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.inline.hpp"
48 #include "runtime/os.inline.hpp"
49 #include "runtime/osThread.hpp"
50 #include "runtime/safepointMechanism.inline.hpp"
51 #include "runtime/safepointVerifiers.hpp"
52 #include "runtime/sharedRuntime.hpp"
53 #include "runtime/stubRoutines.hpp"
54 #include "runtime/synchronizer.inline.hpp"
55 #include "runtime/threads.hpp"
56 #include "runtime/timer.hpp"
57 #include "runtime/trimNativeHeap.hpp"
58 #include "runtime/vframe.hpp"
59 #include "runtime/vmThread.hpp"
60 #include "utilities/align.hpp"
61 #include "utilities/dtrace.hpp"
62 #include "utilities/events.hpp"
63 #include "utilities/globalCounter.inline.hpp"
64 #include "utilities/globalDefinitions.hpp"
65 #include "utilities/linkedlist.hpp"
66 #include "utilities/preserveException.hpp"
67
68 class ObjectMonitorDeflationLogging;
69
70 void MonitorList::add(ObjectMonitor* m) {
71 ObjectMonitor* head;
72 do {
73 head = Atomic::load(&_head);
74 m->set_next_om(head);
75 } while (Atomic::cmpxchg(&_head, head, m) != head);
76
77 size_t count = Atomic::add(&_count, 1u, memory_order_relaxed);
78 size_t old_max;
79 do {
80 old_max = Atomic::load(&_max);
81 if (count <= old_max) {
82 break;
83 }
84 } while (Atomic::cmpxchg(&_max, old_max, count, memory_order_relaxed) != old_max);
85 }
86
87 size_t MonitorList::count() const {
88 return Atomic::load(&_count);
89 }
90
91 size_t MonitorList::max() const {
92 return Atomic::load(&_max);
93 }
94
95 class ObjectMonitorDeflationSafepointer : public StackObj {
96 JavaThread* const _current;
97 ObjectMonitorDeflationLogging* const _log;
98
99 public:
100 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
101 : _current(current), _log(log) {}
102
103 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
104 };
105
106 // Walk the in-use list and unlink deflated ObjectMonitors.
107 // Returns the number of unlinked ObjectMonitors.
108 size_t MonitorList::unlink_deflated(size_t deflated_count,
109 GrowableArray<ObjectMonitor*>* unlinked_list,
110 ObjectMonitorDeflationSafepointer* safepointer) {
111 size_t unlinked_count = 0;
112 ObjectMonitor* prev = nullptr;
113 ObjectMonitor* m = Atomic::load_acquire(&_head);
114
115 while (m != nullptr) {
116 if (m->is_being_async_deflated()) {
117 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
118 // modify the list once per batch. The batch starts at "m".
119 size_t unlinked_batch = 0;
120 ObjectMonitor* next = m;
121 // Look for at most MonitorUnlinkBatch monitors, or the number of
122 // deflated and not unlinked monitors, whatever comes first.
123 assert(deflated_count >= unlinked_count, "Sanity: underflow");
124 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
125 do {
126 ObjectMonitor* next_next = next->next_om();
127 unlinked_batch++;
128 unlinked_list->append(next);
129 next = next_next;
130 if (unlinked_batch >= unlinked_batch_limit) {
131 // Reached the max batch, so bail out of the gathering loop.
132 break;
133 }
134 if (prev == nullptr && Atomic::load(&_head) != m) {
135 // Current batch used to be at head, but it is not at head anymore.
136 // Bail out and figure out where we currently are. This avoids long
137 // walks searching for new prev during unlink under heavy list inserts.
138 break;
139 }
140 } while (next != nullptr && next->is_being_async_deflated());
141
142 // Unlink the found batch.
143 if (prev == nullptr) {
144 // The current batch is the first batch, so there is a chance that it starts at head.
145 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
146 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, m, next);
147 if (prev_head != m) {
148 // Something must have updated the head. Figure out the actual prev for this batch.
149 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
150 prev = n;
151 }
152 assert(prev != nullptr, "Should have found the prev for the current batch");
153 prev->set_next_om(next);
154 }
155 } else {
156 // The current batch is preceded by another batch. This guarantees the current batch
157 // does not start at head. Unlink the entire current batch without updating the head.
158 assert(Atomic::load(&_head) != m, "Sanity");
159 prev->set_next_om(next);
160 }
161
162 unlinked_count += unlinked_batch;
163 if (unlinked_count >= deflated_count) {
164 // Reached the max so bail out of the searching loop.
165 // There should be no more deflated monitors left.
166 break;
167 }
168 m = next;
169 } else {
170 prev = m;
171 m = m->next_om();
172 }
173
174 // Must check for a safepoint/handshake and honor it.
175 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
176 }
177
178 #ifdef ASSERT
179 // Invariant: the code above should unlink all deflated monitors.
180 // The code that runs after this unlinking does not expect deflated monitors.
181 // Notably, attempting to deflate the already deflated monitor would break.
182 {
183 ObjectMonitor* m = Atomic::load_acquire(&_head);
184 while (m != nullptr) {
185 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
186 m = m->next_om();
187 }
188 }
189 #endif
190
191 Atomic::sub(&_count, unlinked_count);
192 return unlinked_count;
193 }
194
195 MonitorList::Iterator MonitorList::iterator() const {
196 return Iterator(Atomic::load_acquire(&_head));
197 }
198
199 ObjectMonitor* MonitorList::Iterator::next() {
200 ObjectMonitor* current = _current;
201 _current = current->next_om();
202 return current;
203 }
204
205 // The "core" versions of monitor enter and exit reside in this file.
206 // The interpreter and compilers contain specialized transliterated
207 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
208 // fast_lock(...) for instance. If you make changes here, make sure to modify the
209 // interpreter, and both C1 and C2 fast-path inline locking code emission.
210 //
211 // -----------------------------------------------------------------------------
212
213 #ifdef DTRACE_ENABLED
214
215 // Only bother with this argument setup if dtrace is available
216 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
217
218 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
219 char* bytes = nullptr; \
220 int len = 0; \
221 jlong jtid = SharedRuntime::get_java_tid(thread); \
222 Symbol* klassname = obj->klass()->name(); \
223 if (klassname != nullptr) { \
224 bytes = (char*)klassname->bytes(); \
225 len = klassname->utf8_length(); \
226 }
227
228 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
229 { \
230 if (DTraceMonitorProbes) { \
231 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
232 HOTSPOT_MONITOR_WAIT(jtid, \
233 (uintptr_t)(monitor), bytes, len, (millis)); \
234 } \
235 }
236
237 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
238 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
239 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
240
241 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
242 { \
243 if (DTraceMonitorProbes) { \
244 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
245 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
246 (uintptr_t)(monitor), bytes, len); \
247 } \
248 }
249
250 #else // ndef DTRACE_ENABLED
251
252 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
253 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
254
255 #endif // ndef DTRACE_ENABLED
256
257 // This exists only as a workaround of dtrace bug 6254741
258 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
259 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
260 return 0;
261 }
262
263 static constexpr size_t inflation_lock_count() {
264 return 256;
265 }
266
267 // Static storage for an array of PlatformMutex.
268 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
269
270 static inline PlatformMutex* inflation_lock(size_t index) {
271 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
272 }
273
274 void ObjectSynchronizer::initialize() {
275 for (size_t i = 0; i < inflation_lock_count(); i++) {
276 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
277 }
278 // Start the ceiling with the estimate for one thread.
279 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
280
281 // Start the timer for deflations, so it does not trigger immediately.
282 _last_async_deflation_time_ns = os::javaTimeNanos();
283
284 if (LockingMode == LM_LIGHTWEIGHT) {
285 LightweightSynchronizer::initialize();
286 }
287 }
288
289 MonitorList ObjectSynchronizer::_in_use_list;
290 // monitors_used_above_threshold() policy is as follows:
291 //
292 // The ratio of the current _in_use_list count to the ceiling is used
293 // to determine if we are above MonitorUsedDeflationThreshold and need
294 // to do an async monitor deflation cycle. The ceiling is increased by
295 // AvgMonitorsPerThreadEstimate when a thread is added to the system
296 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
297 // removed from the system.
298 //
299 // Note: If the _in_use_list max exceeds the ceiling, then
300 // monitors_used_above_threshold() will use the in_use_list max instead
301 // of the thread count derived ceiling because we have used more
302 // ObjectMonitors than the estimated average.
303 //
304 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
305 // no-progress async monitor deflation cycles in a row, then the ceiling
306 // is adjusted upwards by monitors_used_above_threshold().
307 //
308 // Start the ceiling with the estimate for one thread in initialize()
309 // which is called after cmd line options are processed.
