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.RejectedExecutionException;
38 import java.util.concurrent.ScheduledExecutorService;
39 import java.util.concurrent.ScheduledFuture;
40 import java.util.concurrent.ScheduledThreadPoolExecutor;
41 import java.util.concurrent.TimeUnit;
42 import jdk.internal.event.VirtualThreadEndEvent;
43 import jdk.internal.event.VirtualThreadParkEvent;
44 import jdk.internal.event.VirtualThreadStartEvent;
45 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
46 import jdk.internal.invoke.MhUtil;
47 import jdk.internal.misc.CarrierThread;
48 import jdk.internal.misc.InnocuousThread;
49 import jdk.internal.misc.Unsafe;
50 import jdk.internal.vm.Continuation;
51 import jdk.internal.vm.ContinuationScope;
52 import jdk.internal.vm.StackableScope;
53 import jdk.internal.vm.ThreadContainer;
54 import jdk.internal.vm.ThreadContainers;
55 import jdk.internal.vm.annotation.ChangesCurrentThread;
56 import jdk.internal.vm.annotation.Hidden;
57 import jdk.internal.vm.annotation.IntrinsicCandidate;
58 import jdk.internal.vm.annotation.JvmtiHideEvents;
59 import jdk.internal.vm.annotation.JvmtiMountTransition;
60 import jdk.internal.vm.annotation.ReservedStackAccess;
61 import sun.nio.ch.Interruptible;
62 import static java.util.concurrent.TimeUnit.*;
63
64 /**
65 * A thread that is scheduled by the Java virtual machine rather than the operating system.
66 */
67 final class VirtualThread extends BaseVirtualThread {
68 private static final Unsafe U = Unsafe.getUnsafe();
69 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
70
71 private static final BuiltinScheduler BUILTIN_SCHEDULER;
72 private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
73 private static final VirtualThreadScheduler EXTERNAL_VIEW;
74 static {
75 // experimental
76 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
77 if (propValue != null) {
78 BuiltinScheduler builtinScheduler = createBuiltinScheduler(true);
79 VirtualThreadScheduler externalView = builtinScheduler.createExternalView();
80 VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue);
81 BUILTIN_SCHEDULER = builtinScheduler;
82 DEFAULT_SCHEDULER = defaultScheduler;
83 EXTERNAL_VIEW = externalView;
84 } else {
85 var builtinScheduler = createBuiltinScheduler(false);
86 BUILTIN_SCHEDULER = builtinScheduler;
87 DEFAULT_SCHEDULER = builtinScheduler;
88 EXTERNAL_VIEW = builtinScheduler.createExternalView();
89 }
90 }
91
92 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
93 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
94 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
95 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
96 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
97
98 // scheduler and continuation
99 private final VirtualThreadScheduler scheduler;
100 private final Continuation cont;
101 private final VirtualThreadTask runContinuation;
102
103 // virtual thread state, accessed by VM
104 private volatile int state;
105
106 /*
107 * Virtual thread state transitions:
108 *
109 * NEW -> STARTED // Thread.start, schedule to run
110 * STARTED -> TERMINATED // failed to start
111 * STARTED -> RUNNING // first run
112 * RUNNING -> TERMINATED // done
113 *
114 * RUNNING -> PARKING // Thread parking with LockSupport.park
115 * PARKING -> PARKED // cont.yield successful, parked indefinitely
116 * PARKED -> UNPARKED // unparked, may be scheduled to continue
117 * UNPARKED -> RUNNING // continue execution after park
118 *
119 * PARKING -> RUNNING // cont.yield failed, need to park on carrier
120 * RUNNING -> PINNED // park on carrier
121 * PINNED -> RUNNING // unparked, continue execution on same carrier
122 *
123 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
124 * TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked
125 * TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue
126 *
127 * TIMED_PARKING -> RUNNING // cont.yield failed, need to park on carrier
128 * RUNNING -> TIMED_PINNED // park on carrier
129 * TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier
130 *
131 * RUNNING -> BLOCKING // blocking on monitor enter
132 * BLOCKING -> BLOCKED // blocked on monitor enter
133 * BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue
134 * UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter
135 *
136 * RUNNING -> WAITING // transitional state during wait on monitor
137 * WAITING -> WAIT // waiting on monitor
138 * WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
139 * WAIT -> UNBLOCKED // interrupted
140 *
141 * RUNNING -> TIMED_WAITING // transition state during timed-waiting on monitor
142 * TIMED_WAITING -> TIMED_WAIT // timed-waiting on monitor
143 * TIMED_WAIT -> BLOCKED // notified, waiting to be unblocked by monitor owner
144 * TIMED_WAIT -> UNBLOCKED // timed-out/interrupted
145 *
146 * RUNNING -> YIELDING // Thread.yield
147 * YIELDING -> YIELDED // cont.yield successful, may be scheduled to continue
148 * YIELDING -> RUNNING // cont.yield failed
149 * YIELDED -> RUNNING // continue execution after Thread.yield
150 */
151 private static final int NEW = 0;
152 private static final int STARTED = 1;
153 private static final int RUNNING = 2; // runnable-mounted
154
155 // untimed and timed parking
156 private static final int PARKING = 3;
157 private static final int PARKED = 4; // unmounted
158 private static final int PINNED = 5; // mounted
159 private static final int TIMED_PARKING = 6;
160 private static final int TIMED_PARKED = 7; // unmounted
161 private static final int TIMED_PINNED = 8; // mounted
162 private static final int UNPARKED = 9; // unmounted but runnable
163
164 // Thread.yield
165 private static final int YIELDING = 10;
166 private static final int YIELDED = 11; // unmounted but runnable
167
168 // monitor enter
169 private static final int BLOCKING = 12;
170 private static final int BLOCKED = 13; // unmounted
171 private static final int UNBLOCKED = 14; // unmounted but runnable
172
173 // monitor wait/timed-wait
174 private static final int WAITING = 15;
175 private static final int WAIT = 16; // waiting in Object.wait
176 private static final int TIMED_WAITING = 17;
177 private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait
178
179 private static final int TERMINATED = 99; // final state
180
181 // parking permit made available by LockSupport.unpark
182 private volatile boolean parkPermit;
183
184 // blocking permit made available by unblocker thread when another thread exits monitor
185 private volatile boolean blockPermit;
186
187 // true when on the list of virtual threads waiting to be unblocked
188 private volatile boolean onWaitingList;
189
190 // next virtual thread on the list of virtual threads waiting to be unblocked
191 private volatile VirtualThread next;
192
193 // notified by Object.notify/notifyAll while waiting in Object.wait
194 private volatile boolean notified;
195
196 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
197 private volatile boolean interruptibleWait;
198
199 // timed-wait support
200 private byte timedWaitSeqNo;
201
202 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
203 private long timeout;
204
205 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
206 private Future<?> timeoutTask;
207
208 // carrier thread when mounted, accessed by VM
209 private volatile Thread carrierThread;
210
211 // termination object when joining, created lazily if needed
212 private volatile CountDownLatch termination;
213
214 /**
215 * Return the built-in scheduler.
