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 "oops/inlineKlass.hpp"
50 #include "runtime/atomic.hpp"
51 #include "runtime/deoptimization.hpp"
52 #include "runtime/frame.inline.hpp"
53 #include "runtime/globals.hpp"
54 #include "runtime/handles.inline.hpp"
55 #include "runtime/interfaceSupport.inline.hpp"
56 #include "runtime/javaThread.inline.hpp"
57 #include "runtime/mutexLocker.hpp"
58 #include "runtime/orderAccess.hpp"
59 #include "runtime/osThread.hpp"
60 #include "runtime/safepoint.hpp"
61 #include "runtime/safepointMechanism.inline.hpp"
62 #include "runtime/signature.hpp"
63 #include "runtime/stackWatermarkSet.inline.hpp"
64 #include "runtime/stubCodeGenerator.hpp"
65 #include "runtime/stubRoutines.hpp"
66 #include "runtime/synchronizer.hpp"
67 #include "runtime/threads.hpp"
68 #include "runtime/threadSMR.hpp"
69 #include "runtime/threadWXSetters.inline.hpp"
70 #include "runtime/timerTrace.hpp"
71 #include "services/runtimeService.hpp"
72 #include "utilities/events.hpp"
73 #include "utilities/macros.hpp"
74 #include "utilities/systemMemoryBarrier.hpp"
75
76 static void post_safepoint_begin_event(EventSafepointBegin& event,
77 uint64_t safepoint_id,
78 int thread_count,
79 int critical_thread_count) {
80 if (event.should_commit()) {
81 event.set_safepointId(safepoint_id);
82 event.set_totalThreadCount(thread_count);
83 event.set_jniCriticalThreadCount(critical_thread_count);
84 event.commit();
85 }
86 }
87
88 static void post_safepoint_cleanup_event(EventSafepointCleanup& event, uint64_t safepoint_id) {
89 if (event.should_commit()) {
90 event.set_safepointId(safepoint_id);
91 event.commit();
92 }
93 }
94
95 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization& event,
96 uint64_t safepoint_id,
97 int initial_number_of_threads,
98 int threads_waiting_to_block,
99 uint64_t iterations) {
100 if (event.should_commit()) {
101 event.set_safepointId(safepoint_id);
102 event.set_initialThreadCount(initial_number_of_threads);
103 event.set_runningThreadCount(threads_waiting_to_block);
104 event.set_iterations(iterations);
105 event.commit();
106 }
107 }
108
109 static void post_safepoint_cleanup_task_event(EventSafepointCleanupTask& event,
110 uint64_t safepoint_id,
111 const char* name) {
112 if (event.should_commit()) {
113 event.set_safepointId(safepoint_id);
114 event.set_name(name);
115 event.commit();
116 }
117 }
118
119 static void post_safepoint_end_event(EventSafepointEnd& event, uint64_t safepoint_id) {
120 if (event.should_commit()) {
121 event.set_safepointId(safepoint_id);
122 event.commit();
123 }
124 }
125
126 // SafepointCheck
127 SafepointStateTracker::SafepointStateTracker(uint64_t safepoint_id, bool at_safepoint)
128 : _safepoint_id(safepoint_id), _at_safepoint(at_safepoint) {}
129
130 bool SafepointStateTracker::safepoint_state_changed() {
131 return _safepoint_id != SafepointSynchronize::safepoint_id() ||
132 _at_safepoint != SafepointSynchronize::is_at_safepoint();
133 }
134
135 // --------------------------------------------------------------------------------------------------
136 // Implementation of Safepoint begin/end
137
138 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
139 int SafepointSynchronize::_waiting_to_block = 0;
140 volatile uint64_t SafepointSynchronize::_safepoint_counter = 0;
141 uint64_t SafepointSynchronize::_safepoint_id = 0;
142 const uint64_t SafepointSynchronize::InactiveSafepointCounter = 0;
143 int SafepointSynchronize::_current_jni_active_count = 0;
144
145 WaitBarrier* SafepointSynchronize::_wait_barrier;
146
147 static bool timeout_error_printed = false;
148
149 // Statistic related
150 static jlong _safepoint_begin_time = 0;
151 static volatile int _nof_threads_hit_polling_page = 0;
152
153 void SafepointSynchronize::init(Thread* vmthread) {
154 // WaitBarrier should never be destroyed since we will have
155 // threads waiting on it while exiting.
156 _wait_barrier = new WaitBarrier(vmthread);
157 SafepointTracing::init();
158 }
159
160 void SafepointSynchronize::increment_jni_active_count() {
161 assert(Thread::current()->is_VM_thread(), "Only VM thread may increment");
162 ++_current_jni_active_count;
163 }
164
165 void SafepointSynchronize::decrement_waiting_to_block() {
166 assert(_waiting_to_block > 0, "sanity check");
167 assert(Thread::current()->is_VM_thread(), "Only VM thread may decrement");
168 --_waiting_to_block;
169 }
170
171 bool SafepointSynchronize::thread_not_running(ThreadSafepointState *cur_state) {
172 if (!cur_state->is_running()) {
173 // Robustness: asserted in the caller, but handle/tolerate it for release bits.
