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/handles.inline.hpp"
38 #include "runtime/handshake.hpp"
39 #include "runtime/interfaceSupport.inline.hpp"
40 #include "runtime/mutexLocker.hpp"
41 #include "runtime/objectMonitor.hpp"
42 #include "runtime/objectMonitor.inline.hpp"
43 #include "runtime/os.inline.hpp"
44 #include "runtime/osThread.hpp"
45 #include "runtime/perfData.hpp"
46 #include "runtime/safepointMechanism.inline.hpp"
47 #include "runtime/safepointVerifiers.hpp"
48 #include "runtime/sharedRuntime.hpp"
49 #include "runtime/stubRoutines.hpp"
50 #include "runtime/synchronizer.hpp"
51 #include "runtime/thread.inline.hpp"
52 #include "runtime/timer.hpp"
53 #include "runtime/vframe.hpp"
54 #include "runtime/vmThread.hpp"
55 #include "utilities/align.hpp"
56 #include "utilities/dtrace.hpp"
57 #include "utilities/events.hpp"
58 #include "utilities/preserveException.hpp"
59
60 class CleanupObjectMonitorsHashtable: StackObj {
61 public:
62 bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) {
63 list->clear(); // clear the LinkListNodes
64 delete list; // then delete the LinkedList
65 return true;
66 }
67 };
68
69 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() {
70 CleanupObjectMonitorsHashtable cleanup;
71 _ptrs->unlink(&cleanup); // cleanup the LinkedLists
72 delete _ptrs; // then delete the hash table
73 }
74
75 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) {
76 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
77 if (list == nullptr) {
78 // Create new list and add it to the hash table:
79 list = new (ResourceObj::C_HEAP, mtThread) ObjectMonitorsHashtable::PtrList();
80 add_entry(key, list);
81 }
82 list->add(om); // Add the ObjectMonitor to the list.
83 _om_count++;
84 }
85
86 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) {
87 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
88 if (list == nullptr || list->find(om) == nullptr) {
89 return false;
90 }
91 return true;
92 }
93
94 void MonitorList::add(ObjectMonitor* m) {
95 ObjectMonitor* head;
96 do {
97 head = Atomic::load(&_head);
98 m->set_next_om(head);
99 } while (Atomic::cmpxchg(&_head, head, m) != head);
100
101 size_t count = Atomic::add(&_count, 1u);
102 if (count > max()) {
103 Atomic::inc(&_max);
104 }
105 }
106
107 size_t MonitorList::count() const {
108 return Atomic::load(&_count);
109 }
110
111 size_t MonitorList::max() const {
112 return Atomic::load(&_max);
113 }
114
115 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
116 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
117 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
118 elapsedTimer* timer_p,
119 GrowableArray<ObjectMonitor*>* unlinked_list) {
120 size_t unlinked_count = 0;
121 ObjectMonitor* prev = NULL;
122 ObjectMonitor* head = Atomic::load_acquire(&_head);
123 ObjectMonitor* m = head;
124 // The in-use list head can be NULL during the final audit.
125 while (m != NULL) {
126 if (m->is_being_async_deflated()) {
127 // Find next live ObjectMonitor.
128 ObjectMonitor* next = m;
129 do {
130 ObjectMonitor* next_next = next->next_om();
131 unlinked_count++;
132 unlinked_list->append(next);
133 next = next_next;
134 if (unlinked_count >= (size_t)MonitorDeflationMax) {
135 // Reached the max so bail out on the gathering loop.
136 break;
137 }
138 } while (next != NULL && next->is_being_async_deflated());
139 if (prev == NULL) {
140 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
141 if (prev_head != head) {
142 // Find new prev ObjectMonitor that just got inserted.
143 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
144 prev = n;
145 }
146 prev->set_next_om(next);
147 }
148 } else {
149 prev->set_next_om(next);
150 }
151 if (unlinked_count >= (size_t)MonitorDeflationMax) {
152 // Reached the max so bail out on the searching loop.
153 break;
154 }
155 m = next;
156 } else {
157 prev = m;
158 m = m->next_om();
159 }
160
161 if (current->is_Java_thread()) {
162 // A JavaThread must check for a safepoint/handshake and honor it.
163 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking",
164 "unlinked_count", unlinked_count,
165 ls, timer_p);
166 }
167 }
168 Atomic::sub(&_count, unlinked_count);
169 return unlinked_count;
170 }
171
172 MonitorList::Iterator MonitorList::iterator() const {
173 return Iterator(Atomic::load_acquire(&_head));
174 }
175
176 ObjectMonitor* MonitorList::Iterator::next() {
177 ObjectMonitor* current = _current;
178 _current = current->next_om();
179 return current;
180 }
181
182 // The "core" versions of monitor enter and exit reside in this file.
183 // The interpreter and compilers contain specialized transliterated
184 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
185 // fast_lock(...) for instance. If you make changes here, make sure to modify the
186 // interpreter, and both C1 and C2 fast-path inline locking code emission.
