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 // These checks are required for wait, notify and exit to avoid inflating the monitor to
316 // find out this inline type object cannot be locked.
317 #define CHECK_THROW_NOSYNC_IMSE(obj) \
318 if ((obj)->mark().is_inline_type()) { \
319 JavaThread* THREAD = current; \
320 ResourceMark rm(THREAD); \
321 THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
322 }
323
324 #define CHECK_THROW_NOSYNC_IMSE_0(obj) \
325 if ((obj)->mark().is_inline_type()) { \
326 JavaThread* THREAD = current; \
327 ResourceMark rm(THREAD); \
328 THROW_MSG_0(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
329 }
330
331 // =====================> Quick functions
332
333 // The quick_* forms are special fast-path variants used to improve
334 // performance. In the simplest case, a "quick_*" implementation could
335 // simply return false, in which case the caller will perform the necessary
336 // state transitions and call the slow-path form.
337 // The fast-path is designed to handle frequently arising cases in an efficient
338 // manner and is just a degenerate "optimistic" variant of the slow-path.
339 // returns true -- to indicate the call was satisfied.
340 // returns false -- to indicate the call needs the services of the slow-path.
341 // A no-loitering ordinance is in effect for code in the quick_* family
342 // operators: safepoints or indefinite blocking (blocking that might span a
343 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
344 // entry.
345 //
346 // Consider: An interesting optimization is to have the JIT recognize the
347 // following common idiom:
348 // synchronized (someobj) { .... ; notify(); }
349 // That is, we find a notify() or notifyAll() call that immediately precedes
350 // the monitorexit operation. In that case the JIT could fuse the operations
351 // into a single notifyAndExit() runtime primitive.
352
353 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
354 assert(current->thread_state() == _thread_in_Java, "invariant");
355 NoSafepointVerifier nsv;
356 if (obj == nullptr) return false; // slow-path for invalid obj
357 assert(!obj->klass()->is_inline_klass(), "monitor op on inline type");
358 const markWord mark = obj->mark();
359
360 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
361 // Degenerate notify
362 // fast-locked by caller so by definition the implied waitset is empty.
363 return true;
364 }
365
366 if (mark.has_monitor()) {
367 ObjectMonitor* const mon = read_monitor(current, obj, mark);
368 if (mon == nullptr) {
369 // Racing with inflation/deflation go slow path
370 return false;
371 }
372 assert(mon->object() == oop(obj), "invariant");
373 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
374
375 if (mon->first_waiter() != nullptr) {
376 // We have one or more waiters. Since this is an inflated monitor
377 // that we own, we quickly notify them here and now, avoiding the slow-path.
378 if (all) {
379 mon->quick_notifyAll(current);
380 } else {
381 mon->quick_notify(current);
382 }
383 }
384 return true;
385 }
386
387 // other IMS exception states take the slow-path
388 return false;
389 }
390
391 // Handle notifications when synchronizing on value based classes
392 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
393 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
394 frame last_frame = locking_thread->last_frame();
395 bool bcp_was_adjusted = false;
396 // Don't decrement bcp if it points to the frame's first instruction. This happens when
397 // handle_sync_on_value_based_class() is called because of a synchronized method. There
398 // is no actual monitorenter instruction in the byte code in this case.
399 if (last_frame.is_interpreted_frame() &&
400 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
401 // adjust bcp to point back to monitorenter so that we print the correct line numbers
402 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
403 bcp_was_adjusted = true;
404 }
405
406 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
407 ResourceMark rm;
408 stringStream ss;
409 locking_thread->print_active_stack_on(&ss);
410 char* base = (char*)strstr(ss.base(), "at");
411 char* newline = (char*)strchr(ss.base(), '\n');
412 if (newline != nullptr) {
413 *newline = '\0';
414 }
415 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
416 } else {
417 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
418 ResourceMark rm;
419 Log(valuebasedclasses) vblog;
420
421 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
422 if (locking_thread->has_last_Java_frame()) {
423 LogStream info_stream(vblog.info());
424 locking_thread->print_active_stack_on(&info_stream);
425 } else {
426 vblog.info("Cannot find the last Java frame");
427 }
428
429 EventSyncOnValueBasedClass event;
430 if (event.should_commit()) {
431 event.set_valueBasedClass(obj->klass());
432 event.commit();
433 }
434 }
435
436 if (bcp_was_adjusted) {
437 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
438 }
439 }
440
441 // -----------------------------------------------------------------------------
442 // Monitor Enter/Exit
443
444 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
445 // When called with locking_thread != Thread::current() some mechanism must synchronize
446 // the locking_thread with respect to the current thread. Currently only used when
447 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
448 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
449 assert(!obj->klass()->is_inline_klass(), "JITed code should never have locked an instance of a value class");
450 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
451 }
452
453 // -----------------------------------------------------------------------------
454 // JNI locks on java objects
455 // NOTE: must use heavy weight monitor to handle jni monitor enter
456 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
457 JavaThread* THREAD = current;
458 // Top native frames in the stack will not be seen if we attempt
459 // preemption, since we start walking from the last Java anchor.