310 static size_t _in_use_list_ceiling = 0;
311 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
312 bool volatile ObjectSynchronizer::_is_final_audit = false;
313 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
314 static uintx _no_progress_cnt = 0;
315 static bool _no_progress_skip_increment = false;
316
317 // =====================> Quick functions
318
319 // The quick_* forms are special fast-path variants used to improve
320 // performance. In the simplest case, a "quick_*" implementation could
321 // simply return false, in which case the caller will perform the necessary
322 // state transitions and call the slow-path form.
323 // The fast-path is designed to handle frequently arising cases in an efficient
324 // manner and is just a degenerate "optimistic" variant of the slow-path.
325 // returns true -- to indicate the call was satisfied.
326 // returns false -- to indicate the call needs the services of the slow-path.
327 // A no-loitering ordinance is in effect for code in the quick_* family
328 // operators: safepoints or indefinite blocking (blocking that might span a
329 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
330 // entry.
331 //
332 // Consider: An interesting optimization is to have the JIT recognize the
333 // following common idiom:
334 // synchronized (someobj) { .... ; notify(); }
335 // That is, we find a notify() or notifyAll() call that immediately precedes
336 // the monitorexit operation. In that case the JIT could fuse the operations
337 // into a single notifyAndExit() runtime primitive.
338
339 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
340 assert(current->thread_state() == _thread_in_Java, "invariant");
341 NoSafepointVerifier nsv;
342 if (obj == nullptr) return false; // slow-path for invalid obj
343 const markWord mark = obj->mark();
344
345 if (LockingMode == LM_LIGHTWEIGHT) {
346 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
347 // Degenerate notify
348 // fast-locked by caller so by definition the implied waitset is empty.
349 return true;
350 }
351 } else if (LockingMode == LM_LEGACY) {
352 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
353 // Degenerate notify
354 // stack-locked by caller so by definition the implied waitset is empty.
355 return true;
356 }
357 }
358
359 if (mark.has_monitor()) {
360 ObjectMonitor* const mon = read_monitor(current, obj, mark);
361 if (LockingMode == LM_LIGHTWEIGHT && mon == nullptr) {
362 // Racing with inflation/deflation go slow path
363 return false;
364 }
365 assert(mon->object() == oop(obj), "invariant");
366 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
367
368 if (mon->first_waiter() != nullptr) {
369 // We have one or more waiters. Since this is an inflated monitor
370 // that we own, we quickly notify them here and now, avoiding the slow-path.
371 if (all) {
372 mon->quick_notifyAll(current);
373 } else {
374 mon->quick_notify(current);
375 }
376 }
377 return true;
378 }
379
380 // other IMS exception states take the slow-path
381 return false;
382 }
383
384 static bool useHeavyMonitors() {
385 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
386 return LockingMode == LM_MONITOR;
387 #else
388 return false;
389 #endif
390 }
391
392 // The LockNode emitted directly at the synchronization site would have
393 // been too big if it were to have included support for the cases of inflated
394 // recursive enter and exit, so they go here instead.
395 // Note that we can't safely call AsyncPrintJavaStack() from within
396 // quick_enter() as our thread state remains _in_Java.
397
398 bool ObjectSynchronizer::quick_enter_legacy(oop obj, BasicLock* lock, JavaThread* current) {
399 assert(current->thread_state() == _thread_in_Java, "invariant");
400
401 if (useHeavyMonitors()) {
402 return false; // Slow path
403 }
404
405 assert(LockingMode == LM_LEGACY, "legacy mode below");
406
407 const markWord mark = obj->mark();
408
409 if (mark.has_monitor()) {
410
411 ObjectMonitor* const m = read_monitor(mark);
412 // An async deflation or GC can race us before we manage to make
413 // the ObjectMonitor busy by setting the owner below. If we detect
414 // that race we just bail out to the slow-path here.
415 if (m->object_peek() == nullptr) {
416 return false;
417 }
418
419 // Lock contention and Transactional Lock Elision (TLE) diagnostics
420 // and observability
421 // Case: light contention possibly amenable to TLE
422 // Case: TLE inimical operations such as nested/recursive synchronization
423
424 if (m->has_owner(current)) {
425 m->increment_recursions(current);
426 current->inc_held_monitor_count();
427 return true;
428 }
429
430 // This Java Monitor is inflated so obj's header will never be
431 // displaced to this thread's BasicLock. Make the displaced header
432 // non-null so this BasicLock is not seen as recursive nor as
433 // being locked. We do this unconditionally so that this thread's
434 // BasicLock cannot be mis-interpreted by any stack walkers. For
435 // performance reasons, stack walkers generally first check for
436 // stack-locking in the object's header, the second check is for
437 // recursive stack-locking in the displaced header in the BasicLock,
438 // and last are the inflated Java Monitor (ObjectMonitor) checks.
439 lock->set_displaced_header(markWord::unused_mark());
440
441 if (!m->has_owner() && m->try_set_owner(current)) {
442 assert(m->recursions() == 0, "invariant");
443 current->inc_held_monitor_count();
444 return true;
445 }
446 }
447
448 // Note that we could inflate in quick_enter.
449 // This is likely a useful optimization
450 // Critically, in quick_enter() we must not:
451 // -- block indefinitely, or
452 // -- reach a safepoint
453
454 return false; // revert to slow-path
455 }
456
457 // Handle notifications when synchronizing on value based classes
458 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
459 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
460 frame last_frame = locking_thread->last_frame();
461 bool bcp_was_adjusted = false;
462 // Don't decrement bcp if it points to the frame's first instruction. This happens when
463 // handle_sync_on_value_based_class() is called because of a synchronized method. There
464 // is no actual monitorenter instruction in the byte code in this case.
465 if (last_frame.is_interpreted_frame() &&
466 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
467 // adjust bcp to point back to monitorenter so that we print the correct line numbers
468 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
469 bcp_was_adjusted = true;
470 }
471
472 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
473 ResourceMark rm;
474 stringStream ss;
475 locking_thread->print_active_stack_on(&ss);
476 char* base = (char*)strstr(ss.base(), "at");
477 char* newline = (char*)strchr(ss.base(), '\n');
478 if (newline != nullptr) {
479 *newline = '\0';
480 }
481 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
482 } else {
483 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
484 ResourceMark rm;
485 Log(valuebasedclasses) vblog;
486
487 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
488 if (locking_thread->has_last_Java_frame()) {
489 LogStream info_stream(vblog.info());
490 locking_thread->print_active_stack_on(&info_stream);
491 } else {
492 vblog.info("Cannot find the last Java frame");
493 }
494
495 EventSyncOnValueBasedClass event;
496 if (event.should_commit()) {
497 event.set_valueBasedClass(obj->klass());
498 event.commit();
499 }
500 }
501
502 if (bcp_was_adjusted) {
503 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
504 }
505 }
506
507 // -----------------------------------------------------------------------------
508 // Monitor Enter/Exit
509
510 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
511 // When called with locking_thread != Thread::current() some mechanism must synchronize
512 // the locking_thread with respect to the current thread. Currently only used when
513 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
514 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
515
516 if (LockingMode == LM_LIGHTWEIGHT) {
517 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
518 }
519
520 if (!enter_fast_impl(obj, lock, locking_thread)) {
521 // Inflated ObjectMonitor::enter_for is required
522
523 // An async deflation can race after the inflate_for() call and before
524 // enter_for() can make the ObjectMonitor busy. enter_for() returns false
525 // if we have lost the race to async deflation and we simply try again.
526 while (true) {
527 ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
528 if (monitor->enter_for(locking_thread)) {
529 return;
530 }
531 assert(monitor->is_being_async_deflated(), "must be");
532 }
533 }
534 }
535
536 void ObjectSynchronizer::enter_legacy(Handle obj, BasicLock* lock, JavaThread* current) {
537 if (!enter_fast_impl(obj, lock, current)) {
538 // Inflated ObjectMonitor::enter is required
539
540 // An async deflation can race after the inflate() call and before
541 // enter() can make the ObjectMonitor busy. enter() returns false if
542 // we have lost the race to async deflation and we simply try again.
543 while (true) {
544 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
545 if (monitor->enter(current)) {
546 return;
547 }
548 }
549 }
550 }
551
552 // The interpreter and compiler assembly code tries to lock using the fast path
553 // of this algorithm. Make sure to update that code if the following function is
554 // changed. The implementation is extremely sensitive to race condition. Be careful.
555 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
556 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
557
558 if (obj->klass()->is_value_based()) {
559 handle_sync_on_value_based_class(obj, locking_thread);
560 }
561
562 locking_thread->inc_held_monitor_count();
563
564 if (!useHeavyMonitors()) {
565 if (LockingMode == LM_LEGACY) {
566 markWord mark = obj->mark();
567 if (mark.is_unlocked()) {
568 // Anticipate successful CAS -- the ST of the displaced mark must
569 // be visible <= the ST performed by the CAS.
