1 /*
2 * Copyright (c) 1997, 2016, 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/stringTable.hpp"
27 #include "classfile/symbolTable.hpp"
28 #include "classfile/systemDictionary.hpp"
29 #include "code/codeCache.hpp"
30 #include "code/icBuffer.hpp"
31 #include "code/nmethod.hpp"
32 #include "code/pcDesc.hpp"
33 #include "code/scopeDesc.hpp"
34 #include "gc/shared/collectedHeap.hpp"
35 #include "gc/shared/gcLocker.inline.hpp"
36 #include "interpreter/interpreter.hpp"
37 #include "logging/log.hpp"
38 #include "memory/resourceArea.hpp"
39 #include "memory/universe.inline.hpp"
40 #include "oops/oop.inline.hpp"
41 #include "oops/symbol.hpp"
42 #include "runtime/atomic.hpp"
43 #include "runtime/compilationPolicy.hpp"
44 #include "runtime/deoptimization.hpp"
45 #include "runtime/frame.inline.hpp"
46 #include "runtime/interfaceSupport.hpp"
47 #include "runtime/mutexLocker.hpp"
48 #include "runtime/orderAccess.inline.hpp"
49 #include "runtime/osThread.hpp"
50 #include "runtime/safepoint.hpp"
51 #include "runtime/signature.hpp"
52 #include "runtime/stubCodeGenerator.hpp"
53 #include "runtime/stubRoutines.hpp"
54 #include "runtime/sweeper.hpp"
55 #include "runtime/synchronizer.hpp"
56 #include "runtime/thread.inline.hpp"
57 #include "runtime/timerTrace.hpp"
58 #include "services/runtimeService.hpp"
59 #include "trace/tracing.hpp"
60 #include "trace/traceMacros.hpp"
61 #include "utilities/events.hpp"
62 #include "utilities/macros.hpp"
63 #if INCLUDE_ALL_GCS
64 #include "gc/shenandoah/shenandoahConcurrentThread.hpp"
65 #include "gc/cms/concurrentMarkSweepThread.hpp"
66 #include "gc/g1/suspendibleThreadSet.hpp"
67 #endif // INCLUDE_ALL_GCS
68 #ifdef COMPILER1
69 #include "c1/c1_globals.hpp"
70 #endif
71
72 // --------------------------------------------------------------------------------------------------
73 // Implementation of Safepoint begin/end
74
75 WorkGang* SafepointSynchronize::_cleanup_workers = NULL;
76
77 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
78 volatile int SafepointSynchronize::_waiting_to_block = 0;
79 volatile int SafepointSynchronize::_safepoint_counter = 0;
80 int SafepointSynchronize::_current_jni_active_count = 0;
81 long SafepointSynchronize::_end_of_last_safepoint = 0;
82 static volatile int PageArmed = 0 ; // safepoint polling page is RO|RW vs PROT_NONE
83 static volatile int TryingToBlock = 0 ; // proximate value -- for advisory use only
84 static bool timeout_error_printed = false;
85
86 // Roll all threads forward to a safepoint and suspend them all
87 void SafepointSynchronize::begin() {
88 EventSafepointBegin begin_event;
89 Thread* myThread = Thread::current();
90 assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint");
91
92 if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {
93 _safepoint_begin_time = os::javaTimeNanos();
94 _ts_of_current_safepoint = tty->time_stamp().seconds();
95 }
96
97 #if INCLUDE_ALL_GCS
98 if (UseConcMarkSweepGC) {
99 // In the future we should investigate whether CMS can use the
100 // more-general mechanism below. DLD (01/05).
101 ConcurrentMarkSweepThread::synchronize(false);
102 } else if (UseG1GC) {
103 SuspendibleThreadSet::synchronize();
104 }
105 #endif // INCLUDE_ALL_GCS
106
107 // By getting the Threads_lock, we assure that no threads are about to start or
108 // exit. It is released again in SafepointSynchronize::end().
109 Threads_lock->lock();
110
111 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
112
113 int nof_threads = Threads::number_of_threads();
114
115 log_debug(safepoint)("Safepoint synchronization initiated. (%d)", nof_threads);
116
117 RuntimeService::record_safepoint_begin();
118
119 MutexLocker mu(Safepoint_lock);
120
121 // Reset the count of active JNI critical threads
122 _current_jni_active_count = 0;
123
124 // Set number of threads to wait for, before we initiate the callbacks
125 _waiting_to_block = nof_threads;
126 TryingToBlock = 0 ;
127 int still_running = nof_threads;
128
129 // Save the starting time, so that it can be compared to see if this has taken
130 // too long to complete.
131 jlong safepoint_limit_time = 0;
132 timeout_error_printed = false;
133
134 // PrintSafepointStatisticsTimeout can be specified separately. When
135 // specified, PrintSafepointStatistics will be set to true in
136 // deferred_initialize_stat method. The initialization has to be done
137 // early enough to avoid any races. See bug 6880029 for details.
138 if (PrintSafepointStatistics || PrintSafepointStatisticsTimeout > 0) {
139 deferred_initialize_stat();
140 }
141
142 // Begin the process of bringing the system to a safepoint.
143 // Java threads can be in several different states and are
144 // stopped by different mechanisms:
145 //
146 // 1. Running interpreted
147 // The interpreter dispatch table is changed to force it to
148 // check for a safepoint condition between bytecodes.
149 // 2. Running in native code
150 // When returning from the native code, a Java thread must check
151 // the safepoint _state to see if we must block. If the
152 // VM thread sees a Java thread in native, it does
153 // not wait for this thread to block. The order of the memory
154 // writes and reads of both the safepoint state and the Java
155 // threads state is critical. In order to guarantee that the
156 // memory writes are serialized with respect to each other,
157 // the VM thread issues a memory barrier instruction
158 // (on MP systems). In order to avoid the overhead of issuing
159 // a memory barrier for each Java thread making native calls, each Java
160 // thread performs a write to a single memory page after changing
161 // the thread state. The VM thread performs a sequence of
162 // mprotect OS calls which forces all previous writes from all
163 // Java threads to be serialized. This is done in the
164 // os::serialize_thread_states() call. This has proven to be
165 // much more efficient than executing a membar instruction
166 // on every call to native code.
167 // 3. Running compiled Code
168 // Compiled code reads a global (Safepoint Polling) page that
169 // is set to fault if we are trying to get to a safepoint.
170 // 4. Blocked
171 // A thread which is blocked will not be allowed to return from the
172 // block condition until the safepoint operation is complete.
173 // 5. In VM or Transitioning between states
174 // If a Java thread is currently running in the VM or transitioning
175 // between states, the safepointing code will wait for the thread to
176 // block itself when it attempts transitions to a new state.
