1 /*
2 * Copyright (c) 2024, 2025, 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 "classfile/vmSymbols.hpp"
26 #include "jfrfiles/jfrEventClasses.hpp"
27 #include "logging/log.hpp"
28 #include "memory/allStatic.hpp"
29 #include "memory/resourceArea.hpp"
30 #include "nmt/memTag.hpp"
31 #include "oops/oop.inline.hpp"
32 #include "runtime/atomic.hpp"
33 #include "runtime/basicLock.inline.hpp"
34 #include "runtime/globals_extension.hpp"
35 #include "runtime/interfaceSupport.inline.hpp"
36 #include "runtime/javaThread.inline.hpp"
37 #include "runtime/lightweightSynchronizer.hpp"
38 #include "runtime/lockStack.inline.hpp"
39 #include "runtime/mutexLocker.hpp"
40 #include "runtime/objectMonitor.inline.hpp"
41 #include "runtime/os.hpp"
42 #include "runtime/perfData.inline.hpp"
43 #include "runtime/safepointMechanism.inline.hpp"
44 #include "runtime/safepointVerifiers.hpp"
45 #include "runtime/synchronizer.inline.hpp"
46 #include "runtime/timerTrace.hpp"
47 #include "runtime/trimNativeHeap.hpp"
48 #include "utilities/concurrentHashTable.inline.hpp"
49 #include "utilities/concurrentHashTableTasks.inline.hpp"
50 #include "utilities/globalDefinitions.hpp"
51
52 // ConcurrentHashTable storing links from objects to ObjectMonitors
53 class ObjectMonitorTable : AllStatic {
54 struct Config {
55 using Value = ObjectMonitor*;
56 static uintx get_hash(Value const& value, bool* is_dead) {
57 return (uintx)value->hash();
58 }
59 static void* allocate_node(void* context, size_t size, Value const& value) {
60 ObjectMonitorTable::inc_items_count();
61 return AllocateHeap(size, mtObjectMonitor);
62 };
63 static void free_node(void* context, void* memory, Value const& value) {
64 ObjectMonitorTable::dec_items_count();
65 FreeHeap(memory);
66 }
67 };
68 using ConcurrentTable = ConcurrentHashTable<Config, mtObjectMonitor>;
69
70 static ConcurrentTable* _table;
71 static volatile size_t _items_count;
72 static size_t _table_size;
73 static volatile bool _resize;
74
75 class Lookup : public StackObj {
76 oop _obj;
77
78 public:
79 explicit Lookup(oop obj) : _obj(obj) {}
80
81 uintx get_hash() const {
82 uintx hash = _obj->mark().hash();
83 assert(hash != 0, "should have a hash");
84 return hash;
85 }
86
87 bool equals(ObjectMonitor** value) {
88 assert(*value != nullptr, "must be");
89 return (*value)->object_refers_to(_obj);
90 }
91
92 bool is_dead(ObjectMonitor** value) {
93 assert(*value != nullptr, "must be");
94 return false;
95 }
96 };
97
98 class LookupMonitor : public StackObj {
99 ObjectMonitor* _monitor;
100
101 public:
102 explicit LookupMonitor(ObjectMonitor* monitor) : _monitor(monitor) {}
103
104 uintx get_hash() const {
105 return _monitor->hash();
106 }
107
108 bool equals(ObjectMonitor** value) {
109 return (*value) == _monitor;
110 }
111
112 bool is_dead(ObjectMonitor** value) {
113 assert(*value != nullptr, "must be");
114 return (*value)->object_is_dead();
115 }
116 };
117
118 static void inc_items_count() {
119 Atomic::inc(&_items_count);
120 }
121
122 static void dec_items_count() {
123 Atomic::dec(&_items_count);
124 }
125
126 static double get_load_factor() {
127 return (double)_items_count / (double)_table_size;
128 }
129
130 static size_t table_size(Thread* current = Thread::current()) {
131 return ((size_t)1) << _table->get_size_log2(current);
132 }
133
134 static size_t max_log_size() {
135 // TODO[OMTable]: Evaluate the max size.
136 // TODO[OMTable]: Need to fix init order to use Universe::heap()->max_capacity();
137 // Using MaxHeapSize directly this early may be wrong, and there
138 // are definitely rounding errors (alignment).
