1 /*
2 * Copyright (c) 1998, 2014, 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 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
50
51 // Dummy VM operation to act as first element in our circular double-linked list
52 class VM_Dummy: public VM_Operation {
53 VMOp_Type type() const { return VMOp_Dummy; }
54 void doit() {};
55 };
56
57 VMOperationQueue::VMOperationQueue() {
58 // The queue is a circular doubled-linked list, which always contains
59 // one element (i.e., one element means empty).
60 for(int i = 0; i < nof_priorities; i++) {
61 _queue_length[i] = 0;
62 _queue_counter = 0;
63 _queue[i] = new VM_Dummy();
64 _queue[i]->set_next(_queue[i]);
65 _queue[i]->set_prev(_queue[i]);
66 }
67 _drain_list = NULL;
68 }
69
70
71 bool VMOperationQueue::queue_empty(int prio) {
72 // It is empty if there is exactly one element
73 bool empty = (_queue[prio] == _queue[prio]->next());
74 assert( (_queue_length[prio] == 0 && empty) ||
75 (_queue_length[prio] > 0 && !empty), "sanity check");
76 return _queue_length[prio] == 0;
77 }
78
79 // Inserts an element to the right of the q element
80 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
81 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
82 n->set_prev(q);
83 n->set_next(q->next());
84 q->next()->set_prev(n);
85 q->set_next(n);
86 }
87
88 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
89 _queue_length[prio]++;
90 insert(_queue[prio]->next(), op);
91 }
92
93 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
94 _queue_length[prio]++;
95 insert(_queue[prio]->prev(), op);
96 }
97
98
99 void VMOperationQueue::unlink(VM_Operation* q) {
100 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
101 q->prev()->set_next(q->next());
102 q->next()->set_prev(q->prev());
103 }
104
105 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
106 if (queue_empty(prio)) return NULL;
107 assert(_queue_length[prio] >= 0, "sanity check");
108 _queue_length[prio]--;
109 VM_Operation* r = _queue[prio]->next();
110 assert(r != _queue[prio], "cannot remove base element");
111 unlink(r);
112 return r;
113 }
114
115 VM_Operation* VMOperationQueue::queue_drain(int prio) {
116 if (queue_empty(prio)) return NULL;
117 DEBUG_ONLY(int length = _queue_length[prio];);
118 assert(length >= 0, "sanity check");
119 _queue_length[prio] = 0;
120 VM_Operation* r = _queue[prio]->next();
121 assert(r != _queue[prio], "cannot remove base element");
122 // remove links to base element from head and tail
123 r->set_prev(NULL);
124 _queue[prio]->prev()->set_next(NULL);
125 // restore queue to empty state
126 _queue[prio]->set_next(_queue[prio]);
127 _queue[prio]->set_prev(_queue[prio]);
128 assert(queue_empty(prio), "drain corrupted queue");
129 #ifdef ASSERT
130 int len = 0;
131 VM_Operation* cur;
132 for(cur = r; cur != NULL; cur=cur->next()) len++;
133 assert(len == length, "drain lost some ops");
134 #endif
135 return r;
136 }
137
138 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
139 VM_Operation* cur = _queue[queue];
140 cur = cur->next();
141 while (cur != _queue[queue]) {
142 cur->oops_do(f);
143 cur = cur->next();
144 }
145 }
146
147 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
148 VM_Operation* cur = _drain_list;
149 while (cur != NULL) {
150 cur->oops_do(f);
151 cur = cur->next();
152 }
153 }
154
155 //-----------------------------------------------------------------
156 // High-level interface
157 bool VMOperationQueue::add(VM_Operation *op) {
158
159 #ifndef USDT2
160 HS_DTRACE_PROBE3(hotspot, vmops__request, op->name(), strlen(op->name()),
161 op->evaluation_mode());
162 #else /* USDT2 */
163 HOTSPOT_VMOPS_REQUEST(
164 (char *) op->name(), strlen(op->name()),
165 op->evaluation_mode());
166 #endif /* USDT2 */
167
168 // Encapsulates VM queue policy. Currently, that
169 // only involves putting them on the right list
170 if (op->evaluate_at_safepoint()) {
171 queue_add_back(SafepointPriority, op);
172 return true;
173 }
174
175 queue_add_back(MediumPriority, op);
176 return true;
177 }
178
179 VM_Operation* VMOperationQueue::remove_next() {
180 // Assuming VMOperation queue is two-level priority queue. If there are
181 // more than two priorities, we need a different scheduling algorithm.
