591 // Not inflated so there can't be any waiters to notify.
592 return;
593 }
594
595 ObjectMonitor* monitor = ObjectSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
596 monitor->notifyAll(CHECK);
597 }
598
599 // -----------------------------------------------------------------------------
600 // Hash Code handling
601
602 struct SharedGlobals {
603 char _pad_prefix[OM_CACHE_LINE_SIZE];
604 // This is a highly shared mostly-read variable.
605 // To avoid false-sharing it needs to be the sole occupant of a cache line.
606 volatile int stw_random;
607 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
608 // Hot RW variable -- Sequester to avoid false-sharing
609 volatile int hc_sequence;
610 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
611 };
612
613 static SharedGlobals GVars;
614
615 // hashCode() generation :
616 //
617 // Possibilities:
618 // * MD5Digest of {obj,stw_random}
619 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
620 // * A DES- or AES-style SBox[] mechanism
621 // * One of the Phi-based schemes, such as:
622 // 2654435761 = 2^32 * Phi (golden ratio)
623 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
624 // * A variation of Marsaglia's shift-xor RNG scheme.
625 // * (obj ^ stw_random) is appealing, but can result
626 // in undesirable regularity in the hashCode values of adjacent objects
627 // (objects allocated back-to-back, in particular). This could potentially
628 // result in hashtable collisions and reduced hashtable efficiency.
629 // There are simple ways to "diffuse" the middle address bits over the
630 // generated hashCode values:
631
632 static intptr_t get_next_hash(Thread* current, oop obj) {
633 intptr_t value = 0;
634 if (hashCode == 0) {
635 // This form uses global Park-Miller RNG.
636 // On MP system we'll have lots of RW access to a global, so the
637 // mechanism induces lots of coherency traffic.
638 value = os::random();
639 } else if (hashCode == 1) {
640 // This variation has the property of being stable (idempotent)
641 // between STW operations. This can be useful in some of the 1-0
642 // synchronization schemes.
643 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
644 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
645 } else if (hashCode == 2) {
646 value = 1; // for sensitivity testing
647 } else if (hashCode == 3) {
648 value = ++GVars.hc_sequence;
649 } else if (hashCode == 4) {
650 value = cast_from_oop<intptr_t>(obj);
651 } else {
652 // Marsaglia's xor-shift scheme with thread-specific state
653 // This is probably the best overall implementation -- we'll
654 // likely make this the default in future releases.
655 unsigned t = current->_hashStateX;
656 t ^= (t << 11);
657 current->_hashStateX = current->_hashStateY;
658 current->_hashStateY = current->_hashStateZ;
659 current->_hashStateZ = current->_hashStateW;
660 unsigned v = current->_hashStateW;
661 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
662 current->_hashStateW = v;
663 value = v;
664 }
665
666 value &= markWord::hash_mask;
667 if (value == 0) value = 0xBAD;
668 assert(value != markWord::no_hash, "invariant");
669 return value;
670 }
671
672 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
673 // VM should be calling bootstrap method.
674 assert(!obj->klass()->is_inline_klass(), "FastHashCode should not be called for inline classes");
675
676 while (true) {
677 ObjectMonitor* monitor = nullptr;
678 markWord temp, test;
679 intptr_t hash;
680 markWord mark = obj->mark_acquire();
681 // If UseObjectMonitorTable is set the hash can simply be installed in the
682 // object header, since the monitor isn't in the object header.
683 if (UseObjectMonitorTable || !mark.has_monitor()) {
684 hash = mark.hash();
685 if (hash != 0) { // if it has a hash, just return it
686 return hash;
687 }
688 hash = get_next_hash(current, obj); // get a new hash
689 temp = mark.copy_set_hash(hash); // merge the hash into header
690 // try to install the hash
691 test = obj->cas_set_mark(temp, mark);
692 if (test == mark) { // if the hash was installed, return it
693 return hash;
694 }
695 // CAS failed, retry
696 continue;
697
698 // Failed to install the hash. It could be that another thread
699 // installed the hash just before our attempt or inflation has
700 // occurred or... so we fall thru to inflate the monitor for
701 // stability and then install the hash.
702 } else {
703 assert(!mark.is_unlocked() && !mark.is_fast_locked(), "invariant");
704 monitor = mark.monitor();
705 temp = monitor->header();
706 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
707 hash = temp.hash();
708 if (hash != 0) {
709 // It has a hash.
710
711 // Separate load of dmw/header above from the loads in
712 // is_being_async_deflated().
713
714 // dmw/header and _contentions may get written by different threads.
715 // Make sure to observe them in the same order when having several observers.
716 OrderAccess::loadload_for_IRIW();
717
718 if (monitor->is_being_async_deflated()) {
719 // But we can't safely use the hash if we detect that async
720 // deflation has occurred. So we attempt to restore the
721 // header/dmw to the object's header so that we only retry
722 // once if the deflater thread happens to be slow.
723 monitor->install_displaced_markword_in_object(obj);
724 continue;
725 }
726 return hash;
727 }
728 // Fall thru so we only have one place that installs the hash in
729 // the ObjectMonitor.
730 }
731
732 // NOTE: an async deflation can race after we get the monitor and
733 // before we can update the ObjectMonitor's header with the hash
734 // value below.
735 assert(mark.has_monitor(), "must be");
736 monitor = mark.monitor();
737
738 // Load ObjectMonitor's header/dmw field and see if it has a hash.
739 mark = monitor->header();
740 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
741 hash = mark.hash();
742 if (hash == 0) { // if it does not have a hash
743 hash = get_next_hash(current, obj); // get a new hash
744 temp = mark.copy_set_hash(hash) ; // merge the hash into header
745 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
746 uintptr_t v = AtomicAccess::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
747 test = markWord(v);
748 if (test != mark) {
749 // The attempt to update the ObjectMonitor's header/dmw field
750 // did not work. This can happen if another thread managed to
751 // merge in the hash just before our cmpxchg().
752 // If we add any new usages of the header/dmw field, this code
753 // will need to be updated.
754 hash = test.hash();
755 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
756 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
757 }
758 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
759 // If we detect that async deflation has occurred, then we
760 // attempt to restore the header/dmw to the object's header
761 // so that we only retry once if the deflater thread happens
762 // to be slow.
763 monitor->install_displaced_markword_in_object(obj);
764 continue;
765 }
766 }
767 // We finally get the hash.
768 return hash;
769 }
770 }
771
772 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
773 Handle h_obj) {
774 if (h_obj->mark().is_inline_type()) {
775 return false;
776 }
777 assert(current == JavaThread::current(), "Can only be called on current thread");
778 oop obj = h_obj();
779
780 markWord mark = obj->mark_acquire();
781
782 if (mark.is_fast_locked()) {
783 // fast-locking case, see if lock is in current's lock stack
784 return current->lock_stack().contains(h_obj());
785 }
786
787 while (mark.has_monitor()) {
788 ObjectMonitor* monitor = read_monitor(obj, mark);
789 if (monitor != nullptr) {
790 return monitor->is_entered(current) != 0;
791 }
792 // Racing with inflation/deflation, retry
793 mark = obj->mark_acquire();
794
795 if (mark.is_fast_locked()) {
796 // Some other thread fast_locked, current could not have held the lock
797 return false;
798 }
799 }
800
801 // Unlocked case, header in place
802 assert(mark.is_unlocked(), "sanity check");
803 return false;
804 }
805
806 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
807 oop obj = h_obj();
808 markWord mark = obj->mark_acquire();
809
810 if (mark.is_fast_locked()) {
811 // fast-locked so get owner from the object.
812 // owning_thread_from_object() may also return null here:
813 return Threads::owning_thread_from_object(t_list, h_obj());
814 }
815
816 while (mark.has_monitor()) {
817 ObjectMonitor* monitor = read_monitor(obj, mark);
818 if (monitor != nullptr) {
819 return Threads::owning_thread_from_monitor(t_list, monitor);
820 }
821 // Racing with inflation/deflation, retry
822 mark = obj->mark_acquire();
823
824 if (mark.is_fast_locked()) {
825 // Some other thread fast_locked
826 return Threads::owning_thread_from_object(t_list, h_obj());
827 }
828 }
829
830 // Unlocked case, header in place
831 // Cannot have assertion since this object may have been
832 // locked by another thread when reaching here.
