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/workerThread.hpp"
34 #include "gc/shared/workerUtils.hpp"
35 #include "interpreter/interpreter.hpp"
36 #include "jfr/jfrEvents.hpp"
37 #include "logging/log.hpp"
38 #include "logging/logStream.hpp"
39 #include "memory/resourceArea.hpp"
40 #include "memory/universe.hpp"
41 #include "oops/oop.inline.hpp"
42 #include "oops/symbol.hpp"
43 #include "runtime/atomicAccess.hpp"
44 #include "runtime/deoptimization.hpp"
45 #include "runtime/frame.inline.hpp"
46 #include "runtime/globals.hpp"
47 #include "runtime/handles.inline.hpp"
48 #include "runtime/interfaceSupport.inline.hpp"
49 #include "runtime/javaThread.inline.hpp"
50 #include "runtime/mutexLocker.hpp"
51 #include "runtime/orderAccess.hpp"
52 #include "runtime/osThread.hpp"
53 #include "runtime/safepoint.hpp"
54 #include "runtime/safepointMechanism.inline.hpp"
55 #include "runtime/signature.hpp"
56 #include "runtime/stackWatermarkSet.inline.hpp"
57 #include "runtime/stubCodeGenerator.hpp"
58 #include "runtime/stubRoutines.hpp"
59 #include "runtime/synchronizer.hpp"
60 #include "runtime/threads.hpp"
61 #include "runtime/threadSMR.hpp"
62 #include "runtime/threadWXSetters.inline.hpp"
63 #include "runtime/timerTrace.hpp"
64 #include "services/runtimeService.hpp"
65 #include "utilities/events.hpp"
66 #include "utilities/macros.hpp"
67 #include "utilities/systemMemoryBarrier.hpp"
68 #include "utilities/vmError.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 return false;
165 }
166
167 #ifdef ASSERT
168 static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) {
169 int a = 0;
170 const ThreadSafepointState *tmp_tss = tss_head;
171 while (tmp_tss != nullptr) {
172 ++a;
173 assert(tmp_tss->is_running(), "Illegal initial state");
174 tmp_tss = tmp_tss->get_next();
175 }
176 assert(a == still_running, "Must be the same");
177 }
178 #endif // ASSERT
179
180 static void back_off(int64_t start_time) {
181 // We start with fine-grained nanosleeping until a millisecond has
182 // passed, at which point we resort to plain naked_short_sleep.
183 if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) {
184 os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
185 } else {
186 os::naked_short_sleep(1);
187 }
188 }
189
190 int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running)
191 {
192 JavaThreadIteratorWithHandle jtiwh;
193
194 #ifdef ASSERT
195 for (; JavaThread *cur = jtiwh.next(); ) {
196 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
197 }
198 jtiwh.rewind();
199 #endif // ASSERT
200
201 // Iterate through all threads until it has been determined how to stop them all at a safepoint.
202 int still_running = nof_threads;
203 ThreadSafepointState *tss_head = nullptr;
204 ThreadSafepointState **p_prev = &tss_head;
205 for (; JavaThread *cur = jtiwh.next(); ) {
206 ThreadSafepointState *cur_tss = cur->safepoint_state();
207 assert(cur_tss->get_next() == nullptr, "Must be null");
208 if (thread_not_running(cur_tss)) {
209 --still_running;
210 } else {
211 *p_prev = cur_tss;
212 p_prev = cur_tss->next_ptr();
213 }
214 }
215 *p_prev = nullptr;
216
217 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
218
219 *initial_running = still_running;
220
221 log_trace(safepoint)("%d total threads, waiting for %d threads to block", nof_threads, still_running);
222
223 // If there is no thread still running, we are already done.
224 if (still_running <= 0) {
225 assert(tss_head == nullptr, "Must be empty");
226 return 1;
227 }
228
229 int iterations = 1; // The first iteration is above.
