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/suspendibleThreadSet.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 #define CHECK_THROW_NOSYNC_IMSE(obj) \
302 if (EnableValhalla && (obj)->mark().is_inline_type()) { \
303 JavaThread* THREAD = current; \
304 ResourceMark rm(THREAD); \
305 THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
306 }
307
308 #define CHECK_THROW_NOSYNC_IMSE_0(obj) \
309 if (EnableValhalla && (obj)->mark().is_inline_type()) { \
310 JavaThread* THREAD = current; \
311 ResourceMark rm(THREAD); \
312 THROW_MSG_0(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
313 }
314
315 // =====================> Quick functions
316
317 // The quick_* forms are special fast-path variants used to improve
318 // performance. In the simplest case, a "quick_*" implementation could
319 // simply return false, in which case the caller will perform the necessary
320 // state transitions and call the slow-path form.
321 // The fast-path is designed to handle frequently arising cases in an efficient
322 // manner and is just a degenerate "optimistic" variant of the slow-path.
323 // returns true -- to indicate the call was satisfied.
324 // returns false -- to indicate the call needs the services of the slow-path.
325 // A no-loitering ordinance is in effect for code in the quick_* family
326 // operators: safepoints or indefinite blocking (blocking that might span a
327 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
328 // entry.
329 //
330 // Consider: An interesting optimization is to have the JIT recognize the
331 // following common idiom:
332 // synchronized (someobj) { .... ; notify(); }
333 // That is, we find a notify() or notifyAll() call that immediately precedes
334 // the monitorexit operation. In that case the JIT could fuse the operations
335 // into a single notifyAndExit() runtime primitive.
336
337 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
338 assert(current->thread_state() == _thread_in_Java, "invariant");
339 NoSafepointVerifier nsv;
340 if (obj == nullptr) return false; // slow-path for invalid obj
341 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
342 const markWord mark = obj->mark();
343
344 if (LockingMode == LM_LIGHTWEIGHT) {
345 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
346 // Degenerate notify
347 // fast-locked by caller so by definition the implied waitset is empty.
348 return true;
349 }
350 } else if (LockingMode == LM_LEGACY) {
351 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
352 // Degenerate notify
353 // stack-locked by caller so by definition the implied waitset is empty.
354 return true;
355 }
356 }
357
358 if (mark.has_monitor()) {
359 ObjectMonitor* const mon = mark.monitor();
360 assert(mon->object() == oop(obj), "invariant");
361 if (mon->owner() != current) return false; // slow-path for IMS exception
362
363 if (mon->first_waiter() != nullptr) {
364 // We have one or more waiters. Since this is an inflated monitor
365 // that we own, we can transfer one or more threads from the waitset
366 // to the entrylist here and now, avoiding the slow-path.
367 if (all) {
368 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
369 } else {
370 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
371 }
372 int free_count = 0;
373 do {
374 mon->INotify(current);
375 ++free_count;
376 } while (mon->first_waiter() != nullptr && all);
377 OM_PERFDATA_OP(Notifications, inc(free_count));
378 }
379 return true;
380 }
381
382 // other IMS exception states take the slow-path
383 return false;
384 }
385
386
387 // The LockNode emitted directly at the synchronization site would have
388 // been too big if it were to have included support for the cases of inflated
389 // recursive enter and exit, so they go here instead.
390 // Note that we can't safely call AsyncPrintJavaStack() from within
391 // quick_enter() as our thread state remains _in_Java.
392
393 bool ObjectSynchronizer::quick_enter(oop obj, JavaThread* current,
394 BasicLock * lock) {
395 assert(current->thread_state() == _thread_in_Java, "invariant");
396 NoSafepointVerifier nsv;
397 if (obj == nullptr) return false; // Need to throw NPE
398 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
399
400 if (obj->klass()->is_value_based()) {
401 return false;
402 }
403
404 const markWord mark = obj->mark();
405
406 if (mark.has_monitor()) {
407 ObjectMonitor* const m = mark.monitor();
408 // An async deflation or GC can race us before we manage to make
409 // the ObjectMonitor busy by setting the owner below. If we detect
410 // that race we just bail out to the slow-path here.
411 if (m->object_peek() == nullptr) {
412 return false;
413 }
414 JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
415
416 // Lock contention and Transactional Lock Elision (TLE) diagnostics
417 // and observability
418 // Case: light contention possibly amenable to TLE
419 // Case: TLE inimical operations such as nested/recursive synchronization
420
421 if (owner == current) {
422 m->_recursions++;
423 current->inc_held_monitor_count();
424 return true;
425 }
426
427 if (LockingMode != LM_LIGHTWEIGHT) {
428 // This Java Monitor is inflated so obj's header will never be
429 // displaced to this thread's BasicLock. Make the displaced header
430 // non-null so this BasicLock is not seen as recursive nor as
431 // being locked. We do this unconditionally so that this thread's
432 // BasicLock cannot be mis-interpreted by any stack walkers. For
433 // performance reasons, stack walkers generally first check for
434 // stack-locking in the object's header, the second check is for
435 // recursive stack-locking in the displaced header in the BasicLock,
436 // and last are the inflated Java Monitor (ObjectMonitor) checks.
437 lock->set_displaced_header(markWord::unused_mark());
438 }
439
440 if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) {
441 assert(m->_recursions == 0, "invariant");
442 current->inc_held_monitor_count();
443 return true;
444 }
445 }
446
447 // Note that we could inflate in quick_enter.
448 // This is likely a useful optimization
449 // Critically, in quick_enter() we must not:
450 // -- block indefinitely, or
451 // -- reach a safepoint
452
453 return false; // revert to slow-path
454 }
455
456 // Handle notifications when synchronizing on value based classes
457 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* current) {
458 frame last_frame = current->last_frame();
459 bool bcp_was_adjusted = false;
460 // Don't decrement bcp if it points to the frame's first instruction. This happens when
461 // handle_sync_on_value_based_class() is called because of a synchronized method. There
462 // is no actual monitorenter instruction in the byte code in this case.
463 if (last_frame.is_interpreted_frame() &&
464 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
465 // adjust bcp to point back to monitorenter so that we print the correct line numbers
466 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
467 bcp_was_adjusted = true;
468 }
469
470 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
471 ResourceMark rm(current);
472 stringStream ss;
473 current->print_active_stack_on(&ss);
474 char* base = (char*)strstr(ss.base(), "at");
475 char* newline = (char*)strchr(ss.base(), '\n');
476 if (newline != nullptr) {
477 *newline = '\0';
478 }
479 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
480 } else {
481 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
482 ResourceMark rm(current);
483 Log(valuebasedclasses) vblog;
484
485 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
486 if (current->has_last_Java_frame()) {
487 LogStream info_stream(vblog.info());
488 current->print_active_stack_on(&info_stream);
489 } else {
490 vblog.info("Cannot find the last Java frame");
491 }
492
493 EventSyncOnValueBasedClass event;
494 if (event.should_commit()) {
495 event.set_valueBasedClass(obj->klass());
496 event.commit();
497 }
498 }
499
500 if (bcp_was_adjusted) {
501 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
502 }
503 }
504
505 static bool useHeavyMonitors() {
506 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
507 return LockingMode == LM_MONITOR;
508 #else
509 return false;
510 #endif
511 }
512
513 // -----------------------------------------------------------------------------
514 // Monitor Enter/Exit
515 // The interpreter and compiler assembly code tries to lock using the fast path
516 // of this algorithm. Make sure to update that code if the following function is
517 // changed. The implementation is extremely sensitive to race condition. Be careful.
518
519 void ObjectSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
520 CHECK_THROW_NOSYNC_IMSE(obj);
521 if (obj->klass()->is_value_based()) {
522 handle_sync_on_value_based_class(obj, current);
523 }
524
525 current->inc_held_monitor_count();
526
527 if (!useHeavyMonitors()) {
528 if (LockingMode == LM_LIGHTWEIGHT) {
529 // Fast-locking does not use the 'lock' argument.
530 LockStack& lock_stack = current->lock_stack();
531 if (lock_stack.can_push()) {
532 markWord mark = obj()->mark_acquire();
533 if (mark.is_neutral()) {
534 assert(!lock_stack.contains(obj()), "thread must not already hold the lock");
535 // Try to swing into 'fast-locked' state.
