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 // These checks are required for wait, notify and exit to avoid inflating the monitor to
310 // find out this inline type object cannot be locked.
311 #define CHECK_THROW_NOSYNC_IMSE(obj) \
312 if (EnableValhalla && (obj)->mark().is_inline_type()) { \
313 JavaThread* THREAD = current; \
314 ResourceMark rm(THREAD); \
315 THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
316 }
317
318 #define CHECK_THROW_NOSYNC_IMSE_0(obj) \
319 if (EnableValhalla && (obj)->mark().is_inline_type()) { \
320 JavaThread* THREAD = current; \
321 ResourceMark rm(THREAD); \
322 THROW_MSG_0(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
323 }
324
325 // =====================> Quick functions
326
327 // The quick_* forms are special fast-path variants used to improve
328 // performance. In the simplest case, a "quick_*" implementation could
329 // simply return false, in which case the caller will perform the necessary
330 // state transitions and call the slow-path form.
331 // The fast-path is designed to handle frequently arising cases in an efficient
332 // manner and is just a degenerate "optimistic" variant of the slow-path.
333 // returns true -- to indicate the call was satisfied.
334 // returns false -- to indicate the call needs the services of the slow-path.
335 // A no-loitering ordinance is in effect for code in the quick_* family
336 // operators: safepoints or indefinite blocking (blocking that might span a
337 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
338 // entry.
339 //
340 // Consider: An interesting optimization is to have the JIT recognize the
341 // following common idiom:
342 // synchronized (someobj) { .... ; notify(); }
343 // That is, we find a notify() or notifyAll() call that immediately precedes
344 // the monitorexit operation. In that case the JIT could fuse the operations
345 // into a single notifyAndExit() runtime primitive.
346
347 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
348 assert(current->thread_state() == _thread_in_Java, "invariant");
349 NoSafepointVerifier nsv;
350 if (obj == nullptr) return false; // slow-path for invalid obj
351 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
352 const markWord mark = obj->mark();
353
354 if (LockingMode == LM_LIGHTWEIGHT) {
355 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
356 // Degenerate notify
357 // fast-locked by caller so by definition the implied waitset is empty.
358 return true;
359 }
360 } else if (LockingMode == LM_LEGACY) {
361 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
362 // Degenerate notify
363 // stack-locked by caller so by definition the implied waitset is empty.
364 return true;
365 }
366 }
367
368 if (mark.has_monitor()) {
369 ObjectMonitor* const mon = mark.monitor();
370 assert(mon->object() == oop(obj), "invariant");
371 if (mon->owner() != current) return false; // slow-path for IMS exception
372
373 if (mon->first_waiter() != nullptr) {
374 // We have one or more waiters. Since this is an inflated monitor
375 // that we own, we can transfer one or more threads from the waitset
376 // to the entrylist here and now, avoiding the slow-path.
377 if (all) {
378 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
379 } else {
380 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
381 }
382 int free_count = 0;
383 do {
384 mon->INotify(current);
385 ++free_count;
386 } while (mon->first_waiter() != nullptr && all);
387 OM_PERFDATA_OP(Notifications, inc(free_count));
388 }
389 return true;
390 }
391
392 // other IMS exception states take the slow-path
393 return false;
394 }
395
396
397 // The LockNode emitted directly at the synchronization site would have
398 // been too big if it were to have included support for the cases of inflated
399 // recursive enter and exit, so they go here instead.
400 // Note that we can't safely call AsyncPrintJavaStack() from within
401 // quick_enter() as our thread state remains _in_Java.
402
403 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
404 BasicLock * lock) {
405 assert(current->thread_state() == _thread_in_Java, "invariant");
406 NoSafepointVerifier nsv;
407 if (obj == nullptr) return false; // Need to throw NPE
408 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
409
410 if (obj->klass()->is_value_based()) {
411 return false;
412 }
413
414 if (LockingMode == LM_LIGHTWEIGHT) {
415 LockStack& lock_stack = current->lock_stack();
416 if (lock_stack.is_full()) {
417 // Always go into runtime if the lock stack is full.
418 return false;
419 }
420 if (lock_stack.try_recursive_enter(obj)) {
421 // Recursive lock successful.
422 current->inc_held_monitor_count();
423 return true;
424 }
425 }
426
427 const markWord mark = obj->mark();
428
429 if (mark.has_monitor()) {
430 ObjectMonitor* const m = mark.monitor();
431 // An async deflation or GC can race us before we manage to make
432 // the ObjectMonitor busy by setting the owner below. If we detect
433 // that race we just bail out to the slow-path here.
434 if (m->object_peek() == nullptr) {
435 return false;
436 }
437 JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
438
439 // Lock contention and Transactional Lock Elision (TLE) diagnostics
440 // and observability
441 // Case: light contention possibly amenable to TLE
442 // Case: TLE inimical operations such as nested/recursive synchronization
443
444 if (owner == current) {
445 m->_recursions++;
446 current->inc_held_monitor_count();
447 return true;
448 }
449
450 if (LockingMode != LM_LIGHTWEIGHT) {
451 // This Java Monitor is inflated so obj's header will never be
452 // displaced to this thread's BasicLock. Make the displaced header
453 // non-null so this BasicLock is not seen as recursive nor as
454 // being locked. We do this unconditionally so that this thread's
455 // BasicLock cannot be mis-interpreted by any stack walkers. For
456 // performance reasons, stack walkers generally first check for
457 // stack-locking in the object's header, the second check is for
458 // recursive stack-locking in the displaced header in the BasicLock,
459 // and last are the inflated Java Monitor (ObjectMonitor) checks.
460 lock->set_displaced_header(markWord::unused_mark());
461 }
462
463 if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) {
464 assert(m->_recursions == 0, "invariant");
465 current->inc_held_monitor_count();
466 return true;
467 }
468 }
469
470 // Note that we could inflate in quick_enter.
471 // This is likely a useful optimization
472 // Critically, in quick_enter() we must not:
473 // -- block indefinitely, or
474 // -- reach a safepoint
475
476 return false; // revert to slow-path
477 }
478
479 // Handle notifications when synchronizing on value based classes
480 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
481 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
482 frame last_frame = locking_thread->last_frame();
483 bool bcp_was_adjusted = false;
484 // Don't decrement bcp if it points to the frame's first instruction. This happens when
485 // handle_sync_on_value_based_class() is called because of a synchronized method. There
486 // is no actual monitorenter instruction in the byte code in this case.
487 if (last_frame.is_interpreted_frame() &&
488 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
489 // adjust bcp to point back to monitorenter so that we print the correct line numbers
490 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
491 bcp_was_adjusted = true;
492 }
493
494 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
495 ResourceMark rm;
496 stringStream ss;
497 locking_thread->print_active_stack_on(&ss);
498 char* base = (char*)strstr(ss.base(), "at");
499 char* newline = (char*)strchr(ss.base(), '\n');
500 if (newline != nullptr) {
501 *newline = '\0';
502 }
503 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
504 } else {
505 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
506 ResourceMark rm;
507 Log(valuebasedclasses) vblog;
508
509 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
510 if (locking_thread->has_last_Java_frame()) {
511 LogStream info_stream(vblog.info());
512 locking_thread->print_active_stack_on(&info_stream);
513 } else {
514 vblog.info("Cannot find the last Java frame");
515 }
516
517 EventSyncOnValueBasedClass event;
518 if (event.should_commit()) {
519 event.set_valueBasedClass(obj->klass());
520 event.commit();
521 }
522 }
523
524 if (bcp_was_adjusted) {
525 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
526 }
527 }
528
529 static bool useHeavyMonitors() {
530 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
531 return LockingMode == LM_MONITOR;
532 #else
533 return false;
534 #endif
535 }
536
537 // -----------------------------------------------------------------------------
538 // Monitor Enter/Exit
539
540 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
541 // When called with locking_thread != Thread::current() some mechanism must synchronize
542 // the locking_thread with respect to the current thread. Currently only used when
543 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
544 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
545 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "JITed code should never have locked an instance of a value class");
546 if (!enter_fast_impl(obj, lock, locking_thread)) {
547 // Inflated ObjectMonitor::enter_for is required
548
549 // An async deflation can race after the inflate_for() call and before
550 // enter_for() can make the ObjectMonitor busy. enter_for() returns false
551 // if we have lost the race to async deflation and we simply try again.
