1 /*
2 * Copyright (c) 1998, 2025, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "classfile/vmSymbols.hpp"
26 #include "gc/shared/collectedHeap.hpp"
27 #include "jfr/jfrEvents.hpp"
28 #include "logging/log.hpp"
29 #include "logging/logStream.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/padded.hpp"
32 #include "memory/resourceArea.hpp"
33 #include "memory/universe.hpp"
34 #include "oops/markWord.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "runtime/atomic.hpp"
37 #include "runtime/basicLock.inline.hpp"
38 #include "runtime/frame.inline.hpp"
39 #include "runtime/globals.hpp"
40 #include "runtime/handles.inline.hpp"
41 #include "runtime/handshake.hpp"
42 #include "runtime/interfaceSupport.inline.hpp"
43 #include "runtime/javaThread.hpp"
44 #include "runtime/lightweightSynchronizer.hpp"
45 #include "runtime/lockStack.inline.hpp"
46 #include "runtime/mutexLocker.hpp"
47 #include "runtime/objectMonitor.hpp"
48 #include "runtime/objectMonitor.inline.hpp"
49 #include "runtime/os.inline.hpp"
50 #include "runtime/osThread.hpp"
51 #include "runtime/safepointMechanism.inline.hpp"
52 #include "runtime/safepointVerifiers.hpp"
53 #include "runtime/sharedRuntime.hpp"
54 #include "runtime/stubRoutines.hpp"
55 #include "runtime/synchronizer.inline.hpp"
56 #include "runtime/threads.hpp"
57 #include "runtime/timer.hpp"
58 #include "runtime/trimNativeHeap.hpp"
59 #include "runtime/vframe.hpp"
60 #include "runtime/vmThread.hpp"
61 #include "utilities/align.hpp"
62 #include "utilities/dtrace.hpp"
63 #include "utilities/events.hpp"
64 #include "utilities/globalCounter.inline.hpp"
65 #include "utilities/globalDefinitions.hpp"
66 #include "utilities/linkedlist.hpp"
67 #include "utilities/preserveException.hpp"
68
69 class ObjectMonitorDeflationLogging;
70
71 void MonitorList::add(ObjectMonitor* m) {
72 ObjectMonitor* head;
73 do {
74 head = Atomic::load(&_head);
75 m->set_next_om(head);
76 } while (Atomic::cmpxchg(&_head, head, m) != head);
77
78 size_t count = Atomic::add(&_count, 1u, memory_order_relaxed);
79 size_t old_max;
80 do {
81 old_max = Atomic::load(&_max);
82 if (count <= old_max) {
83 break;
84 }
85 } while (Atomic::cmpxchg(&_max, old_max, count, memory_order_relaxed) != old_max);
86 }
87
88 size_t MonitorList::count() const {
89 return Atomic::load(&_count);
90 }
91
92 size_t MonitorList::max() const {
93 return Atomic::load(&_max);
94 }
95
96 class ObjectMonitorDeflationSafepointer : public StackObj {
97 JavaThread* const _current;
98 ObjectMonitorDeflationLogging* const _log;
99
100 public:
101 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
102 : _current(current), _log(log) {}
103
104 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
105 };
106
107 // Walk the in-use list and unlink deflated ObjectMonitors.
108 // Returns the number of unlinked ObjectMonitors.
109 size_t MonitorList::unlink_deflated(size_t deflated_count,
110 GrowableArray<ObjectMonitor*>* unlinked_list,
111 ObjectMonitorDeflationSafepointer* safepointer) {
112 size_t unlinked_count = 0;
113 ObjectMonitor* prev = nullptr;
114 ObjectMonitor* m = Atomic::load_acquire(&_head);
115
116 while (m != nullptr) {
117 if (m->is_being_async_deflated()) {
118 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
119 // modify the list once per batch. The batch starts at "m".
120 size_t unlinked_batch = 0;
121 ObjectMonitor* next = m;
122 // Look for at most MonitorUnlinkBatch monitors, or the number of
123 // deflated and not unlinked monitors, whatever comes first.
124 assert(deflated_count >= unlinked_count, "Sanity: underflow");
125 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
126 do {
127 ObjectMonitor* next_next = next->next_om();
128 unlinked_batch++;
129 unlinked_list->append(next);
130 next = next_next;
131 if (unlinked_batch >= unlinked_batch_limit) {
132 // Reached the max batch, so bail out of the gathering loop.
133 break;
134 }
135 if (prev == nullptr && Atomic::load(&_head) != m) {
136 // Current batch used to be at head, but it is not at head anymore.
137 // Bail out and figure out where we currently are. This avoids long
138 // walks searching for new prev during unlink under heavy list inserts.
139 break;
140 }
141 } while (next != nullptr && next->is_being_async_deflated());
142
143 // Unlink the found batch.
144 if (prev == nullptr) {
145 // The current batch is the first batch, so there is a chance that it starts at head.
146 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
147 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, m, next);
148 if (prev_head != m) {
149 // Something must have updated the head. Figure out the actual prev for this batch.
150 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
151 prev = n;
152 }
153 assert(prev != nullptr, "Should have found the prev for the current batch");
154 prev->set_next_om(next);
155 }
156 } else {
157 // The current batch is preceded by another batch. This guarantees the current batch
158 // does not start at head. Unlink the entire current batch without updating the head.
159 assert(Atomic::load(&_head) != m, "Sanity");
160 prev->set_next_om(next);
161 }
162
163 unlinked_count += unlinked_batch;
164 if (unlinked_count >= deflated_count) {
165 // Reached the max so bail out of the searching loop.
166 // There should be no more deflated monitors left.
167 break;
168 }
169 m = next;
170 } else {
171 prev = m;
172 m = m->next_om();
173 }
174
175 // Must check for a safepoint/handshake and honor it.
176 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
177 }
178
179 #ifdef ASSERT
180 // Invariant: the code above should unlink all deflated monitors.
181 // The code that runs after this unlinking does not expect deflated monitors.
182 // Notably, attempting to deflate the already deflated monitor would break.
183 {
184 ObjectMonitor* m = Atomic::load_acquire(&_head);
185 while (m != nullptr) {
186 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
187 m = m->next_om();
188 }
189 }
190 #endif
191
192 Atomic::sub(&_count, unlinked_count);
193 return unlinked_count;
194 }
195
196 MonitorList::Iterator MonitorList::iterator() const {
197 return Iterator(Atomic::load_acquire(&_head));
198 }
199
200 ObjectMonitor* MonitorList::Iterator::next() {
201 ObjectMonitor* current = _current;
202 _current = current->next_om();
203 return current;
204 }
205
206 // The "core" versions of monitor enter and exit reside in this file.
207 // The interpreter and compilers contain specialized transliterated
208 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
209 // fast_lock(...) for instance. If you make changes here, make sure to modify the
210 // interpreter, and both C1 and C2 fast-path inline locking code emission.
211 //
212 // -----------------------------------------------------------------------------
213
214 #ifdef DTRACE_ENABLED
215
216 // Only bother with this argument setup if dtrace is available
217 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
218
219 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
220 char* bytes = nullptr; \
221 int len = 0; \
222 jlong jtid = SharedRuntime::get_java_tid(thread); \
223 Symbol* klassname = obj->klass()->name(); \
224 if (klassname != nullptr) { \
225 bytes = (char*)klassname->bytes(); \
226 len = klassname->utf8_length(); \
227 }
228
229 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
230 { \
231 if (DTraceMonitorProbes) { \
232 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
233 HOTSPOT_MONITOR_WAIT(jtid, \
234 (uintptr_t)(monitor), bytes, len, (millis)); \
235 } \
236 }
237
238 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
239 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
240 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
241
242 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
243 { \
244 if (DTraceMonitorProbes) { \
245 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
246 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
247 (uintptr_t)(monitor), bytes, len); \
248 } \
249 }
250
251 #else // ndef DTRACE_ENABLED
252
253 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
254 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
255
256 #endif // ndef DTRACE_ENABLED
257
258 // This exists only as a workaround of dtrace bug 6254741
259 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
260 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
261 return 0;
262 }
263
264 static constexpr size_t inflation_lock_count() {
265 return 256;
266 }
267
268 // Static storage for an array of PlatformMutex.
269 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
270
271 static inline PlatformMutex* inflation_lock(size_t index) {
272 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
273 }
274
275 void ObjectSynchronizer::initialize() {
276 for (size_t i = 0; i < inflation_lock_count(); i++) {
277 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
278 }
279 // Start the ceiling with the estimate for one thread.
280 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
281
282 // Start the timer for deflations, so it does not trigger immediately.
