1 /*
2 * Copyright (c) 1998, 2019, 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 "memory/universe.hpp"
35 #include "oops/method.hpp"
36 #include "oops/oop.inline.hpp"
37 #include "oops/verifyOopClosure.hpp"
38 #include "runtime/handles.inline.hpp"
39 #include "runtime/interfaceSupport.inline.hpp"
40 #include "runtime/mutexLocker.hpp"
41 #include "runtime/os.hpp"
42 #include "runtime/safepoint.hpp"
43 #include "runtime/thread.inline.hpp"
44 #include "runtime/vmThread.hpp"
45 #include "runtime/vmOperations.hpp"
46 #include "services/runtimeService.hpp"
47 #include "utilities/dtrace.hpp"
48 #include "utilities/events.hpp"
49 #include "utilities/vmError.hpp"
50 #include "utilities/xmlstream.hpp"
51
52 VM_QueueHead VMOperationQueue::_queue_head[VMOperationQueue::nof_priorities];
53
54 VMOperationQueue::VMOperationQueue() {
55 // The queue is a circular doubled-linked list, which always contains
56 // one element (i.e., one element means empty).
57 for(int i = 0; i < nof_priorities; i++) {
58 _queue_length[i] = 0;
59 _queue_counter = 0;
60 _queue[i] = &_queue_head[i];
61 _queue[i]->set_next(_queue[i]);
62 _queue[i]->set_prev(_queue[i]);
63 }
64 _drain_list = NULL;
65 }
66
67
68 bool VMOperationQueue::queue_empty(int prio) {
69 // It is empty if there is exactly one element
70 bool empty = (_queue[prio] == _queue[prio]->next());
71 assert( (_queue_length[prio] == 0 && empty) ||
72 (_queue_length[prio] > 0 && !empty), "sanity check");
73 return _queue_length[prio] == 0;
74 }
75
76 // Inserts an element to the right of the q element
77 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
78 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
79 n->set_prev(q);
80 n->set_next(q->next());
81 q->next()->set_prev(n);
82 q->set_next(n);
83 }
84
85 void VMOperationQueue::queue_add(int prio, VM_Operation *op) {
86 _queue_length[prio]++;
87 insert(_queue[prio]->prev(), op);
88 }
89
90
91 void VMOperationQueue::unlink(VM_Operation* q) {
92 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
93 q->prev()->set_next(q->next());
94 q->next()->set_prev(q->prev());
95 }
96
97 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
98 if (queue_empty(prio)) return NULL;
99 assert(_queue_length[prio] >= 0, "sanity check");
100 _queue_length[prio]--;
101 VM_Operation* r = _queue[prio]->next();
102 assert(r != _queue[prio], "cannot remove base element");
103 unlink(r);
104 return r;
105 }
106
107 VM_Operation* VMOperationQueue::queue_drain(int prio) {
108 if (queue_empty(prio)) return NULL;
109 DEBUG_ONLY(int length = _queue_length[prio];);
110 assert(length >= 0, "sanity check");
111 _queue_length[prio] = 0;
112 VM_Operation* r = _queue[prio]->next();
113 assert(r != _queue[prio], "cannot remove base element");
114 // remove links to base element from head and tail
115 r->set_prev(NULL);
116 _queue[prio]->prev()->set_next(NULL);
117 // restore queue to empty state
118 _queue[prio]->set_next(_queue[prio]);
119 _queue[prio]->set_prev(_queue[prio]);
120 assert(queue_empty(prio), "drain corrupted queue");
121 #ifdef ASSERT
122 int len = 0;
123 VM_Operation* cur;
124 for(cur = r; cur != NULL; cur=cur->next()) len++;
125 assert(len == length, "drain lost some ops");
126 #endif
127 return r;
128 }
129
130 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
131 VM_Operation* cur = _queue[queue];
132 cur = cur->next();
133 while (cur != _queue[queue]) {
134 cur->oops_do(f);
135 cur = cur->next();
136 }
137 }
138
139 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
140 VM_Operation* cur = _drain_list;
141 while (cur != NULL) {
142 cur->oops_do(f);
143 cur = cur->next();
144 }
145 }
146
147 //-----------------------------------------------------------------
148 // High-level interface
149 void VMOperationQueue::add(VM_Operation *op) {
150
151 HOTSPOT_VMOPS_REQUEST(
152 (char *) op->name(), strlen(op->name()),
153 op->evaluate_at_safepoint() ? 0 : 1);
154
155 // Encapsulates VM queue policy. Currently, that
156 // only involves putting them on the right list
157 queue_add(op->evaluate_at_safepoint() ? SafepointPriority : MediumPriority, op);
158 }
159
160 VM_Operation* VMOperationQueue::remove_next() {
161 // Assuming VMOperation queue is two-level priority queue. If there are
162 // more than two priorities, we need a different scheduling algorithm.