139 const size_t max_capacity = MaxHeapSize;
140 const size_t min_object_size = CollectedHeap::min_dummy_object_size() * HeapWordSize;
141 const size_t max_objects = max_capacity / MAX2(MinObjAlignmentInBytes, checked_cast<int>(min_object_size));
142 const size_t log_max_objects = log2i_graceful(max_objects);
143
144 return MAX2(MIN2<size_t>(SIZE_BIG_LOG2, log_max_objects), min_log_size());
145 }
146
147 static size_t min_log_size() {
148 // ~= log(AvgMonitorsPerThreadEstimate default)
149 return 10;
150 }
151
152 template<typename V>
153 static size_t clamp_log_size(V log_size) {
154 return MAX2(MIN2(log_size, checked_cast<V>(max_log_size())), checked_cast<V>(min_log_size()));
155 }
156
157 static size_t initial_log_size() {
158 const size_t estimate = log2i(MAX2(os::processor_count(), 1)) + log2i(MAX2(AvgMonitorsPerThreadEstimate, size_t(1)));
159 return clamp_log_size(estimate);
160 }
161
162 static size_t grow_hint () {
163 return ConcurrentTable::DEFAULT_GROW_HINT;
164 }
165
166 public:
167 static void create() {
168 _table = new ConcurrentTable(initial_log_size(), max_log_size(), grow_hint());
169 _items_count = 0;
170 _table_size = table_size();
171 _resize = false;
172 }
173
174 static void verify_monitor_get_result(oop obj, ObjectMonitor* monitor) {
175 #ifdef ASSERT
176 if (SafepointSynchronize::is_at_safepoint()) {
177 bool has_monitor = obj->mark().has_monitor();
178 assert(has_monitor == (monitor != nullptr),
179 "Inconsistency between markWord and ObjectMonitorTable has_monitor: %s monitor: " PTR_FORMAT,
180 BOOL_TO_STR(has_monitor), p2i(monitor));
181 }
182 #endif
183 }
184
185 static ObjectMonitor* monitor_get(Thread* current, oop obj) {
186 ObjectMonitor* result = nullptr;
187 Lookup lookup_f(obj);
188 auto found_f = [&](ObjectMonitor** found) {
189 assert((*found)->object_peek() == obj, "must be");
190 result = *found;
191 };
192 _table->get(current, lookup_f, found_f);
193 verify_monitor_get_result(obj, result);
194 return result;
195 }
196
197 static void try_notify_grow() {
198 if (!_table->is_max_size_reached() && !Atomic::load(&_resize)) {
199 Atomic::store(&_resize, true);
200 if (Service_lock->try_lock()) {
201 Service_lock->notify();
202 Service_lock->unlock();
203 }
204 }
205 }
206
207 static bool should_shrink() {
208 // Not implemented;
209 return false;
210 }
211
212 static constexpr double GROW_LOAD_FACTOR = 0.75;
213
214 static bool should_grow() {
215 return get_load_factor() > GROW_LOAD_FACTOR && !_table->is_max_size_reached();
216 }
217
218 static bool should_resize() {
219 return should_grow() || should_shrink() || Atomic::load(&_resize);
220 }
221
222 template<typename Task, typename... Args>
223 static bool run_task(JavaThread* current, Task& task, const char* task_name, Args&... args) {
224 if (task.prepare(current)) {
225 log_trace(monitortable)("Started to %s", task_name);
226 TraceTime timer(task_name, TRACETIME_LOG(Debug, monitortable, perf));
227 while (task.do_task(current, args...)) {
228 task.pause(current);
229 {
230 ThreadBlockInVM tbivm(current);
231 }
232 task.cont(current);
233 }
234 task.done(current);
235 return true;
236 }
237 return false;
238 }
239
240 static bool grow(JavaThread* current) {
241 ConcurrentTable::GrowTask grow_task(_table);
242 if (run_task(current, grow_task, "Grow")) {
243 _table_size = table_size(current);
244 log_info(monitortable)("Grown to size: %zu", _table_size);
245 return true;
246 }
247 return false;
248 }
249
250 static bool clean(JavaThread* current) {
251 ConcurrentTable::BulkDeleteTask clean_task(_table);
252 auto is_dead = [&](ObjectMonitor** monitor) {
253 return (*monitor)->object_is_dead();
254 };
255 auto do_nothing = [&](ObjectMonitor** monitor) {};
256 NativeHeapTrimmer::SuspendMark sm("ObjectMonitorTable");
257 return run_task(current, clean_task, "Clean", is_dead, do_nothing);
258 }
259
260 static bool resize(JavaThread* current) {
261 LogTarget(Info, monitortable) lt;
262 bool success = false;
263
264 if (should_grow()) {
265 lt.print("Start growing with load factor %f", get_load_factor());
266 success = grow(current);
267 } else {
268 if (!_table->is_max_size_reached() && Atomic::load(&_resize)) {
269 lt.print("WARNING: Getting resize hints with load factor %f", get_load_factor());
270 }
271 lt.print("Start cleaning with load factor %f", get_load_factor());
272 success = clean(current);
273 }
274
275 Atomic::store(&_resize, false);
276
277 return success;
278 }
279
280 static ObjectMonitor* monitor_put_get(Thread* current, ObjectMonitor* monitor, oop obj) {
281 // Enter the monitor into the concurrent hashtable.
282 ObjectMonitor* result = monitor;
283 Lookup lookup_f(obj);
284 auto found_f = [&](ObjectMonitor** found) {
285 assert((*found)->object_peek() == obj, "must be");
286 result = *found;
287 };
288 bool grow;
289 _table->insert_get(current, lookup_f, monitor, found_f, &grow);
290 verify_monitor_get_result(obj, result);
291 if (grow) {
292 try_notify_grow();
293 }
294 return result;
295 }
296
297 static bool remove_monitor_entry(Thread* current, ObjectMonitor* monitor) {
298 LookupMonitor lookup_f(monitor);
299 return _table->remove(current, lookup_f);
300 }
301
302 static bool contains_monitor(Thread* current, ObjectMonitor* monitor) {
303 LookupMonitor lookup_f(monitor);
304 bool result = false;
305 auto found_f = [&](ObjectMonitor** found) {
306 result = true;
307 };
308 _table->get(current, lookup_f, found_f);
309 return result;
310 }
311
312 static void print_on(outputStream* st) {
313 auto printer = [&] (ObjectMonitor** entry) {
314 ObjectMonitor* om = *entry;
315 oop obj = om->object_peek();
316 st->print("monitor=" PTR_FORMAT ", ", p2i(om));
317 st->print("object=" PTR_FORMAT, p2i(obj));
318 assert(obj->mark().hash() == om->hash(), "hash must match");
319 st->cr();
320 return true;
321 };
322 if (SafepointSynchronize::is_at_safepoint()) {
323 _table->do_safepoint_scan(printer);
324 } else {
325 _table->do_scan(Thread::current(), printer);
326 }
327 }
328 };
329
330 ObjectMonitorTable::ConcurrentTable* ObjectMonitorTable::_table = nullptr;
