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/classLoaderData.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 int 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 // (on MP systems). In order to avoid the overhead of issuing
218 // a memory barrier for each Java thread making native calls, each Java
219 // thread performs a write to a single memory page after changing
220 // the thread state. The VM thread performs a sequence of
221 // mprotect OS calls which forces all previous writes from all
222 // Java threads to be serialized. This is done in the
223 // os::serialize_thread_states() call. This has proven to be
224 // much more efficient than executing a membar instruction
225 // on every call to native code.
226 // 3. Running compiled Code
227 // Compiled code reads a global (Safepoint Polling) page that
228 // is set to fault if we are trying to get to a safepoint.
229 // 4. Blocked
230 // A thread which is blocked will not be allowed to return from the
231 // block condition until the safepoint operation is complete.
232 // 5. In VM or Transitioning between states
233 // If a Java thread is currently running in the VM or transitioning
234 // between states, the safepointing code will wait for the thread to
235 // block itself when it attempts transitions to a new state.
236 //
237 {
238 EventSafepointStateSynchronization sync_event;
239 int initial_running = 0;
240
241 _state = _synchronizing;
242
243 if (SafepointMechanism::uses_thread_local_poll()) {
244 // Arming the per thread poll while having _state != _not_synchronized means safepointing
245 log_trace(safepoint)("Setting thread local yield flag for threads");
246 OrderAccess::storestore(); // storestore, global state -> local state
247 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
248 // Make sure the threads start polling, it is time to yield.
249 SafepointMechanism::arm_local_poll(cur);
250 }
251 }
252 OrderAccess::fence(); // storestore|storeload, global state -> local state
253
254 // Flush all thread states to memory
255 if (!UseMembar) {
256 os::serialize_thread_states();
257 }
258
259 if (SafepointMechanism::uses_global_page_poll()) {
260 // Make interpreter safepoint aware
261 Interpreter::notice_safepoints();
262
263 // Make polling safepoint aware
264 guarantee (PageArmed == 0, "invariant") ;
265 PageArmed = 1 ;
266 os::make_polling_page_unreadable();
267 }
268
269 // Consider using active_processor_count() ... but that call is expensive.
270 int ncpus = os::processor_count() ;
271 unsigned int iterations = 0;
272
273 {
274 JavaThreadIteratorWithHandle jtiwh;
275 #ifdef ASSERT
276 for (; JavaThread *cur = jtiwh.next(); ) {
277 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
278 // Clear the visited flag to ensure that the critical counts are collected properly.
279 cur->set_visited_for_critical_count(false);
280 }
281 #endif // ASSERT
282
283 if (SafepointTimeout)
284 safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;
285
286 // Iterate through all threads until it have been determined how to stop them all at a safepoint
287 int steps = 0 ;
288 while(still_running > 0) {
289 jtiwh.rewind();
290 for (; JavaThread *cur = jtiwh.next(); ) {
291 assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");
292 ThreadSafepointState *cur_state = cur->safepoint_state();
293 if (cur_state->is_running()) {
294 cur_state->examine_state_of_thread();
295 if (!cur_state->is_running()) {
296 still_running--;
297 // consider adjusting steps downward:
298 // steps = 0
299 // steps -= NNN
300 // steps >>= 1
301 // steps = MIN(steps, 2000-100)
302 // if (iterations != 0) steps -= NNN
303 }
304 LogTarget(Trace, safepoint) lt;
305 if (lt.is_enabled()) {
306 ResourceMark rm;
307 LogStream ls(lt);
308 cur_state->print_on(&ls);
309 }
310 }
311 }
312
313 if (iterations == 0) {
314 initial_running = still_running;
315 if (log_is_enabled(Debug, safepoint, stats)) {
316 begin_statistics(nof_threads, still_running);
317 }
318 }
319
320 if (still_running > 0) {
321 // Check for if it takes to long
322 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
323 print_safepoint_timeout(_spinning_timeout);
324 }
325
326 // Spin to avoid context switching.
327 // There's a tension between allowing the mutators to run (and rendezvous)
328 // vs spinning. As the VM thread spins, wasting cycles, it consumes CPU that
329 // a mutator might otherwise use profitably to reach a safepoint. Excessive
330 // spinning by the VM thread on a saturated system can increase rendezvous latency.
331 // Blocking or yielding incur their own penalties in the form of context switching
332 // and the resultant loss of $ residency.
333 //
334 // Further complicating matters is that yield() does not work as naively expected
335 // on many platforms -- yield() does not guarantee that any other ready threads
336 // will run. As such we revert to naked_short_sleep() after some number of iterations.
337 // nakes_short_sleep() is implemented as a short unconditional sleep.
338 // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping
339 // can actually increase the time it takes the VM thread to detect that a system-wide
340 // stop-the-world safepoint has been reached. In a pathological scenario such as that
341 // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.
342 // In that case the mutators will be stalled waiting for the safepoint to complete and the
343 // the VMthread will be sleeping, waiting for the mutators to rendezvous. The VMthread
344 // will eventually wake up and detect that all mutators are safe, at which point
345 // we'll again make progress.
346 //
347 // Beware too that that the VMThread typically runs at elevated priority.
348 // Its default priority is higher than the default mutator priority.
349 // Obviously, this complicates spinning.
350 //
351 // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).
352 // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.
