1 /*
2 * Copyright (c) 1998, 2022, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "jfr/jfrEvents.hpp"
28 #include "gc/shared/suspendibleThreadSet.hpp"
29 #include "logging/log.hpp"
30 #include "logging/logStream.hpp"
31 #include "memory/allocation.inline.hpp"
32 #include "memory/padded.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/markWord.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "runtime/atomic.hpp"
38 #include "runtime/handles.inline.hpp"
39 #include "runtime/handshake.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "runtime/objectMonitor.hpp"
43 #include "runtime/objectMonitor.inline.hpp"
44 #include "runtime/os.inline.hpp"
45 #include "runtime/osThread.hpp"
46 #include "runtime/perfData.hpp"
47 #include "runtime/safepointMechanism.inline.hpp"
48 #include "runtime/safepointVerifiers.hpp"
49 #include "runtime/sharedRuntime.hpp"
50 #include "runtime/stubRoutines.hpp"
51 #include "runtime/synchronizer.hpp"
52 #include "runtime/thread.inline.hpp"
53 #include "runtime/timer.hpp"
54 #include "runtime/vframe.hpp"
55 #include "runtime/vmThread.hpp"
56 #include "utilities/align.hpp"
57 #include "utilities/dtrace.hpp"
58 #include "utilities/events.hpp"
59 #include "utilities/preserveException.hpp"
60
61 class CleanupObjectMonitorsHashtable: StackObj {
62 public:
63 bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) {
64 list->clear(); // clear the LinkListNodes
65 delete list; // then delete the LinkedList
66 return true;
67 }
68 };
69
70 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() {
71 CleanupObjectMonitorsHashtable cleanup;
72 _ptrs->unlink(&cleanup); // cleanup the LinkedLists
73 delete _ptrs; // then delete the hash table
74 }
75
76 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) {
77 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
78 if (list == nullptr) {
79 // Create new list and add it to the hash table:
80 list = new (ResourceObj::C_HEAP, mtThread) ObjectMonitorsHashtable::PtrList();
81 add_entry(key, list);
82 }
83 list->add(om); // Add the ObjectMonitor to the list.
84 _om_count++;
85 }
86
87 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) {
88 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
89 if (list == nullptr || list->find(om) == nullptr) {
90 return false;
91 }
92 return true;
93 }
94
95 void MonitorList::add(ObjectMonitor* m) {
96 ObjectMonitor* head;
97 do {
98 head = Atomic::load(&_head);
99 m->set_next_om(head);
100 } while (Atomic::cmpxchg(&_head, head, m) != head);
101
102 size_t count = Atomic::add(&_count, 1u);
103 if (count > max()) {
104 Atomic::inc(&_max);
105 }
106 }
107
108 size_t MonitorList::count() const {
109 return Atomic::load(&_count);
110 }
111
112 size_t MonitorList::max() const {
113 return Atomic::load(&_max);
114 }
115
116 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
117 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
118 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
119 elapsedTimer* timer_p,
120 GrowableArray<ObjectMonitor*>* unlinked_list) {
121 size_t unlinked_count = 0;
122 ObjectMonitor* prev = NULL;
123 ObjectMonitor* head = Atomic::load_acquire(&_head);
124 ObjectMonitor* m = head;
125 // The in-use list head can be NULL during the final audit.
126 while (m != NULL) {
127 if (m->is_being_async_deflated()) {
128 // Find next live ObjectMonitor.
129 ObjectMonitor* next = m;
130 do {
131 ObjectMonitor* next_next = next->next_om();
132 unlinked_count++;
133 unlinked_list->append(next);
134 next = next_next;
135 if (unlinked_count >= (size_t)MonitorDeflationMax) {
136 // Reached the max so bail out on the gathering loop.
137 break;
138 }
139 } while (next != NULL && next->is_being_async_deflated());
140 if (prev == NULL) {
141 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
142 if (prev_head != head) {
143 // Find new prev ObjectMonitor that just got inserted.
144 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
145 prev = n;
146 }
147 prev->set_next_om(next);
148 }
149 } else {
150 prev->set_next_om(next);
151 }
152 if (unlinked_count >= (size_t)MonitorDeflationMax) {
153 // Reached the max so bail out on the searching loop.
154 break;
155 }
156 m = next;
157 } else {
158 prev = m;
159 m = m->next_om();
160 }
161
162 if (current->is_Java_thread()) {
163 // A JavaThread must check for a safepoint/handshake and honor it.
164 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking",
165 "unlinked_count", unlinked_count,
166 ls, timer_p);
167 }
168 }
169 Atomic::sub(&_count, unlinked_count);
170 return unlinked_count;
171 }
172
173 MonitorList::Iterator MonitorList::iterator() const {
174 return Iterator(Atomic::load_acquire(&_head));
175 }
176
177 ObjectMonitor* MonitorList::Iterator::next() {
178 ObjectMonitor* current = _current;
179 _current = current->next_om();
180 return current;
181 }
182
183 // The "core" versions of monitor enter and exit reside in this file.
184 // The interpreter and compilers contain specialized transliterated
185 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
186 // fast_lock(...) for instance. If you make changes here, make sure to modify the
187 // interpreter, and both C1 and C2 fast-path inline locking code emission.
188 //
189 // -----------------------------------------------------------------------------
190
191 #ifdef DTRACE_ENABLED
192
193 // Only bother with this argument setup if dtrace is available
194 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
195
196 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
197 char* bytes = NULL; \
198 int len = 0; \
199 jlong jtid = SharedRuntime::get_java_tid(thread); \
200 Symbol* klassname = obj->klass()->name(); \
201 if (klassname != NULL) { \
202 bytes = (char*)klassname->bytes(); \
203 len = klassname->utf8_length(); \
204 }
205
206 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
207 { \
208 if (DTraceMonitorProbes) { \
209 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
210 HOTSPOT_MONITOR_WAIT(jtid, \
211 (uintptr_t)(monitor), bytes, len, (millis)); \
212 } \
213 }
214
215 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
216 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
217 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
218
219 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
220 { \
221 if (DTraceMonitorProbes) { \
222 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
223 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
224 (uintptr_t)(monitor), bytes, len); \
225 } \
226 }
227
228 #else // ndef DTRACE_ENABLED
229
230 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
231 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
232
233 #endif // ndef DTRACE_ENABLED
234
235 // This exists only as a workaround of dtrace bug 6254741
236 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
237 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
238 return 0;
239 }
240
241 static const int NINFLATIONLOCKS = 256;
242 static os::PlatformMutex* gInflationLocks[NINFLATIONLOCKS];
243
244 void ObjectSynchronizer::initialize() {
245 for (int i = 0; i < NINFLATIONLOCKS; i++) {
246 gInflationLocks[i] = new os::PlatformMutex();
247 }
248 // Start the ceiling with the estimate for one thread.
249 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
250 }
251
252 MonitorList ObjectSynchronizer::_in_use_list;
253 // monitors_used_above_threshold() policy is as follows:
254 //
255 // The ratio of the current _in_use_list count to the ceiling is used
256 // to determine if we are above MonitorUsedDeflationThreshold and need
257 // to do an async monitor deflation cycle. The ceiling is increased by
258 // AvgMonitorsPerThreadEstimate when a thread is added to the system
259 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
260 // removed from the system.
261 //
262 // Note: If the _in_use_list max exceeds the ceiling, then
263 // monitors_used_above_threshold() will use the in_use_list max instead
264 // of the thread count derived ceiling because we have used more
265 // ObjectMonitors than the estimated average.
266 //
267 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
268 // no-progress async monitor deflation cycles in a row, then the ceiling
269 // is adjusted upwards by monitors_used_above_threshold().
270 //
271 // Start the ceiling with the estimate for one thread in initialize()
272 // which is called after cmd line options are processed.
