1 /*
2 * Copyright (c) 2018, 2022, 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.lang.ref.Reference;
28 import java.security.AccessController;
29 import java.security.PrivilegedAction;
30 import java.util.Locale;
31 import java.util.Objects;
32 import java.util.concurrent.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.ThreadSleepEvent;
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.ForceInline;
58 import jdk.internal.vm.annotation.Hidden;
59 import jdk.internal.vm.annotation.IntrinsicCandidate;
60 import jdk.internal.vm.annotation.JvmtiMountTransition;
61 import sun.nio.ch.Interruptible;
62 import sun.security.action.GetPropertyAction;
63 import static java.util.concurrent.TimeUnit.*;
64
65 /**
66 * A thread that is scheduled by the Java virtual machine rather than the operating
67 * system.
68 */
69 final class VirtualThread extends BaseVirtualThread {
70 private static final Unsafe U = Unsafe.getUnsafe();
71 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
72 private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();
73 private static final ScheduledExecutorService UNPARKER = createDelayedTaskScheduler();
74 private static final int TRACE_PINNING_MODE = tracePinningMode();
75
76 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
77 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
78 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
79 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
80
81 // scheduler and continuation
82 private final Executor scheduler;
83 private final Continuation cont;
84 private final Runnable runContinuation;
85
86 // virtual thread state, accessed by VM
87 private volatile int state;
88
89 /*
90 * Virtual thread state and transitions:
91 *
92 * NEW -> STARTED // Thread.start
93 * STARTED -> TERMINATED // failed to start
94 * STARTED -> RUNNING // first run
95 *
96 * RUNNING -> PARKING // Thread attempts to park
97 * PARKING -> PARKED // cont.yield successful, thread is parked
98 * PARKING -> PINNED // cont.yield failed, thread is pinned
99 *
100 * PARKED -> RUNNABLE // unpark or interrupted
101 * PINNED -> RUNNABLE // unpark or interrupted
102 *
103 * RUNNABLE -> RUNNING // continue execution
104 *
105 * RUNNING -> YIELDING // Thread.yield
106 * YIELDING -> RUNNABLE // yield successful
107 * YIELDING -> RUNNING // yield failed
108 *
109 * RUNNING -> TERMINATED // done
110 */
111 private static final int NEW = 0;
112 private static final int STARTED = 1;
113 private static final int RUNNABLE = 2; // runnable-unmounted
114 private static final int RUNNING = 3; // runnable-mounted
115 private static final int PARKING = 4;
116 private static final int PARKED = 5; // unmounted
117 private static final int PINNED = 6; // mounted
118 private static final int YIELDING = 7; // Thread.yield
119 private static final int TERMINATED = 99; // final state
120
121 // can be suspended from scheduling when unmounted
122 private static final int SUSPENDED = 1 << 8;
123 private static final int RUNNABLE_SUSPENDED = (RUNNABLE | SUSPENDED);
124 private static final int PARKED_SUSPENDED = (PARKED | SUSPENDED);
125
126 // parking permit
127 private volatile boolean parkPermit;
128
129 // carrier thread when mounted, accessed by VM
130 private volatile Thread carrierThread;
131
132 // termination object when joining, created lazily if needed
133 private volatile CountDownLatch termination;
134
135 /**
136 * Returns the continuation scope used for virtual threads.
137 */
138 static ContinuationScope continuationScope() {
139 return VTHREAD_SCOPE;
140 }
141
142 /**
143 * Creates a new {@code VirtualThread} to run the given task with the given
144 * scheduler. If the given scheduler is {@code null} and the current thread
145 * is a platform thread then the newly created virtual thread will use the
146 * default scheduler. If given scheduler is {@code null} and the current
147 * thread is a virtual thread then the current thread's scheduler is used.
148 *
149 * @param scheduler the scheduler or null
150 * @param name thread name
151 * @param characteristics characteristics
152 * @param task the task to execute
153 */
154 VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
155 super(name, characteristics, /*bound*/ false);
156 Objects.requireNonNull(task);
157
158 // choose scheduler if not specified
159 if (scheduler == null) {
160 Thread parent = Thread.currentThread();
161 if (parent instanceof VirtualThread vparent) {
162 scheduler = vparent.scheduler;
163 } else {
164 scheduler = DEFAULT_SCHEDULER;
165 }
166 }
167
168 this.scheduler = scheduler;
169 this.cont = new VThreadContinuation(this, task);
170 this.runContinuation = this::runContinuation;
171 }
172
173 /**
174 * The continuation that a virtual thread executes.
