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/lockStack.inline.hpp"
44 #include "runtime/mutexLocker.hpp"
45 #include "runtime/objectMonitor.hpp"
46 #include "runtime/objectMonitor.inline.hpp"
47 #include "runtime/os.inline.hpp"
48 #include "runtime/osThread.hpp"
49 #include "runtime/perfData.hpp"
50 #include "runtime/safepointMechanism.inline.hpp"
51 #include "runtime/safepointVerifiers.hpp"
52 #include "runtime/sharedRuntime.hpp"
53 #include "runtime/stubRoutines.hpp"
54 #include "runtime/synchronizer.hpp"
55 #include "runtime/threads.hpp"
56 #include "runtime/timer.hpp"
57 #include "runtime/vframe.hpp"
58 #include "runtime/vmThread.hpp"
59 #include "utilities/align.hpp"
60 #include "utilities/dtrace.hpp"
61 #include "utilities/events.hpp"
62 #include "utilities/linkedlist.hpp"
63 #include "utilities/preserveException.hpp"
64
65 class ObjectMonitorsHashtable::PtrList :
66 public LinkedListImpl<ObjectMonitor*,
67 AnyObj::C_HEAP, mtThread,
68 AllocFailStrategy::RETURN_NULL> {};
69
70 class CleanupObjectMonitorsHashtable: StackObj {
71 public:
72 bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) {
73 list->clear(); // clear the LinkListNodes
74 delete list; // then delete the LinkedList
75 return true;
76 }
77 };
78
79 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() {
80 CleanupObjectMonitorsHashtable cleanup;
81 _ptrs->unlink(&cleanup); // cleanup the LinkedLists
82 delete _ptrs; // then delete the hash table
83 }
84
85 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) {
86 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
87 if (list == nullptr) {
88 // Create new list and add it to the hash table:
89 list = new (mtThread) ObjectMonitorsHashtable::PtrList;
90 add_entry(key, list);
91 }
92 list->add(om); // Add the ObjectMonitor to the list.
93 _om_count++;
94 }
95
96 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) {
97 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
98 if (list == nullptr || list->find(om) == nullptr) {
99 return false;
100 }
101 return true;
102 }
103
104 void MonitorList::add(ObjectMonitor* m) {
105 ObjectMonitor* head;
106 do {
107 head = Atomic::load(&_head);
108 m->set_next_om(head);
109 } while (Atomic::cmpxchg(&_head, head, m) != head);
110
111 size_t count = Atomic::add(&_count, 1u);
112 if (count > max()) {
113 Atomic::inc(&_max);
114 }
115 }
116
117 size_t MonitorList::count() const {
118 return Atomic::load(&_count);
119 }
120
121 size_t MonitorList::max() const {
122 return Atomic::load(&_max);
123 }
124
125 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
126 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
127 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
128 elapsedTimer* timer_p,
129 GrowableArray<ObjectMonitor*>* unlinked_list) {
130 size_t unlinked_count = 0;
131 ObjectMonitor* prev = NULL;
132 ObjectMonitor* head = Atomic::load_acquire(&_head);
133 ObjectMonitor* m = head;
134 // The in-use list head can be NULL during the final audit.
135 while (m != NULL) {
136 if (m->is_being_async_deflated()) {
137 // Find next live ObjectMonitor.
138 ObjectMonitor* next = m;
139 do {
140 ObjectMonitor* next_next = next->next_om();
141 unlinked_count++;
142 unlinked_list->append(next);
143 next = next_next;
144 if (unlinked_count >= (size_t)MonitorDeflationMax) {
145 // Reached the max so bail out on the gathering loop.
146 break;
147 }
148 } while (next != NULL && next->is_being_async_deflated());
149 if (prev == NULL) {
150 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
151 if (prev_head != head) {
152 // Find new prev ObjectMonitor that just got inserted.
153 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
154 prev = n;
155 }
156 prev->set_next_om(next);
157 }
158 } else {
159 prev->set_next_om(next);
160 }
161 if (unlinked_count >= (size_t)MonitorDeflationMax) {
162 // Reached the max so bail out on the searching loop.
163 break;
164 }
165 m = next;
166 } else {
167 prev = m;
168 m = m->next_om();
169 }
170
171 if (current->is_Java_thread()) {
172 // A JavaThread must check for a safepoint/handshake and honor it.
173 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking",
174 "unlinked_count", unlinked_count,
175 ls, timer_p);
176 }
177 }
178 Atomic::sub(&_count, unlinked_count);
179 return unlinked_count;
180 }
181
182 MonitorList::Iterator MonitorList::iterator() const {
183 return Iterator(Atomic::load_acquire(&_head));
184 }
185
186 ObjectMonitor* MonitorList::Iterator::next() {
187 ObjectMonitor* current = _current;
188 _current = current->next_om();
189 return current;
190 }
191
192 // The "core" versions of monitor enter and exit reside in this file.
193 // The interpreter and compilers contain specialized transliterated
194 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
195 // fast_lock(...) for instance. If you make changes here, make sure to modify the
196 // interpreter, and both C1 and C2 fast-path inline locking code emission.
197 //
198 // -----------------------------------------------------------------------------
199
200 #ifdef DTRACE_ENABLED
201
202 // Only bother with this argument setup if dtrace is available
203 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
204
205 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
206 char* bytes = NULL; \
207 int len = 0; \
208 jlong jtid = SharedRuntime::get_java_tid(thread); \
209 Symbol* klassname = obj->klass()->name(); \
210 if (klassname != NULL) { \
211 bytes = (char*)klassname->bytes(); \
212 len = klassname->utf8_length(); \
213 }
214
215 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
216 { \
217 if (DTraceMonitorProbes) { \
218 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
219 HOTSPOT_MONITOR_WAIT(jtid, \
220 (uintptr_t)(monitor), bytes, len, (millis)); \
221 } \
222 }
223
224 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
225 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
226 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
227
228 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
229 { \
230 if (DTraceMonitorProbes) { \
231 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
232 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
233 (uintptr_t)(monitor), bytes, len); \
234 } \
235 }
236
237 #else // ndef DTRACE_ENABLED
238
239 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
240 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
241
242 #endif // ndef DTRACE_ENABLED
243
244 // This exists only as a workaround of dtrace bug 6254741
245 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
246 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
247 return 0;
248 }
249
250 static const int NINFLATIONLOCKS = 256;
251 static PlatformMutex* gInflationLocks[NINFLATIONLOCKS];
252
253 void ObjectSynchronizer::initialize() {
254 for (int i = 0; i < NINFLATIONLOCKS; i++) {
255 gInflationLocks[i] = new PlatformMutex();
256 }
257 // Start the ceiling with the estimate for one thread.
258 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
259 }
260
261 MonitorList ObjectSynchronizer::_in_use_list;
262 // monitors_used_above_threshold() policy is as follows:
263 //
264 // The ratio of the current _in_use_list count to the ceiling is used
265 // to determine if we are above MonitorUsedDeflationThreshold and need
266 // to do an async monitor deflation cycle. The ceiling is increased by
267 // AvgMonitorsPerThreadEstimate when a thread is added to the system
268 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
269 // removed from the system.
270 //
271 // Note: If the _in_use_list max exceeds the ceiling, then
272 // monitors_used_above_threshold() will use the in_use_list max instead
273 // of the thread count derived ceiling because we have used more
274 // ObjectMonitors than the estimated average.
275 //
276 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
277 // no-progress async monitor deflation cycles in a row, then the ceiling
278 // is adjusted upwards by monitors_used_above_threshold().
279 //
280 // Start the ceiling with the estimate for one thread in initialize()
281 // which is called after cmd line options are processed.
282 static size_t _in_use_list_ceiling = 0;
283 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
284 bool volatile ObjectSynchronizer::_is_final_audit = false;
285 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
286 static uintx _no_progress_cnt = 0;
287
288 // =====================> Quick functions
289
290 // The quick_* forms are special fast-path variants used to improve
291 // performance. In the simplest case, a "quick_*" implementation could
292 // simply return false, in which case the caller will perform the necessary
293 // state transitions and call the slow-path form.
294 // The fast-path is designed to handle frequently arising cases in an efficient
295 // manner and is just a degenerate "optimistic" variant of the slow-path.
296 // returns true -- to indicate the call was satisfied.
297 // returns false -- to indicate the call needs the services of the slow-path.
