1 /*
2 * Copyright (c) 1998, 2023, 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/handles.inline.hpp"
40 #include "runtime/handshake.hpp"
41 #include "runtime/interfaceSupport.inline.hpp"
42 #include "runtime/javaThread.hpp"
43 #include "runtime/lockStack.inline.hpp"
44 #include "runtime/mutexLocker.hpp"
45 #include "runtime/objectMonitor.hpp"
46 #include "runtime/objectMonitor.inline.hpp"
47 #include "runtime/os.inline.hpp"
48 #include "runtime/osThread.hpp"
49 #include "runtime/perfData.hpp"
50 #include "runtime/safepointMechanism.inline.hpp"
51 #include "runtime/safepointVerifiers.hpp"
52 #include "runtime/sharedRuntime.hpp"
53 #include "runtime/stubRoutines.hpp"
54 #include "runtime/synchronizer.hpp"
55 #include "runtime/threads.hpp"
56 #include "runtime/timer.hpp"
57 #include "runtime/trimNativeHeap.hpp"
58 #include "runtime/vframe.hpp"
59 #include "runtime/vmThread.hpp"
60 #include "utilities/align.hpp"
61 #include "utilities/dtrace.hpp"
62 #include "utilities/events.hpp"
63 #include "utilities/linkedlist.hpp"
64 #include "utilities/preserveException.hpp"
65
66 void MonitorList::add(ObjectMonitor* m) {
67 ObjectMonitor* head;
68 do {
69 head = Atomic::load(&_head);
70 m->set_next_om(head);
71 } while (Atomic::cmpxchg(&_head, head, m) != head);
72
73 size_t count = Atomic::add(&_count, 1u);
74 if (count > max()) {
75 Atomic::inc(&_max);
76 }
77 }
78
79 size_t MonitorList::count() const {
80 return Atomic::load(&_count);
81 }
82
83 size_t MonitorList::max() const {
84 return Atomic::load(&_max);
85 }
86
87 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
88 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
89 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
90 elapsedTimer* timer_p,
91 GrowableArray<ObjectMonitor*>* unlinked_list) {
92 size_t unlinked_count = 0;
93 ObjectMonitor* prev = nullptr;
94 ObjectMonitor* head = Atomic::load_acquire(&_head);
95 ObjectMonitor* m = head;
96 // The in-use list head can be null during the final audit.
97 while (m != nullptr) {
98 if (m->is_being_async_deflated()) {
99 // Find next live ObjectMonitor.
100 ObjectMonitor* next = m;
101 do {
102 ObjectMonitor* next_next = next->next_om();
103 unlinked_count++;
104 unlinked_list->append(next);
105 next = next_next;
106 if (unlinked_count >= (size_t)MonitorDeflationMax) {
107 // Reached the max so bail out on the gathering loop.
108 break;
109 }
110 } while (next != nullptr && next->is_being_async_deflated());
111 if (prev == nullptr) {
112 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
113 if (prev_head != head) {
114 // Find new prev ObjectMonitor that just got inserted.
115 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
116 prev = n;
117 }
118 prev->set_next_om(next);
119 }
120 } else {
121 prev->set_next_om(next);
122 }
123 if (unlinked_count >= (size_t)MonitorDeflationMax) {
124 // Reached the max so bail out on the searching loop.
125 break;
126 }
127 m = next;
128 } else {
129 prev = m;
130 m = m->next_om();
131 }
132
133 if (current->is_Java_thread()) {
134 // A JavaThread must check for a safepoint/handshake and honor it.
135 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking",
136 "unlinked_count", unlinked_count,
137 ls, timer_p);
138 }
139 }
140 Atomic::sub(&_count, unlinked_count);
141 return unlinked_count;
142 }
143
144 MonitorList::Iterator MonitorList::iterator() const {
145 return Iterator(Atomic::load_acquire(&_head));
146 }
147
148 ObjectMonitor* MonitorList::Iterator::next() {
149 ObjectMonitor* current = _current;
150 _current = current->next_om();
151 return current;
152 }
153
154 // The "core" versions of monitor enter and exit reside in this file.
155 // The interpreter and compilers contain specialized transliterated
156 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
157 // fast_lock(...) for instance. If you make changes here, make sure to modify the
158 // interpreter, and both C1 and C2 fast-path inline locking code emission.
159 //
160 // -----------------------------------------------------------------------------
161
162 #ifdef DTRACE_ENABLED
163
164 // Only bother with this argument setup if dtrace is available
165 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
166
167 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
168 char* bytes = nullptr; \
169 int len = 0; \
170 jlong jtid = SharedRuntime::get_java_tid(thread); \
171 Symbol* klassname = obj->klass()->name(); \
172 if (klassname != nullptr) { \
173 bytes = (char*)klassname->bytes(); \
174 len = klassname->utf8_length(); \
175 }
176
177 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
178 { \
179 if (DTraceMonitorProbes) { \
180 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
181 HOTSPOT_MONITOR_WAIT(jtid, \
182 (uintptr_t)(monitor), bytes, len, (millis)); \
183 } \
184 }
185
186 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
187 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
188 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
189
190 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
191 { \
192 if (DTraceMonitorProbes) { \
193 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
194 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
195 (uintptr_t)(monitor), bytes, len); \
196 } \
197 }
198
199 #else // ndef DTRACE_ENABLED
200
201 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
202 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
203
204 #endif // ndef DTRACE_ENABLED
205
206 // This exists only as a workaround of dtrace bug 6254741
207 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
208 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
209 return 0;
210 }
211
212 static constexpr size_t inflation_lock_count() {
213 return 256;
214 }
215
216 // Static storage for an array of PlatformMutex.
217 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
218
219 static inline PlatformMutex* inflation_lock(size_t index) {
220 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
221 }
222
223 void ObjectSynchronizer::initialize() {
224 for (size_t i = 0; i < inflation_lock_count(); i++) {
225 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
226 }
227 // Start the ceiling with the estimate for one thread.
228 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
229
230 // Start the timer for deflations, so it does not trigger immediately.
231 _last_async_deflation_time_ns = os::javaTimeNanos();
232 }
233
234 MonitorList ObjectSynchronizer::_in_use_list;
235 // monitors_used_above_threshold() policy is as follows:
236 //
237 // The ratio of the current _in_use_list count to the ceiling is used
238 // to determine if we are above MonitorUsedDeflationThreshold and need
239 // to do an async monitor deflation cycle. The ceiling is increased by
240 // AvgMonitorsPerThreadEstimate when a thread is added to the system
241 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
242 // removed from the system.
243 //
244 // Note: If the _in_use_list max exceeds the ceiling, then
245 // monitors_used_above_threshold() will use the in_use_list max instead
246 // of the thread count derived ceiling because we have used more
247 // ObjectMonitors than the estimated average.
248 //
249 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
250 // no-progress async monitor deflation cycles in a row, then the ceiling
251 // is adjusted upwards by monitors_used_above_threshold().
252 //
253 // Start the ceiling with the estimate for one thread in initialize()
254 // which is called after cmd line options are processed.
255 static size_t _in_use_list_ceiling = 0;
256 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
257 bool volatile ObjectSynchronizer::_is_final_audit = false;
258 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
259 static uintx _no_progress_cnt = 0;
260 static bool _no_progress_skip_increment = false;
261
262 // =====================> Quick functions
263
264 // The quick_* forms are special fast-path variants used to improve
265 // performance. In the simplest case, a "quick_*" implementation could
266 // simply return false, in which case the caller will perform the necessary
267 // state transitions and call the slow-path form.
268 // The fast-path is designed to handle frequently arising cases in an efficient
269 // manner and is just a degenerate "optimistic" variant of the slow-path.
270 // returns true -- to indicate the call was satisfied.
271 // returns false -- to indicate the call needs the services of the slow-path.
272 // A no-loitering ordinance is in effect for code in the quick_* family
273 // operators: safepoints or indefinite blocking (blocking that might span a
274 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
275 // entry.
276 //
277 // Consider: An interesting optimization is to have the JIT recognize the
278 // following common idiom:
279 // synchronized (someobj) { .... ; notify(); }
280 // That is, we find a notify() or notifyAll() call that immediately precedes
281 // the monitorexit operation. In that case the JIT could fuse the operations
282 // into a single notifyAndExit() runtime primitive.