536 markWord locked_mark = mark.set_fast_locked();
537 markWord old_mark = obj()->cas_set_mark(locked_mark, mark);
538 if (old_mark == mark) {
539 // Successfully fast-locked, push object to lock-stack and return.
540 lock_stack.push(obj());
541 return;
542 }
543 }
544 }
545 // All other paths fall-through to inflate-enter.
546 } else if (LockingMode == LM_LEGACY) {
547 markWord mark = obj->mark();
548 if (mark.is_neutral()) {
549 // Anticipate successful CAS -- the ST of the displaced mark must
550 // be visible <= the ST performed by the CAS.
551 lock->set_displaced_header(mark);
552 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
553 return;
554 }
555 // Fall through to inflate() ...
556 } else if (mark.has_locker() &&
557 current->is_lock_owned((address) mark.locker())) {
558 assert(lock != mark.locker(), "must not re-lock the same lock");
559 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
560 lock->set_displaced_header(markWord::from_pointer(nullptr));
561 return;
562 }
563
564 // The object header will never be displaced to this lock,
565 // so it does not matter what the value is, except that it
566 // must be non-zero to avoid looking like a re-entrant lock,
567 // and must not look locked either.
568 lock->set_displaced_header(markWord::unused_mark());
569 }
570 } else if (VerifyHeavyMonitors) {
571 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
572 }
573
574 // An async deflation can race after the inflate() call and before
575 // enter() can make the ObjectMonitor busy. enter() returns false if
576 // we have lost the race to async deflation and we simply try again.
577 while (true) {
578 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
579 if (monitor->enter(current)) {
580 return;
581 }
582 }
583 }
584
585 void ObjectSynchronizer::exit(oop object, BasicLock* lock, JavaThread* current) {
586 current->dec_held_monitor_count();
587
588 if (!useHeavyMonitors()) {
589 markWord mark = object->mark();
590 if (EnableValhalla && mark.is_inline_type()) {
591 return;
592 }
593 if (LockingMode == LM_LIGHTWEIGHT) {
594 // Fast-locking does not use the 'lock' argument.
595 if (mark.is_fast_locked()) {
596 markWord unlocked_mark = mark.set_unlocked();
597 markWord old_mark = object->cas_set_mark(unlocked_mark, mark);
598 if (old_mark != mark) {
599 // Another thread won the CAS, it must have inflated the monitor.
600 // It can only have installed an anonymously locked monitor at this point.
601 // Fetch that monitor, set owner correctly to this thread, and
602 // exit it (allowing waiting threads to enter).
603 assert(old_mark.has_monitor(), "must have monitor");
604 ObjectMonitor* monitor = old_mark.monitor();
605 assert(monitor->is_owner_anonymous(), "must be anonymous owner");
606 monitor->set_owner_from_anonymous(current);
607 monitor->exit(current);
608 }
609 LockStack& lock_stack = current->lock_stack();
610 lock_stack.remove(object);
611 return;
612 }
613 } else if (LockingMode == LM_LEGACY) {
614 markWord dhw = lock->displaced_header();
615 if (dhw.value() == 0) {
616 // If the displaced header is null, then this exit matches up with
617 // a recursive enter. No real work to do here except for diagnostics.
618 #ifndef PRODUCT
619 if (mark != markWord::INFLATING()) {
620 // Only do diagnostics if we are not racing an inflation. Simply
621 // exiting a recursive enter of a Java Monitor that is being
622 // inflated is safe; see the has_monitor() comment below.
623 assert(!mark.is_neutral(), "invariant");
624 assert(!mark.has_locker() ||
625 current->is_lock_owned((address)mark.locker()), "invariant");
626 if (mark.has_monitor()) {
627 // The BasicLock's displaced_header is marked as a recursive
628 // enter and we have an inflated Java Monitor (ObjectMonitor).
629 // This is a special case where the Java Monitor was inflated
630 // after this thread entered the stack-lock recursively. When a
631 // Java Monitor is inflated, we cannot safely walk the Java
632 // Monitor owner's stack and update the BasicLocks because a
633 // Java Monitor can be asynchronously inflated by a thread that
634 // does not own the Java Monitor.
635 ObjectMonitor* m = mark.monitor();
636 assert(m->object()->mark() == mark, "invariant");
637 assert(m->is_entered(current), "invariant");
638 }
639 }
640 #endif
641 return;
642 }
643
644 if (mark == markWord::from_pointer(lock)) {
645 // If the object is stack-locked by the current thread, try to
646 // swing the displaced header from the BasicLock back to the mark.
647 assert(dhw.is_neutral(), "invariant");
648 if (object->cas_set_mark(dhw, mark) == mark) {
649 return;
650 }
651 }
652 }
653 } else if (VerifyHeavyMonitors) {
654 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
655 }
656
657 // We have to take the slow-path of possible inflation and then exit.
658 // The ObjectMonitor* can't be async deflated until ownership is
659 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
660 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
661 if (LockingMode == LM_LIGHTWEIGHT && monitor->is_owner_anonymous()) {
662 // It must be owned by us. Pop lock object from lock stack.
663 LockStack& lock_stack = current->lock_stack();
664 oop popped = lock_stack.pop();
665 assert(popped == object, "must be owned by this thread");
666 monitor->set_owner_from_anonymous(current);
667 }
668 monitor->exit(current);
669 }
670
671 // -----------------------------------------------------------------------------
672 // JNI locks on java objects
673 // NOTE: must use heavy weight monitor to handle jni monitor enter
674 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
675 if (obj->klass()->is_value_based()) {
676 handle_sync_on_value_based_class(obj, current);
677 }
678 CHECK_THROW_NOSYNC_IMSE(obj);
679
680 // the current locking is from JNI instead of Java code
681 current->set_current_pending_monitor_is_from_java(false);
682 // An async deflation can race after the inflate() call and before
683 // enter() can make the ObjectMonitor busy. enter() returns false if
684 // we have lost the race to async deflation and we simply try again.
685 while (true) {
686 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_jni_enter);
687 if (monitor->enter(current)) {
688 current->inc_held_monitor_count(1, true);
689 break;
690 }
691 }
692 current->set_current_pending_monitor_is_from_java(true);
693 }
694
695 // NOTE: must use heavy weight monitor to handle jni monitor exit
696 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
697 JavaThread* current = THREAD;
698 CHECK_THROW_NOSYNC_IMSE(obj);
699
700 // The ObjectMonitor* can't be async deflated until ownership is
701 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
702 ObjectMonitor* monitor = inflate(current, obj, inflate_cause_jni_exit);
703 // If this thread has locked the object, exit the monitor. We
704 // intentionally do not use CHECK on check_owner because we must exit the
705 // monitor even if an exception was already pending.
706 if (monitor->check_owner(THREAD)) {
707 monitor->exit(current);
708 current->dec_held_monitor_count(1, true);
709 }
710 }
711
712 // -----------------------------------------------------------------------------
713 // Internal VM locks on java objects
714 // standard constructor, allows locking failures
715 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
716 _thread = thread;
717 _thread->check_for_valid_safepoint_state();
718 _obj = obj;
719
720 if (_obj() != nullptr) {
721 ObjectSynchronizer::enter(_obj, &_lock, _thread);
722 }
723 }
724
725 ObjectLocker::~ObjectLocker() {
726 if (_obj() != nullptr) {
727 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
728 }
729 }
730
731
732 // -----------------------------------------------------------------------------
733 // Wait/Notify/NotifyAll
734 // NOTE: must use heavy weight monitor to handle wait()
735 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
736 JavaThread* current = THREAD;
737 CHECK_THROW_NOSYNC_IMSE_0(obj);
738 if (millis < 0) {
739 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
740 }
741 // The ObjectMonitor* can't be async deflated because the _waiters
742 // field is incremented before ownership is dropped and decremented
743 // after ownership is regained.
744 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_wait);
745
746 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
747 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
748
749 // This dummy call is in place to get around dtrace bug 6254741. Once
750 // that's fixed we can uncomment the following line, remove the call
751 // and change this function back into a "void" func.
