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/atomic.hpp"
39 #include "runtime/handles.inline.hpp"
40 #include "runtime/interfaceSupport.inline.hpp"
41 #include "runtime/mutexLocker.hpp"
42 #include "runtime/os.hpp"
43 #include "runtime/safepoint.hpp"
44 #include "runtime/thread.inline.hpp"
45 #include "runtime/vmThread.hpp"
46 #include "runtime/vmOperations.hpp"
47 #include "services/runtimeService.hpp"
48 #include "utilities/dtrace.hpp"
49 #include "utilities/events.hpp"
50 #include "utilities/vmError.hpp"
51 #include "utilities/xmlstream.hpp"
52
53 VMOperationQueue::VMOperationQueue() {
54 // The queue is a circular doubled-linked list, which always contains
55 // one element (i.e., one element means empty).
56 for(int i = 0; i < nof_priorities; i++) {
57 _queue_length[i] = 0;
58 _queue_counter = 0;
59 _queue[i] = new VM_None("QueueHead");
60 _queue[i]->set_next(_queue[i]);
61 _queue[i]->set_prev(_queue[i]);
62 }
63 _drain_list = NULL;
64 }
65
66
67 bool VMOperationQueue::queue_empty(int prio) {
68 // It is empty if there is exactly one element
69 bool empty = (_queue[prio] == _queue[prio]->next());
70 assert( (_queue_length[prio] == 0 && empty) ||
71 (_queue_length[prio] > 0 && !empty), "sanity check");
72 return _queue_length[prio] == 0;
73 }
74
75 // Inserts an element to the right of the q element
76 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
77 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
78 n->set_prev(q);
79 n->set_next(q->next());
80 q->next()->set_prev(n);
81 q->set_next(n);
82 }
83
84 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {
85 _queue_length[prio]++;
86 insert(_queue[prio]->next(), op);
87 }
88
89 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {
90 _queue_length[prio]++;
91 insert(_queue[prio]->prev(), op);
92 }
93
94
95 void VMOperationQueue::unlink(VM_Operation* q) {
96 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
97 q->prev()->set_next(q->next());
98 q->next()->set_prev(q->prev());
99 }
100
101 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
102 if (queue_empty(prio)) return NULL;
103 assert(_queue_length[prio] >= 0, "sanity check");
104 _queue_length[prio]--;
105 VM_Operation* r = _queue[prio]->next();
106 assert(r != _queue[prio], "cannot remove base element");
107 unlink(r);
108 return r;
109 }
110
111 VM_Operation* VMOperationQueue::queue_drain(int prio) {
112 if (queue_empty(prio)) return NULL;
113 DEBUG_ONLY(int length = _queue_length[prio];);
114 assert(length >= 0, "sanity check");
115 _queue_length[prio] = 0;
116 VM_Operation* r = _queue[prio]->next();
117 assert(r != _queue[prio], "cannot remove base element");
118 // remove links to base element from head and tail
119 r->set_prev(NULL);
120 _queue[prio]->prev()->set_next(NULL);
121 // restore queue to empty state
122 _queue[prio]->set_next(_queue[prio]);
123 _queue[prio]->set_prev(_queue[prio]);
124 assert(queue_empty(prio), "drain corrupted queue");
125 #ifdef ASSERT
126 int len = 0;
127 VM_Operation* cur;
128 for(cur = r; cur != NULL; cur=cur->next()) len++;
129 assert(len == length, "drain lost some ops");
130 #endif
131 return r;
132 }
133
134 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {
135 VM_Operation* cur = _queue[queue];
136 cur = cur->next();
137 while (cur != _queue[queue]) {
138 cur->oops_do(f);
139 cur = cur->next();
140 }
141 }
142
143 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {
144 VM_Operation* cur = _drain_list;
145 while (cur != NULL) {
146 cur->oops_do(f);
147 cur = cur->next();
148 }
149 }
150
151 //-----------------------------------------------------------------
152 // High-level interface
153 void VMOperationQueue::add(VM_Operation *op) {
154
155 HOTSPOT_VMOPS_REQUEST(
156 (char *) op->name(), strlen(op->name()),
157 op->evaluation_mode());
158
159 // Encapsulates VM queue policy. Currently, that
160 // only involves putting them on the right list
161 queue_add_back(op->evaluate_at_safepoint() ? SafepointPriority : MediumPriority, op);
162 }
163
164 VM_Operation* VMOperationQueue::remove_next() {
165 // Assuming VMOperation queue is two-level priority queue. If there are
166 // more than two priorities, we need a different scheduling algorithm.
