1 /*
2 * Copyright (c) 2018, 2024, 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 java.util.concurrent.TimeUnit;
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 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[] DELAYED_TASK_SCHEDULERS = createDelayedTaskSchedulers();
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 -> UNPARKED // unparked, may be scheduled to continue
100 * PINNED -> RUNNING // unparked, continue execution on same carrier
101 * UNPARKED -> RUNNING // continue execution after park
102 *
103 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
104 * TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked
105 * TIMED_PARKING -> TIMED_PINNED // cont.yield failed, timed-parked on carrier
106 * TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue
107 * TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier
108 *
109 * RUNNING -> YIELDING // Thread.yield
110 * YIELDING -> YIELDED // cont.yield successful, may be scheduled to continue
111 * YIELDING -> RUNNING // cont.yield failed
112 * YIELDED -> RUNNING // continue execution after Thread.yield
113 */
114 private static final int NEW = 0;
115 private static final int STARTED = 1;
116 private static final int RUNNING = 2; // runnable-mounted
117
118 // untimed and timed parking
119 private static final int PARKING = 3;
120 private static final int PARKED = 4; // unmounted
121 private static final int PINNED = 5; // mounted
122 private static final int TIMED_PARKING = 6;
123 private static final int TIMED_PARKED = 7; // unmounted
124 private static final int TIMED_PINNED = 8; // mounted
125 private static final int UNPARKED = 9; // unmounted but runnable
126
127 // Thread.yield
128 private static final int YIELDING = 10;
129 private static final int YIELDED = 11; // unmounted but runnable
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 /**
147 * Returns the default scheduler.
148 */
149 static Executor defaultScheduler() {
150 return DEFAULT_SCHEDULER;
151 }
152
153 /**
154 * Returns the continuation scope used for virtual threads.
155 */
156 static ContinuationScope continuationScope() {
157 return VTHREAD_SCOPE;
158 }
159
160 /**
161 * Creates a new {@code VirtualThread} to run the given task with the given
162 * scheduler. If the given scheduler is {@code null} and the current thread
163 * is a platform thread then the newly created virtual thread will use the
164 * default scheduler. If given scheduler is {@code null} and the current
165 * thread is a virtual thread then the current thread's scheduler is used.
166 *
167 * @param scheduler the scheduler or null
168 * @param name thread name
169 * @param characteristics characteristics
170 * @param task the task to execute
171 */
172 VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
173 super(name, characteristics, /*bound*/ false);
174 Objects.requireNonNull(task);
175
176 // choose scheduler if not specified
177 if (scheduler == null) {
178 Thread parent = Thread.currentThread();
179 if (parent instanceof VirtualThread vparent) {
180 scheduler = vparent.scheduler;
181 } else {
182 scheduler = DEFAULT_SCHEDULER;
183 }
184 }
185
186 this.scheduler = scheduler;
187 this.cont = new VThreadContinuation(this, task);
188 this.runContinuation = this::runContinuation;
189 }
190
191 /**
192 * The continuation that a virtual thread executes.
193 */
194 private static class VThreadContinuation extends Continuation {
195 VThreadContinuation(VirtualThread vthread, Runnable task) {
196 super(VTHREAD_SCOPE, wrap(vthread, task));
197 }
198 @Override
199 protected void onPinned(Continuation.Pinned reason) {
200 if (TRACE_PINNING_MODE > 0) {
201 boolean printAll = (TRACE_PINNING_MODE == 1);
202 VirtualThread vthread = (VirtualThread) Thread.currentThread();
203 int oldState = vthread.state();
204 try {
205 // avoid printing when in transition states
206 vthread.setState(RUNNING);
207 PinnedThreadPrinter.printStackTrace(System.out, reason, printAll);
208 } finally {
209 vthread.setState(oldState);
210 }
211 }
212 }
213 private static Runnable wrap(VirtualThread vthread, Runnable task) {
214 return new Runnable() {
215 @Hidden
216 public void run() {
217 vthread.run(task);
218 }
219 };
220 }
221 }
222
223 /**
224 * Runs or continues execution on the current thread. The virtual thread is mounted
225 * on the current thread before the task runs or continues. It unmounts when the
226 * task completes or yields.
227 */
228 @ChangesCurrentThread // allow mount/unmount to be inlined
229 private void runContinuation() {
230 // the carrier must be a platform thread
231 if (Thread.currentThread().isVirtual()) {
232 throw new WrongThreadException();
233 }
234
235 // set state to RUNNING
236 int initialState = state();
237 if (initialState == STARTED || initialState == UNPARKED || initialState == YIELDED) {
238 // newly started or continue after parking/blocking/Thread.yield
239 if (!compareAndSetState(initialState, RUNNING)) {
240 return;
241 }
242 // consume parking permit when continuing after parking
243 if (initialState == UNPARKED) {
244 setParkPermit(false);
245 }
246 } else {
247 // not runnable
248 return;
249 }
250
251 mount();
252 try {
253 cont.run();
254 } finally {
255 unmount();
256 if (cont.isDone()) {
257 afterDone();
258 } else {
259 afterYield();
260 }
261 }
262 }
263
264 /**
265 * Submits the runContinuation task to the scheduler. For the default scheduler,
266 * and calling it on a worker thread, the task will be pushed to the local queue,
267 * otherwise it will be pushed to an external submission queue.