273 static size_t _in_use_list_ceiling = 0;
274 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
275 bool volatile ObjectSynchronizer::_is_final_audit = false;
276 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
277 static uintx _no_progress_cnt = 0;
278
279 // =====================> Quick functions
280
281 // The quick_* forms are special fast-path variants used to improve
282 // performance. In the simplest case, a "quick_*" implementation could
283 // simply return false, in which case the caller will perform the necessary
284 // state transitions and call the slow-path form.
285 // The fast-path is designed to handle frequently arising cases in an efficient
286 // manner and is just a degenerate "optimistic" variant of the slow-path.
287 // returns true -- to indicate the call was satisfied.
288 // returns false -- to indicate the call needs the services of the slow-path.
289 // A no-loitering ordinance is in effect for code in the quick_* family
290 // operators: safepoints or indefinite blocking (blocking that might span a
291 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
292 // entry.
293 //
294 // Consider: An interesting optimization is to have the JIT recognize the
295 // following common idiom:
296 // synchronized (someobj) { .... ; notify(); }
297 // That is, we find a notify() or notifyAll() call that immediately precedes
298 // the monitorexit operation. In that case the JIT could fuse the operations
299 // into a single notifyAndExit() runtime primitive.
300
301 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
302 assert(current->thread_state() == _thread_in_Java, "invariant");
303 NoSafepointVerifier nsv;
304 if (obj == NULL) return false; // slow-path for invalid obj
305 const markWord mark = obj->mark();
306
307 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
308 // Degenerate notify
309 // stack-locked by caller so by definition the implied waitset is empty.
310 return true;
311 }
312
313 if (mark.has_monitor()) {
314 ObjectMonitor* const mon = mark.monitor();
315 assert(mon->object() == oop(obj), "invariant");
316 if (mon->owner() != current) return false; // slow-path for IMS exception
317
318 if (mon->first_waiter() != NULL) {
319 // We have one or more waiters. Since this is an inflated monitor
320 // that we own, we can transfer one or more threads from the waitset
321 // to the entrylist here and now, avoiding the slow-path.
322 if (all) {
323 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
324 } else {
325 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
326 }
327 int free_count = 0;
328 do {
329 mon->INotify(current);
330 ++free_count;
331 } while (mon->first_waiter() != NULL && all);
332 OM_PERFDATA_OP(Notifications, inc(free_count));
333 }
334 return true;
335 }
336
337 // other IMS exception states take the slow-path
338 return false;
339 }
340
341
342 // The LockNode emitted directly at the synchronization site would have
343 // been too big if it were to have included support for the cases of inflated
344 // recursive enter and exit, so they go here instead.
345 // Note that we can't safely call AsyncPrintJavaStack() from within
346 // quick_enter() as our thread state remains _in_Java.
347
348 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
349 BasicLock * lock) {
350 assert(current->thread_state() == _thread_in_Java, "invariant");
351 NoSafepointVerifier nsv;
352 if (obj == NULL) return false; // Need to throw NPE
353
354 if (obj->klass()->is_value_based()) {
355 return false;
356 }
357
358 const markWord mark = obj->mark();
359
360 if (mark.has_monitor()) {
361 ObjectMonitor* const m = mark.monitor();
362 // An async deflation or GC can race us before we manage to make
363 // the ObjectMonitor busy by setting the owner below. If we detect
364 // that race we just bail out to the slow-path here.
365 if (m->object_peek() == NULL) {
366 return false;
367 }
368 JavaThread* const owner = (JavaThread*) m->owner_raw();
369
370 // Lock contention and Transactional Lock Elision (TLE) diagnostics
371 // and observability
372 // Case: light contention possibly amenable to TLE
373 // Case: TLE inimical operations such as nested/recursive synchronization
374
375 if (owner == current) {
376 m->_recursions++;
377 return true;
378 }
379
380 // This Java Monitor is inflated so obj's header will never be
381 // displaced to this thread's BasicLock. Make the displaced header
382 // non-NULL so this BasicLock is not seen as recursive nor as
383 // being locked. We do this unconditionally so that this thread's
384 // BasicLock cannot be mis-interpreted by any stack walkers. For
385 // performance reasons, stack walkers generally first check for
386 // stack-locking in the object's header, the second check is for
387 // recursive stack-locking in the displaced header in the BasicLock,
388 // and last are the inflated Java Monitor (ObjectMonitor) checks.
389 lock->set_displaced_header(markWord::unused_mark());
390
391 if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
392 assert(m->_recursions == 0, "invariant");
393 return true;
394 }
395 }
396
397 // Note that we could inflate in quick_enter.
398 // This is likely a useful optimization
399 // Critically, in quick_enter() we must not:
400 // -- block indefinitely, or
401 // -- reach a safepoint
402
403 return false; // revert to slow-path
404 }
405
406 // Handle notifications when synchronizing on value based classes
407 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
408 frame last_frame = current->last_frame();
409 bool bcp_was_adjusted = false;
410 // Don't decrement bcp if it points to the frame's first instruction. This happens when
411 // handle_sync_on_value_based_class() is called because of a synchronized method. There
412 // is no actual monitorenter instruction in the byte code in this case.
413 if (last_frame.is_interpreted_frame() &&
414 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
415 // adjust bcp to point back to monitorenter so that we print the correct line numbers
416 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
417 bcp_was_adjusted = true;
418 }
419
420 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
421 ResourceMark rm(current);
422 stringStream ss;
423 current->print_stack_on(&ss);
424 char* base = (char*)strstr(ss.base(), "at");
425 char* newline = (char*)strchr(ss.base(), '\n');
426 if (newline != NULL) {
427 *newline = '\0';
428 }
429 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
430 } else {
431 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
432 ResourceMark rm(current);
433 Log(valuebasedclasses) vblog;
434
435 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
436 if (current->has_last_Java_frame()) {
437 LogStream info_stream(vblog.info());
438 current->print_stack_on(&info_stream);
439 } else {
440 vblog.info("Cannot find the last Java frame");
441 }
442
443 EventSyncOnValueBasedClass event;
444 if (event.should_commit()) {
445 event.set_valueBasedClass(obj->klass());
446 event.commit();
447 }
448 }
449
450 if (bcp_was_adjusted) {
451 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
452 }
453 }
454
455 static bool useHeavyMonitors() {
456 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64)
457 return UseHeavyMonitors;
458 #else
459 return false;
460 #endif
461 }
462
463 // -----------------------------------------------------------------------------
464 // Monitor Enter/Exit
465 // The interpreter and compiler assembly code tries to lock using the fast path
466 // of this algorithm. Make sure to update that code if the following function is
467 // changed. The implementation is extremely sensitive to race condition. Be careful.
468
469 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
470 if (obj->klass()->is_value_based()) {
471 handle_sync_on_value_based_class(obj, current);
472 }
473
474 if (!useHeavyMonitors()) {
475 markWord mark = obj->mark();
476 if (mark.is_neutral()) {
477 // Anticipate successful CAS -- the ST of the displaced mark must
478 // be visible <= the ST performed by the CAS.
479 lock->set_displaced_header(mark);
480 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
481 return;
482 }
483 // Fall through to inflate() ...
484 } else if (mark.has_locker() &&
485 current->is_lock_owned((address)mark.locker())) {
486 assert(lock != mark.locker(), "must not re-lock the same lock");
487 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
488 lock->set_displaced_header(markWord::from_pointer(NULL));
489 return;
490 }
491
492 // The object header will never be displaced to this lock,
493 // so it does not matter what the value is, except that it
494 // must be non-zero to avoid looking like a re-entrant lock,
495 // and must not look locked either.
496 lock->set_displaced_header(markWord::unused_mark());
497 } else if (VerifyHeavyMonitors) {
498 guarantee(!obj->mark().has_locker(), "must not be stack-locked");
499 }
500
501 // An async deflation can race after the inflate() call and before
502 // enter() can make the ObjectMonitor busy. enter() returns false if
503 // we have lost the race to async deflation and we simply try again.
