1 /*
2 * Copyright (c) 1998, 2021, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "jfr/jfrEvents.hpp"
28 #include "gc/shared/suspendibleThreadSet.hpp"
29 #include "logging/log.hpp"
30 #include "logging/logStream.hpp"
31 #include "memory/allocation.inline.hpp"
32 #include "memory/padded.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/markWord.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/biasedLocking.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/handshake.hpp"
41 #include "runtime/interfaceSupport.inline.hpp"
42 #include "runtime/lockStack.inline.hpp"
43 #include "runtime/mutexLocker.hpp"
44 #include "runtime/objectMonitor.hpp"
45 #include "runtime/objectMonitor.inline.hpp"
46 #include "runtime/os.inline.hpp"
47 #include "runtime/osThread.hpp"
48 #include "runtime/perfData.hpp"
49 #include "runtime/safepointMechanism.inline.hpp"
50 #include "runtime/safepointVerifiers.hpp"
51 #include "runtime/sharedRuntime.hpp"
52 #include "runtime/stubRoutines.hpp"
53 #include "runtime/synchronizer.hpp"
54 #include "runtime/thread.inline.hpp"
55 #include "runtime/timer.hpp"
56 #include "runtime/vframe.hpp"
57 #include "runtime/vmThread.hpp"
58 #include "utilities/align.hpp"
59 #include "utilities/dtrace.hpp"
60 #include "utilities/events.hpp"
61 #include "utilities/preserveException.hpp"
62
63 void MonitorList::add(ObjectMonitor* m) {
64 ObjectMonitor* head;
65 do {
66 head = Atomic::load(&_head);
67 m->set_next_om(head);
68 } while (Atomic::cmpxchg(&_head, head, m) != head);
69
70 size_t count = Atomic::add(&_count, 1u);
71 if (count > max()) {
72 Atomic::inc(&_max);
73 }
74 }
75
76 size_t MonitorList::count() const {
77 return Atomic::load(&_count);
78 }
79
80 size_t MonitorList::max() const {
81 return Atomic::load(&_max);
82 }
83
84 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
85 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
86 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
87 elapsedTimer* timer_p,
88 GrowableArray<ObjectMonitor*>* unlinked_list) {
89 size_t unlinked_count = 0;
90 ObjectMonitor* prev = NULL;
91 ObjectMonitor* head = Atomic::load_acquire(&_head);
92 ObjectMonitor* m = head;
93 // The in-use list head can be NULL during the final audit.
94 while (m != NULL) {
95 if (m->is_being_async_deflated()) {
96 // Find next live ObjectMonitor.
97 ObjectMonitor* next = m;
98 do {
99 ObjectMonitor* next_next = next->next_om();
100 unlinked_count++;
101 unlinked_list->append(next);
102 next = next_next;
103 if (unlinked_count >= (size_t)MonitorDeflationMax) {
104 // Reached the max so bail out on the gathering loop.
105 break;
106 }
107 } while (next != NULL && next->is_being_async_deflated());
108 if (prev == NULL) {
109 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
110 if (prev_head != head) {
111 // Find new prev ObjectMonitor that just got inserted.
112 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
113 prev = n;
114 }
115 prev->set_next_om(next);
116 }
117 } else {
118 prev->set_next_om(next);
119 }
120 if (unlinked_count >= (size_t)MonitorDeflationMax) {
121 // Reached the max so bail out on the searching loop.
122 break;
123 }
124 m = next;
125 } else {
126 prev = m;
127 m = m->next_om();
128 }
129
130 if (current->is_Java_thread()) {
131 // A JavaThread must check for a safepoint/handshake and honor it.
132 ObjectSynchronizer::chk_for_block_req(current->as_Java_thread(), "unlinking",
133 "unlinked_count", unlinked_count,
134 ls, timer_p);
135 }
136 }
137 Atomic::sub(&_count, unlinked_count);
138 return unlinked_count;
139 }
140
141 MonitorList::Iterator MonitorList::iterator() const {
142 return Iterator(Atomic::load_acquire(&_head));
143 }
144
145 ObjectMonitor* MonitorList::Iterator::next() {
146 ObjectMonitor* current = _current;
147 _current = current->next_om();
148 return current;
149 }
150
151 // The "core" versions of monitor enter and exit reside in this file.
152 // The interpreter and compilers contain specialized transliterated
153 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
154 // fast_lock(...) for instance. If you make changes here, make sure to modify the
155 // interpreter, and both C1 and C2 fast-path inline locking code emission.
156 //
157 // -----------------------------------------------------------------------------
158
159 #ifdef DTRACE_ENABLED
160
161 // Only bother with this argument setup if dtrace is available
162 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
163
164 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
165 char* bytes = NULL; \
166 int len = 0; \
167 jlong jtid = SharedRuntime::get_java_tid(thread); \
168 Symbol* klassname = obj->klass()->name(); \
169 if (klassname != NULL) { \
170 bytes = (char*)klassname->bytes(); \
171 len = klassname->utf8_length(); \
172 }
173
174 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
175 { \
176 if (DTraceMonitorProbes) { \
177 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
178 HOTSPOT_MONITOR_WAIT(jtid, \
179 (uintptr_t)(monitor), bytes, len, (millis)); \
180 } \
181 }
182
183 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
184 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
185 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
186
187 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
188 { \
189 if (DTraceMonitorProbes) { \
190 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
191 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
192 (uintptr_t)(monitor), bytes, len); \
193 } \
194 }
195
196 #else // ndef DTRACE_ENABLED
197
198 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
199 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
200
201 #endif // ndef DTRACE_ENABLED
202
203 // This exists only as a workaround of dtrace bug 6254741
204 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
205 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
206 return 0;
207 }
208
209 static const int NINFLATIONLOCKS = 256;
210 static os::PlatformMutex* gInflationLocks[NINFLATIONLOCKS];
211
212 void ObjectSynchronizer::initialize() {
213 for (int i = 0; i < NINFLATIONLOCKS; i++) {
214 gInflationLocks[i] = new os::PlatformMutex();
215 }
216 // Start the ceiling with the estimate for one thread.
217 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
218 }
219
220 MonitorList ObjectSynchronizer::_in_use_list;
221 // monitors_used_above_threshold() policy is as follows:
222 //
223 // The ratio of the current _in_use_list count to the ceiling is used
224 // to determine if we are above MonitorUsedDeflationThreshold and need
225 // to do an async monitor deflation cycle. The ceiling is increased by
226 // AvgMonitorsPerThreadEstimate when a thread is added to the system
227 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
228 // removed from the system.
229 //
230 // Note: If the _in_use_list max exceeds the ceiling, then
231 // monitors_used_above_threshold() will use the in_use_list max instead
232 // of the thread count derived ceiling because we have used more
233 // ObjectMonitors than the estimated average.
234 //
235 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
236 // no-progress async monitor deflation cycles in a row, then the ceiling
237 // is adjusted upwards by monitors_used_above_threshold().
238 //
239 // Start the ceiling with the estimate for one thread in initialize()
240 // which is called after cmd line options are processed.
241 static size_t _in_use_list_ceiling = 0;
242 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
243 bool volatile ObjectSynchronizer::_is_final_audit = false;
244 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
245 static uintx _no_progress_cnt = 0;
246
247 // =====================> Quick functions
248
249 // The quick_* forms are special fast-path variants used to improve
250 // performance. In the simplest case, a "quick_*" implementation could
251 // simply return false, in which case the caller will perform the necessary
252 // state transitions and call the slow-path form.
253 // The fast-path is designed to handle frequently arising cases in an efficient
254 // manner and is just a degenerate "optimistic" variant of the slow-path.
255 // returns true -- to indicate the call was satisfied.
256 // returns false -- to indicate the call needs the services of the slow-path.
257 // A no-loitering ordinance is in effect for code in the quick_* family
258 // operators: safepoints or indefinite blocking (blocking that might span a
259 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
260 // entry.
261 //
262 // Consider: An interesting optimization is to have the JIT recognize the
263 // following common idiom:
264 // synchronized (someobj) { .... ; notify(); }
265 // That is, we find a notify() or notifyAll() call that immediately precedes
266 // the monitorexit operation. In that case the JIT could fuse the operations
267 // into a single notifyAndExit() runtime primitive.
