1 /*
2 * Copyright (c) 1997, 2018, 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 "classfile/classLoaderDataGraph.inline.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "code/codeCache.hpp"
31 #include "code/icBuffer.hpp"
32 #include "code/nmethod.hpp"
33 #include "code/pcDesc.hpp"
34 #include "code/scopeDesc.hpp"
35 #include "gc/shared/collectedHeap.hpp"
36 #include "gc/shared/gcLocker.hpp"
37 #include "gc/shared/strongRootsScope.hpp"
38 #include "gc/shared/workgroup.hpp"
39 #include "interpreter/interpreter.hpp"
40 #include "jfr/jfrEvents.hpp"
41 #include "logging/log.hpp"
42 #include "logging/logStream.hpp"
43 #include "memory/resourceArea.hpp"
44 #include "memory/universe.hpp"
45 #include "oops/oop.inline.hpp"
46 #include "oops/symbol.hpp"
47 #include "runtime/atomic.hpp"
48 #include "runtime/compilationPolicy.hpp"
49 #include "runtime/deoptimization.hpp"
50 #include "runtime/frame.inline.hpp"
51 #include "runtime/interfaceSupport.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/stubCodeGenerator.hpp"
59 #include "runtime/stubRoutines.hpp"
60 #include "runtime/sweeper.hpp"
61 #include "runtime/synchronizer.hpp"
62 #include "runtime/thread.inline.hpp"
63 #include "runtime/threadSMR.hpp"
64 #include "runtime/timerTrace.hpp"
65 #include "services/runtimeService.hpp"
66 #include "utilities/events.hpp"
67 #include "utilities/macros.hpp"
68 #ifdef COMPILER1
69 #include "c1/c1_globals.hpp"
70 #endif
71
72 template <typename E>
73 static void set_current_safepoint_id(E* event, int adjustment = 0) {
74 assert(event != NULL, "invariant");
75 event->set_safepointId(SafepointSynchronize::safepoint_counter() + adjustment);
76 }
77
78 static void post_safepoint_begin_event(EventSafepointBegin* event,
79 int thread_count,
80 int critical_thread_count) {
81 assert(event != NULL, "invariant");
82 assert(event->should_commit(), "invariant");
83 set_current_safepoint_id(event);
84 event->set_totalThreadCount(thread_count);
85 event->set_jniCriticalThreadCount(critical_thread_count);
86 event->commit();
87 }
88
89 static void post_safepoint_cleanup_event(EventSafepointCleanup* event) {
90 assert(event != NULL, "invariant");
91 assert(event->should_commit(), "invariant");
92 set_current_safepoint_id(event);
93 event->commit();
94 }
95
96 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization* event,
97 int initial_number_of_threads,
98 int threads_waiting_to_block,
99 unsigned int iterations) {
100 assert(event != NULL, "invariant");
101 if (event->should_commit()) {
102 // Group this event together with the ones committed after the counter is increased
103 set_current_safepoint_id(event, 1);
104 event->set_initialThreadCount(initial_number_of_threads);
105 event->set_runningThreadCount(threads_waiting_to_block);
106 event->set_iterations(iterations);
107 event->commit();
108 }
109 }
110
111 static void post_safepoint_wait_blocked_event(EventSafepointWaitBlocked* event,
112 int initial_threads_waiting_to_block) {
113 assert(event != NULL, "invariant");
114 assert(event->should_commit(), "invariant");
115 set_current_safepoint_id(event);
116 event->set_runningThreadCount(initial_threads_waiting_to_block);
117 event->commit();
118 }
119
120 static void post_safepoint_cleanup_task_event(EventSafepointCleanupTask* event,
121 const char* name) {
122 assert(event != NULL, "invariant");
123 if (event->should_commit()) {
124 set_current_safepoint_id(event);
125 event->set_name(name);
126 event->commit();
127 }
128 }
129
130 static void post_safepoint_end_event(EventSafepointEnd* event) {
131 assert(event != NULL, "invariant");
132 if (event->should_commit()) {
133 // Group this event together with the ones committed before the counter increased
134 set_current_safepoint_id(event, -1);
135 event->commit();
136 }
137 }
138
139 // --------------------------------------------------------------------------------------------------
140 // Implementation of Safepoint begin/end
141
142 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
143 volatile int SafepointSynchronize::_waiting_to_block = 0;
144 volatile uint64_t SafepointSynchronize::_safepoint_counter = 0;
145 int SafepointSynchronize::_current_jni_active_count = 0;
146 long SafepointSynchronize::_end_of_last_safepoint = 0;
147 int SafepointSynchronize::_defer_thr_suspend_loop_count = 4000;
148 static const int safepoint_spin_before_yield = 2000;
149 static volatile int PageArmed = 0 ; // safepoint polling page is RO|RW vs PROT_NONE
150 static volatile int TryingToBlock = 0 ; // proximate value -- for advisory use only
151 static bool timeout_error_printed = false;
152
153
154 // Statistic related statics
155 julong SafepointSynchronize::_coalesced_vmop_count = 0;
156 static jlong _safepoint_begin_time = 0;
157 static float _ts_of_current_safepoint = 0.0f;
158 static volatile int _nof_threads_hit_polling_page = 0;
159
160 // Roll all threads forward to a safepoint and suspend them all
161 void SafepointSynchronize::begin() {
162 EventSafepointBegin begin_event;
163 Thread* myThread = Thread::current();
164 assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint");
165
166 if (log_is_enabled(Debug, safepoint, stats)) {
167 _safepoint_begin_time = os::javaTimeNanos();
168 _ts_of_current_safepoint = tty->time_stamp().seconds();
169 _nof_threads_hit_polling_page = 0;
170 }
171
172 Universe::heap()->safepoint_synchronize_begin();
173
174 // By getting the Threads_lock, we assure that no threads are about to start or
175 // exit. It is released again in SafepointSynchronize::end().