552 while (true) {
553 ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
554 if (monitor->enter_for(locking_thread)) {
555 return;
556 }
557 assert(monitor->is_being_async_deflated(), "must be");
558 }
559 }
560 }
561
562 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
563 assert(current == Thread::current(), "must be");
564 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "This method should never be called on an instance of an inline class");
565 if (!enter_fast_impl(obj, lock, current)) {
566 // Inflated ObjectMonitor::enter is required
567
568 // An async deflation can race after the inflate() call and before
569 // enter() can make the ObjectMonitor busy. enter() returns false if
570 // we have lost the race to async deflation and we simply try again.
571 while (true) {
572 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
573 if (monitor->enter(current)) {
574 return;
575 }
576 }
577 }
578 }
579
580 // The interpreter and compiler assembly code tries to lock using the fast path
581 // of this algorithm. Make sure to update that code if the following function is
582 // changed. The implementation is extremely sensitive to race condition. Be careful.
583 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
584 guarantee(!EnableValhalla || !obj->klass()->is_inline_klass(), "Attempt to inflate inline type");
585 if (obj->klass()->is_value_based()) {
586 handle_sync_on_value_based_class(obj, locking_thread);
587 }
588
589 locking_thread->inc_held_monitor_count();
590
591 if (!useHeavyMonitors()) {
592 if (LockingMode == LM_LIGHTWEIGHT) {
593 // Fast-locking does not use the 'lock' argument.
594 LockStack& lock_stack = locking_thread->lock_stack();
595 if (lock_stack.is_full()) {
596 // We unconditionally make room on the lock stack by inflating
597 // the least recently locked object on the lock stack.
598
599 // About the choice to inflate least recently locked object.
600 // First we must chose to inflate a lock, either some lock on
601 // the lock-stack or the lock that is currently being entered
602 // (which may or may not be on the lock-stack).
603 // Second the best lock to inflate is a lock which is entered
604 // in a control flow where there are only a very few locks being
605 // used, as the costly part of inflated locking is inflation,
606 // not locking. But this property is entirely program dependent.
607 // Third inflating the lock currently being entered on when it
608 // is not present on the lock-stack will result in a still full
609 // lock-stack. This creates a scenario where every deeper nested
610 // monitorenter must call into the runtime.
611 // The rational here is as follows:
612 // Because we cannot (currently) figure out the second, and want
613 // to avoid the third, we inflate a lock on the lock-stack.
614 // The least recently locked lock is chosen as it is the lock
615 // with the longest critical section.
616
617 log_info(monitorinflation)("LockStack capacity exceeded, inflating.");
618 ObjectMonitor* monitor = inflate_for(locking_thread, lock_stack.bottom(), inflate_cause_vm_internal);
619 assert(monitor->owner() == Thread::current(), "must be owner=" PTR_FORMAT " current=" PTR_FORMAT " mark=" PTR_FORMAT,
620 p2i(monitor->owner()), p2i(Thread::current()), monitor->object()->mark_acquire().value());
621 assert(!lock_stack.is_full(), "must have made room here");
622 }
623
624 markWord mark = obj()->mark_acquire();
625 while (mark.is_neutral()) {
626 // Retry until a lock state change has been observed. cas_set_mark() may collide with non lock bits modifications.
627 // Try to swing into 'fast-locked' state.
628 assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
629 const markWord locked_mark = mark.set_fast_locked();
630 const markWord old_mark = obj()->cas_set_mark(locked_mark, mark);
631 if (old_mark == mark) {
632 // Successfully fast-locked, push object to lock-stack and return.
633 lock_stack.push(obj());
634 return true;
635 }
636 mark = old_mark;
637 }
638
639 if (mark.is_fast_locked() && lock_stack.try_recursive_enter(obj())) {
640 // Recursive lock successful.
641 return true;
642 }
643
644 // Failed to fast lock.
645 return false;
646 } else if (LockingMode == LM_LEGACY) {
647 markWord mark = obj->mark();
648 if (mark.is_neutral()) {
649 // Anticipate successful CAS -- the ST of the displaced mark must
650 // be visible <= the ST performed by the CAS.
651 lock->set_displaced_header(mark);
652 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
653 return true;
654 }
655 } else if (mark.has_locker() &&
656 locking_thread->is_lock_owned((address) mark.locker())) {
657 assert(lock != mark.locker(), "must not re-lock the same lock");
658 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
659 lock->set_displaced_header(markWord::from_pointer(nullptr));
660 return true;
661 }
662
663 // The object header will never be displaced to this lock,
664 // so it does not matter what the value is, except that it
665 // must be non-zero to avoid looking like a re-entrant lock,
666 // and must not look locked either.
667 lock->set_displaced_header(markWord::unused_mark());
668
669 // Failed to fast lock.
670 return false;
671 }
672 } else if (VerifyHeavyMonitors) {
673 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
674 }
675
676 return false;
677 }
678
679 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
680 current->dec_held_monitor_count();
681
682 if (!useHeavyMonitors()) {
683 markWord mark = object->mark();
684 if (EnableValhalla && mark.is_inline_type()) {
685 return;
686 }
687 if (LockingMode == LM_LIGHTWEIGHT) {
688 // Fast-locking does not use the 'lock' argument.
689 LockStack& lock_stack = current->lock_stack();
690 if (mark.is_fast_locked() && lock_stack.try_recursive_exit(object)) {
691 // Recursively unlocked.
692 return;
693 }
694
695 if (mark.is_fast_locked() && lock_stack.is_recursive(object)) {
696 // This lock is recursive but is not at the top of the lock stack so we're
697 // doing an unbalanced exit. We have to fall thru to inflation below and
698 // let ObjectMonitor::exit() do the unlock.
699 } else {
700 while (mark.is_fast_locked()) {
701 // Retry until a lock state change has been observed. cas_set_mark() may collide with non lock bits modifications.
702 const markWord unlocked_mark = mark.set_unlocked();
703 const markWord old_mark = object->cas_set_mark(unlocked_mark, mark);
704 if (old_mark == mark) {
705 size_t recursions = lock_stack.remove(object) - 1;
706 assert(recursions == 0, "must not be recursive here");
707 return;
708 }
709 mark = old_mark;
710 }
711 }
712 } else if (LockingMode == LM_LEGACY) {
713 markWord dhw = lock->displaced_header();
714 if (dhw.value() == 0) {
715 // If the displaced header is null, then this exit matches up with
716 // a recursive enter. No real work to do here except for diagnostics.
717 #ifndef PRODUCT
718 if (mark != markWord::INFLATING()) {
719 // Only do diagnostics if we are not racing an inflation. Simply
720 // exiting a recursive enter of a Java Monitor that is being
721 // inflated is safe; see the has_monitor() comment below.
722 assert(!mark.is_neutral(), "invariant");
723 assert(!mark.has_locker() ||
724 current->is_lock_owned((address)mark.locker()), "invariant");
725 if (mark.has_monitor()) {
726 // The BasicLock's displaced_header is marked as a recursive
727 // enter and we have an inflated Java Monitor (ObjectMonitor).
728 // This is a special case where the Java Monitor was inflated
729 // after this thread entered the stack-lock recursively. When a
730 // Java Monitor is inflated, we cannot safely walk the Java
731 // Monitor owner's stack and update the BasicLocks because a
732 // Java Monitor can be asynchronously inflated by a thread that
733 // does not own the Java Monitor.
734 ObjectMonitor* m = mark.monitor();
735 assert(m->object()->mark() == mark, "invariant");
736 assert(m->is_entered(current), "invariant");
737 }
738 }
739 #endif
740 return;
741 }
742
743 if (mark == markWord::from_pointer(lock)) {
744 // If the object is stack-locked by the current thread, try to
745 // swing the displaced header from the BasicLock back to the mark.
746 assert(dhw.is_neutral(), "invariant");
747 if (object->cas_set_mark(dhw, mark) == mark) {
748 return;
749 }
750 }
751 }
752 } else if (VerifyHeavyMonitors) {
753 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
754 }
755
756 // We have to take the slow-path of possible inflation and then exit.
