1 /*
2 * Copyright (c) 1997, 2024, 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 "precompiled.hpp"
26 #include "code/codeCache.hpp"
27 #include "code/nmethod.hpp"
28 #include "code/pcDesc.hpp"
29 #include "code/scopeDesc.hpp"
30 #include "compiler/compilationPolicy.hpp"
31 #include "gc/shared/collectedHeap.hpp"
32 #include "gc/shared/gcLocker.hpp"
33 #include "gc/shared/oopStorage.hpp"
34 #include "gc/shared/strongRootsScope.hpp"
35 #include "gc/shared/workerThread.hpp"
36 #include "gc/shared/workerUtils.hpp"
37 #include "interpreter/interpreter.hpp"
38 #include "jfr/jfrEvents.hpp"
39 #include "logging/log.hpp"
40 #include "logging/logStream.hpp"
41 #include "memory/resourceArea.hpp"
42 #include "memory/universe.hpp"
43 #include "oops/oop.inline.hpp"
44 #include "oops/symbol.hpp"
45 #include "oops/inlineKlass.hpp"
46 #include "runtime/atomic.hpp"
47 #include "runtime/deoptimization.hpp"
48 #include "runtime/frame.inline.hpp"
49 #include "runtime/globals.hpp"
50 #include "runtime/handles.inline.hpp"
51 #include "runtime/interfaceSupport.inline.hpp"
52 #include "runtime/javaThread.inline.hpp"
53 #include "runtime/mutexLocker.hpp"
54 #include "runtime/orderAccess.hpp"
55 #include "runtime/osThread.hpp"
56 #include "runtime/safepoint.hpp"
57 #include "runtime/safepointMechanism.inline.hpp"
58 #include "runtime/signature.hpp"
59 #include "runtime/stackWatermarkSet.inline.hpp"
60 #include "runtime/stubCodeGenerator.hpp"
61 #include "runtime/stubRoutines.hpp"
62 #include "runtime/synchronizer.hpp"
63 #include "runtime/threads.hpp"
64 #include "runtime/threadSMR.hpp"
65 #include "runtime/threadWXSetters.inline.hpp"
66 #include "runtime/timerTrace.hpp"
67 #include "services/runtimeService.hpp"
68 #include "utilities/events.hpp"
69 #include "utilities/macros.hpp"
70 #include "utilities/systemMemoryBarrier.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 ResourceMark rm;
157 LogStream ls(lt);
158 ls.print("Illegal initial state detected: ");
159 cur_state->print_on(&ls);
160 }
161 return true;
162 }
163 cur_state->examine_state_of_thread(SafepointSynchronize::safepoint_counter());
164 if (!cur_state->is_running()) {
165 return true;
166 }
167 LogTarget(Trace, safepoint) lt;
168 if (lt.is_enabled()) {
169 ResourceMark rm;
170 LogStream ls(lt);
171 cur_state->print_on(&ls);
172 }
173 return false;
174 }
175
176 #ifdef ASSERT
177 static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) {
178 int a = 0;
179 const ThreadSafepointState *tmp_tss = tss_head;
180 while (tmp_tss != nullptr) {
181 ++a;
182 assert(tmp_tss->is_running(), "Illegal initial state");
183 tmp_tss = tmp_tss->get_next();
184 }
185 assert(a == still_running, "Must be the same");
186 }
187 #endif // ASSERT
188
189 static void back_off(int64_t start_time) {
190 // We start with fine-grained nanosleeping until a millisecond has
191 // passed, at which point we resort to plain naked_short_sleep.
192 if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) {
193 os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
194 } else {
195 os::naked_short_sleep(1);
196 }
197 }
198
199 int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running)
200 {
201 JavaThreadIteratorWithHandle jtiwh;
202
203 #ifdef ASSERT
204 for (; JavaThread *cur = jtiwh.next(); ) {
205 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
206 }
207 jtiwh.rewind();
208 #endif // ASSERT
209
210 // Iterate through all threads until it has been determined how to stop them all at a safepoint.