268
269 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
270 assert(current->thread_state() == _thread_in_Java, "invariant");
271 NoSafepointVerifier nsv;
272 if (obj == NULL) return false; // slow-path for invalid obj
273 const markWord mark = obj->mark();
274
275 if ((mark.is_fast_locked() && current->lock_stack().contains(oop(obj))) ||
276 (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) {
277 // Degenerate notify
278 // stack-locked by caller so by definition the implied waitset is empty.
279 return true;
280 }
281
282 if (mark.has_monitor()) {
283 ObjectMonitor* const mon = mark.monitor();
284 assert(mon->object() == oop(obj), "invariant");
285 if (mon->owner() != current) return false; // slow-path for IMS exception
286
287 if (mon->first_waiter() != NULL) {
288 // We have one or more waiters. Since this is an inflated monitor
289 // that we own, we can transfer one or more threads from the waitset
290 // to the entrylist here and now, avoiding the slow-path.
291 if (all) {
292 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
293 } else {
294 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
295 }
296 int free_count = 0;
297 do {
298 mon->INotify(current);
299 ++free_count;
300 } while (mon->first_waiter() != NULL && all);
301 OM_PERFDATA_OP(Notifications, inc(free_count));
302 }
303 return true;
304 }
305
306 // biased locking and any other IMS exception states take the slow-path
307 return false;
308 }
309
310
311 // The LockNode emitted directly at the synchronization site would have
312 // been too big if it were to have included support for the cases of inflated
313 // recursive enter and exit, so they go here instead.
314 // Note that we can't safely call AsyncPrintJavaStack() from within
315 // quick_enter() as our thread state remains _in_Java.
316
317 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
318 BasicLock * lock) {
319 assert(current->thread_state() == _thread_in_Java, "invariant");
320 NoSafepointVerifier nsv;
321 if (obj == NULL) return false; // Need to throw NPE
322
323 if (obj->klass()->is_value_based()) {
324 return false;
325 }
326
327 const markWord mark = obj->mark();
328
329 if (mark.has_monitor()) {
330 ObjectMonitor* const m = mark.monitor();
331 // An async deflation or GC can race us before we manage to make
332 // the ObjectMonitor busy by setting the owner below. If we detect
333 // that race we just bail out to the slow-path here.
334 if (m->object_peek() == NULL) {
335 return false;
336 }
337 JavaThread* const owner = (JavaThread*) m->owner_raw();
338
339 // Lock contention and Transactional Lock Elision (TLE) diagnostics
340 // and observability
341 // Case: light contention possibly amenable to TLE
342 // Case: TLE inimical operations such as nested/recursive synchronization
343
344 if (owner == current) {
345 m->_recursions++;
346 return true;
347 }
348
349 // This Java Monitor is inflated so obj's header will never be
350 // displaced to this thread's BasicLock. Make the displaced header
351 // non-NULL so this BasicLock is not seen as recursive nor as
352 // being locked. We do this unconditionally so that this thread's
353 // BasicLock cannot be mis-interpreted by any stack walkers. For
354 // performance reasons, stack walkers generally first check for
355 // Biased Locking in the object's header, the second check is for
356 // stack-locking in the object's header, the third check is for
357 // recursive stack-locking in the displaced header in the BasicLock,
358 // and last are the inflated Java Monitor (ObjectMonitor) checks.
359 if (!UseFastLocking) {
360 lock->set_displaced_header(markWord::unused_mark());
361 }
362
363 if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
364 assert(m->_recursions == 0, "invariant");
365 return true;
366 }
367 }
368
369 // Note that we could inflate in quick_enter.
370 // This is likely a useful optimization
371 // Critically, in quick_enter() we must not:
372 // -- perform bias revocation, or
373 // -- block indefinitely, or
374 // -- reach a safepoint
375
376 return false; // revert to slow-path
377 }
378
379 // Handle notifications when synchronizing on value based classes
380 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
381 frame last_frame = current->last_frame();
382 bool bcp_was_adjusted = false;
383 // Don't decrement bcp if it points to the frame's first instruction. This happens when
384 // handle_sync_on_value_based_class() is called because of a synchronized method. There
385 // is no actual monitorenter instruction in the byte code in this case.
386 if (last_frame.is_interpreted_frame() &&
387 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
388 // adjust bcp to point back to monitorenter so that we print the correct line numbers
389 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
390 bcp_was_adjusted = true;
391 }
392
393 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
394 ResourceMark rm(current);
395 stringStream ss;
396 current->print_stack_on(&ss);
397 char* base = (char*)strstr(ss.base(), "at");
398 char* newline = (char*)strchr(ss.base(), '\n');
399 if (newline != NULL) {
400 *newline = '\0';
401 }
402 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
403 } else {
404 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
405 ResourceMark rm(current);
406 Log(valuebasedclasses) vblog;
407
408 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
409 if (current->has_last_Java_frame()) {
410 LogStream info_stream(vblog.info());
411 current->print_stack_on(&info_stream);
412 } else {
413 vblog.info("Cannot find the last Java frame");
414 }
415
416 EventSyncOnValueBasedClass event;
417 if (event.should_commit()) {
418 event.set_valueBasedClass(obj->klass());
419 event.commit();
420 }
421 }
422
423 if (bcp_was_adjusted) {
424 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
425 }
426 }
427
428 // -----------------------------------------------------------------------------
429 // Monitor Enter/Exit
430 // The interpreter and compiler assembly code tries to lock using the fast path
431 // of this algorithm. Make sure to update that code if the following function is
432 // changed. The implementation is extremely sensitive to race condition. Be careful.
433
434 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
435 if (obj->klass()->is_value_based()) {
436 handle_sync_on_value_based_class(obj, current);
437 }
438
439 if (UseFastLocking) {
440 LockStack& lock_stack = current->lock_stack();
441
442 markWord header = obj()->mark_acquire();
443 while (true) {
444 if (header.is_neutral()) {
445 assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
446 // Try to swing into 'fast-locked' state without inflating.
447 markWord locked_header = header.set_fast_locked();
448 markWord witness = obj()->cas_set_mark(locked_header, header);
449 if (witness == header) {
450 // Successfully fast-locked, push object to lock-stack and return.
451 lock_stack.push(obj());
452 return;
453 }
454 // Otherwise retry.
455 header = witness;
456 } else {
457 // Fall-through to inflate-enter.
458 break;
459 }
460 }
461 } else {
462 if (UseBiasedLocking) {
463 BiasedLocking::revoke(current, obj);
464 }
465
466 markWord mark = obj->mark();
467 if (mark.is_neutral()) {
468 // Anticipate successful CAS -- the ST of the displaced mark must
469 // be visible <= the ST performed by the CAS.
470 lock->set_displaced_header(mark);
471 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
472 return;
473 }
474 // Fall through to inflate() ...
475 } else if (mark.has_locker() &&
476 current->is_lock_owned((address) mark.locker())) {
477 assert(lock != mark.locker(), "must not re-lock the same lock");
478 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
479 lock->set_displaced_header(markWord::from_pointer(NULL));
480 return;
481 }
482
483 // The object header will never be displaced to this lock,
484 // so it does not matter what the value is, except that it
485 // must be non-zero to avoid looking like a re-entrant lock,
486 // and must not look locked either.
487 lock->set_displaced_header(markWord::unused_mark());
488 }
489
490 // An async deflation can race after the inflate() call and before
491 // enter() can make the ObjectMonitor busy. enter() returns false if
492 // we have lost the race to async deflation and we simply try again.
493 while (true) {
494 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
495 if (monitor->enter(current)) {
496 return;
497 }
498 }
499 }
500
501 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
502 markWord mark = object->mark();
503 if (UseFastLocking) {
504 if (mark.is_fast_locked()) {
505 markWord unlocked_header = mark.set_unlocked();
506 markWord witness = object->cas_set_mark(unlocked_header, mark);
507 if (witness != mark) {
508 // Another thread beat us, it can only have installed an anonymously locked monitor at this point.
