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.util.Locale;
28 import java.util.Objects;
29 import java.util.concurrent.CountDownLatch;
30 import java.util.concurrent.Executor;
31 import java.util.concurrent.Executors;
32 import java.util.concurrent.ForkJoinPool;
33 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
34 import java.util.concurrent.ForkJoinTask;
35 import java.util.concurrent.Future;
36 import java.util.concurrent.RejectedExecutionException;
37 import java.util.concurrent.ScheduledExecutorService;
38 import java.util.concurrent.ScheduledThreadPoolExecutor;
39 import java.util.concurrent.TimeUnit;
40 import jdk.internal.event.VirtualThreadEndEvent;
41 import jdk.internal.event.VirtualThreadStartEvent;
42 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
43 import jdk.internal.misc.CarrierThread;
44 import jdk.internal.misc.InnocuousThread;
45 import jdk.internal.misc.Unsafe;
46 import jdk.internal.vm.Continuation;
47 import jdk.internal.vm.ContinuationScope;
48 import jdk.internal.vm.StackableScope;
49 import jdk.internal.vm.ThreadContainer;
50 import jdk.internal.vm.ThreadContainers;
51 import jdk.internal.vm.annotation.ChangesCurrentThread;
52 import jdk.internal.vm.annotation.Hidden;
53 import jdk.internal.vm.annotation.IntrinsicCandidate;
54 import jdk.internal.vm.annotation.JvmtiHideEvents;
55 import jdk.internal.vm.annotation.JvmtiMountTransition;
56 import jdk.internal.vm.annotation.ReservedStackAccess;
57 import sun.nio.ch.Interruptible;
58 import static java.util.concurrent.TimeUnit.*;
59
60 /**
61 * A thread that is scheduled by the Java virtual machine rather than the operating system.
62 */
63 final class VirtualThread extends BaseVirtualThread {
64 private static final Unsafe U = Unsafe.getUnsafe();
65 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
66 private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();
67
68 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
69 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
70 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
71 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
72 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
73
74 // scheduler and continuation
75 private final Executor scheduler;
76 private final Continuation cont;
77 private final Runnable runContinuation;
78
79 // virtual thread state, accessed by VM
80 private volatile int state;
81
82 /*
83 * Virtual thread state transitions:
84 *
85 * NEW -> STARTED // Thread.start, schedule to run
86 * STARTED -> TERMINATED // failed to start
87 * STARTED -> RUNNING // first run
88 * RUNNING -> TERMINATED // done
89 *
90 * RUNNING -> PARKING // Thread parking with LockSupport.park
91 * PARKING -> PARKED // cont.yield successful, parked indefinitely
92 * PARKED -> UNPARKED // unparked, may be scheduled to continue
93 * UNPARKED -> RUNNING // continue execution after park
94 *
95 * PARKING -> RUNNING // cont.yield failed, need to park on carrier
96 * RUNNING -> PINNED // park on carrier
97 * PINNED -> RUNNING // unparked, continue execution on same carrier
171
172 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
173 private volatile boolean interruptibleWait;
174
175 // timed-wait support
176 private byte timedWaitSeqNo;
177
178 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
179 private long timeout;
180
181 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
182 private Future<?> timeoutTask;
183
184 // carrier thread when mounted, accessed by VM
185 private volatile Thread carrierThread;
186
187 // termination object when joining, created lazily if needed
188 private volatile CountDownLatch termination;
189
190 /**
191 * Returns the default scheduler.
192 */
193 static Executor defaultScheduler() {
194 return DEFAULT_SCHEDULER;
195 }
196
197 /**
198 * Returns the continuation scope used for virtual threads.
199 */
200 static ContinuationScope continuationScope() {
201 return VTHREAD_SCOPE;
202 }
203
204 /**
205 * Creates a new {@code VirtualThread} to run the given task with the given
206 * scheduler. If the given scheduler is {@code null} and the current thread
207 * is a platform thread then the newly created virtual thread will use the
208 * default scheduler. If given scheduler is {@code null} and the current
209 * thread is a virtual thread then the current thread's scheduler is used.
