1 /*
2 * Copyright (c) 1998, 2025, 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/atomic.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/lightweightSynchronizer.hpp"
45 #include "runtime/lockStack.inline.hpp"
46 #include "runtime/mutexLocker.hpp"
47 #include "runtime/objectMonitor.hpp"
48 #include "runtime/objectMonitor.inline.hpp"
49 #include "runtime/os.inline.hpp"
50 #include "runtime/osThread.hpp"
51 #include "runtime/safepointMechanism.inline.hpp"
52 #include "runtime/safepointVerifiers.hpp"
53 #include "runtime/sharedRuntime.hpp"
54 #include "runtime/stubRoutines.hpp"
55 #include "runtime/synchronizer.inline.hpp"
56 #include "runtime/threads.hpp"
57 #include "runtime/timer.hpp"
58 #include "runtime/trimNativeHeap.hpp"
59 #include "runtime/vframe.hpp"
60 #include "runtime/vmThread.hpp"
61 #include "utilities/align.hpp"
62 #include "utilities/dtrace.hpp"
63 #include "utilities/events.hpp"
64 #include "utilities/globalCounter.inline.hpp"
65 #include "utilities/globalDefinitions.hpp"
66 #include "utilities/linkedlist.hpp"
67 #include "utilities/preserveException.hpp"
68
69 class ObjectMonitorDeflationLogging;
70
71 void MonitorList::add(ObjectMonitor* m) {
72 ObjectMonitor* head;
73 do {
74 head = Atomic::load(&_head);
75 m->set_next_om(head);
76 } while (Atomic::cmpxchg(&_head, head, m) != head);
77
78 size_t count = Atomic::add(&_count, 1u, memory_order_relaxed);
79 size_t old_max;
80 do {
81 old_max = Atomic::load(&_max);
82 if (count <= old_max) {
83 break;
84 }
85 } while (Atomic::cmpxchg(&_max, old_max, count, memory_order_relaxed) != old_max);
86 }
87
88 size_t MonitorList::count() const {
89 return Atomic::load(&_count);
90 }
91
92 size_t MonitorList::max() const {
93 return Atomic::load(&_max);
94 }
95
96 class ObjectMonitorDeflationSafepointer : public StackObj {
97 JavaThread* const _current;
98 ObjectMonitorDeflationLogging* const _log;
99
100 public:
101 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
102 : _current(current), _log(log) {}
103
104 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
105 };
106
107 // Walk the in-use list and unlink deflated ObjectMonitors.
108 // Returns the number of unlinked ObjectMonitors.
109 size_t MonitorList::unlink_deflated(size_t deflated_count,
110 GrowableArray<ObjectMonitor*>* unlinked_list,
111 ObjectMonitorDeflationSafepointer* safepointer) {
112 size_t unlinked_count = 0;
113 ObjectMonitor* prev = nullptr;
114 ObjectMonitor* m = Atomic::load_acquire(&_head);
115
116 while (m != nullptr) {
117 if (m->is_being_async_deflated()) {
118 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
119 // modify the list once per batch. The batch starts at "m".
120 size_t unlinked_batch = 0;
121 ObjectMonitor* next = m;
122 // Look for at most MonitorUnlinkBatch monitors, or the number of
123 // deflated and not unlinked monitors, whatever comes first.
124 assert(deflated_count >= unlinked_count, "Sanity: underflow");
125 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
126 do {
127 ObjectMonitor* next_next = next->next_om();
128 unlinked_batch++;
129 unlinked_list->append(next);
130 next = next_next;
131 if (unlinked_batch >= unlinked_batch_limit) {
132 // Reached the max batch, so bail out of the gathering loop.
133 break;
134 }
135 if (prev == nullptr && Atomic::load(&_head) != m) {
136 // Current batch used to be at head, but it is not at head anymore.
137 // Bail out and figure out where we currently are. This avoids long
138 // walks searching for new prev during unlink under heavy list inserts.
139 break;
140 }
141 } while (next != nullptr && next->is_being_async_deflated());
142
143 // Unlink the found batch.
144 if (prev == nullptr) {
145 // The current batch is the first batch, so there is a chance that it starts at head.
146 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
147 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, m, next);
148 if (prev_head != m) {
149 // Something must have updated the head. Figure out the actual prev for this batch.
150 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
151 prev = n;
152 }
153 assert(prev != nullptr, "Should have found the prev for the current batch");
154 prev->set_next_om(next);
155 }
156 } else {
157 // The current batch is preceded by another batch. This guarantees the current batch
158 // does not start at head. Unlink the entire current batch without updating the head.
159 assert(Atomic::load(&_head) != m, "Sanity");
160 prev->set_next_om(next);
161 }
162
163 unlinked_count += unlinked_batch;
164 if (unlinked_count >= deflated_count) {
165 // Reached the max so bail out of the searching loop.
166 // There should be no more deflated monitors left.
167 break;
168 }
169 m = next;
170 } else {
171 prev = m;
172 m = m->next_om();
173 }
174
175 // Must check for a safepoint/handshake and honor it.
176 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
177 }
178
179 #ifdef ASSERT
180 // Invariant: the code above should unlink all deflated monitors.
181 // The code that runs after this unlinking does not expect deflated monitors.
182 // Notably, attempting to deflate the already deflated monitor would break.
183 {
184 ObjectMonitor* m = Atomic::load_acquire(&_head);
185 while (m != nullptr) {
186 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
187 m = m->next_om();
188 }
189 }
190 #endif
191
192 Atomic::sub(&_count, unlinked_count);
193 return unlinked_count;
194 }
195
196 MonitorList::Iterator MonitorList::iterator() const {
197 return Iterator(Atomic::load_acquire(&_head));
198 }
199
200 ObjectMonitor* MonitorList::Iterator::next() {
201 ObjectMonitor* current = _current;
202 _current = current->next_om();
203 return current;
204 }
205
206 // The "core" versions of monitor enter and exit reside in this file.
207 // The interpreter and compilers contain specialized transliterated
208 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
209 // fast_lock(...) for instance. If you make changes here, make sure to modify the
210 // interpreter, and both C1 and C2 fast-path inline locking code emission.
211 //
212 // -----------------------------------------------------------------------------
213
214 #ifdef DTRACE_ENABLED
215
216 // Only bother with this argument setup if dtrace is available
217 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
218
219 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
220 char* bytes = nullptr; \
221 int len = 0; \
222 jlong jtid = SharedRuntime::get_java_tid(thread); \
223 Symbol* klassname = obj->klass()->name(); \
224 if (klassname != nullptr) { \
225 bytes = (char*)klassname->bytes(); \
226 len = klassname->utf8_length(); \
227 }
228
229 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
230 { \
231 if (DTraceMonitorProbes) { \
232 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
233 HOTSPOT_MONITOR_WAIT(jtid, \
234 (uintptr_t)(monitor), bytes, len, (millis)); \
235 } \
236 }
237
238 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
239 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
240 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
241
242 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
243 { \
244 if (DTraceMonitorProbes) { \
245 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
246 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
247 (uintptr_t)(monitor), bytes, len); \
248 } \
249 }
250
251 #else // ndef DTRACE_ENABLED
252
253 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
254 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
255
256 #endif // ndef DTRACE_ENABLED
257
258 // This exists only as a workaround of dtrace bug 6254741
259 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
260 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
261 return 0;
262 }
263
264 static constexpr size_t inflation_lock_count() {
265 return 256;
266 }
267
268 // Static storage for an array of PlatformMutex.
269 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
270
271 static inline PlatformMutex* inflation_lock(size_t index) {
272 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
273 }
274
275 void ObjectSynchronizer::initialize() {
276 for (size_t i = 0; i < inflation_lock_count(); i++) {
277 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
278 }
279 // Start the ceiling with the estimate for one thread.
280 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
281
282 // Start the timer for deflations, so it does not trigger immediately.
283 _last_async_deflation_time_ns = os::javaTimeNanos();
284
285 if (LockingMode == LM_LIGHTWEIGHT) {
286 LightweightSynchronizer::initialize();
287 }
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 // =====================> Quick functions
319
320 // The quick_* forms are special fast-path variants used to improve
321 // performance. In the simplest case, a "quick_*" implementation could
322 // simply return false, in which case the caller will perform the necessary
323 // state transitions and call the slow-path form.
324 // The fast-path is designed to handle frequently arising cases in an efficient
325 // manner and is just a degenerate "optimistic" variant of the slow-path.
326 // returns true -- to indicate the call was satisfied.
327 // returns false -- to indicate the call needs the services of the slow-path.