268 * @param scheduler the scheduler
269 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
270 * @throws RejectedExecutionException
271 */
272 @ChangesCurrentThread
273 private void submitRunContinuation(Executor scheduler, boolean retryOnOOME) {
274 boolean done = false;
275 while (!done) {
276 try {
277 // The scheduler's execute method is invoked in the context of the
278 // carrier thread. For the default scheduler this ensures that the
279 // current thread is a ForkJoinWorkerThread so the task will be pushed
280 // to the local queue. For other schedulers, it avoids deadlock that
281 // would arise due to platform and virtual threads contending for a
282 // lock on the scheduler's submission queue.
283 if (currentThread() instanceof VirtualThread vthread) {
284 vthread.switchToCarrierThread();
285 try {
286 scheduler.execute(runContinuation);
287 } finally {
288 switchToVirtualThread(vthread);
289 }
290 } else {
291 scheduler.execute(runContinuation);
292 }
293 done = true;
294 } catch (RejectedExecutionException ree) {
295 submitFailed(ree);
296 throw ree;
297 } catch (OutOfMemoryError e) {
298 if (retryOnOOME) {
299 U.park(false, 100_000_000); // 100ms
300 } else {
301 throw e;
302 }
303 }
304 }
305 }
306
307 /**
308 * Submits the runContinuation task to given scheduler with a lazy submit.
309 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
310 * @throws RejectedExecutionException
311 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
312 */
313 private void lazySubmitRunContinuation(ForkJoinPool pool) {
314 assert Thread.currentThread() instanceof CarrierThread;
315 try {
316 pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
317 } catch (RejectedExecutionException ree) {
318 submitFailed(ree);
319 throw ree;
320 } catch (OutOfMemoryError e) {
321 submitRunContinuation(pool, true);
322 }
323 }
324
325 /**
326 * Submits the runContinuation task to the given scheduler as an external submit.
327 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
328 * @throws RejectedExecutionException
329 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
330 */
331 private void externalSubmitRunContinuation(ForkJoinPool pool) {
332 assert Thread.currentThread() instanceof CarrierThread;
333 try {
334 pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
335 } catch (RejectedExecutionException ree) {
336 submitFailed(ree);
337 throw ree;
338 } catch (OutOfMemoryError e) {
339 submitRunContinuation(pool, true);
340 }
341 }
342
343 /**
344 * Submits the runContinuation task to the scheduler. For the default scheduler,
345 * and calling it on a worker thread, the task will be pushed to the local queue,
346 * otherwise it will be pushed to an external submission queue.
347 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
348 * @throws RejectedExecutionException
349 */
350 private void submitRunContinuation() {
351 submitRunContinuation(scheduler, true);
352 }
353
354 /**
355 * Submits the runContinuation task to the scheduler. For the default scheduler, and
356 * calling it a virtual thread that uses the default scheduler, the task will be
357 * pushed to an external submission queue. This method may throw OutOfMemoryError.
358 * @throws RejectedExecutionException
359 * @throws OutOfMemoryError
360 */
361 private void externalSubmitRunContinuationOrThrow() {
362 if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
363 try {
364 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
365 } catch (RejectedExecutionException ree) {
366 submitFailed(ree);
367 throw ree;
368 }
369 } else {
370 submitRunContinuation(scheduler, false);
371 }
372 }
373
374 /**
375 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
376 */
377 private void submitFailed(RejectedExecutionException ree) {
378 var event = new VirtualThreadSubmitFailedEvent();
379 if (event.isEnabled()) {
380 event.javaThreadId = threadId();
381 event.exceptionMessage = ree.getMessage();
382 event.commit();
383 }
384 }
385
386 /**
387 * Runs a task in the context of this virtual thread.
388 */
389 private void run(Runnable task) {
390 assert Thread.currentThread() == this && state == RUNNING;
391
392 // notify JVMTI, may post VirtualThreadStart event
393 notifyJvmtiStart();
394
395 // emit JFR event if enabled
396 if (VirtualThreadStartEvent.isTurnedOn()) {
397 var event = new VirtualThreadStartEvent();
398 event.javaThreadId = threadId();
399 event.commit();
400 }
401
402 Object bindings = Thread.scopedValueBindings();
403 try {
404 runWith(bindings, task);
405 } catch (Throwable exc) {
406 dispatchUncaughtException(exc);
407 } finally {
408 try {
409 // pop any remaining scopes from the stack, this may block
410 StackableScope.popAll();
411
412 // emit JFR event if enabled
413 if (VirtualThreadEndEvent.isTurnedOn()) {
414 var event = new VirtualThreadEndEvent();
415 event.javaThreadId = threadId();
416 event.commit();
417 }
418
419 } finally {
420 // notify JVMTI, may post VirtualThreadEnd event
421 notifyJvmtiEnd();
422 }
423 }
424 }
425
426 /**
427 * Mounts this virtual thread onto the current platform thread. On
428 * return, the current thread is the virtual thread.