216 * @param trusted true if caller is trusted, false if not trusted
217 */
218 static VirtualThreadScheduler builtinScheduler(boolean trusted) {
219 return trusted ? BUILTIN_SCHEDULER : EXTERNAL_VIEW;
220 }
221
222 /**
223 * Returns the default scheduler, usually the same as the built-in scheduler.
224 */
225 static VirtualThreadScheduler defaultScheduler() {
226 return DEFAULT_SCHEDULER;
227 }
228
229 /**
230 * Returns the continuation scope used for virtual threads.
231 */
232 static ContinuationScope continuationScope() {
233 return VTHREAD_SCOPE;
234 }
235
236 /**
237 * Return the scheduler for this thread.
238 * @param trusted true if caller is trusted, false if not trusted
239 */
240 VirtualThreadScheduler scheduler(boolean trusted) {
241 if (scheduler == BUILTIN_SCHEDULER && !trusted) {
242 return EXTERNAL_VIEW;
243 } else {
244 return scheduler;
245 }
246 }
247
248 /**
249 * Returns the task to start/continue this virtual thread.
250 */
251 VirtualThreadTask virtualThreadTask() {
252 return runContinuation;
253 }
254
255 /**
256 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
257 *
258 * @param scheduler the scheduler or null for default scheduler
259 * @param preferredCarrier the preferred carrier or null
260 * @param name thread name
261 * @param characteristics characteristics
262 * @param task the task to execute
263 */
264 VirtualThread(VirtualThreadScheduler scheduler,
265 Thread preferredCarrier,
266 String name,
267 int characteristics,
268 Runnable task) {
269 super(name, characteristics, /*bound*/ false);
270 Objects.requireNonNull(task);
271
272 // use default scheduler if not provided
273 if (scheduler == null) {
274 scheduler = DEFAULT_SCHEDULER;
275 } else if (scheduler == EXTERNAL_VIEW) {
276 throw new UnsupportedOperationException();
277 }
278 this.scheduler = scheduler;
279 this.cont = new VThreadContinuation(this, task);
280
281 if (scheduler == BUILTIN_SCHEDULER) {
282 this.runContinuation = new BuiltinSchedulerTask(this);
283 } else {
284 this.runContinuation = new CustomSchedulerTask(this, preferredCarrier);
285 }
286 }
287
288 /**
289 * The task to execute when using the built-in scheduler.
290 */
291 static final class BuiltinSchedulerTask implements VirtualThreadTask {
292 private final VirtualThread vthread;
293 BuiltinSchedulerTask(VirtualThread vthread) {
294 this.vthread = vthread;
295 }
296 @Override
297 public Thread thread() {
298 return vthread;
299 }
300 @Override
301 public void run() {
302 vthread.runContinuation();;
303 }
304 @Override
305 public Thread preferredCarrier() {
306 throw new UnsupportedOperationException();
307 }
308 @Override
309 public Object attach(Object att) {
310 throw new UnsupportedOperationException();
311 }
312 @Override
313 public Object attachment() {
314 throw new UnsupportedOperationException();
315 }
316 }
317
318 /**
319 * The task to execute when using a custom scheduler.
320 */
321 static final class CustomSchedulerTask implements VirtualThreadTask {
322 private static final VarHandle ATT =
323 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class);
324 private final VirtualThread vthread;
325 private final Thread preferredCarrier;
326 private volatile Object att;
327 CustomSchedulerTask(VirtualThread vthread, Thread preferredCarrier) {
328 this.vthread = vthread;
329 this.preferredCarrier = preferredCarrier;
330 }
331 @Override
332 public Thread thread() {
333 return vthread;
334 }
335 @Override
336 public void run() {
337 vthread.runContinuation();;
338 }
339 @Override
340 public Thread preferredCarrier() {
341 return preferredCarrier;
342 }
343 @Override
344 public Object attach(Object att) {
345 return ATT.getAndSet(this, att);
346 }
347 @Override
348 public Object attachment() {
349 return att;
350 }
351 }
352
353 /**
354 * The continuation that a virtual thread executes.
355 */
356 private static class VThreadContinuation extends Continuation {
357 VThreadContinuation(VirtualThread vthread, Runnable task) {
358 super(VTHREAD_SCOPE, wrap(vthread, task));
359 }
360 @Override
361 protected void onPinned(Continuation.Pinned reason) {
362 }
363 private static Runnable wrap(VirtualThread vthread, Runnable task) {
364 return new Runnable() {
365 @Hidden
366 @JvmtiHideEvents
367 public void run() {
368 vthread.endFirstTransition();
369 try {
370 vthread.run(task);
371 } finally {
372 vthread.startFinalTransition();
373 }
374 }
375 };
376 }
377 }
378
379 /**
380 * Runs or continues execution on the current thread. The virtual thread is mounted
381 * on the current thread before the task runs or continues. It unmounts when the
382 * task completes or yields.
383 */
384 @ChangesCurrentThread // allow mount/unmount to be inlined
385 private void runContinuation() {
386 // the carrier must be a platform thread
387 if (Thread.currentThread().isVirtual()) {
388 throw new WrongThreadException();
389 }
390
391 // set state to RUNNING
392 int initialState = state();
393 if (initialState == STARTED || initialState == UNPARKED
394 || initialState == UNBLOCKED || initialState == YIELDED) {
395 // newly started or continue after parking/blocking/Thread.yield
396 if (!compareAndSetState(initialState, RUNNING)) {
397 return;
398 }
399 // consume permit when continuing after parking or blocking. If continue
400 // after a timed-park or timed-wait then the timeout task is cancelled.
401 if (initialState == UNPARKED) {
402 cancelTimeoutTask();
403 setParkPermit(false);
404 } else if (initialState == UNBLOCKED) {
405 cancelTimeoutTask();
406 blockPermit = false;
407 }
408 } else {
409 // not runnable
410 return;
411 }
412
413 mount();
414 try {
415 cont.run();
416 } finally {
417 unmount();
418 if (cont.isDone()) {
419 afterDone();
420 } else {
421 afterYield();
422 }
423 }
424 }
425
426 /**
427 * Cancel timeout task when continuing after timed-park or timed-wait.
