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/nmethod.hpp"
31 #include "code/pcDesc.hpp"
32 #include "code/scopeDesc.hpp"
33 #include "compiler/compilationPolicy.hpp"
34 #include "gc/shared/collectedHeap.hpp"
35 #include "gc/shared/gcLocker.hpp"
36 #include "gc/shared/oopStorage.hpp"
37 #include "gc/shared/strongRootsScope.hpp"
38 #include "gc/shared/workerThread.hpp"
39 #include "gc/shared/workerUtils.hpp"
40 #include "interpreter/interpreter.hpp"
41 #include "jfr/jfrEvents.hpp"
42 #include "logging/log.hpp"
43 #include "logging/logStream.hpp"
44 #include "memory/resourceArea.hpp"
45 #include "memory/universe.hpp"
46 #include "oops/oop.inline.hpp"
47 #include "oops/symbol.hpp"
48 #include "oops/inlineKlass.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 (StringTable::needs_rehashing()) return true;
517 if (SymbolTable::needs_rehashing()) return true;
518 return false;
519 }
520
521 class ParallelCleanupTask : public WorkerTask {
522 private:
523 SubTasksDone _subtasks;
524 bool _do_lazy_roots;
525
526 class Tracer {
527 private:
528 const char* _name;
529 EventSafepointCleanupTask _event;
530 TraceTime _timer;
531
532 public:
533 Tracer(const char* name) :
534 _name(name),
535 _event(),
536 _timer(name, TRACETIME_LOG(Info, safepoint, cleanup)) {}
537 ~Tracer() {
538 post_safepoint_cleanup_task_event(_event, SafepointSynchronize::safepoint_id(), _name);
539 }
540 };
541
542 public:
543 ParallelCleanupTask() :
544 WorkerTask("Parallel Safepoint Cleanup"),
545 _subtasks(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS),
546 _do_lazy_roots(!VMThread::vm_operation()->skip_thread_oop_barriers() &&
547 Universe::heap()->uses_stack_watermark_barrier()) {}
548
549 uint expected_num_workers() const {
550 uint workers = 0;
551
552 if (SymbolTable::rehash_table_expects_safepoint_rehashing()) {
553 workers++;
554 }
555
556 if (StringTable::rehash_table_expects_safepoint_rehashing()) {
557 workers++;
558 }
559
560 if (_do_lazy_roots) {
561 workers++;
562 }
563
564 return MAX2<uint>(1, workers);
565 }
566
567 void work(uint worker_id) {
568 // These tasks are ordered by relative length of time to execute so that potentially longer tasks start first.
569 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
570 if (SymbolTable::needs_rehashing()) {
571 Tracer t("rehashing symbol table");
572 SymbolTable::rehash_table();
573 }
574 }
575
576 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
577 if (StringTable::needs_rehashing()) {
578 Tracer t("rehashing string table");
579 StringTable::rehash_table();
580 }
581 }
582
583 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_LAZY_ROOT_PROCESSING)) {
584 if (_do_lazy_roots) {
585 Tracer t("lazy partial thread root processing");
586 class LazyRootClosure : public ThreadClosure {
587 public:
588 void do_thread(Thread* thread) {
589 StackWatermarkSet::start_processing(JavaThread::cast(thread), StackWatermarkKind::gc);
590 }
591 };
592 LazyRootClosure cl;
593 Threads::java_threads_do(&cl);
594 }
595 }
596
597 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_REQUEST_OOPSTORAGE_CLEANUP)) {
598 // Don't bother reporting event or time for this very short operation.
599 // To have any utility we'd also want to report whether needed.
600 OopStorage::trigger_cleanup_if_needed();
601 }
602
603 _subtasks.all_tasks_claimed();
604 }
605 };
606
607 // Various cleaning tasks that should be done periodically at safepoints.
608 void SafepointSynchronize::do_cleanup_tasks() {
609
610 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
611
612 CollectedHeap* heap = Universe::heap();
613 assert(heap != nullptr, "heap not initialized yet?");
614 ParallelCleanupTask cleanup;
615 WorkerThreads* cleanup_workers = heap->safepoint_workers();
616 const uint expected_num_workers = cleanup.expected_num_workers();
617 if (cleanup_workers != nullptr && expected_num_workers > 1) {
618 // Parallel cleanup using GC provided thread pool.
619 const uint num_workers = MIN2(expected_num_workers, cleanup_workers->active_workers());
620 cleanup_workers->run_task(&cleanup, num_workers);
621 } else {
622 // Serial cleanup using VMThread.
