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/frame.inline.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/handshake.hpp"
41 #include "runtime/interfaceSupport.inline.hpp"
42 #include "runtime/javaThread.hpp"
43 #include "runtime/mutexLocker.hpp"
44 #include "runtime/objectMonitor.hpp"
45 #include "runtime/objectMonitor.inline.hpp"
46 #include "runtime/os.inline.hpp"
47 #include "runtime/osThread.hpp"
48 #include "runtime/perfData.hpp"
49 #include "runtime/safepointMechanism.inline.hpp"
50 #include "runtime/safepointVerifiers.hpp"
51 #include "runtime/sharedRuntime.hpp"
52 #include "runtime/stubRoutines.hpp"
53 #include "runtime/synchronizer.hpp"
54 #include "runtime/threads.hpp"
55 #include "runtime/timer.hpp"
56 #include "runtime/vframe.hpp"
57 #include "runtime/vmThread.hpp"
58 #include "utilities/align.hpp"
59 #include "utilities/dtrace.hpp"
60 #include "utilities/events.hpp"
61 #include "utilities/preserveException.hpp"
62
63 class CleanupObjectMonitorsHashtable: StackObj {
64 public:
65 bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) {
66 list->clear(); // clear the LinkListNodes
67 delete list; // then delete the LinkedList
68 return true;
69 }
70 };
71
72 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() {
73 CleanupObjectMonitorsHashtable cleanup;
74 _ptrs->unlink(&cleanup); // cleanup the LinkedLists
75 delete _ptrs; // then delete the hash table
76 }
77
78 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) {
79 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
80 if (list == nullptr) {
81 // Create new list and add it to the hash table:
82 list = new (ResourceObj::C_HEAP, mtThread) ObjectMonitorsHashtable::PtrList();
83 add_entry(key, list);
84 }
85 list->add(om); // Add the ObjectMonitor to the list.
86 _om_count++;
87 }
88
89 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) {
90 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
91 if (list == nullptr || list->find(om) == nullptr) {
92 return false;
93 }
94 return true;
95 }
96
97 void MonitorList::add(ObjectMonitor* m) {
98 ObjectMonitor* head;
99 do {
100 head = Atomic::load(&_head);
101 m->set_next_om(head);
102 } while (Atomic::cmpxchg(&_head, head, m) != head);
103
104 size_t count = Atomic::add(&_count, 1u);
105 if (count > max()) {
106 Atomic::inc(&_max);
107 }
108 }
109
110 size_t MonitorList::count() const {
111 return Atomic::load(&_count);
112 }
113
114 size_t MonitorList::max() const {
115 return Atomic::load(&_max);
116 }
117
118 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
119 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
120 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
121 elapsedTimer* timer_p,
122 GrowableArray<ObjectMonitor*>* unlinked_list) {
123 size_t unlinked_count = 0;
124 ObjectMonitor* prev = NULL;
125 ObjectMonitor* head = Atomic::load_acquire(&_head);
126 ObjectMonitor* m = head;
127 // The in-use list head can be NULL during the final audit.
128 while (m != NULL) {
129 if (m->is_being_async_deflated()) {
130 // Find next live ObjectMonitor.
131 ObjectMonitor* next = m;
132 do {
133 ObjectMonitor* next_next = next->next_om();
134 unlinked_count++;
135 unlinked_list->append(next);
136 next = next_next;
137 if (unlinked_count >= (size_t)MonitorDeflationMax) {
138 // Reached the max so bail out on the gathering loop.
139 break;
140 }
141 } while (next != NULL && next->is_being_async_deflated());
142 if (prev == NULL) {
143 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
144 if (prev_head != head) {
145 // Find new prev ObjectMonitor that just got inserted.
146 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
147 prev = n;
148 }
149 prev->set_next_om(next);
150 }
151 } else {
152 prev->set_next_om(next);
153 }
154 if (unlinked_count >= (size_t)MonitorDeflationMax) {
155 // Reached the max so bail out on the searching loop.
156 break;
157 }
158 m = next;
159 } else {
160 prev = m;
161 m = m->next_om();
162 }
163
164 if (current->is_Java_thread()) {
165 // A JavaThread must check for a safepoint/handshake and honor it.
166 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking",
167 "unlinked_count", unlinked_count,
168 ls, timer_p);
169 }
170 }
171 Atomic::sub(&_count, unlinked_count);
172 return unlinked_count;
173 }
174
175 MonitorList::Iterator MonitorList::iterator() const {
176 return Iterator(Atomic::load_acquire(&_head));
177 }
178
179 ObjectMonitor* MonitorList::Iterator::next() {
180 ObjectMonitor* current = _current;
181 _current = current->next_om();
182 return current;
183 }
184
185 // The "core" versions of monitor enter and exit reside in this file.
186 // The interpreter and compilers contain specialized transliterated
187 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
188 // fast_lock(...) for instance. If you make changes here, make sure to modify the
189 // interpreter, and both C1 and C2 fast-path inline locking code emission.
190 //
191 // -----------------------------------------------------------------------------
192
193 #ifdef DTRACE_ENABLED
194
195 // Only bother with this argument setup if dtrace is available
196 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
197
198 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
199 char* bytes = NULL; \
200 int len = 0; \
201 jlong jtid = SharedRuntime::get_java_tid(thread); \
202 Symbol* klassname = obj->klass()->name(); \
203 if (klassname != NULL) { \
204 bytes = (char*)klassname->bytes(); \
205 len = klassname->utf8_length(); \
206 }
207
208 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
209 { \
210 if (DTraceMonitorProbes) { \
211 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
212 HOTSPOT_MONITOR_WAIT(jtid, \
213 (uintptr_t)(monitor), bytes, len, (millis)); \
214 } \
215 }
216
217 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
218 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
219 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
220
221 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
222 { \
223 if (DTraceMonitorProbes) { \
224 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
225 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
226 (uintptr_t)(monitor), bytes, len); \
227 } \
228 }
229
230 #else // ndef DTRACE_ENABLED
231
232 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
233 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
234
235 #endif // ndef DTRACE_ENABLED
236
237 // This exists only as a workaround of dtrace bug 6254741
238 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, Thread* thr) {
239 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
240 return 0;
241 }
242
243 static const int NINFLATIONLOCKS = 256;
244 static PlatformMutex* gInflationLocks[NINFLATIONLOCKS];
245
246 void ObjectSynchronizer::initialize() {
247 for (int i = 0; i < NINFLATIONLOCKS; i++) {
248 gInflationLocks[i] = new PlatformMutex();
249 }
250 // Start the ceiling with the estimate for one thread.
251 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
252 }
253
254 MonitorList ObjectSynchronizer::_in_use_list;
255 // monitors_used_above_threshold() policy is as follows:
256 //
257 // The ratio of the current _in_use_list count to the ceiling is used
258 // to determine if we are above MonitorUsedDeflationThreshold and need
259 // to do an async monitor deflation cycle. The ceiling is increased by
260 // AvgMonitorsPerThreadEstimate when a thread is added to the system
261 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
262 // removed from the system.
263 //
264 // Note: If the _in_use_list max exceeds the ceiling, then
265 // monitors_used_above_threshold() will use the in_use_list max instead
266 // of the thread count derived ceiling because we have used more
267 // ObjectMonitors than the estimated average.
268 //
269 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
270 // no-progress async monitor deflation cycles in a row, then the ceiling
271 // is adjusted upwards by monitors_used_above_threshold().
272 //
273 // Start the ceiling with the estimate for one thread in initialize()
274 // which is called after cmd line options are processed.
275 static size_t _in_use_list_ceiling = 0;
276 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
277 bool volatile ObjectSynchronizer::_is_final_audit = false;
278 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
279 static uintx _no_progress_cnt = 0;
280
281 // =====================> Quick functions
282
283 // The quick_* forms are special fast-path variants used to improve
284 // performance. In the simplest case, a "quick_*" implementation could
285 // simply return false, in which case the caller will perform the necessary
286 // state transitions and call the slow-path form.