757 // The ObjectMonitor* can't be async deflated until ownership is
758 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
759 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
760 assert(!monitor->is_owner_anonymous(), "must not be");
761 monitor->exit(current);
762 }
763
764 // -----------------------------------------------------------------------------
765 // JNI locks on java objects
766 // NOTE: must use heavy weight monitor to handle jni monitor enter
767 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
768 JavaThread* THREAD = current;
769 if (obj->klass()->is_value_based()) {
770 handle_sync_on_value_based_class(obj, current);
771 }
772
773 if (EnableValhalla && obj->klass()->is_inline_klass()) {
774 ResourceMark rm(THREAD);
775 const char* desc = "Cannot synchronize on an instance of value class ";
776 const char* className = obj->klass()->external_name();
777 size_t msglen = strlen(desc) + strlen(className) + 1;
778 char* message = NEW_RESOURCE_ARRAY(char, msglen);
779 assert(message != nullptr, "NEW_RESOURCE_ARRAY should have called vm_exit_out_of_memory and not return nullptr");
780 THROW_MSG(vmSymbols::java_lang_IdentityException(), className);
781 }
782
783 // the current locking is from JNI instead of Java code
784 current->set_current_pending_monitor_is_from_java(false);
785 // An async deflation can race after the inflate() call and before
786 // enter() can make the ObjectMonitor busy. enter() returns false if
787 // we have lost the race to async deflation and we simply try again.
788 while (true) {
789 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
790 if (monitor->enter(current)) {
791 current->inc_held_monitor_count(1, true);
792 break;
793 }
794 }
795 current->set_current_pending_monitor_is_from_java(true);
796 }
797
798 // NOTE: must use heavy weight monitor to handle jni monitor exit
799 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
800 JavaThread* current = THREAD;
801 CHECK_THROW_NOSYNC_IMSE(obj);
802
803 // The ObjectMonitor* can't be async deflated until ownership is
804 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
805 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
806 // If this thread has locked the object, exit the monitor. We
807 // intentionally do not use CHECK on check_owner because we must exit the
808 // monitor even if an exception was already pending.
809 if (monitor->check_owner(THREAD)) {
810 monitor->exit(current);
811 current->dec_held_monitor_count(1, true);
812 }
813 }
814
815 // -----------------------------------------------------------------------------
816 // Internal VM locks on java objects
817 // standard constructor, allows locking failures
818 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
819 _thread = thread;
820 _thread->check_for_valid_safepoint_state();
821 _obj = obj;
822
823 if (_obj() != nullptr) {
824 ObjectSynchronizer::enter(_obj, &_lock, _thread);
825 }
826 }
827
828 ObjectLocker::~ObjectLocker() {
829 if (_obj() != nullptr) {
830 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
831 }
832 }
833
834
835 // -----------------------------------------------------------------------------
836 // Wait/Notify/NotifyAll
837 // NOTE: must use heavy weight monitor to handle wait()
838 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
839 JavaThread* current = THREAD;
840 CHECK_THROW_NOSYNC_IMSE_0(obj);
841 if (millis < 0) {
842 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
843 }
844 // The ObjectMonitor* can't be async deflated because the _waiters
845 // field is incremented before ownership is dropped and decremented
846 // after ownership is regained.
847 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
848
849 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
850 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
851
852 // This dummy call is in place to get around dtrace bug 6254741. Once
853 // that's fixed we can uncomment the following line, remove the call
854 // and change this function back into a "void" func.
855 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
856 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
857 return ret_code;
858 }
859
860 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
861 JavaThread* current = THREAD;
862 CHECK_THROW_NOSYNC_IMSE(obj);
863
864 markWord mark = obj->mark();
865 if (LockingMode == LM_LIGHTWEIGHT) {
866 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
867 // Not inflated so there can't be any waiters to notify.
868 return;
869 }
870 } else if (LockingMode == LM_LEGACY) {
871 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
872 // Not inflated so there can't be any waiters to notify.
873 return;
874 }
875 }
876 // The ObjectMonitor* can't be async deflated until ownership is
877 // dropped by the calling thread.
878 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
879 monitor->notify(CHECK);
880 }
881
882 // NOTE: see comment of notify()
883 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
884 JavaThread* current = THREAD;
885 CHECK_THROW_NOSYNC_IMSE(obj);
886
887 markWord mark = obj->mark();
888 if (LockingMode == LM_LIGHTWEIGHT) {
889 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
890 // Not inflated so there can't be any waiters to notify.
891 return;
892 }
893 } else if (LockingMode == LM_LEGACY) {
894 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
895 // Not inflated so there can't be any waiters to notify.
896 return;
897 }
898 }
899 // The ObjectMonitor* can't be async deflated until ownership is
900 // dropped by the calling thread.
901 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
902 monitor->notifyAll(CHECK);
903 }
904
905 // -----------------------------------------------------------------------------
906 // Hash Code handling
907
908 struct SharedGlobals {
909 char _pad_prefix[OM_CACHE_LINE_SIZE];
910 // This is a highly shared mostly-read variable.
911 // To avoid false-sharing it needs to be the sole occupant of a cache line.
912 volatile int stw_random;
913 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
914 // Hot RW variable -- Sequester to avoid false-sharing
915 volatile int hc_sequence;
916 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
917 };
918
919 static SharedGlobals GVars;
920
921 static markWord read_stable_mark(oop obj) {
922 markWord mark = obj->mark_acquire();
923 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
924 // New lightweight locking does not use the markWord::INFLATING() protocol.
925 return mark; // normal fast-path return
926 }
927
928 int its = 0;
929 for (;;) {
930 markWord mark = obj->mark_acquire();
931 if (!mark.is_being_inflated()) {
932 return mark; // normal fast-path return
933 }
934
935 // The object is being inflated by some other thread.
936 // The caller of read_stable_mark() must wait for inflation to complete.
937 // Avoid live-lock.
938
939 ++its;
940 if (its > 10000 || !os::is_MP()) {
941 if (its & 1) {
942 os::naked_yield();
943 } else {
944 // Note that the following code attenuates the livelock problem but is not
945 // a complete remedy. A more complete solution would require that the inflating
946 // thread hold the associated inflation lock. The following code simply restricts
947 // the number of spinners to at most one. We'll have N-2 threads blocked
948 // on the inflationlock, 1 thread holding the inflation lock and using
949 // a yield/park strategy, and 1 thread in the midst of inflation.
950 // A more refined approach would be to change the encoding of INFLATING
951 // to allow encapsulation of a native thread pointer. Threads waiting for
952 // inflation to complete would use CAS to push themselves onto a singly linked
953 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
954 // and calling park(). When inflation was complete the thread that accomplished inflation
955 // would detach the list and set the markword to inflated with a single CAS and
956 // then for each thread on the list, set the flag and unpark() the thread.
957
958 // Index into the lock array based on the current object address.
959 static_assert(is_power_of_2(inflation_lock_count()), "must be");
960 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
961 int YieldThenBlock = 0;
962 assert(ix < inflation_lock_count(), "invariant");
963 inflation_lock(ix)->lock();
964 while (obj->mark_acquire() == markWord::INFLATING()) {
965 // Beware: naked_yield() is advisory and has almost no effect on some platforms
966 // so we periodically call current->_ParkEvent->park(1).
967 // We use a mixed spin/yield/block mechanism.
968 if ((YieldThenBlock++) >= 16) {
969 Thread::current()->_ParkEvent->park(1);
970 } else {
971 os::naked_yield();
972 }
973 }
974 inflation_lock(ix)->unlock();
975 }
976 } else {
977 SpinPause(); // SMP-polite spinning
978 }
979 }
980 }
981
982 // hashCode() generation :
983 //
984 // Possibilities:
985 // * MD5Digest of {obj,stw_random}
986 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
987 // * A DES- or AES-style SBox[] mechanism
988 // * One of the Phi-based schemes, such as:
989 // 2654435761 = 2^32 * Phi (golden ratio)
990 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
991 // * A variation of Marsaglia's shift-xor RNG scheme.
992 // * (obj ^ stw_random) is appealing, but can result
993 // in undesirable regularity in the hashCode values of adjacent objects
994 // (objects allocated back-to-back, in particular). This could potentially
995 // result in hashtable collisions and reduced hashtable efficiency.