752 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
753 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
754 return ret_code;
755 }
756
757 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
758 JavaThread* current = THREAD;
759 CHECK_THROW_NOSYNC_IMSE(obj);
760
761 markWord mark = obj->mark();
762 if (LockingMode == LM_LIGHTWEIGHT) {
763 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
764 // Not inflated so there can't be any waiters to notify.
765 return;
766 }
767 } else if (LockingMode == LM_LEGACY) {
768 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
769 // Not inflated so there can't be any waiters to notify.
770 return;
771 }
772 }
773 // The ObjectMonitor* can't be async deflated until ownership is
774 // dropped by the calling thread.
775 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
776 monitor->notify(CHECK);
777 }
778
779 // NOTE: see comment of notify()
780 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
781 JavaThread* current = THREAD;
782 CHECK_THROW_NOSYNC_IMSE(obj);
783
784 markWord mark = obj->mark();
785 if (LockingMode == LM_LIGHTWEIGHT) {
786 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
787 // Not inflated so there can't be any waiters to notify.
788 return;
789 }
790 } else if (LockingMode == LM_LEGACY) {
791 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
792 // Not inflated so there can't be any waiters to notify.
793 return;
794 }
795 }
796 // The ObjectMonitor* can't be async deflated until ownership is
797 // dropped by the calling thread.
798 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_notify);
799 monitor->notifyAll(CHECK);
800 }
801
802 // -----------------------------------------------------------------------------
803 // Hash Code handling
804
805 struct SharedGlobals {
806 char _pad_prefix[OM_CACHE_LINE_SIZE];
807 // This is a highly shared mostly-read variable.
808 // To avoid false-sharing it needs to be the sole occupant of a cache line.
809 volatile int stw_random;
810 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
811 // Hot RW variable -- Sequester to avoid false-sharing
812 volatile int hc_sequence;
813 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
814 };
815
816 static SharedGlobals GVars;
817
818 static markWord read_stable_mark(oop obj) {
819 markWord mark = obj->mark_acquire();
820 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
821 // New lightweight locking does not use the markWord::INFLATING() protocol.
822 return mark; // normal fast-path return
823 }
824
825 int its = 0;
826 for (;;) {
827 markWord mark = obj->mark_acquire();
828 if (!mark.is_being_inflated()) {
829 return mark; // normal fast-path return
830 }
831
832 // The object is being inflated by some other thread.
833 // The caller of read_stable_mark() must wait for inflation to complete.
834 // Avoid live-lock.
835
836 ++its;
837 if (its > 10000 || !os::is_MP()) {
838 if (its & 1) {
839 os::naked_yield();
840 } else {
841 // Note that the following code attenuates the livelock problem but is not
842 // a complete remedy. A more complete solution would require that the inflating
843 // thread hold the associated inflation lock. The following code simply restricts
844 // the number of spinners to at most one. We'll have N-2 threads blocked
845 // on the inflationlock, 1 thread holding the inflation lock and using
846 // a yield/park strategy, and 1 thread in the midst of inflation.
847 // A more refined approach would be to change the encoding of INFLATING
848 // to allow encapsulation of a native thread pointer. Threads waiting for
849 // inflation to complete would use CAS to push themselves onto a singly linked
850 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
851 // and calling park(). When inflation was complete the thread that accomplished inflation
852 // would detach the list and set the markword to inflated with a single CAS and
853 // then for each thread on the list, set the flag and unpark() the thread.
854
855 // Index into the lock array based on the current object address.
856 static_assert(is_power_of_2(inflation_lock_count()), "must be");
857 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
858 int YieldThenBlock = 0;
859 assert(ix < inflation_lock_count(), "invariant");
860 inflation_lock(ix)->lock();
861 while (obj->mark_acquire() == markWord::INFLATING()) {
862 // Beware: naked_yield() is advisory and has almost no effect on some platforms
863 // so we periodically call current->_ParkEvent->park(1).
864 // We use a mixed spin/yield/block mechanism.
865 if ((YieldThenBlock++) >= 16) {
866 Thread::current()->_ParkEvent->park(1);
867 } else {
868 os::naked_yield();
869 }
870 }
871 inflation_lock(ix)->unlock();
872 }
873 } else {
874 SpinPause(); // SMP-polite spinning
875 }
876 }
877 }
878
879 // hashCode() generation :
880 //
881 // Possibilities:
882 // * MD5Digest of {obj,stw_random}
883 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
884 // * A DES- or AES-style SBox[] mechanism
885 // * One of the Phi-based schemes, such as:
886 // 2654435761 = 2^32 * Phi (golden ratio)
887 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
888 // * A variation of Marsaglia's shift-xor RNG scheme.
889 // * (obj ^ stw_random) is appealing, but can result
890 // in undesirable regularity in the hashCode values of adjacent objects
891 // (objects allocated back-to-back, in particular). This could potentially
892 // result in hashtable collisions and reduced hashtable efficiency.
893 // There are simple ways to "diffuse" the middle address bits over the
894 // generated hashCode values:
895
896 static inline intptr_t get_next_hash(Thread* current, oop obj) {
897 intptr_t value = 0;
898 if (hashCode == 0) {
899 // This form uses global Park-Miller RNG.
900 // On MP system we'll have lots of RW access to a global, so the
901 // mechanism induces lots of coherency traffic.
902 value = os::random();
903 } else if (hashCode == 1) {
904 // This variation has the property of being stable (idempotent)
905 // between STW operations. This can be useful in some of the 1-0
906 // synchronization schemes.
907 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
908 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
909 } else if (hashCode == 2) {
910 value = 1; // for sensitivity testing
911 } else if (hashCode == 3) {
912 value = ++GVars.hc_sequence;
913 } else if (hashCode == 4) {
914 value = cast_from_oop<intptr_t>(obj);
915 } else {
916 // Marsaglia's xor-shift scheme with thread-specific state
917 // This is probably the best overall implementation -- we'll
918 // likely make this the default in future releases.
919 unsigned t = current->_hashStateX;
920 t ^= (t << 11);
921 current->_hashStateX = current->_hashStateY;
922 current->_hashStateY = current->_hashStateZ;
923 current->_hashStateZ = current->_hashStateW;
924 unsigned v = current->_hashStateW;
925 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
926 current->_hashStateW = v;
927 value = v;
928 }
929
930 value &= markWord::hash_mask;
931 if (value == 0) value = 0xBAD;
932 assert(value != markWord::no_hash, "invariant");
933 return value;
934 }
935
936 // Can be called from non JavaThreads (e.g., VMThread) for FastHashCode
937 // calculations as part of JVM/TI tagging.
938 static bool is_lock_owned(Thread* thread, oop obj) {
939 assert(LockingMode == LM_LIGHTWEIGHT, "only call this with new lightweight locking enabled");
940 return thread->is_Java_thread() ? JavaThread::cast(thread)->lock_stack().contains(obj) : false;
941 }
942
943 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
944 if (EnableValhalla && obj->klass()->is_inline_klass()) {
945 // VM should be calling bootstrap method
946 ShouldNotReachHere();
947 }
948
949 while (true) {
950 ObjectMonitor* monitor = nullptr;
951 markWord temp, test;
952 intptr_t hash;
953 markWord mark = read_stable_mark(obj);
954 if (VerifyHeavyMonitors) {
955 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
956 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
957 }
958 if (mark.is_neutral()) { // if this is a normal header
959 hash = mark.hash();
960 if (hash != 0) { // if it has a hash, just return it
961 return hash;
962 }
963 hash = get_next_hash(current, obj); // get a new hash
964 temp = mark.copy_set_hash(hash); // merge the hash into header
965 // try to install the hash
966 test = obj->cas_set_mark(temp, mark);
967 if (test == mark) { // if the hash was installed, return it
968 return hash;
969 }
970 // Failed to install the hash. It could be that another thread
971 // installed the hash just before our attempt or inflation has
972 // occurred or... so we fall thru to inflate the monitor for
973 // stability and then install the hash.
974 } else if (mark.has_monitor()) {
975 monitor = mark.monitor();
976 temp = monitor->header();
977 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
978 hash = temp.hash();
979 if (hash != 0) {
980 // It has a hash.