429 */
430 @ChangesCurrentThread
431 @ReservedStackAccess
432 private void mount() {
433 // notify JVMTI before mount
434 notifyJvmtiMount(/*hide*/true);
435
436 // sets the carrier thread
437 Thread carrier = Thread.currentCarrierThread();
438 setCarrierThread(carrier);
439
440 // sync up carrier thread interrupt status if needed
441 if (interrupted) {
442 carrier.setInterrupt();
443 } else if (carrier.isInterrupted()) {
444 synchronized (interruptLock) {
445 // need to recheck interrupt status
446 if (!interrupted) {
447 carrier.clearInterrupt();
448 }
449 }
450 }
451
452 // set Thread.currentThread() to return this virtual thread
453 carrier.setCurrentThread(this);
454 }
455
456 /**
457 * Unmounts this virtual thread from the carrier. On return, the
458 * current thread is the current platform thread.
459 */
460 @ChangesCurrentThread
461 @ReservedStackAccess
462 private void unmount() {
463 assert !Thread.holdsLock(interruptLock);
464
465 // set Thread.currentThread() to return the platform thread
466 Thread carrier = this.carrierThread;
467 carrier.setCurrentThread(carrier);
468
469 // break connection to carrier thread, synchronized with interrupt
470 synchronized (interruptLock) {
471 setCarrierThread(null);
472 }
473 carrier.clearInterrupt();
474
475 // notify JVMTI after unmount
476 notifyJvmtiUnmount(/*hide*/false);
477 }
478
479 /**
480 * Sets the current thread to the current carrier thread.
481 */
482 @ChangesCurrentThread
483 @JvmtiMountTransition
484 private void switchToCarrierThread() {
485 notifyJvmtiHideFrames(true);
486 Thread carrier = this.carrierThread;
487 assert Thread.currentThread() == this
488 && carrier == Thread.currentCarrierThread();
489 carrier.setCurrentThread(carrier);
490 }
491
492 /**
493 * Sets the current thread to the given virtual thread.
494 */
495 @ChangesCurrentThread
496 @JvmtiMountTransition
497 private static void switchToVirtualThread(VirtualThread vthread) {
498 Thread carrier = vthread.carrierThread;
499 assert carrier == Thread.currentCarrierThread();
500 carrier.setCurrentThread(vthread);
501 notifyJvmtiHideFrames(false);
502 }
503
504 /**
505 * Executes the given value returning task on the current carrier thread.
506 */
507 @ChangesCurrentThread
508 <V> V executeOnCarrierThread(Callable<V> task) throws Exception {
509 assert Thread.currentThread() == this;
510 switchToCarrierThread();
511 try {
512 return task.call();
513 } finally {
514 switchToVirtualThread(this);
515 }
516 }
517
518 /**
519 * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
520 * the continuation continues.
521 */
522 @Hidden
523 private boolean yieldContinuation() {
524 notifyJvmtiUnmount(/*hide*/true);
525 try {
526 return Continuation.yield(VTHREAD_SCOPE);
527 } finally {
528 notifyJvmtiMount(/*hide*/false);
529 }
530 }
531
532 /**
533 * Invoked after the continuation yields. If parking then it sets the state
534 * and also re-submits the task to continue if unparked while parking.
535 * If yielding due to Thread.yield then it just submits the task to continue.
536 */
537 private void afterYield() {
538 assert carrierThread == null;
539
540 // re-adjust parallelism if the virtual thread yielded when compensating
541 if (currentThread() instanceof CarrierThread ct) {
542 ct.endBlocking();
543 }
544
545 int s = state();
546
547 // LockSupport.park/parkNanos
548 if (s == PARKING || s == TIMED_PARKING) {
549 int newState = (s == PARKING) ? PARKED : TIMED_PARKED;
550 setState(newState);
551
552 // may have been unparked while parking
553 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
554 // lazy submit to continue on the current carrier if possible
555 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
556 lazySubmitRunContinuation(ct.getPool());
557 } else {
558 submitRunContinuation();
559 }
560 }
561 return;
562 }
563
564 // Thread.yield
565 if (s == YIELDING) {
566 setState(YIELDED);
567
568 // external submit if there are no tasks in the local task queue
569 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
570 externalSubmitRunContinuation(ct.getPool());
571 } else {
572 submitRunContinuation();
573 }
574 return;
575 }
576
577 assert false;
578 }
579
580 /**
581 * Invoked after the continuation completes.