353 //
354 // See the comments in synchronizer.cpp for additional remarks on spinning.
355 //
356 // In the future we might:
357 // 1. Modify the safepoint scheme to avoid potentially unbounded spinning.
358 // This is tricky as the path used by a thread exiting the JVM (say on
359 // on JNI call-out) simply stores into its state field. The burden
360 // is placed on the VM thread, which must poll (spin).
361 // 2. Find something useful to do while spinning. If the safepoint is GC-related
362 // we might aggressively scan the stacks of threads that are already safe.
363 // 3. Use Solaris schedctl to examine the state of the still-running mutators.
364 // If all the mutators are ONPROC there's no reason to sleep or yield.
365 // 4. YieldTo() any still-running mutators that are ready but OFFPROC.
366 // 5. Check system saturation. If the system is not fully saturated then
367 // simply spin and avoid sleep/yield.
368 // 6. As still-running mutators rendezvous they could unpark the sleeping
369 // VMthread. This works well for still-running mutators that become
370 // safe. The VMthread must still poll for mutators that call-out.
371 // 7. Drive the policy on time-since-begin instead of iterations.
372 // 8. Consider making the spin duration a function of the # of CPUs:
373 // Spin = (((ncpus-1) * M) + K) + F(still_running)
374 // Alternately, instead of counting iterations of the outer loop
375 // we could count the # of threads visited in the inner loop, above.
376 // 9. On windows consider using the return value from SwitchThreadTo()
377 // to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
378
379 if (int(iterations) == -1) { // overflow - something is wrong.
380 // We can only overflow here when we are using global
381 // polling pages. We keep this guarantee in its original
382 // form so that searches of the bug database for this
383 // failure mode find the right bugs.
384 guarantee (PageArmed == 0, "invariant");
385 }
386
387 // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
388 // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
389 ++steps ;
390 if (ncpus > 1 && steps < safepoint_spin_before_yield) {
391 SpinPause() ; // MP-Polite spin
392 } else
393 if (steps < _defer_thr_suspend_loop_count) {
394 os::naked_yield() ;
395 } else {
396 os::naked_short_sleep(1);
397 }
398
399 iterations ++ ;
400 }
401 assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
402 }
403 } // ThreadsListHandle destroyed here.
404 assert(still_running == 0, "sanity check");
405
406 if (log_is_enabled(Debug, safepoint, stats)) {
407 update_statistics_on_spin_end();
408 }
409 if (sync_event.should_commit()) {
410 post_safepoint_synchronize_event(&sync_event, initial_running, _waiting_to_block, iterations);
411 }
412 }
413
414 // wait until all threads are stopped
415 {
416 EventSafepointWaitBlocked wait_blocked_event;
417 int initial_waiting_to_block = _waiting_to_block;
418
419 while (_waiting_to_block > 0) {
420 log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block);
421 if (!SafepointTimeout || timeout_error_printed) {
422 Safepoint_lock->wait(true); // true, means with no safepoint checks
423 } else {
424 // Compute remaining time
425 jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
426
427 // If there is no remaining time, then there is an error
428 if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
429 print_safepoint_timeout(_blocking_timeout);
430 }
431 }
432 }
433 assert(_waiting_to_block == 0, "sanity check");
434
435 #ifndef PRODUCT
436 if (SafepointTimeout) {
437 jlong current_time = os::javaTimeNanos();
438 if (safepoint_limit_time < current_time) {
439 log_warning(safepoint)("# SafepointSynchronize: Finished after "
440 INT64_FORMAT_W(6) " ms",
441 (int64_t)((current_time - safepoint_limit_time) / MICROUNITS +
442 (jlong)SafepointTimeoutDelay));
443 }
444 }
445 #endif
446
447 assert((_safepoint_counter & 0x1) == 0, "must be even");
448 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
449 _safepoint_counter ++;
450
451 // Record state
452 _state = _synchronized;
453
454 OrderAccess::fence();
455 if (wait_blocked_event.should_commit()) {
456 post_safepoint_wait_blocked_event(&wait_blocked_event, initial_waiting_to_block);
457 }
458 }
459
460 #ifdef ASSERT
461 // Make sure all the threads were visited.
462 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
463 assert(cur->was_visited_for_critical_count(), "missed a thread");
464 }
465 #endif // ASSERT
466
467 // Update the count of active JNI critical regions
468 GCLocker::set_jni_lock_count(_current_jni_active_count);
469
470 log_info(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description());
471
472 RuntimeService::record_safepoint_synchronized();
473 if (log_is_enabled(Debug, safepoint, stats)) {
474 update_statistics_on_sync_end(os::javaTimeNanos());
475 }
476
477 // Call stuff that needs to be run when a safepoint is just about to be completed
478 {
479 EventSafepointCleanup cleanup_event;
480 do_cleanup_tasks();
481 if (cleanup_event.should_commit()) {
482 post_safepoint_cleanup_event(&cleanup_event);
483 }
484 }
485
486 if (log_is_enabled(Debug, safepoint, stats)) {
487 // Record how much time spend on the above cleanup tasks
488 update_statistics_on_cleanup_end(os::javaTimeNanos());
489 }
490
491 if (begin_event.should_commit()) {
492 post_safepoint_begin_event(&begin_event, nof_threads, _current_jni_active_count);
493 }
494 }
495
496 // Wake up all threads, so they are ready to resume execution after the safepoint
497 // operation has been carried out
498 void SafepointSynchronize::end() {
499 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
500 assert((_safepoint_counter & 0x1) == 1, "must be odd");
501 EventSafepointEnd event;
502 _safepoint_counter ++;
503 // memory fence isn't required here since an odd _safepoint_counter
504 // value can do no harm and a fence is issued below anyway.
