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 // These checks are required for wait, notify and exit to avoid inflating the monitor to
319 // find out this inline type object cannot be locked.
320 #define CHECK_THROW_NOSYNC_IMSE(obj) \
321 if (EnableValhalla && (obj)->mark().is_inline_type()) { \
322 JavaThread* THREAD = current; \
323 ResourceMark rm(THREAD); \
324 THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
325 }
326
327 #define CHECK_THROW_NOSYNC_IMSE_0(obj) \
328 if (EnableValhalla && (obj)->mark().is_inline_type()) { \
329 JavaThread* THREAD = current; \
330 ResourceMark rm(THREAD); \
331 THROW_MSG_0(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
332 }
333
334 // =====================> Quick functions
335
336 // The quick_* forms are special fast-path variants used to improve
337 // performance. In the simplest case, a "quick_*" implementation could
338 // simply return false, in which case the caller will perform the necessary
339 // state transitions and call the slow-path form.
340 // The fast-path is designed to handle frequently arising cases in an efficient
341 // manner and is just a degenerate "optimistic" variant of the slow-path.
342 // returns true -- to indicate the call was satisfied.
343 // returns false -- to indicate the call needs the services of the slow-path.
344 // A no-loitering ordinance is in effect for code in the quick_* family
345 // operators: safepoints or indefinite blocking (blocking that might span a
346 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
347 // entry.
348 //
349 // Consider: An interesting optimization is to have the JIT recognize the
350 // following common idiom:
351 // synchronized (someobj) { .... ; notify(); }
352 // That is, we find a notify() or notifyAll() call that immediately precedes
353 // the monitorexit operation. In that case the JIT could fuse the operations
354 // into a single notifyAndExit() runtime primitive.
355
356 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
357 assert(current->thread_state() == _thread_in_Java, "invariant");
358 NoSafepointVerifier nsv;
359 if (obj == nullptr) return false; // slow-path for invalid obj
360 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
361 const markWord mark = obj->mark();
362
363 if (LockingMode == LM_LIGHTWEIGHT) {
364 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
365 // Degenerate notify
366 // fast-locked by caller so by definition the implied waitset is empty.
367 return true;
368 }
369 } else if (LockingMode == LM_LEGACY) {
370 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
371 // Degenerate notify
372 // stack-locked by caller so by definition the implied waitset is empty.
373 return true;
374 }
375 }
376
377 if (mark.has_monitor()) {
378 ObjectMonitor* const mon = read_monitor(current, obj, mark);
379 if (LockingMode == LM_LIGHTWEIGHT && mon == nullptr) {
380 // Racing with inflation/deflation go slow path
381 return false;
382 }
383 assert(mon->object() == oop(obj), "invariant");
384 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
385
386 if (mon->first_waiter() != nullptr) {
387 // We have one or more waiters. Since this is an inflated monitor
388 // that we own, we can transfer one or more threads from the waitset
389 // to the entry_list here and now, avoiding the slow-path.
390 if (all) {
391 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
392 } else {
393 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
394 }
395 do {
396 mon->notify_internal(current);
397 } while (mon->first_waiter() != nullptr && all);
398 }
399 return true;
400 }
401
402 // other IMS exception states take the slow-path
403 return false;
404 }
405
406 static bool useHeavyMonitors() {
407 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
408 return LockingMode == LM_MONITOR;
409 #else
410 return false;
411 #endif
412 }
413
414 // The LockNode emitted directly at the synchronization site would have
415 // been too big if it were to have included support for the cases of inflated
416 // recursive enter and exit, so they go here instead.
417 // Note that we can't safely call AsyncPrintJavaStack() from within
418 // quick_enter() as our thread state remains _in_Java.
419
420 bool ObjectSynchronizer::quick_enter_legacy(oop obj, BasicLock* lock, JavaThread* current) {
421 assert(current->thread_state() == _thread_in_Java, "invariant");
422 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
423
424 if (useHeavyMonitors()) {
425 return false; // Slow path
426 }
427
428 assert(LockingMode == LM_LEGACY, "legacy mode below");
429
430 const markWord mark = obj->mark();
431
432 if (mark.has_monitor()) {
433
434 ObjectMonitor* const m = read_monitor(mark);
435 // An async deflation or GC can race us before we manage to make
436 // the ObjectMonitor busy by setting the owner below. If we detect
437 // that race we just bail out to the slow-path here.
438 if (m->object_peek() == nullptr) {
439 return false;
440 }
441
442 // Lock contention and Transactional Lock Elision (TLE) diagnostics
443 // and observability
444 // Case: light contention possibly amenable to TLE
445 // Case: TLE inimical operations such as nested/recursive synchronization
446
447 if (m->has_owner(current)) {
448 m->_recursions++;
449 current->inc_held_monitor_count();
450 return true;
451 }
452
453 // This Java Monitor is inflated so obj's header will never be
454 // displaced to this thread's BasicLock. Make the displaced header
455 // non-null so this BasicLock is not seen as recursive nor as
456 // being locked. We do this unconditionally so that this thread's
457 // BasicLock cannot be mis-interpreted by any stack walkers. For
458 // performance reasons, stack walkers generally first check for
459 // stack-locking in the object's header, the second check is for
460 // recursive stack-locking in the displaced header in the BasicLock,
461 // and last are the inflated Java Monitor (ObjectMonitor) checks.
462 lock->set_displaced_header(markWord::unused_mark());
463
464 if (!m->has_owner() && m->try_set_owner(current)) {
465 assert(m->_recursions == 0, "invariant");
466 current->inc_held_monitor_count();
467 return true;
468 }
469 }
470
471 // Note that we could inflate in quick_enter.
472 // This is likely a useful optimization
473 // Critically, in quick_enter() we must not:
474 // -- block indefinitely, or
475 // -- reach a safepoint
476
477 return false; // revert to slow-path
478 }
479
480 // Handle notifications when synchronizing on value based classes
481 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
482 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
483 frame last_frame = locking_thread->last_frame();
484 bool bcp_was_adjusted = false;
485 // Don't decrement bcp if it points to the frame's first instruction. This happens when
486 // handle_sync_on_value_based_class() is called because of a synchronized method. There
487 // is no actual monitorenter instruction in the byte code in this case.
488 if (last_frame.is_interpreted_frame() &&
489 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
490 // adjust bcp to point back to monitorenter so that we print the correct line numbers
491 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
492 bcp_was_adjusted = true;
493 }
494
495 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
496 ResourceMark rm;
497 stringStream ss;
498 locking_thread->print_active_stack_on(&ss);
499 char* base = (char*)strstr(ss.base(), "at");
500 char* newline = (char*)strchr(ss.base(), '\n');
501 if (newline != nullptr) {
502 *newline = '\0';
503 }
504 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
505 } else {
506 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
507 ResourceMark rm;
508 Log(valuebasedclasses) vblog;
509
510 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
511 if (locking_thread->has_last_Java_frame()) {
512 LogStream info_stream(vblog.info());
513 locking_thread->print_active_stack_on(&info_stream);
514 } else {
515 vblog.info("Cannot find the last Java frame");
516 }
517
518 EventSyncOnValueBasedClass event;
519 if (event.should_commit()) {
520 event.set_valueBasedClass(obj->klass());
521 event.commit();
522 }
523 }
524
525 if (bcp_was_adjusted) {
526 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
527 }
528 }
529
530 // -----------------------------------------------------------------------------
531 // Monitor Enter/Exit
532
533 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
534 // When called with locking_thread != Thread::current() some mechanism must synchronize
535 // the locking_thread with respect to the current thread. Currently only used when
536 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
537 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
538 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "JITed code should never have locked an instance of a value class");
539
540 if (LockingMode == LM_LIGHTWEIGHT) {
541 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
542 }
543
544 if (!enter_fast_impl(obj, lock, locking_thread)) {
545 // Inflated ObjectMonitor::enter_for is required
546
547 // An async deflation can race after the inflate_for() call and before
548 // enter_for() can make the ObjectMonitor busy. enter_for() returns false
549 // if we have lost the race to async deflation and we simply try again.
