1 /*
2 * Copyright (c) 1998, 2020, 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/synchronizer.hpp"
45 #include "runtime/thread.inline.hpp"
46 #include "runtime/vmThread.hpp"
47 #include "runtime/vmOperations.hpp"
48 #include "services/runtimeService.hpp"
49 #include "utilities/dtrace.hpp"
50 #include "utilities/events.hpp"
51 #include "utilities/vmError.hpp"
52 #include "utilities/xmlstream.hpp"
53
54 VM_QueueHead VMOperationQueue::_queue_head[VMOperationQueue::nof_priorities];
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] = &_queue_head[i];
63 _queue[i]->set_next(_queue[i]);
64 _queue[i]->set_prev(_queue[i]);
65 }
66 }
67
68
69 bool VMOperationQueue::queue_empty(int prio) {
70 // It is empty if there is exactly one element
71 bool empty = (_queue[prio] == _queue[prio]->next());
72 assert( (_queue_length[prio] == 0 && empty) ||
73 (_queue_length[prio] > 0 && !empty), "sanity check");
74 return _queue_length[prio] == 0;
75 }
76
77 // Inserts an element to the right of the q element
78 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {
79 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
80 n->set_prev(q);
81 n->set_next(q->next());
82 q->next()->set_prev(n);
83 q->set_next(n);
84 }
85
86 void VMOperationQueue::queue_add(int prio, VM_Operation *op) {
87 _queue_length[prio]++;
88 insert(_queue[prio]->prev(), op);
89 }
90
91
92 void VMOperationQueue::unlink(VM_Operation* q) {
93 assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");
94 q->prev()->set_next(q->next());
95 q->next()->set_prev(q->prev());
96 }
97
98 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {
99 if (queue_empty(prio)) return NULL;
100 assert(_queue_length[prio] >= 0, "sanity check");
101 _queue_length[prio]--;
102 VM_Operation* r = _queue[prio]->next();
103 assert(r != _queue[prio], "cannot remove base element");
104 unlink(r);
105 return r;
106 }
107
108 //-----------------------------------------------------------------
109 // High-level interface
110 void VMOperationQueue::add(VM_Operation *op) {
111
112 HOTSPOT_VMOPS_REQUEST(
113 (char *) op->name(), strlen(op->name()),
114 op->evaluate_at_safepoint() ? 0 : 1);
115
116 // Encapsulates VM queue policy. Currently, that
117 // only involves putting them on the right list
118 queue_add(op->evaluate_at_safepoint() ? SafepointPriority : MediumPriority, op);
119 }
120
121 VM_Operation* VMOperationQueue::remove_next() {
122 // Assuming VMOperation queue is two-level priority queue. If there are
123 // more than two priorities, we need a different scheduling algorithm.
124 assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,
125 "current algorithm does not work");
126
127 // simple counter based scheduling to prevent starvation of lower priority
128 // queue. -- see 4390175
129 int high_prio, low_prio;
130 if (_queue_counter++ < 10) {
131 high_prio = SafepointPriority;
132 low_prio = MediumPriority;
133 } else {
134 _queue_counter = 0;
135 high_prio = MediumPriority;
136 low_prio = SafepointPriority;
137 }
138
139 return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);
140 }
141
142 //------------------------------------------------------------------------------------------------------------------
143 // Timeout machinery
144
145 void VMOperationTimeoutTask::task() {
146 assert(AbortVMOnVMOperationTimeout, "only if enabled");
147 if (is_armed()) {
148 jlong delay = nanos_to_millis(os::javaTimeNanos() - _arm_time);
149 if (delay > AbortVMOnVMOperationTimeoutDelay) {
150 fatal("VM operation took too long: " JLONG_FORMAT " ms (timeout: " INTX_FORMAT " ms)",
151 delay, AbortVMOnVMOperationTimeoutDelay);
152 }
153 }
154 }
155
156 bool VMOperationTimeoutTask::is_armed() {
157 return Atomic::load_acquire(&_armed) != 0;
158 }
159
160 void VMOperationTimeoutTask::arm() {
161 _arm_time = os::javaTimeNanos();
162 Atomic::release_store_fence(&_armed, 1);
163 }
164
165 void VMOperationTimeoutTask::disarm() {
166 Atomic::release_store_fence(&_armed, 0);
167 }
168
169 //------------------------------------------------------------------------------------------------------------------
170 // Implementation of VMThread stuff
171
172 bool VMThread::_should_terminate = false;
173 bool VMThread::_terminated = false;
174 Monitor* VMThread::_terminate_lock = NULL;
175 VMThread* VMThread::_vm_thread = NULL;
176 VM_Operation* VMThread::_cur_vm_operation = NULL;
177 VMOperationQueue* VMThread::_vm_queue = NULL;
178 PerfCounter* VMThread::_perf_accumulated_vm_operation_time = NULL;
179 VMOperationTimeoutTask* VMThread::_timeout_task = NULL;
180
181
182 void VMThread::create() {
183 assert(vm_thread() == NULL, "we can only allocate one VMThread");
184 _vm_thread = new VMThread();
185
186 if (AbortVMOnVMOperationTimeout) {
187 // Make sure we call the timeout task frequently enough, but not too frequent.
