1 /*
2 * Copyright (c) 1998, 2021, 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 "jfr/jfrEvents.hpp"
28 #include "gc/shared/suspendibleThreadSet.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/biasedLocking.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/handshake.hpp"
41 #include "runtime/interfaceSupport.inline.hpp"
42 #include "runtime/lockStack.inline.hpp"
43 #include "runtime/mutexLocker.hpp"
44 #include "runtime/objectMonitor.hpp"
45 #include "runtime/objectMonitor.inline.hpp"
46 #include "runtime/os.inline.hpp"
47 #include "runtime/osThread.hpp"
48 #include "runtime/perfData.hpp"
49 #include "runtime/safepointMechanism.inline.hpp"
50 #include "runtime/safepointVerifiers.hpp"
51 #include "runtime/sharedRuntime.hpp"
52 #include "runtime/stubRoutines.hpp"
53 #include "runtime/synchronizer.hpp"
54 #include "runtime/thread.inline.hpp"
55 #include "runtime/timer.hpp"
56 #include "runtime/vframe.hpp"
57 #include "runtime/vmThread.hpp"
58 #include "utilities/align.hpp"
59 #include "utilities/dtrace.hpp"
60 #include "utilities/events.hpp"
61 #include "utilities/preserveException.hpp"
62
63 void MonitorList::add(ObjectMonitor* m) {
64 ObjectMonitor* head;
65 do {
66 head = Atomic::load(&_head);
67 m->set_next_om(head);
68 } while (Atomic::cmpxchg(&_head, head, m) != head);
69
70 size_t count = Atomic::add(&_count, 1u);
71 if (count > max()) {
72 Atomic::inc(&_max);
73 }
74 }
75
76 size_t MonitorList::count() const {
77 return Atomic::load(&_count);
78 }
79
80 size_t MonitorList::max() const {
81 return Atomic::load(&_max);
82 }
83
84 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
85 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
86 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
87 elapsedTimer* timer_p,
88 GrowableArray<ObjectMonitor*>* unlinked_list) {
89 size_t unlinked_count = 0;
90 ObjectMonitor* prev = NULL;
91 ObjectMonitor* head = Atomic::load_acquire(&_head);
92 ObjectMonitor* m = head;
93 // The in-use list head can be NULL during the final audit.
94 while (m != NULL) {
95 if (m->is_being_async_deflated()) {
96 // Find next live ObjectMonitor.
97 ObjectMonitor* next = m;
98 do {
99 ObjectMonitor* next_next = next->next_om();
100 unlinked_count++;
101 unlinked_list->append(next);
102 next = next_next;
103 if (unlinked_count >= (size_t)MonitorDeflationMax) {
104 // Reached the max so bail out on the gathering loop.
105 break;
106 }
107 } while (next != NULL && next->is_being_async_deflated());
108 if (prev == NULL) {
109 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
110 if (prev_head != head) {
111 // Find new prev ObjectMonitor that just got inserted.
112 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
113 prev = n;
114 }
115 prev->set_next_om(next);
116 }
117 } else {
118 prev->set_next_om(next);
119 }
120 if (unlinked_count >= (size_t)MonitorDeflationMax) {
121 // Reached the max so bail out on the searching loop.
122 break;
123 }
124 m = next;
125 } else {
126 prev = m;
127 m = m->next_om();
128 }
129
130 if (current->is_Java_thread()) {
131 // A JavaThread must check for a safepoint/handshake and honor it.
132 ObjectSynchronizer::chk_for_block_req(current->as_Java_thread(), "unlinking",
133 "unlinked_count", unlinked_count,
134 ls, timer_p);
135 }
136 }
137 Atomic::sub(&_count, unlinked_count);
138 return unlinked_count;
139 }
140
141 MonitorList::Iterator MonitorList::iterator() const {
142 return Iterator(Atomic::load_acquire(&_head));
143 }
144
145 ObjectMonitor* MonitorList::Iterator::next() {
146 ObjectMonitor* current = _current;
147 _current = current->next_om();
148 return current;
149 }
150
151 // The "core" versions of monitor enter and exit reside in this file.
152 // The interpreter and compilers contain specialized transliterated
153 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
154 // fast_lock(...) for instance. If you make changes here, make sure to modify the
155 // interpreter, and both C1 and C2 fast-path inline locking code emission.
156 //
157 // -----------------------------------------------------------------------------
158
159 #ifdef DTRACE_ENABLED
160
161 // Only bother with this argument setup if dtrace is available
162 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
163
164 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
165 char* bytes = NULL; \
166 int len = 0; \
167 jlong jtid = SharedRuntime::get_java_tid(thread); \
168 Symbol* klassname = obj->klass()->name(); \
169 if (klassname != NULL) { \
170 bytes = (char*)klassname->bytes(); \
171 len = klassname->utf8_length(); \
172 }
173
174 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
175 { \
176 if (DTraceMonitorProbes) { \
177 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
178 HOTSPOT_MONITOR_WAIT(jtid, \
179 (uintptr_t)(monitor), bytes, len, (millis)); \
180 } \
181 }
182
183 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
184 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
185 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
186
187 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
188 { \
189 if (DTraceMonitorProbes) { \
190 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
191 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
192 (uintptr_t)(monitor), bytes, len); \
193 } \
194 }
195
196 #else // ndef DTRACE_ENABLED
197
198 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
199 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
200
201 #endif // ndef DTRACE_ENABLED
202
203 // This exists only as a workaround of dtrace bug 6254741
204 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
205 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
206 return 0;
207 }
208
209 static const int NINFLATIONLOCKS = 256;
210 static os::PlatformMutex* gInflationLocks[NINFLATIONLOCKS];
211
212 void ObjectSynchronizer::initialize() {
213 for (int i = 0; i < NINFLATIONLOCKS; i++) {
214 gInflationLocks[i] = new os::PlatformMutex();
215 }
216 // Start the ceiling with the estimate for one thread.
217 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
218
219 // Start the timer for deflations, so it does not trigger immediately.
220 _last_async_deflation_time_ns = os::javaTimeNanos();
221 }
222
223 MonitorList ObjectSynchronizer::_in_use_list;
224 // monitors_used_above_threshold() policy is as follows:
225 //
226 // The ratio of the current _in_use_list count to the ceiling is used
227 // to determine if we are above MonitorUsedDeflationThreshold and need
228 // to do an async monitor deflation cycle. The ceiling is increased by
229 // AvgMonitorsPerThreadEstimate when a thread is added to the system
230 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
231 // removed from the system.
232 //
233 // Note: If the _in_use_list max exceeds the ceiling, then
234 // monitors_used_above_threshold() will use the in_use_list max instead
235 // of the thread count derived ceiling because we have used more
236 // ObjectMonitors than the estimated average.
237 //
238 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
239 // no-progress async monitor deflation cycles in a row, then the ceiling
240 // is adjusted upwards by monitors_used_above_threshold().
241 //
242 // Start the ceiling with the estimate for one thread in initialize()
243 // which is called after cmd line options are processed.
244 static size_t _in_use_list_ceiling = 0;
245 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
246 bool volatile ObjectSynchronizer::_is_final_audit = false;
247 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
248 static uintx _no_progress_cnt = 0;
249 static bool _no_progress_skip_increment = false;
250
251 // =====================> Quick functions
252
253 // The quick_* forms are special fast-path variants used to improve
254 // performance. In the simplest case, a "quick_*" implementation could
255 // simply return false, in which case the caller will perform the necessary
256 // state transitions and call the slow-path form.
257 // The fast-path is designed to handle frequently arising cases in an efficient
258 // manner and is just a degenerate "optimistic" variant of the slow-path.
259 // returns true -- to indicate the call was satisfied.
260 // returns false -- to indicate the call needs the services of the slow-path.
261 // A no-loitering ordinance is in effect for code in the quick_* family
262 // operators: safepoints or indefinite blocking (blocking that might span a
263 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
264 // entry.
265 //
266 // Consider: An interesting optimization is to have the JIT recognize the
267 // following common idiom:
268 // synchronized (someobj) { .... ; notify(); }
269 // That is, we find a notify() or notifyAll() call that immediately precedes
270 // the monitorexit operation. In that case the JIT could fuse the operations
271 // into a single notifyAndExit() runtime primitive.
272
273 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
274 assert(current->thread_state() == _thread_in_Java, "invariant");
275 NoSafepointVerifier nsv;
276 if (obj == NULL) return false; // slow-path for invalid obj
277 const markWord mark = obj->mark();
278
279 if (LockingMode == LM_LIGHTWEIGHT) {
280 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
281 // Degenerate notify
282 // fast-locked by caller so by definition the implied waitset is empty.