210 *
211 * @param scheduler the scheduler or null
212 * @param name thread name
213 * @param characteristics characteristics
214 * @param task the task to execute
215 */
216 VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
217 super(name, characteristics, /*bound*/ false);
218 Objects.requireNonNull(task);
219
220 // choose scheduler if not specified
221 if (scheduler == null) {
222 Thread parent = Thread.currentThread();
223 if (parent instanceof VirtualThread vparent) {
224 scheduler = vparent.scheduler;
225 } else {
226 scheduler = DEFAULT_SCHEDULER;
227 }
228 }
229
230 this.scheduler = scheduler;
231 this.cont = new VThreadContinuation(this, task);
232 this.runContinuation = this::runContinuation;
233 }
234
235 /**
236 * The continuation that a virtual thread executes.
237 */
238 private static class VThreadContinuation extends Continuation {
239 VThreadContinuation(VirtualThread vthread, Runnable task) {
240 super(VTHREAD_SCOPE, wrap(vthread, task));
241 }
242 @Override
243 protected void onPinned(Continuation.Pinned reason) {
244 }
245 private static Runnable wrap(VirtualThread vthread, Runnable task) {
246 return new Runnable() {
247 @Hidden
248 @JvmtiHideEvents
249 public void run() {
250 vthread.endFirstTransition();
251 try {
252 vthread.run(task);
300 if (cont.isDone()) {
301 afterDone();
302 } else {
303 afterYield();
304 }
305 }
306 }
307
308 /**
309 * Cancel timeout task when continuing after timed-park or timed-wait.
310 * The timeout task may be executing, or may have already completed.
311 */
312 private void cancelTimeoutTask() {
313 if (timeoutTask != null) {
314 timeoutTask.cancel(false);
315 timeoutTask = null;
316 }
317 }
318
319 /**
320 * Submits the given task to the given executor. If the scheduler is a
321 * ForkJoinPool then the task is first adapted to a ForkJoinTask.
322 */
323 private void submit(Executor executor, Runnable task) {
324 if (executor instanceof ForkJoinPool pool) {
325 pool.submit(ForkJoinTask.adapt(task));
326 } else {
327 executor.execute(task);
328 }
329 }
330
331 /**
332 * Submits the runContinuation task to the scheduler. For the default scheduler,
333 * and calling it on a worker thread, the task will be pushed to the local queue,
334 * otherwise it will be pushed to an external submission queue.
335 * @param scheduler the scheduler
336 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
337 * @throws RejectedExecutionException
338 */
339 private void submitRunContinuation(Executor scheduler, boolean retryOnOOME) {
340 boolean done = false;
341 while (!done) {
342 try {
343 // Pin the continuation to prevent the virtual thread from unmounting
344 // when submitting a task. For the default scheduler this ensures that
345 // the carrier doesn't change when pushing a task. For other schedulers
346 // it avoids deadlock that could arise due to carriers and virtual
347 // threads contending for a lock.
348 if (currentThread().isVirtual()) {
349 Continuation.pin();
350 try {
351 submit(scheduler, runContinuation);
352 } finally {
353 Continuation.unpin();
354 }
355 } else {
356 submit(scheduler, runContinuation);
357 }
358 done = true;
359 } catch (RejectedExecutionException ree) {
360 submitFailed(ree);
361 throw ree;
362 } catch (OutOfMemoryError e) {
363 if (retryOnOOME) {
364 U.park(false, 100_000_000); // 100ms
365 } else {
366 throw e;
367 }
368 }
369 }
370 }
371
372 /**
373 * Submits the runContinuation task to the given scheduler as an external submit.
374 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
375 * @throws RejectedExecutionException
376 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
377 */
378 private void externalSubmitRunContinuation(ForkJoinPool pool) {
379 assert Thread.currentThread() instanceof CarrierThread;
380 try {
381 pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
382 } catch (RejectedExecutionException ree) {
383 submitFailed(ree);
384 throw ree;
385 } catch (OutOfMemoryError e) {
386 submitRunContinuation(pool, true);
387 }
388 }
389
390 /**
391 * Submits the runContinuation task to the scheduler. For the default scheduler,
392 * and calling it on a worker thread, the task will be pushed to the local queue,
393 * otherwise it will be pushed to an external submission queue.