981
982 // Separate load of dmw/header above from the loads in
983 // is_being_async_deflated().
984
985 // dmw/header and _contentions may get written by different threads.
986 // Make sure to observe them in the same order when having several observers.
987 OrderAccess::loadload_for_IRIW();
988
989 if (monitor->is_being_async_deflated()) {
990 // But we can't safely use the hash if we detect that async
991 // deflation has occurred. So we attempt to restore the
992 // header/dmw to the object's header so that we only retry
993 // once if the deflater thread happens to be slow.
994 monitor->install_displaced_markword_in_object(obj);
995 continue;
996 }
997 return hash;
998 }
999 // Fall thru so we only have one place that installs the hash in
1000 // the ObjectMonitor.
1001 } else if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked() && is_lock_owned(current, obj)) {
1002 // This is a fast-lock owned by the calling thread so use the
1003 // markWord from the object.
1004 hash = mark.hash();
1005 if (hash != 0) { // if it has a hash, just return it
1006 return hash;
1007 }
1008 } else if (LockingMode == LM_LEGACY && mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
1009 // This is a stack-lock owned by the calling thread so fetch the
1010 // displaced markWord from the BasicLock on the stack.
1011 temp = mark.displaced_mark_helper();
1012 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1013 hash = temp.hash();
1014 if (hash != 0) { // if it has a hash, just return it
1015 return hash;
1016 }
1017 // WARNING:
1018 // The displaced header in the BasicLock on a thread's stack
1019 // is strictly immutable. It CANNOT be changed in ANY cases.
1020 // So we have to inflate the stack-lock into an ObjectMonitor
1021 // even if the current thread owns the lock. The BasicLock on
1022 // a thread's stack can be asynchronously read by other threads
1023 // during an inflate() call so any change to that stack memory
1024 // may not propagate to other threads correctly.
1025 }
1026
1027 // Inflate the monitor to set the hash.
1028
1029 // An async deflation can race after the inflate() call and before we
1030 // can update the ObjectMonitor's header with the hash value below.
1031 monitor = inflate(current, obj, inflate_cause_hash_code);
1032 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1033 mark = monitor->header();
1034 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1035 hash = mark.hash();
1036 if (hash == 0) { // if it does not have a hash
1037 hash = get_next_hash(current, obj); // get a new hash
1038 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1039 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1040 uintptr_t v = Atomic::cmpxchg((volatile uintptr_t*)monitor->header_addr(), mark.value(), temp.value());
1041 test = markWord(v);
1042 if (test != mark) {
1043 // The attempt to update the ObjectMonitor's header/dmw field
1044 // did not work. This can happen if another thread managed to
1045 // merge in the hash just before our cmpxchg().
1046 // If we add any new usages of the header/dmw field, this code
1047 // will need to be updated.
1048 hash = test.hash();
1049 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1050 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1051 }
1052 if (monitor->is_being_async_deflated()) {
1053 // If we detect that async deflation has occurred, then we
1054 // attempt to restore the header/dmw to the object's header
1055 // so that we only retry once if the deflater thread happens
1056 // to be slow.
1057 monitor->install_displaced_markword_in_object(obj);
1058 continue;
1059 }
1060 }
1061 // We finally get the hash.
1062 return hash;
1063 }
1064 }
1065
1066 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1067 Handle h_obj) {
1068 if (EnableValhalla && h_obj->mark().is_inline_type()) {
1069 return false;
1070 }
1071 assert(current == JavaThread::current(), "Can only be called on current thread");
1072 oop obj = h_obj();
1073
1074 markWord mark = read_stable_mark(obj);
1075
1076 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1077 // stack-locked case, header points into owner's stack
1078 return current->is_lock_owned((address)mark.locker());
1079 }
1080
1081 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1082 // fast-locking case, see if lock is in current's lock stack
1083 return current->lock_stack().contains(h_obj());
1084 }
1085
1086 if (mark.has_monitor()) {
1087 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1088 // The first stage of async deflation does not affect any field
1089 // used by this comparison so the ObjectMonitor* is usable here.
1090 ObjectMonitor* monitor = mark.monitor();
1091 return monitor->is_entered(current) != 0;
1092 }
1093 // Unlocked case, header in place
1094 assert(mark.is_neutral(), "sanity check");
1095 return false;
1096 }
1097
1098 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1099 oop obj = h_obj();
1100 markWord mark = read_stable_mark(obj);
1101
1102 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1103 // stack-locked so header points into owner's stack.
1104 // owning_thread_from_monitor_owner() may also return null here:
1105 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1106 }
1107
1108 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1109 // fast-locked so get owner from the object.
1110 // owning_thread_from_object() may also return null here:
1111 return Threads::owning_thread_from_object(t_list, h_obj());
1112 }
1113
1114 if (mark.has_monitor()) {
1115 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1116 // The first stage of async deflation does not affect any field
1117 // used by this comparison so the ObjectMonitor* is usable here.
1118 ObjectMonitor* monitor = mark.monitor();
1119 assert(monitor != nullptr, "monitor should be non-null");
1120 // owning_thread_from_monitor() may also return null here:
1121 return Threads::owning_thread_from_monitor(t_list, monitor);
1122 }
1123
1124 // Unlocked case, header in place
1125 // Cannot have assertion since this object may have been
1126 // locked by another thread when reaching here.
1127 // assert(mark.is_neutral(), "sanity check");
1128
1129 return nullptr;
1130 }
1131
1132 // Visitors ...
1133
1134 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1135 // ObjectMonitors where owner is set to a stack-lock address in thread.
1136 //
1137 // This version of monitors_iterate() works with the in-use monitor list.
1138 //
1139 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1140 MonitorList::Iterator iter = _in_use_list.iterator();
1141 while (iter.has_next()) {
1142 ObjectMonitor* mid = iter.next();
1143 if (mid->owner() != thread) {
1144 // Not owned by the target thread and intentionally skips when owner
1145 // is set to a stack-lock address in the target thread.
1146 continue;
1147 }
1148 if (!mid->is_being_async_deflated() && mid->object_peek() != nullptr) {
1149 // Only process with closure if the object is set.
1150
1151 // monitors_iterate() is only called at a safepoint or when the
1152 // target thread is suspended or when the target thread is
1153 // operating on itself. The current closures in use today are
1154 // only interested in an owned ObjectMonitor and ownership
1155 // cannot be dropped under the calling contexts so the
1156 // ObjectMonitor cannot be async deflated.
1157 closure->do_monitor(mid);
1158 }
1159 }
1160 }
1161
1162 // This version of monitors_iterate() works with the specified linked list.
1163 //
1164 void ObjectSynchronizer::monitors_iterate(MonitorClosure* closure,
1165 ObjectMonitorsHashtable::PtrList* list,
1166 JavaThread* thread) {
1167 typedef LinkedListIterator<ObjectMonitor*> ObjectMonitorIterator;
1168 ObjectMonitorIterator iter(list->head());
1169 while (!iter.is_empty()) {
1170 ObjectMonitor* mid = *iter.next();
1171 // Owner set to a stack-lock address in thread should never be seen here:
1172 assert(mid->owner() == thread, "must be");
1173 if (!mid->is_being_async_deflated() && mid->object_peek() != nullptr) {
1174 // Only process with closure if the object is set.
1175
1176 // monitors_iterate() is only called at a safepoint or when the
1177 // target thread is suspended or when the target thread is
1178 // operating on itself. The current closures in use today are
1179 // only interested in an owned ObjectMonitor and ownership
1180 // cannot be dropped under the calling contexts so the
1181 // ObjectMonitor cannot be async deflated.
