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/fastHash.hpp"
67 #include "utilities/linkedlist.hpp"
68 #include "utilities/preserveException.hpp"
69
70 class ObjectMonitorDeflationLogging;
71
72 void MonitorList::add(ObjectMonitor* m) {
73 ObjectMonitor* head;
74 do {
75 head = Atomic::load(&_head);
76 m->set_next_om(head);
77 } while (Atomic::cmpxchg(&_head, head, m) != head);
78
79 size_t count = Atomic::add(&_count, 1u, memory_order_relaxed);
80 size_t old_max;
81 do {
82 old_max = Atomic::load(&_max);
83 if (count <= old_max) {
84 break;
85 }
86 } while (Atomic::cmpxchg(&_max, old_max, count, memory_order_relaxed) != old_max);
87 }
88
89 size_t MonitorList::count() const {
90 return Atomic::load(&_count);
91 }
92
93 size_t MonitorList::max() const {
94 return Atomic::load(&_max);
95 }
96
97 class ObjectMonitorDeflationSafepointer : public StackObj {
98 JavaThread* const _current;
99 ObjectMonitorDeflationLogging* const _log;
100
101 public:
102 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
103 : _current(current), _log(log) {}
104
105 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
106 };
107
108 // Walk the in-use list and unlink deflated ObjectMonitors.
109 // Returns the number of unlinked ObjectMonitors.
110 size_t MonitorList::unlink_deflated(size_t deflated_count,
111 GrowableArray<ObjectMonitor*>* unlinked_list,
112 ObjectMonitorDeflationSafepointer* safepointer) {
113 size_t unlinked_count = 0;
114 ObjectMonitor* prev = nullptr;
115 ObjectMonitor* m = Atomic::load_acquire(&_head);
116
117 while (m != nullptr) {
118 if (m->is_being_async_deflated()) {
119 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
120 // modify the list once per batch. The batch starts at "m".
121 size_t unlinked_batch = 0;
122 ObjectMonitor* next = m;
123 // Look for at most MonitorUnlinkBatch monitors, or the number of
124 // deflated and not unlinked monitors, whatever comes first.
125 assert(deflated_count >= unlinked_count, "Sanity: underflow");
126 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
127 do {
128 ObjectMonitor* next_next = next->next_om();
129 unlinked_batch++;
130 unlinked_list->append(next);
131 next = next_next;
132 if (unlinked_batch >= unlinked_batch_limit) {
133 // Reached the max batch, so bail out of the gathering loop.
134 break;
135 }
136 if (prev == nullptr && Atomic::load(&_head) != m) {
137 // Current batch used to be at head, but it is not at head anymore.
138 // Bail out and figure out where we currently are. This avoids long
139 // walks searching for new prev during unlink under heavy list inserts.
140 break;
141 }
142 } while (next != nullptr && next->is_being_async_deflated());
143
144 // Unlink the found batch.
145 if (prev == nullptr) {
146 // The current batch is the first batch, so there is a chance that it starts at head.
147 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
148 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, m, next);
149 if (prev_head != m) {
150 // Something must have updated the head. Figure out the actual prev for this batch.
151 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
152 prev = n;
153 }
154 assert(prev != nullptr, "Should have found the prev for the current batch");
155 prev->set_next_om(next);
156 }
157 } else {
158 // The current batch is preceded by another batch. This guarantees the current batch
159 // does not start at head. Unlink the entire current batch without updating the head.
160 assert(Atomic::load(&_head) != m, "Sanity");
161 prev->set_next_om(next);
162 }
163
164 unlinked_count += unlinked_batch;
165 if (unlinked_count >= deflated_count) {
166 // Reached the max so bail out of the searching loop.
167 // There should be no more deflated monitors left.
168 break;
169 }
170 m = next;
171 } else {
172 prev = m;
173 m = m->next_om();
174 }
175
176 // Must check for a safepoint/handshake and honor it.
177 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
178 }
179
180 #ifdef ASSERT
181 // Invariant: the code above should unlink all deflated monitors.
182 // The code that runs after this unlinking does not expect deflated monitors.
183 // Notably, attempting to deflate the already deflated monitor would break.
184 {
185 ObjectMonitor* m = Atomic::load_acquire(&_head);
186 while (m != nullptr) {
187 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
188 m = m->next_om();
189 }
190 }
191 #endif
192
193 Atomic::sub(&_count, unlinked_count);
194 return unlinked_count;
195 }
196
197 MonitorList::Iterator MonitorList::iterator() const {
198 return Iterator(Atomic::load_acquire(&_head));
199 }
200
201 ObjectMonitor* MonitorList::Iterator::next() {
202 ObjectMonitor* current = _current;
203 _current = current->next_om();
204 return current;
205 }
206
207 // The "core" versions of monitor enter and exit reside in this file.
208 // The interpreter and compilers contain specialized transliterated
209 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
210 // fast_lock(...) for instance. If you make changes here, make sure to modify the
211 // interpreter, and both C1 and C2 fast-path inline locking code emission.
212 //
213 // -----------------------------------------------------------------------------
214
215 #ifdef DTRACE_ENABLED
216
217 // Only bother with this argument setup if dtrace is available
218 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
219
220 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
221 char* bytes = nullptr; \
222 int len = 0; \
223 jlong jtid = SharedRuntime::get_java_tid(thread); \
224 Symbol* klassname = obj->klass()->name(); \
225 if (klassname != nullptr) { \
226 bytes = (char*)klassname->bytes(); \
227 len = klassname->utf8_length(); \
228 }
229
230 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
231 { \
232 if (DTraceMonitorProbes) { \
233 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
234 HOTSPOT_MONITOR_WAIT(jtid, \
235 (uintptr_t)(monitor), bytes, len, (millis)); \
236 } \
237 }
238
239 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
240 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
241 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
242
243 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
244 { \
245 if (DTraceMonitorProbes) { \
246 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
247 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
248 (uintptr_t)(monitor), bytes, len); \
249 } \
250 }
251
252 #else // ndef DTRACE_ENABLED
253
254 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
255 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
256
257 #endif // ndef DTRACE_ENABLED
258
259 // This exists only as a workaround of dtrace bug 6254741
260 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
261 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
262 return 0;
263 }
264
265 static constexpr size_t inflation_lock_count() {
266 return 256;
267 }
268
269 // Static storage for an array of PlatformMutex.
270 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
271
272 static inline PlatformMutex* inflation_lock(size_t index) {
273 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
274 }
275
276 void ObjectSynchronizer::initialize() {
277 for (size_t i = 0; i < inflation_lock_count(); i++) {
278 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
279 }
280 // Start the ceiling with the estimate for one thread.
281 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
282
283 // Start the timer for deflations, so it does not trigger immediately.
284 _last_async_deflation_time_ns = os::javaTimeNanos();
285
286 if (LockingMode == LM_LIGHTWEIGHT) {
287 LightweightSynchronizer::initialize();
288 }
289 }
290
291 MonitorList ObjectSynchronizer::_in_use_list;
292 // monitors_used_above_threshold() policy is as follows:
293 //
294 // The ratio of the current _in_use_list count to the ceiling is used
295 // to determine if we are above MonitorUsedDeflationThreshold and need
296 // to do an async monitor deflation cycle. The ceiling is increased by
297 // AvgMonitorsPerThreadEstimate when a thread is added to the system
298 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
299 // removed from the system.
300 //
301 // Note: If the _in_use_list max exceeds the ceiling, then
302 // monitors_used_above_threshold() will use the in_use_list max instead
303 // of the thread count derived ceiling because we have used more
304 // ObjectMonitors than the estimated average.
305 //
306 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
307 // no-progress async monitor deflation cycles in a row, then the ceiling
308 // is adjusted upwards by monitors_used_above_threshold().
309 //
310 // Start the ceiling with the estimate for one thread in initialize()
311 // which is called after cmd line options are processed.
312 static size_t _in_use_list_ceiling = 0;
313 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
314 bool volatile ObjectSynchronizer::_is_final_audit = false;
315 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
316 static uintx _no_progress_cnt = 0;
317 static bool _no_progress_skip_increment = false;
318
319 // =====================> Quick functions
320
321 // The quick_* forms are special fast-path variants used to improve
322 // performance. In the simplest case, a "quick_*" implementation could
323 // simply return false, in which case the caller will perform the necessary
324 // state transitions and call the slow-path form.
325 // The fast-path is designed to handle frequently arising cases in an efficient
326 // manner and is just a degenerate "optimistic" variant of the slow-path.
327 // returns true -- to indicate the call was satisfied.
328 // returns false -- to indicate the call needs the services of the slow-path.
329 // A no-loitering ordinance is in effect for code in the quick_* family
330 // operators: safepoints or indefinite blocking (blocking that might span a
331 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
332 // entry.
