1 /*
2 * Copyright (c) 1998, 2023, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/vmSymbols.hpp"
27 #include "gc/shared/collectedHeap.hpp"
28 #include "jfr/jfrEvents.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/trimNativeHeap.hpp"
58 #include "runtime/vframe.hpp"
59 #include "runtime/vmThread.hpp"
60 #include "utilities/align.hpp"
61 #include "utilities/dtrace.hpp"
62 #include "utilities/events.hpp"
63 #include "utilities/linkedlist.hpp"
64 #include "utilities/preserveException.hpp"
65
66 class ObjectMonitorsHashtable::PtrList :
67 public LinkedListImpl<ObjectMonitor*,
68 AnyObj::C_HEAP, mtThread,
69 AllocFailStrategy::RETURN_NULL> {};
70
71 class CleanupObjectMonitorsHashtable: StackObj {
72 public:
73 bool do_entry(void*& key, ObjectMonitorsHashtable::PtrList*& list) {
74 list->clear(); // clear the LinkListNodes
75 delete list; // then delete the LinkedList
76 return true;
77 }
78 };
79
80 ObjectMonitorsHashtable::~ObjectMonitorsHashtable() {
81 CleanupObjectMonitorsHashtable cleanup;
82 _ptrs->unlink(&cleanup); // cleanup the LinkedLists
83 delete _ptrs; // then delete the hash table
84 }
85
86 void ObjectMonitorsHashtable::add_entry(void* key, ObjectMonitor* om) {
87 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
88 if (list == nullptr) {
89 // Create new list and add it to the hash table:
90 list = new (mtThread) ObjectMonitorsHashtable::PtrList;
91 add_entry(key, list);
92 }
93 list->add(om); // Add the ObjectMonitor to the list.
94 _om_count++;
95 }
96
97 bool ObjectMonitorsHashtable::has_entry(void* key, ObjectMonitor* om) {
98 ObjectMonitorsHashtable::PtrList* list = get_entry(key);
99 if (list == nullptr || list->find(om) == nullptr) {
100 return false;
101 }
102 return true;
103 }
104
105 void MonitorList::add(ObjectMonitor* m) {
106 ObjectMonitor* head;
107 do {
108 head = Atomic::load(&_head);
109 m->set_next_om(head);
110 } while (Atomic::cmpxchg(&_head, head, m) != head);
111
112 size_t count = Atomic::add(&_count, 1u);
113 if (count > max()) {
114 Atomic::inc(&_max);
115 }
116 }
117
118 size_t MonitorList::count() const {
119 return Atomic::load(&_count);
120 }
121
122 size_t MonitorList::max() const {
123 return Atomic::load(&_max);
124 }
125
126 // Walk the in-use list and unlink (at most MonitorDeflationMax) deflated
127 // ObjectMonitors. Returns the number of unlinked ObjectMonitors.
128 size_t MonitorList::unlink_deflated(Thread* current, LogStream* ls,
129 elapsedTimer* timer_p,
130 GrowableArray<ObjectMonitor*>* unlinked_list) {
131 size_t unlinked_count = 0;
132 ObjectMonitor* prev = nullptr;
133 ObjectMonitor* head = Atomic::load_acquire(&_head);
134 ObjectMonitor* m = head;
135 // The in-use list head can be null during the final audit.
136 while (m != nullptr) {
137 if (m->is_being_async_deflated()) {
138 // Find next live ObjectMonitor.
139 ObjectMonitor* next = m;
140 do {
141 ObjectMonitor* next_next = next->next_om();
142 unlinked_count++;
143 unlinked_list->append(next);
144 next = next_next;
145 if (unlinked_count >= (size_t)MonitorDeflationMax) {
146 // Reached the max so bail out on the gathering loop.
147 break;
148 }
149 } while (next != nullptr && next->is_being_async_deflated());
150 if (prev == nullptr) {
151 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, head, next);
152 if (prev_head != head) {
153 // Find new prev ObjectMonitor that just got inserted.
154 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
155 prev = n;
156 }
157 prev->set_next_om(next);
158 }
159 } else {
160 prev->set_next_om(next);
161 }
162 if (unlinked_count >= (size_t)MonitorDeflationMax) {
163 // Reached the max so bail out on the searching loop.
164 break;
165 }
166 m = next;
167 } else {
168 prev = m;
169 m = m->next_om();
170 }
171
172 if (current->is_Java_thread()) {
173 // A JavaThread must check for a safepoint/handshake and honor it.
174 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "unlinking",
175 "unlinked_count", unlinked_count,
176 ls, timer_p);
177 }
178 }
179 Atomic::sub(&_count, unlinked_count);
180 return unlinked_count;
181 }
182
183 MonitorList::Iterator MonitorList::iterator() const {
184 return Iterator(Atomic::load_acquire(&_head));
185 }
186
187 ObjectMonitor* MonitorList::Iterator::next() {
188 ObjectMonitor* current = _current;
189 _current = current->next_om();
190 return current;
191 }
192
193 // The "core" versions of monitor enter and exit reside in this file.
194 // The interpreter and compilers contain specialized transliterated
195 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
196 // fast_lock(...) for instance. If you make changes here, make sure to modify the
197 // interpreter, and both C1 and C2 fast-path inline locking code emission.
198 //
199 // -----------------------------------------------------------------------------
200
201 #ifdef DTRACE_ENABLED
202
203 // Only bother with this argument setup if dtrace is available
204 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
205
206 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
207 char* bytes = nullptr; \
208 int len = 0; \
209 jlong jtid = SharedRuntime::get_java_tid(thread); \
210 Symbol* klassname = obj->klass()->name(); \
211 if (klassname != nullptr) { \
212 bytes = (char*)klassname->bytes(); \
213 len = klassname->utf8_length(); \
214 }
215
216 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
217 { \
218 if (DTraceMonitorProbes) { \
219 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
220 HOTSPOT_MONITOR_WAIT(jtid, \
221 (uintptr_t)(monitor), bytes, len, (millis)); \
222 } \
223 }
224
225 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
226 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
227 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
228
229 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
230 { \
231 if (DTraceMonitorProbes) { \
232 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
233 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
234 (uintptr_t)(monitor), bytes, len); \
235 } \
236 }
237
238 #else // ndef DTRACE_ENABLED
239
240 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
241 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
242
243 #endif // ndef DTRACE_ENABLED
244
245 // This exists only as a workaround of dtrace bug 6254741
246 int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
247 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
248 return 0;
249 }
250
251 static constexpr size_t inflation_lock_count() {
252 return 256;
253 }
254
255 // Static storage for an array of PlatformMutex.
256 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
257
258 static inline PlatformMutex* inflation_lock(size_t index) {
259 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
260 }
261
262 void ObjectSynchronizer::initialize() {
263 for (size_t i = 0; i < inflation_lock_count(); i++) {
264 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
265 }
266 // Start the ceiling with the estimate for one thread.
267 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
268
269 // Start the timer for deflations, so it does not trigger immediately.
270 _last_async_deflation_time_ns = os::javaTimeNanos();
271 }
272
273 MonitorList ObjectSynchronizer::_in_use_list;
274 // monitors_used_above_threshold() policy is as follows:
275 //
276 // The ratio of the current _in_use_list count to the ceiling is used
277 // to determine if we are above MonitorUsedDeflationThreshold and need
278 // to do an async monitor deflation cycle. The ceiling is increased by
279 // AvgMonitorsPerThreadEstimate when a thread is added to the system
280 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
281 // removed from the system.
282 //
283 // Note: If the _in_use_list max exceeds the ceiling, then
284 // monitors_used_above_threshold() will use the in_use_list max instead
285 // of the thread count derived ceiling because we have used more
286 // ObjectMonitors than the estimated average.
287 //
288 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
289 // no-progress async monitor deflation cycles in a row, then the ceiling
290 // is adjusted upwards by monitors_used_above_threshold().
291 //
292 // Start the ceiling with the estimate for one thread in initialize()
293 // which is called after cmd line options are processed.
294 static size_t _in_use_list_ceiling = 0;
295 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
296 bool volatile ObjectSynchronizer::_is_final_audit = false;
297 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
298 static uintx _no_progress_cnt = 0;
299 static bool _no_progress_skip_increment = false;
300
301 // =====================> Quick functions
302
303 // The quick_* forms are special fast-path variants used to improve
304 // performance. In the simplest case, a "quick_*" implementation could
305 // simply return false, in which case the caller will perform the necessary
306 // state transitions and call the slow-path form.
