1 /*
2 * Copyright (c) 2018, 2026, 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.invoke.MethodHandles;
28 import java.lang.invoke.VarHandle;
29 import java.lang.reflect.Constructor;
30 import java.util.Locale;
31 import java.util.Objects;
32 import java.util.concurrent.Executors;
33 import java.util.concurrent.ForkJoinPool;
34 import java.util.concurrent.ForkJoinTask;
35 import java.util.concurrent.Future;
36 import java.util.concurrent.LinkedTransferQueue;
37 import java.util.concurrent.RejectedExecutionException;
38 import java.util.concurrent.ScheduledExecutorService;
39 import java.util.concurrent.ScheduledFuture;
40 import java.util.concurrent.ScheduledThreadPoolExecutor;
41 import java.util.concurrent.ThreadFactory;
42 import java.util.concurrent.ThreadPoolExecutor;
43 import java.util.concurrent.TimeUnit;
44 import jdk.internal.event.VirtualThreadEndEvent;
45 import jdk.internal.event.VirtualThreadStartEvent;
46 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
47 import jdk.internal.invoke.MhUtil;
48 import jdk.internal.misc.CarrierThread;
49 import jdk.internal.misc.InnocuousThread;
50 import jdk.internal.misc.Unsafe;
51 import jdk.internal.vm.Continuation;
52 import jdk.internal.vm.ContinuationScope;
53 import jdk.internal.vm.StackableScope;
54 import jdk.internal.vm.ThreadContainer;
55 import jdk.internal.vm.ThreadContainers;
56 import jdk.internal.vm.annotation.ChangesCurrentThread;
57 import jdk.internal.vm.annotation.Hidden;
58 import jdk.internal.vm.annotation.IntrinsicCandidate;
59 import jdk.internal.vm.annotation.JvmtiHideEvents;
60 import jdk.internal.vm.annotation.JvmtiMountTransition;
61 import jdk.internal.vm.annotation.ReservedStackAccess;
62 import sun.nio.ch.Interruptible;
63 import static java.util.concurrent.TimeUnit.*;
64
65 /**
66 * A thread that is scheduled by the Java virtual machine rather than the operating system.
67 */
68 final class VirtualThread extends BaseVirtualThread {
69 private static final Unsafe U = Unsafe.getUnsafe();
70 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
71
72 private static final VirtualThreadScheduler BUILTIN_SCHEDULER;
73 private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
74 private static final VirtualThreadScheduler EXTERNAL_VIEW;
75 private static final boolean USE_STPE;
76 static {
77 // experimental
78 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
79 if (propValue != null) {
80 VirtualThreadScheduler builtinScheduler = createBuiltinScheduler(true);
81 VirtualThreadScheduler externalView = createExternalView(builtinScheduler);
82 VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue);
83 BUILTIN_SCHEDULER = builtinScheduler;
84 DEFAULT_SCHEDULER = defaultScheduler;
85 EXTERNAL_VIEW = externalView;
86 } else {
87 var builtinScheduler = createBuiltinScheduler(false);
88 BUILTIN_SCHEDULER = builtinScheduler;
89 DEFAULT_SCHEDULER = builtinScheduler;
90 EXTERNAL_VIEW = createExternalView(builtinScheduler);
91 }
92 propValue = System.getProperty("jdk.virtualThreadScheduler.useSTPE");
93 if (propValue != null) {
94 USE_STPE = Boolean.parseBoolean(propValue);
95 } else {
96 USE_STPE = Runtime.getRuntime().availableProcessors() < 4;
97 }
98 }
99
100 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
101 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
102 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
103 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
104
105 // scheduler and continuation
106 private final VirtualThreadScheduler scheduler;
107 private final Continuation cont;
108 private final VThreadTask runContinuation;
109
110 // virtual thread state, accessed by VM
111 private volatile int state;
112
113 /*
114 * Virtual thread state transitions:
115 *
116 * NEW -> STARTED // Thread.start, schedule to run
117 * STARTED -> TERMINATED // failed to start
118 * STARTED -> RUNNING // first run
119 * RUNNING -> TERMINATED // done
120 *
121 * RUNNING -> PARKING // Thread parking with LockSupport.park
122 * PARKING -> PARKED // cont.yield successful, parked indefinitely
123 * PARKED -> UNPARKED // unparked, may be scheduled to continue
124 * UNPARKED -> RUNNING // continue execution after park
125 *
126 * PARKING -> RUNNING // cont.yield failed, need to park on carrier
127 * RUNNING -> PINNED // park on carrier
128 * PINNED -> RUNNING // unparked, continue execution on same carrier
129 *
130 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
131 * TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked
132 * TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue
133 *
134 * TIMED_PARKING -> RUNNING // cont.yield failed, need to park on carrier
135 * RUNNING -> TIMED_PINNED // park on carrier
136 * TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier
137 *
138 * RUNNING -> BLOCKING // blocking on monitor enter
139 * BLOCKING -> BLOCKED // blocked on monitor enter
140 * BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue
141 * UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter
142 *
143 * RUNNING -> WAITING // transitional state during wait on monitor
144 * WAITING -> WAIT // waiting on monitor
145 * WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
146 * WAIT -> UNBLOCKED // interrupted
147 *
148 * RUNNING -> TIMED_WAITING // transition state during timed-waiting on monitor
149 * TIMED_WAITING -> TIMED_WAIT // timed-waiting on monitor
150 * TIMED_WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
151 * TIMED_WAIT -> UNBLOCKED // timed-out/interrupted
152 *
153 * RUNNING -> YIELDING // Thread.yield
154 * YIELDING -> YIELDED // cont.yield successful, may be scheduled to continue
155 * YIELDING -> RUNNING // cont.yield failed
156 * YIELDED -> RUNNING // continue execution after Thread.yield
157 */
158 private static final int NEW = 0;
159 private static final int STARTED = 1;
160 private static final int RUNNING = 2; // runnable-mounted
161
162 // untimed and timed parking
163 private static final int PARKING = 3;
164 private static final int PARKED = 4; // unmounted
165 private static final int PINNED = 5; // mounted
166 private static final int TIMED_PARKING = 6;
167 private static final int TIMED_PARKED = 7; // unmounted
168 private static final int TIMED_PINNED = 8; // mounted
169 private static final int UNPARKED = 9; // unmounted but runnable
170
171 // Thread.yield
172 private static final int YIELDING = 10;
173 private static final int YIELDED = 11; // unmounted but runnable
174
175 // monitor enter
176 private static final int BLOCKING = 12;
177 private static final int BLOCKED = 13; // unmounted
178 private static final int UNBLOCKED = 14; // unmounted but runnable
179
180 // monitor wait/timed-wait
181 private static final int WAITING = 15;
182 private static final int WAIT = 16; // waiting in Object.wait
183 private static final int TIMED_WAITING = 17;
184 private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait
185
186 private static final int TERMINATED = 99; // final state
187
188 // parking permit made available by LockSupport.unpark
189 private volatile boolean parkPermit;
190
191 // blocking permit made available by unblocker thread when another thread exits monitor
192 private volatile boolean blockPermit;
193
194 // true when on the list of virtual threads waiting to be unblocked
195 private volatile boolean onWaitingList;
196
197 // next virtual thread on the list of virtual threads waiting to be unblocked
198 private volatile VirtualThread next;
199
200 // notified by Object.notify/notifyAll while waiting in Object.wait
201 private volatile boolean notified;
202
203 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
204 private volatile boolean interruptibleWait;
205
206 // timed-wait support
207 private byte timedWaitSeqNo;
208
209 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
210 private long timeout;
211
212 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
213 private Future<?> timeoutTask;
214
215 // carrier thread when mounted, accessed by VM
216 private volatile Thread carrierThread;
217
218 // true to notifyAll after this virtual thread terminates
219 private volatile boolean notifyAllAfterTerminate;
220
221 /**
222 * Return the built-in scheduler.