570 lock->set_displaced_header(mark);
571 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
572 return true;
573 }
574 } else if (mark.has_locker() &&
575 locking_thread->is_lock_owned((address) mark.locker())) {
576 assert(lock != mark.locker(), "must not re-lock the same lock");
577 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
578 lock->set_displaced_header(markWord::from_pointer(nullptr));
579 return true;
580 }
581
582 // The object header will never be displaced to this lock,
583 // so it does not matter what the value is, except that it
584 // must be non-zero to avoid looking like a re-entrant lock,
585 // and must not look locked either.
586 lock->set_displaced_header(markWord::unused_mark());
587
588 // Failed to fast lock.
589 return false;
590 }
591 } else if (VerifyHeavyMonitors) {
592 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
593 }
594
595 return false;
596 }
597
598 void ObjectSynchronizer::exit_legacy(oop object, BasicLock* lock, JavaThread* current) {
599 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
600
601 if (!useHeavyMonitors()) {
602 markWord mark = object->mark();
603 if (LockingMode == LM_LEGACY) {
604 markWord dhw = lock->displaced_header();
605 if (dhw.value() == 0) {
606 // If the displaced header is null, then this exit matches up with
607 // a recursive enter. No real work to do here except for diagnostics.
608 #ifndef PRODUCT
609 if (mark != markWord::INFLATING()) {
610 // Only do diagnostics if we are not racing an inflation. Simply
611 // exiting a recursive enter of a Java Monitor that is being
612 // inflated is safe; see the has_monitor() comment below.
613 assert(!mark.is_unlocked(), "invariant");
614 assert(!mark.has_locker() ||
615 current->is_lock_owned((address)mark.locker()), "invariant");
616 if (mark.has_monitor()) {
617 // The BasicLock's displaced_header is marked as a recursive
618 // enter and we have an inflated Java Monitor (ObjectMonitor).
619 // This is a special case where the Java Monitor was inflated
620 // after this thread entered the stack-lock recursively. When a
621 // Java Monitor is inflated, we cannot safely walk the Java
622 // Monitor owner's stack and update the BasicLocks because a
623 // Java Monitor can be asynchronously inflated by a thread that
624 // does not own the Java Monitor.
625 ObjectMonitor* m = read_monitor(mark);
626 assert(m->object()->mark() == mark, "invariant");
627 assert(m->is_entered(current), "invariant");
628 }
629 }
630 #endif
631 return;
632 }
633
634 if (mark == markWord::from_pointer(lock)) {
635 // If the object is stack-locked by the current thread, try to
636 // swing the displaced header from the BasicLock back to the mark.
637 assert(dhw.is_neutral(), "invariant");
638 if (object->cas_set_mark(dhw, mark) == mark) {
639 return;
640 }
641 }
642 }
643 } else if (VerifyHeavyMonitors) {
644 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
645 }
646
647 // We have to take the slow-path of possible inflation and then exit.
648 // The ObjectMonitor* can't be async deflated until ownership is
649 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
650 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
651 assert(!monitor->has_anonymous_owner(), "must not be");
652 monitor->exit(current);
653 }
654
655 // -----------------------------------------------------------------------------
656 // JNI locks on java objects
657 // NOTE: must use heavy weight monitor to handle jni monitor enter
658 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
659 // Top native frames in the stack will not be seen if we attempt
660 // preemption, since we start walking from the last Java anchor.
661 NoPreemptMark npm(current);
662
663 if (obj->klass()->is_value_based()) {
664 handle_sync_on_value_based_class(obj, current);
665 }
666
667 // the current locking is from JNI instead of Java code
668 current->set_current_pending_monitor_is_from_java(false);
669 // An async deflation can race after the inflate() call and before
670 // enter() can make the ObjectMonitor busy. enter() returns false if
671 // we have lost the race to async deflation and we simply try again.
672 while (true) {
673 ObjectMonitor* monitor;
674 bool entered;
675 if (LockingMode == LM_LIGHTWEIGHT) {
676 BasicLock lock;
677 entered = LightweightSynchronizer::inflate_and_enter(obj(), &lock, inflate_cause_jni_enter, current, current) != nullptr;
678 } else {
679 monitor = inflate(current, obj(), inflate_cause_jni_enter);
680 entered = monitor->enter(current);
681 }
682
683 if (entered) {
684 current->inc_held_monitor_count(1, true);
685 break;
686 }
687 }
688 current->set_current_pending_monitor_is_from_java(true);
689 }
690
691 // NOTE: must use heavy weight monitor to handle jni monitor exit
692 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
693 JavaThread* current = THREAD;
694
695 ObjectMonitor* monitor;
696 if (LockingMode == LM_LIGHTWEIGHT) {
697 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
698 } else {
699 // The ObjectMonitor* can't be async deflated until ownership is
700 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
701 monitor = inflate(current, obj, inflate_cause_jni_exit);
702 }
703 // If this thread has locked the object, exit the monitor. We
704 // intentionally do not use CHECK on check_owner because we must exit the
705 // monitor even if an exception was already pending.
706 if (monitor->check_owner(THREAD)) {
707 monitor->exit(current);
708 current->dec_held_monitor_count(1, true);
709 }
710 }
711
712 // -----------------------------------------------------------------------------
713 // Internal VM locks on java objects
714 // standard constructor, allows locking failures
715 ObjectLocker::ObjectLocker(Handle obj, TRAPS) : _thread(THREAD), _obj(obj),
716 _npm(_thread, _thread->at_preemptable_init() /* ignore_mark */), _skip_exit(false) {
717 assert(!_thread->preempting(), "");
718
719 _thread->check_for_valid_safepoint_state();
720
721 if (_obj() != nullptr) {
722 ObjectSynchronizer::enter(_obj, &_lock, _thread);
723
724 if (_thread->preempting()) {
725 // If preemption was cancelled we acquired the monitor after freezing
726 // the frames. Redoing the vm call later in thaw will require us to
727 // release it since the call should look like the original one. We
728 // do it in ~ObjectLocker to reduce the window of time we hold the
729 // monitor since we can't do anything useful with it now, and would
730 // otherwise just force other vthreads to preempt in case they try
731 // to acquire this monitor.
732 _skip_exit = !_thread->preemption_cancelled();
733 _thread->set_pending_preempted_exception();
734 }
735 }
736 }
737
738 ObjectLocker::~ObjectLocker() {
739 if (_obj() != nullptr && !_skip_exit) {
740 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
741 }
742 }
743
744 void ObjectLocker::wait_uninterruptibly(TRAPS) {
745 ObjectSynchronizer::waitUninterruptibly(_obj, 0, _thread);
746 if (_thread->preempting()) {
747 _skip_exit = true;
748 _thread->set_pending_preempted_exception();
749 }
750 }
751
752 // -----------------------------------------------------------------------------
753 // Wait/Notify/NotifyAll
754 // NOTE: must use heavy weight monitor to handle wait()
755
756 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
757 JavaThread* current = THREAD;
758 if (millis < 0) {
759 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
760 }
761
762 ObjectMonitor* monitor;
763 if (LockingMode == LM_LIGHTWEIGHT) {
764 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
765 } else {
766 // The ObjectMonitor* can't be async deflated because the _waiters
767 // field is incremented before ownership is dropped and decremented
768 // after ownership is regained.
769 monitor = inflate(current, obj(), inflate_cause_wait);
770 }
771
772 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
773 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
774
775 // This dummy call is in place to get around dtrace bug 6254741. Once
776 // that's fixed we can uncomment the following line, remove the call
777 // and change this function back into a "void" func.
778 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
779 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
780 return ret_code;
781 }
782
783 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
784 assert(millis >= 0, "timeout value is negative");
785
786 ObjectMonitor* monitor;
787 if (LockingMode == LM_LIGHTWEIGHT) {
788 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
789 } else {
790 monitor = inflate(THREAD, obj(), inflate_cause_wait);
791 }
792 monitor->wait(millis, false, THREAD);
793 }
794
795
796 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
797 JavaThread* current = THREAD;
798
799 markWord mark = obj->mark();
800 if (LockingMode == LM_LIGHTWEIGHT) {
801 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
802 // Not inflated so there can't be any waiters to notify.
803 return;
804 }
805 } else if (LockingMode == LM_LEGACY) {
806 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
807 // Not inflated so there can't be any waiters to notify.
808 return;
809 }
810 }
811
812 ObjectMonitor* monitor;
813 if (LockingMode == LM_LIGHTWEIGHT) {
814 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
815 } else {
816 // The ObjectMonitor* can't be async deflated until ownership is
817 // dropped by the calling thread.
818 monitor = inflate(current, obj(), inflate_cause_notify);
819 }
820 monitor->notify(CHECK);
821 }
822
823 // NOTE: see comment of notify()
824 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
825 JavaThread* current = THREAD;
826
827 markWord mark = obj->mark();
828 if (LockingMode == LM_LIGHTWEIGHT) {
829 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
830 // Not inflated so there can't be any waiters to notify.
