1 /*
2 * Copyright (c) 1998, 2024, 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/basicLock.inline.hpp"
39 #include "runtime/frame.inline.hpp"
40 #include "runtime/globals.hpp"
41 #include "runtime/handles.inline.hpp"
42 #include "runtime/handshake.hpp"
43 #include "runtime/interfaceSupport.inline.hpp"
44 #include "runtime/javaThread.hpp"
45 #include "runtime/lightweightSynchronizer.hpp"
46 #include "runtime/lockStack.inline.hpp"
47 #include "runtime/mutexLocker.hpp"
48 #include "runtime/objectMonitor.hpp"
49 #include "runtime/objectMonitor.inline.hpp"
50 #include "runtime/os.inline.hpp"
51 #include "runtime/osThread.hpp"
52 #include "runtime/perfData.hpp"
53 #include "runtime/safepointMechanism.inline.hpp"
54 #include "runtime/safepointVerifiers.hpp"
55 #include "runtime/sharedRuntime.hpp"
56 #include "runtime/stubRoutines.hpp"
57 #include "runtime/synchronizer.inline.hpp"
58 #include "runtime/threads.hpp"
59 #include "runtime/timer.hpp"
60 #include "runtime/trimNativeHeap.hpp"
61 #include "runtime/vframe.hpp"
62 #include "runtime/vmThread.hpp"
63 #include "utilities/align.hpp"
64 #include "utilities/dtrace.hpp"
65 #include "utilities/events.hpp"
66 #include "utilities/globalDefinitions.hpp"
67 #include "utilities/linkedlist.hpp"
68 #include "utilities/preserveException.hpp"
69
70 class ObjectMonitorDeflationLogging;
71
72 void MonitorList::add(ObjectMonitor* m) {
73 ObjectMonitor* head;
74 do {
75 head = Atomic::load(&_head);
76 m->set_next_om(head);
77 } while (Atomic::cmpxchg(&_head, head, m) != head);
78
79 size_t count = Atomic::add(&_count, 1u);
80 if (count > max()) {
81 Atomic::inc(&_max);
82 }
83 }
84
85 size_t MonitorList::count() const {
86 return Atomic::load(&_count);
87 }
88
89 size_t MonitorList::max() const {
90 return Atomic::load(&_max);
91 }
92
93 class ObjectMonitorDeflationSafepointer : public StackObj {
94 JavaThread* const _current;
95 ObjectMonitorDeflationLogging* const _log;
96
97 public:
98 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
99 : _current(current), _log(log) {}
100
101 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
102 };
103
104 // Walk the in-use list and unlink deflated ObjectMonitors.
105 // Returns the number of unlinked ObjectMonitors.
106 size_t MonitorList::unlink_deflated(size_t deflated_count,
107 GrowableArray<ObjectMonitor*>* unlinked_list,
108 ObjectMonitorDeflationSafepointer* safepointer) {
109 size_t unlinked_count = 0;
110 ObjectMonitor* prev = nullptr;
111 ObjectMonitor* m = Atomic::load_acquire(&_head);
112
113 while (m != nullptr) {
114 if (m->is_being_async_deflated()) {
115 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
116 // modify the list once per batch. The batch starts at "m".
117 size_t unlinked_batch = 0;
118 ObjectMonitor* next = m;
119 // Look for at most MonitorUnlinkBatch monitors, or the number of
120 // deflated and not unlinked monitors, whatever comes first.
121 assert(deflated_count >= unlinked_count, "Sanity: underflow");
122 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
123 do {
124 ObjectMonitor* next_next = next->next_om();
125 unlinked_batch++;
126 unlinked_list->append(next);
127 next = next_next;
128 if (unlinked_batch >= unlinked_batch_limit) {
129 // Reached the max batch, so bail out of the gathering loop.
130 break;
131 }
132 if (prev == nullptr && Atomic::load(&_head) != m) {
133 // Current batch used to be at head, but it is not at head anymore.
134 // Bail out and figure out where we currently are. This avoids long
135 // walks searching for new prev during unlink under heavy list inserts.
136 break;
137 }
138 } while (next != nullptr && next->is_being_async_deflated());
139
140 // Unlink the found batch.
141 if (prev == nullptr) {
142 // The current batch is the first batch, so there is a chance that it starts at head.
143 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
144 ObjectMonitor* prev_head = Atomic::cmpxchg(&_head, m, next);
145 if (prev_head != m) {
146 // Something must have updated the head. Figure out the actual prev for this batch.
147 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
148 prev = n;
149 }
150 assert(prev != nullptr, "Should have found the prev for the current batch");
151 prev->set_next_om(next);
152 }
153 } else {
154 // The current batch is preceded by another batch. This guarantees the current batch
155 // does not start at head. Unlink the entire current batch without updating the head.
156 assert(Atomic::load(&_head) != m, "Sanity");
157 prev->set_next_om(next);
158 }
159
160 unlinked_count += unlinked_batch;
161 if (unlinked_count >= deflated_count) {
162 // Reached the max so bail out of the searching loop.
163 // There should be no more deflated monitors left.
164 break;
165 }
166 m = next;
167 } else {
168 prev = m;
169 m = m->next_om();
170 }
171
172 // Must check for a safepoint/handshake and honor it.
173 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
174 }
175
176 #ifdef ASSERT
177 // Invariant: the code above should unlink all deflated monitors.
178 // The code that runs after this unlinking does not expect deflated monitors.
179 // Notably, attempting to deflate the already deflated monitor would break.
180 {
181 ObjectMonitor* m = Atomic::load_acquire(&_head);
182 while (m != nullptr) {
183 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
184 m = m->next_om();
185 }
186 }
187 #endif
188
189 Atomic::sub(&_count, unlinked_count);
190 return unlinked_count;
191 }
192
193 MonitorList::Iterator MonitorList::iterator() const {
194 return Iterator(Atomic::load_acquire(&_head));
195 }
196
197 ObjectMonitor* MonitorList::Iterator::next() {
198 ObjectMonitor* current = _current;
199 _current = current->next_om();
200 return current;
201 }
202
203 // The "core" versions of monitor enter and exit reside in this file.
204 // The interpreter and compilers contain specialized transliterated
205 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
206 // fast_lock(...) for instance. If you make changes here, make sure to modify the
207 // interpreter, and both C1 and C2 fast-path inline locking code emission.
208 //
209 // -----------------------------------------------------------------------------
210
211 #ifdef DTRACE_ENABLED
212
213 // Only bother with this argument setup if dtrace is available
214 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
215
216 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
217 char* bytes = nullptr; \
218 int len = 0; \
219 jlong jtid = SharedRuntime::get_java_tid(thread); \
220 Symbol* klassname = obj->klass()->name(); \
221 if (klassname != nullptr) { \
222 bytes = (char*)klassname->bytes(); \
223 len = klassname->utf8_length(); \
224 }
225
226 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
227 { \
228 if (DTraceMonitorProbes) { \
229 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
230 HOTSPOT_MONITOR_WAIT(jtid, \
231 (uintptr_t)(monitor), bytes, len, (millis)); \
232 } \
233 }
234
235 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
236 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
237 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
238
239 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
240 { \
241 if (DTraceMonitorProbes) { \
242 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
243 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
244 (uintptr_t)(monitor), bytes, len); \
245 } \
246 }
247
248 #else // ndef DTRACE_ENABLED
249
250 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
251 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
252
253 #endif // ndef DTRACE_ENABLED
254
255 // This exists only as a workaround of dtrace bug 6254741
256 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
257 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
258 return 0;
259 }
260
261 static constexpr size_t inflation_lock_count() {
262 return 256;
263 }
264
265 // Static storage for an array of PlatformMutex.
266 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
267
268 static inline PlatformMutex* inflation_lock(size_t index) {
269 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
270 }
271
272 void ObjectSynchronizer::initialize() {
273 for (size_t i = 0; i < inflation_lock_count(); i++) {
274 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
275 }
276 // Start the ceiling with the estimate for one thread.
277 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
278
279 // Start the timer for deflations, so it does not trigger immediately.
280 _last_async_deflation_time_ns = os::javaTimeNanos();
281
282 if (LockingMode == LM_LIGHTWEIGHT) {
283 LightweightSynchronizer::initialize();
284 }
285 }
286
287 MonitorList ObjectSynchronizer::_in_use_list;
288 // monitors_used_above_threshold() policy is as follows:
289 //
290 // The ratio of the current _in_use_list count to the ceiling is used
291 // to determine if we are above MonitorUsedDeflationThreshold and need
292 // to do an async monitor deflation cycle. The ceiling is increased by
293 // AvgMonitorsPerThreadEstimate when a thread is added to the system
294 // and is decreased by AvgMonitorsPerThreadEstimate when a thread is
295 // removed from the system.
296 //
297 // Note: If the _in_use_list max exceeds the ceiling, then
298 // monitors_used_above_threshold() will use the in_use_list max instead
299 // of the thread count derived ceiling because we have used more
300 // ObjectMonitors than the estimated average.
301 //
302 // Note: If deflate_idle_monitors() has NoAsyncDeflationProgressMax
303 // no-progress async monitor deflation cycles in a row, then the ceiling
304 // is adjusted upwards by monitors_used_above_threshold().
305 //
306 // Start the ceiling with the estimate for one thread in initialize()
307 // which is called after cmd line options are processed.
308 static size_t _in_use_list_ceiling = 0;
309 bool volatile ObjectSynchronizer::_is_async_deflation_requested = false;
310 bool volatile ObjectSynchronizer::_is_final_audit = false;
311 jlong ObjectSynchronizer::_last_async_deflation_time_ns = 0;
312 static uintx _no_progress_cnt = 0;
313 static bool _no_progress_skip_increment = false;
314
315 // These checks are required for wait, notify and exit to avoid inflating the monitor to
316 // find out this inline type object cannot be locked.