996 // There are simple ways to "diffuse" the middle address bits over the
997 // generated hashCode values:
998
999 static inline intptr_t get_next_hash(Thread* current, oop obj) {
1000 intptr_t value = 0;
1001 if (hashCode == 0) {
1002 // This form uses global Park-Miller RNG.
1003 // On MP system we'll have lots of RW access to a global, so the
1004 // mechanism induces lots of coherency traffic.
1005 value = os::random();
1006 } else if (hashCode == 1) {
1007 // This variation has the property of being stable (idempotent)
1008 // between STW operations. This can be useful in some of the 1-0
1009 // synchronization schemes.
1010 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
1011 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
1012 } else if (hashCode == 2) {
1013 value = 1; // for sensitivity testing
1014 } else if (hashCode == 3) {
1015 value = ++GVars.hc_sequence;
1016 } else if (hashCode == 4) {
1017 value = cast_from_oop<intptr_t>(obj);
1018 } else {
1019 // Marsaglia's xor-shift scheme with thread-specific state
1020 // This is probably the best overall implementation -- we'll
1021 // likely make this the default in future releases.
1022 unsigned t = current->_hashStateX;
1023 t ^= (t << 11);
1024 current->_hashStateX = current->_hashStateY;
1025 current->_hashStateY = current->_hashStateZ;
1026 current->_hashStateZ = current->_hashStateW;
1027 unsigned v = current->_hashStateW;
1028 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
1029 current->_hashStateW = v;
1030 value = v;
1031 }
1032
1033 value &= markWord::hash_mask;
1034 if (value == 0) value = 0xBAD;
1035 assert(value != markWord::no_hash, "invariant");
1036 return value;
1037 }
1038
1039 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
1040 if (EnableValhalla && obj->klass()->is_inline_klass()) {
1041 // VM should be calling bootstrap method
1042 ShouldNotReachHere();
1043 }
1044
1045 while (true) {
1046 ObjectMonitor* monitor = nullptr;
1047 markWord temp, test;
1048 intptr_t hash;
1049 markWord mark = read_stable_mark(obj);
1050 if (VerifyHeavyMonitors) {
1051 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
1052 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1053 }
1054 if (mark.is_neutral() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1055 hash = mark.hash();
1056 if (hash != 0) { // if it has a hash, just return it
1057 return hash;
1058 }
1059 hash = get_next_hash(current, obj); // get a new hash
1060 temp = mark.copy_set_hash(hash); // merge the hash into header
1061 // try to install the hash
1062 test = obj->cas_set_mark(temp, mark);
1063 if (test == mark) { // if the hash was installed, return it
1064 return hash;
1065 }
1066 if (LockingMode == LM_LIGHTWEIGHT) {
1067 // CAS failed, retry
1068 continue;
1069 }
1070 // Failed to install the hash. It could be that another thread
1071 // installed the hash just before our attempt or inflation has
1072 // occurred or... so we fall thru to inflate the monitor for
1073 // stability and then install the hash.
1074 } else if (mark.has_monitor()) {
1075 monitor = mark.monitor();
1076 temp = monitor->header();
1077 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1078 hash = temp.hash();
1079 if (hash != 0) {
1080 // It has a hash.
1081
1082 // Separate load of dmw/header above from the loads in
1083 // is_being_async_deflated().
1084
1085 // dmw/header and _contentions may get written by different threads.
1086 // Make sure to observe them in the same order when having several observers.
1087 OrderAccess::loadload_for_IRIW();
1088
1089 if (monitor->is_being_async_deflated()) {
1090 // But we can't safely use the hash if we detect that async
1091 // deflation has occurred. So we attempt to restore the
1092 // header/dmw to the object's header so that we only retry
1093 // once if the deflater thread happens to be slow.
1094 monitor->install_displaced_markword_in_object(obj);
1095 continue;
1096 }
1097 return hash;
1098 }
1099 // Fall thru so we only have one place that installs the hash in
1100 // the ObjectMonitor.
1101 } else if (LockingMode == LM_LEGACY && mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
1102 // This is a stack-lock owned by the calling thread so fetch the
1103 // displaced markWord from the BasicLock on the stack.
1104 temp = mark.displaced_mark_helper();
1105 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1106 hash = temp.hash();
1107 if (hash != 0) { // if it has a hash, just return it
1108 return hash;
1109 }
1110 // WARNING:
1111 // The displaced header in the BasicLock on a thread's stack
1112 // is strictly immutable. It CANNOT be changed in ANY cases.
1113 // So we have to inflate the stack-lock into an ObjectMonitor
1114 // even if the current thread owns the lock. The BasicLock on
1115 // a thread's stack can be asynchronously read by other threads
1116 // during an inflate() call so any change to that stack memory
1117 // may not propagate to other threads correctly.
1118 }
1119
1120 // Inflate the monitor to set the hash.
1121
1122 // An async deflation can race after the inflate() call and before we
1123 // can update the ObjectMonitor's header with the hash value below.
1124 monitor = inflate(current, obj, inflate_cause_hash_code);
1125 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1126 mark = monitor->header();
1127 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1128 hash = mark.hash();
1129 if (hash == 0) { // if it does not have a hash
1130 hash = get_next_hash(current, obj); // get a new hash
1131 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1132 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1133 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1134 test = markWord(v);
1135 if (test != mark) {
1136 // The attempt to update the ObjectMonitor's header/dmw field
1137 // did not work. This can happen if another thread managed to
1138 // merge in the hash just before our cmpxchg().
1139 // If we add any new usages of the header/dmw field, this code
1140 // will need to be updated.
1141 hash = test.hash();
1142 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1143 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1144 }
1145 if (monitor->is_being_async_deflated()) {
1146 // If we detect that async deflation has occurred, then we
1147 // attempt to restore the header/dmw to the object's header
1148 // so that we only retry once if the deflater thread happens
1149 // to be slow.
1150 monitor->install_displaced_markword_in_object(obj);
1151 continue;
1152 }
1153 }
1154 // We finally get the hash.
1155 return hash;
1156 }
1157 }
1158
1159 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1160 Handle h_obj) {
1161 if (EnableValhalla && h_obj->mark().is_inline_type()) {
1162 return false;
1163 }
1164 assert(current == JavaThread::current(), "Can only be called on current thread");
1165 oop obj = h_obj();
1166
1167 markWord mark = read_stable_mark(obj);
1168
1169 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1170 // stack-locked case, header points into owner's stack
1171 return current->is_lock_owned((address)mark.locker());
1172 }
1173
1174 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1175 // fast-locking case, see if lock is in current's lock stack
1176 return current->lock_stack().contains(h_obj());
1177 }
1178
1179 if (mark.has_monitor()) {
1180 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1181 // The first stage of async deflation does not affect any field
1182 // used by this comparison so the ObjectMonitor* is usable here.
1183 ObjectMonitor* monitor = mark.monitor();
1184 return monitor->is_entered(current) != 0;
1185 }
1186 // Unlocked case, header in place
1187 assert(mark.is_neutral(), "sanity check");
1188 return false;
1189 }
1190
1191 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1192 oop obj = h_obj();
1193 markWord mark = read_stable_mark(obj);
1194
1195 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1196 // stack-locked so header points into owner's stack.
1197 // owning_thread_from_monitor_owner() may also return null here:
1198 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1199 }
1200
1201 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1202 // fast-locked so get owner from the object.
1203 // owning_thread_from_object() may also return null here:
1204 return Threads::owning_thread_from_object(t_list, h_obj());
1205 }
1206
1207 if (mark.has_monitor()) {
1208 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1209 // The first stage of async deflation does not affect any field
1210 // used by this comparison so the ObjectMonitor* is usable here.
1211 ObjectMonitor* monitor = mark.monitor();
1212 assert(monitor != nullptr, "monitor should be non-null");
1213 // owning_thread_from_monitor() may also return null here:
1214 return Threads::owning_thread_from_monitor(t_list, monitor);
1215 }
1216
1217 // Unlocked case, header in place
1218 // Cannot have assertion since this object may have been
1219 // locked by another thread when reaching here.
