1 /*
2 * Copyright (c) 1998, 2012, 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/methodOop.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/vmThread.hpp"
35 #include "runtime/vm_operations.hpp"
36 #include "services/runtimeService.hpp"
37 #include "trace/tracing.hpp"
38 #include "utilities/dtrace.hpp"
39 #include "utilities/events.hpp"
40 #include "utilities/xmlstream.hpp"
41 #ifdef TARGET_OS_FAMILY_linux
42 # include "thread_linux.inline.hpp"
43 #endif
44 #ifdef TARGET_OS_FAMILY_solaris
45 # include "thread_solaris.inline.hpp"
46 #endif
47 #ifdef TARGET_OS_FAMILY_windows
48 # include "thread_windows.inline.hpp"
49 #endif
50 #ifdef TARGET_OS_FAMILY_bsd
51 # include "thread_bsd.inline.hpp"
52 #endif
53
54 #ifndef USDT2
55 HS_DTRACE_PROBE_DECL3(hotspot, vmops__request, char *, uintptr_t, int);
56 HS_DTRACE_PROBE_DECL3(hotspot, vmops__begin, char *, uintptr_t, int);
57 HS_DTRACE_PROBE_DECL3(hotspot, vmops__end, char *, uintptr_t, int);
58 #endif /* !USDT2 */
59
60 // Dummy VM operation to act as first element in our circular double-linked list
61 class VM_Dummy: public VM_Operation {
62 VMOp_Type type() const { return VMOp_Dummy; }
63 void doit() {};
64 };
65
66 VMOperationQueue::VMOperationQueue() {
67 // The queue is a circular doubled-linked list, which always contains
68 // one element (i.e., one element means empty).
69 for(int i = 0; i < nof_priorities; i++) {
70 _queue_length[i] = 0;
71 _queue_counter = 0;
72 _queue[i] = new VM_Dummy();
73 _queue[i]->set_next(_queue[i]);
74 _queue[i]->set_prev(_queue[i]);
75 }
76 _drain_list = NULL;
77 }
78
79
80 bool VMOperationQueue::queue_empty(int prio) {
81 // It is empty if there is exactly one element
82 bool empty = (_queue[prio] == _queue[prio]->next());
83 assert( (_queue_length[prio] == 0 && empty) ||
84 (_queue_length[prio] > 0 && !empty), "sanity check");
85 return _queue_length[prio] == 0;
86 }
87
88 // Inserts an element to the right of the q element
89 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
90 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
91 n->set_prev(q);
92 n->set_next(q->next());
93 q->next()->set_prev(n);
94 q->set_next(n);
95 }
96
97 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
98 _queue_length[prio]++;
99 insert(_queue[prio]->next(), op);
100 }
101
102 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
103 _queue_length[prio]++;
104 insert(_queue[prio]->prev(), op);
105 }
106
107
108 void VMOperationQueue::unlink(VM_Operation* q) {
109 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
110 q->prev()->set_next(q->next());
111 q->next()->set_prev(q->prev());
112 }
113
114 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
115 if (queue_empty(prio)) return NULL;
116 assert(_queue_length[prio] >= 0, "sanity check");
117 _queue_length[prio]--;
118 VM_Operation* r = _queue[prio]->next();
119 assert(r != _queue[prio], "cannot remove base element");
120 unlink(r);
121 return r;
122 }
123
124 VM_Operation* VMOperationQueue::queue_drain(int prio) {
125 if (queue_empty(prio)) return NULL;
126 DEBUG_ONLY(int length = _queue_length[prio];);
127 assert(length >= 0, "sanity check");
128 _queue_length[prio] = 0;
129 VM_Operation* r = _queue[prio]->next();
130 assert(r != _queue[prio], "cannot remove base element");
131 // remove links to base element from head and tail
132 r->set_prev(NULL);
133 _queue[prio]->prev()->set_next(NULL);
134 // restore queue to empty state
135 _queue[prio]->set_next(_queue[prio]);
136 _queue[prio]->set_prev(_queue[prio]);
137 assert(queue_empty(prio), "drain corrupted queue");
138 #ifdef DEBUG
139 int len = 0;
140 VM_Operation* cur;
141 for(cur = r; cur != NULL; cur=cur->next()) len++;
142 assert(len == length, "drain lost some ops");
143 #endif
144 return r;
145 }
146
147 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
148 VM_Operation* cur = _queue[queue];
149 cur = cur->next();
150 while (cur != _queue[queue]) {
151 cur->oops_do(f);
152 cur = cur->next();
