1 /*
2 * Copyright (c) 1998, 2016, 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 "trace/tracing.hpp"
41 #include "utilities/dtrace.hpp"
42 #include "utilities/events.hpp"
43 #include "utilities/xmlstream.hpp"
44
45 // Dummy VM operation to act as first element in our circular double-linked list
46 class VM_Dummy: public VM_Operation {
47 VMOp_Type type() const { return VMOp_Dummy; }
48 void doit() {};
49 };
50
51 VMOperationQueue::VMOperationQueue() {
52 // The queue is a circular doubled-linked list, which always contains
53 // one element (i.e., one element means empty).
54 for(int i = 0; i < nof_priorities; i++) {
55 _queue_length[i] = 0;
56 _queue_counter = 0;
57 _queue[i] = new VM_Dummy();
58 _queue[i]->set_next(_queue[i]);
59 _queue[i]->set_prev(_queue[i]);
60 }
61 _drain_list = NULL;
62 }
63
64
65 bool VMOperationQueue::queue_empty(int prio) {
66 // It is empty if there is exactly one element
67 bool empty = (_queue[prio] == _queue[prio]->next());
68 assert( (_queue_length[prio] == 0 && empty) ||
69 (_queue_length[prio] > 0 && !empty), "sanity check");
70 return _queue_length[prio] == 0;
71 }
72
73 // Inserts an element to the right of the q element
74 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
75 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
76 n->set_prev(q);
77 n->set_next(q->next());
78 q->next()->set_prev(n);
79 q->set_next(n);
80 }
81
82 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
83 _queue_length[prio]++;
84 insert(_queue[prio]->next(), op);
85 }
86
87 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
88 _queue_length[prio]++;
89 insert(_queue[prio]->prev(), op);
90 }
91
92
93 void VMOperationQueue::unlink(VM_Operation* q) {
94 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
95 q->prev()->set_next(q->next());
96 q->next()->set_prev(q->prev());
97 }
98
99 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
100 if (queue_empty(prio)) return NULL;
101 assert(_queue_length[prio] >= 0, "sanity check");
102 _queue_length[prio]--;
103 VM_Operation* r = _queue[prio]->next();
104 assert(r != _queue[prio], "cannot remove base element");
105 unlink(r);
106 return r;
107 }
108
109 VM_Operation* VMOperationQueue::queue_drain(int prio) {
110 if (queue_empty(prio)) return NULL;
111 DEBUG_ONLY(int length = _queue_length[prio];);
112 assert(length >= 0, "sanity check");
113 _queue_length[prio] = 0;
114 VM_Operation* r = _queue[prio]->next();
115 assert(r != _queue[prio], "cannot remove base element");
116 // remove links to base element from head and tail
117 r->set_prev(NULL);
118 _queue[prio]->prev()->set_next(NULL);
119 // restore queue to empty state
120 _queue[prio]->set_next(_queue[prio]);
121 _queue[prio]->set_prev(_queue[prio]);
122 assert(queue_empty(prio), "drain corrupted queue");
123 #ifdef ASSERT
124 int len = 0;
125 VM_Operation* cur;
126 for(cur = r; cur != NULL; cur=cur->next()) len++;
127 assert(len == length, "drain lost some ops");
128 #endif
129 return r;
130 }
131
132 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
133 VM_Operation* cur = _queue[queue];
134 cur = cur->next();
135 while (cur != _queue[queue]) {
136 cur->oops_do(f);
137 cur = cur->next();
138 }
139 }
140
141 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
142 VM_Operation* cur = _drain_list;
143 while (cur != NULL) {
144 cur->oops_do(f);
145 cur = cur->next();
146 }
147 }
148
149 //-----------------------------------------------------------------
150 // High-level interface
151 bool VMOperationQueue::add(VM_Operation *op) {
152
153 HOTSPOT_VMOPS_REQUEST(
154 (char *) op->name(), strlen(op->name()),
155 op->evaluation_mode());
156
157 // Encapsulates VM queue policy. Currently, that
158 // only involves putting them on the right list
159 if (op->evaluate_at_safepoint()) {
160 queue_add_back(SafepointPriority, op);
161 return true;
162 }
163
164 queue_add_back(MediumPriority, op);
165 return true;
166 }
167
168 VM_Operation* VMOperationQueue::remove_next() {
169 // Assuming VMOperation queue is two-level priority queue. If there are
170 // more than two priorities, we need a different scheduling algorithm.