505
506 DEBUG_ONLY(Thread* myThread = Thread::current();)
507 assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
508
509 if (log_is_enabled(Debug, safepoint, stats)) {
510 end_statistics(os::javaTimeNanos());
511 }
512
513 {
514 JavaThreadIteratorWithHandle jtiwh;
515 #ifdef ASSERT
516 // A pending_exception cannot be installed during a safepoint. The threads
517 // may install an async exception after they come back from a safepoint into
518 // pending_exception after they unblock. But that should happen later.
519 for (; JavaThread *cur = jtiwh.next(); ) {
520 assert (!(cur->has_pending_exception() &&
521 cur->safepoint_state()->is_at_poll_safepoint()),
522 "safepoint installed a pending exception");
523 }
524 #endif // ASSERT
525
526 if (PageArmed) {
527 assert(SafepointMechanism::uses_global_page_poll(), "sanity");
528 // Make polling safepoint aware
529 os::make_polling_page_readable();
530 PageArmed = 0 ;
531 }
532
533 if (SafepointMechanism::uses_global_page_poll()) {
534 // Remove safepoint check from interpreter
535 Interpreter::ignore_safepoints();
536 }
537
538 {
539 MutexLocker mu(Safepoint_lock);
540
541 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
542
543 if (SafepointMechanism::uses_thread_local_poll()) {
544 _state = _not_synchronized;
545 OrderAccess::storestore(); // global state -> local state
546 jtiwh.rewind();
547 for (; JavaThread *current = jtiwh.next(); ) {
548 ThreadSafepointState* cur_state = current->safepoint_state();
549 cur_state->restart(); // TSS _running
550 SafepointMechanism::disarm_local_poll(current);
551 }
552 log_info(safepoint)("Leaving safepoint region");
553 } else {
554 // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
555 // when they get restarted.
556 _state = _not_synchronized;
557 OrderAccess::fence();
558
559 log_info(safepoint)("Leaving safepoint region");
560
561 // Start suspended threads
562 jtiwh.rewind();
563 for (; JavaThread *current = jtiwh.next(); ) {
564 // A problem occurring on Solaris is when attempting to restart threads
565 // the first #cpus - 1 go well, but then the VMThread is preempted when we get
566 // to the next one (since it has been running the longest). We then have
567 // to wait for a cpu to become available before we can continue restarting
568 // threads.
569 // FIXME: This causes the performance of the VM to degrade when active and with
570 // large numbers of threads. Apparently this is due to the synchronous nature
571 // of suspending threads.
572 //
573 // TODO-FIXME: the comments above are vestigial and no longer apply.
574 // Furthermore, using solaris' schedctl in this particular context confers no benefit
575 if (VMThreadHintNoPreempt) {
576 os::hint_no_preempt();
577 }
578 ThreadSafepointState* cur_state = current->safepoint_state();
579 assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
580 cur_state->restart();
581 assert(cur_state->is_running(), "safepoint state has not been reset");
582 }
583 }
584
585 RuntimeService::record_safepoint_end();
586
587 // Release threads lock, so threads can be created/destroyed again.
588 // It will also release all threads blocked in signal_thread_blocked.
589 Threads_lock->unlock();
590 }
591 } // ThreadsListHandle destroyed here.
592
593 Universe::heap()->safepoint_synchronize_end();
594 // record this time so VMThread can keep track how much time has elapsed
595 // since last safepoint.
596 _end_of_last_safepoint = os::javaTimeMillis();
597 if (event.should_commit()) {
598 post_safepoint_end_event(&event);
599 }
600 }
601
602 bool SafepointSynchronize::is_cleanup_needed() {
603 // Need a safepoint if there are many monitors to deflate.
604 if (ObjectSynchronizer::is_cleanup_needed()) return true;
605 // Need a safepoint if some inline cache buffers is non-empty
606 if (!InlineCacheBuffer::is_empty()) return true;
607 return false;
608 }
609
610 class ParallelSPCleanupThreadClosure : public ThreadClosure {
611 private:
612 CodeBlobClosure* _nmethod_cl;
613 DeflateMonitorCounters* _counters;
614
615 public:
616 ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
617 _counters(counters),
618 _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()) {}
619
620 void do_thread(Thread* thread) {
621 ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
622 if (_nmethod_cl != NULL && thread->is_Java_thread() &&
623 ! thread->is_Code_cache_sweeper_thread()) {
624 JavaThread* jt = (JavaThread*) thread;
625 jt->nmethods_do(_nmethod_cl);
626 }
627 }
628 };
629
630 class ParallelSPCleanupTask : public AbstractGangTask {
631 private:
632 SubTasksDone _subtasks;
633 ParallelSPCleanupThreadClosure _cleanup_threads_cl;
634 uint _num_workers;
635 DeflateMonitorCounters* _counters;
636 public:
637 ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
638 AbstractGangTask("Parallel Safepoint Cleanup"),
639 _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
640 _num_workers(num_workers),
641 _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
642 _counters(counters) {}
643
644 void work(uint worker_id) {
645 // All threads deflate monitors and mark nmethods (if necessary).