333 //
334 // Consider: An interesting optimization is to have the JIT recognize the
335 // following common idiom:
336 // synchronized (someobj) { .... ; notify(); }
337 // That is, we find a notify() or notifyAll() call that immediately precedes
338 // the monitorexit operation. In that case the JIT could fuse the operations
339 // into a single notifyAndExit() runtime primitive.
340
341 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
342 assert(current->thread_state() == _thread_in_Java, "invariant");
343 NoSafepointVerifier nsv;
344 if (obj == nullptr) return false; // slow-path for invalid obj
345 const markWord mark = obj->mark();
346
347 if (LockingMode == LM_LIGHTWEIGHT) {
348 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
349 // Degenerate notify
350 // fast-locked by caller so by definition the implied waitset is empty.
351 return true;
352 }
353 } else if (LockingMode == LM_LEGACY) {
354 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
355 // Degenerate notify
356 // stack-locked by caller so by definition the implied waitset is empty.
357 return true;
358 }
359 }
360
361 if (mark.has_monitor()) {
362 ObjectMonitor* const mon = read_monitor(current, obj, mark);
363 if (LockingMode == LM_LIGHTWEIGHT && mon == nullptr) {
364 // Racing with inflation/deflation go slow path
365 return false;
366 }
367 assert(mon->object() == oop(obj), "invariant");
368 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
369
370 if (mon->first_waiter() != nullptr) {
371 // We have one or more waiters. Since this is an inflated monitor
372 // that we own, we quickly notify them here and now, avoiding the slow-path.
373 if (all) {
374 mon->quick_notifyAll(current);
375 } else {
376 mon->quick_notify(current);
377 }
378 }
379 return true;
380 }
381
382 // other IMS exception states take the slow-path
383 return false;
384 }
385
386 static bool useHeavyMonitors() {
387 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
388 return LockingMode == LM_MONITOR;
389 #else
390 return false;
391 #endif
392 }
393
394 // The LockNode emitted directly at the synchronization site would have
395 // been too big if it were to have included support for the cases of inflated
396 // recursive enter and exit, so they go here instead.
397 // Note that we can't safely call AsyncPrintJavaStack() from within
398 // quick_enter() as our thread state remains _in_Java.
399
400 bool ObjectSynchronizer::quick_enter_legacy(oop obj, BasicLock* lock, JavaThread* current) {
401 assert(current->thread_state() == _thread_in_Java, "invariant");
402
403 if (useHeavyMonitors()) {
404 return false; // Slow path
405 }
406
407 assert(LockingMode == LM_LEGACY, "legacy mode below");
408
409 const markWord mark = obj->mark();
410
411 if (mark.has_monitor()) {
412
413 ObjectMonitor* const m = read_monitor(mark);
414 // An async deflation or GC can race us before we manage to make
415 // the ObjectMonitor busy by setting the owner below. If we detect
416 // that race we just bail out to the slow-path here.
417 if (m->object_peek() == nullptr) {
418 return false;
419 }
420
421 // Lock contention and Transactional Lock Elision (TLE) diagnostics
422 // and observability
423 // Case: light contention possibly amenable to TLE
424 // Case: TLE inimical operations such as nested/recursive synchronization
425
426 if (m->has_owner(current)) {
427 m->increment_recursions(current);
428 current->inc_held_monitor_count();
429 return true;
430 }
431
432 // This Java Monitor is inflated so obj's header will never be
433 // displaced to this thread's BasicLock. Make the displaced header
434 // non-null so this BasicLock is not seen as recursive nor as
435 // being locked. We do this unconditionally so that this thread's
436 // BasicLock cannot be mis-interpreted by any stack walkers. For
437 // performance reasons, stack walkers generally first check for
438 // stack-locking in the object's header, the second check is for
439 // recursive stack-locking in the displaced header in the BasicLock,
440 // and last are the inflated Java Monitor (ObjectMonitor) checks.
441 lock->set_displaced_header(markWord::unused_mark());
442
443 if (!m->has_owner() && m->try_set_owner(current)) {
444 assert(m->recursions() == 0, "invariant");
445 current->inc_held_monitor_count();
446 return true;
447 }
448 }
449
450 // Note that we could inflate in quick_enter.
451 // This is likely a useful optimization
452 // Critically, in quick_enter() we must not:
453 // -- block indefinitely, or
454 // -- reach a safepoint
455
456 return false; // revert to slow-path
457 }
458
459 // Handle notifications when synchronizing on value based classes
460 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
461 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
462 frame last_frame = locking_thread->last_frame();
463 bool bcp_was_adjusted = false;
464 // Don't decrement bcp if it points to the frame's first instruction. This happens when
465 // handle_sync_on_value_based_class() is called because of a synchronized method. There
466 // is no actual monitorenter instruction in the byte code in this case.
467 if (last_frame.is_interpreted_frame() &&
468 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
469 // adjust bcp to point back to monitorenter so that we print the correct line numbers
470 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
471 bcp_was_adjusted = true;
472 }
473
474 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
475 ResourceMark rm;
476 stringStream ss;
477 locking_thread->print_active_stack_on(&ss);
478 char* base = (char*)strstr(ss.base(), "at");
479 char* newline = (char*)strchr(ss.base(), '\n');
480 if (newline != nullptr) {
481 *newline = '\0';
482 }
483 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
484 } else {
485 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
486 ResourceMark rm;
487 Log(valuebasedclasses) vblog;
488
489 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
490 if (locking_thread->has_last_Java_frame()) {
491 LogStream info_stream(vblog.info());
492 locking_thread->print_active_stack_on(&info_stream);
493 } else {
494 vblog.info("Cannot find the last Java frame");
495 }
496
497 EventSyncOnValueBasedClass event;
498 if (event.should_commit()) {
499 event.set_valueBasedClass(obj->klass());
500 event.commit();
501 }
502 }
503
504 if (bcp_was_adjusted) {
505 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
506 }
507 }
508
509 // -----------------------------------------------------------------------------
510 // Monitor Enter/Exit
511
512 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
513 // When called with locking_thread != Thread::current() some mechanism must synchronize
514 // the locking_thread with respect to the current thread. Currently only used when
515 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
516 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
517
518 if (LockingMode == LM_LIGHTWEIGHT) {
519 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
520 }
521
522 if (!enter_fast_impl(obj, lock, locking_thread)) {
523 // Inflated ObjectMonitor::enter_for is required
524
525 // An async deflation can race after the inflate_for() call and before
526 // enter_for() can make the ObjectMonitor busy. enter_for() returns false
527 // if we have lost the race to async deflation and we simply try again.
528 while (true) {
529 ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
530 if (monitor->enter_for(locking_thread)) {
531 return;
532 }
533 assert(monitor->is_being_async_deflated(), "must be");
534 }
535 }
536 }
537
538 void ObjectSynchronizer::enter_legacy(Handle obj, BasicLock* lock, JavaThread* current) {
539 if (!enter_fast_impl(obj, lock, current)) {
540 // Inflated ObjectMonitor::enter is required
541
542 // An async deflation can race after the inflate() call and before
543 // enter() can make the ObjectMonitor busy. enter() returns false if
544 // we have lost the race to async deflation and we simply try again.
545 while (true) {
546 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
547 if (monitor->enter(current)) {
548 return;
549 }
550 }
551 }
552 }
553
554 // The interpreter and compiler assembly code tries to lock using the fast path
555 // of this algorithm. Make sure to update that code if the following function is
556 // changed. The implementation is extremely sensitive to race condition. Be careful.
557 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
558 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
559
560 if (obj->klass()->is_value_based()) {
561 handle_sync_on_value_based_class(obj, locking_thread);
562 }
563
564 locking_thread->inc_held_monitor_count();
565
566 if (!useHeavyMonitors()) {
567 if (LockingMode == LM_LEGACY) {
568 markWord mark = obj->mark();
569 if (mark.is_unlocked()) {
570 // Anticipate successful CAS -- the ST of the displaced mark must
571 // be visible <= the ST performed by the CAS.
572 lock->set_displaced_header(mark);
573 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
574 return true;
575 }
576 } else if (mark.has_locker() &&
577 locking_thread->is_lock_owned((address) mark.locker())) {
578 assert(lock != mark.locker(), "must not re-lock the same lock");
579 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
580 lock->set_displaced_header(markWord::from_pointer(nullptr));
581 return true;
582 }
583
584 // The object header will never be displaced to this lock,
585 // so it does not matter what the value is, except that it
586 // must be non-zero to avoid looking like a re-entrant lock,
587 // and must not look locked either.
588 lock->set_displaced_header(markWord::unused_mark());
589
590 // Failed to fast lock.
