1 /*
2 * Copyright (c) 1998, 2017, 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 "memory/resourceArea.hpp"
29 #include "oops/method.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "oops/verifyOopClosure.hpp"
32 #include "runtime/interfaceSupport.hpp"
33 #include "runtime/mutexLocker.hpp"
34 #include "runtime/os.hpp"
35 #include "runtime/safepoint.hpp"
36 #include "runtime/thread.inline.hpp"
37 #include "runtime/vmThread.hpp"
38 #include "runtime/vm_operations.hpp"
39 #include "services/runtimeService.hpp"
40 #include "utilities/dtrace.hpp"
41 #include "utilities/events.hpp"
42 #include "utilities/xmlstream.hpp"
43 #if INCLUDE_TRACE
44 #include "trace/tracing.hpp"
45 #endif
46
47 // Dummy VM operation to act as first element in our circular double-linked list
48 class VM_Dummy: public VM_Operation {
49 VMOp_Type type() const { return VMOp_Dummy; }
50 void doit() {};
51 };
52
53 VMOperationQueue::VMOperationQueue() {
54 // The queue is a circular doubled-linked list, which always contains
55 // one element (i.e., one element means empty).
56 for(int i = 0; i < nof_priorities; i++) {
57 _queue_length[i] = 0;
58 _queue_counter = 0;
59 _queue[i] = new VM_Dummy();
60 _queue[i]->set_next(_queue[i]);
61 _queue[i]->set_prev(_queue[i]);
62 }
63 _drain_list = NULL;
64 }
65
66
67 bool VMOperationQueue::queue_empty(int prio) {
68 // It is empty if there is exactly one element
69 bool empty = (_queue[prio] == _queue[prio]->next());
70 assert( (_queue_length[prio] == 0 && empty) ||
71 (_queue_length[prio] > 0 && !empty), "sanity check");
72 return _queue_length[prio] == 0;
73 }
74
75 // Inserts an element to the right of the q element
76 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
77 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
78 n->set_prev(q);
79 n->set_next(q->next());
80 q->next()->set_prev(n);
81 q->set_next(n);
82 }
83
84 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
85 _queue_length[prio]++;
86 insert(_queue[prio]->next(), op);
87 }
88
89 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
90 _queue_length[prio]++;
91 insert(_queue[prio]->prev(), op);
92 }
93
94
95 void VMOperationQueue::unlink(VM_Operation* q) {
96 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
97 q->prev()->set_next(q->next());
98 q->next()->set_prev(q->prev());
99 }
100
101 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
102 if (queue_empty(prio)) return NULL;
103 assert(_queue_length[prio] >= 0, "sanity check");
104 _queue_length[prio]--;
105 VM_Operation* r = _queue[prio]->next();
106 assert(r != _queue[prio], "cannot remove base element");
107 unlink(r);
108 return r;
109 }
110
111 VM_Operation* VMOperationQueue::queue_drain(int prio) {
112 if (queue_empty(prio)) return NULL;
113 DEBUG_ONLY(int length = _queue_length[prio];);
114 assert(length >= 0, "sanity check");
115 _queue_length[prio] = 0;
116 VM_Operation* r = _queue[prio]->next();
117 assert(r != _queue[prio], "cannot remove base element");
118 // remove links to base element from head and tail
119 r->set_prev(NULL);
120 _queue[prio]->prev()->set_next(NULL);
121 // restore queue to empty state
122 _queue[prio]->set_next(_queue[prio]);
123 _queue[prio]->set_prev(_queue[prio]);
124 assert(queue_empty(prio), "drain corrupted queue");
125 #ifdef ASSERT
126 int len = 0;
127 VM_Operation* cur;
128 for(cur = r; cur != NULL; cur=cur->next()) len++;
129 assert(len == length, "drain lost some ops");
130 #endif
131 return r;
132 }
133
134 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
135 VM_Operation* cur = _queue[queue];
136 cur = cur->next();
137 while (cur != _queue[queue]) {
138 cur->oops_do(f);
139 cur = cur->next();
140 }
141 }
142
143 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
144 VM_Operation* cur = _drain_list;
145 while (cur != NULL) {
146 cur->oops_do(f);
147 cur = cur->next();
148 }
149 }
150
151 //-----------------------------------------------------------------
152 // High-level interface
153 bool VMOperationQueue::add(VM_Operation *op) {
154
155 HOTSPOT_VMOPS_REQUEST(
156 (char *) op->name(), strlen(op->name()),
157 op->evaluation_mode());
158
159 // Encapsulates VM queue policy. Currently, that
160 // only involves putting them on the right list
161 if (op->evaluate_at_safepoint()) {
162 queue_add_back(SafepointPriority, op);
163 return true;
164 }
165
166 queue_add_back(MediumPriority, op);
167 return true;
168 }
169
170 VM_Operation* VMOperationQueue::remove_next() {
171 // Assuming VMOperation queue is two-level priority queue. If there are
172 // more than two priorities, we need a different scheduling algorithm.