187 //
188 // -----------------------------------------------------------------------------
189
190 #ifdef DTRACE_ENABLED
191
192 // Only bother with this argument setup if dtrace is available
193 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
194
195 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
196 char* bytes = NULL; \
197 int len = 0; \
198 jlong jtid = SharedRuntime::get_java_tid(thread); \
199 Symbol* klassname = obj->klass()->name(); \
200 if (klassname != NULL) { \
201 bytes = (char*)klassname->bytes(); \
202 len = klassname->utf8_length(); \
203 }
204
205 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
206 { \
207 if (DTraceMonitorProbes) { \
208 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
209 HOTSPOT_MONITOR_WAIT(jtid, \
210 (uintptr_t)(monitor), bytes, len, (millis)); \
211 } \
212 }
213
214 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
215 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
216 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
217
218 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
219 { \
220 if (DTraceMonitorProbes) { \
221 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
222 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
223 (uintptr_t)(monitor), bytes, len); \
224 } \
225 }
226
227 #else // ndef DTRACE_ENABLED
228
229 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
230 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
231
232 #endif // ndef DTRACE_ENABLED
233
234 // This exists only as a workaround of dtrace bug 6254741
235 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
236 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
237 return 0;
238 }
239
240 static const int NINFLATIONLOCKS = 256;
241 static os::PlatformMutex* gInflationLocks[NINFLATIONLOCKS];
242
243 void ObjectSynchronizer::initialize() {
244 for (int i = 0; i < NINFLATIONLOCKS; i++) {
245 gInflationLocks[i] = new os::PlatformMutex();
246 }
247 // Start the ceiling with the estimate for one thread.
248 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
249 }
250
251 MonitorList ObjectSynchronizer::_in_use_list;
252 // monitors_used_above_threshold() policy is as follows:
253 //
254 // The ratio of the current _in_use_list count to the ceiling is used
255 // to determine if we are above MonitorUsedDeflationThreshold and need
256 // to do an async monitor deflation cycle. The ceiling is increased by
257 // AvgMonitorsPerThreadEstimate when a thread is added to the system
258 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
259 // removed from the system.
260 //
261 // Note: If the _in_use_list max exceeds the ceiling, then
262 // monitors_used_above_threshold() will use the in_use_list max instead
263 // of the thread count derived ceiling because we have used more
264 // ObjectMonitors than the estimated average.
265 //
266 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
267 // no-progress async monitor deflation cycles in a row, then the ceiling
268 // is adjusted upwards by monitors_used_above_threshold().
269 //
270 // Start the ceiling with the estimate for one thread in initialize()
271 // which is called after cmd line options are processed.
272 static size_t _in_use_list_ceiling = 0;
273 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
274 bool volatile ObjectSynchronizer::_is_final_audit = false;
275 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
276 static uintx _no_progress_cnt = 0;
277
278 // =====================> Quick functions
279
280 // The quick_* forms are special fast-path variants used to improve
281 // performance. In the simplest case, a "quick_*" implementation could
282 // simply return false, in which case the caller will perform the necessary
283 // state transitions and call the slow-path form.
284 // The fast-path is designed to handle frequently arising cases in an efficient
285 // manner and is just a degenerate "optimistic" variant of the slow-path.
286 // returns true -- to indicate the call was satisfied.
287 // returns false -- to indicate the call needs the services of the slow-path.
288 // A no-loitering ordinance is in effect for code in the quick_* family
289 // operators: safepoints or indefinite blocking (blocking that might span a
290 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
291 // entry.
292 //
293 // Consider: An interesting optimization is to have the JIT recognize the
294 // following common idiom:
295 // synchronized (someobj) { .... ; notify(); }
296 // That is, we find a notify() or notifyAll() call that immediately precedes
297 // the monitorexit operation. In that case the JIT could fuse the operations
298 // into a single notifyAndExit() runtime primitive.
299
300 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
301 assert(current->thread_state() == _thread_in_Java, "invariant");
302 NoSafepointVerifier nsv;
303 if (obj == NULL) return false; // slow-path for invalid obj
304 const markWord mark = obj->mark();
305
306 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
307 // Degenerate notify
308 // stack-locked by caller so by definition the implied waitset is empty.
309 return true;
310 }
311
312 if (mark.has_monitor()) {
313 ObjectMonitor* const mon = mark.monitor();
314 assert(mon->object() == oop(obj), "invariant");
315 if (mon->owner() != current) return false; // slow-path for IMS exception
316
317 if (mon->first_waiter() != NULL) {
318 // We have one or more waiters. Since this is an inflated monitor
319 // that we own, we can transfer one or more threads from the waitset
320 // to the entrylist here and now, avoiding the slow-path.
321 if (all) {
322 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
323 } else {
324 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
325 }
326 int free_count = 0;
327 do {
328 mon->INotify(current);
329 ++free_count;
330 } while (mon->first_waiter() != NULL && all);
331 OM_PERFDATA_OP(Notifications, inc(free_count));
332 }
333 return true;
334 }
335
336 // other IMS exception states take the slow-path
337 return false;
338 }
339
340
341 // The LockNode emitted directly at the synchronization site would have
342 // been too big if it were to have included support for the cases of inflated
343 // recursive enter and exit, so they go here instead.
344 // Note that we can't safely call AsyncPrintJavaStack() from within
345 // quick_enter() as our thread state remains _in_Java.
346
347 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
348 BasicLock * lock) {
349 assert(current->thread_state() == _thread_in_Java, "invariant");
350 NoSafepointVerifier nsv;
351 if (obj == NULL) return false; // Need to throw NPE
352
353 if (obj->klass()->is_value_based()) {
354 return false;
355 }
356
357 const markWord mark = obj->mark();
358
359 if (mark.has_monitor()) {
360 ObjectMonitor* const m = mark.monitor();
361 // An async deflation or GC can race us before we manage to make
362 // the ObjectMonitor busy by setting the owner below. If we detect
363 // that race we just bail out to the slow-path here.