223 * @param trusted true if caller is trusted, false if not trusted
224 */
225 static VirtualThreadScheduler builtinScheduler(boolean trusted) {
226 return trusted ? BUILTIN_SCHEDULER : EXTERNAL_VIEW;
227 }
228
229 /**
230 * Returns the default scheduler, usually the same as the built-in scheduler.
231 */
232 static VirtualThreadScheduler defaultScheduler() {
233 return DEFAULT_SCHEDULER;
234 }
235
236 /**
237 * Returns the continuation scope used for virtual threads.
238 */
239 static ContinuationScope continuationScope() {
240 return VTHREAD_SCOPE;
241 }
242
243 /**
244 * Returns the task to start/continue this virtual thread.
245 */
246 VirtualThreadTask virtualThreadTask() {
247 return runContinuation;
248 }
249
250 /**
251 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
252 *
253 * @param scheduler the scheduler or null for default scheduler
254 * @param preferredCarrier the preferred carrier or null
255 * @param name thread name
256 * @param characteristics characteristics
257 * @param task the task to execute
258 */
259 VirtualThread(VirtualThreadScheduler scheduler,
260 Thread preferredCarrier,
261 String name,
262 int characteristics,
263 Runnable task) {
264 super(name, characteristics, /*bound*/ false);
265 Objects.requireNonNull(task);
266
267 // use default scheduler if not provided
268 if (scheduler == null) {
269 scheduler = DEFAULT_SCHEDULER;
270 } else if (scheduler == EXTERNAL_VIEW) {
271 throw new UnsupportedOperationException();
272 }
273 this.scheduler = scheduler;
274 this.cont = new VThreadContinuation(this, task);
275
276 if (scheduler == BUILTIN_SCHEDULER) {
277 this.runContinuation = new VThreadTask(this);
278 } else {
279 this.runContinuation = new CustomVThreadTask(this, preferredCarrier);
280 }
281 }
282
283 /**
284 * The task to start/continue a virtual thread.
285 */
286 static non-sealed class VThreadTask implements VirtualThreadTask {
287 private final VirtualThread vthread;
288 VThreadTask(VirtualThread vthread) {
289 this.vthread = vthread;
290 }
291 @Override
292 public final Thread thread() {
293 return vthread;
294 }
295 @Override
296 public final void run() {
297 vthread.runContinuation();;
298 }
299 @Override
300 public Thread preferredCarrier() {
301 throw new UnsupportedOperationException();
302 }
303 @Override
304 public Object attach(Object att) {
305 throw new UnsupportedOperationException();
306 }
307 @Override
308 public Object attachment() {
309 throw new UnsupportedOperationException();
310 }
311 }
312
313 /**
314 * The task to start/continue a virtual thread when using a custom scheduler.
315 */
316 static final class CustomVThreadTask extends VThreadTask {
317 private static final VarHandle ATT =
318 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class);
319 private final Thread preferredCarrier;
320 private volatile Object att;
321 CustomVThreadTask(VirtualThread vthread, Thread preferredCarrier) {
322 super(vthread);
323 this.preferredCarrier = preferredCarrier;
324 }
325 @Override
326 public Thread preferredCarrier() {
327 return preferredCarrier;
328 }
329 @Override
330 public Object attach(Object att) {
331 return ATT.getAndSet(this, att);
332 }
333 @Override
334 public Object attachment() {
335 return att;
336 }
337 }
338
339 /**
340 * The continuation that a virtual thread executes.
341 */
342 private static class VThreadContinuation extends Continuation {
343 VThreadContinuation(VirtualThread vthread, Runnable task) {
344 super(VTHREAD_SCOPE, wrap(vthread, task));
345 }
346 @Override
347 protected void onPinned(Continuation.Pinned reason) {
348 }
349 private static Runnable wrap(VirtualThread vthread, Runnable task) {
350 return new Runnable() {
351 @Hidden
352 @JvmtiHideEvents
353 public void run() {
354 vthread.endFirstTransition();
355 try {
356 vthread.run(task);
357 } finally {
358 vthread.startFinalTransition();
359 }
360 }
361 };
362 }
363 }
364
365 /**
366 * Runs or continues execution on the current thread. The virtual thread is mounted
367 * on the current thread before the task runs or continues. It unmounts when the
368 * task completes or yields.
369 */
370 @ChangesCurrentThread // allow mount/unmount to be inlined
371 private void runContinuation() {
372 // the carrier must be a platform thread
373 if (Thread.currentThread().isVirtual()) {
374 throw new WrongThreadException();
375 }
376
377 // set state to RUNNING
378 int initialState = state();
379 if (initialState == STARTED || initialState == UNPARKED
380 || initialState == UNBLOCKED || initialState == YIELDED) {
381 // newly started or continue after parking/blocking/Thread.yield
382 if (!compareAndSetState(initialState, RUNNING)) {
383 return;
384 }
385 // consume permit when continuing after parking or blocking. If continue
386 // after a timed-park or timed-wait then the timeout task is cancelled.
