1 /*
2 * Copyright (c) 2018, 2024, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25 package java.lang;
26
27 import java.lang.reflect.Constructor;
28 import java.security.AccessController;
29 import java.security.PrivilegedAction;
30 import java.util.Arrays;
31 import java.util.Locale;
32 import java.util.Objects;
33 import java.util.concurrent.Callable;
34 import java.util.concurrent.CountDownLatch;
35 import java.util.concurrent.Executor;
36 import java.util.concurrent.Executors;
37 import java.util.concurrent.ForkJoinPool;
38 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
39 import java.util.concurrent.ForkJoinTask;
40 import java.util.concurrent.ForkJoinWorkerThread;
41 import java.util.concurrent.Future;
42 import java.util.concurrent.RejectedExecutionException;
43 import java.util.concurrent.ScheduledExecutorService;
44 import java.util.concurrent.ScheduledThreadPoolExecutor;
45 import java.util.concurrent.TimeUnit;
46 import java.util.stream.Stream;
47 import jdk.internal.event.VirtualThreadEndEvent;
48 import jdk.internal.event.VirtualThreadStartEvent;
49 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
50 import jdk.internal.misc.CarrierThread;
51 import jdk.internal.misc.InnocuousThread;
52 import jdk.internal.misc.Unsafe;
53 import jdk.internal.vm.Continuation;
54 import jdk.internal.vm.ContinuationScope;
55 import jdk.internal.vm.StackableScope;
56 import jdk.internal.vm.ThreadContainer;
57 import jdk.internal.vm.ThreadContainers;
58 import jdk.internal.vm.annotation.ChangesCurrentThread;
59 import jdk.internal.vm.annotation.Hidden;
60 import jdk.internal.vm.annotation.IntrinsicCandidate;
61 import jdk.internal.vm.annotation.JvmtiMountTransition;
62 import jdk.internal.vm.annotation.ReservedStackAccess;
63 import sun.nio.ch.Interruptible;
64 import sun.security.action.GetPropertyAction;
65 import static java.util.concurrent.TimeUnit.*;
66
67 /**
68 * A thread that is scheduled by the Java virtual machine rather than the operating system.
69 */
70 final class VirtualThread extends BaseVirtualThread {
71 private static final Unsafe U = Unsafe.getUnsafe();
72 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
73 private static final Executor DEFAULT_SCHEDULER = createDefaultScheduler();
74 private static final ScheduledExecutorService[] DELAYED_TASK_SCHEDULERS = createDelayedTaskSchedulers();
75
76 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
77 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
78 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
79 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
80 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
81
82 // scheduler and continuation
83 private final Executor scheduler;
84 private final Continuation cont;
85 private final Runnable runContinuation;
86
87 // virtual thread state, accessed by VM
88 private volatile int state;
89
90 /*
91 * Virtual thread state transitions:
92 *
93 * NEW -> STARTED // Thread.start, schedule to run
94 * STARTED -> TERMINATED // failed to start
95 * STARTED -> RUNNING // first run
96 * RUNNING -> TERMINATED // done
97 *
98 * RUNNING -> PARKING // Thread parking with LockSupport.park
99 * PARKING -> PARKED // cont.yield successful, parked indefinitely
100 * PARKING -> PINNED // cont.yield failed, parked indefinitely on carrier
101 * PARKED -> UNPARKED // unparked, may be scheduled to continue
102 * PINNED -> RUNNING // unparked, continue execution on same carrier
103 * UNPARKED -> RUNNING // continue execution after park
104 *
105 * RUNNING -> TIMED_PARKING // Thread parking with LockSupport.parkNanos
106 * TIMED_PARKING -> TIMED_PARKED // cont.yield successful, timed-parked
107 * TIMED_PARKING -> TIMED_PINNED // cont.yield failed, timed-parked on carrier
108 * TIMED_PARKED -> UNPARKED // unparked, may be scheduled to continue
109 * TIMED_PINNED -> RUNNING // unparked, continue execution on same carrier
110 *
111 * RUNNING -> BLOCKING // blocking on monitor enter
112 * BLOCKING -> BLOCKED // blocked on monitor enter
113 * BLOCKED -> UNBLOCKED // unblocked, may be scheduled to continue
114 * UNBLOCKED -> RUNNING // continue execution after blocked on monitor enter
115 *
116 * RUNNING -> WAITING // transitional state during wait on monitor
117 * WAITING -> WAITED // waiting on monitor
118 * WAITED -> BLOCKED // notified, waiting to be unblocked by monitor owner
119 * WAITED -> UNBLOCKED // timed-out/interrupted
120 *
121 * RUNNING -> TIMED_WAITING // transition state during timed-waiting on monitor
122 * TIMED_WAITING -> TIMED_WAITED // timed-waiting on monitor
123 * TIMED_WAITED -> BLOCKED // notified, waiting to be unblocked by monitor owner
124 * TIMED_WAITED -> UNBLOCKED // timed-out/interrupted
125 *
126 * RUNNING -> YIELDING // Thread.yield
127 * YIELDING -> YIELDED // cont.yield successful, may be scheduled to continue
128 * YIELDING -> RUNNING // cont.yield failed
129 * YIELDED -> RUNNING // continue execution after Thread.yield
130 */
131 private static final int NEW = 0;
132 private static final int STARTED = 1;
133 private static final int RUNNING = 2; // runnable-mounted
134
135 // untimed and timed parking
136 private static final int PARKING = 3;
137 private static final int PARKED = 4; // unmounted
138 private static final int PINNED = 5; // mounted
139 private static final int TIMED_PARKING = 6;
140 private static final int TIMED_PARKED = 7; // unmounted
141 private static final int TIMED_PINNED = 8; // mounted
142 private static final int UNPARKED = 9; // unmounted but runnable
143
144 // Thread.yield
145 private static final int YIELDING = 10;
146 private static final int YIELDED = 11; // unmounted but runnable
147
148 // monitor enter
149 private static final int BLOCKING = 12;
150 private static final int BLOCKED = 13; // unmounted
151 private static final int UNBLOCKED = 14; // unmounted but runnable
152
153 // monitor wait/timed-wait
154 private static final int WAITING = 15;
155 private static final int WAIT = 16; // waiting in Object.wait
156 private static final int TIMED_WAITING = 17;
157 private static final int TIMED_WAIT = 18; // waiting in timed-Object.wait
158
159 private static final int TERMINATED = 99; // final state
160
161 // can be suspended from scheduling when unmounted
162 private static final int SUSPENDED = 1 << 8;
163
164 // parking permit
165 private volatile boolean parkPermit;
166
167 // used to mark thread as ready to be unblocked
168 private volatile boolean unblocked;
169
170 // notified by Object.notify/notifyAll while waiting in Object.wait
171 private volatile boolean notified;
172
173 // timed-wait support
174 private long waitTimeout;
175 private byte timedWaitNonce;
176 private volatile Future<?> waitTimeoutTask;
177
178 // a positive value if "responsible thread" blocked on monitor enter, accessed by VM
179 private volatile byte recheckInterval;
180
181 // carrier thread when mounted, accessed by VM
182 private volatile Thread carrierThread;
183
184 // termination object when joining, created lazily if needed
185 private volatile CountDownLatch termination;
186
187 // has the value 1 when on the list of virtual threads waiting to be unblocked
188 private volatile byte onWaitingList;
189
190 // next virtual thread on the list of virtual threads waiting to be unblocked
191 private volatile VirtualThread next;
192
193 /**
194 * Returns the default scheduler.
