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/logStream.hpp"
32 #include "logging/logConfiguration.hpp"
33 #include "memory/resourceArea.hpp"
34 #include "oops/method.hpp"
35 #include "oops/oop.inline.hpp"
36 #include "oops/verifyOopClosure.hpp"
37 #include "runtime/interfaceSupport.inline.hpp"
38 #include "runtime/mutexLocker.hpp"
39 #include "runtime/os.hpp"
40 #include "runtime/safepoint.hpp"
41 #include "runtime/thread.inline.hpp"
42 #include "runtime/vmThread.hpp"
43 #include "runtime/vmOperations.hpp"
44 #include "services/runtimeService.hpp"
45 #include "utilities/dtrace.hpp"
46 #include "utilities/events.hpp"
47 #include "utilities/vmError.hpp"
48 #include "utilities/xmlstream.hpp"
49
50 // Dummy VM operation to act as first element in our circular double-linked list
51 class VM_None: public VM_Operation {
52 VMOp_Type type() const { return VMOp_None; }
53 void doit() {};
54 };
55
56 VMOperationQueue::VMOperationQueue() {
57 // The queue is a circular doubled-linked list, which always contains
58 // one element (i.e., one element means empty).
59 for(int i = 0; i < nof_priorities; i++) {
60 _queue_length[i] = 0;
61 _queue_counter = 0;
62 _queue[i] = new VM_None();
63 _queue[i]->set_next(_queue[i]);
64 _queue[i]->set_prev(_queue[i]);
65 }
66 _drain_list = NULL;
67 }
68
69
70 bool VMOperationQueue::queue_empty(int prio) {
71 // It is empty if there is exactly one element
72 bool empty = (_queue[prio] == _queue[prio]->next());
73 assert( (_queue_length[prio] == 0 && empty) ||
74 (_queue_length[prio] > 0 && !empty), "sanity check");
75 return _queue_length[prio] == 0;
76 }
77
78 // Inserts an element to the right of the q element
79 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
80 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
81 n->set_prev(q);
82 n->set_next(q->next());
83 q->next()->set_prev(n);
84 q->set_next(n);
85 }
86
87 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
88 _queue_length[prio]++;
89 insert(_queue[prio]->next(), op);
90 }
91
92 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
93 _queue_length[prio]++;
94 insert(_queue[prio]->prev(), op);
95 }
96
97
98 void VMOperationQueue::unlink(VM_Operation* q) {
99 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
100 q->prev()->set_next(q->next());
101 q->next()->set_prev(q->prev());
102 }
103
104 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
105 if (queue_empty(prio)) return NULL;
106 assert(_queue_length[prio] >= 0, "sanity check");
107 _queue_length[prio]--;
108 VM_Operation* r = _queue[prio]->next();
109 assert(r != _queue[prio], "cannot remove base element");
110 unlink(r);
111 return r;
112 }
113
114 VM_Operation* VMOperationQueue::queue_drain(int prio) {
115 if (queue_empty(prio)) return NULL;
116 DEBUG_ONLY(int length = _queue_length[prio];);
117 assert(length >= 0, "sanity check");
118 _queue_length[prio] = 0;
119 VM_Operation* r = _queue[prio]->next();
120 assert(r != _queue[prio], "cannot remove base element");
121 // remove links to base element from head and tail
122 r->set_prev(NULL);
123 _queue[prio]->prev()->set_next(NULL);
124 // restore queue to empty state
125 _queue[prio]->set_next(_queue[prio]);
126 _queue[prio]->set_prev(_queue[prio]);
127 assert(queue_empty(prio), "drain corrupted queue");
128 #ifdef ASSERT
129 int len = 0;
130 VM_Operation* cur;
131 for(cur = r; cur != NULL; cur=cur->next()) len++;
132 assert(len == length, "drain lost some ops");
133 #endif
134 return r;
135 }
136
137 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
138 VM_Operation* cur = _queue[queue];
139 cur = cur->next();
140 while (cur != _queue[queue]) {
141 cur->oops_do(f);
142 cur = cur->next();
143 }
144 }
145
146 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
147 VM_Operation* cur = _drain_list;
148 while (cur != NULL) {
149 cur->oops_do(f);
150 cur = cur->next();
151 }
152 }
153
154 //-----------------------------------------------------------------
155 // High-level interface
156 bool VMOperationQueue::add(VM_Operation *op) {
157
158 HOTSPOT_VMOPS_REQUEST(
159 (char *) op->name(), strlen(op->name()),
160 op->evaluation_mode());
161
162 // Encapsulates VM queue policy. Currently, that
163 // only involves putting them on the right list
164 if (op->evaluate_at_safepoint()) {
165 queue_add_back(SafepointPriority, op);
166 return true;
167 }
168
169 queue_add_back(MediumPriority, op);
170 return true;
171 }
172
173 VM_Operation* VMOperationQueue::remove_next() {
174 // Assuming VMOperation queue is two-level priority queue. If there are
175 // more than two priorities, we need a different scheduling algorithm.