177 //
178 {
179 EventSafepointStateSynchronization sync_event;
180 int initial_running = 0;
181
182 _state = _synchronizing;
183 OrderAccess::fence();
184
185 // Flush all thread states to memory
186 if (!UseMembar) {
187 os::serialize_thread_states();
188 }
189
190 // Make interpreter safepoint aware
191 Interpreter::notice_safepoints();
192
193 if (DeferPollingPageLoopCount < 0) {
194 // Make polling safepoint aware
195 guarantee (PageArmed == 0, "invariant") ;
196 PageArmed = 1 ;
197 os::make_polling_page_unreadable();
198 }
199
200 // Consider using active_processor_count() ... but that call is expensive.
201 int ncpus = os::processor_count() ;
202
203 #ifdef ASSERT
204 for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
205 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
206 // Clear the visited flag to ensure that the critical counts are collected properly.
207 cur->set_visited_for_critical_count(false);
208 }
209 #endif // ASSERT
210
211 if (SafepointTimeout)
212 safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;
213
214 // Iterate through all threads until it have been determined how to stop them all at a safepoint
215 unsigned int iterations = 0;
216 int steps = 0 ;
217 while(still_running > 0) {
218 for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
219 assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");
220 ThreadSafepointState *cur_state = cur->safepoint_state();
221 if (cur_state->is_running()) {
222 cur_state->examine_state_of_thread();
223 if (!cur_state->is_running()) {
224 still_running--;
225 // consider adjusting steps downward:
226 // steps = 0
227 // steps -= NNN
228 // steps >>= 1
229 // steps = MIN(steps, 2000-100)
230 // if (iterations != 0) steps -= NNN
231 }
232 if (log_is_enabled(Trace, safepoint)) {
233 ResourceMark rm;
234 cur_state->print_on(Log(safepoint)::trace_stream());
235 }
236 }
237 }
238
239 if (iterations == 0) {
240 initial_running = still_running;
241 if (PrintSafepointStatistics) {
242 begin_statistics(nof_threads, still_running);
243 }
244 }
245
246 if (still_running > 0) {
247 // Check for if it takes to long
248 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
249 print_safepoint_timeout(_spinning_timeout);
250 }
251
252 // Spin to avoid context switching.
253 // There's a tension between allowing the mutators to run (and rendezvous)
254 // vs spinning. As the VM thread spins, wasting cycles, it consumes CPU that
255 // a mutator might otherwise use profitably to reach a safepoint. Excessive
256 // spinning by the VM thread on a saturated system can increase rendezvous latency.
257 // Blocking or yielding incur their own penalties in the form of context switching
258 // and the resultant loss of $ residency.
259 //
260 // Further complicating matters is that yield() does not work as naively expected
261 // on many platforms -- yield() does not guarantee that any other ready threads
262 // will run. As such we revert to naked_short_sleep() after some number of iterations.
263 // nakes_short_sleep() is implemented as a short unconditional sleep.
264 // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping
265 // can actually increase the time it takes the VM thread to detect that a system-wide
266 // stop-the-world safepoint has been reached. In a pathological scenario such as that
267 // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.
268 // In that case the mutators will be stalled waiting for the safepoint to complete and the
269 // the VMthread will be sleeping, waiting for the mutators to rendezvous. The VMthread
270 // will eventually wake up and detect that all mutators are safe, at which point
271 // we'll again make progress.
272 //
273 // Beware too that that the VMThread typically runs at elevated priority.
274 // Its default priority is higher than the default mutator priority.
275 // Obviously, this complicates spinning.
276 //
277 // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).
278 // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.
279 //
280 // See the comments in synchronizer.cpp for additional remarks on spinning.
281 //
282 // In the future we might:
283 // 1. Modify the safepoint scheme to avoid potentially unbounded spinning.
284 // This is tricky as the path used by a thread exiting the JVM (say on
285 // on JNI call-out) simply stores into its state field. The burden
286 // is placed on the VM thread, which must poll (spin).
287 // 2. Find something useful to do while spinning. If the safepoint is GC-related
288 // we might aggressively scan the stacks of threads that are already safe.
289 // 3. Use Solaris schedctl to examine the state of the still-running mutators.
290 // If all the mutators are ONPROC there's no reason to sleep or yield.
291 // 4. YieldTo() any still-running mutators that are ready but OFFPROC.
292 // 5. Check system saturation. If the system is not fully saturated then
293 // simply spin and avoid sleep/yield.
294 // 6. As still-running mutators rendezvous they could unpark the sleeping
295 // VMthread. This works well for still-running mutators that become
296 // safe. The VMthread must still poll for mutators that call-out.
297 // 7. Drive the policy on time-since-begin instead of iterations.
298 // 8. Consider making the spin duration a function of the # of CPUs:
299 // Spin = (((ncpus-1) * M) + K) + F(still_running)
300 // Alternately, instead of counting iterations of the outer loop
301 // we could count the # of threads visited in the inner loop, above.
