1 /*
2 * Copyright (c) 2018, 2023, 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. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25 package java.lang;
26
27 import java.nio.charset.StandardCharsets;
28 import java.security.AccessController;
29 import java.security.PrivilegedAction;
30 import java.util.Locale;
31 import java.util.Objects;
32 import java.util.concurrent.Callable;
33 import java.util.concurrent.CountDownLatch;
34 import java.util.concurrent.Executor;
35 import java.util.concurrent.Executors;
36 import java.util.concurrent.ForkJoinPool;
37 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
38 import java.util.concurrent.ForkJoinTask;
39 import java.util.concurrent.ForkJoinWorkerThread;
40 import java.util.concurrent.Future;
41 import java.util.concurrent.RejectedExecutionException;
42 import java.util.concurrent.ScheduledExecutorService;
43 import java.util.concurrent.ScheduledThreadPoolExecutor;
44 import jdk.internal.event.VirtualThreadEndEvent;
45 import jdk.internal.event.VirtualThreadPinnedEvent;
46 import jdk.internal.event.VirtualThreadStartEvent;
47 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
48 import jdk.internal.misc.CarrierThread;
49 import jdk.internal.misc.InnocuousThread;
50 import jdk.internal.misc.Unsafe;
51 import jdk.internal.vm.Continuation;
52 import jdk.internal.vm.ContinuationScope;
53 import jdk.internal.vm.StackableScope;
54 import jdk.internal.vm.ThreadContainer;
55 import jdk.internal.vm.ThreadContainers;
56 import jdk.internal.vm.annotation.ChangesCurrentThread;
57 import jdk.internal.vm.annotation.Hidden;
58 import jdk.internal.vm.annotation.IntrinsicCandidate;
59 import jdk.internal.vm.annotation.JvmtiMountTransition;
60 import jdk.internal.vm.annotation.ReservedStackAccess;
61 import sun.nio.ch.Interruptible;
62 import sun.security.action.GetPropertyAction;
63 import static java.util.concurrent.TimeUnit.*;
64
65 /**
66 * A thread that is scheduled by the Java virtual machine rather than the operating
67 * system.
68 */
69 final class VirtualThread extends BaseVirtualThread {
70 private static final Unsafe U = Unsafe.getUnsafe();
71 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
72 private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();
73 private static final ScheduledExecutorService[] DELAYED_TASK_SCHEDULERS = createDelayedTaskSchedulers();
74 private static final int TRACE_PINNING_MODE = tracePinningMode();
75
76 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
77 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
78 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
79 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
80
81 // scheduler and continuation
82 private final Executor scheduler;
83 private final Continuation cont;
84 private final Runnable runContinuation;
85
86 // virtual thread state, accessed by VM
87 private volatile int state;
88
89 /*
90 * Virtual thread state transitions:
91 *
92 * NEW -> STARTED // Thread.start, schedule to run
93 * STARTED -> TERMINATED // failed to start
94 * STARTED -> RUNNING // first run
95 * RUNNING -> TERMINATED // done
96 *
97 * RUNNING -> PARKING // Thread parking with LockSupport.park
98 * PARKING -> PARKED // cont.yield successful, parked indefinitely
99 * PARKING -> PINNED // cont.yield failed, parked indefinitely on carrier
100 * PARKED -> UNPARKED // unparked, may be scheduled to continue
101 * PINNED -> RUNNING // unparked, continue execution on same carrier
102 * UNPARKED -> RUNNING // continue execution after park
103 *
104 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
105 * TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked
106 * TIMED_PARKING -> TIMED_PINNED // cont.yield failed, timed-parked on carrier
107 * TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue
108 * TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier
109 *
110 * RUNNABLE -> BLOCKING // blocking on monitor enter
111 * BLOCKING -> BLOCKED // blocked on monitor enter
112 * BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue
113 * UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter
114 *
115 * RUNNING -> YIELDING // Thread.yield
116 * YIELDING -> YIELDED // cont.yield successful, may be scheduled to continue
117 * YIELDING -> RUNNING // cont.yield failed
118 * YIELDED -> RUNNING // continue execution after Thread.yield
119 */
120 private static final int NEW = 0;
121 private static final int STARTED = 1;
122 private static final int RUNNING = 2; // runnable-mounted
123
124 // untimed and timed parking
125 private static final int PARKING = 3;
126 private static final int PARKED = 4; // unmounted
127 private static final int PINNED = 5; // mounted
128 private static final int TIMED_PARKING = 6;
129 private static final int TIMED_PARKED = 7; // unmounted
130 private static final int TIMED_PINNED = 8; // mounted
131 private static final int UNPARKED = 9; // unmounted but runnable
132
133 // Thread.yield
134 private static final int YIELDING = 10;
135 private static final int YIELDED = 11; // unmounted but runnable
136
137 // monitor enter
138 private static final int BLOCKING = 12;
139 private static final int BLOCKED = 13; // unmounted
140 private static final int UNBLOCKED = 14; // unmounted but runnable
141
142 private static final int TERMINATED = 99; // final state
143
144 // can be suspended from scheduling when unmounted
145 private static final int SUSPENDED = 1 << 8;
146
147 // parking permit
148 private volatile boolean parkPermit;
149
150 // unblocked
151 private volatile boolean unblocked;
152
153 // carrier thread when mounted, accessed by VM
154 private volatile Thread carrierThread;
155
156 // termination object when joining, created lazily if needed
157 private volatile CountDownLatch termination;
158
159 /**
160 * Returns the continuation scope used for virtual threads.
