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 "jfr/jfrEvents.hpp"
29 #include "jfr/support/jfrThreadId.hpp"
30 #include "memory/resourceArea.hpp"
31 #include "oops/method.hpp"
32 #include "oops/oop.inline.hpp"
33 #include "runtime/interfaceSupport.hpp"
34 #include "runtime/mutexLocker.hpp"
35 #include "runtime/os.hpp"
36 #include "runtime/thread.inline.hpp"
37 #include "runtime/vmThread.hpp"
38 #include "runtime/vm_operations.hpp"
39 #include "services/runtimeService.hpp"
40 #include "utilities/dtrace.hpp"
41 #include "utilities/events.hpp"
42 #include "utilities/xmlstream.hpp"
43
44 #ifndef USDT2
45 HS_DTRACE_PROBE_DECL3(hotspot, vmops__request, char *, uintptr_t, int);
46 HS_DTRACE_PROBE_DECL3(hotspot, vmops__begin, char *, uintptr_t, int);
47 HS_DTRACE_PROBE_DECL3(hotspot, vmops__end, char *, uintptr_t, int);
48 #endif /* !USDT2 */
49
50 PRAGMA_FORMAT_MUTE_WARNINGS_FOR_GCC
51
52 // Dummy VM operation to act as first element in our circular double-linked list
53 class VM_Dummy: public VM_Operation {
54 VMOp_Type type() const { return VMOp_Dummy; }
55 void doit() {};
56 };
57
58 VMOperationQueue::VMOperationQueue() {
59 // The queue is a circular doubled-linked list, which always contains
60 // one element (i.e., one element means empty).
61 for(int i = 0; i < nof_priorities; i++) {
62 _queue_length[i] = 0;
63 _queue_counter = 0;
64 _queue[i] = new VM_Dummy();
65 _queue[i]->set_next(_queue[i]);
66 _queue[i]->set_prev(_queue[i]);
67 }
68 _drain_list = NULL;
69 }
70
71
72 bool VMOperationQueue::queue_empty(int prio) {
73 // It is empty if there is exactly one element
74 bool empty = (_queue[prio] == _queue[prio]->next());
75 assert( (_queue_length[prio] == 0 && empty) ||
76 (_queue_length[prio] > 0 && !empty), "sanity check");
77 return _queue_length[prio] == 0;
78 }
79
80 // Inserts an element to the right of the q element
81 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
82 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
83 n->set_prev(q);
84 n->set_next(q->next());
85 q->next()->set_prev(n);
86 q->set_next(n);
87 }
88
89 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
90 _queue_length[prio]++;
91 insert(_queue[prio]->next(), op);
92 }
93
94 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
95 _queue_length[prio]++;
96 insert(_queue[prio]->prev(), op);
97 }
98
99
100 void VMOperationQueue::unlink(VM_Operation* q) {
101 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
102 q->prev()->set_next(q->next());
103 q->next()->set_prev(q->prev());
104 }
105
106 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
107 if (queue_empty(prio)) return NULL;
108 assert(_queue_length[prio] >= 0, "sanity check");
109 _queue_length[prio]--;
110 VM_Operation* r = _queue[prio]->next();
111 assert(r != _queue[prio], "cannot remove base element");
112 unlink(r);
113 return r;
114 }
115
116 VM_Operation* VMOperationQueue::queue_drain(int prio) {
117 if (queue_empty(prio)) return NULL;
118 DEBUG_ONLY(int length = _queue_length[prio];);
119 assert(length >= 0, "sanity check");
120 _queue_length[prio] = 0;
121 VM_Operation* r = _queue[prio]->next();
122 assert(r != _queue[prio], "cannot remove base element");
123 // remove links to base element from head and tail
124 r->set_prev(NULL);
125 _queue[prio]->prev()->set_next(NULL);
126 // restore queue to empty state
127 _queue[prio]->set_next(_queue[prio]);
128 _queue[prio]->set_prev(_queue[prio]);
129 assert(queue_empty(prio), "drain corrupted queue");
130 #ifdef ASSERT
131 int len = 0;
132 VM_Operation* cur;
133 for(cur = r; cur != NULL; cur=cur->next()) len++;
134 assert(len == length, "drain lost some ops");
135 #endif
136 return r;
137 }
138
139 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
140 VM_Operation* cur = _queue[queue];
141 cur = cur->next();
142 while (cur != _queue[queue]) {
143 cur->oops_do(f);
144 cur = cur->next();
145 }
146 }
147
148 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