504 while (true) {
505 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
506 if (monitor->enter(current)) {
507 return;
508 }
509 }
510 }
511
512 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
513 if (!useHeavyMonitors()) {
514 markWord mark = object->mark();
515
516 markWord dhw = lock->displaced_header();
517 if (dhw.value() == 0) {
518 // If the displaced header is NULL, then this exit matches up with
519 // a recursive enter. No real work to do here except for diagnostics.
520 #ifndef PRODUCT
521 if (mark != markWord::INFLATING()) {
522 // Only do diagnostics if we are not racing an inflation. Simply
523 // exiting a recursive enter of a Java Monitor that is being
524 // inflated is safe; see the has_monitor() comment below.
525 assert(!mark.is_neutral(), "invariant");
526 assert(!mark.has_locker() ||
527 current->is_lock_owned((address)mark.locker()), "invariant");
528 if (mark.has_monitor()) {
529 // The BasicLock's displaced_header is marked as a recursive
530 // enter and we have an inflated Java Monitor (ObjectMonitor).
531 // This is a special case where the Java Monitor was inflated
532 // after this thread entered the stack-lock recursively. When a
533 // Java Monitor is inflated, we cannot safely walk the Java
534 // Monitor owner's stack and update the BasicLocks because a
535 // Java Monitor can be asynchronously inflated by a thread that
536 // does not own the Java Monitor.
537 ObjectMonitor* m = mark.monitor();
538 assert(m->object()->mark() == mark, "invariant");
539 assert(m->is_entered(current), "invariant");
540 }
541 }
542 #endif
543 return;
544 }
545
546 if (mark == markWord::from_pointer(lock)) {
547 // If the object is stack-locked by the current thread, try to
548 // swing the displaced header from the BasicLock back to the mark.
549 assert(dhw.is_neutral(), "invariant");
550 if (object->cas_set_mark(dhw, mark) == mark) {
551 return;
552 }
553 }
554 } else if (VerifyHeavyMonitors) {
555 guarantee(!object->mark().has_locker(), "must not be stack-locked");
556 }
557
558 // We have to take the slow-path of possible inflation and then exit.
559 // The ObjectMonitor* can't be async deflated until ownership is
560 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
561 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
562 monitor->exit(current);
563 }
564
565 // -----------------------------------------------------------------------------
566 // Class Loader support to workaround deadlocks on the class loader lock objects
567 // Also used by GC
568 // complete_exit()/reenter() are used to wait on a nested lock
569 // i.e. to give up an outer lock completely and then re-enter
570 // Used when holding nested locks - lock acquisition order: lock1 then lock2
571 // 1) complete_exit lock1 - saving recursion count
572 // 2) wait on lock2
573 // 3) when notified on lock2, unlock lock2
574 // 4) reenter lock1 with original recursion count
575 // 5) lock lock2
576 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
577 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
578 // The ObjectMonitor* can't be async deflated until ownership is
579 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
580 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
581 intptr_t ret_code = monitor->complete_exit(current);
582 return ret_code;
583 }
584
585 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
586 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
587 // An async deflation can race after the inflate() call and before
588 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
589 // enter() returns false if we have lost the race to async deflation
590 // and we simply try again.
591 while (true) {
592 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
593 if (monitor->reenter(recursions, current)) {
594 return;
595 }
596 }
597 }
598
599 // -----------------------------------------------------------------------------
600 // JNI locks on java objects
601 // NOTE: must use heavy weight monitor to handle jni monitor enter
602 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
603 if (obj->klass()->is_value_based()) {
604 handle_sync_on_value_based_class(obj, current);
605 }
606
607 // the current locking is from JNI instead of Java code
608 current->set_current_pending_monitor_is_from_java(false);
609 // An async deflation can race after the inflate() call and before
610 // enter() can make the ObjectMonitor busy. enter() returns false if
611 // we have lost the race to async deflation and we simply try again.
612 while (true) {
613 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
614 if (monitor->enter(current)) {
615 break;
616 }
617 }
618 current->set_current_pending_monitor_is_from_java(true);
619 }
620
621 // NOTE: must use heavy weight monitor to handle jni monitor exit
622 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
623 JavaThread* current = THREAD;
624
625 // The ObjectMonitor* can't be async deflated until ownership is
626 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
627 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
628 // If this thread has locked the object, exit the monitor. We
629 // intentionally do not use CHECK on check_owner because we must exit the
630 // monitor even if an exception was already pending.
631 if (monitor->check_owner(THREAD)) {
632 monitor->exit(current);
633 }
634 }
635
636 // -----------------------------------------------------------------------------
637 // Internal VM locks on java objects
638 // standard constructor, allows locking failures
639 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
640 _thread = thread;
641 _thread->check_for_valid_safepoint_state();
642 _obj = obj;
643
644 if (_obj() != NULL) {
645 ObjectSynchronizer::enter(_obj, &_lock, _thread);
646 }
647 }
648
649 ObjectLocker::~ObjectLocker() {
650 if (_obj() != NULL) {
651 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
652 }
653 }
654
655
656 // -----------------------------------------------------------------------------
657 // Wait/Notify/NotifyAll
658 // NOTE: must use heavy weight monitor to handle wait()
659 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
660 JavaThread* current = THREAD;
661 if (millis < 0) {
662 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
663 }
664 // The ObjectMonitor* can't be async deflated because the _waiters
665 // field is incremented before ownership is dropped and decremented
666 // after ownership is regained.
667 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
668
669 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
670 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
671
672 // This dummy call is in place to get around dtrace bug 6254741. Once
673 // that's fixed we can uncomment the following line, remove the call
674 // and change this function back into a "void" func.
675 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
676 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
677 return ret_code;
678 }
679
680 // No exception are possible in this case as we only use this internally when locking is
681 // correct and we have to wait until notified - so no interrupts or timeouts.
682 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, JavaThread* current) {
683 // The ObjectMonitor* can't be async deflated because the _waiters
684 // field is incremented before ownership is dropped and decremented
685 // after ownership is regained.
686 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
687 monitor->wait(0 /* wait-forever */, false /* not interruptible */, current);
688 }
689
690 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
691 JavaThread* current = THREAD;
692
693 markWord mark = obj->mark();
694 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
695 // Not inflated so there can't be any waiters to notify.
696 return;
697 }
698 // The ObjectMonitor* can't be async deflated until ownership is
699 // dropped by the calling thread.
700 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
701 monitor->notify(CHECK);
702 }
703
704 // NOTE: see comment of notify()
705 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
706 JavaThread* current = THREAD;
707
708 markWord mark = obj->mark();
709 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
710 // Not inflated so there can't be any waiters to notify.
711 return;
712 }
713 // The ObjectMonitor* can't be async deflated until ownership is
714 // dropped by the calling thread.
715 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
716 monitor->notifyAll(CHECK);
717 }
718
719 // -----------------------------------------------------------------------------
720 // Hash Code handling
721
722 struct SharedGlobals {
723 char _pad_prefix[OM_CACHE_LINE_SIZE];
724 // This is a highly shared mostly-read variable.
725 // To avoid false-sharing it needs to be the sole occupant of a cache line.
726 volatile int stw_random;
727 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
728 // Hot RW variable -- Sequester to avoid false-sharing
729 volatile int hc_sequence;
730 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
731 };
732
733 static SharedGlobals GVars;
734
735 markWord ObjectSynchronizer::read_stable_mark(oop obj) {
736 markWord mark = obj->mark_acquire();
737 if (!mark.is_being_inflated()) {
738 return mark; // normal fast-path return
739 }
740
741 int its = 0;
742 for (;;) {
743 markWord mark = obj->mark_acquire();
744 if (!mark.is_being_inflated()) {
745 return mark; // normal fast-path return
746 }
747
748 // The object is being inflated by some other thread.
749 // The caller of read_stable_mark() must wait for inflation to complete.
750 // Avoid live-lock.