302 // 9. On windows consider using the return value from SwitchThreadTo()
303 // to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
304
305 if (int(iterations) == DeferPollingPageLoopCount) {
306 guarantee (PageArmed == 0, "invariant") ;
307 PageArmed = 1 ;
308 os::make_polling_page_unreadable();
309 }
310
311 // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
312 // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
313 ++steps ;
314 if (ncpus > 1 && steps < SafepointSpinBeforeYield) {
315 SpinPause() ; // MP-Polite spin
316 } else
317 if (steps < DeferThrSuspendLoopCount) {
318 os::naked_yield() ;
319 } else {
320 os::naked_short_sleep(1);
321 }
322
323 iterations ++ ;
324 }
325 assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
326 }
327 assert(still_running == 0, "sanity check");
328
329 if (PrintSafepointStatistics) {
330 update_statistics_on_spin_end();
331 }
332
333 if (sync_event.should_commit()) {
334 sync_event.set_safepointId(safepoint_counter());
335 sync_event.set_initialThreadCount(initial_running);
336 sync_event.set_runningThreadCount(_waiting_to_block);
337 sync_event.set_iterations(iterations);
338 sync_event.commit();
339 }
340 } //EventSafepointStateSync
341
342 // wait until all threads are stopped
343 {
344 EventSafepointWaitBlocked wait_blocked_event;
345 int initial_waiting_to_block = _waiting_to_block;
346
347 while (_waiting_to_block > 0) {
348 log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block);
349 if (!SafepointTimeout || timeout_error_printed) {
350 Safepoint_lock->wait(true); // true, means with no safepoint checks
351 } else {
352 // Compute remaining time
353 jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
354
355 // If there is no remaining time, then there is an error
356 if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
357 print_safepoint_timeout(_blocking_timeout);
358 }
359 }
360 }
361 assert(_waiting_to_block == 0, "sanity check");
362
363 #ifndef PRODUCT
364 if (SafepointTimeout) {
365 jlong current_time = os::javaTimeNanos();
366 if (safepoint_limit_time < current_time) {
367 tty->print_cr("# SafepointSynchronize: Finished after "
368 INT64_FORMAT_W(6) " ms",
369 ((current_time - safepoint_limit_time) / MICROUNITS +
370 (jlong)SafepointTimeoutDelay));
371 }
372 }
373 #endif
374
375 assert((_safepoint_counter & 0x1) == 0, "must be even");
376 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
377 _safepoint_counter ++;
378
379 // Record state
380 _state = _synchronized;
381
382 OrderAccess::fence();
383
384 if (wait_blocked_event.should_commit()) {
385 wait_blocked_event.set_safepointId(safepoint_counter());
386 wait_blocked_event.set_runningThreadCount(initial_waiting_to_block);
387 wait_blocked_event.commit();
388 }
389 } // EventSafepointWaitBlocked
390
391 #ifdef ASSERT
392 for (JavaThread *cur = Threads::first(); cur != NULL; cur = cur->next()) {
393 // make sure all the threads were visited
394 assert(cur->was_visited_for_critical_count(), "missed a thread");
395 }
396 #endif // ASSERT
397
398 // Update the count of active JNI critical regions
399 GCLocker::set_jni_lock_count(_current_jni_active_count);
400
401 if (log_is_enabled(Debug, safepoint)) {
402 VM_Operation *op = VMThread::vm_operation();
403 log_debug(safepoint)("Entering safepoint region: %s",
404 (op != NULL) ? op->name() : "no vm operation");
405 }
406
407 RuntimeService::record_safepoint_synchronized();
408 if (PrintSafepointStatistics) {
409 update_statistics_on_sync_end(os::javaTimeNanos());
410 }
411
412 // Call stuff that needs to be run when a safepoint is just about to be completed
413 {
414 EventSafepointCleanup cleanup_event;
415 do_cleanup_tasks();
416 if (cleanup_event.should_commit()) {
417 cleanup_event.set_safepointId(safepoint_counter());
418 cleanup_event.commit();
419 }
420 }
421
422 if (PrintSafepointStatistics) {
423 // Record how much time spend on the above cleanup tasks
424 update_statistics_on_cleanup_end(os::javaTimeNanos());
425 }
426 if (begin_event.should_commit()) {
427 begin_event.set_safepointId(safepoint_counter());
428 begin_event.set_totalThreadCount(nof_threads);
429 begin_event.set_jniCriticalThreadCount(_current_jni_active_count);
430 begin_event.commit();
431 }
432 }
433
434 // Wake up all threads, so they are ready to resume execution after the safepoint
435 // operation has been carried out
436 void SafepointSynchronize::end() {
437 EventSafepointEnd event;
438 int safepoint_id = safepoint_counter(); // Keep the odd counter as "id"
439
440 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
441 assert((_safepoint_counter & 0x1) == 1, "must be odd");
442 _safepoint_counter ++;
443 // memory fence isn't required here since an odd _safepoint_counter
444 // value can do no harm and a fence is issued below anyway.
445
446 DEBUG_ONLY(Thread* myThread = Thread::current();)
447 assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
448
449 if (PrintSafepointStatistics) {
450 end_statistics(os::javaTimeNanos());
451 }
452
453 #ifdef ASSERT
454 // A pending_exception cannot be installed during a safepoint. The threads
455 // may install an async exception after they come back from a safepoint into
456 // pending_exception after they unblock. But that should happen later.
457 for(JavaThread *cur = Threads::first(); cur; cur = cur->next()) {
458 assert (!(cur->has_pending_exception() &&
459 cur->safepoint_state()->is_at_poll_safepoint()),
460 "safepoint installed a pending exception");
461 }
462 #endif // ASSERT
463
464 if (PageArmed) {
465 // Make polling safepoint aware
466 os::make_polling_page_readable();
467 PageArmed = 0 ;
468 }
469
470 // Remove safepoint check from interpreter
471 Interpreter::ignore_safepoints();
472
473 {
474 MutexLocker mu(Safepoint_lock);
475
476 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
477
478 // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
479 // when they get restarted.
480 _state = _not_synchronized;
481 OrderAccess::fence();
482
483 log_debug(safepoint)("Leaving safepoint region");
484
485 // Start suspended threads
486 for(JavaThread *current = Threads::first(); current; current = current->next()) {
487 // A problem occurring on Solaris is when attempting to restart threads
488 // the first #cpus - 1 go well, but then the VMThread is preempted when we get
489 // to the next one (since it has been running the longest). We then have
490 // to wait for a cpu to become available before we can continue restarting
491 // threads.
492 // FIXME: This causes the performance of the VM to degrade when active and with
493 // large numbers of threads. Apparently this is due to the synchronous nature
494 // of suspending threads.
495 //
496 // TODO-FIXME: the comments above are vestigial and no longer apply.
497 // Furthermore, using solaris' schedctl in this particular context confers no benefit
498 if (VMThreadHintNoPreempt) {
499 os::hint_no_preempt();
500 }
501 ThreadSafepointState* cur_state = current->safepoint_state();
502 assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
503 cur_state->restart();
504 assert(cur_state->is_running(), "safepoint state has not been reset");
505 }
506
507 RuntimeService::record_safepoint_end();
508
509 // Release threads lock, so threads can be created/destroyed again. It will also starts all threads
510 // blocked in signal_thread_blocked
511 Threads_lock->unlock();
512
513 }
514 #if INCLUDE_ALL_GCS
515 // If there are any concurrent GC threads resume them.
516 if (UseConcMarkSweepGC) {
517 ConcurrentMarkSweepThread::desynchronize(false);
518 } else if (UseG1GC) {
519 SuspendibleThreadSet::desynchronize();
520 }
521 #endif // INCLUDE_ALL_GCS
522 // record this time so VMThread can keep track how much time has elapsed
523 // since last safepoint.
524 _end_of_last_safepoint = os::javaTimeMillis();
525
526 if (event.should_commit()) {
527 event.set_safepointId(safepoint_id);
528 event.commit();
529 }
530 }
531
532 bool SafepointSynchronize::is_cleanup_needed() {
533 // Need a safepoint if some inline cache buffers is non-empty
534 if (!InlineCacheBuffer::is_empty()) return true;
535 return false;
536 }
537
538 static void event_safepoint_cleanup_task_commit(EventSafepointCleanupTask& event, const char* name) {
539 if (event.should_commit()) {
540 event.set_safepointId(SafepointSynchronize::safepoint_counter());
541 event.set_name(name);
542 event.commit();
543 }
544 }
545
546 // Various cleaning tasks that should be done periodically at safepoints
547 void SafepointSynchronize::do_cleanup_tasks() {
548 VM_Operation* op = VMThread::vm_operation();
549 // If op does both deflating and nmethod marking, we don't bother firing up
550 // the workers.