394 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
395 * @throws RejectedExecutionException
396 */
397 private void submitRunContinuation() {
398 submitRunContinuation(scheduler, true);
399 }
400
401 /**
402 * Lazy submit the runContinuation task if invoked on a carrier thread and its local
403 * queue is empty. If not empty, or invoked by another thread, then this method works
404 * like submitRunContinuation and just submits the task to the scheduler.
405 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
406 * @throws RejectedExecutionException
407 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
408 */
409 private void lazySubmitRunContinuation() {
410 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
411 ForkJoinPool pool = ct.getPool();
412 try {
413 pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
414 } catch (RejectedExecutionException ree) {
415 submitFailed(ree);
416 throw ree;
417 } catch (OutOfMemoryError e) {
418 submitRunContinuation();
419 }
420 } else {
421 submitRunContinuation();
422 }
423 }
424
425 /**
426 * Submits the runContinuation task to the scheduler. For the default scheduler, and
427 * calling it a virtual thread that uses the default scheduler, the task will be
428 * pushed to an external submission queue. This method may throw OutOfMemoryError.
429 * @throws RejectedExecutionException
430 * @throws OutOfMemoryError
431 */
432 private void externalSubmitRunContinuationOrThrow() {
433 if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
434 try {
435 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
436 } catch (RejectedExecutionException ree) {
437 submitFailed(ree);
438 throw ree;
439 }
440 } else {
441 submitRunContinuation(scheduler, false);
442 }
443 }
444
445 /**
446 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
447 */
448 private void submitFailed(RejectedExecutionException ree) {
449 var event = new VirtualThreadSubmitFailedEvent();
450 if (event.isEnabled()) {
451 event.javaThreadId = threadId();
452 event.exceptionMessage = ree.getMessage();
453 event.commit();
454 }
455 }
456
457 /**
458 * Runs a task in the context of this virtual thread.
459 */
460 private void run(Runnable task) {
461 assert Thread.currentThread() == this && state == RUNNING;
578 long timeout = this.timeout;
579 assert timeout > 0;
580 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
581 setState(newState = TIMED_PARKED);
582 }
583
584 // may have been unparked while parking
585 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
586 // lazy submit if local queue is empty
587 lazySubmitRunContinuation();
588 }
589 return;
590 }
591
592 // Thread.yield
593 if (s == YIELDING) {
594 setState(YIELDED);
595
596 // external submit if there are no tasks in the local task queue
597 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
598 externalSubmitRunContinuation(ct.getPool());
599 } else {
600 submitRunContinuation();
601 }
602 return;
603 }
604
605 // blocking on monitorenter
606 if (s == BLOCKING) {
607 setState(BLOCKED);
608
609 // may have been unblocked while blocking
610 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
611 // lazy submit if local queue is empty
612 lazySubmitRunContinuation();
613 }
614 return;
615 }
616
617 // Object.wait
618 if (s == WAITING || s == TIMED_WAITING) {
738 @Override
739 public void run() {
740 // do nothing
741 }
742
743 /**
744 * Parks until unparked or interrupted. If already unparked then the parking
745 * permit is consumed and this method completes immediately (meaning it doesn't
746 * yield). It also completes immediately if the interrupted status is set.
747 */
748 @Override
749 void park() {
750 assert Thread.currentThread() == this;
751
752 // complete immediately if parking permit available or interrupted
753 if (getAndSetParkPermit(false) || interrupted)
754 return;
755
756 // park the thread
757 boolean yielded = false;
758 setState(PARKING);
759 try {
760 yielded = yieldContinuation();
761 } catch (OutOfMemoryError e) {
762 // park on carrier
763 } finally {
764 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
765 if (!yielded) {
766 assert state() == PARKING;
767 setState(RUNNING);
768 }
769 }
770
771 // park on the carrier thread when pinned
772 if (!yielded) {
773 parkOnCarrierThread(false, 0);
774 }
775 }
776
777 /**
778 * Parks up to the given waiting time or until unparked or interrupted.
779 * If already unparked then the parking permit is consumed and this method
780 * completes immediately (meaning it doesn't yield). It also completes immediately
781 * if the interrupted status is set or the waiting time is {@code <= 0}.
