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 "logging/log.hpp"
29 #include "logging/logStream.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/padded.hpp"
32 #include "memory/resourceArea.hpp"
33 #include "memory/universe.hpp"
34 #include "oops/markWord.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "runtime/atomic.hpp"
37 #include "runtime/biasedLocking.hpp"
38 #include "runtime/handles.inline.hpp"
39 #include "runtime/handshake.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "runtime/objectMonitor.hpp"
43 #include "runtime/objectMonitor.inline.hpp"
44 #include "runtime/os.inline.hpp"
45 #include "runtime/osThread.hpp"
46 #include "runtime/perfData.hpp"
47 #include "runtime/safepointMechanism.inline.hpp"
48 #include "runtime/safepointVerifiers.hpp"
49 #include "runtime/sharedRuntime.hpp"
50 #include "runtime/stubRoutines.hpp"
51 #include "runtime/synchronizer.hpp"
52 #include "runtime/thread.inline.hpp"
53 #include "runtime/timer.hpp"
54 #include "runtime/trimNativeHeap.hpp"
55 #include "runtime/vframe.hpp"
56 #include "runtime/vmThread.hpp"
57 #include "utilities/align.hpp"
58 #include "utilities/dtrace.hpp"
59 #include "utilities/events.hpp"
60 #include "utilities/preserveException.hpp"
61
62 void MonitorList::add(ObjectMonitor* m) {
63 ObjectMonitor* head;
64 do {
65 head = Atomic::load(&_head);
66 m->set_next_om(head);
67 } while (Atomic::cmpxchg(&_head, head, m) != head);
68
69 size_t count = Atomic::add(&_count, 1u);
70 if (count > max()) {
71 Atomic::inc(&_max);
72 }
73 }
74
75 size_t MonitorList::count() const {
76 return Atomic::load(&_count);
77 }
78
79 size_t MonitorList::max() const {
80 return Atomic::load(&_max);
81 }
82
83 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
84 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
85 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
86 elapsedTimer* timer_p,
87 GrowableArray<ObjectMonitor*>* unlinked_list) {
88 size_t unlinked_count = 0;
89 ObjectMonitor* prev = NULL;
90 ObjectMonitor* head = Atomic::load_acquire(&_head);
91 ObjectMonitor* m = head;
92 // The in-use list head can be NULL during the final audit.
93 while (m != NULL) {
94 if (m->is_being_async_deflated()) {
95 // Find next live ObjectMonitor.
96 ObjectMonitor* next = m;
97 do {
98 ObjectMonitor* next_next = next->next_om();
99 unlinked_count++;
100 unlinked_list->append(next);
101 next = next_next;
102 if (unlinked_count >= (size_t)MonitorDeflationMax) {
103 // Reached the max so bail out on the gathering loop.
104 break;
105 }
106 } while (next != NULL && next->is_being_async_deflated());
107 if (prev == NULL) {
108 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
109 if (prev_head != head) {
110 // Find new prev ObjectMonitor that just got inserted.
111 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
112 prev = n;
113 }
114 prev->set_next_om(next);
115 }
116 } else {
117 prev->set_next_om(next);
118 }
119 if (unlinked_count >= (size_t)MonitorDeflationMax) {
120 // Reached the max so bail out on the searching loop.
121 break;
122 }
123 m = next;
124 } else {
125 prev = m;
126 m = m->next_om();
127 }
128
129 if (current->is_Java_thread()) {
130 // A JavaThread must check for a safepoint/handshake and honor it.
131 ObjectSynchronizer::chk_for_block_req(current->as_Java_thread(), "unlinking",
132 "unlinked_count", unlinked_count,
133 ls, timer_p);
134 }
135 }
136 Atomic::sub(&_count, unlinked_count);
137 return unlinked_count;
138 }
139
140 MonitorList::Iterator MonitorList::iterator() const {
141 return Iterator(Atomic::load_acquire(&_head));
142 }
143
144 ObjectMonitor* MonitorList::Iterator::next() {
145 ObjectMonitor* current = _current;
146 _current = current->next_om();
147 return current;
148 }
149
150 // The "core" versions of monitor enter and exit reside in this file.
151 // The interpreter and compilers contain specialized transliterated
152 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
153 // fast_lock(...) for instance. If you make changes here, make sure to modify the
154 // interpreter, and both C1 and C2 fast-path inline locking code emission.
155 //
156 // -----------------------------------------------------------------------------
157
158 #ifdef DTRACE_ENABLED
159
160 // Only bother with this argument setup if dtrace is available
161 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
162
163 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
164 char* bytes = NULL; \
165 int len = 0; \
166 jlong jtid = SharedRuntime::get_java_tid(thread); \
167 Symbol* klassname = obj->klass()->name(); \
168 if (klassname != NULL) { \
169 bytes = (char*)klassname->bytes(); \
170 len = klassname->utf8_length(); \
171 }
172
173 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
174 { \
175 if (DTraceMonitorProbes) { \
176 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
177 HOTSPOT_MONITOR_WAIT(jtid, \
178 (uintptr_t)(monitor), bytes, len, (millis)); \
179 } \
180 }
181
182 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
183 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
184 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
185
186 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
187 { \
188 if (DTraceMonitorProbes) { \
189 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
190 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
191 (uintptr_t)(monitor), bytes, len); \
192 } \
193 }
194
195 #else // ndef DTRACE_ENABLED
196
197 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
198 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
199
200 #endif // ndef DTRACE_ENABLED
201
202 // This exists only as a workaround of dtrace bug 6254741
203 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
204 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
205 return 0;
206 }
207
208 static const int NINFLATIONLOCKS = 256;
209 static os::PlatformMutex* gInflationLocks[NINFLATIONLOCKS];
210
211 void ObjectSynchronizer::initialize() {
212 for (int i = 0; i < NINFLATIONLOCKS; i++) {
213 gInflationLocks[i] = new os::PlatformMutex();
214 }
215 // Start the ceiling with the estimate for one thread.
216 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
217
218 // Start the timer for deflations, so it does not trigger immediately.
219 _last_async_deflation_time_ns = os::javaTimeNanos();
220 }
221
222 MonitorList ObjectSynchronizer::_in_use_list;
223 // monitors_used_above_threshold() policy is as follows:
224 //
225 // The ratio of the current _in_use_list count to the ceiling is used
226 // to determine if we are above MonitorUsedDeflationThreshold and need
227 // to do an async monitor deflation cycle. The ceiling is increased by
228 // AvgMonitorsPerThreadEstimate when a thread is added to the system
229 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
230 // removed from the system.
231 //
232 // Note: If the _in_use_list max exceeds the ceiling, then
233 // monitors_used_above_threshold() will use the in_use_list max instead
234 // of the thread count derived ceiling because we have used more
235 // ObjectMonitors than the estimated average.
236 //
237 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
238 // no-progress async monitor deflation cycles in a row, then the ceiling
239 // is adjusted upwards by monitors_used_above_threshold().
240 //
241 // Start the ceiling with the estimate for one thread in initialize()
242 // which is called after cmd line options are processed.
243 static size_t _in_use_list_ceiling = 0;
244 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
245 bool volatile ObjectSynchronizer::_is_final_audit = false;
246 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
247 static uintx _no_progress_cnt = 0;
248 static bool _no_progress_skip_increment = false;
249
250 // =====================> Quick functions
251
252 // The quick_* forms are special fast-path variants used to improve
253 // performance. In the simplest case, a "quick_*" implementation could
254 // simply return false, in which case the caller will perform the necessary
255 // state transitions and call the slow-path form.
256 // The fast-path is designed to handle frequently arising cases in an efficient
257 // manner and is just a degenerate "optimistic" variant of the slow-path.
