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 VMOperationQueue::VMOperationQueue() {
53 // The queue is a circular doubled-linked list, which always contains
54 // one element (i.e., one element means empty).
55 for(int i = 0; i < nof_priorities; i++) {
56 _queue_length[i] = 0;
57 _queue_counter = 0;
58 _queue[i] = new VM_None("QueueHead");
59 _queue[i]->set_next(_queue[i]);
60 _queue[i]->set_prev(_queue[i]);
61 }
62 _drain_list = NULL;
63 }
64
65
66 bool VMOperationQueue::queue_empty(int prio) {
67 // It is empty if there is exactly one element
68 bool empty = (_queue[prio] == _queue[prio]->next());
69 assert( (_queue_length[prio] == 0 && empty) ||
70 (_queue_length[prio] > 0 && !empty), "sanity check");
71 return _queue_length[prio] == 0;
72 }
73
74 // Inserts an element to the right of the q element
75 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
76 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
77 n->set_prev(q);
78 n->set_next(q->next());
79 q->next()->set_prev(n);
80 q->set_next(n);
81 }
82
83 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
84 _queue_length[prio]++;
85 insert(_queue[prio]->next(), op);
86 }
87
88 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
89 _queue_length[prio]++;
90 insert(_queue[prio]->prev(), op);
91 }
92
93
94 void VMOperationQueue::unlink(VM_Operation* q) {
95 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
96 q->prev()->set_next(q->next());
97 q->next()->set_prev(q->prev());
98 }
99
100 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
101 if (queue_empty(prio)) return NULL;
102 assert(_queue_length[prio] >= 0, "sanity check");
103 _queue_length[prio]--;
104 VM_Operation* r = _queue[prio]->next();
105 assert(r != _queue[prio], "cannot remove base element");
106 unlink(r);
107 return r;
108 }
109
110 VM_Operation* VMOperationQueue::queue_drain(int prio) {
111 if (queue_empty(prio)) return NULL;
112 DEBUG_ONLY(int length = _queue_length[prio];);
113 assert(length >= 0, "sanity check");
114 _queue_length[prio] = 0;
115 VM_Operation* r = _queue[prio]->next();
116 assert(r != _queue[prio], "cannot remove base element");
117 // remove links to base element from head and tail
118 r->set_prev(NULL);
119 _queue[prio]->prev()->set_next(NULL);
120 // restore queue to empty state
121 _queue[prio]->set_next(_queue[prio]);
122 _queue[prio]->set_prev(_queue[prio]);
123 assert(queue_empty(prio), "drain corrupted queue");
124 #ifdef ASSERT
125 int len = 0;
126 VM_Operation* cur;
127 for(cur = r; cur != NULL; cur=cur->next()) len++;
128 assert(len == length, "drain lost some ops");
129 #endif
130 return r;
131 }
132
133 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
134 VM_Operation* cur = _queue[queue];
135 cur = cur->next();
136 while (cur != _queue[queue]) {
137 cur->oops_do(f);
138 cur = cur->next();
139 }
140 }
141
142 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
143 VM_Operation* cur = _drain_list;
144 while (cur != NULL) {
145 cur->oops_do(f);
146 cur = cur->next();
147 }
148 }
149
150 //-----------------------------------------------------------------
151 // High-level interface
152 void VMOperationQueue::add(VM_Operation *op) {
153
154 HOTSPOT_VMOPS_REQUEST(
155 (char *) op->name(), strlen(op->name()),
156 op->evaluation_mode());
157
158 // Encapsulates VM queue policy. Currently, that
159 // only involves putting them on the right list
160 queue_add_back(op->evaluate_at_safepoint() ? SafepointPriority : MediumPriority, op);
161 }
162
163 VM_Operation* VMOperationQueue::remove_next() {
164 // Assuming VMOperation queue is two-level priority queue. If there are
165 // more than two priorities, we need a different scheduling algorithm.