182 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
183 "current algorithm does not work");
184
185 // simple counter based scheduling to prevent starvation of lower priority
186 // queue. -- see 4390175
187 int high_prio, low_prio;
188 if (_queue_counter++ < 10) {
189 high_prio = SafepointPriority;
190 low_prio = MediumPriority;
191 } else {
192 _queue_counter = 0;
193 high_prio = MediumPriority;
194 low_prio = SafepointPriority;
195 }
196
197 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
198 }
199
200 void VMOperationQueue::oops_do(OopClosure* f) {
201 for(int i = 0; i < nof_priorities; i++) {
202 queue_oops_do(i, f);
203 }
204 drain_list_oops_do(f);
205 }
206
207
208 //------------------------------------------------------------------------------------------------------------------
209 // Implementation of VMThread stuff
210
211 bool VMThread::_should_terminate = false;
212 bool VMThread::_terminated = false;
213 Monitor* VMThread::_terminate_lock = NULL;
214 VMThread* VMThread::_vm_thread = NULL;
215 VM_Operation* VMThread::_cur_vm_operation = NULL;
216 VMOperationQueue* VMThread::_vm_queue = NULL;
217 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
218
219
220 void VMThread::create() {
221 assert(vm_thread() == NULL, "we can only allocate one VMThread");
222 _vm_thread = new VMThread();
223
224 // Create VM operation queue
225 _vm_queue = new VMOperationQueue();
226 guarantee(_vm_queue != NULL, "just checking");
227
228 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true);
229
230 if (UsePerfData) {
231 // jvmstat performance counters
232 Thread* THREAD = Thread::current();
233 _perf_accumulated_vm_operation_time =
234 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
235 PerfData::U_Ticks, CHECK);
236 }
237 }
238
239
240 VMThread::VMThread() : NamedThread() {
241 set_name("VM Thread");
242 }
243
244 void VMThread::destroy() {
245 if (_vm_thread != NULL) {
246 delete _vm_thread;
247 _vm_thread = NULL; // VM thread is gone
248 }
249 }
250
251 void VMThread::run() {
252 assert(this == vm_thread(), "check");
253
254 this->initialize_thread_local_storage();
255 this->record_stack_base_and_size();
256 // Notify_lock wait checks on active_handles() to rewait in
257 // case of spurious wakeup, it should wait on the last
258 // value set prior to the notify
259 this->set_active_handles(JNIHandleBlock::allocate_block());
260
261 {
262 MutexLocker ml(Notify_lock);
263 Notify_lock->notify();
264 }
265 // Notify_lock is destroyed by Threads::create_vm()
266
267 int prio = (VMThreadPriority == -1)
268 ? os::java_to_os_priority[NearMaxPriority]
269 : VMThreadPriority;
270 // Note that I cannot call os::set_priority because it expects Java
271 // priorities and I am *explicitly* using OS priorities so that it's
272 // possible to set the VM thread priority higher than any Java thread.
273 os::set_native_priority( this, prio );
274
275 // Wait for VM_Operations until termination
276 this->loop();
277
278 // Note the intention to exit before safepointing.
279 // 6295565 This has the effect of waiting for any large tty
280 // outputs to finish.
281 if (xtty != NULL) {
282 ttyLocker ttyl;
283 xtty->begin_elem("destroy_vm");
284 xtty->stamp();
285 xtty->end_elem();
286 assert(should_terminate(), "termination flag must be set");
287 }
288
289 // 4526887 let VM thread exit at Safepoint
290 SafepointSynchronize::begin();
291
292 if (VerifyBeforeExit) {
293 HandleMark hm(VMThread::vm_thread());
294 // Among other things, this ensures that Eden top is correct.
295 Universe::heap()->prepare_for_verify();
296 os::check_heap();
297 // Silent verification so as not to pollute normal output,
298 // unless we really asked for it.
299 Universe::verify(!(PrintGCDetails || Verbose) || VerifySilently);
300 }
301
302 CompileBroker::set_should_block();
303
304 // wait for threads (compiler threads or daemon threads) in the
305 // _thread_in_native state to block.
306 VM_Exit::wait_for_threads_in_native_to_block();
307
308 // signal other threads that VM process is gone
309 {
310 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
311 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
312 // If that happens after _terminate_lock->wait() has unset _owner
313 // but before it actually drops the lock and waits, the notification below
314 // may get lost and we will have a hang. To avoid this, we need to use
315 // Mutex::lock_without_safepoint_check().
316 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
317 _terminated = true;
318 _terminate_lock->notify();
319 }
320
321 // Thread destructor usually does this.