623 cleanup.work(0);
624 }
625
626 if (log_is_enabled(Debug, monitorinflation)) {
627 // The VMThread calls do_final_audit_and_print_stats() which calls
628 // audit_and_print_stats() at the Info level at VM exit time.
629 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
630 }
631 }
632
633 // Methods for determining if a JavaThread is safepoint safe.
634
635 // False means unsafe with undetermined state.
636 // True means a determined state, but it may be an unsafe state.
637 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
638 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
639 assert((safepoint_count != InactiveSafepointCounter &&
640 Thread::current() == (Thread*)VMThread::vm_thread() &&
641 SafepointSynchronize::_state != _not_synchronized)
642 || safepoint_count == InactiveSafepointCounter, "Invalid check");
643
644 // To handle the thread_blocked state on the backedge of the WaitBarrier from
645 // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
646 // re-read state after we read thread safepoint id. The JavaThread changes its
647 // thread state from thread_blocked before resetting safepoint id to 0.
648 // This guarantees the second read will be from an updated thread state. It can
649 // either be different state making this an unsafe state or it can see blocked
650 // again. When we see blocked twice with a 0 safepoint id, either:
651 // - It is normally blocked, e.g. on Mutex, TBIVM.
652 // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
653 // - It was in SS:block() but now on a Mutex.
654 // All of these cases are safe.
655
656 *state = thread->thread_state();
657 OrderAccess::loadload();
658 uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire
659 if (sid != InactiveSafepointCounter && sid != safepoint_count) {
660 // In an old safepoint, state not relevant.
661 return false;
662 }
663 return *state == thread->thread_state();
664 }
665
666 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
667 switch(state) {
668 case _thread_in_native:
669 // native threads are safe if they have no java stack or have walkable stack
670 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
671
672 case _thread_blocked:
673 // On wait_barrier or blocked.
674 // Blocked threads should already have walkable stack.
675 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
676 return true;
677
678 default:
679 return false;
680 }
681 }
682
683 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
684 if (thread->is_terminated()) {
685 return true;
686 }
687 JavaThreadState stable_state;
688 if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
689 return safepoint_safe_with(thread, stable_state);
690 }
691 return false;
692 }
693
694
695 // -------------------------------------------------------------------------------------------------------
696 // Implementation of Safepoint blocking point
697
698 void SafepointSynchronize::block(JavaThread *thread) {
699 assert(thread != nullptr, "thread must be set");
700
701 // Threads shouldn't block if they are in the middle of printing, but...
702 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
703
704 // Only bail from the block() call if the thread is gone from the
705 // thread list; starting to exit should still block.
706 if (thread->is_terminated()) {
707 // block current thread if we come here from native code when VM is gone
708 thread->block_if_vm_exited();
709
710 // otherwise do nothing
711 return;
712 }
713
714 JavaThreadState state = thread->thread_state();
715 thread->frame_anchor()->make_walkable();
716
717 uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
718
719 // We have no idea where the VMThread is, it might even be at next safepoint.
720 // So we can miss this poll, but stop at next.
721
722 // Load dependent store, it must not pass loading of safepoint_id.
723 thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
724
725 // This part we can skip if we notice we miss or are in a future safepoint.
726 OrderAccess::storestore();
727 // Load in wait barrier should not float up
728 thread->set_thread_state_fence(_thread_blocked);
729
730 _wait_barrier->wait(static_cast<int>(safepoint_id));
731 assert(_state != _synchronized, "Can't be");
732
733 // If barrier is disarmed stop store from floating above loads in barrier.
734 OrderAccess::loadstore();
735 thread->set_thread_state(state);
736
737 // Then we reset the safepoint id to inactive.
738 thread->safepoint_state()->reset_safepoint_id(); // Release store
739
740 OrderAccess::fence();
741
742 guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
743 "The safepoint id should be set only in block path");
744
745 // cross_modify_fence is done by SafepointMechanism::process_if_requested
746 // which is the only caller here.
747 }
748
749 // ------------------------------------------------------------------------------------------------------
750 // Exception handlers
751
752
753 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
754 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
755 thread->set_thread_state(_thread_in_vm);
756
757 // Enable WXWrite: the function is called implicitly from java code.
758 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread));
759
760 if (log_is_enabled(Info, safepoint, stats)) {
761 Atomic::inc(&_nof_threads_hit_polling_page);
762 }
763
764 ThreadSafepointState* state = thread->safepoint_state();
765
766 state->handle_polling_page_exception();
767
768 thread->set_thread_state(_thread_in_Java);
769 }
770
771
772 void SafepointSynchronize::print_safepoint_timeout() {
773 if (!timeout_error_printed) {
774 timeout_error_printed = true;
775 // Print out the thread info which didn't reach the safepoint for debugging
776 // purposes (useful when there are lots of threads in the debugger).