230 int64_t start_time = os::javaTimeNanos();
231
232 do {
233 log_trace(safepoint)("Checking thread status");
234
235 // Check if this has taken too long:
236 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
237 print_safepoint_timeout();
238 }
239
240 p_prev = &tss_head;
241 ThreadSafepointState *cur_tss = tss_head;
242 while (cur_tss != nullptr) {
243 assert(cur_tss->is_running(), "Illegal initial state");
244 if (thread_not_running(cur_tss)) {
245 log_trace(safepoint)("Thread " INTPTR_FORMAT " [%d] is now blocked",
246 p2i(cur_tss->thread()), cur_tss->thread()->osthread()->thread_id());
247 --still_running;
248 *p_prev = nullptr;
249 ThreadSafepointState *tmp = cur_tss;
250 cur_tss = cur_tss->get_next();
251 tmp->set_next(nullptr);
252 } else {
253 log_trace(safepoint)("Thread " INTPTR_FORMAT " [%d] is still running",
254 p2i(cur_tss->thread()), cur_tss->thread()->osthread()->thread_id());
255 *p_prev = cur_tss;
256 p_prev = cur_tss->next_ptr();
257 cur_tss = cur_tss->get_next();
258 }
259 }
260
261 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
262
263 if (still_running > 0) {
264 log_trace(safepoint)("Waiting for %d threads to block", still_running);
265 back_off(start_time);
266 }
267
268 iterations++;
269 } while (still_running > 0);
270
271 assert(tss_head == nullptr, "Must be empty");
272
273 return iterations;
274 }
275
276 void SafepointSynchronize::arm_safepoint() {
277 // Begin the process of bringing the system to a safepoint.
278 // Java threads can be in several different states and are
279 // stopped by different mechanisms:
280 //
281 // 1. Running interpreted
282 // When executing branching/returning byte codes interpreter
283 // checks if the poll is armed, if so blocks in SS::block().
284 // 2. Running in native code
285 // When returning from the native code, a Java thread must check
286 // the safepoint _state to see if we must block. If the
287 // VM thread sees a Java thread in native, it does
288 // not wait for this thread to block. The order of the memory
289 // writes and reads of both the safepoint state and the Java
290 // threads state is critical. In order to guarantee that the
291 // memory writes are serialized with respect to each other,
292 // the VM thread issues a memory barrier instruction.
293 // 3. Running compiled Code
294 // Compiled code reads the local polling page that
295 // is set to fault if we are trying to get to a safepoint.
296 // 4. Blocked
297 // A thread which is blocked will not be allowed to return from the
298 // block condition until the safepoint operation is complete.
299 // 5. In VM or Transitioning between states
300 // If a Java thread is currently running in the VM or transitioning
301 // between states, the safepointing code will poll the thread state
302 // until the thread blocks itself when it attempts transitions to a
303 // new state or locking a safepoint checked monitor.
304
305 // We must never miss a thread with correct safepoint id, so we must make sure we arm
306 // the wait barrier for the next safepoint id/counter.
307 // Arming must be done after resetting _current_jni_active_count, _waiting_to_block.
308 _wait_barrier->arm(static_cast<int>(_safepoint_counter + 1));
309
310 assert((_safepoint_counter & 0x1) == 0, "must be even");
311 // The store to _safepoint_counter must happen after any stores in arming.
312 AtomicAccess::release_store(&_safepoint_counter, _safepoint_counter + 1);
313
314 // We are synchronizing
315 OrderAccess::storestore(); // Ordered with _safepoint_counter
316 _state = _synchronizing;
317
318 // Arming the per thread poll while having _state != _not_synchronized means safepointing
319 log_trace(safepoint)("Setting thread local yield flag for threads");
320 OrderAccess::storestore(); // storestore, global state -> local state
321 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
322 // Make sure the threads start polling, it is time to yield.
