1 /*
2 * Copyright (c) 1998, 2025, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "classfile/vmSymbols.hpp"
26 #include "gc/shared/collectedHeap.hpp"
27 #include "jfr/jfrEvents.hpp"
28 #include "logging/log.hpp"
29 #include "logging/logStream.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/padded.hpp"
32 #include "memory/resourceArea.hpp"
33 #include "memory/universe.hpp"
34 #include "oops/markWord.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "runtime/atomic.hpp"
37 #include "runtime/basicLock.inline.hpp"
38 #include "runtime/frame.inline.hpp"
39 #include "runtime/globals.hpp"
40 #include "runtime/handles.inline.hpp"
41 #include "runtime/handshake.hpp"
42 #include "runtime/interfaceSupport.inline.hpp"
43 #include "runtime/javaThread.hpp"
44 #include "runtime/lightweightSynchronizer.hpp"
45 #include "runtime/lockStack.inline.hpp"
46 #include "runtime/mutexLocker.hpp"
47 #include "runtime/objectMonitor.hpp"
48 #include "runtime/objectMonitor.inline.hpp"
49 #include "runtime/os.inline.hpp"
50 #include "runtime/osThread.hpp"
51 #include "runtime/safepointMechanism.inline.hpp"
52 #include "runtime/safepointVerifiers.hpp"
53 #include "runtime/sharedRuntime.hpp"
54 #include "runtime/stubRoutines.hpp"
55 #include "runtime/synchronizer.inline.hpp"
56 #include "runtime/threads.hpp"
57 #include "runtime/timer.hpp"
58 #include "runtime/trimNativeHeap.hpp"
59 #include "runtime/vframe.hpp"
60 #include "runtime/vmThread.hpp"
61 #include "utilities/align.hpp"
62 #include "utilities/dtrace.hpp"
63 #include "utilities/events.hpp"
64 #include "utilities/globalCounter.inline.hpp"
65 #include "utilities/globalDefinitions.hpp"
66 #include "utilities/linkedlist.hpp"
67 #include "utilities/preserveException.hpp"
68
69 class ObjectMonitorDeflationLogging;
70
71 void MonitorList::add(ObjectMonitor* m) {
72 ObjectMonitor* head;
73 do {
74 head = Atomic::load(&_head);
75 m->set_next_om(head);
76 } while (Atomic::cmpxchg(&_head, head, m) != head);
77
78 size_t count = Atomic::add(&_count, 1u, memory_order_relaxed);
79 size_t old_max;
80 do {
81 old_max = Atomic::load(&_max);
82 if (count <= old_max) {
83 break;
84 }
85 } while (Atomic::cmpxchg(&_max, old_max, count, memory_order_relaxed) != old_max);
86 }
87
88 size_t MonitorList::count() const {
89 return Atomic::load(&_count);
90 }
91
92 size_t MonitorList::max() const {
93 return Atomic::load(&_max);
94 }
95
96 class ObjectMonitorDeflationSafepointer : public StackObj {
97 JavaThread* const _current;
98 ObjectMonitorDeflationLogging* const _log;
99
100 public:
101 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
102 : _current(current), _log(log) {}
103
104 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
105 };
106
107 // Walk the in-use list and unlink deflated ObjectMonitors.
108 // Returns the number of unlinked ObjectMonitors.
109 size_t MonitorList::unlink_deflated(size_t deflated_count,
110 GrowableArray<ObjectMonitor*>* unlinked_list,
111 ObjectMonitorDeflationSafepointer* safepointer) {
112 size_t unlinked_count = 0;
113 ObjectMonitor* prev = nullptr;
114 ObjectMonitor* m = Atomic::load_acquire(&_head);
115
116 while (m != nullptr) {
117 if (m->is_being_async_deflated()) {
118 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
119 // modify the list once per batch. The batch starts at "m".
120 size_t unlinked_batch = 0;
121 ObjectMonitor* next = m;
122 // Look for at most MonitorUnlinkBatch monitors, or the number of
123 // deflated and not unlinked monitors, whatever comes first.
124 assert(deflated_count >= unlinked_count, "Sanity: underflow");
125 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
126 do {
127 ObjectMonitor* next_next = next->next_om();
128 unlinked_batch++;
129 unlinked_list->append(next);
130 next = next_next;
131 if (unlinked_batch >= unlinked_batch_limit) {
132 // Reached the max batch, so bail out of the gathering loop.
133 break;
134 }
135 if (prev == nullptr && Atomic::load(&_head) != m) {
136 // Current batch used to be at head, but it is not at head anymore.
137 // Bail out and figure out where we currently are. This avoids long
138 // walks searching for new prev during unlink under heavy list inserts.
139 break;
140 }
141 } while (next != nullptr && next->is_being_async_deflated());
142
143 // Unlink the found batch.
144 if (prev == nullptr) {
145 // The current batch is the first batch, so there is a chance that it starts at head.
146 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
147 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, m, next);
148 if (prev_head != m) {
149 // Something must have updated the head. Figure out the actual prev for this batch.
150 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
151 prev = n;
152 }
153 assert(prev != nullptr, "Should have found the prev for the current batch");
154 prev->set_next_om(next);
155 }
156 } else {
157 // The current batch is preceded by another batch. This guarantees the current batch
158 // does not start at head. Unlink the entire current batch without updating the head.
159 assert(Atomic::load(&_head) != m, "Sanity");
160 prev->set_next_om(next);
161 }
162
163 unlinked_count += unlinked_batch;
164 if (unlinked_count >= deflated_count) {
165 // Reached the max so bail out of the searching loop.
166 // There should be no more deflated monitors left.
167 break;
168 }
169 m = next;
170 } else {
171 prev = m;
172 m = m->next_om();
173 }
174
175 // Must check for a safepoint/handshake and honor it.
176 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
177 }
178
179 #ifdef ASSERT
180 // Invariant: the code above should unlink all deflated monitors.
181 // The code that runs after this unlinking does not expect deflated monitors.
182 // Notably, attempting to deflate the already deflated monitor would break.
183 {
184 ObjectMonitor* m = Atomic::load_acquire(&_head);
185 while (m != nullptr) {
186 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
187 m = m->next_om();
188 }
189 }
190 #endif
191
192 Atomic::sub(&_count, unlinked_count);
193 return unlinked_count;
194 }
195
196 MonitorList::Iterator MonitorList::iterator() const {
197 return Iterator(Atomic::load_acquire(&_head));
198 }
199
200 ObjectMonitor* MonitorList::Iterator::next() {
201 ObjectMonitor* current = _current;
202 _current = current->next_om();
203 return current;
204 }
205
206 // The "core" versions of monitor enter and exit reside in this file.
207 // The interpreter and compilers contain specialized transliterated
208 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
209 // fast_lock(...) for instance. If you make changes here, make sure to modify the
210 // interpreter, and both C1 and C2 fast-path inline locking code emission.
211 //
212 // -----------------------------------------------------------------------------
213
214 #ifdef DTRACE_ENABLED
215
216 // Only bother with this argument setup if dtrace is available
217 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
218
219 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
220 char* bytes = nullptr; \
221 int len = 0; \
222 jlong jtid = SharedRuntime::get_java_tid(thread); \
223 Symbol* klassname = obj->klass()->name(); \
224 if (klassname != nullptr) { \
225 bytes = (char*)klassname->bytes(); \
226 len = klassname->utf8_length(); \
227 }
228
229 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
230 { \
231 if (DTraceMonitorProbes) { \
232 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
233 HOTSPOT_MONITOR_WAIT(jtid, \
234 (uintptr_t)(monitor), bytes, len, (millis)); \
235 } \
236 }
237
238 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
239 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
240 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
241
242 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
243 { \
244 if (DTraceMonitorProbes) { \
245 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
246 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
247 (uintptr_t)(monitor), bytes, len); \
248 } \
249 }
250
251 #else // ndef DTRACE_ENABLED
252
253 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
254 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
255
256 #endif // ndef DTRACE_ENABLED
257
258 // This exists only as a workaround of dtrace bug 6254741
259 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
260 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
261 return 0;
262 }
263
264 static constexpr size_t inflation_lock_count() {
265 return 256;
266 }
267
268 // Static storage for an array of PlatformMutex.
269 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
270
271 static inline PlatformMutex* inflation_lock(size_t index) {
272 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
273 }
274
275 void ObjectSynchronizer::initialize() {
276 for (size_t i = 0; i < inflation_lock_count(); i++) {
277 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
278 }
279 // Start the ceiling with the estimate for one thread.
280 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
281
282 // Start the timer for deflations, so it does not trigger immediately.
283 _last_async_deflation_time_ns = os::javaTimeNanos();
284
285 if (LockingMode == LM_LIGHTWEIGHT) {
286 LightweightSynchronizer::initialize();
287 }
288 }
289
290 MonitorList ObjectSynchronizer::_in_use_list;
291 // monitors_used_above_threshold() policy is as follows:
292 //
293 // The ratio of the current _in_use_list count to the ceiling is used
294 // to determine if we are above MonitorUsedDeflationThreshold and need
295 // to do an async monitor deflation cycle. The ceiling is increased by
296 // AvgMonitorsPerThreadEstimate when a thread is added to the system
297 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
298 // removed from the system.
