1 /*
2 * Copyright (c) 1998, 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 "gc/shared/collectedHeap.hpp"
27 #include "jfr/jfrEvents.hpp"
28 #include "logging/log.hpp"
29 #include "logging/logStream.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "memory/padded.hpp"
32 #include "memory/resourceArea.hpp"
33 #include "memory/universe.hpp"
34 #include "oops/markWord.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "runtime/atomicAccess.hpp"
37 #include "runtime/basicLock.inline.hpp"
38 #include "runtime/frame.inline.hpp"
39 #include "runtime/globals.hpp"
40 #include "runtime/handles.inline.hpp"
41 #include "runtime/handshake.hpp"
42 #include "runtime/interfaceSupport.inline.hpp"
43 #include "runtime/javaThread.hpp"
44 #include "runtime/lightweightSynchronizer.hpp"
45 #include "runtime/lockStack.inline.hpp"
46 #include "runtime/mutexLocker.hpp"
47 #include "runtime/objectMonitor.inline.hpp"
48 #include "runtime/os.inline.hpp"
49 #include "runtime/osThread.hpp"
50 #include "runtime/safepointMechanism.inline.hpp"
51 #include "runtime/safepointVerifiers.hpp"
52 #include "runtime/sharedRuntime.hpp"
53 #include "runtime/stubRoutines.hpp"
54 #include "runtime/synchronizer.inline.hpp"
55 #include "runtime/threads.hpp"
56 #include "runtime/timer.hpp"
57 #include "runtime/trimNativeHeap.hpp"
58 #include "runtime/vframe.hpp"
59 #include "runtime/vmThread.hpp"
60 #include "utilities/align.hpp"
61 #include "utilities/dtrace.hpp"
62 #include "utilities/events.hpp"
63 #include "utilities/globalCounter.inline.hpp"
64 #include "utilities/globalDefinitions.hpp"
65 #include "utilities/linkedlist.hpp"
66 #include "utilities/preserveException.hpp"
67
68 class ObjectMonitorDeflationLogging;
69
70 void MonitorList::add(ObjectMonitor* m) {
71 ObjectMonitor* head;
72 do {
73 head = AtomicAccess::load(&_head);
74 m->set_next_om(head);
75 } while (AtomicAccess::cmpxchg(&_head, head, m) != head);
76
77 size_t count = AtomicAccess::add(&_count, 1u, memory_order_relaxed);
78 size_t old_max;
79 do {
80 old_max = AtomicAccess::load(&_max);
81 if (count <= old_max) {
82 break;
83 }
84 } while (AtomicAccess::cmpxchg(&_max, old_max, count, memory_order_relaxed) != old_max);
85 }
86
87 size_t MonitorList::count() const {
88 return AtomicAccess::load(&_count);
89 }
90
91 size_t MonitorList::max() const {
92 return AtomicAccess::load(&_max);
93 }
94
95 class ObjectMonitorDeflationSafepointer : public StackObj {
96 JavaThread* const _current;
97 ObjectMonitorDeflationLogging* const _log;
98
99 public:
100 ObjectMonitorDeflationSafepointer(JavaThread* current, ObjectMonitorDeflationLogging* log)
101 : _current(current), _log(log) {}
102
103 void block_for_safepoint(const char* op_name, const char* count_name, size_t counter);
104 };
105
106 // Walk the in-use list and unlink deflated ObjectMonitors.
107 // Returns the number of unlinked ObjectMonitors.
108 size_t MonitorList::unlink_deflated(size_t deflated_count,
109 GrowableArray<ObjectMonitor*>* unlinked_list,
110 ObjectMonitorDeflationSafepointer* safepointer) {
111 size_t unlinked_count = 0;
112 ObjectMonitor* prev = nullptr;
113 ObjectMonitor* m = AtomicAccess::load_acquire(&_head);
114
115 while (m != nullptr) {
116 if (m->is_being_async_deflated()) {
117 // Find next live ObjectMonitor. Batch up the unlinkable monitors, so we can
118 // modify the list once per batch. The batch starts at "m".
119 size_t unlinked_batch = 0;
120 ObjectMonitor* next = m;
121 // Look for at most MonitorUnlinkBatch monitors, or the number of
122 // deflated and not unlinked monitors, whatever comes first.
123 assert(deflated_count >= unlinked_count, "Sanity: underflow");
124 size_t unlinked_batch_limit = MIN2<size_t>(deflated_count - unlinked_count, MonitorUnlinkBatch);
125 do {
126 ObjectMonitor* next_next = next->next_om();
127 unlinked_batch++;
128 unlinked_list->append(next);
129 next = next_next;
130 if (unlinked_batch >= unlinked_batch_limit) {
131 // Reached the max batch, so bail out of the gathering loop.
132 break;
133 }
134 if (prev == nullptr && AtomicAccess::load(&_head) != m) {
135 // Current batch used to be at head, but it is not at head anymore.
136 // Bail out and figure out where we currently are. This avoids long
137 // walks searching for new prev during unlink under heavy list inserts.
138 break;
139 }
140 } while (next != nullptr && next->is_being_async_deflated());
141
142 // Unlink the found batch.
143 if (prev == nullptr) {
144 // The current batch is the first batch, so there is a chance that it starts at head.
145 // Optimistically assume no inserts happened, and try to unlink the entire batch from the head.
146 ObjectMonitor* prev_head = AtomicAccess::cmpxchg(&_head, m, next);
147 if (prev_head != m) {
148 // Something must have updated the head. Figure out the actual prev for this batch.
149 for (ObjectMonitor* n = prev_head; n != m; n = n->next_om()) {
150 prev = n;
151 }
152 assert(prev != nullptr, "Should have found the prev for the current batch");
153 prev->set_next_om(next);
154 }
155 } else {
156 // The current batch is preceded by another batch. This guarantees the current batch
157 // does not start at head. Unlink the entire current batch without updating the head.
158 assert(AtomicAccess::load(&_head) != m, "Sanity");
159 prev->set_next_om(next);
160 }
161
162 unlinked_count += unlinked_batch;
163 if (unlinked_count >= deflated_count) {
164 // Reached the max so bail out of the searching loop.
165 // There should be no more deflated monitors left.
166 break;
167 }
168 m = next;
169 } else {
170 prev = m;
171 m = m->next_om();
172 }
173
174 // Must check for a safepoint/handshake and honor it.
