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 // -- 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 // -- 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 // -- YieldTo() any still-running mutators that are ready but OFFPROC.
364 // -- Check system saturation. If the system is not fully saturated then
365 // simply spin and avoid sleep/yield.
366 // -- As still-running mutators rendezvous they could unpark the sleeping
367 // VMthread. This works well for still-running mutators that become
368 // safe. The VMthread must still poll for mutators that call-out.
369 // -- Drive the policy on time-since-begin instead of iterations.
370 // -- Consider making the spin duration a function of the # of CPUs:
371 // Spin = (((ncpus-1) * M) + K) + F(still_running)
372 // Alternately, instead of counting iterations of the outer loop
373 // we could count the # of threads visited in the inner loop, above.
374 // -- On windows consider using the return value from SwitchThreadTo()
375 // to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
376
377 if (int(iterations) == -1) { // overflow - something is wrong.
378 // We can only overflow here when we are using global
379 // polling pages. We keep this guarantee in its original
380 // form so that searches of the bug database for this
381 // failure mode find the right bugs.
382 guarantee (PageArmed == 0, "invariant");
383 }
384
385 // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
386 // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
387 ++steps ;
388 if (ncpus > 1 && steps < safepoint_spin_before_yield) {
389 SpinPause() ; // MP-Polite spin
390 } else
391 if (steps < _defer_thr_suspend_loop_count) {
392 os::naked_yield() ;
393 } else {
394 os::naked_short_sleep(1);
395 }
396
397 iterations ++ ;
398 }
399 assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
400 }
401 } // ThreadsListHandle destroyed here.
402 assert(still_running == 0, "sanity check");
403
404 if (log_is_enabled(Debug, safepoint, stats)) {
405 update_statistics_on_spin_end();
406 }
407 if (sync_event.should_commit()) {
408 post_safepoint_synchronize_event(&sync_event, initial_running, _waiting_to_block, iterations);
409 }
410 }
411
412 // wait until all threads are stopped
413 {
414 EventSafepointWaitBlocked wait_blocked_event;
415 int initial_waiting_to_block = _waiting_to_block;
416
417 while (_waiting_to_block > 0) {
418 log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block);
419 if (!SafepointTimeout || timeout_error_printed) {
420 Safepoint_lock->wait(true); // true, means with no safepoint checks
421 } else {
422 // Compute remaining time
423 jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
424
425 // If there is no remaining time, then there is an error
426 if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
427 print_safepoint_timeout(_blocking_timeout);
428 }
429 }
430 }
431 assert(_waiting_to_block == 0, "sanity check");
432
433 #ifndef PRODUCT
434 if (SafepointTimeout) {
435 jlong current_time = os::javaTimeNanos();
436 if (safepoint_limit_time < current_time) {
437 log_warning(safepoint)("# SafepointSynchronize: Finished after "
438 INT64_FORMAT_W(6) " ms",
439 (int64_t)((current_time - safepoint_limit_time) / MICROUNITS +
440 (jlong)SafepointTimeoutDelay));
441 }
442 }
443 #endif
444
445 assert((_safepoint_counter & 0x1) == 0, "must be even");
446 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
447 _safepoint_counter ++;
448
449 // Record state
450 _state = _synchronized;
451
452 OrderAccess::fence();
453 if (wait_blocked_event.should_commit()) {
454 post_safepoint_wait_blocked_event(&wait_blocked_event, initial_waiting_to_block);
455 }
456 }
457
458 #ifdef ASSERT
459 // Make sure all the threads were visited.
460 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
461 assert(cur->was_visited_for_critical_count(), "missed a thread");
462 }
463 #endif // ASSERT
464
465 // Update the count of active JNI critical regions
466 GCLocker::set_jni_lock_count(_current_jni_active_count);
467
468 log_info(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description());
469
470 RuntimeService::record_safepoint_synchronized();
471 if (log_is_enabled(Debug, safepoint, stats)) {
472 update_statistics_on_sync_end(os::javaTimeNanos());
473 }
474
475 // Call stuff that needs to be run when a safepoint is just about to be completed
476 {
477 EventSafepointCleanup cleanup_event;
478 do_cleanup_tasks();
479 if (cleanup_event.should_commit()) {
480 post_safepoint_cleanup_event(&cleanup_event);
481 }
482 }
483
484 if (log_is_enabled(Debug, safepoint, stats)) {
485 // Record how much time spend on the above cleanup tasks
486 update_statistics_on_cleanup_end(os::javaTimeNanos());
487 }
488
489 if (begin_event.should_commit()) {
490 post_safepoint_begin_event(&begin_event, nof_threads, _current_jni_active_count);
491 }
492 }
493
494 // Wake up all threads, so they are ready to resume execution after the safepoint
495 // operation has been carried out
496 void SafepointSynchronize::end() {
497 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
498 assert((_safepoint_counter & 0x1) == 1, "must be odd");
499 EventSafepointEnd event;
500 _safepoint_counter ++;
501 // memory fence isn't required here since an odd _safepoint_counter
502 // value can do no harm and a fence is issued below anyway.