211 int still_running = nof_threads;
212 ThreadSafepointState *tss_head = nullptr;
213 ThreadSafepointState **p_prev = &tss_head;
214 for (; JavaThread *cur = jtiwh.next(); ) {
215 ThreadSafepointState *cur_tss = cur->safepoint_state();
216 assert(cur_tss->get_next() == nullptr, "Must be null");
217 if (thread_not_running(cur_tss)) {
218 --still_running;
219 } else {
220 *p_prev = cur_tss;
221 p_prev = cur_tss->next_ptr();
222 }
223 }
224 *p_prev = nullptr;
225
226 DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
227
228 *initial_running = still_running;
229
230 // If there is no thread still running, we are already done.
231 if (still_running <= 0) {
232 assert(tss_head == nullptr, "Must be empty");
233 return 1;
234 }
235
236 int iterations = 1; // The first iteration is above.
237 int64_t start_time = os::javaTimeNanos();
238
239 do {
240 // Check if this has taken too long:
241 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
242 print_safepoint_timeout();
243 }
244
245 p_prev = &tss_head;
246 ThreadSafepointState *cur_tss = tss_head;
247 while (cur_tss != nullptr) {
248 assert(cur_tss->is_running(), "Illegal initial state");
249 if (thread_not_running(cur_tss)) {
250 --still_running;
251 *p_prev = nullptr;
252 ThreadSafepointState *tmp = cur_tss;
253 cur_tss = cur_tss->get_next();
254 tmp->set_next(nullptr);
255 } else {
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 back_off(start_time);
266 }
267
268 iterations++;
269 } while (still_running > 0);
270
271 assert(tss_head == nullptr, "Must be empty");
272
273 return iterations;
274 }
275
276 void SafepointSynchronize::arm_safepoint() {
277 // Begin the process of bringing the system to a safepoint.
278 // Java threads can be in several different states and are
279 // stopped by different mechanisms:
280 //
281 // 1. Running interpreted
282 // When executing branching/returning byte codes interpreter
283 // checks if the poll is armed, if so blocks in SS::block().
284 // 2. Running in native code
285 // When returning from the native code, a Java thread must check
286 // the safepoint _state to see if we must block. If the
287 // VM thread sees a Java thread in native, it does
288 // not wait for this thread to block. The order of the memory
289 // writes and reads of both the safepoint state and the Java
290 // threads state is critical. In order to guarantee that the
291 // memory writes are serialized with respect to each other,
292 // the VM thread issues a memory barrier instruction.
293 // 3. Running compiled Code
294 // Compiled code reads the local polling page that
295 // is set to fault if we are trying to get to a safepoint.
296 // 4. Blocked
297 // A thread which is blocked will not be allowed to return from the
298 // block condition until the safepoint operation is complete.
299 // 5. In VM or Transitioning between states
300 // If a Java thread is currently running in the VM or transitioning
301 // between states, the safepointing code will poll the thread state
302 // until the thread blocks itself when it attempts transitions to a
303 // new state or locking a safepoint checked monitor.
304
305 // We must never miss a thread with correct safepoint id, so we must make sure we arm
306 // the wait barrier for the next safepoint id/counter.
307 // Arming must be done after resetting _current_jni_active_count, _waiting_to_block.
308 _wait_barrier->arm(static_cast<int>(_safepoint_counter + 1));
309
310 assert((_safepoint_counter & 0x1) == 0, "must be even");
311 // The store to _safepoint_counter must happen after any stores in arming.
312 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
313
314 // We are synchronizing
315 OrderAccess::storestore(); // Ordered with _safepoint_counter
316 _state = _synchronizing;
317
318 // Arming the per thread poll while having _state != _not_synchronized means safepointing
319 log_trace(safepoint)("Setting thread local yield flag for threads");
320 OrderAccess::storestore(); // storestore, global state -> local state
321 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
322 // Make sure the threads start polling, it is time to yield.