364 if (m->object_peek() == NULL) {
365 return false;
366 }
367 JavaThread* const owner = (JavaThread*) m->owner_raw();
368
369 // Lock contention and Transactional Lock Elision (TLE) diagnostics
370 // and observability
371 // Case: light contention possibly amenable to TLE
372 // Case: TLE inimical operations such as nested/recursive synchronization
373
374 if (owner == current) {
375 m->_recursions++;
376 return true;
377 }
378
379 // This Java Monitor is inflated so obj's header will never be
380 // displaced to this thread's BasicLock. Make the displaced header
381 // non-NULL so this BasicLock is not seen as recursive nor as
382 // being locked. We do this unconditionally so that this thread's
383 // BasicLock cannot be mis-interpreted by any stack walkers. For
384 // performance reasons, stack walkers generally first check for
385 // stack-locking in the object's header, the second check is for
386 // recursive stack-locking in the displaced header in the BasicLock,
387 // and last are the inflated Java Monitor (ObjectMonitor) checks.
388 lock->set_displaced_header(markWord::unused_mark());
389
390 if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
391 assert(m->_recursions == 0, "invariant");
392 return true;
393 }
394 }
395
396 // Note that we could inflate in quick_enter.
397 // This is likely a useful optimization
398 // Critically, in quick_enter() we must not:
399 // -- block indefinitely, or
400 // -- reach a safepoint
401
402 return false; // revert to slow-path
403 }
404
405 // Handle notifications when synchronizing on value based classes
406 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
407 frame last_frame = current->last_frame();
408 bool bcp_was_adjusted = false;
409 // Don't decrement bcp if it points to the frame's first instruction. This happens when
410 // handle_sync_on_value_based_class() is called because of a synchronized method. There
411 // is no actual monitorenter instruction in the byte code in this case.
412 if (last_frame.is_interpreted_frame() &&
413 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
414 // adjust bcp to point back to monitorenter so that we print the correct line numbers
415 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
416 bcp_was_adjusted = true;
417 }
418
419 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
420 ResourceMark rm(current);
421 stringStream ss;
422 current->print_stack_on(&ss);
423 char* base = (char*)strstr(ss.base(), "at");
424 char* newline = (char*)strchr(ss.base(), '\n');
425 if (newline != NULL) {
426 *newline = '\0';
427 }
428 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
429 } else {
430 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
431 ResourceMark rm(current);
432 Log(valuebasedclasses) vblog;
433
434 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
435 if (current->has_last_Java_frame()) {
436 LogStream info_stream(vblog.info());
437 current->print_stack_on(&info_stream);
438 } else {
439 vblog.info("Cannot find the last Java frame");
440 }
441
442 EventSyncOnValueBasedClass event;
443 if (event.should_commit()) {
444 event.set_valueBasedClass(obj->klass());
445 event.commit();
446 }
447 }
448
449 if (bcp_was_adjusted) {
450 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
451 }
452 }
453
454 static bool useHeavyMonitors() {
455 #if defined(X86) || defined(AARCH64) || defined(PPC64)
456 return UseHeavyMonitors;
457 #else
458 return false;
459 #endif
460 }
461
462 // -----------------------------------------------------------------------------
463 // Monitor Enter/Exit
464 // The interpreter and compiler assembly code tries to lock using the fast path
465 // of this algorithm. Make sure to update that code if the following function is
466 // changed. The implementation is extremely sensitive to race condition. Be careful.
467
468 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
469 if (obj->klass()->is_value_based()) {
470 handle_sync_on_value_based_class(obj, current);
471 }
472
473 if (!useHeavyMonitors()) {
474 markWord mark = obj->mark();
475 if (mark.is_neutral()) {
476 // Anticipate successful CAS -- the ST of the displaced mark must
477 // be visible <= the ST performed by the CAS.
478 lock->set_displaced_header(mark);
479 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
480 return;
481 }
482 // Fall through to inflate() ...
483 } else if (mark.has_locker() &&
484 current->is_lock_owned((address)mark.locker())) {
485 assert(lock != mark.locker(), "must not re-lock the same lock");
486 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
487 lock->set_displaced_header(markWord::from_pointer(NULL));
488 return;
489 }
490
491 // The object header will never be displaced to this lock,
492 // so it does not matter what the value is, except that it
493 // must be non-zero to avoid looking like a re-entrant lock,
494 // and must not look locked either.
495 lock->set_displaced_header(markWord::unused_mark());
496 } else if (VerifyHeavyMonitors) {
497 guarantee(!obj->mark().has_locker(), "must not be stack-locked");
498 }
499
500 // An async deflation can race after the inflate() call and before
501 // enter() can make the ObjectMonitor busy. enter() returns false if
502 // we have lost the race to async deflation and we simply try again.
503 while (true) {
504 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
505 if (monitor->enter(current)) {
506 return;
507 }
508 }
509 }
510
511 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
512 if (!useHeavyMonitors()) {
513 markWord mark = object->mark();
514
515 markWord dhw = lock->displaced_header();
516 if (dhw.value() == 0) {
517 // If the displaced header is NULL, then this exit matches up with
518 // a recursive enter. No real work to do here except for diagnostics.
519 #ifndef PRODUCT
520 if (mark != markWord::INFLATING()) {
521 // Only do diagnostics if we are not racing an inflation. Simply
522 // exiting a recursive enter of a Java Monitor that is being
523 // inflated is safe; see the has_monitor() comment below.
524 assert(!mark.is_neutral(), "invariant");
525 assert(!mark.has_locker() ||
526 current->is_lock_owned((address)mark.locker()), "invariant");
527 if (mark.has_monitor()) {
528 // The BasicLock's displaced_header is marked as a recursive
529 // enter and we have an inflated Java Monitor (ObjectMonitor).