460 NoPreemptMark npm(current);
461
462 if (obj->klass()->is_value_based()) {
463 handle_sync_on_value_based_class(obj, current);
464 }
465
466 if (obj->klass()->is_inline_klass()) {
467 ResourceMark rm(THREAD);
468 const char* desc = "Cannot synchronize on an instance of value class ";
469 const char* className = obj->klass()->external_name();
470 size_t msglen = strlen(desc) + strlen(className) + 1;
471 char* message = NEW_RESOURCE_ARRAY(char, msglen);
472 assert(message != nullptr, "NEW_RESOURCE_ARRAY should have called vm_exit_out_of_memory and not return nullptr");
473 THROW_MSG(vmSymbols::java_lang_IdentityException(), className);
474 }
475
476 // the current locking is from JNI instead of Java code
477 current->set_current_pending_monitor_is_from_java(false);
478 // An async deflation can race after the inflate() call and before
479 // enter() can make the ObjectMonitor busy. enter() returns false if
480 // we have lost the race to async deflation and we simply try again.
481 while (true) {
482 BasicLock lock;
483 if (LightweightSynchronizer::inflate_and_enter(obj(), &lock, inflate_cause_jni_enter, current, current) != nullptr) {
484 break;
485 }
486 }
487 current->set_current_pending_monitor_is_from_java(true);
488 }
489
490 // NOTE: must use heavy weight monitor to handle jni monitor exit
491 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
492 JavaThread* current = THREAD;
493 CHECK_THROW_NOSYNC_IMSE(obj);
494
495 ObjectMonitor* monitor;
496 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
497 // If this thread has locked the object, exit the monitor. We
498 // intentionally do not use CHECK on check_owner because we must exit the
499 // monitor even if an exception was already pending.
500 if (monitor->check_owner(THREAD)) {
501 monitor->exit(current);
502 }
503 }
504
505 // -----------------------------------------------------------------------------
506 // Internal VM locks on java objects
507 // standard constructor, allows locking failures
508 ObjectLocker::ObjectLocker(Handle obj, TRAPS) : _thread(THREAD), _obj(obj),
509 _npm(_thread, _thread->at_preemptable_init() /* ignore_mark */), _skip_exit(false) {
510 assert(!_thread->preempting(), "");
511
512 _thread->check_for_valid_safepoint_state();
513
514 if (_obj() != nullptr) {
515 ObjectSynchronizer::enter(_obj, &_lock, _thread);
516
517 if (_thread->preempting()) {
518 // If preemption was cancelled we acquired the monitor after freezing
519 // the frames. Redoing the vm call later in thaw will require us to
520 // release it since the call should look like the original one. We
521 // do it in ~ObjectLocker to reduce the window of time we hold the
522 // monitor since we can't do anything useful with it now, and would
523 // otherwise just force other vthreads to preempt in case they try
524 // to acquire this monitor.
525 _skip_exit = !_thread->preemption_cancelled();
526 ObjectSynchronizer::read_monitor(_thread, _obj())->set_object_strong();
527 _thread->set_pending_preempted_exception();
528
529 }
530 }
531 }
532
533 ObjectLocker::~ObjectLocker() {
534 if (_obj() != nullptr && !_skip_exit) {
535 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
536 }
537 }
538
539 void ObjectLocker::wait_uninterruptibly(TRAPS) {
540 ObjectSynchronizer::waitUninterruptibly(_obj, 0, _thread);
541 if (_thread->preempting()) {
542 _skip_exit = true;
543 ObjectSynchronizer::read_monitor(_thread, _obj())->set_object_strong();
544 _thread->set_pending_preempted_exception();
545 }
546 }
547
548 // -----------------------------------------------------------------------------
549 // Wait/Notify/NotifyAll
550 // NOTE: must use heavy weight monitor to handle wait()
551
552 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
553 JavaThread* current = THREAD;
554 CHECK_THROW_NOSYNC_IMSE_0(obj);
555 if (millis < 0) {
556 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
557 }
558
559 ObjectMonitor* monitor;
560 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
561
562 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
563 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
564
565 // This dummy call is in place to get around dtrace bug 6254741. Once
566 // that's fixed we can uncomment the following line, remove the call
567 // and change this function back into a "void" func.
568 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
569 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
570 return ret_code;
571 }
572
573 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
574 assert(millis >= 0, "timeout value is negative");
575
576 ObjectMonitor* monitor;
577 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
578 monitor->wait(millis, false, THREAD);
579 }
580
581
582 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
583 JavaThread* current = THREAD;
584 CHECK_THROW_NOSYNC_IMSE(obj);
585
586 markWord mark = obj->mark();
587 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
588 // Not inflated so there can't be any waiters to notify.
589 return;
590 }
591 ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
592 monitor->notify(CHECK);
593 }
594
595 // NOTE: see comment of notify()
596 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
597 JavaThread* current = THREAD;
598 CHECK_THROW_NOSYNC_IMSE(obj);
599
600 markWord mark = obj->mark();
601 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
602 // Not inflated so there can't be any waiters to notify.
