1 /*
2 * Copyright (c) 1998, 2024, 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 "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "gc/shared/collectedHeap.hpp"
28 #include "jfr/jfrEvents.hpp"
29 #include "logging/log.hpp"
30 #include "logging/logStream.hpp"
31 #include "memory/allocation.inline.hpp"
32 #include "memory/padded.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/markWord.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/basicLock.inline.hpp"
39 #include "runtime/frame.inline.hpp"
40 #include "runtime/globals.hpp"
41 #include "runtime/handles.inline.hpp"
42 #include "runtime/handshake.hpp"
43 #include "runtime/interfaceSupport.inline.hpp"
44 #include "runtime/javaThread.hpp"
45 #include "runtime/lightweightSynchronizer.hpp"
46 #include "runtime/lockStack.inline.hpp"
47 #include "runtime/mutexLocker.hpp"
48 #include "runtime/objectMonitor.hpp"
49 #include "runtime/objectMonitor.inline.hpp"
50 #include "runtime/os.inline.hpp"
51 #include "runtime/osThread.hpp"
52 #include "runtime/perfData.hpp"
53 #include "runtime/safepointMechanism.inline.hpp"
54 #include "runtime/safepointVerifiers.hpp"
55 #include "runtime/sharedRuntime.hpp"
56 #include "runtime/stubRoutines.hpp"
57 #include "runtime/synchronizer.hpp"
58 #include "runtime/threads.hpp"
59 #include "runtime/timer.hpp"
60 #include "runtime/trimNativeHeap.hpp"
61 #include "runtime/vframe.hpp"
62 #include "runtime/vmThread.hpp"
63 #include "utilities/align.hpp"
64 #include "utilities/dtrace.hpp"
65 #include "utilities/events.hpp"
66 #include "utilities/globalDefinitions.hpp"
67 #include "utilities/linkedlist.hpp"
68 #include "utilities/preserveException.hpp"
69
70 class ObjectMonitorDeflationLogging;
71
72 ObjectMonitor* ObjectSynchronizer::read_monitor(markWord mark) {
73 assert(LockingMode != LM_LIGHTWEIGHT, "lightweight locking uses table");
74 return mark.monitor();
75 }
76
77 ObjectMonitor* ObjectSynchronizer::read_monitor(Thread* current, oop obj, markWord mark) {
78 if (LockingMode != LM_LIGHTWEIGHT) {
79 return read_monitor(mark);
80 }
81 return LightweightSynchronizer::read_monitor(current, obj);
82 }
83
84 void MonitorList::add(ObjectMonitor* m) {
85 ObjectMonitor* head;
86 do {
87 head = Atomic::load(&_head);
88 m->set_next_om(head);
89 } while (Atomic::cmpxchg(&_head, head, m) != head);
90
91 size_t count = Atomic::add(&_count, 1u);
92 if (count > max()) {
93 Atomic::inc(&_max);
94 }
95 }
96
97 size_t MonitorList::count() const {
98 return Atomic::load(&_count);
99 }
100
101 size_t MonitorList::max() const {
102 return Atomic::load(&_max);
103 }
104
105 class ObjectMonitorDeflationSafepointer : public StackObj {
106 JavaThread* const _current;
107 ObjectMonitorDeflationLogging* const _log;
108
109 public:
110 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
111 : _current(current), _log(log) {}
112
113 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
114 };
115
116 // Walk the in-use list and unlink deflated ObjectMonitors.
117 // Returns the number of unlinked ObjectMonitors.
118 size_t MonitorList::unlink_deflated(size_t deflated_count,
119 GrowableArray<ObjectMonitor*>* unlinked_list,
120 ObjectMonitorDeflationSafepointer* safepointer) {
121 size_t unlinked_count = 0;
122 ObjectMonitor* prev = nullptr;
123 ObjectMonitor* m = Atomic::load_acquire(&_head);
124
125 while (m != nullptr) {
126 if (m->is_being_async_deflated()) {
127 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
128 // modify the list once per batch. The batch starts at "m".
129 size_t unlinked_batch = 0;
130 ObjectMonitor* next = m;
131 // Look for at most MonitorUnlinkBatch monitors, or the number of
132 // deflated and not unlinked monitors, whatever comes first.
133 assert(deflated_count >= unlinked_count, "Sanity: underflow");
134 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
135 do {
136 ObjectMonitor* next_next = next->next_om();
137 unlinked_batch++;
138 unlinked_list->append(next);
139 next = next_next;
140 if (unlinked_batch >= unlinked_batch_limit) {
141 // Reached the max batch, so bail out of the gathering loop.
142 break;
143 }
144 if (prev == nullptr && Atomic::load(&_head) != m) {
145 // Current batch used to be at head, but it is not at head anymore.
146 // Bail out and figure out where we currently are. This avoids long
147 // walks searching for new prev during unlink under heavy list inserts.
148 break;
149 }
150 } while (next != nullptr && next->is_being_async_deflated());
151
152 // Unlink the found batch.
153 if (prev == nullptr) {
154 // The current batch is the first batch, so there is a chance that it starts at head.
155 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
156 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, m, next);
157 if (prev_head != m) {
158 // Something must have updated the head. Figure out the actual prev for this batch.
159 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
160 prev = n;
161 }
162 assert(prev != nullptr, "Should have found the prev for the current batch");
163 prev->set_next_om(next);
164 }
165 } else {
166 // The current batch is preceded by another batch. This guarantees the current batch
167 // does not start at head. Unlink the entire current batch without updating the head.
168 assert(Atomic::load(&_head) != m, "Sanity");
169 prev->set_next_om(next);
170 }
171
172 unlinked_count += unlinked_batch;
173 if (unlinked_count >= deflated_count) {
174 // Reached the max so bail out of the searching loop.
175 // There should be no more deflated monitors left.
176 break;
177 }
178 m = next;
179 } else {
180 prev = m;
181 m = m->next_om();
182 }
183
184 // Must check for a safepoint/handshake and honor it.
185 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
186 }
187
188 #ifdef ASSERT
189 // Invariant: the code above should unlink all deflated monitors.
190 // The code that runs after this unlinking does not expect deflated monitors.
191 // Notably, attempting to deflate the already deflated monitor would break.
192 {
193 ObjectMonitor* m = Atomic::load_acquire(&_head);
194 while (m != nullptr) {
195 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
196 m = m->next_om();
197 }
198 }
199 #endif
200
201 Atomic::sub(&_count, unlinked_count);
202 return unlinked_count;
203 }
204
205 MonitorList::Iterator MonitorList::iterator() const {
206 return Iterator(Atomic::load_acquire(&_head));
207 }
208
209 ObjectMonitor* MonitorList::Iterator::next() {
210 ObjectMonitor* current = _current;
211 _current = current->next_om();
212 return current;
213 }
214
215 // The "core" versions of monitor enter and exit reside in this file.
216 // The interpreter and compilers contain specialized transliterated
217 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
218 // fast_lock(...) for instance. If you make changes here, make sure to modify the
219 // interpreter, and both C1 and C2 fast-path inline locking code emission.
220 //
221 // -----------------------------------------------------------------------------
222
223 #ifdef DTRACE_ENABLED
224
225 // Only bother with this argument setup if dtrace is available
226 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
227
228 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
229 char* bytes = nullptr; \
230 int len = 0; \
231 jlong jtid = SharedRuntime::get_java_tid(thread); \
232 Symbol* klassname = obj->klass()->name(); \
233 if (klassname != nullptr) { \
234 bytes = (char*)klassname->bytes(); \
235 len = klassname->utf8_length(); \
236 }
237
238 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
239 { \
240 if (DTraceMonitorProbes) { \
241 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
242 HOTSPOT_MONITOR_WAIT(jtid, \
243 (uintptr_t)(monitor), bytes, len, (millis)); \
244 } \
245 }
246
247 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
248 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
249 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
250
251 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
252 { \
253 if (DTraceMonitorProbes) { \
254 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
255 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
256 (uintptr_t)(monitor), bytes, len); \
257 } \
258 }
259
260 #else // ndef DTRACE_ENABLED
261
262 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
263 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
264
265 #endif // ndef DTRACE_ENABLED
266
267 // This exists only as a workaround of dtrace bug 6254741
268 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
269 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
270 return 0;
271 }
272
273 static constexpr size_t inflation_lock_count() {
274 return 256;
275 }
276
277 // Static storage for an array of PlatformMutex.