591 return false;
592 }
593 } else if (VerifyHeavyMonitors) {
594 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
595 }
596
597 return false;
598 }
599
600 void ObjectSynchronizer::exit_legacy(oop object, BasicLock* lock, JavaThread* current) {
601 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
602
603 if (!useHeavyMonitors()) {
604 markWord mark = object->mark();
605 if (LockingMode == LM_LEGACY) {
606 markWord dhw = lock->displaced_header();
607 if (dhw.value() == 0) {
608 // If the displaced header is null, then this exit matches up with
609 // a recursive enter. No real work to do here except for diagnostics.
610 #ifndef PRODUCT
611 if (mark != markWord::INFLATING()) {
612 // Only do diagnostics if we are not racing an inflation. Simply
613 // exiting a recursive enter of a Java Monitor that is being
614 // inflated is safe; see the has_monitor() comment below.
615 assert(!mark.is_unlocked(), "invariant");
616 assert(!mark.has_locker() ||
617 current->is_lock_owned((address)mark.locker()), "invariant");
618 if (mark.has_monitor()) {
619 // The BasicLock's displaced_header is marked as a recursive
620 // enter and we have an inflated Java Monitor (ObjectMonitor).
621 // This is a special case where the Java Monitor was inflated
622 // after this thread entered the stack-lock recursively. When a
623 // Java Monitor is inflated, we cannot safely walk the Java
624 // Monitor owner's stack and update the BasicLocks because a
625 // Java Monitor can be asynchronously inflated by a thread that
626 // does not own the Java Monitor.
627 ObjectMonitor* m = read_monitor(mark);
628 assert(m->object()->mark() == mark, "invariant");
629 assert(m->is_entered(current), "invariant");
630 }
631 }
632 #endif
633 return;
634 }
635
636 if (mark == markWord::from_pointer(lock)) {
637 // If the object is stack-locked by the current thread, try to
638 // swing the displaced header from the BasicLock back to the mark.
639 assert(dhw.is_neutral(), "invariant");
640 if (object->cas_set_mark(dhw, mark) == mark) {
641 return;
642 }
643 }
644 }
645 } else if (VerifyHeavyMonitors) {
646 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
647 }
648
649 // We have to take the slow-path of possible inflation and then exit.
650 // The ObjectMonitor* can't be async deflated until ownership is
651 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
652 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
653 assert(!monitor->has_anonymous_owner(), "must not be");
654 monitor->exit(current);
655 }
656
657 // -----------------------------------------------------------------------------
658 // JNI locks on java objects
659 // NOTE: must use heavy weight monitor to handle jni monitor enter
660 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
661 // Top native frames in the stack will not be seen if we attempt
662 // preemption, since we start walking from the last Java anchor.
663 NoPreemptMark npm(current);
664
665 if (obj->klass()->is_value_based()) {
666 handle_sync_on_value_based_class(obj, current);
667 }
668
669 // the current locking is from JNI instead of Java code
670 current->set_current_pending_monitor_is_from_java(false);
671 // An async deflation can race after the inflate() call and before
672 // enter() can make the ObjectMonitor busy. enter() returns false if
673 // we have lost the race to async deflation and we simply try again.
674 while (true) {
675 ObjectMonitor* monitor;
676 bool entered;
677 if (LockingMode == LM_LIGHTWEIGHT) {
678 BasicLock lock;
679 entered = LightweightSynchronizer::inflate_and_enter(obj(), &lock, inflate_cause_jni_enter, current, current) != nullptr;
680 } else {
681 monitor = inflate(current, obj(), inflate_cause_jni_enter);
682 entered = monitor->enter(current);
683 }
684
685 if (entered) {
686 current->inc_held_monitor_count(1, true);
687 break;
688 }
689 }
690 current->set_current_pending_monitor_is_from_java(true);
691 }
692
693 // NOTE: must use heavy weight monitor to handle jni monitor exit
694 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
695 JavaThread* current = THREAD;
696
697 ObjectMonitor* monitor;
698 if (LockingMode == LM_LIGHTWEIGHT) {
699 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
700 } else {
701 // The ObjectMonitor* can't be async deflated until ownership is
702 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
703 monitor = inflate(current, obj, inflate_cause_jni_exit);
704 }
705 // If this thread has locked the object, exit the monitor. We
706 // intentionally do not use CHECK on check_owner because we must exit the
707 // monitor even if an exception was already pending.
708 if (monitor->check_owner(THREAD)) {
709 monitor->exit(current);
710 current->dec_held_monitor_count(1, true);
711 }
712 }
713
714 // -----------------------------------------------------------------------------
715 // Internal VM locks on java objects
716 // standard constructor, allows locking failures
717 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) : _npm(thread) {
718 _thread = thread;
719 _thread->check_for_valid_safepoint_state();
720 _obj = obj;
721
722 if (_obj() != nullptr) {
723 ObjectSynchronizer::enter(_obj, &_lock, _thread);
724 }
725 }
726
727 ObjectLocker::~ObjectLocker() {
728 if (_obj() != nullptr) {
729 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
730 }
731 }
732
733
734 // -----------------------------------------------------------------------------
735 // Wait/Notify/NotifyAll
736 // NOTE: must use heavy weight monitor to handle wait()
737
738 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
739 JavaThread* current = THREAD;
740 if (millis < 0) {
741 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
742 }
743
744 ObjectMonitor* monitor;
745 if (LockingMode == LM_LIGHTWEIGHT) {
746 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
747 } else {
748 // The ObjectMonitor* can't be async deflated because the _waiters
749 // field is incremented before ownership is dropped and decremented
750 // after ownership is regained.
751 monitor = inflate(current, obj(), inflate_cause_wait);
752 }
753
754 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
755 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
756
757 // This dummy call is in place to get around dtrace bug 6254741. Once
758 // that's fixed we can uncomment the following line, remove the call
759 // and change this function back into a "void" func.
760 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
761 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
762 return ret_code;
763 }
764
765 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
766 if (millis < 0) {
767 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
768 }
769
770 ObjectMonitor* monitor;
771 if (LockingMode == LM_LIGHTWEIGHT) {
772 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
773 } else {
774 monitor = inflate(THREAD, obj(), inflate_cause_wait);
775 }
776 monitor->wait(millis, false, THREAD);
777 }
778
779
780 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
781 JavaThread* current = THREAD;
782
783 markWord mark = obj->mark();
784 if (LockingMode == LM_LIGHTWEIGHT) {
785 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
786 // Not inflated so there can't be any waiters to notify.
787 return;
788 }
789 } else if (LockingMode == LM_LEGACY) {
790 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
791 // Not inflated so there can't be any waiters to notify.
792 return;
793 }
794 }
795
796 ObjectMonitor* monitor;
797 if (LockingMode == LM_LIGHTWEIGHT) {
798 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
799 } else {
800 // The ObjectMonitor* can't be async deflated until ownership is
801 // dropped by the calling thread.
802 monitor = inflate(current, obj(), inflate_cause_notify);
803 }
804 monitor->notify(CHECK);
805 }
806
807 // NOTE: see comment of notify()
808 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
809 JavaThread* current = THREAD;
810
811 markWord mark = obj->mark();
812 if (LockingMode == LM_LIGHTWEIGHT) {
813 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
814 // Not inflated so there can't be any waiters to notify.
815 return;
816 }
817 } else if (LockingMode == LM_LEGACY) {
818 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
819 // Not inflated so there can't be any waiters to notify.
820 return;
821 }
822 }
823
824 ObjectMonitor* monitor;
825 if (LockingMode == LM_LIGHTWEIGHT) {
826 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
827 } else {
828 // The ObjectMonitor* can't be async deflated until ownership is
829 // dropped by the calling thread.
830 monitor = inflate(current, obj(), inflate_cause_notify);
831 }
832 monitor->notifyAll(CHECK);
833 }
834
835 // -----------------------------------------------------------------------------
836 // Hash Code handling
837
838 struct SharedGlobals {
839 char _pad_prefix[OM_CACHE_LINE_SIZE];
840 // This is a highly shared mostly-read variable.
841 // To avoid false-sharing it needs to be the sole occupant of a cache line.
842 volatile int stw_random;
843 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
844 // Hot RW variable -- Sequester to avoid false-sharing
845 volatile int hc_sequence;
846 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
847 };
848
849 static SharedGlobals GVars;
850
851 static markWord read_stable_mark(oop obj) {
852 markWord mark = obj->mark_acquire();
853 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
854 // New lightweight locking does not use the markWord::INFLATING() protocol.
855 return mark; // normal fast-path return
856 }
857
858 int its = 0;
859 for (;;) {
860 markWord mark = obj->mark_acquire();
861 if (!mark.is_being_inflated()) {
862 return mark; // normal fast-path return
863 }
864
865 // The object is being inflated by some other thread.
866 // The caller of read_stable_mark() must wait for inflation to complete.
867 // Avoid live-lock.