166 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
167 "current algorithm does not work");
168
169 // simple counter based scheduling to prevent starvation of lower priority
170 // queue. -- see 4390175
171 int high_prio, low_prio;
172 if (_queue_counter++ < 10) {
173 high_prio = SafepointPriority;
174 low_prio = MediumPriority;
175 } else {
176 _queue_counter = 0;
177 high_prio = MediumPriority;
178 low_prio = SafepointPriority;
179 }
180
181 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
182 }
183
184 void VMOperationQueue::oops_do(OopClosure* f) {
185 for(int i = 0; i < nof_priorities; i++) {
186 queue_oops_do(i, f);
187 }
188 drain_list_oops_do(f);
189 }
190
191 //------------------------------------------------------------------------------------------------------------------
192 // Timeout machinery
193
194 void VMOperationTimeoutTask::task() {
195 assert(AbortVMOnVMOperationTimeout, "only if enabled");
196 if (is_armed()) {
197 jlong delay = (os::javaTimeMillis() - _arm_time);
198 if (delay > AbortVMOnVMOperationTimeoutDelay) {
199 fatal("VM operation took too long: " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)",
200 delay, AbortVMOnVMOperationTimeoutDelay);
201 }
202 }
203 }
204
205 bool VMOperationTimeoutTask::is_armed() {
206 return OrderAccess::load_acquire(&_armed) != 0;
207 }
208
209 void VMOperationTimeoutTask::arm() {
210 _arm_time = os::javaTimeMillis();
211 OrderAccess::release_store_fence(&_armed, 1);
212 }
213
214 void VMOperationTimeoutTask::disarm() {
215 OrderAccess::release_store_fence(&_armed, 0);
216 }
217
218 //------------------------------------------------------------------------------------------------------------------
219 // Implementation of VMThread stuff
220
221 bool VMThread::_should_terminate = false;
222 bool VMThread::_terminated = false;
223 Monitor* VMThread::_terminate_lock = NULL;
224 VMThread* VMThread::_vm_thread = NULL;
225 VM_Operation* VMThread::_cur_vm_operation = NULL;
226 VMOperationQueue* VMThread::_vm_queue = NULL;
227 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
228 uint64_t VMThread::_coalesced_count = 0;
229 VMOperationTimeoutTask* VMThread::_timeout_task = NULL;
230
231
232 void VMThread::create() {
233 assert(vm_thread() == NULL, "we can only allocate one VMThread");
234 _vm_thread = new VMThread();
235
236 if (AbortVMOnVMOperationTimeout) {
237 // Make sure we call the timeout task frequently enough, but not too frequent.
238 // Try to make the interval 10% of the timeout delay, so that we miss the timeout
239 // by those 10% at max. Periodic task also expects it to fit min/max intervals.
240 size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10;
241 interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran;
242 interval = MAX2<size_t>(interval, PeriodicTask::min_interval);
243 interval = MIN2<size_t>(interval, PeriodicTask::max_interval);
244
245 _timeout_task = new VMOperationTimeoutTask(interval);
246 _timeout_task->enroll();
247 } else {
248 assert(_timeout_task == NULL, "sanity");
249 }
250
251 // Create VM operation queue
252 _vm_queue = new VMOperationQueue();
253 guarantee(_vm_queue != NULL, "just checking");
254
255 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
256 Monitor::_safepoint_check_never);
257
258 if (UsePerfData) {
259 // jvmstat performance counters
260 Thread* THREAD = Thread::current();
261 _perf_accumulated_vm_operation_time =
262 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
263 PerfData::U_Ticks, CHECK);
264 }
265 }
266
267 VMThread::VMThread() : NamedThread() {
268 set_name("VM Thread");
269 }
270
271 void VMThread::destroy() {
272 _vm_thread = NULL; // VM thread is gone
273 }
274
275 static VM_None halt_op("Halt");
276
277 void VMThread::run() {
278 assert(this == vm_thread(), "check");
279
280 // Notify_lock wait checks on active_handles() to rewait in
281 // case of spurious wakeup, it should wait on the last
282 // value set prior to the notify
283 this->set_active_handles(JNIHandleBlock::allocate_block());
284
285 {
286 MutexLocker ml(Notify_lock);
287 Notify_lock->notify();
288 }
289 // Notify_lock is destroyed by Threads::create_vm()
290
291 int prio = (VMThreadPriority == -1)
292 ? os::java_to_os_priority[NearMaxPriority]
293 : VMThreadPriority;
294 // Note that I cannot call os::set_priority because it expects Java
295 // priorities and I am *explicitly* using OS priorities so that it's
296 // possible to set the VM thread priority higher than any Java thread.