173 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
174 "current algorithm does not work");
175
176 // simple counter based scheduling to prevent starvation of lower priority
177 // queue. -- see 4390175
178 int high_prio, low_prio;
179 if (_queue_counter++ < 10) {
180 high_prio = SafepointPriority;
181 low_prio = MediumPriority;
182 } else {
183 _queue_counter = 0;
184 high_prio = MediumPriority;
185 low_prio = SafepointPriority;
186 }
187
188 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
189 }
190
191 void VMOperationQueue::oops_do(OopClosure* f) {
192 for(int i = 0; i < nof_priorities; i++) {
193 queue_oops_do(i, f);
194 }
195 drain_list_oops_do(f);
196 }
197
198
199 //------------------------------------------------------------------------------------------------------------------
200 // Implementation of VMThread stuff
201
202 bool VMThread::_should_terminate = false;
203 bool VMThread::_terminated = false;
204 Monitor* VMThread::_terminate_lock = NULL;
205 VMThread* VMThread::_vm_thread = NULL;
206 VM_Operation* VMThread::_cur_vm_operation = NULL;
207 VMOperationQueue* VMThread::_vm_queue = NULL;
208 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
209 const char* VMThread::_no_op_reason = NULL;
210
211
212 void VMThread::create() {
213 assert(vm_thread() == NULL, "we can only allocate one VMThread");
214 _vm_thread = new VMThread();
215
216 // Create VM operation queue
217 _vm_queue = new VMOperationQueue();
218 guarantee(_vm_queue != NULL, "just checking");
219
220 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
221 Monitor::_safepoint_check_never);
222
223 if (UsePerfData) {
224 // jvmstat performance counters
225 Thread* THREAD = Thread::current();
226 _perf_accumulated_vm_operation_time =
227 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
228 PerfData::U_Ticks, CHECK);
229 }
230 }
231
232 VMThread::VMThread() : NamedThread() {
233 set_name("VM Thread");
234 }
235
236 void VMThread::destroy() {
237 _vm_thread = NULL; // VM thread is gone
238 }
239
240 void VMThread::run() {
241 assert(this == vm_thread(), "check");
242
243 this->initialize_named_thread();
244 this->record_stack_base_and_size();
245 // Notify_lock wait checks on active_handles() to rewait in
246 // case of spurious wakeup, it should wait on the last
247 // value set prior to the notify
248 this->set_active_handles(JNIHandleBlock::allocate_block());
249
250 {
251 MutexLocker ml(Notify_lock);
252 Notify_lock->notify();
253 }
254 // Notify_lock is destroyed by Threads::create_vm()
255
256 int prio = (VMThreadPriority == -1)
257 ? os::java_to_os_priority[NearMaxPriority]
258 : VMThreadPriority;
259 // Note that I cannot call os::set_priority because it expects Java
260 // priorities and I am *explicitly* using OS priorities so that it's
261 // possible to set the VM thread priority higher than any Java thread.
262 os::set_native_priority( this, prio );
263
264 // Wait for VM_Operations until termination
265 this->loop();
266
267 // Note the intention to exit before safepointing.
268 // 6295565 This has the effect of waiting for any large tty
269 // outputs to finish.
270 if (xtty != NULL) {
271 ttyLocker ttyl;
272 xtty->begin_elem("destroy_vm");
273 xtty->stamp();
274 xtty->end_elem();
275 assert(should_terminate(), "termination flag must be set");
276 }
277
278 // 4526887 let VM thread exit at Safepoint
279 _no_op_reason = "Halt";
280 SafepointSynchronize::begin();
281
282 if (VerifyBeforeExit) {
283 HandleMark hm(VMThread::vm_thread());
284 // Among other things, this ensures that Eden top is correct.
285 Universe::heap()->prepare_for_verify();
286 // Silent verification so as not to pollute normal output,
287 // unless we really asked for it.
288 Universe::verify();
289 }
290
291 CompileBroker::set_should_block();
292
293 // wait for threads (compiler threads or daemon threads) in the
294 // _thread_in_native state to block.