868
869 ++its;
870 if (its > 10000 || !os::is_MP()) {
871 if (its & 1) {
872 os::naked_yield();
873 } else {
874 // Note that the following code attenuates the livelock problem but is not
875 // a complete remedy. A more complete solution would require that the inflating
876 // thread hold the associated inflation lock. The following code simply restricts
877 // the number of spinners to at most one. We'll have N-2 threads blocked
878 // on the inflationlock, 1 thread holding the inflation lock and using
879 // a yield/park strategy, and 1 thread in the midst of inflation.
880 // A more refined approach would be to change the encoding of INFLATING
881 // to allow encapsulation of a native thread pointer. Threads waiting for
882 // inflation to complete would use CAS to push themselves onto a singly linked
883 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
884 // and calling park(). When inflation was complete the thread that accomplished inflation
885 // would detach the list and set the markword to inflated with a single CAS and
886 // then for each thread on the list, set the flag and unpark() the thread.
887
888 // Index into the lock array based on the current object address.
889 static_assert(is_power_of_2(inflation_lock_count()), "must be");
890 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
891 int YieldThenBlock = 0;
892 assert(ix < inflation_lock_count(), "invariant");
893 inflation_lock(ix)->lock();
894 while (obj->mark_acquire() == markWord::INFLATING()) {
895 // Beware: naked_yield() is advisory and has almost no effect on some platforms
896 // so we periodically call current->_ParkEvent->park(1).
897 // We use a mixed spin/yield/block mechanism.
898 if ((YieldThenBlock++) >= 16) {
899 Thread::current()->_ParkEvent->park(1);
900 } else {
901 os::naked_yield();
902 }
903 }
904 inflation_lock(ix)->unlock();
905 }
906 } else {
907 SpinPause(); // SMP-polite spinning
908 }
909 }
910 }
911
912 // hashCode() generation :
913 //
914 // Possibilities:
915 // * MD5Digest of {obj,stw_random}
916 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
917 // * A DES- or AES-style SBox[] mechanism
918 // * One of the Phi-based schemes, such as:
919 // 2654435761 = 2^32 * Phi (golden ratio)
920 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
921 // * A variation of Marsaglia's shift-xor RNG scheme.
922 // * (obj ^ stw_random) is appealing, but can result
923 // in undesirable regularity in the hashCode values of adjacent objects
924 // (objects allocated back-to-back, in particular). This could potentially
925 // result in hashtable collisions and reduced hashtable efficiency.
926 // There are simple ways to "diffuse" the middle address bits over the
927 // generated hashCode values:
928
929 intptr_t ObjectSynchronizer::get_next_hash(Thread* current, oop obj) {
930 intptr_t value = 0;
931 if (hashCode == 0) {
932 // This form uses global Park-Miller RNG.
933 // On MP system we'll have lots of RW access to a global, so the
934 // mechanism induces lots of coherency traffic.
935 value = os::random();
936 } else if (hashCode == 1) {
937 // This variation has the property of being stable (idempotent)
938 // between STW operations. This can be useful in some of the 1-0
939 // synchronization schemes.
940 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
941 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
942 } else if (hashCode == 2) {
943 value = 1; // for sensitivity testing
944 } else if (hashCode == 3) {
945 value = ++GVars.hc_sequence;
946 } else if (hashCode == 4) {
947 value = cast_from_oop<intptr_t>(obj);
948 } else if (hashCode == 5) {
949 // Marsaglia's xor-shift scheme with thread-specific state
950 // This is probably the best overall implementation -- we'll
951 // likely make this the default in future releases.
952 unsigned t = current->_hashStateX;
953 t ^= (t << 11);
954 current->_hashStateX = current->_hashStateY;
955 current->_hashStateY = current->_hashStateZ;
956 current->_hashStateZ = current->_hashStateW;
957 unsigned v = current->_hashStateW;
958 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
959 current->_hashStateW = v;
960 value = v;
961 } else {
962 assert(UseCompactObjectHeaders, "Only with compact i-hash");
963 #ifdef _LP64
964 uint64_t val = cast_from_oop<uint64_t>(obj);
965 uint32_t hash = FastHash::get_hash32((uint32_t)val, (uint32_t)(val >> 32));
966 #else
967 uint32_t val = cast_from_oop<uint32_t>(obj);
968 uint32_t hash = FastHash::get_hash32(val, UCONST64(0xAAAAAAAA));
969 #endif
970 value= static_cast<intptr_t>(hash);
971 }
972
973 value &= markWord::hash_mask;
974 if (hashCode != 6 && value == 0) value = 0xBAD;
975 assert(value != markWord::no_hash || hashCode == 6, "invariant");
976 return value;
977 }
978
979 static intptr_t install_hash_code(Thread* current, oop obj) {
980 assert(UseObjectMonitorTable && LockingMode == LM_LIGHTWEIGHT, "must be");
981
982 markWord mark = obj->mark_acquire();
983 for (;;) {
984 if (UseCompactObjectHeaders) {
985 if (mark.is_hashed()) {
986 return LightweightSynchronizer::get_hash(mark, obj);
987 }
988 intptr_t hash = ObjectSynchronizer::get_next_hash(current, obj); // get a new hash
989 markWord new_mark;
990 if (mark.is_not_hashed_expanded()) {
991 new_mark = mark.set_hashed_expanded();
992 int offset = mark.klass()->hash_offset_in_bytes(obj, mark);
993 obj->int_field_put(offset, (jint) hash);
994 } else {
995 new_mark = mark.set_hashed_not_expanded();
996 }
997 markWord old_mark = obj->cas_set_mark(new_mark, mark);
998 if (old_mark == mark) {
999 return hash;
1000 }
1001 mark = old_mark;
1002 } else {
1003 intptr_t hash = mark.hash();
1004 if (hash != 0) {
1005 return hash;
1006 }
1007
1008 hash = ObjectSynchronizer::get_next_hash(current, obj);
1009 const markWord old_mark = mark;
1010 const markWord new_mark = old_mark.copy_set_hash(hash);
1011
1012 mark = obj->cas_set_mark(new_mark, old_mark);
1013 if (old_mark == mark) {
1014 return hash;
1015 }
1016 }
1017 }
1018 }
1019
1020 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
1021 if (UseObjectMonitorTable) {
1022 // Since the monitor isn't in the object header, the hash can simply be
1023 // installed in the object header.
1024 return install_hash_code(current, obj);
1025 }
1026
1027 while (true) {
1028 ObjectMonitor* monitor = nullptr;
1029 markWord temp, test;
1030 intptr_t hash;
1031 markWord mark = read_stable_mark(obj);
1032 if (VerifyHeavyMonitors) {
1033 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
1034 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1035 }
1036 if (mark.is_unlocked() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1037 hash = mark.hash();
1038 if (hash != 0) { // if it has a hash, just return it
1039 return hash;
1040 }
1041 hash = get_next_hash(current, obj); // get a new hash
1042 temp = mark.copy_set_hash(hash); // merge the hash into header
1043 // try to install the hash
1044 test = obj->cas_set_mark(temp, mark);
1045 if (test == mark) { // if the hash was installed, return it
1046 return hash;
1047 }
1048 if (LockingMode == LM_LIGHTWEIGHT) {
1049 // CAS failed, retry
1050 continue;
1051 }
1052 // Failed to install the hash. It could be that another thread
1053 // installed the hash just before our attempt or inflation has
1054 // occurred or... so we fall thru to inflate the monitor for
1055 // stability and then install the hash.
1056 } else if (mark.has_monitor()) {
1057 monitor = mark.monitor();
1058 temp = monitor->header();
1059 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1060 hash = temp.hash();
1061 if (hash != 0) {
1062 // It has a hash.
1063
1064 // Separate load of dmw/header above from the loads in
1065 // is_being_async_deflated().
1066
1067 // dmw/header and _contentions may get written by different threads.
1068 // Make sure to observe them in the same order when having several observers.
1069 OrderAccess::loadload_for_IRIW();
1070
1071 if (monitor->is_being_async_deflated()) {
1072 // But we can't safely use the hash if we detect that async
1073 // deflation has occurred. So we attempt to restore the
1074 // header/dmw to the object's header so that we only retry
1075 // once if the deflater thread happens to be slow.
1076 monitor->install_displaced_markword_in_object(obj);
1077 continue;
1078 }
1079 return hash;
1080 }
1081 // Fall thru so we only have one place that installs the hash in
1082 // the ObjectMonitor.
1083 } else if (LockingMode == LM_LEGACY && mark.has_locker()
1084 && current->is_Java_thread()
1085 && JavaThread::cast(current)->is_lock_owned((address)mark.locker())) {
1086 // This is a stack-lock owned by the calling thread so fetch the
1087 // displaced markWord from the BasicLock on the stack.
