1 /*
2 * Copyright (c) 1997, 2022, 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 != NULL) {
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 = NULL;
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() == NULL, "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 = NULL;
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 == NULL, "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 != NULL) {
268 assert(cur_tss->is_running(), "Illegal initial state");
269 if (thread_not_running(cur_tss)) {
270 --still_running;
271 *p_prev = NULL;
272 ThreadSafepointState *tmp = cur_tss;
273 cur_tss = cur_tss->get_next();
274 tmp->set_next(NULL);
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 == NULL, "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 * (NANOUNITS / MILLIUNITS);
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 void work(uint worker_id) {
552 // These tasks are ordered by relative length of time to execute so that potentially longer tasks start first.
553 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
554 if (SymbolTable::needs_rehashing()) {
555 Tracer t("rehashing symbol table");
556 SymbolTable::rehash_table();
557 }
558 }
559
560 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
561 if (StringTable::needs_rehashing()) {
562 Tracer t("rehashing string table");
563 StringTable::rehash_table();
564 }
565 }
566
567 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_LAZY_ROOT_PROCESSING)) {
568 if (_do_lazy_roots) {
569 Tracer t("lazy partial thread root processing");
570 class LazyRootClosure : public ThreadClosure {
571 public:
572 void do_thread(Thread* thread) {
573 StackWatermarkSet::start_processing(JavaThread::cast(thread), StackWatermarkKind::gc);
574 }
575 };
576 LazyRootClosure cl;
577 Threads::java_threads_do(&cl);
578 }
579 }
580
581 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
582 Tracer t("updating inline caches");
583 InlineCacheBuffer::update_inline_caches();
584 }
585
586 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_REQUEST_OOPSTORAGE_CLEANUP)) {
587 // Don't bother reporting event or time for this very short operation.
588 // To have any utility we'd also want to report whether needed.
589 OopStorage::trigger_cleanup_if_needed();
590 }
591
592 _subtasks.all_tasks_claimed();
593 }
594 };
595
596 // Various cleaning tasks that should be done periodically at safepoints.
597 void SafepointSynchronize::do_cleanup_tasks() {
598
599 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
600
601 CollectedHeap* heap = Universe::heap();
602 assert(heap != NULL, "heap not initialized yet?");
603 ParallelCleanupTask cleanup;
604 WorkerThreads* cleanup_workers = heap->safepoint_workers();
605 if (cleanup_workers != NULL) {
606 // Parallel cleanup using GC provided thread pool.
607 cleanup_workers->run_task(&cleanup);
608 } else {
609 // Serial cleanup using VMThread.
610 cleanup.work(0);
611 }
612
613 assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
614
615 if (log_is_enabled(Debug, monitorinflation)) {
616 // The VMThread calls do_final_audit_and_print_stats() which calls
617 // audit_and_print_stats() at the Info level at VM exit time.
618 ObjectSynchronizer::audit_and_print_stats(false /* on_exit */);
619 }
620 }
621
622 // Methods for determining if a JavaThread is safepoint safe.
623
624 // False means unsafe with undetermined state.
625 // True means a determined state, but it may be an unsafe state.
626 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
627 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
628 assert((safepoint_count != InactiveSafepointCounter &&
629 Thread::current() == (Thread*)VMThread::vm_thread() &&
630 SafepointSynchronize::_state != _not_synchronized)
631 || safepoint_count == InactiveSafepointCounter, "Invalid check");
632
633 // To handle the thread_blocked state on the backedge of the WaitBarrier from
634 // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
635 // re-read state after we read thread safepoint id. The JavaThread changes its
636 // thread state from thread_blocked before resetting safepoint id to 0.
637 // This guarantees the second read will be from an updated thread state. It can
638 // either be different state making this an unsafe state or it can see blocked
639 // again. When we see blocked twice with a 0 safepoint id, either:
640 // - It is normally blocked, e.g. on Mutex, TBIVM.
641 // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
642 // - It was in SS:block() but now on a Mutex.
643 // All of these cases are safe.
644
645 *state = thread->thread_state();
646 OrderAccess::loadload();
647 uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire
648 if (sid != InactiveSafepointCounter && sid != safepoint_count) {
649 // In an old safepoint, state not relevant.