509 // Fetch that monitor, set owner correctly to this thread, and exit it (allowing waiting threads to enter).
510 assert(witness.has_monitor(), "must have monitor");
511 ObjectMonitor* monitor = witness.monitor();
512 assert(monitor->is_owner_anonymous(), "must be anonymous owner");
513 monitor->set_owner_from_anonymous(current);
514 monitor->exit(current);
515 }
516 LockStack& lock_stack = current->lock_stack();
517 lock_stack.remove(object);
518 return;
519 }
520 } else {
521 markWord dhw = lock->displaced_header();
522 if (dhw.value() == 0) {
523 // If the displaced header is NULL, then this exit matches up with
524 // a recursive enter. No real work to do here except for diagnostics.
525 #ifndef PRODUCT
526 if (mark != markWord::INFLATING()) {
527 // Only do diagnostics if we are not racing an inflation. Simply
528 // exiting a recursive enter of a Java Monitor that is being
529 // inflated is safe; see the has_monitor() comment below.
530 assert(!mark.is_neutral(), "invariant");
531 assert(!mark.has_locker() ||
532 current->is_lock_owned((address)mark.locker()), "invariant");
533 if (mark.has_monitor()) {
534 // The BasicLock's displaced_header is marked as a recursive
535 // enter and we have an inflated Java Monitor (ObjectMonitor).
536 // This is a special case where the Java Monitor was inflated
537 // after this thread entered the stack-lock recursively. When a
538 // Java Monitor is inflated, we cannot safely walk the Java
539 // Monitor owner's stack and update the BasicLocks because a
540 // Java Monitor can be asynchronously inflated by a thread that
541 // does not own the Java Monitor.
542 ObjectMonitor* m = mark.monitor();
543 assert(m->object()->mark() == mark, "invariant");
544 assert(m->is_entered(current), "invariant");
545 }
546 }
547 #endif
548 return;
549 }
550
551 if (mark == markWord::from_pointer(lock)) {
552 // If the object is stack-locked by the current thread, try to
553 // swing the displaced header from the BasicLock back to the mark.
554 assert(dhw.is_neutral(), "invariant");
555 if (object->cas_set_mark(dhw, mark) == mark) {
556 return;
557 }
558 }
559 }
560
561 // We have to take the slow-path of possible inflation and then exit.
562 // The ObjectMonitor* can't be async deflated until ownership is
563 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
564 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
565 if (UseFastLocking && monitor->is_owner_anonymous()) {
566 // It must be us. Pop lock object from lock stack.
567 LockStack& lock_stack = current->lock_stack();
568 oop popped = lock_stack.pop();
569 assert(popped == object, "must be owned by this thread");
570 monitor->set_owner_from_anonymous(current);
571 }
572 monitor->exit(current);
573 }
574
575 // -----------------------------------------------------------------------------
576 // Class Loader support to workaround deadlocks on the class loader lock objects
577 // Also used by GC
578 // complete_exit()/reenter() are used to wait on a nested lock
579 // i.e. to give up an outer lock completely and then re-enter
580 // Used when holding nested locks - lock acquisition order: lock1 then lock2
581 // 1) complete_exit lock1 - saving recursion count
582 // 2) wait on lock2
583 // 3) when notified on lock2, unlock lock2
584 // 4) reenter lock1 with original recursion count
585 // 5) lock lock2
586 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
587 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
588 if (UseBiasedLocking) {
589 BiasedLocking::revoke(current, obj);
590 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
591 }
592
593 // The ObjectMonitor* can't be async deflated until ownership is
594 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
595 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
596 intptr_t ret_code = monitor->complete_exit(current);
597 return ret_code;
598 }
599
600 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
601 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
602 if (UseBiasedLocking) {
603 BiasedLocking::revoke(current, obj);
604 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
605 }
606
607 // An async deflation can race after the inflate() call and before
608 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
609 // enter() returns false if we have lost the race to async deflation
610 // and we simply try again.
611 while (true) {
612 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
613 if (monitor->reenter(recursions, current)) {
614 return;
615 }
616 }
617 }
618
619 // -----------------------------------------------------------------------------
620 // JNI locks on java objects
621 // NOTE: must use heavy weight monitor to handle jni monitor enter
622 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
623 if (obj->klass()->is_value_based()) {
624 handle_sync_on_value_based_class(obj, current);
625 }
626
627 // the current locking is from JNI instead of Java code
628 if (UseBiasedLocking) {
629 BiasedLocking::revoke(current, obj);
630 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
631 }
632 current->set_current_pending_monitor_is_from_java(false);
633 // An async deflation can race after the inflate() call and before
634 // enter() can make the ObjectMonitor busy. enter() returns false if
635 // we have lost the race to async deflation and we simply try again.
636 while (true) {
637 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
638 if (monitor->enter(current)) {
639 break;
640 }
641 }
642 current->set_current_pending_monitor_is_from_java(true);
643 }
644
645 // NOTE: must use heavy weight monitor to handle jni monitor exit
646 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
647 JavaThread* current = THREAD;
648 if (UseBiasedLocking) {
649 Handle h_obj(current, obj);
650 BiasedLocking::revoke(current, h_obj);
651 obj = h_obj();
652 }
653 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
654
655 // The ObjectMonitor* can't be async deflated until ownership is
656 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
657 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
658 // If this thread has locked the object, exit the monitor. We
659 // intentionally do not use CHECK on check_owner because we must exit the
660 // monitor even if an exception was already pending.
661 if (monitor->check_owner(THREAD)) {
662 monitor->exit(current);
663 }
664 }
665
666 // -----------------------------------------------------------------------------
667 // Internal VM locks on java objects
668 // standard constructor, allows locking failures
669 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
670 _thread = thread;
671 _thread->check_for_valid_safepoint_state();
672 _obj = obj;
673
674 if (_obj() != NULL) {
675 ObjectSynchronizer::enter(_obj, &_lock, _thread);
676 }
677 }
678
679 ObjectLocker::~ObjectLocker() {
680 if (_obj() != NULL) {
681 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
682 }
683 }
684
685
686 // -----------------------------------------------------------------------------
687 // Wait/Notify/NotifyAll
688 // NOTE: must use heavy weight monitor to handle wait()
689 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
690 JavaThread* current = THREAD;
691 if (UseBiasedLocking) {
692 BiasedLocking::revoke(current, obj);
693 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
694 }
695 if (millis < 0) {
696 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
697 }
698 // The ObjectMonitor* can't be async deflated because the _waiters
699 // field is incremented before ownership is dropped and decremented
700 // after ownership is regained.
701 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
702
703 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
704 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
705
706 // This dummy call is in place to get around dtrace bug 6254741. Once
707 // that's fixed we can uncomment the following line, remove the call
708 // and change this function back into a "void" func.
709 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
710 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
711 return ret_code;
712 }
713
714 // No exception are possible in this case as we only use this internally when locking is
715 // correct and we have to wait until notified - so no interrupts or timeouts.
716 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, JavaThread* current) {
717 if (UseBiasedLocking) {
718 BiasedLocking::revoke(current, obj);
719 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
720 }
721 // The ObjectMonitor* can't be async deflated because the _waiters
722 // field is incremented before ownership is dropped and decremented
723 // after ownership is regained.
724 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
725 monitor->wait(0 /* wait-forever */, false /* not interruptible */, current);
726 }
727
728 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
729 JavaThread* current = THREAD;
730 if (UseBiasedLocking) {
731 BiasedLocking::revoke(current, obj);
732 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
733 }
734
735 markWord mark = obj->mark();
736 if ((mark.is_fast_locked() && current->lock_stack().contains(obj())) ||
737 (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) {
738 // Not inflated so there can't be any waiters to notify.
739 return;
740 }
741 // The ObjectMonitor* can't be async deflated until ownership is
742 // dropped by the calling thread.
743 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
744 monitor->notify(CHECK);
745 }
746
747 // NOTE: see comment of notify()
748 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
749 JavaThread* current = THREAD;
750 if (UseBiasedLocking) {
751 BiasedLocking::revoke(current, obj);
752 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
753 }
754
755 markWord mark = obj->mark();
756 if ((mark.is_fast_locked() && current->lock_stack().contains(obj())) ||
757 (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) {
758 // Not inflated so there can't be any waiters to notify.