751
752 ++its;
753 if (its > 10000 || !os::is_MP()) {
754 if (its & 1) {
755 os::naked_yield();
756 } else {
757 // Note that the following code attenuates the livelock problem but is not
758 // a complete remedy. A more complete solution would require that the inflating
759 // thread hold the associated inflation lock. The following code simply restricts
760 // the number of spinners to at most one. We'll have N-2 threads blocked
761 // on the inflationlock, 1 thread holding the inflation lock and using
762 // a yield/park strategy, and 1 thread in the midst of inflation.
763 // A more refined approach would be to change the encoding of INFLATING
764 // to allow encapsulation of a native thread pointer. Threads waiting for
765 // inflation to complete would use CAS to push themselves onto a singly linked
766 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
767 // and calling park(). When inflation was complete the thread that accomplished inflation
768 // would detach the list and set the markword to inflated with a single CAS and
769 // then for each thread on the list, set the flag and unpark() the thread.
770
771 // Index into the lock array based on the current object address.
772 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
773 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
774 int YieldThenBlock = 0;
775 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
776 gInflationLocks[ix]->lock();
777 while (obj->mark_acquire() == markWord::INFLATING()) {
778 // Beware: naked_yield() is advisory and has almost no effect on some platforms
779 // so we periodically call current->_ParkEvent->park(1).
780 // We use a mixed spin/yield/block mechanism.
781 if ((YieldThenBlock++) >= 16) {
782 Thread::current()->_ParkEvent->park(1);
783 } else {
784 os::naked_yield();
785 }
786 }
787 gInflationLocks[ix]->unlock();
788 }
789 } else {
790 SpinPause(); // SMP-polite spinning
791 }
792 }
793 }
794
795 // Safely load a mark word from an object, even with racing stack-locking or monitor inflation.
796 // The protocol is a partial inflation-protocol: it installs INFLATING into the object's mark
797 // word in order to prevent an stack-locks or inflations from interferring (or detect such
798 // interference and retry), but then, instead of creating and installing a monitor, simply
799 // read and return the real mark word.
800 markWord ObjectSynchronizer::stable_mark(oop object) {
801 for (;;) {
802 const markWord mark = read_stable_mark(object);
803 assert(!mark.is_being_inflated(), "read_stable_mark must prevent inflating mark");
804
805 // The mark can be in one of the following states:
806 // * Inflated - just return mark from inflated monitor
807 // * Stack-locked - coerce it to inflating, and then return displaced mark
808 // * Neutral - return mark
809 // * Marked - return mark
810
811 // CASE: inflated
812 if (mark.has_monitor()) {
813 ObjectMonitor* inf = mark.monitor();
814 markWord dmw = inf->header();
815 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
816 return dmw;
817 }
818
819 // CASE: stack-locked
820 // Could be stack-locked either by this thread or by some other thread.
821 if (mark.has_locker()) {
822 BasicLock* lock = mark.locker();
823 if (Thread::current()->is_lock_owned((address)lock)) {
824 // If locked by this thread, it is safe to access the displaced header.
825 markWord dmw = lock->displaced_header();
826 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
827 return dmw;
828 }
829
830 // Otherwise, attempt to temporarily install INFLATING into the mark-word,
831 // to prevent inflation or unlocking by competing thread.
832 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
833 if (cmp != mark) {
834 continue; // Interference -- just retry
835 }
836
837 // fetch the displaced mark from the owner's stack.
838 // The owner can't die or unwind past the lock while our INFLATING
839 // object is in the mark. Furthermore the owner can't complete
840 // an unlock on the object, either.
841 markWord dmw = mark.displaced_mark_helper();
842 // Catch if the object's header is not neutral (not locked and
843 // not marked is what we care about here).
844 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
845
846 // Must preserve store ordering. The monitor state must
847 // be stable at the time of publishing the monitor address.
848 assert(object->mark() == markWord::INFLATING(), "invariant");
849 // Release semantics so that above set_object() is seen first.
850 object->release_set_mark(mark);
851
852 return dmw;
853 }
854
855 // CASE: neutral or marked (for GC)
856 // Catch if the object's header is not neutral or marked (it must not be locked).
857 assert(mark.is_neutral() || mark.is_marked(), "invariant: header=" INTPTR_FORMAT, mark.value());
858 return mark;
859 }
860 }
861
862 // hashCode() generation :
863 //
864 // Possibilities:
865 // * MD5Digest of {obj,stw_random}
866 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
867 // * A DES- or AES-style SBox[] mechanism
868 // * One of the Phi-based schemes, such as:
869 // 2654435761 = 2^32 * Phi (golden ratio)
870 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
871 // * A variation of Marsaglia's shift-xor RNG scheme.
872 // * (obj ^ stw_random) is appealing, but can result
873 // in undesirable regularity in the hashCode values of adjacent objects
874 // (objects allocated back-to-back, in particular). This could potentially
875 // result in hashtable collisions and reduced hashtable efficiency.
876 // There are simple ways to "diffuse" the middle address bits over the
877 // generated hashCode values:
878
879 static inline intptr_t get_next_hash(Thread* current, oop obj) {
880 intptr_t value = 0;
881 if (hashCode == 0) {
882 // This form uses global Park-Miller RNG.
883 // On MP system we'll have lots of RW access to a global, so the
884 // mechanism induces lots of coherency traffic.
885 value = os::random();
886 } else if (hashCode == 1) {
887 // This variation has the property of being stable (idempotent)
888 // between STW operations. This can be useful in some of the 1-0
889 // synchronization schemes.
890 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
891 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
892 } else if (hashCode == 2) {
893 value = 1; // for sensitivity testing
894 } else if (hashCode == 3) {
895 value = ++GVars.hc_sequence;
896 } else if (hashCode == 4) {
897 value = cast_from_oop<intptr_t>(obj);
898 } else {
899 // Marsaglia's xor-shift scheme with thread-specific state
900 // This is probably the best overall implementation -- we'll
901 // likely make this the default in future releases.
902 unsigned t = current->_hashStateX;
903 t ^= (t << 11);
904 current->_hashStateX = current->_hashStateY;
905 current->_hashStateY = current->_hashStateZ;
906 current->_hashStateZ = current->_hashStateW;
907 unsigned v = current->_hashStateW;
908 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
909 current->_hashStateW = v;
910 value = v;
911 }
912
913 value &= markWord::hash_mask;
914 if (value == 0) value = 0xBAD;
915 assert(value != markWord::no_hash, "invariant");
916 return value;
917 }
918
919 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
920
921 while (true) {
922 ObjectMonitor* monitor = NULL;
923 markWord temp, test;
924 intptr_t hash;
925 markWord mark = read_stable_mark(obj);
926 if (VerifyHeavyMonitors) {
927 assert(UseHeavyMonitors, "+VerifyHeavyMonitors requires +UseHeavyMonitors");
928 guarantee(!mark.has_locker(), "must not be stack locked");
929 }
930 if (mark.is_neutral()) { // if this is a normal header
931 hash = mark.hash();
932 if (hash != 0) { // if it has a hash, just return it
933 return hash;
934 }
935 hash = get_next_hash(current, obj); // get a new hash
936 temp = mark.copy_set_hash(hash); // merge the hash into header
937 // try to install the hash
938 test = obj->cas_set_mark(temp, mark);
939 if (test == mark) { // if the hash was installed, return it
940 return hash;
941 }
942 // Failed to install the hash. It could be that another thread
943 // installed the hash just before our attempt or inflation has
944 // occurred or... so we fall thru to inflate the monitor for
945 // stability and then install the hash.
946 } else if (mark.has_monitor()) {
947 monitor = mark.monitor();
948 temp = monitor->header();
949 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
950 hash = temp.hash();
951 if (hash != 0) {
952 // It has a hash.
953
954 // Separate load of dmw/header above from the loads in
955 // is_being_async_deflated().
956
957 // dmw/header and _contentions may get written by different threads.
958 // Make sure to observe them in the same order when having several observers.
959 OrderAccess::loadload_for_IRIW();
960
961 if (monitor->is_being_async_deflated()) {
962 // But we can't safely use the hash if we detect that async
963 // deflation has occurred. So we attempt to restore the
964 // header/dmw to the object's header so that we only retry
965 // once if the deflater thread happens to be slow.