550 while (true) {
551 ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
552 if (monitor->enter_for(locking_thread)) {
553 return;
554 }
555 assert(monitor->is_being_async_deflated(), "must be");
556 }
557 }
558 }
559
560 void ObjectSynchronizer::enter_legacy(Handle obj, BasicLock* lock, JavaThread* current) {
561 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "This method should never be called on an instance of an inline class");
562 if (!enter_fast_impl(obj, lock, current)) {
563 // Inflated ObjectMonitor::enter is required
564
565 // An async deflation can race after the inflate() call and before
566 // enter() can make the ObjectMonitor busy. enter() returns false if
567 // we have lost the race to async deflation and we simply try again.
568 while (true) {
569 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
570 if (monitor->enter(current)) {
571 return;
572 }
573 }
574 }
575 }
576
577 // The interpreter and compiler assembly code tries to lock using the fast path
578 // of this algorithm. Make sure to update that code if the following function is
579 // changed. The implementation is extremely sensitive to race condition. Be careful.
580 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
581 guarantee(!EnableValhalla || !obj->klass()->is_inline_klass(), "Attempt to inflate inline type");
582 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
583
584 if (obj->klass()->is_value_based()) {
585 handle_sync_on_value_based_class(obj, locking_thread);
586 }
587
588 locking_thread->inc_held_monitor_count();
589
590 if (!useHeavyMonitors()) {
591 if (LockingMode == LM_LEGACY) {
592 markWord mark = obj->mark();
593 if (mark.is_unlocked()) {
594 // Anticipate successful CAS -- the ST of the displaced mark must
595 // be visible <= the ST performed by the CAS.
596 lock->set_displaced_header(mark);
597 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
598 return true;
599 }
600 } else if (mark.has_locker() &&
601 locking_thread->is_lock_owned((address) mark.locker())) {
602 assert(lock != mark.locker(), "must not re-lock the same lock");
603 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
604 lock->set_displaced_header(markWord::from_pointer(nullptr));
605 return true;
606 }
607
608 // The object header will never be displaced to this lock,
609 // so it does not matter what the value is, except that it
610 // must be non-zero to avoid looking like a re-entrant lock,
611 // and must not look locked either.
612 lock->set_displaced_header(markWord::unused_mark());
613
614 // Failed to fast lock.
615 return false;
616 }
617 } else if (VerifyHeavyMonitors) {
618 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
619 }
620
621 return false;
622 }
623
624 void ObjectSynchronizer::exit_legacy(oop object, BasicLock* lock, JavaThread* current) {
625 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
626
627 if (!useHeavyMonitors()) {
628 markWord mark = object->mark();
629 if (EnableValhalla && mark.is_inline_type()) {
630 return;
631 }
632 if (LockingMode == LM_LEGACY) {
633 markWord dhw = lock->displaced_header();
634 if (dhw.value() == 0) {
635 // If the displaced header is null, then this exit matches up with
636 // a recursive enter. No real work to do here except for diagnostics.
637 #ifndef PRODUCT
638 if (mark != markWord::INFLATING()) {
639 // Only do diagnostics if we are not racing an inflation. Simply
640 // exiting a recursive enter of a Java Monitor that is being
641 // inflated is safe; see the has_monitor() comment below.
642 assert(!mark.is_unlocked(), "invariant");
643 assert(!mark.has_locker() ||
644 current->is_lock_owned((address)mark.locker()), "invariant");
645 if (mark.has_monitor()) {
646 // The BasicLock's displaced_header is marked as a recursive
647 // enter and we have an inflated Java Monitor (ObjectMonitor).
648 // This is a special case where the Java Monitor was inflated
649 // after this thread entered the stack-lock recursively. When a
650 // Java Monitor is inflated, we cannot safely walk the Java
651 // Monitor owner's stack and update the BasicLocks because a
652 // Java Monitor can be asynchronously inflated by a thread that
653 // does not own the Java Monitor.
654 ObjectMonitor* m = read_monitor(mark);
655 assert(m->object()->mark() == mark, "invariant");
656 assert(m->is_entered(current), "invariant");
657 }
658 }
659 #endif
660 return;
661 }
662
663 if (mark == markWord::from_pointer(lock)) {
664 // If the object is stack-locked by the current thread, try to
665 // swing the displaced header from the BasicLock back to the mark.
666 assert(dhw.is_neutral(), "invariant");
667 if (object->cas_set_mark(dhw, mark) == mark) {
668 return;
669 }
670 }
671 }
672 } else if (VerifyHeavyMonitors) {
673 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
674 }
675
676 // We have to take the slow-path of possible inflation and then exit.
677 // The ObjectMonitor* can't be async deflated until ownership is
678 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
679 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
680 assert(!monitor->has_anonymous_owner(), "must not be");
681 monitor->exit(current);
682 }
683
684 // -----------------------------------------------------------------------------
685 // JNI locks on java objects
686 // NOTE: must use heavy weight monitor to handle jni monitor enter
687 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
688 JavaThread* THREAD = current;
689 // Top native frames in the stack will not be seen if we attempt
690 // preemption, since we start walking from the last Java anchor.
691 NoPreemptMark npm(current);
692
693 if (obj->klass()->is_value_based()) {
694 handle_sync_on_value_based_class(obj, current);
695 }
696
697 if (EnableValhalla && obj->klass()->is_inline_klass()) {
698 ResourceMark rm(THREAD);
699 const char* desc = "Cannot synchronize on an instance of value class ";
700 const char* className = obj->klass()->external_name();
701 size_t msglen = strlen(desc) + strlen(className) + 1;
702 char* message = NEW_RESOURCE_ARRAY(char, msglen);
703 assert(message != nullptr, "NEW_RESOURCE_ARRAY should have called vm_exit_out_of_memory and not return nullptr");
704 THROW_MSG(vmSymbols::java_lang_IdentityException(), className);
705 }
706
707 // the current locking is from JNI instead of Java code
708 current->set_current_pending_monitor_is_from_java(false);
709 // An async deflation can race after the inflate() call and before
710 // enter() can make the ObjectMonitor busy. enter() returns false if
711 // we have lost the race to async deflation and we simply try again.
712 while (true) {
713 ObjectMonitor* monitor;
714 bool entered;
715 if (LockingMode == LM_LIGHTWEIGHT) {
716 entered = LightweightSynchronizer::inflate_and_enter(obj(), inflate_cause_jni_enter, current, current) != nullptr;
717 } else {
718 monitor = inflate(current, obj(), inflate_cause_jni_enter);
719 entered = monitor->enter(current);
720 }
721
722 if (entered) {
723 current->inc_held_monitor_count(1, true);
724 break;
725 }
726 }
727 current->set_current_pending_monitor_is_from_java(true);
728 }
729
730 // NOTE: must use heavy weight monitor to handle jni monitor exit
731 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
732 JavaThread* current = THREAD;
733 CHECK_THROW_NOSYNC_IMSE(obj);
734
735 ObjectMonitor* monitor;
736 if (LockingMode == LM_LIGHTWEIGHT) {
737 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
738 } else {
739 // The ObjectMonitor* can't be async deflated until ownership is
740 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
741 monitor = inflate(current, obj, inflate_cause_jni_exit);
742 }
743 // If this thread has locked the object, exit the monitor. We
744 // intentionally do not use CHECK on check_owner because we must exit the
745 // monitor even if an exception was already pending.