331 volatile size_t ObjectMonitorTable::_items_count = 0;
332 size_t ObjectMonitorTable::_table_size = 0;
333 volatile bool ObjectMonitorTable::_resize = false;
334
335 ObjectMonitor* LightweightSynchronizer::get_or_insert_monitor_from_table(oop object, JavaThread* current, bool* inserted) {
336 assert(LockingMode == LM_LIGHTWEIGHT, "must be");
337
338 ObjectMonitor* monitor = get_monitor_from_table(current, object);
339 if (monitor != nullptr) {
340 *inserted = false;
341 return monitor;
342 }
343
344 ObjectMonitor* alloced_monitor = new ObjectMonitor(object);
345 alloced_monitor->set_anonymous_owner();
346
347 // Try insert monitor
348 monitor = add_monitor(current, alloced_monitor, object);
349
350 *inserted = alloced_monitor == monitor;
351 if (!*inserted) {
352 delete alloced_monitor;
353 }
354
355 return monitor;
356 }
357
358 static void log_inflate(Thread* current, oop object, ObjectSynchronizer::InflateCause cause) {
359 if (log_is_enabled(Trace, monitorinflation)) {
360 ResourceMark rm(current);
361 log_trace(monitorinflation)("inflate: object=" INTPTR_FORMAT ", mark="
362 INTPTR_FORMAT ", type='%s' cause=%s", p2i(object),
363 object->mark().value(), object->klass()->external_name(),
364 ObjectSynchronizer::inflate_cause_name(cause));
365 }
366 }
367
368 static void post_monitor_inflate_event(EventJavaMonitorInflate* event,
369 const oop obj,
370 ObjectSynchronizer::InflateCause cause) {
371 assert(event != nullptr, "invariant");
372 event->set_monitorClass(obj->klass());
373 event->set_address((uintptr_t)(void*)obj);
374 event->set_cause((u1)cause);
375 event->commit();
376 }
377
378 ObjectMonitor* LightweightSynchronizer::get_or_insert_monitor(oop object, JavaThread* current, ObjectSynchronizer::InflateCause cause) {
379 assert(UseObjectMonitorTable, "must be");
380
381 EventJavaMonitorInflate event;
382
383 bool inserted;
384 ObjectMonitor* monitor = get_or_insert_monitor_from_table(object, current, &inserted);
385
386 if (inserted) {
387 // Hopefully the performance counters are allocated on distinct
388 // cache lines to avoid false sharing on MP systems ...
389 OM_PERFDATA_OP(Inflations, inc());
390 log_inflate(current, object, cause);
391 if (event.should_commit()) {
392 post_monitor_inflate_event(&event, object, cause);
393 }
394
395 // The monitor has an anonymous owner so it is safe from async deflation.
396 ObjectSynchronizer::_in_use_list.add(monitor);
397 }
398
399 return monitor;
400 }
401
402 // Add the hashcode to the monitor to match the object and put it in the hashtable.
403 ObjectMonitor* LightweightSynchronizer::add_monitor(JavaThread* current, ObjectMonitor* monitor, oop obj) {
404 assert(UseObjectMonitorTable, "must be");
405 assert(obj == monitor->object(), "must be");
406
407 intptr_t hash = obj->mark().hash();
408 assert(hash != 0, "must be set when claiming the object monitor");
409 monitor->set_hash(hash);
410
411 return ObjectMonitorTable::monitor_put_get(current, monitor, obj);
412 }
413
414 bool LightweightSynchronizer::remove_monitor(Thread* current, ObjectMonitor* monitor, oop obj) {
415 assert(UseObjectMonitorTable, "must be");
416 assert(monitor->object_peek() == obj, "must be, cleared objects are removed by is_dead");
417
418 return ObjectMonitorTable::remove_monitor_entry(current, monitor);
419 }
420
421 void LightweightSynchronizer::deflate_mark_word(oop obj) {
422 assert(UseObjectMonitorTable, "must be");
423
424 markWord mark = obj->mark_acquire();
425 assert(!mark.has_no_hash(), "obj with inflated monitor must have had a hash");
426
427 while (mark.has_monitor()) {
428 const markWord new_mark = mark.clear_lock_bits().set_unlocked();
429 mark = obj->cas_set_mark(new_mark, mark);
430 }
431 }
432
433 void LightweightSynchronizer::initialize() {
434 if (!UseObjectMonitorTable) {
435 return;
436 }
437 ObjectMonitorTable::create();
438 }
439
440 bool LightweightSynchronizer::needs_resize() {
441 if (!UseObjectMonitorTable) {
442 return false;
443 }
444 return ObjectMonitorTable::should_resize();
445 }
446
447 bool LightweightSynchronizer::resize_table(JavaThread* current) {
448 if (!UseObjectMonitorTable) {
449 return true;
450 }
451 return ObjectMonitorTable::resize(current);
452 }
453
454 class LightweightSynchronizer::LockStackInflateContendedLocks : private OopClosure {
455 private:
456 oop _contended_oops[LockStack::CAPACITY];
457 int _length;
458
459 void do_oop(oop* o) final {
460 oop obj = *o;
461 if (obj->mark_acquire().has_monitor()) {
462 if (_length > 0 && _contended_oops[_length - 1] == obj) {
463 // Recursive
464 return;
465 }
466 _contended_oops[_length++] = obj;
467 }
468 }
469
470 void do_oop(narrowOop* o) final {
471 ShouldNotReachHere();
472 }
473
474 public:
475 LockStackInflateContendedLocks() :
476 _contended_oops(),
477 _length(0) {};
478
479 void inflate(JavaThread* current) {
480 assert(current == JavaThread::current(), "must be");
481 current->lock_stack().oops_do(this);
482 for (int i = 0; i < _length; i++) {
483 LightweightSynchronizer::
484 inflate_fast_locked_object(_contended_oops[i], ObjectSynchronizer::inflate_cause_vm_internal, current, current);
485 }
486 }
487 };
488
489 void LightweightSynchronizer::ensure_lock_stack_space(JavaThread* current) {
490 assert(current == JavaThread::current(), "must be");
491 LockStack& lock_stack = current->lock_stack();
492
493 // Make room on lock_stack
494 if (lock_stack.is_full()) {
495 // Inflate contended objects
496 LockStackInflateContendedLocks().inflate(current);
497 if (lock_stack.is_full()) {
498 // Inflate the oldest object
499 inflate_fast_locked_object(lock_stack.bottom(), ObjectSynchronizer::inflate_cause_vm_internal, current, current);
500 }
501 }
502 }
503
504 class LightweightSynchronizer::CacheSetter : StackObj {
505 JavaThread* const _thread;
506 BasicLock* const _lock;
507 ObjectMonitor* _monitor;
508
509 NONCOPYABLE(CacheSetter);
510
511 public:
512 CacheSetter(JavaThread* thread, BasicLock* lock) :
513 _thread(thread),
514 _lock(lock),
515 _monitor(nullptr) {}
516
517 ~CacheSetter() {
518 // Only use the cache if using the table.