759 return;
760 }
761 // The ObjectMonitor* can't be async deflated until ownership is
762 // dropped by the calling thread.
763 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
764 monitor->notifyAll(CHECK);
765 }
766
767 // -----------------------------------------------------------------------------
768 // Hash Code handling
769
770 struct SharedGlobals {
771 char _pad_prefix[OM_CACHE_LINE_SIZE];
772 // This is a highly shared mostly-read variable.
773 // To avoid false-sharing it needs to be the sole occupant of a cache line.
774 volatile int stw_random;
775 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
776 // Hot RW variable -- Sequester to avoid false-sharing
777 volatile int hc_sequence;
778 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
779 };
780
781 static SharedGlobals GVars;
782
783 static markWord read_stable_mark(oop obj) {
784 markWord mark = obj->mark();
785 if (!mark.is_being_inflated() || UseFastLocking) {
786 return mark; // normal fast-path return
787 }
788
789 int its = 0;
790 for (;;) {
791 markWord mark = obj->mark();
792 if (!mark.is_being_inflated()) {
793 return mark; // normal fast-path return
794 }
795
796 // The object is being inflated by some other thread.
797 // The caller of read_stable_mark() must wait for inflation to complete.
798 // Avoid live-lock.
799
800 ++its;
801 if (its > 10000 || !os::is_MP()) {
802 if (its & 1) {
803 os::naked_yield();
804 } else {
805 // Note that the following code attenuates the livelock problem but is not
806 // a complete remedy. A more complete solution would require that the inflating
807 // thread hold the associated inflation lock. The following code simply restricts
808 // the number of spinners to at most one. We'll have N-2 threads blocked
809 // on the inflationlock, 1 thread holding the inflation lock and using
810 // a yield/park strategy, and 1 thread in the midst of inflation.
811 // A more refined approach would be to change the encoding of INFLATING
812 // to allow encapsulation of a native thread pointer. Threads waiting for
813 // inflation to complete would use CAS to push themselves onto a singly linked
814 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
815 // and calling park(). When inflation was complete the thread that accomplished inflation
816 // would detach the list and set the markword to inflated with a single CAS and
817 // then for each thread on the list, set the flag and unpark() the thread.
818
819 // Index into the lock array based on the current object address.
820 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
821 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
822 int YieldThenBlock = 0;
823 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
824 gInflationLocks[ix]->lock();
825 while (obj->mark() == markWord::INFLATING()) {
826 // Beware: naked_yield() is advisory and has almost no effect on some platforms
827 // so we periodically call current->_ParkEvent->park(1).
828 // We use a mixed spin/yield/block mechanism.
829 if ((YieldThenBlock++) >= 16) {
830 Thread::current()->_ParkEvent->park(1);
831 } else {
832 os::naked_yield();
833 }
834 }
835 gInflationLocks[ix]->unlock();
836 }
837 } else {
838 SpinPause(); // SMP-polite spinning
839 }
840 }
841 }
842
843 // hashCode() generation :
844 //
845 // Possibilities:
846 // * MD5Digest of {obj,stw_random}
847 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
848 // * A DES- or AES-style SBox[] mechanism
849 // * One of the Phi-based schemes, such as:
850 // 2654435761 = 2^32 * Phi (golden ratio)
851 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
852 // * A variation of Marsaglia's shift-xor RNG scheme.
853 // * (obj ^ stw_random) is appealing, but can result
854 // in undesirable regularity in the hashCode values of adjacent objects
855 // (objects allocated back-to-back, in particular). This could potentially
856 // result in hashtable collisions and reduced hashtable efficiency.
857 // There are simple ways to "diffuse" the middle address bits over the
858 // generated hashCode values:
859
860 static inline intptr_t get_next_hash(Thread* current, oop obj) {
861 intptr_t value = 0;
862 if (hashCode == 0) {
863 // This form uses global Park-Miller RNG.
864 // On MP system we'll have lots of RW access to a global, so the
865 // mechanism induces lots of coherency traffic.
866 value = os::random();
867 } else if (hashCode == 1) {
868 // This variation has the property of being stable (idempotent)
869 // between STW operations. This can be useful in some of the 1-0
870 // synchronization schemes.
871 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
872 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
873 } else if (hashCode == 2) {
874 value = 1; // for sensitivity testing
875 } else if (hashCode == 3) {
876 value = ++GVars.hc_sequence;
877 } else if (hashCode == 4) {
878 value = cast_from_oop<intptr_t>(obj);
879 } else {
880 // Marsaglia's xor-shift scheme with thread-specific state
881 // This is probably the best overall implementation -- we'll
882 // likely make this the default in future releases.
883 unsigned t = current->_hashStateX;
884 t ^= (t << 11);
885 current->_hashStateX = current->_hashStateY;
886 current->_hashStateY = current->_hashStateZ;
887 current->_hashStateZ = current->_hashStateW;
888 unsigned v = current->_hashStateW;
889 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
890 current->_hashStateW = v;
891 value = v;
892 }
893
894 value &= markWord::hash_mask;
895 if (value == 0) value = 0xBAD;
896 assert(value != markWord::no_hash, "invariant");
897 return value;
898 }
899
900 static bool is_lock_owned(Thread* thread, oop obj) {
901 assert(UseFastLocking, "only call this with fast-locking enabled");
902 return thread->is_Java_thread() ? reinterpret_cast<JavaThread*>(thread)->lock_stack().contains(obj) : false;
903 }
904
905 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
906 if (UseBiasedLocking) {
907 // NOTE: many places throughout the JVM do not expect a safepoint
908 // to be taken here. However, we only ever bias Java instances and all
909 // of the call sites of identity_hash that might revoke biases have
910 // been checked to make sure they can handle a safepoint. The
911 // added check of the bias pattern is to avoid useless calls to
912 // thread-local storage.
913 if (obj->mark().has_bias_pattern()) {
914 // Handle for oop obj in case of STW safepoint
915 Handle hobj(current, obj);
916 if (SafepointSynchronize::is_at_safepoint()) {
917 BiasedLocking::revoke_at_safepoint(hobj);
918 } else {
919 BiasedLocking::revoke(current->as_Java_thread(), hobj);
920 }
921 obj = hobj();
922 assert(!obj->mark().has_bias_pattern(), "biases should be revoked by now");
923 }
924 }
925
926 while (true) {
927 ObjectMonitor* monitor = NULL;
928 markWord temp, test;
929 intptr_t hash;
930 markWord mark = read_stable_mark(obj);
931
932 // object should remain ineligible for biased locking
933 assert(!mark.has_bias_pattern(), "invariant");
934
935 if (mark.is_neutral()) { // if this is a normal header
936 hash = mark.hash();
937 if (hash != 0) { // if it has a hash, just return it
938 return hash;
939 }
940 hash = get_next_hash(current, obj); // get a new hash
941 temp = mark.copy_set_hash(hash); // merge the hash into header
942 // try to install the hash
943 test = obj->cas_set_mark(temp, mark);
944 if (test == mark) { // if the hash was installed, return it
945 return hash;
946 }
947 // Failed to install the hash. It could be that another thread
948 // installed the hash just before our attempt or inflation has
949 // occurred or... so we fall thru to inflate the monitor for
950 // stability and then install the hash.
951 } else if (mark.has_monitor()) {
952 monitor = mark.monitor();
953 temp = monitor->header();
954 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
955 hash = temp.hash();
956 if (hash != 0) {
957 // It has a hash.
958
959 // Separate load of dmw/header above from the loads in
960 // is_being_async_deflated().
961
962 // dmw/header and _contentions may get written by different threads.
963 // Make sure to observe them in the same order when having several observers.
964 OrderAccess::loadload_for_IRIW();
965
966 if (monitor->is_being_async_deflated()) {
967 // But we can't safely use the hash if we detect that async
968 // deflation has occurred. So we attempt to restore the
969 // header/dmw to the object's header so that we only retry
970 // once if the deflater thread happens to be slow.
971 monitor->install_displaced_markword_in_object(obj);
972 continue;
973 }
974 return hash;
975 }
976 // Fall thru so we only have one place that installs the hash in
977 // the ObjectMonitor.
