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/inlineKlass.hpp"
42 #include "oops/oop.inline.hpp"
43 #include "oops/symbol.hpp"
44 #include "runtime/atomicAccess.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 #include "utilities/vmError.hpp"
70
71 static void post_safepoint_begin_event(EventSafepointBegin& event,
72 uint64_t safepoint_id,
73 int thread_count,
74 int critical_thread_count) {
75 if (event.should_commit()) {
76 event.set_safepointId(safepoint_id);
77 event.set_totalThreadCount(thread_count);
78 event.set_jniCriticalThreadCount(critical_thread_count);
79 event.commit();
80 }
81 }
82
83
84 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization& event,
85 uint64_t safepoint_id,
86 int initial_number_of_threads,
87 int threads_waiting_to_block,
88 int iterations) {
89 if (event.should_commit()) {
90 event.set_safepointId(safepoint_id);
91 event.set_initialThreadCount(initial_number_of_threads);
92 event.set_runningThreadCount(threads_waiting_to_block);
93 event.set_iterations(checked_cast<u4>(iterations));
94 event.commit();
95 }
96 }
97
98 static void post_safepoint_end_event(EventSafepointEnd& event, uint64_t safepoint_id) {
99 if (event.should_commit()) {
100 event.set_safepointId(safepoint_id);
101 event.commit();
102 }
103 }
104
105 // SafepointCheck
106 SafepointStateTracker::SafepointStateTracker(uint64_t safepoint_id, bool at_safepoint)
107 : _safepoint_id(safepoint_id), _at_safepoint(at_safepoint) {}
108
109 bool SafepointStateTracker::safepoint_state_changed() {
110 return _safepoint_id != SafepointSynchronize::safepoint_id() ||
111 _at_safepoint != SafepointSynchronize::is_at_safepoint();
112 }
113
114 // --------------------------------------------------------------------------------------------------
115 // Implementation of Safepoint begin/end
116
117 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
118 int SafepointSynchronize::_waiting_to_block = 0;
119 volatile uint64_t SafepointSynchronize::_safepoint_counter = 0;
120 uint64_t SafepointSynchronize::_safepoint_id = 0;
121 const uint64_t SafepointSynchronize::InactiveSafepointCounter = 0;
122 int SafepointSynchronize::_current_jni_active_count = 0;
123
124 WaitBarrier* SafepointSynchronize::_wait_barrier;
125
126 static bool timeout_error_printed = false;
127
128 // Statistic related
129 static jlong _safepoint_begin_time = 0;
130 static volatile int _nof_threads_hit_polling_page = 0;
131
132 void SafepointSynchronize::init(Thread* vmthread) {
133 // WaitBarrier should never be destroyed since we will have
134 // threads waiting on it while exiting.
135 _wait_barrier = new WaitBarrier(vmthread);
136 SafepointTracing::init();
137 }
138
139 void SafepointSynchronize::increment_jni_active_count() {
140 assert(Thread::current()->is_VM_thread(), "Only VM thread may increment");
141 ++_current_jni_active_count;
142 }
143
144 void SafepointSynchronize::decrement_waiting_to_block() {
145 assert(_waiting_to_block > 0, "sanity check");
146 assert(Thread::current()->is_VM_thread(), "Only VM thread may decrement");
147 --_waiting_to_block;
148 }
149
150 bool SafepointSynchronize::thread_not_running(ThreadSafepointState *cur_state) {
151 if (!cur_state->is_running()) {
152 // Robustness: asserted in the caller, but handle/tolerate it for release bits.
153 LogTarget(Error, safepoint) lt;
154 if (lt.is_enabled()) {
155 LogStream ls(lt);
156 ls.print("Illegal initial state detected: ");
157 cur_state->print_on(&ls);
158 }
159 return true;
160 }
161 cur_state->examine_state_of_thread(SafepointSynchronize::safepoint_counter());
162 if (!cur_state->is_running()) {
163 return true;
164 }
165 return false;
166 }
167
168 #ifdef ASSERT
169 static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) {
170 int a = 0;
171 const ThreadSafepointState *tmp_tss = tss_head;
172 while (tmp_tss != nullptr) {
173 ++a;
174 assert(tmp_tss->is_running(), "Illegal initial state");
175 tmp_tss = tmp_tss->get_next();
176 }
177 assert(a == still_running, "Must be the same");
178 }
179 #endif // ASSERT
180
181 static void back_off(int64_t start_time) {
182 // We start with fine-grained nanosleeping until a millisecond has
183 // passed, at which point we resort to plain naked_short_sleep.
