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 #include "utilities/vmError.hpp"
71
72 static void post_safepoint_begin_event(EventSafepointBegin& event,
73 uint64_t safepoint_id,
74 int thread_count,
75 int critical_thread_count) {
76 if (event.should_commit()) {
77 event.set_safepointId(safepoint_id);
78 event.set_totalThreadCount(thread_count);
79 event.set_jniCriticalThreadCount(critical_thread_count);
80 event.commit();
81 }
82 }
83
84
85 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization& event,
86 uint64_t safepoint_id,
87 int initial_number_of_threads,
88 int threads_waiting_to_block,
89 int iterations) {
90 if (event.should_commit()) {
91 event.set_safepointId(safepoint_id);
92 event.set_initialThreadCount(initial_number_of_threads);
93 event.set_runningThreadCount(threads_waiting_to_block);
94 event.set_iterations(checked_cast<u4>(iterations));
95 event.commit();
96 }
97 }
98
99 static void post_safepoint_end_event(EventSafepointEnd& event, uint64_t safepoint_id) {
100 if (event.should_commit()) {
101 event.set_safepointId(safepoint_id);
102 event.commit();
103 }
104 }
105
106 // SafepointCheck
107 SafepointStateTracker::SafepointStateTracker(uint64_t safepoint_id, bool at_safepoint)
108 : _safepoint_id(safepoint_id), _at_safepoint(at_safepoint) {}
109
110 bool SafepointStateTracker::safepoint_state_changed() {
111 return _safepoint_id != SafepointSynchronize::safepoint_id() ||
112 _at_safepoint != SafepointSynchronize::is_at_safepoint();
113 }
114
115 // --------------------------------------------------------------------------------------------------
116 // Implementation of Safepoint begin/end
117
118 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
119 int SafepointSynchronize::_waiting_to_block = 0;
120 volatile uint64_t SafepointSynchronize::_safepoint_counter = 0;
121 uint64_t SafepointSynchronize::_safepoint_id = 0;
122 const uint64_t SafepointSynchronize::InactiveSafepointCounter = 0;
123 int SafepointSynchronize::_current_jni_active_count = 0;
124
125 WaitBarrier* SafepointSynchronize::_wait_barrier;
126
127 static bool timeout_error_printed = false;
128
129 // Statistic related
130 static jlong _safepoint_begin_time = 0;
131 static volatile int _nof_threads_hit_polling_page = 0;
132
133 void SafepointSynchronize::init(Thread* vmthread) {
134 // WaitBarrier should never be destroyed since we will have
135 // threads waiting on it while exiting.
136 _wait_barrier = new WaitBarrier(vmthread);
137 SafepointTracing::init();
138 }
139
140 void SafepointSynchronize::increment_jni_active_count() {
141 assert(Thread::current()->is_VM_thread(), "Only VM thread may increment");
142 ++_current_jni_active_count;
143 }
144
145 void SafepointSynchronize::decrement_waiting_to_block() {
146 assert(_waiting_to_block > 0, "sanity check");
147 assert(Thread::current()->is_VM_thread(), "Only VM thread may decrement");
148 --_waiting_to_block;
149 }
150
151 bool SafepointSynchronize::thread_not_running(ThreadSafepointState *cur_state) {
152 if (!cur_state->is_running()) {
153 // Robustness: asserted in the caller, but handle/tolerate it for release bits.
154 LogTarget(Error, safepoint) lt;
155 if (lt.is_enabled()) {
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 LogStream ls(lt);
169 cur_state->print_on(&ls);
170 }
171 return false;
172 }
173
174 #ifdef ASSERT
175 static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) {
176 int a = 0;
177 const ThreadSafepointState *tmp_tss = tss_head;
178 while (tmp_tss != nullptr) {
179 ++a;
180 assert(tmp_tss->is_running(), "Illegal initial state");
181 tmp_tss = tmp_tss->get_next();
182 }
183 assert(a == still_running, "Must be the same");
184 }
185 #endif // ASSERT
186
187 static void back_off(int64_t start_time) {
188 // We start with fine-grained nanosleeping until a millisecond has
189 // passed, at which point we resort to plain naked_short_sleep.
190 if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) {
191 os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
192 } else {
193 os::naked_short_sleep(1);
194 }
195 }
196
197 int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running)
198 {
199 JavaThreadIteratorWithHandle jtiwh;
200
201 #ifdef ASSERT
202 for (; JavaThread *cur = jtiwh.next(); ) {
203 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
204 }
205 jtiwh.rewind();
206 #endif // ASSERT
207
208 // Iterate through all threads until it has been determined how to stop them all at a safepoint.