503
504 DEBUG_ONLY(Thread* myThread = Thread::current();)
505 assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
506
507 if (log_is_enabled(Debug, safepoint, stats)) {
508 end_statistics(os::javaTimeNanos());
509 }
510
511 {
512 JavaThreadIteratorWithHandle jtiwh;
513 #ifdef ASSERT
514 // A pending_exception cannot be installed during a safepoint. The threads
515 // may install an async exception after they come back from a safepoint into
516 // pending_exception after they unblock. But that should happen later.
517 for (; JavaThread *cur = jtiwh.next(); ) {
518 assert (!(cur->has_pending_exception() &&
519 cur->safepoint_state()->is_at_poll_safepoint()),
520 "safepoint installed a pending exception");
521 }
522 #endif // ASSERT
523
524 if (PageArmed) {
525 assert(SafepointMechanism::uses_global_page_poll(), "sanity");
526 // Make polling safepoint aware
527 os::make_polling_page_readable();
528 PageArmed = 0 ;
529 }
530
531 if (SafepointMechanism::uses_global_page_poll()) {
532 // Remove safepoint check from interpreter
533 Interpreter::ignore_safepoints();
534 }
535
536 {
537 MutexLocker mu(Safepoint_lock);
538
539 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
540
541 if (SafepointMechanism::uses_thread_local_poll()) {
542 _state = _not_synchronized;
543 OrderAccess::storestore(); // global state -> local state
544 jtiwh.rewind();
545 for (; JavaThread *current = jtiwh.next(); ) {
546 ThreadSafepointState* cur_state = current->safepoint_state();
547 cur_state->restart(); // TSS _running
548 SafepointMechanism::disarm_local_poll(current);
549 }
550 log_info(safepoint)("Leaving safepoint region");
551 } else {
552 // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
553 // when they get restarted.
554 _state = _not_synchronized;
555 OrderAccess::fence();
556
557 log_info(safepoint)("Leaving safepoint region");
558
559 // Start suspended threads
560 jtiwh.rewind();
561 for (; JavaThread *current = jtiwh.next(); ) {
562 ThreadSafepointState* cur_state = current->safepoint_state();
563 assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
564 cur_state->restart();
565 assert(cur_state->is_running(), "safepoint state has not been reset");
566 }
567 }
568
569 RuntimeService::record_safepoint_end();
570
571 // Release threads lock, so threads can be created/destroyed again.
572 // It will also release all threads blocked in signal_thread_blocked.
573 Threads_lock->unlock();
574 }
575 } // ThreadsListHandle destroyed here.
576
577 Universe::heap()->safepoint_synchronize_end();
578 // record this time so VMThread can keep track how much time has elapsed
579 // since last safepoint.
580 _end_of_last_safepoint = os::javaTimeMillis();
581 if (event.should_commit()) {
582 post_safepoint_end_event(&event);
583 }
584 }
585
586 bool SafepointSynchronize::is_cleanup_needed() {
587 // Need a safepoint if there are many monitors to deflate.
588 if (ObjectSynchronizer::is_cleanup_needed()) return true;
589 // Need a safepoint if some inline cache buffers is non-empty
590 if (!InlineCacheBuffer::is_empty()) return true;
591 return false;
592 }
593
594 class ParallelSPCleanupThreadClosure : public ThreadClosure {
595 private:
596 CodeBlobClosure* _nmethod_cl;
597 DeflateMonitorCounters* _counters;
598
599 public:
600 ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
601 _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()), _counters(counters) {}
602
603 void do_thread(Thread* thread) {
604 ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
605 if (_nmethod_cl != NULL && thread->is_Java_thread() &&
606 ! thread->is_Code_cache_sweeper_thread()) {
607 JavaThread* jt = (JavaThread*) thread;
608 jt->nmethods_do(_nmethod_cl);
609 }
610 }
611 };
612
613 class ParallelSPCleanupTask : public AbstractGangTask {
614 private:
615 SubTasksDone _subtasks;
616 ParallelSPCleanupThreadClosure _cleanup_threads_cl;
617 uint _num_workers;
618 DeflateMonitorCounters* _counters;
619 public:
620 ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
621 AbstractGangTask("Parallel Safepoint Cleanup"),
622 _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
623 _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
624 _num_workers(num_workers),
625 _counters(counters) {}
626
627 void work(uint worker_id) {
628 // All threads deflate monitors and mark nmethods (if necessary).