1088 temp = mark.displaced_mark_helper();
1089 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1090 hash = temp.hash();
1091 if (hash != 0) { // if it has a hash, just return it
1092 return hash;
1093 }
1094 // WARNING:
1095 // The displaced header in the BasicLock on a thread's stack
1096 // is strictly immutable. It CANNOT be changed in ANY cases.
1097 // So we have to inflate the stack-lock into an ObjectMonitor
1098 // even if the current thread owns the lock. The BasicLock on
1099 // a thread's stack can be asynchronously read by other threads
1100 // during an inflate() call so any change to that stack memory
1101 // may not propagate to other threads correctly.
1102 }
1103
1104 // Inflate the monitor to set the hash.
1105
1106 // There's no need to inflate if the mark has already got a monitor.
1107 // NOTE: an async deflation can race after we get the monitor and
1108 // before we can update the ObjectMonitor's header with the hash
1109 // value below.
1110 monitor = mark.has_monitor() ? mark.monitor() : inflate(current, obj, inflate_cause_hash_code);
1111 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1112 mark = monitor->header();
1113 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1114 hash = mark.hash();
1115 if (hash == 0) { // if it does not have a hash
1116 hash = get_next_hash(current, obj); // get a new hash
1117 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1118 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1119 uintptr_t v = Atomic::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
1120 test = markWord(v);
1121 if (test != mark) {
1122 // The attempt to update the ObjectMonitor's header/dmw field
1123 // did not work. This can happen if another thread managed to
1124 // merge in the hash just before our cmpxchg().
1125 // If we add any new usages of the header/dmw field, this code
1126 // will need to be updated.
1127 hash = test.hash();
1128 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1129 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1130 }
1131 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
1132 // If we detect that async deflation has occurred, then we
1133 // attempt to restore the header/dmw to the object's header
1134 // so that we only retry once if the deflater thread happens
1135 // to be slow.
1136 monitor->install_displaced_markword_in_object(obj);
1137 continue;
1138 }
1139 }
1140 // We finally get the hash.
1141 return hash;
1142 }
1143 }
1144
1145 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1146 Handle h_obj) {
1147 assert(current == JavaThread::current(), "Can only be called on current thread");
1148 oop obj = h_obj();
1149
1150 markWord mark = read_stable_mark(obj);
1151
1152 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1153 // stack-locked case, header points into owner's stack
1154 return current->is_lock_owned((address)mark.locker());
1155 }
1156
1157 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1158 // fast-locking case, see if lock is in current's lock stack
1159 return current->lock_stack().contains(h_obj());
1160 }
1161
1162 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1163 ObjectMonitor* monitor = read_monitor(current, obj, mark);
1164 if (monitor != nullptr) {
1165 return monitor->is_entered(current) != 0;
1166 }
1167 // Racing with inflation/deflation, retry
1168 mark = obj->mark_acquire();
1169
1170 if (mark.is_fast_locked()) {
1171 // Some other thread fast_locked, current could not have held the lock
1172 return false;
1173 }
1174 }
1175
1176 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1177 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1178 // The first stage of async deflation does not affect any field
1179 // used by this comparison so the ObjectMonitor* is usable here.
1180 ObjectMonitor* monitor = read_monitor(mark);
1181 return monitor->is_entered(current) != 0;
1182 }
1183 // Unlocked case, header in place
1184 assert(mark.is_unlocked(), "sanity check");
1185 return false;
1186 }
1187
1188 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1189 oop obj = h_obj();
1190 markWord mark = read_stable_mark(obj);
1191
1192 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1193 // stack-locked so header points into owner's stack.
1194 // owning_thread_from_monitor_owner() may also return null here:
1195 return Threads::owning_thread_from_stacklock(t_list, (address) mark.locker());
1196 }
1197
1198 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1199 // fast-locked so get owner from the object.
1200 // owning_thread_from_object() may also return null here:
1201 return Threads::owning_thread_from_object(t_list, h_obj());
1202 }
1203
1204 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1205 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
1206 if (monitor != nullptr) {
1207 return Threads::owning_thread_from_monitor(t_list, monitor);
1208 }
1209 // Racing with inflation/deflation, retry
1210 mark = obj->mark_acquire();
1211
1212 if (mark.is_fast_locked()) {
1213 // Some other thread fast_locked
1214 return Threads::owning_thread_from_object(t_list, h_obj());
1215 }
1216 }
1217
1218 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1219 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1220 // The first stage of async deflation does not affect any field
1221 // used by this comparison so the ObjectMonitor* is usable here.
1222 ObjectMonitor* monitor = read_monitor(mark);
1223 assert(monitor != nullptr, "monitor should be non-null");
1224 // owning_thread_from_monitor() may also return null here:
1225 return Threads::owning_thread_from_monitor(t_list, monitor);
1226 }
1227
1228 // Unlocked case, header in place
1229 // Cannot have assertion since this object may have been
1230 // locked by another thread when reaching here.
1231 // assert(mark.is_unlocked(), "sanity check");
1232
1233 return nullptr;
1234 }
1235
1236 // Visitors ...
1237
1238 // Iterate over all ObjectMonitors.
1239 template <typename Function>
1240 void ObjectSynchronizer::monitors_iterate(Function function) {
1241 MonitorList::Iterator iter = _in_use_list.iterator();
1242 while (iter.has_next()) {
1243 ObjectMonitor* monitor = iter.next();
1244 function(monitor);
1245 }
1246 }
1247
1248 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1249 // returns true.
1250 template <typename OwnerFilter>
1251 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1252 monitors_iterate([&](ObjectMonitor* monitor) {
1253 // This function is only called at a safepoint or when the
1254 // target thread is suspended or when the target thread is
1255 // operating on itself. The current closures in use today are
1256 // only interested in an owned ObjectMonitor and ownership
1257 // cannot be dropped under the calling contexts so the
1258 // ObjectMonitor cannot be async deflated.
1259 if (monitor->has_owner() && filter(monitor)) {
1260 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1261
1262 closure->do_monitor(monitor);
1263 }
1264 });
1265 }
1266
1267 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1268 // ObjectMonitors where owner is set to a stack-lock address in thread.
1269 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1270 int64_t key = ObjectMonitor::owner_id_from(thread);
1271 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1272 return owned_monitors_iterate_filtered(closure, thread_filter);
1273 }
1274
1275 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
1276 int64_t key = ObjectMonitor::owner_id_from(vthread);
1277 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1278 return owned_monitors_iterate_filtered(closure, thread_filter);
1279 }
1280
1281 // Iterate ObjectMonitors owned by any thread.
1282 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1283 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
1284 return owned_monitors_iterate_filtered(closure, all_filter);
1285 }
1286
1287 static bool monitors_used_above_threshold(MonitorList* list) {
1288 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1289 return false;
1290 }
1291 size_t monitors_used = list->count();
1292 if (monitors_used == 0) { // empty list is easy
1293 return false;
1294 }
1295 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
1296 // Make sure that we use a ceiling value that is not lower than
1297 // previous, not lower than the recorded max used by the system, and
1298 // not lower than the current number of monitors in use (which can
1299 // race ahead of max). The result is guaranteed > 0.
1300 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
1301
1302 // Check if our monitor usage is above the threshold:
1303 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1304 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1305 // Deflate monitors if over the threshold percentage, unless no
1306 // progress on previous deflations.
1307 bool is_above_threshold = true;
1308
1309 // Check if it's time to adjust the in_use_list_ceiling up, due
1310 // to too many async deflation attempts without any progress.
1311 if (NoAsyncDeflationProgressMax != 0 &&
1312 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1313 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1314 size_t delta = (size_t)(ceiling * remainder) + 1;
1315 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
1316 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
1317 : ceiling + delta;
1318
1319 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1320 log_info(monitorinflation)("Too many deflations without progress; "
1321 "bumping in_use_list_ceiling from %zu"
1322 " to %zu", old_ceiling, new_ceiling);
1323 _no_progress_cnt = 0;
1324 ceiling = new_ceiling;
1325
1326 // Check if our monitor usage is still above the threshold:
1327 monitor_usage = (monitors_used * 100LL) / ceiling;
1328 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
1329 }
1330 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
1331 ", monitor_usage=%zu, threshold=%d",
1332 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1333 return is_above_threshold;
1334 }
1335
1336 return false;
1337 }
1338
1339 size_t ObjectSynchronizer::in_use_list_count() {
1340 return _in_use_list.count();
1341 }
1342
1343 size_t ObjectSynchronizer::in_use_list_max() {
1344 return _in_use_list.max();
1345 }
1346
1347 size_t ObjectSynchronizer::in_use_list_ceiling() {
1348 return _in_use_list_ceiling;
1349 }
1350
1351 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1352 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1353 }
1354
1355 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1356 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1357 }
1358
1359 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1360 _in_use_list_ceiling = new_value;
1361 }
1362
1363 bool ObjectSynchronizer::is_async_deflation_needed() {
1364 if (is_async_deflation_requested()) {
1365 // Async deflation request.