167 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
168 "current algorithm does not work");
169
170 // simple counter based scheduling to prevent starvation of lower priority
171 // queue. -- see 4390175
172 int high_prio, low_prio;
173 if (_queue_counter++ < 10) {
174 high_prio = SafepointPriority;
175 low_prio = MediumPriority;
176 } else {
177 _queue_counter = 0;
178 high_prio = MediumPriority;
179 low_prio = SafepointPriority;
180 }
181
182 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
183 }
184
185 void VMOperationQueue::oops_do(OopClosure* f) {
186 for(int i = 0; i < nof_priorities; i++) {
187 queue_oops_do(i, f);
188 }
189 drain_list_oops_do(f);
190 }
191
192 //------------------------------------------------------------------------------------------------------------------
193 // Timeout machinery
194
195 void VMOperationTimeoutTask::task() {
196 assert(AbortVMOnVMOperationTimeout, "only if enabled");
197 if (is_armed()) {
198 jlong delay = (os::javaTimeMillis() - _arm_time);
199 if (delay > AbortVMOnVMOperationTimeoutDelay) {
200 fatal("VM operation took too long: " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)",
201 delay, AbortVMOnVMOperationTimeoutDelay);
202 }
203 }
204 }
205
206 bool VMOperationTimeoutTask::is_armed() {
207 return Atomic::load_acquire(&_armed) != 0;
208 }
209
210 void VMOperationTimeoutTask::arm() {
211 _arm_time = os::javaTimeMillis();
212 Atomic::release_store_fence(&_armed, 1);
213 }
214
215 void VMOperationTimeoutTask::disarm() {
216 Atomic::release_store_fence(&_armed, 0);
217 }
218
219 //------------------------------------------------------------------------------------------------------------------
220 // Implementation of VMThread stuff
221
222 bool VMThread::_should_terminate = false;
223 bool VMThread::_terminated = false;
224 Monitor* VMThread::_terminate_lock = NULL;
225 VMThread* VMThread::_vm_thread = NULL;
226 VM_Operation* VMThread::_cur_vm_operation = NULL;
227 VMOperationQueue* VMThread::_vm_queue = NULL;
228 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
229 uint64_t VMThread::_coalesced_count = 0;
230 VMOperationTimeoutTask* VMThread::_timeout_task = NULL;
231
232
233 void VMThread::create() {
234 assert(vm_thread() == NULL, "we can only allocate one VMThread");
235 _vm_thread = new VMThread();
236
237 if (AbortVMOnVMOperationTimeout) {
238 // Make sure we call the timeout task frequently enough, but not too frequent.
239 // Try to make the interval 10% of the timeout delay, so that we miss the timeout
240 // by those 10% at max. Periodic task also expects it to fit min/max intervals.
241 size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10;
242 interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran;
243 interval = MAX2<size_t>(interval, PeriodicTask::min_interval);
244 interval = MIN2<size_t>(interval, PeriodicTask::max_interval);
245
246 _timeout_task = new VMOperationTimeoutTask(interval);
247 _timeout_task->enroll();
248 } else {
249 assert(_timeout_task == NULL, "sanity");
250 }
251
252 // Create VM operation queue
253 _vm_queue = new VMOperationQueue();
254 guarantee(_vm_queue != NULL, "just checking");
255
256 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
257 Monitor::_safepoint_check_never);
258
259 if (UsePerfData) {
260 // jvmstat performance counters
261 Thread* THREAD = Thread::current();
262 _perf_accumulated_vm_operation_time =
263 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
264 PerfData::U_Ticks, CHECK);
265 }
266 }
267
268 VMThread::VMThread() : NamedThread() {
269 set_name("VM Thread");
270 }
271
272 void VMThread::destroy() {
273 _vm_thread = NULL; // VM thread is gone
274 }
275
276 static VM_None halt_op("Halt");
277
278 void VMThread::run() {
279 assert(this == vm_thread(), "check");
280
281 // Notify_lock wait checks on active_handles() to rewait in
282 // case of spurious wakeup, it should wait on the last
283 // value set prior to the notify
284 this->set_active_handles(JNIHandleBlock::allocate_block());
285
286 {
287 MutexLocker ml(Notify_lock);
288 Notify_lock->notify();
289 }
290 // Notify_lock is destroyed by Threads::create_vm()
291
292 int prio = (VMThreadPriority == -1)
293 ? os::java_to_os_priority[NearMaxPriority]
294 : VMThreadPriority;
295 // Note that I cannot call os::set_priority because it expects Java
296 // priorities and I am *explicitly* using OS priorities so that it's
297 // possible to set the VM thread priority higher than any Java thread.