184 if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) {
185 os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
186 } else {
187 os::naked_short_sleep(1);
188 }
189 }
190
191 int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running)
192 {
193 JavaThreadIteratorWithHandle jtiwh;
194
195 #ifdef ASSERT
196 for (; JavaThread *cur = jtiwh.next(); ) {
197 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
198 }
199 jtiwh.rewind();
200 #endif // ASSERT
201
202 // Iterate through all threads until it has been determined how to stop them all at a safepoint.
203 int still_running = nof_threads;
204 ThreadSafepointState *tss_head = nullptr;
205 ThreadSafepointState **p_prev = &tss_head;
206 for (; JavaThread *cur = jtiwh.next(); ) {
207 ThreadSafepointState *cur_tss = cur->safepoint_state();
208 assert(cur_tss->get_next() == nullptr, "Must be null");
209 if (thread_not_running(cur_tss)) {
210 --still_running;
211 } else {
212 *p_prev = cur_tss;
213 p_prev = cur_tss->next_ptr();
214 }
215 }
216 *p_prev = nullptr;
217
218 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
219
220 *initial_running = still_running;
221
222 log_trace(safepoint)("%d total threads, waiting for %d threads to block", nof_threads, still_running);
223
224 // If there is no thread still running, we are already done.
225 if (still_running <= 0) {
226 assert(tss_head == nullptr, "Must be empty");
227 return 1;
228 }
229
230 int iterations = 1; // The first iteration is above.
231 int64_t start_time = os::javaTimeNanos();
232
233 do {
234 log_trace(safepoint)("Checking thread status");
235
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 log_trace(safepoint)("Thread " INTPTR_FORMAT " [%d] is now blocked",
247 p2i(cur_tss->thread()), cur_tss->thread()->osthread()->thread_id());
248 --still_running;
249 *p_prev = nullptr;
250 ThreadSafepointState *tmp = cur_tss;
251 cur_tss = cur_tss->get_next();
252 tmp->set_next(nullptr);
253 } else {
254 log_trace(safepoint)("Thread " INTPTR_FORMAT " [%d] is still running",
255 p2i(cur_tss->thread()), cur_tss->thread()->osthread()->thread_id());
256 *p_prev = cur_tss;
257 p_prev = cur_tss->next_ptr();
258 cur_tss = cur_tss->get_next();
259 }
260 }
261
262 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
263
264 if (still_running > 0) {
265 log_trace(safepoint)("Waiting for %d threads to block", still_running);
266 back_off(start_time);
267 }
268
269 iterations++;
270 } while (still_running > 0);
271
272 assert(tss_head == nullptr, "Must be empty");
273
274 return iterations;
275 }
276
277 void SafepointSynchronize::arm_safepoint() {
278 // Begin the process of bringing the system to a safepoint.
279 // Java threads can be in several different states and are
280 // stopped by different mechanisms:
281 //
282 // 1. Running interpreted
283 // When executing branching/returning byte codes interpreter
284 // checks if the poll is armed, if so blocks in SS::block().
285 // 2. Running in native code
286 // When returning from the native code, a Java thread must check
287 // the safepoint _state to see if we must block. If the
288 // VM thread sees a Java thread in native, it does
289 // not wait for this thread to block. The order of the memory
290 // writes and reads of both the safepoint state and the Java
291 // threads state is critical. In order to guarantee that the
292 // memory writes are serialized with respect to each other,
293 // the VM thread issues a memory barrier instruction.
294 // 3. Running compiled Code
295 // Compiled code reads the local polling page that
296 // is set to fault if we are trying to get to a safepoint.
297 // 4. Blocked
298 // A thread which is blocked will not be allowed to return from the
299 // block condition until the safepoint operation is complete.
300 // 5. In VM or Transitioning between states
301 // If a Java thread is currently running in the VM or transitioning
302 // between states, the safepointing code will poll the thread state
303 // until the thread blocks itself when it attempts transitions to a
304 // new state or locking a safepoint checked monitor.