582 */
583 private void afterDone() {
584 afterDone(true);
585 }
586
587 /**
588 * Invoked after the continuation completes (or start failed). Sets the thread
589 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
590 *
591 * @param notifyContainer true if its container should be notified
592 */
593 private void afterDone(boolean notifyContainer) {
594 assert carrierThread == null;
595 setState(TERMINATED);
596
597 // notify anyone waiting for this virtual thread to terminate
598 CountDownLatch termination = this.termination;
599 if (termination != null) {
600 assert termination.getCount() == 1;
601 termination.countDown();
602 }
603
604 // notify container
605 if (notifyContainer) {
606 threadContainer().onExit(this);
607 }
608
609 // clear references to thread locals
610 clearReferences();
611 }
612
613 /**
614 * Schedules this {@code VirtualThread} to execute.
615 *
616 * @throws IllegalStateException if the container is shutdown or closed
617 * @throws IllegalThreadStateException if the thread has already been started
618 * @throws RejectedExecutionException if the scheduler cannot accept a task
619 */
620 @Override
621 void start(ThreadContainer container) {
622 if (!compareAndSetState(NEW, STARTED)) {
623 throw new IllegalThreadStateException("Already started");
624 }
625
626 // bind thread to container
627 assert threadContainer() == null;
628 setThreadContainer(container);
629
630 // start thread
631 boolean addedToContainer = false;
632 boolean started = false;
633 try {
634 container.onStart(this); // may throw
635 addedToContainer = true;
636
637 // scoped values may be inherited
638 inheritScopedValueBindings(container);
639
640 // submit task to run thread, using externalSubmit if possible
641 externalSubmitRunContinuationOrThrow();
642 started = true;
643 } finally {
644 if (!started) {
645 afterDone(addedToContainer);
646 }
647 }
648 }
649
650 @Override
651 public void start() {
652 start(ThreadContainers.root());
653 }
654
655 @Override
656 public void run() {
657 // do nothing
658 }
659
660 /**
661 * Parks until unparked or interrupted. If already unparked then the parking
662 * permit is consumed and this method completes immediately (meaning it doesn't
663 * yield). It also completes immediately if the interrupt status is set.
664 */
665 @Override
666 void park() {
667 assert Thread.currentThread() == this;
668
669 // complete immediately if parking permit available or interrupted
670 if (getAndSetParkPermit(false) || interrupted)
671 return;
672
673 // park the thread
674 boolean yielded = false;
675 setState(PARKING);
676 try {
677 yielded = yieldContinuation(); // may throw
678 } finally {
679 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
680 if (!yielded) {
681 assert state() == PARKING;
682 setState(RUNNING);
683 }
684 }
685
686 // park on the carrier thread when pinned
687 if (!yielded) {
688 parkOnCarrierThread(false, 0);
689 }
690 }
691
692 /**
693 * Parks up to the given waiting time or until unparked or interrupted.
694 * If already unparked then the parking permit is consumed and this method
695 * completes immediately (meaning it doesn't yield). It also completes immediately
696 * if the interrupt status is set or the waiting time is {@code <= 0}.
697 *
698 * @param nanos the maximum number of nanoseconds to wait.
699 */
700 @Override
701 void parkNanos(long nanos) {
702 assert Thread.currentThread() == this;
703
704 // complete immediately if parking permit available or interrupted
705 if (getAndSetParkPermit(false) || interrupted)
706 return;
707
708 // park the thread for the waiting time
709 if (nanos > 0) {
710 long startTime = System.nanoTime();
711
712 boolean yielded = false;
713 Future<?> unparker = scheduleUnpark(nanos); // may throw OOME
714 setState(TIMED_PARKING);
715 try {
716 yielded = yieldContinuation(); // may throw
717 } finally {
718 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
719 if (!yielded) {
720 assert state() == TIMED_PARKING;
721 setState(RUNNING);
722 }
723 cancel(unparker);
724 }
725
726 // park on carrier thread for remaining time when pinned
727 if (!yielded) {
728 long remainingNanos = nanos - (System.nanoTime() - startTime);
729 parkOnCarrierThread(true, remainingNanos);
730 }
731 }
732 }
733
734 /**
735 * Parks the current carrier thread up to the given waiting time or until
736 * unparked or interrupted. If the virtual thread is interrupted then the
737 * interrupt status will be propagated to the carrier thread.
738 * @param timed true for a timed park, false for untimed
739 * @param nanos the waiting time in nanoseconds
740 */
741 private void parkOnCarrierThread(boolean timed, long nanos) {
742 assert state() == RUNNING;
743
744 VirtualThreadPinnedEvent event;
745 try {
746 event = new VirtualThreadPinnedEvent();
747 event.begin();
748 } catch (OutOfMemoryError e) {
749 event = null;
750 }
751
752 setState(timed ? TIMED_PINNED : PINNED);
753 try {
754 if (!parkPermit) {
755 if (!timed) {
756 U.park(false, 0);
757 } else if (nanos > 0) {
758 U.park(false, nanos);
759 }
760 }
761 } finally {
762 setState(RUNNING);
763 }
764
765 // consume parking permit
766 setParkPermit(false);
767
768 if (event != null) {
769 try {
770 event.commit();
771 } catch (OutOfMemoryError e) {
772 // ignore
773 }
774 }
775 }
776
777 /**
778 * Schedule this virtual thread to be unparked after a given delay.
