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/atomic.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.hpp"
48 #include "runtime/objectMonitor.inline.hpp"
49 #include "runtime/os.inline.hpp"
50 #include "runtime/osThread.hpp"
51 #include "runtime/perfData.hpp"
52 #include "runtime/safepointMechanism.inline.hpp"
53 #include "runtime/safepointVerifiers.hpp"
54 #include "runtime/sharedRuntime.hpp"
55 #include "runtime/stubRoutines.hpp"
56 #include "runtime/synchronizer.inline.hpp"
57 #include "runtime/threads.hpp"
58 #include "runtime/timer.hpp"
59 #include "runtime/trimNativeHeap.hpp"
60 #include "runtime/vframe.hpp"
61 #include "runtime/vmThread.hpp"
62 #include "utilities/align.hpp"
63 #include "utilities/dtrace.hpp"
64 #include "utilities/events.hpp"
65 #include "utilities/globalCounter.inline.hpp"
66 #include "utilities/globalDefinitions.hpp"
67 #include "utilities/linkedlist.hpp"
68 #include "utilities/preserveException.hpp"
69
70 class ObjectMonitorDeflationLogging;
71
72 void MonitorList::add(ObjectMonitor* m) {
73 ObjectMonitor* head;
74 do {
75 head = Atomic::load(&_head);
76 m->set_next_om(head);
77 } while (Atomic::cmpxchg(&_head, head, m) != head);
78
79 size_t count = Atomic::add(&_count, 1u);
80 if (count > max()) {
81 Atomic::inc(&_max);
82 }
83 }
84
85 size_t MonitorList::count() const {
86 return Atomic::load(&_count);
87 }
88
89 size_t MonitorList::max() const {
90 return Atomic::load(&_max);
91 }
92
93 class ObjectMonitorDeflationSafepointer : public StackObj {
94 JavaThread* const _current;
95 ObjectMonitorDeflationLogging* const _log;
96
97 public:
98 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
99 : _current(current), _log(log) {}
100
101 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
102 };
103
104 // Walk the in-use list and unlink deflated ObjectMonitors.
105 // Returns the number of unlinked ObjectMonitors.
106 size_t MonitorList::unlink_deflated(size_t deflated_count,
107 GrowableArray<ObjectMonitor*>* unlinked_list,
108 ObjectMonitorDeflationSafepointer* safepointer) {
109 size_t unlinked_count = 0;
110 ObjectMonitor* prev = nullptr;
111 ObjectMonitor* m = Atomic::load_acquire(&_head);
112
113 while (m != nullptr) {
114 if (m->is_being_async_deflated()) {
115 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
116 // modify the list once per batch. The batch starts at "m".
117 size_t unlinked_batch = 0;
118 ObjectMonitor* next = m;
119 // Look for at most MonitorUnlinkBatch monitors, or the number of
120 // deflated and not unlinked monitors, whatever comes first.
121 assert(deflated_count >= unlinked_count, "Sanity: underflow");
122 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
123 do {
124 ObjectMonitor* next_next = next->next_om();
125 unlinked_batch++;
126 unlinked_list->append(next);
127 next = next_next;
128 if (unlinked_batch >= unlinked_batch_limit) {
129 // Reached the max batch, so bail out of the gathering loop.
130 break;
131 }
132 if (prev == nullptr && Atomic::load(&_head) != m) {
133 // Current batch used to be at head, but it is not at head anymore.
134 // Bail out and figure out where we currently are. This avoids long
135 // walks searching for new prev during unlink under heavy list inserts.
136 break;
137 }
138 } while (next != nullptr && next->is_being_async_deflated());
139
140 // Unlink the found batch.
141 if (prev == nullptr) {
142 // The current batch is the first batch, so there is a chance that it starts at head.
143 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
144 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, m, next);
145 if (prev_head != m) {
146 // Something must have updated the head. Figure out the actual prev for this batch.
147 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
148 prev = n;
149 }
150 assert(prev != nullptr, "Should have found the prev for the current batch");
151 prev->set_next_om(next);
152 }
153 } else {
154 // The current batch is preceded by another batch. This guarantees the current batch
155 // does not start at head. Unlink the entire current batch without updating the head.
156 assert(Atomic::load(&_head) != m, "Sanity");
157 prev->set_next_om(next);
158 }
159
160 unlinked_count += unlinked_batch;
161 if (unlinked_count >= deflated_count) {
162 // Reached the max so bail out of the searching loop.
163 // There should be no more deflated monitors left.
164 break;
165 }
166 m = next;
167 } else {
168 prev = m;
169 m = m->next_om();
170 }
171
172 // Must check for a safepoint/handshake and honor it.
173 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
174 }
175
176 #ifdef ASSERT
177 // Invariant: the code above should unlink all deflated monitors.
178 // The code that runs after this unlinking does not expect deflated monitors.
179 // Notably, attempting to deflate the already deflated monitor would break.
180 {
181 ObjectMonitor* m = Atomic::load_acquire(&_head);
182 while (m != nullptr) {
183 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
184 m = m->next_om();
185 }
186 }
187 #endif
188
189 Atomic::sub(&_count, unlinked_count);
190 return unlinked_count;
191 }
192
193 MonitorList::Iterator MonitorList::iterator() const {
194 return Iterator(Atomic::load_acquire(&_head));
195 }
196
197 ObjectMonitor* MonitorList::Iterator::next() {
198 ObjectMonitor* current = _current;
199 _current = current->next_om();
200 return current;
201 }
202
203 // The "core" versions of monitor enter and exit reside in this file.
204 // The interpreter and compilers contain specialized transliterated
205 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
206 // fast_lock(...) for instance. If you make changes here, make sure to modify the
207 // interpreter, and both C1 and C2 fast-path inline locking code emission.
208 //
209 // -----------------------------------------------------------------------------
210
211 #ifdef DTRACE_ENABLED
212
213 // Only bother with this argument setup if dtrace is available
214 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
215
216 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
217 char* bytes = nullptr; \
218 int len = 0; \
219 jlong jtid = SharedRuntime::get_java_tid(thread); \
220 Symbol* klassname = obj->klass()->name(); \
221 if (klassname != nullptr) { \
222 bytes = (char*)klassname->bytes(); \
223 len = klassname->utf8_length(); \
224 }
225
226 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
227 { \
228 if (DTraceMonitorProbes) { \
229 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
230 HOTSPOT_MONITOR_WAIT(jtid, \
231 (uintptr_t)(monitor), bytes, len, (millis)); \
232 } \
233 }
234
235 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
236 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
237 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
238
239 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
240 { \
241 if (DTraceMonitorProbes) { \
242 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
243 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
244 (uintptr_t)(monitor), bytes, len); \
245 } \
246 }
247
248 #else // ndef DTRACE_ENABLED
249
250 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
251 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
252
253 #endif // ndef DTRACE_ENABLED
254
255 // This exists only as a workaround of dtrace bug 6254741
256 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
257 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
258 return 0;
259 }
260
261 static constexpr size_t inflation_lock_count() {
262 return 256;
263 }
264
265 // Static storage for an array of PlatformMutex.
266 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
267
268 static inline PlatformMutex* inflation_lock(size_t index) {
269 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
270 }
271
272 void ObjectSynchronizer::initialize() {
273 for (size_t i = 0; i < inflation_lock_count(); i++) {
274 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
275 }
276 // Start the ceiling with the estimate for one thread.
277 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
278
279 // Start the timer for deflations, so it does not trigger immediately.
280 _last_async_deflation_time_ns = os::javaTimeNanos();
281
282 if (LockingMode == LM_LIGHTWEIGHT) {
283 LightweightSynchronizer::initialize();
284 }
285 }
286
287 MonitorList ObjectSynchronizer::_in_use_list;
288 // monitors_used_above_threshold() policy is as follows:
289 //
290 // The ratio of the current _in_use_list count to the ceiling is used
291 // to determine if we are above MonitorUsedDeflationThreshold and need
292 // to do an async monitor deflation cycle. The ceiling is increased by
293 // AvgMonitorsPerThreadEstimate when a thread is added to the system
294 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
295 // removed from the system.
296 //
297 // Note: If the _in_use_list max exceeds the ceiling, then
298 // monitors_used_above_threshold() will use the in_use_list max instead
299 // of the thread count derived ceiling because we have used more
300 // ObjectMonitors than the estimated average.
301 //
302 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
303 // no-progress async monitor deflation cycles in a row, then the ceiling
304 // is adjusted upwards by monitors_used_above_threshold().
305 //
306 // Start the ceiling with the estimate for one thread in initialize()
307 // which is called after cmd line options are processed.