966 monitor->install_displaced_markword_in_object(obj);
967 continue;
968 }
969 return hash;
970 }
971 // Fall thru so we only have one place that installs the hash in
972 // the ObjectMonitor.
973 } else if (current->is_lock_owned((address)mark.locker())) {
974 // This is a stack lock owned by the calling thread so fetch the
975 // displaced markWord from the BasicLock on the stack.
976 temp = mark.displaced_mark_helper();
977 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
978 hash = temp.hash();
979 if (hash != 0) { // if it has a hash, just return it
980 return hash;
981 }
982 // WARNING:
983 // The displaced header in the BasicLock on a thread's stack
984 // is strictly immutable. It CANNOT be changed in ANY cases.
985 // So we have to inflate the stack lock into an ObjectMonitor
986 // even if the current thread owns the lock. The BasicLock on
987 // a thread's stack can be asynchronously read by other threads
988 // during an inflate() call so any change to that stack memory
989 // may not propagate to other threads correctly.
990 }
991
992 // Inflate the monitor to set the hash.
993
994 // An async deflation can race after the inflate() call and before we
995 // can update the ObjectMonitor's header with the hash value below.
996 monitor = inflate(current, obj, inflate_cause_hash_code);
997 // Load ObjectMonitor's header/dmw field and see if it has a hash.
998 mark = monitor->header();
999 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1000 hash = mark.hash();
1001 if (hash == 0) { // if it does not have a hash
1002 hash = get_next_hash(current, obj); // get a new hash
1003 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1004 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1005 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1006 test = markWord(v);
1007 if (test != mark) {
1008 // The attempt to update the ObjectMonitor's header/dmw field
1009 // did not work. This can happen if another thread managed to
1010 // merge in the hash just before our cmpxchg().
1011 // If we add any new usages of the header/dmw field, this code
1012 // will need to be updated.
1013 hash = test.hash();
1014 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1015 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1016 }
1017 if (monitor->is_being_async_deflated()) {
1018 // If we detect that async deflation has occurred, then we
1019 // attempt to restore the header/dmw to the object's header
1020 // so that we only retry once if the deflater thread happens
1021 // to be slow.
1022 monitor->install_displaced_markword_in_object(obj);
1023 continue;
1024 }
1025 }
1026 // We finally get the hash.
1027 return hash;
1028 }
1029 }
1030
1031 // Deprecated -- use FastHashCode() instead.
1032
1033 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1034 return FastHashCode(Thread::current(), obj());
1035 }
1036
1037
1038 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1039 Handle h_obj) {
1040 assert(current == JavaThread::current(), "Can only be called on current thread");
1041 oop obj = h_obj();
1042
1043 markWord mark = read_stable_mark(obj);
1044
1045 // Uncontended case, header points to stack
1046 if (mark.has_locker()) {
1047 return current->is_lock_owned((address)mark.locker());
1048 }
1049 // Contended case, header points to ObjectMonitor (tagged pointer)
1050 if (mark.has_monitor()) {
1051 // The first stage of async deflation does not affect any field
1052 // used by this comparison so the ObjectMonitor* is usable here.
1053 ObjectMonitor* monitor = mark.monitor();
1054 return monitor->is_entered(current) != 0;
1055 }
1056 // Unlocked case, header in place
1057 assert(mark.is_neutral(), "sanity check");
1058 return false;
1059 }
1060
1061 // FIXME: jvmti should call this
1062 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1063 oop obj = h_obj();
1064 address owner = NULL;
1065
1066 markWord mark = read_stable_mark(obj);
1067
1068 // Uncontended case, header points to stack
1069 if (mark.has_locker()) {
1070 owner = (address) mark.locker();
1071 }
1072
1073 // Contended case, header points to ObjectMonitor (tagged pointer)
1074 else if (mark.has_monitor()) {
1075 // The first stage of async deflation does not affect any field
1076 // used by this comparison so the ObjectMonitor* is usable here.
1077 ObjectMonitor* monitor = mark.monitor();
1078 assert(monitor != NULL, "monitor should be non-null");
1079 owner = (address) monitor->owner();
1080 }
1081
1082 if (owner != NULL) {
1083 // owning_thread_from_monitor_owner() may also return NULL here
1084 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1085 }
1086
1087 // Unlocked case, header in place
1088 // Cannot have assertion since this object may have been
1089 // locked by another thread when reaching here.
1090 // assert(mark.is_neutral(), "sanity check");
1091
1092 return NULL;
1093 }
1094
1095 // Visitors ...
1096
1097 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1098 // ObjectMonitors where owner is set to a stack lock address in thread.
1099 //
1100 // This version of monitors_iterate() works with the in-use monitor list.
1101 //
1102 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1103 MonitorList::Iterator iter = _in_use_list.iterator();
1104 while (iter.has_next()) {
1105 ObjectMonitor* mid = iter.next();
1106 if (mid->owner() != thread) {
1107 // Not owned by the target thread and intentionally skips when owner
1108 // is set to a stack lock address in the target thread.
1109 continue;
1110 }
1111 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1112 // Only process with closure if the object is set.
1113
1114 // monitors_iterate() is only called at a safepoint or when the
1115 // target thread is suspended or when the target thread is
1116 // operating on itself. The current closures in use today are
1117 // only interested in an owned ObjectMonitor and ownership
1118 // cannot be dropped under the calling contexts so the
1119 // ObjectMonitor cannot be async deflated.
1120 closure->do_monitor(mid);
1121 }
1122 }
1123 }
1124
1125 // This version of monitors_iterate() works with the specified linked list.
1126 //
1127 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure,
1128 ObjectMonitorsHashtable::PtrList* list,
1129 JavaThread* thread) {
1130 typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator;
1131 ObjectMonitorIterator iter(list->head());
1132 while (!iter.is_empty()) {
1133 ObjectMonitor* mid = *iter.next();
1134 // Owner set to a stack lock address in thread should never be seen here:
1135 assert(mid->owner() == thread, "must be");
1136 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1137 // Only process with closure if the object is set.
1138
1139 // monitors_iterate() is only called at a safepoint or when the
1140 // target thread is suspended or when the target thread is
1141 // operating on itself. The current closures in use today are
1142 // only interested in an owned ObjectMonitor and ownership
1143 // cannot be dropped under the calling contexts so the
1144 // ObjectMonitor cannot be async deflated.
1145 closure->do_monitor(mid);
1146 }
1147 }
1148 }
1149
1150 static bool monitors_used_above_threshold(MonitorList* list) {
1151 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1152 return false;
1153 }
1154 // Start with ceiling based on a per-thread estimate:
1155 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1156 size_t old_ceiling = ceiling;
1157 if (ceiling < list->max()) {
1158 // The max used by the system has exceeded the ceiling so use that:
1159 ceiling = list->max();
1160 }
1161 size_t monitors_used = list->count();
1162 if (monitors_used == 0) { // empty list is easy
1163 return false;
1164 }
1165 if (NoAsyncDeflationProgressMax != 0 &&
1166 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1167 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1168 size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1169 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1170 log_info(monitorinflation)("Too many deflations without progress; "
1171 "bumping in_use_list_ceiling from " SIZE_FORMAT
1172 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1173 _no_progress_cnt = 0;
1174 ceiling = new_ceiling;
1175 }
1176
1177 // Check if our monitor usage is above the threshold:
1178 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1179 return int(monitor_usage) > MonitorUsedDeflationThreshold;
1180 }
1181
1182 size_t ObjectSynchronizer::in_use_list_ceiling() {
1183 return _in_use_list_ceiling;
1184 }
1185
1186 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1187 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1188 }
1189
1190 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1191 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1192 }
1193
1194 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1195 _in_use_list_ceiling = new_value;
1196 }
1197
1198 bool ObjectSynchronizer::is_async_deflation_needed() {
1199 if (is_async_deflation_requested()) {
1200 // Async deflation request.