519 if (UseObjectMonitorTable) {
520 if (_monitor != nullptr) {
521 _thread->om_set_monitor_cache(_monitor);
522 _lock->set_object_monitor_cache(_monitor);
523 } else {
524 _lock->clear_object_monitor_cache();
525 }
526 }
527 }
528
529 void set_monitor(ObjectMonitor* monitor) {
530 assert(_monitor == nullptr, "only set once");
531 _monitor = monitor;
532 }
533
534 };
535
536 class LightweightSynchronizer::VerifyThreadState {
537 bool _no_safepoint;
538
539 public:
540 VerifyThreadState(JavaThread* locking_thread, JavaThread* current) : _no_safepoint(locking_thread != current) {
541 assert(current == Thread::current(), "must be");
542 assert(locking_thread == current || locking_thread->is_obj_deopt_suspend(), "locking_thread may not run concurrently");
543 if (_no_safepoint) {
544 DEBUG_ONLY(JavaThread::current()->inc_no_safepoint_count();)
545 }
546 }
547 ~VerifyThreadState() {
548 if (_no_safepoint){
549 DEBUG_ONLY(JavaThread::current()->dec_no_safepoint_count();)
550 }
551 }
552 };
553
554 inline bool LightweightSynchronizer::fast_lock_try_enter(oop obj, LockStack& lock_stack, JavaThread* current) {
555 markWord mark = obj->mark();
556 while (mark.is_unlocked()) {
557 ensure_lock_stack_space(current);
558 assert(!lock_stack.is_full(), "must have made room on the lock stack");
559 assert(!lock_stack.contains(obj), "thread must not already hold the lock");
560 // Try to swing into 'fast-locked' state.
561 markWord locked_mark = mark.set_fast_locked();
562 markWord old_mark = mark;
563 mark = obj->cas_set_mark(locked_mark, old_mark);
564 if (old_mark == mark) {
565 // Successfully fast-locked, push object to lock-stack and return.
566 lock_stack.push(obj);
567 return true;
568 }
569 }
570 return false;
571 }
572
573 bool LightweightSynchronizer::fast_lock_spin_enter(oop obj, LockStack& lock_stack, JavaThread* current, bool observed_deflation) {
574 assert(UseObjectMonitorTable, "must be");
575 // Will spin with exponential backoff with an accumulative O(2^spin_limit) spins.
576 const int log_spin_limit = os::is_MP() ? LightweightFastLockingSpins : 1;
577 const int log_min_safepoint_check_interval = 10;
578
579 markWord mark = obj->mark();
580 const auto should_spin = [&]() {
581 if (!mark.has_monitor()) {
582 // Spin while not inflated.
583 return true;
584 } else if (observed_deflation) {
585 // Spin while monitor is being deflated.
586 ObjectMonitor* monitor = ObjectSynchronizer::read_monitor(current, obj, mark);
587 return monitor == nullptr || monitor->is_being_async_deflated();
588 }
589 // Else stop spinning.
590 return false;
591 };
592 // Always attempt to lock once even when safepoint synchronizing.
593 bool should_process = false;
594 for (int i = 0; should_spin() && !should_process && i < log_spin_limit; i++) {
595 // Spin with exponential backoff.
596 const int total_spin_count = 1 << i;
597 const int inner_spin_count = MIN2(1 << log_min_safepoint_check_interval, total_spin_count);
598 const int outer_spin_count = total_spin_count / inner_spin_count;
599 for (int outer = 0; outer < outer_spin_count; outer++) {
600 should_process = SafepointMechanism::should_process(current);
601 if (should_process) {
602 // Stop spinning for safepoint.
603 break;
604 }
605 for (int inner = 1; inner < inner_spin_count; inner++) {
606 SpinPause();
607 }
608 }
609
610 if (fast_lock_try_enter(obj, lock_stack, current)) return true;
611 }
612 return false;
613 }
614
615 void LightweightSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
616 assert(LockingMode == LM_LIGHTWEIGHT, "must be");
617 JavaThread* current = JavaThread::current();
618 VerifyThreadState vts(locking_thread, current);
619
620 if (obj->klass()->is_value_based()) {
621 ObjectSynchronizer::handle_sync_on_value_based_class(obj, locking_thread);
622 }
623
624 CacheSetter cache_setter(locking_thread, lock);
625
626 LockStack& lock_stack = locking_thread->lock_stack();
627
628 ObjectMonitor* monitor = nullptr;
629 if (lock_stack.contains(obj())) {
630 monitor = inflate_fast_locked_object(obj(), ObjectSynchronizer::inflate_cause_monitor_enter, locking_thread, current);
631 bool entered = monitor->enter_for(locking_thread);
632 assert(entered, "recursive ObjectMonitor::enter_for must succeed");
633 } else {
634 do {
635 // It is assumed that enter_for must enter on an object without contention.
636 monitor = inflate_and_enter(obj(), ObjectSynchronizer::inflate_cause_monitor_enter, locking_thread, current);
637 // But there may still be a race with deflation.