283 return true;
284 }
285 } else if (LockingMode == LM_LEGACY) {
286 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
287 // Degenerate notify
288 // stack-locked by caller so by definition the implied waitset is empty.
289 return true;
290 }
291 }
292
293 if (mark.has_monitor()) {
294 ObjectMonitor* const mon = mark.monitor();
295 assert(mon->object() == oop(obj), "invariant");
296 if (mon->owner() != current) return false; // slow-path for IMS exception
297
298 if (mon->first_waiter() != NULL) {
299 // We have one or more waiters. Since this is an inflated monitor
300 // that we own, we can transfer one or more threads from the waitset
301 // to the entrylist here and now, avoiding the slow-path.
302 if (all) {
303 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
304 } else {
305 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
306 }
307 int free_count = 0;
308 do {
309 mon->INotify(current);
310 ++free_count;
311 } while (mon->first_waiter() != NULL && all);
312 OM_PERFDATA_OP(Notifications, inc(free_count));
313 }
314 return true;
315 }
316
317 // biased locking and any other IMS exception states take the slow-path
318 return false;
319 }
320
321
322 // The LockNode emitted directly at the synchronization site would have
323 // been too big if it were to have included support for the cases of inflated
324 // recursive enter and exit, so they go here instead.
325 // Note that we can't safely call AsyncPrintJavaStack() from within
326 // quick_enter() as our thread state remains _in_Java.
327
328 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
329 BasicLock * lock) {
330 assert(current->thread_state() == _thread_in_Java, "invariant");
331 NoSafepointVerifier nsv;
332 if (obj == NULL) return false; // Need to throw NPE
333
334 if (obj->klass()->is_value_based()) {
335 return false;
336 }
337
338 const markWord mark = obj->mark();
339
340 if (mark.has_monitor()) {
341 ObjectMonitor* const m = mark.monitor();
342 // An async deflation or GC can race us before we manage to make
343 // the ObjectMonitor busy by setting the owner below. If we detect
344 // that race we just bail out to the slow-path here.
345 if (m->object_peek() == NULL) {
346 return false;
347 }
348 JavaThread* const owner = (JavaThread*) m->owner_raw();
349
350 // Lock contention and Transactional Lock Elision (TLE) diagnostics
351 // and observability
352 // Case: light contention possibly amenable to TLE
353 // Case: TLE inimical operations such as nested/recursive synchronization
354
355 if (owner == current) {
356 m->_recursions++;
357 return true;
358 }
359
360 if (LockingMode != LM_LIGHTWEIGHT) {
361 // This Java Monitor is inflated so obj's header will never be
362 // displaced to this thread's BasicLock. Make the displaced header
363 // non-NULL so this BasicLock is not seen as recursive nor as
364 // being locked. We do this unconditionally so that this thread's
365 // BasicLock cannot be mis-interpreted by any stack walkers. For
366 // performance reasons, stack walkers generally first check for
367 // Biased Locking in the object's header, the second check is for
368 // stack-locking in the object's header, the third check is for
369 // recursive stack-locking in the displaced header in the BasicLock,
370 // and last are the inflated Java Monitor (ObjectMonitor) checks.
371 lock->set_displaced_header(markWord::unused_mark());
372 }
373
374 if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
375 assert(m->_recursions == 0, "invariant");
376 return true;
377 }
378 }
379
380 // Note that we could inflate in quick_enter.
381 // This is likely a useful optimization
382 // Critically, in quick_enter() we must not:
383 // -- perform bias revocation, or
384 // -- block indefinitely, or
385 // -- reach a safepoint
386
387 return false; // revert to slow-path
388 }
389
390 // Handle notifications when synchronizing on value based classes
391 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
392 frame last_frame = current->last_frame();
393 bool bcp_was_adjusted = false;
394 // Don't decrement bcp if it points to the frame's first instruction. This happens when
395 // handle_sync_on_value_based_class() is called because of a synchronized method. There
396 // is no actual monitorenter instruction in the byte code in this case.
397 if (last_frame.is_interpreted_frame() &&
398 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
399 // adjust bcp to point back to monitorenter so that we print the correct line numbers
400 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
401 bcp_was_adjusted = true;
402 }
403
404 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
405 ResourceMark rm(current);
406 stringStream ss;
407 current->print_stack_on(&ss);
408 char* base = (char*)strstr(ss.base(), "at");
409 char* newline = (char*)strchr(ss.base(), '\n');
410 if (newline != NULL) {
411 *newline = '\0';
412 }
413 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
414 } else {
415 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
416 ResourceMark rm(current);
417 Log(valuebasedclasses) vblog;
418
419 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
420 if (current->has_last_Java_frame()) {
421 LogStream info_stream(vblog.info());
422 current->print_stack_on(&info_stream);
423 } else {
424 vblog.info("Cannot find the last Java frame");
425 }
426
427 EventSyncOnValueBasedClass event;
428 if (event.should_commit()) {
429 event.set_valueBasedClass(obj->klass());
430 event.commit();
431 }
432 }
433
434 if (bcp_was_adjusted) {
435 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
436 }
437 }
438
439 static bool useHeavyMonitors() {
440 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64)
441 return LockingMode == LM_MONITOR;
442 #else
443 return false;
444 #endif
445 }
446
447 // -----------------------------------------------------------------------------
448 // Monitor Enter/Exit
449 // The interpreter and compiler assembly code tries to lock using the fast path
450 // of this algorithm. Make sure to update that code if the following function is
451 // changed. The implementation is extremely sensitive to race condition. Be careful.
452
453 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
454 if (obj->klass()->is_value_based()) {
455 handle_sync_on_value_based_class(obj, current);
456 }
457
458 if (!useHeavyMonitors()) {
459 if (LockingMode == LM_LIGHTWEIGHT) {
460 // Fast-locking does not use the 'lock' argument.
461 LockStack& lock_stack = current->lock_stack();
462 if (lock_stack.can_push()) {
463 markWord mark = obj()->mark_acquire();
464 if (mark.is_neutral()) {
465 assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
466 // Try to swing into 'fast-locked' state.
467 markWord locked_mark = mark.set_fast_locked();
468 markWord old_mark = obj()->cas_set_mark(locked_mark, mark);
469 if (old_mark == mark) {
470 // Successfully fast-locked, push object to lock-stack and return.
471 lock_stack.push(obj());
472 return;
473 }
474 }
475 }
476 // All other paths fall-through to inflate-enter.
477 } else if (LockingMode == LM_LEGACY) {
478 if (UseBiasedLocking) {
479 BiasedLocking::revoke(current, obj);
480 }
481
482 markWord mark = obj->mark();
483 if (mark.is_neutral()) {
484 // Anticipate successful CAS -- the ST of the displaced mark must
485 // be visible <= the ST performed by the CAS.
486 lock->set_displaced_header(mark);
487 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
488 return;
489 }
490 // Fall through to inflate() ...
491 } else if (mark.has_locker() &&
492 current->is_lock_owned((address) mark.locker())) {
493 assert(lock != mark.locker(), "must not re-lock the same lock");
494 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
495 lock->set_displaced_header(markWord::from_pointer(NULL));
496 return;
497 }
498
499 // The object header will never be displaced to this lock,
500 // so it does not matter what the value is, except that it
501 // must be non-zero to avoid looking like a re-entrant lock,
502 // and must not look locked either.
503 lock->set_displaced_header(markWord::unused_mark());
504 }
505 }
506
507 // An async deflation can race after the inflate() call and before
508 // enter() can make the ObjectMonitor busy. enter() returns false if
509 // we have lost the race to async deflation and we simply try again.
510 while (true) {
511 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
512 if (monitor->enter(current)) {
513 return;
514 }
515 }
516 }
517
518 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
519 if (!useHeavyMonitors()) {
520 markWord mark = object->mark();
521 if (LockingMode == LM_LIGHTWEIGHT) {
522 // Fast-locking does not use the 'lock' argument.
523 if (mark.is_fast_locked()) {
524 markWord unlocked_mark = mark.set_unlocked();
525 markWord old_mark = object->cas_set_mark(unlocked_mark, mark);
526 if (old_mark != mark) {
527 // Another thread won the CAS, it must have inflated the monitor.
528 // It can only have installed an anonymously locked monitor at this point.
529 // Fetch that monitor, set owner correctly to this thread, and
530 // exit it (allowing waiting threads to enter).