305
306 // We must never miss a thread with correct safepoint id, so we must make sure we arm
307 // the wait barrier for the next safepoint id/counter.
308 // Arming must be done after resetting _current_jni_active_count, _waiting_to_block.
309 _wait_barrier->arm(static_cast<int>(_safepoint_counter + 1));
310
311 assert((_safepoint_counter & 0x1) == 0, "must be even");
312 // The store to _safepoint_counter must happen after any stores in arming.
313 AtomicAccess::release_store(&_safepoint_counter, _safepoint_counter + 1);
314
315 // We are synchronizing
316 OrderAccess::storestore(); // Ordered with _safepoint_counter
317 _state = _synchronizing;
318
319 // Arming the per thread poll while having _state != _not_synchronized means safepointing
320 log_trace(safepoint)("Setting thread local yield flag for threads");
321 OrderAccess::storestore(); // storestore, global state -> local state
322 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
323 // Make sure the threads start polling, it is time to yield.
324 SafepointMechanism::arm_local_poll(cur);
325 }
326 if (UseSystemMemoryBarrier) {
327 SystemMemoryBarrier::emit(); // storestore|storeload, global state -> local state
328 } else {
329 OrderAccess::fence(); // storestore|storeload, global state -> local state
330 }
331 }
332
333 // Roll all threads forward to a safepoint and suspend them all
334 void SafepointSynchronize::begin() {
335 assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint");
336
337 EventSafepointBegin begin_event;
338 SafepointTracing::begin(VMThread::vm_op_type());
339
340 log_trace(safepoint)("Suspending GC threads");
341 Universe::heap()->safepoint_synchronize_begin();
342
343 // By getting the Threads_lock, we assure that no threads are about to start or
344 // exit. It is released again in SafepointSynchronize::end().
345 log_trace(safepoint)("Blocking threads from starting/exiting");
346 Threads_lock->lock();
347
348 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
349
350 int nof_threads = Threads::number_of_threads();
351
352 _nof_threads_hit_polling_page = 0;
353
354 // Reset the count of active JNI critical threads
355 _current_jni_active_count = 0;
356
357 // Set number of threads to wait for
358 _waiting_to_block = nof_threads;
359
360 jlong safepoint_limit_time = 0;
361 if (SafepointTimeout) {
362 // Set the limit time, so that it can be compared to see if this has taken
363 // too long to complete.
364 safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)(SafepointTimeoutDelay * NANOSECS_PER_MILLISEC);
365 timeout_error_printed = false;
366 }
367
368 EventSafepointStateSynchronization sync_event;
369 int initial_running = 0;
370
371 // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before.
372 log_trace(safepoint)("Arming safepoint using %s wait barrier", _wait_barrier->description());
373 arm_safepoint();
374
375 // Will spin until all threads are safe.
376 int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running);
377 assert(_waiting_to_block == 0, "No thread should be running");
378
379 #ifndef PRODUCT
380 // Mark all threads
381 if (VerifyCrossModifyFence) {
382 JavaThreadIteratorWithHandle jtiwh;
383 for (; JavaThread *cur = jtiwh.next(); ) {
384 cur->set_requires_cross_modify_fence(true);
385 }
386 }
387
388 if (safepoint_limit_time != 0) {
389 jlong current_time = os::javaTimeNanos();
390 if (safepoint_limit_time < current_time) {
391 log_warning(safepoint)("# SafepointSynchronize: Finished after "
392 INT64_FORMAT_W(6) " ms",
393 (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS));
394 }
395 }
396 #endif
397
398 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
399
400 // Record state
401 _state = _synchronized;
402
403 OrderAccess::fence();
404
405 // Set the new id
406 ++_safepoint_id;
407
408 #ifdef ASSERT
409 // Make sure all the threads were visited.
