1 /*
2 * Copyright (c) 1998, 2020, 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 "compiler/compileBroker.hpp"
27 #include "gc/shared/collectedHeap.hpp"
28 #include "jfr/jfrEvents.hpp"
29 #include "jfr/support/jfrThreadId.hpp"
30 #include "logging/log.hpp"
31 #include "logging/logStream.hpp"
32 #include "logging/logConfiguration.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "memory/universe.hpp"
35 #include "oops/method.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "oops/verifyOopClosure.hpp"
38 #include "runtime/atomic.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "runtime/os.hpp"
43 #include "runtime/safepoint.hpp"
44 #include "runtime/synchronizer.hpp"
45 #include "runtime/thread.inline.hpp"
46 #include "runtime/vmThread.hpp"
47 #include "runtime/vmOperations.hpp"
48 #include "services/runtimeService.hpp"
49 #include "utilities/dtrace.hpp"
50 #include "utilities/events.hpp"
51 #include "utilities/vmError.hpp"
52 #include "utilities/xmlstream.hpp"
53
54 VM_QueueHead VMOperationQueue::_queue_head[VMOperationQueue::nof_priorities];
55
56 VMOperationQueue::VMOperationQueue() {
57 // The queue is a circular doubled-linked list, which always contains
58 // one element (i.e., one element means empty).
59 for(int i = 0; i < nof_priorities; i++) {
60 _queue_length[i] = 0;
61 _queue_counter = 0;
62 _queue[i] = &_queue_head[i];
63 _queue[i]->set_next(_queue[i]);
64 _queue[i]->set_prev(_queue[i]);
65 }
66 }
67
68
69 bool VMOperationQueue::queue_empty(int prio) {
70 // It is empty if there is exactly one element
71 bool empty = (_queue[prio] == _queue[prio]->next());
72 assert( (_queue_length[prio] == 0 && empty) ||
73 (_queue_length[prio] > 0 && !empty), "sanity check");
74 return _queue_length[prio] == 0;
75 }
76
77 // Inserts an element to the right of the q element
78 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
79 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
80 n->set_prev(q);
81 n->set_next(q->next());
82 q->next()->set_prev(n);
83 q->set_next(n);
84 }
85
86 void VMOperationQueue::queue_add(int prio, VM_Operation *op) {
87 _queue_length[prio]++;
88 insert(_queue[prio]->prev(), op);
89 }
90
91
92 void VMOperationQueue::unlink(VM_Operation* q) {
93 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
94 q->prev()->set_next(q->next());
95 q->next()->set_prev(q->prev());
96 }
97
98 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
99 if (queue_empty(prio)) return NULL;
100 assert(_queue_length[prio] >= 0, "sanity check");
101 _queue_length[prio]--;
102 VM_Operation* r = _queue[prio]->next();
103 assert(r != _queue[prio], "cannot remove base element");
104 unlink(r);
105 return r;
106 }
107
108 VM_Operation* VMOperationQueue::queue_drain(int prio) {
109 if (queue_empty(prio)) return NULL;
110 DEBUG_ONLY(int length = _queue_length[prio];);
111 assert(length >= 0, "sanity check");
112 _queue_length[prio] = 0;
113 VM_Operation* r = _queue[prio]->next();
114 assert(r != _queue[prio], "cannot remove base element");
115 // remove links to base element from head and tail
116 r->set_prev(NULL);
117 _queue[prio]->prev()->set_next(NULL);
118 // restore queue to empty state
119 _queue[prio]->set_next(_queue[prio]);
120 _queue[prio]->set_prev(_queue[prio]);
121 assert(queue_empty(prio), "drain corrupted queue");
122 #ifdef ASSERT
123 int len = 0;
124 VM_Operation* cur;
125 for(cur = r; cur != NULL; cur=cur->next()) len++;
126 assert(len == length, "drain lost some ops");
127 #endif
128 return r;
129 }
130
131 //-----------------------------------------------------------------
132 // High-level interface
133 void VMOperationQueue::add(VM_Operation *op) {
134
135 HOTSPOT_VMOPS_REQUEST(
136 (char *) op->name(), strlen(op->name()),
137 op->evaluate_at_safepoint() ? 0 : 1);
138
139 // Encapsulates VM queue policy. Currently, that
140 // only involves putting them on the right list
141 queue_add(op->evaluate_at_safepoint() ? SafepointPriority : MediumPriority, op);
142 }
143
144 VM_Operation* VMOperationQueue::remove_next() {
145 // Assuming VMOperation queue is two-level priority queue. If there are
146 // more than two priorities, we need a different scheduling algorithm.