283
284 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
285 assert(current->thread_state() == _thread_in_Java, "invariant");
286 NoSafepointVerifier nsv;
287 if (obj == nullptr) return false; // slow-path for invalid obj
288 const markWord mark = obj->mark();
289
290 if (LockingMode == LM_LIGHTWEIGHT) {
291 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
292 // Degenerate notify
293 // fast-locked by caller so by definition the implied waitset is empty.
294 return true;
295 }
296 } else if (LockingMode == LM_LEGACY) {
297 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
298 // Degenerate notify
299 // stack-locked by caller so by definition the implied waitset is empty.
300 return true;
301 }
302 }
303
304 if (mark.has_monitor()) {
305 ObjectMonitor* const mon = mark.monitor();
306 assert(mon->object() == oop(obj), "invariant");
307 if (mon->owner() != current) return false; // slow-path for IMS exception
308
309 if (mon->first_waiter() != nullptr) {
310 // We have one or more waiters. Since this is an inflated monitor
311 // that we own, we can transfer one or more threads from the waitset
312 // to the entrylist here and now, avoiding the slow-path.
313 if (all) {
314 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
315 } else {
316 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
317 }
318 int free_count = 0;
319 do {
320 mon->INotify(current);
321 ++free_count;
322 } while (mon->first_waiter() != nullptr && all);
323 OM_PERFDATA_OP(Notifications, inc(free_count));
324 }
325 return true;
326 }
327
328 // other IMS exception states take the slow-path
329 return false;
330 }
331
332
333 // The LockNode emitted directly at the synchronization site would have
334 // been too big if it were to have included support for the cases of inflated
335 // recursive enter and exit, so they go here instead.
336 // Note that we can't safely call AsyncPrintJavaStack() from within
337 // quick_enter() as our thread state remains _in_Java.
338
339 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
340 BasicLock * lock) {
341 assert(current->thread_state() == _thread_in_Java, "invariant");
342 NoSafepointVerifier nsv;
343 if (obj == nullptr) return false; // Need to throw NPE
344
345 if (obj->klass()->is_value_based()) {
346 return false;
347 }
348
349 const markWord mark = obj->mark();
350
351 if (mark.has_monitor()) {
352 ObjectMonitor* const m = mark.monitor();
353 // An async deflation or GC can race us before we manage to make
354 // the ObjectMonitor busy by setting the owner below. If we detect
355 // that race we just bail out to the slow-path here.
356 if (m->object_peek() == nullptr) {
357 return false;
358 }
359 JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
360
361 // Lock contention and Transactional Lock Elision (TLE) diagnostics
362 // and observability
363 // Case: light contention possibly amenable to TLE
364 // Case: TLE inimical operations such as nested/recursive synchronization
365
366 if (owner == current) {
367 m->_recursions++;
368 current->inc_held_monitor_count();
369 return true;
370 }
371
372 if (LockingMode != LM_LIGHTWEIGHT) {
373 // This Java Monitor is inflated so obj's header will never be
374 // displaced to this thread's BasicLock. Make the displaced header
375 // non-null so this BasicLock is not seen as recursive nor as
376 // being locked. We do this unconditionally so that this thread's
377 // BasicLock cannot be mis-interpreted by any stack walkers. For
378 // performance reasons, stack walkers generally first check for
379 // stack-locking in the object's header, the second check is for
380 // recursive stack-locking in the displaced header in the BasicLock,
381 // and last are the inflated Java Monitor (ObjectMonitor) checks.
382 lock->set_displaced_header(markWord::unused_mark());
383 }
384
385 if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) {
386 assert(m->_recursions == 0, "invariant");
387 current->inc_held_monitor_count();
388 return true;
389 }
390 }
391
392 // Note that we could inflate in quick_enter.
393 // This is likely a useful optimization
394 // Critically, in quick_enter() we must not:
395 // -- block indefinitely, or
396 // -- reach a safepoint
397
398 return false; // revert to slow-path
399 }
400
401 // Handle notifications when synchronizing on value based classes
402 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
403 frame last_frame = current->last_frame();
404 bool bcp_was_adjusted = false;
405 // Don't decrement bcp if it points to the frame's first instruction. This happens when
406 // handle_sync_on_value_based_class() is called because of a synchronized method. There
407 // is no actual monitorenter instruction in the byte code in this case.
408 if (last_frame.is_interpreted_frame() &&
409 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
410 // adjust bcp to point back to monitorenter so that we print the correct line numbers
411 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
412 bcp_was_adjusted = true;
413 }
414
415 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
416 ResourceMark rm(current);
417 stringStream ss;
418 current->print_active_stack_on(&ss);
419 char* base = (char*)strstr(ss.base(), "at");
420 char* newline = (char*)strchr(ss.base(), '\n');
421 if (newline != nullptr) {
422 *newline = '\0';
423 }
424 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
425 } else {
426 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
427 ResourceMark rm(current);
428 Log(valuebasedclasses) vblog;
429
430 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
431 if (current->has_last_Java_frame()) {
432 LogStream info_stream(vblog.info());
433 current->print_active_stack_on(&info_stream);
434 } else {
435 vblog.info("Cannot find the last Java frame");
436 }
437
438 EventSyncOnValueBasedClass event;
439 if (event.should_commit()) {
440 event.set_valueBasedClass(obj->klass());
441 event.commit();
442 }
443 }
444
445 if (bcp_was_adjusted) {
446 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
447 }
448 }
449
450 static bool useHeavyMonitors() {
451 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
452 return LockingMode == LM_MONITOR;
453 #else
454 return false;
455 #endif
456 }
457
458 // -----------------------------------------------------------------------------
459 // Monitor Enter/Exit
460 // The interpreter and compiler assembly code tries to lock using the fast path
461 // of this algorithm. Make sure to update that code if the following function is
462 // changed. The implementation is extremely sensitive to race condition. Be careful.
463
464 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
465 if (obj->klass()->is_value_based()) {
466 handle_sync_on_value_based_class(obj, current);
467 }
468
469 current->inc_held_monitor_count();
470
471 if (!useHeavyMonitors()) {
472 if (LockingMode == LM_LIGHTWEIGHT) {
473 // Fast-locking does not use the 'lock' argument.
474 LockStack& lock_stack = current->lock_stack();
475 if (lock_stack.can_push()) {
476 markWord mark = obj()->mark_acquire();
477 if (mark.is_neutral()) {
478 assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
479 // Try to swing into 'fast-locked' state.
480 markWord locked_mark = mark.set_fast_locked();
481 markWord old_mark = obj()->cas_set_mark(locked_mark, mark);
482 if (old_mark == mark) {
483 // Successfully fast-locked, push object to lock-stack and return.
484 lock_stack.push(obj());
485 return;
486 }
487 }
488 }
489 // All other paths fall-through to inflate-enter.
490 } else if (LockingMode == LM_LEGACY) {
491 markWord mark = obj->mark();
492 if (mark.is_neutral()) {
493 // Anticipate successful CAS -- the ST of the displaced mark must
494 // be visible <= the ST performed by the CAS.
495 lock->set_displaced_header(mark);
496 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
497 return;
498 }
499 // Fall through to inflate() ...
500 } else if (mark.has_locker() &&
501 current->is_lock_owned((address) mark.locker())) {
502 assert(lock != mark.locker(), "must not re-lock the same lock");
503 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
504 lock->set_displaced_header(markWord::from_pointer(nullptr));
505 return;
506 }
507
508 // The object header will never be displaced to this lock,
509 // so it does not matter what the value is, except that it
510 // must be non-zero to avoid looking like a re-entrant lock,
511 // and must not look locked either.
512 lock->set_displaced_header(markWord::unused_mark());
513 }
514 } else if (VerifyHeavyMonitors) {
515 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
516 }
517
518 // An async deflation can race after the inflate() call and before
519 // enter() can make the ObjectMonitor busy. enter() returns false if
520 // we have lost the race to async deflation and we simply try again.
521 while (true) {
522 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
523 if (monitor->enter(current)) {
524 return;
525 }
526 }
527 }
528
529 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
530 current->dec_held_monitor_count();
531
532 if (!useHeavyMonitors()) {
533 markWord mark = object->mark();
534 if (LockingMode == LM_LIGHTWEIGHT) {
535 // Fast-locking does not use the 'lock' argument.
