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.CountDownLatch;
33 import java.util.concurrent.Executors;
34 import java.util.concurrent.ForkJoinPool;
35 import java.util.concurrent.ForkJoinTask;
36 import java.util.concurrent.Future;
37 import java.util.concurrent.LinkedTransferQueue;
38 import java.util.concurrent.RejectedExecutionException;
39 import java.util.concurrent.ScheduledExecutorService;
40 import java.util.concurrent.ScheduledFuture;
41 import java.util.concurrent.ScheduledThreadPoolExecutor;
42 import java.util.concurrent.ThreadFactory;
43 import java.util.concurrent.ThreadPoolExecutor;
44 import java.util.concurrent.TimeUnit;
45 import jdk.internal.event.VirtualThreadEndEvent;
46 import jdk.internal.event.VirtualThreadParkEvent;
47 import jdk.internal.event.VirtualThreadStartEvent;
48 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
49 import jdk.internal.invoke.MhUtil;
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.JvmtiHideEvents;
62 import jdk.internal.vm.annotation.JvmtiMountTransition;
63 import jdk.internal.vm.annotation.ReservedStackAccess;
64 import sun.nio.ch.Interruptible;
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
74 private static final VirtualThreadScheduler BUILTIN_SCHEDULER;
75 private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
76 private static final VirtualThreadScheduler EXTERNAL_VIEW;
77 private static final boolean USE_STPE;
78 static {
79 // experimental
80 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
81 if (propValue != null) {
82 VirtualThreadScheduler builtinScheduler = createBuiltinScheduler(true);
83 VirtualThreadScheduler externalView = createExternalView(builtinScheduler);
84 VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue);
85 BUILTIN_SCHEDULER = builtinScheduler;
86 DEFAULT_SCHEDULER = defaultScheduler;
87 EXTERNAL_VIEW = externalView;
88 } else {
89 var builtinScheduler = createBuiltinScheduler(false);
90 BUILTIN_SCHEDULER = builtinScheduler;
91 DEFAULT_SCHEDULER = builtinScheduler;
92 EXTERNAL_VIEW = createExternalView(builtinScheduler);
93 }
94 USE_STPE = Boolean.getBoolean("jdk.virtualThreadScheduler.useSTPE");
95 }
96
97 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
98 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
99 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
100 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
101 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
102
103 // scheduler and continuation
104 private final VirtualThreadScheduler scheduler;
105 private final Continuation cont;
106 private final VThreadRunner runContinuation;
107
108 // virtual thread state, accessed by VM
109 private volatile int state;
110
111 /*
112 * Virtual thread state transitions:
113 *
114 * NEW -> STARTED // Thread.start, schedule to run
115 * STARTED -> TERMINATED // failed to start
116 * STARTED -> RUNNING // first run
117 * RUNNING -> TERMINATED // done
118 *
119 * RUNNING -> PARKING // Thread parking with LockSupport.park
120 * PARKING -> PARKED // cont.yield successful, parked indefinitely
121 * PARKED -> UNPARKED // unparked, may be scheduled to continue
122 * UNPARKED -> RUNNING // continue execution after park
123 *
124 * PARKING -> RUNNING // cont.yield failed, need to park on carrier
125 * RUNNING -> PINNED // park on carrier
126 * PINNED -> RUNNING // unparked, continue execution on same carrier
127 *
128 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
129 * TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked
130 * TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue
131 *
132 * TIMED_PARKING -> RUNNING // cont.yield failed, need to park on carrier
133 * RUNNING -> TIMED_PINNED // park on carrier
134 * TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier
135 *
136 * RUNNING -> BLOCKING // blocking on monitor enter
137 * BLOCKING -> BLOCKED // blocked on monitor enter
138 * BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue
139 * UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter
140 *
141 * RUNNING -> WAITING // transitional state during wait on monitor
142 * WAITING -> WAIT // waiting on monitor
143 * WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
144 * WAIT -> UNBLOCKED // interrupted
145 *
146 * RUNNING -> TIMED_WAITING // transition state during timed-waiting on monitor
147 * TIMED_WAITING -> TIMED_WAIT // timed-waiting on monitor
148 * TIMED_WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
149 * TIMED_WAIT -> UNBLOCKED // timed-out/interrupted
150 *
151 * RUNNING -> YIELDING // Thread.yield
152 * YIELDING -> YIELDED // cont.yield successful, may be scheduled to continue
153 * YIELDING -> RUNNING // cont.yield failed
154 * YIELDED -> RUNNING // continue execution after Thread.yield
155 */
156 private static final int NEW = 0;
157 private static final int STARTED = 1;
158 private static final int RUNNING = 2; // runnable-mounted
159
160 // untimed and timed parking
161 private static final int PARKING = 3;
162 private static final int PARKED = 4; // unmounted
163 private static final int PINNED = 5; // mounted
164 private static final int TIMED_PARKING = 6;
165 private static final int TIMED_PARKED = 7; // unmounted
166 private static final int TIMED_PINNED = 8; // mounted
167 private static final int UNPARKED = 9; // unmounted but runnable
168
169 // Thread.yield
170 private static final int YIELDING = 10;
171 private static final int YIELDED = 11; // unmounted but runnable
172
173 // monitor enter
174 private static final int BLOCKING = 12;
175 private static final int BLOCKED = 13; // unmounted
176 private static final int UNBLOCKED = 14; // unmounted but runnable
177
178 // monitor wait/timed-wait
179 private static final int WAITING = 15;
180 private static final int WAIT = 16; // waiting in Object.wait
181 private static final int TIMED_WAITING = 17;
182 private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait
183
184 private static final int TERMINATED = 99; // final state
185
186 // parking permit made available by LockSupport.unpark
187 private volatile boolean parkPermit;
188
189 // blocking permit made available by unblocker thread when another thread exits monitor
190 private volatile boolean blockPermit;
191
192 // true when on the list of virtual threads waiting to be unblocked
193 private volatile boolean onWaitingList;
194
195 // next virtual thread on the list of virtual threads waiting to be unblocked
196 private volatile VirtualThread next;
197
198 // notified by Object.notify/notifyAll while waiting in Object.wait
199 private volatile boolean notified;
200
201 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
202 private volatile boolean interruptibleWait;
203
204 // timed-wait support
205 private byte timedWaitSeqNo;
206
207 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
208 private long timeout;
209
210 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
211 private Future<?> timeoutTask;
212
213 // carrier thread when mounted, accessed by VM
214 private volatile Thread carrierThread;
215
216 // termination object when joining, created lazily if needed
217 private volatile CountDownLatch termination;
218
219 /**
220 * Return the built-in scheduler.