295 VM_Exit::wait_for_threads_in_native_to_block();
296
297 // signal other threads that VM process is gone
298 {
299 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
300 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
301 // If that happens after _terminate_lock->wait() has unset _owner
302 // but before it actually drops the lock and waits, the notification below
303 // may get lost and we will have a hang. To avoid this, we need to use
304 // Mutex::lock_without_safepoint_check().
305 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
306 _terminated = true;
307 _terminate_lock->notify();
308 }
309
310 // We are now racing with the VM termination being carried out in
311 // another thread, so we don't "delete this". Numerous threads don't
312 // get deleted when the VM terminates
313
314 }
315
316
317 // Notify the VMThread that the last non-daemon JavaThread has terminated,
318 // and wait until operation is performed.
319 void VMThread::wait_for_vm_thread_exit() {
320 { MutexLocker mu(VMOperationQueue_lock);
321 _should_terminate = true;
322 VMOperationQueue_lock->notify();
323 }
324
325 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
326 // because this thread has been removed from the threads list. But anything
327 // that could get blocked by Safepoint should not be used after this point,
328 // otherwise we will hang, since there is no one can end the safepoint.
329
330 // Wait until VM thread is terminated
331 // Note: it should be OK to use Terminator_lock here. But this is called
332 // at a very delicate time (VM shutdown) and we are operating in non- VM
333 // thread at Safepoint. It's safer to not share lock with other threads.
334 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
335 while(!VMThread::is_terminated()) {
336 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
337 }
338 }
339 }
340
341 #if INCLUDE_TRACE
342 static void post_vm_operation_event(EventExecuteVMOperation* event,
343 VM_Operation* op) {
344 assert(event != NULL, "invariant");
345 assert(op != NULL, "invariant");
346 if (event->should_commit()) {
347 const bool is_concurrent = op->evaluate_concurrently();
348 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
349 event->set_operation(op->type());
350 event->set_safepoint(evaluate_at_safepoint);
351 event->set_blocking(!is_concurrent);
352 // Only write caller thread information for non-concurrent vm operations.
353 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
354 // This is because the caller thread could have exited already.
355 event->set_caller(is_concurrent ? 0 : THREAD_TRACE_ID(op->calling_thread()));
356 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0);
357 event->commit();
358 }
359 }
360 #endif // INCLUDE_TRACE
361
362 void VMThread::evaluate_operation(VM_Operation* op) {
363 ResourceMark rm;
364
365 {
366 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
367 HOTSPOT_VMOPS_BEGIN(
368 (char *) op->name(), strlen(op->name()),
369 op->evaluation_mode());
370 TRACE_ONLY(EventExecuteVMOperation event;)
371
372 op->evaluate();
373
374 TRACE_ONLY(post_vm_operation_event(&event, op);)
375
376 HOTSPOT_VMOPS_END(
377 (char *) op->name(), strlen(op->name()),
378 op->evaluation_mode());
379 }
380
381 // Last access of info in _cur_vm_operation!
382 bool c_heap_allocated = op->is_cheap_allocated();
383
384 // Mark as completed
385 if (!op->evaluate_concurrently()) {
386 op->calling_thread()->increment_vm_operation_completed_count();
387 }
388 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
389 // since if it is stack allocated the calling thread might have deallocated
390 if (c_heap_allocated) {
391 delete _cur_vm_operation;
392 }
393 }
394
395 bool VMThread::no_op_safepoint_needed(bool check_time) {
396 if (SafepointALot) {
397 _no_op_reason = "SafepointALot";
398 return true;
399 }
400 if (!SafepointSynchronize::is_cleanup_needed()) {
401 return false;
402 }
403 if (check_time) {
404 long interval = SafepointSynchronize::last_non_safepoint_interval();
405 bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
406 (interval > GuaranteedSafepointInterval);
407 if (!max_time_exceeded) {
408 return false;
409 }
410 }
411 _no_op_reason = "Cleanup";
412 return true;
413 }
414
415 void VMThread::loop() {
416 assert(_cur_vm_operation == NULL, "no current one should be executing");
417
418 while(true) {
419 VM_Operation* safepoint_ops = NULL;
420 //
421 // Wait for VM operation
422 //
423 // use no_safepoint_check to get lock without attempting to "sneak"
424 { MutexLockerEx mu_queue(VMOperationQueue_lock,
425 Mutex::_no_safepoint_check_flag);
426
427 // Look for new operation
428 assert(_cur_vm_operation == NULL, "no current one should be executing");
429 _cur_vm_operation = _vm_queue->remove_next();
430
431 // Stall time tracking code
432 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
433 !_cur_vm_operation->evaluate_concurrently()) {
434 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