831 return;
832 }
833 } else if (LockingMode == LM_LEGACY) {
834 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
835 // Not inflated so there can't be any waiters to notify.
836 return;
837 }
838 }
839
840 ObjectMonitor* monitor;
841 if (LockingMode == LM_LIGHTWEIGHT) {
842 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
843 } else {
844 // The ObjectMonitor* can't be async deflated until ownership is
845 // dropped by the calling thread.
846 monitor = inflate(current, obj(), inflate_cause_notify);
847 }
848 monitor->notifyAll(CHECK);
849 }
850
851 // -----------------------------------------------------------------------------
852 // Hash Code handling
853
854 struct SharedGlobals {
855 char _pad_prefix[OM_CACHE_LINE_SIZE];
856 // This is a highly shared mostly-read variable.
857 // To avoid false-sharing it needs to be the sole occupant of a cache line.
858 volatile int stw_random;
859 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
860 // Hot RW variable -- Sequester to avoid false-sharing
861 volatile int hc_sequence;
862 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
863 };
864
865 static SharedGlobals GVars;
866
867 static markWord read_stable_mark(oop obj) {
868 markWord mark = obj->mark_acquire();
869 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
870 // New lightweight locking does not use the markWord::INFLATING() protocol.
871 return mark; // normal fast-path return
872 }
873
874 int its = 0;
875 for (;;) {
876 markWord mark = obj->mark_acquire();
877 if (!mark.is_being_inflated()) {
878 return mark; // normal fast-path return
879 }
880
881 // The object is being inflated by some other thread.
882 // The caller of read_stable_mark() must wait for inflation to complete.
883 // Avoid live-lock.
884
885 ++its;
886 if (its > 10000 || !os::is_MP()) {
887 if (its & 1) {
888 os::naked_yield();
889 } else {
890 // Note that the following code attenuates the livelock problem but is not
891 // a complete remedy. A more complete solution would require that the inflating
892 // thread hold the associated inflation lock. The following code simply restricts
893 // the number of spinners to at most one. We'll have N-2 threads blocked
894 // on the inflationlock, 1 thread holding the inflation lock and using
895 // a yield/park strategy, and 1 thread in the midst of inflation.
896 // A more refined approach would be to change the encoding of INFLATING
897 // to allow encapsulation of a native thread pointer. Threads waiting for
898 // inflation to complete would use CAS to push themselves onto a singly linked
899 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
900 // and calling park(). When inflation was complete the thread that accomplished inflation
901 // would detach the list and set the markword to inflated with a single CAS and
902 // then for each thread on the list, set the flag and unpark() the thread.
903
904 // Index into the lock array based on the current object address.
905 static_assert(is_power_of_2(inflation_lock_count()), "must be");
906 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
907 int YieldThenBlock = 0;
908 assert(ix < inflation_lock_count(), "invariant");
909 inflation_lock(ix)->lock();
910 while (obj->mark_acquire() == markWord::INFLATING()) {
911 // Beware: naked_yield() is advisory and has almost no effect on some platforms
912 // so we periodically call current->_ParkEvent->park(1).
913 // We use a mixed spin/yield/block mechanism.
914 if ((YieldThenBlock++) >= 16) {
915 Thread::current()->_ParkEvent->park(1);
916 } else {
917 os::naked_yield();
918 }
919 }
920 inflation_lock(ix)->unlock();
921 }
922 } else {
923 SpinPause(); // SMP-polite spinning
924 }
925 }
926 }
927
928 // hashCode() generation :
929 //
930 // Possibilities:
931 // * MD5Digest of {obj,stw_random}
932 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
933 // * A DES- or AES-style SBox[] mechanism
934 // * One of the Phi-based schemes, such as:
935 // 2654435761 = 2^32 * Phi (golden ratio)
936 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
937 // * A variation of Marsaglia's shift-xor RNG scheme.
938 // * (obj ^ stw_random) is appealing, but can result
939 // in undesirable regularity in the hashCode values of adjacent objects
940 // (objects allocated back-to-back, in particular). This could potentially
941 // result in hashtable collisions and reduced hashtable efficiency.
942 // There are simple ways to "diffuse" the middle address bits over the
943 // generated hashCode values:
944
945 static intptr_t get_next_hash(Thread* current, oop obj) {
946 intptr_t value = 0;
947 if (hashCode == 0) {
948 // This form uses global Park-Miller RNG.
949 // On MP system we'll have lots of RW access to a global, so the
950 // mechanism induces lots of coherency traffic.
951 value = os::random();
952 } else if (hashCode == 1) {
953 // This variation has the property of being stable (idempotent)
954 // between STW operations. This can be useful in some of the 1-0
955 // synchronization schemes.
956 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
957 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
958 } else if (hashCode == 2) {
959 value = 1; // for sensitivity testing
960 } else if (hashCode == 3) {
961 value = ++GVars.hc_sequence;
962 } else if (hashCode == 4) {
963 value = cast_from_oop<intptr_t>(obj);
964 } else {
965 // Marsaglia's xor-shift scheme with thread-specific state
966 // This is probably the best overall implementation -- we'll
967 // likely make this the default in future releases.
968 unsigned t = current->_hashStateX;
969 t ^= (t << 11);
970 current->_hashStateX = current->_hashStateY;
971 current->_hashStateY = current->_hashStateZ;
972 current->_hashStateZ = current->_hashStateW;
973 unsigned v = current->_hashStateW;
974 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
975 current->_hashStateW = v;
976 value = v;
977 }
978
979 value &= markWord::hash_mask;
980 if (value == 0) value = 0xBAD;
981 assert(value != markWord::no_hash, "invariant");
982 return value;
983 }
984
985 static intptr_t install_hash_code(Thread* current, oop obj) {
986 assert(UseObjectMonitorTable && LockingMode == LM_LIGHTWEIGHT, "must be");
987
988 markWord mark = obj->mark_acquire();
989 for (;;) {
990 intptr_t hash = mark.hash();
991 if (hash != 0) {
992 return hash;
993 }
994
995 hash = get_next_hash(current, obj);
996 const markWord old_mark = mark;
997 const markWord new_mark = old_mark.copy_set_hash(hash);
998
999 mark = obj->cas_set_mark(new_mark, old_mark);
1000 if (old_mark == mark) {
1001 return hash;
1002 }
1003 }
1004 }
1005
1006 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
1007 if (UseObjectMonitorTable) {
1008 // Since the monitor isn't in the object header, the hash can simply be
1009 // installed in the object header.
1010 return install_hash_code(current, obj);
1011 }
1012
1013 while (true) {
1014 ObjectMonitor* monitor = nullptr;
1015 markWord temp, test;
1016 intptr_t hash;
1017 markWord mark = read_stable_mark(obj);
1018 if (VerifyHeavyMonitors) {
1019 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
1020 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1021 }
1022 if (mark.is_unlocked() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1023 hash = mark.hash();
1024 if (hash != 0) { // if it has a hash, just return it
1025 return hash;
1026 }
1027 hash = get_next_hash(current, obj); // get a new hash
1028 temp = mark.copy_set_hash(hash); // merge the hash into header
1029 // try to install the hash
1030 test = obj->cas_set_mark(temp, mark);
1031 if (test == mark) { // if the hash was installed, return it
1032 return hash;
1033 }
1034 if (LockingMode == LM_LIGHTWEIGHT) {
1035 // CAS failed, retry
1036 continue;
1037 }
1038 // Failed to install the hash. It could be that another thread
1039 // installed the hash just before our attempt or inflation has
1040 // occurred or... so we fall thru to inflate the monitor for
1041 // stability and then install the hash.
1042 } else if (mark.has_monitor()) {
1043 monitor = mark.monitor();
1044 temp = monitor->header();
1045 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1046 hash = temp.hash();
1047 if (hash != 0) {
1048 // It has a hash.
1049
1050 // Separate load of dmw/header above from the loads in
1051 // is_being_async_deflated().
1052
1053 // dmw/header and _contentions may get written by different threads.
1054 // Make sure to observe them in the same order when having several observers.
1055 OrderAccess::loadload_for_IRIW();
1056
1057 if (monitor->is_being_async_deflated()) {
1058 // But we can't safely use the hash if we detect that async
1059 // deflation has occurred. So we attempt to restore the
1060 // header/dmw to the object's header so that we only retry
1061 // once if the deflater thread happens to be slow.
1062 monitor->install_displaced_markword_in_object(obj);
1063 continue;
1064 }
1065 return hash;
1066 }
1067 // Fall thru so we only have one place that installs the hash in
1068 // the ObjectMonitor.
1069 } else if (LockingMode == LM_LEGACY && mark.has_locker()
1070 && current->is_Java_thread()
1071 && JavaThread::cast(current)->is_lock_owned((address)mark.locker())) {
1072 // This is a stack-lock owned by the calling thread so fetch the
1073 // displaced markWord from the BasicLock on the stack.