323 SafepointMechanism::arm_local_poll(cur);
324 }
325 if (UseSystemMemoryBarrier) {
326 SystemMemoryBarrier::emit(); // storestore|storeload, global state -> local state
327 } else {
328 OrderAccess::fence(); // storestore|storeload, global state -> local state
329 }
330 }
331
332 // Roll all threads forward to a safepoint and suspend them all
333 void SafepointSynchronize::begin() {
334 assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint");
335
336 EventSafepointBegin begin_event;
337 SafepointTracing::begin(VMThread::vm_op_type());
338
339 Universe::heap()->safepoint_synchronize_begin();
340
341 // By getting the Threads_lock, we assure that no threads are about to start or
342 // exit. It is released again in SafepointSynchronize::end().
343 Threads_lock->lock();
344
345 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
346
347 int nof_threads = Threads::number_of_threads();
348
349 _nof_threads_hit_polling_page = 0;
350
351 log_debug(safepoint)("Safepoint synchronization initiated using %s wait barrier. (%d threads)", _wait_barrier->description(), nof_threads);
352
353 // Reset the count of active JNI critical threads
354 _current_jni_active_count = 0;
355
356 // Set number of threads to wait for
357 _waiting_to_block = nof_threads;
358
359 jlong safepoint_limit_time = 0;
360 if (SafepointTimeout) {
361 // Set the limit time, so that it can be compared to see if this has taken
362 // too long to complete.
363 safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)(SafepointTimeoutDelay * NANOSECS_PER_MILLISEC);
364 timeout_error_printed = false;
365 }
366
367 EventSafepointStateSynchronization sync_event;
368 int initial_running = 0;
369
370 // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before.
371 arm_safepoint();
372
373 // Will spin until all threads are safe.
374 int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running);
375 assert(_waiting_to_block == 0, "No thread should be running");
376
377 #ifndef PRODUCT
378 // Mark all threads
379 if (VerifyCrossModifyFence) {
380 JavaThreadIteratorWithHandle jtiwh;
381 for (; JavaThread *cur = jtiwh.next(); ) {
382 cur->set_requires_cross_modify_fence(true);
383 }
384 }
385
386 if (safepoint_limit_time != 0) {
387 jlong current_time = os::javaTimeNanos();
388 if (safepoint_limit_time < current_time) {
389 log_warning(safepoint)("# SafepointSynchronize: Finished after "
390 INT64_FORMAT_W(6) " ms",
391 (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS));
392 }
393 }
394 #endif
395
396 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
397
398 // Record state
399 _state = _synchronized;
400
401 OrderAccess::fence();
402
403 // Set the new id
404 ++_safepoint_id;
405
406 #ifdef ASSERT
407 // Make sure all the threads were visited.
408 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
409 assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread");
410 }
411 #endif // ASSERT
412
413 // Update the count of active JNI critical regions
414 GCLocker::set_jni_lock_count(_current_jni_active_count);
415
416 post_safepoint_synchronize_event(sync_event,
417 _safepoint_id,
418 initial_running,
419 _waiting_to_block, iterations);
420
421 SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page);
422
423 post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count);
424 }
425
426 void SafepointSynchronize::disarm_safepoint() {
427 uint64_t active_safepoint_counter = _safepoint_counter;
428 {
429 JavaThreadIteratorWithHandle jtiwh;
430 #ifdef ASSERT
431 // A pending_exception cannot be installed during a safepoint. The threads
432 // may install an async exception after they come back from a safepoint into
433 // pending_exception after they unblock. But that should happen later.