328 // A no-loitering ordinance is in effect for code in the quick_* family
329 // operators: safepoints or indefinite blocking (blocking that might span a
330 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
331 // entry.
332 //
333 // Consider: An interesting optimization is to have the JIT recognize the
334 // following common idiom:
335 // synchronized (someobj) { .... ; notify(); }
336 // That is, we find a notify() or notifyAll() call that immediately precedes
337 // the monitorexit operation. In that case the JIT could fuse the operations
338 // into a single notifyAndExit() runtime primitive.
339
340 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
341 assert(current->thread_state() == _thread_in_Java, "invariant");
342 NoSafepointVerifier nsv;
343 if (obj == nullptr) return false; // slow-path for invalid obj
344 const markWord mark = obj->mark();
345
346 if (LockingMode == LM_LIGHTWEIGHT) {
347 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
348 // Degenerate notify
349 // fast-locked by caller so by definition the implied waitset is empty.
350 return true;
351 }
352 } else if (LockingMode == LM_LEGACY) {
353 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
354 // Degenerate notify
355 // stack-locked by caller so by definition the implied waitset is empty.
356 return true;
357 }
358 }
359
360 if (mark.has_monitor()) {
361 ObjectMonitor* const mon = read_monitor(current, obj, mark);
362 if (LockingMode == LM_LIGHTWEIGHT && mon == nullptr) {
363 // Racing with inflation/deflation go slow path
364 return false;
365 }
366 assert(mon->object() == oop(obj), "invariant");
367 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
368
369 if (mon->first_waiter() != nullptr) {
370 // We have one or more waiters. Since this is an inflated monitor
371 // that we own, we can transfer one or more threads from the waitset
372 // to the entry_list here and now, avoiding the slow-path.
373 if (all) {
374 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
375 } else {
376 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
377 }
378 do {
379 mon->notify_internal(current);
380 } while (mon->first_waiter() != nullptr && all);
381 }
382 return true;
383 }
384
385 // other IMS exception states take the slow-path
386 return false;
387 }
388
389 static bool useHeavyMonitors() {
390 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
391 return LockingMode == LM_MONITOR;
392 #else
393 return false;
394 #endif
395 }
396
397 // The LockNode emitted directly at the synchronization site would have
398 // been too big if it were to have included support for the cases of inflated
399 // recursive enter and exit, so they go here instead.
400 // Note that we can't safely call AsyncPrintJavaStack() from within
401 // quick_enter() as our thread state remains _in_Java.
402
403 bool ObjectSynchronizer::quick_enter_legacy(oop obj, BasicLock* lock, JavaThread* current) {
404 assert(current->thread_state() == _thread_in_Java, "invariant");
405
406 if (useHeavyMonitors()) {
407 return false; // Slow path
408 }
409
410 assert(LockingMode == LM_LEGACY, "legacy mode below");
411
412 const markWord mark = obj->mark();
413
414 if (mark.has_monitor()) {
415
416 ObjectMonitor* const m = read_monitor(mark);
417 // An async deflation or GC can race us before we manage to make
418 // the ObjectMonitor busy by setting the owner below. If we detect
419 // that race we just bail out to the slow-path here.
420 if (m->object_peek() == nullptr) {
421 return false;
422 }
423
424 // Lock contention and Transactional Lock Elision (TLE) diagnostics
425 // and observability
426 // Case: light contention possibly amenable to TLE
427 // Case: TLE inimical operations such as nested/recursive synchronization
428
429 if (m->has_owner(current)) {
430 m->_recursions++;
431 current->inc_held_monitor_count();
432 return true;
433 }
434
435 // This Java Monitor is inflated so obj's header will never be
436 // displaced to this thread's BasicLock. Make the displaced header
437 // non-null so this BasicLock is not seen as recursive nor as
438 // being locked. We do this unconditionally so that this thread's
439 // BasicLock cannot be mis-interpreted by any stack walkers. For
440 // performance reasons, stack walkers generally first check for
441 // stack-locking in the object's header, the second check is for
442 // recursive stack-locking in the displaced header in the BasicLock,
443 // and last are the inflated Java Monitor (ObjectMonitor) checks.
444 lock->set_displaced_header(markWord::unused_mark());
445
446 if (!m->has_owner() && m->try_set_owner(current)) {
447 assert(m->_recursions == 0, "invariant");
448 current->inc_held_monitor_count();
449 return true;
450 }
451 }
452
453 // Note that we could inflate in quick_enter.
454 // This is likely a useful optimization
455 // Critically, in quick_enter() we must not:
456 // -- block indefinitely, or
457 // -- reach a safepoint
458
459 return false; // revert to slow-path
460 }
461
462 // Handle notifications when synchronizing on value based classes
463 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
464 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
465 frame last_frame = locking_thread->last_frame();
466 bool bcp_was_adjusted = false;
467 // Don't decrement bcp if it points to the frame's first instruction. This happens when
468 // handle_sync_on_value_based_class() is called because of a synchronized method. There
469 // is no actual monitorenter instruction in the byte code in this case.
470 if (last_frame.is_interpreted_frame() &&
471 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
472 // adjust bcp to point back to monitorenter so that we print the correct line numbers
473 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
474 bcp_was_adjusted = true;
475 }
476
477 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
478 ResourceMark rm;
479 stringStream ss;
480 locking_thread->print_active_stack_on(&ss);
481 char* base = (char*)strstr(ss.base(), "at");
482 char* newline = (char*)strchr(ss.base(), '\n');
483 if (newline != nullptr) {
484 *newline = '\0';
485 }
486 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
487 } else {
488 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
489 ResourceMark rm;
490 Log(valuebasedclasses) vblog;
491
492 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
493 if (locking_thread->has_last_Java_frame()) {
494 LogStream info_stream(vblog.info());
495 locking_thread->print_active_stack_on(&info_stream);
496 } else {
497 vblog.info("Cannot find the last Java frame");
498 }
499
500 EventSyncOnValueBasedClass event;
501 if (event.should_commit()) {
502 event.set_valueBasedClass(obj->klass());
503 event.commit();
504 }
505 }
506
507 if (bcp_was_adjusted) {
508 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
509 }
510 }
511
512 // -----------------------------------------------------------------------------
513 // Monitor Enter/Exit
514
515 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
516 // When called with locking_thread != Thread::current() some mechanism must synchronize
517 // the locking_thread with respect to the current thread. Currently only used when
518 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
519 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
520
521 if (LockingMode == LM_LIGHTWEIGHT) {
522 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
523 }
524
525 if (!enter_fast_impl(obj, lock, locking_thread)) {
526 // Inflated ObjectMonitor::enter_for is required
527
528 // An async deflation can race after the inflate_for() call and before
529 // enter_for() can make the ObjectMonitor busy. enter_for() returns false
530 // if we have lost the race to async deflation and we simply try again.
531 while (true) {
532 ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
533 if (monitor->enter_for(locking_thread)) {
534 return;
535 }
536 assert(monitor->is_being_async_deflated(), "must be");
537 }
538 }
539 }
540
541 void ObjectSynchronizer::enter_legacy(Handle obj, BasicLock* lock, JavaThread* current) {
542 if (!enter_fast_impl(obj, lock, current)) {
543 // Inflated ObjectMonitor::enter is required
544
545 // An async deflation can race after the inflate() call and before
546 // enter() can make the ObjectMonitor busy. enter() returns false if
547 // we have lost the race to async deflation and we simply try again.
548 while (true) {
549 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
550 if (monitor->enter(current)) {
551 return;
552 }
553 }
554 }
555 }
556
557 // The interpreter and compiler assembly code tries to lock using the fast path
558 // of this algorithm. Make sure to update that code if the following function is
559 // changed. The implementation is extremely sensitive to race condition. Be careful.
560 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
561 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
562
563 if (obj->klass()->is_value_based()) {
564 handle_sync_on_value_based_class(obj, locking_thread);
565 }
566
567 locking_thread->inc_held_monitor_count();
568
569 if (!useHeavyMonitors()) {
570 if (LockingMode == LM_LEGACY) {
571 markWord mark = obj->mark();
572 if (mark.is_unlocked()) {
573 // Anticipate successful CAS -- the ST of the displaced mark must
574 // be visible <= the ST performed by the CAS.
575 lock->set_displaced_header(mark);
576 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
577 return true;
578 }
579 } else if (mark.has_locker() &&
580 locking_thread->is_lock_owned((address) mark.locker())) {
581 assert(lock != mark.locker(), "must not re-lock the same lock");
582 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
583 lock->set_displaced_header(markWord::from_pointer(nullptr));
584 return true;
585 }
586
587 // The object header will never be displaced to this lock,
588 // so it does not matter what the value is, except that it
589 // must be non-zero to avoid looking like a re-entrant lock,
590 // and must not look locked either.
