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 "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   // Update the count of active JNI critical regions
413   GCLocker::set_jni_lock_count(_current_jni_active_count);
414 
415   post_safepoint_synchronize_event(sync_event,
416                                    _safepoint_id,
417                                    initial_running,
418                                    _waiting_to_block, iterations);
419 
420   SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page);
421 
422   post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count);
423 }
424 
425 void SafepointSynchronize::disarm_safepoint() {
426   uint64_t active_safepoint_counter = _safepoint_counter;
427   {
428     JavaThreadIteratorWithHandle jtiwh;
429 #ifdef ASSERT
430     // A pending_exception cannot be installed during a safepoint.  The threads
431     // may install an async exception after they come back from a safepoint into
432     // pending_exception after they unblock.  But that should happen later.
433     for (; JavaThread *cur = jtiwh.next(); ) {
434       assert (!(cur->has_pending_exception() &&
435                 cur->safepoint_state()->is_at_poll_safepoint()),
436               "safepoint installed a pending exception");
437     }
438 #endif // ASSERT
439 
440     OrderAccess::fence(); // keep read and write of _state from floating up
441     assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
442 
443     // Change state first to _not_synchronized.
444     // No threads should see _synchronized when running.
445     _state = _not_synchronized;
446 
447     // Set the next dormant (even) safepoint id.
448     assert((_safepoint_counter & 0x1) == 1, "must be odd");
449     Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
450 
451     OrderAccess::fence(); // Keep the local state from floating up.
452 
453     jtiwh.rewind();
454     for (; JavaThread *current = jtiwh.next(); ) {
455       // Clear the visited flag to ensure that the critical counts are collected properly.
456       DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);)
457       ThreadSafepointState* cur_state = current->safepoint_state();
458       assert(!cur_state->is_running(), "Thread not suspended at safepoint");
459       cur_state->restart(); // TSS _running
460       assert(cur_state->is_running(), "safepoint state has not been reset");
461     }
462   } // ~JavaThreadIteratorWithHandle
463 
464   // Release threads lock, so threads can be created/destroyed again.
465   Threads_lock->unlock();
466 
467   // Wake threads after local state is correctly set.
468   _wait_barrier->disarm();
469 }
470 
471 // Wake up all threads, so they are ready to resume execution after the safepoint
472 // operation has been carried out
473 void SafepointSynchronize::end() {
474   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
475   EventSafepointEnd event;
476   assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint");
477 
478   disarm_safepoint();
479 
480   Universe::heap()->safepoint_synchronize_end();
481 
482   SafepointTracing::end();
483 
484   post_safepoint_end_event(event, safepoint_id());
485 }
486 
487 // Methods for determining if a JavaThread is safepoint safe.
488 
489 // False means unsafe with undetermined state.
490 // True means a determined state, but it may be an unsafe state.
491 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
492 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
493   assert((safepoint_count != InactiveSafepointCounter &&
494           Thread::current() == (Thread*)VMThread::vm_thread() &&
495           SafepointSynchronize::_state != _not_synchronized)
496          || safepoint_count == InactiveSafepointCounter, "Invalid check");
497 
498   // To handle the thread_blocked state on the backedge of the WaitBarrier from
499   // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
500   // re-read state after we read thread safepoint id. The JavaThread changes its
501   // thread state from thread_blocked before resetting safepoint id to 0.
502   // This guarantees the second read will be from an updated thread state. It can
503   // either be different state making this an unsafe state or it can see blocked
504   // again. When we see blocked twice with a 0 safepoint id, either:
505   // - It is normally blocked, e.g. on Mutex, TBIVM.
506   // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
507   // - It was in SS:block() but now on a Mutex.
508   // All of these cases are safe.
509 
510   *state = thread->thread_state();
511   OrderAccess::loadload();
512   uint64_t sid = thread->safepoint_state()->get_safepoint_id();  // Load acquire
513   if (sid != InactiveSafepointCounter && sid != safepoint_count) {
514     // In an old safepoint, state not relevant.