551 bool op_does_cleanup = op != NULL && op->marks_nmethods() && op->deflates_idle_monitors();
552 if (ParallelSPCleanup && ! op_does_cleanup) {
553 parallel_cleanup();
554 } else {
555 serial_cleanup();
556 }
557 }
558
559 void SafepointSynchronize::serial_cleanup() {
560 VM_Operation* op = VMThread::vm_operation();
561 {
562 const char* name = "deflating idle monitors";
563 EventSafepointCleanupTask event;
564 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
565 ObjectSynchronizer::deflate_idle_monitors(op == NULL || ! op->deflates_idle_monitors());
566 event_safepoint_cleanup_task_commit(event, name);
567 }
568
569 {
570 const char* name = "updating inline caches";
571 EventSafepointCleanupTask event;
572 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
573 InlineCacheBuffer::update_inline_caches();
574 event_safepoint_cleanup_task_commit(event, name);
575 }
576 {
577 const char* name = "compilation policy safepoint handler";
578 EventSafepointCleanupTask event;
579 TraceTime timer("compilation policy safepoint handler", TRACETIME_LOG(Info, safepoint, cleanup));
580 CompilationPolicy::policy()->do_safepoint_work();
581 event_safepoint_cleanup_task_commit(event, name);
582 }
583
584 if (op == NULL || ! op->marks_nmethods()) {
585 const char* name = "mark nmethods";
586 EventSafepointCleanupTask event;
587 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
588 NMethodSweeper::mark_active_nmethods();
589 event_safepoint_cleanup_task_commit(event, name);
590 }
591
592 if (SymbolTable::needs_rehashing()) {
593 const char* name = "rehashing symbol table";
594 EventSafepointCleanupTask event;
595 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
596 SymbolTable::rehash_table();
597 event_safepoint_cleanup_task_commit(event, name);
598 }
599
600 if (StringTable::needs_rehashing()) {
601 const char* name = "rehashing string table";
602 EventSafepointCleanupTask event;
603 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
604 StringTable::rehash_table();
605 event_safepoint_cleanup_task_commit(event, name);
606 }
607
608 {
609 // CMS delays purging the CLDG until the beginning of the next safepoint and to
610 // make sure concurrent sweep is done
611 const char* name = "purging class loader data graph";
612 EventSafepointCleanupTask event;
613 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
614 ClassLoaderDataGraph::purge_if_needed();
615 event_safepoint_cleanup_task_commit(event, name);
616 }
617 }
618
619 class ParallelSPCleanupThreadClosure : public ThreadClosure {
620 private:
621 bool _do_deflate_idle_monitors;
622 CodeBlobClosure* _nmethod_cl;
623
624 public:
625 ParallelSPCleanupThreadClosure() {
626 VM_Operation* op = VMThread::vm_operation();
627 _do_deflate_idle_monitors = op == NULL || ! op->deflates_idle_monitors();
628 if (op == NULL || ! op->marks_nmethods()) {
629 _nmethod_cl = NMethodSweeper::prepare_mark_active_nmethods();
630 } else {
631 _nmethod_cl = NULL;
632 }
633 }
634
635 void do_thread(Thread* thread) {
636 if (_do_deflate_idle_monitors) {
637 ObjectSynchronizer::deflate_idle_monitors_and_oops_do(thread, NULL);
638 }
639 if (_nmethod_cl != NULL) {
640 if (thread->is_Java_thread()) {
641 JavaThread* jt = (JavaThread*) thread;
642 if(! jt->is_Code_cache_sweeper_thread()) {
643 jt->nmethods_do(_nmethod_cl);
644 }
645 }
646 }
647 }
648 };
649
650 class ParallelSPCleanupTask : public AbstractGangTask {
651 private:
652 SubTasksDone _subtasks;
653 public:
654 ParallelSPCleanupTask() :
655 AbstractGangTask("Parallel Safepoint Cleanup"),
656 _subtasks(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS) {}
657
658 void work(uint worker_id) {
659 // All threads deflate monitors and mark nmethods (if necessary).
660 ParallelSPCleanupThreadClosure cleanup_threads_cl;
661 Threads::parallel_java_threads_do(&cleanup_threads_cl);
662
663 if (! _subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
664 const char* name = "deflating idle monitors";
665 EventSafepointCleanupTask event;
666 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
667 ObjectSynchronizer::deflate_idle_monitors(false);
668 event_safepoint_cleanup_task_commit(event, name);
669 }
670 if (! _subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
671 const char* name = "updating inline caches";
672 EventSafepointCleanupTask event;
673 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
674 InlineCacheBuffer::update_inline_caches();
675 event_safepoint_cleanup_task_commit(event, name);
676 }
677
678 if (! _subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
679 const char* name = "rehashing symbol table";
680 EventSafepointCleanupTask event;
681 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
682 SymbolTable::rehash_table();
683 event_safepoint_cleanup_task_commit(event, name);
684 }
685
686 if (! _subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
687 const char* name = "rehashing string table";
688 EventSafepointCleanupTask event;
689 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
690 StringTable::rehash_table();
691 event_safepoint_cleanup_task_commit(event, name);
692 }
693
694 if (! _subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
695 // CMS delays purging the CLDG until the beginning of the next safepoint and to
696 // make sure concurrent sweep is done
697 const char* name = "purging class loader data graph";
698 EventSafepointCleanupTask event;
699 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
700 ClassLoaderDataGraph::purge_if_needed();
701 event_safepoint_cleanup_task_commit(event, name);
702 }
703 }
704 };
705
706 void SafepointSynchronize::parallel_cleanup() {
707 // Deferred init
708 if (_cleanup_workers == NULL) {
709 _cleanup_workers = new WorkGang("Parallel Safepoint Cleanup", ParallelSPCleanupThreads, false, false);
710 _cleanup_workers->initialize_workers();
711 }
712
713 StrongRootsScope srs(_cleanup_workers->active_workers());
714 ParallelSPCleanupTask cleanup_task;
715 _cleanup_workers->run_task(&cleanup_task);
716 }
717
718 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
719 switch(state) {
720 case _thread_in_native:
721 // native threads are safe if they have no java stack or have walkable stack
722 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
723
724 // blocked threads should have already have walkable stack
725 case _thread_blocked:
726 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
727 return true;
728
729 default:
730 return false;
731 }
732 }
733
734
735 // See if the thread is running inside a lazy critical native and
736 // update the thread critical count if so. Also set a suspend flag to
737 // cause the native wrapper to return into the JVM to do the unlock
738 // once the native finishes.