308 static size_t _in_use_list_ceiling = 0;
309 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
310 bool volatile ObjectSynchronizer::_is_final_audit = false;
311 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
312 static uintx _no_progress_cnt = 0;
313 static bool _no_progress_skip_increment = false;
314
315 // 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 (EnableValhalla && (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 (EnableValhalla && (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(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
358 const markWord mark = obj->mark();
359
360 if (LockingMode == LM_LIGHTWEIGHT) {
361 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
362 // Degenerate notify
363 // fast-locked by caller so by definition the implied waitset is empty.
364 return true;
365 }
366 } else if (LockingMode == LM_LEGACY) {
367 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
368 // Degenerate notify
369 // stack-locked by caller so by definition the implied waitset is empty.
370 return true;
371 }
372 }
373
374 if (mark.has_monitor()) {
375 ObjectMonitor* const mon = read_monitor(current, obj, mark);
376 if (LockingMode == LM_LIGHTWEIGHT && mon == nullptr) {
377 // Racing with inflation/deflation go slow path
378 return false;
379 }
380 assert(mon->object() == oop(obj), "invariant");
381 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
382
383 if (mon->first_waiter() != nullptr) {
384 // We have one or more waiters. Since this is an inflated monitor
385 // that we own, we can transfer one or more threads from the waitset
386 // to the entrylist here and now, avoiding the slow-path.
387 if (all) {
388 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
389 } else {
390 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
391 }
392 int free_count = 0;
393 do {
394 mon->INotify(current);
395 ++free_count;
396 } while (mon->first_waiter() != nullptr && all);
397 OM_PERFDATA_OP(Notifications, inc(free_count));
398 }
399 return true;
400 }
401
402 // other IMS exception states take the slow-path
403 return false;
404 }
405
406 static bool useHeavyMonitors() {
407 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
408 return LockingMode == LM_MONITOR;
409 #else
410 return false;
411 #endif
412 }
413
414 // The LockNode emitted directly at the synchronization site would have
415 // been too big if it were to have included support for the cases of inflated
416 // recursive enter and exit, so they go here instead.
417 // Note that we can't safely call AsyncPrintJavaStack() from within
418 // quick_enter() as our thread state remains _in_Java.
419
420 bool ObjectSynchronizer::quick_enter_legacy(oop obj, BasicLock* lock, JavaThread* current) {
421 assert(current->thread_state() == _thread_in_Java, "invariant");
422 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
423
424 if (useHeavyMonitors()) {
425 return false; // Slow path
426 }
427
428 if (LockingMode == LM_LIGHTWEIGHT) {
429 return LightweightSynchronizer::quick_enter(obj, lock, current);
430 }
431
432 assert(LockingMode == LM_LEGACY, "legacy mode below");
433
434 const markWord mark = obj->mark();
435
436 if (mark.has_monitor()) {
437
438 ObjectMonitor* const m = read_monitor(mark);
439 // An async deflation or GC can race us before we manage to make
440 // the ObjectMonitor busy by setting the owner below. If we detect
441 // that race we just bail out to the slow-path here.
442 if (m->object_peek() == nullptr) {
443 return false;
444 }
445
446 // Lock contention and Transactional Lock Elision (TLE) diagnostics
447 // and observability
448 // Case: light contention possibly amenable to TLE
449 // Case: TLE inimical operations such as nested/recursive synchronization
450
451 if (m->has_owner(current)) {
452 m->_recursions++;
453 current->inc_held_monitor_count();
454 return true;
455 }
456
457 // This Java Monitor is inflated so obj's header will never be
458 // displaced to this thread's BasicLock. Make the displaced header
459 // non-null so this BasicLock is not seen as recursive nor as
460 // being locked. We do this unconditionally so that this thread's
461 // BasicLock cannot be mis-interpreted by any stack walkers. For
462 // performance reasons, stack walkers generally first check for
463 // stack-locking in the object's header, the second check is for
464 // recursive stack-locking in the displaced header in the BasicLock,
465 // and last are the inflated Java Monitor (ObjectMonitor) checks.
466 lock->set_displaced_header(markWord::unused_mark());
467
468 if (!m->has_owner() && m->try_set_owner(current)) {
469 assert(m->_recursions == 0, "invariant");
470 current->inc_held_monitor_count();
471 return true;
472 }
473 }
474
475 // Note that we could inflate in quick_enter.
476 // This is likely a useful optimization
477 // Critically, in quick_enter() we must not:
478 // -- block indefinitely, or
479 // -- reach a safepoint
480
481 return false; // revert to slow-path
482 }
483
484 // Handle notifications when synchronizing on value based classes
485 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
486 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
487 frame last_frame = locking_thread->last_frame();
488 bool bcp_was_adjusted = false;
489 // Don't decrement bcp if it points to the frame's first instruction. This happens when
490 // handle_sync_on_value_based_class() is called because of a synchronized method. There
491 // is no actual monitorenter instruction in the byte code in this case.
492 if (last_frame.is_interpreted_frame() &&
493 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
494 // adjust bcp to point back to monitorenter so that we print the correct line numbers
495 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
496 bcp_was_adjusted = true;
497 }
498
499 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
500 ResourceMark rm;
501 stringStream ss;
502 locking_thread->print_active_stack_on(&ss);
503 char* base = (char*)strstr(ss.base(), "at");
504 char* newline = (char*)strchr(ss.base(), '\n');
505 if (newline != nullptr) {
506 *newline = '\0';
507 }
508 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
509 } else {
510 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
511 ResourceMark rm;
512 Log(valuebasedclasses) vblog;
513
514 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
515 if (locking_thread->has_last_Java_frame()) {
516 LogStream info_stream(vblog.info());
517 locking_thread->print_active_stack_on(&info_stream);
518 } else {
519 vblog.info("Cannot find the last Java frame");
520 }
521
522 EventSyncOnValueBasedClass event;
523 if (event.should_commit()) {
524 event.set_valueBasedClass(obj->klass());
525 event.commit();
526 }
527 }
528
529 if (bcp_was_adjusted) {
530 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
531 }
532 }
533
534 // -----------------------------------------------------------------------------
535 // Monitor Enter/Exit
536
537 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
538 // When called with locking_thread != Thread::current() some mechanism must synchronize
539 // the locking_thread with respect to the current thread. Currently only used when
540 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
541 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
542 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "JITed code should never have locked an instance of a value class");
543
544 if (LockingMode == LM_LIGHTWEIGHT) {
545 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
546 }
547
548 if (!enter_fast_impl(obj, lock, locking_thread)) {
549 // Inflated ObjectMonitor::enter_for is required
550
551 // An async deflation can race after the inflate_for() call and before
552 // enter_for() can make the ObjectMonitor busy. enter_for() returns false
553 // if we have lost the race to async deflation and we simply try again.
554 while (true) {
555 ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
556 if (monitor->enter_for(locking_thread)) {
557 return;
558 }
559 assert(monitor->is_being_async_deflated(), "must be");
560 }
561 }
562 }
563
564 void ObjectSynchronizer::enter_legacy(Handle obj, BasicLock* lock, JavaThread* current) {
565 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "This method should never be called on an instance of an inline class");
566 if (!enter_fast_impl(obj, lock, current)) {
567 // Inflated ObjectMonitor::enter is required
568
569 // An async deflation can race after the inflate() call and before
570 // enter() can make the ObjectMonitor busy. enter() returns false if
571 // we have lost the race to async deflation and we simply try again.
572 while (true) {
573 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
574 if (monitor->enter(current)) {
575 return;
576 }
577 }
578 }
579 }
580
581 // The interpreter and compiler assembly code tries to lock using the fast path
582 // of this algorithm. Make sure to update that code if the following function is
583 // changed. The implementation is extremely sensitive to race condition. Be careful.
584 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
585 guarantee(!EnableValhalla || !obj->klass()->is_inline_klass(), "Attempt to inflate inline type");
586 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
587
588 if (obj->klass()->is_value_based()) {
589 handle_sync_on_value_based_class(obj, locking_thread);
590 }
591
592 locking_thread->inc_held_monitor_count();
593
594 if (!useHeavyMonitors()) {
595 if (LockingMode == LM_LEGACY) {
596 markWord mark = obj->mark();
597 if (mark.is_unlocked()) {
598 // Anticipate successful CAS -- the ST of the displaced mark must
599 // be visible <= the ST performed by the CAS.
600 lock->set_displaced_header(mark);
601 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
602 return true;
603 }
604 } else if (mark.has_locker() &&
605 locking_thread->is_lock_owned((address) mark.locker())) {
606 assert(lock != mark.locker(), "must not re-lock the same lock");
607 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
608 lock->set_displaced_header(markWord::from_pointer(nullptr));
609 return true;
610 }
611
612 // The object header will never be displaced to this lock,
613 // so it does not matter what the value is, except that it
614 // must be non-zero to avoid looking like a re-entrant lock,
615 // and must not look locked either.
616 lock->set_displaced_header(markWord::unused_mark());
617
618 // Failed to fast lock.