833 // assert(mark.is_unlocked(), "sanity check");
834
835 return nullptr;
836 }
837
838 // Visitors ...
839
840 // Iterate over all ObjectMonitors.
841 template <typename Function>
842 void ObjectSynchronizer::monitors_iterate(Function function) {
843 MonitorList::Iterator iter = _in_use_list.iterator();
844 while (iter.has_next()) {
845 ObjectMonitor* monitor = iter.next();
846 function(monitor);
847 }
848 }
849
850 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
851 // returns true.
852 template <typename OwnerFilter>
853 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
854 monitors_iterate([&](ObjectMonitor* monitor) {
855 // This function is only called at a safepoint or when the
856 // target thread is suspended or when the target thread is
857 // operating on itself. The current closures in use today are
858 // only interested in an owned ObjectMonitor and ownership
859 // cannot be dropped under the calling contexts so the
860 // ObjectMonitor cannot be async deflated.
861 if (monitor->has_owner() && filter(monitor)) {
862 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
863
864 closure->do_monitor(monitor);
865 }
866 });
867 }
868
869 // Iterate ObjectMonitors where the owner == thread; this does NOT include
870 // ObjectMonitors where owner is set to a stack-lock address in thread.
871 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
872 int64_t key = ObjectMonitor::owner_id_from(thread);
873 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
874 return owned_monitors_iterate_filtered(closure, thread_filter);
875 }
876
877 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
878 int64_t key = ObjectMonitor::owner_id_from(vthread);
879 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
880 return owned_monitors_iterate_filtered(closure, thread_filter);
881 }
882
883 // Iterate ObjectMonitors owned by any thread.
884 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
885 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
886 return owned_monitors_iterate_filtered(closure, all_filter);
887 }
888
889 static bool monitors_used_above_threshold(MonitorList* list) {
890 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
891 return false;
892 }
893 size_t monitors_used = list->count();
894 if (monitors_used == 0) { // empty list is easy
895 return false;
896 }
897 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
898 // Make sure that we use a ceiling value that is not lower than
899 // previous, not lower than the recorded max used by the system, and
900 // not lower than the current number of monitors in use (which can
901 // race ahead of max). The result is guaranteed > 0.
902 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
903
904 // Check if our monitor usage is above the threshold:
905 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
906 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
907 // Deflate monitors if over the threshold percentage, unless no
908 // progress on previous deflations.
909 bool is_above_threshold = true;
910
911 // Check if it's time to adjust the in_use_list_ceiling up, due
912 // to too many async deflation attempts without any progress.
913 if (NoAsyncDeflationProgressMax != 0 &&
914 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
915 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
916 size_t delta = (size_t)(ceiling * remainder) + 1;
917 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
918 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
919 : ceiling + delta;
920
921 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
922 log_info(monitorinflation)("Too many deflations without progress; "
923 "bumping in_use_list_ceiling from %zu"
924 " to %zu", old_ceiling, new_ceiling);
925 _no_progress_cnt = 0;
926 ceiling = new_ceiling;
927
928 // Check if our monitor usage is still above the threshold:
929 monitor_usage = (monitors_used * 100LL) / ceiling;
930 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
931 }
932 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
933 ", monitor_usage=%zu, threshold=%d",
934 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
935 return is_above_threshold;
936 }
937
938 return false;
939 }
940
941 size_t ObjectSynchronizer::in_use_list_count() {
942 return _in_use_list.count();
943 }
944
945 size_t ObjectSynchronizer::in_use_list_max() {
946 return _in_use_list.max();
947 }
948
949 size_t ObjectSynchronizer::in_use_list_ceiling() {
950 return _in_use_list_ceiling;
951 }
952
953 void ObjectSynchronizer::dec_in_use_list_ceiling() {
954 AtomicAccess::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
955 }
956
957 void ObjectSynchronizer::inc_in_use_list_ceiling() {
958 AtomicAccess::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
959 }
960
961 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
962 _in_use_list_ceiling = new_value;
963 }
964
965 bool ObjectSynchronizer::is_async_deflation_needed() {
966 if (is_async_deflation_requested()) {
967 // Async deflation request.
968 log_info(monitorinflation)("Async deflation needed: explicit request");
969 return true;
970 }
971
972 jlong time_since_last = time_since_last_async_deflation_ms();
973
974 if (AsyncDeflationInterval > 0 &&
975 time_since_last > AsyncDeflationInterval &&
976 monitors_used_above_threshold(&_in_use_list)) {
977 // It's been longer than our specified deflate interval and there
978 // are too many monitors in use. We don't deflate more frequently
979 // than AsyncDeflationInterval (unless is_async_deflation_requested)
980 // in order to not swamp the MonitorDeflationThread.
981 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
982 return true;
983 }
984
985 if (GuaranteedAsyncDeflationInterval > 0 &&
986 time_since_last > GuaranteedAsyncDeflationInterval) {
987 // It's been longer than our specified guaranteed deflate interval.
988 // We need to clean up the used monitors even if the threshold is
989 // not reached, to keep the memory utilization at bay when many threads
990 // touched many monitors.
991 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
992 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
993 GuaranteedAsyncDeflationInterval, time_since_last);
994
995 // If this deflation has no progress, then it should not affect the no-progress
996 // tracking, otherwise threshold heuristics would think it was triggered, experienced
997 // no progress, and needs to backoff more aggressively. In this "no progress" case,
998 // the generic code would bump the no-progress counter, and we compensate for that
999 // by telling it to skip the update.
1000 //
1001 // If this deflation has progress, then it should let non-progress tracking
1002 // know about this, otherwise the threshold heuristics would kick in, potentially
1003 // experience no-progress due to aggressive cleanup by this deflation, and think
1004 // it is still in no-progress stride. In this "progress" case, the generic code would
1005 // zero the counter, and we allow it to happen.
1006 _no_progress_skip_increment = true;
1007
1008 return true;
1009 }
1010
1011 return false;
1012 }
1013
1014 void ObjectSynchronizer::request_deflate_idle_monitors() {
1015 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1016 set_is_async_deflation_requested(true);
1017 ml.notify_all();
1018 }
1019
1020 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1021 JavaThread* current = JavaThread::current();
1022 bool ret_code = false;
1023
1024 jlong last_time = last_async_deflation_time_ns();
1025
1026 request_deflate_idle_monitors();
1027
1028 const int N_CHECKS = 5;
1029 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1030 if (last_async_deflation_time_ns() > last_time) {
1031 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1032 ret_code = true;
1033 break;
1034 }
1035 {
1036 // JavaThread has to honor the blocking protocol.
1037 ThreadBlockInVM tbivm(current);
1038 os::naked_short_sleep(999); // sleep for almost 1 second
1039 }
1040 }
1041 if (!ret_code) {
1042 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1043 }
1044
1045 return ret_code;
1046 }
1047
1048 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1049 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1050 }
1051
1052 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1053 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1054 //
1055 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1056 MonitorList::Iterator iter = _in_use_list.iterator();
1057 size_t deflated_count = 0;
1058 Thread* current = Thread::current();
1059
1060 while (iter.has_next()) {
1061 if (deflated_count >= (size_t)MonitorDeflationMax) {
1062 break;
1063 }
1064 ObjectMonitor* mid = iter.next();
1065 if (mid->deflate_monitor(current)) {
1066 deflated_count++;
1067 }
1068
1069 // Must check for a safepoint/handshake and honor it.
1070 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1071 }
1072
1073 return deflated_count;
1074 }
1075
1076 class DeflationHandshakeClosure : public HandshakeClosure {
1077 public:
1078 DeflationHandshakeClosure() : HandshakeClosure("DeflationHandshakeClosure") {}
1079
1080 void do_thread(Thread* thread) {
1081 log_trace(monitorinflation)("DeflationHandshakeClosure::do_thread: thread="
1082 INTPTR_FORMAT, p2i(thread));
1083 if (thread->is_Java_thread()) {
1084 // Clear OM cache
1085 JavaThread* jt = JavaThread::cast(thread);
1086 jt->om_clear_monitor_cache();
1087 }
1088 }
1089 };
1090
1091 class VM_RendezvousGCThreads : public VM_Operation {
1092 public:
1093 bool evaluate_at_safepoint() const override { return false; }
1094 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1095 void doit() override {
1096 Universe::heap()->safepoint_synchronize_begin();
1097 Universe::heap()->safepoint_synchronize_end();
1098 };
1099 };
1100
1101 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1102 ObjectMonitorDeflationSafepointer* safepointer) {
1103 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1104 size_t deleted_count = 0;
1105 for (ObjectMonitor* monitor: *delete_list) {
1106 delete monitor;
1107 deleted_count++;
1108 // A JavaThread must check for a safepoint/handshake and honor it.