298 os::set_native_priority( this, prio );
299
300 // Wait for VM_Operations until termination
301 this->loop();
302
303 // Note the intention to exit before safepointing.
304 // 6295565 This has the effect of waiting for any large tty
305 // outputs to finish.
306 if (xtty != NULL) {
307 ttyLocker ttyl;
308 xtty->begin_elem("destroy_vm");
309 xtty->stamp();
310 xtty->end_elem();
311 assert(should_terminate(), "termination flag must be set");
312 }
313
314 // 4526887 let VM thread exit at Safepoint
315 _cur_vm_operation = &halt_op;
316 SafepointSynchronize::begin();
317
318 if (VerifyBeforeExit) {
319 HandleMark hm(VMThread::vm_thread());
320 // Among other things, this ensures that Eden top is correct.
321 Universe::heap()->prepare_for_verify();
322 // Silent verification so as not to pollute normal output,
323 // unless we really asked for it.
324 Universe::verify();
325 }
326
327 CompileBroker::set_should_block();
328
329 // wait for threads (compiler threads or daemon threads) in the
330 // _thread_in_native state to block.
331 VM_Exit::wait_for_threads_in_native_to_block();
332
333 // signal other threads that VM process is gone
334 {
335 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
336 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
337 // If that happens after _terminate_lock->wait() has unset _owner
338 // but before it actually drops the lock and waits, the notification below
339 // may get lost and we will have a hang. To avoid this, we need to use
340 // Mutex::lock_without_safepoint_check().
341 MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
342 _terminated = true;
343 ml.notify();
344 }
345
346 // We are now racing with the VM termination being carried out in
347 // another thread, so we don't "delete this". Numerous threads don't
348 // get deleted when the VM terminates
349
350 }
351
352
353 // Notify the VMThread that the last non-daemon JavaThread has terminated,
354 // and wait until operation is performed.
355 void VMThread::wait_for_vm_thread_exit() {
356 assert(Thread::current()->is_Java_thread(), "Should be a JavaThread");
357 assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated");
358 { MonitorLocker mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
359 _should_terminate = true;
360 mu.notify();
361 }
362
363 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
364 // because this thread has been removed from the threads list. But anything
365 // that could get blocked by Safepoint should not be used after this point,
366 // otherwise we will hang, since there is no one can end the safepoint.
367
368 // Wait until VM thread is terminated
369 // Note: it should be OK to use Terminator_lock here. But this is called
370 // at a very delicate time (VM shutdown) and we are operating in non- VM
371 // thread at Safepoint. It's safer to not share lock with other threads.
372 { MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
373 while(!VMThread::is_terminated()) {
374 ml.wait();
375 }
376 }
377 }
378
379 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
380 assert(event != NULL, "invariant");
381 assert(event->should_commit(), "invariant");
382 assert(op != NULL, "invariant");
383 const bool is_concurrent = op->evaluate_concurrently();
384 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
385 event->set_operation(op->type());
386 event->set_safepoint(evaluate_at_safepoint);
387 event->set_blocking(!is_concurrent);
388 // Only write caller thread information for non-concurrent vm operations.
389 // For concurrent vm operations, the thread id is set to 0 indicating thread is unknown.
390 // This is because the caller thread could have exited already.
391 event->set_caller(is_concurrent ? 0 : JFR_THREAD_ID(op->calling_thread()));
392 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0);
393 event->commit();
394 }
395
396 void VMThread::evaluate_operation(VM_Operation* op) {
397 ResourceMark rm;
398
399 {
400 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
401 HOTSPOT_VMOPS_BEGIN(
402 (char *) op->name(), strlen(op->name()),
403 op->evaluation_mode());
404
405 EventExecuteVMOperation event;
406 op->evaluate();
407 if (event.should_commit()) {
408 post_vm_operation_event(&event, op);
409 }
410
411 HOTSPOT_VMOPS_END(
412 (char *) op->name(), strlen(op->name()),
413 op->evaluation_mode());
414 }
415
416 // Last access of info in _cur_vm_operation!
