1 /*
2 * Copyright (c) 2018, 2025, 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.RejectedExecutionException;
38 import java.util.concurrent.ScheduledExecutorService;
39 import java.util.concurrent.ScheduledThreadPoolExecutor;
40 import java.util.concurrent.TimeUnit;
41 import jdk.internal.event.VirtualThreadEndEvent;
42 import jdk.internal.event.VirtualThreadParkEvent;
43 import jdk.internal.event.VirtualThreadStartEvent;
44 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
45 import jdk.internal.invoke.MhUtil;
46 import jdk.internal.misc.CarrierThread;
47 import jdk.internal.misc.InnocuousThread;
48 import jdk.internal.misc.Unsafe;
49 import jdk.internal.vm.Continuation;
50 import jdk.internal.vm.ContinuationScope;
51 import jdk.internal.vm.StackableScope;
52 import jdk.internal.vm.ThreadContainer;
53 import jdk.internal.vm.ThreadContainers;
54 import jdk.internal.vm.annotation.ChangesCurrentThread;
55 import jdk.internal.vm.annotation.Hidden;
56 import jdk.internal.vm.annotation.IntrinsicCandidate;
57 import jdk.internal.vm.annotation.JvmtiHideEvents;
58 import jdk.internal.vm.annotation.JvmtiMountTransition;
59 import jdk.internal.vm.annotation.ReservedStackAccess;
60 import sun.nio.ch.Interruptible;
61 import static java.util.concurrent.TimeUnit.*;
62
63 /**
64 * A thread that is scheduled by the Java virtual machine rather than the operating system.
65 */
66 final class VirtualThread extends BaseVirtualThread {
67 private static final Unsafe U = Unsafe.getUnsafe();
68 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
69
70 private static final BuiltinScheduler BUILTIN_SCHEDULER;
71 private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
72 private static final VirtualThreadScheduler EXTERNAL_VIEW;
73 static {
74 // experimental
75 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
76 if (propValue != null) {
77 BuiltinScheduler builtinScheduler = createBuiltinScheduler(true);
78 VirtualThreadScheduler externalView = builtinScheduler.createExternalView();
79 VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue);
80 BUILTIN_SCHEDULER = builtinScheduler;
81 DEFAULT_SCHEDULER = defaultScheduler;
82 EXTERNAL_VIEW = externalView;
83 } else {
84 var builtinScheduler = createBuiltinScheduler(false);
85 BUILTIN_SCHEDULER = builtinScheduler;
86 DEFAULT_SCHEDULER = builtinScheduler;
87 EXTERNAL_VIEW = builtinScheduler.createExternalView();
88 }
89 }
90
91 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
92 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
93 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
94 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
95 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
96
97 // scheduler and continuation
98 private final VirtualThreadScheduler scheduler;
99 private final Continuation cont;
100 private final VirtualThreadTask runContinuation;
101
102 // virtual thread state, accessed by VM
103 private volatile int state;
104
105 /*
106 * Virtual thread state transitions:
107 *
108 * NEW -> STARTED // Thread.start, schedule to run
109 * STARTED -> TERMINATED // failed to start
110 * STARTED -> RUNNING // first run
111 * RUNNING -> TERMINATED // done
112 *
113 * RUNNING -> PARKING // Thread parking with LockSupport.park
114 * PARKING -> PARKED // cont.yield successful, parked indefinitely
115 * PARKING -> PINNED // cont.yield failed, parked indefinitely on carrier
116 * PARKED -> UNPARKED // unparked, may be scheduled to continue
117 * PINNED -> RUNNING // unparked, continue execution on same carrier
118 * UNPARKED -> RUNNING // continue execution after park
119 *
120 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
121 * TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked
122 * TIMED_PARKING -> TIMED_PINNED // cont.yield failed, timed-parked on carrier
123 * TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue
124 * TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier
125 *
126 * RUNNING -> BLOCKING // blocking on monitor enter
127 * BLOCKING -> BLOCKED // blocked on monitor enter
128 * BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue
129 * UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter
130 *
131 * RUNNING -> WAITING // transitional state during wait on monitor
132 * WAITING -> WAIT // waiting on monitor
133 * WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
134 * WAIT -> UNBLOCKED // timed-out/interrupted
135 *
136 * RUNNING -> TIMED_WAITING // transition state during timed-waiting on monitor
137 * TIMED_WAITING -> TIMED_WAIT // timed-waiting on monitor
138 * TIMED_WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
139 * TIMED_WAIT -> UNBLOCKED // timed-out/interrupted
140 *
141 * RUNNING -> YIELDING // Thread.yield
142 * YIELDING -> YIELDED // cont.yield successful, may be scheduled to continue
143 * YIELDING -> RUNNING // cont.yield failed
144 * YIELDED -> RUNNING // continue execution after Thread.yield
145 */
146 private static final int NEW = 0;
147 private static final int STARTED = 1;
148 private static final int RUNNING = 2; // runnable-mounted
149
150 // untimed and timed parking
151 private static final int PARKING = 3;
152 private static final int PARKED = 4; // unmounted
153 private static final int PINNED = 5; // mounted
154 private static final int TIMED_PARKING = 6;
155 private static final int TIMED_PARKED = 7; // unmounted
156 private static final int TIMED_PINNED = 8; // mounted
157 private static final int UNPARKED = 9; // unmounted but runnable
158
159 // Thread.yield
160 private static final int YIELDING = 10;
161 private static final int YIELDED = 11; // unmounted but runnable
162
163 // monitor enter
164 private static final int BLOCKING = 12;
165 private static final int BLOCKED = 13; // unmounted
166 private static final int UNBLOCKED = 14; // unmounted but runnable
167
168 // monitor wait/timed-wait
169 private static final int WAITING = 15;
170 private static final int WAIT = 16; // waiting in Object.wait
171 private static final int TIMED_WAITING = 17;
172 private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait
173
174 private static final int TERMINATED = 99; // final state
175
176 // parking permit made available by LockSupport.unpark
177 private volatile boolean parkPermit;
178
179 // blocking permit made available by unblocker thread when another thread exits monitor
180 private volatile boolean blockPermit;
181
182 // true when on the list of virtual threads waiting to be unblocked
183 private volatile boolean onWaitingList;
184
185 // next virtual thread on the list of virtual threads waiting to be unblocked
186 private volatile VirtualThread next;
187
188 // notified by Object.notify/notifyAll while waiting in Object.wait
189 private volatile boolean notified;
190
191 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
192 private volatile boolean interruptibleWait;
193
194 // timed-wait support
195 private byte timedWaitSeqNo;
196
197 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
198 private long timeout;
199
200 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
201 private Future<?> timeoutTask;
202
203 // carrier thread when mounted, accessed by VM
204 private volatile Thread carrierThread;
205
206 // termination object when joining, created lazily if needed
207 private volatile CountDownLatch termination;
208
209 /**
210 * Return the built-in scheduler.
