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.inline.hpp"
27 #include "classfile/stringTable.hpp"
28 #include "classfile/symbolTable.hpp"
29 #include "classfile/systemDictionary.hpp"
30 #include "code/codeCache.hpp"
31 #include "code/icBuffer.hpp"
32 #include "code/nmethod.hpp"
33 #include "code/pcDesc.hpp"
34 #include "code/scopeDesc.hpp"
35 #include "gc/shared/collectedHeap.hpp"
36 #include "gc/shared/gcLocker.hpp"
37 #include "gc/shared/strongRootsScope.hpp"
38 #include "gc/shared/workgroup.hpp"
39 #include "interpreter/interpreter.hpp"
40 #include "jfr/jfrEvents.hpp"
41 #include "logging/log.hpp"
42 #include "logging/logStream.hpp"
43 #include "memory/resourceArea.hpp"
44 #include "memory/universe.hpp"
45 #include "oops/oop.inline.hpp"
46 #include "oops/symbol.hpp"
47 #include "oops/valueKlass.hpp"
48 #include "runtime/atomic.hpp"
49 #include "runtime/compilationPolicy.hpp"
50 #include "runtime/deoptimization.hpp"
51 #include "runtime/frame.inline.hpp"
52 #include "runtime/interfaceSupport.inline.hpp"
53 #include "runtime/mutexLocker.hpp"
54 #include "runtime/orderAccess.hpp"
55 #include "runtime/osThread.hpp"
56 #include "runtime/safepoint.hpp"
57 #include "runtime/safepointMechanism.inline.hpp"
58 #include "runtime/signature.hpp"
59 #include "runtime/stubCodeGenerator.hpp"
60 #include "runtime/stubRoutines.hpp"
61 #include "runtime/sweeper.hpp"
62 #include "runtime/synchronizer.hpp"
63 #include "runtime/thread.inline.hpp"
64 #include "runtime/threadSMR.hpp"
65 #include "runtime/timerTrace.hpp"
66 #include "services/runtimeService.hpp"
67 #include "utilities/events.hpp"
68 #include "utilities/macros.hpp"
69 #ifdef COMPILER1
70 #include "c1/c1_globals.hpp"
71 #endif
72
73 template <typename E>
74 static void set_current_safepoint_id(E* event, int adjustment = 0) {
75 assert(event != NULL, "invariant");
76 event->set_safepointId(SafepointSynchronize::safepoint_counter() + adjustment);
77 }
78
79 static void post_safepoint_begin_event(EventSafepointBegin* event,
80 int thread_count,
81 int critical_thread_count) {
82 assert(event != NULL, "invariant");
83 assert(event->should_commit(), "invariant");
84 set_current_safepoint_id(event);
85 event->set_totalThreadCount(thread_count);
86 event->set_jniCriticalThreadCount(critical_thread_count);
87 event->commit();
88 }
89
90 static void post_safepoint_cleanup_event(EventSafepointCleanup* event) {
91 assert(event != NULL, "invariant");
92 assert(event->should_commit(), "invariant");
93 set_current_safepoint_id(event);
94 event->commit();
95 }
96
97 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization* event,
98 int initial_number_of_threads,
99 int threads_waiting_to_block,
100 unsigned int iterations) {
101 assert(event != NULL, "invariant");
102 if (event->should_commit()) {
103 // Group this event together with the ones committed after the counter is increased
104 set_current_safepoint_id(event, 1);
105 event->set_initialThreadCount(initial_number_of_threads);
106 event->set_runningThreadCount(threads_waiting_to_block);
107 event->set_iterations(iterations);
108 event->commit();
109 }
110 }
111
112 static void post_safepoint_wait_blocked_event(EventSafepointWaitBlocked* event,
113 int initial_threads_waiting_to_block) {
114 assert(event != NULL, "invariant");
115 assert(event->should_commit(), "invariant");
116 set_current_safepoint_id(event);
117 event->set_runningThreadCount(initial_threads_waiting_to_block);
118 event->commit();
119 }
120
121 static void post_safepoint_cleanup_task_event(EventSafepointCleanupTask* event,
122 const char* name) {
123 assert(event != NULL, "invariant");
124 if (event->should_commit()) {
125 set_current_safepoint_id(event);
126 event->set_name(name);
127 event->commit();
128 }
129 }
130
131 static void post_safepoint_end_event(EventSafepointEnd* event) {
132 assert(event != NULL, "invariant");
133 if (event->should_commit()) {
134 // Group this event together with the ones committed before the counter increased
135 set_current_safepoint_id(event, -1);
136 event->commit();
137 }
138 }
139
140 // --------------------------------------------------------------------------------------------------
141 // Implementation of Safepoint begin/end
142
143 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
144 volatile int SafepointSynchronize::_waiting_to_block = 0;
145 volatile int SafepointSynchronize::_safepoint_counter = 0;
146 int SafepointSynchronize::_current_jni_active_count = 0;
147 long SafepointSynchronize::_end_of_last_safepoint = 0;
148 int SafepointSynchronize::_defer_thr_suspend_loop_count = 4000;
149 static const int safepoint_spin_before_yield = 2000;
150 static volatile int PageArmed = 0 ; // safepoint polling page is RO|RW vs PROT_NONE
151 static volatile int TryingToBlock = 0 ; // proximate value -- for advisory use only
152 static bool timeout_error_printed = false;
153
154
155 // Statistic related statics
156 julong SafepointSynchronize::_coalesced_vmop_count = 0;
157 static jlong _safepoint_begin_time = 0;
158 static float _ts_of_current_safepoint = 0.0f;
159 static volatile int _nof_threads_hit_polling_page = 0;
160
161 // Roll all threads forward to a safepoint and suspend them all
162 void SafepointSynchronize::begin() {
163 EventSafepointBegin begin_event;
164 Thread* myThread = Thread::current();
165 assert(myThread->is_VM_thread(), "Only VM thread may execute a safepoint");
166
167 if (log_is_enabled(Debug, safepoint, stats)) {
168 _safepoint_begin_time = os::javaTimeNanos();
169 _ts_of_current_safepoint = tty->time_stamp().seconds();
170 _nof_threads_hit_polling_page = 0;
171 }
172
173 Universe::heap()->safepoint_synchronize_begin();
174
175 // By getting the Threads_lock, we assure that no threads are about to start or
176 // exit. It is released again in SafepointSynchronize::end().
177 Threads_lock->lock();
178
179 assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
180
181 int nof_threads = Threads::number_of_threads();
182
183 log_debug(safepoint)("Safepoint synchronization initiated. (%d threads)", nof_threads);
184
185 RuntimeService::record_safepoint_begin();
186
187 MutexLocker mu(Safepoint_lock);
188
189 // Reset the count of active JNI critical threads
190 _current_jni_active_count = 0;
191
192 // Set number of threads to wait for, before we initiate the callbacks
193 _waiting_to_block = nof_threads;
194 TryingToBlock = 0 ;
195 int still_running = nof_threads;
196
197 // Save the starting time, so that it can be compared to see if this has taken
198 // too long to complete.
