1 /*
2 * Copyright (c) 1997, 2025, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 *
23 */
24
25 #include "code/codeCache.hpp"
26 #include "code/nmethod.hpp"
27 #include "code/pcDesc.hpp"
28 #include "code/scopeDesc.hpp"
29 #include "compiler/compilationPolicy.hpp"
30 #include "gc/shared/collectedHeap.hpp"
31 #include "gc/shared/gcLocker.hpp"
32 #include "gc/shared/oopStorage.hpp"
33 #include "gc/shared/strongRootsScope.hpp"
34 #include "gc/shared/workerThread.hpp"
35 #include "gc/shared/workerUtils.hpp"
36 #include "interpreter/interpreter.hpp"
37 #include "jfr/jfrEvents.hpp"
38 #include "logging/log.hpp"
39 #include "logging/logStream.hpp"
40 #include "memory/resourceArea.hpp"
41 #include "memory/universe.hpp"
42 #include "oops/oop.inline.hpp"
43 #include "oops/symbol.hpp"
44 #include "runtime/atomic.hpp"
45 #include "runtime/deoptimization.hpp"
46 #include "runtime/frame.inline.hpp"
47 #include "runtime/globals.hpp"
48 #include "runtime/handles.inline.hpp"
49 #include "runtime/interfaceSupport.inline.hpp"
50 #include "runtime/javaThread.inline.hpp"
51 #include "runtime/mutexLocker.hpp"
52 #include "runtime/orderAccess.hpp"
53 #include "runtime/osThread.hpp"
54 #include "runtime/safepoint.hpp"
55 #include "runtime/safepointMechanism.inline.hpp"
56 #include "runtime/signature.hpp"
57 #include "runtime/stackWatermarkSet.inline.hpp"
58 #include "runtime/stubCodeGenerator.hpp"
59 #include "runtime/stubRoutines.hpp"
60 #include "runtime/synchronizer.hpp"
61 #include "runtime/threads.hpp"
62 #include "runtime/threadSMR.hpp"
63 #include "runtime/threadWXSetters.inline.hpp"
64 #include "runtime/timerTrace.hpp"
65 #include "services/runtimeService.hpp"
66 #include "utilities/events.hpp"
67 #include "utilities/macros.hpp"
68 #include "utilities/systemMemoryBarrier.hpp"
69
70 static void post_safepoint_begin_event(EventSafepointBegin& event,
71 uint64_t safepoint_id,
72 int thread_count,
73 int critical_thread_count) {
74 if (event.should_commit()) {
75 event.set_safepointId(safepoint_id);
76 event.set_totalThreadCount(thread_count);
77 event.set_jniCriticalThreadCount(critical_thread_count);
78 event.commit();
79 }
80 }
81
82
83 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization& event,
84 uint64_t safepoint_id,
85 int initial_number_of_threads,
86 int threads_waiting_to_block,
87 int iterations) {
88 if (event.should_commit()) {
89 event.set_safepointId(safepoint_id);
90 event.set_initialThreadCount(initial_number_of_threads);
91 event.set_runningThreadCount(threads_waiting_to_block);
92 event.set_iterations(checked_cast<u4>(iterations));
93 event.commit();
94 }
95 }
96
97 static void post_safepoint_end_event(EventSafepointEnd& event, uint64_t safepoint_id) {
98 if (event.should_commit()) {
99 event.set_safepointId(safepoint_id);
100 event.commit();
101 }
102 }
103
104 // SafepointCheck
105 SafepointStateTracker::SafepointStateTracker(uint64_t safepoint_id, bool at_safepoint)
106 : _safepoint_id(safepoint_id), _at_safepoint(at_safepoint) {}
107
108 bool SafepointStateTracker::safepoint_state_changed() {
109 return _safepoint_id != SafepointSynchronize::safepoint_id() ||
110 _at_safepoint != SafepointSynchronize::is_at_safepoint();
111 }
112
113 // --------------------------------------------------------------------------------------------------
114 // Implementation of Safepoint begin/end
115
116 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
117 int SafepointSynchronize::_waiting_to_block = 0;
118 volatile uint64_t SafepointSynchronize::_safepoint_counter = 0;
119 uint64_t SafepointSynchronize::_safepoint_id = 0;
120 const uint64_t SafepointSynchronize::InactiveSafepointCounter = 0;
121 int SafepointSynchronize::_current_jni_active_count = 0;
122
123 WaitBarrier* SafepointSynchronize::_wait_barrier;
124
125 static bool timeout_error_printed = false;
126
127 // Statistic related
128 static jlong _safepoint_begin_time = 0;
129 static volatile int _nof_threads_hit_polling_page = 0;
130
131 void SafepointSynchronize::init(Thread* vmthread) {
132 // WaitBarrier should never be destroyed since we will have
133 // threads waiting on it while exiting.