299 //
300 // Note: If the _in_use_list max exceeds the ceiling, then
301 // monitors_used_above_threshold() will use the in_use_list max instead
302 // of the thread count derived ceiling because we have used more
303 // ObjectMonitors than the estimated average.
304 //
305 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
306 // no-progress async monitor deflation cycles in a row, then the ceiling
307 // is adjusted upwards by monitors_used_above_threshold().
308 //
309 // Start the ceiling with the estimate for one thread in initialize()
310 // which is called after cmd line options are processed.
311 static size_t _in_use_list_ceiling = 0;
312 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
313 bool volatile ObjectSynchronizer::_is_final_audit = false;
314 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
315 static uintx _no_progress_cnt = 0;
316 static bool _no_progress_skip_increment = false;
317
318 // These checks are required for wait, notify and exit to avoid inflating the monitor to
319 // find out this inline type object cannot be locked.
320 #define CHECK_THROW_NOSYNC_IMSE(obj) \
321 if (EnableValhalla && (obj)->mark().is_inline_type()) { \
322 JavaThread* THREAD = current; \
323 ResourceMark rm(THREAD); \
324 THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
325 }
326
327 #define CHECK_THROW_NOSYNC_IMSE_0(obj) \
328 if (EnableValhalla && (obj)->mark().is_inline_type()) { \
329 JavaThread* THREAD = current; \
330 ResourceMark rm(THREAD); \
331 THROW_MSG_0(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
332 }
333
334 // =====================> Quick functions
335
336 // The quick_* forms are special fast-path variants used to improve
337 // performance. In the simplest case, a "quick_*" implementation could
338 // simply return false, in which case the caller will perform the necessary
339 // state transitions and call the slow-path form.
340 // The fast-path is designed to handle frequently arising cases in an efficient
341 // manner and is just a degenerate "optimistic" variant of the slow-path.
342 // returns true -- to indicate the call was satisfied.
343 // returns false -- to indicate the call needs the services of the slow-path.
344 // A no-loitering ordinance is in effect for code in the quick_* family
345 // operators: safepoints or indefinite blocking (blocking that might span a
346 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
347 // entry.
348 //
349 // Consider: An interesting optimization is to have the JIT recognize the
350 // following common idiom:
351 // synchronized (someobj) { .... ; notify(); }
352 // That is, we find a notify() or notifyAll() call that immediately precedes
353 // the monitorexit operation. In that case the JIT could fuse the operations
354 // into a single notifyAndExit() runtime primitive.
355
356 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
357 assert(current->thread_state() == _thread_in_Java, "invariant");
358 NoSafepointVerifier nsv;
359 if (obj == nullptr) return false; // slow-path for invalid obj
360 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
361 const markWord mark = obj->mark();
362
363 if (LockingMode == LM_LIGHTWEIGHT) {
364 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
365 // Degenerate notify
366 // fast-locked by caller so by definition the implied waitset is empty.
367 return true;
368 }
369 } else if (LockingMode == LM_LEGACY) {
370 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
371 // Degenerate notify
372 // stack-locked by caller so by definition the implied waitset is empty.
373 return true;
374 }
375 }
376
377 if (mark.has_monitor()) {
378 ObjectMonitor* const mon = read_monitor(current, obj, mark);
379 if (LockingMode == LM_LIGHTWEIGHT && mon == nullptr) {
380 // Racing with inflation/deflation go slow path
381 return false;
382 }
383 assert(mon->object() == oop(obj), "invariant");
384 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
385
386 if (mon->first_waiter() != nullptr) {
387 // We have one or more waiters. Since this is an inflated monitor
388 // that we own, we quickly notify them here and now, avoiding the slow-path.
389 if (all) {
390 mon->quick_notifyAll(current);
391 } else {
392 mon->quick_notify(current);
393 }
394 }
395 return true;
396 }
397
398 // other IMS exception states take the slow-path
399 return false;
400 }
401
402 static bool useHeavyMonitors() {
403 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
404 return LockingMode == LM_MONITOR;
405 #else
406 return false;
407 #endif
408 }
409
410 // The LockNode emitted directly at the synchronization site would have
411 // been too big if it were to have included support for the cases of inflated
412 // recursive enter and exit, so they go here instead.
413 // Note that we can't safely call AsyncPrintJavaStack() from within
414 // quick_enter() as our thread state remains _in_Java.
415
416 bool ObjectSynchronizer::quick_enter_legacy(oop obj, BasicLock* lock, JavaThread* current) {
417 assert(current->thread_state() == _thread_in_Java, "invariant");
418 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
419
420 if (useHeavyMonitors()) {
421 return false; // Slow path
422 }
423
424 assert(LockingMode == LM_LEGACY, "legacy mode below");
425
426 const markWord mark = obj->mark();
427
428 if (mark.has_monitor()) {
429
430 ObjectMonitor* const m = read_monitor(mark);
431 // An async deflation or GC can race us before we manage to make
432 // the ObjectMonitor busy by setting the owner below. If we detect
433 // that race we just bail out to the slow-path here.
434 if (m->object_peek() == nullptr) {
435 return false;
436 }
437
438 // Lock contention and Transactional Lock Elision (TLE) diagnostics
439 // and observability
440 // Case: light contention possibly amenable to TLE
441 // Case: TLE inimical operations such as nested/recursive synchronization
442
443 if (m->has_owner(current)) {
444 m->increment_recursions(current);
445 current->inc_held_monitor_count();
446 return true;
447 }
448
449 // This Java Monitor is inflated so obj's header will never be
450 // displaced to this thread's BasicLock. Make the displaced header
451 // non-null so this BasicLock is not seen as recursive nor as
452 // being locked. We do this unconditionally so that this thread's
453 // BasicLock cannot be mis-interpreted by any stack walkers. For
454 // performance reasons, stack walkers generally first check for
455 // stack-locking in the object's header, the second check is for
456 // recursive stack-locking in the displaced header in the BasicLock,
457 // and last are the inflated Java Monitor (ObjectMonitor) checks.
458 lock->set_displaced_header(markWord::unused_mark());
459
460 if (!m->has_owner() && m->try_set_owner(current)) {
461 assert(m->recursions() == 0, "invariant");
462 current->inc_held_monitor_count();
463 return true;
464 }
465 }
466
467 // Note that we could inflate in quick_enter.
468 // This is likely a useful optimization
469 // Critically, in quick_enter() we must not:
470 // -- block indefinitely, or
471 // -- reach a safepoint
472
473 return false; // revert to slow-path
474 }
475
476 // Handle notifications when synchronizing on value based classes
477 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
478 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
479 frame last_frame = locking_thread->last_frame();
480 bool bcp_was_adjusted = false;
481 // Don't decrement bcp if it points to the frame's first instruction. This happens when
482 // handle_sync_on_value_based_class() is called because of a synchronized method. There
483 // is no actual monitorenter instruction in the byte code in this case.
484 if (last_frame.is_interpreted_frame() &&
485 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
486 // adjust bcp to point back to monitorenter so that we print the correct line numbers
487 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
488 bcp_was_adjusted = true;
489 }
490
491 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
492 ResourceMark rm;
493 stringStream ss;
494 locking_thread->print_active_stack_on(&ss);
495 char* base = (char*)strstr(ss.base(), "at");
496 char* newline = (char*)strchr(ss.base(), '\n');
497 if (newline != nullptr) {
498 *newline = '\0';
499 }
500 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
501 } else {
502 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
503 ResourceMark rm;
504 Log(valuebasedclasses) vblog;
505
506 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
507 if (locking_thread->has_last_Java_frame()) {
508 LogStream info_stream(vblog.info());
509 locking_thread->print_active_stack_on(&info_stream);
510 } else {
511 vblog.info("Cannot find the last Java frame");
512 }
513
514 EventSyncOnValueBasedClass event;
515 if (event.should_commit()) {
516 event.set_valueBasedClass(obj->klass());
517 event.commit();
518 }
519 }
520
521 if (bcp_was_adjusted) {
522 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
523 }
524 }
525
526 // -----------------------------------------------------------------------------
527 // Monitor Enter/Exit
528
529 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
530 // When called with locking_thread != Thread::current() some mechanism must synchronize
531 // the locking_thread with respect to the current thread. Currently only used when
532 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
533 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
534 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "JITed code should never have locked an instance of a value class");
535
536 if (LockingMode == LM_LIGHTWEIGHT) {
537 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
538 }
539
540 if (!enter_fast_impl(obj, lock, locking_thread)) {
541 // Inflated ObjectMonitor::enter_for is required
542
543 // An async deflation can race after the inflate_for() call and before
544 // enter_for() can make the ObjectMonitor busy. enter_for() returns false
545 // if we have lost the race to async deflation and we simply try again.