298 // A no-loitering ordinance is in effect for code in the quick_* family
299 // operators: safepoints or indefinite blocking (blocking that might span a
300 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
301 // entry.
302 //
303 // Consider: An interesting optimization is to have the JIT recognize the
304 // following common idiom:
305 // synchronized (someobj) { .... ; notify(); }
306 // That is, we find a notify() or notifyAll() call that immediately precedes
307 // the monitorexit operation. In that case the JIT could fuse the operations
308 // into a single notifyAndExit() runtime primitive.
309
310 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
311 assert(current->thread_state() == _thread_in_Java, "invariant");
312 NoSafepointVerifier nsv;
313 if (obj == NULL) return false; // slow-path for invalid obj
314 const markWord mark = obj->mark();
315
316 if ((mark.is_fast_locked() && current->lock_stack().contains(oop(obj))) ||
317 (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) {
318 // Degenerate notify
319 // stack-locked by caller so by definition the implied waitset is empty.
320 return true;
321 }
322
323 if (mark.has_monitor()) {
324 ObjectMonitor* const mon = mark.monitor();
325 assert(mon->object() == oop(obj), "invariant");
326 if (mon->owner() != current) return false; // slow-path for IMS exception
327
328 if (mon->first_waiter() != NULL) {
329 // We have one or more waiters. Since this is an inflated monitor
330 // that we own, we can transfer one or more threads from the waitset
331 // to the entrylist here and now, avoiding the slow-path.
332 if (all) {
333 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
334 } else {
335 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
336 }
337 int free_count = 0;
338 do {
339 mon->INotify(current);
340 ++free_count;
341 } while (mon->first_waiter() != NULL && all);
342 OM_PERFDATA_OP(Notifications, inc(free_count));
343 }
344 return true;
345 }
346
347 // other IMS exception states take the slow-path
348 return false;
349 }
350
351
352 // The LockNode emitted directly at the synchronization site would have
353 // been too big if it were to have included support for the cases of inflated
354 // recursive enter and exit, so they go here instead.
355 // Note that we can't safely call AsyncPrintJavaStack() from within
356 // quick_enter() as our thread state remains _in_Java.
357
358 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
359 BasicLock * lock) {
360 assert(current->thread_state() == _thread_in_Java, "invariant");
361 NoSafepointVerifier nsv;
362 if (obj == NULL) return false; // Need to throw NPE
363
364 if (obj->klass()->is_value_based()) {
365 return false;
366 }
367
368 const markWord mark = obj->mark();
369
370 if (mark.has_monitor()) {
371 ObjectMonitor* const m = mark.monitor();
372 // An async deflation or GC can race us before we manage to make
373 // the ObjectMonitor busy by setting the owner below. If we detect
374 // that race we just bail out to the slow-path here.
375 if (m->object_peek() == NULL) {
376 return false;
377 }
378 JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
379
380 // Lock contention and Transactional Lock Elision (TLE) diagnostics
381 // and observability
382 // Case: light contention possibly amenable to TLE
383 // Case: TLE inimical operations such as nested/recursive synchronization
384
385 if (owner == current) {
386 m->_recursions++;
387 current->inc_held_monitor_count();
388 return true;
389 }
390
391 // This Java Monitor is inflated so obj's header will never be
392 // displaced to this thread's BasicLock. Make the displaced header
393 // non-NULL so this BasicLock is not seen as recursive nor as
394 // being locked. We do this unconditionally so that this thread's
395 // BasicLock cannot be mis-interpreted by any stack walkers. For
396 // performance reasons, stack walkers generally first check for
397 // stack-locking in the object's header, the second check is for
398 // recursive stack-locking in the displaced header in the BasicLock,
399 // and last are the inflated Java Monitor (ObjectMonitor) checks.
400 if (!UseFastLocking) {
401 lock->set_displaced_header(markWord::unused_mark());
402 }
403
404 if (owner == NULL && m->try_set_owner_from(NULL, current) == NULL) {
405 assert(m->_recursions == 0, "invariant");
406 current->inc_held_monitor_count();
407 return true;
408 }
409 }
410
411 // Note that we could inflate in quick_enter.
412 // This is likely a useful optimization
413 // Critically, in quick_enter() we must not:
414 // -- block indefinitely, or
415 // -- reach a safepoint
416
417 return false; // revert to slow-path
418 }
419
420 // Handle notifications when synchronizing on value based classes
421 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
422 frame last_frame = current->last_frame();
423 bool bcp_was_adjusted = false;
424 // Don't decrement bcp if it points to the frame's first instruction. This happens when
425 // handle_sync_on_value_based_class() is called because of a synchronized method. There
426 // is no actual monitorenter instruction in the byte code in this case.
427 if (last_frame.is_interpreted_frame() &&
428 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
429 // adjust bcp to point back to monitorenter so that we print the correct line numbers
430 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
431 bcp_was_adjusted = true;
432 }
433
434 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
435 ResourceMark rm(current);
436 stringStream ss;
437 current->print_active_stack_on(&ss);
438 char* base = (char*)strstr(ss.base(), "at");
439 char* newline = (char*)strchr(ss.base(), '\n');
440 if (newline != NULL) {
441 *newline = '\0';
442 }
443 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
444 } else {
445 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
446 ResourceMark rm(current);
447 Log(valuebasedclasses) vblog;
448
449 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
450 if (current->has_last_Java_frame()) {
451 LogStream info_stream(vblog.info());
452 current->print_active_stack_on(&info_stream);
453 } else {
454 vblog.info("Cannot find the last Java frame");
455 }
456
457 EventSyncOnValueBasedClass event;
458 if (event.should_commit()) {
459 event.set_valueBasedClass(obj->klass());
460 event.commit();
461 }
462 }
463
464 if (bcp_was_adjusted) {
465 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
466 }
467 }
468
469 static bool useHeavyMonitors() {
470 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64)
471 return UseHeavyMonitors;
472 #else
473 return false;
474 #endif
475 }
476
477 // -----------------------------------------------------------------------------
478 // Monitor Enter/Exit
479 // The interpreter and compiler assembly code tries to lock using the fast path
480 // of this algorithm. Make sure to update that code if the following function is
481 // changed. The implementation is extremely sensitive to race condition. Be careful.
482
483 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
484 if (obj->klass()->is_value_based()) {
485 handle_sync_on_value_based_class(obj, current);
486 }
487
488 current->inc_held_monitor_count();
489
490 if (!useHeavyMonitors()) {
491 if (UseFastLocking) {
492 LockStack& lock_stack = current->lock_stack();
493
494 markWord header = obj()->mark_acquire();
495 while (true) {
496 if (header.is_neutral()) {
497 assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
498 // Try to swing into 'fast-locked' state without inflating.
499 markWord locked_header = header.set_fast_locked();
500 markWord witness = obj()->cas_set_mark(locked_header, header);
501 if (witness == header) {
502 // Successfully fast-locked, push object to lock-stack and return.
503 lock_stack.push(obj());
504 return;
505 }
506 // Otherwise retry.
507 header = witness;
508 } else {
509 // Fall-through to inflate-enter.
510 break;
511 }
512 }
513 } else {
514 markWord mark = obj->mark();
515 if (mark.is_neutral()) {
516 // Anticipate successful CAS -- the ST of the displaced mark must
517 // be visible <= the ST performed by the CAS.
518 lock->set_displaced_header(mark);
519 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
520 return;
521 }
522 // Fall through to inflate() ...
523 } else if (mark.has_locker() &&
524 current->is_lock_owned((address) mark.locker())) {
525 assert(lock != mark.locker(), "must not re-lock the same lock");
526 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
527 lock->set_displaced_header(markWord::from_pointer(NULL));
528 return;
529 }
530
531 // The object header will never be displaced to this lock,
532 // so it does not matter what the value is, except that it
533 // must be non-zero to avoid looking like a re-entrant lock,
534 // and must not look locked either.
535 lock->set_displaced_header(markWord::unused_mark());
536 }
537 } else if (VerifyHeavyMonitors) {
538 guarantee(!obj->mark().has_locker() && !obj->mark().is_fast_locked(), "must not be stack-locked");
539 }
540
541 // An async deflation can race after the inflate() call and before
542 // enter() can make the ObjectMonitor busy. enter() returns false if
543 // we have lost the race to async deflation and we simply try again.