209 int still_running = nof_threads;
210 ThreadSafepointState *tss_head = nullptr;
211 ThreadSafepointState **p_prev = &tss_head;
212 for (; JavaThread *cur = jtiwh.next(); ) {
213 ThreadSafepointState *cur_tss = cur->safepoint_state();
214 assert(cur_tss->get_next() == nullptr, "Must be null");
215 if (thread_not_running(cur_tss)) {
216 --still_running;
217 } else {
218 *p_prev = cur_tss;
219 p_prev = cur_tss->next_ptr();
220 }
221 }
222 *p_prev = nullptr;
223
224 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
225
226 *initial_running = still_running;
227
228 // If there is no thread still running, we are already done.
229 if (still_running <= 0) {
230 assert(tss_head == nullptr, "Must be empty");
231 return 1;
232 }
233
234 int iterations = 1; // The first iteration is above.
235 int64_t start_time = os::javaTimeNanos();
236
237 do {
238 // Check if this has taken too long:
239 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
240 print_safepoint_timeout();
241 }
242
243 p_prev = &tss_head;
244 ThreadSafepointState *cur_tss = tss_head;
245 while (cur_tss != nullptr) {
246 assert(cur_tss->is_running(), "Illegal initial state");
247 if (thread_not_running(cur_tss)) {
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 *p_prev = cur_tss;
255 p_prev = cur_tss->next_ptr();
256 cur_tss = cur_tss->get_next();
257 }
258 }
259
260 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
261
262 if (still_running > 0) {
263 back_off(start_time);
264 }
265
266 iterations++;
267 } while (still_running > 0);
268
269 assert(tss_head == nullptr, "Must be empty");
270
271 return iterations;
272 }
273
274 void SafepointSynchronize::arm_safepoint() {
275 // Begin the process of bringing the system to a safepoint.
276 // Java threads can be in several different states and are
277 // stopped by different mechanisms:
278 //
279 // 1. Running interpreted
280 // When executing branching/returning byte codes interpreter
281 // checks if the poll is armed, if so blocks in SS::block().
282 // 2. Running in native code
283 // When returning from the native code, a Java thread must check
284 // the safepoint _state to see if we must block. If the
285 // VM thread sees a Java thread in native, it does
286 // not wait for this thread to block. The order of the memory
287 // writes and reads of both the safepoint state and the Java
288 // threads state is critical. In order to guarantee that the
289 // memory writes are serialized with respect to each other,
290 // the VM thread issues a memory barrier instruction.
291 // 3. Running compiled Code
292 // Compiled code reads the local polling page that
293 // is set to fault if we are trying to get to a safepoint.
294 // 4. Blocked
295 // A thread which is blocked will not be allowed to return from the
296 // block condition until the safepoint operation is complete.
297 // 5. In VM or Transitioning between states
298 // If a Java thread is currently running in the VM or transitioning
299 // between states, the safepointing code will poll the thread state
300 // until the thread blocks itself when it attempts transitions to a
301 // new state or locking a safepoint checked monitor.
302
303 // We must never miss a thread with correct safepoint id, so we must make sure we arm
304 // the wait barrier for the next safepoint id/counter.
305 // Arming must be done after resetting _current_jni_active_count, _waiting_to_block.
306 _wait_barrier->arm(static_cast<int>(_safepoint_counter + 1));
307
308 assert((_safepoint_counter & 0x1) == 0, "must be even");
309 // The store to _safepoint_counter must happen after any stores in arming.
310 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
311
312 // We are synchronizing
313 OrderAccess::storestore(); // Ordered with _safepoint_counter
314 _state = _synchronizing;
315
316 // Arming the per thread poll while having _state != _not_synchronized means safepointing
317 log_trace(safepoint)("Setting thread local yield flag for threads");
318 OrderAccess::storestore(); // storestore, global state -> local state
319 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
320 // Make sure the threads start polling, it is time to yield.
321 SafepointMechanism::arm_local_poll(cur);
322 }
323 if (UseSystemMemoryBarrier) {
324 SystemMemoryBarrier::emit(); // storestore|storeload, global state -> local state
325 } else {
326 OrderAccess::fence(); // storestore|storeload, global state -> local state
327 }
328 }
329
330 // Roll all threads forward to a safepoint and suspend them all
331 void SafepointSynchronize::begin() {
332 assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint");
333
334 EventSafepointBegin begin_event;
335 SafepointTracing::begin(VMThread::vm_op_type());
336
337 Universe::heap()->safepoint_synchronize_begin();
338
339 // By getting the Threads_lock, we assure that no threads are about to start or
340 // exit. It is released again in SafepointSynchronize::end().
