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->record_stack_base_and_size();
257 // Notify_lock wait checks on active_handles() to rewait in
258 // case of spurious wakeup, it should wait on the last
259 // value set prior to the notify
260 this->set_active_handles(JNIHandleBlock::allocate_block());
261
262 {
263 MutexLocker ml(Notify_lock);
264 Notify_lock->notify();
265 }
266 // Notify_lock is destroyed by Threads::create_vm()
267
268 int prio = (VMThreadPriority == -1)
269 ? os::java_to_os_priority[NearMaxPriority]
270 : VMThreadPriority;
271 // Note that I cannot call os::set_priority because it expects Java
272 // priorities and I am *explicitly* using OS priorities so that it's
273 // possible to set the VM thread priority higher than any Java thread.
274 os::set_native_priority( this, prio );
275
276 // Wait for VM_Operations until termination
277 this->loop();
278
279 // Note the intention to exit before safepointing.
280 // 6295565 This has the effect of waiting for any large tty
281 // outputs to finish.
282 if (xtty != NULL) {
283 ttyLocker ttyl;
284 xtty->begin_elem("destroy_vm");
285 xtty->stamp();
286 xtty->end_elem();
287 assert(should_terminate(), "termination flag must be set");
288 }
289
290 // 4526887 let VM thread exit at Safepoint
291 SafepointSynchronize::begin();
292
293 if (VerifyBeforeExit) {
294 HandleMark hm(VMThread::vm_thread());
295 // Among other things, this ensures that Eden top is correct.
296 Universe::heap()->prepare_for_verify();
297 os::check_heap();
298 // Silent verification so as not to pollute normal output,
299 // unless we really asked for it.
300 Universe::verify(!(PrintGCDetails || Verbose) || VerifySilently);
301 }
302
303 CompileBroker::set_should_block();
304
305 // wait for threads (compiler threads or daemon threads) in the
306 // _thread_in_native state to block.
307 VM_Exit::wait_for_threads_in_native_to_block();
308
309 // signal other threads that VM process is gone
310 {
311 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
312 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
313 // If that happens after _terminate_lock->wait() has unset _owner
314 // but before it actually drops the lock and waits, the notification below
315 // may get lost and we will have a hang. To avoid this, we need to use
316 // Mutex::lock_without_safepoint_check().
317 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
318 _terminated = true;
319 _terminate_lock->notify();
320 }
321
322 // Thread destructor usually does this.
323 ThreadLocalStorage::set_thread(NULL);
324
325 // Deletion must be done synchronously by the JNI DestroyJavaVM thread
326 // so that the VMThread deletion completes before the main thread frees
327 // up the CodeHeap.
328
329 }
330
331
332 // Notify the VMThread that the last non-daemon JavaThread has terminated,
333 // and wait until operation is performed.
334 void VMThread::wait_for_vm_thread_exit() {
335 { MutexLocker mu(VMOperationQueue_lock);
336 _should_terminate = true;
337 VMOperationQueue_lock->notify();
338 }
339
340 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
341 // because this thread has been removed from the threads list. But anything
342 // that could get blocked by Safepoint should not be used after this point,
343 // otherwise we will hang, since there is no one can end the safepoint.
344
345 // Wait until VM thread is terminated
346 // Note: it should be OK to use Terminator_lock here. But this is called
347 // at a very delicate time (VM shutdown) and we are operating in non- VM
348 // thread at Safepoint. It's safer to not share lock with other threads.
349 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
350 while(!VMThread::is_terminated()) {
351 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
352 }
353 }
354 }
355
356 void VMThread::print_on(outputStream* st) const {
357 st->print("\"%s\" ", name());
358 Thread::print_on(st);
359 st->cr();
360 }
361
362 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
363 assert(event != NULL, "invariant");
364 assert(event->should_commit(), "invariant");
365 assert(op != NULL, "invariant");
366 const bool is_concurrent = op->evaluate_concurrently();
367 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
368 event->set_operation(op->type());
369 event->set_safepoint(evaluate_at_safepoint);
370 event->set_blocking(!is_concurrent);
371 // Only write caller thread information for non-concurrent vm operations.
