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/atomicAccess.hpp"
37 #include "runtime/basicLock.inline.hpp"
38 #include "runtime/frame.inline.hpp"
39 #include "runtime/globals.hpp"
40 #include "runtime/handles.inline.hpp"
41 #include "runtime/handshake.hpp"
42 #include "runtime/interfaceSupport.inline.hpp"
43 #include "runtime/javaThread.hpp"
44 #include "runtime/lightweightSynchronizer.hpp"
45 #include "runtime/lockStack.inline.hpp"
46 #include "runtime/mutexLocker.hpp"
47 #include "runtime/objectMonitor.inline.hpp"
48 #include "runtime/os.inline.hpp"
49 #include "runtime/osThread.hpp"
50 #include "runtime/safepointMechanism.inline.hpp"
51 #include "runtime/safepointVerifiers.hpp"
52 #include "runtime/sharedRuntime.hpp"
53 #include "runtime/stubRoutines.hpp"
54 #include "runtime/synchronizer.inline.hpp"
55 #include "runtime/threads.hpp"
56 #include "runtime/timer.hpp"
57 #include "runtime/trimNativeHeap.hpp"
58 #include "runtime/vframe.hpp"
59 #include "runtime/vmThread.hpp"
60 #include "utilities/align.hpp"
61 #include "utilities/dtrace.hpp"
62 #include "utilities/events.hpp"
63 #include "utilities/globalCounter.inline.hpp"
64 #include "utilities/globalDefinitions.hpp"
65 #include "utilities/linkedlist.hpp"
66 #include "utilities/preserveException.hpp"
67
68 class ObjectMonitorDeflationLogging;
69
70 void MonitorList::add(ObjectMonitor* m) {
71 ObjectMonitor* head;
72 do {
73 head = AtomicAccess::load(&_head);
74 m->set_next_om(head);
75 } while (AtomicAccess::cmpxchg(&_head, head, m) != head);
76
77 size_t count = AtomicAccess::add(&_count, 1u, memory_order_relaxed);
78 size_t old_max;
79 do {
80 old_max = AtomicAccess::load(&_max);
81 if (count <= old_max) {
82 break;
83 }
84 } while (AtomicAccess::cmpxchg(&_max, old_max, count, memory_order_relaxed) != old_max);
85 }
86
87 size_t MonitorList::count() const {
88 return AtomicAccess::load(&_count);
89 }
90
91 size_t MonitorList::max() const {
92 return AtomicAccess::load(&_max);
93 }
94
95 class ObjectMonitorDeflationSafepointer : public StackObj {
96 JavaThread* const _current;
97 ObjectMonitorDeflationLogging* const _log;
98
99 public:
100 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
101 : _current(current), _log(log) {}
102
103 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
104 };
105
106 // Walk the in-use list and unlink deflated ObjectMonitors.
107 // Returns the number of unlinked ObjectMonitors.
108 size_t MonitorList::unlink_deflated(size_t deflated_count,
109 GrowableArray<ObjectMonitor*>* unlinked_list,
110 ObjectMonitorDeflationSafepointer* safepointer) {
111 size_t unlinked_count = 0;
112 ObjectMonitor* prev = nullptr;
113 ObjectMonitor* m = AtomicAccess::load_acquire(&_head);
114
115 while (m != nullptr) {
116 if (m->is_being_async_deflated()) {
117 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
118 // modify the list once per batch. The batch starts at "m".
119 size_t unlinked_batch = 0;
120 ObjectMonitor* next = m;
121 // Look for at most MonitorUnlinkBatch monitors, or the number of
122 // deflated and not unlinked monitors, whatever comes first.
123 assert(deflated_count >= unlinked_count, "Sanity: underflow");
124 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
125 do {
126 ObjectMonitor* next_next = next->next_om();
127 unlinked_batch++;
128 unlinked_list->append(next);
129 next = next_next;
130 if (unlinked_batch >= unlinked_batch_limit) {
131 // Reached the max batch, so bail out of the gathering loop.
132 break;
133 }
134 if (prev == nullptr && AtomicAccess::load(&_head) != m) {
135 // Current batch used to be at head, but it is not at head anymore.
136 // Bail out and figure out where we currently are. This avoids long
137 // walks searching for new prev during unlink under heavy list inserts.
138 break;
139 }
140 } while (next != nullptr && next->is_being_async_deflated());
141
142 // Unlink the found batch.
143 if (prev == nullptr) {
144 // The current batch is the first batch, so there is a chance that it starts at head.
145 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
146 ObjectMonitor* prev_head = AtomicAccess::cmpxchg(&_head, m, next);
147 if (prev_head != m) {
148 // Something must have updated the head. Figure out the actual prev for this batch.
149 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
150 prev = n;
151 }
152 assert(prev != nullptr, "Should have found the prev for the current batch");
153 prev->set_next_om(next);
154 }
155 } else {
156 // The current batch is preceded by another batch. This guarantees the current batch
157 // does not start at head. Unlink the entire current batch without updating the head.
158 assert(AtomicAccess::load(&_head) != m, "Sanity");
159 prev->set_next_om(next);
160 }
161
162 unlinked_count += unlinked_batch;
163 if (unlinked_count >= deflated_count) {
164 // Reached the max so bail out of the searching loop.
165 // There should be no more deflated monitors left.
166 break;
167 }
168 m = next;
169 } else {
170 prev = m;
171 m = m->next_om();
172 }
173
174 // Must check for a safepoint/handshake and honor it.
175 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
176 }
177
178 #ifdef ASSERT
179 // Invariant: the code above should unlink all deflated monitors.
180 // The code that runs after this unlinking does not expect deflated monitors.
181 // Notably, attempting to deflate the already deflated monitor would break.