739 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
740 if (state == _thread_in_native &&
741 thread->has_last_Java_frame() &&
742 thread->frame_anchor()->walkable()) {
743 // This thread might be in a critical native nmethod so look at
744 // the top of the stack and increment the critical count if it
745 // is.
746 frame wrapper_frame = thread->last_frame();
747 CodeBlob* stub_cb = wrapper_frame.cb();
748 if (stub_cb != NULL &&
749 stub_cb->is_nmethod() &&
750 stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
751 // A thread could potentially be in a critical native across
752 // more than one safepoint, so only update the critical state on
753 // the first one. When it returns it will perform the unlock.
754 if (!thread->do_critical_native_unlock()) {
755 #ifdef ASSERT
756 if (!thread->in_critical()) {
757 GCLocker::increment_debug_jni_lock_count();
758 }
759 #endif
760 thread->enter_critical();
761 // Make sure the native wrapper calls back on return to
762 // perform the needed critical unlock.
763 thread->set_critical_native_unlock();
764 }
765 }
766 }
767 }
768
769
770
771 // -------------------------------------------------------------------------------------------------------
772 // Implementation of Safepoint callback point
773
774 void SafepointSynchronize::block(JavaThread *thread) {
775 assert(thread != NULL, "thread must be set");
776 assert(thread->is_Java_thread(), "not a Java thread");
777
778 // Threads shouldn't block if they are in the middle of printing, but...
779 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
780
781 // Only bail from the block() call if the thread is gone from the
782 // thread list; starting to exit should still block.
783 if (thread->is_terminated()) {
784 // block current thread if we come here from native code when VM is gone
785 thread->block_if_vm_exited();
786
787 // otherwise do nothing
788 return;
789 }
790
791 JavaThreadState state = thread->thread_state();
792 thread->frame_anchor()->make_walkable(thread);
793
794 // Check that we have a valid thread_state at this point
795 switch(state) {
796 case _thread_in_vm_trans:
797 case _thread_in_Java: // From compiled code
798
799 // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
800 // we pretend we are still in the VM.
801 thread->set_thread_state(_thread_in_vm);
802
803 if (is_synchronizing()) {
804 Atomic::inc (&TryingToBlock) ;
805 }
806
807 // We will always be holding the Safepoint_lock when we are examine the state
808 // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
809 // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
810 Safepoint_lock->lock_without_safepoint_check();
811 if (is_synchronizing()) {
812 // Decrement the number of threads to wait for and signal vm thread
813 assert(_waiting_to_block > 0, "sanity check");
814 _waiting_to_block--;
815 thread->safepoint_state()->set_has_called_back(true);
816
817 DEBUG_ONLY(thread->set_visited_for_critical_count(true));
818 if (thread->in_critical()) {
819 // Notice that this thread is in a critical section
820 increment_jni_active_count();
821 }
822
823 // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
824 if (_waiting_to_block == 0) {
825 Safepoint_lock->notify_all();
826 }
827 }
828
829 // We transition the thread to state _thread_blocked here, but
830 // we can't do our usual check for external suspension and then
831 // self-suspend after the lock_without_safepoint_check() call
832 // below because we are often called during transitions while
833 // we hold different locks. That would leave us suspended while
834 // holding a resource which results in deadlocks.
835 thread->set_thread_state(_thread_blocked);
836 Safepoint_lock->unlock();
837
838 // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
839 // the entire safepoint, the threads will all line up here during the safepoint.
840 Threads_lock->lock_without_safepoint_check();
841 // restore original state. This is important if the thread comes from compiled code, so it
842 // will continue to execute with the _thread_in_Java state.
843 thread->set_thread_state(state);
844 Threads_lock->unlock();
845 break;
846
847 case _thread_in_native_trans:
848 case _thread_blocked_trans:
849 case _thread_new_trans:
850 if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
851 thread->print_thread_state();
852 fatal("Deadlock in safepoint code. "
853 "Should have called back to the VM before blocking.");
854 }
855
856 // We transition the thread to state _thread_blocked here, but
857 // we can't do our usual check for external suspension and then
858 // self-suspend after the lock_without_safepoint_check() call
859 // below because we are often called during transitions while
860 // we hold different locks. That would leave us suspended while
861 // holding a resource which results in deadlocks.
862 thread->set_thread_state(_thread_blocked);
863
864 // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
865 // the safepoint code might still be waiting for it to block. We need to change the state here,
866 // so it can see that it is at a safepoint.
867
868 // Block until the safepoint operation is completed.
869 Threads_lock->lock_without_safepoint_check();
870
871 // Restore state
872 thread->set_thread_state(state);
873
874 Threads_lock->unlock();
875 break;
876
877 default:
878 fatal("Illegal threadstate encountered: %d", state);
879 }
880
881 // Check for pending. async. exceptions or suspends - except if the
882 // thread was blocked inside the VM. has_special_runtime_exit_condition()
883 // is called last since it grabs a lock and we only want to do that when
884 // we must.
885 //
886 // Note: we never deliver an async exception at a polling point as the
887 // compiler may not have an exception handler for it. The polling
888 // code will notice the async and deoptimize and the exception will
889 // be delivered. (Polling at a return point is ok though). Sure is
890 // a lot of bother for a deprecated feature...
891 //
892 // We don't deliver an async exception if the thread state is
893 // _thread_in_native_trans so JNI functions won't be called with
894 // a surprising pending exception. If the thread state is going back to java,
895 // async exception is checked in check_special_condition_for_native_trans().
896
897 if (state != _thread_blocked_trans &&
898 state != _thread_in_vm_trans &&
899 thread->has_special_runtime_exit_condition()) {
900 thread->handle_special_runtime_exit_condition(
901 !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
902 }
903 }
904
905 // ------------------------------------------------------------------------------------------------------
906 // Exception handlers
907
908
909 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
910 assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
911 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
912 assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
913
914 if (ShowSafepointMsgs) {
915 tty->print("handle_polling_page_exception: ");
916 }
917
918 if (PrintSafepointStatistics) {
919 inc_page_trap_count();
920 }
921
922 ThreadSafepointState* state = thread->safepoint_state();
923
924 state->handle_polling_page_exception();
925 }
926
927
928 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
929 if (!timeout_error_printed) {
930 timeout_error_printed = true;
931 // Print out the thread info which didn't reach the safepoint for debugging
932 // purposes (useful when there are lots of threads in the debugger).