410 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
411 assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread");
412 }
413 #endif // ASSERT
414
415 post_safepoint_synchronize_event(sync_event,
416 _safepoint_id,
417 initial_running,
418 _waiting_to_block, iterations);
419
420 SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page);
421
422 post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count);
423 }
424
425 void SafepointSynchronize::disarm_safepoint() {
426 uint64_t active_safepoint_counter = _safepoint_counter;
427 {
428 JavaThreadIteratorWithHandle jtiwh;
429 #ifdef ASSERT
430 // A pending_exception cannot be installed during a safepoint. The threads
431 // may install an async exception after they come back from a safepoint into
432 // pending_exception after they unblock. But that should happen later.
433 for (; JavaThread *cur = jtiwh.next(); ) {
434 assert (!(cur->has_pending_exception() &&
435 cur->safepoint_state()->is_at_poll_safepoint()),
436 "safepoint installed a pending exception");
437 }
438 #endif // ASSERT
439
440 OrderAccess::fence(); // keep read and write of _state from floating up
441 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
442
443 // Change state first to _not_synchronized.
444 // No threads should see _synchronized when running.
445 _state = _not_synchronized;
446
447 // Set the next dormant (even) safepoint id.
448 assert((_safepoint_counter & 0x1) == 1, "must be odd");
449 AtomicAccess::release_store(&_safepoint_counter, _safepoint_counter + 1);
450
451 OrderAccess::fence(); // Keep the local state from floating up.
452
453 jtiwh.rewind();
454 for (; JavaThread *current = jtiwh.next(); ) {
455 // Clear the visited flag to ensure that the critical counts are collected properly.
456 DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);)
457 ThreadSafepointState* cur_state = current->safepoint_state();
458 assert(!cur_state->is_running(), "Thread not suspended at safepoint");
459 cur_state->restart(); // TSS _running
460 assert(cur_state->is_running(), "safepoint state has not been reset");
461 }
462 } // ~JavaThreadIteratorWithHandle
463
464 // Release threads lock, so threads can be created/destroyed again.
465 Threads_lock->unlock();
466
467 // Wake threads after local state is correctly set.
468 _wait_barrier->disarm();
469 }
470
471 // Wake up all threads, so they are ready to resume execution after the safepoint
472 // operation has been carried out
473 void SafepointSynchronize::end() {
474 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
475 SafepointTracing::leave();
476
477 EventSafepointEnd event;
478 assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint");
479
480 log_trace(safepoint)("Disarming safepoint");
481 disarm_safepoint();
482
483 log_trace(safepoint)("Resuming GC threads");
484 Universe::heap()->safepoint_synchronize_end();
485
486 SafepointTracing::end();
487
488 post_safepoint_end_event(event, safepoint_id());
489 }
490
491 // Methods for determining if a JavaThread is safepoint safe.
492
493 // False means unsafe with undetermined state.
494 // True means a determined state, but it may be an unsafe state.
495 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
496 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
497 assert((safepoint_count != InactiveSafepointCounter &&
498 Thread::current() == (Thread*)VMThread::vm_thread() &&
499 SafepointSynchronize::_state != _not_synchronized)
500 || safepoint_count == InactiveSafepointCounter, "Invalid check");
501
502 // To handle the thread_blocked state on the backedge of the WaitBarrier from
503 // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
504 // re-read state after we read thread safepoint id. The JavaThread changes its
505 // thread state from thread_blocked before resetting safepoint id to 0.
506 // This guarantees the second read will be from an updated thread state. It can
507 // either be different state making this an unsafe state or it can see blocked
508 // again. When we see blocked twice with a 0 safepoint id, either:
509 // - It is normally blocked, e.g. on Mutex, TBIVM.
510 // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
511 // - It was in SS:block() but now on a Mutex.
512 // All of these cases are safe.
513
514 *state = thread->thread_state();
515 OrderAccess::loadload();
516 uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire
517 if (sid != InactiveSafepointCounter && sid != safepoint_count) {
518 // In an old safepoint, state not relevant.
519 return false;
520 }
521 return *state == thread->thread_state();
522 }
523
524 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
525 switch(state) {
526 case _thread_in_native:
527 // native threads are safe if they have no java stack or have walkable stack
528 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
529
530 case _thread_blocked:
531 // On wait_barrier or blocked.
532 // Blocked threads should already have walkable stack.