1109 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1110 }
1111 return deleted_count;
1112 }
1113
1114 class ObjectMonitorDeflationLogging: public StackObj {
1115 LogStreamHandle(Debug, monitorinflation) _debug;
1116 LogStreamHandle(Info, monitorinflation) _info;
1117 LogStream* _stream;
1118 elapsedTimer _timer;
1119
1120 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1121 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1122 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1123
1124 public:
1125 ObjectMonitorDeflationLogging()
1126 : _debug(), _info(), _stream(nullptr) {
1127 if (_debug.is_enabled()) {
1128 _stream = &_debug;
1129 } else if (_info.is_enabled()) {
1130 _stream = &_info;
1131 }
1132 }
1133
1134 void begin() {
1135 if (_stream != nullptr) {
1136 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1137 ceiling(), count(), max());
1138 _timer.start();
1139 }
1140 }
1141
1142 void before_handshake(size_t unlinked_count) {
1143 if (_stream != nullptr) {
1144 _timer.stop();
1145 _stream->print_cr("before handshaking: unlinked_count=%zu"
1146 ", in_use_list stats: ceiling=%zu, count="
1147 "%zu, max=%zu",
1148 unlinked_count, ceiling(), count(), max());
1149 }
1150 }
1151
1152 void after_handshake() {
1153 if (_stream != nullptr) {
1154 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1155 "%zu, count=%zu, max=%zu",
1156 ceiling(), count(), max());
1157 _timer.start();
1158 }
1159 }
1160
1161 void end(size_t deflated_count, size_t unlinked_count) {
1162 if (_stream != nullptr) {
1163 _timer.stop();
1164 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1165 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1166 deflated_count, unlinked_count, _timer.seconds());
1167 }
1168 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1169 ceiling(), count(), max());
1170 }
1171 }
1172
1173 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1174 if (_stream != nullptr) {
1175 _timer.stop();
1176 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1177 "%zu, count=%zu, max=%zu",
1178 op_name, cnt_name, cnt, ceiling(), count(), max());
1179 }
1180 }
1181
1182 void after_block_for_safepoint(const char* op_name) {
1183 if (_stream != nullptr) {
1184 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1185 ", count=%zu, max=%zu", op_name,
1186 ceiling(), count(), max());
1187 _timer.start();
1188 }
1189 }
1190 };
1191
1192 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1193 if (!SafepointMechanism::should_process(_current)) {
1194 return;
1195 }
1196
1197 // A safepoint/handshake has started.
1198 _log->before_block_for_safepoint(op_name, count_name, counter);
1199
1200 {
1201 // Honor block request.
1202 ThreadBlockInVM tbivm(_current);
1203 }
1204
1205 _log->after_block_for_safepoint(op_name);
1206 }
1207
1208 // This function is called by the MonitorDeflationThread to deflate
1209 // ObjectMonitors.
1210 size_t ObjectSynchronizer::deflate_idle_monitors() {
1211 JavaThread* current = JavaThread::current();
1212 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1213
1214 // The async deflation request has been processed.
1215 _last_async_deflation_time_ns = os::javaTimeNanos();
1216 set_is_async_deflation_requested(false);
1217
1218 ObjectMonitorDeflationLogging log;
1219 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1220
1221 log.begin();
1222
1223 // Deflate some idle ObjectMonitors.
1224 size_t deflated_count = deflate_monitor_list(&safepointer);
1225
1226 // Unlink the deflated ObjectMonitors from the in-use list.
1227 size_t unlinked_count = 0;
1228 size_t deleted_count = 0;
1229 if (deflated_count > 0) {
1230 ResourceMark rm(current);
1231 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1232 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1233
1234 GrowableArray<ObjectMonitorTable::Table*> table_delete_list;
1235 if (UseObjectMonitorTable) {
1236 ObjectMonitorTable::rebuild(&table_delete_list);
1237 }
1238
1239 log.before_handshake(unlinked_count);
1240
1241 // A JavaThread needs to handshake in order to safely free the
1242 // ObjectMonitors that were deflated in this cycle.
1243 DeflationHandshakeClosure dhc;
1244 Handshake::execute(&dhc);
1245 // Also, we sync and desync GC threads around the handshake, so that they can
1246 // safely read the mark-word and look-through to the object-monitor, without
1247 // being afraid that the object-monitor is going away.
1248 VM_RendezvousGCThreads sync_gc;
1249 VMThread::execute(&sync_gc);
1250
1251 log.after_handshake();
1252
1253 // After the handshake, safely free the ObjectMonitors that were
1254 // deflated and unlinked in this cycle.
1255
1256 // Delete the unlinked ObjectMonitors.
1257 deleted_count = delete_monitors(&delete_list, &safepointer);
1258 if (UseObjectMonitorTable) {
1259 ObjectMonitorTable::destroy(&table_delete_list);
1260 }
1261 assert(unlinked_count == deleted_count, "must be");
1262 }
1263
1264 log.end(deflated_count, unlinked_count);
1265
1266 GVars.stw_random = os::random();
1267
1268 if (deflated_count != 0) {
1269 _no_progress_cnt = 0;
1270 } else if (_no_progress_skip_increment) {
1271 _no_progress_skip_increment = false;
1272 } else {
1273 _no_progress_cnt++;
1274 }
1275
1276 return deflated_count;
1277 }
1278
1279 // Monitor cleanup on JavaThread::exit
1280
1281 // Iterate through monitor cache and attempt to release thread's monitors
1282 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1283 private:
1284 JavaThread* _thread;
1285
1286 public:
1287 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1288 void do_monitor(ObjectMonitor* mid) {
1289 mid->complete_exit(_thread);
1290 }
1291 };
1292
1293 // Release all inflated monitors owned by current thread. Lightweight monitors are
1294 // ignored. This is meant to be called during JNI thread detach which assumes
1295 // all remaining monitors are heavyweight. All exceptions are swallowed.
1296 // Scanning the extant monitor list can be time consuming.
1297 // A simple optimization is to add a per-thread flag that indicates a thread
1298 // called jni_monitorenter() during its lifetime.
1299 //
1300 // Instead of NoSafepointVerifier it might be cheaper to
1301 // use an idiom of the form:
1302 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1303 // <code that must not run at safepoint>
1304 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1305 // Since the tests are extremely cheap we could leave them enabled
1306 // for normal product builds.
1307
1308 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1309 assert(current == JavaThread::current(), "must be current Java thread");
1310 NoSafepointVerifier nsv;
1311 ReleaseJavaMonitorsClosure rjmc(current);
1312 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1313 assert(!current->has_pending_exception(), "Should not be possible");
1314 current->clear_pending_exception();
1315 }
1316
1317 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1318 switch (cause) {
1319 case inflate_cause_vm_internal: return "VM Internal";
1320 case inflate_cause_monitor_enter: return "Monitor Enter";
1321 case inflate_cause_wait: return "Monitor Wait";
1322 case inflate_cause_notify: return "Monitor Notify";
1323 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1324 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1325 default:
1326 ShouldNotReachHere();
1327 }
1328 return "Unknown";
1329 }
1330
1331 //------------------------------------------------------------------------------
1332 // Debugging code
1333
1334 u_char* ObjectSynchronizer::get_gvars_addr() {
1335 return (u_char*)&GVars;
1336 }
1337
1338 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1339 return (u_char*)&GVars.hc_sequence;
1340 }
1341
1342 size_t ObjectSynchronizer::get_gvars_size() {
1343 return sizeof(SharedGlobals);
1344 }
1345
1346 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1347 return (u_char*)&GVars.stw_random;
1348 }
1349
1350 // Do the final audit and print of ObjectMonitor stats; must be done
1351 // by the VMThread at VM exit time.
1352 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1353 assert(Thread::current()->is_VM_thread(), "sanity check");
1354
1355 if (is_final_audit()) { // Only do the audit once.
