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 break;
456 }
457 }
458 current->set_current_pending_monitor_is_from_java(true);
459 }
460
461 // NOTE: must use heavy weight monitor to handle jni monitor exit
462 void ObjectSynchronizer::jni_exit(oop obj, TRAPS) {
463 JavaThread* current = THREAD;
464
465 ObjectMonitor* monitor;
466 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj, inflate_cause_jni_exit, CHECK);
467 // If this thread has locked the object, exit the monitor. We
468 // intentionally do not use CHECK on check_owner because we must exit the
469 // monitor even if an exception was already pending.
470 if (monitor->check_owner(THREAD)) {
471 monitor->exit(current);
472 }
473 }
474
475 // -----------------------------------------------------------------------------
476 // Internal VM locks on java objects
477 // standard constructor, allows locking failures
478 ObjectLocker::ObjectLocker(Handle obj, JavaThread* thread) : _npm(thread) {
479 _thread = thread;
480 _thread->check_for_valid_safepoint_state();
481 _obj = obj;
482
483 if (_obj() != nullptr) {
484 ObjectSynchronizer::enter(_obj, &_lock, _thread);
485 }
486 }
487
488 ObjectLocker::~ObjectLocker() {
489 if (_obj() != nullptr) {
490 ObjectSynchronizer::exit(_obj(), &_lock, _thread);
491 }
492 }
493
494
495 // -----------------------------------------------------------------------------
496 // Wait/Notify/NotifyAll
497 // NOTE: must use heavy weight monitor to handle wait()
498
499 int ObjectSynchronizer::wait(Handle obj, jlong millis, TRAPS) {
500 JavaThread* current = THREAD;
501 if (millis < 0) {
502 THROW_MSG_0(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
503 }
504
505 ObjectMonitor* monitor;
506 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK_0);
507
508 DTRACE_MONITOR_WAIT_PROBE(monitor, obj(), current, millis);
509 monitor->wait(millis, true, THREAD); // Not CHECK as we need following code
510
511 // This dummy call is in place to get around dtrace bug 6254741. Once
512 // that's fixed we can uncomment the following line, remove the call
513 // and change this function back into a "void" func.
514 // DTRACE_MONITOR_PROBE(waited, monitor, obj(), THREAD);
515 int ret_code = dtrace_waited_probe(monitor, obj, THREAD);
516 return ret_code;
517 }
518
519 void ObjectSynchronizer::waitUninterruptibly(Handle obj, jlong millis, TRAPS) {
520 if (millis < 0) {
521 THROW_MSG(vmSymbols::java_lang_IllegalArgumentException(), "timeout value is negative");
522 }
523
524 ObjectMonitor* monitor;
525 monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_wait, CHECK);
526 monitor->wait(millis, false, THREAD);
527 }
528
529
530 void ObjectSynchronizer::notify(Handle obj, TRAPS) {
531 JavaThread* current = THREAD;
532
533 markWord mark = obj->mark();
534 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
535 // Not inflated so there can't be any waiters to notify.
536 return;
537 }
538 ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
539 monitor->notify(CHECK);
540 }
541
542 // NOTE: see comment of notify()
543 void ObjectSynchronizer::notifyall(Handle obj, TRAPS) {
544 JavaThread* current = THREAD;
545
546 markWord mark = obj->mark();
547 if ((mark.is_fast_locked() && current->lock_stack().contains(obj()))) {
548 // Not inflated so there can't be any waiters to notify.
549 return;
550 }
551
552 ObjectMonitor* monitor = LightweightSynchronizer::inflate_locked_or_imse(obj(), inflate_cause_notify, CHECK);
553 monitor->notifyAll(CHECK);
554 }
555
556 // -----------------------------------------------------------------------------
557 // Hash Code handling
558
559 struct SharedGlobals {
560 char _pad_prefix[OM_CACHE_LINE_SIZE];
561 // This is a highly shared mostly-read variable.
562 // To avoid false-sharing it needs to be the sole occupant of a cache line.
563 volatile int stw_random;
564 DEFINE_PAD_MINUS_SIZE(1, OM_CACHE_LINE_SIZE, sizeof(volatile int));
565 // Hot RW variable -- Sequester to avoid false-sharing
566 volatile int hc_sequence;
567 DEFINE_PAD_MINUS_SIZE(2, OM_CACHE_LINE_SIZE, sizeof(volatile int));
568 };
569
570 static SharedGlobals GVars;
571
572 // hashCode() generation :
573 //
574 // Possibilities:
575 // * MD5Digest of {obj,stw_random}
576 // * CRC32 of {obj,stw_random} or any linear-feedback shift register function.
577 // * A DES- or AES-style SBox[] mechanism
578 // * One of the Phi-based schemes, such as:
579 // 2654435761 = 2^32 * Phi (golden ratio)
580 // HashCodeValue = ((uintptr_t(obj) >> 3) * 2654435761) ^ GVars.stw_random ;
581 // * A variation of Marsaglia's shift-xor RNG scheme.
582 // * (obj ^ stw_random) is appealing, but can result
583 // in undesirable regularity in the hashCode values of adjacent objects
584 // (objects allocated back-to-back, in particular). This could potentially
585 // result in hashtable collisions and reduced hashtable efficiency.