174 LogTarget(Error, safepoint) lt;
175 if (lt.is_enabled()) {
176 ResourceMark rm;
177 LogStream ls(lt);
178 ls.print("Illegal initial state detected: ");
179 cur_state->print_on(&ls);
180 }
181 return true;
182 }
183 cur_state->examine_state_of_thread(SafepointSynchronize::safepoint_counter());
184 if (!cur_state->is_running()) {
185 return true;
186 }
187 LogTarget(Trace, safepoint) lt;
188 if (lt.is_enabled()) {
189 ResourceMark rm;
190 LogStream ls(lt);
191 cur_state->print_on(&ls);
192 }
193 return false;
194 }
195
196 #ifdef ASSERT
197 static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) {
198 int a = 0;
199 const ThreadSafepointState *tmp_tss = tss_head;
200 while (tmp_tss != nullptr) {
201 ++a;
202 assert(tmp_tss->is_running(), "Illegal initial state");
203 tmp_tss = tmp_tss->get_next();
204 }
205 assert(a == still_running, "Must be the same");
206 }
207 #endif // ASSERT
208
209 static void back_off(int64_t start_time) {
210 // We start with fine-grained nanosleeping until a millisecond has
211 // passed, at which point we resort to plain naked_short_sleep.
212 if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) {
213 os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
214 } else {
215 os::naked_short_sleep(1);
216 }
217 }
218
219 int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running)
220 {
221 JavaThreadIteratorWithHandle jtiwh;
222
223 #ifdef ASSERT
224 for (; JavaThread *cur = jtiwh.next(); ) {
225 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
226 }
227 jtiwh.rewind();
228 #endif // ASSERT
229
230 // Iterate through all threads until it has been determined how to stop them all at a safepoint.
231 int still_running = nof_threads;
232 ThreadSafepointState *tss_head = nullptr;
233 ThreadSafepointState **p_prev = &tss_head;
234 for (; JavaThread *cur = jtiwh.next(); ) {
235 ThreadSafepointState *cur_tss = cur->safepoint_state();
236 assert(cur_tss->get_next() == nullptr, "Must be null");
237 if (thread_not_running(cur_tss)) {
238 --still_running;
239 } else {
240 *p_prev = cur_tss;
241 p_prev = cur_tss->next_ptr();
242 }
243 }
244 *p_prev = nullptr;
245
246 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
247
248 *initial_running = still_running;
249
250 // If there is no thread still running, we are already done.
251 if (still_running <= 0) {
252 assert(tss_head == nullptr, "Must be empty");
253 return 1;
254 }
255
256 int iterations = 1; // The first iteration is above.
257 int64_t start_time = os::javaTimeNanos();
258
259 do {
260 // Check if this has taken too long:
261 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
262 print_safepoint_timeout();
263 }
264
265 p_prev = &tss_head;
266 ThreadSafepointState *cur_tss = tss_head;
267 while (cur_tss != nullptr) {
268 assert(cur_tss->is_running(), "Illegal initial state");
269 if (thread_not_running(cur_tss)) {
270 --still_running;
271 *p_prev = nullptr;
272 ThreadSafepointState *tmp = cur_tss;
273 cur_tss = cur_tss->get_next();
274 tmp->set_next(nullptr);
275 } else {
276 *p_prev = cur_tss;
277 p_prev = cur_tss->next_ptr();
278 cur_tss = cur_tss->get_next();
279 }
280 }
281
282 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
283
284 if (still_running > 0) {
285 back_off(start_time);
286 }
287
288 iterations++;
289 } while (still_running > 0);
290
291 assert(tss_head == nullptr, "Must be empty");
292
293 return iterations;
294 }
295
296 void SafepointSynchronize::arm_safepoint() {
297 // Begin the process of bringing the system to a safepoint.
298 // Java threads can be in several different states and are
299 // stopped by different mechanisms:
300 //
301 // 1. Running interpreted
302 // When executing branching/returning byte codes interpreter
303 // checks if the poll is armed, if so blocks in SS::block().
304 // 2. Running in native code
305 // When returning from the native code, a Java thread must check
306 // the safepoint _state to see if we must block. If the
307 // VM thread sees a Java thread in native, it does
308 // not wait for this thread to block. The order of the memory
309 // writes and reads of both the safepoint state and the Java
310 // threads state is critical. In order to guarantee that the
311 // memory writes are serialized with respect to each other,
312 // the VM thread issues a memory barrier instruction.
313 // 3. Running compiled Code
314 // Compiled code reads the local polling page that
315 // is set to fault if we are trying to get to a safepoint.
316 // 4. Blocked
317 // A thread which is blocked will not be allowed to return from the
318 // block condition until the safepoint operation is complete.