323 SafepointMechanism::arm_local_poll(cur);
324 }
325 if (UseSystemMemoryBarrier) {
326 SystemMemoryBarrier::emit(); // storestore|storeload, global state -> local state
327 } else {
328 OrderAccess::fence(); // storestore|storeload, global state -> local state
329 }
330 }
331
332 // Roll all threads forward to a safepoint and suspend them all
333 void SafepointSynchronize::begin() {
334 assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint");
335
336 EventSafepointBegin begin_event;
337 SafepointTracing::begin(VMThread::vm_op_type());
338
339 log_trace(safepoint)("Suspending GC threads");
340 Universe::heap()->safepoint_synchronize_begin();
341
342 // By getting the Threads_lock, we assure that no threads are about to start or
343 // exit. It is released again in SafepointSynchronize::end().
344 log_trace(safepoint)("Blocking threads from starting/exiting");
345 Threads_lock->lock();
346
347 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
348
349 int nof_threads = Threads::number_of_threads();
350
351 _nof_threads_hit_polling_page = 0;
352
353 // Reset the count of active JNI critical threads
354 _current_jni_active_count = 0;
355
356 // Set number of threads to wait for
357 _waiting_to_block = nof_threads;
358
359 jlong safepoint_limit_time = 0;
360 if (SafepointTimeout) {
361 // Set the limit time, so that it can be compared to see if this has taken
362 // too long to complete.
363 safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)(SafepointTimeoutDelay * NANOSECS_PER_MILLISEC);
364 timeout_error_printed = false;
365 }
366
367 EventSafepointStateSynchronization sync_event;
368 int initial_running = 0;
369
370 // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before.
371 log_trace(safepoint)("Arming safepoint using %s wait barrier", _wait_barrier->description());
372 arm_safepoint();
373
374 // Will spin until all threads are safe.
375 int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running);
376 assert(_waiting_to_block == 0, "No thread should be running");
377
378 #ifndef PRODUCT
379 // Mark all threads
380 if (VerifyCrossModifyFence) {
381 JavaThreadIteratorWithHandle jtiwh;
382 for (; JavaThread *cur = jtiwh.next(); ) {
383 cur->set_requires_cross_modify_fence(true);
384 }
385 }
386
387 if (safepoint_limit_time != 0) {
388 jlong current_time = os::javaTimeNanos();
389 if (safepoint_limit_time < current_time) {
390 log_warning(safepoint)("# SafepointSynchronize: Finished after "
391 INT64_FORMAT_W(6) " ms",
392 (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS));
393 }
394 }
395 #endif
396
397 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
398
399 // Record state
400 _state = _synchronized;
401
402 OrderAccess::fence();
403
404 // Set the new id
405 ++_safepoint_id;
406
407 #ifdef ASSERT
408 // Make sure all the threads were visited.
409 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
410 assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread");
411 }
412 #endif // ASSERT
413
414 post_safepoint_synchronize_event(sync_event,
415 _safepoint_id,
416 initial_running,
417 _waiting_to_block, iterations);
418
419 SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page);
420
421 post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count);
422 }
423
424 void SafepointSynchronize::disarm_safepoint() {
425 uint64_t active_safepoint_counter = _safepoint_counter;
426 {
427 JavaThreadIteratorWithHandle jtiwh;
428 #ifdef ASSERT
429 // A pending_exception cannot be installed during a safepoint. The threads
430 // may install an async exception after they come back from a safepoint into
431 // pending_exception after they unblock. But that should happen later.
432 for (; JavaThread *cur = jtiwh.next(); ) {
433 assert (!(cur->has_pending_exception() &&
434 cur->safepoint_state()->is_at_poll_safepoint()),
435 "safepoint installed a pending exception");
436 }
437 #endif // ASSERT
438
439 OrderAccess::fence(); // keep read and write of _state from floating up
440 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
441
442 // Change state first to _not_synchronized.
443 // No threads should see _synchronized when running.