317 #define CHECK_THROW_NOSYNC_IMSE(obj) \
318 if (EnableValhalla && (obj)->mark().is_inline_type()) { \
319 JavaThread* THREAD = current; \
320 ResourceMark rm(THREAD); \
321 THROW_MSG(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
322 }
323
324 #define CHECK_THROW_NOSYNC_IMSE_0(obj) \
325 if (EnableValhalla && (obj)->mark().is_inline_type()) { \
326 JavaThread* THREAD = current; \
327 ResourceMark rm(THREAD); \
328 THROW_MSG_0(vmSymbols::java_lang_IllegalMonitorStateException(), obj->klass()->external_name()); \
329 }
330
331 // =====================> Quick functions
332
333 // The quick_* forms are special fast-path variants used to improve
334 // performance. In the simplest case, a "quick_*" implementation could
335 // simply return false, in which case the caller will perform the necessary
336 // state transitions and call the slow-path form.
337 // The fast-path is designed to handle frequently arising cases in an efficient
338 // manner and is just a degenerate "optimistic" variant of the slow-path.
339 // returns true -- to indicate the call was satisfied.
340 // returns false -- to indicate the call needs the services of the slow-path.
341 // A no-loitering ordinance is in effect for code in the quick_* family
342 // operators: safepoints or indefinite blocking (blocking that might span a
343 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
344 // entry.
345 //
346 // Consider: An interesting optimization is to have the JIT recognize the
347 // following common idiom:
348 // synchronized (someobj) { .... ; notify(); }
349 // That is, we find a notify() or notifyAll() call that immediately precedes
350 // the monitorexit operation. In that case the JIT could fuse the operations
351 // into a single notifyAndExit() runtime primitive.
352
353 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
354 assert(current->thread_state() == _thread_in_Java, "invariant");
355 NoSafepointVerifier nsv;
356 if (obj == nullptr) return false; // slow-path for invalid obj
357 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
358 const markWord mark = obj->mark();
359
360 if (LockingMode == LM_LIGHTWEIGHT) {
361 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
362 // Degenerate notify
363 // fast-locked by caller so by definition the implied waitset is empty.
364 return true;
365 }
366 } else if (LockingMode == LM_LEGACY) {
367 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
368 // Degenerate notify
369 // stack-locked by caller so by definition the implied waitset is empty.
370 return true;
371 }
372 }
373
374 if (mark.has_monitor()) {
375 ObjectMonitor* const mon = read_monitor(current, obj, mark);
376 if (LockingMode == LM_LIGHTWEIGHT && mon == nullptr) {
377 // Racing with inflation/deflation go slow path
378 return false;
379 }
380 assert(mon->object() == oop(obj), "invariant");
381 if (mon->owner() != current) return false; // slow-path for IMS exception
382
383 if (mon->first_waiter() != nullptr) {
384 // We have one or more waiters. Since this is an inflated monitor
385 // that we own, we can transfer one or more threads from the waitset
386 // to the entrylist here and now, avoiding the slow-path.
387 if (all) {
388 DTRACE_MONITOR_PROBE(notifyAll, mon, obj, current);
389 } else {
390 DTRACE_MONITOR_PROBE(notify, mon, obj, current);
391 }
392 int free_count = 0;
393 do {
394 mon->INotify(current);
395 ++free_count;
396 } while (mon->first_waiter() != nullptr && all);
397 OM_PERFDATA_OP(Notifications, inc(free_count));
398 }
399 return true;
400 }
401
402 // other IMS exception states take the slow-path
403 return false;
404 }
405
406 static bool useHeavyMonitors() {
407 #if defined(X86) || defined(AARCH64) || defined(PPC64) || defined(RISCV64) || defined(S390)
408 return LockingMode == LM_MONITOR;
409 #else
410 return false;
411 #endif
412 }
413
414 // The LockNode emitted directly at the synchronization site would have
415 // been too big if it were to have included support for the cases of inflated
416 // recursive enter and exit, so they go here instead.
417 // Note that we can't safely call AsyncPrintJavaStack() from within
418 // quick_enter() as our thread state remains _in_Java.
419
420 bool ObjectSynchronizer::quick_enter_legacy(oop obj, BasicLock* lock, JavaThread* current) {
421 assert(current->thread_state() == _thread_in_Java, "invariant");
422 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "monitor op on inline type");
423
424 if (useHeavyMonitors()) {
425 return false; // Slow path
426 }
427
428 if (LockingMode == LM_LIGHTWEIGHT) {
429 return LightweightSynchronizer::quick_enter(obj, lock, current);
430 }
431
432 assert(LockingMode == LM_LEGACY, "legacy mode below");
433
434 const markWord mark = obj->mark();
435
436 if (mark.has_monitor()) {
437
438 ObjectMonitor* const m = read_monitor(mark);
439 // An async deflation or GC can race us before we manage to make
440 // the ObjectMonitor busy by setting the owner below. If we detect
441 // that race we just bail out to the slow-path here.
442 if (m->object_peek() == nullptr) {
443 return false;
444 }
445 JavaThread* const owner = static_cast<JavaThread*>(m->owner_raw());
446
447 // Lock contention and Transactional Lock Elision (TLE) diagnostics
448 // and observability
449 // Case: light contention possibly amenable to TLE
450 // Case: TLE inimical operations such as nested/recursive synchronization
451
452 if (owner == current) {
453 m->_recursions++;
454 current->inc_held_monitor_count();
455 return true;
456 }
457
458 // This Java Monitor is inflated so obj's header will never be
459 // displaced to this thread's BasicLock. Make the displaced header
460 // non-null so this BasicLock is not seen as recursive nor as
461 // being locked. We do this unconditionally so that this thread's
462 // BasicLock cannot be mis-interpreted by any stack walkers. For
463 // performance reasons, stack walkers generally first check for
464 // stack-locking in the object's header, the second check is for
465 // recursive stack-locking in the displaced header in the BasicLock,
466 // and last are the inflated Java Monitor (ObjectMonitor) checks.
467 lock->set_displaced_header(markWord::unused_mark());
468
469 if (owner == nullptr && m->try_set_owner_from(nullptr, current) == nullptr) {
470 assert(m->_recursions == 0, "invariant");
471 current->inc_held_monitor_count();
472 return true;
473 }
474 }
475
476 // Note that we could inflate in quick_enter.
477 // This is likely a useful optimization
478 // Critically, in quick_enter() we must not:
479 // -- block indefinitely, or
480 // -- reach a safepoint
481
482 return false; // revert to slow-path
483 }
484
485 // Handle notifications when synchronizing on value based classes
486 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
487 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
488 frame last_frame = locking_thread->last_frame();
489 bool bcp_was_adjusted = false;
490 // Don't decrement bcp if it points to the frame's first instruction. This happens when
491 // handle_sync_on_value_based_class() is called because of a synchronized method. There
492 // is no actual monitorenter instruction in the byte code in this case.
493 if (last_frame.is_interpreted_frame() &&
494 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
495 // adjust bcp to point back to monitorenter so that we print the correct line numbers
496 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
497 bcp_was_adjusted = true;
498 }
499
500 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
501 ResourceMark rm;
502 stringStream ss;
503 locking_thread->print_active_stack_on(&ss);
504 char* base = (char*)strstr(ss.base(), "at");
505 char* newline = (char*)strchr(ss.base(), '\n');
506 if (newline != nullptr) {
507 *newline = '\0';
508 }
509 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
510 } else {
511 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
512 ResourceMark rm;
513 Log(valuebasedclasses) vblog;
514
515 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
516 if (locking_thread->has_last_Java_frame()) {
517 LogStream info_stream(vblog.info());
518 locking_thread->print_active_stack_on(&info_stream);
519 } else {
520 vblog.info("Cannot find the last Java frame");
521 }
522
523 EventSyncOnValueBasedClass event;
524 if (event.should_commit()) {
525 event.set_valueBasedClass(obj->klass());
526 event.commit();
527 }
528 }
529
530 if (bcp_was_adjusted) {
531 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
532 }
533 }
534
535 // -----------------------------------------------------------------------------
536 // Monitor Enter/Exit
537
538 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
539 // When called with locking_thread != Thread::current() some mechanism must synchronize
540 // the locking_thread with respect to the current thread. Currently only used when
541 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
542 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
543 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "JITed code should never have locked an instance of a value class");
544
545 if (LockingMode == LM_LIGHTWEIGHT) {
546 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
547 }
548
549 if (!enter_fast_impl(obj, lock, locking_thread)) {
550 // Inflated ObjectMonitor::enter_for is required
551
552 // An async deflation can race after the inflate_for() call and before
553 // enter_for() can make the ObjectMonitor busy. enter_for() returns false
554 // if we have lost the race to async deflation and we simply try again.
555 while (true) {
556 ObjectMonitor* monitor = inflate_for(locking_thread, obj(), inflate_cause_monitor_enter);
557 if (monitor->enter_for(locking_thread)) {
558 return;
559 }
560 assert(monitor->is_being_async_deflated(), "must be");
561 }
562 }
563 }
564
565 void ObjectSynchronizer::enter_legacy(Handle obj, BasicLock* lock, JavaThread* current) {
566 assert(!EnableValhalla || !obj->klass()->is_inline_klass(), "This method should never be called on an instance of an inline class");
567 if (!enter_fast_impl(obj, lock, current)) {
568 // Inflated ObjectMonitor::enter is required
569
570 // An async deflation can race after the inflate() call and before
571 // enter() can make the ObjectMonitor busy. enter() returns false if
572 // we have lost the race to async deflation and we simply try again.