319 // 5. In VM or Transitioning between states
320 // If a Java thread is currently running in the VM or transitioning
321 // between states, the safepointing code will poll the thread state
322 // until the thread blocks itself when it attempts transitions to a
323 // new state or locking a safepoint checked monitor.
324
325 // We must never miss a thread with correct safepoint id, so we must make sure we arm
326 // the wait barrier for the next safepoint id/counter.
327 // Arming must be done after resetting _current_jni_active_count, _waiting_to_block.
328 _wait_barrier->arm(static_cast<int>(_safepoint_counter + 1));
329
330 assert((_safepoint_counter & 0x1) == 0, "must be even");
331 // The store to _safepoint_counter must happen after any stores in arming.
332 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
333
334 // We are synchronizing
335 OrderAccess::storestore(); // Ordered with _safepoint_counter
336 _state = _synchronizing;
337
338 // Arming the per thread poll while having _state != _not_synchronized means safepointing
339 log_trace(safepoint)("Setting thread local yield flag for threads");
340 OrderAccess::storestore(); // storestore, global state -> local state
341 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
342 // Make sure the threads start polling, it is time to yield.
343 SafepointMechanism::arm_local_poll(cur);
344 }
345 if (UseSystemMemoryBarrier) {
346 SystemMemoryBarrier::emit(); // storestore|storeload, global state -> local state
347 } else {
348 OrderAccess::fence(); // storestore|storeload, global state -> local state
349 }
350 }
351
352 // Roll all threads forward to a safepoint and suspend them all
353 void SafepointSynchronize::begin() {
354 assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint");
355
356 EventSafepointBegin begin_event;
357 SafepointTracing::begin(VMThread::vm_op_type());
358
359 Universe::heap()->safepoint_synchronize_begin();
360
361 // By getting the Threads_lock, we assure that no threads are about to start or
362 // exit. It is released again in SafepointSynchronize::end().
363 Threads_lock->lock();
364
365 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
366
367 int nof_threads = Threads::number_of_threads();
368
369 _nof_threads_hit_polling_page = 0;
370
371 log_debug(safepoint)("Safepoint synchronization initiated using %s wait barrier. (%d threads)", _wait_barrier->description(), nof_threads);
372
373 // Reset the count of active JNI critical threads
374 _current_jni_active_count = 0;
375
376 // Set number of threads to wait for
377 _waiting_to_block = nof_threads;
378
379 jlong safepoint_limit_time = 0;
380 if (SafepointTimeout) {
381 // Set the limit time, so that it can be compared to see if this has taken
382 // too long to complete.
383 safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)(SafepointTimeoutDelay * NANOSECS_PER_MILLISEC);
384 timeout_error_printed = false;
385 }
386
387 EventSafepointStateSynchronization sync_event;
388 int initial_running = 0;
389
390 // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before.
391 arm_safepoint();
392
393 // Will spin until all threads are safe.
394 int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running);
395 assert(_waiting_to_block == 0, "No thread should be running");
396
397 #ifndef PRODUCT
398 // Mark all threads
399 if (VerifyCrossModifyFence) {
400 JavaThreadIteratorWithHandle jtiwh;
401 for (; JavaThread *cur = jtiwh.next(); ) {
402 cur->set_requires_cross_modify_fence(true);
403 }
404 }
405
406 if (safepoint_limit_time != 0) {
407 jlong current_time = os::javaTimeNanos();
408 if (safepoint_limit_time < current_time) {
409 log_warning(safepoint)("# SafepointSynchronize: Finished after "
410 INT64_FORMAT_W(6) " ms",
411 (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS));
412 }
413 }
414 #endif
415
416 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
417
418 // Record state
419 _state = _synchronized;
420
421 OrderAccess::fence();
422
423 // Set the new id
424 ++_safepoint_id;
425
426 #ifdef ASSERT
427 // Make sure all the threads were visited.
428 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
429 assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread");
430 }
431 #endif // ASSERT
432
433 // Update the count of active JNI critical regions
434 GCLocker::set_jni_lock_count(_current_jni_active_count);
435
436 post_safepoint_synchronize_event(sync_event,
437 _safepoint_id,
438 initial_running,
439 _waiting_to_block, iterations);
440
441 SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page);
442
443 // We do the safepoint cleanup first since a GC related safepoint
444 // needs cleanup to be completed before running the GC op.
445 EventSafepointCleanup cleanup_event;
446 do_cleanup_tasks();
447 post_safepoint_cleanup_event(cleanup_event, _safepoint_id);
448
449 post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count);
450 SafepointTracing::cleanup();
451 }
452
453 void SafepointSynchronize::disarm_safepoint() {
454 uint64_t active_safepoint_counter = _safepoint_counter;
455 {
456 JavaThreadIteratorWithHandle jtiwh;
457 #ifdef ASSERT
458 // A pending_exception cannot be installed during a safepoint. The threads
459 // may install an async exception after they come back from a safepoint into
460 // pending_exception after they unblock. But that should happen later.