211 */
212 static VirtualThreadScheduler builtinScheduler() {
213 return BUILTIN_SCHEDULER;
214 }
215
216 /**
217 * Returns the default scheduler, usually the same as the built-in scheduler.
218 */
219 static VirtualThreadScheduler defaultScheduler() {
220 return DEFAULT_SCHEDULER;
221 }
222
223 /**
224 * Returns the continuation scope used for virtual threads.
225 */
226 static ContinuationScope continuationScope() {
227 return VTHREAD_SCOPE;
228 }
229
230 /**
231 * Return the scheduler for this thread.
232 * @param trusted true if caller is trusted, false if not trusted
233 */
234 VirtualThreadScheduler scheduler(boolean trusted) {
235 if (scheduler == BUILTIN_SCHEDULER && !trusted) {
236 return EXTERNAL_VIEW;
237 } else {
238 return scheduler;
239 }
240 }
241
242 /**
243 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
244 *
245 * @param scheduler the scheduler or null for default scheduler
246 * @param preferredCarrier the preferred carrier or null
247 * @param name thread name
248 * @param characteristics characteristics
249 * @param task the task to execute
250 */
251 VirtualThread(VirtualThreadScheduler scheduler,
252 Thread preferredCarrier,
253 String name,
254 int characteristics,
255 Runnable task,
256 Object att) {
257 super(name, characteristics, /*bound*/ false);
258 Objects.requireNonNull(task);
259
260 // use default scheduler if not provided
261 if (scheduler == null) {
262 scheduler = DEFAULT_SCHEDULER;
263 } else if (scheduler == EXTERNAL_VIEW) {
264 throw new UnsupportedOperationException();
265 }
266 this.scheduler = scheduler;
267 this.cont = new VThreadContinuation(this, task);
268
269 if (scheduler == BUILTIN_SCHEDULER) {
270 this.runContinuation = new BuiltinSchedulerTask(this);
271 } else {
272 this.runContinuation = new CustomSchedulerTask(this, preferredCarrier, att);
273 }
274 }
275
276 /**
277 * The task to execute when using the built-in scheduler.
278 */
279 static final class BuiltinSchedulerTask implements VirtualThreadTask {
280 private final VirtualThread vthread;
281 BuiltinSchedulerTask(VirtualThread vthread) {
282 this.vthread = vthread;
283 }
284 @Override
285 public Thread thread() {
286 return vthread;
287 }
288 @Override
289 public void run() {
290 vthread.runContinuation();;
291 }
292 @Override
293 public Thread preferredCarrier() {
294 throw new UnsupportedOperationException();
295 }
296 @Override
297 public Object attach(Object att) {
298 throw new UnsupportedOperationException();
299 }
300 @Override
301 public Object attachment() {
302 throw new UnsupportedOperationException();
303 }
304 }
305
306 /**
307 * The task to execute when using a custom scheduler.
308 */
309 static final class CustomSchedulerTask implements VirtualThreadTask {
310 private static final VarHandle ATT =
311 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class);
312 private final VirtualThread vthread;
313 private final Thread preferredCarrier;
314 private volatile Object att;
315 CustomSchedulerTask(VirtualThread vthread, Thread preferredCarrier, Object att) {
316 this.vthread = vthread;
317 this.preferredCarrier = preferredCarrier;
318 if (att != null) {
319 this.att = att;
320 }
321 }
322 @Override
323 public Thread thread() {
324 return vthread;
325 }
326 @Override
327 public void run() {
328 vthread.runContinuation();;
329 }
330 @Override
331 public Thread preferredCarrier() {
332 return preferredCarrier;
333 }
334 @Override
335 public Object attach(Object att) {
336 return ATT.getAndSet(this, att);
337 }
338 @Override
339 public Object attachment() {
340 return att;
341 }
342 }
343
344 /**
345 * The continuation that a virtual thread executes.
346 */
347 private static class VThreadContinuation extends Continuation {
348 VThreadContinuation(VirtualThread vthread, Runnable task) {
349 super(VTHREAD_SCOPE, wrap(vthread, task));
350 }
351 @Override
352 protected void onPinned(Continuation.Pinned reason) {
353 }
354 private static Runnable wrap(VirtualThread vthread, Runnable task) {
355 return new Runnable() {
356 @Hidden
357 @JvmtiHideEvents
358 public void run() {
359 vthread.endFirstTransition();
360 try {
361 vthread.run(task);
362 } finally {
363 vthread.startFinalTransition();
364 }
365 }
366 };
367 }
368 }
369
370 /**
371 * Runs or continues execution on the current thread. The virtual thread is mounted
372 * on the current thread before the task runs or continues. It unmounts when the
373 * task completes or yields.
374 */
375 @ChangesCurrentThread // allow mount/unmount to be inlined
376 private void runContinuation() {
377 // the carrier must be a platform thread
378 if (Thread.currentThread().isVirtual()) {
379 throw new WrongThreadException();
380 }
381
382 // set state to RUNNING
383 int initialState = state();
384 if (initialState == STARTED || initialState == UNPARKED
385 || initialState == UNBLOCKED || initialState == YIELDED) {
386 // newly started or continue after parking/blocking/Thread.yield
387 if (!compareAndSetState(initialState, RUNNING)) {
388 return;
389 }
390 // consume permit when continuing after parking or blocking. If continue
391 // after a timed-park or timed-wait then the timeout task is cancelled.
392 if (initialState == UNPARKED) {
393 cancelTimeoutTask();
394 setParkPermit(false);
395 } else if (initialState == UNBLOCKED) {
396 cancelTimeoutTask();
397 blockPermit = false;
398 }
399 } else {
400 // not runnable
401 return;
402 }
403
404 mount();
405 try {
406 cont.run();
407 } finally {
408 unmount();
409 if (cont.isDone()) {
410 afterDone();
411 } else {
412 afterYield();
413 }
414 }
415 }
416
417 /**
418 * Cancel timeout task when continuing after timed-park or timed-wait.
419 * The timeout task may be executing, or may have already completed.