307 // The fast-path is designed to handle frequently arising cases in an efficient
308 // manner and is just a degenerate "optimistic" variant of the slow-path.
309 // returns true -- to indicate the call was satisfied.
310 // returns false -- to indicate the call needs the services of the slow-path.
311 // A no-loitering ordinance is in effect for code in the quick_* family
312 // operators: safepoints or indefinite blocking (blocking that might span a
313 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
314 // entry.
315 //
316 // Consider: An interesting optimization is to have the JIT recognize the
317 // following common idiom:
318 // synchronized (someobj) { .... ; notify(); }
319 // That is, we find a notify() or notifyAll() call that immediately precedes
320 // the monitorexit operation. In that case the JIT could fuse the operations
321 // into a single notifyAndExit() runtime primitive.
322
323 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
324 assert(current->thread_state() == _thread_in_Java, "invariant");
325 NoSafepointVerifier nsv;
326 if (obj == nullptr) return false; // slow-path for invalid obj
327 const markWord mark = obj->mark();
328
329 if (LockingMode == LM_LIGHTWEIGHT) {
330 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
331 // Degenerate notify
332 // fast-locked by caller so by definition the implied waitset is empty.
333 return true;
334 }
335 } else if (LockingMode == LM_LEGACY) {
336 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
337 // Degenerate notify
338 // stack-locked by caller so by definition the implied waitset is empty.
339 return true;
340 }
341 }
342
343 if (mark.has_monitor()) {
344 ObjectMonitor* const mon = mark.monitor();
345 assert(mon->object() == oop(obj), "invariant");
346 if (mon->owner() != current) return false; // slow-path for IMS exception
347
348 if (mon->first_waiter() != nullptr) {
349 // We have one or more waiters. Since this is an inflated monitor
350 // that we own, we can transfer one or more threads from the waitset
351 // to the entrylist here and now, avoiding the slow-path.
352 if (all) {
353 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
354 } else {
355 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
356 }
357 int free_count = 0;
358 do {
359 mon->INotify(current);
360 ++free_count;
361 } while (mon->first_waiter() != nullptr && all);
362 OM_PERFDATA_OP(Notifications, inc(free_count));
363 }
364 return true;
365 }
366
367 // other IMS exception states take the slow-path
368 return false;
369 }
370
371
372 // The LockNode emitted directly at the synchronization site would have
373 // been too big if it were to have included support for the cases of inflated
374 // recursive enter and exit, so they go here instead.
375 // Note that we can't safely call AsyncPrintJavaStack() from within
376 // quick_enter() as our thread state remains _in_Java.
377
378 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
379 BasicLock * lock) {
380 assert(current->thread_state() == _thread_in_Java, "invariant");
381 NoSafepointVerifier nsv;
382 if (obj == nullptr) return false; // Need to throw NPE
383
384 if (obj->klass()->is_value_based()) {
385 return false;
386 }
387
388 const markWord mark = obj->mark();
389
390 if (mark.has_monitor()) {
391 ObjectMonitor* const m = mark.monitor();
392 // An async deflation or GC can race us before we manage to make
393 // the ObjectMonitor busy by setting the owner below. If we detect
394 // that race we just bail out to the slow-path here.
395 if (m->object_peek() == nullptr) {
396 return false;
397 }
398 JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
399
400 // Lock contention and Transactional Lock Elision (TLE) diagnostics
401 // and observability
402 // Case: light contention possibly amenable to TLE
403 // Case: TLE inimical operations such as nested/recursive synchronization
404
405 if (owner == current) {
406 m->_recursions++;
407 current->inc_held_monitor_count();
408 return true;
409 }
410
411 if (LockingMode != LM_LIGHTWEIGHT) {
412 // This Java Monitor is inflated so obj's header will never be
413 // displaced to this thread's BasicLock. Make the displaced header
414 // non-null so this BasicLock is not seen as recursive nor as
415 // being locked. We do this unconditionally so that this thread's
416 // BasicLock cannot be mis-interpreted by any stack walkers. For
417 // performance reasons, stack walkers generally first check for
418 // stack-locking in the object's header, the second check is for
419 // recursive stack-locking in the displaced header in the BasicLock,
420 // and last are the inflated Java Monitor (ObjectMonitor) checks.
421 lock->set_displaced_header(markWord::unused_mark());
422 }
423
424 if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) {
425 assert(m->_recursions == 0, "invariant");
426 current->inc_held_monitor_count();
427 return true;
428 }
429 }
430
431 // Note that we could inflate in quick_enter.
432 // This is likely a useful optimization
433 // Critically, in quick_enter() we must not:
434 // -- block indefinitely, or
435 // -- reach a safepoint
436
437 return false; // revert to slow-path
438 }
439
440 // Handle notifications when synchronizing on value based classes
441 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
442 frame last_frame = current->last_frame();
443 bool bcp_was_adjusted = false;
444 // Don't decrement bcp if it points to the frame's first instruction. This happens when
445 // handle_sync_on_value_based_class() is called because of a synchronized method. There
446 // is no actual monitorenter instruction in the byte code in this case.
447 if (last_frame.is_interpreted_frame() &&
448 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
449 // adjust bcp to point back to monitorenter so that we print the correct line numbers
450 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
451 bcp_was_adjusted = true;
452 }
453
454 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
455 ResourceMark rm(current);
456 stringStream ss;
457 current->print_active_stack_on(&ss);
458 char* base = (char*)strstr(ss.base(), "at");
459 char* newline = (char*)strchr(ss.base(), '\n');
460 if (newline != nullptr) {
461 *newline = '\0';
462 }
463 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
464 } else {
465 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
466 ResourceMark rm(current);
467 Log(valuebasedclasses) vblog;
468
469 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
470 if (current->has_last_Java_frame()) {
471 LogStream info_stream(vblog.info());
472 current->print_active_stack_on(&info_stream);
473 } else {
474 vblog.info("Cannot find the last Java frame");
475 }
476
477 EventSyncOnValueBasedClass event;
478 if (event.should_commit()) {
479 event.set_valueBasedClass(obj->klass());
480 event.commit();
481 }
482 }
483
484 if (bcp_was_adjusted) {
485 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
486 }
487 }
488
489 static bool useHeavyMonitors() {
490 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
491 return LockingMode == LM_MONITOR;
492 #else
493 return false;
494 #endif
495 }
496
497 // -----------------------------------------------------------------------------
498 // Monitor Enter/Exit
499 // The interpreter and compiler assembly code tries to lock using the fast path
500 // of this algorithm. Make sure to update that code if the following function is
501 // changed. The implementation is extremely sensitive to race condition. Be careful.
502
503 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
504 if (obj->klass()->is_value_based()) {
505 handle_sync_on_value_based_class(obj, current);
506 }
507
508 current->inc_held_monitor_count();
509
510 if (!useHeavyMonitors()) {
511 if (LockingMode == LM_LIGHTWEIGHT) {
512 // Fast-locking does not use the 'lock' argument.
513 LockStack& lock_stack = current->lock_stack();
514 if (lock_stack.can_push()) {
515 markWord mark = obj()->mark_acquire();
516 if (mark.is_neutral()) {
517 assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
518 // Try to swing into 'fast-locked' state.
519 markWord locked_mark = mark.set_fast_locked();
520 markWord old_mark = obj()->cas_set_mark(locked_mark, mark);
521 if (old_mark == mark) {
522 // Successfully fast-locked, push object to lock-stack and return.
523 lock_stack.push(obj());
524 return;
525 }
526 }
527 }
528 // All other paths fall-through to inflate-enter.
529 } else if (LockingMode == LM_LEGACY) {
530 markWord mark = obj->mark();
531 if (mark.is_neutral()) {
532 // Anticipate successful CAS -- the ST of the displaced mark must
533 // be visible <= the ST performed by the CAS.
534 lock->set_displaced_header(mark);
535 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
536 return;
537 }
538 // Fall through to inflate() ...
539 } else if (mark.has_locker() &&
540 current->is_lock_owned((address) mark.locker())) {
541 assert(lock != mark.locker(), "must not re-lock the same lock");
542 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
543 lock->set_displaced_header(markWord::from_pointer(nullptr));
544 return;
545 }
546
547 // The object header will never be displaced to this lock,
548 // so it does not matter what the value is, except that it
549 // must be non-zero to avoid looking like a re-entrant lock,
550 // and must not look locked either.
551 lock->set_displaced_header(markWord::unused_mark());
552 }
553 } else if (VerifyHeavyMonitors) {
554 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
555 }
556
557 // An async deflation can race after the inflate() call and before
558 // enter() can make the ObjectMonitor busy. enter() returns false if
559 // we have lost the race to async deflation and we simply try again.