161 */
162 static ContinuationScope continuationScope() {
163 return VTHREAD_SCOPE;
164 }
165
166 /**
167 * Creates a new {@code VirtualThread} to run the given task with the given
168 * scheduler. If the given scheduler is {@code null} and the current thread
169 * is a platform thread then the newly created virtual thread will use the
170 * default scheduler. If given scheduler is {@code null} and the current
171 * thread is a virtual thread then the current thread's scheduler is used.
172 *
173 * @param scheduler the scheduler or null
174 * @param name thread name
175 * @param characteristics characteristics
176 * @param task the task to execute
177 */
178 VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
179 super(name, characteristics, /*bound*/ false);
180 Objects.requireNonNull(task);
181
182 // choose scheduler if not specified
183 if (scheduler == null) {
184 Thread parent = Thread.currentThread();
185 if (parent instanceof VirtualThread vparent) {
186 scheduler = vparent.scheduler;
187 } else {
188 scheduler = DEFAULT_SCHEDULER;
189 }
190 }
191
192 this.scheduler = scheduler;
193 this.cont = new VThreadContinuation(this, task);
194 this.runContinuation = this::runContinuation;
195 }
196
197 /**
198 * The continuation that a virtual thread executes.
199 */
200 private static class VThreadContinuation extends Continuation {
201 VThreadContinuation(VirtualThread vthread, Runnable task) {
202 super(VTHREAD_SCOPE, wrap(vthread, task));
203 }
204 @Override
205 protected void onPinned(Continuation.Pinned reason) {
206 if (TRACE_PINNING_MODE > 0) {
207 boolean printAll = (TRACE_PINNING_MODE == 1);
208 VirtualThread vthread = (VirtualThread) Thread.currentThread();
209 int oldState = vthread.state();
210 try {
211 // avoid printing when in transition states
212 vthread.setState(RUNNING);
213 PinnedThreadPrinter.printStackTrace(System.out, printAll);
214 } finally {
215 vthread.setState(oldState);
216 }
217 }
218 }
219 private static Runnable wrap(VirtualThread vthread, Runnable task) {
220 return new Runnable() {
221 @Hidden
222 public void run() {
223 vthread.run(task);
224 }
225 };
226 }
227 }
228
229 /**
230 * Runs or continues execution on the current thread. The virtual thread is mounted
231 * on the current thread before the task runs or continues. It unmounts when the
232 * task completes or yields.
233 */
234 @ChangesCurrentThread
235 private void runContinuation() {
236 // the carrier must be a platform thread
237 if (Thread.currentThread().isVirtual()) {
238 throw new WrongThreadException();
239 }
240
241 // set state to RUNNING
242 int initialState = state();
243 if (initialState == STARTED || initialState == UNPARKED
244 || initialState == UNBLOCKED || initialState == YIELDED) {
245 // newly started or continue after parking/blocking/Thread.yield
246 if (!compareAndSetState(initialState, RUNNING)) {
247 return;
248 }
249 // consume parking permit when continuing after parking
250 if (initialState == UNPARKED) {
251 setParkPermit(false);
252 }
253 } else {
254 // not runnable
255 return;
256 }
257
258 mount();
259 try {
260 cont.run();
261 } finally {
262 unmount();
263 if (cont.isDone()) {
264 afterDone();
265 } else {
266 afterYield();
267 }
268 }
269 }
270
271 /**
272 * Submits the runContinuation task to the scheduler. For the default scheduler,
273 * and calling it on a worker thread, the task will be pushed to the local queue,
274 * otherwise it will be pushed to an external submission queue.
275 * @throws RejectedExecutionException
276 */
277 private void submitRunContinuation() {
278 try {
279 scheduler.execute(runContinuation);
280 } catch (RejectedExecutionException ree) {
281 submitFailed(ree);
282 throw ree;
283 }
284 }
285
286 /**
287 * Submits the runContinuation task the scheduler. For the default scheduler, the task
288 * will be pushed to an external submission queue.
289 * @throws RejectedExecutionException
290 */
291 private void externalSubmitRunContinuation() {
292 if (scheduler == DEFAULT_SCHEDULER
293 && currentCarrierThread() instanceof CarrierThread ct) {
294 externalSubmitRunContinuation(ct.getPool());
295 } else {
296 submitRunContinuation();
297 }
298 }
299
300 /**
301 * Submits the runContinuation task to given scheduler with a lazy submit.
302 * @throws RejectedExecutionException
303 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
304 */
305 private void lazySubmitRunContinuation(ForkJoinPool pool) {
306 try {
307 pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
308 } catch (RejectedExecutionException ree) {
309 submitFailed(ree);
310 throw ree;
311 }
312 }
313
314 /**
315 * Submits the runContinuation task to the given scheduler as an external submit.