420 */
421 private void cancelTimeoutTask() {
422 if (timeoutTask != null) {
423 timeoutTask.cancel(false);
424 timeoutTask = null;
425 }
426 }
427
428 /**
429 * Submits the runContinuation task to the scheduler. For the built-in scheduler,
430 * the task will be pushed to the local queue if possible, otherwise it will be
431 * pushed to an external submission queue.
432 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
433 * @throws RejectedExecutionException
434 */
435 private void submitRunContinuation(boolean retryOnOOME) {
436 boolean done = false;
437 while (!done) {
438 try {
439 // Pin the continuation to prevent the virtual thread from unmounting
440 // when submitting a task. For the default scheduler this ensures that
441 // the carrier doesn't change when pushing a task. For other schedulers
442 // it avoids deadlock that could arise due to carriers and virtual
443 // threads contending for a lock.
444 if (currentThread().isVirtual()) {
445 Continuation.pin();
446 try {
447 scheduler.onContinue(runContinuation);
448 } finally {
449 Continuation.unpin();
450 }
451 } else {
452 scheduler.onContinue(runContinuation);
453 }
454 done = true;
455 } catch (RejectedExecutionException ree) {
456 submitFailed(ree);
457 throw ree;
458 } catch (OutOfMemoryError e) {
459 if (retryOnOOME) {
460 U.park(false, 100_000_000); // 100ms
461 } else {
462 throw e;
463 }
464 }
465 }
466 }
467
468 /**
469 * Submits the runContinuation task to the scheduler. For the default scheduler,
470 * and calling it on a worker thread, the task will be pushed to the local queue,
471 * otherwise it will be pushed to an external submission queue.
472 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
473 * @throws RejectedExecutionException
474 */
475 private void submitRunContinuation() {
476 submitRunContinuation(true);
477 }
478
479 /**
480 * Invoked from a carrier thread to lazy submit the runContinuation task to the
481 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
482 * for a custom scheduler, then it just submits the task to the scheduler.
483 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
484 * @throws RejectedExecutionException
485 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
486 */
487 private void lazySubmitRunContinuation() {
488 assert !currentThread().isVirtual();
489 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
490 try {
491 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
492 } catch (RejectedExecutionException ree) {
493 submitFailed(ree);
494 throw ree;
495 } catch (OutOfMemoryError e) {
496 submitRunContinuation();
497 }
498 } else {
499 submitRunContinuation();
500 }
501 }
502
503 /**
504 * Invoked from a carrier thread to externally submit the runContinuation task to the
505 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
506 * task to the scheduler.
507 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
508 * @throws RejectedExecutionException
509 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
510 */
511 private void externalSubmitRunContinuation() {
512 assert !currentThread().isVirtual();
513 if (currentThread() instanceof CarrierThread ct) {
514 try {
515 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
516 } catch (RejectedExecutionException ree) {
517 submitFailed(ree);
518 throw ree;
519 } catch (OutOfMemoryError e) {
520 submitRunContinuation();
521 }
522 } else {
523 submitRunContinuation();
524 }
525 }
526
527 /**
528 * Invoked from Thread.start to externally submit the runContinuation task to the
529 * scheduler. If this virtual thread is scheduled by the built-in scheduler,
530 * and this method is called from a virtual thread scheduled by the built-in
531 * scheduler, then it uses externalSubmit to ensure that the task is pushed to an
532 * external submission queue rather than the local queue.
533 * @throws RejectedExecutionException
534 * @throws OutOfMemoryError
535 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
536 */
537 private void externalSubmitRunContinuationOrThrow() {
538 try {
539 if (currentThread().isVirtual()) {
540 // Pin the continuation to prevent the virtual thread from unmounting
541 // when submitting a task. This avoids deadlock that could arise due to
542 // carriers and virtual threads contending for a lock.
543 Continuation.pin();
544 try {
545 if (scheduler == BUILTIN_SCHEDULER
546 && currentCarrierThread() instanceof CarrierThread ct) {
547 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
548 } else {
549 scheduler.onStart(runContinuation);
550 }
551 } finally {
552 Continuation.unpin();
553 }
554 } else {
555 scheduler.onStart(runContinuation);
556 }
557 } catch (RejectedExecutionException ree) {
558 submitFailed(ree);
559 throw ree;
560 }
561 }
562
563 /**
564 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
565 */
566 private void submitFailed(RejectedExecutionException ree) {
567 var event = new VirtualThreadSubmitFailedEvent();
568 if (event.isEnabled()) {
569 event.javaThreadId = threadId();
570 event.exceptionMessage = ree.getMessage();
571 event.commit();
572 }
573 }
574
575 /**
576 * Runs a task in the context of this virtual thread.
577 */
578 private void run(Runnable task) {
579 assert Thread.currentThread() == this && state == RUNNING;
580
581 // emit JFR event if enabled
582 if (VirtualThreadStartEvent.isTurnedOn()) {
583 var event = new VirtualThreadStartEvent();
584 event.javaThreadId = threadId();
585 event.commit();
586 }
587
588 Object bindings = Thread.scopedValueBindings();
589 try {
590 runWith(bindings, task);
591 } catch (Throwable exc) {
592 dispatchUncaughtException(exc);
593 } finally {
594 // pop any remaining scopes from the stack, this may block
595 StackableScope.popAll();
596
597 // emit JFR event if enabled
598 if (VirtualThreadEndEvent.isTurnedOn()) {
599 var event = new VirtualThreadEndEvent();
600 event.javaThreadId = threadId();
601 event.commit();
602 }
603 }
604 }
605
606 /**
607 * Mounts this virtual thread onto the current platform thread. On
608 * return, the current thread is the virtual thread.
609 */
610 @ChangesCurrentThread
611 @ReservedStackAccess
612 private void mount() {
613 startTransition(/*is_mount*/true);
614 // We assume following volatile accesses provide equivalent
615 // of acquire ordering, otherwise we need U.loadFence() here.
616
617 // sets the carrier thread
618 Thread carrier = Thread.currentCarrierThread();
619 setCarrierThread(carrier);
620
621 // sync up carrier thread interrupted status if needed
622 if (interrupted) {
623 carrier.setInterrupt();
624 } else if (carrier.isInterrupted()) {
625 synchronized (interruptLock) {
626 // need to recheck interrupted status
627 if (!interrupted) {
628 carrier.clearInterrupt();
629 }
630 }
631 }
632
633 // set Thread.currentThread() to return this virtual thread
634 carrier.setCurrentThread(this);
635 }
636
637 /**
638 * Unmounts this virtual thread from the carrier. On return, the
639 * current thread is the current platform thread.