428 * The timeout task may be executing, or may have already completed.
429 */
430 private void cancelTimeoutTask() {
431 if (timeoutTask != null) {
432 timeoutTask.cancel(false);
433 timeoutTask = null;
434 }
435 }
436
437 /**
438 * Submits the runContinuation task to the scheduler. For the built-in scheduler,
439 * the task will be pushed to the local queue if possible, otherwise it will be
440 * pushed to an external submission queue.
441 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
442 * @throws RejectedExecutionException
443 */
444 private void submitRunContinuation(boolean retryOnOOME) {
445 boolean done = false;
446 while (!done) {
447 try {
448 // Pin the continuation to prevent the virtual thread from unmounting
449 // when submitting a task. For the default scheduler this ensures that
450 // the carrier doesn't change when pushing a task. For other schedulers
451 // it avoids deadlock that could arise due to carriers and virtual
452 // threads contending for a lock.
453 if (currentThread().isVirtual()) {
454 Continuation.pin();
455 try {
456 scheduler.onContinue(runContinuation);
457 } finally {
458 Continuation.unpin();
459 }
460 } else {
461 scheduler.onContinue(runContinuation);
462 }
463 done = true;
464 } catch (RejectedExecutionException ree) {
465 submitFailed(ree);
466 throw ree;
467 } catch (OutOfMemoryError e) {
468 if (retryOnOOME) {
469 U.park(false, 100_000_000); // 100ms
470 } else {
471 throw e;
472 }
473 }
474 }
475 }
476
477 /**
478 * Submits the runContinuation task to the scheduler. For the default scheduler,
479 * and calling it on a worker thread, the task will be pushed to the local queue,
480 * otherwise it will be pushed to an external submission queue.
481 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
482 * @throws RejectedExecutionException
483 */
484 private void submitRunContinuation() {
485 submitRunContinuation(true);
486 }
487
488 /**
489 * Invoked from a carrier thread to lazy submit the runContinuation task to the
490 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
491 * for a custom scheduler, then it just submits the task to the scheduler.
492 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
493 * @throws RejectedExecutionException
494 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
495 */
496 private void lazySubmitRunContinuation() {
497 assert !currentThread().isVirtual();
498 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
499 try {
500 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
501 } catch (RejectedExecutionException ree) {
502 submitFailed(ree);
503 throw ree;
504 } catch (OutOfMemoryError e) {
505 submitRunContinuation();
506 }
507 } else {
508 submitRunContinuation();
509 }
510 }
511
512 /**
513 * Invoked from a carrier thread to externally submit the runContinuation task to the
514 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
515 * task to the scheduler.
516 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
517 * @throws RejectedExecutionException
518 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
519 */
520 private void externalSubmitRunContinuation() {
521 assert !currentThread().isVirtual();
522 if (currentThread() instanceof CarrierThread ct) {
523 try {
524 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
525 } catch (RejectedExecutionException ree) {
526 submitFailed(ree);
527 throw ree;
528 } catch (OutOfMemoryError e) {
529 submitRunContinuation();
530 }
531 } else {
532 submitRunContinuation();
533 }
534 }
535
536 /**
537 * Invoked from Thread.start to externally submit the runContinuation task to the
538 * scheduler. If this virtual thread is scheduled by the built-in scheduler,
539 * and this method is called from a virtual thread scheduled by the built-in
540 * scheduler, then it uses externalSubmit to ensure that the task is pushed to an
541 * external submission queue rather than the local queue.
542 * @throws RejectedExecutionException
543 * @throws OutOfMemoryError
544 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
545 */
546 private void externalSubmitRunContinuationOrThrow() {
547 try {
548 if (currentThread().isVirtual()) {
549 // Pin the continuation to prevent the virtual thread from unmounting
550 // when submitting a task. This avoids deadlock that could arise due to
551 // carriers and virtual threads contending for a lock.
552 Continuation.pin();
553 try {
554 if (scheduler == BUILTIN_SCHEDULER
555 && currentCarrierThread() instanceof CarrierThread ct) {
556 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
557 } else {
558 scheduler.onStart(runContinuation);
559 }
560 } finally {
561 Continuation.unpin();
562 }
563 } else {
564 scheduler.onStart(runContinuation);
565 }
566 } catch (RejectedExecutionException ree) {
567 submitFailed(ree);
568 throw ree;
569 }
570 }
571
572 /**
573 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
574 */
575 private void submitFailed(RejectedExecutionException ree) {
576 var event = new VirtualThreadSubmitFailedEvent();
577 if (event.isEnabled()) {
578 event.javaThreadId = threadId();
579 event.exceptionMessage = ree.getMessage();
580 event.commit();
581 }
582 }
583
584 /**
585 * Runs a task in the context of this virtual thread.
586 */
587 private void run(Runnable task) {
588 assert Thread.currentThread() == this && state == RUNNING;
589
590 // emit JFR event if enabled
591 if (VirtualThreadStartEvent.isTurnedOn()) {
592 var event = new VirtualThreadStartEvent();
593 event.javaThreadId = threadId();
594 event.commit();
595 }
596
597 Object bindings = Thread.scopedValueBindings();
598 try {
599 runWith(bindings, task);
600 } catch (Throwable exc) {
601 dispatchUncaughtException(exc);
602 } finally {
603 // pop any remaining scopes from the stack, this may block
604 StackableScope.popAll();
605
606 // emit JFR event if enabled
607 if (VirtualThreadEndEvent.isTurnedOn()) {
608 var event = new VirtualThreadEndEvent();
609 event.javaThreadId = threadId();
610 event.commit();
611 }
612 }
613 }
614
615 /**
616 * Mounts this virtual thread onto the current platform thread. On
617 * return, the current thread is the virtual thread.
618 */
619 @ChangesCurrentThread
620 @ReservedStackAccess
621 private void mount() {
622 startTransition(/*mount*/true);
623 // We assume following volatile accesses provide equivalent
624 // of acquire ordering, otherwise we need U.loadFence() here.
625
626 // sets the carrier thread
627 Thread carrier = Thread.currentCarrierThread();
628 setCarrierThread(carrier);
629
630 // sync up carrier thread interrupted status if needed
631 if (interrupted) {
632 carrier.setInterrupt();
633 } else if (carrier.isInterrupted()) {
634 synchronized (interruptLock) {
635 // need to recheck interrupted status
636 if (!interrupted) {
637 carrier.clearInterrupt();
638 }
639 }
640 }
641
642 // set Thread.currentThread() to return this virtual thread
643 carrier.setCurrentThread(this);
644 }
645
646 /**
647 * Unmounts this virtual thread from the carrier. On return, the
648 * current thread is the current platform thread.