933 tty->cr();
934 tty->print_cr("# SafepointSynchronize::begin: Timeout detected:");
935 if (reason == _spinning_timeout) {
936 tty->print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
937 } else if (reason == _blocking_timeout) {
938 tty->print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
939 }
940
941 tty->print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
942 ThreadSafepointState *cur_state;
943 ResourceMark rm;
944 for(JavaThread *cur_thread = Threads::first(); cur_thread;
945 cur_thread = cur_thread->next()) {
946 cur_state = cur_thread->safepoint_state();
947
948 if (cur_thread->thread_state() != _thread_blocked &&
949 ((reason == _spinning_timeout && cur_state->is_running()) ||
950 (reason == _blocking_timeout && !cur_state->has_called_back()))) {
951 tty->print("# ");
952 cur_thread->print();
953 tty->cr();
954 }
955 }
956 tty->print_cr("# SafepointSynchronize::begin: (End of list)");
957 }
958
959 // To debug the long safepoint, specify both DieOnSafepointTimeout &
960 // ShowMessageBoxOnError.
961 if (DieOnSafepointTimeout) {
962 VM_Operation *op = VMThread::vm_operation();
963 fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
964 SafepointTimeoutDelay,
965 op != NULL ? op->name() : "no vm operation");
966 }
967 }
968
969
970 // -------------------------------------------------------------------------------------------------------
971 // Implementation of ThreadSafepointState
972
973 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
974 _thread = thread;
975 _type = _running;
976 _has_called_back = false;
977 _at_poll_safepoint = false;
978 }
979
980 void ThreadSafepointState::create(JavaThread *thread) {
981 ThreadSafepointState *state = new ThreadSafepointState(thread);
982 thread->set_safepoint_state(state);
983 }
984
985 void ThreadSafepointState::destroy(JavaThread *thread) {
986 if (thread->safepoint_state()) {
987 delete(thread->safepoint_state());
988 thread->set_safepoint_state(NULL);
989 }
990 }
991
992 void ThreadSafepointState::examine_state_of_thread() {
993 assert(is_running(), "better be running or just have hit safepoint poll");
994
995 JavaThreadState state = _thread->thread_state();
996
997 // Save the state at the start of safepoint processing.
998 _orig_thread_state = state;
999
1000 // Check for a thread that is suspended. Note that thread resume tries
1001 // to grab the Threads_lock which we own here, so a thread cannot be
1002 // resumed during safepoint synchronization.
1003
1004 // We check to see if this thread is suspended without locking to
1005 // avoid deadlocking with a third thread that is waiting for this
1006 // thread to be suspended. The third thread can notice the safepoint
1007 // that we're trying to start at the beginning of its SR_lock->wait()
1008 // call. If that happens, then the third thread will block on the
1009 // safepoint while still holding the underlying SR_lock. We won't be
1010 // able to get the SR_lock and we'll deadlock.
1011 //
1012 // We don't need to grab the SR_lock here for two reasons:
1013 // 1) The suspend flags are both volatile and are set with an
1014 // Atomic::cmpxchg() call so we should see the suspended
1015 // state right away.
1016 // 2) We're being called from the safepoint polling loop; if
1017 // we don't see the suspended state on this iteration, then
1018 // we'll come around again.
1019 //
1020 bool is_suspended = _thread->is_ext_suspended();
1021 if (is_suspended) {
1022 roll_forward(_at_safepoint);
1023 return;
1024 }
1025
1026 // Some JavaThread states have an initial safepoint state of
1027 // running, but are actually at a safepoint. We will happily
1028 // agree and update the safepoint state here.
1029 if (SafepointSynchronize::safepoint_safe(_thread, state)) {
1030 SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
1031 roll_forward(_at_safepoint);
1032 return;
1033 }
1034
1035 if (state == _thread_in_vm) {
1036 roll_forward(_call_back);
1037 return;
1038 }
1039
1040 // All other thread states will continue to run until they
1041 // transition and self-block in state _blocked
1042 // Safepoint polling in compiled code causes the Java threads to do the same.
1043 // Note: new threads may require a malloc so they must be allowed to finish
1044
1045 assert(is_running(), "examine_state_of_thread on non-running thread");
1046 return;
1047 }
1048
1049 // Returns true is thread could not be rolled forward at present position.
1050 void ThreadSafepointState::roll_forward(suspend_type type) {
1051 _type = type;
1052
1053 switch(_type) {
1054 case _at_safepoint:
1055 SafepointSynchronize::signal_thread_at_safepoint();
1056 DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
1057 if (_thread->in_critical()) {
1058 // Notice that this thread is in a critical section
1059 SafepointSynchronize::increment_jni_active_count();
1060 }
1061 break;
1062
1063 case _call_back:
1064 set_has_called_back(false);
1065 break;
1066
1067 case _running:
1068 default:
1069 ShouldNotReachHere();
1070 }
1071 }
1072
1073 void ThreadSafepointState::restart() {
1074 switch(type()) {
1075 case _at_safepoint:
1076 case _call_back:
1077 break;
1078
1079 case _running:
1080 default:
1081 tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
1082 p2i(_thread), _type);
1083 _thread->print();
1084 ShouldNotReachHere();
1085 }
1086 _type = _running;
1087 set_has_called_back(false);
1088 }
1089
1090
1091 void ThreadSafepointState::print_on(outputStream *st) const {
1092 const char *s = NULL;
1093
1094 switch(_type) {
1095 case _running : s = "_running"; break;
1096 case _at_safepoint : s = "_at_safepoint"; break;
1097 case _call_back : s = "_call_back"; break;
1098 default:
1099 ShouldNotReachHere();
1100 }
1101
1102 st->print_cr("Thread: " INTPTR_FORMAT
1103 " [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
1104 p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back,
1105 _at_poll_safepoint);
1106
1107 _thread->print_thread_state_on(st);
1108 }
1109
1110 // ---------------------------------------------------------------------------------------------------------------------
1111
1112 // Block the thread at the safepoint poll or poll return.
1113 void ThreadSafepointState::handle_polling_page_exception() {
1114
1115 // Check state. block() will set thread state to thread_in_vm which will
1116 // cause the safepoint state _type to become _call_back.
1117 assert(type() == ThreadSafepointState::_running,
1118 "polling page exception on thread not running state");
1119
1120 // Step 1: Find the nmethod from the return address
1121 if (ShowSafepointMsgs && Verbose) {
1122 tty->print_cr("Polling page exception at " INTPTR_FORMAT, p2i(thread()->saved_exception_pc()));
1123 }
1124 address real_return_addr = thread()->saved_exception_pc();
1125
1126 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1127 assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1128 CompiledMethod* nm = (CompiledMethod*)cb;
1129
1130 // Find frame of caller
1131 frame stub_fr = thread()->last_frame();
1132 CodeBlob* stub_cb = stub_fr.cb();
1133 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1134 RegisterMap map(thread(), true);
1135 frame caller_fr = stub_fr.sender(&map);
1136
1137 // Should only be poll_return or poll
1138 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1139
1140 // This is a poll immediately before a return. The exception handling code
1141 // has already had the effect of causing the return to occur, so the execution
1142 // will continue immediately after the call. In addition, the oopmap at the
1143 // return point does not mark the return value as an oop (if it is), so
1144 // it needs a handle here to be updated.