591 lock->set_displaced_header(markWord::unused_mark());
592
593 // Failed to fast lock.
594 return false;
595 }
596 } else if (VerifyHeavyMonitors) {
597 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
598 }
599
600 return false;
601 }
602
603 void ObjectSynchronizer::exit_legacy(oop object, BasicLock* lock, JavaThread* current) {
604 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
605
606 if (!useHeavyMonitors()) {
607 markWord mark = object->mark();
608 if (LockingMode == LM_LEGACY) {
609 markWord dhw = lock->displaced_header();
610 if (dhw.value() == 0) {
611 // If the displaced header is null, then this exit matches up with
612 // a recursive enter. No real work to do here except for diagnostics.
613 #ifndef PRODUCT
614 if (mark != markWord::INFLATING()) {
615 // Only do diagnostics if we are not racing an inflation. Simply
616 // exiting a recursive enter of a Java Monitor that is being
617 // inflated is safe; see the has_monitor() comment below.
618 assert(!mark.is_unlocked(), "invariant");
619 assert(!mark.has_locker() ||
620 current->is_lock_owned((address)mark.locker()), "invariant");
621 if (mark.has_monitor()) {
622 // The BasicLock's displaced_header is marked as a recursive
623 // enter and we have an inflated Java Monitor (ObjectMonitor).
624 // This is a special case where the Java Monitor was inflated
625 // after this thread entered the stack-lock recursively. When a
626 // Java Monitor is inflated, we cannot safely walk the Java
627 // Monitor owner's stack and update the BasicLocks because a
628 // Java Monitor can be asynchronously inflated by a thread that
629 // does not own the Java Monitor.
630 ObjectMonitor* m = read_monitor(mark);
631 assert(m->object()->mark() == mark, "invariant");
632 assert(m->is_entered(current), "invariant");
633 }
634 }
635 #endif
636 return;
637 }
638
639 if (mark == markWord::from_pointer(lock)) {
640 // If the object is stack-locked by the current thread, try to
641 // swing the displaced header from the BasicLock back to the mark.
642 assert(dhw.is_neutral(), "invariant");
643 if (object->cas_set_mark(dhw, mark) == mark) {
644 return;
645 }
646 }
647 }
648 } else if (VerifyHeavyMonitors) {
649 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
650 }
651
652 // We have to take the slow-path of possible inflation and then exit.
653 // The ObjectMonitor* can't be async deflated until ownership is
654 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
655 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
656 assert(!monitor->has_anonymous_owner(), "must not be");
657 monitor->exit(current);
658 }
659
660 // -----------------------------------------------------------------------------
661 // JNI locks on java objects
662 // NOTE: must use heavy weight monitor to handle jni monitor enter
663 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
664 // Top native frames in the stack will not be seen if we attempt
665 // preemption, since we start walking from the last Java anchor.
666 NoPreemptMark npm(current);
667
668 if (obj->klass()->is_value_based()) {
669 handle_sync_on_value_based_class(obj, current);
670 }
671
672 // the current locking is from JNI instead of Java code
673 current->set_current_pending_monitor_is_from_java(false);
674 // An async deflation can race after the inflate() call and before
675 // enter() can make the ObjectMonitor busy. enter() returns false if
676 // we have lost the race to async deflation and we simply try again.
677 while (true) {
678 ObjectMonitor* monitor;
679 bool entered;
680 if (LockingMode == LM_LIGHTWEIGHT) {
681 entered = LightweightSynchronizer::inflate_and_enter(obj(), inflate_cause_jni_enter, current, current) != nullptr;
682 } else {
683 monitor = inflate(current, obj(), inflate_cause_jni_enter);
684 entered = monitor->enter(current);
685 }
686
687 if (entered) {
688 current->inc_held_monitor_count(1, true);
689 break;
690 }
691 }
692 current->set_current_pending_monitor_is_from_java(true);
693 }
694
695 // NOTE: must use heavy weight monitor to handle jni monitor exit
696 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
697 JavaThread* current = THREAD;
698
699 ObjectMonitor* monitor;
700 if (LockingMode == LM_LIGHTWEIGHT) {
701 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
702 } else {
703 // The ObjectMonitor* can't be async deflated until ownership is
704 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
705 monitor = inflate(current, obj, inflate_cause_jni_exit);
706 }
707 // If this thread has locked the object, exit the monitor. We
708 // intentionally do not use CHECK on check_owner because we must exit the
709 // monitor even if an exception was already pending.
710 if (monitor->check_owner(THREAD)) {
711 monitor->exit(current);
712 current->dec_held_monitor_count(1, true);
713 }
714 }
715
716 // -----------------------------------------------------------------------------
717 // Internal VM locks on java objects
718 // standard constructor, allows locking failures
719 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) : _npm(thread) {
720 _thread = thread;
721 _thread->check_for_valid_safepoint_state();
722 _obj = obj;
723
724 if (_obj() != nullptr) {
725 ObjectSynchronizer::enter(_obj, &_lock, _thread);
726 }
727 }
728
729 ObjectLocker::~ObjectLocker() {
730 if (_obj() != nullptr) {
731 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
732 }
733 }
734
735
736 // -----------------------------------------------------------------------------
737 // Wait/Notify/NotifyAll
738 // NOTE: must use heavy weight monitor to handle wait()
739
740 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
741 JavaThread* current = THREAD;
742 if (millis < 0) {
743 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
744 }
745
746 ObjectMonitor* monitor;
747 if (LockingMode == LM_LIGHTWEIGHT) {
748 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
749 } else {
750 // The ObjectMonitor* can't be async deflated because the _waiters
751 // field is incremented before ownership is dropped and decremented
752 // after ownership is regained.
753 monitor = inflate(current, obj(), inflate_cause_wait);
754 }
755
756 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
757 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
758
759 // This dummy call is in place to get around dtrace bug 6254741. Once
760 // that's fixed we can uncomment the following line, remove the call
761 // and change this function back into a "void" func.
762 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
763 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
764 return ret_code;
765 }
766
767 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
768 if (millis < 0) {
769 THROW_MSG(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);
775 } else {
776 monitor = inflate(THREAD, obj(), inflate_cause_wait);
777 }
778 monitor->wait(millis, false, THREAD);
779 }
780
781
782 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
783 JavaThread* current = THREAD;
784
785 markWord mark = obj->mark();
786 if (LockingMode == LM_LIGHTWEIGHT) {
787 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
788 // Not inflated so there can't be any waiters to notify.
789 return;
790 }
791 } else if (LockingMode == LM_LEGACY) {
792 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
793 // Not inflated so there can't be any waiters to notify.
794 return;
795 }
796 }
797
798 ObjectMonitor* monitor;
799 if (LockingMode == LM_LIGHTWEIGHT) {
800 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
801 } else {
802 // The ObjectMonitor* can't be async deflated until ownership is
803 // dropped by the calling thread.
804 monitor = inflate(current, obj(), inflate_cause_notify);
805 }
806 monitor->notify(CHECK);
807 }
808
809 // NOTE: see comment of notify()
810 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
811 JavaThread* current = THREAD;
812
813 markWord mark = obj->mark();
814 if (LockingMode == LM_LIGHTWEIGHT) {
815 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
816 // Not inflated so there can't be any waiters to notify.
817 return;
818 }
819 } else if (LockingMode == LM_LEGACY) {
820 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
821 // Not inflated so there can't be any waiters to notify.
822 return;
823 }
824 }
825
826 ObjectMonitor* monitor;
827 if (LockingMode == LM_LIGHTWEIGHT) {
828 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
829 } else {
830 // The ObjectMonitor* can't be async deflated until ownership is
831 // dropped by the calling thread.
832 monitor = inflate(current, obj(), inflate_cause_notify);
833 }
834 monitor->notifyAll(CHECK);
835 }
836
837 // -----------------------------------------------------------------------------
838 // Hash Code handling
839
840 struct SharedGlobals {
841 char _pad_prefix[OM_CACHE_LINE_SIZE];
842 // This is a highly shared mostly-read variable.
843 // To avoid false-sharing it needs to be the sole occupant of a cache line.
844 volatile int stw_random;
845 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
846 // Hot RW variable -- Sequester to avoid false-sharing
847 volatile int hc_sequence;
848 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
849 };
850
851 static SharedGlobals GVars;
852
853 static markWord read_stable_mark(oop obj) {
854 markWord mark = obj->mark_acquire();
855 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
856 // New lightweight locking does not use the markWord::INFLATING() protocol.