573 while (true) {
574 ObjectMonitor* monitor = inflate(current, obj(), inflate_cause_monitor_enter);
575 if (monitor->enter(current)) {
576 return;
577 }
578 }
579 }
580 }
581
582 // The interpreter and compiler assembly code tries to lock using the fast path
583 // of this algorithm. Make sure to update that code if the following function is
584 // changed. The implementation is extremely sensitive to race condition. Be careful.
585 bool ObjectSynchronizer::enter_fast_impl(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
586 guarantee(!EnableValhalla || !obj->klass()->is_inline_klass(), "Attempt to inflate inline type");
587 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
588
589 if (obj->klass()->is_value_based()) {
590 handle_sync_on_value_based_class(obj, locking_thread);
591 }
592
593 locking_thread->inc_held_monitor_count();
594
595 if (!useHeavyMonitors()) {
596 if (LockingMode == LM_LEGACY) {
597 markWord mark = obj->mark();
598 if (mark.is_unlocked()) {
599 // Anticipate successful CAS -- the ST of the displaced mark must
600 // be visible <= the ST performed by the CAS.
601 lock->set_displaced_header(mark);
602 if (mark == obj()->cas_set_mark(markWord::from_pointer(lock), mark)) {
603 return true;
604 }
605 } else if (mark.has_locker() &&
606 locking_thread->is_lock_owned((address) mark.locker())) {
607 assert(lock != mark.locker(), "must not re-lock the same lock");
608 assert(lock != (BasicLock*) obj->mark().value(), "don't relock with same BasicLock");
609 lock->set_displaced_header(markWord::from_pointer(nullptr));
610 return true;
611 }
612
613 // The object header will never be displaced to this lock,
614 // so it does not matter what the value is, except that it
615 // must be non-zero to avoid looking like a re-entrant lock,
616 // and must not look locked either.
617 lock->set_displaced_header(markWord::unused_mark());
618
619 // Failed to fast lock.
620 return false;
621 }
622 } else if (VerifyHeavyMonitors) {
623 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
624 }
625
626 return false;
627 }
628
629 void ObjectSynchronizer::exit_legacy(oop object, BasicLock* lock, JavaThread* current) {
630 assert(LockingMode != LM_LIGHTWEIGHT, "Use LightweightSynchronizer");
631
632 if (!useHeavyMonitors()) {
633 markWord mark = object->mark();
634 if (EnableValhalla && mark.is_inline_type()) {
635 return;
636 }
637 if (LockingMode == LM_LEGACY) {
638 markWord dhw = lock->displaced_header();
639 if (dhw.value() == 0) {
640 // If the displaced header is null, then this exit matches up with
641 // a recursive enter. No real work to do here except for diagnostics.
642 #ifndef PRODUCT
643 if (mark != markWord::INFLATING()) {
644 // Only do diagnostics if we are not racing an inflation. Simply
645 // exiting a recursive enter of a Java Monitor that is being
646 // inflated is safe; see the has_monitor() comment below.
647 assert(!mark.is_unlocked(), "invariant");
648 assert(!mark.has_locker() ||
649 current->is_lock_owned((address)mark.locker()), "invariant");
650 if (mark.has_monitor()) {
651 // The BasicLock's displaced_header is marked as a recursive
652 // enter and we have an inflated Java Monitor (ObjectMonitor).
653 // This is a special case where the Java Monitor was inflated
654 // after this thread entered the stack-lock recursively. When a
655 // Java Monitor is inflated, we cannot safely walk the Java
656 // Monitor owner's stack and update the BasicLocks because a
657 // Java Monitor can be asynchronously inflated by a thread that
658 // does not own the Java Monitor.
659 ObjectMonitor* m = read_monitor(mark);
660 assert(m->object()->mark() == mark, "invariant");
661 assert(m->is_entered(current), "invariant");
662 }
663 }
664 #endif
665 return;
666 }
667
668 if (mark == markWord::from_pointer(lock)) {
669 // If the object is stack-locked by the current thread, try to
670 // swing the displaced header from the BasicLock back to the mark.
671 assert(dhw.is_neutral(), "invariant");
672 if (object->cas_set_mark(dhw, mark) == mark) {
673 return;
674 }
675 }
676 }
677 } else if (VerifyHeavyMonitors) {
678 guarantee((object->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
679 }
680
681 // We have to take the slow-path of possible inflation and then exit.
682 // The ObjectMonitor* can't be async deflated until ownership is
683 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
684 ObjectMonitor* monitor = inflate(current, object, inflate_cause_vm_internal);
685 assert(!monitor->is_owner_anonymous(), "must not be");
686 monitor->exit(current);
687 }
688
689 // -----------------------------------------------------------------------------
690 // JNI locks on java objects
691 // NOTE: must use heavy weight monitor to handle jni monitor enter
692 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
693 JavaThread* THREAD = current;
694 if (obj->klass()->is_value_based()) {
695 handle_sync_on_value_based_class(obj, current);
696 }
697
698 if (EnableValhalla && obj->klass()->is_inline_klass()) {
699 ResourceMark rm(THREAD);
700 const char* desc = "Cannot synchronize on an instance of value class ";
701 const char* className = obj->klass()->external_name();
702 size_t msglen = strlen(desc) + strlen(className) + 1;
703 char* message = NEW_RESOURCE_ARRAY(char, msglen);
704 assert(message != nullptr, "NEW_RESOURCE_ARRAY should have called vm_exit_out_of_memory and not return nullptr");
705 THROW_MSG(vmSymbols::java_lang_IdentityException(), className);
706 }
707
708 // the current locking is from JNI instead of Java code
709 current->set_current_pending_monitor_is_from_java(false);
710 // An async deflation can race after the inflate() call and before
711 // enter() can make the ObjectMonitor busy. enter() returns false if
712 // we have lost the race to async deflation and we simply try again.
713 while (true) {
714 ObjectMonitor* monitor;
715 bool entered;
716 if (LockingMode == LM_LIGHTWEIGHT) {
717 entered = LightweightSynchronizer::inflate_and_enter(obj(), inflate_cause_jni_enter, current, current) != nullptr;
718 } else {
719 monitor = inflate(current, obj(), inflate_cause_jni_enter);
720 entered = monitor->enter(current);
721 }
722
723 if (entered) {
724 current->inc_held_monitor_count(1, true);
725 break;
726 }
727 }
728 current->set_current_pending_monitor_is_from_java(true);
729 }
730
731 // NOTE: must use heavy weight monitor to handle jni monitor exit
732 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
733 JavaThread* current = THREAD;
734 CHECK_THROW_NOSYNC_IMSE(obj);
735
736 ObjectMonitor* monitor;
737 if (LockingMode == LM_LIGHTWEIGHT) {
738 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
739 } else {
740 // The ObjectMonitor* can't be async deflated until ownership is
741 // dropped inside exit() and the ObjectMonitor* must be !is_busy().
742 monitor = inflate(current, obj, inflate_cause_jni_exit);
743 }
744 // If this thread has locked the object, exit the monitor. We
745 // intentionally do not use CHECK on check_owner because we must exit the
746 // monitor even if an exception was already pending.
747 if (monitor->check_owner(THREAD)) {
748 monitor->exit(current);
749 current->dec_held_monitor_count(1, true);
750 }
751 }
752
753 // -----------------------------------------------------------------------------
754 // Internal VM locks on java objects
755 // standard constructor, allows locking failures
756 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) {
757 _thread = thread;
758 _thread->check_for_valid_safepoint_state();
759 _obj = obj;
760
761 if (_obj() != nullptr) {
762 ObjectSynchronizer::enter(_obj, &_lock, _thread);
763 }
764 }
765
766 ObjectLocker::~ObjectLocker() {
767 if (_obj() != nullptr) {
768 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
769 }
770 }
771
772
773 // -----------------------------------------------------------------------------
774 // Wait/Notify/NotifyAll
775 // NOTE: must use heavy weight monitor to handle wait()
776
777 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
778 JavaThread* current = THREAD;
779 CHECK_THROW_NOSYNC_IMSE_0(obj);
780 if (millis < 0) {
781 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
782 }
783
784 ObjectMonitor* monitor;
785 if (LockingMode == LM_LIGHTWEIGHT) {
786 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
787 } else {
788 // The ObjectMonitor* can't be async deflated because the _waiters
789 // field is incremented before ownership is dropped and decremented
790 // after ownership is regained.
791 monitor = inflate(current, obj(), inflate_cause_wait);
792 }
793
794 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
795 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
796
797 // This dummy call is in place to get around dtrace bug 6254741. Once
798 // that's fixed we can uncomment the following line, remove the call
799 // and change this function back into a "void" func.
800 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
801 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
802 return ret_code;
803 }
804
805 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
806 if (millis < 0) {
807 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
808 }
809
810 ObjectMonitor* monitor;
811 if (LockingMode == LM_LIGHTWEIGHT) {
812 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
813 } else {
814 monitor = inflate(THREAD, obj(), inflate_cause_wait);
815 }
816 monitor->wait(millis, false, THREAD);
817 }
818
819
820 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
821 JavaThread* current = THREAD;
822 CHECK_THROW_NOSYNC_IMSE(obj);
823
824 markWord mark = obj->mark();
825 if (LockingMode == LM_LIGHTWEIGHT) {
826 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
827 // Not inflated so there can't be any waiters to notify.
828 return;
829 }
830 } else if (LockingMode == LM_LEGACY) {
831 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
832 // Not inflated so there can't be any waiters to notify.
833 return;
834 }
835 }
836
837 ObjectMonitor* monitor;
838 if (LockingMode == LM_LIGHTWEIGHT) {
839 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
840 } else {
841 // The ObjectMonitor* can't be async deflated until ownership is
842 // dropped by the calling thread.