1145 if( nm->is_at_poll_return(real_return_addr) ) {
1146 // See if return type is an oop.
1147 bool return_oop = nm->method()->is_returning_oop();
1148 Handle return_value;
1149 if (return_oop) {
1150 // The oop result has been saved on the stack together with all
1151 // the other registers. In order to preserve it over GCs we need
1152 // to keep it in a handle.
1153 oop result = caller_fr.saved_oop_result(&map);
1154 assert(result == NULL || result->is_oop(), "must be oop");
1155 return_value = Handle(thread(), result);
1156 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1157 }
1158
1159 // Block the thread
1160 SafepointSynchronize::block(thread());
1161
1162 // restore oop result, if any
1163 if (return_oop) {
1164 caller_fr.set_saved_oop_result(&map, return_value());
1165 }
1166 }
1167
1168 // This is a safepoint poll. Verify the return address and block.
1169 else {
1170 set_at_poll_safepoint(true);
1171
1172 // verify the blob built the "return address" correctly
1173 assert(real_return_addr == caller_fr.pc(), "must match");
1174
1175 // Block the thread
1176 SafepointSynchronize::block(thread());
1177 set_at_poll_safepoint(false);
1178
1179 // If we have a pending async exception deoptimize the frame
1180 // as otherwise we may never deliver it.
1181 if (thread()->has_async_condition()) {
1182 ThreadInVMfromJavaNoAsyncException __tiv(thread());
1183 Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1184 }
1185
1186 // If an exception has been installed we must check for a pending deoptimization
1187 // Deoptimize frame if exception has been thrown.
1188
1189 if (thread()->has_pending_exception() ) {
1190 RegisterMap map(thread(), true);
1191 frame caller_fr = stub_fr.sender(&map);
1192 if (caller_fr.is_deoptimized_frame()) {
1193 // The exception patch will destroy registers that are still
1194 // live and will be needed during deoptimization. Defer the
1195 // Async exception should have deferred the exception until the
1196 // next safepoint which will be detected when we get into
1197 // the interpreter so if we have an exception now things
1198 // are messed up.
1199
1200 fatal("Exception installed and deoptimization is pending");
1201 }
1202 }
1203 }
1204 }
1205
1206
1207 //
1208 // Statistics & Instrumentations
1209 //
1210 SafepointSynchronize::SafepointStats* SafepointSynchronize::_safepoint_stats = NULL;
1211 jlong SafepointSynchronize::_safepoint_begin_time = 0;
1212 int SafepointSynchronize::_cur_stat_index = 0;
1213 julong SafepointSynchronize::_safepoint_reasons[VM_Operation::VMOp_Terminating];
1214 julong SafepointSynchronize::_coalesced_vmop_count = 0;
1215 jlong SafepointSynchronize::_max_sync_time = 0;
1216 jlong SafepointSynchronize::_max_vmop_time = 0;
1217 float SafepointSynchronize::_ts_of_current_safepoint = 0.0f;
1218
1219 static jlong cleanup_end_time = 0;
1220 static bool need_to_track_page_armed_status = false;
1221 static bool init_done = false;
1222
1223 // Helper method to print the header.
1224 static void print_header() {
1225 tty->print(" vmop "
1226 "[threads: total initially_running wait_to_block] ");
1227 tty->print("[time: spin block sync cleanup vmop] ");
1228
1229 // no page armed status printed out if it is always armed.
1230 if (need_to_track_page_armed_status) {
1231 tty->print("page_armed ");
1232 }
1233
1234 tty->print_cr("page_trap_count");
1235 }
1236
1237 void SafepointSynchronize::deferred_initialize_stat() {
1238 if (init_done) return;
1239
1240 // If PrintSafepointStatisticsTimeout is specified, the statistics data will
1241 // be printed right away, in which case, _safepoint_stats will regress to
1242 // a single element array. Otherwise, it is a circular ring buffer with default
1243 // size of PrintSafepointStatisticsCount.
1244 int stats_array_size;
1245 if (PrintSafepointStatisticsTimeout > 0) {
1246 stats_array_size = 1;
1247 PrintSafepointStatistics = true;
1248 } else {
1249 stats_array_size = PrintSafepointStatisticsCount;
1250 }
1251 _safepoint_stats = (SafepointStats*)os::malloc(stats_array_size
1252 * sizeof(SafepointStats), mtInternal);
1253 guarantee(_safepoint_stats != NULL,
1254 "not enough memory for safepoint instrumentation data");
1255
1256 if (DeferPollingPageLoopCount >= 0) {
1257 need_to_track_page_armed_status = true;
1258 }
1259 init_done = true;
1260 }
1261
1262 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1263 assert(init_done, "safepoint statistics array hasn't been initialized");
1264 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1265
1266 spstat->_time_stamp = _ts_of_current_safepoint;
1267
1268 VM_Operation *op = VMThread::vm_operation();
1269 spstat->_vmop_type = (op != NULL ? op->type() : -1);
1270 if (op != NULL) {
1271 _safepoint_reasons[spstat->_vmop_type]++;
1272 }
1273
1274 spstat->_nof_total_threads = nof_threads;
1275 spstat->_nof_initial_running_threads = nof_running;
1276 spstat->_nof_threads_hit_page_trap = 0;
1277
1278 // Records the start time of spinning. The real time spent on spinning
1279 // will be adjusted when spin is done. Same trick is applied for time
1280 // spent on waiting for threads to block.
1281 if (nof_running != 0) {
1282 spstat->_time_to_spin = os::javaTimeNanos();
1283 } else {
1284 spstat->_time_to_spin = 0;
1285 }
1286 }
1287
1288 void SafepointSynchronize::update_statistics_on_spin_end() {
1289 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1290
1291 jlong cur_time = os::javaTimeNanos();
1292
1293 spstat->_nof_threads_wait_to_block = _waiting_to_block;
1294 if (spstat->_nof_initial_running_threads != 0) {
1295 spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
1296 }
1297
1298 if (need_to_track_page_armed_status) {
1299 spstat->_page_armed = (PageArmed == 1);
1300 }
1301
1302 // Records the start time of waiting for to block. Updated when block is done.