278 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
279
280 static inline PlatformMutex* inflation_lock(size_t index) {
281 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
282 }
283
284 void ObjectSynchronizer::initialize() {
285 for (size_t i = 0; i < inflation_lock_count(); i++) {
286 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
287 }
288 // Start the ceiling with the estimate for one thread.
289 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
290
291 // Start the timer for deflations, so it does not trigger immediately.
292 _last_async_deflation_time_ns = os::javaTimeNanos();
293
294 if (LockingMode == LM_LIGHTWEIGHT) {
295 LightweightSynchronizer::initialize();
296 }
297 }
298
299 MonitorList ObjectSynchronizer::_in_use_list;
300 // monitors_used_above_threshold() policy is as follows:
301 //
302 // The ratio of the current _in_use_list count to the ceiling is used
303 // to determine if we are above MonitorUsedDeflationThreshold and need
304 // to do an async monitor deflation cycle. The ceiling is increased by
305 // AvgMonitorsPerThreadEstimate when a thread is added to the system
306 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
307 // removed from the system.
308 //
309 // Note: If the _in_use_list max exceeds the ceiling, then
310 // monitors_used_above_threshold() will use the in_use_list max instead
311 // of the thread count derived ceiling because we have used more
312 // ObjectMonitors than the estimated average.
313 //
314 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
315 // no-progress async monitor deflation cycles in a row, then the ceiling
316 // is adjusted upwards by monitors_used_above_threshold().
317 //
318 // Start the ceiling with the estimate for one thread in initialize()
319 // which is called after cmd line options are processed.
320 static size_t _in_use_list_ceiling = 0;
321 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
322 bool volatile ObjectSynchronizer::_is_final_audit = false;
323 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
324 static uintx _no_progress_cnt = 0;
325 static bool _no_progress_skip_increment = false;
326
327 // =====================> Quick functions
328
329 // The quick_* forms are special fast-path variants used to improve
330 // performance. In the simplest case, a "quick_*" implementation could
331 // simply return false, in which case the caller will perform the necessary
332 // state transitions and call the slow-path form.
333 // The fast-path is designed to handle frequently arising cases in an efficient
334 // manner and is just a degenerate "optimistic" variant of the slow-path.
335 // returns true -- to indicate the call was satisfied.
336 // returns false -- to indicate the call needs the services of the slow-path.
337 // A no-loitering ordinance is in effect for code in the quick_* family
338 // operators: safepoints or indefinite blocking (blocking that might span a
339 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
340 // entry.
341 //
342 // Consider: An interesting optimization is to have the JIT recognize the
343 // following common idiom:
344 // synchronized (someobj) { .... ; notify(); }
345 // That is, we find a notify() or notifyAll() call that immediately precedes
346 // the monitorexit operation. In that case the JIT could fuse the operations
347 // into a single notifyAndExit() runtime primitive.
348
349 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
350 assert(current->thread_state() == _thread_in_Java, "invariant");
351 NoSafepointVerifier nsv;
352 if (obj == nullptr) return false; // slow-path for invalid obj
353 const markWord mark = obj->mark();
354
355 if (LockingMode == LM_LIGHTWEIGHT) {
356 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
357 // Degenerate notify
358 // fast-locked by caller so by definition the implied waitset is empty.
359 return true;
360 }
361 } else if (LockingMode == LM_LEGACY) {
362 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
363 // Degenerate notify
364 // stack-locked by caller so by definition the implied waitset is empty.
365 return true;
366 }
367 }
368
369 if (mark.has_monitor()) {
370 ObjectMonitor* const mon = read_monitor(current, obj, mark);
371 if (LockingMode == LM_LIGHTWEIGHT && mon == nullptr) {
372 // Racing with inflation/deflation go slow path
373 return false;
374 }
375 assert(mon->object() == oop(obj), "invariant");
376 if (mon->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 can transfer one or more threads from the waitset
381 // to the entrylist here and now, avoiding the slow-path.
382 if (all) {
383 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
384 } else {
385 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
386 }
387 int free_count = 0;
388 do {
389 mon->INotify(current);
390 ++free_count;
391 } while (mon->first_waiter() != nullptr && all);
392 OM_PERFDATA_OP(Notifications, inc(free_count));
393 }
394 return true;
395 }
396
397 // other IMS exception states take the slow-path
398 return false;
399 }
400
401
402 // The LockNode emitted directly at the synchronization site would have
403 // been too big if it were to have included support for the cases of inflated
404 // recursive enter and exit, so they go here instead.
405 // Note that we can't safely call AsyncPrintJavaStack() from within
406 // quick_enter() as our thread state remains _in_Java.
407
408 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
409 BasicLock * lock) {
410 assert(current->thread_state() == _thread_in_Java, "invariant");
411 NoSafepointVerifier nsv;
412 if (obj == nullptr) return false; // Need to throw NPE
413
414 if (obj->klass()->is_value_based()) {
415 return false;
416 }
417
418 if (LockingMode == LM_LIGHTWEIGHT) {
419 return LightweightSynchronizer::quick_enter(obj, current, lock);
420 }
421
422 const markWord mark = obj->mark();
423
424 if (mark.has_monitor()) {
425 ObjectMonitor* const m = ObjectSynchronizer::read_monitor(mark);
426 // An async deflation or GC can race us before we manage to make
427 // the ObjectMonitor busy by setting the owner below. If we detect
428 // that race we just bail out to the slow-path here.
429 if (m->object_peek() == nullptr) {
430 return false;
431 }
432 JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
433
434 // Lock contention and Transactional Lock Elision (TLE) diagnostics
435 // and observability
436 // Case: light contention possibly amenable to TLE
437 // Case: TLE inimical operations such as nested/recursive synchronization
438
439 if (owner == current) {
440 m->_recursions++;
441 current->inc_held_monitor_count();
442 return true;
443 }
444
445 if (LockingMode == LM_LEGACY) {
446 // This Java Monitor is inflated so obj's header will never be
447 // displaced to this thread's BasicLock. Make the displaced header
448 // non-null so this BasicLock is not seen as recursive nor as
449 // being locked. We do this unconditionally so that this thread's
450 // BasicLock cannot be mis-interpreted by any stack walkers. For
451 // performance reasons, stack walkers generally first check for
452 // stack-locking in the object's header, the second check is for
453 // recursive stack-locking in the displaced header in the BasicLock,
454 // and last are the inflated Java Monitor (ObjectMonitor) checks.
455 lock->set_displaced_header(markWord::unused_mark());
456 }
457
458 if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) {
459 assert(m->_recursions == 0, "invariant");
460 current->inc_held_monitor_count();
461 return true;
462 }
463 }
464
465 // Note that we could inflate in quick_enter.
466 // This is likely a useful optimization
467 // Critically, in quick_enter() we must not:
468 // -- block indefinitely, or
469 // -- reach a safepoint
470
471 return false; // revert to slow-path
472 }
473
474 // Handle notifications when synchronizing on value based classes
475 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
476 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
477 frame last_frame = locking_thread->last_frame();
478 bool bcp_was_adjusted = false;
479 // Don't decrement bcp if it points to the frame's first instruction. This happens when
480 // handle_sync_on_value_based_class() is called because of a synchronized method. There
481 // is no actual monitorenter instruction in the byte code in this case.
482 if (last_frame.is_interpreted_frame() &&
483 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
484 // adjust bcp to point back to monitorenter so that we print the correct line numbers
485 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
486 bcp_was_adjusted = true;
487 }
488
489 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
490 ResourceMark rm;
491 stringStream ss;
492 locking_thread->print_active_stack_on(&ss);
493 char* base = (char*)strstr(ss.base(), "at");
494 char* newline = (char*)strchr(ss.base(), '\n');
495 if (newline != nullptr) {
496 *newline = '\0';
497 }
498 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
499 } else {
500 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
501 ResourceMark rm;
502 Log(valuebasedclasses) vblog;
503
504 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
505 if (locking_thread->has_last_Java_frame()) {
506 LogStream info_stream(vblog.info());
507 locking_thread->print_active_stack_on(&info_stream);
508 } else {
509 vblog.info("Cannot find the last Java frame");
510 }
511
512 EventSyncOnValueBasedClass event;
513 if (event.should_commit()) {
514 event.set_valueBasedClass(obj->klass());
515 event.commit();
516 }
517 }
518
519 if (bcp_was_adjusted) {
520 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
521 }
522 }
523
524 static bool useHeavyMonitors() {
525 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
526 return LockingMode == LM_MONITOR;
527 #else
528 return false;
529 #endif
530 }
531
532 // -----------------------------------------------------------------------------
533 // Monitor Enter/Exit
534
535 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
536 // When called with locking_thread != Thread::current() some mechanism must synchronize
537 // the locking_thread with respect to the current thread. Currently only used when
538 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
539 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
540
541 if (LockingMode == LM_LIGHTWEIGHT) {
542 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
543 }
544
545 if (!enter_fast_impl(obj, lock, locking_thread)) {
546 // Inflated ObjectMonitor::enter_for is required
547
548 // An async deflation can race after the inflate_for() call and before
549 // enter_for() can make the ObjectMonitor busy. enter_for() returns false
550 // if we have lost the race to async deflation and we simply try again.