1201 return true;
1202 }
1203 if (AsyncDeflationInterval > 0 &&
1204 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1205 monitors_used_above_threshold(&_in_use_list)) {
1206 // It's been longer than our specified deflate interval and there
1207 // are too many monitors in use. We don't deflate more frequently
1208 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1209 // in order to not swamp the MonitorDeflationThread.
1210 return true;
1211 }
1212 return false;
1213 }
1214
1215 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1216 JavaThread* current = JavaThread::current();
1217 bool ret_code = false;
1218
1219 jlong last_time = last_async_deflation_time_ns();
1220 set_is_async_deflation_requested(true);
1221 {
1222 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1223 ml.notify_all();
1224 }
1225 const int N_CHECKS = 5;
1226 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1227 if (last_async_deflation_time_ns() > last_time) {
1228 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1229 ret_code = true;
1230 break;
1231 }
1232 {
1233 // JavaThread has to honor the blocking protocol.
1234 ThreadBlockInVM tbivm(current);
1235 os::naked_short_sleep(999); // sleep for almost 1 second
1236 }
1237 }
1238 if (!ret_code) {
1239 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1240 }
1241
1242 return ret_code;
1243 }
1244
1245 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1246 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1247 }
1248
1249 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1250 const oop obj,
1251 ObjectSynchronizer::InflateCause cause) {
1252 assert(event != NULL, "invariant");
1253 assert(event->should_commit(), "invariant");
1254 event->set_monitorClass(obj->klass());
1255 event->set_address((uintptr_t)(void*)obj);
1256 event->set_cause((u1)cause);
1257 event->commit();
1258 }
1259
1260 // Fast path code shared by multiple functions
1261 void ObjectSynchronizer::inflate_helper(oop obj) {
1262 markWord mark = obj->mark_acquire();
1263 if (mark.has_monitor()) {
1264 ObjectMonitor* monitor = mark.monitor();
1265 markWord dmw = monitor->header();
1266 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1267 return;
1268 }
1269 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1270 }
1271
1272 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1273 const InflateCause cause) {
1274 EventJavaMonitorInflate event;
1275
1276 for (;;) {
1277 const markWord mark = object->mark_acquire();
1278
1279 // The mark can be in one of the following states:
1280 // * Inflated - just return
1281 // * Stack-locked - coerce it to inflated
1282 // * INFLATING - busy wait for conversion to complete
1283 // * Neutral - aggressively inflate the object.
1284
1285 // CASE: inflated
1286 if (mark.has_monitor()) {
1287 ObjectMonitor* inf = mark.monitor();
1288 markWord dmw = inf->header();
1289 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1290 return inf;
1291 }
1292
1293 // CASE: inflation in progress - inflating over a stack-lock.
1294 // Some other thread is converting from stack-locked to inflated.
1295 // Only that thread can complete inflation -- other threads must wait.
1296 // The INFLATING value is transient.
1297 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1298 // We could always eliminate polling by parking the thread on some auxiliary list.
1299 if (mark == markWord::INFLATING()) {
1300 read_stable_mark(object);
1301 continue;
1302 }
1303
1304 // CASE: stack-locked
1305 // Could be stack-locked either by this thread or by some other thread.
1306 //
1307 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1308 // to install INFLATING into the mark word. We originally installed INFLATING,
1309 // allocated the ObjectMonitor, and then finally STed the address of the
1310 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1311 // the interval in which INFLATING appeared in the mark, thus increasing
1312 // the odds of inflation contention.
1313
1314 LogStreamHandle(Trace, monitorinflation) lsh;
1315
1316 if (mark.has_locker()) {
1317 ObjectMonitor* m = new ObjectMonitor(object);
1318 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1319 // We do this before the CAS in order to minimize the length of time
1320 // in which INFLATING appears in the mark.
1321
1322 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1323 if (cmp != mark) {
1324 delete m;
1325 continue; // Interference -- just retry
1326 }
1327
1328 // We've successfully installed INFLATING (0) into the mark-word.
1329 // This is the only case where 0 will appear in a mark-word.
1330 // Only the singular thread that successfully swings the mark-word
1331 // to 0 can perform (or more precisely, complete) inflation.
1332 //
1333 // Why do we CAS a 0 into the mark-word instead of just CASing the
1334 // mark-word from the stack-locked value directly to the new inflated state?
1335 // Consider what happens when a thread unlocks a stack-locked object.
1336 // It attempts to use CAS to swing the displaced header value from the
1337 // on-stack BasicLock back into the object header. Recall also that the
1338 // header value (hash code, etc) can reside in (a) the object header, or
1339 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1340 // header in an ObjectMonitor. The inflate() routine must copy the header
1341 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1342 // the while preserving the hashCode stability invariants. If the owner
1343 // decides to release the lock while the value is 0, the unlock will fail
1344 // and control will eventually pass from slow_exit() to inflate. The owner
1345 // will then spin, waiting for the 0 value to disappear. Put another way,
1346 // the 0 causes the owner to stall if the owner happens to try to
1347 // drop the lock (restoring the header from the BasicLock to the object)
1348 // while inflation is in-progress. This protocol avoids races that might
1349 // would otherwise permit hashCode values to change or "flicker" for an object.
1350 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1351 // 0 serves as a "BUSY" inflate-in-progress indicator.
1352
1353
1354 // fetch the displaced mark from the owner's stack.
1355 // The owner can't die or unwind past the lock while our INFLATING
1356 // object is in the mark. Furthermore the owner can't complete
1357 // an unlock on the object, either.
1358 markWord dmw = mark.displaced_mark_helper();
1359 // Catch if the object's header is not neutral (not locked and
1360 // not marked is what we care about here).
1361 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1362
1363 // Setup monitor fields to proper values -- prepare the monitor
1364 m->set_header(dmw);
1365
1366 // Optimization: if the mark.locker stack address is associated
1367 // with this thread we could simply set m->_owner = current.
1368 // Note that a thread can inflate an object
1369 // that it has stack-locked -- as might happen in wait() -- directly
1370 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1371 m->set_owner_from(NULL, mark.locker());
1372 // TODO-FIXME: assert BasicLock->dhw != 0.
1373
1374 // Must preserve store ordering. The monitor state must
1375 // be stable at the time of publishing the monitor address.
1376 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1377 // Release semantics so that above set_object() is seen first.
1378 object->release_set_mark(markWord::encode(m));
1379
1380 // Once ObjectMonitor is configured and the object is associated
1381 // with the ObjectMonitor, it is safe to allow async deflation:
1382 _in_use_list.add(m);
1383
1384 // Hopefully the performance counters are allocated on distinct cache lines
1385 // to avoid false sharing on MP systems ...
1386 OM_PERFDATA_OP(Inflations, inc());
1387 if (log_is_enabled(Trace, monitorinflation)) {
1388 ResourceMark rm(current);
1389 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1390 INTPTR_FORMAT ", type='%s'", p2i(object),
1391 object->mark().value(), object->klass()->external_name());
1392 }
1393 if (event.should_commit()) {
1394 post_monitor_inflate_event(&event, object, cause);
1395 }
1396 return m;
1397 }
1398
1399 // CASE: neutral
1400 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1401 // If we know we're inflating for entry it's better to inflate by swinging a
1402 // pre-locked ObjectMonitor pointer into the object header. A successful
1403 // CAS inflates the object *and* confers ownership to the inflating thread.
1404 // In the current implementation we use a 2-step mechanism where we CAS()
1405 // to inflate and then CAS() again to try to swing _owner from NULL to current.
1406 // An inflateTry() method that we could call from enter() would be useful.
1407
1408 // Catch if the object's header is not neutral (not locked and
1409 // not marked is what we care about here).
1410 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1411 ObjectMonitor* m = new ObjectMonitor(object);
1412 // prepare m for installation - set monitor to initial state
1413 m->set_header(mark);
1414
1415 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1416 delete m;
1417 m = NULL;
1418 continue;
1419 // interference - the markword changed - just retry.