1303 if (_waiting_to_block != 0) {
1304 spstat->_time_to_wait_to_block = cur_time;
1305 } else {
1306 spstat->_time_to_wait_to_block = 0;
1307 }
1308 }
1309
1310 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {
1311 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1312
1313 if (spstat->_nof_threads_wait_to_block != 0) {
1314 spstat->_time_to_wait_to_block = end_time -
1315 spstat->_time_to_wait_to_block;
1316 }
1317
1318 // Records the end time of sync which will be used to calculate the total
1319 // vm operation time. Again, the real time spending in syncing will be deducted
1320 // from the start of the sync time later when end_statistics is called.
1321 spstat->_time_to_sync = end_time - _safepoint_begin_time;
1322 if (spstat->_time_to_sync > _max_sync_time) {
1323 _max_sync_time = spstat->_time_to_sync;
1324 }
1325
1326 spstat->_time_to_do_cleanups = end_time;
1327 }
1328
1329 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1330 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1331
1332 // Record how long spent in cleanup tasks.
1333 spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1334
1335 cleanup_end_time = end_time;
1336 }
1337
1338 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1339 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1340
1341 // Update the vm operation time.
1342 spstat->_time_to_exec_vmop = vmop_end_time - cleanup_end_time;
1343 if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1344 _max_vmop_time = spstat->_time_to_exec_vmop;
1345 }
1346 // Only the sync time longer than the specified
1347 // PrintSafepointStatisticsTimeout will be printed out right away.
1348 // By default, it is -1 meaning all samples will be put into the list.
1349 if ( PrintSafepointStatisticsTimeout > 0) {
1350 if (spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1351 print_statistics();
1352 }
1353 } else {
1354 // The safepoint statistics will be printed out when the _safepoin_stats
1355 // array fills up.
1356 if (_cur_stat_index == PrintSafepointStatisticsCount - 1) {
1357 print_statistics();
1358 _cur_stat_index = 0;
1359 } else {
1360 _cur_stat_index++;
1361 }
1362 }
1363 }
1364
1365 void SafepointSynchronize::print_statistics() {
1366 SafepointStats* sstats = _safepoint_stats;
1367
1368 for (int index = 0; index <= _cur_stat_index; index++) {
1369 if (index % 30 == 0) {
1370 print_header();
1371 }
1372 sstats = &_safepoint_stats[index];
1373 tty->print("%.3f: ", sstats->_time_stamp);
1374 tty->print("%-26s ["
1375 INT32_FORMAT_W(8) INT32_FORMAT_W(11) INT32_FORMAT_W(15)
1376 " ] ",
1377 sstats->_vmop_type == -1 ? "no vm operation" :
1378 VM_Operation::name(sstats->_vmop_type),
1379 sstats->_nof_total_threads,
1380 sstats->_nof_initial_running_threads,
1381 sstats->_nof_threads_wait_to_block);
1382 // "/ MICROUNITS " is to convert the unit from nanos to millis.
1383 tty->print(" ["
1384 INT64_FORMAT_W(6) INT64_FORMAT_W(6)
1385 INT64_FORMAT_W(6) INT64_FORMAT_W(6)
1386 INT64_FORMAT_W(6) " ] ",
1387 sstats->_time_to_spin / MICROUNITS,
1388 sstats->_time_to_wait_to_block / MICROUNITS,
1389 sstats->_time_to_sync / MICROUNITS,
1390 sstats->_time_to_do_cleanups / MICROUNITS,
1391 sstats->_time_to_exec_vmop / MICROUNITS);
1392
1393 if (need_to_track_page_armed_status) {
1394 tty->print(INT32_FORMAT " ", sstats->_page_armed);
1395 }
1396 tty->print_cr(INT32_FORMAT " ", sstats->_nof_threads_hit_page_trap);
1397 }
1398 }
1399
1400 // This method will be called when VM exits. It will first call
1401 // print_statistics to print out the rest of the sampling. Then
1402 // it tries to summarize the sampling.
1403 void SafepointSynchronize::print_stat_on_exit() {
1404 if (_safepoint_stats == NULL) return;
1405
1406 SafepointStats *spstat = &_safepoint_stats[_cur_stat_index];
1407
1408 // During VM exit, end_statistics may not get called and in that
1409 // case, if the sync time is less than PrintSafepointStatisticsTimeout,
1410 // don't print it out.
1411 // Approximate the vm op time.
1412 _safepoint_stats[_cur_stat_index]._time_to_exec_vmop =
1413 os::javaTimeNanos() - cleanup_end_time;
1414
1415 if ( PrintSafepointStatisticsTimeout < 0 ||
1416 spstat->_time_to_sync > (jlong)PrintSafepointStatisticsTimeout * MICROUNITS) {
1417 print_statistics();
1418 }
1419 tty->cr();
1420
1421 // Print out polling page sampling status.
1422 if (!need_to_track_page_armed_status) {
1423 tty->print_cr("Polling page always armed");
1424 } else {
1425 tty->print_cr("Defer polling page loop count = " INTX_FORMAT "\n",
1426 DeferPollingPageLoopCount);
1427 }
1428
1429 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1430 if (_safepoint_reasons[index] != 0) {
1431 tty->print_cr("%-26s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1432 _safepoint_reasons[index]);
1433 }
1434 }
1435
1436 tty->print_cr(UINT64_FORMAT_W(5) " VM operations coalesced during safepoint",
1437 _coalesced_vmop_count);
1438 tty->print_cr("Maximum sync time " INT64_FORMAT_W(5) " ms",
1439 _max_sync_time / MICROUNITS);
1440 tty->print_cr("Maximum vm operation time (except for Exit VM operation) "
1441 INT64_FORMAT_W(5) " ms",
1442 _max_vmop_time / MICROUNITS);
1443 }
1444
1445 // ------------------------------------------------------------------------------------------------
1446 // Non-product code
1447
1448 #ifndef PRODUCT
1449
1450 void SafepointSynchronize::print_state() {
1451 if (_state == _not_synchronized) {
1452 tty->print_cr("not synchronized");
1453 } else if (_state == _synchronizing || _state == _synchronized) {
1454 tty->print_cr("State: %s", (_state == _synchronizing) ? "synchronizing" :
1455 "synchronized");
1456
1457 for(JavaThread *cur = Threads::first(); cur; cur = cur->next()) {
1458 cur->safepoint_state()->print();
1459 }
1460 }
1461 }
1462
1463 void SafepointSynchronize::safepoint_msg(const char* format, ...) {
1464 if (ShowSafepointMsgs) {
1465 va_list ap;
1466 va_start(ap, format);
1467 tty->vprint_cr(format, ap);
1468 va_end(ap);
1469 }
1470 }
1471
1472 #endif // !PRODUCT