182 {
183 ObjectMonitor* m = AtomicAccess::load_acquire(&_head);
184 while (m != nullptr) {
185 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
186 m = m->next_om();
187 }
188 }
189 #endif
190
191 AtomicAccess::sub(&_count, unlinked_count);
192 return unlinked_count;
193 }
194
195 MonitorList::Iterator MonitorList::iterator() const {
196 return Iterator(AtomicAccess::load_acquire(&_head));
197 }
198
199 ObjectMonitor* MonitorList::Iterator::next() {
200 ObjectMonitor* current = _current;
201 _current = current->next_om();
202 return current;
203 }
204
205 // The "core" versions of monitor enter and exit reside in this file.
206 // The interpreter and compilers contain specialized transliterated
207 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
208 // fast_lock(...) for instance. If you make changes here, make sure to modify the
209 // interpreter, and both C1 and C2 fast-path inline locking code emission.
210 //
211 // -----------------------------------------------------------------------------
212
213 #ifdef DTRACE_ENABLED
214
215 // Only bother with this argument setup if dtrace is available
216 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
217
218 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
219 char* bytes = nullptr; \
220 int len = 0; \
221 jlong jtid = SharedRuntime::get_java_tid(thread); \
222 Symbol* klassname = obj->klass()->name(); \
223 if (klassname != nullptr) { \
224 bytes = (char*)klassname->bytes(); \
225 len = klassname->utf8_length(); \
226 }
227
228 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
229 { \
230 if (DTraceMonitorProbes) { \
231 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
232 HOTSPOT_MONITOR_WAIT(jtid, \
233 (uintptr_t)(monitor), bytes, len, (millis)); \
234 } \
235 }
236
237 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
238 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
239 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
240
241 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
242 { \
243 if (DTraceMonitorProbes) { \
244 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
245 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
246 (uintptr_t)(monitor), bytes, len); \
247 } \
248 }
249
250 #else // ndef DTRACE_ENABLED
251
252 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
253 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
254
255 #endif // ndef DTRACE_ENABLED
256
257 // This exists only as a workaround of dtrace bug 6254741
258 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
259 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
260 return 0;
261 }
262
263 static constexpr size_t inflation_lock_count() {
264 return 256;
265 }
266
267 // Static storage for an array of PlatformMutex.
268 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
269
270 static inline PlatformMutex* inflation_lock(size_t index) {
271 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
272 }
273
274 void ObjectSynchronizer::initialize() {
275 for (size_t i = 0; i < inflation_lock_count(); i++) {
276 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
277 }
278 // Start the ceiling with the estimate for one thread.
279 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
280
281 // Start the timer for deflations, so it does not trigger immediately.
282 _last_async_deflation_time_ns = os::javaTimeNanos();
283
284 LightweightSynchronizer::initialize();
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 (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
344 // Degenerate notify
345 // fast-locked by caller so by definition the implied waitset is empty.
346 return true;
347 }
348
349 if (mark.has_monitor()) {
350 ObjectMonitor* const mon = read_monitor(current, obj, mark);
351 if (mon == nullptr) {
352 // Racing with inflation/deflation go slow path
353 return false;
354 }
355 assert(mon->object() == oop(obj), "invariant");
356 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
357
358 if (mon->first_waiter() != nullptr) {
359 // We have one or more waiters. Since this is an inflated monitor
360 // that we own, we quickly notify them here and now, avoiding the slow-path.
361 if (all) {
362 mon->quick_notifyAll(current);
363 } else {
364 mon->quick_notify(current);
365 }
366 }
367 return true;
368 }
369
370 // other IMS exception states take the slow-path
371 return false;
372 }
373
374 // Handle notifications when synchronizing on value based classes
375 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
376 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
377 frame last_frame = locking_thread->last_frame();
378 bool bcp_was_adjusted = false;
379 // Don't decrement bcp if it points to the frame's first instruction. This happens when
380 // handle_sync_on_value_based_class() is called because of a synchronized method. There
381 // is no actual monitorenter instruction in the byte code in this case.
382 if (last_frame.is_interpreted_frame() &&
383 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
384 // adjust bcp to point back to monitorenter so that we print the correct line numbers
385 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
386 bcp_was_adjusted = true;
387 }
388
389 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
390 ResourceMark rm;
391 stringStream ss;
392 locking_thread->print_active_stack_on(&ss);
393 char* base = (char*)strstr(ss.base(), "at");
394 char* newline = (char*)strchr(ss.base(), '\n');
395 if (newline != nullptr) {
396 *newline = '\0';
397 }
398 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
399 } else {
400 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
401 ResourceMark rm;
402 Log(valuebasedclasses) vblog;
403
404 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
405 if (locking_thread->has_last_Java_frame()) {
406 LogStream info_stream(vblog.info());
407 locking_thread->print_active_stack_on(&info_stream);
408 } else {
409 vblog.info("Cannot find the last Java frame");
410 }
411
412 EventSyncOnValueBasedClass event;
413 if (event.should_commit()) {
414 event.set_valueBasedClass(obj->klass());
415 event.commit();
416 }
417 }
418
419 if (bcp_was_adjusted) {
420 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
421 }
422 }
423
424 // -----------------------------------------------------------------------------
425 // Monitor Enter/Exit
426
427 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
428 // When called with locking_thread != Thread::current() some mechanism must synchronize
429 // the locking_thread with respect to the current thread. Currently only used when
430 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
431 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
432 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
433 }
434
435 // -----------------------------------------------------------------------------
436 // JNI locks on java objects
437 // NOTE: must use heavy weight monitor to handle jni monitor enter
438 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
439 // Top native frames in the stack will not be seen if we attempt
440 // preemption, since we start walking from the last Java anchor.