551 while (true) {
552 ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
553 if (monitor->enter_for(locking_thread)) {
554 return;
555 }
556 assert(monitor->is_being_async_deflated(), "must be");
557 }
558 }
559 }
560
561 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
562 assert(current == Thread::current(), "must be");
563
564 if (LockingMode == LM_LIGHTWEIGHT) {
565 return LightweightSynchronizer::enter(obj, lock, current);
566 }
567
568 if (!enter_fast_impl(obj, lock, current)) {
569 // Inflated ObjectMonitor::enter is required
570
571 // An async deflation can race after the inflate() call and before
572 // enter() can make the ObjectMonitor busy. enter() returns false if
573 // we have lost the race to async deflation and we simply try again.
574 while (true) {
575 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
576 if (monitor->enter(current)) {
577 return;
578 }
579 }
580 }
581 }
582
583 // The interpreter and compiler assembly code tries to lock using the fast path
584 // of this algorithm. Make sure to update that code if the following function is
585 // changed. The implementation is extremely sensitive to race condition. Be careful.
586 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
587 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
588
589 if (obj->klass()->is_value_based()) {
590 handle_sync_on_value_based_class(obj, locking_thread);
591 }
592
593 locking_thread->inc_held_monitor_count();
594
595 if (!useHeavyMonitors()) {
596 if (LockingMode == LM_LEGACY) {
597 markWord mark = obj->mark();
598 if (mark.is_unlocked()) {
599 // Anticipate successful CAS -- the ST of the displaced mark must
600 // be visible <= the ST performed by the CAS.
601 lock->set_displaced_header(mark);
602 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
603 return true;
604 }
605 } else if (mark.has_locker() &&
606 locking_thread->is_lock_owned((address) mark.locker())) {
607 assert(lock != mark.locker(), "must not re-lock the same lock");
608 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
609 lock->set_displaced_header(markWord::from_pointer(nullptr));
610 return true;
611 }
612
613 // The object header will never be displaced to this lock,
614 // so it does not matter what the value is, except that it
615 // must be non-zero to avoid looking like a re-entrant lock,
616 // and must not look locked either.
617 lock->set_displaced_header(markWord::unused_mark());
618
619 // Failed to fast lock.
620 return false;
621 }
622 } else if (VerifyHeavyMonitors) {
623 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
624 }
625
626 return false;
627 }
628
629 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
630 current->dec_held_monitor_count();
631
632 if (LockingMode == LM_LIGHTWEIGHT) {
633 return LightweightSynchronizer::exit(object, current);
634 }
635
636 if (!useHeavyMonitors()) {
637 markWord mark = object->mark();
638 if (LockingMode == LM_LEGACY) {
639 markWord dhw = lock->displaced_header();
640 if (dhw.value() == 0) {
641 // If the displaced header is null, then this exit matches up with
642 // a recursive enter. No real work to do here except for diagnostics.
643 #ifndef PRODUCT
644 if (mark != markWord::INFLATING()) {
645 // Only do diagnostics if we are not racing an inflation. Simply
646 // exiting a recursive enter of a Java Monitor that is being
647 // inflated is safe; see the has_monitor() comment below.
648 assert(!mark.is_unlocked(), "invariant");
649 assert(!mark.has_locker() ||
650 current->is_lock_owned((address)mark.locker()), "invariant");
651 if (mark.has_monitor()) {
652 // The BasicLock's displaced_header is marked as a recursive
653 // enter and we have an inflated Java Monitor (ObjectMonitor).
654 // This is a special case where the Java Monitor was inflated
655 // after this thread entered the stack-lock recursively. When a
656 // Java Monitor is inflated, we cannot safely walk the Java
657 // Monitor owner's stack and update the BasicLocks because a
658 // Java Monitor can be asynchronously inflated by a thread that
659 // does not own the Java Monitor.
660 ObjectMonitor* m = read_monitor(mark);
661 assert(m->object()->mark() == mark, "invariant");
662 assert(m->is_entered(current), "invariant");
663 }
664 }
665 #endif
666 return;
667 }
668
669 if (mark == markWord::from_pointer(lock)) {
670 // If the object is stack-locked by the current thread, try to
671 // swing the displaced header from the BasicLock back to the mark.
672 assert(dhw.is_neutral(), "invariant");
673 if (object->cas_set_mark(dhw, mark) == mark) {
674 return;
675 }
676 }
677 }
678 } else if (VerifyHeavyMonitors) {
679 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
680 }
681
682 // We have to take the slow-path of possible inflation and then exit.
683 // The ObjectMonitor* can't be async deflated until ownership is
684 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
685 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
686 assert(!monitor->is_owner_anonymous(), "must not be");
687 monitor->exit(current);
688 }
689
690 // -----------------------------------------------------------------------------
691 // JNI locks on java objects
692 // NOTE: must use heavy weight monitor to handle jni monitor enter
693 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
694 if (obj->klass()->is_value_based()) {
695 handle_sync_on_value_based_class(obj, current);
696 }
697
698 // the current locking is from JNI instead of Java code
699 current->set_current_pending_monitor_is_from_java(false);
700 // An async deflation can race after the inflate() call and before
701 // enter() can make the ObjectMonitor busy. enter() returns false if
702 // we have lost the race to async deflation and we simply try again.
703 while (true) {
704 ObjectMonitor* monitor;
705 bool entered;
706 if (LockingMode == LM_LIGHTWEIGHT) {
707 entered = LightweightSynchronizer::inflate_and_enter(obj(), current, current, inflate_cause_jni_enter) != nullptr;
708 } else {
709 monitor = inflate(current, obj(), inflate_cause_jni_enter);
710 entered = monitor->enter(current);
711 }
712
713 if (entered) {
714 current->inc_held_monitor_count(1, true);
715 break;
716 }
717 }
718 current->set_current_pending_monitor_is_from_java(true);
719 }
720
721 // NOTE: must use heavy weight monitor to handle jni monitor exit
722 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
723 JavaThread* current = THREAD;
724
725 ObjectMonitor* monitor;
726 if (LockingMode == LM_LIGHTWEIGHT) {
727 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
728 } else {
729 // The ObjectMonitor* can't be async deflated until ownership is
730 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
731 monitor = inflate(current, obj, inflate_cause_jni_exit);
732 }
733 // If this thread has locked the object, exit the monitor. We
734 // intentionally do not use CHECK on check_owner because we must exit the
735 // monitor even if an exception was already pending.
736 if (monitor->check_owner(THREAD)) {
737 monitor->exit(current);
738 current->dec_held_monitor_count(1, true);
739 }
740 }
741
742 // -----------------------------------------------------------------------------
743 // Internal VM locks on java objects
744 // standard constructor, allows locking failures
745 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
746 _thread = thread;
747 _thread->check_for_valid_safepoint_state();
748 _obj = obj;
749
750 if (_obj() != nullptr) {
751 ObjectSynchronizer::enter(_obj, &_lock, _thread);
752 }
753 }
754
755 ObjectLocker::~ObjectLocker() {
756 if (_obj() != nullptr) {
757 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
758 }
759 }
760
761
762 // -----------------------------------------------------------------------------
763 // Wait/Notify/NotifyAll
764 // NOTE: must use heavy weight monitor to handle wait()
765
766 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
767 JavaThread* current = THREAD;
768 if (millis < 0) {
769 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
770 }
771
772 ObjectMonitor* monitor;
773 if (LockingMode == LM_LIGHTWEIGHT) {
774 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
775 } else {
776 // The ObjectMonitor* can't be async deflated because the _waiters
777 // field is incremented before ownership is dropped and decremented
778 // after ownership is regained.
779 monitor = inflate(current, obj(), inflate_cause_wait);
780 }
781
782 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
783 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
784
785 // This dummy call is in place to get around dtrace bug 6254741. Once
786 // that's fixed we can uncomment the following line, remove the call
787 // and change this function back into a "void" func.