434 for (; JavaThread *cur = jtiwh.next(); ) {
435 assert (!(cur->has_pending_exception() &&
436 cur->safepoint_state()->is_at_poll_safepoint()),
437 "safepoint installed a pending exception");
438 }
439 #endif // ASSERT
440
441 OrderAccess::fence(); // keep read and write of _state from floating up
442 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
443
444 // Change state first to _not_synchronized.
445 // No threads should see _synchronized when running.
446 _state = _not_synchronized;
447
448 // Set the next dormant (even) safepoint id.
449 assert((_safepoint_counter & 0x1) == 1, "must be odd");
450 Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
451
452 OrderAccess::fence(); // Keep the local state from floating up.
453
454 jtiwh.rewind();
455 for (; JavaThread *current = jtiwh.next(); ) {
456 // Clear the visited flag to ensure that the critical counts are collected properly.
457 DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);)
458 ThreadSafepointState* cur_state = current->safepoint_state();
459 assert(!cur_state->is_running(), "Thread not suspended at safepoint");
460 cur_state->restart(); // TSS _running
461 assert(cur_state->is_running(), "safepoint state has not been reset");
462 }
463 } // ~JavaThreadIteratorWithHandle
464
465 // Release threads lock, so threads can be created/destroyed again.
466 Threads_lock->unlock();
467
468 // Wake threads after local state is correctly set.
469 _wait_barrier->disarm();
470 }
471
472 // Wake up all threads, so they are ready to resume execution after the safepoint
473 // operation has been carried out
474 void SafepointSynchronize::end() {
475 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
476 EventSafepointEnd event;
477 assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint");
478
479 disarm_safepoint();
480
481 Universe::heap()->safepoint_synchronize_end();
482
483 SafepointTracing::end();
484
485 post_safepoint_end_event(event, safepoint_id());
486 }
487
488 // Methods for determining if a JavaThread is safepoint safe.
489
490 // False means unsafe with undetermined state.
491 // True means a determined state, but it may be an unsafe state.
492 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
493 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
494 assert((safepoint_count != InactiveSafepointCounter &&
495 Thread::current() == (Thread*)VMThread::vm_thread() &&
496 SafepointSynchronize::_state != _not_synchronized)
497 || safepoint_count == InactiveSafepointCounter, "Invalid check");
498
499 // To handle the thread_blocked state on the backedge of the WaitBarrier from
500 // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
501 // re-read state after we read thread safepoint id. The JavaThread changes its
502 // thread state from thread_blocked before resetting safepoint id to 0.
503 // This guarantees the second read will be from an updated thread state. It can
504 // either be different state making this an unsafe state or it can see blocked
505 // again. When we see blocked twice with a 0 safepoint id, either:
506 // - It is normally blocked, e.g. on Mutex, TBIVM.
507 // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
508 // - It was in SS:block() but now on a Mutex.
509 // All of these cases are safe.
510
511 *state = thread->thread_state();
512 OrderAccess::loadload();
513 uint64_t sid = thread->safepoint_state()->get_safepoint_id(); // Load acquire
514 if (sid != InactiveSafepointCounter && sid != safepoint_count) {
515 // In an old safepoint, state not relevant.
516 return false;
517 }
518 return *state == thread->thread_state();
519 }
520
521 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
522 switch(state) {
523 case _thread_in_native:
524 // native threads are safe if they have no java stack or have walkable stack
525 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
526
527 case _thread_blocked:
528 // On wait_barrier or blocked.
529 // Blocked threads should already have walkable stack.
530 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
531 return true;
532
533 default:
534 return false;
535 }
536 }
537
538 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
539 if (thread->is_terminated()) {
540 return true;
541 }
542 JavaThreadState stable_state;
543 if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
544 return safepoint_safe_with(thread, stable_state);
545 }
546 return false;
547 }
548
549
550 // -------------------------------------------------------------------------------------------------------
551 // Implementation of Safepoint blocking point
552
553 void SafepointSynchronize::block(JavaThread *thread) {
554 assert(thread != nullptr, "thread must be set");
555
556 // Threads shouldn't block if they are in the middle of printing, but...
