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