788 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
789 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
790 return ret_code;
791 }
792
793 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
794 JavaThread* current = THREAD;
795
796 markWord mark = obj->mark();
797 if (LockingMode == LM_LIGHTWEIGHT) {
798 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
799 // Not inflated so there can't be any waiters to notify.
800 return;
801 }
802 } else if (LockingMode == LM_LEGACY) {
803 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
804 // Not inflated so there can't be any waiters to notify.
805 return;
806 }
807 }
808
809 ObjectMonitor* monitor;
810 if (LockingMode == LM_LIGHTWEIGHT) {
811 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
812 } else {
813 // The ObjectMonitor* can't be async deflated until ownership is
814 // dropped by the calling thread.
815 monitor = inflate(current, obj(), inflate_cause_notify);
816 }
817 monitor->notify(CHECK);
818 }
819
820 // NOTE: see comment of notify()
821 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
822 JavaThread* current = THREAD;
823
824 markWord mark = obj->mark();
825 if (LockingMode == LM_LIGHTWEIGHT) {
826 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
827 // Not inflated so there can't be any waiters to notify.
828 return;
829 }
830 } else if (LockingMode == LM_LEGACY) {
831 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
832 // Not inflated so there can't be any waiters to notify.
833 return;
834 }
835 }
836
837 ObjectMonitor* monitor;
838 if (LockingMode == LM_LIGHTWEIGHT) {
839 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
840 } else {
841 // The ObjectMonitor* can't be async deflated until ownership is
842 // dropped by the calling thread.
843 monitor = inflate(current, obj(), inflate_cause_notify);
844 }
845 monitor->notifyAll(CHECK);
846 }
847
848 // -----------------------------------------------------------------------------
849 // Hash Code handling
850
851 struct SharedGlobals {
852 char _pad_prefix[OM_CACHE_LINE_SIZE];
853 // This is a highly shared mostly-read variable.
854 // To avoid false-sharing it needs to be the sole occupant of a cache line.
855 volatile int stw_random;
856 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
857 // Hot RW variable -- Sequester to avoid false-sharing
858 volatile int hc_sequence;
859 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
860 };
861
862 static SharedGlobals GVars;
863
864 static markWord read_stable_mark(oop obj) {
865 markWord mark = obj->mark_acquire();
866 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
867 // New lightweight locking does not use the markWord::INFLATING() protocol.
868 return mark; // normal fast-path return
869 }
870
871 int its = 0;
872 for (;;) {
873 markWord mark = obj->mark_acquire();
874 if (!mark.is_being_inflated()) {
875 return mark; // normal fast-path return
876 }
877
878 // The object is being inflated by some other thread.
879 // The caller of read_stable_mark() must wait for inflation to complete.
880 // Avoid live-lock.
881
882 ++its;
883 if (its > 10000 || !os::is_MP()) {
884 if (its & 1) {
885 os::naked_yield();
886 } else {
887 // Note that the following code attenuates the livelock problem but is not
888 // a complete remedy. A more complete solution would require that the inflating
889 // thread hold the associated inflation lock. The following code simply restricts
890 // the number of spinners to at most one. We'll have N-2 threads blocked
891 // on the inflationlock, 1 thread holding the inflation lock and using
892 // a yield/park strategy, and 1 thread in the midst of inflation.
893 // A more refined approach would be to change the encoding of INFLATING
894 // to allow encapsulation of a native thread pointer. Threads waiting for
895 // inflation to complete would use CAS to push themselves onto a singly linked
896 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
897 // and calling park(). When inflation was complete the thread that accomplished inflation
898 // would detach the list and set the markword to inflated with a single CAS and
899 // then for each thread on the list, set the flag and unpark() the thread.
900
901 // Index into the lock array based on the current object address.
902 static_assert(is_power_of_2(inflation_lock_count()), "must be");
903 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
904 int YieldThenBlock = 0;
905 assert(ix < inflation_lock_count(), "invariant");
906 inflation_lock(ix)->lock();
907 while (obj->mark_acquire() == markWord::INFLATING()) {
908 // Beware: naked_yield() is advisory and has almost no effect on some platforms
909 // so we periodically call current->_ParkEvent->park(1).
910 // We use a mixed spin/yield/block mechanism.
911 if ((YieldThenBlock++) >= 16) {
912 Thread::current()->_ParkEvent->park(1);
913 } else {
914 os::naked_yield();
915 }
916 }
917 inflation_lock(ix)->unlock();
918 }
919 } else {
920 SpinPause(); // SMP-polite spinning
921 }
922 }
923 }
924
925 // hashCode() generation :
926 //
927 // Possibilities:
928 // * MD5Digest of {obj,stw_random}
929 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
930 // * A DES- or AES-style SBox[] mechanism
931 // * One of the Phi-based schemes, such as:
932 // 2654435761 = 2^32 * Phi (golden ratio)
933 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
934 // * A variation of Marsaglia's shift-xor RNG scheme.
935 // * (obj ^ stw_random) is appealing, but can result
936 // in undesirable regularity in the hashCode values of adjacent objects
937 // (objects allocated back-to-back, in particular). This could potentially
938 // result in hashtable collisions and reduced hashtable efficiency.
939 // There are simple ways to "diffuse" the middle address bits over the
940 // generated hashCode values:
941
942 static inline intptr_t get_next_hash(Thread* current, oop obj) {
943 intptr_t value = 0;
944 if (hashCode == 0) {
945 // This form uses global Park-Miller RNG.
946 // On MP system we'll have lots of RW access to a global, so the
947 // mechanism induces lots of coherency traffic.
948 value = os::random();
949 } else if (hashCode == 1) {
950 // This variation has the property of being stable (idempotent)
951 // between STW operations. This can be useful in some of the 1-0
952 // synchronization schemes.
953 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
954 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
955 } else if (hashCode == 2) {
956 value = 1; // for sensitivity testing
957 } else if (hashCode == 3) {
958 value = ++GVars.hc_sequence;
959 } else if (hashCode == 4) {
960 value = cast_from_oop<intptr_t>(obj);
961 } else {
962 // Marsaglia's xor-shift scheme with thread-specific state
963 // This is probably the best overall implementation -- we'll
964 // likely make this the default in future releases.
965 unsigned t = current->_hashStateX;
966 t ^= (t << 11);
967 current->_hashStateX = current->_hashStateY;
968 current->_hashStateY = current->_hashStateZ;
969 current->_hashStateZ = current->_hashStateW;
970 unsigned v = current->_hashStateW;
971 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
972 current->_hashStateW = v;
973 value = v;
974 }
975
976 value &= UseCompactObjectHeaders ? markWord::hash_mask_compact : markWord::hash_mask;
977 if (value == 0) value = 0xBAD;
978 assert(value != markWord::no_hash, "invariant");
979 return value;
980 }
981
982 intptr_t ObjectSynchronizer::get_next_hash(Thread* current, oop obj) {
983 // CLEANUP[Axel]: hack for LightweightSynchronizer being in different translation unit
984 return ::get_next_hash(current, obj);
985 }
986
987 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
988 if (LockingMode == LM_LIGHTWEIGHT) {
989 return LightweightSynchronizer::FastHashCode(current, obj);
990 }
991
992 while (true) {
993 ObjectMonitor* monitor = nullptr;
994 markWord temp, test;
995 intptr_t hash;
996 markWord mark = read_stable_mark(obj);
997 if (VerifyHeavyMonitors) {
998 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
999 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1000 }
1001 if (mark.is_unlocked() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1002 hash = mark.hash();
1003 if (hash != 0) { // if it has a hash, just return it
1004 return hash;
1005 }
1006 hash = get_next_hash(current, obj); // get a new hash
1007 temp = mark.copy_set_hash(hash); // merge the hash into header
1008 // try to install the hash
1009 test = obj->cas_set_mark(temp, mark);
1010 if (test == mark) { // if the hash was installed, return it
1011 return hash;
1012 }
1013 if (LockingMode == LM_LIGHTWEIGHT) {
1014 // CAS failed, retry
1015 continue;
1016 }
1017 // Failed to install the hash. It could be that another thread
1018 // installed the hash just before our attempt or inflation has
1019 // occurred or... so we fall thru to inflate the monitor for
1020 // stability and then install the hash.
1021 } else if (mark.has_monitor()) {
1022 monitor = mark.monitor();
1023 temp = monitor->header();
1024 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1025 hash = temp.hash();
1026 if (hash != 0) {
1027 // It has a hash.
1028
1029 // Separate load of dmw/header above from the loads in
1030 // is_being_async_deflated().
1031
1032 // dmw/header and _contentions may get written by different threads.
1033 // Make sure to observe them in the same order when having several observers.