560 while (true) {
561 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
562 if (monitor->enter(current)) {
563 return;
564 }
565 }
566 }
567
568 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
569 current->dec_held_monitor_count();
570
571 if (!useHeavyMonitors()) {
572 markWord mark = object->mark();
573 if (LockingMode == LM_LIGHTWEIGHT) {
574 // Fast-locking does not use the 'lock' argument.
575 if (mark.is_fast_locked()) {
576 markWord unlocked_mark = mark.set_unlocked();
577 markWord old_mark = object->cas_set_mark(unlocked_mark, mark);
578 if (old_mark != mark) {
579 // Another thread won the CAS, it must have inflated the monitor.
580 // It can only have installed an anonymously locked monitor at this point.
581 // Fetch that monitor, set owner correctly to this thread, and
582 // exit it (allowing waiting threads to enter).
583 assert(old_mark.has_monitor(), "must have monitor");
584 ObjectMonitor* monitor = old_mark.monitor();
585 assert(monitor->is_owner_anonymous(), "must be anonymous owner");
586 monitor->set_owner_from_anonymous(current);
587 monitor->exit(current);
588 }
589 LockStack& lock_stack = current->lock_stack();
590 lock_stack.remove(object);
591 return;
592 }
593 } else if (LockingMode == LM_LEGACY) {
594 markWord dhw = lock->displaced_header();
595 if (dhw.value() == 0) {
596 // If the displaced header is null, then this exit matches up with
597 // a recursive enter. No real work to do here except for diagnostics.
598 #ifndef PRODUCT
599 if (mark != markWord::INFLATING()) {
600 // Only do diagnostics if we are not racing an inflation. Simply
601 // exiting a recursive enter of a Java Monitor that is being
602 // inflated is safe; see the has_monitor() comment below.
603 assert(!mark.is_neutral(), "invariant");
604 assert(!mark.has_locker() ||
605 current->is_lock_owned((address)mark.locker()), "invariant");
606 if (mark.has_monitor()) {
607 // The BasicLock's displaced_header is marked as a recursive
608 // enter and we have an inflated Java Monitor (ObjectMonitor).
609 // This is a special case where the Java Monitor was inflated
610 // after this thread entered the stack-lock recursively. When a
611 // Java Monitor is inflated, we cannot safely walk the Java
612 // Monitor owner's stack and update the BasicLocks because a
613 // Java Monitor can be asynchronously inflated by a thread that
614 // does not own the Java Monitor.
615 ObjectMonitor* m = mark.monitor();
616 assert(m->object()->mark() == mark, "invariant");
617 assert(m->is_entered(current), "invariant");
618 }
619 }
620 #endif
621 return;
622 }
623
624 if (mark == markWord::from_pointer(lock)) {
625 // If the object is stack-locked by the current thread, try to
626 // swing the displaced header from the BasicLock back to the mark.
627 assert(dhw.is_neutral(), "invariant");
628 if (object->cas_set_mark(dhw, mark) == mark) {
629 return;
630 }
631 }
632 }
633 } else if (VerifyHeavyMonitors) {
634 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
635 }
636
637 // We have to take the slow-path of possible inflation and then exit.
638 // The ObjectMonitor* can't be async deflated until ownership is
639 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
640 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
641 if (LockingMode == LM_LIGHTWEIGHT && monitor->is_owner_anonymous()) {
642 // It must be owned by us. Pop lock object from lock stack.
643 LockStack& lock_stack = current->lock_stack();
644 oop popped = lock_stack.pop();
645 assert(popped == object, "must be owned by this thread");
646 monitor->set_owner_from_anonymous(current);
647 }
648 monitor->exit(current);
649 }
650
651 // -----------------------------------------------------------------------------
652 // JNI locks on java objects
653 // NOTE: must use heavy weight monitor to handle jni monitor enter
654 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
655 if (obj->klass()->is_value_based()) {
656 handle_sync_on_value_based_class(obj, current);
657 }
658
659 // the current locking is from JNI instead of Java code
660 current->set_current_pending_monitor_is_from_java(false);
661 // An async deflation can race after the inflate() call and before
662 // enter() can make the ObjectMonitor busy. enter() returns false if
663 // we have lost the race to async deflation and we simply try again.
664 while (true) {
665 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
666 if (monitor->enter(current)) {
667 current->inc_held_monitor_count(1, true);
668 break;
669 }
670 }
671 current->set_current_pending_monitor_is_from_java(true);
672 }
673
674 // NOTE: must use heavy weight monitor to handle jni monitor exit
675 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
676 JavaThread* current = THREAD;
677
678 // The ObjectMonitor* can't be async deflated until ownership is
679 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
680 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
681 // If this thread has locked the object, exit the monitor. We
682 // intentionally do not use CHECK on check_owner because we must exit the
683 // monitor even if an exception was already pending.
684 if (monitor->check_owner(THREAD)) {
685 monitor->exit(current);
686 current->dec_held_monitor_count(1, true);
687 }
688 }
689
690 // -----------------------------------------------------------------------------
691 // Internal VM locks on java objects
692 // standard constructor, allows locking failures
693 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
694 _thread = thread;
695 _thread->check_for_valid_safepoint_state();
696 _obj = obj;
697
698 if (_obj() != nullptr) {
699 ObjectSynchronizer::enter(_obj, &_lock, _thread);
700 }
701 }
702
703 ObjectLocker::~ObjectLocker() {
704 if (_obj() != nullptr) {
705 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
706 }
707 }
708
709
710 // -----------------------------------------------------------------------------
711 // Wait/Notify/NotifyAll
712 // NOTE: must use heavy weight monitor to handle wait()
713 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
714 JavaThread* current = THREAD;
715 if (millis < 0) {
716 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
717 }
718 // The ObjectMonitor* can't be async deflated because the _waiters
719 // field is incremented before ownership is dropped and decremented
720 // after ownership is regained.
721 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
722
723 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
724 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
725
726 // This dummy call is in place to get around dtrace bug 6254741. Once
727 // that's fixed we can uncomment the following line, remove the call
728 // and change this function back into a "void" func.
729 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
730 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
731 return ret_code;
732 }
733
734 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
735 JavaThread* current = THREAD;
736
737 markWord mark = obj->mark();
738 if (LockingMode == LM_LIGHTWEIGHT) {
739 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
740 // Not inflated so there can't be any waiters to notify.
741 return;
742 }
743 } else if (LockingMode == LM_LEGACY) {
744 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
745 // Not inflated so there can't be any waiters to notify.
746 return;
747 }
748 }
749 // The ObjectMonitor* can't be async deflated until ownership is
750 // dropped by the calling thread.
751 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
752 monitor->notify(CHECK);
753 }
754
755 // NOTE: see comment of notify()
756 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
757 JavaThread* current = THREAD;
758
759 markWord mark = obj->mark();
760 if (LockingMode == LM_LIGHTWEIGHT) {
761 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
762 // Not inflated so there can't be any waiters to notify.
763 return;
764 }
765 } else if (LockingMode == LM_LEGACY) {
766 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
767 // Not inflated so there can't be any waiters to notify.
768 return;
769 }
770 }
771 // The ObjectMonitor* can't be async deflated until ownership is
772 // dropped by the calling thread.
773 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
774 monitor->notifyAll(CHECK);
775 }
776
777 // -----------------------------------------------------------------------------
778 // Hash Code handling
779
780 struct SharedGlobals {
781 char _pad_prefix[OM_CACHE_LINE_SIZE];
782 // This is a highly shared mostly-read variable.
783 // To avoid false-sharing it needs to be the sole occupant of a cache line.
784 volatile int stw_random;
785 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
786 // Hot RW variable -- Sequester to avoid false-sharing
787 volatile int hc_sequence;
788 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
789 };
790
791 static SharedGlobals GVars;
792
793 static markWord read_stable_mark(oop obj) {
794 markWord mark = obj->mark_acquire();
795 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
796 // New lightweight locking does not use the markWord::INFLATING() protocol.
797 return mark; // normal fast-path return
798 }
799
800 int its = 0;
801 for (;;) {
802 markWord mark = obj->mark_acquire();
803 if (!mark.is_being_inflated()) {
804 return mark; // normal fast-path return
805 }
806
807 // The object is being inflated by some other thread.
808 // The caller of read_stable_mark() must wait for inflation to complete.
809 // Avoid live-lock.