619 return false;
620 }
621 } else if (VerifyHeavyMonitors) {
622 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
623 }
624
625 return false;
626 }
627
628 void ObjectSynchronizer::exit_legacy(oop object, BasicLock* lock, JavaThread* current) {
629 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
630
631 if (!useHeavyMonitors()) {
632 markWord mark = object->mark();
633 if (EnableValhalla && mark.is_inline_type()) {
634 return;
635 }
636 if (LockingMode == LM_LEGACY) {
637 markWord dhw = lock->displaced_header();
638 if (dhw.value() == 0) {
639 // If the displaced header is null, then this exit matches up with
640 // a recursive enter. No real work to do here except for diagnostics.
641 #ifndef PRODUCT
642 if (mark != markWord::INFLATING()) {
643 // Only do diagnostics if we are not racing an inflation. Simply
644 // exiting a recursive enter of a Java Monitor that is being
645 // inflated is safe; see the has_monitor() comment below.
646 assert(!mark.is_unlocked(), "invariant");
647 assert(!mark.has_locker() ||
648 current->is_lock_owned((address)mark.locker()), "invariant");
649 if (mark.has_monitor()) {
650 // The BasicLock's displaced_header is marked as a recursive
651 // enter and we have an inflated Java Monitor (ObjectMonitor).
652 // This is a special case where the Java Monitor was inflated
653 // after this thread entered the stack-lock recursively. When a
654 // Java Monitor is inflated, we cannot safely walk the Java
655 // Monitor owner's stack and update the BasicLocks because a
656 // Java Monitor can be asynchronously inflated by a thread that
657 // does not own the Java Monitor.
658 ObjectMonitor* m = read_monitor(mark);
659 assert(m->object()->mark() == mark, "invariant");
660 assert(m->is_entered(current), "invariant");
661 }
662 }
663 #endif
664 return;
665 }
666
667 if (mark == markWord::from_pointer(lock)) {
668 // If the object is stack-locked by the current thread, try to
669 // swing the displaced header from the BasicLock back to the mark.
670 assert(dhw.is_neutral(), "invariant");
671 if (object->cas_set_mark(dhw, mark) == mark) {
672 return;
673 }
674 }
675 }
676 } else if (VerifyHeavyMonitors) {
677 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
678 }
679
680 // We have to take the slow-path of possible inflation and then exit.
681 // The ObjectMonitor* can't be async deflated until ownership is
682 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
683 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
684 assert(!monitor->has_anonymous_owner(), "must not be");
685 monitor->exit(current);
686 }
687
688 // -----------------------------------------------------------------------------
689 // JNI locks on java objects
690 // NOTE: must use heavy weight monitor to handle jni monitor enter
691 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
692 JavaThread* THREAD = current;
693 // Top native frames in the stack will not be seen if we attempt
694 // preemption, since we start walking from the last Java anchor.
695 NoPreemptMark npm(current);
696
697 if (obj->klass()->is_value_based()) {
698 handle_sync_on_value_based_class(obj, current);
699 }
700
701 if (EnableValhalla && obj->klass()->is_inline_klass()) {
702 ResourceMark rm(THREAD);
703 const char* desc = "Cannot synchronize on an instance of value class ";
704 const char* className = obj->klass()->external_name();
705 size_t msglen = strlen(desc) + strlen(className) + 1;
706 char* message = NEW_RESOURCE_ARRAY(char, msglen);
707 assert(message != nullptr, "NEW_RESOURCE_ARRAY should have called vm_exit_out_of_memory and not return nullptr");
708 THROW_MSG(vmSymbols::java_lang_IdentityException(), className);
709 }
710
711 // the current locking is from JNI instead of Java code
712 current->set_current_pending_monitor_is_from_java(false);
713 // An async deflation can race after the inflate() call and before
714 // enter() can make the ObjectMonitor busy. enter() returns false if
715 // we have lost the race to async deflation and we simply try again.
716 while (true) {
717 ObjectMonitor* monitor;
718 bool entered;
719 if (LockingMode == LM_LIGHTWEIGHT) {
720 entered = LightweightSynchronizer::inflate_and_enter(obj(), inflate_cause_jni_enter, current, current) != nullptr;
721 } else {
722 monitor = inflate(current, obj(), inflate_cause_jni_enter);
723 entered = monitor->enter(current);
724 }
725
726 if (entered) {
727 current->inc_held_monitor_count(1, true);
728 break;
729 }
730 }
731 current->set_current_pending_monitor_is_from_java(true);
732 }
733
734 // NOTE: must use heavy weight monitor to handle jni monitor exit
735 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
736 JavaThread* current = THREAD;
737 CHECK_THROW_NOSYNC_IMSE(obj);
738
739 ObjectMonitor* monitor;
740 if (LockingMode == LM_LIGHTWEIGHT) {
741 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
742 } else {
743 // The ObjectMonitor* can't be async deflated until ownership is
744 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
745 monitor = inflate(current, obj, inflate_cause_jni_exit);
746 }
747 // If this thread has locked the object, exit the monitor. We
748 // intentionally do not use CHECK on check_owner because we must exit the
749 // monitor even if an exception was already pending.
750 if (monitor->check_owner(THREAD)) {
751 monitor->exit(current);
752 current->dec_held_monitor_count(1, true);
753 }
754 }
755
756 // -----------------------------------------------------------------------------
757 // Internal VM locks on java objects
758 // standard constructor, allows locking failures
759 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) : _npm(thread) {
760 _thread = thread;
761 _thread->check_for_valid_safepoint_state();
762 _obj = obj;
763
764 if (_obj() != nullptr) {
765 ObjectSynchronizer::enter(_obj, &_lock, _thread);
766 }
767 }
768
769 ObjectLocker::~ObjectLocker() {
770 if (_obj() != nullptr) {
771 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
772 }
773 }
774
775
776 // -----------------------------------------------------------------------------
777 // Wait/Notify/NotifyAll
778 // NOTE: must use heavy weight monitor to handle wait()
779
780 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
781 JavaThread* current = THREAD;
782 CHECK_THROW_NOSYNC_IMSE_0(obj);
783 if (millis < 0) {
784 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
785 }
786
787 ObjectMonitor* monitor;
788 if (LockingMode == LM_LIGHTWEIGHT) {
789 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
790 } else {
791 // The ObjectMonitor* can't be async deflated because the _waiters
792 // field is incremented before ownership is dropped and decremented
793 // after ownership is regained.
794 monitor = inflate(current, obj(), inflate_cause_wait);
795 }
796
797 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
798 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
799
800 // This dummy call is in place to get around dtrace bug 6254741. Once
801 // that's fixed we can uncomment the following line, remove the call
802 // and change this function back into a "void" func.
803 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
804 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
805 return ret_code;
806 }
807
808 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
809 if (millis < 0) {
810 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
811 }
812
813 ObjectMonitor* monitor;
814 if (LockingMode == LM_LIGHTWEIGHT) {
815 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
816 } else {
817 monitor = inflate(THREAD, obj(), inflate_cause_wait);
818 }
819 monitor->wait(millis, false, THREAD);
820 }
821
822
823 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
824 JavaThread* current = THREAD;
825 CHECK_THROW_NOSYNC_IMSE(obj);
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
840 ObjectMonitor* monitor;
841 if (LockingMode == LM_LIGHTWEIGHT) {
842 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
843 } else {
844 // The ObjectMonitor* can't be async deflated until ownership is
845 // dropped by the calling thread.
846 monitor = inflate(current, obj(), inflate_cause_notify);
847 }
848 monitor->notify(CHECK);
849 }
850
851 // NOTE: see comment of notify()
852 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
853 JavaThread* current = THREAD;
854 CHECK_THROW_NOSYNC_IMSE(obj);
855
856 markWord mark = obj->mark();
857 if (LockingMode == LM_LIGHTWEIGHT) {
858 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
859 // Not inflated so there can't be any waiters to notify.
860 return;
861 }
862 } else if (LockingMode == LM_LEGACY) {
863 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
864 // Not inflated so there can't be any waiters to notify.
865 return;
866 }
867 }
868
869 ObjectMonitor* monitor;
870 if (LockingMode == LM_LIGHTWEIGHT) {
871 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
872 } else {
873 // The ObjectMonitor* can't be async deflated until ownership is
874 // dropped by the calling thread.
875 monitor = inflate(current, obj(), inflate_cause_notify);
876 }
877 monitor->notifyAll(CHECK);
878 }
879
880 // -----------------------------------------------------------------------------
881 // Hash Code handling
882
883 struct SharedGlobals {
884 char _pad_prefix[OM_CACHE_LINE_SIZE];
885 // This is a highly shared mostly-read variable.
886 // To avoid false-sharing it needs to be the sole occupant of a cache line.