857 return mark; // normal fast-path return
858 }
859
860 int its = 0;
861 for (;;) {
862 markWord mark = obj->mark_acquire();
863 if (!mark.is_being_inflated()) {
864 return mark; // normal fast-path return
865 }
866
867 // The object is being inflated by some other thread.
868 // The caller of read_stable_mark() must wait for inflation to complete.
869 // Avoid live-lock.
870
871 ++its;
872 if (its > 10000 || !os::is_MP()) {
873 if (its & 1) {
874 os::naked_yield();
875 } else {
876 // Note that the following code attenuates the livelock problem but is not
877 // a complete remedy. A more complete solution would require that the inflating
878 // thread hold the associated inflation lock. The following code simply restricts
879 // the number of spinners to at most one. We'll have N-2 threads blocked
880 // on the inflationlock, 1 thread holding the inflation lock and using
881 // a yield/park strategy, and 1 thread in the midst of inflation.
882 // A more refined approach would be to change the encoding of INFLATING
883 // to allow encapsulation of a native thread pointer. Threads waiting for
884 // inflation to complete would use CAS to push themselves onto a singly linked
885 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
886 // and calling park(). When inflation was complete the thread that accomplished inflation
887 // would detach the list and set the markword to inflated with a single CAS and
888 // then for each thread on the list, set the flag and unpark() the thread.
889
890 // Index into the lock array based on the current object address.
891 static_assert(is_power_of_2(inflation_lock_count()), "must be");
892 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
893 int YieldThenBlock = 0;
894 assert(ix < inflation_lock_count(), "invariant");
895 inflation_lock(ix)->lock();
896 while (obj->mark_acquire() == markWord::INFLATING()) {
897 // Beware: naked_yield() is advisory and has almost no effect on some platforms
898 // so we periodically call current->_ParkEvent->park(1).
899 // We use a mixed spin/yield/block mechanism.
900 if ((YieldThenBlock++) >= 16) {
901 Thread::current()->_ParkEvent->park(1);
902 } else {
903 os::naked_yield();
904 }
905 }
906 inflation_lock(ix)->unlock();
907 }
908 } else {
909 SpinPause(); // SMP-polite spinning
910 }
911 }
912 }
913
914 // hashCode() generation :
915 //
916 // Possibilities:
917 // * MD5Digest of {obj,stw_random}
918 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
919 // * A DES- or AES-style SBox[] mechanism
920 // * One of the Phi-based schemes, such as:
921 // 2654435761 = 2^32 * Phi (golden ratio)
922 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
923 // * A variation of Marsaglia's shift-xor RNG scheme.
924 // * (obj ^ stw_random) is appealing, but can result
925 // in undesirable regularity in the hashCode values of adjacent objects
926 // (objects allocated back-to-back, in particular). This could potentially
927 // result in hashtable collisions and reduced hashtable efficiency.
928 // There are simple ways to "diffuse" the middle address bits over the
929 // generated hashCode values:
930
931 static intptr_t get_next_hash(Thread* current, oop obj) {
932 intptr_t value = 0;
933 if (hashCode == 0) {
934 // This form uses global Park-Miller RNG.
935 // On MP system we'll have lots of RW access to a global, so the
936 // mechanism induces lots of coherency traffic.
937 value = os::random();
938 } else if (hashCode == 1) {
939 // This variation has the property of being stable (idempotent)
940 // between STW operations. This can be useful in some of the 1-0
941 // synchronization schemes.
942 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
943 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
944 } else if (hashCode == 2) {
945 value = 1; // for sensitivity testing
946 } else if (hashCode == 3) {
947 value = ++GVars.hc_sequence;
948 } else if (hashCode == 4) {
949 value = cast_from_oop<intptr_t>(obj);
950 } else {
951 // Marsaglia's xor-shift scheme with thread-specific state
952 // This is probably the best overall implementation -- we'll
953 // likely make this the default in future releases.
954 unsigned t = current->_hashStateX;
955 t ^= (t << 11);
956 current->_hashStateX = current->_hashStateY;
957 current->_hashStateY = current->_hashStateZ;
958 current->_hashStateZ = current->_hashStateW;
959 unsigned v = current->_hashStateW;
960 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
961 current->_hashStateW = v;
962 value = v;
963 }
964
965 value &= markWord::hash_mask;
966 if (value == 0) value = 0xBAD;
967 assert(value != markWord::no_hash, "invariant");
968 return value;
969 }
970
971 static intptr_t install_hash_code(Thread* current, oop obj) {
972 assert(UseObjectMonitorTable && LockingMode == LM_LIGHTWEIGHT, "must be");
973
974 markWord mark = obj->mark_acquire();
975 for (;;) {
976 intptr_t hash = mark.hash();
977 if (hash != 0) {
978 return hash;
979 }
980
981 hash = get_next_hash(current, obj);
982 const markWord old_mark = mark;
983 const markWord new_mark = old_mark.copy_set_hash(hash);
984
985 mark = obj->cas_set_mark(new_mark, old_mark);
986 if (old_mark == mark) {
987 return hash;
988 }
989 }
990 }
991
992 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
993 if (UseObjectMonitorTable) {
994 // Since the monitor isn't in the object header, the hash can simply be
995 // installed in the object header.
996 return install_hash_code(current, obj);
997 }
998
999 while (true) {
1000 ObjectMonitor* monitor = nullptr;
1001 markWord temp, test;
1002 intptr_t hash;
1003 markWord mark = read_stable_mark(obj);
1004 if (VerifyHeavyMonitors) {
1005 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
1006 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1007 }
1008 if (mark.is_unlocked() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1009 hash = mark.hash();
1010 if (hash != 0) { // if it has a hash, just return it
1011 return hash;
1012 }
1013 hash = get_next_hash(current, obj); // get a new hash
1014 temp = mark.copy_set_hash(hash); // merge the hash into header
1015 // try to install the hash
1016 test = obj->cas_set_mark(temp, mark);
1017 if (test == mark) { // if the hash was installed, return it
1018 return hash;
1019 }
1020 if (LockingMode == LM_LIGHTWEIGHT) {
1021 // CAS failed, retry
1022 continue;
1023 }
1024 // Failed to install the hash. It could be that another thread
1025 // installed the hash just before our attempt or inflation has
1026 // occurred or... so we fall thru to inflate the monitor for
1027 // stability and then install the hash.
1028 } else if (mark.has_monitor()) {
1029 monitor = mark.monitor();
1030 temp = monitor->header();
1031 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1032 hash = temp.hash();
1033 if (hash != 0) {
1034 // It has a hash.
1035
1036 // Separate load of dmw/header above from the loads in
1037 // is_being_async_deflated().
1038
1039 // dmw/header and _contentions may get written by different threads.
1040 // Make sure to observe them in the same order when having several observers.
1041 OrderAccess::loadload_for_IRIW();
1042
1043 if (monitor->is_being_async_deflated()) {
1044 // But we can't safely use the hash if we detect that async
1045 // deflation has occurred. So we attempt to restore the
1046 // header/dmw to the object's header so that we only retry
1047 // once if the deflater thread happens to be slow.
1048 monitor->install_displaced_markword_in_object(obj);
1049 continue;
1050 }
1051 return hash;
1052 }
1053 // Fall thru so we only have one place that installs the hash in
1054 // the ObjectMonitor.
1055 } else if (LockingMode == LM_LEGACY && mark.has_locker()
1056 && current->is_Java_thread()
1057 && JavaThread::cast(current)->is_lock_owned((address)mark.locker())) {
1058 // This is a stack-lock owned by the calling thread so fetch the
1059 // displaced markWord from the BasicLock on the stack.
1060 temp = mark.displaced_mark_helper();
1061 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1062 hash = temp.hash();
1063 if (hash != 0) { // if it has a hash, just return it
1064 return hash;
1065 }
1066 // WARNING:
1067 // The displaced header in the BasicLock on a thread's stack
1068 // is strictly immutable. It CANNOT be changed in ANY cases.
1069 // So we have to inflate the stack-lock into an ObjectMonitor
1070 // even if the current thread owns the lock. The BasicLock on
1071 // a thread's stack can be asynchronously read by other threads
1072 // during an inflate() call so any change to that stack memory
1073 // may not propagate to other threads correctly.
1074 }
1075
1076 // Inflate the monitor to set the hash.
1077
1078 // There's no need to inflate if the mark has already got a monitor.
1079 // NOTE: an async deflation can race after we get the monitor and
1080 // before we can update the ObjectMonitor's header with the hash
1081 // value below.