779 */
780 @ChangesCurrentThread
781 private Future<?> scheduleUnpark(long nanos) {
782 assert Thread.currentThread() == this;
783 // need to switch to current carrier thread to avoid nested parking
784 switchToCarrierThread();
785 try {
786 return schedule(this::unpark, nanos, NANOSECONDS);
787 } finally {
788 switchToVirtualThread(this);
789 }
790 }
791
792 /**
793 * Cancels a task if it has not completed.
794 */
795 @ChangesCurrentThread
796 private void cancel(Future<?> future) {
797 assert Thread.currentThread() == this;
798 if (!future.isDone()) {
799 // need to switch to current carrier thread to avoid nested parking
800 switchToCarrierThread();
801 try {
802 future.cancel(false);
803 } finally {
804 switchToVirtualThread(this);
805 }
806 }
807 }
808
809 /**
810 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
811 * then its task is scheduled to continue, otherwise its next call to {@code park} or
812 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
813 * @throws RejectedExecutionException if the scheduler cannot accept a task
814 */
815 @Override
816 void unpark() {
817 if (!getAndSetParkPermit(true) && currentThread() != this) {
818 int s = state();
819
820 // unparked while parked
821 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
822 submitRunContinuation();
823 return;
824 }
825
826 // unparked while parked when pinned
827 if (s == PINNED || s == TIMED_PINNED) {
828 // unpark carrier thread when pinned
829 disableSuspendAndPreempt();
830 try {
831 synchronized (carrierThreadAccessLock()) {
832 Thread carrier = carrierThread;
833 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
834 U.unpark(carrier);
835 }
836 }
837 } finally {
838 enableSuspendAndPreempt();
839 }
840 return;
841 }
842 }
843 }
844
845 /**
846 * Attempts to yield the current virtual thread (Thread.yield).
847 */
848 void tryYield() {
849 assert Thread.currentThread() == this;
850 setState(YIELDING);
851 boolean yielded = false;
852 try {
853 yielded = yieldContinuation(); // may throw
854 } finally {
855 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
856 if (!yielded) {
857 assert state() == YIELDING;
858 setState(RUNNING);
859 }
860 }
861 }
862
863 /**
864 * Sleep the current thread for the given sleep time (in nanoseconds). If
865 * nanos is 0 then the thread will attempt to yield.
866 *
867 * @implNote This implementation parks the thread for the given sleeping time
868 * and will therefore be observed in PARKED state during the sleep. Parking
869 * will consume the parking permit so this method makes available the parking
870 * permit after the sleep. This may be observed as a spurious, but benign,
871 * wakeup when the thread subsequently attempts to park.
872 *
873 * @param nanos the maximum number of nanoseconds to sleep
874 * @throws InterruptedException if interrupted while sleeping
875 */
876 void sleepNanos(long nanos) throws InterruptedException {
877 assert Thread.currentThread() == this && nanos >= 0;
878 if (getAndClearInterrupt())
879 throw new InterruptedException();
880 if (nanos == 0) {
881 tryYield();
882 } else {
883 // park for the sleep time
884 try {
885 long remainingNanos = nanos;
886 long startNanos = System.nanoTime();
887 while (remainingNanos > 0) {
888 parkNanos(remainingNanos);
889 if (getAndClearInterrupt()) {
890 throw new InterruptedException();
891 }
892 remainingNanos = nanos - (System.nanoTime() - startNanos);
893 }
894 } finally {
895 // may have been unparked while sleeping
896 setParkPermit(true);
897 }
898 }
899 }
900
901 /**
902 * Waits up to {@code nanos} nanoseconds for this virtual thread to terminate.
903 * A timeout of {@code 0} means to wait forever.