1220 // assert(mark.is_neutral(), "sanity check");
1221
1222 return nullptr;
1223 }
1224
1225 // Visitors ...
1226
1227 // Iterate over all ObjectMonitors.
1228 template <typename Function>
1229 void ObjectSynchronizer::monitors_iterate(Function function) {
1230 MonitorList::Iterator iter = _in_use_list.iterator();
1231 while (iter.has_next()) {
1232 ObjectMonitor* monitor = iter.next();
1233 function(monitor);
1234 }
1235 }
1236
1237 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1238 // returns true.
1239 template <typename OwnerFilter>
1240 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1241 monitors_iterate([&](ObjectMonitor* monitor) {
1242 // This function is only called at a safepoint or when the
1243 // target thread is suspended or when the target thread is
1244 // operating on itself. The current closures in use today are
1245 // only interested in an owned ObjectMonitor and ownership
1246 // cannot be dropped under the calling contexts so the
1247 // ObjectMonitor cannot be async deflated.
1248 if (monitor->has_owner() && filter(monitor->owner_raw())) {
1249 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1250
1251 closure->do_monitor(monitor);
1252 }
1253 });
1254 }
1255
1256 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1257 // ObjectMonitors where owner is set to a stack-lock address in thread.
1258 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1259 auto thread_filter = [&](void* owner) { return owner == thread; };
1260 return owned_monitors_iterate_filtered(closure, thread_filter);
1261 }
1262
1263 // Iterate ObjectMonitors owned by any thread.
1264 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1265 auto all_filter = [&](void* owner) { return true; };
1266 return owned_monitors_iterate_filtered(closure, all_filter);
1267 }
1268
1269 static bool monitors_used_above_threshold(MonitorList* list) {
1270 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1271 return false;
1272 }
1273 // Start with ceiling based on a per-thread estimate:
1274 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1275 size_t old_ceiling = ceiling;
1276 if (ceiling < list->max()) {
1277 // The max used by the system has exceeded the ceiling so use that:
1278 ceiling = list->max();
1279 }
1280 size_t monitors_used = list->count();
1281 if (monitors_used == 0) { // empty list is easy
1282 return false;
1283 }
1284 if (NoAsyncDeflationProgressMax != 0 &&
1285 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1286 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1287 size_t new_ceiling = ceiling + (size_t)((double)ceiling * remainder) + 1;
1288 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1289 log_info(monitorinflation)("Too many deflations without progress; "
1290 "bumping in_use_list_ceiling from " SIZE_FORMAT
1291 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1292 _no_progress_cnt = 0;
1293 ceiling = new_ceiling;
1294 }
1295
1296 // Check if our monitor usage is above the threshold:
1297 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1298 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1299 log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
1300 ", monitor_usage=" SIZE_FORMAT ", threshold=%d",
1301 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1302 return true;
1303 }
1304
1305 return false;
1306 }
1307
1308 size_t ObjectSynchronizer::in_use_list_ceiling() {
1309 return _in_use_list_ceiling;
1310 }
1311
1312 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1313 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1314 }
1315
1316 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1317 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1318 }
1319
1320 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1321 _in_use_list_ceiling = new_value;
1322 }
1323
1324 bool ObjectSynchronizer::is_async_deflation_needed() {
1325 if (is_async_deflation_requested()) {
1326 // Async deflation request.
1327 log_info(monitorinflation)("Async deflation needed: explicit request");
1328 return true;
1329 }
1330
1331 jlong time_since_last = time_since_last_async_deflation_ms();
1332
1333 if (AsyncDeflationInterval > 0 &&
1334 time_since_last > AsyncDeflationInterval &&
1335 monitors_used_above_threshold(&_in_use_list)) {
1336 // It's been longer than our specified deflate interval and there
1337 // are too many monitors in use. We don't deflate more frequently
1338 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1339 // in order to not swamp the MonitorDeflationThread.
1340 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1341 return true;
1342 }
1343
1344 if (GuaranteedAsyncDeflationInterval > 0 &&
1345 time_since_last > GuaranteedAsyncDeflationInterval) {
1346 // It's been longer than our specified guaranteed deflate interval.
1347 // We need to clean up the used monitors even if the threshold is
1348 // not reached, to keep the memory utilization at bay when many threads
1349 // touched many monitors.
1350 log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) "
1351 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1352 GuaranteedAsyncDeflationInterval, time_since_last);
1353
1354 // If this deflation has no progress, then it should not affect the no-progress
1355 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1356 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1357 // the generic code would bump the no-progress counter, and we compensate for that
1358 // by telling it to skip the update.
1359 //
1360 // If this deflation has progress, then it should let non-progress tracking
1361 // know about this, otherwise the threshold heuristics would kick in, potentially
1362 // experience no-progress due to aggressive cleanup by this deflation, and think
1363 // it is still in no-progress stride. In this "progress" case, the generic code would
1364 // zero the counter, and we allow it to happen.
1365 _no_progress_skip_increment = true;
1366
1367 return true;
1368 }
1369
1370 return false;
1371 }
1372
1373 void ObjectSynchronizer::request_deflate_idle_monitors() {
1374 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1375 set_is_async_deflation_requested(true);
1376 ml.notify_all();
1377 }
1378
1379 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1380 JavaThread* current = JavaThread::current();
1381 bool ret_code = false;
1382
1383 jlong last_time = last_async_deflation_time_ns();
1384
1385 request_deflate_idle_monitors();
1386
1387 const int N_CHECKS = 5;
1388 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1389 if (last_async_deflation_time_ns() > last_time) {
1390 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1391 ret_code = true;
1392 break;
1393 }
1394 {
1395 // JavaThread has to honor the blocking protocol.
1396 ThreadBlockInVM tbivm(current);
1397 os::naked_short_sleep(999); // sleep for almost 1 second
1398 }
1399 }
1400 if (!ret_code) {
1401 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1402 }
1403
1404 return ret_code;
1405 }
1406
1407 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1408 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1409 }
1410
1411 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1412 const oop obj,
1413 ObjectSynchronizer::InflateCause cause) {
1414 assert(event != nullptr, "invariant");
1415 event->set_monitorClass(obj->klass());
1416 event->set_address((uintptr_t)(void*)obj);
1417 event->set_cause((u1)cause);
1418 event->commit();
1419 }
1420
1421 // Fast path code shared by multiple functions
1422 void ObjectSynchronizer::inflate_helper(oop obj) {
1423 markWord mark = obj->mark_acquire();
1424 if (mark.has_monitor()) {
1425 ObjectMonitor* monitor = mark.monitor();
1426 markWord dmw = monitor->header();
1427 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1428 return;
1429 }
1430 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1431 }
1432
1433 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1434 assert(current == Thread::current(), "must be");
1435 if (LockingMode == LM_LIGHTWEIGHT && current->is_Java_thread()) {
1436 return inflate_impl(JavaThread::cast(current), obj, cause);
1437 }
1438 return inflate_impl(nullptr, obj, cause);
1439 }
1440
1441 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1442 assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1443 return inflate_impl(thread, obj, cause);
1444 }
1445
1446 ObjectMonitor* ObjectSynchronizer::inflate_impl(JavaThread* inflating_thread, oop object, const InflateCause cause) {
1447 if (EnableValhalla) {
1448 guarantee(!object->klass()->is_inline_klass(), "Attempt to inflate inline type");
1449 }
1450 // The JavaThread* inflating_thread parameter is only used by LM_LIGHTWEIGHT and requires
1451 // that the inflating_thread == Thread::current() or is suspended throughout the call by
1452 // some other mechanism.
1453 // Even with LM_LIGHTWEIGHT the thread might be nullptr when called from a non
1454 // JavaThread. (As may still be the case from FastHashCode). However it is only
1455 // important for the correctness of the LM_LIGHTWEIGHT algorithm that the thread
1456 // is set when called from ObjectSynchronizer::enter from the owning thread,
1457 // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
1458 EventJavaMonitorInflate event;
1459
1460 for (;;) {
1461 const markWord mark = object->mark_acquire();
1462
1463 // The mark can be in one of the following states:
1464 // * inflated - Just return if using stack-locking.