544 while (true) {
545 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
546 if (monitor->enter(current)) {
547 return;
548 }
549 }
550 }
551
552 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
553 current->dec_held_monitor_count();
554
555 if (!useHeavyMonitors()) {
556 markWord mark = object->mark();
557 if (UseFastLocking) {
558 if (mark.is_fast_locked()) {
559 markWord unlocked_header = mark.set_unlocked();
560 markWord witness = object->cas_set_mark(unlocked_header, mark);
561 if (witness != mark) {
562 // Another thread beat us, it can only have installed an anonymously locked monitor at this point.
563 // Fetch that monitor, set owner correctly to this thread, and exit it (allowing waiting threads to enter).
564 assert(witness.has_monitor(), "must have monitor");
565 ObjectMonitor* monitor = witness.monitor();
566 assert(monitor->is_owner_anonymous(), "must be anonymous owner");
567 monitor->set_owner_from_anonymous(current);
568 monitor->exit(current);
569 }
570 LockStack& lock_stack = current->lock_stack();
571 lock_stack.remove(object);
572 return;
573 }
574 } else {
575 markWord dhw = lock->displaced_header();
576 if (dhw.value() == 0) {
577 // If the displaced header is NULL, then this exit matches up with
578 // a recursive enter. No real work to do here except for diagnostics.
579 #ifndef PRODUCT
580 if (mark != markWord::INFLATING()) {
581 // Only do diagnostics if we are not racing an inflation. Simply
582 // exiting a recursive enter of a Java Monitor that is being
583 // inflated is safe; see the has_monitor() comment below.
584 assert(!mark.is_neutral(), "invariant");
585 assert(!mark.has_locker() ||
586 current->is_lock_owned((address)mark.locker()), "invariant");
587 if (mark.has_monitor()) {
588 // The BasicLock's displaced_header is marked as a recursive
589 // enter and we have an inflated Java Monitor (ObjectMonitor).
590 // This is a special case where the Java Monitor was inflated
591 // after this thread entered the stack-lock recursively. When a
592 // Java Monitor is inflated, we cannot safely walk the Java
593 // Monitor owner's stack and update the BasicLocks because a
594 // Java Monitor can be asynchronously inflated by a thread that
595 // does not own the Java Monitor.
596 ObjectMonitor* m = mark.monitor();
597 assert(m->object()->mark() == mark, "invariant");
598 assert(m->is_entered(current), "invariant");
599 }
600 }
601 #endif
602 return;
603 }
604
605 if (mark == markWord::from_pointer(lock)) {
606 // If the object is stack-locked by the current thread, try to
607 // swing the displaced header from the BasicLock back to the mark.
608 assert(dhw.is_neutral(), "invariant");
609 if (object->cas_set_mark(dhw, mark) == mark) {
610 return;
611 }
612 }
613 }
614 } else if (VerifyHeavyMonitors) {
615 guarantee(!object->mark().has_locker(), "must not be stack-locked");
616 }
617
618 // We have to take the slow-path of possible inflation and then exit.
619 // The ObjectMonitor* can't be async deflated until ownership is
620 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
621 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
622 if (UseFastLocking && monitor->is_owner_anonymous()) {
623 // It must be us. Pop lock object from lock stack.
624 LockStack& lock_stack = current->lock_stack();
625 oop popped = lock_stack.pop();
626 assert(popped == object, "must be owned by this thread");
627 monitor->set_owner_from_anonymous(current);
628 }
629 monitor->exit(current);
630 }
631
632 // -----------------------------------------------------------------------------
633 // Class Loader support to workaround deadlocks on the class loader lock objects
634 // Also used by GC
635 // complete_exit()/reenter() are used to wait on a nested lock
636 // i.e. to give up an outer lock completely and then re-enter
637 // Used when holding nested locks - lock acquisition order: lock1 then lock2
638 // 1) complete_exit lock1 - saving recursion count
639 // 2) wait on lock2
640 // 3) when notified on lock2, unlock lock2
641 // 4) reenter lock1 with original recursion count
642 // 5) lock lock2
643 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
644 intx ObjectSynchronizer::complete_exit(Handle obj, JavaThread* current) {
645 // The ObjectMonitor* can't be async deflated until ownership is
646 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
647 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
648 intx recur_count = monitor->complete_exit(current);
649 current->dec_held_monitor_count(recur_count + 1);
650 return recur_count;
651 }
652
653 // NOTE: must use heavy weight monitor to handle complete_exit/reenter()
654 void ObjectSynchronizer::reenter(Handle obj, intx recursions, JavaThread* current) {
655 // An async deflation can race after the inflate() call and before
656 // reenter() -> enter() can make the ObjectMonitor busy. reenter() ->
657 // enter() returns false if we have lost the race to async deflation
658 // and we simply try again.
659 while (true) {
660 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_vm_internal);
661 if (monitor->reenter(recursions, current)) {
662 current->inc_held_monitor_count(recursions + 1);
663 return;
664 }
665 }
666 }
667
668 // -----------------------------------------------------------------------------
669 // JNI locks on java objects
670 // NOTE: must use heavy weight monitor to handle jni monitor enter
671 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
672 if (obj->klass()->is_value_based()) {
673 handle_sync_on_value_based_class(obj, current);
674 }
675
676 // the current locking is from JNI instead of Java code
677 current->set_current_pending_monitor_is_from_java(false);
678 // An async deflation can race after the inflate() call and before
679 // enter() can make the ObjectMonitor busy. enter() returns false if
680 // we have lost the race to async deflation and we simply try again.
681 while (true) {
682 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
683 if (monitor->enter(current)) {
684 current->inc_held_monitor_count(1, true);
685 break;
686 }
687 }
688 current->set_current_pending_monitor_is_from_java(true);
689 }
690
691 // NOTE: must use heavy weight monitor to handle jni monitor exit
692 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
693 JavaThread* current = THREAD;
694
695 // The ObjectMonitor* can't be async deflated until ownership is
696 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
697 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
698 // If this thread has locked the object, exit the monitor. We
699 // intentionally do not use CHECK on check_owner because we must exit the
700 // monitor even if an exception was already pending.
701 if (monitor->check_owner(THREAD)) {
702 monitor->exit(current);
703 current->dec_held_monitor_count(1, true);
704 }
705 }
706
707 // -----------------------------------------------------------------------------
708 // Internal VM locks on java objects
709 // standard constructor, allows locking failures
710 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
711 _thread = thread;
712 _thread->check_for_valid_safepoint_state();
713 _obj = obj;
714
715 if (_obj() != NULL) {
716 ObjectSynchronizer::enter(_obj, &_lock, _thread);
717 }
718 }
719
720 ObjectLocker::~ObjectLocker() {
721 if (_obj() != NULL) {
722 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
723 }
724 }
725
726
727 // -----------------------------------------------------------------------------
728 // Wait/Notify/NotifyAll
729 // NOTE: must use heavy weight monitor to handle wait()
730 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
731 JavaThread* current = THREAD;
732 if (millis < 0) {
733 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
734 }
735 // The ObjectMonitor* can't be async deflated because the _waiters
736 // field is incremented before ownership is dropped and decremented
737 // after ownership is regained.
738 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
739
740 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
741 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
742
743 // This dummy call is in place to get around dtrace bug 6254741. Once
744 // that's fixed we can uncomment the following line, remove the call
745 // and change this function back into a "void" func.
746 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
747 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
748 return ret_code;
749 }
750
751 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
752 JavaThread* current = THREAD;
753
754 markWord mark = obj->mark();
755 if ((mark.is_fast_locked() && current->lock_stack().contains(obj())) ||
756 (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) {
757 // Not inflated so there can't be any waiters to notify.
758 return;
759 }
760 // The ObjectMonitor* can't be async deflated until ownership is
761 // dropped by the calling thread.
762 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
763 monitor->notify(CHECK);
764 }
765
766 // NOTE: see comment of notify()
767 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
768 JavaThread* current = THREAD;
769
770 markWord mark = obj->mark();
771 if ((mark.is_fast_locked() && current->lock_stack().contains(obj())) ||
772 (mark.has_locker() && current->is_lock_owned((address)mark.locker()))) {
773 // Not inflated so there can't be any waiters to notify.
774 return;
775 }
776 // The ObjectMonitor* can't be async deflated until ownership is
777 // dropped by the calling thread.
