1 /*
2 * Copyright (c) 1998, 2018, 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/shared/collectedHeap.hpp"
28 #include "jfr/jfrEvents.hpp"
29 #include "jfr/support/jfrThreadId.hpp"
30 #include "logging/log.hpp"
31 #include "logging/logConfiguration.hpp"
32 #include "memory/resourceArea.hpp"
33 #include "oops/method.hpp"
34 #include "oops/oop.inline.hpp"
35 #include "oops/verifyOopClosure.hpp"
36 #include "runtime/interfaceSupport.inline.hpp"
37 #include "runtime/mutexLocker.hpp"
38 #include "runtime/os.hpp"
39 #include "runtime/safepoint.hpp"
40 #include "runtime/thread.inline.hpp"
41 #include "runtime/vmThread.hpp"
42 #include "runtime/vm_operations.hpp"
43 #include "services/runtimeService.hpp"
44 #include "utilities/dtrace.hpp"
45 #include "utilities/events.hpp"
46 #include "utilities/vmError.hpp"
47 #include "utilities/xmlstream.hpp"
48
49 // Dummy VM operation to act as first element in our circular double-linked list
50 class VM_None: public VM_Operation {
51 VMOp_Type type() const { return VMOp_None; }
52 void doit() {};
53 };
54
55 VMOperationQueue::VMOperationQueue() {
56 // The queue is a circular doubled-linked list, which always contains
57 // one element (i.e., one element means empty).
58 for(int i = 0; i < nof_priorities; i++) {
59 _queue_length[i] = 0;
60 _queue_counter = 0;
61 _queue[i] = new VM_None();
62 _queue[i]->set_next(_queue[i]);
63 _queue[i]->set_prev(_queue[i]);
64 }
65 _drain_list = NULL;
66 }
67
68
69 bool VMOperationQueue::queue_empty(int prio) {
70 // It is empty if there is exactly one element
71 bool empty = (_queue[prio] == _queue[prio]->next());
72 assert( (_queue_length[prio] == 0 && empty) ||
73 (_queue_length[prio] > 0 && !empty), "sanity check");
74 return _queue_length[prio] == 0;
75 }
76
77 // Inserts an element to the right of the q element
78 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
79 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
80 n->set_prev(q);
81 n->set_next(q->next());
82 q->next()->set_prev(n);
83 q->set_next(n);
84 }
85
86 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
87 _queue_length[prio]++;
88 insert(_queue[prio]->next(), op);
89 }
90
91 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
92 _queue_length[prio]++;
93 insert(_queue[prio]->prev(), op);
94 }
95
96
97 void VMOperationQueue::unlink(VM_Operation* q) {
98 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
99 q->prev()->set_next(q->next());
100 q->next()->set_prev(q->prev());
101 }
102
103 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
104 if (queue_empty(prio)) return NULL;
105 assert(_queue_length[prio] >= 0, "sanity check");
106 _queue_length[prio]--;
107 VM_Operation* r = _queue[prio]->next();
108 assert(r != _queue[prio], "cannot remove base element");
109 unlink(r);
110 return r;
111 }
112
113 VM_Operation* VMOperationQueue::queue_drain(int prio) {
114 if (queue_empty(prio)) return NULL;
115 DEBUG_ONLY(int length = _queue_length[prio];);
116 assert(length >= 0, "sanity check");
117 _queue_length[prio] = 0;
118 VM_Operation* r = _queue[prio]->next();
119 assert(r != _queue[prio], "cannot remove base element");
120 // remove links to base element from head and tail
121 r->set_prev(NULL);
122 _queue[prio]->prev()->set_next(NULL);
123 // restore queue to empty state
124 _queue[prio]->set_next(_queue[prio]);
125 _queue[prio]->set_prev(_queue[prio]);
126 assert(queue_empty(prio), "drain corrupted queue");
127 #ifdef ASSERT
128 int len = 0;
129 VM_Operation* cur;
130 for(cur = r; cur != NULL; cur=cur->next()) len++;
131 assert(len == length, "drain lost some ops");
132 #endif
133 return r;
134 }
135
136 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
137 VM_Operation* cur = _queue[queue];
138 cur = cur->next();
139 while (cur != _queue[queue]) {
140 cur->oops_do(f);
141 cur = cur->next();