904 *
905 * @throws InterruptedException if interrupted while waiting
906 * @return true if the thread has terminated
907 */
908 boolean joinNanos(long nanos) throws InterruptedException {
909 if (state() == TERMINATED)
910 return true;
911
912 // ensure termination object exists, then re-check state
913 CountDownLatch termination = getTermination();
914 if (state() == TERMINATED)
915 return true;
916
917 // wait for virtual thread to terminate
918 if (nanos == 0) {
919 termination.await();
920 } else {
921 boolean terminated = termination.await(nanos, NANOSECONDS);
922 if (!terminated) {
923 // waiting time elapsed
924 return false;
925 }
926 }
927 assert state() == TERMINATED;
928 return true;
929 }
930
931 @Override
932 void blockedOn(Interruptible b) {
933 disableSuspendAndPreempt();
934 try {
935 super.blockedOn(b);
936 } finally {
937 enableSuspendAndPreempt();
938 }
939 }
940
941 @Override
942 @SuppressWarnings("removal")
943 public void interrupt() {
944 if (Thread.currentThread() != this) {
945 checkAccess();
946
947 // if current thread is a virtual thread then prevent it from being
948 // suspended or unmounted when entering or holding interruptLock
949 Interruptible blocker;
950 disableSuspendAndPreempt();
951 try {
952 synchronized (interruptLock) {
953 interrupted = true;
954 blocker = nioBlocker();
955 if (blocker != null) {
956 blocker.interrupt(this);
957 }
958
959 // interrupt carrier thread if mounted
960 Thread carrier = carrierThread;
961 if (carrier != null) carrier.setInterrupt();
962 }
963 } finally {
964 enableSuspendAndPreempt();
965 }
966
967 // notify blocker after releasing interruptLock
968 if (blocker != null) {
969 blocker.postInterrupt();
970 }
971
972 // make available parking permit, unpark thread if parked
973 unpark();
974
975 } else {
976 interrupted = true;
977 carrierThread.setInterrupt();
978 setParkPermit(true);
979 }
980 }
981
982 @Override
983 public boolean isInterrupted() {
984 return interrupted;
985 }
986
987 @Override
988 boolean getAndClearInterrupt() {
989 assert Thread.currentThread() == this;
990 boolean oldValue = interrupted;
991 if (oldValue) {
992 disableSuspendAndPreempt();
993 try {
994 synchronized (interruptLock) {
995 interrupted = false;
996 carrierThread.clearInterrupt();
997 }
998 } finally {
999 enableSuspendAndPreempt();
1000 }
1001 }
1002 return oldValue;
1003 }
1004
1005 @Override
1006 Thread.State threadState() {
1007 int s = state();
1008 switch (s & ~SUSPENDED) {
1009 case NEW:
1010 return Thread.State.NEW;
1011 case STARTED:
1012 // return NEW if thread container not yet set
1013 if (threadContainer() == null) {
1014 return Thread.State.NEW;
1015 } else {
1016 return Thread.State.RUNNABLE;
1017 }
1018 case UNPARKED:
1019 case YIELDED:
1020 // runnable, not mounted
1021 return Thread.State.RUNNABLE;
1022 case RUNNING:
1023 // if mounted then return state of carrier thread
1024 if (Thread.currentThread() != this) {
1025 disableSuspendAndPreempt();
1026 try {
1027 synchronized (carrierThreadAccessLock()) {
1028 Thread carrierThread = this.carrierThread;
1029 if (carrierThread != null) {
1030 return carrierThread.threadState();
1031 }
1032 }
1033 } finally {
1034 enableSuspendAndPreempt();
1035 }
1036 }
1037 // runnable, mounted
1038 return Thread.State.RUNNABLE;
1039 case PARKING:
1040 case TIMED_PARKING:
1041 case YIELDING:
1042 // runnable, in transition
1043 return Thread.State.RUNNABLE;
1044 case PARKED:
1045 case PINNED:
1046 return State.WAITING;
1047 case TIMED_PARKED:
1048 case TIMED_PINNED:
1049 return State.TIMED_WAITING;
1050 case TERMINATED:
1051 return Thread.State.TERMINATED;
1052 default:
1053 throw new InternalError();
1054 }
1055 }
1056
1057 @Override
1058 boolean alive() {
1059 int s = state;
1060 return (s != NEW && s != TERMINATED);
1061 }
1062
1063 @Override
1064 boolean isTerminated() {
1065 return (state == TERMINATED);
1066 }
1067
1068 @Override
1069 StackTraceElement[] asyncGetStackTrace() {
1070 StackTraceElement[] stackTrace;
1071 do {
1072 stackTrace = (carrierThread != null)
1073 ? super.asyncGetStackTrace() // mounted
1074 : tryGetStackTrace(); // unmounted
1075 if (stackTrace == null) {
1076 Thread.yield();
1077 }
1078 } while (stackTrace == null);
1079 return stackTrace;
1080 }
1081
1082 /**
1083 * Returns the stack trace for this virtual thread if it is unmounted.
1084 * Returns null if the thread is mounted or in transition.