782 *
783 * @param nanos the maximum number of nanoseconds to wait.
784 */
785 @Override
786 void parkNanos(long nanos) {
787 assert Thread.currentThread() == this;
788
789 // complete immediately if parking permit available or interrupted
790 if (getAndSetParkPermit(false) || interrupted)
791 return;
792
793 // park the thread for the waiting time
794 if (nanos > 0) {
795 long startTime = System.nanoTime();
796
797 // park the thread, afterYield will schedule the thread to unpark
798 boolean yielded = false;
799 timeout = nanos;
800 setState(TIMED_PARKING);
801 try {
802 yielded = yieldContinuation();
803 } catch (OutOfMemoryError e) {
804 // park on carrier
805 } finally {
806 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
807 if (!yielded) {
808 assert state() == TIMED_PARKING;
809 setState(RUNNING);
810 }
811 }
812
813 // park on carrier thread for remaining time when pinned (or OOME)
814 if (!yielded) {
815 long remainingNanos = nanos - (System.nanoTime() - startTime);
816 parkOnCarrierThread(true, remainingNanos);
817 }
818 }
819 }
820
821 /**
822 * Parks the current carrier thread up to the given waiting time or until
823 * unparked or interrupted. If the virtual thread is interrupted then the
824 * interrupted status will be propagated to the carrier thread.
825 * @param timed true for a timed park, false for untimed
826 * @param nanos the waiting time in nanoseconds
827 */
1344 @JvmtiMountTransition
1345 private native void startFinalTransition();
1346
1347 @IntrinsicCandidate
1348 @JvmtiMountTransition
1349 private native void startTransition(boolean mount);
1350
1351 @IntrinsicCandidate
1352 @JvmtiMountTransition
1353 private native void endTransition(boolean mount);
1354
1355 @IntrinsicCandidate
1356 private static native void notifyJvmtiDisableSuspend(boolean enter);
1357
1358 private static native void registerNatives();
1359 static {
1360 registerNatives();
1361
1362 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1363 var group = Thread.virtualThreadGroup();
1364 }
1365
1366 /**
1367 * Creates the default ForkJoinPool scheduler.
1368 */
1369 private static ForkJoinPool createDefaultScheduler() {
1370 ForkJoinWorkerThreadFactory factory = pool -> new CarrierThread(pool);
1371 int parallelism, maxPoolSize, minRunnable;
1372 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1373 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1374 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1375 if (parallelismValue != null) {
1376 parallelism = Integer.parseInt(parallelismValue);
1377 } else {
1378 parallelism = Runtime.getRuntime().availableProcessors();
1379 }
1380 if (maxPoolSizeValue != null) {
1381 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1382 parallelism = Integer.min(parallelism, maxPoolSize);
1383 } else {
1384 maxPoolSize = Integer.max(parallelism, 256);
1385 }
1386 if (minRunnableValue != null) {
1387 minRunnable = Integer.parseInt(minRunnableValue);
1388 } else {
1389 minRunnable = Integer.max(parallelism / 2, 1);
1390 }
1391 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1392 boolean asyncMode = true; // FIFO
1393 return new ForkJoinPool(parallelism, factory, handler, asyncMode,
1394 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1395 }
1396
1397 /**
1398 * Schedule a runnable task to run after a delay.
1399 */
1400 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1401 if (scheduler instanceof ForkJoinPool pool) {
1402 return pool.schedule(command, delay, unit);
1403 } else {
1404 return DelayedTaskSchedulers.schedule(command, delay, unit);
1405 }
1406 }
1407
1408 /**
1409 * Supports scheduling a runnable task to run after a delay. It uses a number
1410 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1411 * work queue used. This class is used when using a custom scheduler.