153 }
154 }
155
156 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
157 VM_Operation* cur = _drain_list;
158 while (cur != NULL) {
159 cur->oops_do(f);
160 cur = cur->next();
161 }
162 }
163
164 //-----------------------------------------------------------------
165 // High-level interface
166 bool VMOperationQueue::add(VM_Operation *op) {
167
168 #ifndef USDT2
169 HS_DTRACE_PROBE3(hotspot, vmops__request, op->name(), strlen(op->name()),
170 op->evaluation_mode());
171 #else /* USDT2 */
172 HOTSPOT_VMOPS_REQUEST(
173 (char *) op->name(), strlen(op->name()),
174 op->evaluation_mode());
175 #endif /* USDT2 */
176
177 // Encapsulates VM queue policy. Currently, that
178 // only involves putting them on the right list
179 if (op->evaluate_at_safepoint()) {
180 queue_add_back(SafepointPriority, op);
181 return true;
182 }
183
184 queue_add_back(MediumPriority, op);
185 return true;
186 }
187
188 VM_Operation* VMOperationQueue::remove_next() {
189 // Assuming VMOperation queue is two-level priority queue. If there are
190 // more than two priorities, we need a different scheduling algorithm.
191 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
192 "current algorithm does not work");
193
194 // simple counter based scheduling to prevent starvation of lower priority
195 // queue. -- see 4390175
196 int high_prio, low_prio;
197 if (_queue_counter++ < 10) {
198 high_prio = SafepointPriority;
199 low_prio = MediumPriority;
200 } else {
201 _queue_counter = 0;
202 high_prio = MediumPriority;
203 low_prio = SafepointPriority;
204 }
205
206 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
207 }
208
209 void VMOperationQueue::oops_do(OopClosure* f) {
210 for(int i = 0; i < nof_priorities; i++) {
211 queue_oops_do(i, f);
212 }
213 drain_list_oops_do(f);
214 }
215
216
217 //------------------------------------------------------------------------------------------------------------------
218 // Implementation of VMThread stuff
219
220 bool VMThread::_should_terminate = false;
221 bool VMThread::_terminated = false;
222 Monitor* VMThread::_terminate_lock = NULL;
223 VMThread* VMThread::_vm_thread = NULL;
224 VM_Operation* VMThread::_cur_vm_operation = NULL;
225 VMOperationQueue* VMThread::_vm_queue = NULL;
226 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
227
228
229 void VMThread::create() {
230 assert(vm_thread() == NULL, "we can only allocate one VMThread");
231 _vm_thread = new VMThread();
232
233 // Create VM operation queue
234 _vm_queue = new VMOperationQueue();
235 guarantee(_vm_queue != NULL, "just checking");
236
237 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true);
238
239 if (UsePerfData) {
240 // jvmstat performance counters
241 Thread* THREAD = Thread::current();
242 _perf_accumulated_vm_operation_time =
243 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
244 PerfData::U_Ticks, CHECK);
245 }
246 }
247
248
249 VMThread::VMThread() : NamedThread() {
250 set_name("VM Thread");
251 }
252
253 void VMThread::destroy() {
254 if (_vm_thread != NULL) {
255 delete _vm_thread;
256 _vm_thread = NULL; // VM thread is gone
257 }
258 }
259
260 void VMThread::run() {
261 assert(this == vm_thread(), "check");
262
263 this->initialize_thread_local_storage();
264 this->record_stack_base_and_size();
265 // Notify_lock wait checks on active_handles() to rewait in
266 // case of spurious wakeup, it should wait on the last
267 // value set prior to the notify
268 this->set_active_handles(JNIHandleBlock::allocate_block());
269
270 {
271 MutexLocker ml(Notify_lock);
272 Notify_lock->notify();
273 }
274 // Notify_lock is destroyed by Threads::create_vm()
275
276 int prio = (VMThreadPriority == -1)
277 ? os::java_to_os_priority[NearMaxPriority]
278 : VMThreadPriority;
279 // Note that I cannot call os::set_priority because it expects Java
280 // priorities and I am *explicitly* using OS priorities so that it's
281 // possible to set the VM thread priority higher than any Java thread.