283 _last_async_deflation_time_ns = os::javaTimeNanos();
284
285 if (LockingMode == LM_LIGHTWEIGHT) {
286 LightweightSynchronizer::initialize();
287 }
288 }
289
290 MonitorList ObjectSynchronizer::_in_use_list;
291 // monitors_used_above_threshold() policy is as follows:
292 //
293 // The ratio of the current _in_use_list count to the ceiling is used
294 // to determine if we are above MonitorUsedDeflationThreshold and need
295 // to do an async monitor deflation cycle. The ceiling is increased by
296 // AvgMonitorsPerThreadEstimate when a thread is added to the system
297 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
298 // removed from the system.
299 //
300 // Note: If the _in_use_list max exceeds the ceiling, then
301 // monitors_used_above_threshold() will use the in_use_list max instead
302 // of the thread count derived ceiling because we have used more
303 // ObjectMonitors than the estimated average.
304 //
305 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
306 // no-progress async monitor deflation cycles in a row, then the ceiling
307 // is adjusted upwards by monitors_used_above_threshold().
308 //
309 // Start the ceiling with the estimate for one thread in initialize()
310 // which is called after cmd line options are processed.
311 static size_t _in_use_list_ceiling = 0;
312 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
313 bool volatile ObjectSynchronizer::_is_final_audit = false;
314 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
315 static uintx _no_progress_cnt = 0;
316 static bool _no_progress_skip_increment = false;
317
318 // =====================> Quick functions
319
320 // The quick_* forms are special fast-path variants used to improve
321 // performance. In the simplest case, a "quick_*" implementation could
322 // simply return false, in which case the caller will perform the necessary
323 // state transitions and call the slow-path form.
324 // The fast-path is designed to handle frequently arising cases in an efficient
325 // manner and is just a degenerate "optimistic" variant of the slow-path.
326 // returns true -- to indicate the call was satisfied.
327 // returns false -- to indicate the call needs the services of the slow-path.
328 // A no-loitering ordinance is in effect for code in the quick_* family
329 // operators: safepoints or indefinite blocking (blocking that might span a
330 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
331 // entry.
332 //
333 // Consider: An interesting optimization is to have the JIT recognize the
334 // following common idiom:
335 // synchronized (someobj) { .... ; notify(); }
336 // That is, we find a notify() or notifyAll() call that immediately precedes
337 // the monitorexit operation. In that case the JIT could fuse the operations
338 // into a single notifyAndExit() runtime primitive.
339
340 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
341 assert(current->thread_state() == _thread_in_Java, "invariant");
342 NoSafepointVerifier nsv;
343 if (obj == nullptr) return false; // slow-path for invalid obj
344 const markWord mark = obj->mark();
345
346 if (LockingMode == LM_LIGHTWEIGHT) {
347 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
348 // Degenerate notify
349 // fast-locked by caller so by definition the implied waitset is empty.
350 return true;
351 }
352 } else if (LockingMode == LM_LEGACY) {
353 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
354 // Degenerate notify
355 // stack-locked by caller so by definition the implied waitset is empty.
356 return true;
357 }
358 }
359
360 if (mark.has_monitor()) {
361 ObjectMonitor* const mon = read_monitor(current, obj, mark);
362 if (LockingMode == LM_LIGHTWEIGHT && mon == nullptr) {
363 // Racing with inflation/deflation go slow path
364 return false;
365 }
366 assert(mon->object() == oop(obj), "invariant");
367 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
368
369 if (mon->first_waiter() != nullptr) {
370 // We have one or more waiters. Since this is an inflated monitor
371 // that we own, we quickly notify them here and now, avoiding the slow-path.
372 if (all) {
373 mon->quick_notifyAll(current);
374 } else {
375 mon->quick_notify(current);
376 }
377 }
378 return true;
379 }
380
381 // other IMS exception states take the slow-path
382 return false;
383 }
384
385 static bool useHeavyMonitors() {
386 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
387 return LockingMode == LM_MONITOR;
388 #else
389 return false;
390 #endif
391 }
392
393 // The LockNode emitted directly at the synchronization site would have
394 // been too big if it were to have included support for the cases of inflated
395 // recursive enter and exit, so they go here instead.
396 // Note that we can't safely call AsyncPrintJavaStack() from within
397 // quick_enter() as our thread state remains _in_Java.
398
399 bool ObjectSynchronizer::quick_enter_legacy(oop obj, BasicLock* lock, JavaThread* current) {
400 assert(current->thread_state() == _thread_in_Java, "invariant");
401
402 if (useHeavyMonitors()) {
403 return false; // Slow path
404 }
405
406 assert(LockingMode == LM_LEGACY, "legacy mode below");
407
408 const markWord mark = obj->mark();
409
410 if (mark.has_monitor()) {
411
412 ObjectMonitor* const m = read_monitor(mark);
413 // An async deflation or GC can race us before we manage to make
414 // the ObjectMonitor busy by setting the owner below. If we detect
415 // that race we just bail out to the slow-path here.
416 if (m->object_peek() == nullptr) {
417 return false;
418 }
419
420 // Lock contention and Transactional Lock Elision (TLE) diagnostics
421 // and observability
422 // Case: light contention possibly amenable to TLE
423 // Case: TLE inimical operations such as nested/recursive synchronization
424
425 if (m->has_owner(current)) {
426 m->increment_recursions(current);
427 current->inc_held_monitor_count();
428 return true;
429 }
430
431 // This Java Monitor is inflated so obj's header will never be
432 // displaced to this thread's BasicLock. Make the displaced header
433 // non-null so this BasicLock is not seen as recursive nor as
434 // being locked. We do this unconditionally so that this thread's
435 // BasicLock cannot be mis-interpreted by any stack walkers. For
436 // performance reasons, stack walkers generally first check for
437 // stack-locking in the object's header, the second check is for
438 // recursive stack-locking in the displaced header in the BasicLock,
439 // and last are the inflated Java Monitor (ObjectMonitor) checks.
440 lock->set_displaced_header(markWord::unused_mark());
441
442 if (!m->has_owner() && m->try_set_owner(current)) {
443 assert(m->recursions() == 0, "invariant");
444 current->inc_held_monitor_count();
445 return true;
446 }
447 }
448
449 // Note that we could inflate in quick_enter.
450 // This is likely a useful optimization
451 // Critically, in quick_enter() we must not:
452 // -- block indefinitely, or
453 // -- reach a safepoint
454
455 return false; // revert to slow-path
456 }
457
458 // Handle notifications when synchronizing on value based classes
459 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
460 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
461 frame last_frame = locking_thread->last_frame();
462 bool bcp_was_adjusted = false;
463 // Don't decrement bcp if it points to the frame's first instruction. This happens when
464 // handle_sync_on_value_based_class() is called because of a synchronized method. There
465 // is no actual monitorenter instruction in the byte code in this case.
466 if (last_frame.is_interpreted_frame() &&
467 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
468 // adjust bcp to point back to monitorenter so that we print the correct line numbers
469 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
470 bcp_was_adjusted = true;
471 }
472
473 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
474 ResourceMark rm;
475 stringStream ss;
476 locking_thread->print_active_stack_on(&ss);
477 char* base = (char*)strstr(ss.base(), "at");
478 char* newline = (char*)strchr(ss.base(), '\n');
479 if (newline != nullptr) {
480 *newline = '\0';
481 }
482 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
483 } else {
484 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
485 ResourceMark rm;
486 Log(valuebasedclasses) vblog;
487
488 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
489 if (locking_thread->has_last_Java_frame()) {
490 LogStream info_stream(vblog.info());
491 locking_thread->print_active_stack_on(&info_stream);
492 } else {
493 vblog.info("Cannot find the last Java frame");
494 }
495
496 EventSyncOnValueBasedClass event;
497 if (event.should_commit()) {
498 event.set_valueBasedClass(obj->klass());
499 event.commit();
500 }
501 }
502
503 if (bcp_was_adjusted) {
504 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
505 }
506 }
507
508 // -----------------------------------------------------------------------------
509 // Monitor Enter/Exit
510
511 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
512 // When called with locking_thread != Thread::current() some mechanism must synchronize
513 // the locking_thread with respect to the current thread. Currently only used when
514 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
515 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
516
517 if (LockingMode == LM_LIGHTWEIGHT) {
518 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
519 }
520
521 if (!enter_fast_impl(obj, lock, locking_thread)) {
522 // Inflated ObjectMonitor::enter_for is required
523
524 // An async deflation can race after the inflate_for() call and before
525 // enter_for() can make the ObjectMonitor busy. enter_for() returns false
526 // if we have lost the race to async deflation and we simply try again.
527 while (true) {
528 ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
529 if (monitor->enter_for(locking_thread)) {
530 return;
531 }
532 assert(monitor->is_being_async_deflated(), "must be");
533 }
534 }
535 }
536
537 void ObjectSynchronizer::enter_legacy(Handle obj, BasicLock* lock, JavaThread* current) {
538 if (!enter_fast_impl(obj, lock, current)) {
539 // Inflated ObjectMonitor::enter is required
540
541 // An async deflation can race after the inflate() call and before
542 // enter() can make the ObjectMonitor busy. enter() returns false if
543 // we have lost the race to async deflation and we simply try again.