638 } while (monitor == nullptr);
639 }
640
641 assert(monitor != nullptr, "LightweightSynchronizer::enter_for must succeed");
642 cache_setter.set_monitor(monitor);
643 }
644
645 void LightweightSynchronizer::enter(Handle obj, BasicLock* lock, JavaThread* current) {
646 assert(LockingMode == LM_LIGHTWEIGHT, "must be");
647 assert(current == JavaThread::current(), "must be");
648
649 if (obj->klass()->is_value_based()) {
650 ObjectSynchronizer::handle_sync_on_value_based_class(obj, current);
651 }
652
653 CacheSetter cache_setter(current, lock);
654
655 // Used when deflation is observed. Progress here requires progress
656 // from the deflator. After observing that the deflator is not
657 // making progress (after two yields), switch to sleeping.
658 SpinYield spin_yield(0, 2);
659 bool observed_deflation = false;
660
661 LockStack& lock_stack = current->lock_stack();
662
663 if (!lock_stack.is_full() && lock_stack.try_recursive_enter(obj())) {
664 // Recursively fast locked
665 return;
666 }
667
668 if (lock_stack.contains(obj())) {
669 ObjectMonitor* monitor = inflate_fast_locked_object(obj(), ObjectSynchronizer::inflate_cause_monitor_enter, current, current);
670 bool entered = monitor->enter(current);
671 assert(entered, "recursive ObjectMonitor::enter must succeed");
672 cache_setter.set_monitor(monitor);
673 return;
674 }
675
676 while (true) {
677 // Fast-locking does not use the 'lock' argument.
678 // Fast-lock spinning to avoid inflating for short critical sections.
679 // The goal is to only inflate when the extra cost of using ObjectMonitors
680 // is worth it.
681 // If deflation has been observed we also spin while deflation is ongoing.
682 if (fast_lock_try_enter(obj(), lock_stack, current)) {
683 return;
684 } else if (UseObjectMonitorTable && fast_lock_spin_enter(obj(), lock_stack, current, observed_deflation)) {
685 return;
686 }
687
688 if (observed_deflation) {
689 spin_yield.wait();
690 }
691
692 ObjectMonitor* monitor = inflate_and_enter(obj(), ObjectSynchronizer::inflate_cause_monitor_enter, current, current);
693 if (monitor != nullptr) {
694 cache_setter.set_monitor(monitor);
695 return;
696 }
697
698 // If inflate_and_enter returns nullptr it is because a deflated monitor
699 // was encountered. Fallback to fast locking. The deflater is responsible
700 // for clearing out the monitor and transitioning the markWord back to
701 // fast locking.
702 observed_deflation = true;
703 }
704 }
705
706 void LightweightSynchronizer::exit(oop object, JavaThread* current) {
707 assert(LockingMode == LM_LIGHTWEIGHT, "must be");
708 assert(current == Thread::current(), "must be");
709
710 markWord mark = object->mark();
711 assert(!mark.is_unlocked(), "must be");
712
713 LockStack& lock_stack = current->lock_stack();
714 if (mark.is_fast_locked()) {
715 if (lock_stack.try_recursive_exit(object)) {
716 // This is a recursive exit which succeeded
717 return;
718 }
719 if (lock_stack.is_recursive(object)) {
720 // Must inflate recursive locks if try_recursive_exit fails
721 // This happens for un-structured unlocks, could potentially
722 // fix try_recursive_exit to handle these.
723 inflate_fast_locked_object(object, ObjectSynchronizer::inflate_cause_vm_internal, current, current);
724 }
725 }
726
727 while (mark.is_fast_locked()) {
728 markWord unlocked_mark = mark.set_unlocked();
729 markWord old_mark = mark;
730 mark = object->cas_set_mark(unlocked_mark, old_mark);
731 if (old_mark == mark) {
732 // CAS successful, remove from lock_stack
733 size_t recursion = lock_stack.remove(object) - 1;
734 assert(recursion == 0, "Should not have unlocked here");
735 return;
736 }
737 }
738
739 assert(mark.has_monitor(), "must be");
740 // The monitor exists
741 ObjectMonitor* monitor = ObjectSynchronizer::read_monitor(current, object, mark);
742 if (monitor->has_anonymous_owner()) {
743 assert(current->lock_stack().contains(object), "current must have object on its lock stack");
744 monitor->set_owner_from_anonymous(current);
745 monitor->set_recursions(current->lock_stack().remove(object) - 1);
746 }
747
748 monitor->exit(current);
749 }
750
751 // LightweightSynchronizer::inflate_locked_or_imse is used to to get an inflated
752 // ObjectMonitor* with LM_LIGHTWEIGHT. It is used from contexts which require
753 // an inflated ObjectMonitor* for a monitor, and expects to throw a
754 // java.lang.IllegalMonitorStateException if it is not held by the current
755 // thread. Such as notify/wait and jni_exit. LM_LIGHTWEIGHT keeps it invariant
756 // that it only inflates if it is already locked by the current thread or the
757 // current thread is in the process of entering. To maintain this invariant we
758 // need to throw a java.lang.IllegalMonitorStateException before inflating if
759 // the current thread is not the owner.
760 // LightweightSynchronizer::inflate_locked_or_imse facilitates this.
761 ObjectMonitor* LightweightSynchronizer::inflate_locked_or_imse(oop obj, ObjectSynchronizer::InflateCause cause, TRAPS) {
762 assert(LockingMode == LM_LIGHTWEIGHT, "must be");
763 JavaThread* current = THREAD;
764
765 for (;;) {
766 markWord mark = obj->mark_acquire();
767 if (mark.is_unlocked()) {
768 // No lock, IMSE.
769 THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
770 "current thread is not owner", nullptr);
771 }
772
773 if (mark.is_fast_locked()) {
774 if (!current->lock_stack().contains(obj)) {
775 // Fast locked by other thread, IMSE.
