1 /*
2 * Copyright (c) 1998, 2023, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "jfr/jfrEvents.hpp"
28 #include "logging/log.hpp"
29 #include "logging/logStream.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/padded.hpp"
32 #include "memory/resourceArea.hpp"
33 #include "memory/universe.hpp"
34 #include "oops/markWord.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "runtime/atomic.hpp"
37 #include "runtime/frame.inline.hpp"
38 #include "runtime/handles.inline.hpp"
39 #include "runtime/handshake.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/javaThread.hpp"
42 #include "runtime/mutexLocker.hpp"
43 #include "runtime/objectMonitor.hpp"
44 #include "runtime/objectMonitor.inline.hpp"
45 #include "runtime/os.inline.hpp"
46 #include "runtime/osThread.hpp"
47 #include "runtime/perfData.hpp"
48 #include "runtime/safepointMechanism.inline.hpp"
49 #include "runtime/safepointVerifiers.hpp"
50 #include "runtime/sharedRuntime.hpp"
51 #include "runtime/stubRoutines.hpp"
52 #include "runtime/synchronizer.hpp"
53 #include "runtime/threads.hpp"
54 #include "runtime/timer.hpp"
55 #include "runtime/vframe.hpp"
56 #include "runtime/vmThread.hpp"
57 #include "utilities/align.hpp"
58 #include "utilities/dtrace.hpp"
59 #include "utilities/events.hpp"
60 #include "utilities/linkedlist.hpp"
61 #include "utilities/preserveException.hpp"
62
63 class ObjectMonitorsHashtable::PtrList :
64 public LinkedListImpl<ObjectMonitor*,
65 AnyObj::C_HEAP, mtThread,
66 AllocFailStrategy::RETURN_NULL> {};
67
68 class CleanupObjectMonitorsHashtable: StackObj {
69 public:
70 bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) {
71 list->clear(); // clear the LinkListNodes
72 delete list; // then delete the LinkedList
73 return true;
74 }
75 };
76
77 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() {
78 CleanupObjectMonitorsHashtable cleanup;
79 _ptrs->unlink(&cleanup); // cleanup the LinkedLists
80 delete _ptrs; // then delete the hash table
81 }
82
83 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) {
84 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
85 if (list == nullptr) {
86 // Create new list and add it to the hash table:
87 list = new (mtThread) ObjectMonitorsHashtable::PtrList;
88 add_entry(key, list);
89 }
90 list->add(om); // Add the ObjectMonitor to the list.
91 _om_count++;
92 }
93
94 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) {
95 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
96 if (list == nullptr || list->find(om) == nullptr) {
97 return false;
98 }
99 return true;
100 }
101
102 void MonitorList::add(ObjectMonitor* m) {
103 ObjectMonitor* head;
104 do {
105 head = Atomic::load(&_head);
106 m->set_next_om(head);
107 } while (Atomic::cmpxchg(&_head, head, m) != head);
108
109 size_t count = Atomic::add(&_count, 1u);
110 if (count > max()) {
111 Atomic::inc(&_max);
112 }
113 }
114
115 size_t MonitorList::count() const {
116 return Atomic::load(&_count);
117 }
118
119 size_t MonitorList::max() const {
120 return Atomic::load(&_max);
121 }
122
123 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
124 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
125 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
126 elapsedTimer* timer_p,
127 GrowableArray<ObjectMonitor*>* unlinked_list) {
128 size_t unlinked_count = 0;
129 ObjectMonitor* prev = nullptr;
130 ObjectMonitor* head = Atomic::load_acquire(&_head);
131 ObjectMonitor* m = head;
132 // The in-use list head can be null during the final audit.
133 while (m != nullptr) {
134 if (m->is_being_async_deflated()) {
135 // Find next live ObjectMonitor.
136 ObjectMonitor* next = m;
137 do {
138 ObjectMonitor* next_next = next->next_om();
139 unlinked_count++;
140 unlinked_list->append(next);
141 next = next_next;
142 if (unlinked_count >= (size_t)MonitorDeflationMax) {
143 // Reached the max so bail out on the gathering loop.
144 break;
145 }
146 } while (next != nullptr && next->is_being_async_deflated());
147 if (prev == nullptr) {
148 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
149 if (prev_head != head) {
150 // Find new prev ObjectMonitor that just got inserted.
151 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
152 prev = n;
153 }
154 prev->set_next_om(next);
155 }
156 } else {
157 prev->set_next_om(next);
158 }
159 if (unlinked_count >= (size_t)MonitorDeflationMax) {
160 // Reached the max so bail out on the searching loop.
161 break;
162 }
163 m = next;
164 } else {
165 prev = m;
166 m = m->next_om();
167 }
168
169 if (current->is_Java_thread()) {
170 // A JavaThread must check for a safepoint/handshake and honor it.
171 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking",
172 "unlinked_count", unlinked_count,
173 ls, timer_p);
174 }
175 }
176 Atomic::sub(&_count, unlinked_count);
177 return unlinked_count;
178 }
179
180 MonitorList::Iterator MonitorList::iterator() const {
181 return Iterator(Atomic::load_acquire(&_head));
182 }
183
184 ObjectMonitor* MonitorList::Iterator::next() {
185 ObjectMonitor* current = _current;
186 _current = current->next_om();
187 return current;
188 }
189
190 // The "core" versions of monitor enter and exit reside in this file.
191 // The interpreter and compilers contain specialized transliterated
192 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
193 // fast_lock(...) for instance. If you make changes here, make sure to modify the
194 // interpreter, and both C1 and C2 fast-path inline locking code emission.
195 //
196 // -----------------------------------------------------------------------------
197
198 #ifdef DTRACE_ENABLED
199
200 // Only bother with this argument setup if dtrace is available
201 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
202
203 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
204 char* bytes = nullptr; \
205 int len = 0; \
206 jlong jtid = SharedRuntime::get_java_tid(thread); \
207 Symbol* klassname = obj->klass()->name(); \
208 if (klassname != nullptr) { \
209 bytes = (char*)klassname->bytes(); \
210 len = klassname->utf8_length(); \
211 }
212
213 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
214 { \
215 if (DTraceMonitorProbes) { \
216 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
217 HOTSPOT_MONITOR_WAIT(jtid, \
218 (uintptr_t)(monitor), bytes, len, (millis)); \
219 } \
220 }
221
222 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
223 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
224 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
225
226 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
227 { \
228 if (DTraceMonitorProbes) { \
229 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
230 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
231 (uintptr_t)(monitor), bytes, len); \
232 } \
233 }
234
235 #else // ndef DTRACE_ENABLED
236
237 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
238 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
239
240 #endif // ndef DTRACE_ENABLED
241
242 // This exists only as a workaround of dtrace bug 6254741
243 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
244 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
245 return 0;
246 }
247
248 static const int NINFLATIONLOCKS = 256;
249 static PlatformMutex* gInflationLocks[NINFLATIONLOCKS];
250
251 void ObjectSynchronizer::initialize() {
252 for (int i = 0; i < NINFLATIONLOCKS; i++) {
253 gInflationLocks[i] = new PlatformMutex();
254 }
255 // Start the ceiling with the estimate for one thread.
256 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
257 }
258
259 MonitorList ObjectSynchronizer::_in_use_list;
260 // monitors_used_above_threshold() policy is as follows:
261 //
262 // The ratio of the current _in_use_list count to the ceiling is used
263 // to determine if we are above MonitorUsedDeflationThreshold and need
264 // to do an async monitor deflation cycle. The ceiling is increased by
265 // AvgMonitorsPerThreadEstimate when a thread is added to the system
266 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
267 // removed from the system.
