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.lang.reflect.Constructor;
28 import java.security.AccessController;
29 import java.security.PrivilegedAction;
30 import java.util.Arrays;
31 import java.util.Locale;
32 import java.util.Objects;
33 import java.util.concurrent.Callable;
34 import java.util.concurrent.CountDownLatch;
35 import java.util.concurrent.Executor;
36 import java.util.concurrent.Executors;
37 import java.util.concurrent.ForkJoinPool;
38 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
39 import java.util.concurrent.ForkJoinTask;
40 import java.util.concurrent.ForkJoinWorkerThread;
41 import java.util.concurrent.Future;
42 import java.util.concurrent.RejectedExecutionException;
43 import java.util.concurrent.ScheduledExecutorService;
44 import java.util.concurrent.ScheduledThreadPoolExecutor;
45 import java.util.concurrent.TimeUnit;
46 import java.util.stream.Stream;
47 import jdk.internal.event.VirtualThreadEndEvent;
48 import jdk.internal.event.VirtualThreadStartEvent;
49 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
50 import jdk.internal.misc.CarrierThread;
51 import jdk.internal.misc.InnocuousThread;
52 import jdk.internal.misc.Unsafe;
53 import jdk.internal.vm.Continuation;
54 import jdk.internal.vm.ContinuationScope;
55 import jdk.internal.vm.StackableScope;
56 import jdk.internal.vm.ThreadContainer;
57 import jdk.internal.vm.ThreadContainers;
58 import jdk.internal.vm.annotation.ChangesCurrentThread;
59 import jdk.internal.vm.annotation.Hidden;
60 import jdk.internal.vm.annotation.IntrinsicCandidate;
61 import jdk.internal.vm.annotation.JvmtiMountTransition;
62 import jdk.internal.vm.annotation.ReservedStackAccess;
63 import sun.nio.ch.Interruptible;
64 import sun.security.action.GetPropertyAction;
65 import static java.util.concurrent.TimeUnit.*;
66
67 /**
68 * A thread that is scheduled by the Java virtual machine rather than the operating system.
69 */
70 final class VirtualThread extends BaseVirtualThread {
71 private static final Unsafe U = Unsafe.getUnsafe();
72 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
73 private static final Executor DEFAULT_SCHEDULER = createDefaultScheduler();
74 private static final ScheduledExecutorService[] DELAYED_TASK_SCHEDULERS = createDelayedTaskSchedulers();
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 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
81
82 // scheduler and continuation
83 private final Executor scheduler;
84 private final Continuation cont;
85 private final Runnable runContinuation;
86
87 // virtual thread state, accessed by VM
88 private volatile int state;
89
90 /*
91 * Virtual thread state transitions:
92 *
93 * NEW -> STARTED // Thread.start, schedule to run
94 * STARTED -> TERMINATED // failed to start
95 * STARTED -> RUNNING // first run
96 * RUNNING -> TERMINATED // done
97 *
98 * RUNNING -> PARKING // Thread parking with LockSupport.park
99 * PARKING -> PARKED // cont.yield successful, parked indefinitely
100 * PARKING -> PINNED // cont.yield failed, parked indefinitely on carrier
101 * PARKED -> UNPARKED // unparked, may be scheduled to continue
102 * PINNED -> RUNNING // unparked, continue execution on same carrier
103 * UNPARKED -> RUNNING // continue execution after park
104 *
105 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
106 * TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked
107 * TIMED_PARKING -> TIMED_PINNED // cont.yield failed, timed-parked on carrier
108 * TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue
109 * TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier
110 *
111 * RUNNING -> BLOCKING // blocking on monitor enter
112 * BLOCKING -> BLOCKED // blocked on monitor enter
113 * BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue
114 * UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter
115 *
116 * RUNNING -> WAITING // transitional state during wait on monitor
117 * WAITING -> WAITED // waiting on monitor
118 * WAITED -> BLOCKED // notified, waiting to be unblocked by monitor owner
119 * WAITED -> UNBLOCKED // timed-out/interrupted
120 *
121 * RUNNING -> TIMED_WAITING // transition state during timed-waiting on monitor
122 * TIMED_WAITING -> TIMED_WAITED // timed-waiting on monitor
123 * TIMED_WAITED -> BLOCKED // notified, waiting to be unblocked by monitor owner
124 * TIMED_WAITED -> UNBLOCKED // timed-out/interrupted
125 *
126 * RUNNING -> YIELDING // Thread.yield
127 * YIELDING -> YIELDED // cont.yield successful, may be scheduled to continue
128 * YIELDING -> RUNNING // cont.yield failed
129 * YIELDED -> RUNNING // continue execution after Thread.yield
130 */
131 private static final int NEW = 0;
132 private static final int STARTED = 1;
133 private static final int RUNNING = 2; // runnable-mounted
134
135 // untimed and timed parking
136 private static final int PARKING = 3;
137 private static final int PARKED = 4; // unmounted
138 private static final int PINNED = 5; // mounted
139 private static final int TIMED_PARKING = 6;
140 private static final int TIMED_PARKED = 7; // unmounted
141 private static final int TIMED_PINNED = 8; // mounted
142 private static final int UNPARKED = 9; // unmounted but runnable
143
144 // Thread.yield
145 private static final int YIELDING = 10;
146 private static final int YIELDED = 11; // unmounted but runnable
147
148 // monitor enter
149 private static final int BLOCKING = 12;
150 private static final int BLOCKED = 13; // unmounted
151 private static final int UNBLOCKED = 14; // unmounted but runnable
152
153 // monitor wait/timed-wait
154 private static final int WAITING = 15;
155 private static final int WAIT = 16; // waiting in Object.wait
156 private static final int TIMED_WAITING = 17;
157 private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait
158
159 private static final int TERMINATED = 99; // final state
160
161 // can be suspended from scheduling when unmounted
162 private static final int SUSPENDED = 1 << 8;
163
164 // parking permit made available by LockSupport.unpark
165 private volatile boolean parkPermit;
166
167 // blocking permit made available by unblocker thread when another thread exits monitor
168 private volatile boolean blockPermit;
169
170 // true when on the list of virtual threads waiting to be unblocked
171 private volatile boolean onWaitingList;
172
173 // next virtual thread on the list of virtual threads waiting to be unblocked
174 private volatile VirtualThread next;
175
176 // notified by Object.notify/notifyAll while waiting in Object.wait
177 private volatile boolean notified;
178
179 // timed-wait support
180 private long waitTimeout;
181 private byte timedWaitNonce;
182 private volatile Future<?> waitTimeoutTask;
183
184 // carrier thread when mounted, accessed by VM
185 private volatile Thread carrierThread;
186
187 // termination object when joining, created lazily if needed
188 private volatile CountDownLatch termination;
189
190 /**
191 * Returns the default scheduler.