176 Threads_lock->lock();
177
178 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
179
180 int nof_threads = Threads::number_of_threads();
181
182 log_debug(safepoint)("Safepoint synchronization initiated. (%d threads)", nof_threads);
183
184 RuntimeService::record_safepoint_begin();
185
186 MutexLocker mu(Safepoint_lock);
187
188 // Reset the count of active JNI critical threads
189 _current_jni_active_count = 0;
190
191 // Set number of threads to wait for, before we initiate the callbacks
192 _waiting_to_block = nof_threads;
193 TryingToBlock = 0 ;
194 int still_running = nof_threads;
195
196 // Save the starting time, so that it can be compared to see if this has taken
197 // too long to complete.
198 jlong safepoint_limit_time = 0;
199 timeout_error_printed = false;
200
201 // Begin the process of bringing the system to a safepoint.
202 // Java threads can be in several different states and are
203 // stopped by different mechanisms:
204 //
205 // 1. Running interpreted
206 // The interpreter dispatch table is changed to force it to
207 // check for a safepoint condition between bytecodes.
208 // 2. Running in native code
209 // When returning from the native code, a Java thread must check
210 // the safepoint _state to see if we must block. If the
211 // VM thread sees a Java thread in native, it does
212 // not wait for this thread to block. The order of the memory
213 // writes and reads of both the safepoint state and the Java
214 // threads state is critical. In order to guarantee that the
215 // memory writes are serialized with respect to each other,
216 // the VM thread issues a memory barrier instruction.
217 // 3. Running compiled Code
218 // Compiled code reads a global (Safepoint Polling) page that
219 // is set to fault if we are trying to get to a safepoint.
220 // 4. Blocked
221 // A thread which is blocked will not be allowed to return from the
222 // block condition until the safepoint operation is complete.
223 // 5. In VM or Transitioning between states
224 // If a Java thread is currently running in the VM or transitioning
225 // between states, the safepointing code will wait for the thread to
226 // block itself when it attempts transitions to a new state.
227 //
228 {
229 EventSafepointStateSynchronization sync_event;
230 int initial_running = 0;
231
232 _state = _synchronizing;
233
234 if (SafepointMechanism::uses_thread_local_poll()) {
235 // Arming the per thread poll while having _state != _not_synchronized means safepointing
236 log_trace(safepoint)("Setting thread local yield flag for threads");
237 OrderAccess::storestore(); // storestore, global state -> local state
238 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
239 // Make sure the threads start polling, it is time to yield.
240 SafepointMechanism::arm_local_poll(cur);
241 }
242 }
243 OrderAccess::fence(); // storestore|storeload, global state -> local state
244
245 if (SafepointMechanism::uses_global_page_poll()) {
246 // Make interpreter safepoint aware
247 Interpreter::notice_safepoints();
248
249 // Make polling safepoint aware
250 guarantee (PageArmed == 0, "invariant") ;
251 PageArmed = 1 ;
252 os::make_polling_page_unreadable();
253 }
254
255 // Consider using active_processor_count() ... but that call is expensive.
256 int ncpus = os::processor_count() ;
257 unsigned int iterations = 0;
258
259 {
260 JavaThreadIteratorWithHandle jtiwh;
261 #ifdef ASSERT
262 for (; JavaThread *cur = jtiwh.next(); ) {
263 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
264 // Clear the visited flag to ensure that the critical counts are collected properly.
265 cur->set_visited_for_critical_count(false);
266 }
267 #endif // ASSERT
268
269 if (SafepointTimeout)
270 safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;
271
272 // Iterate through all threads until it have been determined how to stop them all at a safepoint
273 int steps = 0 ;
274 while(still_running > 0) {
275 jtiwh.rewind();
276 for (; JavaThread *cur = jtiwh.next(); ) {
277 assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");
278 ThreadSafepointState *cur_state = cur->safepoint_state();
279 if (cur_state->is_running()) {
280 cur_state->examine_state_of_thread();
281 if (!cur_state->is_running()) {
282 still_running--;
283 // consider adjusting steps downward:
284 // steps = 0
285 // steps -= NNN
286 // steps >>= 1
287 // steps = MIN(steps, 2000-100)
288 // if (iterations != 0) steps -= NNN
289 }
290 LogTarget(Trace, safepoint) lt;
291 if (lt.is_enabled()) {
292 ResourceMark rm;
293 LogStream ls(lt);
294 cur_state->print_on(&ls);
295 }
296 }
297 }
298
299 if (iterations == 0) {
300 initial_running = still_running;
301 if (log_is_enabled(Debug, safepoint, stats)) {
302 begin_statistics(nof_threads, still_running);
303 }
304 }
305
306 if (still_running > 0) {
307 // Check for if it takes to long
308 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
309 print_safepoint_timeout(_spinning_timeout);
310 }
311
312 // Spin to avoid context switching.
313 // There's a tension between allowing the mutators to run (and rendezvous)
314 // vs spinning. As the VM thread spins, wasting cycles, it consumes CPU that
315 // a mutator might otherwise use profitably to reach a safepoint. Excessive
316 // spinning by the VM thread on a saturated system can increase rendezvous latency.
317 // Blocking or yielding incur their own penalties in the form of context switching
318 // and the resultant loss of $ residency.
319 //
320 // Further complicating matters is that yield() does not work as naively expected
321 // on many platforms -- yield() does not guarantee that any other ready threads
322 // will run. As such we revert to naked_short_sleep() after some number of iterations.
323 // nakes_short_sleep() is implemented as a short unconditional sleep.
324 // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping
325 // can actually increase the time it takes the VM thread to detect that a system-wide
326 // stop-the-world safepoint has been reached. In a pathological scenario such as that
327 // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.
328 // In that case the mutators will be stalled waiting for the safepoint to complete and the
329 // the VMthread will be sleeping, waiting for the mutators to rendezvous. The VMthread
330 // will eventually wake up and detect that all mutators are safe, at which point
331 // we'll again make progress.
332 //
333 // Beware too that that the VMThread typically runs at elevated priority.
334 // Its default priority is higher than the default mutator priority.
335 // Obviously, this complicates spinning.
336 //
337 // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).
338 // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.
339 //
340 // See the comments in synchronizer.cpp for additional remarks on spinning.
341 //
342 // In the future we might:
343 // -- Modify the safepoint scheme to avoid potentially unbounded spinning.