387 if (initialState == UNPARKED) {
388 cancelTimeoutTask();
389 setParkPermit(false);
390 } else if (initialState == UNBLOCKED) {
391 cancelTimeoutTask();
392 blockPermit = false;
393 }
394 } else {
395 // not runnable
396 return;
397 }
398
399 mount();
400 try {
401 cont.run();
402 } finally {
403 unmount();
404 if (cont.isDone()) {
405 afterDone();
406 } else {
407 afterYield();
408 }
409 }
410 }
411
412 /**
413 * Cancel timeout task when continuing after timed-park or timed-wait.
414 * The timeout task may be executing, or may have already completed.
415 */
416 private void cancelTimeoutTask() {
417 if (timeoutTask != null) {
418 timeoutTask.cancel(false);
419 timeoutTask = null;
420 }
421 }
422
423 /**
424 * Submits the runContinuation task to the scheduler. For the built-in scheduler,
425 * the task will be pushed to the local queue if possible, otherwise it will be
426 * pushed to an external submission queue.
427 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
428 * @throws RejectedExecutionException
429 */
430 private void submitRunContinuation(boolean retryOnOOME) {
431 boolean done = false;
432 while (!done) {
433 try {
434 // Pin the continuation to prevent the virtual thread from unmounting
435 // when submitting a task. For the default scheduler this ensures that
436 // the carrier doesn't change when pushing a task. For other schedulers
437 // it avoids deadlock that could arise due to carriers and virtual
438 // threads contending for a lock.
439 if (currentThread().isVirtual()) {
440 Continuation.pin();
441 try {
442 scheduler.onContinue(runContinuation);
443 } finally {
444 Continuation.unpin();
445 }
446 } else {
447 scheduler.onContinue(runContinuation);
448 }
449 done = true;
450 } catch (RejectedExecutionException ree) {
451 submitFailed(ree);
452 throw ree;
453 } catch (OutOfMemoryError e) {
454 if (retryOnOOME) {
455 U.park(false, 100_000_000); // 100ms
456 } else {
457 throw e;
458 }
459 }
460 }
461 }
462
463 /**
464 * Submits the runContinuation task to the scheduler. For the default scheduler,
465 * and calling it on a worker thread, the task will be pushed to the local queue,
466 * otherwise it will be pushed to an external submission queue.
467 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
468 * @throws RejectedExecutionException
469 */
470 private void submitRunContinuation() {
471 submitRunContinuation(true);
472 }
473
474 /**
475 * Invoked from a carrier thread to lazy submit the runContinuation task to the
476 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
477 * for a custom scheduler, then it just submits the task to the scheduler.
478 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
479 * @throws RejectedExecutionException
480 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
481 */
482 private void lazySubmitRunContinuation() {
483 assert !currentThread().isVirtual();
484 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
485 try {
486 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
487 } catch (RejectedExecutionException ree) {
488 submitFailed(ree);
489 throw ree;
490 } catch (OutOfMemoryError e) {
491 submitRunContinuation();
492 }
493 } else {
494 submitRunContinuation();
495 }
496 }
497
498 /**
499 * Invoked from a carrier thread to externally submit the runContinuation task to the
500 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
501 * task to the scheduler.
502 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
503 * @throws RejectedExecutionException
504 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
505 */
506 private void externalSubmitRunContinuation() {
507 assert !currentThread().isVirtual();
508 if (currentThread() instanceof CarrierThread ct) {
509 try {
510 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
511 } catch (RejectedExecutionException ree) {
512 submitFailed(ree);
513 throw ree;
514 } catch (OutOfMemoryError e) {
515 submitRunContinuation();
516 }
517 } else {
518 submitRunContinuation();
519 }
520 }
521
522 /**
523 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
524 */
525 private void submitFailed(RejectedExecutionException ree) {
526 var event = new VirtualThreadSubmitFailedEvent();
527 if (event.isEnabled()) {
528 event.javaThreadId = threadId();
529 event.exceptionMessage = ree.getMessage();
530 event.commit();
531 }
532 }
533
534 /**
535 * Runs a task in the context of this virtual thread.
536 */
537 private void run(Runnable task) {
538 assert Thread.currentThread() == this && state == RUNNING;
539
540 // emit JFR event if enabled
541 if (VirtualThreadStartEvent.isTurnedOn()) {
542 var event = new VirtualThreadStartEvent();
543 event.javaThreadId = threadId();
544 event.commit();
545 }
546
547 Object bindings = Thread.scopedValueBindings();
548 try {
549 runWith(bindings, task);
550 } catch (Throwable exc) {
551 dispatchUncaughtException(exc);
552 } finally {
553 // pop any remaining scopes from the stack, this may block
554 StackableScope.popAll();
555
556 // emit JFR event if enabled
557 if (VirtualThreadEndEvent.isTurnedOn()) {
558 var event = new VirtualThreadEndEvent();
559 event.javaThreadId = threadId();
560 event.commit();
561 }
562 }
563 }
564
565 /**
566 * Mounts this virtual thread onto the current platform thread. On
567 * return, the current thread is the virtual thread.
568 */
569 @ChangesCurrentThread
570 @ReservedStackAccess
571 private void mount() {
572 startTransition(/*mount*/true);
573 // We assume following volatile accesses provide equivalent
574 // of acquire ordering, otherwise we need U.loadFence() here.
575
576 // sets the carrier thread
577 Thread carrier = Thread.currentCarrierThread();
578 setCarrierThread(carrier);
579
580 // sync up carrier thread interrupted status if needed
581 if (interrupted) {
582 carrier.setInterrupt();
583 } else if (carrier.isInterrupted()) {
584 synchronized (interruptLock) {
585 // need to recheck interrupted status
586 if (!interrupted) {
587 carrier.clearInterrupt();
588 }
589 }
590 }
591
592 // set Thread.currentThread() to return this virtual thread
593 carrier.setCurrentThread(this);
594 }
595
596 /**
597 * Unmounts this virtual thread from the carrier. On return, the
598 * current thread is the current platform thread.
599 */
600 @ChangesCurrentThread
601 @ReservedStackAccess
602 private void unmount() {
603 assert !Thread.holdsLock(interruptLock);
604
605 // set Thread.currentThread() to return the platform thread
606 Thread carrier = this.carrierThread;
607 carrier.setCurrentThread(carrier);
608
609 // break connection to carrier thread, synchronized with interrupt
610 synchronized (interruptLock) {
611 setCarrierThread(null);
612 }
613 carrier.clearInterrupt();
614
615 // We assume previous volatile accesses provide equivalent
616 // of release ordering, otherwise we need U.storeFence() here.
617 endTransition(/*mount*/false);
618 }
619
620 /**
621 * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
622 * the continuation continues.