316 * @throws RejectedExecutionException
317 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
318 */
319 private void externalSubmitRunContinuation(ForkJoinPool pool) {
320 try {
321 pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
322 } catch (RejectedExecutionException ree) {
323 submitFailed(ree);
324 throw ree;
325 }
326 }
327
328 /**
329 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
330 */
331 private void submitFailed(RejectedExecutionException ree) {
332 var event = new VirtualThreadSubmitFailedEvent();
333 if (event.isEnabled()) {
334 event.javaThreadId = threadId();
335 event.exceptionMessage = ree.getMessage();
336 event.commit();
337 }
338 }
339
340 /**
341 * Runs a task in the context of this virtual thread.
342 */
343 private void run(Runnable task) {
344 assert Thread.currentThread() == this && state == RUNNING;
345
346 // notify JVMTI, may post VirtualThreadStart event
347 notifyJvmtiStart();
348
349 // emit JFR event if enabled
350 if (VirtualThreadStartEvent.isTurnedOn()) {
351 var event = new VirtualThreadStartEvent();
352 event.javaThreadId = threadId();
353 event.commit();
354 }
355
356 Object bindings = Thread.scopedValueBindings();
357 try {
358 runWith(bindings, task);
359 } catch (Throwable exc) {
360 dispatchUncaughtException(exc);
361 } finally {
362 try {
363 // pop any remaining scopes from the stack, this may block
364 StackableScope.popAll();
365
366 // emit JFR event if enabled
367 if (VirtualThreadEndEvent.isTurnedOn()) {
368 var event = new VirtualThreadEndEvent();
369 event.javaThreadId = threadId();
370 event.commit();
371 }
372
373 } finally {
374 // notify JVMTI, may post VirtualThreadEnd event
375 notifyJvmtiEnd();
376 }
377 }
378 }
379
380 /**
381 * Mounts this virtual thread onto the current platform thread. On
382 * return, the current thread is the virtual thread.
383 */
384 @ChangesCurrentThread
385 @ReservedStackAccess
386 private void mount() {
387 // notify JVMTI before mount
388 notifyJvmtiMount(/*hide*/true);
389
390 // sets the carrier thread
391 Thread carrier = Thread.currentCarrierThread();
392 setCarrierThread(carrier);
393
394 // sync up carrier thread interrupt status if needed
395 if (interrupted) {
396 carrier.setInterrupt();
397 } else if (carrier.isInterrupted()) {
398 synchronized (interruptLock) {
399 // need to recheck interrupt status
400 if (!interrupted) {
401 carrier.clearInterrupt();
402 }
403 }
404 }
405
406 // set Thread.currentThread() to return this virtual thread
407 carrier.setCurrentThread(this);
408 }
409
410 /**
411 * Unmounts this virtual thread from the carrier. On return, the
412 * current thread is the current platform thread.
413 */
414 @ChangesCurrentThread
415 @ReservedStackAccess
416 private void unmount() {
417 assert !Thread.holdsLock(interruptLock);
418
419 // set Thread.currentThread() to return the platform thread
420 Thread carrier = this.carrierThread;
421 carrier.setCurrentThread(carrier);
422
423 // break connection to carrier thread, synchronized with interrupt
424 synchronized (interruptLock) {
425 setCarrierThread(null);
426 }
427 carrier.clearInterrupt();
428
429 // notify JVMTI after unmount
430 notifyJvmtiUnmount(/*hide*/false);
431 }
432
433 /**
434 * Sets the current thread to the current carrier thread.
435 */
436 @ChangesCurrentThread
437 @JvmtiMountTransition
438 private void switchToCarrierThread() {
439 notifyJvmtiHideFrames(true);
440 Thread carrier = this.carrierThread;
441 assert Thread.currentThread() == this
442 && carrier == Thread.currentCarrierThread();
443 carrier.setCurrentThread(carrier);
444 }
445
446 /**
447 * Sets the current thread to the given virtual thread.
448 */
449 @ChangesCurrentThread
450 @JvmtiMountTransition
451 private void switchToVirtualThread(VirtualThread vthread) {
452 Thread carrier = vthread.carrierThread;
453 assert carrier == Thread.currentCarrierThread();
454 carrier.setCurrentThread(vthread);
455 notifyJvmtiHideFrames(false);
456 }
457
458 /**
459 * Executes the given value returning task on the current carrier thread.
460 */
461 @ChangesCurrentThread
462 <V> V executeOnCarrierThread(Callable<V> task) throws Exception {
463 assert Thread.currentThread() == this;
464 switchToCarrierThread();
465 try {
466 return task.call();
467 } finally {
468 switchToVirtualThread(this);
469 }
470 }
471
472 /**
473 * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
474 * the continuation continues.
475 */
476 @Hidden
477 private boolean yieldContinuation() {
478 notifyJvmtiUnmount(/*hide*/true);
479 try {
480 return Continuation.yield(VTHREAD_SCOPE);
481 } finally {
482 notifyJvmtiMount(/*hide*/false);
483 }
484 }
485
486 /**
487 * Invoked after the continuation yields. If parking then it sets the state
488 * and also re-submits the task to continue if unparked while parking.
489 * If yielding due to Thread.yield then it just submits the task to continue.