1074 temp = mark.displaced_mark_helper();
1075 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1076 hash = temp.hash();
1077 if (hash != 0) { // if it has a hash, just return it
1078 return hash;
1079 }
1080 // WARNING:
1081 // The displaced header in the BasicLock on a thread's stack
1082 // is strictly immutable. It CANNOT be changed in ANY cases.
1083 // So we have to inflate the stack-lock into an ObjectMonitor
1084 // even if the current thread owns the lock. The BasicLock on
1085 // a thread's stack can be asynchronously read by other threads
1086 // during an inflate() call so any change to that stack memory
1087 // may not propagate to other threads correctly.
1088 }
1089
1090 // Inflate the monitor to set the hash.
1091
1092 // There's no need to inflate if the mark has already got a monitor.
1093 // NOTE: an async deflation can race after we get the monitor and
1094 // before we can update the ObjectMonitor's header with the hash
1095 // value below.
1096 monitor = mark.has_monitor() ? mark.monitor() : inflate(current, obj, inflate_cause_hash_code);
1097 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1098 mark = monitor->header();
1099 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1100 hash = mark.hash();
1101 if (hash == 0) { // if it does not have a hash
1102 hash = get_next_hash(current, obj); // get a new hash
1103 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1104 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1105 uintptr_t v = Atomic::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
1106 test = markWord(v);
1107 if (test != mark) {
1108 // The attempt to update the ObjectMonitor's header/dmw field
1109 // did not work. This can happen if another thread managed to
1110 // merge in the hash just before our cmpxchg().
1111 // If we add any new usages of the header/dmw field, this code
1112 // will need to be updated.
1113 hash = test.hash();
1114 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1115 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1116 }
1117 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
1118 // If we detect that async deflation has occurred, then we
1119 // attempt to restore the header/dmw to the object's header
1120 // so that we only retry once if the deflater thread happens
1121 // to be slow.
1122 monitor->install_displaced_markword_in_object(obj);
1123 continue;
1124 }
1125 }
1126 // We finally get the hash.
1127 return hash;
1128 }
1129 }
1130
1131 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1132 Handle h_obj) {
1133 assert(current == JavaThread::current(), "Can only be called on current thread");
1134 oop obj = h_obj();
1135
1136 markWord mark = read_stable_mark(obj);
1137
1138 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1139 // stack-locked case, header points into owner's stack
1140 return current->is_lock_owned((address)mark.locker());
1141 }
1142
1143 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1144 // fast-locking case, see if lock is in current's lock stack
1145 return current->lock_stack().contains(h_obj());
1146 }
1147
1148 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1149 ObjectMonitor* monitor = read_monitor(current, obj, mark);
1150 if (monitor != nullptr) {
1151 return monitor->is_entered(current) != 0;
1152 }
1153 // Racing with inflation/deflation, retry
1154 mark = obj->mark_acquire();
1155
1156 if (mark.is_fast_locked()) {
1157 // Some other thread fast_locked, current could not have held the lock
1158 return false;
1159 }
1160 }
1161
1162 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1163 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1164 // The first stage of async deflation does not affect any field
1165 // used by this comparison so the ObjectMonitor* is usable here.
1166 ObjectMonitor* monitor = read_monitor(mark);
1167 return monitor->is_entered(current) != 0;
1168 }
1169 // Unlocked case, header in place
1170 assert(mark.is_unlocked(), "sanity check");
1171 return false;
1172 }
1173
1174 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1175 oop obj = h_obj();
1176 markWord mark = read_stable_mark(obj);
1177
1178 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1179 // stack-locked so header points into owner's stack.
1180 // owning_thread_from_monitor_owner() may also return null here:
1181 return Threads::owning_thread_from_stacklock(t_list, (address) mark.locker());
1182 }
1183
1184 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1185 // fast-locked so get owner from the object.
1186 // owning_thread_from_object() may also return null here:
1187 return Threads::owning_thread_from_object(t_list, h_obj());
1188 }
1189
1190 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1191 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
1192 if (monitor != nullptr) {
1193 return Threads::owning_thread_from_monitor(t_list, monitor);
1194 }
1195 // Racing with inflation/deflation, retry
1196 mark = obj->mark_acquire();
1197
1198 if (mark.is_fast_locked()) {
1199 // Some other thread fast_locked
1200 return Threads::owning_thread_from_object(t_list, h_obj());
1201 }
1202 }
1203
1204 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1205 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1206 // The first stage of async deflation does not affect any field
1207 // used by this comparison so the ObjectMonitor* is usable here.
1208 ObjectMonitor* monitor = read_monitor(mark);
1209 assert(monitor != nullptr, "monitor should be non-null");
1210 // owning_thread_from_monitor() may also return null here:
1211 return Threads::owning_thread_from_monitor(t_list, monitor);
1212 }
1213
1214 // Unlocked case, header in place
1215 // Cannot have assertion since this object may have been
1216 // locked by another thread when reaching here.
1217 // assert(mark.is_unlocked(), "sanity check");
1218
1219 return nullptr;
1220 }
1221
1222 // Visitors ...
1223
1224 // Iterate over all ObjectMonitors.
1225 template <typename Function>
1226 void ObjectSynchronizer::monitors_iterate(Function function) {
1227 MonitorList::Iterator iter = _in_use_list.iterator();
1228 while (iter.has_next()) {
1229 ObjectMonitor* monitor = iter.next();
1230 function(monitor);
1231 }
1232 }
1233
1234 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1235 // returns true.
1236 template <typename OwnerFilter>
1237 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1238 monitors_iterate([&](ObjectMonitor* monitor) {
1239 // This function is only called at a safepoint or when the
1240 // target thread is suspended or when the target thread is
1241 // operating on itself. The current closures in use today are
1242 // only interested in an owned ObjectMonitor and ownership
1243 // cannot be dropped under the calling contexts so the
1244 // ObjectMonitor cannot be async deflated.
1245 if (monitor->has_owner() && filter(monitor)) {
1246 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1247
1248 closure->do_monitor(monitor);
1249 }
1250 });
1251 }
1252
1253 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1254 // ObjectMonitors where owner is set to a stack-lock address in thread.
1255 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1256 int64_t key = ObjectMonitor::owner_id_from(thread);
1257 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1258 return owned_monitors_iterate_filtered(closure, thread_filter);
1259 }
1260
1261 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
1262 int64_t key = ObjectMonitor::owner_id_from(vthread);
1263 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1264 return owned_monitors_iterate_filtered(closure, thread_filter);
1265 }
1266
1267 // Iterate ObjectMonitors owned by any thread.
1268 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1269 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
1270 return owned_monitors_iterate_filtered(closure, all_filter);
1271 }
1272
1273 static bool monitors_used_above_threshold(MonitorList* list) {
1274 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1275 return false;
1276 }
1277 size_t monitors_used = list->count();
1278 if (monitors_used == 0) { // empty list is easy
1279 return false;
1280 }
1281 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
1282 // Make sure that we use a ceiling value that is not lower than
1283 // previous, not lower than the recorded max used by the system, and
1284 // not lower than the current number of monitors in use (which can
1285 // race ahead of max). The result is guaranteed > 0.
1286 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
1287
1288 // Check if our monitor usage is above the threshold:
1289 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1290 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1291 // Deflate monitors if over the threshold percentage, unless no
1292 // progress on previous deflations.
1293 bool is_above_threshold = true;
1294
1295 // Check if it's time to adjust the in_use_list_ceiling up, due
1296 // to too many async deflation attempts without any progress.
1297 if (NoAsyncDeflationProgressMax != 0 &&
1298 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1299 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1300 size_t delta = (size_t)(ceiling * remainder) + 1;
1301 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
1302 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
1303 : ceiling + delta;
1304
1305 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1306 log_info(monitorinflation)("Too many deflations without progress; "
1307 "bumping in_use_list_ceiling from %zu"
1308 " to %zu", old_ceiling, new_ceiling);
1309 _no_progress_cnt = 0;
1310 ceiling = new_ceiling;
1311
1312 // Check if our monitor usage is still above the threshold:
1313 monitor_usage = (monitors_used * 100LL) / ceiling;
1314 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
1315 }
1316 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
1317 ", monitor_usage=%zu, threshold=%d",
1318 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1319 return is_above_threshold;
1320 }
1321
1322 return false;
1323 }
1324
1325 size_t ObjectSynchronizer::in_use_list_count() {
1326 return _in_use_list.count();
1327 }
1328
1329 size_t ObjectSynchronizer::in_use_list_max() {
1330 return _in_use_list.max();
1331 }
1332
1333 size_t ObjectSynchronizer::in_use_list_ceiling() {
1334 return _in_use_list_ceiling;
1335 }
1336
1337 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1338 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1339 }
1340
1341 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1342 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1343 }
1344
1345 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1346 _in_use_list_ceiling = new_value;
1347 }
1348
1349 bool ObjectSynchronizer::is_async_deflation_needed() {
1350 if (is_async_deflation_requested()) {
1351 // Async deflation request.