199 jlong safepoint_limit_time = 0;
200 timeout_error_printed = false;
201
202 // Begin the process of bringing the system to a safepoint.
203 // Java threads can be in several different states and are
204 // stopped by different mechanisms:
205 //
206 // 1. Running interpreted
207 // The interpreter dispatch table is changed to force it to
208 // check for a safepoint condition between bytecodes.
209 // 2. Running in native code
210 // When returning from the native code, a Java thread must check
211 // the safepoint _state to see if we must block. If the
212 // VM thread sees a Java thread in native, it does
213 // not wait for this thread to block. The order of the memory
214 // writes and reads of both the safepoint state and the Java
215 // threads state is critical. In order to guarantee that the
216 // memory writes are serialized with respect to each other,
217 // the VM thread issues a memory barrier instruction
218 // (on MP systems). In order to avoid the overhead of issuing
219 // a memory barrier for each Java thread making native calls, each Java
220 // thread performs a write to a single memory page after changing
221 // the thread state. The VM thread performs a sequence of
222 // mprotect OS calls which forces all previous writes from all
223 // Java threads to be serialized. This is done in the
224 // os::serialize_thread_states() call. This has proven to be
225 // much more efficient than executing a membar instruction
226 // on every call to native code.
227 // 3. Running compiled Code
228 // Compiled code reads a global (Safepoint Polling) page that
229 // is set to fault if we are trying to get to a safepoint.
230 // 4. Blocked
231 // A thread which is blocked will not be allowed to return from the
232 // block condition until the safepoint operation is complete.
233 // 5. In VM or Transitioning between states
234 // If a Java thread is currently running in the VM or transitioning
235 // between states, the safepointing code will wait for the thread to
236 // block itself when it attempts transitions to a new state.
237 //
238 {
239 EventSafepointStateSynchronization sync_event;
240 int initial_running = 0;
241
242 _state = _synchronizing;
243
244 if (SafepointMechanism::uses_thread_local_poll()) {
245 // Arming the per thread poll while having _state != _not_synchronized means safepointing
246 log_trace(safepoint)("Setting thread local yield flag for threads");
247 OrderAccess::storestore(); // storestore, global state -> local state
248 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
249 // Make sure the threads start polling, it is time to yield.
250 SafepointMechanism::arm_local_poll(cur);
251 }
252 }
253 OrderAccess::fence(); // storestore|storeload, global state -> local state
254
255 // Flush all thread states to memory
256 if (!UseMembar) {
257 os::serialize_thread_states();
258 }
259
260 if (SafepointMechanism::uses_global_page_poll()) {
261 // Make interpreter safepoint aware
262 Interpreter::notice_safepoints();
263
264 // Make polling safepoint aware
265 guarantee (PageArmed == 0, "invariant") ;
266 PageArmed = 1 ;
267 os::make_polling_page_unreadable();
268 }
269
270 // Consider using active_processor_count() ... but that call is expensive.
271 int ncpus = os::processor_count() ;
272 unsigned int iterations = 0;
273
274 {
275 JavaThreadIteratorWithHandle jtiwh;
276 #ifdef ASSERT
277 for (; JavaThread *cur = jtiwh.next(); ) {
278 assert(cur->safepoint_state()->is_running(), "Illegal initial state");
279 // Clear the visited flag to ensure that the critical counts are collected properly.
280 cur->set_visited_for_critical_count(false);
281 }
282 #endif // ASSERT
283
284 if (SafepointTimeout)
285 safepoint_limit_time = os::javaTimeNanos() + (jlong)SafepointTimeoutDelay * MICROUNITS;
286
287 // Iterate through all threads until it have been determined how to stop them all at a safepoint
288 int steps = 0 ;
289 while(still_running > 0) {
290 jtiwh.rewind();
291 for (; JavaThread *cur = jtiwh.next(); ) {
292 assert(!cur->is_ConcurrentGC_thread(), "A concurrent GC thread is unexpectly being suspended");
293 ThreadSafepointState *cur_state = cur->safepoint_state();
294 if (cur_state->is_running()) {
295 cur_state->examine_state_of_thread();
296 if (!cur_state->is_running()) {
297 still_running--;
298 // consider adjusting steps downward:
299 // steps = 0
300 // steps -= NNN
301 // steps >>= 1
302 // steps = MIN(steps, 2000-100)
303 // if (iterations != 0) steps -= NNN
304 }
305 LogTarget(Trace, safepoint) lt;
306 if (lt.is_enabled()) {
307 ResourceMark rm;
308 LogStream ls(lt);
309 cur_state->print_on(&ls);
310 }
311 }
312 }
313
314 if (iterations == 0) {
315 initial_running = still_running;
316 if (log_is_enabled(Debug, safepoint, stats)) {
317 begin_statistics(nof_threads, still_running);
318 }
319 }
320
321 if (still_running > 0) {
322 // Check for if it takes to long
323 if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
324 print_safepoint_timeout(_spinning_timeout);
325 }
326
327 // Spin to avoid context switching.
328 // There's a tension between allowing the mutators to run (and rendezvous)
329 // vs spinning. As the VM thread spins, wasting cycles, it consumes CPU that
330 // a mutator might otherwise use profitably to reach a safepoint. Excessive
331 // spinning by the VM thread on a saturated system can increase rendezvous latency.
332 // Blocking or yielding incur their own penalties in the form of context switching
333 // and the resultant loss of $ residency.
334 //
335 // Further complicating matters is that yield() does not work as naively expected
336 // on many platforms -- yield() does not guarantee that any other ready threads
337 // will run. As such we revert to naked_short_sleep() after some number of iterations.
338 // nakes_short_sleep() is implemented as a short unconditional sleep.
339 // Typical operating systems round a "short" sleep period up to 10 msecs, so sleeping
340 // can actually increase the time it takes the VM thread to detect that a system-wide
341 // stop-the-world safepoint has been reached. In a pathological scenario such as that
342 // described in CR6415670 the VMthread may sleep just before the mutator(s) become safe.
343 // In that case the mutators will be stalled waiting for the safepoint to complete and the
344 // the VMthread will be sleeping, waiting for the mutators to rendezvous. The VMthread
345 // will eventually wake up and detect that all mutators are safe, at which point
346 // we'll again make progress.
347 //
348 // Beware too that that the VMThread typically runs at elevated priority.
349 // Its default priority is higher than the default mutator priority.
350 // Obviously, this complicates spinning.
351 //
352 // Note too that on Windows XP SwitchThreadTo() has quite different behavior than Sleep(0).
353 // Sleep(0) will _not yield to lower priority threads, while SwitchThreadTo() will.