490 */
491 private void afterYield() {
492 assert carrierThread == null;
493
494 int s = state();
495
496 // LockSupport.park/parkNanos
497 if (s == PARKING || s == TIMED_PARKING) {
498 int newState = (s == PARKING) ? PARKED : TIMED_PARKED;
499 setState(newState);
500
501 // may have been unparked while parking
502 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
503 // lazy submit to continue on the current thread as carrier if possible
504 if (currentThread() instanceof CarrierThread ct) {
505 lazySubmitRunContinuation(ct.getPool());
506 } else {
507 submitRunContinuation();
508 }
509
510 }
511 return;
512 }
513
514 // Thread.yield
515 if (s == YIELDING) {
516 setState(YIELDED);
517
518 // external submit if there are no tasks in the local task queue
519 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
520 externalSubmitRunContinuation(ct.getPool());
521 } else {
522 submitRunContinuation();
523 }
524 return;
525 }
526
527 // blocking on monitorenter
528 if (s == BLOCKING) {
529 setState(BLOCKED);
530 if (unblocked && compareAndSetState(BLOCKED, UNBLOCKED)) {
531 unblocked = false;
532 submitRunContinuation();
533 }
534 return;
535 }
536
537 assert false;
538 }
539
540 /**
541 * Invoked after the continuation completes.
542 */
543 private void afterDone() {
544 afterDone(true);
545 }
546
547 /**
548 * Invoked after the continuation completes (or start failed). Sets the thread
549 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
550 *
551 * @param notifyContainer true if its container should be notified
552 */
553 private void afterDone(boolean notifyContainer) {
554 assert carrierThread == null;
555 setState(TERMINATED);
556
557 // notify anyone waiting for this virtual thread to terminate
558 CountDownLatch termination = this.termination;
559 if (termination != null) {
560 assert termination.getCount() == 1;
561 termination.countDown();
562 }
563
564 // notify container
565 if (notifyContainer) {
566 threadContainer().onExit(this);
567 }
568
569 // clear references to thread locals
570 clearReferences();
571 }
572
573 /**
574 * Schedules this {@code VirtualThread} to execute.
575 *
576 * @throws IllegalStateException if the container is shutdown or closed
577 * @throws IllegalThreadStateException if the thread has already been started
578 * @throws RejectedExecutionException if the scheduler cannot accept a task
579 */
580 @Override
581 void start(ThreadContainer container) {
582 if (!compareAndSetState(NEW, STARTED)) {
583 throw new IllegalThreadStateException("Already started");
584 }
585
586 // bind thread to container
587 assert threadContainer() == null;
588 setThreadContainer(container);
589
590 // start thread
591 boolean addedToContainer = false;
592 boolean started = false;
593 try {
594 container.onStart(this); // may throw
595 addedToContainer = true;
596
597 // scoped values may be inherited
598 inheritScopedValueBindings(container);
599
600 // submit task to run thread, using externalSubmit if possible
601 externalSubmitRunContinuation();
602 started = true;
603 } finally {
604 if (!started) {
605 afterDone(addedToContainer);
606 }
607 }
608 }
609
610 @Override
611 public void start() {
612 start(ThreadContainers.root());
613 }
614
615 @Override
616 public void run() {
617 // do nothing
618 }
619
620 /**
621 * Parks until unparked or interrupted. If already unparked then the parking
622 * permit is consumed and this method completes immediately (meaning it doesn't
623 * yield). It also completes immediately if the interrupt status is set.
624 */
625 @Override
626 void park() {
627 assert Thread.currentThread() == this;
628
629 // complete immediately if parking permit available or interrupted
630 if (getAndSetParkPermit(false) || interrupted)
631 return;
632
633 // park the thread
634 boolean yielded = false;
635 setState(PARKING);
636 try {
637 yielded = yieldContinuation(); // may throw
638 } finally {
639 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
640 if (!yielded) {
641 assert state() == PARKING;
642 setState(RUNNING);
643 }
644 }
645
646 // park on the carrier thread when pinned
647 if (!yielded) {
648 parkOnCarrierThread(false, 0);
649 }
650 }
651
652 /**
653 * Parks up to the given waiting time or until unparked or interrupted.
654 * If already unparked then the parking permit is consumed and this method
655 * completes immediately (meaning it doesn't yield). It also completes immediately
656 * if the interrupt status is set or the waiting time is {@code <= 0}.
657 *
658 * @param nanos the maximum number of nanoseconds to wait.
659 */
660 @Override
661 void parkNanos(long nanos) {
662 assert Thread.currentThread() == this;
663
664 // complete immediately if parking permit available or interrupted
665 if (getAndSetParkPermit(false) || interrupted)
666 return;
667
668 // park the thread for the waiting time
669 if (nanos > 0) {
670 long startTime = System.nanoTime();
671
672 boolean yielded = false;
673 Future<?> unparker = scheduleUnpark(nanos); // may throw OOME
674 setState(TIMED_PARKING);
675 try {
676 yielded = yieldContinuation(); // may throw
677 } finally {
678 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
679 if (!yielded) {
680 assert state() == TIMED_PARKING;
681 setState(RUNNING);
682 }
683 cancel(unparker);
684 }
685
686 // park on carrier thread for remaining time when pinned
687 if (!yielded) {
688 long remainingNanos = nanos - (System.nanoTime() - startTime);
689 parkOnCarrierThread(true, remainingNanos);
690 }
691 }
692 }
693
694 /**
695 * Parks the current carrier thread up to the given waiting time or until
696 * unparked or interrupted. If the virtual thread is interrupted then the
697 * interrupt status will be propagated to the carrier thread.