163 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
164 "current algorithm does not work");
165
166 // simple counter based scheduling to prevent starvation of lower priority
167 // queue. -- see 4390175
168 int high_prio, low_prio;
169 if (_queue_counter++ < 10) {
170 high_prio = SafepointPriority;
171 low_prio = MediumPriority;
172 } else {
173 _queue_counter = 0;
174 high_prio = MediumPriority;
175 low_prio = SafepointPriority;
176 }
177
178 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
179 }
180
181 void VMOperationQueue::oops_do(OopClosure* f) {
182 for(int i = 0; i < nof_priorities; i++) {
183 queue_oops_do(i, f);
184 }
185 drain_list_oops_do(f);
186 }
187
188 //------------------------------------------------------------------------------------------------------------------
189 // Timeout machinery
190
191 void VMOperationTimeoutTask::task() {
192 assert(AbortVMOnVMOperationTimeout, "only if enabled");
193 if (is_armed()) {
194 jlong delay = (os::javaTimeMillis() - _arm_time);
195 if (delay > AbortVMOnVMOperationTimeoutDelay) {
196 fatal("VM operation took too long: " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)",
197 delay, AbortVMOnVMOperationTimeoutDelay);
198 }
199 }
200 }
201
202 bool VMOperationTimeoutTask::is_armed() {
203 return OrderAccess::load_acquire(&_armed) != 0;
204 }
205
206 void VMOperationTimeoutTask::arm() {
207 _arm_time = os::javaTimeMillis();
208 OrderAccess::release_store_fence(&_armed, 1);
209 }
210
211 void VMOperationTimeoutTask::disarm() {
212 OrderAccess::release_store_fence(&_armed, 0);
213 }
214
215 //------------------------------------------------------------------------------------------------------------------
216 // Implementation of VMThread stuff
217
218 bool VMThread::_should_terminate = false;
219 bool VMThread::_terminated = false;
220 Monitor* VMThread::_terminate_lock = NULL;
221 VMThread* VMThread::_vm_thread = NULL;
222 VM_Operation* VMThread::_cur_vm_operation = NULL;
223 VMOperationQueue* VMThread::_vm_queue = NULL;
224 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
225 uint64_t VMThread::_coalesced_count = 0;
226 VMOperationTimeoutTask* VMThread::_timeout_task = NULL;
227
228
229 void VMThread::create() {
230 assert(vm_thread() == NULL, "we can only allocate one VMThread");
231 _vm_thread = new VMThread();
232
233 if (AbortVMOnVMOperationTimeout) {
234 // Make sure we call the timeout task frequently enough, but not too frequent.
235 // Try to make the interval 10% of the timeout delay, so that we miss the timeout
236 // by those 10% at max. Periodic task also expects it to fit min/max intervals.
237 size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10;
238 interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran;
239 interval = MAX2<size_t>(interval, PeriodicTask::min_interval);
240 interval = MIN2<size_t>(interval, PeriodicTask::max_interval);
241
242 _timeout_task = new VMOperationTimeoutTask(interval);
243 _timeout_task->enroll();
244 } else {
245 assert(_timeout_task == NULL, "sanity");
246 }
247
248 // Create VM operation queue
249 _vm_queue = new VMOperationQueue();
250 guarantee(_vm_queue != NULL, "just checking");
251
252 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
253 Monitor::_safepoint_check_never);
254
255 if (UsePerfData) {
256 // jvmstat performance counters
257 Thread* THREAD = Thread::current();
258 _perf_accumulated_vm_operation_time =
259 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
260 PerfData::U_Ticks, CHECK);
261 }
262 }
263
264 VMThread::VMThread() : NamedThread() {
265 set_name("VM Thread");
266 }
267
268 void VMThread::destroy() {
269 _vm_thread = NULL; // VM thread is gone
270 }
271
272 static VM_None halt_op("Halt");
273
274 void VMThread::run() {
275 assert(this == vm_thread(), "check");
276
277 // Notify_lock wait checks on active_handles() to rewait in
278 // case of spurious wakeup, it should wait on the last
279 // value set prior to the notify
280 this->set_active_handles(JNIHandleBlock::allocate_block());
281
282 {
283 MutexLocker ml(Notify_lock);
284 Notify_lock->notify();
285 }
286 // Notify_lock is destroyed by Threads::create_vm()
287
288 int prio = (VMThreadPriority == -1)
289 ? os::java_to_os_priority[NearMaxPriority]
290 : VMThreadPriority;
291 // Note that I cannot call os::set_priority because it expects Java
292 // priorities and I am *explicitly* using OS priorities so that it's
293 // possible to set the VM thread priority higher than any Java thread.