287 // The fast-path is designed to handle frequently arising cases in an efficient
288 // manner and is just a degenerate "optimistic" variant of the slow-path.
289 // returns true -- to indicate the call was satisfied.
290 // returns false -- to indicate the call needs the services of the slow-path.
291 // A no-loitering ordinance is in effect for code in the quick_* family
292 // operators: safepoints or indefinite blocking (blocking that might span a
293 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
294 // entry.
295 //
296 // Consider: An interesting optimization is to have the JIT recognize the
297 // following common idiom:
298 // synchronized (someobj) { .... ; notify(); }
299 // That is, we find a notify() or notifyAll() call that immediately precedes
300 // the monitorexit operation. In that case the JIT could fuse the operations
301 // into a single notifyAndExit() runtime primitive.
302
303 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
304 assert(current->thread_state() == _thread_in_Java, "invariant");
305 NoSafepointVerifier nsv;
306 if (obj == NULL) return false; // slow-path for invalid obj
307 const markWord mark = obj->mark();
308
309 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
310 // Degenerate notify
311 // stack-locked by caller so by definition the implied waitset is empty.
312 return true;
313 }
314
315 if (mark.has_monitor()) {
316 ObjectMonitor* const mon = mark.monitor();
317 assert(mon->object() == oop(obj), "invariant");
318 if (mon->owner() != current) return false; // slow-path for IMS exception
319
320 if (mon->first_waiter() != NULL) {
321 // We have one or more waiters. Since this is an inflated monitor
322 // that we own, we can transfer one or more threads from the waitset
323 // to the entrylist here and now, avoiding the slow-path.
324 if (all) {
325 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
326 } else {
327 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
328 }
329 int free_count = 0;
330 do {
331 mon->INotify(current);
332 ++free_count;
333 } while (mon->first_waiter() != NULL && all);
334 OM_PERFDATA_OP(Notifications, inc(free_count));
335 }
336 return true;
337 }
338
339 // other IMS exception states take the slow-path
340 return false;
341 }
342
343
344 // The LockNode emitted directly at the synchronization site would have
345 // been too big if it were to have included support for the cases of inflated
346 // recursive enter and exit, so they go here instead.
347 // Note that we can't safely call AsyncPrintJavaStack() from within
348 // quick_enter() as our thread state remains _in_Java.
349
350 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
351 BasicLock * lock) {
352 assert(current->thread_state() == _thread_in_Java, "invariant");
353 NoSafepointVerifier nsv;
354 if (obj == NULL) return false; // Need to throw NPE
355
356 if (obj->klass()->is_value_based()) {
357 return false;
358 }
359
360 const markWord mark = obj->mark();
361
362 if (mark.has_monitor()) {
363 ObjectMonitor* const m = mark.monitor();
364 // An async deflation or GC can race us before we manage to make
365 // the ObjectMonitor busy by setting the owner below. If we detect
366 // that race we just bail out to the slow-path here.
367 if (m->object_peek() == NULL) {
368 return false;
369 }
370 JavaThread* const owner = (JavaThread*) m->owner_raw();
371
372 // Lock contention and Transactional Lock Elision (TLE) diagnostics
373 // and observability
374 // Case: light contention possibly amenable to TLE
375 // Case: TLE inimical operations such as nested/recursive synchronization
376
377 if (owner == current) {
378 m->_recursions++;
379 current->inc_held_monitor_count();
380 return true;
381 }
382
383 // This Java Monitor is inflated so obj's header will never be
384 // displaced to this thread's BasicLock. Make the displaced header
385 // non-NULL so this BasicLock is not seen as recursive nor as
386 // being locked. We do this unconditionally so that this thread's
387 // BasicLock cannot be mis-interpreted by any stack walkers. For
388 // performance reasons, stack walkers generally first check for
389 // stack-locking in the object's header, the second check is for
390 // recursive stack-locking in the displaced header in the BasicLock,
391 // and last are the inflated Java Monitor (ObjectMonitor) checks.
392 lock->set_displaced_header(markWord::unused_mark());
393
394 if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
395 assert(m->_recursions == 0, "invariant");
396 current->inc_held_monitor_count();
397 return true;
398 }
399 }
400
401 // Note that we could inflate in quick_enter.
402 // This is likely a useful optimization
403 // Critically, in quick_enter() we must not:
404 // -- block indefinitely, or
405 // -- reach a safepoint
406
407 return false; // revert to slow-path
408 }
409
410 // Handle notifications when synchronizing on value based classes
411 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
412 frame last_frame = current->last_frame();
413 bool bcp_was_adjusted = false;
414 // Don't decrement bcp if it points to the frame's first instruction. This happens when
415 // handle_sync_on_value_based_class() is called because of a synchronized method. There
416 // is no actual monitorenter instruction in the byte code in this case.
417 if (last_frame.is_interpreted_frame() &&
418 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
419 // adjust bcp to point back to monitorenter so that we print the correct line numbers
420 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
421 bcp_was_adjusted = true;
422 }
423
424 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
425 ResourceMark rm(current);
426 stringStream ss;
427 current->print_stack_on(&ss);
428 char* base = (char*)strstr(ss.base(), "at");
429 char* newline = (char*)strchr(ss.base(), '\n');
430 if (newline != NULL) {
431 *newline = '\0';
432 }
433 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
434 } else {
435 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
436 ResourceMark rm(current);
437 Log(valuebasedclasses) vblog;
438
439 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
440 if (current->has_last_Java_frame()) {
441 LogStream info_stream(vblog.info());
442 current->print_stack_on(&info_stream);
443 } else {
444 vblog.info("Cannot find the last Java frame");
445 }
446
447 EventSyncOnValueBasedClass event;
448 if (event.should_commit()) {
449 event.set_valueBasedClass(obj->klass());
450 event.commit();
451 }
452 }
453
454 if (bcp_was_adjusted) {
455 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
456 }
457 }
458
459 static bool useHeavyMonitors() {
460 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64)
461 return UseHeavyMonitors;
462 #else
463 return false;
464 #endif
465 }
466
467 // -----------------------------------------------------------------------------
468 // Monitor Enter/Exit
469 // The interpreter and compiler assembly code tries to lock using the fast path
470 // of this algorithm. Make sure to update that code if the following function is
471 // changed. The implementation is extremely sensitive to race condition. Be careful.
472
473 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
474 if (obj->klass()->is_value_based()) {
475 handle_sync_on_value_based_class(obj, current);
476 }
477
478 current->inc_held_monitor_count();
479
480 if (!useHeavyMonitors()) {
481 markWord mark = obj->mark();
482 if (mark.is_neutral()) {
483 // Anticipate successful CAS -- the ST of the displaced mark must
484 // be visible <= the ST performed by the CAS.
485 lock->set_displaced_header(mark);
486 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
487 return;
488 }
489 // Fall through to inflate() ...
490 } else if (mark.has_locker() &&
491 current->is_lock_owned((address)mark.locker())) {
492 assert(lock != mark.locker(), "must not re-lock the same lock");
493 assert(lock != (BasicLock*)obj->mark().value(), "don't relock with same BasicLock");
494 lock->set_displaced_header(markWord::from_pointer(NULL));
495 return;
496 }
497
498 // The object header will never be displaced to this lock,
499 // so it does not matter what the value is, except that it
500 // must be non-zero to avoid looking like a re-entrant lock,
501 // and must not look locked either.
502 lock->set_displaced_header(markWord::unused_mark());
503 } else if (VerifyHeavyMonitors) {
504 guarantee(!obj->mark().has_locker(), "must not be stack-locked");
505 }
506
507 // An async deflation can race after the inflate() call and before
508 // enter() can make the ObjectMonitor busy. enter() returns false if
509 // we have lost the race to async deflation and we simply try again.
510 while (true) {
511 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
512 if (monitor->enter(current)) {
513 return;
514 }
515 }
516 }
517
518 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
519 current->dec_held_monitor_count();
520
521 if (!useHeavyMonitors()) {
522 markWord mark = object->mark();
523
524 markWord dhw = lock->displaced_header();
525 if (dhw.value() == 0) {
526 // If the displaced header is NULL, then this exit matches up with
527 // a recursive enter. No real work to do here except for diagnostics.