544 while (true) {
545 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
546 if (monitor->enter(current)) {
547 return;
548 }
549 }
550 }
551 }
552
553 // The interpreter and compiler assembly code tries to lock using the fast path
554 // of this algorithm. Make sure to update that code if the following function is
555 // changed. The implementation is extremely sensitive to race condition. Be careful.
556 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
557 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
558
559 if (obj->klass()->is_value_based()) {
560 handle_sync_on_value_based_class(obj, locking_thread);
561 }
562
563 locking_thread->inc_held_monitor_count();
564
565 if (!useHeavyMonitors()) {
566 if (LockingMode == LM_LEGACY) {
567 markWord mark = obj->mark();
568 if (mark.is_unlocked()) {
569 // Anticipate successful CAS -- the ST of the displaced mark must
570 // be visible <= the ST performed by the CAS.
571 lock->set_displaced_header(mark);
572 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
573 return true;
574 }
575 } else if (mark.has_locker() &&
576 locking_thread->is_lock_owned((address) mark.locker())) {
577 assert(lock != mark.locker(), "must not re-lock the same lock");
578 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
579 lock->set_displaced_header(markWord::from_pointer(nullptr));
580 return true;
581 }
582
583 // The object header will never be displaced to this lock,
584 // so it does not matter what the value is, except that it
585 // must be non-zero to avoid looking like a re-entrant lock,
586 // and must not look locked either.
587 lock->set_displaced_header(markWord::unused_mark());
588
589 // Failed to fast lock.
590 return false;
591 }
592 } else if (VerifyHeavyMonitors) {
593 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
594 }
595
596 return false;
597 }
598
599 void ObjectSynchronizer::exit_legacy(oop object, BasicLock* lock, JavaThread* current) {
600 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
601
602 if (!useHeavyMonitors()) {
603 markWord mark = object->mark();
604 if (LockingMode == LM_LEGACY) {
605 markWord dhw = lock->displaced_header();
606 if (dhw.value() == 0) {
607 // If the displaced header is null, then this exit matches up with
608 // a recursive enter. No real work to do here except for diagnostics.
609 #ifndef PRODUCT
610 if (mark != markWord::INFLATING()) {
611 // Only do diagnostics if we are not racing an inflation. Simply
612 // exiting a recursive enter of a Java Monitor that is being
613 // inflated is safe; see the has_monitor() comment below.
614 assert(!mark.is_unlocked(), "invariant");
615 assert(!mark.has_locker() ||
616 current->is_lock_owned((address)mark.locker()), "invariant");
617 if (mark.has_monitor()) {
618 // The BasicLock's displaced_header is marked as a recursive
619 // enter and we have an inflated Java Monitor (ObjectMonitor).
620 // This is a special case where the Java Monitor was inflated
621 // after this thread entered the stack-lock recursively. When a
622 // Java Monitor is inflated, we cannot safely walk the Java
623 // Monitor owner's stack and update the BasicLocks because a
624 // Java Monitor can be asynchronously inflated by a thread that
625 // does not own the Java Monitor.
626 ObjectMonitor* m = read_monitor(mark);
627 assert(m->object()->mark() == mark, "invariant");
628 assert(m->is_entered(current), "invariant");
629 }
630 }
631 #endif
632 return;
633 }
634
635 if (mark == markWord::from_pointer(lock)) {
636 // If the object is stack-locked by the current thread, try to
637 // swing the displaced header from the BasicLock back to the mark.
638 assert(dhw.is_neutral(), "invariant");
639 if (object->cas_set_mark(dhw, mark) == mark) {
640 return;
641 }
642 }
643 }
644 } else if (VerifyHeavyMonitors) {
645 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
646 }
647
648 // We have to take the slow-path of possible inflation and then exit.
649 // The ObjectMonitor* can't be async deflated until ownership is
650 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
651 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
652 assert(!monitor->has_anonymous_owner(), "must not be");
653 monitor->exit(current);
654 }
655
656 // -----------------------------------------------------------------------------
657 // JNI locks on java objects
658 // NOTE: must use heavy weight monitor to handle jni monitor enter
659 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
660 // Top native frames in the stack will not be seen if we attempt
661 // preemption, since we start walking from the last Java anchor.
662 NoPreemptMark npm(current);
663
664 if (obj->klass()->is_value_based()) {
665 handle_sync_on_value_based_class(obj, current);
666 }
667
668 // the current locking is from JNI instead of Java code
669 current->set_current_pending_monitor_is_from_java(false);
670 // An async deflation can race after the inflate() call and before
671 // enter() can make the ObjectMonitor busy. enter() returns false if
672 // we have lost the race to async deflation and we simply try again.
673 while (true) {
674 ObjectMonitor* monitor;
675 bool entered;
676 if (LockingMode == LM_LIGHTWEIGHT) {
677 BasicLock lock;
678 entered = LightweightSynchronizer::inflate_and_enter(obj(), &lock, inflate_cause_jni_enter, current, current) != nullptr;
679 } else {
680 monitor = inflate(current, obj(), inflate_cause_jni_enter);
681 entered = monitor->enter(current);
682 }
683
684 if (entered) {
685 current->inc_held_monitor_count(1, true);
686 break;
687 }
688 }
689 current->set_current_pending_monitor_is_from_java(true);
690 }
691
692 // NOTE: must use heavy weight monitor to handle jni monitor exit
693 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
694 JavaThread* current = THREAD;
695
696 ObjectMonitor* monitor;
697 if (LockingMode == LM_LIGHTWEIGHT) {
698 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
699 } else {
700 // The ObjectMonitor* can't be async deflated until ownership is
701 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
702 monitor = inflate(current, obj, inflate_cause_jni_exit);
703 }
704 // If this thread has locked the object, exit the monitor. We
705 // intentionally do not use CHECK on check_owner because we must exit the
706 // monitor even if an exception was already pending.
707 if (monitor->check_owner(THREAD)) {
708 monitor->exit(current);
709 current->dec_held_monitor_count(1, true);
710 }
711 }
712
713 // -----------------------------------------------------------------------------
714 // Internal VM locks on java objects
715 // standard constructor, allows locking failures
716 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) : _npm(thread) {
717 _thread = thread;
718 _thread->check_for_valid_safepoint_state();
719 _obj = obj;
720
721 if (_obj() != nullptr) {
722 ObjectSynchronizer::enter(_obj, &_lock, _thread);
723 }
724 }
725
726 ObjectLocker::~ObjectLocker() {
727 if (_obj() != nullptr) {
728 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
729 }
730 }
731
732
733 // -----------------------------------------------------------------------------
734 // Wait/Notify/NotifyAll
735 // NOTE: must use heavy weight monitor to handle wait()
736
737 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
738 JavaThread* current = THREAD;
739 if (millis < 0) {
740 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
741 }
742
743 ObjectMonitor* monitor;
744 if (LockingMode == LM_LIGHTWEIGHT) {
745 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
746 } else {
747 // The ObjectMonitor* can't be async deflated because the _waiters
748 // field is incremented before ownership is dropped and decremented
749 // after ownership is regained.
750 monitor = inflate(current, obj(), inflate_cause_wait);
751 }
752
753 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
754 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
755
756 // This dummy call is in place to get around dtrace bug 6254741. Once
757 // that's fixed we can uncomment the following line, remove the call
758 // and change this function back into a "void" func.
759 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
760 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
761 return ret_code;
762 }
763
764 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
765 if (millis < 0) {
766 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
767 }
768
769 ObjectMonitor* monitor;
770 if (LockingMode == LM_LIGHTWEIGHT) {
771 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
772 } else {
773 monitor = inflate(THREAD, obj(), inflate_cause_wait);
774 }
775 monitor->wait(millis, false, THREAD);
776 }
777
778
779 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
780 JavaThread* current = THREAD;
781
782 markWord mark = obj->mark();
783 if (LockingMode == LM_LIGHTWEIGHT) {
784 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
785 // Not inflated so there can't be any waiters to notify.
786 return;
787 }
788 } else if (LockingMode == LM_LEGACY) {
789 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
790 // Not inflated so there can't be any waiters to notify.
791 return;
792 }
793 }
794
795 ObjectMonitor* monitor;
796 if (LockingMode == LM_LIGHTWEIGHT) {
797 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
798 } else {
799 // The ObjectMonitor* can't be async deflated until ownership is
800 // dropped by the calling thread.
801 monitor = inflate(current, obj(), inflate_cause_notify);
802 }
803 monitor->notify(CHECK);
804 }
805
806 // NOTE: see comment of notify()
807 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
808 JavaThread* current = THREAD;
809
810 markWord mark = obj->mark();
811 if (LockingMode == LM_LIGHTWEIGHT) {
812 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
813 // Not inflated so there can't be any waiters to notify.