776 THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
777 "current thread is not owner", nullptr);
778 } else {
779 // Current thread owns the lock, must inflate
780 return inflate_fast_locked_object(obj, cause, current, current);
781 }
782 }
783
784 assert(mark.has_monitor(), "must be");
785 ObjectMonitor* monitor = ObjectSynchronizer::read_monitor(current, obj, mark);
786 if (monitor != nullptr) {
787 if (monitor->has_anonymous_owner()) {
788 LockStack& lock_stack = current->lock_stack();
789 if (lock_stack.contains(obj)) {
790 // Current thread owns the lock but someone else inflated it.
791 // Fix owner and pop lock stack.
792 monitor->set_owner_from_anonymous(current);
793 monitor->set_recursions(lock_stack.remove(obj) - 1);
794 } else {
795 // Fast locked (and inflated) by other thread, or deflation in progress, IMSE.
796 THROW_MSG_(vmSymbols::java_lang_IllegalMonitorStateException(),
797 "current thread is not owner", nullptr);
798 }
799 }
800 return monitor;
801 }
802 }
803 }
804
805 ObjectMonitor* LightweightSynchronizer::inflate_into_object_header(oop object, ObjectSynchronizer::InflateCause cause, JavaThread* locking_thread, Thread* current) {
806
807 // The JavaThread* locking_thread parameter is only used by LM_LIGHTWEIGHT and requires
808 // that the locking_thread == Thread::current() or is suspended throughout the call by
809 // some other mechanism.
810 // Even with LM_LIGHTWEIGHT the thread might be nullptr when called from a non
811 // JavaThread. (As may still be the case from FastHashCode). However it is only
812 // important for the correctness of the LM_LIGHTWEIGHT algorithm that the thread
813 // is set when called from ObjectSynchronizer::enter from the owning thread,
814 // ObjectSynchronizer::enter_for from any thread, or ObjectSynchronizer::exit.
815 EventJavaMonitorInflate event;
816
817 for (;;) {
818 const markWord mark = object->mark_acquire();
819
820 // The mark can be in one of the following states:
821 // * inflated - Just return if using stack-locking.
822 // If using fast-locking and the ObjectMonitor owner
823 // is anonymous and the locking_thread owns the
824 // object lock, then we make the locking_thread
825 // the ObjectMonitor owner and remove the lock from
826 // the locking_thread's lock stack.
827 // * fast-locked - Coerce it to inflated from fast-locked.
828 // * unlocked - Aggressively inflate the object.
829
830 // CASE: inflated
831 if (mark.has_monitor()) {
832 ObjectMonitor* inf = mark.monitor();
833 markWord dmw = inf->header();
834 assert(dmw.is_neutral(), "invariant: header=" INTPTR_FORMAT, dmw.value());
835 if (inf->has_anonymous_owner() &&
836 locking_thread != nullptr && locking_thread->lock_stack().contains(object)) {
837 inf->set_owner_from_anonymous(locking_thread);
838 size_t removed = locking_thread->lock_stack().remove(object);
839 inf->set_recursions(removed - 1);
840 }
841 return inf;
842 }
843
844 // CASE: fast-locked
845 // Could be fast-locked either by the locking_thread or by some other thread.
846 //
847 // Note that we allocate the ObjectMonitor speculatively, _before_
848 // attempting to set the object's mark to the new ObjectMonitor. If
849 // the locking_thread owns the monitor, then we set the ObjectMonitor's
850 // owner to the locking_thread. Otherwise, we set the ObjectMonitor's owner
851 // to anonymous. If we lose the race to set the object's mark to the
852 // new ObjectMonitor, then we just delete it and loop around again.
853 //
854 if (mark.is_fast_locked()) {
855 ObjectMonitor* monitor = new ObjectMonitor(object);
856 monitor->set_header(mark.set_unlocked());
857 bool own = locking_thread != nullptr && locking_thread->lock_stack().contains(object);
858 if (own) {
859 // Owned by locking_thread.
860 monitor->set_owner(locking_thread);
861 } else {
862 // Owned by somebody else.
863 monitor->set_anonymous_owner();
864 }
865 markWord monitor_mark = markWord::encode(monitor);
866 markWord old_mark = object->cas_set_mark(monitor_mark, mark);
867 if (old_mark == mark) {
868 // Success! Return inflated monitor.
869 if (own) {
870 size_t removed = locking_thread->lock_stack().remove(object);
871 monitor->set_recursions(removed - 1);
872 }
873 // Once the ObjectMonitor is configured and object is associated
874 // with the ObjectMonitor, it is safe to allow async deflation:
875 ObjectSynchronizer::_in_use_list.add(monitor);
876
877 // Hopefully the performance counters are allocated on distinct
878 // cache lines to avoid false sharing on MP systems ...
879 OM_PERFDATA_OP(Inflations, inc());
880 log_inflate(current, object, cause);
881 if (event.should_commit()) {
882 post_monitor_inflate_event(&event, object, cause);
883 }
884 return monitor;
885 } else {
886 delete monitor;
887 continue; // Interference -- just retry
888 }
889 }
890
891 // CASE: unlocked
892 // TODO-FIXME: for entry we currently inflate and then try to CAS _owner.
893 // If we know we're inflating for entry it's better to inflate by swinging a
894 // pre-locked ObjectMonitor pointer into the object header. A successful
895 // CAS inflates the object *and* confers ownership to the inflating thread.
896 // In the current implementation we use a 2-step mechanism where we CAS()
897 // to inflate and then CAS() again to try to swing _owner from null to current.
898 // An inflateTry() method that we could call from enter() would be useful.
899
900 assert(mark.is_unlocked(), "invariant: header=" INTPTR_FORMAT, mark.value());
901 ObjectMonitor* m = new ObjectMonitor(object);
902 // prepare m for installation - set monitor to initial state
903 m->set_header(mark);
904
905 if (object->cas_set_mark(markWord::encode(m), mark) != mark) {
906 delete m;
907 m = nullptr;
908 continue;
909 // interference - the markword changed - just retry.