1034 OrderAccess::loadload_for_IRIW();
1035
1036 if (monitor->is_being_async_deflated()) {
1037 // But we can't safely use the hash if we detect that async
1038 // deflation has occurred. So we attempt to restore the
1039 // header/dmw to the object's header so that we only retry
1040 // once if the deflater thread happens to be slow.
1041 monitor->install_displaced_markword_in_object(obj);
1042 continue;
1043 }
1044 return hash;
1045 }
1046 // Fall thru so we only have one place that installs the hash in
1047 // the ObjectMonitor.
1048 } else if (LockingMode == LM_LEGACY && mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
1049 // This is a stack-lock owned by the calling thread so fetch the
1050 // displaced markWord from the BasicLock on the stack.
1051 temp = mark.displaced_mark_helper();
1052 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1053 hash = temp.hash();
1054 if (hash != 0) { // if it has a hash, just return it
1055 return hash;
1056 }
1057 // WARNING:
1058 // The displaced header in the BasicLock on a thread's stack
1059 // is strictly immutable. It CANNOT be changed in ANY cases.
1060 // So we have to inflate the stack-lock into an ObjectMonitor
1061 // even if the current thread owns the lock. The BasicLock on
1062 // a thread's stack can be asynchronously read by other threads
1063 // during an inflate() call so any change to that stack memory
1064 // may not propagate to other threads correctly.
1065 }
1066
1067 // Inflate the monitor to set the hash.
1068
1069 // An async deflation can race after the inflate() call and before we
1070 // can update the ObjectMonitor's header with the hash value below.
1071 monitor = inflate(current, obj, inflate_cause_hash_code);
1072 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1073 mark = monitor->header();
1074 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1075 hash = mark.hash();
1076 if (hash == 0) { // if it does not have a hash
1077 hash = get_next_hash(current, obj); // get a new hash
1078 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1079 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1080 uintptr_t v = Atomic::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
1081 test = markWord(v);
1082 if (test != mark) {
1083 // The attempt to update the ObjectMonitor's header/dmw field
1084 // did not work. This can happen if another thread managed to
1085 // merge in the hash just before our cmpxchg().
1086 // If we add any new usages of the header/dmw field, this code
1087 // will need to be updated.
1088 hash = test.hash();
1089 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1090 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1091 }
1092 if (monitor->is_being_async_deflated()) {
1093 // If we detect that async deflation has occurred, then we
1094 // attempt to restore the header/dmw to the object's header
1095 // so that we only retry once if the deflater thread happens
1096 // to be slow.
1097 monitor->install_displaced_markword_in_object(obj);
1098 continue;
1099 }
1100 }
1101 // We finally get the hash.
1102 return hash;
1103 }
1104 }
1105
1106 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1107 Handle h_obj) {
1108 assert(current == JavaThread::current(), "Can only be called on current thread");
1109 oop obj = h_obj();
1110
1111 markWord mark = read_stable_mark(obj);
1112
1113 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1114 // stack-locked case, header points into owner's stack
1115 return current->is_lock_owned((address)mark.locker());
1116 }
1117
1118 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1119 // fast-locking case, see if lock is in current's lock stack
1120 return current->lock_stack().contains(h_obj());
1121 }
1122
1123 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1124 ObjectMonitor* monitor = LightweightSynchronizer::read_monitor(current, obj);
1125 if (monitor != nullptr) {
1126 return monitor->is_entered(current) != 0;
1127 }
1128 // Racing with inflation/deflation, retry
1129 mark = obj->mark_acquire();
1130
1131 if (mark.is_fast_locked()) {
1132 // Some other thread fast_locked, current could not have held the lock
1133 return false;
1134 }
1135 }
1136
1137 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1138 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1139 // The first stage of async deflation does not affect any field
1140 // used by this comparison so the ObjectMonitor* is usable here.
1141 ObjectMonitor* monitor = read_monitor(mark);
1142 return monitor->is_entered(current) != 0;
1143 }
1144 // Unlocked case, header in place
1145 assert(mark.is_unlocked(), "sanity check");
1146 return false;
1147 }
1148
1149 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1150 oop obj = h_obj();
1151 markWord mark = read_stable_mark(obj);
1152
1153 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1154 // stack-locked so header points into owner's stack.
1155 // owning_thread_from_monitor_owner() may also return null here:
1156 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1157 }
1158
1159 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1160 // fast-locked so get owner from the object.
1161 // owning_thread_from_object() may also return null here:
1162 return Threads::owning_thread_from_object(t_list, h_obj());
1163 }
1164
1165 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1166 ObjectMonitor* monitor = LightweightSynchronizer::read_monitor(Thread::current(), obj);
1167 if (monitor != nullptr) {
1168 return Threads::owning_thread_from_monitor(t_list, monitor);
1169 }
1170 // Racing with inflation/deflation, retry
1171 mark = obj->mark_acquire();
1172
1173 if (mark.is_fast_locked()) {
1174 // Some other thread fast_locked
1175 return Threads::owning_thread_from_object(t_list, h_obj());
1176 }
1177 }
1178
1179 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1180 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1181 // The first stage of async deflation does not affect any field
1182 // used by this comparison so the ObjectMonitor* is usable here.
1183 ObjectMonitor* monitor = read_monitor(mark);
1184 assert(monitor != nullptr, "monitor should be non-null");
1185 // owning_thread_from_monitor() may also return null here:
1186 return Threads::owning_thread_from_monitor(t_list, monitor);
1187 }
1188
1189 // Unlocked case, header in place
1190 // Cannot have assertion since this object may have been
1191 // locked by another thread when reaching here.
1192 // assert(mark.is_unlocked(), "sanity check");
1193
1194 return nullptr;
1195 }
1196
1197 // Visitors ...
1198
1199 // Iterate over all ObjectMonitors.
1200 template <typename Function>
1201 void ObjectSynchronizer::monitors_iterate(Function function) {
1202 MonitorList::Iterator iter = _in_use_list.iterator();
1203 while (iter.has_next()) {
1204 ObjectMonitor* monitor = iter.next();
1205 function(monitor);
1206 }
1207 }
1208
1209 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1210 // returns true.
1211 template <typename OwnerFilter>
1212 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1213 monitors_iterate([&](ObjectMonitor* monitor) {
1214 // This function is only called at a safepoint or when the
1215 // target thread is suspended or when the target thread is
1216 // operating on itself. The current closures in use today are
1217 // only interested in an owned ObjectMonitor and ownership
1218 // cannot be dropped under the calling contexts so the
1219 // ObjectMonitor cannot be async deflated.
1220 if (monitor->has_owner() && filter(monitor->owner_raw())) {
1221 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1222
1223 closure->do_monitor(monitor);
1224 }
1225 });
1226 }
1227
1228 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1229 // ObjectMonitors where owner is set to a stack-lock address in thread.
1230 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1231 auto thread_filter = [&](void* owner) { return owner == thread; };
1232 return owned_monitors_iterate_filtered(closure, thread_filter);
1233 }
1234
1235 // Iterate ObjectMonitors owned by any thread.
1236 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1237 auto all_filter = [&](void* owner) { return true; };
1238 return owned_monitors_iterate_filtered(closure, all_filter);
1239 }
1240
1241 static bool monitors_used_above_threshold(MonitorList* list) {
1242 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1243 return false;
1244 }
1245 // Start with ceiling based on a per-thread estimate:
1246 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1247 size_t old_ceiling = ceiling;
1248 if (ceiling < list->max()) {
1249 // The max used by the system has exceeded the ceiling so use that:
1250 ceiling = list->max();
1251 }
1252 size_t monitors_used = list->count();
1253 if (monitors_used == 0) { // empty list is easy
1254 return false;
1255 }
1256 if (NoAsyncDeflationProgressMax != 0 &&
1257 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1258 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1259 size_t new_ceiling = ceiling / remainder + 1;
1260 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1261 log_info(monitorinflation)("Too many deflations without progress; "
1262 "bumping in_use_list_ceiling from " SIZE_FORMAT
1263 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1264 _no_progress_cnt = 0;
1265 ceiling = new_ceiling;
1266 }
1267
1268 // Check if our monitor usage is above the threshold:
1269 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1270 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1271 log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
1272 ", monitor_usage=" SIZE_FORMAT ", threshold=%d",
1273 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1274 return true;
1275 }
1276
1277 return false;
1278 }
1279
1280 size_t ObjectSynchronizer::in_use_list_ceiling() {
1281 return _in_use_list_ceiling;
1282 }
1283
1284 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1285 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1286 }
1287
1288 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1289 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1290 }
1291
1292 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1293 _in_use_list_ceiling = new_value;
1294 }
1295
1296 bool ObjectSynchronizer::is_async_deflation_needed() {
1297 if (is_async_deflation_requested()) {
1298 // Async deflation request.