134 _wait_barrier = new WaitBarrier(vmthread);
135 SafepointTracing::init();
136 }
137
138 void SafepointSynchronize::increment_jni_active_count() {
139 assert(Thread::current()->is_VM_thread(), "Only VM thread may increment");
140 ++_current_jni_active_count;
141 }
142
143 void SafepointSynchronize::decrement_waiting_to_block() {
144 assert(_waiting_to_block > 0, "sanity check");
145 assert(Thread::current()->is_VM_thread(), "Only VM thread may decrement");
146 --_waiting_to_block;
147 }
148
149 bool SafepointSynchronize::thread_not_running(ThreadSafepointState *cur_state) {
150 if (!cur_state->is_running()) {
151 // Robustness: asserted in the caller, but handle/tolerate it for release bits.
152 LogTarget(Error, safepoint) lt;
153 if (lt.is_enabled()) {
154 LogStream ls(lt);
155 ls.print("Illegal initial state detected: ");
156 cur_state->print_on(&ls);
157 }
158 return true;
159 }
160 cur_state->examine_state_of_thread(SafepointSynchronize::safepoint_counter());
161 if (!cur_state->is_running()) {
162 return true;
163 }
164 LogTarget(Trace, safepoint) lt;
165 if (lt.is_enabled()) {
166 LogStream ls(lt);
167 cur_state->print_on(&ls);
168 }
169 return false;
170 }
171
172 #ifdef ASSERT
173 static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) {
174 int a = 0;
175 const ThreadSafepointState *tmp_tss = tss_head;
176 while (tmp_tss != nullptr) {
177 ++a;
178 assert(tmp_tss->is_running(), "Illegal initial state");
179 tmp_tss = tmp_tss->get_next();
180 }
181 assert(a == still_running, "Must be the same");
182 }
183 #endif // ASSERT
184
185 static void back_off(int64_t start_time) {
186 // We start with fine-grained nanosleeping until a millisecond has
187 // passed, at which point we resort to plain naked_short_sleep.
188 if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) {
189 os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
190 } else {
191 os::naked_short_sleep(1);
192 }
193 }
194
195 int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running)
196 {
197 JavaThreadIteratorWithHandle jtiwh;
198
199 #ifdef ASSERT
200 for (; JavaThread *cur = jtiwh.next(); ) {
201 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
202 }
203 jtiwh.rewind();
204 #endif // ASSERT
205
206 // Iterate through all threads until it has been determined how to stop them all at a safepoint.
207 int still_running = nof_threads;
208 ThreadSafepointState *tss_head = nullptr;
209 ThreadSafepointState **p_prev = &tss_head;
210 for (; JavaThread *cur = jtiwh.next(); ) {
211 ThreadSafepointState *cur_tss = cur->safepoint_state();
212 assert(cur_tss->get_next() == nullptr, "Must be null");
213 if (thread_not_running(cur_tss)) {
214 --still_running;
215 } else {
216 *p_prev = cur_tss;
217 p_prev = cur_tss->next_ptr();
218 }
219 }
220 *p_prev = nullptr;
221
222 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
223
224 *initial_running = still_running;
225
226 // If there is no thread still running, we are already done.
227 if (still_running <= 0) {
228 assert(tss_head == nullptr, "Must be empty");
229 return 1;
230 }
231
232 int iterations = 1; // The first iteration is above.