910 // The state-transitions are one-way, so there's no chance of
911 // live-lock -- "Inflated" is an absorbing state.
912 }
913
914 // Once the ObjectMonitor is configured and object is associated
915 // with the ObjectMonitor, it is safe to allow async deflation:
916 ObjectSynchronizer::_in_use_list.add(m);
917
918 // Hopefully the performance counters are allocated on distinct
919 // cache lines to avoid false sharing on MP systems ...
920 OM_PERFDATA_OP(Inflations, inc());
921 log_inflate(current, object, cause);
922 if (event.should_commit()) {
923 post_monitor_inflate_event(&event, object, cause);
924 }
925 return m;
926 }
927 }
928
929 ObjectMonitor* LightweightSynchronizer::inflate_fast_locked_object(oop object, ObjectSynchronizer::InflateCause cause, JavaThread* locking_thread, JavaThread* current) {
930 assert(LockingMode == LM_LIGHTWEIGHT, "only used for lightweight");
931 VerifyThreadState vts(locking_thread, current);
932 assert(locking_thread->lock_stack().contains(object), "locking_thread must have object on its lock stack");
933
934 ObjectMonitor* monitor;
935
936 if (!UseObjectMonitorTable) {
937 return inflate_into_object_header(object, cause, locking_thread, current);
938 }
939
940 // Inflating requires a hash code
941 ObjectSynchronizer::FastHashCode(current, object);
942
943 markWord mark = object->mark_acquire();
944 assert(!mark.is_unlocked(), "Cannot be unlocked");
945
946 for (;;) {
947 // Fetch the monitor from the table
948 monitor = get_or_insert_monitor(object, current, cause);
949
950 // ObjectMonitors are always inserted as anonymously owned, this thread is
951 // the current holder of the monitor. So unless the entry is stale and
952 // contains a deflating monitor it must be anonymously owned.
953 if (monitor->has_anonymous_owner()) {
954 // The monitor must be anonymously owned if it was added
955 assert(monitor == get_monitor_from_table(current, object), "The monitor must be found");
956 // New fresh monitor
957 break;
958 }
959
960 // If the monitor was not anonymously owned then we got a deflating monitor
961 // from the table. We need to let the deflator make progress and remove this
962 // entry before we are allowed to add a new one.
963 os::naked_yield();
964 assert(monitor->is_being_async_deflated(), "Should be the reason");
965 }
966
967 // Set the mark word; loop to handle concurrent updates to other parts of the mark word
968 while (mark.is_fast_locked()) {
969 mark = object->cas_set_mark(mark.set_has_monitor(), mark);
970 }
971
972 // Indicate that the monitor now has a known owner
973 monitor->set_owner_from_anonymous(locking_thread);
974
975 // Remove the entry from the thread's lock stack
976 monitor->set_recursions(locking_thread->lock_stack().remove(object) - 1);
977
978 if (locking_thread == current) {
979 // Only change the thread local state of the current thread.
980 locking_thread->om_set_monitor_cache(monitor);
981 }
982
983 return monitor;
984 }
985
986 ObjectMonitor* LightweightSynchronizer::inflate_and_enter(oop object, ObjectSynchronizer::InflateCause cause, JavaThread* locking_thread, JavaThread* current) {
987 assert(LockingMode == LM_LIGHTWEIGHT, "only used for lightweight");
988 VerifyThreadState vts(locking_thread, current);
989
990 // Note: In some paths (deoptimization) the 'current' thread inflates and
991 // enters the lock on behalf of the 'locking_thread' thread.
992
993 ObjectMonitor* monitor = nullptr;
994
995 if (!UseObjectMonitorTable) {
996 // Do the old inflate and enter.
997 monitor = inflate_into_object_header(object, cause, locking_thread, current);
998
999 bool entered;
1000 if (locking_thread == current) {
1001 entered = monitor->enter(locking_thread);
1002 } else {
1003 entered = monitor->enter_for(locking_thread);
1004 }
1005
1006 // enter returns false for deflation found.
1007 return entered ? monitor : nullptr;
1008 }
1009
1010 NoSafepointVerifier nsv;
1011
1012 // Lightweight monitors require that hash codes are installed first
1013 ObjectSynchronizer::FastHashCode(locking_thread, object);
1014
1015 // Try to get the monitor from the thread-local cache.
1016 // There's no need to use the cache if we are locking
1017 // on behalf of another thread.
1018 if (current == locking_thread) {
1019 monitor = current->om_get_from_monitor_cache(object);
1020 }
1021
1022 // Get or create the monitor
1023 if (monitor == nullptr) {
1024 monitor = get_or_insert_monitor(object, current, cause);
1025 }
1026
1027 if (monitor->try_enter(locking_thread)) {
1028 return monitor;
1029 }
1030
1031 // Holds is_being_async_deflated() stable throughout this function.
1032 ObjectMonitorContentionMark contention_mark(monitor);
1033
1034 /// First handle the case where the monitor from the table is deflated
1035 if (monitor->is_being_async_deflated()) {
1036 // The MonitorDeflation thread is deflating the monitor. The locking thread
1037 // must spin until further progress has been made.
1038
1039 const markWord mark = object->mark_acquire();
1040
1041 if (mark.has_monitor()) {
1042 // Waiting on the deflation thread to remove the deflated monitor from the table.
1043 os::naked_yield();
1044
1045 } else if (mark.is_fast_locked()) {
1046 // Some other thread managed to fast-lock the lock, or this is a
1047 // recursive lock from the same thread; yield for the deflation
1048 // thread to remove the deflated monitor from the table.
1049 os::naked_yield();
1050
1051 } else {
1052 assert(mark.is_unlocked(), "Implied");
1053 // Retry immediately
1054 }
1055
1056 // Retry
1057 return nullptr;
1058 }
1059
1060 for (;;) {
1061 const markWord mark = object->mark_acquire();
1062 // The mark can be in one of the following states:
1063 // * inflated - If the ObjectMonitor owner is anonymous
1064 // and the locking_thread owns the object
1065 // lock, then we make the locking_thread
1066 // the ObjectMonitor owner and remove the
1067 // lock from the locking_thread's lock stack.