142 }
143 }
144
145 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
146 VM_Operation* cur = _drain_list;
147 while (cur != NULL) {
148 cur->oops_do(f);
149 cur = cur->next();
150 }
151 }
152
153 //-----------------------------------------------------------------
154 // High-level interface
155 bool VMOperationQueue::add(VM_Operation *op) {
156
157 HOTSPOT_VMOPS_REQUEST(
158 (char *) op->name(), strlen(op->name()),
159 op->evaluation_mode());
160
161 // Encapsulates VM queue policy. Currently, that
162 // only involves putting them on the right list
163 if (op->evaluate_at_safepoint()) {
164 queue_add_back(SafepointPriority, op);
165 return true;
166 }
167
168 queue_add_back(MediumPriority, op);
169 return true;
170 }
171
172 VM_Operation* VMOperationQueue::remove_next() {
173 // Assuming VMOperation queue is two-level priority queue. If there are
174 // more than two priorities, we need a different scheduling algorithm.
175 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
176 "current algorithm does not work");
177
178 // simple counter based scheduling to prevent starvation of lower priority
179 // queue. -- see 4390175
180 int high_prio, low_prio;
181 if (_queue_counter++ < 10) {
182 high_prio = SafepointPriority;
183 low_prio = MediumPriority;
184 } else {
185 _queue_counter = 0;
186 high_prio = MediumPriority;
187 low_prio = SafepointPriority;
188 }
189
190 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
191 }
192
193 void VMOperationQueue::oops_do(OopClosure* f) {
194 for(int i = 0; i < nof_priorities; i++) {
195 queue_oops_do(i, f);
196 }
197 drain_list_oops_do(f);
198 }
199
200
201 //------------------------------------------------------------------------------------------------------------------
202 // Implementation of VMThread stuff
203
204 bool VMThread::_should_terminate = false;
205 bool VMThread::_terminated = false;
206 Monitor* VMThread::_terminate_lock = NULL;
207 VMThread* VMThread::_vm_thread = NULL;
208 VM_Operation* VMThread::_cur_vm_operation = NULL;
209 VMOperationQueue* VMThread::_vm_queue = NULL;
210 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
211 const char* VMThread::_no_op_reason = NULL;
212
213
214 void VMThread::create() {
215 assert(vm_thread() == NULL, "we can only allocate one VMThread");
216 _vm_thread = new VMThread();
217
218 // Create VM operation queue
219 _vm_queue = new VMOperationQueue();
220 guarantee(_vm_queue != NULL, "just checking");
221
222 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
223 Monitor::_safepoint_check_never);
224
225 if (UsePerfData) {
226 // jvmstat performance counters
227 Thread* THREAD = Thread::current();
228 _perf_accumulated_vm_operation_time =
229 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
230 PerfData::U_Ticks, CHECK);
231 }
232 }
233
234 VMThread::VMThread() : NamedThread() {
235 set_name("VM Thread");
236 }
237
238 void VMThread::destroy() {
239 _vm_thread = NULL; // VM thread is gone
240 }
241
242 void VMThread::run() {
243 assert(this == vm_thread(), "check");
244
245 this->initialize_named_thread();
246 this->record_stack_base_and_size();
247 // Notify_lock wait checks on active_handles() to rewait in
248 // case of spurious wakeup, it should wait on the last
249 // value set prior to the notify
250 this->set_active_handles(JNIHandleBlock::allocate_block());
251
252 {
253 MutexLocker ml(Notify_lock);
254 Notify_lock->notify();
255 }
256 // Notify_lock is destroyed by Threads::create_vm()
257
258 int prio = (VMThreadPriority == -1)
259 ? os::java_to_os_priority[NearMaxPriority]
260 : VMThreadPriority;
261 // Note that I cannot call os::set_priority because it expects Java
262 // priorities and I am *explicitly* using OS priorities so that it's
263 // possible to set the VM thread priority higher than any Java thread.