258 // returns true -- to indicate the call was satisfied.
259 // returns false -- to indicate the call needs the services of the slow-path.
260 // A no-loitering ordinance is in effect for code in the quick_* family
261 // operators: safepoints or indefinite blocking (blocking that might span a
262 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
263 // entry.
264 //
265 // Consider: An interesting optimization is to have the JIT recognize the
266 // following common idiom:
267 // synchronized (someobj) { .... ; notify(); }
268 // That is, we find a notify() or notifyAll() call that immediately precedes
269 // the monitorexit operation. In that case the JIT could fuse the operations
270 // into a single notifyAndExit() runtime primitive.
271
272 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
273 assert(current->thread_state() == _thread_in_Java, "invariant");
274 NoSafepointVerifier nsv;
275 if (obj == NULL) return false; // slow-path for invalid obj
276 const markWord mark = obj->mark();
277
278 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
279 // Degenerate notify
280 // stack-locked by caller so by definition the implied waitset is empty.
281 return true;
282 }
283
284 if (mark.has_monitor()) {
285 ObjectMonitor* const mon = mark.monitor();
286 assert(mon->object() == oop(obj), "invariant");
287 if (mon->owner() != current) return false; // slow-path for IMS exception
288
289 if (mon->first_waiter() != NULL) {
290 // We have one or more waiters. Since this is an inflated monitor
291 // that we own, we can transfer one or more threads from the waitset
292 // to the entrylist here and now, avoiding the slow-path.
293 if (all) {
294 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
295 } else {
296 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
297 }
298 int free_count = 0;
299 do {
300 mon->INotify(current);
301 ++free_count;
302 } while (mon->first_waiter() != NULL && all);
303 OM_PERFDATA_OP(Notifications, inc(free_count));
304 }
305 return true;
306 }
307
308 // biased locking and any other IMS exception states take the slow-path
309 return false;
310 }
311
312
313 // The LockNode emitted directly at the synchronization site would have
314 // been too big if it were to have included support for the cases of inflated
315 // recursive enter and exit, so they go here instead.
316 // Note that we can't safely call AsyncPrintJavaStack() from within
317 // quick_enter() as our thread state remains _in_Java.
318
319 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
320 BasicLock * lock) {
321 assert(current->thread_state() == _thread_in_Java, "invariant");
322 NoSafepointVerifier nsv;
323 if (obj == NULL) return false; // Need to throw NPE
324
325 if (obj->klass()->is_value_based()) {
326 return false;
327 }
328
329 const markWord mark = obj->mark();
330
331 if (mark.has_monitor()) {
332 ObjectMonitor* const m = mark.monitor();
333 // An async deflation or GC can race us before we manage to make
334 // the ObjectMonitor busy by setting the owner below. If we detect
335 // that race we just bail out to the slow-path here.
336 if (m->object_peek() == NULL) {
337 return false;
338 }
339 JavaThread* const owner = (JavaThread*) m->owner_raw();
340
341 // Lock contention and Transactional Lock Elision (TLE) diagnostics
342 // and observability
343 // Case: light contention possibly amenable to TLE
344 // Case: TLE inimical operations such as nested/recursive synchronization
345
346 if (owner == current) {
347 m->_recursions++;
348 return true;
349 }
350
351 // This Java Monitor is inflated so obj's header will never be
352 // displaced to this thread's BasicLock. Make the displaced header
353 // non-NULL so this BasicLock is not seen as recursive nor as
354 // being locked. We do this unconditionally so that this thread's
355 // BasicLock cannot be mis-interpreted by any stack walkers. For
356 // performance reasons, stack walkers generally first check for
357 // Biased Locking in the object's header, the second check is for
358 // stack-locking in the object's header, the third check is for
359 // recursive stack-locking in the displaced header in the BasicLock,
360 // and last are the inflated Java Monitor (ObjectMonitor) checks.
361 lock->set_displaced_header(markWord::unused_mark());
362
363 if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
364 assert(m->_recursions == 0, "invariant");
365 return true;
366 }
367 }
368
369 // Note that we could inflate in quick_enter.
370 // This is likely a useful optimization
371 // Critically, in quick_enter() we must not:
372 // -- perform bias revocation, or
373 // -- block indefinitely, or
374 // -- reach a safepoint
375
376 return false; // revert to slow-path
377 }
378
379 // Handle notifications when synchronizing on value based classes
380 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
381 frame last_frame = current->last_frame();
382 bool bcp_was_adjusted = false;
383 // Don't decrement bcp if it points to the frame's first instruction. This happens when
384 // handle_sync_on_value_based_class() is called because of a synchronized method. There
385 // is no actual monitorenter instruction in the byte code in this case.
386 if (last_frame.is_interpreted_frame() &&
387 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
388 // adjust bcp to point back to monitorenter so that we print the correct line numbers
389 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
390 bcp_was_adjusted = true;
391 }
392
393 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
394 ResourceMark rm(current);
395 stringStream ss;
396 current->print_stack_on(&ss);
397 char* base = (char*)strstr(ss.base(), "at");
398 char* newline = (char*)strchr(ss.base(), '\n');
399 if (newline != NULL) {
400 *newline = '\0';
401 }
402 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
403 } else {
404 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
405 ResourceMark rm(current);
406 Log(valuebasedclasses) vblog;
407
408 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
409 if (current->has_last_Java_frame()) {
410 LogStream info_stream(vblog.info());
411 current->print_stack_on(&info_stream);
412 } else {
413 vblog.info("Cannot find the last Java frame");
414 }
415
416 EventSyncOnValueBasedClass event;
417 if (event.should_commit()) {
418 event.set_valueBasedClass(obj->klass());
419 event.commit();
420 }
421 }
422
423 if (bcp_was_adjusted) {
424 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
425 }
426 }
427
428 // -----------------------------------------------------------------------------
429 // Monitor Enter/Exit
430 // The interpreter and compiler assembly code tries to lock using the fast path
431 // of this algorithm. Make sure to update that code if the following function is
432 // changed. The implementation is extremely sensitive to race condition. Be careful.
433
434 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
435 if (obj->klass()->is_value_based()) {
436 handle_sync_on_value_based_class(obj, current);
437 }
438
439 if (UseBiasedLocking) {
440 BiasedLocking::revoke(current, obj);
441 }
442
443 markWord mark = obj->mark();
444 assert(!mark.has_bias_pattern(), "should not see bias pattern here");
445
446 if (mark.is_neutral()) {
447 // Anticipate successful CAS -- the ST of the displaced mark must
448 // be visible <= the ST performed by the CAS.
449 lock->set_displaced_header(mark);
450 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
451 return;
452 }
453 // Fall through to inflate() ...
454 } else if (mark.has_locker() &&
455 current->is_lock_owned((address)mark.locker())) {
456 assert(lock != mark.locker(), "must not re-lock the same lock");
457 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
458 lock->set_displaced_header(markWord::from_pointer(NULL));
459 return;
460 }
461
462 // The object header will never be displaced to this lock,
463 // so it does not matter what the value is, except that it
464 // must be non-zero to avoid looking like a re-entrant lock,
465 // and must not look locked either.
466 lock->set_displaced_header(markWord::unused_mark());
467 // An async deflation can race after the inflate() call and before
468 // enter() can make the ObjectMonitor busy. enter() returns false if
469 // we have lost the race to async deflation and we simply try again.
470 while (true) {
471 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
472 if (monitor->enter(current)) {
473 return;
474 }
475 }
476 }
477
478 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
479 markWord mark = object->mark();
480 // We cannot check for Biased Locking if we are racing an inflation.