372 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
373 // This is because the caller thread could have exited already.
374 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread()));
375 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0);
376 event->commit();
377 }
378
379 void VMThread::evaluate_operation(VM_Operation* op) {
380 ResourceMark rm;
381
382 {
383 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
384 #ifndef USDT2
385 HS_DTRACE_PROBE3(hotspot, vmops__begin, op->name(), strlen(op->name()),
386 op->evaluation_mode());
387 #else /* USDT2 */
388 HOTSPOT_VMOPS_BEGIN(
389 (char *) op->name(), strlen(op->name()),
390 op->evaluation_mode());
391 #endif /* USDT2 */
392
393 EventExecuteVMOperation event;
394 op->evaluate();
395 if (event.should_commit()) {
396 post_vm_operation_event(&event, op);
397 }
398
399 #ifndef USDT2
400 HS_DTRACE_PROBE3(hotspot, vmops__end, op->name(), strlen(op->name()),
401 op->evaluation_mode());
402 #else /* USDT2 */
403 HOTSPOT_VMOPS_END(
404 (char *) op->name(), strlen(op->name()),
405 op->evaluation_mode());
406 #endif /* USDT2 */
407 }
408
409 // Last access of info in _cur_vm_operation!
410 bool c_heap_allocated = op->is_cheap_allocated();
411
412 // Mark as completed
413 if (!op->evaluate_concurrently()) {
414 op->calling_thread()->increment_vm_operation_completed_count();
415 }
416 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
417 // since if it is stack allocated the calling thread might have deallocated
418 if (c_heap_allocated) {
419 delete _cur_vm_operation;
420 }
421 }
422
423
424 void VMThread::loop() {
425 assert(_cur_vm_operation == NULL, "no current one should be executing");
426
427 while(true) {
428 VM_Operation* safepoint_ops = NULL;
429 //
430 // Wait for VM operation
431 //
432 // use no_safepoint_check to get lock without attempting to "sneak"
433 { MutexLockerEx mu_queue(VMOperationQueue_lock,
434 Mutex::_no_safepoint_check_flag);
435
436 // Look for new operation
437 assert(_cur_vm_operation == NULL, "no current one should be executing");
438 _cur_vm_operation = _vm_queue->remove_next();
439
440 // Stall time tracking code
441 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
442 !_cur_vm_operation->evaluate_concurrently()) {
443 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
444 if (stall > 0)
445 tty->print_cr("%s stall: %Ld", _cur_vm_operation->name(), stall);
446 }
447
448 while (!should_terminate() && _cur_vm_operation == NULL) {
449 // wait with a timeout to guarantee safepoints at regular intervals
450 bool timedout =
451 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
452 GuaranteedSafepointInterval);
453
454 // Support for self destruction
455 if ((SelfDestructTimer != 0) && !is_error_reported() &&
456 (os::elapsedTime() > SelfDestructTimer * 60)) {
457 tty->print_cr("VM self-destructed");
458 exit(-1);
459 }
460
461 if (timedout && (SafepointALot ||
462 SafepointSynchronize::is_cleanup_needed())) {
463 MutexUnlockerEx mul(VMOperationQueue_lock,
464 Mutex::_no_safepoint_check_flag);
465 // Force a safepoint since we have not had one for at least
466 // 'GuaranteedSafepointInterval' milliseconds. This will run all
467 // the clean-up processing that needs to be done regularly at a
468 // safepoint
469 SafepointSynchronize::begin();
470 #ifdef ASSERT
471 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
472 #endif
473 SafepointSynchronize::end();
474 }
475 _cur_vm_operation = _vm_queue->remove_next();
476
477 // If we are at a safepoint we will evaluate all the operations that
478 // follow that also require a safepoint
479 if (_cur_vm_operation != NULL &&
480 _cur_vm_operation->evaluate_at_safepoint()) {
481 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
482 }
483 }
484
485 if (should_terminate()) break;
486 } // Release mu_queue_lock
487
488 //
489 // Execute VM operation
490 //
491 { HandleMark hm(VMThread::vm_thread());
492
493 EventMark em("Executing VM operation: %s", vm_operation()->name());
494 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
495
496 // Give the VM thread an extra quantum. Jobs tend to be bursty and this
497 // helps the VM thread to finish up the job.