536 if (mark.is_fast_locked()) {
537 markWord unlocked_mark = mark.set_unlocked();
538 markWord old_mark = object->cas_set_mark(unlocked_mark, mark);
539 if (old_mark != mark) {
540 // Another thread won the CAS, it must have inflated the monitor.
541 // It can only have installed an anonymously locked monitor at this point.
542 // Fetch that monitor, set owner correctly to this thread, and
543 // exit it (allowing waiting threads to enter).
544 assert(old_mark.has_monitor(), "must have monitor");
545 ObjectMonitor* monitor = old_mark.monitor();
546 assert(monitor->is_owner_anonymous(), "must be anonymous owner");
547 monitor->set_owner_from_anonymous(current);
548 monitor->exit(current);
549 }
550 LockStack& lock_stack = current->lock_stack();
551 lock_stack.remove(object);
552 return;
553 }
554 } else if (LockingMode == LM_LEGACY) {
555 markWord dhw = lock->displaced_header();
556 if (dhw.value() == 0) {
557 // If the displaced header is null, then this exit matches up with
558 // a recursive enter. No real work to do here except for diagnostics.
559 #ifndef PRODUCT
560 if (mark != markWord::INFLATING()) {
561 // Only do diagnostics if we are not racing an inflation. Simply
562 // exiting a recursive enter of a Java Monitor that is being
563 // inflated is safe; see the has_monitor() comment below.
564 assert(!mark.is_neutral(), "invariant");
565 assert(!mark.has_locker() ||
566 current->is_lock_owned((address)mark.locker()), "invariant");
567 if (mark.has_monitor()) {
568 // The BasicLock's displaced_header is marked as a recursive
569 // enter and we have an inflated Java Monitor (ObjectMonitor).
570 // This is a special case where the Java Monitor was inflated
571 // after this thread entered the stack-lock recursively. When a
572 // Java Monitor is inflated, we cannot safely walk the Java
573 // Monitor owner's stack and update the BasicLocks because a
574 // Java Monitor can be asynchronously inflated by a thread that
575 // does not own the Java Monitor.
576 ObjectMonitor* m = mark.monitor();
577 assert(m->object()->mark() == mark, "invariant");
578 assert(m->is_entered(current), "invariant");
579 }
580 }
581 #endif
582 return;
583 }
584
585 if (mark == markWord::from_pointer(lock)) {
586 // If the object is stack-locked by the current thread, try to
587 // swing the displaced header from the BasicLock back to the mark.
588 assert(dhw.is_neutral(), "invariant");
589 if (object->cas_set_mark(dhw, mark) == mark) {
590 return;
591 }
592 }
593 }
594 } else if (VerifyHeavyMonitors) {
595 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
596 }
597
598 // We have to take the slow-path of possible inflation and then exit.
599 // The ObjectMonitor* can't be async deflated until ownership is
600 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
601 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
602 if (LockingMode == LM_LIGHTWEIGHT && monitor->is_owner_anonymous()) {
603 // It must be owned by us. Pop lock object from lock stack.
604 LockStack& lock_stack = current->lock_stack();
605 oop popped = lock_stack.pop();
606 assert(popped == object, "must be owned by this thread");
607 monitor->set_owner_from_anonymous(current);
608 }
609 monitor->exit(current);
610 }
611
612 // -----------------------------------------------------------------------------
613 // JNI locks on java objects
614 // NOTE: must use heavy weight monitor to handle jni monitor enter
615 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
616 if (obj->klass()->is_value_based()) {
617 handle_sync_on_value_based_class(obj, current);
618 }
619
620 // the current locking is from JNI instead of Java code
621 current->set_current_pending_monitor_is_from_java(false);
622 // An async deflation can race after the inflate() call and before
623 // enter() can make the ObjectMonitor busy. enter() returns false if
624 // we have lost the race to async deflation and we simply try again.
625 while (true) {
626 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
627 if (monitor->enter(current)) {
628 current->inc_held_monitor_count(1, true);
629 break;
630 }
631 }
632 current->set_current_pending_monitor_is_from_java(true);
633 }
634
635 // NOTE: must use heavy weight monitor to handle jni monitor exit
636 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
637 JavaThread* current = THREAD;
638
639 // The ObjectMonitor* can't be async deflated until ownership is
640 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
641 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
642 // If this thread has locked the object, exit the monitor. We
643 // intentionally do not use CHECK on check_owner because we must exit the
644 // monitor even if an exception was already pending.
645 if (monitor->check_owner(THREAD)) {
646 monitor->exit(current);
647 current->dec_held_monitor_count(1, true);
648 }
649 }
650
651 // -----------------------------------------------------------------------------
652 // Internal VM locks on java objects
653 // standard constructor, allows locking failures
654 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
655 _thread = thread;
656 _thread->check_for_valid_safepoint_state();
657 _obj = obj;
658
659 if (_obj() != nullptr) {
660 ObjectSynchronizer::enter(_obj, &_lock, _thread);
661 }
662 }
663
664 ObjectLocker::~ObjectLocker() {
665 if (_obj() != nullptr) {
666 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
667 }
668 }
669
670
671 // -----------------------------------------------------------------------------
672 // Wait/Notify/NotifyAll
673 // NOTE: must use heavy weight monitor to handle wait()
674 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
675 JavaThread* current = THREAD;
676 if (millis < 0) {
677 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
678 }
679 // The ObjectMonitor* can't be async deflated because the _waiters
680 // field is incremented before ownership is dropped and decremented
681 // after ownership is regained.
682 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
683
684 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
685 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
686
687 // This dummy call is in place to get around dtrace bug 6254741. Once
688 // that's fixed we can uncomment the following line, remove the call
689 // and change this function back into a "void" func.
690 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
691 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
692 return ret_code;
693 }
694
695 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
696 JavaThread* current = THREAD;
697
698 markWord mark = obj->mark();
699 if (LockingMode == LM_LIGHTWEIGHT) {
700 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
701 // Not inflated so there can't be any waiters to notify.
702 return;
703 }
704 } else if (LockingMode == LM_LEGACY) {
705 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
706 // Not inflated so there can't be any waiters to notify.
707 return;
708 }
709 }
710 // The ObjectMonitor* can't be async deflated until ownership is
711 // dropped by the calling thread.
712 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
713 monitor->notify(CHECK);
714 }
715
716 // NOTE: see comment of notify()
717 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
718 JavaThread* current = THREAD;
719
720 markWord mark = obj->mark();
721 if (LockingMode == LM_LIGHTWEIGHT) {
722 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
723 // Not inflated so there can't be any waiters to notify.
724 return;
725 }
726 } else if (LockingMode == LM_LEGACY) {
727 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
728 // Not inflated so there can't be any waiters to notify.
729 return;
730 }
731 }
732 // The ObjectMonitor* can't be async deflated until ownership is
733 // dropped by the calling thread.
734 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
735 monitor->notifyAll(CHECK);
736 }
737
738 // -----------------------------------------------------------------------------
739 // Hash Code handling
740
741 struct SharedGlobals {
742 char _pad_prefix[OM_CACHE_LINE_SIZE];
743 // This is a highly shared mostly-read variable.
744 // To avoid false-sharing it needs to be the sole occupant of a cache line.
745 volatile int stw_random;
746 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
747 // Hot RW variable -- Sequester to avoid false-sharing
748 volatile int hc_sequence;
749 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
750 };
751
752 static SharedGlobals GVars;
753
754 static markWord read_stable_mark(oop obj) {
755 markWord mark = obj->mark_acquire();
756 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
757 // New lightweight locking does not use the markWord::INFLATING() protocol.
758 return mark; // normal fast-path return
759 }
760
761 int its = 0;
762 for (;;) {
763 markWord mark = obj->mark_acquire();
764 if (!mark.is_being_inflated()) {
765 return mark; // normal fast-path return
766 }
767
768 // The object is being inflated by some other thread.
769 // The caller of read_stable_mark() must wait for inflation to complete.
770 // Avoid live-lock.
771
772 ++its;
773 if (its > 10000 || !os::is_MP()) {
774 if (its & 1) {
775 os::naked_yield();
776 } else {
777 // Note that the following code attenuates the livelock problem but is not
778 // a complete remedy. A more complete solution would require that the inflating
779 // thread hold the associated inflation lock. The following code simply restricts
780 // the number of spinners to at most one. We'll have N-2 threads blocked
781 // on the inflationlock, 1 thread holding the inflation lock and using
782 // a yield/park strategy, and 1 thread in the midst of inflation.