195 */
196 static Executor defaultScheduler() {
197 return DEFAULT_SCHEDULER;
198 }
199
200 /**
201 * Returns a stream of the delayed task schedulers used to support timed operations.
202 */
203 static Stream<ScheduledExecutorService> delayedTaskSchedulers() {
204 return Arrays.stream(DELAYED_TASK_SCHEDULERS);
205 }
206
207 /**
208 * Returns the continuation scope used for virtual threads.
209 */
210 static ContinuationScope continuationScope() {
211 return VTHREAD_SCOPE;
212 }
213
214 /**
215 * Creates a new {@code VirtualThread} to run the given task with the given
216 * scheduler. If the given scheduler is {@code null} and the current thread
217 * is a platform thread then the newly created virtual thread will use the
218 * default scheduler. If given scheduler is {@code null} and the current
219 * thread is a virtual thread then the current thread's scheduler is used.
220 *
221 * @param scheduler the scheduler or null
222 * @param name thread name
223 * @param characteristics characteristics
224 * @param task the task to execute
225 */
226 VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
227 super(name, characteristics, /*bound*/ false);
228 Objects.requireNonNull(task);
229
230 // choose scheduler if not specified
231 if (scheduler == null) {
232 Thread parent = Thread.currentThread();
233 if (parent instanceof VirtualThread vparent) {
234 scheduler = vparent.scheduler;
235 } else {
236 scheduler = DEFAULT_SCHEDULER;
237 }
238 }
239
240 this.scheduler = scheduler;
241 this.cont = new VThreadContinuation(this, task);
242 this.runContinuation = this::runContinuation;
243 }
244
245 /**
246 * The continuation that a virtual thread executes.
247 */
248 private static class VThreadContinuation extends Continuation {
249 VThreadContinuation(VirtualThread vthread, Runnable task) {
250 super(VTHREAD_SCOPE, wrap(vthread, task));
251 }
252 @Override
253 protected void onPinned(Continuation.Pinned reason) {
254 // emit JFR event
255 virtualThreadPinnedEvent(reason.reasonCode(), reason.reasonString());
256 }
257 private static Runnable wrap(VirtualThread vthread, Runnable task) {
258 return new Runnable() {
259 @Hidden
260 public void run() {
261 vthread.run(task);
262 }
263 };
264 }
265 }
266
267 /**
268 * jdk.VirtualThreadPinned is emitted by HotSpot VM when pinned. Call into VM to
269 * emit event to avoid having a JFR event in Java with the same name (but different ID)
270 * to events emitted by the VM.
271 */
272 private static native void virtualThreadPinnedEvent(int reason, String reasonString);
273
274 /**
275 * Runs or continues execution on the current thread. The virtual thread is mounted
276 * on the current thread before the task runs or continues. It unmounts when the
277 * task completes or yields.
278 */
279 @ChangesCurrentThread // allow mount/unmount to be inlined
280 private void runContinuation() {
281 // the carrier must be a platform thread
282 if (Thread.currentThread().isVirtual()) {
283 throw new WrongThreadException();
284 }
285
286 // set state to RUNNING
287 int initialState = state();
288 if (initialState == STARTED || initialState == UNPARKED
289 || initialState == UNBLOCKED || initialState == YIELDED) {
290 // newly started or continue after parking/blocking/Thread.yield
291 if (!compareAndSetState(initialState, RUNNING)) {
292 return;
293 }
294 // consume parking permit when continuing after parking
295 if (initialState == UNPARKED) {
296 setParkPermit(false);
297 }
298 } else {
299 // not runnable
300 return;
301 }
302
303 mount();
304 try {
305 cont.run();
306 } finally {
307 unmount();
308 if (cont.isDone()) {
309 afterDone();
310 } else {
311 afterYield();
312 }
313 }
314 }
315
316 /**
317 * Submits the runContinuation task to the scheduler. For the default scheduler,
318 * and calling it on a worker thread, the task will be pushed to the local queue,
319 * otherwise it will be pushed to an external submission queue.
320 * @param scheduler the scheduler
321 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
322 * @throws RejectedExecutionException
323 */
324 @ChangesCurrentThread
325 private void submitRunContinuation(Executor scheduler, boolean retryOnOOME) {
326 boolean done = false;
327 while (!done) {
328 try {
329 // The scheduler's execute method is invoked in the context of the
330 // carrier thread. For the default scheduler this ensures that the
331 // current thread is a ForkJoinWorkerThread so the task will be pushed
332 // to the local queue. For other schedulers, it avoids deadlock that
333 // would arise due to platform and virtual threads contending for a
334 // lock on the scheduler's submission queue.
335 if (currentThread() instanceof VirtualThread vthread) {
336 vthread.switchToCarrierThread();
337 try {
338 scheduler.execute(runContinuation);
339 } finally {
340 switchToVirtualThread(vthread);
341 }
342 } else {
343 scheduler.execute(runContinuation);
344 }
345 done = true;
346 } catch (RejectedExecutionException ree) {
347 submitFailed(ree);
348 throw ree;
349 } catch (OutOfMemoryError e) {
350 if (retryOnOOME) {
351 U.park(false, 100_000_000); // 100ms
352 } else {
353 throw e;
354 }
355 }
356 }
357 }
358
359 /**
360 * Submits the runContinuation task to given scheduler with a lazy submit.
361 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
362 * @throws RejectedExecutionException
363 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
364 */
365 private void lazySubmitRunContinuation(ForkJoinPool pool) {
366 assert Thread.currentThread() instanceof CarrierThread;
367 try {
368 pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
369 } catch (RejectedExecutionException ree) {
370 submitFailed(ree);
371 throw ree;
372 } catch (OutOfMemoryError e) {
373 submitRunContinuation(pool, true);
374 }
375 }
376
377 /**
378 * Submits the runContinuation task to the given scheduler as an external submit.