264 os::set_native_priority( this, prio );
265
266 // Wait for VM_Operations until termination
267 this->loop();
268
269 // Note the intention to exit before safepointing.
270 // 6295565 This has the effect of waiting for any large tty
271 // outputs to finish.
272 if (xtty != NULL) {
273 ttyLocker ttyl;
274 xtty->begin_elem("destroy_vm");
275 xtty->stamp();
276 xtty->end_elem();
277 assert(should_terminate(), "termination flag must be set");
278 }
279
280 // 4526887 let VM thread exit at Safepoint
281 _no_op_reason = "Halt";
282 SafepointSynchronize::begin();
283
284 if (VerifyBeforeExit) {
285 HandleMark hm(VMThread::vm_thread());
286 // Among other things, this ensures that Eden top is correct.
287 Universe::heap()->prepare_for_verify();
288 // Silent verification so as not to pollute normal output,
289 // unless we really asked for it.
290 Universe::verify();
291 }
292
293 CompileBroker::set_should_block();
294
295 // wait for threads (compiler threads or daemon threads) in the
296 // _thread_in_native state to block.
297 VM_Exit::wait_for_threads_in_native_to_block();
298
299 // signal other threads that VM process is gone
300 {
301 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
302 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
303 // If that happens after _terminate_lock->wait() has unset _owner
304 // but before it actually drops the lock and waits, the notification below
305 // may get lost and we will have a hang. To avoid this, we need to use
306 // Mutex::lock_without_safepoint_check().
307 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
308 _terminated = true;
309 _terminate_lock->notify();
310 }
311
312 // We are now racing with the VM termination being carried out in
313 // another thread, so we don't "delete this". Numerous threads don't
314 // get deleted when the VM terminates
315
316 }
317
318
319 // Notify the VMThread that the last non-daemon JavaThread has terminated,
320 // and wait until operation is performed.
321 void VMThread::wait_for_vm_thread_exit() {
322 { MutexLocker mu(VMOperationQueue_lock);
323 _should_terminate = true;
324 VMOperationQueue_lock->notify();
325 }
326
327 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
328 // because this thread has been removed from the threads list. But anything
329 // that could get blocked by Safepoint should not be used after this point,
330 // otherwise we will hang, since there is no one can end the safepoint.
331
332 // Wait until VM thread is terminated
333 // Note: it should be OK to use Terminator_lock here. But this is called
334 // at a very delicate time (VM shutdown) and we are operating in non- VM
335 // thread at Safepoint. It's safer to not share lock with other threads.
336 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
337 while(!VMThread::is_terminated()) {
338 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
339 }
340 }
341 }
342
343 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
344 assert(event != NULL, "invariant");
345 assert(event->should_commit(), "invariant");
346 assert(op != NULL, "invariant");
347 const bool is_concurrent = op->evaluate_concurrently();
348 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
349 event->set_operation(op->type());
350 event->set_safepoint(evaluate_at_safepoint);
351 event->set_blocking(!is_concurrent);
352 // Only write caller thread information for non-concurrent vm operations.
353 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
354 // This is because the caller thread could have exited already.
355 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread()));
356 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0);
357 event->commit();
358 }
359
360 void VMThread::evaluate_operation(VM_Operation* op) {
361 ResourceMark rm;
362
363 {
364 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
365 HOTSPOT_VMOPS_BEGIN(
366 (char *) op->name(), strlen(op->name()),
367 op->evaluation_mode());
368
369 EventExecuteVMOperation event;
370 op->evaluate();
371 if (event.should_commit()) {
372 post_vm_operation_event(&event, op);
373 }
374
375 HOTSPOT_VMOPS_END(
376 (char *) op->name(), strlen(op->name()),
377 op->evaluation_mode());
378 }
379
380 // Last access of info in _cur_vm_operation!