778 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
779 monitor->notifyAll(CHECK);
780 }
781
782 // -----------------------------------------------------------------------------
783 // Hash Code handling
784
785 struct SharedGlobals {
786 char _pad_prefix[OM_CACHE_LINE_SIZE];
787 // This is a highly shared mostly-read variable.
788 // To avoid false-sharing it needs to be the sole occupant of a cache line.
789 volatile int stw_random;
790 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
791 // Hot RW variable -- Sequester to avoid false-sharing
792 volatile int hc_sequence;
793 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
794 };
795
796 static SharedGlobals GVars;
797
798 static markWord read_stable_mark(oop obj) {
799 markWord mark = obj->mark_acquire();
800 if (!mark.is_being_inflated() || UseFastLocking) {
801 return mark; // normal fast-path return
802 }
803
804 int its = 0;
805 for (;;) {
806 markWord mark = obj->mark_acquire();
807 if (!mark.is_being_inflated()) {
808 return mark; // normal fast-path return
809 }
810
811 // The object is being inflated by some other thread.
812 // The caller of read_stable_mark() must wait for inflation to complete.
813 // Avoid live-lock.
814
815 ++its;
816 if (its > 10000 || !os::is_MP()) {
817 if (its & 1) {
818 os::naked_yield();
819 } else {
820 // Note that the following code attenuates the livelock problem but is not
821 // a complete remedy. A more complete solution would require that the inflating
822 // thread hold the associated inflation lock. The following code simply restricts
823 // the number of spinners to at most one. We'll have N-2 threads blocked
824 // on the inflationlock, 1 thread holding the inflation lock and using
825 // a yield/park strategy, and 1 thread in the midst of inflation.
826 // A more refined approach would be to change the encoding of INFLATING
827 // to allow encapsulation of a native thread pointer. Threads waiting for
828 // inflation to complete would use CAS to push themselves onto a singly linked
829 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
830 // and calling park(). When inflation was complete the thread that accomplished inflation
831 // would detach the list and set the markword to inflated with a single CAS and
832 // then for each thread on the list, set the flag and unpark() the thread.
833
834 // Index into the lock array based on the current object address.
835 static_assert(is_power_of_2(NINFLATIONLOCKS), "must be");
836 int ix = (cast_from_oop<intptr_t>(obj) >> 5) & (NINFLATIONLOCKS-1);
837 int YieldThenBlock = 0;
838 assert(ix >= 0 && ix < NINFLATIONLOCKS, "invariant");
839 gInflationLocks[ix]->lock();
840 while (obj->mark_acquire() == markWord::INFLATING()) {
841 // Beware: naked_yield() is advisory and has almost no effect on some platforms
842 // so we periodically call current->_ParkEvent->park(1).
843 // We use a mixed spin/yield/block mechanism.
844 if ((YieldThenBlock++) >= 16) {
845 Thread::current()->_ParkEvent->park(1);
846 } else {
847 os::naked_yield();
848 }
849 }
850 gInflationLocks[ix]->unlock();
851 }
852 } else {
853 SpinPause(); // SMP-polite spinning
854 }
855 }
856 }
857
858 // hashCode() generation :
859 //
860 // Possibilities:
861 // * MD5Digest of {obj,stw_random}
862 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
863 // * A DES- or AES-style SBox[] mechanism
864 // * One of the Phi-based schemes, such as:
865 // 2654435761 = 2^32 * Phi (golden ratio)
866 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
867 // * A variation of Marsaglia's shift-xor RNG scheme.
868 // * (obj ^ stw_random) is appealing, but can result
869 // in undesirable regularity in the hashCode values of adjacent objects
870 // (objects allocated back-to-back, in particular). This could potentially
871 // result in hashtable collisions and reduced hashtable efficiency.
872 // There are simple ways to "diffuse" the middle address bits over the
873 // generated hashCode values:
874
875 static inline intptr_t get_next_hash(Thread* current, oop obj) {
876 intptr_t value = 0;
877 if (hashCode == 0) {
878 // This form uses global Park-Miller RNG.
879 // On MP system we'll have lots of RW access to a global, so the
880 // mechanism induces lots of coherency traffic.
881 value = os::random();
882 } else if (hashCode == 1) {
883 // This variation has the property of being stable (idempotent)
884 // between STW operations. This can be useful in some of the 1-0
885 // synchronization schemes.
886 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
887 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
888 } else if (hashCode == 2) {
889 value = 1; // for sensitivity testing
890 } else if (hashCode == 3) {
891 value = ++GVars.hc_sequence;
892 } else if (hashCode == 4) {
893 value = cast_from_oop<intptr_t>(obj);
894 } else {
895 // Marsaglia's xor-shift scheme with thread-specific state
896 // This is probably the best overall implementation -- we'll
897 // likely make this the default in future releases.
898 unsigned t = current->_hashStateX;
899 t ^= (t << 11);
900 current->_hashStateX = current->_hashStateY;
901 current->_hashStateY = current->_hashStateZ;
902 current->_hashStateZ = current->_hashStateW;
903 unsigned v = current->_hashStateW;
904 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
905 current->_hashStateW = v;
906 value = v;
907 }
908
909 value &= markWord::hash_mask;
910 if (value == 0) value = 0xBAD;
911 assert(value != markWord::no_hash, "invariant");
912 return value;
913 }
914
915 static bool is_lock_owned(Thread* thread, oop obj) {
916 assert(UseFastLocking, "only call this with fast-locking enabled");
917 return thread->is_Java_thread() ? reinterpret_cast<JavaThread*>(thread)->lock_stack().contains(obj) : false;
918 }
919
920 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
921
922 while (true) {
923 ObjectMonitor* monitor = NULL;
924 markWord temp, test;
925 intptr_t hash;
926 markWord mark = read_stable_mark(obj);
927 if (VerifyHeavyMonitors) {
928 assert(UseHeavyMonitors, "+VerifyHeavyMonitors requires +UseHeavyMonitors");
929 guarantee(!mark.has_locker(), "must not be stack locked");
930 }
931 if (mark.is_neutral()) { // if this is a normal header
932 hash = mark.hash();
933 if (hash != 0) { // if it has a hash, just return it
934 return hash;
935 }
936 hash = get_next_hash(current, obj); // get a new hash
937 temp = mark.copy_set_hash(hash); // merge the hash into header
938 // try to install the hash
939 test = obj->cas_set_mark(temp, mark);
940 if (test == mark) { // if the hash was installed, return it
941 return hash;
942 }
943 // Failed to install the hash. It could be that another thread
944 // installed the hash just before our attempt or inflation has
945 // occurred or... so we fall thru to inflate the monitor for
946 // stability and then install the hash.
947 } else if (mark.has_monitor()) {
948 monitor = mark.monitor();
949 temp = monitor->header();
950 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
951 hash = temp.hash();
952 if (hash != 0) {
953 // It has a hash.
954
955 // Separate load of dmw/header above from the loads in
956 // is_being_async_deflated().
957
958 // dmw/header and _contentions may get written by different threads.
959 // Make sure to observe them in the same order when having several observers.
960 OrderAccess::loadload_for_IRIW();
961
962 if (monitor->is_being_async_deflated()) {
963 // But we can't safely use the hash if we detect that async
964 // deflation has occurred. So we attempt to restore the
965 // header/dmw to the object's header so that we only retry
966 // once if the deflater thread happens to be slow.
967 monitor->install_displaced_markword_in_object(obj);
968 continue;
969 }
970 return hash;
971 }
972 // Fall thru so we only have one place that installs the hash in
973 // the ObjectMonitor.
974 } else if (mark.is_fast_locked() && is_lock_owned(current, obj)) {
975 // This is a fast lock owned by the calling thread so use the
976 // markWord from the object.
977 hash = mark.hash();
978 if (hash != 0) { // if it has a hash, just return it
979 return hash;
980 }
981 } else if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
982 // This is a stack lock owned by the calling thread so fetch the
983 // displaced markWord from the BasicLock on the stack.
984 temp = mark.displaced_mark_helper();
985 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
986 hash = temp.hash();
987 if (hash != 0) { // if it has a hash, just return it
988 return hash;
989 }
990 // WARNING:
991 // The displaced header in the BasicLock on a thread's stack
992 // is strictly immutable. It CANNOT be changed in ANY cases.