887 volatile int stw_random;
888 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
889 // Hot RW variable -- Sequester to avoid false-sharing
890 volatile int hc_sequence;
891 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
892 };
893
894 static SharedGlobals GVars;
895
896 static markWord read_stable_mark(oop obj) {
897 markWord mark = obj->mark_acquire();
898 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
899 // New lightweight locking does not use the markWord::INFLATING() protocol.
900 return mark; // normal fast-path return
901 }
902
903 int its = 0;
904 for (;;) {
905 markWord mark = obj->mark_acquire();
906 if (!mark.is_being_inflated()) {
907 return mark; // normal fast-path return
908 }
909
910 // The object is being inflated by some other thread.
911 // The caller of read_stable_mark() must wait for inflation to complete.
912 // Avoid live-lock.
913
914 ++its;
915 if (its > 10000 || !os::is_MP()) {
916 if (its & 1) {
917 os::naked_yield();
918 } else {
919 // Note that the following code attenuates the livelock problem but is not
920 // a complete remedy. A more complete solution would require that the inflating
921 // thread hold the associated inflation lock. The following code simply restricts
922 // the number of spinners to at most one. We'll have N-2 threads blocked
923 // on the inflationlock, 1 thread holding the inflation lock and using
924 // a yield/park strategy, and 1 thread in the midst of inflation.
925 // A more refined approach would be to change the encoding of INFLATING
926 // to allow encapsulation of a native thread pointer. Threads waiting for
927 // inflation to complete would use CAS to push themselves onto a singly linked
928 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
929 // and calling park(). When inflation was complete the thread that accomplished inflation
930 // would detach the list and set the markword to inflated with a single CAS and
931 // then for each thread on the list, set the flag and unpark() the thread.
932
933 // Index into the lock array based on the current object address.
934 static_assert(is_power_of_2(inflation_lock_count()), "must be");
935 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
936 int YieldThenBlock = 0;
937 assert(ix < inflation_lock_count(), "invariant");
938 inflation_lock(ix)->lock();
939 while (obj->mark_acquire() == markWord::INFLATING()) {
940 // Beware: naked_yield() is advisory and has almost no effect on some platforms
941 // so we periodically call current->_ParkEvent->park(1).
942 // We use a mixed spin/yield/block mechanism.
943 if ((YieldThenBlock++) >= 16) {
944 Thread::current()->_ParkEvent->park(1);
945 } else {
946 os::naked_yield();
947 }
948 }
949 inflation_lock(ix)->unlock();
950 }
951 } else {
952 SpinPause(); // SMP-polite spinning
953 }
954 }
955 }
956
957 // hashCode() generation :
958 //
959 // Possibilities:
960 // * MD5Digest of {obj,stw_random}
961 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
962 // * A DES- or AES-style SBox[] mechanism
963 // * One of the Phi-based schemes, such as:
964 // 2654435761 = 2^32 * Phi (golden ratio)
965 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
966 // * A variation of Marsaglia's shift-xor RNG scheme.
967 // * (obj ^ stw_random) is appealing, but can result
968 // in undesirable regularity in the hashCode values of adjacent objects
969 // (objects allocated back-to-back, in particular). This could potentially
970 // result in hashtable collisions and reduced hashtable efficiency.
971 // There are simple ways to "diffuse" the middle address bits over the
972 // generated hashCode values:
973
974 static intptr_t get_next_hash(Thread* current, oop obj) {
975 intptr_t value = 0;
976 if (hashCode == 0) {
977 // This form uses global Park-Miller RNG.
978 // On MP system we'll have lots of RW access to a global, so the
979 // mechanism induces lots of coherency traffic.
980 value = os::random();
981 } else if (hashCode == 1) {
982 // This variation has the property of being stable (idempotent)
983 // between STW operations. This can be useful in some of the 1-0
984 // synchronization schemes.
985 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
986 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
987 } else if (hashCode == 2) {
988 value = 1; // for sensitivity testing
989 } else if (hashCode == 3) {
990 value = ++GVars.hc_sequence;
991 } else if (hashCode == 4) {
992 value = cast_from_oop<intptr_t>(obj);
993 } else {
994 // Marsaglia's xor-shift scheme with thread-specific state
995 // This is probably the best overall implementation -- we'll
996 // likely make this the default in future releases.
997 unsigned t = current->_hashStateX;
998 t ^= (t << 11);
999 current->_hashStateX = current->_hashStateY;
1000 current->_hashStateY = current->_hashStateZ;
1001 current->_hashStateZ = current->_hashStateW;
1002 unsigned v = current->_hashStateW;
1003 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
1004 current->_hashStateW = v;
1005 value = v;
1006 }
1007
1008 value &= markWord::hash_mask;
1009 if (value == 0) value = 0xBAD;
1010 assert(value != markWord::no_hash, "invariant");
1011 return value;
1012 }
1013
1014 static intptr_t install_hash_code(Thread* current, oop obj) {
1015 assert(UseObjectMonitorTable && LockingMode == LM_LIGHTWEIGHT, "must be");
1016
1017 markWord mark = obj->mark_acquire();
1018 for (;;) {
1019 intptr_t hash = mark.hash();
1020 if (hash != 0) {
1021 return hash;
1022 }
1023
1024 hash = get_next_hash(current, obj);
1025 const markWord old_mark = mark;
1026 const markWord new_mark = old_mark.copy_set_hash(hash);
1027
1028 mark = obj->cas_set_mark(new_mark, old_mark);
1029 if (old_mark == mark) {
1030 return hash;
1031 }
1032 }
1033 }
1034
1035 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
1036 if (EnableValhalla && obj->klass()->is_inline_klass()) {
1037 // VM should be calling bootstrap method
1038 ShouldNotReachHere();
1039 }
1040 if (UseObjectMonitorTable) {
1041 // Since the monitor isn't in the object header, the hash can simply be
1042 // installed in the object header.
1043 return install_hash_code(current, obj);
1044 }
1045
1046 while (true) {
1047 ObjectMonitor* monitor = nullptr;
1048 markWord temp, test;
1049 intptr_t hash;
1050 markWord mark = read_stable_mark(obj);
1051 if (VerifyHeavyMonitors) {
1052 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
1053 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1054 }
1055 if (mark.is_unlocked() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1056 hash = mark.hash();
1057 if (hash != 0) { // if it has a hash, just return it
1058 return hash;
1059 }
1060 hash = get_next_hash(current, obj); // get a new hash
1061 temp = mark.copy_set_hash(hash); // merge the hash into header
1062 // try to install the hash
1063 test = obj->cas_set_mark(temp, mark);
1064 if (test == mark) { // if the hash was installed, return it
1065 return hash;
1066 }
1067 if (LockingMode == LM_LIGHTWEIGHT) {
1068 // CAS failed, retry
1069 continue;
1070 }
1071 // Failed to install the hash. It could be that another thread
1072 // installed the hash just before our attempt or inflation has
1073 // occurred or... so we fall thru to inflate the monitor for
1074 // stability and then install the hash.
1075 } else if (mark.has_monitor()) {
1076 monitor = mark.monitor();
1077 temp = monitor->header();
1078 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1079 hash = temp.hash();
1080 if (hash != 0) {
1081 // It has a hash.
1082
1083 // Separate load of dmw/header above from the loads in
1084 // is_being_async_deflated().
1085
1086 // dmw/header and _contentions may get written by different threads.
1087 // Make sure to observe them in the same order when having several observers.
1088 OrderAccess::loadload_for_IRIW();
1089
1090 if (monitor->is_being_async_deflated()) {
1091 // But we can't safely use the hash if we detect that async
1092 // deflation has occurred. So we attempt to restore the
1093 // header/dmw to the object's header so that we only retry
1094 // once if the deflater thread happens to be slow.
1095 monitor->install_displaced_markword_in_object(obj);
1096 continue;
1097 }
1098 return hash;
1099 }
1100 // Fall thru so we only have one place that installs the hash in
1101 // the ObjectMonitor.
1102 } else if (LockingMode == LM_LEGACY && mark.has_locker()
1103 && current->is_Java_thread()
1104 && JavaThread::cast(current)->is_lock_owned((address)mark.locker())) {
1105 // This is a stack-lock owned by the calling thread so fetch the
1106 // displaced markWord from the BasicLock on the stack.
1107 temp = mark.displaced_mark_helper();
1108 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1109 hash = temp.hash();
1110 if (hash != 0) { // if it has a hash, just return it
1111 return hash;
1112 }
1113 // WARNING:
1114 // The displaced header in the BasicLock on a thread's stack
1115 // is strictly immutable. It CANNOT be changed in ANY cases.
1116 // So we have to inflate the stack-lock into an ObjectMonitor
1117 // even if the current thread owns the lock. The BasicLock on
1118 // a thread's stack can be asynchronously read by other threads
1119 // during an inflate() call so any change to that stack memory
1120 // may not propagate to other threads correctly.