746 if (monitor->check_owner(THREAD)) {
747 monitor->exit(current);
748 current->dec_held_monitor_count(1, true);
749 }
750 }
751
752 // -----------------------------------------------------------------------------
753 // Internal VM locks on java objects
754 // standard constructor, allows locking failures
755 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) : _npm(thread) {
756 _thread = thread;
757 _thread->check_for_valid_safepoint_state();
758 _obj = obj;
759
760 if (_obj() != nullptr) {
761 ObjectSynchronizer::enter(_obj, &_lock, _thread);
762 }
763 }
764
765 ObjectLocker::~ObjectLocker() {
766 if (_obj() != nullptr) {
767 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
768 }
769 }
770
771
772 // -----------------------------------------------------------------------------
773 // Wait/Notify/NotifyAll
774 // NOTE: must use heavy weight monitor to handle wait()
775
776 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
777 JavaThread* current = THREAD;
778 CHECK_THROW_NOSYNC_IMSE_0(obj);
779 if (millis < 0) {
780 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
781 }
782
783 ObjectMonitor* monitor;
784 if (LockingMode == LM_LIGHTWEIGHT) {
785 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
786 } else {
787 // The ObjectMonitor* can't be async deflated because the _waiters
788 // field is incremented before ownership is dropped and decremented
789 // after ownership is regained.
790 monitor = inflate(current, obj(), inflate_cause_wait);
791 }
792
793 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
794 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
795
796 // This dummy call is in place to get around dtrace bug 6254741. Once
797 // that's fixed we can uncomment the following line, remove the call
798 // and change this function back into a "void" func.
799 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
800 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
801 return ret_code;
802 }
803
804 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
805 if (millis < 0) {
806 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
807 }
808
809 ObjectMonitor* monitor;
810 if (LockingMode == LM_LIGHTWEIGHT) {
811 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
812 } else {
813 monitor = inflate(THREAD, obj(), inflate_cause_wait);
814 }
815 monitor->wait(millis, false, THREAD);
816 }
817
818
819 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
820 JavaThread* current = THREAD;
821 CHECK_THROW_NOSYNC_IMSE(obj);
822
823 markWord mark = obj->mark();
824 if (LockingMode == LM_LIGHTWEIGHT) {
825 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
826 // Not inflated so there can't be any waiters to notify.
827 return;
828 }
829 } else if (LockingMode == LM_LEGACY) {
830 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
831 // Not inflated so there can't be any waiters to notify.
832 return;
833 }
834 }
835
836 ObjectMonitor* monitor;
837 if (LockingMode == LM_LIGHTWEIGHT) {
838 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
839 } else {
840 // The ObjectMonitor* can't be async deflated until ownership is
841 // dropped by the calling thread.
842 monitor = inflate(current, obj(), inflate_cause_notify);
843 }
844 monitor->notify(CHECK);
845 }
846
847 // NOTE: see comment of notify()
848 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
849 JavaThread* current = THREAD;
850 CHECK_THROW_NOSYNC_IMSE(obj);
851
852 markWord mark = obj->mark();
853 if (LockingMode == LM_LIGHTWEIGHT) {
854 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
855 // Not inflated so there can't be any waiters to notify.
856 return;
857 }
858 } else if (LockingMode == LM_LEGACY) {
859 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
860 // Not inflated so there can't be any waiters to notify.
861 return;
862 }
863 }
864
865 ObjectMonitor* monitor;
866 if (LockingMode == LM_LIGHTWEIGHT) {
867 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
868 } else {
869 // The ObjectMonitor* can't be async deflated until ownership is
870 // dropped by the calling thread.
871 monitor = inflate(current, obj(), inflate_cause_notify);
872 }
873 monitor->notifyAll(CHECK);
874 }
875
876 // -----------------------------------------------------------------------------
877 // Hash Code handling
878
879 struct SharedGlobals {
880 char _pad_prefix[OM_CACHE_LINE_SIZE];
881 // This is a highly shared mostly-read variable.
882 // To avoid false-sharing it needs to be the sole occupant of a cache line.
883 volatile int stw_random;
884 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
885 // Hot RW variable -- Sequester to avoid false-sharing
886 volatile int hc_sequence;
887 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
888 };
889
890 static SharedGlobals GVars;
891
892 static markWord read_stable_mark(oop obj) {
893 markWord mark = obj->mark_acquire();
894 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
895 // New lightweight locking does not use the markWord::INFLATING() protocol.
896 return mark; // normal fast-path return
897 }
898
899 int its = 0;
900 for (;;) {
901 markWord mark = obj->mark_acquire();
902 if (!mark.is_being_inflated()) {
903 return mark; // normal fast-path return
904 }
905
906 // The object is being inflated by some other thread.
907 // The caller of read_stable_mark() must wait for inflation to complete.
908 // Avoid live-lock.
909
910 ++its;
911 if (its > 10000 || !os::is_MP()) {
912 if (its & 1) {
913 os::naked_yield();
914 } else {
915 // Note that the following code attenuates the livelock problem but is not
916 // a complete remedy. A more complete solution would require that the inflating
917 // thread hold the associated inflation lock. The following code simply restricts
918 // the number of spinners to at most one. We'll have N-2 threads blocked
919 // on the inflationlock, 1 thread holding the inflation lock and using
920 // a yield/park strategy, and 1 thread in the midst of inflation.
921 // A more refined approach would be to change the encoding of INFLATING
922 // to allow encapsulation of a native thread pointer. Threads waiting for
923 // inflation to complete would use CAS to push themselves onto a singly linked
924 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
925 // and calling park(). When inflation was complete the thread that accomplished inflation
926 // would detach the list and set the markword to inflated with a single CAS and
927 // then for each thread on the list, set the flag and unpark() the thread.
928
929 // Index into the lock array based on the current object address.
930 static_assert(is_power_of_2(inflation_lock_count()), "must be");
931 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
932 int YieldThenBlock = 0;
933 assert(ix < inflation_lock_count(), "invariant");
934 inflation_lock(ix)->lock();
935 while (obj->mark_acquire() == markWord::INFLATING()) {
936 // Beware: naked_yield() is advisory and has almost no effect on some platforms
937 // so we periodically call current->_ParkEvent->park(1).
938 // We use a mixed spin/yield/block mechanism.
939 if ((YieldThenBlock++) >= 16) {
940 Thread::current()->_ParkEvent->park(1);
941 } else {
942 os::naked_yield();
943 }
944 }
945 inflation_lock(ix)->unlock();
946 }
947 } else {
948 SpinPause(); // SMP-polite spinning
949 }
950 }
951 }
952
953 // hashCode() generation :
954 //
955 // Possibilities:
956 // * MD5Digest of {obj,stw_random}
957 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
958 // * A DES- or AES-style SBox[] mechanism
959 // * One of the Phi-based schemes, such as:
960 // 2654435761 = 2^32 * Phi (golden ratio)
961 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
962 // * A variation of Marsaglia's shift-xor RNG scheme.
963 // * (obj ^ stw_random) is appealing, but can result
964 // in undesirable regularity in the hashCode values of adjacent objects
965 // (objects allocated back-to-back, in particular). This could potentially
966 // result in hashtable collisions and reduced hashtable efficiency.
967 // There are simple ways to "diffuse" the middle address bits over the
968 // generated hashCode values:
969
970 static intptr_t get_next_hash(Thread* current, oop obj) {
971 intptr_t value = 0;
972 if (hashCode == 0) {
973 // This form uses global Park-Miller RNG.
974 // On MP system we'll have lots of RW access to a global, so the
975 // mechanism induces lots of coherency traffic.
976 value = os::random();
977 } else if (hashCode == 1) {
978 // This variation has the property of being stable (idempotent)
979 // between STW operations. This can be useful in some of the 1-0
980 // synchronization schemes.
981 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
982 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
983 } else if (hashCode == 2) {
984 value = 1; // for sensitivity testing
985 } else if (hashCode == 3) {
986 value = ++GVars.hc_sequence;
987 } else if (hashCode == 4) {
988 value = cast_from_oop<intptr_t>(obj);
989 } else {
990 // Marsaglia's xor-shift scheme with thread-specific state
991 // This is probably the best overall implementation -- we'll
992 // likely make this the default in future releases.