444 _state = _not_synchronized;
445
446 // Set the next dormant (even) safepoint id.
447 assert((_safepoint_counter & 0x1) == 1, "must be odd");
448 AtomicAccess::release_store(&_safepoint_counter, _safepoint_counter + 1);
449
450 OrderAccess::fence(); // Keep the local state from floating up.
451
452 jtiwh.rewind();
453 for (; JavaThread *current = jtiwh.next(); ) {
454 // Clear the visited flag to ensure that the critical counts are collected properly.
455 DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);)
456 ThreadSafepointState* cur_state = current->safepoint_state();
457 assert(!cur_state->is_running(), "Thread not suspended at safepoint");
458 cur_state->restart(); // TSS _running
459 assert(cur_state->is_running(), "safepoint state has not been reset");
460 }
461 } // ~JavaThreadIteratorWithHandle
462
463 // Release threads lock, so threads can be created/destroyed again.
464 Threads_lock->unlock();
465
466 // Wake threads after local state is correctly set.
467 _wait_barrier->disarm();
468 }
469
470 // Wake up all threads, so they are ready to resume execution after the safepoint
471 // operation has been carried out
472 void SafepointSynchronize::end() {
473 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
474 SafepointTracing::leave();
475
476 EventSafepointEnd event;
477 assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint");
478
479 log_trace(safepoint)("Disarming safepoint");
480 disarm_safepoint();
481
482 log_trace(safepoint)("Resuming GC threads");
483 Universe::heap()->safepoint_synchronize_end();
484
485 SafepointTracing::end();
486
487 post_safepoint_end_event(event, safepoint_id());
488 }
489
490 // Methods for determining if a JavaThread is safepoint safe.
491
492 // False means unsafe with undetermined state.
493 // True means a determined state, but it may be an unsafe state.
494 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
495 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
496 assert((safepoint_count != InactiveSafepointCounter &&
497 Thread::current() == (Thread*)VMThread::vm_thread() &&
498 SafepointSynchronize::_state != _not_synchronized)
499 || safepoint_count == InactiveSafepointCounter, "Invalid check");
500
501 // To handle the thread_blocked state on the backedge of the WaitBarrier from
502 // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
503 // re-read state after we read thread safepoint id. The JavaThread changes its
504 // thread state from thread_blocked before resetting safepoint id to 0.
505 // This guarantees the second read will be from an updated thread state. It can
506 // either be different state making this an unsafe state or it can see blocked
507 // again. When we see blocked twice with a 0 safepoint id, either:
508 // - It is normally blocked, e.g. on Mutex, TBIVM.
509 // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
510 // - It was in SS:block() but now on a Mutex.
511 // All of these cases are safe.
512
513 *state = thread->thread_state();
514 OrderAccess::loadload();
515 uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire
516 if (sid != InactiveSafepointCounter && sid != safepoint_count) {
517 // In an old safepoint, state not relevant.
518 return false;
519 }
520 return *state == thread->thread_state();
521 }
522
523 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
524 switch(state) {
525 case _thread_in_native:
526 // native threads are safe if they have no java stack or have walkable stack
527 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
528
529 case _thread_blocked:
530 // On wait_barrier or blocked.
531 // Blocked threads should already have walkable stack.
532 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
533 return true;
534
535 default:
536 return false;
537 }
538 }
539
540 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
541 if (thread->is_terminated()) {
542 return true;
543 }
544 JavaThreadState stable_state;
545 if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
546 return safepoint_safe_with(thread, stable_state);
547 }
548 return false;
549 }
550
551
552 // -------------------------------------------------------------------------------------------------------
553 // Implementation of Safepoint blocking point
554
555 void SafepointSynchronize::block(JavaThread *thread) {
556 assert(thread != nullptr, "thread must be set");
557
558 // Threads shouldn't block if they are in the middle of printing, but...