481 assert(mark == markWord::INFLATING() ||
482 !mark.has_bias_pattern(), "should not see bias pattern here");
483
484 markWord dhw = lock->displaced_header();
485 if (dhw.value() == 0) {
486 // If the displaced header is NULL, then this exit matches up with
487 // a recursive enter. No real work to do here except for diagnostics.
488 #ifndef PRODUCT
489 if (mark != markWord::INFLATING()) {
490 // Only do diagnostics if we are not racing an inflation. Simply
491 // exiting a recursive enter of a Java Monitor that is being
492 // inflated is safe; see the has_monitor() comment below.
493 assert(!mark.is_neutral(), "invariant");
494 assert(!mark.has_locker() ||
495 current->is_lock_owned((address)mark.locker()), "invariant");
496 if (mark.has_monitor()) {
497 // The BasicLock's displaced_header is marked as a recursive
498 // enter and we have an inflated Java Monitor (ObjectMonitor).
499 // This is a special case where the Java Monitor was inflated
500 // after this thread entered the stack-lock recursively. When a
501 // Java Monitor is inflated, we cannot safely walk the Java
502 // Monitor owner's stack and update the BasicLocks because a
503 // Java Monitor can be asynchronously inflated by a thread that
504 // does not own the Java Monitor.
505 ObjectMonitor* m = mark.monitor();
506 assert(m->object()->mark() == mark, "invariant");
507 assert(m->is_entered(current), "invariant");
508 }
509 }
510 #endif
511 return;
512 }
513
514 if (mark == markWord::from_pointer(lock)) {
515 // If the object is stack-locked by the current thread, try to
516 // swing the displaced header from the BasicLock back to the mark.
517 assert(dhw.is_neutral(), "invariant");
518 if (object->cas_set_mark(dhw, mark) == mark) {
519 return;
520 }
521 }
522
523 // We have to take the slow-path of possible inflation and then exit.
524 // The ObjectMonitor* can't be async deflated until ownership is
525 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
526 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
527 monitor->exit(current);
528 }
529
530 // -----------------------------------------------------------------------------
531 // Class Loader support to workaround deadlocks on the class loader lock objects
532 // Also used by GC
533 // complete_exit()/reenter() are used to wait on a nested lock
534 // i.e. to give up an outer lock completely and then re-enter
535 // Used when holding nested locks - lock acquisition order: lock1 then lock2
536 // 1) complete_exit lock1 - saving recursion count
537 // 2) wait on lock2
538 // 3) when notified on lock2, unlock lock2
539 // 4) reenter lock1 with original recursion count
540 // 5) lock lock2
541 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
542 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
543 if (UseBiasedLocking) {
544 BiasedLocking::revoke(current, obj);
545 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
546 }
547
548 // The ObjectMonitor* can't be async deflated until ownership is
549 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
550 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
551 intptr_t ret_code = monitor->complete_exit(current);
552 return ret_code;
553 }
554
555 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
556 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
557 if (UseBiasedLocking) {
558 BiasedLocking::revoke(current, obj);
559 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
560 }
561
562 // An async deflation can race after the inflate() call and before
563 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
564 // enter() returns false if we have lost the race to async deflation
565 // and we simply try again.
566 while (true) {
567 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
568 if (monitor->reenter(recursions, current)) {
569 return;
570 }
571 }
572 }
573
574 // -----------------------------------------------------------------------------
575 // JNI locks on java objects
576 // NOTE: must use heavy weight monitor to handle jni monitor enter
577 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
578 if (obj->klass()->is_value_based()) {
579 handle_sync_on_value_based_class(obj, current);
580 }
581
582 // the current locking is from JNI instead of Java code
583 if (UseBiasedLocking) {
584 BiasedLocking::revoke(current, obj);
585 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
586 }
587 current->set_current_pending_monitor_is_from_java(false);
588 // An async deflation can race after the inflate() call and before
589 // enter() can make the ObjectMonitor busy. enter() returns false if
590 // we have lost the race to async deflation and we simply try again.
591 while (true) {
592 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
593 if (monitor->enter(current)) {
594 break;
595 }
596 }
597 current->set_current_pending_monitor_is_from_java(true);
598 }
599
600 // NOTE: must use heavy weight monitor to handle jni monitor exit
601 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
602 JavaThread* current = THREAD;
603 if (UseBiasedLocking) {
604 Handle h_obj(current, obj);
605 BiasedLocking::revoke(current, h_obj);
606 obj = h_obj();
607 }
608 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
609
610 // The ObjectMonitor* can't be async deflated until ownership is
611 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
612 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
613 // If this thread has locked the object, exit the monitor. We
614 // intentionally do not use CHECK on check_owner because we must exit the
615 // monitor even if an exception was already pending.
616 if (monitor->check_owner(THREAD)) {
617 monitor->exit(current);
618 }
619 }
620
621 // -----------------------------------------------------------------------------
622 // Internal VM locks on java objects
623 // standard constructor, allows locking failures
624 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
625 _thread = thread;
626 _thread->check_for_valid_safepoint_state();
627 _obj = obj;
628
629 if (_obj() != NULL) {
630 ObjectSynchronizer::enter(_obj, &_lock, _thread);
631 }
632 }
633
634 ObjectLocker::~ObjectLocker() {
635 if (_obj() != NULL) {
636 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
637 }
638 }
639
640
641 // -----------------------------------------------------------------------------
642 // Wait/Notify/NotifyAll
643 // NOTE: must use heavy weight monitor to handle wait()
644 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
645 JavaThread* current = THREAD;
646 if (UseBiasedLocking) {
647 BiasedLocking::revoke(current, obj);
648 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
649 }
650 if (millis < 0) {
651 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
652 }
653 // The ObjectMonitor* can't be async deflated because the _waiters
654 // field is incremented before ownership is dropped and decremented
655 // after ownership is regained.
656 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
657
658 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
659 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
660
661 // This dummy call is in place to get around dtrace bug 6254741. Once
662 // that's fixed we can uncomment the following line, remove the call
663 // and change this function back into a "void" func.
664 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
665 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
666 return ret_code;
667 }
668
669 // No exception are possible in this case as we only use this internally when locking is
670 // correct and we have to wait until notified - so no interrupts or timeouts.
671 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, JavaThread* current) {
672 if (UseBiasedLocking) {
673 BiasedLocking::revoke(current, obj);
674 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
675 }
676 // The ObjectMonitor* can't be async deflated because the _waiters
677 // field is incremented before ownership is dropped and decremented
678 // after ownership is regained.
679 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
680 monitor->wait(0 /* wait-forever */, false /* not interruptible */, current);
681 }
682
683 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
684 JavaThread* current = THREAD;
685 if (UseBiasedLocking) {
686 BiasedLocking::revoke(current, obj);
687 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
688 }
689
690 markWord mark = obj->mark();
691 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
692 // Not inflated so there can't be any waiters to notify.
693 return;
694 }
695 // The ObjectMonitor* can't be async deflated until ownership is
696 // dropped by the calling thread.
697 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
698 monitor->notify(CHECK);
699 }
700
701 // NOTE: see comment of notify()
702 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
703 JavaThread* current = THREAD;
704 if (UseBiasedLocking) {
705 BiasedLocking::revoke(current, obj);
706 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
707 }
708
709 markWord mark = obj->mark();
710 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
711 // Not inflated so there can't be any waiters to notify.
712 return;
713 }
714 // The ObjectMonitor* can't be async deflated until ownership is
715 // dropped by the calling thread.