221 * @param trusted true if caller is trusted, false if not trusted
222 */
223 static VirtualThreadScheduler builtinScheduler(boolean trusted) {
224 return trusted ? BUILTIN_SCHEDULER : EXTERNAL_VIEW;
225 }
226
227 /**
228 * Returns the default scheduler, usually the same as the built-in scheduler.
229 */
230 static VirtualThreadScheduler defaultScheduler() {
231 return DEFAULT_SCHEDULER;
232 }
233
234 /**
235 * Returns the continuation scope used for virtual threads.
236 */
237 static ContinuationScope continuationScope() {
238 return VTHREAD_SCOPE;
239 }
240
241 /**
242 * Returns the task to start/continue this virtual thread.
243 */
244 VirtualThreadTask virtualThreadTask() {
245 return runContinuation;
246 }
247
248 /**
249 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
250 *
251 * @param scheduler the scheduler or null for default scheduler
252 * @param preferredCarrier the preferred carrier or null
253 * @param name thread name
254 * @param characteristics characteristics
255 * @param task the task to execute
256 */
257 VirtualThread(VirtualThreadScheduler scheduler,
258 Thread preferredCarrier,
259 String name,
260 int characteristics,
261 Runnable task) {
262 super(name, characteristics, /*bound*/ false);
263 Objects.requireNonNull(task);
264
265 // use default scheduler if not provided
266 if (scheduler == null) {
267 scheduler = DEFAULT_SCHEDULER;
268 } else if (scheduler == EXTERNAL_VIEW) {
269 throw new UnsupportedOperationException();
270 }
271 this.scheduler = scheduler;
272 this.cont = new VThreadContinuation(this, task);
273
274 if (scheduler == BUILTIN_SCHEDULER) {
275 this.runContinuation = new VThreadRunner(this);
276 } else {
277 this.runContinuation = new CustomSchedulerVThreadRunner(this, preferredCarrier);
278 }
279 }
280
281 /**
282 * The task to start/continue a virtual thread.
283 */
284 static non-sealed class VThreadRunner implements VirtualThreadTask {
285 private final VirtualThread vthread;
286 VThreadRunner(VirtualThread vthread) {
287 this.vthread = vthread;
288 }
289 @Override
290 public final Thread thread() {
291 return vthread;
292 }
293 @Override
294 public final void run() {
295 vthread.runContinuation();;
296 }
297 @Override
298 public Thread preferredCarrier() {
299 throw new UnsupportedOperationException();
300 }
301 @Override
302 public Object attach(Object att) {
303 throw new UnsupportedOperationException();
304 }
305 @Override
306 public Object attachment() {
307 throw new UnsupportedOperationException();
308 }
309 }
310
311 /**
312 * The task to start/continue a virtual thread when using a custom scheduler.
313 */
314 static final class CustomSchedulerVThreadRunner extends VThreadRunner {
315 private static final VarHandle ATT =
316 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class);
317 private final Thread preferredCarrier;
318 private volatile Object att;
319 CustomSchedulerVThreadRunner(VirtualThread vthread, Thread preferredCarrier) {
320 super(vthread);
321 this.preferredCarrier = preferredCarrier;
322 }
323 @Override
324 public Thread preferredCarrier() {
325 return preferredCarrier;
326 }
327 @Override
328 public Object attach(Object att) {
329 return ATT.getAndSet(this, att);
330 }
331 @Override
332 public Object attachment() {
333 return att;
334 }
335 }
336
337 /**
338 * The continuation that a virtual thread executes.
339 */
340 private static class VThreadContinuation extends Continuation {
341 VThreadContinuation(VirtualThread vthread, Runnable task) {
342 super(VTHREAD_SCOPE, wrap(vthread, task));
343 }
344 @Override
345 protected void onPinned(Continuation.Pinned reason) {
346 }
347 private static Runnable wrap(VirtualThread vthread, Runnable task) {
348 return new Runnable() {
349 @Hidden
350 @JvmtiHideEvents
351 public void run() {
352 vthread.endFirstTransition();
353 try {
354 vthread.run(task);
355 } finally {
356 vthread.startFinalTransition();
357 }
358 }
359 };
360 }
361 }
362
363 /**
364 * Runs or continues execution on the current thread. The virtual thread is mounted
365 * on the current thread before the task runs or continues. It unmounts when the
366 * task completes or yields.
367 */
368 @ChangesCurrentThread // allow mount/unmount to be inlined
369 private void runContinuation() {
370 // the carrier must be a platform thread
371 if (Thread.currentThread().isVirtual()) {
372 throw new WrongThreadException();
373 }
374
375 // set state to RUNNING
376 int initialState = state();
377 if (initialState == STARTED || initialState == UNPARKED
378 || initialState == UNBLOCKED || initialState == YIELDED) {
379 // newly started or continue after parking/blocking/Thread.yield
380 if (!compareAndSetState(initialState, RUNNING)) {
381 return;
382 }
383 // consume permit when continuing after parking or blocking. If continue
384 // after a timed-park or timed-wait then the timeout task is cancelled.
385 if (initialState == UNPARKED) {
386 cancelTimeoutTask();
387 setParkPermit(false);
388 } else if (initialState == UNBLOCKED) {
389 cancelTimeoutTask();
390 blockPermit = false;
391 }
392 } else {
393 // not runnable
394 return;
395 }
396
397 mount();
398 try {
399 cont.run();
400 } finally {
401 unmount();
402 if (cont.isDone()) {
403 afterDone();
404 } else {
405 afterYield();
406 }
407 }
408 }
409
410 /**
411 * Cancel timeout task when continuing after timed-park or timed-wait.
412 * The timeout task may be executing, or may have already completed.
413 */
414 private void cancelTimeoutTask() {
415 if (timeoutTask != null) {
416 timeoutTask.cancel(false);
417 timeoutTask = null;
418 }
419 }
420
421 /**
422 * Submits the runContinuation task to the scheduler. For the built-in scheduler,
423 * the task will be pushed to the local queue if possible, otherwise it will be
424 * pushed to an external submission queue.
425 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
426 * @throws RejectedExecutionException
427 */
428 private void submitRunContinuation(boolean retryOnOOME) {
429 boolean done = false;
430 while (!done) {
431 try {
432 // Pin the continuation to prevent the virtual thread from unmounting
433 // when submitting a task. For the default scheduler this ensures that
434 // the carrier doesn't change when pushing a task. For other schedulers
435 // it avoids deadlock that could arise due to carriers and virtual
436 // threads contending for a lock.