1420 // The state-transitions are one-way, so there's no chance of
1421 // live-lock -- "Inflated" is an absorbing state.
1422 }
1423
1424 // Once the ObjectMonitor is configured and object is associated
1425 // with the ObjectMonitor, it is safe to allow async deflation:
1426 _in_use_list.add(m);
1427
1428 // Hopefully the performance counters are allocated on distinct
1429 // cache lines to avoid false sharing on MP systems ...
1430 OM_PERFDATA_OP(Inflations, inc());
1431 if (log_is_enabled(Trace, monitorinflation)) {
1432 ResourceMark rm(current);
1433 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1434 INTPTR_FORMAT ", type='%s'", p2i(object),
1435 object->mark().value(), object->klass()->external_name());
1436 }
1437 if (event.should_commit()) {
1438 post_monitor_inflate_event(&event, object, cause);
1439 }
1440 return m;
1441 }
1442 }
1443
1444 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1445 const char* cnt_name, size_t cnt,
1446 LogStream* ls, elapsedTimer* timer_p) {
1447 if (!SafepointMechanism::should_process(current)) {
1448 return;
1449 }
1450
1451 // A safepoint/handshake has started.
1452 if (ls != NULL) {
1453 timer_p->stop();
1454 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1455 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1456 op_name, cnt_name, cnt, in_use_list_ceiling(),
1457 _in_use_list.count(), _in_use_list.max());
1458 }
1459
1460 {
1461 // Honor block request.
1462 ThreadBlockInVM tbivm(current);
1463 }
1464
1465 if (ls != NULL) {
1466 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1467 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1468 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1469 timer_p->start();
1470 }
1471 }
1472
1473 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1474 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1475 //
1476 // If table != nullptr, we gather owned ObjectMonitors indexed by the
1477 // owner in the table. Please note that ObjectMonitors where the owner
1478 // is set to a stack lock address are NOT associated with the JavaThread
1479 // that holds that stack lock. All of the current consumers of
1480 // ObjectMonitorsHashtable info only care about JNI locked monitors and
1481 // those do not have the owner set to a stack lock address.
1482 //
1483 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1484 elapsedTimer* timer_p,
1485 ObjectMonitorsHashtable* table) {
1486 MonitorList::Iterator iter = _in_use_list.iterator();
1487 size_t deflated_count = 0;
1488
1489 while (iter.has_next()) {
1490 if (deflated_count >= (size_t)MonitorDeflationMax) {
1491 break;
1492 }
1493 ObjectMonitor* mid = iter.next();
1494 if (mid->deflate_monitor()) {
1495 deflated_count++;
1496 } else if (table != nullptr) {
1497 // The caller is interested in the owned ObjectMonitors. This does
1498 // not include when owner is set to a stack lock address in thread.
1499 // This also does not capture unowned ObjectMonitors that cannot be
1500 // deflated because of a waiter.
1501 void* key = mid->owner();
1502 // Since deflate_idle_monitors() and deflate_monitor_list() can be
1503 // called more than once, we have to make sure the entry has not
1504 // already been added.
1505 if (key != nullptr && !table->has_entry(key, mid)) {
1506 table->add_entry(key, mid);
1507 }
1508 }
1509
1510 if (current->is_Java_thread()) {
1511 // A JavaThread must check for a safepoint/handshake and honor it.
1512 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1513 deflated_count, ls, timer_p);
1514 }
1515 }
1516
1517 return deflated_count;
1518 }
1519
1520 class HandshakeForDeflation : public HandshakeClosure {
1521 public:
1522 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1523
1524 void do_thread(Thread* thread) {
1525 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1526 INTPTR_FORMAT, p2i(thread));
1527 }
1528 };
1529
1530 class VM_RendezvousGCThreads : public VM_Operation {
1531 public:
1532 bool evaluate_at_safepoint() const override { return false; }
1533 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1534 void doit() override {
1535 SuspendibleThreadSet::synchronize();
1536 SuspendibleThreadSet::desynchronize();
1537 };
1538 };
1539
1540 // This function is called by the MonitorDeflationThread to deflate
1541 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1542 // and VM_ThreadDump::doit() by the VMThread.
1543 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) {
1544 Thread* current = Thread::current();
1545 if (current->is_Java_thread()) {
1546 // The async deflation request has been processed.
1547 _last_async_deflation_time_ns = os::javaTimeNanos();
1548 set_is_async_deflation_requested(false);
1549 }
1550
1551 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1552 LogStreamHandle(Info, monitorinflation) lsh_info;
1553 LogStream* ls = NULL;
1554 if (log_is_enabled(Debug, monitorinflation)) {
1555 ls = &lsh_debug;
1556 } else if (log_is_enabled(Info, monitorinflation)) {
1557 ls = &lsh_info;
1558 }
1559
1560 elapsedTimer timer;
1561 if (ls != NULL) {
1562 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1563 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1564 timer.start();
1565 }
1566
1567 // Deflate some idle ObjectMonitors.
1568 size_t deflated_count = deflate_monitor_list(current, ls, &timer, table);
1569 if (deflated_count > 0 || is_final_audit()) {
1570 // There are ObjectMonitors that have been deflated or this is the
1571 // final audit and all the remaining ObjectMonitors have been
1572 // deflated, BUT the MonitorDeflationThread blocked for the final
1573 // safepoint during unlinking.
1574
1575 // Unlink deflated ObjectMonitors from the in-use list.
1576 ResourceMark rm;
1577 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1578 size_t unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer,
1579 &delete_list);
1580 if (current->is_Java_thread()) {
1581 if (ls != NULL) {
1582 timer.stop();
1583 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1584 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1585 SIZE_FORMAT ", max=" SIZE_FORMAT,
1586 unlinked_count, in_use_list_ceiling(),
1587 _in_use_list.count(), _in_use_list.max());
1588 }
1589
1590 // A JavaThread needs to handshake in order to safely free the
1591 // ObjectMonitors that were deflated in this cycle.
1592 // Also, we sync and desync GC threads around the handshake, so that they can
1593 // safely read the mark-word and look-through to the object-monitor, without
1594 // being afraid that the object-monitor is going away.
1595 HandshakeForDeflation hfd_hc;
1596 Handshake::execute(&hfd_hc);
1597 VM_RendezvousGCThreads sync_gc;
1598 VMThread::execute(&sync_gc);
1599
1600 if (ls != NULL) {
1601 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1602 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1603 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1604 timer.start();
1605 }
1606 }
1607
1608 // After the handshake, safely free the ObjectMonitors that were
1609 // deflated in this cycle.
1610 size_t deleted_count = 0;
1611 for (ObjectMonitor* monitor: delete_list) {
1612 delete monitor;
1613 deleted_count++;
1614
1615 if (current->is_Java_thread()) {
1616 // A JavaThread must check for a safepoint/handshake and honor it.
1617 chk_for_block_req(JavaThread::cast(current), "deletion", "deleted_count",
1618 deleted_count, ls, &timer);
1619 }
1620 }
1621 }
1622
1623 if (ls != NULL) {
1624 timer.stop();
1625 if (deflated_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1626 ls->print_cr("deflated " SIZE_FORMAT " monitors in %3.7f secs",
1627 deflated_count, timer.seconds());
1628 }
1629 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1630 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1631 if (table != nullptr) {
1632 ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT,
1633 table->key_count(), table->om_count());
1634 }
1635 }
1636
1637 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1638 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1639
1640 GVars.stw_random = os::random();
1641
1642 if (deflated_count != 0) {
1643 _no_progress_cnt = 0;
1644 } else {
1645 _no_progress_cnt++;
1646 }
1647
1648 return deflated_count;
1649 }
1650
1651 // Monitor cleanup on JavaThread::exit
1652
1653 // Iterate through monitor cache and attempt to release thread's monitors
1654 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1655 private:
1656 JavaThread* _thread;
1657
1658 public:
1659 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1660 void do_monitor(ObjectMonitor* mid) {
1661 (void)mid->complete_exit(_thread);
1662 }
1663 };
1664
1665 // Release all inflated monitors owned by current thread. Lightweight monitors are
1666 // ignored. This is meant to be called during JNI thread detach which assumes
1667 // all remaining monitors are heavyweight. All exceptions are swallowed.