603 return;
604 }
605
606 ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
607 monitor->notifyAll(CHECK);
608 }
609
610 // -----------------------------------------------------------------------------
611 // Hash Code handling
612
613 struct SharedGlobals {
614 char _pad_prefix[OM_CACHE_LINE_SIZE];
615 // This is a highly shared mostly-read variable.
616 // To avoid false-sharing it needs to be the sole occupant of a cache line.
617 volatile int stw_random;
618 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
619 // Hot RW variable -- Sequester to avoid false-sharing
620 volatile int hc_sequence;
621 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
622 };
623
624 static SharedGlobals GVars;
625
626 // hashCode() generation :
627 //
628 // Possibilities:
629 // * MD5Digest of {obj,stw_random}
630 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
631 // * A DES- or AES-style SBox[] mechanism
632 // * One of the Phi-based schemes, such as:
633 // 2654435761 = 2^32 * Phi (golden ratio)
634 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
635 // * A variation of Marsaglia's shift-xor RNG scheme.
636 // * (obj ^ stw_random) is appealing, but can result
637 // in undesirable regularity in the hashCode values of adjacent objects
638 // (objects allocated back-to-back, in particular). This could potentially
639 // result in hashtable collisions and reduced hashtable efficiency.
640 // There are simple ways to "diffuse" the middle address bits over the
641 // generated hashCode values:
642
643 static intptr_t get_next_hash(Thread* current, oop obj) {
644 intptr_t value = 0;
645 if (hashCode == 0) {
646 // This form uses global Park-Miller RNG.
647 // On MP system we'll have lots of RW access to a global, so the
648 // mechanism induces lots of coherency traffic.
649 value = os::random();
650 } else if (hashCode == 1) {
651 // This variation has the property of being stable (idempotent)
652 // between STW operations. This can be useful in some of the 1-0
653 // synchronization schemes.
654 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
655 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
656 } else if (hashCode == 2) {
657 value = 1; // for sensitivity testing
658 } else if (hashCode == 3) {
659 value = ++GVars.hc_sequence;
660 } else if (hashCode == 4) {
661 value = cast_from_oop<intptr_t>(obj);
662 } else {
663 // Marsaglia's xor-shift scheme with thread-specific state
664 // This is probably the best overall implementation -- we'll
665 // likely make this the default in future releases.
666 unsigned t = current->_hashStateX;
667 t ^= (t << 11);
668 current->_hashStateX = current->_hashStateY;
669 current->_hashStateY = current->_hashStateZ;
670 current->_hashStateZ = current->_hashStateW;
671 unsigned v = current->_hashStateW;
672 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
673 current->_hashStateW = v;
674 value = v;
675 }
676
677 value &= markWord::hash_mask;
678 if (value == 0) value = 0xBAD;
679 assert(value != markWord::no_hash, "invariant");
680 return value;
681 }
682
683 static intptr_t install_hash_code(Thread* current, oop obj) {
684 assert(UseObjectMonitorTable, "must be");
685
686 markWord mark = obj->mark_acquire();
687 for (;;) {
688 intptr_t hash = mark.hash();
689 if (hash != 0) {
690 return hash;
691 }
692
693 hash = get_next_hash(current, obj);
694 const markWord old_mark = mark;
695 const markWord new_mark = old_mark.copy_set_hash(hash);
696
697 mark = obj->cas_set_mark(new_mark, old_mark);
698 if (old_mark == mark) {
699 return hash;
700 }
701 }
702 }
703
704 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
705 // VM should be calling bootstrap method.
706 assert(!obj->klass()->is_inline_klass(), "FastHashCode should not be called for inline classes");
707
708 if (UseObjectMonitorTable) {
709 // Since the monitor isn't in the object header, the hash can simply be
710 // installed in the object header.
711 return install_hash_code(current, obj);
712 }
713
714 while (true) {
715 ObjectMonitor* monitor = nullptr;
716 markWord temp, test;
717 intptr_t hash;
718 markWord mark = obj->mark_acquire();
719 if (mark.is_unlocked() || mark.is_fast_locked()) {
720 hash = mark.hash();
721 if (hash != 0) { // if it has a hash, just return it
722 return hash;
723 }
724 hash = get_next_hash(current, obj); // get a new hash
725 temp = mark.copy_set_hash(hash); // merge the hash into header
726 // try to install the hash
727 test = obj->cas_set_mark(temp, mark);
728 if (test == mark) { // if the hash was installed, return it
729 return hash;
730 }
731 // CAS failed, retry
732 continue;
733
734 // Failed to install the hash. It could be that another thread
735 // installed the hash just before our attempt or inflation has
736 // occurred or... so we fall thru to inflate the monitor for
737 // stability and then install the hash.
738 } else if (mark.has_monitor()) {
739 monitor = mark.monitor();
740 temp = monitor->header();
741 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
742 hash = temp.hash();
743 if (hash != 0) {
744 // It has a hash.
745
746 // Separate load of dmw/header above from the loads in
747 // is_being_async_deflated().
748
749 // dmw/header and _contentions may get written by different threads.