379 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
380 * @throws RejectedExecutionException
381 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
382 */
383 private void externalSubmitRunContinuation(ForkJoinPool pool) {
384 assert Thread.currentThread() instanceof CarrierThread;
385 try {
386 pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
387 } catch (RejectedExecutionException ree) {
388 submitFailed(ree);
389 throw ree;
390 } catch (OutOfMemoryError e) {
391 submitRunContinuation(pool, true);
392 }
393 }
394
395 /**
396 * Submits the runContinuation task to the scheduler. For the default scheduler,
397 * and calling it on a worker thread, the task will be pushed to the local queue,
398 * otherwise it will be pushed to an external submission queue.
399 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
400 * @throws RejectedExecutionException
401 */
402 private void submitRunContinuation() {
403 submitRunContinuation(scheduler, true);
404 }
405
406 /**
407 * Submits the runContinuation task to the scheduler. For the default scheduler, and
408 * calling it a virtual thread that uses the default scheduler, the task will be
409 * pushed to an external submission queue. This method may throw OutOfMemoryError.
410 * @throws RejectedExecutionException
411 * @throws OutOfMemoryError
412 */
413 private void externalSubmitRunContinuationOrThrow() {
414 if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
415 try {
416 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
417 } catch (RejectedExecutionException ree) {
418 submitFailed(ree);
419 throw ree;
420 }
421 } else {
422 submitRunContinuation(scheduler, false);
423 }
424 }
425
426 /**
427 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
428 */
429 private void submitFailed(RejectedExecutionException ree) {
430 var event = new VirtualThreadSubmitFailedEvent();
431 if (event.isEnabled()) {
432 event.javaThreadId = threadId();
433 event.exceptionMessage = ree.getMessage();
434 event.commit();
435 }
436 }
437
438 /**
439 * Runs a task in the context of this virtual thread.
440 */
441 private void run(Runnable task) {
442 assert Thread.currentThread() == this && state == RUNNING;
443
444 // notify JVMTI, may post VirtualThreadStart event
445 notifyJvmtiStart();
446
447 // emit JFR event if enabled
448 if (VirtualThreadStartEvent.isTurnedOn()) {
449 var event = new VirtualThreadStartEvent();
450 event.javaThreadId = threadId();
451 event.commit();
452 }
453
454 Object bindings = Thread.scopedValueBindings();
455 try {
456 runWith(bindings, task);
457 } catch (Throwable exc) {
458 dispatchUncaughtException(exc);
459 } finally {
460 try {
461 // pop any remaining scopes from the stack, this may block
462 StackableScope.popAll();
463
464 // emit JFR event if enabled
465 if (VirtualThreadEndEvent.isTurnedOn()) {
466 var event = new VirtualThreadEndEvent();
467 event.javaThreadId = threadId();
468 event.commit();
469 }
470
471 } finally {
472 // notify JVMTI, may post VirtualThreadEnd event
473 notifyJvmtiEnd();
474 }
475 }
476 }
477
478 /**
479 * Mounts this virtual thread onto the current platform thread. On
480 * return, the current thread is the virtual thread.
481 */
482 @ChangesCurrentThread
483 @ReservedStackAccess
484 private void mount() {
485 // notify JVMTI before mount
486 notifyJvmtiMount(/*hide*/true);
487
488 // sets the carrier thread
489 Thread carrier = Thread.currentCarrierThread();
490 setCarrierThread(carrier);
491
492 // sync up carrier thread interrupt status if needed
493 if (interrupted) {
494 carrier.setInterrupt();
495 } else if (carrier.isInterrupted()) {
496 synchronized (interruptLock) {
497 // need to recheck interrupt status
498 if (!interrupted) {
499 carrier.clearInterrupt();
500 }
501 }
502 }
503
504 // set Thread.currentThread() to return this virtual thread
505 carrier.setCurrentThread(this);
506 }
507
508 /**
509 * Unmounts this virtual thread from the carrier. On return, the
510 * current thread is the current platform thread.
511 */
512 @ChangesCurrentThread
513 @ReservedStackAccess
514 private void unmount() {
515 assert !Thread.holdsLock(interruptLock);
516
517 // set Thread.currentThread() to return the platform thread
518 Thread carrier = this.carrierThread;
519 carrier.setCurrentThread(carrier);
520
521 // break connection to carrier thread, synchronized with interrupt
522 synchronized (interruptLock) {
523 setCarrierThread(null);
524 }
525 carrier.clearInterrupt();
526
527 // notify JVMTI after unmount
528 notifyJvmtiUnmount(/*hide*/false);
529 }
530
531 /**
532 * Sets the current thread to the current carrier thread.
533 */
534 @ChangesCurrentThread
535 @JvmtiMountTransition
536 private void switchToCarrierThread() {
537 notifyJvmtiHideFrames(true);
538 Thread carrier = this.carrierThread;
539 assert Thread.currentThread() == this
540 && carrier == Thread.currentCarrierThread();
541 carrier.setCurrentThread(carrier);
542 setLockId(this.threadId()); // keep lockid of vthread
543 }
544
545 /**
546 * Sets the current thread to the given virtual thread.
547 */
548 @ChangesCurrentThread
549 @JvmtiMountTransition
550 private static void switchToVirtualThread(VirtualThread vthread) {
551 Thread carrier = vthread.carrierThread;
552 assert carrier == Thread.currentCarrierThread();
553 carrier.setCurrentThread(vthread);
554 notifyJvmtiHideFrames(false);
555 }
556
557 /**
558 * Executes the given value returning task on the current carrier thread.
559 */
560 @ChangesCurrentThread
561 <V> V executeOnCarrierThread(Callable<V> task) throws Exception {
562 assert Thread.currentThread() == this;
563 switchToCarrierThread();
564 try {
565 return task.call();
566 } finally {
567 switchToVirtualThread(this);
568 }
569 }
570
571 /**
572 * Invokes Continuation.yield, notifying JVMTI (if enabled) to hide frames until
573 * the continuation continues.
574 */
575 @Hidden
576 private boolean yieldContinuation() {
577 notifyJvmtiUnmount(/*hide*/true);
578 try {
579 return Continuation.yield(VTHREAD_SCOPE);
580 } finally {
581 notifyJvmtiMount(/*hide*/false);
582 }
583 }
584
585 /**
586 * Invoked after the continuation yields. If parking then it sets the state
587 * and also re-submits the task to continue if unparked while parking.
588 * If yielding due to Thread.yield then it just submits the task to continue.
