1 /*
2 * Copyright (c) 1997, 2023, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "classfile/classLoaderDataGraph.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/symbolTable.hpp"
29 #include "code/codeCache.hpp"
30 #include "code/icBuffer.hpp"
31 #include "code/nmethod.hpp"
32 #include "code/pcDesc.hpp"
33 #include "code/scopeDesc.hpp"
34 #include "compiler/compilationPolicy.hpp"
35 #include "gc/shared/collectedHeap.hpp"
36 #include "gc/shared/gcLocker.hpp"
37 #include "gc/shared/oopStorage.hpp"
38 #include "gc/shared/strongRootsScope.hpp"
39 #include "gc/shared/workerThread.hpp"
40 #include "gc/shared/workerUtils.hpp"
41 #include "interpreter/interpreter.hpp"
42 #include "jfr/jfrEvents.hpp"
43 #include "logging/log.hpp"
44 #include "logging/logStream.hpp"
45 #include "memory/resourceArea.hpp"
46 #include "memory/universe.hpp"
47 #include "oops/oop.inline.hpp"
48 #include "oops/symbol.hpp"
49 #include "runtime/atomic.hpp"
50 #include "runtime/deoptimization.hpp"
51 #include "runtime/frame.inline.hpp"
52 #include "runtime/globals.hpp"
53 #include "runtime/handles.inline.hpp"
54 #include "runtime/interfaceSupport.inline.hpp"
55 #include "runtime/javaThread.inline.hpp"
56 #include "runtime/mutexLocker.hpp"
57 #include "runtime/orderAccess.hpp"
58 #include "runtime/osThread.hpp"
59 #include "runtime/safepoint.hpp"
60 #include "runtime/safepointMechanism.inline.hpp"
61 #include "runtime/signature.hpp"
62 #include "runtime/stackWatermarkSet.inline.hpp"
63 #include "runtime/stubCodeGenerator.hpp"
64 #include "runtime/stubRoutines.hpp"
65 #include "runtime/synchronizer.hpp"
66 #include "runtime/threads.hpp"
67 #include "runtime/threadSMR.hpp"
68 #include "runtime/threadWXSetters.inline.hpp"
69 #include "runtime/timerTrace.hpp"
70 #include "services/runtimeService.hpp"
71 #include "utilities/events.hpp"
72 #include "utilities/macros.hpp"
73 #include "utilities/systemMemoryBarrier.hpp"
74
75 static void post_safepoint_begin_event(EventSafepointBegin& event,
76 uint64_t safepoint_id,
77 int thread_count,
78 int critical_thread_count) {
79 if (event.should_commit()) {
80 event.set_safepointId(safepoint_id);
81 event.set_totalThreadCount(thread_count);
82 event.set_jniCriticalThreadCount(critical_thread_count);
83 event.commit();
84 }
85 }
86
87 static void post_safepoint_cleanup_event(EventSafepointCleanup& event, uint64_t safepoint_id) {
88 if (event.should_commit()) {
89 event.set_safepointId(safepoint_id);
90 event.commit();
91 }
92 }
93
94 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization& event,
95 uint64_t safepoint_id,
96 int initial_number_of_threads,
97 int threads_waiting_to_block,
98 int iterations) {
99 if (event.should_commit()) {
100 event.set_safepointId(safepoint_id);
101 event.set_initialThreadCount(initial_number_of_threads);
102 event.set_runningThreadCount(threads_waiting_to_block);
103 event.set_iterations(checked_cast<u4>(iterations));
104 event.commit();
105 }
106 }
107
108 static void post_safepoint_cleanup_task_event(EventSafepointCleanupTask& event,
109 uint64_t safepoint_id,
110 const char* name) {
111 if (event.should_commit()) {
112 event.set_safepointId(safepoint_id);
113 event.set_name(name);
114 event.commit();
115 }
116 }
117
118 static void post_safepoint_end_event(EventSafepointEnd& event, uint64_t safepoint_id) {
119 if (event.should_commit()) {
120 event.set_safepointId(safepoint_id);
121 event.commit();
122 }
123 }
124
125 // SafepointCheck
126 SafepointStateTracker::SafepointStateTracker(uint64_t safepoint_id, bool at_safepoint)
127 : _safepoint_id(safepoint_id), _at_safepoint(at_safepoint) {}
128
129 bool SafepointStateTracker::safepoint_state_changed() {
130 return _safepoint_id != SafepointSynchronize::safepoint_id() ||
131 _at_safepoint != SafepointSynchronize::is_at_safepoint();
132 }
133
134 // --------------------------------------------------------------------------------------------------
135 // Implementation of Safepoint begin/end
136
137 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
138 int SafepointSynchronize::_waiting_to_block = 0;
139 volatile uint64_t SafepointSynchronize::_safepoint_counter = 0;
140 uint64_t SafepointSynchronize::_safepoint_id = 0;
141 const uint64_t SafepointSynchronize::InactiveSafepointCounter = 0;
142 int SafepointSynchronize::_current_jni_active_count = 0;
143
144 WaitBarrier* SafepointSynchronize::_wait_barrier;
145
146 static bool timeout_error_printed = false;
147
148 // Statistic related
149 static jlong _safepoint_begin_time = 0;
150 static volatile int _nof_threads_hit_polling_page = 0;
151
152 void SafepointSynchronize::init(Thread* vmthread) {
153 // WaitBarrier should never be destroyed since we will have
154 // threads waiting on it while exiting.