716 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
717 monitor->notifyAll(CHECK);
718 }
719
720 // -----------------------------------------------------------------------------
721 // Hash Code handling
722
723 struct SharedGlobals {
724 char _pad_prefix[OM_CACHE_LINE_SIZE];
725 // This is a highly shared mostly-read variable.
726 // To avoid false-sharing it needs to be the sole occupant of a cache line.
727 volatile int stw_random;
728 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
729 // Hot RW variable -- Sequester to avoid false-sharing
730 volatile int hc_sequence;
731 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
732 };
733
734 static SharedGlobals GVars;
735
736 static markWord read_stable_mark(oop obj) {
737 markWord mark = obj->mark_acquire();
738 if (!mark.is_being_inflated()) {
739 return mark; // normal fast-path return
740 }
741
742 int its = 0;
743 for (;;) {
744 markWord mark = obj->mark_acquire();
745 if (!mark.is_being_inflated()) {
746 return mark; // normal fast-path return
747 }
748
749 // The object is being inflated by some other thread.
750 // The caller of read_stable_mark() must wait for inflation to complete.
751 // Avoid live-lock.
752
753 ++its;
754 if (its > 10000 || !os::is_MP()) {
755 if (its & 1) {
756 os::naked_yield();
757 } else {
758 // Note that the following code attenuates the livelock problem but is not
759 // a complete remedy. A more complete solution would require that the inflating
760 // thread hold the associated inflation lock. The following code simply restricts
761 // the number of spinners to at most one. We'll have N-2 threads blocked
762 // on the inflationlock, 1 thread holding the inflation lock and using
763 // a yield/park strategy, and 1 thread in the midst of inflation.
764 // A more refined approach would be to change the encoding of INFLATING
765 // to allow encapsulation of a native thread pointer. Threads waiting for
766 // inflation to complete would use CAS to push themselves onto a singly linked
767 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
768 // and calling park(). When inflation was complete the thread that accomplished inflation
769 // would detach the list and set the markword to inflated with a single CAS and
770 // then for each thread on the list, set the flag and unpark() the thread.
771
772 // Index into the lock array based on the current object address.
773 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
774 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
775 int YieldThenBlock = 0;
776 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
777 gInflationLocks[ix]->lock();
778 while (obj->mark_acquire() == markWord::INFLATING()) {
779 // Beware: naked_yield() is advisory and has almost no effect on some platforms
780 // so we periodically call current->_ParkEvent->park(1).
781 // We use a mixed spin/yield/block mechanism.
782 if ((YieldThenBlock++) >= 16) {
783 Thread::current()->_ParkEvent->park(1);
784 } else {
785 os::naked_yield();
786 }
787 }
788 gInflationLocks[ix]->unlock();
789 }
790 } else {
791 SpinPause(); // SMP-polite spinning
792 }
793 }
794 }
795
796 // hashCode() generation :
797 //
798 // Possibilities:
799 // * MD5Digest of {obj,stw_random}
800 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
801 // * A DES- or AES-style SBox[] mechanism
802 // * One of the Phi-based schemes, such as:
803 // 2654435761 = 2^32 * Phi (golden ratio)
804 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
805 // * A variation of Marsaglia's shift-xor RNG scheme.
806 // * (obj ^ stw_random) is appealing, but can result
807 // in undesirable regularity in the hashCode values of adjacent objects
808 // (objects allocated back-to-back, in particular). This could potentially
809 // result in hashtable collisions and reduced hashtable efficiency.
810 // There are simple ways to "diffuse" the middle address bits over the
811 // generated hashCode values:
812
813 static inline intptr_t get_next_hash(Thread* current, oop obj) {
814 intptr_t value = 0;
815 if (hashCode == 0) {
816 // This form uses global Park-Miller RNG.
817 // On MP system we'll have lots of RW access to a global, so the
818 // mechanism induces lots of coherency traffic.
819 value = os::random();
820 } else if (hashCode == 1) {
821 // This variation has the property of being stable (idempotent)
822 // between STW operations. This can be useful in some of the 1-0
823 // synchronization schemes.
824 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
825 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
826 } else if (hashCode == 2) {
827 value = 1; // for sensitivity testing
828 } else if (hashCode == 3) {
829 value = ++GVars.hc_sequence;
830 } else if (hashCode == 4) {
831 value = cast_from_oop<intptr_t>(obj);
832 } else {
833 // Marsaglia's xor-shift scheme with thread-specific state
834 // This is probably the best overall implementation -- we'll
835 // likely make this the default in future releases.
836 unsigned t = current->_hashStateX;
837 t ^= (t << 11);
838 current->_hashStateX = current->_hashStateY;
839 current->_hashStateY = current->_hashStateZ;
840 current->_hashStateZ = current->_hashStateW;
841 unsigned v = current->_hashStateW;
842 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
843 current->_hashStateW = v;
844 value = v;
845 }
846
847 value &= markWord::hash_mask;
848 if (value == 0) value = 0xBAD;
849 assert(value != markWord::no_hash, "invariant");
850 return value;
851 }
852
853 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
854 if (UseBiasedLocking) {
855 // NOTE: many places throughout the JVM do not expect a safepoint
856 // to be taken here. However, we only ever bias Java instances and all
857 // of the call sites of identity_hash that might revoke biases have
858 // been checked to make sure they can handle a safepoint. The
859 // added check of the bias pattern is to avoid useless calls to
860 // thread-local storage.
861 if (obj->mark().has_bias_pattern()) {
862 // Handle for oop obj in case of STW safepoint
863 Handle hobj(current, obj);
864 if (SafepointSynchronize::is_at_safepoint()) {
865 BiasedLocking::revoke_at_safepoint(hobj);
866 } else {
867 BiasedLocking::revoke(current->as_Java_thread(), hobj);
868 }
869 obj = hobj();
870 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
871 }
872 }
873
874 while (true) {
875 ObjectMonitor* monitor = NULL;
876 markWord temp, test;
877 intptr_t hash;
878 markWord mark = read_stable_mark(obj);
879
880 // object should remain ineligible for biased locking
881 assert(!mark.has_bias_pattern(), "invariant");
882
883 if (mark.is_neutral()) { // if this is a normal header
884 hash = mark.hash();
885 if (hash != 0) { // if it has a hash, just return it
886 return hash;
887 }
888 hash = get_next_hash(current, obj); // get a new hash
889 temp = mark.copy_set_hash(hash); // merge the hash into header
890 // try to install the hash
891 test = obj->cas_set_mark(temp, mark);
892 if (test == mark) { // if the hash was installed, return it
893 return hash;
894 }
895 // Failed to install the hash. It could be that another thread
896 // installed the hash just before our attempt or inflation has
897 // occurred or... so we fall thru to inflate the monitor for
898 // stability and then install the hash.
899 } else if (mark.has_monitor()) {
900 monitor = mark.monitor();
901 temp = monitor->header();
902 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
903 hash = temp.hash();
904 if (hash != 0) {
905 // It has a hash.
906
907 // Separate load of dmw/header above from the loads in
908 // is_being_async_deflated().
909
910 // dmw/header and _contentions may get written by different threads.
911 // Make sure to observe them in the same order when having several observers.
912 OrderAccess::loadload_for_IRIW();
913
914 if (monitor->is_being_async_deflated()) {
915 // But we can't safely use the hash if we detect that async
916 // deflation has occurred. So we attempt to restore the
917 // header/dmw to the object's header so that we only retry
918 // once if the deflater thread happens to be slow.
919 monitor->install_displaced_markword_in_object(obj);
920 continue;
921 }
922 return hash;
923 }
924 // Fall thru so we only have one place that installs the hash in
925 // the ObjectMonitor.
926 } else if (current->is_lock_owned((address)mark.locker())) {
927 // This is a stack lock owned by the calling thread so fetch the
928 // displaced markWord from the BasicLock on the stack.