589 */
590 private void afterYield() {
591 assert carrierThread == null;
592
593 // re-adjust parallelism if the virtual thread yielded when compensating
594 if (currentThread() instanceof CarrierThread ct) {
595 ct.endBlocking();
596 }
597
598 int s = state();
599
600 // LockSupport.park/parkNanos
601 if (s == PARKING || s == TIMED_PARKING) {
602 int newState = (s == PARKING) ? PARKED : TIMED_PARKED;
603 setState(newState);
604
605 // may have been unparked while parking
606 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
607 // lazy submit to continue on the current carrier if possible
608 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
609 lazySubmitRunContinuation(ct.getPool());
610 } else {
611 submitRunContinuation();
612 }
613 }
614 return;
615 }
616
617 // Thread.yield
618 if (s == YIELDING) {
619 setState(YIELDED);
620
621 // external submit if there are no tasks in the local task queue
622 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
623 externalSubmitRunContinuation(ct.getPool());
624 } else {
625 submitRunContinuation();
626 }
627 return;
628 }
629
630 // blocking on monitorenter
631 if (s == BLOCKING) {
632 setState(BLOCKED);
633
634 // may have been unblocked while blocking
635 if (unblocked && compareAndSetState(BLOCKED, UNBLOCKED)) {
636 unblocked = false;
637 submitRunContinuation();
638 return;
639 }
640
641 // if thread is the designated responsible thread for a monitor then schedule
642 // it to wakeup so that it can check and recover. See objectMonitor.cpp.
643 int recheckInterval = this.recheckInterval;
644 if (recheckInterval > 0) {
645 assert recheckInterval >= 1 && recheckInterval <= 6;
646 // 4 ^ (recheckInterval - 1) = 1, 4, 16, ... 1024
647 long delay = 1 << (recheckInterval - 1) << (recheckInterval - 1);
648 schedule(this::unblock, delay, MILLISECONDS);
649 }
650 return;
651 }
652
653 // Object.wait
654 if (s == WAITING || s == TIMED_WAITING) {
655 byte nonce;
656 int newState;
657 if (s == WAITING) {
658 nonce = 0; // not used
659 setState(newState = WAIT);
660 } else {
661 // synchronize with timeout task (previous timed-wait may be running)
662 synchronized (timedWaitLock()) {
663 nonce = ++timedWaitNonce;
664 setState(newState = TIMED_WAIT);
665 }
666 }
667
668 // may have been notified while in transition to wait state
669 if (notified && compareAndSetState(newState, BLOCKED)) {
670 // may have even been unblocked already
671 if (unblocked && compareAndSetState(BLOCKED, UNBLOCKED)) {
672 unblocked = false;
673 submitRunContinuation();
674 }
675 return;
676 }
677
678 // may have been interrupted while in transition to wait state
679 if (interrupted && compareAndSetState(newState, UNBLOCKED)) {
680 submitRunContinuation();
681 return;
682 }
683
684 // schedule wakeup
685 if (newState == TIMED_WAIT) {
686 assert waitTimeout > 0;
687 waitTimeoutTask = schedule(() -> waitTimeoutExpired(nonce), waitTimeout, MILLISECONDS);
688 }
689 return;
690 }
691
692 assert false;
693 }
694
695 /**
696 * Invoked after the continuation completes.
697 */
698 private void afterDone() {
699 afterDone(true);
700 }
701
702 /**
703 * Invoked after the continuation completes (or start failed). Sets the thread
704 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
705 *
706 * @param notifyContainer true if its container should be notified
707 */
708 private void afterDone(boolean notifyContainer) {
709 assert carrierThread == null;
710 setState(TERMINATED);
711
712 // notify anyone waiting for this virtual thread to terminate
713 CountDownLatch termination = this.termination;
714 if (termination != null) {
715 assert termination.getCount() == 1;
716 termination.countDown();
717 }
718
719 // notify container
720 if (notifyContainer) {
721 threadContainer().onExit(this);
722 }
723
724 // clear references to thread locals
725 clearReferences();
726 }
727
728 /**
729 * Schedules this {@code VirtualThread} to execute.
730 *
731 * @throws IllegalStateException if the container is shutdown or closed
732 * @throws IllegalThreadStateException if the thread has already been started
733 * @throws RejectedExecutionException if the scheduler cannot accept a task
734 */
735 @Override
736 void start(ThreadContainer container) {
737 if (!compareAndSetState(NEW, STARTED)) {
738 throw new IllegalThreadStateException("Already started");
739 }
740
741 // bind thread to container
742 assert threadContainer() == null;
743 setThreadContainer(container);
744
745 // start thread
746 boolean addedToContainer = false;
747 boolean started = false;
748 try {
749 container.onStart(this); // may throw
750 addedToContainer = true;
751
752 // scoped values may be inherited
753 inheritScopedValueBindings(container);
754
755 // submit task to run thread, using externalSubmit if possible
756 externalSubmitRunContinuationOrThrow();
757 started = true;
758 } finally {
759 if (!started) {
760 afterDone(addedToContainer);
761 }
762 }
763 }
764
765 @Override
766 public void start() {
767 start(ThreadContainers.root());
768 }
769
770 @Override
771 public void run() {
772 // do nothing
773 }
774
775 /**
776 * Parks until unparked or interrupted. If already unparked then the parking
777 * permit is consumed and this method completes immediately (meaning it doesn't
778 * yield). It also completes immediately if the interrupt status is set.
779 */
780 @Override
781 void park() {
782 assert Thread.currentThread() == this;
783
784 // complete immediately if parking permit available or interrupted
785 if (getAndSetParkPermit(false) || interrupted)
786 return;
787
788 // park the thread
789 boolean yielded = false;
790 setState(PARKING);
791 try {
792 yielded = yieldContinuation(); // may throw
793 } finally {
794 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
795 if (!yielded) {
796 assert state() == PARKING;
797 setState(RUNNING);
798 }
799 }
800
801 // park on the carrier thread when pinned
802 if (!yielded) {
803 parkOnCarrierThread(false, 0);
804 }
805 }
806
807 /**
808 * Parks up to the given waiting time or until unparked or interrupted.
809 * If already unparked then the parking permit is consumed and this method
810 * completes immediately (meaning it doesn't yield). It also completes immediately
811 * if the interrupt status is set or the waiting time is {@code <= 0}.
812 *
813 * @param nanos the maximum number of nanoseconds to wait.
814 */
815 @Override
816 void parkNanos(long nanos) {
817 assert Thread.currentThread() == this;
818
819 // complete immediately if parking permit available or interrupted
820 if (getAndSetParkPermit(false) || interrupted)
821 return;
822
823 // park the thread for the waiting time
824 if (nanos > 0) {
825 long startTime = System.nanoTime();
826
827 boolean yielded = false;
828 Future<?> unparker = scheduleUnpark(nanos); // may throw OOME
829 setState(TIMED_PARKING);
830 try {
831 yielded = yieldContinuation(); // may throw
832 } finally {
833 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
834 if (!yielded) {
835 assert state() == TIMED_PARKING;
836 setState(RUNNING);
837 }
838 cancel(unparker);
839 }
840
841 // park on carrier thread for remaining time when pinned
842 if (!yielded) {
843 long remainingNanos = nanos - (System.nanoTime() - startTime);
844 parkOnCarrierThread(true, remainingNanos);
845 }
846 }
847 }
848
849 /**
850 * Parks the current carrier thread up to the given waiting time or until
851 * unparked or interrupted. If the virtual thread is interrupted then the
852 * interrupt status will be propagated to the carrier thread.