546 while (true) {
547 ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
548 if (monitor->enter_for(locking_thread)) {
549 return;
550 }
551 assert(monitor->is_being_async_deflated(), "must be");
552 }
553 }
554 }
555
556 void ObjectSynchronizer::enter_legacy(Handle obj, BasicLock* lock, JavaThread* current) {
557 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "This method should never be called on an instance of an inline class");
558 if (!enter_fast_impl(obj, lock, current)) {
559 // Inflated ObjectMonitor::enter is required
560
561 // An async deflation can race after the inflate() call and before
562 // enter() can make the ObjectMonitor busy. enter() returns false if
563 // we have lost the race to async deflation and we simply try again.
564 while (true) {
565 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
566 if (monitor->enter(current)) {
567 return;
568 }
569 }
570 }
571 }
572
573 // The interpreter and compiler assembly code tries to lock using the fast path
574 // of this algorithm. Make sure to update that code if the following function is
575 // changed. The implementation is extremely sensitive to race condition. Be careful.
576 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
577 guarantee(!EnableValhalla || !obj->klass()->is_inline_klass(), "Attempt to inflate inline type");
578 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
579
580 if (obj->klass()->is_value_based()) {
581 handle_sync_on_value_based_class(obj, locking_thread);
582 }
583
584 locking_thread->inc_held_monitor_count();
585
586 if (!useHeavyMonitors()) {
587 if (LockingMode == LM_LEGACY) {
588 markWord mark = obj->mark();
589 if (mark.is_unlocked()) {
590 // Anticipate successful CAS -- the ST of the displaced mark must
591 // be visible <= the ST performed by the CAS.
592 lock->set_displaced_header(mark);
593 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
594 return true;
595 }
596 } else if (mark.has_locker() &&
597 locking_thread->is_lock_owned((address) mark.locker())) {
598 assert(lock != mark.locker(), "must not re-lock the same lock");
599 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
600 lock->set_displaced_header(markWord::from_pointer(nullptr));
601 return true;
602 }
603
604 // The object header will never be displaced to this lock,
605 // so it does not matter what the value is, except that it
606 // must be non-zero to avoid looking like a re-entrant lock,
607 // and must not look locked either.
608 lock->set_displaced_header(markWord::unused_mark());
609
610 // Failed to fast lock.
611 return false;
612 }
613 } else if (VerifyHeavyMonitors) {
614 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
615 }
616
617 return false;
618 }
619
620 void ObjectSynchronizer::exit_legacy(oop object, BasicLock* lock, JavaThread* current) {
621 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
622
623 if (!useHeavyMonitors()) {
624 markWord mark = object->mark();
625 if (EnableValhalla && mark.is_inline_type()) {
626 return;
627 }
628 if (LockingMode == LM_LEGACY) {
629 markWord dhw = lock->displaced_header();
630 if (dhw.value() == 0) {
631 // If the displaced header is null, then this exit matches up with
632 // a recursive enter. No real work to do here except for diagnostics.
633 #ifndef PRODUCT
634 if (mark != markWord::INFLATING()) {
635 // Only do diagnostics if we are not racing an inflation. Simply
636 // exiting a recursive enter of a Java Monitor that is being
637 // inflated is safe; see the has_monitor() comment below.
638 assert(!mark.is_unlocked(), "invariant");
639 assert(!mark.has_locker() ||
640 current->is_lock_owned((address)mark.locker()), "invariant");
641 if (mark.has_monitor()) {
642 // The BasicLock's displaced_header is marked as a recursive
643 // enter and we have an inflated Java Monitor (ObjectMonitor).
644 // This is a special case where the Java Monitor was inflated
645 // after this thread entered the stack-lock recursively. When a
646 // Java Monitor is inflated, we cannot safely walk the Java
647 // Monitor owner's stack and update the BasicLocks because a
648 // Java Monitor can be asynchronously inflated by a thread that
649 // does not own the Java Monitor.
650 ObjectMonitor* m = read_monitor(mark);
651 assert(m->object()->mark() == mark, "invariant");
652 assert(m->is_entered(current), "invariant");
653 }
654 }
655 #endif
656 return;
657 }
658
659 if (mark == markWord::from_pointer(lock)) {
660 // If the object is stack-locked by the current thread, try to
661 // swing the displaced header from the BasicLock back to the mark.
662 assert(dhw.is_neutral(), "invariant");
663 if (object->cas_set_mark(dhw, mark) == mark) {
664 return;
665 }
666 }
667 }
668 } else if (VerifyHeavyMonitors) {
669 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
670 }
671
672 // We have to take the slow-path of possible inflation and then exit.
673 // The ObjectMonitor* can't be async deflated until ownership is
674 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
675 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
676 assert(!monitor->has_anonymous_owner(), "must not be");
677 monitor->exit(current);
678 }
679
680 // -----------------------------------------------------------------------------
681 // JNI locks on java objects
682 // NOTE: must use heavy weight monitor to handle jni monitor enter
683 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
684 JavaThread* THREAD = current;
685 // Top native frames in the stack will not be seen if we attempt
686 // preemption, since we start walking from the last Java anchor.
687 NoPreemptMark npm(current);
688
689 if (obj->klass()->is_value_based()) {
690 handle_sync_on_value_based_class(obj, current);
691 }
692
693 if (EnableValhalla && obj->klass()->is_inline_klass()) {
694 ResourceMark rm(THREAD);
695 const char* desc = "Cannot synchronize on an instance of value class ";
696 const char* className = obj->klass()->external_name();
697 size_t msglen = strlen(desc) + strlen(className) + 1;
698 char* message = NEW_RESOURCE_ARRAY(char, msglen);
699 assert(message != nullptr, "NEW_RESOURCE_ARRAY should have called vm_exit_out_of_memory and not return nullptr");
700 THROW_MSG(vmSymbols::java_lang_IdentityException(), className);
701 }
702
703 // the current locking is from JNI instead of Java code
704 current->set_current_pending_monitor_is_from_java(false);
705 // An async deflation can race after the inflate() call and before
706 // enter() can make the ObjectMonitor busy. enter() returns false if
707 // we have lost the race to async deflation and we simply try again.
708 while (true) {
709 ObjectMonitor* monitor;
710 bool entered;
711 if (LockingMode == LM_LIGHTWEIGHT) {
712 BasicLock lock;
713 entered = LightweightSynchronizer::inflate_and_enter(obj(), &lock, inflate_cause_jni_enter, current, current) != nullptr;
714 } else {
715 monitor = inflate(current, obj(), inflate_cause_jni_enter);
716 entered = monitor->enter(current);
717 }
718
719 if (entered) {
720 current->inc_held_monitor_count(1, true);
721 break;
722 }
723 }
724 current->set_current_pending_monitor_is_from_java(true);
725 }
726
727 // NOTE: must use heavy weight monitor to handle jni monitor exit
728 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
729 JavaThread* current = THREAD;
730 CHECK_THROW_NOSYNC_IMSE(obj);
731
732 ObjectMonitor* monitor;
733 if (LockingMode == LM_LIGHTWEIGHT) {
734 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
735 } else {
736 // The ObjectMonitor* can't be async deflated until ownership is
737 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
738 monitor = inflate(current, obj, inflate_cause_jni_exit);
739 }
740 // If this thread has locked the object, exit the monitor. We
741 // intentionally do not use CHECK on check_owner because we must exit the
742 // monitor even if an exception was already pending.
743 if (monitor->check_owner(THREAD)) {
744 monitor->exit(current);
745 current->dec_held_monitor_count(1, true);
746 }
747 }
748
749 // -----------------------------------------------------------------------------
750 // Internal VM locks on java objects
751 // standard constructor, allows locking failures
752 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) : _npm(thread) {
753 _thread = thread;
754 _thread->check_for_valid_safepoint_state();
755 _obj = obj;
756
757 if (_obj() != nullptr) {
758 ObjectSynchronizer::enter(_obj, &_lock, _thread);
759 }
760 }
761
762 ObjectLocker::~ObjectLocker() {
763 if (_obj() != nullptr) {
764 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
765 }
766 }
767
768
769 // -----------------------------------------------------------------------------
770 // Wait/Notify/NotifyAll
771 // NOTE: must use heavy weight monitor to handle wait()
772
773 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
774 JavaThread* current = THREAD;
775 CHECK_THROW_NOSYNC_IMSE_0(obj);
776 if (millis < 0) {
777 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
778 }
779
780 ObjectMonitor* monitor;
781 if (LockingMode == LM_LIGHTWEIGHT) {
782 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
783 } else {
784 // The ObjectMonitor* can't be async deflated because the _waiters
785 // field is incremented before ownership is dropped and decremented
786 // after ownership is regained.
787 monitor = inflate(current, obj(), inflate_cause_wait);
788 }
789
790 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
791 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
792
793 // This dummy call is in place to get around dtrace bug 6254741. Once
794 // that's fixed we can uncomment the following line, remove the call
795 // and change this function back into a "void" func.
796 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
797 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
798 return ret_code;
799 }
800
801 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
802 if (millis < 0) {
803 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
804 }
805
806 ObjectMonitor* monitor;
807 if (LockingMode == LM_LIGHTWEIGHT) {
808 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
809 } else {
810 monitor = inflate(THREAD, obj(), inflate_cause_wait);
811 }
812 monitor->wait(millis, false, THREAD);
813 }
814
815
816 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
817 JavaThread* current = THREAD;
818 CHECK_THROW_NOSYNC_IMSE(obj);
819
820 markWord mark = obj->mark();
821 if (LockingMode == LM_LIGHTWEIGHT) {
822 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
823 // Not inflated so there can't be any waiters to notify.