586 // There are simple ways to "diffuse" the middle address bits over the
587 // generated hashCode values:
588
589 static intptr_t get_next_hash(Thread* current, oop obj) {
590 intptr_t value = 0;
591 if (hashCode == 0) {
592 // This form uses global Park-Miller RNG.
593 // On MP system we'll have lots of RW access to a global, so the
594 // mechanism induces lots of coherency traffic.
595 value = os::random();
596 } else if (hashCode == 1) {
597 // This variation has the property of being stable (idempotent)
598 // between STW operations. This can be useful in some of the 1-0
599 // synchronization schemes.
600 intptr_t addr_bits = cast_from_oop<intptr_t>(obj) >> 3;
601 value = addr_bits ^ (addr_bits >> 5) ^ GVars.stw_random;
602 } else if (hashCode == 2) {
603 value = 1; // for sensitivity testing
604 } else if (hashCode == 3) {
605 value = ++GVars.hc_sequence;
606 } else if (hashCode == 4) {
607 value = cast_from_oop<intptr_t>(obj);
608 } else {
609 // Marsaglia's xor-shift scheme with thread-specific state
610 // This is probably the best overall implementation -- we'll
611 // likely make this the default in future releases.
612 unsigned t = current->_hashStateX;
613 t ^= (t << 11);
614 current->_hashStateX = current->_hashStateY;
615 current->_hashStateY = current->_hashStateZ;
616 current->_hashStateZ = current->_hashStateW;
617 unsigned v = current->_hashStateW;
618 v = (v ^ (v >> 19)) ^ (t ^ (t >> 8));
619 current->_hashStateW = v;
620 value = v;
621 }
622
623 value &= markWord::hash_mask;
624 if (value == 0) value = 0xBAD;
625 assert(value != markWord::no_hash, "invariant");
626 return value;
627 }
628
629 static intptr_t install_hash_code(Thread* current, oop obj) {
630 assert(UseObjectMonitorTable, "must be");
631
632 markWord mark = obj->mark_acquire();
633 for (;;) {
634 intptr_t hash = mark.hash();
635 if (hash != 0) {
636 return hash;
637 }
638
639 hash = get_next_hash(current, obj);
640 const markWord old_mark = mark;
641 const markWord new_mark = old_mark.copy_set_hash(hash);
642
643 mark = obj->cas_set_mark(new_mark, old_mark);
644 if (old_mark == mark) {
645 return hash;
646 }
647 }
648 }
649
650 intptr_t ObjectSynchronizer::FastHashCode(Thread* current, oop obj) {
651 if (UseObjectMonitorTable) {
652 // Since the monitor isn't in the object header, the hash can simply be
653 // installed in the object header.
654 return install_hash_code(current, obj);
655 }
656
657 while (true) {
658 ObjectMonitor* monitor = nullptr;
659 markWord temp, test;
660 intptr_t hash;
661 markWord mark = obj->mark_acquire();
662 if (mark.is_unlocked() || mark.is_fast_locked()) {
663 hash = mark.hash();
664 if (hash != 0) { // if it has a hash, just return it
665 return hash;
666 }
667 hash = get_next_hash(current, obj); // get a new hash
668 temp = mark.copy_set_hash(hash); // merge the hash into header
669 // try to install the hash
670 test = obj->cas_set_mark(temp, mark);
671 if (test == mark) { // if the hash was installed, return it
672 return hash;
673 }
674 // CAS failed, retry
675 continue;
676
677 // Failed to install the hash. It could be that another thread
678 // installed the hash just before our attempt or inflation has
679 // occurred or... so we fall thru to inflate the monitor for
680 // stability and then install the hash.
681 } else if (mark.has_monitor()) {
682 monitor = mark.monitor();
683 temp = monitor->header();
684 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
685 hash = temp.hash();
686 if (hash != 0) {
687 // It has a hash.
688
689 // Separate load of dmw/header above from the loads in
690 // is_being_async_deflated().
691
692 // dmw/header and _contentions may get written by different threads.
693 // Make sure to observe them in the same order when having several observers.
694 OrderAccess::loadload_for_IRIW();
695
696 if (monitor->is_being_async_deflated()) {
697 // But we can't safely use the hash if we detect that async
698 // deflation has occurred. So we attempt to restore the
699 // header/dmw to the object's header so that we only retry
700 // once if the deflater thread happens to be slow.
701 monitor->install_displaced_markword_in_object(obj);
702 continue;
703 }
704 return hash;
705 }
706 // Fall thru so we only have one place that installs the hash in
707 // the ObjectMonitor.
708 }
709
710 // NOTE: an async deflation can race after we get the monitor and
711 // before we can update the ObjectMonitor's header with the hash
712 // value below.
713 assert(mark.has_monitor(), "must be");
714 monitor = mark.monitor();
715
716 // Load ObjectMonitor's header/dmw field and see if it has a hash.
717 mark = monitor->header();
718 assert(mark.is_neutral(), "invariant: header=" INTPTR_FORMAT, mark.value());
719 hash = mark.hash();
720 if (hash == 0) { // if it does not have a hash
721 hash = get_next_hash(current, obj); // get a new hash
722 temp = mark.copy_set_hash(hash) ; // merge the hash into header
723 assert(temp.is_neutral(), "invariant: header=" INTPTR_FORMAT, temp.value());
724 uintptr_t v = AtomicAccess::cmpxchg(monitor->metadata_addr(), mark.value(), temp.value());
725 test = markWord(v);
726 if (test != mark) {
727 // The attempt to update the ObjectMonitor's header/dmw field
728 // did not work. This can happen if another thread managed to
729 // merge in the hash just before our cmpxchg().