814 return;
815 }
816 } else if (LockingMode == LM_LEGACY) {
817 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
818 // Not inflated so there can't be any waiters to notify.
819 return;
820 }
821 }
822
823 ObjectMonitor* monitor;
824 if (LockingMode == LM_LIGHTWEIGHT) {
825 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
826 } else {
827 // The ObjectMonitor* can't be async deflated until ownership is
828 // dropped by the calling thread.
829 monitor = inflate(current, obj(), inflate_cause_notify);
830 }
831 monitor->notifyAll(CHECK);
832 }
833
834 // -----------------------------------------------------------------------------
835 // Hash Code handling
836
837 struct SharedGlobals {
838 char _pad_prefix[OM_CACHE_LINE_SIZE];
839 // This is a highly shared mostly-read variable.
840 // To avoid false-sharing it needs to be the sole occupant of a cache line.
841 volatile int stw_random;
842 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
843 // Hot RW variable -- Sequester to avoid false-sharing
844 volatile int hc_sequence;
845 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
846 };
847
848 static SharedGlobals GVars;
849
850 static markWord read_stable_mark(oop obj) {
851 markWord mark = obj->mark_acquire();
852 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
853 // New lightweight locking does not use the markWord::INFLATING() protocol.
854 return mark; // normal fast-path return
855 }
856
857 int its = 0;
858 for (;;) {
859 markWord mark = obj->mark_acquire();
860 if (!mark.is_being_inflated()) {
861 return mark; // normal fast-path return
862 }
863
864 // The object is being inflated by some other thread.
865 // The caller of read_stable_mark() must wait for inflation to complete.
866 // Avoid live-lock.
867
868 ++its;
869 if (its > 10000 || !os::is_MP()) {
870 if (its & 1) {
871 os::naked_yield();
872 } else {
873 // Note that the following code attenuates the livelock problem but is not
874 // a complete remedy. A more complete solution would require that the inflating
875 // thread hold the associated inflation lock. The following code simply restricts
876 // the number of spinners to at most one. We'll have N-2 threads blocked
877 // on the inflationlock, 1 thread holding the inflation lock and using
878 // a yield/park strategy, and 1 thread in the midst of inflation.
879 // A more refined approach would be to change the encoding of INFLATING
880 // to allow encapsulation of a native thread pointer. Threads waiting for
881 // inflation to complete would use CAS to push themselves onto a singly linked
882 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
883 // and calling park(). When inflation was complete the thread that accomplished inflation
884 // would detach the list and set the markword to inflated with a single CAS and
885 // then for each thread on the list, set the flag and unpark() the thread.
886
887 // Index into the lock array based on the current object address.
888 static_assert(is_power_of_2(inflation_lock_count()), "must be");
889 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
890 int YieldThenBlock = 0;
891 assert(ix < inflation_lock_count(), "invariant");
892 inflation_lock(ix)->lock();
893 while (obj->mark_acquire() == markWord::INFLATING()) {
894 // Beware: naked_yield() is advisory and has almost no effect on some platforms
895 // so we periodically call current->_ParkEvent->park(1).
896 // We use a mixed spin/yield/block mechanism.
897 if ((YieldThenBlock++) >= 16) {
898 Thread::current()->_ParkEvent->park(1);
899 } else {
900 os::naked_yield();
901 }
902 }
903 inflation_lock(ix)->unlock();
904 }
905 } else {
906 SpinPause(); // SMP-polite spinning
907 }
908 }
909 }
910
911 // hashCode() generation :
912 //
913 // Possibilities:
914 // * MD5Digest of {obj,stw_random}
915 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
916 // * A DES- or AES-style SBox[] mechanism
917 // * One of the Phi-based schemes, such as:
918 // 2654435761 = 2^32 * Phi (golden ratio)
919 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
920 // * A variation of Marsaglia's shift-xor RNG scheme.
921 // * (obj ^ stw_random) is appealing, but can result
922 // in undesirable regularity in the hashCode values of adjacent objects
923 // (objects allocated back-to-back, in particular). This could potentially
924 // result in hashtable collisions and reduced hashtable efficiency.
925 // There are simple ways to "diffuse" the middle address bits over the
926 // generated hashCode values:
927
928 static intptr_t get_next_hash(Thread* current, oop obj) {
929 intptr_t value = 0;
930 if (hashCode == 0) {
931 // This form uses global Park-Miller RNG.
932 // On MP system we'll have lots of RW access to a global, so the
933 // mechanism induces lots of coherency traffic.
934 value = os::random();
935 } else if (hashCode == 1) {
936 // This variation has the property of being stable (idempotent)
937 // between STW operations. This can be useful in some of the 1-0
938 // synchronization schemes.
939 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
940 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
941 } else if (hashCode == 2) {
942 value = 1; // for sensitivity testing
943 } else if (hashCode == 3) {
944 value = ++GVars.hc_sequence;
945 } else if (hashCode == 4) {
946 value = cast_from_oop<intptr_t>(obj);
947 } else {
948 // Marsaglia's xor-shift scheme with thread-specific state
949 // This is probably the best overall implementation -- we'll
950 // likely make this the default in future releases.
951 unsigned t = current->_hashStateX;
952 t ^= (t << 11);
953 current->_hashStateX = current->_hashStateY;
954 current->_hashStateY = current->_hashStateZ;
955 current->_hashStateZ = current->_hashStateW;
956 unsigned v = current->_hashStateW;
957 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
958 current->_hashStateW = v;
959 value = v;
960 }
961
962 value &= markWord::hash_mask;
963 if (value == 0) value = 0xBAD;
964 assert(value != markWord::no_hash, "invariant");
965 return value;
966 }
967
968 static intptr_t install_hash_code(Thread* current, oop obj) {
969 assert(UseObjectMonitorTable && LockingMode == LM_LIGHTWEIGHT, "must be");
970
971 markWord mark = obj->mark_acquire();
972 for (;;) {
973 intptr_t hash = mark.hash();
974 if (hash != 0) {
975 return hash;
976 }
977
978 hash = get_next_hash(current, obj);
979 const markWord old_mark = mark;
980 const markWord new_mark = old_mark.copy_set_hash(hash);
981
982 mark = obj->cas_set_mark(new_mark, old_mark);
983 if (old_mark == mark) {
984 return hash;
985 }
986 }
987 }
988
989 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
990 if (UseObjectMonitorTable) {
991 // Since the monitor isn't in the object header, the hash can simply be
992 // installed in the object header.
993 return install_hash_code(current, obj);
994 }
995
996 while (true) {
997 ObjectMonitor* monitor = nullptr;
998 markWord temp, test;
999 intptr_t hash;
1000 markWord mark = read_stable_mark(obj);
1001 if (VerifyHeavyMonitors) {
1002 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
1003 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1004 }
1005 if (mark.is_unlocked() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1006 hash = mark.hash();
1007 if (hash != 0) { // if it has a hash, just return it
1008 return hash;
1009 }
1010 hash = get_next_hash(current, obj); // get a new hash
1011 temp = mark.copy_set_hash(hash); // merge the hash into header
1012 // try to install the hash
1013 test = obj->cas_set_mark(temp, mark);
1014 if (test == mark) { // if the hash was installed, return it
1015 return hash;
1016 }
1017 if (LockingMode == LM_LIGHTWEIGHT) {
1018 // CAS failed, retry
1019 continue;
1020 }
1021 // Failed to install the hash. It could be that another thread
1022 // installed the hash just before our attempt or inflation has
1023 // occurred or... so we fall thru to inflate the monitor for
1024 // stability and then install the hash.
1025 } else if (mark.has_monitor()) {
1026 monitor = mark.monitor();
1027 temp = monitor->header();
1028 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1029 hash = temp.hash();
1030 if (hash != 0) {
1031 // It has a hash.
1032
1033 // Separate load of dmw/header above from the loads in
1034 // is_being_async_deflated().
1035
1036 // dmw/header and _contentions may get written by different threads.
1037 // Make sure to observe them in the same order when having several observers.
1038 OrderAccess::loadload_for_IRIW();
1039
1040 if (monitor->is_being_async_deflated()) {
1041 // But we can't safely use the hash if we detect that async
1042 // deflation has occurred. So we attempt to restore the
1043 // header/dmw to the object's header so that we only retry
1044 // once if the deflater thread happens to be slow.
1045 monitor->install_displaced_markword_in_object(obj);
1046 continue;
1047 }
1048 return hash;
1049 }
1050 // Fall thru so we only have one place that installs the hash in
1051 // the ObjectMonitor.
1052 } else if (LockingMode == LM_LEGACY && mark.has_locker()
1053 && current->is_Java_thread()
1054 && JavaThread::cast(current)->is_lock_owned((address)mark.locker())) {
1055 // This is a stack-lock owned by the calling thread so fetch the
1056 // displaced markWord from the BasicLock on the stack.