777 LogTarget(Warning, safepoint) lt;
778 if (lt.is_enabled()) {
779 ResourceMark rm;
780 LogStream ls(lt);
781
782 ls.cr();
783 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
784 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
785 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
786 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
787 if (cur_thread->safepoint_state()->is_running()) {
788 ls.print("# ");
789 cur_thread->print_on(&ls);
790 ls.cr();
791 }
792 }
793 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
794 }
795 }
796
797 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
798 // ShowMessageBoxOnError.
799 if (AbortVMOnSafepointTimeout && (os::elapsedTime() * MILLIUNITS > AbortVMOnSafepointTimeoutDelay)) {
800 // Send the blocking thread a signal to terminate and write an error file.
801 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
802 if (cur_thread->safepoint_state()->is_running()) {
803 if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
804 break; // Could not send signal. Report fatal error.
805 }
806 // Give cur_thread a chance to report the error and terminate the VM.
807 os::naked_sleep(3000);
808 }
809 }
810 fatal("Safepoint sync time longer than %.6f ms detected when executing %s.",
811 SafepointTimeoutDelay, VMThread::vm_operation()->name());
812 }
813 }
814
815 // -------------------------------------------------------------------------------------------------------
816 // Implementation of ThreadSafepointState
817
818 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
819 : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
820 _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(nullptr) {
821 }
822
823 void ThreadSafepointState::create(JavaThread *thread) {
824 ThreadSafepointState *state = new ThreadSafepointState(thread);
825 thread->set_safepoint_state(state);
826 }
827
828 void ThreadSafepointState::destroy(JavaThread *thread) {
829 if (thread->safepoint_state()) {
830 delete(thread->safepoint_state());
831 thread->set_safepoint_state(nullptr);
832 }
833 }
834
835 uint64_t ThreadSafepointState::get_safepoint_id() const {
836 return Atomic::load_acquire(&_safepoint_id);
837 }
838
839 void ThreadSafepointState::reset_safepoint_id() {
840 Atomic::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
841 }
842
843 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
844 Atomic::release_store(&_safepoint_id, safepoint_id);
845 }
846
847 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
848 assert(is_running(), "better be running or just have hit safepoint poll");
849
850 JavaThreadState stable_state;
851 if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
852 // We could not get stable state of the JavaThread.
853 // Consider it running and just return.
854 return;
855 }
856
857 if (safepoint_safe_with(_thread, stable_state)) {
858 account_safe_thread();
859 return;
860 }
861
862 // All other thread states will continue to run until they
863 // transition and self-block in state _blocked
864 // Safepoint polling in compiled code causes the Java threads to do the same.
865 // Note: new threads may require a malloc so they must be allowed to finish
866
867 assert(is_running(), "examine_state_of_thread on non-running thread");
868 return;
869 }
870
871 void ThreadSafepointState::account_safe_thread() {
872 SafepointSynchronize::decrement_waiting_to_block();
873 if (_thread->in_critical()) {
874 // Notice that this thread is in a critical section
875 SafepointSynchronize::increment_jni_active_count();
876 }
877 DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
878 assert(!_safepoint_safe, "Must be unsafe before safe");
879 _safepoint_safe = true;
880 }
881
882 void ThreadSafepointState::restart() {
883 assert(_safepoint_safe, "Must be safe before unsafe");
884 _safepoint_safe = false;
885 }
886
887 void ThreadSafepointState::print_on(outputStream *st) const {
888 const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
889
890 st->print_cr("Thread: " INTPTR_FORMAT
891 " [0x%2x] State: %s _at_poll_safepoint %d",
892 p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
893
894 _thread->print_thread_state_on(st);
895 }
896
897 // ---------------------------------------------------------------------------------------------------------------------
898
899 // Process pending operation.
900 void ThreadSafepointState::handle_polling_page_exception() {
901 JavaThread* self = thread();
902 assert(self == JavaThread::current(), "must be self");
903
904 // Step 1: Find the nmethod from the return address
905 address real_return_addr = self->saved_exception_pc();
906
907 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
908 assert(cb != nullptr && cb->is_compiled(), "return address should be in nmethod");
909 CompiledMethod* nm = (CompiledMethod*)cb;
910
911 // Find frame of caller
912 frame stub_fr = self->last_frame();
913 CodeBlob* stub_cb = stub_fr.cb();
914 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
915 RegisterMap map(self,
916 RegisterMap::UpdateMap::include,
917 RegisterMap::ProcessFrames::skip,
918 RegisterMap::WalkContinuation::skip);
919 frame caller_fr = stub_fr.sender(&map);
920
921 // Should only be poll_return or poll
922 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
923
924 // This is a poll immediately before a return. The exception handling code
925 // has already had the effect of causing the return to occur, so the execution
926 // will continue immediately after the call. In addition, the oopmap at the
927 // return point does not mark the return value as an oop (if it is), so
928 // it needs a handle here to be updated.