531 assert(old_mark.has_monitor(), "must have monitor");
532 ObjectMonitor* monitor = old_mark.monitor();
533 assert(monitor->is_owner_anonymous(), "must be anonymous owner");
534 monitor->set_owner_from_anonymous(current);
535 monitor->exit(current);
536 }
537 LockStack& lock_stack = current->lock_stack();
538 lock_stack.remove(object);
539 return;
540 }
541 } else if (LockingMode == LM_LEGACY) {
542 markWord dhw = lock->displaced_header();
543 if (dhw.value() == 0) {
544 // If the displaced header is NULL, then this exit matches up with
545 // a recursive enter. No real work to do here except for diagnostics.
546 #ifndef PRODUCT
547 if (mark != markWord::INFLATING()) {
548 // Only do diagnostics if we are not racing an inflation. Simply
549 // exiting a recursive enter of a Java Monitor that is being
550 // inflated is safe; see the has_monitor() comment below.
551 assert(!mark.is_neutral(), "invariant");
552 assert(!mark.has_locker() ||
553 current->is_lock_owned((address)mark.locker()), "invariant");
554 if (mark.has_monitor()) {
555 // The BasicLock's displaced_header is marked as a recursive
556 // enter and we have an inflated Java Monitor (ObjectMonitor).
557 // This is a special case where the Java Monitor was inflated
558 // after this thread entered the stack-lock recursively. When a
559 // Java Monitor is inflated, we cannot safely walk the Java
560 // Monitor owner's stack and update the BasicLocks because a
561 // Java Monitor can be asynchronously inflated by a thread that
562 // does not own the Java Monitor.
563 ObjectMonitor* m = mark.monitor();
564 assert(m->object()->mark() == mark, "invariant");
565 assert(m->is_entered(current), "invariant");
566 }
567 }
568 #endif
569 return;
570 }
571
572 if (mark == markWord::from_pointer(lock)) {
573 // If the object is stack-locked by the current thread, try to
574 // swing the displaced header from the BasicLock back to the mark.
575 assert(dhw.is_neutral(), "invariant");
576 if (object->cas_set_mark(dhw, mark) == mark) {
577 return;
578 }
579 }
580 }
581 }
582
583 // We have to take the slow-path of possible inflation and then exit.
584 // The ObjectMonitor* can't be async deflated until ownership is
585 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
586 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
587 if (LockingMode == LM_LIGHTWEIGHT && monitor->is_owner_anonymous()) {
588 // It must be us. Pop lock object from lock stack.
589 LockStack& lock_stack = current->lock_stack();
590 oop popped = lock_stack.pop();
591 assert(popped == object, "must be owned by this thread");
592 monitor->set_owner_from_anonymous(current);
593 }
594 monitor->exit(current);
595 }
596
597 // -----------------------------------------------------------------------------
598 // Class Loader support to workaround deadlocks on the class loader lock objects
599 // Also used by GC
600 // complete_exit()/reenter() are used to wait on a nested lock
601 // i.e. to give up an outer lock completely and then re-enter
602 // Used when holding nested locks - lock acquisition order: lock1 then lock2
603 // 1) complete_exit lock1 - saving recursion count
604 // 2) wait on lock2
605 // 3) when notified on lock2, unlock lock2
606 // 4) reenter lock1 with original recursion count
607 // 5) lock lock2
608 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
609 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
610 if (UseBiasedLocking) {
611 BiasedLocking::revoke(current, obj);
612 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
613 }
614
615 // The ObjectMonitor* can't be async deflated until ownership is
616 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
617 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
618 intptr_t ret_code = monitor->complete_exit(current);
619 return ret_code;
620 }
621
622 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
623 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
624 if (UseBiasedLocking) {
625 BiasedLocking::revoke(current, obj);
626 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
627 }
628
629 // An async deflation can race after the inflate() call and before
630 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
631 // enter() returns false if we have lost the race to async deflation
632 // and we simply try again.
633 while (true) {
634 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
635 if (monitor->reenter(recursions, current)) {
636 return;
637 }
638 }
639 }
640
641 // -----------------------------------------------------------------------------
642 // JNI locks on java objects
643 // NOTE: must use heavy weight monitor to handle jni monitor enter
644 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
645 if (obj->klass()->is_value_based()) {
646 handle_sync_on_value_based_class(obj, current);
647 }
648
649 // the current locking is from JNI instead of Java code
650 if (UseBiasedLocking) {
651 BiasedLocking::revoke(current, obj);
652 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
653 }
654 current->set_current_pending_monitor_is_from_java(false);
655 // An async deflation can race after the inflate() call and before
656 // enter() can make the ObjectMonitor busy. enter() returns false if
657 // we have lost the race to async deflation and we simply try again.
658 while (true) {
659 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
660 if (monitor->enter(current)) {
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 if (UseBiasedLocking) {
671 Handle h_obj(current, obj);
672 BiasedLocking::revoke(current, h_obj);
673 obj = h_obj();
674 }
675 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
676
677 // The ObjectMonitor* can't be async deflated until ownership is
678 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
679 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
680 // If this thread has locked the object, exit the monitor. We
681 // intentionally do not use CHECK on check_owner because we must exit the
682 // monitor even if an exception was already pending.
683 if (monitor->check_owner(THREAD)) {
684 monitor->exit(current);
685 }
686 }
687
688 // -----------------------------------------------------------------------------
689 // Internal VM locks on java objects
690 // standard constructor, allows locking failures
691 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
692 _thread = thread;
693 _thread->check_for_valid_safepoint_state();
694 _obj = obj;
695
696 if (_obj() != NULL) {
697 ObjectSynchronizer::enter(_obj, &_lock, _thread);
698 }
699 }
700
701 ObjectLocker::~ObjectLocker() {
702 if (_obj() != NULL) {
703 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
704 }
705 }
706
707
708 // -----------------------------------------------------------------------------
709 // Wait/Notify/NotifyAll
710 // NOTE: must use heavy weight monitor to handle wait()
711 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
712 JavaThread* current = THREAD;
713 if (UseBiasedLocking) {
714 BiasedLocking::revoke(current, obj);
715 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
716 }
717 if (millis < 0) {
718 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
719 }
720 // The ObjectMonitor* can't be async deflated because the _waiters
721 // field is incremented before ownership is dropped and decremented
722 // after ownership is regained.
723 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
724
725 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
726 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
727
728 // This dummy call is in place to get around dtrace bug 6254741. Once
729 // that's fixed we can uncomment the following line, remove the call
730 // and change this function back into a "void" func.
731 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
732 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
733 return ret_code;
734 }
735
736 // No exception are possible in this case as we only use this internally when locking is
737 // correct and we have to wait until notified - so no interrupts or timeouts.
738 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, JavaThread* current) {
739 if (UseBiasedLocking) {
740 BiasedLocking::revoke(current, obj);
741 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
742 }
743 // The ObjectMonitor* can't be async deflated because the _waiters
744 // field is incremented before ownership is dropped and decremented
745 // after ownership is regained.
746 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
747 monitor->wait(0 /* wait-forever */, false /* not interruptible */, current);
748 }
749
750 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
751 JavaThread* current = THREAD;
752 if (UseBiasedLocking) {
753 BiasedLocking::revoke(current, obj);
754 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
755 }
756
757 markWord mark = obj->mark();
758 if (LockingMode == LM_LIGHTWEIGHT) {
759 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
760 // Not inflated so there can't be any waiters to notify.
761 return;
762 }
763 } else if (LockingMode == LM_LEGACY) {
764 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
765 // Not inflated so there can't be any waiters to notify.
766 return;
767 }
768 }
769 // The ObjectMonitor* can't be async deflated until ownership is
770 // dropped by the calling thread.
771 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
772 monitor->notify(CHECK);
773 }
774
775 // NOTE: see comment of notify()
776 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
777 JavaThread* current = THREAD;
778 if (UseBiasedLocking) {
779 BiasedLocking::revoke(current, obj);
780 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
781 }
782
783 markWord mark = obj->mark();
784 if (LockingMode == LM_LIGHTWEIGHT) {
785 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
786 // Not inflated so there can't be any waiters to notify.
787 return;
788 }
789 } else if (LockingMode == LM_LEGACY) {
790 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
791 // Not inflated so there can't be any waiters to notify.
792 return;
793 }
794 }
795 // The ObjectMonitor* can't be async deflated until ownership is
796 // dropped by the calling thread.
797 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
798 monitor->notifyAll(CHECK);
799 }
800
801 // -----------------------------------------------------------------------------
802 // Hash Code handling
803
804 struct SharedGlobals {
805 char _pad_prefix[OM_CACHE_LINE_SIZE];
806 // This is a highly shared mostly-read variable.
807 // To avoid false-sharing it needs to be the sole occupant of a cache line.