623 */
624 @Hidden
625 private boolean yieldContinuation() {
626 startTransition(/*mount*/false);
627 try {
628 return Continuation.yield(VTHREAD_SCOPE);
629 } finally {
630 endTransition(/*mount*/true);
631 }
632 }
633
634 /**
635 * Invoked in the context of the carrier thread after the Continuation yields when
636 * parking, blocking on monitor enter, Object.wait, or Thread.yield.
637 */
638 private void afterYield() {
639 assert carrierThread == null;
640
641 // re-adjust parallelism if the virtual thread yielded when compensating
642 if (currentThread() instanceof CarrierThread ct) {
643 ct.endBlocking();
644 }
645
646 int s = state();
647
648 // LockSupport.park/parkNanos
649 if (s == PARKING || s == TIMED_PARKING) {
650 int newState;
651 if (s == PARKING) {
652 setState(newState = PARKED);
653 } else {
654 // schedule unpark
655 long timeout = this.timeout;
656 assert timeout > 0;
657 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
658 setState(newState = TIMED_PARKED);
659 }
660
661 // may have been unparked while parking
662 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
663 // lazy submit if local queue is empty
664 lazySubmitRunContinuation();
665 }
666 return;
667 }
668
669 // Thread.yield
670 if (s == YIELDING) {
671 setState(YIELDED);
672
673 // external submit if there are no tasks in the local task queue
674 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
675 externalSubmitRunContinuation();
676 } else {
677 submitRunContinuation();
678 }
679 return;
680 }
681
682 // blocking on monitorenter
683 if (s == BLOCKING) {
684 setState(BLOCKED);
685
686 // may have been unblocked while blocking
687 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
688 // lazy submit if local queue is empty
689 lazySubmitRunContinuation();
690 }
691 return;
692 }
693
694 // Object.wait
695 if (s == WAITING || s == TIMED_WAITING) {
696 int newState;
697 boolean blocked;
698 boolean interruptible = interruptibleWait;
699 if (s == WAITING) {
700 setState(newState = WAIT);
701 // may have been notified while in transition
702 blocked = notified && compareAndSetState(WAIT, BLOCKED);
703 } else {
704 // For timed-wait, a timeout task is scheduled to execute. The timeout
705 // task will change the thread state to UNBLOCKED and submit the thread
706 // to the scheduler. A sequence number is used to ensure that the timeout
707 // task only unblocks the thread for this timed-wait. We synchronize with
708 // the timeout task to coordinate access to the sequence number and to
709 // ensure the timeout task doesn't execute until the thread has got to
710 // the TIMED_WAIT state.
711 long timeout = this.timeout;
712 assert timeout > 0;
713 synchronized (timedWaitLock()) {
714 byte seqNo = ++timedWaitSeqNo;
715 timeoutTask = schedule(() -> waitTimeoutExpired(seqNo), timeout, MILLISECONDS);
716 setState(newState = TIMED_WAIT);
717 // May have been notified while in transition. This must be done while
718 // holding the monitor to avoid changing the state of a new timed wait call.
719 blocked = notified && compareAndSetState(TIMED_WAIT, BLOCKED);
720 }
721 }
722
723 if (blocked) {
724 // may have been unblocked already
725 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
726 lazySubmitRunContinuation();
727 }
728 } else {
729 // may have been interrupted while in transition to wait state
730 if (interruptible && interrupted && compareAndSetState(newState, UNBLOCKED)) {
731 lazySubmitRunContinuation();
732 }
733 }
734 return;
735 }
736
737 assert false;
738 }
739
740 /**
741 * Invoked after the continuation completes.
742 */
743 private void afterDone() {
744 afterDone(true);
745 }
746
747 /**
748 * Invoked after the continuation completes (or start failed). Sets the thread
749 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
750 *
751 * @param notifyContainer true if its container should be notified
752 */
753 private void afterDone(boolean notifyContainer) {
754 assert carrierThread == null;
755 setState(TERMINATED);
756
757 // notifyAll to wakeup any threads waiting for this thread to terminate
758 if (notifyAllAfterTerminate) {
759 synchronized (this) {
760 notifyAll();
761 }
762 }
763
764 // notify container
765 if (notifyContainer) {
766 threadContainer().remove(this);
767 }
768
769 // clear references to thread locals
770 clearReferences();
771 }
772
773 /**
774 * Schedules this {@code VirtualThread} to execute.
775 *
776 * @throws IllegalStateException if the container is shutdown or closed
777 * @throws IllegalThreadStateException if the thread has already been started
778 * @throws RejectedExecutionException if the scheduler cannot accept a task
779 */
780 @Override
781 void start(ThreadContainer container) {
782 if (!compareAndSetState(NEW, STARTED)) {
783 throw new IllegalThreadStateException("Already started");
784 }
785
786 // bind thread to container
787 assert threadContainer() == null;
788 setThreadContainer(container);
789
790 // start thread
791 boolean addedToContainer = false;
792 boolean started = false;
793 try {
794 container.add(this); // may throw
795 addedToContainer = true;
796
797 // scoped values may be inherited
798 inheritScopedValueBindings(container);
799
800 // submit task to schedule
801 try {
802 if (currentThread().isVirtual()) {
803 Continuation.pin();
804 try {
805 if (scheduler == BUILTIN_SCHEDULER
806 && currentCarrierThread() instanceof CarrierThread ct) {
807 ForkJoinPool pool = ct.getPool();
808 ForkJoinTask<?> task = ForkJoinTask.adapt(runContinuation);
809 pool.externalSubmit(task);
810 } else {
811 scheduler.onStart(runContinuation);
812 }
813 } finally {
814 Continuation.unpin();
815 }
816 } else {
817 scheduler.onStart(runContinuation);
818 }
819 } catch (RejectedExecutionException ree) {
820 submitFailed(ree);
821 throw ree;
822 }
823
824 started = true;
825 } finally {
826 if (!started) {
827 afterDone(addedToContainer);
828 }
829 }
830 }
831
832 @Override
833 public void start() {
834 start(ThreadContainers.root());
835 }
836
837 @Override
838 public void run() {
839 // do nothing
840 }
841
842 /**
843 * Invoked by Thread.join before a thread waits for this virtual thread to terminate.
844 */
845 void beforeJoin() {
846 notifyAllAfterTerminate = true;
847 }
848
849 /**
850 * Parks until unparked or interrupted. If already unparked then the parking
851 * permit is consumed and this method completes immediately (meaning it doesn't
852 * yield). It also completes immediately if the interrupted status is set.