176 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
177 "current algorithm does not work");
178
179 // simple counter based scheduling to prevent starvation of lower priority
180 // queue. -- see 4390175
181 int high_prio, low_prio;
182 if (_queue_counter++ < 10) {
183 high_prio = SafepointPriority;
184 low_prio = MediumPriority;
185 } else {
186 _queue_counter = 0;
187 high_prio = MediumPriority;
188 low_prio = SafepointPriority;
189 }
190
191 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
192 }
193
194 void VMOperationQueue::oops_do(OopClosure* f) {
195 for(int i = 0; i < nof_priorities; i++) {
196 queue_oops_do(i, f);
197 }
198 drain_list_oops_do(f);
199 }
200
201 //------------------------------------------------------------------------------------------------------------------
202 // Timeout machinery
203
204 void VMOperationTimeoutTask::task() {
205 assert(AbortVMOnVMOperationTimeout, "only if enabled");
206 if (is_armed()) {
207 jlong delay = (os::javaTimeMillis() - _arm_time);
208 if (delay > AbortVMOnVMOperationTimeoutDelay) {
209 fatal("VM operation took too long: " SIZE_FORMAT " ms (timeout: " SIZE_FORMAT " ms)",
210 delay, AbortVMOnVMOperationTimeoutDelay);
211 }
212 }
213 }
214
215 bool VMOperationTimeoutTask::is_armed() {
216 return OrderAccess::load_acquire(&_armed) != 0;
217 }
218
219 void VMOperationTimeoutTask::arm() {
220 _arm_time = os::javaTimeMillis();
221 OrderAccess::release_store_fence(&_armed, 1);
222 }
223
224 void VMOperationTimeoutTask::disarm() {
225 OrderAccess::release_store_fence(&_armed, 0);
226 }
227
228 //------------------------------------------------------------------------------------------------------------------
229 // Implementation of VMThread stuff
230
231 bool VMThread::_should_terminate = false;
232 bool VMThread::_terminated = false;
233 Monitor* VMThread::_terminate_lock = NULL;
234 VMThread* VMThread::_vm_thread = NULL;
235 VM_Operation* VMThread::_cur_vm_operation = NULL;
236 VMOperationQueue* VMThread::_vm_queue = NULL;
237 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
238 const char* VMThread::_no_op_reason = NULL;
239 VMOperationTimeoutTask* VMThread::_timeout_task = NULL;
240
241
242 void VMThread::create() {
243 assert(vm_thread() == NULL, "we can only allocate one VMThread");
244 _vm_thread = new VMThread();
245
246 if (AbortVMOnVMOperationTimeout) {
247 // Make sure we call the timeout task frequently enough, but not too frequent.
248 // Try to make the interval 10% of the timeout delay, so that we miss the timeout
249 // by those 10% at max. Periodic task also expects it to fit min/max intervals.