381 bool c_heap_allocated = op->is_cheap_allocated();
382
383 // Mark as completed
384 if (!op->evaluate_concurrently()) {
385 op->calling_thread()->increment_vm_operation_completed_count();
386 }
387 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
388 // since if it is stack allocated the calling thread might have deallocated
389 if (c_heap_allocated) {
390 delete _cur_vm_operation;
391 }
392 }
393
394 bool VMThread::no_op_safepoint_needed(bool check_time) {
395 if (SafepointALot) {
396 _no_op_reason = "SafepointALot";
397 return true;
398 }
399 if (!SafepointSynchronize::is_cleanup_needed()) {
400 return false;
401 }
402 if (check_time) {
403 long interval = SafepointSynchronize::last_non_safepoint_interval();
404 bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
405 (interval > GuaranteedSafepointInterval);
406 if (!max_time_exceeded) {
407 return false;
408 }
409 }
410 _no_op_reason = "Cleanup";
411 return true;
412 }
413
414 void VMThread::loop() {
415 assert(_cur_vm_operation == NULL, "no current one should be executing");
416
417 while(true) {
418 VM_Operation* safepoint_ops = NULL;
419 //
420 // Wait for VM operation
421 //
422 // use no_safepoint_check to get lock without attempting to "sneak"
423 { MutexLockerEx mu_queue(VMOperationQueue_lock,
424 Mutex::_no_safepoint_check_flag);
425
426 // Look for new operation
427 assert(_cur_vm_operation == NULL, "no current one should be executing");
428 _cur_vm_operation = _vm_queue->remove_next();
429
430 // Stall time tracking code
431 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
432 !_cur_vm_operation->evaluate_concurrently()) {
433 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
434 if (stall > 0)
435 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall);
436 }
437
438 while (!should_terminate() && _cur_vm_operation == NULL) {
439 // wait with a timeout to guarantee safepoints at regular intervals
440 bool timedout =
441 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
442 GuaranteedSafepointInterval);
443
444 // Support for self destruction
445 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() &&
446 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
447 tty->print_cr("VM self-destructed");
448 exit(-1);
449 }
450
451 if (timedout && VMThread::no_op_safepoint_needed(false)) {
452 MutexUnlockerEx mul(VMOperationQueue_lock,
453 Mutex::_no_safepoint_check_flag);
454 // Force a safepoint since we have not had one for at least
455 // 'GuaranteedSafepointInterval' milliseconds. This will run all
456 // the clean-up processing that needs to be done regularly at a
457 // safepoint
458 SafepointSynchronize::begin();
459 #ifdef ASSERT
460 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
461 #endif
462 SafepointSynchronize::end();
463 }
464 _cur_vm_operation = _vm_queue->remove_next();
465
466 // If we are at a safepoint we will evaluate all the operations that
467 // follow that also require a safepoint
468 if (_cur_vm_operation != NULL &&
469 _cur_vm_operation->evaluate_at_safepoint()) {
470 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
471 }
472 }
473
474 if (should_terminate()) break;
475 } // Release mu_queue_lock
476
477 //
478 // Execute VM operation
479 //
480 { HandleMark hm(VMThread::vm_thread());
481
482 EventMark em("Executing VM operation: %s", vm_operation()->name());
483 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
484
485 // If we are at a safepoint we will evaluate all the operations that
486 // follow that also require a safepoint
487 if (_cur_vm_operation->evaluate_at_safepoint()) {
488 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name());
489
490 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
491
492 SafepointSynchronize::begin();
493 evaluate_operation(_cur_vm_operation);
494 // now process all queued safepoint ops, iteratively draining
495 // the queue until there are none left
496 do {
497 _cur_vm_operation = safepoint_ops;
498 if (_cur_vm_operation != NULL) {
499 do {
500 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name());
501 // evaluate_operation deletes the op object so we have
502 // to grab the next op now
503 VM_Operation* next = _cur_vm_operation->next();
504 _vm_queue->set_drain_list(next);
505 evaluate_operation(_cur_vm_operation);
506 _cur_vm_operation = next;
507 if (log_is_enabled(Debug, safepoint, stats)) {
508 SafepointSynchronize::inc_vmop_coalesced_count();
509 }
510 } while (_cur_vm_operation != NULL);
511 }
512 // There is a chance that a thread enqueued a safepoint op
513 // since we released the op-queue lock and initiated the safepoint.
