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