192 */
193 static Executor defaultScheduler() {
194 return DEFAULT_SCHEDULER;
195 }
196
197 /**
198 * Returns a stream of the delayed task schedulers used to support timed operations.
199 */
200 static Stream<ScheduledExecutorService> delayedTaskSchedulers() {
201 return Arrays.stream(DELAYED_TASK_SCHEDULERS);
202 }
203
204 /**
205 * Returns the continuation scope used for virtual threads.
206 */
207 static ContinuationScope continuationScope() {
208 return VTHREAD_SCOPE;
209 }
210
211 /**
212 * Creates a new {@code VirtualThread} to run the given task with the given
213 * scheduler. If the given scheduler is {@code null} and the current thread
214 * is a platform thread then the newly created virtual thread will use the
215 * default scheduler. If given scheduler is {@code null} and the current
216 * thread is a virtual thread then the current thread's scheduler is used.
217 *
218 * @param scheduler the scheduler or null
219 * @param name thread name
220 * @param characteristics characteristics
221 * @param task the task to execute
222 */
223 VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
224 super(name, characteristics, /*bound*/ false);
225 Objects.requireNonNull(task);
226
227 // choose scheduler if not specified
228 if (scheduler == null) {
229 Thread parent = Thread.currentThread();
230 if (parent instanceof VirtualThread vparent) {
231 scheduler = vparent.scheduler;
232 } else {
233 scheduler = DEFAULT_SCHEDULER;
234 }
235 }
236
237 this.scheduler = scheduler;
238 this.cont = new VThreadContinuation(this, task);
239 this.runContinuation = this::runContinuation;
240 }
241
242 /**
243 * The continuation that a virtual thread executes.
244 */
245 private static class VThreadContinuation extends Continuation {
246 VThreadContinuation(VirtualThread vthread, Runnable task) {
247 super(VTHREAD_SCOPE, wrap(vthread, task));
248 }
249 @Override
250 protected void onPinned(Continuation.Pinned reason) {
251 // emit JFR event
252 virtualThreadPinnedEvent(reason.reasonCode(), reason.reasonString());
253 }
254 private static Runnable wrap(VirtualThread vthread, Runnable task) {
255 return new Runnable() {
256 @Hidden
257 public void run() {
258 vthread.run(task);
259 }
260 };
261 }
262 }
263
264 /**
265 * jdk.VirtualThreadPinned is emitted by HotSpot VM when pinned. Call into VM to
266 * emit event to avoid having a JFR event in Java with the same name (but different ID)
267 * to events emitted by the VM.
268 */
269 private static native void virtualThreadPinnedEvent(int reason, String reasonString);
270
271 /**
272 * Runs or continues execution on the current thread. The virtual thread is mounted
273 * on the current thread before the task runs or continues. It unmounts when the
274 * task completes or yields.
275 */
276 @ChangesCurrentThread // allow mount/unmount to be inlined
277 private void runContinuation() {
278 // the carrier must be a platform thread
279 if (Thread.currentThread().isVirtual()) {
280 throw new WrongThreadException();
281 }
282
283 // set state to RUNNING
284 int initialState = state();
285 if (initialState == STARTED || initialState == UNPARKED
286 || initialState == UNBLOCKED || initialState == YIELDED) {
287 // newly started or continue after parking/blocking/Thread.yield
288 if (!compareAndSetState(initialState, RUNNING)) {
289 return;
290 }
291 // consume permit when continuing after parking or blocking
292 if (initialState == UNPARKED) {
293 setParkPermit(false);
294 } if (initialState == UNBLOCKED) {
295 blockPermit = false;
296 }
297 } else {
298 // not runnable
299 return;
300 }
301
302 mount();
303 try {
304 cont.run();
305 } finally {
306 unmount();
307 if (cont.isDone()) {
308 afterDone();
309 } else {
310 afterYield();
311 }
312 }
313 }
314
315 /**
316 * Submits the runContinuation task to the scheduler. For the default scheduler,
317 * and calling it on a worker thread, the task will be pushed to the local queue,
318 * otherwise it will be pushed to an external submission queue.
319 * @param scheduler the scheduler
320 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
321 * @throws RejectedExecutionException
322 */
323 @ChangesCurrentThread
324 private void submitRunContinuation(Executor scheduler, boolean retryOnOOME) {
325 boolean done = false;
326 while (!done) {
327 try {
328 // Pin the continuation to prevent the virtual thread from unmounting
329 // when submitting a task. For the default scheduler this ensures that
330 // the carrier doesn't change when pushing a task. For other schedulers
331 // it avoids deadlock that could arise due to carriers and virtual
332 // threads contending for a lock.
333 if (currentThread().isVirtual()) {
334 Continuation.pin();
335 try {
336 scheduler.execute(runContinuation);
337 } finally {
338 Continuation.unpin();
339 }
340 } else {
341 scheduler.execute(runContinuation);
342 }
343 done = true;
344 } catch (RejectedExecutionException ree) {
345 submitFailed(ree);
346 throw ree;
347 } catch (OutOfMemoryError e) {
348 if (retryOnOOME) {
349 U.park(false, 100_000_000); // 100ms
350 } else {
351 throw e;
352 }
353 }
354 }
355 }
356
357 /**
358 * Submits the runContinuation task to given scheduler with a lazy submit.
359 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
360 * @throws RejectedExecutionException
361 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
362 */
363 private void lazySubmitRunContinuation(ForkJoinPool pool) {
364 assert Thread.currentThread() instanceof CarrierThread;
365 try {
366 pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
367 } catch (RejectedExecutionException ree) {
368 submitFailed(ree);
369 throw ree;
370 } catch (OutOfMemoryError e) {
371 submitRunContinuation(pool, true);
372 }
373 }
374
375 /**
376 * Submits the runContinuation task to the given scheduler as an external submit.