175 */
176 private static class VThreadContinuation extends Continuation {
177 VThreadContinuation(VirtualThread vthread, Runnable task) {
178 super(VTHREAD_SCOPE, () -> vthread.run(task));
179 }
180 @Override
181 protected void onPinned(Continuation.Pinned reason) {
182 if (TRACE_PINNING_MODE > 0) {
183 boolean printAll = (TRACE_PINNING_MODE == 1);
184 PinnedThreadPrinter.printStackTrace(System.out, printAll);
185 }
186 }
187 }
188
189 /**
190 * Runs or continues execution of the continuation on the current thread.
191 */
192 private void runContinuation() {
193 // the carrier must be a platform thread
194 if (Thread.currentThread().isVirtual()) {
195 throw new WrongThreadException();
196 }
197
198 // set state to RUNNING
199 boolean firstRun;
200 int initialState = state();
201 if (initialState == STARTED && compareAndSetState(STARTED, RUNNING)) {
202 // first run
203 firstRun = true;
204 } else if (initialState == RUNNABLE && compareAndSetState(RUNNABLE, RUNNING)) {
205 // consume parking permit
206 setParkPermit(false);
207 firstRun = false;
208 } else {
209 // not runnable
210 return;
211 }
212
213 // notify JVMTI before mount
214 notifyJvmtiMount(true, firstRun);
215
216 try {
217 cont.run();
218 } finally {
219 if (cont.isDone()) {
220 afterTerminate(/*executed*/ true);
221 } else {
222 afterYield();
223 }
224 }
225 }
226
227 /**
228 * Submits the runContinuation task to the scheduler. For the default scheduler,
229 * and calling it on a worker thread, the task will be pushed to the local queue,
230 * otherwise it will be pushed to a submission queue.
231 *
232 * @throws RejectedExecutionException
233 */
234 private void submitRunContinuation() {
235 try {
236 scheduler.execute(runContinuation);
237 } catch (RejectedExecutionException ree) {
238 submitFailed(ree);
239 throw ree;
240 }
241 }
242
243 /**
244 * Submits the runContinuation task to the scheduler with a lazy submit.
245 * @throws RejectedExecutionException
246 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
247 */
248 private void lazySubmitRunContinuation(ForkJoinPool pool) {
249 try {
250 pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
251 } catch (RejectedExecutionException ree) {
252 submitFailed(ree);
253 throw ree;
254 }
255 }
256
257 /**
258 * Submits the runContinuation task to the scheduler as an external submit.
259 * @throws RejectedExecutionException
260 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
261 */
262 private void externalSubmitRunContinuation(ForkJoinPool pool) {
263 try {
264 pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
265 } catch (RejectedExecutionException ree) {
266 submitFailed(ree);
267 throw ree;
268 }
269 }
270
271 /**
272 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
273 */
274 private void submitFailed(RejectedExecutionException ree) {
275 var event = new VirtualThreadSubmitFailedEvent();
276 if (event.isEnabled()) {
277 event.javaThreadId = threadId();
278 event.exceptionMessage = ree.getMessage();
279 event.commit();
280 }
281 }
282
283 /**
284 * Runs a task in the context of this virtual thread. The virtual thread is
285 * mounted on the current (carrier) thread before the task runs. It unmounts
286 * from its carrier thread when the task completes.