853 */
854 @Override
855 void park() {
856 assert Thread.currentThread() == this;
857
858 // complete immediately if parking permit available or interrupted
859 if (getAndSetParkPermit(false) || interrupted)
860 return;
861
862 // park the thread
863 boolean yielded = false;
864 setState(PARKING);
865 try {
866 yielded = yieldContinuation();
867 } catch (OutOfMemoryError e) {
868 // park on carrier
869 } finally {
870 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
871 if (!yielded) {
872 assert state() == PARKING;
873 setState(RUNNING);
874 }
875 }
876
877 // park on the carrier thread when pinned
878 if (!yielded) {
879 parkOnCarrierThread(false, 0);
880 }
881 }
882
883 /**
884 * Parks up to the given waiting time or until unparked or interrupted.
885 * If already unparked then the parking permit is consumed and this method
886 * completes immediately (meaning it doesn't yield). It also completes immediately
887 * if the interrupted status is set or the waiting time is {@code <= 0}.
888 *
889 * @param nanos the maximum number of nanoseconds to wait.
890 */
891 @Override
892 void parkNanos(long nanos) {
893 assert Thread.currentThread() == this;
894
895 // complete immediately if parking permit available or interrupted
896 if (getAndSetParkPermit(false) || interrupted)
897 return;
898
899 // park the thread for the waiting time
900 if (nanos > 0) {
901 long startTime = System.nanoTime();
902
903 // park the thread, afterYield will schedule the thread to unpark
904 boolean yielded = false;
905 timeout = nanos;
906 setState(TIMED_PARKING);
907 try {
908 yielded = yieldContinuation();
909 } catch (OutOfMemoryError e) {
910 // park on carrier
911 } finally {
912 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
913 if (!yielded) {
914 assert state() == TIMED_PARKING;
915 setState(RUNNING);
916 }
917 }
918
919 // park on carrier thread for remaining time when pinned (or OOME)
920 if (!yielded) {
921 long remainingNanos = nanos - (System.nanoTime() - startTime);
922 parkOnCarrierThread(true, remainingNanos);
923 }
924 }
925 }
926
927 /**
928 * Parks the current carrier thread up to the given waiting time or until
929 * unparked or interrupted. If the virtual thread is interrupted then the
930 * interrupted status will be propagated to the carrier thread.
931 * @param timed true for a timed park, false for untimed
932 * @param nanos the waiting time in nanoseconds
933 */
934 private void parkOnCarrierThread(boolean timed, long nanos) {
935 assert state() == RUNNING;
936
937 setState(timed ? TIMED_PINNED : PINNED);
938 try {
939 if (!parkPermit) {
940 if (!timed) {
941 U.park(false, 0);
942 } else if (nanos > 0) {
943 U.park(false, nanos);
944 }
945 }
946 } finally {
947 setState(RUNNING);
948 }
949
950 // consume parking permit
951 setParkPermit(false);
952
953 // JFR jdk.VirtualThreadPinned event
954 postPinnedEvent("LockSupport.park");
955 }
956
957 /**
958 * Call into VM when pinned to record a JFR jdk.VirtualThreadPinned event.
959 * Recording the event in the VM avoids having JFR event recorded in Java
960 * with the same name, but different ID, to events recorded by the VM.
961 */
962 @Hidden
963 private static native void postPinnedEvent(String op);
964
965 /**
966 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
967 * then its task is scheduled to continue, otherwise its next call to {@code park} or
968 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
969 * @param lazySubmit to use lazySubmit if possible
970 * @throws RejectedExecutionException if the scheduler cannot accept a task
971 */
972 private void unpark(boolean lazySubmit) {
973 if (!getAndSetParkPermit(true) && currentThread() != this) {
974 int s = state();
975
976 // unparked while parked
977 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
978
979 if (lazySubmit && currentThread().isVirtual()) {
980 Continuation.pin();
981 try {
982 if (scheduler == BUILTIN_SCHEDULER
983 && currentCarrierThread() instanceof CarrierThread ct) {
984 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
985 return;
986 }
987 } catch (RejectedExecutionException ree) {
988 submitFailed(ree);
989 throw ree;
990 } catch (OutOfMemoryError e) {
991 // fall-though
992 } finally {
993 Continuation.unpin();
994 }
995 }
996
997 submitRunContinuation();
998 return;
999 }
1000
1001 // unparked while parked when pinned
1002 if (s == PINNED || s == TIMED_PINNED) {
1003 // unpark carrier thread when pinned
1004 disableSuspendAndPreempt();
1005 try {
1006 synchronized (carrierThreadAccessLock()) {
1007 Thread carrier = carrierThread;
1008 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
1009 U.unpark(carrier);
1010 }
1011 }
1012 } finally {
1013 enableSuspendAndPreempt();
1014 }
1015 return;
1016 }
1017 }
1018 }
1019
1020 @Override
1021 void unpark() {
1022 unpark(false);
1023 }
1024
1025 /**
1026 * Invoked by unblocker thread to unblock this virtual thread.
1027 */
1028 private void unblock() {
1029 assert !Thread.currentThread().isVirtual();
1030 blockPermit = true;
1031 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) {
1032 submitRunContinuation();
1033 }
1034 }
1035
1036 /**
1037 * Invoked by FJP worker thread or STPE thread when park timeout expires.
1038 */
1039 private void parkTimeoutExpired() {
1040 assert !VirtualThread.currentThread().isVirtual();
1041 unpark(true);
1042 }
1043
1044 /**
1045 * Invoked by FJP worker thread or STPE thread when wait timeout expires.
1046 * If the virtual thread is in timed-wait then this method will unblock the thread
1047 * and submit its task so that it continues and attempts to reenter the monitor.
1048 * This method does nothing if the thread has been woken by notify or interrupt.
1049 */
1050 private void waitTimeoutExpired(byte seqNo) {
1051 assert !Thread.currentThread().isVirtual();
1052
1053 synchronized (timedWaitLock()) {
1054 if (seqNo != timedWaitSeqNo) {
1055 // this timeout task is for a past timed-wait
1056 return;
1057 }
1058 if (!compareAndSetState(TIMED_WAIT, UNBLOCKED)) {
1059 // already notified (or interrupted)
1060 return;
1061 }
1062 }
1063
1064 lazySubmitRunContinuation();
1065 }
1066
1067 /**
1068 * Attempts to yield the current virtual thread (Thread.yield).