810
811 ++its;
812 if (its > 10000 || !os::is_MP()) {
813 if (its & 1) {
814 os::naked_yield();
815 } else {
816 // Note that the following code attenuates the livelock problem but is not
817 // a complete remedy. A more complete solution would require that the inflating
818 // thread hold the associated inflation lock. The following code simply restricts
819 // the number of spinners to at most one. We'll have N-2 threads blocked
820 // on the inflationlock, 1 thread holding the inflation lock and using
821 // a yield/park strategy, and 1 thread in the midst of inflation.
822 // A more refined approach would be to change the encoding of INFLATING
823 // to allow encapsulation of a native thread pointer. Threads waiting for
824 // inflation to complete would use CAS to push themselves onto a singly linked
825 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
826 // and calling park(). When inflation was complete the thread that accomplished inflation
827 // would detach the list and set the markword to inflated with a single CAS and
828 // then for each thread on the list, set the flag and unpark() the thread.
829
830 // Index into the lock array based on the current object address.
831 static_assert(is_power_of_2(inflation_lock_count()), "must be");
832 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
833 int YieldThenBlock = 0;
834 assert(ix < inflation_lock_count(), "invariant");
835 inflation_lock(ix)->lock();
836 while (obj->mark_acquire() == markWord::INFLATING()) {
837 // Beware: naked_yield() is advisory and has almost no effect on some platforms
838 // so we periodically call current->_ParkEvent->park(1).
839 // We use a mixed spin/yield/block mechanism.
840 if ((YieldThenBlock++) >= 16) {
841 Thread::current()->_ParkEvent->park(1);
842 } else {
843 os::naked_yield();
844 }
845 }
846 inflation_lock(ix)->unlock();
847 }
848 } else {
849 SpinPause(); // SMP-polite spinning
850 }
851 }
852 }
853
854 // hashCode() generation :
855 //
856 // Possibilities:
857 // * MD5Digest of {obj,stw_random}
858 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
859 // * A DES- or AES-style SBox[] mechanism
860 // * One of the Phi-based schemes, such as:
861 // 2654435761 = 2^32 * Phi (golden ratio)
862 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
863 // * A variation of Marsaglia's shift-xor RNG scheme.
864 // * (obj ^ stw_random) is appealing, but can result
865 // in undesirable regularity in the hashCode values of adjacent objects
866 // (objects allocated back-to-back, in particular). This could potentially
867 // result in hashtable collisions and reduced hashtable efficiency.
868 // There are simple ways to "diffuse" the middle address bits over the
869 // generated hashCode values:
870
871 static inline intptr_t get_next_hash(Thread* current, oop obj) {
872 intptr_t value = 0;
873 if (hashCode == 0) {
874 // This form uses global Park-Miller RNG.
875 // On MP system we'll have lots of RW access to a global, so the
876 // mechanism induces lots of coherency traffic.
877 value = os::random();
878 } else if (hashCode == 1) {
879 // This variation has the property of being stable (idempotent)
880 // between STW operations. This can be useful in some of the 1-0
881 // synchronization schemes.
882 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
883 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
884 } else if (hashCode == 2) {
885 value = 1; // for sensitivity testing
886 } else if (hashCode == 3) {
887 value = ++GVars.hc_sequence;
888 } else if (hashCode == 4) {
889 value = cast_from_oop<intptr_t>(obj);
890 } else {
891 // Marsaglia's xor-shift scheme with thread-specific state
892 // This is probably the best overall implementation -- we'll
893 // likely make this the default in future releases.
894 unsigned t = current->_hashStateX;
895 t ^= (t << 11);
896 current->_hashStateX = current->_hashStateY;
897 current->_hashStateY = current->_hashStateZ;
898 current->_hashStateZ = current->_hashStateW;
899 unsigned v = current->_hashStateW;
900 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
901 current->_hashStateW = v;
902 value = v;
903 }
904
905 value &= markWord::hash_mask;
906 if (value == 0) value = 0xBAD;
907 assert(value != markWord::no_hash, "invariant");
908 return value;
909 }
910
911 // Can be called from non JavaThreads (e.g., VMThread) for FastHashCode
912 // calculations as part of JVM/TI tagging.
913 static bool is_lock_owned(Thread* thread, oop obj) {
914 assert(LockingMode == LM_LIGHTWEIGHT, "only call this with new lightweight locking enabled");
915 return thread->is_Java_thread() ? JavaThread::cast(thread)->lock_stack().contains(obj) : false;
916 }
917
918 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
919
920 while (true) {
921 ObjectMonitor* monitor = nullptr;
922 markWord temp, test;
923 intptr_t hash;
924 markWord mark = read_stable_mark(obj);
925 if (VerifyHeavyMonitors) {
926 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
927 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
928 }
929 if (mark.is_neutral()) { // if this is a normal header
930 hash = mark.hash();
931 if (hash != 0) { // if it has a hash, just return it
932 return hash;
933 }
934 hash = get_next_hash(current, obj); // get a new hash
935 temp = mark.copy_set_hash(hash); // merge the hash into header
936 // try to install the hash
937 test = obj->cas_set_mark(temp, mark);
938 if (test == mark) { // if the hash was installed, return it
939 return hash;
940 }
941 // Failed to install the hash. It could be that another thread
942 // installed the hash just before our attempt or inflation has
943 // occurred or... so we fall thru to inflate the monitor for
944 // stability and then install the hash.
945 } else if (mark.has_monitor()) {
946 monitor = mark.monitor();
947 temp = monitor->header();
948 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
949 hash = temp.hash();
950 if (hash != 0) {
951 // It has a hash.
952
953 // Separate load of dmw/header above from the loads in
954 // is_being_async_deflated().
955
956 // dmw/header and _contentions may get written by different threads.
957 // Make sure to observe them in the same order when having several observers.
958 OrderAccess::loadload_for_IRIW();
959
960 if (monitor->is_being_async_deflated()) {
961 // But we can't safely use the hash if we detect that async
962 // deflation has occurred. So we attempt to restore the
963 // header/dmw to the object's header so that we only retry
964 // once if the deflater thread happens to be slow.
965 monitor->install_displaced_markword_in_object(obj);
966 continue;
967 }
968 return hash;
969 }
970 // Fall thru so we only have one place that installs the hash in
971 // the ObjectMonitor.
972 } else if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked() && is_lock_owned(current, obj)) {
973 // This is a fast-lock owned by the calling thread so use the
974 // markWord from the object.
975 hash = mark.hash();
976 if (hash != 0) { // if it has a hash, just return it
977 return hash;
978 }
979 } else if (LockingMode == LM_LEGACY && mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
980 // This is a stack-lock owned by the calling thread so fetch the
981 // displaced markWord from the BasicLock on the stack.
982 temp = mark.displaced_mark_helper();
983 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
984 hash = temp.hash();
985 if (hash != 0) { // if it has a hash, just return it
986 return hash;
987 }
988 // WARNING:
989 // The displaced header in the BasicLock on a thread's stack
990 // is strictly immutable. It CANNOT be changed in ANY cases.
991 // So we have to inflate the stack-lock into an ObjectMonitor
992 // even if the current thread owns the lock. The BasicLock on
993 // a thread's stack can be asynchronously read by other threads
994 // during an inflate() call so any change to that stack memory
995 // may not propagate to other threads correctly.
996 }
997
998 // Inflate the monitor to set the hash.
999
1000 // An async deflation can race after the inflate() call and before we
1001 // can update the ObjectMonitor's header with the hash value below.
1002 monitor = inflate(current, obj, inflate_cause_hash_code);
1003 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1004 mark = monitor->header();
1005 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1006 hash = mark.hash();
1007 if (hash == 0) { // if it does not have a hash
1008 hash = get_next_hash(current, obj); // get a new hash
1009 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1010 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1011 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1012 test = markWord(v);
1013 if (test != mark) {
1014 // The attempt to update the ObjectMonitor's header/dmw field
1015 // did not work. This can happen if another thread managed to
1016 // merge in the hash just before our cmpxchg().
1017 // If we add any new usages of the header/dmw field, this code
1018 // will need to be updated.
1019 hash = test.hash();
1020 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1021 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1022 }
1023 if (monitor->is_being_async_deflated()) {
1024 // If we detect that async deflation has occurred, then we
1025 // attempt to restore the header/dmw to the object's header
1026 // so that we only retry once if the deflater thread happens
1027 // to be slow.
1028 monitor->install_displaced_markword_in_object(obj);
1029 continue;
1030 }
1031 }
1032 // We finally get the hash.