1356 return;
1357 }
1358 set_is_final_audit();
1359 log_info(monitorinflation)("Starting the final audit.");
1360
1361 if (log_is_enabled(Info, monitorinflation)) {
1362 LogStreamHandle(Info, monitorinflation) ls;
1363 audit_and_print_stats(&ls, true /* on_exit */);
1364 }
1365 }
1366
1367 // This function can be called by the MonitorDeflationThread or it can be called when
1368 // we are trying to exit the VM. The list walker functions can run in parallel with
1369 // the other list operations.
1370 // Calls to this function can be added in various places as a debugging
1371 // aid.
1372 //
1373 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1374 int error_cnt = 0;
1375
1376 ls->print_cr("Checking in_use_list:");
1377 chk_in_use_list(ls, &error_cnt);
1378
1379 if (error_cnt == 0) {
1380 ls->print_cr("No errors found in in_use_list checks.");
1381 } else {
1382 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1383 }
1384
1385 // When exiting, only log the interesting entries at the Info level.
1386 // When called at intervals by the MonitorDeflationThread, log output
1387 // at the Trace level since there can be a lot of it.
1388 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1389 LogStreamHandle(Trace, monitorinflation) ls_tr;
1390 log_in_use_monitor_details(&ls_tr, true /* log_all */);
1391 } else if (on_exit) {
1392 log_in_use_monitor_details(ls, false /* log_all */);
1393 }
1394
1395 ls->flush();
1396
1397 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1398 }
1399
1400 // Check the in_use_list; log the results of the checks.
1401 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1402 size_t l_in_use_count = _in_use_list.count();
1403 size_t l_in_use_max = _in_use_list.max();
1404 out->print_cr("count=%zu, max=%zu", l_in_use_count,
1405 l_in_use_max);
1406
1407 size_t ck_in_use_count = 0;
1408 MonitorList::Iterator iter = _in_use_list.iterator();
1409 while (iter.has_next()) {
1410 ObjectMonitor* mid = iter.next();
1411 chk_in_use_entry(mid, out, error_cnt_p);
1412 ck_in_use_count++;
1413 }
1414
1415 if (l_in_use_count == ck_in_use_count) {
1416 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
1417 l_in_use_count, ck_in_use_count);
1418 } else {
1419 out->print_cr("WARNING: in_use_count=%zu is not equal to "
1420 "ck_in_use_count=%zu", l_in_use_count,
1421 ck_in_use_count);
1422 }
1423
1424 size_t ck_in_use_max = _in_use_list.max();
1425 if (l_in_use_max == ck_in_use_max) {
1426 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
1427 l_in_use_max, ck_in_use_max);
1428 } else {
1429 out->print_cr("WARNING: in_use_max=%zu is not equal to "
1430 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
1431 }
1432 }
1433
1434 // Check an in-use monitor entry; log any errors.
1435 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1436 int* error_cnt_p) {
1437 if (n->owner_is_DEFLATER_MARKER()) {
1438 // This could happen when monitor deflation blocks for a safepoint.
1439 return;
1440 }
1441
1442
1443 if (n->metadata() == 0) {
1444 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1445 "have non-null _metadata (header/hash) field.", p2i(n));
1446 *error_cnt_p = *error_cnt_p + 1;
1447 }
1448
1449 const oop obj = n->object_peek();
1450 if (obj == nullptr) {
1451 return;
1452 }
1453
1454 const markWord mark = obj->mark();
1455 if (!mark.has_monitor()) {
1456 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1457 "object does not think it has a monitor: obj="
1458 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1459 p2i(obj), mark.value());
1460 *error_cnt_p = *error_cnt_p + 1;
1461 return;
1462 }
1463
1464 ObjectMonitor* const obj_mon = read_monitor(obj, mark);
1465 if (n != obj_mon) {
1466 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1467 "object does not refer to the same monitor: obj="
1468 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1469 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1470 *error_cnt_p = *error_cnt_p + 1;
1471 }
1472 }
1473
1474 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1475 // flags indicate why the entry is in-use, 'object' and 'object type'
1476 // indicate the associated object and its type.
1477 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
1478 if (_in_use_list.count() > 0) {
1479 stringStream ss;
1480 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
1481 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1482 out->print_cr("%18s %s %18s %18s",
1483 "monitor", "BHL", "object", "object type");
1484 out->print_cr("================== === ================== ==================");
1485
1486 auto is_interesting = [&](ObjectMonitor* monitor) {
1487 return log_all || monitor->has_owner() || monitor->is_busy();
1488 };
1489
1490 monitors_iterate([&](ObjectMonitor* monitor) {
1491 if (is_interesting(monitor)) {
1492 const oop obj = monitor->object_peek();
1493 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
1494 ResourceMark rm;
1495 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
1496 monitor->is_busy(), hash != 0, monitor->has_owner(),
1497 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
1498 if (monitor->is_busy()) {
1499 out->print(" (%s)", monitor->is_busy_to_string(&ss));
1500 ss.reset();
1501 }
1502 out->cr();
1503 }
1504 });
1505 }
1506
1507 out->flush();
1508 }
1509
1510 ObjectMonitor* ObjectSynchronizer::get_or_insert_monitor_from_table(oop object, bool* inserted) {
1511 ObjectMonitor* monitor = get_monitor_from_table(object);
1512 if (monitor != nullptr) {
1513 *inserted = false;
1514 return monitor;
1515 }
1516
1517 ObjectMonitor* alloced_monitor = new ObjectMonitor(object);
1518 alloced_monitor->set_anonymous_owner();
1519
1520 // Try insert monitor
1521 monitor = add_monitor(alloced_monitor, object);
1522
1523 *inserted = alloced_monitor == monitor;
1524 if (!*inserted) {
1525 delete alloced_monitor;
1526 }
1527
1528 return monitor;
1529 }
1530
1531 static void log_inflate(Thread* current, oop object, ObjectSynchronizer::InflateCause cause) {
1532 if (log_is_enabled(Trace, monitorinflation)) {
1533 ResourceMark rm(current);
1534 log_trace(monitorinflation)("inflate: object=" INTPTR_FORMAT ", mark="
1535 INTPTR_FORMAT ", type='%s' cause=%s", p2i(object),
1536 object->mark().value(), object->klass()->external_name(),
1537 ObjectSynchronizer::inflate_cause_name(cause));
1538 }
1539 }
1540
1541 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1542 const oop obj,
1543 ObjectSynchronizer::InflateCause cause) {
1544 assert(event != nullptr, "invariant");
1545 const Klass* monitor_klass = obj->klass();
1546 if (ObjectMonitor::is_jfr_excluded(monitor_klass)) {
1547 return;
1548 }
1549 event->set_monitorClass(monitor_klass);
1550 event->set_address((uintptr_t)(void*)obj);
1551 event->set_cause((u1)cause);
1552 event->commit();
1553 }
1554
1555 ObjectMonitor* ObjectSynchronizer::get_or_insert_monitor(oop object, JavaThread* current, ObjectSynchronizer::InflateCause cause) {
1556 assert(UseObjectMonitorTable, "must be");
1557
1558 EventJavaMonitorInflate event;
1559
1560 bool inserted;
1561 ObjectMonitor* monitor = get_or_insert_monitor_from_table(object, &inserted);
1562
1563 if (inserted) {
1564 log_inflate(current, object, cause);
1565 if (event.should_commit()) {
1566 post_monitor_inflate_event(&event, object, cause);
1567 }
1568
1569 // The monitor has an anonymous owner so it is safe from async deflation.
1570 ObjectSynchronizer::_in_use_list.add(monitor);
1571 }
1572
1573 return monitor;
1574 }
1575
1576 // Add the hashcode to the monitor to match the object and put it in the hashtable.