808 volatile int stw_random;
809 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
810 // Hot RW variable -- Sequester to avoid false-sharing
811 volatile int hc_sequence;
812 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
813 };
814
815 static SharedGlobals GVars;
816
817 static markWord read_stable_mark(oop obj) {
818 markWord mark = obj->mark();
819 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
820 // New lightweight locking does not use the markWord::INFLATING() protocol.
821 return mark; // normal fast-path return
822 }
823
824 int its = 0;
825 for (;;) {
826 markWord mark = obj->mark();
827 if (!mark.is_being_inflated()) {
828 return mark; // normal fast-path return
829 }
830
831 // The object is being inflated by some other thread.
832 // The caller of read_stable_mark() must wait for inflation to complete.
833 // Avoid live-lock.
834
835 ++its;
836 if (its > 10000 || !os::is_MP()) {
837 if (its & 1) {
838 os::naked_yield();
839 } else {
840 // Note that the following code attenuates the livelock problem but is not
841 // a complete remedy. A more complete solution would require that the inflating
842 // thread hold the associated inflation lock. The following code simply restricts
843 // the number of spinners to at most one. We'll have N-2 threads blocked
844 // on the inflationlock, 1 thread holding the inflation lock and using
845 // a yield/park strategy, and 1 thread in the midst of inflation.
846 // A more refined approach would be to change the encoding of INFLATING
847 // to allow encapsulation of a native thread pointer. Threads waiting for
848 // inflation to complete would use CAS to push themselves onto a singly linked
849 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
850 // and calling park(). When inflation was complete the thread that accomplished inflation
851 // would detach the list and set the markword to inflated with a single CAS and
852 // then for each thread on the list, set the flag and unpark() the thread.
853
854 // Index into the lock array based on the current object address.
855 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
856 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
857 int YieldThenBlock = 0;
858 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
859 gInflationLocks[ix]->lock();
860 while (obj->mark() == markWord::INFLATING()) {
861 // Beware: naked_yield() is advisory and has almost no effect on some platforms
862 // so we periodically call current->_ParkEvent->park(1).
863 // We use a mixed spin/yield/block mechanism.
864 if ((YieldThenBlock++) >= 16) {
865 Thread::current()->_ParkEvent->park(1);
866 } else {
867 os::naked_yield();
868 }
869 }
870 gInflationLocks[ix]->unlock();
871 }
872 } else {
873 SpinPause(); // SMP-polite spinning
874 }
875 }
876 }
877
878 // hashCode() generation :
879 //
880 // Possibilities:
881 // * MD5Digest of {obj,stw_random}
882 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
883 // * A DES- or AES-style SBox[] mechanism
884 // * One of the Phi-based schemes, such as:
885 // 2654435761 = 2^32 * Phi (golden ratio)
886 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
887 // * A variation of Marsaglia's shift-xor RNG scheme.
888 // * (obj ^ stw_random) is appealing, but can result
889 // in undesirable regularity in the hashCode values of adjacent objects
890 // (objects allocated back-to-back, in particular). This could potentially
891 // result in hashtable collisions and reduced hashtable efficiency.
892 // There are simple ways to "diffuse" the middle address bits over the
893 // generated hashCode values:
894
895 static inline intptr_t get_next_hash(Thread* current, oop obj) {
896 intptr_t value = 0;
897 if (hashCode == 0) {
898 // This form uses global Park-Miller RNG.
899 // On MP system we'll have lots of RW access to a global, so the
900 // mechanism induces lots of coherency traffic.
901 value = os::random();
902 } else if (hashCode == 1) {
903 // This variation has the property of being stable (idempotent)
904 // between STW operations. This can be useful in some of the 1-0
905 // synchronization schemes.
906 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
907 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
908 } else if (hashCode == 2) {
909 value = 1; // for sensitivity testing
910 } else if (hashCode == 3) {
911 value = ++GVars.hc_sequence;
912 } else if (hashCode == 4) {
913 value = cast_from_oop<intptr_t>(obj);
914 } else {
915 // Marsaglia's xor-shift scheme with thread-specific state
916 // This is probably the best overall implementation -- we'll
917 // likely make this the default in future releases.
918 unsigned t = current->_hashStateX;
919 t ^= (t << 11);
920 current->_hashStateX = current->_hashStateY;
921 current->_hashStateY = current->_hashStateZ;
922 current->_hashStateZ = current->_hashStateW;
923 unsigned v = current->_hashStateW;
924 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
925 current->_hashStateW = v;
926 value = v;
927 }
928
929 value &= UseCompactObjectHeaders ? markWord::hash_mask_compact : markWord::hash_mask;
930 if (value == 0) value = 0xBAD;
931 assert(value != markWord::no_hash, "invariant");
932 return value;
933 }
934
935 // Can be called from non JavaThreads (e.g., VMThread) for FastHashCode
936 // calculations as part of JVM/TI tagging.
937 static bool is_lock_owned(Thread* thread, oop obj) {
938 assert(LockingMode == LM_LIGHTWEIGHT, "only call this with new lightweight locking enabled");
939 return thread->is_Java_thread() ? reinterpret_cast<JavaThread*>(thread)->lock_stack().contains(obj) : false;
940 }
941
942 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
943 if (UseBiasedLocking) {
944 // NOTE: many places throughout the JVM do not expect a safepoint
945 // to be taken here. However, we only ever bias Java instances and all
946 // of the call sites of identity_hash that might revoke biases have
947 // been checked to make sure they can handle a safepoint. The
948 // added check of the bias pattern is to avoid useless calls to
949 // thread-local storage.
950 if (obj->mark().has_bias_pattern()) {
951 // Handle for oop obj in case of STW safepoint
952 Handle hobj(current, obj);
953 if (SafepointSynchronize::is_at_safepoint()) {
954 BiasedLocking::revoke_at_safepoint(hobj);
955 } else {
956 BiasedLocking::revoke(current->as_Java_thread(), hobj);
957 }
958 obj = hobj();
959 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
960 }
961 }
962
963 while (true) {
964 ObjectMonitor* monitor = NULL;
965 markWord temp, test;
966 intptr_t hash;
967 markWord mark = read_stable_mark(obj);
968
969 // object should remain ineligible for biased locking
970 assert(!mark.has_bias_pattern(), "invariant");
971
972 if (mark.is_neutral()) { // if this is a normal header
973 hash = mark.hash();
974 if (hash != 0) { // if it has a hash, just return it
975 return hash;
976 }
977 hash = get_next_hash(current, obj); // get a new hash
978 temp = mark.copy_set_hash(hash); // merge the hash into header
979 // try to install the hash
980 test = obj->cas_set_mark(temp, mark);
981 if (test == mark) { // if the hash was installed, return it
982 return hash;
983 }
984 // Failed to install the hash. It could be that another thread
985 // installed the hash just before our attempt or inflation has
986 // occurred or... so we fall thru to inflate the monitor for
987 // stability and then install the hash.
988 } else if (mark.has_monitor()) {
989 monitor = mark.monitor();
990 temp = monitor->header();
991 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
992 hash = temp.hash();
993 if (hash != 0) {
994 // It has a hash.
995
996 // Separate load of dmw/header above from the loads in
997 // is_being_async_deflated().
998
999 // dmw/header and _contentions may get written by different threads.
1000 // Make sure to observe them in the same order when having several observers.
1001 OrderAccess::loadload_for_IRIW();
1002
1003 if (monitor->is_being_async_deflated()) {
1004 // But we can't safely use the hash if we detect that async
1005 // deflation has occurred. So we attempt to restore the
1006 // header/dmw to the object's header so that we only retry
1007 // once if the deflater thread happens to be slow.
1008 monitor->install_displaced_markword_in_object(obj);
1009 continue;
1010 }
1011 return hash;
1012 }
1013 // Fall thru so we only have one place that installs the hash in
1014 // the ObjectMonitor.
1015 } else if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked() && is_lock_owned(current, obj)) {
1016 // This is a fast lock owned by the calling thread so use the
1017 // markWord from the object.
1018 hash = mark.hash();
1019 if (hash != 0) { // if it has a hash, just return it
1020 return hash;
1021 }
1022 } else if (LockingMode == LM_LEGACY && mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
1023 // This is a stack lock owned by the calling thread so fetch the
1024 // displaced markWord from the BasicLock on the stack.
1025 temp = mark.displaced_mark_helper();
1026 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1027 hash = temp.hash();
1028 if (hash != 0) { // if it has a hash, just return it
1029 return hash;
1030 }
1031 // WARNING:
1032 // The displaced header in the BasicLock on a thread's stack
1033 // is strictly immutable. It CANNOT be changed in ANY cases.