783 // A more refined approach would be to change the encoding of INFLATING
784 // to allow encapsulation of a native thread pointer. Threads waiting for
785 // inflation to complete would use CAS to push themselves onto a singly linked
786 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
787 // and calling park(). When inflation was complete the thread that accomplished inflation
788 // would detach the list and set the markword to inflated with a single CAS and
789 // then for each thread on the list, set the flag and unpark() the thread.
790
791 // Index into the lock array based on the current object address.
792 static_assert(is_power_of_2(inflation_lock_count()), "must be");
793 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
794 int YieldThenBlock = 0;
795 assert(ix < inflation_lock_count(), "invariant");
796 inflation_lock(ix)->lock();
797 while (obj->mark_acquire() == markWord::INFLATING()) {
798 // Beware: naked_yield() is advisory and has almost no effect on some platforms
799 // so we periodically call current->_ParkEvent->park(1).
800 // We use a mixed spin/yield/block mechanism.
801 if ((YieldThenBlock++) >= 16) {
802 Thread::current()->_ParkEvent->park(1);
803 } else {
804 os::naked_yield();
805 }
806 }
807 inflation_lock(ix)->unlock();
808 }
809 } else {
810 SpinPause(); // SMP-polite spinning
811 }
812 }
813 }
814
815 // hashCode() generation :
816 //
817 // Possibilities:
818 // * MD5Digest of {obj,stw_random}
819 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
820 // * A DES- or AES-style SBox[] mechanism
821 // * One of the Phi-based schemes, such as:
822 // 2654435761 = 2^32 * Phi (golden ratio)
823 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
824 // * A variation of Marsaglia's shift-xor RNG scheme.
825 // * (obj ^ stw_random) is appealing, but can result
826 // in undesirable regularity in the hashCode values of adjacent objects
827 // (objects allocated back-to-back, in particular). This could potentially
828 // result in hashtable collisions and reduced hashtable efficiency.
829 // There are simple ways to "diffuse" the middle address bits over the
830 // generated hashCode values:
831
832 static inline intptr_t get_next_hash(Thread* current, oop obj) {
833 intptr_t value = 0;
834 if (hashCode == 0) {
835 // This form uses global Park-Miller RNG.
836 // On MP system we'll have lots of RW access to a global, so the
837 // mechanism induces lots of coherency traffic.
838 value = os::random();
839 } else if (hashCode == 1) {
840 // This variation has the property of being stable (idempotent)
841 // between STW operations. This can be useful in some of the 1-0
842 // synchronization schemes.
843 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
844 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
845 } else if (hashCode == 2) {
846 value = 1; // for sensitivity testing
847 } else if (hashCode == 3) {
848 value = ++GVars.hc_sequence;
849 } else if (hashCode == 4) {
850 value = cast_from_oop<intptr_t>(obj);
851 } else {
852 // Marsaglia's xor-shift scheme with thread-specific state
853 // This is probably the best overall implementation -- we'll
854 // likely make this the default in future releases.
855 unsigned t = current->_hashStateX;
856 t ^= (t << 11);
857 current->_hashStateX = current->_hashStateY;
858 current->_hashStateY = current->_hashStateZ;
859 current->_hashStateZ = current->_hashStateW;
860 unsigned v = current->_hashStateW;
861 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
862 current->_hashStateW = v;
863 value = v;
864 }
865
866 value &= markWord::hash_mask;
867 if (value == 0) value = 0xBAD;
868 assert(value != markWord::no_hash, "invariant");
869 return value;
870 }
871
872 // Can be called from non JavaThreads (e.g., VMThread) for FastHashCode
873 // calculations as part of JVM/TI tagging.
874 static bool is_lock_owned(Thread* thread, oop obj) {
875 assert(LockingMode == LM_LIGHTWEIGHT, "only call this with new lightweight locking enabled");
876 return thread->is_Java_thread() ? JavaThread::cast(thread)->lock_stack().contains(obj) : false;
877 }
878
879 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
880
881 while (true) {
882 ObjectMonitor* monitor = nullptr;
883 markWord temp, test;
884 intptr_t hash;
885 markWord mark = read_stable_mark(obj);
886 if (VerifyHeavyMonitors) {
887 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
888 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
889 }
890 if (mark.is_neutral()) { // if this is a normal header
891 hash = mark.hash();
892 if (hash != 0) { // if it has a hash, just return it
893 return hash;
894 }
895 hash = get_next_hash(current, obj); // get a new hash
896 temp = mark.copy_set_hash(hash); // merge the hash into header
897 // try to install the hash
898 test = obj->cas_set_mark(temp, mark);
899 if (test == mark) { // if the hash was installed, return it
900 return hash;
901 }
902 // Failed to install the hash. It could be that another thread
903 // installed the hash just before our attempt or inflation has
904 // occurred or... so we fall thru to inflate the monitor for
905 // stability and then install the hash.
906 } else if (mark.has_monitor()) {
907 monitor = mark.monitor();
908 temp = monitor->header();
909 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
910 hash = temp.hash();
911 if (hash != 0) {
912 // It has a hash.
913
914 // Separate load of dmw/header above from the loads in
915 // is_being_async_deflated().
916
917 // dmw/header and _contentions may get written by different threads.
918 // Make sure to observe them in the same order when having several observers.
919 OrderAccess::loadload_for_IRIW();
920
921 if (monitor->is_being_async_deflated()) {
922 // But we can't safely use the hash if we detect that async
923 // deflation has occurred. So we attempt to restore the
924 // header/dmw to the object's header so that we only retry
925 // once if the deflater thread happens to be slow.
926 monitor->install_displaced_markword_in_object(obj);
927 continue;
928 }
929 return hash;
930 }
931 // Fall thru so we only have one place that installs the hash in
932 // the ObjectMonitor.
933 } else if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked() && is_lock_owned(current, obj)) {
934 // This is a fast-lock owned by the calling thread so use the
935 // markWord from the object.
936 hash = mark.hash();
937 if (hash != 0) { // if it has a hash, just return it
938 return hash;
939 }
940 } else if (LockingMode == LM_LEGACY && mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
941 // This is a stack-lock owned by the calling thread so fetch the
942 // displaced markWord from the BasicLock on the stack.
943 temp = mark.displaced_mark_helper();
944 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
945 hash = temp.hash();
946 if (hash != 0) { // if it has a hash, just return it
947 return hash;
948 }
949 // WARNING:
950 // The displaced header in the BasicLock on a thread's stack
951 // is strictly immutable. It CANNOT be changed in ANY cases.
952 // So we have to inflate the stack-lock into an ObjectMonitor
953 // even if the current thread owns the lock. The BasicLock on
954 // a thread's stack can be asynchronously read by other threads
955 // during an inflate() call so any change to that stack memory
956 // may not propagate to other threads correctly.
957 }
958
959 // Inflate the monitor to set the hash.
960
961 // An async deflation can race after the inflate() call and before we
962 // can update the ObjectMonitor's header with the hash value below.
963 monitor = inflate(current, obj, inflate_cause_hash_code);
964 // Load ObjectMonitor's header/dmw field and see if it has a hash.
965 mark = monitor->header();
966 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
967 hash = mark.hash();
968 if (hash == 0) { // if it does not have a hash
969 hash = get_next_hash(current, obj); // get a new hash
970 temp = mark.copy_set_hash(hash) ; // merge the hash into header
971 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
972 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
973 test = markWord(v);
974 if (test != mark) {
975 // The attempt to update the ObjectMonitor's header/dmw field
976 // did not work. This can happen if another thread managed to
977 // merge in the hash just before our cmpxchg().
978 // If we add any new usages of the header/dmw field, this code
979 // will need to be updated.
980 hash = test.hash();
981 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
982 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
983 }
984 if (monitor->is_being_async_deflated()) {
985 // If we detect that async deflation has occurred, then we
986 // attempt to restore the header/dmw to the object's header
987 // so that we only retry once if the deflater thread happens
988 // to be slow.
989 monitor->install_displaced_markword_in_object(obj);
990 continue;
991 }
992 }
993 // We finally get the hash.