1465 // If using fast-locking and the ObjectMonitor owner
1466 // is anonymous and the inflating_thread owns the
1467 // object lock, then we make the inflating_thread
1468 // the ObjectMonitor owner and remove the lock from
1469 // the inflating_thread's lock stack.
1470 // * fast-locked - Coerce it to inflated from fast-locked.
1471 // * stack-locked - Coerce it to inflated from stack-locked.
1472 // * INFLATING - Busy wait for conversion from stack-locked to
1473 // inflated.
1474 // * neutral - Aggressively inflate the object.
1475
1476 // CASE: inflated
1477 if (mark.has_monitor()) {
1478 ObjectMonitor* inf = mark.monitor();
1479 markWord dmw = inf->header();
1480 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1481 if (LockingMode == LM_LIGHTWEIGHT && inf->is_owner_anonymous() &&
1482 inflating_thread != nullptr && inflating_thread->lock_stack().contains(object)) {
1483 inf->set_owner_from_anonymous(inflating_thread);
1484 size_t removed = inflating_thread->lock_stack().remove(object);
1485 inf->set_recursions(removed - 1);
1486 }
1487 return inf;
1488 }
1489
1490 if (LockingMode != LM_LIGHTWEIGHT) {
1491 // New lightweight locking does not use INFLATING.
1492 // CASE: inflation in progress - inflating over a stack-lock.
1493 // Some other thread is converting from stack-locked to inflated.
1494 // Only that thread can complete inflation -- other threads must wait.
1495 // The INFLATING value is transient.
1496 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1497 // We could always eliminate polling by parking the thread on some auxiliary list.
1498 if (mark == markWord::INFLATING()) {
1499 read_stable_mark(object);
1500 continue;
1501 }
1502 }
1503
1504 // CASE: fast-locked
1505 // Could be fast-locked either by the inflating_thread or by some other thread.
1506 //
1507 // Note that we allocate the ObjectMonitor speculatively, _before_
1508 // attempting to set the object's mark to the new ObjectMonitor. If
1509 // the inflating_thread owns the monitor, then we set the ObjectMonitor's
1510 // owner to the inflating_thread. Otherwise, we set the ObjectMonitor's owner
1511 // to anonymous. If we lose the race to set the object's mark to the
1512 // new ObjectMonitor, then we just delete it and loop around again.
1513 //
1514 LogStreamHandle(Trace, monitorinflation) lsh;
1515 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1516 ObjectMonitor* monitor = new ObjectMonitor(object);
1517 monitor->set_header(mark.set_unlocked());
1518 bool own = inflating_thread != nullptr && inflating_thread->lock_stack().contains(object);
1519 if (own) {
1520 // Owned by inflating_thread.
1521 monitor->set_owner_from(nullptr, inflating_thread);
1522 } else {
1523 // Owned by somebody else.
1524 monitor->set_owner_anonymous();
1525 }
1526 markWord monitor_mark = markWord::encode(monitor);
1527 markWord old_mark = object->cas_set_mark(monitor_mark, mark);
1528 if (old_mark == mark) {
1529 // Success! Return inflated monitor.
1530 if (own) {
1531 size_t removed = inflating_thread->lock_stack().remove(object);
1532 monitor->set_recursions(removed - 1);
1533 }
1534 // Once the ObjectMonitor is configured and object is associated
1535 // with the ObjectMonitor, it is safe to allow async deflation:
1536 _in_use_list.add(monitor);
1537
1538 // Hopefully the performance counters are allocated on distinct
1539 // cache lines to avoid false sharing on MP systems ...
1540 OM_PERFDATA_OP(Inflations, inc());
1541 if (log_is_enabled(Trace, monitorinflation)) {
1542 ResourceMark rm;
1543 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1544 INTPTR_FORMAT ", type='%s'", p2i(object),
1545 object->mark().value(), object->klass()->external_name());
1546 }
1547 if (event.should_commit()) {
1548 post_monitor_inflate_event(&event, object, cause);
1549 }
1550 return monitor;
1551 } else {
1552 delete monitor;
1553 continue; // Interference -- just retry
1554 }
1555 }
1556
1557 // CASE: stack-locked
1558 // Could be stack-locked either by current or by some other thread.
1559 //
1560 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1561 // to install INFLATING into the mark word. We originally installed INFLATING,
1562 // allocated the ObjectMonitor, and then finally STed the address of the
1563 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1564 // the interval in which INFLATING appeared in the mark, thus increasing
1565 // the odds of inflation contention. If we lose the race to set INFLATING,
1566 // then we just delete the ObjectMonitor and loop around again.
1567 //
1568 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1569 assert(LockingMode != LM_LIGHTWEIGHT, "cannot happen with new lightweight locking");
1570 ObjectMonitor* m = new ObjectMonitor(object);
1571 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1572 // We do this before the CAS in order to minimize the length of time
1573 // in which INFLATING appears in the mark.
1574
1575 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1576 if (cmp != mark) {
1577 delete m;
1578 continue; // Interference -- just retry
1579 }
1580
1581 // We've successfully installed INFLATING (0) into the mark-word.
1582 // This is the only case where 0 will appear in a mark-word.
1583 // Only the singular thread that successfully swings the mark-word
1584 // to 0 can perform (or more precisely, complete) inflation.
1585 //
1586 // Why do we CAS a 0 into the mark-word instead of just CASing the
1587 // mark-word from the stack-locked value directly to the new inflated state?
1588 // Consider what happens when a thread unlocks a stack-locked object.
1589 // It attempts to use CAS to swing the displaced header value from the
1590 // on-stack BasicLock back into the object header. Recall also that the
1591 // header value (hash code, etc) can reside in (a) the object header, or
1592 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1593 // header in an ObjectMonitor. The inflate() routine must copy the header
1594 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1595 // the while preserving the hashCode stability invariants. If the owner
1596 // decides to release the lock while the value is 0, the unlock will fail
1597 // and control will eventually pass from slow_exit() to inflate. The owner
1598 // will then spin, waiting for the 0 value to disappear. Put another way,
1599 // the 0 causes the owner to stall if the owner happens to try to
1600 // drop the lock (restoring the header from the BasicLock to the object)
1601 // while inflation is in-progress. This protocol avoids races that might
1602 // would otherwise permit hashCode values to change or "flicker" for an object.
1603 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1604 // 0 serves as a "BUSY" inflate-in-progress indicator.
1605
1606
1607 // fetch the displaced mark from the owner's stack.
1608 // The owner can't die or unwind past the lock while our INFLATING
1609 // object is in the mark. Furthermore the owner can't complete
1610 // an unlock on the object, either.
1611 markWord dmw = mark.displaced_mark_helper();
1612 // Catch if the object's header is not neutral (not locked and
1613 // not marked is what we care about here).
1614 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1615
1616 // Setup monitor fields to proper values -- prepare the monitor
1617 m->set_header(dmw);
1618
1619 // Optimization: if the mark.locker stack address is associated
1620 // with this thread we could simply set m->_owner = current.
1621 // Note that a thread can inflate an object
1622 // that it has stack-locked -- as might happen in wait() -- directly
1623 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1624 m->set_owner_from(nullptr, mark.locker());
1625 // TODO-FIXME: assert BasicLock->dhw != 0.
1626
1627 // Must preserve store ordering. The monitor state must
1628 // be stable at the time of publishing the monitor address.
1629 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1630 // Release semantics so that above set_object() is seen first.
1631 object->release_set_mark(markWord::encode(m));
1632
1633 // Once ObjectMonitor is configured and the object is associated
1634 // with the ObjectMonitor, it is safe to allow async deflation:
1635 _in_use_list.add(m);
1636
1637 // Hopefully the performance counters are allocated on distinct cache lines
1638 // to avoid false sharing on MP systems ...
1639 OM_PERFDATA_OP(Inflations, inc());
1640 if (log_is_enabled(Trace, monitorinflation)) {
1641 ResourceMark rm;
1642 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1643 INTPTR_FORMAT ", type='%s'", p2i(object),
1644 object->mark().value(), object->klass()->external_name());
1645 }
1646 if (event.should_commit()) {
1647 post_monitor_inflate_event(&event, object, cause);
1648 }
1649 return m;
1650 }
1651
1652 // CASE: neutral
1653 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1654 // If we know we're inflating for entry it's better to inflate by swinging a
1655 // pre-locked ObjectMonitor pointer into the object header. A successful
1656 // CAS inflates the object *and* confers ownership to the inflating thread.