461 for (; JavaThread *cur = jtiwh.next(); ) {
462 assert (!(cur->has_pending_exception() &&
463 cur->safepoint_state()->is_at_poll_safepoint()),
464 "safepoint installed a pending exception");
465 }
466 #endif // ASSERT
467
468 OrderAccess::fence(); // keep read and write of _state from floating up
469 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
470
471 // Change state first to _not_synchronized.
472 // No threads should see _synchronized when running.
473 _state = _not_synchronized;
474
475 // Set the next dormant (even) safepoint id.
476 assert((_safepoint_counter & 0x1) == 1, "must be odd");
477 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
478
479 OrderAccess::fence(); // Keep the local state from floating up.
480
481 jtiwh.rewind();
482 for (; JavaThread *current = jtiwh.next(); ) {
483 // Clear the visited flag to ensure that the critical counts are collected properly.
484 DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);)
485 ThreadSafepointState* cur_state = current->safepoint_state();
486 assert(!cur_state->is_running(), "Thread not suspended at safepoint");
487 cur_state->restart(); // TSS _running
488 assert(cur_state->is_running(), "safepoint state has not been reset");
489 }
490 } // ~JavaThreadIteratorWithHandle
491
492 // Release threads lock, so threads can be created/destroyed again.
493 Threads_lock->unlock();
494
495 // Wake threads after local state is correctly set.
496 _wait_barrier->disarm();
497 }
498
499 // Wake up all threads, so they are ready to resume execution after the safepoint
500 // operation has been carried out
501 void SafepointSynchronize::end() {
502 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
503 EventSafepointEnd event;
504 assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint");
505
506 disarm_safepoint();
507
508 Universe::heap()->safepoint_synchronize_end();
509
510 SafepointTracing::end();
511
512 post_safepoint_end_event(event, safepoint_id());
513 }
514
515 bool SafepointSynchronize::is_cleanup_needed() {
516 // Need a safepoint if some inline cache buffers is non-empty
517 if (!InlineCacheBuffer::is_empty()) return true;
518 if (StringTable::needs_rehashing()) return true;
519 if (SymbolTable::needs_rehashing()) return true;
520 return false;
521 }
522
523 class ParallelCleanupTask : public WorkerTask {
524 private:
525 SubTasksDone _subtasks;
526 bool _do_lazy_roots;
527
528 class Tracer {
529 private:
530 const char* _name;
531 EventSafepointCleanupTask _event;
532 TraceTime _timer;
533
534 public:
535 Tracer(const char* name) :
536 _name(name),
537 _event(),
538 _timer(name, TRACETIME_LOG(Info, safepoint, cleanup)) {}
539 ~Tracer() {
540 post_safepoint_cleanup_task_event(_event, SafepointSynchronize::safepoint_id(), _name);
541 }
542 };
543
544 public:
545 ParallelCleanupTask() :
546 WorkerTask("Parallel Safepoint Cleanup"),
547 _subtasks(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS),
548 _do_lazy_roots(!VMThread::vm_operation()->skip_thread_oop_barriers() &&
549 Universe::heap()->uses_stack_watermark_barrier()) {}
550
551 uint expected_num_workers() const {
552 uint workers = 0;
553
554 if (SymbolTable::rehash_table_expects_safepoint_rehashing()) {
555 workers++;
556 }
557
558 if (StringTable::rehash_table_expects_safepoint_rehashing()) {
559 workers++;
560 }
561
562 if (InlineCacheBuffer::needs_update_inline_caches()) {
563 workers++;
564 }
565
566 if (_do_lazy_roots) {
567 workers++;
568 }
569
570 return MAX2<uint>(1, workers);
571 }
572
573 void work(uint worker_id) {
574 // These tasks are ordered by relative length of time to execute so that potentially longer tasks start first.
575 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
576 if (SymbolTable::needs_rehashing()) {
577 Tracer t("rehashing symbol table");
578 SymbolTable::rehash_table();
579 }
580 }
581
582 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
583 if (StringTable::needs_rehashing()) {
584 Tracer t("rehashing string table");
585 StringTable::rehash_table();
586 }
587 }
588
589 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_LAZY_ROOT_PROCESSING)) {
590 if (_do_lazy_roots) {
591 Tracer t("lazy partial thread root processing");
592 class LazyRootClosure : public ThreadClosure {
593 public:
594 void do_thread(Thread* thread) {
595 StackWatermarkSet::start_processing(JavaThread::cast(thread), StackWatermarkKind::gc);
596 }
597 };
598 LazyRootClosure cl;
599 Threads::java_threads_do(&cl);
600 }
601 }
602
603 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
604 Tracer t("updating inline caches");
605 InlineCacheBuffer::update_inline_caches();
606 }
607
608 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_REQUEST_OOPSTORAGE_CLEANUP)) {
609 // Don't bother reporting event or time for this very short operation.