287 */
288 @ChangesCurrentThread
289 private void run(Runnable task) {
290 assert state == RUNNING;
291
292 // first mount
293 mount();
294 notifyJvmtiMount(false, true);
295
296 // emit JFR event if enabled
297 if (VirtualThreadStartEvent.isTurnedOn()) {
298 var event = new VirtualThreadStartEvent();
299 event.javaThreadId = threadId();
300 event.commit();
301 }
302
303 Object bindings = scopedValueBindings();
304 try {
305 runWith(bindings, task);
306 } catch (Throwable exc) {
307 dispatchUncaughtException(exc);
308 } finally {
309 try {
310 // pop any remaining scopes from the stack, this may block
311 StackableScope.popAll();
312
313 // emit JFR event if enabled
314 if (VirtualThreadEndEvent.isTurnedOn()) {
315 var event = new VirtualThreadEndEvent();
316 event.javaThreadId = threadId();
317 event.commit();
318 }
319
320 } finally {
321 // last unmount
322 notifyJvmtiUnmount(true, true);
323 unmount();
324
325 // final state
326 setState(TERMINATED);
327 }
328 }
329 }
330
331 @Hidden
332 @ForceInline
333 private void runWith(Object bindings, Runnable op) {
334 ensureMaterializedForStackWalk(bindings);
335 op.run();
336 Reference.reachabilityFence(bindings);
337 }
338
339 /**
340 * Mounts this virtual thread onto the current platform thread. On
341 * return, the current thread is the virtual thread.
342 */
343 @ChangesCurrentThread
344 private void mount() {
345 // sets the carrier thread
346 Thread carrier = Thread.currentCarrierThread();
347 setCarrierThread(carrier);
348
349 // sync up carrier thread interrupt status if needed
350 if (interrupted) {
351 carrier.setInterrupt();
352 } else if (carrier.isInterrupted()) {
353 synchronized (interruptLock) {
354 // need to recheck interrupt status
355 if (!interrupted) {
356 carrier.clearInterrupt();
357 }
358 }
359 }
360
361 // set Thread.currentThread() to return this virtual thread
362 carrier.setCurrentThread(this);
363 }
364
365 /**
366 * Unmounts this virtual thread from the carrier. On return, the
367 * current thread is the current platform thread.
368 */
369 @ChangesCurrentThread
370 private void unmount() {
371 // set Thread.currentThread() to return the platform thread
372 Thread carrier = this.carrierThread;
373 carrier.setCurrentThread(carrier);
374
375 // break connection to carrier thread, synchronized with interrupt
376 synchronized (interruptLock) {
377 setCarrierThread(null);
378 }
379 carrier.clearInterrupt();
380 }
381
382 /**
383 * Sets the current thread to the current carrier thread.
384 */
385 @ChangesCurrentThread
386 @JvmtiMountTransition
387 private void switchToCarrierThread() {
388 notifyJvmtiHideFrames(true);
389 Thread carrier = this.carrierThread;
390 assert Thread.currentThread() == this
391 && carrier == Thread.currentCarrierThread();
392 carrier.setCurrentThread(carrier);
393 }
394
395 /**
396 * Sets the current thread to the given virtual thread.
397 */
398 @ChangesCurrentThread
399 @JvmtiMountTransition
400 private void switchToVirtualThread(VirtualThread vthread) {
401 Thread carrier = vthread.carrierThread;
402 assert carrier == Thread.currentCarrierThread();
403 carrier.setCurrentThread(vthread);
404 notifyJvmtiHideFrames(false);
405 }
406
407 /**
408 * Unmounts this virtual thread, invokes Continuation.yield, and re-mounts the
409 * thread when continued. When enabled, JVMTI must be notified from this method.
410 * @return true if the yield was successful
411 */
412 @ChangesCurrentThread
413 private boolean yieldContinuation() {
414 // unmount
415 notifyJvmtiUnmount(true, false);
416 unmount();
417 try {
418 return Continuation.yield(VTHREAD_SCOPE);
419 } finally {
420 // re-mount
421 mount();
422 notifyJvmtiMount(false, false);
423 }
424 }
425
426 /**
427 * Invoked after the continuation yields. If parking then it sets the state
428 * and also re-submits the task to continue if unparked while parking.
429 * If yielding due to Thread.yield then it just submits the task to continue.