533 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
534 return true;
535
536 default:
537 return false;
538 }
539 }
540
541 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
542 if (thread->is_terminated()) {
543 return true;
544 }
545 JavaThreadState stable_state;
546 if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
547 return safepoint_safe_with(thread, stable_state);
548 }
549 return false;
550 }
551
552
553 // -------------------------------------------------------------------------------------------------------
554 // Implementation of Safepoint blocking point
555
556 void SafepointSynchronize::block(JavaThread *thread) {
557 assert(thread != nullptr, "thread must be set");
558
559 // Threads shouldn't block if they are in the middle of printing, but...
560 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
561
562 log_trace(safepoint)("Blocking thread " INTPTR_FORMAT " [%d]",
563 p2i(thread), thread->osthread()->thread_id());
564
565 // Only bail from the block() call if the thread is gone from the
566 // thread list; starting to exit should still block.
567 if (thread->is_terminated()) {
568 // block current thread if we come here from native code when VM is gone
569 thread->block_if_vm_exited();
570
571 // otherwise do nothing
572 return;
573 }
574
575 JavaThreadState state = thread->thread_state();
576 thread->frame_anchor()->make_walkable();
577
578 uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
579
580 // We have no idea where the VMThread is, it might even be at next safepoint.
581 // So we can miss this poll, but stop at next.
582
583 // Load dependent store, it must not pass loading of safepoint_id.
584 thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
585
586 // This part we can skip if we notice we miss or are in a future safepoint.
587 OrderAccess::storestore();
588 // Load in wait barrier should not float up
589 thread->set_thread_state_fence(_thread_blocked);
590
591 _wait_barrier->wait(static_cast<int>(safepoint_id));
592 assert(_state != _synchronized, "Can't be");
593
594 // If barrier is disarmed stop store from floating above loads in barrier.
595 OrderAccess::loadstore();
596 thread->set_thread_state(state);
597
598 // Then we reset the safepoint id to inactive.
599 thread->safepoint_state()->reset_safepoint_id(); // Release store
600
601 OrderAccess::fence();
602
603 guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
604 "The safepoint id should be set only in block path");
605
606 // cross_modify_fence is done by SafepointMechanism::process_if_requested
607 // which is the only caller here.
608
609 log_trace(safepoint)("Unblocking thread " INTPTR_FORMAT " [%d]",
610 p2i(thread), thread->osthread()->thread_id());
611 }
612
613 // ------------------------------------------------------------------------------------------------------
614 // Exception handlers
615
616
617 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
618 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
619 thread->set_thread_state(_thread_in_vm);
620
621 // Enable WXWrite: the function is called implicitly from java code.
622 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread));
623
624 if (log_is_enabled(Info, safepoint, stats)) {
625 AtomicAccess::inc(&_nof_threads_hit_polling_page);
626 }
627
628 ThreadSafepointState* state = thread->safepoint_state();
629
630 state->handle_polling_page_exception();
631
632 thread->set_thread_state(_thread_in_Java);
633 }
634
635
636 void SafepointSynchronize::print_safepoint_timeout() {
637 if (!timeout_error_printed) {
638 timeout_error_printed = true;
639 // Print out the thread info which didn't reach the safepoint for debugging
640 // purposes (useful when there are lots of threads in the debugger).
641 LogTarget(Warning, safepoint) lt;
642 if (lt.is_enabled()) {
643 ResourceMark rm;
644 LogStream ls(lt);
645
646 ls.cr();
647 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
648 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
649 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
650 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
651 if (cur_thread->safepoint_state()->is_running()) {
652 ls.print("# ");
653 cur_thread->print_on(&ls);
654 ls.cr();
655 }
656 }
657 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
658 }
659 }
660
661 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
662 // ShowMessageBoxOnError.
663 if (AbortVMOnSafepointTimeout && (os::elapsedTime() * MILLIUNITS > AbortVMOnSafepointTimeoutDelay)) {
664 // Send the blocking thread a signal to terminate and write an error file.
665 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
666 if (cur_thread->safepoint_state()->is_running()) {
667 VMError::set_safepoint_timed_out_thread(cur_thread);
668 if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
669 break; // Could not send signal. Report fatal error.
670 }
671 // Give cur_thread a chance to report the error and terminate the VM.