843 monitor = inflate(current, obj(), inflate_cause_notify);
844 }
845 monitor->notify(CHECK);
846 }
847
848 // NOTE: see comment of notify()
849 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
850 JavaThread* current = THREAD;
851 CHECK_THROW_NOSYNC_IMSE(obj);
852
853 markWord mark = obj->mark();
854 if (LockingMode == LM_LIGHTWEIGHT) {
855 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
856 // Not inflated so there can't be any waiters to notify.
857 return;
858 }
859 } else if (LockingMode == LM_LEGACY) {
860 if (mark.has_locker() && current->is_lock_owned((address)mark.locker())) {
861 // Not inflated so there can't be any waiters to notify.
862 return;
863 }
864 }
865
866 ObjectMonitor* monitor;
867 if (LockingMode == LM_LIGHTWEIGHT) {
868 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
869 } else {
870 // The ObjectMonitor* can't be async deflated until ownership is
871 // dropped by the calling thread.
872 monitor = inflate(current, obj(), inflate_cause_notify);
873 }
874 monitor->notifyAll(CHECK);
875 }
876
877 // -----------------------------------------------------------------------------
878 // Hash Code handling
879
880 struct SharedGlobals {
881 char _pad_prefix[OM_CACHE_LINE_SIZE];
882 // This is a highly shared mostly-read variable.
883 // To avoid false-sharing it needs to be the sole occupant of a cache line.
884 volatile int stw_random;
885 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
886 // Hot RW variable -- Sequester to avoid false-sharing
887 volatile int hc_sequence;
888 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
889 };
890
891 static SharedGlobals GVars;
892
893 static markWord read_stable_mark(oop obj) {
894 markWord mark = obj->mark_acquire();
895 if (!mark.is_being_inflated() || LockingMode == LM_LIGHTWEIGHT) {
896 // New lightweight locking does not use the markWord::INFLATING() protocol.
897 return mark; // normal fast-path return
898 }
899
900 int its = 0;
901 for (;;) {
902 markWord mark = obj->mark_acquire();
903 if (!mark.is_being_inflated()) {
904 return mark; // normal fast-path return
905 }
906
907 // The object is being inflated by some other thread.
908 // The caller of read_stable_mark() must wait for inflation to complete.
909 // Avoid live-lock.
910
911 ++its;
912 if (its > 10000 || !os::is_MP()) {
913 if (its & 1) {
914 os::naked_yield();
915 } else {
916 // Note that the following code attenuates the livelock problem but is not
917 // a complete remedy. A more complete solution would require that the inflating
918 // thread hold the associated inflation lock. The following code simply restricts
919 // the number of spinners to at most one. We'll have N-2 threads blocked
920 // on the inflationlock, 1 thread holding the inflation lock and using
921 // a yield/park strategy, and 1 thread in the midst of inflation.
922 // A more refined approach would be to change the encoding of INFLATING
923 // to allow encapsulation of a native thread pointer. Threads waiting for
924 // inflation to complete would use CAS to push themselves onto a singly linked
925 // list rooted at the markword. Once enqueued, they'd loop, checking a per-thread flag
926 // and calling park(). When inflation was complete the thread that accomplished inflation
927 // would detach the list and set the markword to inflated with a single CAS and
928 // then for each thread on the list, set the flag and unpark() the thread.
929
930 // Index into the lock array based on the current object address.
931 static_assert(is_power_of_2(inflation_lock_count()), "must be");
932 size_t ix = (cast_from_oop<intptr_t>(obj) >> 5) & (inflation_lock_count() - 1);
933 int YieldThenBlock = 0;
934 assert(ix < inflation_lock_count(), "invariant");
935 inflation_lock(ix)->lock();
936 while (obj->mark_acquire() == markWord::INFLATING()) {
937 // Beware: naked_yield() is advisory and has almost no effect on some platforms
938 // so we periodically call current->_ParkEvent->park(1).
939 // We use a mixed spin/yield/block mechanism.
940 if ((YieldThenBlock++) >= 16) {
941 Thread::current()->_ParkEvent->park(1);
942 } else {
943 os::naked_yield();
944 }
945 }
946 inflation_lock(ix)->unlock();
947 }
948 } else {
949 SpinPause(); // SMP-polite spinning
950 }
951 }
952 }
953
954 // hashCode() generation :
955 //
956 // Possibilities:
957 // * MD5Digest of {obj,stw_random}
958 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
959 // * A DES- or AES-style SBox[] mechanism
960 // * One of the Phi-based schemes, such as:
961 // 2654435761 = 2^32 * Phi (golden ratio)
962 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
963 // * A variation of Marsaglia's shift-xor RNG scheme.
964 // * (obj ^ stw_random) is appealing, but can result
965 // in undesirable regularity in the hashCode values of adjacent objects
966 // (objects allocated back-to-back, in particular). This could potentially
967 // result in hashtable collisions and reduced hashtable efficiency.
968 // There are simple ways to "diffuse" the middle address bits over the
969 // generated hashCode values:
970
971 static intptr_t get_next_hash(Thread* current, oop obj) {
972 intptr_t value = 0;
973 if (hashCode == 0) {
974 // This form uses global Park-Miller RNG.
975 // On MP system we'll have lots of RW access to a global, so the
976 // mechanism induces lots of coherency traffic.
977 value = os::random();
978 } else if (hashCode == 1) {
979 // This variation has the property of being stable (idempotent)
980 // between STW operations. This can be useful in some of the 1-0
981 // synchronization schemes.
982 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
983 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
984 } else if (hashCode == 2) {
985 value = 1; // for sensitivity testing
986 } else if (hashCode == 3) {
987 value = ++GVars.hc_sequence;
988 } else if (hashCode == 4) {
989 value = cast_from_oop<intptr_t>(obj);
990 } else {
991 // Marsaglia's xor-shift scheme with thread-specific state
992 // This is probably the best overall implementation -- we'll
993 // likely make this the default in future releases.
994 unsigned t = current->_hashStateX;
995 t ^= (t << 11);
996 current->_hashStateX = current->_hashStateY;
997 current->_hashStateY = current->_hashStateZ;
998 current->_hashStateZ = current->_hashStateW;
999 unsigned v = current->_hashStateW;
1000 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
1001 current->_hashStateW = v;
1002 value = v;
1003 }
1004
1005 value &= markWord::hash_mask;
1006 if (value == 0) value = 0xBAD;
1007 assert(value != markWord::no_hash, "invariant");
1008 return value;
1009 }
1010
1011 static intptr_t install_hash_code(Thread* current, oop obj) {
1012 assert(UseObjectMonitorTable && LockingMode == LM_LIGHTWEIGHT, "must be");
1013
1014 markWord mark = obj->mark_acquire();
1015 for (;;) {
1016 intptr_t hash = mark.hash();
1017 if (hash != 0) {
1018 return hash;
1019 }
1020
1021 hash = get_next_hash(current, obj);
1022 const markWord old_mark = mark;
1023 const markWord new_mark = old_mark.copy_set_hash(hash);
1024
1025 mark = obj->cas_set_mark(new_mark, old_mark);
1026 if (old_mark == mark) {
1027 return hash;
1028 }
1029 }
1030 }
1031
1032 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
1033 if (EnableValhalla && obj->klass()->is_inline_klass()) {
1034 // VM should be calling bootstrap method
1035 ShouldNotReachHere();
1036 }
1037 if (UseObjectMonitorTable) {
1038 // Since the monitor isn't in the object header, the hash can simply be
1039 // installed in the object header.
1040 return install_hash_code(current, obj);
1041 }
1042
1043 while (true) {
1044 ObjectMonitor* monitor = nullptr;
1045 markWord temp, test;
1046 intptr_t hash;
1047 markWord mark = read_stable_mark(obj);
1048 if (VerifyHeavyMonitors) {
1049 assert(LockingMode == LM_MONITOR, "+VerifyHeavyMonitors requires LockingMode == 0 (LM_MONITOR)");
1050 guarantee((obj->mark().value() & markWord::lock_mask_in_place) != markWord::locked_value, "must not be lightweight/stack-locked");
1051 }
1052 if (mark.is_unlocked() || (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked())) {
1053 hash = mark.hash();
1054 if (hash != 0) { // if it has a hash, just return it
1055 return hash;
1056 }
1057 hash = get_next_hash(current, obj); // get a new hash
1058 temp = mark.copy_set_hash(hash); // merge the hash into header
1059 // try to install the hash
1060 test = obj->cas_set_mark(temp, mark);
1061 if (test == mark) { // if the hash was installed, return it
1062 return hash;
1063 }
1064 if (LockingMode == LM_LIGHTWEIGHT) {
1065 // CAS failed, retry
1066 continue;
1067 }
1068 // Failed to install the hash. It could be that another thread
1069 // installed the hash just before our attempt or inflation has
1070 // occurred or... so we fall thru to inflate the monitor for
1071 // stability and then install the hash.
1072 } else if (mark.has_monitor()) {
1073 monitor = mark.monitor();
1074 temp = monitor->header();
1075 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1076 hash = temp.hash();
1077 if (hash != 0) {
1078 // It has a hash.
1079
1080 // Separate load of dmw/header above from the loads in
1081 // is_being_async_deflated().
1082
1083 // dmw/header and _contentions may get written by different threads.
1084 // Make sure to observe them in the same order when having several observers.
1085 OrderAccess::loadload_for_IRIW();
1086
1087 if (monitor->is_being_async_deflated()) {
1088 // But we can't safely use the hash if we detect that async
1089 // deflation has occurred. So we attempt to restore the
1090 // header/dmw to the object's header so that we only retry
1091 // once if the deflater thread happens to be slow.