649 */
650 @ChangesCurrentThread
651 @ReservedStackAccess
652 private void unmount() {
653 assert !Thread.holdsLock(interruptLock);
654
655 // set Thread.currentThread() to return the platform thread
656 Thread carrier = this.carrierThread;
657 carrier.setCurrentThread(carrier);
658
659 // break connection to carrier thread, synchronized with interrupt
660 synchronized (interruptLock) {
661 setCarrierThread(null);
662 }
663 carrier.clearInterrupt();
664
665 // We assume previous volatile accesses provide equivalent
666 // of release ordering, otherwise we need U.storeFence() here.
667 endTransition(/*mount*/false);
668 }
669
670 /**
671 * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
672 * the continuation continues.
673 */
674 @Hidden
675 private boolean yieldContinuation() {
676 startTransition(/*mount*/false);
677 try {
678 return Continuation.yield(VTHREAD_SCOPE);
679 } finally {
680 endTransition(/*mount*/true);
681 }
682 }
683
684 /**
685 * Invoked in the context of the carrier thread after the Continuation yields when
686 * parking, blocking on monitor enter, Object.wait, or Thread.yield.
687 */
688 private void afterYield() {
689 assert carrierThread == null;
690
691 // re-adjust parallelism if the virtual thread yielded when compensating
692 if (currentThread() instanceof CarrierThread ct) {
693 ct.endBlocking();
694 }
695
696 int s = state();
697
698 // LockSupport.park/parkNanos
699 if (s == PARKING || s == TIMED_PARKING) {
700 int newState;
701 if (s == PARKING) {
702 setState(newState = PARKED);
703 } else {
704 // schedule unpark
705 long timeout = this.timeout;
706 assert timeout > 0;
707 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
708 setState(newState = TIMED_PARKED);
709 }
710
711 // may have been unparked while parking
712 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
713 // lazy submit if local queue is empty
714 lazySubmitRunContinuation();
715 }
716 return;
717 }
718
719 // Thread.yield
720 if (s == YIELDING) {
721 setState(YIELDED);
722
723 // external submit if there are no tasks in the local task queue
724 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
725 externalSubmitRunContinuation();
726 } else {
727 submitRunContinuation();
728 }
729 return;
730 }
731
732 // blocking on monitorenter
733 if (s == BLOCKING) {
734 setState(BLOCKED);
735
736 // may have been unblocked while blocking
737 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
738 // lazy submit if local queue is empty
739 lazySubmitRunContinuation();
740 }
741 return;
742 }
743
744 // Object.wait
745 if (s == WAITING || s == TIMED_WAITING) {
746 int newState;
747 boolean blocked;
748 boolean interruptible = interruptibleWait;
749 if (s == WAITING) {
750 setState(newState = WAIT);
751 // may have been notified while in transition
752 blocked = notified && compareAndSetState(WAIT, BLOCKED);
753 } else {
754 // For timed-wait, a timeout task is scheduled to execute. The timeout
755 // task will change the thread state to UNBLOCKED and submit the thread
756 // to the scheduler. A sequence number is used to ensure that the timeout
757 // task only unblocks the thread for this timed-wait. We synchronize with
758 // the timeout task to coordinate access to the sequence number and to
759 // ensure the timeout task doesn't execute until the thread has got to
760 // the TIMED_WAIT state.
761 long timeout = this.timeout;
762 assert timeout > 0;
763 synchronized (timedWaitLock()) {
764 byte seqNo = ++timedWaitSeqNo;
765 timeoutTask = schedule(() -> waitTimeoutExpired(seqNo), timeout, MILLISECONDS);
766 setState(newState = TIMED_WAIT);
767 // May have been notified while in transition. This must be done while
768 // holding the monitor to avoid changing the state of a new timed wait call.
769 blocked = notified && compareAndSetState(TIMED_WAIT, BLOCKED);
770 }
771 }
772
773 if (blocked) {
774 // may have been unblocked already
775 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
776 lazySubmitRunContinuation();
777 }
778 } else {
779 // may have been interrupted while in transition to wait state
780 if (interruptible && interrupted && compareAndSetState(newState, UNBLOCKED)) {
781 lazySubmitRunContinuation();
782 }
783 }
784 return;
785 }
786
787 assert false;
788 }
789
790 /**
791 * Invoked after the continuation completes.
792 */
793 private void afterDone() {
794 afterDone(true);
795 }
796
797 /**
798 * Invoked after the continuation completes (or start failed). Sets the thread
799 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
800 *
801 * @param notifyContainer true if its container should be notified
802 */
803 private void afterDone(boolean notifyContainer) {
804 assert carrierThread == null;
805 setState(TERMINATED);
806
807 // notify anyone waiting for this virtual thread to terminate
808 CountDownLatch termination = this.termination;
809 if (termination != null) {
810 assert termination.getCount() == 1;
811 termination.countDown();
812 }
813
814 // notify container
815 if (notifyContainer) {
816 threadContainer().remove(this);
817 }
818
819 // clear references to thread locals
820 clearReferences();
821 }
822
823 /**
824 * Schedules this {@code VirtualThread} to execute.
825 *
826 * @throws IllegalStateException if the container is shutdown or closed
827 * @throws IllegalThreadStateException if the thread has already been started
828 * @throws RejectedExecutionException if the scheduler cannot accept a task
829 */
830 @Override
831 void start(ThreadContainer container) {
832 if (!compareAndSetState(NEW, STARTED)) {
833 throw new IllegalThreadStateException("Already started");
834 }
835
836 // bind thread to container
837 assert threadContainer() == null;
838 setThreadContainer(container);
839
840 // start thread
841 boolean addedToContainer = false;
842 boolean started = false;
843 try {
844 container.add(this); // may throw
845 addedToContainer = true;
846
847 // scoped values may be inherited
848 inheritScopedValueBindings(container);
849
850 // submit task to run thread, using externalSubmit if possible
851 externalSubmitRunContinuationOrThrow();
852 started = true;
853 } finally {
854 if (!started) {
855 afterDone(addedToContainer);
856 }
857 }
858 }
859
860 @Override
861 public void start() {
862 start(ThreadContainers.root());
863 }
864
865 @Override
866 public void run() {
867 // do nothing
868 }
869
870 /**
871 * Parks until unparked or interrupted. If already unparked then the parking
872 * permit is consumed and this method completes immediately (meaning it doesn't
873 * yield). It also completes immediately if the interrupted status is set.