610 // To have any utility we'd also want to report whether needed.
611 OopStorage::trigger_cleanup_if_needed();
612 }
613
614 _subtasks.all_tasks_claimed();
615 }
616 };
617
618 // Various cleaning tasks that should be done periodically at safepoints.
619 void SafepointSynchronize::do_cleanup_tasks() {
620
621 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
622
623 CollectedHeap* heap = Universe::heap();
624 assert(heap != nullptr, "heap not initialized yet?");
625 ParallelCleanupTask cleanup;
626 WorkerThreads* cleanup_workers = heap->safepoint_workers();
627 const uint expected_num_workers = cleanup.expected_num_workers();
628 if (cleanup_workers != nullptr && expected_num_workers > 1) {
629 // Parallel cleanup using GC provided thread pool.
630 const uint num_workers = MIN2(expected_num_workers, cleanup_workers->active_workers());
631 cleanup_workers->run_task(&cleanup, num_workers);
632 } else {
633 // Serial cleanup using VMThread.
634 cleanup.work(0);
635 }
636
637 assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
638
639 if (log_is_enabled(Debug, monitorinflation)) {
640 // The VMThread calls do_final_audit_and_print_stats() which calls
641 // audit_and_print_stats() at the Info level at VM exit time.
642 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
643 }
644 }
645
646 // Methods for determining if a JavaThread is safepoint safe.
647
648 // False means unsafe with undetermined state.
649 // True means a determined state, but it may be an unsafe state.
650 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
651 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
652 assert((safepoint_count != InactiveSafepointCounter &&
653 Thread::current() == (Thread*)VMThread::vm_thread() &&
654 SafepointSynchronize::_state != _not_synchronized)
655 || safepoint_count == InactiveSafepointCounter, "Invalid check");
656
657 // To handle the thread_blocked state on the backedge of the WaitBarrier from
658 // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
659 // re-read state after we read thread safepoint id. The JavaThread changes its
660 // thread state from thread_blocked before resetting safepoint id to 0.
661 // This guarantees the second read will be from an updated thread state. It can
662 // either be different state making this an unsafe state or it can see blocked
663 // again. When we see blocked twice with a 0 safepoint id, either:
664 // - It is normally blocked, e.g. on Mutex, TBIVM.
665 // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
666 // - It was in SS:block() but now on a Mutex.
667 // All of these cases are safe.
668
669 *state = thread->thread_state();
670 OrderAccess::loadload();
671 uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire
672 if (sid != InactiveSafepointCounter && sid != safepoint_count) {
673 // In an old safepoint, state not relevant.
674 return false;
675 }
676 return *state == thread->thread_state();
677 }
678
679 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
680 switch(state) {
681 case _thread_in_native:
682 // native threads are safe if they have no java stack or have walkable stack
683 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
684
685 case _thread_blocked:
686 // On wait_barrier or blocked.
687 // Blocked threads should already have walkable stack.
688 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
689 return true;
690
691 default:
692 return false;
693 }
694 }
695
696 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
697 if (thread->is_terminated()) {
698 return true;
699 }
700 JavaThreadState stable_state;
701 if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
702 return safepoint_safe_with(thread, stable_state);
703 }
704 return false;
705 }
706
707
708 // -------------------------------------------------------------------------------------------------------
709 // Implementation of Safepoint blocking point
710
711 void SafepointSynchronize::block(JavaThread *thread) {
712 assert(thread != nullptr, "thread must be set");
713
714 // Threads shouldn't block if they are in the middle of printing, but...
715 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
716
717 // Only bail from the block() call if the thread is gone from the
718 // thread list; starting to exit should still block.
719 if (thread->is_terminated()) {
720 // block current thread if we come here from native code when VM is gone
721 thread->block_if_vm_exited();
722
723 // otherwise do nothing
724 return;
725 }
726
727 JavaThreadState state = thread->thread_state();
728 thread->frame_anchor()->make_walkable();
729
730 uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
731
732 // We have no idea where the VMThread is, it might even be at next safepoint.
733 // So we can miss this poll, but stop at next.
734
735 // Load dependent store, it must not pass loading of safepoint_id.
736 thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
737
738 // This part we can skip if we notice we miss or are in a future safepoint.
739 OrderAccess::storestore();
740 // Load in wait barrier should not float up
741 thread->set_thread_state_fence(_thread_blocked);
742
743 _wait_barrier->wait(static_cast<int>(safepoint_id));
744 assert(_state != _synchronized, "Can't be");
745
746 // If barrier is disarmed stop store from floating above loads in barrier.
747 OrderAccess::loadstore();
748 thread->set_thread_state(state);
749
750 // Then we reset the safepoint id to inactive.
751 thread->safepoint_state()->reset_safepoint_id(); // Release store
752
753 OrderAccess::fence();
754
755 guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
756 "The safepoint id should be set only in block path");
757
758 // cross_modify_fence is done by SafepointMechanism::process_if_requested
759 // which is the only caller here.