978 } else if (mark.is_fast_locked() && is_lock_owned(current, obj)) {
979 // This is a fast lock owned by the calling thread so use the
980 // markWord from the object.
981 hash = mark.hash();
982 if (hash != 0) { // if it has a hash, just return it
983 return hash;
984 }
985 } else if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
986 // This is a stack lock owned by the calling thread so fetch the
987 // displaced markWord from the BasicLock on the stack.
988 temp = mark.displaced_mark_helper();
989 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
990 hash = temp.hash();
991 if (hash != 0) { // if it has a hash, just return it
992 return hash;
993 }
994 // WARNING:
995 // The displaced header in the BasicLock on a thread's stack
996 // is strictly immutable. It CANNOT be changed in ANY cases.
997 // So we have to inflate the stack lock into an ObjectMonitor
998 // even if the current thread owns the lock. The BasicLock on
999 // a thread's stack can be asynchronously read by other threads
1000 // during an inflate() call so any change to that stack memory
1001 // may not propagate to other threads correctly.
1002 }
1003
1004 // Inflate the monitor to set the hash.
1005
1006 // An async deflation can race after the inflate() call and before we
1007 // can update the ObjectMonitor's header with the hash value below.
1008 monitor = inflate(current, obj, inflate_cause_hash_code);
1009 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1010 mark = monitor->header();
1011 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1012 hash = mark.hash();
1013 if (hash == 0) { // if it does not have a hash
1014 hash = get_next_hash(current, obj); // get a new hash
1015 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1016 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1017 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1018 test = markWord(v);
1019 if (test != mark) {
1020 // The attempt to update the ObjectMonitor's header/dmw field
1021 // did not work. This can happen if another thread managed to
1022 // merge in the hash just before our cmpxchg().
1023 // If we add any new usages of the header/dmw field, this code
1024 // will need to be updated.
1025 hash = test.hash();
1026 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1027 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1028 }
1029 if (monitor->is_being_async_deflated()) {
1030 // If we detect that async deflation has occurred, then we
1031 // attempt to restore the header/dmw to the object's header
1032 // so that we only retry once if the deflater thread happens
1033 // to be slow.
1034 monitor->install_displaced_markword_in_object(obj);
1035 continue;
1036 }
1037 }
1038 // We finally get the hash.
1039 return hash;
1040 }
1041 }
1042
1043 // Deprecated -- use FastHashCode() instead.
1044
1045 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1046 return FastHashCode(Thread::current(), obj());
1047 }
1048
1049
1050 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1051 Handle h_obj) {
1052 if (UseBiasedLocking) {
1053 BiasedLocking::revoke(current, h_obj);
1054 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1055 }
1056
1057 assert(current == JavaThread::current(), "Can only be called on current thread");
1058 oop obj = h_obj();
1059
1060 markWord mark = read_stable_mark(obj);
1061
1062 // Uncontended case, header points to stack
1063 if (mark.has_locker()) {
1064 return current->is_lock_owned((address)mark.locker());
1065 }
1066
1067 // Fast-locking case.
1068 if (mark.is_fast_locked()) {
1069 return current->lock_stack().contains(h_obj());
1070 }
1071
1072 // Contended case, header points to ObjectMonitor (tagged pointer)
1073 if (mark.has_monitor()) {
1074 // The first stage of async deflation does not affect any field
1075 // used by this comparison so the ObjectMonitor* is usable here.
1076 ObjectMonitor* monitor = mark.monitor();
1077 return monitor->is_entered(current) != 0;
1078 }
1079 // Unlocked case, header in place
1080 assert(mark.is_neutral(), "sanity check");
1081 return false;
1082 }
1083
1084 // FIXME: jvmti should call this
1085 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1086 if (UseBiasedLocking) {
1087 if (SafepointSynchronize::is_at_safepoint()) {
1088 BiasedLocking::revoke_at_safepoint(h_obj);
1089 } else {
1090 BiasedLocking::revoke(JavaThread::current(), h_obj);
1091 }
1092 assert(!h_obj->mark().has_bias_pattern(), "biases should be revoked by now");
1093 }
1094
1095 oop obj = h_obj();
1096 markWord mark = read_stable_mark(obj);
1097
1098 // Uncontended case, header points to stack
1099 if (mark.has_locker()) {
1100 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1101 }
1102
1103 if (mark.is_fast_locked()) {
1104 return Threads::owning_thread_from_object(t_list, h_obj());
1105 }
1106
1107 // Contended case, header points to ObjectMonitor (tagged pointer)
1108 if (mark.has_monitor()) {
1109 // The first stage of async deflation does not affect any field
1110 // used by this comparison so the ObjectMonitor* is usable here.
1111 ObjectMonitor* monitor = mark.monitor();
1112 assert(monitor != NULL, "monitor should be non-null");
1113 return Threads::owning_thread_from_monitor(t_list, monitor);
1114 }
1115
1116 return NULL;
1117 }
1118
1119 // Visitors ...
1120
1121 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1122 MonitorList::Iterator iter = _in_use_list.iterator();
1123 while (iter.has_next()) {
1124 ObjectMonitor* mid = iter.next();
1125 if (mid->owner() != thread) {
1126 continue;
1127 }
1128 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1129 // Only process with closure if the object is set.
1130
1131 // monitors_iterate() is only called at a safepoint or when the
1132 // target thread is suspended or when the target thread is
1133 // operating on itself. The current closures in use today are
1134 // only interested in an owned ObjectMonitor and ownership
1135 // cannot be dropped under the calling contexts so the
1136 // ObjectMonitor cannot be async deflated.
1137 closure->do_monitor(mid);
1138 }
1139 }
1140 }
1141
1142 static bool monitors_used_above_threshold(MonitorList* list) {
1143 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1144 return false;
1145 }
1146 // Start with ceiling based on a per-thread estimate:
1147 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1148 size_t old_ceiling = ceiling;
1149 if (ceiling < list->max()) {
1150 // The max used by the system has exceeded the ceiling so use that:
1151 ceiling = list->max();
1152 }
1153 size_t monitors_used = list->count();
1154 if (monitors_used == 0) { // empty list is easy
1155 return false;
1156 }
1157 if (NoAsyncDeflationProgressMax != 0 &&
1158 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1159 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1160 size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1161 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1162 log_info(monitorinflation)("Too many deflations without progress; "
1163 "bumping in_use_list_ceiling from " SIZE_FORMAT
1164 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1165 _no_progress_cnt = 0;
1166 ceiling = new_ceiling;
1167 }
1168
1169 // Check if our monitor usage is above the threshold:
1170 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1171 return int(monitor_usage) > MonitorUsedDeflationThreshold;
1172 }
1173
1174 size_t ObjectSynchronizer::in_use_list_ceiling() {
1175 return _in_use_list_ceiling;
1176 }
1177
1178 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1179 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1180 }
1181
1182 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1183 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1184 }
1185
1186 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1187 _in_use_list_ceiling = new_value;
1188 }
1189
1190 bool ObjectSynchronizer::is_async_deflation_needed() {
1191 if (is_async_deflation_requested()) {
1192 // Async deflation request.
1193 return true;
1194 }
1195 if (AsyncDeflationInterval > 0 &&
1196 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1197 monitors_used_above_threshold(&_in_use_list)) {
1198 // It's been longer than our specified deflate interval and there
1199 // are too many monitors in use. We don't deflate more frequently
1200 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1201 // in order to not swamp the MonitorDeflationThread.
1202 return true;
1203 }
1204 return false;
1205 }
1206
1207 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1208 JavaThread* current = JavaThread::current();
1209 bool ret_code = false;
1210
1211 jlong last_time = last_async_deflation_time_ns();
1212 set_is_async_deflation_requested(true);
1213 {
1214 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1215 ml.notify_all();
1216 }
1217 const int N_CHECKS = 5;
1218 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1219 if (last_async_deflation_time_ns() > last_time) {
1220 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1221 ret_code = true;
1222 break;
1223 }
1224 {
1225 // JavaThread has to honor the blocking protocol.