233 int64_t start_time = os::javaTimeNanos();
234
235 do {
236 // Check if this has taken too long:
237 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
238 print_safepoint_timeout();
239 }
240
241 p_prev = &tss_head;
242 ThreadSafepointState *cur_tss = tss_head;
243 while (cur_tss != nullptr) {
244 assert(cur_tss->is_running(), "Illegal initial state");
245 if (thread_not_running(cur_tss)) {
246 --still_running;
247 *p_prev = nullptr;
248 ThreadSafepointState *tmp = cur_tss;
249 cur_tss = cur_tss->get_next();
250 tmp->set_next(nullptr);
251 } else {
252 *p_prev = cur_tss;
253 p_prev = cur_tss->next_ptr();
254 cur_tss = cur_tss->get_next();
255 }
256 }
257
258 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
259
260 if (still_running > 0) {
261 back_off(start_time);
262 }
263
264 iterations++;
265 } while (still_running > 0);
266
267 assert(tss_head == nullptr, "Must be empty");
268
269 return iterations;
270 }
271
272 void SafepointSynchronize::arm_safepoint() {
273 // Begin the process of bringing the system to a safepoint.
274 // Java threads can be in several different states and are
275 // stopped by different mechanisms:
276 //
277 // 1. Running interpreted
278 // When executing branching/returning byte codes interpreter
279 // checks if the poll is armed, if so blocks in SS::block().
280 // 2. Running in native code
281 // When returning from the native code, a Java thread must check
282 // the safepoint _state to see if we must block. If the
283 // VM thread sees a Java thread in native, it does
284 // not wait for this thread to block. The order of the memory
285 // writes and reads of both the safepoint state and the Java
286 // threads state is critical. In order to guarantee that the
287 // memory writes are serialized with respect to each other,
288 // the VM thread issues a memory barrier instruction.
289 // 3. Running compiled Code
290 // Compiled code reads the local polling page that
291 // is set to fault if we are trying to get to a safepoint.
292 // 4. Blocked
293 // A thread which is blocked will not be allowed to return from the
294 // block condition until the safepoint operation is complete.
295 // 5. In VM or Transitioning between states
296 // If a Java thread is currently running in the VM or transitioning
297 // between states, the safepointing code will poll the thread state
298 // until the thread blocks itself when it attempts transitions to a
299 // new state or locking a safepoint checked monitor.
300
301 // We must never miss a thread with correct safepoint id, so we must make sure we arm
302 // the wait barrier for the next safepoint id/counter.
303 // Arming must be done after resetting _current_jni_active_count, _waiting_to_block.
304 _wait_barrier->arm(static_cast<int>(_safepoint_counter + 1));
305
306 assert((_safepoint_counter & 0x1) == 0, "must be even");
307 // The store to _safepoint_counter must happen after any stores in arming.
308 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
309
310 // We are synchronizing
311 OrderAccess::storestore(); // Ordered with _safepoint_counter
312 _state = _synchronizing;
313
314 // Arming the per thread poll while having _state != _not_synchronized means safepointing
315 log_trace(safepoint)("Setting thread local yield flag for threads");
316 OrderAccess::storestore(); // storestore, global state -> local state
317 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
318 // Make sure the threads start polling, it is time to yield.
319 SafepointMechanism::arm_local_poll(cur);
320 }
321 if (UseSystemMemoryBarrier) {
322 SystemMemoryBarrier::emit(); // storestore|storeload, global state -> local state
323 } else {
324 OrderAccess::fence(); // storestore|storeload, global state -> local state
325 }
326 }
327
328 // Roll all threads forward to a safepoint and suspend them all
329 void SafepointSynchronize::begin() {
330 assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint");
331
332 EventSafepointBegin begin_event;
333 SafepointTracing::begin(VMThread::vm_op_type());
334
335 Universe::heap()->safepoint_synchronize_begin();
336
337 // By getting the Threads_lock, we assure that no threads are about to start or
338 // exit. It is released again in SafepointSynchronize::end().
339 Threads_lock->lock();
340
341 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
342
343 int nof_threads = Threads::number_of_threads();
344
345 _nof_threads_hit_polling_page = 0;
346
347 log_debug(safepoint)("Safepoint synchronization initiated using %s wait barrier. (%d threads)", _wait_barrier->description(), nof_threads);
348
349 // Reset the count of active JNI critical threads
350 _current_jni_active_count = 0;
351
352 // Set number of threads to wait for
353 _waiting_to_block = nof_threads;
354
355 jlong safepoint_limit_time = 0;
356 if (SafepointTimeout) {
357 // Set the limit time, so that it can be compared to see if this has taken
358 // too long to complete.