1069 */
1070 void tryYield() {
1071 assert Thread.currentThread() == this;
1072 setState(YIELDING);
1073 boolean yielded = false;
1074 try {
1075 yielded = yieldContinuation(); // may throw
1076 } finally {
1077 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
1078 if (!yielded) {
1079 assert state() == YIELDING;
1080 setState(RUNNING);
1081 }
1082 }
1083 }
1084
1085 /**
1086 * Sleep the current thread for the given sleep time (in nanoseconds). If
1087 * nanos is 0 then the thread will attempt to yield.
1088 *
1089 * @implNote This implementation parks the thread for the given sleeping time
1090 * and will therefore be observed in PARKED state during the sleep. Parking
1091 * will consume the parking permit so this method makes available the parking
1092 * permit after the sleep. This may be observed as a spurious, but benign,
1093 * wakeup when the thread subsequently attempts to park.
1094 *
1095 * @param nanos the maximum number of nanoseconds to sleep
1096 * @throws InterruptedException if interrupted while sleeping
1097 */
1098 void sleepNanos(long nanos) throws InterruptedException {
1099 assert Thread.currentThread() == this && nanos >= 0;
1100 if (getAndClearInterrupt())
1101 throw new InterruptedException();
1102 if (nanos == 0) {
1103 tryYield();
1104 } else {
1105 // park for the sleep time
1106 try {
1107 long remainingNanos = nanos;
1108 long startNanos = System.nanoTime();
1109 while (remainingNanos > 0) {
1110 parkNanos(remainingNanos);
1111 if (getAndClearInterrupt()) {
1112 throw new InterruptedException();
1113 }
1114 remainingNanos = nanos - (System.nanoTime() - startNanos);
1115 }
1116 } finally {
1117 // may have been unparked while sleeping
1118 setParkPermit(true);
1119 }
1120 }
1121 }
1122
1123 @Override
1124 void blockedOn(Interruptible b) {
1125 disableSuspendAndPreempt();
1126 try {
1127 super.blockedOn(b);
1128 } finally {
1129 enableSuspendAndPreempt();
1130 }
1131 }
1132
1133 @Override
1134 public void interrupt() {
1135 if (Thread.currentThread() != this) {
1136 // if current thread is a virtual thread then prevent it from being
1137 // suspended or unmounted when entering or holding interruptLock
1138 Interruptible blocker;
1139 disableSuspendAndPreempt();
1140 try {
1141 synchronized (interruptLock) {
1142 interrupted = true;
1143 blocker = nioBlocker();
1144 if (blocker != null) {
1145 blocker.interrupt(this);
1146 }
1147
1148 // interrupt carrier thread if mounted
1149 Thread carrier = carrierThread;
1150 if (carrier != null) carrier.setInterrupt();
1151 }
1152 } finally {
1153 enableSuspendAndPreempt();
1154 }
1155
1156 // notify blocker after releasing interruptLock
1157 if (blocker != null) {
1158 blocker.postInterrupt();
1159 }
1160
1161 // make available parking permit, unpark thread if parked
1162 unpark();
1163
1164 // if thread is waiting in Object.wait then schedule to try to reenter
1165 int s = state();
1166 if ((s == WAIT || s == TIMED_WAIT) && compareAndSetState(s, UNBLOCKED)) {
1167 submitRunContinuation();
1168 }
1169
1170 } else {
1171 interrupted = true;
1172 carrierThread.setInterrupt();
1173 setParkPermit(true);
1174 }
1175 }
1176
1177 @Override
1178 public boolean isInterrupted() {
1179 return interrupted;
1180 }
1181
1182 @Override
1183 boolean getAndClearInterrupt() {
1184 assert Thread.currentThread() == this;
1185 boolean oldValue = interrupted;
1186 if (oldValue) {
1187 disableSuspendAndPreempt();
1188 try {
1189 synchronized (interruptLock) {
1190 interrupted = false;
1191 carrierThread.clearInterrupt();
1192 }
1193 } finally {
1194 enableSuspendAndPreempt();
1195 }
1196 }
1197 return oldValue;
1198 }
1199
1200 @Override
1201 Thread.State threadState() {
1202 switch (state()) {
1203 case NEW:
1204 return Thread.State.NEW;
1205 case STARTED:
1206 // return NEW if thread container not yet set
1207 if (threadContainer() == null) {
1208 return Thread.State.NEW;
1209 } else {
1210 return Thread.State.RUNNABLE;
1211 }
1212 case UNPARKED:
1213 case UNBLOCKED:
1214 case YIELDED:
1215 // runnable, not mounted
1216 return Thread.State.RUNNABLE;
1217 case RUNNING:
1218 // if mounted then return state of carrier thread
1219 if (Thread.currentThread() != this) {
1220 disableSuspendAndPreempt();
1221 try {
1222 synchronized (carrierThreadAccessLock()) {
1223 Thread carrierThread = this.carrierThread;
1224 if (carrierThread != null) {
1225 return carrierThread.threadState();
1226 }
1227 }
1228 } finally {
1229 enableSuspendAndPreempt();
1230 }
1231 }
1232 // runnable, mounted
1233 return Thread.State.RUNNABLE;
1234 case PARKING:
1235 case TIMED_PARKING:
1236 case WAITING:
1237 case TIMED_WAITING:
1238 case YIELDING:
1239 // runnable, in transition
1240 return Thread.State.RUNNABLE;
1241 case PARKED:
1242 case PINNED:
1243 case WAIT:
1244 return Thread.State.WAITING;
1245 case TIMED_PARKED:
1246 case TIMED_PINNED:
1247 case TIMED_WAIT:
1248 return Thread.State.TIMED_WAITING;
1249 case BLOCKING:
1250 case BLOCKED:
1251 return Thread.State.BLOCKED;
1252 case TERMINATED:
1253 return Thread.State.TERMINATED;
1254 default:
1255 throw new InternalError();
1256 }
1257 }
1258
1259 @Override
1260 boolean alive() {
1261 int s = state;
1262 return (s != NEW && s != TERMINATED);
1263 }
1264
1265 @Override
1266 boolean isTerminated() {
1267 return (state == TERMINATED);
1268 }
1269
1270 @Override
1271 public String toString() {
1272 StringBuilder sb = new StringBuilder("VirtualThread[#");
1273 sb.append(threadId());
1274 String name = getName();
1275 if (!name.isEmpty()) {
1276 sb.append(",");
1277 sb.append(name);
1278 }
1279 sb.append("]/");
1280
1281 // add the carrier state and thread name when mounted
1282 boolean mounted;
1283 if (Thread.currentThread() == this) {
1284 mounted = appendCarrierInfo(sb);
1285 } else {
1286 disableSuspendAndPreempt();
1287 try {
1288 synchronized (carrierThreadAccessLock()) {
1289 mounted = appendCarrierInfo(sb);
1290 }
1291 } finally {
1292 enableSuspendAndPreempt();
1293 }
1294 }
1295
1296 // add virtual thread state when not mounted
1297 if (!mounted) {
1298 String stateAsString = threadState().toString();
1299 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1300 }
1301
1302 return sb.toString();
1303 }
1304
1305 /**
1306 * Appends the carrier state and thread name to the string buffer if mounted.