149 VM_Operation* cur = _drain_list;
150 while (cur != NULL) {
151 cur->oops_do(f);
152 cur = cur->next();
153 }
154 }
155
156 //-----------------------------------------------------------------
157 // High-level interface
158 bool VMOperationQueue::add(VM_Operation *op) {
159
160 #ifndef USDT2
161 HS_DTRACE_PROBE3(hotspot, vmops__request, op->name(), strlen(op->name()),
162 op->evaluation_mode());
163 #else /* USDT2 */
164 HOTSPOT_VMOPS_REQUEST(
165 (char *) op->name(), strlen(op->name()),
166 op->evaluation_mode());
167 #endif /* USDT2 */
168
169 // Encapsulates VM queue policy. Currently, that
170 // only involves putting them on the right list
171 if (op->evaluate_at_safepoint()) {
172 queue_add_back(SafepointPriority, op);
173 return true;
174 }
175
176 queue_add_back(MediumPriority, op);
177 return true;
178 }
179
180 VM_Operation* VMOperationQueue::remove_next() {
181 // Assuming VMOperation queue is two-level priority queue. If there are
182 // more than two priorities, we need a different scheduling algorithm.
183 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
184 "current algorithm does not work");
185
186 // simple counter based scheduling to prevent starvation of lower priority
187 // queue. -- see 4390175
188 int high_prio, low_prio;
189 if (_queue_counter++ < 10) {
190 high_prio = SafepointPriority;
191 low_prio = MediumPriority;
192 } else {
193 _queue_counter = 0;
194 high_prio = MediumPriority;
195 low_prio = SafepointPriority;
196 }
197
198 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
199 }
200
201 void VMOperationQueue::oops_do(OopClosure* f) {
202 for(int i = 0; i < nof_priorities; i++) {
203 queue_oops_do(i, f);
204 }
205 drain_list_oops_do(f);
206 }
207
208
209 //------------------------------------------------------------------------------------------------------------------
210 // Implementation of VMThread stuff
211
212 bool VMThread::_should_terminate = false;
213 bool VMThread::_terminated = false;
214 Monitor* VMThread::_terminate_lock = NULL;
215 VMThread* VMThread::_vm_thread = NULL;
216 VM_Operation* VMThread::_cur_vm_operation = NULL;
217 VMOperationQueue* VMThread::_vm_queue = NULL;
218 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
219
220
221 void VMThread::create() {
222 assert(vm_thread() == NULL, "we can only allocate one VMThread");
223 _vm_thread = new VMThread();
224
225 // Create VM operation queue
226 _vm_queue = new VMOperationQueue();
227 guarantee(_vm_queue != NULL, "just checking");
228
229 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true);
230
231 if (UsePerfData) {
232 // jvmstat performance counters
233 Thread* THREAD = Thread::current();
234 _perf_accumulated_vm_operation_time =
235 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
236 PerfData::U_Ticks, CHECK);
237 }
238 }
239
240
241 VMThread::VMThread() : NamedThread() {
242 set_name("VM Thread");
243 }
244
245 void VMThread::destroy() {
246 if (_vm_thread != NULL) {
247 delete _vm_thread;
248 _vm_thread = NULL; // VM thread is gone
249 }
250 }
251
252 void VMThread::run() {
253 assert(this == vm_thread(), "check");
254
255 this->initialize_thread_local_storage();
256 this->set_native_thread_name(this->name());
257 this->record_stack_base_and_size();
258 // Notify_lock wait checks on active_handles() to rewait in
259 // case of spurious wakeup, it should wait on the last
260 // value set prior to the notify
261 this->set_active_handles(JNIHandleBlock::allocate_block());
262
263 {
264 MutexLocker ml(Notify_lock);
265 Notify_lock->notify();
266 }
267 // Notify_lock is destroyed by Threads::create_vm()
268
269 int prio = (VMThreadPriority == -1)
270 ? os::java_to_os_priority[NearMaxPriority]
271 : VMThreadPriority;
272 // Note that I cannot call os::set_priority because it expects Java
273 // priorities and I am *explicitly* using OS priorities so that it's
274 // possible to set the VM thread priority higher than any Java thread.