341 Threads_lock->lock();
342
343 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
344
345 int nof_threads = Threads::number_of_threads();
346
347 _nof_threads_hit_polling_page = 0;
348
349 log_debug(safepoint)("Safepoint synchronization initiated using %s wait barrier. (%d threads)", _wait_barrier->description(), nof_threads);
350
351 // Reset the count of active JNI critical threads
352 _current_jni_active_count = 0;
353
354 // Set number of threads to wait for
355 _waiting_to_block = nof_threads;
356
357 jlong safepoint_limit_time = 0;
358 if (SafepointTimeout) {
359 // Set the limit time, so that it can be compared to see if this has taken
360 // too long to complete.
361 safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)(SafepointTimeoutDelay * NANOSECS_PER_MILLISEC);
362 timeout_error_printed = false;
363 }
364
365 EventSafepointStateSynchronization sync_event;
366 int initial_running = 0;
367
368 // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before.
369 arm_safepoint();
370
371 // Will spin until all threads are safe.
372 int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running);
373 assert(_waiting_to_block == 0, "No thread should be running");
374
375 #ifndef PRODUCT
376 // Mark all threads
377 if (VerifyCrossModifyFence) {
378 JavaThreadIteratorWithHandle jtiwh;
379 for (; JavaThread *cur = jtiwh.next(); ) {
380 cur->set_requires_cross_modify_fence(true);
381 }
382 }
383
384 if (safepoint_limit_time != 0) {
385 jlong current_time = os::javaTimeNanos();
386 if (safepoint_limit_time < current_time) {
387 log_warning(safepoint)("# SafepointSynchronize: Finished after "
388 INT64_FORMAT_W(6) " ms",
389 (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS));
390 }
391 }
392 #endif
393
394 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
395
396 // Record state
397 _state = _synchronized;
398
399 OrderAccess::fence();
400
401 // Set the new id
402 ++_safepoint_id;
403
404 #ifdef ASSERT
405 // Make sure all the threads were visited.
406 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
407 assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread");
408 }
409 #endif // ASSERT
410
411 post_safepoint_synchronize_event(sync_event,
412 _safepoint_id,
413 initial_running,
414 _waiting_to_block, iterations);
415
416 SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page);
417
418 post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count);
419 }
420
421 void SafepointSynchronize::disarm_safepoint() {
422 uint64_t active_safepoint_counter = _safepoint_counter;
423 {
424 JavaThreadIteratorWithHandle jtiwh;
425 #ifdef ASSERT
426 // A pending_exception cannot be installed during a safepoint. The threads
427 // may install an async exception after they come back from a safepoint into
428 // pending_exception after they unblock. But that should happen later.
429 for (; JavaThread *cur = jtiwh.next(); ) {
430 assert (!(cur->has_pending_exception() &&
431 cur->safepoint_state()->is_at_poll_safepoint()),
432 "safepoint installed a pending exception");
433 }
434 #endif // ASSERT
435
436 OrderAccess::fence(); // keep read and write of _state from floating up
437 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
438
439 // Change state first to _not_synchronized.
440 // No threads should see _synchronized when running.
441 _state = _not_synchronized;
442
443 // Set the next dormant (even) safepoint id.
444 assert((_safepoint_counter & 0x1) == 1, "must be odd");
445 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
446
447 OrderAccess::fence(); // Keep the local state from floating up.
448
449 jtiwh.rewind();
450 for (; JavaThread *current = jtiwh.next(); ) {
451 // Clear the visited flag to ensure that the critical counts are collected properly.
452 DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);)
453 ThreadSafepointState* cur_state = current->safepoint_state();
454 assert(!cur_state->is_running(), "Thread not suspended at safepoint");
455 cur_state->restart(); // TSS _running
456 assert(cur_state->is_running(), "safepoint state has not been reset");
457 }
458 } // ~JavaThreadIteratorWithHandle
459
460 // Release threads lock, so threads can be created/destroyed again.
461 Threads_lock->unlock();
462
463 // Wake threads after local state is correctly set.