1307 * @return true if mounted, false if not mounted
1308 */
1309 private boolean appendCarrierInfo(StringBuilder sb) {
1310 assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock());
1311 Thread carrier = carrierThread;
1312 if (carrier != null) {
1313 String stateAsString = carrier.threadState().toString();
1314 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1315 sb.append('@');
1316 sb.append(carrier.getName());
1317 return true;
1318 } else {
1319 return false;
1320 }
1321 }
1322
1323 @Override
1324 public int hashCode() {
1325 return (int) threadId();
1326 }
1327
1328 @Override
1329 public boolean equals(Object obj) {
1330 return obj == this;
1331 }
1332
1333 /**
1334 * Returns the lock object to synchronize on when accessing carrierThread.
1335 * The lock prevents carrierThread from being reset to null during unmount.
1336 */
1337 private Object carrierThreadAccessLock() {
1338 // return interruptLock as unmount has to coordinate with interrupt
1339 return interruptLock;
1340 }
1341
1342 /**
1343 * Returns a lock object for coordinating timed-wait setup and timeout handling.
1344 */
1345 private Object timedWaitLock() {
1346 // use this object for now to avoid the overhead of introducing another lock
1347 return runContinuation;
1348 }
1349
1350 /**
1351 * Disallow the current thread be suspended or preempted.
1352 */
1353 private void disableSuspendAndPreempt() {
1354 notifyJvmtiDisableSuspend(true);
1355 Continuation.pin();
1356 }
1357
1358 /**
1359 * Allow the current thread be suspended or preempted.
1360 */
1361 private void enableSuspendAndPreempt() {
1362 Continuation.unpin();
1363 notifyJvmtiDisableSuspend(false);
1364 }
1365
1366 // -- wrappers for get/set of state, parking permit, and carrier thread --
1367
1368 private int state() {
1369 return state; // volatile read
1370 }
1371
1372 private void setState(int newValue) {
1373 state = newValue; // volatile write
1374 }
1375
1376 private boolean compareAndSetState(int expectedValue, int newValue) {
1377 return U.compareAndSetInt(this, STATE, expectedValue, newValue);
1378 }
1379
1380 private boolean compareAndSetOnWaitingList(boolean expectedValue, boolean newValue) {
1381 return U.compareAndSetBoolean(this, ON_WAITING_LIST, expectedValue, newValue);
1382 }
1383
1384 private void setParkPermit(boolean newValue) {
1385 if (parkPermit != newValue) {
1386 parkPermit = newValue;
1387 }
1388 }
1389
1390 private boolean getAndSetParkPermit(boolean newValue) {
1391 if (parkPermit != newValue) {
1392 return U.getAndSetBoolean(this, PARK_PERMIT, newValue);
1393 } else {
1394 return newValue;
1395 }
1396 }
1397
1398 private void setCarrierThread(Thread carrier) {
1399 // U.putReferenceRelease(this, CARRIER_THREAD, carrier);
1400 this.carrierThread = carrier;
1401 }
1402
1403 // The following four methods notify the VM when a "transition" starts and ends.
1404 // A "mount transition" embodies the steps to transfer control from a platform
1405 // thread to a virtual thread, changing the thread identity, and starting or
1406 // resuming the virtual thread's continuation on the carrier.
1407 // An "unmount transition" embodies the steps to transfer control from a virtual
1408 // thread to its carrier, suspending the virtual thread's continuation, and
1409 // restoring the thread identity to the platform thread.
1410 // The notifications to the VM are necessary in order to coordinate with functions
1411 // (JVMTI mostly) that disable transitions for one or all virtual threads. Starting
1412 // a transition may block if transitions are disabled. Ending a transition may
1413 // notify a thread that is waiting to disable transitions. The notifications are
1414 // also used to post JVMTI events for virtual thread start and end.
1415
1416 @IntrinsicCandidate
1417 @JvmtiMountTransition
1418 private native void endFirstTransition();
1419
1420 @IntrinsicCandidate
1421 @JvmtiMountTransition
1422 private native void startFinalTransition();
1423
1424 @IntrinsicCandidate
1425 @JvmtiMountTransition
1426 private native void startTransition(boolean mount);
1427
1428 @IntrinsicCandidate
1429 @JvmtiMountTransition
1430 private native void endTransition(boolean mount);
1431
1432 @IntrinsicCandidate
1433 private static native void notifyJvmtiDisableSuspend(boolean enter);
1434
1435 private static native void registerNatives();
1436 static {
1437 registerNatives();
1438
1439 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1440 var group = Thread.virtualThreadGroup();
1441 }
1442
1443 /**
1444 * Loads a VirtualThreadScheduler with the given class name. The class must be public
1445 * in an exported package, with public one-arg or no-arg constructor, and be visible
1446 * to the system class loader.
1447 * @param delegate the scheduler that the custom scheduler may delegate to
1448 * @param cn the class name of the custom scheduler
1449 */
1450 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
1451 VirtualThreadScheduler scheduler;
1452 try {
1453 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1454 // 1-arg constructor
1455 try {
1456 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1457 return (VirtualThreadScheduler) ctor.newInstance(delegate);
1458 } catch (NoSuchMethodException e) {
1459 // 0-arg constructor
1460 Constructor<?> ctor = clazz.getConstructor();
1461 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1462 }
1463 } catch (Exception ex) {
1464 throw new Error(ex);
1465 }
1466 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!");
1467 return scheduler;
1468 }
1469
1470 /**
1471 * Creates the built-in ForkJoinPool scheduler.