430 */
431 private void afterYield() {
432 int s = state();
433 assert (s == PARKING || s == YIELDING) && (carrierThread == null);
434
435 if (s == PARKING) {
436 setState(PARKED);
437
438 // notify JVMTI that unmount has completed, thread is parked
439 notifyJvmtiUnmount(false, false);
440
441 // may have been unparked while parking
442 if (parkPermit && compareAndSetState(PARKED, RUNNABLE)) {
443 // lazy submit to continue on the current thread as carrier if possible
444 if (currentThread() instanceof CarrierThread ct) {
445 lazySubmitRunContinuation(ct.getPool());
446 } else {
447 submitRunContinuation();
448 }
449
450 }
451 } else if (s == YIELDING) { // Thread.yield
452 setState(RUNNABLE);
453
454 // notify JVMTI that unmount has completed, thread is runnable
455 notifyJvmtiUnmount(false, false);
456
457 // external submit if there are no tasks in the local task queue
458 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
459 externalSubmitRunContinuation(ct.getPool());
460 } else {
461 submitRunContinuation();
462 }
463 }
464 }
465
466 /**
467 * Invoked after the thread terminates (or start failed). This method
468 * notifies anyone waiting for the thread to terminate.
469 *
470 * @param executed true if the thread executed, false if it failed to start
471 */
472 private void afterTerminate(boolean executed) {
473 assert (state() == TERMINATED) && (carrierThread == null);
474
475 if (executed) {
476 notifyJvmtiUnmount(false, true);
477 }
478
479 // notify anyone waiting for this virtual thread to terminate
480 CountDownLatch termination = this.termination;
481 if (termination != null) {
482 assert termination.getCount() == 1;
483 termination.countDown();
484 }
485
486 if (executed) {
487 // notify container if thread executed
488 threadContainer().onExit(this);
489
490 // clear references to thread locals
491 clearReferences();
492 }
493 }
494
495 /**
496 * Schedules this {@code VirtualThread} to execute.
497 *
498 * @throws IllegalStateException if the container is shutdown or closed
499 * @throws IllegalThreadStateException if the thread has already been started
500 * @throws RejectedExecutionException if the scheduler cannot accept a task
501 */
502 @Override
503 void start(ThreadContainer container) {
504 if (!compareAndSetState(NEW, STARTED)) {
505 throw new IllegalThreadStateException("Already started");
506 }
507
508 // bind thread to container
509 setThreadContainer(container);
510
511 // start thread
512 boolean started = false;
513 container.onStart(this); // may throw
514 try {
515 // scoped values may be inherited
516 inheritScopedValueBindings(container);
517
518 // submit task to run thread
519 submitRunContinuation();
520 started = true;
521 } finally {
522 if (!started) {
523 setState(TERMINATED);
524 container.onExit(this);
525 afterTerminate(/*executed*/ false);
526 }
527 }
528 }
529
530 @Override
531 public void start() {
532 start(ThreadContainers.root());
533 }
534
535 @Override
536 public void run() {
537 // do nothing
538 }
539
540 /**
541 * Parks until unparked or interrupted. If already unparked then the parking
542 * permit is consumed and this method completes immediately (meaning it doesn't
543 * yield). It also completes immediately if the interrupt status is set.
544 */
545 @Override
546 void park() {
547 assert Thread.currentThread() == this;
548
549 // complete immediately if parking permit available or interrupted
550 if (getAndSetParkPermit(false) || interrupted)
551 return;
552
553 // park the thread
554 setState(PARKING);
555 try {
556 if (!yieldContinuation()) {
557 // park on the carrier thread when pinned
558 parkOnCarrierThread(false, 0);
559 }
560 } finally {
561 assert (Thread.currentThread() == this) && (state() == RUNNING);
562 }
563 }
564
565 /**
566 * Parks up to the given waiting time or until unparked or interrupted.
567 * If already unparked then the parking permit is consumed and this method
568 * completes immediately (meaning it doesn't yield). It also completes immediately
569 * if the interrupt status is set or the waiting time is {@code <= 0}.
570 *
571 * @param nanos the maximum number of nanoseconds to wait.
572 */
573 @Override
574 void parkNanos(long nanos) {
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 for the waiting time
582 if (nanos > 0) {
583 long startTime = System.nanoTime();
584
585 boolean yielded;
586 Future<?> unparker = scheduleUnpark(this::unpark, nanos);
587 setState(PARKING);
588 try {
589 yielded = yieldContinuation();
590 } finally {
591 assert (Thread.currentThread() == this)
592 && (state() == RUNNING || state() == PARKING);
593 cancel(unparker);
594 }
595
596 // park on carrier thread for remaining time when pinned
597 if (!yielded) {
598 long deadline = startTime + nanos;
599 if (deadline < 0L)
600 deadline = Long.MAX_VALUE;
601 parkOnCarrierThread(true, deadline - System.nanoTime());
602 }
603 }
604 }
605
606 /**
607 * Parks the current carrier thread up to the given waiting time or until
608 * unparked or interrupted. If the virtual thread is interrupted then the
609 * interrupt status will be propagated to the carrier thread.