730 // If we add any new usages of the header/dmw field, this code
731 // will need to be updated.
732 hash = test.hash();
733 assert(test.is_neutral(), "invariant: header=" INTPTR_FORMAT, test.value());
734 assert(hash != 0, "should only have lost the race to a thread that set a non-zero hash");
735 }
736 if (monitor->is_being_async_deflated() && !UseObjectMonitorTable) {
737 // If we detect that async deflation has occurred, then we
738 // attempt to restore the header/dmw to the object's header
739 // so that we only retry once if the deflater thread happens
740 // to be slow.
741 monitor->install_displaced_markword_in_object(obj);
742 continue;
743 }
744 }
745 // We finally get the hash.
746 return hash;
747 }
748 }
749
750 bool ObjectSynchronizer::current_thread_holds_lock(JavaThread* current,
751 Handle h_obj) {
752 assert(current == JavaThread::current(), "Can only be called on current thread");
753 oop obj = h_obj();
754
755 markWord mark = obj->mark_acquire();
756
757 if (mark.is_fast_locked()) {
758 // fast-locking case, see if lock is in current's lock stack
759 return current->lock_stack().contains(h_obj());
760 }
761
762 while (mark.has_monitor()) {
763 ObjectMonitor* monitor = read_monitor(current, obj, mark);
764 if (monitor != nullptr) {
765 return monitor->is_entered(current) != 0;
766 }
767 // Racing with inflation/deflation, retry
768 mark = obj->mark_acquire();
769
770 if (mark.is_fast_locked()) {
771 // Some other thread fast_locked, current could not have held the lock
772 return false;
773 }
774 }
775
776 // Unlocked case, header in place
777 assert(mark.is_unlocked(), "sanity check");
778 return false;
779 }
780
781 JavaThread* ObjectSynchronizer::get_lock_owner(ThreadsList * t_list, Handle h_obj) {
782 oop obj = h_obj();
783 markWord mark = obj->mark_acquire();
784
785 if (mark.is_fast_locked()) {
786 // fast-locked so get owner from the object.
787 // owning_thread_from_object() may also return null here:
788 return Threads::owning_thread_from_object(t_list, h_obj());
789 }
790
791 while (mark.has_monitor()) {
792 ObjectMonitor* monitor = read_monitor(Thread::current(), obj, mark);
793 if (monitor != nullptr) {
794 return Threads::owning_thread_from_monitor(t_list, monitor);
795 }
796 // Racing with inflation/deflation, retry
797 mark = obj->mark_acquire();
798
799 if (mark.is_fast_locked()) {
800 // Some other thread fast_locked
801 return Threads::owning_thread_from_object(t_list, h_obj());
802 }
803 }
804
805 // Unlocked case, header in place
806 // Cannot have assertion since this object may have been
807 // locked by another thread when reaching here.
808 // assert(mark.is_unlocked(), "sanity check");
809
810 return nullptr;
811 }
812
813 // Visitors ...
814
815 // Iterate over all ObjectMonitors.
816 template <typename Function>
817 void ObjectSynchronizer::monitors_iterate(Function function) {
818 MonitorList::Iterator iter = _in_use_list.iterator();
819 while (iter.has_next()) {
820 ObjectMonitor* monitor = iter.next();
821 function(monitor);
822 }
823 }
824
825 // Iterate ObjectMonitors owned by any thread and where the owner `filter`
826 // returns true.
827 template <typename OwnerFilter>
828 void ObjectSynchronizer::owned_monitors_iterate_filtered(MonitorClosure* closure, OwnerFilter filter) {
829 monitors_iterate([&](ObjectMonitor* monitor) {
830 // This function is only called at a safepoint or when the
831 // target thread is suspended or when the target thread is
832 // operating on itself. The current closures in use today are
833 // only interested in an owned ObjectMonitor and ownership
834 // cannot be dropped under the calling contexts so the
835 // ObjectMonitor cannot be async deflated.
836 if (monitor->has_owner() && filter(monitor)) {
837 assert(!monitor->is_being_async_deflated(), "Owned monitors should not be deflating");
838
839 closure->do_monitor(monitor);
840 }
841 });
842 }
843
844 // Iterate ObjectMonitors where the owner == thread; this does NOT include
845 // ObjectMonitors where owner is set to a stack-lock address in thread.
846 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, JavaThread* thread) {
847 int64_t key = ObjectMonitor::owner_id_from(thread);
848 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
849 return owned_monitors_iterate_filtered(closure, thread_filter);
850 }
851
852 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure, oop vthread) {
853 int64_t key = ObjectMonitor::owner_id_from(vthread);
854 auto thread_filter = [&](ObjectMonitor* monitor) { return monitor->owner() == key; };
855 return owned_monitors_iterate_filtered(closure, thread_filter);
856 }
857
858 // Iterate ObjectMonitors owned by any thread.