1092 monitor->install_displaced_markword_in_object(obj);
1093 continue;
1094 }
1095 return hash;
1096 }
1097 // Fall thru so we only have one place that installs the hash in
1098 // the ObjectMonitor.
1099 } else if (LockingMode == LM_LEGACY && mark.has_locker()
1100 && current->is_Java_thread()
1101 && JavaThread::cast(current)->is_lock_owned((address)mark.locker())) {
1102 // This is a stack-lock owned by the calling thread so fetch the
1103 // displaced markWord from the BasicLock on the stack.
1104 temp = mark.displaced_mark_helper();
1105 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1106 hash = temp.hash();
1107 if (hash != 0) { // if it has a hash, just return it
1108 return hash;
1109 }
1110 // WARNING:
1111 // The displaced header in the BasicLock on a thread's stack
1112 // is strictly immutable. It CANNOT be changed in ANY cases.
1113 // So we have to inflate the stack-lock into an ObjectMonitor
1114 // even if the current thread owns the lock. The BasicLock on
1115 // a thread's stack can be asynchronously read by other threads
1116 // during an inflate() call so any change to that stack memory
1117 // may not propagate to other threads correctly.
1118 }
1119
1120 // Inflate the monitor to set the hash.
1121
1122 // There's no need to inflate if the mark has already got a monitor.
1123 // NOTE: an async deflation can race after we get the monitor and
1124 // before we can update the ObjectMonitor's header with the hash
1125 // value below.
1126 monitor = mark.has_monitor() ? mark.monitor() : inflate(current, obj, inflate_cause_hash_code);
1127 // Load ObjectMonitor's header/dmw field and see if it has a hash.
1128 mark = monitor->header();
1129 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1130 hash = mark.hash();
1131 if (hash == 0) { // if it does not have a hash
1132 hash = get_next_hash(current, obj); // get a new hash
1133 temp = mark.copy_set_hash(hash) ; // merge the hash into header
1134 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
1135 uintptr_t v = Atomic::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
1136 test = markWord(v);
1137 if (test != mark) {
1138 // The attempt to update the ObjectMonitor's header/dmw field
1139 // did not work. This can happen if another thread managed to
1140 // merge in the hash just before our cmpxchg().
1141 // If we add any new usages of the header/dmw field, this code
1142 // will need to be updated.
1143 hash = test.hash();
1144 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
1145 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
1146 }
1147 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
1148 // If we detect that async deflation has occurred, then we
1149 // attempt to restore the header/dmw to the object's header
1150 // so that we only retry once if the deflater thread happens
1151 // to be slow.
1152 monitor->install_displaced_markword_in_object(obj);
1153 continue;
1154 }
1155 }
1156 // We finally get the hash.
1157 return hash;
1158 }
1159 }
1160
1161 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
1162 Handle h_obj) {
1163 if (EnableValhalla && h_obj->mark().is_inline_type()) {
1164 return false;
1165 }
1166 assert(current == JavaThread::current(), "Can only be called on current thread");
1167 oop obj = h_obj();
1168
1169 markWord mark = read_stable_mark(obj);
1170
1171 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1172 // stack-locked case, header points into owner's stack
1173 return current->is_lock_owned((address)mark.locker());
1174 }
1175
1176 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1177 // fast-locking case, see if lock is in current's lock stack
1178 return current->lock_stack().contains(h_obj());
1179 }
1180
1181 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1182 ObjectMonitor* monitor = read_monitor(current, obj, mark);
1183 if (monitor != nullptr) {
1184 return monitor->is_entered(current) != 0;
1185 }
1186 // Racing with inflation/deflation, retry
1187 mark = obj->mark_acquire();
1188
1189 if (mark.is_fast_locked()) {
1190 // Some other thread fast_locked, current could not have held the lock
1191 return false;
1192 }
1193 }
1194
1195 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1196 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1197 // The first stage of async deflation does not affect any field
1198 // used by this comparison so the ObjectMonitor* is usable here.
1199 ObjectMonitor* monitor = read_monitor(mark);
1200 return monitor->is_entered(current) != 0;
1201 }
1202 // Unlocked case, header in place
1203 assert(mark.is_unlocked(), "sanity check");
1204 return false;
1205 }
1206
1207 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
1208 oop obj = h_obj();
1209 markWord mark = read_stable_mark(obj);
1210
1211 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1212 // stack-locked so header points into owner's stack.
1213 // owning_thread_from_monitor_owner() may also return null here:
1214 return Threads::owning_thread_from_monitor_owner(t_list, (address) mark.locker());
1215 }
1216
1217 if (LockingMode == LM_LIGHTWEIGHT && mark.is_fast_locked()) {
1218 // fast-locked so get owner from the object.
1219 // owning_thread_from_object() may also return null here:
1220 return Threads::owning_thread_from_object(t_list, h_obj());
1221 }
1222
1223 while (LockingMode == LM_LIGHTWEIGHT && mark.has_monitor()) {
1224 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
1225 if (monitor != nullptr) {
1226 return Threads::owning_thread_from_monitor(t_list, monitor);
1227 }
1228 // Racing with inflation/deflation, retry
1229 mark = obj->mark_acquire();
1230
1231 if (mark.is_fast_locked()) {
1232 // Some other thread fast_locked
1233 return Threads::owning_thread_from_object(t_list, h_obj());
1234 }
1235 }
1236
1237 if (LockingMode != LM_LIGHTWEIGHT && mark.has_monitor()) {
1238 // Inflated monitor so header points to ObjectMonitor (tagged pointer).
1239 // The first stage of async deflation does not affect any field
1240 // used by this comparison so the ObjectMonitor* is usable here.
1241 ObjectMonitor* monitor = read_monitor(mark);
1242 assert(monitor != nullptr, "monitor should be non-null");
1243 // owning_thread_from_monitor() may also return null here:
1244 return Threads::owning_thread_from_monitor(t_list, monitor);
1245 }
1246
1247 // Unlocked case, header in place
1248 // Cannot have assertion since this object may have been
1249 // locked by another thread when reaching here.
1250 // assert(mark.is_unlocked(), "sanity check");
1251
1252 return nullptr;
1253 }
1254
1255 // Visitors ...
1256
1257 // Iterate over all ObjectMonitors.
1258 template <typename Function>
1259 void ObjectSynchronizer::monitors_iterate(Function function) {
1260 MonitorList::Iterator iter = _in_use_list.iterator();
1261 while (iter.has_next()) {
1262 ObjectMonitor* monitor = iter.next();
1263 function(monitor);
1264 }
1265 }
1266
1267 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
1268 // returns true.
1269 template <typename OwnerFilter>
1270 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
1271 monitors_iterate([&](ObjectMonitor* monitor) {
1272 // This function is only called at a safepoint or when the
1273 // target thread is suspended or when the target thread is
1274 // operating on itself. The current closures in use today are
1275 // only interested in an owned ObjectMonitor and ownership
1276 // cannot be dropped under the calling contexts so the
1277 // ObjectMonitor cannot be async deflated.
1278 if (monitor->has_owner() && filter(monitor->owner_raw())) {
1279 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
1280
1281 closure->do_monitor(monitor);
1282 }
1283 });
1284 }
1285
1286 // Iterate ObjectMonitors where the owner == thread; this does NOT include
1287 // ObjectMonitors where owner is set to a stack-lock address in thread.
1288 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
1289 auto thread_filter = [&](void* owner) { return owner == thread; };
1290 return owned_monitors_iterate_filtered(closure, thread_filter);
1291 }
1292
1293 // Iterate ObjectMonitors owned by any thread.
1294 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
1295 auto all_filter = [&](void* owner) { return true; };
1296 return owned_monitors_iterate_filtered(closure, all_filter);
1297 }
1298
1299 static bool monitors_used_above_threshold(MonitorList* list) {
1300 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
1301 return false;
1302 }
1303 // Start with ceiling based on a per-thread estimate:
1304 size_t ceiling = ObjectSynchronizer::in_use_list_ceiling();
1305 size_t old_ceiling = ceiling;
1306 if (ceiling < list->max()) {
1307 // The max used by the system has exceeded the ceiling so use that:
1308 ceiling = list->max();
1309 }
1310 size_t monitors_used = list->count();
1311 if (monitors_used == 0) { // empty list is easy
1312 return false;
1313 }
1314 if (NoAsyncDeflationProgressMax != 0 &&
1315 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
1316 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
1317 size_t new_ceiling = ceiling + (size_t)((double)ceiling * remainder) + 1;
1318 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
1319 log_info(monitorinflation)("Too many deflations without progress; "
1320 "bumping in_use_list_ceiling from " SIZE_FORMAT
1321 " to " SIZE_FORMAT, old_ceiling, new_ceiling);
1322 _no_progress_cnt = 0;
1323 ceiling = new_ceiling;
1324 }
1325
1326 // Check if our monitor usage is above the threshold:
1327 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
1328 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
1329 log_info(monitorinflation)("monitors_used=" SIZE_FORMAT ", ceiling=" SIZE_FORMAT
1330 ", monitor_usage=" SIZE_FORMAT ", threshold=%d",
1331 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
1332 return true;
1333 }
1334
1335 return false;
1336 }
1337
1338 size_t ObjectSynchronizer::in_use_list_ceiling() {
1339 return _in_use_list_ceiling;
1340 }
1341
1342 void ObjectSynchronizer::dec_in_use_list_ceiling() {
1343 Atomic::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1344 }
1345
1346 void ObjectSynchronizer::inc_in_use_list_ceiling() {
1347 Atomic::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
1348 }
1349
1350 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
1351 _in_use_list_ceiling = new_value;
1352 }
1353
1354 bool ObjectSynchronizer::is_async_deflation_needed() {
1355 if (is_async_deflation_requested()) {
1356 // Async deflation request.