344 // This is tricky as the path used by a thread exiting the JVM (say on
345 // on JNI call-out) simply stores into its state field. The burden
346 // is placed on the VM thread, which must poll (spin).
347 // -- Find something useful to do while spinning. If the safepoint is GC-related
348 // we might aggressively scan the stacks of threads that are already safe.
349 // -- YieldTo() any still-running mutators that are ready but OFFPROC.
350 // -- Check system saturation. If the system is not fully saturated then
351 // simply spin and avoid sleep/yield.
352 // -- As still-running mutators rendezvous they could unpark the sleeping
353 // VMthread. This works well for still-running mutators that become
354 // safe. The VMthread must still poll for mutators that call-out.
355 // -- Drive the policy on time-since-begin instead of iterations.
356 // -- Consider making the spin duration a function of the # of CPUs:
357 // Spin = (((ncpus-1) * M) + K) + F(still_running)
358 // Alternately, instead of counting iterations of the outer loop
359 // we could count the # of threads visited in the inner loop, above.
360 // -- On windows consider using the return value from SwitchThreadTo()
361 // to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
362
363 if (int(iterations) == -1) { // overflow - something is wrong.
364 // We can only overflow here when we are using global
365 // polling pages. We keep this guarantee in its original
366 // form so that searches of the bug database for this
367 // failure mode find the right bugs.
368 guarantee (PageArmed == 0, "invariant");
369 }
370
371 // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
372 // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
373 ++steps ;
374 if (ncpus > 1 && steps < safepoint_spin_before_yield) {
375 SpinPause() ; // MP-Polite spin
376 } else
377 if (steps < _defer_thr_suspend_loop_count) {
378 os::naked_yield() ;
379 } else {
380 os::naked_short_sleep(1);
381 }
382
383 iterations ++ ;
384 }
385 assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
386 }
387 } // ThreadsListHandle destroyed here.
388 assert(still_running == 0, "sanity check");
389
390 if (log_is_enabled(Debug, safepoint, stats)) {
391 update_statistics_on_spin_end();
392 }
393 if (sync_event.should_commit()) {
394 post_safepoint_synchronize_event(&sync_event, initial_running, _waiting_to_block, iterations);
395 }
396 }
397
398 // wait until all threads are stopped
399 {
400 EventSafepointWaitBlocked wait_blocked_event;
401 int initial_waiting_to_block = _waiting_to_block;
402
403 while (_waiting_to_block > 0) {
404 log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block);
405 if (!SafepointTimeout || timeout_error_printed) {
406 Safepoint_lock->wait(true); // true, means with no safepoint checks
407 } else {
408 // Compute remaining time
409 jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
410
411 // If there is no remaining time, then there is an error
412 if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
413 print_safepoint_timeout(_blocking_timeout);
414 }
415 }
416 }
417 assert(_waiting_to_block == 0, "sanity check");
418
419 #ifndef PRODUCT
420 if (SafepointTimeout) {
421 jlong current_time = os::javaTimeNanos();
422 if (safepoint_limit_time < current_time) {
423 log_warning(safepoint)("# SafepointSynchronize: Finished after "
424 INT64_FORMAT_W(6) " ms",
425 (int64_t)((current_time - safepoint_limit_time) / MICROUNITS +
426 (jlong)SafepointTimeoutDelay));
427 }
428 }
429 #endif
430
431 assert((_safepoint_counter & 0x1) == 0, "must be even");
432 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
433 _safepoint_counter ++;
434
435 // Record state
436 _state = _synchronized;
437
438 OrderAccess::fence();
439 if (wait_blocked_event.should_commit()) {
440 post_safepoint_wait_blocked_event(&wait_blocked_event, initial_waiting_to_block);
441 }
442 }
443
444 #ifdef ASSERT
445 // Make sure all the threads were visited.
446 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
447 assert(cur->was_visited_for_critical_count(), "missed a thread");
448 }
449 #endif // ASSERT
450
451 // Update the count of active JNI critical regions
452 GCLocker::set_jni_lock_count(_current_jni_active_count);
453
454 log_info(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description());
455
456 RuntimeService::record_safepoint_synchronized();
457 if (log_is_enabled(Debug, safepoint, stats)) {
458 update_statistics_on_sync_end(os::javaTimeNanos());
459 }
460
461 // Call stuff that needs to be run when a safepoint is just about to be completed
462 {
463 EventSafepointCleanup cleanup_event;
464 do_cleanup_tasks();
465 if (cleanup_event.should_commit()) {
466 post_safepoint_cleanup_event(&cleanup_event);
467 }
468 }
469
470 if (log_is_enabled(Debug, safepoint, stats)) {
471 // Record how much time spend on the above cleanup tasks
472 update_statistics_on_cleanup_end(os::javaTimeNanos());
473 }
474
475 if (begin_event.should_commit()) {
476 post_safepoint_begin_event(&begin_event, nof_threads, _current_jni_active_count);
477 }
478 }
479
480 // Wake up all threads, so they are ready to resume execution after the safepoint
481 // operation has been carried out
482 void SafepointSynchronize::end() {
483 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
484 assert((_safepoint_counter & 0x1) == 1, "must be odd");
485 EventSafepointEnd event;
486 _safepoint_counter ++;
487 // memory fence isn't required here since an odd _safepoint_counter
488 // value can do no harm and a fence is issued below anyway.
489
490 DEBUG_ONLY(Thread* myThread = Thread::current();)
491 assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
492
493 if (log_is_enabled(Debug, safepoint, stats)) {
494 end_statistics(os::javaTimeNanos());
495 }
496
497 {
498 JavaThreadIteratorWithHandle jtiwh;
499 #ifdef ASSERT
500 // A pending_exception cannot be installed during a safepoint. The threads
501 // may install an async exception after they come back from a safepoint into
502 // pending_exception after they unblock. But that should happen later.