929 if( nm->is_at_poll_return(real_return_addr) ) {
930 ResourceMark rm;
931 // See if return type is an oop.
932 Method* method = nm->method();
933 bool return_oop = method->is_returning_oop();
934 HandleMark hm(self);
935 GrowableArray<Handle> return_values;
936 InlineKlass* vk = nullptr;
937 if (return_oop && InlineTypeReturnedAsFields &&
938 (method->result_type() == T_OBJECT)) {
939 // Check if an inline type is returned as fields
940 vk = InlineKlass::returned_inline_klass(map);
941 if (vk != nullptr) {
942 // We're at a safepoint at the return of a method that returns
943 // multiple values. We must make sure we preserve the oop values
944 // across the safepoint.
945 assert(vk == method->returns_inline_type(thread()), "bad inline klass");
946 vk->save_oop_fields(map, return_values);
947 return_oop = false;
948 }
949 }
950
951 if (return_oop) {
952 // The oop result has been saved on the stack together with all
953 // the other registers. In order to preserve it over GCs we need
954 // to keep it in a handle.
955 oop result = caller_fr.saved_oop_result(&map);
956 assert(oopDesc::is_oop_or_null(result), "must be oop");
957 return_values.push(Handle(self, result));
958 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
959 }
960
961 // We get here if compiled return polls found a reason to call into the VM.
962 // One condition for that is that the top frame is not yet safe to use.
963 // The following stack watermark barrier poll will catch such situations.
964 StackWatermarkSet::after_unwind(self);
965
966 // Process pending operation
967 SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */);
968
969 // restore oop result, if any
970 if (return_oop) {
971 assert(return_values.length() == 1, "only one return value");
972 caller_fr.set_saved_oop_result(&map, return_values.pop()());
973 } else if (vk != nullptr) {
974 vk->restore_oop_results(map, return_values);
975 }
976 }
977
978 // This is a safepoint poll. Verify the return address and block.
979 else {
980
981 // verify the blob built the "return address" correctly
982 assert(real_return_addr == caller_fr.pc(), "must match");
983
984 set_at_poll_safepoint(true);
985 // Process pending operation
986 // We never deliver an async exception at a polling point as the
987 // compiler may not have an exception handler for it (polling at
988 // a return point is ok though). We will check for a pending async
989 // exception below and deoptimize if needed. We also cannot deoptimize
990 // and still install the exception here because live registers needed
991 // during deoptimization are clobbered by the exception path. The
992 // exception will just be delivered once we get into the interpreter.
993 SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */);
994 set_at_poll_safepoint(false);
995
996 if (self->has_async_exception_condition()) {
997 Deoptimization::deoptimize_frame(self, caller_fr.id());
998 log_info(exceptions)("deferred async exception at compiled safepoint");
999 }
1000
1001 // If an exception has been installed we must verify that the top frame wasn't deoptimized.
1002 if (self->has_pending_exception() ) {
1003 RegisterMap map(self,
1004 RegisterMap::UpdateMap::include,
1005 RegisterMap::ProcessFrames::skip,
1006 RegisterMap::WalkContinuation::skip);
1007 frame caller_fr = stub_fr.sender(&map);
1008 if (caller_fr.is_deoptimized_frame()) {
1009 // The exception path will destroy registers that are still
1010 // live and will be needed during deoptimization, so if we
1011 // have an exception now things are messed up. We only check
1012 // at this scope because for a poll return it is ok to deoptimize
1013 // while having a pending exception since the call we are returning
1014 // from already collides with exception handling registers and
1015 // so there is no issue (the exception handling path kills call
1016 // result registers but this is ok since the exception kills
1017 // the result anyway).
1018 fatal("Exception installed and deoptimization is pending");
1019 }
1020 }
1021 }
1022 }
1023
1024
1025 // -------------------------------------------------------------------------------------------------------
1026 // Implementation of SafepointTracing
1027
1028 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
1029 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
1030 jlong SafepointTracing::_last_safepoint_cleanup_time_ns = 0;
1031 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
1032 jlong SafepointTracing::_last_app_time_ns = 0;
1033 int SafepointTracing::_nof_threads = 0;
1034 int SafepointTracing::_nof_running = 0;
1035 int SafepointTracing::_page_trap = 0;
1036 VM_Operation::VMOp_Type SafepointTracing::_current_type;
1037 jlong SafepointTracing::_max_sync_time = 0;
1038 jlong SafepointTracing::_max_cleanup_time = 0;
1039 jlong SafepointTracing::_max_vmop_time = 0;
1040 uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
1041
1042 void SafepointTracing::init() {
1043 // Application start
1044 _last_safepoint_end_time_ns = os::javaTimeNanos();
1045 }
1046
1047 // Helper method to print the header.
