1 /*
2 * Copyright (c) 1998, 2013, 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_interface/collectedHeap.hpp"
28 #include "memory/resourceArea.hpp"
29 #include "oops/method.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/interfaceSupport.hpp"
32 #include "runtime/mutexLocker.hpp"
33 #include "runtime/os.hpp"
34 #include "runtime/thread.inline.hpp"
35 #include "runtime/vmThread.hpp"
36 #include "runtime/vm_operations.hpp"
37 #include "services/runtimeService.hpp"
38 #include "trace/tracing.hpp"
39 #include "utilities/dtrace.hpp"
40 #include "utilities/events.hpp"
41 #include "utilities/xmlstream.hpp"
42
43 #ifndef USDT2
44 HS_DTRACE_PROBE_DECL3(hotspot, vmops__request, char *, uintptr_t, int);
45 HS_DTRACE_PROBE_DECL3(hotspot, vmops__begin, char *, uintptr_t, int);
46 HS_DTRACE_PROBE_DECL3(hotspot, vmops__end, char *, uintptr_t, int);
47 #endif /* !USDT2 */
48
49 // Dummy VM operation to act as first element in our circular double-linked list
50 class VM_Dummy: public VM_Operation {
51 VMOp_Type type() const { return VMOp_Dummy; }
52 void doit() {};
53 };
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] = new VM_Dummy();
62 _queue[i]->set_next(_queue[i]);
63 _queue[i]->set_prev(_queue[i]);
64 }
65 _drain_list = NULL;
66 }
67
68
69 bool VMOperationQueue::queue_empty(int prio) {
70 // It is empty if there is exactly one element
71 bool empty = (_queue[prio] == _queue[prio]->next());
72 assert( (_queue_length[prio] == 0 && empty) ||
73 (_queue_length[prio] > 0 && !empty), "sanity check");
74 return _queue_length[prio] == 0;
75 }
76
77 // Inserts an element to the right of the q element
78 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
79 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
80 n->set_prev(q);
81 n->set_next(q->next());
82 q->next()->set_prev(n);
83 q->set_next(n);
84 }
85
86 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
87 _queue_length[prio]++;
88 insert(_queue[prio]->next(), op);
89 }
90
91 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
92 _queue_length[prio]++;
93 insert(_queue[prio]->prev(), op);
94 }
95
96
97 void VMOperationQueue::unlink(VM_Operation* q) {
98 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
99 q->prev()->set_next(q->next());
100 q->next()->set_prev(q->prev());
101 }
102
103 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
104 if (queue_empty(prio)) return NULL;
105 assert(_queue_length[prio] >= 0, "sanity check");
106 _queue_length[prio]--;
107 VM_Operation* r = _queue[prio]->next();
108 assert(r != _queue[prio], "cannot remove base element");
109 unlink(r);
110 return r;
111 }
112
113 VM_Operation* VMOperationQueue::queue_drain(int prio) {
114 if (queue_empty(prio)) return NULL;
115 DEBUG_ONLY(int length = _queue_length[prio];);
116 assert(length >= 0, "sanity check");
117 _queue_length[prio] = 0;
118 VM_Operation* r = _queue[prio]->next();
119 assert(r != _queue[prio], "cannot remove base element");
120 // remove links to base element from head and tail
121 r->set_prev(NULL);
122 _queue[prio]->prev()->set_next(NULL);
123 // restore queue to empty state
124 _queue[prio]->set_next(_queue[prio]);
125 _queue[prio]->set_prev(_queue[prio]);
126 assert(queue_empty(prio), "drain corrupted queue");
127 #ifdef ASSERT
128 int len = 0;
129 VM_Operation* cur;
130 for(cur = r; cur != NULL; cur=cur->next()) len++;
131 assert(len == length, "drain lost some ops");
132 #endif
133 return r;
134 }
135
136 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
137 VM_Operation* cur = _queue[queue];
138 cur = cur->next();
139 while (cur != _queue[queue]) {
140 cur->oops_do(f);
141 cur = cur->next();
142 }
143 }
144
145 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
146 VM_Operation* cur = _drain_list;
147 while (cur != NULL) {
148 cur->oops_do(f);
149 cur = cur->next();
150 }
151 }
152
153 //-----------------------------------------------------------------
154 // High-level interface
155 bool VMOperationQueue::add(VM_Operation *op) {
156
157 #ifndef USDT2
158 HS_DTRACE_PROBE3(hotspot, vmops__request, op->name(), strlen(op->name()),
159 op->evaluation_mode());
160 #else /* USDT2 */
161 HOTSPOT_VMOPS_REQUEST(
162 (char *) op->name(), strlen(op->name()),
163 op->evaluation_mode());
164 #endif /* USDT2 */
165
166 // Encapsulates VM queue policy. Currently, that
167 // only involves putting them on the right list
168 if (op->evaluate_at_safepoint()) {
169 queue_add_back(SafepointPriority, op);
170 return true;
171 }
172
173 queue_add_back(MediumPriority, op);
174 return true;
175 }
176
177 VM_Operation* VMOperationQueue::remove_next() {
178 // Assuming VMOperation queue is two-level priority queue. If there are
179 // more than two priorities, we need a different scheduling algorithm.