629 Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl);
630
631 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
632 const char* name = "deflating idle monitors";
633 EventSafepointCleanupTask event;
634 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
635 ObjectSynchronizer::deflate_idle_monitors(_counters);
636 if (event.should_commit()) {
637 post_safepoint_cleanup_task_event(&event, name);
638 }
639 }
640
641 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
642 const char* name = "updating inline caches";
643 EventSafepointCleanupTask event;
644 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
645 InlineCacheBuffer::update_inline_caches();
646 if (event.should_commit()) {
647 post_safepoint_cleanup_task_event(&event, name);
648 }
649 }
650
651 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
652 const char* name = "compilation policy safepoint handler";
653 EventSafepointCleanupTask event;
654 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
655 CompilationPolicy::policy()->do_safepoint_work();
656 if (event.should_commit()) {
657 post_safepoint_cleanup_task_event(&event, name);
658 }
659 }
660
661 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
662 if (SymbolTable::needs_rehashing()) {
663 const char* name = "rehashing symbol table";
664 EventSafepointCleanupTask event;
665 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
666 SymbolTable::rehash_table();
667 if (event.should_commit()) {
668 post_safepoint_cleanup_task_event(&event, name);
669 }
670 }
671 }
672
673 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
674 if (StringTable::needs_rehashing()) {
675 const char* name = "rehashing string table";
676 EventSafepointCleanupTask event;
677 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
678 StringTable::rehash_table();
679 if (event.should_commit()) {
680 post_safepoint_cleanup_task_event(&event, name);
681 }
682 }
683 }
684
685 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
686 // CMS delays purging the CLDG until the beginning of the next safepoint and to
687 // make sure concurrent sweep is done
688 const char* name = "purging class loader data graph";
689 EventSafepointCleanupTask event;
690 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
691 ClassLoaderDataGraph::purge_if_needed();
692 if (event.should_commit()) {
693 post_safepoint_cleanup_task_event(&event, name);
694 }
695 }
696
697 if (!_subtasks.is_task_claimed(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) {
698 const char* name = "resizing system dictionaries";
699 EventSafepointCleanupTask event;
700 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
701 ClassLoaderDataGraph::resize_if_needed();
702 if (event.should_commit()) {
703 post_safepoint_cleanup_task_event(&event, name);
704 }
705 }
706 _subtasks.all_tasks_completed(_num_workers);
707 }
708 };
709
710 // Various cleaning tasks that should be done periodically at safepoints.
711 void SafepointSynchronize::do_cleanup_tasks() {
712
713 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
714
715 // Prepare for monitor deflation.
716 DeflateMonitorCounters deflate_counters;
717 ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
718
719 CollectedHeap* heap = Universe::heap();
720 assert(heap != NULL, "heap not initialized yet?");
721 WorkGang* cleanup_workers = heap->get_safepoint_workers();
722 if (cleanup_workers != NULL) {
723 // Parallel cleanup using GC provided thread pool.
724 uint num_cleanup_workers = cleanup_workers->active_workers();
725 ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
726 StrongRootsScope srs(num_cleanup_workers);
727 cleanup_workers->run_task(&cleanup);
728 } else {
729 // Serial cleanup using VMThread.
730 ParallelSPCleanupTask cleanup(1, &deflate_counters);
731 StrongRootsScope srs(1);
732 cleanup.work(0);
733 }
734
735 // Finish monitor deflation.
736 ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
737 }
738
739
740 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
741 switch(state) {
742 case _thread_in_native:
743 // native threads are safe if they have no java stack or have walkable stack
744 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
745
746 // blocked threads should have already have walkable stack
747 case _thread_blocked:
748 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
749 return true;
750
751 default:
752 return false;
753 }
754 }
755
756
757 // See if the thread is running inside a lazy critical native and
758 // update the thread critical count if so. Also set a suspend flag to
759 // cause the native wrapper to return into the JVM to do the unlock
760 // once the native finishes.
761 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
762 if (state == _thread_in_native &&
763 thread->has_last_Java_frame() &&
764 thread->frame_anchor()->walkable()) {
765 // This thread might be in a critical native nmethod so look at
766 // the top of the stack and increment the critical count if it
767 // is.