1033 return hash;
1034 }
1035 }
1036
1037 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1038 Handle h_obj) {
1039 assert(current == JavaThread::current(), "Can only be called on current thread");
1040 oop obj = h_obj();
1041
1042 markWord mark = read_stable_mark(obj);
1043
1044 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1045 // stack-locked case, header points into owner's stack
1046 return current->is_lock_owned((address)mark.locker());
1047 }
1048
1049 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1050 // fast-locking case, see if lock is in current's lock stack
1051 return current->lock_stack().contains(h_obj());
1052 }
1053
1054 if (mark.has_monitor()) {
1055 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1056 // The first stage of async deflation does not affect any field
1057 // used by this comparison so the ObjectMonitor* is usable here.
1058 ObjectMonitor* monitor = mark.monitor();
1059 return monitor->is_entered(current) != 0;
1060 }
1061 // Unlocked case, header in place
1062 assert(mark.is_neutral(), "sanity check");
1063 return false;
1064 }
1065
1066 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1067 oop obj = h_obj();
1068 markWord mark = read_stable_mark(obj);
1069
1070 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1071 // stack-locked so header points into owner's stack.
1072 // owning_thread_from_monitor_owner() may also return null here:
1073 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1074 }
1075
1076 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1077 // fast-locked so get owner from the object.
1078 // owning_thread_from_object() may also return null here:
1079 return Threads::owning_thread_from_object(t_list, h_obj());
1080 }
1081
1082 if (mark.has_monitor()) {
1083 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1084 // The first stage of async deflation does not affect any field
1085 // used by this comparison so the ObjectMonitor* is usable here.
1086 ObjectMonitor* monitor = mark.monitor();
1087 assert(monitor != nullptr, "monitor should be non-null");
1088 // owning_thread_from_monitor() may also return null here:
1089 return Threads::owning_thread_from_monitor(t_list, monitor);
1090 }
1091
1092 // Unlocked case, header in place
1093 // Cannot have assertion since this object may have been
1094 // locked by another thread when reaching here.
1095 // assert(mark.is_neutral(), "sanity check");
1096
1097 return nullptr;
1098 }
1099
1100 // Visitors ...
1101
1102 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1103 // ObjectMonitors where owner is set to a stack-lock address in thread.
1104 //
1105 // This version of monitors_iterate() works with the in-use monitor list.
1106 //
1107 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1108 MonitorList::Iterator iter = _in_use_list.iterator();
1109 while (iter.has_next()) {
1110 ObjectMonitor* mid = iter.next();
1111 if (mid->owner() != thread) {
1112 // Not owned by the target thread and intentionally skips when owner
1113 // is set to a stack-lock address in the target thread.
1114 continue;
1115 }
1116 if (!mid->is_being_async_deflated() && mid->object_peek() != nullptr) {
1117 // Only process with closure if the object is set.
1118
1119 // monitors_iterate() is only called at a safepoint or when the
1120 // target thread is suspended or when the target thread is
1121 // operating on itself. The current closures in use today are
1122 // only interested in an owned ObjectMonitor and ownership
1123 // cannot be dropped under the calling contexts so the
1124 // ObjectMonitor cannot be async deflated.
1125 closure->do_monitor(mid);
1126 }
1127 }
1128 }
1129
1130 // This version of monitors_iterate() works with the specified linked list.
1131 //
1132 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure,
1133 ObjectMonitorsHashtable::PtrList* list,
1134 JavaThread* thread) {
1135 typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator;
1136 ObjectMonitorIterator iter(list->head());
1137 while (!iter.is_empty()) {
1138 ObjectMonitor* mid = *iter.next();
1139 // Owner set to a stack-lock address in thread should never be seen here:
1140 assert(mid->owner() == thread, "must be");
1141 if (!mid->is_being_async_deflated() && mid->object_peek() != nullptr) {
1142 // Only process with closure if the object is set.
1143
1144 // monitors_iterate() is only called at a safepoint or when the
1145 // target thread is suspended or when the target thread is
1146 // operating on itself. The current closures in use today are
1147 // only interested in an owned ObjectMonitor and ownership
1148 // cannot be dropped under the calling contexts so the
1149 // ObjectMonitor cannot be async deflated.
1150 closure->do_monitor(mid);
1151 }
1152 }
1153 }
1154
1155 static bool monitors_used_above_threshold(MonitorList* list) {
1156 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1157 return false;
1158 }
1159 // Start with ceiling based on a per-thread estimate:
1160 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1161 size_t old_ceiling = ceiling;
1162 if (ceiling < list->max()) {
1163 // The max used by the system has exceeded the ceiling so use that:
1164 ceiling = list->max();
1165 }
1166 size_t monitors_used = list->count();
1167 if (monitors_used == 0) { // empty list is easy
1168 return false;
1169 }
1170 if (NoAsyncDeflationProgressMax != 0 &&
1171 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1172 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1173 size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1174 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1175 log_info(monitorinflation)("Too many deflations without progress; "
1176 "bumping in_use_list_ceiling from " SIZE_FORMAT
1177 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1178 _no_progress_cnt = 0;
1179 ceiling = new_ceiling;
1180 }
1181
1182 // Check if our monitor usage is above the threshold:
1183 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1184 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1185 log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
1186 ", monitor_usage=" SIZE_FORMAT ", threshold=" INTX_FORMAT,
1187 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1188 return true;
1189 }
1190
1191 return false;
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 log_info(monitorinflation)("Async deflation needed: explicit request");
1214 return true;
1215 }
1216
1217 jlong time_since_last = time_since_last_async_deflation_ms();
1218
1219 if (AsyncDeflationInterval > 0 &&
1220 time_since_last > AsyncDeflationInterval &&
1221 monitors_used_above_threshold(&_in_use_list)) {
1222 // It's been longer than our specified deflate interval and there
1223 // are too many monitors in use. We don't deflate more frequently
1224 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1225 // in order to not swamp the MonitorDeflationThread.
1226 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1227 return true;
1228 }
1229
1230 if (GuaranteedAsyncDeflationInterval > 0 &&
1231 time_since_last > GuaranteedAsyncDeflationInterval) {
1232 // It's been longer than our specified guaranteed deflate interval.
1233 // We need to clean up the used monitors even if the threshold is
1234 // not reached, to keep the memory utilization at bay when many threads
1235 // touched many monitors.
1236 log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) "
1237 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1238 GuaranteedAsyncDeflationInterval, time_since_last);
1239
1240 // If this deflation has no progress, then it should not affect the no-progress
1241 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1242 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1243 // the generic code would bump the no-progress counter, and we compensate for that
1244 // by telling it to skip the update.
1245 //
1246 // If this deflation has progress, then it should let non-progress tracking
1247 // know about this, otherwise the threshold heuristics would kick in, potentially
1248 // experience no-progress due to aggressive cleanup by this deflation, and think
1249 // it is still in no-progress stride. In this "progress" case, the generic code would
1250 // zero the counter, and we allow it to happen.
1251 _no_progress_skip_increment = true;
1252
1253 return true;
1254 }
1255
1256 return false;
1257 }
1258
1259 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1260 JavaThread* current = JavaThread::current();
1261 bool ret_code = false;
1262
1263 jlong last_time = last_async_deflation_time_ns();
1264 set_is_async_deflation_requested(true);
1265 {
1266 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1267 ml.notify_all();
1268 }
1269 const int N_CHECKS = 5;
1270 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1271 if (last_async_deflation_time_ns() > last_time) {
1272 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1273 ret_code = true;
1274 break;
1275 }
1276 {
1277 // JavaThread has to honor the blocking protocol.
1278 ThreadBlockInVM tbivm(current);
1279 os::naked_short_sleep(999); // sleep for almost 1 second
1280 }
1281 }
1282 if (!ret_code) {
1283 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1284 }
1285
1286 return ret_code;
1287 }
1288
1289 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1290 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1291 }
1292
1293 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1294 const oop obj,
1295 ObjectSynchronizer::InflateCause cause) {
1296 assert(event != nullptr, "invariant");
1297 event->set_monitorClass(obj->klass());
1298 event->set_address((uintptr_t)(void*)obj);
1299 event->set_cause((u1)cause);
1300 event->commit();
1301 }
1302
1303 // Fast path code shared by multiple functions
1304 void ObjectSynchronizer::inflate_helper(oop obj) {
1305 markWord mark = obj->mark_acquire();
1306 if (mark.has_monitor()) {
1307 ObjectMonitor* monitor = mark.monitor();
1308 markWord dmw = monitor->header();
1309 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1310 return;
1311 }
1312 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1313 }
1314
1315 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1316 const InflateCause cause) {
1317 EventJavaMonitorInflate event;
1318
1319 for (;;) {
1320 const markWord mark = object->mark_acquire();
1321
1322 // The mark can be in one of the following states:
1323 // * inflated - Just return if using stack-locking.