672 os::naked_sleep(3000);
673 }
674 }
675 fatal("Safepoint sync time longer than %.6f ms detected when executing %s.",
676 SafepointTimeoutDelay, VMThread::vm_operation()->name());
677 }
678 }
679
680 // -------------------------------------------------------------------------------------------------------
681 // Implementation of ThreadSafepointState
682
683 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
684 : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
685 _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(nullptr) {
686 }
687
688 void ThreadSafepointState::create(JavaThread *thread) {
689 ThreadSafepointState *state = new ThreadSafepointState(thread);
690 thread->set_safepoint_state(state);
691 }
692
693 void ThreadSafepointState::destroy(JavaThread *thread) {
694 if (thread->safepoint_state()) {
695 delete(thread->safepoint_state());
696 thread->set_safepoint_state(nullptr);
697 }
698 }
699
700 uint64_t ThreadSafepointState::get_safepoint_id() const {
701 return AtomicAccess::load_acquire(&_safepoint_id);
702 }
703
704 void ThreadSafepointState::reset_safepoint_id() {
705 AtomicAccess::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
706 }
707
708 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
709 AtomicAccess::release_store(&_safepoint_id, safepoint_id);
710 }
711
712 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
713 assert(is_running(), "better be running or just have hit safepoint poll");
714
715 JavaThreadState stable_state;
716 if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
717 // We could not get stable state of the JavaThread.
718 // Consider it running and just return.
719 return;
720 }
721
722 if (safepoint_safe_with(_thread, stable_state)) {
723 account_safe_thread();
724 return;
725 }
726
727 // All other thread states will continue to run until they
728 // transition and self-block in state _blocked
729 // Safepoint polling in compiled code causes the Java threads to do the same.
730 // Note: new threads may require a malloc so they must be allowed to finish
731
732 assert(is_running(), "examine_state_of_thread on non-running thread");
733 return;
734 }
735
736 void ThreadSafepointState::account_safe_thread() {
737 SafepointSynchronize::decrement_waiting_to_block();
738 if (_thread->in_critical()) {
739 // Notice that this thread is in a critical section
740 SafepointSynchronize::increment_jni_active_count();
741 }
742 DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
743 assert(!_safepoint_safe, "Must be unsafe before safe");
744 _safepoint_safe = true;
745
746 // The oops in the monitor cache are cleared to prevent stale cache entries
747 // from keeping dead objects alive. Because these oops are always cleared
748 // before safepoint operations they are not visited in JavaThread::oops_do.
749 _thread->om_clear_monitor_cache();
750 }
751
752 void ThreadSafepointState::restart() {
753 assert(_safepoint_safe, "Must be safe before unsafe");
754 _safepoint_safe = false;
755 }
756
757 void ThreadSafepointState::print_on(outputStream *st) const {
758 const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
759
760 st->print_cr("Thread: " INTPTR_FORMAT
761 " [0x%2x] State: %s _at_poll_safepoint %d",
762 p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
763
764 _thread->print_thread_state_on(st);
765 }
766
767 // ---------------------------------------------------------------------------------------------------------------------
768
769 // Process pending operation.
770 void ThreadSafepointState::handle_polling_page_exception() {
771 JavaThread* self = thread();
772 assert(self == JavaThread::current(), "must be self");
773
774 // Step 1: Find the nmethod from the return address
775 address real_return_addr = self->saved_exception_pc();
776
777 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
778 assert(cb != nullptr && cb->is_nmethod(), "return address should be in nmethod");
779 nmethod* nm = cb->as_nmethod();
780
781 // Find frame of caller
782 frame stub_fr = self->last_frame();
783 CodeBlob* stub_cb = stub_fr.cb();
784 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
785 RegisterMap map(self,
786 RegisterMap::UpdateMap::include,
787 RegisterMap::ProcessFrames::skip,
788 RegisterMap::WalkContinuation::skip);
789 frame caller_fr = stub_fr.sender(&map);
790
791 // Should only be poll_return or poll
792 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
793
794 // This is a poll immediately before a return. The exception handling code
795 // has already had the effect of causing the return to occur, so the execution
796 // will continue immediately after the call. In addition, the oopmap at the
797 // return point does not mark the return value as an oop (if it is), so
798 // it needs a handle here to be updated.