1034 // So we have to inflate the stack lock into an ObjectMonitor
1035 // even if the current thread owns the lock. The BasicLock on
1036 // a thread's stack can be asynchronously read by other threads
1037 // during an inflate() call so any change to that stack memory
1038 // may not propagate to other threads correctly.
1039 }
1040
1041 // Inflate the monitor to set the hash.
1042
1043 // An async deflation can race after the inflate() call and before we
1044 // can update the ObjectMonitor's header with the hash value below.
1045 monitor = inflate(current, obj, inflate_cause_hash_code);
1046 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1047 mark = monitor->header();
1048 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1049 hash = mark.hash();
1050 if (hash == 0) { // if it does not have a hash
1051 hash = get_next_hash(current, obj); // get a new hash
1052 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1053 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1054 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1055 test = markWord(v);
1056 if (test != mark) {
1057 // The attempt to update the ObjectMonitor's header/dmw field
1058 // did not work. This can happen if another thread managed to
1059 // merge in the hash just before our cmpxchg().
1060 // If we add any new usages of the header/dmw field, this code
1061 // will need to be updated.
1062 hash = test.hash();
1063 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1064 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1065 }
1066 if (monitor->is_being_async_deflated()) {
1067 // If we detect that async deflation has occurred, then we
1068 // attempt to restore the header/dmw to the object's header
1069 // so that we only retry once if the deflater thread happens
1070 // to be slow.
1071 monitor->install_displaced_markword_in_object(obj);
1072 continue;
1073 }
1074 }
1075 // We finally get the hash.
1076 return hash;
1077 }
1078 }
1079
1080 // Deprecated -- use FastHashCode() instead.
1081
1082 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1083 return FastHashCode(Thread::current(), obj());
1084 }
1085
1086
1087 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1088 Handle h_obj) {
1089 if (UseBiasedLocking) {
1090 BiasedLocking::revoke(current, h_obj);
1091 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1092 }
1093
1094 assert(current == JavaThread::current(), "Can only be called on current thread");
1095 oop obj = h_obj();
1096
1097 markWord mark = read_stable_mark(obj);
1098
1099 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1100 // stack-locked case, header points into owner's stack
1101 return current->is_lock_owned((address)mark.locker());
1102 }
1103
1104 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1105 // fast-locking case, see if lock is in current's lock stack
1106 return current->lock_stack().contains(h_obj());
1107 }
1108
1109 // Contended case, header points to ObjectMonitor (tagged pointer)
1110 if (mark.has_monitor()) {
1111 // The first stage of async deflation does not affect any field
1112 // used by this comparison so the ObjectMonitor* is usable here.
1113 ObjectMonitor* monitor = mark.monitor();
1114 return monitor->is_entered(current) != 0;
1115 }
1116 // Unlocked case, header in place
1117 assert(mark.is_neutral(), "sanity check");
1118 return false;
1119 }
1120
1121 // FIXME: jvmti should call this
1122 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1123 if (UseBiasedLocking) {
1124 if (SafepointSynchronize::is_at_safepoint()) {
1125 BiasedLocking::revoke_at_safepoint(h_obj);
1126 } else {
1127 BiasedLocking::revoke(JavaThread::current(), h_obj);
1128 }
1129 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1130 }
1131
1132 oop obj = h_obj();
1133 markWord mark = read_stable_mark(obj);
1134
1135 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1136 // stack-locked so header points into owner's stack.
1137 // owning_thread_from_monitor_owner() may also return null here:
1138 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1139 }
1140
1141 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1142 // fast-locked so get owner from the object.
1143 // owning_thread_from_object() may also return null here:
1144 return Threads::owning_thread_from_object(t_list, h_obj());
1145 }
1146
1147 // Contended case, header points to ObjectMonitor (tagged pointer)
1148 if (mark.has_monitor()) {
1149 // The first stage of async deflation does not affect any field
1150 // used by this comparison so the ObjectMonitor* is usable here.
1151 ObjectMonitor* monitor = mark.monitor();
1152 assert(monitor != NULL, "monitor should be non-null");
1153 // owning_thread_from_monitor() may also return null here:
1154 return Threads::owning_thread_from_monitor(t_list, monitor);
1155 }
1156
1157 // Unlocked case, header in place
1158 // Cannot have assertion since this object may have been
1159 // locked by another thread when reaching here.
1160 // assert(mark.is_neutral(), "sanity check");
1161
1162 return NULL;
1163 }
1164
1165 // Visitors ...
1166
1167 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1168 MonitorList::Iterator iter = _in_use_list.iterator();
1169 while (iter.has_next()) {
1170 ObjectMonitor* mid = iter.next();
1171 if (mid->owner() != thread) {
1172 continue;
1173 }
1174 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1175 // Only process with closure if the object is set.
1176
1177 // monitors_iterate() is only called at a safepoint or when the
1178 // target thread is suspended or when the target thread is
1179 // operating on itself. The current closures in use today are
1180 // only interested in an owned ObjectMonitor and ownership
1181 // cannot be dropped under the calling contexts so the
1182 // ObjectMonitor cannot be async deflated.
1183 closure->do_monitor(mid);
1184 }
1185 }
1186 }
1187
1188 static bool monitors_used_above_threshold(MonitorList* list) {
1189 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1190 return false;
1191 }
1192 // Start with ceiling based on a per-thread estimate:
1193 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1194 size_t old_ceiling = ceiling;
1195 if (ceiling < list->max()) {
1196 // The max used by the system has exceeded the ceiling so use that:
1197 ceiling = list->max();
1198 }
1199 size_t monitors_used = list->count();
1200 if (monitors_used == 0) { // empty list is easy
1201 return false;
1202 }
1203 if (NoAsyncDeflationProgressMax != 0 &&
1204 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1205 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1206 size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1207 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1208 log_info(monitorinflation)("Too many deflations without progress; "
1209 "bumping in_use_list_ceiling from " SIZE_FORMAT
1210 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1211 _no_progress_cnt = 0;
1212 ceiling = new_ceiling;
1213 }
1214
1215 // Check if our monitor usage is above the threshold:
1216 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1217 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1218 log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
1219 ", monitor_usage=" SIZE_FORMAT ", threshold=" INTX_FORMAT,
1220 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1221 return true;
1222 }
1223
1224 return false;
1225 }
1226
1227 size_t ObjectSynchronizer::in_use_list_ceiling() {
1228 return _in_use_list_ceiling;
1229 }
1230
1231 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1232 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1233 }
1234
1235 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1236 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1237 }
1238
1239 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1240 _in_use_list_ceiling = new_value;
1241 }
1242
1243 bool ObjectSynchronizer::is_async_deflation_needed() {
1244 if (is_async_deflation_requested()) {
1245 // Async deflation request.
1246 log_info(monitorinflation)("Async deflation needed: explicit request");
1247 return true;
1248 }
1249
1250 jlong time_since_last = time_since_last_async_deflation_ms();
1251
1252 if (AsyncDeflationInterval > 0 &&
1253 time_since_last > AsyncDeflationInterval &&
1254 monitors_used_above_threshold(&_in_use_list)) {
1255 // It's been longer than our specified deflate interval and there
1256 // are too many monitors in use. We don't deflate more frequently
1257 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1258 // in order to not swamp the MonitorDeflationThread.
1259 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1260 return true;
1261 }
1262
1263 if (GuaranteedAsyncDeflationInterval > 0 &&
1264 time_since_last > GuaranteedAsyncDeflationInterval) {
1265 // It's been longer than our specified guaranteed deflate interval.
1266 // We need to clean up the used monitors even if the threshold is
1267 // not reached, to keep the memory utilization at bay when many threads
1268 // touched many monitors.
1269 log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) "
1270 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1271 GuaranteedAsyncDeflationInterval, time_since_last);
1272
1273 // If this deflation has no progress, then it should not affect the no-progress
1274 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1275 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1276 // the generic code would bump the no-progress counter, and we compensate for that
1277 // by telling it to skip the update.
1278 //
1279 // If this deflation has progress, then it should let non-progress tracking
1280 // know about this, otherwise the threshold heuristics would kick in, potentially
1281 // experience no-progress due to aggressive cleanup by this deflation, and think
1282 // it is still in no-progress stride. In this "progress" case, the generic code would
1283 // zero the counter, and we allow it to happen.