268 //
269 // Note: If the _in_use_list max exceeds the ceiling, then
270 // monitors_used_above_threshold() will use the in_use_list max instead
271 // of the thread count derived ceiling because we have used more
272 // ObjectMonitors than the estimated average.
273 //
274 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
275 // no-progress async monitor deflation cycles in a row, then the ceiling
276 // is adjusted upwards by monitors_used_above_threshold().
277 //
278 // Start the ceiling with the estimate for one thread in initialize()
279 // which is called after cmd line options are processed.
280 static size_t _in_use_list_ceiling = 0;
281 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
282 bool volatile ObjectSynchronizer::_is_final_audit = false;
283 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
284 static uintx _no_progress_cnt = 0;
285
286 // =====================> Quick functions
287
288 // The quick_* forms are special fast-path variants used to improve
289 // performance. In the simplest case, a "quick_*" implementation could
290 // simply return false, in which case the caller will perform the necessary
291 // state transitions and call the slow-path form.
292 // The fast-path is designed to handle frequently arising cases in an efficient
293 // manner and is just a degenerate "optimistic" variant of the slow-path.
294 // returns true -- to indicate the call was satisfied.
295 // returns false -- to indicate the call needs the services of the slow-path.
296 // A no-loitering ordinance is in effect for code in the quick_* family
297 // operators: safepoints or indefinite blocking (blocking that might span a
298 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
299 // entry.
300 //
301 // Consider: An interesting optimization is to have the JIT recognize the
302 // following common idiom:
303 // synchronized (someobj) { .... ; notify(); }
304 // That is, we find a notify() or notifyAll() call that immediately precedes
305 // the monitorexit operation. In that case the JIT could fuse the operations
306 // into a single notifyAndExit() runtime primitive.
307
308 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
309 assert(current->thread_state() == _thread_in_Java, "invariant");
310 NoSafepointVerifier nsv;
311 if (obj == nullptr) return false; // slow-path for invalid obj
312 const markWord mark = obj->mark();
313
314 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
315 // Degenerate notify
316 // stack-locked by caller so by definition the implied waitset is empty.
317 return true;
318 }
319
320 if (mark.has_monitor()) {
321 ObjectMonitor* const mon = mark.monitor();
322 assert(mon->object() == oop(obj), "invariant");
323 if (mon->owner() != current) return false; // slow-path for IMS exception
324
325 if (mon->first_waiter() != nullptr) {
326 // We have one or more waiters. Since this is an inflated monitor
327 // that we own, we can transfer one or more threads from the waitset
328 // to the entrylist here and now, avoiding the slow-path.
329 if (all) {
330 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
331 } else {
332 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
333 }
334 int free_count = 0;
335 do {
336 mon->INotify(current);
337 ++free_count;
338 } while (mon->first_waiter() != nullptr && all);
339 OM_PERFDATA_OP(Notifications, inc(free_count));
340 }
341 return true;
342 }
343
344 // other IMS exception states take the slow-path
345 return false;
346 }
347
348
349 // The LockNode emitted directly at the synchronization site would have
350 // been too big if it were to have included support for the cases of inflated
351 // recursive enter and exit, so they go here instead.
352 // Note that we can't safely call AsyncPrintJavaStack() from within
353 // quick_enter() as our thread state remains _in_Java.
354
355 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
356 BasicLock * lock) {
357 assert(current->thread_state() == _thread_in_Java, "invariant");
358 NoSafepointVerifier nsv;
359 if (obj == nullptr) return false; // Need to throw NPE
360
361 if (obj->klass()->is_value_based()) {
362 return false;
363 }
364
365 const markWord mark = obj->mark();
366
367 if (mark.has_monitor()) {
368 ObjectMonitor* const m = mark.monitor();
369 // An async deflation or GC can race us before we manage to make
370 // the ObjectMonitor busy by setting the owner below. If we detect
371 // that race we just bail out to the slow-path here.
372 if (m->object_peek() == nullptr) {
373 return false;
374 }
375 JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
376
377 // Lock contention and Transactional Lock Elision (TLE) diagnostics
378 // and observability
379 // Case: light contention possibly amenable to TLE
380 // Case: TLE inimical operations such as nested/recursive synchronization
381
382 if (owner == current) {
383 m->_recursions++;
384 current->inc_held_monitor_count();
385 return true;
386 }
387
388 // This Java Monitor is inflated so obj's header will never be
389 // displaced to this thread's BasicLock. Make the displaced header
390 // non-null so this BasicLock is not seen as recursive nor as
391 // being locked. We do this unconditionally so that this thread's
392 // BasicLock cannot be mis-interpreted by any stack walkers. For
393 // performance reasons, stack walkers generally first check for
394 // stack-locking in the object's header, the second check is for
395 // recursive stack-locking in the displaced header in the BasicLock,
396 // and last are the inflated Java Monitor (ObjectMonitor) checks.
397 lock->set_displaced_header(markWord::unused_mark());
398
399 if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) {
400 assert(m->_recursions == 0, "invariant");
401 current->inc_held_monitor_count();
402 return true;
403 }
404 }
405
406 // Note that we could inflate in quick_enter.
407 // This is likely a useful optimization
408 // Critically, in quick_enter() we must not:
409 // -- block indefinitely, or
410 // -- reach a safepoint
411
412 return false; // revert to slow-path
413 }
414
415 // Handle notifications when synchronizing on value based classes
416 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
417 frame last_frame = current->last_frame();
418 bool bcp_was_adjusted = false;
419 // Don't decrement bcp if it points to the frame's first instruction. This happens when
420 // handle_sync_on_value_based_class() is called because of a synchronized method. There
421 // is no actual monitorenter instruction in the byte code in this case.
422 if (last_frame.is_interpreted_frame() &&
423 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
424 // adjust bcp to point back to monitorenter so that we print the correct line numbers
425 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
426 bcp_was_adjusted = true;
427 }
428
429 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
430 ResourceMark rm(current);
431 stringStream ss;
432 current->print_active_stack_on(&ss);
433 char* base = (char*)strstr(ss.base(), "at");
434 char* newline = (char*)strchr(ss.base(), '\n');
435 if (newline != nullptr) {
436 *newline = '\0';
437 }
438 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
439 } else {
440 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
441 ResourceMark rm(current);
442 Log(valuebasedclasses) vblog;
443
444 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
445 if (current->has_last_Java_frame()) {
446 LogStream info_stream(vblog.info());
447 current->print_active_stack_on(&info_stream);
448 } else {
449 vblog.info("Cannot find the last Java frame");
450 }
451
452 EventSyncOnValueBasedClass event;
453 if (event.should_commit()) {
454 event.set_valueBasedClass(obj->klass());
455 event.commit();
456 }
457 }
458
459 if (bcp_was_adjusted) {
460 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
461 }
462 }
463
464 static bool useHeavyMonitors() {
465 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64)
466 return UseHeavyMonitors;
467 #else
468 return false;
469 #endif
470 }
471
472 // -----------------------------------------------------------------------------
473 // Monitor Enter/Exit
474 // The interpreter and compiler assembly code tries to lock using the fast path
475 // of this algorithm. Make sure to update that code if the following function is
476 // changed. The implementation is extremely sensitive to race condition. Be careful.
477
478 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
479 if (obj->klass()->is_value_based()) {
480 handle_sync_on_value_based_class(obj, current);
481 }
482
483 current->inc_held_monitor_count();
484
485 if (!useHeavyMonitors()) {
486 markWord mark = obj->mark();
487 if (mark.is_neutral()) {
488 // Anticipate successful CAS -- the ST of the displaced mark must
489 // be visible <= the ST performed by the CAS.