1082 monitor = mark.has_monitor() ? mark.monitor() : inflate(current, obj, inflate_cause_hash_code);
1083 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1084 mark = monitor->header();
1085 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1086 hash = mark.hash();
1087 if (hash == 0) { // if it does not have a hash
1088 hash = get_next_hash(current, obj); // get a new hash
1089 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1090 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1091 uintptr_t v = Atomic::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
1092 test = markWord(v);
1093 if (test != mark) {
1094 // The attempt to update the ObjectMonitor's header/dmw field
1095 // did not work. This can happen if another thread managed to
1096 // merge in the hash just before our cmpxchg().
1097 // If we add any new usages of the header/dmw field, this code
1098 // will need to be updated.
1099 hash = test.hash();
1100 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1101 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1102 }
1103 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
1104 // If we detect that async deflation has occurred, then we
1105 // attempt to restore the header/dmw to the object's header
1106 // so that we only retry once if the deflater thread happens
1107 // to be slow.
1108 monitor->install_displaced_markword_in_object(obj);
1109 continue;
1110 }
1111 }
1112 // We finally get the hash.
1113 return hash;
1114 }
1115 }
1116
1117 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1118 Handle h_obj) {
1119 assert(current == JavaThread::current(), "Can only be called on current thread");
1120 oop obj = h_obj();
1121
1122 markWord mark = read_stable_mark(obj);
1123
1124 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1125 // stack-locked case, header points into owner's stack
1126 return current->is_lock_owned((address)mark.locker());
1127 }
1128
1129 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1130 // fast-locking case, see if lock is in current's lock stack
1131 return current->lock_stack().contains(h_obj());
1132 }
1133
1134 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1135 ObjectMonitor* monitor = read_monitor(current, obj, mark);
1136 if (monitor != nullptr) {
1137 return monitor->is_entered(current) != 0;
1138 }
1139 // Racing with inflation/deflation, retry
1140 mark = obj->mark_acquire();
1141
1142 if (mark.is_fast_locked()) {
1143 // Some other thread fast_locked, current could not have held the lock
1144 return false;
1145 }
1146 }
1147
1148 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1149 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1150 // The first stage of async deflation does not affect any field
1151 // used by this comparison so the ObjectMonitor* is usable here.
1152 ObjectMonitor* monitor = read_monitor(mark);
1153 return monitor->is_entered(current) != 0;
1154 }
1155 // Unlocked case, header in place
1156 assert(mark.is_unlocked(), "sanity check");
1157 return false;
1158 }
1159
1160 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1161 oop obj = h_obj();
1162 markWord mark = read_stable_mark(obj);
1163
1164 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1165 // stack-locked so header points into owner's stack.
1166 // owning_thread_from_monitor_owner() may also return null here:
1167 return Threads::owning_thread_from_stacklock(t_list, (address) mark.locker());
1168 }
1169
1170 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1171 // fast-locked so get owner from the object.
1172 // owning_thread_from_object() may also return null here:
1173 return Threads::owning_thread_from_object(t_list, h_obj());
1174 }
1175
1176 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1177 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
1178 if (monitor != nullptr) {
1179 return Threads::owning_thread_from_monitor(t_list, monitor);
1180 }
1181 // Racing with inflation/deflation, retry
1182 mark = obj->mark_acquire();
1183
1184 if (mark.is_fast_locked()) {
1185 // Some other thread fast_locked
1186 return Threads::owning_thread_from_object(t_list, h_obj());
1187 }
1188 }
1189
1190 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1191 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1192 // The first stage of async deflation does not affect any field
1193 // used by this comparison so the ObjectMonitor* is usable here.
1194 ObjectMonitor* monitor = read_monitor(mark);
1195 assert(monitor != nullptr, "monitor should be non-null");
1196 // owning_thread_from_monitor() may also return null here:
1197 return Threads::owning_thread_from_monitor(t_list, monitor);
1198 }
1199
1200 // Unlocked case, header in place
1201 // Cannot have assertion since this object may have been
1202 // locked by another thread when reaching here.
1203 // assert(mark.is_unlocked(), "sanity check");
1204
1205 return nullptr;
1206 }
1207
1208 // Visitors ...
1209
1210 // Iterate over all ObjectMonitors.
1211 template <typename Function>
1212 void ObjectSynchronizer::monitors_iterate(Function function) {
1213 MonitorList::Iterator iter = _in_use_list.iterator();
1214 while (iter.has_next()) {
1215 ObjectMonitor* monitor = iter.next();
1216 function(monitor);
1217 }
1218 }
1219
1220 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1221 // returns true.
1222 template <typename OwnerFilter>
1223 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1224 monitors_iterate([&](ObjectMonitor* monitor) {
1225 // This function is only called at a safepoint or when the
1226 // target thread is suspended or when the target thread is
1227 // operating on itself. The current closures in use today are
1228 // only interested in an owned ObjectMonitor and ownership
1229 // cannot be dropped under the calling contexts so the
1230 // ObjectMonitor cannot be async deflated.
1231 if (monitor->has_owner() && filter(monitor)) {
1232 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1233
1234 closure->do_monitor(monitor);
1235 }
1236 });
1237 }
1238
1239 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1240 // ObjectMonitors where owner is set to a stack-lock address in thread.
1241 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1242 int64_t key = ObjectMonitor::owner_id_from(thread);
1243 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1244 return owned_monitors_iterate_filtered(closure, thread_filter);
1245 }
1246
1247 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
1248 int64_t key = ObjectMonitor::owner_id_from(vthread);
1249 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1250 return owned_monitors_iterate_filtered(closure, thread_filter);
1251 }
1252
1253 // Iterate ObjectMonitors owned by any thread.
1254 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1255 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
1256 return owned_monitors_iterate_filtered(closure, all_filter);
1257 }
1258
1259 static bool monitors_used_above_threshold(MonitorList* list) {
1260 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1261 return false;
1262 }
1263 size_t monitors_used = list->count();
1264 if (monitors_used == 0) { // empty list is easy
1265 return false;
1266 }
1267 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
1268 // Make sure that we use a ceiling value that is not lower than
1269 // previous, not lower than the recorded max used by the system, and
1270 // not lower than the current number of monitors in use (which can
1271 // race ahead of max). The result is guaranteed > 0.
1272 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
1273
1274 // Check if our monitor usage is above the threshold:
1275 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1276 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1277 // Deflate monitors if over the threshold percentage, unless no
1278 // progress on previous deflations.
1279 bool is_above_threshold = true;
1280
1281 // Check if it's time to adjust the in_use_list_ceiling up, due
1282 // to too many async deflation attempts without any progress.
1283 if (NoAsyncDeflationProgressMax != 0 &&
1284 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1285 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1286 size_t delta = (size_t)(ceiling * remainder) + 1;
1287 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
1288 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
1289 : ceiling + delta;
1290
1291 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1292 log_info(monitorinflation)("Too many deflations without progress; "
1293 "bumping in_use_list_ceiling from %zu"
1294 " to %zu", old_ceiling, new_ceiling);
1295 _no_progress_cnt = 0;
1296 ceiling = new_ceiling;
1297
1298 // Check if our monitor usage is still above the threshold:
1299 monitor_usage = (monitors_used * 100LL) / ceiling;
1300 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
1301 }
1302 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
1303 ", monitor_usage=%zu, threshold=%d",
1304 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1305 return is_above_threshold;
1306 }
1307
1308 return false;
1309 }
1310
1311 size_t ObjectSynchronizer::in_use_list_count() {
1312 return _in_use_list.count();
1313 }
1314
1315 size_t ObjectSynchronizer::in_use_list_max() {
1316 return _in_use_list.max();
1317 }
1318
1319 size_t ObjectSynchronizer::in_use_list_ceiling() {
1320 return _in_use_list_ceiling;
1321 }
1322
1323 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1324 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1325 }
1326
1327 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1328 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1329 }
1330
1331 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1332 _in_use_list_ceiling = new_value;
1333 }
1334
1335 bool ObjectSynchronizer::is_async_deflation_needed() {
1336 if (is_async_deflation_requested()) {
1337 // Async deflation request.
1338 log_info(monitorinflation)("Async deflation needed: explicit request");
1339 return true;
1340 }
1341
1342 jlong time_since_last = time_since_last_async_deflation_ms();
1343
1344 if (AsyncDeflationInterval > 0 &&
1345 time_since_last > AsyncDeflationInterval &&
1346 monitors_used_above_threshold(&_in_use_list)) {
1347 // It's been longer than our specified deflate interval and there
1348 // are too many monitors in use. We don't deflate more frequently
1349 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1350 // in order to not swamp the MonitorDeflationThread.