175 safepointer->block_for_safepoint("unlinking", "unlinked_count", unlinked_count);
176 }
177
178 #ifdef ASSERT
179 // Invariant: the code above should unlink all deflated monitors.
180 // The code that runs after this unlinking does not expect deflated monitors.
181 // Notably, attempting to deflate the already deflated monitor would break.
182 {
183 ObjectMonitor* m = AtomicAccess::load_acquire(&_head);
184 while (m != nullptr) {
185 assert(!m->is_being_async_deflated(), "All deflated monitors should be unlinked");
186 m = m->next_om();
187 }
188 }
189 #endif
190
191 AtomicAccess::sub(&_count, unlinked_count);
192 return unlinked_count;
193 }
194
195 MonitorList::Iterator MonitorList::iterator() const {
196 return Iterator(AtomicAccess::load_acquire(&_head));
197 }
198
199 ObjectMonitor* MonitorList::Iterator::next() {
200 ObjectMonitor* current = _current;
201 _current = current->next_om();
202 return current;
203 }
204
205 // The "core" versions of monitor enter and exit reside in this file.
206 // The interpreter and compilers contain specialized transliterated
207 // variants of the enter-exit fast-path operations. See c2_MacroAssembler_x86.cpp
208 // fast_lock(...) for instance. If you make changes here, make sure to modify the
209 // interpreter, and both C1 and C2 fast-path inline locking code emission.
210 //
211 // -----------------------------------------------------------------------------
212
213 #ifdef DTRACE_ENABLED
214
215 // Only bother with this argument setup if dtrace is available
216 // TODO-FIXME: probes should not fire when caller is _blocked. assert() accordingly.
217
218 #define DTRACE_MONITOR_PROBE_COMMON(obj, thread) \
219 char* bytes = nullptr; \
220 int len = 0; \
221 jlong jtid = SharedRuntime::get_java_tid(thread); \
222 Symbol* klassname = obj->klass()->name(); \
223 if (klassname != nullptr) { \
224 bytes = (char*)klassname->bytes(); \
225 len = klassname->utf8_length(); \
226 }
227
228 #define DTRACE_MONITOR_WAIT_PROBE(monitor, obj, thread, millis) \
229 { \
230 if (DTraceMonitorProbes) { \
231 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
232 HOTSPOT_MONITOR_WAIT(jtid, \
233 (uintptr_t)(monitor), bytes, len, (millis)); \
234 } \
235 }
236
237 #define HOTSPOT_MONITOR_PROBE_notify HOTSPOT_MONITOR_NOTIFY
238 #define HOTSPOT_MONITOR_PROBE_notifyAll HOTSPOT_MONITOR_NOTIFYALL
239 #define HOTSPOT_MONITOR_PROBE_waited HOTSPOT_MONITOR_WAITED
240
241 #define DTRACE_MONITOR_PROBE(probe, monitor, obj, thread) \
242 { \
243 if (DTraceMonitorProbes) { \
244 DTRACE_MONITOR_PROBE_COMMON(obj, thread); \
245 HOTSPOT_MONITOR_PROBE_##probe(jtid, /* probe = waited */ \
246 (uintptr_t)(monitor), bytes, len); \
247 } \
248 }
249
250 #else // ndef DTRACE_ENABLED
251
252 #define DTRACE_MONITOR_WAIT_PROBE(obj, thread, millis, mon) {;}
253 #define DTRACE_MONITOR_PROBE(probe, obj, thread, mon) {;}
254
255 #endif // ndef DTRACE_ENABLED
256
257 // This exists only as a workaround of dtrace bug 6254741
258 static int dtrace_waited_probe(ObjectMonitor* monitor, Handle obj, JavaThread* thr) {
259 DTRACE_MONITOR_PROBE(waited, monitor, obj(), thr);
260 return 0;
261 }
262
263 static constexpr size_t inflation_lock_count() {
264 return 256;
265 }
266
267 // Static storage for an array of PlatformMutex.
268 alignas(PlatformMutex) static uint8_t _inflation_locks[inflation_lock_count()][sizeof(PlatformMutex)];
269
270 static inline PlatformMutex* inflation_lock(size_t index) {
271 return reinterpret_cast<PlatformMutex*>(_inflation_locks[index]);
272 }
273
274 void ObjectSynchronizer::initialize() {
275 for (size_t i = 0; i < inflation_lock_count(); i++) {
276 ::new(static_cast<void*>(inflation_lock(i))) PlatformMutex();
277 }
278 // Start the ceiling with the estimate for one thread.
279 set_in_use_list_ceiling(AvgMonitorsPerThreadEstimate);
280
281 // Start the timer for deflations, so it does not trigger immediately.
282 _last_async_deflation_time_ns = os::javaTimeNanos();
283
284 LightweightSynchronizer::initialize();
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 // =====================> Quick functions
316
317 // The quick_* forms are special fast-path variants used to improve
318 // performance. In the simplest case, a "quick_*" implementation could
319 // simply return false, in which case the caller will perform the necessary
320 // state transitions and call the slow-path form.
321 // The fast-path is designed to handle frequently arising cases in an efficient
322 // manner and is just a degenerate "optimistic" variant of the slow-path.
323 // returns true -- to indicate the call was satisfied.
324 // returns false -- to indicate the call needs the services of the slow-path.
325 // A no-loitering ordinance is in effect for code in the quick_* family
326 // operators: safepoints or indefinite blocking (blocking that might span a
327 // safepoint) are forbidden. Generally the thread_state() is _in_Java upon
328 // entry.
329 //
330 // Consider: An interesting optimization is to have the JIT recognize the
331 // following common idiom:
332 // synchronized (someobj) { .... ; notify(); }
333 // That is, we find a notify() or notifyAll() call that immediately precedes
334 // the monitorexit operation. In that case the JIT could fuse the operations
335 // into a single notifyAndExit() runtime primitive.
336
337 bool ObjectSynchronizer::quick_notify(oopDesc* obj, JavaThread* current, bool all) {
338 assert(current->thread_state() == _thread_in_Java, "invariant");
339 NoSafepointVerifier nsv;
340 if (obj == nullptr) return false; // slow-path for invalid obj
341 const markWord mark = obj->mark();
342
343 if (mark.is_fast_locked() && current->lock_stack().contains(cast_to_oop(obj))) {
344 // Degenerate notify
345 // fast-locked by caller so by definition the implied waitset is empty.