1121 }
1122
1123 // Inflate the monitor to set the hash.
1124
1125 // There's no need to inflate if the mark has already got a monitor.
1126 // NOTE: an async deflation can race after we get the monitor and
1127 // before we can update the ObjectMonitor's header with the hash
1128 // value below.
1129 monitor = mark.has_monitor() ? mark.monitor() : inflate(current, obj, inflate_cause_hash_code);
1130 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1131 mark = monitor->header();
1132 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1133 hash = mark.hash();
1134 if (hash == 0) { // if it does not have a hash
1135 hash = get_next_hash(current, obj); // get a new hash
1136 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1137 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1138 uintptr_t v = Atomic::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
1139 test = markWord(v);
1140 if (test != mark) {
1141 // The attempt to update the ObjectMonitor's header/dmw field
1142 // did not work. This can happen if another thread managed to
1143 // merge in the hash just before our cmpxchg().
1144 // If we add any new usages of the header/dmw field, this code
1145 // will need to be updated.
1146 hash = test.hash();
1147 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1148 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1149 }
1150 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
1151 // If we detect that async deflation has occurred, then we
1152 // attempt to restore the header/dmw to the object's header
1153 // so that we only retry once if the deflater thread happens
1154 // to be slow.
1155 monitor->install_displaced_markword_in_object(obj);
1156 continue;
1157 }
1158 }
1159 // We finally get the hash.
1160 return hash;
1161 }
1162 }
1163
1164 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1165 Handle h_obj) {
1166 if (EnableValhalla && h_obj->mark().is_inline_type()) {
1167 return false;
1168 }
1169 assert(current == JavaThread::current(), "Can only be called on current thread");
1170 oop obj = h_obj();
1171
1172 markWord mark = read_stable_mark(obj);
1173
1174 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1175 // stack-locked case, header points into owner's stack
1176 return current->is_lock_owned((address)mark.locker());
1177 }
1178
1179 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1180 // fast-locking case, see if lock is in current's lock stack
1181 return current->lock_stack().contains(h_obj());
1182 }
1183
1184 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1185 ObjectMonitor* monitor = read_monitor(current, obj, mark);
1186 if (monitor != nullptr) {
1187 return monitor->is_entered(current) != 0;
1188 }
1189 // Racing with inflation/deflation, retry
1190 mark = obj->mark_acquire();
1191
1192 if (mark.is_fast_locked()) {
1193 // Some other thread fast_locked, current could not have held the lock
1194 return false;
1195 }
1196 }
1197
1198 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1199 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1200 // The first stage of async deflation does not affect any field
1201 // used by this comparison so the ObjectMonitor* is usable here.
1202 ObjectMonitor* monitor = read_monitor(mark);
1203 return monitor->is_entered(current) != 0;
1204 }
1205 // Unlocked case, header in place
1206 assert(mark.is_unlocked(), "sanity check");
1207 return false;
1208 }
1209
1210 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1211 oop obj = h_obj();
1212 markWord mark = read_stable_mark(obj);
1213
1214 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1215 // stack-locked so header points into owner's stack.
1216 // owning_thread_from_monitor_owner() may also return null here:
1217 return Threads::owning_thread_from_stacklock(t_list, (address) mark.locker());
1218 }
1219
1220 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1221 // fast-locked so get owner from the object.
1222 // owning_thread_from_object() may also return null here:
1223 return Threads::owning_thread_from_object(t_list, h_obj());
1224 }
1225
1226 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1227 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
1228 if (monitor != nullptr) {
1229 return Threads::owning_thread_from_monitor(t_list, monitor);
1230 }
1231 // Racing with inflation/deflation, retry
1232 mark = obj->mark_acquire();
1233
1234 if (mark.is_fast_locked()) {
1235 // Some other thread fast_locked
1236 return Threads::owning_thread_from_object(t_list, h_obj());
1237 }
1238 }
1239
1240 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1241 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1242 // The first stage of async deflation does not affect any field
1243 // used by this comparison so the ObjectMonitor* is usable here.
1244 ObjectMonitor* monitor = read_monitor(mark);
1245 assert(monitor != nullptr, "monitor should be non-null");
1246 // owning_thread_from_monitor() may also return null here:
1247 return Threads::owning_thread_from_monitor(t_list, monitor);
1248 }
1249
1250 // Unlocked case, header in place
1251 // Cannot have assertion since this object may have been
1252 // locked by another thread when reaching here.
1253 // assert(mark.is_unlocked(), "sanity check");
1254
1255 return nullptr;
1256 }
1257
1258 // Visitors ...
1259
1260 // Iterate over all ObjectMonitors.
1261 template <typename Function>
1262 void ObjectSynchronizer::monitors_iterate(Function function) {
1263 MonitorList::Iterator iter = _in_use_list.iterator();
1264 while (iter.has_next()) {
1265 ObjectMonitor* monitor = iter.next();
1266 function(monitor);
1267 }
1268 }
1269
1270 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1271 // returns true.
1272 template <typename OwnerFilter>
1273 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1274 monitors_iterate([&](ObjectMonitor* monitor) {
1275 // This function is only called at a safepoint or when the
1276 // target thread is suspended or when the target thread is
1277 // operating on itself. The current closures in use today are
1278 // only interested in an owned ObjectMonitor and ownership
1279 // cannot be dropped under the calling contexts so the
1280 // ObjectMonitor cannot be async deflated.
1281 if (monitor->has_owner() && filter(monitor)) {
1282 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1283
1284 closure->do_monitor(monitor);
1285 }
1286 });
1287 }
1288
1289 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1290 // ObjectMonitors where owner is set to a stack-lock address in thread.
1291 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1292 int64_t key = ObjectMonitor::owner_id_from(thread);
1293 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1294 return owned_monitors_iterate_filtered(closure, thread_filter);
1295 }
1296
1297 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
1298 int64_t key = ObjectMonitor::owner_id_from(vthread);
1299 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
1300 return owned_monitors_iterate_filtered(closure, thread_filter);
1301 }
1302
1303 // Iterate ObjectMonitors owned by any thread.
1304 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1305 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
1306 return owned_monitors_iterate_filtered(closure, all_filter);
1307 }
1308
1309 static bool monitors_used_above_threshold(MonitorList* list) {
1310 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1311 return false;
1312 }
1313 size_t monitors_used = list->count();
1314 if (monitors_used == 0) { // empty list is easy
1315 return false;
1316 }
1317 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
1318 // Make sure that we use a ceiling value that is not lower than
1319 // previous, not lower than the recorded max used by the system, and
1320 // not lower than the current number of monitors in use (which can
1321 // race ahead of max). The result is guaranteed > 0.
1322 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
1323
1324 // Check if our monitor usage is above the threshold:
1325 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1326 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1327 // Deflate monitors if over the threshold percentage, unless no
1328 // progress on previous deflations.
1329 bool is_above_threshold = true;
1330
1331 // Check if it's time to adjust the in_use_list_ceiling up, due
1332 // to too many async deflation attempts without any progress.
1333 if (NoAsyncDeflationProgressMax != 0 &&
1334 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1335 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1336 size_t delta = (size_t)(ceiling * remainder) + 1;
1337 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
1338 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
1339 : ceiling + delta;
1340
1341 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1342 log_info(monitorinflation)("Too many deflations without progress; "
1343 "bumping in_use_list_ceiling from %zu"
1344 " to %zu", old_ceiling, new_ceiling);
1345 _no_progress_cnt = 0;
1346 ceiling = new_ceiling;
1347
1348 // Check if our monitor usage is still above the threshold:
1349 monitor_usage = (monitors_used * 100LL) / ceiling;
1350 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
1351 }
1352 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
1353 ", monitor_usage=%zu, threshold=%d",
1354 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1355 return is_above_threshold;
1356 }
1357
1358 return false;
1359 }
1360
1361 size_t ObjectSynchronizer::in_use_list_ceiling() {
1362 return _in_use_list_ceiling;
1363 }
1364
1365 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1366 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1367 }
1368
1369 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1370 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1371 }
1372
1373 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1374 _in_use_list_ceiling = new_value;
1375 }
1376
1377 bool ObjectSynchronizer::is_async_deflation_needed() {
1378 if (is_async_deflation_requested()) {
1379 // Async deflation request.
1380 log_info(monitorinflation)("Async deflation needed: explicit request");
1381 return true;
1382 }
1383
1384 jlong time_since_last = time_since_last_async_deflation_ms();
1385
1386 if (AsyncDeflationInterval > 0 &&
1387 time_since_last > AsyncDeflationInterval &&
1388 monitors_used_above_threshold(&_in_use_list)) {
1389 // It's been longer than our specified deflate interval and there
1390 // are too many monitors in use. We don't deflate more frequently
1391 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1392 // in order to not swamp the MonitorDeflationThread.