1284 _no_progress_skip_increment = true;
1285
1286 return true;
1287 }
1288
1289 return false;
1290 }
1291
1292 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1293 JavaThread* current = JavaThread::current();
1294 bool ret_code = false;
1295
1296 jlong last_time = last_async_deflation_time_ns();
1297 set_is_async_deflation_requested(true);
1298 {
1299 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1300 ml.notify_all();
1301 }
1302 const int N_CHECKS = 5;
1303 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1304 if (last_async_deflation_time_ns() > last_time) {
1305 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1306 ret_code = true;
1307 break;
1308 }
1309 {
1310 // JavaThread has to honor the blocking protocol.
1311 ThreadBlockInVM tbivm(current);
1312 os::naked_short_sleep(999); // sleep for almost 1 second
1313 }
1314 }
1315 if (!ret_code) {
1316 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1317 }
1318
1319 return ret_code;
1320 }
1321
1322 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1323 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1324 }
1325
1326 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1327 const oop obj,
1328 ObjectSynchronizer::InflateCause cause) {
1329 assert(event != NULL, "invariant");
1330 assert(event->should_commit(), "invariant");
1331 event->set_monitorClass(obj->klass());
1332 event->set_address((uintptr_t)(void*)obj);
1333 event->set_cause((u1)cause);
1334 event->commit();
1335 }
1336
1337 // Fast path code shared by multiple functions
1338 void ObjectSynchronizer::inflate_helper(oop obj) {
1339 markWord mark = obj->mark();
1340 if (mark.has_monitor()) {
1341 ObjectMonitor* monitor = mark.monitor();
1342 markWord dmw = monitor->header();
1343 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1344 return;
1345 }
1346 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1347 }
1348
1349 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1350 const InflateCause cause) {
1351 EventJavaMonitorInflate event;
1352
1353 for (;;) {
1354 const markWord mark = object->mark();
1355 assert(!mark.has_bias_pattern(), "invariant");
1356
1357 // The mark can be in one of the following states:
1358 // * inflated - Just return if using stack-locking.
1359 // If using fast-locking and the ObjectMonitor owner
1360 // is anonymous and the current thread owns the
1361 // object lock, then we make the current thread the
1362 // ObjectMonitor owner and remove the lock from the
1363 // current thread's lock stack.
1364 // * fast-locked - Coerce it to inflated from fast-locked.
1365 // * stack-locked - Coerce it to inflated from stack-locked.
1366 // * INFLATING - busy wait for conversion to complete
1367 // * Neutral - aggressively inflate the object.
1368 // * BIASED - Illegal. We should never see this
1369
1370 // CASE: inflated
1371 if (mark.has_monitor()) {
1372 ObjectMonitor* inf = mark.monitor();
1373 markWord dmw = inf->header();
1374 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1375 if (LockingMode == LM_LIGHTWEIGHT && inf->is_owner_anonymous() && is_lock_owned(current, object)) {
1376 inf->set_owner_from_anonymous(current);
1377 assert(current->is_Java_thread(), "must be Java thread");
1378 reinterpret_cast<JavaThread*>(current)->lock_stack().remove(object);
1379 }
1380 return inf;
1381 }
1382
1383 // CASE: inflation in progress - inflating over a stack-lock.
1384 // Some other thread is converting from stack-locked to inflated.
1385 // Only that thread can complete inflation -- other threads must wait.
1386 // The INFLATING value is transient.
1387 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1388 // We could always eliminate polling by parking the thread on some auxiliary list.
1389 if (LockingMode != LM_LIGHTWEIGHT) {
1390 // New lightweight locking does not use INFLATING.
1391 // CASE: inflation in progress - inflating over a stack-lock.
1392 // Some other thread is converting from stack-locked to inflated.
1393 // Only that thread can complete inflation -- other threads must wait.
1394 // The INFLATING value is transient.
1395 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1396 // We could always eliminate polling by parking the thread on some auxiliary list.
1397 if (mark == markWord::INFLATING()) {
1398 read_stable_mark(object);
1399 continue;
1400 }
1401 }
1402
1403 // CASE: fast-locked
1404 // Could be fast-locked either by current or by some other thread.
1405 //
1406 // Note that we allocate the ObjectMonitor speculatively, _before_
1407 // attempting to set the object's mark to the new ObjectMonitor. If
1408 // this thread owns the monitor, then we set the ObjectMonitor's
1409 // owner to this thread. Otherwise, we set the ObjectMonitor's owner
1410 // to anonymous. If we lose the race to set the object's mark to the
1411 // new ObjectMonitor, then we just delete it and loop around again.
1412 //
1413 LogStreamHandle(Trace, monitorinflation) lsh;
1414 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1415 ObjectMonitor* monitor = new ObjectMonitor(object);
1416 monitor->set_header(mark.set_unlocked());
1417 bool own = is_lock_owned(current, object);
1418 if (own) {
1419 // Owned by us.
1420 monitor->set_owner_from(NULL, current);
1421 } else {
1422 // Owned by somebody else.
1423 monitor->set_owner_anonymous();
1424 }
1425 markWord monitor_mark = markWord::encode(monitor);
1426 markWord old_mark = object->cas_set_mark(monitor_mark, mark);
1427 if (old_mark == mark) {
1428 // Success! Return inflated monitor.
1429 if (own) {
1430 assert(current->is_Java_thread(), "must be Java thread");
1431 reinterpret_cast<JavaThread*>(current)->lock_stack().remove(object);
1432 }
1433 // Once the ObjectMonitor is configured and object is associated
1434 // with the ObjectMonitor, it is safe to allow async deflation:
1435 _in_use_list.add(monitor);
1436
1437 // Hopefully the performance counters are allocated on distinct
1438 // cache lines to avoid false sharing on MP systems ...
1439 OM_PERFDATA_OP(Inflations, inc());
1440 if (log_is_enabled(Trace, monitorinflation)) {
1441 ResourceMark rm(current);
1442 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1443 INTPTR_FORMAT ", type='%s'", p2i(object),
1444 object->mark().value(), object->klass()->external_name());
1445 }
1446 if (event.should_commit()) {
1447 post_monitor_inflate_event(&event, object, cause);
1448 }
1449 return monitor;
1450 } else {
1451 delete monitor;
1452 continue; // Interference -- just retry
1453 }
1454 }
1455
1456 // CASE: stack-locked
1457 // Could be stack-locked either by this thread or by some other thread.
1458 //
1459 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1460 // to install INFLATING into the mark word. We originally installed INFLATING,
1461 // allocated the ObjectMonitor, and then finally STed the address of the
1462 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1463 // the interval in which INFLATING appeared in the mark, thus increasing
1464 // the odds of inflation contention.
1465
1466 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1467 assert(LockingMode != LM_LIGHTWEIGHT, "cannot happen with new lightweight locking");
1468 ObjectMonitor* m = new ObjectMonitor(object);
1469 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1470 // We do this before the CAS in order to minimize the length of time
1471 // in which INFLATING appears in the mark.
1472
1473 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1474 if (cmp != mark) {
1475 delete m;
1476 continue; // Interference -- just retry
1477 }
1478
1479 // We've successfully installed INFLATING (0) into the mark-word.
1480 // This is the only case where 0 will appear in a mark-word.
1481 // Only the singular thread that successfully swings the mark-word
1482 // to 0 can perform (or more precisely, complete) inflation.
1483 //
1484 // Why do we CAS a 0 into the mark-word instead of just CASing the
1485 // mark-word from the stack-locked value directly to the new inflated state?
1486 // Consider what happens when a thread unlocks a stack-locked object.
1487 // It attempts to use CAS to swing the displaced header value from the
1488 // on-stack BasicLock back into the object header. Recall also that the
1489 // header value (hash code, etc) can reside in (a) the object header, or
1490 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1491 // header in an ObjectMonitor. The inflate() routine must copy the header
1492 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1493 // the while preserving the hashCode stability invariants. If the owner
1494 // decides to release the lock while the value is 0, the unlock will fail
1495 // and control will eventually pass from slow_exit() to inflate. The owner
1496 // will then spin, waiting for the 0 value to disappear. Put another way,
1497 // the 0 causes the owner to stall if the owner happens to try to
1498 // drop the lock (restoring the header from the BasicLock to the object)
1499 // while inflation is in-progress. This protocol avoids races that might
1500 // would otherwise permit hashCode values to change or "flicker" for an object.
1501 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1502 // 0 serves as a "BUSY" inflate-in-progress indicator.
1503
1504
1505 // fetch the displaced mark from the owner's stack.
1506 // The owner can't die or unwind past the lock while our INFLATING
1507 // object is in the mark. Furthermore the owner can't complete
1508 // an unlock on the object, either.
1509 markWord dmw = mark.displaced_mark_helper();
1510 // Catch if the object's header is not neutral (not locked and
1511 // not marked is what we care about here).