993 unsigned t = current->_hashStateX;
994 t ^= (t << 11);
995 current->_hashStateX = current->_hashStateY;
996 current->_hashStateY = current->_hashStateZ;
997 current->_hashStateZ = current->_hashStateW;
998 unsigned v = current->_hashStateW;
999 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
1000 current->_hashStateW = v;
1001 value = v;
1002 }
1003
1004 value &= markWord::hash_mask;
1005 if (value == 0) value = 0xBAD;
1006 assert(value != markWord::no_hash, "invariant");
1007 return value;
1008 }
1009
1010 static intptr_t install_hash_code(Thread* current, oop obj) {
1011 assert(UseObjectMonitorTable && LockingMode == LM_LIGHTWEIGHT, "must be");
1012
1013 markWord mark = obj->mark_acquire();
1014 for (;;) {
1015 intptr_t hash = mark.hash();
1016 if (hash != 0) {
1017 return hash;
1018 }
1019
1020 hash = get_next_hash(current, obj);
1021 const markWord old_mark = mark;
1022 const markWord new_mark = old_mark.copy_set_hash(hash);
1023
1024 mark = obj->cas_set_mark(new_mark, old_mark);
1025 if (old_mark == mark) {
1026 return hash;
1027 }
1028 }
1029 }
1030
1031 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
1032 if (EnableValhalla && obj->klass()->is_inline_klass()) {
1033 // VM should be calling bootstrap method
1034 ShouldNotReachHere();
1035 }
1036 if (UseObjectMonitorTable) {
1037 // Since the monitor isn't in the object header, the hash can simply be
1038 // installed in the object header.
1039 return install_hash_code(current, obj);
1040 }
1041
1042 while (true) {
1043 ObjectMonitor* monitor = nullptr;
1044 markWord temp, test;
1045 intptr_t hash;
1046 markWord mark = read_stable_mark(obj);
1047 if (VerifyHeavyMonitors) {
1048 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
1049 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1050 }
1051 if (mark.is_unlocked() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1052 hash = mark.hash();
1053 if (hash != 0) { // if it has a hash, just return it
1054 return hash;
1055 }
1056 hash = get_next_hash(current, obj); // get a new hash
1057 temp = mark.copy_set_hash(hash); // merge the hash into header
1058 // try to install the hash
1059 test = obj->cas_set_mark(temp, mark);
1060 if (test == mark) { // if the hash was installed, return it
1061 return hash;
1062 }
1063 if (LockingMode == LM_LIGHTWEIGHT) {
1064 // CAS failed, retry
1065 continue;
1066 }
1067 // Failed to install the hash. It could be that another thread
1068 // installed the hash just before our attempt or inflation has
1069 // occurred or... so we fall thru to inflate the monitor for
1070 // stability and then install the hash.
1071 } else if (mark.has_monitor()) {
1072 monitor = mark.monitor();
1073 temp = monitor->header();
1074 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1075 hash = temp.hash();
1076 if (hash != 0) {
1077 // It has a hash.
1078
1079 // Separate load of dmw/header above from the loads in
1080 // is_being_async_deflated().
1081
1082 // dmw/header and _contentions may get written by different threads.
1083 // Make sure to observe them in the same order when having several observers.
1084 OrderAccess::loadload_for_IRIW();
1085
1086 if (monitor->is_being_async_deflated()) {
1087 // But we can't safely use the hash if we detect that async
1088 // deflation has occurred. So we attempt to restore the
1089 // header/dmw to the object's header so that we only retry
1090 // once if the deflater thread happens to be slow.
1091 monitor->install_displaced_markword_in_object(obj);
1092 continue;
1093 }
1094 return hash;
1095 }
1096 // Fall thru so we only have one place that installs the hash in
1097 // the ObjectMonitor.
1098 } else if (LockingMode == LM_LEGACY && mark.has_locker()
1099 && current->is_Java_thread()
1100 && JavaThread::cast(current)->is_lock_owned((address)mark.locker())) {
1101 // This is a stack-lock owned by the calling thread so fetch the
1102 // displaced markWord from the BasicLock on the stack.
1103 temp = mark.displaced_mark_helper();
1104 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1105 hash = temp.hash();
1106 if (hash != 0) { // if it has a hash, just return it
1107 return hash;
1108 }
1109 // WARNING:
1110 // The displaced header in the BasicLock on a thread's stack
1111 // is strictly immutable. It CANNOT be changed in ANY cases.
1112 // So we have to inflate the stack-lock into an ObjectMonitor
1113 // even if the current thread owns the lock. The BasicLock on
1114 // a thread's stack can be asynchronously read by other threads
1115 // during an inflate() call so any change to that stack memory
1116 // may not propagate to other threads correctly.
1117 }
1118
1119 // Inflate the monitor to set the hash.
1120
1121 // There's no need to inflate if the mark has already got a monitor.
1122 // NOTE: an async deflation can race after we get the monitor and
1123 // before we can update the ObjectMonitor's header with the hash
1124 // value below.
1125 monitor = mark.has_monitor() ? mark.monitor() : inflate(current, obj, inflate_cause_hash_code);
1126 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1127 mark = monitor->header();
1128 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1129 hash = mark.hash();
1130 if (hash == 0) { // if it does not have a hash
1131 hash = get_next_hash(current, obj); // get a new hash
1132 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1133 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1134 uintptr_t v = Atomic::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
1135 test = markWord(v);
1136 if (test != mark) {
1137 // The attempt to update the ObjectMonitor's header/dmw field
1138 // did not work. This can happen if another thread managed to
1139 // merge in the hash just before our cmpxchg().
1140 // If we add any new usages of the header/dmw field, this code
1141 // will need to be updated.
1142 hash = test.hash();
1143 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1144 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1145 }
1146 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
1147 // If we detect that async deflation has occurred, then we
1148 // attempt to restore the header/dmw to the object's header
1149 // so that we only retry once if the deflater thread happens
1150 // to be slow.
1151 monitor->install_displaced_markword_in_object(obj);
1152 continue;
1153 }
1154 }
1155 // We finally get the hash.
1156 return hash;
1157 }
1158 }
1159
1160 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1161 Handle h_obj) {
1162 if (EnableValhalla && h_obj->mark().is_inline_type()) {
1163 return false;
1164 }
1165 assert(current == JavaThread::current(), "Can only be called on current thread");
1166 oop obj = h_obj();
1167
1168 markWord mark = read_stable_mark(obj);
1169
1170 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1171 // stack-locked case, header points into owner's stack
1172 return current->is_lock_owned((address)mark.locker());
1173 }
1174
1175 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1176 // fast-locking case, see if lock is in current's lock stack
1177 return current->lock_stack().contains(h_obj());
1178 }
1179
1180 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1181 ObjectMonitor* monitor = read_monitor(current, obj, mark);
1182 if (monitor != nullptr) {
1183 return monitor->is_entered(current) != 0;
1184 }
1185 // Racing with inflation/deflation, retry
1186 mark = obj->mark_acquire();
1187
1188 if (mark.is_fast_locked()) {
1189 // Some other thread fast_locked, current could not have held the lock
1190 return false;
1191 }
1192 }
1193
1194 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1195 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1196 // The first stage of async deflation does not affect any field
1197 // used by this comparison so the ObjectMonitor* is usable here.
1198 ObjectMonitor* monitor = read_monitor(mark);
1199 return monitor->is_entered(current) != 0;
1200 }
1201 // Unlocked case, header in place
1202 assert(mark.is_unlocked(), "sanity check");
1203 return false;
1204 }
1205
1206 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1207 oop obj = h_obj();
1208 markWord mark = read_stable_mark(obj);
1209
1210 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1211 // stack-locked so header points into owner's stack.
1212 // owning_thread_from_monitor_owner() may also return null here:
1213 return Threads::owning_thread_from_stacklock(t_list, (address) mark.locker());
1214 }
1215
1216 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1217 // fast-locked so get owner from the object.