464 _wait_barrier->disarm();
465 }
466
467 // Wake up all threads, so they are ready to resume execution after the safepoint
468 // operation has been carried out
469 void SafepointSynchronize::end() {
470 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
471 SafepointTracing::leave();
472
473 EventSafepointEnd event;
474 assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint");
475
476 disarm_safepoint();
477
478 Universe::heap()->safepoint_synchronize_end();
479
480 SafepointTracing::end();
481
482 post_safepoint_end_event(event, safepoint_id());
483 }
484
485 // Methods for determining if a JavaThread is safepoint safe.
486
487 // False means unsafe with undetermined state.
488 // True means a determined state, but it may be an unsafe state.
489 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
490 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
491 assert((safepoint_count != InactiveSafepointCounter &&
492 Thread::current() == (Thread*)VMThread::vm_thread() &&
493 SafepointSynchronize::_state != _not_synchronized)
494 || safepoint_count == InactiveSafepointCounter, "Invalid check");
495
496 // To handle the thread_blocked state on the backedge of the WaitBarrier from
497 // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
498 // re-read state after we read thread safepoint id. The JavaThread changes its
499 // thread state from thread_blocked before resetting safepoint id to 0.
500 // This guarantees the second read will be from an updated thread state. It can
501 // either be different state making this an unsafe state or it can see blocked
502 // again. When we see blocked twice with a 0 safepoint id, either:
503 // - It is normally blocked, e.g. on Mutex, TBIVM.
504 // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
505 // - It was in SS:block() but now on a Mutex.
506 // All of these cases are safe.
507
508 *state = thread->thread_state();
509 OrderAccess::loadload();
510 uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire
511 if (sid != InactiveSafepointCounter && sid != safepoint_count) {
512 // In an old safepoint, state not relevant.
513 return false;
514 }
515 return *state == thread->thread_state();
516 }
517
518 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
519 switch(state) {
520 case _thread_in_native:
521 // native threads are safe if they have no java stack or have walkable stack
522 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
523
524 case _thread_blocked:
525 // On wait_barrier or blocked.
526 // Blocked threads should already have walkable stack.
527 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
528 return true;
529
530 default:
531 return false;
532 }
533 }
534
535 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
536 if (thread->is_terminated()) {
537 return true;
538 }
539 JavaThreadState stable_state;
540 if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
541 return safepoint_safe_with(thread, stable_state);
542 }
543 return false;
544 }
545
546
547 // -------------------------------------------------------------------------------------------------------
548 // Implementation of Safepoint blocking point
549
550 void SafepointSynchronize::block(JavaThread *thread) {
551 assert(thread != nullptr, "thread must be set");
552
553 // Threads shouldn't block if they are in the middle of printing, but...
554 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
555
556 // Only bail from the block() call if the thread is gone from the
557 // thread list; starting to exit should still block.
558 if (thread->is_terminated()) {
559 // block current thread if we come here from native code when VM is gone
560 thread->block_if_vm_exited();
561
562 // otherwise do nothing
563 return;
564 }
565
566 JavaThreadState state = thread->thread_state();
567 thread->frame_anchor()->make_walkable();
568
569 uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
570
571 // We have no idea where the VMThread is, it might even be at next safepoint.
572 // So we can miss this poll, but stop at next.
573
574 // Load dependent store, it must not pass loading of safepoint_id.
575 thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
576
577 // This part we can skip if we notice we miss or are in a future safepoint.
578 OrderAccess::storestore();
579 // Load in wait barrier should not float up
580 thread->set_thread_state_fence(_thread_blocked);
581
582 _wait_barrier->wait(static_cast<int>(safepoint_id));
583 assert(_state != _synchronized, "Can't be");
584
585 // If barrier is disarmed stop store from floating above loads in barrier.
586 OrderAccess::loadstore();
587 thread->set_thread_state(state);
588
589 // Then we reset the safepoint id to inactive.
590 thread->safepoint_state()->reset_safepoint_id(); // Release store
591
592 OrderAccess::fence();
593
594 guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
595 "The safepoint id should be set only in block path");
596
597 // cross_modify_fence is done by SafepointMechanism::process_if_requested
598 // which is the only caller here.
599 }
600
601 // ------------------------------------------------------------------------------------------------------
602 // Exception handlers
603
604
605 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
606 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
607 thread->set_thread_state(_thread_in_vm);
608
609 // Enable WXWrite: the function is called implicitly from java code.