528 #ifndef PRODUCT
529 if (mark != markWord::INFLATING()) {
530 // Only do diagnostics if we are not racing an inflation. Simply
531 // exiting a recursive enter of a Java Monitor that is being
532 // inflated is safe; see the has_monitor() comment below.
533 assert(!mark.is_neutral(), "invariant");
534 assert(!mark.has_locker() ||
535 current->is_lock_owned((address)mark.locker()), "invariant");
536 if (mark.has_monitor()) {
537 // The BasicLock's displaced_header is marked as a recursive
538 // enter and we have an inflated Java Monitor (ObjectMonitor).
539 // This is a special case where the Java Monitor was inflated
540 // after this thread entered the stack-lock recursively. When a
541 // Java Monitor is inflated, we cannot safely walk the Java
542 // Monitor owner's stack and update the BasicLocks because a
543 // Java Monitor can be asynchronously inflated by a thread that
544 // does not own the Java Monitor.
545 ObjectMonitor* m = mark.monitor();
546 assert(m->object()->mark() == mark, "invariant");
547 assert(m->is_entered(current), "invariant");
548 }
549 }
550 #endif
551 return;
552 }
553
554 if (mark == markWord::from_pointer(lock)) {
555 // If the object is stack-locked by the current thread, try to
556 // swing the displaced header from the BasicLock back to the mark.
557 assert(dhw.is_neutral(), "invariant");
558 if (object->cas_set_mark(dhw, mark) == mark) {
559 return;
560 }
561 }
562 } else if (VerifyHeavyMonitors) {
563 guarantee(!object->mark().has_locker(), "must not be stack-locked");
564 }
565
566 // We have to take the slow-path of possible inflation and then exit.
567 // The ObjectMonitor* can't be async deflated until ownership is
568 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
569 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
570 monitor->exit(current);
571 }
572
573 // -----------------------------------------------------------------------------
574 // Class Loader support to workaround deadlocks on the class loader lock objects
575 // Also used by GC
576 // complete_exit()/reenter() are used to wait on a nested lock
577 // i.e. to give up an outer lock completely and then re-enter
578 // Used when holding nested locks - lock acquisition order: lock1 then lock2
579 // 1) complete_exit lock1 - saving recursion count
580 // 2) wait on lock2
581 // 3) when notified on lock2, unlock lock2
582 // 4) reenter lock1 with original recursion count
583 // 5) lock lock2
584 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
585 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
586 // The ObjectMonitor* can't be async deflated until ownership is
587 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
588 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
589 intx recur_count = monitor->complete_exit(current);
590 current->dec_held_monitor_count(recur_count + 1);
591 return recur_count;
592 }
593
594 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
595 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
596 // An async deflation can race after the inflate() call and before
597 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
598 // enter() returns false if we have lost the race to async deflation
599 // and we simply try again.
600 while (true) {
601 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
602 if (monitor->reenter(recursions, current)) {
603 current->inc_held_monitor_count(recursions + 1);
604 return;
605 }
606 }
607 }
608
609 // -----------------------------------------------------------------------------
610 // JNI locks on java objects
611 // NOTE: must use heavy weight monitor to handle jni monitor enter
612 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
613 if (obj->klass()->is_value_based()) {
614 handle_sync_on_value_based_class(obj, current);
615 }
616
617 // the current locking is from JNI instead of Java code
618 current->set_current_pending_monitor_is_from_java(false);
619 // An async deflation can race after the inflate() call and before
620 // enter() can make the ObjectMonitor busy. enter() returns false if
621 // we have lost the race to async deflation and we simply try again.
622 while (true) {
623 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
624 if (monitor->enter(current)) {
625 current->inc_held_monitor_count(1, true);
626 break;
627 }
628 }
629 current->set_current_pending_monitor_is_from_java(true);
630 }
631
632 // NOTE: must use heavy weight monitor to handle jni monitor exit
633 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
634 JavaThread* current = THREAD;
635
636 // The ObjectMonitor* can't be async deflated until ownership is
637 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
638 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
639 // If this thread has locked the object, exit the monitor. We
640 // intentionally do not use CHECK on check_owner because we must exit the
641 // monitor even if an exception was already pending.
642 if (monitor->check_owner(THREAD)) {
643 monitor->exit(current);
644 current->dec_held_monitor_count(1, true);
645 }
646 }
647
648 // -----------------------------------------------------------------------------
649 // Internal VM locks on java objects
650 // standard constructor, allows locking failures
651 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
652 _thread = thread;
653 _thread->check_for_valid_safepoint_state();
654 _obj = obj;
655
656 if (_obj() != NULL) {
657 ObjectSynchronizer::enter(_obj, &_lock, _thread);
658 }
659 }
660
661 ObjectLocker::~ObjectLocker() {
662 if (_obj() != NULL) {
663 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
664 }
665 }
666
667
668 // -----------------------------------------------------------------------------
669 // Wait/Notify/NotifyAll
670 // NOTE: must use heavy weight monitor to handle wait()
671 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
672 JavaThread* current = THREAD;
673 if (millis < 0) {
674 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
675 }
676 // The ObjectMonitor* can't be async deflated because the _waiters
677 // field is incremented before ownership is dropped and decremented
678 // after ownership is regained.
679 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
680
681 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
682 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
683
684 // This dummy call is in place to get around dtrace bug 6254741. Once
685 // that's fixed we can uncomment the following line, remove the call
686 // and change this function back into a "void" func.
687 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
688 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
689 return ret_code;
690 }
691
692 // No exception are possible in this case as we only use this internally when locking is
693 // correct and we have to wait until notified - so no interrupts or timeouts.
694 void ObjectSynchronizer::wait_uninterruptibly(Handle obj, JavaThread* current) {
695 // The ObjectMonitor* can't be async deflated because the _waiters
696 // field is incremented before ownership is dropped and decremented
697 // after ownership is regained.
698 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
699 monitor->wait(0 /* wait-forever */, false /* not interruptible */, current);
700 }
701
702 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
703 JavaThread* current = THREAD;
704
705 markWord mark = obj->mark();
706 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
707 // Not inflated so there can't be any waiters to notify.
708 return;
709 }
710 // The ObjectMonitor* can't be async deflated until ownership is
711 // dropped by the calling thread.
712 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
713 monitor->notify(CHECK);
714 }
715
716 // NOTE: see comment of notify()
717 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
718 JavaThread* current = THREAD;
719
720 markWord mark = obj->mark();
721 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
722 // Not inflated so there can't be any waiters to notify.
723 return;
724 }
725 // The ObjectMonitor* can't be async deflated until ownership is
726 // dropped by the calling thread.
727 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
728 monitor->notifyAll(CHECK);
729 }
730
731 // -----------------------------------------------------------------------------
732 // Hash Code handling
733
734 struct SharedGlobals {
735 char _pad_prefix[OM_CACHE_LINE_SIZE];
736 // This is a highly shared mostly-read variable.
737 // To avoid false-sharing it needs to be the sole occupant of a cache line.
738 volatile int stw_random;
739 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
740 // Hot RW variable -- Sequester to avoid false-sharing
741 volatile int hc_sequence;
742 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
743 };
744
745 static SharedGlobals GVars;
746
747 markWord ObjectSynchronizer::read_stable_mark(oop obj) {
748 markWord mark = obj->mark_acquire();
749 if (!mark.is_being_inflated()) {
750 return mark; // normal fast-path return
751 }
752
753 int its = 0;
754 for (;;) {
755 markWord mark = obj->mark_acquire();
756 if (!mark.is_being_inflated()) {
757 return mark; // normal fast-path return
758 }
759
760 // The object is being inflated by some other thread.
761 // The caller of read_stable_mark() must wait for inflation to complete.
762 // Avoid live-lock.