188 // Try to make the interval 10% of the timeout delay, so that we miss the timeout
189 // by those 10% at max. Periodic task also expects it to fit min/max intervals.
190 size_t interval = (size_t)AbortVMOnVMOperationTimeoutDelay / 10;
191 interval = interval / PeriodicTask::interval_gran * PeriodicTask::interval_gran;
192 interval = MAX2<size_t>(interval, PeriodicTask::min_interval);
193 interval = MIN2<size_t>(interval, PeriodicTask::max_interval);
194
195 _timeout_task = new VMOperationTimeoutTask(interval);
196 _timeout_task->enroll();
197 } else {
198 assert(_timeout_task == NULL, "sanity");
199 }
200
201 // Create VM operation queue
202 _vm_queue = new VMOperationQueue();
203 guarantee(_vm_queue != NULL, "just checking");
204
205 _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true,
206 Monitor::_safepoint_check_never);
207
208 if (UsePerfData) {
209 // jvmstat performance counters
210 Thread* THREAD = Thread::current();
211 _perf_accumulated_vm_operation_time =
212 PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",
213 PerfData::U_Ticks, CHECK);
214 }
215 }
216
217 VMThread::VMThread() : NamedThread() {
218 set_name("VM Thread");
219 }
220
221 void VMThread::destroy() {
222 _vm_thread = NULL; // VM thread is gone
223 }
224
225 static VM_None halt_op("Halt");
226
227 void VMThread::run() {
228 assert(this == vm_thread(), "check");
229
230 // Notify_lock wait checks on active_handles() to rewait in
231 // case of spurious wakeup, it should wait on the last
232 // value set prior to the notify
233 this->set_active_handles(JNIHandleBlock::allocate_block());
234
235 {
236 MutexLocker ml(Notify_lock);
237 Notify_lock->notify();
238 }
239 // Notify_lock is destroyed by Threads::create_vm()
240
241 int prio = (VMThreadPriority == -1)
242 ? os::java_to_os_priority[NearMaxPriority]
243 : VMThreadPriority;
244 // Note that I cannot call os::set_priority because it expects Java
245 // priorities and I am *explicitly* using OS priorities so that it's
246 // possible to set the VM thread priority higher than any Java thread.
247 os::set_native_priority( this, prio );
248
249 // Wait for VM_Operations until termination
250 this->loop();
251
252 // Note the intention to exit before safepointing.
253 // 6295565 This has the effect of waiting for any large tty
254 // outputs to finish.
255 if (xtty != NULL) {
256 ttyLocker ttyl;
257 xtty->begin_elem("destroy_vm");
258 xtty->stamp();
259 xtty->end_elem();
260 assert(should_terminate(), "termination flag must be set");
261 }
262
263 if (log_is_enabled(Info, monitorinflation)) {
264 // Do a deflation in order to reduce the in-use monitor population
265 // that is reported by ObjectSynchronizer::log_in_use_monitor_details()
266 // at VM exit.