1366 log_info(monitorinflation)("Async deflation needed: explicit request");
1367 return true;
1368 }
1369
1370 jlong time_since_last = time_since_last_async_deflation_ms();
1371
1372 if (AsyncDeflationInterval > 0 &&
1373 time_since_last > AsyncDeflationInterval &&
1374 monitors_used_above_threshold(&_in_use_list)) {
1375 // It's been longer than our specified deflate interval and there
1376 // are too many monitors in use. We don't deflate more frequently
1377 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1378 // in order to not swamp the MonitorDeflationThread.
1379 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1380 return true;
1381 }
1382
1383 if (GuaranteedAsyncDeflationInterval > 0 &&
1384 time_since_last > GuaranteedAsyncDeflationInterval) {
1385 // It's been longer than our specified guaranteed deflate interval.
1386 // We need to clean up the used monitors even if the threshold is
1387 // not reached, to keep the memory utilization at bay when many threads
1388 // touched many monitors.
1389 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
1390 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1391 GuaranteedAsyncDeflationInterval, time_since_last);
1392
1393 // If this deflation has no progress, then it should not affect the no-progress
1394 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1395 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1396 // the generic code would bump the no-progress counter, and we compensate for that
1397 // by telling it to skip the update.
1398 //
1399 // If this deflation has progress, then it should let non-progress tracking
1400 // know about this, otherwise the threshold heuristics would kick in, potentially
1401 // experience no-progress due to aggressive cleanup by this deflation, and think
1402 // it is still in no-progress stride. In this "progress" case, the generic code would
1403 // zero the counter, and we allow it to happen.
1404 _no_progress_skip_increment = true;
1405
1406 return true;
1407 }
1408
1409 return false;
1410 }
1411
1412 void ObjectSynchronizer::request_deflate_idle_monitors() {
1413 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1414 set_is_async_deflation_requested(true);
1415 ml.notify_all();
1416 }
1417
1418 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1419 JavaThread* current = JavaThread::current();
1420 bool ret_code = false;
1421
1422 jlong last_time = last_async_deflation_time_ns();
1423
1424 request_deflate_idle_monitors();
1425
1426 const int N_CHECKS = 5;
1427 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1428 if (last_async_deflation_time_ns() > last_time) {
1429 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1430 ret_code = true;
1431 break;
1432 }
1433 {
1434 // JavaThread has to honor the blocking protocol.
1435 ThreadBlockInVM tbivm(current);
1436 os::naked_short_sleep(999); // sleep for almost 1 second
1437 }
1438 }
1439 if (!ret_code) {
1440 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1441 }
1442
1443 return ret_code;
1444 }
1445
1446 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1447 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1448 }
1449
1450 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1451 const oop obj,
1452 ObjectSynchronizer::InflateCause cause) {
1453 assert(event != nullptr, "invariant");
1454 const Klass* monitor_klass = obj->klass();
1455 if (ObjectMonitor::is_jfr_excluded(monitor_klass)) {
1456 return;
1457 }
1458 event->set_monitorClass(monitor_klass);
1459 event->set_address((uintptr_t)(void*)obj);
1460 event->set_cause((u1)cause);
1461 event->commit();
1462 }
1463
1464 // Fast path code shared by multiple functions
1465 void ObjectSynchronizer::inflate_helper(oop obj) {
1466 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1467 markWord mark = obj->mark_acquire();
1468 if (mark.has_monitor()) {
1469 ObjectMonitor* monitor = read_monitor(mark);
1470 markWord dmw = monitor->header();
1471 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1472 return;
1473 }
1474 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1475 }
1476
1477 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1478 assert(current == Thread::current(), "must be");
1479 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1480 return inflate_impl(current->is_Java_thread() ? JavaThread::cast(current) : nullptr, obj, cause);
1481 }
1482
1483 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1484 assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1485 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_for");
1486 return inflate_impl(thread, obj, cause);
1487 }
1488
1489 ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* locking_thread, oop object, const InflateCause cause) {
1490 // The JavaThread* locking_thread requires that the locking_thread == Thread::current() or
1491 // is suspended throughout the call by some other mechanism.
1492 // The thread might be nullptr when called from a non JavaThread. (As may still be
1493 // the case from FastHashCode). However it is only important for correctness that the
1494 // thread is set when called from ObjectSynchronizer::enter from the owning thread,
1495 // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
1496 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_impl");
1497 EventJavaMonitorInflate event;
1498
1499 for (;;) {
1500 const markWord mark = object->mark_acquire();
1501
1502 // The mark can be in one of the following states:
1503 // * inflated - If the ObjectMonitor owner is anonymous and the
1504 // locking_thread owns the object lock, then we
1505 // make the locking_thread the ObjectMonitor owner.
1506 // * stack-locked - Coerce it to inflated from stack-locked.
1507 // * INFLATING - Busy wait for conversion from stack-locked to
1508 // inflated.
1509 // * unlocked - Aggressively inflate the object.
1510
1511 // CASE: inflated
1512 if (mark.has_monitor()) {
1513 ObjectMonitor* inf = mark.monitor();
1514 markWord dmw = inf->header();
1515 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1516 if (inf->has_anonymous_owner() && locking_thread != nullptr) {
1517 assert(LockingMode == LM_LEGACY, "invariant");
1518 if (locking_thread->is_lock_owned((address)inf->stack_locker())) {
1519 inf->set_stack_locker(nullptr);
1520 inf->set_owner_from_anonymous(locking_thread);
1521 }
1522 }
1523 return inf;
1524 }
1525
1526 // CASE: inflation in progress - inflating over a stack-lock.
1527 // Some other thread is converting from stack-locked to inflated.
1528 // Only that thread can complete inflation -- other threads must wait.
1529 // The INFLATING value is transient.
1530 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1531 // We could always eliminate polling by parking the thread on some auxiliary list.
1532 if (mark == markWord::INFLATING()) {
1533 read_stable_mark(object);
1534 continue;
1535 }
1536
1537 // CASE: stack-locked
1538 // Could be stack-locked either by current or by some other thread.
1539 //
1540 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1541 // to install INFLATING into the mark word. We originally installed INFLATING,
1542 // allocated the ObjectMonitor, and then finally STed the address of the
1543 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1544 // the interval in which INFLATING appeared in the mark, thus increasing
1545 // the odds of inflation contention. If we lose the race to set INFLATING,
1546 // then we just delete the ObjectMonitor and loop around again.
1547 //
1548 LogStreamHandle(Trace, monitorinflation) lsh;
1549 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1550 ObjectMonitor* m = new ObjectMonitor(object);
1551 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1552 // We do this before the CAS in order to minimize the length of time
1553 // in which INFLATING appears in the mark.
1554
1555 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1556 if (cmp != mark) {
1557 delete m;
1558 continue; // Interference -- just retry
1559 }
1560
1561 // We've successfully installed INFLATING (0) into the mark-word.
1562 // This is the only case where 0 will appear in a mark-word.
1563 // Only the singular thread that successfully swings the mark-word
1564 // to 0 can perform (or more precisely, complete) inflation.
1565 //
1566 // Why do we CAS a 0 into the mark-word instead of just CASing the
1567 // mark-word from the stack-locked value directly to the new inflated state?
1568 // Consider what happens when a thread unlocks a stack-locked object.
1569 // It attempts to use CAS to swing the displaced header value from the
1570 // on-stack BasicLock back into the object header. Recall also that the
1571 // header value (hash code, etc) can reside in (a) the object header, or
1572 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1573 // header in an ObjectMonitor. The inflate() routine must copy the header
1574 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1575 // the while preserving the hashCode stability invariants. If the owner
1576 // decides to release the lock while the value is 0, the unlock will fail
1577 // and control will eventually pass from slow_exit() to inflate. The owner
1578 // will then spin, waiting for the 0 value to disappear. Put another way,
1579 // the 0 causes the owner to stall if the owner happens to try to
1580 // drop the lock (restoring the header from the BasicLock to the object)
1581 // while inflation is in-progress. This protocol avoids races that might
1582 // would otherwise permit hashCode values to change or "flicker" for an object.
1583 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1584 // 0 serves as a "BUSY" inflate-in-progress indicator.
1585
1586
1587 // fetch the displaced mark from the owner's stack.
1588 // The owner can't die or unwind past the lock while our INFLATING
1589 // object is in the mark. Furthermore the owner can't complete
1590 // an unlock on the object, either.
1591 markWord dmw = mark.displaced_mark_helper();
1592 // Catch if the object's header is not neutral (not locked and
1593 // not marked is what we care about here).