490 lock->set_displaced_header(mark);
491 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
492 return;
493 }
494 // Fall through to inflate() ...
495 } else if (mark.has_locker() &&
496 current->is_lock_owned((address)mark.locker())) {
497 assert(lock != mark.locker(), "must not re-lock the same lock");
498 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
499 lock->set_displaced_header(markWord::from_pointer(nullptr));
500 return;
501 }
502
503 // The object header will never be displaced to this lock,
504 // so it does not matter what the value is, except that it
505 // must be non-zero to avoid looking like a re-entrant lock,
506 // and must not look locked either.
507 lock->set_displaced_header(markWord::unused_mark());
508 } else if (VerifyHeavyMonitors) {
509 guarantee(!obj->mark().has_locker(), "must not be stack-locked");
510 }
511
512 // An async deflation can race after the inflate() call and before
513 // enter() can make the ObjectMonitor busy. enter() returns false if
514 // we have lost the race to async deflation and we simply try again.
515 while (true) {
516 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
517 if (monitor->enter(current)) {
518 return;
519 }
520 }
521 }
522
523 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
524 current->dec_held_monitor_count();
525
526 if (!useHeavyMonitors()) {
527 markWord mark = object->mark();
528
529 markWord dhw = lock->displaced_header();
530 if (dhw.value() == 0) {
531 // If the displaced header is null, then this exit matches up with
532 // a recursive enter. No real work to do here except for diagnostics.
533 #ifndef PRODUCT
534 if (mark != markWord::INFLATING()) {
535 // Only do diagnostics if we are not racing an inflation. Simply
536 // exiting a recursive enter of a Java Monitor that is being
537 // inflated is safe; see the has_monitor() comment below.
538 assert(!mark.is_neutral(), "invariant");
539 assert(!mark.has_locker() ||
540 current->is_lock_owned((address)mark.locker()), "invariant");
541 if (mark.has_monitor()) {
542 // The BasicLock's displaced_header is marked as a recursive
543 // enter and we have an inflated Java Monitor (ObjectMonitor).
544 // This is a special case where the Java Monitor was inflated
545 // after this thread entered the stack-lock recursively. When a
546 // Java Monitor is inflated, we cannot safely walk the Java
547 // Monitor owner's stack and update the BasicLocks because a
548 // Java Monitor can be asynchronously inflated by a thread that
549 // does not own the Java Monitor.
550 ObjectMonitor* m = mark.monitor();
551 assert(m->object()->mark() == mark, "invariant");
552 assert(m->is_entered(current), "invariant");
553 }
554 }
555 #endif
556 return;
557 }
558
559 if (mark == markWord::from_pointer(lock)) {
560 // If the object is stack-locked by the current thread, try to
561 // swing the displaced header from the BasicLock back to the mark.
562 assert(dhw.is_neutral(), "invariant");
563 if (object->cas_set_mark(dhw, mark) == mark) {
564 return;
565 }
566 }
567 } else if (VerifyHeavyMonitors) {
568 guarantee(!object->mark().has_locker(), "must not be stack-locked");
569 }
570
571 // We have to take the slow-path of possible inflation and then exit.
572 // The ObjectMonitor* can't be async deflated until ownership is
573 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
574 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
575 monitor->exit(current);
576 }
577
578 // -----------------------------------------------------------------------------
579 // Class Loader support to workaround deadlocks on the class loader lock objects
580 // Also used by GC
581 // complete_exit()/reenter() are used to wait on a nested lock
582 // i.e. to give up an outer lock completely and then re-enter
583 // Used when holding nested locks - lock acquisition order: lock1 then lock2
584 // 1) complete_exit lock1 - saving recursion count
585 // 2) wait on lock2
586 // 3) when notified on lock2, unlock lock2
587 // 4) reenter lock1 with original recursion count
588 // 5) lock lock2
589 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
590 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
591 // The ObjectMonitor* can't be async deflated until ownership is
592 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
593 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
594 intx recur_count = monitor->complete_exit(current);
595 current->dec_held_monitor_count(recur_count + 1);
596 return recur_count;
597 }
598
599 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
600 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
601 // An async deflation can race after the inflate() call and before
602 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
603 // enter() returns false if we have lost the race to async deflation
604 // and we simply try again.
605 while (true) {
606 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
607 if (monitor->reenter(recursions, current)) {
608 current->inc_held_monitor_count(recursions + 1);
609 return;
610 }
611 }
612 }
613
614 // -----------------------------------------------------------------------------
615 // JNI locks on java objects
616 // NOTE: must use heavy weight monitor to handle jni monitor enter
617 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
618 if (obj->klass()->is_value_based()) {
619 handle_sync_on_value_based_class(obj, current);
620 }
621
622 // the current locking is from JNI instead of Java code
623 current->set_current_pending_monitor_is_from_java(false);
624 // An async deflation can race after the inflate() call and before
625 // enter() can make the ObjectMonitor busy. enter() returns false if
626 // we have lost the race to async deflation and we simply try again.
627 while (true) {
628 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
629 if (monitor->enter(current)) {
630 current->inc_held_monitor_count(1, true);
631 break;
632 }
633 }
634 current->set_current_pending_monitor_is_from_java(true);
635 }
636
637 // NOTE: must use heavy weight monitor to handle jni monitor exit
638 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
639 JavaThread* current = THREAD;
640
641 // The ObjectMonitor* can't be async deflated until ownership is
642 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
643 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
644 // If this thread has locked the object, exit the monitor. We
645 // intentionally do not use CHECK on check_owner because we must exit the
646 // monitor even if an exception was already pending.
647 if (monitor->check_owner(THREAD)) {
648 monitor->exit(current);
649 current->dec_held_monitor_count(1, true);
650 }
651 }
652
653 // -----------------------------------------------------------------------------
654 // Internal VM locks on java objects
655 // standard constructor, allows locking failures
656 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
657 _thread = thread;
658 _thread->check_for_valid_safepoint_state();
659 _obj = obj;
660
661 if (_obj() != nullptr) {
662 ObjectSynchronizer::enter(_obj, &_lock, _thread);
663 }
664 }
665
666 ObjectLocker::~ObjectLocker() {
667 if (_obj() != nullptr) {
668 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
669 }
670 }
671
672
673 // -----------------------------------------------------------------------------
674 // Wait/Notify/NotifyAll
675 // NOTE: must use heavy weight monitor to handle wait()
676 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
677 JavaThread* current = THREAD;
678 if (millis < 0) {
679 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
680 }
681 // The ObjectMonitor* can't be async deflated because the _waiters
682 // field is incremented before ownership is dropped and decremented
683 // after ownership is regained.
684 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
685
686 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
687 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
688
689 // This dummy call is in place to get around dtrace bug 6254741. Once
690 // that's fixed we can uncomment the following line, remove the call
691 // and change this function back into a "void" func.
692 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
693 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
694 return ret_code;
695 }
696
697 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
698 JavaThread* current = THREAD;
699
700 markWord mark = obj->mark();
701 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
702 // Not inflated so there can't be any waiters to notify.
703 return;
704 }
705 // The ObjectMonitor* can't be async deflated until ownership is
706 // dropped by the calling thread.
707 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
708 monitor->notify(CHECK);
709 }
710
711 // NOTE: see comment of notify()
712 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
713 JavaThread* current = THREAD;
714
715 markWord mark = obj->mark();
716 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
717 // Not inflated so there can't be any waiters to notify.
718 return;
719 }
720 // The ObjectMonitor* can't be async deflated until ownership is
721 // dropped by the calling thread.