435 if (stall > 0)
436 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall);
437 }
438
439 while (!should_terminate() && _cur_vm_operation == NULL) {
440 // wait with a timeout to guarantee safepoints at regular intervals
441 bool timedout =
442 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
443 GuaranteedSafepointInterval);
444
445 // Support for self destruction
446 if ((SelfDestructTimer != 0) && !is_error_reported() &&
447 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
448 tty->print_cr("VM self-destructed");
449 exit(-1);
450 }
451
452 if (timedout && VMThread::no_op_safepoint_needed(false)) {
453 MutexUnlockerEx mul(VMOperationQueue_lock,
454 Mutex::_no_safepoint_check_flag);
455 // Force a safepoint since we have not had one for at least
456 // 'GuaranteedSafepointInterval' milliseconds. This will run all
457 // the clean-up processing that needs to be done regularly at a
458 // safepoint
459 SafepointSynchronize::begin();
460 #ifdef ASSERT
461 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
462 #endif
463 SafepointSynchronize::end();
464 }
465 _cur_vm_operation = _vm_queue->remove_next();
466
467 // If we are at a safepoint we will evaluate all the operations that
468 // follow that also require a safepoint
469 if (_cur_vm_operation != NULL &&
470 _cur_vm_operation->evaluate_at_safepoint()) {
471 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
472 }
473 }
474
475 if (should_terminate()) break;
476 } // Release mu_queue_lock
477
478 //
479 // Execute VM operation
480 //
481 { HandleMark hm(VMThread::vm_thread());
482
483 EventMark em("Executing VM operation: %s", vm_operation()->name());
484 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
485
486 // Give the VM thread an extra quantum. Jobs tend to be bursty and this
487 // helps the VM thread to finish up the job.
488 // FIXME: When this is enabled and there are many threads, this can degrade
489 // performance significantly.
490 if( VMThreadHintNoPreempt )
491 os::hint_no_preempt();
492
493 // If we are at a safepoint we will evaluate all the operations that
494 // follow that also require a safepoint
495 if (_cur_vm_operation->evaluate_at_safepoint()) {
496
497 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
498
499 SafepointSynchronize::begin();
500 evaluate_operation(_cur_vm_operation);
501 // now process all queued safepoint ops, iteratively draining
502 // the queue until there are none left
503 do {
504 _cur_vm_operation = safepoint_ops;
505 if (_cur_vm_operation != NULL) {
506 do {
507 // evaluate_operation deletes the op object so we have
508 // to grab the next op now
509 VM_Operation* next = _cur_vm_operation->next();
510 _vm_queue->set_drain_list(next);
511 evaluate_operation(_cur_vm_operation);
512 _cur_vm_operation = next;
513 if (PrintSafepointStatistics) {
514 SafepointSynchronize::inc_vmop_coalesced_count();
515 }
516 } while (_cur_vm_operation != NULL);
517 }
518 // There is a chance that a thread enqueued a safepoint op
519 // since we released the op-queue lock and initiated the safepoint.
520 // So we drain the queue again if there is anything there, as an
521 // optimization to try and reduce the number of safepoints.
522 // As the safepoint synchronizes us with JavaThreads we will see
523 // any enqueue made by a JavaThread, but the peek will not
524 // necessarily detect a concurrent enqueue by a GC thread, but
525 // that simply means the op will wait for the next major cycle of the
526 // VMThread - just as it would if the GC thread lost the race for
527 // the lock.
528 if (_vm_queue->peek_at_safepoint_priority()) {
529 // must hold lock while draining queue
530 MutexLockerEx mu_queue(VMOperationQueue_lock,
531 Mutex::_no_safepoint_check_flag);
532 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
533 } else {
534 safepoint_ops = NULL;
535 }
536 } while(safepoint_ops != NULL);
537
538 _vm_queue->set_drain_list(NULL);
539
540 // Complete safepoint synchronization
541 SafepointSynchronize::end();
542
543 } else { // not a safepoint operation
544 if (TraceLongCompiles) {
545 elapsedTimer t;
546 t.start();
547 evaluate_operation(_cur_vm_operation);
548 t.stop();
549 double secs = t.seconds();
550 if (secs * 1e3 > LongCompileThreshold) {
551 // XXX - _cur_vm_operation should not be accessed after
552 // the completed count has been incremented; the waiting
553 // thread may have already freed this memory.
554 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
555 }
556 } else {
557 evaluate_operation(_cur_vm_operation);
558 }
559
560 _cur_vm_operation = NULL;
561 }
562 }
563
564 //
565 // Notify (potential) waiting Java thread(s) - lock without safepoint
566 // check so that sneaking is not possible
567 { MutexLockerEx mu(VMOperationRequest_lock,
568 Mutex::_no_safepoint_check_flag);
569 VMOperationRequest_lock->notify_all();
570 }
571
572 //
573 // We want to make sure that we get to a safepoint regularly.
