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