147 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
148 "current algorithm does not work");
149
150 // simple counter based scheduling to prevent starvation of lower priority
151 // queue. -- see 4390175
152 int high_prio, low_prio;
153 if (_queue_counter++ < 10) {
154 high_prio = SafepointPriority;
155 low_prio = MediumPriority;
156 } else {
157 _queue_counter = 0;
158 high_prio = MediumPriority;
159 low_prio = SafepointPriority;
160 }
161
162 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
163 }
164
165 //------------------------------------------------------------------------------------------------------------------
166 // Timeout machinery
167
168 void VMOperationTimeoutTask::task() {
169 assert(AbortVMOnVMOperationTimeout, "only if enabled");
170 if (is_armed()) {
171 jlong delay = nanos_to_millis(os::javaTimeNanos() - _arm_time);
172 if (delay > AbortVMOnVMOperationTimeoutDelay) {
173 fatal("VM operation took too long: " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)",
174 delay, AbortVMOnVMOperationTimeoutDelay);
175 }
176 }
177 }
178
179 bool VMOperationTimeoutTask::is_armed() {
180 return Atomic::load_acquire(&_armed) != 0;
181 }
182
183 void VMOperationTimeoutTask::arm() {
184 _arm_time = os::javaTimeNanos();
185 Atomic::release_store_fence(&_armed, 1);
186 }
187
188 void VMOperationTimeoutTask::disarm() {
189 Atomic::release_store_fence(&_armed, 0);
190 }
191
192 //------------------------------------------------------------------------------------------------------------------
193 // Implementation of VMThread stuff
194
195 bool VMThread::_should_terminate = false;
196 bool VMThread::_terminated = false;
197 Monitor* VMThread::_terminate_lock = NULL;
198 VMThread* VMThread::_vm_thread = NULL;
199 VM_Operation* VMThread::_cur_vm_operation = NULL;
200 VMOperationQueue* VMThread::_vm_queue = NULL;
201 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
202 uint64_t VMThread::_coalesced_count = 0;
203 VMOperationTimeoutTask* VMThread::_timeout_task = NULL;
204
205
206 void VMThread::create() {
207 assert(vm_thread() == NULL, "we can only allocate one VMThread");
208 _vm_thread = new VMThread();
209
210 if (AbortVMOnVMOperationTimeout) {
211 // Make sure we call the timeout task frequently enough, but not too frequent.
212 // Try to make the interval 10% of the timeout delay, so that we miss the timeout
213 // by those 10% at max. Periodic task also expects it to fit min/max intervals.