610 * @param timed true for a timed park, false for untimed
611 * @param nanos the waiting time in nanoseconds
612 */
613 private void parkOnCarrierThread(boolean timed, long nanos) {
614 assert state() == PARKING;
615
616 var pinnedEvent = new VirtualThreadPinnedEvent();
617 pinnedEvent.begin();
618
619 setState(PINNED);
620 try {
621 if (!parkPermit) {
622 if (!timed) {
623 U.park(false, 0);
624 } else if (nanos > 0) {
625 U.park(false, nanos);
626 }
627 }
628 } finally {
629 setState(RUNNING);
630 }
631
632 // consume parking permit
633 setParkPermit(false);
634
635 pinnedEvent.commit();
636 }
637
638 /**
639 * Schedule an unpark task to run after a given delay.
640 */
641 @ChangesCurrentThread
642 private Future<?> scheduleUnpark(Runnable unparker, long nanos) {
643 // need to switch to current carrier thread to avoid nested parking
644 switchToCarrierThread();
645 try {
646 return UNPARKER.schedule(unparker, nanos, NANOSECONDS);
647 } finally {
648 switchToVirtualThread(this);
649 }
650 }
651
652 /**
653 * Cancels a task if it has not completed.
654 */
655 @ChangesCurrentThread
656 private void cancel(Future<?> future) {
657 if (!future.isDone()) {
658 // need to switch to current carrier thread to avoid nested parking
659 switchToCarrierThread();
660 try {
661 future.cancel(false);
662 } finally {
663 switchToVirtualThread(this);
664 }
665 }
666 }
667
668 /**
669 * Re-enables this virtual thread for scheduling. If the virtual thread was
670 * {@link #park() parked} then it will be unblocked, otherwise its next call
671 * to {@code park} or {@linkplain #parkNanos(long) parkNanos} is guaranteed
672 * not to block.
673 * @throws RejectedExecutionException if the scheduler cannot accept a task
674 */
675 @Override
676 @ChangesCurrentThread
677 void unpark() {
678 Thread currentThread = Thread.currentThread();
679 if (!getAndSetParkPermit(true) && currentThread != this) {
680 int s = state();
681 if (s == PARKED && compareAndSetState(PARKED, RUNNABLE)) {
682 if (currentThread instanceof VirtualThread vthread) {
683 vthread.switchToCarrierThread();
684 try {
685 submitRunContinuation();
686 } finally {
687 switchToVirtualThread(vthread);
688 }
689 } else {
690 submitRunContinuation();
691 }
692 } else if (s == PINNED) {
693 // unpark carrier thread when pinned.
694 synchronized (carrierThreadAccessLock()) {
695 Thread carrier = carrierThread;
696 if (carrier != null && state() == PINNED) {
697 U.unpark(carrier);
698 }
699 }
700 }
701 }
702 }
703
704 /**
705 * Attempts to yield the current virtual thread (Thread.yield).
706 */
707 void tryYield() {
708 assert Thread.currentThread() == this;
709 setState(YIELDING);
710 try {
711 yieldContinuation();
712 } finally {
713 assert Thread.currentThread() == this;
714 if (state() != RUNNING) {
715 assert state() == YIELDING;
716 setState(RUNNING);
717 }
718 }
719 }
720
721 /**
722 * Sleep the current virtual thread for the given sleep time.
723 *
724 * @param nanos the maximum number of nanoseconds to sleep
725 * @throws InterruptedException if interrupted while sleeping
726 */
727 void sleepNanos(long nanos) throws InterruptedException {
728 assert Thread.currentThread() == this;
729 if (nanos >= 0) {
730 if (ThreadSleepEvent.isTurnedOn()) {
731 ThreadSleepEvent event = new ThreadSleepEvent();
732 try {
733 event.time = nanos;
734 event.begin();
735 doSleepNanos(nanos);
736 } finally {
737 event.commit();
738 }
739 } else {
740 doSleepNanos(nanos);
741 }
742 }
743 }
744
745 /**
746 * Sleep the current thread for the given sleep time (in nanoseconds). If
747 * nanos is 0 then the thread will attempt to yield.