559 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
560
561 log_trace(safepoint)("Blocking thread " INTPTR_FORMAT " [%d]",
562 p2i(thread), thread->osthread()->thread_id());
563
564 // Only bail from the block() call if the thread is gone from the
565 // thread list; starting to exit should still block.
566 if (thread->is_terminated()) {
567 // block current thread if we come here from native code when VM is gone
568 thread->block_if_vm_exited();
569
570 // otherwise do nothing
571 return;
572 }
573
574 JavaThreadState state = thread->thread_state();
575 thread->frame_anchor()->make_walkable();
576
577 uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
578
579 // We have no idea where the VMThread is, it might even be at next safepoint.
580 // So we can miss this poll, but stop at next.
581
582 // Load dependent store, it must not pass loading of safepoint_id.
583 thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
584
585 // This part we can skip if we notice we miss or are in a future safepoint.
586 OrderAccess::storestore();
587 // Load in wait barrier should not float up
588 thread->set_thread_state_fence(_thread_blocked);
589
590 _wait_barrier->wait(static_cast<int>(safepoint_id));
591 assert(_state != _synchronized, "Can't be");
592
593 // If barrier is disarmed stop store from floating above loads in barrier.
594 OrderAccess::loadstore();
595 thread->set_thread_state(state);
596
597 // Then we reset the safepoint id to inactive.
598 thread->safepoint_state()->reset_safepoint_id(); // Release store
599
600 OrderAccess::fence();
601
602 guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
603 "The safepoint id should be set only in block path");
604
605 // cross_modify_fence is done by SafepointMechanism::process_if_requested
606 // which is the only caller here.
607
608 log_trace(safepoint)("Unblocking thread " INTPTR_FORMAT " [%d]",
609 p2i(thread), thread->osthread()->thread_id());
610 }
611
612 // ------------------------------------------------------------------------------------------------------
613 // Exception handlers
614
615
616 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
617 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
618 thread->set_thread_state(_thread_in_vm);
619
620 // Enable WXWrite: the function is called implicitly from java code.
621 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread));
622
623 if (log_is_enabled(Info, safepoint, stats)) {
624 AtomicAccess::inc(&_nof_threads_hit_polling_page);
625 }
626
627 ThreadSafepointState* state = thread->safepoint_state();
628
629 state->handle_polling_page_exception();
630
631 thread->set_thread_state(_thread_in_Java);
632 }
633
634
635 void SafepointSynchronize::print_safepoint_timeout() {
636 if (!timeout_error_printed) {
637 timeout_error_printed = true;
638 // Print out the thread info which didn't reach the safepoint for debugging
639 // purposes (useful when there are lots of threads in the debugger).
640 LogTarget(Warning, safepoint) lt;
641 if (lt.is_enabled()) {
642 ResourceMark rm;
643 LogStream ls(lt);
644
645 ls.cr();
646 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
647 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
648 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
649 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
650 if (cur_thread->safepoint_state()->is_running()) {
651 ls.print("# ");
652 cur_thread->print_on(&ls);
653 ls.cr();
654 }
655 }
656 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
657 }
658 }
659
660 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
661 // ShowMessageBoxOnError.
662 if (AbortVMOnSafepointTimeout && (os::elapsedTime() * MILLIUNITS > AbortVMOnSafepointTimeoutDelay)) {
663 // Send the blocking thread a signal to terminate and write an error file.
664 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
665 if (cur_thread->safepoint_state()->is_running()) {
666 VMError::set_safepoint_timed_out_thread(cur_thread);
667 if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
668 break; // Could not send signal. Report fatal error.
669 }
670 // Give cur_thread a chance to report the error and terminate the VM.