346 return true;
347 }
348
349 if (mark.has_monitor()) {
350 ObjectMonitor* const mon = read_monitor(current, obj, mark);
351 if (mon == nullptr) {
352 // Racing with inflation/deflation go slow path
353 return false;
354 }
355 assert(mon->object() == oop(obj), "invariant");
356 if (!mon->has_owner(current)) return false; // slow-path for IMS exception
357
358 if (mon->first_waiter() != nullptr) {
359 // We have one or more waiters. Since this is an inflated monitor
360 // that we own, we quickly notify them here and now, avoiding the slow-path.
361 if (all) {
362 mon->quick_notifyAll(current);
363 } else {
364 mon->quick_notify(current);
365 }
366 }
367 return true;
368 }
369
370 // other IMS exception states take the slow-path
371 return false;
372 }
373
374 // Handle notifications when synchronizing on value based classes
375 void ObjectSynchronizer::handle_sync_on_value_based_class(Handle obj, JavaThread* locking_thread) {
376 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
377 frame last_frame = locking_thread->last_frame();
378 bool bcp_was_adjusted = false;
379 // Don't decrement bcp if it points to the frame's first instruction. This happens when
380 // handle_sync_on_value_based_class() is called because of a synchronized method. There
381 // is no actual monitorenter instruction in the byte code in this case.
382 if (last_frame.is_interpreted_frame() &&
383 (last_frame.interpreter_frame_method()->code_base() < last_frame.interpreter_frame_bcp())) {
384 // adjust bcp to point back to monitorenter so that we print the correct line numbers
385 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() - 1);
386 bcp_was_adjusted = true;
387 }
388
389 if (DiagnoseSyncOnValueBasedClasses == FATAL_EXIT) {
390 ResourceMark rm;
391 stringStream ss;
392 locking_thread->print_active_stack_on(&ss);
393 char* base = (char*)strstr(ss.base(), "at");
394 char* newline = (char*)strchr(ss.base(), '\n');
395 if (newline != nullptr) {
396 *newline = '\0';
397 }
398 fatal("Synchronizing on object " INTPTR_FORMAT " of klass %s %s", p2i(obj()), obj->klass()->external_name(), base);
399 } else {
400 assert(DiagnoseSyncOnValueBasedClasses == LOG_WARNING, "invalid value for DiagnoseSyncOnValueBasedClasses");
401 ResourceMark rm;
402 Log(valuebasedclasses) vblog;
403
404 vblog.info("Synchronizing on object " INTPTR_FORMAT " of klass %s", p2i(obj()), obj->klass()->external_name());
405 if (locking_thread->has_last_Java_frame()) {
406 LogStream info_stream(vblog.info());
407 locking_thread->print_active_stack_on(&info_stream);
408 } else {
409 vblog.info("Cannot find the last Java frame");
410 }
411
412 EventSyncOnValueBasedClass event;
413 if (event.should_commit()) {
414 event.set_valueBasedClass(obj->klass());
415 event.commit();
416 }
417 }
418
419 if (bcp_was_adjusted) {
420 last_frame.interpreter_frame_set_bcp(last_frame.interpreter_frame_bcp() + 1);
421 }
422 }
423
424 // -----------------------------------------------------------------------------
425 // Monitor Enter/Exit
426
427 void ObjectSynchronizer::enter_for(Handle obj, BasicLock* lock, JavaThread* locking_thread) {
428 // When called with locking_thread != Thread::current() some mechanism must synchronize
429 // the locking_thread with respect to the current thread. Currently only used when
430 // deoptimizing and re-locking locks. See Deoptimization::relock_objects
431 assert(locking_thread == Thread::current() || locking_thread->is_obj_deopt_suspend(), "must be");
432 return LightweightSynchronizer::enter_for(obj, lock, locking_thread);
433 }
434
435 // -----------------------------------------------------------------------------
436 // JNI locks on java objects
437 // NOTE: must use heavy weight monitor to handle jni monitor enter
438 void ObjectSynchronizer::jni_enter(Handle obj, JavaThread* current) {
439 // Top native frames in the stack will not be seen if we attempt
440 // preemption, since we start walking from the last Java anchor.
441 NoPreemptMark npm(current);
442
443 if (obj->klass()->is_value_based()) {
444 handle_sync_on_value_based_class(obj, current);
445 }
446
447 // the current locking is from JNI instead of Java code
448 current->set_current_pending_monitor_is_from_java(false);
449 // An async deflation can race after the inflate() call and before
450 // enter() can make the ObjectMonitor busy. enter() returns false if
451 // we have lost the race to async deflation and we simply try again.
452 while (true) {
453 BasicLock lock;
454 if (LightweightSynchronizer::inflate_and_enter(obj(), &lock, inflate_cause_jni_enter, current, current) != nullptr) {
455 current->inc_held_monitor_count(1, true);
456 break;
457 }
458 }
459 current->set_current_pending_monitor_is_from_java(true);
460 }
461
462 // NOTE: must use heavy weight monitor to handle jni monitor exit
463 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
464 JavaThread* current = THREAD;
465
466 ObjectMonitor* monitor;
467 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
468 // If this thread has locked the object, exit the monitor. We
469 // intentionally do not use CHECK on check_owner because we must exit the
470 // monitor even if an exception was already pending.
471 if (monitor->check_owner(THREAD)) {
472 monitor->exit(current);
473 current->dec_held_monitor_count(1, true);
474 }
475 }
476
477 // -----------------------------------------------------------------------------
478 // Internal VM locks on java objects
479 // standard constructor, allows locking failures
480 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) : _npm(thread) {
481 _thread = thread;
482 _thread->check_for_valid_safepoint_state();
483 _obj = obj;
484
485 if (_obj() != nullptr) {
486 ObjectSynchronizer::enter(_obj, &_lock, _thread);
487 }
488 }
489
490 ObjectLocker::~ObjectLocker() {
491 if (_obj() != nullptr) {
492 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
493 }
494 }
495
496
497 // -----------------------------------------------------------------------------
498 // Wait/Notify/NotifyAll
499 // NOTE: must use heavy weight monitor to handle wait()
500
501 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
502 JavaThread* current = THREAD;
503 if (millis < 0) {
504 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
505 }
506
507 ObjectMonitor* monitor;
508 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
509
510 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
511 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
512
513 // This dummy call is in place to get around dtrace bug 6254741. Once
514 // that's fixed we can uncomment the following line, remove the call
515 // and change this function back into a "void" func.