557 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
558
559 // Only bail from the block() call if the thread is gone from the
560 // thread list; starting to exit should still block.
561 if (thread->is_terminated()) {
562 // block current thread if we come here from native code when VM is gone
563 thread->block_if_vm_exited();
564
565 // otherwise do nothing
566 return;
567 }
568
569 JavaThreadState state = thread->thread_state();
570 thread->frame_anchor()->make_walkable();
571
572 uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
573
574 // We have no idea where the VMThread is, it might even be at next safepoint.
575 // So we can miss this poll, but stop at next.
576
577 // Load dependent store, it must not pass loading of safepoint_id.
578 thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
579
580 // This part we can skip if we notice we miss or are in a future safepoint.
581 OrderAccess::storestore();
582 // Load in wait barrier should not float up
583 thread->set_thread_state_fence(_thread_blocked);
584
585 _wait_barrier->wait(static_cast<int>(safepoint_id));
586 assert(_state != _synchronized, "Can't be");
587
588 // If barrier is disarmed stop store from floating above loads in barrier.
589 OrderAccess::loadstore();
590 thread->set_thread_state(state);
591
592 // Then we reset the safepoint id to inactive.
593 thread->safepoint_state()->reset_safepoint_id(); // Release store
594
595 OrderAccess::fence();
596
597 guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
598 "The safepoint id should be set only in block path");
599
600 // cross_modify_fence is done by SafepointMechanism::process_if_requested
601 // which is the only caller here.
602 }
603
604 // ------------------------------------------------------------------------------------------------------
605 // Exception handlers
606
607
608 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
609 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
610 thread->set_thread_state(_thread_in_vm);
611
612 // Enable WXWrite: the function is called implicitly from java code.
613 MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread));
614
615 if (log_is_enabled(Info, safepoint, stats)) {
616 Atomic::inc(&_nof_threads_hit_polling_page);
617 }
618
619 ThreadSafepointState* state = thread->safepoint_state();
620
621 state->handle_polling_page_exception();
622
623 thread->set_thread_state(_thread_in_Java);
624 }
625
626
627 void SafepointSynchronize::print_safepoint_timeout() {
628 if (!timeout_error_printed) {
629 timeout_error_printed = true;
630 // Print out the thread info which didn't reach the safepoint for debugging
631 // purposes (useful when there are lots of threads in the debugger).
632 LogTarget(Warning, safepoint) lt;
633 if (lt.is_enabled()) {
634 ResourceMark rm;
635 LogStream ls(lt);
636
637 ls.cr();
638 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
639 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
640 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
641 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
642 if (cur_thread->safepoint_state()->is_running()) {
643 ls.print("# ");
644 cur_thread->print_on(&ls);
645 ls.cr();
646 }
647 }
648 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
649 }
650 }
651
652 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
653 // ShowMessageBoxOnError.
654 if (AbortVMOnSafepointTimeout && (os::elapsedTime() * MILLIUNITS > AbortVMOnSafepointTimeoutDelay)) {
655 // Send the blocking thread a signal to terminate and write an error file.
656 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
657 if (cur_thread->safepoint_state()->is_running()) {
658 if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
659 break; // Could not send signal. Report fatal error.
660 }
661 // Give cur_thread a chance to report the error and terminate the VM.