1657 // In the current implementation we use a 2-step mechanism where we CAS()
1658 // to inflate and then CAS() again to try to swing _owner from null to current.
1659 // An inflateTry() method that we could call from enter() would be useful.
1660
1661 // Catch if the object's header is not neutral (not locked and
1662 // not marked is what we care about here).
1663 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1664 ObjectMonitor* m = new ObjectMonitor(object);
1665 // prepare m for installation - set monitor to initial state
1666 m->set_header(mark);
1667
1668 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1669 delete m;
1670 m = nullptr;
1671 continue;
1672 // interference - the markword changed - just retry.
1673 // The state-transitions are one-way, so there's no chance of
1674 // live-lock -- "Inflated" is an absorbing state.
1675 }
1676
1677 // Once the ObjectMonitor is configured and object is associated
1678 // with the ObjectMonitor, it is safe to allow async deflation:
1679 _in_use_list.add(m);
1680
1681 // Hopefully the performance counters are allocated on distinct
1682 // cache lines to avoid false sharing on MP systems ...
1683 OM_PERFDATA_OP(Inflations, inc());
1684 if (log_is_enabled(Trace, monitorinflation)) {
1685 ResourceMark rm;
1686 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1687 INTPTR_FORMAT ", type='%s'", p2i(object),
1688 object->mark().value(), object->klass()->external_name());
1689 }
1690 if (event.should_commit()) {
1691 post_monitor_inflate_event(&event, object, cause);
1692 }
1693 return m;
1694 }
1695 }
1696
1697 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1698 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1699 //
1700 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1701 MonitorList::Iterator iter = _in_use_list.iterator();
1702 size_t deflated_count = 0;
1703
1704 while (iter.has_next()) {
1705 if (deflated_count >= (size_t)MonitorDeflationMax) {
1706 break;
1707 }
1708 ObjectMonitor* mid = iter.next();
1709 if (mid->deflate_monitor()) {
1710 deflated_count++;
1711 }
1712
1713 // Must check for a safepoint/handshake and honor it.
1714 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1715 }
1716
1717 return deflated_count;
1718 }
1719
1720 class HandshakeForDeflation : public HandshakeClosure {
1721 public:
1722 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1723
1724 void do_thread(Thread* thread) {
1725 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1726 INTPTR_FORMAT, p2i(thread));
1727 }
1728 };
1729
1730 class VM_RendezvousGCThreads : public VM_Operation {
1731 public:
1732 bool evaluate_at_safepoint() const override { return false; }
1733 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1734 void doit() override {
1735 Universe::heap()->safepoint_synchronize_begin();
1736 Universe::heap()->safepoint_synchronize_end();
1737 };
1738 };
1739
1740 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1741 ObjectMonitorDeflationSafepointer* safepointer) {
1742 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1743 size_t deleted_count = 0;
1744 for (ObjectMonitor* monitor: *delete_list) {
1745 delete monitor;
1746 deleted_count++;
1747 // A JavaThread must check for a safepoint/handshake and honor it.
1748 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1749 }
1750 return deleted_count;
1751 }
1752
1753 class ObjectMonitorDeflationLogging: public StackObj {
1754 LogStreamHandle(Debug, monitorinflation) _debug;
1755 LogStreamHandle(Info, monitorinflation) _info;
1756 LogStream* _stream;
1757 elapsedTimer _timer;
1758
1759 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1760 size_t count() const { return ObjectSynchronizer::_in_use_list.count(); }
1761 size_t max() const { return ObjectSynchronizer::_in_use_list.max(); }
1762
1763 public:
1764 ObjectMonitorDeflationLogging()
1765 : _debug(), _info(), _stream(nullptr) {
1766 if (_debug.is_enabled()) {
1767 _stream = &_debug;
1768 } else if (_info.is_enabled()) {
1769 _stream = &_info;
1770 }
1771 }
1772
1773 void begin() {
1774 if (_stream != nullptr) {
1775 _stream->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1776 ceiling(), count(), max());
1777 _timer.start();
1778 }
1779 }
1780
1781 void before_handshake(size_t unlinked_count) {
1782 if (_stream != nullptr) {
1783 _timer.stop();
1784 _stream->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1785 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1786 SIZE_FORMAT ", max=" SIZE_FORMAT,
1787 unlinked_count, ceiling(), count(), max());
1788 }
1789 }
1790
1791 void after_handshake() {
1792 if (_stream != nullptr) {
1793 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1794 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1795 ceiling(), count(), max());
1796 _timer.start();
1797 }
1798 }
1799
1800 void end(size_t deflated_count, size_t unlinked_count) {
1801 if (_stream != nullptr) {
1802 _timer.stop();
1803 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1804 _stream->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1805 deflated_count, unlinked_count, _timer.seconds());
1806 }
1807 _stream->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1808 ceiling(), count(), max());
1809 }
1810 }
1811
1812 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1813 if (_stream != nullptr) {
1814 _timer.stop();
1815 _stream->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1816 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1817 op_name, cnt_name, cnt, ceiling(), count(), max());
1818 }
1819 }
1820
1821 void after_block_for_safepoint(const char* op_name) {
1822 if (_stream != nullptr) {
1823 _stream->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1824 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1825 ceiling(), count(), max());
1826 _timer.start();
1827 }
1828 }
1829 };
1830
1831 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1832 if (!SafepointMechanism::should_process(_current)) {
1833 return;
1834 }
1835
1836 // A safepoint/handshake has started.
1837 _log->before_block_for_safepoint(op_name, count_name, counter);
1838
1839 {
1840 // Honor block request.
1841 ThreadBlockInVM tbivm(_current);
1842 }
1843
1844 _log->after_block_for_safepoint(op_name);
1845 }
1846
1847 // This function is called by the MonitorDeflationThread to deflate
1848 // ObjectMonitors.
1849 size_t ObjectSynchronizer::deflate_idle_monitors() {
1850 JavaThread* current = JavaThread::current();
1851 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1852
1853 // The async deflation request has been processed.
1854 _last_async_deflation_time_ns = os::javaTimeNanos();
1855 set_is_async_deflation_requested(false);
1856
1857 ObjectMonitorDeflationLogging log;
1858 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1859
1860 log.begin();
1861
1862 // Deflate some idle ObjectMonitors.
1863 size_t deflated_count = deflate_monitor_list(&safepointer);
1864
1865 // Unlink the deflated ObjectMonitors from the in-use list.
1866 size_t unlinked_count = 0;
1867 size_t deleted_count = 0;
1868 if (deflated_count > 0) {
1869 ResourceMark rm(current);
1870 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1871 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1872
1873 log.before_handshake(unlinked_count);
1874
1875 // A JavaThread needs to handshake in order to safely free the
1876 // ObjectMonitors that were deflated in this cycle.
1877 HandshakeForDeflation hfd_hc;
1878 Handshake::execute(&hfd_hc);
1879 // Also, we sync and desync GC threads around the handshake, so that they can
1880 // safely read the mark-word and look-through to the object-monitor, without
1881 // being afraid that the object-monitor is going away.
1882 VM_RendezvousGCThreads sync_gc;
1883 VMThread::execute(&sync_gc);
1884
1885 log.after_handshake();
1886
1887 // After the handshake, safely free the ObjectMonitors that were
1888 // deflated and unlinked in this cycle.
1889
1890 // Delete the unlinked ObjectMonitors.
1891 deleted_count = delete_monitors(&delete_list, &safepointer);
1892 assert(unlinked_count == deleted_count, "must be");
1893 }
1894
1895 log.end(deflated_count, unlinked_count);
1896
1897 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1898 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1899
1900 GVars.stw_random = os::random();
1901
1902 if (deflated_count != 0) {
1903 _no_progress_cnt = 0;
1904 } else if (_no_progress_skip_increment) {
1905 _no_progress_skip_increment = false;
1906 } else {
1907 _no_progress_cnt++;
1908 }
1909
1910 return deflated_count;
1911 }
1912
1913 // Monitor cleanup on JavaThread::exit
1914
1915 // Iterate through monitor cache and attempt to release thread's monitors
1916 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1917 private:
1918 JavaThread* _thread;
1919
1920 public:
1921 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1922 void do_monitor(ObjectMonitor* mid) {
1923 intx rec = mid->complete_exit(_thread);
1924 _thread->dec_held_monitor_count(rec + 1);
1925 }
1926 };
1927
1928 // Release all inflated monitors owned by current thread. Lightweight monitors are
1929 // ignored. This is meant to be called during JNI thread detach which assumes
1930 // all remaining monitors are heavyweight. All exceptions are swallowed.