650 return false;
651 }
652 return *state == thread->thread_state();
653 }
654
655 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
656 switch(state) {
657 case _thread_in_native:
658 // native threads are safe if they have no java stack or have walkable stack
659 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
660
661 case _thread_blocked:
662 // On wait_barrier or blocked.
663 // Blocked threads should already have walkable stack.
664 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
665 return true;
666
667 default:
668 return false;
669 }
670 }
671
672 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
673 if (thread->is_terminated()) {
674 return true;
675 }
676 JavaThreadState stable_state;
677 if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
678 return safepoint_safe_with(thread, stable_state);
679 }
680 return false;
681 }
682
683
684 // -------------------------------------------------------------------------------------------------------
685 // Implementation of Safepoint blocking point
686
687 void SafepointSynchronize::block(JavaThread *thread) {
688 assert(thread != NULL, "thread must be set");
689
690 // Threads shouldn't block if they are in the middle of printing, but...
691 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
692
693 // Only bail from the block() call if the thread is gone from the
694 // thread list; starting to exit should still block.
695 if (thread->is_terminated()) {
696 // block current thread if we come here from native code when VM is gone
697 thread->block_if_vm_exited();
698
699 // otherwise do nothing
700 return;
701 }
702
703 JavaThreadState state = thread->thread_state();
704 thread->frame_anchor()->make_walkable();
705
706 uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
707
708 // We have no idea where the VMThread is, it might even be at next safepoint.
709 // So we can miss this poll, but stop at next.
710
711 // Load dependent store, it must not pass loading of safepoint_id.
712 thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
713
714 // This part we can skip if we notice we miss or are in a future safepoint.
715 OrderAccess::storestore();
716 // Load in wait barrier should not float up
717 thread->set_thread_state_fence(_thread_blocked);
718
719 _wait_barrier->wait(static_cast<int>(safepoint_id));
720 assert(_state != _synchronized, "Can't be");
721
722 // If barrier is disarmed stop store from floating above loads in barrier.
723 OrderAccess::loadstore();
724 thread->set_thread_state(state);
725
726 // Then we reset the safepoint id to inactive.
727 thread->safepoint_state()->reset_safepoint_id(); // Release store
728
729 OrderAccess::fence();
730
731 guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
732 "The safepoint id should be set only in block path");
733
734 // cross_modify_fence is done by SafepointMechanism::process_if_requested
735 // which is the only caller here.
736 }
737
738 // ------------------------------------------------------------------------------------------------------
739 // Exception handlers
740
741
742 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
743 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
744 thread->set_thread_state(_thread_in_vm);
745
746 // Enable WXWrite: the function is called implicitly from java code.
747 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread));
748
749 if (log_is_enabled(Info, safepoint, stats)) {
750 Atomic::inc(&_nof_threads_hit_polling_page);
751 }
752
753 ThreadSafepointState* state = thread->safepoint_state();
754
755 state->handle_polling_page_exception();
756
757 thread->set_thread_state(_thread_in_Java);
758 }
759
760
761 void SafepointSynchronize::print_safepoint_timeout() {
762 if (!timeout_error_printed) {
763 timeout_error_printed = true;
764 // Print out the thread info which didn't reach the safepoint for debugging
765 // purposes (useful when there are lots of threads in the debugger).
766 LogTarget(Warning, safepoint) lt;
767 if (lt.is_enabled()) {
768 ResourceMark rm;
769 LogStream ls(lt);
770
771 ls.cr();
772 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
773 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
774 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
775 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
776 if (cur_thread->safepoint_state()->is_running()) {
777 ls.print("# ");
778 cur_thread->print_on(&ls);
779 ls.cr();
780 }
781 }
782 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
783 }
784 }
785
786 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
787 // ShowMessageBoxOnError.
788 if (AbortVMOnSafepointTimeout) {
789 // Send the blocking thread a signal to terminate and write an error file.
790 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
791 if (cur_thread->safepoint_state()->is_running()) {
792 if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
793 break; // Could not send signal. Report fatal error.
794 }
795 // Give cur_thread a chance to report the error and terminate the VM.