993 // So we have to inflate the stack lock into an ObjectMonitor
994 // even if the current thread owns the lock. The BasicLock on
995 // a thread's stack can be asynchronously read by other threads
996 // during an inflate() call so any change to that stack memory
997 // may not propagate to other threads correctly.
998 }
999
1000 // Inflate the monitor to set the hash.
1001
1002 // An async deflation can race after the inflate() call and before we
1003 // can update the ObjectMonitor's header with the hash value below.
1004 monitor = inflate(current, obj, inflate_cause_hash_code);
1005 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1006 mark = monitor->header();
1007 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1008 hash = mark.hash();
1009 if (hash == 0) { // if it does not have a hash
1010 hash = get_next_hash(current, obj); // get a new hash
1011 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1012 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1013 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1014 test = markWord(v);
1015 if (test != mark) {
1016 // The attempt to update the ObjectMonitor's header/dmw field
1017 // did not work. This can happen if another thread managed to
1018 // merge in the hash just before our cmpxchg().
1019 // If we add any new usages of the header/dmw field, this code
1020 // will need to be updated.
1021 hash = test.hash();
1022 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1023 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1024 }
1025 if (monitor->is_being_async_deflated()) {
1026 // If we detect that async deflation has occurred, then we
1027 // attempt to restore the header/dmw to the object's header
1028 // so that we only retry once if the deflater thread happens
1029 // to be slow.
1030 monitor->install_displaced_markword_in_object(obj);
1031 continue;
1032 }
1033 }
1034 // We finally get the hash.
1035 return hash;
1036 }
1037 }
1038
1039 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1040 Handle h_obj) {
1041 assert(current == JavaThread::current(), "Can only be called on current thread");
1042 oop obj = h_obj();
1043
1044 markWord mark = read_stable_mark(obj);
1045
1046 // Uncontended case, header points to stack
1047 if (mark.has_locker()) {
1048 return current->is_lock_owned((address)mark.locker());
1049 }
1050
1051 // Fast-locking case.
1052 if (mark.is_fast_locked()) {
1053 return current->lock_stack().contains(h_obj());
1054 }
1055
1056 // Contended case, header points to ObjectMonitor (tagged pointer)
1057 if (mark.has_monitor()) {
1058 // The first stage of async deflation does not affect any field
1059 // used by this comparison so the ObjectMonitor* is usable here.
1060 ObjectMonitor* monitor = mark.monitor();
1061 return monitor->is_entered(current) != 0;
1062 }
1063 // Unlocked case, header in place
1064 assert(mark.is_neutral(), "sanity check");
1065 return false;
1066 }
1067
1068 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1069 oop obj = h_obj();
1070 markWord mark = read_stable_mark(obj);
1071
1072 // Uncontended case, header points to stack
1073 if (mark.has_locker()) {
1074 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1075 }
1076
1077 if (mark.is_fast_locked()) {
1078 return Threads::owning_thread_from_object(t_list, h_obj());
1079 }
1080
1081 // Contended case, header points to ObjectMonitor (tagged pointer)
1082 if (mark.has_monitor()) {
1083 // The first stage of async deflation does not affect any field
1084 // used by this comparison so the ObjectMonitor* is usable here.
1085 ObjectMonitor* monitor = mark.monitor();
1086 assert(monitor != NULL, "monitor should be non-null");
1087 return Threads::owning_thread_from_monitor(t_list, monitor);
1088 }
1089
1090 return NULL;
1091 }
1092
1093 // Visitors ...
1094
1095 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1096 // ObjectMonitors where owner is set to a stack lock address in thread.
1097 //
1098 // This version of monitors_iterate() works with the in-use monitor list.
1099 //
1100 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1101 MonitorList::Iterator iter = _in_use_list.iterator();
1102 while (iter.has_next()) {
1103 ObjectMonitor* mid = iter.next();
1104 if (mid->owner() != thread) {
1105 // Not owned by the target thread and intentionally skips when owner
1106 // is set to a stack lock address in the target thread.
1107 continue;
1108 }
1109 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1110 // Only process with closure if the object is set.
1111
1112 // monitors_iterate() is only called at a safepoint or when the
1113 // target thread is suspended or when the target thread is
1114 // operating on itself. The current closures in use today are
1115 // only interested in an owned ObjectMonitor and ownership
1116 // cannot be dropped under the calling contexts so the
1117 // ObjectMonitor cannot be async deflated.
1118 closure->do_monitor(mid);
1119 }
1120 }
1121 }
1122
1123 // This version of monitors_iterate() works with the specified linked list.
1124 //
1125 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure,
1126 ObjectMonitorsHashtable::PtrList* list,
1127 JavaThread* thread) {
1128 typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator;
1129 ObjectMonitorIterator iter(list->head());
1130 while (!iter.is_empty()) {
1131 ObjectMonitor* mid = *iter.next();
1132 // Owner set to a stack lock address in thread should never be seen here:
1133 assert(mid->owner() == thread, "must be");
1134 if (!mid->is_being_async_deflated() && mid->object_peek() != NULL) {
1135 // Only process with closure if the object is set.
1136
1137 // monitors_iterate() is only called at a safepoint or when the
1138 // target thread is suspended or when the target thread is
1139 // operating on itself. The current closures in use today are
1140 // only interested in an owned ObjectMonitor and ownership
1141 // cannot be dropped under the calling contexts so the
1142 // ObjectMonitor cannot be async deflated.
1143 closure->do_monitor(mid);
1144 }
1145 }
1146 }
1147
1148 static bool monitors_used_above_threshold(MonitorList* list) {
1149 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1150 return false;
1151 }
1152 // Start with ceiling based on a per-thread estimate:
1153 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1154 size_t old_ceiling = ceiling;
1155 if (ceiling < list->max()) {
1156 // The max used by the system has exceeded the ceiling so use that:
1157 ceiling = list->max();
1158 }
1159 size_t monitors_used = list->count();
1160 if (monitors_used == 0) { // empty list is easy
1161 return false;
1162 }
1163 if (NoAsyncDeflationProgressMax != 0 &&
1164 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1165 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1166 size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1167 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1168 log_info(monitorinflation)("Too many deflations without progress; "
1169 "bumping in_use_list_ceiling from " SIZE_FORMAT
1170 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1171 _no_progress_cnt = 0;
1172 ceiling = new_ceiling;
1173 }
1174
1175 // Check if our monitor usage is above the threshold:
1176 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1177 return int(monitor_usage) > MonitorUsedDeflationThreshold;
1178 }
1179
1180 size_t ObjectSynchronizer::in_use_list_ceiling() {
1181 return _in_use_list_ceiling;
1182 }
1183
1184 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1185 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1186 }
1187
1188 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1189 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1190 }
1191
1192 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1193 _in_use_list_ceiling = new_value;
1194 }
1195
1196 bool ObjectSynchronizer::is_async_deflation_needed() {
1197 if (is_async_deflation_requested()) {
1198 // Async deflation request.
1199 return true;
1200 }
1201 if (AsyncDeflationInterval > 0 &&
1202 time_since_last_async_deflation_ms() > AsyncDeflationInterval &&
1203 monitors_used_above_threshold(&_in_use_list)) {
1204 // It's been longer than our specified deflate interval and there
1205 // are too many monitors in use. We don't deflate more frequently
1206 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1207 // in order to not swamp the MonitorDeflationThread.
1208 return true;
1209 }
1210 return false;
1211 }
1212
1213 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1214 JavaThread* current = JavaThread::current();
1215 bool ret_code = false;
1216
1217 jlong last_time = last_async_deflation_time_ns();
1218 set_is_async_deflation_requested(true);
1219 {
1220 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1221 ml.notify_all();
1222 }
1223 const int N_CHECKS = 5;
1224 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1225 if (last_async_deflation_time_ns() > last_time) {
1226 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1227 ret_code = true;
1228 break;
1229 }
1230 {
1231 // JavaThread has to honor the blocking protocol.