354 //
355 // See the comments in synchronizer.cpp for additional remarks on spinning.
356 //
357 // In the future we might:
358 // -- Modify the safepoint scheme to avoid potentially unbounded spinning.
359 // This is tricky as the path used by a thread exiting the JVM (say on
360 // on JNI call-out) simply stores into its state field. The burden
361 // is placed on the VM thread, which must poll (spin).
362 // -- Find something useful to do while spinning. If the safepoint is GC-related
363 // we might aggressively scan the stacks of threads that are already safe.
364 // -- YieldTo() any still-running mutators that are ready but OFFPROC.
365 // -- Check system saturation. If the system is not fully saturated then
366 // simply spin and avoid sleep/yield.
367 // -- As still-running mutators rendezvous they could unpark the sleeping
368 // VMthread. This works well for still-running mutators that become
369 // safe. The VMthread must still poll for mutators that call-out.
370 // -- Drive the policy on time-since-begin instead of iterations.
371 // -- Consider making the spin duration a function of the # of CPUs:
372 // Spin = (((ncpus-1) * M) + K) + F(still_running)
373 // Alternately, instead of counting iterations of the outer loop
374 // we could count the # of threads visited in the inner loop, above.
375 // -- On windows consider using the return value from SwitchThreadTo()
376 // to drive subsequent spin/SwitchThreadTo()/Sleep(N) decisions.
377
378 if (int(iterations) == -1) { // overflow - something is wrong.
379 // We can only overflow here when we are using global
380 // polling pages. We keep this guarantee in its original
381 // form so that searches of the bug database for this
382 // failure mode find the right bugs.
383 guarantee (PageArmed == 0, "invariant");
384 }
385
386 // Instead of (ncpus > 1) consider either (still_running < (ncpus + EPSILON)) or
387 // ((still_running + _waiting_to_block - TryingToBlock)) < ncpus)
388 ++steps ;
389 if (ncpus > 1 && steps < safepoint_spin_before_yield) {
390 SpinPause() ; // MP-Polite spin
391 } else
392 if (steps < _defer_thr_suspend_loop_count) {
393 os::naked_yield() ;
394 } else {
395 os::naked_short_sleep(1);
396 }
397
398 iterations ++ ;
399 }
400 assert(iterations < (uint)max_jint, "We have been iterating in the safepoint loop too long");
401 }
402 } // ThreadsListHandle destroyed here.
403 assert(still_running == 0, "sanity check");
404
405 if (log_is_enabled(Debug, safepoint, stats)) {
406 update_statistics_on_spin_end();
407 }
408 if (sync_event.should_commit()) {
409 post_safepoint_synchronize_event(&sync_event, initial_running, _waiting_to_block, iterations);
410 }
411 }
412
413 // wait until all threads are stopped
414 {
415 EventSafepointWaitBlocked wait_blocked_event;
416 int initial_waiting_to_block = _waiting_to_block;
417
418 while (_waiting_to_block > 0) {
419 log_debug(safepoint)("Waiting for %d thread(s) to block", _waiting_to_block);
420 if (!SafepointTimeout || timeout_error_printed) {
421 Safepoint_lock->wait(true); // true, means with no safepoint checks
422 } else {
423 // Compute remaining time
424 jlong remaining_time = safepoint_limit_time - os::javaTimeNanos();
425
426 // If there is no remaining time, then there is an error
427 if (remaining_time < 0 || Safepoint_lock->wait(true, remaining_time / MICROUNITS)) {
428 print_safepoint_timeout(_blocking_timeout);
429 }
430 }
431 }
432 assert(_waiting_to_block == 0, "sanity check");
433
434 #ifndef PRODUCT
435 if (SafepointTimeout) {
436 jlong current_time = os::javaTimeNanos();
437 if (safepoint_limit_time < current_time) {
438 log_warning(safepoint)("# SafepointSynchronize: Finished after "
439 INT64_FORMAT_W(6) " ms",
440 (int64_t)((current_time - safepoint_limit_time) / MICROUNITS +
441 (jlong)SafepointTimeoutDelay));
442 }
443 }
444 #endif
445
446 assert((_safepoint_counter & 0x1) == 0, "must be even");
447 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
448 _safepoint_counter ++;
449
450 // Record state
451 _state = _synchronized;
452
453 OrderAccess::fence();
454 if (wait_blocked_event.should_commit()) {
455 post_safepoint_wait_blocked_event(&wait_blocked_event, initial_waiting_to_block);
456 }
457 }
458
459 #ifdef ASSERT
460 // Make sure all the threads were visited.
461 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
462 assert(cur->was_visited_for_critical_count(), "missed a thread");
463 }
464 #endif // ASSERT
465
466 // Update the count of active JNI critical regions
467 GCLocker::set_jni_lock_count(_current_jni_active_count);
468
469 log_info(safepoint)("Entering safepoint region: %s", VMThread::vm_safepoint_description());
470
471 RuntimeService::record_safepoint_synchronized();
472 if (log_is_enabled(Debug, safepoint, stats)) {
473 update_statistics_on_sync_end(os::javaTimeNanos());
474 }
475
476 // Call stuff that needs to be run when a safepoint is just about to be completed
477 {
478 EventSafepointCleanup cleanup_event;
479 do_cleanup_tasks();
480 if (cleanup_event.should_commit()) {
481 post_safepoint_cleanup_event(&cleanup_event);
482 }
483 }
484
485 if (log_is_enabled(Debug, safepoint, stats)) {
486 // Record how much time spend on the above cleanup tasks
487 update_statistics_on_cleanup_end(os::javaTimeNanos());
488 }
489
490 if (begin_event.should_commit()) {
491 post_safepoint_begin_event(&begin_event, nof_threads, _current_jni_active_count);
492 }
493 }
494
495 // Wake up all threads, so they are ready to resume execution after the safepoint
496 // operation has been carried out
497 void SafepointSynchronize::end() {
498 assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
499 assert((_safepoint_counter & 0x1) == 1, "must be odd");
500 EventSafepointEnd event;
501 _safepoint_counter ++;
502 // memory fence isn't required here since an odd _safepoint_counter
503 // value can do no harm and a fence is issued below anyway.
504
505 DEBUG_ONLY(Thread* myThread = Thread::current();)
506 assert(myThread->is_VM_thread(), "Only VM thread can execute a safepoint");
507
508 if (log_is_enabled(Debug, safepoint, stats)) {
509 end_statistics(os::javaTimeNanos());
510 }
511
512 {
513 JavaThreadIteratorWithHandle jtiwh;
514 #ifdef ASSERT
515 // A pending_exception cannot be installed during a safepoint. The threads
516 // may install an async exception after they come back from a safepoint into
517 // pending_exception after they unblock. But that should happen later.