1324 // If using fast-locking and the ObjectMonitor owner
1325 // is anonymous and the current thread owns the
1326 // object lock, then we make the current thread the
1327 // ObjectMonitor owner and remove the lock from the
1328 // current thread's lock stack.
1329 // * fast-locked - Coerce it to inflated from fast-locked.
1330 // * stack-locked - Coerce it to inflated from stack-locked.
1331 // * INFLATING - Busy wait for conversion from stack-locked to
1332 // inflated.
1333 // * neutral - Aggressively inflate the object.
1334
1335 // CASE: inflated
1336 if (mark.has_monitor()) {
1337 ObjectMonitor* inf = mark.monitor();
1338 markWord dmw = inf->header();
1339 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1340 if (LockingMode == LM_LIGHTWEIGHT && inf->is_owner_anonymous() && is_lock_owned(current, object)) {
1341 inf->set_owner_from_anonymous(current);
1342 JavaThread::cast(current)->lock_stack().remove(object);
1343 }
1344 return inf;
1345 }
1346
1347 if (LockingMode != LM_LIGHTWEIGHT) {
1348 // New lightweight locking does not use INFLATING.
1349 // CASE: inflation in progress - inflating over a stack-lock.
1350 // Some other thread is converting from stack-locked to inflated.
1351 // Only that thread can complete inflation -- other threads must wait.
1352 // The INFLATING value is transient.
1353 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1354 // We could always eliminate polling by parking the thread on some auxiliary list.
1355 if (mark == markWord::INFLATING()) {
1356 read_stable_mark(object);
1357 continue;
1358 }
1359 }
1360
1361 // CASE: fast-locked
1362 // Could be fast-locked either by current or by some other thread.
1363 //
1364 // Note that we allocate the ObjectMonitor speculatively, _before_
1365 // attempting to set the object's mark to the new ObjectMonitor. If
1366 // this thread owns the monitor, then we set the ObjectMonitor's
1367 // owner to this thread. Otherwise, we set the ObjectMonitor's owner
1368 // to anonymous. If we lose the race to set the object's mark to the
1369 // new ObjectMonitor, then we just delete it and loop around again.
1370 //
1371 LogStreamHandle(Trace, monitorinflation) lsh;
1372 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1373 ObjectMonitor* monitor = new ObjectMonitor(object);
1374 monitor->set_header(mark.set_unlocked());
1375 bool own = is_lock_owned(current, object);
1376 if (own) {
1377 // Owned by us.
1378 monitor->set_owner_from(nullptr, current);
1379 } else {
1380 // Owned by somebody else.
1381 monitor->set_owner_anonymous();
1382 }
1383 markWord monitor_mark = markWord::encode(monitor);
1384 markWord old_mark = object->cas_set_mark(monitor_mark, mark);
1385 if (old_mark == mark) {
1386 // Success! Return inflated monitor.
1387 if (own) {
1388 JavaThread::cast(current)->lock_stack().remove(object);
1389 }
1390 // Once the ObjectMonitor is configured and object is associated
1391 // with the ObjectMonitor, it is safe to allow async deflation:
1392 _in_use_list.add(monitor);
1393
1394 // Hopefully the performance counters are allocated on distinct
1395 // cache lines to avoid false sharing on MP systems ...
1396 OM_PERFDATA_OP(Inflations, inc());
1397 if (log_is_enabled(Trace, monitorinflation)) {
1398 ResourceMark rm(current);
1399 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1400 INTPTR_FORMAT ", type='%s'", p2i(object),
1401 object->mark().value(), object->klass()->external_name());
1402 }
1403 if (event.should_commit()) {
1404 post_monitor_inflate_event(&event, object, cause);
1405 }
1406 return monitor;
1407 } else {
1408 delete monitor;
1409 continue; // Interference -- just retry
1410 }
1411 }
1412
1413 // CASE: stack-locked
1414 // Could be stack-locked either by current or by some other thread.
1415 //
1416 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1417 // to install INFLATING into the mark word. We originally installed INFLATING,
1418 // allocated the ObjectMonitor, and then finally STed the address of the
1419 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1420 // the interval in which INFLATING appeared in the mark, thus increasing
1421 // the odds of inflation contention. If we lose the race to set INFLATING,
1422 // then we just delete the ObjectMonitor and loop around again.
1423 //
1424 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1425 assert(LockingMode != LM_LIGHTWEIGHT, "cannot happen with new lightweight locking");
1426 ObjectMonitor* m = new ObjectMonitor(object);
1427 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1428 // We do this before the CAS in order to minimize the length of time
1429 // in which INFLATING appears in the mark.
1430
1431 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1432 if (cmp != mark) {
1433 delete m;
1434 continue; // Interference -- just retry
1435 }
1436
1437 // We've successfully installed INFLATING (0) into the mark-word.
1438 // This is the only case where 0 will appear in a mark-word.
1439 // Only the singular thread that successfully swings the mark-word
1440 // to 0 can perform (or more precisely, complete) inflation.
1441 //
1442 // Why do we CAS a 0 into the mark-word instead of just CASing the
1443 // mark-word from the stack-locked value directly to the new inflated state?
1444 // Consider what happens when a thread unlocks a stack-locked object.
1445 // It attempts to use CAS to swing the displaced header value from the
1446 // on-stack BasicLock back into the object header. Recall also that the
1447 // header value (hash code, etc) can reside in (a) the object header, or
1448 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1449 // header in an ObjectMonitor. The inflate() routine must copy the header
1450 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1451 // the while preserving the hashCode stability invariants. If the owner
1452 // decides to release the lock while the value is 0, the unlock will fail
1453 // and control will eventually pass from slow_exit() to inflate. The owner
1454 // will then spin, waiting for the 0 value to disappear. Put another way,
1455 // the 0 causes the owner to stall if the owner happens to try to
1456 // drop the lock (restoring the header from the BasicLock to the object)
1457 // while inflation is in-progress. This protocol avoids races that might
1458 // would otherwise permit hashCode values to change or "flicker" for an object.
1459 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1460 // 0 serves as a "BUSY" inflate-in-progress indicator.
1461
1462
1463 // fetch the displaced mark from the owner's stack.
1464 // The owner can't die or unwind past the lock while our INFLATING
1465 // object is in the mark. Furthermore the owner can't complete
1466 // an unlock on the object, either.
1467 markWord dmw = mark.displaced_mark_helper();
1468 // Catch if the object's header is not neutral (not locked and
1469 // not marked is what we care about here).
1470 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1471
1472 // Setup monitor fields to proper values -- prepare the monitor
1473 m->set_header(dmw);
1474
1475 // Optimization: if the mark.locker stack address is associated
1476 // with this thread we could simply set m->_owner = current.
1477 // Note that a thread can inflate an object
1478 // that it has stack-locked -- as might happen in wait() -- directly
1479 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1480 m->set_owner_from(nullptr, mark.locker());
1481 // TODO-FIXME: assert BasicLock->dhw != 0.
1482
1483 // Must preserve store ordering. The monitor state must
1484 // be stable at the time of publishing the monitor address.
1485 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1486 // Release semantics so that above set_object() is seen first.
1487 object->release_set_mark(markWord::encode(m));
1488
1489 // Once ObjectMonitor is configured and the object is associated
1490 // with the ObjectMonitor, it is safe to allow async deflation:
1491 _in_use_list.add(m);
1492
1493 // Hopefully the performance counters are allocated on distinct cache lines
1494 // to avoid false sharing on MP systems ...
1495 OM_PERFDATA_OP(Inflations, inc());
1496 if (log_is_enabled(Trace, monitorinflation)) {
1497 ResourceMark rm(current);
1498 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1499 INTPTR_FORMAT ", type='%s'", p2i(object),
1500 object->mark().value(), object->klass()->external_name());
1501 }
1502 if (event.should_commit()) {
1503 post_monitor_inflate_event(&event, object, cause);
1504 }
1505 return m;
1506 }
1507
1508 // CASE: neutral
1509 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1510 // If we know we're inflating for entry it's better to inflate by swinging a
1511 // pre-locked ObjectMonitor pointer into the object header. A successful
1512 // CAS inflates the object *and* confers ownership to the inflating thread.
1513 // In the current implementation we use a 2-step mechanism where we CAS()
1514 // to inflate and then CAS() again to try to swing _owner from null to current.
