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