1068 // * fast-locked - Coerce it to inflated from fast-locked.
1069 // * neutral - Inflate the object. Successful CAS is locked
1070
1071 // CASE: inflated
1072 if (mark.has_monitor()) {
1073 LockStack& lock_stack = locking_thread->lock_stack();
1074 if (monitor->has_anonymous_owner() && lock_stack.contains(object)) {
1075 // The lock is fast-locked by the locking thread,
1076 // convert it to a held monitor with a known owner.
1077 monitor->set_owner_from_anonymous(locking_thread);
1078 monitor->set_recursions(lock_stack.remove(object) - 1);
1079 }
1080
1081 break; // Success
1082 }
1083
1084 // CASE: fast-locked
1085 // Could be fast-locked either by locking_thread or by some other thread.
1086 //
1087 if (mark.is_fast_locked()) {
1088 markWord old_mark = object->cas_set_mark(mark.set_has_monitor(), mark);
1089 if (old_mark != mark) {
1090 // CAS failed
1091 continue;
1092 }
1093
1094 // Success! Return inflated monitor.
1095 LockStack& lock_stack = locking_thread->lock_stack();
1096 if (lock_stack.contains(object)) {
1097 // The lock is fast-locked by the locking thread,
1098 // convert it to a held monitor with a known owner.
1099 monitor->set_owner_from_anonymous(locking_thread);
1100 monitor->set_recursions(lock_stack.remove(object) - 1);
1101 }
1102
1103 break; // Success
1104 }
1105
1106 // CASE: neutral (unlocked)
1107
1108 // Catch if the object's header is not neutral (not locked and
1109 // not marked is what we care about here).
1110 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
1111 markWord old_mark = object->cas_set_mark(mark.set_has_monitor(), mark);
1112 if (old_mark != mark) {
1113 // CAS failed
1114 continue;
1115 }
1116
1117 // Transitioned from unlocked to monitor means locking_thread owns the lock.
1118 monitor->set_owner_from_anonymous(locking_thread);
1119
1120 return monitor;
1121 }
1122
1123 if (current == locking_thread) {
1124 // One round of spinning
1125 if (monitor->spin_enter(locking_thread)) {
1126 return monitor;
1127 }
1128
1129 // Monitor is contended, take the time before entering to fix the lock stack.
1130 LockStackInflateContendedLocks().inflate(current);
1131 }
1132
1133 // enter can block for safepoints; clear the unhandled object oop
1134 PauseNoSafepointVerifier pnsv(&nsv);
1135 object = nullptr;
1136
1137 if (current == locking_thread) {
1138 monitor->enter_with_contention_mark(locking_thread, contention_mark);
1139 } else {
1140 monitor->enter_for_with_contention_mark(locking_thread, contention_mark);
1141 }
1142
1143 return monitor;
1144 }
1145
1146 void LightweightSynchronizer::deflate_monitor(Thread* current, oop obj, ObjectMonitor* monitor) {
1147 if (obj != nullptr) {
1148 deflate_mark_word(obj);
1149 }
1150 bool removed = remove_monitor(current, monitor, obj);
1151 if (obj != nullptr) {
1152 assert(removed, "Should have removed the entry if obj was alive");
1153 }
1154 }
1155
1156 ObjectMonitor* LightweightSynchronizer::get_monitor_from_table(Thread* current, oop obj) {
1157 assert(UseObjectMonitorTable, "must be");
1158 return ObjectMonitorTable::monitor_get(current, obj);
1159 }
1160
1161 bool LightweightSynchronizer::contains_monitor(Thread* current, ObjectMonitor* monitor) {
1162 assert(UseObjectMonitorTable, "must be");
1163 return ObjectMonitorTable::contains_monitor(current, monitor);
1164 }
1165
1166 bool LightweightSynchronizer::quick_enter(oop obj, BasicLock* lock, JavaThread* current) {
1167 assert(current->thread_state() == _thread_in_Java, "must be");
1168 assert(obj != nullptr, "must be");
1169 NoSafepointVerifier nsv;
1170
1171 // If quick_enter succeeds with entering, the cache should be in a valid initialized state.
1172 CacheSetter cache_setter(current, lock);
1173
1174 LockStack& lock_stack = current->lock_stack();
1175 if (lock_stack.is_full()) {
1176 // Always go into runtime if the lock stack is full.
1177 return false;
1178 }
1179
1180 const markWord mark = obj->mark();
1181
1182 #ifndef _LP64
1183 // Only for 32bit which has limited support for fast locking outside the runtime.
1184 if (lock_stack.try_recursive_enter(obj)) {
1185 // Recursive lock successful.
1186 return true;
1187 }
1188
1189 if (mark.is_unlocked()) {
1190 markWord locked_mark = mark.set_fast_locked();
1191 if (obj->cas_set_mark(locked_mark, mark) == mark) {
1192 // Successfully fast-locked, push object to lock-stack and return.
1193 lock_stack.push(obj);
1194 return true;
1195 }
1196 }
1197 #endif
1198
1199 if (mark.has_monitor()) {
1200 ObjectMonitor* const monitor = UseObjectMonitorTable ? current->om_get_from_monitor_cache(obj) :
1201 ObjectSynchronizer::read_monitor(mark);
1202
1203 if (monitor == nullptr) {
1204 // Take the slow-path on a cache miss.
1205 return false;
1206 }
1207
1208 if (monitor->try_enter(current)) {
1209 // ObjectMonitor enter successful.
1210 cache_setter.set_monitor(monitor);
1211 return true;
1212 }
1213 }
1214
1215 // Slow-path.
1216 return false;
1217 }