763
764 ++its;
765 if (its > 10000 || !os::is_MP()) {
766 if (its & 1) {
767 os::naked_yield();
768 } else {
769 // Note that the following code attenuates the livelock problem but is not
770 // a complete remedy. A more complete solution would require that the inflating
771 // thread hold the associated inflation lock. The following code simply restricts
772 // the number of spinners to at most one. We'll have N-2 threads blocked
773 // on the inflationlock, 1 thread holding the inflation lock and using
774 // a yield/park strategy, and 1 thread in the midst of inflation.
775 // A more refined approach would be to change the encoding of INFLATING
776 // to allow encapsulation of a native thread pointer. Threads waiting for
777 // inflation to complete would use CAS to push themselves onto a singly linked
778 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
779 // and calling park(). When inflation was complete the thread that accomplished inflation
780 // would detach the list and set the markword to inflated with a single CAS and
781 // then for each thread on the list, set the flag and unpark() the thread.
782
783 // Index into the lock array based on the current object address.
784 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
785 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
786 int YieldThenBlock = 0;
787 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
788 gInflationLocks[ix]->lock();
789 while (obj->mark_acquire() == markWord::INFLATING()) {
790 // Beware: naked_yield() is advisory and has almost no effect on some platforms
791 // so we periodically call current->_ParkEvent->park(1).
792 // We use a mixed spin/yield/block mechanism.
793 if ((YieldThenBlock++) >= 16) {
794 Thread::current()->_ParkEvent->park(1);
795 } else {
796 os::naked_yield();
797 }
798 }
799 gInflationLocks[ix]->unlock();
800 }
801 } else {
802 SpinPause(); // SMP-polite spinning
803 }
804 }
805 }
806
807 // Safely load a mark word from an object, even with racing stack-locking or monitor inflation.
808 // The protocol is a partial inflation-protocol: it installs INFLATING into the object's mark
809 // word in order to prevent an stack-locks or inflations from interferring (or detect such
810 // interference and retry), but then, instead of creating and installing a monitor, simply
811 // read and return the real mark word.
812 markWord ObjectSynchronizer::stable_mark(oop object) {
813 for (;;) {
814 const markWord mark = read_stable_mark(object);
815 assert(!mark.is_being_inflated(), "read_stable_mark must prevent inflating mark");
816
817 // The mark can be in one of the following states:
818 // * Inflated - just return mark from inflated monitor
819 // * Stack-locked - coerce it to inflating, and then return displaced mark
820 // * Neutral - return mark
821 // * Marked - return mark
822
823 // CASE: inflated
824 if (mark.has_monitor()) {
825 ObjectMonitor* inf = mark.monitor();
826 markWord dmw = inf->header();
827 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
828 return dmw;
829 }
830
831 // CASE: stack-locked
832 // Could be stack-locked either by this thread or by some other thread.
833 if (mark.has_locker()) {
834 BasicLock* lock = mark.locker();
835 if (Thread::current()->is_lock_owned((address)lock)) {
836 // If locked by this thread, it is safe to access the displaced header.
837 markWord dmw = lock->displaced_header();
838 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
839 return dmw;
840 }
841
842 // Otherwise, attempt to temporarily install INFLATING into the mark-word,
843 // to prevent inflation or unlocking by competing thread.
844 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
845 if (cmp != mark) {
846 continue; // Interference -- just retry
847 }
848
849 // fetch the displaced mark from the owner's stack.
850 // The owner can't die or unwind past the lock while our INFLATING
851 // object is in the mark. Furthermore the owner can't complete
852 // an unlock on the object, either.
853 markWord dmw = mark.displaced_mark_helper();
854 // Catch if the object's header is not neutral (not locked and
855 // not marked is what we care about here).
856 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
857
858 // Must preserve store ordering. The monitor state must
859 // be stable at the time of publishing the monitor address.
860 assert(object->mark() == markWord::INFLATING(), "invariant");
861 // Release semantics so that above set_object() is seen first.
862 object->release_set_mark(mark);
863
864 return dmw;
865 }
866
867 // CASE: neutral or marked (for GC)
868 // Catch if the object's header is not neutral or marked (it must not be locked).
869 assert(mark.is_neutral() || mark.is_marked(), "invariant: header=" INTPTR_FORMAT, mark.value());
870 return mark;
871 }
872 }
873
874 // hashCode() generation :
875 //
876 // Possibilities:
877 // * MD5Digest of {obj,stw_random}
878 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
879 // * A DES- or AES-style SBox[] mechanism
880 // * One of the Phi-based schemes, such as:
881 // 2654435761 = 2^32 * Phi (golden ratio)
882 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
883 // * A variation of Marsaglia's shift-xor RNG scheme.
884 // * (obj ^ stw_random) is appealing, but can result
885 // in undesirable regularity in the hashCode values of adjacent objects
886 // (objects allocated back-to-back, in particular). This could potentially
887 // result in hashtable collisions and reduced hashtable efficiency.
888 // There are simple ways to "diffuse" the middle address bits over the
889 // generated hashCode values:
890
891 static inline intptr_t get_next_hash(Thread* current, oop obj) {
892 intptr_t value = 0;
893 if (hashCode == 0) {
894 // This form uses global Park-Miller RNG.
895 // On MP system we'll have lots of RW access to a global, so the
896 // mechanism induces lots of coherency traffic.
897 value = os::random();
898 } else if (hashCode == 1) {
899 // This variation has the property of being stable (idempotent)
900 // between STW operations. This can be useful in some of the 1-0
901 // synchronization schemes.
902 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
903 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
904 } else if (hashCode == 2) {
905 value = 1; // for sensitivity testing
906 } else if (hashCode == 3) {
907 value = ++GVars.hc_sequence;
908 } else if (hashCode == 4) {
909 value = cast_from_oop<intptr_t>(obj);
910 } else {
911 // Marsaglia's xor-shift scheme with thread-specific state
912 // This is probably the best overall implementation -- we'll
913 // likely make this the default in future releases.
914 unsigned t = current->_hashStateX;
915 t ^= (t << 11);
916 current->_hashStateX = current->_hashStateY;
917 current->_hashStateY = current->_hashStateZ;
918 current->_hashStateZ = current->_hashStateW;
919 unsigned v = current->_hashStateW;
920 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
921 current->_hashStateW = v;
922 value = v;
923 }
924
925 value &= markWord::hash_mask;
926 if (value == 0) value = 0xBAD;
927 assert(value != markWord::no_hash, "invariant");
928 return value;
929 }
930
931 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
932
933 while (true) {
934 ObjectMonitor* monitor = NULL;
935 markWord temp, test;
936 intptr_t hash;
937 markWord mark = read_stable_mark(obj);
938 if (VerifyHeavyMonitors) {
939 assert(UseHeavyMonitors, "+VerifyHeavyMonitors requires +UseHeavyMonitors");
940 guarantee(!mark.has_locker(), "must not be stack locked");
941 }
942 if (mark.is_neutral()) { // if this is a normal header
943 hash = mark.hash();
944 if (hash != 0) { // if it has a hash, just return it
945 return hash;
946 }
947 hash = get_next_hash(current, obj); // get a new hash
948 temp = mark.copy_set_hash(hash); // merge the hash into header
949 // try to install the hash
950 test = obj->cas_set_mark(temp, mark);
951 if (test == mark) { // if the hash was installed, return it
952 return hash;
953 }
954 // Failed to install the hash. It could be that another thread
955 // installed the hash just before our attempt or inflation has
956 // occurred or... so we fall thru to inflate the monitor for
957 // stability and then install the hash.
958 } else if (mark.has_monitor()) {
959 monitor = mark.monitor();
960 temp = monitor->header();
961 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
962 hash = temp.hash();
963 if (hash != 0) {
964 // It has a hash.
965
966 // Separate load of dmw/header above from the loads in
967 // is_being_async_deflated().
968
969 // dmw/header and _contentions may get written by different threads.
970 // Make sure to observe them in the same order when having several observers.