796 os::naked_sleep(3000);
797 }
798 }
799 fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
800 SafepointTimeoutDelay, VMThread::vm_operation()->name());
801 }
802 }
803
804 // -------------------------------------------------------------------------------------------------------
805 // Implementation of ThreadSafepointState
806
807 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
808 : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
809 _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(NULL) {
810 }
811
812 void ThreadSafepointState::create(JavaThread *thread) {
813 ThreadSafepointState *state = new ThreadSafepointState(thread);
814 thread->set_safepoint_state(state);
815 }
816
817 void ThreadSafepointState::destroy(JavaThread *thread) {
818 if (thread->safepoint_state()) {
819 delete(thread->safepoint_state());
820 thread->set_safepoint_state(NULL);
821 }
822 }
823
824 uint64_t ThreadSafepointState::get_safepoint_id() const {
825 return Atomic::load_acquire(&_safepoint_id);
826 }
827
828 void ThreadSafepointState::reset_safepoint_id() {
829 Atomic::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
830 }
831
832 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
833 Atomic::release_store(&_safepoint_id, safepoint_id);
834 }
835
836 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
837 assert(is_running(), "better be running or just have hit safepoint poll");
838
839 JavaThreadState stable_state;
840 if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
841 // We could not get stable state of the JavaThread.
842 // Consider it running and just return.
843 return;
844 }
845
846 if (safepoint_safe_with(_thread, stable_state)) {
847 account_safe_thread();
848 return;
849 }
850
851 // All other thread states will continue to run until they
852 // transition and self-block in state _blocked
853 // Safepoint polling in compiled code causes the Java threads to do the same.
854 // Note: new threads may require a malloc so they must be allowed to finish
855
856 assert(is_running(), "examine_state_of_thread on non-running thread");
857 return;
858 }
859
860 void ThreadSafepointState::account_safe_thread() {
861 SafepointSynchronize::decrement_waiting_to_block();
862 if (_thread->in_critical()) {
863 // Notice that this thread is in a critical section
864 SafepointSynchronize::increment_jni_active_count();
865 }
866 DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
867 assert(!_safepoint_safe, "Must be unsafe before safe");
868 _safepoint_safe = true;
869 }
870
871 void ThreadSafepointState::restart() {
872 assert(_safepoint_safe, "Must be safe before unsafe");
873 _safepoint_safe = false;
874 }
875
876 void ThreadSafepointState::print_on(outputStream *st) const {
877 const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
878
879 st->print_cr("Thread: " INTPTR_FORMAT
880 " [0x%2x] State: %s _at_poll_safepoint %d",
881 p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
882
883 _thread->print_thread_state_on(st);
884 }
885
886 // ---------------------------------------------------------------------------------------------------------------------
887
888 // Process pending operation.
889 void ThreadSafepointState::handle_polling_page_exception() {
890 JavaThread* self = thread();
891 assert(self == JavaThread::current(), "must be self");
892
893 // Step 1: Find the nmethod from the return address
894 address real_return_addr = self->saved_exception_pc();
895
896 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
897 assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
898 CompiledMethod* nm = (CompiledMethod*)cb;
899
900 // Find frame of caller
901 frame stub_fr = self->last_frame();
902 CodeBlob* stub_cb = stub_fr.cb();
903 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
904 RegisterMap map(self,
905 RegisterMap::UpdateMap::include,
906 RegisterMap::ProcessFrames::skip,
907 RegisterMap::WalkContinuation::skip);
908 frame caller_fr = stub_fr.sender(&map);
909
910 // Should only be poll_return or poll
911 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
912
913 // This is a poll immediately before a return. The exception handling code
914 // has already had the effect of causing the return to occur, so the execution
915 // will continue immediately after the call. In addition, the oopmap at the
916 // return point does not mark the return value as an oop (if it is), so
917 // it needs a handle here to be updated.
918 if( nm->is_at_poll_return(real_return_addr) ) {
919 ResourceMark rm;
920 // See if return type is an oop.
921 Method* method = nm->method();
922 bool return_oop = method->is_returning_oop();
923 HandleMark hm(self);
924
925 GrowableArray<Handle> return_values;
926 InlineKlass* vk = NULL;
927 if (return_oop && InlineTypeReturnedAsFields &&
928 (method->result_type() == T_PRIMITIVE_OBJECT || method->result_type() == T_OBJECT)) {
929 // Check if an inline type is returned as fields
930 vk = InlineKlass::returned_inline_klass(map);
931 if (vk != NULL) {
932 // We're at a safepoint at the return of a method that returns
933 // multiple values. We must make sure we preserve the oop values
934 // across the safepoint.