1182 closure->do_monitor(mid);
1183 }
1184 }
1185 }
1186
1187 static bool monitors_used_above_threshold(MonitorList* list) {
1188 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1189 return false;
1190 }
1191 // Start with ceiling based on a per-thread estimate:
1192 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1193 size_t old_ceiling = ceiling;
1194 if (ceiling < list->max()) {
1195 // The max used by the system has exceeded the ceiling so use that:
1196 ceiling = list->max();
1197 }
1198 size_t monitors_used = list->count();
1199 if (monitors_used == 0) { // empty list is easy
1200 return false;
1201 }
1202 if (NoAsyncDeflationProgressMax != 0 &&
1203 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1204 float remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1205 size_t new_ceiling = ceiling + (ceiling * remainder) + 1;
1206 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1207 log_info(monitorinflation)("Too many deflations without progress; "
1208 "bumping in_use_list_ceiling from " SIZE_FORMAT
1209 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1210 _no_progress_cnt = 0;
1211 ceiling = new_ceiling;
1212 }
1213
1214 // Check if our monitor usage is above the threshold:
1215 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1216 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1217 log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
1218 ", monitor_usage=" SIZE_FORMAT ", threshold=" INTX_FORMAT,
1219 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1220 return true;
1221 }
1222
1223 return false;
1224 }
1225
1226 size_t ObjectSynchronizer::in_use_list_ceiling() {
1227 return _in_use_list_ceiling;
1228 }
1229
1230 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1231 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1232 }
1233
1234 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1235 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1236 }
1237
1238 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1239 _in_use_list_ceiling = new_value;
1240 }
1241
1242 bool ObjectSynchronizer::is_async_deflation_needed() {
1243 if (is_async_deflation_requested()) {
1244 // Async deflation request.
1245 log_info(monitorinflation)("Async deflation needed: explicit request");
1246 return true;
1247 }
1248
1249 jlong time_since_last = time_since_last_async_deflation_ms();
1250
1251 if (AsyncDeflationInterval > 0 &&
1252 time_since_last > AsyncDeflationInterval &&
1253 monitors_used_above_threshold(&_in_use_list)) {
1254 // It's been longer than our specified deflate interval and there
1255 // are too many monitors in use. We don't deflate more frequently
1256 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1257 // in order to not swamp the MonitorDeflationThread.
1258 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1259 return true;
1260 }
1261
1262 if (GuaranteedAsyncDeflationInterval > 0 &&
1263 time_since_last > GuaranteedAsyncDeflationInterval) {
1264 // It's been longer than our specified guaranteed deflate interval.
1265 // We need to clean up the used monitors even if the threshold is
1266 // not reached, to keep the memory utilization at bay when many threads
1267 // touched many monitors.
1268 log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) "
1269 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1270 GuaranteedAsyncDeflationInterval, time_since_last);
1271
1272 // If this deflation has no progress, then it should not affect the no-progress
1273 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1274 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1275 // the generic code would bump the no-progress counter, and we compensate for that
1276 // by telling it to skip the update.
1277 //
1278 // If this deflation has progress, then it should let non-progress tracking
1279 // know about this, otherwise the threshold heuristics would kick in, potentially
1280 // experience no-progress due to aggressive cleanup by this deflation, and think
1281 // it is still in no-progress stride. In this "progress" case, the generic code would
1282 // zero the counter, and we allow it to happen.
1283 _no_progress_skip_increment = true;
1284
1285 return true;
1286 }
1287
1288 return false;
1289 }
1290
1291 bool ObjectSynchronizer::request_deflate_idle_monitors() {
1292 JavaThread* current = JavaThread::current();
1293 bool ret_code = false;
1294
1295 jlong last_time = last_async_deflation_time_ns();
1296 set_is_async_deflation_requested(true);
1297 {
1298 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1299 ml.notify_all();
1300 }
1301 const int N_CHECKS = 5;
1302 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1303 if (last_async_deflation_time_ns() > last_time) {
1304 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1305 ret_code = true;
1306 break;
1307 }
1308 {
1309 // JavaThread has to honor the blocking protocol.
1310 ThreadBlockInVM tbivm(current);
1311 os::naked_short_sleep(999); // sleep for almost 1 second
1312 }
1313 }
1314 if (!ret_code) {
1315 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1316 }
1317
1318 return ret_code;
1319 }
1320
1321 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1322 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1323 }
1324
1325 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1326 const oop obj,
1327 ObjectSynchronizer::InflateCause cause) {
1328 assert(event != nullptr, "invariant");
1329 event->set_monitorClass(obj->klass());
1330 event->set_address((uintptr_t)(void*)obj);
1331 event->set_cause((u1)cause);
1332 event->commit();
1333 }
1334
1335 // Fast path code shared by multiple functions
1336 void ObjectSynchronizer::inflate_helper(oop obj) {
1337 markWord mark = obj->mark_acquire();
1338 if (mark.has_monitor()) {
1339 ObjectMonitor* monitor = mark.monitor();
1340 markWord dmw = monitor->header();
1341 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1342 return;
1343 }
1344 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1345 }
1346
1347 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop object,
1348 const InflateCause cause) {
1349 if (EnableValhalla) {
1350 guarantee(!object->klass()->is_inline_klass(), "Attempt to inflate inline type");
1351 }
1352
1353 EventJavaMonitorInflate event;
1354
1355 for (;;) {
1356 const markWord mark = object->mark_acquire();
1357
1358 // The mark can be in one of the following states:
1359 // * inflated - Just return if using stack-locking.
1360 // If using fast-locking and the ObjectMonitor owner
1361 // is anonymous and the current thread owns the
1362 // object lock, then we make the current thread the
1363 // ObjectMonitor owner and remove the lock from the
1364 // current thread's lock stack.
1365 // * fast-locked - Coerce it to inflated from fast-locked.
1366 // * stack-locked - Coerce it to inflated from stack-locked.
1367 // * INFLATING - Busy wait for conversion from stack-locked to
1368 // inflated.
1369 // * neutral - Aggressively inflate the object.
1370
1371 // CASE: inflated
1372 if (mark.has_monitor()) {
1373 ObjectMonitor* inf = mark.monitor();
1374 markWord dmw = inf->header();
1375 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1376 if (LockingMode == LM_LIGHTWEIGHT && inf->is_owner_anonymous() && is_lock_owned(current, object)) {
1377 inf->set_owner_from_anonymous(current);
1378 JavaThread::cast(current)->lock_stack().remove(object);
1379 }
1380 return inf;
1381 }
1382
1383 if (LockingMode != LM_LIGHTWEIGHT) {
1384 // New lightweight locking does not use INFLATING.
1385 // CASE: inflation in progress - inflating over a stack-lock.
1386 // Some other thread is converting from stack-locked to inflated.
1387 // Only that thread can complete inflation -- other threads must wait.
1388 // The INFLATING value is transient.
1389 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1390 // We could always eliminate polling by parking the thread on some auxiliary list.
1391 if (mark == markWord::INFLATING()) {
1392 read_stable_mark(object);
1393 continue;
1394 }
1395 }
1396
1397 // CASE: fast-locked
1398 // Could be fast-locked either by current or by some other thread.
1399 //
1400 // Note that we allocate the ObjectMonitor speculatively, _before_
1401 // attempting to set the object's mark to the new ObjectMonitor. If
1402 // this thread owns the monitor, then we set the ObjectMonitor's
1403 // owner to this thread. Otherwise, we set the ObjectMonitor's owner
1404 // to anonymous. If we lose the race to set the object's mark to the
1405 // new ObjectMonitor, then we just delete it and loop around again.
1406 //
1407 LogStreamHandle(Trace, monitorinflation) lsh;
1408 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1409 ObjectMonitor* monitor = new ObjectMonitor(object);
1410 monitor->set_header(mark.set_unlocked());
1411 bool own = is_lock_owned(current, object);
1412 if (own) {
1413 // Owned by us.
1414 monitor->set_owner_from(nullptr, current);
1415 } else {
1416 // Owned by somebody else.
1417 monitor->set_owner_anonymous();
1418 }
1419 markWord monitor_mark = markWord::encode(monitor);
1420 markWord old_mark = object->cas_set_mark(monitor_mark, mark);
1421 if (old_mark == mark) {
1422 // Success! Return inflated monitor.
1423 if (own) {
1424 JavaThread::cast(current)->lock_stack().remove(object);
1425 }
1426 // Once the ObjectMonitor is configured and object is associated
1427 // with the ObjectMonitor, it is safe to allow async deflation:
1428 _in_use_list.add(monitor);
1429
1430 // Hopefully the performance counters are allocated on distinct
1431 // cache lines to avoid false sharing on MP systems ...