530 // This is a special case where the Java Monitor was inflated
531 // after this thread entered the stack-lock recursively. When a
532 // Java Monitor is inflated, we cannot safely walk the Java
533 // Monitor owner's stack and update the BasicLocks because a
534 // Java Monitor can be asynchronously inflated by a thread that
535 // does not own the Java Monitor.
536 ObjectMonitor* m = mark.monitor();
537 assert(m->object()->mark() == mark, "invariant");
538 assert(m->is_entered(current), "invariant");
539 }
540 }
541 #endif
542 return;
543 }
544
545 if (mark == markWord::from_pointer(lock)) {
546 // If the object is stack-locked by the current thread, try to
547 // swing the displaced header from the BasicLock back to the mark.
548 assert(dhw.is_neutral(), "invariant");
549 if (object->cas_set_mark(dhw, mark) == mark) {
550 return;
551 }
552 }
553 } else if (VerifyHeavyMonitors) {
554 guarantee(!object->mark().has_locker(), "must not be stack-locked");
555 }
556
557 // We have to take the slow-path of possible inflation and then exit.
558 // The ObjectMonitor* can't be async deflated until ownership is
559 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
560 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
561 monitor->exit(current);
562 }
563
564 // -----------------------------------------------------------------------------
565 // Class Loader support to workaround deadlocks on the class loader lock objects
566 // Also used by GC
567 // complete_exit()/reenter() are used to wait on a nested lock
568 // i.e. to give up an outer lock completely and then re-enter
569 // Used when holding nested locks - lock acquisition order: lock1 then lock2
570 // 1) complete_exit lock1 - saving recursion count
571 // 2) wait on lock2
572 // 3) when notified on lock2, unlock lock2
573 // 4) reenter lock1 with original recursion count
574 // 5) lock lock2
575 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
576 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
577 // The ObjectMonitor* can't be async deflated until ownership is
578 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
579 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
580 intptr_t ret_code = monitor->complete_exit(current);
581 return ret_code;
582 }
583
584 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
585 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
586 // An async deflation can race after the inflate() call and before
587 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
588 // enter() returns false if we have lost the race to async deflation
589 // and we simply try again.
590 while (true) {
591 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
592 if (monitor->reenter(recursions, current)) {
593 return;
594 }
595 }
596 }
597
598 // -----------------------------------------------------------------------------
599 // JNI locks on java objects
600 // NOTE: must use heavy weight monitor to handle jni monitor enter
601 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
602 if (obj->klass()->is_value_based()) {
603 handle_sync_on_value_based_class(obj, current);
604 }
605
606 // the current locking is from JNI instead of Java code
607 current->set_current_pending_monitor_is_from_java(false);
608 // An async deflation can race after the inflate() call and before
609 // enter() can make the ObjectMonitor busy. enter() returns false if
610 // we have lost the race to async deflation and we simply try again.
611 while (true) {
612 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
613 if (monitor->enter(current)) {
614 break;
615 }
616 }
617 current->set_current_pending_monitor_is_from_java(true);
618 }
619
620 // NOTE: must use heavy weight monitor to handle jni monitor exit
621 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
622 JavaThread* current = THREAD;
623
624 // The ObjectMonitor* can't be async deflated until ownership is
625 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
626 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
627 // If this thread has locked the object, exit the monitor. We
628 // intentionally do not use CHECK on check_owner because we must exit the
629 // monitor even if an exception was already pending.
630 if (monitor->check_owner(THREAD)) {
631 monitor->exit(current);
632 }
633 }
634
635 // -----------------------------------------------------------------------------
636 // Internal VM locks on java objects
637 // standard constructor, allows locking failures
638 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
639 _thread = thread;
640 _thread->check_for_valid_safepoint_state();
641 _obj = obj;
642
643 if (_obj() != NULL) {
644 ObjectSynchronizer::enter(_obj, &_lock, _thread);
645 }
646 }
647
648 ObjectLocker::~ObjectLocker() {
649 if (_obj() != NULL) {
650 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
651 }
652 }
653
654
655 // -----------------------------------------------------------------------------
656 // Wait/Notify/NotifyAll
657 // NOTE: must use heavy weight monitor to handle wait()
658 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
659 JavaThread* current = THREAD;
660 if (millis < 0) {
661 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
662 }
663 // The ObjectMonitor* can't be async deflated because the _waiters
664 // field is incremented before ownership is dropped and decremented
665 // after ownership is regained.
666 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
667
668 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
669 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
670
671 // This dummy call is in place to get around dtrace bug 6254741. Once
672 // that's fixed we can uncomment the following line, remove the call
673 // and change this function back into a "void" func.
674 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
675 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
676 return ret_code;
677 }
678
679 // No exception are possible in this case as we only use this internally when locking is
680 // correct and we have to wait until notified - so no interrupts or timeouts.
681 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, JavaThread* current) {
682 // The ObjectMonitor* can't be async deflated because the _waiters
683 // field is incremented before ownership is dropped and decremented
684 // after ownership is regained.
685 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
686 monitor->wait(0 /* wait-forever */, false /* not interruptible */, current);
687 }
688
689 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
690 JavaThread* current = THREAD;
691
692 markWord mark = obj->mark();
693 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
694 // Not inflated so there can't be any waiters to notify.
695 return;
696 }
697 // The ObjectMonitor* can't be async deflated until ownership is
698 // dropped by the calling thread.
699 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
700 monitor->notify(CHECK);
701 }
702
703 // NOTE: see comment of notify()
704 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
705 JavaThread* current = THREAD;
706
707 markWord mark = obj->mark();
708 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
709 // Not inflated so there can't be any waiters to notify.
710 return;
711 }
712 // The ObjectMonitor* can't be async deflated until ownership is
713 // dropped by the calling thread.