824 return;
825 }
826 } else if (LockingMode == LM_LEGACY) {
827 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
828 // Not inflated so there can't be any waiters to notify.
829 return;
830 }
831 }
832
833 ObjectMonitor* monitor;
834 if (LockingMode == LM_LIGHTWEIGHT) {
835 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
836 } else {
837 // The ObjectMonitor* can't be async deflated until ownership is
838 // dropped by the calling thread.
839 monitor = inflate(current, obj(), inflate_cause_notify);
840 }
841 monitor->notify(CHECK);
842 }
843
844 // NOTE: see comment of notify()
845 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
846 JavaThread* current = THREAD;
847 CHECK_THROW_NOSYNC_IMSE(obj);
848
849 markWord mark = obj->mark();
850 if (LockingMode == LM_LIGHTWEIGHT) {
851 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
852 // Not inflated so there can't be any waiters to notify.
853 return;
854 }
855 } else if (LockingMode == LM_LEGACY) {
856 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
857 // Not inflated so there can't be any waiters to notify.
858 return;
859 }
860 }
861
862 ObjectMonitor* monitor;
863 if (LockingMode == LM_LIGHTWEIGHT) {
864 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
865 } else {
866 // The ObjectMonitor* can't be async deflated until ownership is
867 // dropped by the calling thread.
868 monitor = inflate(current, obj(), inflate_cause_notify);
869 }
870 monitor->notifyAll(CHECK);
871 }
872
873 // -----------------------------------------------------------------------------
874 // Hash Code handling
875
876 struct SharedGlobals {
877 char _pad_prefix[OM_CACHE_LINE_SIZE];
878 // This is a highly shared mostly-read variable.
879 // To avoid false-sharing it needs to be the sole occupant of a cache line.
880 volatile int stw_random;
881 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
882 // Hot RW variable -- Sequester to avoid false-sharing
883 volatile int hc_sequence;
884 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
885 };
886
887 static SharedGlobals GVars;
888
889 static markWord read_stable_mark(oop obj) {
890 markWord mark = obj->mark_acquire();
891 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
892 // New lightweight locking does not use the markWord::INFLATING() protocol.
893 return mark; // normal fast-path return
894 }
895
896 int its = 0;
897 for (;;) {
898 markWord mark = obj->mark_acquire();
899 if (!mark.is_being_inflated()) {
900 return mark; // normal fast-path return
901 }
902
903 // The object is being inflated by some other thread.
904 // The caller of read_stable_mark() must wait for inflation to complete.
905 // Avoid live-lock.
906
907 ++its;
908 if (its > 10000 || !os::is_MP()) {
909 if (its & 1) {
910 os::naked_yield();
911 } else {
912 // Note that the following code attenuates the livelock problem but is not
913 // a complete remedy. A more complete solution would require that the inflating
914 // thread hold the associated inflation lock. The following code simply restricts
915 // the number of spinners to at most one. We'll have N-2 threads blocked
916 // on the inflationlock, 1 thread holding the inflation lock and using
917 // a yield/park strategy, and 1 thread in the midst of inflation.
918 // A more refined approach would be to change the encoding of INFLATING
919 // to allow encapsulation of a native thread pointer. Threads waiting for
920 // inflation to complete would use CAS to push themselves onto a singly linked
921 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
922 // and calling park(). When inflation was complete the thread that accomplished inflation
923 // would detach the list and set the markword to inflated with a single CAS and
924 // then for each thread on the list, set the flag and unpark() the thread.
925
926 // Index into the lock array based on the current object address.
927 static_assert(is_power_of_2(inflation_lock_count()), "must be");
928 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
929 int YieldThenBlock = 0;
930 assert(ix < inflation_lock_count(), "invariant");
931 inflation_lock(ix)->lock();
932 while (obj->mark_acquire() == markWord::INFLATING()) {
933 // Beware: naked_yield() is advisory and has almost no effect on some platforms
934 // so we periodically call current->_ParkEvent->park(1).
935 // We use a mixed spin/yield/block mechanism.
936 if ((YieldThenBlock++) >= 16) {
937 Thread::current()->_ParkEvent->park(1);
938 } else {
939 os::naked_yield();
940 }
941 }
942 inflation_lock(ix)->unlock();
943 }
944 } else {
945 SpinPause(); // SMP-polite spinning
946 }
947 }
948 }
949
950 // hashCode() generation :
951 //
952 // Possibilities:
953 // * MD5Digest of {obj,stw_random}
954 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
955 // * A DES- or AES-style SBox[] mechanism
956 // * One of the Phi-based schemes, such as:
957 // 2654435761 = 2^32 * Phi (golden ratio)
958 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
959 // * A variation of Marsaglia's shift-xor RNG scheme.
960 // * (obj ^ stw_random) is appealing, but can result
961 // in undesirable regularity in the hashCode values of adjacent objects
962 // (objects allocated back-to-back, in particular). This could potentially
963 // result in hashtable collisions and reduced hashtable efficiency.
964 // There are simple ways to "diffuse" the middle address bits over the
965 // generated hashCode values:
966
967 static intptr_t get_next_hash(Thread* current, oop obj) {
968 intptr_t value = 0;
969 if (hashCode == 0) {
970 // This form uses global Park-Miller RNG.
971 // On MP system we'll have lots of RW access to a global, so the
972 // mechanism induces lots of coherency traffic.
973 value = os::random();
974 } else if (hashCode == 1) {
975 // This variation has the property of being stable (idempotent)
976 // between STW operations. This can be useful in some of the 1-0
977 // synchronization schemes.
978 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
979 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
980 } else if (hashCode == 2) {
981 value = 1; // for sensitivity testing
982 } else if (hashCode == 3) {
983 value = ++GVars.hc_sequence;
984 } else if (hashCode == 4) {
985 value = cast_from_oop<intptr_t>(obj);
986 } else {
987 // Marsaglia's xor-shift scheme with thread-specific state
988 // This is probably the best overall implementation -- we'll
989 // likely make this the default in future releases.
990 unsigned t = current->_hashStateX;
991 t ^= (t << 11);
992 current->_hashStateX = current->_hashStateY;
993 current->_hashStateY = current->_hashStateZ;
994 current->_hashStateZ = current->_hashStateW;
995 unsigned v = current->_hashStateW;
996 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
997 current->_hashStateW = v;
998 value = v;
999 }
1000
1001 value &= markWord::hash_mask;
1002 if (value == 0) value = 0xBAD;
1003 assert(value != markWord::no_hash, "invariant");
1004 return value;
1005 }
1006
1007 static intptr_t install_hash_code(Thread* current, oop obj) {
1008 assert(UseObjectMonitorTable && LockingMode == LM_LIGHTWEIGHT, "must be");
1009
1010 markWord mark = obj->mark_acquire();
1011 for (;;) {
1012 intptr_t hash = mark.hash();
1013 if (hash != 0) {
1014 return hash;
1015 }
1016
1017 hash = get_next_hash(current, obj);
1018 const markWord old_mark = mark;
1019 const markWord new_mark = old_mark.copy_set_hash(hash);
1020
1021 mark = obj->cas_set_mark(new_mark, old_mark);
1022 if (old_mark == mark) {
1023 return hash;
1024 }
1025 }
1026 }
1027
1028 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
1029 if (EnableValhalla && obj->klass()->is_inline_klass()) {
1030 // VM should be calling bootstrap method
1031 ShouldNotReachHere();
1032 }
1033 if (UseObjectMonitorTable) {
1034 // Since the monitor isn't in the object header, the hash can simply be
1035 // installed in the object header.
1036 return install_hash_code(current, obj);
1037 }
1038
1039 while (true) {
1040 ObjectMonitor* monitor = nullptr;
1041 markWord temp, test;
1042 intptr_t hash;
1043 markWord mark = read_stable_mark(obj);
1044 if (VerifyHeavyMonitors) {
1045 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
1046 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1047 }
1048 if (mark.is_unlocked() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1049 hash = mark.hash();
1050 if (hash != 0) { // if it has a hash, just return it
1051 return hash;
1052 }
1053 hash = get_next_hash(current, obj); // get a new hash
1054 temp = mark.copy_set_hash(hash); // merge the hash into header
1055 // try to install the hash
1056 test = obj->cas_set_mark(temp, mark);
1057 if (test == mark) { // if the hash was installed, return it
1058 return hash;
1059 }
1060 if (LockingMode == LM_LIGHTWEIGHT) {
1061 // CAS failed, retry
1062 continue;
1063 }
1064 // Failed to install the hash. It could be that another thread
1065 // installed the hash just before our attempt or inflation has
1066 // occurred or... so we fall thru to inflate the monitor for
1067 // stability and then install the hash.
1068 } else if (mark.has_monitor()) {
1069 monitor = mark.monitor();
1070 temp = monitor->header();
1071 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1072 hash = temp.hash();
1073 if (hash != 0) {
1074 // It has a hash.
1075
1076 // Separate load of dmw/header above from the loads in
1077 // is_being_async_deflated().