1218 // owning_thread_from_object() may also return null here:
1219 return Threads::owning_thread_from_object(t_list, h_obj());
1220 }
1221
1222 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1223 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
1224 if (monitor != nullptr) {
1225 return Threads::owning_thread_from_monitor(t_list, monitor);
1226 }
1227 // Racing with inflation/deflation, retry
1228 mark = obj->mark_acquire();
1229
1230 if (mark.is_fast_locked()) {
1231 // Some other thread fast_locked
1232 return Threads::owning_thread_from_object(t_list, h_obj());
1233 }
1234 }
1235
1236 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1237 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1238 // The first stage of async deflation does not affect any field
1239 // used by this comparison so the ObjectMonitor* is usable here.
1240 ObjectMonitor* monitor = read_monitor(mark);
1241 assert(monitor != nullptr, "monitor should be non-null");
1242 // owning_thread_from_monitor() may also return null here:
1243 return Threads::owning_thread_from_monitor(t_list, monitor);
1244 }
1245
1246 // Unlocked case, header in place
1247 // Cannot have assertion since this object may have been
1248 // locked by another thread when reaching here.
1249 // assert(mark.is_unlocked(), "sanity check");
1250
1251 return nullptr;
1252 }
1253
1254 // Visitors ...
1255
1256 // Iterate over all ObjectMonitors.
1257 template <typename Function>
1258 void ObjectSynchronizer::monitors_iterate(Function function) {
1259 MonitorList::Iterator iter = _in_use_list.iterator();
1260 while (iter.has_next()) {
1261 ObjectMonitor* monitor = iter.next();
1262 function(monitor);
1263 }
1264 }
1265
1266 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1267 // returns true.
1268 template <typename OwnerFilter>
1269 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1270 monitors_iterate([&](ObjectMonitor* monitor) {
1271 // This function is only called at a safepoint or when the
1272 // target thread is suspended or when the target thread is
1273 // operating on itself. The current closures in use today are
1274 // only interested in an owned ObjectMonitor and ownership
1275 // cannot be dropped under the calling contexts so the
1276 // ObjectMonitor cannot be async deflated.
1277 if (monitor->has_owner() && filter(monitor)) {
1278 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1279
1280 closure->do_monitor(monitor);
1281 }
1282 });
1283 }
1284
1285 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1286 // ObjectMonitors where owner is set to a stack-lock address in thread.
1287 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1288 int64_t key = ObjectMonitor::owner_id_from(thread);
1289 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1290 return owned_monitors_iterate_filtered(closure, thread_filter);
1291 }
1292
1293 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
1294 int64_t key = ObjectMonitor::owner_id_from(vthread);
1295 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1296 return owned_monitors_iterate_filtered(closure, thread_filter);
1297 }
1298
1299 // Iterate ObjectMonitors owned by any thread.
1300 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1301 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
1302 return owned_monitors_iterate_filtered(closure, all_filter);
1303 }
1304
1305 static bool monitors_used_above_threshold(MonitorList* list) {
1306 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1307 return false;
1308 }
1309 size_t monitors_used = list->count();
1310 if (monitors_used == 0) { // empty list is easy
1311 return false;
1312 }
1313 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
1314 // Make sure that we use a ceiling value that is not lower than
1315 // previous, not lower than the recorded max used by the system, and
1316 // not lower than the current number of monitors in use (which can
1317 // race ahead of max). The result is guaranteed > 0.
1318 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
1319
1320 // Check if our monitor usage is above the threshold:
1321 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1322 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1323 // Deflate monitors if over the threshold percentage, unless no
1324 // progress on previous deflations.
1325 bool is_above_threshold = true;
1326
1327 // Check if it's time to adjust the in_use_list_ceiling up, due
1328 // to too many async deflation attempts without any progress.
1329 if (NoAsyncDeflationProgressMax != 0 &&
1330 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1331 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1332 size_t delta = (size_t)(ceiling * remainder) + 1;
1333 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
1334 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
1335 : ceiling + delta;
1336
1337 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1338 log_info(monitorinflation)("Too many deflations without progress; "
1339 "bumping in_use_list_ceiling from %zu"
1340 " to %zu", old_ceiling, new_ceiling);
1341 _no_progress_cnt = 0;
1342 ceiling = new_ceiling;
1343
1344 // Check if our monitor usage is still above the threshold:
1345 monitor_usage = (monitors_used * 100LL) / ceiling;
1346 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
1347 }
1348 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
1349 ", monitor_usage=%zu, threshold=%d",
1350 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1351 return is_above_threshold;
1352 }
1353
1354 return false;
1355 }
1356
1357 size_t ObjectSynchronizer::in_use_list_count() {
1358 return _in_use_list.count();
1359 }
1360
1361 size_t ObjectSynchronizer::in_use_list_max() {
1362 return _in_use_list.max();
1363 }
1364
1365 size_t ObjectSynchronizer::in_use_list_ceiling() {
1366 return _in_use_list_ceiling;
1367 }
1368
1369 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1370 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1371 }
1372
1373 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1374 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1375 }
1376
1377 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1378 _in_use_list_ceiling = new_value;
1379 }
1380
1381 bool ObjectSynchronizer::is_async_deflation_needed() {
1382 if (is_async_deflation_requested()) {
1383 // Async deflation request.
1384 log_info(monitorinflation)("Async deflation needed: explicit request");
1385 return true;
1386 }
1387
1388 jlong time_since_last = time_since_last_async_deflation_ms();
1389
1390 if (AsyncDeflationInterval > 0 &&
1391 time_since_last > AsyncDeflationInterval &&
1392 monitors_used_above_threshold(&_in_use_list)) {
1393 // It's been longer than our specified deflate interval and there
1394 // are too many monitors in use. We don't deflate more frequently
1395 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1396 // in order to not swamp the MonitorDeflationThread.
1397 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1398 return true;
1399 }
1400
1401 if (GuaranteedAsyncDeflationInterval > 0 &&
1402 time_since_last > GuaranteedAsyncDeflationInterval) {
1403 // It's been longer than our specified guaranteed deflate interval.
1404 // We need to clean up the used monitors even if the threshold is
1405 // not reached, to keep the memory utilization at bay when many threads
1406 // touched many monitors.
1407 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
1408 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1409 GuaranteedAsyncDeflationInterval, time_since_last);
1410
1411 // If this deflation has no progress, then it should not affect the no-progress
1412 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1413 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1414 // the generic code would bump the no-progress counter, and we compensate for that
1415 // by telling it to skip the update.
1416 //
1417 // If this deflation has progress, then it should let non-progress tracking
1418 // know about this, otherwise the threshold heuristics would kick in, potentially
1419 // experience no-progress due to aggressive cleanup by this deflation, and think
1420 // it is still in no-progress stride. In this "progress" case, the generic code would
1421 // zero the counter, and we allow it to happen.
1422 _no_progress_skip_increment = true;
1423
1424 return true;
1425 }
1426
1427 return false;
1428 }
1429
1430 void ObjectSynchronizer::request_deflate_idle_monitors() {
1431 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1432 set_is_async_deflation_requested(true);
1433 ml.notify_all();
1434 }
1435
1436 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1437 JavaThread* current = JavaThread::current();
1438 bool ret_code = false;
1439
1440 jlong last_time = last_async_deflation_time_ns();
1441
1442 request_deflate_idle_monitors();
1443
1444 const int N_CHECKS = 5;
1445 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1446 if (last_async_deflation_time_ns() > last_time) {
1447 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1448 ret_code = true;
1449 break;
1450 }
1451 {
1452 // JavaThread has to honor the blocking protocol.