359 safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)(SafepointTimeoutDelay * NANOSECS_PER_MILLISEC);
360 timeout_error_printed = false;
361 }
362
363 EventSafepointStateSynchronization sync_event;
364 int initial_running = 0;
365
366 // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before.
367 arm_safepoint();
368
369 // Will spin until all threads are safe.
370 int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running);
371 assert(_waiting_to_block == 0, "No thread should be running");
372
373 #ifndef PRODUCT
374 // Mark all threads
375 if (VerifyCrossModifyFence) {
376 JavaThreadIteratorWithHandle jtiwh;
377 for (; JavaThread *cur = jtiwh.next(); ) {
378 cur->set_requires_cross_modify_fence(true);
379 }
380 }
381
382 if (safepoint_limit_time != 0) {
383 jlong current_time = os::javaTimeNanos();
384 if (safepoint_limit_time < current_time) {
385 log_warning(safepoint)("# SafepointSynchronize: Finished after "
386 INT64_FORMAT_W(6) " ms",
387 (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS));
388 }
389 }
390 #endif
391
392 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
393
394 // Record state
395 _state = _synchronized;
396
397 OrderAccess::fence();
398
399 // Set the new id
400 ++_safepoint_id;
401
402 #ifdef ASSERT
403 // Make sure all the threads were visited.
404 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
405 assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread");
406 }
407 #endif // ASSERT
408
409 post_safepoint_synchronize_event(sync_event,
410 _safepoint_id,
411 initial_running,
412 _waiting_to_block, iterations);
413
414 SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page);
415
416 post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count);
417 }
418
419 void SafepointSynchronize::disarm_safepoint() {
420 uint64_t active_safepoint_counter = _safepoint_counter;
421 {
422 JavaThreadIteratorWithHandle jtiwh;
423 #ifdef ASSERT
424 // A pending_exception cannot be installed during a safepoint. The threads
425 // may install an async exception after they come back from a safepoint into
426 // pending_exception after they unblock. But that should happen later.
427 for (; JavaThread *cur = jtiwh.next(); ) {
428 assert (!(cur->has_pending_exception() &&
429 cur->safepoint_state()->is_at_poll_safepoint()),
430 "safepoint installed a pending exception");
431 }
432 #endif // ASSERT
433
434 OrderAccess::fence(); // keep read and write of _state from floating up
435 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
436
437 // Change state first to _not_synchronized.
438 // No threads should see _synchronized when running.
439 _state = _not_synchronized;
440
441 // Set the next dormant (even) safepoint id.
442 assert((_safepoint_counter & 0x1) == 1, "must be odd");
443 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
444
445 OrderAccess::fence(); // Keep the local state from floating up.
446
447 jtiwh.rewind();
448 for (; JavaThread *current = jtiwh.next(); ) {
449 // Clear the visited flag to ensure that the critical counts are collected properly.
450 DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);)
451 ThreadSafepointState* cur_state = current->safepoint_state();
452 assert(!cur_state->is_running(), "Thread not suspended at safepoint");
453 cur_state->restart(); // TSS _running
454 assert(cur_state->is_running(), "safepoint state has not been reset");
455 }
456 } // ~JavaThreadIteratorWithHandle
457
458 // Release threads lock, so threads can be created/destroyed again.
459 Threads_lock->unlock();
460
461 // Wake threads after local state is correctly set.
462 _wait_barrier->disarm();
463 }
464
465 // Wake up all threads, so they are ready to resume execution after the safepoint
466 // operation has been carried out
467 void SafepointSynchronize::end() {
468 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
469 SafepointTracing::leave();
470
471 EventSafepointEnd event;
472 assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint");
473
474 disarm_safepoint();
475
476 Universe::heap()->safepoint_synchronize_end();
477
478 SafepointTracing::end();
479
480 post_safepoint_end_event(event, safepoint_id());
481 }
482
483 // Methods for determining if a JavaThread is safepoint safe.
484
485 // False means unsafe with undetermined state.
486 // True means a determined state, but it may be an unsafe state.