1078
1079 // dmw/header and _contentions may get written by different threads.
1080 // Make sure to observe them in the same order when having several observers.
1081 OrderAccess::loadload_for_IRIW();
1082
1083 if (monitor->is_being_async_deflated()) {
1084 // But we can't safely use the hash if we detect that async
1085 // deflation has occurred. So we attempt to restore the
1086 // header/dmw to the object's header so that we only retry
1087 // once if the deflater thread happens to be slow.
1088 monitor->install_displaced_markword_in_object(obj);
1089 continue;
1090 }
1091 return hash;
1092 }
1093 // Fall thru so we only have one place that installs the hash in
1094 // the ObjectMonitor.
1095 } else if (LockingMode == LM_LEGACY && mark.has_locker()
1096 && current->is_Java_thread()
1097 && JavaThread::cast(current)->is_lock_owned((address)mark.locker())) {
1098 // This is a stack-lock owned by the calling thread so fetch the
1099 // displaced markWord from the BasicLock on the stack.
1100 temp = mark.displaced_mark_helper();
1101 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1102 hash = temp.hash();
1103 if (hash != 0) { // if it has a hash, just return it
1104 return hash;
1105 }
1106 // WARNING:
1107 // The displaced header in the BasicLock on a thread's stack
1108 // is strictly immutable. It CANNOT be changed in ANY cases.
1109 // So we have to inflate the stack-lock into an ObjectMonitor
1110 // even if the current thread owns the lock. The BasicLock on
1111 // a thread's stack can be asynchronously read by other threads
1112 // during an inflate() call so any change to that stack memory
1113 // may not propagate to other threads correctly.
1114 }
1115
1116 // Inflate the monitor to set the hash.
1117
1118 // There's no need to inflate if the mark has already got a monitor.
1119 // NOTE: an async deflation can race after we get the monitor and
1120 // before we can update the ObjectMonitor's header with the hash
1121 // value below.
1122 monitor = mark.has_monitor() ? mark.monitor() : inflate(current, obj, inflate_cause_hash_code);
1123 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1124 mark = monitor->header();
1125 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1126 hash = mark.hash();
1127 if (hash == 0) { // if it does not have a hash
1128 hash = get_next_hash(current, obj); // get a new hash
1129 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1130 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1131 uintptr_t v = Atomic::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
1132 test = markWord(v);
1133 if (test != mark) {
1134 // The attempt to update the ObjectMonitor's header/dmw field
1135 // did not work. This can happen if another thread managed to
1136 // merge in the hash just before our cmpxchg().
1137 // If we add any new usages of the header/dmw field, this code
1138 // will need to be updated.
1139 hash = test.hash();
1140 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1141 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1142 }
1143 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
1144 // If we detect that async deflation has occurred, then we
1145 // attempt to restore the header/dmw to the object's header
1146 // so that we only retry once if the deflater thread happens
1147 // to be slow.
1148 monitor->install_displaced_markword_in_object(obj);
1149 continue;
1150 }
1151 }
1152 // We finally get the hash.
1153 return hash;
1154 }
1155 }
1156
1157 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1158 Handle h_obj) {
1159 if (EnableValhalla && h_obj->mark().is_inline_type()) {
1160 return false;
1161 }
1162 assert(current == JavaThread::current(), "Can only be called on current thread");
1163 oop obj = h_obj();
1164
1165 markWord mark = read_stable_mark(obj);
1166
1167 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1168 // stack-locked case, header points into owner's stack
1169 return current->is_lock_owned((address)mark.locker());
1170 }
1171
1172 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1173 // fast-locking case, see if lock is in current's lock stack
1174 return current->lock_stack().contains(h_obj());
1175 }
1176
1177 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1178 ObjectMonitor* monitor = read_monitor(current, obj, mark);
1179 if (monitor != nullptr) {
1180 return monitor->is_entered(current) != 0;
1181 }
1182 // Racing with inflation/deflation, retry
1183 mark = obj->mark_acquire();
1184
1185 if (mark.is_fast_locked()) {
1186 // Some other thread fast_locked, current could not have held the lock
1187 return false;
1188 }
1189 }
1190
1191 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1192 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1193 // The first stage of async deflation does not affect any field
1194 // used by this comparison so the ObjectMonitor* is usable here.
1195 ObjectMonitor* monitor = read_monitor(mark);
1196 return monitor->is_entered(current) != 0;
1197 }
1198 // Unlocked case, header in place
1199 assert(mark.is_unlocked(), "sanity check");
1200 return false;
1201 }
1202
1203 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1204 oop obj = h_obj();
1205 markWord mark = read_stable_mark(obj);
1206
1207 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1208 // stack-locked so header points into owner's stack.
1209 // owning_thread_from_monitor_owner() may also return null here:
1210 return Threads::owning_thread_from_stacklock(t_list, (address) mark.locker());
1211 }
1212
1213 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1214 // fast-locked so get owner from the object.
1215 // owning_thread_from_object() may also return null here:
1216 return Threads::owning_thread_from_object(t_list, h_obj());
1217 }
1218
1219 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1220 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
1221 if (monitor != nullptr) {
1222 return Threads::owning_thread_from_monitor(t_list, monitor);
1223 }
1224 // Racing with inflation/deflation, retry
1225 mark = obj->mark_acquire();
1226
1227 if (mark.is_fast_locked()) {
1228 // Some other thread fast_locked
1229 return Threads::owning_thread_from_object(t_list, h_obj());
1230 }
1231 }
1232
1233 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1234 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1235 // The first stage of async deflation does not affect any field
1236 // used by this comparison so the ObjectMonitor* is usable here.
1237 ObjectMonitor* monitor = read_monitor(mark);
1238 assert(monitor != nullptr, "monitor should be non-null");
1239 // owning_thread_from_monitor() may also return null here:
1240 return Threads::owning_thread_from_monitor(t_list, monitor);
1241 }
1242
1243 // Unlocked case, header in place
1244 // Cannot have assertion since this object may have been
1245 // locked by another thread when reaching here.
1246 // assert(mark.is_unlocked(), "sanity check");
1247
1248 return nullptr;
1249 }
1250
1251 // Visitors ...
1252
1253 // Iterate over all ObjectMonitors.
1254 template <typename Function>
1255 void ObjectSynchronizer::monitors_iterate(Function function) {
1256 MonitorList::Iterator iter = _in_use_list.iterator();
1257 while (iter.has_next()) {
1258 ObjectMonitor* monitor = iter.next();
1259 function(monitor);
1260 }
1261 }
1262
1263 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1264 // returns true.
1265 template <typename OwnerFilter>
1266 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1267 monitors_iterate([&](ObjectMonitor* monitor) {
1268 // This function is only called at a safepoint or when the
1269 // target thread is suspended or when the target thread is
1270 // operating on itself. The current closures in use today are
1271 // only interested in an owned ObjectMonitor and ownership
1272 // cannot be dropped under the calling contexts so the
1273 // ObjectMonitor cannot be async deflated.
1274 if (monitor->has_owner() && filter(monitor)) {
1275 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1276
1277 closure->do_monitor(monitor);
1278 }
1279 });
1280 }
1281
1282 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1283 // ObjectMonitors where owner is set to a stack-lock address in thread.
1284 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1285 int64_t key = ObjectMonitor::owner_id_from(thread);
1286 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1287 return owned_monitors_iterate_filtered(closure, thread_filter);
1288 }
1289
1290 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
1291 int64_t key = ObjectMonitor::owner_id_from(vthread);
1292 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1293 return owned_monitors_iterate_filtered(closure, thread_filter);
1294 }
1295
1296 // Iterate ObjectMonitors owned by any thread.
1297 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1298 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
1299 return owned_monitors_iterate_filtered(closure, all_filter);
1300 }
1301
1302 static bool monitors_used_above_threshold(MonitorList* list) {
1303 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1304 return false;
1305 }
1306 size_t monitors_used = list->count();
1307 if (monitors_used == 0) { // empty list is easy
1308 return false;
1309 }
1310 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
1311 // Make sure that we use a ceiling value that is not lower than
1312 // previous, not lower than the recorded max used by the system, and
1313 // not lower than the current number of monitors in use (which can
1314 // race ahead of max). The result is guaranteed > 0.
1315 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
1316
1317 // Check if our monitor usage is above the threshold:
1318 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1319 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1320 // Deflate monitors if over the threshold percentage, unless no
1321 // progress on previous deflations.
1322 bool is_above_threshold = true;
1323
1324 // Check if it's time to adjust the in_use_list_ceiling up, due
1325 // to too many async deflation attempts without any progress.