1226 ThreadBlockInVM tbivm(current);
1227 os::naked_short_sleep(999); // sleep for almost 1 second
1228 }
1229 }
1230 if (!ret_code) {
1231 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1232 }
1233
1234 return ret_code;
1235 }
1236
1237 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1238 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1239 }
1240
1241 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1242 const oop obj,
1243 ObjectSynchronizer::InflateCause cause) {
1244 assert(event != NULL, "invariant");
1245 assert(event->should_commit(), "invariant");
1246 event->set_monitorClass(obj->klass());
1247 event->set_address((uintptr_t)(void*)obj);
1248 event->set_cause((u1)cause);
1249 event->commit();
1250 }
1251
1252 // Fast path code shared by multiple functions
1253 void ObjectSynchronizer::inflate_helper(oop obj) {
1254 markWord mark = obj->mark();
1255 if (mark.has_monitor()) {
1256 ObjectMonitor* monitor = mark.monitor();
1257 markWord dmw = monitor->header();
1258 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1259 return;
1260 }
1261 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1262 }
1263
1264 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1265 const InflateCause cause) {
1266 EventJavaMonitorInflate event;
1267
1268 for (;;) {
1269 const markWord mark = object->mark();
1270 assert(!mark.has_bias_pattern(), "invariant");
1271
1272 // The mark can be in one of the following states:
1273 // * Inflated - just return
1274 // * Stack-locked - coerce it to inflated
1275 // * INFLATING - busy wait for conversion to complete
1276 // * Neutral - aggressively inflate the object.
1277 // * BIASED - Illegal. We should never see this
1278
1279 // CASE: inflated
1280 if (mark.has_monitor()) {
1281 ObjectMonitor* inf = mark.monitor();
1282 markWord dmw = inf->header();
1283 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1284 if (UseFastLocking && inf->is_owner_anonymous() && is_lock_owned(current, object)) {
1285 inf->set_owner_from_anonymous(current);
1286 assert(current->is_Java_thread(), "must be Java thread");
1287 reinterpret_cast<JavaThread*>(current)->lock_stack().remove(object);
1288 }
1289 return inf;
1290 }
1291
1292 // CASE: inflation in progress - inflating over a stack-lock.
1293 // Some other thread is converting from stack-locked to inflated.
1294 // Only that thread can complete inflation -- other threads must wait.
1295 // The INFLATING value is transient.
1296 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1297 // We could always eliminate polling by parking the thread on some auxiliary list.
1298 // NOTE: We need to check UseFastLocking here, because with fast-locking, the header
1299 // may legitimately be zero: cleared lock-bits and all upper header bits zero.
1300 // With fast-locking, the INFLATING protocol is not used.
1301 if (mark == markWord::INFLATING() && !UseFastLocking) {
1302 read_stable_mark(object);
1303 continue;
1304 }
1305
1306 // CASE: stack-locked
1307 // Could be stack-locked either by this thread or by some other thread.
1308 //
1309 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1310 // to install INFLATING into the mark word. We originally installed INFLATING,
1311 // allocated the ObjectMonitor, and then finally STed the address of the
1312 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1313 // the interval in which INFLATING appeared in the mark, thus increasing
1314 // the odds of inflation contention.
1315
1316 LogStreamHandle(Trace, monitorinflation) lsh;
1317 if (mark.is_fast_locked()) {
1318 assert(UseFastLocking, "can only happen with fast-locking");
1319 ObjectMonitor* monitor = new ObjectMonitor(object);
1320 monitor->set_header(mark.set_unlocked());
1321 bool own = is_lock_owned(current, object);
1322 if (own) {
1323 // Owned by us.
1324 monitor->set_owner_from(NULL, current);
1325 } else {
1326 // Owned by somebody else.
1327 monitor->set_owner_anonymous();
1328 }
1329 markWord monitor_mark = markWord::encode(monitor);
1330 markWord witness = object->cas_set_mark(monitor_mark, mark);
1331 if (witness == mark) {
1332 // Success! Return inflated monitor.
1333 if (own) {
1334 assert(current->is_Java_thread(), "must be: checked in is_lock_owned()");
1335 reinterpret_cast<JavaThread*>(current)->lock_stack().remove(object);
1336 }
1337 // Once the ObjectMonitor is configured and object is associated
1338 // with the ObjectMonitor, it is safe to allow async deflation:
1339 _in_use_list.add(monitor);
1340
1341 // Hopefully the performance counters are allocated on distinct
1342 // cache lines to avoid false sharing on MP systems ...
1343 OM_PERFDATA_OP(Inflations, inc());
1344 if (log_is_enabled(Trace, monitorinflation)) {
1345 ResourceMark rm(current);
1346 lsh.print_cr("inflate(locked): object=" INTPTR_FORMAT ", mark="
1347 INTPTR_FORMAT ", type='%s'", p2i(object),
1348 object->mark().value(), object->klass()->external_name());
1349 }
1350 if (event.should_commit()) {
1351 post_monitor_inflate_event(&event, object, cause);
1352 }
1353 return monitor;
1354 } else {
1355 delete monitor;
1356 continue;
1357 }
1358 }
1359
1360 if (mark.has_locker()) {
1361 assert(!UseFastLocking, "can not happen with fast-locking");
1362 ObjectMonitor* m = new ObjectMonitor(object);
1363 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1364 // We do this before the CAS in order to minimize the length of time
1365 // in which INFLATING appears in the mark.
1366
1367 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1368 if (cmp != mark) {
1369 delete m;
1370 continue; // Interference -- just retry
1371 }
1372
1373 // We've successfully installed INFLATING (0) into the mark-word.
1374 // This is the only case where 0 will appear in a mark-word.
1375 // Only the singular thread that successfully swings the mark-word
1376 // to 0 can perform (or more precisely, complete) inflation.
1377 //
1378 // Why do we CAS a 0 into the mark-word instead of just CASing the
1379 // mark-word from the stack-locked value directly to the new inflated state?
1380 // Consider what happens when a thread unlocks a stack-locked object.
1381 // It attempts to use CAS to swing the displaced header value from the
1382 // on-stack BasicLock back into the object header. Recall also that the
1383 // header value (hash code, etc) can reside in (a) the object header, or
1384 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1385 // header in an ObjectMonitor. The inflate() routine must copy the header
1386 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1387 // the while preserving the hashCode stability invariants. If the owner
1388 // decides to release the lock while the value is 0, the unlock will fail
1389 // and control will eventually pass from slow_exit() to inflate. The owner
1390 // will then spin, waiting for the 0 value to disappear. Put another way,
1391 // the 0 causes the owner to stall if the owner happens to try to
1392 // drop the lock (restoring the header from the BasicLock to the object)
1393 // while inflation is in-progress. This protocol avoids races that might
1394 // would otherwise permit hashCode values to change or "flicker" for an object.
1395 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1396 // 0 serves as a "BUSY" inflate-in-progress indicator.
1397
1398
1399 // fetch the displaced mark from the owner's stack.
1400 // The owner can't die or unwind past the lock while our INFLATING
1401 // object is in the mark. Furthermore the owner can't complete
1402 // an unlock on the object, either.
1403 markWord dmw = mark.displaced_mark_helper();
1404 // Catch if the object's header is not neutral (not locked and
1405 // not marked is what we care about here).
1406 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1407
1408 // Setup monitor fields to proper values -- prepare the monitor
1409 m->set_header(dmw);
1410
1411 // Optimization: if the mark.locker stack address is associated
1412 // with this thread we could simply set m->_owner = current.
1413 // Note that a thread can inflate an object
1414 // that it has stack-locked -- as might happen in wait() -- directly
1415 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1416 m->set_owner_from(NULL, mark.locker());
1417 // TODO-FIXME: assert BasicLock->dhw != 0.
1418
1419 // Must preserve store ordering. The monitor state must
1420 // be stable at the time of publishing the monitor address.
1421 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1422 // Release semantics so that above set_object() is seen first.
1423 object->release_set_mark(markWord::encode(m));
1424
1425 // Once ObjectMonitor is configured and the object is associated
1426 // with the ObjectMonitor, it is safe to allow async deflation:
1427 _in_use_list.add(m);
1428
1429 // Hopefully the performance counters are allocated on distinct cache lines
1430 // to avoid false sharing on MP systems ...