935 assert(vk == method->returns_inline_type(thread()), "bad inline klass");
936 vk->save_oop_fields(map, return_values);
937 return_oop = false;
938 }
939 }
940
941 if (return_oop) {
942 // The oop result has been saved on the stack together with all
943 // the other registers. In order to preserve it over GCs we need
944 // to keep it in a handle.
945 oop result = caller_fr.saved_oop_result(&map);
946 assert(oopDesc::is_oop_or_null(result), "must be oop");
947 return_values.push(Handle(self, result));
948 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
949 }
950
951 // We get here if compiled return polls found a reason to call into the VM.
952 // One condition for that is that the top frame is not yet safe to use.
953 // The following stack watermark barrier poll will catch such situations.
954 StackWatermarkSet::after_unwind(self);
955
956 // Process pending operation
957 SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */);
958
959 // restore oop result, if any
960 if (return_oop) {
961 assert(return_values.length() == 1, "only one return value");
962 caller_fr.set_saved_oop_result(&map, return_values.pop()());
963 } else if (vk != NULL) {
964 vk->restore_oop_results(map, return_values);
965 }
966 }
967
968 // This is a safepoint poll. Verify the return address and block.
969 else {
970
971 // verify the blob built the "return address" correctly
972 assert(real_return_addr == caller_fr.pc(), "must match");
973
974 set_at_poll_safepoint(true);
975 // Process pending operation
976 // We never deliver an async exception at a polling point as the
977 // compiler may not have an exception handler for it (polling at
978 // a return point is ok though). We will check for a pending async
979 // exception below and deoptimize if needed. We also cannot deoptimize
980 // and still install the exception here because live registers needed
981 // during deoptimization are clobbered by the exception path. The
982 // exception will just be delivered once we get into the interpreter.
983 SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */);
984 set_at_poll_safepoint(false);
985
986 if (self->has_async_exception_condition()) {
987 Deoptimization::deoptimize_frame(self, caller_fr.id());
988 log_info(exceptions)("deferred async exception at compiled safepoint");
989 }
990
991 // If an exception has been installed we must verify that the top frame wasn't deoptimized.
992 if (self->has_pending_exception() ) {
993 RegisterMap map(self,
994 RegisterMap::UpdateMap::include,
995 RegisterMap::ProcessFrames::skip,
996 RegisterMap::WalkContinuation::skip);
997 frame caller_fr = stub_fr.sender(&map);
998 if (caller_fr.is_deoptimized_frame()) {
999 // The exception path will destroy registers that are still
1000 // live and will be needed during deoptimization, so if we
1001 // have an exception now things are messed up. We only check
1002 // at this scope because for a poll return it is ok to deoptimize
1003 // while having a pending exception since the call we are returning
1004 // from already collides with exception handling registers and
1005 // so there is no issue (the exception handling path kills call
1006 // result registers but this is ok since the exception kills
1007 // the result anyway).
1008 fatal("Exception installed and deoptimization is pending");
1009 }
1010 }
1011 }
1012 }
1013
1014
1015 // -------------------------------------------------------------------------------------------------------
1016 // Implementation of SafepointTracing
1017
1018 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
1019 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
1020 jlong SafepointTracing::_last_safepoint_cleanup_time_ns = 0;
1021 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
1022 jlong SafepointTracing::_last_app_time_ns = 0;
1023 int SafepointTracing::_nof_threads = 0;
1024 int SafepointTracing::_nof_running = 0;
1025 int SafepointTracing::_page_trap = 0;
1026 VM_Operation::VMOp_Type SafepointTracing::_current_type;
1027 jlong SafepointTracing::_max_sync_time = 0;
1028 jlong SafepointTracing::_max_cleanup_time = 0;
1029 jlong SafepointTracing::_max_vmop_time = 0;
1030 uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
1031
1032 void SafepointTracing::init() {
1033 // Application start
1034 _last_safepoint_end_time_ns = os::javaTimeNanos();
1035 }
1036
1037 // Helper method to print the header.