994 return hash;
995 }
996 }
997
998 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
999 Handle h_obj) {
1000 assert(current == JavaThread::current(), "Can only be called on current thread");
1001 oop obj = h_obj();
1002
1003 markWord mark = read_stable_mark(obj);
1004
1005 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1006 // stack-locked case, header points into owner's stack
1007 return current->is_lock_owned((address)mark.locker());
1008 }
1009
1010 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1011 // fast-locking case, see if lock is in current's lock stack
1012 return current->lock_stack().contains(h_obj());
1013 }
1014
1015 if (mark.has_monitor()) {
1016 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1017 // The first stage of async deflation does not affect any field
1018 // used by this comparison so the ObjectMonitor* is usable here.
1019 ObjectMonitor* monitor = mark.monitor();
1020 return monitor->is_entered(current) != 0;
1021 }
1022 // Unlocked case, header in place
1023 assert(mark.is_neutral(), "sanity check");
1024 return false;
1025 }
1026
1027 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1028 oop obj = h_obj();
1029 markWord mark = read_stable_mark(obj);
1030
1031 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1032 // stack-locked so header points into owner's stack.
1033 // owning_thread_from_monitor_owner() may also return null here:
1034 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1035 }
1036
1037 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1038 // fast-locked so get owner from the object.
1039 // owning_thread_from_object() may also return null here:
1040 return Threads::owning_thread_from_object(t_list, h_obj());
1041 }
1042
1043 if (mark.has_monitor()) {
1044 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1045 // The first stage of async deflation does not affect any field
1046 // used by this comparison so the ObjectMonitor* is usable here.
1047 ObjectMonitor* monitor = mark.monitor();
1048 assert(monitor != nullptr, "monitor should be non-null");
1049 // owning_thread_from_monitor() may also return null here:
1050 return Threads::owning_thread_from_monitor(t_list, monitor);
1051 }
1052
1053 // Unlocked case, header in place
1054 // Cannot have assertion since this object may have been
1055 // locked by another thread when reaching here.
1056 // assert(mark.is_neutral(), "sanity check");
1057
1058 return nullptr;
1059 }
1060
1061 // Visitors ...
1062
1063 // Iterate over all ObjectMonitors.
1064 template <typename Function>
1065 void ObjectSynchronizer::monitors_iterate(Function function) {
1066 MonitorList::Iterator iter = _in_use_list.iterator();
1067 while (iter.has_next()) {
1068 ObjectMonitor* monitor = iter.next();
1069 function(monitor);
1070 }
1071 }
1072
1073 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1074 // returns true.
1075 template <typename OwnerFilter>
1076 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1077 monitors_iterate([&](ObjectMonitor* monitor) {
1078 // This function is only called at a safepoint or when the
1079 // target thread is suspended or when the target thread is
1080 // operating on itself. The current closures in use today are
1081 // only interested in an owned ObjectMonitor and ownership
1082 // cannot be dropped under the calling contexts so the
1083 // ObjectMonitor cannot be async deflated.
1084 if (monitor->has_owner() && filter(monitor->owner_raw())) {
1085 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1086 assert(monitor->object_peek() != nullptr, "Owned monitors should not have a dead object");
1087
1088 closure->do_monitor(monitor);
1089 }
1090 });
1091 }
1092
1093 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1094 // ObjectMonitors where owner is set to a stack-lock address in thread.
1095 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1096 auto thread_filter = [&](void* owner) { return owner == thread; };
1097 return owned_monitors_iterate_filtered(closure, thread_filter);
1098 }
1099
1100 // Iterate ObjectMonitors owned by any thread.
1101 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1102 auto all_filter = [&](void* owner) { return true; };
1103 return owned_monitors_iterate_filtered(closure, all_filter);
1104 }
1105
1106 static bool monitors_used_above_threshold(MonitorList* list) {
1107 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1108 return false;
1109 }
1110 // Start with ceiling based on a per-thread estimate:
1111 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1112 size_t old_ceiling = ceiling;
1113 if (ceiling < list->max()) {
1114 // The max used by the system has exceeded the ceiling so use that:
1115 ceiling = list->max();
1116 }
1117 size_t monitors_used = list->count();
1118 if (monitors_used == 0) { // empty list is easy
1119 return false;
1120 }
1121 if (NoAsyncDeflationProgressMax != 0 &&
1122 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1123 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1124 size_t new_ceiling = ceiling + (size_t)((double)ceiling * remainder) + 1;
1125 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1126 log_info(monitorinflation)("Too many deflations without progress; "
1127 "bumping in_use_list_ceiling from " SIZE_FORMAT
1128 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1129 _no_progress_cnt = 0;
1130 ceiling = new_ceiling;
1131 }
1132
1133 // Check if our monitor usage is above the threshold:
1134 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1135 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1136 log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
1137 ", monitor_usage=" SIZE_FORMAT ", threshold=%d",
1138 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1139 return true;
1140 }
1141
1142 return false;
1143 }
1144
1145 size_t ObjectSynchronizer::in_use_list_ceiling() {
1146 return _in_use_list_ceiling;
1147 }
1148
1149 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1150 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1151 }
1152
1153 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1154 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1155 }
1156
1157 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1158 _in_use_list_ceiling = new_value;
1159 }
1160
1161 bool ObjectSynchronizer::is_async_deflation_needed() {
1162 if (is_async_deflation_requested()) {
1163 // Async deflation request.
1164 log_info(monitorinflation)("Async deflation needed: explicit request");
1165 return true;
1166 }
1167
1168 jlong time_since_last = time_since_last_async_deflation_ms();
1169
1170 if (AsyncDeflationInterval > 0 &&
1171 time_since_last > AsyncDeflationInterval &&
1172 monitors_used_above_threshold(&_in_use_list)) {
1173 // It's been longer than our specified deflate interval and there
1174 // are too many monitors in use. We don't deflate more frequently
1175 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1176 // in order to not swamp the MonitorDeflationThread.
1177 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1178 return true;
1179 }
1180
1181 if (GuaranteedAsyncDeflationInterval > 0 &&
1182 time_since_last > GuaranteedAsyncDeflationInterval) {
1183 // It's been longer than our specified guaranteed deflate interval.
1184 // We need to clean up the used monitors even if the threshold is
1185 // not reached, to keep the memory utilization at bay when many threads
1186 // touched many monitors.
1187 log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) "
1188 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1189 GuaranteedAsyncDeflationInterval, time_since_last);
1190
1191 // If this deflation has no progress, then it should not affect the no-progress
1192 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1193 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1194 // the generic code would bump the no-progress counter, and we compensate for that
1195 // by telling it to skip the update.
1196 //
1197 // If this deflation has progress, then it should let non-progress tracking
1198 // know about this, otherwise the threshold heuristics would kick in, potentially
1199 // experience no-progress due to aggressive cleanup by this deflation, and think
1200 // it is still in no-progress stride. In this "progress" case, the generic code would
1201 // zero the counter, and we allow it to happen.
1202 _no_progress_skip_increment = true;
1203
1204 return true;
1205 }
1206
1207 return false;
1208 }
1209
1210 void ObjectSynchronizer::request_deflate_idle_monitors() {
1211 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1212 set_is_async_deflation_requested(true);
1213 ml.notify_all();
1214 }
1215
1216 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1217 JavaThread* current = JavaThread::current();
1218 bool ret_code = false;
1219
1220 jlong last_time = last_async_deflation_time_ns();
1221
1222 request_deflate_idle_monitors();
1223
1224 const int N_CHECKS = 5;
1225 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1226 if (last_async_deflation_time_ns() > last_time) {
1227 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1228 ret_code = true;
1229 break;
1230 }
1231 {
1232 // JavaThread has to honor the blocking protocol.
1233 ThreadBlockInVM tbivm(current);
1234 os::naked_short_sleep(999); // sleep for almost 1 second
1235 }
1236 }
1237 if (!ret_code) {
1238 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1239 }
1240
1241 return ret_code;
1242 }
1243
1244 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1245 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1246 }
1247
1248 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1249 const oop obj,
1250 ObjectSynchronizer::InflateCause cause) {
1251 assert(event != nullptr, "invariant");
1252 event->set_monitorClass(obj->klass());
1253 event->set_address((uintptr_t)(void*)obj);
1254 event->set_cause((u1)cause);
1255 event->commit();
1256 }
1257
1258 // Fast path code shared by multiple functions
1259 void ObjectSynchronizer::inflate_helper(oop obj) {
1260 markWord mark = obj->mark_acquire();
1261 if (mark.has_monitor()) {
1262 ObjectMonitor* monitor = mark.monitor();
1263 markWord dmw = monitor->header();
1264 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1265 return;
1266 }
1267 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1268 }
1269
1270 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1271 const InflateCause cause) {
1272 EventJavaMonitorInflate event;
1273
1274 for (;;) {
1275 const markWord mark = object->mark_acquire();
1276
1277 // The mark can be in one of the following states:
1278 // * inflated - Just return if using stack-locking.
