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 "evtrace/traceEvents.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 if (EnableEventTracing) {
277 TraceEvents::write_thread_start();
278 }
279
280 // Wait for VM_Operations until termination
281 this->loop();
282
283 // Note the intention to exit before safepointing.
284 // 6295565 This has the effect of waiting for any large tty
285 // outputs to finish.
286 if (xtty != NULL) {
287 ttyLocker ttyl;
288 xtty->begin_elem("destroy_vm");
289 xtty->stamp();
290 xtty->end_elem();
291 assert(should_terminate(), "termination flag must be set");
292 }
293
294 // 4526887 let VM thread exit at Safepoint
295 SafepointSynchronize::begin();
296
297 if (VerifyBeforeExit) {
298 HandleMark hm(VMThread::vm_thread());
299 // Among other things, this ensures that Eden top is correct.
300 Universe::heap()->prepare_for_verify();
301 os::check_heap();
302 // Silent verification so as not to pollute normal output,
303 // unless we really asked for it.
304 Universe::verify(!(PrintGCDetails || Verbose) || VerifySilently);
305 }
306
307 CompileBroker::set_should_block();
308
309 // wait for threads (compiler threads or daemon threads) in the
310 // _thread_in_native state to block.
311 VM_Exit::wait_for_threads_in_native_to_block();
312
313 // signal other threads that VM process is gone
314 {
315 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
316 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
317 // If that happens after _terminate_lock->wait() has unset _owner
318 // but before it actually drops the lock and waits, the notification below
319 // may get lost and we will have a hang. To avoid this, we need to use
320 // Mutex::lock_without_safepoint_check().
321 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
322 _terminated = true;
323 _terminate_lock->notify();
324 }
325
326 // Thread destructor usually does this.
327 ThreadLocalStorage::set_thread(NULL);
328
329 // Deletion must be done synchronously by the JNI DestroyJavaVM thread
330 // so that the VMThread deletion completes before the main thread frees
331 // up the CodeHeap.
332
333 }
334
335
336 // Notify the VMThread that the last non-daemon JavaThread has terminated,
337 // and wait until operation is performed.
338 void VMThread::wait_for_vm_thread_exit() {
339 { MutexLocker mu(VMOperationQueue_lock);
340 _should_terminate = true;
341 VMOperationQueue_lock->notify();
342 }
343
344 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
345 // because this thread has been removed from the threads list. But anything
346 // that could get blocked by Safepoint should not be used after this point,
347 // otherwise we will hang, since there is no one can end the safepoint.
348
349 // Wait until VM thread is terminated
350 // Note: it should be OK to use Terminator_lock here. But this is called
351 // at a very delicate time (VM shutdown) and we are operating in non- VM
352 // thread at Safepoint. It's safer to not share lock with other threads.
353 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
354 while(!VMThread::is_terminated()) {
355 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
356 }
357 }
358 }
359
360 void VMThread::print_on(outputStream* st) const {
361 st->print("\"%s\" ", name());
362 Thread::print_on(st);
363 st->cr();
364 }
365
366 void VMThread::evaluate_operation(VM_Operation* op) {
367 ResourceMark rm;
368
369 {
370 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
371 #ifndef USDT2
372 HS_DTRACE_PROBE3(hotspot, vmops__begin, op->name(), strlen(op->name()),
373 op->evaluation_mode());
374 #else /* USDT2 */
375 HOTSPOT_VMOPS_BEGIN(
376 (char *) op->name(), strlen(op->name()),
377 op->evaluation_mode());
378 #endif /* USDT2 */
379
380 EventExecuteVMOperation event;
381
382 op->evaluate();
383
384 if (event.should_commit()) {
385 bool is_concurrent = op->evaluate_concurrently();
386 event.set_operation(op->type());
387 event.set_safepoint(op->evaluate_at_safepoint());
388 event.set_blocking(!is_concurrent);
389 // Only write caller thread information for non-concurrent vm operations.
390 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
391 // This is because the caller thread could have exited already.