714 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
715 monitor->notifyAll(CHECK);
716 }
717
718 // -----------------------------------------------------------------------------
719 // Hash Code handling
720
721 struct SharedGlobals {
722 char _pad_prefix[OM_CACHE_LINE_SIZE];
723 // This is a highly shared mostly-read variable.
724 // To avoid false-sharing it needs to be the sole occupant of a cache line.
725 volatile int stw_random;
726 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
727 // Hot RW variable -- Sequester to avoid false-sharing
728 volatile int hc_sequence;
729 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
730 };
731
732 static SharedGlobals GVars;
733
734 static markWord read_stable_mark(oop obj) {
735 markWord mark = obj->mark_acquire();
736 if (!mark.is_being_inflated()) {
737 return mark; // normal fast-path return
738 }
739
740 int its = 0;
741 for (;;) {
742 markWord mark = obj->mark_acquire();
743 if (!mark.is_being_inflated()) {
744 return mark; // normal fast-path return
745 }
746
747 // The object is being inflated by some other thread.
748 // The caller of read_stable_mark() must wait for inflation to complete.
749 // Avoid live-lock.
750
751 ++its;
752 if (its > 10000 || !os::is_MP()) {
753 if (its & 1) {
754 os::naked_yield();
755 } else {
756 // Note that the following code attenuates the livelock problem but is not
757 // a complete remedy. A more complete solution would require that the inflating
758 // thread hold the associated inflation lock. The following code simply restricts
759 // the number of spinners to at most one. We'll have N-2 threads blocked
760 // on the inflationlock, 1 thread holding the inflation lock and using
761 // a yield/park strategy, and 1 thread in the midst of inflation.
762 // A more refined approach would be to change the encoding of INFLATING
763 // to allow encapsulation of a native thread pointer. Threads waiting for
764 // inflation to complete would use CAS to push themselves onto a singly linked
765 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
766 // and calling park(). When inflation was complete the thread that accomplished inflation
767 // would detach the list and set the markword to inflated with a single CAS and
768 // then for each thread on the list, set the flag and unpark() the thread.
769
770 // Index into the lock array based on the current object address.
771 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
772 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
773 int YieldThenBlock = 0;
774 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
775 gInflationLocks[ix]->lock();
776 while (obj->mark_acquire() == markWord::INFLATING()) {
777 // Beware: naked_yield() is advisory and has almost no effect on some platforms
778 // so we periodically call current->_ParkEvent->park(1).
779 // We use a mixed spin/yield/block mechanism.
780 if ((YieldThenBlock++) >= 16) {
781 Thread::current()->_ParkEvent->park(1);
782 } else {
783 os::naked_yield();
784 }
785 }
786 gInflationLocks[ix]->unlock();
787 }
788 } else {
789 SpinPause(); // SMP-polite spinning
790 }
791 }
792 }
793
794 // hashCode() generation :
795 //
796 // Possibilities:
797 // * MD5Digest of {obj,stw_random}
798 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
799 // * A DES- or AES-style SBox[] mechanism
800 // * One of the Phi-based schemes, such as:
801 // 2654435761 = 2^32 * Phi (golden ratio)
802 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
803 // * A variation of Marsaglia's shift-xor RNG scheme.
804 // * (obj ^ stw_random) is appealing, but can result
805 // in undesirable regularity in the hashCode values of adjacent objects
806 // (objects allocated back-to-back, in particular). This could potentially
807 // result in hashtable collisions and reduced hashtable efficiency.
808 // There are simple ways to "diffuse" the middle address bits over the
809 // generated hashCode values:
810
811 static inline intptr_t get_next_hash(Thread* current, oop obj) {
812 intptr_t value = 0;
813 if (hashCode == 0) {
814 // This form uses global Park-Miller RNG.
815 // On MP system we'll have lots of RW access to a global, so the
816 // mechanism induces lots of coherency traffic.
817 value = os::random();
818 } else if (hashCode == 1) {
819 // This variation has the property of being stable (idempotent)
820 // between STW operations. This can be useful in some of the 1-0
821 // synchronization schemes.
822 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
823 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
824 } else if (hashCode == 2) {
825 value = 1; // for sensitivity testing
826 } else if (hashCode == 3) {
827 value = ++GVars.hc_sequence;
828 } else if (hashCode == 4) {
829 value = cast_from_oop<intptr_t>(obj);
830 } else {
831 // Marsaglia's xor-shift scheme with thread-specific state
832 // This is probably the best overall implementation -- we'll
833 // likely make this the default in future releases.
834 unsigned t = current->_hashStateX;
835 t ^= (t << 11);
836 current->_hashStateX = current->_hashStateY;
837 current->_hashStateY = current->_hashStateZ;
838 current->_hashStateZ = current->_hashStateW;
839 unsigned v = current->_hashStateW;
840 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
841 current->_hashStateW = v;
842 value = v;
843 }
844
845 value &= markWord::hash_mask;
846 if (value == 0) value = 0xBAD;
847 assert(value != markWord::no_hash, "invariant");
848 return value;
849 }
850
851 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
852
853 while (true) {
854 ObjectMonitor* monitor = NULL;
855 markWord temp, test;
856 intptr_t hash;
857 markWord mark = read_stable_mark(obj);
858 if (VerifyHeavyMonitors) {
859 assert(UseHeavyMonitors, "+VerifyHeavyMonitors requires +UseHeavyMonitors");
860 guarantee(!mark.has_locker(), "must not be stack locked");
861 }
862 if (mark.is_neutral()) { // if this is a normal header
863 hash = mark.hash();
864 if (hash != 0) { // if it has a hash, just return it
865 return hash;
866 }
867 hash = get_next_hash(current, obj); // get a new hash
868 temp = mark.copy_set_hash(hash); // merge the hash into header
869 // try to install the hash
870 test = obj->cas_set_mark(temp, mark);
871 if (test == mark) { // if the hash was installed, return it
872 return hash;
873 }
874 // Failed to install the hash. It could be that another thread
875 // installed the hash just before our attempt or inflation has
876 // occurred or... so we fall thru to inflate the monitor for
877 // stability and then install the hash.