750 // Make sure to observe them in the same order when having several observers.
751 OrderAccess::loadload_for_IRIW();
752
753 if (monitor->is_being_async_deflated()) {
754 // But we can't safely use the hash if we detect that async
755 // deflation has occurred. So we attempt to restore the
756 // header/dmw to the object's header so that we only retry
757 // once if the deflater thread happens to be slow.
758 monitor->install_displaced_markword_in_object(obj);
759 continue;
760 }
761 return hash;
762 }
763 // Fall thru so we only have one place that installs the hash in
764 // the ObjectMonitor.
765 }
766
767 // NOTE: an async deflation can race after we get the monitor and
768 // before we can update the ObjectMonitor's header with the hash
769 // value below.
770 assert(mark.has_monitor(), "must be");
771 monitor = mark.monitor();
772
773 // Load ObjectMonitor's header/dmw field and see if it has a hash.
774 mark = monitor->header();
775 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
776 hash = mark.hash();
777 if (hash == 0) { // if it does not have a hash
778 hash = get_next_hash(current, obj); // get a new hash
779 temp = mark.copy_set_hash(hash) ; // merge the hash into header
780 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
781 uintptr_t v = AtomicAccess::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
782 test = markWord(v);
783 if (test != mark) {
784 // The attempt to update the ObjectMonitor's header/dmw field
785 // did not work. This can happen if another thread managed to
786 // merge in the hash just before our cmpxchg().
787 // If we add any new usages of the header/dmw field, this code
788 // will need to be updated.
789 hash = test.hash();
790 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
791 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
792 }
793 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
794 // If we detect that async deflation has occurred, then we
795 // attempt to restore the header/dmw to the object's header
796 // so that we only retry once if the deflater thread happens
797 // to be slow.
798 monitor->install_displaced_markword_in_object(obj);
799 continue;
800 }
801 }
802 // We finally get the hash.
803 return hash;
804 }
805 }
806
807 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
808 Handle h_obj) {
809 if (h_obj->mark().is_inline_type()) {
810 return false;
811 }
812 assert(current == JavaThread::current(), "Can only be called on current thread");
813 oop obj = h_obj();
814
815 markWord mark = obj->mark_acquire();
816
817 if (mark.is_fast_locked()) {
818 // fast-locking case, see if lock is in current's lock stack
819 return current->lock_stack().contains(h_obj());
820 }
821
822 while (mark.has_monitor()) {
823 ObjectMonitor* monitor = read_monitor(current, obj, mark);
824 if (monitor != nullptr) {
825 return monitor->is_entered(current) != 0;
826 }
827 // Racing with inflation/deflation, retry
828 mark = obj->mark_acquire();
829
830 if (mark.is_fast_locked()) {
831 // Some other thread fast_locked, current could not have held the lock
832 return false;
833 }
834 }
835
836 // Unlocked case, header in place
837 assert(mark.is_unlocked(), "sanity check");
838 return false;
839 }
840
841 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
842 oop obj = h_obj();
843 markWord mark = obj->mark_acquire();
844
845 if (mark.is_fast_locked()) {
846 // fast-locked so get owner from the object.
847 // owning_thread_from_object() may also return null here:
848 return Threads::owning_thread_from_object(t_list, h_obj());
849 }
850
851 while (mark.has_monitor()) {
852 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
853 if (monitor != nullptr) {
854 return Threads::owning_thread_from_monitor(t_list, monitor);
855 }
856 // Racing with inflation/deflation, retry
857 mark = obj->mark_acquire();
858
859 if (mark.is_fast_locked()) {
860 // Some other thread fast_locked
861 return Threads::owning_thread_from_object(t_list, h_obj());
862 }
863 }
864
865 // Unlocked case, header in place
866 // Cannot have assertion since this object may have been
867 // locked by another thread when reaching here.
868 // assert(mark.is_unlocked(), "sanity check");
869
870 return nullptr;
871 }
872
873 // Visitors ...
874
875 // Iterate over all ObjectMonitors.
876 template <typename Function>
877 void ObjectSynchronizer::monitors_iterate(Function function) {
878 MonitorList::Iterator iter = _in_use_list.iterator();
879 while (iter.has_next()) {
880 ObjectMonitor* monitor = iter.next();
881 function(monitor);
882 }
883 }
884
885 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
886 // returns true.
887 template <typename OwnerFilter>
888 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
889 monitors_iterate([&](ObjectMonitor* monitor) {
890 // This function is only called at a safepoint or when the
891 // target thread is suspended or when the target thread is
892 // operating on itself. The current closures in use today are
893 // only interested in an owned ObjectMonitor and ownership
894 // cannot be dropped under the calling contexts so the
895 // ObjectMonitor cannot be async deflated.
896 if (monitor->has_owner() && filter(monitor)) {
897 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
898
899 closure->do_monitor(monitor);
900 }
901 });
902 }
903
904 // Iterate ObjectMonitors where the owner == thread; this does NOT include
905 // ObjectMonitors where owner is set to a stack-lock address in thread.