498 // FIXME: When this is enabled and there are many threads, this can degrade
499 // performance significantly.
500 if( VMThreadHintNoPreempt )
501 os::hint_no_preempt();
502
503 // If we are at a safepoint we will evaluate all the operations that
504 // follow that also require a safepoint
505 if (_cur_vm_operation->evaluate_at_safepoint()) {
506
507 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
508
509 SafepointSynchronize::begin();
510 evaluate_operation(_cur_vm_operation);
511 // now process all queued safepoint ops, iteratively draining
512 // the queue until there are none left
513 do {
514 _cur_vm_operation = safepoint_ops;
515 if (_cur_vm_operation != NULL) {
516 do {
517 // evaluate_operation deletes the op object so we have
518 // to grab the next op now
519 VM_Operation* next = _cur_vm_operation->next();
520 _vm_queue->set_drain_list(next);
521 evaluate_operation(_cur_vm_operation);
522 _cur_vm_operation = next;
523 if (PrintSafepointStatistics) {
524 SafepointSynchronize::inc_vmop_coalesced_count();
525 }
526 } while (_cur_vm_operation != NULL);
527 }
528 // There is a chance that a thread enqueued a safepoint op
529 // since we released the op-queue lock and initiated the safepoint.
530 // So we drain the queue again if there is anything there, as an
531 // optimization to try and reduce the number of safepoints.
532 // As the safepoint synchronizes us with JavaThreads we will see
533 // any enqueue made by a JavaThread, but the peek will not
534 // necessarily detect a concurrent enqueue by a GC thread, but
535 // that simply means the op will wait for the next major cycle of the
536 // VMThread - just as it would if the GC thread lost the race for
537 // the lock.
538 if (_vm_queue->peek_at_safepoint_priority()) {
539 // must hold lock while draining queue
540 MutexLockerEx mu_queue(VMOperationQueue_lock,
541 Mutex::_no_safepoint_check_flag);
542 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
543 } else {
544 safepoint_ops = NULL;
545 }
546 } while(safepoint_ops != NULL);
547
548 _vm_queue->set_drain_list(NULL);
549
550 // Complete safepoint synchronization
551 SafepointSynchronize::end();
552
553 } else { // not a safepoint operation
554 if (TraceLongCompiles) {
555 elapsedTimer t;
556 t.start();
557 evaluate_operation(_cur_vm_operation);
558 t.stop();
559 double secs = t.seconds();
560 if (secs * 1e3 > LongCompileThreshold) {
561 // XXX - _cur_vm_operation should not be accessed after
562 // the completed count has been incremented; the waiting
563 // thread may have already freed this memory.
564 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
565 }
566 } else {
567 evaluate_operation(_cur_vm_operation);
568 }
569
570 _cur_vm_operation = NULL;
571 }
572 }
573
574 //
575 // Notify (potential) waiting Java thread(s) - lock without safepoint
576 // check so that sneaking is not possible
577 { MutexLockerEx mu(VMOperationRequest_lock,
578 Mutex::_no_safepoint_check_flag);
579 VMOperationRequest_lock->notify_all();
580 }
581
582 //
583 // We want to make sure that we get to a safepoint regularly.
584 //
585 if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) {
586 long interval = SafepointSynchronize::last_non_safepoint_interval();
587 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval);
588 if (SafepointALot || max_time_exceeded) {
589 HandleMark hm(VMThread::vm_thread());
590 SafepointSynchronize::begin();
591 SafepointSynchronize::end();
592 }
593 }
594 }
595 }
596
597 void VMThread::execute(VM_Operation* op) {
598 Thread* t = Thread::current();
599
600 if (!t->is_VM_thread()) {
601 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
602 // JavaThread or WatcherThread
603 bool concurrent = op->evaluate_concurrently();
604 // only blocking VM operations need to verify the caller's safepoint state:
605 if (!concurrent) {
606 t->check_for_valid_safepoint_state(true);
607 }
608
609 // New request from Java thread, evaluate prologue
610 if (!op->doit_prologue()) {
611 return; // op was cancelled
612 }
613
614 // Setup VM_operations for execution
615 op->set_calling_thread(t, Thread::get_priority(t));
616
617 // It does not make sense to execute the epilogue, if the VM operation object is getting
618 // deallocated by the VM thread.