441 NoPreemptMark npm(current);
442
443 if (obj->klass()->is_value_based()) {
444 handle_sync_on_value_based_class(obj, current);
445 }
446
447 // the current locking is from JNI instead of Java code
448 current->set_current_pending_monitor_is_from_java(false);
449 // An async deflation can race after the inflate() call and before
450 // enter() can make the ObjectMonitor busy. enter() returns false if
451 // we have lost the race to async deflation and we simply try again.
452 while (true) {
453 BasicLock lock;
454 if (LightweightSynchronizer::inflate_and_enter(obj(), &lock, inflate_cause_jni_enter, current, current) != nullptr) {
455 current->inc_held_monitor_count(1, true);
456 break;
457 }
458 }
459 current->set_current_pending_monitor_is_from_java(true);
460 }
461
462 // NOTE: must use heavy weight monitor to handle jni monitor exit
463 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
464 JavaThread* current = THREAD;
465
466 ObjectMonitor* monitor;
467 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
468 // If this thread has locked the object, exit the monitor. We
469 // intentionally do not use CHECK on check_owner because we must exit the
470 // monitor even if an exception was already pending.
471 if (monitor->check_owner(THREAD)) {
472 monitor->exit(current);
473 current->dec_held_monitor_count(1, true);
474 }
475 }
476
477 // -----------------------------------------------------------------------------
478 // Internal VM locks on java objects
479 // standard constructor, allows locking failures
480 ObjectLocker::ObjectLocker(Handle obj, TRAPS) : _thread(THREAD), _obj(obj),
481 _npm(_thread, _thread->at_preemptable_init() /* ignore_mark */), _skip_exit(false) {
482 assert(!_thread->preempting(), "");
483
484 _thread->check_for_valid_safepoint_state();
485
486 if (_obj() != nullptr) {
487 ObjectSynchronizer::enter(_obj, &_lock, _thread);
488
489 if (_thread->preempting()) {
490 // If preemption was cancelled we acquired the monitor after freezing
491 // the frames. Redoing the vm call later in thaw will require us to
492 // release it since the call should look like the original one. We
493 // do it in ~ObjectLocker to reduce the window of time we hold the
494 // monitor since we can't do anything useful with it now, and would
495 // otherwise just force other vthreads to preempt in case they try
496 // to acquire this monitor.
497 _skip_exit = !_thread->preemption_cancelled();
498 ObjectSynchronizer::read_monitor(_thread, _obj())->set_object_strong();
499 _thread->set_pending_preempted_exception();
500
501 }
502 }
503 }
504
505 ObjectLocker::~ObjectLocker() {
506 if (_obj() != nullptr && !_skip_exit) {
507 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
508 }
509 }
510
511 void ObjectLocker::wait_uninterruptibly(TRAPS) {
512 ObjectSynchronizer::waitUninterruptibly(_obj, 0, _thread);
513 if (_thread->preempting()) {
514 _skip_exit = true;
515 ObjectSynchronizer::read_monitor(_thread, _obj())->set_object_strong();
516 _thread->set_pending_preempted_exception();
517 }
518 }
519
520 // -----------------------------------------------------------------------------
521 // Wait/Notify/NotifyAll
522 // NOTE: must use heavy weight monitor to handle wait()
523
524 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
525 JavaThread* current = THREAD;
526 if (millis < 0) {
527 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
528 }
529
530 ObjectMonitor* monitor;
531 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
532
533 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
534 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
535
536 // This dummy call is in place to get around dtrace bug 6254741. Once
537 // that's fixed we can uncomment the following line, remove the call
538 // and change this function back into a "void" func.
539 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
540 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
541 return ret_code;
542 }
543
544 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
545 assert(millis >= 0, "timeout value is negative");
546
547 ObjectMonitor* monitor;
548 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
549 monitor->wait(millis, false, THREAD);
550 }
551
552
553 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
554 JavaThread* current = THREAD;
555
556 markWord mark = obj->mark();
557 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
558 // Not inflated so there can't be any waiters to notify.
559 return;
560 }
561 ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
562 monitor->notify(CHECK);
563 }
564
565 // NOTE: see comment of notify()
566 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
567 JavaThread* current = THREAD;
568
569 markWord mark = obj->mark();
570 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
571 // Not inflated so there can't be any waiters to notify.
572 return;
573 }
574
575 ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
576 monitor->notifyAll(CHECK);
577 }
578
579 // -----------------------------------------------------------------------------
580 // Hash Code handling
581
582 struct SharedGlobals {
583 char _pad_prefix[OM_CACHE_LINE_SIZE];
584 // This is a highly shared mostly-read variable.
585 // To avoid false-sharing it needs to be the sole occupant of a cache line.
586 volatile int stw_random;
587 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
588 // Hot RW variable -- Sequester to avoid false-sharing
589 volatile int hc_sequence;
590 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
591 };
592
593 static SharedGlobals GVars;
594
595 // hashCode() generation :
596 //
597 // Possibilities:
598 // * MD5Digest of {obj,stw_random}
599 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
600 // * A DES- or AES-style SBox[] mechanism
601 // * One of the Phi-based schemes, such as:
602 // 2654435761 = 2^32 * Phi (golden ratio)
603 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
604 // * A variation of Marsaglia's shift-xor RNG scheme.
605 // * (obj ^ stw_random) is appealing, but can result
606 // in undesirable regularity in the hashCode values of adjacent objects
607 // (objects allocated back-to-back, in particular). This could potentially
608 // result in hashtable collisions and reduced hashtable efficiency.
609 // There are simple ways to "diffuse" the middle address bits over the
610 // generated hashCode values:
611
612 static intptr_t get_next_hash(Thread* current, oop obj) {
613 intptr_t value = 0;
614 if (hashCode == 0) {
615 // This form uses global Park-Miller RNG.