515     return false;
516   }
517   return *state == thread->thread_state();
518 }
519 
520 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
521   switch(state) {
522   case _thread_in_native:
523     // native threads are safe if they have no java stack or have walkable stack
524     return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
525 
526   case _thread_blocked:
527     // On wait_barrier or blocked.
528     // Blocked threads should already have walkable stack.
529     assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
530     return true;
531 
532   default:
533     return false;
534   }
535 }
536 
537 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
538   if (thread->is_terminated()) {
539     return true;
540   }
541   JavaThreadState stable_state;
542   if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
543     return safepoint_safe_with(thread, stable_state);
544   }
545   return false;
546 }
547 
548 
549 // -------------------------------------------------------------------------------------------------------
550 // Implementation of Safepoint blocking point
551 
552 void SafepointSynchronize::block(JavaThread *thread) {
553   assert(thread != nullptr, "thread must be set");
554 
555   // Threads shouldn't block if they are in the middle of printing, but...
556   ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
557 
558   // Only bail from the block() call if the thread is gone from the
559   // thread list; starting to exit should still block.
560   if (thread->is_terminated()) {
561      // block current thread if we come here from native code when VM is gone
562      thread->block_if_vm_exited();
563 
564      // otherwise do nothing
565      return;
566   }
567 
568   JavaThreadState state = thread->thread_state();
569   thread->frame_anchor()->make_walkable();
570 
571   uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
572 
573   // We have no idea where the VMThread is, it might even be at next safepoint.
574   // So we can miss this poll, but stop at next.
575 
576   // Load dependent store, it must not pass loading of safepoint_id.
577   thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
578 
579   // This part we can skip if we notice we miss or are in a future safepoint.
580   OrderAccess::storestore();
581   // Load in wait barrier should not float up
582   thread->set_thread_state_fence(_thread_blocked);
583 
584   _wait_barrier->wait(static_cast<int>(safepoint_id));
585   assert(_state != _synchronized, "Can't be");
586 
587   // If barrier is disarmed stop store from floating above loads in barrier.
588   OrderAccess::loadstore();
589   thread->set_thread_state(state);
590 
591   // Then we reset the safepoint id to inactive.
592   thread->safepoint_state()->reset_safepoint_id(); // Release store
593 
594   OrderAccess::fence();
595 
596   guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
597             "The safepoint id should be set only in block path");
598 
599   // cross_modify_fence is done by SafepointMechanism::process_if_requested
600   // which is the only caller here.
601 }
602 
603 // ------------------------------------------------------------------------------------------------------
604 // Exception handlers
605 
606 
607 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
608   assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
609   thread->set_thread_state(_thread_in_vm);
610 
611   // Enable WXWrite: the function is called implicitly from java code.
612   MACOS_AARCH64_ONLY(ThreadWXEnable wx(WXWrite, thread));
613 
614   if (log_is_enabled(Info, safepoint, stats)) {
615     Atomic::inc(&_nof_threads_hit_polling_page);
616   }
617 
618   ThreadSafepointState* state = thread->safepoint_state();
619 
620   state->handle_polling_page_exception();
621 
622   thread->set_thread_state(_thread_in_Java);
623 }
624 
625 
626 void SafepointSynchronize::print_safepoint_timeout() {
627   if (!timeout_error_printed) {
628     timeout_error_printed = true;
629     // Print out the thread info which didn't reach the safepoint for debugging
630     // purposes (useful when there are lots of threads in the debugger).
631     LogTarget(Warning, safepoint) lt;
632     if (lt.is_enabled()) {
633       ResourceMark rm;
634       LogStream ls(lt);
635 
636       ls.cr();
637       ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
638       ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
639       ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
640       for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
641         if (cur_thread->safepoint_state()->is_running()) {
642           ls.print("# ");
643           cur_thread->print_on(&ls);
644           ls.cr();
645         }
646       }
647       ls.print_cr("# SafepointSynchronize::begin: (End of list)");
648     }
649   }
650 
651   // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
652   // ShowMessageBoxOnError.
653   if (AbortVMOnSafepointTimeout && (os::elapsedTime() * MILLIUNITS > AbortVMOnSafepointTimeoutDelay)) {
654     // Send the blocking thread a signal to terminate and write an error file.