1326 if (NoAsyncDeflationProgressMax != 0 &&
1327 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1328 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1329 size_t delta = (size_t)(ceiling * remainder) + 1;
1330 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
1331 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
1332 : ceiling + delta;
1333
1334 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1335 log_info(monitorinflation)("Too many deflations without progress; "
1336 "bumping in_use_list_ceiling from %zu"
1337 " to %zu", old_ceiling, new_ceiling);
1338 _no_progress_cnt = 0;
1339 ceiling = new_ceiling;
1340
1341 // Check if our monitor usage is still above the threshold:
1342 monitor_usage = (monitors_used * 100LL) / ceiling;
1343 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
1344 }
1345 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
1346 ", monitor_usage=%zu, threshold=%d",
1347 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1348 return is_above_threshold;
1349 }
1350
1351 return false;
1352 }
1353
1354 size_t ObjectSynchronizer::in_use_list_count() {
1355 return _in_use_list.count();
1356 }
1357
1358 size_t ObjectSynchronizer::in_use_list_max() {
1359 return _in_use_list.max();
1360 }
1361
1362 size_t ObjectSynchronizer::in_use_list_ceiling() {
1363 return _in_use_list_ceiling;
1364 }
1365
1366 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1367 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1368 }
1369
1370 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1371 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1372 }
1373
1374 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1375 _in_use_list_ceiling = new_value;
1376 }
1377
1378 bool ObjectSynchronizer::is_async_deflation_needed() {
1379 if (is_async_deflation_requested()) {
1380 // Async deflation request.
1381 log_info(monitorinflation)("Async deflation needed: explicit request");
1382 return true;
1383 }
1384
1385 jlong time_since_last = time_since_last_async_deflation_ms();
1386
1387 if (AsyncDeflationInterval > 0 &&
1388 time_since_last > AsyncDeflationInterval &&
1389 monitors_used_above_threshold(&_in_use_list)) {
1390 // It's been longer than our specified deflate interval and there
1391 // are too many monitors in use. We don't deflate more frequently
1392 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1393 // in order to not swamp the MonitorDeflationThread.
1394 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1395 return true;
1396 }
1397
1398 if (GuaranteedAsyncDeflationInterval > 0 &&
1399 time_since_last > GuaranteedAsyncDeflationInterval) {
1400 // It's been longer than our specified guaranteed deflate interval.
1401 // We need to clean up the used monitors even if the threshold is
1402 // not reached, to keep the memory utilization at bay when many threads
1403 // touched many monitors.
1404 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
1405 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1406 GuaranteedAsyncDeflationInterval, time_since_last);
1407
1408 // If this deflation has no progress, then it should not affect the no-progress
1409 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1410 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1411 // the generic code would bump the no-progress counter, and we compensate for that
1412 // by telling it to skip the update.
1413 //
1414 // If this deflation has progress, then it should let non-progress tracking
1415 // know about this, otherwise the threshold heuristics would kick in, potentially
1416 // experience no-progress due to aggressive cleanup by this deflation, and think
1417 // it is still in no-progress stride. In this "progress" case, the generic code would
1418 // zero the counter, and we allow it to happen.
1419 _no_progress_skip_increment = true;
1420
1421 return true;
1422 }
1423
1424 return false;
1425 }
1426
1427 void ObjectSynchronizer::request_deflate_idle_monitors() {
1428 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1429 set_is_async_deflation_requested(true);
1430 ml.notify_all();
1431 }
1432
1433 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1434 JavaThread* current = JavaThread::current();
1435 bool ret_code = false;
1436
1437 jlong last_time = last_async_deflation_time_ns();
1438
1439 request_deflate_idle_monitors();
1440
1441 const int N_CHECKS = 5;
1442 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1443 if (last_async_deflation_time_ns() > last_time) {
1444 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1445 ret_code = true;
1446 break;
1447 }
1448 {
1449 // JavaThread has to honor the blocking protocol.
1450 ThreadBlockInVM tbivm(current);
1451 os::naked_short_sleep(999); // sleep for almost 1 second
1452 }
1453 }
1454 if (!ret_code) {
1455 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1456 }
1457
1458 return ret_code;
1459 }
1460
1461 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1462 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1463 }
1464
1465 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1466 const oop obj,
1467 ObjectSynchronizer::InflateCause cause) {
1468 assert(event != nullptr, "invariant");
1469 const Klass* monitor_klass = obj->klass();
1470 if (ObjectMonitor::is_jfr_excluded(monitor_klass)) {
1471 return;
1472 }
1473 event->set_monitorClass(monitor_klass);
1474 event->set_address((uintptr_t)(void*)obj);
1475 event->set_cause((u1)cause);
1476 event->commit();
1477 }
1478
1479 // Fast path code shared by multiple functions
1480 void ObjectSynchronizer::inflate_helper(oop obj) {
1481 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1482 markWord mark = obj->mark_acquire();
1483 if (mark.has_monitor()) {
1484 ObjectMonitor* monitor = read_monitor(mark);
1485 markWord dmw = monitor->header();
1486 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1487 return;
1488 }
1489 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1490 }
1491
1492 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1493 assert(current == Thread::current(), "must be");
1494 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1495 return inflate_impl(current->is_Java_thread() ? JavaThread::cast(current) : nullptr, obj, cause);
1496 }
1497
1498 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1499 assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1500 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_for");
1501 return inflate_impl(thread, obj, cause);
1502 }
1503
1504 ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* locking_thread, oop object, const InflateCause cause) {
1505 if (EnableValhalla) {
1506 guarantee(!object->klass()->is_inline_klass(), "Attempt to inflate inline type");
1507 }
1508 // The JavaThread* locking_thread requires that the locking_thread == Thread::current() or
1509 // is suspended throughout the call by some other mechanism.
1510 // The thread might be nullptr when called from a non JavaThread. (As may still be
1511 // the case from FastHashCode). However it is only important for correctness that the
1512 // thread is set when called from ObjectSynchronizer::enter from the owning thread,
1513 // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
1514 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_impl");
1515 EventJavaMonitorInflate event;
1516
1517 for (;;) {
1518 const markWord mark = object->mark_acquire();
1519
1520 // The mark can be in one of the following states:
1521 // * inflated - If the ObjectMonitor owner is anonymous and the
1522 // locking_thread owns the object lock, then we
1523 // make the locking_thread the ObjectMonitor owner.
1524 // * stack-locked - Coerce it to inflated from stack-locked.
1525 // * INFLATING - Busy wait for conversion from stack-locked to
1526 // inflated.
1527 // * unlocked - Aggressively inflate the object.
1528
1529 // CASE: inflated
1530 if (mark.has_monitor()) {
1531 ObjectMonitor* inf = mark.monitor();
1532 markWord dmw = inf->header();
1533 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1534 if (inf->has_anonymous_owner() && locking_thread != nullptr) {
1535 assert(LockingMode == LM_LEGACY, "invariant");
1536 if (locking_thread->is_lock_owned((address)inf->stack_locker())) {
1537 inf->set_stack_locker(nullptr);
1538 inf->set_owner_from_anonymous(locking_thread);
1539 }
1540 }
1541 return inf;
1542 }
1543
1544 // CASE: inflation in progress - inflating over a stack-lock.
1545 // Some other thread is converting from stack-locked to inflated.
1546 // Only that thread can complete inflation -- other threads must wait.
1547 // The INFLATING value is transient.
1548 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1549 // We could always eliminate polling by parking the thread on some auxiliary list.
1550 if (mark == markWord::INFLATING()) {
1551 read_stable_mark(object);
1552 continue;
1553 }
1554
1555 // CASE: stack-locked
1556 // Could be stack-locked either by current or by some other thread.
1557 //
1558 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1559 // to install INFLATING into the mark word. We originally installed INFLATING,
1560 // allocated the ObjectMonitor, and then finally STed the address of the
1561 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1562 // the interval in which INFLATING appeared in the mark, thus increasing
1563 // the odds of inflation contention. If we lose the race to set INFLATING,
1564 // then we just delete the ObjectMonitor and loop around again.
1565 //
1566 LogStreamHandle(Trace, monitorinflation) lsh;
1567 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1568 ObjectMonitor* m = new ObjectMonitor(object);
1569 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1570 // We do this before the CAS in order to minimize the length of time
1571 // in which INFLATING appears in the mark.
1572
1573 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1574 if (cmp != mark) {
1575 delete m;
1576 continue; // Interference -- just retry
1577 }
1578
1579 // We've successfully installed INFLATING (0) into the mark-word.
1580 // This is the only case where 0 will appear in a mark-word.
1581 // Only the singular thread that successfully swings the mark-word
1582 // to 0 can perform (or more precisely, complete) inflation.
1583 //
1584 // Why do we CAS a 0 into the mark-word instead of just CASing the
1585 // mark-word from the stack-locked value directly to the new inflated state?
1586 // Consider what happens when a thread unlocks a stack-locked object.
1587 // It attempts to use CAS to swing the displaced header value from the
1588 // on-stack BasicLock back into the object header. Recall also that the
1589 // header value (hash code, etc) can reside in (a) the object header, or
1590 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1591 // header in an ObjectMonitor. The inflate() routine must copy the header
1592 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1593 // the while preserving the hashCode stability invariants. If the owner
1594 // decides to release the lock while the value is 0, the unlock will fail
1595 // and control will eventually pass from slow_exit() to inflate. The owner
1596 // will then spin, waiting for the 0 value to disappear. Put another way,
1597 // the 0 causes the owner to stall if the owner happens to try to
1598 // drop the lock (restoring the header from the BasicLock to the object)
1599 // while inflation is in-progress. This protocol avoids races that might
1600 // would otherwise permit hashCode values to change or "flicker" for an object.
