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