906 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
907 int64_t key = ObjectMonitor::owner_id_from(thread);
908 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
909 return owned_monitors_iterate_filtered(closure, thread_filter);
910 }
911
912 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
913 int64_t key = ObjectMonitor::owner_id_from(vthread);
914 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
915 return owned_monitors_iterate_filtered(closure, thread_filter);
916 }
917
918 // Iterate ObjectMonitors owned by any thread.
919 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
920 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
921 return owned_monitors_iterate_filtered(closure, all_filter);
922 }
923
924 static bool monitors_used_above_threshold(MonitorList* list) {
925 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
926 return false;
927 }
928 size_t monitors_used = list->count();
929 if (monitors_used == 0) { // empty list is easy
930 return false;
931 }
932 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
933 // Make sure that we use a ceiling value that is not lower than
934 // previous, not lower than the recorded max used by the system, and
935 // not lower than the current number of monitors in use (which can
936 // race ahead of max). The result is guaranteed > 0.
937 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
938
939 // Check if our monitor usage is above the threshold:
940 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
941 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
942 // Deflate monitors if over the threshold percentage, unless no
943 // progress on previous deflations.
944 bool is_above_threshold = true;
945
946 // Check if it's time to adjust the in_use_list_ceiling up, due
947 // to too many async deflation attempts without any progress.
948 if (NoAsyncDeflationProgressMax != 0 &&
949 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
950 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
951 size_t delta = (size_t)(ceiling * remainder) + 1;
952 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
953 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
954 : ceiling + delta;
955
956 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
957 log_info(monitorinflation)("Too many deflations without progress; "
958 "bumping in_use_list_ceiling from %zu"
959 " to %zu", old_ceiling, new_ceiling);
960 _no_progress_cnt = 0;
961 ceiling = new_ceiling;
962
963 // Check if our monitor usage is still above the threshold:
964 monitor_usage = (monitors_used * 100LL) / ceiling;
965 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
966 }
967 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
968 ", monitor_usage=%zu, threshold=%d",
969 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
970 return is_above_threshold;
971 }
972
973 return false;
974 }
975
976 size_t ObjectSynchronizer::in_use_list_count() {
977 return _in_use_list.count();
978 }
979
980 size_t ObjectSynchronizer::in_use_list_max() {
981 return _in_use_list.max();
982 }
983
984 size_t ObjectSynchronizer::in_use_list_ceiling() {
985 return _in_use_list_ceiling;
986 }
987
988 void ObjectSynchronizer::dec_in_use_list_ceiling() {
989 AtomicAccess::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
990 }
991
992 void ObjectSynchronizer::inc_in_use_list_ceiling() {
993 AtomicAccess::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
994 }
995
996 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
997 _in_use_list_ceiling = new_value;
998 }
999
1000 bool ObjectSynchronizer::is_async_deflation_needed() {
1001 if (is_async_deflation_requested()) {
1002 // Async deflation request.
1003 log_info(monitorinflation)("Async deflation needed: explicit request");
1004 return true;
1005 }
1006
1007 jlong time_since_last = time_since_last_async_deflation_ms();
1008
1009 if (AsyncDeflationInterval > 0 &&
1010 time_since_last > AsyncDeflationInterval &&
1011 monitors_used_above_threshold(&_in_use_list)) {
1012 // It's been longer than our specified deflate interval and there
1013 // are too many monitors in use. We don't deflate more frequently
1014 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1015 // in order to not swamp the MonitorDeflationThread.
1016 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1017 return true;
1018 }
1019
1020 if (GuaranteedAsyncDeflationInterval > 0 &&
1021 time_since_last > GuaranteedAsyncDeflationInterval) {
1022 // It's been longer than our specified guaranteed deflate interval.
1023 // We need to clean up the used monitors even if the threshold is
1024 // not reached, to keep the memory utilization at bay when many threads
1025 // touched many monitors.
1026 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
1027 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1028 GuaranteedAsyncDeflationInterval, time_since_last);
1029
1030 // If this deflation has no progress, then it should not affect the no-progress
1031 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1032 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1033 // the generic code would bump the no-progress counter, and we compensate for that
1034 // by telling it to skip the update.
1035 //
1036 // If this deflation has progress, then it should let non-progress tracking
1037 // know about this, otherwise the threshold heuristics would kick in, potentially
1038 // experience no-progress due to aggressive cleanup by this deflation, and think
1039 // it is still in no-progress stride. In this "progress" case, the generic code would
1040 // zero the counter, and we allow it to happen.
1041 _no_progress_skip_increment = true;
1042
1043 return true;
1044 }
1045
1046 return false;
1047 }
1048
1049 void ObjectSynchronizer::request_deflate_idle_monitors() {
1050 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1051 set_is_async_deflation_requested(true);
1052 ml.notify_all();
1053 }
1054
1055 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1056 JavaThread* current = JavaThread::current();
1057 bool ret_code = false;
1058
1059 jlong last_time = last_async_deflation_time_ns();
1060
1061 request_deflate_idle_monitors();
1062
1063 const int N_CHECKS = 5;
1064 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1065 if (last_async_deflation_time_ns() > last_time) {
1066 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1067 ret_code = true;
1068 break;
1069 }
1070 {
1071 // JavaThread has to honor the blocking protocol.