1577 ObjectMonitor* ObjectSynchronizer::add_monitor(ObjectMonitor* monitor, oop obj) {
1578 assert(UseObjectMonitorTable, "must be");
1579 assert(obj == monitor->object(), "must be");
1580
1581 intptr_t hash = obj->mark().hash();
1582 assert(hash != 0, "must be set when claiming the object monitor");
1583 monitor->set_hash(hash);
1584
1585 return ObjectMonitorTable::monitor_put_get(monitor, obj);
1586 }
1587
1588 void ObjectSynchronizer::remove_monitor(ObjectMonitor* monitor, oop obj) {
1589 assert(UseObjectMonitorTable, "must be");
1590 assert(monitor->object_peek() == obj, "must be, cleared objects are removed by is_dead");
1591
1592 ObjectMonitorTable::remove_monitor_entry(monitor);
1593 }
1594
1595 void ObjectSynchronizer::deflate_mark_word(oop obj) {
1596 assert(UseObjectMonitorTable, "must be");
1597
1598 markWord mark = obj->mark_acquire();
1599 assert(!mark.has_no_hash(), "obj with inflated monitor must have had a hash");
1600
1601 while (mark.has_monitor()) {
1602 const markWord new_mark = mark.clear_lock_bits().set_unlocked();
1603 mark = obj->cas_set_mark(new_mark, mark);
1604 }
1605 }
1606
1607 void ObjectSynchronizer::create_om_table() {
1608 if (!UseObjectMonitorTable) {
1609 return;
1610 }
1611 ObjectMonitorTable::create();
1612 }
1613
1614 class ObjectSynchronizer::LockStackInflateContendedLocks : private OopClosure {
1615 private:
1616 oop _contended_oops[LockStack::CAPACITY];
1617 int _length;
1618
1619 void do_oop(oop* o) final {
1620 oop obj = *o;
1621 if (obj->mark_acquire().has_monitor()) {
1622 if (_length > 0 && _contended_oops[_length - 1] == obj) {
1623 // Recursive
1624 return;
1625 }
1626 _contended_oops[_length++] = obj;
1627 }
1628 }
1629
1630 void do_oop(narrowOop* o) final {
1631 ShouldNotReachHere();
1632 }
1633
1634 public:
1635 LockStackInflateContendedLocks() :
1636 _contended_oops(),
1637 _length(0) {};
1638
1639 void inflate(JavaThread* current) {
1640 assert(current == JavaThread::current(), "must be");
1641 current->lock_stack().oops_do(this);
1642 for (int i = 0; i < _length; i++) {
1643 ObjectSynchronizer::
1644 inflate_fast_locked_object(_contended_oops[i], ObjectSynchronizer::inflate_cause_vm_internal, current, current);
1645 }
1646 }
1647 };
1648
1649 void ObjectSynchronizer::ensure_lock_stack_space(JavaThread* current) {
1650 assert(current == JavaThread::current(), "must be");
1651 LockStack& lock_stack = current->lock_stack();
1652
1653 // Make room on lock_stack
1654 if (lock_stack.is_full()) {
1655 // Inflate contended objects
1656 LockStackInflateContendedLocks().inflate(current);
1657 if (lock_stack.is_full()) {
1658 // Inflate the oldest object
1659 inflate_fast_locked_object(lock_stack.bottom(), ObjectSynchronizer::inflate_cause_vm_internal, current, current);
1660 }
1661 }
1662 }
1663
1664 class ObjectSynchronizer::CacheSetter : StackObj {
1665 JavaThread* const _thread;
1666 BasicLock* const _lock;
1667 ObjectMonitor* _monitor;
1668
1669 NONCOPYABLE(CacheSetter);
1670
1671 public:
1672 CacheSetter(JavaThread* thread, BasicLock* lock) :
1673 _thread(thread),
1674 _lock(lock),
1675 _monitor(nullptr) {}
1676
1677 ~CacheSetter() {
1678 // Only use the cache if using the table.
1679 if (UseObjectMonitorTable) {
1680 if (_monitor != nullptr) {
1681 // If the monitor is already in the BasicLock cache then it is most
1682 // likely in the thread cache, do not set it again to avoid reordering.
1683 if (_monitor != _lock->object_monitor_cache()) {
1684 _thread->om_set_monitor_cache(_monitor);
1685 _lock->set_object_monitor_cache(_monitor);
1686 }
1687 } else {
1688 _lock->clear_object_monitor_cache();
1689 }
1690 }
1691 }
1692
1693 void set_monitor(ObjectMonitor* monitor) {
1694 assert(_monitor == nullptr, "only set once");
1695 _monitor = monitor;
1696 }
1697
1698 };
1699
1700 // Reads first from the BasicLock cache then from the OMCache in the current thread.
1701 // C2 fast-path may have put the monitor in the cache in the BasicLock.
1702 inline static ObjectMonitor* read_caches(JavaThread* current, BasicLock* lock, oop object) {
1703 ObjectMonitor* monitor = lock->object_monitor_cache();
1704 if (monitor == nullptr) {
1705 monitor = current->om_get_from_monitor_cache(object);
1706 }
1707 return monitor;
1708 }
1709
1710 class ObjectSynchronizer::VerifyThreadState {
1711 bool _no_safepoint;
1712
1713 public:
1714 VerifyThreadState(JavaThread* locking_thread, JavaThread* current) : _no_safepoint(locking_thread != current) {
1715 assert(current == Thread::current(), "must be");
1716 assert(locking_thread == current || locking_thread->is_obj_deopt_suspend(), "locking_thread may not run concurrently");
1717 if (_no_safepoint) {
1718 DEBUG_ONLY(JavaThread::current()->inc_no_safepoint_count();)
1719 }
1720 }
1721 ~VerifyThreadState() {
1722 if (_no_safepoint){
1723 DEBUG_ONLY(JavaThread::current()->dec_no_safepoint_count();)
1724 }
1725 }
1726 };
1727
1728 inline bool ObjectSynchronizer::fast_lock_try_enter(oop obj, LockStack& lock_stack, JavaThread* current) {
1729 markWord mark = obj->mark();
1730 while (mark.is_unlocked()) {
1731 ensure_lock_stack_space(current);
1732 assert(!lock_stack.is_full(), "must have made room on the lock stack");
1733 assert(!lock_stack.contains(obj), "thread must not already hold the lock");
1734 // Try to swing into 'fast-locked' state.
1735 markWord locked_mark = mark.set_fast_locked();
1736 markWord old_mark = mark;
1737 mark = obj->cas_set_mark(locked_mark, old_mark);
1738 if (old_mark == mark) {
1739 // Successfully fast-locked, push object to lock-stack and return.
1740 lock_stack.push(obj);
1741 return true;
1742 }
1743 }
1744 return false;
1745 }
1746
1747 bool ObjectSynchronizer::fast_lock_spin_enter(oop obj, LockStack& lock_stack, JavaThread* current, bool observed_deflation) {
1748 assert(UseObjectMonitorTable, "must be");
1749 // Will spin with exponential backoff with an accumulative O(2^spin_limit) spins.
1750 const int log_spin_limit = os::is_MP() ? FastLockingSpins : 1;
1751 const int log_min_safepoint_check_interval = 10;
1752
1753 markWord mark = obj->mark();
1754 const auto should_spin = [&]() {
1755 if (!mark.has_monitor()) {
1756 // Spin while not inflated.
1757 return true;
1758 } else if (observed_deflation) {
1759 // Spin while monitor is being deflated.
1760 ObjectMonitor* monitor = ObjectSynchronizer::read_monitor(obj, mark);
1761 return monitor == nullptr || monitor->is_being_async_deflated();
1762 }
1763 // Else stop spinning.
1764 return false;
1765 };
1766 // Always attempt to lock once even when safepoint synchronizing.
1767 bool should_process = false;
1768 for (int i = 0; should_spin() && !should_process && i < log_spin_limit; i++) {
1769 // Spin with exponential backoff.
1770 const int total_spin_count = 1 << i;
1771 const int inner_spin_count = MIN2(1 << log_min_safepoint_check_interval, total_spin_count);
1772 const int outer_spin_count = total_spin_count / inner_spin_count;
1773 for (int outer = 0; outer < outer_spin_count; outer++) {
1774 should_process = SafepointMechanism::should_process(current);
1775 if (should_process) {
1776 // Stop spinning for safepoint.