297 os::set_native_priority( this, prio );
298
299 // Wait for VM_Operations until termination
300 this->loop();
301
302 // Note the intention to exit before safepointing.
303 // 6295565 This has the effect of waiting for any large tty
304 // outputs to finish.
305 if (xtty != NULL) {
306 ttyLocker ttyl;
307 xtty->begin_elem("destroy_vm");
308 xtty->stamp();
309 xtty->end_elem();
310 assert(should_terminate(), "termination flag must be set");
311 }
312
313 // 4526887 let VM thread exit at Safepoint
314 _cur_vm_operation = &halt_op;
315 SafepointSynchronize::begin();
316
317 if (VerifyBeforeExit) {
318 HandleMark hm(VMThread::vm_thread());
319 // Among other things, this ensures that Eden top is correct.
320 Universe::heap()->prepare_for_verify();
321 // Silent verification so as not to pollute normal output,
322 // unless we really asked for it.
323 Universe::verify();
324 }
325
326 CompileBroker::set_should_block();
327
328 // wait for threads (compiler threads or daemon threads) in the
329 // _thread_in_native state to block.
330 VM_Exit::wait_for_threads_in_native_to_block();
331
332 // signal other threads that VM process is gone
333 {
334 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
335 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
336 // If that happens after _terminate_lock->wait() has unset _owner
337 // but before it actually drops the lock and waits, the notification below
338 // may get lost and we will have a hang. To avoid this, we need to use
339 // Mutex::lock_without_safepoint_check().
340 MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
341 _terminated = true;
342 ml.notify();
343 }
344
345 // We are now racing with the VM termination being carried out in
346 // another thread, so we don't "delete this". Numerous threads don't
347 // get deleted when the VM terminates
348
349 }
350
351
352 // Notify the VMThread that the last non-daemon JavaThread has terminated,
353 // and wait until operation is performed.
354 void VMThread::wait_for_vm_thread_exit() {
355 assert(Thread::current()->is_Java_thread(), "Should be a JavaThread");
356 assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated");
357 { MutexLocker mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
358 _should_terminate = true;
359 VMOperationQueue_lock->notify();
360 }
361
362 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
363 // because this thread has been removed from the threads list. But anything
364 // that could get blocked by Safepoint should not be used after this point,
365 // otherwise we will hang, since there is no one can end the safepoint.
366
367 // Wait until VM thread is terminated
368 // Note: it should be OK to use Terminator_lock here. But this is called
369 // at a very delicate time (VM shutdown) and we are operating in non- VM
370 // thread at Safepoint. It's safer to not share lock with other threads.
371 { MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
372 while(!VMThread::is_terminated()) {
373 ml.wait();
374 }
375 }
376 }
377
378 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
379 assert(event != NULL, "invariant");
380 assert(event->should_commit(), "invariant");
381 assert(op != NULL, "invariant");
382 const bool is_concurrent = op->evaluate_concurrently();
383 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
384 event->set_operation(op->type());
385 event->set_safepoint(evaluate_at_safepoint);
386 event->set_blocking(!is_concurrent);
387 // Only write caller thread information for non-concurrent vm operations.
388 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
389 // This is because the caller thread could have exited already.
390 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread()));
391 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0);
392 event->commit();
393 }
394
395 void VMThread::evaluate_operation(VM_Operation* op) {
396 ResourceMark rm;
397
398 {
399 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
400 HOTSPOT_VMOPS_BEGIN(
401 (char *) op->name(), strlen(op->name()),
402 op->evaluation_mode());
403
404 EventExecuteVMOperation event;
405 op->evaluate();
406 if (event.should_commit()) {
407 post_vm_operation_event(&event, op);
408 }
409
410 HOTSPOT_VMOPS_END(
411 (char *) op->name(), strlen(op->name()),
412 op->evaluation_mode());
413 }
414
415 // Last access of info in _cur_vm_operation!