377 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
378 * @throws RejectedExecutionException
379 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
380 */
381 private void externalSubmitRunContinuation(ForkJoinPool pool) {
382 assert Thread.currentThread() instanceof CarrierThread;
383 try {
384 pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
385 } catch (RejectedExecutionException ree) {
386 submitFailed(ree);
387 throw ree;
388 } catch (OutOfMemoryError e) {
389 submitRunContinuation(pool, true);
390 }
391 }
392
393 /**
394 * Submits the runContinuation task to the scheduler. For the default scheduler,
395 * and calling it on a worker thread, the task will be pushed to the local queue,
396 * otherwise it will be pushed to an external submission queue.
397 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
398 * @throws RejectedExecutionException
399 */
400 private void submitRunContinuation() {
401 submitRunContinuation(scheduler, true);
402 }
403
404 /**
405 * Submits the runContinuation task to the scheduler. For the default scheduler, and
406 * calling it a virtual thread that uses the default scheduler, the task will be
407 * pushed to an external submission queue. This method may throw OutOfMemoryError.
408 * @throws RejectedExecutionException
409 * @throws OutOfMemoryError
410 */
411 private void externalSubmitRunContinuationOrThrow() {
412 if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
413 try {
414 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
415 } catch (RejectedExecutionException ree) {
416 submitFailed(ree);
417 throw ree;
418 }
419 } else {
420 submitRunContinuation(scheduler, false);
421 }
422 }
423
424 /**
425 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
426 */
427 private void submitFailed(RejectedExecutionException ree) {
428 var event = new VirtualThreadSubmitFailedEvent();
429 if (event.isEnabled()) {
430 event.javaThreadId = threadId();
431 event.exceptionMessage = ree.getMessage();
432 event.commit();
433 }
434 }
435
436 /**
437 * Runs a task in the context of this virtual thread.
438 */
439 private void run(Runnable task) {
440 assert Thread.currentThread() == this && state == RUNNING;
441
442 // notify JVMTI, may post VirtualThreadStart event
443 notifyJvmtiStart();
444
445 // emit JFR event if enabled
446 if (VirtualThreadStartEvent.isTurnedOn()) {
447 var event = new VirtualThreadStartEvent();
448 event.javaThreadId = threadId();
449 event.commit();
450 }
451
452 Object bindings = Thread.scopedValueBindings();
453 try {
454 runWith(bindings, task);
455 } catch (Throwable exc) {
456 dispatchUncaughtException(exc);
457 } finally {
458 try {
459 // pop any remaining scopes from the stack, this may block
460 StackableScope.popAll();
461
462 // emit JFR event if enabled
463 if (VirtualThreadEndEvent.isTurnedOn()) {
464 var event = new VirtualThreadEndEvent();
465 event.javaThreadId = threadId();
466 event.commit();
467 }
468
469 } finally {
470 // notify JVMTI, may post VirtualThreadEnd event
471 notifyJvmtiEnd();
472 }
473 }
474 }
475
476 /**
477 * Mounts this virtual thread onto the current platform thread. On
478 * return, the current thread is the virtual thread.
479 */
480 @ChangesCurrentThread
481 @ReservedStackAccess
482 private void mount() {
483 // notify JVMTI before mount
484 notifyJvmtiMount(/*hide*/true);
485
486 // sets the carrier thread
487 Thread carrier = Thread.currentCarrierThread();
488 setCarrierThread(carrier);
489
490 // sync up carrier thread interrupt status if needed
491 if (interrupted) {
492 carrier.setInterrupt();
493 } else if (carrier.isInterrupted()) {
494 synchronized (interruptLock) {
495 // need to recheck interrupt status
496 if (!interrupted) {
497 carrier.clearInterrupt();
498 }
499 }
500 }
501
502 // set Thread.currentThread() to return this virtual thread
503 carrier.setCurrentThread(this);
504 }
505
506 /**
507 * Unmounts this virtual thread from the carrier. On return, the
508 * current thread is the current platform thread.
509 */
510 @ChangesCurrentThread
511 @ReservedStackAccess
512 private void unmount() {
513 assert !Thread.holdsLock(interruptLock);
514
515 // set Thread.currentThread() to return the platform thread
516 Thread carrier = this.carrierThread;
517 carrier.setCurrentThread(carrier);
518
519 // break connection to carrier thread, synchronized with interrupt
520 synchronized (interruptLock) {
521 setCarrierThread(null);
522 }
523 carrier.clearInterrupt();
524
525 // notify JVMTI after unmount
526 notifyJvmtiUnmount(/*hide*/false);
527 }
528
529 /**
530 * Sets the current thread to the current carrier thread.
531 */
532 @ChangesCurrentThread
533 @JvmtiMountTransition
534 private void switchToCarrierThread() {
535 notifyJvmtiHideFrames(true);
536 Thread carrier = this.carrierThread;
537 assert Thread.currentThread() == this
538 && carrier == Thread.currentCarrierThread();
539 carrier.setCurrentThread(carrier);
540 Thread.setCurrentLockId(this.threadId()); // keep lock ID of virtual thread
541 }
542
543 /**
544 * Sets the current thread to the given virtual thread.
545 */
546 @ChangesCurrentThread
547 @JvmtiMountTransition
548 private static void switchToVirtualThread(VirtualThread vthread) {
549 Thread carrier = vthread.carrierThread;
550 assert carrier == Thread.currentCarrierThread();
551 carrier.setCurrentThread(vthread);
552 notifyJvmtiHideFrames(false);
553 }
554
555 /**
556 * Executes the given value returning task on the current carrier thread.
557 */
558 @ChangesCurrentThread
559 <V> V executeOnCarrierThread(Callable<V> task) throws Exception {
560 assert Thread.currentThread() == this;
561 switchToCarrierThread();
562 try {
563 return task.call();
564 } finally {
565 switchToVirtualThread(this);
566 }
567 }
568
569 /**
570 * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
571 * the continuation continues.
572 */
573 @Hidden
574 private boolean yieldContinuation() {
575 notifyJvmtiUnmount(/*hide*/true);
576 try {
577 return Continuation.yield(VTHREAD_SCOPE);
578 } finally {
579 notifyJvmtiMount(/*hide*/false);
580 }
581 }
582
583 /**
584 * Invoked after the continuation yields. If parking then it sets the state
585 * and also re-submits the task to continue if unparked while parking.
586 * If yielding due to Thread.yield then it just submits the task to continue.