1777 break;
1778 }
1779 for (int inner = 1; inner < inner_spin_count; inner++) {
1780 SpinPause();
1781 }
1782 }
1783
1784 if (fast_lock_try_enter(obj, lock_stack, current)) return true;
1785 }
1786 return false;
1787 }
1788
1789 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
1790 // When called with locking_thread != Thread::current() some mechanism must synchronize
1791 // the locking_thread with respect to the current thread. Currently only used when
1792 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
1793 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
1794
1795 assert(!UseObjectMonitorTable || lock->object_monitor_cache() == nullptr, "must be cleared");
1796 JavaThread* current = JavaThread::current();
1797 VerifyThreadState vts(locking_thread, current);
1798
1799 if (obj->klass()->is_value_based()) {
1800 ObjectSynchronizer::handle_sync_on_value_based_class(obj, locking_thread);
1801 }
1802
1803 LockStack& lock_stack = locking_thread->lock_stack();
1804
1805 ObjectMonitor* monitor = nullptr;
1806 if (lock_stack.contains(obj())) {
1807 monitor = inflate_fast_locked_object(obj(), ObjectSynchronizer::inflate_cause_monitor_enter, locking_thread, current);
1808 bool entered = monitor->enter_for(locking_thread);
1809 assert(entered, "recursive ObjectMonitor::enter_for must succeed");
1810 } else {
1811 do {
1812 // It is assumed that enter_for must enter on an object without contention.
1813 monitor = inflate_and_enter(obj(), lock, ObjectSynchronizer::inflate_cause_monitor_enter, locking_thread, current);
1814 // But there may still be a race with deflation.
1815 } while (monitor == nullptr);
1816 }
1817
1818 assert(monitor != nullptr, "ObjectSynchronizer::enter_for must succeed");
1819 assert(!UseObjectMonitorTable || lock->object_monitor_cache() == nullptr, "unused. already cleared");
1820 }
1821
1822 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
1823 assert(current == JavaThread::current(), "must be");
1824
1825 if (obj->klass()->is_value_based()) {
1826 ObjectSynchronizer::handle_sync_on_value_based_class(obj, current);
1827 }
1828
1829 CacheSetter cache_setter(current, lock);
1830
1831 // Used when deflation is observed. Progress here requires progress
1832 // from the deflator. After observing that the deflator is not
1833 // making progress (after two yields), switch to sleeping.
1834 SpinYield spin_yield(0, 2);
1835 bool observed_deflation = false;
1836
1837 LockStack& lock_stack = current->lock_stack();
1838
1839 if (!lock_stack.is_full() && lock_stack.try_recursive_enter(obj())) {
1840 // Recursively fast locked
1841 return;
1842 }
1843
1844 if (lock_stack.contains(obj())) {
1845 ObjectMonitor* monitor = inflate_fast_locked_object(obj(), ObjectSynchronizer::inflate_cause_monitor_enter, current, current);
1846 bool entered = monitor->enter(current);
1847 assert(entered, "recursive ObjectMonitor::enter must succeed");
1848 cache_setter.set_monitor(monitor);
1849 return;
1850 }
1851
1852 while (true) {
1853 // Fast-locking does not use the 'lock' argument.
1854 // Fast-lock spinning to avoid inflating for short critical sections.
1855 // The goal is to only inflate when the extra cost of using ObjectMonitors
1856 // is worth it.
1857 // If deflation has been observed we also spin while deflation is ongoing.
1858 if (fast_lock_try_enter(obj(), lock_stack, current)) {
1859 return;
1860 } else if (UseObjectMonitorTable && fast_lock_spin_enter(obj(), lock_stack, current, observed_deflation)) {
1861 return;
1862 }
1863
1864 if (observed_deflation) {
1865 spin_yield.wait();
1866 }
1867
1868 ObjectMonitor* monitor = inflate_and_enter(obj(), lock, ObjectSynchronizer::inflate_cause_monitor_enter, current, current);
1869 if (monitor != nullptr) {
1870 cache_setter.set_monitor(monitor);
1871 return;
1872 }
1873
1874 // If inflate_and_enter returns nullptr it is because a deflated monitor
1875 // was encountered. Fallback to fast locking. The deflater is responsible
1876 // for clearing out the monitor and transitioning the markWord back to
1877 // fast locking.
1878 observed_deflation = true;
1879 }
1880 }
1881
1882 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
1883 assert(current == Thread::current(), "must be");
1884
1885 markWord mark = object->mark();
1886 assert(!mark.is_unlocked(), "must be");
1887
1888 LockStack& lock_stack = current->lock_stack();
1889 if (mark.is_fast_locked()) {
1890 if (lock_stack.try_recursive_exit(object)) {
1891 // This is a recursive exit which succeeded
1892 return;
1893 }
1894 if (lock_stack.is_recursive(object)) {
1895 // Must inflate recursive locks if try_recursive_exit fails
1896 // This happens for un-structured unlocks, could potentially
1897 // fix try_recursive_exit to handle these.
1898 inflate_fast_locked_object(object, ObjectSynchronizer::inflate_cause_vm_internal, current, current);
1899 }
1900 }
1901
1902 while (mark.is_fast_locked()) {
1903 markWord unlocked_mark = mark.set_unlocked();
1904 markWord old_mark = mark;
1905 mark = object->cas_set_mark(unlocked_mark, old_mark);
1906 if (old_mark == mark) {
1907 // CAS successful, remove from lock_stack
1908 size_t recursion = lock_stack.remove(object) - 1;
1909 assert(recursion == 0, "Should not have unlocked here");
1910 return;
1911 }
1912 }
1913
1914 assert(mark.has_monitor(), "must be");
1915 // The monitor exists
1916 ObjectMonitor* monitor;
1917 if (UseObjectMonitorTable) {
1918 monitor = read_caches(current, lock, object);
1919 if (monitor == nullptr) {
1920 monitor = get_monitor_from_table(object);
1921 }
1922 } else {
1923 monitor = ObjectSynchronizer::read_monitor(mark);
1924 }
1925 if (monitor->has_anonymous_owner()) {
1926 assert(current->lock_stack().contains(object), "current must have object on its lock stack");
1927 monitor->set_owner_from_anonymous(current);
1928 monitor->set_recursions(current->lock_stack().remove(object) - 1);
1929 }
1930
1931 monitor->exit(current);
1932 }
1933
1934 // ObjectSynchronizer::inflate_locked_or_imse is used to get an
1935 // inflated ObjectMonitor* from contexts which require that, such as
1936 // notify/wait and jni_exit. Fast locking keeps the invariant that it
1937 // only inflates if it is already locked by the current thread or the current
1938 // thread is in the process of entering. To maintain this invariant we need to
1939 // throw a java.lang.IllegalMonitorStateException before inflating if the
1940 // current thread is not the owner.
1941 ObjectMonitor* ObjectSynchronizer::inflate_locked_or_imse(oop obj, ObjectSynchronizer::InflateCause cause, TRAPS) {
1942 JavaThread* current = THREAD;
1943
1944 for (;;) {
1945 markWord mark = obj->mark_acquire();
1946 if (mark.is_unlocked()) {
1947 // No lock, IMSE.
1948 THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
1949 "current thread is not owner", nullptr);
1950 }
1951
1952 if (mark.is_fast_locked()) {
1953 if (!current->lock_stack().contains(obj)) {
1954 // Fast locked by other thread, IMSE.
1955 THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
1956 "current thread is not owner", nullptr);
1957 } else {
1958 // Current thread owns the lock, must inflate
1959 return inflate_fast_locked_object(obj, cause, current, current);
1960 }
1961 }
1962
1963 assert(mark.has_monitor(), "must be");
1964 ObjectMonitor* monitor = ObjectSynchronizer::read_monitor(obj, mark);
1965 if (monitor != nullptr) {
1966 if (monitor->has_anonymous_owner()) {
1967 LockStack& lock_stack = current->lock_stack();
1968 if (lock_stack.contains(obj)) {
1969 // Current thread owns the lock but someone else inflated it.
1970 // Fix owner and pop lock stack.
1971 monitor->set_owner_from_anonymous(current);
1972 monitor->set_recursions(lock_stack.remove(obj) - 1);
1973 } else {
1974 // Fast locked (and inflated) by other thread, or deflation in progress, IMSE.
1975 THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
1976 "current thread is not owner", nullptr);
1977 }
1978 }
1979 return monitor;
1980 }
1981 }
1982 }
1983
1984 ObjectMonitor* ObjectSynchronizer::inflate_into_object_header(oop object, ObjectSynchronizer::InflateCause cause, JavaThread* locking_thread, Thread* current) {
1985
1986 // The JavaThread* locking parameter requires that the locking_thread == JavaThread::current,
1987 // or is suspended throughout the call by some other mechanism.