1515 // An inflateTry() method that we could call from enter() would be useful.
1516
1517 // Catch if the object's header is not neutral (not locked and
1518 // not marked is what we care about here).
1519 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1520 ObjectMonitor* m = new ObjectMonitor(object);
1521 // prepare m for installation - set monitor to initial state
1522 m->set_header(mark);
1523
1524 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1525 delete m;
1526 m = nullptr;
1527 continue;
1528 // interference - the markword changed - just retry.
1529 // The state-transitions are one-way, so there's no chance of
1530 // live-lock -- "Inflated" is an absorbing state.
1531 }
1532
1533 // Once the ObjectMonitor is configured and object is associated
1534 // with the ObjectMonitor, it is safe to allow async deflation:
1535 _in_use_list.add(m);
1536
1537 // Hopefully the performance counters are allocated on distinct
1538 // cache lines to avoid false sharing on MP systems ...
1539 OM_PERFDATA_OP(Inflations, inc());
1540 if (log_is_enabled(Trace, monitorinflation)) {
1541 ResourceMark rm(current);
1542 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1543 INTPTR_FORMAT ", type='%s'", p2i(object),
1544 object->mark().value(), object->klass()->external_name());
1545 }
1546 if (event.should_commit()) {
1547 post_monitor_inflate_event(&event, object, cause);
1548 }
1549 return m;
1550 }
1551 }
1552
1553 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1554 const char* cnt_name, size_t cnt,
1555 LogStream* ls, elapsedTimer* timer_p) {
1556 if (!SafepointMechanism::should_process(current)) {
1557 return;
1558 }
1559
1560 // A safepoint/handshake has started.
1561 if (ls != nullptr) {
1562 timer_p->stop();
1563 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1564 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1565 op_name, cnt_name, cnt, in_use_list_ceiling(),
1566 _in_use_list.count(), _in_use_list.max());
1567 }
1568
1569 {
1570 // Honor block request.
1571 ThreadBlockInVM tbivm(current);
1572 }
1573
1574 if (ls != nullptr) {
1575 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1576 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1577 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1578 timer_p->start();
1579 }
1580 }
1581
1582 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1583 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1584 //
1585 // If table != nullptr, we gather owned ObjectMonitors indexed by the
1586 // owner in the table. Please note that ObjectMonitors where the owner
1587 // is set to a stack-lock address are NOT associated with the JavaThread
1588 // that holds that stack-lock. All of the current consumers of
1589 // ObjectMonitorsHashtable info only care about JNI locked monitors and
1590 // those do not have the owner set to a stack-lock address.
1591 //
1592 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1593 elapsedTimer* timer_p,
1594 ObjectMonitorsHashtable* table) {
1595 MonitorList::Iterator iter = _in_use_list.iterator();
1596 size_t deflated_count = 0;
1597
1598 while (iter.has_next()) {
1599 if (deflated_count >= (size_t)MonitorDeflationMax) {
1600 break;
1601 }
1602 ObjectMonitor* mid = iter.next();
1603 if (mid->deflate_monitor()) {
1604 deflated_count++;
1605 } else if (table != nullptr) {
1606 // The caller is interested in the owned ObjectMonitors. This does
1607 // not include when owner is set to a stack-lock address in thread.
1608 // This also does not capture unowned ObjectMonitors that cannot be
1609 // deflated because of a waiter.
1610 void* key = mid->owner();
1611 // Since deflate_idle_monitors() and deflate_monitor_list() can be
1612 // called more than once, we have to make sure the entry has not
1613 // already been added.
1614 if (key != nullptr && !table->has_entry(key, mid)) {
1615 table->add_entry(key, mid);
1616 }
1617 }
1618
1619 if (current->is_Java_thread()) {
1620 // A JavaThread must check for a safepoint/handshake and honor it.
1621 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1622 deflated_count, ls, timer_p);
1623 }
1624 }
1625
1626 return deflated_count;
1627 }
1628
1629 class HandshakeForDeflation : public HandshakeClosure {
1630 public:
1631 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1632
1633 void do_thread(Thread* thread) {
1634 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1635 INTPTR_FORMAT, p2i(thread));
1636 }
1637 };
1638
1639 class VM_RendezvousGCThreads : public VM_Operation {
1640 public:
1641 bool evaluate_at_safepoint() const override { return false; }
1642 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1643 void doit() override {
1644 Universe::heap()->safepoint_synchronize_begin();
1645 Universe::heap()->safepoint_synchronize_end();
1646 };
1647 };
1648
1649 static size_t delete_monitors(Thread* current, GrowableArray<ObjectMonitor*>* delete_list,
1650 LogStream* ls, elapsedTimer* timer_p) {
1651 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1652 size_t deleted_count = 0;
1653 for (ObjectMonitor* monitor: *delete_list) {
1654 delete monitor;
1655 deleted_count++;
1656 if (current->is_Java_thread()) {
1657 // A JavaThread must check for a safepoint/handshake and honor it.
1658 ObjectSynchronizer::chk_for_block_req(JavaThread::cast(current), "deletion", "deleted_count",
1659 deleted_count, ls, timer_p);
1660 }
1661 }
1662 return deleted_count;
1663 }
1664
1665 // This function is called by the MonitorDeflationThread to deflate
1666 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1667 // and VM_ThreadDump::doit() by the VMThread.
1668 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) {
1669 Thread* current = Thread::current();
1670 if (current->is_Java_thread()) {
1671 // The async deflation request has been processed.
1672 _last_async_deflation_time_ns = os::javaTimeNanos();
1673 set_is_async_deflation_requested(false);
1674 }
1675
1676 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1677 LogStreamHandle(Info, monitorinflation) lsh_info;
1678 LogStream* ls = nullptr;
1679 if (log_is_enabled(Debug, monitorinflation)) {
1680 ls = &lsh_debug;
1681 } else if (log_is_enabled(Info, monitorinflation)) {
1682 ls = &lsh_info;
1683 }
1684
1685 elapsedTimer timer;
1686 if (ls != nullptr) {
1687 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1688 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1689 timer.start();
1690 }
1691
1692 // Deflate some idle ObjectMonitors.
1693 size_t deflated_count = deflate_monitor_list(current, ls, &timer, table);
1694 size_t unlinked_count = 0;
1695 size_t deleted_count = 0;
1696 if (deflated_count > 0 || is_final_audit()) {
1697 // There are ObjectMonitors that have been deflated or this is the
1698 // final audit and all the remaining ObjectMonitors have been
1699 // deflated, BUT the MonitorDeflationThread blocked for the final
1700 // safepoint during unlinking.
1701
1702 // Unlink deflated ObjectMonitors from the in-use list.
1703 ResourceMark rm;
1704 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1705 unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, &delete_list);
1706 if (current->is_monitor_deflation_thread()) {
1707 if (ls != nullptr) {
1708 timer.stop();
1709 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1710 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1711 SIZE_FORMAT ", max=" SIZE_FORMAT,
1712 unlinked_count, in_use_list_ceiling(),
1713 _in_use_list.count(), _in_use_list.max());
1714 }
1715
1716 // A JavaThread needs to handshake in order to safely free the
1717 // ObjectMonitors that were deflated in this cycle.
1718 HandshakeForDeflation hfd_hc;
1719 Handshake::execute(&hfd_hc);
1720 // Also, we sync and desync GC threads around the handshake, so that they can
1721 // safely read the mark-word and look-through to the object-monitor, without
1722 // being afraid that the object-monitor is going away.
1723 VM_RendezvousGCThreads sync_gc;
1724 VMThread::execute(&sync_gc);
1725
1726 if (ls != nullptr) {
1727 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1728 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1729 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1730 timer.start();
1731 }
1732 } else {
1733 // This is not a monitor deflation thread.
1734 // No handshake or rendezvous is needed when we are already at safepoint.
1735 assert_at_safepoint();
1736 }
1737
1738 // After the handshake, safely free the ObjectMonitors that were
1739 // deflated and unlinked in this cycle.