417 bool c_heap_allocated = op->is_cheap_allocated();
418
419 // Mark as completed
420 if (!op->evaluate_concurrently()) {
421 op->calling_thread()->increment_vm_operation_completed_count();
422 }
423 // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,
424 // since if it is stack allocated the calling thread might have deallocated
425 if (c_heap_allocated) {
426 delete _cur_vm_operation;
427 }
428 }
429
430 static VM_None safepointALot_op("SafepointALot");
431 static VM_Cleanup cleanup_op;
432
433 class HandshakeALotTC : public ThreadClosure {
434 public:
435 virtual void do_thread(Thread* thread) {
436 #ifdef ASSERT
437 assert(thread->is_Java_thread(), "must be");
438 JavaThread* jt = (JavaThread*)thread;
439 jt->verify_states_for_handshake();
440 #endif
441 }
442 };
443
444 VM_Operation* VMThread::no_op_safepoint() {
445 // Check for handshakes first since we may need to return a VMop.
446 if (HandshakeALot) {
447 HandshakeALotTC haltc;
448 Handshake::execute(&haltc);
449 }
450 // Check for a cleanup before SafepointALot to keep stats correct.
451 long interval_ms = SafepointTracing::time_since_last_safepoint_ms();
452 bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
453 (interval_ms >= GuaranteedSafepointInterval);
454 if (max_time_exceeded && SafepointSynchronize::is_cleanup_needed()) {
455 return &cleanup_op;
456 }
457 if (SafepointALot) {
458 return &safepointALot_op;
459 }
460 // Nothing to be done.
461 return NULL;
462 }
463
464 void VMThread::loop() {
465 assert(_cur_vm_operation == NULL, "no current one should be executing");
466
467 SafepointSynchronize::init(_vm_thread);
468
469 while(true) {
470 VM_Operation* safepoint_ops = NULL;
471 //
472 // Wait for VM operation
473 //
474 // use no_safepoint_check to get lock without attempting to "sneak"
475 { MonitorLocker mu_queue(VMOperationQueue_lock,
476 Mutex::_no_safepoint_check_flag);
477
478 // Look for new operation
479 assert(_cur_vm_operation == NULL, "no current one should be executing");
480 _cur_vm_operation = _vm_queue->remove_next();
481
482 // Stall time tracking code
483 if (PrintVMQWaitTime && _cur_vm_operation != NULL &&
484 !_cur_vm_operation->evaluate_concurrently()) {
485 long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();
486 if (stall > 0)
487 tty->print_cr("%s stall: %ld", _cur_vm_operation->name(), stall);
488 }
489
490 while (!should_terminate() && _cur_vm_operation == NULL) {
491 // wait with a timeout to guarantee safepoints at regular intervals
492 bool timedout =
493 mu_queue.wait(GuaranteedSafepointInterval);
494
495 // Support for self destruction
496 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() &&
497 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
498 tty->print_cr("VM self-destructed");
499 exit(-1);
500 }
501
502 if (timedout) {
503 // Have to unlock VMOperationQueue_lock just in case no_op_safepoint()
504 // has to do a handshake.
505 MutexUnlocker mul(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
506 if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
507 // Force a safepoint since we have not had one for at least
508 // 'GuaranteedSafepointInterval' milliseconds and we need to clean
509 // something. This will run all the clean-up processing that needs
510 // to be done at a safepoint.