437 if (currentThread().isVirtual()) {
438 Continuation.pin();
439 try {
440 scheduler.onContinue(runContinuation);
441 } finally {
442 Continuation.unpin();
443 }
444 } else {
445 scheduler.onContinue(runContinuation);
446 }
447 done = true;
448 } catch (RejectedExecutionException ree) {
449 submitFailed(ree);
450 throw ree;
451 } catch (OutOfMemoryError e) {
452 if (retryOnOOME) {
453 U.park(false, 100_000_000); // 100ms
454 } else {
455 throw e;
456 }
457 }
458 }
459 }
460
461 /**
462 * Submits the runContinuation task to the scheduler. For the default scheduler,
463 * and calling it on a worker thread, the task will be pushed to the local queue,
464 * otherwise it will be pushed to an external submission queue.
465 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
466 * @throws RejectedExecutionException
467 */
468 private void submitRunContinuation() {
469 submitRunContinuation(true);
470 }
471
472 /**
473 * Invoked from a carrier thread to lazy submit the runContinuation task to the
474 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
475 * for a custom scheduler, then it just submits the task to the scheduler.
476 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
477 * @throws RejectedExecutionException
478 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
479 */
480 private void lazySubmitRunContinuation() {
481 assert !currentThread().isVirtual();
482 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
483 try {
484 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
485 } catch (RejectedExecutionException ree) {
486 submitFailed(ree);
487 throw ree;
488 } catch (OutOfMemoryError e) {
489 submitRunContinuation();
490 }
491 } else {
492 submitRunContinuation();
493 }
494 }
495
496 /**
497 * Invoked from a carrier thread to externally submit the runContinuation task to the
498 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
499 * task to the scheduler.
500 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
501 * @throws RejectedExecutionException
502 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
503 */
504 private void externalSubmitRunContinuation() {
505 assert !currentThread().isVirtual();
506 if (currentThread() instanceof CarrierThread ct) {
507 try {
508 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
509 } catch (RejectedExecutionException ree) {
510 submitFailed(ree);
511 throw ree;
512 } catch (OutOfMemoryError e) {
513 submitRunContinuation();
514 }
515 } else {
516 submitRunContinuation();
517 }
518 }
519
520 /**
521 * Invoked from Thread.start to externally submit the runContinuation task to the
522 * scheduler. If this virtual thread is scheduled by the built-in scheduler,
523 * and this method is called from a virtual thread scheduled by the built-in
524 * scheduler, then it uses externalSubmit to ensure that the task is pushed to an
525 * external submission queue rather than the local queue.
526 * @throws RejectedExecutionException
527 * @throws OutOfMemoryError
528 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
529 */
530 private void externalSubmitRunContinuationOrThrow() {
531 try {
532 if (currentThread().isVirtual()) {
533 // Pin the continuation to prevent the virtual thread from unmounting
534 // when submitting a task. This avoids deadlock that could arise due to
535 // carriers and virtual threads contending for a lock.
536 Continuation.pin();
537 try {
538 if (scheduler == BUILTIN_SCHEDULER
539 && currentCarrierThread() instanceof CarrierThread ct) {
540 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
541 } else {
542 scheduler.onStart(runContinuation);
543 }
544 } finally {
545 Continuation.unpin();
546 }
547 } else {
548 scheduler.onStart(runContinuation);
549 }
550 } catch (RejectedExecutionException ree) {
551 submitFailed(ree);
552 throw ree;
553 }
554 }
555
556 /**
557 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
558 */
559 private void submitFailed(RejectedExecutionException ree) {
560 var event = new VirtualThreadSubmitFailedEvent();
561 if (event.isEnabled()) {
562 event.javaThreadId = threadId();
563 event.exceptionMessage = ree.getMessage();
564 event.commit();
565 }
566 }
567
568 /**
569 * Runs a task in the context of this virtual thread.
570 */
571 private void run(Runnable task) {
572 assert Thread.currentThread() == this && state == RUNNING;
573
574 // emit JFR event if enabled
575 if (VirtualThreadStartEvent.isTurnedOn()) {
576 var event = new VirtualThreadStartEvent();
577 event.javaThreadId = threadId();
578 event.commit();
579 }
580
581 Object bindings = Thread.scopedValueBindings();
582 try {
583 runWith(bindings, task);
584 } catch (Throwable exc) {
585 dispatchUncaughtException(exc);
586 } finally {
587 // pop any remaining scopes from the stack, this may block
588 StackableScope.popAll();
589
590 // emit JFR event if enabled
591 if (VirtualThreadEndEvent.isTurnedOn()) {
592 var event = new VirtualThreadEndEvent();
593 event.javaThreadId = threadId();
594 event.commit();
595 }
596 }
597 }
598
599 /**
600 * Mounts this virtual thread onto the current platform thread. On
601 * return, the current thread is the virtual thread.
602 */
603 @ChangesCurrentThread
604 @ReservedStackAccess
605 private void mount() {
606 startTransition(/*mount*/true);
607 // We assume following volatile accesses provide equivalent
608 // of acquire ordering, otherwise we need U.loadFence() here.
609
610 // sets the carrier thread
611 Thread carrier = Thread.currentCarrierThread();
612 setCarrierThread(carrier);
613
614 // sync up carrier thread interrupted status if needed
615 if (interrupted) {
616 carrier.setInterrupt();
617 } else if (carrier.isInterrupted()) {
618 synchronized (interruptLock) {
619 // need to recheck interrupted status
620 if (!interrupted) {
621 carrier.clearInterrupt();
622 }
623 }
624 }
625
626 // set Thread.currentThread() to return this virtual thread
627 carrier.setCurrentThread(this);
628 }
629
630 /**
631 * Unmounts this virtual thread from the carrier. On return, the
632 * current thread is the current platform thread.
633 */
634 @ChangesCurrentThread
635 @ReservedStackAccess
636 private void unmount() {
637 assert !Thread.holdsLock(interruptLock);
638
639 // set Thread.currentThread() to return the platform thread
640 Thread carrier = this.carrierThread;
641 carrier.setCurrentThread(carrier);
642
643 // break connection to carrier thread, synchronized with interrupt
644 synchronized (interruptLock) {
645 setCarrierThread(null);
646 }
647 carrier.clearInterrupt();
648
649 // We assume previous volatile accesses provide equivalent
650 // of release ordering, otherwise we need U.storeFence() here.
651 endTransition(/*mount*/false);
652 }
653
654 /**
655 * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
656 * the continuation continues.
657 */
658 @Hidden
659 private boolean yieldContinuation() {
660 startTransition(/*mount*/false);
661 try {
662 return Continuation.yield(VTHREAD_SCOPE);
663 } finally {
664 endTransition(/*mount*/true);
665 }
666 }
667
668 /**
669 * Invoked in the context of the carrier thread after the Continuation yields when
670 * parking, blocking on monitor enter, Object.wait, or Thread.yield.