1988 // Even with fast locking the thread might be nullptr when called from a non
1989 // JavaThread. (As may still be the case from FastHashCode). However it is only
1990 // important for the correctness of the fast locking algorithm that the thread
1991 // is set when called from ObjectSynchronizer::enter from the owning thread,
1992 // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
1993 EventJavaMonitorInflate event;
1994
1995 for (;;) {
1996 const markWord mark = object->mark_acquire();
1997
1998 // The mark can be in one of the following states:
1999 // * inflated - Just return if using stack-locking.
2000 // If using fast-locking and the ObjectMonitor owner
2001 // is anonymous and the locking_thread owns the
2002 // object lock, then we make the locking_thread
2003 // the ObjectMonitor owner and remove the lock from
2004 // the locking_thread's lock stack.
2005 // * fast-locked - Coerce it to inflated from fast-locked.
2006 // * unlocked - Aggressively inflate the object.
2007
2008 // CASE: inflated
2009 if (mark.has_monitor()) {
2010 ObjectMonitor* inf = mark.monitor();
2011 markWord dmw = inf->header();
2012 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
2013 if (inf->has_anonymous_owner() &&
2014 locking_thread != nullptr && locking_thread->lock_stack().contains(object)) {
2015 inf->set_owner_from_anonymous(locking_thread);
2016 size_t removed = locking_thread->lock_stack().remove(object);
2017 inf->set_recursions(removed - 1);
2018 }
2019 return inf;
2020 }
2021
2022 // CASE: fast-locked
2023 // Could be fast-locked either by the locking_thread or by some other thread.
2024 //
2025 // Note that we allocate the ObjectMonitor speculatively, _before_
2026 // attempting to set the object's mark to the new ObjectMonitor. If
2027 // the locking_thread owns the monitor, then we set the ObjectMonitor's
2028 // owner to the locking_thread. Otherwise, we set the ObjectMonitor's owner
2029 // to anonymous. If we lose the race to set the object's mark to the
2030 // new ObjectMonitor, then we just delete it and loop around again.
2031 //
2032 if (mark.is_fast_locked()) {
2033 ObjectMonitor* monitor = new ObjectMonitor(object);
2034 monitor->set_header(mark.set_unlocked());
2035 bool own = locking_thread != nullptr && locking_thread->lock_stack().contains(object);
2036 if (own) {
2037 // Owned by locking_thread.
2038 monitor->set_owner(locking_thread);
2039 } else {
2040 // Owned by somebody else.
2041 monitor->set_anonymous_owner();
2042 }
2043 markWord monitor_mark = markWord::encode(monitor);
2044 markWord old_mark = object->cas_set_mark(monitor_mark, mark);
2045 if (old_mark == mark) {
2046 // Success! Return inflated monitor.
2047 if (own) {
2048 size_t removed = locking_thread->lock_stack().remove(object);
2049 monitor->set_recursions(removed - 1);
2050 }
2051 // Once the ObjectMonitor is configured and object is associated
2052 // with the ObjectMonitor, it is safe to allow async deflation:
2053 ObjectSynchronizer::_in_use_list.add(monitor);
2054
2055 log_inflate(current, object, cause);
2056 if (event.should_commit()) {
2057 post_monitor_inflate_event(&event, object, cause);
2058 }
2059 return monitor;
2060 } else {
2061 delete monitor;
2062 continue; // Interference -- just retry
2063 }
2064 }
2065
2066 // CASE: unlocked
2067 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
2068 // If we know we're inflating for entry it's better to inflate by swinging a
2069 // pre-locked ObjectMonitor pointer into the object header. A successful
2070 // CAS inflates the object *and* confers ownership to the inflating thread.
2071 // In the current implementation we use a 2-step mechanism where we CAS()
2072 // to inflate and then CAS() again to try to swing _owner from null to current.
2073 // An inflateTry() method that we could call from enter() would be useful.
2074
2075 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
2076 ObjectMonitor* m = new ObjectMonitor(object);
2077 // prepare m for installation - set monitor to initial state
2078 m->set_header(mark);
2079
2080 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
2081 delete m;
2082 m = nullptr;
2083 continue;
2084 // interference - the markword changed - just retry.
2085 // The state-transitions are one-way, so there's no chance of
2086 // live-lock -- "Inflated" is an absorbing state.
2087 }
2088
2089 // Once the ObjectMonitor is configured and object is associated
2090 // with the ObjectMonitor, it is safe to allow async deflation:
2091 ObjectSynchronizer::_in_use_list.add(m);
2092
2093 log_inflate(current, object, cause);
2094 if (event.should_commit()) {
2095 post_monitor_inflate_event(&event, object, cause);
2096 }
2097 return m;
2098 }
2099 }
2100
2101 ObjectMonitor* ObjectSynchronizer::inflate_fast_locked_object(oop object, ObjectSynchronizer::InflateCause cause, JavaThread* locking_thread, JavaThread* current) {
2102 VerifyThreadState vts(locking_thread, current);
2103 assert(locking_thread->lock_stack().contains(object), "locking_thread must have object on its lock stack");
2104
2105 ObjectMonitor* monitor;
2106
2107 if (!UseObjectMonitorTable) {
2108 return inflate_into_object_header(object, cause, locking_thread, current);
2109 }
2110
2111 // Inflating requires a hash code
2112 ObjectSynchronizer::FastHashCode(current, object);
2113
2114 markWord mark = object->mark_acquire();
2115 assert(!mark.is_unlocked(), "Cannot be unlocked");
2116
2117 for (;;) {
2118 // Fetch the monitor from the table
2119 monitor = get_or_insert_monitor(object, current, cause);
2120
2121 // ObjectMonitors are always inserted as anonymously owned, this thread is
2122 // the current holder of the monitor. So unless the entry is stale and
2123 // contains a deflating monitor it must be anonymously owned.
2124 if (monitor->has_anonymous_owner()) {
2125 // The monitor must be anonymously owned if it was added
2126 assert(monitor == get_monitor_from_table(object), "The monitor must be found");
2127 // New fresh monitor
2128 break;
2129 }
2130
2131 // If the monitor was not anonymously owned then we got a deflating monitor
2132 // from the table. We need to let the deflator make progress and remove this
2133 // entry before we are allowed to add a new one.
2134 os::naked_yield();
2135 assert(monitor->is_being_async_deflated(), "Should be the reason");
2136 }
2137
2138 // Set the mark word; loop to handle concurrent updates to other parts of the mark word
2139 while (mark.is_fast_locked()) {
2140 mark = object->cas_set_mark(mark.set_has_monitor(), mark);
2141 }
2142
2143 // Indicate that the monitor now has a known owner
2144 monitor->set_owner_from_anonymous(locking_thread);
2145
2146 // Remove the entry from the thread's lock stack
2147 monitor->set_recursions(locking_thread->lock_stack().remove(object) - 1);
2148
2149 if (locking_thread == current) {
2150 // Only change the thread local state of the current thread.
2151 locking_thread->om_set_monitor_cache(monitor);
2152 }
2153
2154 return monitor;
2155 }
2156
2157 ObjectMonitor* ObjectSynchronizer::inflate_and_enter(oop object, BasicLock* lock, ObjectSynchronizer::InflateCause cause, JavaThread* locking_thread, JavaThread* current) {
2158 VerifyThreadState vts(locking_thread, current);
2159
2160 // Note: In some paths (deoptimization) the 'current' thread inflates and
2161 // enters the lock on behalf of the 'locking_thread' thread.
2162
2163 ObjectMonitor* monitor = nullptr;
2164
2165 if (!UseObjectMonitorTable) {
2166 // Do the old inflate and enter.
2167 monitor = inflate_into_object_header(object, cause, locking_thread, current);
2168
2169 bool entered;
2170 if (locking_thread == current) {
2171 entered = monitor->enter(locking_thread);
2172 } else {
2173 entered = monitor->enter_for(locking_thread);
2174 }
2175
2176 // enter returns false for deflation found.
2177 return entered ? monitor : nullptr;
2178 }
2179
2180 NoSafepointVerifier nsv;
2181
2182 // Try to get the monitor from the thread-local cache.
2183 // There's no need to use the cache if we are locking
2184 // on behalf of another thread.