698 * @param timed true for a timed park, false for untimed
699 * @param nanos the waiting time in nanoseconds
700 */
701 private void parkOnCarrierThread(boolean timed, long nanos) {
702 assert state() == RUNNING;
703
704 VirtualThreadPinnedEvent event;
705 try {
706 event = new VirtualThreadPinnedEvent();
707 event.begin();
708 } catch (OutOfMemoryError e) {
709 event = null;
710 }
711
712 setState(timed ? TIMED_PINNED : PINNED);
713 try {
714 if (!parkPermit) {
715 if (!timed) {
716 U.park(false, 0);
717 } else if (nanos > 0) {
718 U.park(false, nanos);
719 }
720 }
721 } finally {
722 setState(RUNNING);
723 }
724
725 // consume parking permit
726 setParkPermit(false);
727
728 if (event != null) {
729 try {
730 event.commit();
731 } catch (OutOfMemoryError e) {
732 // ignore
733 }
734 }
735 }
736
737 /**
738 * Schedule this virtual thread to be unparked after a given delay.
739 */
740 @ChangesCurrentThread
741 private Future<?> scheduleUnpark(long nanos) {
742 assert Thread.currentThread() == this;
743 // need to switch to current carrier thread to avoid nested parking
744 switchToCarrierThread();
745 try {
746 return delayedTaskScheduler().schedule(this::unpark, nanos, NANOSECONDS);
747 } finally {
748 switchToVirtualThread(this);
749 }
750 }
751
752 /**
753 * Cancels a task if it has not completed.
754 */
755 @ChangesCurrentThread
756 private void cancel(Future<?> future) {
757 assert Thread.currentThread() == this;
758 if (!future.isDone()) {
759 // need to switch to current carrier thread to avoid nested parking
760 switchToCarrierThread();
761 try {
762 future.cancel(false);
763 } finally {
764 switchToVirtualThread(this);
765 }
766 }
767 }
768
769 /**
770 * Re-enables this virtual thread for scheduling. If the virtual thread was
771 * {@link #park() parked} then it will be unblocked, otherwise its next call
772 * to {@code park} or {@linkplain #parkNanos(long) parkNanos} is guaranteed
773 * not to block.
774 * @throws RejectedExecutionException if the scheduler cannot accept a task
775 */
776 @Override
777 @ChangesCurrentThread
778 void unpark() {
779 Thread currentThread = Thread.currentThread();
780 if (!getAndSetParkPermit(true) && currentThread != this) {
781 int s = state();
782 boolean parked = (s == PARKED) || (s == TIMED_PARKED);
783 if (parked && compareAndSetState(s, UNPARKED)) {
784 if (currentThread instanceof VirtualThread vthread) {
785 vthread.switchToCarrierThread();
786 try {
787 submitRunContinuation();
788 } finally {
789 switchToVirtualThread(vthread);
790 }
791 } else {
792 submitRunContinuation();
793 }
794 } else if ((s == PINNED) || (s == TIMED_PINNED)) {
795 // unpark carrier thread when pinned
796 synchronized (carrierThreadAccessLock()) {
797 Thread carrier = carrierThread;
798 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
799 U.unpark(carrier);
800 }
801 }
802 }
803 }
804 }
805
806 /**
807 * Re-enables this virtual thread for scheduling after blocking on monitor enter.
808 * @throws RejectedExecutionException if the scheduler cannot accept a task
809 */
810 private void unblock() {
811 assert !Thread.currentThread().isVirtual();
812 unblocked = true;
813 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) {
814 unblocked = false;
815 submitRunContinuation();
816 }
817 }
818
819 /**
820 * Attempts to yield the current virtual thread (Thread.yield).
821 */
822 void tryYield() {
823 assert Thread.currentThread() == this;
824 setState(YIELDING);
825 boolean yielded = false;
826 try {
827 yielded = yieldContinuation(); // may throw
828 } finally {
829 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
830 if (!yielded) {
831 assert state() == YIELDING;
832 setState(RUNNING);
833 }
834 }
835 }
836
837 /**
838 * Sleep the current thread for the given sleep time (in nanoseconds). If
839 * nanos is 0 then the thread will attempt to yield.
840 *
841 * @implNote This implementation parks the thread for the given sleeping time
842 * and will therefore be observed in PARKED state during the sleep. Parking
843 * will consume the parking permit so this method makes available the parking
844 * permit after the sleep. This may be observed as a spurious, but benign,
845 * wakeup when the thread subsequently attempts to park.