587 */
588 private void afterYield() {
589 assert carrierThread == null;
590
591 // re-adjust parallelism if the virtual thread yielded when compensating
592 if (currentThread() instanceof CarrierThread ct) {
593 ct.endBlocking();
594 }
595
596 int s = state();
597
598 // LockSupport.park/parkNanos
599 if (s == PARKING || s == TIMED_PARKING) {
600 int newState = (s == PARKING) ? PARKED : TIMED_PARKED;
601 setState(newState);
602
603 // may have been unparked while parking
604 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
605 // lazy submit to continue on the current carrier if possible
606 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
607 lazySubmitRunContinuation(ct.getPool());
608 } else {
609 submitRunContinuation();
610 }
611 }
612 return;
613 }
614
615 // Thread.yield
616 if (s == YIELDING) {
617 setState(YIELDED);
618
619 // external submit if there are no tasks in the local task queue
620 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
621 externalSubmitRunContinuation(ct.getPool());
622 } else {
623 submitRunContinuation();
624 }
625 return;
626 }
627
628 // blocking on monitorenter
629 if (s == BLOCKING) {
630 setState(BLOCKED);
631
632 // may have been unblocked while blocking
633 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
634 submitRunContinuation();
635 }
636 return;
637 }
638
639 // Object.wait
640 if (s == WAITING || s == TIMED_WAITING) {
641 byte nonce;
642 int newState;
643 if (s == WAITING) {
644 nonce = 0; // not used
645 setState(newState = WAIT);
646 } else {
647 // synchronize with timeout task (previous timed-wait may be running)
648 synchronized (timedWaitLock()) {
649 nonce = ++timedWaitNonce;
650 setState(newState = TIMED_WAIT);
651 }
652 }
653
654 // may have been notified while in transition to wait state
655 if (notified && compareAndSetState(newState, BLOCKED)) {
656 // may have even been unblocked already
657 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
658 submitRunContinuation();
659 }
660 return;
661 }
662
663 // may have been interrupted while in transition to wait state
664 if (interrupted && compareAndSetState(newState, UNBLOCKED)) {
665 submitRunContinuation();
666 return;
667 }
668
669 // schedule wakeup
670 if (newState == TIMED_WAIT) {
671 assert waitTimeout > 0;
672 waitTimeoutTask = schedule(() -> waitTimeoutExpired(nonce), waitTimeout, MILLISECONDS);
673 }
674 return;
675 }
676
677 assert false;
678 }
679
680 /**
681 * Invoked after the continuation completes.
682 */
683 private void afterDone() {
684 afterDone(true);
685 }
686
687 /**
688 * Invoked after the continuation completes (or start failed). Sets the thread
689 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
690 *
691 * @param notifyContainer true if its container should be notified
692 */
693 private void afterDone(boolean notifyContainer) {
694 assert carrierThread == null;
695 setState(TERMINATED);
696
697 // notify anyone waiting for this virtual thread to terminate
698 CountDownLatch termination = this.termination;
699 if (termination != null) {
700 assert termination.getCount() == 1;
701 termination.countDown();
702 }
703
704 // notify container
705 if (notifyContainer) {
706 threadContainer().onExit(this);
707 }
708
709 // clear references to thread locals
710 clearReferences();
711 }
712
713 /**
714 * Schedules this {@code VirtualThread} to execute.
715 *
716 * @throws IllegalStateException if the container is shutdown or closed
717 * @throws IllegalThreadStateException if the thread has already been started
718 * @throws RejectedExecutionException if the scheduler cannot accept a task
719 */
720 @Override
721 void start(ThreadContainer container) {
722 if (!compareAndSetState(NEW, STARTED)) {
723 throw new IllegalThreadStateException("Already started");
724 }
725
726 // bind thread to container
727 assert threadContainer() == null;
728 setThreadContainer(container);
729
730 // start thread
731 boolean addedToContainer = false;
732 boolean started = false;
733 try {
734 container.onStart(this); // may throw
735 addedToContainer = true;
736
737 // scoped values may be inherited
738 inheritScopedValueBindings(container);
739
740 // submit task to run thread, using externalSubmit if possible
741 externalSubmitRunContinuationOrThrow();
742 started = true;
743 } finally {
744 if (!started) {
745 afterDone(addedToContainer);
746 }
747 }
748 }
749
750 @Override
751 public void start() {
752 start(ThreadContainers.root());
753 }
754
755 @Override
756 public void run() {
757 // do nothing
758 }
759
760 /**
761 * Parks until unparked or interrupted. If already unparked then the parking
762 * permit is consumed and this method completes immediately (meaning it doesn't
763 * yield). It also completes immediately if the interrupt status is set.
764 */
765 @Override
766 void park() {
767 assert Thread.currentThread() == this;
768
769 // complete immediately if parking permit available or interrupted
770 if (getAndSetParkPermit(false) || interrupted)
771 return;
772
773 // park the thread
774 boolean yielded = false;
775 setState(PARKING);
776 try {
777 yielded = yieldContinuation();
778 } catch (OutOfMemoryError e) {
779 // park on carrier
780 } finally {
781 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
782 if (!yielded) {
783 assert state() == PARKING;
784 setState(RUNNING);
785 }
786 }
787
788 // park on the carrier thread when pinned
789 if (!yielded) {
790 parkOnCarrierThread(false, 0);
791 }
792 }
793
794 /**
795 * Parks up to the given waiting time or until unparked or interrupted.
796 * If already unparked then the parking permit is consumed and this method
797 * completes immediately (meaning it doesn't yield). It also completes immediately
798 * if the interrupt status is set or the waiting time is {@code <= 0}.
799 *
800 * @param nanos the maximum number of nanoseconds to wait.
801 */
802 @Override
803 void parkNanos(long nanos) {
804 assert Thread.currentThread() == this;
805
806 // complete immediately if parking permit available or interrupted
807 if (getAndSetParkPermit(false) || interrupted)
808 return;
809
810 // park the thread for the waiting time
811 if (nanos > 0) {
812 long startTime = System.nanoTime();
813
814 boolean yielded = false;
815 Future<?> unparker = null;
816 try {
817 unparker = scheduleUnpark(nanos);
818 } catch (OutOfMemoryError e) {
819 // park on carrier
820 }
821 if (unparker != null) {
822 setState(TIMED_PARKING);
823 try {
824 yielded = yieldContinuation();
825 } catch (OutOfMemoryError e) {
826 // park on carrier
827 } finally {
828 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
829 if (!yielded) {
830 assert state() == TIMED_PARKING;
831 setState(RUNNING);
832 }
833 cancel(unparker);
834 }
835 }
836
837 // park on carrier thread for remaining time when pinned (or OOME)
838 if (!yielded) {
839 long remainingNanos = nanos - (System.nanoTime() - startTime);
840 parkOnCarrierThread(true, remainingNanos);
841 }
842 }
843 }
844
845 /**
846 * Parks the current carrier thread up to the given waiting time or until
847 * unparked or interrupted. If the virtual thread is interrupted then the
848 * interrupt status will be propagated to the carrier thread.