155 _wait_barrier = new WaitBarrier(vmthread);
156 SafepointTracing::init();
157 }
158
159 void SafepointSynchronize::increment_jni_active_count() {
160 assert(Thread::current()->is_VM_thread(), "Only VM thread may increment");
161 ++_current_jni_active_count;
162 }
163
164 void SafepointSynchronize::decrement_waiting_to_block() {
165 assert(_waiting_to_block > 0, "sanity check");
166 assert(Thread::current()->is_VM_thread(), "Only VM thread may decrement");
167 --_waiting_to_block;
168 }
169
170 bool SafepointSynchronize::thread_not_running(ThreadSafepointState *cur_state) {
171 if (!cur_state->is_running()) {
172 // Robustness: asserted in the caller, but handle/tolerate it for release bits.
173 LogTarget(Error, safepoint) lt;
174 if (lt.is_enabled()) {
175 ResourceMark rm;
176 LogStream ls(lt);
177 ls.print("Illegal initial state detected: ");
178 cur_state->print_on(&ls);
179 }
180 return true;
181 }
182 cur_state->examine_state_of_thread(SafepointSynchronize::safepoint_counter());
183 if (!cur_state->is_running()) {
184 return true;
185 }
186 LogTarget(Trace, safepoint) lt;
187 if (lt.is_enabled()) {
188 ResourceMark rm;
189 LogStream ls(lt);
190 cur_state->print_on(&ls);
191 }
192 return false;
193 }
194
195 #ifdef ASSERT
196 static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) {
197 int a = 0;
198 const ThreadSafepointState *tmp_tss = tss_head;
199 while (tmp_tss != nullptr) {
200 ++a;
201 assert(tmp_tss->is_running(), "Illegal initial state");
202 tmp_tss = tmp_tss->get_next();
203 }
204 assert(a == still_running, "Must be the same");
205 }
206 #endif // ASSERT
207
208 static void back_off(int64_t start_time) {
209 // We start with fine-grained nanosleeping until a millisecond has
210 // passed, at which point we resort to plain naked_short_sleep.
211 if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) {
212 os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
213 } else {
214 os::naked_short_sleep(1);
215 }
216 }
217
218 int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running)
219 {
220 JavaThreadIteratorWithHandle jtiwh;
221
222 #ifdef ASSERT
223 for (; JavaThread *cur = jtiwh.next(); ) {
224 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
225 }
226 jtiwh.rewind();
227 #endif // ASSERT
228
229 // Iterate through all threads until it has been determined how to stop them all at a safepoint.
230 int still_running = nof_threads;
231 ThreadSafepointState *tss_head = nullptr;
232 ThreadSafepointState **p_prev = &tss_head;
233 for (; JavaThread *cur = jtiwh.next(); ) {
234 ThreadSafepointState *cur_tss = cur->safepoint_state();
235 assert(cur_tss->get_next() == nullptr, "Must be null");
236 if (thread_not_running(cur_tss)) {
237 --still_running;
238 } else {
239 *p_prev = cur_tss;
240 p_prev = cur_tss->next_ptr();
241 }
242 }
243 *p_prev = nullptr;
244
245 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
246
247 *initial_running = still_running;
248
249 // If there is no thread still running, we are already done.
250 if (still_running <= 0) {
251 assert(tss_head == nullptr, "Must be empty");
252 return 1;
253 }
254
255 int iterations = 1; // The first iteration is above.
256 int64_t start_time = os::javaTimeNanos();
257
258 do {
259 // Check if this has taken too long:
260 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
261 print_safepoint_timeout();
262 }
263
264 p_prev = &tss_head;
265 ThreadSafepointState *cur_tss = tss_head;
266 while (cur_tss != nullptr) {
267 assert(cur_tss->is_running(), "Illegal initial state");
268 if (thread_not_running(cur_tss)) {
269 --still_running;
270 *p_prev = nullptr;
271 ThreadSafepointState *tmp = cur_tss;
272 cur_tss = cur_tss->get_next();
273 tmp->set_next(nullptr);
274 } else {
275 *p_prev = cur_tss;
276 p_prev = cur_tss->next_ptr();
277 cur_tss = cur_tss->get_next();
278 }
279 }
280
281 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
282
283 if (still_running > 0) {
284 back_off(start_time);
285 }
286
287 iterations++;
288 } while (still_running > 0);
289
290 assert(tss_head == nullptr, "Must be empty");
291
292 return iterations;
293 }
294
295 void SafepointSynchronize::arm_safepoint() {
296 // Begin the process of bringing the system to a safepoint.