859 void ObjectSynchronizer::owned_monitors_iterate(MonitorClosure* closure) {
860 auto all_filter = [&](ObjectMonitor* monitor) { return true; };
861 return owned_monitors_iterate_filtered(closure, all_filter);
862 }
863
864 static bool monitors_used_above_threshold(MonitorList* list) {
865 if (MonitorUsedDeflationThreshold == 0) { // disabled case is easy
866 return false;
867 }
868 size_t monitors_used = list->count();
869 if (monitors_used == 0) { // empty list is easy
870 return false;
871 }
872 size_t old_ceiling = ObjectSynchronizer::in_use_list_ceiling();
873 // Make sure that we use a ceiling value that is not lower than
874 // previous, not lower than the recorded max used by the system, and
875 // not lower than the current number of monitors in use (which can
876 // race ahead of max). The result is guaranteed > 0.
877 size_t ceiling = MAX3(old_ceiling, list->max(), monitors_used);
878
879 // Check if our monitor usage is above the threshold:
880 size_t monitor_usage = (monitors_used * 100LL) / ceiling;
881 if (int(monitor_usage) > MonitorUsedDeflationThreshold) {
882 // Deflate monitors if over the threshold percentage, unless no
883 // progress on previous deflations.
884 bool is_above_threshold = true;
885
886 // Check if it's time to adjust the in_use_list_ceiling up, due
887 // to too many async deflation attempts without any progress.
888 if (NoAsyncDeflationProgressMax != 0 &&
889 _no_progress_cnt >= NoAsyncDeflationProgressMax) {
890 double remainder = (100.0 - MonitorUsedDeflationThreshold) / 100.0;
891 size_t delta = (size_t)(ceiling * remainder) + 1;
892 size_t new_ceiling = (ceiling > SIZE_MAX - delta)
893 ? SIZE_MAX // Overflow, let's clamp new_ceiling.
894 : ceiling + delta;
895
896 ObjectSynchronizer::set_in_use_list_ceiling(new_ceiling);
897 log_info(monitorinflation)("Too many deflations without progress; "
898 "bumping in_use_list_ceiling from %zu"
899 " to %zu", old_ceiling, new_ceiling);
900 _no_progress_cnt = 0;
901 ceiling = new_ceiling;
902
903 // Check if our monitor usage is still above the threshold:
904 monitor_usage = (monitors_used * 100LL) / ceiling;
905 is_above_threshold = int(monitor_usage) > MonitorUsedDeflationThreshold;
906 }
907 log_info(monitorinflation)("monitors_used=%zu, ceiling=%zu"
908 ", monitor_usage=%zu, threshold=%d",
909 monitors_used, ceiling, monitor_usage, MonitorUsedDeflationThreshold);
910 return is_above_threshold;
911 }
912
913 return false;
914 }
915
916 size_t ObjectSynchronizer::in_use_list_count() {
917 return _in_use_list.count();
918 }
919
920 size_t ObjectSynchronizer::in_use_list_max() {
921 return _in_use_list.max();
922 }
923
924 size_t ObjectSynchronizer::in_use_list_ceiling() {
925 return _in_use_list_ceiling;
926 }
927
928 void ObjectSynchronizer::dec_in_use_list_ceiling() {
929 AtomicAccess::sub(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
930 }
931
932 void ObjectSynchronizer::inc_in_use_list_ceiling() {
933 AtomicAccess::add(&_in_use_list_ceiling, AvgMonitorsPerThreadEstimate);
934 }
935
936 void ObjectSynchronizer::set_in_use_list_ceiling(size_t new_value) {
937 _in_use_list_ceiling = new_value;
938 }
939
940 bool ObjectSynchronizer::is_async_deflation_needed() {
941 if (is_async_deflation_requested()) {
942 // Async deflation request.
943 log_info(monitorinflation)("Async deflation needed: explicit request");
944 return true;
945 }
946
947 jlong time_since_last = time_since_last_async_deflation_ms();
948
949 if (AsyncDeflationInterval > 0 &&
950 time_since_last > AsyncDeflationInterval &&
951 monitors_used_above_threshold(&_in_use_list)) {
952 // It's been longer than our specified deflate interval and there
953 // are too many monitors in use. We don't deflate more frequently
954 // than AsyncDeflationInterval (unless is_async_deflation_requested)
955 // in order to not swamp the MonitorDeflationThread.
956 log_info(monitorinflation)("Async deflation needed: monitors used are above the threshold");
957 return true;
958 }
959
960 if (GuaranteedAsyncDeflationInterval > 0 &&
961 time_since_last > GuaranteedAsyncDeflationInterval) {
962 // It's been longer than our specified guaranteed deflate interval.
963 // We need to clean up the used monitors even if the threshold is
964 // not reached, to keep the memory utilization at bay when many threads
965 // touched many monitors.
966 log_info(monitorinflation)("Async deflation needed: guaranteed interval (%zd ms) "
967 "is greater than time since last deflation (" JLONG_FORMAT " ms)",
968 GuaranteedAsyncDeflationInterval, time_since_last);
969
970 // If this deflation has no progress, then it should not affect the no-progress
971 // tracking, otherwise threshold heuristics would think it was triggered, experienced
972 // no progress, and needs to backoff more aggressively. In this "no progress" case,
973 // the generic code would bump the no-progress counter, and we compensate for that
974 // by telling it to skip the update.
975 //
976 // If this deflation has progress, then it should let non-progress tracking
977 // know about this, otherwise the threshold heuristics would kick in, potentially
978 // experience no-progress due to aggressive cleanup by this deflation, and think
979 // it is still in no-progress stride. In this "progress" case, the generic code would
980 // zero the counter, and we allow it to happen.