1352 log_info(monitorinflation)("Async deflation needed: explicit request");
1353 return true;
1354 }
1355
1356 jlong time_since_last = time_since_last_async_deflation_ms();
1357
1358 if (AsyncDeflationInterval > 0 &&
1359 time_since_last > AsyncDeflationInterval &&
1360 monitors_used_above_threshold(&_in_use_list)) {
1361 // It's been longer than our specified deflate interval and there
1362 // are too many monitors in use. We don't deflate more frequently
1363 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1364 // in order to not swamp the MonitorDeflationThread.
1365 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1366 return true;
1367 }
1368
1369 if (GuaranteedAsyncDeflationInterval > 0 &&
1370 time_since_last > GuaranteedAsyncDeflationInterval) {
1371 // It's been longer than our specified guaranteed deflate interval.
1372 // We need to clean up the used monitors even if the threshold is
1373 // not reached, to keep the memory utilization at bay when many threads
1374 // touched many monitors.
1375 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
1376 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1377 GuaranteedAsyncDeflationInterval, time_since_last);
1378
1379 // If this deflation has no progress, then it should not affect the no-progress
1380 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1381 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1382 // the generic code would bump the no-progress counter, and we compensate for that
1383 // by telling it to skip the update.
1384 //
1385 // If this deflation has progress, then it should let non-progress tracking
1386 // know about this, otherwise the threshold heuristics would kick in, potentially
1387 // experience no-progress due to aggressive cleanup by this deflation, and think
1388 // it is still in no-progress stride. In this "progress" case, the generic code would
1389 // zero the counter, and we allow it to happen.
1390 _no_progress_skip_increment = true;
1391
1392 return true;
1393 }
1394
1395 return false;
1396 }
1397
1398 void ObjectSynchronizer::request_deflate_idle_monitors() {
1399 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1400 set_is_async_deflation_requested(true);
1401 ml.notify_all();
1402 }
1403
1404 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1405 JavaThread* current = JavaThread::current();
1406 bool ret_code = false;
1407
1408 jlong last_time = last_async_deflation_time_ns();
1409
1410 request_deflate_idle_monitors();
1411
1412 const int N_CHECKS = 5;
1413 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1414 if (last_async_deflation_time_ns() > last_time) {
1415 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1416 ret_code = true;
1417 break;
1418 }
1419 {
1420 // JavaThread has to honor the blocking protocol.
1421 ThreadBlockInVM tbivm(current);
1422 os::naked_short_sleep(999); // sleep for almost 1 second
1423 }
1424 }
1425 if (!ret_code) {
1426 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1427 }
1428
1429 return ret_code;
1430 }
1431
1432 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1433 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1434 }
1435
1436 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1437 const oop obj,
1438 ObjectSynchronizer::InflateCause cause) {
1439 assert(event != nullptr, "invariant");
1440 const Klass* monitor_klass = obj->klass();
1441 if (ObjectMonitor::is_jfr_excluded(monitor_klass)) {
1442 return;
1443 }
1444 event->set_monitorClass(monitor_klass);
1445 event->set_address((uintptr_t)(void*)obj);
1446 event->set_cause((u1)cause);
1447 event->commit();
1448 }
1449
1450 // Fast path code shared by multiple functions
1451 void ObjectSynchronizer::inflate_helper(oop obj) {
1452 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1453 markWord mark = obj->mark_acquire();
1454 if (mark.has_monitor()) {
1455 ObjectMonitor* monitor = read_monitor(mark);
1456 markWord dmw = monitor->header();
1457 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1458 return;
1459 }
1460 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1461 }
1462
1463 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1464 assert(current == Thread::current(), "must be");
1465 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1466 return inflate_impl(current->is_Java_thread() ? JavaThread::cast(current) : nullptr, obj, cause);
1467 }
1468
1469 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1470 assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1471 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_for");
1472 return inflate_impl(thread, obj, cause);
1473 }
1474
1475 ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* locking_thread, oop object, const InflateCause cause) {
1476 // The JavaThread* locking_thread requires that the locking_thread == Thread::current() or
1477 // is suspended throughout the call by some other mechanism.
1478 // The thread might be nullptr when called from a non JavaThread. (As may still be
1479 // the case from FastHashCode). However it is only important for correctness that the
1480 // thread is set when called from ObjectSynchronizer::enter from the owning thread,
1481 // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
1482 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_impl");
1483 EventJavaMonitorInflate event;
1484
1485 for (;;) {
1486 const markWord mark = object->mark_acquire();
1487
1488 // The mark can be in one of the following states:
1489 // * inflated - If the ObjectMonitor owner is anonymous and the
1490 // locking_thread owns the object lock, then we
1491 // make the locking_thread the ObjectMonitor owner.
1492 // * stack-locked - Coerce it to inflated from stack-locked.
1493 // * INFLATING - Busy wait for conversion from stack-locked to
1494 // inflated.
1495 // * unlocked - Aggressively inflate the object.
1496
1497 // CASE: inflated
1498 if (mark.has_monitor()) {
1499 ObjectMonitor* inf = mark.monitor();
1500 markWord dmw = inf->header();
1501 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1502 if (inf->has_anonymous_owner() && locking_thread != nullptr) {
1503 assert(LockingMode == LM_LEGACY, "invariant");
1504 if (locking_thread->is_lock_owned((address)inf->stack_locker())) {
1505 inf->set_stack_locker(nullptr);
1506 inf->set_owner_from_anonymous(locking_thread);
1507 }
1508 }
1509 return inf;
1510 }
1511
1512 // CASE: inflation in progress - inflating over a stack-lock.
1513 // Some other thread is converting from stack-locked to inflated.
1514 // Only that thread can complete inflation -- other threads must wait.
1515 // The INFLATING value is transient.
1516 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1517 // We could always eliminate polling by parking the thread on some auxiliary list.
1518 if (mark == markWord::INFLATING()) {
1519 read_stable_mark(object);
1520 continue;
1521 }
1522
1523 // CASE: stack-locked
1524 // Could be stack-locked either by current or by some other thread.
1525 //
1526 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1527 // to install INFLATING into the mark word. We originally installed INFLATING,
1528 // allocated the ObjectMonitor, and then finally STed the address of the
1529 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1530 // the interval in which INFLATING appeared in the mark, thus increasing
1531 // the odds of inflation contention. If we lose the race to set INFLATING,
1532 // then we just delete the ObjectMonitor and loop around again.
1533 //
1534 LogStreamHandle(Trace, monitorinflation) lsh;
1535 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1536 ObjectMonitor* m = new ObjectMonitor(object);
1537 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1538 // We do this before the CAS in order to minimize the length of time
1539 // in which INFLATING appears in the mark.
1540
1541 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1542 if (cmp != mark) {
1543 delete m;
1544 continue; // Interference -- just retry
1545 }
1546
1547 // We've successfully installed INFLATING (0) into the mark-word.
1548 // This is the only case where 0 will appear in a mark-word.
1549 // Only the singular thread that successfully swings the mark-word
1550 // to 0 can perform (or more precisely, complete) inflation.
1551 //
1552 // Why do we CAS a 0 into the mark-word instead of just CASing the
1553 // mark-word from the stack-locked value directly to the new inflated state?
1554 // Consider what happens when a thread unlocks a stack-locked object.
1555 // It attempts to use CAS to swing the displaced header value from the
1556 // on-stack BasicLock back into the object header. Recall also that the
1557 // header value (hash code, etc) can reside in (a) the object header, or
1558 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1559 // header in an ObjectMonitor. The inflate() routine must copy the header
1560 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1561 // the while preserving the hashCode stability invariants. If the owner
1562 // decides to release the lock while the value is 0, the unlock will fail
1563 // and control will eventually pass from slow_exit() to inflate. The owner
1564 // will then spin, waiting for the 0 value to disappear. Put another way,
1565 // the 0 causes the owner to stall if the owner happens to try to
1566 // drop the lock (restoring the header from the BasicLock to the object)
1567 // while inflation is in-progress. This protocol avoids races that might
1568 // would otherwise permit hashCode values to change or "flicker" for an object.
1569 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1570 // 0 serves as a "BUSY" inflate-in-progress indicator.
1571
1572
1573 // fetch the displaced mark from the owner's stack.
1574 // The owner can't die or unwind past the lock while our INFLATING
1575 // object is in the mark. Furthermore the owner can't complete
1576 // an unlock on the object, either.
1577 markWord dmw = mark.displaced_mark_helper();
1578 // Catch if the object's header is not neutral (not locked and
1579 // not marked is what we care about here).