971 OrderAccess::loadload_for_IRIW();
972
973 if (monitor->is_being_async_deflated()) {
974 // But we can't safely use the hash if we detect that async
975 // deflation has occurred. So we attempt to restore the
976 // header/dmw to the object's header so that we only retry
977 // once if the deflater thread happens to be slow.
978 monitor->install_displaced_markword_in_object(obj);
979 continue;
980 }
981 return hash;
982 }
983 // Fall thru so we only have one place that installs the hash in
984 // the ObjectMonitor.
985 } else if (current->is_lock_owned((address)mark.locker())) {
986 // This is a stack lock owned by the calling thread so fetch the
987 // displaced markWord from the BasicLock on the stack.
988 temp = mark.displaced_mark_helper();
989 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
990 hash = temp.hash();
991 if (hash != 0) { // if it has a hash, just return it
992 return hash;
993 }
994 // WARNING:
995 // The displaced header in the BasicLock on a thread's stack
996 // is strictly immutable. It CANNOT be changed in ANY cases.
997 // So we have to inflate the stack lock into an ObjectMonitor
998 // even if the current thread owns the lock. The BasicLock on
999 // a thread's stack can be asynchronously read by other threads
1000 // during an inflate() call so any change to that stack memory
1001 // may not propagate to other threads correctly.
1002 }
1003
1004 // Inflate the monitor to set the hash.
1005
1006 // An async deflation can race after the inflate() call and before we
1007 // can update the ObjectMonitor's header with the hash value below.
1008 monitor = inflate(current, obj, inflate_cause_hash_code);
1009 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1010 mark = monitor->header();
1011 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1012 hash = mark.hash();
1013 if (hash == 0) { // if it does not have a hash
1014 hash = get_next_hash(current, obj); // get a new hash
1015 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1016 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1017 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1018 test = markWord(v);
1019 if (test != mark) {
1020 // The attempt to update the ObjectMonitor's header/dmw field
1021 // did not work. This can happen if another thread managed to
1022 // merge in the hash just before our cmpxchg().
1023 // If we add any new usages of the header/dmw field, this code
1024 // will need to be updated.
1025 hash = test.hash();
1026 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1027 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1028 }
1029 if (monitor->is_being_async_deflated()) {
1030 // If we detect that async deflation has occurred, then we
1031 // attempt to restore the header/dmw to the object's header
1032 // so that we only retry once if the deflater thread happens
1033 // to be slow.
1034 monitor->install_displaced_markword_in_object(obj);
1035 continue;
1036 }
1037 }
1038 // We finally get the hash.
1039 return hash;
1040 }
1041 }
1042
1043 // Deprecated -- use FastHashCode() instead.
1044
1045 intptr_t ObjectSynchronizer::identity_hash_value_for(Handle obj) {
1046 return FastHashCode(Thread::current(), obj());
1047 }
1048
1049
1050 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1051 Handle h_obj) {
1052 assert(current == JavaThread::current(), "Can only be called on current thread");
1053 oop obj = h_obj();
1054
1055 markWord mark = read_stable_mark(obj);
1056
1057 // Uncontended case, header points to stack
1058 if (mark.has_locker()) {
1059 return current->is_lock_owned((address)mark.locker());
1060 }
1061 // Contended case, header points to ObjectMonitor (tagged pointer)
1062 if (mark.has_monitor()) {
1063 // The first stage of async deflation does not affect any field
1064 // used by this comparison so the ObjectMonitor* is usable here.
1065 ObjectMonitor* monitor = mark.monitor();
1066 return monitor->is_entered(current) != 0;
1067 }
1068 // Unlocked case, header in place
1069 assert(mark.is_neutral(), "sanity check");
1070 return false;
1071 }
1072
1073 // FIXME: jvmti should call this
1074 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1075 oop obj = h_obj();
1076 address owner = NULL;
1077
1078 markWord mark = read_stable_mark(obj);
1079
1080 // Uncontended case, header points to stack
1081 if (mark.has_locker()) {
1082 owner = (address) mark.locker();
1083 }
1084
1085 // Contended case, header points to ObjectMonitor (tagged pointer)
1086 else if (mark.has_monitor()) {
1087 // The first stage of async deflation does not affect any field
1088 // used by this comparison so the ObjectMonitor* is usable here.
1089 ObjectMonitor* monitor = mark.monitor();
1090 assert(monitor != NULL, "monitor should be non-null");
1091 owner = (address) monitor->owner();
1092 }
1093
1094 if (owner != NULL) {
1095 // owning_thread_from_monitor_owner() may also return NULL here
1096 return Threads::owning_thread_from_monitor_owner(t_list, owner);
1097 }
1098
1099 // Unlocked case, header in place
1100 // Cannot have assertion since this object may have been
1101 // locked by another thread when reaching here.
1102 // assert(mark.is_neutral(), "sanity check");
1103
1104 return NULL;
1105 }
1106
1107 // Visitors ...
1108
1109 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1110 // ObjectMonitors where owner is set to a stack lock address in thread.
1111 //
1112 // This version of monitors_iterate() works with the in-use monitor list.
1113 //
1114 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1115 MonitorList::Iterator iter = _in_use_list.iterator();
1116 while (iter.has_next()) {
1117 ObjectMonitor* mid = iter.next();
1118 if (mid->owner() != thread) {
1119 // Not owned by the target thread and intentionally skips when owner
1120 // is set to a stack lock address in the target thread.
1121 continue;
1122 }
1123 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1124 // Only process with closure if the object is set.
1125
1126 // monitors_iterate() is only called at a safepoint or when the
1127 // target thread is suspended or when the target thread is
1128 // operating on itself. The current closures in use today are
1129 // only interested in an owned ObjectMonitor and ownership
1130 // cannot be dropped under the calling contexts so the
1131 // ObjectMonitor cannot be async deflated.
1132 closure->do_monitor(mid);
1133 }
1134 }
1135 }
1136
1137 // This version of monitors_iterate() works with the specified linked list.
1138 //
1139 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure,
1140 ObjectMonitorsHashtable::PtrList* list,
1141 JavaThread* thread) {
1142 typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator;
1143 ObjectMonitorIterator iter(list->head());
1144 while (!iter.is_empty()) {
1145 ObjectMonitor* mid = *iter.next();
1146 // Owner set to a stack lock address in thread should never be seen here:
1147 assert(mid->owner() == thread, "must be");
1148 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1149 // Only process with closure if the object is set.
1150
1151 // monitors_iterate() is only called at a safepoint or when the
1152 // target thread is suspended or when the target thread is
1153 // operating on itself. The current closures in use today are
1154 // only interested in an owned ObjectMonitor and ownership
1155 // cannot be dropped under the calling contexts so the
1156 // ObjectMonitor cannot be async deflated.
1157 closure->do_monitor(mid);
1158 }
1159 }
1160 }
1161
1162 static bool monitors_used_above_threshold(MonitorList* list) {
1163 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1164 return false;
1165 }
1166 // Start with ceiling based on a per-thread estimate:
1167 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1168 size_t old_ceiling = ceiling;
1169 if (ceiling < list->max()) {
1170 // The max used by the system has exceeded the ceiling so use that:
1171 ceiling = list->max();
1172 }
1173 size_t monitors_used = list->count();
1174 if (monitors_used == 0) { // empty list is easy
1175 return false;
1176 }
1177 if (NoAsyncDeflationProgressMax != 0 &&
1178 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1179 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1180 size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1181 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1182 log_info(monitorinflation)("Too many deflations without progress; "
1183 "bumping in_use_list_ceiling from " SIZE_FORMAT
1184 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1185 _no_progress_cnt = 0;
1186 ceiling = new_ceiling;
1187 }
1188
1189 // Check if our monitor usage is above the threshold:
1190 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1191 return int(monitor_usage) > MonitorUsedDeflationThreshold;
1192 }
1193
1194 size_t ObjectSynchronizer::in_use_list_ceiling() {
1195 return _in_use_list_ceiling;
1196 }
1197
1198 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1199 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1200 }
1201
1202 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1203 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1204 }
1205
1206 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1207 _in_use_list_ceiling = new_value;
1208 }
1209
1210 bool ObjectSynchronizer::is_async_deflation_needed() {
1211 if (is_async_deflation_requested()) {
1212 // Async deflation request.