1668 // Scanning the extant monitor list can be time consuming.
1669 // A simple optimization is to add a per-thread flag that indicates a thread
1670 // called jni_monitorenter() during its lifetime.
1671 //
1672 // Instead of NoSafepointVerifier it might be cheaper to
1673 // use an idiom of the form:
1674 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1675 // <code that must not run at safepoint>
1676 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1677 // Since the tests are extremely cheap we could leave them enabled
1678 // for normal product builds.
1679
1680 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1681 assert(current == JavaThread::current(), "must be current Java thread");
1682 NoSafepointVerifier nsv;
1683 ReleaseJavaMonitorsClosure rjmc(current);
1684 ObjectSynchronizer::monitors_iterate(&rjmc, current);
1685 assert(!current->has_pending_exception(), "Should not be possible");
1686 current->clear_pending_exception();
1687 }
1688
1689 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1690 switch (cause) {
1691 case inflate_cause_vm_internal: return "VM Internal";
1692 case inflate_cause_monitor_enter: return "Monitor Enter";
1693 case inflate_cause_wait: return "Monitor Wait";
1694 case inflate_cause_notify: return "Monitor Notify";
1695 case inflate_cause_hash_code: return "Monitor Hash Code";
1696 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1697 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1698 default:
1699 ShouldNotReachHere();
1700 }
1701 return "Unknown";
1702 }
1703
1704 //------------------------------------------------------------------------------
1705 // Debugging code
1706
1707 u_char* ObjectSynchronizer::get_gvars_addr() {
1708 return (u_char*)&GVars;
1709 }
1710
1711 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1712 return (u_char*)&GVars.hc_sequence;
1713 }
1714
1715 size_t ObjectSynchronizer::get_gvars_size() {
1716 return sizeof(SharedGlobals);
1717 }
1718
1719 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1720 return (u_char*)&GVars.stw_random;
1721 }
1722
1723 // Do the final audit and print of ObjectMonitor stats; must be done
1724 // by the VMThread at VM exit time.
1725 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1726 assert(Thread::current()->is_VM_thread(), "sanity check");
1727
1728 if (is_final_audit()) { // Only do the audit once.
1729 return;
1730 }
1731 set_is_final_audit();
1732
1733 if (log_is_enabled(Info, monitorinflation)) {
1734 // Do a deflation in order to reduce the in-use monitor population
1735 // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1736 // which is called by ObjectSynchronizer::audit_and_print_stats().
1737 while (ObjectSynchronizer::deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) >= (size_t)MonitorDeflationMax) {
1738 ; // empty
1739 }
1740 // The other audit_and_print_stats() call is done at the Debug
1741 // level at a safepoint in ObjectSynchronizer::do_safepoint_work().
1742 ObjectSynchronizer::audit_and_print_stats(true /* on_exit */);
1743 }
1744 }
1745
1746 // This function can be called at a safepoint or it can be called when
1747 // we are trying to exit the VM. When we are trying to exit the VM, the
1748 // list walker functions can run in parallel with the other list
1749 // operations so spin-locking is used for safety.
1750 //
1751 // Calls to this function can be added in various places as a debugging
1752 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1753 // details logged at the Info level and 'false' for the 'on_exit'
1754 // parameter to have in-use monitor details logged at the Trace level.
1755 //
1756 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1757 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1758
1759 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1760 LogStreamHandle(Info, monitorinflation) lsh_info;
1761 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1762 LogStream* ls = NULL;
1763 if (log_is_enabled(Trace, monitorinflation)) {
1764 ls = &lsh_trace;
1765 } else if (log_is_enabled(Debug, monitorinflation)) {
1766 ls = &lsh_debug;
1767 } else if (log_is_enabled(Info, monitorinflation)) {
1768 ls = &lsh_info;
1769 }
1770 assert(ls != NULL, "sanity check");
1771
1772 int error_cnt = 0;
1773
1774 ls->print_cr("Checking in_use_list:");
1775 chk_in_use_list(ls, &error_cnt);
1776
1777 if (error_cnt == 0) {
1778 ls->print_cr("No errors found in in_use_list checks.");
1779 } else {
1780 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1781 }
1782
1783 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1784 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1785 // When exiting this log output is at the Info level. When called
1786 // at a safepoint, this log output is at the Trace level since
1787 // there can be a lot of it.
1788 log_in_use_monitor_details(ls);
1789 }
1790
1791 ls->flush();
1792
1793 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1794 }
1795
1796 // Check the in_use_list; log the results of the checks.
1797 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1798 size_t l_in_use_count = _in_use_list.count();
1799 size_t l_in_use_max = _in_use_list.max();
1800 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1801 l_in_use_max);
1802
1803 size_t ck_in_use_count = 0;
1804 MonitorList::Iterator iter = _in_use_list.iterator();
1805 while (iter.has_next()) {
1806 ObjectMonitor* mid = iter.next();
1807 chk_in_use_entry(mid, out, error_cnt_p);
1808 ck_in_use_count++;
1809 }
1810
1811 if (l_in_use_count == ck_in_use_count) {
1812 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1813 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1814 } else {
1815 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1816 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1817 ck_in_use_count);
1818 }
1819
1820 size_t ck_in_use_max = _in_use_list.max();
1821 if (l_in_use_max == ck_in_use_max) {
1822 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1823 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1824 } else {
1825 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1826 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1827 }
1828 }
1829
1830 // Check an in-use monitor entry; log any errors.
1831 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1832 int* error_cnt_p) {
1833 if (n->owner_is_DEFLATER_MARKER()) {
1834 // This should not happen, but if it does, it is not fatal.
1835 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1836 "deflated.", p2i(n));
1837 return;
1838 }
1839 if (n->header().value() == 0) {
1840 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1841 "have non-NULL _header field.", p2i(n));
1842 *error_cnt_p = *error_cnt_p + 1;
1843 }
1844 const oop obj = n->object_peek();
1845 if (obj != NULL) {
1846 const markWord mark = obj->mark();
1847 if (!mark.has_monitor()) {
1848 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1849 "object does not think it has a monitor: obj="
1850 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1851 p2i(obj), mark.value());
1852 *error_cnt_p = *error_cnt_p + 1;
1853 }
1854 ObjectMonitor* const obj_mon = mark.monitor();
1855 if (n != obj_mon) {
1856 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1857 "object does not refer to the same monitor: obj="
1858 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1859 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1860 *error_cnt_p = *error_cnt_p + 1;
1861 }
1862 }
1863 }
1864
1865 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1866 // flags indicate why the entry is in-use, 'object' and 'object type'
1867 // indicate the associated object and its type.
1868 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
1869 stringStream ss;
1870 if (_in_use_list.count() > 0) {
1871 out->print_cr("In-use monitor info:");
1872 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1873 out->print_cr("%18s %s %18s %18s",
1874 "monitor", "BHL", "object", "object type");
1875 out->print_cr("================== === ================== ==================");
1876 MonitorList::Iterator iter = _in_use_list.iterator();
1877 while (iter.has_next()) {
1878 ObjectMonitor* mid = iter.next();
1879 const oop obj = mid->object_peek();
1880 const markWord mark = mid->header();
1881 ResourceMark rm;
1882 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid),
1883 mid->is_busy(), mark.hash() != 0, mid->owner() != NULL,
1884 p2i(obj), obj == NULL ? "" : obj->klass()->external_name());
1885 if (mid->is_busy()) {
1886 out->print(" (%s)", mid->is_busy_to_string(&ss));
1887 ss.reset();
1888 }
1889 out->cr();
1890 }
1891 }
1892
1893 out->flush();
1894 }