275 os::set_native_priority( this, prio );
276
277 // Wait for VM_Operations until termination
278 this->loop();
279
280 // Note the intention to exit before safepointing.
281 // 6295565 This has the effect of waiting for any large tty
282 // outputs to finish.
283 if (xtty != NULL) {
284 ttyLocker ttyl;
285 xtty->begin_elem("destroy_vm");
286 xtty->stamp();
287 xtty->end_elem();
288 assert(should_terminate(), "termination flag must be set");
289 }
290
291 // 4526887 let VM thread exit at Safepoint
292 SafepointSynchronize::begin();
293
294 if (VerifyBeforeExit) {
295 HandleMark hm(VMThread::vm_thread());
296 // Among other things, this ensures that Eden top is correct.
297 Universe::heap()->prepare_for_verify();
298 os::check_heap();
299 // Silent verification so as not to pollute normal output,
300 // unless we really asked for it.
301 Universe::verify(!(PrintGCDetails || Verbose) || VerifySilently);
302 }
303
304 CompileBroker::set_should_block();
305
306 // wait for threads (compiler threads or daemon threads) in the
307 // _thread_in_native state to block.
308 VM_Exit::wait_for_threads_in_native_to_block();
309
310 // signal other threads that VM process is gone
311 {
312 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
313 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
314 // If that happens after _terminate_lock->wait() has unset _owner
315 // but before it actually drops the lock and waits, the notification below
316 // may get lost and we will have a hang. To avoid this, we need to use
317 // Mutex::lock_without_safepoint_check().
318 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
319 _terminated = true;
320 _terminate_lock->notify();
321 }
322
323 // Thread destructor usually does this.
324 ThreadLocalStorage::set_thread(NULL);
325
326 // Deletion must be done synchronously by the JNI DestroyJavaVM thread
327 // so that the VMThread deletion completes before the main thread frees
328 // up the CodeHeap.
329
330 }
331
332
333 // Notify the VMThread that the last non-daemon JavaThread has terminated,
334 // and wait until operation is performed.
335 void VMThread::wait_for_vm_thread_exit() {
336 { MutexLocker mu(VMOperationQueue_lock);
337 _should_terminate = true;
338 VMOperationQueue_lock->notify();
339 }
340
341 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
342 // because this thread has been removed from the threads list. But anything
343 // that could get blocked by Safepoint should not be used after this point,
344 // otherwise we will hang, since there is no one can end the safepoint.
345
346 // Wait until VM thread is terminated
347 // Note: it should be OK to use Terminator_lock here. But this is called
348 // at a very delicate time (VM shutdown) and we are operating in non- VM
349 // thread at Safepoint. It's safer to not share lock with other threads.
350 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
351 while(!VMThread::is_terminated()) {
352 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
353 }
354 }
355 }
356
357 void VMThread::print_on(outputStream* st) const {
358 st->print("\"%s\" ", name());
359 Thread::print_on(st);
360 st->cr();
361 }
362
363 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
364 assert(event != NULL, "invariant");
365 assert(event->should_commit(), "invariant");
366 assert(op != NULL, "invariant");
367 const bool is_concurrent = op->evaluate_concurrently();
368 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
369 event->set_operation(op->type());
370 event->set_safepoint(evaluate_at_safepoint);
371 event->set_blocking(!is_concurrent);
372 // Only write caller thread information for non-concurrent vm operations.