487 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
488 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
489 assert((safepoint_count != InactiveSafepointCounter &&
490 Thread::current() == (Thread*)VMThread::vm_thread() &&
491 SafepointSynchronize::_state != _not_synchronized)
492 || safepoint_count == InactiveSafepointCounter, "Invalid check");
493
494 // To handle the thread_blocked state on the backedge of the WaitBarrier from
495 // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
496 // re-read state after we read thread safepoint id. The JavaThread changes its
497 // thread state from thread_blocked before resetting safepoint id to 0.
498 // This guarantees the second read will be from an updated thread state. It can
499 // either be different state making this an unsafe state or it can see blocked
500 // again. When we see blocked twice with a 0 safepoint id, either:
501 // - It is normally blocked, e.g. on Mutex, TBIVM.
502 // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
503 // - It was in SS:block() but now on a Mutex.
504 // All of these cases are safe.
505
506 *state = thread->thread_state();
507 OrderAccess::loadload();
508 uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire
509 if (sid != InactiveSafepointCounter && sid != safepoint_count) {
510 // In an old safepoint, state not relevant.
511 return false;
512 }
513 return *state == thread->thread_state();
514 }
515
516 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
517 switch(state) {
518 case _thread_in_native:
519 // native threads are safe if they have no java stack or have walkable stack
520 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
521
522 case _thread_blocked:
523 // On wait_barrier or blocked.
524 // Blocked threads should already have walkable stack.
525 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
526 return true;
527
528 default:
529 return false;
530 }
531 }
532
533 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
534 if (thread->is_terminated()) {
535 return true;
536 }
537 JavaThreadState stable_state;
538 if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
539 return safepoint_safe_with(thread, stable_state);
540 }
541 return false;
542 }
543
544
545 // -------------------------------------------------------------------------------------------------------
546 // Implementation of Safepoint blocking point
547
548 void SafepointSynchronize::block(JavaThread *thread) {
549 assert(thread != nullptr, "thread must be set");
550
551 // Threads shouldn't block if they are in the middle of printing, but...
552 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
553
554 // Only bail from the block() call if the thread is gone from the
555 // thread list; starting to exit should still block.
556 if (thread->is_terminated()) {
557 // block current thread if we come here from native code when VM is gone
558 thread->block_if_vm_exited();
559
560 // otherwise do nothing
561 return;
562 }
563
564 JavaThreadState state = thread->thread_state();
565 thread->frame_anchor()->make_walkable();
566
567 uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
568
569 // We have no idea where the VMThread is, it might even be at next safepoint.
570 // So we can miss this poll, but stop at next.
571
572 // Load dependent store, it must not pass loading of safepoint_id.
573 thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
574
575 // This part we can skip if we notice we miss or are in a future safepoint.
576 OrderAccess::storestore();
577 // Load in wait barrier should not float up
578 thread->set_thread_state_fence(_thread_blocked);
579
580 _wait_barrier->wait(static_cast<int>(safepoint_id));
581 assert(_state != _synchronized, "Can't be");
582
583 // If barrier is disarmed stop store from floating above loads in barrier.
584 OrderAccess::loadstore();
585 thread->set_thread_state(state);
586
587 // Then we reset the safepoint id to inactive.
588 thread->safepoint_state()->reset_safepoint_id(); // Release store
589
590 OrderAccess::fence();
591
592 guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
593 "The safepoint id should be set only in block path");
594
595 // cross_modify_fence is done by SafepointMechanism::process_if_requested
596 // which is the only caller here.
597 }
598
599 // ------------------------------------------------------------------------------------------------------
600 // Exception handlers
601
602
603 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
604 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
605 thread->set_thread_state(_thread_in_vm);
606
607 // Enable WXWrite: the function is called implicitly from java code.
608 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread));
609
610 if (log_is_enabled(Info, safepoint, stats)) {
611 Atomic::inc(&_nof_threads_hit_polling_page);
612 }
613
614 ThreadSafepointState* state = thread->safepoint_state();
615
616 state->handle_polling_page_exception();
617
618 thread->set_thread_state(_thread_in_Java);
619 }
620
621
622 void SafepointSynchronize::print_safepoint_timeout() {
623 if (!timeout_error_printed) {
624 timeout_error_printed = true;
625 // Print out the thread info which didn't reach the safepoint for debugging
626 // purposes (useful when there are lots of threads in the debugger).