297 // Java threads can be in several different states and are
298 // stopped by different mechanisms:
299 //
300 // 1. Running interpreted
301 // When executing branching/returning byte codes interpreter
302 // checks if the poll is armed, if so blocks in SS::block().
303 // 2. Running in native code
304 // When returning from the native code, a Java thread must check
305 // the safepoint _state to see if we must block. If the
306 // VM thread sees a Java thread in native, it does
307 // not wait for this thread to block. The order of the memory
308 // writes and reads of both the safepoint state and the Java
309 // threads state is critical. In order to guarantee that the
310 // memory writes are serialized with respect to each other,
311 // the VM thread issues a memory barrier instruction.
312 // 3. Running compiled Code
313 // Compiled code reads the local polling page that
314 // is set to fault if we are trying to get to a safepoint.
315 // 4. Blocked
316 // A thread which is blocked will not be allowed to return from the
317 // block condition until the safepoint operation is complete.
318 // 5. In VM or Transitioning between states
319 // If a Java thread is currently running in the VM or transitioning
320 // between states, the safepointing code will poll the thread state
321 // until the thread blocks itself when it attempts transitions to a
322 // new state or locking a safepoint checked monitor.
323
324 // We must never miss a thread with correct safepoint id, so we must make sure we arm
325 // the wait barrier for the next safepoint id/counter.
326 // Arming must be done after resetting _current_jni_active_count, _waiting_to_block.
327 _wait_barrier->arm(static_cast<int>(_safepoint_counter + 1));
328
329 assert((_safepoint_counter & 0x1) == 0, "must be even");
330 // The store to _safepoint_counter must happen after any stores in arming.
331 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
332
333 // We are synchronizing
334 OrderAccess::storestore(); // Ordered with _safepoint_counter
335 _state = _synchronizing;
336
337 // Arming the per thread poll while having _state != _not_synchronized means safepointing
338 log_trace(safepoint)("Setting thread local yield flag for threads");
339 OrderAccess::storestore(); // storestore, global state -> local state
340 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
341 // Make sure the threads start polling, it is time to yield.
342 SafepointMechanism::arm_local_poll(cur);
343 }
344 if (UseSystemMemoryBarrier) {
345 SystemMemoryBarrier::emit(); // storestore|storeload, global state -> local state
346 } else {
347 OrderAccess::fence(); // storestore|storeload, global state -> local state
348 }
349 }
350
351 // Roll all threads forward to a safepoint and suspend them all
352 void SafepointSynchronize::begin() {
353 assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint");
354
355 EventSafepointBegin begin_event;
356 SafepointTracing::begin(VMThread::vm_op_type());
357
358 Universe::heap()->safepoint_synchronize_begin();
359
360 // By getting the Threads_lock, we assure that no threads are about to start or
361 // exit. It is released again in SafepointSynchronize::end().
362 Threads_lock->lock();
363
364 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
365
366 int nof_threads = Threads::number_of_threads();
367
368 _nof_threads_hit_polling_page = 0;
369
370 log_debug(safepoint)("Safepoint synchronization initiated using %s wait barrier. (%d threads)", _wait_barrier->description(), nof_threads);
371
372 // Reset the count of active JNI critical threads
373 _current_jni_active_count = 0;
374
375 // Set number of threads to wait for
376 _waiting_to_block = nof_threads;
377
378 jlong safepoint_limit_time = 0;
379 if (SafepointTimeout) {
380 // Set the limit time, so that it can be compared to see if this has taken
381 // too long to complete.
382 safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)(SafepointTimeoutDelay * NANOSECS_PER_MILLISEC);
383 timeout_error_printed = false;
384 }
385
386 EventSafepointStateSynchronization sync_event;
387 int initial_running = 0;
388
389 // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before.
390 arm_safepoint();
391
392 // Will spin until all threads are safe.
393 int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running);
394 assert(_waiting_to_block == 0, "No thread should be running");
395
396 #ifndef PRODUCT
397 // Mark all threads
398 if (VerifyCrossModifyFence) {
399 JavaThreadIteratorWithHandle jtiwh;
400 for (; JavaThread *cur = jtiwh.next(); ) {
401 cur->set_requires_cross_modify_fence(true);
402 }
403 }
404
405 if (safepoint_limit_time != 0) {
406 jlong current_time = os::javaTimeNanos();
407 if (safepoint_limit_time < current_time) {
408 log_warning(safepoint)("# SafepointSynchronize: Finished after "
409 INT64_FORMAT_W(6) " ms",
410 (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS));
411 }
412 }
413 #endif
414
415 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
416
417 // Record state
418 _state = _synchronized;
419
420 OrderAccess::fence();
421
422 // Set the new id
423 ++_safepoint_id;
424
425 #ifdef ASSERT
426 // Make sure all the threads were visited.