322 ThreadLocalStorage::set_thread(NULL);
323
324 // Deletion must be done synchronously by the JNI DestroyJavaVM thread
325 // so that the VMThread deletion completes before the main thread frees
326 // up the CodeHeap.
327
328 }
329
330
331 // Notify the VMThread that the last non-daemon JavaThread has terminated,
332 // and wait until operation is performed.
333 void VMThread::wait_for_vm_thread_exit() {
334 { MutexLocker mu(VMOperationQueue_lock);
335 _should_terminate = true;
336 VMOperationQueue_lock->notify();
337 }
338
339 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
340 // because this thread has been removed from the threads list. But anything
341 // that could get blocked by Safepoint should not be used after this point,
342 // otherwise we will hang, since there is no one can end the safepoint.
343
344 // Wait until VM thread is terminated
345 // Note: it should be OK to use Terminator_lock here. But this is called
346 // at a very delicate time (VM shutdown) and we are operating in non- VM
347 // thread at Safepoint. It's safer to not share lock with other threads.
348 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
349 while(!VMThread::is_terminated()) {
350 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
351 }
352 }
353 }
354
355 void VMThread::print_on(outputStream* st) const {
356 st->print("\"%s\" ", name());
357 Thread::print_on(st);
358 st->cr();
359 }
360
361 void VMThread::evaluate_operation(VM_Operation* op) {
362 ResourceMark rm;
363
364 {
365 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
366 #ifndef USDT2
367 HS_DTRACE_PROBE3(hotspot, vmops__begin, op->name(), strlen(op->name()),
368 op->evaluation_mode());
369 #else /* USDT2 */
370 HOTSPOT_VMOPS_BEGIN(
371 (char *) op->name(), strlen(op->name()),
372 op->evaluation_mode());
373 #endif /* USDT2 */
374
375 EventExecuteVMOperation event;
376
377 op->evaluate();
378
379 if (event.should_commit()) {
380 bool is_concurrent = op->evaluate_concurrently();
381 event.set_operation(op->type());
382 event.set_safepoint(op->evaluate_at_safepoint());
383 event.set_blocking(!is_concurrent);
384 // Only write caller thread information for non-concurrent vm operations.
385 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
386 // This is because the caller thread could have exited already.
387 event.set_caller(is_concurrent ? 0 : op->calling_thread()->osthread()->thread_id());
388 event.commit();
389 }
390
391 #ifndef USDT2
392 HS_DTRACE_PROBE3(hotspot, vmops__end, op->name(), strlen(op->name()),
393 op->evaluation_mode());
394 #else /* USDT2 */
395 HOTSPOT_VMOPS_END(
396 (char *) op->name(), strlen(op->name()),
397 op->evaluation_mode());
398 #endif /* USDT2 */
399 }
400
401 // Last access of info in _cur_vm_operation!
402 bool c_heap_allocated = op->is_cheap_allocated();
403
404 // Mark as completed
405 if (!op->evaluate_concurrently()) {
406 op->calling_thread()->increment_vm_operation_completed_count();
407 }
408 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
409 // since if it is stack allocated the calling thread might have deallocated
410 if (c_heap_allocated) {
411 delete _cur_vm_operation;
412 }
413 }
414
415
416 void VMThread::loop() {
417 assert(_cur_vm_operation == NULL, "no current one should be executing");
418
419 while(true) {
420 VM_Operation* safepoint_ops = NULL;
421 //
422 // Wait for VM operation
423 //
424 // use no_safepoint_check to get lock without attempting to "sneak"
425 { MutexLockerEx mu_queue(VMOperationQueue_lock,
426 Mutex::_no_safepoint_check_flag);
427
428 // Look for new operation
429 assert(_cur_vm_operation == NULL, "no current one should be executing");
430 _cur_vm_operation = _vm_queue->remove_next();
431
432 // Stall time tracking code
433 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
434 !_cur_vm_operation->evaluate_concurrently()) {
435 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
436 if (stall > 0)
437 tty->print_cr("%s stall: %Ld", _cur_vm_operation->name(), stall);
438 }
439
440 while (!should_terminate() && _cur_vm_operation == NULL) {
441 // wait with a timeout to guarantee safepoints at regular intervals
442 bool timedout =
443 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
444 GuaranteedSafepointInterval);
445
446 // Support for self destruction
447 if ((SelfDestructTimer != 0) && !is_error_reported() &&
448 (os::elapsedTime() > SelfDestructTimer * 60)) {
449 tty->print_cr("VM self-destructed");
450 exit(-1);
451 }
452
453 if (timedout && (SafepointALot ||
454 SafepointSynchronize::is_cleanup_needed())) {
455 MutexUnlockerEx mul(VMOperationQueue_lock,
456 Mutex::_no_safepoint_check_flag);
457 // Force a safepoint since we have not had one for at least
458 // 'GuaranteedSafepointInterval' milliseconds. This will run all
459 // the clean-up processing that needs to be done regularly at a
460 // safepoint
461 SafepointSynchronize::begin();
462 #ifdef ASSERT
463 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
464 #endif
465 SafepointSynchronize::end();
466 }
467 _cur_vm_operation = _vm_queue->remove_next();
468
469 // If we are at a safepoint we will evaluate all the operations that
470 // follow that also require a safepoint
471 if (_cur_vm_operation != NULL &&
472 _cur_vm_operation->evaluate_at_safepoint()) {
473 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
474 }
475 }
476
477 if (should_terminate()) break;
478 } // Release mu_queue_lock
479
480 //
481 // Execute VM operation
482 //
483 { HandleMark hm(VMThread::vm_thread());
484
485 EventMark em("Executing VM operation: %s", vm_operation()->name());
486 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
487
488 // Give the VM thread an extra quantum. Jobs tend to be bursty and this
489 // helps the VM thread to finish up the job.