511 SafepointSynchronize::begin();
512 #ifdef ASSERT
513 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
514 #endif
515 SafepointSynchronize::end();
516 _cur_vm_operation = NULL;
517 }
518 }
519 _cur_vm_operation = _vm_queue->remove_next();
520
521 // If we are at a safepoint we will evaluate all the operations that
522 // follow that also require a safepoint
523 if (_cur_vm_operation != NULL &&
524 _cur_vm_operation->evaluate_at_safepoint()) {
525 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
526 }
527 }
528
529 if (should_terminate()) break;
530 } // Release mu_queue_lock
531
532 //
533 // Execute VM operation
534 //
535 { HandleMark hm(VMThread::vm_thread());
536
537 EventMark em("Executing VM operation: %s", vm_operation()->name());
538 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
539
540 // If we are at a safepoint we will evaluate all the operations that
541 // follow that also require a safepoint
542 if (_cur_vm_operation->evaluate_at_safepoint()) {
543 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name());
544
545 _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned
546
547 SafepointSynchronize::begin();
548
549 if (_timeout_task != NULL) {
550 _timeout_task->arm();
551 }
552
553 evaluate_operation(_cur_vm_operation);
554 // now process all queued safepoint ops, iteratively draining
555 // the queue until there are none left
556 do {
557 _cur_vm_operation = safepoint_ops;
558 if (_cur_vm_operation != NULL) {
559 do {
560 EventMark em("Executing coalesced safepoint VM operation: %s", _cur_vm_operation->name());
561 log_debug(vmthread)("Evaluating coalesced safepoint VM operation: %s", _cur_vm_operation->name());
562 // evaluate_operation deletes the op object so we have
563 // to grab the next op now
564 VM_Operation* next = _cur_vm_operation->next();
565 _vm_queue->set_drain_list(next);
566 evaluate_operation(_cur_vm_operation);
567 _cur_vm_operation = next;
568 _coalesced_count++;
569 } while (_cur_vm_operation != NULL);
570 }
571 // There is a chance that a thread enqueued a safepoint op
572 // since we released the op-queue lock and initiated the safepoint.
573 // So we drain the queue again if there is anything there, as an
574 // optimization to try and reduce the number of safepoints.
575 // As the safepoint synchronizes us with JavaThreads we will see
576 // any enqueue made by a JavaThread, but the peek will not
577 // necessarily detect a concurrent enqueue by a GC thread, but
578 // that simply means the op will wait for the next major cycle of the
579 // VMThread - just as it would if the GC thread lost the race for
580 // the lock.
581 if (_vm_queue->peek_at_safepoint_priority()) {
582 // must hold lock while draining queue
583 MutexLocker mu_queue(VMOperationQueue_lock,
584 Mutex::_no_safepoint_check_flag);
585 safepoint_ops = _vm_queue->drain_at_safepoint_priority();
586 } else {
587 safepoint_ops = NULL;
588 }
589 } while(safepoint_ops != NULL);
590
591 _vm_queue->set_drain_list(NULL);
592
593 if (_timeout_task != NULL) {
594 _timeout_task->disarm();
595 }
596
597 // Complete safepoint synchronization
598 SafepointSynchronize::end();
599
600 } else { // not a safepoint operation
601 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name());
602 if (TraceLongCompiles) {
603 elapsedTimer t;
604 t.start();
605 evaluate_operation(_cur_vm_operation);
606 t.stop();
607 double secs = t.seconds();
608 if (secs * 1e3 > LongCompileThreshold) {
609 // XXX - _cur_vm_operation should not be accessed after
610 // the completed count has been incremented; the waiting
611 // thread may have already freed this memory.
612 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
613 }
614 } else {
615 evaluate_operation(_cur_vm_operation);
616 }
617
618 _cur_vm_operation = NULL;
619 }
620 }
621
622 //
623 // Notify (potential) waiting Java thread(s)
624 { MonitorLocker mu(VMOperationRequest_lock, Mutex::_no_safepoint_check_flag);
625 mu.notify_all();
626 }
627
628 // We want to make sure that we get to a safepoint regularly
629 // even when executing VMops that don't require safepoints.
630 if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
631 HandleMark hm(VMThread::vm_thread());
632 SafepointSynchronize::begin();
633 SafepointSynchronize::end();
634 _cur_vm_operation = NULL;
635 }
636 }
637 }
638
639 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
640 // over a section of execution by a thread. Currently, it's used only to
641 // prevent re-entrant calls to GC.