294 os::set_native_priority( this, prio );
295
296 // Wait for VM_Operations until termination
297 this->loop();
298
299 // Note the intention to exit before safepointing.
300 // 6295565 This has the effect of waiting for any large tty
301 // outputs to finish.
302 if (xtty != NULL) {
303 ttyLocker ttyl;
304 xtty->begin_elem("destroy_vm");
305 xtty->stamp();
306 xtty->end_elem();
307 assert(should_terminate(), "termination flag must be set");
308 }
309
310 // 4526887 let VM thread exit at Safepoint
311 _cur_vm_operation = &halt_op;
312 SafepointSynchronize::begin();
313
314 if (VerifyBeforeExit) {
315 HandleMark hm(VMThread::vm_thread());
316 // Among other things, this ensures that Eden top is correct.
317 Universe::heap()->prepare_for_verify();
318 // Silent verification so as not to pollute normal output,
319 // unless we really asked for it.
320 Universe::verify();
321 }
322
323 CompileBroker::set_should_block();
324
325 // wait for threads (compiler threads or daemon threads) in the
326 // _thread_in_native state to block.
327 VM_Exit::wait_for_threads_in_native_to_block();
328
329 // signal other threads that VM process is gone
330 {
331 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
332 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
333 // If that happens after _terminate_lock->wait() has unset _owner
334 // but before it actually drops the lock and waits, the notification below
335 // may get lost and we will have a hang. To avoid this, we need to use
336 // Mutex::lock_without_safepoint_check().
337 MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
338 _terminated = true;
339 ml.notify();
340 }
341
342 // We are now racing with the VM termination being carried out in
343 // another thread, so we don't "delete this". Numerous threads don't
344 // get deleted when the VM terminates
345
346 }
347
348
349 // Notify the VMThread that the last non-daemon JavaThread has terminated,
350 // and wait until operation is performed.
351 void VMThread::wait_for_vm_thread_exit() {
352 assert(Thread::current()->is_Java_thread(), "Should be a JavaThread");
353 assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated");
354 { MonitorLocker mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
355 _should_terminate = true;
356 mu.notify();
357 }
358
359 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
360 // because this thread has been removed from the threads list. But anything
361 // that could get blocked by Safepoint should not be used after this point,
362 // otherwise we will hang, since there is no one can end the safepoint.
363
364 // Wait until VM thread is terminated
365 // Note: it should be OK to use Terminator_lock here. But this is called
366 // at a very delicate time (VM shutdown) and we are operating in non- VM
367 // thread at Safepoint. It's safer to not share lock with other threads.
368 { MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
369 while(!VMThread::is_terminated()) {
370 ml.wait();
371 }
372 }
373 }
374
375 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
376 assert(event != NULL, "invariant");
377 assert(event->should_commit(), "invariant");
378 assert(op != NULL, "invariant");
379 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
380 event->set_operation(op->type());
381 event->set_safepoint(evaluate_at_safepoint);
382 event->set_blocking(true);
383 event->set_caller(JFR_THREAD_ID(op->calling_thread()));
384 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0);
385 event->commit();
386 }
387
388 void VMThread::evaluate_operation(VM_Operation* op) {
389 ResourceMark rm;
390
391 {
392 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
393 HOTSPOT_VMOPS_BEGIN(
394 (char *) op->name(), strlen(op->name()),
395 op->evaluate_at_safepoint() ? 0 : 1);
396
397 EventExecuteVMOperation event;
398 op->evaluate();
399 if (event.should_commit()) {
400 post_vm_operation_event(&event, op);
401 }
402
403 HOTSPOT_VMOPS_END(
404 (char *) op->name(), strlen(op->name()),
405 op->evaluate_at_safepoint() ? 0 : 1);
406 }
407
408 // Mark as completed
409 op->calling_thread()->increment_vm_operation_completed_count();
410 }
411
412 static VM_None safepointALot_op("SafepointALot");
413 static VM_Cleanup cleanup_op;
414
415 class HandshakeALotTC : public ThreadClosure {
416 public:
417 virtual void do_thread(Thread* thread) {
418 #ifdef ASSERT
419 assert(thread->is_Java_thread(), "must be");
420 JavaThread* jt = (JavaThread*)thread;
421 jt->verify_states_for_handshake();
422 #endif
423 }
424 };
425
426 void VMThread::check_cleanup() {
427 MonitorLocker mq(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
428 mq.notify();
429 }
430
431 VM_Operation* VMThread::no_op_safepoint() {
432 // Check for handshakes first since we may need to return a VMop.