671 os::naked_sleep(3000);
672 }
673 }
674 fatal("Safepoint sync time longer than %.6f ms detected when executing %s.",
675 SafepointTimeoutDelay, VMThread::vm_operation()->name());
676 }
677 }
678
679 // -------------------------------------------------------------------------------------------------------
680 // Implementation of ThreadSafepointState
681
682 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
683 : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
684 _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(nullptr) {
685 }
686
687 void ThreadSafepointState::create(JavaThread *thread) {
688 ThreadSafepointState *state = new ThreadSafepointState(thread);
689 thread->set_safepoint_state(state);
690 }
691
692 void ThreadSafepointState::destroy(JavaThread *thread) {
693 if (thread->safepoint_state()) {
694 delete(thread->safepoint_state());
695 thread->set_safepoint_state(nullptr);
696 }
697 }
698
699 uint64_t ThreadSafepointState::get_safepoint_id() const {
700 return AtomicAccess::load_acquire(&_safepoint_id);
701 }
702
703 void ThreadSafepointState::reset_safepoint_id() {
704 AtomicAccess::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
705 }
706
707 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
708 AtomicAccess::release_store(&_safepoint_id, safepoint_id);
709 }
710
711 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
712 assert(is_running(), "better be running or just have hit safepoint poll");
713
714 JavaThreadState stable_state;
715 if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
716 // We could not get stable state of the JavaThread.
717 // Consider it running and just return.
718 return;
719 }
720
721 if (safepoint_safe_with(_thread, stable_state)) {
722 account_safe_thread();
723 return;
724 }
725
726 // All other thread states will continue to run until they
727 // transition and self-block in state _blocked
728 // Safepoint polling in compiled code causes the Java threads to do the same.
729 // Note: new threads may require a malloc so they must be allowed to finish
730
731 assert(is_running(), "examine_state_of_thread on non-running thread");
732 return;
733 }
734
735 void ThreadSafepointState::account_safe_thread() {
736 SafepointSynchronize::decrement_waiting_to_block();
737 if (_thread->in_critical()) {
738 // Notice that this thread is in a critical section
739 SafepointSynchronize::increment_jni_active_count();
740 }
741 DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
742 assert(!_safepoint_safe, "Must be unsafe before safe");
743 _safepoint_safe = true;
744
745 // The oops in the monitor cache are cleared to prevent stale cache entries
746 // from keeping dead objects alive. Because these oops are always cleared
747 // before safepoint operations they are not visited in JavaThread::oops_do.
748 _thread->om_clear_monitor_cache();
749 }
750
751 void ThreadSafepointState::restart() {
752 assert(_safepoint_safe, "Must be safe before unsafe");
753 _safepoint_safe = false;
754 }
755
756 void ThreadSafepointState::print_on(outputStream *st) const {
757 const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
758
759 st->print_cr("Thread: " INTPTR_FORMAT
760 " [0x%2x] State: %s _at_poll_safepoint %d",
761 p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
762
763 _thread->print_thread_state_on(st);
764 }
765
766 // ---------------------------------------------------------------------------------------------------------------------
767
768 // Process pending operation.
769 void ThreadSafepointState::handle_polling_page_exception() {
770 JavaThread* self = thread();
771 assert(self == JavaThread::current(), "must be self");
772
773 // Step 1: Find the nmethod from the return address
774 address real_return_addr = self->saved_exception_pc();
775
776 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
777 assert(cb != nullptr && cb->is_nmethod(), "return address should be in nmethod");
778 nmethod* nm = cb->as_nmethod();
779
780 // Find frame of caller
781 frame stub_fr = self->last_frame();
782 CodeBlob* stub_cb = stub_fr.cb();
783 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
784 RegisterMap map(self,
785 RegisterMap::UpdateMap::include,
786 RegisterMap::ProcessFrames::skip,
787 RegisterMap::WalkContinuation::skip);
788 frame caller_fr = stub_fr.sender(&map);
789
790 // Should only be poll_return or poll
791 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
792
793 // This is a poll immediately before a return. The exception handling code
794 // has already had the effect of causing the return to occur, so the execution
795 // will continue immediately after the call. In addition, the oopmap at the
796 // return point does not mark the return value as an oop (if it is), so
797 // it needs a handle here to be updated.