250 size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10;
251 interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran;
252 interval = MAX2<size_t>(interval, PeriodicTask::min_interval);
253 interval = MIN2<size_t>(interval, PeriodicTask::max_interval);
254
255 _timeout_task = new VMOperationTimeoutTask(interval);
256 _timeout_task->enroll();
257 } else {
258 assert(_timeout_task == NULL, "sanity");
259 }
260
261 // Create VM operation queue
262 _vm_queue = new VMOperationQueue();
263 guarantee(_vm_queue != NULL, "just checking");
264
265 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
266 Monitor::_safepoint_check_never);
267
268 if (UsePerfData) {
269 // jvmstat performance counters
270 Thread* THREAD = Thread::current();
271 _perf_accumulated_vm_operation_time =
272 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
273 PerfData::U_Ticks, CHECK);
274 }
275 }
276
277 VMThread::VMThread() : NamedThread() {
278 set_name("VM Thread");
279 }
280
281 void VMThread::destroy() {
282 _vm_thread = NULL; // VM thread is gone
283 }
284
285 void VMThread::run() {
286 assert(this == vm_thread(), "check");
287
288 // Notify_lock wait checks on active_handles() to rewait in
289 // case of spurious wakeup, it should wait on the last
290 // value set prior to the notify
291 this->set_active_handles(JNIHandleBlock::allocate_block());
292
293 {
294 MutexLocker ml(Notify_lock);
295 Notify_lock->notify();
296 }
297 // Notify_lock is destroyed by Threads::create_vm()
298
299 int prio = (VMThreadPriority == -1)
300 ? os::java_to_os_priority[NearMaxPriority]
301 : VMThreadPriority;
302 // Note that I cannot call os::set_priority because it expects Java
303 // priorities and I am *explicitly* using OS priorities so that it's
304 // possible to set the VM thread priority higher than any Java thread.
305 os::set_native_priority( this, prio );
306
307 // Wait for VM_Operations until termination
308 this->loop();
309
310 // Note the intention to exit before safepointing.
311 // 6295565 This has the effect of waiting for any large tty
312 // outputs to finish.
313 if (xtty != NULL) {
314 ttyLocker ttyl;
315 xtty->begin_elem("destroy_vm");
316 xtty->stamp();
317 xtty->end_elem();
318 assert(should_terminate(), "termination flag must be set");
319 }
320
321 // 4526887 let VM thread exit at Safepoint
322 _no_op_reason = "Halt";
323 SafepointSynchronize::begin();
324
325 if (VerifyBeforeExit) {
326 HandleMark hm(VMThread::vm_thread());
327 // Among other things, this ensures that Eden top is correct.
328 Universe::heap()->prepare_for_verify();
329 // Silent verification so as not to pollute normal output,
330 // unless we really asked for it.
331 Universe::verify();
332 }
333
334 CompileBroker::set_should_block();
335
336 // wait for threads (compiler threads or daemon threads) in the
337 // _thread_in_native state to block.
338 VM_Exit::wait_for_threads_in_native_to_block();
339
340 // signal other threads that VM process is gone
341 {
342 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
343 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
344 // If that happens after _terminate_lock->wait() has unset _owner
345 // but before it actually drops the lock and waits, the notification below
346 // may get lost and we will have a hang. To avoid this, we need to use
347 // Mutex::lock_without_safepoint_check().
348 MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
349 _terminated = true;
350 _terminate_lock->notify();
351 }
352
353 // We are now racing with the VM termination being carried out in
354 // another thread, so we don't "delete this". Numerous threads don't
355 // get deleted when the VM terminates
356
357 }
358
359
360 // Notify the VMThread that the last non-daemon JavaThread has terminated,
361 // and wait until operation is performed.
362 void VMThread::wait_for_vm_thread_exit() {
363 assert(Thread::current()->is_Java_thread(), "Should be a JavaThread");
364 assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated");
365 { MutexLockerEx mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
366 _should_terminate = true;
367 VMOperationQueue_lock->notify();
368 }
369
370 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
371 // because this thread has been removed from the threads list. But anything
372 // that could get blocked by Safepoint should not be used after this point,
373 // otherwise we will hang, since there is no one can end the safepoint.
374
375 // Wait until VM thread is terminated
376 // Note: it should be OK to use Terminator_lock here. But this is called
377 // at a very delicate time (VM shutdown) and we are operating in non- VM
378 // thread at Safepoint. It's safer to not share lock with other threads.