1453 ThreadBlockInVM tbivm(current);
1454 os::naked_short_sleep(999); // sleep for almost 1 second
1455 }
1456 }
1457 if (!ret_code) {
1458 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1459 }
1460
1461 return ret_code;
1462 }
1463
1464 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1465 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1466 }
1467
1468 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1469 const oop obj,
1470 ObjectSynchronizer::InflateCause cause) {
1471 assert(event != nullptr, "invariant");
1472 const Klass* monitor_klass = obj->klass();
1473 if (ObjectMonitor::is_jfr_excluded(monitor_klass)) {
1474 return;
1475 }
1476 event->set_monitorClass(monitor_klass);
1477 event->set_address((uintptr_t)(void*)obj);
1478 event->set_cause((u1)cause);
1479 event->commit();
1480 }
1481
1482 // Fast path code shared by multiple functions
1483 void ObjectSynchronizer::inflate_helper(oop obj) {
1484 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1485 markWord mark = obj->mark_acquire();
1486 if (mark.has_monitor()) {
1487 ObjectMonitor* monitor = read_monitor(mark);
1488 markWord dmw = monitor->header();
1489 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1490 return;
1491 }
1492 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1493 }
1494
1495 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1496 assert(current == Thread::current(), "must be");
1497 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1498 return inflate_impl(current->is_Java_thread() ? JavaThread::cast(current) : nullptr, obj, cause);
1499 }
1500
1501 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1502 assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1503 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_for");
1504 return inflate_impl(thread, obj, cause);
1505 }
1506
1507 ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* locking_thread, oop object, const InflateCause cause) {
1508 if (EnableValhalla) {
1509 guarantee(!object->klass()->is_inline_klass(), "Attempt to inflate inline type");
1510 }
1511 // The JavaThread* locking_thread requires that the locking_thread == Thread::current() or
1512 // is suspended throughout the call by some other mechanism.
1513 // The thread might be nullptr when called from a non JavaThread. (As may still be
1514 // the case from FastHashCode). However it is only important for correctness that the
1515 // thread is set when called from ObjectSynchronizer::enter from the owning thread,
1516 // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
1517 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_impl");
1518 EventJavaMonitorInflate event;
1519
1520 for (;;) {
1521 const markWord mark = object->mark_acquire();
1522
1523 // The mark can be in one of the following states:
1524 // * inflated - If the ObjectMonitor owner is anonymous and the
1525 // locking_thread owns the object lock, then we
1526 // make the locking_thread the ObjectMonitor owner.
1527 // * stack-locked - Coerce it to inflated from stack-locked.
1528 // * INFLATING - Busy wait for conversion from stack-locked to
1529 // inflated.
1530 // * unlocked - Aggressively inflate the object.
1531
1532 // CASE: inflated
1533 if (mark.has_monitor()) {
1534 ObjectMonitor* inf = mark.monitor();
1535 markWord dmw = inf->header();
1536 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1537 if (inf->has_anonymous_owner() && locking_thread != nullptr) {
1538 assert(LockingMode == LM_LEGACY, "invariant");
1539 if (locking_thread->is_lock_owned((address)inf->stack_locker())) {
1540 inf->set_stack_locker(nullptr);
1541 inf->set_owner_from_anonymous(locking_thread);
1542 }
1543 }
1544 return inf;
1545 }
1546
1547 // CASE: inflation in progress - inflating over a stack-lock.
1548 // Some other thread is converting from stack-locked to inflated.
1549 // Only that thread can complete inflation -- other threads must wait.
1550 // The INFLATING value is transient.
1551 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1552 // We could always eliminate polling by parking the thread on some auxiliary list.
1553 if (mark == markWord::INFLATING()) {
1554 read_stable_mark(object);
1555 continue;
1556 }
1557
1558 // CASE: stack-locked
1559 // Could be stack-locked either by current or by some other thread.
1560 //
1561 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1562 // to install INFLATING into the mark word. We originally installed INFLATING,
1563 // allocated the ObjectMonitor, and then finally STed the address of the
1564 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1565 // the interval in which INFLATING appeared in the mark, thus increasing
1566 // the odds of inflation contention. If we lose the race to set INFLATING,
1567 // then we just delete the ObjectMonitor and loop around again.
1568 //
1569 LogStreamHandle(Trace, monitorinflation) lsh;
1570 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1571 ObjectMonitor* m = new ObjectMonitor(object);
1572 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1573 // We do this before the CAS in order to minimize the length of time
1574 // in which INFLATING appears in the mark.
1575
1576 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1577 if (cmp != mark) {
1578 delete m;
1579 continue; // Interference -- just retry
1580 }
1581
1582 // We've successfully installed INFLATING (0) into the mark-word.
1583 // This is the only case where 0 will appear in a mark-word.
1584 // Only the singular thread that successfully swings the mark-word
1585 // to 0 can perform (or more precisely, complete) inflation.
1586 //
1587 // Why do we CAS a 0 into the mark-word instead of just CASing the
1588 // mark-word from the stack-locked value directly to the new inflated state?
1589 // Consider what happens when a thread unlocks a stack-locked object.
1590 // It attempts to use CAS to swing the displaced header value from the
1591 // on-stack BasicLock back into the object header. Recall also that the
1592 // header value (hash code, etc) can reside in (a) the object header, or
1593 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1594 // header in an ObjectMonitor. The inflate() routine must copy the header
1595 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1596 // the while preserving the hashCode stability invariants. If the owner
1597 // decides to release the lock while the value is 0, the unlock will fail
1598 // and control will eventually pass from slow_exit() to inflate. The owner
1599 // will then spin, waiting for the 0 value to disappear. Put another way,
1600 // the 0 causes the owner to stall if the owner happens to try to
1601 // drop the lock (restoring the header from the BasicLock to the object)
1602 // while inflation is in-progress. This protocol avoids races that might
1603 // would otherwise permit hashCode values to change or "flicker" for an object.
1604 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1605 // 0 serves as a "BUSY" inflate-in-progress indicator.
1606
1607
1608 // fetch the displaced mark from the owner's stack.
1609 // The owner can't die or unwind past the lock while our INFLATING
1610 // object is in the mark. Furthermore the owner can't complete
1611 // an unlock on the object, either.
1612 markWord dmw = mark.displaced_mark_helper();
1613 // Catch if the object's header is not neutral (not locked and
1614 // not marked is what we care about here).
1615 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1616
1617 // Setup monitor fields to proper values -- prepare the monitor
1618 m->set_header(dmw);
1619
1620 // Note that a thread can inflate an object
1621 // that it has stack-locked -- as might happen in wait() -- directly
1622 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1623 if (locking_thread != nullptr && locking_thread->is_lock_owned((address)mark.locker())) {
1624 m->set_owner(locking_thread);
1625 } else {
1626 // Use ANONYMOUS_OWNER to indicate that the owner is the BasicLock on the stack,
1627 // and set the stack locker field in the monitor.
1628 m->set_stack_locker(mark.locker());
1629 m->set_anonymous_owner();
1630 }
1631 // TODO-FIXME: assert BasicLock->dhw != 0.
1632
1633 // Must preserve store ordering. The monitor state must
1634 // be stable at the time of publishing the monitor address.
1635 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1636 // Release semantics so that above set_object() is seen first.
1637 object->release_set_mark(markWord::encode(m));
1638
1639 // Once ObjectMonitor is configured and the object is associated
1640 // with the ObjectMonitor, it is safe to allow async deflation:
1641 _in_use_list.add(m);
1642
1643 if (log_is_enabled(Trace, monitorinflation)) {
1644 ResourceMark rm;
1645 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1646 INTPTR_FORMAT ", type='%s'", p2i(object),
1647 object->mark().value(), object->klass()->external_name());
1648 }
1649 if (event.should_commit()) {
1650 post_monitor_inflate_event(&event, object, cause);
1651 }
1652 return m;
1653 }
1654
1655 // CASE: unlocked
1656 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1657 // If we know we're inflating for entry it's better to inflate by swinging a
1658 // pre-locked ObjectMonitor pointer into the object header. A successful
1659 // CAS inflates the object *and* confers ownership to the inflating thread.
1660 // In the current implementation we use a 2-step mechanism where we CAS()
1661 // to inflate and then CAS() again to try to swing _owner from null to current.
1662 // An inflateTry() method that we could call from enter() would be useful.