671 */
672 private void afterYield() {
673 assert carrierThread == null;
674
675 // re-adjust parallelism if the virtual thread yielded when compensating
676 if (currentThread() instanceof CarrierThread ct) {
677 ct.endBlocking();
678 }
679
680 int s = state();
681
682 // LockSupport.park/parkNanos
683 if (s == PARKING || s == TIMED_PARKING) {
684 int newState;
685 if (s == PARKING) {
686 setState(newState = PARKED);
687 } else {
688 // schedule unpark
689 long timeout = this.timeout;
690 assert timeout > 0;
691 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
692 setState(newState = TIMED_PARKED);
693 }
694
695 // may have been unparked while parking
696 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
697 // lazy submit if local queue is empty
698 lazySubmitRunContinuation();
699 }
700 return;
701 }
702
703 // Thread.yield
704 if (s == YIELDING) {
705 setState(YIELDED);
706
707 // external submit if there are no tasks in the local task queue
708 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
709 externalSubmitRunContinuation();
710 } else {
711 submitRunContinuation();
712 }
713 return;
714 }
715
716 // blocking on monitorenter
717 if (s == BLOCKING) {
718 setState(BLOCKED);
719
720 // may have been unblocked while blocking
721 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
722 // lazy submit if local queue is empty
723 lazySubmitRunContinuation();
724 }
725 return;
726 }
727
728 // Object.wait
729 if (s == WAITING || s == TIMED_WAITING) {
730 int newState;
731 boolean blocked;
732 boolean interruptible = interruptibleWait;
733 if (s == WAITING) {
734 setState(newState = WAIT);
735 // may have been notified while in transition
736 blocked = notified && compareAndSetState(WAIT, BLOCKED);
737 } else {
738 // For timed-wait, a timeout task is scheduled to execute. The timeout
739 // task will change the thread state to UNBLOCKED and submit the thread
740 // to the scheduler. A sequence number is used to ensure that the timeout
741 // task only unblocks the thread for this timed-wait. We synchronize with
742 // the timeout task to coordinate access to the sequence number and to
743 // ensure the timeout task doesn't execute until the thread has got to
744 // the TIMED_WAIT state.
745 long timeout = this.timeout;
746 assert timeout > 0;
747 synchronized (timedWaitLock()) {
748 byte seqNo = ++timedWaitSeqNo;
749 timeoutTask = schedule(() -> waitTimeoutExpired(seqNo), timeout, MILLISECONDS);
750 setState(newState = TIMED_WAIT);
751 // May have been notified while in transition. This must be done while
752 // holding the monitor to avoid changing the state of a new timed wait call.
753 blocked = notified && compareAndSetState(TIMED_WAIT, BLOCKED);
754 }
755 }
756
757 if (blocked) {
758 // may have been unblocked already
759 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
760 lazySubmitRunContinuation();
761 }
762 } else {
763 // may have been interrupted while in transition to wait state
764 if (interruptible && interrupted && compareAndSetState(newState, UNBLOCKED)) {
765 lazySubmitRunContinuation();
766 }
767 }
768 return;
769 }
770
771 assert false;
772 }
773
774 /**
775 * Invoked after the continuation completes.
776 */
777 private void afterDone() {
778 afterDone(true);
779 }
780
781 /**
782 * Invoked after the continuation completes (or start failed). Sets the thread
783 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
784 *
785 * @param notifyContainer true if its container should be notified
786 */
787 private void afterDone(boolean notifyContainer) {
788 assert carrierThread == null;
789 setState(TERMINATED);
790
791 // notify anyone waiting for this virtual thread to terminate
792 CountDownLatch termination = this.termination;
793 if (termination != null) {
794 assert termination.getCount() == 1;
795 termination.countDown();
796 }
797
798 // notify container
799 if (notifyContainer) {
800 threadContainer().remove(this);
801 }
802
803 // clear references to thread locals
804 clearReferences();
805 }
806
807 /**
808 * Schedules this {@code VirtualThread} to execute.
809 *
810 * @throws IllegalStateException if the container is shutdown or closed
811 * @throws IllegalThreadStateException if the thread has already been started
812 * @throws RejectedExecutionException if the scheduler cannot accept a task
813 */
814 @Override
815 void start(ThreadContainer container) {
816 if (!compareAndSetState(NEW, STARTED)) {
817 throw new IllegalThreadStateException("Already started");
818 }
819
820 // bind thread to container
821 assert threadContainer() == null;
822 setThreadContainer(container);
823
824 // start thread
825 boolean addedToContainer = false;
826 boolean started = false;
827 try {
828 container.add(this); // may throw
829 addedToContainer = true;
830
831 // scoped values may be inherited
832 inheritScopedValueBindings(container);
833
834 // submit task to run thread, using externalSubmit if possible
835 externalSubmitRunContinuationOrThrow();
836 started = true;
837 } finally {
838 if (!started) {
839 afterDone(addedToContainer);
840 }
841 }
842 }
843
844 @Override
845 public void start() {
846 start(ThreadContainers.root());
847 }
848
849 @Override
850 public void run() {
851 // do nothing
852 }
853
854 /**
855 * Parks until unparked or interrupted. If already unparked then the parking
856 * permit is consumed and this method completes immediately (meaning it doesn't
857 * yield). It also completes immediately if the interrupted status is set.
858 */
859 @Override
860 void park() {
861 assert Thread.currentThread() == this;
862
863 // complete immediately if parking permit available or interrupted
864 if (getAndSetParkPermit(false) || interrupted)
865 return;
866
867 // park the thread
868 boolean yielded = false;
869 long eventStartTime = VirtualThreadParkEvent.eventStartTime();
870 setState(PARKING);
871 try {
872 yielded = yieldContinuation();
873 } catch (OutOfMemoryError e) {
874 // park on carrier
875 } finally {
876 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
877 if (yielded) {
878 VirtualThreadParkEvent.offer(eventStartTime, Long.MIN_VALUE);
879 } else {
880 assert state() == PARKING;
881 setState(RUNNING);
882 }
883 }
884
885 // park on the carrier thread when pinned
886 if (!yielded) {
887 parkOnCarrierThread(false, 0);
888 }
889 }
890
891 /**
892 * Parks up to the given waiting time or until unparked or interrupted.
893 * If already unparked then the parking permit is consumed and this method
894 * completes immediately (meaning it doesn't yield). It also completes immediately
895 * if the interrupted status is set or the waiting time is {@code <= 0}.
896 *
897 * @param nanos the maximum number of nanoseconds to wait.