379 { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
380 while(!VMThread::is_terminated()) {
381 _terminate_lock->wait(Mutex::_no_safepoint_check_flag);
382 }
383 }
384 }
385
386 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
387 assert(event != NULL, "invariant");
388 assert(event->should_commit(), "invariant");
389 assert(op != NULL, "invariant");
390 const bool is_concurrent = op->evaluate_concurrently();
391 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
392 event->set_operation(op->type());
393 event->set_safepoint(evaluate_at_safepoint);
394 event->set_blocking(!is_concurrent);
395 // Only write caller thread information for non-concurrent vm operations.
396 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
397 // This is because the caller thread could have exited already.
398 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread()));
399 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_counter() : 0);
400 event->commit();
401 }
402
403 void VMThread::evaluate_operation(VM_Operation* op) {
404 ResourceMark rm;
405
406 {
407 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
408 HOTSPOT_VMOPS_BEGIN(
409 (char *) op->name(), strlen(op->name()),
410 op->evaluation_mode());
411
412 EventExecuteVMOperation event;
413 op->evaluate();
414 if (event.should_commit()) {
415 post_vm_operation_event(&event, op);
416 }
417
418 HOTSPOT_VMOPS_END(
419 (char *) op->name(), strlen(op->name()),
420 op->evaluation_mode());
421 }
422
423 // Last access of info in _cur_vm_operation!
424 bool c_heap_allocated = op->is_cheap_allocated();
425
426 // Mark as completed
427 if (!op->evaluate_concurrently()) {
428 op->calling_thread()->increment_vm_operation_completed_count();
429 }
430 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
431 // since if it is stack allocated the calling thread might have deallocated
432 if (c_heap_allocated) {
433 delete _cur_vm_operation;
434 }
435 }
436
437 bool VMThread::no_op_safepoint_needed(bool check_time) {
438 if (SafepointALot) {
439 _no_op_reason = "SafepointALot";
440 return true;
441 }
442 if (!SafepointSynchronize::is_cleanup_needed()) {
443 return false;
444 }
445 if (check_time) {
446 long interval = SafepointSynchronize::last_non_safepoint_interval();
447 bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
448 (interval > GuaranteedSafepointInterval);
449 if (!max_time_exceeded) {
450 return false;
451 }
452 }
453 _no_op_reason = "Cleanup";
454 return true;
455 }
456
457 void VMThread::loop() {
458 assert(_cur_vm_operation == NULL, "no current one should be executing");
459
460 while(true) {
461 VM_Operation* safepoint_ops = NULL;
462 //
463 // Wait for VM operation
464 //
465 // use no_safepoint_check to get lock without attempting to "sneak"
466 { MutexLockerEx mu_queue(VMOperationQueue_lock,
467 Mutex::_no_safepoint_check_flag);
468
469 // Look for new operation
470 assert(_cur_vm_operation == NULL, "no current one should be executing");
471 _cur_vm_operation = _vm_queue->remove_next();
472
473 // Stall time tracking code
474 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
475 !_cur_vm_operation->evaluate_concurrently()) {
476 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
477 if (stall > 0)
478 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall);
479 }
480
481 while (!should_terminate() && _cur_vm_operation == NULL) {
482 // wait with a timeout to guarantee safepoints at regular intervals
483 bool timedout =
484 VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,
485 GuaranteedSafepointInterval);
486
487 // Support for self destruction
488 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() &&
489 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
490 tty->print_cr("VM self-destructed");
491 exit(-1);
492 }
493
494 if (timedout && VMThread::no_op_safepoint_needed(false)) {
495 MutexUnlockerEx mul(VMOperationQueue_lock,
496 Mutex::_no_safepoint_check_flag);
497 // Force a safepoint since we have not had one for at least
498 // 'GuaranteedSafepointInterval' milliseconds. This will run all
499 // the clean-up processing that needs to be done regularly at a
500 // safepoint
501 SafepointSynchronize::begin();
502 #ifdef ASSERT
503 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