878 } else if (mark.has_monitor()) {
879 monitor = mark.monitor();
880 temp = monitor->header();
881 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
882 hash = temp.hash();
883 if (hash != 0) {
884 // It has a hash.
885
886 // Separate load of dmw/header above from the loads in
887 // is_being_async_deflated().
888
889 // dmw/header and _contentions may get written by different threads.
890 // Make sure to observe them in the same order when having several observers.
891 OrderAccess::loadload_for_IRIW();
892
893 if (monitor->is_being_async_deflated()) {
894 // But we can't safely use the hash if we detect that async
895 // deflation has occurred. So we attempt to restore the
896 // header/dmw to the object's header so that we only retry
897 // once if the deflater thread happens to be slow.
898 monitor->install_displaced_markword_in_object(obj);
899 continue;
900 }
901 return hash;
902 }
903 // Fall thru so we only have one place that installs the hash in
904 // the ObjectMonitor.
905 } else if (current->is_lock_owned((address)mark.locker())) {
906 // This is a stack lock owned by the calling thread so fetch the
907 // displaced markWord from the BasicLock on the stack.
908 temp = mark.displaced_mark_helper();
909 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
910 hash = temp.hash();
911 if (hash != 0) { // if it has a hash, just return it
912 return hash;
913 }
914 // WARNING:
915 // The displaced header in the BasicLock on a thread's stack
916 // is strictly immutable. It CANNOT be changed in ANY cases.
917 // So we have to inflate the stack lock into an ObjectMonitor
918 // even if the current thread owns the lock. The BasicLock on
919 // a thread's stack can be asynchronously read by other threads
920 // during an inflate() call so any change to that stack memory
921 // may not propagate to other threads correctly.
922 }
923
924 // Inflate the monitor to set the hash.
925
926 // An async deflation can race after the inflate() call and before we
927 // can update the ObjectMonitor's header with the hash value below.
928 monitor = inflate(current, obj, inflate_cause_hash_code);
929 // Load ObjectMonitor's header/dmw field and see if it has a hash.
930 mark = monitor->header();
931 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
932 hash = mark.hash();
933 if (hash == 0) { // if it does not have a hash
934 hash = get_next_hash(current, obj); // get a new hash
935 temp = mark.copy_set_hash(hash) ; // merge the hash into header
936 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
937 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
938 test = markWord(v);
939 if (test != mark) {
940 // The attempt to update the ObjectMonitor's header/dmw field
941 // did not work. This can happen if another thread managed to
942 // merge in the hash just before our cmpxchg().
943 // If we add any new usages of the header/dmw field, this code
944 // will need to be updated.
945 hash = test.hash();
946 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
947 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
948 }
949 if (monitor->is_being_async_deflated()) {
950 // If we detect that async deflation has occurred, then we
951 // attempt to restore the header/dmw to the object's header
952 // so that we only retry once if the deflater thread happens
953 // to be slow.
954 monitor->install_displaced_markword_in_object(obj);
955 continue;
956 }
957 }
958 // We finally get the hash.
959 return hash;
960 }
961 }
962
963 // Deprecated -- use FastHashCode() instead.
964
965 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
966 return FastHashCode(Thread::current(), obj());
967 }
968
969
970 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
971 Handle h_obj) {
972 assert(current == JavaThread::current(), "Can only be called on current thread");
973 oop obj = h_obj();
974
975 markWord mark = read_stable_mark(obj);
976
977 // Uncontended case, header points to stack
978 if (mark.has_locker()) {
979 return current->is_lock_owned((address)mark.locker());
980 }
981 // Contended case, header points to ObjectMonitor (tagged pointer)
982 if (mark.has_monitor()) {
983 // The first stage of async deflation does not affect any field
984 // used by this comparison so the ObjectMonitor* is usable here.
985 ObjectMonitor* monitor = mark.monitor();
986 return monitor->is_entered(current) != 0;
987 }
988 // Unlocked case, header in place
989 assert(mark.is_neutral(), "sanity check");
990 return false;
991 }
992
993 // FIXME: jvmti should call this
994 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
995 oop obj = h_obj();
996 address owner = NULL;
997
998 markWord mark = read_stable_mark(obj);
999
1000 // Uncontended case, header points to stack
1001 if (mark.has_locker()) {
1002 owner = (address) mark.locker();
1003 }
1004
1005 // Contended case, header points to ObjectMonitor (tagged pointer)
1006 else if (mark.has_monitor()) {
1007 // The first stage of async deflation does not affect any field
1008 // used by this comparison so the ObjectMonitor* is usable here.
1009 ObjectMonitor* monitor = mark.monitor();
1010 assert(monitor != NULL, "monitor should be non-null");
1011 owner = (address) monitor->owner();
1012 }
1013
1014 if (owner != NULL) {
1015 // owning_thread_from_monitor_owner() may also return NULL here
1016 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1017 }
1018
1019 // Unlocked case, header in place
1020 // Cannot have assertion since this object may have been
1021 // locked by another thread when reaching here.