1072 ThreadBlockInVM tbivm(current);
1073 os::naked_short_sleep(999); // sleep for almost 1 second
1074 }
1075 }
1076 if (!ret_code) {
1077 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1078 }
1079
1080 return ret_code;
1081 }
1082
1083 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1084 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1085 }
1086
1087 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1088 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1089 //
1090 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1091 MonitorList::Iterator iter = _in_use_list.iterator();
1092 size_t deflated_count = 0;
1093 Thread* current = Thread::current();
1094
1095 while (iter.has_next()) {
1096 if (deflated_count >= (size_t)MonitorDeflationMax) {
1097 break;
1098 }
1099 ObjectMonitor* mid = iter.next();
1100 if (mid->deflate_monitor(current)) {
1101 deflated_count++;
1102 }
1103
1104 // Must check for a safepoint/handshake and honor it.
1105 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1106 }
1107
1108 return deflated_count;
1109 }
1110
1111 class DeflationHandshakeClosure : public HandshakeClosure {
1112 public:
1113 DeflationHandshakeClosure() : HandshakeClosure("DeflationHandshakeClosure") {}
1114
1115 void do_thread(Thread* thread) {
1116 log_trace(monitorinflation)("DeflationHandshakeClosure::do_thread: thread="
1117 INTPTR_FORMAT, p2i(thread));
1118 if (thread->is_Java_thread()) {
1119 // Clear OM cache
1120 JavaThread* jt = JavaThread::cast(thread);
1121 jt->om_clear_monitor_cache();
1122 }
1123 }
1124 };
1125
1126 class VM_RendezvousGCThreads : public VM_Operation {
1127 public:
1128 bool evaluate_at_safepoint() const override { return false; }
1129 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1130 void doit() override {
1131 Universe::heap()->safepoint_synchronize_begin();
1132 Universe::heap()->safepoint_synchronize_end();
1133 };
1134 };
1135
1136 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1137 ObjectMonitorDeflationSafepointer* safepointer) {
1138 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1139 size_t deleted_count = 0;
1140 for (ObjectMonitor* monitor: *delete_list) {
1141 delete monitor;
1142 deleted_count++;
1143 // A JavaThread must check for a safepoint/handshake and honor it.
1144 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1145 }
1146 return deleted_count;
1147 }
1148
1149 class ObjectMonitorDeflationLogging: public StackObj {
1150 LogStreamHandle(Debug, monitorinflation) _debug;
1151 LogStreamHandle(Info, monitorinflation) _info;
1152 LogStream* _stream;
1153 elapsedTimer _timer;
1154
1155 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1156 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1157 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1158
1159 public:
1160 ObjectMonitorDeflationLogging()
1161 : _debug(), _info(), _stream(nullptr) {
1162 if (_debug.is_enabled()) {
1163 _stream = &_debug;
1164 } else if (_info.is_enabled()) {
1165 _stream = &_info;
1166 }
1167 }
1168
1169 void begin() {
1170 if (_stream != nullptr) {
1171 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1172 ceiling(), count(), max());
1173 _timer.start();
1174 }
1175 }
1176
1177 void before_handshake(size_t unlinked_count) {
1178 if (_stream != nullptr) {
1179 _timer.stop();
1180 _stream->print_cr("before handshaking: unlinked_count=%zu"
1181 ", in_use_list stats: ceiling=%zu, count="
1182 "%zu, max=%zu",
1183 unlinked_count, ceiling(), count(), max());
1184 }
1185 }
1186
1187 void after_handshake() {
1188 if (_stream != nullptr) {
1189 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1190 "%zu, count=%zu, max=%zu",
1191 ceiling(), count(), max());
1192 _timer.start();
1193 }
1194 }
1195
1196 void end(size_t deflated_count, size_t unlinked_count) {
1197 if (_stream != nullptr) {
1198 _timer.stop();
1199 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1200 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1201 deflated_count, unlinked_count, _timer.seconds());
1202 }
1203 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1204 ceiling(), count(), max());
1205 }
1206 }
1207
1208 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1209 if (_stream != nullptr) {
1210 _timer.stop();
1211 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1212 "%zu, count=%zu, max=%zu",
1213 op_name, cnt_name, cnt, ceiling(), count(), max());
1214 }
1215 }
1216
1217 void after_block_for_safepoint(const char* op_name) {
1218 if (_stream != nullptr) {
1219 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1220 ", count=%zu, max=%zu", op_name,
1221 ceiling(), count(), max());
1222 _timer.start();
1223 }
1224 }
1225 };
1226
1227 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1228 if (!SafepointMechanism::should_process(_current)) {
1229 return;
1230 }
1231
1232 // A safepoint/handshake has started.
1233 _log->before_block_for_safepoint(op_name, count_name, counter);
1234
1235 {
1236 // Honor block request.