1512 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1513
1514 // Setup monitor fields to proper values -- prepare the monitor
1515 m->set_header(dmw);
1516
1517 // Optimization: if the mark.locker stack address is associated
1518 // with this thread we could simply set m->_owner = current.
1519 // Note that a thread can inflate an object
1520 // that it has stack-locked -- as might happen in wait() -- directly
1521 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1522 m->set_owner_from(NULL, mark.locker());
1523 // TODO-FIXME: assert BasicLock->dhw != 0.
1524
1525 // Must preserve store ordering. The monitor state must
1526 // be stable at the time of publishing the monitor address.
1527 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1528 // Release semantics so that above set_object() is seen first.
1529 object->release_set_mark(markWord::encode(m));
1530
1531 // Once ObjectMonitor is configured and the object is associated
1532 // with the ObjectMonitor, it is safe to allow async deflation:
1533 _in_use_list.add(m);
1534
1535 // Hopefully the performance counters are allocated on distinct cache lines
1536 // to avoid false sharing on MP systems ...
1537 OM_PERFDATA_OP(Inflations, inc());
1538 if (log_is_enabled(Trace, monitorinflation)) {
1539 ResourceMark rm(current);
1540 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1541 INTPTR_FORMAT ", type='%s'", p2i(object),
1542 object->mark().value(), object->klass()->external_name());
1543 }
1544 if (event.should_commit()) {
1545 post_monitor_inflate_event(&event, object, cause);
1546 }
1547 return m;
1548 }
1549
1550 // CASE: neutral
1551 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1552 // If we know we're inflating for entry it's better to inflate by swinging a
1553 // pre-locked ObjectMonitor pointer into the object header. A successful
1554 // CAS inflates the object *and* confers ownership to the inflating thread.
1555 // In the current implementation we use a 2-step mechanism where we CAS()
1556 // to inflate and then CAS() again to try to swing _owner from NULL to current.
1557 // An inflateTry() method that we could call from enter() would be useful.
1558
1559 // Catch if the object's header is not neutral (not locked and
1560 // not marked is what we care about here).
1561 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1562 ObjectMonitor* m = new ObjectMonitor(object);
1563 // prepare m for installation - set monitor to initial state
1564 m->set_header(mark);
1565
1566 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1567 delete m;
1568 m = NULL;
1569 continue;
1570 // interference - the markword changed - just retry.
1571 // The state-transitions are one-way, so there's no chance of
1572 // live-lock -- "Inflated" is an absorbing state.
1573 }
1574
1575 // Once the ObjectMonitor is configured and object is associated
1576 // with the ObjectMonitor, it is safe to allow async deflation:
1577 _in_use_list.add(m);
1578
1579 // Hopefully the performance counters are allocated on distinct
1580 // cache lines to avoid false sharing on MP systems ...
1581 OM_PERFDATA_OP(Inflations, inc());
1582 if (log_is_enabled(Trace, monitorinflation)) {
1583 ResourceMark rm(current);
1584 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1585 INTPTR_FORMAT ", type='%s'", p2i(object),
1586 object->mark().value(), object->klass()->external_name());
1587 }
1588 if (event.should_commit()) {
1589 post_monitor_inflate_event(&event, object, cause);
1590 }
1591 return m;
1592 }
1593 }
1594
1595 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1596 const char* cnt_name, size_t cnt,
1597 LogStream* ls, elapsedTimer* timer_p) {
1598 if (!SafepointMechanism::should_process(current)) {
1599 return;
1600 }
1601
1602 // A safepoint/handshake has started.
1603 if (ls != NULL) {
1604 timer_p->stop();
1605 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1606 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1607 op_name, cnt_name, cnt, in_use_list_ceiling(),
1608 _in_use_list.count(), _in_use_list.max());
1609 }
1610
1611 {
1612 // Honor block request.
1613 ThreadBlockInVM tbivm(current);
1614 }
1615
1616 if (ls != NULL) {
1617 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1618 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1619 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1620 timer_p->start();
1621 }
1622 }
1623
1624 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1625 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1626 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1627 elapsedTimer* timer_p) {
1628 MonitorList::Iterator iter = _in_use_list.iterator();
1629 size_t deflated_count = 0;
1630
1631 while (iter.has_next()) {
1632 if (deflated_count >= (size_t)MonitorDeflationMax) {
1633 break;
1634 }
1635 ObjectMonitor* mid = iter.next();
1636 if (mid->deflate_monitor()) {
1637 deflated_count++;
1638 }
1639
1640 if (current->is_Java_thread()) {
1641 // A JavaThread must check for a safepoint/handshake and honor it.
1642 chk_for_block_req(current->as_Java_thread(), "deflation", "deflated_count",
1643 deflated_count, ls, timer_p);
1644 }
1645 }
1646
1647 return deflated_count;
1648 }
1649
1650 class HandshakeForDeflation : public HandshakeClosure {
1651 public:
1652 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1653
1654 void do_thread(Thread* thread) {
1655 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1656 INTPTR_FORMAT, p2i(thread));
1657 }
1658 };
1659
1660 class VM_RendezvousGCThreads : public VM_Operation {
1661 public:
1662 bool evaluate_at_safepoint() const override { return false; }
1663 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1664 void doit() override {
1665 SuspendibleThreadSet::synchronize();
1666 SuspendibleThreadSet::desynchronize();
1667 };
1668 };
1669
1670 // This function is called by the MonitorDeflationThread to deflate
1671 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1672 // by the VMThread.
1673 size_t ObjectSynchronizer::deflate_idle_monitors() {
1674 Thread* current = Thread::current();
1675 if (current->is_Java_thread()) {
1676 // The async deflation request has been processed.
1677 _last_async_deflation_time_ns = os::javaTimeNanos();
1678 set_is_async_deflation_requested(false);
1679 }
1680
1681 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1682 LogStreamHandle(Info, monitorinflation) lsh_info;
1683 LogStream* ls = NULL;
1684 if (log_is_enabled(Debug, monitorinflation)) {
1685 ls = &lsh_debug;
1686 } else if (log_is_enabled(Info, monitorinflation)) {
1687 ls = &lsh_info;
1688 }
1689
1690 elapsedTimer timer;
1691 if (ls != NULL) {
1692 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1693 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1694 timer.start();
1695 }
1696
1697 // Deflate some idle ObjectMonitors.
1698 size_t deflated_count = deflate_monitor_list(current, ls, &timer);
1699 if (deflated_count > 0 || is_final_audit()) {
1700 // There are ObjectMonitors that have been deflated or this is the
1701 // final audit and all the remaining ObjectMonitors have been
1702 // deflated, BUT the MonitorDeflationThread blocked for the final
1703 // safepoint during unlinking.
1704
1705 // Unlink deflated ObjectMonitors from the in-use list.
1706 ResourceMark rm;
1707 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1708 size_t unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer,
1709 &delete_list);
1710 if (current->is_Java_thread()) {
1711 if (ls != NULL) {
1712 timer.stop();
1713 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1714 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1715 SIZE_FORMAT ", max=" SIZE_FORMAT,
1716 unlinked_count, in_use_list_ceiling(),
1717 _in_use_list.count(), _in_use_list.max());
1718 }
1719
1720 // A JavaThread needs to handshake in order to safely free the
1721 // ObjectMonitors that were deflated in this cycle.
1722 // Also, we sync and desync GC threads around the handshake, so that they can
1723 // safely read the mark-word and look-through to the object-monitor, without
1724 // being afraid that the object-monitor is going away.
1725 HandshakeForDeflation hfd_hc;
1726 Handshake::execute(&hfd_hc);
1727 VM_RendezvousGCThreads sync_gc;
1728 VMThread::execute(&sync_gc);
1729
1730 if (ls != NULL) {
1731 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1732 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1733 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1734 timer.start();
1735 }
1736 }
1737
1738 // After the handshake, safely free the ObjectMonitors that were
1739 // deflated in this cycle.
1740 size_t deleted_count = 0;
1741 for (ObjectMonitor* monitor: delete_list) {
1742 delete monitor;
1743 deleted_count++;
1744
1745 if (current->is_Java_thread()) {
1746 // A JavaThread must check for a safepoint/handshake and honor it.