427 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
428 assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread");
429 }
430 #endif // ASSERT
431
432 // Update the count of active JNI critical regions
433 GCLocker::set_jni_lock_count(_current_jni_active_count);
434
435 post_safepoint_synchronize_event(sync_event,
436 _safepoint_id,
437 initial_running,
438 _waiting_to_block, iterations);
439
440 SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page);
441
442 // We do the safepoint cleanup first since a GC related safepoint
443 // needs cleanup to be completed before running the GC op.
444 EventSafepointCleanup cleanup_event;
445 do_cleanup_tasks();
446 post_safepoint_cleanup_event(cleanup_event, _safepoint_id);
447
448 post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count);
449 SafepointTracing::cleanup();
450 }
451
452 void SafepointSynchronize::disarm_safepoint() {
453 uint64_t active_safepoint_counter = _safepoint_counter;
454 {
455 JavaThreadIteratorWithHandle jtiwh;
456 #ifdef ASSERT
457 // A pending_exception cannot be installed during a safepoint. The threads
458 // may install an async exception after they come back from a safepoint into
459 // pending_exception after they unblock. But that should happen later.
460 for (; JavaThread *cur = jtiwh.next(); ) {
461 assert (!(cur->has_pending_exception() &&
462 cur->safepoint_state()->is_at_poll_safepoint()),
463 "safepoint installed a pending exception");
464 }
465 #endif // ASSERT
466
467 OrderAccess::fence(); // keep read and write of _state from floating up
468 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
469
470 // Change state first to _not_synchronized.
471 // No threads should see _synchronized when running.
472 _state = _not_synchronized;
473
474 // Set the next dormant (even) safepoint id.
475 assert((_safepoint_counter & 0x1) == 1, "must be odd");
476 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
477
478 OrderAccess::fence(); // Keep the local state from floating up.
479
480 jtiwh.rewind();
481 for (; JavaThread *current = jtiwh.next(); ) {
482 // Clear the visited flag to ensure that the critical counts are collected properly.
483 DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);)
484 ThreadSafepointState* cur_state = current->safepoint_state();
485 assert(!cur_state->is_running(), "Thread not suspended at safepoint");
486 cur_state->restart(); // TSS _running
487 assert(cur_state->is_running(), "safepoint state has not been reset");
488 }
489 } // ~JavaThreadIteratorWithHandle
490
491 // Release threads lock, so threads can be created/destroyed again.
492 Threads_lock->unlock();
493
494 // Wake threads after local state is correctly set.
495 _wait_barrier->disarm();
496 }
497
498 // Wake up all threads, so they are ready to resume execution after the safepoint
499 // operation has been carried out
500 void SafepointSynchronize::end() {
501 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
502 EventSafepointEnd event;
503 assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint");
504
505 disarm_safepoint();
506
507 Universe::heap()->safepoint_synchronize_end();
508
509 SafepointTracing::end();
510
511 post_safepoint_end_event(event, safepoint_id());
512 }
513
514 bool SafepointSynchronize::is_cleanup_needed() {
515 // Need a safepoint if some inline cache buffers is non-empty
516 if (!InlineCacheBuffer::is_empty()) return true;
517 if (StringTable::needs_rehashing()) return true;
518 if (SymbolTable::needs_rehashing()) return true;
519 return false;
520 }
521
522 class ParallelCleanupTask : public WorkerTask {
523 private:
524 SubTasksDone _subtasks;
525 bool _do_lazy_roots;
526
527 class Tracer {
528 private:
529 const char* _name;
530 EventSafepointCleanupTask _event;
531 TraceTime _timer;
532
533 public:
534 Tracer(const char* name) :
535 _name(name),
536 _event(),
537 _timer(name, TRACETIME_LOG(Info, safepoint, cleanup)) {}
538 ~Tracer() {
539 post_safepoint_cleanup_task_event(_event, SafepointSynchronize::safepoint_id(), _name);
540 }
541 };
542
543 public:
544 ParallelCleanupTask() :
545 WorkerTask("Parallel Safepoint Cleanup"),
546 _subtasks(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS),
547 _do_lazy_roots(!VMThread::vm_operation()->skip_thread_oop_barriers() &&
548 Universe::heap()->uses_stack_watermark_barrier()) {}
549
550 uint expected_num_workers() const {
551 uint workers = 0;
552
553 if (SymbolTable::rehash_table_expects_safepoint_rehashing()) {
554 workers++;
555 }
556
557 if (StringTable::rehash_table_expects_safepoint_rehashing()) {
558 workers++;
559 }
560
561 if (InlineCacheBuffer::needs_update_inline_caches()) {
562 workers++;
563 }
564
565 if (_do_lazy_roots) {
566 workers++;
567 }
568
569 return MAX2<uint>(1, workers);
570 }
571
572 void work(uint worker_id) {
573 // These tasks are ordered by relative length of time to execute so that potentially longer tasks start first.