929 temp = mark.displaced_mark_helper();
930 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
931 hash = temp.hash();
932 if (hash != 0) { // if it has a hash, just return it
933 return hash;
934 }
935 // WARNING:
936 // The displaced header in the BasicLock on a thread's stack
937 // is strictly immutable. It CANNOT be changed in ANY cases.
938 // So we have to inflate the stack lock into an ObjectMonitor
939 // even if the current thread owns the lock. The BasicLock on
940 // a thread's stack can be asynchronously read by other threads
941 // during an inflate() call so any change to that stack memory
942 // may not propagate to other threads correctly.
943 }
944
945 // Inflate the monitor to set the hash.
946
947 // An async deflation can race after the inflate() call and before we
948 // can update the ObjectMonitor's header with the hash value below.
949 monitor = inflate(current, obj, inflate_cause_hash_code);
950 // Load ObjectMonitor's header/dmw field and see if it has a hash.
951 mark = monitor->header();
952 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
953 hash = mark.hash();
954 if (hash == 0) { // if it does not have a hash
955 hash = get_next_hash(current, obj); // get a new hash
956 temp = mark.copy_set_hash(hash) ; // merge the hash into header
957 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
958 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
959 test = markWord(v);
960 if (test != mark) {
961 // The attempt to update the ObjectMonitor's header/dmw field
962 // did not work. This can happen if another thread managed to
963 // merge in the hash just before our cmpxchg().
964 // If we add any new usages of the header/dmw field, this code
965 // will need to be updated.
966 hash = test.hash();
967 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
968 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
969 }
970 if (monitor->is_being_async_deflated()) {
971 // If we detect that async deflation has occurred, then we
972 // attempt to restore the header/dmw to the object's header
973 // so that we only retry once if the deflater thread happens
974 // to be slow.
975 monitor->install_displaced_markword_in_object(obj);
976 continue;
977 }
978 }
979 // We finally get the hash.
980 return hash;
981 }
982 }
983
984 // Deprecated -- use FastHashCode() instead.
985
986 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
987 return FastHashCode(Thread::current(), obj());
988 }
989
990
991 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
992 Handle h_obj) {
993 if (UseBiasedLocking) {
994 BiasedLocking::revoke(current, h_obj);
995 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
996 }
997
998 assert(current == JavaThread::current(), "Can only be called on current thread");
999 oop obj = h_obj();
1000
1001 markWord mark = read_stable_mark(obj);
1002
1003 // Uncontended case, header points to stack
1004 if (mark.has_locker()) {
1005 return current->is_lock_owned((address)mark.locker());
1006 }
1007 // Contended case, header points to ObjectMonitor (tagged pointer)
1008 if (mark.has_monitor()) {
1009 // The first stage of async deflation does not affect any field
1010 // used by this comparison so the ObjectMonitor* is usable here.
1011 ObjectMonitor* monitor = mark.monitor();
1012 return monitor->is_entered(current) != 0;
1013 }
1014 // Unlocked case, header in place
1015 assert(mark.is_neutral(), "sanity check");
1016 return false;
1017 }
1018
1019 // FIXME: jvmti should call this
1020 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1021 if (UseBiasedLocking) {
1022 if (SafepointSynchronize::is_at_safepoint()) {
1023 BiasedLocking::revoke_at_safepoint(h_obj);
1024 } else {
1025 BiasedLocking::revoke(JavaThread::current(), h_obj);
1026 }
1027 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1028 }
1029
1030 oop obj = h_obj();
1031 address owner = NULL;
1032
1033 markWord mark = read_stable_mark(obj);
1034
1035 // Uncontended case, header points to stack
1036 if (mark.has_locker()) {
1037 owner = (address) mark.locker();
1038 }
1039
1040 // Contended case, header points to ObjectMonitor (tagged pointer)
1041 else if (mark.has_monitor()) {
1042 // The first stage of async deflation does not affect any field
1043 // used by this comparison so the ObjectMonitor* is usable here.
1044 ObjectMonitor* monitor = mark.monitor();
1045 assert(monitor != NULL, "monitor should be non-null");
1046 owner = (address) monitor->owner();
1047 }
1048
1049 if (owner != NULL) {
1050 // owning_thread_from_monitor_owner() may also return NULL here
1051 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1052 }
1053
1054 // Unlocked case, header in place
1055 // Cannot have assertion since this object may have been
1056 // locked by another thread when reaching here.
1057 // assert(mark.is_neutral(), "sanity check");
1058
1059 return NULL;
1060 }
1061
1062 // Visitors ...
1063
1064 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1065 MonitorList::Iterator iter = _in_use_list.iterator();
1066 while (iter.has_next()) {
1067 ObjectMonitor* mid = iter.next();
1068 if (mid->owner() != thread) {
1069 continue;
1070 }
1071 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1072 // Only process with closure if the object is set.
1073
1074 // monitors_iterate() is only called at a safepoint or when the
1075 // target thread is suspended or when the target thread is
1076 // operating on itself. The current closures in use today are
1077 // only interested in an owned ObjectMonitor and ownership
1078 // cannot be dropped under the calling contexts so the
1079 // ObjectMonitor cannot be async deflated.
1080 closure->do_monitor(mid);
1081 }
1082 }
1083 }
1084
1085 static bool monitors_used_above_threshold(MonitorList* list) {
1086 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1087 return false;
1088 }
1089 // Start with ceiling based on a per-thread estimate:
1090 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1091 size_t old_ceiling = ceiling;
1092 if (ceiling < list->max()) {
1093 // The max used by the system has exceeded the ceiling so use that:
1094 ceiling = list->max();
1095 }
1096 size_t monitors_used = list->count();
1097 if (monitors_used == 0) { // empty list is easy
1098 return false;
1099 }
1100 if (NoAsyncDeflationProgressMax != 0 &&
1101 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1102 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1103 size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1104 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1105 log_info(monitorinflation)("Too many deflations without progress; "
1106 "bumping in_use_list_ceiling from " SIZE_FORMAT
1107 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1108 _no_progress_cnt = 0;
1109 ceiling = new_ceiling;
1110 }
1111
1112 // Check if our monitor usage is above the threshold:
1113 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1114 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1115 log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
1116 ", monitor_usage=" SIZE_FORMAT ", threshold=" INTX_FORMAT,
1117 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1118 return true;
1119 }
1120
1121 return false;
1122 }
1123
1124 size_t ObjectSynchronizer::in_use_list_ceiling() {
1125 return _in_use_list_ceiling;
1126 }
1127
1128 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1129 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1130 }
1131
1132 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1133 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1134 }
1135
1136 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1137 _in_use_list_ceiling = new_value;
1138 }
1139
1140 bool ObjectSynchronizer::is_async_deflation_needed() {
1141 if (is_async_deflation_requested()) {
1142 // Async deflation request.
1143 log_info(monitorinflation)("Async deflation needed: explicit request");
1144 return true;
1145 }
1146
1147 jlong time_since_last = time_since_last_async_deflation_ms();
1148
1149 if (AsyncDeflationInterval > 0 &&
1150 time_since_last > AsyncDeflationInterval &&
1151 monitors_used_above_threshold(&_in_use_list)) {
1152 // It's been longer than our specified deflate interval and there
1153 // are too many monitors in use. We don't deflate more frequently
1154 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1155 // in order to not swamp the MonitorDeflationThread.
1156 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1157 return true;
1158 }
1159
1160 if (GuaranteedAsyncDeflationInterval > 0 &&
1161 time_since_last > GuaranteedAsyncDeflationInterval) {
1162 // It's been longer than our specified guaranteed deflate interval.