640 */
641 @ChangesCurrentThread
642 @ReservedStackAccess
643 private void unmount() {
644 assert !Thread.holdsLock(interruptLock);
645
646 // set Thread.currentThread() to return the platform thread
647 Thread carrier = this.carrierThread;
648 carrier.setCurrentThread(carrier);
649
650 // break connection to carrier thread, synchronized with interrupt
651 synchronized (interruptLock) {
652 setCarrierThread(null);
653 }
654 carrier.clearInterrupt();
655
656 // We assume previous volatile accesses provide equivalent
657 // of release ordering, otherwise we need U.storeFence() here.
658 endTransition(/*is_mount*/false);
659 }
660
661 /**
662 * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
663 * the continuation continues.
664 */
665 @Hidden
666 private boolean yieldContinuation() {
667 startTransition(/*is_mount*/false);
668 try {
669 return Continuation.yield(VTHREAD_SCOPE);
670 } finally {
671 endTransition(/*is_mount*/true);
672 }
673 }
674
675 /**
676 * Invoked in the context of the carrier thread after the Continuation yields when
677 * parking, blocking on monitor enter, Object.wait, or Thread.yield.
678 */
679 private void afterYield() {
680 assert carrierThread == null;
681
682 // re-adjust parallelism if the virtual thread yielded when compensating
683 if (currentThread() instanceof CarrierThread ct) {
684 ct.endBlocking();
685 }
686
687 int s = state();
688
689 // LockSupport.park/parkNanos
690 if (s == PARKING || s == TIMED_PARKING) {
691 int newState;
692 if (s == PARKING) {
693 setState(newState = PARKED);
694 } else {
695 // schedule unpark
696 long timeout = this.timeout;
697 assert timeout > 0;
698 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
699 setState(newState = TIMED_PARKED);
700 }
701
702 // may have been unparked while parking
703 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
704 // lazy submit if local queue is empty
705 lazySubmitRunContinuation();
706 }
707 return;
708 }
709
710 // Thread.yield
711 if (s == YIELDING) {
712 setState(YIELDED);
713
714 // external submit if there are no tasks in the local task queue
715 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
716 externalSubmitRunContinuation();
717 } else {
718 submitRunContinuation();
719 }
720 return;
721 }
722
723 // blocking on monitorenter
724 if (s == BLOCKING) {
725 setState(BLOCKED);
726
727 // may have been unblocked while blocking
728 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
729 // lazy submit if local queue is empty
730 lazySubmitRunContinuation();
731 }
732 return;
733 }
734
735 // Object.wait
736 if (s == WAITING || s == TIMED_WAITING) {
737 int newState;
738 boolean interruptible = interruptibleWait;
739 if (s == WAITING) {
740 setState(newState = WAIT);
741 } else {
742 // For timed-wait, a timeout task is scheduled to execute. The timeout
743 // task will change the thread state to UNBLOCKED and submit the thread
744 // to the scheduler. A sequence number is used to ensure that the timeout
745 // task only unblocks the thread for this timed-wait. We synchronize with
746 // the timeout task to coordinate access to the sequence number and to
747 // ensure the timeout task doesn't execute until the thread has got to
748 // the TIMED_WAIT state.
749 long timeout = this.timeout;
750 assert timeout > 0;
751 synchronized (timedWaitLock()) {
752 byte seqNo = ++timedWaitSeqNo;
753 timeoutTask = schedule(() -> waitTimeoutExpired(seqNo), timeout, MILLISECONDS);
754 setState(newState = TIMED_WAIT);
755 }
756 }
757
758 // may have been notified while in transition to wait state
759 if (notified && compareAndSetState(newState, BLOCKED)) {
760 // may have even been unblocked already
761 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
762 submitRunContinuation();
763 }
764 return;
765 }
766
767 // may have been interrupted while in transition to wait state
768 if (interruptible && interrupted && compareAndSetState(newState, UNBLOCKED)) {
769 submitRunContinuation();
770 return;
771 }
772 return;
773 }
774
775 assert false;
776 }
777
778 /**
779 * Invoked after the continuation completes.
780 */
781 private void afterDone() {
782 afterDone(true);
783 }
784
785 /**
786 * Invoked after the continuation completes (or start failed). Sets the thread
787 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
788 *
789 * @param notifyContainer true if its container should be notified
790 */
791 private void afterDone(boolean notifyContainer) {
792 assert carrierThread == null;
793 setState(TERMINATED);
794
795 // notify anyone waiting for this virtual thread to terminate
796 CountDownLatch termination = this.termination;
797 if (termination != null) {
798 assert termination.getCount() == 1;
799 termination.countDown();
800 }
801
802 // notify container
803 if (notifyContainer) {
804 threadContainer().remove(this);
805 }
806
807 // clear references to thread locals
808 clearReferences();
809 }
810
811 /**
812 * Schedules this {@code VirtualThread} to execute.
813 *
814 * @throws IllegalStateException if the container is shutdown or closed
815 * @throws IllegalThreadStateException if the thread has already been started
816 * @throws RejectedExecutionException if the scheduler cannot accept a task
817 */
818 @Override
819 void start(ThreadContainer container) {
820 if (!compareAndSetState(NEW, STARTED)) {
821 throw new IllegalThreadStateException("Already started");
822 }
823
824 // bind thread to container
825 assert threadContainer() == null;
826 setThreadContainer(container);
827
828 // start thread
829 boolean addedToContainer = false;
830 boolean started = false;
831 try {
832 container.add(this); // may throw
833 addedToContainer = true;
834
835 // scoped values may be inherited
836 inheritScopedValueBindings(container);
837
838 // submit task to run thread, using externalSubmit if possible
839 externalSubmitRunContinuationOrThrow();
840 started = true;
841 } finally {
842 if (!started) {
843 afterDone(addedToContainer);
844 }
845 }
846 }
847
848 @Override
849 public void start() {
850 start(ThreadContainers.root());
851 }
852
853 @Override
854 public void run() {
855 // do nothing
856 }
857
858 /**
859 * Parks until unparked or interrupted. If already unparked then the parking
860 * permit is consumed and this method completes immediately (meaning it doesn't
861 * yield). It also completes immediately if the interrupted status is set.