518 for (; JavaThread *cur = jtiwh.next(); ) {
519 assert (!(cur->has_pending_exception() &&
520 cur->safepoint_state()->is_at_poll_safepoint()),
521 "safepoint installed a pending exception");
522 }
523 #endif // ASSERT
524
525 if (PageArmed) {
526 assert(SafepointMechanism::uses_global_page_poll(), "sanity");
527 // Make polling safepoint aware
528 os::make_polling_page_readable();
529 PageArmed = 0 ;
530 }
531
532 if (SafepointMechanism::uses_global_page_poll()) {
533 // Remove safepoint check from interpreter
534 Interpreter::ignore_safepoints();
535 }
536
537 {
538 MutexLocker mu(Safepoint_lock);
539
540 assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
541
542 if (SafepointMechanism::uses_thread_local_poll()) {
543 _state = _not_synchronized;
544 OrderAccess::storestore(); // global state -> local state
545 jtiwh.rewind();
546 for (; JavaThread *current = jtiwh.next(); ) {
547 ThreadSafepointState* cur_state = current->safepoint_state();
548 cur_state->restart(); // TSS _running
549 SafepointMechanism::disarm_local_poll(current);
550 }
551 log_info(safepoint)("Leaving safepoint region");
552 } else {
553 // Set to not synchronized, so the threads will not go into the signal_thread_blocked method
554 // when they get restarted.
555 _state = _not_synchronized;
556 OrderAccess::fence();
557
558 log_info(safepoint)("Leaving safepoint region");
559
560 // Start suspended threads
561 jtiwh.rewind();
562 for (; JavaThread *current = jtiwh.next(); ) {
563 ThreadSafepointState* cur_state = current->safepoint_state();
564 assert(cur_state->type() != ThreadSafepointState::_running, "Thread not suspended at safepoint");
565 cur_state->restart();
566 assert(cur_state->is_running(), "safepoint state has not been reset");
567 }
568 }
569
570 RuntimeService::record_safepoint_end();
571
572 // Release threads lock, so threads can be created/destroyed again.
573 // It will also release all threads blocked in signal_thread_blocked.
574 Threads_lock->unlock();
575 }
576 } // ThreadsListHandle destroyed here.
577
578 Universe::heap()->safepoint_synchronize_end();
579 // record this time so VMThread can keep track how much time has elapsed
580 // since last safepoint.
581 _end_of_last_safepoint = os::javaTimeMillis();
582 if (event.should_commit()) {
583 post_safepoint_end_event(&event);
584 }
585 }
586
587 bool SafepointSynchronize::is_cleanup_needed() {
588 // Need a safepoint if there are many monitors to deflate.
589 if (ObjectSynchronizer::is_cleanup_needed()) return true;
590 // Need a safepoint if some inline cache buffers is non-empty
591 if (!InlineCacheBuffer::is_empty()) return true;
592 return false;
593 }
594
595 class ParallelSPCleanupThreadClosure : public ThreadClosure {
596 private:
597 CodeBlobClosure* _nmethod_cl;
598 DeflateMonitorCounters* _counters;
599
600 public:
601 ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
602 _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()), _counters(counters) {}
603
604 void do_thread(Thread* thread) {
605 ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
606 if (_nmethod_cl != NULL && thread->is_Java_thread() &&
607 ! thread->is_Code_cache_sweeper_thread()) {
608 JavaThread* jt = (JavaThread*) thread;
609 jt->nmethods_do(_nmethod_cl);
610 }
611 }
612 };
613
614 class ParallelSPCleanupTask : public AbstractGangTask {
615 private:
616 SubTasksDone _subtasks;
617 ParallelSPCleanupThreadClosure _cleanup_threads_cl;
618 uint _num_workers;
619 DeflateMonitorCounters* _counters;
620 public:
621 ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
622 AbstractGangTask("Parallel Safepoint Cleanup"),
623 _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
624 _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
625 _num_workers(num_workers),
626 _counters(counters) {}
627
628 void work(uint worker_id) {
629 // All threads deflate monitors and mark nmethods (if necessary).
630 Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl);
631
632 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
633 const char* name = "deflating idle monitors";
634 EventSafepointCleanupTask event;
635 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
636 ObjectSynchronizer::deflate_idle_monitors(_counters);
637 if (event.should_commit()) {
638 post_safepoint_cleanup_task_event(&event, name);
639 }
640 }
641
642 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
643 const char* name = "updating inline caches";
644 EventSafepointCleanupTask event;
645 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
646 InlineCacheBuffer::update_inline_caches();
647 if (event.should_commit()) {
648 post_safepoint_cleanup_task_event(&event, name);
649 }
650 }
651
652 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
653 const char* name = "compilation policy safepoint handler";
654 EventSafepointCleanupTask event;
655 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
656 CompilationPolicy::policy()->do_safepoint_work();
657 if (event.should_commit()) {
658 post_safepoint_cleanup_task_event(&event, name);
659 }
660 }
661
662 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
663 if (SymbolTable::needs_rehashing()) {
664 const char* name = "rehashing symbol table";
665 EventSafepointCleanupTask event;
666 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
667 SymbolTable::rehash_table();
668 if (event.should_commit()) {
669 post_safepoint_cleanup_task_event(&event, name);
670 }
671 }
672 }
673
674 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
675 if (StringTable::needs_rehashing()) {
676 const char* name = "rehashing string table";
677 EventSafepointCleanupTask event;
678 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
679 StringTable::rehash_table();
680 if (event.should_commit()) {
681 post_safepoint_cleanup_task_event(&event, name);
682 }
683 }
684 }
685
686 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
687 // CMS delays purging the CLDG until the beginning of the next safepoint and to
688 // make sure concurrent sweep is done
689 const char* name = "purging class loader data graph";
690 EventSafepointCleanupTask event;
691 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
692 ClassLoaderDataGraph::purge_if_needed();
693 if (event.should_commit()) {
694 post_safepoint_cleanup_task_event(&event, name);
695 }
696 }
697
698 if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) {
699 const char* name = "resizing system dictionaries";
700 EventSafepointCleanupTask event;
701 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
702 ClassLoaderDataGraph::resize_if_needed();
703 if (event.should_commit()) {
704 post_safepoint_cleanup_task_event(&event, name);
705 }
706 }
707
708 _subtasks.all_tasks_completed(_num_workers);
709 }
710 };
711
712 // Various cleaning tasks that should be done periodically at safepoints.
713 void SafepointSynchronize::do_cleanup_tasks() {
714
715 TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
716
717 // Prepare for monitor deflation.
718 DeflateMonitorCounters deflate_counters;
719 ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
720
721 CollectedHeap* heap = Universe::heap();
722 assert(heap != NULL, "heap not initialized yet?");
723 WorkGang* cleanup_workers = heap->get_safepoint_workers();
724 if (cleanup_workers != NULL) {
725 // Parallel cleanup using GC provided thread pool.