514 // So we drain the queue again if there is anything there, as an
515 // optimization to try and reduce the number of safepoints.
516 // As the safepoint synchronizes us with JavaThreads we will see
517 // any enqueue made by a JavaThread, but the peek will not
518 // necessarily detect a concurrent enqueue by a GC thread, but
519 // that simply means the op will wait for the next major cycle of the
520 // VMThread - just as it would if the GC thread lost the race for
521 // the lock.
522 if (_vm_queue->peek_at_safepoint_priority()) {
523 // must hold lock while draining queue
524 MutexLockerEx mu_queue(VMOperationQueue_lock,
525 Mutex::_no_safepoint_check_flag);
526 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
527 } else {
528 safepoint_ops = NULL;
529 }
530 } while(safepoint_ops != NULL);
531
532 _vm_queue->set_drain_list(NULL);
533
534 // Complete safepoint synchronization
535 SafepointSynchronize::end();
536
537 } else { // not a safepoint operation
538 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name());
539 if (TraceLongCompiles) {
540 elapsedTimer t;
541 t.start();
542 evaluate_operation(_cur_vm_operation);
543 t.stop();
544 double secs = t.seconds();
545 if (secs * 1e3 > LongCompileThreshold) {
546 // XXX - _cur_vm_operation should not be accessed after
547 // the completed count has been incremented; the waiting
548 // thread may have already freed this memory.
549 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
550 }
551 } else {
552 evaluate_operation(_cur_vm_operation);
553 }
554
555 _cur_vm_operation = NULL;
556 }
557 }
558
559 //
560 // Notify (potential) waiting Java thread(s) - lock without safepoint
561 // check so that sneaking is not possible
562 { MutexLockerEx mu(VMOperationRequest_lock,
563 Mutex::_no_safepoint_check_flag);
564 VMOperationRequest_lock->notify_all();
565 }
566
567 //
568 // We want to make sure that we get to a safepoint regularly.
569 //
570 if (VMThread::no_op_safepoint_needed(true)) {
571 HandleMark hm(VMThread::vm_thread());
572 SafepointSynchronize::begin();
573 SafepointSynchronize::end();
574 }
575 }
576 }
577
578 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
579 // over a section of execution by a thread. Currently, it's used only to
580 // prevent re-entrant calls to GC.
581 class SkipGCALot : public StackObj {
582 private:
583 bool _saved;
584 Thread* _t;
585
586 public:
587 #ifdef ASSERT
588 SkipGCALot(Thread* t) : _t(t) {
589 _saved = _t->skip_gcalot();
590 _t->set_skip_gcalot(true);
591 }
592
593 ~SkipGCALot() {
594 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
595 _t->set_skip_gcalot(_saved);
596 }
597 #else
598 SkipGCALot(Thread* t) { }
599 ~SkipGCALot() { }
600 #endif
601 };
602
603 void VMThread::execute(VM_Operation* op) {
604 Thread* t = Thread::current();
605
606 if (!t->is_VM_thread()) {
607 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
608 // JavaThread or WatcherThread
609 bool concurrent = op->evaluate_concurrently();
610 // only blocking VM operations need to verify the caller's safepoint state:
611 if (!concurrent) {
612 t->check_for_valid_safepoint_state(true);
613 }
614
615 // New request from Java thread, evaluate prologue
616 if (!op->doit_prologue()) {
617 return; // op was cancelled
618 }
619
620 // Setup VM_operations for execution
621 op->set_calling_thread(t, Thread::get_priority(t));
622
623 // It does not make sense to execute the epilogue, if the VM operation object is getting
624 // deallocated by the VM thread.