1299 log_info(monitorinflation)("Async deflation needed: explicit request");
1300 return true;
1301 }
1302
1303 jlong time_since_last = time_since_last_async_deflation_ms();
1304
1305 if (AsyncDeflationInterval > 0 &&
1306 time_since_last > AsyncDeflationInterval &&
1307 monitors_used_above_threshold(&_in_use_list)) {
1308 // It's been longer than our specified deflate interval and there
1309 // are too many monitors in use. We don't deflate more frequently
1310 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1311 // in order to not swamp the MonitorDeflationThread.
1312 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1313 return true;
1314 }
1315
1316 if (GuaranteedAsyncDeflationInterval > 0 &&
1317 time_since_last > GuaranteedAsyncDeflationInterval) {
1318 // It's been longer than our specified guaranteed deflate interval.
1319 // We need to clean up the used monitors even if the threshold is
1320 // not reached, to keep the memory utilization at bay when many threads
1321 // touched many monitors.
1322 log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) "
1323 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1324 GuaranteedAsyncDeflationInterval, time_since_last);
1325
1326 // If this deflation has no progress, then it should not affect the no-progress
1327 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1328 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1329 // the generic code would bump the no-progress counter, and we compensate for that
1330 // by telling it to skip the update.
1331 //
1332 // If this deflation has progress, then it should let non-progress tracking
1333 // know about this, otherwise the threshold heuristics would kick in, potentially
1334 // experience no-progress due to aggressive cleanup by this deflation, and think
1335 // it is still in no-progress stride. In this "progress" case, the generic code would
1336 // zero the counter, and we allow it to happen.
1337 _no_progress_skip_increment = true;
1338
1339 return true;
1340 }
1341
1342 return false;
1343 }
1344
1345 void ObjectSynchronizer::request_deflate_idle_monitors() {
1346 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1347 set_is_async_deflation_requested(true);
1348 ml.notify_all();
1349 }
1350
1351 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1352 JavaThread* current = JavaThread::current();
1353 bool ret_code = false;
1354
1355 jlong last_time = last_async_deflation_time_ns();
1356
1357 request_deflate_idle_monitors();
1358
1359 const int N_CHECKS = 5;
1360 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1361 if (last_async_deflation_time_ns() > last_time) {
1362 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1363 ret_code = true;
1364 break;
1365 }
1366 {
1367 // JavaThread has to honor the blocking protocol.
1368 ThreadBlockInVM tbivm(current);
1369 os::naked_short_sleep(999); // sleep for almost 1 second
1370 }
1371 }
1372 if (!ret_code) {
1373 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1374 }
1375
1376 return ret_code;
1377 }
1378
1379 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1380 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1381 }
1382
1383 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1384 const oop obj,
1385 ObjectSynchronizer::InflateCause cause) {
1386 assert(event != nullptr, "invariant");
1387 event->set_monitorClass(obj->klass());
1388 event->set_address((uintptr_t)(void*)obj);
1389 event->set_cause((u1)cause);
1390 event->commit();
1391 }
1392
1393 // Fast path code shared by multiple functions
1394 void ObjectSynchronizer::inflate_helper(oop obj) {
1395 if (LockingMode == LM_LIGHTWEIGHT) {
1396 return;
1397 }
1398 markWord mark = obj->mark_acquire();
1399 if (mark.has_monitor()) {
1400 ObjectMonitor* monitor = read_monitor(mark);
1401 markWord dmw = monitor->header();
1402 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1403 return;
1404 }
1405 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1406 }
1407
1408 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1409 assert(current == Thread::current(), "must be");
1410 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate");
1411 return inflate_impl(obj, cause);
1412 }
1413
1414 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1415 assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1416 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_for");
1417 return inflate_impl(obj, cause);
1418 }
1419
1420 ObjectMonitor* ObjectSynchronizer::inflate_impl(oop object, const InflateCause cause) {
1421 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_impl");
1422 EventJavaMonitorInflate event;
1423
1424 for (;;) {
1425 const markWord mark = object->mark_acquire();
1426
1427 // The mark can be in one of the following states:
1428 // * inflated - Just return it.
1429 // * stack-locked - Coerce it to inflated from stack-locked.
1430 // * INFLATING - Busy wait for conversion from stack-locked to
1431 // inflated.
1432 // * unlocked - Aggressively inflate the object.
1433
1434 // CASE: inflated
1435 if (mark.has_monitor()) {
1436 ObjectMonitor* inf = mark.monitor();
1437 markWord dmw = inf->header();
1438 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1439 return inf;
1440 }
1441
1442 // CASE: inflation in progress - inflating over a stack-lock.
1443 // Some other thread is converting from stack-locked to inflated.
1444 // Only that thread can complete inflation -- other threads must wait.
1445 // The INFLATING value is transient.
1446 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1447 // We could always eliminate polling by parking the thread on some auxiliary list.
1448 if (mark == markWord::INFLATING()) {
1449 read_stable_mark(object);
1450 continue;
1451 }
1452
1453 // CASE: stack-locked
1454 // Could be stack-locked either by current or by some other thread.
1455 //
1456 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1457 // to install INFLATING into the mark word. We originally installed INFLATING,
1458 // allocated the ObjectMonitor, and then finally STed the address of the
1459 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1460 // the interval in which INFLATING appeared in the mark, thus increasing
1461 // the odds of inflation contention. If we lose the race to set INFLATING,
1462 // then we just delete the ObjectMonitor and loop around again.
1463 //
1464 LogStreamHandle(Trace, monitorinflation) lsh;
1465 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1466 ObjectMonitor* m = new ObjectMonitor(object);
1467 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1468 // We do this before the CAS in order to minimize the length of time
1469 // in which INFLATING appears in the mark.
1470
1471 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1472 if (cmp != mark) {
1473 delete m;
1474 continue; // Interference -- just retry
1475 }
1476
1477 // We've successfully installed INFLATING (0) into the mark-word.
1478 // This is the only case where 0 will appear in a mark-word.
1479 // Only the singular thread that successfully swings the mark-word
1480 // to 0 can perform (or more precisely, complete) inflation.
1481 //
1482 // Why do we CAS a 0 into the mark-word instead of just CASing the
1483 // mark-word from the stack-locked value directly to the new inflated state?
1484 // Consider what happens when a thread unlocks a stack-locked object.
1485 // It attempts to use CAS to swing the displaced header value from the
1486 // on-stack BasicLock back into the object header. Recall also that the
1487 // header value (hash code, etc) can reside in (a) the object header, or
1488 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1489 // header in an ObjectMonitor. The inflate() routine must copy the header
1490 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1491 // the while preserving the hashCode stability invariants. If the owner
1492 // decides to release the lock while the value is 0, the unlock will fail
1493 // and control will eventually pass from slow_exit() to inflate. The owner
1494 // will then spin, waiting for the 0 value to disappear. Put another way,
1495 // the 0 causes the owner to stall if the owner happens to try to
1496 // drop the lock (restoring the header from the BasicLock to the object)
1497 // while inflation is in-progress. This protocol avoids races that might
1498 // would otherwise permit hashCode values to change or "flicker" for an object.
1499 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1500 // 0 serves as a "BUSY" inflate-in-progress indicator.
1501
1502
1503 // fetch the displaced mark from the owner's stack.
1504 // The owner can't die or unwind past the lock while our INFLATING
1505 // object is in the mark. Furthermore the owner can't complete
1506 // an unlock on the object, either.
1507 markWord dmw = mark.displaced_mark_helper();
1508 // Catch if the object's header is not neutral (not locked and
1509 // not marked is what we care about here).
1510 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1511
1512 // Setup monitor fields to proper values -- prepare the monitor
1513 m->set_header(dmw);
1514
1515 // Optimization: if the mark.locker stack address is associated
1516 // with this thread we could simply set m->_owner = current.
1517 // Note that a thread can inflate an object
1518 // that it has stack-locked -- as might happen in wait() -- directly
1519 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1520 m->set_owner_from(nullptr, mark.locker());
1521 // TODO-FIXME: assert BasicLock->dhw != 0.
1522
1523 // Must preserve store ordering. The monitor state must
1524 // be stable at the time of publishing the monitor address.
1525 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1526 // Release semantics so that above set_object() is seen first.