726 uint num_cleanup_workers = cleanup_workers->active_workers();
727 ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
728 StrongRootsScope srs(num_cleanup_workers);
729 cleanup_workers->run_task(&cleanup);
730 } else {
731 // Serial cleanup using VMThread.
732 ParallelSPCleanupTask cleanup(1, &deflate_counters);
733 StrongRootsScope srs(1);
734 cleanup.work(0);
735 }
736
737 // Needs to be done single threaded by the VMThread. This walks
738 // the thread stacks looking for references to metadata before
739 // deciding to remove it from the metaspaces.
740 if (ClassLoaderDataGraph::should_clean_metaspaces_and_reset()) {
741 const char* name = "cleanup live ClassLoaderData metaspaces";
742 TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
743 ClassLoaderDataGraph::walk_metadata_and_clean_metaspaces();
744 }
745
746 // Finish monitor deflation.
747 ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
748
749 }
750
751
752 bool SafepointSynchronize::safepoint_safe(JavaThread *thread, JavaThreadState state) {
753 switch(state) {
754 case _thread_in_native:
755 // native threads are safe if they have no java stack or have walkable stack
756 return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
757
758 // blocked threads should have already have walkable stack
759 case _thread_blocked:
760 assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
761 return true;
762
763 default:
764 return false;
765 }
766 }
767
768
769 // See if the thread is running inside a lazy critical native and
770 // update the thread critical count if so. Also set a suspend flag to
771 // cause the native wrapper to return into the JVM to do the unlock
772 // once the native finishes.
773 void SafepointSynchronize::check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
774 if (state == _thread_in_native &&
775 thread->has_last_Java_frame() &&
776 thread->frame_anchor()->walkable()) {
777 // This thread might be in a critical native nmethod so look at
778 // the top of the stack and increment the critical count if it
779 // is.
780 frame wrapper_frame = thread->last_frame();
781 CodeBlob* stub_cb = wrapper_frame.cb();
782 if (stub_cb != NULL &&
783 stub_cb->is_nmethod() &&
784 stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
785 // A thread could potentially be in a critical native across
786 // more than one safepoint, so only update the critical state on
787 // the first one. When it returns it will perform the unlock.
788 if (!thread->do_critical_native_unlock()) {
789 #ifdef ASSERT
790 if (!thread->in_critical()) {
791 GCLocker::increment_debug_jni_lock_count();
792 }
793 #endif
794 thread->enter_critical();
795 // Make sure the native wrapper calls back on return to
796 // perform the needed critical unlock.
797 thread->set_critical_native_unlock();
798 }
799 }
800 }
801 }
802
803
804
805 // -------------------------------------------------------------------------------------------------------
806 // Implementation of Safepoint callback point
807
808 void SafepointSynchronize::block(JavaThread *thread) {
809 assert(thread != NULL, "thread must be set");
810 assert(thread->is_Java_thread(), "not a Java thread");
811
812 // Threads shouldn't block if they are in the middle of printing, but...
813 ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
814
815 // Only bail from the block() call if the thread is gone from the
816 // thread list; starting to exit should still block.
817 if (thread->is_terminated()) {
818 // block current thread if we come here from native code when VM is gone
819 thread->block_if_vm_exited();
820
821 // otherwise do nothing
822 return;
823 }
824
825 JavaThreadState state = thread->thread_state();
826 thread->frame_anchor()->make_walkable(thread);
827
828 // Check that we have a valid thread_state at this point
829 switch(state) {
830 case _thread_in_vm_trans:
831 case _thread_in_Java: // From compiled code
832
833 // We are highly likely to block on the Safepoint_lock. In order to avoid blocking in this case,
834 // we pretend we are still in the VM.
835 thread->set_thread_state(_thread_in_vm);
836
837 if (is_synchronizing()) {
838 Atomic::inc (&TryingToBlock) ;
839 }
840
841 // We will always be holding the Safepoint_lock when we are examine the state
842 // of a thread. Hence, the instructions between the Safepoint_lock->lock() and
843 // Safepoint_lock->unlock() are happening atomic with regards to the safepoint code
844 Safepoint_lock->lock_without_safepoint_check();
845 if (is_synchronizing()) {
846 // Decrement the number of threads to wait for and signal vm thread
847 assert(_waiting_to_block > 0, "sanity check");
848 _waiting_to_block--;
849 thread->safepoint_state()->set_has_called_back(true);
850
851 DEBUG_ONLY(thread->set_visited_for_critical_count(true));
852 if (thread->in_critical()) {
853 // Notice that this thread is in a critical section
854 increment_jni_active_count();
855 }
856
857 // Consider (_waiting_to_block < 2) to pipeline the wakeup of the VM thread
858 if (_waiting_to_block == 0) {
859 Safepoint_lock->notify_all();
860 }
861 }
862
863 // We transition the thread to state _thread_blocked here, but
864 // we can't do our usual check for external suspension and then
865 // self-suspend after the lock_without_safepoint_check() call
866 // below because we are often called during transitions while
867 // we hold different locks. That would leave us suspended while
868 // holding a resource which results in deadlocks.
869 thread->set_thread_state(_thread_blocked);
870 Safepoint_lock->unlock();
871
872 // We now try to acquire the threads lock. Since this lock is hold by the VM thread during
873 // the entire safepoint, the threads will all line up here during the safepoint.
874 Threads_lock->lock_without_safepoint_check();
875 // restore original state. This is important if the thread comes from compiled code, so it
876 // will continue to execute with the _thread_in_Java state.
877 thread->set_thread_state(state);
878 Threads_lock->unlock();
879 break;
880
881 case _thread_in_native_trans:
882 case _thread_blocked_trans:
883 case _thread_new_trans:
884 if (thread->safepoint_state()->type() == ThreadSafepointState::_call_back) {
885 thread->print_thread_state();
886 fatal("Deadlock in safepoint code. "
887 "Should have called back to the VM before blocking.");
888 }
889
890 // We transition the thread to state _thread_blocked here, but
891 // we can't do our usual check for external suspension and then
892 // self-suspend after the lock_without_safepoint_check() call
893 // below because we are often called during transitions while
894 // we hold different locks. That would leave us suspended while
895 // holding a resource which results in deadlocks.
896 thread->set_thread_state(_thread_blocked);
897
898 // It is not safe to suspend a thread if we discover it is in _thread_in_native_trans. Hence,
899 // the safepoint code might still be waiting for it to block. We need to change the state here,
900 // so it can see that it is at a safepoint.
901
902 // Block until the safepoint operation is completed.
903 Threads_lock->lock_without_safepoint_check();
904
905 // Restore state
906 thread->set_thread_state(state);
907
908 Threads_lock->unlock();
909 break;
910
911 default:
912 fatal("Illegal threadstate encountered: %d", state);
913 }
914
915 // Check for pending. async. exceptions or suspends - except if the
916 // thread was blocked inside the VM. has_special_runtime_exit_condition()
917 // is called last since it grabs a lock and we only want to do that when
918 // we must.