1057 temp = mark.displaced_mark_helper();
1058 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1059 hash = temp.hash();
1060 if (hash != 0) { // if it has a hash, just return it
1061 return hash;
1062 }
1063 // WARNING:
1064 // The displaced header in the BasicLock on a thread's stack
1065 // is strictly immutable. It CANNOT be changed in ANY cases.
1066 // So we have to inflate the stack-lock into an ObjectMonitor
1067 // even if the current thread owns the lock. The BasicLock on
1068 // a thread's stack can be asynchronously read by other threads
1069 // during an inflate() call so any change to that stack memory
1070 // may not propagate to other threads correctly.
1071 }
1072
1073 // Inflate the monitor to set the hash.
1074
1075 // There's no need to inflate if the mark has already got a monitor.
1076 // NOTE: an async deflation can race after we get the monitor and
1077 // before we can update the ObjectMonitor's header with the hash
1078 // value below.
1079 monitor = mark.has_monitor() ? mark.monitor() : inflate(current, obj, inflate_cause_hash_code);
1080 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1081 mark = monitor->header();
1082 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1083 hash = mark.hash();
1084 if (hash == 0) { // if it does not have a hash
1085 hash = get_next_hash(current, obj); // get a new hash
1086 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1087 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1088 uintptr_t v = Atomic::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
1089 test = markWord(v);
1090 if (test != mark) {
1091 // The attempt to update the ObjectMonitor's header/dmw field
1092 // did not work. This can happen if another thread managed to
1093 // merge in the hash just before our cmpxchg().
1094 // If we add any new usages of the header/dmw field, this code
1095 // will need to be updated.
1096 hash = test.hash();
1097 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1098 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1099 }
1100 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
1101 // If we detect that async deflation has occurred, then we
1102 // attempt to restore the header/dmw to the object's header
1103 // so that we only retry once if the deflater thread happens
1104 // to be slow.
1105 monitor->install_displaced_markword_in_object(obj);
1106 continue;
1107 }
1108 }
1109 // We finally get the hash.
1110 return hash;
1111 }
1112 }
1113
1114 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1115 Handle h_obj) {
1116 assert(current == JavaThread::current(), "Can only be called on current thread");
1117 oop obj = h_obj();
1118
1119 markWord mark = read_stable_mark(obj);
1120
1121 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1122 // stack-locked case, header points into owner's stack
1123 return current->is_lock_owned((address)mark.locker());
1124 }
1125
1126 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1127 // fast-locking case, see if lock is in current's lock stack
1128 return current->lock_stack().contains(h_obj());
1129 }
1130
1131 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1132 ObjectMonitor* monitor = read_monitor(current, obj, mark);
1133 if (monitor != nullptr) {
1134 return monitor->is_entered(current) != 0;
1135 }
1136 // Racing with inflation/deflation, retry
1137 mark = obj->mark_acquire();
1138
1139 if (mark.is_fast_locked()) {
1140 // Some other thread fast_locked, current could not have held the lock
1141 return false;
1142 }
1143 }
1144
1145 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1146 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1147 // The first stage of async deflation does not affect any field
1148 // used by this comparison so the ObjectMonitor* is usable here.
1149 ObjectMonitor* monitor = read_monitor(mark);
1150 return monitor->is_entered(current) != 0;
1151 }
1152 // Unlocked case, header in place
1153 assert(mark.is_unlocked(), "sanity check");
1154 return false;
1155 }
1156
1157 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1158 oop obj = h_obj();
1159 markWord mark = read_stable_mark(obj);
1160
1161 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1162 // stack-locked so header points into owner's stack.
1163 // owning_thread_from_monitor_owner() may also return null here:
1164 return Threads::owning_thread_from_stacklock(t_list, (address) mark.locker());
1165 }
1166
1167 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1168 // fast-locked so get owner from the object.
1169 // owning_thread_from_object() may also return null here:
1170 return Threads::owning_thread_from_object(t_list, h_obj());
1171 }
1172
1173 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1174 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
1175 if (monitor != nullptr) {
1176 return Threads::owning_thread_from_monitor(t_list, monitor);
1177 }
1178 // Racing with inflation/deflation, retry
1179 mark = obj->mark_acquire();
1180
1181 if (mark.is_fast_locked()) {
1182 // Some other thread fast_locked
1183 return Threads::owning_thread_from_object(t_list, h_obj());
1184 }
1185 }
1186
1187 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1188 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1189 // The first stage of async deflation does not affect any field
1190 // used by this comparison so the ObjectMonitor* is usable here.
1191 ObjectMonitor* monitor = read_monitor(mark);
1192 assert(monitor != nullptr, "monitor should be non-null");
1193 // owning_thread_from_monitor() may also return null here:
1194 return Threads::owning_thread_from_monitor(t_list, monitor);
1195 }
1196
1197 // Unlocked case, header in place
1198 // Cannot have assertion since this object may have been
1199 // locked by another thread when reaching here.
1200 // assert(mark.is_unlocked(), "sanity check");
1201
1202 return nullptr;
1203 }
1204
1205 // Visitors ...
1206
1207 // Iterate over all ObjectMonitors.
1208 template <typename Function>
1209 void ObjectSynchronizer::monitors_iterate(Function function) {
1210 MonitorList::Iterator iter = _in_use_list.iterator();
1211 while (iter.has_next()) {
1212 ObjectMonitor* monitor = iter.next();
1213 function(monitor);
1214 }
1215 }
1216
1217 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1218 // returns true.
1219 template <typename OwnerFilter>
1220 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1221 monitors_iterate([&](ObjectMonitor* monitor) {
1222 // This function is only called at a safepoint or when the
1223 // target thread is suspended or when the target thread is
1224 // operating on itself. The current closures in use today are
1225 // only interested in an owned ObjectMonitor and ownership
1226 // cannot be dropped under the calling contexts so the
1227 // ObjectMonitor cannot be async deflated.
1228 if (monitor->has_owner() && filter(monitor)) {
1229 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1230
1231 closure->do_monitor(monitor);
1232 }
1233 });
1234 }
1235
1236 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1237 // ObjectMonitors where owner is set to a stack-lock address in thread.
1238 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1239 int64_t key = ObjectMonitor::owner_id_from(thread);
1240 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1241 return owned_monitors_iterate_filtered(closure, thread_filter);
1242 }
1243
1244 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
1245 int64_t key = ObjectMonitor::owner_id_from(vthread);
1246 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1247 return owned_monitors_iterate_filtered(closure, thread_filter);
1248 }
1249
1250 // Iterate ObjectMonitors owned by any thread.
1251 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1252 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
1253 return owned_monitors_iterate_filtered(closure, all_filter);
1254 }
1255
1256 static bool monitors_used_above_threshold(MonitorList* list) {
1257 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1258 return false;
1259 }
1260 size_t monitors_used = list->count();
1261 if (monitors_used == 0) { // empty list is easy
1262 return false;
1263 }
1264 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
1265 // Make sure that we use a ceiling value that is not lower than
1266 // previous, not lower than the recorded max used by the system, and
1267 // not lower than the current number of monitors in use (which can
1268 // race ahead of max). The result is guaranteed > 0.
1269 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
1270
1271 // Check if our monitor usage is above the threshold:
1272 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1273 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1274 // Deflate monitors if over the threshold percentage, unless no
1275 // progress on previous deflations.
1276 bool is_above_threshold = true;
1277
1278 // Check if it's time to adjust the in_use_list_ceiling up, due
1279 // to too many async deflation attempts without any progress.
1280 if (NoAsyncDeflationProgressMax != 0 &&
1281 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1282 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1283 size_t delta = (size_t)(ceiling * remainder) + 1;
1284 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
1285 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
1286 : ceiling + delta;
1287
1288 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1289 log_info(monitorinflation)("Too many deflations without progress; "
1290 "bumping in_use_list_ceiling from %zu"
1291 " to %zu", old_ceiling, new_ceiling);
1292 _no_progress_cnt = 0;
1293 ceiling = new_ceiling;
1294
1295 // Check if our monitor usage is still above the threshold:
1296 monitor_usage = (monitors_used * 100LL) / ceiling;
1297 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
1298 }
1299 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
1300 ", monitor_usage=%zu, threshold=%d",
1301 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1302 return is_above_threshold;
1303 }
1304
1305 return false;
1306 }
1307
1308 size_t ObjectSynchronizer::in_use_list_count() {
1309 return _in_use_list.count();
1310 }
1311
1312 size_t ObjectSynchronizer::in_use_list_max() {
1313 return _in_use_list.max();
1314 }
1315
1316 size_t ObjectSynchronizer::in_use_list_ceiling() {
1317 return _in_use_list_ceiling;
1318 }
1319
1320 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1321 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1322 }
1323
1324 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1325 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1326 }
1327
1328 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1329 _in_use_list_ceiling = new_value;
1330 }
1331
1332 bool ObjectSynchronizer::is_async_deflation_needed() {
1333 if (is_async_deflation_requested()) {
1334 // Async deflation request.