722 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
723 monitor->notifyAll(CHECK);
724 }
725
726 // -----------------------------------------------------------------------------
727 // Hash Code handling
728
729 struct SharedGlobals {
730 char _pad_prefix[OM_CACHE_LINE_SIZE];
731 // This is a highly shared mostly-read variable.
732 // To avoid false-sharing it needs to be the sole occupant of a cache line.
733 volatile int stw_random;
734 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
735 // Hot RW variable -- Sequester to avoid false-sharing
736 volatile int hc_sequence;
737 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
738 };
739
740 static SharedGlobals GVars;
741
742 static markWord read_stable_mark(oop obj) {
743 markWord mark = obj->mark_acquire();
744 if (!mark.is_being_inflated()) {
745 return mark; // normal fast-path return
746 }
747
748 int its = 0;
749 for (;;) {
750 markWord mark = obj->mark_acquire();
751 if (!mark.is_being_inflated()) {
752 return mark; // normal fast-path return
753 }
754
755 // The object is being inflated by some other thread.
756 // The caller of read_stable_mark() must wait for inflation to complete.
757 // Avoid live-lock.
758
759 ++its;
760 if (its > 10000 || !os::is_MP()) {
761 if (its & 1) {
762 os::naked_yield();
763 } else {
764 // Note that the following code attenuates the livelock problem but is not
765 // a complete remedy. A more complete solution would require that the inflating
766 // thread hold the associated inflation lock. The following code simply restricts
767 // the number of spinners to at most one. We'll have N-2 threads blocked
768 // on the inflationlock, 1 thread holding the inflation lock and using
769 // a yield/park strategy, and 1 thread in the midst of inflation.
770 // A more refined approach would be to change the encoding of INFLATING
771 // to allow encapsulation of a native thread pointer. Threads waiting for
772 // inflation to complete would use CAS to push themselves onto a singly linked
773 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
774 // and calling park(). When inflation was complete the thread that accomplished inflation
775 // would detach the list and set the markword to inflated with a single CAS and
776 // then for each thread on the list, set the flag and unpark() the thread.
777
778 // Index into the lock array based on the current object address.
779 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
780 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
781 int YieldThenBlock = 0;
782 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
783 gInflationLocks[ix]->lock();
784 while (obj->mark_acquire() == markWord::INFLATING()) {
785 // Beware: naked_yield() is advisory and has almost no effect on some platforms
786 // so we periodically call current->_ParkEvent->park(1).
787 // We use a mixed spin/yield/block mechanism.
788 if ((YieldThenBlock++) >= 16) {
789 Thread::current()->_ParkEvent->park(1);
790 } else {
791 os::naked_yield();
792 }
793 }
794 gInflationLocks[ix]->unlock();
795 }
796 } else {
797 SpinPause(); // SMP-polite spinning
798 }
799 }
800 }
801
802 // hashCode() generation :
803 //
804 // Possibilities:
805 // * MD5Digest of {obj,stw_random}
806 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
807 // * A DES- or AES-style SBox[] mechanism
808 // * One of the Phi-based schemes, such as:
809 // 2654435761 = 2^32 * Phi (golden ratio)
810 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
811 // * A variation of Marsaglia's shift-xor RNG scheme.
812 // * (obj ^ stw_random) is appealing, but can result
813 // in undesirable regularity in the hashCode values of adjacent objects
814 // (objects allocated back-to-back, in particular). This could potentially
815 // result in hashtable collisions and reduced hashtable efficiency.
816 // There are simple ways to "diffuse" the middle address bits over the
817 // generated hashCode values:
818
819 static inline intptr_t get_next_hash(Thread* current, oop obj) {
820 intptr_t value = 0;
821 if (hashCode == 0) {
822 // This form uses global Park-Miller RNG.
823 // On MP system we'll have lots of RW access to a global, so the
824 // mechanism induces lots of coherency traffic.
825 value = os::random();
826 } else if (hashCode == 1) {
827 // This variation has the property of being stable (idempotent)
828 // between STW operations. This can be useful in some of the 1-0
829 // synchronization schemes.
830 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
831 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
832 } else if (hashCode == 2) {
833 value = 1; // for sensitivity testing
834 } else if (hashCode == 3) {
835 value = ++GVars.hc_sequence;
836 } else if (hashCode == 4) {
837 value = cast_from_oop<intptr_t>(obj);
838 } else {
839 // Marsaglia's xor-shift scheme with thread-specific state
840 // This is probably the best overall implementation -- we'll
841 // likely make this the default in future releases.
842 unsigned t = current->_hashStateX;
843 t ^= (t << 11);
844 current->_hashStateX = current->_hashStateY;
845 current->_hashStateY = current->_hashStateZ;
846 current->_hashStateZ = current->_hashStateW;
847 unsigned v = current->_hashStateW;
848 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
849 current->_hashStateW = v;
850 value = v;
851 }
852
853 value &= markWord::hash_mask;
854 if (value == 0) value = 0xBAD;
855 assert(value != markWord::no_hash, "invariant");
856 return value;
857 }
858
859 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
860
861 while (true) {
862 ObjectMonitor* monitor = nullptr;
863 markWord temp, test;
864 intptr_t hash;
865 markWord mark = read_stable_mark(obj);
866 if (VerifyHeavyMonitors) {
867 assert(UseHeavyMonitors, "+VerifyHeavyMonitors requires +UseHeavyMonitors");
868 guarantee(!mark.has_locker(), "must not be stack locked");
869 }
870 if (mark.is_neutral()) { // if this is a normal header
871 hash = mark.hash();
872 if (hash != 0) { // if it has a hash, just return it
873 return hash;
874 }
875 hash = get_next_hash(current, obj); // get a new hash
876 temp = mark.copy_set_hash(hash); // merge the hash into header
877 // try to install the hash
878 test = obj->cas_set_mark(temp, mark);
879 if (test == mark) { // if the hash was installed, return it
880 return hash;
881 }
882 // Failed to install the hash. It could be that another thread
883 // installed the hash just before our attempt or inflation has
884 // occurred or... so we fall thru to inflate the monitor for
885 // stability and then install the hash.
886 } else if (mark.has_monitor()) {
887 monitor = mark.monitor();
888 temp = monitor->header();
889 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
890 hash = temp.hash();
891 if (hash != 0) {
892 // It has a hash.
893
894 // Separate load of dmw/header above from the loads in
895 // is_being_async_deflated().
896
897 // dmw/header and _contentions may get written by different threads.
898 // Make sure to observe them in the same order when having several observers.
899 OrderAccess::loadload_for_IRIW();
900
901 if (monitor->is_being_async_deflated()) {
902 // But we can't safely use the hash if we detect that async
903 // deflation has occurred. So we attempt to restore the
904 // header/dmw to the object's header so that we only retry
905 // once if the deflater thread happens to be slow.
906 monitor->install_displaced_markword_in_object(obj);
907 continue;
908 }
909 return hash;
910 }
911 // Fall thru so we only have one place that installs the hash in
912 // the ObjectMonitor.
913 } else if (current->is_lock_owned((address)mark.locker())) {
914 // This is a stack lock owned by the calling thread so fetch the
915 // displaced markWord from the BasicLock on the stack.
916 temp = mark.displaced_mark_helper();
917 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
918 hash = temp.hash();
919 if (hash != 0) { // if it has a hash, just return it
920 return hash;
921 }
922 // WARNING:
923 // The displaced header in the BasicLock on a thread's stack
924 // is strictly immutable. It CANNOT be changed in ANY cases.