862 */
863 @Override
864 void park() {
865 assert Thread.currentThread() == this;
866
867 // complete immediately if parking permit available or interrupted
868 if (getAndSetParkPermit(false) || interrupted)
869 return;
870
871 // park the thread
872 boolean yielded = false;
873 long eventStartTime = VirtualThreadParkEvent.eventStartTime();
874 setState(PARKING);
875 try {
876 yielded = yieldContinuation();
877 } catch (OutOfMemoryError e) {
878 // park on carrier
879 } finally {
880 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
881 if (yielded) {
882 VirtualThreadParkEvent.offer(eventStartTime, Long.MIN_VALUE);
883 } else {
884 assert state() == PARKING;
885 setState(RUNNING);
886 }
887 }
888
889 // park on the carrier thread when pinned
890 if (!yielded) {
891 parkOnCarrierThread(false, 0);
892 }
893 }
894
895 /**
896 * Parks up to the given waiting time or until unparked or interrupted.
897 * If already unparked then the parking permit is consumed and this method
898 * completes immediately (meaning it doesn't yield). It also completes immediately
899 * if the interrupted status is set or the waiting time is {@code <= 0}.
900 *
901 * @param nanos the maximum number of nanoseconds to wait.
902 */
903 @Override
904 void parkNanos(long nanos) {
905 assert Thread.currentThread() == this;
906
907 // complete immediately if parking permit available or interrupted
908 if (getAndSetParkPermit(false) || interrupted)
909 return;
910
911 // park the thread for the waiting time
912 if (nanos > 0) {
913 long startTime = System.nanoTime();
914
915 // park the thread, afterYield will schedule the thread to unpark
916 boolean yielded = false;
917 long eventStartTime = VirtualThreadParkEvent.eventStartTime();
918 timeout = nanos;
919 setState(TIMED_PARKING);
920 try {
921 yielded = yieldContinuation();
922 } catch (OutOfMemoryError e) {
923 // park on carrier
924 } finally {
925 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
926 if (yielded) {
927 VirtualThreadParkEvent.offer(eventStartTime, nanos);
928 } else {
929 assert state() == TIMED_PARKING;
930 setState(RUNNING);
931 }
932 }
933
934 // park on carrier thread for remaining time when pinned (or OOME)
935 if (!yielded) {
936 long remainingNanos = nanos - (System.nanoTime() - startTime);
937 parkOnCarrierThread(true, remainingNanos);
938 }
939 }
940 }
941
942 /**
943 * Parks the current carrier thread up to the given waiting time or until
944 * unparked or interrupted. If the virtual thread is interrupted then the
945 * interrupted status will be propagated to the carrier thread.
946 * @param timed true for a timed park, false for untimed
947 * @param nanos the waiting time in nanoseconds
948 */
949 private void parkOnCarrierThread(boolean timed, long nanos) {
950 assert state() == RUNNING;
951
952 setState(timed ? TIMED_PINNED : PINNED);
953 try {
954 if (!parkPermit) {
955 if (!timed) {
956 U.park(false, 0);
957 } else if (nanos > 0) {
958 U.park(false, nanos);
959 }
960 }
961 } finally {
962 setState(RUNNING);
963 }
964
965 // consume parking permit
966 setParkPermit(false);
967
968 // JFR jdk.VirtualThreadPinned event
969 postPinnedEvent("LockSupport.park");
970 }
971
972 /**
973 * Call into VM when pinned to record a JFR jdk.VirtualThreadPinned event.
974 * Recording the event in the VM avoids having JFR event recorded in Java
975 * with the same name, but different ID, to events recorded by the VM.
976 */
977 @Hidden
978 private static native void postPinnedEvent(String op);
979
980 /**
981 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
982 * then its task is scheduled to continue, otherwise its next call to {@code park} or
983 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
984 * @throws RejectedExecutionException if the scheduler cannot accept a task
985 */
986 @Override
987 void unpark() {
988 if (!getAndSetParkPermit(true) && currentThread() != this) {
989 int s = state();
990
991 // unparked while parked
992 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
993 submitRunContinuation();
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 /**
1017 * Invoked by unblocker thread to unblock this virtual thread.
1018 */
1019 private void unblock() {
1020 assert !Thread.currentThread().isVirtual();
1021 blockPermit = true;
1022 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) {
1023 submitRunContinuation();
1024 }
1025 }
1026
1027 /**
1028 * Invoked by FJP worker thread or STPE thread when park timeout expires.
1029 */
1030 private void parkTimeoutExpired() {
1031 assert !VirtualThread.currentThread().isVirtual();
1032 if (!getAndSetParkPermit(true)
1033 && (state() == TIMED_PARKED)
1034 && compareAndSetState(TIMED_PARKED, UNPARKED)) {
1035 lazySubmitRunContinuation();
1036 }
1037 }
1038
1039 /**
1040 * Invoked by FJP worker thread or STPE thread when wait timeout expires.
1041 * If the virtual thread is in timed-wait then this method will unblock the thread
1042 * and submit its task so that it continues and attempts to reenter the monitor.
1043 * This method does nothing if the thread has been woken by notify or interrupt.
1044 */
1045 private void waitTimeoutExpired(byte seqNo) {
1046 assert !Thread.currentThread().isVirtual();
1047
1048 synchronized (timedWaitLock()) {
1049 if (seqNo != timedWaitSeqNo) {
1050 // this timeout task is for a past timed-wait
1051 return;
1052 }
1053 if (compareAndSetState(TIMED_WAIT, UNBLOCKED)) {
1054 lazySubmitRunContinuation();
1055 }
1056 }
1057 }
1058
1059 /**
1060 * Attempts to yield the current virtual thread (Thread.yield).
1061 */
1062 void tryYield() {
1063 assert Thread.currentThread() == this;
1064 setState(YIELDING);
1065 boolean yielded = false;
1066 try {
1067 yielded = yieldContinuation(); // may throw
1068 } finally {
1069 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
1070 if (!yielded) {
1071 assert state() == YIELDING;
1072 setState(RUNNING);
1073 }
1074 }
1075 }
1076
1077 /**
1078 * Sleep the current thread for the given sleep time (in nanoseconds). If
1079 * nanos is 0 then the thread will attempt to yield.
1080 *
1081 * @implNote This implementation parks the thread for the given sleeping time
1082 * and will therefore be observed in PARKED state during the sleep. Parking
1083 * will consume the parking permit so this method makes available the parking
1084 * permit after the sleep. This may be observed as a spurious, but benign,
1085 * wakeup when the thread subsequently attempts to park.