1432 OM_PERFDATA_OP(Inflations, inc());
1433 if (log_is_enabled(Trace, monitorinflation)) {
1434 ResourceMark rm(current);
1435 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1436 INTPTR_FORMAT ", type='%s'", p2i(object),
1437 object->mark().value(), object->klass()->external_name());
1438 }
1439 if (event.should_commit()) {
1440 post_monitor_inflate_event(&event, object, cause);
1441 }
1442 return monitor;
1443 } else {
1444 delete monitor;
1445 continue; // Interference -- just retry
1446 }
1447 }
1448
1449 // CASE: stack-locked
1450 // Could be stack-locked either by current or by some other thread.
1451 //
1452 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1453 // to install INFLATING into the mark word. We originally installed INFLATING,
1454 // allocated the ObjectMonitor, and then finally STed the address of the
1455 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1456 // the interval in which INFLATING appeared in the mark, thus increasing
1457 // the odds of inflation contention. If we lose the race to set INFLATING,
1458 // then we just delete the ObjectMonitor and loop around again.
1459 //
1460 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1461 assert(LockingMode != LM_LIGHTWEIGHT, "cannot happen with new lightweight locking");
1462 ObjectMonitor* m = new ObjectMonitor(object);
1463 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1464 // We do this before the CAS in order to minimize the length of time
1465 // in which INFLATING appears in the mark.
1466
1467 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1468 if (cmp != mark) {
1469 delete m;
1470 continue; // Interference -- just retry
1471 }
1472
1473 // We've successfully installed INFLATING (0) into the mark-word.
1474 // This is the only case where 0 will appear in a mark-word.
1475 // Only the singular thread that successfully swings the mark-word
1476 // to 0 can perform (or more precisely, complete) inflation.
1477 //
1478 // Why do we CAS a 0 into the mark-word instead of just CASing the
1479 // mark-word from the stack-locked value directly to the new inflated state?
1480 // Consider what happens when a thread unlocks a stack-locked object.
1481 // It attempts to use CAS to swing the displaced header value from the
1482 // on-stack BasicLock back into the object header. Recall also that the
1483 // header value (hash code, etc) can reside in (a) the object header, or
1484 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1485 // header in an ObjectMonitor. The inflate() routine must copy the header
1486 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1487 // the while preserving the hashCode stability invariants. If the owner
1488 // decides to release the lock while the value is 0, the unlock will fail
1489 // and control will eventually pass from slow_exit() to inflate. The owner
1490 // will then spin, waiting for the 0 value to disappear. Put another way,
1491 // the 0 causes the owner to stall if the owner happens to try to
1492 // drop the lock (restoring the header from the BasicLock to the object)
1493 // while inflation is in-progress. This protocol avoids races that might
1494 // would otherwise permit hashCode values to change or "flicker" for an object.
1495 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1496 // 0 serves as a "BUSY" inflate-in-progress indicator.
1497
1498
1499 // fetch the displaced mark from the owner's stack.
1500 // The owner can't die or unwind past the lock while our INFLATING
1501 // object is in the mark. Furthermore the owner can't complete
1502 // an unlock on the object, either.
1503 markWord dmw = mark.displaced_mark_helper();
1504 // Catch if the object's header is not neutral (not locked and
1505 // not marked is what we care about here).
1506 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1507
1508 // Setup monitor fields to proper values -- prepare the monitor
1509 m->set_header(dmw);
1510
1511 // Optimization: if the mark.locker stack address is associated
1512 // with this thread we could simply set m->_owner = current.
1513 // Note that a thread can inflate an object
1514 // that it has stack-locked -- as might happen in wait() -- directly
1515 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1516 m->set_owner_from(nullptr, mark.locker());
1517 // TODO-FIXME: assert BasicLock->dhw != 0.
1518
1519 // Must preserve store ordering. The monitor state must
1520 // be stable at the time of publishing the monitor address.
1521 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1522 // Release semantics so that above set_object() is seen first.
1523 object->release_set_mark(markWord::encode(m));
1524
1525 // Once ObjectMonitor is configured and the object is associated
1526 // with the ObjectMonitor, it is safe to allow async deflation:
1527 _in_use_list.add(m);
1528
1529 // Hopefully the performance counters are allocated on distinct cache lines
1530 // to avoid false sharing on MP systems ...
1531 OM_PERFDATA_OP(Inflations, inc());
1532 if (log_is_enabled(Trace, monitorinflation)) {
1533 ResourceMark rm(current);
1534 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1535 INTPTR_FORMAT ", type='%s'", p2i(object),
1536 object->mark().value(), object->klass()->external_name());
1537 }
1538 if (event.should_commit()) {
1539 post_monitor_inflate_event(&event, object, cause);
1540 }
1541 return m;
1542 }
1543
1544 // CASE: neutral
1545 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1546 // If we know we're inflating for entry it's better to inflate by swinging a
1547 // pre-locked ObjectMonitor pointer into the object header. A successful
1548 // CAS inflates the object *and* confers ownership to the inflating thread.
1549 // In the current implementation we use a 2-step mechanism where we CAS()
1550 // to inflate and then CAS() again to try to swing _owner from null to current.
1551 // An inflateTry() method that we could call from enter() would be useful.
1552
1553 // Catch if the object's header is not neutral (not locked and
1554 // not marked is what we care about here).
1555 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1556 ObjectMonitor* m = new ObjectMonitor(object);
1557 // prepare m for installation - set monitor to initial state
1558 m->set_header(mark);
1559
1560 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1561 delete m;
1562 m = nullptr;
1563 continue;
1564 // interference - the markword changed - just retry.
1565 // The state-transitions are one-way, so there's no chance of
1566 // live-lock -- "Inflated" is an absorbing state.
1567 }
1568
1569 // Once the ObjectMonitor is configured and object is associated
1570 // with the ObjectMonitor, it is safe to allow async deflation:
1571 _in_use_list.add(m);
1572
1573 // Hopefully the performance counters are allocated on distinct
1574 // cache lines to avoid false sharing on MP systems ...
1575 OM_PERFDATA_OP(Inflations, inc());
1576 if (log_is_enabled(Trace, monitorinflation)) {
1577 ResourceMark rm(current);
1578 lsh.print_cr("inflate(neutral): object=" INTPTR_FORMAT ", mark="
1579 INTPTR_FORMAT ", type='%s'", p2i(object),
1580 object->mark().value(), object->klass()->external_name());
1581 }
1582 if (event.should_commit()) {
1583 post_monitor_inflate_event(&event, object, cause);
1584 }
1585 return m;
1586 }
1587 }
1588
1589 void ObjectSynchronizer::chk_for_block_req(JavaThread* current, const char* op_name,
1590 const char* cnt_name, size_t cnt,
1591 LogStream* ls, elapsedTimer* timer_p) {
1592 if (!SafepointMechanism::should_process(current)) {
1593 return;
1594 }
1595
1596 // A safepoint/handshake has started.
1597 if (ls != nullptr) {
1598 timer_p->stop();
1599 ls->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1600 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1601 op_name, cnt_name, cnt, in_use_list_ceiling(),
1602 _in_use_list.count(), _in_use_list.max());
1603 }
1604
1605 {
1606 // Honor block request.
1607 ThreadBlockInVM tbivm(current);
1608 }
1609
1610 if (ls != nullptr) {
1611 ls->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1612 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1613 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1614 timer_p->start();
1615 }
1616 }
1617
1618 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1619 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1620 //
1621 // If table != nullptr, we gather owned ObjectMonitors indexed by the
1622 // owner in the table. Please note that ObjectMonitors where the owner
1623 // is set to a stack-lock address are NOT associated with the JavaThread
1624 // that holds that stack-lock. All of the current consumers of
1625 // ObjectMonitorsHashtable info only care about JNI locked monitors and
1626 // those do not have the owner set to a stack-lock address.
