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