619 bool execute_epilog = !op->is_cheap_allocated();
620 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
621
622 // Get ticket number for non-concurrent VM operations
623 int ticket = 0;
624 if (!concurrent) {
625 ticket = t->vm_operation_ticket();
626 }
627
628 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
629 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
630 // to be queued up during a safepoint synchronization.
631 {
632 VMOperationQueue_lock->lock_without_safepoint_check();
633 bool ok = _vm_queue->add(op);
634 op->set_timestamp(os::javaTimeMillis());
635 VMOperationQueue_lock->notify();
636 VMOperationQueue_lock->unlock();
637 // VM_Operation got skipped
638 if (!ok) {
639 assert(concurrent, "can only skip concurrent tasks");
640 if (op->is_cheap_allocated()) delete op;
641 return;
642 }
643 }
644
645 if (!concurrent) {
646 // Wait for completion of request (non-concurrent)
647 // Note: only a JavaThread triggers the safepoint check when locking
648 MutexLocker mu(VMOperationRequest_lock);
649 while(t->vm_operation_completed_count() < ticket) {
650 VMOperationRequest_lock->wait(!t->is_Java_thread());
651 }
652 }
653
654 if (execute_epilog) {
655 op->doit_epilogue();
656 }
657 } else {
658 // invoked by VM thread; usually nested VM operation
659 assert(t->is_VM_thread(), "must be a VM thread");
660 VM_Operation* prev_vm_operation = vm_operation();
661 if (prev_vm_operation != NULL) {
662 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
663 // does not allow nested scavenges or compiles.
664 if (!prev_vm_operation->allow_nested_vm_operations()) {
665 fatal(err_msg("Nested VM operation %s requested by operation %s",
666 op->name(), vm_operation()->name()));
667 }
668 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
669 }
670
671 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
672
673 // Release all internal handles after operation is evaluated
674 HandleMark hm(t);
675 _cur_vm_operation = op;
676
677 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
678 SafepointSynchronize::begin();
679 op->evaluate();
680 SafepointSynchronize::end();
681 } else {
682 op->evaluate();
683 }
684
685 // Free memory if needed
686 if (op->is_cheap_allocated()) delete op;
687
688 _cur_vm_operation = prev_vm_operation;
689 }
690 }
691
692
693 void VMThread::oops_do(OopClosure* f, CLDClosure* cld_f, CodeBlobClosure* cf) {
694 Thread::oops_do(f, cld_f, cf);
695 _vm_queue->oops_do(f);
696 }
697
698 //------------------------------------------------------------------------------------------------------------------
699 #ifndef PRODUCT
700
701 void VMOperationQueue::verify_queue(int prio) {
702 // Check that list is correctly linked
703 int length = _queue_length[prio];
704 VM_Operation *cur = _queue[prio];
705 int i;
706
707 // Check forward links
708 for(i = 0; i < length; i++) {
709 cur = cur->next();
710 assert(cur != _queue[prio], "list to short (forward)");
711 }
712 assert(cur->next() == _queue[prio], "list to long (forward)");
713
714 // Check backwards links
715 cur = _queue[prio];
716 for(i = 0; i < length; i++) {
717 cur = cur->prev();
718 assert(cur != _queue[prio], "list to short (backwards)");
719 }
720 assert(cur->prev() == _queue[prio], "list to long (backwards)");
721 }
722
723 #endif
724
725 void VMThread::verify() {
726 oops_do(&VerifyOopClosure::verify_oop, NULL, NULL);
727 }