981 _no_progress_skip_increment = true;
982
983 return true;
984 }
985
986 return false;
987 }
988
989 void ObjectSynchronizer::request_deflate_idle_monitors() {
990 MonitorLocker ml(MonitorDeflation_lock, Mutex::_no_safepoint_check_flag);
991 set_is_async_deflation_requested(true);
992 ml.notify_all();
993 }
994
995 bool ObjectSynchronizer::request_deflate_idle_monitors_from_wb() {
996 JavaThread* current = JavaThread::current();
997 bool ret_code = false;
998
999 jlong last_time = last_async_deflation_time_ns();
1000
1001 request_deflate_idle_monitors();
1002
1003 const int N_CHECKS = 5;
1004 for (int i = 0; i < N_CHECKS; i++) { // sleep for at most 5 seconds
1005 if (last_async_deflation_time_ns() > last_time) {
1006 log_info(monitorinflation)("Async Deflation happened after %d check(s).", i);
1007 ret_code = true;
1008 break;
1009 }
1010 {
1011 // JavaThread has to honor the blocking protocol.
1012 ThreadBlockInVM tbivm(current);
1013 os::naked_short_sleep(999); // sleep for almost 1 second
1014 }
1015 }
1016 if (!ret_code) {
1017 log_info(monitorinflation)("Async Deflation DID NOT happen after %d checks.", N_CHECKS);
1018 }
1019
1020 return ret_code;
1021 }
1022
1023 jlong ObjectSynchronizer::time_since_last_async_deflation_ms() {
1024 return (os::javaTimeNanos() - last_async_deflation_time_ns()) / (NANOUNITS / MILLIUNITS);
1025 }
1026
1027 // Walk the in-use list and deflate (at most MonitorDeflationMax) idle
1028 // ObjectMonitors. Returns the number of deflated ObjectMonitors.
1029 //
1030 size_t ObjectSynchronizer::deflate_monitor_list(ObjectMonitorDeflationSafepointer* safepointer) {
1031 MonitorList::Iterator iter = _in_use_list.iterator();
1032 size_t deflated_count = 0;
1033 Thread* current = Thread::current();
1034
1035 while (iter.has_next()) {
1036 if (deflated_count >= (size_t)MonitorDeflationMax) {
1037 break;
1038 }
1039 ObjectMonitor* mid = iter.next();
1040 if (mid->deflate_monitor(current)) {
1041 deflated_count++;
1042 }
1043
1044 // Must check for a safepoint/handshake and honor it.
1045 safepointer->block_for_safepoint("deflation", "deflated_count", deflated_count);
1046 }
1047
1048 return deflated_count;
1049 }
1050
1051 class DeflationHandshakeClosure : public HandshakeClosure {
1052 public:
1053 DeflationHandshakeClosure() : HandshakeClosure("DeflationHandshakeClosure") {}
1054
1055 void do_thread(Thread* thread) {
1056 log_trace(monitorinflation)("DeflationHandshakeClosure::do_thread: thread="
1057 INTPTR_FORMAT, p2i(thread));
1058 if (thread->is_Java_thread()) {
1059 // Clear OM cache
1060 JavaThread* jt = JavaThread::cast(thread);
1061 jt->om_clear_monitor_cache();
1062 }
1063 }
1064 };
1065
1066 class VM_RendezvousGCThreads : public VM_Operation {
1067 public:
1068 bool evaluate_at_safepoint() const override { return false; }
1069 VMOp_Type type() const override { return VMOp_RendezvousGCThreads; }
1070 void doit() override {
1071 Universe::heap()->safepoint_synchronize_begin();
1072 Universe::heap()->safepoint_synchronize_end();
1073 };
1074 };
1075
1076 static size_t delete_monitors(GrowableArray<ObjectMonitor*>* delete_list,
1077 ObjectMonitorDeflationSafepointer* safepointer) {
1078 NativeHeapTrimmer::SuspendMark sm("monitor deletion");
1079 size_t deleted_count = 0;
1080 for (ObjectMonitor* monitor: *delete_list) {
1081 delete monitor;
1082 deleted_count++;
1083 // A JavaThread must check for a safepoint/handshake and honor it.