1213 return true;
1214 }
1215 if (AsyncDeflationInterval > 0 &&
1216 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1217 monitors_used_above_threshold(&_in_use_list)) {
1218 // It's been longer than our specified deflate interval and there
1219 // are too many monitors in use. We don't deflate more frequently
1220 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1221 // in order to not swamp the MonitorDeflationThread.
1222 return true;
1223 }
1224 return false;
1225 }
1226
1227 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1228 JavaThread* current = JavaThread::current();
1229 bool ret_code = false;
1230
1231 jlong last_time = last_async_deflation_time_ns();
1232 set_is_async_deflation_requested(true);
1233 {
1234 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1235 ml.notify_all();
1236 }
1237 const int N_CHECKS = 5;
1238 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1239 if (last_async_deflation_time_ns() > last_time) {
1240 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1241 ret_code = true;
1242 break;
1243 }
1244 {
1245 // JavaThread has to honor the blocking protocol.
1246 ThreadBlockInVM tbivm(current);
1247 os::naked_short_sleep(999); // sleep for almost 1 second
1248 }
1249 }
1250 if (!ret_code) {
1251 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1252 }
1253
1254 return ret_code;
1255 }
1256
1257 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1258 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1259 }
1260
1261 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1262 const oop obj,
1263 ObjectSynchronizer::InflateCause cause) {
1264 assert(event != NULL, "invariant");
1265 assert(event->should_commit(), "invariant");
1266 event->set_monitorClass(obj->klass());
1267 event->set_address((uintptr_t)(void*)obj);
1268 event->set_cause((u1)cause);
1269 event->commit();
1270 }
1271
1272 // Fast path code shared by multiple functions
1273 void ObjectSynchronizer::inflate_helper(oop obj) {
1274 markWord mark = obj->mark_acquire();
1275 if (mark.has_monitor()) {
1276 ObjectMonitor* monitor = mark.monitor();
1277 markWord dmw = monitor->header();
1278 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1279 return;
1280 }
1281 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1282 }
1283
1284 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1285 const InflateCause cause) {
1286 EventJavaMonitorInflate event;
1287
1288 for (;;) {
1289 const markWord mark = object->mark_acquire();
1290
1291 // The mark can be in one of the following states:
1292 // * Inflated - just return
1293 // * Stack-locked - coerce it to inflated
1294 // * INFLATING - busy wait for conversion to complete
1295 // * Neutral - aggressively inflate the object.
1296
1297 // CASE: inflated
1298 if (mark.has_monitor()) {
1299 ObjectMonitor* inf = mark.monitor();
1300 markWord dmw = inf->header();
1301 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1302 return inf;
1303 }
1304
1305 // CASE: inflation in progress - inflating over a stack-lock.
1306 // Some other thread is converting from stack-locked to inflated.
1307 // Only that thread can complete inflation -- other threads must wait.
1308 // The INFLATING value is transient.
1309 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1310 // We could always eliminate polling by parking the thread on some auxiliary list.
1311 if (mark == markWord::INFLATING()) {
1312 read_stable_mark(object);
1313 continue;
1314 }
1315
1316 // CASE: stack-locked
1317 // Could be stack-locked either by this thread or by some other thread.
1318 //
1319 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1320 // to install INFLATING into the mark word. We originally installed INFLATING,
1321 // allocated the ObjectMonitor, and then finally STed the address of the
1322 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1323 // the interval in which INFLATING appeared in the mark, thus increasing
1324 // the odds of inflation contention.
1325
1326 LogStreamHandle(Trace, monitorinflation) lsh;
1327
1328 if (mark.has_locker()) {
1329 ObjectMonitor* m = new ObjectMonitor(object);
1330 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1331 // We do this before the CAS in order to minimize the length of time
1332 // in which INFLATING appears in the mark.
1333
1334 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1335 if (cmp != mark) {
1336 delete m;
1337 continue; // Interference -- just retry
1338 }
1339
1340 // We've successfully installed INFLATING (0) into the mark-word.
1341 // This is the only case where 0 will appear in a mark-word.
1342 // Only the singular thread that successfully swings the mark-word
1343 // to 0 can perform (or more precisely, complete) inflation.
1344 //
1345 // Why do we CAS a 0 into the mark-word instead of just CASing the
1346 // mark-word from the stack-locked value directly to the new inflated state?
1347 // Consider what happens when a thread unlocks a stack-locked object.
1348 // It attempts to use CAS to swing the displaced header value from the
1349 // on-stack BasicLock back into the object header. Recall also that the
1350 // header value (hash code, etc) can reside in (a) the object header, or
1351 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1352 // header in an ObjectMonitor. The inflate() routine must copy the header
1353 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1354 // the while preserving the hashCode stability invariants. If the owner
1355 // decides to release the lock while the value is 0, the unlock will fail
1356 // and control will eventually pass from slow_exit() to inflate. The owner
1357 // will then spin, waiting for the 0 value to disappear. Put another way,
1358 // the 0 causes the owner to stall if the owner happens to try to
1359 // drop the lock (restoring the header from the BasicLock to the object)
1360 // while inflation is in-progress. This protocol avoids races that might
1361 // would otherwise permit hashCode values to change or "flicker" for an object.
1362 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1363 // 0 serves as a "BUSY" inflate-in-progress indicator.
1364
1365
1366 // fetch the displaced mark from the owner's stack.
1367 // The owner can't die or unwind past the lock while our INFLATING
1368 // object is in the mark. Furthermore the owner can't complete
1369 // an unlock on the object, either.
1370 markWord dmw = mark.displaced_mark_helper();
1371 // Catch if the object's header is not neutral (not locked and
1372 // not marked is what we care about here).
1373 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1374
1375 // Setup monitor fields to proper values -- prepare the monitor
1376 m->set_header(dmw);
1377
1378 // Optimization: if the mark.locker stack address is associated
1379 // with this thread we could simply set m->_owner = current.
1380 // Note that a thread can inflate an object
1381 // that it has stack-locked -- as might happen in wait() -- directly
1382 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1383 m->set_owner_from(NULL, mark.locker());
1384 // TODO-FIXME: assert BasicLock->dhw != 0.
1385
1386 // Must preserve store ordering. The monitor state must
1387 // be stable at the time of publishing the monitor address.
1388 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1389 // Release semantics so that above set_object() is seen first.
1390 object->release_set_mark(markWord::encode(m));
1391
1392 // Once ObjectMonitor is configured and the object is associated
1393 // with the ObjectMonitor, it is safe to allow async deflation:
1394 _in_use_list.add(m);
1395
1396 // Hopefully the performance counters are allocated on distinct cache lines
1397 // to avoid false sharing on MP systems ...
1398 OM_PERFDATA_OP(Inflations, inc());
1399 if (log_is_enabled(Trace, monitorinflation)) {
1400 ResourceMark rm(current);
1401 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1402 INTPTR_FORMAT ", type='%s'", p2i(object),
1403 object->mark().value(), object->klass()->external_name());
1404 }
1405 if (event.should_commit()) {
1406 post_monitor_inflate_event(&event, object, cause);
1407 }
1408 return m;
1409 }
1410
1411 // CASE: neutral
1412 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1413 // If we know we're inflating for entry it's better to inflate by swinging a
1414 // pre-locked ObjectMonitor pointer into the object header. A successful
1415 // CAS inflates the object *and* confers ownership to the inflating thread.
1416 // In the current implementation we use a 2-step mechanism where we CAS()
1417 // to inflate and then CAS() again to try to swing _owner from NULL to current.
1418 // An inflateTry() method that we could call from enter() would be useful.
1419
1420 // Catch if the object's header is not neutral (not locked and
1421 // not marked is what we care about here).
1422 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1423 ObjectMonitor* m = new ObjectMonitor(object);
1424 // prepare m for installation - set monitor to initial state
1425 m->set_header(mark);
1426
1427 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1428 delete m;
1429 m = NULL;
1430 continue;
1431 // interference - the markword changed - just retry.