642 class SkipGCALot : public StackObj {
643 private:
644 bool _saved;
645 Thread* _t;
646
647 public:
648 #ifdef ASSERT
649 SkipGCALot(Thread* t) : _t(t) {
650 _saved = _t->skip_gcalot();
651 _t->set_skip_gcalot(true);
652 }
653
654 ~SkipGCALot() {
655 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
656 _t->set_skip_gcalot(_saved);
657 }
658 #else
659 SkipGCALot(Thread* t) { }
660 ~SkipGCALot() { }
661 #endif
662 };
663
664 void VMThread::execute(VM_Operation* op) {
665 Thread* t = Thread::current();
666
667 if (!t->is_VM_thread()) {
668 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
669 // JavaThread or WatcherThread
670 bool concurrent = op->evaluate_concurrently();
671 // only blocking VM operations need to verify the caller's safepoint state:
672 if (!concurrent) {
673 t->check_for_valid_safepoint_state();
674 }
675
676 // New request from Java thread, evaluate prologue
677 if (!op->doit_prologue()) {
678 return; // op was cancelled
679 }
680
681 // Setup VM_operations for execution
682 op->set_calling_thread(t);
683
684 // It does not make sense to execute the epilogue, if the VM operation object is getting
685 // deallocated by the VM thread.
686 bool execute_epilog = !op->is_cheap_allocated();
687 assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");
688
689 // Get ticket number for non-concurrent VM operations
690 int ticket = 0;
691 if (!concurrent) {
692 ticket = t->vm_operation_ticket();
693 }
694
695 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
696 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
697 // to be queued up during a safepoint synchronization.
698 {
699 MonitorLocker ml(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
700 log_debug(vmthread)("Adding VM operation: %s", op->name());
701 _vm_queue->add(op);
702 op->set_timestamp(os::javaTimeMillis());
703 ml.notify();
704 }
705
706 if (!concurrent) {
707 // Wait for completion of request (non-concurrent)
708 // Note: only a JavaThread triggers the safepoint check when locking
709 MonitorLocker ml(VMOperationRequest_lock,
710 t->is_Java_thread() ? Mutex::_safepoint_check_flag : Mutex::_no_safepoint_check_flag);
711 while(t->vm_operation_completed_count() < ticket) {
712 ml.wait();
713 }
714 }
715
716 if (execute_epilog) {
717 op->doit_epilogue();
718 }
719 } else {
720 // invoked by VM thread; usually nested VM operation
721 assert(t->is_VM_thread(), "must be a VM thread");
722 VM_Operation* prev_vm_operation = vm_operation();
723 if (prev_vm_operation != NULL) {
724 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
725 // does not allow nested scavenges or compiles.
726 if (!prev_vm_operation->allow_nested_vm_operations()) {
727 fatal("Nested VM operation %s requested by operation %s",
728 op->name(), vm_operation()->name());
729 }
730 op->set_calling_thread(prev_vm_operation->calling_thread());
731 }
732
733 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
734
735 // Release all internal handles after operation is evaluated
736 HandleMark hm(t);
737 _cur_vm_operation = op;
738
739 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
740 SafepointSynchronize::begin();
741 op->evaluate();
742 SafepointSynchronize::end();
743 } else {
744 op->evaluate();
745 }
746
747 // Free memory if needed
748 if (op->is_cheap_allocated()) delete op;
749
750 _cur_vm_operation = prev_vm_operation;
751 }
752 }
753
754
755 void VMThread::oops_do(OopClosure* f, CodeBlobClosure* cf) {
756 Thread::oops_do(f, cf);
757 _vm_queue->oops_do(f);
758 }
759
760 //------------------------------------------------------------------------------------------------------------------
761 #ifndef PRODUCT
762
763 void VMOperationQueue::verify_queue(int prio) {
764 // Check that list is correctly linked
765 int length = _queue_length[prio];
766 VM_Operation *cur = _queue[prio];
767 int i;
768
769 // Check forward links
770 for(i = 0; i < length; i++) {
771 cur = cur->next();
772 assert(cur != _queue[prio], "list to short (forward)");
773 }
774 assert(cur->next() == _queue[prio], "list to long (forward)");
775
776 // Check backwards links
777 cur = _queue[prio];
778 for(i = 0; i < length; i++) {
779 cur = cur->prev();
780 assert(cur != _queue[prio], "list to short (backwards)");
781 }
782 assert(cur->prev() == _queue[prio], "list to long (backwards)");
783 }
784
785 #endif
786
787 void VMThread::verify() {
788 oops_do(&VerifyOopClosure::verify_oop, NULL);
789 }