662 os::naked_sleep(3000);
663 }
664 }
665 fatal("Safepoint sync time longer than %.6f ms detected when executing %s.",
666 SafepointTimeoutDelay, VMThread::vm_operation()->name());
667 }
668 }
669
670 // -------------------------------------------------------------------------------------------------------
671 // Implementation of ThreadSafepointState
672
673 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
674 : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
675 _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(nullptr) {
676 }
677
678 void ThreadSafepointState::create(JavaThread *thread) {
679 ThreadSafepointState *state = new ThreadSafepointState(thread);
680 thread->set_safepoint_state(state);
681 }
682
683 void ThreadSafepointState::destroy(JavaThread *thread) {
684 if (thread->safepoint_state()) {
685 delete(thread->safepoint_state());
686 thread->set_safepoint_state(nullptr);
687 }
688 }
689
690 uint64_t ThreadSafepointState::get_safepoint_id() const {
691 return Atomic::load_acquire(&_safepoint_id);
692 }
693
694 void ThreadSafepointState::reset_safepoint_id() {
695 Atomic::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
696 }
697
698 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
699 Atomic::release_store(&_safepoint_id, safepoint_id);
700 }
701
702 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
703 assert(is_running(), "better be running or just have hit safepoint poll");
704
705 JavaThreadState stable_state;
706 if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
707 // We could not get stable state of the JavaThread.
708 // Consider it running and just return.
709 return;
710 }
711
712 if (safepoint_safe_with(_thread, stable_state)) {
713 account_safe_thread();
714 return;
715 }
716
717 // All other thread states will continue to run until they
718 // transition and self-block in state _blocked
719 // Safepoint polling in compiled code causes the Java threads to do the same.
720 // Note: new threads may require a malloc so they must be allowed to finish
721
722 assert(is_running(), "examine_state_of_thread on non-running thread");
723 return;
724 }
725
726 void ThreadSafepointState::account_safe_thread() {
727 SafepointSynchronize::decrement_waiting_to_block();
728 if (_thread->in_critical()) {
729 // Notice that this thread is in a critical section
730 SafepointSynchronize::increment_jni_active_count();
731 }
732 DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
733 assert(!_safepoint_safe, "Must be unsafe before safe");
734 _safepoint_safe = true;
735
736 // The oops in the monitor cache are cleared to prevent stale cache entries
737 // from keeping dead objects alive. Because these oops are always cleared
738 // before safepoint operations they are not visited in JavaThread::oops_do.
739 _thread->om_clear_monitor_cache();
740 }
741
742 void ThreadSafepointState::restart() {
743 assert(_safepoint_safe, "Must be safe before unsafe");
744 _safepoint_safe = false;
745 }
746
747 void ThreadSafepointState::print_on(outputStream *st) const {
748 const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
749
750 st->print_cr("Thread: " INTPTR_FORMAT
751 " [0x%2x] State: %s _at_poll_safepoint %d",
752 p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
753
754 _thread->print_thread_state_on(st);
755 }
756
757 // ---------------------------------------------------------------------------------------------------------------------
758
759 // Process pending operation.
760 void ThreadSafepointState::handle_polling_page_exception() {
761 JavaThread* self = thread();
762 assert(self == JavaThread::current(), "must be self");
763
764 // Step 1: Find the nmethod from the return address
765 address real_return_addr = self->saved_exception_pc();
766
767 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
768 assert(cb != nullptr && cb->is_nmethod(), "return address should be in nmethod");
769 nmethod* nm = cb->as_nmethod();
770
771 // Find frame of caller
772 frame stub_fr = self->last_frame();
773 CodeBlob* stub_cb = stub_fr.cb();
774 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
775 RegisterMap map(self,
776 RegisterMap::UpdateMap::include,
777 RegisterMap::ProcessFrames::skip,
778 RegisterMap::WalkContinuation::skip);
779 frame caller_fr = stub_fr.sender(&map);
780
781 // Should only be poll_return or poll
782 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
783
784 // This is a poll immediately before a return. The exception handling code
785 // has already had the effect of causing the return to occur, so the execution
786 // will continue immediately after the call. In addition, the oopmap at the
787 // return point does not mark the return value as an oop (if it is), so
788 // it needs a handle here to be updated.
789 if( nm->is_at_poll_return(real_return_addr) ) {
790 ResourceMark rm;
791 // See if return type is an oop.