849 * @param timed true for a timed park, false for untimed
850 * @param nanos the waiting time in nanoseconds
851 */
852 private void parkOnCarrierThread(boolean timed, long nanos) {
853 assert state() == RUNNING;
854
855 setState(timed ? TIMED_PINNED : PINNED);
856 try {
857 if (!parkPermit) {
858 if (!timed) {
859 U.park(false, 0);
860 } else if (nanos > 0) {
861 U.park(false, nanos);
862 }
863 }
864 } finally {
865 setState(RUNNING);
866 }
867
868 // consume parking permit
869 setParkPermit(false);
870 }
871
872 /**
873 * Invoked by parkNanos to schedule this virtual thread to be unparked after
874 * a given delay.
875 */
876 @ChangesCurrentThread
877 private Future<?> scheduleUnpark(long nanos) {
878 assert Thread.currentThread() == this;
879 // need to switch to current carrier thread to avoid nested parking
880 switchToCarrierThread();
881 try {
882 return schedule(this::unpark, nanos, NANOSECONDS);
883 } finally {
884 switchToVirtualThread(this);
885 }
886 }
887
888 /**
889 * Invoked by parkNanos to cancel the unpark timer.
890 */
891 @ChangesCurrentThread
892 private void cancel(Future<?> future) {
893 assert Thread.currentThread() == this;
894 if (!future.isDone()) {
895 // need to switch to current carrier thread to avoid nested parking
896 switchToCarrierThread();
897 try {
898 future.cancel(false);
899 } finally {
900 switchToVirtualThread(this);
901 }
902 }
903 }
904
905 /**
906 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
907 * then its task is scheduled to continue, otherwise its next call to {@code park} or
908 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
909 * @throws RejectedExecutionException if the scheduler cannot accept a task
910 */
911 @Override
912 void unpark() {
913 if (!getAndSetParkPermit(true) && currentThread() != this) {
914 int s = state();
915
916 // unparked while parked
917 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
918 submitRunContinuation();
919 return;
920 }
921
922 // unparked while parked when pinned
923 if (s == PINNED || s == TIMED_PINNED) {
924 // unpark carrier thread when pinned
925 disableSuspendAndPreempt();
926 try {
927 synchronized (carrierThreadAccessLock()) {
928 Thread carrier = carrierThread;
929 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
930 U.unpark(carrier);
931 }
932 }
933 } finally {
934 enableSuspendAndPreempt();
935 }
936 return;
937 }
938 }
939 }
940
941 /**
942 * Invoked by unblocker thread to unblock this virtual thread.
943 */
944 private void unblock() {
945 assert !Thread.currentThread().isVirtual();
946 blockPermit = true;
947 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) {
948 submitRunContinuation();
949 }
950 }
951
952 /**
953 * Invoked by timer thread when wait timeout for virtual thread has expired.
954 * If the virtual thread is in timed-wait then this method will unblock the thread
955 * and submit its task so that it continues and attempts to reenter the monitor.
956 * This method does nothing if the thread has been woken by notify or interrupt.
957 */
958 private void waitTimeoutExpired(byte nounce) {
959 assert !Thread.currentThread().isVirtual();
960 for (;;) {
961 boolean unblocked = false;
962 synchronized (timedWaitLock()) {
963 if (nounce != timedWaitNonce) {
964 // this timeout task is for a past timed-wait
965 return;
966 }
967 int s = state();
968 if (s == TIMED_WAIT) {
969 unblocked = compareAndSetState(TIMED_WAIT, UNBLOCKED);
970 } else if (s != (TIMED_WAIT | SUSPENDED)) {
971 // notified or interrupted, no longer waiting
972 return;
973 }
974 }
975 if (unblocked) {
976 submitRunContinuation();
977 return;
978 }
979 // need to retry when thread is suspended in time-wait
980 Thread.yield();
981 }
982 }
983
984 /**
985 * Invoked by Object.wait to cancel the wait timer.
986 */
987 void cancelWaitTimeout() {
988 assert Thread.currentThread() == this;
989 Future<?> timeoutTask = this.waitTimeoutTask;
990 if (timeoutTask != null) {
991 // Pin the continuation to prevent the virtual thread from unmounting
992 // when there is contention removing the task. This avoids deadlock that
993 // could arise due to carriers and virtual threads contending for a
994 // lock on the delay queue.
995 Continuation.pin();
996 try {
997 timeoutTask.cancel(false);
998 } finally {
999 Continuation.unpin();
1000 }
1001 }
1002 }
1003
1004 /**
1005 * Attempts to yield the current virtual thread (Thread.yield).
1006 */
1007 void tryYield() {
1008 assert Thread.currentThread() == this;
1009 setState(YIELDING);
1010 boolean yielded = false;
1011 try {
1012 yielded = yieldContinuation(); // may throw
1013 } finally {
1014 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
1015 if (!yielded) {
1016 assert state() == YIELDING;
1017 setState(RUNNING);
1018 }
1019 }
1020 }
1021
1022 /**
1023 * Sleep the current thread for the given sleep time (in nanoseconds). If
1024 * nanos is 0 then the thread will attempt to yield.
1025 *
1026 * @implNote This implementation parks the thread for the given sleeping time
1027 * and will therefore be observed in PARKED state during the sleep. Parking
1028 * will consume the parking permit so this method makes available the parking
1029 * permit after the sleep. This may be observed as a spurious, but benign,
1030 * wakeup when the thread subsequently attempts to park.
1031 *
1032 * @param nanos the maximum number of nanoseconds to sleep
1033 * @throws InterruptedException if interrupted while sleeping
1034 */
1035 void sleepNanos(long nanos) throws InterruptedException {
1036 assert Thread.currentThread() == this && nanos >= 0;
1037 if (getAndClearInterrupt())
1038 throw new InterruptedException();
1039 if (nanos == 0) {
1040 tryYield();
1041 } else {
1042 // park for the sleep time
1043 try {
1044 long remainingNanos = nanos;
1045 long startNanos = System.nanoTime();
1046 while (remainingNanos > 0) {
1047 parkNanos(remainingNanos);
1048 if (getAndClearInterrupt()) {
1049 throw new InterruptedException();
1050 }
1051 remainingNanos = nanos - (System.nanoTime() - startNanos);
1052 }
1053 } finally {
1054 // may have been unparked while sleeping
1055 setParkPermit(true);
1056 }
1057 }
1058 }
1059
1060 /**
1061 * Waits up to {@code nanos} nanoseconds for this virtual thread to terminate.