214 size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10;
215 interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran;
216 interval = MAX2<size_t>(interval, PeriodicTask::min_interval);
217 interval = MIN2<size_t>(interval, PeriodicTask::max_interval);
218
219 _timeout_task = new VMOperationTimeoutTask(interval);
220 _timeout_task->enroll();
221 } else {
222 assert(_timeout_task == NULL, "sanity");
223 }
224
225 // Create VM operation queue
226 _vm_queue = new VMOperationQueue();
227 guarantee(_vm_queue != NULL, "just checking");
228
229 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
230 Monitor::_safepoint_check_never);
231
232 if (UsePerfData) {
233 // jvmstat performance counters
234 Thread* THREAD = Thread::current();
235 _perf_accumulated_vm_operation_time =
236 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
237 PerfData::U_Ticks, CHECK);
238 }
239 }
240
241 VMThread::VMThread() : NamedThread() {
242 set_name("VM Thread");
243 }
244
245 void VMThread::destroy() {
246 _vm_thread = NULL; // VM thread is gone
247 }
248
249 static VM_None halt_op("Halt");
250
251 void VMThread::run() {
252 assert(this == vm_thread(), "check");
253
254 // Notify_lock wait checks on active_handles() to rewait in
255 // case of spurious wakeup, it should wait on the last
256 // value set prior to the notify
257 this->set_active_handles(JNIHandleBlock::allocate_block());
258
259 {
260 MutexLocker ml(Notify_lock);
261 Notify_lock->notify();
262 }
263 // Notify_lock is destroyed by Threads::create_vm()
264
265 int prio = (VMThreadPriority == -1)
266 ? os::java_to_os_priority[NearMaxPriority]
267 : VMThreadPriority;
268 // Note that I cannot call os::set_priority because it expects Java
269 // priorities and I am *explicitly* using OS priorities so that it's
270 // possible to set the VM thread priority higher than any Java thread.
271 os::set_native_priority( this, prio );
272
273 // Wait for VM_Operations until termination
274 this->loop();
275
276 // Note the intention to exit before safepointing.
277 // 6295565 This has the effect of waiting for any large tty
278 // outputs to finish.
279 if (xtty != NULL) {
280 ttyLocker ttyl;
281 xtty->begin_elem("destroy_vm");
282 xtty->stamp();
283 xtty->end_elem();
284 assert(should_terminate(), "termination flag must be set");
285 }
286
287 if (AsyncDeflateIdleMonitors && log_is_enabled(Info, monitorinflation)) {
288 // AsyncDeflateIdleMonitors does a special deflation in order
289 // to reduce the in-use monitor population that is reported by
290 // ObjectSynchronizer::log_in_use_monitor_details() at VM exit.
291 ObjectSynchronizer::request_deflate_idle_monitors();
292 }
293
294 // 4526887 let VM thread exit at Safepoint
295 _cur_vm_operation = &halt_op;
296 SafepointSynchronize::begin();
297
298 if (VerifyBeforeExit) {
299 HandleMark hm(VMThread::vm_thread());
300 // Among other things, this ensures that Eden top is correct.
301 Universe::heap()->prepare_for_verify();
302 // Silent verification so as not to pollute normal output,
303 // unless we really asked for it.
304 Universe::verify();
305 }
306
307 CompileBroker::set_should_block();
308
309 // wait for threads (compiler threads or daemon threads) in the
310 // _thread_in_native state to block.
311 VM_Exit::wait_for_threads_in_native_to_block();
312
313 // signal other threads that VM process is gone
314 {
315 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
316 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
317 // If that happens after _terminate_lock->wait() has unset _owner
318 // but before it actually drops the lock and waits, the notification below
319 // may get lost and we will have a hang. To avoid this, we need to use
320 // Mutex::lock_without_safepoint_check().
321 MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
322 _terminated = true;
323 ml.notify();
324 }
325
326 // We are now racing with the VM termination being carried out in
327 // another thread, so we don't "delete this". Numerous threads don't
328 // get deleted when the VM terminates
329
330 }
331
332
333 // Notify the VMThread that the last non-daemon JavaThread has terminated,
334 // and wait until operation is performed.
335 void VMThread::wait_for_vm_thread_exit() {
336 assert(Thread::current()->is_Java_thread(), "Should be a JavaThread");
337 assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated");
338 { MonitorLocker mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
339 _should_terminate = true;
340 mu.notify();
341 }
342
343 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
344 // because this thread has been removed from the threads list. But anything
345 // that could get blocked by Safepoint should not be used after this point,
346 // otherwise we will hang, since there is no one can end the safepoint.