1601 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1602 // 0 serves as a "BUSY" inflate-in-progress indicator.
1603
1604
1605 // fetch the displaced mark from the owner's stack.
1606 // The owner can't die or unwind past the lock while our INFLATING
1607 // object is in the mark. Furthermore the owner can't complete
1608 // an unlock on the object, either.
1609 markWord dmw = mark.displaced_mark_helper();
1610 // Catch if the object's header is not neutral (not locked and
1611 // not marked is what we care about here).
1612 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1613
1614 // Setup monitor fields to proper values -- prepare the monitor
1615 m->set_header(dmw);
1616
1617 // Note that a thread can inflate an object
1618 // that it has stack-locked -- as might happen in wait() -- directly
1619 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1620 if (locking_thread != nullptr && locking_thread->is_lock_owned((address)mark.locker())) {
1621 m->set_owner(locking_thread);
1622 } else {
1623 // Use ANONYMOUS_OWNER to indicate that the owner is the BasicLock on the stack,
1624 // and set the stack locker field in the monitor.
1625 m->set_stack_locker(mark.locker());
1626 m->set_anonymous_owner();
1627 }
1628 // TODO-FIXME: assert BasicLock->dhw != 0.
1629
1630 // Must preserve store ordering. The monitor state must
1631 // be stable at the time of publishing the monitor address.
1632 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1633 // Release semantics so that above set_object() is seen first.
1634 object->release_set_mark(markWord::encode(m));
1635
1636 // Once ObjectMonitor is configured and the object is associated
1637 // with the ObjectMonitor, it is safe to allow async deflation:
1638 _in_use_list.add(m);
1639
1640 if (log_is_enabled(Trace, monitorinflation)) {
1641 ResourceMark rm;
1642 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1643 INTPTR_FORMAT ", type='%s'", p2i(object),
1644 object->mark().value(), object->klass()->external_name());
1645 }
1646 if (event.should_commit()) {
1647 post_monitor_inflate_event(&event, object, cause);
1648 }
1649 return m;
1650 }
1651
1652 // CASE: unlocked
1653 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1654 // If we know we're inflating for entry it's better to inflate by swinging a
1655 // pre-locked ObjectMonitor pointer into the object header. A successful
1656 // CAS inflates the object *and* confers ownership to the inflating thread.
1657 // In the current implementation we use a 2-step mechanism where we CAS()
1658 // to inflate and then CAS() again to try to swing _owner from null to current.
1659 // An inflateTry() method that we could call from enter() would be useful.
1660
1661 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
1662 ObjectMonitor* m = new ObjectMonitor(object);
1663 // prepare m for installation - set monitor to initial state
1664 m->set_header(mark);
1665
1666 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1667 delete m;
1668 m = nullptr;
1669 continue;
1670 // interference - the markword changed - just retry.
1671 // The state-transitions are one-way, so there's no chance of
1672 // live-lock -- "Inflated" is an absorbing state.
1673 }
1674
1675 // Once the ObjectMonitor is configured and object is associated
1676 // with the ObjectMonitor, it is safe to allow async deflation:
1677 _in_use_list.add(m);
1678
1679 if (log_is_enabled(Trace, monitorinflation)) {
1680 ResourceMark rm;
1681 lsh.print_cr("inflate(unlocked): object=" INTPTR_FORMAT ", mark="
1682 INTPTR_FORMAT ", type='%s'", p2i(object),
1683 object->mark().value(), object->klass()->external_name());
1684 }
1685 if (event.should_commit()) {
1686 post_monitor_inflate_event(&event, object, cause);
1687 }
1688 return m;
1689 }
1690 }
1691
1692 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1693 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1694 //
1695 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1696 MonitorList::Iterator iter = _in_use_list.iterator();
1697 size_t deflated_count = 0;
1698 Thread* current = Thread::current();
1699
1700 while (iter.has_next()) {
1701 if (deflated_count >= (size_t)MonitorDeflationMax) {
1702 break;
1703 }
1704 ObjectMonitor* mid = iter.next();
1705 if (mid->deflate_monitor(current)) {
1706 deflated_count++;
1707 }
1708
1709 // Must check for a safepoint/handshake and honor it.
1710 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1711 }
1712
1713 return deflated_count;
1714 }
1715
1716 class HandshakeForDeflation : public HandshakeClosure {
1717 public:
1718 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1719
1720 void do_thread(Thread* thread) {
1721 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1722 INTPTR_FORMAT, p2i(thread));
1723 if (thread->is_Java_thread()) {
1724 // Clear OM cache
1725 JavaThread* jt = JavaThread::cast(thread);
1726 jt->om_clear_monitor_cache();
1727 }
1728 }
1729 };
1730
1731 class VM_RendezvousGCThreads : public VM_Operation {
1732 public:
1733 bool evaluate_at_safepoint() const override { return false; }
1734 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1735 void doit() override {
1736 Universe::heap()->safepoint_synchronize_begin();
1737 Universe::heap()->safepoint_synchronize_end();
1738 };
1739 };
1740
1741 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1742 ObjectMonitorDeflationSafepointer* safepointer) {
1743 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1744 size_t deleted_count = 0;
1745 for (ObjectMonitor* monitor: *delete_list) {
1746 delete monitor;
1747 deleted_count++;
1748 // A JavaThread must check for a safepoint/handshake and honor it.
1749 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1750 }
1751 return deleted_count;
1752 }
1753
1754 class ObjectMonitorDeflationLogging: public StackObj {
1755 LogStreamHandle(Debug, monitorinflation) _debug;
1756 LogStreamHandle(Info, monitorinflation) _info;
1757 LogStream* _stream;
1758 elapsedTimer _timer;
1759
1760 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1761 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1762 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1763
1764 public:
1765 ObjectMonitorDeflationLogging()
1766 : _debug(), _info(), _stream(nullptr) {
1767 if (_debug.is_enabled()) {
1768 _stream = &_debug;
1769 } else if (_info.is_enabled()) {
1770 _stream = &_info;
1771 }
1772 }
1773
1774 void begin() {
1775 if (_stream != nullptr) {
1776 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1777 ceiling(), count(), max());
1778 _timer.start();
1779 }
1780 }
1781
1782 void before_handshake(size_t unlinked_count) {
1783 if (_stream != nullptr) {
1784 _timer.stop();
1785 _stream->print_cr("before handshaking: unlinked_count=%zu"
1786 ", in_use_list stats: ceiling=%zu, count="
1787 "%zu, max=%zu",
1788 unlinked_count, ceiling(), count(), max());
1789 }
1790 }
1791
1792 void after_handshake() {
1793 if (_stream != nullptr) {
1794 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1795 "%zu, count=%zu, max=%zu",
1796 ceiling(), count(), max());
1797 _timer.start();
1798 }
1799 }
1800
1801 void end(size_t deflated_count, size_t unlinked_count) {
1802 if (_stream != nullptr) {
1803 _timer.stop();
1804 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1805 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1806 deflated_count, unlinked_count, _timer.seconds());
1807 }
1808 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1809 ceiling(), count(), max());
1810 }
1811 }
1812
1813 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1814 if (_stream != nullptr) {
1815 _timer.stop();
1816 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1817 "%zu, count=%zu, max=%zu",
1818 op_name, cnt_name, cnt, ceiling(), count(), max());
1819 }
1820 }
1821
1822 void after_block_for_safepoint(const char* op_name) {
1823 if (_stream != nullptr) {
1824 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1825 ", count=%zu, max=%zu", op_name,
1826 ceiling(), count(), max());
1827 _timer.start();
1828 }
1829 }
1830 };
1831
1832 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1833 if (!SafepointMechanism::should_process(_current)) {
1834 return;
1835 }
1836
1837 // A safepoint/handshake has started.
1838 _log->before_block_for_safepoint(op_name, count_name, counter);
1839
1840 {
1841 // Honor block request.
1842 ThreadBlockInVM tbivm(_current);
1843 }
1844
1845 _log->after_block_for_safepoint(op_name);
1846 }
1847
1848 // This function is called by the MonitorDeflationThread to deflate
1849 // ObjectMonitors.
1850 size_t ObjectSynchronizer::deflate_idle_monitors() {
1851 JavaThread* current = JavaThread::current();
1852 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1853
1854 // The async deflation request has been processed.
1855 _last_async_deflation_time_ns = os::javaTimeNanos();
1856 set_is_async_deflation_requested(false);
1857
1858 ObjectMonitorDeflationLogging log;
1859 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1860
1861 log.begin();
1862
1863 // Deflate some idle ObjectMonitors.
1864 size_t deflated_count = deflate_monitor_list(&safepointer);
1865
1866 // Unlink the deflated ObjectMonitors from the in-use list.
1867 size_t unlinked_count = 0;
1868 size_t deleted_count = 0;
1869 if (deflated_count > 0) {
1870 ResourceMark rm(current);
1871 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1872 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1873
1874 #ifdef ASSERT
1875 if (UseObjectMonitorTable) {
1876 for (ObjectMonitor* monitor : delete_list) {
1877 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1878 }
1879 }
1880 #endif
1881
1882 log.before_handshake(unlinked_count);
1883
1884 // A JavaThread needs to handshake in order to safely free the
1885 // ObjectMonitors that were deflated in this cycle.