646 Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl);
647
648 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
649 const char* name = "deflating idle monitors";
650 EventSafepointCleanupTask event;
651 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
652 ObjectSynchronizer::deflate_idle_monitors(_counters);
653 if (event.should_commit()) {
654 post_safepoint_cleanup_task_event(&event, name);
655 }
656 }
657
658 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
659 const char* name = "updating inline caches";
660 EventSafepointCleanupTask event;
661 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
662 InlineCacheBuffer::update_inline_caches();
663 if (event.should_commit()) {
664 post_safepoint_cleanup_task_event(&event, name);
665 }
666 }
667
668 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
669 const char* name = "compilation policy safepoint handler";
670 EventSafepointCleanupTask event;
671 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
672 CompilationPolicy::policy()->do_safepoint_work();
673 if (event.should_commit()) {
674 post_safepoint_cleanup_task_event(&event, name);
675 }
676 }
677
678 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
679 if (SymbolTable::needs_rehashing()) {
680 const char* name = "rehashing symbol table";
681 EventSafepointCleanupTask event;
682 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
683 SymbolTable::rehash_table();
684 if (event.should_commit()) {
685 post_safepoint_cleanup_task_event(&event, name);
686 }
687 }
688 }
689
690 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
691 if (StringTable::needs_rehashing()) {
692 const char* name = "rehashing string table";
693 EventSafepointCleanupTask event;
694 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
695 StringTable::rehash_table();
696 if (event.should_commit()) {
697 post_safepoint_cleanup_task_event(&event, name);
698 }
699 }
700 }
701
702 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
703 // CMS delays purging the CLDG until the beginning of the next safepoint and to
704 // make sure concurrent sweep is done
705 const char* name = "purging class loader data graph";
706 EventSafepointCleanupTask event;
707 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
708 ClassLoaderDataGraph::purge_if_needed();
709 if (event.should_commit()) {
710 post_safepoint_cleanup_task_event(&event, name);
711 }
712 }
713
714 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) {
715 const char* name = "resizing system dictionaries";
716 EventSafepointCleanupTask event;
717 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
718 ClassLoaderDataGraph::resize_if_needed();
719 if (event.should_commit()) {
720 post_safepoint_cleanup_task_event(&event, name);
721 }
722 }
723 _subtasks.all_tasks_completed(_num_workers);
724 }
725 };
726
727 // Various cleaning tasks that should be done periodically at safepoints.
728 void SafepointSynchronize::do_cleanup_tasks() {
729
730 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
731
732 // Prepare for monitor deflation.
733 DeflateMonitorCounters deflate_counters;
734 ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
735
736 CollectedHeap* heap = Universe::heap();
737 assert(heap != NULL, "heap not initialized yet?");
738 WorkGang* cleanup_workers = heap->get_safepoint_workers();
739 if (cleanup_workers != NULL) {
740 // Parallel cleanup using GC provided thread pool.
741 uint num_cleanup_workers = cleanup_workers->active_workers();
742 ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
743 StrongRootsScope srs(num_cleanup_workers);
744 cleanup_workers->run_task(&cleanup);
745 } else {
746 // Serial cleanup using VMThread.
747 ParallelSPCleanupTask cleanup(1, &deflate_counters);
748 StrongRootsScope srs(1);
749 cleanup.work(0);
750 }
751
752 // Finish monitor deflation.
753 ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
754 }
755
756
757 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
758 switch(state) {
759 case _thread_in_native:
760 // native threads are safe if they have no java stack or have walkable stack
761 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
762
763 // blocked threads should have already have walkable stack
764 case _thread_blocked:
765 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
766 return true;
767
768 default:
769 return false;
770 }
771 }
772
773
774 // See if the thread is running inside a lazy critical native and
775 // update the thread critical count if so. Also set a suspend flag to
776 // cause the native wrapper to return into the JVM to do the unlock
777 // once the native finishes.
778 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
779 if (state == _thread_in_native &&
780 thread->has_last_Java_frame() &&
781 thread->frame_anchor()->walkable()) {
782 // This thread might be in a critical native nmethod so look at
783 // the top of the stack and increment the critical count if it
784 // is.
785 frame wrapper_frame = thread->last_frame();
786 CodeBlob* stub_cb = wrapper_frame.cb();
787 if (stub_cb != NULL &&
788 stub_cb->is_nmethod() &&
789 stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
790 // A thread could potentially be in a critical native across
791 // more than one safepoint, so only update the critical state on
792 // the first one. When it returns it will perform the unlock.
793 if (!thread->do_critical_native_unlock()) {
794 #ifdef ASSERT
795 if (!thread->in_critical()) {
796 GCLocker::increment_debug_jni_lock_count();
797 }
798 #endif
799 thread->enter_critical();
800 // Make sure the native wrapper calls back on return to
801 // perform the needed critical unlock.
802 thread->set_critical_native_unlock();
803 }
804 }
805 }
806 }
807
808
809
810 // -------------------------------------------------------------------------------------------------------
811 // Implementation of Safepoint callback point
812
813 void SafepointSynchronize::block(JavaThread *thread) {
814 assert(thread != NULL, "thread must be set");
815 assert(thread->is_Java_thread(), "not a Java thread");
816
817 // Threads shouldn't block if they are in the middle of printing, but...