627 LogTarget(Warning, safepoint) lt;
628 if (lt.is_enabled()) {
629 ResourceMark rm;
630 LogStream ls(lt);
631
632 ls.cr();
633 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
634 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
635 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
636 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
637 if (cur_thread->safepoint_state()->is_running()) {
638 ls.print("# ");
639 cur_thread->print_on(&ls);
640 ls.cr();
641 }
642 }
643 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
644 }
645 }
646
647 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
648 // ShowMessageBoxOnError.
649 if (AbortVMOnSafepointTimeout && (os::elapsedTime() * MILLIUNITS > AbortVMOnSafepointTimeoutDelay)) {
650 // Send the blocking thread a signal to terminate and write an error file.
651 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
652 if (cur_thread->safepoint_state()->is_running()) {
653 if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
654 break; // Could not send signal. Report fatal error.
655 }
656 // Give cur_thread a chance to report the error and terminate the VM.
657 os::naked_sleep(3000);
658 }
659 }
660 fatal("Safepoint sync time longer than %.6f ms detected when executing %s.",
661 SafepointTimeoutDelay, VMThread::vm_operation()->name());
662 }
663 }
664
665 // -------------------------------------------------------------------------------------------------------
666 // Implementation of ThreadSafepointState
667
668 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
669 : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
670 _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(nullptr) {
671 }
672
673 void ThreadSafepointState::create(JavaThread *thread) {
674 ThreadSafepointState *state = new ThreadSafepointState(thread);
675 thread->set_safepoint_state(state);
676 }
677
678 void ThreadSafepointState::destroy(JavaThread *thread) {
679 if (thread->safepoint_state()) {
680 delete(thread->safepoint_state());
681 thread->set_safepoint_state(nullptr);
682 }
683 }
684
685 uint64_t ThreadSafepointState::get_safepoint_id() const {
686 return Atomic::load_acquire(&_safepoint_id);
687 }
688
689 void ThreadSafepointState::reset_safepoint_id() {
690 Atomic::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
691 }
692
693 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
694 Atomic::release_store(&_safepoint_id, safepoint_id);
695 }
696
697 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
698 assert(is_running(), "better be running or just have hit safepoint poll");
699
700 JavaThreadState stable_state;
701 if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
702 // We could not get stable state of the JavaThread.
703 // Consider it running and just return.
704 return;
705 }
706
707 if (safepoint_safe_with(_thread, stable_state)) {
708 account_safe_thread();
709 return;
710 }
711
712 // All other thread states will continue to run until they
713 // transition and self-block in state _blocked
714 // Safepoint polling in compiled code causes the Java threads to do the same.
715 // Note: new threads may require a malloc so they must be allowed to finish
716
717 assert(is_running(), "examine_state_of_thread on non-running thread");
718 return;
719 }
720
721 void ThreadSafepointState::account_safe_thread() {
722 SafepointSynchronize::decrement_waiting_to_block();
723 if (_thread->in_critical()) {
724 // Notice that this thread is in a critical section
725 SafepointSynchronize::increment_jni_active_count();
726 }
727 DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
728 assert(!_safepoint_safe, "Must be unsafe before safe");
729 _safepoint_safe = true;
730
731 // The oops in the monitor cache are cleared to prevent stale cache entries
732 // from keeping dead objects alive. Because these oops are always cleared
733 // before safepoint operations they are not visited in JavaThread::oops_do.
734 _thread->om_clear_monitor_cache();
735 }
736
737 void ThreadSafepointState::restart() {
738 assert(_safepoint_safe, "Must be safe before unsafe");
739 _safepoint_safe = false;
740 }
741
742 void ThreadSafepointState::print_on(outputStream *st) const {
743 const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
744
745 st->print_cr("Thread: " INTPTR_FORMAT
746 " [0x%2x] State: %s _at_poll_safepoint %d",
747 p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
748
749 _thread->print_thread_state_on(st);
750 }
751
752 // ---------------------------------------------------------------------------------------------------------------------
753
754 // Process pending operation.