416 bool c_heap_allocated = op->is_cheap_allocated();
417
418 // Mark as completed
419 if (!op->evaluate_concurrently()) {
420 op->calling_thread()->increment_vm_operation_completed_count();
421 }
422 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
423 // since if it is stack allocated the calling thread might have deallocated
424 if (c_heap_allocated) {
425 delete _cur_vm_operation;
426 }
427 }
428
429 static VM_None safepointALot_op("SafepointALot");
430 static VM_Cleanup cleanup_op;
431
432 class HandshakeALotTC : public ThreadClosure {
433 public:
434 virtual void do_thread(Thread* thread) {
435 #ifdef ASSERT
436 assert(thread->is_Java_thread(), "must be");
437 JavaThread* jt = (JavaThread*)thread;
438 jt->verify_states_for_handshake();
439 #endif
440 }
441 };
442
443 VM_Operation* VMThread::no_op_safepoint() {
444 // Check for handshakes first since we may need to return a VMop.
445 if (HandshakeALot) {
446 HandshakeALotTC haltc;
447 Handshake::execute(&haltc);
448 }
449 // Check for a cleanup before SafepointALot to keep stats correct.
450 long interval_ms = SafepointTracing::time_since_last_safepoint_ms();
451 bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
452 (interval_ms >= GuaranteedSafepointInterval);
453 if (max_time_exceeded && SafepointSynchronize::is_cleanup_needed()) {
454 return &cleanup_op;
455 }
456 if (SafepointALot) {
457 return &safepointALot_op;
458 }
459 // Nothing to be done.
460 return NULL;
461 }
462
463 void VMThread::loop() {
464 assert(_cur_vm_operation == NULL, "no current one should be executing");
465
466 SafepointSynchronize::init(_vm_thread);
467
468 while(true) {
469 VM_Operation* safepoint_ops = NULL;
470 //
471 // Wait for VM operation
472 //
473 // use no_safepoint_check to get lock without attempting to "sneak"
474 { MonitorLocker mu_queue(VMOperationQueue_lock,
475 Mutex::_no_safepoint_check_flag);
476
477 // Look for new operation
478 assert(_cur_vm_operation == NULL, "no current one should be executing");
479 _cur_vm_operation = _vm_queue->remove_next();
480
481 // Stall time tracking code
482 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
483 !_cur_vm_operation->evaluate_concurrently()) {
484 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
485 if (stall > 0)
486 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall);
487 }
488
489 while (!should_terminate() && _cur_vm_operation == NULL) {
490 // wait with a timeout to guarantee safepoints at regular intervals
491 bool timedout =
492 mu_queue.wait(GuaranteedSafepointInterval);
493
494 // Support for self destruction
495 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() &&
496 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
497 tty->print_cr("VM self-destructed");
498 exit(-1);
499 }
500
501 if (timedout) {
502 // Have to unlock VMOperationQueue_lock just in case no_op_safepoint()
503 // has to do a handshake.
504 MutexUnlocker mul(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
505 if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
506 // Force a safepoint since we have not had one for at least
507 // 'GuaranteedSafepointInterval' milliseconds and we need to clean
508 // something. This will run all the clean-up processing that needs
509 // to be done at a safepoint.