1663
1664 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
1665 ObjectMonitor* m = new ObjectMonitor(object);
1666 // prepare m for installation - set monitor to initial state
1667 m->set_header(mark);
1668
1669 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1670 delete m;
1671 m = nullptr;
1672 continue;
1673 // interference - the markword changed - just retry.
1674 // The state-transitions are one-way, so there's no chance of
1675 // live-lock -- "Inflated" is an absorbing state.
1676 }
1677
1678 // Once the ObjectMonitor is configured and object is associated
1679 // with the ObjectMonitor, it is safe to allow async deflation:
1680 _in_use_list.add(m);
1681
1682 if (log_is_enabled(Trace, monitorinflation)) {
1683 ResourceMark rm;
1684 lsh.print_cr("inflate(unlocked): object=" INTPTR_FORMAT ", mark="
1685 INTPTR_FORMAT ", type='%s'", p2i(object),
1686 object->mark().value(), object->klass()->external_name());
1687 }
1688 if (event.should_commit()) {
1689 post_monitor_inflate_event(&event, object, cause);
1690 }
1691 return m;
1692 }
1693 }
1694
1695 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1696 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1697 //
1698 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1699 MonitorList::Iterator iter = _in_use_list.iterator();
1700 size_t deflated_count = 0;
1701 Thread* current = Thread::current();
1702
1703 while (iter.has_next()) {
1704 if (deflated_count >= (size_t)MonitorDeflationMax) {
1705 break;
1706 }
1707 ObjectMonitor* mid = iter.next();
1708 if (mid->deflate_monitor(current)) {
1709 deflated_count++;
1710 }
1711
1712 // Must check for a safepoint/handshake and honor it.
1713 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1714 }
1715
1716 return deflated_count;
1717 }
1718
1719 class HandshakeForDeflation : public HandshakeClosure {
1720 public:
1721 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1722
1723 void do_thread(Thread* thread) {
1724 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1725 INTPTR_FORMAT, p2i(thread));
1726 if (thread->is_Java_thread()) {
1727 // Clear OM cache
1728 JavaThread* jt = JavaThread::cast(thread);
1729 jt->om_clear_monitor_cache();
1730 }
1731 }
1732 };
1733
1734 class VM_RendezvousGCThreads : public VM_Operation {
1735 public:
1736 bool evaluate_at_safepoint() const override { return false; }
1737 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1738 void doit() override {
1739 Universe::heap()->safepoint_synchronize_begin();
1740 Universe::heap()->safepoint_synchronize_end();
1741 };
1742 };
1743
1744 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1745 ObjectMonitorDeflationSafepointer* safepointer) {
1746 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1747 size_t deleted_count = 0;
1748 for (ObjectMonitor* monitor: *delete_list) {
1749 delete monitor;
1750 deleted_count++;
1751 // A JavaThread must check for a safepoint/handshake and honor it.
1752 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1753 }
1754 return deleted_count;
1755 }
1756
1757 class ObjectMonitorDeflationLogging: public StackObj {
1758 LogStreamHandle(Debug, monitorinflation) _debug;
1759 LogStreamHandle(Info, monitorinflation) _info;
1760 LogStream* _stream;
1761 elapsedTimer _timer;
1762
1763 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1764 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1765 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1766
1767 public:
1768 ObjectMonitorDeflationLogging()
1769 : _debug(), _info(), _stream(nullptr) {
1770 if (_debug.is_enabled()) {
1771 _stream = &_debug;
1772 } else if (_info.is_enabled()) {
1773 _stream = &_info;
1774 }
1775 }
1776
1777 void begin() {
1778 if (_stream != nullptr) {
1779 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1780 ceiling(), count(), max());
1781 _timer.start();
1782 }
1783 }
1784
1785 void before_handshake(size_t unlinked_count) {
1786 if (_stream != nullptr) {
1787 _timer.stop();
1788 _stream->print_cr("before handshaking: unlinked_count=%zu"
1789 ", in_use_list stats: ceiling=%zu, count="
1790 "%zu, max=%zu",
1791 unlinked_count, ceiling(), count(), max());
1792 }
1793 }
1794
1795 void after_handshake() {
1796 if (_stream != nullptr) {
1797 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1798 "%zu, count=%zu, max=%zu",
1799 ceiling(), count(), max());
1800 _timer.start();
1801 }
1802 }
1803
1804 void end(size_t deflated_count, size_t unlinked_count) {
1805 if (_stream != nullptr) {
1806 _timer.stop();
1807 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1808 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1809 deflated_count, unlinked_count, _timer.seconds());
1810 }
1811 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1812 ceiling(), count(), max());
1813 }
1814 }
1815
1816 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1817 if (_stream != nullptr) {
1818 _timer.stop();
1819 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1820 "%zu, count=%zu, max=%zu",
1821 op_name, cnt_name, cnt, ceiling(), count(), max());
1822 }
1823 }
1824
1825 void after_block_for_safepoint(const char* op_name) {
1826 if (_stream != nullptr) {
1827 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1828 ", count=%zu, max=%zu", op_name,
1829 ceiling(), count(), max());
1830 _timer.start();
1831 }
1832 }
1833 };
1834
1835 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1836 if (!SafepointMechanism::should_process(_current)) {
1837 return;
1838 }
1839
1840 // A safepoint/handshake has started.
1841 _log->before_block_for_safepoint(op_name, count_name, counter);
1842
1843 {
1844 // Honor block request.
1845 ThreadBlockInVM tbivm(_current);
1846 }
1847
1848 _log->after_block_for_safepoint(op_name);
1849 }
1850
1851 // This function is called by the MonitorDeflationThread to deflate
1852 // ObjectMonitors.
1853 size_t ObjectSynchronizer::deflate_idle_monitors() {
1854 JavaThread* current = JavaThread::current();
1855 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1856
1857 // The async deflation request has been processed.
1858 _last_async_deflation_time_ns = os::javaTimeNanos();
1859 set_is_async_deflation_requested(false);
1860
1861 ObjectMonitorDeflationLogging log;
1862 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1863
1864 log.begin();
1865
1866 // Deflate some idle ObjectMonitors.
1867 size_t deflated_count = deflate_monitor_list(&safepointer);
1868
1869 // Unlink the deflated ObjectMonitors from the in-use list.
1870 size_t unlinked_count = 0;
1871 size_t deleted_count = 0;
1872 if (deflated_count > 0) {
1873 ResourceMark rm(current);
1874 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1875 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1876
1877 #ifdef ASSERT
1878 if (UseObjectMonitorTable) {
1879 for (ObjectMonitor* monitor : delete_list) {
1880 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1881 }
1882 }
1883 #endif
1884
1885 log.before_handshake(unlinked_count);
1886
1887 // A JavaThread needs to handshake in order to safely free the
1888 // ObjectMonitors that were deflated in this cycle.
1889 HandshakeForDeflation hfd_hc;
1890 Handshake::execute(&hfd_hc);
1891 // Also, we sync and desync GC threads around the handshake, so that they can
1892 // safely read the mark-word and look-through to the object-monitor, without
1893 // being afraid that the object-monitor is going away.
1894 VM_RendezvousGCThreads sync_gc;
1895 VMThread::execute(&sync_gc);
1896
1897 log.after_handshake();
1898
1899 // After the handshake, safely free the ObjectMonitors that were
1900 // deflated and unlinked in this cycle.
1901
1902 // Delete the unlinked ObjectMonitors.