1335 log_info(monitorinflation)("Async deflation needed: explicit request");
1336 return true;
1337 }
1338
1339 jlong time_since_last = time_since_last_async_deflation_ms();
1340
1341 if (AsyncDeflationInterval > 0 &&
1342 time_since_last > AsyncDeflationInterval &&
1343 monitors_used_above_threshold(&_in_use_list)) {
1344 // It's been longer than our specified deflate interval and there
1345 // are too many monitors in use. We don't deflate more frequently
1346 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1347 // in order to not swamp the MonitorDeflationThread.
1348 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1349 return true;
1350 }
1351
1352 if (GuaranteedAsyncDeflationInterval > 0 &&
1353 time_since_last > GuaranteedAsyncDeflationInterval) {
1354 // It's been longer than our specified guaranteed deflate interval.
1355 // We need to clean up the used monitors even if the threshold is
1356 // not reached, to keep the memory utilization at bay when many threads
1357 // touched many monitors.
1358 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
1359 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1360 GuaranteedAsyncDeflationInterval, time_since_last);
1361
1362 // If this deflation has no progress, then it should not affect the no-progress
1363 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1364 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1365 // the generic code would bump the no-progress counter, and we compensate for that
1366 // by telling it to skip the update.
1367 //
1368 // If this deflation has progress, then it should let non-progress tracking
1369 // know about this, otherwise the threshold heuristics would kick in, potentially
1370 // experience no-progress due to aggressive cleanup by this deflation, and think
1371 // it is still in no-progress stride. In this "progress" case, the generic code would
1372 // zero the counter, and we allow it to happen.
1373 _no_progress_skip_increment = true;
1374
1375 return true;
1376 }
1377
1378 return false;
1379 }
1380
1381 void ObjectSynchronizer::request_deflate_idle_monitors() {
1382 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1383 set_is_async_deflation_requested(true);
1384 ml.notify_all();
1385 }
1386
1387 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1388 JavaThread* current = JavaThread::current();
1389 bool ret_code = false;
1390
1391 jlong last_time = last_async_deflation_time_ns();
1392
1393 request_deflate_idle_monitors();
1394
1395 const int N_CHECKS = 5;
1396 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1397 if (last_async_deflation_time_ns() > last_time) {
1398 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1399 ret_code = true;
1400 break;
1401 }
1402 {
1403 // JavaThread has to honor the blocking protocol.
1404 ThreadBlockInVM tbivm(current);
1405 os::naked_short_sleep(999); // sleep for almost 1 second
1406 }
1407 }
1408 if (!ret_code) {
1409 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1410 }
1411
1412 return ret_code;
1413 }
1414
1415 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1416 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1417 }
1418
1419 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1420 const oop obj,
1421 ObjectSynchronizer::InflateCause cause) {
1422 assert(event != nullptr, "invariant");
1423 const Klass* monitor_klass = obj->klass();
1424 if (ObjectMonitor::is_jfr_excluded(monitor_klass)) {
1425 return;
1426 }
1427 event->set_monitorClass(monitor_klass);
1428 event->set_address((uintptr_t)(void*)obj);
1429 event->set_cause((u1)cause);
1430 event->commit();
1431 }
1432
1433 // Fast path code shared by multiple functions
1434 void ObjectSynchronizer::inflate_helper(oop obj) {
1435 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1436 markWord mark = obj->mark_acquire();
1437 if (mark.has_monitor()) {
1438 ObjectMonitor* monitor = read_monitor(mark);
1439 markWord dmw = monitor->header();
1440 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1441 return;
1442 }
1443 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1444 }
1445
1446 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1447 assert(current == Thread::current(), "must be");
1448 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1449 return inflate_impl(current->is_Java_thread() ? JavaThread::cast(current) : nullptr, obj, cause);
1450 }
1451
1452 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1453 assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1454 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_for");
1455 return inflate_impl(thread, obj, cause);
1456 }
1457
1458 ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* locking_thread, oop object, const InflateCause cause) {
1459 // The JavaThread* locking_thread requires that the locking_thread == Thread::current() or
1460 // is suspended throughout the call by some other mechanism.
1461 // The thread might be nullptr when called from a non JavaThread. (As may still be
1462 // the case from FastHashCode). However it is only important for correctness that the
1463 // thread is set when called from ObjectSynchronizer::enter from the owning thread,
1464 // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
1465 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_impl");
1466 EventJavaMonitorInflate event;
1467
1468 for (;;) {
1469 const markWord mark = object->mark_acquire();
1470
1471 // The mark can be in one of the following states:
1472 // * inflated - If the ObjectMonitor owner is anonymous and the
1473 // locking_thread owns the object lock, then we
1474 // make the locking_thread the ObjectMonitor owner.
1475 // * stack-locked - Coerce it to inflated from stack-locked.
1476 // * INFLATING - Busy wait for conversion from stack-locked to
1477 // inflated.
1478 // * unlocked - Aggressively inflate the object.
1479
1480 // CASE: inflated
1481 if (mark.has_monitor()) {
1482 ObjectMonitor* inf = mark.monitor();
1483 markWord dmw = inf->header();
1484 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1485 if (inf->has_anonymous_owner() && locking_thread != nullptr) {
1486 assert(LockingMode == LM_LEGACY, "invariant");
1487 if (locking_thread->is_lock_owned((address)inf->stack_locker())) {
1488 inf->set_stack_locker(nullptr);
1489 inf->set_owner_from_anonymous(locking_thread);
1490 }
1491 }
1492 return inf;
1493 }
1494
1495 // CASE: inflation in progress - inflating over a stack-lock.
1496 // Some other thread is converting from stack-locked to inflated.
1497 // Only that thread can complete inflation -- other threads must wait.
1498 // The INFLATING value is transient.
1499 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1500 // We could always eliminate polling by parking the thread on some auxiliary list.
1501 if (mark == markWord::INFLATING()) {
1502 read_stable_mark(object);
1503 continue;
1504 }
1505
1506 // CASE: stack-locked
1507 // Could be stack-locked either by current or by some other thread.
1508 //
1509 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1510 // to install INFLATING into the mark word. We originally installed INFLATING,
1511 // allocated the ObjectMonitor, and then finally STed the address of the
1512 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1513 // the interval in which INFLATING appeared in the mark, thus increasing
1514 // the odds of inflation contention. If we lose the race to set INFLATING,
1515 // then we just delete the ObjectMonitor and loop around again.
1516 //
1517 LogStreamHandle(Trace, monitorinflation) lsh;
1518 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1519 ObjectMonitor* m = new ObjectMonitor(object);
1520 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1521 // We do this before the CAS in order to minimize the length of time
1522 // in which INFLATING appears in the mark.
1523
1524 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1525 if (cmp != mark) {
1526 delete m;
1527 continue; // Interference -- just retry
1528 }
1529
1530 // We've successfully installed INFLATING (0) into the mark-word.
1531 // This is the only case where 0 will appear in a mark-word.
1532 // Only the singular thread that successfully swings the mark-word
1533 // to 0 can perform (or more precisely, complete) inflation.
1534 //
1535 // Why do we CAS a 0 into the mark-word instead of just CASing the
1536 // mark-word from the stack-locked value directly to the new inflated state?
1537 // Consider what happens when a thread unlocks a stack-locked object.
1538 // It attempts to use CAS to swing the displaced header value from the
1539 // on-stack BasicLock back into the object header. Recall also that the
1540 // header value (hash code, etc) can reside in (a) the object header, or
1541 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1542 // header in an ObjectMonitor. The inflate() routine must copy the header
1543 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1544 // the while preserving the hashCode stability invariants. If the owner
1545 // decides to release the lock while the value is 0, the unlock will fail
1546 // and control will eventually pass from slow_exit() to inflate. The owner
1547 // will then spin, waiting for the 0 value to disappear. Put another way,
1548 // the 0 causes the owner to stall if the owner happens to try to
1549 // drop the lock (restoring the header from the BasicLock to the object)
1550 // while inflation is in-progress. This protocol avoids races that might
1551 // would otherwise permit hashCode values to change or "flicker" for an object.
1552 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1553 // 0 serves as a "BUSY" inflate-in-progress indicator.
1554
1555
1556 // fetch the displaced mark from the owner's stack.
1557 // The owner can't die or unwind past the lock while our INFLATING
1558 // object is in the mark. Furthermore the owner can't complete
1559 // an unlock on the object, either.
1560 markWord dmw = mark.displaced_mark_helper();
1561 // Catch if the object's header is not neutral (not locked and
1562 // not marked is what we care about here).