799 if( nm->is_at_poll_return(real_return_addr) ) {
800 ResourceMark rm;
801 // See if return type is an oop.
802 Method* method = nm->method();
803 bool return_oop = method->is_returning_oop();
804 HandleMark hm(self);
805 GrowableArray<Handle> return_values;
806 InlineKlass* vk = nullptr;
807 if (InlineTypeReturnedAsFields && return_oop) {
808 // Check if an inline type is returned as fields
809 vk = InlineKlass::returned_inline_klass(map, &return_oop, method);
810 if (vk != nullptr) {
811 // We're at a safepoint at the return of a method that returns
812 // multiple values. We must make sure we preserve the oop values
813 // across the safepoint.
814 vk->save_oop_fields(map, return_values);
815 }
816 }
817
818 if (return_oop) {
819 // The oop result has been saved on the stack together with all
820 // the other registers. In order to preserve it over GCs we need
821 // to keep it in a handle.
822 oop result = caller_fr.saved_oop_result(&map);
823 assert(oopDesc::is_oop_or_null(result), "must be oop");
824 return_values.push(Handle(self, result));
825 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
826 }
827
828 // We get here if compiled return polls found a reason to call into the VM.
829 // One condition for that is that the top frame is not yet safe to use.
830 // The following stack watermark barrier poll will catch such situations.
831 StackWatermarkSet::after_unwind(self);
832
833 // Process pending operation
834 SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */);
835
836 // restore oop result, if any
837 if (return_oop) {
838 assert(vk != nullptr || return_values.length() == 1, "only one return value");
839 caller_fr.set_saved_oop_result(&map, return_values.pop()());
840 }
841 // restore oops in scalarized fields
842 if (vk != nullptr) {
843 vk->restore_oop_results(map, return_values);
844 }
845 }
846
847 // This is a safepoint poll. Verify the return address and block.
848 else {
849
850 // verify the blob built the "return address" correctly
851 assert(real_return_addr == caller_fr.pc(), "must match");
852
853 set_at_poll_safepoint(true);
854 // Process pending operation
855 // We never deliver an async exception at a polling point as the
856 // compiler may not have an exception handler for it (polling at
857 // a return point is ok though). We will check for a pending async
858 // exception below and deoptimize if needed. We also cannot deoptimize
859 // and still install the exception here because live registers needed
860 // during deoptimization are clobbered by the exception path. The
861 // exception will just be delivered once we get into the interpreter.
862 SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */);
863 set_at_poll_safepoint(false);
864
865 if (self->has_async_exception_condition()) {
866 Deoptimization::deoptimize_frame(self, caller_fr.id());
867 log_info(exceptions)("deferred async exception at compiled safepoint");
868 }
869
870 // If an exception has been installed we must verify that the top frame wasn't deoptimized.
871 if (self->has_pending_exception() ) {
872 RegisterMap map(self,
873 RegisterMap::UpdateMap::include,
874 RegisterMap::ProcessFrames::skip,
875 RegisterMap::WalkContinuation::skip);
876 frame caller_fr = stub_fr.sender(&map);
877 if (caller_fr.is_deoptimized_frame()) {
878 // The exception path will destroy registers that are still
879 // live and will be needed during deoptimization, so if we
880 // have an exception now things are messed up. We only check
881 // at this scope because for a poll return it is ok to deoptimize
882 // while having a pending exception since the call we are returning
883 // from already collides with exception handling registers and
884 // so there is no issue (the exception handling path kills call
885 // result registers but this is ok since the exception kills
886 // the result anyway).
887 fatal("Exception installed and deoptimization is pending");
888 }
889 }
890 }
891 }
892
893
894 // -------------------------------------------------------------------------------------------------------
895 // Implementation of SafepointTracing
896
897 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
898 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
899 jlong SafepointTracing::_last_safepoint_leave_time_ns = 0;
900 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
901 jlong SafepointTracing::_last_app_time_ns = 0;
902 int SafepointTracing::_nof_threads = 0;
903 int SafepointTracing::_nof_running = 0;
904 int SafepointTracing::_page_trap = 0;
905 VM_Operation::VMOp_Type SafepointTracing::_current_type;
906 jlong SafepointTracing::_max_sync_time = 0;
907 jlong SafepointTracing::_max_vmop_time = 0;
908 uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
909
910 void SafepointTracing::init() {
911 // Application start
912 _last_safepoint_end_time_ns = os::javaTimeNanos();
913 }
914
915 // Helper method to print the header.