853 * @param timed true for a timed park, false for untimed
854 * @param nanos the waiting time in nanoseconds
855 */
856 private void parkOnCarrierThread(boolean timed, long nanos) {
857 assert state() == RUNNING;
858
859 setState(timed ? TIMED_PINNED : PINNED);
860 try {
861 if (!parkPermit) {
862 if (!timed) {
863 U.park(false, 0);
864 } else if (nanos > 0) {
865 U.park(false, nanos);
866 }
867 }
868 } finally {
869 setState(RUNNING);
870 }
871
872 // consume parking permit
873 setParkPermit(false);
874 }
875
876 /**
877 * Invoked by parkNanos to schedule this virtual thread to be unparked after
878 * a given delay.
879 */
880 @ChangesCurrentThread
881 private Future<?> scheduleUnpark(long nanos) {
882 assert Thread.currentThread() == this;
883 // need to switch to current carrier thread to avoid nested parking
884 switchToCarrierThread();
885 try {
886 return schedule(this::unpark, nanos, NANOSECONDS);
887 } finally {
888 switchToVirtualThread(this);
889 }
890 }
891
892 /**
893 * Invoked by parkNanos to cancel the unpark timer.
894 */
895 @ChangesCurrentThread
896 private void cancel(Future<?> future) {
897 assert Thread.currentThread() == this;
898 if (!future.isDone()) {
899 // need to switch to current carrier thread to avoid nested parking
900 switchToCarrierThread();
901 try {
902 future.cancel(false);
903 } finally {
904 switchToVirtualThread(this);
905 }
906 }
907 }
908
909 /**
910 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
911 * then its task is scheduled to continue, otherwise its next call to {@code park} or
912 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
913 * @throws RejectedExecutionException if the scheduler cannot accept a task
914 */
915 @Override
916 void unpark() {
917 if (!getAndSetParkPermit(true) && currentThread() != this) {
918 int s = state();
919
920 // unparked while parked
921 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
922 submitRunContinuation();
923 return;
924 }
925
926 // unparked while parked when pinned
927 if (s == PINNED || s == TIMED_PINNED) {
928 // unpark carrier thread when pinned
929 disableSuspendAndPreempt();
930 try {
931 synchronized (carrierThreadAccessLock()) {
932 Thread carrier = carrierThread;
933 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
934 U.unpark(carrier);
935 }
936 }
937 } finally {
938 enableSuspendAndPreempt();
939 }
940 return;
941 }
942 }
943 }
944
945 /**
946 * Invoked by unblocker thread to unblock this virtual thread.
947 */
948 private void unblock() {
949 assert !Thread.currentThread().isVirtual();
950 unblocked = true;
951 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) {
952 unblocked = false;
953 submitRunContinuation();
954 }
955 }
956
957 /**
958 * Invoked by timer thread when wait timeout for virtual thread has expired.
959 * If the virtual thread is in timed-wait then this method will unblock the thread
960 * and submit its task so that it continues and attempts to reenter the monitor.
961 * This method does nothing if the thread has been woken by notify or interrupt.
962 */
963 private void waitTimeoutExpired(byte nounce) {
964 assert !Thread.currentThread().isVirtual();
965 for (;;) {
966 boolean unblocked = false;
967 synchronized (timedWaitLock()) {
968 if (nounce != timedWaitNonce) {
969 // this timeout task is for a past timed-wait
970 return;
971 }
972 int s = state();
973 if (s == TIMED_WAIT) {
974 unblocked = compareAndSetState(TIMED_WAIT, UNBLOCKED);
975 } else if (s != (TIMED_WAIT | SUSPENDED)) {
976 // notified or interrupted, no longer waiting
977 return;
978 }
979 }
980 if (unblocked) {
981 submitRunContinuation();
982 return;
983 }
984 // need to retry when thread is suspended in time-wait
985 Thread.yield();
986 }
987 }
988
989 /**
990 * Invoked by Object.wait to cancel the wait timer.
991 */
992 void cancelWaitTimeout() {
993 assert Thread.currentThread() == this;
994 Future<?> timeoutTask = this.waitTimeoutTask;
995 if (timeoutTask != null) {
996 // Pin the continuation to prevent the virtual thread from unmounting
997 // when there is contention removing the task. This avoids deadlock that
998 // could arise due to carriers and virtual threads contending for a
999 // lock on the delay queue.
1000 Continuation.pin();
1001 try {
1002 timeoutTask.cancel(false);
1003 } finally {
1004 Continuation.unpin();
1005 }
1006 }
1007 }
1008
1009 /**
1010 * Attempts to yield the current virtual thread (Thread.yield).
1011 */
1012 void tryYield() {
1013 assert Thread.currentThread() == this;
1014 setState(YIELDING);
1015 boolean yielded = false;
1016 try {
1017 yielded = yieldContinuation(); // may throw
1018 } finally {
1019 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
1020 if (!yielded) {
1021 assert state() == YIELDING;
1022 setState(RUNNING);
1023 }
1024 }
1025 }
1026
1027 /**
1028 * Sleep the current thread for the given sleep time (in nanoseconds). If
1029 * nanos is 0 then the thread will attempt to yield.
1030 *
1031 * @implNote This implementation parks the thread for the given sleeping time
1032 * and will therefore be observed in PARKED state during the sleep. Parking
1033 * will consume the parking permit so this method makes available the parking
1034 * permit after the sleep. This may be observed as a spurious, but benign,
1035 * wakeup when the thread subsequently attempts to park.
1036 *
1037 * @param nanos the maximum number of nanoseconds to sleep
1038 * @throws InterruptedException if interrupted while sleeping
1039 */
1040 void sleepNanos(long nanos) throws InterruptedException {
1041 assert Thread.currentThread() == this && nanos >= 0;
1042 if (getAndClearInterrupt())
1043 throw new InterruptedException();
1044 if (nanos == 0) {
1045 tryYield();
1046 } else {
1047 // park for the sleep time
1048 try {
1049 long remainingNanos = nanos;
1050 long startNanos = System.nanoTime();
1051 while (remainingNanos > 0) {
1052 parkNanos(remainingNanos);
1053 if (getAndClearInterrupt()) {
1054 throw new InterruptedException();
1055 }
1056 remainingNanos = nanos - (System.nanoTime() - startNanos);
1057 }
1058 } finally {
1059 // may have been unparked while sleeping
1060 setParkPermit(true);
1061 }
1062 }
1063 }
1064
1065 /**
1066 * Waits up to {@code nanos} nanoseconds for this virtual thread to terminate.