1279 // If using fast-locking and the ObjectMonitor owner
1280 // is anonymous and the current thread owns the
1281 // object lock, then we make the current thread the
1282 // ObjectMonitor owner and remove the lock from the
1283 // current thread's lock stack.
1284 // * fast-locked - Coerce it to inflated from fast-locked.
1285 // * stack-locked - Coerce it to inflated from stack-locked.
1286 // * INFLATING - Busy wait for conversion from stack-locked to
1287 // inflated.
1288 // * neutral - Aggressively inflate the object.
1289
1290 // CASE: inflated
1291 if (mark.has_monitor()) {
1292 ObjectMonitor* inf = mark.monitor();
1293 markWord dmw = inf->header();
1294 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1295 if (LockingMode == LM_LIGHTWEIGHT && inf->is_owner_anonymous() && is_lock_owned(current, object)) {
1296 inf->set_owner_from_anonymous(current);
1297 JavaThread::cast(current)->lock_stack().remove(object);
1298 }
1299 return inf;
1300 }
1301
1302 if (LockingMode != LM_LIGHTWEIGHT) {
1303 // New lightweight locking does not use INFLATING.
1304 // CASE: inflation in progress - inflating over a stack-lock.
1305 // Some other thread is converting from stack-locked to inflated.
1306 // Only that thread can complete inflation -- other threads must wait.
1307 // The INFLATING value is transient.
1308 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1309 // We could always eliminate polling by parking the thread on some auxiliary list.
1310 if (mark == markWord::INFLATING()) {
1311 read_stable_mark(object);
1312 continue;
1313 }
1314 }
1315
1316 // CASE: fast-locked
1317 // Could be fast-locked either by current or by some other thread.
1318 //
1319 // Note that we allocate the ObjectMonitor speculatively, _before_
1320 // attempting to set the object's mark to the new ObjectMonitor. If
1321 // this thread owns the monitor, then we set the ObjectMonitor's
1322 // owner to this thread. Otherwise, we set the ObjectMonitor's owner
1323 // to anonymous. If we lose the race to set the object's mark to the
1324 // new ObjectMonitor, then we just delete it and loop around again.
1325 //
1326 LogStreamHandle(Trace, monitorinflation) lsh;
1327 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1328 ObjectMonitor* monitor = new ObjectMonitor(object);
1329 monitor->set_header(mark.set_unlocked());
1330 bool own = is_lock_owned(current, object);
1331 if (own) {
1332 // Owned by us.
1333 monitor->set_owner_from(nullptr, current);
1334 } else {
1335 // Owned by somebody else.
1336 monitor->set_owner_anonymous();
1337 }
1338 markWord monitor_mark = markWord::encode(monitor);
1339 markWord old_mark = object->cas_set_mark(monitor_mark, mark);
1340 if (old_mark == mark) {
1341 // Success! Return inflated monitor.
1342 if (own) {
1343 JavaThread::cast(current)->lock_stack().remove(object);
1344 }
1345 // Once the ObjectMonitor is configured and object is associated
1346 // with the ObjectMonitor, it is safe to allow async deflation:
1347 _in_use_list.add(monitor);
1348
1349 // Hopefully the performance counters are allocated on distinct
1350 // cache lines to avoid false sharing on MP systems ...
1351 OM_PERFDATA_OP(Inflations, inc());
1352 if (log_is_enabled(Trace, monitorinflation)) {
1353 ResourceMark rm(current);
1354 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1355 INTPTR_FORMAT ", type='%s'", p2i(object),
1356 object->mark().value(), object->klass()->external_name());
1357 }
1358 if (event.should_commit()) {
1359 post_monitor_inflate_event(&event, object, cause);
1360 }
1361 return monitor;
1362 } else {
1363 delete monitor;
1364 continue; // Interference -- just retry
1365 }
1366 }
1367
1368 // CASE: stack-locked
1369 // Could be stack-locked either by current or by some other thread.
1370 //
1371 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1372 // to install INFLATING into the mark word. We originally installed INFLATING,
1373 // allocated the ObjectMonitor, and then finally STed the address of the
1374 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1375 // the interval in which INFLATING appeared in the mark, thus increasing
1376 // the odds of inflation contention. If we lose the race to set INFLATING,
1377 // then we just delete the ObjectMonitor and loop around again.
1378 //
1379 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1380 assert(LockingMode != LM_LIGHTWEIGHT, "cannot happen with new lightweight locking");
1381 ObjectMonitor* m = new ObjectMonitor(object);
1382 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1383 // We do this before the CAS in order to minimize the length of time
1384 // in which INFLATING appears in the mark.
1385
1386 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1387 if (cmp != mark) {
1388 delete m;
1389 continue; // Interference -- just retry
1390 }
1391
1392 // We've successfully installed INFLATING (0) into the mark-word.
1393 // This is the only case where 0 will appear in a mark-word.
1394 // Only the singular thread that successfully swings the mark-word
1395 // to 0 can perform (or more precisely, complete) inflation.
1396 //
1397 // Why do we CAS a 0 into the mark-word instead of just CASing the
1398 // mark-word from the stack-locked value directly to the new inflated state?
1399 // Consider what happens when a thread unlocks a stack-locked object.
1400 // It attempts to use CAS to swing the displaced header value from the
1401 // on-stack BasicLock back into the object header. Recall also that the
1402 // header value (hash code, etc) can reside in (a) the object header, or
1403 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1404 // header in an ObjectMonitor. The inflate() routine must copy the header
1405 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1406 // the while preserving the hashCode stability invariants. If the owner
1407 // decides to release the lock while the value is 0, the unlock will fail
1408 // and control will eventually pass from slow_exit() to inflate. The owner
1409 // will then spin, waiting for the 0 value to disappear. Put another way,
1410 // the 0 causes the owner to stall if the owner happens to try to
1411 // drop the lock (restoring the header from the BasicLock to the object)
1412 // while inflation is in-progress. This protocol avoids races that might
1413 // would otherwise permit hashCode values to change or "flicker" for an object.
1414 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1415 // 0 serves as a "BUSY" inflate-in-progress indicator.
1416
1417
1418 // fetch the displaced mark from the owner's stack.
1419 // The owner can't die or unwind past the lock while our INFLATING
1420 // object is in the mark. Furthermore the owner can't complete
1421 // an unlock on the object, either.
1422 markWord dmw = mark.displaced_mark_helper();
1423 // Catch if the object's header is not neutral (not locked and
1424 // not marked is what we care about here).
1425 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1426
1427 // Setup monitor fields to proper values -- prepare the monitor
1428 m->set_header(dmw);
1429
1430 // Optimization: if the mark.locker stack address is associated
1431 // with this thread we could simply set m->_owner = current.
1432 // Note that a thread can inflate an object
1433 // that it has stack-locked -- as might happen in wait() -- directly
1434 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1435 m->set_owner_from(nullptr, mark.locker());
1436 // TODO-FIXME: assert BasicLock->dhw != 0.
1437
1438 // Must preserve store ordering. The monitor state must
1439 // be stable at the time of publishing the monitor address.
1440 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1441 // Release semantics so that above set_object() is seen first.
1442 object->release_set_mark(markWord::encode(m));
1443
1444 // Once ObjectMonitor is configured and the object is associated
1445 // with the ObjectMonitor, it is safe to allow async deflation:
1446 _in_use_list.add(m);
1447
1448 // Hopefully the performance counters are allocated on distinct cache lines
1449 // to avoid false sharing on MP systems ...