1086 *
1087 * @param nanos the maximum number of nanoseconds to sleep
1088 * @throws InterruptedException if interrupted while sleeping
1089 */
1090 void sleepNanos(long nanos) throws InterruptedException {
1091 assert Thread.currentThread() == this && nanos >= 0;
1092 if (getAndClearInterrupt())
1093 throw new InterruptedException();
1094 if (nanos == 0) {
1095 tryYield();
1096 } else {
1097 // park for the sleep time
1098 try {
1099 long remainingNanos = nanos;
1100 long startNanos = System.nanoTime();
1101 while (remainingNanos > 0) {
1102 parkNanos(remainingNanos);
1103 if (getAndClearInterrupt()) {
1104 throw new InterruptedException();
1105 }
1106 remainingNanos = nanos - (System.nanoTime() - startNanos);
1107 }
1108 } finally {
1109 // may have been unparked while sleeping
1110 setParkPermit(true);
1111 }
1112 }
1113 }
1114
1115 /**
1116 * Waits up to {@code nanos} nanoseconds for this virtual thread to terminate.
1117 * A timeout of {@code 0} means to wait forever.
1118 *
1119 * @throws InterruptedException if interrupted while waiting
1120 * @return true if the thread has terminated
1121 */
1122 boolean joinNanos(long nanos) throws InterruptedException {
1123 if (state() == TERMINATED)
1124 return true;
1125
1126 // ensure termination object exists, then re-check state
1127 CountDownLatch termination = getTermination();
1128 if (state() == TERMINATED)
1129 return true;
1130
1131 // wait for virtual thread to terminate
1132 if (nanos == 0) {
1133 termination.await();
1134 } else {
1135 boolean terminated = termination.await(nanos, NANOSECONDS);
1136 if (!terminated) {
1137 // waiting time elapsed
1138 return false;
1139 }
1140 }
1141 assert state() == TERMINATED;
1142 return true;
1143 }
1144
1145 @Override
1146 void blockedOn(Interruptible b) {
1147 disableSuspendAndPreempt();
1148 try {
1149 super.blockedOn(b);
1150 } finally {
1151 enableSuspendAndPreempt();
1152 }
1153 }
1154
1155 @Override
1156 public void interrupt() {
1157 if (Thread.currentThread() != this) {
1158 // if current thread is a virtual thread then prevent it from being
1159 // suspended or unmounted when entering or holding interruptLock
1160 Interruptible blocker;
1161 disableSuspendAndPreempt();
1162 try {
1163 synchronized (interruptLock) {
1164 interrupted = true;
1165 blocker = nioBlocker();
1166 if (blocker != null) {
1167 blocker.interrupt(this);
1168 }
1169
1170 // interrupt carrier thread if mounted
1171 Thread carrier = carrierThread;
1172 if (carrier != null) carrier.setInterrupt();
1173 }
1174 } finally {
1175 enableSuspendAndPreempt();
1176 }
1177
1178 // notify blocker after releasing interruptLock
1179 if (blocker != null) {
1180 blocker.postInterrupt();
1181 }
1182
1183 // make available parking permit, unpark thread if parked
1184 unpark();
1185
1186 // if thread is waiting in Object.wait then schedule to try to reenter
1187 int s = state();
1188 if ((s == WAIT || s == TIMED_WAIT) && compareAndSetState(s, UNBLOCKED)) {
1189 submitRunContinuation();
1190 }
1191
1192 } else {
1193 interrupted = true;
1194 carrierThread.setInterrupt();
1195 setParkPermit(true);
1196 }
1197 }
1198
1199 @Override
1200 public boolean isInterrupted() {
1201 return interrupted;
1202 }
1203
1204 @Override
1205 boolean getAndClearInterrupt() {
1206 assert Thread.currentThread() == this;
1207 boolean oldValue = interrupted;
1208 if (oldValue) {
1209 disableSuspendAndPreempt();
1210 try {
1211 synchronized (interruptLock) {
1212 interrupted = false;
1213 carrierThread.clearInterrupt();
1214 }
1215 } finally {
1216 enableSuspendAndPreempt();
1217 }
1218 }
1219 return oldValue;
1220 }
1221
1222 @Override
1223 Thread.State threadState() {
1224 switch (state()) {
1225 case NEW:
1226 return Thread.State.NEW;
1227 case STARTED:
1228 // return NEW if thread container not yet set
1229 if (threadContainer() == null) {
1230 return Thread.State.NEW;
1231 } else {
1232 return Thread.State.RUNNABLE;
1233 }
1234 case UNPARKED:
1235 case UNBLOCKED:
1236 case YIELDED:
1237 // runnable, not mounted
1238 return Thread.State.RUNNABLE;
1239 case RUNNING:
1240 // if mounted then return state of carrier thread
1241 if (Thread.currentThread() != this) {
1242 disableSuspendAndPreempt();
1243 try {
1244 synchronized (carrierThreadAccessLock()) {
1245 Thread carrierThread = this.carrierThread;
1246 if (carrierThread != null) {
1247 return carrierThread.threadState();
1248 }
1249 }
1250 } finally {
1251 enableSuspendAndPreempt();
1252 }
1253 }
1254 // runnable, mounted
1255 return Thread.State.RUNNABLE;
1256 case PARKING:
1257 case TIMED_PARKING:
1258 case WAITING:
1259 case TIMED_WAITING:
1260 case YIELDING:
1261 // runnable, in transition
1262 return Thread.State.RUNNABLE;
1263 case PARKED:
1264 case PINNED:
1265 case WAIT:
1266 return Thread.State.WAITING;
1267 case TIMED_PARKED:
1268 case TIMED_PINNED:
1269 case TIMED_WAIT:
1270 return Thread.State.TIMED_WAITING;
1271 case BLOCKING:
1272 case BLOCKED:
1273 return Thread.State.BLOCKED;
1274 case TERMINATED:
1275 return Thread.State.TERMINATED;
1276 default:
1277 throw new InternalError();
1278 }
1279 }
1280
1281 @Override
1282 boolean alive() {
1283 int s = state;
1284 return (s != NEW && s != TERMINATED);
1285 }
1286
1287 @Override
1288 boolean isTerminated() {
1289 return (state == TERMINATED);
1290 }
1291
1292 @Override
1293 public String toString() {
1294 StringBuilder sb = new StringBuilder("VirtualThread[#");
1295 sb.append(threadId());
1296 String name = getName();
1297 if (!name.isEmpty()) {
1298 sb.append(",");
1299 sb.append(name);
1300 }
1301 sb.append("]/");
1302
1303 // add the carrier state and thread name when mounted
1304 boolean mounted;
1305 if (Thread.currentThread() == this) {
1306 mounted = appendCarrierInfo(sb);
1307 } else {
1308 disableSuspendAndPreempt();
1309 try {
1310 synchronized (carrierThreadAccessLock()) {
1311 mounted = appendCarrierInfo(sb);
1312 }
1313 } finally {
1314 enableSuspendAndPreempt();
1315 }
1316 }
1317
1318 // add virtual thread state when not mounted
1319 if (!mounted) {
1320 String stateAsString = threadState().toString();
1321 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1322 }
1323
1324 return sb.toString();
1325 }
1326
1327 /**
1328 * Appends the carrier state and thread name to the string buffer if mounted.