655     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
656       if (cur_thread->safepoint_state()->is_running()) {
657         if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
658           break; // Could not send signal. Report fatal error.
659         }
660         // Give cur_thread a chance to report the error and terminate the VM.
661         os::naked_sleep(3000);
662       }
663     }
664     fatal("Safepoint sync time longer than %.6f ms detected when executing %s.",
665           SafepointTimeoutDelay, VMThread::vm_operation()->name());
666   }
667 }
668 
669 // -------------------------------------------------------------------------------------------------------
670 // Implementation of ThreadSafepointState
671 
672 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
673   : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
674     _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(nullptr) {
675 }
676 
677 void ThreadSafepointState::create(JavaThread *thread) {
678   ThreadSafepointState *state = new ThreadSafepointState(thread);
679   thread->set_safepoint_state(state);
680 }
681 
682 void ThreadSafepointState::destroy(JavaThread *thread) {
683   if (thread->safepoint_state()) {
684     delete(thread->safepoint_state());
685     thread->set_safepoint_state(nullptr);
686   }
687 }
688 
689 uint64_t ThreadSafepointState::get_safepoint_id() const {
690   return Atomic::load_acquire(&_safepoint_id);
691 }
692 
693 void ThreadSafepointState::reset_safepoint_id() {
694   Atomic::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
695 }
696 
697 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
698   Atomic::release_store(&_safepoint_id, safepoint_id);
699 }
700 
701 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
702   assert(is_running(), "better be running or just have hit safepoint poll");
703 
704   JavaThreadState stable_state;
705   if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
706     // We could not get stable state of the JavaThread.
707     // Consider it running and just return.
708     return;
709   }
710 
711   if (safepoint_safe_with(_thread, stable_state)) {
712     account_safe_thread();
713     return;
714   }
715 
716   // All other thread states will continue to run until they
717   // transition and self-block in state _blocked
718   // Safepoint polling in compiled code causes the Java threads to do the same.
719   // Note: new threads may require a malloc so they must be allowed to finish
720 
721   assert(is_running(), "examine_state_of_thread on non-running thread");
722   return;
723 }
724 
725 void ThreadSafepointState::account_safe_thread() {
726   SafepointSynchronize::decrement_waiting_to_block();
727   if (_thread->in_critical()) {
728     // Notice that this thread is in a critical section
729     SafepointSynchronize::increment_jni_active_count();
730   }
731   DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
732   assert(!_safepoint_safe, "Must be unsafe before safe");
733   _safepoint_safe = true;
734 
735   // The oops in the monitor cache are cleared to prevent stale cache entries
736   // from keeping dead objects alive. Because these oops are always cleared
737   // before safepoint operations they are not visited in JavaThread::oops_do.
738   _thread->om_clear_monitor_cache();
739 }
740 
741 void ThreadSafepointState::restart() {
742   assert(_safepoint_safe, "Must be safe before unsafe");
743   _safepoint_safe = false;
744 }
745 
746 void ThreadSafepointState::print_on(outputStream *st) const {
747   const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
748 
749   st->print_cr("Thread: " INTPTR_FORMAT
750               "  [0x%2x] State: %s _at_poll_safepoint %d",
751                p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
752 
753   _thread->print_thread_state_on(st);
754 }
755 
756 // ---------------------------------------------------------------------------------------------------------------------
757 
758 // Process pending operation.
759 void ThreadSafepointState::handle_polling_page_exception() {
760   JavaThread* self = thread();
761   assert(self == JavaThread::current(), "must be self");
762 
763   // Step 1: Find the nmethod from the return address
764   address real_return_addr = self->saved_exception_pc();
765 
766   CodeBlob *cb = CodeCache::find_blob(real_return_addr);
767   assert(cb != nullptr && cb->is_nmethod(), "return address should be in nmethod");
768   nmethod* nm = cb->as_nmethod();
769 
770   // Find frame of caller
771   frame stub_fr = self->last_frame();
772   CodeBlob* stub_cb = stub_fr.cb();
773   assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
774   RegisterMap map(self,
775                   RegisterMap::UpdateMap::include,
776                   RegisterMap::ProcessFrames::skip,
777                   RegisterMap::WalkContinuation::skip);
778   frame caller_fr = stub_fr.sender(&map);
779 
780   // Should only be poll_return or poll
781   assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
782 
783   // This is a poll immediately before a return. The exception handling code
784   // has already had the effect of causing the return to occur, so the execution
785   // will continue immediately after the call. In addition, the oopmap at the
786   // return point does not mark the return value as an oop (if it is), so
787   // it needs a handle here to be updated.