392 event.set_caller(is_concurrent ? 0 : op->calling_thread()->osthread()->thread_id());
393 event.commit();
394 }
395
396 #ifndef USDT2
397 HS_DTRACE_PROBE3(hotspot, vmops__end, op->name(), strlen(op->name()),
398 op->evaluation_mode());
399 #else /* USDT2 */
400 HOTSPOT_VMOPS_END(
401 (char *) op->name(), strlen(op->name()),
402 op->evaluation_mode());
403 #endif /* USDT2 */
404 }
405
406 // Last access of info in _cur_vm_operation!
407 bool c_heap_allocated = op->is_cheap_allocated();
408
409 // Mark as completed
410 if (!op->evaluate_concurrently()) {
411 op->calling_thread()->increment_vm_operation_completed_count();
412 }
413 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
414 // since if it is stack allocated the calling thread might have deallocated
415 if (c_heap_allocated) {
416 delete _cur_vm_operation;
417 }
418 }
419
420
421 void VMThread::loop() {
422 assert(_cur_vm_operation == NULL, "no current one should be executing");
423
424 while(true) {
425 VM_Operation* safepoint_ops = NULL;
426 //
427 // Wait for VM operation
428 //
429 // use no_safepoint_check to get lock without attempting to "sneak"
430 { MutexLockerEx mu_queue(VMOperationQueue_lock,
431 Mutex::_no_safepoint_check_flag);
432
433 // Look for new operation
434 assert(_cur_vm_operation == NULL, "no current one should be executing");
435 _cur_vm_operation = _vm_queue->remove_next();
436
437 // Stall time tracking code
438 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
439 !_cur_vm_operation->evaluate_concurrently()) {
440 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
441 if (stall > 0)
442 tty->print_cr("%s stall: %Ld", _cur_vm_operation->name(), stall);
443 }
444
445 while (!should_terminate() && _cur_vm_operation == NULL) {
446 // wait with a timeout to guarantee safepoints at regular intervals
447 bool timedout =
448 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
449 GuaranteedSafepointInterval);
450
451 // Support for self destruction
452 if ((SelfDestructTimer != 0) && !is_error_reported() &&
453 (os::elapsedTime() > SelfDestructTimer * 60)) {
454 tty->print_cr("VM self-destructed");
455 exit(-1);
456 }
457
458 if (timedout && (SafepointALot ||
459 SafepointSynchronize::is_cleanup_needed())) {
460 MutexUnlockerEx mul(VMOperationQueue_lock,
461 Mutex::_no_safepoint_check_flag);
462 // Force a safepoint since we have not had one for at least
463 // 'GuaranteedSafepointInterval' milliseconds. This will run all
464 // the clean-up processing that needs to be done regularly at a
465 // safepoint
466
467 if (EnableEventTracing) {
468 TraceEvents::write_safepoint_begin(TraceTypes::safepoint_periodic);
469 }
470
471 SafepointSynchronize::begin();
472 #ifdef ASSERT
473 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
474 #endif
475 SafepointSynchronize::end();
476
477 if (EnableEventTracing) {
478 TraceEvents::write_safepoint_end(0);
479 }
480 }
481 _cur_vm_operation = _vm_queue->remove_next();
482
483 // If we are at a safepoint we will evaluate all the operations that
484 // follow that also require a safepoint
485 if (_cur_vm_operation != NULL &&
486 _cur_vm_operation->evaluate_at_safepoint()) {
487 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
488 }
489 }
490
491 if (should_terminate()) break;
492 } // Release mu_queue_lock
493
494 //
495 // Execute VM operation
496 //
497 { HandleMark hm(VMThread::vm_thread());
498
499 EventMark em("Executing VM operation: %s", vm_operation()->name());
500 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
501
502 // Give the VM thread an extra quantum. Jobs tend to be bursty and this
503 // helps the VM thread to finish up the job.
504 // FIXME: When this is enabled and there are many threads, this can degrade
505 // performance significantly.