1237 ThreadBlockInVM tbivm(_current);
1238 }
1239
1240 _log->after_block_for_safepoint(op_name);
1241 }
1242
1243 // This function is called by the MonitorDeflationThread to deflate
1244 // ObjectMonitors.
1245 size_t ObjectSynchronizer::deflate_idle_monitors() {
1246 JavaThread* current = JavaThread::current();
1247 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1248
1249 // The async deflation request has been processed.
1250 _last_async_deflation_time_ns = os::javaTimeNanos();
1251 set_is_async_deflation_requested(false);
1252
1253 ObjectMonitorDeflationLogging log;
1254 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1255
1256 log.begin();
1257
1258 // Deflate some idle ObjectMonitors.
1259 size_t deflated_count = deflate_monitor_list(&safepointer);
1260
1261 // Unlink the deflated ObjectMonitors from the in-use list.
1262 size_t unlinked_count = 0;
1263 size_t deleted_count = 0;
1264 if (deflated_count > 0) {
1265 ResourceMark rm(current);
1266 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1267 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1268
1269 #ifdef ASSERT
1270 if (UseObjectMonitorTable) {
1271 for (ObjectMonitor* monitor : delete_list) {
1272 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1273 }
1274 }
1275 #endif
1276
1277 log.before_handshake(unlinked_count);
1278
1279 // A JavaThread needs to handshake in order to safely free the
1280 // ObjectMonitors that were deflated in this cycle.
1281 DeflationHandshakeClosure dhc;
1282 Handshake::execute(&dhc);
1283 // Also, we sync and desync GC threads around the handshake, so that they can
1284 // safely read the mark-word and look-through to the object-monitor, without
1285 // being afraid that the object-monitor is going away.
1286 VM_RendezvousGCThreads sync_gc;
1287 VMThread::execute(&sync_gc);
1288
1289 log.after_handshake();
1290
1291 // After the handshake, safely free the ObjectMonitors that were
1292 // deflated and unlinked in this cycle.
1293
1294 // Delete the unlinked ObjectMonitors.
1295 deleted_count = delete_monitors(&delete_list, &safepointer);
1296 assert(unlinked_count == deleted_count, "must be");
1297 }
1298
1299 log.end(deflated_count, unlinked_count);
1300
1301 GVars.stw_random = os::random();
1302
1303 if (deflated_count != 0) {
1304 _no_progress_cnt = 0;
1305 } else if (_no_progress_skip_increment) {
1306 _no_progress_skip_increment = false;
1307 } else {
1308 _no_progress_cnt++;
1309 }
1310
1311 return deflated_count;
1312 }
1313
1314 // Monitor cleanup on JavaThread::exit
1315
1316 // Iterate through monitor cache and attempt to release thread's monitors
1317 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1318 private:
1319 JavaThread* _thread;
1320
1321 public:
1322 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1323 void do_monitor(ObjectMonitor* mid) {
1324 mid->complete_exit(_thread);
1325 }
1326 };
1327
1328 // Release all inflated monitors owned by current thread. Lightweight monitors are
1329 // ignored. This is meant to be called during JNI thread detach which assumes
1330 // all remaining monitors are heavyweight. All exceptions are swallowed.
1331 // Scanning the extant monitor list can be time consuming.
1332 // A simple optimization is to add a per-thread flag that indicates a thread
1333 // called jni_monitorenter() during its lifetime.
1334 //
1335 // Instead of NoSafepointVerifier it might be cheaper to
1336 // use an idiom of the form:
1337 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1338 // <code that must not run at safepoint>
1339 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1340 // Since the tests are extremely cheap we could leave them enabled
1341 // for normal product builds.
1342
1343 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1344 assert(current == JavaThread::current(), "must be current Java thread");
1345 NoSafepointVerifier nsv;
1346 ReleaseJavaMonitorsClosure rjmc(current);
1347 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1348 assert(!current->has_pending_exception(), "Should not be possible");
1349 current->clear_pending_exception();
1350 }
1351
1352 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1353 switch (cause) {
1354 case inflate_cause_vm_internal: return "VM Internal";
1355 case inflate_cause_monitor_enter: return "Monitor Enter";
1356 case inflate_cause_wait: return "Monitor Wait";
1357 case inflate_cause_notify: return "Monitor Notify";
1358 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1359 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1360 default:
1361 ShouldNotReachHere();
1362 }
1363 return "Unknown";
1364 }
1365
1366 //------------------------------------------------------------------------------
1367 // Debugging code
1368
1369 u_char* ObjectSynchronizer::get_gvars_addr() {
1370 return (u_char*)&GVars;
1371 }
1372
1373 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1374 return (u_char*)&GVars.hc_sequence;
1375 }
1376
1377 size_t ObjectSynchronizer::get_gvars_size() {
1378 return sizeof(SharedGlobals);
1379 }
1380
1381 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1382 return (u_char*)&GVars.stw_random;
1383 }
1384
1385 // Do the final audit and print of ObjectMonitor stats; must be done
1386 // by the VMThread at VM exit time.
1387 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1388 assert(Thread::current()->is_VM_thread(), "sanity check");
1389
1390 if (is_final_audit()) { // Only do the audit once.