1084 safepointer->block_for_safepoint("deletion", "deleted_count", deleted_count);
1085 }
1086 return deleted_count;
1087 }
1088
1089 class ObjectMonitorDeflationLogging: public StackObj {
1090 LogStreamHandle(Debug, monitorinflation) _debug;
1091 LogStreamHandle(Info, monitorinflation) _info;
1092 LogStream* _stream;
1093 elapsedTimer _timer;
1094
1095 size_t ceiling() const { return ObjectSynchronizer::in_use_list_ceiling(); }
1096 size_t count() const { return ObjectSynchronizer::in_use_list_count(); }
1097 size_t max() const { return ObjectSynchronizer::in_use_list_max(); }
1098
1099 public:
1100 ObjectMonitorDeflationLogging()
1101 : _debug(), _info(), _stream(nullptr) {
1102 if (_debug.is_enabled()) {
1103 _stream = &_debug;
1104 } else if (_info.is_enabled()) {
1105 _stream = &_info;
1106 }
1107 }
1108
1109 void begin() {
1110 if (_stream != nullptr) {
1111 _stream->print_cr("begin deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1112 ceiling(), count(), max());
1113 _timer.start();
1114 }
1115 }
1116
1117 void before_handshake(size_t unlinked_count) {
1118 if (_stream != nullptr) {
1119 _timer.stop();
1120 _stream->print_cr("before handshaking: unlinked_count=%zu"
1121 ", in_use_list stats: ceiling=%zu, count="
1122 "%zu, max=%zu",
1123 unlinked_count, ceiling(), count(), max());
1124 }
1125 }
1126
1127 void after_handshake() {
1128 if (_stream != nullptr) {
1129 _stream->print_cr("after handshaking: in_use_list stats: ceiling="
1130 "%zu, count=%zu, max=%zu",
1131 ceiling(), count(), max());
1132 _timer.start();
1133 }
1134 }
1135
1136 void end(size_t deflated_count, size_t unlinked_count) {
1137 if (_stream != nullptr) {
1138 _timer.stop();
1139 if (deflated_count != 0 || unlinked_count != 0 || _debug.is_enabled()) {
1140 _stream->print_cr("deflated_count=%zu, {unlinked,deleted}_count=%zu monitors in %3.7f secs",
1141 deflated_count, unlinked_count, _timer.seconds());
1142 }
1143 _stream->print_cr("end deflating: in_use_list stats: ceiling=%zu, count=%zu, max=%zu",
1144 ceiling(), count(), max());
1145 }
1146 }
1147
1148 void before_block_for_safepoint(const char* op_name, const char* cnt_name, size_t cnt) {
1149 if (_stream != nullptr) {
1150 _timer.stop();
1151 _stream->print_cr("pausing %s: %s=%zu, in_use_list stats: ceiling="
1152 "%zu, count=%zu, max=%zu",
1153 op_name, cnt_name, cnt, ceiling(), count(), max());
1154 }
1155 }
1156
1157 void after_block_for_safepoint(const char* op_name) {
1158 if (_stream != nullptr) {
1159 _stream->print_cr("resuming %s: in_use_list stats: ceiling=%zu"
1160 ", count=%zu, max=%zu", op_name,
1161 ceiling(), count(), max());
1162 _timer.start();
1163 }
1164 }
1165 };
1166
1167 void ObjectMonitorDeflationSafepointer::block_for_safepoint(const char* op_name, const char* count_name, size_t counter) {
1168 if (!SafepointMechanism::should_process(_current)) {
1169 return;
1170 }
1171
1172 // A safepoint/handshake has started.
1173 _log->before_block_for_safepoint(op_name, count_name, counter);
1174
1175 {
1176 // Honor block request.
1177 ThreadBlockInVM tbivm(_current);
1178 }
1179
1180 _log->after_block_for_safepoint(op_name);
1181 }
1182
1183 // This function is called by the MonitorDeflationThread to deflate
1184 // ObjectMonitors.
1185 size_t ObjectSynchronizer::deflate_idle_monitors() {
1186 JavaThread* current = JavaThread::current();
1187 assert(current->is_monitor_deflation_thread(), "The only monitor deflater");
1188
1189 // The async deflation request has been processed.
1190 _last_async_deflation_time_ns = os::javaTimeNanos();
1191 set_is_async_deflation_requested(false);
1192
1193 ObjectMonitorDeflationLogging log;
1194 ObjectMonitorDeflationSafepointer safepointer(current, &log);
1195
1196 log.begin();
1197
1198 // Deflate some idle ObjectMonitors.
1199 size_t deflated_count = deflate_monitor_list(&safepointer);
1200
1201 // Unlink the deflated ObjectMonitors from the in-use list.
1202 size_t unlinked_count = 0;
1203 size_t deleted_count = 0;
1204 if (deflated_count > 0) {
1205 ResourceMark rm(current);
1206 GrowableArray<ObjectMonitor*> delete_list((int)deflated_count);
1207 unlinked_count = _in_use_list.unlink_deflated(deflated_count, &delete_list, &safepointer);
1208
1209 #ifdef ASSERT
1210 if (UseObjectMonitorTable) {
1211 for (ObjectMonitor* monitor : delete_list) {
1212 assert(!LightweightSynchronizer::contains_monitor(current, monitor), "Should have been removed");
1213 }
1214 }
1215 #endif
1216
1217 log.before_handshake(unlinked_count);
1218
1219 // A JavaThread needs to handshake in order to safely free the
1220 // ObjectMonitors that were deflated in this cycle.
1221 DeflationHandshakeClosure dhc;
1222 Handshake::execute(&dhc);
1223 // Also, we sync and desync GC threads around the handshake, so that they can
1224 // safely read the mark-word and look-through to the object-monitor, without
1225 // being afraid that the object-monitor is going away.
1226 VM_RendezvousGCThreads sync_gc;
1227 VMThread::execute(&sync_gc);
1228
1229 log.after_handshake();
1230
1231 // After the handshake, safely free the ObjectMonitors that were
1232 // deflated and unlinked in this cycle.
1233
1234 // Delete the unlinked ObjectMonitors.