510 SafepointSynchronize::begin();
511 #ifdef ASSERT
512 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
513 #endif
514 SafepointSynchronize::end();
515 _cur_vm_operation = NULL;
516 }
517 }
518 _cur_vm_operation = _vm_queue->remove_next();
519
520 // If we are at a safepoint we will evaluate all the operations that
521 // follow that also require a safepoint
522 if (_cur_vm_operation != NULL &&
523 _cur_vm_operation->evaluate_at_safepoint()) {
524 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
525 }
526 }
527
528 if (should_terminate()) break;
529 } // Release mu_queue_lock
530
531 //
532 // Execute VM operation
533 //
534 { HandleMark hm(VMThread::vm_thread());
535
536 EventMark em("Executing VM operation: %s", vm_operation()->name());
537 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
538
539 // If we are at a safepoint we will evaluate all the operations that
540 // follow that also require a safepoint
541 if (_cur_vm_operation->evaluate_at_safepoint()) {
542 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name());
543
544 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
545
546 SafepointSynchronize::begin();
547
548 if (_timeout_task != NULL) {
549 _timeout_task->arm();
550 }
551
552 evaluate_operation(_cur_vm_operation);
553 // now process all queued safepoint ops, iteratively draining
554 // the queue until there are none left
555 do {
556 _cur_vm_operation = safepoint_ops;
557 if (_cur_vm_operation != NULL) {
558 do {
559 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name());
560 // evaluate_operation deletes the op object so we have
561 // to grab the next op now
562 VM_Operation* next = _cur_vm_operation->next();
563 _vm_queue->set_drain_list(next);
564 evaluate_operation(_cur_vm_operation);
565 _cur_vm_operation = next;
566 _coalesced_count++;
567 } while (_cur_vm_operation != NULL);
568 }
569 // There is a chance that a thread enqueued a safepoint op
570 // since we released the op-queue lock and initiated the safepoint.
571 // So we drain the queue again if there is anything there, as an
572 // optimization to try and reduce the number of safepoints.
573 // As the safepoint synchronizes us with JavaThreads we will see
574 // any enqueue made by a JavaThread, but the peek will not
575 // necessarily detect a concurrent enqueue by a GC thread, but
576 // that simply means the op will wait for the next major cycle of the
577 // VMThread - just as it would if the GC thread lost the race for
578 // the lock.
579 if (_vm_queue->peek_at_safepoint_priority()) {
580 // must hold lock while draining queue
581 MutexLocker mu_queue(VMOperationQueue_lock,
582 Mutex::_no_safepoint_check_flag);
583 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
584 } else {
585 safepoint_ops = NULL;
586 }
587 } while(safepoint_ops != NULL);
588
589 _vm_queue->set_drain_list(NULL);
590
591 if (_timeout_task != NULL) {
592 _timeout_task->disarm();
593 }
594
595 // Complete safepoint synchronization
596 SafepointSynchronize::end();
597
598 } else { // not a safepoint operation
599 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name());
600 if (TraceLongCompiles) {
601 elapsedTimer t;
602 t.start();
603 evaluate_operation(_cur_vm_operation);
604 t.stop();
605 double secs = t.seconds();
606 if (secs * 1e3 > LongCompileThreshold) {
607 // XXX - _cur_vm_operation should not be accessed after
608 // the completed count has been incremented; the waiting
609 // thread may have already freed this memory.
610 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
611 }
612 } else {
613 evaluate_operation(_cur_vm_operation);
614 }
615
616 _cur_vm_operation = NULL;
617 }
618 }
619
620 //
621 // Notify (potential) waiting Java thread(s)
622 { MutexLocker mu(VMOperationRequest_lock, Mutex::_no_safepoint_check_flag);
623 VMOperationRequest_lock->notify_all();
624 }
625
626 // We want to make sure that we get to a safepoint regularly
627 // even when executing VMops that don't require safepoints.
628 if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
629 HandleMark hm(VMThread::vm_thread());
630 SafepointSynchronize::begin();
631 SafepointSynchronize::end();
632 _cur_vm_operation = NULL;
633 }
634 }
635 }
636
637 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
638 // over a section of execution by a thread. Currently, it's used only to
639 // prevent re-entrant calls to GC.