180 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
181 "current algorithm does not work");
182
183 // simple counter based scheduling to prevent starvation of lower priority
184 // queue. -- see 4390175
185 int high_prio, low_prio;
186 if (_queue_counter++ < 10) {
187 high_prio = SafepointPriority;
188 low_prio = MediumPriority;
189 } else {
190 _queue_counter = 0;
191 high_prio = MediumPriority;
192 low_prio = SafepointPriority;
193 }
194
195 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
196 }
197
198 void VMOperationQueue::oops_do(OopClosure* f) {
199 for(int i = 0; i < nof_priorities; i++) {
200 queue_oops_do(i, f);
201 }
202 drain_list_oops_do(f);
203 }
204
205
206 //------------------------------------------------------------------------------------------------------------------
207 // Implementation of VMThread stuff
208
209 bool VMThread::_should_terminate = false;
210 bool VMThread::_terminated = false;
211 Monitor* VMThread::_terminate_lock = NULL;
212 VMThread* VMThread::_vm_thread = NULL;
213 VM_Operation* VMThread::_cur_vm_operation = NULL;
214 VMOperationQueue* VMThread::_vm_queue = NULL;
215 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
216
217
218 void VMThread::create() {
219 assert(vm_thread() == NULL, "we can only allocate one VMThread");
220 _vm_thread = new VMThread();
221
222 // Create VM operation queue
223 _vm_queue = new VMOperationQueue();
224 guarantee(_vm_queue != NULL, "just checking");
225
226 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true);
227
228 if (UsePerfData) {
229 // jvmstat performance counters
230 Thread* THREAD = Thread::current();
231 _perf_accumulated_vm_operation_time =
232 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
233 PerfData::U_Ticks, CHECK);
234 }
235 }
236
237
238 VMThread::VMThread() : NamedThread() {
239 set_name("VM Thread");
240 }
241
242 void VMThread::destroy() {
243 if (_vm_thread != NULL) {
244 delete _vm_thread;
245 _vm_thread = NULL; // VM thread is gone
246 }
247 }
248
249 void VMThread::run() {
250 assert(this == vm_thread(), "check");
251
252 this->initialize_thread_local_storage();
253 this->record_stack_base_and_size();
254 // Notify_lock wait checks on active_handles() to rewait in
255 // case of spurious wakeup, it should wait on the last
256 // value set prior to the notify
257 this->set_active_handles(JNIHandleBlock::allocate_block());
258
259 {
260 MutexLocker ml(Notify_lock);
261 Notify_lock->notify();
262 }
263 // Notify_lock is destroyed by Threads::create_vm()
264
265 int prio = (VMThreadPriority == -1)
266 ? os::java_to_os_priority[NearMaxPriority]
267 : VMThreadPriority;
268 // Note that I cannot call os::set_priority because it expects Java
269 // priorities and I am *explicitly* using OS priorities so that it's
270 // possible to set the VM thread priority higher than any Java thread.
271 os::set_native_priority( this, prio );
272
273 // Wait for VM_Operations until termination
274 this->loop();
275
276 // Note the intention to exit before safepointing.
277 // 6295565 This has the effect of waiting for any large tty
278 // outputs to finish.
279 if (xtty != NULL) {
280 ttyLocker ttyl;
281 xtty->begin_elem("destroy_vm");
282 xtty->stamp();
283 xtty->end_elem();
284 assert(should_terminate(), "termination flag must be set");
285 }
286
287 // 4526887 let VM thread exit at Safepoint
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 os::check_heap();
295 // Silent verification so as not to pollute normal output,
296 // unless we really asked for it.
297 Universe::verify(!(PrintGCDetails || Verbose) || VerifySilently);
298 }
299
300 CompileBroker::set_should_block();
301
302 // wait for threads (compiler threads or daemon threads) in the
303 // _thread_in_native state to block.