1235 deleted_count = delete_monitors(&delete_list, &safepointer);
1236 assert(unlinked_count == deleted_count, "must be");
1237 }
1238
1239 log.end(deflated_count, unlinked_count);
1240
1241 GVars.stw_random = os::random();
1242
1243 if (deflated_count != 0) {
1244 _no_progress_cnt = 0;
1245 } else if (_no_progress_skip_increment) {
1246 _no_progress_skip_increment = false;
1247 } else {
1248 _no_progress_cnt++;
1249 }
1250
1251 return deflated_count;
1252 }
1253
1254 // Monitor cleanup on JavaThread::exit
1255
1256 // Iterate through monitor cache and attempt to release thread's monitors
1257 class ReleaseJavaMonitorsClosure: public MonitorClosure {
1258 private:
1259 JavaThread* _thread;
1260
1261 public:
1262 ReleaseJavaMonitorsClosure(JavaThread* thread) : _thread(thread) {}
1263 void do_monitor(ObjectMonitor* mid) {
1264 mid->complete_exit(_thread);
1265 }
1266 };
1267
1268 // Release all inflated monitors owned by current thread. Lightweight monitors are
1269 // ignored. This is meant to be called during JNI thread detach which assumes
1270 // all remaining monitors are heavyweight. All exceptions are swallowed.
1271 // Scanning the extant monitor list can be time consuming.
1272 // A simple optimization is to add a per-thread flag that indicates a thread
1273 // called jni_monitorenter() during its lifetime.
1274 //
1275 // Instead of NoSafepointVerifier it might be cheaper to
1276 // use an idiom of the form:
1277 // auto int tmp = SafepointSynchronize::_safepoint_counter ;
1278 // <code that must not run at safepoint>
1279 // guarantee (((tmp ^ _safepoint_counter) | (tmp & 1)) == 0) ;
1280 // Since the tests are extremely cheap we could leave them enabled
1281 // for normal product builds.
1282
1283 void ObjectSynchronizer::release_monitors_owned_by_thread(JavaThread* current) {
1284 assert(current == JavaThread::current(), "must be current Java thread");
1285 NoSafepointVerifier nsv;
1286 ReleaseJavaMonitorsClosure rjmc(current);
1287 ObjectSynchronizer::owned_monitors_iterate(&rjmc, current);
1288 assert(!current->has_pending_exception(), "Should not be possible");
1289 current->clear_pending_exception();
1290 }
1291
1292 const char* ObjectSynchronizer::inflate_cause_name(const InflateCause cause) {
1293 switch (cause) {
1294 case inflate_cause_vm_internal: return "VM Internal";
1295 case inflate_cause_monitor_enter: return "Monitor Enter";
1296 case inflate_cause_wait: return "Monitor Wait";
1297 case inflate_cause_notify: return "Monitor Notify";
1298 case inflate_cause_jni_enter: return "JNI Monitor Enter";
1299 case inflate_cause_jni_exit: return "JNI Monitor Exit";
1300 default:
1301 ShouldNotReachHere();
1302 }
1303 return "Unknown";
1304 }
1305
1306 //------------------------------------------------------------------------------
1307 // Debugging code
1308
1309 u_char* ObjectSynchronizer::get_gvars_addr() {
1310 return (u_char*)&GVars;
1311 }
1312
1313 u_char* ObjectSynchronizer::get_gvars_hc_sequence_addr() {
1314 return (u_char*)&GVars.hc_sequence;
1315 }
1316
1317 size_t ObjectSynchronizer::get_gvars_size() {
1318 return sizeof(SharedGlobals);
1319 }
1320
1321 u_char* ObjectSynchronizer::get_gvars_stw_random_addr() {
1322 return (u_char*)&GVars.stw_random;
1323 }
1324
1325 // Do the final audit and print of ObjectMonitor stats; must be done
1326 // by the VMThread at VM exit time.
1327 void ObjectSynchronizer::do_final_audit_and_print_stats() {
1328 assert(Thread::current()->is_VM_thread(), "sanity check");
1329
1330 if (is_final_audit()) { // Only do the audit once.
1331 return;
1332 }
1333 set_is_final_audit();
1334 log_info(monitorinflation)("Starting the final audit.");
1335
1336 if (log_is_enabled(Info, monitorinflation)) {
1337 LogStreamHandle(Info, monitorinflation) ls;
1338 audit_and_print_stats(&ls, true /* on_exit */);
1339 }
1340 }
1341
1342 // This function can be called by the MonitorDeflationThread or it can be called when
1343 // we are trying to exit the VM. The list walker functions can run in parallel with
1344 // the other list operations.
1345 // Calls to this function can be added in various places as a debugging
1346 // aid.
1347 //
1348 void ObjectSynchronizer::audit_and_print_stats(outputStream* ls, bool on_exit) {
1349 int error_cnt = 0;
1350
1351 ls->print_cr("Checking in_use_list:");
1352 chk_in_use_list(ls, &error_cnt);
1353
1354 if (error_cnt == 0) {
1355 ls->print_cr("No errors found in in_use_list checks.");
1356 } else {
1357 log_error(monitorinflation)("found in_use_list errors: error_cnt=%d", error_cnt);
1358 }
1359
1360 // When exiting, only log the interesting entries at the Info level.
1361 // When called at intervals by the MonitorDeflationThread, log output
1362 // at the Trace level since there can be a lot of it.