1067 * A timeout of {@code 0} means to wait forever.
1068 *
1069 * @throws InterruptedException if interrupted while waiting
1070 * @return true if the thread has terminated
1071 */
1072 boolean joinNanos(long nanos) throws InterruptedException {
1073 if (state() == TERMINATED)
1074 return true;
1075
1076 // ensure termination object exists, then re-check state
1077 CountDownLatch termination = getTermination();
1078 if (state() == TERMINATED)
1079 return true;
1080
1081 // wait for virtual thread to terminate
1082 if (nanos == 0) {
1083 termination.await();
1084 } else {
1085 boolean terminated = termination.await(nanos, NANOSECONDS);
1086 if (!terminated) {
1087 // waiting time elapsed
1088 return false;
1089 }
1090 }
1091 assert state() == TERMINATED;
1092 return true;
1093 }
1094
1095 @Override
1096 void blockedOn(Interruptible b) {
1097 disableSuspendAndPreempt();
1098 try {
1099 super.blockedOn(b);
1100 } finally {
1101 enableSuspendAndPreempt();
1102 }
1103 }
1104
1105 @Override
1106 @SuppressWarnings("removal")
1107 public void interrupt() {
1108 if (Thread.currentThread() != this) {
1109 checkAccess();
1110
1111 // if current thread is a virtual thread then prevent it from being
1112 // suspended or unmounted when entering or holding interruptLock
1113 Interruptible blocker;
1114 disableSuspendAndPreempt();
1115 try {
1116 synchronized (interruptLock) {
1117 interrupted = true;
1118 blocker = nioBlocker();
1119 if (blocker != null) {
1120 blocker.interrupt(this);
1121 }
1122
1123 // interrupt carrier thread if mounted
1124 Thread carrier = carrierThread;
1125 if (carrier != null) carrier.setInterrupt();
1126 }
1127 } finally {
1128 enableSuspendAndPreempt();
1129 }
1130
1131 // notify blocker after releasing interruptLock
1132 if (blocker != null) {
1133 blocker.postInterrupt();
1134 }
1135
1136 // make available parking permit, unpark thread if parked
1137 unpark();
1138
1139 // if thread is waiting in Object.wait then schedule to try to reenter
1140 int s = state();
1141 if ((s == WAIT || s == TIMED_WAIT) && compareAndSetState(s, UNBLOCKED)) {
1142 submitRunContinuation();
1143 }
1144
1145 } else {
1146 interrupted = true;
1147 carrierThread.setInterrupt();
1148 setParkPermit(true);
1149 }
1150 }
1151
1152 @Override
1153 public boolean isInterrupted() {
1154 return interrupted;
1155 }
1156
1157 @Override
1158 boolean getAndClearInterrupt() {
1159 assert Thread.currentThread() == this;
1160 boolean oldValue = interrupted;
1161 if (oldValue) {
1162 disableSuspendAndPreempt();
1163 try {
1164 synchronized (interruptLock) {
1165 interrupted = false;
1166 carrierThread.clearInterrupt();
1167 }
1168 } finally {
1169 enableSuspendAndPreempt();
1170 }
1171 }
1172 return oldValue;
1173 }
1174
1175 @Override
1176 Thread.State threadState() {
1177 int s = state();
1178 switch (s & ~SUSPENDED) {
1179 case NEW:
1180 return Thread.State.NEW;
1181 case STARTED:
1182 // return NEW if thread container not yet set
1183 if (threadContainer() == null) {
1184 return Thread.State.NEW;
1185 } else {
1186 return Thread.State.RUNNABLE;
1187 }
1188 case UNPARKED:
1189 case YIELDED:
1190 // runnable, not mounted
1191 return Thread.State.RUNNABLE;
1192 case UNBLOCKED:
1193 // if designated responsible thread for monitor then thread is blocked
1194 if (isResponsibleForMonitor()) {
1195 return Thread.State.BLOCKED;
1196 } else {
1197 return Thread.State.RUNNABLE;
1198 }
1199 case RUNNING:
1200 // if designated responsible thread for monitor then thread is blocked
1201 if (isResponsibleForMonitor()) {
1202 return Thread.State.BLOCKED;
1203 }
1204 // if mounted then return state of carrier thread
1205 if (Thread.currentThread() != this) {
1206 disableSuspendAndPreempt();
1207 try {
1208 synchronized (carrierThreadAccessLock()) {
1209 Thread carrierThread = this.carrierThread;
1210 if (carrierThread != null) {
1211 return carrierThread.threadState();
1212 }
1213 }
1214 } finally {
1215 enableSuspendAndPreempt();
1216 }
1217 }
1218 // runnable, mounted
1219 return Thread.State.RUNNABLE;
1220 case PARKING:
1221 case TIMED_PARKING:
1222 case YIELDING:
1223 case WAITING:
1224 case TIMED_WAITING:
1225 // runnable, in transition
1226 return Thread.State.RUNNABLE;
1227 case PARKED:
1228 case PINNED:
1229 case WAIT:
1230 return State.WAITING;
1231 case TIMED_PARKED:
1232 case TIMED_PINNED:
1233 case TIMED_WAIT:
1234 return State.TIMED_WAITING;
1235 case BLOCKING:
1236 case BLOCKED:
1237 return State.BLOCKED;
1238 case TERMINATED:
1239 return Thread.State.TERMINATED;
1240 default:
1241 throw new InternalError();
1242 }
1243 }
1244
1245 /**
1246 * Returns true if thread is the designated responsible thread for a monitor.
1247 * See objectMonitor.cpp for details.
1248 */
1249 private boolean isResponsibleForMonitor() {
1250 return (recheckInterval > 0);
1251 }
1252
1253 @Override
1254 boolean alive() {
1255 int s = state;
1256 return (s != NEW && s != TERMINATED);
1257 }
1258
1259 @Override
1260 boolean isTerminated() {
1261 return (state == TERMINATED);
1262 }
1263
1264 @Override
1265 StackTraceElement[] asyncGetStackTrace() {
1266 StackTraceElement[] stackTrace;
1267 do {
1268 stackTrace = (carrierThread != null)
1269 ? super.asyncGetStackTrace() // mounted
1270 : tryGetStackTrace(); // unmounted
1271 if (stackTrace == null) {
1272 Thread.yield();
1273 }
1274 } while (stackTrace == null);
1275 return stackTrace;
1276 }
1277
1278 /**
1279 * Returns the stack trace for this virtual thread if it is unmounted.