504 #endif
505 SafepointSynchronize::end();
506 }
507 _cur_vm_operation = _vm_queue->remove_next();
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 != NULL &&
512 _cur_vm_operation->evaluate_at_safepoint()) {
513 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
514 }
515 }
516
517 if (should_terminate()) break;
518 } // Release mu_queue_lock
519
520 //
521 // Execute VM operation
522 //
523 { HandleMark hm(VMThread::vm_thread());
524
525 EventMark em("Executing VM operation: %s", vm_operation()->name());
526 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
527
528 // If we are at a safepoint we will evaluate all the operations that
529 // follow that also require a safepoint
530 if (_cur_vm_operation->evaluate_at_safepoint()) {
531 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name());
532
533 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
534
535 SafepointSynchronize::begin();
536
537 if (_timeout_task != NULL) {
538 _timeout_task->arm();
539 }
540
541 evaluate_operation(_cur_vm_operation);
542 // now process all queued safepoint ops, iteratively draining
543 // the queue until there are none left
544 do {
545 _cur_vm_operation = safepoint_ops;
546 if (_cur_vm_operation != NULL) {
547 do {
548 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name());
549 // evaluate_operation deletes the op object so we have
550 // to grab the next op now
551 VM_Operation* next = _cur_vm_operation->next();
552 _vm_queue->set_drain_list(next);
553 evaluate_operation(_cur_vm_operation);
554 _cur_vm_operation = next;
555 if (log_is_enabled(Debug, safepoint, stats)) {
556 SafepointSynchronize::inc_vmop_coalesced_count();
557 }
558 } while (_cur_vm_operation != NULL);
559 }
560 // There is a chance that a thread enqueued a safepoint op
561 // since we released the op-queue lock and initiated the safepoint.
562 // So we drain the queue again if there is anything there, as an
563 // optimization to try and reduce the number of safepoints.
564 // As the safepoint synchronizes us with JavaThreads we will see
565 // any enqueue made by a JavaThread, but the peek will not
566 // necessarily detect a concurrent enqueue by a GC thread, but
567 // that simply means the op will wait for the next major cycle of the
568 // VMThread - just as it would if the GC thread lost the race for
569 // the lock.
570 if (_vm_queue->peek_at_safepoint_priority()) {
571 // must hold lock while draining queue
572 MutexLockerEx mu_queue(VMOperationQueue_lock,
573 Mutex::_no_safepoint_check_flag);
574 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
575 } else {
576 safepoint_ops = NULL;
577 }
578 } while(safepoint_ops != NULL);
579
580 _vm_queue->set_drain_list(NULL);
581
582 if (_timeout_task != NULL) {
583 _timeout_task->disarm();
584 }
585
586 // Complete safepoint synchronization
587 SafepointSynchronize::end();
588
589 } else { // not a safepoint operation
590 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name());
591 if (TraceLongCompiles) {
592 elapsedTimer t;
593 t.start();
594 evaluate_operation(_cur_vm_operation);
595 t.stop();
596 double secs = t.seconds();
597 if (secs * 1e3 > LongCompileThreshold) {
598 // XXX - _cur_vm_operation should not be accessed after
599 // the completed count has been incremented; the waiting
600 // thread may have already freed this memory.
601 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
602 }
603 } else {
604 evaluate_operation(_cur_vm_operation);
605 }
606
607 _cur_vm_operation = NULL;
608 }
609 }
610
611 //
612 // Notify (potential) waiting Java thread(s) - lock without safepoint
613 // check so that sneaking is not possible
614 { MutexLockerEx mu(VMOperationRequest_lock,
615 Mutex::_no_safepoint_check_flag);
616 VMOperationRequest_lock->notify_all();
617 }
618
619 //
620 // We want to make sure that we get to a safepoint regularly.
621 //
622 if (VMThread::no_op_safepoint_needed(true)) {
623 HandleMark hm(VMThread::vm_thread());
624 SafepointSynchronize::begin();
625 SafepointSynchronize::end();
626 }
627 }
628 }
629
630 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
631 // over a section of execution by a thread. Currently, it's used only to
632 // prevent re-entrant calls to GC.