1357 log_info(monitorinflation)("Async deflation needed: explicit request");
1358 return true;
1359 }
1360
1361 jlong time_since_last = time_since_last_async_deflation_ms();
1362
1363 if (AsyncDeflationInterval > 0 &&
1364 time_since_last > AsyncDeflationInterval &&
1365 monitors_used_above_threshold(&_in_use_list)) {
1366 // It's been longer than our specified deflate interval and there
1367 // are too many monitors in use. We don't deflate more frequently
1368 // than AsyncDeflationInterval (unless is_async_deflation_requested)
1369 // in order to not swamp the MonitorDeflationThread.
1370 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
1371 return true;
1372 }
1373
1374 if (GuaranteedAsyncDeflationInterval > 0 &&
1375 time_since_last > GuaranteedAsyncDeflationInterval) {
1376 // It's been longer than our specified guaranteed deflate interval.
1377 // We need to clean up the used monitors even if the threshold is
1378 // not reached, to keep the memory utilization at bay when many threads
1379 // touched many monitors.
1380 log_info(monitorinflation)("Async deflation needed: guaranteed interval (" INTX_FORMAT " ms) "
1381 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
1382 GuaranteedAsyncDeflationInterval, time_since_last);
1383
1384 // If this deflation has no progress, then it should not affect the no-progress
1385 // tracking, otherwise threshold heuristics would think it was triggered, experienced
1386 // no progress, and needs to backoff more aggressively. In this "no progress" case,
1387 // the generic code would bump the no-progress counter, and we compensate for that
1388 // by telling it to skip the update.
1389 //
1390 // If this deflation has progress, then it should let non-progress tracking
1391 // know about this, otherwise the threshold heuristics would kick in, potentially
1392 // experience no-progress due to aggressive cleanup by this deflation, and think
1393 // it is still in no-progress stride. In this "progress" case, the generic code would
1394 // zero the counter, and we allow it to happen.
1395 _no_progress_skip_increment = true;
1396
1397 return true;
1398 }
1399
1400 return false;
1401 }
1402
1403 void ObjectSynchronizer::request_deflate_idle_monitors() {
1404 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
1405 set_is_async_deflation_requested(true);
1406 ml.notify_all();
1407 }
1408
1409 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
1410 JavaThread* current = JavaThread::current();
1411 bool ret_code = false;
1412
1413 jlong last_time = last_async_deflation_time_ns();
1414
1415 request_deflate_idle_monitors();
1416
1417 const int N_CHECKS = 5;
1418 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1419 if (last_async_deflation_time_ns() > last_time) {
1420 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1421 ret_code = true;
1422 break;
1423 }
1424 {
1425 // JavaThread has to honor the blocking protocol.
1426 ThreadBlockInVM tbivm(current);
1427 os::naked_short_sleep(999); // sleep for almost 1 second
1428 }
1429 }
1430 if (!ret_code) {
1431 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1432 }
1433
1434 return ret_code;
1435 }
1436
1437 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1438 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1439 }
1440
1441 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
1442 const oop obj,
1443 ObjectSynchronizer::InflateCause cause) {
1444 assert(event != nullptr, "invariant");
1445 event->set_monitorClass(obj->klass());
1446 event->set_address((uintptr_t)(void*)obj);
1447 event->set_cause((u1)cause);
1448 event->commit();
1449 }
1450
1451 // Fast path code shared by multiple functions
1452 void ObjectSynchronizer::inflate_helper(oop obj) {
1453 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1454 markWord mark = obj->mark_acquire();
1455 if (mark.has_monitor()) {
1456 ObjectMonitor* monitor = read_monitor(mark);
1457 markWord dmw = monitor->header();
1458 assert(dmw.is_neutral(), "sanity check: header=" INTPTR_FORMAT, dmw.value());
1459 return;
1460 }
1461 (void)inflate(Thread::current(), obj, inflate_cause_vm_internal);
1462 }
1463
1464 ObjectMonitor* ObjectSynchronizer::inflate(Thread* current, oop obj, const InflateCause cause) {
1465 assert(current == Thread::current(), "must be");
1466 assert(LockingMode != LM_LIGHTWEIGHT, "only inflate through enter");
1467 return inflate_impl(obj, cause);
1468 }
1469
1470 ObjectMonitor* ObjectSynchronizer::inflate_for(JavaThread* thread, oop obj, const InflateCause cause) {
1471 assert(thread == Thread::current() || thread->is_obj_deopt_suspend(), "must be");
1472 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_for");
1473 return inflate_impl(obj, cause);
1474 }
1475
1476 ObjectMonitor* ObjectSynchronizer::inflate_impl(oop object, const InflateCause cause) {
1477 if (EnableValhalla) {
1478 guarantee(!object->klass()->is_inline_klass(), "Attempt to inflate inline type");
1479 }
1480 assert(LockingMode != LM_LIGHTWEIGHT, "LM_LIGHTWEIGHT cannot use inflate_impl");
1481 EventJavaMonitorInflate event;
1482
1483 for (;;) {
1484 const markWord mark = object->mark_acquire();
1485
1486 // The mark can be in one of the following states:
1487 // * inflated - Just return it.
1488 // * stack-locked - Coerce it to inflated from stack-locked.
1489 // * INFLATING - Busy wait for conversion from stack-locked to
1490 // inflated.
1491 // * unlocked - Aggressively inflate the object.
1492
1493 // CASE: inflated
1494 if (mark.has_monitor()) {
1495 ObjectMonitor* inf = mark.monitor();
1496 markWord dmw = inf->header();
1497 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1498 return inf;
1499 }
1500
1501 // CASE: inflation in progress - inflating over a stack-lock.
1502 // Some other thread is converting from stack-locked to inflated.
1503 // Only that thread can complete inflation -- other threads must wait.
1504 // The INFLATING value is transient.
1505 // Currently, we spin/yield/park and poll the markword, waiting for inflation to finish.
1506 // We could always eliminate polling by parking the thread on some auxiliary list.
1507 if (mark == markWord::INFLATING()) {
1508 read_stable_mark(object);
1509 continue;
1510 }
1511
1512 // CASE: stack-locked
1513 // Could be stack-locked either by current or by some other thread.
1514 //
1515 // Note that we allocate the ObjectMonitor speculatively, _before_ attempting
1516 // to install INFLATING into the mark word. We originally installed INFLATING,
1517 // allocated the ObjectMonitor, and then finally STed the address of the
1518 // ObjectMonitor into the mark. This was correct, but artificially lengthened
1519 // the interval in which INFLATING appeared in the mark, thus increasing
1520 // the odds of inflation contention. If we lose the race to set INFLATING,
1521 // then we just delete the ObjectMonitor and loop around again.
1522 //
1523 LogStreamHandle(Trace, monitorinflation) lsh;
1524 if (LockingMode == LM_LEGACY && mark.has_locker()) {
1525 ObjectMonitor* m = new ObjectMonitor(object);
1526 // Optimistically prepare the ObjectMonitor - anticipate successful CAS
1527 // We do this before the CAS in order to minimize the length of time
1528 // in which INFLATING appears in the mark.
1529
1530 markWord cmp = object->cas_set_mark(markWord::INFLATING(), mark);
1531 if (cmp != mark) {
1532 delete m;
1533 continue; // Interference -- just retry
1534 }
1535
1536 // We've successfully installed INFLATING (0) into the mark-word.
1537 // This is the only case where 0 will appear in a mark-word.
1538 // Only the singular thread that successfully swings the mark-word
1539 // to 0 can perform (or more precisely, complete) inflation.
1540 //
1541 // Why do we CAS a 0 into the mark-word instead of just CASing the
1542 // mark-word from the stack-locked value directly to the new inflated state?
1543 // Consider what happens when a thread unlocks a stack-locked object.
1544 // It attempts to use CAS to swing the displaced header value from the
1545 // on-stack BasicLock back into the object header. Recall also that the
1546 // header value (hash code, etc) can reside in (a) the object header, or
1547 // (b) a displaced header associated with the stack-lock, or (c) a displaced
1548 // header in an ObjectMonitor. The inflate() routine must copy the header
1549 // value from the BasicLock on the owner's stack to the ObjectMonitor, all
1550 // the while preserving the hashCode stability invariants. If the owner
1551 // decides to release the lock while the value is 0, the unlock will fail
1552 // and control will eventually pass from slow_exit() to inflate. The owner
1553 // will then spin, waiting for the 0 value to disappear. Put another way,
1554 // the 0 causes the owner to stall if the owner happens to try to
1555 // drop the lock (restoring the header from the BasicLock to the object)
1556 // while inflation is in-progress. This protocol avoids races that might
1557 // would otherwise permit hashCode values to change or "flicker" for an object.
1558 // Critically, while object->mark is 0 mark.displaced_mark_helper() is stable.
1559 // 0 serves as a "BUSY" inflate-in-progress indicator.
1560
1561
1562 // fetch the displaced mark from the owner's stack.
1563 // The owner can't die or unwind past the lock while our INFLATING
1564 // object is in the mark. Furthermore the owner can't complete
1565 // an unlock on the object, either.
1566 markWord dmw = mark.displaced_mark_helper();
1567 // Catch if the object's header is not neutral (not locked and
1568 // not marked is what we care about here).
1569 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
1570
1571 // Setup monitor fields to proper values -- prepare the monitor
1572 m->set_header(dmw);
1573
1574 // Optimization: if the mark.locker stack address is associated
1575 // with this thread we could simply set m->_owner = current.