516 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
517 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
518 return ret_code;
519 }
520
521 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
522 if (millis < 0) {
523 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
524 }
525
526 ObjectMonitor* monitor;
527 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
528 monitor->wait(millis, false, THREAD);
529 }
530
531
532 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
533 JavaThread* current = THREAD;
534
535 markWord mark = obj->mark();
536 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
537 // Not inflated so there can't be any waiters to notify.
538 return;
539 }
540 ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
541 monitor->notify(CHECK);
542 }
543
544 // NOTE: see comment of notify()
545 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
546 JavaThread* current = THREAD;
547
548 markWord mark = obj->mark();
549 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
550 // Not inflated so there can't be any waiters to notify.
551 return;
552 }
553
554 ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
555 monitor->notifyAll(CHECK);
556 }
557
558 // -----------------------------------------------------------------------------
559 // Hash Code handling
560
561 struct SharedGlobals {
562 char _pad_prefix[OM_CACHE_LINE_SIZE];
563 // This is a highly shared mostly-read variable.
564 // To avoid false-sharing it needs to be the sole occupant of a cache line.
565 volatile int stw_random;
566 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
567 // Hot RW variable -- Sequester to avoid false-sharing
568 volatile int hc_sequence;
569 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
570 };
571
572 static SharedGlobals GVars;
573
574 // hashCode() generation :
575 //
576 // Possibilities:
577 // * MD5Digest of {obj,stw_random}
578 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
579 // * A DES- or AES-style SBox[] mechanism
580 // * One of the Phi-based schemes, such as:
581 // 2654435761 = 2^32 * Phi (golden ratio)
582 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
583 // * A variation of Marsaglia's shift-xor RNG scheme.
584 // * (obj ^ stw_random) is appealing, but can result
585 // in undesirable regularity in the hashCode values of adjacent objects
586 // (objects allocated back-to-back, in particular). This could potentially
587 // result in hashtable collisions and reduced hashtable efficiency.
588 // There are simple ways to "diffuse" the middle address bits over the
589 // generated hashCode values:
590
591 static intptr_t get_next_hash(Thread* current, oop obj) {
592 intptr_t value = 0;
593 if (hashCode == 0) {
594 // This form uses global Park-Miller RNG.
595 // On MP system we'll have lots of RW access to a global, so the
596 // mechanism induces lots of coherency traffic.
597 value = os::random();
598 } else if (hashCode == 1) {
599 // This variation has the property of being stable (idempotent)
600 // between STW operations. This can be useful in some of the 1-0
601 // synchronization schemes.
602 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
603 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
604 } else if (hashCode == 2) {
605 value = 1; // for sensitivity testing
606 } else if (hashCode == 3) {
607 value = ++GVars.hc_sequence;
608 } else if (hashCode == 4) {
609 value = cast_from_oop<intptr_t>(obj);
610 } else {
611 // Marsaglia's xor-shift scheme with thread-specific state
612 // This is probably the best overall implementation -- we'll
613 // likely make this the default in future releases.
614 unsigned t = current->_hashStateX;
615 t ^= (t << 11);
616 current->_hashStateX = current->_hashStateY;
617 current->_hashStateY = current->_hashStateZ;
618 current->_hashStateZ = current->_hashStateW;
619 unsigned v = current->_hashStateW;
620 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
621 current->_hashStateW = v;
622 value = v;
623 }
624
625 value &= markWord::hash_mask;
626 if (value == 0) value = 0xBAD;
627 assert(value != markWord::no_hash, "invariant");
628 return value;
629 }
630
631 static intptr_t install_hash_code(Thread* current, oop obj) {
632 assert(UseObjectMonitorTable, "must be");
633
634 markWord mark = obj->mark_acquire();
635 for (;;) {
636 intptr_t hash = mark.hash();
637 if (hash != 0) {
638 return hash;
639 }
640
641 hash = get_next_hash(current, obj);
642 const markWord old_mark = mark;
643 const markWord new_mark = old_mark.copy_set_hash(hash);
644
645 mark = obj->cas_set_mark(new_mark, old_mark);
646 if (old_mark == mark) {
647 return hash;
648 }
649 }
650 }
651
652 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
653 if (UseObjectMonitorTable) {
654 // Since the monitor isn't in the object header, the hash can simply be
655 // installed in the object header.
656 return install_hash_code(current, obj);
657 }
658
659 while (true) {
660 ObjectMonitor* monitor = nullptr;
661 markWord temp, test;
662 intptr_t hash;
663 markWord mark = obj->mark_acquire();
664 if (mark.is_unlocked() || mark.is_fast_locked()) {
665 hash = mark.hash();
666 if (hash != 0) { // if it has a hash, just return it
667 return hash;
668 }
669 hash = get_next_hash(current, obj); // get a new hash
670 temp = mark.copy_set_hash(hash); // merge the hash into header
671 // try to install the hash
672 test = obj->cas_set_mark(temp, mark);
673 if (test == mark) { // if the hash was installed, return it
674 return hash;
675 }
676 // CAS failed, retry
677 continue;
678
679 // Failed to install the hash. It could be that another thread
680 // installed the hash just before our attempt or inflation has
681 // occurred or... so we fall thru to inflate the monitor for
682 // stability and then install the hash.
683 } else if (mark.has_monitor()) {
684 monitor = mark.monitor();
685 temp = monitor->header();
686 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
687 hash = temp.hash();
688 if (hash != 0) {
689 // It has a hash.
690
691 // Separate load of dmw/header above from the loads in
692 // is_being_async_deflated().
693
694 // dmw/header and _contentions may get written by different threads.
695 // Make sure to observe them in the same order when having several observers.
696 OrderAccess::loadload_for_IRIW();
697
698 if (monitor->is_being_async_deflated()) {
699 // But we can't safely use the hash if we detect that async
700 // deflation has occurred. So we attempt to restore the
701 // header/dmw to the object's header so that we only retry
702 // once if the deflater thread happens to be slow.