347
348 // Wait until VM thread is terminated
349 // Note: it should be OK to use Terminator_lock here. But this is called
350 // at a very delicate time (VM shutdown) and we are operating in non- VM
351 // thread at Safepoint. It's safer to not share lock with other threads.
352 { MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
353 while(!VMThread::is_terminated()) {
354 ml.wait();
355 }
356 }
357 }
358
359 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
360 assert(event != NULL, "invariant");
361 assert(event->should_commit(), "invariant");
362 assert(op != NULL, "invariant");
363 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
364 event->set_operation(op->type());
365 event->set_safepoint(evaluate_at_safepoint);
366 event->set_blocking(true);
367 event->set_caller(JFR_THREAD_ID(op->calling_thread()));
368 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0);
369 event->commit();
370 }
371
372 void VMThread::evaluate_operation(VM_Operation* op) {
373 ResourceMark rm;
374
375 {
376 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
377 HOTSPOT_VMOPS_BEGIN(
378 (char *) op->name(), strlen(op->name()),
379 op->evaluate_at_safepoint() ? 0 : 1);
380
381 EventExecuteVMOperation event;
382 op->evaluate();
383 if (event.should_commit()) {
384 post_vm_operation_event(&event, op);
385 }
386
387 HOTSPOT_VMOPS_END(
388 (char *) op->name(), strlen(op->name()),
389 op->evaluate_at_safepoint() ? 0 : 1);
390 }
391
392 // Mark as completed
393 op->calling_thread()->increment_vm_operation_completed_count();
394 }
395
396 static VM_None safepointALot_op("SafepointALot");
397 static VM_Cleanup cleanup_op;
398
399 class HandshakeALotClosure : public HandshakeClosure {
400 public:
401 HandshakeALotClosure() : HandshakeClosure("HandshakeALot") {}
402 void do_thread(Thread* thread) {
403 #ifdef ASSERT
404 assert(thread->is_Java_thread(), "must be");
405 JavaThread* jt = (JavaThread*)thread;
406 jt->verify_states_for_handshake();
407 #endif
408 }
409 };
410
411 VM_Operation* VMThread::no_op_safepoint() {
412 // Check for handshakes first since we may need to return a VMop.
413 if (HandshakeALot) {
414 HandshakeALotClosure hal_cl;
415 Handshake::execute(&hal_cl);
416 }
417 // Check for a cleanup before SafepointALot to keep stats correct.
418 long interval_ms = SafepointTracing::time_since_last_safepoint_ms();
419 bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
420 (interval_ms >= GuaranteedSafepointInterval);
421 if (max_time_exceeded && SafepointSynchronize::is_cleanup_needed()) {
422 return &cleanup_op;
423 }
424 if (SafepointALot) {
425 return &safepointALot_op;
426 }
427 // Nothing to be done.
428 return NULL;
429 }
430
431 void VMThread::loop() {
432 assert(_cur_vm_operation == NULL, "no current one should be executing");
433
434 SafepointSynchronize::init(_vm_thread);
435
436 while(true) {
437 VM_Operation* safepoint_ops = NULL;
438 //
439 // Wait for VM operation
440 //
441 // use no_safepoint_check to get lock without attempting to "sneak"
442 { MonitorLocker mu_queue(VMOperationQueue_lock,
443 Mutex::_no_safepoint_check_flag);
444
445 // Look for new operation
446 assert(_cur_vm_operation == NULL, "no current one should be executing");
447 _cur_vm_operation = _vm_queue->remove_next();
448
449 // Stall time tracking code
450 if (PrintVMQWaitTime && _cur_vm_operation != NULL) {
451 jlong stall = nanos_to_millis(os::javaTimeNanos() - _cur_vm_operation->timestamp());
452 if (stall > 0)
453 tty->print_cr("%s stall: " JLONG_FORMAT, _cur_vm_operation->name(), stall);
454 }
455
456 while (!should_terminate() && _cur_vm_operation == NULL) {
457 // wait with a timeout to guarantee safepoints at regular intervals
458 // (if there is cleanup work to do)
459 (void)mu_queue.wait(GuaranteedSafepointInterval);
460
461 // Support for self destruction
462 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() &&
463 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
464 tty->print_cr("VM self-destructed");
465 exit(-1);
466 }
467
468 // If the queue contains a safepoint VM op,
469 // clean up will be done so we can skip this part.