925 // So we have to inflate the stack lock into an ObjectMonitor
926 // even if the current thread owns the lock. The BasicLock on
927 // a thread's stack can be asynchronously read by other threads
928 // during an inflate() call so any change to that stack memory
929 // may not propagate to other threads correctly.
930 }
931
932 // Inflate the monitor to set the hash.
933
934 // An async deflation can race after the inflate() call and before we
935 // can update the ObjectMonitor's header with the hash value below.
936 monitor = inflate(current, obj, inflate_cause_hash_code);
937 // Load ObjectMonitor's header/dmw field and see if it has a hash.
938 mark = monitor->header();
939 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
940 hash = mark.hash();
941 if (hash == 0) { // if it does not have a hash
942 hash = get_next_hash(current, obj); // get a new hash
943 temp = mark.copy_set_hash(hash) ; // merge the hash into header
944 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
945 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
946 test = markWord(v);
947 if (test != mark) {
948 // The attempt to update the ObjectMonitor's header/dmw field
949 // did not work. This can happen if another thread managed to
950 // merge in the hash just before our cmpxchg().
951 // If we add any new usages of the header/dmw field, this code
952 // will need to be updated.
953 hash = test.hash();
954 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
955 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
956 }
957 if (monitor->is_being_async_deflated()) {
958 // If we detect that async deflation has occurred, then we
959 // attempt to restore the header/dmw to the object's header
960 // so that we only retry once if the deflater thread happens
961 // to be slow.
962 monitor->install_displaced_markword_in_object(obj);
963 continue;
964 }
965 }
966 // We finally get the hash.
967 return hash;
968 }
969 }
970
971 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
972 Handle h_obj) {
973 assert(current == JavaThread::current(), "Can only be called on current thread");
974 oop obj = h_obj();
975
976 markWord mark = read_stable_mark(obj);
977
978 // Uncontended case, header points to stack
979 if (mark.has_locker()) {
980 return current->is_lock_owned((address)mark.locker());
981 }
982 // Contended case, header points to ObjectMonitor (tagged pointer)
983 if (mark.has_monitor()) {
984 // The first stage of async deflation does not affect any field
985 // used by this comparison so the ObjectMonitor* is usable here.
986 ObjectMonitor* monitor = mark.monitor();
987 return monitor->is_entered(current) != 0;
988 }
989 // Unlocked case, header in place
990 assert(mark.is_neutral(), "sanity check");
991 return false;
992 }
993
994 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
995 oop obj = h_obj();
996 address owner = nullptr;
997
998 markWord mark = read_stable_mark(obj);
999
1000 // Uncontended case, header points to stack
1001 if (mark.has_locker()) {
1002 owner = (address) mark.locker();
1003 }
1004
1005 // Contended case, header points to ObjectMonitor (tagged pointer)
1006 else if (mark.has_monitor()) {
1007 // The first stage of async deflation does not affect any field
1008 // used by this comparison so the ObjectMonitor* is usable here.
1009 ObjectMonitor* monitor = mark.monitor();
1010 assert(monitor != nullptr, "monitor should be non-null");
1011 owner = (address) monitor->owner();
1012 }
1013
1014 if (owner != nullptr) {
1015 // owning_thread_from_monitor_owner() may also return null here
1016 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1017 }
1018
1019 // Unlocked case, header in place
1020 // Cannot have assertion since this object may have been
1021 // locked by another thread when reaching here.
1022 // assert(mark.is_neutral(), "sanity check");
1023
1024 return nullptr;
1025 }
1026
1027 // Visitors ...
1028
1029 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1030 // ObjectMonitors where owner is set to a stack lock address in thread.
1031 //
1032 // This version of monitors_iterate() works with the in-use monitor list.
1033 //
1034 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1035 MonitorList::Iterator iter = _in_use_list.iterator();
1036 while (iter.has_next()) {
1037 ObjectMonitor* mid = iter.next();
1038 if (mid->owner() != thread) {
1039 // Not owned by the target thread and intentionally skips when owner
1040 // is set to a stack lock address in the target thread.
1041 continue;
1042 }
1043 if (!mid->is_being_async_deflated() && mid->object_peek() != nullptr) {
1044 // Only process with closure if the object is set.
1045
1046 // monitors_iterate() is only called at a safepoint or when the
1047 // target thread is suspended or when the target thread is
1048 // operating on itself. The current closures in use today are
1049 // only interested in an owned ObjectMonitor and ownership
1050 // cannot be dropped under the calling contexts so the
1051 // ObjectMonitor cannot be async deflated.
1052 closure->do_monitor(mid);
1053 }
1054 }
1055 }
1056
1057 // This version of monitors_iterate() works with the specified linked list.
1058 //
1059 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure,
1060 ObjectMonitorsHashtable::PtrList* list,
1061 JavaThread* thread) {
1062 typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator;
1063 ObjectMonitorIterator iter(list->head());
1064 while (!iter.is_empty()) {
1065 ObjectMonitor* mid = *iter.next();
1066 // Owner set to a stack lock address in thread should never be seen here:
1067 assert(mid->owner() == thread, "must be");
1068 if (!mid->is_being_async_deflated() && mid->object_peek() != nullptr) {
1069 // Only process with closure if the object is set.
1070
1071 // monitors_iterate() is only called at a safepoint or when the
1072 // target thread is suspended or when the target thread is
1073 // operating on itself. The current closures in use today are
1074 // only interested in an owned ObjectMonitor and ownership
1075 // cannot be dropped under the calling contexts so the
1076 // ObjectMonitor cannot be async deflated.
1077 closure->do_monitor(mid);
1078 }
1079 }
1080 }
1081
1082 static bool monitors_used_above_threshold(MonitorList* list) {
1083 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1084 return false;
1085 }
1086 // Start with ceiling based on a per-thread estimate:
1087 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1088 size_t old_ceiling = ceiling;
1089 if (ceiling < list->max()) {
1090 // The max used by the system has exceeded the ceiling so use that:
1091 ceiling = list->max();
1092 }
1093 size_t monitors_used = list->count();
1094 if (monitors_used == 0) { // empty list is easy
1095 return false;
1096 }
1097 if (NoAsyncDeflationProgressMax != 0 &&
1098 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1099 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1100 size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1101 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1102 log_info(monitorinflation)("Too many deflations without progress; "
1103 "bumping in_use_list_ceiling from " SIZE_FORMAT
1104 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1105 _no_progress_cnt = 0;
1106 ceiling = new_ceiling;
1107 }
1108
1109 // Check if our monitor usage is above the threshold:
1110 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1111 return int(monitor_usage) > MonitorUsedDeflationThreshold;
1112 }
1113
1114 size_t ObjectSynchronizer::in_use_list_ceiling() {
1115 return _in_use_list_ceiling;
1116 }
1117
1118 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1119 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1120 }
1121
1122 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1123 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1124 }
1125
1126 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1127 _in_use_list_ceiling = new_value;
1128 }
1129
1130 bool ObjectSynchronizer::is_async_deflation_needed() {
1131 if (is_async_deflation_requested()) {
1132 // Async deflation request.
1133 return true;
1134 }
1135 if (AsyncDeflationInterval > 0 &&
1136 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1137 monitors_used_above_threshold(&_in_use_list)) {
1138 // It's been longer than our specified deflate interval and there
1139 // are too many monitors in use. We don't deflate more frequently
1140 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1141 // in order to not swamp the MonitorDeflationThread.