1627 //
1628 size_t ObjectSynchronizer::deflate_monitor_list(Thread* current, LogStream* ls,
1629 elapsedTimer* timer_p,
1630 ObjectMonitorsHashtable* table) {
1631 MonitorList::Iterator iter = _in_use_list.iterator();
1632 size_t deflated_count = 0;
1633
1634 while (iter.has_next()) {
1635 if (deflated_count >= (size_t)MonitorDeflationMax) {
1636 break;
1637 }
1638 ObjectMonitor* mid = iter.next();
1639 if (mid->deflate_monitor()) {
1640 deflated_count++;
1641 } else if (table != nullptr) {
1642 // The caller is interested in the owned ObjectMonitors. This does
1643 // not include when owner is set to a stack-lock address in thread.
1644 // This also does not capture unowned ObjectMonitors that cannot be
1645 // deflated because of a waiter.
1646 void* key = mid->owner();
1647 // Since deflate_idle_monitors() and deflate_monitor_list() can be
1648 // called more than once, we have to make sure the entry has not
1649 // already been added.
1650 if (key != nullptr && !table->has_entry(key, mid)) {
1651 table->add_entry(key, mid);
1652 }
1653 }
1654
1655 if (current->is_Java_thread()) {
1656 // A JavaThread must check for a safepoint/handshake and honor it.
1657 chk_for_block_req(JavaThread::cast(current), "deflation", "deflated_count",
1658 deflated_count, ls, timer_p);
1659 }
1660 }
1661
1662 return deflated_count;
1663 }
1664
1665 class HandshakeForDeflation : public HandshakeClosure {
1666 public:
1667 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1668
1669 void do_thread(Thread* thread) {
1670 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1671 INTPTR_FORMAT, p2i(thread));
1672 }
1673 };
1674
1675 class VM_RendezvousGCThreads : public VM_Operation {
1676 public:
1677 bool evaluate_at_safepoint() const override { return false; }
1678 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1679 void doit() override {
1680 SuspendibleThreadSet::synchronize();
1681 SuspendibleThreadSet::desynchronize();
1682 };
1683 };
1684
1685 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list) {
1686 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1687 size_t count = 0;
1688 for (ObjectMonitor* monitor: *delete_list) {
1689 delete monitor;
1690 count++;
1691 }
1692 return count;
1693 }
1694
1695 // This function is called by the MonitorDeflationThread to deflate
1696 // ObjectMonitors. It is also called via do_final_audit_and_print_stats()
1697 // and VM_ThreadDump::doit() by the VMThread.
1698 size_t ObjectSynchronizer::deflate_idle_monitors(ObjectMonitorsHashtable* table) {
1699 Thread* current = Thread::current();
1700 if (current->is_Java_thread()) {
1701 // The async deflation request has been processed.
1702 _last_async_deflation_time_ns = os::javaTimeNanos();
1703 set_is_async_deflation_requested(false);
1704 }
1705
1706 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1707 LogStreamHandle(Info, monitorinflation) lsh_info;
1708 LogStream* ls = nullptr;
1709 if (log_is_enabled(Debug, monitorinflation)) {
1710 ls = &lsh_debug;
1711 } else if (log_is_enabled(Info, monitorinflation)) {
1712 ls = &lsh_info;
1713 }
1714
1715 elapsedTimer timer;
1716 if (ls != nullptr) {
1717 ls->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1718 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1719 timer.start();
1720 }
1721
1722 // Deflate some idle ObjectMonitors.
1723 size_t deflated_count = deflate_monitor_list(current, ls, &timer, table);
1724 size_t unlinked_count = 0;
1725 size_t deleted_count = 0;
1726 if (deflated_count > 0 || is_final_audit()) {
1727 // There are ObjectMonitors that have been deflated or this is the
1728 // final audit and all the remaining ObjectMonitors have been
1729 // deflated, BUT the MonitorDeflationThread blocked for the final
1730 // safepoint during unlinking.
1731
1732 // Unlink deflated ObjectMonitors from the in-use list.
1733 ResourceMark rm;
1734 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1735 unlinked_count = _in_use_list.unlink_deflated(current, ls, &timer, &delete_list);
1736 if (current->is_monitor_deflation_thread()) {
1737 if (ls != nullptr) {
1738 timer.stop();
1739 ls->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1740 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1741 SIZE_FORMAT ", max=" SIZE_FORMAT,
1742 unlinked_count, in_use_list_ceiling(),
1743 _in_use_list.count(), _in_use_list.max());
1744 }
1745
1746 // A JavaThread needs to handshake in order to safely free the
1747 // ObjectMonitors that were deflated in this cycle.
1748 HandshakeForDeflation hfd_hc;
1749 Handshake::execute(&hfd_hc);
1750 // Also, we sync and desync GC threads around the handshake, so that they can
1751 // safely read the mark-word and look-through to the object-monitor, without
1752 // being afraid that the object-monitor is going away.
1753 VM_RendezvousGCThreads sync_gc;
1754 VMThread::execute(&sync_gc);
1755
1756 if (ls != nullptr) {
1757 ls->print_cr("after handshaking: in_use_list stats: ceiling="
1758 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1759 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1760 timer.start();
1761 }
1762 } else {
1763 // This is not a monitor deflation thread.
1764 // No handshake or rendezvous is needed when we are already at safepoint.
1765 assert_at_safepoint();
1766 }
1767
1768 // After the handshake, safely free the ObjectMonitors that were
1769 // deflated and unlinked in this cycle.
1770 if (current->is_Java_thread()) {
1771 if (ls != nullptr) {
1772 timer.stop();
1773 ls->print_cr("before setting blocked: unlinked_count=" SIZE_FORMAT
1774 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1775 SIZE_FORMAT ", max=" SIZE_FORMAT,
1776 unlinked_count, in_use_list_ceiling(),
1777 _in_use_list.count(), _in_use_list.max());
1778 }
1779 // Mark the calling JavaThread blocked (safepoint safe) while we free
1780 // the ObjectMonitors so we don't delay safepoints whilst doing that.
1781 ThreadBlockInVM tbivm(JavaThread::cast(current));
1782 if (ls != nullptr) {
1783 ls->print_cr("after setting blocked: in_use_list stats: ceiling="
1784 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1785 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1786 timer.start();
1787 }
1788 deleted_count = delete_monitors(&delete_list);
1789 // ThreadBlockInVM is destroyed here
1790 } else {
1791 // A non-JavaThread can just free the ObjectMonitors:
1792 deleted_count = delete_monitors(&delete_list);
1793 }
1794 assert(unlinked_count == deleted_count, "must be");
1795 }
1796
1797 if (ls != nullptr) {
1798 timer.stop();
1799 if (deflated_count != 0 || unlinked_count != 0 || log_is_enabled(Debug, monitorinflation)) {
1800 ls->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1801 deflated_count, unlinked_count, timer.seconds());
1802 }
1803 ls->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1804 in_use_list_ceiling(), _in_use_list.count(), _in_use_list.max());
1805 if (table != nullptr) {
1806 ls->print_cr("ObjectMonitorsHashtable: key_count=" SIZE_FORMAT ", om_count=" SIZE_FORMAT,
1807 table->key_count(), table->om_count());
1808 }
1809 }
1810
1811 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1812 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1813
1814 GVars.stw_random = os::random();
1815
1816 if (deflated_count != 0) {
1817 _no_progress_cnt = 0;
1818 } else if (_no_progress_skip_increment) {
1819 _no_progress_skip_increment = false;
1820 } else {
1821 _no_progress_cnt++;
1822 }
1823
1824 return deflated_count;
1825 }
1826
1827 // Monitor cleanup on JavaThread::exit
1828
1829 // Iterate through monitor cache and attempt to release thread's monitors
1830 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1831 private:
1832 JavaThread* _thread;
1833
1834 public:
1835 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1836 void do_monitor(ObjectMonitor* mid) {
1837 intx rec = mid->complete_exit(_thread);
1838 _thread->dec_held_monitor_count(rec + 1);
1839 }
1840 };
1841
1842 // Release all inflated monitors owned by current thread. Lightweight monitors are
1843 // ignored. This is meant to be called during JNI thread detach which assumes
1844 // all remaining monitors are heavyweight. All exceptions are swallowed.
1845 // Scanning the extant monitor list can be time consuming.
1846 // A simple optimization is to add a per-thread flag that indicates a thread
1847 // called jni_monitorenter() during its lifetime.