818 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
819
820 // Only bail from the block() call if the thread is gone from the
821 // thread list; starting to exit should still block.
822 if (thread->is_terminated()) {
823 // block current thread if we come here from native code when VM is gone
824 thread->block_if_vm_exited();
825
826 // otherwise do nothing
827 return;
828 }
829
830 JavaThreadState state = thread->thread_state();
831 thread->frame_anchor()->make_walkable(thread);
832
833 // Check that we have a valid thread_state at this point
834 switch(state) {
835 case _thread_in_vm_trans:
836 case _thread_in_Java: // From compiled code
837
838 // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
839 // we pretend we are still in the VM.
840 thread->set_thread_state(_thread_in_vm);
841
842 if (is_synchronizing()) {
843 Atomic::inc (&TryingToBlock) ;
844 }
845
846 // We will always be holding the Safepoint_lock when we are examine the state
847 // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
848 // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
849 Safepoint_lock->lock_without_safepoint_check();
850 if (is_synchronizing()) {
851 // Decrement the number of threads to wait for and signal vm thread
852 assert(_waiting_to_block > 0, "sanity check");
853 _waiting_to_block--;
854 thread->safepoint_state()->set_has_called_back(true);
855
856 DEBUG_ONLY(thread->set_visited_for_critical_count(true));
857 if (thread->in_critical()) {
858 // Notice that this thread is in a critical section
859 increment_jni_active_count();
860 }
861
862 // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
863 if (_waiting_to_block == 0) {
864 Safepoint_lock->notify_all();
865 }
866 }
867
868 // We transition the thread to state _thread_blocked here, but
869 // we can't do our usual check for external suspension and then
870 // self-suspend after the lock_without_safepoint_check() call
871 // below because we are often called during transitions while
872 // we hold different locks. That would leave us suspended while
873 // holding a resource which results in deadlocks.
874 thread->set_thread_state(_thread_blocked);
875 Safepoint_lock->unlock();
876
877 // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
878 // the entire safepoint, the threads will all line up here during the safepoint.
879 Threads_lock->lock_without_safepoint_check();
880 // restore original state. This is important if the thread comes from compiled code, so it
881 // will continue to execute with the _thread_in_Java state.
882 thread->set_thread_state(state);
883 Threads_lock->unlock();
884 break;
885
886 case _thread_in_native_trans:
887 case _thread_blocked_trans:
888 case _thread_new_trans:
889 if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
890 thread->print_thread_state();
891 fatal("Deadlock in safepoint code. "
892 "Should have called back to the VM before blocking.");
893 }
894
895 // We transition the thread to state _thread_blocked here, but
896 // we can't do our usual check for external suspension and then
897 // self-suspend after the lock_without_safepoint_check() call
898 // below because we are often called during transitions while
899 // we hold different locks. That would leave us suspended while
900 // holding a resource which results in deadlocks.
901 thread->set_thread_state(_thread_blocked);
902
903 // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
904 // the safepoint code might still be waiting for it to block. We need to change the state here,
905 // so it can see that it is at a safepoint.
906
907 // Block until the safepoint operation is completed.
908 Threads_lock->lock_without_safepoint_check();
909
910 // Restore state
911 thread->set_thread_state(state);
912
913 Threads_lock->unlock();
914 break;
915
916 default:
917 fatal("Illegal threadstate encountered: %d", state);
918 }
919
920 // Check for pending. async. exceptions or suspends - except if the
921 // thread was blocked inside the VM. has_special_runtime_exit_condition()
922 // is called last since it grabs a lock and we only want to do that when
923 // we must.
924 //
925 // Note: we never deliver an async exception at a polling point as the
926 // compiler may not have an exception handler for it. The polling
927 // code will notice the async and deoptimize and the exception will
928 // be delivered. (Polling at a return point is ok though). Sure is
929 // a lot of bother for a deprecated feature...
930 //
931 // We don't deliver an async exception if the thread state is
932 // _thread_in_native_trans so JNI functions won't be called with
933 // a surprising pending exception. If the thread state is going back to java,
934 // async exception is checked in check_special_condition_for_native_trans().
935
936 if (state != _thread_blocked_trans &&
937 state != _thread_in_vm_trans &&
938 thread->has_special_runtime_exit_condition()) {
939 thread->handle_special_runtime_exit_condition(
940 !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
941 }
942 }
943
944 // ------------------------------------------------------------------------------------------------------
945 // Exception handlers
946
947
948 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
949 assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
950 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
951 if (!ThreadLocalHandshakes) {
952 assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
953 }
954
955 if (log_is_enabled(Debug, safepoint, stats)) {
956 Atomic::inc(&_nof_threads_hit_polling_page);
957 }
958
959 ThreadSafepointState* state = thread->safepoint_state();
960
961 state->handle_polling_page_exception();
962 }
963
964
965 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
966 if (!timeout_error_printed) {
967 timeout_error_printed = true;
968 // Print out the thread info which didn't reach the safepoint for debugging
969 // purposes (useful when there are lots of threads in the debugger).