1431 OM_PERFDATA_OP(Inflations, inc());
1432 if (log_is_enabled(Trace, monitorinflation)) {
1433 ResourceMark rm(current);
1434 lsh.print_cr("inflate(locked): object=" INTPTR_FORMAT ", mark="
1435 INTPTR_FORMAT ", type='%s'", p2i(object),
1436 object->mark().value(), object->klass()->external_name());
1437 }
1438 if (event.should_commit()) {
1439 post_monitor_inflate_event(&event, object, cause);
1440 }
1441 return m;
1442 }
1443
1444 // CASE: neutral
1445 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1446 // If we know we're inflating for entry it's better to inflate by swinging a
1447 // pre-locked ObjectMonitor pointer into the object header. A successful
1448 // CAS inflates the object *and* confers ownership to the inflating thread.
1449 // In the current implementation we use a 2-step mechanism where we CAS()
1450 // to inflate and then CAS() again to try to swing _owner from NULL to current.
1451 // An inflateTry() method that we could call from enter() would be useful.
1452
1453 // Catch if the object's header is not neutral (not locked and
1454 // not marked is what we care about here).
1455 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1456 ObjectMonitor* m = new ObjectMonitor(object);
1457 // prepare m for installation - set monitor to initial state
1458 m->set_header(mark);
1459
1460 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1461 delete m;
1462 m = NULL;
1463 continue;
1464 // interference - the markword changed - just retry.
1465 // The state-transitions are one-way, so there's no chance of
1466 // live-lock -- "Inflated" is an absorbing state.
1467 }
1468
1469 // Once the ObjectMonitor is configured and object is associated
1470 // with the ObjectMonitor, it is safe to allow async deflation:
1471 _in_use_list.add(m);
1472
1473 // Hopefully the performance counters are allocated on distinct
1474 // cache lines to avoid false sharing on MP systems ...
1475 OM_PERFDATA_OP(Inflations, inc());
1476 if (log_is_enabled(Trace, monitorinflation)) {
1477 ResourceMark rm(current);
1478 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1479 INTPTR_FORMAT ", type='%s'", p2i(object),
1480 object->mark().value(), object->klass()->external_name());
1481 }
1482 if (event.should_commit()) {
1483 post_monitor_inflate_event(&event, object, cause);
1484 }
1485 return m;
1486 }
1487 }
1488
1489 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1490 const char* cnt_name, size_t cnt,
1491 LogStream* ls, elapsedTimer* timer_p) {
1492 if (!SafepointMechanism::should_process(current)) {
1493 return;
1494 }
1495
1496 // A safepoint/handshake has started.
1497 if (ls != NULL) {
1498 timer_p->stop();
1499 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1500 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1501 op_name, cnt_name, cnt, in_use_list_ceiling(),
1502 _in_use_list.count(), _in_use_list.max());
1503 }
1504
1505 {
1506 // Honor block request.
1507 ThreadBlockInVM tbivm(current);
1508 }
1509
1510 if (ls != NULL) {
1511 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1512 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1513 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1514 timer_p->start();
1515 }
1516 }
1517
1518 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1519 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1520 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1521 elapsedTimer* timer_p) {
1522 MonitorList::Iterator iter = _in_use_list.iterator();
1523 size_t deflated_count = 0;
1524
1525 while (iter.has_next()) {
1526 if (deflated_count >= (size_t)MonitorDeflationMax) {
1527 break;
1528 }
1529 ObjectMonitor* mid = iter.next();
1530 if (mid->deflate_monitor()) {
1531 deflated_count++;
1532 }
1533
1534 if (current->is_Java_thread()) {
1535 // A JavaThread must check for a safepoint/handshake and honor it.
1536 chk_for_block_req(current->as_Java_thread(), "deflation", "deflated_count",
1537 deflated_count, ls, timer_p);
1538 }
1539 }
1540
1541 return deflated_count;
1542 }
1543
1544 class HandshakeForDeflation : public HandshakeClosure {
1545 public:
1546 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1547
1548 void do_thread(Thread* thread) {
1549 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1550 INTPTR_FORMAT, p2i(thread));
1551 }
1552 };
1553
1554 class VM_RendezvousGCThreads : public VM_Operation {
1555 public:
1556 bool evaluate_at_safepoint() const override { return false; }
1557 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1558 void doit() override {
1559 SuspendibleThreadSet::synchronize();
1560 SuspendibleThreadSet::desynchronize();
1561 };
1562 };
1563
1564 // This function is called by the MonitorDeflationThread to deflate
1565 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1566 // by the VMThread.
1567 size_t ObjectSynchronizer::deflate_idle_monitors() {
1568 Thread* current = Thread::current();
1569 if (current->is_Java_thread()) {
1570 // The async deflation request has been processed.
1571 _last_async_deflation_time_ns = os::javaTimeNanos();
1572 set_is_async_deflation_requested(false);
1573 }
1574
1575 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1576 LogStreamHandle(Info, monitorinflation) lsh_info;
1577 LogStream* ls = NULL;
1578 if (log_is_enabled(Debug, monitorinflation)) {
1579 ls = &lsh_debug;
1580 } else if (log_is_enabled(Info, monitorinflation)) {
1581 ls = &lsh_info;
1582 }
1583
1584 elapsedTimer timer;
1585 if (ls != NULL) {
1586 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1587 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1588 timer.start();
1589 }
1590
1591 // Deflate some idle ObjectMonitors.
1592 size_t deflated_count = deflate_monitor_list(current, ls, &timer);
1593 if (deflated_count > 0 || is_final_audit()) {
1594 // There are ObjectMonitors that have been deflated or this is the
1595 // final audit and all the remaining ObjectMonitors have been
1596 // deflated, BUT the MonitorDeflationThread blocked for the final
1597 // safepoint during unlinking.
1598
1599 // Unlink deflated ObjectMonitors from the in-use list.
1600 ResourceMark rm;
1601 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1602 size_t unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer,
1603 &delete_list);
1604 if (current->is_Java_thread()) {
1605 if (ls != NULL) {
1606 timer.stop();
1607 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1608 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1609 SIZE_FORMAT ", max=" SIZE_FORMAT,
1610 unlinked_count, in_use_list_ceiling(),
1611 _in_use_list.count(), _in_use_list.max());
1612 }
1613
1614 // A JavaThread needs to handshake in order to safely free the
1615 // ObjectMonitors that were deflated in this cycle.
1616 // Also, we sync and desync GC threads around the handshake, so that they can
1617 // safely read the mark-word and look-through to the object-monitor, without
1618 // being afraid that the object-monitor is going away.
1619 HandshakeForDeflation hfd_hc;
1620 Handshake::execute(&hfd_hc);
1621 VM_RendezvousGCThreads sync_gc;
1622 VMThread::execute(&sync_gc);
1623
1624 if (ls != NULL) {
1625 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1626 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1627 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1628 timer.start();
1629 }
1630 }
1631
1632 // After the handshake, safely free the ObjectMonitors that were
1633 // deflated in this cycle.
1634 size_t deleted_count = 0;
1635 for (ObjectMonitor* monitor: delete_list) {
1636 delete monitor;
1637 deleted_count++;
1638
1639 if (current->is_Java_thread()) {
1640 // A JavaThread must check for a safepoint/handshake and honor it.
1641 chk_for_block_req(current->as_Java_thread(), "deletion", "deleted_count",
1642 deleted_count, ls, &timer);
1643 }
1644 }
1645 }
1646
1647 if (ls != NULL) {
1648 timer.stop();
1649 if (deflated_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1650 ls->print_cr("deflated " SIZE_FORMAT " monitors in %3.7f secs",
1651 deflated_count, timer.seconds());
1652 }
1653 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1654 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1655 }
1656
1657 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1658 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1659
1660 GVars.stw_random = os::random();
1661
1662 if (deflated_count != 0) {
1663 _no_progress_cnt = 0;
1664 } else {
1665 _no_progress_cnt++;
1666 }
1667
1668 return deflated_count;
1669 }
1670
1671 // Monitor cleanup on JavaThread::exit
1672
1673 // Iterate through monitor cache and attempt to release thread's monitors
1674 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1675 private:
1676 JavaThread* _thread;
1677
1678 public:
1679 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1680 void do_monitor(ObjectMonitor* mid) {
1681 (void)mid->complete_exit(_thread);
1682 }
1683 };
1684
1685 // Release all inflated monitors owned by current thread. Lightweight monitors are
1686 // ignored. This is meant to be called during JNI thread detach which assumes
1687 // all remaining monitors are heavyweight. All exceptions are swallowed.