1142 return true;
1143 }
1144 return false;
1145 }
1146
1147 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1148 JavaThread* current = JavaThread::current();
1149 bool ret_code = false;
1150
1151 jlong last_time = last_async_deflation_time_ns();
1152 set_is_async_deflation_requested(true);
1153 {
1154 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1155 ml.notify_all();
1156 }
1157 const int N_CHECKS = 5;
1158 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1159 if (last_async_deflation_time_ns() > last_time) {
1160 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1161 ret_code = true;
1162 break;
1163 }
1164 {
1165 // JavaThread has to honor the blocking protocol.
1166 ThreadBlockInVM tbivm(current);
1167 os::naked_short_sleep(999); // sleep for almost 1 second
1168 }
1169 }
1170 if (!ret_code) {
1171 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1172 }
1173
1174 return ret_code;
1175 }
1176
1177 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1178 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1179 }
1180
1181 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1182 const oop obj,
1183 ObjectSynchronizer::InflateCause cause) {
1184 assert(event != nullptr, "invariant");
1185 event->set_monitorClass(obj->klass());
1186 event->set_address((uintptr_t)(void*)obj);
1187 event->set_cause((u1)cause);
1188 event->commit();
1189 }
1190
1191 // Fast path code shared by multiple functions
1192 void ObjectSynchronizer::inflate_helper(oop obj) {
1193 markWord mark = obj->mark_acquire();
1194 if (mark.has_monitor()) {
1195 ObjectMonitor* monitor = mark.monitor();
1196 markWord dmw = monitor->header();
1197 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1198 return;
1199 }
1200 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1201 }
1202
1203 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1204 const InflateCause cause) {
1205 EventJavaMonitorInflate event;
1206
1207 for (;;) {
1208 const markWord mark = object->mark_acquire();
1209
1210 // The mark can be in one of the following states:
1211 // * Inflated - just return
1212 // * Stack-locked - coerce it to inflated
1213 // * INFLATING - busy wait for conversion to complete
1214 // * Neutral - aggressively inflate the object.
1215
1216 // CASE: inflated
1217 if (mark.has_monitor()) {
1218 ObjectMonitor* inf = mark.monitor();
1219 markWord dmw = inf->header();
1220 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1221 return inf;
1222 }
1223
1224 // CASE: inflation in progress - inflating over a stack-lock.
1225 // Some other thread is converting from stack-locked to inflated.
1226 // Only that thread can complete inflation -- other threads must wait.
1227 // The INFLATING value is transient.
1228 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1229 // We could always eliminate polling by parking the thread on some auxiliary list.
1230 if (mark == markWord::INFLATING()) {
1231 read_stable_mark(object);
1232 continue;
1233 }
1234
1235 // CASE: stack-locked
1236 // Could be stack-locked either by this thread or by some other thread.
1237 //
1238 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1239 // to install INFLATING into the mark word. We originally installed INFLATING,
1240 // allocated the ObjectMonitor, and then finally STed the address of the
1241 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1242 // the interval in which INFLATING appeared in the mark, thus increasing
1243 // the odds of inflation contention.
1244
1245 LogStreamHandle(Trace, monitorinflation) lsh;
1246
1247 if (mark.has_locker()) {
1248 ObjectMonitor* m = new ObjectMonitor(object);
1249 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1250 // We do this before the CAS in order to minimize the length of time
1251 // in which INFLATING appears in the mark.
1252
1253 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1254 if (cmp != mark) {
1255 delete m;
1256 continue; // Interference -- just retry
1257 }
1258
1259 // We've successfully installed INFLATING (0) into the mark-word.
1260 // This is the only case where 0 will appear in a mark-word.
1261 // Only the singular thread that successfully swings the mark-word
1262 // to 0 can perform (or more precisely, complete) inflation.
1263 //
1264 // Why do we CAS a 0 into the mark-word instead of just CASing the
1265 // mark-word from the stack-locked value directly to the new inflated state?
1266 // Consider what happens when a thread unlocks a stack-locked object.
1267 // It attempts to use CAS to swing the displaced header value from the
1268 // on-stack BasicLock back into the object header. Recall also that the
1269 // header value (hash code, etc) can reside in (a) the object header, or
1270 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1271 // header in an ObjectMonitor. The inflate() routine must copy the header
1272 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1273 // the while preserving the hashCode stability invariants. If the owner
1274 // decides to release the lock while the value is 0, the unlock will fail
1275 // and control will eventually pass from slow_exit() to inflate. The owner
1276 // will then spin, waiting for the 0 value to disappear. Put another way,
1277 // the 0 causes the owner to stall if the owner happens to try to
1278 // drop the lock (restoring the header from the BasicLock to the object)
1279 // while inflation is in-progress. This protocol avoids races that might
1280 // would otherwise permit hashCode values to change or "flicker" for an object.
1281 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1282 // 0 serves as a "BUSY" inflate-in-progress indicator.
1283
1284
1285 // fetch the displaced mark from the owner's stack.
1286 // The owner can't die or unwind past the lock while our INFLATING
1287 // object is in the mark. Furthermore the owner can't complete
1288 // an unlock on the object, either.
1289 markWord dmw = mark.displaced_mark_helper();
1290 // Catch if the object's header is not neutral (not locked and
1291 // not marked is what we care about here).
1292 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1293
1294 // Setup monitor fields to proper values -- prepare the monitor
1295 m->set_header(dmw);
1296
1297 // Optimization: if the mark.locker stack address is associated
1298 // with this thread we could simply set m->_owner = current.
1299 // Note that a thread can inflate an object
1300 // that it has stack-locked -- as might happen in wait() -- directly
1301 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1302 m->set_owner_from(nullptr, mark.locker());
1303 // TODO-FIXME: assert BasicLock->dhw != 0.
1304
1305 // Must preserve store ordering. The monitor state must
1306 // be stable at the time of publishing the monitor address.
1307 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1308 // Release semantics so that above set_object() is seen first.
1309 object->release_set_mark(markWord::encode(m));
1310
1311 // Once ObjectMonitor is configured and the object is associated
1312 // with the ObjectMonitor, it is safe to allow async deflation:
1313 _in_use_list.add(m);
1314
1315 // Hopefully the performance counters are allocated on distinct cache lines
1316 // to avoid false sharing on MP systems ...
1317 OM_PERFDATA_OP(Inflations, inc());
1318 if (log_is_enabled(Trace, monitorinflation)) {
1319 ResourceMark rm(current);
1320 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1321 INTPTR_FORMAT ", type='%s'", p2i(object),
1322 object->mark().value(), object->klass()->external_name());
1323 }
1324 if (event.should_commit()) {
1325 post_monitor_inflate_event(&event, object, cause);
1326 }
1327 return m;
1328 }
1329
1330 // CASE: neutral
1331 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1332 // If we know we're inflating for entry it's better to inflate by swinging a
1333 // pre-locked ObjectMonitor pointer into the object header. A successful
1334 // CAS inflates the object *and* confers ownership to the inflating thread.
1335 // In the current implementation we use a 2-step mechanism where we CAS()
1336 // to inflate and then CAS() again to try to swing _owner from null to current.
1337 // An inflateTry() method that we could call from enter() would be useful.
1338
1339 // Catch if the object's header is not neutral (not locked and
1340 // not marked is what we care about here).
1341 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1342 ObjectMonitor* m = new ObjectMonitor(object);
1343 // prepare m for installation - set monitor to initial state
1344 m->set_header(mark);
1345
1346 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1347 delete m;
1348 m = nullptr;
1349 continue;
1350 // interference - the markword changed - just retry.
1351 // The state-transitions are one-way, so there's no chance of
1352 // live-lock -- "Inflated" is an absorbing state.