898 */
899 @Override
900 void parkNanos(long nanos) {
901 assert Thread.currentThread() == this;
902
903 // complete immediately if parking permit available or interrupted
904 if (getAndSetParkPermit(false) || interrupted)
905 return;
906
907 // park the thread for the waiting time
908 if (nanos > 0) {
909 long startTime = System.nanoTime();
910
911 // park the thread, afterYield will schedule the thread to unpark
912 boolean yielded = false;
913 long eventStartTime = VirtualThreadParkEvent.eventStartTime();
914 timeout = nanos;
915 setState(TIMED_PARKING);
916 try {
917 yielded = yieldContinuation();
918 } catch (OutOfMemoryError e) {
919 // park on carrier
920 } finally {
921 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
922 if (yielded) {
923 VirtualThreadParkEvent.offer(eventStartTime, nanos);
924 } else {
925 assert state() == TIMED_PARKING;
926 setState(RUNNING);
927 }
928 }
929
930 // park on carrier thread for remaining time when pinned (or OOME)
931 if (!yielded) {
932 long remainingNanos = nanos - (System.nanoTime() - startTime);
933 parkOnCarrierThread(true, remainingNanos);
934 }
935 }
936 }
937
938 /**
939 * Parks the current carrier thread up to the given waiting time or until
940 * unparked or interrupted. If the virtual thread is interrupted then the
941 * interrupted status will be propagated to the carrier thread.
942 * @param timed true for a timed park, false for untimed
943 * @param nanos the waiting time in nanoseconds
944 */
945 private void parkOnCarrierThread(boolean timed, long nanos) {
946 assert state() == RUNNING;
947
948 setState(timed ? TIMED_PINNED : PINNED);
949 try {
950 if (!parkPermit) {
951 if (!timed) {
952 U.park(false, 0);
953 } else if (nanos > 0) {
954 U.park(false, nanos);
955 }
956 }
957 } finally {
958 setState(RUNNING);
959 }
960
961 // consume parking permit
962 setParkPermit(false);
963
964 // JFR jdk.VirtualThreadPinned event
965 postPinnedEvent("LockSupport.park");
966 }
967
968 /**
969 * Call into VM when pinned to record a JFR jdk.VirtualThreadPinned event.
970 * Recording the event in the VM avoids having JFR event recorded in Java
971 * with the same name, but different ID, to events recorded by the VM.
972 */
973 @Hidden
974 private static native void postPinnedEvent(String op);
975
976 /**
977 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
978 * then its task is scheduled to continue, otherwise its next call to {@code park} or
979 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
980 * @param lazySubmit to use lazySubmit if possible
981 * @throws RejectedExecutionException if the scheduler cannot accept a task
982 */
983 private void unpark(boolean lazySubmit) {
984 if (!getAndSetParkPermit(true) && currentThread() != this) {
985 int s = state();
986
987 // unparked while parked
988 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
989 if (lazySubmit) {
990 lazySubmitRunContinuation();
991 } else {
992 submitRunContinuation();
993 }
994 return;
995 }
996
997 // unparked while parked when pinned
998 if (s == PINNED || s == TIMED_PINNED) {
999 // unpark carrier thread when pinned
1000 disableSuspendAndPreempt();
1001 try {
1002 synchronized (carrierThreadAccessLock()) {
1003 Thread carrier = carrierThread;
1004 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
1005 U.unpark(carrier);
1006 }
1007 }
1008 } finally {
1009 enableSuspendAndPreempt();
1010 }
1011 return;
1012 }
1013 }
1014 }
1015
1016 @Override
1017 void unpark() {
1018 unpark(false);
1019 }
1020
1021 /**
1022 * Invoked by unblocker thread to unblock this virtual thread.
1023 */
1024 private void unblock() {
1025 assert !Thread.currentThread().isVirtual();
1026 blockPermit = true;
1027 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) {
1028 submitRunContinuation();
1029 }
1030 }
1031
1032 /**
1033 * Invoked by FJP worker thread or STPE thread when park timeout expires.
1034 */
1035 private void parkTimeoutExpired() {
1036 assert !VirtualThread.currentThread().isVirtual();
1037 unpark(true);
1038 }
1039
1040 /**
1041 * Invoked by FJP worker thread or STPE thread when wait timeout expires.
1042 * If the virtual thread is in timed-wait then this method will unblock the thread
1043 * and submit its task so that it continues and attempts to reenter the monitor.
1044 * This method does nothing if the thread has been woken by notify or interrupt.
1045 */
1046 private void waitTimeoutExpired(byte seqNo) {
1047 assert !Thread.currentThread().isVirtual();
1048
1049 synchronized (timedWaitLock()) {
1050 if (seqNo != timedWaitSeqNo) {
1051 // this timeout task is for a past timed-wait
1052 return;
1053 }
1054 if (!compareAndSetState(TIMED_WAIT, UNBLOCKED)) {
1055 // already notified (or interrupted)
1056 return;
1057 }
1058 }
1059
1060 lazySubmitRunContinuation();
1061 }
1062
1063 /**
1064 * Attempts to yield the current virtual thread (Thread.yield).
1065 */
1066 void tryYield() {
1067 assert Thread.currentThread() == this;
1068 setState(YIELDING);
1069 boolean yielded = false;
1070 try {
1071 yielded = yieldContinuation(); // may throw
1072 } finally {
1073 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
1074 if (!yielded) {
1075 assert state() == YIELDING;
1076 setState(RUNNING);
1077 }
1078 }
1079 }
1080
1081 /**
1082 * Sleep the current thread for the given sleep time (in nanoseconds). If
1083 * nanos is 0 then the thread will attempt to yield.
1084 *
1085 * @implNote This implementation parks the thread for the given sleeping time
1086 * and will therefore be observed in PARKED state during the sleep. Parking
1087 * will consume the parking permit so this method makes available the parking
1088 * permit after the sleep. This may be observed as a spurious, but benign,
1089 * wakeup when the thread subsequently attempts to park.
1090 *
1091 * @param nanos the maximum number of nanoseconds to sleep
1092 * @throws InterruptedException if interrupted while sleeping
1093 */
1094 void sleepNanos(long nanos) throws InterruptedException {
1095 assert Thread.currentThread() == this && nanos >= 0;
1096 if (getAndClearInterrupt())
1097 throw new InterruptedException();
1098 if (nanos == 0) {
1099 tryYield();
1100 } else {
1101 // park for the sleep time
1102 try {
1103 long remainingNanos = nanos;
1104 long startNanos = System.nanoTime();
1105 while (remainingNanos > 0) {
1106 parkNanos(remainingNanos);
1107 if (getAndClearInterrupt()) {
1108 throw new InterruptedException();
1109 }
1110 remainingNanos = nanos - (System.nanoTime() - startNanos);
1111 }
1112 } finally {
1113 // may have been unparked while sleeping
1114 setParkPermit(true);
1115 }
1116 }
1117 }
1118
1119 /**
1120 * Waits up to {@code nanos} nanoseconds for this virtual thread to terminate.