1580 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1581
1582 // Setup monitor fields to proper values -- prepare the monitor
1583 m->set_header(dmw);
1584
1585 // Note that a thread can inflate an object
1586 // that it has stack-locked -- as might happen in wait() -- directly
1587 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1588 if (locking_thread != nullptr && locking_thread->is_lock_owned((address)mark.locker())) {
1589 m->set_owner(locking_thread);
1590 } else {
1591 // Use ANONYMOUS_OWNER to indicate that the owner is the BasicLock on the stack,
1592 // and set the stack locker field in the monitor.
1593 m->set_stack_locker(mark.locker());
1594 m->set_anonymous_owner();
1595 }
1596 // TODO-FIXME: assert BasicLock->dhw != 0.
1597
1598 // Must preserve store ordering. The monitor state must
1599 // be stable at the time of publishing the monitor address.
1600 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1601 // Release semantics so that above set_object() is seen first.
1602 object->release_set_mark(markWord::encode(m));
1603
1604 // Once ObjectMonitor is configured and the object is associated
1605 // with the ObjectMonitor, it is safe to allow async deflation:
1606 _in_use_list.add(m);
1607
1608 if (log_is_enabled(Trace, monitorinflation)) {
1609 ResourceMark rm;
1610 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1611 INTPTR_FORMAT ", type='%s'", p2i(object),
1612 object->mark().value(), object->klass()->external_name());
1613 }
1614 if (event.should_commit()) {
1615 post_monitor_inflate_event(&event, object, cause);
1616 }
1617 return m;
1618 }
1619
1620 // CASE: unlocked
1621 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1622 // If we know we're inflating for entry it's better to inflate by swinging a
1623 // pre-locked ObjectMonitor pointer into the object header. A successful
1624 // CAS inflates the object *and* confers ownership to the inflating thread.
1625 // In the current implementation we use a 2-step mechanism where we CAS()
1626 // to inflate and then CAS() again to try to swing _owner from null to current.
1627 // An inflateTry() method that we could call from enter() would be useful.
1628
1629 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
1630 ObjectMonitor* m = new ObjectMonitor(object);
1631 // prepare m for installation - set monitor to initial state
1632 m->set_header(mark);
1633
1634 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1635 delete m;
1636 m = nullptr;
1637 continue;
1638 // interference - the markword changed - just retry.
1639 // The state-transitions are one-way, so there's no chance of
1640 // live-lock -- "Inflated" is an absorbing state.
1641 }
1642
1643 // Once the ObjectMonitor is configured and object is associated
1644 // with the ObjectMonitor, it is safe to allow async deflation:
1645 _in_use_list.add(m);
1646
1647 if (log_is_enabled(Trace, monitorinflation)) {
1648 ResourceMark rm;
1649 lsh.print_cr("inflate(unlocked): object=" INTPTR_FORMAT ", mark="
1650 INTPTR_FORMAT ", type='%s'", p2i(object),
1651 object->mark().value(), object->klass()->external_name());
1652 }
1653 if (event.should_commit()) {
1654 post_monitor_inflate_event(&event, object, cause);
1655 }
1656 return m;
1657 }
1658 }
1659
1660 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1661 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1662 //
1663 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1664 MonitorList::Iterator iter = _in_use_list.iterator();
1665 size_t deflated_count = 0;
1666 Thread* current = Thread::current();
1667
1668 while (iter.has_next()) {
1669 if (deflated_count >= (size_t)MonitorDeflationMax) {
1670 break;
1671 }
1672 ObjectMonitor* mid = iter.next();
1673 if (mid->deflate_monitor(current)) {
1674 deflated_count++;
1675 }
1676
1677 // Must check for a safepoint/handshake and honor it.
1678 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1679 }
1680
1681 return deflated_count;
1682 }
1683
1684 class DeflationHandshakeClosure : public HandshakeClosure {
1685 public:
1686 DeflationHandshakeClosure() : HandshakeClosure("DeflationHandshakeClosure") {}
1687
1688 void do_thread(Thread* thread) {
1689 log_trace(monitorinflation)("DeflationHandshakeClosure::do_thread: thread="
1690 INTPTR_FORMAT, p2i(thread));
1691 if (thread->is_Java_thread()) {
1692 // Clear OM cache
1693 JavaThread* jt = JavaThread::cast(thread);
1694 jt->om_clear_monitor_cache();
1695 }
1696 }
1697 };
1698
1699 class VM_RendezvousGCThreads : public VM_Operation {
1700 public:
1701 bool evaluate_at_safepoint() const override { return false; }
1702 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1703 void doit() override {
1704 Universe::heap()->safepoint_synchronize_begin();
1705 Universe::heap()->safepoint_synchronize_end();
1706 };
1707 };
1708
1709 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1710 ObjectMonitorDeflationSafepointer* safepointer) {
1711 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1712 size_t deleted_count = 0;
1713 for (ObjectMonitor* monitor: *delete_list) {
1714 delete monitor;
1715 deleted_count++;
1716 // A JavaThread must check for a safepoint/handshake and honor it.
1717 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1718 }
1719 return deleted_count;
1720 }
1721
1722 class ObjectMonitorDeflationLogging: public StackObj {
1723 LogStreamHandle(Debug, monitorinflation) _debug;
1724 LogStreamHandle(Info, monitorinflation) _info;
1725 LogStream* _stream;
1726 elapsedTimer _timer;
1727
1728 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1729 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1730 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1731
1732 public:
1733 ObjectMonitorDeflationLogging()
1734 : _debug(), _info(), _stream(nullptr) {
1735 if (_debug.is_enabled()) {
1736 _stream = &_debug;
1737 } else if (_info.is_enabled()) {
1738 _stream = &_info;
1739 }
1740 }
1741
1742 void begin() {
1743 if (_stream != nullptr) {
1744 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1745 ceiling(), count(), max());
1746 _timer.start();
1747 }
1748 }
1749
1750 void before_handshake(size_t unlinked_count) {
1751 if (_stream != nullptr) {
1752 _timer.stop();
1753 _stream->print_cr("before handshaking: unlinked_count=%zu"
1754 ", in_use_list stats: ceiling=%zu, count="
1755 "%zu, max=%zu",
1756 unlinked_count, ceiling(), count(), max());
1757 }
1758 }
1759
1760 void after_handshake() {
1761 if (_stream != nullptr) {
1762 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1763 "%zu, count=%zu, max=%zu",
1764 ceiling(), count(), max());
1765 _timer.start();
1766 }
1767 }
1768
1769 void end(size_t deflated_count, size_t unlinked_count) {
1770 if (_stream != nullptr) {
1771 _timer.stop();
1772 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1773 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1774 deflated_count, unlinked_count, _timer.seconds());
1775 }
1776 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1777 ceiling(), count(), max());
1778 }
1779 }
1780
1781 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1782 if (_stream != nullptr) {
1783 _timer.stop();
1784 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1785 "%zu, count=%zu, max=%zu",
1786 op_name, cnt_name, cnt, ceiling(), count(), max());
1787 }
1788 }
1789
1790 void after_block_for_safepoint(const char* op_name) {
1791 if (_stream != nullptr) {
1792 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1793 ", count=%zu, max=%zu", op_name,
1794 ceiling(), count(), max());
1795 _timer.start();
1796 }
1797 }
1798 };
1799
1800 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1801 if (!SafepointMechanism::should_process(_current)) {
1802 return;
1803 }
1804
1805 // A safepoint/handshake has started.
1806 _log->before_block_for_safepoint(op_name, count_name, counter);
1807
1808 {
1809 // Honor block request.
1810 ThreadBlockInVM tbivm(_current);
1811 }
1812
1813 _log->after_block_for_safepoint(op_name);
1814 }
1815
1816 // This function is called by the MonitorDeflationThread to deflate
1817 // ObjectMonitors.
1818 size_t ObjectSynchronizer::deflate_idle_monitors() {
1819 JavaThread* current = JavaThread::current();
1820 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1821
1822 // The async deflation request has been processed.
1823 _last_async_deflation_time_ns = os::javaTimeNanos();
1824 set_is_async_deflation_requested(false);
1825
1826 ObjectMonitorDeflationLogging log;
1827 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1828
1829 log.begin();
1830
1831 // Deflate some idle ObjectMonitors.
1832 size_t deflated_count = deflate_monitor_list(&safepointer);
1833
1834 // Unlink the deflated ObjectMonitors from the in-use list.
1835 size_t unlinked_count = 0;
1836 size_t deleted_count = 0;
1837 if (deflated_count > 0) {
1838 ResourceMark rm(current);
1839 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1840 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1841
1842 #ifdef ASSERT
1843 if (UseObjectMonitorTable) {
1844 for (ObjectMonitor* monitor : delete_list) {
1845 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1846 }
1847 }
1848 #endif
1849
1850 log.before_handshake(unlinked_count);
1851
1852 // A JavaThread needs to handshake in order to safely free the
1853 // ObjectMonitors that were deflated in this cycle.