1232 ThreadBlockInVM tbivm(current);
1233 os::naked_short_sleep(999); // sleep for almost 1 second
1234 }
1235 }
1236 if (!ret_code) {
1237 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1238 }
1239
1240 return ret_code;
1241 }
1242
1243 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1244 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1245 }
1246
1247 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1248 const oop obj,
1249 ObjectSynchronizer::InflateCause cause) {
1250 assert(event != NULL, "invariant");
1251 event->set_monitorClass(obj->klass());
1252 event->set_address((uintptr_t)(void*)obj);
1253 event->set_cause((u1)cause);
1254 event->commit();
1255 }
1256
1257 // Fast path code shared by multiple functions
1258 void ObjectSynchronizer::inflate_helper(oop obj) {
1259 markWord mark = obj->mark_acquire();
1260 if (mark.has_monitor()) {
1261 ObjectMonitor* monitor = mark.monitor();
1262 markWord dmw = monitor->header();
1263 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1264 return;
1265 }
1266 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1267 }
1268
1269 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1270 const InflateCause cause) {
1271 EventJavaMonitorInflate event;
1272
1273 for (;;) {
1274 const markWord mark = object->mark_acquire();
1275
1276 // The mark can be in one of the following states:
1277 // * Inflated - just return
1278 // * Stack-locked - coerce it to inflated
1279 // * INFLATING - busy wait for conversion to complete
1280 // * Neutral - aggressively inflate the object.
1281
1282 // CASE: inflated
1283 if (mark.has_monitor()) {
1284 ObjectMonitor* inf = mark.monitor();
1285 markWord dmw = inf->header();
1286 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1287 if (UseFastLocking && inf->is_owner_anonymous() && is_lock_owned(current, object)) {
1288 inf->set_owner_from_anonymous(current);
1289 assert(current->is_Java_thread(), "must be Java thread");
1290 reinterpret_cast<JavaThread*>(current)->lock_stack().remove(object);
1291 }
1292 return inf;
1293 }
1294
1295 // CASE: inflation in progress - inflating over a stack-lock.
1296 // Some other thread is converting from stack-locked to inflated.
1297 // Only that thread can complete inflation -- other threads must wait.
1298 // The INFLATING value is transient.
1299 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1300 // We could always eliminate polling by parking the thread on some auxiliary list.
1301 // NOTE: We need to check UseFastLocking here, because with fast-locking, the header
1302 // may legitimately be zero: cleared lock-bits and all upper header bits zero.
1303 // With fast-locking, the INFLATING protocol is not used.
1304 if (mark == markWord::INFLATING() && !UseFastLocking) {
1305 read_stable_mark(object);
1306 continue;
1307 }
1308
1309 // CASE: stack-locked
1310 // Could be stack-locked either by this thread or by some other thread.
1311 //
1312 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1313 // to install INFLATING into the mark word. We originally installed INFLATING,
1314 // allocated the ObjectMonitor, and then finally STed the address of the
1315 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1316 // the interval in which INFLATING appeared in the mark, thus increasing
1317 // the odds of inflation contention.
1318
1319 LogStreamHandle(Trace, monitorinflation) lsh;
1320 if (mark.is_fast_locked()) {
1321 assert(UseFastLocking, "can only happen with fast-locking");
1322 ObjectMonitor* monitor = new ObjectMonitor(object);
1323 monitor->set_header(mark.set_unlocked());
1324 bool own = is_lock_owned(current, object);
1325 if (own) {
1326 // Owned by us.
1327 monitor->set_owner_from(NULL, current);
1328 } else {
1329 // Owned by somebody else.
1330 monitor->set_owner_anonymous();
1331 }
1332 markWord monitor_mark = markWord::encode(monitor);
1333 markWord witness = object->cas_set_mark(monitor_mark, mark);
1334 if (witness == mark) {
1335 // Success! Return inflated monitor.
1336 if (own) {
1337 assert(current->is_Java_thread(), "must be: checked in is_lock_owned()");
1338 reinterpret_cast<JavaThread*>(current)->lock_stack().remove(object);
1339 }
1340 // Once the ObjectMonitor is configured and object is associated
1341 // with the ObjectMonitor, it is safe to allow async deflation:
1342 _in_use_list.add(monitor);
1343
1344 // Hopefully the performance counters are allocated on distinct
1345 // cache lines to avoid false sharing on MP systems ...
1346 OM_PERFDATA_OP(Inflations, inc());
1347 if (log_is_enabled(Trace, monitorinflation)) {
1348 ResourceMark rm(current);
1349 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1350 INTPTR_FORMAT ", type='%s'", p2i(object),
1351 object->mark().value(), object->klass()->external_name());
1352 }
1353 if (event.should_commit()) {
1354 post_monitor_inflate_event(&event, object, cause);
1355 }
1356 return monitor;
1357 } else {
1358 delete monitor;
1359 continue;
1360 }
1361 }
1362
1363 if (mark.has_locker()) {
1364 assert(!UseFastLocking, "can not happen with fast-locking");
1365 ObjectMonitor* m = new ObjectMonitor(object);
1366 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1367 // We do this before the CAS in order to minimize the length of time
1368 // in which INFLATING appears in the mark.
1369
1370 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1371 if (cmp != mark) {
1372 delete m;
1373 continue; // Interference -- just retry
1374 }
1375
1376 // We've successfully installed INFLATING (0) into the mark-word.
1377 // This is the only case where 0 will appear in a mark-word.
1378 // Only the singular thread that successfully swings the mark-word
1379 // to 0 can perform (or more precisely, complete) inflation.
1380 //
1381 // Why do we CAS a 0 into the mark-word instead of just CASing the
1382 // mark-word from the stack-locked value directly to the new inflated state?
1383 // Consider what happens when a thread unlocks a stack-locked object.
1384 // It attempts to use CAS to swing the displaced header value from the
1385 // on-stack BasicLock back into the object header. Recall also that the
1386 // header value (hash code, etc) can reside in (a) the object header, or
1387 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1388 // header in an ObjectMonitor. The inflate() routine must copy the header
1389 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1390 // the while preserving the hashCode stability invariants. If the owner
1391 // decides to release the lock while the value is 0, the unlock will fail
1392 // and control will eventually pass from slow_exit() to inflate. The owner
1393 // will then spin, waiting for the 0 value to disappear. Put another way,
1394 // the 0 causes the owner to stall if the owner happens to try to
1395 // drop the lock (restoring the header from the BasicLock to the object)
1396 // while inflation is in-progress. This protocol avoids races that might
1397 // would otherwise permit hashCode values to change or "flicker" for an object.
1398 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1399 // 0 serves as a "BUSY" inflate-in-progress indicator.
1400
1401
1402 // fetch the displaced mark from the owner's stack.
1403 // The owner can't die or unwind past the lock while our INFLATING
1404 // object is in the mark. Furthermore the owner can't complete
1405 // an unlock on the object, either.
1406 markWord dmw = mark.displaced_mark_helper();
1407 // Catch if the object's header is not neutral (not locked and
1408 // not marked is what we care about here).
1409 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1410
1411 // Setup monitor fields to proper values -- prepare the monitor
1412 m->set_header(dmw);
1413
1414 // Optimization: if the mark.locker stack address is associated
1415 // with this thread we could simply set m->_owner = current.
1416 // Note that a thread can inflate an object
1417 // that it has stack-locked -- as might happen in wait() -- directly
1418 // with CAS. That is, we can avoid the xchg-NULL .... ST idiom.
1419 m->set_owner_from(NULL, mark.locker());
1420 // TODO-FIXME: assert BasicLock->dhw != 0.
1421
1422 // Must preserve store ordering. The monitor state must
1423 // be stable at the time of publishing the monitor address.
1424 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1425 // Release semantics so that above set_object() is seen first.
1426 object->release_set_mark(markWord::encode(m));
1427
1428 // Once ObjectMonitor is configured and the object is associated
1429 // with the ObjectMonitor, it is safe to allow async deflation:
1430 _in_use_list.add(m);
1431
1432 // Hopefully the performance counters are allocated on distinct cache lines
1433 // to avoid false sharing on MP systems ...
1434 OM_PERFDATA_OP(Inflations, inc());
1435 if (log_is_enabled(Trace, monitorinflation)) {
1436 ResourceMark rm(current);
1437 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1438 INTPTR_FORMAT ", type='%s'", p2i(object),
1439 object->mark().value(), object->klass()->external_name());
1440 }
1441 if (event.should_commit()) {
1442 post_monitor_inflate_event(&event, object, cause);
1443 }
1444 return m;
1445 }
1446
1447 // CASE: neutral
1448 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1449 // If we know we're inflating for entry it's better to inflate by swinging a
1450 // pre-locked ObjectMonitor pointer into the object header. A successful
1451 // CAS inflates the object *and* confers ownership to the inflating thread.