1432 // The state-transitions are one-way, so there's no chance of
1433 // live-lock -- "Inflated" is an absorbing state.
1434 }
1435
1436 // Once the ObjectMonitor is configured and object is associated
1437 // with the ObjectMonitor, it is safe to allow async deflation:
1438 _in_use_list.add(m);
1439
1440 // Hopefully the performance counters are allocated on distinct
1441 // cache lines to avoid false sharing on MP systems ...
1442 OM_PERFDATA_OP(Inflations, inc());
1443 if (log_is_enabled(Trace, monitorinflation)) {
1444 ResourceMark rm(current);
1445 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1446 INTPTR_FORMAT ", type='%s'", p2i(object),
1447 object->mark().value(), object->klass()->external_name());
1448 }
1449 if (event.should_commit()) {
1450 post_monitor_inflate_event(&event, object, cause);
1451 }
1452 return m;
1453 }
1454 }
1455
1456 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1457 const char* cnt_name, size_t cnt,
1458 LogStream* ls, elapsedTimer* timer_p) {
1459 if (!SafepointMechanism::should_process(current)) {
1460 return;
1461 }
1462
1463 // A safepoint/handshake has started.
1464 if (ls != NULL) {
1465 timer_p->stop();
1466 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1467 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1468 op_name, cnt_name, cnt, in_use_list_ceiling(),
1469 _in_use_list.count(), _in_use_list.max());
1470 }
1471
1472 {
1473 // Honor block request.
1474 ThreadBlockInVM tbivm(current);
1475 }
1476
1477 if (ls != NULL) {
1478 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1479 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1480 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1481 timer_p->start();
1482 }
1483 }
1484
1485 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1486 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1487 //
1488 // If table != nullptr, we gather owned ObjectMonitors indexed by the
1489 // owner in the table. Please note that ObjectMonitors where the owner
1490 // is set to a stack lock address are NOT associated with the JavaThread
1491 // that holds that stack lock. All of the current consumers of
1492 // ObjectMonitorsHashtable info only care about JNI locked monitors and
1493 // those do not have the owner set to a stack lock address.
1494 //
1495 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1496 elapsedTimer* timer_p,
1497 ObjectMonitorsHashtable* table) {
1498 MonitorList::Iterator iter = _in_use_list.iterator();
1499 size_t deflated_count = 0;
1500
1501 while (iter.has_next()) {
1502 if (deflated_count >= (size_t)MonitorDeflationMax) {
1503 break;
1504 }
1505 ObjectMonitor* mid = iter.next();
1506 if (mid->deflate_monitor()) {
1507 deflated_count++;
1508 } else if (table != nullptr) {
1509 // The caller is interested in the owned ObjectMonitors. This does
1510 // not include when owner is set to a stack lock address in thread.
1511 // This also does not capture unowned ObjectMonitors that cannot be
1512 // deflated because of a waiter.
1513 void* key = mid->owner();
1514 // Since deflate_idle_monitors() and deflate_monitor_list() can be
1515 // called more than once, we have to make sure the entry has not
1516 // already been added.
1517 if (key != nullptr && !table->has_entry(key, mid)) {
1518 table->add_entry(key, mid);
1519 }
1520 }
1521
1522 if (current->is_Java_thread()) {
1523 // A JavaThread must check for a safepoint/handshake and honor it.
1524 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1525 deflated_count, ls, timer_p);
1526 }
1527 }
1528
1529 return deflated_count;
1530 }
1531
1532 class HandshakeForDeflation : public HandshakeClosure {
1533 public:
1534 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1535
1536 void do_thread(Thread* thread) {
1537 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1538 INTPTR_FORMAT, p2i(thread));
1539 }
1540 };
1541
1542 class VM_RendezvousGCThreads : public VM_Operation {
1543 public:
1544 bool evaluate_at_safepoint() const override { return false; }
1545 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1546 void doit() override {
1547 SuspendibleThreadSet::synchronize();
1548 SuspendibleThreadSet::desynchronize();
1549 };
1550 };
1551
1552 // This function is called by the MonitorDeflationThread to deflate
1553 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1554 // and VM_ThreadDump::doit() by the VMThread.
1555 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) {
1556 Thread* current = Thread::current();
1557 if (current->is_Java_thread()) {
1558 // The async deflation request has been processed.
1559 _last_async_deflation_time_ns = os::javaTimeNanos();
1560 set_is_async_deflation_requested(false);
1561 }
1562
1563 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1564 LogStreamHandle(Info, monitorinflation) lsh_info;
1565 LogStream* ls = NULL;
1566 if (log_is_enabled(Debug, monitorinflation)) {
1567 ls = &lsh_debug;
1568 } else if (log_is_enabled(Info, monitorinflation)) {
1569 ls = &lsh_info;
1570 }
1571
1572 elapsedTimer timer;
1573 if (ls != NULL) {
1574 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1575 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1576 timer.start();
1577 }
1578
1579 // Deflate some idle ObjectMonitors.
1580 size_t deflated_count = deflate_monitor_list(current, ls, &timer, table);
1581 if (deflated_count > 0 || is_final_audit()) {
1582 // There are ObjectMonitors that have been deflated or this is the
1583 // final audit and all the remaining ObjectMonitors have been
1584 // deflated, BUT the MonitorDeflationThread blocked for the final
1585 // safepoint during unlinking.
1586
1587 // Unlink deflated ObjectMonitors from the in-use list.
1588 ResourceMark rm;
1589 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1590 size_t unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer,
1591 &delete_list);
1592 if (current->is_Java_thread()) {
1593 if (ls != NULL) {
1594 timer.stop();
1595 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1596 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1597 SIZE_FORMAT ", max=" SIZE_FORMAT,
1598 unlinked_count, in_use_list_ceiling(),
1599 _in_use_list.count(), _in_use_list.max());
1600 }
1601
1602 // A JavaThread needs to handshake in order to safely free the
1603 // ObjectMonitors that were deflated in this cycle.
1604 // Also, we sync and desync GC threads around the handshake, so that they can
1605 // safely read the mark-word and look-through to the object-monitor, without
1606 // being afraid that the object-monitor is going away.
1607 HandshakeForDeflation hfd_hc;
1608 Handshake::execute(&hfd_hc);
1609 VM_RendezvousGCThreads sync_gc;
1610 VMThread::execute(&sync_gc);
1611
1612 if (ls != NULL) {
1613 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1614 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1615 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1616 timer.start();
1617 }
1618 }
1619
1620 // After the handshake, safely free the ObjectMonitors that were
1621 // deflated in this cycle.
1622 size_t deleted_count = 0;
1623 for (ObjectMonitor* monitor: delete_list) {
1624 delete monitor;
1625 deleted_count++;
1626
1627 if (current->is_Java_thread()) {
1628 // A JavaThread must check for a safepoint/handshake and honor it.
1629 chk_for_block_req(JavaThread::cast(current), "deletion", "deleted_count",
1630 deleted_count, ls, &timer);
1631 }
1632 }
1633 }
1634
1635 if (ls != NULL) {
1636 timer.stop();
1637 if (deflated_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1638 ls->print_cr("deflated " SIZE_FORMAT " monitors in %3.7f secs",
1639 deflated_count, timer.seconds());
1640 }
1641 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1642 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1643 if (table != nullptr) {
1644 ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT,
1645 table->key_count(), table->om_count());
1646 }
1647 }
1648
1649 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1650 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1651
1652 GVars.stw_random = os::random();
1653
1654 if (deflated_count != 0) {
1655 _no_progress_cnt = 0;
1656 } else {
1657 _no_progress_cnt++;
1658 }
1659
1660 return deflated_count;
1661 }
1662
1663 // Monitor cleanup on JavaThread::exit
1664
1665 // Iterate through monitor cache and attempt to release thread's monitors
1666 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1667 private:
1668 JavaThread* _thread;
1669
1670 public:
1671 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1672 void do_monitor(ObjectMonitor* mid) {
1673 intx rec = mid->complete_exit(_thread);
1674 _thread->dec_held_monitor_count(rec + 1);
1675 }
1676 };
1677
1678 // Release all inflated monitors owned by current thread. Lightweight monitors are
1679 // ignored. This is meant to be called during JNI thread detach which assumes
1680 // all remaining monitors are heavyweight. All exceptions are swallowed.