1854 DeflationHandshakeClosure dhc;
1855 Handshake::execute(&dhc);
1856 // Also, we sync and desync GC threads around the handshake, so that they can
1857 // safely read the mark-word and look-through to the object-monitor, without
1858 // being afraid that the object-monitor is going away.
1859 VM_RendezvousGCThreads sync_gc;
1860 VMThread::execute(&sync_gc);
1861
1862 log.after_handshake();
1863
1864 // After the handshake, safely free the ObjectMonitors that were
1865 // deflated and unlinked in this cycle.
1866
1867 // Delete the unlinked ObjectMonitors.
1868 deleted_count = delete_monitors(&delete_list, &safepointer);
1869 assert(unlinked_count == deleted_count, "must be");
1870 }
1871
1872 log.end(deflated_count, unlinked_count);
1873
1874 GVars.stw_random = os::random();
1875
1876 if (deflated_count != 0) {
1877 _no_progress_cnt = 0;
1878 } else if (_no_progress_skip_increment) {
1879 _no_progress_skip_increment = false;
1880 } else {
1881 _no_progress_cnt++;
1882 }
1883
1884 return deflated_count;
1885 }
1886
1887 // Monitor cleanup on JavaThread::exit
1888
1889 // Iterate through monitor cache and attempt to release thread's monitors
1890 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1891 private:
1892 JavaThread* _thread;
1893
1894 public:
1895 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1896 void do_monitor(ObjectMonitor* mid) {
1897 intx rec = mid->complete_exit(_thread);
1898 _thread->dec_held_monitor_count(rec + 1);
1899 }
1900 };
1901
1902 // Release all inflated monitors owned by current thread. Lightweight monitors are
1903 // ignored. This is meant to be called during JNI thread detach which assumes
1904 // all remaining monitors are heavyweight. All exceptions are swallowed.
1905 // Scanning the extant monitor list can be time consuming.
1906 // A simple optimization is to add a per-thread flag that indicates a thread
1907 // called jni_monitorenter() during its lifetime.
1908 //
1909 // Instead of NoSafepointVerifier it might be cheaper to
1910 // use an idiom of the form:
1911 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1912 // <code that must not run at safepoint>
1913 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1914 // Since the tests are extremely cheap we could leave them enabled
1915 // for normal product builds.
1916
1917 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1918 assert(current == JavaThread::current(), "must be current Java thread");
1919 NoSafepointVerifier nsv;
1920 ReleaseJavaMonitorsClosure rjmc(current);
1921 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1922 assert(!current->has_pending_exception(), "Should not be possible");
1923 current->clear_pending_exception();
1924 assert(current->held_monitor_count() == 0, "Should not be possible");
1925 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1926 current->clear_jni_monitor_count();
1927 }
1928
1929 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1930 switch (cause) {
1931 case inflate_cause_vm_internal: return "VM Internal";
1932 case inflate_cause_monitor_enter: return "Monitor Enter";
1933 case inflate_cause_wait: return "Monitor Wait";
1934 case inflate_cause_notify: return "Monitor Notify";
1935 case inflate_cause_hash_code: return "Monitor Hash Code";
1936 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1937 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1938 default:
1939 ShouldNotReachHere();
1940 }
1941 return "Unknown";
1942 }
1943
1944 //------------------------------------------------------------------------------
1945 // Debugging code
1946
1947 u_char* ObjectSynchronizer::get_gvars_addr() {
1948 return (u_char*)&GVars;
1949 }
1950
1951 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1952 return (u_char*)&GVars.hc_sequence;
1953 }
1954
1955 size_t ObjectSynchronizer::get_gvars_size() {
1956 return sizeof(SharedGlobals);
1957 }
1958
1959 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1960 return (u_char*)&GVars.stw_random;
1961 }
1962
1963 // Do the final audit and print of ObjectMonitor stats; must be done
1964 // by the VMThread at VM exit time.
1965 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1966 assert(Thread::current()->is_VM_thread(), "sanity check");
1967
1968 if (is_final_audit()) { // Only do the audit once.
1969 return;
1970 }
1971 set_is_final_audit();
1972 log_info(monitorinflation)("Starting the final audit.");
1973
1974 if (log_is_enabled(Info, monitorinflation)) {
1975 LogStreamHandle(Info, monitorinflation) ls;
1976 audit_and_print_stats(&ls, true /* on_exit */);
1977 }
1978 }
1979
1980 // This function can be called by the MonitorDeflationThread or it can be called when
1981 // we are trying to exit the VM. The list walker functions can run in parallel with
1982 // the other list operations.
1983 // Calls to this function can be added in various places as a debugging
1984 // aid.
1985 //
1986 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1987 int error_cnt = 0;
1988
1989 ls->print_cr("Checking in_use_list:");
1990 chk_in_use_list(ls, &error_cnt);
1991
1992 if (error_cnt == 0) {
1993 ls->print_cr("No errors found in in_use_list checks.");
1994 } else {
1995 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1996 }
1997
1998 // When exiting, only log the interesting entries at the Info level.
1999 // When called at intervals by the MonitorDeflationThread, log output
2000 // at the Trace level since there can be a lot of it.
2001 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
2002 LogStreamHandle(Trace, monitorinflation) ls_tr;
2003 log_in_use_monitor_details(&ls_tr, true /* log_all */);
2004 } else if (on_exit) {
2005 log_in_use_monitor_details(ls, false /* log_all */);
2006 }
2007
2008 ls->flush();
2009
2010 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2011 }
2012
2013 // Check the in_use_list; log the results of the checks.
2014 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
2015 size_t l_in_use_count = _in_use_list.count();
2016 size_t l_in_use_max = _in_use_list.max();
2017 out->print_cr("count=%zu, max=%zu", l_in_use_count,
2018 l_in_use_max);
2019
2020 size_t ck_in_use_count = 0;
2021 MonitorList::Iterator iter = _in_use_list.iterator();
2022 while (iter.has_next()) {
2023 ObjectMonitor* mid = iter.next();
2024 chk_in_use_entry(mid, out, error_cnt_p);
2025 ck_in_use_count++;
2026 }
2027
2028 if (l_in_use_count == ck_in_use_count) {
2029 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
2030 l_in_use_count, ck_in_use_count);
2031 } else {
2032 out->print_cr("WARNING: in_use_count=%zu is not equal to "
2033 "ck_in_use_count=%zu", l_in_use_count,
2034 ck_in_use_count);
2035 }
2036
2037 size_t ck_in_use_max = _in_use_list.max();
2038 if (l_in_use_max == ck_in_use_max) {
2039 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
2040 l_in_use_max, ck_in_use_max);
2041 } else {
2042 out->print_cr("WARNING: in_use_max=%zu is not equal to "
2043 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
2044 }
2045 }
2046
2047 // Check an in-use monitor entry; log any errors.
2048 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2049 int* error_cnt_p) {
2050 if (n->owner_is_DEFLATER_MARKER()) {
2051 // This could happen when monitor deflation blocks for a safepoint.
2052 return;
2053 }
2054
2055
2056 if (n->metadata() == 0) {
2057 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2058 "have non-null _metadata (header/hash) field.", p2i(n));
2059 *error_cnt_p = *error_cnt_p + 1;
2060 }
2061
2062 const oop obj = n->object_peek();
2063 if (obj == nullptr) {
2064 return;
2065 }
2066
2067 const markWord mark = obj->mark();
2068 if (!mark.has_monitor()) {
2069 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2070 "object does not think it has a monitor: obj="
2071 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2072 p2i(obj), mark.value());
2073 *error_cnt_p = *error_cnt_p + 1;
2074 return;
2075 }
2076
2077 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
2078 if (n != obj_mon) {
2079 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2080 "object does not refer to the same monitor: obj="
2081 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2082 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2083 *error_cnt_p = *error_cnt_p + 1;
2084 }
2085 }
2086
2087 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2088 // flags indicate why the entry is in-use, 'object' and 'object type'
2089 // indicate the associated object and its type.
2090 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2091 if (_in_use_list.count() > 0) {
2092 stringStream ss;
2093 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
2094 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2095 out->print_cr("%18s %s %18s %18s",
2096 "monitor", "BHL", "object", "object type");
2097 out->print_cr("================== === ================== ==================");
2098
2099 auto is_interesting = [&](ObjectMonitor* monitor) {
2100 return log_all || monitor->has_owner() || monitor->is_busy();
2101 };
2102
2103 monitors_iterate([&](ObjectMonitor* monitor) {
2104 if (is_interesting(monitor)) {
2105 const oop obj = monitor->object_peek();
2106 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
2107 ResourceMark rm;
2108 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
2109 monitor->is_busy(), hash != 0, monitor->has_owner(),
2110 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2111 if (monitor->is_busy()) {
2112 out->print(" (%s)", monitor->is_busy_to_string(&ss));
2113 ss.reset();
2114 }
2115 out->cr();
2116 }
2117 });
2118 }
2119
2120 out->flush();
2121 }