1353 }
1354
1355 // Once the ObjectMonitor is configured and object is associated
1356 // with the ObjectMonitor, it is safe to allow async deflation:
1357 _in_use_list.add(m);
1358
1359 // Hopefully the performance counters are allocated on distinct
1360 // cache lines to avoid false sharing on MP systems ...
1361 OM_PERFDATA_OP(Inflations, inc());
1362 if (log_is_enabled(Trace, monitorinflation)) {
1363 ResourceMark rm(current);
1364 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1365 INTPTR_FORMAT ", type='%s'", p2i(object),
1366 object->mark().value(), object->klass()->external_name());
1367 }
1368 if (event.should_commit()) {
1369 post_monitor_inflate_event(&event, object, cause);
1370 }
1371 return m;
1372 }
1373 }
1374
1375 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1376 const char* cnt_name, size_t cnt,
1377 LogStream* ls, elapsedTimer* timer_p) {
1378 if (!SafepointMechanism::should_process(current)) {
1379 return;
1380 }
1381
1382 // A safepoint/handshake has started.
1383 if (ls != nullptr) {
1384 timer_p->stop();
1385 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1386 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1387 op_name, cnt_name, cnt, in_use_list_ceiling(),
1388 _in_use_list.count(), _in_use_list.max());
1389 }
1390
1391 {
1392 // Honor block request.
1393 ThreadBlockInVM tbivm(current);
1394 }
1395
1396 if (ls != nullptr) {
1397 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1398 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1399 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1400 timer_p->start();
1401 }
1402 }
1403
1404 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1405 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1406 //
1407 // If table != nullptr, we gather owned ObjectMonitors indexed by the
1408 // owner in the table. Please note that ObjectMonitors where the owner
1409 // is set to a stack lock address are NOT associated with the JavaThread
1410 // that holds that stack lock. All of the current consumers of
1411 // ObjectMonitorsHashtable info only care about JNI locked monitors and
1412 // those do not have the owner set to a stack lock address.
1413 //
1414 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1415 elapsedTimer* timer_p,
1416 ObjectMonitorsHashtable* table) {
1417 MonitorList::Iterator iter = _in_use_list.iterator();
1418 size_t deflated_count = 0;
1419
1420 while (iter.has_next()) {
1421 if (deflated_count >= (size_t)MonitorDeflationMax) {
1422 break;
1423 }
1424 ObjectMonitor* mid = iter.next();
1425 if (mid->deflate_monitor()) {
1426 deflated_count++;
1427 } else if (table != nullptr) {
1428 // The caller is interested in the owned ObjectMonitors. This does
1429 // not include when owner is set to a stack lock address in thread.
1430 // This also does not capture unowned ObjectMonitors that cannot be
1431 // deflated because of a waiter.
1432 void* key = mid->owner();
1433 // Since deflate_idle_monitors() and deflate_monitor_list() can be
1434 // called more than once, we have to make sure the entry has not
1435 // already been added.
1436 if (key != nullptr && !table->has_entry(key, mid)) {
1437 table->add_entry(key, mid);
1438 }
1439 }
1440
1441 if (current->is_Java_thread()) {
1442 // A JavaThread must check for a safepoint/handshake and honor it.
1443 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1444 deflated_count, ls, timer_p);
1445 }
1446 }
1447
1448 return deflated_count;
1449 }
1450
1451 class HandshakeForDeflation : public HandshakeClosure {
1452 public:
1453 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1454
1455 void do_thread(Thread* thread) {
1456 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1457 INTPTR_FORMAT, p2i(thread));
1458 }
1459 };
1460
1461 // This function is called by the MonitorDeflationThread to deflate
1462 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1463 // and VM_ThreadDump::doit() by the VMThread.
1464 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) {
1465 Thread* current = Thread::current();
1466 if (current->is_Java_thread()) {
1467 // The async deflation request has been processed.
1468 _last_async_deflation_time_ns = os::javaTimeNanos();
1469 set_is_async_deflation_requested(false);
1470 }
1471
1472 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1473 LogStreamHandle(Info, monitorinflation) lsh_info;
1474 LogStream* ls = nullptr;
1475 if (log_is_enabled(Debug, monitorinflation)) {
1476 ls = &lsh_debug;
1477 } else if (log_is_enabled(Info, monitorinflation)) {
1478 ls = &lsh_info;
1479 }
1480
1481 elapsedTimer timer;
1482 if (ls != nullptr) {
1483 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1484 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1485 timer.start();
1486 }
1487
1488 // Deflate some idle ObjectMonitors.
1489 size_t deflated_count = deflate_monitor_list(current, ls, &timer, table);
1490 size_t unlinked_count = 0;
1491 size_t deleted_count = 0;
1492 if (deflated_count > 0 || is_final_audit()) {
1493 // There are ObjectMonitors that have been deflated or this is the
1494 // final audit and all the remaining ObjectMonitors have been
1495 // deflated, BUT the MonitorDeflationThread blocked for the final
1496 // safepoint during unlinking.
1497
1498 // Unlink deflated ObjectMonitors from the in-use list.
1499 ResourceMark rm;
1500 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1501 unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, &delete_list);
1502 if (current->is_Java_thread()) {
1503 if (ls != nullptr) {
1504 timer.stop();
1505 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1506 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1507 SIZE_FORMAT ", max=" SIZE_FORMAT,
1508 unlinked_count, in_use_list_ceiling(),
1509 _in_use_list.count(), _in_use_list.max());
1510 }
1511
1512 // A JavaThread needs to handshake in order to safely free the
1513 // ObjectMonitors that were deflated in this cycle.
1514 HandshakeForDeflation hfd_hc;
1515 Handshake::execute(&hfd_hc);
1516
1517 if (ls != nullptr) {
1518 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1519 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1520 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1521 timer.start();
1522 }
1523 }
1524
1525 // After the handshake, safely free the ObjectMonitors that were
1526 // deflated in this cycle.
1527 for (ObjectMonitor* monitor: delete_list) {
1528 delete monitor;
1529 deleted_count++;
1530
1531 if (current->is_Java_thread()) {
1532 // A JavaThread must check for a safepoint/handshake and honor it.
1533 chk_for_block_req(JavaThread::cast(current), "deletion", "deleted_count",
1534 deleted_count, ls, &timer);
1535 }
1536 }
1537 assert(unlinked_count == deleted_count, "must be");
1538 }
1539
1540 if (ls != nullptr) {
1541 timer.stop();
1542 if (deflated_count != 0 || unlinked_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1543 ls->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1544 deflated_count, unlinked_count, timer.seconds());
1545 }
1546 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1547 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1548 if (table != nullptr) {
1549 ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT,
1550 table->key_count(), table->om_count());
1551 }
1552 }
1553
1554 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1555 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1556
1557 GVars.stw_random = os::random();
1558
1559 if (deflated_count != 0) {
1560 _no_progress_cnt = 0;
1561 } else {
1562 _no_progress_cnt++;
1563 }
1564
1565 return deflated_count;
1566 }
1567
1568 // Monitor cleanup on JavaThread::exit
1569
1570 // Iterate through monitor cache and attempt to release thread's monitors
1571 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1572 private:
1573 JavaThread* _thread;
1574
1575 public:
1576 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1577 void do_monitor(ObjectMonitor* mid) {
1578 intx rec = mid->complete_exit(_thread);
1579 _thread->dec_held_monitor_count(rec + 1);
1580 }
1581 };
1582
1583 // Release all inflated monitors owned by current thread. Lightweight monitors are
1584 // ignored. This is meant to be called during JNI thread detach which assumes
1585 // all remaining monitors are heavyweight. All exceptions are swallowed.