1848 //
1849 // Instead of NoSafepointVerifier it might be cheaper to
1850 // use an idiom of the form:
1851 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1852 // <code that must not run at safepoint>
1853 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1854 // Since the tests are extremely cheap we could leave them enabled
1855 // for normal product builds.
1856
1857 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1858 assert(current == JavaThread::current(), "must be current Java thread");
1859 NoSafepointVerifier nsv;
1860 ReleaseJavaMonitorsClosure rjmc(current);
1861 ObjectSynchronizer::monitors_iterate(&rjmc, current);
1862 assert(!current->has_pending_exception(), "Should not be possible");
1863 current->clear_pending_exception();
1864 assert(current->held_monitor_count() == 0, "Should not be possible");
1865 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1866 current->clear_jni_monitor_count();
1867 }
1868
1869 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1870 switch (cause) {
1871 case inflate_cause_vm_internal: return "VM Internal";
1872 case inflate_cause_monitor_enter: return "Monitor Enter";
1873 case inflate_cause_wait: return "Monitor Wait";
1874 case inflate_cause_notify: return "Monitor Notify";
1875 case inflate_cause_hash_code: return "Monitor Hash Code";
1876 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1877 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1878 default:
1879 ShouldNotReachHere();
1880 }
1881 return "Unknown";
1882 }
1883
1884 //------------------------------------------------------------------------------
1885 // Debugging code
1886
1887 u_char* ObjectSynchronizer::get_gvars_addr() {
1888 return (u_char*)&GVars;
1889 }
1890
1891 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1892 return (u_char*)&GVars.hc_sequence;
1893 }
1894
1895 size_t ObjectSynchronizer::get_gvars_size() {
1896 return sizeof(SharedGlobals);
1897 }
1898
1899 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1900 return (u_char*)&GVars.stw_random;
1901 }
1902
1903 // Do the final audit and print of ObjectMonitor stats; must be done
1904 // by the VMThread at VM exit time.
1905 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1906 assert(Thread::current()->is_VM_thread(), "sanity check");
1907
1908 if (is_final_audit()) { // Only do the audit once.
1909 return;
1910 }
1911 set_is_final_audit();
1912 log_info(monitorinflation)("Starting the final audit.");
1913
1914 if (log_is_enabled(Info, monitorinflation)) {
1915 // Do deflations in order to reduce the in-use monitor population
1916 // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
1917 // which is called by ObjectSynchronizer::audit_and_print_stats().
1918 while (deflate_idle_monitors(/* ObjectMonitorsHashtable is not needed here */ nullptr) > 0) {
1919 ; // empty
1920 }
1921 // The other audit_and_print_stats() call is done at the Debug
1922 // level at a safepoint in SafepointSynchronize::do_cleanup_tasks.
1923 audit_and_print_stats(true /* on_exit */);
1924 }
1925 }
1926
1927 // This function can be called at a safepoint or it can be called when
1928 // we are trying to exit the VM. When we are trying to exit the VM, the
1929 // list walker functions can run in parallel with the other list
1930 // operations so spin-locking is used for safety.
1931 //
1932 // Calls to this function can be added in various places as a debugging
1933 // aid; pass 'true' for the 'on_exit' parameter to have in-use monitor
1934 // details logged at the Info level and 'false' for the 'on_exit'
1935 // parameter to have in-use monitor details logged at the Trace level.
1936 //
1937 void ObjectSynchronizer::audit_and_print_stats(bool on_exit) {
1938 assert(on_exit || SafepointSynchronize::is_at_safepoint(), "invariant");
1939
1940 LogStreamHandle(Debug, monitorinflation) lsh_debug;
1941 LogStreamHandle(Info, monitorinflation) lsh_info;
1942 LogStreamHandle(Trace, monitorinflation) lsh_trace;
1943 LogStream* ls = nullptr;
1944 if (log_is_enabled(Trace, monitorinflation)) {
1945 ls = &lsh_trace;
1946 } else if (log_is_enabled(Debug, monitorinflation)) {
1947 ls = &lsh_debug;
1948 } else if (log_is_enabled(Info, monitorinflation)) {
1949 ls = &lsh_info;
1950 }
1951 assert(ls != nullptr, "sanity check");
1952
1953 int error_cnt = 0;
1954
1955 ls->print_cr("Checking in_use_list:");
1956 chk_in_use_list(ls, &error_cnt);
1957
1958 if (error_cnt == 0) {
1959 ls->print_cr("No errors found in in_use_list checks.");
1960 } else {
1961 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1962 }
1963
1964 if ((on_exit && log_is_enabled(Info, monitorinflation)) ||
1965 (!on_exit && log_is_enabled(Trace, monitorinflation))) {
1966 // When exiting this log output is at the Info level. When called
1967 // at a safepoint, this log output is at the Trace level since
1968 // there can be a lot of it.
1969 log_in_use_monitor_details(ls);
1970 }
1971
1972 ls->flush();
1973
1974 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1975 }
1976
1977 // Check the in_use_list; log the results of the checks.
1978 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1979 size_t l_in_use_count = _in_use_list.count();
1980 size_t l_in_use_max = _in_use_list.max();
1981 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
1982 l_in_use_max);
1983
1984 size_t ck_in_use_count = 0;
1985 MonitorList::Iterator iter = _in_use_list.iterator();
1986 while (iter.has_next()) {
1987 ObjectMonitor* mid = iter.next();
1988 chk_in_use_entry(mid, out, error_cnt_p);
1989 ck_in_use_count++;
1990 }
1991
1992 if (l_in_use_count == ck_in_use_count) {
1993 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
1994 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
1995 } else {
1996 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
1997 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
1998 ck_in_use_count);
1999 }
2000
2001 size_t ck_in_use_max = _in_use_list.max();
2002 if (l_in_use_max == ck_in_use_max) {
2003 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
2004 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
2005 } else {
2006 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
2007 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
2008 }
2009 }
2010
2011 // Check an in-use monitor entry; log any errors.
2012 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2013 int* error_cnt_p) {
2014 if (n->owner_is_DEFLATER_MARKER()) {
2015 // This should not happen, but if it does, it is not fatal.
2016 out->print_cr("WARNING: monitor=" INTPTR_FORMAT ": in-use monitor is "
2017 "deflated.", p2i(n));
2018 return;
2019 }
2020 if (n->header().value() == 0) {
2021 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2022 "have non-null _header field.", p2i(n));
2023 *error_cnt_p = *error_cnt_p + 1;
2024 }
2025 const oop obj = n->object_peek();
2026 if (obj != nullptr) {
2027 const markWord mark = obj->mark();
2028 if (!mark.has_monitor()) {
2029 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2030 "object does not think it has a monitor: obj="
2031 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2032 p2i(obj), mark.value());
2033 *error_cnt_p = *error_cnt_p + 1;
2034 }
2035 ObjectMonitor* const obj_mon = mark.monitor();
2036 if (n != obj_mon) {
2037 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2038 "object does not refer to the same monitor: obj="
2039 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2040 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2041 *error_cnt_p = *error_cnt_p + 1;
2042 }
2043 }
2044 }
2045
2046 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2047 // flags indicate why the entry is in-use, 'object' and 'object type'
2048 // indicate the associated object and its type.
2049 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out) {
2050 stringStream ss;
2051 if (_in_use_list.count() > 0) {
2052 out->print_cr("In-use monitor info:");
2053 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2054 out->print_cr("%18s %s %18s %18s",
2055 "monitor", "BHL", "object", "object type");
2056 out->print_cr("================== === ================== ==================");
2057 MonitorList::Iterator iter = _in_use_list.iterator();
2058 while (iter.has_next()) {
2059 ObjectMonitor* mid = iter.next();
2060 const oop obj = mid->object_peek();
2061 const markWord mark = mid->header();
2062 ResourceMark rm;
2063 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(mid),
2064 mid->is_busy(), mark.hash() != 0, mid->owner() != nullptr,
2065 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2066 if (mid->is_busy()) {
2067 out->print(" (%s)", mid->is_busy_to_string(&ss));
2068 ss.reset();
2069 }
2070 out->cr();
2071 }
2072 }
2073
2074 out->flush();
2075 }