703 monitor->install_displaced_markword_in_object(obj);
704 continue;
705 }
706 return hash;
707 }
708 // Fall thru so we only have one place that installs the hash in
709 // the ObjectMonitor.
710 }
711
712 // NOTE: an async deflation can race after we get the monitor and
713 // before we can update the ObjectMonitor's header with the hash
714 // value below.
715 assert(mark.has_monitor(), "must be");
716 monitor = mark.monitor();
717
718 // Load ObjectMonitor's header/dmw field and see if it has a hash.
719 mark = monitor->header();
720 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
721 hash = mark.hash();
722 if (hash == 0) { // if it does not have a hash
723 hash = get_next_hash(current, obj); // get a new hash
724 temp = mark.copy_set_hash(hash) ; // merge the hash into header
725 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
726 uintptr_t v = AtomicAccess::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
727 test = markWord(v);
728 if (test != mark) {
729 // The attempt to update the ObjectMonitor's header/dmw field
730 // did not work. This can happen if another thread managed to
731 // merge in the hash just before our cmpxchg().
732 // If we add any new usages of the header/dmw field, this code
733 // will need to be updated.
734 hash = test.hash();
735 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
736 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
737 }
738 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
739 // If we detect that async deflation has occurred, then we
740 // attempt to restore the header/dmw to the object's header
741 // so that we only retry once if the deflater thread happens
742 // to be slow.
743 monitor->install_displaced_markword_in_object(obj);
744 continue;
745 }
746 }
747 // We finally get the hash.
748 return hash;
749 }
750 }
751
752 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
753 Handle h_obj) {
754 assert(current == JavaThread::current(), "Can only be called on current thread");
755 oop obj = h_obj();
756
757 markWord mark = obj->mark_acquire();
758
759 if (mark.is_fast_locked()) {
760 // fast-locking case, see if lock is in current's lock stack
761 return current->lock_stack().contains(h_obj());
762 }
763
764 while (mark.has_monitor()) {
765 ObjectMonitor* monitor = read_monitor(current, obj, mark);
766 if (monitor != nullptr) {
767 return monitor->is_entered(current) != 0;
768 }
769 // Racing with inflation/deflation, retry
770 mark = obj->mark_acquire();
771
772 if (mark.is_fast_locked()) {
773 // Some other thread fast_locked, current could not have held the lock
774 return false;
775 }
776 }
777
778 // Unlocked case, header in place
779 assert(mark.is_unlocked(), "sanity check");
780 return false;
781 }
782
783 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
784 oop obj = h_obj();
785 markWord mark = obj->mark_acquire();
786
787 if (mark.is_fast_locked()) {
788 // fast-locked so get owner from the object.
789 // owning_thread_from_object() may also return null here:
790 return Threads::owning_thread_from_object(t_list, h_obj());
791 }
792
793 while (mark.has_monitor()) {
794 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
795 if (monitor != nullptr) {
796 return Threads::owning_thread_from_monitor(t_list, monitor);
797 }
798 // Racing with inflation/deflation, retry
799 mark = obj->mark_acquire();
800
801 if (mark.is_fast_locked()) {
802 // Some other thread fast_locked
803 return Threads::owning_thread_from_object(t_list, h_obj());
804 }
805 }
806
807 // Unlocked case, header in place
808 // Cannot have assertion since this object may have been
809 // locked by another thread when reaching here.
810 // assert(mark.is_unlocked(), "sanity check");
811
812 return nullptr;
813 }
814
815 // Visitors ...
816
817 // Iterate over all ObjectMonitors.
818 template <typename Function>
819 void ObjectSynchronizer::monitors_iterate(Function function) {
820 MonitorList::Iterator iter = _in_use_list.iterator();
821 while (iter.has_next()) {
822 ObjectMonitor* monitor = iter.next();
823 function(monitor);
824 }
825 }
826
827 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
828 // returns true.
829 template <typename OwnerFilter>
830 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
831 monitors_iterate([&](ObjectMonitor* monitor) {
832 // This function is only called at a safepoint or when the
833 // target thread is suspended or when the target thread is
834 // operating on itself. The current closures in use today are
835 // only interested in an owned ObjectMonitor and ownership
836 // cannot be dropped under the calling contexts so the
837 // ObjectMonitor cannot be async deflated.
838 if (monitor->has_owner() && filter(monitor)) {
839 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
840
841 closure->do_monitor(monitor);
842 }
843 });
844 }
845
846 // Iterate ObjectMonitors where the owner == thread; this does NOT include
847 // ObjectMonitors where owner is set to a stack-lock address in thread.
848 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
849 int64_t key = ObjectMonitor::owner_id_from(thread);
850 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
851 return owned_monitors_iterate_filtered(closure, thread_filter);
852 }
853
854 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
855 int64_t key = ObjectMonitor::owner_id_from(vthread);
856 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
857 return owned_monitors_iterate_filtered(closure, thread_filter);
858 }
859
860 // Iterate ObjectMonitors owned by any thread.
861 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
862 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
863 return owned_monitors_iterate_filtered(closure, all_filter);
864 }
865
866 static bool monitors_used_above_threshold(MonitorList* list) {
867 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
868 return false;
869 }
870 size_t monitors_used = list->count();
871 if (monitors_used == 0) { // empty list is easy
872 return false;
873 }
874 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
875 // Make sure that we use a ceiling value that is not lower than
876 // previous, not lower than the recorded max used by the system, and
877 // not lower than the current number of monitors in use (which can
878 // race ahead of max). The result is guaranteed > 0.
879 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
880
881 // Check if our monitor usage is above the threshold:
882 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
883 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
884 // Deflate monitors if over the threshold percentage, unless no
885 // progress on previous deflations.
886 bool is_above_threshold = true;
887
888 // Check if it's time to adjust the in_use_list_ceiling up, due
889 // to too many async deflation attempts without any progress.