970 LogTarget(Warning, safepoint) lt;
971 if (lt.is_enabled()) {
972 ResourceMark rm;
973 LogStream ls(lt);
974
975 ls.cr();
976 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
977 if (reason == _spinning_timeout) {
978 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
979 } else if (reason == _blocking_timeout) {
980 ls.print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
981 }
982
983 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
984 ThreadSafepointState *cur_state;
985 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
986 cur_state = cur_thread->safepoint_state();
987
988 if (cur_thread->thread_state() != _thread_blocked &&
989 ((reason == _spinning_timeout && cur_state->is_running()) ||
990 (reason == _blocking_timeout && !cur_state->has_called_back()))) {
991 ls.print("# ");
992 cur_thread->print_on(&ls);
993 ls.cr();
994 }
995 }
996 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
997 }
998 }
999
1000 // To debug the long safepoint, specify both DieOnSafepointTimeout &
1001 // ShowMessageBoxOnError.
1002 if (DieOnSafepointTimeout) {
1003 fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
1004 SafepointTimeoutDelay, VMThread::vm_safepoint_description());
1005 }
1006 }
1007
1008
1009 // -------------------------------------------------------------------------------------------------------
1010 // Implementation of ThreadSafepointState
1011
1012 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
1013 _thread = thread;
1014 _type = _running;
1015 _has_called_back = false;
1016 _at_poll_safepoint = false;
1017 }
1018
1019 void ThreadSafepointState::create(JavaThread *thread) {
1020 ThreadSafepointState *state = new ThreadSafepointState(thread);
1021 thread->set_safepoint_state(state);
1022 }
1023
1024 void ThreadSafepointState::destroy(JavaThread *thread) {
1025 if (thread->safepoint_state()) {
1026 delete(thread->safepoint_state());
1027 thread->set_safepoint_state(NULL);
1028 }
1029 }
1030
1031 void ThreadSafepointState::examine_state_of_thread() {
1032 assert(is_running(), "better be running or just have hit safepoint poll");
1033
1034 JavaThreadState state = _thread->thread_state();
1035
1036 // Save the state at the start of safepoint processing.
1037 _orig_thread_state = state;
1038
1039 // Check for a thread that is suspended. Note that thread resume tries
1040 // to grab the Threads_lock which we own here, so a thread cannot be
1041 // resumed during safepoint synchronization.
1042
1043 // We check to see if this thread is suspended without locking to
1044 // avoid deadlocking with a third thread that is waiting for this
1045 // thread to be suspended. The third thread can notice the safepoint
1046 // that we're trying to start at the beginning of its SR_lock->wait()
1047 // call. If that happens, then the third thread will block on the
1048 // safepoint while still holding the underlying SR_lock. We won't be
1049 // able to get the SR_lock and we'll deadlock.
1050 //
1051 // We don't need to grab the SR_lock here for two reasons:
1052 // 1) The suspend flags are both volatile and are set with an
1053 // Atomic::cmpxchg() call so we should see the suspended
1054 // state right away.
1055 // 2) We're being called from the safepoint polling loop; if
1056 // we don't see the suspended state on this iteration, then
1057 // we'll come around again.
1058 //
1059 bool is_suspended = _thread->is_ext_suspended();
1060 if (is_suspended) {
1061 roll_forward(_at_safepoint);
1062 return;
1063 }
1064
1065 // Some JavaThread states have an initial safepoint state of
1066 // running, but are actually at a safepoint. We will happily
1067 // agree and update the safepoint state here.
1068 if (SafepointSynchronize::safepoint_safe(_thread, state)) {
1069 SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
1070 roll_forward(_at_safepoint);
1071 return;
1072 }
1073
1074 if (state == _thread_in_vm) {
1075 roll_forward(_call_back);
1076 return;
1077 }
1078
1079 // All other thread states will continue to run until they
1080 // transition and self-block in state _blocked
1081 // Safepoint polling in compiled code causes the Java threads to do the same.
1082 // Note: new threads may require a malloc so they must be allowed to finish
1083
1084 assert(is_running(), "examine_state_of_thread on non-running thread");
1085 return;
1086 }
1087
1088 // Returns true is thread could not be rolled forward at present position.
1089 void ThreadSafepointState::roll_forward(suspend_type type) {
1090 _type = type;
1091
1092 switch(_type) {
1093 case _at_safepoint:
1094 SafepointSynchronize::signal_thread_at_safepoint();
1095 DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
1096 if (_thread->in_critical()) {
1097 // Notice that this thread is in a critical section
1098 SafepointSynchronize::increment_jni_active_count();
1099 }
1100 break;
1101
1102 case _call_back:
1103 set_has_called_back(false);
1104 break;
1105
1106 case _running:
1107 default:
1108 ShouldNotReachHere();
1109 }
1110 }
1111
1112 void ThreadSafepointState::restart() {
1113 switch(type()) {
1114 case _at_safepoint:
1115 case _call_back:
1116 break;
1117
1118 case _running:
1119 default:
1120 tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
1121 p2i(_thread), _type);
1122 _thread->print();
1123 ShouldNotReachHere();
1124 }
1125 _type = _running;
1126 set_has_called_back(false);
1127 }
1128
1129
1130 void ThreadSafepointState::print_on(outputStream *st) const {
1131 const char *s = NULL;
1132
1133 switch(_type) {
1134 case _running : s = "_running"; break;
1135 case _at_safepoint : s = "_at_safepoint"; break;
1136 case _call_back : s = "_call_back"; break;
1137 default:
1138 ShouldNotReachHere();
1139 }
1140
1141 st->print_cr("Thread: " INTPTR_FORMAT
1142 " [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
1143 p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back,
1144 _at_poll_safepoint);
1145
1146 _thread->print_thread_state_on(st);
1147 }
1148
1149 // ---------------------------------------------------------------------------------------------------------------------
1150
1151 // Block the thread at poll or poll return for safepoint/handshake.