267 ObjectSynchronizer::request_deflate_idle_monitors();
268 }
269
270 // 4526887 let VM thread exit at Safepoint
271 _cur_vm_operation = &halt_op;
272 SafepointSynchronize::begin();
273
274 if (VerifyBeforeExit) {
275 HandleMark hm(VMThread::vm_thread());
276 // Among other things, this ensures that Eden top is correct.
277 Universe::heap()->prepare_for_verify();
278 // Silent verification so as not to pollute normal output,
279 // unless we really asked for it.
280 Universe::verify();
281 }
282
283 CompileBroker::set_should_block();
284
285 // wait for threads (compiler threads or daemon threads) in the
286 // _thread_in_native state to block.
287 VM_Exit::wait_for_threads_in_native_to_block();
288
289 // signal other threads that VM process is gone
290 {
291 // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows
292 // VM thread to enter any lock at Safepoint as long as its _owner is NULL.
293 // If that happens after _terminate_lock->wait() has unset _owner
294 // but before it actually drops the lock and waits, the notification below
295 // may get lost and we will have a hang. To avoid this, we need to use
296 // Mutex::lock_without_safepoint_check().
297 MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
298 _terminated = true;
299 ml.notify();
300 }
301
302 // We are now racing with the VM termination being carried out in
303 // another thread, so we don't "delete this". Numerous threads don't
304 // get deleted when the VM terminates
305
306 }
307
308
309 // Notify the VMThread that the last non-daemon JavaThread has terminated,
310 // and wait until operation is performed.
311 void VMThread::wait_for_vm_thread_exit() {
312 assert(Thread::current()->is_Java_thread(), "Should be a JavaThread");
313 assert(((JavaThread*)Thread::current())->is_terminated(), "Should be terminated");
314 { MonitorLocker mu(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
315 _should_terminate = true;
316 mu.notify();
317 }
318
319 // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint
320 // because this thread has been removed from the threads list. But anything
321 // that could get blocked by Safepoint should not be used after this point,
322 // otherwise we will hang, since there is no one can end the safepoint.
323
324 // Wait until VM thread is terminated
325 // Note: it should be OK to use Terminator_lock here. But this is called
326 // at a very delicate time (VM shutdown) and we are operating in non- VM
327 // thread at Safepoint. It's safer to not share lock with other threads.
328 { MonitorLocker ml(_terminate_lock, Mutex::_no_safepoint_check_flag);
329 while(!VMThread::is_terminated()) {
330 ml.wait();
331 }
332 }
333 }
334
335 static void post_vm_operation_event(EventExecuteVMOperation* event, VM_Operation* op) {
336 assert(event != NULL, "invariant");
337 assert(event->should_commit(), "invariant");
338 assert(op != NULL, "invariant");
339 const bool evaluate_at_safepoint = op->evaluate_at_safepoint();
340 event->set_operation(op->type());
341 event->set_safepoint(evaluate_at_safepoint);
342 event->set_blocking(true);
343 event->set_caller(JFR_THREAD_ID(op->calling_thread()));
344 event->set_safepointId(evaluate_at_safepoint ? SafepointSynchronize::safepoint_id() : 0);
345 event->commit();
346 }
347
348 void VMThread::evaluate_operation(VM_Operation* op) {
349 ResourceMark rm;
350
351 {
352 PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());
353 HOTSPOT_VMOPS_BEGIN(
354 (char *) op->name(), strlen(op->name()),
355 op->evaluate_at_safepoint() ? 0 : 1);
356
357 EventExecuteVMOperation event;
358 op->evaluate();
359 if (event.should_commit()) {
360 post_vm_operation_event(&event, op);
361 }
362
363 HOTSPOT_VMOPS_END(
364 (char *) op->name(), strlen(op->name()),
365 op->evaluate_at_safepoint() ? 0 : 1);
366 }
367
368 // Mark as completed
369 op->calling_thread()->increment_vm_operation_completed_count();
370 }
371
372 static VM_None safepointALot_op("SafepointALot");
373 static VM_Cleanup cleanup_op;
374
375 class HandshakeALotClosure : public HandshakeClosure {
376 public:
377 HandshakeALotClosure() : HandshakeClosure("HandshakeALot") {}
378 void do_thread(Thread* thread) {
379 #ifdef ASSERT
380 assert(thread->is_Java_thread(), "must be");
381 JavaThread* jt = (JavaThread*)thread;
382 jt->verify_states_for_handshake();
383 #endif
384 }
385 };
386
387 VM_Operation* VMThread::no_op_safepoint() {
388 // Check for handshakes first since we may need to return a VMop.