616 // On MP system we'll have lots of RW access to a global, so the
617 // mechanism induces lots of coherency traffic.
618 value = os::random();
619 } else if (hashCode == 1) {
620 // This variation has the property of being stable (idempotent)
621 // between STW operations. This can be useful in some of the 1-0
622 // synchronization schemes.
623 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
624 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
625 } else if (hashCode == 2) {
626 value = 1; // for sensitivity testing
627 } else if (hashCode == 3) {
628 value = ++GVars.hc_sequence;
629 } else if (hashCode == 4) {
630 value = cast_from_oop<intptr_t>(obj);
631 } else {
632 // Marsaglia's xor-shift scheme with thread-specific state
633 // This is probably the best overall implementation -- we'll
634 // likely make this the default in future releases.
635 unsigned t = current->_hashStateX;
636 t ^= (t << 11);
637 current->_hashStateX = current->_hashStateY;
638 current->_hashStateY = current->_hashStateZ;
639 current->_hashStateZ = current->_hashStateW;
640 unsigned v = current->_hashStateW;
641 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
642 current->_hashStateW = v;
643 value = v;
644 }
645
646 value &= markWord::hash_mask;
647 if (value == 0) value = 0xBAD;
648 assert(value != markWord::no_hash, "invariant");
649 return value;
650 }
651
652 static intptr_t install_hash_code(Thread* current, oop obj) {
653 assert(UseObjectMonitorTable, "must be");
654
655 markWord mark = obj->mark_acquire();
656 for (;;) {
657 intptr_t hash = mark.hash();
658 if (hash != 0) {
659 return hash;
660 }
661
662 hash = get_next_hash(current, obj);
663 const markWord old_mark = mark;
664 const markWord new_mark = old_mark.copy_set_hash(hash);
665
666 mark = obj->cas_set_mark(new_mark, old_mark);
667 if (old_mark == mark) {
668 return hash;
669 }
670 }
671 }
672
673 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
674 if (UseObjectMonitorTable) {
675 // Since the monitor isn't in the object header, the hash can simply be
676 // installed in the object header.
677 return install_hash_code(current, obj);
678 }
679
680 while (true) {
681 ObjectMonitor* monitor = nullptr;
682 markWord temp, test;
683 intptr_t hash;
684 markWord mark = obj->mark_acquire();
685 if (mark.is_unlocked() || mark.is_fast_locked()) {
686 hash = mark.hash();
687 if (hash != 0) { // if it has a hash, just return it
688 return hash;
689 }
690 hash = get_next_hash(current, obj); // get a new hash
691 temp = mark.copy_set_hash(hash); // merge the hash into header
692 // try to install the hash
693 test = obj->cas_set_mark(temp, mark);
694 if (test == mark) { // if the hash was installed, return it
695 return hash;
696 }
697 // CAS failed, retry
698 continue;
699
700 // Failed to install the hash. It could be that another thread
701 // installed the hash just before our attempt or inflation has
702 // occurred or... so we fall thru to inflate the monitor for
703 // stability and then install the hash.
704 } else if (mark.has_monitor()) {
705 monitor = mark.monitor();
706 temp = monitor->header();
707 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
708 hash = temp.hash();
709 if (hash != 0) {
710 // It has a hash.
711
712 // Separate load of dmw/header above from the loads in
713 // is_being_async_deflated().
714
715 // dmw/header and _contentions may get written by different threads.
716 // Make sure to observe them in the same order when having several observers.
717 OrderAccess::loadload_for_IRIW();
718
719 if (monitor->is_being_async_deflated()) {
720 // But we can't safely use the hash if we detect that async
721 // deflation has occurred. So we attempt to restore the
722 // header/dmw to the object's header so that we only retry
723 // once if the deflater thread happens to be slow.
724 monitor->install_displaced_markword_in_object(obj);
725 continue;
726 }
727 return hash;
728 }
729 // Fall thru so we only have one place that installs the hash in
730 // the ObjectMonitor.
731 }
732
733 // NOTE: an async deflation can race after we get the monitor and
734 // before we can update the ObjectMonitor's header with the hash
735 // value below.
736 assert(mark.has_monitor(), "must be");
737 monitor = mark.monitor();
738
739 // Load ObjectMonitor's header/dmw field and see if it has a hash.
740 mark = monitor->header();
741 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
742 hash = mark.hash();
743 if (hash == 0) { // if it does not have a hash
744 hash = get_next_hash(current, obj); // get a new hash
745 temp = mark.copy_set_hash(hash) ; // merge the hash into header
746 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
747 uintptr_t v = AtomicAccess::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
748 test = markWord(v);
749 if (test != mark) {
750 // The attempt to update the ObjectMonitor's header/dmw field
751 // did not work. This can happen if another thread managed to
752 // merge in the hash just before our cmpxchg().
753 // If we add any new usages of the header/dmw field, this code
754 // will need to be updated.
755 hash = test.hash();
756 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
757 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
758 }
759 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
760 // If we detect that async deflation has occurred, then we
761 // attempt to restore the header/dmw to the object's header
762 // so that we only retry once if the deflater thread happens
763 // to be slow.
764 monitor->install_displaced_markword_in_object(obj);
765 continue;
766 }
767 }
768 // We finally get the hash.