640 class SkipGCALot : public StackObj {
641 private:
642 bool _saved;
643 Thread* _t;
644
645 public:
646 #ifdef ASSERT
647 SkipGCALot(Thread* t) : _t(t) {
648 _saved = _t->skip_gcalot();
649 _t->set_skip_gcalot(true);
650 }
651
652 ~SkipGCALot() {
653 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
654 _t->set_skip_gcalot(_saved);
655 }
656 #else
657 SkipGCALot(Thread* t) { }
658 ~SkipGCALot() { }
659 #endif
660 };
661
662 void VMThread::execute(VM_Operation* op) {
663 Thread* t = Thread::current();
664
665 if (!t->is_VM_thread()) {
666 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
667 // JavaThread or WatcherThread
668 bool concurrent = op->evaluate_concurrently();
669 // only blocking VM operations need to verify the caller's safepoint state:
670 if (!concurrent) {
671 t->check_for_valid_safepoint_state(true);
672 }
673
674 // New request from Java thread, evaluate prologue
675 if (!op->doit_prologue()) {
676 return; // op was cancelled
677 }
678
679 // Setup VM_operations for execution
680 op->set_calling_thread(t, Thread::get_priority(t));
681
682 // It does not make sense to execute the epilogue, if the VM operation object is getting
683 // deallocated by the VM thread.
684 bool execute_epilog = !op->is_cheap_allocated();
685 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
686
687 // Get ticket number for non-concurrent VM operations
688 int ticket = 0;
689 if (!concurrent) {
690 ticket = t->vm_operation_ticket();
691 }
692
693 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
694 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
695 // to be queued up during a safepoint synchronization.
696 {
697 VMOperationQueue_lock->lock_without_safepoint_check();
698 log_debug(vmthread)("Adding VM operation: %s", op->name());
699 _vm_queue->add(op);
700 op->set_timestamp(os::javaTimeMillis());
701 VMOperationQueue_lock->notify();
702 VMOperationQueue_lock->unlock();
703 }
704
705 if (!concurrent) {
706 // Wait for completion of request (non-concurrent)
707 // Note: only a JavaThread triggers the safepoint check when locking
708 MonitorLocker ml(VMOperationRequest_lock,
709 t->is_Java_thread() ? Mutex::_safepoint_check_flag : Mutex::_no_safepoint_check_flag);
710 while(t->vm_operation_completed_count() < ticket) {
711 ml.wait();
712 }
713 }
714
715 if (execute_epilog) {
716 op->doit_epilogue();
717 }
718 } else {
719 // invoked by VM thread; usually nested VM operation
720 assert(t->is_VM_thread(), "must be a VM thread");
721 VM_Operation* prev_vm_operation = vm_operation();
722 if (prev_vm_operation != NULL) {
723 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
724 // does not allow nested scavenges or compiles.
725 if (!prev_vm_operation->allow_nested_vm_operations()) {
726 fatal("Nested VM operation %s requested by operation %s",
727 op->name(), vm_operation()->name());
728 }
729 op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());
730 }
731
732 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
733
734 // Release all internal handles after operation is evaluated
735 HandleMark hm(t);
736 _cur_vm_operation = op;
737
738 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
739 SafepointSynchronize::begin();
740 op->evaluate();
741 SafepointSynchronize::end();
742 } else {
743 op->evaluate();
744 }
745
746 // Free memory if needed
747 if (op->is_cheap_allocated()) delete op;
748
749 _cur_vm_operation = prev_vm_operation;
750 }
751 }
752
753
754 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
755 Thread::oops_do(f, cf);
756 _vm_queue->oops_do(f);
757 }
758
759 //------------------------------------------------------------------------------------------------------------------
760 #ifndef PRODUCT
761
762 void VMOperationQueue::verify_queue(int prio) {
763 // Check that list is correctly linked
764 int length = _queue_length[prio];
765 VM_Operation *cur = _queue[prio];
766 int i;
767
768 // Check forward links
769 for(i = 0; i < length; i++) {
770 cur = cur->next();
771 assert(cur != _queue[prio], "list to short (forward)");
772 }
773 assert(cur->next() == _queue[prio], "list to long (forward)");
774
775 // Check backwards links
776 cur = _queue[prio];
777 for(i = 0; i < length; i++) {
778 cur = cur->prev();
779 assert(cur != _queue[prio], "list to short (backwards)");
780 }
781 assert(cur->prev() == _queue[prio], "list to long (backwards)");
782 }
783
784 #endif
785
786 void VMThread::verify() {
787 oops_do(&VerifyOopClosure::verify_oop, NULL);
788 }