1563 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1564
1565 // Setup monitor fields to proper values -- prepare the monitor
1566 m->set_header(dmw);
1567
1568 // Note that a thread can inflate an object
1569 // that it has stack-locked -- as might happen in wait() -- directly
1570 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1571 if (locking_thread != nullptr && locking_thread->is_lock_owned((address)mark.locker())) {
1572 m->set_owner(locking_thread);
1573 } else {
1574 // Use ANONYMOUS_OWNER to indicate that the owner is the BasicLock on the stack,
1575 // and set the stack locker field in the monitor.
1576 m->set_stack_locker(mark.locker());
1577 m->set_anonymous_owner();
1578 }
1579 // TODO-FIXME: assert BasicLock->dhw != 0.
1580
1581 // Must preserve store ordering. The monitor state must
1582 // be stable at the time of publishing the monitor address.
1583 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1584 // Release semantics so that above set_object() is seen first.
1585 object->release_set_mark(markWord::encode(m));
1586
1587 // Once ObjectMonitor is configured and the object is associated
1588 // with the ObjectMonitor, it is safe to allow async deflation:
1589 _in_use_list.add(m);
1590
1591 if (log_is_enabled(Trace, monitorinflation)) {
1592 ResourceMark rm;
1593 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1594 INTPTR_FORMAT ", type='%s'", p2i(object),
1595 object->mark().value(), object->klass()->external_name());
1596 }
1597 if (event.should_commit()) {
1598 post_monitor_inflate_event(&event, object, cause);
1599 }
1600 return m;
1601 }
1602
1603 // CASE: unlocked
1604 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1605 // If we know we're inflating for entry it's better to inflate by swinging a
1606 // pre-locked ObjectMonitor pointer into the object header. A successful
1607 // CAS inflates the object *and* confers ownership to the inflating thread.
1608 // In the current implementation we use a 2-step mechanism where we CAS()
1609 // to inflate and then CAS() again to try to swing _owner from null to current.
1610 // An inflateTry() method that we could call from enter() would be useful.
1611
1612 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
1613 ObjectMonitor* m = new ObjectMonitor(object);
1614 // prepare m for installation - set monitor to initial state
1615 m->set_header(mark);
1616
1617 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1618 delete m;
1619 m = nullptr;
1620 continue;
1621 // interference - the markword changed - just retry.
1622 // The state-transitions are one-way, so there's no chance of
1623 // live-lock -- "Inflated" is an absorbing state.
1624 }
1625
1626 // Once the ObjectMonitor is configured and object is associated
1627 // with the ObjectMonitor, it is safe to allow async deflation:
1628 _in_use_list.add(m);
1629
1630 if (log_is_enabled(Trace, monitorinflation)) {
1631 ResourceMark rm;
1632 lsh.print_cr("inflate(unlocked): object=" INTPTR_FORMAT ", mark="
1633 INTPTR_FORMAT ", type='%s'", p2i(object),
1634 object->mark().value(), object->klass()->external_name());
1635 }
1636 if (event.should_commit()) {
1637 post_monitor_inflate_event(&event, object, cause);
1638 }
1639 return m;
1640 }
1641 }
1642
1643 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1644 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1645 //
1646 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1647 MonitorList::Iterator iter = _in_use_list.iterator();
1648 size_t deflated_count = 0;
1649 Thread* current = Thread::current();
1650
1651 while (iter.has_next()) {
1652 if (deflated_count >= (size_t)MonitorDeflationMax) {
1653 break;
1654 }
1655 ObjectMonitor* mid = iter.next();
1656 if (mid->deflate_monitor(current)) {
1657 deflated_count++;
1658 }
1659
1660 // Must check for a safepoint/handshake and honor it.
1661 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1662 }
1663
1664 return deflated_count;
1665 }
1666
1667 class HandshakeForDeflation : public HandshakeClosure {
1668 public:
1669 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1670
1671 void do_thread(Thread* thread) {
1672 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1673 INTPTR_FORMAT, p2i(thread));
1674 if (thread->is_Java_thread()) {
1675 // Clear OM cache
1676 JavaThread* jt = JavaThread::cast(thread);
1677 jt->om_clear_monitor_cache();
1678 }
1679 }
1680 };
1681
1682 class VM_RendezvousGCThreads : public VM_Operation {
1683 public:
1684 bool evaluate_at_safepoint() const override { return false; }
1685 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1686 void doit() override {
1687 Universe::heap()->safepoint_synchronize_begin();
1688 Universe::heap()->safepoint_synchronize_end();
1689 };
1690 };
1691
1692 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1693 ObjectMonitorDeflationSafepointer* safepointer) {
1694 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1695 size_t deleted_count = 0;
1696 for (ObjectMonitor* monitor: *delete_list) {
1697 delete monitor;
1698 deleted_count++;
1699 // A JavaThread must check for a safepoint/handshake and honor it.
1700 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1701 }
1702 return deleted_count;
1703 }
1704
1705 class ObjectMonitorDeflationLogging: public StackObj {
1706 LogStreamHandle(Debug, monitorinflation) _debug;
1707 LogStreamHandle(Info, monitorinflation) _info;
1708 LogStream* _stream;
1709 elapsedTimer _timer;
1710
1711 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1712 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1713 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1714
1715 public:
1716 ObjectMonitorDeflationLogging()
1717 : _debug(), _info(), _stream(nullptr) {
1718 if (_debug.is_enabled()) {
1719 _stream = &_debug;
1720 } else if (_info.is_enabled()) {
1721 _stream = &_info;
1722 }
1723 }
1724
1725 void begin() {
1726 if (_stream != nullptr) {
1727 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1728 ceiling(), count(), max());
1729 _timer.start();
1730 }
1731 }
1732
1733 void before_handshake(size_t unlinked_count) {
1734 if (_stream != nullptr) {
1735 _timer.stop();
1736 _stream->print_cr("before handshaking: unlinked_count=%zu"
1737 ", in_use_list stats: ceiling=%zu, count="
1738 "%zu, max=%zu",
1739 unlinked_count, ceiling(), count(), max());
1740 }
1741 }
1742
1743 void after_handshake() {
1744 if (_stream != nullptr) {
1745 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1746 "%zu, count=%zu, max=%zu",
1747 ceiling(), count(), max());
1748 _timer.start();
1749 }
1750 }
1751
1752 void end(size_t deflated_count, size_t unlinked_count) {
1753 if (_stream != nullptr) {
1754 _timer.stop();
1755 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1756 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1757 deflated_count, unlinked_count, _timer.seconds());
1758 }
1759 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1760 ceiling(), count(), max());
1761 }
1762 }
1763
1764 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1765 if (_stream != nullptr) {
1766 _timer.stop();
1767 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1768 "%zu, count=%zu, max=%zu",
1769 op_name, cnt_name, cnt, ceiling(), count(), max());
1770 }
1771 }
1772
1773 void after_block_for_safepoint(const char* op_name) {
1774 if (_stream != nullptr) {
1775 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1776 ", count=%zu, max=%zu", op_name,
1777 ceiling(), count(), max());
1778 _timer.start();
1779 }
1780 }
1781 };
1782
1783 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1784 if (!SafepointMechanism::should_process(_current)) {
1785 return;
1786 }
1787
1788 // A safepoint/handshake has started.
1789 _log->before_block_for_safepoint(op_name, count_name, counter);
1790
1791 {
1792 // Honor block request.
1793 ThreadBlockInVM tbivm(_current);
1794 }
1795
1796 _log->after_block_for_safepoint(op_name);
1797 }
1798
1799 // This function is called by the MonitorDeflationThread to deflate
1800 // ObjectMonitors.
1801 size_t ObjectSynchronizer::deflate_idle_monitors() {
1802 JavaThread* current = JavaThread::current();
1803 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1804
1805 // The async deflation request has been processed.
1806 _last_async_deflation_time_ns = os::javaTimeNanos();
1807 set_is_async_deflation_requested(false);
1808
1809 ObjectMonitorDeflationLogging log;
1810 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1811
1812 log.begin();
1813
1814 // Deflate some idle ObjectMonitors.
1815 size_t deflated_count = deflate_monitor_list(&safepointer);
1816
1817 // Unlink the deflated ObjectMonitors from the in-use list.
1818 size_t unlinked_count = 0;
1819 size_t deleted_count = 0;
1820 if (deflated_count > 0) {
1821 ResourceMark rm(current);
1822 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1823 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1824
1825 #ifdef ASSERT
1826 if (UseObjectMonitorTable) {
1827 for (ObjectMonitor* monitor : delete_list) {
1828 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1829 }
1830 }
1831 #endif
1832
1833 log.before_handshake(unlinked_count);
1834
1835 // A JavaThread needs to handshake in order to safely free the
1836 // ObjectMonitors that were deflated in this cycle.