1329 * @return true if mounted, false if not mounted
1330 */
1331 private boolean appendCarrierInfo(StringBuilder sb) {
1332 assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock());
1333 Thread carrier = carrierThread;
1334 if (carrier != null) {
1335 String stateAsString = carrier.threadState().toString();
1336 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1337 sb.append('@');
1338 sb.append(carrier.getName());
1339 return true;
1340 } else {
1341 return false;
1342 }
1343 }
1344
1345 @Override
1346 public int hashCode() {
1347 return (int) threadId();
1348 }
1349
1350 @Override
1351 public boolean equals(Object obj) {
1352 return obj == this;
1353 }
1354
1355 /**
1356 * Returns the termination object, creating it if needed.
1357 */
1358 private CountDownLatch getTermination() {
1359 CountDownLatch termination = this.termination;
1360 if (termination == null) {
1361 termination = new CountDownLatch(1);
1362 if (!U.compareAndSetReference(this, TERMINATION, null, termination)) {
1363 termination = this.termination;
1364 }
1365 }
1366 return termination;
1367 }
1368
1369 /**
1370 * Returns the lock object to synchronize on when accessing carrierThread.
1371 * The lock prevents carrierThread from being reset to null during unmount.
1372 */
1373 private Object carrierThreadAccessLock() {
1374 // return interruptLock as unmount has to coordinate with interrupt
1375 return interruptLock;
1376 }
1377
1378 /**
1379 * Returns a lock object for coordinating timed-wait setup and timeout handling.
1380 */
1381 private Object timedWaitLock() {
1382 // use this object for now to avoid the overhead of introducing another lock
1383 return runContinuation;
1384 }
1385
1386 /**
1387 * Disallow the current thread be suspended or preempted.
1388 */
1389 private void disableSuspendAndPreempt() {
1390 notifyJvmtiDisableSuspend(true);
1391 Continuation.pin();
1392 }
1393
1394 /**
1395 * Allow the current thread be suspended or preempted.
1396 */
1397 private void enableSuspendAndPreempt() {
1398 Continuation.unpin();
1399 notifyJvmtiDisableSuspend(false);
1400 }
1401
1402 // -- wrappers for get/set of state, parking permit, and carrier thread --
1403
1404 private int state() {
1405 return state; // volatile read
1406 }
1407
1408 private void setState(int newValue) {
1409 state = newValue; // volatile write
1410 }
1411
1412 private boolean compareAndSetState(int expectedValue, int newValue) {
1413 return U.compareAndSetInt(this, STATE, expectedValue, newValue);
1414 }
1415
1416 private boolean compareAndSetOnWaitingList(boolean expectedValue, boolean newValue) {
1417 return U.compareAndSetBoolean(this, ON_WAITING_LIST, expectedValue, newValue);
1418 }
1419
1420 private void setParkPermit(boolean newValue) {
1421 if (parkPermit != newValue) {
1422 parkPermit = newValue;
1423 }
1424 }
1425
1426 private boolean getAndSetParkPermit(boolean newValue) {
1427 if (parkPermit != newValue) {
1428 return U.getAndSetBoolean(this, PARK_PERMIT, newValue);
1429 } else {
1430 return newValue;
1431 }
1432 }
1433
1434 private void setCarrierThread(Thread carrier) {
1435 // U.putReferenceRelease(this, CARRIER_THREAD, carrier);
1436 this.carrierThread = carrier;
1437 }
1438
1439 // The following four methods notify the VM when a "transition" starts and ends.
1440 // A "mount transition" embodies the steps to transfer control from a platform
1441 // thread to a virtual thread, changing the thread identity, and starting or
1442 // resuming the virtual thread's continuation on the carrier.
1443 // An "unmount transition" embodies the steps to transfer control from a virtual
1444 // thread to its carrier, suspending the virtual thread's continuation, and
1445 // restoring the thread identity to the platform thread.
1446 // The notifications to the VM are necessary in order to coordinate with functions
1447 // (JVMTI mostly) that disable transitions for one or all virtual threads. Starting
1448 // a transition may block if transitions are disabled. Ending a transition may
1449 // notify a thread that is waiting to disable transitions. The notifications are
1450 // also used to post JVMTI events for virtual thread start and end.
1451
1452 @IntrinsicCandidate
1453 @JvmtiMountTransition
1454 private native void endFirstTransition();
1455
1456 @IntrinsicCandidate
1457 @JvmtiMountTransition
1458 private native void startFinalTransition();
1459
1460 @IntrinsicCandidate
1461 @JvmtiMountTransition
1462 private native void startTransition(boolean is_mount);
1463
1464 @IntrinsicCandidate
1465 @JvmtiMountTransition
1466 private native void endTransition(boolean is_mount);
1467
1468 @IntrinsicCandidate
1469 private static native void notifyJvmtiDisableSuspend(boolean enter);
1470
1471 private static native void registerNatives();
1472 static {
1473 registerNatives();
1474
1475 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1476 var group = Thread.virtualThreadGroup();
1477
1478 // ensure event class is initialized
1479 try {
1480 MethodHandles.lookup().ensureInitialized(VirtualThreadParkEvent.class);
1481 } catch (IllegalAccessException e) {
1482 throw new ExceptionInInitializerError(e);
1483 }
1484 }
1485
1486 /**
1487 * Loads a VirtualThreadScheduler with the given class name. The class must be public
1488 * in an exported package, with public one-arg or no-arg constructor, and be visible
1489 * to the system class loader.