1681 // Scanning the extant monitor list can be time consuming.
1682 // A simple optimization is to add a per-thread flag that indicates a thread
1683 // called jni_monitorenter() during its lifetime.
1684 //
1685 // Instead of NoSafepointVerifier it might be cheaper to
1686 // use an idiom of the form:
1687 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1688 // <code that must not run at safepoint>
1689 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1690 // Since the tests are extremely cheap we could leave them enabled
1691 // for normal product builds.
1692
1693 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1694 assert(current == JavaThread::current(), "must be current Java thread");
1695 NoSafepointVerifier nsv;
1696 ReleaseJavaMonitorsClosure rjmc(current);
1697 ObjectSynchronizer::monitors_iterate(&rjmc, current);
1698 assert(!current->has_pending_exception(), "Should not be possible");
1699 current->clear_pending_exception();
1700 assert(current->held_monitor_count() == 0, "Should not be possible");
1701 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1702 current->clear_jni_monitor_count();
1703 }
1704
1705 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1706 switch (cause) {
1707 case inflate_cause_vm_internal: return "VM Internal";
1708 case inflate_cause_monitor_enter: return "Monitor Enter";
1709 case inflate_cause_wait: return "Monitor Wait";
1710 case inflate_cause_notify: return "Monitor Notify";
1711 case inflate_cause_hash_code: return "Monitor Hash Code";
1712 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1713 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1714 default:
1715 ShouldNotReachHere();
1716 }
1717 return "Unknown";
1718 }
1719
1720 //------------------------------------------------------------------------------
1721 // Debugging code
1722
1723 u_char* ObjectSynchronizer::get_gvars_addr() {
1724 return (u_char*)&GVars;
1725 }
1726
1727 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1728 return (u_char*)&GVars.hc_sequence;
1729 }
1730
1731 size_t ObjectSynchronizer::get_gvars_size() {
1732 return sizeof(SharedGlobals);
1733 }
1734
1735 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1736 return (u_char*)&GVars.stw_random;
1737 }
1738
1739 // Do the final audit and print of ObjectMonitor stats; must be done
1740 // by the VMThread at VM exit time.
1741 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1742 assert(Thread::current()->is_VM_thread(), "sanity check");
1743
1744 if (is_final_audit()) { // Only do the audit once.
1745 return;
1746 }
1747 set_is_final_audit();
1748
1749 if (log_is_enabled(Info, monitorinflation)) {
1750 // Do a deflation in order to reduce the in-use monitor population
1751 // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1752 // which is called by ObjectSynchronizer::audit_and_print_stats().
1753 while (ObjectSynchronizer::deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) >= (size_t)MonitorDeflationMax) {
1754 ; // empty
1755 }
1756 // The other audit_and_print_stats() call is done at the Debug
1757 // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
1758 ObjectSynchronizer::audit_and_print_stats(true /* on_exit */);
1759 }
1760 }
1761
1762 // This function can be called at a safepoint or it can be called when
1763 // we are trying to exit the VM. When we are trying to exit the VM, the
1764 // list walker functions can run in parallel with the other list
1765 // operations so spin-locking is used for safety.
1766 //
1767 // Calls to this function can be added in various places as a debugging
1768 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1769 // details logged at the Info level and 'false' for the 'on_exit'
1770 // parameter to have in-use monitor details logged at the Trace level.
1771 //
1772 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1773 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1774
1775 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1776 LogStreamHandle(Info, monitorinflation) lsh_info;
1777 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1778 LogStream* ls = NULL;
1779 if (log_is_enabled(Trace, monitorinflation)) {
1780 ls = &lsh_trace;
1781 } else if (log_is_enabled(Debug, monitorinflation)) {
1782 ls = &lsh_debug;
1783 } else if (log_is_enabled(Info, monitorinflation)) {
1784 ls = &lsh_info;
1785 }
1786 assert(ls != NULL, "sanity check");
1787
1788 int error_cnt = 0;
1789
1790 ls->print_cr("Checking in_use_list:");
1791 chk_in_use_list(ls, &error_cnt);
1792
1793 if (error_cnt == 0) {
1794 ls->print_cr("No errors found in in_use_list checks.");
1795 } else {
1796 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1797 }
1798
1799 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1800 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1801 // When exiting this log output is at the Info level. When called
1802 // at a safepoint, this log output is at the Trace level since
1803 // there can be a lot of it.
1804 log_in_use_monitor_details(ls);
1805 }
1806
1807 ls->flush();
1808
1809 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1810 }
1811
1812 // Check the in_use_list; log the results of the checks.
1813 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1814 size_t l_in_use_count = _in_use_list.count();
1815 size_t l_in_use_max = _in_use_list.max();
1816 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1817 l_in_use_max);
1818
1819 size_t ck_in_use_count = 0;
1820 MonitorList::Iterator iter = _in_use_list.iterator();
1821 while (iter.has_next()) {
1822 ObjectMonitor* mid = iter.next();
1823 chk_in_use_entry(mid, out, error_cnt_p);
1824 ck_in_use_count++;
1825 }
1826
1827 if (l_in_use_count == ck_in_use_count) {
1828 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1829 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1830 } else {
1831 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1832 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1833 ck_in_use_count);
1834 }
1835
1836 size_t ck_in_use_max = _in_use_list.max();
1837 if (l_in_use_max == ck_in_use_max) {
1838 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1839 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1840 } else {
1841 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1842 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1843 }
1844 }
1845
1846 // Check an in-use monitor entry; log any errors.
1847 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1848 int* error_cnt_p) {
1849 if (n->owner_is_DEFLATER_MARKER()) {
1850 // This should not happen, but if it does, it is not fatal.
1851 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1852 "deflated.", p2i(n));
1853 return;
1854 }
1855 if (n->header().value() == 0) {
1856 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1857 "have non-NULL _header field.", p2i(n));
1858 *error_cnt_p = *error_cnt_p + 1;
1859 }
1860 const oop obj = n->object_peek();
1861 if (obj != NULL) {
1862 const markWord mark = obj->mark();
1863 if (!mark.has_monitor()) {
1864 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1865 "object does not think it has a monitor: obj="
1866 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1867 p2i(obj), mark.value());
1868 *error_cnt_p = *error_cnt_p + 1;
1869 }
1870 ObjectMonitor* const obj_mon = mark.monitor();
1871 if (n != obj_mon) {
1872 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1873 "object does not refer to the same monitor: obj="
1874 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1875 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1876 *error_cnt_p = *error_cnt_p + 1;
1877 }
1878 }
1879 }
1880
1881 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1882 // flags indicate why the entry is in-use, 'object' and 'object type'
1883 // indicate the associated object and its type.
1884 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
1885 stringStream ss;
1886 if (_in_use_list.count() > 0) {
1887 out->print_cr("In-use monitor info:");
1888 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1889 out->print_cr("%18s %s %18s %18s",
1890 "monitor", "BHL", "object", "object type");
1891 out->print_cr("================== === ================== ==================");
1892 MonitorList::Iterator iter = _in_use_list.iterator();
1893 while (iter.has_next()) {
1894 ObjectMonitor* mid = iter.next();
1895 const oop obj = mid->object_peek();
1896 const markWord mark = mid->header();
1897 ResourceMark rm;
1898 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid),
1899 mid->is_busy(), mark.hash() != 0, mid->owner() != NULL,
1900 p2i(obj), obj == NULL ? "" : obj->klass()->external_name());
1901 if (mid->is_busy()) {
1902 out->print(" (%s)", mid->is_busy_to_string(&ss));
1903 ss.reset();
1904 }
1905 out->cr();
1906 }
1907 }
1908
1909 out->flush();
1910 }