768 frame wrapper_frame = thread->last_frame();
769 CodeBlob* stub_cb = wrapper_frame.cb();
770 if (stub_cb != NULL &&
771 stub_cb->is_nmethod() &&
772 stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
773 // A thread could potentially be in a critical native across
774 // more than one safepoint, so only update the critical state on
775 // the first one. When it returns it will perform the unlock.
776 if (!thread->do_critical_native_unlock()) {
777 #ifdef ASSERT
778 if (!thread->in_critical()) {
779 GCLocker::increment_debug_jni_lock_count();
780 }
781 #endif
782 thread->enter_critical();
783 // Make sure the native wrapper calls back on return to
784 // perform the needed critical unlock.
785 thread->set_critical_native_unlock();
786 }
787 }
788 }
789 }
790
791
792
793 // -------------------------------------------------------------------------------------------------------
794 // Implementation of Safepoint callback point
795
796 void SafepointSynchronize::block(JavaThread *thread) {
797 assert(thread != NULL, "thread must be set");
798 assert(thread->is_Java_thread(), "not a Java thread");
799
800 // Threads shouldn't block if they are in the middle of printing, but...
801 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
802
803 // Only bail from the block() call if the thread is gone from the
804 // thread list; starting to exit should still block.
805 if (thread->is_terminated()) {
806 // block current thread if we come here from native code when VM is gone
807 thread->block_if_vm_exited();
808
809 // otherwise do nothing
810 return;
811 }
812
813 JavaThreadState state = thread->thread_state();
814 thread->frame_anchor()->make_walkable(thread);
815
816 // Check that we have a valid thread_state at this point
817 switch(state) {
818 case _thread_in_vm_trans:
819 case _thread_in_Java: // From compiled code
820
821 // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
822 // we pretend we are still in the VM.
823 thread->set_thread_state(_thread_in_vm);
824
825 if (is_synchronizing()) {
826 Atomic::inc (&TryingToBlock) ;
827 }
828
829 // We will always be holding the Safepoint_lock when we are examine the state
830 // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
831 // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
832 Safepoint_lock->lock_without_safepoint_check();
833 if (is_synchronizing()) {
834 // Decrement the number of threads to wait for and signal vm thread
835 assert(_waiting_to_block > 0, "sanity check");
836 _waiting_to_block--;
837 thread->safepoint_state()->set_has_called_back(true);
838
839 DEBUG_ONLY(thread->set_visited_for_critical_count(true));
840 if (thread->in_critical()) {
841 // Notice that this thread is in a critical section
842 increment_jni_active_count();
843 }
844
845 // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
846 if (_waiting_to_block == 0) {
847 Safepoint_lock->notify_all();
848 }
849 }
850
851 // We transition the thread to state _thread_blocked here, but
852 // we can't do our usual check for external suspension and then
853 // self-suspend after the lock_without_safepoint_check() call
854 // below because we are often called during transitions while
855 // we hold different locks. That would leave us suspended while
856 // holding a resource which results in deadlocks.
857 thread->set_thread_state(_thread_blocked);
858 Safepoint_lock->unlock();
859
860 // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
861 // the entire safepoint, the threads will all line up here during the safepoint.
862 Threads_lock->lock_without_safepoint_check();
863 // restore original state. This is important if the thread comes from compiled code, so it
864 // will continue to execute with the _thread_in_Java state.
865 thread->set_thread_state(state);
866 Threads_lock->unlock();
867 break;
868
869 case _thread_in_native_trans:
870 case _thread_blocked_trans:
871 case _thread_new_trans:
872 if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
873 thread->print_thread_state();
874 fatal("Deadlock in safepoint code. "
875 "Should have called back to the VM before blocking.");
876 }
877
878 // We transition the thread to state _thread_blocked here, but
879 // we can't do our usual check for external suspension and then
880 // self-suspend after the lock_without_safepoint_check() call
881 // below because we are often called during transitions while
882 // we hold different locks. That would leave us suspended while
883 // holding a resource which results in deadlocks.
884 thread->set_thread_state(_thread_blocked);
885
886 // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
887 // the safepoint code might still be waiting for it to block. We need to change the state here,
888 // so it can see that it is at a safepoint.
889
890 // Block until the safepoint operation is completed.
891 Threads_lock->lock_without_safepoint_check();
892
893 // Restore state
894 thread->set_thread_state(state);
895
896 Threads_lock->unlock();
897 break;
898
899 default:
900 fatal("Illegal threadstate encountered: %d", state);
901 }
902
903 // Check for pending. async. exceptions or suspends - except if the
904 // thread was blocked inside the VM. has_special_runtime_exit_condition()
905 // is called last since it grabs a lock and we only want to do that when
906 // we must.