1740 deleted_count = delete_monitors(current, &delete_list, ls, &timer);
1741 assert(unlinked_count == deleted_count, "must be");
1742 }
1743
1744 if (ls != nullptr) {
1745 timer.stop();
1746 if (deflated_count != 0 || unlinked_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1747 ls->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1748 deflated_count, unlinked_count, timer.seconds());
1749 }
1750 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1751 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1752 if (table != nullptr) {
1753 ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT,
1754 table->key_count(), table->om_count());
1755 }
1756 }
1757
1758 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1759 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1760
1761 GVars.stw_random = os::random();
1762
1763 if (deflated_count != 0) {
1764 _no_progress_cnt = 0;
1765 } else if (_no_progress_skip_increment) {
1766 _no_progress_skip_increment = false;
1767 } else {
1768 _no_progress_cnt++;
1769 }
1770
1771 return deflated_count;
1772 }
1773
1774 // Monitor cleanup on JavaThread::exit
1775
1776 // Iterate through monitor cache and attempt to release thread's monitors
1777 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1778 private:
1779 JavaThread* _thread;
1780
1781 public:
1782 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1783 void do_monitor(ObjectMonitor* mid) {
1784 intx rec = mid->complete_exit(_thread);
1785 _thread->dec_held_monitor_count(rec + 1);
1786 }
1787 };
1788
1789 // Release all inflated monitors owned by current thread. Lightweight monitors are
1790 // ignored. This is meant to be called during JNI thread detach which assumes
1791 // all remaining monitors are heavyweight. All exceptions are swallowed.
1792 // Scanning the extant monitor list can be time consuming.
1793 // A simple optimization is to add a per-thread flag that indicates a thread
1794 // called jni_monitorenter() during its lifetime.
1795 //
1796 // Instead of NoSafepointVerifier it might be cheaper to
1797 // use an idiom of the form:
1798 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1799 // <code that must not run at safepoint>
1800 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1801 // Since the tests are extremely cheap we could leave them enabled
1802 // for normal product builds.
1803
1804 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1805 assert(current == JavaThread::current(), "must be current Java thread");
1806 NoSafepointVerifier nsv;
1807 ReleaseJavaMonitorsClosure rjmc(current);
1808 ObjectSynchronizer::monitors_iterate(&rjmc, current);
1809 assert(!current->has_pending_exception(), "Should not be possible");
1810 current->clear_pending_exception();
1811 assert(current->held_monitor_count() == 0, "Should not be possible");
1812 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1813 current->clear_jni_monitor_count();
1814 }
1815
1816 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1817 switch (cause) {
1818 case inflate_cause_vm_internal: return "VM Internal";
1819 case inflate_cause_monitor_enter: return "Monitor Enter";
1820 case inflate_cause_wait: return "Monitor Wait";
1821 case inflate_cause_notify: return "Monitor Notify";
1822 case inflate_cause_hash_code: return "Monitor Hash Code";
1823 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1824 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1825 default:
1826 ShouldNotReachHere();
1827 }
1828 return "Unknown";
1829 }
1830
1831 //------------------------------------------------------------------------------
1832 // Debugging code
1833
1834 u_char* ObjectSynchronizer::get_gvars_addr() {
1835 return (u_char*)&GVars;
1836 }
1837
1838 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1839 return (u_char*)&GVars.hc_sequence;
1840 }
1841
1842 size_t ObjectSynchronizer::get_gvars_size() {
1843 return sizeof(SharedGlobals);
1844 }
1845
1846 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1847 return (u_char*)&GVars.stw_random;
1848 }
1849
1850 // Do the final audit and print of ObjectMonitor stats; must be done
1851 // by the VMThread at VM exit time.
1852 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1853 assert(Thread::current()->is_VM_thread(), "sanity check");
1854
1855 if (is_final_audit()) { // Only do the audit once.
1856 return;
1857 }
1858 set_is_final_audit();
1859 log_info(monitorinflation)("Starting the final audit.");
1860
1861 if (log_is_enabled(Info, monitorinflation)) {
1862 // Do deflations in order to reduce the in-use monitor population
1863 // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1864 // which is called by ObjectSynchronizer::audit_and_print_stats().
1865 while (deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) > 0) {
1866 ; // empty
1867 }
1868 // The other audit_and_print_stats() call is done at the Debug
1869 // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
1870 audit_and_print_stats(true /* on_exit */);
1871 }
1872 }
1873
1874 // This function can be called at a safepoint or it can be called when
1875 // we are trying to exit the VM. When we are trying to exit the VM, the
1876 // list walker functions can run in parallel with the other list
1877 // operations so spin-locking is used for safety.
1878 //
1879 // Calls to this function can be added in various places as a debugging
1880 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1881 // details logged at the Info level and 'false' for the 'on_exit'
1882 // parameter to have in-use monitor details logged at the Trace level.
1883 //
1884 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1885 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1886
1887 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1888 LogStreamHandle(Info, monitorinflation) lsh_info;
1889 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1890 LogStream* ls = nullptr;
1891 if (log_is_enabled(Trace, monitorinflation)) {
1892 ls = &lsh_trace;
1893 } else if (log_is_enabled(Debug, monitorinflation)) {
1894 ls = &lsh_debug;
1895 } else if (log_is_enabled(Info, monitorinflation)) {
1896 ls = &lsh_info;
1897 }
1898 assert(ls != nullptr, "sanity check");
1899
1900 int error_cnt = 0;
1901
1902 ls->print_cr("Checking in_use_list:");
1903 chk_in_use_list(ls, &error_cnt);
1904
1905 if (error_cnt == 0) {
1906 ls->print_cr("No errors found in in_use_list checks.");
1907 } else {
1908 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1909 }
1910
1911 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1912 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1913 // When exiting this log output is at the Info level. When called
1914 // at a safepoint, this log output is at the Trace level since
1915 // there can be a lot of it.
1916 log_in_use_monitor_details(ls);
1917 }
1918
1919 ls->flush();
1920
1921 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1922 }
1923
1924 // Check the in_use_list; log the results of the checks.
1925 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1926 size_t l_in_use_count = _in_use_list.count();
1927 size_t l_in_use_max = _in_use_list.max();
1928 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1929 l_in_use_max);
1930
1931 size_t ck_in_use_count = 0;
1932 MonitorList::Iterator iter = _in_use_list.iterator();
1933 while (iter.has_next()) {
1934 ObjectMonitor* mid = iter.next();
1935 chk_in_use_entry(mid, out, error_cnt_p);
1936 ck_in_use_count++;
1937 }
1938
1939 if (l_in_use_count == ck_in_use_count) {
1940 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1941 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1942 } else {
1943 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1944 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1945 ck_in_use_count);
1946 }
1947
1948 size_t ck_in_use_max = _in_use_list.max();
1949 if (l_in_use_max == ck_in_use_max) {
1950 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
1951 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1952 } else {
1953 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
1954 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
1955 }
1956 }
1957
1958 // Check an in-use monitor entry; log any errors.
1959 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1960 int* error_cnt_p) {
1961 if (n->owner_is_DEFLATER_MARKER()) {
1962 // This should not happen, but if it does, it is not fatal.
1963 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
1964 "deflated.", p2i(n));
1965 return;
1966 }
1967 if (n->header().value() == 0) {
1968 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1969 "have non-null _header field.", p2i(n));
1970 *error_cnt_p = *error_cnt_p + 1;
1971 }
1972 const oop obj = n->object_peek();
1973 if (obj != nullptr) {
1974 const markWord mark = obj->mark();
1975 if (!mark.has_monitor()) {
1976 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1977 "object does not think it has a monitor: obj="
1978 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1979 p2i(obj), mark.value());
1980 *error_cnt_p = *error_cnt_p + 1;
1981 }
1982 ObjectMonitor* const obj_mon = mark.monitor();
1983 if (n != obj_mon) {
1984 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1985 "object does not refer to the same monitor: obj="
1986 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1987 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1988 *error_cnt_p = *error_cnt_p + 1;
1989 }
1990 }
1991 }
1992
1993 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1994 // flags indicate why the entry is in-use, 'object' and 'object type'
1995 // indicate the associated object and its type.
1996 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
1997 stringStream ss;
1998 if (_in_use_list.count() > 0) {
1999 out->print_cr("In-use monitor info:");
2000 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2001 out->print_cr("%18s %s %18s %18s",
2002 "monitor", "BHL", "object", "object type");
2003 out->print_cr("================== === ================== ==================");
2004 MonitorList::Iterator iter = _in_use_list.iterator();
2005 while (iter.has_next()) {
2006 ObjectMonitor* mid = iter.next();
2007 const oop obj = mid->object_peek();
2008 const markWord mark = mid->header();
2009 ResourceMark rm;
2010 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid),
2011 mid->is_busy(), mark.hash() != 0, mid->owner() != nullptr,
2012 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2013 if (mid->is_busy()) {
2014 out->print(" (%s)", mid->is_busy_to_string(&ss));
2015 ss.reset();
2016 }
2017 out->cr();
2018 }
2019 }
2020
2021 out->flush();
2022 }