171 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
172 "current algorithm does not work");
173
174 // simple counter based scheduling to prevent starvation of lower priority
175 // queue. -- see 4390175
176 int high_prio, low_prio;
177 if (_queue_counter++ < 10) {
178 high_prio = SafepointPriority;
179 low_prio = MediumPriority;
180 } else {
181 _queue_counter = 0;
182 high_prio = MediumPriority;
183 low_prio = SafepointPriority;
184 }
185
186 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
187 }
188
189 void VMOperationQueue::oops_do(OopClosure* f) {
190 for(int i = 0; i < nof_priorities; i++) {
191 queue_oops_do(i, f);
192 }
193 drain_list_oops_do(f);
194 }
195
196
197 //------------------------------------------------------------------------------------------------------------------
198 // Implementation of VMThread stuff
199
200 bool VMThread::_should_terminate = false;
201 bool VMThread::_terminated = false;
202 Monitor* VMThread::_terminate_lock = NULL;
203 VMThread* VMThread::_vm_thread = NULL;
204 VM_Operation* VMThread::_cur_vm_operation = NULL;
205 VMOperationQueue* VMThread::_vm_queue = NULL;
206 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
207 const char* VMThread::_no_op_reason = NULL;
208
209
210 void VMThread::create() {
211 assert(vm_thread() == NULL, "we can only allocate one VMThread");
212 _vm_thread = new VMThread();
213
214 // Create VM operation queue
215 _vm_queue = new VMOperationQueue();
216 guarantee(_vm_queue != NULL, "just checking");
217
218 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
219 Monitor::_safepoint_check_never);
220
221 if (UsePerfData) {
222 // jvmstat performance counters
223 Thread* THREAD = Thread::current();
224 _perf_accumulated_vm_operation_time =
225 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
226 PerfData::U_Ticks, CHECK);
227 }
228 }
229
230 VMThread::VMThread() : NamedThread() {
231 set_name("VM Thread");
232 }
233
234 void VMThread::destroy() {
235 _vm_thread = NULL; // VM thread is gone
236 }
237
238 void VMThread::run() {
239 assert(this == vm_thread(), "check");
240
241 this->initialize_named_thread();
242 this->record_stack_base_and_size();
243 // Notify_lock wait checks on active_handles() to rewait in
244 // case of spurious wakeup, it should wait on the last
245 // value set prior to the notify
246 this->set_active_handles(JNIHandleBlock::allocate_block());
247
248 {
249 MutexLocker ml(Notify_lock);
250 Notify_lock->notify();
251 }
252 // Notify_lock is destroyed by Threads::create_vm()
253
254 int prio = (VMThreadPriority == -1)
255 ? os::java_to_os_priority[NearMaxPriority]
256 : VMThreadPriority;
257 // Note that I cannot call os::set_priority because it expects Java
258 // priorities and I am *explicitly* using OS priorities so that it's
259 // possible to set the VM thread priority higher than any Java thread.
260 os::set_native_priority( this, prio );
261
262 // Wait for VM_Operations until termination
263 this->loop();
264
265 // Note the intention to exit before safepointing.
266 // 6295565 This has the effect of waiting for any large tty
267 // outputs to finish.
268 if (xtty != NULL) {
269 ttyLocker ttyl;
270 xtty->begin_elem("destroy_vm");
271 xtty->stamp();
272 xtty->end_elem();
273 assert(should_terminate(), "termination flag must be set");
274 }
275
276 // 4526887 let VM thread exit at Safepoint
277 _no_op_reason = "Halt";
278 SafepointSynchronize::begin();
279
280 if (VerifyBeforeExit) {
281 HandleMark hm(VMThread::vm_thread());
282 // Among other things, this ensures that Eden top is correct.
283 Universe::heap()->prepare_for_verify();
284 // Silent verification so as not to pollute normal output,
285 // unless we really asked for it.
286 Universe::verify();
287 }
288
289 CompileBroker::set_should_block();
290
291 // wait for threads (compiler threads or daemon threads) in the
292 // _thread_in_native state to block.
293 VM_Exit::wait_for_threads_in_native_to_block();
294
295 // signal other threads that VM process is gone
296 {
297 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
298 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
299 // If that happens after _terminate_lock->wait() has unset _owner
300 // but before it actually drops the lock and waits, the notification below
301 // may get lost and we will have a hang. To avoid this, we need to use
302 // Mutex::lock_without_safepoint_check().