919 //
920 // Note: we never deliver an async exception at a polling point as the
921 // compiler may not have an exception handler for it. The polling
922 // code will notice the async and deoptimize and the exception will
923 // be delivered. (Polling at a return point is ok though). Sure is
924 // a lot of bother for a deprecated feature...
925 //
926 // We don't deliver an async exception if the thread state is
927 // _thread_in_native_trans so JNI functions won't be called with
928 // a surprising pending exception. If the thread state is going back to java,
929 // async exception is checked in check_special_condition_for_native_trans().
930
931 if (state != _thread_blocked_trans &&
932 state != _thread_in_vm_trans &&
933 thread->has_special_runtime_exit_condition()) {
934 thread->handle_special_runtime_exit_condition(
935 !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
936 }
937 }
938
939 // ------------------------------------------------------------------------------------------------------
940 // Exception handlers
941
942
943 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
944 assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
945 assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
946 if (!ThreadLocalHandshakes) {
947 assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
948 }
949
950 if (log_is_enabled(Debug, safepoint, stats)) {
951 Atomic::inc(&_nof_threads_hit_polling_page);
952 }
953
954 ThreadSafepointState* state = thread->safepoint_state();
955
956 state->handle_polling_page_exception();
957 }
958
959
960 void SafepointSynchronize::print_safepoint_timeout(SafepointTimeoutReason reason) {
961 if (!timeout_error_printed) {
962 timeout_error_printed = true;
963 // Print out the thread info which didn't reach the safepoint for debugging
964 // purposes (useful when there are lots of threads in the debugger).
965 LogTarget(Warning, safepoint) lt;
966 if (lt.is_enabled()) {
967 ResourceMark rm;
968 LogStream ls(lt);
969
970 ls.cr();
971 ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
972 if (reason == _spinning_timeout) {
973 ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
974 } else if (reason == _blocking_timeout) {
975 ls.print_cr("# SafepointSynchronize::begin: Timed out while waiting for threads to stop.");
976 }
977
978 ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
979 ThreadSafepointState *cur_state;
980 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
981 cur_state = cur_thread->safepoint_state();
982
983 if (cur_thread->thread_state() != _thread_blocked &&
984 ((reason == _spinning_timeout && cur_state->is_running()) ||
985 (reason == _blocking_timeout && !cur_state->has_called_back()))) {
986 ls.print("# ");
987 cur_thread->print_on(&ls);
988 ls.cr();
989 }
990 }
991 ls.print_cr("# SafepointSynchronize::begin: (End of list)");
992 }
993 }
994
995 // To debug the long safepoint, specify both DieOnSafepointTimeout &
996 // ShowMessageBoxOnError.
997 if (DieOnSafepointTimeout) {
998 fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
999 SafepointTimeoutDelay, VMThread::vm_safepoint_description());
1000 }
1001 }
1002
1003
1004 // -------------------------------------------------------------------------------------------------------
1005 // Implementation of ThreadSafepointState
1006
1007 ThreadSafepointState::ThreadSafepointState(JavaThread *thread) {
1008 _thread = thread;
1009 _type = _running;
1010 _has_called_back = false;
1011 _at_poll_safepoint = false;
1012 }
1013
1014 void ThreadSafepointState::create(JavaThread *thread) {
1015 ThreadSafepointState *state = new ThreadSafepointState(thread);
1016 thread->set_safepoint_state(state);
1017 }
1018
1019 void ThreadSafepointState::destroy(JavaThread *thread) {
1020 if (thread->safepoint_state()) {
1021 delete(thread->safepoint_state());
1022 thread->set_safepoint_state(NULL);
1023 }
1024 }
1025
1026 void ThreadSafepointState::examine_state_of_thread() {
1027 assert(is_running(), "better be running or just have hit safepoint poll");
1028
1029 JavaThreadState state = _thread->thread_state();
1030
1031 // Save the state at the start of safepoint processing.
1032 _orig_thread_state = state;
1033
1034 // Check for a thread that is suspended. Note that thread resume tries
1035 // to grab the Threads_lock which we own here, so a thread cannot be
1036 // resumed during safepoint synchronization.
1037
1038 // We check to see if this thread is suspended without locking to
1039 // avoid deadlocking with a third thread that is waiting for this
1040 // thread to be suspended. The third thread can notice the safepoint
1041 // that we're trying to start at the beginning of its SR_lock->wait()
1042 // call. If that happens, then the third thread will block on the
1043 // safepoint while still holding the underlying SR_lock. We won't be
1044 // able to get the SR_lock and we'll deadlock.
1045 //
1046 // We don't need to grab the SR_lock here for two reasons:
1047 // 1) The suspend flags are both volatile and are set with an
1048 // Atomic::cmpxchg() call so we should see the suspended
1049 // state right away.
1050 // 2) We're being called from the safepoint polling loop; if
1051 // we don't see the suspended state on this iteration, then
1052 // we'll come around again.
1053 //
1054 bool is_suspended = _thread->is_ext_suspended();
1055 if (is_suspended) {
1056 roll_forward(_at_safepoint);
1057 return;
1058 }
1059
1060 // Some JavaThread states have an initial safepoint state of
1061 // running, but are actually at a safepoint. We will happily
1062 // agree and update the safepoint state here.
1063 if (SafepointSynchronize::safepoint_safe(_thread, state)) {
1064 SafepointSynchronize::check_for_lazy_critical_native(_thread, state);
1065 roll_forward(_at_safepoint);
1066 return;
1067 }
1068
1069 if (state == _thread_in_vm) {
1070 roll_forward(_call_back);
1071 return;
1072 }
1073
1074 // All other thread states will continue to run until they
1075 // transition and self-block in state _blocked
1076 // Safepoint polling in compiled code causes the Java threads to do the same.
1077 // Note: new threads may require a malloc so they must be allowed to finish
1078
1079 assert(is_running(), "examine_state_of_thread on non-running thread");
1080 return;
1081 }
1082
1083 // Returns true is thread could not be rolled forward at present position.