1576 // Note that a thread can inflate an object
1577 // that it has stack-locked -- as might happen in wait() -- directly
1578 // with CAS. That is, we can avoid the xchg-nullptr .... ST idiom.
1579 m->set_owner_from(nullptr, mark.locker());
1580 // TODO-FIXME: assert BasicLock->dhw != 0.
1581
1582 // Must preserve store ordering. The monitor state must
1583 // be stable at the time of publishing the monitor address.
1584 guarantee(object->mark() == markWord::INFLATING(), "invariant");
1585 // Release semantics so that above set_object() is seen first.
1586 object->release_set_mark(markWord::encode(m));
1587
1588 // Once ObjectMonitor is configured and the object is associated
1589 // with the ObjectMonitor, it is safe to allow async deflation:
1590 _in_use_list.add(m);
1591
1592 // Hopefully the performance counters are allocated on distinct cache lines
1593 // to avoid false sharing on MP systems ...
1594 OM_PERFDATA_OP(Inflations, inc());
1595 if (log_is_enabled(Trace, monitorinflation)) {
1596 ResourceMark rm;
1597 lsh.print_cr("inflate(has_locker): object=" INTPTR_FORMAT ", mark="
1598 INTPTR_FORMAT ", type='%s'", p2i(object),
1599 object->mark().value(), object->klass()->external_name());
1600 }
1601 if (event.should_commit()) {
1602 post_monitor_inflate_event(&event, object, cause);
1603 }
1604 return m;
1605 }
1606
1607 // CASE: unlocked
1608 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
1609 // If we know we're inflating for entry it's better to inflate by swinging a
1610 // pre-locked ObjectMonitor pointer into the object header. A successful
1611 // CAS inflates the object *and* confers ownership to the inflating thread.
1612 // In the current implementation we use a 2-step mechanism where we CAS()
1613 // to inflate and then CAS() again to try to swing _owner from null to current.
1614 // An inflateTry() method that we could call from enter() would be useful.
1615
1616 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
1617 ObjectMonitor* m = new ObjectMonitor(object);
1618 // prepare m for installation - set monitor to initial state
1619 m->set_header(mark);
1620
1621 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
1622 delete m;
1623 m = nullptr;
1624 continue;
1625 // interference - the markword changed - just retry.
1626 // The state-transitions are one-way, so there's no chance of
1627 // live-lock -- "Inflated" is an absorbing state.
1628 }
1629
1630 // Once the ObjectMonitor is configured and object is associated
1631 // with the ObjectMonitor, it is safe to allow async deflation:
1632 _in_use_list.add(m);
1633
1634 // Hopefully the performance counters are allocated on distinct
1635 // cache lines to avoid false sharing on MP systems ...
1636 OM_PERFDATA_OP(Inflations, inc());
1637 if (log_is_enabled(Trace, monitorinflation)) {
1638 ResourceMark rm;
1639 lsh.print_cr("inflate(unlocked): object=" INTPTR_FORMAT ", mark="
1640 INTPTR_FORMAT ", type='%s'", p2i(object),
1641 object->mark().value(), object->klass()->external_name());
1642 }
1643 if (event.should_commit()) {
1644 post_monitor_inflate_event(&event, object, cause);
1645 }
1646 return m;
1647 }
1648 }
1649
1650 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1651 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1652 //
1653 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1654 MonitorList::Iterator iter = _in_use_list.iterator();
1655 size_t deflated_count = 0;
1656 Thread* current = Thread::current();
1657
1658 while (iter.has_next()) {
1659 if (deflated_count >= (size_t)MonitorDeflationMax) {
1660 break;
1661 }
1662 ObjectMonitor* mid = iter.next();
1663 if (mid->deflate_monitor(current)) {
1664 deflated_count++;
1665 }
1666
1667 // Must check for a safepoint/handshake and honor it.
1668 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1669 }
1670
1671 return deflated_count;
1672 }
1673
1674 class HandshakeForDeflation : public HandshakeClosure {
1675 public:
1676 HandshakeForDeflation() : HandshakeClosure("HandshakeForDeflation") {}
1677
1678 void do_thread(Thread* thread) {
1679 log_trace(monitorinflation)("HandshakeForDeflation::do_thread: thread="
1680 INTPTR_FORMAT, p2i(thread));
1681 if (thread->is_Java_thread()) {
1682 // Clear OM cache
1683 JavaThread* jt = JavaThread::cast(thread);
1684 jt->om_clear_monitor_cache();
1685 }
1686 }
1687 };
1688
1689 class VM_RendezvousGCThreads : public VM_Operation {
1690 public:
1691 bool evaluate_at_safepoint() const override { return false; }
1692 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1693 void doit() override {
1694 Universe::heap()->safepoint_synchronize_begin();
1695 Universe::heap()->safepoint_synchronize_end();
1696 };
1697 };
1698
1699 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1700 ObjectMonitorDeflationSafepointer* safepointer) {
1701 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1702 size_t deleted_count = 0;
1703 for (ObjectMonitor* monitor: *delete_list) {
1704 delete monitor;
1705 deleted_count++;
1706 // A JavaThread must check for a safepoint/handshake and honor it.
1707 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1708 }
1709 return deleted_count;
1710 }
1711
1712 class ObjectMonitorDeflationLogging: public StackObj {
1713 LogStreamHandle(Debug, monitorinflation) _debug;
1714 LogStreamHandle(Info, monitorinflation) _info;
1715 LogStream* _stream;
1716 elapsedTimer _timer;
1717
1718 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1719 size_t count() const { return ObjectSynchronizer::_in_use_list.count(); }
1720 size_t max() const { return ObjectSynchronizer::_in_use_list.max(); }
1721
1722 public:
1723 ObjectMonitorDeflationLogging()
1724 : _debug(), _info(), _stream(nullptr) {
1725 if (_debug.is_enabled()) {
1726 _stream = &_debug;
1727 } else if (_info.is_enabled()) {
1728 _stream = &_info;
1729 }
1730 }
1731
1732 void begin() {
1733 if (_stream != nullptr) {
1734 _stream->print_cr("begin deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1735 ceiling(), count(), max());
1736 _timer.start();
1737 }
1738 }
1739
1740 void before_handshake(size_t unlinked_count) {
1741 if (_stream != nullptr) {
1742 _timer.stop();
1743 _stream->print_cr("before handshaking: unlinked_count=" SIZE_FORMAT
1744 ", in_use_list stats: ceiling=" SIZE_FORMAT ", count="
1745 SIZE_FORMAT ", max=" SIZE_FORMAT,
1746 unlinked_count, ceiling(), count(), max());
1747 }
1748 }
1749
1750 void after_handshake() {
1751 if (_stream != nullptr) {
1752 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1753 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1754 ceiling(), count(), max());
1755 _timer.start();
1756 }
1757 }
1758
1759 void end(size_t deflated_count, size_t unlinked_count) {
1760 if (_stream != nullptr) {
1761 _timer.stop();
1762 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1763 _stream->print_cr("deflated_count=" SIZE_FORMAT ", {unlinked,deleted}_count=" SIZE_FORMAT " monitors in %3.7f secs",
1764 deflated_count, unlinked_count, _timer.seconds());
1765 }
1766 _stream->print_cr("end deflating: in_use_list stats: ceiling=" SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1767 ceiling(), count(), max());
1768 }
1769 }
1770
1771 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1772 if (_stream != nullptr) {
1773 _timer.stop();
1774 _stream->print_cr("pausing %s: %s=" SIZE_FORMAT ", in_use_list stats: ceiling="
1775 SIZE_FORMAT ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT,
1776 op_name, cnt_name, cnt, ceiling(), count(), max());
1777 }
1778 }
1779
1780 void after_block_for_safepoint(const char* op_name) {
1781 if (_stream != nullptr) {
1782 _stream->print_cr("resuming %s: in_use_list stats: ceiling=" SIZE_FORMAT
1783 ", count=" SIZE_FORMAT ", max=" SIZE_FORMAT, op_name,
1784 ceiling(), count(), max());
1785 _timer.start();
1786 }
1787 }
1788 };
1789
1790 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1791 if (!SafepointMechanism::should_process(_current)) {
1792 return;
1793 }
1794
1795 // A safepoint/handshake has started.
1796 _log->before_block_for_safepoint(op_name, count_name, counter);
1797
1798 {
1799 // Honor block request.
1800 ThreadBlockInVM tbivm(_current);
1801 }
1802
1803 _log->after_block_for_safepoint(op_name);
1804 }
1805
1806 // This function is called by the MonitorDeflationThread to deflate
1807 // ObjectMonitors.
1808 size_t ObjectSynchronizer::deflate_idle_monitors() {
1809 JavaThread* current = JavaThread::current();
1810 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1811
1812 // The async deflation request has been processed.
1813 _last_async_deflation_time_ns = os::javaTimeNanos();
1814 set_is_async_deflation_requested(false);
1815
1816 ObjectMonitorDeflationLogging log;
1817 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1818
1819 log.begin();
1820
1821 // Deflate some idle ObjectMonitors.
1822 size_t deflated_count = deflate_monitor_list(&safepointer);
1823
1824 // Unlink the deflated ObjectMonitors from the in-use list.
1825 size_t unlinked_count = 0;
1826 size_t deleted_count = 0;
1827 if (deflated_count > 0) {
1828 ResourceMark rm(current);
1829 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1830 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1831
1832 #ifdef ASSERT
1833 if (UseObjectMonitorTable) {
1834 for (ObjectMonitor* monitor : delete_list) {
1835 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1836 }
1837 }
1838 #endif
1839
1840 log.before_handshake(unlinked_count);
1841
1842 // A JavaThread needs to handshake in order to safely free the
1843 // ObjectMonitors that were deflated in this cycle.