282 os::set_native_priority( this, prio );
283
284 // Wait for VM_Operations until termination
285 this->loop();
286
287 // Note the intention to exit before safepointing.
288 // 6295565 This has the effect of waiting for any large tty
289 // outputs to finish.
290 if (xtty != NULL) {
291 ttyLocker ttyl;
292 xtty->begin_elem("destroy_vm");
293 xtty->stamp();
294 xtty->end_elem();
295 assert(should_terminate(), "termination flag must be set");
296 }
297
298 // 4526887 let VM thread exit at Safepoint
299 SafepointSynchronize::begin();
300
301 if (VerifyBeforeExit) {
302 HandleMark hm(VMThread::vm_thread());
303 // Among other things, this ensures that Eden top is correct.
304 Universe::heap()->prepare_for_verify();
305 os::check_heap();
306 // Silent verification so as not to pollute normal output,
307 // unless we really asked for it.
308 Universe::verify(!(PrintGCDetails || Verbose));
309 }
310
311 CompileBroker::set_should_block();
312
313 // wait for threads (compiler threads or daemon threads) in the
314 // _thread_in_native state to block.
315 VM_Exit::wait_for_threads_in_native_to_block();
316
317 // signal other threads that VM process is gone
318 {
319 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
320 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
321 // If that happens after _terminate_lock->wait() has unset _owner
322 // but before it actually drops the lock and waits, the notification below
323 // may get lost and we will have a hang. To avoid this, we need to use
324 // Mutex::lock_without_safepoint_check().
325 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
326 _terminated = true;
327 _terminate_lock->notify();
328 }
329
330 // Deletion must be done synchronously by the JNI DestroyJavaVM thread
331 // so that the VMThread deletion completes before the main thread frees
332 // up the CodeHeap.
333
334 }
335
336
337 // Notify the VMThread that the last non-daemon JavaThread has terminated,
338 // and wait until operation is performed.
339 void VMThread::wait_for_vm_thread_exit() {
340 { MutexLocker mu(VMOperationQueue_lock);
341 _should_terminate = true;
342 VMOperationQueue_lock->notify();
343 }
344
345 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
346 // because this thread has been removed from the threads list. But anything
347 // that could get blocked by Safepoint should not be used after this point,
348 // otherwise we will hang, since there is no one can end the safepoint.
349
350 // Wait until VM thread is terminated
351 // Note: it should be OK to use Terminator_lock here. But this is called
352 // at a very delicate time (VM shutdown) and we are operating in non- VM
353 // thread at Safepoint. It's safer to not share lock with other threads.