890 if (NoAsyncDeflationProgressMax != 0 &&
891 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
892 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
893 size_t delta = (size_t)(ceiling * remainder) + 1;
894 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
895 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
896 : ceiling + delta;
897
898 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
899 log_info(monitorinflation)("Too many deflations without progress; "
900 "bumping in_use_list_ceiling from %zu"
901 " to %zu", old_ceiling, new_ceiling);
902 _no_progress_cnt = 0;
903 ceiling = new_ceiling;
904
905 // Check if our monitor usage is still above the threshold:
906 monitor_usage = (monitors_used * 100LL) / ceiling;
907 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
908 }
909 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
910 ", monitor_usage=%zu, threshold=%d",
911 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
912 return is_above_threshold;
913 }
914
915 return false;
916 }
917
918 size_t ObjectSynchronizer::in_use_list_count() {
919 return _in_use_list.count();
920 }
921
922 size_t ObjectSynchronizer::in_use_list_max() {
923 return _in_use_list.max();
924 }
925
926 size_t ObjectSynchronizer::in_use_list_ceiling() {
927 return _in_use_list_ceiling;
928 }
929
930 void ObjectSynchronizer::dec_in_use_list_ceiling() {
931 AtomicAccess::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
932 }
933
934 void ObjectSynchronizer::inc_in_use_list_ceiling() {
935 AtomicAccess::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
936 }
937
938 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
939 _in_use_list_ceiling = new_value;
940 }
941
942 bool ObjectSynchronizer::is_async_deflation_needed() {
943 if (is_async_deflation_requested()) {
944 // Async deflation request.
945 log_info(monitorinflation)("Async deflation needed: explicit request");
946 return true;
947 }
948
949 jlong time_since_last = time_since_last_async_deflation_ms();
950
951 if (AsyncDeflationInterval > 0 &&
952 time_since_last > AsyncDeflationInterval &&
953 monitors_used_above_threshold(&_in_use_list)) {
954 // It's been longer than our specified deflate interval and there
955 // are too many monitors in use. We don't deflate more frequently
956 // than AsyncDeflationInterval (unless is_async_deflation_requested)
957 // in order to not swamp the MonitorDeflationThread.
958 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
959 return true;
960 }
961
962 if (GuaranteedAsyncDeflationInterval > 0 &&
963 time_since_last > GuaranteedAsyncDeflationInterval) {
964 // It's been longer than our specified guaranteed deflate interval.
965 // We need to clean up the used monitors even if the threshold is
966 // not reached, to keep the memory utilization at bay when many threads
967 // touched many monitors.
968 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
969 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
970 GuaranteedAsyncDeflationInterval, time_since_last);
971
972 // If this deflation has no progress, then it should not affect the no-progress
973 // tracking, otherwise threshold heuristics would think it was triggered, experienced
974 // no progress, and needs to backoff more aggressively. In this "no progress" case,
975 // the generic code would bump the no-progress counter, and we compensate for that
976 // by telling it to skip the update.
977 //
978 // If this deflation has progress, then it should let non-progress tracking
979 // know about this, otherwise the threshold heuristics would kick in, potentially
980 // experience no-progress due to aggressive cleanup by this deflation, and think
981 // it is still in no-progress stride. In this "progress" case, the generic code would
982 // zero the counter, and we allow it to happen.
983 _no_progress_skip_increment = true;
984
985 return true;
986 }
987
988 return false;
989 }
990
991 void ObjectSynchronizer::request_deflate_idle_monitors() {
992 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
993 set_is_async_deflation_requested(true);
994 ml.notify_all();
995 }
996
997 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
998 JavaThread* current = JavaThread::current();
999 bool ret_code = false;
1000
1001 jlong last_time = last_async_deflation_time_ns();
1002
1003 request_deflate_idle_monitors();
1004
1005 const int N_CHECKS = 5;
1006 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1007 if (last_async_deflation_time_ns() > last_time) {
1008 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1009 ret_code = true;
1010 break;
1011 }
1012 {
1013 // JavaThread has to honor the blocking protocol.
1014 ThreadBlockInVM tbivm(current);
1015 os::naked_short_sleep(999); // sleep for almost 1 second
1016 }
1017 }
1018 if (!ret_code) {
1019 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1020 }
1021
1022 return ret_code;
1023 }
1024
1025 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1026 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1027 }
1028
1029 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1030 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1031 //
1032 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1033 MonitorList::Iterator iter = _in_use_list.iterator();
1034 size_t deflated_count = 0;
1035 Thread* current = Thread::current();
1036
1037 while (iter.has_next()) {
1038 if (deflated_count >= (size_t)MonitorDeflationMax) {
1039 break;
1040 }
1041 ObjectMonitor* mid = iter.next();
1042 if (mid->deflate_monitor(current)) {
1043 deflated_count++;
1044 }
1045
1046 // Must check for a safepoint/handshake and honor it.
1047 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1048 }
1049
1050 return deflated_count;
1051 }
1052
1053 class DeflationHandshakeClosure : public HandshakeClosure {
1054 public:
1055 DeflationHandshakeClosure() : HandshakeClosure("DeflationHandshakeClosure") {}
1056
1057 void do_thread(Thread* thread) {
1058 log_trace(monitorinflation)("DeflationHandshakeClosure::do_thread: thread="
1059 INTPTR_FORMAT, p2i(thread));
1060 if (thread->is_Java_thread()) {
1061 // Clear OM cache
1062 JavaThread* jt = JavaThread::cast(thread);
1063 jt->om_clear_monitor_cache();
1064 }
1065 }
1066 };
1067
1068 class VM_RendezvousGCThreads : public VM_Operation {
1069 public:
1070 bool evaluate_at_safepoint() const override { return false; }
1071 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1072 void doit() override {
1073 Universe::heap()->safepoint_synchronize_begin();
1074 Universe::heap()->safepoint_synchronize_end();
1075 };
1076 };
1077
1078 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1079 ObjectMonitorDeflationSafepointer* safepointer) {
1080 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1081 size_t deleted_count = 0;
1082 for (ObjectMonitor* monitor: *delete_list) {
1083 delete monitor;
1084 deleted_count++;
1085 // A JavaThread must check for a safepoint/handshake and honor it.
