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