1527 object->release_set_mark(markWord::encode(m));
1528
1529 // Once ObjectMonitor is configured and the object is associated
1530 // with the ObjectMonitor, it is safe to allow async deflation:
1531 _in_use_list.add(m);
1532
1533 // Hopefully the performance counters are allocated on distinct cache lines
1534 // to avoid false sharing on MP systems ...
1535 OM_PERFDATA_OP(Inflations, inc());
1536 if (log_is_enabled(Trace, monitorinflation)) {
1537 ResourceMark rm;
1538 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1539 INTPTR_FORMAT ", type='%s'", p2i(object),
1540 object->mark().value(), object->klass()->external_name());
1541 }
1542 if (event.should_commit()) {
1543 post_monitor_inflate_event(&event, object, cause);
1544 }
1545 return m;
1546 }
1547
1548 // CASE: unlocked
1549 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1550 // If we know we're inflating for entry it's better to inflate by swinging a
1551 // pre-locked ObjectMonitor pointer into the object header. A successful
1552 // CAS inflates the object *and* confers ownership to the inflating thread.
1553 // In the current implementation we use a 2-step mechanism where we CAS()
1554 // to inflate and then CAS() again to try to swing _owner from null to current.
1555 // An inflateTry() method that we could call from enter() would be useful.
1556
1557 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
1558 ObjectMonitor* m = new ObjectMonitor(object);
1559 // prepare m for installation - set monitor to initial state
1560 m->set_header(mark);
1561
1562 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1563 delete m;
1564 m = nullptr;
1565 continue;
1566 // interference - the markword changed - just retry.
1567 // The state-transitions are one-way, so there's no chance of
1568 // live-lock -- "Inflated" is an absorbing state.
1569 }
1570
1571 // Once the ObjectMonitor is configured and object is associated
1572 // with the ObjectMonitor, it is safe to allow async deflation:
1573 _in_use_list.add(m);
1574
1575 // Hopefully the performance counters are allocated on distinct
1576 // cache lines to avoid false sharing on MP systems ...
1577 OM_PERFDATA_OP(Inflations, inc());
1578 if (log_is_enabled(Trace, monitorinflation)) {
1579 ResourceMark rm;
1580 lsh.print_cr("inflate(unlocked): object=" INTPTR_FORMAT ", mark="
1581 INTPTR_FORMAT ", type='%s'", p2i(object),
1582 object->mark().value(), object->klass()->external_name());
1583 }
1584 if (event.should_commit()) {
1585 post_monitor_inflate_event(&event, object, cause);
1586 }
1587 return m;
1588 }
1589 }
1590
1591 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1592 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1593 //
1594 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1595 MonitorList::Iterator iter = _in_use_list.iterator();
1596 size_t deflated_count = 0;
1597 Thread* current = Thread::current();
1598
1599 while (iter.has_next()) {
1600 if (deflated_count >= (size_t)MonitorDeflationMax) {
1601 break;
1602 }
1603 ObjectMonitor* mid = iter.next();
1604 if (mid->deflate_monitor(current)) {
1605 deflated_count++;
1606 }
1607
1608 // Must check for a safepoint/handshake and honor it.
1609 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1610 }
1611
1612 return deflated_count;
1613 }
1614
1615 class HandshakeForDeflation : public HandshakeClosure {
1616 public:
1617 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1618
1619 void do_thread(Thread* thread) {
1620 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1621 INTPTR_FORMAT, p2i(thread));
1622 if (thread->is_Java_thread()) {
1623 // Clear OM cache
1624 JavaThread* jt = JavaThread::cast(thread);
1625 jt->om_clear_monitor_cache();
1626 }
1627 }
1628 };
1629
1630 class VM_RendezvousGCThreads : public VM_Operation {
1631 public:
1632 bool evaluate_at_safepoint() const override { return false; }
1633 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1634 void doit() override {
1635 Universe::heap()->safepoint_synchronize_begin();
1636 Universe::heap()->safepoint_synchronize_end();
1637 };
1638 };
1639
1640 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1641 ObjectMonitorDeflationSafepointer* safepointer) {
1642 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1643 size_t deleted_count = 0;
1644 for (ObjectMonitor* monitor: *delete_list) {
1645 delete monitor;
1646 deleted_count++;
1647 // A JavaThread must check for a safepoint/handshake and honor it.
1648 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1649 }
1650 return deleted_count;
1651 }
1652
1653 class ObjectMonitorDeflationLogging: public StackObj {
1654 LogStreamHandle(Debug, monitorinflation) _debug;
1655 LogStreamHandle(Info, monitorinflation) _info;
1656 LogStream* _stream;
1657 elapsedTimer _timer;
1658
1659 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1660 size_t count() const { return ObjectSynchronizer::_in_use_list.count(); }
1661 size_t max() const { return ObjectSynchronizer::_in_use_list.max(); }
1662
1663 public:
1664 ObjectMonitorDeflationLogging()
1665 : _debug(), _info(), _stream(nullptr) {
1666 if (_debug.is_enabled()) {
1667 _stream = &_debug;
1668 } else if (_info.is_enabled()) {
1669 _stream = &_info;
1670 }
1671 }
1672
1673 void begin() {
1674 if (_stream != nullptr) {
1675 _stream->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1676 ceiling(), count(), max());
1677 _timer.start();
1678 }
1679 }
1680
1681 void before_handshake(size_t unlinked_count) {
1682 if (_stream != nullptr) {
1683 _timer.stop();
1684 _stream->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1685 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1686 SIZE_FORMAT ", max=" SIZE_FORMAT,
1687 unlinked_count, ceiling(), count(), max());
1688 }
1689 }
1690
1691 void after_handshake() {
1692 if (_stream != nullptr) {
1693 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1694 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1695 ceiling(), count(), max());
1696 _timer.start();
1697 }
1698 }
1699
1700 void end(size_t deflated_count, size_t unlinked_count) {
1701 if (_stream != nullptr) {
1702 _timer.stop();
1703 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1704 _stream->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1705 deflated_count, unlinked_count, _timer.seconds());
1706 }
1707 _stream->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1708 ceiling(), count(), max());
1709 }
1710 }
1711
1712 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1713 if (_stream != nullptr) {
1714 _timer.stop();
1715 _stream->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1716 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1717 op_name, cnt_name, cnt, ceiling(), count(), max());
1718 }
1719 }
1720
1721 void after_block_for_safepoint(const char* op_name) {
1722 if (_stream != nullptr) {
1723 _stream->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1724 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1725 ceiling(), count(), max());
1726 _timer.start();
1727 }
1728 }
1729 };
1730
1731 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1732 if (!SafepointMechanism::should_process(_current)) {
1733 return;
1734 }
1735
1736 // A safepoint/handshake has started.
1737 _log->before_block_for_safepoint(op_name, count_name, counter);
1738
1739 {
1740 // Honor block request.
1741 ThreadBlockInVM tbivm(_current);
1742 }
1743
1744 _log->after_block_for_safepoint(op_name);
1745 }
1746
1747 // This function is called by the MonitorDeflationThread to deflate
1748 // ObjectMonitors.
1749 size_t ObjectSynchronizer::deflate_idle_monitors() {
1750 JavaThread* current = JavaThread::current();
1751 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1752
1753 // The async deflation request has been processed.
1754 _last_async_deflation_time_ns = os::javaTimeNanos();
1755 set_is_async_deflation_requested(false);
1756
1757 ObjectMonitorDeflationLogging log;
1758 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1759
1760 log.begin();
1761
1762 // Deflate some idle ObjectMonitors.
1763 size_t deflated_count = deflate_monitor_list(&safepointer);
1764
1765 // Unlink the deflated ObjectMonitors from the in-use list.
1766 size_t unlinked_count = 0;
1767 size_t deleted_count = 0;
1768 if (deflated_count > 0) {
1769 ResourceMark rm(current);
1770 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1771 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1772
1773 #ifdef ASSERT
1774 if (LockingMode == LM_LIGHTWEIGHT) {
1775 for (ObjectMonitor* monitor : delete_list) {
1776 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1777 }
1778 }
1779 #endif
1780
1781 log.before_handshake(unlinked_count);
1782
1783 // A JavaThread needs to handshake in order to safely free the
1784 // ObjectMonitors that were deflated in this cycle.
1785 HandshakeForDeflation hfd_hc;
1786 Handshake::execute(&hfd_hc);
1787 // Also, we sync and desync GC threads around the handshake, so that they can
1788 // safely read the mark-word and look-through to the object-monitor, without
1789 // being afraid that the object-monitor is going away.