1412 */
1413 private static class DelayedTaskSchedulers {
1414 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1415
1416 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1417 long tid = Thread.currentThread().threadId();
1418 int index = (int) tid & (INSTANCE.length - 1);
1419 return INSTANCE[index].schedule(command, delay, unit);
1420 }
1421
1422 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1423 String propName = "jdk.virtualThreadScheduler.timerQueues";
1424 String propValue = System.getProperty(propName);
1425 int queueCount;
1426 if (propValue != null) {
1427 queueCount = Integer.parseInt(propValue);
1428 if (queueCount != Integer.highestOneBit(queueCount)) {
1429 throw new RuntimeException("Value of " + propName + " must be power of 2");
1430 }
1431 } else {
1432 int ncpus = Runtime.getRuntime().availableProcessors();
1433 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
|
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25 package java.lang;
26
27 import java.lang.invoke.MethodHandles;
28 import java.lang.invoke.VarHandle;
29 import java.lang.reflect.Constructor;
30 import java.util.Locale;
31 import java.util.Objects;
32 import java.util.concurrent.CountDownLatch;
33 import java.util.concurrent.Executors;
34 import java.util.concurrent.ForkJoinPool;
35 import java.util.concurrent.ForkJoinTask;
36 import java.util.concurrent.Future;
37 import java.util.concurrent.LinkedTransferQueue;
38 import java.util.concurrent.RejectedExecutionException;
39 import java.util.concurrent.ScheduledExecutorService;
40 import java.util.concurrent.ScheduledFuture;
41 import java.util.concurrent.ScheduledThreadPoolExecutor;
42 import java.util.concurrent.ThreadFactory;
43 import java.util.concurrent.ThreadPoolExecutor;
44 import java.util.concurrent.TimeUnit;
45 import jdk.internal.event.VirtualThreadEndEvent;
46 import jdk.internal.event.VirtualThreadParkEvent;
47 import jdk.internal.event.VirtualThreadStartEvent;
48 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
49 import jdk.internal.invoke.MhUtil;
50 import jdk.internal.misc.CarrierThread;
51 import jdk.internal.misc.InnocuousThread;
52 import jdk.internal.misc.Unsafe;
53 import jdk.internal.vm.Continuation;
54 import jdk.internal.vm.ContinuationScope;
55 import jdk.internal.vm.StackableScope;
56 import jdk.internal.vm.ThreadContainer;
57 import jdk.internal.vm.ThreadContainers;
58 import jdk.internal.vm.annotation.ChangesCurrentThread;
59 import jdk.internal.vm.annotation.Hidden;
60 import jdk.internal.vm.annotation.IntrinsicCandidate;
61 import jdk.internal.vm.annotation.JvmtiHideEvents;
62 import jdk.internal.vm.annotation.JvmtiMountTransition;
63 import jdk.internal.vm.annotation.ReservedStackAccess;
64 import sun.nio.ch.Interruptible;
65 import static java.util.concurrent.TimeUnit.*;
66
67 /**
68 * A thread that is scheduled by the Java virtual machine rather than the operating system.
69 */
70 final class VirtualThread extends BaseVirtualThread {
71 private static final Unsafe U = Unsafe.getUnsafe();
72 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
73
74 private static final VirtualThreadScheduler BUILTIN_SCHEDULER;
75 private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
76 private static final VirtualThreadScheduler EXTERNAL_VIEW;
77 private static final boolean USE_STPE;
78 static {
79 // experimental
80 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
81 if (propValue != null) {
82 VirtualThreadScheduler builtinScheduler = createBuiltinScheduler(true);
83 VirtualThreadScheduler externalView = createExternalView(builtinScheduler);
84 VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue);
85 BUILTIN_SCHEDULER = builtinScheduler;
86 DEFAULT_SCHEDULER = defaultScheduler;
87 EXTERNAL_VIEW = externalView;
88 } else {
89 var builtinScheduler = createBuiltinScheduler(false);
90 BUILTIN_SCHEDULER = builtinScheduler;
91 DEFAULT_SCHEDULER = builtinScheduler;
92 EXTERNAL_VIEW = createExternalView(builtinScheduler);
93 }
94 USE_STPE = Boolean.getBoolean("jdk.virtualThreadScheduler.useSTPE");
95 }
96
97 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
98 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
99 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