748 *
749 * @implNote This implementation parks the thread for the given sleeping time
750 * and will therefore be observed in PARKED state during the sleep. Parking
751 * will consume the parking permit so this method makes available the parking
752 * permit after the sleep. This may be observed as a spurious, but benign,
753 * wakeup when the thread subsequently attempts to park.
754 */
755 private void doSleepNanos(long nanos) throws InterruptedException {
756 assert nanos >= 0;
757 if (getAndClearInterrupt())
758 throw new InterruptedException();
759 if (nanos == 0) {
760 tryYield();
761 } else {
762 // park for the sleep time
763 try {
764 long remainingNanos = nanos;
765 long startNanos = System.nanoTime();
766 while (remainingNanos > 0) {
767 parkNanos(remainingNanos);
768 if (getAndClearInterrupt()) {
769 throw new InterruptedException();
770 }
771 remainingNanos = nanos - (System.nanoTime() - startNanos);
772 }
773 } finally {
774 // may have been unparked while sleeping
775 setParkPermit(true);
776 }
777 }
778 }
779
780 /**
781 * Waits up to {@code nanos} nanoseconds for this virtual thread to terminate.
782 * A timeout of {@code 0} means to wait forever.
783 *
784 * @throws InterruptedException if interrupted while waiting
785 * @return true if the thread has terminated
786 */
787 boolean joinNanos(long nanos) throws InterruptedException {
788 if (state() == TERMINATED)
789 return true;
790
791 // ensure termination object exists, then re-check state
792 CountDownLatch termination = getTermination();
793 if (state() == TERMINATED)
794 return true;
795
796 // wait for virtual thread to terminate
797 if (nanos == 0) {
798 termination.await();
799 } else {
800 boolean terminated = termination.await(nanos, NANOSECONDS);
801 if (!terminated) {
802 // waiting time elapsed
803 return false;
804 }
805 }
806 assert state() == TERMINATED;
807 return true;
808 }
809
810 @Override
811 @SuppressWarnings("removal")
812 public void interrupt() {
813 if (Thread.currentThread() != this) {
814 checkAccess();
815 synchronized (interruptLock) {
816 interrupted = true;
817 Interruptible b = nioBlocker;
818 if (b != null) {
819 b.interrupt(this);
820 }
821
822 // interrupt carrier thread if mounted
823 Thread carrier = carrierThread;
824 if (carrier != null) carrier.setInterrupt();
825 }
826 } else {
827 interrupted = true;
828 carrierThread.setInterrupt();
829 }
830 unpark();
831 }
832
833 @Override
834 public boolean isInterrupted() {
835 return interrupted;
836 }
837
838 @Override
839 boolean getAndClearInterrupt() {
840 assert Thread.currentThread() == this;
841 synchronized (interruptLock) {
842 boolean oldValue = interrupted;
843 if (oldValue)
844 interrupted = false;
845 carrierThread.clearInterrupt();
846 return oldValue;
847 }
848 }
849
850 @Override
851 Thread.State threadState() {
852 switch (state()) {
853 case NEW:
854 return Thread.State.NEW;
855 case STARTED:
856 // return NEW if thread container not yet set
857 if (threadContainer() == null) {
858 return Thread.State.NEW;
859 } else {
860 return Thread.State.RUNNABLE;
861 }
862 case RUNNABLE:
863 case RUNNABLE_SUSPENDED:
864 // runnable, not mounted
865 return Thread.State.RUNNABLE;
866 case RUNNING:
867 // if mounted then return state of carrier thread
868 synchronized (carrierThreadAccessLock()) {
869 Thread carrierThread = this.carrierThread;
870 if (carrierThread != null) {
871 return carrierThread.threadState();
872 }
873 }
874 // runnable, mounted
875 return Thread.State.RUNNABLE;
876 case PARKING:
877 case YIELDING:
878 // runnable, mounted, not yet waiting
879 return Thread.State.RUNNABLE;
880 case PARKED:
881 case PARKED_SUSPENDED:
882 case PINNED:
883 return Thread.State.WAITING;
884 case TERMINATED:
885 return Thread.State.TERMINATED;
886 default:
887 throw new InternalError();
888 }
889 }
890
891 @Override
892 boolean alive() {
893 int s = state;
894 return (s != NEW && s != TERMINATED);
895 }
896
897 @Override
898 boolean isTerminated() {
899 return (state == TERMINATED);
900 }
901
902 @Override
903 StackTraceElement[] asyncGetStackTrace() {
904 StackTraceElement[] stackTrace;
905 do {
906 stackTrace = (carrierThread != null)
907 ? super.asyncGetStackTrace() // mounted
908 : tryGetStackTrace(); // unmounted
909 if (stackTrace == null) {
910 Thread.yield();
911 }
912 } while (stackTrace == null);
913 return stackTrace;
914 }
915
916 /**
917 * Returns the stack trace for this virtual thread if it is unmounted.