846 *
847 * @param nanos the maximum number of nanoseconds to sleep
848 * @throws InterruptedException if interrupted while sleeping
849 */
850 void sleepNanos(long nanos) throws InterruptedException {
851 assert Thread.currentThread() == this && nanos >= 0;
852 if (getAndClearInterrupt())
853 throw new InterruptedException();
854 if (nanos == 0) {
855 tryYield();
856 } else {
857 // park for the sleep time
858 try {
859 long remainingNanos = nanos;
860 long startNanos = System.nanoTime();
861 while (remainingNanos > 0) {
862 parkNanos(remainingNanos);
863 if (getAndClearInterrupt()) {
864 throw new InterruptedException();
865 }
866 remainingNanos = nanos - (System.nanoTime() - startNanos);
867 }
868 } finally {
869 // may have been unparked while sleeping
870 setParkPermit(true);
871 }
872 }
873 }
874
875 /**
876 * Waits up to {@code nanos} nanoseconds for this virtual thread to terminate.
877 * A timeout of {@code 0} means to wait forever.
878 *
879 * @throws InterruptedException if interrupted while waiting
880 * @return true if the thread has terminated
881 */
882 boolean joinNanos(long nanos) throws InterruptedException {
883 if (state() == TERMINATED)
884 return true;
885
886 // ensure termination object exists, then re-check state
887 CountDownLatch termination = getTermination();
888 if (state() == TERMINATED)
889 return true;
890
891 // wait for virtual thread to terminate
892 if (nanos == 0) {
893 termination.await();
894 } else {
895 boolean terminated = termination.await(nanos, NANOSECONDS);
896 if (!terminated) {
897 // waiting time elapsed
898 return false;
899 }
900 }
901 assert state() == TERMINATED;
902 return true;
903 }
904
905 @Override
906 @SuppressWarnings("removal")
907 public void interrupt() {
908 if (Thread.currentThread() != this) {
909 checkAccess();
910 synchronized (interruptLock) {
911 interrupted = true;
912 Interruptible b = nioBlocker;
913 if (b != null) {
914 // ensure current thread doesn't unmount while holding interruptLock
915 Continuation.pin();
916 try {
917 b.interrupt(this);
918 } finally {
919 Continuation.unpin();
920 }
921 }
922
923 // interrupt carrier thread if mounted
924 Thread carrier = carrierThread;
925 if (carrier != null) carrier.setInterrupt();
926 }
927 } else {
928 interrupted = true;
929 carrierThread.setInterrupt();
930 }
931 unpark();
932 }
933
934 @Override
935 public boolean isInterrupted() {
936 return interrupted;
937 }
938
939 @Override
940 boolean getAndClearInterrupt() {
941 assert Thread.currentThread() == this;
942 boolean oldValue = interrupted;
943 if (oldValue) {
944 // ensure current thread doesn't unmount trying to enter interruptLock
945 Continuation.pin();
946 try {
947 synchronized (interruptLock) {
948 interrupted = false;
949 carrierThread.clearInterrupt();
950 }
951 } finally {
952 Continuation.unpin();
953 }
954 }
955 return oldValue;
956 }
957
958 @Override
959 Thread.State threadState() {
960 int s = state();
961 switch (s & ~SUSPENDED) {
962 case NEW:
963 return Thread.State.NEW;
964 case STARTED:
965 // return NEW if thread container not yet set
966 if (threadContainer() == null) {
967 return Thread.State.NEW;
968 } else {
969 return Thread.State.RUNNABLE;
970 }
971 case UNPARKED:
972 case UNBLOCKED:
973 case YIELDED:
974 // runnable, not mounted
975 return Thread.State.RUNNABLE;
976 case RUNNING:
977 // if mounted then return state of carrier thread
978 if (Thread.currentThread() != this) {
979 synchronized (carrierThreadAccessLock()) {
980 Thread carrier = this.carrierThread;
981 if (carrier != null) {
982 return carrier.threadState();
983 }
984 }
985 }
986 // runnable, mounted
987 return Thread.State.RUNNABLE;
988 case PARKING:
989 case TIMED_PARKING:
990 case YIELDING:
991 case BLOCKING:
992 // runnable, in transition
993 return Thread.State.RUNNABLE;
994 case PARKED:
995 case PINNED:
996 return State.WAITING;
997 case TIMED_PARKED:
998 case TIMED_PINNED:
999 return State.TIMED_WAITING;
1000 case BLOCKED:
1001 return State.BLOCKED;
1002 case TERMINATED:
1003 return Thread.State.TERMINATED;
1004 default:
1005 throw new InternalError();
1006 }
1007 }
1008
1009 @Override
1010 boolean alive() {
1011 int s = state;
1012 return (s != NEW && s != TERMINATED);
1013 }
1014
1015 @Override
1016 boolean isTerminated() {
1017 return (state == TERMINATED);
1018 }
1019
1020 @Override
1021 StackTraceElement[] asyncGetStackTrace() {
1022 StackTraceElement[] stackTrace;
1023 do {
1024 stackTrace = (carrierThread != null)
1025 ? super.asyncGetStackTrace() // mounted
1026 : tryGetStackTrace(); // unmounted
1027 if (stackTrace == null) {
1028 Thread.yield();
1029 }
1030 } while (stackTrace == null);
1031 return stackTrace;
1032 }
1033
1034 /**
1035 * Returns the stack trace for this virtual thread if it is unmounted.
1036 * Returns null if the thread is mounted or in transition.