1163 // We need to clean up the used monitors even if the threshold is
1164 // not reached, to keep the memory utilization at bay when many threads
1165 // touched many monitors.
1166 log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) "
1167 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1168 GuaranteedAsyncDeflationInterval, time_since_last);
1169
1170 // If this deflation has no progress, then it should not affect the no-progress
1171 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1172 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1173 // the generic code would bump the no-progress counter, and we compensate for that
1174 // by telling it to skip the update.
1175 //
1176 // If this deflation has progress, then it should let non-progress tracking
1177 // know about this, otherwise the threshold heuristics would kick in, potentially
1178 // experience no-progress due to aggressive cleanup by this deflation, and think
1179 // it is still in no-progress stride. In this "progress" case, the generic code would
1180 // zero the counter, and we allow it to happen.
1181 _no_progress_skip_increment = true;
1182
1183 return true;
1184 }
1185
1186 return false;
1187 }
1188
1189 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1190 JavaThread* current = JavaThread::current();
1191 bool ret_code = false;
1192
1193 jlong last_time = last_async_deflation_time_ns();
1194 set_is_async_deflation_requested(true);
1195 {
1196 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1197 ml.notify_all();
1198 }
1199 const int N_CHECKS = 5;
1200 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1201 if (last_async_deflation_time_ns() > last_time) {
1202 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1203 ret_code = true;
1204 break;
1205 }
1206 {
1207 // JavaThread has to honor the blocking protocol.
1208 ThreadBlockInVM tbivm(current);
1209 os::naked_short_sleep(999); // sleep for almost 1 second
1210 }
1211 }
1212 if (!ret_code) {
1213 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1214 }
1215
1216 return ret_code;
1217 }
1218
1219 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1220 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1221 }
1222
1223 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1224 const oop obj,
1225 ObjectSynchronizer::InflateCause cause) {
1226 assert(event != NULL, "invariant");
1227 assert(event->should_commit(), "invariant");
1228 event->set_monitorClass(obj->klass());
1229 event->set_address((uintptr_t)(void*)obj);
1230 event->set_cause((u1)cause);
1231 event->commit();
1232 }
1233
1234 // Fast path code shared by multiple functions
1235 void ObjectSynchronizer::inflate_helper(oop obj) {
1236 markWord mark = obj->mark_acquire();
1237 if (mark.has_monitor()) {
1238 ObjectMonitor* monitor = mark.monitor();
1239 markWord dmw = monitor->header();
1240 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1241 return;
1242 }
1243 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1244 }
1245
1246 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1247 const InflateCause cause) {
1248 EventJavaMonitorInflate event;
1249
1250 for (;;) {
1251 const markWord mark = object->mark_acquire();
1252 assert(!mark.has_bias_pattern(), "invariant");
1253
1254 // The mark can be in one of the following states:
1255 // * Inflated - just return
1256 // * Stack-locked - coerce it to inflated
1257 // * INFLATING - busy wait for conversion to complete
1258 // * Neutral - aggressively inflate the object.
1259 // * BIASED - Illegal. We should never see this
1260
1261 // CASE: inflated
1262 if (mark.has_monitor()) {
1263 ObjectMonitor* inf = mark.monitor();
1264 markWord dmw = inf->header();
1265 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1266 return inf;
1267 }
1268
1269 // CASE: inflation in progress - inflating over a stack-lock.
1270 // Some other thread is converting from stack-locked to inflated.
1271 // Only that thread can complete inflation -- other threads must wait.
1272 // The INFLATING value is transient.
1273 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1274 // We could always eliminate polling by parking the thread on some auxiliary list.
1275 if (mark == markWord::INFLATING()) {
1276 read_stable_mark(object);
1277 continue;
1278 }
1279
1280 // CASE: stack-locked
1281 // Could be stack-locked either by this thread or by some other thread.
1282 //
1283 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1284 // to install INFLATING into the mark word. We originally installed INFLATING,
1285 // allocated the ObjectMonitor, and then finally STed the address of the
1286 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1287 // the interval in which INFLATING appeared in the mark, thus increasing
1288 // the odds of inflation contention.
1289
1290 LogStreamHandle(Trace, monitorinflation) lsh;
1291
1292 if (mark.has_locker()) {
1293 ObjectMonitor* m = new ObjectMonitor(object);
1294 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1295 // We do this before the CAS in order to minimize the length of time
1296 // in which INFLATING appears in the mark.
1297
1298 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1299 if (cmp != mark) {
1300 delete m;
1301 continue; // Interference -- just retry
1302 }
1303
1304 // We've successfully installed INFLATING (0) into the mark-word.
1305 // This is the only case where 0 will appear in a mark-word.
1306 // Only the singular thread that successfully swings the mark-word
1307 // to 0 can perform (or more precisely, complete) inflation.
1308 //
1309 // Why do we CAS a 0 into the mark-word instead of just CASing the
1310 // mark-word from the stack-locked value directly to the new inflated state?
1311 // Consider what happens when a thread unlocks a stack-locked object.
1312 // It attempts to use CAS to swing the displaced header value from the
1313 // on-stack BasicLock back into the object header. Recall also that the
1314 // header value (hash code, etc) can reside in (a) the object header, or
1315 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1316 // header in an ObjectMonitor. The inflate() routine must copy the header
1317 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1318 // the while preserving the hashCode stability invariants. If the owner
1319 // decides to release the lock while the value is 0, the unlock will fail
1320 // and control will eventually pass from slow_exit() to inflate. The owner
1321 // will then spin, waiting for the 0 value to disappear. Put another way,
1322 // the 0 causes the owner to stall if the owner happens to try to
1323 // drop the lock (restoring the header from the BasicLock to the object)
1324 // while inflation is in-progress. This protocol avoids races that might
1325 // would otherwise permit hashCode values to change or "flicker" for an object.
1326 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1327 // 0 serves as a "BUSY" inflate-in-progress indicator.
1328
1329
1330 // fetch the displaced mark from the owner's stack.
1331 // The owner can't die or unwind past the lock while our INFLATING
1332 // object is in the mark. Furthermore the owner can't complete
1333 // an unlock on the object, either.
1334 markWord dmw = mark.displaced_mark_helper();
1335 // Catch if the object's header is not neutral (not locked and
1336 // not marked is what we care about here).
1337 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1338
1339 // Setup monitor fields to proper values -- prepare the monitor
1340 m->set_header(dmw);
1341
1342 // Optimization: if the mark.locker stack address is associated
1343 // with this thread we could simply set m->_owner = current.
1344 // Note that a thread can inflate an object
1345 // that it has stack-locked -- as might happen in wait() -- directly
1346 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1347 m->set_owner_from(NULL, mark.locker());
1348 // TODO-FIXME: assert BasicLock->dhw != 0.
1349
1350 // Must preserve store ordering. The monitor state must
1351 // be stable at the time of publishing the monitor address.
1352 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1353 // Release semantics so that above set_object() is seen first.
1354 object->release_set_mark(markWord::encode(m));
1355
1356 // Once ObjectMonitor is configured and the object is associated
1357 // with the ObjectMonitor, it is safe to allow async deflation:
1358 _in_use_list.add(m);
1359
1360 // Hopefully the performance counters are allocated on distinct cache lines
1361 // to avoid false sharing on MP systems ...