874 */
875 @Override
876 void park() {
877 assert Thread.currentThread() == this;
878
879 // complete immediately if parking permit available or interrupted
880 if (getAndSetParkPermit(false) || interrupted)
881 return;
882
883 // park the thread
884 boolean yielded = false;
885 long eventStartTime = VirtualThreadParkEvent.eventStartTime();
886 setState(PARKING);
887 try {
888 yielded = yieldContinuation();
889 } catch (OutOfMemoryError e) {
890 // park on carrier
891 } finally {
892 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
893 if (yielded) {
894 VirtualThreadParkEvent.offer(eventStartTime, Long.MIN_VALUE);
895 } else {
896 assert state() == PARKING;
897 setState(RUNNING);
898 }
899 }
900
901 // park on the carrier thread when pinned
902 if (!yielded) {
903 parkOnCarrierThread(false, 0);
904 }
905 }
906
907 /**
908 * Parks up to the given waiting time or until unparked or interrupted.
909 * If already unparked then the parking permit is consumed and this method
910 * completes immediately (meaning it doesn't yield). It also completes immediately
911 * if the interrupted status is set or the waiting time is {@code <= 0}.
912 *
913 * @param nanos the maximum number of nanoseconds to wait.
914 */
915 @Override
916 void parkNanos(long nanos) {
917 assert Thread.currentThread() == this;
918
919 // complete immediately if parking permit available or interrupted
920 if (getAndSetParkPermit(false) || interrupted)
921 return;
922
923 // park the thread for the waiting time
924 if (nanos > 0) {
925 long startTime = System.nanoTime();
926
927 // park the thread, afterYield will schedule the thread to unpark
928 boolean yielded = false;
929 long eventStartTime = VirtualThreadParkEvent.eventStartTime();
930 timeout = nanos;
931 setState(TIMED_PARKING);
932 try {
933 yielded = yieldContinuation();
934 } catch (OutOfMemoryError e) {
935 // park on carrier
936 } finally {
937 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
938 if (yielded) {
939 VirtualThreadParkEvent.offer(eventStartTime, nanos);
940 } else {
941 assert state() == TIMED_PARKING;
942 setState(RUNNING);
943 }
944 }
945
946 // park on carrier thread for remaining time when pinned (or OOME)
947 if (!yielded) {
948 long remainingNanos = nanos - (System.nanoTime() - startTime);
949 parkOnCarrierThread(true, remainingNanos);
950 }
951 }
952 }
953
954 /**
955 * Parks the current carrier thread up to the given waiting time or until
956 * unparked or interrupted. If the virtual thread is interrupted then the
957 * interrupted status will be propagated to the carrier thread.
958 * @param timed true for a timed park, false for untimed
959 * @param nanos the waiting time in nanoseconds
960 */
961 private void parkOnCarrierThread(boolean timed, long nanos) {
962 assert state() == RUNNING;
963
964 setState(timed ? TIMED_PINNED : PINNED);
965 try {
966 if (!parkPermit) {
967 if (!timed) {
968 U.park(false, 0);
969 } else if (nanos > 0) {
970 U.park(false, nanos);
971 }
972 }
973 } finally {
974 setState(RUNNING);
975 }
976
977 // consume parking permit
978 setParkPermit(false);
979
980 // JFR jdk.VirtualThreadPinned event
981 postPinnedEvent("LockSupport.park");
982 }
983
984 /**
985 * Call into VM when pinned to record a JFR jdk.VirtualThreadPinned event.
986 * Recording the event in the VM avoids having JFR event recorded in Java
987 * with the same name, but different ID, to events recorded by the VM.
988 */
989 @Hidden
990 private static native void postPinnedEvent(String op);
991
992 /**
993 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
994 * then its task is scheduled to continue, otherwise its next call to {@code park} or
995 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
996 * @param lazySubmit to use lazySubmit if possible
997 * @throws RejectedExecutionException if the scheduler cannot accept a task
998 */
999 private void unpark(boolean lazySubmit) {
1000 if (!getAndSetParkPermit(true) && currentThread() != this) {
1001 int s = state();
1002
1003 // unparked while parked
1004 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
1005 if (lazySubmit) {
1006 lazySubmitRunContinuation();
1007 } else {
1008 submitRunContinuation();
1009 }
1010 return;
1011 }
1012
1013 // unparked while parked when pinned
1014 if (s == PINNED || s == TIMED_PINNED) {
1015 // unpark carrier thread when pinned
1016 disableSuspendAndPreempt();
1017 try {
1018 synchronized (carrierThreadAccessLock()) {
1019 Thread carrier = carrierThread;
1020 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
1021 U.unpark(carrier);
1022 }
1023 }
1024 } finally {
1025 enableSuspendAndPreempt();
1026 }
1027 return;
1028 }
1029 }
1030 }
1031
1032 @Override
1033 void unpark() {
1034 unpark(false);
1035 }
1036
1037 /**
1038 * Invoked by unblocker thread to unblock this virtual thread.
1039 */
1040 private void unblock() {
1041 assert !Thread.currentThread().isVirtual();
1042 blockPermit = true;
1043 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) {
1044 submitRunContinuation();
1045 }
1046 }
1047
1048 /**
1049 * Invoked by FJP worker thread or STPE thread when park timeout expires.
1050 */
1051 private void parkTimeoutExpired() {
1052 assert !VirtualThread.currentThread().isVirtual();
1053 unpark(true);
1054 }
1055
1056 /**
1057 * Invoked by FJP worker thread or STPE thread when wait timeout expires.
1058 * If the virtual thread is in timed-wait then this method will unblock the thread
1059 * and submit its task so that it continues and attempts to reenter the monitor.
1060 * This method does nothing if the thread has been woken by notify or interrupt.
1061 */
1062 private void waitTimeoutExpired(byte seqNo) {
1063 assert !Thread.currentThread().isVirtual();
1064
1065 synchronized (timedWaitLock()) {
1066 if (seqNo != timedWaitSeqNo) {
1067 // this timeout task is for a past timed-wait
1068 return;
1069 }
1070 if (!compareAndSetState(TIMED_WAIT, UNBLOCKED)) {
1071 // already unblocked
1072 return;
1073 }
1074 }
1075
1076 lazySubmitRunContinuation();
1077 }
1078
1079 /**
1080 * Attempts to yield the current virtual thread (Thread.yield).
1081 */
1082 void tryYield() {
1083 assert Thread.currentThread() == this;
1084 setState(YIELDING);
1085 boolean yielded = false;
1086 try {
1087 yielded = yieldContinuation(); // may throw
1088 } finally {
1089 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
1090 if (!yielded) {
1091 assert state() == YIELDING;
1092 setState(RUNNING);
1093 }
1094 }
1095 }
1096
1097 /**
1098 * Sleep the current thread for the given sleep time (in nanoseconds). If
1099 * nanos is 0 then the thread will attempt to yield.