574 //
575 if (VMThread::no_op_safepoint_needed(true)) {
576 HandleMark hm(VMThread::vm_thread());
577 SafepointSynchronize::begin();
578 SafepointSynchronize::end();
579 }
580 }
581 }
582
583 void VMThread::execute(VM_Operation* op) {
584 Thread* t = Thread::current();
585
586 if (!t->is_VM_thread()) {
587 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
588 // JavaThread or WatcherThread
589 bool concurrent = op->evaluate_concurrently();
590 // only blocking VM operations need to verify the caller's safepoint state:
591 if (!concurrent) {
592 t->check_for_valid_safepoint_state(true);
593 }
594
595 // New request from Java thread, evaluate prologue
596 if (!op->doit_prologue()) {
597 return; // op was cancelled
598 }
599
600 // Setup VM_operations for execution
601 op->set_calling_thread(t, Thread::get_priority(t));
602
603 // It does not make sense to execute the epilogue, if the VM operation object is getting
604 // deallocated by the VM thread.
605 bool execute_epilog = !op->is_cheap_allocated();
606 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
607
608 // Get ticket number for non-concurrent VM operations
609 int ticket = 0;
610 if (!concurrent) {
611 ticket = t->vm_operation_ticket();
612 }
613
614 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
615 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
616 // to be queued up during a safepoint synchronization.
617 {
618 VMOperationQueue_lock->lock_without_safepoint_check();
619 bool ok = _vm_queue->add(op);
620 op->set_timestamp(os::javaTimeMillis());
621 VMOperationQueue_lock->notify();
622 VMOperationQueue_lock->unlock();
623 // VM_Operation got skipped
624 if (!ok) {
625 assert(concurrent, "can only skip concurrent tasks");
626 if (op->is_cheap_allocated()) delete op;
627 return;
628 }
629 }
630
631 if (!concurrent) {
632 // Wait for completion of request (non-concurrent)
633 // Note: only a JavaThread triggers the safepoint check when locking
634 MutexLocker mu(VMOperationRequest_lock);
635 while(t->vm_operation_completed_count() < ticket) {
636 VMOperationRequest_lock->wait(!t->is_Java_thread());
637 }
638 }
639
640 if (execute_epilog) {
641 op->doit_epilogue();
642 }
643 } else {
644 // invoked by VM thread; usually nested VM operation
645 assert(t->is_VM_thread(), "must be a VM thread");
646 VM_Operation* prev_vm_operation = vm_operation();
647 if (prev_vm_operation != NULL) {
648 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
649 // does not allow nested scavenges or compiles.
650 if (!prev_vm_operation->allow_nested_vm_operations()) {
651 fatal("Nested VM operation %s requested by operation %s",
652 op->name(), vm_operation()->name());
653 }
654 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
655 }
656
657 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
658
659 // Release all internal handles after operation is evaluated
660 HandleMark hm(t);
661 _cur_vm_operation = op;
662
663 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
664 SafepointSynchronize::begin();
665 op->evaluate();
666 SafepointSynchronize::end();
667 } else {
668 op->evaluate();
669 }
670
671 // Free memory if needed
672 if (op->is_cheap_allocated()) delete op;
673
674 _cur_vm_operation = prev_vm_operation;
675 }
676 }
677
678
679 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
680 Thread::oops_do(f, cf);
681 _vm_queue->oops_do(f);
682 }
683
684 //------------------------------------------------------------------------------------------------------------------
685 #ifndef PRODUCT
686
687 void VMOperationQueue::verify_queue(int prio) {
688 // Check that list is correctly linked
689 int length = _queue_length[prio];
690 VM_Operation *cur = _queue[prio];
691 int i;
692
693 // Check forward links
694 for(i = 0; i < length; i++) {
695 cur = cur->next();
696 assert(cur != _queue[prio], "list to short (forward)");
697 }
698 assert(cur->next() == _queue[prio], "list to long (forward)");
699
700 // Check backwards links
701 cur = _queue[prio];
702 for(i = 0; i < length; i++) {
703 cur = cur->prev();
704 assert(cur != _queue[prio], "list to short (backwards)");
705 }
706 assert(cur->prev() == _queue[prio], "list to long (backwards)");
707 }
708
709 #endif
710
711 void VMThread::verify() {
712 oops_do(&VerifyOopClosure::verify_oop, NULL);
713 }