373 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
374 // This is because the caller thread could have exited already.
375 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread()));
376 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0);
377 event->commit();
378 }
379
380 void VMThread::evaluate_operation(VM_Operation* op) {
381 ResourceMark rm;
382
383 {
384 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
385 #ifndef USDT2
386 HS_DTRACE_PROBE3(hotspot, vmops__begin, op->name(), strlen(op->name()),
387 op->evaluation_mode());
388 #else /* USDT2 */
389 HOTSPOT_VMOPS_BEGIN(
390 (char *) op->name(), strlen(op->name()),
391 op->evaluation_mode());
392 #endif /* USDT2 */
393
394 EventExecuteVMOperation event;
395 op->evaluate();
396 if (event.should_commit()) {
397 post_vm_operation_event(&event, op);
398 }
399
400 #ifndef USDT2
401 HS_DTRACE_PROBE3(hotspot, vmops__end, op->name(), strlen(op->name()),
402 op->evaluation_mode());
403 #else /* USDT2 */
404 HOTSPOT_VMOPS_END(
405 (char *) op->name(), strlen(op->name()),
406 op->evaluation_mode());
407 #endif /* USDT2 */
408 }
409
410 // Last access of info in _cur_vm_operation!
411 bool c_heap_allocated = op->is_cheap_allocated();
412
413 // Mark as completed
414 if (!op->evaluate_concurrently()) {
415 op->calling_thread()->increment_vm_operation_completed_count();
416 }
417 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
418 // since if it is stack allocated the calling thread might have deallocated
419 if (c_heap_allocated) {
420 delete _cur_vm_operation;
421 }
422 }
423
424
425 void VMThread::loop() {
426 assert(_cur_vm_operation == NULL, "no current one should be executing");
427
428 while(true) {
429 VM_Operation* safepoint_ops = NULL;
430 //
431 // Wait for VM operation
432 //
433 // use no_safepoint_check to get lock without attempting to "sneak"
434 { MutexLockerEx mu_queue(VMOperationQueue_lock,
435 Mutex::_no_safepoint_check_flag);
436
437 // Look for new operation
438 assert(_cur_vm_operation == NULL, "no current one should be executing");
439 _cur_vm_operation = _vm_queue->remove_next();
440
441 // Stall time tracking code
442 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
443 !_cur_vm_operation->evaluate_concurrently()) {
444 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
445 if (stall > 0)
446 tty->print_cr("%s stall: %Ld", _cur_vm_operation->name(), stall);
447 }
448
449 while (!should_terminate() && _cur_vm_operation == NULL) {
450 // wait with a timeout to guarantee safepoints at regular intervals
451 bool timedout =
452 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
453 GuaranteedSafepointInterval);
454
455 // Support for self destruction
456 if ((SelfDestructTimer != 0) && !is_error_reported() &&
457 (os::elapsedTime() > SelfDestructTimer * 60)) {
458 tty->print_cr("VM self-destructed");
459 exit(-1);
460 }
461
462 if (timedout && (SafepointALot ||
463 SafepointSynchronize::is_cleanup_needed())) {
464 MutexUnlockerEx mul(VMOperationQueue_lock,
465 Mutex::_no_safepoint_check_flag);
466 // Force a safepoint since we have not had one for at least
467 // 'GuaranteedSafepointInterval' milliseconds. This will run all
468 // the clean-up processing that needs to be done regularly at a
469 // safepoint
470 SafepointSynchronize::begin();
471 #ifdef ASSERT
472 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
473 #endif
474 SafepointSynchronize::end();
475 }
476 _cur_vm_operation = _vm_queue->remove_next();
477
478 // If we are at a safepoint we will evaluate all the operations that
479 // follow that also require a safepoint
480 if (_cur_vm_operation != NULL &&
481 _cur_vm_operation->evaluate_at_safepoint()) {
482 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
483 }
484 }
485
486 if (should_terminate()) break;
487 } // Release mu_queue_lock
488
489 //
490 // Execute VM operation
491 //
492 { HandleMark hm(VMThread::vm_thread());
493
494 EventMark em("Executing VM operation: %s", vm_operation()->name());
495 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
496
497 // Give the VM thread an extra quantum. Jobs tend to be bursty and this
498 // helps the VM thread to finish up the job.