1280 * Returns null if the thread is mounted or in transition.
1281 */
1282 private StackTraceElement[] tryGetStackTrace() {
1283 int initialState = state() & ~SUSPENDED;
1284 switch (initialState) {
1285 case NEW, STARTED, TERMINATED -> {
1286 return new StackTraceElement[0]; // unmounted, empty stack
1287 }
1288 case RUNNING, PINNED, TIMED_PINNED -> {
1289 return null; // mounted
1290 }
1291 case PARKED, TIMED_PARKED, BLOCKED, WAIT, TIMED_WAIT -> {
1292 // unmounted, not runnable
1293 }
1294 case UNPARKED, UNBLOCKED, YIELDED -> {
1295 // unmounted, runnable
1296 }
1297 case PARKING, TIMED_PARKING, BLOCKING, YIELDING, WAITING, TIMED_WAITING -> {
1298 return null; // in transition
1299 }
1300 default -> throw new InternalError("" + initialState);
1301 }
1302
1303 // thread is unmounted, prevent it from continuing
1304 int suspendedState = initialState | SUSPENDED;
1305 if (!compareAndSetState(initialState, suspendedState)) {
1306 return null;
1307 }
1308
1309 // get stack trace and restore state
1310 StackTraceElement[] stack;
1311 try {
1312 stack = cont.getStackTrace();
1313 } finally {
1314 assert state == suspendedState;
1315 setState(initialState);
1316 }
1317 boolean resubmit = switch (initialState) {
1318 case UNPARKED, UNBLOCKED, YIELDED -> {
1319 // resubmit as task may have run while suspended
1320 yield true;
1321 }
1322 case PARKED, TIMED_PARKED -> {
1323 // resubmit if unparked while suspended
1324 yield parkPermit && compareAndSetState(initialState, UNPARKED);
1325 }
1326 case BLOCKED -> {
1327 // resubmit if unblocked while suspended
1328 yield unblocked && compareAndSetState(BLOCKED, UNBLOCKED);
1329 }
1330 case WAIT, TIMED_WAIT -> {
1331 // resubmit if notified or interrupted while waiting (Object.wait)
1332 // waitTimeoutExpired will retry if the timed expired when suspended
1333 yield (notified || interrupted) && compareAndSetState(initialState, UNBLOCKED);
1334 }
1335 default -> throw new InternalError();
1336 };
1337 if (resubmit) {
1338 submitRunContinuation();
1339 }
1340 return stack;
1341 }
1342
1343 @Override
1344 public String toString() {
1345 StringBuilder sb = new StringBuilder("VirtualThread[#");
1346 sb.append(threadId());
1347 String name = getName();
1348 if (!name.isEmpty()) {
1349 sb.append(",");
1350 sb.append(name);
1351 }
1352 sb.append("]/");
1353
1354 // add the carrier state and thread name when mounted
1355 boolean mounted;
1356 if (Thread.currentThread() == this) {
1357 mounted = appendCarrierInfo(sb);
1358 } else {
1359 disableSuspendAndPreempt();
1360 try {
1361 synchronized (carrierThreadAccessLock()) {
1362 mounted = appendCarrierInfo(sb);
1363 }
1364 } finally {
1365 enableSuspendAndPreempt();
1366 }
1367 }
1368
1369 // add virtual thread state when not mounted
1370 if (!mounted) {
1371 String stateAsString = threadState().toString();
1372 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1373 }
1374
1375 return sb.toString();
1376 }
1377
1378 /**
1379 * Appends the carrier state and thread name to the string buffer if mounted.
1380 * @return true if mounted, false if not mounted
1381 */
1382 private boolean appendCarrierInfo(StringBuilder sb) {
1383 assert Thread.currentThread() == this || Thread.holdsLock(carrierThreadAccessLock());
1384 Thread carrier = carrierThread;
1385 if (carrier != null) {
1386 String stateAsString = carrier.threadState().toString();
1387 sb.append(stateAsString.toLowerCase(Locale.ROOT));
1388 sb.append('@');
1389 sb.append(carrier.getName());
1390 return true;
1391 } else {
1392 return false;
1393 }
1394 }
1395
1396 @Override
1397 public int hashCode() {
1398 return (int) threadId();
1399 }
1400
1401 @Override
1402 public boolean equals(Object obj) {
1403 return obj == this;
1404 }
1405
1406 /**
1407 * Returns the termination object, creating it if needed.
1408 */
1409 private CountDownLatch getTermination() {
1410 CountDownLatch termination = this.termination;
1411 if (termination == null) {
1412 termination = new CountDownLatch(1);
1413 if (!U.compareAndSetReference(this, TERMINATION, null, termination)) {
1414 termination = this.termination;
1415 }
1416 }
1417 return termination;
1418 }
1419
1420 /**
1421 * Returns the lock object to synchronize on when accessing carrierThread.
1422 * The lock prevents carrierThread from being reset to null during unmount.
1423 */
1424 private Object carrierThreadAccessLock() {
1425 // return interruptLock as unmount has to coordinate with interrupt
1426 return interruptLock;
1427 }
1428
1429 /**
1430 * Returns a lock object to coordinating timed-wait setup and timeout handling.
1431 */
1432 private Object timedWaitLock() {
1433 // use this object for now to avoid the overhead of introducing another lock
1434 return runContinuation;
1435 }
1436
1437 /**
1438 * Disallow the current thread be suspended or preempted.
1439 */
1440 private void disableSuspendAndPreempt() {
1441 notifyJvmtiDisableSuspend(true);
1442 Continuation.pin();
1443 }
1444
1445 /**
1446 * Allow the current thread be suspended or preempted.