1472 * @param wrapped true if wrapped by a custom default scheduler
1473 */
1474 private static VirtualThreadScheduler createBuiltinScheduler(boolean wrapped) {
1475 int parallelism, maxPoolSize, minRunnable;
1476 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1477 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1478 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1479 if (parallelismValue != null) {
1480 parallelism = Integer.parseInt(parallelismValue);
1481 } else {
1482 parallelism = Runtime.getRuntime().availableProcessors();
1483 }
1484 if (maxPoolSizeValue != null) {
1485 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1486 parallelism = Integer.min(parallelism, maxPoolSize);
1487 } else {
1488 maxPoolSize = Integer.max(parallelism, 256);
1489 }
1490 if (minRunnableValue != null) {
1491 minRunnable = Integer.parseInt(minRunnableValue);
1492 } else {
1493 minRunnable = Integer.max(parallelism / 2, 1);
1494 }
1495 if (Boolean.getBoolean("jdk.virtualThreadScheduler.useTPE")) {
1496 return new BuiltinThreadPoolExecutorScheduler(parallelism);
1497 } else {
1498 return new BuiltinForkJoinPoolScheduler(parallelism, maxPoolSize, minRunnable, wrapped);
1499 }
1500 }
1501
1502 /**
1503 * The built-in ForkJoinPool scheduler.
1504 */
1505 private static class BuiltinForkJoinPoolScheduler
1506 extends ForkJoinPool implements VirtualThreadScheduler {
1507
1508 BuiltinForkJoinPoolScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) {
1509 ForkJoinWorkerThreadFactory factory = wrapped
1510 ? ForkJoinPool.defaultForkJoinWorkerThreadFactory
1511 : CarrierThread::new;
1512 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1513 boolean asyncMode = true; // FIFO
1514 super(parallelism, factory, handler, asyncMode,
1515 0, maxPoolSize, minRunnable, pool -> true, 30L, SECONDS);
1516 }
1517
1518 @Override
1519 public void onStart(VirtualThreadTask task) {
1520 execute(ForkJoinTask.adapt(task));
1521 }
1522
1523 @Override
1524 public void onContinue(VirtualThreadTask task) {
1525 execute(ForkJoinTask.adapt(task));
1526 }
1527
1528 @Override
1529 public ScheduledFuture<?> schedule(Runnable task, long delay, TimeUnit unit) {
1530 return super.schedule(task, delay, unit);
1531 }
1532 }
1533
1534 /**
1535 * Built-in ThreadPoolExecutor scheduler.
1536 */
1537 private static class BuiltinThreadPoolExecutorScheduler
1538 extends ThreadPoolExecutor implements VirtualThreadScheduler {
1539
1540 BuiltinThreadPoolExecutorScheduler(int maxPoolSize) {
1541 ThreadFactory factory = task -> {
1542 Thread t = InnocuousThread.newThread(task);
1543 t.setDaemon(true);
1544 return t;
1545 };
1546 super(maxPoolSize, maxPoolSize,
1547 0L, SECONDS,
1548 new LinkedTransferQueue<>(),
1549 factory);
1550 }
1551
1552 @Override
1553 public void onStart(VirtualThreadTask task) {
1554 execute(task);
1555 }
1556
1557 @Override
1558 public void onContinue(VirtualThreadTask task) {
1559 execute(task);
1560 }
1561 }
1562
1563 /**
1564 * Wraps the scheduler to avoid leaking a direct reference to built-in scheduler.
1565 */
1566 static VirtualThreadScheduler createExternalView(VirtualThreadScheduler delegate) {
1567 return new VirtualThreadScheduler() {
1568 private void check(VirtualThreadTask task) {
1569 var vthread = (VirtualThread) task.thread();
1570 VirtualThreadScheduler scheduler = vthread.scheduler;
1571 if (scheduler != this && scheduler != DEFAULT_SCHEDULER) {
1572 throw new IllegalArgumentException();
1573 }
1574 }
1575 @Override
1576 public void onStart(VirtualThreadTask task) {
1577 check(task);
1578 delegate.onStart(task);
1579 }
1580 @Override
1581 public void onContinue(VirtualThreadTask task) {
1582 check(task);
1583 delegate.onContinue(task);
1584 }
1585 @Override
1586 public String toString() {
1587 return delegate.toString();
1588 }
1589 };
1590 }
1591
1592 /**
1593 * Schedule a runnable task to run after a delay.
1594 */
1595 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1596 if (USE_STPE) {
1597 return DelayedTaskSchedulers.schedule(command, delay, unit);
1598 } else {
1599 return scheduler.schedule(command, delay, unit);
1600 }
1601 }
1602
1603 /**
1604 * Supports scheduling a runnable task to run after a delay. It uses a number
1605 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1606 * work queue used. This class is used when using a custom scheduler.
1607 */
1608 static class DelayedTaskSchedulers {
1609 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1610
1611 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1612 long tid = Thread.currentThread().threadId();
1613 int index = (int) tid & (INSTANCE.length - 1);
1614 return INSTANCE[index].schedule(command, delay, unit);
1615 }
1616
1617 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1618 String propName = "jdk.virtualThreadScheduler.timerQueues";
1619 String propValue = System.getProperty(propName);
1620 int queueCount;
1621 if (propValue != null) {
1622 queueCount = Integer.parseInt(propValue);
1623 if (queueCount != Integer.highestOneBit(queueCount)) {
1624 throw new RuntimeException("Value of " + propName + " must be power of 2");
1625 }
1626 } else {
1627 int ncpus = Runtime.getRuntime().availableProcessors();
1628 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
1629 }
1630 var schedulers = new ScheduledExecutorService[queueCount];
1631 for (int i = 0; i < queueCount; i++) {
1632 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
1633 Executors.newScheduledThreadPool(1, task -> {
1634 Thread t = InnocuousThread.newThread("VirtualThread-unparker", task);
1635 t.setDaemon(true);
1636 return t;
1637 });
1638 stpe.setRemoveOnCancelPolicy(true);
1639 schedulers[i] = stpe;
1640 }
1641 return schedulers;
1642 }
1643 }
1644
1645 /**
1646 * Schedule virtual threads that are ready to be scheduled after they blocked on
1647 * monitor enter.
1648 */
1649 private static void unblockVirtualThreads() {
1650 while (true) {
1651 VirtualThread vthread = takeVirtualThreadListToUnblock();
1652 while (vthread != null) {
1653 assert vthread.onWaitingList;
1654 VirtualThread nextThread = vthread.next;
1655
1656 // remove from list and unblock
1657 vthread.next = null;
1658 boolean changed = vthread.compareAndSetOnWaitingList(true, false);
1659 assert changed;
1660 vthread.unblock();
1661
1662 vthread = nextThread;
1663 }
1664 }
1665 }
1666
1667 /**
1668 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting
1669 * if necessary until a list of one or more threads becomes available.
1670 */
1671 private static native VirtualThread takeVirtualThreadListToUnblock();
1672
1673 static {
1674 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker",
1675 VirtualThread::unblockVirtualThreads);
1676 unblocker.setDaemon(true);
1677 unblocker.start();
1678 }
1679 }