1062 * A timeout of {@code 0} means to wait forever.
1063 *
1064 * @throws InterruptedException if interrupted while waiting
1065 * @return true if the thread has terminated
1066 */
1067 boolean joinNanos(long nanos) throws InterruptedException {
1068 if (state() == TERMINATED)
1069 return true;
1070
1071 // ensure termination object exists, then re-check state
1072 CountDownLatch termination = getTermination();
1073 if (state() == TERMINATED)
1074 return true;
1075
1076 // wait for virtual thread to terminate
1077 if (nanos == 0) {
1078 termination.await();
1079 } else {
1080 boolean terminated = termination.await(nanos, NANOSECONDS);
1081 if (!terminated) {
1082 // waiting time elapsed
1083 return false;
1084 }
1085 }
1086 assert state() == TERMINATED;
1087 return true;
1088 }
1089
1090 @Override
1091 void blockedOn(Interruptible b) {
1092 disableSuspendAndPreempt();
1093 try {
1094 super.blockedOn(b);
1095 } finally {
1096 enableSuspendAndPreempt();
1097 }
1098 }
1099
1100 @Override
1101 @SuppressWarnings("removal")
1102 public void interrupt() {
1103 if (Thread.currentThread() != this) {
1104 checkAccess();
1105
1106 // if current thread is a virtual thread then prevent it from being
1107 // suspended or unmounted when entering or holding interruptLock
1108 Interruptible blocker;
1109 disableSuspendAndPreempt();
1110 try {
1111 synchronized (interruptLock) {
1112 interrupted = true;
1113 blocker = nioBlocker();
1114 if (blocker != null) {
1115 blocker.interrupt(this);
1116 }
1117
1118 // interrupt carrier thread if mounted
1119 Thread carrier = carrierThread;
1120 if (carrier != null) carrier.setInterrupt();
1121 }
1122 } finally {
1123 enableSuspendAndPreempt();
1124 }
1125
1126 // notify blocker after releasing interruptLock
1127 if (blocker != null) {
1128 blocker.postInterrupt();
1129 }
1130
1131 // make available parking permit, unpark thread if parked
1132 unpark();
1133
1134 // if thread is waiting in Object.wait then schedule to try to reenter
1135 int s = state();
1136 if ((s == WAIT || s == TIMED_WAIT) && compareAndSetState(s, UNBLOCKED)) {
1137 submitRunContinuation();
1138 }
1139
1140 } else {
1141 interrupted = true;
1142 carrierThread.setInterrupt();
1143 setParkPermit(true);
1144 }
1145 }
1146
1147 @Override
1148 public boolean isInterrupted() {
1149 return interrupted;
1150 }
1151
1152 @Override
1153 boolean getAndClearInterrupt() {
1154 assert Thread.currentThread() == this;
1155 boolean oldValue = interrupted;
1156 if (oldValue) {
1157 disableSuspendAndPreempt();
1158 try {
1159 synchronized (interruptLock) {
1160 interrupted = false;
1161 carrierThread.clearInterrupt();
1162 }
1163 } finally {
1164 enableSuspendAndPreempt();
1165 }
1166 }
1167 return oldValue;
1168 }
1169
1170 @Override
1171 Thread.State threadState() {
1172 int s = state();
1173 switch (s & ~SUSPENDED) {
1174 case NEW:
1175 return Thread.State.NEW;
1176 case STARTED:
1177 // return NEW if thread container not yet set
1178 if (threadContainer() == null) {
1179 return Thread.State.NEW;
1180 } else {
1181 return Thread.State.RUNNABLE;
1182 }
1183 case UNPARKED:
1184 case UNBLOCKED:
1185 case YIELDED:
1186 // runnable, not mounted
1187 return Thread.State.RUNNABLE;
1188 case RUNNING:
1189 // if mounted then return state of carrier thread
1190 if (Thread.currentThread() != this) {
1191 disableSuspendAndPreempt();
1192 try {
1193 synchronized (carrierThreadAccessLock()) {
1194 Thread carrierThread = this.carrierThread;
1195 if (carrierThread != null) {
1196 return carrierThread.threadState();
1197 }
1198 }
1199 } finally {
1200 enableSuspendAndPreempt();
1201 }
1202 }
1203 // runnable, mounted
1204 return Thread.State.RUNNABLE;
1205 case PARKING:
1206 case TIMED_PARKING:
1207 case BLOCKING:
1208 case WAITING:
1209 case TIMED_WAITING:
1210 case YIELDING:
1211 // runnable, in transition
1212 return Thread.State.RUNNABLE;
1213 case PARKED:
1214 case PINNED:
1215 case WAIT:
1216 return Thread.State.WAITING;
1217 case TIMED_PARKED:
1218 case TIMED_PINNED:
1219 case TIMED_WAIT:
1220 return Thread.State.TIMED_WAITING;
1221 case BLOCKED:
1222 return Thread.State.BLOCKED;
1223 case TERMINATED:
1224 return Thread.State.TERMINATED;
1225 default:
1226 throw new InternalError();
1227 }
1228 }
1229
1230 @Override
1231 boolean alive() {
1232 int s = state;
1233 return (s != NEW && s != TERMINATED);
1234 }
1235
1236 @Override
1237 boolean isTerminated() {
1238 return (state == TERMINATED);
1239 }
1240
1241 @Override
1242 StackTraceElement[] asyncGetStackTrace() {
1243 StackTraceElement[] stackTrace;
1244 do {
1245 stackTrace = (carrierThread != null)
1246 ? super.asyncGetStackTrace() // mounted
1247 : tryGetStackTrace(); // unmounted
1248 if (stackTrace == null) {
1249 Thread.yield();
1250 }
1251 } while (stackTrace == null);
1252 return stackTrace;
1253 }
1254
1255 /**
1256 * Returns the stack trace for this virtual thread if it is unmounted.
1257 * Returns null if the thread is mounted or in transition.