1086 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1087 }
1088 return deleted_count;
1089 }
1090
1091 class ObjectMonitorDeflationLogging: public StackObj {
1092 LogStreamHandle(Debug, monitorinflation) _debug;
1093 LogStreamHandle(Info, monitorinflation) _info;
1094 LogStream* _stream;
1095 elapsedTimer _timer;
1096
1097 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1098 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1099 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1100
1101 public:
1102 ObjectMonitorDeflationLogging()
1103 : _debug(), _info(), _stream(nullptr) {
1104 if (_debug.is_enabled()) {
1105 _stream = &_debug;
1106 } else if (_info.is_enabled()) {
1107 _stream = &_info;
1108 }
1109 }
1110
1111 void begin() {
1112 if (_stream != nullptr) {
1113 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1114 ceiling(), count(), max());
1115 _timer.start();
1116 }
1117 }
1118
1119 void before_handshake(size_t unlinked_count) {
1120 if (_stream != nullptr) {
1121 _timer.stop();
1122 _stream->print_cr("before handshaking: unlinked_count=%zu"
1123 ", in_use_list stats: ceiling=%zu, count="
1124 "%zu, max=%zu",
1125 unlinked_count, ceiling(), count(), max());
1126 }
1127 }
1128
1129 void after_handshake() {
1130 if (_stream != nullptr) {
1131 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1132 "%zu, count=%zu, max=%zu",
1133 ceiling(), count(), max());
1134 _timer.start();
1135 }
1136 }
1137
1138 void end(size_t deflated_count, size_t unlinked_count) {
1139 if (_stream != nullptr) {
1140 _timer.stop();
1141 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1142 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1143 deflated_count, unlinked_count, _timer.seconds());
1144 }
1145 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1146 ceiling(), count(), max());
1147 }
1148 }
1149
1150 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1151 if (_stream != nullptr) {
1152 _timer.stop();
1153 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1154 "%zu, count=%zu, max=%zu",
1155 op_name, cnt_name, cnt, ceiling(), count(), max());
1156 }
1157 }
1158
1159 void after_block_for_safepoint(const char* op_name) {
1160 if (_stream != nullptr) {
1161 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1162 ", count=%zu, max=%zu", op_name,
1163 ceiling(), count(), max());
1164 _timer.start();
1165 }
1166 }
1167 };
1168
1169 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1170 if (!SafepointMechanism::should_process(_current)) {
1171 return;
1172 }
1173
1174 // A safepoint/handshake has started.
1175 _log->before_block_for_safepoint(op_name, count_name, counter);
1176
1177 {
1178 // Honor block request.
1179 ThreadBlockInVM tbivm(_current);
1180 }
1181
1182 _log->after_block_for_safepoint(op_name);
1183 }
1184
1185 // This function is called by the MonitorDeflationThread to deflate
1186 // ObjectMonitors.
1187 size_t ObjectSynchronizer::deflate_idle_monitors() {
1188 JavaThread* current = JavaThread::current();
1189 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1190
1191 // The async deflation request has been processed.
1192 _last_async_deflation_time_ns = os::javaTimeNanos();
1193 set_is_async_deflation_requested(false);
1194
1195 ObjectMonitorDeflationLogging log;
1196 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1197
1198 log.begin();
1199
1200 // Deflate some idle ObjectMonitors.
1201 size_t deflated_count = deflate_monitor_list(&safepointer);
1202
1203 // Unlink the deflated ObjectMonitors from the in-use list.
1204 size_t unlinked_count = 0;
1205 size_t deleted_count = 0;
1206 if (deflated_count > 0) {
1207 ResourceMark rm(current);
1208 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1209 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1210
1211 #ifdef ASSERT
1212 if (UseObjectMonitorTable) {
1213 for (ObjectMonitor* monitor : delete_list) {
1214 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1215 }
1216 }
1217 #endif
1218
1219 log.before_handshake(unlinked_count);
1220
1221 // A JavaThread needs to handshake in order to safely free the
1222 // ObjectMonitors that were deflated in this cycle.
1223 DeflationHandshakeClosure dhc;
1224 Handshake::execute(&dhc);
1225 // Also, we sync and desync GC threads around the handshake, so that they can
1226 // safely read the mark-word and look-through to the object-monitor, without
1227 // being afraid that the object-monitor is going away.
1228 VM_RendezvousGCThreads sync_gc;
1229 VMThread::execute(&sync_gc);
1230
1231 log.after_handshake();
1232
1233 // After the handshake, safely free the ObjectMonitors that were
1234 // deflated and unlinked in this cycle.
1235
1236 // Delete the unlinked ObjectMonitors.
1237 deleted_count = delete_monitors(&delete_list, &safepointer);
1238 assert(unlinked_count == deleted_count, "must be");
1239 }
1240
1241 log.end(deflated_count, unlinked_count);
1242
1243 GVars.stw_random = os::random();
1244
1245 if (deflated_count != 0) {
1246 _no_progress_cnt = 0;
1247 } else if (_no_progress_skip_increment) {
1248 _no_progress_skip_increment = false;
1249 } else {
1250 _no_progress_cnt++;
1251 }
1252
1253 return deflated_count;
1254 }
1255
1256 // Monitor cleanup on JavaThread::exit
1257
1258 // Iterate through monitor cache and attempt to release thread's monitors
1259 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1260 private:
1261 JavaThread* _thread;
1262
1263 public:
1264 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1265 void do_monitor(ObjectMonitor* mid) {
1266 intx rec = mid->complete_exit(_thread);
1267 _thread->dec_held_monitor_count(rec + 1);
1268 }
1269 };
1270
1271 // Release all inflated monitors owned by current thread. Lightweight monitors are
1272 // ignored. This is meant to be called during JNI thread detach which assumes
1273 // all remaining monitors are heavyweight. All exceptions are swallowed.
1274 // Scanning the extant monitor list can be time consuming.
1275 // A simple optimization is to add a per-thread flag that indicates a thread
1276 // called jni_monitorenter() during its lifetime.
1277 //
1278 // Instead of NoSafepointVerifier it might be cheaper to
1279 // use an idiom of the form:
1280 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1281 // <code that must not run at safepoint>
1282 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1283 // Since the tests are extremely cheap we could leave them enabled
1284 // for normal product builds.
1285
1286 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1287 assert(current == JavaThread::current(), "must be current Java thread");
1288 NoSafepointVerifier nsv;
1289 ReleaseJavaMonitorsClosure rjmc(current);
1290 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1291 assert(!current->has_pending_exception(), "Should not be possible");
1292 current->clear_pending_exception();
1293 assert(current->held_monitor_count() == 0, "Should not be possible");
1294 // All monitors (including entered via JNI) have been unlocked above, so we need to clear jni count.