769 return hash;
770 }
771 }
772
773 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
774 Handle h_obj) {
775 assert(current == JavaThread::current(), "Can only be called on current thread");
776 oop obj = h_obj();
777
778 markWord mark = obj->mark_acquire();
779
780 if (mark.is_fast_locked()) {
781 // fast-locking case, see if lock is in current's lock stack
782 return current->lock_stack().contains(h_obj());
783 }
784
785 while (mark.has_monitor()) {
786 ObjectMonitor* monitor = read_monitor(current, obj, mark);
787 if (monitor != nullptr) {
788 return monitor->is_entered(current) != 0;
789 }
790 // Racing with inflation/deflation, retry
791 mark = obj->mark_acquire();
792
793 if (mark.is_fast_locked()) {
794 // Some other thread fast_locked, current could not have held the lock
795 return false;
796 }
797 }
798
799 // Unlocked case, header in place
800 assert(mark.is_unlocked(), "sanity check");
801 return false;
802 }
803
804 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
805 oop obj = h_obj();
806 markWord mark = obj->mark_acquire();
807
808 if (mark.is_fast_locked()) {
809 // fast-locked so get owner from the object.
810 // owning_thread_from_object() may also return null here:
811 return Threads::owning_thread_from_object(t_list, h_obj());
812 }
813
814 while (mark.has_monitor()) {
815 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
816 if (monitor != nullptr) {
817 return Threads::owning_thread_from_monitor(t_list, monitor);
818 }
819 // Racing with inflation/deflation, retry
820 mark = obj->mark_acquire();
821
822 if (mark.is_fast_locked()) {
823 // Some other thread fast_locked
824 return Threads::owning_thread_from_object(t_list, h_obj());
825 }
826 }
827
828 // Unlocked case, header in place
829 // Cannot have assertion since this object may have been
830 // locked by another thread when reaching here.
831 // assert(mark.is_unlocked(), "sanity check");
832
833 return nullptr;
834 }
835
836 // Visitors ...
837
838 // Iterate over all ObjectMonitors.
839 template <typename Function>
840 void ObjectSynchronizer::monitors_iterate(Function function) {
841 MonitorList::Iterator iter = _in_use_list.iterator();
842 while (iter.has_next()) {
843 ObjectMonitor* monitor = iter.next();
844 function(monitor);
845 }
846 }
847
848 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
849 // returns true.
850 template <typename OwnerFilter>
851 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
852 monitors_iterate([&](ObjectMonitor* monitor) {
853 // This function is only called at a safepoint or when the
854 // target thread is suspended or when the target thread is
855 // operating on itself. The current closures in use today are
856 // only interested in an owned ObjectMonitor and ownership
857 // cannot be dropped under the calling contexts so the
858 // ObjectMonitor cannot be async deflated.
859 if (monitor->has_owner() && filter(monitor)) {
860 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
861
862 closure->do_monitor(monitor);
863 }
864 });
865 }
866
867 // Iterate ObjectMonitors where the owner == thread; this does NOT include
868 // ObjectMonitors where owner is set to a stack-lock address in thread.
869 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
870 int64_t key = ObjectMonitor::owner_id_from(thread);
871 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
872 return owned_monitors_iterate_filtered(closure, thread_filter);
873 }
874
875 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
876 int64_t key = ObjectMonitor::owner_id_from(vthread);
877 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
878 return owned_monitors_iterate_filtered(closure, thread_filter);
879 }
880
881 // Iterate ObjectMonitors owned by any thread.
882 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
883 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
884 return owned_monitors_iterate_filtered(closure, all_filter);
885 }
886
887 static bool monitors_used_above_threshold(MonitorList* list) {
888 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
889 return false;
890 }
891 size_t monitors_used = list->count();
892 if (monitors_used == 0) { // empty list is easy
893 return false;
894 }
895 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
896 // Make sure that we use a ceiling value that is not lower than
897 // previous, not lower than the recorded max used by the system, and
898 // not lower than the current number of monitors in use (which can
899 // race ahead of max). The result is guaranteed > 0.
900 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
901
902 // Check if our monitor usage is above the threshold:
903 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
904 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
905 // Deflate monitors if over the threshold percentage, unless no
906 // progress on previous deflations.
907 bool is_above_threshold = true;
908
909 // Check if it's time to adjust the in_use_list_ceiling up, due
910 // to too many async deflation attempts without any progress.
911 if (NoAsyncDeflationProgressMax != 0 &&
912 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
913 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
914 size_t delta = (size_t)(ceiling * remainder) + 1;
915 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
916 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
917 : ceiling + delta;
918
919 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
920 log_info(monitorinflation)("Too many deflations without progress; "
921 "bumping in_use_list_ceiling from %zu"
922 " to %zu", old_ceiling, new_ceiling);
923 _no_progress_cnt = 0;
924 ceiling = new_ceiling;
925
926 // Check if our monitor usage is still above the threshold:
927 monitor_usage = (monitors_used * 100LL) / ceiling;
928 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
929 }
930 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
931 ", monitor_usage=%zu, threshold=%d",
932 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
933 return is_above_threshold;
934 }
935
936 return false;
937 }
938
939 size_t ObjectSynchronizer::in_use_list_count() {
940 return _in_use_list.count();
941 }
942
943 size_t ObjectSynchronizer::in_use_list_max() {
944 return _in_use_list.max();
945 }
946
947 size_t ObjectSynchronizer::in_use_list_ceiling() {
948 return _in_use_list_ceiling;
949 }
950
951 void ObjectSynchronizer::dec_in_use_list_ceiling() {
952 AtomicAccess::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
953 }
954
955 void ObjectSynchronizer::inc_in_use_list_ceiling() {
956 AtomicAccess::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
957 }
958
959 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
960 _in_use_list_ceiling = new_value;
961 }
962
963 bool ObjectSynchronizer::is_async_deflation_needed() {
964 if (is_async_deflation_requested()) {
965 // Async deflation request.
966 log_info(monitorinflation)("Async deflation needed: explicit request");
967 return true;
968 }
969
970 jlong time_since_last = time_since_last_async_deflation_ms();
971
972 if (AsyncDeflationInterval > 0 &&
973 time_since_last > AsyncDeflationInterval &&
974 monitors_used_above_threshold(&_in_use_list)) {
975 // It's been longer than our specified deflate interval and there
976 // are too many monitors in use. We don't deflate more frequently
977 // than AsyncDeflationInterval (unless is_async_deflation_requested)
978 // in order to not swamp the MonitorDeflationThread.
