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