100 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
101 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
102
103 // scheduler and continuation
104 private final VirtualThreadScheduler scheduler;
105 private final Continuation cont;
106 private final VThreadRunner runContinuation;
107
108 // virtual thread state, accessed by VM
109 private volatile int state;
110
111 /*
112 * Virtual thread state transitions:
113 *
114 * NEW -> STARTED // Thread.start, schedule to run
115 * STARTED -> TERMINATED // failed to start
116 * STARTED -> RUNNING // first run
117 * RUNNING -> TERMINATED // done
118 *
119 * RUNNING -> PARKING // Thread parking with LockSupport.park
120 * PARKING -> PARKED // cont.yield successful, parked indefinitely
121 * PARKED -> UNPARKED // unparked, may be scheduled to continue
122 * UNPARKED -> RUNNING // continue execution after park
123 *
124 * PARKING -> RUNNING // cont.yield failed, need to park on carrier
125 * RUNNING -> PINNED // park on carrier
126 * PINNED -> RUNNING // unparked, continue execution on same carrier
200
201 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
202 private volatile boolean interruptibleWait;
203
204 // timed-wait support
205 private byte timedWaitSeqNo;
206
207 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
208 private long timeout;
209
210 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
211 private Future<?> timeoutTask;
212
213 // carrier thread when mounted, accessed by VM
214 private volatile Thread carrierThread;
215
216 // termination object when joining, created lazily if needed
217 private volatile CountDownLatch termination;
218
219 /**
220 * Return the built-in scheduler.
221 * @param trusted true if caller is trusted, false if not trusted
222 */
223 static VirtualThreadScheduler builtinScheduler(boolean trusted) {
224 return trusted ? BUILTIN_SCHEDULER : EXTERNAL_VIEW;
225 }
226
227 /**
228 * Returns the default scheduler, usually the same as the built-in scheduler.
229 */
230 static VirtualThreadScheduler defaultScheduler() {
231 return DEFAULT_SCHEDULER;
232 }
233
234 /**
235 * Returns the continuation scope used for virtual threads.
236 */
237 static ContinuationScope continuationScope() {
238 return VTHREAD_SCOPE;
239 }
240
241 /**
242 * Returns the task to start/continue this virtual thread.
243 */
244 VirtualThreadTask virtualThreadTask() {
245 return runContinuation;
246 }
247
248 /**
249 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
250 *
251 * @param scheduler the scheduler or null for default scheduler
252 * @param preferredCarrier the preferred carrier or null
253 * @param name thread name
254 * @param characteristics characteristics
255 * @param task the task to execute
256 */
257 VirtualThread(VirtualThreadScheduler scheduler,
258 Thread preferredCarrier,
259 String name,
260 int characteristics,
261 Runnable task) {
262 super(name, characteristics, /*bound*/ false);
263 Objects.requireNonNull(task);
264
265 // use default scheduler if not provided
266 if (scheduler == null) {
267 scheduler = DEFAULT_SCHEDULER;
268 } else if (scheduler == EXTERNAL_VIEW) {
269 throw new UnsupportedOperationException();
270 }
271 this.scheduler = scheduler;
272 this.cont = new VThreadContinuation(this, task);
273
274 if (scheduler == BUILTIN_SCHEDULER) {
275 this.runContinuation = new VThreadRunner(this);
276 } else {
277 this.runContinuation = new CustomSchedulerVThreadRunner(this, preferredCarrier);
278 }
279 }
280
281 /**
282 * The task to start/continue a virtual thread.
283 */
284 static non-sealed class VThreadRunner implements VirtualThreadTask {
285 private final VirtualThread vthread;
286 VThreadRunner(VirtualThread vthread) {
287 this.vthread = vthread;
288 }
289 @Override
290 public final Thread thread() {
291 return vthread;
292 }
293 @Override
294 public final void run() {
295 vthread.runContinuation();;
296 }
297 @Override
298 public Thread preferredCarrier() {
299 throw new UnsupportedOperationException();
300 }
301 @Override
302 public Object attach(Object att) {
303 throw new UnsupportedOperationException();
304 }
305 @Override
306 public Object attachment() {
307 throw new UnsupportedOperationException();
308 }
309 }
310
311 /**
312 * The task to start/continue a virtual thread when using a custom scheduler.