1085 */
1086 private StackTraceElement[] tryGetStackTrace() {
1087 int initialState = state() & ~SUSPENDED;
1088 switch (initialState) {
1089 case NEW, STARTED, TERMINATED -> {
1090 return new StackTraceElement[0]; // unmounted, empty stack
1091 }
1092 case RUNNING, PINNED, TIMED_PINNED -> {
1093 return null; // mounted
1094 }
1095 case PARKED, TIMED_PARKED -> {
1096 // unmounted, not runnable
1097 }
1098 case UNPARKED, YIELDED -> {
1099 // unmounted, runnable
1100 }
1101 case PARKING, TIMED_PARKING, YIELDING -> {
1102 return null; // in transition
1103 }
1104 default -> throw new InternalError("" + initialState);
1105 }
1106
1107 // thread is unmounted, prevent it from continuing
1108 int suspendedState = initialState | SUSPENDED;
1109 if (!compareAndSetState(initialState, suspendedState)) {
1110 return null;
1111 }
1112
1113 // get stack trace and restore state
1114 StackTraceElement[] stack;
1115 try {
1116 stack = cont.getStackTrace();
1117 } finally {
1118 assert state == suspendedState;
1119 setState(initialState);
1120 }
1121 boolean resubmit = switch (initialState) {
1122 case UNPARKED, YIELDED -> {
1123 // resubmit as task may have run while suspended
1124 yield true;
1125 }
1126 case PARKED, TIMED_PARKED -> {
1127 // resubmit if unparked while suspended
1128 yield parkPermit && compareAndSetState(initialState, UNPARKED);
1129 }
1130 default -> throw new InternalError();
1131 };
1132 if (resubmit) {
1133 submitRunContinuation();
1134 }
1135 return stack;
1136 }
1137
1138 @Override
1139 public String toString() {
1140 StringBuilder sb = new StringBuilder("VirtualThread[#");
1141 sb.append(threadId());
1142 String name = getName();
1143 if (!name.isEmpty()) {
1144 sb.append(",");
1145 sb.append(name);
1146 }
1147 sb.append("]/");
1148
1149 // add the carrier state and thread name when mounted
1150 boolean mounted;
1151 if (Thread.currentThread() == this) {
1152 mounted = appendCarrierInfo(sb);
1153 } else {
1154 disableSuspendAndPreempt();
1155 try {
1156 synchronized (carrierThreadAccessLock()) {
1157 mounted = appendCarrierInfo(sb);
1158 }
1159 } finally {
1160 enableSuspendAndPreempt();
1161 }
1162 }
1163
1164 // add virtual thread state when not mounted
1165 if (!mounted) {
1166 String stateAsString = threadState().toString();
1167 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1168 }
1169
1170 return sb.toString();
1171 }
1172
1173 /**
1174 * Appends the carrier state and thread name to the string buffer if mounted.
1175 * @return true if mounted, false if not mounted
1176 */
1177 private boolean appendCarrierInfo(StringBuilder sb) {
1178 assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock());
1179 Thread carrier = carrierThread;
1180 if (carrier != null) {
1181 String stateAsString = carrier.threadState().toString();
1182 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1183 sb.append('@');
1184 sb.append(carrier.getName());
1185 return true;
1186 } else {
1187 return false;
1188 }
1189 }
1190
1191 @Override
1192 public int hashCode() {
1193 return (int) threadId();
1194 }
1195
1196 @Override
1197 public boolean equals(Object obj) {
1198 return obj == this;
1199 }
1200
1201 /**
1202 * Returns the termination object, creating it if needed.
1203 */
1204 private CountDownLatch getTermination() {
1205 CountDownLatch termination = this.termination;
1206 if (termination == null) {
1207 termination = new CountDownLatch(1);
1208 if (!U.compareAndSetReference(this, TERMINATION, null, termination)) {
1209 termination = this.termination;
1210 }
1211 }
1212 return termination;
1213 }
1214
1215 /**
1216 * Returns the lock object to synchronize on when accessing carrierThread.
1217 * The lock prevents carrierThread from being reset to null during unmount.
1218 */
1219 private Object carrierThreadAccessLock() {
1220 // return interruptLock as unmount has to coordinate with interrupt
1221 return interruptLock;
1222 }
1223
1224 /**
1225 * Disallow the current thread be suspended or preempted.
1226 */
1227 private void disableSuspendAndPreempt() {
1228 notifyJvmtiDisableSuspend(true);
1229 Continuation.pin();
1230 }
1231
1232 /**
1233 * Allow the current thread be suspended or preempted.