1295 current->clear_jni_monitor_count();
1296 }
1297
1298 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1299 switch (cause) {
1300 case inflate_cause_vm_internal: return "VM Internal";
1301 case inflate_cause_monitor_enter: return "Monitor Enter";
1302 case inflate_cause_wait: return "Monitor Wait";
1303 case inflate_cause_notify: return "Monitor Notify";
1304 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1305 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1306 default:
1307 ShouldNotReachHere();
1308 }
1309 return "Unknown";
1310 }
1311
1312 //------------------------------------------------------------------------------
1313 // Debugging code
1314
1315 u_char* ObjectSynchronizer::get_gvars_addr() {
1316 return (u_char*)&GVars;
1317 }
1318
1319 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1320 return (u_char*)&GVars.hc_sequence;
1321 }
1322
1323 size_t ObjectSynchronizer::get_gvars_size() {
1324 return sizeof(SharedGlobals);
1325 }
1326
1327 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1328 return (u_char*)&GVars.stw_random;
1329 }
1330
1331 // Do the final audit and print of ObjectMonitor stats; must be done
1332 // by the VMThread at VM exit time.
1333 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1334 assert(Thread::current()->is_VM_thread(), "sanity check");
1335
1336 if (is_final_audit()) { // Only do the audit once.
1337 return;
1338 }
1339 set_is_final_audit();
1340 log_info(monitorinflation)("Starting the final audit.");
1341
1342 if (log_is_enabled(Info, monitorinflation)) {
1343 LogStreamHandle(Info, monitorinflation) ls;
1344 audit_and_print_stats(&ls, true /* on_exit */);
1345 }
1346 }
1347
1348 // This function can be called by the MonitorDeflationThread or it can be called when
1349 // we are trying to exit the VM. The list walker functions can run in parallel with
1350 // the other list operations.
1351 // Calls to this function can be added in various places as a debugging
1352 // aid.
1353 //
1354 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1355 int error_cnt = 0;
1356
1357 ls->print_cr("Checking in_use_list:");
1358 chk_in_use_list(ls, &error_cnt);
1359
1360 if (error_cnt == 0) {
1361 ls->print_cr("No errors found in in_use_list checks.");
1362 } else {
1363 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1364 }
1365
1366 // When exiting, only log the interesting entries at the Info level.
1367 // When called at intervals by the MonitorDeflationThread, log output
1368 // at the Trace level since there can be a lot of it.
1369 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1370 LogStreamHandle(Trace, monitorinflation) ls_tr;
1371 log_in_use_monitor_details(&ls_tr, true /* log_all */);
1372 } else if (on_exit) {
1373 log_in_use_monitor_details(ls, false /* log_all */);
1374 }
1375
1376 ls->flush();
1377
1378 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1379 }
1380
1381 // Check the in_use_list; log the results of the checks.
1382 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1383 size_t l_in_use_count = _in_use_list.count();
1384 size_t l_in_use_max = _in_use_list.max();
1385 out->print_cr("count=%zu, max=%zu", l_in_use_count,
1386 l_in_use_max);
1387
1388 size_t ck_in_use_count = 0;
1389 MonitorList::Iterator iter = _in_use_list.iterator();
1390 while (iter.has_next()) {
1391 ObjectMonitor* mid = iter.next();
1392 chk_in_use_entry(mid, out, error_cnt_p);
1393 ck_in_use_count++;
1394 }
1395
1396 if (l_in_use_count == ck_in_use_count) {
1397 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
1398 l_in_use_count, ck_in_use_count);
1399 } else {
1400 out->print_cr("WARNING: in_use_count=%zu is not equal to "
1401 "ck_in_use_count=%zu", l_in_use_count,
1402 ck_in_use_count);
1403 }
1404
1405 size_t ck_in_use_max = _in_use_list.max();
1406 if (l_in_use_max == ck_in_use_max) {
1407 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
1408 l_in_use_max, ck_in_use_max);
1409 } else {
1410 out->print_cr("WARNING: in_use_max=%zu is not equal to "
1411 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
1412 }
1413 }
1414
1415 // Check an in-use monitor entry; log any errors.
1416 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1417 int* error_cnt_p) {
1418 if (n->owner_is_DEFLATER_MARKER()) {
1419 // This could happen when monitor deflation blocks for a safepoint.
1420 return;
1421 }
1422
1423
1424 if (n->metadata() == 0) {
1425 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1426 "have non-null _metadata (header/hash) field.", p2i(n));
1427 *error_cnt_p = *error_cnt_p + 1;
1428 }
1429
1430 const oop obj = n->object_peek();
1431 if (obj == nullptr) {
1432 return;
1433 }
1434
1435 const markWord mark = obj->mark();
1436 if (!mark.has_monitor()) {
1437 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1438 "object does not think it has a monitor: obj="
1439 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1440 p2i(obj), mark.value());
1441 *error_cnt_p = *error_cnt_p + 1;
1442 return;
1443 }
1444
1445 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
1446 if (n != obj_mon) {
1447 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1448 "object does not refer to the same monitor: obj="
1449 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1450 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1451 *error_cnt_p = *error_cnt_p + 1;
1452 }
1453 }
1454
1455 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1456 // flags indicate why the entry is in-use, 'object' and 'object type'
1457 // indicate the associated object and its type.
1458 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
1459 if (_in_use_list.count() > 0) {
1460 stringStream ss;
1461 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
1462 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1463 out->print_cr("%18s %s %18s %18s",
1464 "monitor", "BHL", "object", "object type");
1465 out->print_cr("================== === ================== ==================");
1466
1467 auto is_interesting = [&](ObjectMonitor* monitor) {
1468 return log_all || monitor->has_owner() || monitor->is_busy();
1469 };
1470
1471 monitors_iterate([&](ObjectMonitor* monitor) {
1472 if (is_interesting(monitor)) {
1473 const oop obj = monitor->object_peek();
1474 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
1475 ResourceMark rm;
1476 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
1477 monitor->is_busy(), hash != 0, monitor->has_owner(),
1478 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
1479 if (monitor->is_busy()) {
1480 out->print(" (%s)", monitor->is_busy_to_string(&ss));
1481 ss.reset();
1482 }
1483 out->cr();
1484 }
1485 });
1486 }
1487
1488 out->flush();
1489 }