2185 if (current == locking_thread) {
2186 monitor = read_caches(current, lock, object);
2187 }
2188
2189 // Get or create the monitor
2190 if (monitor == nullptr) {
2191 // Lightweight monitors require that hash codes are installed first
2192 ObjectSynchronizer::FastHashCode(locking_thread, object);
2193 monitor = get_or_insert_monitor(object, current, cause);
2194 }
2195
2196 if (monitor->try_enter(locking_thread)) {
2197 return monitor;
2198 }
2199
2200 // Holds is_being_async_deflated() stable throughout this function.
2201 ObjectMonitorContentionMark contention_mark(monitor);
2202
2203 /// First handle the case where the monitor from the table is deflated
2204 if (monitor->is_being_async_deflated()) {
2205 // The MonitorDeflation thread is deflating the monitor. The locking thread
2206 // must spin until further progress has been made.
2207
2208 // Clear the BasicLock cache as it may contain this monitor.
2209 lock->clear_object_monitor_cache();
2210
2211 const markWord mark = object->mark_acquire();
2212
2213 if (mark.has_monitor()) {
2214 // Waiting on the deflation thread to remove the deflated monitor from the table.
2215 os::naked_yield();
2216
2217 } else if (mark.is_fast_locked()) {
2218 // Some other thread managed to fast-lock the lock, or this is a
2219 // recursive lock from the same thread; yield for the deflation
2220 // thread to remove the deflated monitor from the table.
2221 os::naked_yield();
2222
2223 } else {
2224 assert(mark.is_unlocked(), "Implied");
2225 // Retry immediately
2226 }
2227
2228 // Retry
2229 return nullptr;
2230 }
2231
2232 for (;;) {
2233 const markWord mark = object->mark_acquire();
2234 // The mark can be in one of the following states:
2235 // * inflated - If the ObjectMonitor owner is anonymous
2236 // and the locking_thread owns the object
2237 // lock, then we make the locking_thread
2238 // the ObjectMonitor owner and remove the
2239 // lock from the locking_thread's lock stack.
2240 // * fast-locked - Coerce it to inflated from fast-locked.
2241 // * neutral - Inflate the object. Successful CAS is locked
2242
2243 // CASE: inflated
2244 if (mark.has_monitor()) {
2245 LockStack& lock_stack = locking_thread->lock_stack();
2246 if (monitor->has_anonymous_owner() && lock_stack.contains(object)) {
2247 // The lock is fast-locked by the locking thread,
2248 // convert it to a held monitor with a known owner.
2249 monitor->set_owner_from_anonymous(locking_thread);
2250 monitor->set_recursions(lock_stack.remove(object) - 1);
2251 }
2252
2253 break; // Success
2254 }
2255
2256 // CASE: fast-locked
2257 // Could be fast-locked either by locking_thread or by some other thread.
2258 //
2259 if (mark.is_fast_locked()) {
2260 markWord old_mark = object->cas_set_mark(mark.set_has_monitor(), mark);
2261 if (old_mark != mark) {
2262 // CAS failed
2263 continue;
2264 }
2265
2266 // Success! Return inflated monitor.
2267 LockStack& lock_stack = locking_thread->lock_stack();
2268 if (lock_stack.contains(object)) {
2269 // The lock is fast-locked by the locking thread,
2270 // convert it to a held monitor with a known owner.
2271 monitor->set_owner_from_anonymous(locking_thread);
2272 monitor->set_recursions(lock_stack.remove(object) - 1);
2273 }
2274
2275 break; // Success
2276 }
2277
2278 // CASE: neutral (unlocked)
2279
2280 // Catch if the object's header is not neutral (not locked and
2281 // not marked is what we care about here).
2282 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
2283 markWord old_mark = object->cas_set_mark(mark.set_has_monitor(), mark);
2284 if (old_mark != mark) {
2285 // CAS failed
2286 continue;
2287 }
2288
2289 // Transitioned from unlocked to monitor means locking_thread owns the lock.
2290 monitor->set_owner_from_anonymous(locking_thread);
2291
2292 return monitor;
2293 }
2294
2295 if (current == locking_thread) {
2296 // One round of spinning
2297 if (monitor->spin_enter(locking_thread)) {
2298 return monitor;
2299 }
2300
2301 // Monitor is contended, take the time before entering to fix the lock stack.
2302 LockStackInflateContendedLocks().inflate(current);
2303 }
2304
2305 // enter can block for safepoints; clear the unhandled object oop
2306 PauseNoSafepointVerifier pnsv(&nsv);
2307 object = nullptr;
2308
2309 if (current == locking_thread) {
2310 monitor->enter_with_contention_mark(locking_thread, contention_mark);
2311 } else {
2312 monitor->enter_for_with_contention_mark(locking_thread, contention_mark);
2313 }
2314
2315 return monitor;
2316 }
2317
2318 void ObjectSynchronizer::deflate_monitor(oop obj, ObjectMonitor* monitor) {
2319 if (obj != nullptr) {
2320 deflate_mark_word(obj);
2321 remove_monitor(monitor, obj);
2322 }
2323 }
2324
2325 ObjectMonitor* ObjectSynchronizer::get_monitor_from_table(oop obj) {
2326 assert(UseObjectMonitorTable, "must be");
2327 return ObjectMonitorTable::monitor_get(obj);
2328 }
2329
2330 ObjectMonitor* ObjectSynchronizer::read_monitor(markWord mark) {
2331 return mark.monitor();
2332 }
2333
2334 ObjectMonitor* ObjectSynchronizer::read_monitor(oop obj) {
2335 return ObjectSynchronizer::read_monitor(obj, obj->mark());
2336 }
2337
2338 ObjectMonitor* ObjectSynchronizer::read_monitor(oop obj, markWord mark) {
2339 if (!UseObjectMonitorTable) {
2340 return read_monitor(mark);
2341 } else {
2342 return ObjectSynchronizer::get_monitor_from_table(obj);
2343 }
2344 }
2345
2346 bool ObjectSynchronizer::quick_enter_internal(oop obj, BasicLock* lock, JavaThread* current) {
2347 assert(current->thread_state() == _thread_in_Java, "must be");
2348 assert(obj != nullptr, "must be");
2349 NoSafepointVerifier nsv;
2350
2351 LockStack& lock_stack = current->lock_stack();
2352 if (lock_stack.is_full()) {
2353 // Always go into runtime if the lock stack is full.
2354 return false;
2355 }
2356
2357 const markWord mark = obj->mark();
2358
2359 #ifndef _LP64
2360 // Only for 32bit which has limited support for fast locking outside the runtime.
2361 if (lock_stack.try_recursive_enter(obj)) {
2362 // Recursive lock successful.
2363 return true;
2364 }
2365
2366 if (mark.is_unlocked()) {
2367 markWord locked_mark = mark.set_fast_locked();
2368 if (obj->cas_set_mark(locked_mark, mark) == mark) {
2369 // Successfully fast-locked, push object to lock-stack and return.
2370 lock_stack.push(obj);
2371 return true;
2372 }
2373 }
2374 #endif
2375
2376 if (mark.has_monitor()) {
2377 ObjectMonitor* monitor;
2378 if (UseObjectMonitorTable) {
2379 monitor = read_caches(current, lock, obj);
2380 } else {
2381 monitor = ObjectSynchronizer::read_monitor(mark);
2382 }
2383
2384 if (monitor == nullptr) {
2385 // Take the slow-path on a cache miss.
2386 return false;
2387 }
2388
2389 if (UseObjectMonitorTable) {
2390 // Set the monitor regardless of success.
2391 // Either we successfully lock on the monitor, or we retry with the
2392 // monitor in the slow path. If the monitor gets deflated, it will be
2393 // cleared, either by the CacheSetter if we fast lock in enter or in
2394 // inflate_and_enter when we see that the monitor is deflated.
2395 lock->set_object_monitor_cache(monitor);
2396 }
2397
2398 if (monitor->spin_enter(current)) {
2399 return true;
2400 }
2401 }
2402
2403 // Slow-path.
2404 return false;
2405 }
2406
2407 bool ObjectSynchronizer::quick_enter(oop obj, BasicLock* lock, JavaThread* current) {
2408 assert(current->thread_state() == _thread_in_Java, "invariant");
2409 NoSafepointVerifier nsv;
2410 if (obj == nullptr) return false; // Need to throw NPE
2411
2412 if (obj->klass()->is_value_based()) {
2413 return false;
2414 }
2415
2416 return ObjectSynchronizer::quick_enter_internal(obj, lock, current);
2417 }