755 void ThreadSafepointState::handle_polling_page_exception() {
756 JavaThread* self = thread();
757 assert(self == JavaThread::current(), "must be self");
758
759 // Step 1: Find the nmethod from the return address
760 address real_return_addr = self->saved_exception_pc();
761
762 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
763 assert(cb != nullptr && cb->is_nmethod(), "return address should be in nmethod");
764 nmethod* nm = cb->as_nmethod();
765
766 // Find frame of caller
767 frame stub_fr = self->last_frame();
768 CodeBlob* stub_cb = stub_fr.cb();
769 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
770 RegisterMap map(self,
771 RegisterMap::UpdateMap::include,
772 RegisterMap::ProcessFrames::skip,
773 RegisterMap::WalkContinuation::skip);
774 frame caller_fr = stub_fr.sender(&map);
775
776 // Should only be poll_return or poll
777 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
778
779 // This is a poll immediately before a return. The exception handling code
780 // has already had the effect of causing the return to occur, so the execution
781 // will continue immediately after the call. In addition, the oopmap at the
782 // return point does not mark the return value as an oop (if it is), so
783 // it needs a handle here to be updated.
784 if( nm->is_at_poll_return(real_return_addr) ) {
785 // See if return type is an oop.
786 bool return_oop = nm->method()->is_returning_oop();
787 HandleMark hm(self);
788 Handle return_value;
789 if (return_oop) {
790 // The oop result has been saved on the stack together with all
791 // the other registers. In order to preserve it over GCs we need
792 // to keep it in a handle.
793 oop result = caller_fr.saved_oop_result(&map);
794 assert(oopDesc::is_oop_or_null(result), "must be oop");
795 return_value = Handle(self, result);
796 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
797 }
798
799 // We get here if compiled return polls found a reason to call into the VM.
800 // One condition for that is that the top frame is not yet safe to use.
801 // The following stack watermark barrier poll will catch such situations.
802 StackWatermarkSet::after_unwind(self);
803
804 // Process pending operation
805 SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */);
806
807 // restore oop result, if any
808 if (return_oop) {
809 caller_fr.set_saved_oop_result(&map, return_value());
810 }
811 }
812
813 // This is a safepoint poll. Verify the return address and block.
814 else {
815
816 // verify the blob built the "return address" correctly
817 assert(real_return_addr == caller_fr.pc(), "must match");
818
819 set_at_poll_safepoint(true);
820 // Process pending operation
821 // We never deliver an async exception at a polling point as the
822 // compiler may not have an exception handler for it (polling at
823 // a return point is ok though). We will check for a pending async
824 // exception below and deoptimize if needed. We also cannot deoptimize
825 // and still install the exception here because live registers needed
826 // during deoptimization are clobbered by the exception path. The
827 // exception will just be delivered once we get into the interpreter.
828 SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */);
829 set_at_poll_safepoint(false);
830
831 if (self->has_async_exception_condition()) {
832 Deoptimization::deoptimize_frame(self, caller_fr.id());
833 log_info(exceptions)("deferred async exception at compiled safepoint");
834 }
835
836 // If an exception has been installed we must verify that the top frame wasn't deoptimized.
837 if (self->has_pending_exception() ) {
838 RegisterMap map(self,
839 RegisterMap::UpdateMap::include,
840 RegisterMap::ProcessFrames::skip,
841 RegisterMap::WalkContinuation::skip);
842 frame caller_fr = stub_fr.sender(&map);
843 if (caller_fr.is_deoptimized_frame()) {
844 // The exception path will destroy registers that are still
845 // live and will be needed during deoptimization, so if we
846 // have an exception now things are messed up. We only check
847 // at this scope because for a poll return it is ok to deoptimize
848 // while having a pending exception since the call we are returning
849 // from already collides with exception handling registers and
850 // so there is no issue (the exception handling path kills call
851 // result registers but this is ok since the exception kills
852 // the result anyway).