907 //
908 // Note: we never deliver an async exception at a polling point as the
909 // compiler may not have an exception handler for it. The polling
910 // code will notice the async and deoptimize and the exception will
911 // be delivered. (Polling at a return point is ok though). Sure is
912 // a lot of bother for a deprecated feature...
913 //
914 // We don't deliver an async exception if the thread state is
915 // _thread_in_native_trans so JNI functions won't be called with
916 // a surprising pending exception. If the thread state is going back to java,
917 // async exception is checked in check_special_condition_for_native_trans().
918
919 if (state != _thread_blocked_trans &&
920 state != _thread_in_vm_trans &&
921 thread->has_special_runtime_exit_condition()) {
922 thread->handle_special_runtime_exit_condition(
923 !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
924 }
925 }
926
927 // ------------------------------------------------------------------------------------------------------
928 // Exception handlers
929
930
931 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
932 assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
933 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
934 if (!ThreadLocalHandshakes) {
935 assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
936 }
937
938 if (log_is_enabled(Debug, safepoint, stats)) {
939 Atomic::inc(&_nof_threads_hit_polling_page);
940 }
941
942 ThreadSafepointState* state = thread->safepoint_state();
943
944 state->handle_polling_page_exception();
945 }
946
947
948 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
949 if (!timeout_error_printed) {
950 timeout_error_printed = true;
951 // Print out the thread info which didn't reach the safepoint for debugging
952 // purposes (useful when there are lots of threads in the debugger).
953 LogTarget(Warning, safepoint) lt;
954 if (lt.is_enabled()) {
955 ResourceMark rm;
956 LogStream ls(lt);
957
958 ls.cr();
959 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
960 if (reason == _spinning_timeout) {
961 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
962 } else if (reason == _blocking_timeout) {
963 ls.print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
964 }
965
966 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
967 ThreadSafepointState *cur_state;
968 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
969 cur_state = cur_thread->safepoint_state();
970
971 if (cur_thread->thread_state() != _thread_blocked &&
972 ((reason == _spinning_timeout && cur_state->is_running()) ||
973 (reason == _blocking_timeout && !cur_state->has_called_back()))) {
974 ls.print("# ");
975 cur_thread->print_on(&ls);
976 ls.cr();
977 }
978 }
979 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
980 }
981 }
982
983 // To debug the long safepoint, specify both DieOnSafepointTimeout &
984 // ShowMessageBoxOnError.
985 if (DieOnSafepointTimeout) {
986 fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
987 SafepointTimeoutDelay, VMThread::vm_safepoint_description());
988 }
989 }
990
991
992 // -------------------------------------------------------------------------------------------------------
993 // Implementation of ThreadSafepointState
994
995 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
996 _thread = thread;
997 _type = _running;
998 _has_called_back = false;
999 _at_poll_safepoint = false;
1000 }
1001
1002 void ThreadSafepointState::create(JavaThread *thread) {
1003 ThreadSafepointState *state = new ThreadSafepointState(thread);
1004 thread->set_safepoint_state(state);
1005 }
1006
1007 void ThreadSafepointState::destroy(JavaThread *thread) {
1008 if (thread->safepoint_state()) {
1009 delete(thread->safepoint_state());
1010 thread->set_safepoint_state(NULL);
1011 }
1012 }
1013
1014 void ThreadSafepointState::examine_state_of_thread() {
1015 assert(is_running(), "better be running or just have hit safepoint poll");
1016
1017 JavaThreadState state = _thread->thread_state();
1018
1019 // Save the state at the start of safepoint processing.
1020 _orig_thread_state = state;
1021
1022 // Check for a thread that is suspended. Note that thread resume tries
1023 // to grab the Threads_lock which we own here, so a thread cannot be
1024 // resumed during safepoint synchronization.
1025
1026 // We check to see if this thread is suspended without locking to
1027 // avoid deadlocking with a third thread that is waiting for this
1028 // thread to be suspended. The third thread can notice the safepoint
1029 // that we're trying to start at the beginning of its SR_lock->wait()
1030 // call. If that happens, then the third thread will block on the
1031 // safepoint while still holding the underlying SR_lock. We won't be
1032 // able to get the SR_lock and we'll deadlock.
1033 //
1034 // We don't need to grab the SR_lock here for two reasons:
1035 // 1) The suspend flags are both volatile and are set with an
1036 // Atomic::cmpxchg() call so we should see the suspended
1037 // state right away.