792 Method* method = nm->method();
793 bool return_oop = method->is_returning_oop();
794 HandleMark hm(self);
795 GrowableArray<Handle> return_values;
796 InlineKlass* vk = nullptr;
797 if (return_oop && InlineTypeReturnedAsFields &&
798 (method->result_type() == T_OBJECT)) {
799 // Check if an inline type is returned as fields
800 vk = InlineKlass::returned_inline_klass(map);
801 if (vk != nullptr) {
802 // We're at a safepoint at the return of a method that returns
803 // multiple values. We must make sure we preserve the oop values
804 // across the safepoint.
805 assert(vk == method->returns_inline_type(thread()), "bad inline klass");
806 vk->save_oop_fields(map, return_values);
807 return_oop = false;
808 }
809 }
810
811 if (return_oop) {
812 // The oop result has been saved on the stack together with all
813 // the other registers. In order to preserve it over GCs we need
814 // to keep it in a handle.
815 oop result = caller_fr.saved_oop_result(&map);
816 assert(oopDesc::is_oop_or_null(result), "must be oop");
817 return_values.push(Handle(self, result));
818 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
819 }
820
821 // We get here if compiled return polls found a reason to call into the VM.
822 // One condition for that is that the top frame is not yet safe to use.
823 // The following stack watermark barrier poll will catch such situations.
824 StackWatermarkSet::after_unwind(self);
825
826 // Process pending operation
827 SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */);
828
829 // restore oop result, if any
830 if (return_oop) {
831 assert(return_values.length() == 1, "only one return value");
832 caller_fr.set_saved_oop_result(&map, return_values.pop()());
833 } else if (vk != nullptr) {
834 vk->restore_oop_results(map, return_values);
835 }
836 }
837
838 // This is a safepoint poll. Verify the return address and block.
839 else {
840
841 // verify the blob built the "return address" correctly
842 assert(real_return_addr == caller_fr.pc(), "must match");
843
844 set_at_poll_safepoint(true);
845 // Process pending operation
846 // We never deliver an async exception at a polling point as the
847 // compiler may not have an exception handler for it (polling at
848 // a return point is ok though). We will check for a pending async
849 // exception below and deoptimize if needed. We also cannot deoptimize
850 // and still install the exception here because live registers needed
851 // during deoptimization are clobbered by the exception path. The
852 // exception will just be delivered once we get into the interpreter.
853 SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */);
854 set_at_poll_safepoint(false);
855
856 if (self->has_async_exception_condition()) {
857 Deoptimization::deoptimize_frame(self, caller_fr.id());
858 log_info(exceptions)("deferred async exception at compiled safepoint");
859 }
860
861 // If an exception has been installed we must verify that the top frame wasn't deoptimized.
862 if (self->has_pending_exception() ) {
863 RegisterMap map(self,
864 RegisterMap::UpdateMap::include,
865 RegisterMap::ProcessFrames::skip,
866 RegisterMap::WalkContinuation::skip);
867 frame caller_fr = stub_fr.sender(&map);
868 if (caller_fr.is_deoptimized_frame()) {
869 // The exception path will destroy registers that are still
870 // live and will be needed during deoptimization, so if we
871 // have an exception now things are messed up. We only check
872 // at this scope because for a poll return it is ok to deoptimize
873 // while having a pending exception since the call we are returning
874 // from already collides with exception handling registers and
875 // so there is no issue (the exception handling path kills call
876 // result registers but this is ok since the exception kills
877 // the result anyway).
878 fatal("Exception installed and deoptimization is pending");
879 }
880 }
881 }
882 }
883
884
885 // -------------------------------------------------------------------------------------------------------
886 // Implementation of SafepointTracing
887
888 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
889 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
890 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
891 jlong SafepointTracing::_last_app_time_ns = 0;
892 int SafepointTracing::_nof_threads = 0;
893 int SafepointTracing::_nof_running = 0;
894 int SafepointTracing::_page_trap = 0;
895 VM_Operation::VMOp_Type SafepointTracing::_current_type;
896 jlong SafepointTracing::_max_sync_time = 0;
897 jlong SafepointTracing::_max_vmop_time = 0;
898 uint64_t SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
899
900 void SafepointTracing::init() {
901 // Application start
902 _last_safepoint_end_time_ns = os::javaTimeNanos();
903 }
904
905 // Helper method to print the header.