503 for (; JavaThread *cur = jtiwh.next(); ) {
504 assert (!(cur->has_pending_exception() &&
505 cur->safepoint_state()->is_at_poll_safepoint()),
506 "safepoint installed a pending exception");
507 }
508 #endif // ASSERT
509
510 if (PageArmed) {
511 assert(SafepointMechanism::uses_global_page_poll(), "sanity");
512 // Make polling safepoint aware
513 os::make_polling_page_readable();
514 PageArmed = 0 ;
515 }
516
517 if (SafepointMechanism::uses_global_page_poll()) {
518 // Remove safepoint check from interpreter
519 Interpreter::ignore_safepoints();
520 }
521
522 {
523 MutexLocker mu(Safepoint_lock);
524
525 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
526
527 if (SafepointMechanism::uses_thread_local_poll()) {
528 _state = _not_synchronized;
529 OrderAccess::storestore(); // global state -> local state
530 jtiwh.rewind();
531 for (; JavaThread *current = jtiwh.next(); ) {
532 ThreadSafepointState* cur_state = current->safepoint_state();
533 cur_state->restart(); // TSS _running
534 SafepointMechanism::disarm_local_poll(current);
535 }
536 log_info(safepoint)("Leaving safepoint region");
537 } else {
538 // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
539 // when they get restarted.
540 _state = _not_synchronized;
541 OrderAccess::fence();
542
543 log_info(safepoint)("Leaving safepoint region");
544
545 // Start suspended threads
546 jtiwh.rewind();
547 for (; JavaThread *current = jtiwh.next(); ) {
548 ThreadSafepointState* cur_state = current->safepoint_state();
549 assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
550 cur_state->restart();
551 assert(cur_state->is_running(), "safepoint state has not been reset");
552 }
553 }
554
555 RuntimeService::record_safepoint_end();
556
557 // Release threads lock, so threads can be created/destroyed again.
558 // It will also release all threads blocked in signal_thread_blocked.
559 Threads_lock->unlock();
560 }
561 } // ThreadsListHandle destroyed here.
562
563 Universe::heap()->safepoint_synchronize_end();
564 // record this time so VMThread can keep track how much time has elapsed
565 // since last safepoint.
566 _end_of_last_safepoint = os::javaTimeMillis();
567 if (event.should_commit()) {
568 post_safepoint_end_event(&event);
569 }
570 }
571
572 bool SafepointSynchronize::is_cleanup_needed() {
573 // Need a safepoint if there are many monitors to deflate.
574 if (ObjectSynchronizer::is_cleanup_needed()) return true;
575 // Need a safepoint if some inline cache buffers is non-empty
576 if (!InlineCacheBuffer::is_empty()) return true;
577 return false;
578 }
579
580 class ParallelSPCleanupThreadClosure : public ThreadClosure {
581 private:
582 CodeBlobClosure* _nmethod_cl;
583 DeflateMonitorCounters* _counters;
584
585 public:
586 ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
587 _nmethod_cl(UseCodeAging ? NMethodSweeper::prepare_reset_hotness_counters() : NULL),
588 _counters(counters) {}
589
590 void do_thread(Thread* thread) {
591 ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
592 if (_nmethod_cl != NULL && thread->is_Java_thread() &&
593 ! thread->is_Code_cache_sweeper_thread()) {
594 JavaThread* jt = (JavaThread*) thread;
595 jt->nmethods_do(_nmethod_cl);
596 }
597 }
598 };
599
600 class ParallelSPCleanupTask : public AbstractGangTask {
601 private:
602 SubTasksDone _subtasks;
603 ParallelSPCleanupThreadClosure _cleanup_threads_cl;
604 uint _num_workers;
605 DeflateMonitorCounters* _counters;
606 public:
607 ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
608 AbstractGangTask("Parallel Safepoint Cleanup"),
609 _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
610 _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
611 _num_workers(num_workers),
612 _counters(counters) {}
613
614 void work(uint worker_id) {
615 // All threads deflate monitors and mark nmethods (if necessary).
616 Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl);
617
618 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
619 const char* name = "deflating global idle monitors";
620 EventSafepointCleanupTask event;
621 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
622 ObjectSynchronizer::deflate_idle_monitors(_counters);
623 if (event.should_commit()) {
624 post_safepoint_cleanup_task_event(&event, name);
625 }
626 }
627
628 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
629 const char* name = "updating inline caches";
630 EventSafepointCleanupTask event;
631 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
632 InlineCacheBuffer::update_inline_caches();
633 if (event.should_commit()) {
634 post_safepoint_cleanup_task_event(&event, name);
635 }
636 }
637
638 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
639 const char* name = "compilation policy safepoint handler";
640 EventSafepointCleanupTask event;
641 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
642 CompilationPolicy::policy()->do_safepoint_work();
643 if (event.should_commit()) {
644 post_safepoint_cleanup_task_event(&event, name);
645 }
646 }
647
648 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
649 if (SymbolTable::needs_rehashing()) {
650 const char* name = "rehashing symbol table";
651 EventSafepointCleanupTask event;
652 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
653 SymbolTable::rehash_table();
654 if (event.should_commit()) {
655 post_safepoint_cleanup_task_event(&event, name);
656 }
657 }
658 }
659
660 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
661 if (StringTable::needs_rehashing()) {
662 const char* name = "rehashing string table";
663 EventSafepointCleanupTask event;
664 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
665 StringTable::rehash_table();
666 if (event.should_commit()) {
667 post_safepoint_cleanup_task_event(&event, name);
668 }
669 }
670 }
671
672 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
673 // CMS delays purging the CLDG until the beginning of the next safepoint and to
674 // make sure concurrent sweep is done
675 const char* name = "purging class loader data graph";
676 EventSafepointCleanupTask event;
677 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
678 ClassLoaderDataGraph::purge_if_needed();
679 if (event.should_commit()) {
680 post_safepoint_cleanup_task_event(&event, name);
681 }
682 }
683
684 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) {
685 const char* name = "resizing system dictionaries";
686 EventSafepointCleanupTask event;
687 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
688 ClassLoaderDataGraph::resize_if_needed();
689 if (event.should_commit()) {
690 post_safepoint_cleanup_task_event(&event, name);
691 }
692 }
693
694 _subtasks.all_tasks_completed(_num_workers);
695 }
696 };
697
698 // Various cleaning tasks that should be done periodically at safepoints.
699 void SafepointSynchronize::do_cleanup_tasks() {
700
701 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
702
703 // Prepare for monitor deflation.
