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