1594 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1595
1596 // Setup monitor fields to proper values -- prepare the monitor
1597 m->set_header(dmw);
1598
1599 // Note that a thread can inflate an object
1600 // that it has stack-locked -- as might happen in wait() -- directly
1601 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1602 if (locking_thread != nullptr && locking_thread->is_lock_owned((address)mark.locker())) {
1603 m->set_owner(locking_thread);
1604 } else {
1605 // Use ANONYMOUS_OWNER to indicate that the owner is the BasicLock on the stack,
1606 // and set the stack locker field in the monitor.
1607 m->set_stack_locker(mark.locker());
1608 m->set_anonymous_owner();
1609 }
1610 // TODO-FIXME: assert BasicLock->dhw != 0.
1611
1612 // Must preserve store ordering. The monitor state must
1613 // be stable at the time of publishing the monitor address.
1614 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1615 // Release semantics so that above set_object() is seen first.
1616 object->release_set_mark(markWord::encode(m));
1617
1618 // Once ObjectMonitor is configured and the object is associated
1619 // with the ObjectMonitor, it is safe to allow async deflation:
1620 _in_use_list.add(m);
1621
1622 if (log_is_enabled(Trace, monitorinflation)) {
1623 ResourceMark rm;
1624 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1625 INTPTR_FORMAT ", type='%s'", p2i(object),
1626 object->mark().value(), object->klass()->external_name());
1627 }
1628 if (event.should_commit()) {
1629 post_monitor_inflate_event(&event, object, cause);
1630 }
1631 return m;
1632 }
1633
1634 // CASE: unlocked
1635 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1636 // If we know we're inflating for entry it's better to inflate by swinging a
1637 // pre-locked ObjectMonitor pointer into the object header. A successful
1638 // CAS inflates the object *and* confers ownership to the inflating thread.
1639 // In the current implementation we use a 2-step mechanism where we CAS()
1640 // to inflate and then CAS() again to try to swing _owner from null to current.
1641 // An inflateTry() method that we could call from enter() would be useful.
1642
1643 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
1644 ObjectMonitor* m = new ObjectMonitor(object);
1645 // prepare m for installation - set monitor to initial state
1646 m->set_header(mark);
1647
1648 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1649 delete m;
1650 m = nullptr;
1651 continue;
1652 // interference - the markword changed - just retry.
1653 // The state-transitions are one-way, so there's no chance of
1654 // live-lock -- "Inflated" is an absorbing state.
1655 }
1656
1657 // Once the ObjectMonitor is configured and object is associated
1658 // with the ObjectMonitor, it is safe to allow async deflation:
1659 _in_use_list.add(m);
1660
1661 if (log_is_enabled(Trace, monitorinflation)) {
1662 ResourceMark rm;
1663 lsh.print_cr("inflate(unlocked): object=" INTPTR_FORMAT ", mark="
1664 INTPTR_FORMAT ", type='%s'", p2i(object),
1665 object->mark().value(), object->klass()->external_name());
1666 }
1667 if (event.should_commit()) {
1668 post_monitor_inflate_event(&event, object, cause);
1669 }
1670 return m;
1671 }
1672 }
1673
1674 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1675 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1676 //
1677 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1678 MonitorList::Iterator iter = _in_use_list.iterator();
1679 size_t deflated_count = 0;
1680 Thread* current = Thread::current();
1681
1682 while (iter.has_next()) {
1683 if (deflated_count >= (size_t)MonitorDeflationMax) {
1684 break;
1685 }
1686 ObjectMonitor* mid = iter.next();
1687 if (mid->deflate_monitor(current)) {
1688 deflated_count++;
1689 }
1690
1691 // Must check for a safepoint/handshake and honor it.
1692 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1693 }
1694
1695 return deflated_count;
1696 }
1697
1698 class HandshakeForDeflation : public HandshakeClosure {
1699 public:
1700 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1701
1702 void do_thread(Thread* thread) {
1703 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1704 INTPTR_FORMAT, p2i(thread));
1705 if (thread->is_Java_thread()) {
1706 // Clear OM cache
1707 JavaThread* jt = JavaThread::cast(thread);
1708 jt->om_clear_monitor_cache();
1709 }
1710 }
1711 };
1712
1713 class VM_RendezvousGCThreads : public VM_Operation {
1714 public:
1715 bool evaluate_at_safepoint() const override { return false; }
1716 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1717 void doit() override {
1718 Universe::heap()->safepoint_synchronize_begin();
1719 Universe::heap()->safepoint_synchronize_end();
1720 };
1721 };
1722
1723 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1724 ObjectMonitorDeflationSafepointer* safepointer) {
1725 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1726 size_t deleted_count = 0;
1727 for (ObjectMonitor* monitor: *delete_list) {
1728 delete monitor;
1729 deleted_count++;
1730 // A JavaThread must check for a safepoint/handshake and honor it.
1731 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1732 }
1733 return deleted_count;
1734 }
1735
1736 class ObjectMonitorDeflationLogging: public StackObj {
1737 LogStreamHandle(Debug, monitorinflation) _debug;
1738 LogStreamHandle(Info, monitorinflation) _info;
1739 LogStream* _stream;
1740 elapsedTimer _timer;
1741
1742 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1743 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1744 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1745
1746 public:
1747 ObjectMonitorDeflationLogging()
1748 : _debug(), _info(), _stream(nullptr) {
1749 if (_debug.is_enabled()) {
1750 _stream = &_debug;
1751 } else if (_info.is_enabled()) {
1752 _stream = &_info;
1753 }
1754 }
1755
1756 void begin() {
1757 if (_stream != nullptr) {
1758 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1759 ceiling(), count(), max());
1760 _timer.start();
1761 }
1762 }
1763
1764 void before_handshake(size_t unlinked_count) {
1765 if (_stream != nullptr) {
1766 _timer.stop();
1767 _stream->print_cr("before handshaking: unlinked_count=%zu"
1768 ", in_use_list stats: ceiling=%zu, count="
1769 "%zu, max=%zu",
1770 unlinked_count, ceiling(), count(), max());
1771 }
1772 }
1773
1774 void after_handshake() {
1775 if (_stream != nullptr) {
1776 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1777 "%zu, count=%zu, max=%zu",
1778 ceiling(), count(), max());
1779 _timer.start();
1780 }
1781 }
1782
1783 void end(size_t deflated_count, size_t unlinked_count) {
1784 if (_stream != nullptr) {
1785 _timer.stop();
1786 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1787 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1788 deflated_count, unlinked_count, _timer.seconds());
1789 }
1790 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1791 ceiling(), count(), max());
1792 }
1793 }
1794
1795 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1796 if (_stream != nullptr) {
1797 _timer.stop();
1798 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1799 "%zu, count=%zu, max=%zu",
1800 op_name, cnt_name, cnt, ceiling(), count(), max());
1801 }
1802 }
1803
1804 void after_block_for_safepoint(const char* op_name) {
1805 if (_stream != nullptr) {
1806 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1807 ", count=%zu, max=%zu", op_name,
1808 ceiling(), count(), max());
1809 _timer.start();
1810 }
1811 }
1812 };
1813
1814 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1815 if (!SafepointMechanism::should_process(_current)) {
1816 return;
1817 }
1818
1819 // A safepoint/handshake has started.
1820 _log->before_block_for_safepoint(op_name, count_name, counter);
1821
1822 {
1823 // Honor block request.
1824 ThreadBlockInVM tbivm(_current);
1825 }
1826
1827 _log->after_block_for_safepoint(op_name);
1828 }
1829
1830 // This function is called by the MonitorDeflationThread to deflate
1831 // ObjectMonitors.
1832 size_t ObjectSynchronizer::deflate_idle_monitors() {
1833 JavaThread* current = JavaThread::current();
1834 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1835
1836 // The async deflation request has been processed.
1837 _last_async_deflation_time_ns = os::javaTimeNanos();
1838 set_is_async_deflation_requested(false);
1839
1840 ObjectMonitorDeflationLogging log;
1841 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1842
1843 log.begin();
1844
1845 // Deflate some idle ObjectMonitors.
1846 size_t deflated_count = deflate_monitor_list(&safepointer);
1847
1848 // Unlink the deflated ObjectMonitors from the in-use list.
1849 size_t unlinked_count = 0;
1850 size_t deleted_count = 0;
1851 if (deflated_count > 0) {
1852 ResourceMark rm(current);
1853 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1854 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1855
1856 #ifdef ASSERT
1857 if (UseObjectMonitorTable) {
1858 for (ObjectMonitor* monitor : delete_list) {
1859 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1860 }
1861 }
1862 #endif
1863
1864 log.before_handshake(unlinked_count);
1865
1866 // A JavaThread needs to handshake in order to safely free the
1867 // ObjectMonitors that were deflated in this cycle.
1868 HandshakeForDeflation hfd_hc;
1869 Handshake::execute(&hfd_hc);
1870 // Also, we sync and desync GC threads around the handshake, so that they can
1871 // safely read the mark-word and look-through to the object-monitor, without
1872 // being afraid that the object-monitor is going away.