1038 // 2) We're being called from the safepoint polling loop; if
1039 // we don't see the suspended state on this iteration, then
1040 // we'll come around again.
1041 //
1042 bool is_suspended = _thread->is_ext_suspended();
1043 if (is_suspended) {
1044 roll_forward(_at_safepoint);
1045 return;
1046 }
1047
1048 // Some JavaThread states have an initial safepoint state of
1049 // running, but are actually at a safepoint. We will happily
1050 // agree and update the safepoint state here.
1051 if (SafepointSynchronize::safepoint_safe(_thread, state)) {
1052 SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
1053 roll_forward(_at_safepoint);
1054 return;
1055 }
1056
1057 if (state == _thread_in_vm) {
1058 roll_forward(_call_back);
1059 return;
1060 }
1061
1062 // All other thread states will continue to run until they
1063 // transition and self-block in state _blocked
1064 // Safepoint polling in compiled code causes the Java threads to do the same.
1065 // Note: new threads may require a malloc so they must be allowed to finish
1066
1067 assert(is_running(), "examine_state_of_thread on non-running thread");
1068 return;
1069 }
1070
1071 // Returns true is thread could not be rolled forward at present position.
1072 void ThreadSafepointState::roll_forward(suspend_type type) {
1073 _type = type;
1074
1075 switch(_type) {
1076 case _at_safepoint:
1077 SafepointSynchronize::signal_thread_at_safepoint();
1078 DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
1079 if (_thread->in_critical()) {
1080 // Notice that this thread is in a critical section
1081 SafepointSynchronize::increment_jni_active_count();
1082 }
1083 break;
1084
1085 case _call_back:
1086 set_has_called_back(false);
1087 break;
1088
1089 case _running:
1090 default:
1091 ShouldNotReachHere();
1092 }
1093 }
1094
1095 void ThreadSafepointState::restart() {
1096 switch(type()) {
1097 case _at_safepoint:
1098 case _call_back:
1099 break;
1100
1101 case _running:
1102 default:
1103 tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
1104 p2i(_thread), _type);
1105 _thread->print();
1106 ShouldNotReachHere();
1107 }
1108 _type = _running;
1109 set_has_called_back(false);
1110 }
1111
1112
1113 void ThreadSafepointState::print_on(outputStream *st) const {
1114 const char *s = NULL;
1115
1116 switch(_type) {
1117 case _running : s = "_running"; break;
1118 case _at_safepoint : s = "_at_safepoint"; break;
1119 case _call_back : s = "_call_back"; break;
1120 default:
1121 ShouldNotReachHere();
1122 }
1123
1124 st->print_cr("Thread: " INTPTR_FORMAT
1125 " [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
1126 p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back,
1127 _at_poll_safepoint);
1128
1129 _thread->print_thread_state_on(st);
1130 }
1131
1132 // ---------------------------------------------------------------------------------------------------------------------
1133
1134 // Block the thread at poll or poll return for safepoint/handshake.
1135 void ThreadSafepointState::handle_polling_page_exception() {
1136
1137 // Check state. block() will set thread state to thread_in_vm which will
1138 // cause the safepoint state _type to become _call_back.
1139 suspend_type t = type();
1140 assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running,
1141 "polling page exception on thread not running state: %u", uint(t));
1142
1143 // Step 1: Find the nmethod from the return address
1144 address real_return_addr = thread()->saved_exception_pc();
1145
1146 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1147 assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1148 CompiledMethod* nm = (CompiledMethod*)cb;
1149
1150 // Find frame of caller
1151 frame stub_fr = thread()->last_frame();
1152 CodeBlob* stub_cb = stub_fr.cb();
1153 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1154 RegisterMap map(thread(), true);
1155 frame caller_fr = stub_fr.sender(&map);
1156
1157 // Should only be poll_return or poll
1158 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1159
1160 // This is a poll immediately before a return. The exception handling code
1161 // has already had the effect of causing the return to occur, so the execution
1162 // will continue immediately after the call. In addition, the oopmap at the
1163 // return point does not mark the return value as an oop (if it is), so
1164 // it needs a handle here to be updated.
1165 if( nm->is_at_poll_return(real_return_addr) ) {
1166 // See if return type is an oop.
1167 bool return_oop = nm->method()->is_returning_oop();
1168 Handle return_value;
1169 if (return_oop) {
1170 // The oop result has been saved on the stack together with all
1171 // the other registers. In order to preserve it over GCs we need
1172 // to keep it in a handle.