906 static void print_header(outputStream* st) {
907 // The number of spaces is significant here, and should match the format
908 // specifiers in print_statistics().
909
910 st->print("VM Operation "
911 "[ threads: total initial_running ]"
912 "[ time: sync vmop total ]");
913
914 st->print_cr(" page_trap_count");
915 }
916
917 // This prints a nice table. To get the statistics to not shift due to the logging uptime
918 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
919 void SafepointTracing::statistics_log() {
920 LogTarget(Info, safepoint, stats) lt;
921 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
922 LogStream ls(lt);
923
924 static int _cur_stat_index = 0;
925
926 // Print header every 30 entries
927 if ((_cur_stat_index % 30) == 0) {
928 print_header(&ls);
929 _cur_stat_index = 1; // wrap
930 } else {
931 _cur_stat_index++;
932 }
933
934 ls.print("%-28s [ "
935 INT32_FORMAT_W(8) " " INT32_FORMAT_W(8) " "
936 "]",
937 VM_Operation::name(_current_type),
938 _nof_threads,
939 _nof_running);
940 ls.print("[ "
941 INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
942 (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
943 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns),
944 (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
945
946 ls.print_cr(INT32_FORMAT_W(16), _page_trap);
947 }
948
949 // This method will be called when VM exits. This tries to summarize the sampling.
950 // Current thread may already be deleted, so don't use ResourceMark.
951 void SafepointTracing::statistics_exit_log() {
952 if (!log_is_enabled(Info, safepoint, stats)) {
953 return;
954 }
955 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
956 if (_op_count[index] != 0) {
957 log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
958 _op_count[index]);
959 }
960 }
961
962 log_info(safepoint, stats)("Maximum sync time " INT64_FORMAT" ns",
963 (int64_t)(_max_sync_time));
964 log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
965 INT64_FORMAT " ns",
966 (int64_t)(_max_vmop_time));
967 }
968
969 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
970 _op_count[type]++;
971 _current_type = type;
972
973 // update the time stamp to begin recording safepoint time
974 _last_safepoint_begin_time_ns = os::javaTimeNanos();
975 _last_safepoint_sync_time_ns = 0;
976
977 _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
978 _last_safepoint_end_time_ns = 0;
979
980 RuntimeService::record_safepoint_begin(_last_app_time_ns);
981 }
982
983 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
984 _last_safepoint_sync_time_ns = os::javaTimeNanos();
985 _nof_threads = nof_threads;
986 _nof_running = nof_running;
987 _page_trap = traps;
988 RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
989 }
990
991 void SafepointTracing::end() {
992 _last_safepoint_end_time_ns = os::javaTimeNanos();
993
994 if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
995 _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
996 }
997 if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
998 _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
999 }
1000 if (log_is_enabled(Info, safepoint, stats)) {
1001 statistics_log();
1002 }
1003
1004 log_info(safepoint)(
1005 "Safepoint \"%s\", "
1006 "Time since last: " JLONG_FORMAT " ns, "
1007 "Reaching safepoint: " JLONG_FORMAT " ns, "
1008 "At safepoint: " JLONG_FORMAT " ns, "
1009 "Total: " JLONG_FORMAT " ns",
1010 VM_Operation::name(_current_type),
1011 _last_app_time_ns,
1012 _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns,
1013 _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns,
1014 _last_safepoint_end_time_ns - _last_safepoint_begin_time_ns
1015 );
1016
1017 RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns);
1018 }