610 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread));
611
612 if (log_is_enabled(Info, safepoint, stats)) {
613 Atomic::inc(&_nof_threads_hit_polling_page);
614 }
615
616 ThreadSafepointState* state = thread->safepoint_state();
617
618 state->handle_polling_page_exception();
619
620 thread->set_thread_state(_thread_in_Java);
621 }
622
623
624 void SafepointSynchronize::print_safepoint_timeout() {
625 if (!timeout_error_printed) {
626 timeout_error_printed = true;
627 // Print out the thread info which didn't reach the safepoint for debugging
628 // purposes (useful when there are lots of threads in the debugger).
629 LogTarget(Warning, safepoint) lt;
630 if (lt.is_enabled()) {
631 ResourceMark rm;
632 LogStream ls(lt);
633
634 ls.cr();
635 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
636 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
637 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
638 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
639 if (cur_thread->safepoint_state()->is_running()) {
640 ls.print("# ");
641 cur_thread->print_on(&ls);
642 ls.cr();
643 }
644 }
645 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
646 }
647 }
648
649 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
650 // ShowMessageBoxOnError.
651 if (AbortVMOnSafepointTimeout && (os::elapsedTime() * MILLIUNITS > AbortVMOnSafepointTimeoutDelay)) {
652 // Send the blocking thread a signal to terminate and write an error file.
653 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
654 if (cur_thread->safepoint_state()->is_running()) {
655 VMError::set_safepoint_timed_out_thread(cur_thread);
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 (InlineTypeReturnedAsFields && return_oop) {
796 // Check if an inline type is returned as fields
797 vk = InlineKlass::returned_inline_klass(map, &return_oop, method);
798 if (vk != nullptr) {
799 // We're at a safepoint at the return of a method that returns
800 // multiple values. We must make sure we preserve the oop values
801 // across the safepoint.
802 vk->save_oop_fields(map, return_values);
803 }
804 }
805
806 if (return_oop) {
807 // The oop result has been saved on the stack together with all
808 // the other registers. In order to preserve it over GCs we need
809 // to keep it in a handle.
810 oop result = caller_fr.saved_oop_result(&map);
811 assert(oopDesc::is_oop_or_null(result), "must be oop");
812 return_values.push(Handle(self, result));
813 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
814 }
815
816 // We get here if compiled return polls found a reason to call into the VM.
817 // One condition for that is that the top frame is not yet safe to use.
818 // The following stack watermark barrier poll will catch such situations.
819 StackWatermarkSet::after_unwind(self);
820
821 // Process pending operation
822 SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */);
823
824 // restore oop result, if any
825 if (return_oop) {
826 assert(vk != nullptr || return_values.length() == 1, "only one return value");
827 caller_fr.set_saved_oop_result(&map, return_values.pop()());
828 }
829 // restore oops in scalarized fields
830 if (vk != nullptr) {
831 vk->restore_oop_results(map, return_values);
832 }
833 }
834
835 // This is a safepoint poll. Verify the return address and block.
836 else {
837
838 // verify the blob built the "return address" correctly
839 assert(real_return_addr == caller_fr.pc(), "must match");
840
841 set_at_poll_safepoint(true);
842 // Process pending operation
843 // We never deliver an async exception at a polling point as the
844 // compiler may not have an exception handler for it (polling at
845 // a return point is ok though). We will check for a pending async
846 // exception below and deoptimize if needed. We also cannot deoptimize
847 // and still install the exception here because live registers needed
848 // during deoptimization are clobbered by the exception path. The
849 // exception will just be delivered once we get into the interpreter.
850 SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */);
851 set_at_poll_safepoint(false);
852
853 if (self->has_async_exception_condition()) {
854 Deoptimization::deoptimize_frame(self, caller_fr.id());
855 log_info(exceptions)("deferred async exception at compiled safepoint");
856 }
857
858 // If an exception has been installed we must verify that the top frame wasn't deoptimized.
859 if (self->has_pending_exception() ) {
860 RegisterMap map(self,
861 RegisterMap::UpdateMap::include,
862 RegisterMap::ProcessFrames::skip,
863 RegisterMap::WalkContinuation::skip);
864 frame caller_fr = stub_fr.sender(&map);
865 if (caller_fr.is_deoptimized_frame()) {
866 // The exception path will destroy registers that are still
867 // live and will be needed during deoptimization, so if we
868 // have an exception now things are messed up. We only check
869 // at this scope because for a poll return it is ok to deoptimize
870 // while having a pending exception since the call we are returning
871 // from already collides with exception handling registers and
872 // so there is no issue (the exception handling path kills call
873 // result registers but this is ok since the exception kills
874 // the result anyway).