853 fatal("Exception installed and deoptimization is pending");
854 }
855 }
856 }
857 }
858
859
860 // -------------------------------------------------------------------------------------------------------
861 // Implementation of SafepointTracing
862
863 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
864 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
865 jlong SafepointTracing::_last_safepoint_leave_time_ns = 0;
866 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
867 jlong SafepointTracing::_last_app_time_ns = 0;
868 int SafepointTracing::_nof_threads = 0;
869 int SafepointTracing::_nof_running = 0;
870 int SafepointTracing::_page_trap = 0;
871 VM_Operation::VMOp_Type SafepointTracing::_current_type;
872 jlong SafepointTracing::_max_sync_time = 0;
873 jlong SafepointTracing::_max_vmop_time = 0;
874 uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
875
876 void SafepointTracing::init() {
877 // Application start
878 _last_safepoint_end_time_ns = os::javaTimeNanos();
879 }
880
881 // Helper method to print the header.
882 static void print_header(outputStream* st) {
883 // The number of spaces is significant here, and should match the format
884 // specifiers in print_statistics().
885
886 st->print("VM Operation "
887 "[ threads: total initial_running ]"
888 "[ time: sync vmop total ]");
889
890 st->print_cr(" page_trap_count");
891 }
892
893 // This prints a nice table. To get the statistics to not shift due to the logging uptime
894 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
895 void SafepointTracing::statistics_log() {
896 LogTarget(Info, safepoint, stats) lt;
897 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
898 LogStream ls(lt);
899
900 static int _cur_stat_index = 0;
901
902 // Print header every 30 entries
903 if ((_cur_stat_index % 30) == 0) {
904 print_header(&ls);
905 _cur_stat_index = 1; // wrap
906 } else {
907 _cur_stat_index++;
908 }
909
910 ls.print("%-28s [ "
911 INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " "
912 "]",
913 VM_Operation::name(_current_type),
914 _nof_threads,
915 _nof_running);
916 ls.print("[ "
917 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
918 (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
919 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns),
920 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
921
922 ls.print_cr(INT32_FORMAT_W(16), _page_trap);
923 }
924
925 // This method will be called when VM exits. This tries to summarize the sampling.
926 // Current thread may already be deleted, so don't use ResourceMark.
927 void SafepointTracing::statistics_exit_log() {
928 if (!log_is_enabled(Info, safepoint, stats)) {
929 return;
930 }
931 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
932 if (_op_count[index] != 0) {
933 log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
934 _op_count[index]);
935 }
936 }
937
938 log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns",
939 (int64_t)(_max_sync_time));
940 log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
941 INT64_FORMAT " ns",
942 (int64_t)(_max_vmop_time));
943 }
944
945 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
946 _op_count[type]++;
947 _current_type = type;
948
949 // update the time stamp to begin recording safepoint time
950 _last_safepoint_begin_time_ns = os::javaTimeNanos();
951 _last_safepoint_sync_time_ns = 0;
952
953 _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
954 _last_safepoint_end_time_ns = 0;
955
956 RuntimeService::record_safepoint_begin(_last_app_time_ns);
957 }
958
959 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
960 _last_safepoint_sync_time_ns = os::javaTimeNanos();
961 _nof_threads = nof_threads;
962 _nof_running = nof_running;
963 _page_trap = traps;
964 RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
965 }
966
967 void SafepointTracing::leave() {
968 _last_safepoint_leave_time_ns = os::javaTimeNanos();
969 }
970
971 void SafepointTracing::end() {
972 _last_safepoint_end_time_ns = os::javaTimeNanos();
973
974 if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
975 _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
976 }
977 if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
978 _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
979 }
980 if (log_is_enabled(Info, safepoint, stats)) {
981 statistics_log();
982 }
983
984 log_info(safepoint)(
985 "Safepoint \"%s\", "
986 "Time since last: " JLONG_FORMAT " ns, "
987 "Reaching safepoint: " JLONG_FORMAT " ns, "
988 "At safepoint: " JLONG_FORMAT " ns, "
989 "Leaving safepoint: " JLONG_FORMAT " ns, "
990 "Total: " JLONG_FORMAT " ns, "
991 "Threads: %d runnable, %d total",
992 VM_Operation::name(_current_type),
993 _last_app_time_ns,
994 _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns,
995 _last_safepoint_leave_time_ns - _last_safepoint_sync_time_ns,
996 _last_safepoint_end_time_ns - _last_safepoint_leave_time_ns,
997 _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns,
998 _nof_running,
999 _nof_threads
1000 );
1001
1002 RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns);
1003 }