499 // FIXME: When this is enabled and there are many threads, this can degrade
500 // performance significantly.
501 if( VMThreadHintNoPreempt )
502 os::hint_no_preempt();
503
504 // If we are at a safepoint we will evaluate all the operations that
505 // follow that also require a safepoint
506 if (_cur_vm_operation->evaluate_at_safepoint()) {
507
508 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
509
510 SafepointSynchronize::begin();
511 evaluate_operation(_cur_vm_operation);
512 // now process all queued safepoint ops, iteratively draining
513 // the queue until there are none left
514 do {
515 _cur_vm_operation = safepoint_ops;
516 if (_cur_vm_operation != NULL) {
517 do {
518 // evaluate_operation deletes the op object so we have
519 // to grab the next op now
520 VM_Operation* next = _cur_vm_operation->next();
521 _vm_queue->set_drain_list(next);
522 evaluate_operation(_cur_vm_operation);
523 _cur_vm_operation = next;
524 if (PrintSafepointStatistics) {
525 SafepointSynchronize::inc_vmop_coalesced_count();
526 }
527 } while (_cur_vm_operation != NULL);
528 }
529 // There is a chance that a thread enqueued a safepoint op
530 // since we released the op-queue lock and initiated the safepoint.
531 // So we drain the queue again if there is anything there, as an
532 // optimization to try and reduce the number of safepoints.
533 // As the safepoint synchronizes us with JavaThreads we will see
534 // any enqueue made by a JavaThread, but the peek will not
535 // necessarily detect a concurrent enqueue by a GC thread, but
536 // that simply means the op will wait for the next major cycle of the
537 // VMThread - just as it would if the GC thread lost the race for
538 // the lock.
539 if (_vm_queue->peek_at_safepoint_priority()) {
540 // must hold lock while draining queue
541 MutexLockerEx mu_queue(VMOperationQueue_lock,
542 Mutex::_no_safepoint_check_flag);
543 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
544 } else {
545 safepoint_ops = NULL;
546 }
547 } while(safepoint_ops != NULL);
548
549 _vm_queue->set_drain_list(NULL);
550
551 // Complete safepoint synchronization
552 SafepointSynchronize::end();
553
554 } else { // not a safepoint operation
555 if (TraceLongCompiles) {
556 elapsedTimer t;
557 t.start();
558 evaluate_operation(_cur_vm_operation);
559 t.stop();
560 double secs = t.seconds();
561 if (secs * 1e3 > LongCompileThreshold) {
562 // XXX - _cur_vm_operation should not be accessed after
563 // the completed count has been incremented; the waiting
564 // thread may have already freed this memory.
565 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
566 }
567 } else {
568 evaluate_operation(_cur_vm_operation);
569 }
570
571 _cur_vm_operation = NULL;
572 }
573 }
574
575 //
576 // Notify (potential) waiting Java thread(s) - lock without safepoint
577 // check so that sneaking is not possible
578 { MutexLockerEx mu(VMOperationRequest_lock,
579 Mutex::_no_safepoint_check_flag);
580 VMOperationRequest_lock->notify_all();
581 }
582
583 //
584 // We want to make sure that we get to a safepoint regularly.
585 //
586 if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) {
587 long interval = SafepointSynchronize::last_non_safepoint_interval();
588 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval);
589 if (SafepointALot || max_time_exceeded) {
590 HandleMark hm(VMThread::vm_thread());
591 SafepointSynchronize::begin();
592 SafepointSynchronize::end();
593 }
594 }
595 }
596 }
597
598 void VMThread::execute(VM_Operation* op) {
599 Thread* t = Thread::current();
600
601 if (!t->is_VM_thread()) {
602 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
603 // JavaThread or WatcherThread
604 bool concurrent = op->evaluate_concurrently();
605 // only blocking VM operations need to verify the caller's safepoint state:
606 if (!concurrent) {
607 t->check_for_valid_safepoint_state(true);
608 }
609
610 // New request from Java thread, evaluate prologue
611 if (!op->doit_prologue()) {
612 return; // op was cancelled
613 }
614
615 // Setup VM_operations for execution
616 op->set_calling_thread(t, Thread::get_priority(t));
617
618 // It does not make sense to execute the epilogue, if the VM operation object is getting
619 // deallocated by the VM thread.