1450 OM_PERFDATA_OP(Inflations, inc());
1451 if (log_is_enabled(Trace, monitorinflation)) {
1452 ResourceMark rm(current);
1453 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1454 INTPTR_FORMAT ", type='%s'", p2i(object),
1455 object->mark().value(), object->klass()->external_name());
1456 }
1457 if (event.should_commit()) {
1458 post_monitor_inflate_event(&event, object, cause);
1459 }
1460 return m;
1461 }
1462
1463 // CASE: neutral
1464 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1465 // If we know we're inflating for entry it's better to inflate by swinging a
1466 // pre-locked ObjectMonitor pointer into the object header. A successful
1467 // CAS inflates the object *and* confers ownership to the inflating thread.
1468 // In the current implementation we use a 2-step mechanism where we CAS()
1469 // to inflate and then CAS() again to try to swing _owner from null to current.
1470 // An inflateTry() method that we could call from enter() would be useful.
1471
1472 // Catch if the object's header is not neutral (not locked and
1473 // not marked is what we care about here).
1474 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1475 ObjectMonitor* m = new ObjectMonitor(object);
1476 // prepare m for installation - set monitor to initial state
1477 m->set_header(mark);
1478
1479 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1480 delete m;
1481 m = nullptr;
1482 continue;
1483 // interference - the markword changed - just retry.
1484 // The state-transitions are one-way, so there's no chance of
1485 // live-lock -- "Inflated" is an absorbing state.
1486 }
1487
1488 // Once the ObjectMonitor is configured and object is associated
1489 // with the ObjectMonitor, it is safe to allow async deflation:
1490 _in_use_list.add(m);
1491
1492 // Hopefully the performance counters are allocated on distinct
1493 // cache lines to avoid false sharing on MP systems ...
1494 OM_PERFDATA_OP(Inflations, inc());
1495 if (log_is_enabled(Trace, monitorinflation)) {
1496 ResourceMark rm(current);
1497 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1498 INTPTR_FORMAT ", type='%s'", p2i(object),
1499 object->mark().value(), object->klass()->external_name());
1500 }
1501 if (event.should_commit()) {
1502 post_monitor_inflate_event(&event, object, cause);
1503 }
1504 return m;
1505 }
1506 }
1507
1508 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1509 const char* cnt_name, size_t cnt,
1510 LogStream* ls, elapsedTimer* timer_p) {
1511 if (!SafepointMechanism::should_process(current)) {
1512 return;
1513 }
1514
1515 // A safepoint/handshake has started.
1516 if (ls != nullptr) {
1517 timer_p->stop();
1518 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1519 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1520 op_name, cnt_name, cnt, in_use_list_ceiling(),
1521 _in_use_list.count(), _in_use_list.max());
1522 }
1523
1524 {
1525 // Honor block request.
1526 ThreadBlockInVM tbivm(current);
1527 }
1528
1529 if (ls != nullptr) {
1530 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1531 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1532 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1533 timer_p->start();
1534 }
1535 }
1536
1537 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1538 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1539 //
1540 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1541 elapsedTimer* timer_p) {
1542 MonitorList::Iterator iter = _in_use_list.iterator();
1543 size_t deflated_count = 0;
1544
1545 while (iter.has_next()) {
1546 if (deflated_count >= (size_t)MonitorDeflationMax) {
1547 break;
1548 }
1549 ObjectMonitor* mid = iter.next();
1550 if (mid->deflate_monitor()) {
1551 deflated_count++;
1552 }
1553
1554 if (current->is_Java_thread()) {
1555 // A JavaThread must check for a safepoint/handshake and honor it.
1556 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1557 deflated_count, ls, timer_p);
1558 }
1559 }
1560
1561 return deflated_count;
1562 }
1563
1564 class HandshakeForDeflation : public HandshakeClosure {
1565 public:
1566 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1567
1568 void do_thread(Thread* thread) {
1569 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1570 INTPTR_FORMAT, p2i(thread));
1571 }
1572 };
1573
1574 class VM_RendezvousGCThreads : public VM_Operation {
1575 public:
1576 bool evaluate_at_safepoint() const override { return false; }
1577 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1578 void doit() override {
1579 Universe::heap()->safepoint_synchronize_begin();
1580 Universe::heap()->safepoint_synchronize_end();
1581 };
1582 };
1583
1584 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list) {
1585 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1586 size_t count = 0;
1587 for (ObjectMonitor* monitor: *delete_list) {
1588 delete monitor;
1589 count++;
1590 }
1591 return count;
1592 }
1593
1594 // This function is called by the MonitorDeflationThread to deflate
1595 // ObjectMonitors.
1596 size_t ObjectSynchronizer::deflate_idle_monitors() {
1597 Thread* current = Thread::current();
1598 if (current->is_Java_thread()) {
1599 // The async deflation request has been processed.
1600 _last_async_deflation_time_ns = os::javaTimeNanos();
1601 set_is_async_deflation_requested(false);
1602 }
1603
1604 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1605 LogStreamHandle(Info, monitorinflation) lsh_info;
1606 LogStream* ls = nullptr;
1607 if (log_is_enabled(Debug, monitorinflation)) {
1608 ls = &lsh_debug;
1609 } else if (log_is_enabled(Info, monitorinflation)) {
1610 ls = &lsh_info;
1611 }
1612
1613 elapsedTimer timer;
1614 if (ls != nullptr) {
1615 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1616 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1617 timer.start();
1618 }
1619
1620 // Deflate some idle ObjectMonitors.
1621 size_t deflated_count = deflate_monitor_list(current, ls, &timer);
1622 size_t unlinked_count = 0;
1623 size_t deleted_count = 0;
1624 if (deflated_count > 0) {
1625 // There are ObjectMonitors that have been deflated.
1626
1627 // Unlink deflated ObjectMonitors from the in-use list.
1628 ResourceMark rm;
1629 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1630 unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, &delete_list);
1631 if (current->is_monitor_deflation_thread()) {
1632 if (ls != nullptr) {
1633 timer.stop();
1634 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1635 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1636 SIZE_FORMAT ", max=" SIZE_FORMAT,
1637 unlinked_count, in_use_list_ceiling(),
1638 _in_use_list.count(), _in_use_list.max());
1639 }
1640
1641 // A JavaThread needs to handshake in order to safely free the
1642 // ObjectMonitors that were deflated in this cycle.
1643 HandshakeForDeflation hfd_hc;
1644 Handshake::execute(&hfd_hc);
1645 // Also, we sync and desync GC threads around the handshake, so that they can
1646 // safely read the mark-word and look-through to the object-monitor, without
1647 // being afraid that the object-monitor is going away.
1648 VM_RendezvousGCThreads sync_gc;
1649 VMThread::execute(&sync_gc);
1650
1651 if (ls != nullptr) {
1652 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1653 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1654 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1655 timer.start();
1656 }
1657 } else {
1658 // This is not a monitor deflation thread.
1659 // No handshake or rendezvous is needed when we are already at safepoint.
1660 assert_at_safepoint();
1661 }
1662
1663 // After the handshake, safely free the ObjectMonitors that were
1664 // deflated and unlinked in this cycle.
1665 if (current->is_Java_thread()) {
1666 if (ls != NULL) {
1667 timer.stop();
1668 ls->print_cr("before setting blocked: unlinked_count=" SIZE_FORMAT
1669 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1670 SIZE_FORMAT ", max=" SIZE_FORMAT,
1671 unlinked_count, in_use_list_ceiling(),
1672 _in_use_list.count(), _in_use_list.max());
1673 }
1674 // Mark the calling JavaThread blocked (safepoint safe) while we free
1675 // the ObjectMonitors so we don't delay safepoints whilst doing that.
1676 ThreadBlockInVM tbivm(JavaThread::cast(current));
1677 if (ls != NULL) {
1678 ls->print_cr("after setting blocked: in_use_list stats: ceiling="
1679 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1680 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1681 timer.start();
1682 }
1683 deleted_count = delete_monitors(&delete_list);
1684 // ThreadBlockInVM is destroyed here
1685 } else {
1686 // A non-JavaThread can just free the ObjectMonitors:
1687 deleted_count = delete_monitors(&delete_list);
1688 }
1689 assert(unlinked_count == deleted_count, "must be");
1690 }
1691
1692 if (ls != nullptr) {
1693 timer.stop();
1694 if (deflated_count != 0 || unlinked_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1695 ls->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1696 deflated_count, unlinked_count, timer.seconds());
1697 }
1698 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1699 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1700 }
1701
1702 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1703 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1704
1705 GVars.stw_random = os::random();
1706
1707 if (deflated_count != 0) {
1708 _no_progress_cnt = 0;
1709 } else if (_no_progress_skip_increment) {
1710 _no_progress_skip_increment = false;
1711 } else {
1712 _no_progress_cnt++;
1713 }
1714
1715 return deflated_count;
1716 }
1717
1718 // Monitor cleanup on JavaThread::exit
1719
1720 // Iterate through monitor cache and attempt to release thread's monitors
1721 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1722 private:
1723 JavaThread* _thread;
1724
1725 public:
1726 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1727 void do_monitor(ObjectMonitor* mid) {
1728 intx rec = mid->complete_exit(_thread);
1729 _thread->dec_held_monitor_count(rec + 1);
1730 }
1731 };
1732
1733 // Release all inflated monitors owned by current thread. Lightweight monitors are
1734 // ignored. This is meant to be called during JNI thread detach which assumes
1735 // all remaining monitors are heavyweight. All exceptions are swallowed.