704 DeflateMonitorCounters deflate_counters;
705 ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
706
707 CollectedHeap* heap = Universe::heap();
708 assert(heap != NULL, "heap not initialized yet?");
709 WorkGang* cleanup_workers = heap->get_safepoint_workers();
710 if (cleanup_workers != NULL) {
711 // Parallel cleanup using GC provided thread pool.
712 uint num_cleanup_workers = cleanup_workers->active_workers();
713 ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
714 StrongRootsScope srs(num_cleanup_workers);
715 cleanup_workers->run_task(&cleanup);
716 } else {
717 // Serial cleanup using VMThread.
718 ParallelSPCleanupTask cleanup(1, &deflate_counters);
719 StrongRootsScope srs(1);
720 cleanup.work(0);
721 }
722
723 // Needs to be done single threaded by the VMThread. This walks
724 // the thread stacks looking for references to metadata before
725 // deciding to remove it from the metaspaces.
726 if (ClassLoaderDataGraph::should_clean_metaspaces_and_reset()) {
727 const char* name = "cleanup live ClassLoaderData metaspaces";
728 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
729 ClassLoaderDataGraph::walk_metadata_and_clean_metaspaces();
730 }
731
732 // Finish monitor deflation.
733 ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
734
735 }
736
737
738 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
739 switch(state) {
740 case _thread_in_native:
741 // native threads are safe if they have no java stack or have walkable stack
742 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
743
744 // blocked threads should have already have walkable stack
745 case _thread_blocked:
746 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
747 return true;
748
749 default:
750 return false;
751 }
752 }
753
754
755 // See if the thread is running inside a lazy critical native and
756 // update the thread critical count if so. Also set a suspend flag to
757 // cause the native wrapper to return into the JVM to do the unlock
758 // once the native finishes.
759 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
760 if (state == _thread_in_native &&
761 thread->has_last_Java_frame() &&
762 thread->frame_anchor()->walkable()) {
763 // This thread might be in a critical native nmethod so look at
764 // the top of the stack and increment the critical count if it
765 // is.
766 frame wrapper_frame = thread->last_frame();
767 CodeBlob* stub_cb = wrapper_frame.cb();
768 if (stub_cb != NULL &&
769 stub_cb->is_nmethod() &&
770 stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
771 // A thread could potentially be in a critical native across
772 // more than one safepoint, so only update the critical state on
773 // the first one. When it returns it will perform the unlock.
774 if (!thread->do_critical_native_unlock()) {
775 #ifdef ASSERT
776 if (!thread->in_critical()) {
777 GCLocker::increment_debug_jni_lock_count();
778 }
779 #endif
780 thread->enter_critical();
781 // Make sure the native wrapper calls back on return to
782 // perform the needed critical unlock.
783 thread->set_critical_native_unlock();
784 }
785 }
786 }
787 }
788
789
790
791 // -------------------------------------------------------------------------------------------------------
792 // Implementation of Safepoint callback point
793
794 void SafepointSynchronize::block(JavaThread *thread) {
795 assert(thread != NULL, "thread must be set");
796 assert(thread->is_Java_thread(), "not a Java thread");
797
798 // Threads shouldn't block if they are in the middle of printing, but...
799 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
800
801 // Only bail from the block() call if the thread is gone from the
802 // thread list; starting to exit should still block.
803 if (thread->is_terminated()) {
804 // block current thread if we come here from native code when VM is gone
805 thread->block_if_vm_exited();
806
807 // otherwise do nothing
808 return;
809 }
810
811 JavaThreadState state = thread->thread_state();
812 thread->frame_anchor()->make_walkable(thread);
813
814 // Check that we have a valid thread_state at this point
815 switch(state) {
816 case _thread_in_vm_trans:
817 case _thread_in_Java: // From compiled code
818
819 // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
820 // we pretend we are still in the VM.
821 thread->set_thread_state(_thread_in_vm);
822
823 if (is_synchronizing()) {
824 Atomic::inc (&TryingToBlock) ;
825 }
826
827 // We will always be holding the Safepoint_lock when we are examine the state
828 // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
829 // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
830 Safepoint_lock->lock_without_safepoint_check();
831 if (is_synchronizing()) {
832 // Decrement the number of threads to wait for and signal vm thread
833 assert(_waiting_to_block > 0, "sanity check");
834 _waiting_to_block--;
835 thread->safepoint_state()->set_has_called_back(true);
836
837 DEBUG_ONLY(thread->set_visited_for_critical_count(true));
838 if (thread->in_critical()) {
839 // Notice that this thread is in a critical section
840 increment_jni_active_count();
841 }
842
843 // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
844 if (_waiting_to_block == 0) {
845 Safepoint_lock->notify_all();
846 }
847 }
848
849 // We transition the thread to state _thread_blocked here, but
850 // we can't do our usual check for external suspension and then
851 // self-suspend after the lock_without_safepoint_check() call
852 // below because we are often called during transitions while
853 // we hold different locks. That would leave us suspended while
854 // holding a resource which results in deadlocks.
855 thread->set_thread_state(_thread_blocked);
856 Safepoint_lock->unlock();
857
858 // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
859 // the entire safepoint, the threads will all line up here during the safepoint.
860 Threads_lock->lock_without_safepoint_check();
861 // restore original state. This is important if the thread comes from compiled code, so it
862 // will continue to execute with the _thread_in_Java state.
863 thread->set_thread_state(state);
864 Threads_lock->unlock();
865 break;
866
867 case _thread_in_native_trans:
868 case _thread_blocked_trans:
869 case _thread_new_trans:
870 if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
871 thread->print_thread_state();
872 fatal("Deadlock in safepoint code. "
873 "Should have called back to the VM before blocking.");
874 }
875
876 // We transition the thread to state _thread_blocked here, but
877 // we can't do our usual check for external suspension and then
878 // self-suspend after the lock_without_safepoint_check() call
879 // below because we are often called during transitions while
880 // we hold different locks. That would leave us suspended while
881 // holding a resource which results in deadlocks.