490 // FIXME: When this is enabled and there are many threads, this can degrade
491 // performance significantly.
492 if( VMThreadHintNoPreempt )
493 os::hint_no_preempt();
494
495 // If we are at a safepoint we will evaluate all the operations that
496 // follow that also require a safepoint
497 if (_cur_vm_operation->evaluate_at_safepoint()) {
498
499 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
500
501 SafepointSynchronize::begin();
502 evaluate_operation(_cur_vm_operation);
503 // now process all queued safepoint ops, iteratively draining
504 // the queue until there are none left
505 do {
506 _cur_vm_operation = safepoint_ops;
507 if (_cur_vm_operation != NULL) {
508 do {
509 // evaluate_operation deletes the op object so we have
510 // to grab the next op now
511 VM_Operation* next = _cur_vm_operation->next();
512 _vm_queue->set_drain_list(next);
513 evaluate_operation(_cur_vm_operation);
514 _cur_vm_operation = next;
515 if (PrintSafepointStatistics) {
516 SafepointSynchronize::inc_vmop_coalesced_count();
517 }
518 } while (_cur_vm_operation != NULL);
519 }
520 // There is a chance that a thread enqueued a safepoint op
521 // since we released the op-queue lock and initiated the safepoint.
522 // So we drain the queue again if there is anything there, as an
523 // optimization to try and reduce the number of safepoints.
524 // As the safepoint synchronizes us with JavaThreads we will see
525 // any enqueue made by a JavaThread, but the peek will not
526 // necessarily detect a concurrent enqueue by a GC thread, but
527 // that simply means the op will wait for the next major cycle of the
528 // VMThread - just as it would if the GC thread lost the race for
529 // the lock.
530 if (_vm_queue->peek_at_safepoint_priority()) {
531 // must hold lock while draining queue
532 MutexLockerEx mu_queue(VMOperationQueue_lock,
533 Mutex::_no_safepoint_check_flag);
534 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
535 } else {
536 safepoint_ops = NULL;
537 }
538 } while(safepoint_ops != NULL);
539
540 _vm_queue->set_drain_list(NULL);
541
542 // Complete safepoint synchronization
543 SafepointSynchronize::end();
544
545 } else { // not a safepoint operation
546 if (TraceLongCompiles) {
547 elapsedTimer t;
548 t.start();
549 evaluate_operation(_cur_vm_operation);
550 t.stop();
551 double secs = t.seconds();
552 if (secs * 1e3 > LongCompileThreshold) {
553 // XXX - _cur_vm_operation should not be accessed after
554 // the completed count has been incremented; the waiting
555 // thread may have already freed this memory.
556 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
557 }
558 } else {
559 evaluate_operation(_cur_vm_operation);
560 }
561
562 _cur_vm_operation = NULL;
563 }
564 }
565
566 //
567 // Notify (potential) waiting Java thread(s) - lock without safepoint
568 // check so that sneaking is not possible
569 { MutexLockerEx mu(VMOperationRequest_lock,
570 Mutex::_no_safepoint_check_flag);
571 VMOperationRequest_lock->notify_all();
572 }
573
574 //
575 // We want to make sure that we get to a safepoint regularly.