1844 HandshakeForDeflation hfd_hc;
1845 Handshake::execute(&hfd_hc);
1846 // Also, we sync and desync GC threads around the handshake, so that they can
1847 // safely read the mark-word and look-through to the object-monitor, without
1848 // being afraid that the object-monitor is going away.
1849 VM_RendezvousGCThreads sync_gc;
1850 VMThread::execute(&sync_gc);
1851
1852 log.after_handshake();
1853
1854 // After the handshake, safely free the ObjectMonitors that were
1855 // deflated and unlinked in this cycle.
1856
1857 // Delete the unlinked ObjectMonitors.
1858 deleted_count = delete_monitors(&delete_list, &safepointer);
1859 assert(unlinked_count == deleted_count, "must be");
1860 }
1861
1862 log.end(deflated_count, unlinked_count);
1863
1864 OM_PERFDATA_OP(MonExtant, set_value(_in_use_list.count()));
1865 OM_PERFDATA_OP(Deflations, inc(deflated_count));
1866
1867 GVars.stw_random = os::random();
1868
1869 if (deflated_count != 0) {
1870 _no_progress_cnt = 0;
1871 } else if (_no_progress_skip_increment) {
1872 _no_progress_skip_increment = false;
1873 } else {
1874 _no_progress_cnt++;
1875 }
1876
1877 return deflated_count;
1878 }
1879
1880 // Monitor cleanup on JavaThread::exit
1881
1882 // Iterate through monitor cache and attempt to release thread's monitors
1883 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1884 private:
1885 JavaThread* _thread;
1886
1887 public:
1888 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1889 void do_monitor(ObjectMonitor* mid) {
1890 intx rec = mid->complete_exit(_thread);
1891 _thread->dec_held_monitor_count(rec + 1);
1892 }
1893 };
1894
1895 // Release all inflated monitors owned by current thread. Lightweight monitors are
1896 // ignored. This is meant to be called during JNI thread detach which assumes
1897 // all remaining monitors are heavyweight. All exceptions are swallowed.
1898 // Scanning the extant monitor list can be time consuming.
1899 // A simple optimization is to add a per-thread flag that indicates a thread
1900 // called jni_monitorenter() during its lifetime.
1901 //
1902 // Instead of NoSafepointVerifier it might be cheaper to
1903 // use an idiom of the form:
1904 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1905 // <code that must not run at safepoint>
1906 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1907 // Since the tests are extremely cheap we could leave them enabled
1908 // for normal product builds.
1909
1910 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1911 assert(current == JavaThread::current(), "must be current Java thread");
1912 NoSafepointVerifier nsv;
1913 ReleaseJavaMonitorsClosure rjmc(current);
1914 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1915 assert(!current->has_pending_exception(), "Should not be possible");
1916 current->clear_pending_exception();
1917 assert(current->held_monitor_count() == 0, "Should not be possible");
1918 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1919 current->clear_jni_monitor_count();
1920 }
1921
1922 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1923 switch (cause) {
1924 case inflate_cause_vm_internal: return "VM Internal";
1925 case inflate_cause_monitor_enter: return "Monitor Enter";
1926 case inflate_cause_wait: return "Monitor Wait";
1927 case inflate_cause_notify: return "Monitor Notify";
1928 case inflate_cause_hash_code: return "Monitor Hash Code";
1929 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1930 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1931 default:
1932 ShouldNotReachHere();
1933 }
1934 return "Unknown";
1935 }
1936
1937 //------------------------------------------------------------------------------
1938 // Debugging code
1939
1940 u_char* ObjectSynchronizer::get_gvars_addr() {
1941 return (u_char*)&GVars;
1942 }
1943
1944 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1945 return (u_char*)&GVars.hc_sequence;
1946 }
1947
1948 size_t ObjectSynchronizer::get_gvars_size() {
1949 return sizeof(SharedGlobals);
1950 }
1951
1952 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1953 return (u_char*)&GVars.stw_random;
1954 }
1955
1956 // Do the final audit and print of ObjectMonitor stats; must be done
1957 // by the VMThread at VM exit time.
1958 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1959 assert(Thread::current()->is_VM_thread(), "sanity check");
1960
1961 if (is_final_audit()) { // Only do the audit once.
1962 return;
1963 }
1964 set_is_final_audit();
1965 log_info(monitorinflation)("Starting the final audit.");
1966
1967 if (log_is_enabled(Info, monitorinflation)) {
1968 LogStreamHandle(Info, monitorinflation) ls;
1969 audit_and_print_stats(&ls, true /* on_exit */);
1970 }
1971 }
1972
1973 // This function can be called by the MonitorDeflationThread or it can be called when
1974 // we are trying to exit the VM. The list walker functions can run in parallel with
1975 // the other list operations.
1976 // Calls to this function can be added in various places as a debugging
1977 // aid.
1978 //
1979 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1980 int error_cnt = 0;
1981
1982 ls->print_cr("Checking in_use_list:");
1983 chk_in_use_list(ls, &error_cnt);
1984
1985 if (error_cnt == 0) {
1986 ls->print_cr("No errors found in in_use_list checks.");
1987 } else {
1988 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1989 }
1990
1991 // When exiting, only log the interesting entries at the Info level.
1992 // When called at intervals by the MonitorDeflationThread, log output
1993 // at the Trace level since there can be a lot of it.
1994 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1995 LogStreamHandle(Trace, monitorinflation) ls_tr;
1996 log_in_use_monitor_details(&ls_tr, true /* log_all */);
1997 } else if (on_exit) {
1998 log_in_use_monitor_details(ls, false /* log_all */);
1999 }
2000
2001 ls->flush();
2002
2003 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
2004 }
2005
2006 // Check the in_use_list; log the results of the checks.
2007 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
2008 size_t l_in_use_count = _in_use_list.count();
2009 size_t l_in_use_max = _in_use_list.max();
2010 out->print_cr("count=" SIZE_FORMAT ", max=" SIZE_FORMAT, l_in_use_count,
2011 l_in_use_max);
2012
2013 size_t ck_in_use_count = 0;
2014 MonitorList::Iterator iter = _in_use_list.iterator();
2015 while (iter.has_next()) {
2016 ObjectMonitor* mid = iter.next();
2017 chk_in_use_entry(mid, out, error_cnt_p);
2018 ck_in_use_count++;
2019 }
2020
2021 if (l_in_use_count == ck_in_use_count) {
2022 out->print_cr("in_use_count=" SIZE_FORMAT " equals ck_in_use_count="
2023 SIZE_FORMAT, l_in_use_count, ck_in_use_count);
2024 } else {
2025 out->print_cr("WARNING: in_use_count=" SIZE_FORMAT " is not equal to "
2026 "ck_in_use_count=" SIZE_FORMAT, l_in_use_count,
2027 ck_in_use_count);
2028 }
2029
2030 size_t ck_in_use_max = _in_use_list.max();
2031 if (l_in_use_max == ck_in_use_max) {
2032 out->print_cr("in_use_max=" SIZE_FORMAT " equals ck_in_use_max="
2033 SIZE_FORMAT, l_in_use_max, ck_in_use_max);
2034 } else {
2035 out->print_cr("WARNING: in_use_max=" SIZE_FORMAT " is not equal to "
2036 "ck_in_use_max=" SIZE_FORMAT, l_in_use_max, ck_in_use_max);
2037 }
2038 }
2039
2040 // Check an in-use monitor entry; log any errors.
2041 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
2042 int* error_cnt_p) {
2043 if (n->owner_is_DEFLATER_MARKER()) {
2044 // This could happen when monitor deflation blocks for a safepoint.
2045 return;
2046 }
2047
2048
2049 if (n->metadata() == 0) {
2050 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
2051 "have non-null _metadata (header/hash) field.", p2i(n));
2052 *error_cnt_p = *error_cnt_p + 1;
2053 }
2054
2055 const oop obj = n->object_peek();
2056 if (obj == nullptr) {
2057 return;
2058 }
2059
2060 const markWord mark = obj->mark();
2061 if (!mark.has_monitor()) {
2062 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2063 "object does not think it has a monitor: obj="
2064 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
2065 p2i(obj), mark.value());
2066 *error_cnt_p = *error_cnt_p + 1;
2067 return;
2068 }
2069
2070 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
2071 if (n != obj_mon) {
2072 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
2073 "object does not refer to the same monitor: obj="
2074 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
2075 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
2076 *error_cnt_p = *error_cnt_p + 1;
2077 }
2078 }
2079
2080 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
2081 // flags indicate why the entry is in-use, 'object' and 'object type'
2082 // indicate the associated object and its type.
2083 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
2084 if (_in_use_list.count() > 0) {
2085 stringStream ss;
2086 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
2087 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
2088 out->print_cr("%18s %s %18s %18s",
2089 "monitor", "BHL", "object", "object type");
2090 out->print_cr("================== === ================== ==================");
2091
2092 auto is_interesting = [&](ObjectMonitor* monitor) {
2093 return log_all || monitor->has_owner() || monitor->is_busy();
2094 };
2095
2096 monitors_iterate([&](ObjectMonitor* monitor) {
2097 if (is_interesting(monitor)) {
2098 const oop obj = monitor->object_peek();
2099 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
2100 ResourceMark rm;
2101 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
2102 monitor->is_busy(), hash != 0, monitor->owner() != nullptr,
2103 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
2104 if (monitor->is_busy()) {
2105 out->print(" (%s)", monitor->is_busy_to_string(&ss));
2106 ss.reset();
2107 }
2108 out->cr();
2109 }
2110 });
2111 }
2112
2113 out->flush();
2114 }