620 bool execute_epilog = !op->is_cheap_allocated();
621 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
622
623 // Get ticket number for non-concurrent VM operations
624 int ticket = 0;
625 if (!concurrent) {
626 ticket = t->vm_operation_ticket();
627 }
628
629 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
630 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
631 // to be queued up during a safepoint synchronization.
632 {
633 VMOperationQueue_lock->lock_without_safepoint_check();
634 bool ok = _vm_queue->add(op);
635 op->set_timestamp(os::javaTimeMillis());
636 VMOperationQueue_lock->notify();
637 VMOperationQueue_lock->unlock();
638 // VM_Operation got skipped
639 if (!ok) {
640 assert(concurrent, "can only skip concurrent tasks");
641 if (op->is_cheap_allocated()) delete op;
642 return;
643 }
644 }
645
646 if (!concurrent) {
647 // Wait for completion of request (non-concurrent)
648 // Note: only a JavaThread triggers the safepoint check when locking
649 MutexLocker mu(VMOperationRequest_lock);
650 while(t->vm_operation_completed_count() < ticket) {
651 VMOperationRequest_lock->wait(!t->is_Java_thread());
652 }
653 }
654
655 if (execute_epilog) {
656 op->doit_epilogue();
657 }
658 } else {
659 // invoked by VM thread; usually nested VM operation
660 assert(t->is_VM_thread(), "must be a VM thread");
661 VM_Operation* prev_vm_operation = vm_operation();
662 if (prev_vm_operation != NULL) {
663 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
664 // does not allow nested scavenges or compiles.
665 if (!prev_vm_operation->allow_nested_vm_operations()) {
666 fatal(err_msg("Nested VM operation %s requested by operation %s",
667 op->name(), vm_operation()->name()));
668 }
669 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
670 }
671
672 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
673
674 // Release all internal handles after operation is evaluated
675 HandleMark hm(t);
676 _cur_vm_operation = op;
677
678 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
679 SafepointSynchronize::begin();
680 op->evaluate();
681 SafepointSynchronize::end();
682 } else {
683 op->evaluate();
684 }
685
686 // Free memory if needed
687 if (op->is_cheap_allocated()) delete op;
688
689 _cur_vm_operation = prev_vm_operation;
690 }
691 }
692
693
694 void VMThread::oops_do(OopClosure* f, CLDClosure* cld_f, CodeBlobClosure* cf) {
695 Thread::oops_do(f, cld_f, cf);
696 _vm_queue->oops_do(f);
697 }
698
699 //------------------------------------------------------------------------------------------------------------------
700 #ifndef PRODUCT
701
702 void VMOperationQueue::verify_queue(int prio) {
703 // Check that list is correctly linked
704 int length = _queue_length[prio];
705 VM_Operation *cur = _queue[prio];
706 int i;
707
708 // Check forward links
709 for(i = 0; i < length; i++) {
710 cur = cur->next();
711 assert(cur != _queue[prio], "list to short (forward)");
712 }
713 assert(cur->next() == _queue[prio], "list to long (forward)");
714
715 // Check backwards links
716 cur = _queue[prio];
717 for(i = 0; i < length; i++) {
718 cur = cur->prev();
719 assert(cur != _queue[prio], "list to short (backwards)");
720 }
721 assert(cur->prev() == _queue[prio], "list to long (backwards)");
722 }
723
724 #endif
725
726 void VMThread::verify() {
727 oops_do(&VerifyOopClosure::verify_oop, NULL, NULL);
728 }