1121 * A timeout of {@code 0} means to wait forever.
1122 *
1123 * @throws InterruptedException if interrupted while waiting
1124 * @return true if the thread has terminated
1125 */
1126 boolean joinNanos(long nanos) throws InterruptedException {
1127 if (state() == TERMINATED)
1128 return true;
1129
1130 // ensure termination object exists, then re-check state
1131 CountDownLatch termination = getTermination();
1132 if (state() == TERMINATED)
1133 return true;
1134
1135 // wait for virtual thread to terminate
1136 if (nanos == 0) {
1137 termination.await();
1138 } else {
1139 boolean terminated = termination.await(nanos, NANOSECONDS);
1140 if (!terminated) {
1141 // waiting time elapsed
1142 return false;
1143 }
1144 }
1145 assert state() == TERMINATED;
1146 return true;
1147 }
1148
1149 @Override
1150 void blockedOn(Interruptible b) {
1151 disableSuspendAndPreempt();
1152 try {
1153 super.blockedOn(b);
1154 } finally {
1155 enableSuspendAndPreempt();
1156 }
1157 }
1158
1159 @Override
1160 public void interrupt() {
1161 if (Thread.currentThread() != this) {
1162 // if current thread is a virtual thread then prevent it from being
1163 // suspended or unmounted when entering or holding interruptLock
1164 Interruptible blocker;
1165 disableSuspendAndPreempt();
1166 try {
1167 synchronized (interruptLock) {
1168 interrupted = true;
1169 blocker = nioBlocker();
1170 if (blocker != null) {
1171 blocker.interrupt(this);
1172 }
1173
1174 // interrupt carrier thread if mounted
1175 Thread carrier = carrierThread;
1176 if (carrier != null) carrier.setInterrupt();
1177 }
1178 } finally {
1179 enableSuspendAndPreempt();
1180 }
1181
1182 // notify blocker after releasing interruptLock
1183 if (blocker != null) {
1184 blocker.postInterrupt();
1185 }
1186
1187 // make available parking permit, unpark thread if parked
1188 unpark();
1189
1190 // if thread is waiting in Object.wait then schedule to try to reenter
1191 int s = state();
1192 if ((s == WAIT || s == TIMED_WAIT) && compareAndSetState(s, UNBLOCKED)) {
1193 submitRunContinuation();
1194 }
1195
1196 } else {
1197 interrupted = true;
1198 carrierThread.setInterrupt();
1199 setParkPermit(true);
1200 }
1201 }
1202
1203 @Override
1204 public boolean isInterrupted() {
1205 return interrupted;
1206 }
1207
1208 @Override
1209 boolean getAndClearInterrupt() {
1210 assert Thread.currentThread() == this;
1211 boolean oldValue = interrupted;
1212 if (oldValue) {
1213 disableSuspendAndPreempt();
1214 try {
1215 synchronized (interruptLock) {
1216 interrupted = false;
1217 carrierThread.clearInterrupt();
1218 }
1219 } finally {
1220 enableSuspendAndPreempt();
1221 }
1222 }
1223 return oldValue;
1224 }
1225
1226 @Override
1227 Thread.State threadState() {
1228 switch (state()) {
1229 case NEW:
1230 return Thread.State.NEW;
1231 case STARTED:
1232 // return NEW if thread container not yet set
1233 if (threadContainer() == null) {
1234 return Thread.State.NEW;
1235 } else {
1236 return Thread.State.RUNNABLE;
1237 }
1238 case UNPARKED:
1239 case UNBLOCKED:
1240 case YIELDED:
1241 // runnable, not mounted
1242 return Thread.State.RUNNABLE;
1243 case RUNNING:
1244 // if mounted then return state of carrier thread
1245 if (Thread.currentThread() != this) {
1246 disableSuspendAndPreempt();
1247 try {
1248 synchronized (carrierThreadAccessLock()) {
1249 Thread carrierThread = this.carrierThread;
1250 if (carrierThread != null) {
1251 return carrierThread.threadState();
1252 }
1253 }
1254 } finally {
1255 enableSuspendAndPreempt();
1256 }
1257 }
1258 // runnable, mounted
1259 return Thread.State.RUNNABLE;
1260 case PARKING:
1261 case TIMED_PARKING:
1262 case WAITING:
1263 case TIMED_WAITING:
1264 case YIELDING:
1265 // runnable, in transition
1266 return Thread.State.RUNNABLE;
1267 case PARKED:
1268 case PINNED:
1269 case WAIT:
1270 return Thread.State.WAITING;
1271 case TIMED_PARKED:
1272 case TIMED_PINNED:
1273 case TIMED_WAIT:
1274 return Thread.State.TIMED_WAITING;
1275 case BLOCKING:
1276 case BLOCKED:
1277 return Thread.State.BLOCKED;
1278 case TERMINATED:
1279 return Thread.State.TERMINATED;
1280 default:
1281 throw new InternalError();
1282 }
1283 }
1284
1285 @Override
1286 boolean alive() {
1287 int s = state;
1288 return (s != NEW && s != TERMINATED);
1289 }
1290
1291 @Override
1292 boolean isTerminated() {
1293 return (state == TERMINATED);
1294 }
1295
1296 @Override
1297 public String toString() {
1298 StringBuilder sb = new StringBuilder("VirtualThread[#");
1299 sb.append(threadId());
1300 String name = getName();
1301 if (!name.isEmpty()) {
1302 sb.append(",");
1303 sb.append(name);
1304 }
1305 sb.append("]/");
1306
1307 // add the carrier state and thread name when mounted
1308 boolean mounted;
1309 if (Thread.currentThread() == this) {
1310 mounted = appendCarrierInfo(sb);
1311 } else {
1312 disableSuspendAndPreempt();
1313 try {
1314 synchronized (carrierThreadAccessLock()) {
1315 mounted = appendCarrierInfo(sb);
1316 }
1317 } finally {
1318 enableSuspendAndPreempt();
1319 }
1320 }
1321
1322 // add virtual thread state when not mounted
1323 if (!mounted) {
1324 String stateAsString = threadState().toString();
1325 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1326 }
1327
1328 return sb.toString();
1329 }
1330
1331 /**
1332 * Appends the carrier state and thread name to the string buffer if mounted.