788   if( nm->is_at_poll_return(real_return_addr) ) {

789     // See if return type is an oop.
790     bool return_oop = nm->method()->is_returning_oop();

791     HandleMark hm(self);
792     Handle return_value;















793     if (return_oop) {
794       // The oop result has been saved on the stack together with all
795       // the other registers. In order to preserve it over GCs we need
796       // to keep it in a handle.
797       oop result = caller_fr.saved_oop_result(&map);
798       assert(oopDesc::is_oop_or_null(result), "must be oop");
799       return_value = Handle(self, result);
800       assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
801     }
802 
803     // We get here if compiled return polls found a reason to call into the VM.
804     // One condition for that is that the top frame is not yet safe to use.
805     // The following stack watermark barrier poll will catch such situations.
806     StackWatermarkSet::after_unwind(self);
807 
808     // Process pending operation
809     SafepointMechanism::process_if_requested_with_exit_check(self, true /* check asyncs */);
810 
811     // restore oop result, if any
812     if (return_oop) {
813       caller_fr.set_saved_oop_result(&map, return_value());



814     }
815   }
816 
817   // This is a safepoint poll. Verify the return address and block.
818   else {
819 
820     // verify the blob built the "return address" correctly
821     assert(real_return_addr == caller_fr.pc(), "must match");
822 
823     set_at_poll_safepoint(true);
824     // Process pending operation
825     // We never deliver an async exception at a polling point as the
826     // compiler may not have an exception handler for it (polling at
827     // a return point is ok though). We will check for a pending async
828     // exception below and deoptimize if needed. We also cannot deoptimize
829     // and still install the exception here because live registers needed
830     // during deoptimization are clobbered by the exception path. The
831     // exception will just be delivered once we get into the interpreter.
832     SafepointMechanism::process_if_requested_with_exit_check(self, false /* check asyncs */);
833     set_at_poll_safepoint(false);
834 
835     if (self->has_async_exception_condition()) {
836       Deoptimization::deoptimize_frame(self, caller_fr.id());
837       log_info(exceptions)("deferred async exception at compiled safepoint");
838     }
839 
840     // If an exception has been installed we must verify that the top frame wasn't deoptimized.
841     if (self->has_pending_exception() ) {
842       RegisterMap map(self,
843                       RegisterMap::UpdateMap::include,
844                       RegisterMap::ProcessFrames::skip,
845                       RegisterMap::WalkContinuation::skip);
846       frame caller_fr = stub_fr.sender(&map);
847       if (caller_fr.is_deoptimized_frame()) {
848         // The exception path will destroy registers that are still
849         // live and will be needed during deoptimization, so if we
850         // have an exception now things are messed up. We only check
851         // at this scope because for a poll return it is ok to deoptimize
852         // while having a pending exception since the call we are returning
853         // from already collides with exception handling registers and
854         // so there is no issue (the exception handling path kills call
855         // result registers but this is ok since the exception kills
856         // the result anyway).
857         fatal("Exception installed and deoptimization is pending");
858       }
859     }
860   }
861 }
862 
863 
864 // -------------------------------------------------------------------------------------------------------
865 // Implementation of SafepointTracing
866 
867 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
868 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
869 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
870 jlong SafepointTracing::_last_app_time_ns = 0;
871 int SafepointTracing::_nof_threads = 0;
872 int SafepointTracing::_nof_running = 0;
873 int SafepointTracing::_page_trap = 0;
874 VM_Operation::VMOp_Type SafepointTracing::_current_type;
875 jlong     SafepointTracing::_max_sync_time = 0;
876 jlong     SafepointTracing::_max_vmop_time = 0;
877 uint64_t  SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
878 
879 void SafepointTracing::init() {
880   // Application start
881   _last_safepoint_end_time_ns = os::javaTimeNanos();
882 }
883 
884 // Helper method to print the header.