1100 *
1101 * @implNote This implementation parks the thread for the given sleeping time
1102 * and will therefore be observed in PARKED state during the sleep. Parking
1103 * will consume the parking permit so this method makes available the parking
1104 * permit after the sleep. This may be observed as a spurious, but benign,
1105 * wakeup when the thread subsequently attempts to park.
1106 *
1107 * @param nanos the maximum number of nanoseconds to sleep
1108 * @throws InterruptedException if interrupted while sleeping
1109 */
1110 void sleepNanos(long nanos) throws InterruptedException {
1111 assert Thread.currentThread() == this && nanos >= 0;
1112 if (getAndClearInterrupt())
1113 throw new InterruptedException();
1114 if (nanos == 0) {
1115 tryYield();
1116 } else {
1117 // park for the sleep time
1118 try {
1119 long remainingNanos = nanos;
1120 long startNanos = System.nanoTime();
1121 while (remainingNanos > 0) {
1122 parkNanos(remainingNanos);
1123 if (getAndClearInterrupt()) {
1124 throw new InterruptedException();
1125 }
1126 remainingNanos = nanos - (System.nanoTime() - startNanos);
1127 }
1128 } finally {
1129 // may have been unparked while sleeping
1130 setParkPermit(true);
1131 }
1132 }
1133 }
1134
1135 /**
1136 * Waits up to {@code nanos} nanoseconds for this virtual thread to terminate.
1137 * A timeout of {@code 0} means to wait forever.
1138 *
1139 * @throws InterruptedException if interrupted while waiting
1140 * @return true if the thread has terminated
1141 */
1142 boolean joinNanos(long nanos) throws InterruptedException {
1143 if (state() == TERMINATED)
1144 return true;
1145
1146 // ensure termination object exists, then re-check state
1147 CountDownLatch termination = getTermination();
1148 if (state() == TERMINATED)
1149 return true;
1150
1151 // wait for virtual thread to terminate
1152 if (nanos == 0) {
1153 termination.await();
1154 } else {
1155 boolean terminated = termination.await(nanos, NANOSECONDS);
1156 if (!terminated) {
1157 // waiting time elapsed
1158 return false;
1159 }
1160 }
1161 assert state() == TERMINATED;
1162 return true;
1163 }
1164
1165 @Override
1166 void blockedOn(Interruptible b) {
1167 disableSuspendAndPreempt();
1168 try {
1169 super.blockedOn(b);
1170 } finally {
1171 enableSuspendAndPreempt();
1172 }
1173 }
1174
1175 @Override
1176 public void interrupt() {
1177 if (Thread.currentThread() != this) {
1178 // if current thread is a virtual thread then prevent it from being
1179 // suspended or unmounted when entering or holding interruptLock
1180 Interruptible blocker;
1181 disableSuspendAndPreempt();
1182 try {
1183 synchronized (interruptLock) {
1184 interrupted = true;
1185 blocker = nioBlocker();
1186 if (blocker != null) {
1187 blocker.interrupt(this);
1188 }
1189
1190 // interrupt carrier thread if mounted
1191 Thread carrier = carrierThread;
1192 if (carrier != null) carrier.setInterrupt();
1193 }
1194 } finally {
1195 enableSuspendAndPreempt();
1196 }
1197
1198 // notify blocker after releasing interruptLock
1199 if (blocker != null) {
1200 blocker.postInterrupt();
1201 }
1202
1203 // make available parking permit, unpark thread if parked
1204 unpark();
1205
1206 // if thread is waiting in Object.wait then schedule to try to reenter
1207 int s = state();
1208 if ((s == WAIT || s == TIMED_WAIT) && compareAndSetState(s, UNBLOCKED)) {
1209 submitRunContinuation();
1210 }
1211
1212 } else {
1213 interrupted = true;
1214 carrierThread.setInterrupt();
1215 setParkPermit(true);
1216 }
1217 }
1218
1219 @Override
1220 public boolean isInterrupted() {
1221 return interrupted;
1222 }
1223
1224 @Override
1225 boolean getAndClearInterrupt() {
1226 assert Thread.currentThread() == this;
1227 boolean oldValue = interrupted;
1228 if (oldValue) {
1229 disableSuspendAndPreempt();
1230 try {
1231 synchronized (interruptLock) {
1232 interrupted = false;
1233 carrierThread.clearInterrupt();
1234 }
1235 } finally {
1236 enableSuspendAndPreempt();
1237 }
1238 }
1239 return oldValue;
1240 }
1241
1242 @Override
1243 Thread.State threadState() {
1244 switch (state()) {
1245 case NEW:
1246 return Thread.State.NEW;
1247 case STARTED:
1248 // return NEW if thread container not yet set
1249 if (threadContainer() == null) {
1250 return Thread.State.NEW;
1251 } else {
1252 return Thread.State.RUNNABLE;
1253 }
1254 case UNPARKED:
1255 case UNBLOCKED:
1256 case YIELDED:
1257 // runnable, not mounted
1258 return Thread.State.RUNNABLE;
1259 case RUNNING:
1260 // if mounted then return state of carrier thread
1261 if (Thread.currentThread() != this) {
1262 disableSuspendAndPreempt();
1263 try {
1264 synchronized (carrierThreadAccessLock()) {
1265 Thread carrierThread = this.carrierThread;
1266 if (carrierThread != null) {
1267 return carrierThread.threadState();
1268 }
1269 }
1270 } finally {
1271 enableSuspendAndPreempt();
1272 }
1273 }
1274 // runnable, mounted
1275 return Thread.State.RUNNABLE;
1276 case PARKING:
1277 case TIMED_PARKING:
1278 case WAITING:
1279 case TIMED_WAITING:
1280 case YIELDING:
1281 // runnable, in transition
1282 return Thread.State.RUNNABLE;
1283 case PARKED:
1284 case PINNED:
1285 case WAIT:
1286 return Thread.State.WAITING;
1287 case TIMED_PARKED:
1288 case TIMED_PINNED:
1289 case TIMED_WAIT:
1290 return Thread.State.TIMED_WAITING;
1291 case BLOCKING:
1292 case BLOCKED:
1293 return Thread.State.BLOCKED;
1294 case TERMINATED:
1295 return Thread.State.TERMINATED;
1296 default:
1297 throw new InternalError();
1298 }
1299 }
1300
1301 @Override
1302 boolean alive() {
1303 int s = state;
1304 return (s != NEW && s != TERMINATED);
1305 }
1306
1307 @Override
1308 boolean isTerminated() {
1309 return (state == TERMINATED);
1310 }
1311
1312 @Override
1313 public String toString() {
1314 StringBuilder sb = new StringBuilder("VirtualThread[#");
1315 sb.append(threadId());
1316 String name = getName();
1317 if (!name.isEmpty()) {
1318 sb.append(",");
1319 sb.append(name);
1320 }
1321 sb.append("]/");
1322
1323 // add the carrier state and thread name when mounted
1324 boolean mounted;
1325 if (Thread.currentThread() == this) {
1326 mounted = appendCarrierInfo(sb);
1327 } else {
1328 disableSuspendAndPreempt();
1329 try {
1330 synchronized (carrierThreadAccessLock()) {
1331 mounted = appendCarrierInfo(sb);
1332 }
1333 } finally {
1334 enableSuspendAndPreempt();
1335 }
1336 }
1337
1338 // add virtual thread state when not mounted
1339 if (!mounted) {
1340 String stateAsString = threadState().toString();
1341 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1342 }
1343
1344 return sb.toString();
1345 }
1346
1347 /**
1348 * Appends the carrier state and thread name to the string buffer if mounted.