304 VM_Exit::wait_for_threads_in_native_to_block();
305
306 // signal other threads that VM process is gone
307 {
308 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
309 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
310 // If that happens after _terminate_lock->wait() has unset _owner
311 // but before it actually drops the lock and waits, the notification below
312 // may get lost and we will have a hang. To avoid this, we need to use
313 // Mutex::lock_without_safepoint_check().
314 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
315 _terminated = true;
316 _terminate_lock->notify();
317 }
318
319 // Deletion must be done synchronously by the JNI DestroyJavaVM thread
320 // so that the VMThread deletion completes before the main thread frees
321 // up the CodeHeap.
322
323 }
324
325
326 // Notify the VMThread that the last non-daemon JavaThread has terminated,
327 // and wait until operation is performed.
328 void VMThread::wait_for_vm_thread_exit() {
329 { MutexLocker mu(VMOperationQueue_lock);
330 _should_terminate = true;
331 VMOperationQueue_lock->notify();
332 }
333
334 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
335 // because this thread has been removed from the threads list. But anything
336 // that could get blocked by Safepoint should not be used after this point,
337 // otherwise we will hang, since there is no one can end the safepoint.
338
339 // Wait until VM thread is terminated
340 // Note: it should be OK to use Terminator_lock here. But this is called
341 // at a very delicate time (VM shutdown) and we are operating in non- VM
342 // thread at Safepoint. It's safer to not share lock with other threads.
343 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
344 while(!VMThread::is_terminated()) {
345 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
346 }
347 }
348 }
349
350 void VMThread::print_on(outputStream* st) const {
351 st->print("\"%s\" ", name());
352 Thread::print_on(st);
353 st->cr();
354 }
355
356 void VMThread::evaluate_operation(VM_Operation* op) {
357 ResourceMark rm;
358
359 {
360 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
361 #ifndef USDT2
362 HS_DTRACE_PROBE3(hotspot, vmops__begin, op->name(), strlen(op->name()),
363 op->evaluation_mode());
364 #else /* USDT2 */
365 HOTSPOT_VMOPS_BEGIN(
366 (char *) op->name(), strlen(op->name()),
367 op->evaluation_mode());
368 #endif /* USDT2 */
369
370 EventExecuteVMOperation event;
371
372 op->evaluate();
373
374 if (event.should_commit()) {
375 bool is_concurrent = op->evaluate_concurrently();
376 event.set_operation(op->type());
377 event.set_safepoint(op->evaluate_at_safepoint());
378 event.set_blocking(!is_concurrent);
379 // Only write caller thread information for non-concurrent vm operations.
380 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
381 // This is because the caller thread could have exited already.
382 event.set_caller(is_concurrent ? 0 : op->calling_thread()->osthread()->thread_id());
383 event.commit();
384 }
385
386 #ifndef USDT2
387 HS_DTRACE_PROBE3(hotspot, vmops__end, op->name(), strlen(op->name()),
388 op->evaluation_mode());
389 #else /* USDT2 */
390 HOTSPOT_VMOPS_END(
391 (char *) op->name(), strlen(op->name()),
392 op->evaluation_mode());
393 #endif /* USDT2 */
394 }
395
396 // Last access of info in _cur_vm_operation!
397 bool c_heap_allocated = op->is_cheap_allocated();
398
399 // Mark as completed
400 if (!op->evaluate_concurrently()) {
401 op->calling_thread()->increment_vm_operation_completed_count();
402 }
403 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
404 // since if it is stack allocated the calling thread might have deallocated
405 if (c_heap_allocated) {
406 delete _cur_vm_operation;
407 }
408 }
409
410
411 void VMThread::loop() {
412 assert(_cur_vm_operation == NULL, "no current one should be executing");
413
414 while(true) {
415 VM_Operation* safepoint_ops = NULL;
416 //
417 // Wait for VM operation
418 //
419 // use no_safepoint_check to get lock without attempting to "sneak"
420 { MutexLockerEx mu_queue(VMOperationQueue_lock,
421 Mutex::_no_safepoint_check_flag);
422
423 // Look for new operation
424 assert(_cur_vm_operation == NULL, "no current one should be executing");
425 _cur_vm_operation = _vm_queue->remove_next();
426
427 // Stall time tracking code
428 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
429 !_cur_vm_operation->evaluate_concurrently()) {
430 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
431 if (stall > 0)
432 tty->print_cr("%s stall: %Ld", _cur_vm_operation->name(), stall);
433 }
434
435 while (!should_terminate() && _cur_vm_operation == NULL) {
436 // wait with a timeout to guarantee safepoints at regular intervals