574 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
575 if (SymbolTable::needs_rehashing()) {
576 Tracer t("rehashing symbol table");
577 SymbolTable::rehash_table();
578 }
579 }
580
581 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
582 if (StringTable::needs_rehashing()) {
583 Tracer t("rehashing string table");
584 StringTable::rehash_table();
585 }
586 }
587
588 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_LAZY_ROOT_PROCESSING)) {
589 if (_do_lazy_roots) {
590 Tracer t("lazy partial thread root processing");
591 class LazyRootClosure : public ThreadClosure {
592 public:
593 void do_thread(Thread* thread) {
594 StackWatermarkSet::start_processing(JavaThread::cast(thread), StackWatermarkKind::gc);
595 }
596 };
597 LazyRootClosure cl;
598 Threads::java_threads_do(&cl);
599 }
600 }
601
602 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
603 Tracer t("updating inline caches");
604 InlineCacheBuffer::update_inline_caches();
605 }
606
607 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_REQUEST_OOPSTORAGE_CLEANUP)) {
608 // Don't bother reporting event or time for this very short operation.
609 // To have any utility we'd also want to report whether needed.
610 OopStorage::trigger_cleanup_if_needed();
611 }
612
613 _subtasks.all_tasks_claimed();
614 }
615 };
616
617 // Various cleaning tasks that should be done periodically at safepoints.
618 void SafepointSynchronize::do_cleanup_tasks() {
619
620 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
621
622 CollectedHeap* heap = Universe::heap();
623 assert(heap != nullptr, "heap not initialized yet?");
624 ParallelCleanupTask cleanup;
625 WorkerThreads* cleanup_workers = heap->safepoint_workers();
626 const uint expected_num_workers = cleanup.expected_num_workers();
627 if (cleanup_workers != nullptr && expected_num_workers > 1) {
628 // Parallel cleanup using GC provided thread pool.
629 const uint num_workers = MIN2(expected_num_workers, cleanup_workers->active_workers());
630 cleanup_workers->run_task(&cleanup, num_workers);
631 } else {
632 // Serial cleanup using VMThread.
633 cleanup.work(0);
634 }
635
636 assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
637
638 if (log_is_enabled(Debug, monitorinflation)) {
639 // The VMThread calls do_final_audit_and_print_stats() which calls
640 // audit_and_print_stats() at the Info level at VM exit time.
641 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
642 }
643 }
644
645 // Methods for determining if a JavaThread is safepoint safe.
646
647 // False means unsafe with undetermined state.
648 // True means a determined state, but it may be an unsafe state.
649 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
650 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
651 assert((safepoint_count != InactiveSafepointCounter &&
652 Thread::current() == (Thread*)VMThread::vm_thread() &&
653 SafepointSynchronize::_state != _not_synchronized)
654 || safepoint_count == InactiveSafepointCounter, "Invalid check");
655
656 // To handle the thread_blocked state on the backedge of the WaitBarrier from
657 // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
658 // re-read state after we read thread safepoint id. The JavaThread changes its
659 // thread state from thread_blocked before resetting safepoint id to 0.
660 // This guarantees the second read will be from an updated thread state. It can
661 // either be different state making this an unsafe state or it can see blocked
662 // again. When we see blocked twice with a 0 safepoint id, either:
663 // - It is normally blocked, e.g. on Mutex, TBIVM.
664 // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
665 // - It was in SS:block() but now on a Mutex.
666 // All of these cases are safe.
667
668 *state = thread->thread_state();
669 OrderAccess::loadload();
670 uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire
671 if (sid != InactiveSafepointCounter && sid != safepoint_count) {
672 // In an old safepoint, state not relevant.
673 return false;
674 }
675 return *state == thread->thread_state();
676 }
677
678 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
679 switch(state) {
680 case _thread_in_native:
681 // native threads are safe if they have no java stack or have walkable stack
682 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
683
684 case _thread_blocked:
685 // On wait_barrier or blocked.
686 // Blocked threads should already have walkable stack.
687 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
688 return true;
689
690 default:
691 return false;
692 }
693 }
694
695 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
696 if (thread->is_terminated()) {
697 return true;
698 }
699 JavaThreadState stable_state;
700 if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
701 return safepoint_safe_with(thread, stable_state);
702 }
703 return false;
704 }
705
706
707 // -------------------------------------------------------------------------------------------------------
708 // Implementation of Safepoint blocking point
709
710 void SafepointSynchronize::block(JavaThread *thread) {
711 assert(thread != nullptr, "thread must be set");
712
713 // Threads shouldn't block if they are in the middle of printing, but...
714 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
715
716 // Only bail from the block() call if the thread is gone from the
717 // thread list; starting to exit should still block.
718 if (thread->is_terminated()) {
719 // block current thread if we come here from native code when VM is gone
720 thread->block_if_vm_exited();
721
722 // otherwise do nothing
723 return;
724 }
725
726 JavaThreadState state = thread->thread_state();
727 thread->frame_anchor()->make_walkable();
728
729 uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
730
731 // We have no idea where the VMThread is, it might even be at next safepoint.