1447 */
1448 private void enableSuspendAndPreempt() {
1449 Continuation.unpin();
1450 notifyJvmtiDisableSuspend(false);
1451 }
1452
1453 // -- wrappers for get/set of state, parking permit, and carrier thread --
1454
1455 private int state() {
1456 return state; // volatile read
1457 }
1458
1459 private void setState(int newValue) {
1460 state = newValue; // volatile write
1461 }
1462
1463 private boolean compareAndSetState(int expectedValue, int newValue) {
1464 return U.compareAndSetInt(this, STATE, expectedValue, newValue);
1465 }
1466
1467 private boolean compareAndSetOnWaitingList(byte expectedValue, byte newValue) {
1468 return U.compareAndSetByte(this, ON_WAITING_LIST, expectedValue, newValue);
1469 }
1470
1471 private void setParkPermit(boolean newValue) {
1472 if (parkPermit != newValue) {
1473 parkPermit = newValue;
1474 }
1475 }
1476
1477 private boolean getAndSetParkPermit(boolean newValue) {
1478 if (parkPermit != newValue) {
1479 return U.getAndSetBoolean(this, PARK_PERMIT, newValue);
1480 } else {
1481 return newValue;
1482 }
1483 }
1484
1485 private void setCarrierThread(Thread carrier) {
1486 // U.putReferenceRelease(this, CARRIER_THREAD, carrier);
1487 this.carrierThread = carrier;
1488 }
1489
1490 @IntrinsicCandidate
1491 private static native void setLockId(long tid);
1492
1493 // -- JVM TI support --
1494
1495 @IntrinsicCandidate
1496 @JvmtiMountTransition
1497 private native void notifyJvmtiStart();
1498
1499 @IntrinsicCandidate
1500 @JvmtiMountTransition
1501 private native void notifyJvmtiEnd();
1502
1503 @IntrinsicCandidate
1504 @JvmtiMountTransition
1505 private native void notifyJvmtiMount(boolean hide);
1506
1507 @IntrinsicCandidate
1508 @JvmtiMountTransition
1509 private native void notifyJvmtiUnmount(boolean hide);
1510
1511 @IntrinsicCandidate
1512 @JvmtiMountTransition
1513 private static native void notifyJvmtiHideFrames(boolean hide);
1514
1515 @IntrinsicCandidate
1516 private static native void notifyJvmtiDisableSuspend(boolean enter);
1517
1518 private static native void registerNatives();
1519 static {
1520 registerNatives();
1521
1522 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1523 var group = Thread.virtualThreadGroup();
1524 }
1525
1526 /**
1527 * Creates the default scheduler.
1528 * If the system property {@code jdk.virtualThreadScheduler.implClass} is set then
1529 * its value is the name of a class that implements java.util.concurrent.Executor.
1530 * The class is public in an exported package, has a public no-arg constructor,
1531 * and is visible to the system class loader.
1532 * If the system property is not set then the default scheduler will be a
1533 * ForkJoinPool instance.
1534 */
1535 private static Executor createDefaultScheduler() {
1536 String propName = "jdk.virtualThreadScheduler.implClass";
1537 String propValue = GetPropertyAction.privilegedGetProperty(propName);
1538 if (propValue != null) {
1539 try {
1540 Class<?> clazz = Class.forName(propValue, true,
1541 ClassLoader.getSystemClassLoader());
1542 Constructor<?> ctor = clazz.getConstructor();
1543 return (Executor) ctor.newInstance();
1544 } catch (Exception ex) {
1545 throw new Error(ex);
1546 }
1547 } else {
1548 return createDefaultForkJoinPoolScheduler();
1549 }
1550 }
1551
1552 /**
1553 * Creates the default ForkJoinPool scheduler.
1554 */
1555 @SuppressWarnings("removal")
1556 private static ForkJoinPool createDefaultForkJoinPoolScheduler() {
1557 ForkJoinWorkerThreadFactory factory = pool -> {
1558 PrivilegedAction<ForkJoinWorkerThread> pa = () -> new CarrierThread(pool);
1559 return AccessController.doPrivileged(pa);
1560 };
1561 PrivilegedAction<ForkJoinPool> pa = () -> {
1562 int parallelism, maxPoolSize, minRunnable;
1563 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1564 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1565 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1566 if (parallelismValue != null) {
1567 parallelism = Integer.parseInt(parallelismValue);
1568 } else {
1569 parallelism = Runtime.getRuntime().availableProcessors();
1570 }
1571 if (maxPoolSizeValue != null) {
1572 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1573 parallelism = Integer.min(parallelism, maxPoolSize);
1574 } else {
1575 maxPoolSize = Integer.max(parallelism, 256);
1576 }
1577 if (minRunnableValue != null) {
1578 minRunnable = Integer.parseInt(minRunnableValue);
1579 } else {
1580 minRunnable = Integer.max(parallelism / 2, 1);
1581 }
1582 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1583 boolean asyncMode = true; // FIFO
1584 return new ForkJoinPool(parallelism, factory, handler, asyncMode,
1585 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1586 };
1587 return AccessController.doPrivileged(pa);
1588 }
1589
1590 /**
1591 * Schedule a runnable task to run after a delay.
1592 */
1593 private static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1594 long tid = Thread.currentThread().threadId();
1595 int index = (int) tid & (DELAYED_TASK_SCHEDULERS.length - 1);
1596 return DELAYED_TASK_SCHEDULERS[index].schedule(command, delay, unit);
1597 }
1598
1599 /**
1600 * Creates the ScheduledThreadPoolExecutors used to execute delayed tasks.
1601 */
1602 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1603 String propName = "jdk.virtualThreadScheduler.timerQueues";
1604 String propValue = GetPropertyAction.privilegedGetProperty(propName);
1605 int queueCount;
1606 if (propValue != null) {
1607 queueCount = Integer.parseInt(propValue);
1608 if (queueCount != Integer.highestOneBit(queueCount)) {
1609 throw new RuntimeException("Value of " + propName + " must be power of 2");
1610 }
1611 } else {
1612 int ncpus = Runtime.getRuntime().availableProcessors();
1613 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
1614 }
1615 var schedulers = new ScheduledExecutorService[queueCount];
1616 for (int i = 0; i < queueCount; i++) {
1617 ScheduledThreadPoolExecutor stpe = (ScheduledThreadPoolExecutor)
1618 Executors.newScheduledThreadPool(1, task -> {
1619 Thread t = InnocuousThread.newThread("VirtualThread-unparker", task);
1620 t.setDaemon(true);
1621 return t;
1622 });
1623 stpe.setRemoveOnCancelPolicy(true);
1624 schedulers[i] = stpe;
1625 }
1626 return schedulers;
1627 }
1628
1629 /**
1630 * Schedule virtual threads that are ready to be scheduled after they blocked on
1631 * monitor enter.
1632 */
1633 private static void unblockVirtualThreads() {
1634 while (true) {
1635 VirtualThread vthread = takeVirtualThreadListToUnblock();
1636 while (vthread != null) {
1637 assert vthread.onWaitingList == 1;
1638 VirtualThread nextThread = vthread.next;
1639
1640 // remove from list and unblock
1641 vthread.next = null;
1642 boolean changed = vthread.compareAndSetOnWaitingList((byte) 1, (byte) 0);
1643 assert changed;
1644 vthread.unblock();
1645
1646 vthread = nextThread;
1647 }
1648 }
1649 }
1650
1651 /**
1652 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting
1653 * if necessary until a list of one or more threads becomes available.
1654 */
1655 private static native VirtualThread takeVirtualThreadListToUnblock();
1656
1657 static {
1658 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker",
1659 VirtualThread::unblockVirtualThreads);
1660 unblocker.setDaemon(true);
1661 unblocker.start();
1662 }
1663 }