760 }
761
762 // ------------------------------------------------------------------------------------------------------
763 // Exception handlers
764
765
766 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
767 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
768 thread->set_thread_state(_thread_in_vm);
769
770 // Enable WXWrite: the function is called implicitly from java code.
771 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread));
772
773 if (log_is_enabled(Info, safepoint, stats)) {
774 Atomic::inc(&_nof_threads_hit_polling_page);
775 }
776
777 ThreadSafepointState* state = thread->safepoint_state();
778
779 state->handle_polling_page_exception();
780
781 thread->set_thread_state(_thread_in_Java);
782 }
783
784
785 void SafepointSynchronize::print_safepoint_timeout() {
786 if (!timeout_error_printed) {
787 timeout_error_printed = true;
788 // Print out the thread info which didn't reach the safepoint for debugging
789 // purposes (useful when there are lots of threads in the debugger).
790 LogTarget(Warning, safepoint) lt;
791 if (lt.is_enabled()) {
792 ResourceMark rm;
793 LogStream ls(lt);
794
795 ls.cr();
796 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
797 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
798 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
799 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
800 if (cur_thread->safepoint_state()->is_running()) {
801 ls.print("# ");
802 cur_thread->print_on(&ls);
803 ls.cr();
804 }
805 }
806 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
807 }
808 }
809
810 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
811 // ShowMessageBoxOnError.
812 if (AbortVMOnSafepointTimeout) {
813 // Send the blocking thread a signal to terminate and write an error file.
814 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
815 if (cur_thread->safepoint_state()->is_running()) {
816 if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
817 break; // Could not send signal. Report fatal error.
818 }
819 // Give cur_thread a chance to report the error and terminate the VM.
820 os::naked_sleep(3000);
821 }
822 }
823 fatal("Safepoint sync time longer than %.6f ms detected when executing %s.",
824 SafepointTimeoutDelay, VMThread::vm_operation()->name());
825 }
826 }
827
828 // -------------------------------------------------------------------------------------------------------
829 // Implementation of ThreadSafepointState
830
831 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
832 : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
833 _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(nullptr) {
834 }
835
836 void ThreadSafepointState::create(JavaThread *thread) {
837 ThreadSafepointState *state = new ThreadSafepointState(thread);
838 thread->set_safepoint_state(state);
839 }
840
841 void ThreadSafepointState::destroy(JavaThread *thread) {
842 if (thread->safepoint_state()) {
843 delete(thread->safepoint_state());
844 thread->set_safepoint_state(nullptr);
845 }
846 }
847
848 uint64_t ThreadSafepointState::get_safepoint_id() const {
849 return Atomic::load_acquire(&_safepoint_id);
850 }
851
852 void ThreadSafepointState::reset_safepoint_id() {
853 Atomic::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
854 }
855
856 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
857 Atomic::release_store(&_safepoint_id, safepoint_id);
858 }
859
860 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
861 assert(is_running(), "better be running or just have hit safepoint poll");
862
863 JavaThreadState stable_state;
864 if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
865 // We could not get stable state of the JavaThread.
866 // Consider it running and just return.
867 return;
868 }
869
870 if (safepoint_safe_with(_thread, stable_state)) {
871 account_safe_thread();
872 return;
873 }
874
875 // All other thread states will continue to run until they
876 // transition and self-block in state _blocked
877 // Safepoint polling in compiled code causes the Java threads to do the same.
878 // Note: new threads may require a malloc so they must be allowed to finish
879
880 assert(is_running(), "examine_state_of_thread on non-running thread");
881 return;
882 }
883
884 void ThreadSafepointState::account_safe_thread() {
885 SafepointSynchronize::decrement_waiting_to_block();
886 if (_thread->in_critical()) {
887 // Notice that this thread is in a critical section
888 SafepointSynchronize::increment_jni_active_count();
889 }
890 DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
891 assert(!_safepoint_safe, "Must be unsafe before safe");
892 _safepoint_safe = true;
893 }
894
895 void ThreadSafepointState::restart() {
896 assert(_safepoint_safe, "Must be safe before unsafe");
897 _safepoint_safe = false;
898 }
899
900 void ThreadSafepointState::print_on(outputStream *st) const {
901 const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
902
903 st->print_cr("Thread: " INTPTR_FORMAT
904 " [0x%2x] State: %s _at_poll_safepoint %d",
905 p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
906
907 _thread->print_thread_state_on(st);
908 }
909
910 // ---------------------------------------------------------------------------------------------------------------------
911
912 // Process pending operation.