354 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
355 while(!VMThread::is_terminated()) {
356 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
357 }
358 }
359 }
360
361 void VMThread::print_on(outputStream* st) const {
362 st->print("\"%s\" ", name());
363 Thread::print_on(st);
364 st->cr();
365 }
366
367 void VMThread::evaluate_operation(VM_Operation* op) {
368 ResourceMark rm;
369
370 {
371 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
372 #ifndef USDT2
373 HS_DTRACE_PROBE3(hotspot, vmops__begin, op->name(), strlen(op->name()),
374 op->evaluation_mode());
375 #else /* USDT2 */
376 HOTSPOT_VMOPS_BEGIN(
377 (char *) op->name(), strlen(op->name()),
378 op->evaluation_mode());
379 #endif /* USDT2 */
380
381 EventExecuteVMOperation event;
382
383 op->evaluate();
384
385 if (event.should_commit()) {
386 event.set_operation(op->type());
387 event.set_safepoint(op->evaluate_at_safepoint());
388 event.set_blocking(!op->evaluate_concurrently());
389 event.set_caller(op->calling_thread()->osthread()->thread_id());
390 event.commit();
391 }
392
393 #ifndef USDT2
394 HS_DTRACE_PROBE3(hotspot, vmops__end, op->name(), strlen(op->name()),
395 op->evaluation_mode());
396 #else /* USDT2 */
397 HOTSPOT_VMOPS_END(
398 (char *) op->name(), strlen(op->name()),
399 op->evaluation_mode());
400 #endif /* USDT2 */
401 }
402
403 // Last access of info in _cur_vm_operation!
404 bool c_heap_allocated = op->is_cheap_allocated();
405
406 // Mark as completed
407 if (!op->evaluate_concurrently()) {
408 op->calling_thread()->increment_vm_operation_completed_count();
409 }
410 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
411 // since if it is stack allocated the calling thread might have deallocated
412 if (c_heap_allocated) {
413 delete _cur_vm_operation;
414 }
415 }
416
417
418 void VMThread::loop() {
419 assert(_cur_vm_operation == NULL, "no current one should be executing");
420
421 while(true) {
422 VM_Operation* safepoint_ops = NULL;
423 //
424 // Wait for VM operation
425 //
426 // use no_safepoint_check to get lock without attempting to "sneak"
427 { MutexLockerEx mu_queue(VMOperationQueue_lock,
428 Mutex::_no_safepoint_check_flag);
429
430 // Look for new operation
431 assert(_cur_vm_operation == NULL, "no current one should be executing");
432 _cur_vm_operation = _vm_queue->remove_next();
433
434 // Stall time tracking code
435 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
436 !_cur_vm_operation->evaluate_concurrently()) {
437 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
438 if (stall > 0)
439 tty->print_cr("%s stall: %Ld", _cur_vm_operation->name(), stall);
440 }
441
442 while (!should_terminate() && _cur_vm_operation == NULL) {
443 // wait with a timeout to guarantee safepoints at regular intervals
444 bool timedout =
445 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
446 GuaranteedSafepointInterval);
447
448 // Support for self destruction
449 if ((SelfDestructTimer != 0) && !is_error_reported() &&
450 (os::elapsedTime() > SelfDestructTimer * 60)) {
451 tty->print_cr("VM self-destructed");
452 exit(-1);
453 }
454
455 if (timedout && (SafepointALot ||
456 SafepointSynchronize::is_cleanup_needed())) {
457 MutexUnlockerEx mul(VMOperationQueue_lock,
458 Mutex::_no_safepoint_check_flag);
459 // Force a safepoint since we have not had one for at least
460 // 'GuaranteedSafepointInterval' milliseconds. This will run all
461 // the clean-up processing that needs to be done regularly at a
462 // safepoint
463 SafepointSynchronize::begin();
464 #ifdef ASSERT
465 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
466 #endif
467 SafepointSynchronize::end();
468 }
469 _cur_vm_operation = _vm_queue->remove_next();
470
471 // If we are at a safepoint we will evaluate all the operations that
472 // follow that also require a safepoint
473 if (_cur_vm_operation != NULL &&
474 _cur_vm_operation->evaluate_at_safepoint()) {
475 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
476 }
477 }
478
479 if (should_terminate()) break;
480 } // Release mu_queue_lock
481
482 //
483 // Execute VM operation
484 //
485 { HandleMark hm(VMThread::vm_thread());
486
487 EventMark em("Executing VM operation: %s", vm_operation()->name());
488 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
489
490 // Give the VM thread an extra quantum. Jobs tend to be bursty and this
491 // helps the VM thread to finish up the job.