1393 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1394 return true;
1395 }
1396
1397 if (GuaranteedAsyncDeflationInterval > 0 &&
1398 time_since_last > GuaranteedAsyncDeflationInterval) {
1399 // It's been longer than our specified guaranteed deflate interval.
1400 // We need to clean up the used monitors even if the threshold is
1401 // not reached, to keep the memory utilization at bay when many threads
1402 // touched many monitors.
1403 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
1404 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1405 GuaranteedAsyncDeflationInterval, time_since_last);
1406
1407 // If this deflation has no progress, then it should not affect the no-progress
1408 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1409 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1410 // the generic code would bump the no-progress counter, and we compensate for that
1411 // by telling it to skip the update.
1412 //
1413 // If this deflation has progress, then it should let non-progress tracking
1414 // know about this, otherwise the threshold heuristics would kick in, potentially
1415 // experience no-progress due to aggressive cleanup by this deflation, and think
1416 // it is still in no-progress stride. In this "progress" case, the generic code would
1417 // zero the counter, and we allow it to happen.
1418 _no_progress_skip_increment = true;
1419
1420 return true;
1421 }
1422
1423 return false;
1424 }
1425
1426 void ObjectSynchronizer::request_deflate_idle_monitors() {
1427 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1428 set_is_async_deflation_requested(true);
1429 ml.notify_all();
1430 }
1431
1432 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1433 JavaThread* current = JavaThread::current();
1434 bool ret_code = false;
1435
1436 jlong last_time = last_async_deflation_time_ns();
1437
1438 request_deflate_idle_monitors();
1439
1440 const int N_CHECKS = 5;
1441 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1442 if (last_async_deflation_time_ns() > last_time) {
1443 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1444 ret_code = true;
1445 break;
1446 }
1447 {
1448 // JavaThread has to honor the blocking protocol.
1449 ThreadBlockInVM tbivm(current);
1450 os::naked_short_sleep(999); // sleep for almost 1 second
1451 }
1452 }
1453 if (!ret_code) {
1454 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1455 }
1456
1457 return ret_code;
1458 }
1459
1460 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1461 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1462 }
1463
1464 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1465 const oop obj,
1466 ObjectSynchronizer::InflateCause cause) {
1467 assert(event != nullptr, "invariant");
1468 event->set_monitorClass(obj->klass());
1469 event->set_address((uintptr_t)(void*)obj);
1470 event->set_cause((u1)cause);
1471 event->commit();
1472 }
1473
1474 // Fast path code shared by multiple functions
1475 void ObjectSynchronizer::inflate_helper(oop obj) {
1476 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1477 markWord mark = obj->mark_acquire();
1478 if (mark.has_monitor()) {
1479 ObjectMonitor* monitor = read_monitor(mark);
1480 markWord dmw = monitor->header();
1481 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1482 return;
1483 }
1484 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1485 }
1486
1487 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1488 assert(current == Thread::current(), "must be");
1489 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1490 return inflate_impl(current->is_Java_thread() ? JavaThread::cast(current) : nullptr, obj, cause);
1491 }
1492
1493 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1494 assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1495 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_for");
1496 return inflate_impl(thread, obj, cause);
1497 }
1498
1499 ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* locking_thread, oop object, const InflateCause cause) {
1500 if (EnableValhalla) {
1501 guarantee(!object->klass()->is_inline_klass(), "Attempt to inflate inline type");
1502 }
1503 // The JavaThread* locking_thread requires that the locking_thread == Thread::current() or
1504 // is suspended throughout the call by some other mechanism.
1505 // The thread might be nullptr when called from a non JavaThread. (As may still be
1506 // the case from FastHashCode). However it is only important for correctness that the
1507 // thread is set when called from ObjectSynchronizer::enter from the owning thread,
1508 // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
1509 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_impl");
1510 EventJavaMonitorInflate event;
1511
1512 for (;;) {
1513 const markWord mark = object->mark_acquire();
1514
1515 // The mark can be in one of the following states:
1516 // * inflated - If the ObjectMonitor owner is anonymous and the
1517 // locking_thread owns the object lock, then we
1518 // make the locking_thread the ObjectMonitor owner.
1519 // * stack-locked - Coerce it to inflated from stack-locked.
1520 // * INFLATING - Busy wait for conversion from stack-locked to
1521 // inflated.
1522 // * unlocked - Aggressively inflate the object.
1523
1524 // CASE: inflated
1525 if (mark.has_monitor()) {
1526 ObjectMonitor* inf = mark.monitor();
1527 markWord dmw = inf->header();
1528 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1529 if (inf->has_anonymous_owner() && locking_thread != nullptr) {
1530 assert(LockingMode == LM_LEGACY, "invariant");
1531 if (locking_thread->is_lock_owned((address)inf->stack_locker())) {
1532 inf->set_stack_locker(nullptr);
1533 inf->set_owner_from_anonymous(locking_thread);
1534 }
1535 }
1536 return inf;
1537 }
1538
1539 // CASE: inflation in progress - inflating over a stack-lock.
1540 // Some other thread is converting from stack-locked to inflated.
1541 // Only that thread can complete inflation -- other threads must wait.
1542 // The INFLATING value is transient.
1543 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1544 // We could always eliminate polling by parking the thread on some auxiliary list.
1545 if (mark == markWord::INFLATING()) {
1546 read_stable_mark(object);
1547 continue;
1548 }
1549
1550 // CASE: stack-locked
1551 // Could be stack-locked either by current or by some other thread.
1552 //
1553 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1554 // to install INFLATING into the mark word. We originally installed INFLATING,
1555 // allocated the ObjectMonitor, and then finally STed the address of the
1556 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1557 // the interval in which INFLATING appeared in the mark, thus increasing
1558 // the odds of inflation contention. If we lose the race to set INFLATING,
1559 // then we just delete the ObjectMonitor and loop around again.
1560 //
1561 LogStreamHandle(Trace, monitorinflation) lsh;
1562 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1563 ObjectMonitor* m = new ObjectMonitor(object);
1564 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1565 // We do this before the CAS in order to minimize the length of time
1566 // in which INFLATING appears in the mark.
1567
1568 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1569 if (cmp != mark) {
1570 delete m;
1571 continue; // Interference -- just retry
1572 }
1573
1574 // We've successfully installed INFLATING (0) into the mark-word.
1575 // This is the only case where 0 will appear in a mark-word.
1576 // Only the singular thread that successfully swings the mark-word
1577 // to 0 can perform (or more precisely, complete) inflation.
1578 //
1579 // Why do we CAS a 0 into the mark-word instead of just CASing the
1580 // mark-word from the stack-locked value directly to the new inflated state?
1581 // Consider what happens when a thread unlocks a stack-locked object.
1582 // It attempts to use CAS to swing the displaced header value from the
1583 // on-stack BasicLock back into the object header. Recall also that the
1584 // header value (hash code, etc) can reside in (a) the object header, or
1585 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1586 // header in an ObjectMonitor. The inflate() routine must copy the header
1587 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1588 // the while preserving the hashCode stability invariants. If the owner
1589 // decides to release the lock while the value is 0, the unlock will fail
1590 // and control will eventually pass from slow_exit() to inflate. The owner
1591 // will then spin, waiting for the 0 value to disappear. Put another way,
1592 // the 0 causes the owner to stall if the owner happens to try to
1593 // drop the lock (restoring the header from the BasicLock to the object)
1594 // while inflation is in-progress. This protocol avoids races that might
1595 // would otherwise permit hashCode values to change or "flicker" for an object.
1596 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1597 // 0 serves as a "BUSY" inflate-in-progress indicator.
1598
1599
1600 // fetch the displaced mark from the owner's stack.
1601 // The owner can't die or unwind past the lock while our INFLATING
1602 // object is in the mark. Furthermore the owner can't complete
1603 // an unlock on the object, either.
1604 markWord dmw = mark.displaced_mark_helper();
1605 // Catch if the object's header is not neutral (not locked and
1606 // not marked is what we care about here).
1607 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1608
1609 // Setup monitor fields to proper values -- prepare the monitor
1610 m->set_header(dmw);
1611
1612 // Note that a thread can inflate an object
1613 // that it has stack-locked -- as might happen in wait() -- directly
1614 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1615 if (locking_thread != nullptr && locking_thread->is_lock_owned((address)mark.locker())) {
1616 m->set_owner(locking_thread);
1617 } else {
1618 // Use ANONYMOUS_OWNER to indicate that the owner is the BasicLock on the stack,
1619 // and set the stack locker field in the monitor.
1620 m->set_stack_locker(mark.locker());
1621 m->set_anonymous_owner();
1622 }
1623 // TODO-FIXME: assert BasicLock->dhw != 0.