1747 chk_for_block_req(current->as_Java_thread(), "deletion", "deleted_count",
1748 deleted_count, ls, &timer);
1749 }
1750 }
1751 }
1752
1753 if (ls != NULL) {
1754 timer.stop();
1755 if (deflated_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1756 ls->print_cr("deflated " SIZE_FORMAT " monitors in %3.7f secs",
1757 deflated_count, timer.seconds());
1758 }
1759 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1760 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1761 }
1762
1763 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1764 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1765
1766 GVars.stw_random = os::random();
1767
1768 if (deflated_count != 0) {
1769 _no_progress_cnt = 0;
1770 } else if (_no_progress_skip_increment) {
1771 _no_progress_skip_increment = false;
1772 } else {
1773 _no_progress_cnt++;
1774 }
1775
1776 return deflated_count;
1777 }
1778
1779 // Monitor cleanup on JavaThread::exit
1780
1781 // Iterate through monitor cache and attempt to release thread's monitors
1782 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1783 private:
1784 JavaThread* _thread;
1785
1786 public:
1787 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1788 void do_monitor(ObjectMonitor* mid) {
1789 (void)mid->complete_exit(_thread);
1790 }
1791 };
1792
1793 // Release all inflated monitors owned by current thread. Lightweight monitors are
1794 // ignored. This is meant to be called during JNI thread detach which assumes
1795 // all remaining monitors are heavyweight. All exceptions are swallowed.
1796 // Scanning the extant monitor list can be time consuming.
1797 // A simple optimization is to add a per-thread flag that indicates a thread
1798 // called jni_monitorenter() during its lifetime.
1799 //
1800 // Instead of NoSafepointVerifier it might be cheaper to
1801 // use an idiom of the form:
1802 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1803 // <code that must not run at safepoint>
1804 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1805 // Since the tests are extremely cheap we could leave them enabled
1806 // for normal product builds.
1807
1808 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1809 assert(current == JavaThread::current(), "must be current Java thread");
1810 NoSafepointVerifier nsv;
1811 ReleaseJavaMonitorsClosure rjmc(current);
1812 ObjectSynchronizer::monitors_iterate(&rjmc, current);
1813 assert(!current->has_pending_exception(), "Should not be possible");
1814 current->clear_pending_exception();
1815 }
1816
1817 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1818 switch (cause) {
1819 case inflate_cause_vm_internal: return "VM Internal";
1820 case inflate_cause_monitor_enter: return "Monitor Enter";
1821 case inflate_cause_wait: return "Monitor Wait";
1822 case inflate_cause_notify: return "Monitor Notify";
1823 case inflate_cause_hash_code: return "Monitor Hash Code";
1824 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1825 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1826 default:
1827 ShouldNotReachHere();
1828 }
1829 return "Unknown";
1830 }
1831
1832 //------------------------------------------------------------------------------
1833 // Debugging code
1834
1835 u_char* ObjectSynchronizer::get_gvars_addr() {
1836 return (u_char*)&GVars;
1837 }
1838
1839 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1840 return (u_char*)&GVars.hc_sequence;
1841 }
1842
1843 size_t ObjectSynchronizer::get_gvars_size() {
1844 return sizeof(SharedGlobals);
1845 }
1846
1847 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1848 return (u_char*)&GVars.stw_random;
1849 }
1850
1851 // Do the final audit and print of ObjectMonitor stats; must be done
1852 // by the VMThread at VM exit time.
1853 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1854 assert(Thread::current()->is_VM_thread(), "sanity check");
1855
1856 if (is_final_audit()) { // Only do the audit once.
1857 return;
1858 }
1859 set_is_final_audit();
1860 log_info(monitorinflation)("Starting the final audit.");
1861
1862 if (log_is_enabled(Info, monitorinflation)) {
1863 // Do a deflation in order to reduce the in-use monitor population
1864 // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1865 // which is called by ObjectSynchronizer::audit_and_print_stats().
1866 while (ObjectSynchronizer::deflate_idle_monitors() != 0) {
1867 ; // empty
1868 }
1869 // The other audit_and_print_stats() call is done at the Debug
1870 // level at a safepoint in ObjectSynchronizer::do_safepoint_work().
1871 ObjectSynchronizer::audit_and_print_stats(true /* on_exit */);
1872 }
1873 }
1874
1875 // This function can be called at a safepoint or it can be called when
1876 // we are trying to exit the VM. When we are trying to exit the VM, the
1877 // list walker functions can run in parallel with the other list
1878 // operations so spin-locking is used for safety.
1879 //
1880 // Calls to this function can be added in various places as a debugging
1881 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1882 // details logged at the Info level and 'false' for the 'on_exit'
1883 // parameter to have in-use monitor details logged at the Trace level.
1884 //
1885 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1886 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1887
1888 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1889 LogStreamHandle(Info, monitorinflation) lsh_info;
1890 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1891 LogStream* ls = NULL;
1892 if (log_is_enabled(Trace, monitorinflation)) {
1893 ls = &lsh_trace;
1894 } else if (log_is_enabled(Debug, monitorinflation)) {
1895 ls = &lsh_debug;
1896 } else if (log_is_enabled(Info, monitorinflation)) {
1897 ls = &lsh_info;
1898 }
1899 assert(ls != NULL, "sanity check");
1900
1901 int error_cnt = 0;
1902
1903 ls->print_cr("Checking in_use_list:");
1904 chk_in_use_list(ls, &error_cnt);
1905
1906 if (error_cnt == 0) {
1907 ls->print_cr("No errors found in in_use_list checks.");
1908 } else {
1909 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1910 }
1911
1912 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1913 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1914 // When exiting this log output is at the Info level. When called
1915 // at a safepoint, this log output is at the Trace level since
1916 // there can be a lot of it.
1917 log_in_use_monitor_details(ls);
1918 }
1919
1920 ls->flush();
1921
1922 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1923 }
1924
1925 // Check the in_use_list; log the results of the checks.
1926 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1927 size_t l_in_use_count = _in_use_list.count();
1928 size_t l_in_use_max = _in_use_list.max();
1929 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1930 l_in_use_max);
1931
1932 size_t ck_in_use_count = 0;
1933 MonitorList::Iterator iter = _in_use_list.iterator();
1934 while (iter.has_next()) {
1935 ObjectMonitor* mid = iter.next();
1936 chk_in_use_entry(mid, out, error_cnt_p);
1937 ck_in_use_count++;
1938 }
1939
1940 if (l_in_use_count == ck_in_use_count) {
1941 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1942 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1943 } else {
1944 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1945 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1946 ck_in_use_count);
1947 }
1948
1949 size_t ck_in_use_max = _in_use_list.max();
1950 if (l_in_use_max == ck_in_use_max) {
1951 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1952 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1953 } else {
1954 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1955 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1956 }
1957 }
1958
1959 // Check an in-use monitor entry; log any errors.
1960 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1961 int* error_cnt_p) {
1962 if (n->owner_is_DEFLATER_MARKER()) {
1963 // This should not happen, but if it does, it is not fatal.
1964 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1965 "deflated.", p2i(n));
1966 return;
1967 }
1968 if (n->header().value() == 0) {
1969 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1970 "have non-NULL _header field.", p2i(n));
1971 *error_cnt_p = *error_cnt_p + 1;
1972 }
1973 const oop obj = n->object_peek();
1974 if (obj != NULL) {
1975 const markWord mark = obj->mark();
1976 if (!mark.has_monitor()) {
1977 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1978 "object does not think it has a monitor: obj="
1979 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1980 p2i(obj), mark.value());
1981 *error_cnt_p = *error_cnt_p + 1;
1982 }
1983 ObjectMonitor* const obj_mon = mark.monitor();
1984 if (n != obj_mon) {
1985 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1986 "object does not refer to the same monitor: obj="
1987 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1988 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1989 *error_cnt_p = *error_cnt_p + 1;
1990 }
1991 }
1992 }
1993
1994 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1995 // flags indicate why the entry is in-use, 'object' and 'object type'
1996 // indicate the associated object and its type.
1997 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
1998 stringStream ss;
1999 if (_in_use_list.count() > 0) {
2000 out->print_cr("In-use monitor info:");
2001 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2002 out->print_cr("%18s %s %18s %18s",
2003 "monitor", "BHL", "object", "object type");
2004 out->print_cr("================== === ================== ==================");
2005 MonitorList::Iterator iter = _in_use_list.iterator();
2006 while (iter.has_next()) {
2007 ObjectMonitor* mid = iter.next();
2008 const oop obj = mid->object_peek();
2009 const markWord mark = mid->header();
2010 ResourceMark rm;
2011 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid),
2012 mid->is_busy(), mark.hash() != 0, mid->owner() != NULL,
2013 p2i(obj), obj == NULL ? "" : obj->klass()->external_name());
2014 if (mid->is_busy()) {
2015 out->print(" (%s)", mid->is_busy_to_string(&ss));
2016 ss.reset();
2017 }
2018 out->cr();
2019 }
2020 }
2021
2022 out->flush();
2023 }