1586 // Scanning the extant monitor list can be time consuming.
1587 // A simple optimization is to add a per-thread flag that indicates a thread
1588 // called jni_monitorenter() during its lifetime.
1589 //
1590 // Instead of NoSafepointVerifier it might be cheaper to
1591 // use an idiom of the form:
1592 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1593 // <code that must not run at safepoint>
1594 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1595 // Since the tests are extremely cheap we could leave them enabled
1596 // for normal product builds.
1597
1598 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1599 assert(current == JavaThread::current(), "must be current Java thread");
1600 NoSafepointVerifier nsv;
1601 ReleaseJavaMonitorsClosure rjmc(current);
1602 ObjectSynchronizer::monitors_iterate(&rjmc, current);
1603 assert(!current->has_pending_exception(), "Should not be possible");
1604 current->clear_pending_exception();
1605 assert(current->held_monitor_count() == 0, "Should not be possible");
1606 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1607 current->clear_jni_monitor_count();
1608 }
1609
1610 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1611 switch (cause) {
1612 case inflate_cause_vm_internal: return "VM Internal";
1613 case inflate_cause_monitor_enter: return "Monitor Enter";
1614 case inflate_cause_wait: return "Monitor Wait";
1615 case inflate_cause_notify: return "Monitor Notify";
1616 case inflate_cause_hash_code: return "Monitor Hash Code";
1617 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1618 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1619 default:
1620 ShouldNotReachHere();
1621 }
1622 return "Unknown";
1623 }
1624
1625 //------------------------------------------------------------------------------
1626 // Debugging code
1627
1628 u_char* ObjectSynchronizer::get_gvars_addr() {
1629 return (u_char*)&GVars;
1630 }
1631
1632 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1633 return (u_char*)&GVars.hc_sequence;
1634 }
1635
1636 size_t ObjectSynchronizer::get_gvars_size() {
1637 return sizeof(SharedGlobals);
1638 }
1639
1640 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1641 return (u_char*)&GVars.stw_random;
1642 }
1643
1644 // Do the final audit and print of ObjectMonitor stats; must be done
1645 // by the VMThread at VM exit time.
1646 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1647 assert(Thread::current()->is_VM_thread(), "sanity check");
1648
1649 if (is_final_audit()) { // Only do the audit once.
1650 return;
1651 }
1652 set_is_final_audit();
1653 log_info(monitorinflation)("Starting the final audit.");
1654
1655 if (log_is_enabled(Info, monitorinflation)) {
1656 // Do deflations in order to reduce the in-use monitor population
1657 // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1658 // which is called by ObjectSynchronizer::audit_and_print_stats().
1659 while (deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) > 0) {
1660 ; // empty
1661 }
1662 // The other audit_and_print_stats() call is done at the Debug
1663 // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
1664 audit_and_print_stats(true /* on_exit */);
1665 }
1666 }
1667
1668 // This function can be called at a safepoint or it can be called when
1669 // we are trying to exit the VM. When we are trying to exit the VM, the
1670 // list walker functions can run in parallel with the other list
1671 // operations so spin-locking is used for safety.
1672 //
1673 // Calls to this function can be added in various places as a debugging
1674 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1675 // details logged at the Info level and 'false' for the 'on_exit'
1676 // parameter to have in-use monitor details logged at the Trace level.
1677 //
1678 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1679 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1680
1681 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1682 LogStreamHandle(Info, monitorinflation) lsh_info;
1683 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1684 LogStream* ls = nullptr;
1685 if (log_is_enabled(Trace, monitorinflation)) {
1686 ls = &lsh_trace;
1687 } else if (log_is_enabled(Debug, monitorinflation)) {
1688 ls = &lsh_debug;
1689 } else if (log_is_enabled(Info, monitorinflation)) {
1690 ls = &lsh_info;
1691 }
1692 assert(ls != nullptr, "sanity check");
1693
1694 int error_cnt = 0;
1695
1696 ls->print_cr("Checking in_use_list:");
1697 chk_in_use_list(ls, &error_cnt);
1698
1699 if (error_cnt == 0) {
1700 ls->print_cr("No errors found in in_use_list checks.");
1701 } else {
1702 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1703 }
1704
1705 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1706 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1707 // When exiting this log output is at the Info level. When called
1708 // at a safepoint, this log output is at the Trace level since
1709 // there can be a lot of it.
1710 log_in_use_monitor_details(ls);
1711 }
1712
1713 ls->flush();
1714
1715 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1716 }
1717
1718 // Check the in_use_list; log the results of the checks.
1719 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1720 size_t l_in_use_count = _in_use_list.count();
1721 size_t l_in_use_max = _in_use_list.max();
1722 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1723 l_in_use_max);
1724
1725 size_t ck_in_use_count = 0;
1726 MonitorList::Iterator iter = _in_use_list.iterator();
1727 while (iter.has_next()) {
1728 ObjectMonitor* mid = iter.next();
1729 chk_in_use_entry(mid, out, error_cnt_p);
1730 ck_in_use_count++;
1731 }
1732
1733 if (l_in_use_count == ck_in_use_count) {
1734 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1735 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1736 } else {
1737 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1738 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1739 ck_in_use_count);
1740 }
1741
1742 size_t ck_in_use_max = _in_use_list.max();
1743 if (l_in_use_max == ck_in_use_max) {
1744 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1745 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1746 } else {
1747 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1748 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1749 }
1750 }
1751
1752 // Check an in-use monitor entry; log any errors.
1753 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1754 int* error_cnt_p) {
1755 if (n->owner_is_DEFLATER_MARKER()) {
1756 // This should not happen, but if it does, it is not fatal.
1757 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1758 "deflated.", p2i(n));
1759 return;
1760 }
1761 if (n->header().value() == 0) {
1762 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1763 "have non-null _header field.", p2i(n));
1764 *error_cnt_p = *error_cnt_p + 1;
1765 }
1766 const oop obj = n->object_peek();
1767 if (obj != nullptr) {
1768 const markWord mark = obj->mark();
1769 if (!mark.has_monitor()) {
1770 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1771 "object does not think it has a monitor: obj="
1772 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1773 p2i(obj), mark.value());
1774 *error_cnt_p = *error_cnt_p + 1;
1775 }
1776 ObjectMonitor* const obj_mon = mark.monitor();
1777 if (n != obj_mon) {
1778 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1779 "object does not refer to the same monitor: obj="
1780 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1781 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1782 *error_cnt_p = *error_cnt_p + 1;
1783 }
1784 }
1785 }
1786
1787 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1788 // flags indicate why the entry is in-use, 'object' and 'object type'
1789 // indicate the associated object and its type.
1790 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
1791 stringStream ss;
1792 if (_in_use_list.count() > 0) {
1793 out->print_cr("In-use monitor info:");
1794 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1795 out->print_cr("%18s %s %18s %18s",
1796 "monitor", "BHL", "object", "object type");
1797 out->print_cr("================== === ================== ==================");
1798 MonitorList::Iterator iter = _in_use_list.iterator();
1799 while (iter.has_next()) {
1800 ObjectMonitor* mid = iter.next();
1801 const oop obj = mid->object_peek();
1802 const markWord mark = mid->header();
1803 ResourceMark rm;
1804 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid),
1805 mid->is_busy(), mark.hash() != 0, mid->owner() != nullptr,
1806 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
1807 if (mid->is_busy()) {
1808 out->print(" (%s)", mid->is_busy_to_string(&ss));
1809 ss.reset();
1810 }
1811 out->cr();
1812 }
1813 }
1814
1815 out->flush();
1816 }