979 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
980 return true;
981 }
982
983 if (GuaranteedAsyncDeflationInterval > 0 &&
984 time_since_last > GuaranteedAsyncDeflationInterval) {
985 // It's been longer than our specified guaranteed deflate interval.
986 // We need to clean up the used monitors even if the threshold is
987 // not reached, to keep the memory utilization at bay when many threads
988 // touched many monitors.
989 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
990 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
991 GuaranteedAsyncDeflationInterval, time_since_last);
992
993 // If this deflation has no progress, then it should not affect the no-progress
994 // tracking, otherwise threshold heuristics would think it was triggered, experienced
995 // no progress, and needs to backoff more aggressively. In this "no progress" case,
996 // the generic code would bump the no-progress counter, and we compensate for that
997 // by telling it to skip the update.
998 //
999 // If this deflation has progress, then it should let non-progress tracking
1000 // know about this, otherwise the threshold heuristics would kick in, potentially
1001 // experience no-progress due to aggressive cleanup by this deflation, and think
1002 // it is still in no-progress stride. In this "progress" case, the generic code would
1003 // zero the counter, and we allow it to happen.
1004 _no_progress_skip_increment = true;
1005
1006 return true;
1007 }
1008
1009 return false;
1010 }
1011
1012 void ObjectSynchronizer::request_deflate_idle_monitors() {
1013 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1014 set_is_async_deflation_requested(true);
1015 ml.notify_all();
1016 }
1017
1018 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1019 JavaThread* current = JavaThread::current();
1020 bool ret_code = false;
1021
1022 jlong last_time = last_async_deflation_time_ns();
1023
1024 request_deflate_idle_monitors();
1025
1026 const int N_CHECKS = 5;
1027 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1028 if (last_async_deflation_time_ns() > last_time) {
1029 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1030 ret_code = true;
1031 break;
1032 }
1033 {
1034 // JavaThread has to honor the blocking protocol.
1035 ThreadBlockInVM tbivm(current);
1036 os::naked_short_sleep(999); // sleep for almost 1 second
1037 }
1038 }
1039 if (!ret_code) {
1040 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1041 }
1042
1043 return ret_code;
1044 }
1045
1046 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1047 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1048 }
1049
1050 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1051 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1052 //
1053 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1054 MonitorList::Iterator iter = _in_use_list.iterator();
1055 size_t deflated_count = 0;
1056 Thread* current = Thread::current();
1057
1058 while (iter.has_next()) {
1059 if (deflated_count >= (size_t)MonitorDeflationMax) {
1060 break;
1061 }
1062 ObjectMonitor* mid = iter.next();
1063 if (mid->deflate_monitor(current)) {
1064 deflated_count++;
1065 }
1066
1067 // Must check for a safepoint/handshake and honor it.
1068 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1069 }
1070
1071 return deflated_count;
1072 }
1073
1074 class DeflationHandshakeClosure : public HandshakeClosure {
1075 public:
1076 DeflationHandshakeClosure() : HandshakeClosure("DeflationHandshakeClosure") {}
1077
1078 void do_thread(Thread* thread) {
1079 log_trace(monitorinflation)("DeflationHandshakeClosure::do_thread: thread="
1080 INTPTR_FORMAT, p2i(thread));
1081 if (thread->is_Java_thread()) {
1082 // Clear OM cache
1083 JavaThread* jt = JavaThread::cast(thread);
1084 jt->om_clear_monitor_cache();
1085 }
1086 }
1087 };
1088
1089 class VM_RendezvousGCThreads : public VM_Operation {
1090 public:
1091 bool evaluate_at_safepoint() const override { return false; }
1092 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1093 void doit() override {
1094 Universe::heap()->safepoint_synchronize_begin();
1095 Universe::heap()->safepoint_synchronize_end();
1096 };
1097 };
1098
1099 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1100 ObjectMonitorDeflationSafepointer* safepointer) {
1101 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1102 size_t deleted_count = 0;
1103 for (ObjectMonitor* monitor: *delete_list) {
1104 delete monitor;
1105 deleted_count++;
1106 // A JavaThread must check for a safepoint/handshake and honor it.
1107 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1108 }
1109 return deleted_count;
1110 }
1111
1112 class ObjectMonitorDeflationLogging: public StackObj {
1113 LogStreamHandle(Debug, monitorinflation) _debug;
1114 LogStreamHandle(Info, monitorinflation) _info;
1115 LogStream* _stream;
1116 elapsedTimer _timer;
1117
1118 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1119 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1120 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1121
1122 public:
1123 ObjectMonitorDeflationLogging()
1124 : _debug(), _info(), _stream(nullptr) {
1125 if (_debug.is_enabled()) {
1126 _stream = &_debug;
1127 } else if (_info.is_enabled()) {
1128 _stream = &_info;
1129 }
1130 }
1131
1132 void begin() {
1133 if (_stream != nullptr) {
1134 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1135 ceiling(), count(), max());
1136 _timer.start();
1137 }
1138 }
1139
1140 void before_handshake(size_t unlinked_count) {
1141 if (_stream != nullptr) {
1142 _timer.stop();
1143 _stream->print_cr("before handshaking: unlinked_count=%zu"
1144 ", in_use_list stats: ceiling=%zu, count="
1145 "%zu, max=%zu",
1146 unlinked_count, ceiling(), count(), max());
1147 }
1148 }
1149
1150 void after_handshake() {
1151 if (_stream != nullptr) {
1152 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1153 "%zu, count=%zu, max=%zu",
1154 ceiling(), count(), max());
1155 _timer.start();
1156 }
1157 }
1158
1159 void end(size_t deflated_count, size_t unlinked_count) {
1160 if (_stream != nullptr) {
1161 _timer.stop();
1162 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1163 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1164 deflated_count, unlinked_count, _timer.seconds());
1165 }
1166 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1167 ceiling(), count(), max());
1168 }
1169 }
1170
1171 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1172 if (_stream != nullptr) {
1173 _timer.stop();
1174 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1175 "%zu, count=%zu, max=%zu",
1176 op_name, cnt_name, cnt, ceiling(), count(), max());
1177 }
1178 }
1179
1180 void after_block_for_safepoint(const char* op_name) {
1181 if (_stream != nullptr) {
1182 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1183 ", count=%zu, max=%zu", op_name,
1184 ceiling(), count(), max());
1185 _timer.start();
1186 }
1187 }
1188 };
1189
1190 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1191 if (!SafepointMechanism::should_process(_current)) {
1192 return;
1193 }
1194
1195 // A safepoint/handshake has started.