916 static void print_header(outputStream* st) {
917 // The number of spaces is significant here, and should match the format
918 // specifiers in print_statistics().
919
920 st->print("VM Operation "
921 "[ threads: total initial_running ]"
922 "[ time: sync vmop total ]");
923
924 st->print_cr(" page_trap_count");
925 }
926
927 // This prints a nice table. To get the statistics to not shift due to the logging uptime
928 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
929 void SafepointTracing::statistics_log() {
930 LogTarget(Info, safepoint, stats) lt;
931 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
932 LogStream ls(lt);
933
934 static int _cur_stat_index = 0;
935
936 // Print header every 30 entries
937 if ((_cur_stat_index % 30) == 0) {
938 print_header(&ls);
939 _cur_stat_index = 1; // wrap
940 } else {
941 _cur_stat_index++;
942 }
943
944 ls.print("%-28s [ "
945 INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " "
946 "]",
947 VM_Operation::name(_current_type),
948 _nof_threads,
949 _nof_running);
950 ls.print("[ "
951 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
952 (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
953 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns),
954 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
955
956 ls.print_cr(INT32_FORMAT_W(16), _page_trap);
957 }
958
959 // This method will be called when VM exits. This tries to summarize the sampling.
960 // Current thread may already be deleted, so don't use ResourceMark.
961 void SafepointTracing::statistics_exit_log() {
962 if (!log_is_enabled(Info, safepoint, stats)) {
963 return;
964 }
965 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
966 if (_op_count[index] != 0) {
967 log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
968 _op_count[index]);
969 }
970 }
971
972 log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns",
973 (int64_t)(_max_sync_time));
974 log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
975 INT64_FORMAT " ns",
976 (int64_t)(_max_vmop_time));
977 }
978
979 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
980 _op_count[type]++;
981 _current_type = type;
982
983 // update the time stamp to begin recording safepoint time
984 _last_safepoint_begin_time_ns = os::javaTimeNanos();
985 _last_safepoint_sync_time_ns = 0;
986
987 _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
988 _last_safepoint_end_time_ns = 0;
989
990 RuntimeService::record_safepoint_begin(_last_app_time_ns);
991 log_debug(safepoint)("Safepoint synchronization initiated");
992 }
993
994 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
995 _last_safepoint_sync_time_ns = os::javaTimeNanos();
996 _nof_threads = nof_threads;
997 _nof_running = nof_running;
998 _page_trap = traps;
999 RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
1000 log_debug(safepoint)("Safepoint synchronization complete");
1001 }
1002
1003 void SafepointTracing::leave() {
1004 _last_safepoint_leave_time_ns = os::javaTimeNanos();
1005 log_debug(safepoint)("Leaving safepoint");
1006 }
1007
1008 void SafepointTracing::end() {
1009 _last_safepoint_end_time_ns = os::javaTimeNanos();
1010
1011 if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
1012 _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
1013 }
1014 if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
1015 _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
1016 }
1017 if (log_is_enabled(Info, safepoint, stats)) {
1018 statistics_log();
1019 }
1020
1021 log_info(safepoint)(
1022 "Safepoint \"%s\", "
1023 "Time since last: " JLONG_FORMAT " ns, "
1024 "Reaching safepoint: " JLONG_FORMAT " ns, "
1025 "At safepoint: " JLONG_FORMAT " ns, "
1026 "Leaving safepoint: " JLONG_FORMAT " ns, "
1027 "Total: " JLONG_FORMAT " ns, "
1028 "Threads: %d runnable, %d total",
1029 VM_Operation::name(_current_type),
1030 _last_app_time_ns,
1031 _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns,
1032 _last_safepoint_leave_time_ns - _last_safepoint_sync_time_ns,
1033 _last_safepoint_end_time_ns - _last_safepoint_leave_time_ns,
1034 _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns,
1035 _nof_running,
1036 _nof_threads
1037 );
1038
1039 RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns);
1040 log_debug(safepoint)("Safepoint complete");
1041 }