303 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
304 _terminated = true;
305 _terminate_lock->notify();
306 }
307
308 // We are now racing with the VM termination being carried out in
309 // another thread, so we don't "delete this". Numerous threads don't
310 // get deleted when the VM terminates
311
312 }
313
314
315 // Notify the VMThread that the last non-daemon JavaThread has terminated,
316 // and wait until operation is performed.
317 void VMThread::wait_for_vm_thread_exit() {
318 { MutexLocker mu(VMOperationQueue_lock);
319 _should_terminate = true;
320 VMOperationQueue_lock->notify();
321 }
322
323 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
324 // because this thread has been removed from the threads list. But anything
325 // that could get blocked by Safepoint should not be used after this point,
326 // otherwise we will hang, since there is no one can end the safepoint.
327
328 // Wait until VM thread is terminated
329 // Note: it should be OK to use Terminator_lock here. But this is called
330 // at a very delicate time (VM shutdown) and we are operating in non- VM
331 // thread at Safepoint. It's safer to not share lock with other threads.
332 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
333 while(!VMThread::is_terminated()) {
334 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
335 }
336 }
337 }
338
339 void VMThread::evaluate_operation(VM_Operation* op) {
340 ResourceMark rm;
341
342 {
343 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
344 HOTSPOT_VMOPS_BEGIN(
345 (char *) op->name(), strlen(op->name()),
346 op->evaluation_mode());
347
348 EventExecuteVMOperation event;
349
350 op->evaluate();
351
352 if (event.should_commit()) {
353 const bool is_concurrent = op->evaluate_concurrently();
354 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
355 event.set_operation(op->type());
356 event.set_safepoint(evaluate_at_safepoint);
357 event.set_blocking(!is_concurrent);
358 // Only write caller thread information for non-concurrent vm operations.
359 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
360 // This is because the caller thread could have exited already.
361 event.set_caller(is_concurrent ? 0 : THREAD_TRACE_ID(op->calling_thread()));
362 event.set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0);
363 event.commit();
364 }
365
366 HOTSPOT_VMOPS_END(
367 (char *) op->name(), strlen(op->name()),
368 op->evaluation_mode());
369 }
370
371 // Last access of info in _cur_vm_operation!
372 bool c_heap_allocated = op->is_cheap_allocated();
373
374 // Mark as completed
375 if (!op->evaluate_concurrently()) {
376 op->calling_thread()->increment_vm_operation_completed_count();
377 }
378 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
379 // since if it is stack allocated the calling thread might have deallocated
380 if (c_heap_allocated) {
381 delete _cur_vm_operation;
382 }
383 }
384
385 bool VMThread::no_op_safepoint_needed(bool check_time) {
386 if (SafepointALot) {
387 _no_op_reason = "SafepointALot";
388 return true;
389 }
390 if (!SafepointSynchronize::is_cleanup_needed()) {
391 return false;
392 }
393 if (check_time) {
394 long interval = SafepointSynchronize::last_non_safepoint_interval();
395 bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
396 (interval > GuaranteedSafepointInterval);
397 if (!max_time_exceeded) {
398 return false;
399 }
400 }
401 _no_op_reason = "Cleanup";
402 return true;
403 }
404
405 void VMThread::loop() {
406 assert(_cur_vm_operation == NULL, "no current one should be executing");
407
408 while(true) {
409 VM_Operation* safepoint_ops = NULL;
410 //
411 // Wait for VM operation
412 //
413 // use no_safepoint_check to get lock without attempting to "sneak"
414 { MutexLockerEx mu_queue(VMOperationQueue_lock,
415 Mutex::_no_safepoint_check_flag);
416
417 // Look for new operation
418 assert(_cur_vm_operation == NULL, "no current one should be executing");
419 _cur_vm_operation = _vm_queue->remove_next();
420
421 // Stall time tracking code
422 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
423 !_cur_vm_operation->evaluate_concurrently()) {
424 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
425 if (stall > 0)
426 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall);
427 }
428
429 while (!should_terminate() && _cur_vm_operation == NULL) {
430 // wait with a timeout to guarantee safepoints at regular intervals
431 bool timedout =
432 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
433 GuaranteedSafepointInterval);
434
435 // Support for self destruction
436 if ((SelfDestructTimer != 0) && !is_error_reported() &&
437 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
438 tty->print_cr("VM self-destructed");
439 exit(-1);
440 }
441
442 if (timedout && VMThread::no_op_safepoint_needed(false)) {
443 MutexUnlockerEx mul(VMOperationQueue_lock,
444 Mutex::_no_safepoint_check_flag);
445 // Force a safepoint since we have not had one for at least
446 // 'GuaranteedSafepointInterval' milliseconds. This will run all
447 // the clean-up processing that needs to be done regularly at a
448 // safepoint
449 SafepointSynchronize::begin();
450 #ifdef ASSERT
451 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
452 #endif
453 SafepointSynchronize::end();
454 }
455 _cur_vm_operation = _vm_queue->remove_next();
456
457 // If we are at a safepoint we will evaluate all the operations that
458 // follow that also require a safepoint
459 if (_cur_vm_operation != NULL &&
460 _cur_vm_operation->evaluate_at_safepoint()) {
461 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
462 }
463 }
464
465 if (should_terminate()) break;
466 } // Release mu_queue_lock
467
468 //
469 // Execute VM operation
470 //
471 { HandleMark hm(VMThread::vm_thread());
472
473 EventMark em("Executing VM operation: %s", vm_operation()->name());
474 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
475
476 // Give the VM thread an extra quantum. Jobs tend to be bursty and this
477 // helps the VM thread to finish up the job.