1022 // assert(mark.is_neutral(), "sanity check");
1023
1024 return NULL;
1025 }
1026
1027 // Visitors ...
1028
1029 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1030 // ObjectMonitors where owner is set to a stack lock address in thread.
1031 //
1032 // This version of monitors_iterate() works with the in-use monitor list.
1033 //
1034 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1035 MonitorList::Iterator iter = _in_use_list.iterator();
1036 while (iter.has_next()) {
1037 ObjectMonitor* mid = iter.next();
1038 if (mid->owner() != thread) {
1039 // Not owned by the target thread and intentionally skips when owner
1040 // is set to a stack lock address in the target thread.
1041 continue;
1042 }
1043 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1044 // Only process with closure if the object is set.
1045
1046 // monitors_iterate() is only called at a safepoint or when the
1047 // target thread is suspended or when the target thread is
1048 // operating on itself. The current closures in use today are
1049 // only interested in an owned ObjectMonitor and ownership
1050 // cannot be dropped under the calling contexts so the
1051 // ObjectMonitor cannot be async deflated.
1052 closure->do_monitor(mid);
1053 }
1054 }
1055 }
1056
1057 // This version of monitors_iterate() works with the specified linked list.
1058 //
1059 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure,
1060 ObjectMonitorsHashtable::PtrList* list,
1061 JavaThread* thread) {
1062 typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator;
1063 ObjectMonitorIterator iter(list->head());
1064 while (!iter.is_empty()) {
1065 ObjectMonitor* mid = *iter.next();
1066 // Owner set to a stack lock address in thread should never be seen here:
1067 assert(mid->owner() == thread, "must be");
1068 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1069 // Only process with closure if the object is set.
1070
1071 // monitors_iterate() is only called at a safepoint or when the
1072 // target thread is suspended or when the target thread is
1073 // operating on itself. The current closures in use today are
1074 // only interested in an owned ObjectMonitor and ownership
1075 // cannot be dropped under the calling contexts so the
1076 // ObjectMonitor cannot be async deflated.
1077 closure->do_monitor(mid);
1078 }
1079 }
1080 }
1081
1082 static bool monitors_used_above_threshold(MonitorList* list) {
1083 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1084 return false;
1085 }
1086 // Start with ceiling based on a per-thread estimate:
1087 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1088 size_t old_ceiling = ceiling;
1089 if (ceiling < list->max()) {
1090 // The max used by the system has exceeded the ceiling so use that:
1091 ceiling = list->max();
1092 }
1093 size_t monitors_used = list->count();
1094 if (monitors_used == 0) { // empty list is easy
1095 return false;
1096 }
1097 if (NoAsyncDeflationProgressMax != 0 &&
1098 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1099 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1100 size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1101 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1102 log_info(monitorinflation)("Too many deflations without progress; "
1103 "bumping in_use_list_ceiling from " SIZE_FORMAT
1104 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1105 _no_progress_cnt = 0;
1106 ceiling = new_ceiling;
1107 }
1108
1109 // Check if our monitor usage is above the threshold:
1110 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1111 return int(monitor_usage) > MonitorUsedDeflationThreshold;
1112 }
1113
1114 size_t ObjectSynchronizer::in_use_list_ceiling() {
1115 return _in_use_list_ceiling;
1116 }
1117
1118 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1119 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1120 }
1121
1122 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1123 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1124 }
1125
1126 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1127 _in_use_list_ceiling = new_value;
1128 }
1129
1130 bool ObjectSynchronizer::is_async_deflation_needed() {
1131 if (is_async_deflation_requested()) {
1132 // Async deflation request.
1133 return true;
1134 }
1135 if (AsyncDeflationInterval > 0 &&
1136 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1137 monitors_used_above_threshold(&_in_use_list)) {
1138 // It's been longer than our specified deflate interval and there
1139 // are too many monitors in use. We don't deflate more frequently
1140 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1141 // in order to not swamp the MonitorDeflationThread.
1142 return true;
1143 }
1144 return false;
1145 }
1146
1147 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1148 JavaThread* current = JavaThread::current();
1149 bool ret_code = false;
1150
1151 jlong last_time = last_async_deflation_time_ns();
1152 set_is_async_deflation_requested(true);
1153 {
1154 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1155 ml.notify_all();
1156 }
1157 const int N_CHECKS = 5;
1158 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1159 if (last_async_deflation_time_ns() > last_time) {
1160 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1161 ret_code = true;
1162 break;
1163 }
1164 {
1165 // JavaThread has to honor the blocking protocol.
1166 ThreadBlockInVM tbivm(current);
1167 os::naked_short_sleep(999); // sleep for almost 1 second
1168 }
1169 }
1170 if (!ret_code) {
1171 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1172 }
1173
1174 return ret_code;
1175 }
1176
1177 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1178 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1179 }
1180
1181 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1182 const oop obj,
1183 ObjectSynchronizer::InflateCause cause) {
1184 assert(event != NULL, "invariant");
1185 assert(event->should_commit(), "invariant");
1186 event->set_monitorClass(obj->klass());
1187 event->set_address((uintptr_t)(void*)obj);
1188 event->set_cause((u1)cause);
1189 event->commit();
1190 }
1191
1192 // Fast path code shared by multiple functions
1193 void ObjectSynchronizer::inflate_helper(oop obj) {
1194 markWord mark = obj->mark_acquire();
1195 if (mark.has_monitor()) {
1196 ObjectMonitor* monitor = mark.monitor();
1197 markWord dmw = monitor->header();
1198 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1199 return;
1200 }
1201 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1202 }
1203
1204 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1205 const InflateCause cause) {
1206 EventJavaMonitorInflate event;
1207
1208 for (;;) {
1209 const markWord mark = object->mark_acquire();
1210
1211 // The mark can be in one of the following states:
1212 // * Inflated - just return
1213 // * Stack-locked - coerce it to inflated
1214 // * INFLATING - busy wait for conversion to complete
1215 // * Neutral - aggressively inflate the object.