1234 */
1235 private void enableSuspendAndPreempt() {
1236 Continuation.unpin();
1237 notifyJvmtiDisableSuspend(false);
1238 }
1239
1240 // -- wrappers for get/set of state, parking permit, and carrier thread --
1241
1242 private int state() {
1243 return state; // volatile read
1244 }
1245
1246 private void setState(int newValue) {
1247 state = newValue; // volatile write
1248 }
1249
1250 private boolean compareAndSetState(int expectedValue, int newValue) {
1251 return U.compareAndSetInt(this, STATE, expectedValue, newValue);
1252 }
1253
1254 private void setParkPermit(boolean newValue) {
1255 if (parkPermit != newValue) {
1256 parkPermit = newValue;
1257 }
1258 }
1259
1260 private boolean getAndSetParkPermit(boolean newValue) {
1261 if (parkPermit != newValue) {
1262 return U.getAndSetBoolean(this, PARK_PERMIT, newValue);
1263 } else {
1264 return newValue;
1265 }
1266 }
1267
1268 private void setCarrierThread(Thread carrier) {
1269 // U.putReferenceRelease(this, CARRIER_THREAD, carrier);
1270 this.carrierThread = carrier;
1271 }
1272
1273 // -- JVM TI support --
1274
1275 @IntrinsicCandidate
1276 @JvmtiMountTransition
1277 private native void notifyJvmtiStart();
1278
1279 @IntrinsicCandidate
1280 @JvmtiMountTransition
1281 private native void notifyJvmtiEnd();
1282
1283 @IntrinsicCandidate
1284 @JvmtiMountTransition
1285 private native void notifyJvmtiMount(boolean hide);
1286
1287 @IntrinsicCandidate
1288 @JvmtiMountTransition
1289 private native void notifyJvmtiUnmount(boolean hide);
1290
1291 @IntrinsicCandidate
1292 @JvmtiMountTransition
1293 private static native void notifyJvmtiHideFrames(boolean hide);
1294
1295 @IntrinsicCandidate
1296 private static native void notifyJvmtiDisableSuspend(boolean enter);
1297
1298 private static native void registerNatives();
1299 static {
1300 registerNatives();
1301
1302 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1303 var group = Thread.virtualThreadGroup();
1304
1305 // ensure VirtualThreadPinnedEvent is loaded/initialized
1306 U.ensureClassInitialized(VirtualThreadPinnedEvent.class);
1307 }
1308
1309 /**
1310 * Creates the default ForkJoinPool scheduler.
1311 */
1312 @SuppressWarnings("removal")
1313 private static ForkJoinPool createDefaultScheduler() {
1314 ForkJoinWorkerThreadFactory factory = pool -> {
1315 PrivilegedAction<ForkJoinWorkerThread> pa = () -> new CarrierThread(pool);
1316 return AccessController.doPrivileged(pa);
1317 };
1318 PrivilegedAction<ForkJoinPool> pa = () -> {
1319 int parallelism, maxPoolSize, minRunnable;
1320 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1321 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1322 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1323 if (parallelismValue != null) {
1324 parallelism = Integer.parseInt(parallelismValue);
1325 } else {
1326 parallelism = Runtime.getRuntime().availableProcessors();
1327 }
1328 if (maxPoolSizeValue != null) {
1329 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1330 parallelism = Integer.min(parallelism, maxPoolSize);
1331 } else {
1332 maxPoolSize = Integer.max(parallelism, 256);
1333 }
1334 if (minRunnableValue != null) {
1335 minRunnable = Integer.parseInt(minRunnableValue);
1336 } else {
1337 minRunnable = Integer.max(parallelism / 2, 1);
1338 }
1339 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1340 boolean asyncMode = true; // FIFO
1341 return new ForkJoinPool(parallelism, factory, handler, asyncMode,
1342 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1343 };
1344 return AccessController.doPrivileged(pa);
1345 }
1346
1347 /**
1348 * Schedule a runnable task to run after a delay.
1349 */
1350 private static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1351 long tid = Thread.currentThread().threadId();
1352 int index = (int) tid & (DELAYED_TASK_SCHEDULERS.length - 1);
1353 return DELAYED_TASK_SCHEDULERS[index].schedule(command, delay, unit);
1354 }
1355
1356 /**
1357 * Creates the ScheduledThreadPoolExecutors used to execute delayed tasks.
1358 */
1359 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1360 String propName = "jdk.virtualThreadScheduler.timerQueues";
1361 String propValue = GetPropertyAction.privilegedGetProperty(propName);
1362 int queueCount;
1363 if (propValue != null) {
1364 queueCount = Integer.parseInt(propValue);
1365 if (queueCount != Integer.highestOneBit(queueCount)) {
1366 throw new RuntimeException("Value of " + propName + " must be power of 2");
1367 }
1368 } else {
1369 int ncpus = Runtime.getRuntime().availableProcessors();
1370 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
1371 }
1372 var schedulers = new ScheduledExecutorService[queueCount];
1373 for (int i = 0; i < queueCount; i++) {
1374 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
1375 Executors.newScheduledThreadPool(1, task -> {
1376 Thread t = InnocuousThread.newThread("VirtualThread-unparker", task);
1377 t.setDaemon(true);
1378 return t;
1379 });
1380 stpe.setRemoveOnCancelPolicy(true);
1381 schedulers[i] = stpe;
1382 }
1383 return schedulers;
1384 }
1385
1386 /**
1387 * Reads the value of the jdk.tracePinnedThreads property to determine if stack
1388 * traces should be printed when a carrier thread is pinned when a virtual thread
1389 * attempts to park.
1390 */
1391 private static int tracePinningMode() {
1392 String propValue = GetPropertyAction.privilegedGetProperty("jdk.tracePinnedThreads");
1393 if (propValue != null) {
1394 if (propValue.length() == 0 || "full".equalsIgnoreCase(propValue))
1395 return 1;
1396 if ("short".equalsIgnoreCase(propValue))
1397 return 2;
1398 }
1399 return 0;
1400 }
1401 }