470 if (!_vm_queue->peek_at_safepoint_priority()) {
471
472 // Have to unlock VMOperationQueue_lock just in case no_op_safepoint()
473 // has to do a handshake when HandshakeALot is enabled.
474 MutexUnlocker mul(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
475 if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
476 // Force a safepoint since we have not had one for at least
477 // 'GuaranteedSafepointInterval' milliseconds and we need to clean
478 // something. This will run all the clean-up processing that needs
479 // to be done at a safepoint.
480 SafepointSynchronize::begin();
481 #ifdef ASSERT
482 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
483 #endif
484 SafepointSynchronize::end();
485 _cur_vm_operation = NULL;
486 }
487 }
488 _cur_vm_operation = _vm_queue->remove_next();
489
490 // If we are at a safepoint we will evaluate all the operations that
491 // follow that also require a safepoint
492 if (_cur_vm_operation != NULL &&
493 _cur_vm_operation->evaluate_at_safepoint()) {
494 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
495 }
496 }
497
498 if (should_terminate()) break;
499 } // Release mu_queue_lock
500
501 //
502 // Execute VM operation
503 //
504 { HandleMark hm(VMThread::vm_thread());
505
506 EventMark em("Executing VM operation: %s", vm_operation()->name());
507 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
508
509 // If we are at a safepoint we will evaluate all the operations that
510 // follow that also require a safepoint
511 if (_cur_vm_operation->evaluate_at_safepoint()) {
512 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name());
513
514 SafepointSynchronize::begin();
515
516 if (_timeout_task != NULL) {
517 _timeout_task->arm();
518 }
519
520 evaluate_operation(_cur_vm_operation);
521 // now process all queued safepoint ops, iteratively draining
522 // the queue until there are none left
523 do {
524 _cur_vm_operation = safepoint_ops;
525 if (_cur_vm_operation != NULL) {
526 do {
527 EventMark em("Executing coalesced safepoint VM operation: %s", _cur_vm_operation->name());
528 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name());
529 // evaluate_operation deletes the op object so we have
530 // to grab the next op now
531 VM_Operation* next = _cur_vm_operation->next();
532 evaluate_operation(_cur_vm_operation);
533 _cur_vm_operation = next;
534 _coalesced_count++;
535 } while (_cur_vm_operation != NULL);
536 }
537 // There is a chance that a thread enqueued a safepoint op
538 // since we released the op-queue lock and initiated the safepoint.
539 // So we drain the queue again if there is anything there, as an
540 // optimization to try and reduce the number of safepoints.
541 // As the safepoint synchronizes us with JavaThreads we will see
542 // any enqueue made by a JavaThread, but the peek will not
543 // necessarily detect a concurrent enqueue by a GC thread, but
544 // that simply means the op will wait for the next major cycle of the
545 // VMThread - just as it would if the GC thread lost the race for
546 // the lock.
547 if (_vm_queue->peek_at_safepoint_priority()) {
548 // must hold lock while draining queue
549 MutexLocker mu_queue(VMOperationQueue_lock,
550 Mutex::_no_safepoint_check_flag);
551 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
552 } else {
553 safepoint_ops = NULL;
554 }
555 } while(safepoint_ops != NULL);
556
557 if (_timeout_task != NULL) {
558 _timeout_task->disarm();
559 }
560
561 // Complete safepoint synchronization
562 SafepointSynchronize::end();
563
564 } else { // not a safepoint operation
565 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name());
566 if (TraceLongCompiles) {
567 elapsedTimer t;
568 t.start();
569 evaluate_operation(_cur_vm_operation);
570 t.stop();
571 double secs = t.seconds();
572 if (secs * 1e3 > LongCompileThreshold) {
573 // XXX - _cur_vm_operation should not be accessed after
574 // the completed count has been incremented; the waiting
575 // thread may have already freed this memory.