1452 // In the current implementation we use a 2-step mechanism where we CAS()
1453 // to inflate and then CAS() again to try to swing _owner from NULL to current.
1454 // An inflateTry() method that we could call from enter() would be useful.
1455
1456 // Catch if the object's header is not neutral (not locked and
1457 // not marked is what we care about here).
1458 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1459 ObjectMonitor* m = new ObjectMonitor(object);
1460 // prepare m for installation - set monitor to initial state
1461 m->set_header(mark);
1462
1463 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1464 delete m;
1465 m = NULL;
1466 continue;
1467 // interference - the markword changed - just retry.
1468 // The state-transitions are one-way, so there's no chance of
1469 // live-lock -- "Inflated" is an absorbing state.
1470 }
1471
1472 // Once the ObjectMonitor is configured and object is associated
1473 // with the ObjectMonitor, it is safe to allow async deflation:
1474 _in_use_list.add(m);
1475
1476 // Hopefully the performance counters are allocated on distinct
1477 // cache lines to avoid false sharing on MP systems ...
1478 OM_PERFDATA_OP(Inflations, inc());
1479 if (log_is_enabled(Trace, monitorinflation)) {
1480 ResourceMark rm(current);
1481 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1482 INTPTR_FORMAT ", type='%s'", p2i(object),
1483 object->mark().value(), object->klass()->external_name());
1484 }
1485 if (event.should_commit()) {
1486 post_monitor_inflate_event(&event, object, cause);
1487 }
1488 return m;
1489 }
1490 }
1491
1492 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1493 const char* cnt_name, size_t cnt,
1494 LogStream* ls, elapsedTimer* timer_p) {
1495 if (!SafepointMechanism::should_process(current)) {
1496 return;
1497 }
1498
1499 // A safepoint/handshake has started.
1500 if (ls != NULL) {
1501 timer_p->stop();
1502 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1503 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1504 op_name, cnt_name, cnt, in_use_list_ceiling(),
1505 _in_use_list.count(), _in_use_list.max());
1506 }
1507
1508 {
1509 // Honor block request.
1510 ThreadBlockInVM tbivm(current);
1511 }
1512
1513 if (ls != NULL) {
1514 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1515 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1516 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1517 timer_p->start();
1518 }
1519 }
1520
1521 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1522 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1523 //
1524 // If table != nullptr, we gather owned ObjectMonitors indexed by the
1525 // owner in the table. Please note that ObjectMonitors where the owner
1526 // is set to a stack lock address are NOT associated with the JavaThread
1527 // that holds that stack lock. All of the current consumers of
1528 // ObjectMonitorsHashtable info only care about JNI locked monitors and
1529 // those do not have the owner set to a stack lock address.
1530 //
1531 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1532 elapsedTimer* timer_p,
1533 ObjectMonitorsHashtable* table) {
1534 MonitorList::Iterator iter = _in_use_list.iterator();
1535 size_t deflated_count = 0;
1536
1537 while (iter.has_next()) {
1538 if (deflated_count >= (size_t)MonitorDeflationMax) {
1539 break;
1540 }
1541 ObjectMonitor* mid = iter.next();
1542 if (mid->deflate_monitor()) {
1543 deflated_count++;
1544 } else if (table != nullptr) {
1545 // The caller is interested in the owned ObjectMonitors. This does
1546 // not include when owner is set to a stack lock address in thread.
1547 // This also does not capture unowned ObjectMonitors that cannot be
1548 // deflated because of a waiter.
1549 void* key = mid->owner();
1550 // Since deflate_idle_monitors() and deflate_monitor_list() can be
1551 // called more than once, we have to make sure the entry has not
1552 // already been added.
1553 if (key != nullptr && !table->has_entry(key, mid)) {
1554 table->add_entry(key, mid);
1555 }
1556 }
1557
1558 if (current->is_Java_thread()) {
1559 // A JavaThread must check for a safepoint/handshake and honor it.
1560 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1561 deflated_count, ls, timer_p);
1562 }
1563 }
1564
1565 return deflated_count;
1566 }
1567
1568 class HandshakeForDeflation : public HandshakeClosure {
1569 public:
1570 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1571
1572 void do_thread(Thread* thread) {
1573 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1574 INTPTR_FORMAT, p2i(thread));
1575 }
1576 };
1577
1578 class VM_RendezvousGCThreads : public VM_Operation {
1579 public:
1580 bool evaluate_at_safepoint() const override { return false; }
1581 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1582 void doit() override {
1583 SuspendibleThreadSet::synchronize();
1584 SuspendibleThreadSet::desynchronize();
1585 };
1586 };
1587
1588 // This function is called by the MonitorDeflationThread to deflate
1589 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1590 // and VM_ThreadDump::doit() by the VMThread.
1591 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) {
1592 Thread* current = Thread::current();
1593 if (current->is_Java_thread()) {
1594 // The async deflation request has been processed.
1595 _last_async_deflation_time_ns = os::javaTimeNanos();
1596 set_is_async_deflation_requested(false);
1597 }
1598
1599 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1600 LogStreamHandle(Info, monitorinflation) lsh_info;
1601 LogStream* ls = NULL;
1602 if (log_is_enabled(Debug, monitorinflation)) {
1603 ls = &lsh_debug;
1604 } else if (log_is_enabled(Info, monitorinflation)) {
1605 ls = &lsh_info;
1606 }
1607
1608 elapsedTimer timer;
1609 if (ls != NULL) {
1610 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1611 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1612 timer.start();
1613 }
1614
1615 // Deflate some idle ObjectMonitors.
1616 size_t deflated_count = deflate_monitor_list(current, ls, &timer, table);
1617 size_t unlinked_count = 0;
1618 size_t deleted_count = 0;
1619 if (deflated_count > 0 || is_final_audit()) {
1620 // There are ObjectMonitors that have been deflated or this is the
1621 // final audit and all the remaining ObjectMonitors have been
1622 // deflated, BUT the MonitorDeflationThread blocked for the final
1623 // safepoint during unlinking.
1624
1625 // Unlink deflated ObjectMonitors from the in-use list.
1626 ResourceMark rm;
1627 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1628 unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, &delete_list);
1629 if (current->is_Java_thread()) {
1630 if (ls != NULL) {
1631 timer.stop();
1632 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1633 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1634 SIZE_FORMAT ", max=" SIZE_FORMAT,
1635 unlinked_count, in_use_list_ceiling(),
1636 _in_use_list.count(), _in_use_list.max());
1637 }
1638
1639 // A JavaThread needs to handshake in order to safely free the
1640 // ObjectMonitors that were deflated in this cycle.
1641 // Also, we sync and desync GC threads around the handshake, so that they can
1642 // safely read the mark-word and look-through to the object-monitor, without
1643 // being afraid that the object-monitor is going away.
1644 HandshakeForDeflation hfd_hc;
1645 Handshake::execute(&hfd_hc);
1646 VM_RendezvousGCThreads sync_gc;
1647 VMThread::execute(&sync_gc);
1648
1649 if (ls != NULL) {
1650 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1651 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1652 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1653 timer.start();
1654 }
1655 }
1656
1657 // After the handshake, safely free the ObjectMonitors that were
1658 // deflated in this cycle.
1659 for (ObjectMonitor* monitor: delete_list) {
1660 delete monitor;
1661 deleted_count++;
1662
1663 if (current->is_Java_thread()) {
1664 // A JavaThread must check for a safepoint/handshake and honor it.
1665 chk_for_block_req(JavaThread::cast(current), "deletion", "deleted_count",
1666 deleted_count, ls, &timer);
1667 }
1668 }
1669 assert(unlinked_count == deleted_count, "must be");
1670 }
1671
1672 if (ls != NULL) {
1673 timer.stop();
1674 if (deflated_count != 0 || unlinked_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1675 ls->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1676 deflated_count, unlinked_count, timer.seconds());
1677 }
1678 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1679 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1680 if (table != nullptr) {
1681 ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT,
1682 table->key_count(), table->om_count());
1683 }
1684 }
1685
1686 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1687 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1688
1689 GVars.stw_random = os::random();
1690
1691 if (deflated_count != 0) {
1692 _no_progress_cnt = 0;
1693 } else {
1694 _no_progress_cnt++;
1695 }
1696
1697 return deflated_count;
1698 }
1699
1700 // Monitor cleanup on JavaThread::exit
1701
1702 // Iterate through monitor cache and attempt to release thread's monitors
1703 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1704 private:
1705 JavaThread* _thread;
1706
1707 public:
1708 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1709 void do_monitor(ObjectMonitor* mid) {
1710 intx rec = mid->complete_exit(_thread);
1711 _thread->dec_held_monitor_count(rec + 1);
1712 }
1713 };
1714
1715 // Release all inflated monitors owned by current thread. Lightweight monitors are
1716 // ignored. This is meant to be called during JNI thread detach which assumes
1717 // all remaining monitors are heavyweight. All exceptions are swallowed.