433 if (HandshakeALot) {
434 HandshakeALotTC haltc;
435 Handshake::execute(&haltc);
436 }
437 // Check for a cleanup before SafepointALot to keep stats correct.
438 long interval_ms = SafepointTracing::time_since_last_safepoint_ms();
439 bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
440 (interval_ms >= GuaranteedSafepointInterval);
441 if ((max_time_exceeded && SafepointSynchronize::is_cleanup_needed()) ||
442 SafepointSynchronize::is_forced_cleanup_needed()) {
443 return &cleanup_op;
444 }
445 if (SafepointALot) {
446 return &safepointALot_op;
447 }
448 // Nothing to be done.
449 return NULL;
450 }
451
452 void VMThread::loop() {
453 assert(_cur_vm_operation == NULL, "no current one should be executing");
454
455 SafepointSynchronize::init(_vm_thread);
456
457 while(true) {
458 VM_Operation* safepoint_ops = NULL;
459 //
460 // Wait for VM operation
461 //
462 // use no_safepoint_check to get lock without attempting to "sneak"
463 { MonitorLocker mu_queue(VMOperationQueue_lock,
464 Mutex::_no_safepoint_check_flag);
465
466 // Look for new operation
467 assert(_cur_vm_operation == NULL, "no current one should be executing");
468 _cur_vm_operation = _vm_queue->remove_next();
469
470 // Stall time tracking code
471 if (PrintVMQWaitTime && _cur_vm_operation != NULL) {
472 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
473 if (stall > 0)
474 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall);
475 }
476
477 while (!should_terminate() && _cur_vm_operation == NULL) {
478 // wait with a timeout to guarantee safepoints at regular intervals
479 mu_queue.wait(GuaranteedSafepointInterval);
480
481 // Support for self destruction
482 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() &&
483 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
484 tty->print_cr("VM self-destructed");
485 exit(-1);
486 }
487
488 // If the queue contains a safepoint VM op,
489 // clean up will be done so we can skip this part.
490 if (!_vm_queue->peek_at_safepoint_priority()) {
491
492 // Have to unlock VMOperationQueue_lock just in case no_op_safepoint()
493 // has to do a handshake when HandshakeALot is enabled.
494 MutexUnlocker mul(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
495 if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
496 // Force a safepoint since we have not had one for at least
497 // 'GuaranteedSafepointInterval' milliseconds and we need to clean
498 // something. This will run all the clean-up processing that needs
499 // to be done at a safepoint.
500 SafepointSynchronize::begin();
501 #ifdef ASSERT
502 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
503 #endif
504 SafepointSynchronize::end();
505 _cur_vm_operation = NULL;
506 }
507 }
508 _cur_vm_operation = _vm_queue->remove_next();
509
510 // If we are at a safepoint we will evaluate all the operations that
511 // follow that also require a safepoint
512 if (_cur_vm_operation != NULL &&
513 _cur_vm_operation->evaluate_at_safepoint()) {
514 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
515 }
516 }
517
518 if (should_terminate()) break;
519 } // Release mu_queue_lock
520
521 //
522 // Execute VM operation
523 //
524 { HandleMark hm(VMThread::vm_thread());
525
526 EventMark em("Executing VM operation: %s", vm_operation()->name());
527 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
528
529 // If we are at a safepoint we will evaluate all the operations that
530 // follow that also require a safepoint
531 if (_cur_vm_operation->evaluate_at_safepoint()) {
532 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name());
533
534 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
535
536 SafepointSynchronize::begin();
537
538 if (_timeout_task != NULL) {
539 _timeout_task->arm();
540 }
541
542 evaluate_operation(_cur_vm_operation);
543 // now process all queued safepoint ops, iteratively draining
544 // the queue until there are none left
545 do {
546 _cur_vm_operation = safepoint_ops;
547 if (_cur_vm_operation != NULL) {
548 do {
549 EventMark em("Executing coalesced safepoint VM operation: %s", _cur_vm_operation->name());
550 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name());
551 // evaluate_operation deletes the op object so we have
552 // to grab the next op now
553 VM_Operation* next = _cur_vm_operation->next();
554 _vm_queue->set_drain_list(next);
555 evaluate_operation(_cur_vm_operation);
556 _cur_vm_operation = next;
557 _coalesced_count++;
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 MutexLocker 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)
613 { MonitorLocker mu(VMOperationRequest_lock, Mutex::_no_safepoint_check_flag);
614 mu.notify_all();
615 }
616 }
617 }
618
619 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
620 // over a section of execution by a thread. Currently, it's used only to
621 // prevent re-entrant calls to GC.