1084 void ThreadSafepointState::roll_forward(suspend_type type) {
1085 _type = type;
1086
1087 switch(_type) {
1088 case _at_safepoint:
1089 SafepointSynchronize::signal_thread_at_safepoint();
1090 DEBUG_ONLY(_thread->set_visited_for_critical_count(true));
1091 if (_thread->in_critical()) {
1092 // Notice that this thread is in a critical section
1093 SafepointSynchronize::increment_jni_active_count();
1094 }
1095 break;
1096
1097 case _call_back:
1098 set_has_called_back(false);
1099 break;
1100
1101 case _running:
1102 default:
1103 ShouldNotReachHere();
1104 }
1105 }
1106
1107 void ThreadSafepointState::restart() {
1108 switch(type()) {
1109 case _at_safepoint:
1110 case _call_back:
1111 break;
1112
1113 case _running:
1114 default:
1115 tty->print_cr("restart thread " INTPTR_FORMAT " with state %d",
1116 p2i(_thread), _type);
1117 _thread->print();
1118 ShouldNotReachHere();
1119 }
1120 _type = _running;
1121 set_has_called_back(false);
1122 }
1123
1124
1125 void ThreadSafepointState::print_on(outputStream *st) const {
1126 const char *s = NULL;
1127
1128 switch(_type) {
1129 case _running : s = "_running"; break;
1130 case _at_safepoint : s = "_at_safepoint"; break;
1131 case _call_back : s = "_call_back"; break;
1132 default:
1133 ShouldNotReachHere();
1134 }
1135
1136 st->print_cr("Thread: " INTPTR_FORMAT
1137 " [0x%2x] State: %s _has_called_back %d _at_poll_safepoint %d",
1138 p2i(_thread), _thread->osthread()->thread_id(), s, _has_called_back,
1139 _at_poll_safepoint);
1140
1141 _thread->print_thread_state_on(st);
1142 }
1143
1144 // ---------------------------------------------------------------------------------------------------------------------
1145
1146 // Block the thread at poll or poll return for safepoint/handshake.
1147 void ThreadSafepointState::handle_polling_page_exception() {
1148
1149 // Check state. block() will set thread state to thread_in_vm which will
1150 // cause the safepoint state _type to become _call_back.
1151 suspend_type t = type();
1152 assert(!SafepointMechanism::uses_global_page_poll() || t == ThreadSafepointState::_running,
1153 "polling page exception on thread not running state: %u", uint(t));
1154
1155 // Step 1: Find the nmethod from the return address
1156 address real_return_addr = thread()->saved_exception_pc();
1157
1158 CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1159 assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1160 CompiledMethod* nm = (CompiledMethod*)cb;
1161
1162 // Find frame of caller
1163 frame stub_fr = thread()->last_frame();
1164 CodeBlob* stub_cb = stub_fr.cb();
1165 assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1166 RegisterMap map(thread(), true);
1167 frame caller_fr = stub_fr.sender(&map);
1168
1169 // Should only be poll_return or poll
1170 assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1171
1172 // This is a poll immediately before a return. The exception handling code
1173 // has already had the effect of causing the return to occur, so the execution
1174 // will continue immediately after the call. In addition, the oopmap at the
1175 // return point does not mark the return value as an oop (if it is), so
1176 // it needs a handle here to be updated.
1177 if( nm->is_at_poll_return(real_return_addr) ) {
1178 ResourceMark rm;
1179 // See if return type is an oop.
1180 Method* method = nm->method();
1181 bool return_oop = method->may_return_oop();
1182
1183 GrowableArray<Handle> return_values;
1184 ValueKlass* vk = NULL;
1185
1186 if (return_oop && ValueTypeReturnedAsFields) {
1187 SignatureStream ss(method->signature());
1188 while (!ss.at_return_type()) {
1189 ss.next();
1190 }
1191 Symbol* sym = ss.as_symbol_or_null();
1192 if (sym != NULL && method->method_holder()->is_declared_value_type(sym)) {
1193 // Check if value type is returned as fields
1194 vk = ValueKlass::returned_value_klass(map);
1195 if (vk != NULL) {
1196 // We're at a safepoint at the return of a method that returns
1197 // multiple values. We must make sure we preserve the oop values
1198 // across the safepoint.
1199 assert(vk == method->returned_value_type(thread()), "bad value klass");
1200 vk->save_oop_fields(map, return_values);
1201 return_oop = false;
1202 }
1203 }
1204 }
1205
1206 if (return_oop) {
1207 // The oop result has been saved on the stack together with all
1208 // the other registers. In order to preserve it over GCs we need
1209 // to keep it in a handle.
1210 oop result = caller_fr.saved_oop_result(&map);
1211 assert(oopDesc::is_oop_or_null(result), "must be oop");
1212 return_values.push(Handle(thread(), result));
1213 assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1214 }
1215
1216 // Block the thread
1217 SafepointMechanism::block_if_requested(thread());
1218
1219 // restore oop result, if any
1220 if (return_oop) {
1221 assert(return_values.length() == 1, "only one return value");
1222 caller_fr.set_saved_oop_result(&map, return_values.pop()());
1223 } else if (vk != NULL) {
1224 vk->restore_oop_results(map, return_values);
1225 }
1226 }
1227
1228 // This is a safepoint poll. Verify the return address and block.
1229 else {
1230 set_at_poll_safepoint(true);
1231
1232 // verify the blob built the "return address" correctly
1233 assert(real_return_addr == caller_fr.pc(), "must match");
1234
1235 // Block the thread
1236 SafepointMechanism::block_if_requested(thread());
1237 set_at_poll_safepoint(false);
1238
1239 // If we have a pending async exception deoptimize the frame
1240 // as otherwise we may never deliver it.
1241 if (thread()->has_async_condition()) {
1242 ThreadInVMfromJavaNoAsyncException __tiv(thread());
1243 Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1244 }
1245
1246 // If an exception has been installed we must check for a pending deoptimization
1247 // Deoptimize frame if exception has been thrown.
1248
1249 if (thread()->has_pending_exception() ) {
1250 RegisterMap map(thread(), true);
1251 frame caller_fr = stub_fr.sender(&map);
1252 if (caller_fr.is_deoptimized_frame()) {
1253 // The exception patch will destroy registers that are still
1254 // live and will be needed during deoptimization. Defer the
1255 // Async exception should have deferred the exception until the
1256 // next safepoint which will be detected when we get into
1257 // the interpreter so if we have an exception now things
1258 // are messed up.
1259
1260 fatal("Exception installed and deoptimization is pending");
1261 }
1262 }
1263 }
1264 }
1265
1266
1267 //
1268 // Statistics & Instrumentations
1269 //
1270 struct SafepointStats {
1271 float _time_stamp; // record when the current safepoint occurs in seconds
1272 int _vmop_type; // tyep of VM operation triggers the safepoint
1273 int _nof_total_threads; // total number of Java threads
1274 int _nof_initial_running_threads; // total number of initially seen running threads
1275 int _nof_threads_wait_to_block; // total number of threads waiting for to block
1276 bool _page_armed; // true if polling page is armed, false otherwise
1277 int _nof_threads_hit_page_trap; // total number of threads hitting the page trap
1278 jlong _time_to_spin; // total time in millis spent in spinning
1279 jlong _time_to_wait_to_block; // total time in millis spent in waiting for to block
1280 jlong _time_to_do_cleanups; // total time in millis spent in performing cleanups
1281 jlong _time_to_sync; // total time in millis spent in getting to _synchronized
1282 jlong _time_to_exec_vmop; // total time in millis spent in vm operation itself
1283 };
1284
1285 static const int _statistics_header_count = 30;
1286 static int _cur_stat_index = 0;
1287 static SafepointStats safepoint_stats = {0}; // zero initialize
1288 static SafepointStats* spstat = &safepoint_stats;
1289
1290 static julong _safepoint_reasons[VM_Operation::VMOp_Terminating];
1291 static jlong _max_sync_time = 0;
1292 static jlong _max_vmop_time = 0;
1293
1294 static jlong cleanup_end_time = 0;
1295
1296 void SafepointSynchronize::begin_statistics(int nof_threads, int nof_running) {
1297
1298 spstat->_time_stamp = _ts_of_current_safepoint;
1299
1300 VM_Operation *op = VMThread::vm_operation();
1301 spstat->_vmop_type = op != NULL ? op->type() : VM_Operation::VMOp_None;
1302 _safepoint_reasons[spstat->_vmop_type]++;
1303
1304 spstat->_nof_total_threads = nof_threads;
1305 spstat->_nof_initial_running_threads = nof_running;
1306
1307 // Records the start time of spinning. The real time spent on spinning
1308 // will be adjusted when spin is done. Same trick is applied for time
1309 // spent on waiting for threads to block.