506 if( VMThreadHintNoPreempt )
507 os::hint_no_preempt();
508
509 // If we are at a safepoint we will evaluate all the operations that
510 // follow that also require a safepoint
511 if (_cur_vm_operation->evaluate_at_safepoint()) {
512
513 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
514
515 if (EnableEventTracing) {
516 TraceEvents::write_safepoint_begin(TraceTypes::safepoint_for_vm_op);
517 }
518
519 int vm_ops_evaluated = 1;
520 SafepointSynchronize::begin();
521 evaluate_operation(_cur_vm_operation);
522 // now process all queued safepoint ops, iteratively draining
523 // the queue until there are none left
524 do {
525 _cur_vm_operation = safepoint_ops;
526 if (_cur_vm_operation != NULL) {
527 do {
528 // evaluate_operation deletes the op object so we have
529 // to grab the next op now
530 VM_Operation* next = _cur_vm_operation->next();
531 _vm_queue->set_drain_list(next);
532 evaluate_operation(_cur_vm_operation);
533 _cur_vm_operation = next;
534 if (PrintSafepointStatistics) {
535 SafepointSynchronize::inc_vmop_coalesced_count();
536 }
537 vm_ops_evaluated++;
538 } while (_cur_vm_operation != NULL);
539 }
540 // There is a chance that a thread enqueued a safepoint op
541 // since we released the op-queue lock and initiated the safepoint.
542 // So we drain the queue again if there is anything there, as an
543 // optimization to try and reduce the number of safepoints.
544 // As the safepoint synchronizes us with JavaThreads we will see
545 // any enqueue made by a JavaThread, but the peek will not
546 // necessarily detect a concurrent enqueue by a GC thread, but
547 // that simply means the op will wait for the next major cycle of the
548 // VMThread - just as it would if the GC thread lost the race for
549 // the lock.
550 if (_vm_queue->peek_at_safepoint_priority()) {
551 // must hold lock while draining queue
552 MutexLockerEx mu_queue(VMOperationQueue_lock,
553 Mutex::_no_safepoint_check_flag);
554 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
555 } else {
556 safepoint_ops = NULL;
557 }
558 } while(safepoint_ops != NULL);
559
560 _vm_queue->set_drain_list(NULL);
561
562 // Complete safepoint synchronization
563 SafepointSynchronize::end();
564
565 if (EnableEventTracing) {
566 TraceEvents::write_safepoint_end((u4) vm_ops_evaluated);
567 }
568
569 } else { // not a safepoint operation
570 if (TraceLongCompiles) {
571 elapsedTimer t;
572 t.start();
573 evaluate_operation(_cur_vm_operation);
574 t.stop();
575 double secs = t.seconds();
576 if (secs * 1e3 > LongCompileThreshold) {
577 // XXX - _cur_vm_operation should not be accessed after
578 // the completed count has been incremented; the waiting
579 // thread may have already freed this memory.
580 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
581 }
582 } else {
583 evaluate_operation(_cur_vm_operation);
584 }
585
586 _cur_vm_operation = NULL;
587 }
588 }
589
590 //
591 // Notify (potential) waiting Java thread(s) - lock without safepoint
592 // check so that sneaking is not possible
593 { MutexLockerEx mu(VMOperationRequest_lock,
594 Mutex::_no_safepoint_check_flag);
595 VMOperationRequest_lock->notify_all();
596 }
597
598 //
599 // We want to make sure that we get to a safepoint regularly.
600 //
601 if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) {
602 long interval = SafepointSynchronize::last_non_safepoint_interval();
603 bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval);
604 if (SafepointALot || max_time_exceeded) {
605 if (EnableEventTracing) {
606 TraceEvents::write_safepoint_begin(TraceTypes::safepoint_periodic);
607 }
608
609 HandleMark hm(VMThread::vm_thread());
610 SafepointSynchronize::begin();
611 SafepointSynchronize::end();
612
613 if (EnableEventTracing) {
614 TraceEvents::write_safepoint_end(0);
615 }
616 }
617 }
618 }
619 }
620
621 void VMThread::execute(VM_Operation* op) {
622 Thread* t = Thread::current();
623
624 if (!t->is_VM_thread()) {
625 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
626 // JavaThread or WatcherThread
627 bool concurrent = op->evaluate_concurrently();
628 // only blocking VM operations need to verify the caller's safepoint state:
629 if (!concurrent) {
630 t->check_for_valid_safepoint_state(true);
631 }
632
633 // New request from Java thread, evaluate prologue
634 if (!op->doit_prologue()) {
635 return; // op was cancelled
636 }
637
638 // Setup VM_operations for execution
639 op->set_calling_thread(t, Thread::get_priority(t));
640
641 // It does not make sense to execute the epilogue, if the VM operation object is getting
642 // deallocated by the VM thread.