1736 // Scanning the extant monitor list can be time consuming.
1737 // A simple optimization is to add a per-thread flag that indicates a thread
1738 // called jni_monitorenter() during its lifetime.
1739 //
1740 // Instead of NoSafepointVerifier it might be cheaper to
1741 // use an idiom of the form:
1742 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1743 // <code that must not run at safepoint>
1744 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1745 // Since the tests are extremely cheap we could leave them enabled
1746 // for normal product builds.
1747
1748 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1749 assert(current == JavaThread::current(), "must be current Java thread");
1750 NoSafepointVerifier nsv;
1751 ReleaseJavaMonitorsClosure rjmc(current);
1752 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1753 assert(!current->has_pending_exception(), "Should not be possible");
1754 current->clear_pending_exception();
1755 assert(current->held_monitor_count() == 0, "Should not be possible");
1756 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1757 current->clear_jni_monitor_count();
1758 }
1759
1760 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1761 switch (cause) {
1762 case inflate_cause_vm_internal: return "VM Internal";
1763 case inflate_cause_monitor_enter: return "Monitor Enter";
1764 case inflate_cause_wait: return "Monitor Wait";
1765 case inflate_cause_notify: return "Monitor Notify";
1766 case inflate_cause_hash_code: return "Monitor Hash Code";
1767 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1768 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1769 default:
1770 ShouldNotReachHere();
1771 }
1772 return "Unknown";
1773 }
1774
1775 //------------------------------------------------------------------------------
1776 // Debugging code
1777
1778 u_char* ObjectSynchronizer::get_gvars_addr() {
1779 return (u_char*)&GVars;
1780 }
1781
1782 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1783 return (u_char*)&GVars.hc_sequence;
1784 }
1785
1786 size_t ObjectSynchronizer::get_gvars_size() {
1787 return sizeof(SharedGlobals);
1788 }
1789
1790 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1791 return (u_char*)&GVars.stw_random;
1792 }
1793
1794 // Do the final audit and print of ObjectMonitor stats; must be done
1795 // by the VMThread at VM exit time.
1796 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1797 assert(Thread::current()->is_VM_thread(), "sanity check");
1798
1799 if (is_final_audit()) { // Only do the audit once.
1800 return;
1801 }
1802 set_is_final_audit();
1803 log_info(monitorinflation)("Starting the final audit.");
1804
1805 if (log_is_enabled(Info, monitorinflation)) {
1806 // The other audit_and_print_stats() call is done at the Debug
1807 // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
1808 audit_and_print_stats(true /* on_exit */);
1809 }
1810 }
1811
1812 // This function can be called at a safepoint or it can be called when
1813 // we are trying to exit the VM. When we are trying to exit the VM, the
1814 // list walker functions can run in parallel with the other list
1815 // operations so spin-locking is used for safety.
1816 //
1817 // Calls to this function can be added in various places as a debugging
1818 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1819 // details logged at the Info level and 'false' for the 'on_exit'
1820 // parameter to have in-use monitor details logged at the Trace level.
1821 //
1822 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1823 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1824
1825 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1826 LogStreamHandle(Info, monitorinflation) lsh_info;
1827 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1828 LogStream* ls = nullptr;
1829 if (log_is_enabled(Trace, monitorinflation)) {
1830 ls = &lsh_trace;
1831 } else if (log_is_enabled(Debug, monitorinflation)) {
1832 ls = &lsh_debug;
1833 } else if (log_is_enabled(Info, monitorinflation)) {
1834 ls = &lsh_info;
1835 }
1836 assert(ls != nullptr, "sanity check");
1837
1838 int error_cnt = 0;
1839
1840 ls->print_cr("Checking in_use_list:");
1841 chk_in_use_list(ls, &error_cnt);
1842
1843 if (error_cnt == 0) {
1844 ls->print_cr("No errors found in in_use_list checks.");
1845 } else {
1846 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1847 }
1848
1849 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1850 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1851 // When exiting this log output is at the Info level. When called
1852 // at a safepoint, this log output is at the Trace level since
1853 // there can be a lot of it.
1854 log_in_use_monitor_details(ls, !on_exit /* log_all */);
1855 }
1856
1857 ls->flush();
1858
1859 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1860 }
1861
1862 // Check the in_use_list; log the results of the checks.
1863 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1864 size_t l_in_use_count = _in_use_list.count();
1865 size_t l_in_use_max = _in_use_list.max();
1866 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1867 l_in_use_max);
1868
1869 size_t ck_in_use_count = 0;
1870 MonitorList::Iterator iter = _in_use_list.iterator();
1871 while (iter.has_next()) {
1872 ObjectMonitor* mid = iter.next();
1873 chk_in_use_entry(mid, out, error_cnt_p);
1874 ck_in_use_count++;
1875 }
1876
1877 if (l_in_use_count == ck_in_use_count) {
1878 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1879 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1880 } else {
1881 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1882 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1883 ck_in_use_count);
1884 }
1885
1886 size_t ck_in_use_max = _in_use_list.max();
1887 if (l_in_use_max == ck_in_use_max) {
1888 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1889 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1890 } else {
1891 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1892 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1893 }
1894 }
1895
1896 // Check an in-use monitor entry; log any errors.
1897 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1898 int* error_cnt_p) {
1899 if (n->owner_is_DEFLATER_MARKER()) {
1900 // This should not happen, but if it does, it is not fatal.
1901 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1902 "deflated.", p2i(n));
1903 return;
1904 }
1905 if (n->header().value() == 0) {
1906 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1907 "have non-null _header field.", p2i(n));
1908 *error_cnt_p = *error_cnt_p + 1;
1909 }
1910 const oop obj = n->object_peek();
1911 if (obj != nullptr) {
1912 const markWord mark = obj->mark();
1913 if (!mark.has_monitor()) {
1914 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1915 "object does not think it has a monitor: obj="
1916 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1917 p2i(obj), mark.value());
1918 *error_cnt_p = *error_cnt_p + 1;
1919 }
1920 ObjectMonitor* const obj_mon = mark.monitor();
1921 if (n != obj_mon) {
1922 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1923 "object does not refer to the same monitor: obj="
1924 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1925 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1926 *error_cnt_p = *error_cnt_p + 1;
1927 }
1928 }
1929 }
1930
1931 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1932 // flags indicate why the entry is in-use, 'object' and 'object type'
1933 // indicate the associated object and its type.
1934 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
1935 if (_in_use_list.count() > 0) {
1936 stringStream ss;
1937 out->print_cr("In-use monitor info:");
1938 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1939 out->print_cr("%18s %s %18s %18s",
1940 "monitor", "BHL", "object", "object type");
1941 out->print_cr("================== === ================== ==================");
1942
1943 auto is_interesting = [&](ObjectMonitor* monitor) {
1944 return log_all || monitor->has_owner() || monitor->is_busy();
1945 };
1946
1947 monitors_iterate([&](ObjectMonitor* monitor) {
1948 if (is_interesting(monitor)) {
1949 const oop obj = monitor->object_peek();
1950 const markWord mark = monitor->header();
1951 ResourceMark rm;
1952 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
1953 monitor->is_busy(), mark.hash() != 0, monitor->owner() != nullptr,
1954 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
1955 if (monitor->is_busy()) {
1956 out->print(" (%s)", monitor->is_busy_to_string(&ss));
1957 ss.reset();
1958 }
1959 out->cr();
1960 }
1961 });
1962 }
1963
1964 out->flush();
1965 }