1688 // Scanning the extant monitor list can be time consuming.
1689 // A simple optimization is to add a per-thread flag that indicates a thread
1690 // called jni_monitorenter() during its lifetime.
1691 //
1692 // Instead of NoSafepointVerifier it might be cheaper to
1693 // use an idiom of the form:
1694 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1695 // <code that must not run at safepoint>
1696 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1697 // Since the tests are extremely cheap we could leave them enabled
1698 // for normal product builds.
1699
1700 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1701 assert(current == JavaThread::current(), "must be current Java thread");
1702 NoSafepointVerifier nsv;
1703 ReleaseJavaMonitorsClosure rjmc(current);
1704 ObjectSynchronizer::monitors_iterate(&rjmc, current);
1705 assert(!current->has_pending_exception(), "Should not be possible");
1706 current->clear_pending_exception();
1707 }
1708
1709 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1710 switch (cause) {
1711 case inflate_cause_vm_internal: return "VM Internal";
1712 case inflate_cause_monitor_enter: return "Monitor Enter";
1713 case inflate_cause_wait: return "Monitor Wait";
1714 case inflate_cause_notify: return "Monitor Notify";
1715 case inflate_cause_hash_code: return "Monitor Hash Code";
1716 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1717 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1718 default:
1719 ShouldNotReachHere();
1720 }
1721 return "Unknown";
1722 }
1723
1724 //------------------------------------------------------------------------------
1725 // Debugging code
1726
1727 u_char* ObjectSynchronizer::get_gvars_addr() {
1728 return (u_char*)&GVars;
1729 }
1730
1731 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1732 return (u_char*)&GVars.hc_sequence;
1733 }
1734
1735 size_t ObjectSynchronizer::get_gvars_size() {
1736 return sizeof(SharedGlobals);
1737 }
1738
1739 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1740 return (u_char*)&GVars.stw_random;
1741 }
1742
1743 // Do the final audit and print of ObjectMonitor stats; must be done
1744 // by the VMThread at VM exit time.
1745 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1746 assert(Thread::current()->is_VM_thread(), "sanity check");
1747
1748 if (is_final_audit()) { // Only do the audit once.
1749 return;
1750 }
1751 set_is_final_audit();
1752
1753 if (log_is_enabled(Info, monitorinflation)) {
1754 // Do a deflation in order to reduce the in-use monitor population
1755 // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1756 // which is called by ObjectSynchronizer::audit_and_print_stats().
1757 while (ObjectSynchronizer::deflate_idle_monitors() != 0) {
1758 ; // empty
1759 }
1760 // The other audit_and_print_stats() call is done at the Debug
1761 // level at a safepoint in ObjectSynchronizer::do_safepoint_work().
1762 ObjectSynchronizer::audit_and_print_stats(true /* on_exit */);
1763 }
1764 }
1765
1766 // This function can be called at a safepoint or it can be called when
1767 // we are trying to exit the VM. When we are trying to exit the VM, the
1768 // list walker functions can run in parallel with the other list
1769 // operations so spin-locking is used for safety.
1770 //
1771 // Calls to this function can be added in various places as a debugging
1772 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1773 // details logged at the Info level and 'false' for the 'on_exit'
1774 // parameter to have in-use monitor details logged at the Trace level.
1775 //
1776 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1777 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1778
1779 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1780 LogStreamHandle(Info, monitorinflation) lsh_info;
1781 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1782 LogStream* ls = NULL;
1783 if (log_is_enabled(Trace, monitorinflation)) {
1784 ls = &lsh_trace;
1785 } else if (log_is_enabled(Debug, monitorinflation)) {
1786 ls = &lsh_debug;
1787 } else if (log_is_enabled(Info, monitorinflation)) {
1788 ls = &lsh_info;
1789 }
1790 assert(ls != NULL, "sanity check");
1791
1792 int error_cnt = 0;
1793
1794 ls->print_cr("Checking in_use_list:");
1795 chk_in_use_list(ls, &error_cnt);
1796
1797 if (error_cnt == 0) {
1798 ls->print_cr("No errors found in in_use_list checks.");
1799 } else {
1800 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1801 }
1802
1803 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1804 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1805 // When exiting this log output is at the Info level. When called
1806 // at a safepoint, this log output is at the Trace level since
1807 // there can be a lot of it.
1808 log_in_use_monitor_details(ls);
1809 }
1810
1811 ls->flush();
1812
1813 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1814 }
1815
1816 // Check the in_use_list; log the results of the checks.
1817 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1818 size_t l_in_use_count = _in_use_list.count();
1819 size_t l_in_use_max = _in_use_list.max();
1820 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1821 l_in_use_max);
1822
1823 size_t ck_in_use_count = 0;
1824 MonitorList::Iterator iter = _in_use_list.iterator();
1825 while (iter.has_next()) {
1826 ObjectMonitor* mid = iter.next();
1827 chk_in_use_entry(mid, out, error_cnt_p);
1828 ck_in_use_count++;
1829 }
1830
1831 if (l_in_use_count == ck_in_use_count) {
1832 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1833 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1834 } else {
1835 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1836 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1837 ck_in_use_count);
1838 }
1839
1840 size_t ck_in_use_max = _in_use_list.max();
1841 if (l_in_use_max == ck_in_use_max) {
1842 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1843 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1844 } else {
1845 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1846 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1847 }
1848 }
1849
1850 // Check an in-use monitor entry; log any errors.
1851 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1852 int* error_cnt_p) {
1853 if (n->owner_is_DEFLATER_MARKER()) {
1854 // This should not happen, but if it does, it is not fatal.
1855 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1856 "deflated.", p2i(n));
1857 return;
1858 }
1859 if (n->header().value() == 0) {
1860 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1861 "have non-NULL _header field.", p2i(n));
1862 *error_cnt_p = *error_cnt_p + 1;
1863 }
1864 const oop obj = n->object_peek();
1865 if (obj != NULL) {
1866 const markWord mark = obj->mark();
1867 if (!mark.has_monitor()) {
1868 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1869 "object does not think it has a monitor: obj="
1870 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1871 p2i(obj), mark.value());
1872 *error_cnt_p = *error_cnt_p + 1;
1873 }
1874 ObjectMonitor* const obj_mon = mark.monitor();
1875 if (n != obj_mon) {
1876 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1877 "object does not refer to the same monitor: obj="
1878 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1879 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1880 *error_cnt_p = *error_cnt_p + 1;
1881 }
1882 }
1883 }
1884
1885 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1886 // flags indicate why the entry is in-use, 'object' and 'object type'
1887 // indicate the associated object and its type.
1888 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
1889 stringStream ss;
1890 if (_in_use_list.count() > 0) {
1891 out->print_cr("In-use monitor info:");
1892 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1893 out->print_cr("%18s %s %18s %18s",
1894 "monitor", "BHL", "object", "object type");
1895 out->print_cr("================== === ================== ==================");
1896 MonitorList::Iterator iter = _in_use_list.iterator();
1897 while (iter.has_next()) {
1898 ObjectMonitor* mid = iter.next();
1899 const oop obj = mid->object_peek();
1900 const markWord mark = mid->header();
1901 ResourceMark rm;
1902 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid),
1903 mid->is_busy(), mark.hash() != 0, mid->owner() != NULL,
1904 p2i(obj), obj == NULL ? "" : obj->klass()->external_name());
1905 if (mid->is_busy()) {
1906 out->print(" (%s)", mid->is_busy_to_string(&ss));
1907 ss.reset();
1908 }
1909 out->cr();
1910 }
1911 }
1912
1913 out->flush();
1914 }