1351 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1352 return true;
1353 }
1354
1355 if (GuaranteedAsyncDeflationInterval > 0 &&
1356 time_since_last > GuaranteedAsyncDeflationInterval) {
1357 // It's been longer than our specified guaranteed deflate interval.
1358 // We need to clean up the used monitors even if the threshold is
1359 // not reached, to keep the memory utilization at bay when many threads
1360 // touched many monitors.
1361 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
1362 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1363 GuaranteedAsyncDeflationInterval, time_since_last);
1364
1365 // If this deflation has no progress, then it should not affect the no-progress
1366 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1367 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1368 // the generic code would bump the no-progress counter, and we compensate for that
1369 // by telling it to skip the update.
1370 //
1371 // If this deflation has progress, then it should let non-progress tracking
1372 // know about this, otherwise the threshold heuristics would kick in, potentially
1373 // experience no-progress due to aggressive cleanup by this deflation, and think
1374 // it is still in no-progress stride. In this "progress" case, the generic code would
1375 // zero the counter, and we allow it to happen.
1376 _no_progress_skip_increment = true;
1377
1378 return true;
1379 }
1380
1381 return false;
1382 }
1383
1384 void ObjectSynchronizer::request_deflate_idle_monitors() {
1385 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1386 set_is_async_deflation_requested(true);
1387 ml.notify_all();
1388 }
1389
1390 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1391 JavaThread* current = JavaThread::current();
1392 bool ret_code = false;
1393
1394 jlong last_time = last_async_deflation_time_ns();
1395
1396 request_deflate_idle_monitors();
1397
1398 const int N_CHECKS = 5;
1399 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1400 if (last_async_deflation_time_ns() > last_time) {
1401 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1402 ret_code = true;
1403 break;
1404 }
1405 {
1406 // JavaThread has to honor the blocking protocol.
1407 ThreadBlockInVM tbivm(current);
1408 os::naked_short_sleep(999); // sleep for almost 1 second
1409 }
1410 }
1411 if (!ret_code) {
1412 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1413 }
1414
1415 return ret_code;
1416 }
1417
1418 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1419 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1420 }
1421
1422 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1423 const oop obj,
1424 ObjectSynchronizer::InflateCause cause) {
1425 assert(event != nullptr, "invariant");
1426 const Klass* monitor_klass = obj->klass();
1427 if (ObjectMonitor::is_jfr_excluded(monitor_klass)) {
1428 return;
1429 }
1430 event->set_monitorClass(monitor_klass);
1431 event->set_address((uintptr_t)(void*)obj);
1432 event->set_cause((u1)cause);
1433 event->commit();
1434 }
1435
1436 // Fast path code shared by multiple functions
1437 void ObjectSynchronizer::inflate_helper(oop obj) {
1438 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1439 markWord mark = obj->mark_acquire();
1440 if (mark.has_monitor()) {
1441 ObjectMonitor* monitor = read_monitor(mark);
1442 markWord dmw = monitor->header();
1443 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1444 return;
1445 }
1446 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1447 }
1448
1449 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1450 assert(current == Thread::current(), "must be");
1451 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1452 return inflate_impl(current->is_Java_thread() ? JavaThread::cast(current) : nullptr, obj, cause);
1453 }
1454
1455 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1456 assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1457 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_for");
1458 return inflate_impl(thread, obj, cause);
1459 }
1460
1461 ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* locking_thread, oop object, const InflateCause cause) {
1462 // The JavaThread* locking_thread requires that the locking_thread == Thread::current() or
1463 // is suspended throughout the call by some other mechanism.
1464 // The thread might be nullptr when called from a non JavaThread. (As may still be
1465 // the case from FastHashCode). However it is only important for correctness that the
1466 // thread is set when called from ObjectSynchronizer::enter from the owning thread,
1467 // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
1468 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_impl");
1469 EventJavaMonitorInflate event;
1470
1471 for (;;) {
1472 const markWord mark = object->mark_acquire();
1473
1474 // The mark can be in one of the following states:
1475 // * inflated - If the ObjectMonitor owner is anonymous and the
1476 // locking_thread owns the object lock, then we
1477 // make the locking_thread the ObjectMonitor owner.
1478 // * stack-locked - Coerce it to inflated from stack-locked.
1479 // * INFLATING - Busy wait for conversion from stack-locked to
1480 // inflated.
1481 // * unlocked - Aggressively inflate the object.
1482
1483 // CASE: inflated
1484 if (mark.has_monitor()) {
1485 ObjectMonitor* inf = mark.monitor();
1486 markWord dmw = inf->header();
1487 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1488 if (inf->has_anonymous_owner() && locking_thread != nullptr) {
1489 assert(LockingMode == LM_LEGACY, "invariant");
1490 if (locking_thread->is_lock_owned((address)inf->stack_locker())) {
1491 inf->set_stack_locker(nullptr);
1492 inf->set_owner_from_anonymous(locking_thread);
1493 }
1494 }
1495 return inf;
1496 }
1497
1498 // CASE: inflation in progress - inflating over a stack-lock.
1499 // Some other thread is converting from stack-locked to inflated.
1500 // Only that thread can complete inflation -- other threads must wait.
1501 // The INFLATING value is transient.
1502 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1503 // We could always eliminate polling by parking the thread on some auxiliary list.
1504 if (mark == markWord::INFLATING()) {
1505 read_stable_mark(object);
1506 continue;
1507 }
1508
1509 // CASE: stack-locked
1510 // Could be stack-locked either by current or by some other thread.
1511 //
1512 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1513 // to install INFLATING into the mark word. We originally installed INFLATING,
1514 // allocated the ObjectMonitor, and then finally STed the address of the
1515 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1516 // the interval in which INFLATING appeared in the mark, thus increasing
1517 // the odds of inflation contention. If we lose the race to set INFLATING,
1518 // then we just delete the ObjectMonitor and loop around again.
1519 //
1520 LogStreamHandle(Trace, monitorinflation) lsh;
1521 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1522 ObjectMonitor* m = new ObjectMonitor(object);
1523 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1524 // We do this before the CAS in order to minimize the length of time
1525 // in which INFLATING appears in the mark.
1526
1527 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1528 if (cmp != mark) {
1529 delete m;
1530 continue; // Interference -- just retry
1531 }
1532
1533 // We've successfully installed INFLATING (0) into the mark-word.
1534 // This is the only case where 0 will appear in a mark-word.
1535 // Only the singular thread that successfully swings the mark-word
1536 // to 0 can perform (or more precisely, complete) inflation.
1537 //
1538 // Why do we CAS a 0 into the mark-word instead of just CASing the
1539 // mark-word from the stack-locked value directly to the new inflated state?
1540 // Consider what happens when a thread unlocks a stack-locked object.
1541 // It attempts to use CAS to swing the displaced header value from the
1542 // on-stack BasicLock back into the object header. Recall also that the
1543 // header value (hash code, etc) can reside in (a) the object header, or
1544 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1545 // header in an ObjectMonitor. The inflate() routine must copy the header
1546 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1547 // the while preserving the hashCode stability invariants. If the owner
1548 // decides to release the lock while the value is 0, the unlock will fail
1549 // and control will eventually pass from slow_exit() to inflate. The owner
1550 // will then spin, waiting for the 0 value to disappear. Put another way,
1551 // the 0 causes the owner to stall if the owner happens to try to
1552 // drop the lock (restoring the header from the BasicLock to the object)
1553 // while inflation is in-progress. This protocol avoids races that might
1554 // would otherwise permit hashCode values to change or "flicker" for an object.
1555 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1556 // 0 serves as a "BUSY" inflate-in-progress indicator.
1557
1558
1559 // fetch the displaced mark from the owner's stack.
1560 // The owner can't die or unwind past the lock while our INFLATING
1561 // object is in the mark. Furthermore the owner can't complete
1562 // an unlock on the object, either.
1563 markWord dmw = mark.displaced_mark_helper();
1564 // Catch if the object's header is not neutral (not locked and
1565 // not marked is what we care about here).
1566 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1567
1568 // Setup monitor fields to proper values -- prepare the monitor
1569 m->set_header(dmw);
1570
1571 // Note that a thread can inflate an object
1572 // that it has stack-locked -- as might happen in wait() -- directly
1573 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1574 if (locking_thread != nullptr && locking_thread->is_lock_owned((address)mark.locker())) {
1575 m->set_owner(locking_thread);
1576 } else {
1577 // Use ANONYMOUS_OWNER to indicate that the owner is the BasicLock on the stack,
1578 // and set the stack locker field in the monitor.
