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