798 if( nm->is_at_poll_return(real_return_addr) ) {
799 // See if return type is an oop.
800 bool return_oop = nm->method()->is_returning_oop();
801 HandleMark hm(self);
802 Handle return_value;
803 if (return_oop) {
804 // The oop result has been saved on the stack together with all
805 // the other registers. In order to preserve it over GCs we need
806 // to keep it in a handle.
807 oop result = caller_fr.saved_oop_result(&map);
808 assert(oopDesc::is_oop_or_null(result), "must be oop");
809 return_value = Handle(self, result);
810 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
811 }
812
813 // We get here if compiled return polls found a reason to call into the VM.
814 // One condition for that is that the top frame is not yet safe to use.
815 // The following stack watermark barrier poll will catch such situations.
816 StackWatermarkSet::after_unwind(self);
817
818 // Process pending operation
819 SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */);
820
821 // restore oop result, if any
822 if (return_oop) {
823 caller_fr.set_saved_oop_result(&map, return_value());
824 }
825 }
826
827 // This is a safepoint poll. Verify the return address and block.
828 else {
829
830 // verify the blob built the "return address" correctly
831 assert(real_return_addr == caller_fr.pc(), "must match");
832
833 set_at_poll_safepoint(true);
834 // Process pending operation
835 // We never deliver an async exception at a polling point as the
836 // compiler may not have an exception handler for it (polling at
837 // a return point is ok though). We will check for a pending async
838 // exception below and deoptimize if needed. We also cannot deoptimize
839 // and still install the exception here because live registers needed
840 // during deoptimization are clobbered by the exception path. The
841 // exception will just be delivered once we get into the interpreter.
842 SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */);
843 set_at_poll_safepoint(false);
844
845 if (self->has_async_exception_condition()) {
846 Deoptimization::deoptimize_frame(self, caller_fr.id());
847 log_info(exceptions)("deferred async exception at compiled safepoint");
848 }
849
850 // If an exception has been installed we must verify that the top frame wasn't deoptimized.
851 if (self->has_pending_exception() ) {
852 RegisterMap map(self,
853 RegisterMap::UpdateMap::include,
854 RegisterMap::ProcessFrames::skip,
855 RegisterMap::WalkContinuation::skip);
856 frame caller_fr = stub_fr.sender(&map);
857 if (caller_fr.is_deoptimized_frame()) {
858 // The exception path will destroy registers that are still
859 // live and will be needed during deoptimization, so if we
860 // have an exception now things are messed up. We only check
861 // at this scope because for a poll return it is ok to deoptimize
862 // while having a pending exception since the call we are returning
863 // from already collides with exception handling registers and
864 // so there is no issue (the exception handling path kills call
865 // result registers but this is ok since the exception kills
866 // the result anyway).
867 fatal("Exception installed and deoptimization is pending");
868 }
869 }
870 }
871 }
872
873
874 // -------------------------------------------------------------------------------------------------------
875 // Implementation of SafepointTracing
876
877 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
878 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
879 jlong SafepointTracing::_last_safepoint_leave_time_ns = 0;
880 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
881 jlong SafepointTracing::_last_app_time_ns = 0;
882 int SafepointTracing::_nof_threads = 0;
883 int SafepointTracing::_nof_running = 0;
884 int SafepointTracing::_page_trap = 0;
885 VM_Operation::VMOp_Type SafepointTracing::_current_type;
886 jlong SafepointTracing::_max_sync_time = 0;
887 jlong SafepointTracing::_max_vmop_time = 0;
888 uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
889
890 void SafepointTracing::init() {
891 // Application start
892 _last_safepoint_end_time_ns = os::javaTimeNanos();
893 }
894
895 // Helper method to print the header.