918 * Returns null if the thread is in another state.
919 */
920 private StackTraceElement[] tryGetStackTrace() {
921 int initialState = state();
922 return switch (initialState) {
923 case RUNNABLE, PARKED -> {
924 int suspendedState = initialState | SUSPENDED;
925 if (compareAndSetState(initialState, suspendedState)) {
926 try {
927 yield cont.getStackTrace();
928 } finally {
929 assert state == suspendedState;
930 setState(initialState);
931
932 // re-submit if runnable
933 // re-submit if unparked while suspended
934 if (initialState == RUNNABLE
935 || (parkPermit && compareAndSetState(PARKED, RUNNABLE))) {
936 try {
937 submitRunContinuation();
938 } catch (RejectedExecutionException ignore) { }
939 }
940 }
941 }
942 yield null;
943 }
944 case NEW, STARTED, TERMINATED -> new StackTraceElement[0]; // empty stack
945 default -> null;
946 };
947 }
948
949 @Override
950 public String toString() {
951 StringBuilder sb = new StringBuilder("VirtualThread[#");
952 sb.append(threadId());
953 String name = getName();
954 if (!name.isEmpty()) {
955 sb.append(",");
956 sb.append(name);
957 }
958 sb.append("]/");
959 Thread carrier = carrierThread;
960 if (carrier != null) {
961 // include the carrier thread state and name when mounted
962 synchronized (carrierThreadAccessLock()) {
963 carrier = carrierThread;
964 if (carrier != null) {
965 String stateAsString = carrier.threadState().toString();
966 sb.append(stateAsString.toLowerCase(Locale.ROOT));
967 sb.append('@');
968 sb.append(carrier.getName());
969 }
970 }
971 }
972 // include virtual thread state when not mounted
973 if (carrier == null) {
974 String stateAsString = threadState().toString();
975 sb.append(stateAsString.toLowerCase(Locale.ROOT));
976 }
977 return sb.toString();
978 }
979
980 @Override
981 public int hashCode() {
982 return (int) threadId();
983 }
984
985 @Override
986 public boolean equals(Object obj) {
987 return obj == this;
988 }
989
990 /**
991 * Returns the termination object, creating it if needed.
992 */
993 private CountDownLatch getTermination() {
994 CountDownLatch termination = this.termination;
995 if (termination == null) {
996 termination = new CountDownLatch(1);
997 if (!U.compareAndSetReference(this, TERMINATION, null, termination)) {
998 termination = this.termination;
999 }
1000 }
1001 return termination;
1002 }
1003
1004 /**
1005 * Returns the lock object to synchronize on when accessing carrierThread.
1006 * The lock prevents carrierThread from being reset to null during unmount.