1579 m->set_stack_locker(mark.locker());
1580 m->set_anonymous_owner();
1581 }
1582 // TODO-FIXME: assert BasicLock->dhw != 0.
1583
1584 // Must preserve store ordering. The monitor state must
1585 // be stable at the time of publishing the monitor address.
1586 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1587 // Release semantics so that above set_object() is seen first.
1588 object->release_set_mark(markWord::encode(m));
1589
1590 // Once ObjectMonitor is configured and the object is associated
1591 // with the ObjectMonitor, it is safe to allow async deflation:
1592 _in_use_list.add(m);
1593
1594 if (log_is_enabled(Trace, monitorinflation)) {
1595 ResourceMark rm;
1596 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1597 INTPTR_FORMAT ", type='%s'", p2i(object),
1598 object->mark().value(), object->klass()->external_name());
1599 }
1600 if (event.should_commit()) {
1601 post_monitor_inflate_event(&event, object, cause);
1602 }
1603 return m;
1604 }
1605
1606 // CASE: unlocked
1607 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1608 // If we know we're inflating for entry it's better to inflate by swinging a
1609 // pre-locked ObjectMonitor pointer into the object header. A successful
1610 // CAS inflates the object *and* confers ownership to the inflating thread.
1611 // In the current implementation we use a 2-step mechanism where we CAS()
1612 // to inflate and then CAS() again to try to swing _owner from null to current.
1613 // An inflateTry() method that we could call from enter() would be useful.
1614
1615 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
1616 ObjectMonitor* m = new ObjectMonitor(object);
1617 // prepare m for installation - set monitor to initial state
1618 m->set_header(mark);
1619
1620 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1621 delete m;
1622 m = nullptr;
1623 continue;
1624 // interference - the markword changed - just retry.
1625 // The state-transitions are one-way, so there's no chance of
1626 // live-lock -- "Inflated" is an absorbing state.
1627 }
1628
1629 // Once the ObjectMonitor is configured and object is associated
1630 // with the ObjectMonitor, it is safe to allow async deflation:
1631 _in_use_list.add(m);
1632
1633 if (log_is_enabled(Trace, monitorinflation)) {
1634 ResourceMark rm;
1635 lsh.print_cr("inflate(unlocked): object=" INTPTR_FORMAT ", mark="
1636 INTPTR_FORMAT ", type='%s'", p2i(object),
1637 object->mark().value(), object->klass()->external_name());
1638 }
1639 if (event.should_commit()) {
1640 post_monitor_inflate_event(&event, object, cause);
1641 }
1642 return m;
1643 }
1644 }
1645
1646 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1647 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1648 //
1649 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1650 MonitorList::Iterator iter = _in_use_list.iterator();
1651 size_t deflated_count = 0;
1652 Thread* current = Thread::current();
1653
1654 while (iter.has_next()) {
1655 if (deflated_count >= (size_t)MonitorDeflationMax) {
1656 break;
1657 }
1658 ObjectMonitor* mid = iter.next();
1659 if (mid->deflate_monitor(current)) {
1660 deflated_count++;
1661 }
1662
1663 // Must check for a safepoint/handshake and honor it.
1664 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1665 }
1666
1667 return deflated_count;
1668 }
1669
1670 class HandshakeForDeflation : public HandshakeClosure {
1671 public:
1672 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1673
1674 void do_thread(Thread* thread) {
1675 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1676 INTPTR_FORMAT, p2i(thread));
1677 if (thread->is_Java_thread()) {
1678 // Clear OM cache
1679 JavaThread* jt = JavaThread::cast(thread);
1680 jt->om_clear_monitor_cache();
1681 }
1682 }
1683 };
1684
1685 class VM_RendezvousGCThreads : public VM_Operation {
1686 public:
1687 bool evaluate_at_safepoint() const override { return false; }
1688 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1689 void doit() override {
1690 Universe::heap()->safepoint_synchronize_begin();
1691 Universe::heap()->safepoint_synchronize_end();
1692 };
1693 };
1694
1695 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1696 ObjectMonitorDeflationSafepointer* safepointer) {
1697 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1698 size_t deleted_count = 0;
1699 for (ObjectMonitor* monitor: *delete_list) {
1700 delete monitor;
1701 deleted_count++;
1702 // A JavaThread must check for a safepoint/handshake and honor it.
1703 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1704 }
1705 return deleted_count;
1706 }
1707
1708 class ObjectMonitorDeflationLogging: public StackObj {
1709 LogStreamHandle(Debug, monitorinflation) _debug;
1710 LogStreamHandle(Info, monitorinflation) _info;
1711 LogStream* _stream;
1712 elapsedTimer _timer;
1713
1714 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1715 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1716 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1717
1718 public:
1719 ObjectMonitorDeflationLogging()
1720 : _debug(), _info(), _stream(nullptr) {
1721 if (_debug.is_enabled()) {
1722 _stream = &_debug;
1723 } else if (_info.is_enabled()) {
1724 _stream = &_info;
1725 }
1726 }
1727
1728 void begin() {
1729 if (_stream != nullptr) {
1730 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1731 ceiling(), count(), max());
1732 _timer.start();
1733 }
1734 }
1735
1736 void before_handshake(size_t unlinked_count) {
1737 if (_stream != nullptr) {
1738 _timer.stop();
1739 _stream->print_cr("before handshaking: unlinked_count=%zu"
1740 ", in_use_list stats: ceiling=%zu, count="
1741 "%zu, max=%zu",
1742 unlinked_count, ceiling(), count(), max());
1743 }
1744 }
1745
1746 void after_handshake() {
1747 if (_stream != nullptr) {
1748 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1749 "%zu, count=%zu, max=%zu",
1750 ceiling(), count(), max());
1751 _timer.start();
1752 }
1753 }
1754
1755 void end(size_t deflated_count, size_t unlinked_count) {
1756 if (_stream != nullptr) {
1757 _timer.stop();
1758 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1759 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1760 deflated_count, unlinked_count, _timer.seconds());
1761 }
1762 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1763 ceiling(), count(), max());
1764 }
1765 }
1766
1767 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1768 if (_stream != nullptr) {
1769 _timer.stop();
1770 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1771 "%zu, count=%zu, max=%zu",
1772 op_name, cnt_name, cnt, ceiling(), count(), max());
1773 }
1774 }
1775
1776 void after_block_for_safepoint(const char* op_name) {
1777 if (_stream != nullptr) {
1778 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1779 ", count=%zu, max=%zu", op_name,
1780 ceiling(), count(), max());
1781 _timer.start();
1782 }
1783 }
1784 };
1785
1786 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1787 if (!SafepointMechanism::should_process(_current)) {
1788 return;
1789 }
1790
1791 // A safepoint/handshake has started.
1792 _log->before_block_for_safepoint(op_name, count_name, counter);
1793
1794 {
1795 // Honor block request.
1796 ThreadBlockInVM tbivm(_current);
1797 }
1798
1799 _log->after_block_for_safepoint(op_name);
1800 }
1801
1802 // This function is called by the MonitorDeflationThread to deflate
1803 // ObjectMonitors.
1804 size_t ObjectSynchronizer::deflate_idle_monitors() {
1805 JavaThread* current = JavaThread::current();
1806 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1807
1808 // The async deflation request has been processed.
1809 _last_async_deflation_time_ns = os::javaTimeNanos();
1810 set_is_async_deflation_requested(false);
1811
1812 ObjectMonitorDeflationLogging log;
1813 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1814
1815 log.begin();
1816
1817 // Deflate some idle ObjectMonitors.
1818 size_t deflated_count = deflate_monitor_list(&safepointer);
1819
1820 // Unlink the deflated ObjectMonitors from the in-use list.
1821 size_t unlinked_count = 0;
1822 size_t deleted_count = 0;
1823 if (deflated_count > 0) {
1824 ResourceMark rm(current);
1825 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1826 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1827
1828 #ifdef ASSERT
1829 if (UseObjectMonitorTable) {
1830 for (ObjectMonitor* monitor : delete_list) {
1831 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1832 }
1833 }
1834 #endif
1835
1836 log.before_handshake(unlinked_count);
1837
1838 // A JavaThread needs to handshake in order to safely free the
1839 // ObjectMonitors that were deflated in this cycle.
1840 HandshakeForDeflation hfd_hc;
1841 Handshake::execute(&hfd_hc);
1842 // Also, we sync and desync GC threads around the handshake, so that they can
1843 // safely read the mark-word and look-through to the object-monitor, without
1844 // being afraid that the object-monitor is going away.