1903 deleted_count = delete_monitors(&delete_list, &safepointer);
1904 assert(unlinked_count == deleted_count, "must be");
1905 }
1906
1907 log.end(deflated_count, unlinked_count);
1908
1909 GVars.stw_random = os::random();
1910
1911 if (deflated_count != 0) {
1912 _no_progress_cnt = 0;
1913 } else if (_no_progress_skip_increment) {
1914 _no_progress_skip_increment = false;
1915 } else {
1916 _no_progress_cnt++;
1917 }
1918
1919 return deflated_count;
1920 }
1921
1922 // Monitor cleanup on JavaThread::exit
1923
1924 // Iterate through monitor cache and attempt to release thread's monitors
1925 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1926 private:
1927 JavaThread* _thread;
1928
1929 public:
1930 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1931 void do_monitor(ObjectMonitor* mid) {
1932 intx rec = mid->complete_exit(_thread);
1933 _thread->dec_held_monitor_count(rec + 1);
1934 }
1935 };
1936
1937 // Release all inflated monitors owned by current thread. Lightweight monitors are
1938 // ignored. This is meant to be called during JNI thread detach which assumes
1939 // all remaining monitors are heavyweight. All exceptions are swallowed.
1940 // Scanning the extant monitor list can be time consuming.
1941 // A simple optimization is to add a per-thread flag that indicates a thread
1942 // called jni_monitorenter() during its lifetime.
1943 //
1944 // Instead of NoSafepointVerifier it might be cheaper to
1945 // use an idiom of the form:
1946 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1947 // <code that must not run at safepoint>
1948 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1949 // Since the tests are extremely cheap we could leave them enabled
1950 // for normal product builds.
1951
1952 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1953 assert(current == JavaThread::current(), "must be current Java thread");
1954 NoSafepointVerifier nsv;
1955 ReleaseJavaMonitorsClosure rjmc(current);
1956 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1957 assert(!current->has_pending_exception(), "Should not be possible");
1958 current->clear_pending_exception();
1959 assert(current->held_monitor_count() == 0, "Should not be possible");
1960 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1961 current->clear_jni_monitor_count();
1962 }
1963
1964 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1965 switch (cause) {
1966 case inflate_cause_vm_internal: return "VM Internal";
1967 case inflate_cause_monitor_enter: return "Monitor Enter";
1968 case inflate_cause_wait: return "Monitor Wait";
1969 case inflate_cause_notify: return "Monitor Notify";
1970 case inflate_cause_hash_code: return "Monitor Hash Code";
1971 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1972 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1973 default:
1974 ShouldNotReachHere();
1975 }
1976 return "Unknown";
1977 }
1978
1979 //------------------------------------------------------------------------------
1980 // Debugging code
1981
1982 u_char* ObjectSynchronizer::get_gvars_addr() {
1983 return (u_char*)&GVars;
1984 }
1985
1986 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1987 return (u_char*)&GVars.hc_sequence;
1988 }
1989
1990 size_t ObjectSynchronizer::get_gvars_size() {
1991 return sizeof(SharedGlobals);
1992 }
1993
1994 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1995 return (u_char*)&GVars.stw_random;
1996 }
1997
1998 // Do the final audit and print of ObjectMonitor stats; must be done
1999 // by the VMThread at VM exit time.
2000 void ObjectSynchronizer::do_final_audit_and_print_stats() {
2001 assert(Thread::current()->is_VM_thread(), "sanity check");
2002
2003 if (is_final_audit()) { // Only do the audit once.
2004 return;
2005 }
2006 set_is_final_audit();
2007 log_info(monitorinflation)("Starting the final audit.");
2008
2009 if (log_is_enabled(Info, monitorinflation)) {
2010 LogStreamHandle(Info, monitorinflation) ls;
2011 audit_and_print_stats(&ls, true /* on_exit */);
2012 }
2013 }
2014
2015 // This function can be called by the MonitorDeflationThread or it can be called when
2016 // we are trying to exit the VM. The list walker functions can run in parallel with
2017 // the other list operations.
2018 // Calls to this function can be added in various places as a debugging
2019 // aid.
2020 //
2021 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
2022 int error_cnt = 0;
2023
2024 ls->print_cr("Checking in_use_list:");
2025 chk_in_use_list(ls, &error_cnt);
2026
2027 if (error_cnt == 0) {
2028 ls->print_cr("No errors found in in_use_list checks.");
2029 } else {
2030 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
2031 }
2032
2033 // When exiting, only log the interesting entries at the Info level.
2034 // When called at intervals by the MonitorDeflationThread, log output
2035 // at the Trace level since there can be a lot of it.
2036 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
2037 LogStreamHandle(Trace, monitorinflation) ls_tr;
2038 log_in_use_monitor_details(&ls_tr, true /* log_all */);
2039 } else if (on_exit) {
2040 log_in_use_monitor_details(ls, false /* log_all */);
2041 }
2042
2043 ls->flush();
2044
2045 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2046 }
2047
2048 // Check the in_use_list; log the results of the checks.
2049 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
2050 size_t l_in_use_count = _in_use_list.count();
2051 size_t l_in_use_max = _in_use_list.max();
2052 out->print_cr("count=%zu, max=%zu", l_in_use_count,
2053 l_in_use_max);
2054
2055 size_t ck_in_use_count = 0;
2056 MonitorList::Iterator iter = _in_use_list.iterator();
2057 while (iter.has_next()) {
2058 ObjectMonitor* mid = iter.next();
2059 chk_in_use_entry(mid, out, error_cnt_p);
2060 ck_in_use_count++;
2061 }
2062
2063 if (l_in_use_count == ck_in_use_count) {
2064 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
2065 l_in_use_count, ck_in_use_count);
2066 } else {
2067 out->print_cr("WARNING: in_use_count=%zu is not equal to "
2068 "ck_in_use_count=%zu", l_in_use_count,
2069 ck_in_use_count);
2070 }
2071
2072 size_t ck_in_use_max = _in_use_list.max();
2073 if (l_in_use_max == ck_in_use_max) {
2074 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
2075 l_in_use_max, ck_in_use_max);
2076 } else {
2077 out->print_cr("WARNING: in_use_max=%zu is not equal to "
2078 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
2079 }
2080 }
2081
2082 // Check an in-use monitor entry; log any errors.
2083 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2084 int* error_cnt_p) {
2085 if (n->owner_is_DEFLATER_MARKER()) {
2086 // This could happen when monitor deflation blocks for a safepoint.
2087 return;
2088 }
2089
2090
2091 if (n->metadata() == 0) {
2092 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2093 "have non-null _metadata (header/hash) field.", p2i(n));
2094 *error_cnt_p = *error_cnt_p + 1;
2095 }
2096
2097 const oop obj = n->object_peek();
2098 if (obj == nullptr) {
2099 return;
2100 }
2101
2102 const markWord mark = obj->mark();
2103 if (!mark.has_monitor()) {
2104 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2105 "object does not think it has a monitor: obj="
2106 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2107 p2i(obj), mark.value());
2108 *error_cnt_p = *error_cnt_p + 1;
2109 return;
2110 }
2111
2112 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
2113 if (n != obj_mon) {
2114 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2115 "object does not refer to the same monitor: obj="
2116 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2117 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2118 *error_cnt_p = *error_cnt_p + 1;
2119 }
2120 }
2121
2122 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2123 // flags indicate why the entry is in-use, 'object' and 'object type'
2124 // indicate the associated object and its type.
2125 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2126 if (_in_use_list.count() > 0) {
2127 stringStream ss;
2128 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
2129 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2130 out->print_cr("%18s %s %18s %18s",
2131 "monitor", "BHL", "object", "object type");
2132 out->print_cr("================== === ================== ==================");
2133
2134 auto is_interesting = [&](ObjectMonitor* monitor) {
2135 return log_all || monitor->has_owner() || monitor->is_busy();
2136 };
2137
2138 monitors_iterate([&](ObjectMonitor* monitor) {
2139 if (is_interesting(monitor)) {
2140 const oop obj = monitor->object_peek();
2141 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
2142 ResourceMark rm;
2143 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
2144 monitor->is_busy(), hash != 0, monitor->has_owner(),
2145 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2146 if (monitor->is_busy()) {
2147 out->print(" (%s)", monitor->is_busy_to_string(&ss));
2148 ss.reset();
2149 }
2150 out->cr();
2151 }
2152 });
2153 }
2154
2155 out->flush();
2156 }