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