633 class SkipGCALot : public StackObj {
634 private:
635 bool _saved;
636 Thread* _t;
637
638 public:
639 #ifdef ASSERT
640 SkipGCALot(Thread* t) : _t(t) {
641 _saved = _t->skip_gcalot();
642 _t->set_skip_gcalot(true);
643 }
644
645 ~SkipGCALot() {
646 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
647 _t->set_skip_gcalot(_saved);
648 }
649 #else
650 SkipGCALot(Thread* t) { }
651 ~SkipGCALot() { }
652 #endif
653 };
654
655 void VMThread::execute(VM_Operation* op) {
656 Thread* t = Thread::current();
657
658 if (!t->is_VM_thread()) {
659 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
660 // JavaThread or WatcherThread
661 bool concurrent = op->evaluate_concurrently();
662 // only blocking VM operations need to verify the caller's safepoint state:
663 if (!concurrent) {
664 t->check_for_valid_safepoint_state(true);
665 }
666
667 // New request from Java thread, evaluate prologue
668 if (!op->doit_prologue()) {
669 return; // op was cancelled
670 }
671
672 // Setup VM_operations for execution
673 op->set_calling_thread(t, Thread::get_priority(t));
674
675 // It does not make sense to execute the epilogue, if the VM operation object is getting
676 // deallocated by the VM thread.
677 bool execute_epilog = !op->is_cheap_allocated();
678 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
679
680 // Get ticket number for non-concurrent VM operations
681 int ticket = 0;
682 if (!concurrent) {
683 ticket = t->vm_operation_ticket();
684 }
685
686 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
687 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
688 // to be queued up during a safepoint synchronization.
689 {
690 VMOperationQueue_lock->lock_without_safepoint_check();
691 log_debug(vmthread)("Adding VM operation: %s", op->name());
692 bool ok = _vm_queue->add(op);
693 op->set_timestamp(os::javaTimeMillis());
694 VMOperationQueue_lock->notify();
695 VMOperationQueue_lock->unlock();
696 // VM_Operation got skipped
697 if (!ok) {
698 assert(concurrent, "can only skip concurrent tasks");
699 if (op->is_cheap_allocated()) delete op;
700 return;
701 }
702 }
703
704 if (!concurrent) {
705 // Wait for completion of request (non-concurrent)
706 // Note: only a JavaThread triggers the safepoint check when locking
707 MutexLocker mu(VMOperationRequest_lock);
708 while(t->vm_operation_completed_count() < ticket) {
709 VMOperationRequest_lock->wait(!t->is_Java_thread());
710 }
711 }
712
713 if (execute_epilog) {
714 op->doit_epilogue();
715 }
716 } else {
717 // invoked by VM thread; usually nested VM operation
718 assert(t->is_VM_thread(), "must be a VM thread");
719 VM_Operation* prev_vm_operation = vm_operation();
720 if (prev_vm_operation != NULL) {
721 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
722 // does not allow nested scavenges or compiles.
723 if (!prev_vm_operation->allow_nested_vm_operations()) {
724 fatal("Nested VM operation %s requested by operation %s",
725 op->name(), vm_operation()->name());
726 }
727 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
728 }
729
730 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
731
732 // Release all internal handles after operation is evaluated
733 HandleMark hm(t);
734 _cur_vm_operation = op;
735
736 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
737 SafepointSynchronize::begin();
738 op->evaluate();
739 SafepointSynchronize::end();
740 } else {
741 op->evaluate();
742 }
743
744 // Free memory if needed
745 if (op->is_cheap_allocated()) delete op;
746
747 _cur_vm_operation = prev_vm_operation;
748 }
749 }
750
751
752 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
753 Thread::oops_do(f, cf);
754 _vm_queue->oops_do(f);
755 }
756
757 //------------------------------------------------------------------------------------------------------------------
758 #ifndef PRODUCT
759
760 void VMOperationQueue::verify_queue(int prio) {
761 // Check that list is correctly linked
762 int length = _queue_length[prio];
763 VM_Operation *cur = _queue[prio];
764 int i;
765
766 // Check forward links
767 for(i = 0; i < length; i++) {
768 cur = cur->next();
769 assert(cur != _queue[prio], "list to short (forward)");
770 }
771 assert(cur->next() == _queue[prio], "list to long (forward)");
772
773 // Check backwards links
774 cur = _queue[prio];
775 for(i = 0; i < length; i++) {
776 cur = cur->prev();
777 assert(cur != _queue[prio], "list to short (backwards)");
778 }
779 assert(cur->prev() == _queue[prio], "list to long (backwards)");
780 }
781
782 #endif
783
784 void VMThread::verify() {
785 oops_do(&VerifyOopClosure::verify_oop, NULL);
786 }