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 //
1408 // If table != nullptr, we gather owned ObjectMonitors indexed by the
1409 // owner in the table. Please note that ObjectMonitors where the owner
1410 // is set to a stack lock address are NOT associated with the JavaThread
1411 // that holds that stack lock. All of the current consumers of
1412 // ObjectMonitorsHashtable info only care about JNI locked monitors and
1413 // those do not have the owner set to a stack lock address.
1414 //
1415 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1416 elapsedTimer* timer_p,
1417 ObjectMonitorsHashtable* table) {
1418 MonitorList::Iterator iter = _in_use_list.iterator();
1419 size_t deflated_count = 0;
1420
1421 while (iter.has_next()) {
1422 if (deflated_count >= (size_t)MonitorDeflationMax) {
1423 break;
1424 }
1425 ObjectMonitor* mid = iter.next();
1426 if (mid->deflate_monitor()) {
1427 deflated_count++;
1428 } else if (table != nullptr) {
1429 // The caller is interested in the owned ObjectMonitors. This does
1430 // not include when owner is set to a stack lock address in thread.
1431 // This also does not capture unowned ObjectMonitors that cannot be
1432 // deflated because of a waiter.
1433 void* key = mid->owner();
1434 // Since deflate_idle_monitors() and deflate_monitor_list() can be
1435 // called more than once, we have to make sure the entry has not
1436 // already been added.
1437 if (key != nullptr && !table->has_entry(key, mid)) {
1438 table->add_entry(key, mid);
1439 }
1440 }
1441
1442 if (current->is_Java_thread()) {
1443 // A JavaThread must check for a safepoint/handshake and honor it.
1444 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1445 deflated_count, ls, timer_p);
1446 }
1447 }
1448
1449 return deflated_count;
1450 }
1451
1452 class HandshakeForDeflation : public HandshakeClosure {
1453 public:
1454 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1455
1456 void do_thread(Thread* thread) {
1457 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1458 INTPTR_FORMAT, p2i(thread));
1459 }
1460 };
1461
1462 // This function is called by the MonitorDeflationThread to deflate
1463 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1464 // and VM_ThreadDump::doit() by the VMThread.
1465 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) {
1466 Thread* current = Thread::current();
1467 if (current->is_Java_thread()) {
1468 // The async deflation request has been processed.
1469 _last_async_deflation_time_ns = os::javaTimeNanos();
1470 set_is_async_deflation_requested(false);
1471 }
1472
1473 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1474 LogStreamHandle(Info, monitorinflation) lsh_info;
1475 LogStream* ls = NULL;
1476 if (log_is_enabled(Debug, monitorinflation)) {
1477 ls = &lsh_debug;
1478 } else if (log_is_enabled(Info, monitorinflation)) {
1479 ls = &lsh_info;
1480 }
1481
1482 elapsedTimer timer;
1483 if (ls != NULL) {
1484 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1485 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1486 timer.start();
1487 }
1488
1489 // Deflate some idle ObjectMonitors.
1490 size_t deflated_count = deflate_monitor_list(current, ls, &timer, table);
1491 if (deflated_count > 0 || is_final_audit()) {
1492 // There are ObjectMonitors that have been deflated or this is the
1493 // final audit and all the remaining ObjectMonitors have been
1494 // deflated, BUT the MonitorDeflationThread blocked for the final
1495 // safepoint during unlinking.
1496
1497 // Unlink deflated ObjectMonitors from the in-use list.
1498 ResourceMark rm;
1499 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1500 size_t unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer,
1501 &delete_list);
1502 if (current->is_Java_thread()) {
1503 if (ls != NULL) {
1504 timer.stop();
1505 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1506 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1507 SIZE_FORMAT ", max=" SIZE_FORMAT,
1508 unlinked_count, in_use_list_ceiling(),
1509 _in_use_list.count(), _in_use_list.max());
1510 }
1511
1512 // A JavaThread needs to handshake in order to safely free the
1513 // ObjectMonitors that were deflated in this cycle.
1514 HandshakeForDeflation hfd_hc;
1515 Handshake::execute(&hfd_hc);
1516
1517 if (ls != NULL) {
1518 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1519 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1520 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1521 timer.start();
1522 }
1523 }
1524
1525 // After the handshake, safely free the ObjectMonitors that were
1526 // deflated in this cycle.
1527 size_t deleted_count = 0;
1528 for (ObjectMonitor* monitor: delete_list) {
1529 delete monitor;
1530 deleted_count++;
1531
1532 if (current->is_Java_thread()) {
1533 // A JavaThread must check for a safepoint/handshake and honor it.
1534 chk_for_block_req(JavaThread::cast(current), "deletion", "deleted_count",
1535 deleted_count, ls, &timer);
1536 }
1537 }
1538 }
1539
1540 if (ls != NULL) {
1541 timer.stop();
1542 if (deflated_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1543 ls->print_cr("deflated " SIZE_FORMAT " monitors in %3.7f secs",
1544 deflated_count, timer.seconds());
1545 }
1546 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1547 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1548 if (table != nullptr) {
1549 ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT,
1550 table->key_count(), table->om_count());
1551 }
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(/* ObjectMonitorsHashtable is not needed here */ nullptr) >= (size_t)MonitorDeflationMax) {
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 }