1845 VM_RendezvousGCThreads sync_gc;
1846 VMThread::execute(&sync_gc);
1847
1848 log.after_handshake();
1849
1850 // After the handshake, safely free the ObjectMonitors that were
1851 // deflated and unlinked in this cycle.
1852
1853 // Delete the unlinked ObjectMonitors.
1854 deleted_count = delete_monitors(&delete_list, &safepointer);
1855 assert(unlinked_count == deleted_count, "must be");
1856 }
1857
1858 log.end(deflated_count, unlinked_count);
1859
1860 GVars.stw_random = os::random();
1861
1862 if (deflated_count != 0) {
1863 _no_progress_cnt = 0;
1864 } else if (_no_progress_skip_increment) {
1865 _no_progress_skip_increment = false;
1866 } else {
1867 _no_progress_cnt++;
1868 }
1869
1870 return deflated_count;
1871 }
1872
1873 // Monitor cleanup on JavaThread::exit
1874
1875 // Iterate through monitor cache and attempt to release thread's monitors
1876 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1877 private:
1878 JavaThread* _thread;
1879
1880 public:
1881 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1882 void do_monitor(ObjectMonitor* mid) {
1883 intx rec = mid->complete_exit(_thread);
1884 _thread->dec_held_monitor_count(rec + 1);
1885 }
1886 };
1887
1888 // Release all inflated monitors owned by current thread. Lightweight monitors are
1889 // ignored. This is meant to be called during JNI thread detach which assumes
1890 // all remaining monitors are heavyweight. All exceptions are swallowed.
1891 // Scanning the extant monitor list can be time consuming.
1892 // A simple optimization is to add a per-thread flag that indicates a thread
1893 // called jni_monitorenter() during its lifetime.
1894 //
1895 // Instead of NoSafepointVerifier it might be cheaper to
1896 // use an idiom of the form:
1897 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1898 // <code that must not run at safepoint>
1899 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1900 // Since the tests are extremely cheap we could leave them enabled
1901 // for normal product builds.
1902
1903 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1904 assert(current == JavaThread::current(), "must be current Java thread");
1905 NoSafepointVerifier nsv;
1906 ReleaseJavaMonitorsClosure rjmc(current);
1907 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1908 assert(!current->has_pending_exception(), "Should not be possible");
1909 current->clear_pending_exception();
1910 assert(current->held_monitor_count() == 0, "Should not be possible");
1911 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1912 current->clear_jni_monitor_count();
1913 }
1914
1915 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1916 switch (cause) {
1917 case inflate_cause_vm_internal: return "VM Internal";
1918 case inflate_cause_monitor_enter: return "Monitor Enter";
1919 case inflate_cause_wait: return "Monitor Wait";
1920 case inflate_cause_notify: return "Monitor Notify";
1921 case inflate_cause_hash_code: return "Monitor Hash Code";
1922 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1923 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1924 default:
1925 ShouldNotReachHere();
1926 }
1927 return "Unknown";
1928 }
1929
1930 //------------------------------------------------------------------------------
1931 // Debugging code
1932
1933 u_char* ObjectSynchronizer::get_gvars_addr() {
1934 return (u_char*)&GVars;
1935 }
1936
1937 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1938 return (u_char*)&GVars.hc_sequence;
1939 }
1940
1941 size_t ObjectSynchronizer::get_gvars_size() {
1942 return sizeof(SharedGlobals);
1943 }
1944
1945 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1946 return (u_char*)&GVars.stw_random;
1947 }
1948
1949 // Do the final audit and print of ObjectMonitor stats; must be done
1950 // by the VMThread at VM exit time.
1951 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1952 assert(Thread::current()->is_VM_thread(), "sanity check");
1953
1954 if (is_final_audit()) { // Only do the audit once.
1955 return;
1956 }
1957 set_is_final_audit();
1958 log_info(monitorinflation)("Starting the final audit.");
1959
1960 if (log_is_enabled(Info, monitorinflation)) {
1961 LogStreamHandle(Info, monitorinflation) ls;
1962 audit_and_print_stats(&ls, true /* on_exit */);
1963 }
1964 }
1965
1966 // This function can be called by the MonitorDeflationThread or it can be called when
1967 // we are trying to exit the VM. The list walker functions can run in parallel with
1968 // the other list operations.
1969 // Calls to this function can be added in various places as a debugging
1970 // aid.
1971 //
1972 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1973 int error_cnt = 0;
1974
1975 ls->print_cr("Checking in_use_list:");
1976 chk_in_use_list(ls, &error_cnt);
1977
1978 if (error_cnt == 0) {
1979 ls->print_cr("No errors found in in_use_list checks.");
1980 } else {
1981 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1982 }
1983
1984 // When exiting, only log the interesting entries at the Info level.
1985 // When called at intervals by the MonitorDeflationThread, log output
1986 // at the Trace level since there can be a lot of it.
1987 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1988 LogStreamHandle(Trace, monitorinflation) ls_tr;
1989 log_in_use_monitor_details(&ls_tr, true /* log_all */);
1990 } else if (on_exit) {
1991 log_in_use_monitor_details(ls, false /* log_all */);
1992 }
1993
1994 ls->flush();
1995
1996 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1997 }
1998
1999 // Check the in_use_list; log the results of the checks.
2000 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
2001 size_t l_in_use_count = _in_use_list.count();
2002 size_t l_in_use_max = _in_use_list.max();
2003 out->print_cr("count=%zu, max=%zu", l_in_use_count,
2004 l_in_use_max);
2005
2006 size_t ck_in_use_count = 0;
2007 MonitorList::Iterator iter = _in_use_list.iterator();
2008 while (iter.has_next()) {
2009 ObjectMonitor* mid = iter.next();
2010 chk_in_use_entry(mid, out, error_cnt_p);
2011 ck_in_use_count++;
2012 }
2013
2014 if (l_in_use_count == ck_in_use_count) {
2015 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
2016 l_in_use_count, ck_in_use_count);
2017 } else {
2018 out->print_cr("WARNING: in_use_count=%zu is not equal to "
2019 "ck_in_use_count=%zu", l_in_use_count,
2020 ck_in_use_count);
2021 }
2022
2023 size_t ck_in_use_max = _in_use_list.max();
2024 if (l_in_use_max == ck_in_use_max) {
2025 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
2026 l_in_use_max, ck_in_use_max);
2027 } else {
2028 out->print_cr("WARNING: in_use_max=%zu is not equal to "
2029 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
2030 }
2031 }
2032
2033 // Check an in-use monitor entry; log any errors.
2034 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2035 int* error_cnt_p) {
2036 if (n->owner_is_DEFLATER_MARKER()) {
2037 // This could happen when monitor deflation blocks for a safepoint.
2038 return;
2039 }
2040
2041
2042 if (n->metadata() == 0) {
2043 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2044 "have non-null _metadata (header/hash) field.", p2i(n));
2045 *error_cnt_p = *error_cnt_p + 1;
2046 }
2047
2048 const oop obj = n->object_peek();
2049 if (obj == nullptr) {
2050 return;
2051 }
2052
2053 const markWord mark = obj->mark();
2054 if (!mark.has_monitor()) {
2055 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2056 "object does not think it has a monitor: obj="
2057 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2058 p2i(obj), mark.value());
2059 *error_cnt_p = *error_cnt_p + 1;
2060 return;
2061 }
2062
2063 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
2064 if (n != obj_mon) {
2065 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2066 "object does not refer to the same monitor: obj="
2067 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2068 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2069 *error_cnt_p = *error_cnt_p + 1;
2070 }
2071 }
2072
2073 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2074 // flags indicate why the entry is in-use, 'object' and 'object type'
2075 // indicate the associated object and its type.
2076 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2077 if (_in_use_list.count() > 0) {
2078 stringStream ss;
2079 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
2080 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2081 out->print_cr("%18s %s %18s %18s",
2082 "monitor", "BHL", "object", "object type");
2083 out->print_cr("================== === ================== ==================");
2084
2085 auto is_interesting = [&](ObjectMonitor* monitor) {
2086 return log_all || monitor->has_owner() || monitor->is_busy();
2087 };
2088
2089 monitors_iterate([&](ObjectMonitor* monitor) {
2090 if (is_interesting(monitor)) {
2091 const oop obj = monitor->object_peek();
2092 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
2093 ResourceMark rm;
2094 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
2095 monitor->is_busy(), hash != 0, monitor->has_owner(),
2096 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2097 if (monitor->is_busy()) {
2098 out->print(" (%s)", monitor->is_busy_to_string(&ss));
2099 ss.reset();
2100 }
2101 out->cr();
2102 }
2103 });
2104 }
2105
2106 out->flush();
2107 }