1873 VM_RendezvousGCThreads sync_gc;
1874 VMThread::execute(&sync_gc);
1875
1876 log.after_handshake();
1877
1878 // After the handshake, safely free the ObjectMonitors that were
1879 // deflated and unlinked in this cycle.
1880
1881 // Delete the unlinked ObjectMonitors.
1882 deleted_count = delete_monitors(&delete_list, &safepointer);
1883 assert(unlinked_count == deleted_count, "must be");
1884 }
1885
1886 log.end(deflated_count, unlinked_count);
1887
1888 GVars.stw_random = os::random();
1889
1890 if (deflated_count != 0) {
1891 _no_progress_cnt = 0;
1892 } else if (_no_progress_skip_increment) {
1893 _no_progress_skip_increment = false;
1894 } else {
1895 _no_progress_cnt++;
1896 }
1897
1898 return deflated_count;
1899 }
1900
1901 // Monitor cleanup on JavaThread::exit
1902
1903 // Iterate through monitor cache and attempt to release thread's monitors
1904 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1905 private:
1906 JavaThread* _thread;
1907
1908 public:
1909 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1910 void do_monitor(ObjectMonitor* mid) {
1911 intx rec = mid->complete_exit(_thread);
1912 _thread->dec_held_monitor_count(rec + 1);
1913 }
1914 };
1915
1916 // Release all inflated monitors owned by current thread. Lightweight monitors are
1917 // ignored. This is meant to be called during JNI thread detach which assumes
1918 // all remaining monitors are heavyweight. All exceptions are swallowed.
1919 // Scanning the extant monitor list can be time consuming.
1920 // A simple optimization is to add a per-thread flag that indicates a thread
1921 // called jni_monitorenter() during its lifetime.
1922 //
1923 // Instead of NoSafepointVerifier it might be cheaper to
1924 // use an idiom of the form:
1925 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1926 // <code that must not run at safepoint>
1927 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1928 // Since the tests are extremely cheap we could leave them enabled
1929 // for normal product builds.
1930
1931 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1932 assert(current == JavaThread::current(), "must be current Java thread");
1933 NoSafepointVerifier nsv;
1934 ReleaseJavaMonitorsClosure rjmc(current);
1935 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1936 assert(!current->has_pending_exception(), "Should not be possible");
1937 current->clear_pending_exception();
1938 assert(current->held_monitor_count() == 0, "Should not be possible");
1939 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1940 current->clear_jni_monitor_count();
1941 }
1942
1943 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1944 switch (cause) {
1945 case inflate_cause_vm_internal: return "VM Internal";
1946 case inflate_cause_monitor_enter: return "Monitor Enter";
1947 case inflate_cause_wait: return "Monitor Wait";
1948 case inflate_cause_notify: return "Monitor Notify";
1949 case inflate_cause_hash_code: return "Monitor Hash Code";
1950 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1951 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1952 default:
1953 ShouldNotReachHere();
1954 }
1955 return "Unknown";
1956 }
1957
1958 //------------------------------------------------------------------------------
1959 // Debugging code
1960
1961 u_char* ObjectSynchronizer::get_gvars_addr() {
1962 return (u_char*)&GVars;
1963 }
1964
1965 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1966 return (u_char*)&GVars.hc_sequence;
1967 }
1968
1969 size_t ObjectSynchronizer::get_gvars_size() {
1970 return sizeof(SharedGlobals);
1971 }
1972
1973 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1974 return (u_char*)&GVars.stw_random;
1975 }
1976
1977 // Do the final audit and print of ObjectMonitor stats; must be done
1978 // by the VMThread at VM exit time.
1979 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1980 assert(Thread::current()->is_VM_thread(), "sanity check");
1981
1982 if (is_final_audit()) { // Only do the audit once.
1983 return;
1984 }
1985 set_is_final_audit();
1986 log_info(monitorinflation)("Starting the final audit.");
1987
1988 if (log_is_enabled(Info, monitorinflation)) {
1989 LogStreamHandle(Info, monitorinflation) ls;
1990 audit_and_print_stats(&ls, true /* on_exit */);
1991 }
1992 }
1993
1994 // This function can be called by the MonitorDeflationThread or it can be called when
1995 // we are trying to exit the VM. The list walker functions can run in parallel with
1996 // the other list operations.
1997 // Calls to this function can be added in various places as a debugging
1998 // aid.
1999 //
2000 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
2001 int error_cnt = 0;
2002
2003 ls->print_cr("Checking in_use_list:");
2004 chk_in_use_list(ls, &error_cnt);
2005
2006 if (error_cnt == 0) {
2007 ls->print_cr("No errors found in in_use_list checks.");
2008 } else {
2009 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
2010 }
2011
2012 // When exiting, only log the interesting entries at the Info level.
2013 // When called at intervals by the MonitorDeflationThread, log output
2014 // at the Trace level since there can be a lot of it.
2015 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
2016 LogStreamHandle(Trace, monitorinflation) ls_tr;
2017 log_in_use_monitor_details(&ls_tr, true /* log_all */);
2018 } else if (on_exit) {
2019 log_in_use_monitor_details(ls, false /* log_all */);
2020 }
2021
2022 ls->flush();
2023
2024 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2025 }
2026
2027 // Check the in_use_list; log the results of the checks.
2028 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
2029 size_t l_in_use_count = _in_use_list.count();
2030 size_t l_in_use_max = _in_use_list.max();
2031 out->print_cr("count=%zu, max=%zu", l_in_use_count,
2032 l_in_use_max);
2033
2034 size_t ck_in_use_count = 0;
2035 MonitorList::Iterator iter = _in_use_list.iterator();
2036 while (iter.has_next()) {
2037 ObjectMonitor* mid = iter.next();
2038 chk_in_use_entry(mid, out, error_cnt_p);
2039 ck_in_use_count++;
2040 }
2041
2042 if (l_in_use_count == ck_in_use_count) {
2043 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
2044 l_in_use_count, ck_in_use_count);
2045 } else {
2046 out->print_cr("WARNING: in_use_count=%zu is not equal to "
2047 "ck_in_use_count=%zu", l_in_use_count,
2048 ck_in_use_count);
2049 }
2050
2051 size_t ck_in_use_max = _in_use_list.max();
2052 if (l_in_use_max == ck_in_use_max) {
2053 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
2054 l_in_use_max, ck_in_use_max);
2055 } else {
2056 out->print_cr("WARNING: in_use_max=%zu is not equal to "
2057 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
2058 }
2059 }
2060
2061 // Check an in-use monitor entry; log any errors.
2062 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2063 int* error_cnt_p) {
2064 if (n->owner_is_DEFLATER_MARKER()) {
2065 // This could happen when monitor deflation blocks for a safepoint.
2066 return;
2067 }
2068
2069
2070 if (n->metadata() == 0) {
2071 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2072 "have non-null _metadata (header/hash) field.", p2i(n));
2073 *error_cnt_p = *error_cnt_p + 1;
2074 }
2075
2076 const oop obj = n->object_peek();
2077 if (obj == nullptr) {
2078 return;
2079 }
2080
2081 const markWord mark = obj->mark();
2082 if (!mark.has_monitor()) {
2083 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2084 "object does not think it has a monitor: obj="
2085 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2086 p2i(obj), mark.value());
2087 *error_cnt_p = *error_cnt_p + 1;
2088 return;
2089 }
2090
2091 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
2092 if (n != obj_mon) {
2093 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2094 "object does not refer to the same monitor: obj="
2095 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2096 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2097 *error_cnt_p = *error_cnt_p + 1;
2098 }
2099 }
2100
2101 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2102 // flags indicate why the entry is in-use, 'object' and 'object type'
2103 // indicate the associated object and its type.
2104 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2105 if (_in_use_list.count() > 0) {
2106 stringStream ss;
2107 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
2108 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2109 out->print_cr("%18s %s %18s %18s",
2110 "monitor", "BHL", "object", "object type");
2111 out->print_cr("================== === ================== ==================");
2112
2113 auto is_interesting = [&](ObjectMonitor* monitor) {
2114 return log_all || monitor->has_owner() || monitor->is_busy();
2115 };
2116
2117 monitors_iterate([&](ObjectMonitor* monitor) {
2118 if (is_interesting(monitor)) {
2119 const oop obj = monitor->object_peek();
2120 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
2121 ResourceMark rm;
2122 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
2123 monitor->is_busy(), hash != 0, monitor->has_owner(),
2124 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2125 if (monitor->is_busy()) {
2126 out->print(" (%s)", monitor->is_busy_to_string(&ss));
2127 ss.reset();
2128 }
2129 out->cr();
2130 }
2131 });
2132 }
2133
2134 out->flush();
2135 }