732 // So we can miss this poll, but stop at next.
733
734 // Load dependent store, it must not pass loading of safepoint_id.
735 thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
736
737 // This part we can skip if we notice we miss or are in a future safepoint.
738 OrderAccess::storestore();
739 // Load in wait barrier should not float up
740 thread->set_thread_state_fence(_thread_blocked);
741
742 _wait_barrier->wait(static_cast<int>(safepoint_id));
743 assert(_state != _synchronized, "Can't be");
744
745 // If barrier is disarmed stop store from floating above loads in barrier.
746 OrderAccess::loadstore();
747 thread->set_thread_state(state);
748
749 // Then we reset the safepoint id to inactive.
750 thread->safepoint_state()->reset_safepoint_id(); // Release store
751
752 OrderAccess::fence();
753
754 guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
755 "The safepoint id should be set only in block path");
756
757 // cross_modify_fence is done by SafepointMechanism::process_if_requested
758 // which is the only caller here.
759 }
760
761 // ------------------------------------------------------------------------------------------------------
762 // Exception handlers
763
764
765 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
766 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
767 thread->set_thread_state(_thread_in_vm);
768
769 // Enable WXWrite: the function is called implicitly from java code.
770 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread));
771
772 if (log_is_enabled(Info, safepoint, stats)) {
773 Atomic::inc(&_nof_threads_hit_polling_page);
774 }
775
776 ThreadSafepointState* state = thread->safepoint_state();
777
778 state->handle_polling_page_exception();
779
780 thread->set_thread_state(_thread_in_Java);
781 }
782
783
784 void SafepointSynchronize::print_safepoint_timeout() {
785 if (!timeout_error_printed) {
786 timeout_error_printed = true;
787 // Print out the thread info which didn't reach the safepoint for debugging
788 // purposes (useful when there are lots of threads in the debugger).
789 LogTarget(Warning, safepoint) lt;
790 if (lt.is_enabled()) {
791 ResourceMark rm;
792 LogStream ls(lt);
793
794 ls.cr();
795 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
796 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
797 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
798 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
799 if (cur_thread->safepoint_state()->is_running()) {
800 ls.print("# ");
801 cur_thread->print_on(&ls);
802 ls.cr();
803 }
804 }
805 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
806 }
807 }
808
809 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
810 // ShowMessageBoxOnError.
811 if (AbortVMOnSafepointTimeout && (os::elapsedTime() * MILLIUNITS > AbortVMOnSafepointTimeoutDelay)) {
812 // Send the blocking thread a signal to terminate and write an error file.
813 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
814 if (cur_thread->safepoint_state()->is_running()) {
815 if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
816 break; // Could not send signal. Report fatal error.
817 }
818 // Give cur_thread a chance to report the error and terminate the VM.
819 os::naked_sleep(3000);
820 }
821 }
822 fatal("Safepoint sync time longer than %.6f ms detected when executing %s.",
823 SafepointTimeoutDelay, VMThread::vm_operation()->name());
824 }
825 }
826
827 // -------------------------------------------------------------------------------------------------------
828 // Implementation of ThreadSafepointState
829
830 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
831 : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
832 _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(nullptr) {
833 }
834
835 void ThreadSafepointState::create(JavaThread *thread) {
836 ThreadSafepointState *state = new ThreadSafepointState(thread);
837 thread->set_safepoint_state(state);
838 }
839
840 void ThreadSafepointState::destroy(JavaThread *thread) {
841 if (thread->safepoint_state()) {
842 delete(thread->safepoint_state());
843 thread->set_safepoint_state(nullptr);
844 }
845 }
846
847 uint64_t ThreadSafepointState::get_safepoint_id() const {
848 return Atomic::load_acquire(&_safepoint_id);
849 }
850
851 void ThreadSafepointState::reset_safepoint_id() {
852 Atomic::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
853 }
854
855 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
856 Atomic::release_store(&_safepoint_id, safepoint_id);
857 }
858
859 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
860 assert(is_running(), "better be running or just have hit safepoint poll");
861
862 JavaThreadState stable_state;
863 if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
864 // We could not get stable state of the JavaThread.
865 // Consider it running and just return.
866 return;
867 }
868
869 if (safepoint_safe_with(_thread, stable_state)) {
870 account_safe_thread();
871 return;
872 }
873
874 // All other thread states will continue to run until they
875 // transition and self-block in state _blocked
876 // Safepoint polling in compiled code causes the Java threads to do the same.