1362 OM_PERFDATA_OP(Inflations, inc());
1363 if (log_is_enabled(Trace, monitorinflation)) {
1364 ResourceMark rm(current);
1365 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1366 INTPTR_FORMAT ", type='%s'", p2i(object),
1367 object->mark().value(), object->klass()->external_name());
1368 }
1369 if (event.should_commit()) {
1370 post_monitor_inflate_event(&event, object, cause);
1371 }
1372 return m;
1373 }
1374
1375 // CASE: neutral
1376 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1377 // If we know we're inflating for entry it's better to inflate by swinging a
1378 // pre-locked ObjectMonitor pointer into the object header. A successful
1379 // CAS inflates the object *and* confers ownership to the inflating thread.
1380 // In the current implementation we use a 2-step mechanism where we CAS()
1381 // to inflate and then CAS() again to try to swing _owner from NULL to current.
1382 // An inflateTry() method that we could call from enter() would be useful.
1383
1384 // Catch if the object's header is not neutral (not locked and
1385 // not marked is what we care about here).
1386 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1387 ObjectMonitor* m = new ObjectMonitor(object);
1388 // prepare m for installation - set monitor to initial state
1389 m->set_header(mark);
1390
1391 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1392 delete m;
1393 m = NULL;
1394 continue;
1395 // interference - the markword changed - just retry.
1396 // The state-transitions are one-way, so there's no chance of
1397 // live-lock -- "Inflated" is an absorbing state.
1398 }
1399
1400 // Once the ObjectMonitor is configured and object is associated
1401 // with the ObjectMonitor, it is safe to allow async deflation:
1402 _in_use_list.add(m);
1403
1404 // Hopefully the performance counters are allocated on distinct
1405 // cache lines to avoid false sharing on MP systems ...
1406 OM_PERFDATA_OP(Inflations, inc());
1407 if (log_is_enabled(Trace, monitorinflation)) {
1408 ResourceMark rm(current);
1409 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1410 INTPTR_FORMAT ", type='%s'", p2i(object),
1411 object->mark().value(), object->klass()->external_name());
1412 }
1413 if (event.should_commit()) {
1414 post_monitor_inflate_event(&event, object, cause);
1415 }
1416 return m;
1417 }
1418 }
1419
1420 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1421 const char* cnt_name, size_t cnt,
1422 LogStream* ls, elapsedTimer* timer_p) {
1423 if (!SafepointMechanism::should_process(current)) {
1424 return;
1425 }
1426
1427 // A safepoint/handshake has started.
1428 if (ls != NULL) {
1429 timer_p->stop();
1430 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1431 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1432 op_name, cnt_name, cnt, in_use_list_ceiling(),
1433 _in_use_list.count(), _in_use_list.max());
1434 }
1435
1436 {
1437 // Honor block request.
1438 ThreadBlockInVM tbivm(current);
1439 }
1440
1441 if (ls != NULL) {
1442 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1443 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1444 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1445 timer_p->start();
1446 }
1447 }
1448
1449 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1450 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1451 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1452 elapsedTimer* timer_p) {
1453 MonitorList::Iterator iter = _in_use_list.iterator();
1454 size_t deflated_count = 0;
1455
1456 while (iter.has_next()) {
1457 if (deflated_count >= (size_t)MonitorDeflationMax) {
1458 break;
1459 }
1460 ObjectMonitor* mid = iter.next();
1461 if (mid->deflate_monitor()) {
1462 deflated_count++;
1463 }
1464
1465 if (current->is_Java_thread()) {
1466 // A JavaThread must check for a safepoint/handshake and honor it.
1467 chk_for_block_req(current->as_Java_thread(), "deflation", "deflated_count",
1468 deflated_count, ls, timer_p);
1469 }
1470 }
1471
1472 return deflated_count;
1473 }
1474
1475 class HandshakeForDeflation : public HandshakeClosure {
1476 public:
1477 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1478
1479 void do_thread(Thread* thread) {
1480 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1481 INTPTR_FORMAT, p2i(thread));
1482 }
1483 };
1484
1485 // This function is called by the MonitorDeflationThread to deflate
1486 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1487 // by the VMThread.
1488 size_t ObjectSynchronizer::deflate_idle_monitors() {
1489 Thread* current = Thread::current();
1490 if (current->is_Java_thread()) {
1491 // The async deflation request has been processed.
1492 _last_async_deflation_time_ns = os::javaTimeNanos();
1493 set_is_async_deflation_requested(false);
1494 }
1495
1496 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1497 LogStreamHandle(Info, monitorinflation) lsh_info;
1498 LogStream* ls = NULL;
1499 if (log_is_enabled(Debug, monitorinflation)) {
1500 ls = &lsh_debug;
1501 } else if (log_is_enabled(Info, monitorinflation)) {
1502 ls = &lsh_info;
1503 }
1504
1505 elapsedTimer timer;
1506 if (ls != NULL) {
1507 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1508 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1509 timer.start();
1510 }
1511
1512 // Deflate some idle ObjectMonitors.
1513 size_t deflated_count = deflate_monitor_list(current, ls, &timer);
1514 if (deflated_count > 0 || is_final_audit()) {
1515 // There are ObjectMonitors that have been deflated or this is the
1516 // final audit and all the remaining ObjectMonitors have been
1517 // deflated, BUT the MonitorDeflationThread blocked for the final
1518 // safepoint during unlinking.
1519
1520 // Unlink deflated ObjectMonitors from the in-use list.
1521 ResourceMark rm;
1522 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1523 size_t unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer,
1524 &delete_list);
1525 if (current->is_Java_thread()) {
1526 if (ls != NULL) {
1527 timer.stop();
1528 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1529 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1530 SIZE_FORMAT ", max=" SIZE_FORMAT,
1531 unlinked_count, in_use_list_ceiling(),
1532 _in_use_list.count(), _in_use_list.max());
1533 }
1534
1535 // A JavaThread needs to handshake in order to safely free the
1536 // ObjectMonitors that were deflated in this cycle.
1537 HandshakeForDeflation hfd_hc;
1538 Handshake::execute(&hfd_hc);
1539
1540 if (ls != NULL) {
1541 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1542 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1543 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1544 timer.start();
1545 }
1546 }
1547
1548 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1549
1550 // After the handshake, safely free the ObjectMonitors that were
1551 // deflated in this cycle.
1552 size_t deleted_count = 0;
1553 for (ObjectMonitor* monitor: delete_list) {
1554 delete monitor;
1555 deleted_count++;
1556
1557 if (current->is_Java_thread()) {
1558 // A JavaThread must check for a safepoint/handshake and honor it.
1559 chk_for_block_req(current->as_Java_thread(), "deletion", "deleted_count",
1560 deleted_count, ls, &timer);
1561 }
1562 }
1563 }
1564
1565 if (ls != NULL) {
1566 timer.stop();
1567 if (deflated_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1568 ls->print_cr("deflated " SIZE_FORMAT " monitors in %3.7f secs",
1569 deflated_count, timer.seconds());
1570 }
1571 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1572 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1573 }
1574
1575 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1576 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1577
1578 GVars.stw_random = os::random();
1579
1580 if (deflated_count != 0) {
1581 _no_progress_cnt = 0;
1582 } else if (_no_progress_skip_increment) {
1583 _no_progress_skip_increment = false;
1584 } else {
1585 _no_progress_cnt++;
1586 }
1587
1588 return deflated_count;
1589 }
1590
1591 // Monitor cleanup on JavaThread::exit
1592
1593 // Iterate through monitor cache and attempt to release thread's monitors
1594 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1595 private:
1596 JavaThread* _thread;
1597
1598 public:
1599 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1600 void do_monitor(ObjectMonitor* mid) {
1601 (void)mid->complete_exit(_thread);
1602 }
1603 };
1604
1605 // Release all inflated monitors owned by current thread. Lightweight monitors are
1606 // ignored. This is meant to be called during JNI thread detach which assumes
1607 // all remaining monitors are heavyweight. All exceptions are swallowed.