1037 */
1038 private StackTraceElement[] tryGetStackTrace() {
1039 int initialState = state();
1040 switch (initialState) {
1041 case NEW, STARTED, TERMINATED -> {
1042 return new StackTraceElement[0]; // unmounted, empty stack
1043 }
1044 case RUNNING, PINNED -> {
1045 return null; // mounted
1046 }
1047 case PARKED, TIMED_PARKED, BLOCKED -> {
1048 // unmounted, not runnable
1049 }
1050 case UNPARKED, UNBLOCKED, YIELDED -> {
1051 // unmounted, runnable
1052 }
1053 case PARKING, TIMED_PARKING, BLOCKING, YIELDING -> {
1054 return null; // in transition
1055 }
1056 default -> throw new InternalError();
1057 }
1058
1059 // thread is unmounted, prevent it from continuing
1060 int suspendedState = initialState | SUSPENDED;
1061 if (!compareAndSetState(initialState, suspendedState)) {
1062 return null;
1063 }
1064
1065 // get stack trace and restore state
1066 StackTraceElement[] stack;
1067 try {
1068 stack = cont.getStackTrace();
1069 } finally {
1070 assert state == suspendedState;
1071 setState(initialState);
1072 }
1073 boolean resubmit = switch (initialState) {
1074 case UNPARKED, UNBLOCKED, YIELDED -> {
1075 // resubmit as task may have run while suspended
1076 yield true;
1077 }
1078 case PARKED, TIMED_PARKED -> {
1079 // resubmit if unparked while suspended
1080 yield parkPermit && compareAndSetState(initialState, UNPARKED);
1081 }
1082 case BLOCKED -> {
1083 // resubmit if unblocked while suspended
1084 yield unblocked && compareAndSetState(BLOCKED, UNBLOCKED);
1085 }
1086 default -> throw new InternalError();
1087 };
1088 if (resubmit) {
1089 submitRunContinuation();
1090 }
1091 return stack;
1092 }
1093
1094 @Override
1095 public String toString() {
1096 StringBuilder sb = new StringBuilder("VirtualThread[#");
1097 sb.append(threadId());
1098 String name = getName();
1099 if (!name.isEmpty()) {
1100 sb.append(",");
1101 sb.append(name);
1102 }
1103 sb.append("]/");
1104
1105 // add the carrier state and thread name when mounted
1106 boolean mounted;
1107 if (Thread.currentThread() == this) {
1108 mounted = appendCarrierInfo(sb);
1109 } else {
1110 synchronized (carrierThreadAccessLock()) {
1111 mounted = appendCarrierInfo(sb);
1112 }
1113 }
1114
1115 // add virtual thread state when not mounted
1116 if (!mounted) {
1117 String stateAsString = threadState().toString();
1118 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1119 }
1120
1121 return sb.toString();
1122 }
1123
1124 /**
1125 * Appends the carrier state and thread name to the string buffer if mounted.
1126 * @return true if mounted, false if not mounted
1127 */
1128 private boolean appendCarrierInfo(StringBuilder sb) {
1129 assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock());
1130 Thread carrier = carrierThread;
1131 if (carrier != null) {
1132 String stateAsString = carrier.threadState().toString();
1133 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1134 sb.append('@');
1135 sb.append(carrier.getName());
1136 return true;
1137 } else {
1138 return false;
1139 }
1140 }
1141
1142 @Override
1143 public int hashCode() {
1144 return (int) threadId();
1145 }
1146
1147 @Override
1148 public boolean equals(Object obj) {
1149 return obj == this;
1150 }
1151
1152 /**
1153 * Returns a ScheduledExecutorService to execute a delayed task.
1154 */
1155 private ScheduledExecutorService delayedTaskScheduler() {
1156 long tid = Thread.currentThread().threadId();
1157 int index = (int) tid & (DELAYED_TASK_SCHEDULERS.length - 1);
1158 return DELAYED_TASK_SCHEDULERS[index];
1159 }
1160
1161 /**
1162 * Returns the termination object, creating it if needed.
1163 */
1164 private CountDownLatch getTermination() {
1165 CountDownLatch termination = this.termination;
1166 if (termination == null) {
1167 termination = new CountDownLatch(1);
1168 if (!U.compareAndSetReference(this, TERMINATION, null, termination)) {
1169 termination = this.termination;
1170 }
1171 }
1172 return termination;
1173 }
1174
1175 /**
1176 * Returns the lock object to synchronize on when accessing carrierThread.
1177 * The lock prevents carrierThread from being reset to null during unmount.