437 bool timedout =
438 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
439 GuaranteedSafepointInterval);
440
441 // Support for self destruction
442 if ((SelfDestructTimer != 0) && !is_error_reported() &&
443 (os::elapsedTime() > SelfDestructTimer * 60)) {
444 tty->print_cr("VM self-destructed");
445 exit(-1);
446 }
447
448 if (timedout && (SafepointALot ||
449 SafepointSynchronize::is_cleanup_needed())) {
450 MutexUnlockerEx mul(VMOperationQueue_lock,
451 Mutex::_no_safepoint_check_flag);
452 // Force a safepoint since we have not had one for at least
453 // 'GuaranteedSafepointInterval' milliseconds. This will run all
454 // the clean-up processing that needs to be done regularly at a
455 // safepoint
456 SafepointSynchronize::begin();
457 #ifdef ASSERT
458 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
459 #endif
460 SafepointSynchronize::end();
461 }
462 _cur_vm_operation = _vm_queue->remove_next();
463
464 // If we are at a safepoint we will evaluate all the operations that
465 // follow that also require a safepoint
466 if (_cur_vm_operation != NULL &&
467 _cur_vm_operation->evaluate_at_safepoint()) {
468 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
469 }
470 }
471
472 if (should_terminate()) break;
473 } // Release mu_queue_lock
474
475 //
476 // Execute VM operation
477 //
478 { HandleMark hm(VMThread::vm_thread());
479
480 EventMark em("Executing VM operation: %s", vm_operation()->name());
481 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
482
483 // Give the VM thread an extra quantum. Jobs tend to be bursty and this
484 // helps the VM thread to finish up the job.
485 // FIXME: When this is enabled and there are many threads, this can degrade
486 // performance significantly.
487 if( VMThreadHintNoPreempt )
488 os::hint_no_preempt();
489
490 // If we are at a safepoint we will evaluate all the operations that
491 // follow that also require a safepoint
492 if (_cur_vm_operation->evaluate_at_safepoint()) {
493
494 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
495
496 SafepointSynchronize::begin();
497 evaluate_operation(_cur_vm_operation);
498 // now process all queued safepoint ops, iteratively draining
499 // the queue until there are none left
500 do {
501 _cur_vm_operation = safepoint_ops;
502 if (_cur_vm_operation != NULL) {
503 do {
504 // evaluate_operation deletes the op object so we have
505 // to grab the next op now
506 VM_Operation* next = _cur_vm_operation->next();
507 _vm_queue->set_drain_list(next);
508 evaluate_operation(_cur_vm_operation);
509 _cur_vm_operation = next;
510 if (PrintSafepointStatistics) {
511 SafepointSynchronize::inc_vmop_coalesced_count();
512 }
513 } while (_cur_vm_operation != NULL);
514 }
515 // There is a chance that a thread enqueued a safepoint op
516 // since we released the op-queue lock and initiated the safepoint.
517 // So we drain the queue again if there is anything there, as an
518 // optimization to try and reduce the number of safepoints.
519 // As the safepoint synchronizes us with JavaThreads we will see
520 // any enqueue made by a JavaThread, but the peek will not
521 // necessarily detect a concurrent enqueue by a GC thread, but
522 // that simply means the op will wait for the next major cycle of the
523 // VMThread - just as it would if the GC thread lost the race for
524 // the lock.
525 if (_vm_queue->peek_at_safepoint_priority()) {
526 // must hold lock while draining queue
527 MutexLockerEx mu_queue(VMOperationQueue_lock,
528 Mutex::_no_safepoint_check_flag);
529 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
530 } else {
531 safepoint_ops = NULL;
532 }
533 } while(safepoint_ops != NULL);
534
535 _vm_queue->set_drain_list(NULL);
536
537 // Complete safepoint synchronization
538 SafepointSynchronize::end();
539
540 } else { // not a safepoint operation
541 if (TraceLongCompiles) {
542 elapsedTimer t;
543 t.start();
544 evaluate_operation(_cur_vm_operation);
545 t.stop();
546 double secs = t.seconds();
547 if (secs * 1e3 > LongCompileThreshold) {
548 // XXX - _cur_vm_operation should not be accessed after
549 // the completed count has been incremented; the waiting
550 // thread may have already freed this memory.
551 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
552 }
553 } else {
554 evaluate_operation(_cur_vm_operation);
555 }
556
557 _cur_vm_operation = NULL;
558 }
559 }
560
561 //
562 // Notify (potential) waiting Java thread(s) - lock without safepoint
563 // check so that sneaking is not possible
564 { MutexLockerEx mu(VMOperationRequest_lock,
565 Mutex::_no_safepoint_check_flag);
566 VMOperationRequest_lock->notify_all();
567 }
568
569 //
570 // We want to make sure that we get to a safepoint regularly.