1790 VM_RendezvousGCThreads sync_gc;
1791 VMThread::execute(&sync_gc);
1792
1793 log.after_handshake();
1794
1795 // After the handshake, safely free the ObjectMonitors that were
1796 // deflated and unlinked in this cycle.
1797
1798 // Delete the unlinked ObjectMonitors.
1799 deleted_count = delete_monitors(&delete_list, &safepointer);
1800 assert(unlinked_count == deleted_count, "must be");
1801 }
1802
1803 log.end(deflated_count, unlinked_count);
1804
1805 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1806 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1807
1808 GVars.stw_random = os::random();
1809
1810 if (deflated_count != 0) {
1811 _no_progress_cnt = 0;
1812 } else if (_no_progress_skip_increment) {
1813 _no_progress_skip_increment = false;
1814 } else {
1815 _no_progress_cnt++;
1816 }
1817
1818 return deflated_count;
1819 }
1820
1821 // Monitor cleanup on JavaThread::exit
1822
1823 // Iterate through monitor cache and attempt to release thread's monitors
1824 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1825 private:
1826 JavaThread* _thread;
1827
1828 public:
1829 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1830 void do_monitor(ObjectMonitor* mid) {
1831 intx rec = mid->complete_exit(_thread);
1832 _thread->dec_held_monitor_count(rec + 1);
1833 }
1834 };
1835
1836 // Release all inflated monitors owned by current thread. Lightweight monitors are
1837 // ignored. This is meant to be called during JNI thread detach which assumes
1838 // all remaining monitors are heavyweight. All exceptions are swallowed.
1839 // Scanning the extant monitor list can be time consuming.
1840 // A simple optimization is to add a per-thread flag that indicates a thread
1841 // called jni_monitorenter() during its lifetime.
1842 //
1843 // Instead of NoSafepointVerifier it might be cheaper to
1844 // use an idiom of the form:
1845 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1846 // <code that must not run at safepoint>
1847 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1848 // Since the tests are extremely cheap we could leave them enabled
1849 // for normal product builds.
1850
1851 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1852 assert(current == JavaThread::current(), "must be current Java thread");
1853 NoSafepointVerifier nsv;
1854 ReleaseJavaMonitorsClosure rjmc(current);
1855 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1856 assert(!current->has_pending_exception(), "Should not be possible");
1857 current->clear_pending_exception();
1858 assert(current->held_monitor_count() == 0, "Should not be possible");
1859 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1860 current->clear_jni_monitor_count();
1861 }
1862
1863 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1864 switch (cause) {
1865 case inflate_cause_vm_internal: return "VM Internal";
1866 case inflate_cause_monitor_enter: return "Monitor Enter";
1867 case inflate_cause_wait: return "Monitor Wait";
1868 case inflate_cause_notify: return "Monitor Notify";
1869 case inflate_cause_hash_code: return "Monitor Hash Code";
1870 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1871 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1872 default:
1873 ShouldNotReachHere();
1874 }
1875 return "Unknown";
1876 }
1877
1878 //------------------------------------------------------------------------------
1879 // Debugging code
1880
1881 u_char* ObjectSynchronizer::get_gvars_addr() {
1882 return (u_char*)&GVars;
1883 }
1884
1885 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1886 return (u_char*)&GVars.hc_sequence;
1887 }
1888
1889 size_t ObjectSynchronizer::get_gvars_size() {
1890 return sizeof(SharedGlobals);
1891 }
1892
1893 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1894 return (u_char*)&GVars.stw_random;
1895 }
1896
1897 // Do the final audit and print of ObjectMonitor stats; must be done
1898 // by the VMThread at VM exit time.
1899 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1900 assert(Thread::current()->is_VM_thread(), "sanity check");
1901
1902 if (is_final_audit()) { // Only do the audit once.
1903 return;
1904 }
1905 set_is_final_audit();
1906 log_info(monitorinflation)("Starting the final audit.");
1907
1908 if (log_is_enabled(Info, monitorinflation)) {
1909 LogStreamHandle(Info, monitorinflation) ls;
1910 audit_and_print_stats(&ls, true /* on_exit */);
1911 }
1912 }
1913
1914 // This function can be called by the MonitorDeflationThread or it can be called when
1915 // we are trying to exit the VM. The list walker functions can run in parallel with
1916 // the other list operations.
1917 // Calls to this function can be added in various places as a debugging
1918 // aid.
1919 //
1920 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1921 int error_cnt = 0;
1922
1923 ls->print_cr("Checking in_use_list:");
1924 chk_in_use_list(ls, &error_cnt);
1925
1926 if (error_cnt == 0) {
1927 ls->print_cr("No errors found in in_use_list checks.");
1928 } else {
1929 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1930 }
1931
1932 // When exiting, only log the interesting entries at the Info level.
1933 // When called at intervals by the MonitorDeflationThread, log output
1934 // at the Trace level since there can be a lot of it.
1935 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1936 LogStreamHandle(Trace, monitorinflation) ls_tr;
1937 log_in_use_monitor_details(&ls_tr, true /* log_all */);
1938 } else if (on_exit) {
1939 log_in_use_monitor_details(ls, false /* log_all */);
1940 }
1941
1942 ls->flush();
1943
1944 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1945 }
1946
1947 // Check the in_use_list; log the results of the checks.
1948 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1949 size_t l_in_use_count = _in_use_list.count();
1950 size_t l_in_use_max = _in_use_list.max();
1951 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1952 l_in_use_max);
1953
1954 size_t ck_in_use_count = 0;
1955 MonitorList::Iterator iter = _in_use_list.iterator();
1956 while (iter.has_next()) {
1957 ObjectMonitor* mid = iter.next();
1958 chk_in_use_entry(mid, out, error_cnt_p);
1959 ck_in_use_count++;
1960 }
1961
1962 if (l_in_use_count == ck_in_use_count) {
1963 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1964 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1965 } else {
1966 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1967 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1968 ck_in_use_count);
1969 }
1970
1971 size_t ck_in_use_max = _in_use_list.max();
1972 if (l_in_use_max == ck_in_use_max) {
1973 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1974 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1975 } else {
1976 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1977 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1978 }
1979 }
1980
1981 // Check an in-use monitor entry; log any errors.
1982 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1983 int* error_cnt_p) {
1984 if (n->owner_is_DEFLATER_MARKER()) {
1985 // This could happen when monitor deflation blocks for a safepoint.
1986 return;
1987 }
1988
1989
1990 if (n->metadata() == 0) {
1991 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1992 "have non-null _metadata (header/hash) field.", p2i(n));
1993 *error_cnt_p = *error_cnt_p + 1;
1994 }
1995
1996 const oop obj = n->object_peek();
1997 if (obj == nullptr) {
1998 return;
1999 }
2000
2001 const markWord mark = obj->mark();
2002 if (!mark.has_monitor()) {
2003 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2004 "object does not think it has a monitor: obj="
2005 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2006 p2i(obj), mark.value());
2007 *error_cnt_p = *error_cnt_p + 1;
2008 return;
2009 }
2010
2011 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
2012 if (n != obj_mon) {
2013 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2014 "object does not refer to the same monitor: obj="
2015 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2016 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2017 *error_cnt_p = *error_cnt_p + 1;
2018 }
2019 }
2020
2021 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2022 // flags indicate why the entry is in-use, 'object' and 'object type'
2023 // indicate the associated object and its type.
2024 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2025 if (_in_use_list.count() > 0) {
2026 stringStream ss;
2027 out->print_cr("In-use monitor info:");
2028 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2029 out->print_cr("%18s %s %18s %18s",
2030 "monitor", "BHL", "object", "object type");
2031 out->print_cr("================== === ================== ==================");
2032
2033 auto is_interesting = [&](ObjectMonitor* monitor) {
2034 return log_all || monitor->has_owner() || monitor->is_busy();
2035 };
2036
2037 monitors_iterate([&](ObjectMonitor* monitor) {
2038 if (is_interesting(monitor)) {
2039 const oop obj = monitor->object_peek();
2040 const intptr_t hash = LockingMode == LM_LIGHTWEIGHT ? monitor->hash() : monitor->header().hash();
2041 ResourceMark rm;
2042 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
2043 monitor->is_busy(), hash != 0, monitor->owner() != nullptr,
2044 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2045 if (monitor->is_busy()) {
2046 out->print(" (%s)", monitor->is_busy_to_string(&ss));
2047 ss.reset();
2048 }
2049 out->cr();
2050 }
2051 });
2052 }
2053
2054 out->flush();
2055 }