1178 */
1179 private Object carrierThreadAccessLock() {
1180 // return interruptLock as unmount has to coordinate with interrupt
1181 return interruptLock;
1182 }
1183
1184 // -- wrappers for get/set of state, parking permit, and carrier thread --
1185
1186 private int state() {
1187 return state; // volatile read
1188 }
1189
1190 private void setState(int newValue) {
1191 state = newValue; // volatile write
1192 }
1193
1194 private boolean compareAndSetState(int expectedValue, int newValue) {
1195 return U.compareAndSetInt(this, STATE, expectedValue, newValue);
1196 }
1197
1198 private void setParkPermit(boolean newValue) {
1199 if (parkPermit != newValue) {
1200 parkPermit = newValue;
1201 }
1202 }
1203
1204 private boolean getAndSetParkPermit(boolean newValue) {
1205 if (parkPermit != newValue) {
1206 return U.getAndSetBoolean(this, PARK_PERMIT, newValue);
1207 } else {
1208 return newValue;
1209 }
1210 }
1211
1212 private void setCarrierThread(Thread carrier) {
1213 // U.putReferenceRelease(this, CARRIER_THREAD, carrier);
1214 this.carrierThread = carrier;
1215 }
1216
1217 // -- JVM TI support --
1218
1219 @IntrinsicCandidate
1220 @JvmtiMountTransition
1221 private native void notifyJvmtiStart();
1222
1223 @IntrinsicCandidate
1224 @JvmtiMountTransition
1225 private native void notifyJvmtiEnd();
1226
1227 @IntrinsicCandidate
1228 @JvmtiMountTransition
1229 private native void notifyJvmtiMount(boolean hide);
1230
1231 @IntrinsicCandidate
1232 @JvmtiMountTransition
1233 private native void notifyJvmtiUnmount(boolean hide);
1234
1235 @IntrinsicCandidate
1236 @JvmtiMountTransition
1237 private native void notifyJvmtiHideFrames(boolean hide);
1238
1239 private static native void registerNatives();
1240 static {
1241 registerNatives();
1242 }
1243
1244 /**
1245 * Creates the default scheduler.
1246 */
1247 @SuppressWarnings("removal")
1248 private static ForkJoinPool createDefaultScheduler() {
1249 ForkJoinWorkerThreadFactory factory = pool -> {
1250 PrivilegedAction<ForkJoinWorkerThread> pa = () -> new CarrierThread(pool);
1251 return AccessController.doPrivileged(pa);
1252 };
1253 PrivilegedAction<ForkJoinPool> pa = () -> {
1254 int parallelism, maxPoolSize, minRunnable;
1255 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1256 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1257 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1258 if (parallelismValue != null) {
1259 parallelism = Integer.max(Integer.parseInt(parallelismValue), 1);
1260 } else {
1261 parallelism = Runtime.getRuntime().availableProcessors();
1262 }
1263 if (maxPoolSizeValue != null) {
1264 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1265 if (maxPoolSize > 0) {
1266 parallelism = Integer.min(parallelism, maxPoolSize);
1267 } else {
1268 maxPoolSize = parallelism; // no spares
1269 }
1270 } else {
1271 maxPoolSize = Integer.max(parallelism, 256);
1272 }
1273 if (minRunnableValue != null) {
1274 minRunnable = Integer.parseInt(minRunnableValue);
1275 } else {
1276 minRunnable = Integer.max(parallelism / 2, 1);
1277 }
1278 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1279 boolean asyncMode = true; // FIFO
1280 return new ForkJoinPool(parallelism, factory, handler, asyncMode,
1281 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1282 };
1283 return AccessController.doPrivileged(pa);
1284 }
1285
1286 /**
1287 * Invoked by the VM for the Thread.vthread_scheduler diagnostic command.
1288 */
1289 private static byte[] printDefaultScheduler() {
1290 return String.format("%s%n", DEFAULT_SCHEDULER.toString())
1291 .getBytes(StandardCharsets.UTF_8);
1292 }
1293
1294 /**
1295 * Creates the ScheduledThreadPoolExecutors used to execute delayed tasks.
1296 */
1297 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1298 String propName = "jdk.virtualThreadScheduler.timerQueues";
1299 String propValue = GetPropertyAction.privilegedGetProperty(propName);
1300 int queueCount;
1301 if (propValue != null) {
1302 queueCount = Integer.parseInt(propValue);
1303 if (queueCount != Integer.highestOneBit(queueCount)) {
1304 throw new RuntimeException("Value of " + propName + " must be power of 2");
1305 }
1306 } else {
1307 int ncpus = Runtime.getRuntime().availableProcessors();
1308 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
1309 }
1310 var schedulers = new ScheduledExecutorService[queueCount];
1311 for (int i = 0; i < queueCount; i++) {
1312 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
1313 Executors.newScheduledThreadPool(1, task -> {
1314 Thread t = InnocuousThread.newThread("VirtualThread-unparker", task);
1315 t.setDaemon(true);
1316 return t;
1317 });
1318 stpe.setRemoveOnCancelPolicy(true);
1319 schedulers[i] = stpe;
1320 }
1321 return schedulers;
1322 }
1323
1324 /**
1325 * Reads the value of the jdk.tracePinnedThreads property to determine if stack
1326 * traces should be printed when a carrier thread is pinned when a virtual thread
1327 * attempts to park.
1328 */
1329 private static int tracePinningMode() {
1330 String propValue = GetPropertyAction.privilegedGetProperty("jdk.tracePinnedThreads");
1331 if (propValue != null) {
1332 if (propValue.length() == 0 || "full".equalsIgnoreCase(propValue))
1333 return 1;
1334 if ("short".equalsIgnoreCase(propValue))
1335 return 2;
1336 }
1337 return 0;
1338 }
1339
1340 /**
1341 * Unblock virtual threads that are ready to be scheduled again.
1342 */
1343 private static void processPendingList() {
1344 // TBD invoke unblock
1345 }
1346
1347 static {
1348 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker",
1349 VirtualThread::processPendingList);
1350 unblocker.setDaemon(true);
1351 unblocker.start();
1352 }
1353 }