1258 */
1259 private StackTraceElement[] tryGetStackTrace() {
1260 int initialState = state() & ~SUSPENDED;
1261 switch (initialState) {
1262 case NEW, STARTED, TERMINATED -> {
1263 return new StackTraceElement[0]; // unmounted, empty stack
1264 }
1265 case RUNNING, PINNED, TIMED_PINNED -> {
1266 return null; // mounted
1267 }
1268 case PARKED, TIMED_PARKED, BLOCKED, WAIT, TIMED_WAIT -> {
1269 // unmounted, not runnable
1270 }
1271 case UNPARKED, UNBLOCKED, YIELDED -> {
1272 // unmounted, runnable
1273 }
1274 case PARKING, TIMED_PARKING, BLOCKING, YIELDING, WAITING, TIMED_WAITING -> {
1275 return null; // in transition
1276 }
1277 default -> throw new InternalError("" + initialState);
1278 }
1279
1280 // thread is unmounted, prevent it from continuing
1281 int suspendedState = initialState | SUSPENDED;
1282 if (!compareAndSetState(initialState, suspendedState)) {
1283 return null;
1284 }
1285
1286 // get stack trace and restore state
1287 StackTraceElement[] stack;
1288 try {
1289 stack = cont.getStackTrace();
1290 } finally {
1291 assert state == suspendedState;
1292 setState(initialState);
1293 }
1294 boolean resubmit = switch (initialState) {
1295 case UNPARKED, UNBLOCKED, YIELDED -> {
1296 // resubmit as task may have run while suspended
1297 yield true;
1298 }
1299 case PARKED, TIMED_PARKED -> {
1300 // resubmit if unparked while suspended
1301 yield parkPermit && compareAndSetState(initialState, UNPARKED);
1302 }
1303 case BLOCKED -> {
1304 // resubmit if unblocked while suspended
1305 yield blockPermit && compareAndSetState(BLOCKED, UNBLOCKED);
1306 }
1307 case WAIT, TIMED_WAIT -> {
1308 // resubmit if notified or interrupted while waiting (Object.wait)
1309 // waitTimeoutExpired will retry if the timed expired when suspended
1310 yield (notified || interrupted) && compareAndSetState(initialState, UNBLOCKED);
1311 }
1312 default -> throw new InternalError();
1313 };
1314 if (resubmit) {
1315 submitRunContinuation();
1316 }
1317 return stack;
1318 }
1319
1320 @Override
1321 public String toString() {
1322 StringBuilder sb = new StringBuilder("VirtualThread[#");
1323 sb.append(threadId());
1324 String name = getName();
1325 if (!name.isEmpty()) {
1326 sb.append(",");
1327 sb.append(name);
1328 }
1329 sb.append("]/");
1330
1331 // add the carrier state and thread name when mounted
1332 boolean mounted;
1333 if (Thread.currentThread() == this) {
1334 mounted = appendCarrierInfo(sb);
1335 } else {
1336 disableSuspendAndPreempt();
1337 try {
1338 synchronized (carrierThreadAccessLock()) {
1339 mounted = appendCarrierInfo(sb);
1340 }
1341 } finally {
1342 enableSuspendAndPreempt();
1343 }
1344 }
1345
1346 // add virtual thread state when not mounted
1347 if (!mounted) {
1348 String stateAsString = threadState().toString();
1349 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1350 }
1351
1352 return sb.toString();
1353 }
1354
1355 /**
1356 * Appends the carrier state and thread name to the string buffer if mounted.
1357 * @return true if mounted, false if not mounted
1358 */
1359 private boolean appendCarrierInfo(StringBuilder sb) {
1360 assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock());
1361 Thread carrier = carrierThread;
1362 if (carrier != null) {
1363 String stateAsString = carrier.threadState().toString();
1364 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1365 sb.append('@');
1366 sb.append(carrier.getName());
1367 return true;
1368 } else {
1369 return false;
1370 }
1371 }
1372
1373 @Override
1374 public int hashCode() {
1375 return (int) threadId();
1376 }
1377
1378 @Override
1379 public boolean equals(Object obj) {
1380 return obj == this;
1381 }
1382
1383 /**
1384 * Returns the termination object, creating it if needed.
1385 */
1386 private CountDownLatch getTermination() {
1387 CountDownLatch termination = this.termination;
1388 if (termination == null) {
1389 termination = new CountDownLatch(1);
1390 if (!U.compareAndSetReference(this, TERMINATION, null, termination)) {
1391 termination = this.termination;
1392 }
1393 }
1394 return termination;
1395 }
1396
1397 /**
1398 * Returns the lock object to synchronize on when accessing carrierThread.
1399 * The lock prevents carrierThread from being reset to null during unmount.
1400 */
1401 private Object carrierThreadAccessLock() {
1402 // return interruptLock as unmount has to coordinate with interrupt
1403 return interruptLock;
1404 }
1405
1406 /**
1407 * Returns a lock object to coordinating timed-wait setup and timeout handling.
1408 */
1409 private Object timedWaitLock() {
1410 // use this object for now to avoid the overhead of introducing another lock
1411 return runContinuation;
1412 }
1413
1414 /**
1415 * Disallow the current thread be suspended or preempted.
1416 */
1417 private void disableSuspendAndPreempt() {
1418 notifyJvmtiDisableSuspend(true);
1419 Continuation.pin();
1420 }
1421
1422 /**
1423 * Allow the current thread be suspended or preempted.
1424 */
1425 private void enableSuspendAndPreempt() {
1426 Continuation.unpin();
1427 notifyJvmtiDisableSuspend(false);
1428 }
1429
1430 // -- wrappers for get/set of state, parking permit, and carrier thread --
1431
1432 private int state() {
1433 return state; // volatile read
1434 }
1435
1436 private void setState(int newValue) {
1437 state = newValue; // volatile write
1438 }
1439
1440 private boolean compareAndSetState(int expectedValue, int newValue) {
1441 return U.compareAndSetInt(this, STATE, expectedValue, newValue);
1442 }
1443
1444 private boolean compareAndSetOnWaitingList(boolean expectedValue, boolean newValue) {
1445 return U.compareAndSetBoolean(this, ON_WAITING_LIST, expectedValue, newValue);
1446 }
1447
1448 private void setParkPermit(boolean newValue) {
1449 if (parkPermit != newValue) {
1450 parkPermit = newValue;
1451 }
1452 }
1453
1454 private boolean getAndSetParkPermit(boolean newValue) {
1455 if (parkPermit != newValue) {
1456 return U.getAndSetBoolean(this, PARK_PERMIT, newValue);
1457 } else {
1458 return newValue;
1459 }
1460 }
1461
1462 private void setCarrierThread(Thread carrier) {
1463 // U.putReferenceRelease(this, CARRIER_THREAD, carrier);
1464 this.carrierThread = carrier;
1465 }
1466
1467 // -- JVM TI support --
1468
1469 @IntrinsicCandidate
1470 @JvmtiMountTransition
1471 private native void notifyJvmtiStart();
1472
1473 @IntrinsicCandidate
1474 @JvmtiMountTransition
1475 private native void notifyJvmtiEnd();
1476
1477 @IntrinsicCandidate
1478 @JvmtiMountTransition
1479 private native void notifyJvmtiMount(boolean hide);
1480
1481 @IntrinsicCandidate
1482 @JvmtiMountTransition
1483 private native void notifyJvmtiUnmount(boolean hide);
1484
1485 @IntrinsicCandidate
1486 @JvmtiMountTransition
1487 private static native void notifyJvmtiHideFrames(boolean hide);
1488
1489 @IntrinsicCandidate
1490 private static native void notifyJvmtiDisableSuspend(boolean enter);
1491
1492 private static native void registerNatives();
1493 static {
1494 registerNatives();
1495
1496 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1497 var group = Thread.virtualThreadGroup();
1498 }
1499
1500 /**
1501 * Creates the default scheduler.