1173 oop result = caller_fr.saved_oop_result(&map);
1174 assert(oopDesc::is_oop_or_null(result), "must be oop");
1175 return_value = Handle(thread(), result);
1176 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1177 }
1178
1179 // Block the thread
1180 SafepointMechanism::block_if_requested(thread());
1181
1182 // restore oop result, if any
1183 if (return_oop) {
1184 caller_fr.set_saved_oop_result(&map, return_value());
1185 }
1186 }
1187
1188 // This is a safepoint poll. Verify the return address and block.
1189 else {
1190 set_at_poll_safepoint(true);
1191
1192 // verify the blob built the "return address" correctly
1193 assert(real_return_addr == caller_fr.pc(), "must match");
1194
1195 // Block the thread
1196 SafepointMechanism::block_if_requested(thread());
1197 set_at_poll_safepoint(false);
1198
1199 // If we have a pending async exception deoptimize the frame
1200 // as otherwise we may never deliver it.
1201 if (thread()->has_async_condition()) {
1202 ThreadInVMfromJavaNoAsyncException __tiv(thread());
1203 Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1204 }
1205
1206 // If an exception has been installed we must check for a pending deoptimization
1207 // Deoptimize frame if exception has been thrown.
1208
1209 if (thread()->has_pending_exception() ) {
1210 RegisterMap map(thread(), true);
1211 frame caller_fr = stub_fr.sender(&map);
1212 if (caller_fr.is_deoptimized_frame()) {
1213 // The exception patch will destroy registers that are still
1214 // live and will be needed during deoptimization. Defer the
1215 // Async exception should have deferred the exception until the
1216 // next safepoint which will be detected when we get into
1217 // the interpreter so if we have an exception now things
1218 // are messed up.
1219
1220 fatal("Exception installed and deoptimization is pending");
1221 }
1222 }
1223 }
1224 }
1225
1226
1227 //
1228 // Statistics & Instrumentations
1229 //
1230 struct SafepointStats {
1231 float _time_stamp; // record when the current safepoint occurs in seconds
1232 int _vmop_type; // tyep of VM operation triggers the safepoint
1233 int _nof_total_threads; // total number of Java threads
1234 int _nof_initial_running_threads; // total number of initially seen running threads
1235 int _nof_threads_wait_to_block; // total number of threads waiting for to block
1236 bool _page_armed; // true if polling page is armed, false otherwise
1237 int _nof_threads_hit_page_trap; // total number of threads hitting the page trap
1238 jlong _time_to_spin; // total time in millis spent in spinning
1239 jlong _time_to_wait_to_block; // total time in millis spent in waiting for to block
1240 jlong _time_to_do_cleanups; // total time in millis spent in performing cleanups
1241 jlong _time_to_sync; // total time in millis spent in getting to _synchronized
1242 jlong _time_to_exec_vmop; // total time in millis spent in vm operation itself
1243 };
1244
1245 static const int _statistics_header_count = 30;
1246 static int _cur_stat_index = 0;
1247 static SafepointStats safepoint_stats = {0}; // zero initialize
1248 static SafepointStats* spstat = &safepoint_stats;
1249
1250 static julong _safepoint_reasons[VM_Operation::VMOp_Terminating];
1251 static jlong _max_sync_time = 0;
1252 static jlong _max_vmop_time = 0;
1253
1254 static jlong cleanup_end_time = 0;
1255
1256 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1257
1258 spstat->_time_stamp = _ts_of_current_safepoint;
1259
1260 VM_Operation *op = VMThread::vm_operation();
1261 spstat->_vmop_type = op != NULL ? op->type() : VM_Operation::VMOp_None;
1262 _safepoint_reasons[spstat->_vmop_type]++;
1263
1264 spstat->_nof_total_threads = nof_threads;
1265 spstat->_nof_initial_running_threads = nof_running;
1266
1267 // Records the start time of spinning. The real time spent on spinning
1268 // will be adjusted when spin is done. Same trick is applied for time
1269 // spent on waiting for threads to block.
1270 if (nof_running != 0) {
1271 spstat->_time_to_spin = os::javaTimeNanos();
1272 } else {
1273 spstat->_time_to_spin = 0;
1274 }
1275 }
1276
1277 void SafepointSynchronize::update_statistics_on_spin_end() {
1278 jlong cur_time = os::javaTimeNanos();
1279
1280 spstat->_nof_threads_wait_to_block = _waiting_to_block;
1281 if (spstat->_nof_initial_running_threads != 0) {
1282 spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
1283 }
1284
1285 // Records the start time of waiting for to block. Updated when block is done.