643 bool execute_epilog = !op->is_cheap_allocated();
644 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
645
646 // Get ticket number for non-concurrent VM operations
647 int ticket = 0;
648 if (!concurrent) {
649 ticket = t->vm_operation_ticket();
650 }
651
652 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
653 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
654 // to be queued up during a safepoint synchronization.
655 {
656 VMOperationQueue_lock->lock_without_safepoint_check();
657 bool ok = _vm_queue->add(op);
658 op->set_timestamp(os::javaTimeMillis());
659 VMOperationQueue_lock->notify();
660 VMOperationQueue_lock->unlock();
661 // VM_Operation got skipped
662 if (!ok) {
663 assert(concurrent, "can only skip concurrent tasks");
664 if (op->is_cheap_allocated()) delete op;
665 return;
666 }
667 }
668
669 if (!concurrent) {
670 // Wait for completion of request (non-concurrent)
671 // Note: only a JavaThread triggers the safepoint check when locking
672 MutexLocker mu(VMOperationRequest_lock);
673 while(t->vm_operation_completed_count() < ticket) {
674 VMOperationRequest_lock->wait(!t->is_Java_thread());
675 }
676 }
677
678 if (execute_epilog) {
679 op->doit_epilogue();
680 }
681 } else {
682 // invoked by VM thread; usually nested VM operation
683 assert(t->is_VM_thread(), "must be a VM thread");
684 VM_Operation* prev_vm_operation = vm_operation();
685 if (prev_vm_operation != NULL) {
686 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
687 // does not allow nested scavenges or compiles.
688 if (!prev_vm_operation->allow_nested_vm_operations()) {
689 fatal(err_msg("Nested VM operation %s requested by operation %s",
690 op->name(), vm_operation()->name()));
691 }
692 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
693 }
694
695 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
696
697 // Release all internal handles after operation is evaluated
698 HandleMark hm(t);
699 _cur_vm_operation = op;
700
701 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
702 if (EnableEventTracing) {
703 TraceEvents::write_safepoint_begin(TraceTypes::safepoint_for_vm_op);
704 }
705
706 SafepointSynchronize::begin();
707 op->evaluate();
708 SafepointSynchronize::end();
709
710 if (EnableEventTracing) {
711 TraceEvents::write_safepoint_end(1);
712 }
713 } else {
714 op->evaluate();
715 }
716
717 // Free memory if needed
718 if (op->is_cheap_allocated()) delete op;
719
720 _cur_vm_operation = prev_vm_operation;
721 }
722 }
723
724
725 void VMThread::oops_do(OopClosure* f, CLDClosure* cld_f, CodeBlobClosure* cf) {
726 Thread::oops_do(f, cld_f, cf);
727 _vm_queue->oops_do(f);
728 }
729
730 //------------------------------------------------------------------------------------------------------------------
731 #ifndef PRODUCT
732
733 void VMOperationQueue::verify_queue(int prio) {
734 // Check that list is correctly linked
735 int length = _queue_length[prio];
736 VM_Operation *cur = _queue[prio];
737 int i;
738
739 // Check forward links
740 for(i = 0; i < length; i++) {
741 cur = cur->next();
742 assert(cur != _queue[prio], "list to short (forward)");
743 }
744 assert(cur->next() == _queue[prio], "list to long (forward)");
745
746 // Check backwards links
747 cur = _queue[prio];
748 for(i = 0; i < length; i++) {
749 cur = cur->prev();
750 assert(cur != _queue[prio], "list to short (backwards)");
751 }
752 assert(cur->prev() == _queue[prio], "list to long (backwards)");
753 }
754
755 #endif
756
757 void VMThread::verify() {
758 oops_do(&VerifyOopClosure::verify_oop, NULL, NULL);
759 }