478 // FIXME: When this is enabled and there are many threads, this can degrade
479 // performance significantly.
480 if( VMThreadHintNoPreempt )
481 os::hint_no_preempt();
482
483 // If we are at a safepoint we will evaluate all the operations that
484 // follow that also require a safepoint
485 if (_cur_vm_operation->evaluate_at_safepoint()) {
486
487 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
488
489 SafepointSynchronize::begin();
490 evaluate_operation(_cur_vm_operation);
491 // now process all queued safepoint ops, iteratively draining
492 // the queue until there are none left
493 do {
494 _cur_vm_operation = safepoint_ops;
495 if (_cur_vm_operation != NULL) {
496 do {
497 // evaluate_operation deletes the op object so we have
498 // to grab the next op now
499 VM_Operation* next = _cur_vm_operation->next();
500 _vm_queue->set_drain_list(next);
501 evaluate_operation(_cur_vm_operation);
502 _cur_vm_operation = next;
503 if (PrintSafepointStatistics) {
504 SafepointSynchronize::inc_vmop_coalesced_count();
505 }
506 } while (_cur_vm_operation != NULL);
507 }
508 // There is a chance that a thread enqueued a safepoint op
509 // since we released the op-queue lock and initiated the safepoint.
510 // So we drain the queue again if there is anything there, as an
511 // optimization to try and reduce the number of safepoints.
512 // As the safepoint synchronizes us with JavaThreads we will see
513 // any enqueue made by a JavaThread, but the peek will not
514 // necessarily detect a concurrent enqueue by a GC thread, but
515 // that simply means the op will wait for the next major cycle of the
516 // VMThread - just as it would if the GC thread lost the race for
517 // the lock.
518 if (_vm_queue->peek_at_safepoint_priority()) {
519 // must hold lock while draining queue
520 MutexLockerEx mu_queue(VMOperationQueue_lock,
521 Mutex::_no_safepoint_check_flag);
522 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
523 } else {
524 safepoint_ops = NULL;
525 }
526 } while(safepoint_ops != NULL);
527
528 _vm_queue->set_drain_list(NULL);
529
530 // Complete safepoint synchronization
531 SafepointSynchronize::end();
532
533 } else { // not a safepoint operation
534 if (TraceLongCompiles) {
535 elapsedTimer t;
536 t.start();
537 evaluate_operation(_cur_vm_operation);
538 t.stop();
539 double secs = t.seconds();
540 if (secs * 1e3 > LongCompileThreshold) {
541 // XXX - _cur_vm_operation should not be accessed after
542 // the completed count has been incremented; the waiting
543 // thread may have already freed this memory.
544 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
545 }
546 } else {
547 evaluate_operation(_cur_vm_operation);
548 }
549
550 _cur_vm_operation = NULL;
551 }
552 }
553
554 //
555 // Notify (potential) waiting Java thread(s) - lock without safepoint
556 // check so that sneaking is not possible
557 { MutexLockerEx mu(VMOperationRequest_lock,
558 Mutex::_no_safepoint_check_flag);
559 VMOperationRequest_lock->notify_all();
560 }
561
562 //
563 // We want to make sure that we get to a safepoint regularly.