877 // Note: new threads may require a malloc so they must be allowed to finish
878
879 assert(is_running(), "examine_state_of_thread on non-running thread");
880 return;
881 }
882
883 void ThreadSafepointState::account_safe_thread() {
884 SafepointSynchronize::decrement_waiting_to_block();
885 if (_thread->in_critical()) {
886 // Notice that this thread is in a critical section
887 SafepointSynchronize::increment_jni_active_count();
888 }
889 DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
890 assert(!_safepoint_safe, "Must be unsafe before safe");
891 _safepoint_safe = true;
892 }
893
894 void ThreadSafepointState::restart() {
895 assert(_safepoint_safe, "Must be safe before unsafe");
896 _safepoint_safe = false;
897 }
898
899 void ThreadSafepointState::print_on(outputStream *st) const {
900 const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
901
902 st->print_cr("Thread: " INTPTR_FORMAT
903 " [0x%2x] State: %s _at_poll_safepoint %d",
904 p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
905
906 _thread->print_thread_state_on(st);
907 }
908
909 // ---------------------------------------------------------------------------------------------------------------------
910
911 // Process pending operation.
912 void ThreadSafepointState::handle_polling_page_exception() {
913 JavaThread* self = thread();
914 assert(self == JavaThread::current(), "must be self");
915
916 // Step 1: Find the nmethod from the return address
917 address real_return_addr = self->saved_exception_pc();
918
919 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
920 assert(cb != nullptr && cb->is_compiled(), "return address should be in nmethod");
921 CompiledMethod* nm = (CompiledMethod*)cb;
922
923 // Find frame of caller
924 frame stub_fr = self->last_frame();
925 CodeBlob* stub_cb = stub_fr.cb();
926 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
927 RegisterMap map(self,
928 RegisterMap::UpdateMap::include,
929 RegisterMap::ProcessFrames::skip,
930 RegisterMap::WalkContinuation::skip);
931 frame caller_fr = stub_fr.sender(&map);
932
933 // Should only be poll_return or poll
934 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
935
936 // This is a poll immediately before a return. The exception handling code
937 // has already had the effect of causing the return to occur, so the execution
938 // will continue immediately after the call. In addition, the oopmap at the
939 // return point does not mark the return value as an oop (if it is), so
940 // it needs a handle here to be updated.
941 if( nm->is_at_poll_return(real_return_addr) ) {
942 // See if return type is an oop.
943 bool return_oop = nm->method()->is_returning_oop();
944 HandleMark hm(self);
945 Handle return_value;
946 if (return_oop) {
947 // The oop result has been saved on the stack together with all
948 // the other registers. In order to preserve it over GCs we need
949 // to keep it in a handle.
950 oop result = caller_fr.saved_oop_result(&map);
951 assert(oopDesc::is_oop_or_null(result), "must be oop");
952 return_value = Handle(self, result);
953 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
954 }
955
956 // We get here if compiled return polls found a reason to call into the VM.
957 // One condition for that is that the top frame is not yet safe to use.
958 // The following stack watermark barrier poll will catch such situations.
959 StackWatermarkSet::after_unwind(self);
960
961 // Process pending operation
962 SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */);
963
964 // restore oop result, if any
965 if (return_oop) {
966 caller_fr.set_saved_oop_result(&map, return_value());
967 }
968 }
969
970 // This is a safepoint poll. Verify the return address and block.
971 else {
972
973 // verify the blob built the "return address" correctly
974 assert(real_return_addr == caller_fr.pc(), "must match");
975
976 set_at_poll_safepoint(true);
977 // Process pending operation
978 // We never deliver an async exception at a polling point as the
979 // compiler may not have an exception handler for it (polling at
980 // a return point is ok though). We will check for a pending async
981 // exception below and deoptimize if needed. We also cannot deoptimize
982 // and still install the exception here because live registers needed
983 // during deoptimization are clobbered by the exception path. The
984 // exception will just be delivered once we get into the interpreter.
985 SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */);
986 set_at_poll_safepoint(false);
987
988 if (self->has_async_exception_condition()) {
989 Deoptimization::deoptimize_frame(self, caller_fr.id());
990 log_info(exceptions)("deferred async exception at compiled safepoint");
991 }
992
993 // If an exception has been installed we must verify that the top frame wasn't deoptimized.
994 if (self->has_pending_exception() ) {
995 RegisterMap map(self,
996 RegisterMap::UpdateMap::include,
997 RegisterMap::ProcessFrames::skip,
998 RegisterMap::WalkContinuation::skip);
999 frame caller_fr = stub_fr.sender(&map);
1000 if (caller_fr.is_deoptimized_frame()) {
1001 // The exception path will destroy registers that are still
1002 // live and will be needed during deoptimization, so if we
1003 // have an exception now things are messed up. We only check
1004 // at this scope because for a poll return it is ok to deoptimize
1005 // while having a pending exception since the call we are returning
1006 // from already collides with exception handling registers and
1007 // so there is no issue (the exception handling path kills call
1008 // result registers but this is ok since the exception kills
1009 // the result anyway).