1286 if (_waiting_to_block != 0) {
1287 spstat->_time_to_wait_to_block = cur_time;
1288 } else {
1289 spstat->_time_to_wait_to_block = 0;
1290 }
1291 }
1292
1293 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {
1294
1295 if (spstat->_nof_threads_wait_to_block != 0) {
1296 spstat->_time_to_wait_to_block = end_time -
1297 spstat->_time_to_wait_to_block;
1298 }
1299
1300 // Records the end time of sync which will be used to calculate the total
1301 // vm operation time. Again, the real time spending in syncing will be deducted
1302 // from the start of the sync time later when end_statistics is called.
1303 spstat->_time_to_sync = end_time - _safepoint_begin_time;
1304 if (spstat->_time_to_sync > _max_sync_time) {
1305 _max_sync_time = spstat->_time_to_sync;
1306 }
1307
1308 spstat->_time_to_do_cleanups = end_time;
1309 }
1310
1311 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1312
1313 // Record how long spent in cleanup tasks.
1314 spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1315 cleanup_end_time = end_time;
1316 }
1317
1318 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1319
1320 // Update the vm operation time.
1321 spstat->_time_to_exec_vmop = vmop_end_time - cleanup_end_time;
1322 if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1323 _max_vmop_time = spstat->_time_to_exec_vmop;
1324 }
1325
1326 spstat->_nof_threads_hit_page_trap = _nof_threads_hit_polling_page;
1327
1328 print_statistics();
1329 }
1330
1331 // Helper method to print the header.
1332 static void print_header(outputStream* st) {
1333 // The number of spaces is significant here, and should match the format
1334 // specifiers in print_statistics().
1335
1336 st->print(" vmop "
1337 "[ threads: total initially_running wait_to_block ]"
1338 "[ time: spin block sync cleanup vmop ] ");
1339
1340 st->print_cr("page_trap_count");
1341 }
1342
1343 // This prints a nice table. To get the statistics to not shift due to the logging uptime
1344 // decorator, use the option as: -Xlog:safepoint+stats=debug:[outputfile]:none
1345 void SafepointSynchronize::print_statistics() {
1346 LogTarget(Debug, safepoint, stats) lt;
1347 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
1348 LogStream ls(lt);
1349
1350 // Print header every 30 entries
1351 if ((_cur_stat_index % _statistics_header_count) == 0) {
1352 print_header(&ls);
1353 _cur_stat_index = 1; // wrap
1354 } else {
1355 _cur_stat_index++;
1356 }
1357
1358 ls.print("%8.3f: ", spstat->_time_stamp);
1359 ls.print("%-28s [ "
1360 INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " "
1361 "]",
1362 VM_Operation::name(spstat->_vmop_type),
1363 spstat->_nof_total_threads,
1364 spstat->_nof_initial_running_threads,
1365 spstat->_nof_threads_wait_to_block);
1366 // "/ MICROUNITS " is to convert the unit from nanos to millis.
1367 ls.print("[ "
1368 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1369 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1370 INT64_FORMAT_W(7) " ] ",
1371 (int64_t)(spstat->_time_to_spin / MICROUNITS),
1372 (int64_t)(spstat->_time_to_wait_to_block / MICROUNITS),
1373 (int64_t)(spstat->_time_to_sync / MICROUNITS),
1374 (int64_t)(spstat->_time_to_do_cleanups / MICROUNITS),
1375 (int64_t)(spstat->_time_to_exec_vmop / MICROUNITS));
1376
1377 ls.print_cr(INT32_FORMAT_W(15) " ", spstat->_nof_threads_hit_page_trap);
1378 }
1379
1380 // This method will be called when VM exits. This tries to summarize the sampling.
1381 // Current thread may already be deleted, so don't use ResourceMark.
1382 void SafepointSynchronize::print_stat_on_exit() {
1383
1384 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1385 if (_safepoint_reasons[index] != 0) {
1386 log_debug(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1387 _safepoint_reasons[index]);
1388 }
1389 }
1390
1391 log_debug(safepoint, stats)("VM operations coalesced during safepoint " INT64_FORMAT,
1392 _coalesced_vmop_count);
1393 log_debug(safepoint, stats)("Maximum sync time " INT64_FORMAT" ms",
1394 (int64_t)(_max_sync_time / MICROUNITS));
1395 log_debug(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
1396 INT64_FORMAT " ms",
1397 (int64_t)(_max_vmop_time / MICROUNITS));
1398 }