1333 * @return true if mounted, false if not mounted
1334 */
1335 private boolean appendCarrierInfo(StringBuilder sb) {
1336 assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock());
1337 Thread carrier = carrierThread;
1338 if (carrier != null) {
1339 String stateAsString = carrier.threadState().toString();
1340 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1341 sb.append('@');
1342 sb.append(carrier.getName());
1343 return true;
1344 } else {
1345 return false;
1346 }
1347 }
1348
1349 @Override
1350 public int hashCode() {
1351 return (int) threadId();
1352 }
1353
1354 @Override
1355 public boolean equals(Object obj) {
1356 return obj == this;
1357 }
1358
1359 /**
1360 * Returns the termination object, creating it if needed.
1361 */
1362 private CountDownLatch getTermination() {
1363 CountDownLatch termination = this.termination;
1364 if (termination == null) {
1365 termination = new CountDownLatch(1);
1366 if (!U.compareAndSetReference(this, TERMINATION, null, termination)) {
1367 termination = this.termination;
1368 }
1369 }
1370 return termination;
1371 }
1372
1373 /**
1374 * Returns the lock object to synchronize on when accessing carrierThread.
1375 * The lock prevents carrierThread from being reset to null during unmount.
1376 */
1377 private Object carrierThreadAccessLock() {
1378 // return interruptLock as unmount has to coordinate with interrupt
1379 return interruptLock;
1380 }
1381
1382 /**
1383 * Returns a lock object for coordinating timed-wait setup and timeout handling.
1384 */
1385 private Object timedWaitLock() {
1386 // use this object for now to avoid the overhead of introducing another lock
1387 return runContinuation;
1388 }
1389
1390 /**
1391 * Disallow the current thread be suspended or preempted.
1392 */
1393 private void disableSuspendAndPreempt() {
1394 notifyJvmtiDisableSuspend(true);
1395 Continuation.pin();
1396 }
1397
1398 /**
1399 * Allow the current thread be suspended or preempted.
1400 */
1401 private void enableSuspendAndPreempt() {
1402 Continuation.unpin();
1403 notifyJvmtiDisableSuspend(false);
1404 }
1405
1406 // -- wrappers for get/set of state, parking permit, and carrier thread --
1407
1408 private int state() {
1409 return state; // volatile read
1410 }
1411
1412 private void setState(int newValue) {
1413 state = newValue; // volatile write
1414 }
1415
1416 private boolean compareAndSetState(int expectedValue, int newValue) {
1417 return U.compareAndSetInt(this, STATE, expectedValue, newValue);
1418 }
1419
1420 private boolean compareAndSetOnWaitingList(boolean expectedValue, boolean newValue) {
1421 return U.compareAndSetBoolean(this, ON_WAITING_LIST, expectedValue, newValue);
1422 }
1423
1424 private void setParkPermit(boolean newValue) {
1425 if (parkPermit != newValue) {
1426 parkPermit = newValue;
1427 }
1428 }
1429
1430 private boolean getAndSetParkPermit(boolean newValue) {
1431 if (parkPermit != newValue) {
1432 return U.getAndSetBoolean(this, PARK_PERMIT, newValue);
1433 } else {
1434 return newValue;
1435 }
1436 }
1437
1438 private void setCarrierThread(Thread carrier) {
1439 // U.putReferenceRelease(this, CARRIER_THREAD, carrier);
1440 this.carrierThread = carrier;
1441 }
1442
1443 // The following four methods notify the VM when a "transition" starts and ends.
1444 // A "mount transition" embodies the steps to transfer control from a platform
1445 // thread to a virtual thread, changing the thread identity, and starting or
1446 // resuming the virtual thread's continuation on the carrier.
1447 // An "unmount transition" embodies the steps to transfer control from a virtual
1448 // thread to its carrier, suspending the virtual thread's continuation, and
1449 // restoring the thread identity to the platform thread.
1450 // The notifications to the VM are necessary in order to coordinate with functions
1451 // (JVMTI mostly) that disable transitions for one or all virtual threads. Starting
1452 // a transition may block if transitions are disabled. Ending a transition may
1453 // notify a thread that is waiting to disable transitions. The notifications are
1454 // also used to post JVMTI events for virtual thread start and end.
1455
1456 @IntrinsicCandidate
1457 @JvmtiMountTransition
1458 private native void endFirstTransition();
1459
1460 @IntrinsicCandidate
1461 @JvmtiMountTransition
1462 private native void startFinalTransition();
1463
1464 @IntrinsicCandidate
1465 @JvmtiMountTransition
1466 private native void startTransition(boolean mount);
1467
1468 @IntrinsicCandidate
1469 @JvmtiMountTransition
1470 private native void endTransition(boolean mount);
1471
1472 @IntrinsicCandidate
1473 private static native void notifyJvmtiDisableSuspend(boolean enter);
1474
1475 private static native void registerNatives();
1476 static {
1477 registerNatives();
1478
1479 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1480 var group = Thread.virtualThreadGroup();
1481
1482 // ensure event class is initialized
1483 try {
1484 MethodHandles.lookup().ensureInitialized(VirtualThreadParkEvent.class);
1485 } catch (IllegalAccessException e) {
1486 throw new ExceptionInInitializerError(e);
1487 }
1488 }
1489
1490 /**
1491 * Loads a VirtualThreadScheduler with the given class name. The class must be public
1492 * in an exported package, with public one-arg or no-arg constructor, and be visible
1493 * to the system class loader.
1494 * @param delegate the scheduler that the custom scheduler may delegate to
1495 * @param cn the class name of the custom scheduler
1496 */
1497 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
1498 VirtualThreadScheduler scheduler;
1499 try {
1500 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1501 // 1-arg constructor
1502 try {
1503 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1504 return (VirtualThreadScheduler) ctor.newInstance(delegate);
1505 } catch (NoSuchMethodException e) {
1506 // 0-arg constructor
1507 Constructor<?> ctor = clazz.getConstructor();
1508 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1509 }
1510 } catch (Exception ex) {
1511 throw new Error(ex);
1512 }
1513 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!");
1514 return scheduler;
1515 }
1516
1517 /**
1518 * Creates the built-in ForkJoinPool scheduler.