1310 if (nof_running != 0) {
1311 spstat->_time_to_spin = os::javaTimeNanos();
1312 } else {
1313 spstat->_time_to_spin = 0;
1314 }
1315 }
1316
1317 void SafepointSynchronize::update_statistics_on_spin_end() {
1318 jlong cur_time = os::javaTimeNanos();
1319
1320 spstat->_nof_threads_wait_to_block = _waiting_to_block;
1321 if (spstat->_nof_initial_running_threads != 0) {
1322 spstat->_time_to_spin = cur_time - spstat->_time_to_spin;
1323 }
1324
1325 // Records the start time of waiting for to block. Updated when block is done.
1326 if (_waiting_to_block != 0) {
1327 spstat->_time_to_wait_to_block = cur_time;
1328 } else {
1329 spstat->_time_to_wait_to_block = 0;
1330 }
1331 }
1332
1333 void SafepointSynchronize::update_statistics_on_sync_end(jlong end_time) {
1334
1335 if (spstat->_nof_threads_wait_to_block != 0) {
1336 spstat->_time_to_wait_to_block = end_time -
1337 spstat->_time_to_wait_to_block;
1338 }
1339
1340 // Records the end time of sync which will be used to calculate the total
1341 // vm operation time. Again, the real time spending in syncing will be deducted
1342 // from the start of the sync time later when end_statistics is called.
1343 spstat->_time_to_sync = end_time - _safepoint_begin_time;
1344 if (spstat->_time_to_sync > _max_sync_time) {
1345 _max_sync_time = spstat->_time_to_sync;
1346 }
1347
1348 spstat->_time_to_do_cleanups = end_time;
1349 }
1350
1351 void SafepointSynchronize::update_statistics_on_cleanup_end(jlong end_time) {
1352
1353 // Record how long spent in cleanup tasks.
1354 spstat->_time_to_do_cleanups = end_time - spstat->_time_to_do_cleanups;
1355 cleanup_end_time = end_time;
1356 }
1357
1358 void SafepointSynchronize::end_statistics(jlong vmop_end_time) {
1359
1360 // Update the vm operation time.
1361 spstat->_time_to_exec_vmop = vmop_end_time - cleanup_end_time;
1362 if (spstat->_time_to_exec_vmop > _max_vmop_time) {
1363 _max_vmop_time = spstat->_time_to_exec_vmop;
1364 }
1365
1366 spstat->_nof_threads_hit_page_trap = _nof_threads_hit_polling_page;
1367
1368 print_statistics();
1369 }
1370
1371 // Helper method to print the header.
1372 static void print_header(outputStream* st) {
1373 // The number of spaces is significant here, and should match the format
1374 // specifiers in print_statistics().
1375
1376 st->print(" vmop "
1377 "[ threads: total initially_running wait_to_block ]"
1378 "[ time: spin block sync cleanup vmop ] ");
1379
1380 st->print_cr("page_trap_count");
1381 }
1382
1383 // This prints a nice table. To get the statistics to not shift due to the logging uptime
1384 // decorator, use the option as: -Xlog:safepoint+stats=debug:[outputfile]:none
1385 void SafepointSynchronize::print_statistics() {
1386 LogTarget(Debug, safepoint, stats) lt;
1387 assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
1388 LogStream ls(lt);
1389
1390 // Print header every 30 entries
1391 if ((_cur_stat_index % _statistics_header_count) == 0) {
1392 print_header(&ls);
1393 _cur_stat_index = 1; // wrap
1394 } else {
1395 _cur_stat_index++;
1396 }
1397
1398 ls.print("%8.3f: ", spstat->_time_stamp);
1399 ls.print("%-28s [ "
1400 INT32_FORMAT_W(8) " " INT32_FORMAT_W(17) " " INT32_FORMAT_W(13) " "
1401 "]",
1402 VM_Operation::name(spstat->_vmop_type),
1403 spstat->_nof_total_threads,
1404 spstat->_nof_initial_running_threads,
1405 spstat->_nof_threads_wait_to_block);
1406 // "/ MICROUNITS " is to convert the unit from nanos to millis.
1407 ls.print("[ "
1408 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1409 INT64_FORMAT_W(7) " " INT64_FORMAT_W(7) " "
1410 INT64_FORMAT_W(7) " ] ",
1411 (int64_t)(spstat->_time_to_spin / MICROUNITS),
1412 (int64_t)(spstat->_time_to_wait_to_block / MICROUNITS),
1413 (int64_t)(spstat->_time_to_sync / MICROUNITS),
1414 (int64_t)(spstat->_time_to_do_cleanups / MICROUNITS),
1415 (int64_t)(spstat->_time_to_exec_vmop / MICROUNITS));
1416
1417 ls.print_cr(INT32_FORMAT_W(15) " ", spstat->_nof_threads_hit_page_trap);
1418 }
1419
1420 // This method will be called when VM exits. This tries to summarize the sampling.
1421 // Current thread may already be deleted, so don't use ResourceMark.
1422 void SafepointSynchronize::print_stat_on_exit() {
1423
1424 for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1425 if (_safepoint_reasons[index] != 0) {
1426 log_debug(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1427 _safepoint_reasons[index]);
1428 }
1429 }
1430
1431 log_debug(safepoint, stats)("VM operations coalesced during safepoint " INT64_FORMAT,
1432 _coalesced_vmop_count);
1433 log_debug(safepoint, stats)("Maximum sync time " INT64_FORMAT" ms",
1434 (int64_t)(_max_sync_time / MICROUNITS));
1435 log_debug(safepoint, stats)("Maximum vm operation time (except for Exit VM operation) "
1436 INT64_FORMAT " ms",
1437 (int64_t)(_max_vmop_time / MICROUNITS));
1438 }