622 class SkipGCALot : public StackObj {
623 private:
624 bool _saved;
625 Thread* _t;
626
627 public:
628 #ifdef ASSERT
629 SkipGCALot(Thread* t) : _t(t) {
630 _saved = _t->skip_gcalot();
631 _t->set_skip_gcalot(true);
632 }
633
634 ~SkipGCALot() {
635 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
636 _t->set_skip_gcalot(_saved);
637 }
638 #else
639 SkipGCALot(Thread* t) { }
640 ~SkipGCALot() { }
641 #endif
642 };
643
644 void VMThread::execute(VM_Operation* op) {
645 Thread* t = Thread::current();
646
647 if (!t->is_VM_thread()) {
648 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
649 // JavaThread or WatcherThread
650 t->check_for_valid_safepoint_state();
651
652 // New request from Java thread, evaluate prologue
653 if (!op->doit_prologue()) {
654 return; // op was cancelled
655 }
656
657 // Setup VM_operations for execution
658 op->set_calling_thread(t);
659
660 // Get ticket number for the VM operation
661 int ticket = t->vm_operation_ticket();
662
663 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
664 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
665 // to be queued up during a safepoint synchronization.
666 {
667 MonitorLocker ml(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
668 log_debug(vmthread)("Adding VM operation: %s", op->name());
669 _vm_queue->add(op);
670 op->set_timestamp(os::javaTimeMillis());
671 ml.notify();
672 }
673 {
674 // Wait for completion of request
675 // Note: only a JavaThread triggers the safepoint check when locking
676 MonitorLocker ml(VMOperationRequest_lock,
677 t->is_Java_thread() ? Mutex::_safepoint_check_flag : Mutex::_no_safepoint_check_flag);
678 while(t->vm_operation_completed_count() < ticket) {
679 ml.wait();
680 }
681 }
682 op->doit_epilogue();
683 } else {
684 // invoked by VM thread; usually nested VM operation
685 assert(t->is_VM_thread(), "must be a VM thread");
686 VM_Operation* prev_vm_operation = vm_operation();
687 if (prev_vm_operation != NULL) {
688 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
689 // does not allow nested scavenges or compiles.
690 if (!prev_vm_operation->allow_nested_vm_operations()) {
691 fatal("Nested VM operation %s requested by operation %s",
692 op->name(), vm_operation()->name());
693 }
694 op->set_calling_thread(prev_vm_operation->calling_thread());
695 }
696
697 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
698
699 // Release all internal handles after operation is evaluated
700 HandleMark hm(t);
701 _cur_vm_operation = op;
702
703 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
704 SafepointSynchronize::begin();
705 op->evaluate();
706 SafepointSynchronize::end();
707 } else {
708 op->evaluate();
709 }
710
711 _cur_vm_operation = prev_vm_operation;
712 }
713 }
714
715
716 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
717 Thread::oops_do(f, cf);
718 _vm_queue->oops_do(f);
719 }
720
721 //------------------------------------------------------------------------------------------------------------------
722 #ifndef PRODUCT
723
724 void VMOperationQueue::verify_queue(int prio) {
725 // Check that list is correctly linked
726 int length = _queue_length[prio];
727 VM_Operation *cur = _queue[prio];
728 int i;
729
730 // Check forward links
731 for(i = 0; i < length; i++) {
732 cur = cur->next();
733 assert(cur != _queue[prio], "list to short (forward)");
734 }
735 assert(cur->next() == _queue[prio], "list to long (forward)");
736
737 // Check backwards links
738 cur = _queue[prio];
739 for(i = 0; i < length; i++) {
740 cur = cur->prev();
741 assert(cur != _queue[prio], "list to short (backwards)");
742 }
743 assert(cur->prev() == _queue[prio], "list to long (backwards)");
744 }
745
746 #endif
747
748 void VMThread::verify() {
749 oops_do(&VerifyOopClosure::verify_oop, NULL);
750 }