1624
1625 // Must preserve store ordering. The monitor state must
1626 // be stable at the time of publishing the monitor address.
1627 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1628 // Release semantics so that above set_object() is seen first.
1629 object->release_set_mark(markWord::encode(m));
1630
1631 // Once ObjectMonitor is configured and the object is associated
1632 // with the ObjectMonitor, it is safe to allow async deflation:
1633 _in_use_list.add(m);
1634
1635 // Hopefully the performance counters are allocated on distinct cache lines
1636 // to avoid false sharing on MP systems ...
1637 OM_PERFDATA_OP(Inflations, inc());
1638 if (log_is_enabled(Trace, monitorinflation)) {
1639 ResourceMark rm;
1640 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1641 INTPTR_FORMAT ", type='%s'", p2i(object),
1642 object->mark().value(), object->klass()->external_name());
1643 }
1644 if (event.should_commit()) {
1645 post_monitor_inflate_event(&event, object, cause);
1646 }
1647 return m;
1648 }
1649
1650 // CASE: unlocked
1651 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1652 // If we know we're inflating for entry it's better to inflate by swinging a
1653 // pre-locked ObjectMonitor pointer into the object header. A successful
1654 // CAS inflates the object *and* confers ownership to the inflating thread.
1655 // In the current implementation we use a 2-step mechanism where we CAS()
1656 // to inflate and then CAS() again to try to swing _owner from null to current.
1657 // An inflateTry() method that we could call from enter() would be useful.
1658
1659 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
1660 ObjectMonitor* m = new ObjectMonitor(object);
1661 // prepare m for installation - set monitor to initial state
1662 m->set_header(mark);
1663
1664 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1665 delete m;
1666 m = nullptr;
1667 continue;
1668 // interference - the markword changed - just retry.
1669 // The state-transitions are one-way, so there's no chance of
1670 // live-lock -- "Inflated" is an absorbing state.
1671 }
1672
1673 // Once the ObjectMonitor is configured and object is associated
1674 // with the ObjectMonitor, it is safe to allow async deflation:
1675 _in_use_list.add(m);
1676
1677 // Hopefully the performance counters are allocated on distinct
1678 // cache lines to avoid false sharing on MP systems ...
1679 OM_PERFDATA_OP(Inflations, inc());
1680 if (log_is_enabled(Trace, monitorinflation)) {
1681 ResourceMark rm;
1682 lsh.print_cr("inflate(unlocked): object=" INTPTR_FORMAT ", mark="
1683 INTPTR_FORMAT ", type='%s'", p2i(object),
1684 object->mark().value(), object->klass()->external_name());
1685 }
1686 if (event.should_commit()) {
1687 post_monitor_inflate_event(&event, object, cause);
1688 }
1689 return m;
1690 }
1691 }
1692
1693 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1694 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1695 //
1696 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1697 MonitorList::Iterator iter = _in_use_list.iterator();
1698 size_t deflated_count = 0;
1699 Thread* current = Thread::current();
1700
1701 while (iter.has_next()) {
1702 if (deflated_count >= (size_t)MonitorDeflationMax) {
1703 break;
1704 }
1705 ObjectMonitor* mid = iter.next();
1706 if (mid->deflate_monitor(current)) {
1707 deflated_count++;
1708 }
1709
1710 // Must check for a safepoint/handshake and honor it.
1711 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1712 }
1713
1714 return deflated_count;
1715 }
1716
1717 class HandshakeForDeflation : public HandshakeClosure {
1718 public:
1719 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1720
1721 void do_thread(Thread* thread) {
1722 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1723 INTPTR_FORMAT, p2i(thread));
1724 if (thread->is_Java_thread()) {
1725 // Clear OM cache
1726 JavaThread* jt = JavaThread::cast(thread);
1727 jt->om_clear_monitor_cache();
1728 }
1729 }
1730 };
1731
1732 class VM_RendezvousGCThreads : public VM_Operation {
1733 public:
1734 bool evaluate_at_safepoint() const override { return false; }
1735 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1736 void doit() override {
1737 Universe::heap()->safepoint_synchronize_begin();
1738 Universe::heap()->safepoint_synchronize_end();
1739 };
1740 };
1741
1742 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1743 ObjectMonitorDeflationSafepointer* safepointer) {
1744 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1745 size_t deleted_count = 0;
1746 for (ObjectMonitor* monitor: *delete_list) {
1747 delete monitor;
1748 deleted_count++;
1749 // A JavaThread must check for a safepoint/handshake and honor it.
1750 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1751 }
1752 return deleted_count;
1753 }
1754
1755 class ObjectMonitorDeflationLogging: public StackObj {
1756 LogStreamHandle(Debug, monitorinflation) _debug;
1757 LogStreamHandle(Info, monitorinflation) _info;
1758 LogStream* _stream;
1759 elapsedTimer _timer;
1760
1761 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1762 size_t count() const { return ObjectSynchronizer::_in_use_list.count(); }
1763 size_t max() const { return ObjectSynchronizer::_in_use_list.max(); }
1764
1765 public:
1766 ObjectMonitorDeflationLogging()
1767 : _debug(), _info(), _stream(nullptr) {
1768 if (_debug.is_enabled()) {
1769 _stream = &_debug;
1770 } else if (_info.is_enabled()) {
1771 _stream = &_info;
1772 }
1773 }
1774
1775 void begin() {
1776 if (_stream != nullptr) {
1777 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1778 ceiling(), count(), max());
1779 _timer.start();
1780 }
1781 }
1782
1783 void before_handshake(size_t unlinked_count) {
1784 if (_stream != nullptr) {
1785 _timer.stop();
1786 _stream->print_cr("before handshaking: unlinked_count=%zu"
1787 ", in_use_list stats: ceiling=%zu, count="
1788 "%zu, max=%zu",
1789 unlinked_count, ceiling(), count(), max());
1790 }
1791 }
1792
1793 void after_handshake() {
1794 if (_stream != nullptr) {
1795 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1796 "%zu, count=%zu, max=%zu",
1797 ceiling(), count(), max());
1798 _timer.start();
1799 }
1800 }
1801
1802 void end(size_t deflated_count, size_t unlinked_count) {
1803 if (_stream != nullptr) {
1804 _timer.stop();
1805 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1806 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1807 deflated_count, unlinked_count, _timer.seconds());
1808 }
1809 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1810 ceiling(), count(), max());
1811 }
1812 }
1813
1814 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1815 if (_stream != nullptr) {
1816 _timer.stop();
1817 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1818 "%zu, count=%zu, max=%zu",
1819 op_name, cnt_name, cnt, ceiling(), count(), max());
1820 }
1821 }
1822
1823 void after_block_for_safepoint(const char* op_name) {
1824 if (_stream != nullptr) {
1825 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1826 ", count=%zu, max=%zu", op_name,
1827 ceiling(), count(), max());
1828 _timer.start();
1829 }
1830 }
1831 };
1832
1833 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1834 if (!SafepointMechanism::should_process(_current)) {
1835 return;
1836 }
1837
1838 // A safepoint/handshake has started.
1839 _log->before_block_for_safepoint(op_name, count_name, counter);
1840
1841 {
1842 // Honor block request.
1843 ThreadBlockInVM tbivm(_current);
1844 }
1845
1846 _log->after_block_for_safepoint(op_name);
1847 }
1848
1849 // This function is called by the MonitorDeflationThread to deflate
1850 // ObjectMonitors.
1851 size_t ObjectSynchronizer::deflate_idle_monitors() {
1852 JavaThread* current = JavaThread::current();
1853 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1854
1855 // The async deflation request has been processed.
1856 _last_async_deflation_time_ns = os::javaTimeNanos();
1857 set_is_async_deflation_requested(false);
1858
1859 ObjectMonitorDeflationLogging log;
1860 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1861
1862 log.begin();
1863
1864 // Deflate some idle ObjectMonitors.
1865 size_t deflated_count = deflate_monitor_list(&safepointer);
1866
1867 // Unlink the deflated ObjectMonitors from the in-use list.
1868 size_t unlinked_count = 0;
1869 size_t deleted_count = 0;
1870 if (deflated_count > 0) {
1871 ResourceMark rm(current);
1872 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1873 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1874
1875 #ifdef ASSERT
1876 if (UseObjectMonitorTable) {
1877 for (ObjectMonitor* monitor : delete_list) {
1878 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1879 }
1880 }
1881 #endif
1882
1883 log.before_handshake(unlinked_count);
1884
1885 // A JavaThread needs to handshake in order to safely free the
1886 // ObjectMonitors that were deflated in this cycle.
1887 HandshakeForDeflation hfd_hc;
1888 Handshake::execute(&hfd_hc);
1889 // Also, we sync and desync GC threads around the handshake, so that they can
1890 // safely read the mark-word and look-through to the object-monitor, without
1891 // being afraid that the object-monitor is going away.