571 //
572 if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) {
573 long interval = SafepointSynchronize::last_non_safepoint_interval();
574 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval);
575 if (SafepointALot || max_time_exceeded) {
576 HandleMark hm(VMThread::vm_thread());
577 SafepointSynchronize::begin();
578 SafepointSynchronize::end();
579 }
580 }
581 }
582 }
583
584 void VMThread::execute(VM_Operation* op) {
585 Thread* t = Thread::current();
586
587 if (!t->is_VM_thread()) {
588 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
589 // JavaThread or WatcherThread
590 bool concurrent = op->evaluate_concurrently();
591 // only blocking VM operations need to verify the caller's safepoint state:
592 if (!concurrent) {
593 t->check_for_valid_safepoint_state(true);
594 }
595
596 // New request from Java thread, evaluate prologue
597 if (!op->doit_prologue()) {
598 return; // op was cancelled
599 }
600
601 // Setup VM_operations for execution
602 op->set_calling_thread(t, Thread::get_priority(t));
603
604 // It does not make sense to execute the epilogue, if the VM operation object is getting
605 // deallocated by the VM thread.
606 bool execute_epilog = !op->is_cheap_allocated();
607 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
608
609 // Get ticket number for non-concurrent VM operations
610 int ticket = 0;
611 if (!concurrent) {
612 ticket = t->vm_operation_ticket();
613 }
614
615 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
616 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
617 // to be queued up during a safepoint synchronization.
618 {
619 VMOperationQueue_lock->lock_without_safepoint_check();
620 bool ok = _vm_queue->add(op);
621 op->set_timestamp(os::javaTimeMillis());
622 VMOperationQueue_lock->notify();
623 VMOperationQueue_lock->unlock();
624 // VM_Operation got skipped
625 if (!ok) {
626 assert(concurrent, "can only skip concurrent tasks");
627 if (op->is_cheap_allocated()) delete op;
628 return;
629 }
630 }
631
632 if (!concurrent) {
633 // Wait for completion of request (non-concurrent)
634 // Note: only a JavaThread triggers the safepoint check when locking
635 MutexLocker mu(VMOperationRequest_lock);
636 while(t->vm_operation_completed_count() < ticket) {
637 VMOperationRequest_lock->wait(!t->is_Java_thread());
638 }
639 }
640
641 if (execute_epilog) {
642 op->doit_epilogue();
643 }
644 } else {
645 // invoked by VM thread; usually nested VM operation
646 assert(t->is_VM_thread(), "must be a VM thread");
647 VM_Operation* prev_vm_operation = vm_operation();
648 if (prev_vm_operation != NULL) {
649 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
650 // does not allow nested scavenges or compiles.
651 if (!prev_vm_operation->allow_nested_vm_operations()) {
652 fatal(err_msg("Nested VM operation %s requested by operation %s",
653 op->name(), vm_operation()->name()));
654 }
655 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
656 }
657
658 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
659
660 // Release all internal handles after operation is evaluated
661 HandleMark hm(t);
662 _cur_vm_operation = op;
663
664 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
665 SafepointSynchronize::begin();
666 op->evaluate();
667 SafepointSynchronize::end();
668 } else {
669 op->evaluate();
670 }
671
672 // Free memory if needed
673 if (op->is_cheap_allocated()) delete op;
674
675 _cur_vm_operation = prev_vm_operation;
676 }
677 }
678
679
680 void VMThread::oops_do(OopClosure* f, CLDToOopClosure* cld_f, CodeBlobClosure* cf) {
681 Thread::oops_do(f, cld_f, cf);
682 _vm_queue->oops_do(f);
683 }
684
685 //------------------------------------------------------------------------------------------------------------------
686 #ifndef PRODUCT
687
688 void VMOperationQueue::verify_queue(int prio) {
689 // Check that list is correctly linked
690 int length = _queue_length[prio];
691 VM_Operation *cur = _queue[prio];
692 int i;
693
694 // Check forward links
695 for(i = 0; i < length; i++) {
696 cur = cur->next();
697 assert(cur != _queue[prio], "list to short (forward)");
698 }
699 assert(cur->next() == _queue[prio], "list to long (forward)");
700
701 // Check backwards links
702 cur = _queue[prio];
703 for(i = 0; i < length; i++) {
704 cur = cur->prev();
705 assert(cur != _queue[prio], "list to short (backwards)");
706 }
707 assert(cur->prev() == _queue[prio], "list to long (backwards)");
708 }
709
710 #endif
711
712 void VMThread::verify() {
713 oops_do(&VerifyOopClosure::verify_oop, NULL, NULL);
714 }