492 // FIXME: When this is enabled and there are many threads, this can degrade
493 // performance significantly.
494 if( VMThreadHintNoPreempt )
495 os::hint_no_preempt();
496
497 // If we are at a safepoint we will evaluate all the operations that
498 // follow that also require a safepoint
499 if (_cur_vm_operation->evaluate_at_safepoint()) {
500
501 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
502
503 SafepointSynchronize::begin();
504 evaluate_operation(_cur_vm_operation);
505 // now process all queued safepoint ops, iteratively draining
506 // the queue until there are none left
507 do {
508 _cur_vm_operation = safepoint_ops;
509 if (_cur_vm_operation != NULL) {
510 do {
511 // evaluate_operation deletes the op object so we have
512 // to grab the next op now
513 VM_Operation* next = _cur_vm_operation->next();
514 _vm_queue->set_drain_list(next);
515 evaluate_operation(_cur_vm_operation);
516 _cur_vm_operation = next;
517 if (PrintSafepointStatistics) {
518 SafepointSynchronize::inc_vmop_coalesced_count();
519 }
520 } while (_cur_vm_operation != NULL);
521 }
522 // There is a chance that a thread enqueued a safepoint op
523 // since we released the op-queue lock and initiated the safepoint.
524 // So we drain the queue again if there is anything there, as an
525 // optimization to try and reduce the number of safepoints.
526 // As the safepoint synchronizes us with JavaThreads we will see
527 // any enqueue made by a JavaThread, but the peek will not
528 // necessarily detect a concurrent enqueue by a GC thread, but
529 // that simply means the op will wait for the next major cycle of the
530 // VMThread - just as it would if the GC thread lost the race for
531 // the lock.
532 if (_vm_queue->peek_at_safepoint_priority()) {
533 // must hold lock while draining queue
534 MutexLockerEx mu_queue(VMOperationQueue_lock,
535 Mutex::_no_safepoint_check_flag);
536 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
537 } else {
538 safepoint_ops = NULL;
539 }
540 } while(safepoint_ops != NULL);
541
542 _vm_queue->set_drain_list(NULL);
543
544 // Complete safepoint synchronization
545 SafepointSynchronize::end();
546
547 } else { // not a safepoint operation
548 if (TraceLongCompiles) {
549 elapsedTimer t;
550 t.start();
551 evaluate_operation(_cur_vm_operation);
552 t.stop();
553 double secs = t.seconds();
554 if (secs * 1e3 > LongCompileThreshold) {
555 // XXX - _cur_vm_operation should not be accessed after
556 // the completed count has been incremented; the waiting
557 // thread may have already freed this memory.
558 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
559 }
560 } else {
561 evaluate_operation(_cur_vm_operation);
562 }
563
564 _cur_vm_operation = NULL;
565 }
566 }
567
568 //
569 // Notify (potential) waiting Java thread(s) - lock without safepoint
570 // check so that sneaking is not possible
571 { MutexLockerEx mu(VMOperationRequest_lock,
572 Mutex::_no_safepoint_check_flag);
573 VMOperationRequest_lock->notify_all();
574 }
575
576 //
577 // We want to make sure that we get to a safepoint regularly.