1007 */
1008 private Object carrierThreadAccessLock() {
1009 // return interruptLock as unmount has to coordinate with interrupt
1010 return interruptLock;
1011 }
1012
1013 // -- wrappers for get/set of state, parking permit, and carrier thread --
1014
1015 private int state() {
1016 return state; // volatile read
1017 }
1018
1019 private void setState(int newValue) {
1020 state = newValue; // volatile write
1021 }
1022
1023 private boolean compareAndSetState(int expectedValue, int newValue) {
1024 return U.compareAndSetInt(this, STATE, expectedValue, newValue);
1025 }
1026
1027 private void setParkPermit(boolean newValue) {
1028 if (parkPermit != newValue) {
1029 parkPermit = newValue;
1030 }
1031 }
1032
1033 private boolean getAndSetParkPermit(boolean newValue) {
1034 if (parkPermit != newValue) {
1035 return U.getAndSetBoolean(this, PARK_PERMIT, newValue);
1036 } else {
1037 return newValue;
1038 }
1039 }
1040
1041 private void setCarrierThread(Thread carrier) {
1042 // U.putReferenceRelease(this, CARRIER_THREAD, carrier);
1043 this.carrierThread = carrier;
1044 }
1045
1046 // -- JVM TI support --
1047
1048 @IntrinsicCandidate
1049 @JvmtiMountTransition
1050 private native void notifyJvmtiMount(boolean hide, boolean firstMount);
1051
1052 @IntrinsicCandidate
1053 @JvmtiMountTransition
1054 private native void notifyJvmtiUnmount(boolean hide, boolean lastUnmount);
1055
1056 @IntrinsicCandidate
1057 @JvmtiMountTransition
1058 private native void notifyJvmtiHideFrames(boolean hide);
1059
1060 private static native void registerNatives();
1061 static {
1062 registerNatives();
1063 }
1064
1065 /**
1066 * Creates the default scheduler.
1067 */
1068 @SuppressWarnings("removal")
1069 private static ForkJoinPool createDefaultScheduler() {
1070 ForkJoinWorkerThreadFactory factory = pool -> {
1071 PrivilegedAction<ForkJoinWorkerThread> pa = () -> new CarrierThread(pool);
1072 return AccessController.doPrivileged(pa);
1073 };
1074 PrivilegedAction<ForkJoinPool> pa = () -> {
1075 int parallelism, maxPoolSize, minRunnable;
1076 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1077 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1078 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1079 if (parallelismValue != null) {
1080 parallelism = Integer.parseInt(parallelismValue);
1081 } else {
1082 parallelism = Runtime.getRuntime().availableProcessors();
1083 }
1084 if (maxPoolSizeValue != null) {
1085 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1086 parallelism = Integer.min(parallelism, maxPoolSize);
1087 } else {
1088 maxPoolSize = Integer.max(parallelism, 256);
1089 }
1090 if (minRunnableValue != null) {
1091 minRunnable = Integer.parseInt(minRunnableValue);
1092 } else {
1093 minRunnable = Integer.max(parallelism / 2, 1);
1094 }
1095 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1096 boolean asyncMode = true; // FIFO
1097 return new ForkJoinPool(parallelism, factory, handler, asyncMode,
1098 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1099 };
1100 return AccessController.doPrivileged(pa);
1101 }
1102
1103 /**
1104 * Creates the ScheduledThreadPoolExecutor used for timed unpark.
1105 */
1106 private static ScheduledExecutorService createDelayedTaskScheduler() {
1107 String propValue = GetPropertyAction.privilegedGetProperty("jdk.unparker.maxPoolSize");
1108 int poolSize;
1109 if (propValue != null) {
1110 poolSize = Integer.parseInt(propValue);
1111 } else {
1112 poolSize = 1;
1113 }
1114 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
1115 Executors.newScheduledThreadPool(poolSize, task -> {
1116 return InnocuousThread.newThread("VirtualThread-unparker", task);
1117 });
1118 stpe.setRemoveOnCancelPolicy(true);
1119 return stpe;
1120 }
1121
1122 /**
1123 * Reads the value of the jdk.tracePinnedThreads property to determine if stack
1124 * traces should be printed when a carrier thread is pinned when a virtual thread
1125 * attempts to park.
1126 */
1127 private static int tracePinningMode() {
1128 String propValue = GetPropertyAction.privilegedGetProperty("jdk.tracePinnedThreads");
1129 if (propValue != null) {
1130 if (propValue.length() == 0 || "full".equalsIgnoreCase(propValue))
1131 return 1;
1132 if ("short".equalsIgnoreCase(propValue))
1133 return 2;
1134 }
1135 return 0;
1136 }
1137 }