1886 HandshakeForDeflation hfd_hc;
1887 Handshake::execute(&hfd_hc);
1888 // Also, we sync and desync GC threads around the handshake, so that they can
1889 // safely read the mark-word and look-through to the object-monitor, without
1890 // being afraid that the object-monitor is going away.
1891 VM_RendezvousGCThreads sync_gc;
1892 VMThread::execute(&sync_gc);
1893
1894 log.after_handshake();
1895
1896 // After the handshake, safely free the ObjectMonitors that were
1897 // deflated and unlinked in this cycle.
1898
1899 // Delete the unlinked ObjectMonitors.
1900 deleted_count = delete_monitors(&delete_list, &safepointer);
1901 assert(unlinked_count == deleted_count, "must be");
1902 }
1903
1904 log.end(deflated_count, unlinked_count);
1905
1906 GVars.stw_random = os::random();
1907
1908 if (deflated_count != 0) {
1909 _no_progress_cnt = 0;
1910 } else if (_no_progress_skip_increment) {
1911 _no_progress_skip_increment = false;
1912 } else {
1913 _no_progress_cnt++;
1914 }
1915
1916 return deflated_count;
1917 }
1918
1919 // Monitor cleanup on JavaThread::exit
1920
1921 // Iterate through monitor cache and attempt to release thread's monitors
1922 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1923 private:
1924 JavaThread* _thread;
1925
1926 public:
1927 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1928 void do_monitor(ObjectMonitor* mid) {
1929 intx rec = mid->complete_exit(_thread);
1930 _thread->dec_held_monitor_count(rec + 1);
1931 }
1932 };
1933
1934 // Release all inflated monitors owned by current thread. Lightweight monitors are
1935 // ignored. This is meant to be called during JNI thread detach which assumes
1936 // all remaining monitors are heavyweight. All exceptions are swallowed.
1937 // Scanning the extant monitor list can be time consuming.
1938 // A simple optimization is to add a per-thread flag that indicates a thread
1939 // called jni_monitorenter() during its lifetime.
1940 //
1941 // Instead of NoSafepointVerifier it might be cheaper to
1942 // use an idiom of the form:
1943 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1944 // <code that must not run at safepoint>
1945 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1946 // Since the tests are extremely cheap we could leave them enabled
1947 // for normal product builds.
1948
1949 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1950 assert(current == JavaThread::current(), "must be current Java thread");
1951 NoSafepointVerifier nsv;
1952 ReleaseJavaMonitorsClosure rjmc(current);
1953 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1954 assert(!current->has_pending_exception(), "Should not be possible");
1955 current->clear_pending_exception();
1956 assert(current->held_monitor_count() == 0, "Should not be possible");
1957 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1958 current->clear_jni_monitor_count();
1959 }
1960
1961 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1962 switch (cause) {
1963 case inflate_cause_vm_internal: return "VM Internal";
1964 case inflate_cause_monitor_enter: return "Monitor Enter";
1965 case inflate_cause_wait: return "Monitor Wait";
1966 case inflate_cause_notify: return "Monitor Notify";
1967 case inflate_cause_hash_code: return "Monitor Hash Code";
1968 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1969 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1970 default:
1971 ShouldNotReachHere();
1972 }
1973 return "Unknown";
1974 }
1975
1976 //------------------------------------------------------------------------------
1977 // Debugging code
1978
1979 u_char* ObjectSynchronizer::get_gvars_addr() {
1980 return (u_char*)&GVars;
1981 }
1982
1983 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1984 return (u_char*)&GVars.hc_sequence;
1985 }
1986
1987 size_t ObjectSynchronizer::get_gvars_size() {
1988 return sizeof(SharedGlobals);
1989 }
1990
1991 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1992 return (u_char*)&GVars.stw_random;
1993 }
1994
1995 // Do the final audit and print of ObjectMonitor stats; must be done
1996 // by the VMThread at VM exit time.
1997 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1998 assert(Thread::current()->is_VM_thread(), "sanity check");
1999
2000 if (is_final_audit()) { // Only do the audit once.
2001 return;
2002 }
2003 set_is_final_audit();
2004 log_info(monitorinflation)("Starting the final audit.");
2005
2006 if (log_is_enabled(Info, monitorinflation)) {
2007 LogStreamHandle(Info, monitorinflation) ls;
2008 audit_and_print_stats(&ls, true /* on_exit */);
2009 }
2010 }
2011
2012 // This function can be called by the MonitorDeflationThread or it can be called when
2013 // we are trying to exit the VM. The list walker functions can run in parallel with
2014 // the other list operations.
2015 // Calls to this function can be added in various places as a debugging
2016 // aid.
2017 //
2018 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
2019 int error_cnt = 0;
2020
2021 ls->print_cr("Checking in_use_list:");
2022 chk_in_use_list(ls, &error_cnt);
2023
2024 if (error_cnt == 0) {
2025 ls->print_cr("No errors found in in_use_list checks.");
2026 } else {
2027 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
2028 }
2029
2030 // When exiting, only log the interesting entries at the Info level.
2031 // When called at intervals by the MonitorDeflationThread, log output
2032 // at the Trace level since there can be a lot of it.
2033 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
2034 LogStreamHandle(Trace, monitorinflation) ls_tr;
2035 log_in_use_monitor_details(&ls_tr, true /* log_all */);
2036 } else if (on_exit) {
2037 log_in_use_monitor_details(ls, false /* log_all */);
2038 }
2039
2040 ls->flush();
2041
2042 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2043 }
2044
2045 // Check the in_use_list; log the results of the checks.
2046 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
2047 size_t l_in_use_count = _in_use_list.count();
2048 size_t l_in_use_max = _in_use_list.max();
2049 out->print_cr("count=%zu, max=%zu", l_in_use_count,
2050 l_in_use_max);
2051
2052 size_t ck_in_use_count = 0;
2053 MonitorList::Iterator iter = _in_use_list.iterator();
2054 while (iter.has_next()) {
2055 ObjectMonitor* mid = iter.next();
2056 chk_in_use_entry(mid, out, error_cnt_p);
2057 ck_in_use_count++;
2058 }
2059
2060 if (l_in_use_count == ck_in_use_count) {
2061 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
2062 l_in_use_count, ck_in_use_count);
2063 } else {
2064 out->print_cr("WARNING: in_use_count=%zu is not equal to "
2065 "ck_in_use_count=%zu", l_in_use_count,
2066 ck_in_use_count);
2067 }
2068
2069 size_t ck_in_use_max = _in_use_list.max();
2070 if (l_in_use_max == ck_in_use_max) {
2071 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
2072 l_in_use_max, ck_in_use_max);
2073 } else {
2074 out->print_cr("WARNING: in_use_max=%zu is not equal to "
2075 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
2076 }
2077 }
2078
2079 // Check an in-use monitor entry; log any errors.
2080 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2081 int* error_cnt_p) {
2082 if (n->owner_is_DEFLATER_MARKER()) {
2083 // This could happen when monitor deflation blocks for a safepoint.
2084 return;
2085 }
2086
2087
2088 if (n->metadata() == 0) {
2089 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2090 "have non-null _metadata (header/hash) field.", p2i(n));
2091 *error_cnt_p = *error_cnt_p + 1;
2092 }
2093
2094 const oop obj = n->object_peek();
2095 if (obj == nullptr) {
2096 return;
2097 }
2098
2099 const markWord mark = obj->mark();
2100 if (!mark.has_monitor()) {
2101 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2102 "object does not think it has a monitor: obj="
2103 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2104 p2i(obj), mark.value());
2105 *error_cnt_p = *error_cnt_p + 1;
2106 return;
2107 }
2108
2109 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
2110 if (n != obj_mon) {
2111 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2112 "object does not refer to the same monitor: obj="
2113 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2114 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2115 *error_cnt_p = *error_cnt_p + 1;
2116 }
2117 }
2118
2119 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2120 // flags indicate why the entry is in-use, 'object' and 'object type'
2121 // indicate the associated object and its type.
2122 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2123 if (_in_use_list.count() > 0) {
2124 stringStream ss;
2125 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
2126 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2127 out->print_cr("%18s %s %18s %18s",
2128 "monitor", "BHL", "object", "object type");
2129 out->print_cr("================== === ================== ==================");
2130
2131 auto is_interesting = [&](ObjectMonitor* monitor) {
2132 return log_all || monitor->has_owner() || monitor->is_busy();
2133 };
2134
2135 monitors_iterate([&](ObjectMonitor* monitor) {
2136 if (is_interesting(monitor)) {
2137 const oop obj = monitor->object_peek();
2138 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
2139 ResourceMark rm;
2140 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
2141 monitor->is_busy(), hash != 0, monitor->has_owner(),
2142 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2143 if (monitor->is_busy()) {
2144 out->print(" (%s)", monitor->is_busy_to_string(&ss));
2145 ss.reset();
2146 }
2147 out->cr();
2148 }
2149 });
2150 }
2151
2152 out->flush();
2153 }