1152 void ThreadSafepointState::handle_polling_page_exception() {
1153
1154 // Check state. block() will set thread state to thread_in_vm which will
1155 // cause the safepoint state _type to become _call_back.
1156 suspend_type t = type();
1157 assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running,
1158 "polling page exception on thread not running state: %u", uint(t));
1159
1160 // Step 1: Find the nmethod from the return address
1161 address real_return_addr = thread()->saved_exception_pc();
1162
1163 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1164 assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1165 CompiledMethod* nm = (CompiledMethod*)cb;
1166
1167 // Find frame of caller
1168 frame stub_fr = thread()->last_frame();
1169 CodeBlob* stub_cb = stub_fr.cb();
1170 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1171 RegisterMap map(thread(), true);
1172 frame caller_fr = stub_fr.sender(&map);
1173
1174 // Should only be poll_return or poll
1175 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1176
1177 // This is a poll immediately before a return. The exception handling code
1178 // has already had the effect of causing the return to occur, so the execution
1179 // will continue immediately after the call. In addition, the oopmap at the
1180 // return point does not mark the return value as an oop (if it is), so
1181 // it needs a handle here to be updated.
1182 if( nm->is_at_poll_return(real_return_addr) ) {
1183 // See if return type is an oop.
1184 bool return_oop = nm->method()->is_returning_oop();
1185 Handle return_value;
1186 if (return_oop) {
1187 // The oop result has been saved on the stack together with all
1188 // the other registers. In order to preserve it over GCs we need
1189 // to keep it in a handle.
1190 oop result = caller_fr.saved_oop_result(&map);
1191 assert(oopDesc::is_oop_or_null(result), "must be oop");
1192 return_value = Handle(thread(), result);
1193 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1194 }
1195
1196 // Block the thread
1197 SafepointMechanism::block_if_requested(thread());
1198
1199 // restore oop result, if any
1200 if (return_oop) {
1201 caller_fr.set_saved_oop_result(&map, return_value());
1202 }
1203 }
1204
1205 // This is a safepoint poll. Verify the return address and block.
1206 else {
1207 set_at_poll_safepoint(true);
1208
1209 // verify the blob built the "return address" correctly
1210 assert(real_return_addr == caller_fr.pc(), "must match");
1211
1212 // Block the thread
1213 SafepointMechanism::block_if_requested(thread());
1214 set_at_poll_safepoint(false);
1215
1216 // If we have a pending async exception deoptimize the frame
1217 // as otherwise we may never deliver it.
1218 if (thread()->has_async_condition()) {
1219 ThreadInVMfromJavaNoAsyncException __tiv(thread());
1220 Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1221 }
1222
1223 // If an exception has been installed we must check for a pending deoptimization
1224 // Deoptimize frame if exception has been thrown.
1225
1226 if (thread()->has_pending_exception() ) {
1227 RegisterMap map(thread(), true);
1228 frame caller_fr = stub_fr.sender(&map);
1229 if (caller_fr.is_deoptimized_frame()) {
1230 // The exception patch will destroy registers that are still
1231 // live and will be needed during deoptimization. Defer the
1232 // Async exception should have deferred the exception until the
1233 // next safepoint which will be detected when we get into
1234 // the interpreter so if we have an exception now things
1235 // are messed up.
1236
1237 fatal("Exception installed and deoptimization is pending");
1238 }
1239 }
1240 }
1241 }
1242
1243
1244 //
1245 // Statistics & Instrumentations
1246 //
1247 struct SafepointStats {
1248 float _time_stamp; // record when the current safepoint occurs in seconds
1249 int _vmop_type; // tyep of VM operation triggers the safepoint
1250 int _nof_total_threads; // total number of Java threads
1251 int _nof_initial_running_threads; // total number of initially seen running threads
1252 int _nof_threads_wait_to_block; // total number of threads waiting for to block
1253 bool _page_armed; // true if polling page is armed, false otherwise
1254 int _nof_threads_hit_page_trap; // total number of threads hitting the page trap
1255 jlong _time_to_spin; // total time in millis spent in spinning
1256 jlong _time_to_wait_to_block; // total time in millis spent in waiting for to block
1257 jlong _time_to_do_cleanups; // total time in millis spent in performing cleanups
1258 jlong _time_to_sync; // total time in millis spent in getting to _synchronized
1259 jlong _time_to_exec_vmop; // total time in millis spent in vm operation itself
1260 };
1261
1262 static const int _statistics_header_count = 30;
1263 static int _cur_stat_index = 0;
1264 static SafepointStats safepoint_stats = {0}; // zero initialize
1265 static SafepointStats* spstat = &safepoint_stats;
1266
1267 static julong _safepoint_reasons[VM_Operation::VMOp_Terminating];
1268 static jlong _max_sync_time = 0;
1269 static jlong _max_vmop_time = 0;
1270
1271 static jlong cleanup_end_time = 0;
1272
1273 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1274
1275 spstat->_time_stamp = _ts_of_current_safepoint;
1276
1277 VM_Operation *op = VMThread::vm_operation();
1278 spstat->_vmop_type = op != NULL ? op->type() : VM_Operation::VMOp_None;
1279 _safepoint_reasons[spstat->_vmop_type]++;
1280
1281 spstat->_nof_total_threads = nof_threads;
1282 spstat->_nof_initial_running_threads = nof_running;
1283
1284 // Records the start time of spinning. The real time spent on spinning
1285 // will be adjusted when spin is done. Same trick is applied for time
1286 // spent on waiting for threads to block.