625 bool execute_epilog = !op->is_cheap_allocated();
626 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
627
628 // Get ticket number for non-concurrent VM operations
629 int ticket = 0;
630 if (!concurrent) {
631 ticket = t->vm_operation_ticket();
632 }
633
634 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
635 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
636 // to be queued up during a safepoint synchronization.
637 {
638 VMOperationQueue_lock->lock_without_safepoint_check();
639 log_debug(vmthread)("Adding VM operation: %s", op->name());
640 bool ok = _vm_queue->add(op);
641 op->set_timestamp(os::javaTimeMillis());
642 VMOperationQueue_lock->notify();
643 VMOperationQueue_lock->unlock();
644 // VM_Operation got skipped
645 if (!ok) {
646 assert(concurrent, "can only skip concurrent tasks");
647 if (op->is_cheap_allocated()) delete op;
648 return;
649 }
650 }
651
652 if (!concurrent) {
653 // Wait for completion of request (non-concurrent)
654 // Note: only a JavaThread triggers the safepoint check when locking
655 MutexLocker mu(VMOperationRequest_lock);
656 while(t->vm_operation_completed_count() < ticket) {
657 VMOperationRequest_lock->wait(!t->is_Java_thread());
658 }
659 }
660
661 if (execute_epilog) {
662 op->doit_epilogue();
663 }
664 } else {
665 // invoked by VM thread; usually nested VM operation
666 assert(t->is_VM_thread(), "must be a VM thread");
667 VM_Operation* prev_vm_operation = vm_operation();
668 if (prev_vm_operation != NULL) {
669 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
670 // does not allow nested scavenges or compiles.
671 if (!prev_vm_operation->allow_nested_vm_operations()) {
672 fatal("Nested VM operation %s requested by operation %s",
673 op->name(), vm_operation()->name());
674 }
675 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
676 }
677
678 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
679
680 // Release all internal handles after operation is evaluated
681 HandleMark hm(t);
682 _cur_vm_operation = op;
683
684 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
685 SafepointSynchronize::begin();
686 op->evaluate();
687 SafepointSynchronize::end();
688 } else {
689 op->evaluate();
690 }
691
692 // Free memory if needed
693 if (op->is_cheap_allocated()) delete op;
694
695 _cur_vm_operation = prev_vm_operation;
696 }
697 }
698
699
700 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
701 Thread::oops_do(f, cf);
702 _vm_queue->oops_do(f);
703 }
704
705 //------------------------------------------------------------------------------------------------------------------
706 #ifndef PRODUCT
707
708 void VMOperationQueue::verify_queue(int prio) {
709 // Check that list is correctly linked
710 int length = _queue_length[prio];
711 VM_Operation *cur = _queue[prio];
712 int i;
713
714 // Check forward links
715 for(i = 0; i < length; i++) {
716 cur = cur->next();
717 assert(cur != _queue[prio], "list to short (forward)");
718 }
719 assert(cur->next() == _queue[prio], "list to long (forward)");
720
721 // Check backwards links
722 cur = _queue[prio];
723 for(i = 0; i < length; i++) {
724 cur = cur->prev();
725 assert(cur != _queue[prio], "list to short (backwards)");
726 }
727 assert(cur->prev() == _queue[prio], "list to long (backwards)");
728 }
729
730 #endif
731
732 void VMThread::verify() {
733 oops_do(&VerifyOopClosure::verify_oop, NULL);
734 }