913 void ThreadSafepointState::handle_polling_page_exception() {
914 JavaThread* self = thread();
915 assert(self == JavaThread::current(), "must be self");
916
917 // Step 1: Find the nmethod from the return address
918 address real_return_addr = self->saved_exception_pc();
919
920 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
921 assert(cb != nullptr && cb->is_compiled(), "return address should be in nmethod");
922 CompiledMethod* nm = (CompiledMethod*)cb;
923
924 // Find frame of caller
925 frame stub_fr = self->last_frame();
926 CodeBlob* stub_cb = stub_fr.cb();
927 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
928 RegisterMap map(self,
929 RegisterMap::UpdateMap::include,
930 RegisterMap::ProcessFrames::skip,
931 RegisterMap::WalkContinuation::skip);
932 frame caller_fr = stub_fr.sender(&map);
933
934 // Should only be poll_return or poll
935 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
936
937 // This is a poll immediately before a return. The exception handling code
938 // has already had the effect of causing the return to occur, so the execution
939 // will continue immediately after the call. In addition, the oopmap at the
940 // return point does not mark the return value as an oop (if it is), so
941 // it needs a handle here to be updated.
942 if( nm->is_at_poll_return(real_return_addr) ) {
943 ResourceMark rm;
944 // See if return type is an oop.
945 Method* method = nm->method();
946 bool return_oop = method->is_returning_oop();
947 HandleMark hm(self);
948
949 GrowableArray<Handle> return_values;
950 InlineKlass* vk = nullptr;
951 if (return_oop && InlineTypeReturnedAsFields &&
952 (method->result_type() == T_PRIMITIVE_OBJECT || method->result_type() == T_OBJECT)) {
953 // Check if an inline type is returned as fields
954 vk = InlineKlass::returned_inline_klass(map);
955 if (vk != nullptr) {
956 // We're at a safepoint at the return of a method that returns
957 // multiple values. We must make sure we preserve the oop values
958 // across the safepoint.
959 assert(vk == method->returns_inline_type(thread()), "bad inline klass");
960 vk->save_oop_fields(map, return_values);
961 return_oop = false;
962 }
963 }
964
965 if (return_oop) {
966 // The oop result has been saved on the stack together with all
967 // the other registers. In order to preserve it over GCs we need
968 // to keep it in a handle.
969 oop result = caller_fr.saved_oop_result(&map);
970 assert(oopDesc::is_oop_or_null(result), "must be oop");
971 return_values.push(Handle(self, result));
972 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
973 }
974
975 // We get here if compiled return polls found a reason to call into the VM.
976 // One condition for that is that the top frame is not yet safe to use.
977 // The following stack watermark barrier poll will catch such situations.
978 StackWatermarkSet::after_unwind(self);
979
980 // Process pending operation
981 SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */);
982
983 // restore oop result, if any
984 if (return_oop) {
985 assert(return_values.length() == 1, "only one return value");
986 caller_fr.set_saved_oop_result(&map, return_values.pop()());
987 } else if (vk != nullptr) {
988 vk->restore_oop_results(map, return_values);
989 }
990 }
991
992 // This is a safepoint poll. Verify the return address and block.
993 else {
994
995 // verify the blob built the "return address" correctly
996 assert(real_return_addr == caller_fr.pc(), "must match");
997
998 set_at_poll_safepoint(true);
999 // Process pending operation
1000 // We never deliver an async exception at a polling point as the
1001 // compiler may not have an exception handler for it (polling at
1002 // a return point is ok though). We will check for a pending async
1003 // exception below and deoptimize if needed. We also cannot deoptimize
1004 // and still install the exception here because live registers needed
1005 // during deoptimization are clobbered by the exception path. The
1006 // exception will just be delivered once we get into the interpreter.
1007 SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */);
1008 set_at_poll_safepoint(false);
1009
1010 if (self->has_async_exception_condition()) {
1011 Deoptimization::deoptimize_frame(self, caller_fr.id());
1012 log_info(exceptions)("deferred async exception at compiled safepoint");
1013 }
1014
1015 // If an exception has been installed we must verify that the top frame wasn't deoptimized.
1016 if (self->has_pending_exception() ) {
1017 RegisterMap map(self,
1018 RegisterMap::UpdateMap::include,
1019 RegisterMap::ProcessFrames::skip,
1020 RegisterMap::WalkContinuation::skip);
1021 frame caller_fr = stub_fr.sender(&map);
1022 if (caller_fr.is_deoptimized_frame()) {
1023 // The exception path will destroy registers that are still
1024 // live and will be needed during deoptimization, so if we
1025 // have an exception now things are messed up. We only check
1026 // at this scope because for a poll return it is ok to deoptimize
1027 // while having a pending exception since the call we are returning
1028 // from already collides with exception handling registers and
1029 // so there is no issue (the exception handling path kills call
1030 // result registers but this is ok since the exception kills
1031 // the result anyway).