1391 return;
1392 }
1393 set_is_final_audit();
1394 log_info(monitorinflation)("Starting the final audit.");
1395
1396 if (log_is_enabled(Info, monitorinflation)) {
1397 LogStreamHandle(Info, monitorinflation) ls;
1398 audit_and_print_stats(&ls, true /* on_exit */);
1399 }
1400 }
1401
1402 // This function can be called by the MonitorDeflationThread or it can be called when
1403 // we are trying to exit the VM. The list walker functions can run in parallel with
1404 // the other list operations.
1405 // Calls to this function can be added in various places as a debugging
1406 // aid.
1407 //
1408 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1409 int error_cnt = 0;
1410
1411 ls->print_cr("Checking in_use_list:");
1412 chk_in_use_list(ls, &error_cnt);
1413
1414 if (error_cnt == 0) {
1415 ls->print_cr("No errors found in in_use_list checks.");
1416 } else {
1417 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1418 }
1419
1420 // When exiting, only log the interesting entries at the Info level.
1421 // When called at intervals by the MonitorDeflationThread, log output
1422 // at the Trace level since there can be a lot of it.
1423 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1424 LogStreamHandle(Trace, monitorinflation) ls_tr;
1425 log_in_use_monitor_details(&ls_tr, true /* log_all */);
1426 } else if (on_exit) {
1427 log_in_use_monitor_details(ls, false /* log_all */);
1428 }
1429
1430 ls->flush();
1431
1432 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1433 }
1434
1435 // Check the in_use_list; log the results of the checks.
1436 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1437 size_t l_in_use_count = _in_use_list.count();
1438 size_t l_in_use_max = _in_use_list.max();
1439 out->print_cr("count=%zu, max=%zu", l_in_use_count,
1440 l_in_use_max);
1441
1442 size_t ck_in_use_count = 0;
1443 MonitorList::Iterator iter = _in_use_list.iterator();
1444 while (iter.has_next()) {
1445 ObjectMonitor* mid = iter.next();
1446 chk_in_use_entry(mid, out, error_cnt_p);
1447 ck_in_use_count++;
1448 }
1449
1450 if (l_in_use_count == ck_in_use_count) {
1451 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
1452 l_in_use_count, ck_in_use_count);
1453 } else {
1454 out->print_cr("WARNING: in_use_count=%zu is not equal to "
1455 "ck_in_use_count=%zu", l_in_use_count,
1456 ck_in_use_count);
1457 }
1458
1459 size_t ck_in_use_max = _in_use_list.max();
1460 if (l_in_use_max == ck_in_use_max) {
1461 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
1462 l_in_use_max, ck_in_use_max);
1463 } else {
1464 out->print_cr("WARNING: in_use_max=%zu is not equal to "
1465 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
1466 }
1467 }
1468
1469 // Check an in-use monitor entry; log any errors.
1470 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1471 int* error_cnt_p) {
1472 if (n->owner_is_DEFLATER_MARKER()) {
1473 // This could happen when monitor deflation blocks for a safepoint.
1474 return;
1475 }
1476
1477
1478 if (n->metadata() == 0) {
1479 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1480 "have non-null _metadata (header/hash) field.", p2i(n));
1481 *error_cnt_p = *error_cnt_p + 1;
1482 }
1483
1484 const oop obj = n->object_peek();
1485 if (obj == nullptr) {
1486 return;
1487 }
1488
1489 const markWord mark = obj->mark();
1490 if (!mark.has_monitor()) {
1491 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1492 "object does not think it has a monitor: obj="
1493 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1494 p2i(obj), mark.value());
1495 *error_cnt_p = *error_cnt_p + 1;
1496 return;
1497 }
1498
1499 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
1500 if (n != obj_mon) {
1501 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1502 "object does not refer to the same monitor: obj="
1503 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1504 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1505 *error_cnt_p = *error_cnt_p + 1;
1506 }
1507 }
1508
1509 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1510 // flags indicate why the entry is in-use, 'object' and 'object type'
1511 // indicate the associated object and its type.
1512 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
1513 if (_in_use_list.count() > 0) {
1514 stringStream ss;
1515 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
1516 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1517 out->print_cr("%18s %s %18s %18s",
1518 "monitor", "BHL", "object", "object type");
1519 out->print_cr("================== === ================== ==================");
1520
1521 auto is_interesting = [&](ObjectMonitor* monitor) {
1522 return log_all || monitor->has_owner() || monitor->is_busy();
1523 };
1524
1525 monitors_iterate([&](ObjectMonitor* monitor) {
1526 if (is_interesting(monitor)) {
1527 const oop obj = monitor->object_peek();
1528 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
1529 ResourceMark rm;
1530 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
1531 monitor->is_busy(), hash != 0, monitor->has_owner(),
1532 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
1533 if (monitor->is_busy()) {
1534 out->print(" (%s)", monitor->is_busy_to_string(&ss));
1535 ss.reset();
1536 }
1537 out->cr();
1538 }
1539 });
1540 }
1541
1542 out->flush();
1543 }