1718 // Scanning the extant monitor list can be time consuming.
1719 // A simple optimization is to add a per-thread flag that indicates a thread
1720 // called jni_monitorenter() during its lifetime.
1721 //
1722 // Instead of NoSafepointVerifier it might be cheaper to
1723 // use an idiom of the form:
1724 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1725 // <code that must not run at safepoint>
1726 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1727 // Since the tests are extremely cheap we could leave them enabled
1728 // for normal product builds.
1729
1730 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1731 assert(current == JavaThread::current(), "must be current Java thread");
1732 NoSafepointVerifier nsv;
1733 ReleaseJavaMonitorsClosure rjmc(current);
1734 ObjectSynchronizer::monitors_iterate(&rjmc, current);
1735 assert(!current->has_pending_exception(), "Should not be possible");
1736 current->clear_pending_exception();
1737 assert(current->held_monitor_count() == 0, "Should not be possible");
1738 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1739 current->clear_jni_monitor_count();
1740 }
1741
1742 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1743 switch (cause) {
1744 case inflate_cause_vm_internal: return "VM Internal";
1745 case inflate_cause_monitor_enter: return "Monitor Enter";
1746 case inflate_cause_wait: return "Monitor Wait";
1747 case inflate_cause_notify: return "Monitor Notify";
1748 case inflate_cause_hash_code: return "Monitor Hash Code";
1749 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1750 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1751 default:
1752 ShouldNotReachHere();
1753 }
1754 return "Unknown";
1755 }
1756
1757 //------------------------------------------------------------------------------
1758 // Debugging code
1759
1760 u_char* ObjectSynchronizer::get_gvars_addr() {
1761 return (u_char*)&GVars;
1762 }
1763
1764 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1765 return (u_char*)&GVars.hc_sequence;
1766 }
1767
1768 size_t ObjectSynchronizer::get_gvars_size() {
1769 return sizeof(SharedGlobals);
1770 }
1771
1772 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1773 return (u_char*)&GVars.stw_random;
1774 }
1775
1776 // Do the final audit and print of ObjectMonitor stats; must be done
1777 // by the VMThread at VM exit time.
1778 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1779 assert(Thread::current()->is_VM_thread(), "sanity check");
1780
1781 if (is_final_audit()) { // Only do the audit once.
1782 return;
1783 }
1784 set_is_final_audit();
1785 log_info(monitorinflation)("Starting the final audit.");
1786
1787 if (log_is_enabled(Info, monitorinflation)) {
1788 // Do deflations in order to reduce the in-use monitor population
1789 // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1790 // which is called by ObjectSynchronizer::audit_and_print_stats().
1791 while (deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) > 0) {
1792 ; // empty
1793 }
1794 // The other audit_and_print_stats() call is done at the Debug
1795 // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
1796 audit_and_print_stats(true /* on_exit */);
1797 }
1798 }
1799
1800 // This function can be called at a safepoint or it can be called when
1801 // we are trying to exit the VM. When we are trying to exit the VM, the
1802 // list walker functions can run in parallel with the other list
1803 // operations so spin-locking is used for safety.
1804 //
1805 // Calls to this function can be added in various places as a debugging
1806 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1807 // details logged at the Info level and 'false' for the 'on_exit'
1808 // parameter to have in-use monitor details logged at the Trace level.
1809 //
1810 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1811 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1812
1813 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1814 LogStreamHandle(Info, monitorinflation) lsh_info;
1815 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1816 LogStream* ls = NULL;
1817 if (log_is_enabled(Trace, monitorinflation)) {
1818 ls = &lsh_trace;
1819 } else if (log_is_enabled(Debug, monitorinflation)) {
1820 ls = &lsh_debug;
1821 } else if (log_is_enabled(Info, monitorinflation)) {
1822 ls = &lsh_info;
1823 }
1824 assert(ls != NULL, "sanity check");
1825
1826 int error_cnt = 0;
1827
1828 ls->print_cr("Checking in_use_list:");
1829 chk_in_use_list(ls, &error_cnt);
1830
1831 if (error_cnt == 0) {
1832 ls->print_cr("No errors found in in_use_list checks.");
1833 } else {
1834 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1835 }
1836
1837 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1838 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1839 // When exiting this log output is at the Info level. When called
1840 // at a safepoint, this log output is at the Trace level since
1841 // there can be a lot of it.
1842 log_in_use_monitor_details(ls);
1843 }
1844
1845 ls->flush();
1846
1847 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1848 }
1849
1850 // Check the in_use_list; log the results of the checks.
1851 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1852 size_t l_in_use_count = _in_use_list.count();
1853 size_t l_in_use_max = _in_use_list.max();
1854 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1855 l_in_use_max);
1856
1857 size_t ck_in_use_count = 0;
1858 MonitorList::Iterator iter = _in_use_list.iterator();
1859 while (iter.has_next()) {
1860 ObjectMonitor* mid = iter.next();
1861 chk_in_use_entry(mid, out, error_cnt_p);
1862 ck_in_use_count++;
1863 }
1864
1865 if (l_in_use_count == ck_in_use_count) {
1866 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1867 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1868 } else {
1869 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1870 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1871 ck_in_use_count);
1872 }
1873
1874 size_t ck_in_use_max = _in_use_list.max();
1875 if (l_in_use_max == ck_in_use_max) {
1876 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1877 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1878 } else {
1879 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1880 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1881 }
1882 }
1883
1884 // Check an in-use monitor entry; log any errors.
1885 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1886 int* error_cnt_p) {
1887 if (n->owner_is_DEFLATER_MARKER()) {
1888 // This should not happen, but if it does, it is not fatal.
1889 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1890 "deflated.", p2i(n));
1891 return;
1892 }
1893 if (n->header().value() == 0) {
1894 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1895 "have non-NULL _header field.", p2i(n));
1896 *error_cnt_p = *error_cnt_p + 1;
1897 }
1898 const oop obj = n->object_peek();
1899 if (obj != NULL) {
1900 const markWord mark = obj->mark();
1901 if (!mark.has_monitor()) {
1902 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1903 "object does not think it has a monitor: obj="
1904 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1905 p2i(obj), mark.value());
1906 *error_cnt_p = *error_cnt_p + 1;
1907 }
1908 ObjectMonitor* const obj_mon = mark.monitor();
1909 if (n != obj_mon) {
1910 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1911 "object does not refer to the same monitor: obj="
1912 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1913 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1914 *error_cnt_p = *error_cnt_p + 1;
1915 }
1916 }
1917 }
1918
1919 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1920 // flags indicate why the entry is in-use, 'object' and 'object type'
1921 // indicate the associated object and its type.
1922 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
1923 stringStream ss;
1924 if (_in_use_list.count() > 0) {
1925 out->print_cr("In-use monitor info:");
1926 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1927 out->print_cr("%18s %s %18s %18s",
1928 "monitor", "BHL", "object", "object type");
1929 out->print_cr("================== === ================== ==================");
1930 MonitorList::Iterator iter = _in_use_list.iterator();
1931 while (iter.has_next()) {
1932 ObjectMonitor* mid = iter.next();
1933 const oop obj = mid->object_peek();
1934 const markWord mark = mid->header();
1935 ResourceMark rm;
1936 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid),
1937 mid->is_busy(), mark.hash() != 0, mid->owner() != NULL,
1938 p2i(obj), obj == NULL ? "" : obj->klass()->external_name());
1939 if (mid->is_busy()) {
1940 out->print(" (%s)", mid->is_busy_to_string(&ss));
1941 ss.reset();
1942 }
1943 out->cr();
1944 }
1945 }
1946
1947 out->flush();
1948 }