1032 fatal("Exception installed and deoptimization is pending");
1033 }
1034 }
1035 }
1036 }
1037
1038
1039 // -------------------------------------------------------------------------------------------------------
1040 // Implementation of SafepointTracing
1041
1042 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
1043 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
1044 jlong SafepointTracing::_last_safepoint_cleanup_time_ns = 0;
1045 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
1046 jlong SafepointTracing::_last_app_time_ns = 0;
1047 int SafepointTracing::_nof_threads = 0;
1048 int SafepointTracing::_nof_running = 0;
1049 int SafepointTracing::_page_trap = 0;
1050 VM_Operation::VMOp_Type SafepointTracing::_current_type;
1051 jlong SafepointTracing::_max_sync_time = 0;
1052 jlong SafepointTracing::_max_cleanup_time = 0;
1053 jlong SafepointTracing::_max_vmop_time = 0;
1054 uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
1055
1056 void SafepointTracing::init() {
1057 // Application start
1058 _last_safepoint_end_time_ns = os::javaTimeNanos();
1059 }
1060
1061 // Helper method to print the header.
1062 static void print_header(outputStream* st) {
1063 // The number of spaces is significant here, and should match the format
1064 // specifiers in print_statistics().
1065
1066 st->print("VM Operation "
1067 "[ threads: total initial_running ]"
1068 "[ time: sync cleanup vmop total ]");
1069
1070 st->print_cr(" page_trap_count");
1071 }
1072
1073 // This prints a nice table. To get the statistics to not shift due to the logging uptime
1074 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
1075 void SafepointTracing::statistics_log() {
1076 LogTarget(Info, safepoint, stats) lt;
1077 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
1078 LogStream ls(lt);
1079
1080 static int _cur_stat_index = 0;
1081
1082 // Print header every 30 entries
1083 if ((_cur_stat_index % 30) == 0) {
1084 print_header(&ls);
1085 _cur_stat_index = 1; // wrap
1086 } else {
1087 _cur_stat_index++;
1088 }
1089
1090 ls.print("%-28s [ "
1091 INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " "
1092 "]",
1093 VM_Operation::name(_current_type),
1094 _nof_threads,
1095 _nof_running);
1096 ls.print("[ "
1097 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " "
1098 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
1099 (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
1100 (int64_t)(_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns),
1101 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns),
1102 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
1103
1104 ls.print_cr(INT32_FORMAT_W(16), _page_trap);
1105 }
1106
1107 // This method will be called when VM exits. This tries to summarize the sampling.
1108 // Current thread may already be deleted, so don't use ResourceMark.
1109 void SafepointTracing::statistics_exit_log() {
1110 if (!log_is_enabled(Info, safepoint, stats)) {
1111 return;
1112 }
1113 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1114 if (_op_count[index] != 0) {
1115 log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1116 _op_count[index]);
1117 }
1118 }
1119
1120 log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns",
1121 (int64_t)(_max_sync_time));
1122 log_info(safepoint, stats)("Maximum cleanup time " INT64_FORMAT" ns",
1123 (int64_t)(_max_cleanup_time));
1124 log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
1125 INT64_FORMAT " ns",
1126 (int64_t)(_max_vmop_time));
1127 }
1128
1129 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
1130 _op_count[type]++;
1131 _current_type = type;
1132
1133 // update the time stamp to begin recording safepoint time
1134 _last_safepoint_begin_time_ns = os::javaTimeNanos();
1135 _last_safepoint_sync_time_ns = 0;
1136 _last_safepoint_cleanup_time_ns = 0;
1137
1138 _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
1139 _last_safepoint_end_time_ns = 0;
1140
1141 RuntimeService::record_safepoint_begin(_last_app_time_ns);
1142 }
1143
1144 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
1145 _last_safepoint_sync_time_ns = os::javaTimeNanos();
1146 _nof_threads = nof_threads;
1147 _nof_running = nof_running;
1148 _page_trap = traps;
1149 RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
1150 }
1151
1152 void SafepointTracing::cleanup() {
1153 _last_safepoint_cleanup_time_ns = os::javaTimeNanos();
1154 }
1155
1156 void SafepointTracing::end() {
1157 _last_safepoint_end_time_ns = os::javaTimeNanos();
1158
1159 if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
1160 _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
1161 }
1162 if (_max_cleanup_time < (_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns)) {
1163 _max_cleanup_time = _last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns;
1164 }
1165 if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
1166 _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
1167 }
1168 if (log_is_enabled(Info, safepoint, stats)) {
1169 statistics_log();
1170 }
1171
1172 log_info(safepoint)(
1173 "Safepoint \"%s\", "
1174 "Time since last: " JLONG_FORMAT " ns, "
1175 "Reaching safepoint: " JLONG_FORMAT " ns, "
1176 "Cleanup: " JLONG_FORMAT " ns, "
1177 "At safepoint: " JLONG_FORMAT " ns, "
1178 "Total: " JLONG_FORMAT " ns",
1179 VM_Operation::name(_current_type),
1180 _last_app_time_ns,
1181 _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns,
1182 _last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns,
1183 _last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns,
1184 _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns
1185 );
1186
1187 RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns);
1188 }