1038 static void print_header(outputStream* st) {
1039 // The number of spaces is significant here, and should match the format
1040 // specifiers in print_statistics().
1041
1042 st->print("VM Operation "
1043 "[ threads: total initial_running ]"
1044 "[ time: sync cleanup vmop total ]");
1045
1046 st->print_cr(" page_trap_count");
1047 }
1048
1049 // This prints a nice table. To get the statistics to not shift due to the logging uptime
1050 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
1051 void SafepointTracing::statistics_log() {
1052 LogTarget(Info, safepoint, stats) lt;
1053 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
1054 LogStream ls(lt);
1055
1056 static int _cur_stat_index = 0;
1057
1058 // Print header every 30 entries
1059 if ((_cur_stat_index % 30) == 0) {
1060 print_header(&ls);
1061 _cur_stat_index = 1; // wrap
1062 } else {
1063 _cur_stat_index++;
1064 }
1065
1066 ls.print("%-28s [ "
1067 INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " "
1068 "]",
1069 VM_Operation::name(_current_type),
1070 _nof_threads,
1071 _nof_running);
1072 ls.print("[ "
1073 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " "
1074 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
1075 (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
1076 (int64_t)(_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns),
1077 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns),
1078 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
1079
1080 ls.print_cr(INT32_FORMAT_W(16), _page_trap);
1081 }
1082
1083 // This method will be called when VM exits. This tries to summarize the sampling.
1084 // Current thread may already be deleted, so don't use ResourceMark.
1085 void SafepointTracing::statistics_exit_log() {
1086 if (!log_is_enabled(Info, safepoint, stats)) {
1087 return;
1088 }
1089 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1090 if (_op_count[index] != 0) {
1091 log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1092 _op_count[index]);
1093 }
1094 }
1095
1096 log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns",
1097 (int64_t)(_max_sync_time));
1098 log_info(safepoint, stats)("Maximum cleanup time " INT64_FORMAT" ns",
1099 (int64_t)(_max_cleanup_time));
1100 log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
1101 INT64_FORMAT " ns",
1102 (int64_t)(_max_vmop_time));
1103 }
1104
1105 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
1106 _op_count[type]++;
1107 _current_type = type;
1108
1109 // update the time stamp to begin recording safepoint time
1110 _last_safepoint_begin_time_ns = os::javaTimeNanos();
1111 _last_safepoint_sync_time_ns = 0;
1112 _last_safepoint_cleanup_time_ns = 0;
1113
1114 _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
1115 _last_safepoint_end_time_ns = 0;
1116
1117 RuntimeService::record_safepoint_begin(_last_app_time_ns);
1118 }
1119
1120 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
1121 _last_safepoint_sync_time_ns = os::javaTimeNanos();
1122 _nof_threads = nof_threads;
1123 _nof_running = nof_running;
1124 _page_trap = traps;
1125 RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
1126 }
1127
1128 void SafepointTracing::cleanup() {
1129 _last_safepoint_cleanup_time_ns = os::javaTimeNanos();
1130 }
1131
1132 void SafepointTracing::end() {
1133 _last_safepoint_end_time_ns = os::javaTimeNanos();
1134
1135 if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
1136 _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
1137 }
1138 if (_max_cleanup_time < (_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns)) {
1139 _max_cleanup_time = _last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns;
1140 }
1141 if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
1142 _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
1143 }
1144 if (log_is_enabled(Info, safepoint, stats)) {
1145 statistics_log();
1146 }
1147
1148 log_info(safepoint)(
1149 "Safepoint \"%s\", "
1150 "Time since last: " JLONG_FORMAT " ns, "
1151 "Reaching safepoint: " JLONG_FORMAT " ns, "
1152 "Cleanup: " JLONG_FORMAT " ns, "
1153 "At safepoint: " JLONG_FORMAT " ns, "
1154 "Total: " JLONG_FORMAT " ns",
1155 VM_Operation::name(_current_type),
1156 _last_app_time_ns,
1157 _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns,
1158 _last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns,
1159 _last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns,
1160 _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns
1161 );
1162
1163 RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns);
1164 }