1287 if (nof_running != 0) {
1288 spstat->_time_to_spin = os::javaTimeNanos();
1289 } else {
1290 spstat->_time_to_spin = 0;
1291 }
1292 }
1293
1294 void SafepointSynchronize::update_statistics_on_spin_end() {
1295 jlong cur_time = os::javaTimeNanos();
1296
1297 spstat->_nof_threads_wait_to_block = _waiting_to_block;
1298 if (spstat->_nof_initial_running_threads != 0) {
1299 spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
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
1312 if (spstat->_nof_threads_wait_to_block != 0) {
1313 spstat->_time_to_wait_to_block = end_time -
1314 spstat->_time_to_wait_to_block;
1315 }
1316
1317 // Records the end time of sync which will be used to calculate the total
1318 // vm operation time. Again, the real time spending in syncing will be deducted
1319 // from the start of the sync time later when end_statistics is called.
1320 spstat->_time_to_sync = end_time - _safepoint_begin_time;
1321 if (spstat->_time_to_sync > _max_sync_time) {
1322 _max_sync_time = spstat->_time_to_sync;
1323 }
1324
1325 spstat->_time_to_do_cleanups = end_time;
1326 }
1327
1328 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1329
1330 // Record how long spent in cleanup tasks.
1331 spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1332 cleanup_end_time = end_time;
1333 }
1334
1335 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1336
1337 // Update the vm operation time.
1338 spstat->_time_to_exec_vmop = vmop_end_time - cleanup_end_time;
1339 if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1340 _max_vmop_time = spstat->_time_to_exec_vmop;
1341 }
1342
1343 spstat->_nof_threads_hit_page_trap = _nof_threads_hit_polling_page;
1344
1345 print_statistics();
1346 }
1347
1348 // Helper method to print the header.
1349 static void print_header(outputStream* st) {
1350 // The number of spaces is significant here, and should match the format
1351 // specifiers in print_statistics().
1352
1353 st->print(" vmop "
1354 "[ threads: total initially_running wait_to_block ]"
1355 "[ time: spin block sync cleanup vmop ] ");
1356
1357 st->print_cr("page_trap_count");
1358 }
1359
1360 // This prints a nice table. To get the statistics to not shift due to the logging uptime
1361 // decorator, use the option as: -Xlog:safepoint+stats=debug:[outputfile]:none
1362 void SafepointSynchronize::print_statistics() {
1363 LogTarget(Debug, safepoint, stats) lt;
1364 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
1365 LogStream ls(lt);
1366
1367 // Print header every 30 entries
1368 if ((_cur_stat_index % _statistics_header_count) == 0) {
1369 print_header(&ls);
1370 _cur_stat_index = 1; // wrap
1371 } else {
1372 _cur_stat_index++;
1373 }
1374
1375 ls.print("%8.3f: ", spstat->_time_stamp);
1376 ls.print("%-28s [ "
1377 INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " "
1378 "]",
1379 VM_Operation::name(spstat->_vmop_type),
1380 spstat->_nof_total_threads,
1381 spstat->_nof_initial_running_threads,
1382 spstat->_nof_threads_wait_to_block);
1383 // "/ MICROUNITS " is to convert the unit from nanos to millis.
1384 ls.print("[ "
1385 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1386 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1387 INT64_FORMAT_W(7) " ] ",
1388 (int64_t)(spstat->_time_to_spin / MICROUNITS),
1389 (int64_t)(spstat->_time_to_wait_to_block / MICROUNITS),
1390 (int64_t)(spstat->_time_to_sync / MICROUNITS),
1391 (int64_t)(spstat->_time_to_do_cleanups / MICROUNITS),
1392 (int64_t)(spstat->_time_to_exec_vmop / MICROUNITS));
1393
1394 ls.print_cr(INT32_FORMAT_W(15) " ", spstat->_nof_threads_hit_page_trap);
1395 }
1396
1397 // This method will be called when VM exits. This tries to summarize the sampling.
1398 // Current thread may already be deleted, so don't use ResourceMark.
1399 void SafepointSynchronize::print_stat_on_exit() {
1400
1401 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1402 if (_safepoint_reasons[index] != 0) {
1403 log_debug(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1404 _safepoint_reasons[index]);
1405 }
1406 }
1407
1408 log_debug(safepoint, stats)("VM operations coalesced during safepoint " INT64_FORMAT,
1409 _coalesced_vmop_count);
1410 log_debug(safepoint, stats)("Maximum sync time " INT64_FORMAT" ms",
1411 (int64_t)(_max_sync_time / MICROUNITS));
1412 log_debug(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
1413 INT64_FORMAT " ms",
1414 (int64_t)(_max_vmop_time / MICROUNITS));
1415 }