1196 _log->before_block_for_safepoint(op_name, count_name, counter);
1197
1198 {
1199 // Honor block request.
1200 ThreadBlockInVM tbivm(_current);
1201 }
1202
1203 _log->after_block_for_safepoint(op_name);
1204 }
1205
1206 // This function is called by the MonitorDeflationThread to deflate
1207 // ObjectMonitors.
1208 size_t ObjectSynchronizer::deflate_idle_monitors() {
1209 JavaThread* current = JavaThread::current();
1210 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1211
1212 // The async deflation request has been processed.
1213 _last_async_deflation_time_ns = os::javaTimeNanos();
1214 set_is_async_deflation_requested(false);
1215
1216 ObjectMonitorDeflationLogging log;
1217 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1218
1219 log.begin();
1220
1221 // Deflate some idle ObjectMonitors.
1222 size_t deflated_count = deflate_monitor_list(&safepointer);
1223
1224 // Unlink the deflated ObjectMonitors from the in-use list.
1225 size_t unlinked_count = 0;
1226 size_t deleted_count = 0;
1227 if (deflated_count > 0) {
1228 ResourceMark rm(current);
1229 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1230 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1231
1232 #ifdef ASSERT
1233 if (UseObjectMonitorTable) {
1234 for (ObjectMonitor* monitor : delete_list) {
1235 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1236 }
1237 }
1238 #endif
1239
1240 log.before_handshake(unlinked_count);
1241
1242 // A JavaThread needs to handshake in order to safely free the
1243 // ObjectMonitors that were deflated in this cycle.
1244 DeflationHandshakeClosure dhc;
1245 Handshake::execute(&dhc);
1246 // Also, we sync and desync GC threads around the handshake, so that they can
1247 // safely read the mark-word and look-through to the object-monitor, without
1248 // being afraid that the object-monitor is going away.
1249 VM_RendezvousGCThreads sync_gc;
1250 VMThread::execute(&sync_gc);
1251
1252 log.after_handshake();
1253
1254 // After the handshake, safely free the ObjectMonitors that were
1255 // deflated and unlinked in this cycle.
1256
1257 // Delete the unlinked ObjectMonitors.
1258 deleted_count = delete_monitors(&delete_list, &safepointer);
1259 assert(unlinked_count == deleted_count, "must be");
1260 }
1261
1262 log.end(deflated_count, unlinked_count);
1263
1264 GVars.stw_random = os::random();
1265
1266 if (deflated_count != 0) {
1267 _no_progress_cnt = 0;
1268 } else if (_no_progress_skip_increment) {
1269 _no_progress_skip_increment = false;
1270 } else {
1271 _no_progress_cnt++;
1272 }
1273
1274 return deflated_count;
1275 }
1276
1277 // Monitor cleanup on JavaThread::exit
1278
1279 // Iterate through monitor cache and attempt to release thread's monitors
1280 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1281 private:
1282 JavaThread* _thread;
1283
1284 public:
1285 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1286 void do_monitor(ObjectMonitor* mid) {
1287 intx rec = mid->complete_exit(_thread);
1288 _thread->dec_held_monitor_count(rec + 1);
1289 }
1290 };
1291
1292 // Release all inflated monitors owned by current thread. Lightweight monitors are
1293 // ignored. This is meant to be called during JNI thread detach which assumes
1294 // all remaining monitors are heavyweight. All exceptions are swallowed.
1295 // Scanning the extant monitor list can be time consuming.
1296 // A simple optimization is to add a per-thread flag that indicates a thread
1297 // called jni_monitorenter() during its lifetime.
1298 //
1299 // Instead of NoSafepointVerifier it might be cheaper to
1300 // use an idiom of the form:
1301 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1302 // <code that must not run at safepoint>
1303 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1304 // Since the tests are extremely cheap we could leave them enabled
1305 // for normal product builds.
1306
1307 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1308 assert(current == JavaThread::current(), "must be current Java thread");
1309 NoSafepointVerifier nsv;
1310 ReleaseJavaMonitorsClosure rjmc(current);
1311 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1312 assert(!current->has_pending_exception(), "Should not be possible");
1313 current->clear_pending_exception();
1314 assert(current->held_monitor_count() == 0, "Should not be possible");
1315 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1316 current->clear_jni_monitor_count();
1317 }
1318
1319 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1320 switch (cause) {
1321 case inflate_cause_vm_internal: return "VM Internal";
1322 case inflate_cause_monitor_enter: return "Monitor Enter";
1323 case inflate_cause_wait: return "Monitor Wait";
1324 case inflate_cause_notify: return "Monitor Notify";
1325 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1326 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1327 default:
1328 ShouldNotReachHere();
1329 }
1330 return "Unknown";
1331 }
1332
1333 //------------------------------------------------------------------------------
1334 // Debugging code
1335
1336 u_char* ObjectSynchronizer::get_gvars_addr() {
1337 return (u_char*)&GVars;
1338 }
1339
1340 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1341 return (u_char*)&GVars.hc_sequence;
1342 }
1343
1344 size_t ObjectSynchronizer::get_gvars_size() {
1345 return sizeof(SharedGlobals);
1346 }
1347
1348 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1349 return (u_char*)&GVars.stw_random;
1350 }
1351
1352 // Do the final audit and print of ObjectMonitor stats; must be done
1353 // by the VMThread at VM exit time.