1608 // Scanning the extant monitor list can be time consuming.
1609 // A simple optimization is to add a per-thread flag that indicates a thread
1610 // called jni_monitorenter() during its lifetime.
1611 //
1612 // Instead of NoSafepointVerifier it might be cheaper to
1613 // use an idiom of the form:
1614 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1615 // <code that must not run at safepoint>
1616 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1617 // Since the tests are extremely cheap we could leave them enabled
1618 // for normal product builds.
1619
1620 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1621 assert(current == JavaThread::current(), "must be current Java thread");
1622 NoSafepointVerifier nsv;
1623 ReleaseJavaMonitorsClosure rjmc(current);
1624 ObjectSynchronizer::monitors_iterate(&rjmc, current);
1625 assert(!current->has_pending_exception(), "Should not be possible");
1626 current->clear_pending_exception();
1627 }
1628
1629 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1630 switch (cause) {
1631 case inflate_cause_vm_internal: return "VM Internal";
1632 case inflate_cause_monitor_enter: return "Monitor Enter";
1633 case inflate_cause_wait: return "Monitor Wait";
1634 case inflate_cause_notify: return "Monitor Notify";
1635 case inflate_cause_hash_code: return "Monitor Hash Code";
1636 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1637 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1638 default:
1639 ShouldNotReachHere();
1640 }
1641 return "Unknown";
1642 }
1643
1644 //------------------------------------------------------------------------------
1645 // Debugging code
1646
1647 u_char* ObjectSynchronizer::get_gvars_addr() {
1648 return (u_char*)&GVars;
1649 }
1650
1651 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1652 return (u_char*)&GVars.hc_sequence;
1653 }
1654
1655 size_t ObjectSynchronizer::get_gvars_size() {
1656 return sizeof(SharedGlobals);
1657 }
1658
1659 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1660 return (u_char*)&GVars.stw_random;
1661 }
1662
1663 // Do the final audit and print of ObjectMonitor stats; must be done
1664 // by the VMThread at VM exit time.
1665 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1666 assert(Thread::current()->is_VM_thread(), "sanity check");
1667
1668 if (is_final_audit()) { // Only do the audit once.
1669 return;
1670 }
1671 set_is_final_audit();
1672 log_info(monitorinflation)("Starting the final audit.");
1673
1674 if (log_is_enabled(Info, monitorinflation)) {
1675 // Do a deflation in order to reduce the in-use monitor population
1676 // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1677 // which is called by ObjectSynchronizer::audit_and_print_stats().
1678 while (ObjectSynchronizer::deflate_idle_monitors() != 0) {
1679 ; // empty
1680 }
1681 // The other audit_and_print_stats() call is done at the Debug
1682 // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
1683 ObjectSynchronizer::audit_and_print_stats(true /* on_exit */);
1684 }
1685 }
1686
1687 // This function can be called at a safepoint or it can be called when
1688 // we are trying to exit the VM. When we are trying to exit the VM, the
1689 // list walker functions can run in parallel with the other list
1690 // operations so spin-locking is used for safety.
1691 //
1692 // Calls to this function can be added in various places as a debugging
1693 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1694 // details logged at the Info level and 'false' for the 'on_exit'
1695 // parameter to have in-use monitor details logged at the Trace level.
1696 //
1697 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1698 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1699
1700 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1701 LogStreamHandle(Info, monitorinflation) lsh_info;
1702 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1703 LogStream* ls = NULL;
1704 if (log_is_enabled(Trace, monitorinflation)) {
1705 ls = &lsh_trace;
1706 } else if (log_is_enabled(Debug, monitorinflation)) {
1707 ls = &lsh_debug;
1708 } else if (log_is_enabled(Info, monitorinflation)) {
1709 ls = &lsh_info;
1710 }
1711 assert(ls != NULL, "sanity check");
1712
1713 int error_cnt = 0;
1714
1715 ls->print_cr("Checking in_use_list:");
1716 chk_in_use_list(ls, &error_cnt);
1717
1718 if (error_cnt == 0) {
1719 ls->print_cr("No errors found in in_use_list checks.");
1720 } else {
1721 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1722 }
1723
1724 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1725 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1726 // When exiting this log output is at the Info level. When called
1727 // at a safepoint, this log output is at the Trace level since
1728 // there can be a lot of it.
1729 log_in_use_monitor_details(ls);
1730 }
1731
1732 ls->flush();
1733
1734 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1735 }
1736
1737 // Check the in_use_list; log the results of the checks.
1738 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1739 size_t l_in_use_count = _in_use_list.count();
1740 size_t l_in_use_max = _in_use_list.max();
1741 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1742 l_in_use_max);
1743
1744 size_t ck_in_use_count = 0;
1745 MonitorList::Iterator iter = _in_use_list.iterator();
1746 while (iter.has_next()) {
1747 ObjectMonitor* mid = iter.next();
1748 chk_in_use_entry(mid, out, error_cnt_p);
1749 ck_in_use_count++;
1750 }
1751
1752 if (l_in_use_count == ck_in_use_count) {
1753 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1754 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1755 } else {
1756 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1757 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1758 ck_in_use_count);
1759 }
1760
1761 size_t ck_in_use_max = _in_use_list.max();
1762 if (l_in_use_max == ck_in_use_max) {
1763 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1764 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1765 } else {
1766 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1767 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1768 }
1769 }
1770
1771 // Check an in-use monitor entry; log any errors.
1772 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1773 int* error_cnt_p) {
1774 if (n->owner_is_DEFLATER_MARKER()) {
1775 // This should not happen, but if it does, it is not fatal.
1776 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1777 "deflated.", p2i(n));
1778 return;
1779 }
1780 if (n->header().value() == 0) {
1781 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1782 "have non-NULL _header field.", p2i(n));
1783 *error_cnt_p = *error_cnt_p + 1;
1784 }
1785 const oop obj = n->object_peek();
1786 if (obj != NULL) {
1787 const markWord mark = obj->mark();
1788 if (!mark.has_monitor()) {
1789 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1790 "object does not think it has a monitor: obj="
1791 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1792 p2i(obj), mark.value());
1793 *error_cnt_p = *error_cnt_p + 1;
1794 }
1795 ObjectMonitor* const obj_mon = mark.monitor();
1796 if (n != obj_mon) {
1797 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1798 "object does not refer to the same monitor: obj="
1799 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1800 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1801 *error_cnt_p = *error_cnt_p + 1;
1802 }
1803 }
1804 }
1805
1806 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1807 // flags indicate why the entry is in-use, 'object' and 'object type'
1808 // indicate the associated object and its type.
1809 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
1810 stringStream ss;
1811 if (_in_use_list.count() > 0) {
1812 out->print_cr("In-use monitor info:");
1813 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1814 out->print_cr("%18s %s %18s %18s",
1815 "monitor", "BHL", "object", "object type");
1816 out->print_cr("================== === ================== ==================");
1817 MonitorList::Iterator iter = _in_use_list.iterator();
1818 while (iter.has_next()) {
1819 ObjectMonitor* mid = iter.next();
1820 const oop obj = mid->object_peek();
1821 const markWord mark = mid->header();
1822 ResourceMark rm;
1823 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid),
1824 mid->is_busy(), mark.hash() != 0, mid->owner() != NULL,
1825 p2i(obj), obj == NULL ? "" : obj->klass()->external_name());
1826 if (mid->is_busy()) {
1827 out->print(" (%s)", mid->is_busy_to_string(&ss));
1828 ss.reset();
1829 }
1830 out->cr();
1831 }
1832 }
1833
1834 out->flush();
1835 }