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