1931 // Scanning the extant monitor list can be time consuming.
1932 // A simple optimization is to add a per-thread flag that indicates a thread
1933 // called jni_monitorenter() during its lifetime.
1934 //
1935 // Instead of NoSafepointVerifier it might be cheaper to
1936 // use an idiom of the form:
1937 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1938 // <code that must not run at safepoint>
1939 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1940 // Since the tests are extremely cheap we could leave them enabled
1941 // for normal product builds.
1942
1943 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1944 assert(current == JavaThread::current(), "must be current Java thread");
1945 NoSafepointVerifier nsv;
1946 ReleaseJavaMonitorsClosure rjmc(current);
1947 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1948 assert(!current->has_pending_exception(), "Should not be possible");
1949 current->clear_pending_exception();
1950 assert(current->held_monitor_count() == 0, "Should not be possible");
1951 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1952 current->clear_jni_monitor_count();
1953 }
1954
1955 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1956 switch (cause) {
1957 case inflate_cause_vm_internal: return "VM Internal";
1958 case inflate_cause_monitor_enter: return "Monitor Enter";
1959 case inflate_cause_wait: return "Monitor Wait";
1960 case inflate_cause_notify: return "Monitor Notify";
1961 case inflate_cause_hash_code: return "Monitor Hash Code";
1962 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1963 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1964 default:
1965 ShouldNotReachHere();
1966 }
1967 return "Unknown";
1968 }
1969
1970 //------------------------------------------------------------------------------
1971 // Debugging code
1972
1973 u_char* ObjectSynchronizer::get_gvars_addr() {
1974 return (u_char*)&GVars;
1975 }
1976
1977 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1978 return (u_char*)&GVars.hc_sequence;
1979 }
1980
1981 size_t ObjectSynchronizer::get_gvars_size() {
1982 return sizeof(SharedGlobals);
1983 }
1984
1985 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1986 return (u_char*)&GVars.stw_random;
1987 }
1988
1989 // Do the final audit and print of ObjectMonitor stats; must be done
1990 // by the VMThread at VM exit time.
1991 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1992 assert(Thread::current()->is_VM_thread(), "sanity check");
1993
1994 if (is_final_audit()) { // Only do the audit once.
1995 return;
1996 }
1997 set_is_final_audit();
1998 log_info(monitorinflation)("Starting the final audit.");
1999
2000 if (log_is_enabled(Info, monitorinflation)) {
2001 // The other audit_and_print_stats() call is done at the Debug
2002 // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
2003 audit_and_print_stats(true /* on_exit */);
2004 }
2005 }
2006
2007 // This function can be called at a safepoint or it can be called when
2008 // we are trying to exit the VM. When we are trying to exit the VM, the
2009 // list walker functions can run in parallel with the other list
2010 // operations so spin-locking is used for safety.
2011 //
2012 // Calls to this function can be added in various places as a debugging
2013 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
2014 // details logged at the Info level and 'false' for the 'on_exit'
2015 // parameter to have in-use monitor details logged at the Trace level.
2016 //
2017 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
2018 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
2019
2020 LogStreamHandle(Debug, monitorinflation) lsh_debug;
2021 LogStreamHandle(Info, monitorinflation) lsh_info;
2022 LogStreamHandle(Trace, monitorinflation) lsh_trace;
2023 LogStream* ls = nullptr;
2024 if (log_is_enabled(Trace, monitorinflation)) {
2025 ls = &lsh_trace;
2026 } else if (log_is_enabled(Debug, monitorinflation)) {
2027 ls = &lsh_debug;
2028 } else if (log_is_enabled(Info, monitorinflation)) {
2029 ls = &lsh_info;
2030 }
2031 assert(ls != nullptr, "sanity check");
2032
2033 int error_cnt = 0;
2034
2035 ls->print_cr("Checking in_use_list:");
2036 chk_in_use_list(ls, &error_cnt);
2037
2038 if (error_cnt == 0) {
2039 ls->print_cr("No errors found in in_use_list checks.");
2040 } else {
2041 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
2042 }
2043
2044 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
2045 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
2046 // When exiting this log output is at the Info level. When called
2047 // at a safepoint, this log output is at the Trace level since
2048 // there can be a lot of it.
2049 log_in_use_monitor_details(ls, !on_exit /* log_all */);
2050 }
2051
2052 ls->flush();
2053
2054 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2055 }
2056
2057 // Check the in_use_list; log the results of the checks.
2058 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
2059 size_t l_in_use_count = _in_use_list.count();
2060 size_t l_in_use_max = _in_use_list.max();
2061 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
2062 l_in_use_max);
2063
2064 size_t ck_in_use_count = 0;
2065 MonitorList::Iterator iter = _in_use_list.iterator();
2066 while (iter.has_next()) {
2067 ObjectMonitor* mid = iter.next();
2068 chk_in_use_entry(mid, out, error_cnt_p);
2069 ck_in_use_count++;
2070 }
2071
2072 if (l_in_use_count == ck_in_use_count) {
2073 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
2074 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
2075 } else {
2076 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
2077 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
2078 ck_in_use_count);
2079 }
2080
2081 size_t ck_in_use_max = _in_use_list.max();
2082 if (l_in_use_max == ck_in_use_max) {
2083 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
2084 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
2085 } else {
2086 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
2087 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
2088 }
2089 }
2090
2091 // Check an in-use monitor entry; log any errors.
2092 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2093 int* error_cnt_p) {
2094 if (n->owner_is_DEFLATER_MARKER()) {
2095 // This could happen when monitor deflation blocks for a safepoint.
2096 return;
2097 }
2098
2099 if (n->header().value() == 0) {
2100 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2101 "have non-null _header field.", p2i(n));
2102 *error_cnt_p = *error_cnt_p + 1;
2103 }
2104 const oop obj = n->object_peek();
2105 if (obj != nullptr) {
2106 const markWord mark = obj->mark();
2107 if (!mark.has_monitor()) {
2108 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2109 "object does not think it has a monitor: obj="
2110 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2111 p2i(obj), mark.value());
2112 *error_cnt_p = *error_cnt_p + 1;
2113 }
2114 ObjectMonitor* const obj_mon = mark.monitor();
2115 if (n != obj_mon) {
2116 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2117 "object does not refer to the same monitor: obj="
2118 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2119 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2120 *error_cnt_p = *error_cnt_p + 1;
2121 }
2122 }
2123 }
2124
2125 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2126 // flags indicate why the entry is in-use, 'object' and 'object type'
2127 // indicate the associated object and its type.
2128 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2129 if (_in_use_list.count() > 0) {
2130 stringStream ss;
2131 out->print_cr("In-use monitor info:");
2132 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2133 out->print_cr("%18s %s %18s %18s",
2134 "monitor", "BHL", "object", "object type");
2135 out->print_cr("================== === ================== ==================");
2136
2137 auto is_interesting = [&](ObjectMonitor* monitor) {
2138 return log_all || monitor->has_owner() || monitor->is_busy();
2139 };
2140
2141 monitors_iterate([&](ObjectMonitor* monitor) {
2142 if (is_interesting(monitor)) {
2143 const oop obj = monitor->object_peek();
2144 const markWord mark = monitor->header();
2145 ResourceMark rm;
2146 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
2147 monitor->is_busy(), mark.hash() != 0, monitor->owner() != nullptr,
2148 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2149 if (monitor->is_busy()) {
2150 out->print(" (%s)", monitor->is_busy_to_string(&ss));
2151 ss.reset();
2152 }
2153 out->cr();
2154 }
2155 });
2156 }
2157
2158 out->flush();
2159 }