882 thread->set_thread_state(_thread_blocked);
883
884 // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
885 // the safepoint code might still be waiting for it to block. We need to change the state here,
886 // so it can see that it is at a safepoint.
887
888 // Block until the safepoint operation is completed.
889 Threads_lock->lock_without_safepoint_check();
890
891 // Restore state
892 thread->set_thread_state(state);
893
894 Threads_lock->unlock();
895 break;
896
897 default:
898 fatal("Illegal threadstate encountered: %d", state);
899 }
900
901 // Check for pending. async. exceptions or suspends - except if the
902 // thread was blocked inside the VM. has_special_runtime_exit_condition()
903 // is called last since it grabs a lock and we only want to do that when
904 // we must.
905 //
906 // Note: we never deliver an async exception at a polling point as the
907 // compiler may not have an exception handler for it. The polling
908 // code will notice the async and deoptimize and the exception will
909 // be delivered. (Polling at a return point is ok though). Sure is
910 // a lot of bother for a deprecated feature...
911 //
912 // We don't deliver an async exception if the thread state is
913 // _thread_in_native_trans so JNI functions won't be called with
914 // a surprising pending exception. If the thread state is going back to java,
915 // async exception is checked in check_special_condition_for_native_trans().
916
917 if (state != _thread_blocked_trans &&
918 state != _thread_in_vm_trans &&
919 thread->has_special_runtime_exit_condition()) {
920 thread->handle_special_runtime_exit_condition(
921 !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
922 }
923 }
924
925 // ------------------------------------------------------------------------------------------------------
926 // Exception handlers
927
928
929 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
930 assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
931 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
932 if (!ThreadLocalHandshakes) {
933 assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
934 }
935
936 if (log_is_enabled(Debug, safepoint, stats)) {
937 Atomic::inc(&_nof_threads_hit_polling_page);
938 }
939
940 ThreadSafepointState* state = thread->safepoint_state();
941
942 state->handle_polling_page_exception();
943 }
944
945
946 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
947 if (!timeout_error_printed) {
948 timeout_error_printed = true;
949 // Print out the thread info which didn't reach the safepoint for debugging
950 // purposes (useful when there are lots of threads in the debugger).
951 LogTarget(Warning, safepoint) lt;
952 if (lt.is_enabled()) {
953 ResourceMark rm;
954 LogStream ls(lt);
955
956 ls.cr();
957 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
958 if (reason == _spinning_timeout) {
959 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
960 } else if (reason == _blocking_timeout) {
961 ls.print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
962 }
963
964 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
965 ThreadSafepointState *cur_state;
966 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
967 cur_state = cur_thread->safepoint_state();
968
969 if (cur_thread->thread_state() != _thread_blocked &&
970 ((reason == _spinning_timeout && cur_state->is_running()) ||
971 (reason == _blocking_timeout && !cur_state->has_called_back()))) {
972 ls.print("# ");
973 cur_thread->print_on(&ls);
974 ls.cr();
975 }
976 }
977 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
978 }
979 }
980
981 // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
982 // ShowMessageBoxOnError.
983 if (AbortVMOnSafepointTimeout) {
984 fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
985 SafepointTimeoutDelay, VMThread::vm_safepoint_description());
986 }
987 }
988
989
990 // -------------------------------------------------------------------------------------------------------
991 // Implementation of ThreadSafepointState
992
993 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
994 _thread = thread;
995 _type = _running;
996 _has_called_back = false;
997 _at_poll_safepoint = false;
998 }
999
1000 void ThreadSafepointState::create(JavaThread *thread) {
1001 ThreadSafepointState *state = new ThreadSafepointState(thread);
1002 thread->set_safepoint_state(state);
1003 }
1004
1005 void ThreadSafepointState::destroy(JavaThread *thread) {
1006 if (thread->safepoint_state()) {
1007 delete(thread->safepoint_state());
1008 thread->set_safepoint_state(NULL);
1009 }
1010 }
1011
1012 void ThreadSafepointState::examine_state_of_thread() {
1013 assert(is_running(), "better be running or just have hit safepoint poll");
1014
1015 JavaThreadState state = _thread->thread_state();
1016
1017 // Save the state at the start of safepoint processing.
1018 _orig_thread_state = state;
1019
1020 // Check for a thread that is suspended. Note that thread resume tries
1021 // to grab the Threads_lock which we own here, so a thread cannot be
1022 // resumed during safepoint synchronization.
1023
1024 // We check to see if this thread is suspended without locking to
1025 // avoid deadlocking with a third thread that is waiting for this
1026 // thread to be suspended. The third thread can notice the safepoint
1027 // that we're trying to start at the beginning of its SR_lock->wait()
1028 // call. If that happens, then the third thread will block on the
1029 // safepoint while still holding the underlying SR_lock. We won't be
1030 // able to get the SR_lock and we'll deadlock.
1031 //
1032 // We don't need to grab the SR_lock here for two reasons:
1033 // 1) The suspend flags are both volatile and are set with an
1034 // Atomic::cmpxchg() call so we should see the suspended
1035 // state right away.
1036 // 2) We're being called from the safepoint polling loop; if
1037 // we don't see the suspended state on this iteration, then
1038 // we'll come around again.
1039 //
1040 bool is_suspended = _thread->is_ext_suspended();
1041 if (is_suspended) {
1042 roll_forward(_at_safepoint);
1043 return;
1044 }
1045
1046 // Some JavaThread states have an initial safepoint state of
1047 // running, but are actually at a safepoint. We will happily
1048 // agree and update the safepoint state here.
1049 if (SafepointSynchronize::safepoint_safe(_thread, state)) {
1050 SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
1051 roll_forward(_at_safepoint);
1052 return;
1053 }
1054
1055 if (state == _thread_in_vm) {
1056 roll_forward(_call_back);
1057 return;
1058 }
1059
1060 // All other thread states will continue to run until they
1061 // transition and self-block in state _blocked
1062 // Safepoint polling in compiled code causes the Java threads to do the same.
1063 // Note: new threads may require a malloc so they must be allowed to finish
1064
1065 assert(is_running(), "examine_state_of_thread on non-running thread");
1066 return;
1067 }
1068
1069 // Returns true is thread could not be rolled forward at present position.