1490 * @param delegate the scheduler that the custom scheduler may delegate to
1491 * @param cn the class name of the custom scheduler
1492 */
1493 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
1494 VirtualThreadScheduler scheduler;
1495 try {
1496 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1497 // 1-arg constructor
1498 try {
1499 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1500 return (VirtualThreadScheduler) ctor.newInstance(delegate);
1501 } catch (NoSuchMethodException e) {
1502 // 0-arg constructor
1503 Constructor<?> ctor = clazz.getConstructor();
1504 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1505 }
1506 } catch (Exception ex) {
1507 throw new Error(ex);
1508 }
1509 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!");
1510 return scheduler;
1511 }
1512
1513 /**
1514 * Creates the built-in ForkJoinPool scheduler.
1515 * @param wrapped true if wrapped by a custom default scheduler
1516 */
1517 private static BuiltinScheduler createBuiltinScheduler(boolean wrapped) {
1518 int parallelism, maxPoolSize, minRunnable;
1519 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1520 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1521 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1522 if (parallelismValue != null) {
1523 parallelism = Integer.parseInt(parallelismValue);
1524 } else {
1525 parallelism = Runtime.getRuntime().availableProcessors();
1526 }
1527 if (maxPoolSizeValue != null) {
1528 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1529 parallelism = Integer.min(parallelism, maxPoolSize);
1530 } else {
1531 maxPoolSize = Integer.max(parallelism, 256);
1532 }
1533 if (minRunnableValue != null) {
1534 minRunnable = Integer.parseInt(minRunnableValue);
1535 } else {
1536 minRunnable = Integer.max(parallelism / 2, 1);
1537 }
1538 return new BuiltinScheduler(parallelism, maxPoolSize, minRunnable, wrapped);
1539 }
1540
1541 /**
1542 * The built-in ForkJoinPool scheduler.
1543 */
1544 private static class BuiltinScheduler
1545 extends ForkJoinPool implements VirtualThreadScheduler {
1546
1547 BuiltinScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) {
1548 ForkJoinWorkerThreadFactory factory = wrapped
1549 ? ForkJoinPool.defaultForkJoinWorkerThreadFactory
1550 : CarrierThread::new;
1551 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1552 boolean asyncMode = true; // FIFO
1553 super(parallelism, factory, handler, asyncMode,
1554 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1555 }
1556
1557 private void adaptAndExecute(Runnable task) {
1558 execute(ForkJoinTask.adapt(task));
1559 }
1560
1561 @Override
1562 public void onStart(VirtualThreadTask task) {
1563 adaptAndExecute(task);
1564 }
1565
1566 @Override
1567 public void onContinue(VirtualThreadTask task) {
1568 adaptAndExecute(task);
1569 }
1570
1571 /**
1572 * Wraps the scheduler to avoid leaking a direct reference with
1573 * {@link VirtualThreadScheduler#current()}.
1574 */
1575 VirtualThreadScheduler createExternalView() {
1576 BuiltinScheduler builtin = this;
1577 return new VirtualThreadScheduler() {
1578 private void execute(VirtualThreadTask task) {
1579 var vthread = (VirtualThread) task.thread();
1580 VirtualThreadScheduler scheduler = vthread.scheduler;
1581 if (scheduler == this || scheduler == DEFAULT_SCHEDULER) {
1582 builtin.adaptAndExecute(task);
1583 } else {
1584 throw new IllegalArgumentException();
1585 }
1586 }
1587 @Override
1588 public void onStart(VirtualThreadTask task) {
1589 execute(task);
1590 }
1591 @Override
1592 public void onContinue(VirtualThreadTask task) {
1593 execute(task);
1594 }
1595 @Override
1596 public String toString() {
1597 return builtin.toString();
1598 }
1599 };
1600 }
1601 }
1602
1603 /**
1604 * Schedule a runnable task to run after a delay.
1605 */
1606 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1607 if (scheduler == BUILTIN_SCHEDULER) {
1608 return BUILTIN_SCHEDULER.schedule(command, delay, unit);
1609 } else {
1610 return DelayedTaskSchedulers.schedule(command, delay, unit);
1611 }
1612 }
1613
1614 /**
1615 * Supports scheduling a runnable task to run after a delay. It uses a number
1616 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1617 * work queue used. This class is used when using a custom scheduler.
1618 */
1619 private static class DelayedTaskSchedulers {
1620 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1621
1622 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1623 long tid = Thread.currentThread().threadId();
1624 int index = (int) tid & (INSTANCE.length - 1);
1625 return INSTANCE[index].schedule(command, delay, unit);
1626 }
1627
1628 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1629 String propName = "jdk.virtualThreadScheduler.timerQueues";
1630 String propValue = System.getProperty(propName);
1631 int queueCount;
1632 if (propValue != null) {
1633 queueCount = Integer.parseInt(propValue);
1634 if (queueCount != Integer.highestOneBit(queueCount)) {
1635 throw new RuntimeException("Value of " + propName + " must be power of 2");
1636 }
1637 } else {
1638 int ncpus = Runtime.getRuntime().availableProcessors();
1639 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
1640 }
1641 var schedulers = new ScheduledExecutorService[queueCount];
1642 for (int i = 0; i < queueCount; i++) {
1643 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
1644 Executors.newScheduledThreadPool(1, task -> {
1645 Thread t = InnocuousThread.newThread("VirtualThread-unparker", task);
1646 t.setDaemon(true);
1647 return t;
1648 });
1649 stpe.setRemoveOnCancelPolicy(true);
1650 schedulers[i] = stpe;
1651 }
1652 return schedulers;
1653 }
1654 }
1655
1656 /**
1657 * Schedule virtual threads that are ready to be scheduled after they blocked on
1658 * monitor enter.
1659 */
1660 private static void unblockVirtualThreads() {
1661 while (true) {
1662 VirtualThread vthread = takeVirtualThreadListToUnblock();
1663 while (vthread != null) {
1664 assert vthread.onWaitingList;
1665 VirtualThread nextThread = vthread.next;
1666
1667 // remove from list and unblock
1668 vthread.next = null;
1669 boolean changed = vthread.compareAndSetOnWaitingList(true, false);
1670 assert changed;
1671 vthread.unblock();
1672
1673 vthread = nextThread;
1674 }
1675 }
1676 }
1677
1678 /**
1679 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting
1680 * if necessary until a list of one or more threads becomes available.
1681 */
1682 private static native VirtualThread takeVirtualThreadListToUnblock();
1683
1684 static {
1685 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker",
1686 VirtualThread::unblockVirtualThreads);
1687 unblocker.setDaemon(true);
1688 unblocker.start();
1689 }
1690 }