1363 if (!on_exit && log_is_enabled(Trace, monitorinflation)) {
1364 LogStreamHandle(Trace, monitorinflation) ls_tr;
1365 log_in_use_monitor_details(&ls_tr, true /* log_all */);
1366 } else if (on_exit) {
1367 log_in_use_monitor_details(ls, false /* log_all */);
1368 }
1369
1370 ls->flush();
1371
1372 guarantee(error_cnt == 0, "ERROR: found monitor list errors: error_cnt=%d", error_cnt);
1373 }
1374
1375 // Check the in_use_list; log the results of the checks.
1376 void ObjectSynchronizer::chk_in_use_list(outputStream* out, int *error_cnt_p) {
1377 size_t l_in_use_count = _in_use_list.count();
1378 size_t l_in_use_max = _in_use_list.max();
1379 out->print_cr("count=%zu, max=%zu", l_in_use_count,
1380 l_in_use_max);
1381
1382 size_t ck_in_use_count = 0;
1383 MonitorList::Iterator iter = _in_use_list.iterator();
1384 while (iter.has_next()) {
1385 ObjectMonitor* mid = iter.next();
1386 chk_in_use_entry(mid, out, error_cnt_p);
1387 ck_in_use_count++;
1388 }
1389
1390 if (l_in_use_count == ck_in_use_count) {
1391 out->print_cr("in_use_count=%zu equals ck_in_use_count=%zu",
1392 l_in_use_count, ck_in_use_count);
1393 } else {
1394 out->print_cr("WARNING: in_use_count=%zu is not equal to "
1395 "ck_in_use_count=%zu", l_in_use_count,
1396 ck_in_use_count);
1397 }
1398
1399 size_t ck_in_use_max = _in_use_list.max();
1400 if (l_in_use_max == ck_in_use_max) {
1401 out->print_cr("in_use_max=%zu equals ck_in_use_max=%zu",
1402 l_in_use_max, ck_in_use_max);
1403 } else {
1404 out->print_cr("WARNING: in_use_max=%zu is not equal to "
1405 "ck_in_use_max=%zu", l_in_use_max, ck_in_use_max);
1406 }
1407 }
1408
1409 // Check an in-use monitor entry; log any errors.
1410 void ObjectSynchronizer::chk_in_use_entry(ObjectMonitor* n, outputStream* out,
1411 int* error_cnt_p) {
1412 if (n->owner_is_DEFLATER_MARKER()) {
1413 // This could happen when monitor deflation blocks for a safepoint.
1414 return;
1415 }
1416
1417
1418 if (n->metadata() == 0) {
1419 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor must "
1420 "have non-null _metadata (header/hash) field.", p2i(n));
1421 *error_cnt_p = *error_cnt_p + 1;
1422 }
1423
1424 const oop obj = n->object_peek();
1425 if (obj == nullptr) {
1426 return;
1427 }
1428
1429 const markWord mark = obj->mark();
1430 if (!mark.has_monitor()) {
1431 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1432 "object does not think it has a monitor: obj="
1433 INTPTR_FORMAT ", mark=" INTPTR_FORMAT, p2i(n),
1434 p2i(obj), mark.value());
1435 *error_cnt_p = *error_cnt_p + 1;
1436 return;
1437 }
1438
1439 ObjectMonitor* const obj_mon = read_monitor(Thread::current(), obj, mark);
1440 if (n != obj_mon) {
1441 out->print_cr("ERROR: monitor=" INTPTR_FORMAT ": in-use monitor's "
1442 "object does not refer to the same monitor: obj="
1443 INTPTR_FORMAT ", mark=" INTPTR_FORMAT ", obj_mon="
1444 INTPTR_FORMAT, p2i(n), p2i(obj), mark.value(), p2i(obj_mon));
1445 *error_cnt_p = *error_cnt_p + 1;
1446 }
1447 }
1448
1449 // Log details about ObjectMonitors on the in_use_list. The 'BHL'
1450 // flags indicate why the entry is in-use, 'object' and 'object type'
1451 // indicate the associated object and its type.
1452 void ObjectSynchronizer::log_in_use_monitor_details(outputStream* out, bool log_all) {
1453 if (_in_use_list.count() > 0) {
1454 stringStream ss;
1455 out->print_cr("In-use monitor info%s:", log_all ? "" : " (eliding idle monitors)");
1456 out->print_cr("(B -> is_busy, H -> has hash code, L -> lock status)");
1457 out->print_cr("%18s %s %18s %18s",
1458 "monitor", "BHL", "object", "object type");
1459 out->print_cr("================== === ================== ==================");
1460
1461 auto is_interesting = [&](ObjectMonitor* monitor) {
1462 return log_all || monitor->has_owner() || monitor->is_busy();
1463 };
1464
1465 monitors_iterate([&](ObjectMonitor* monitor) {
1466 if (is_interesting(monitor)) {
1467 const oop obj = monitor->object_peek();
1468 const intptr_t hash = UseObjectMonitorTable ? monitor->hash() : monitor->header().hash();
1469 ResourceMark rm;
1470 out->print(INTPTR_FORMAT " %d%d%d " INTPTR_FORMAT " %s", p2i(monitor),
1471 monitor->is_busy(), hash != 0, monitor->has_owner(),
1472 p2i(obj), obj == nullptr ? "" : obj->klass()->external_name());
1473 if (monitor->is_busy()) {
1474 out->print(" (%s)", monitor->is_busy_to_string(&ss));
1475 ss.reset();
1476 }
1477 out->cr();
1478 }
1479 });
1480 }
1481
1482 out->flush();
1483 }