1502 * If the system property {@code jdk.virtualThreadScheduler.implClass} is set then
1503 * its value is the name of a class that implements java.util.concurrent.Executor.
1504 * The class is public in an exported package, has a public no-arg constructor,
1505 * and is visible to the system class loader.
1506 * If the system property is not set then the default scheduler will be a
1507 * ForkJoinPool instance.
1508 */
1509 private static Executor createDefaultScheduler() {
1510 String propName = "jdk.virtualThreadScheduler.implClass";
1511 String propValue = GetPropertyAction.privilegedGetProperty(propName);
1512 if (propValue != null) {
1513 try {
1514 Class<?> clazz = Class.forName(propValue, true,
1515 ClassLoader.getSystemClassLoader());
1516 Constructor<?> ctor = clazz.getConstructor();
1517 var scheduler = (Executor) ctor.newInstance();
1518 System.err.println("""
1519 WARNING: Using custom scheduler, this is an experimental feature.""");
1520 return scheduler;
1521 } catch (Exception ex) {
1522 throw new Error(ex);
1523 }
1524 } else {
1525 return createDefaultForkJoinPoolScheduler();
1526 }
1527 }
1528
1529 /**
1530 * Creates the default ForkJoinPool scheduler.
1531 */
1532 @SuppressWarnings("removal")
1533 private static ForkJoinPool createDefaultForkJoinPoolScheduler() {
1534 ForkJoinWorkerThreadFactory factory = pool -> {
1535 PrivilegedAction<ForkJoinWorkerThread> pa = () -> new CarrierThread(pool);
1536 return AccessController.doPrivileged(pa);
1537 };
1538 PrivilegedAction<ForkJoinPool> pa = () -> {
1539 int parallelism, maxPoolSize, minRunnable;
1540 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1541 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1542 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1543 if (parallelismValue != null) {
1544 parallelism = Integer.parseInt(parallelismValue);
1545 } else {
1546 parallelism = Runtime.getRuntime().availableProcessors();
1547 }
1548 if (maxPoolSizeValue != null) {
1549 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1550 parallelism = Integer.min(parallelism, maxPoolSize);
1551 } else {
1552 maxPoolSize = Integer.max(parallelism, 256);
1553 }
1554 if (minRunnableValue != null) {
1555 minRunnable = Integer.parseInt(minRunnableValue);
1556 } else {
1557 minRunnable = Integer.max(parallelism / 2, 1);
1558 }
1559 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1560 boolean asyncMode = true; // FIFO
1561 return new ForkJoinPool(parallelism, factory, handler, asyncMode,
1562 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1563 };
1564 return AccessController.doPrivileged(pa);
1565 }
1566
1567 /**
1568 * Schedule a runnable task to run after a delay.
1569 */
1570 private static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1571 long tid = Thread.currentThread().threadId();
1572 int index = (int) tid & (DELAYED_TASK_SCHEDULERS.length - 1);
1573 return DELAYED_TASK_SCHEDULERS[index].schedule(command, delay, unit);
1574 }
1575
1576 /**
1577 * Creates the ScheduledThreadPoolExecutors used to execute delayed tasks.
1578 */
1579 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1580 String propName = "jdk.virtualThreadScheduler.timerQueues";
1581 String propValue = GetPropertyAction.privilegedGetProperty(propName);
1582 int queueCount;
1583 if (propValue != null) {
1584 queueCount = Integer.parseInt(propValue);
1585 if (queueCount != Integer.highestOneBit(queueCount)) {
1586 throw new RuntimeException("Value of " + propName + " must be power of 2");
1587 }
1588 } else {
1589 int ncpus = Runtime.getRuntime().availableProcessors();
1590 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
1591 }
1592 var schedulers = new ScheduledExecutorService[queueCount];
1593 for (int i = 0; i < queueCount; i++) {
1594 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
1595 Executors.newScheduledThreadPool(1, task -> {
1596 Thread t = InnocuousThread.newThread("VirtualThread-unparker", task);
1597 t.setDaemon(true);
1598 return t;
1599 });
1600 stpe.setRemoveOnCancelPolicy(true);
1601 schedulers[i] = stpe;
1602 }
1603 return schedulers;
1604 }
1605
1606 /**
1607 * Schedule virtual threads that are ready to be scheduled after they blocked on
1608 * monitor enter.
1609 */
1610 private static void unblockVirtualThreads() {
1611 while (true) {
1612 VirtualThread vthread = takeVirtualThreadListToUnblock();
1613 while (vthread != null) {
1614 assert vthread.onWaitingList;
1615 VirtualThread nextThread = vthread.next;
1616
1617 // remove from list and unblock
1618 vthread.next = null;
1619 boolean changed = vthread.compareAndSetOnWaitingList(true, false);
1620 assert changed;
1621 vthread.unblock();
1622
1623 vthread = nextThread;
1624 }
1625 }
1626 }
1627
1628 /**
1629 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting
1630 * if necessary until a list of one or more threads becomes available.
1631 */
1632 private static native VirtualThread takeVirtualThreadListToUnblock();
1633
1634 static {
1635 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker",
1636 VirtualThread::unblockVirtualThreads);
1637 unblocker.setDaemon(true);
1638 unblocker.start();
1639 }
1640 }