1519 * @param wrapped true if wrapped by a custom default scheduler
1520 */
1521 private static VirtualThreadScheduler createBuiltinScheduler(boolean wrapped) {
1522 int parallelism, maxPoolSize, minRunnable;
1523 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1524 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1525 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1526 if (parallelismValue != null) {
1527 parallelism = Integer.parseInt(parallelismValue);
1528 } else {
1529 parallelism = Runtime.getRuntime().availableProcessors();
1530 }
1531 if (maxPoolSizeValue != null) {
1532 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1533 parallelism = Integer.min(parallelism, maxPoolSize);
1534 } else {
1535 maxPoolSize = Integer.max(parallelism, 256);
1536 }
1537 if (minRunnableValue != null) {
1538 minRunnable = Integer.parseInt(minRunnableValue);
1539 } else {
1540 minRunnable = Integer.max(parallelism / 2, 1);
1541 }
1542 if (Boolean.getBoolean("jdk.virtualThreadScheduler.useTPE")) {
1543 return new BuiltinThreadPoolExecutorScheduler(parallelism);
1544 } else {
1545 return new BuiltinForkJoinPoolScheduler(parallelism, maxPoolSize, minRunnable, wrapped);
1546 }
1547 }
1548
1549 /**
1550 * The built-in ForkJoinPool scheduler.
1551 */
1552 private static class BuiltinForkJoinPoolScheduler
1553 extends ForkJoinPool implements VirtualThreadScheduler {
1554
1555 BuiltinForkJoinPoolScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) {
1556 ForkJoinWorkerThreadFactory factory = wrapped
1557 ? ForkJoinPool.defaultForkJoinWorkerThreadFactory
1558 : CarrierThread::new;
1559 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1560 boolean asyncMode = true; // FIFO
1561 super(parallelism, factory, handler, asyncMode,
1562 0, maxPoolSize, minRunnable, pool -> true, 30L, SECONDS);
1563 }
1564
1565 @Override
1566 public void onStart(VirtualThreadTask task) {
1567 execute(ForkJoinTask.adapt(task));
1568 }
1569
1570 @Override
1571 public void onContinue(VirtualThreadTask task) {
1572 execute(ForkJoinTask.adapt(task));
1573 }
1574
1575 @Override
1576 public ScheduledFuture<?> schedule(Runnable task, long delay, TimeUnit unit) {
1577 return super.schedule(task, delay, unit);
1578 }
1579 }
1580
1581 /**
1582 * Built-in ThreadPoolExecutor scheduler.
1583 */
1584 private static class BuiltinThreadPoolExecutorScheduler
1585 extends ThreadPoolExecutor implements VirtualThreadScheduler {
1586
1587 BuiltinThreadPoolExecutorScheduler(int maxPoolSize) {
1588 ThreadFactory factory = task -> {
1589 Thread t = InnocuousThread.newThread(task);
1590 t.setDaemon(true);
1591 return t;
1592 };
1593 super(maxPoolSize, maxPoolSize,
1594 0L, SECONDS,
1595 new LinkedTransferQueue<>(),
1596 factory);
1597 }
1598
1599 @Override
1600 public void onStart(VirtualThreadTask task) {
1601 execute(task);
1602 }
1603
1604 @Override
1605 public void onContinue(VirtualThreadTask task) {
1606 execute(task);
1607 }
1608 }
1609
1610 /**
1611 * Wraps the scheduler to avoid leaking a direct reference with
1612 * {@link VirtualThreadScheduler#current()}.
1613 */
1614 static VirtualThreadScheduler createExternalView(VirtualThreadScheduler delegate) {
1615 return new VirtualThreadScheduler() {
1616 private void check(VirtualThreadTask task) {
1617 var vthread = (VirtualThread) task.thread();
1618 VirtualThreadScheduler scheduler = vthread.scheduler;
1619 if (scheduler != this && scheduler != DEFAULT_SCHEDULER) {
1620 throw new IllegalArgumentException();
1621 }
1622 }
1623 @Override
1624 public void onStart(VirtualThreadTask task) {
1625 check(task);
1626 delegate.onStart(task);
1627 }
1628 @Override
1629 public void onContinue(VirtualThreadTask task) {
1630 check(task);
1631 delegate.onContinue(task);
1632 }
1633 @Override
1634 public String toString() {
1635 return delegate.toString();
1636 }
1637 };
1638 }
1639
1640 /**
1641 * Schedule a runnable task to run after a delay.
1642 */
1643 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1644 if (USE_STPE) {
1645 return DelayedTaskSchedulers.schedule(command, delay, unit);
1646 } else {
1647 return scheduler.schedule(command, delay, unit);
1648 }
1649 }
1650
1651 /**
1652 * Supports scheduling a runnable task to run after a delay. It uses a number
1653 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1654 * work queue used. This class is used when using a custom scheduler.
1655 */
1656 static class DelayedTaskSchedulers {
1657 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1658
1659 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1660 long tid = Thread.currentThread().threadId();
1661 int index = (int) tid & (INSTANCE.length - 1);
1662 return INSTANCE[index].schedule(command, delay, unit);
1663 }
1664
1665 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1666 String propName = "jdk.virtualThreadScheduler.timerQueues";
1667 String propValue = System.getProperty(propName);
1668 int queueCount;
1669 if (propValue != null) {
1670 queueCount = Integer.parseInt(propValue);
1671 if (queueCount != Integer.highestOneBit(queueCount)) {
1672 throw new RuntimeException("Value of " + propName + " must be power of 2");
1673 }
1674 } else {
1675 int ncpus = Runtime.getRuntime().availableProcessors();
1676 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
1677 }
1678 var schedulers = new ScheduledExecutorService[queueCount];
1679 for (int i = 0; i < queueCount; i++) {
1680 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
1681 Executors.newScheduledThreadPool(1, task -> {
1682 Thread t = InnocuousThread.newThread("VirtualThread-unparker", task);
1683 t.setDaemon(true);
1684 return t;
1685 });
1686 stpe.setRemoveOnCancelPolicy(true);
1687 schedulers[i] = stpe;
1688 }
1689 return schedulers;
1690 }
1691 }
1692
1693 /**
1694 * Schedule virtual threads that are ready to be scheduled after they blocked on
1695 * monitor enter.
1696 */
1697 private static void unblockVirtualThreads() {
1698 while (true) {
1699 VirtualThread vthread = takeVirtualThreadListToUnblock();
1700 while (vthread != null) {
1701 assert vthread.onWaitingList;
1702 VirtualThread nextThread = vthread.next;
1703
1704 // remove from list and unblock
1705 vthread.next = null;
1706 boolean changed = vthread.compareAndSetOnWaitingList(true, false);
1707 assert changed;
1708 vthread.unblock();
1709
1710 vthread = nextThread;
1711 }
1712 }
1713 }
1714
1715 /**
1716 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting
1717 * if necessary until a list of one or more threads becomes available.
1718 */
1719 private static native VirtualThread takeVirtualThreadListToUnblock();
1720
1721 static {
1722 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker",
1723 VirtualThread::unblockVirtualThreads);
1724 unblocker.setDaemon(true);
1725 unblocker.start();
1726 }
1727 }