576 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
577 }
578 } else {
579 evaluate_operation(_cur_vm_operation);
580 }
581
582 _cur_vm_operation = NULL;
583 }
584 }
585
586 //
587 // Notify (potential) waiting Java thread(s)
588 { MonitorLocker mu(VMOperationRequest_lock, Mutex::_no_safepoint_check_flag);
589 mu.notify_all();
590 }
591 }
592 }
593
594 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
595 // over a section of execution by a thread. Currently, it's used only to
596 // prevent re-entrant calls to GC.
597 class SkipGCALot : public StackObj {
598 private:
599 bool _saved;
600 Thread* _t;
601
602 public:
603 #ifdef ASSERT
604 SkipGCALot(Thread* t) : _t(t) {
605 _saved = _t->skip_gcalot();
606 _t->set_skip_gcalot(true);
607 }
608
609 ~SkipGCALot() {
610 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
611 _t->set_skip_gcalot(_saved);
612 }
613 #else
614 SkipGCALot(Thread* t) { }
615 ~SkipGCALot() { }
616 #endif
617 };
618
619 void VMThread::execute(VM_Operation* op) {
620 Thread* t = Thread::current();
621
622 if (!t->is_VM_thread()) {
623 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
624 // JavaThread or WatcherThread
625 t->check_for_valid_safepoint_state();
626
627 // New request from Java thread, evaluate prologue
628 if (!op->doit_prologue()) {
629 return; // op was cancelled
630 }
631
632 // Setup VM_operations for execution
633 op->set_calling_thread(t);
634
635 // Get ticket number for the VM operation
636 int ticket = t->vm_operation_ticket();
637
638 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
639 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
640 // to be queued up during a safepoint synchronization.
641 {
642 MonitorLocker ml(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
643 log_debug(vmthread)("Adding VM operation: %s", op->name());
644 _vm_queue->add(op);
645 op->set_timestamp(os::javaTimeNanos());
646 ml.notify();
647 }
648 {
649 // Wait for completion of request
650 // Note: only a JavaThread triggers the safepoint check when locking
651 MonitorLocker ml(VMOperationRequest_lock,
652 t->is_Java_thread() ? Mutex::_safepoint_check_flag : Mutex::_no_safepoint_check_flag);
653 while(t->vm_operation_completed_count() < ticket) {
654 ml.wait();
655 }
656 }
657 op->doit_epilogue();
658 } else {
659 // invoked by VM thread; usually nested VM operation
660 assert(t->is_VM_thread(), "must be a VM thread");
661 VM_Operation* prev_vm_operation = vm_operation();
662 if (prev_vm_operation != NULL) {
663 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
664 // does not allow nested scavenges or compiles.
665 if (!prev_vm_operation->allow_nested_vm_operations()) {
666 fatal("Nested VM operation %s requested by operation %s",
667 op->name(), vm_operation()->name());
668 }
669 op->set_calling_thread(prev_vm_operation->calling_thread());
670 }
671
672 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
673
674 // Release all internal handles after operation is evaluated
675 HandleMark hm(t);
676 _cur_vm_operation = op;
677
678 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
679 SafepointSynchronize::begin();
680 op->evaluate();
681 SafepointSynchronize::end();
682 } else {
683 op->evaluate();
684 }
685
686 _cur_vm_operation = prev_vm_operation;
687 }
688 }
689
690 void VMThread::verify() {
691 oops_do(&VerifyOopClosure::verify_oop, NULL);
692 }