578 //
579 if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) {
580 long interval = SafepointSynchronize::last_non_safepoint_interval();
581 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval);
582 if (SafepointALot || max_time_exceeded) {
583 HandleMark hm(VMThread::vm_thread());
584 SafepointSynchronize::begin();
585 SafepointSynchronize::end();
586 }
587 }
588 }
589 }
590
591 void VMThread::execute(VM_Operation* op) {
592 Thread* t = Thread::current();
593
594 if (!t->is_VM_thread()) {
595 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
596 // JavaThread or WatcherThread
597 t->check_for_valid_safepoint_state(true);
598
599 // New request from Java thread, evaluate prologue
600 if (!op->doit_prologue()) {
601 return; // op was cancelled
602 }
603
604 // Setup VM_operations for execution
605 op->set_calling_thread(t, Thread::get_priority(t));
606
607 // It does not make sense to execute the epilogue, if the VM operation object is getting
608 // deallocated by the VM thread.
609 bool concurrent = op->evaluate_concurrently();
610 bool execute_epilog = !op->is_cheap_allocated();
611 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
612
613 // Get ticket number for non-concurrent VM operations
614 int ticket = 0;
615 if (!concurrent) {
616 ticket = t->vm_operation_ticket();
617 }
618
619 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
620 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
621 // to be queued up during a safepoint synchronization.
622 {
623 VMOperationQueue_lock->lock_without_safepoint_check();
624 bool ok = _vm_queue->add(op);
625 op->set_timestamp(os::javaTimeMillis());
626 VMOperationQueue_lock->notify();
627 VMOperationQueue_lock->unlock();
628 // VM_Operation got skipped
629 if (!ok) {
630 assert(concurrent, "can only skip concurrent tasks");
631 if (op->is_cheap_allocated()) delete op;
632 return;
633 }
634 }
635
636 if (!concurrent) {
637 // Wait for completion of request (non-concurrent)
638 // Note: only a JavaThread triggers the safepoint check when locking
639 MutexLocker mu(VMOperationRequest_lock);
640 while(t->vm_operation_completed_count() < ticket) {
641 VMOperationRequest_lock->wait(!t->is_Java_thread());
642 }
643 }
644
645 if (execute_epilog) {
646 op->doit_epilogue();
647 }
648 } else {
649 // invoked by VM thread; usually nested VM operation
650 assert(t->is_VM_thread(), "must be a VM thread");
651 VM_Operation* prev_vm_operation = vm_operation();
652 if (prev_vm_operation != NULL) {
653 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
654 // does not allow nested scavenges or compiles.
655 if (!prev_vm_operation->allow_nested_vm_operations()) {
656 fatal(err_msg("Nested VM operation %s requested by operation %s",
657 op->name(), vm_operation()->name()));
658 }
659 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
660 }
661
662 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
663
664 // Release all internal handles after operation is evaluated
665 HandleMark hm(t);
666 _cur_vm_operation = op;
667
668 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
669 SafepointSynchronize::begin();
670 op->evaluate();
671 SafepointSynchronize::end();
672 } else {
673 op->evaluate();
674 }
675
676 // Free memory if needed
677 if (op->is_cheap_allocated()) delete op;
678
679 _cur_vm_operation = prev_vm_operation;
680 }
681 }
682
683
684 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
685 Thread::oops_do(f, cf);
686 _vm_queue->oops_do(f);
687 }
688
689 //------------------------------------------------------------------------------------------------------------------
690 #ifndef PRODUCT
691
692 void VMOperationQueue::verify_queue(int prio) {
693 // Check that list is correctly linked
694 int length = _queue_length[prio];
695 VM_Operation *cur = _queue[prio];
696 int i;
697
698 // Check forward links
699 for(i = 0; i < length; i++) {
700 cur = cur->next();
701 assert(cur != _queue[prio], "list to short (forward)");
702 }
703 assert(cur->next() == _queue[prio], "list to long (forward)");
704
705 // Check backwards links
706 cur = _queue[prio];
707 for(i = 0; i < length; i++) {
708 cur = cur->prev();
709 assert(cur != _queue[prio], "list to short (backwards)");
710 }
711 assert(cur->prev() == _queue[prio], "list to long (backwards)");
712 }
713
714 #endif
715
716 void VMThread::verify() {
717 oops_do(&VerifyOopClosure::verify_oop, NULL);
718 }