564 //
565 if (VMThread::no_op_safepoint_needed(true)) {
566 HandleMark hm(VMThread::vm_thread());
567 SafepointSynchronize::begin();
568 SafepointSynchronize::end();
569 }
570 }
571 }
572
573 void VMThread::execute(VM_Operation* op) {
574 Thread* t = Thread::current();
575
576 if (!t->is_VM_thread()) {
577 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
578 // JavaThread or WatcherThread
579 bool concurrent = op->evaluate_concurrently();
580 // only blocking VM operations need to verify the caller's safepoint state:
581 if (!concurrent) {
582 t->check_for_valid_safepoint_state(true);
583 }
584
585 // New request from Java thread, evaluate prologue
586 if (!op->doit_prologue()) {
587 return; // op was cancelled
588 }
589
590 // Setup VM_operations for execution
591 op->set_calling_thread(t, Thread::get_priority(t));
592
593 // It does not make sense to execute the epilogue, if the VM operation object is getting
594 // deallocated by the VM thread.
595 bool execute_epilog = !op->is_cheap_allocated();
596 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
597
598 // Get ticket number for non-concurrent VM operations
599 int ticket = 0;
600 if (!concurrent) {
601 ticket = t->vm_operation_ticket();
602 }
603
604 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
605 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
606 // to be queued up during a safepoint synchronization.
607 {
608 VMOperationQueue_lock->lock_without_safepoint_check();
609 bool ok = _vm_queue->add(op);
610 op->set_timestamp(os::javaTimeMillis());
611 VMOperationQueue_lock->notify();
612 VMOperationQueue_lock->unlock();
613 // VM_Operation got skipped
614 if (!ok) {
615 assert(concurrent, "can only skip concurrent tasks");
616 if (op->is_cheap_allocated()) delete op;
617 return;
618 }
619 }
620
621 if (!concurrent) {
622 // Wait for completion of request (non-concurrent)
623 // Note: only a JavaThread triggers the safepoint check when locking
624 MutexLocker mu(VMOperationRequest_lock);
625 while(t->vm_operation_completed_count() < ticket) {
626 VMOperationRequest_lock->wait(!t->is_Java_thread());
627 }
628 }
629
630 if (execute_epilog) {
631 op->doit_epilogue();
632 }
633 } else {
634 // invoked by VM thread; usually nested VM operation
635 assert(t->is_VM_thread(), "must be a VM thread");
636 VM_Operation* prev_vm_operation = vm_operation();
637 if (prev_vm_operation != NULL) {
638 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
639 // does not allow nested scavenges or compiles.
640 if (!prev_vm_operation->allow_nested_vm_operations()) {
641 fatal("Nested VM operation %s requested by operation %s",
642 op->name(), vm_operation()->name());
643 }
644 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
645 }
646
647 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
648
649 // Release all internal handles after operation is evaluated
650 HandleMark hm(t);
651 _cur_vm_operation = op;
652
653 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
654 SafepointSynchronize::begin();
655 op->evaluate();
656 SafepointSynchronize::end();
657 } else {
658 op->evaluate();
659 }
660
661 // Free memory if needed
662 if (op->is_cheap_allocated()) delete op;
663
664 _cur_vm_operation = prev_vm_operation;
665 }
666 }
667
668
669 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
670 Thread::oops_do(f, cf);
671 _vm_queue->oops_do(f);
672 }
673
674 //------------------------------------------------------------------------------------------------------------------
675 #ifndef PRODUCT
676
677 void VMOperationQueue::verify_queue(int prio) {
678 // Check that list is correctly linked
679 int length = _queue_length[prio];
680 VM_Operation *cur = _queue[prio];
681 int i;
682
683 // Check forward links
684 for(i = 0; i < length; i++) {
685 cur = cur->next();
686 assert(cur != _queue[prio], "list to short (forward)");
687 }
688 assert(cur->next() == _queue[prio], "list to long (forward)");
689
690 // Check backwards links
691 cur = _queue[prio];
692 for(i = 0; i < length; i++) {
693 cur = cur->prev();
694 assert(cur != _queue[prio], "list to short (backwards)");
695 }
696 assert(cur->prev() == _queue[prio], "list to long (backwards)");
697 }
698
699 #endif
700
701 void VMThread::verify() {
702 oops_do(&VerifyOopClosure::verify_oop, NULL);
703 }