885 static void print_header(outputStream* st) {
886   // The number of spaces is significant here, and should match the format
887   // specifiers in print_statistics().
888 
889   st->print("VM Operation                 "
890             "[ threads: total initial_running ]"
891             "[ time:       sync    vmop      total ]");
892 
893   st->print_cr(" page_trap_count");
894 }
895 
896 // This prints a nice table.  To get the statistics to not shift due to the logging uptime
897 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
898 void SafepointTracing::statistics_log() {
899   LogTarget(Info, safepoint, stats) lt;
900   assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
901   LogStream ls(lt);
902 
903   static int _cur_stat_index = 0;
904 
905   // Print header every 30 entries
906   if ((_cur_stat_index % 30) == 0) {
907     print_header(&ls);
908     _cur_stat_index = 1;  // wrap
909   } else {
910     _cur_stat_index++;
911   }
912 
913   ls.print("%-28s [       "
914            INT32_FORMAT_W(8) "        " INT32_FORMAT_W(8) " "
915            "]",
916            VM_Operation::name(_current_type),
917            _nof_threads,
918            _nof_running);
919   ls.print("[       "
920            INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
921            (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
922            (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns),
923            (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
924 
925   ls.print_cr(INT32_FORMAT_W(16), _page_trap);
926 }
927 
928 // This method will be called when VM exits. This tries to summarize the sampling.
929 // Current thread may already be deleted, so don't use ResourceMark.
930 void SafepointTracing::statistics_exit_log() {
931   if (!log_is_enabled(Info, safepoint, stats)) {
932     return;
933   }
934   for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
935     if (_op_count[index] != 0) {
936       log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
937                _op_count[index]);
938     }
939   }
940 
941   log_info(safepoint, stats)("Maximum sync time  " INT64_FORMAT" ns",
942                               (int64_t)(_max_sync_time));
943   log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation)  "
944                               INT64_FORMAT " ns",
945                               (int64_t)(_max_vmop_time));
946 }
947 
948 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
949   _op_count[type]++;
950   _current_type = type;
951 
952   // update the time stamp to begin recording safepoint time
953   _last_safepoint_begin_time_ns = os::javaTimeNanos();
954   _last_safepoint_sync_time_ns = 0;
955 
956   _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
957   _last_safepoint_end_time_ns = 0;
958 
959   RuntimeService::record_safepoint_begin(_last_app_time_ns);
960 }
961 
962 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
963   _last_safepoint_sync_time_ns = os::javaTimeNanos();
964   _nof_threads = nof_threads;
965   _nof_running = nof_running;
966   _page_trap   = traps;
967   RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
968 }
969 
970 void SafepointTracing::end() {
971   _last_safepoint_end_time_ns = os::javaTimeNanos();
972 
973   if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
974     _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
975   }
976   if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
977     _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
978   }
979   if (log_is_enabled(Info, safepoint, stats)) {
980     statistics_log();
981   }
982 
983   log_info(safepoint)(
984      "Safepoint \"%s\", "
985      "Time since last: " JLONG_FORMAT " ns, "
986      "Reaching safepoint: " JLONG_FORMAT " ns, "
987      "At safepoint: " JLONG_FORMAT " ns, "
988      "Total: " JLONG_FORMAT " ns",
989       VM_Operation::name(_current_type),
990       _last_app_time_ns,
991       _last_safepoint_sync_time_ns    - _last_safepoint_begin_time_ns,
992       _last_safepoint_end_time_ns     - _last_safepoint_sync_time_ns,
993       _last_safepoint_end_time_ns     - _last_safepoint_begin_time_ns
994      );
995 
996   RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns);
997 }
--- EOF ---