1892 VM_RendezvousGCThreads sync_gc;
1893 VMThread::execute(&sync_gc);
1894
1895 log.after_handshake();
1896
1897 // After the handshake, safely free the ObjectMonitors that were
1898 // deflated and unlinked in this cycle.
1899
1900 // Delete the unlinked ObjectMonitors.
1901 deleted_count = delete_monitors(&delete_list, &safepointer);
1902 assert(unlinked_count == deleted_count, "must be");
1903 }
1904
1905 log.end(deflated_count, unlinked_count);
1906
1907 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1908 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1909
1910 GVars.stw_random = os::random();
1911
1912 if (deflated_count != 0) {
1913 _no_progress_cnt = 0;
1914 } else if (_no_progress_skip_increment) {
1915 _no_progress_skip_increment = false;
1916 } else {
1917 _no_progress_cnt++;
1918 }
1919
1920 return deflated_count;
1921 }
1922
1923 // Monitor cleanup on JavaThread::exit
1924
1925 // Iterate through monitor cache and attempt to release thread's monitors
1926 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1927 private:
1928 JavaThread* _thread;
1929
1930 public:
1931 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1932 void do_monitor(ObjectMonitor* mid) {
1933 intx rec = mid->complete_exit(_thread);
1934 _thread->dec_held_monitor_count(rec + 1);
1935 }
1936 };
1937
1938 // Release all inflated monitors owned by current thread. Lightweight monitors are
1939 // ignored. This is meant to be called during JNI thread detach which assumes
1940 // all remaining monitors are heavyweight. All exceptions are swallowed.
1941 // Scanning the extant monitor list can be time consuming.
1942 // A simple optimization is to add a per-thread flag that indicates a thread
1943 // called jni_monitorenter() during its lifetime.
1944 //
1945 // Instead of NoSafepointVerifier it might be cheaper to
1946 // use an idiom of the form:
1947 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1948 // <code that must not run at safepoint>
1949 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1950 // Since the tests are extremely cheap we could leave them enabled
1951 // for normal product builds.
1952
1953 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1954 assert(current == JavaThread::current(), "must be current Java thread");
1955 NoSafepointVerifier nsv;
1956 ReleaseJavaMonitorsClosure rjmc(current);
1957 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1958 assert(!current->has_pending_exception(), "Should not be possible");
1959 current->clear_pending_exception();
1960 assert(current->held_monitor_count() == 0, "Should not be possible");
1961 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1962 current->clear_jni_monitor_count();
1963 }
1964
1965 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1966 switch (cause) {
1967 case inflate_cause_vm_internal: return "VM Internal";
1968 case inflate_cause_monitor_enter: return "Monitor Enter";
1969 case inflate_cause_wait: return "Monitor Wait";
1970 case inflate_cause_notify: return "Monitor Notify";
1971 case inflate_cause_hash_code: return "Monitor Hash Code";
1972 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1973 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1974 default:
1975 ShouldNotReachHere();
1976 }
1977 return "Unknown";
1978 }
1979
1980 //------------------------------------------------------------------------------
1981 // Debugging code
1982
1983 u_char* ObjectSynchronizer::get_gvars_addr() {
1984 return (u_char*)&GVars;
1985 }
1986
1987 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1988 return (u_char*)&GVars.hc_sequence;
1989 }
1990
1991 size_t ObjectSynchronizer::get_gvars_size() {
1992 return sizeof(SharedGlobals);
1993 }
1994
1995 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1996 return (u_char*)&GVars.stw_random;
1997 }
1998
1999 // Do the final audit and print of ObjectMonitor stats; must be done
2000 // by the VMThread at VM exit time.
2001 void ObjectSynchronizer::do_final_audit_and_print_stats() {
2002 assert(Thread::current()->is_VM_thread(), "sanity check");
2003
2004 if (is_final_audit()) { // Only do the audit once.
2005 return;
2006 }
2007 set_is_final_audit();
2008 log_info(monitorinflation)("Starting the final audit.");
2009
2010 if (log_is_enabled(Info, monitorinflation)) {
2011 LogStreamHandle(Info, monitorinflation) ls;
2012 audit_and_print_stats(&ls, true /* on_exit */);
2013 }
2014 }
2015
2016 // This function can be called by the MonitorDeflationThread or it can be called when
2017 // we are trying to exit the VM. The list walker functions can run in parallel with
2018 // the other list operations.
2019 // Calls to this function can be added in various places as a debugging
2020 // aid.
2021 //
2022 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
2023 int error_cnt = 0;
2024
2025 ls->print_cr("Checking in_use_list:");
2026 chk_in_use_list(ls, &error_cnt);
2027
2028 if (error_cnt == 0) {
2029 ls->print_cr("No errors found in in_use_list checks.");
2030 } else {
2031 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
2032 }
2033
2034 // When exiting, only log the interesting entries at the Info level.
2035 // When called at intervals by the MonitorDeflationThread, log output
2036 // at the Trace level since there can be a lot of it.
2037 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
2038 LogStreamHandle(Trace, monitorinflation) ls_tr;
2039 log_in_use_monitor_details(&ls_tr, true /* log_all */);
2040 } else if (on_exit) {
2041 log_in_use_monitor_details(ls, false /* log_all */);
2042 }
2043
2044 ls->flush();
2045
2046 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2047 }
2048
2049 // Check the in_use_list; log the results of the checks.
2050 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
2051 size_t l_in_use_count = _in_use_list.count();
2052 size_t l_in_use_max = _in_use_list.max();
2053 out->print_cr("count=%zu, max=%zu", l_in_use_count,
2054 l_in_use_max);
2055
2056 size_t ck_in_use_count = 0;
2057 MonitorList::Iterator iter = _in_use_list.iterator();
2058 while (iter.has_next()) {
2059 ObjectMonitor* mid = iter.next();
2060 chk_in_use_entry(mid, out, error_cnt_p);
2061 ck_in_use_count++;
2062 }
2063
2064 if (l_in_use_count == ck_in_use_count) {
2065 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
2066 l_in_use_count, ck_in_use_count);
2067 } else {
2068 out->print_cr("WARNING: in_use_count=%zu is not equal to "
2069 "ck_in_use_count=%zu", l_in_use_count,
2070 ck_in_use_count);
2071 }
2072
2073 size_t ck_in_use_max = _in_use_list.max();
2074 if (l_in_use_max == ck_in_use_max) {
2075 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
2076 l_in_use_max, ck_in_use_max);
2077 } else {
2078 out->print_cr("WARNING: in_use_max=%zu is not equal to "
2079 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
2080 }
2081 }
2082
2083 // Check an in-use monitor entry; log any errors.
2084 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2085 int* error_cnt_p) {
2086 if (n->owner_is_DEFLATER_MARKER()) {
2087 // This could happen when monitor deflation blocks for a safepoint.
2088 return;
2089 }
2090
2091
2092 if (n->metadata() == 0) {
2093 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2094 "have non-null _metadata (header/hash) field.", p2i(n));
2095 *error_cnt_p = *error_cnt_p + 1;
2096 }
2097
2098 const oop obj = n->object_peek();
2099 if (obj == nullptr) {
2100 return;
2101 }
2102
2103 const markWord mark = obj->mark();
2104 if (!mark.has_monitor()) {
2105 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2106 "object does not think it has a monitor: obj="
2107 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2108 p2i(obj), mark.value());
2109 *error_cnt_p = *error_cnt_p + 1;
2110 return;
2111 }
2112
2113 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
2114 if (n != obj_mon) {
2115 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2116 "object does not refer to the same monitor: obj="
2117 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2118 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2119 *error_cnt_p = *error_cnt_p + 1;
2120 }
2121 }
2122
2123 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2124 // flags indicate why the entry is in-use, 'object' and 'object type'
2125 // indicate the associated object and its type.
2126 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2127 if (_in_use_list.count() > 0) {
2128 stringStream ss;
2129 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
2130 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2131 out->print_cr("%18s %s %18s %18s",
2132 "monitor", "BHL", "object", "object type");
2133 out->print_cr("================== === ================== ==================");
2134
2135 auto is_interesting = [&](ObjectMonitor* monitor) {
2136 return log_all || monitor->has_owner() || monitor->is_busy();
2137 };
2138
2139 monitors_iterate([&](ObjectMonitor* monitor) {
2140 if (is_interesting(monitor)) {
2141 const oop obj = monitor->object_peek();
2142 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
2143 ResourceMark rm;
2144 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
2145 monitor->is_busy(), hash != 0, monitor->has_owner(),
2146 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2147 if (monitor->is_busy()) {
2148 out->print(" (%s)", monitor->is_busy_to_string(&ss));
2149 ss.reset();
2150 }
2151 out->cr();
2152 }
2153 });
2154 }
2155
2156 out->flush();
2157 }