1070 void ThreadSafepointState::roll_forward(suspend_type type) {
1071 _type = type;
1072
1073 switch(_type) {
1074 case _at_safepoint:
1075 SafepointSynchronize::signal_thread_at_safepoint();
1076 DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
1077 if (_thread->in_critical()) {
1078 // Notice that this thread is in a critical section
1079 SafepointSynchronize::increment_jni_active_count();
1080 }
1081 break;
1082
1083 case _call_back:
1084 set_has_called_back(false);
1085 break;
1086
1087 case _running:
1088 default:
1089 ShouldNotReachHere();
1090 }
1091 }
1092
1093 void ThreadSafepointState::restart() {
1094 switch(type()) {
1095 case _at_safepoint:
1096 case _call_back:
1097 break;
1098
1099 case _running:
1100 default:
1101 tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
1102 p2i(_thread), _type);
1103 _thread->print();
1104 ShouldNotReachHere();
1105 }
1106 _type = _running;
1107 set_has_called_back(false);
1108 }
1109
1110
1111 void ThreadSafepointState::print_on(outputStream *st) const {
1112 const char *s = NULL;
1113
1114 switch(_type) {
1115 case _running : s = "_running"; break;
1116 case _at_safepoint : s = "_at_safepoint"; break;
1117 case _call_back : s = "_call_back"; break;
1118 default:
1119 ShouldNotReachHere();
1120 }
1121
1122 st->print_cr("Thread: " INTPTR_FORMAT
1123 " [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
1124 p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back,
1125 _at_poll_safepoint);
1126
1127 _thread->print_thread_state_on(st);
1128 }
1129
1130 // ---------------------------------------------------------------------------------------------------------------------
1131
1132 // Block the thread at poll or poll return for safepoint/handshake.
1133 void ThreadSafepointState::handle_polling_page_exception() {
1134
1135 // Check state. block() will set thread state to thread_in_vm which will
1136 // cause the safepoint state _type to become _call_back.
1137 suspend_type t = type();
1138 assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running,
1139 "polling page exception on thread not running state: %u", uint(t));
1140
1141 // Step 1: Find the nmethod from the return address
1142 address real_return_addr = thread()->saved_exception_pc();
1143
1144 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1145 assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1146 CompiledMethod* nm = (CompiledMethod*)cb;
1147
1148 // Find frame of caller
1149 frame stub_fr = thread()->last_frame();
1150 CodeBlob* stub_cb = stub_fr.cb();
1151 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1152 RegisterMap map(thread(), true);
1153 frame caller_fr = stub_fr.sender(&map);
1154
1155 // Should only be poll_return or poll
1156 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1157
1158 // This is a poll immediately before a return. The exception handling code
1159 // has already had the effect of causing the return to occur, so the execution
1160 // will continue immediately after the call. In addition, the oopmap at the
1161 // return point does not mark the return value as an oop (if it is), so
1162 // it needs a handle here to be updated.
1163 if( nm->is_at_poll_return(real_return_addr) ) {
1164 // See if return type is an oop.
1165 bool return_oop = nm->method()->is_returning_oop();
1166 Handle return_value;
1167 if (return_oop) {
1168 // The oop result has been saved on the stack together with all
1169 // the other registers. In order to preserve it over GCs we need
1170 // to keep it in a handle.
1171 oop result = caller_fr.saved_oop_result(&map);
1172 assert(oopDesc::is_oop_or_null(result), "must be oop");
1173 return_value = Handle(thread(), result);
1174 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1175 }
1176
1177 // Block the thread
1178 SafepointMechanism::block_if_requested(thread());
1179
1180 // restore oop result, if any
1181 if (return_oop) {
1182 caller_fr.set_saved_oop_result(&map, return_value());
1183 }
1184 }
1185
1186 // This is a safepoint poll. Verify the return address and block.
1187 else {
1188 set_at_poll_safepoint(true);
1189
1190 // verify the blob built the "return address" correctly
1191 assert(real_return_addr == caller_fr.pc(), "must match");
1192
1193 // Block the thread
1194 SafepointMechanism::block_if_requested(thread());
1195 set_at_poll_safepoint(false);
1196
1197 // If we have a pending async exception deoptimize the frame
1198 // as otherwise we may never deliver it.
1199 if (thread()->has_async_condition()) {
1200 ThreadInVMfromJavaNoAsyncException __tiv(thread());
1201 Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1202 }
1203
1204 // If an exception has been installed we must check for a pending deoptimization
1205 // Deoptimize frame if exception has been thrown.
1206
1207 if (thread()->has_pending_exception() ) {
1208 RegisterMap map(thread(), true);
1209 frame caller_fr = stub_fr.sender(&map);
1210 if (caller_fr.is_deoptimized_frame()) {
1211 // The exception patch will destroy registers that are still
1212 // live and will be needed during deoptimization. Defer the
1213 // Async exception should have deferred the exception until the
1214 // next safepoint which will be detected when we get into
1215 // the interpreter so if we have an exception now things
1216 // are messed up.
1217
1218 fatal("Exception installed and deoptimization is pending");
1219 }
1220 }
1221 }
1222 }
1223
1224
1225 //
1226 // Statistics & Instrumentations
1227 //
1228 struct SafepointStats {
1229 float _time_stamp; // record when the current safepoint occurs in seconds
1230 int _vmop_type; // tyep of VM operation triggers the safepoint
1231 int _nof_total_threads; // total number of Java threads
1232 int _nof_initial_running_threads; // total number of initially seen running threads
1233 int _nof_threads_wait_to_block; // total number of threads waiting for to block
1234 bool _page_armed; // true if polling page is armed, false otherwise
1235 int _nof_threads_hit_page_trap; // total number of threads hitting the page trap
1236 jlong _time_to_spin; // total time in millis spent in spinning
1237 jlong _time_to_wait_to_block; // total time in millis spent in waiting for to block
1238 jlong _time_to_do_cleanups; // total time in millis spent in performing cleanups
1239 jlong _time_to_sync; // total time in millis spent in getting to _synchronized
1240 jlong _time_to_exec_vmop; // total time in millis spent in vm operation itself
1241 };
1242
1243 static const int _statistics_header_count = 30;
1244 static int _cur_stat_index = 0;
1245 static SafepointStats safepoint_stats = {0}; // zero initialize
1246 static SafepointStats* spstat = &safepoint_stats;
1247
1248 static julong _safepoint_reasons[VM_Operation::VMOp_Terminating];
1249 static jlong _max_sync_time = 0;
1250 static jlong _max_vmop_time = 0;
1251
1252 static jlong cleanup_end_time = 0;
1253
1254 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1255
1256 spstat->_time_stamp = _ts_of_current_safepoint;
1257
1258 VM_Operation *op = VMThread::vm_operation();
1259 spstat->_vmop_type = op != NULL ? op->type() : VM_Operation::VMOp_None;
1260 _safepoint_reasons[spstat->_vmop_type]++;
1261
1262 spstat->_nof_total_threads = nof_threads;
1263 spstat->_nof_initial_running_threads = nof_running;
1264
1265 // Records the start time of spinning. The real time spent on spinning
1266 // will be adjusted when spin is done. Same trick is applied for time
1267 // spent on waiting for threads to block.