1354 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1355 assert(Thread::current()->is_VM_thread(), "sanity check");
1356
1357 if (is_final_audit()) { // Only do the audit once.
1358 return;
1359 }
1360 set_is_final_audit();
1361 log_info(monitorinflation)("Starting the final audit.");
1362
1363 if (log_is_enabled(Info, monitorinflation)) {
1364 LogStreamHandle(Info, monitorinflation) ls;
1365 audit_and_print_stats(&ls, true /* on_exit */);
1366 }
1367 }
1368
1369 // This function can be called by the MonitorDeflationThread or it can be called when
1370 // we are trying to exit the VM. The list walker functions can run in parallel with
1371 // the other list operations.
1372 // Calls to this function can be added in various places as a debugging
1373 // aid.
1374 //
1375 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1376 int error_cnt = 0;
1377
1378 ls->print_cr("Checking in_use_list:");
1379 chk_in_use_list(ls, &error_cnt);
1380
1381 if (error_cnt == 0) {
1382 ls->print_cr("No errors found in in_use_list checks.");
1383 } else {
1384 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1385 }
1386
1387 // When exiting, only log the interesting entries at the Info level.
1388 // When called at intervals by the MonitorDeflationThread, log output
1389 // at the Trace level since there can be a lot of it.
1390 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1391 LogStreamHandle(Trace, monitorinflation) ls_tr;
1392 log_in_use_monitor_details(&ls_tr, true /* log_all */);
1393 } else if (on_exit) {
1394 log_in_use_monitor_details(ls, false /* log_all */);
1395 }
1396
1397 ls->flush();
1398
1399 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1400 }
1401
1402 // Check the in_use_list; log the results of the checks.
1403 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1404 size_t l_in_use_count = _in_use_list.count();
1405 size_t l_in_use_max = _in_use_list.max();
1406 out->print_cr("count=%zu, max=%zu", l_in_use_count,
1407 l_in_use_max);
1408
1409 size_t ck_in_use_count = 0;
1410 MonitorList::Iterator iter = _in_use_list.iterator();
1411 while (iter.has_next()) {
1412 ObjectMonitor* mid = iter.next();
1413 chk_in_use_entry(mid, out, error_cnt_p);
1414 ck_in_use_count++;
1415 }
1416
1417 if (l_in_use_count == ck_in_use_count) {
1418 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
1419 l_in_use_count, ck_in_use_count);
1420 } else {
1421 out->print_cr("WARNING: in_use_count=%zu is not equal to "
1422 "ck_in_use_count=%zu", l_in_use_count,
1423 ck_in_use_count);
1424 }
1425
1426 size_t ck_in_use_max = _in_use_list.max();
1427 if (l_in_use_max == ck_in_use_max) {
1428 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
1429 l_in_use_max, ck_in_use_max);
1430 } else {
1431 out->print_cr("WARNING: in_use_max=%zu is not equal to "
1432 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
1433 }
1434 }
1435
1436 // Check an in-use monitor entry; log any errors.
1437 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1438 int* error_cnt_p) {
1439 if (n->owner_is_DEFLATER_MARKER()) {
1440 // This could happen when monitor deflation blocks for a safepoint.
1441 return;
1442 }
1443
1444
1445 if (n->metadata() == 0) {
1446 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1447 "have non-null _metadata (header/hash) field.", p2i(n));
1448 *error_cnt_p = *error_cnt_p + 1;
1449 }
1450
1451 const oop obj = n->object_peek();
1452 if (obj == nullptr) {
1453 return;
1454 }
1455
1456 const markWord mark = obj->mark();
1457 if (!mark.has_monitor()) {
1458 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1459 "object does not think it has a monitor: obj="
1460 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1461 p2i(obj), mark.value());
1462 *error_cnt_p = *error_cnt_p + 1;
1463 return;
1464 }
1465
1466 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
1467 if (n != obj_mon) {
1468 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1469 "object does not refer to the same monitor: obj="
1470 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1471 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1472 *error_cnt_p = *error_cnt_p + 1;
1473 }
1474 }
1475
1476 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1477 // flags indicate why the entry is in-use, 'object' and 'object type'
1478 // indicate the associated object and its type.
1479 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
1480 if (_in_use_list.count() > 0) {
1481 stringStream ss;
1482 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
1483 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1484 out->print_cr("%18s %s %18s %18s",
1485 "monitor", "BHL", "object", "object type");
1486 out->print_cr("================== === ================== ==================");
1487
1488 auto is_interesting = [&](ObjectMonitor* monitor) {
1489 return log_all || monitor->has_owner() || monitor->is_busy();
1490 };
1491
1492 monitors_iterate([&](ObjectMonitor* monitor) {
1493 if (is_interesting(monitor)) {
1494 const oop obj = monitor->object_peek();
1495 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
1496 ResourceMark rm;
1497 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
1498 monitor->is_busy(), hash != 0, monitor->has_owner(),
1499 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
1500 if (monitor->is_busy()) {
1501 out->print(" (%s)", monitor->is_busy_to_string(&ss));
1502 ss.reset();
1503 }
1504 out->cr();
1505 }
1506 });
1507 }
1508
1509 out->flush();
1510 }