1010 fatal("Exception installed and deoptimization is pending");
1011 }
1012 }
1013 }
1014 }
1015
1016
1017 // -------------------------------------------------------------------------------------------------------
1018 // Implementation of SafepointTracing
1019
1020 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
1021 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
1022 jlong SafepointTracing::_last_safepoint_cleanup_time_ns = 0;
1023 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
1024 jlong SafepointTracing::_last_app_time_ns = 0;
1025 int SafepointTracing::_nof_threads = 0;
1026 int SafepointTracing::_nof_running = 0;
1027 int SafepointTracing::_page_trap = 0;
1028 VM_Operation::VMOp_Type SafepointTracing::_current_type;
1029 jlong SafepointTracing::_max_sync_time = 0;
1030 jlong SafepointTracing::_max_cleanup_time = 0;
1031 jlong SafepointTracing::_max_vmop_time = 0;
1032 uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
1033
1034 void SafepointTracing::init() {
1035 // Application start
1036 _last_safepoint_end_time_ns = os::javaTimeNanos();
1037 }
1038
1039 // Helper method to print the header.
1040 static void print_header(outputStream* st) {
1041 // The number of spaces is significant here, and should match the format
1042 // specifiers in print_statistics().
1043
1044 st->print("VM Operation "
1045 "[ threads: total initial_running ]"
1046 "[ time: sync cleanup vmop total ]");
1047
1048 st->print_cr(" page_trap_count");
1049 }
1050
1051 // This prints a nice table. To get the statistics to not shift due to the logging uptime
1052 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
1053 void SafepointTracing::statistics_log() {
1054 LogTarget(Info, safepoint, stats) lt;
1055 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
1056 LogStream ls(lt);
1057
1058 static int _cur_stat_index = 0;
1059
1060 // Print header every 30 entries
1061 if ((_cur_stat_index % 30) == 0) {
1062 print_header(&ls);
1063 _cur_stat_index = 1; // wrap
1064 } else {
1065 _cur_stat_index++;
1066 }
1067
1068 ls.print("%-28s [ "
1069 INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " "
1070 "]",
1071 VM_Operation::name(_current_type),
1072 _nof_threads,
1073 _nof_running);
1074 ls.print("[ "
1075 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " "
1076 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
1077 (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
1078 (int64_t)(_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns),
1079 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns),
1080 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
1081
1082 ls.print_cr(INT32_FORMAT_W(16), _page_trap);
1083 }
1084
1085 // This method will be called when VM exits. This tries to summarize the sampling.
1086 // Current thread may already be deleted, so don't use ResourceMark.
1087 void SafepointTracing::statistics_exit_log() {
1088 if (!log_is_enabled(Info, safepoint, stats)) {
1089 return;
1090 }
1091 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1092 if (_op_count[index] != 0) {
1093 log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1094 _op_count[index]);
1095 }
1096 }
1097
1098 log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns",
1099 (int64_t)(_max_sync_time));
1100 log_info(safepoint, stats)("Maximum cleanup time " INT64_FORMAT" ns",
1101 (int64_t)(_max_cleanup_time));
1102 log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
1103 INT64_FORMAT " ns",
1104 (int64_t)(_max_vmop_time));
1105 }
1106
1107 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
1108 _op_count[type]++;
1109 _current_type = type;
1110
1111 // update the time stamp to begin recording safepoint time
1112 _last_safepoint_begin_time_ns = os::javaTimeNanos();
1113 _last_safepoint_sync_time_ns = 0;
1114 _last_safepoint_cleanup_time_ns = 0;
1115
1116 _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
1117 _last_safepoint_end_time_ns = 0;
1118
1119 RuntimeService::record_safepoint_begin(_last_app_time_ns);
1120 }
1121
1122 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
1123 _last_safepoint_sync_time_ns = os::javaTimeNanos();
1124 _nof_threads = nof_threads;
1125 _nof_running = nof_running;
1126 _page_trap = traps;
1127 RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
1128 }
1129
1130 void SafepointTracing::cleanup() {
1131 _last_safepoint_cleanup_time_ns = os::javaTimeNanos();
1132 }
1133
1134 void SafepointTracing::end() {
1135 _last_safepoint_end_time_ns = os::javaTimeNanos();
1136
1137 if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
1138 _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
1139 }
1140 if (_max_cleanup_time < (_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns)) {
1141 _max_cleanup_time = _last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns;
1142 }
1143 if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
1144 _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
1145 }
1146 if (log_is_enabled(Info, safepoint, stats)) {
1147 statistics_log();
1148 }
1149
1150 log_info(safepoint)(
1151 "Safepoint \"%s\", "
1152 "Time since last: " JLONG_FORMAT " ns, "
1153 "Reaching safepoint: " JLONG_FORMAT " ns, "
1154 "Cleanup: " JLONG_FORMAT " ns, "
1155 "At safepoint: " JLONG_FORMAT " ns, "
1156 "Total: " JLONG_FORMAT " ns",
1157 VM_Operation::name(_current_type),
1158 _last_app_time_ns,
1159 _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns,
1160 _last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns,
1161 _last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns,
1162 _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns
1163 );
1164
1165 RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns);
1166 }