875 fatal("Exception installed and deoptimization is pending");
876 }
877 }
878 }
879 }
880
881
882 // -------------------------------------------------------------------------------------------------------
883 // Implementation of SafepointTracing
884
885 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
886 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
887 jlong SafepointTracing::_last_safepoint_leave_time_ns = 0;
888 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
889 jlong SafepointTracing::_last_app_time_ns = 0;
890 int SafepointTracing::_nof_threads = 0;
891 int SafepointTracing::_nof_running = 0;
892 int SafepointTracing::_page_trap = 0;
893 VM_Operation::VMOp_Type SafepointTracing::_current_type;
894 jlong SafepointTracing::_max_sync_time = 0;
895 jlong SafepointTracing::_max_vmop_time = 0;
896 uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
897
898 void SafepointTracing::init() {
899 // Application start
900 _last_safepoint_end_time_ns = os::javaTimeNanos();
901 }
902
903 // Helper method to print the header.
904 static void print_header(outputStream* st) {
905 // The number of spaces is significant here, and should match the format
906 // specifiers in print_statistics().
907
908 st->print("VM Operation "
909 "[ threads: total initial_running ]"
910 "[ time: sync vmop total ]");
911
912 st->print_cr(" page_trap_count");
913 }
914
915 // This prints a nice table. To get the statistics to not shift due to the logging uptime
916 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
917 void SafepointTracing::statistics_log() {
918 LogTarget(Info, safepoint, stats) lt;
919 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
920 LogStream ls(lt);
921
922 static int _cur_stat_index = 0;
923
924 // Print header every 30 entries
925 if ((_cur_stat_index % 30) == 0) {
926 print_header(&ls);
927 _cur_stat_index = 1; // wrap
928 } else {
929 _cur_stat_index++;
930 }
931
932 ls.print("%-28s [ "
933 INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " "
934 "]",
935 VM_Operation::name(_current_type),
936 _nof_threads,
937 _nof_running);
938 ls.print("[ "
939 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
940 (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
941 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns),
942 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
943
944 ls.print_cr(INT32_FORMAT_W(16), _page_trap);
945 }
946
947 // This method will be called when VM exits. This tries to summarize the sampling.
948 // Current thread may already be deleted, so don't use ResourceMark.
949 void SafepointTracing::statistics_exit_log() {
950 if (!log_is_enabled(Info, safepoint, stats)) {
951 return;
952 }
953 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
954 if (_op_count[index] != 0) {
955 log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
956 _op_count[index]);
957 }
958 }
959
960 log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns",
961 (int64_t)(_max_sync_time));
962 log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
963 INT64_FORMAT " ns",
964 (int64_t)(_max_vmop_time));
965 }
966
967 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
968 _op_count[type]++;
969 _current_type = type;
970
971 // update the time stamp to begin recording safepoint time
972 _last_safepoint_begin_time_ns = os::javaTimeNanos();
973 _last_safepoint_sync_time_ns = 0;
974
975 _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
976 _last_safepoint_end_time_ns = 0;
977
978 RuntimeService::record_safepoint_begin(_last_app_time_ns);
979 }
980
981 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
982 _last_safepoint_sync_time_ns = os::javaTimeNanos();
983 _nof_threads = nof_threads;
984 _nof_running = nof_running;
985 _page_trap = traps;
986 RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
987 }
988
989 void SafepointTracing::leave() {
990 _last_safepoint_leave_time_ns = os::javaTimeNanos();
991 }
992
993 void SafepointTracing::end() {
994 _last_safepoint_end_time_ns = os::javaTimeNanos();
995
996 if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
997 _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
998 }
999 if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
1000 _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
1001 }
1002 if (log_is_enabled(Info, safepoint, stats)) {
1003 statistics_log();
1004 }
1005
1006 log_info(safepoint)(
1007 "Safepoint \"%s\", "
1008 "Time since last: " JLONG_FORMAT " ns, "
1009 "Reaching safepoint: " JLONG_FORMAT " ns, "
1010 "At safepoint: " JLONG_FORMAT " ns, "
1011 "Leaving safepoint: " JLONG_FORMAT " ns, "
1012 "Total: " JLONG_FORMAT " ns, "
1013 "Threads: %d runnable, %d total",
1014 VM_Operation::name(_current_type),
1015 _last_app_time_ns,
1016 _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns,
1017 _last_safepoint_leave_time_ns - _last_safepoint_sync_time_ns,
1018 _last_safepoint_end_time_ns - _last_safepoint_leave_time_ns,
1019 _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns,
1020 _nof_running,
1021 _nof_threads
1022 );
1023
1024 RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns);
1025 }