1349 * @return true if mounted, false if not mounted
1350 */
1351 private boolean appendCarrierInfo(StringBuilder sb) {
1352 assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock());
1353 Thread carrier = carrierThread;
1354 if (carrier != null) {
1355 String stateAsString = carrier.threadState().toString();
1356 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1357 sb.append('@');
1358 sb.append(carrier.getName());
1359 return true;
1360 } else {
1361 return false;
1362 }
1363 }
1364
1365 @Override
1366 public int hashCode() {
1367 return (int) threadId();
1368 }
1369
1370 @Override
1371 public boolean equals(Object obj) {
1372 return obj == this;
1373 }
1374
1375 /**
1376 * Returns the termination object, creating it if needed.
1377 */
1378 private CountDownLatch getTermination() {
1379 CountDownLatch termination = this.termination;
1380 if (termination == null) {
1381 termination = new CountDownLatch(1);
1382 if (!U.compareAndSetReference(this, TERMINATION, null, termination)) {
1383 termination = this.termination;
1384 }
1385 }
1386 return termination;
1387 }
1388
1389 /**
1390 * Returns the lock object to synchronize on when accessing carrierThread.
1391 * The lock prevents carrierThread from being reset to null during unmount.
1392 */
1393 private Object carrierThreadAccessLock() {
1394 // return interruptLock as unmount has to coordinate with interrupt
1395 return interruptLock;
1396 }
1397
1398 /**
1399 * Returns a lock object for coordinating timed-wait setup and timeout handling.
1400 */
1401 private Object timedWaitLock() {
1402 // use this object for now to avoid the overhead of introducing another lock
1403 return runContinuation;
1404 }
1405
1406 /**
1407 * Disallow the current thread be suspended or preempted.
1408 */
1409 private void disableSuspendAndPreempt() {
1410 notifyJvmtiDisableSuspend(true);
1411 Continuation.pin();
1412 }
1413
1414 /**
1415 * Allow the current thread be suspended or preempted.
1416 */
1417 private void enableSuspendAndPreempt() {
1418 Continuation.unpin();
1419 notifyJvmtiDisableSuspend(false);
1420 }
1421
1422 // -- wrappers for get/set of state, parking permit, and carrier thread --
1423
1424 private int state() {
1425 return state; // volatile read
1426 }
1427
1428 private void setState(int newValue) {
1429 state = newValue; // volatile write
1430 }
1431
1432 private boolean compareAndSetState(int expectedValue, int newValue) {
1433 return U.compareAndSetInt(this, STATE, expectedValue, newValue);
1434 }
1435
1436 private boolean compareAndSetOnWaitingList(boolean expectedValue, boolean newValue) {
1437 return U.compareAndSetBoolean(this, ON_WAITING_LIST, expectedValue, newValue);
1438 }
1439
1440 private void setParkPermit(boolean newValue) {
1441 if (parkPermit != newValue) {
1442 parkPermit = newValue;
1443 }
1444 }
1445
1446 private boolean getAndSetParkPermit(boolean newValue) {
1447 if (parkPermit != newValue) {
1448 return U.getAndSetBoolean(this, PARK_PERMIT, newValue);
1449 } else {
1450 return newValue;
1451 }
1452 }
1453
1454 private void setCarrierThread(Thread carrier) {
1455 // U.putReferenceRelease(this, CARRIER_THREAD, carrier);
1456 this.carrierThread = carrier;
1457 }
1458
1459 // The following four methods notify the VM when a "transition" starts and ends.
1460 // A "mount transition" embodies the steps to transfer control from a platform
1461 // thread to a virtual thread, changing the thread identity, and starting or
1462 // resuming the virtual thread's continuation on the carrier.
1463 // An "unmount transition" embodies the steps to transfer control from a virtual
1464 // thread to its carrier, suspending the virtual thread's continuation, and
1465 // restoring the thread identity to the platform thread.
1466 // The notifications to the VM are necessary in order to coordinate with functions
1467 // (JVMTI mostly) that disable transitions for one or all virtual threads. Starting
1468 // a transition may block if transitions are disabled. Ending a transition may
1469 // notify a thread that is waiting to disable transitions. The notifications are
1470 // also used to post JVMTI events for virtual thread start and end.
1471
1472 @IntrinsicCandidate
1473 @JvmtiMountTransition
1474 private native void endFirstTransition();
1475
1476 @IntrinsicCandidate
1477 @JvmtiMountTransition
1478 private native void startFinalTransition();
1479
1480 @IntrinsicCandidate
1481 @JvmtiMountTransition
1482 private native void startTransition(boolean mount);
1483
1484 @IntrinsicCandidate
1485 @JvmtiMountTransition
1486 private native void endTransition(boolean mount);
1487
1488 @IntrinsicCandidate
1489 private static native void notifyJvmtiDisableSuspend(boolean enter);
1490
1491 private static native void registerNatives();
1492 static {
1493 registerNatives();
1494
1495 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1496 var group = Thread.virtualThreadGroup();
1497
1498 // ensure event class is initialized
1499 try {
1500 MethodHandles.lookup().ensureInitialized(VirtualThreadParkEvent.class);
1501 } catch (IllegalAccessException e) {
1502 throw new ExceptionInInitializerError(e);
1503 }
1504 }
1505
1506 /**
1507 * Loads a VirtualThreadScheduler with the given class name. The class must be public
1508 * in an exported package, with public one-arg or no-arg constructor, and be visible
1509 * to the system class loader.
