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