1048 static void print_header(outputStream* st) {
1049 // The number of spaces is significant here, and should match the format
1050 // specifiers in print_statistics().
1051
1052 st->print("VM Operation "
1053 "[ threads: total initial_running ]"
1054 "[ time: sync cleanup vmop total ]");
1055
1056 st->print_cr(" page_trap_count");
1057 }
1058
1059 // This prints a nice table. To get the statistics to not shift due to the logging uptime
1060 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
1061 void SafepointTracing::statistics_log() {
1062 LogTarget(Info, safepoint, stats) lt;
1063 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
1064 LogStream ls(lt);
1065
1066 static int _cur_stat_index = 0;
1067
1068 // Print header every 30 entries
1069 if ((_cur_stat_index % 30) == 0) {
1070 print_header(&ls);
1071 _cur_stat_index = 1; // wrap
1072 } else {
1073 _cur_stat_index++;
1074 }
1075
1076 ls.print("%-28s [ "
1077 INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " "
1078 "]",
1079 VM_Operation::name(_current_type),
1080 _nof_threads,
1081 _nof_running);
1082 ls.print("[ "
1083 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " "
1084 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
1085 (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
1086 (int64_t)(_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns),
1087 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns),
1088 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
1089
1090 ls.print_cr(INT32_FORMAT_W(16), _page_trap);
1091 }
1092
1093 // This method will be called when VM exits. This tries to summarize the sampling.
1094 // Current thread may already be deleted, so don't use ResourceMark.
1095 void SafepointTracing::statistics_exit_log() {
1096 if (!log_is_enabled(Info, safepoint, stats)) {
1097 return;
1098 }
1099 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1100 if (_op_count[index] != 0) {
1101 log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1102 _op_count[index]);
1103 }
1104 }
1105
1106 log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns",
1107 (int64_t)(_max_sync_time));
1108 log_info(safepoint, stats)("Maximum cleanup time " INT64_FORMAT" ns",
1109 (int64_t)(_max_cleanup_time));
1110 log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
1111 INT64_FORMAT " ns",
1112 (int64_t)(_max_vmop_time));
1113 }
1114
1115 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
1116 _op_count[type]++;
1117 _current_type = type;
1118
1119 // update the time stamp to begin recording safepoint time
1120 _last_safepoint_begin_time_ns = os::javaTimeNanos();
1121 _last_safepoint_sync_time_ns = 0;
1122 _last_safepoint_cleanup_time_ns = 0;
1123
1124 _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
1125 _last_safepoint_end_time_ns = 0;
1126
1127 RuntimeService::record_safepoint_begin(_last_app_time_ns);
1128 }
1129
1130 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
1131 _last_safepoint_sync_time_ns = os::javaTimeNanos();
1132 _nof_threads = nof_threads;
1133 _nof_running = nof_running;
1134 _page_trap = traps;
1135 RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
1136 }
1137
1138 void SafepointTracing::cleanup() {
1139 _last_safepoint_cleanup_time_ns = os::javaTimeNanos();
1140 }
1141
1142 void SafepointTracing::end() {
1143 _last_safepoint_end_time_ns = os::javaTimeNanos();
1144
1145 if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
1146 _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
1147 }
1148 if (_max_cleanup_time < (_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns)) {
1149 _max_cleanup_time = _last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns;
1150 }
1151 if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
1152 _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
1153 }
1154 if (log_is_enabled(Info, safepoint, stats)) {
1155 statistics_log();
1156 }
1157
1158 log_info(safepoint)(
1159 "Safepoint \"%s\", "
1160 "Time since last: " JLONG_FORMAT " ns, "
1161 "Reaching safepoint: " JLONG_FORMAT " ns, "
1162 "Cleanup: " JLONG_FORMAT " ns, "
1163 "At safepoint: " JLONG_FORMAT " ns, "
1164 "Total: " JLONG_FORMAT " ns",
1165 VM_Operation::name(_current_type),
1166 _last_app_time_ns,
1167 _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns,
1168 _last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns,
1169 _last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns,
1170 _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns
1171 );
1172
1173 RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns);
1174 }