1510 * @param delegate the scheduler that the custom scheduler may delegate to
1511 * @param cn the class name of the custom scheduler
1512 */
1513 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
1514 VirtualThreadScheduler scheduler;
1515 try {
1516 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1517 // 1-arg constructor
1518 try {
1519 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1520 return (VirtualThreadScheduler) ctor.newInstance(delegate);
1521 } catch (NoSuchMethodException e) {
1522 // 0-arg constructor
1523 Constructor<?> ctor = clazz.getConstructor();
1524 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1525 }
1526 } catch (Exception ex) {
1527 throw new Error(ex);
1528 }
1529 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!");
1530 return scheduler;
1531 }
1532
1533 /**
1534 * Creates the built-in ForkJoinPool scheduler.
1535 * @param wrapped true if wrapped by a custom default scheduler
1536 */
1537 private static BuiltinScheduler createBuiltinScheduler(boolean wrapped) {
1538 int parallelism, maxPoolSize, minRunnable;
1539 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1540 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1541 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1542 if (parallelismValue != null) {
1543 parallelism = Integer.parseInt(parallelismValue);
1544 } else {
1545 parallelism = Runtime.getRuntime().availableProcessors();
1546 }
1547 if (maxPoolSizeValue != null) {
1548 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1549 parallelism = Integer.min(parallelism, maxPoolSize);
1550 } else {
1551 maxPoolSize = Integer.max(parallelism, 256);
1552 }
1553 if (minRunnableValue != null) {
1554 minRunnable = Integer.parseInt(minRunnableValue);
1555 } else {
1556 minRunnable = Integer.max(parallelism / 2, 1);
1557 }
1558 return new BuiltinScheduler(parallelism, maxPoolSize, minRunnable, wrapped);
1559 }
1560
1561 /**
1562 * The built-in ForkJoinPool scheduler.
1563 */
1564 private static class BuiltinScheduler
1565 extends ForkJoinPool implements VirtualThreadScheduler {
1566
1567 BuiltinScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) {
1568 ForkJoinWorkerThreadFactory factory = wrapped
1569 ? ForkJoinPool.defaultForkJoinWorkerThreadFactory
1570 : CarrierThread::new;
1571 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1572 boolean asyncMode = true; // FIFO
1573 super(parallelism, factory, handler, asyncMode,
1574 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1575 }
1576
1577 private void adaptAndExecute(Runnable task) {
1578 execute(ForkJoinTask.adapt(task));
1579 }
1580
1581 @Override
1582 public void onStart(VirtualThreadTask task) {
1583 adaptAndExecute(task);
1584 }
1585
1586 @Override
1587 public void onContinue(VirtualThreadTask task) {
1588 adaptAndExecute(task);
1589 }
1590
1591 @Override
1592 public ScheduledFuture<?> schedule(Runnable task, long delay, TimeUnit unit) {
1593 return super.schedule(task, delay, unit);
1594 }
1595
1596 /**
1597 * Wraps the scheduler to avoid leaking a direct reference with
1598 * {@link VirtualThreadScheduler#current()}.
1599 */
1600 VirtualThreadScheduler createExternalView() {
1601 BuiltinScheduler builtin = this;
1602 return new VirtualThreadScheduler() {
1603 private void execute(VirtualThreadTask task) {
1604 var vthread = (VirtualThread) task.thread();
1605 VirtualThreadScheduler scheduler = vthread.scheduler;
1606 if (scheduler == this || scheduler == DEFAULT_SCHEDULER) {
1607 builtin.adaptAndExecute(task);
1608 } else {
1609 throw new IllegalArgumentException();
1610 }
1611 }
1612 @Override
1613 public void onStart(VirtualThreadTask task) {
1614 execute(task);
1615 }
1616 @Override
1617 public void onContinue(VirtualThreadTask task) {
1618 execute(task);
1619 }
1620 @Override
1621 public String toString() {
1622 return builtin.toString();
1623 }
1624 };
1625 }
1626 }
1627
1628 /**
1629 * Schedule a runnable task to run after a delay.
1630 */
1631 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1632 return scheduler.schedule(command, delay, unit);
1633 }
1634
1635 /**
1636 * Supports scheduling a runnable task to run after a delay. It uses a number
1637 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1638 * work queue used. This class is used when using a custom scheduler.
1639 */
1640 static class DelayedTaskSchedulers {
1641 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1642
1643 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1644 long tid = Thread.currentThread().threadId();
1645 int index = (int) tid & (INSTANCE.length - 1);
1646 return INSTANCE[index].schedule(command, delay, unit);
1647 }
1648
1649 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1650 String propName = "jdk.virtualThreadScheduler.timerQueues";
1651 String propValue = System.getProperty(propName);
1652 int queueCount;
1653 if (propValue != null) {
1654 queueCount = Integer.parseInt(propValue);
1655 if (queueCount != Integer.highestOneBit(queueCount)) {
1656 throw new RuntimeException("Value of " + propName + " must be power of 2");
1657 }
1658 } else {
1659 int ncpus = Runtime.getRuntime().availableProcessors();
1660 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
1661 }
1662 var schedulers = new ScheduledExecutorService[queueCount];
1663 for (int i = 0; i < queueCount; i++) {
1664 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
1665 Executors.newScheduledThreadPool(1, task -> {
1666 Thread t = InnocuousThread.newThread("VirtualThread-unparker", task);
1667 t.setDaemon(true);
1668 return t;
1669 });
1670 stpe.setRemoveOnCancelPolicy(true);
1671 schedulers[i] = stpe;
1672 }
1673 return schedulers;
1674 }
1675 }
1676
1677 /**
1678 * Schedule virtual threads that are ready to be scheduled after they blocked on
1679 * monitor enter.
1680 */
1681 private static void unblockVirtualThreads() {
1682 while (true) {
1683 VirtualThread vthread = takeVirtualThreadListToUnblock();
1684 while (vthread != null) {
1685 assert vthread.onWaitingList;
1686 VirtualThread nextThread = vthread.next;
1687
1688 // remove from list and unblock
1689 vthread.next = null;
1690 boolean changed = vthread.compareAndSetOnWaitingList(true, false);
1691 assert changed;
1692 vthread.unblock();
1693
1694 vthread = nextThread;
1695 }
1696 }
1697 }
1698
1699 /**
1700 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting
1701 * if necessary until a list of one or more threads becomes available.
1702 */
1703 private static native VirtualThread takeVirtualThreadListToUnblock();
1704
1705 static {
1706 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker",
1707 VirtualThread::unblockVirtualThreads);
1708 unblocker.setDaemon(true);
1709 unblocker.start();
1710 }
1711 }