896 static void print_header(outputStream* st) {
897 // The number of spaces is significant here, and should match the format
898 // specifiers in print_statistics().
899
900 st->print("VM Operation "
901 "[ threads: total initial_running ]"
902 "[ time: sync vmop total ]");
903
904 st->print_cr(" page_trap_count");
905 }
906
907 // This prints a nice table. To get the statistics to not shift due to the logging uptime
908 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
909 void SafepointTracing::statistics_log() {
910 LogTarget(Info, safepoint, stats) lt;
911 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
912 LogStream ls(lt);
913
914 static int _cur_stat_index = 0;
915
916 // Print header every 30 entries
917 if ((_cur_stat_index % 30) == 0) {
918 print_header(&ls);
919 _cur_stat_index = 1; // wrap
920 } else {
921 _cur_stat_index++;
922 }
923
924 ls.print("%-28s [ "
925 INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " "
926 "]",
927 VM_Operation::name(_current_type),
928 _nof_threads,
929 _nof_running);
930 ls.print("[ "
931 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
932 (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
933 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns),
934 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
935
936 ls.print_cr(INT32_FORMAT_W(16), _page_trap);
937 }
938
939 // This method will be called when VM exits. This tries to summarize the sampling.
940 // Current thread may already be deleted, so don't use ResourceMark.
941 void SafepointTracing::statistics_exit_log() {
942 if (!log_is_enabled(Info, safepoint, stats)) {
943 return;
944 }
945 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
946 if (_op_count[index] != 0) {
947 log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
948 _op_count[index]);
949 }
950 }
951
952 log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns",
953 (int64_t)(_max_sync_time));
954 log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
955 INT64_FORMAT " ns",
956 (int64_t)(_max_vmop_time));
957 }
958
959 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
960 _op_count[type]++;
961 _current_type = type;
962
963 // update the time stamp to begin recording safepoint time
964 _last_safepoint_begin_time_ns = os::javaTimeNanos();
965 _last_safepoint_sync_time_ns = 0;
966
967 _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
968 _last_safepoint_end_time_ns = 0;
969
970 RuntimeService::record_safepoint_begin(_last_app_time_ns);
971 log_debug(safepoint)("Safepoint synchronization initiated");
972 }
973
974 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
975 _last_safepoint_sync_time_ns = os::javaTimeNanos();
976 _nof_threads = nof_threads;
977 _nof_running = nof_running;
978 _page_trap = traps;
979 RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
980 log_debug(safepoint)("Safepoint synchronization complete");
981 }
982
983 void SafepointTracing::leave() {
984 _last_safepoint_leave_time_ns = os::javaTimeNanos();
985 log_debug(safepoint)("Leaving safepoint");
986 }
987
988 void SafepointTracing::end() {
989 _last_safepoint_end_time_ns = os::javaTimeNanos();
990
991 if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
992 _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
993 }
994 if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
995 _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
996 }
997 if (log_is_enabled(Info, safepoint, stats)) {
998 statistics_log();
999 }
1000
1001 log_info(safepoint)(
1002 "Safepoint \"%s\", "
1003 "Time since last: " JLONG_FORMAT " ns, "
1004 "Reaching safepoint: " JLONG_FORMAT " ns, "
1005 "At safepoint: " JLONG_FORMAT " ns, "
1006 "Leaving safepoint: " JLONG_FORMAT " ns, "
1007 "Total: " JLONG_FORMAT " ns, "
1008 "Threads: %d runnable, %d total",
1009 VM_Operation::name(_current_type),
1010 _last_app_time_ns,
1011 _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns,
1012 _last_safepoint_leave_time_ns - _last_safepoint_sync_time_ns,
1013 _last_safepoint_end_time_ns - _last_safepoint_leave_time_ns,
1014 _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns,
1015 _nof_running,
1016 _nof_threads
1017 );
1018
1019 RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns);
1020 log_debug(safepoint)("Safepoint complete");
1021 }