389 if (HandshakeALot) {
390 HandshakeALotClosure hal_cl;
391 Handshake::execute(&hal_cl);
392 }
393 // Check for a cleanup before SafepointALot to keep stats correct.
394 long interval_ms = SafepointTracing::time_since_last_safepoint_ms();
395 bool max_time_exceeded = GuaranteedSafepointInterval != 0 &&
396 (interval_ms >= GuaranteedSafepointInterval);
397 if (max_time_exceeded && SafepointSynchronize::is_cleanup_needed()) {
398 return &cleanup_op;
399 }
400 if (SafepointALot) {
401 return &safepointALot_op;
402 }
403 // Nothing to be done.
404 return NULL;
405 }
406
407 void VMThread::loop() {
408 assert(_cur_vm_operation == NULL, "no current one should be executing");
409
410 SafepointSynchronize::init(_vm_thread);
411
412 while(true) {
413 //
414 // Wait for VM operation
415 //
416 // use no_safepoint_check to get lock without attempting to "sneak"
417 { MonitorLocker mu_queue(VMOperationQueue_lock,
418 Mutex::_no_safepoint_check_flag);
419
420 // Look for new operation
421 assert(_cur_vm_operation == NULL, "no current one should be executing");
422 _cur_vm_operation = _vm_queue->remove_next();
423
424 while (!should_terminate() && _cur_vm_operation == NULL) {
425 // wait with a timeout to guarantee safepoints at regular intervals
426 // (if there is cleanup work to do)
427 (void)mu_queue.wait(GuaranteedSafepointInterval);
428
429 // Support for self destruction
430 if ((SelfDestructTimer != 0) && !VMError::is_error_reported() &&
431 (os::elapsedTime() > (double)SelfDestructTimer * 60.0)) {
432 tty->print_cr("VM self-destructed");
433 exit(-1);
434 }
435
436 // If the queue contains a safepoint VM op,
437 // clean up will be done so we can skip this part.
438 if (!_vm_queue->peek_at_safepoint_priority()) {
439
440 // Have to unlock VMOperationQueue_lock just in case no_op_safepoint()
441 // has to do a handshake when HandshakeALot is enabled.
442 MutexUnlocker mul(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
443 if ((_cur_vm_operation = VMThread::no_op_safepoint()) != NULL) {
444 // Force a safepoint since we have not had one for at least
445 // 'GuaranteedSafepointInterval' milliseconds and we need to clean
446 // something. This will run all the clean-up processing that needs
447 // to be done at a safepoint.
448 SafepointSynchronize::begin();
449 #ifdef ASSERT
450 if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();
451 #endif
452 SafepointSynchronize::end();
453 _cur_vm_operation = NULL;
454 }
455 }
456 _cur_vm_operation = _vm_queue->remove_next();
457 }
458
459 if (should_terminate()) break;
460 } // Release mu_queue_lock
461
462 //
463 // Execute VM operation
464 //
465 { HandleMark hm(VMThread::vm_thread());
466
467 EventMark em("Executing VM operation: %s", vm_operation()->name());
468 assert(_cur_vm_operation != NULL, "we should have found an operation to execute");
469
470 // If we are at a safepoint we will evaluate all the operations that
471 // follow that also require a safepoint
472 if (_cur_vm_operation->evaluate_at_safepoint()) {
473 log_debug(vmthread)("Evaluating safepoint VM operation: %s", _cur_vm_operation->name());
474
475 SafepointSynchronize::begin();
476
477 if (_timeout_task != NULL) {
478 _timeout_task->arm();
479 }
480
481 evaluate_operation(_cur_vm_operation);
482 _cur_vm_operation = NULL;
483
484 if (_timeout_task != NULL) {
485 _timeout_task->disarm();
486 }
487
488 // Complete safepoint synchronization
489 SafepointSynchronize::end();
490
491 } else { // not a safepoint operation
492 log_debug(vmthread)("Evaluating non-safepoint VM operation: %s", _cur_vm_operation->name());
493 if (TraceLongCompiles) {
494 elapsedTimer t;
495 t.start();
496 evaluate_operation(_cur_vm_operation);
497 t.stop();
498 double secs = t.seconds();
499 if (secs * 1e3 > LongCompileThreshold) {
500 // XXX - _cur_vm_operation should not be accessed after
501 // the completed count has been incremented; the waiting
502 // thread may have already freed this memory.