576 //
577 if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) {
578 long interval = SafepointSynchronize::last_non_safepoint_interval();
579 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval);
580 if (SafepointALot || max_time_exceeded) {
581 HandleMark hm(VMThread::vm_thread());
582 SafepointSynchronize::begin();
583 SafepointSynchronize::end();
584 }
585 }
586 }
587 }
588
589 void VMThread::execute(VM_Operation* op) {
590 Thread* t = Thread::current();
591
592 if (!t->is_VM_thread()) {
593 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
594 // JavaThread or WatcherThread
595 bool concurrent = op->evaluate_concurrently();
596 // only blocking VM operations need to verify the caller's safepoint state:
597 if (!concurrent) {
598 t->check_for_valid_safepoint_state(true);
599 }
600
601 // New request from Java thread, evaluate prologue
602 if (!op->doit_prologue()) {
603 return; // op was cancelled
604 }
605
606 // Setup VM_operations for execution
607 op->set_calling_thread(t, Thread::get_priority(t));
608
609 // It does not make sense to execute the epilogue, if the VM operation object is getting
610 // deallocated by the VM thread.
611 bool execute_epilog = !op->is_cheap_allocated();
612 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
613
614 // Get ticket number for non-concurrent VM operations
615 int ticket = 0;
616 if (!concurrent) {
617 ticket = t->vm_operation_ticket();
618 }
619
620 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
621 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
622 // to be queued up during a safepoint synchronization.
623 {
624 VMOperationQueue_lock->lock_without_safepoint_check();
625 bool ok = _vm_queue->add(op);
626 op->set_timestamp(os::javaTimeMillis());
627 VMOperationQueue_lock->notify();
628 VMOperationQueue_lock->unlock();
629 // VM_Operation got skipped
630 if (!ok) {
631 assert(concurrent, "can only skip concurrent tasks");
632 if (op->is_cheap_allocated()) delete op;
633 return;
634 }
635 }
636
637 if (!concurrent) {
638 // Wait for completion of request (non-concurrent)
639 // Note: only a JavaThread triggers the safepoint check when locking
640 MutexLocker mu(VMOperationRequest_lock);
641 while(t->vm_operation_completed_count() < ticket) {
642 VMOperationRequest_lock->wait(!t->is_Java_thread());
643 }
644 }
645
646 if (execute_epilog) {
647 op->doit_epilogue();
648 }
649 } else {
650 // invoked by VM thread; usually nested VM operation
651 assert(t->is_VM_thread(), "must be a VM thread");
652 VM_Operation* prev_vm_operation = vm_operation();
653 if (prev_vm_operation != NULL) {
654 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
655 // does not allow nested scavenges or compiles.
656 if (!prev_vm_operation->allow_nested_vm_operations()) {
657 fatal(err_msg("Nested VM operation %s requested by operation %s",
658 op->name(), vm_operation()->name()));
659 }
660 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
661 }
662
663 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
664
665 // Release all internal handles after operation is evaluated
666 HandleMark hm(t);
667 _cur_vm_operation = op;
668
669 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
670 SafepointSynchronize::begin();
671 op->evaluate();
672 SafepointSynchronize::end();
673 } else {
674 op->evaluate();
675 }
676
677 // Free memory if needed
678 if (op->is_cheap_allocated()) delete op;
679
680 _cur_vm_operation = prev_vm_operation;
681 }
682 }
683
684
685 void VMThread::oops_do(OopClosure* f, CLDClosure* cld_f, CodeBlobClosure* cf) {
686 Thread::oops_do(f, cld_f, cf);
687 _vm_queue->oops_do(f);
688 }
689
690 //------------------------------------------------------------------------------------------------------------------
691 #ifndef PRODUCT
692
693 void VMOperationQueue::verify_queue(int prio) {
694 // Check that list is correctly linked
695 int length = _queue_length[prio];
696 VM_Operation *cur = _queue[prio];
697 int i;
698
699 // Check forward links
700 for(i = 0; i < length; i++) {
701 cur = cur->next();
702 assert(cur != _queue[prio], "list to short (forward)");
703 }
704 assert(cur->next() == _queue[prio], "list to long (forward)");
705
706 // Check backwards links
707 cur = _queue[prio];
708 for(i = 0; i < length; i++) {
709 cur = cur->prev();
710 assert(cur != _queue[prio], "list to short (backwards)");
711 }
712 assert(cur->prev() == _queue[prio], "list to long (backwards)");
713 }
714
715 #endif
716
717 void VMThread::verify() {
718 oops_do(&VerifyOopClosure::verify_oop, NULL, NULL);
719 }