1268 if (nof_running != 0) {
1269 spstat->_time_to_spin = os::javaTimeNanos();
1270 } else {
1271 spstat->_time_to_spin = 0;
1272 }
1273 }
1274
1275 void SafepointSynchronize::update_statistics_on_spin_end() {
1276 jlong cur_time = os::javaTimeNanos();
1277
1278 spstat->_nof_threads_wait_to_block = _waiting_to_block;
1279 if (spstat->_nof_initial_running_threads != 0) {
1280 spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
1281 }
1282
1283 // Records the start time of waiting for to block. Updated when block is done.
1284 if (_waiting_to_block != 0) {
1285 spstat->_time_to_wait_to_block = cur_time;
1286 } else {
1287 spstat->_time_to_wait_to_block = 0;
1288 }
1289 }
1290
1291 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {
1292
1293 if (spstat->_nof_threads_wait_to_block != 0) {
1294 spstat->_time_to_wait_to_block = end_time -
1295 spstat->_time_to_wait_to_block;
1296 }
1297
1298 // Records the end time of sync which will be used to calculate the total
1299 // vm operation time. Again, the real time spending in syncing will be deducted
1300 // from the start of the sync time later when end_statistics is called.
1301 spstat->_time_to_sync = end_time - _safepoint_begin_time;
1302 if (spstat->_time_to_sync > _max_sync_time) {
1303 _max_sync_time = spstat->_time_to_sync;
1304 }
1305
1306 spstat->_time_to_do_cleanups = end_time;
1307 }
1308
1309 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1310
1311 // Record how long spent in cleanup tasks.
1312 spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1313 cleanup_end_time = end_time;
1314 }
1315
1316 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1317
1318 // Update the vm operation time.
1319 spstat->_time_to_exec_vmop = vmop_end_time - cleanup_end_time;
1320 if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1321 _max_vmop_time = spstat->_time_to_exec_vmop;
1322 }
1323
1324 spstat->_nof_threads_hit_page_trap = _nof_threads_hit_polling_page;
1325
1326 print_statistics();
1327 }
1328
1329 // Helper method to print the header.
1330 static void print_header(outputStream* st) {
1331 // The number of spaces is significant here, and should match the format
1332 // specifiers in print_statistics().
1333
1334 st->print(" vmop "
1335 "[ threads: total initially_running wait_to_block ]"
1336 "[ time: spin block sync cleanup vmop ] ");
1337
1338 st->print_cr("page_trap_count");
1339 }
1340
1341 // This prints a nice table. To get the statistics to not shift due to the logging uptime
1342 // decorator, use the option as: -Xlog:safepoint+stats=debug:[outputfile]:none
1343 void SafepointSynchronize::print_statistics() {
1344 LogTarget(Debug, safepoint, stats) lt;
1345 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
1346 LogStream ls(lt);
1347
1348 // Print header every 30 entries
1349 if ((_cur_stat_index % _statistics_header_count) == 0) {
1350 print_header(&ls);
1351 _cur_stat_index = 1; // wrap
1352 } else {
1353 _cur_stat_index++;
1354 }
1355
1356 ls.print("%8.3f: ", spstat->_time_stamp);
1357 ls.print("%-28s [ "
1358 INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " "
1359 "]",
1360 VM_Operation::name(spstat->_vmop_type),
1361 spstat->_nof_total_threads,
1362 spstat->_nof_initial_running_threads,
1363 spstat->_nof_threads_wait_to_block);
1364 // "/ MICROUNITS " is to convert the unit from nanos to millis.
1365 ls.print("[ "
1366 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1367 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1368 INT64_FORMAT_W(7) " ] ",
1369 (int64_t)(spstat->_time_to_spin / MICROUNITS),
1370 (int64_t)(spstat->_time_to_wait_to_block / MICROUNITS),
1371 (int64_t)(spstat->_time_to_sync / MICROUNITS),
1372 (int64_t)(spstat->_time_to_do_cleanups / MICROUNITS),
1373 (int64_t)(spstat->_time_to_exec_vmop / MICROUNITS));
1374
1375 ls.print_cr(INT32_FORMAT_W(15) " ", spstat->_nof_threads_hit_page_trap);
1376 }
1377
1378 // This method will be called when VM exits. This tries to summarize the sampling.
1379 // Current thread may already be deleted, so don't use ResourceMark.
1380 void SafepointSynchronize::print_stat_on_exit() {
1381
1382 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1383 if (_safepoint_reasons[index] != 0) {
1384 log_debug(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1385 _safepoint_reasons[index]);
1386 }
1387 }
1388
1389 log_debug(safepoint, stats)("VM operations coalesced during safepoint " INT64_FORMAT,
1390 _coalesced_vmop_count);
1391 log_debug(safepoint, stats)("Maximum sync time " INT64_FORMAT" ms",
1392 (int64_t)(_max_sync_time / MICROUNITS));
1393 log_debug(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
1394 INT64_FORMAT " ms",
1395 (int64_t)(_max_vmop_time / MICROUNITS));
1396 }