503 tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);
504 }
505 } else {
506 evaluate_operation(_cur_vm_operation);
507 }
508
509 _cur_vm_operation = NULL;
510 }
511 }
512
513 //
514 // Notify (potential) waiting Java thread(s)
515 { MonitorLocker mu(VMOperationRequest_lock, Mutex::_no_safepoint_check_flag);
516 mu.notify_all();
517 }
518 }
519 }
520
521 // A SkipGCALot object is used to elide the usual effect of gc-a-lot
522 // over a section of execution by a thread. Currently, it's used only to
523 // prevent re-entrant calls to GC.
524 class SkipGCALot : public StackObj {
525 private:
526 bool _saved;
527 Thread* _t;
528
529 public:
530 #ifdef ASSERT
531 SkipGCALot(Thread* t) : _t(t) {
532 _saved = _t->skip_gcalot();
533 _t->set_skip_gcalot(true);
534 }
535
536 ~SkipGCALot() {
537 assert(_t->skip_gcalot(), "Save-restore protocol invariant");
538 _t->set_skip_gcalot(_saved);
539 }
540 #else
541 SkipGCALot(Thread* t) { }
542 ~SkipGCALot() { }
543 #endif
544 };
545
546 void VMThread::execute(VM_Operation* op) {
547 Thread* t = Thread::current();
548
549 if (!t->is_VM_thread()) {
550 SkipGCALot sgcalot(t); // avoid re-entrant attempts to gc-a-lot
551 // JavaThread or WatcherThread
552 t->check_for_valid_safepoint_state();
553
554 // New request from Java thread, evaluate prologue
555 if (!op->doit_prologue()) {
556 return; // op was cancelled
557 }
558
559 // Setup VM_operations for execution
560 op->set_calling_thread(t);
561
562 // Get ticket number for the VM operation
563 int ticket = t->vm_operation_ticket();
564
565 // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the
566 // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests
567 // to be queued up during a safepoint synchronization.
568 {
569 MonitorLocker ml(VMOperationQueue_lock, Mutex::_no_safepoint_check_flag);
570 log_debug(vmthread)("Adding VM operation: %s", op->name());
571 _vm_queue->add(op);
572 ml.notify();
573 }
574 {
575 // Wait for completion of request
576 // Note: only a JavaThread triggers the safepoint check when locking
577 MonitorLocker ml(VMOperationRequest_lock,
578 t->is_Java_thread() ? Mutex::_safepoint_check_flag : Mutex::_no_safepoint_check_flag);
579 while(t->vm_operation_completed_count() < ticket) {
580 ml.wait();
581 }
582 }
583 op->doit_epilogue();
584 } else {
585 // invoked by VM thread; usually nested VM operation
586 assert(t->is_VM_thread(), "must be a VM thread");
587 VM_Operation* prev_vm_operation = vm_operation();
588 if (prev_vm_operation != NULL) {
589 // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler
590 // does not allow nested scavenges or compiles.
591 if (!prev_vm_operation->allow_nested_vm_operations()) {
592 fatal("Nested VM operation %s requested by operation %s",
593 op->name(), vm_operation()->name());
594 }
595 op->set_calling_thread(prev_vm_operation->calling_thread());
596 }
597
598 EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());
599
600 // Release all internal handles after operation is evaluated
601 HandleMark hm(t);
602 _cur_vm_operation = op;
603
604 if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {
605 SafepointSynchronize::begin();
606 op->evaluate();
607 SafepointSynchronize::end();
608 } else {
609 op->evaluate();
610 }
611
612 _cur_vm_operation = prev_vm_operation;
613 }
614 }
615
616 void VMThread::verify() {
617 oops_do(&VerifyOopClosure::verify_oop, NULL);
618 }