1837 HandshakeForDeflation hfd_hc;
1838 Handshake::execute(&hfd_hc);
1839 // Also, we sync and desync GC threads around the handshake, so that they can
1840 // safely read the mark-word and look-through to the object-monitor, without
1841 // being afraid that the object-monitor is going away.
1842 VM_RendezvousGCThreads sync_gc;
1843 VMThread::execute(&sync_gc);
1844
1845 log.after_handshake();
1846
1847 // After the handshake, safely free the ObjectMonitors that were
1848 // deflated and unlinked in this cycle.
1849
1850 // Delete the unlinked ObjectMonitors.
1851 deleted_count = delete_monitors(&delete_list, &safepointer);
1852 assert(unlinked_count == deleted_count, "must be");
1853 }
1854
1855 log.end(deflated_count, unlinked_count);
1856
1857 GVars.stw_random = os::random();
1858
1859 if (deflated_count != 0) {
1860 _no_progress_cnt = 0;
1861 } else if (_no_progress_skip_increment) {
1862 _no_progress_skip_increment = false;
1863 } else {
1864 _no_progress_cnt++;
1865 }
1866
1867 return deflated_count;
1868 }
1869
1870 // Monitor cleanup on JavaThread::exit
1871
1872 // Iterate through monitor cache and attempt to release thread's monitors
1873 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1874 private:
1875 JavaThread* _thread;
1876
1877 public:
1878 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1879 void do_monitor(ObjectMonitor* mid) {
1880 intx rec = mid->complete_exit(_thread);
1881 _thread->dec_held_monitor_count(rec + 1);
1882 }
1883 };
1884
1885 // Release all inflated monitors owned by current thread. Lightweight monitors are
1886 // ignored. This is meant to be called during JNI thread detach which assumes
1887 // all remaining monitors are heavyweight. All exceptions are swallowed.
1888 // Scanning the extant monitor list can be time consuming.
1889 // A simple optimization is to add a per-thread flag that indicates a thread
1890 // called jni_monitorenter() during its lifetime.
1891 //
1892 // Instead of NoSafepointVerifier it might be cheaper to
1893 // use an idiom of the form:
1894 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1895 // <code that must not run at safepoint>
1896 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1897 // Since the tests are extremely cheap we could leave them enabled
1898 // for normal product builds.
1899
1900 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1901 assert(current == JavaThread::current(), "must be current Java thread");
1902 NoSafepointVerifier nsv;
1903 ReleaseJavaMonitorsClosure rjmc(current);
1904 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1905 assert(!current->has_pending_exception(), "Should not be possible");
1906 current->clear_pending_exception();
1907 assert(current->held_monitor_count() == 0, "Should not be possible");
1908 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1909 current->clear_jni_monitor_count();
1910 }
1911
1912 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1913 switch (cause) {
1914 case inflate_cause_vm_internal: return "VM Internal";
1915 case inflate_cause_monitor_enter: return "Monitor Enter";
1916 case inflate_cause_wait: return "Monitor Wait";
1917 case inflate_cause_notify: return "Monitor Notify";
1918 case inflate_cause_hash_code: return "Monitor Hash Code";
1919 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1920 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1921 default:
1922 ShouldNotReachHere();
1923 }
1924 return "Unknown";
1925 }
1926
1927 //------------------------------------------------------------------------------
1928 // Debugging code
1929
1930 u_char* ObjectSynchronizer::get_gvars_addr() {
1931 return (u_char*)&GVars;
1932 }
1933
1934 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1935 return (u_char*)&GVars.hc_sequence;
1936 }
1937
1938 size_t ObjectSynchronizer::get_gvars_size() {
1939 return sizeof(SharedGlobals);
1940 }
1941
1942 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1943 return (u_char*)&GVars.stw_random;
1944 }
1945
1946 // Do the final audit and print of ObjectMonitor stats; must be done
1947 // by the VMThread at VM exit time.
1948 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1949 assert(Thread::current()->is_VM_thread(), "sanity check");
1950
1951 if (is_final_audit()) { // Only do the audit once.
1952 return;
1953 }
1954 set_is_final_audit();
1955 log_info(monitorinflation)("Starting the final audit.");
1956
1957 if (log_is_enabled(Info, monitorinflation)) {
1958 LogStreamHandle(Info, monitorinflation) ls;
1959 audit_and_print_stats(&ls, true /* on_exit */);
1960 }
1961 }
1962
1963 // This function can be called by the MonitorDeflationThread or it can be called when
1964 // we are trying to exit the VM. The list walker functions can run in parallel with
1965 // the other list operations.
1966 // Calls to this function can be added in various places as a debugging
1967 // aid.
1968 //
1969 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1970 int error_cnt = 0;
1971
1972 ls->print_cr("Checking in_use_list:");
1973 chk_in_use_list(ls, &error_cnt);
1974
1975 if (error_cnt == 0) {
1976 ls->print_cr("No errors found in in_use_list checks.");
1977 } else {
1978 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1979 }
1980
1981 // When exiting, only log the interesting entries at the Info level.
1982 // When called at intervals by the MonitorDeflationThread, log output
1983 // at the Trace level since there can be a lot of it.
1984 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1985 LogStreamHandle(Trace, monitorinflation) ls_tr;
1986 log_in_use_monitor_details(&ls_tr, true /* log_all */);
1987 } else if (on_exit) {
1988 log_in_use_monitor_details(ls, false /* log_all */);
1989 }
1990
1991 ls->flush();
1992
1993 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1994 }
1995
1996 // Check the in_use_list; log the results of the checks.
1997 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1998 size_t l_in_use_count = _in_use_list.count();
1999 size_t l_in_use_max = _in_use_list.max();
2000 out->print_cr("count=%zu, max=%zu", l_in_use_count,
2001 l_in_use_max);
2002
2003 size_t ck_in_use_count = 0;
2004 MonitorList::Iterator iter = _in_use_list.iterator();
2005 while (iter.has_next()) {
2006 ObjectMonitor* mid = iter.next();
2007 chk_in_use_entry(mid, out, error_cnt_p);
2008 ck_in_use_count++;
2009 }
2010
2011 if (l_in_use_count == ck_in_use_count) {
2012 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
2013 l_in_use_count, ck_in_use_count);
2014 } else {
2015 out->print_cr("WARNING: in_use_count=%zu is not equal to "
2016 "ck_in_use_count=%zu", l_in_use_count,
2017 ck_in_use_count);
2018 }
2019
2020 size_t ck_in_use_max = _in_use_list.max();
2021 if (l_in_use_max == ck_in_use_max) {
2022 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
2023 l_in_use_max, ck_in_use_max);
2024 } else {
2025 out->print_cr("WARNING: in_use_max=%zu is not equal to "
2026 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
2027 }
2028 }
2029
2030 // Check an in-use monitor entry; log any errors.
2031 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2032 int* error_cnt_p) {
2033 if (n->owner_is_DEFLATER_MARKER()) {
2034 // This could happen when monitor deflation blocks for a safepoint.
2035 return;
2036 }
2037
2038
2039 if (n->metadata() == 0) {
2040 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2041 "have non-null _metadata (header/hash) field.", p2i(n));
2042 *error_cnt_p = *error_cnt_p + 1;
2043 }
2044
2045 const oop obj = n->object_peek();
2046 if (obj == nullptr) {
2047 return;
2048 }
2049
2050 const markWord mark = obj->mark();
2051 if (!mark.has_monitor()) {
2052 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2053 "object does not think it has a monitor: obj="
2054 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2055 p2i(obj), mark.value());
2056 *error_cnt_p = *error_cnt_p + 1;
2057 return;
2058 }
2059
2060 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
2061 if (n != obj_mon) {
2062 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2063 "object does not refer to the same monitor: obj="
2064 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2065 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2066 *error_cnt_p = *error_cnt_p + 1;
2067 }
2068 }
2069
2070 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2071 // flags indicate why the entry is in-use, 'object' and 'object type'
2072 // indicate the associated object and its type.
2073 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2074 if (_in_use_list.count() > 0) {
2075 stringStream ss;
2076 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
2077 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2078 out->print_cr("%18s %s %18s %18s",
2079 "monitor", "BHL", "object", "object type");
2080 out->print_cr("================== === ================== ==================");
2081
2082 auto is_interesting = [&](ObjectMonitor* monitor) {
2083 return log_all || monitor->has_owner() || monitor->is_busy();
2084 };
2085
2086 monitors_iterate([&](ObjectMonitor* monitor) {
2087 if (is_interesting(monitor)) {
2088 const oop obj = monitor->object_peek();
2089 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
2090 ResourceMark rm;
2091 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
2092 monitor->is_busy(), hash != 0, monitor->has_owner(),
2093 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2094 if (monitor->is_busy()) {
2095 out->print(" (%s)", monitor->is_busy_to_string(&ss));
2096 ss.reset();
2097 }
2098 out->cr();
2099 }
2100 });
2101 }
2102
2103 out->flush();
2104 }