313 */
314 static final class CustomSchedulerVThreadRunner extends VThreadRunner {
315 private static final VarHandle ATT =
316 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class);
317 private final Thread preferredCarrier;
318 private volatile Object att;
319 CustomSchedulerVThreadRunner(VirtualThread vthread, Thread preferredCarrier) {
320 super(vthread);
321 this.preferredCarrier = preferredCarrier;
322 }
323 @Override
324 public Thread preferredCarrier() {
325 return preferredCarrier;
326 }
327 @Override
328 public Object attach(Object att) {
329 return ATT.getAndSet(this, att);
330 }
331 @Override
332 public Object attachment() {
333 return att;
334 }
335 }
336
337 /**
338 * The continuation that a virtual thread executes.
339 */
340 private static class VThreadContinuation extends Continuation {
341 VThreadContinuation(VirtualThread vthread, Runnable task) {
342 super(VTHREAD_SCOPE, wrap(vthread, task));
343 }
344 @Override
345 protected void onPinned(Continuation.Pinned reason) {
346 }
347 private static Runnable wrap(VirtualThread vthread, Runnable task) {
348 return new Runnable() {
349 @Hidden
350 @JvmtiHideEvents
351 public void run() {
352 vthread.endFirstTransition();
353 try {
354 vthread.run(task);
402 if (cont.isDone()) {
403 afterDone();
404 } else {
405 afterYield();
406 }
407 }
408 }
409
410 /**
411 * Cancel timeout task when continuing after timed-park or timed-wait.
412 * The timeout task may be executing, or may have already completed.
413 */
414 private void cancelTimeoutTask() {
415 if (timeoutTask != null) {
416 timeoutTask.cancel(false);
417 timeoutTask = null;
418 }
419 }
420
421 /**
422 * Submits the runContinuation task to the scheduler. For the built-in scheduler,
423 * the task will be pushed to the local queue if possible, otherwise it will be
424 * pushed to an external submission queue.
425 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
426 * @throws RejectedExecutionException
427 */
428 private void submitRunContinuation(boolean retryOnOOME) {
429 boolean done = false;
430 while (!done) {
431 try {
432 // Pin the continuation to prevent the virtual thread from unmounting
433 // when submitting a task. For the default scheduler this ensures that
434 // the carrier doesn't change when pushing a task. For other schedulers
435 // it avoids deadlock that could arise due to carriers and virtual
436 // threads contending for a lock.
437 if (currentThread().isVirtual()) {
438 Continuation.pin();
439 try {
440 scheduler.onContinue(runContinuation);
441 } finally {
442 Continuation.unpin();
443 }
444 } else {
445 scheduler.onContinue(runContinuation);
446 }
447 done = true;
448 } catch (RejectedExecutionException ree) {
449 submitFailed(ree);
450 throw ree;
451 } catch (OutOfMemoryError e) {
452 if (retryOnOOME) {
453 U.park(false, 100_000_000); // 100ms
454 } else {
455 throw e;
456 }
457 }
458 }
459 }
460
461 /**
462 * Submits the runContinuation task to the scheduler. For the default scheduler,
463 * and calling it on a worker thread, the task will be pushed to the local queue,
464 * otherwise it will be pushed to an external submission queue.
465 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
466 * @throws RejectedExecutionException
467 */
468 private void submitRunContinuation() {
469 submitRunContinuation(true);
470 }
471
472 /**
473 * Invoked from a carrier thread to lazy submit the runContinuation task to the
474 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
475 * for a custom scheduler, then it just submits the task to the scheduler.
476 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
477 * @throws RejectedExecutionException
478 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
479 */
480 private void lazySubmitRunContinuation() {
481 assert !currentThread().isVirtual();
482 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
483 try {
484 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
485 } catch (RejectedExecutionException ree) {
486 submitFailed(ree);
487 throw ree;
488 } catch (OutOfMemoryError e) {
489 submitRunContinuation();
490 }
491 } else {
492 submitRunContinuation();
493 }
494 }
495
496 /**
497 * Invoked from a carrier thread to externally submit the runContinuation task to the
498 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
499 * task to the scheduler.
500 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
501 * @throws RejectedExecutionException
502 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
503 */
504 private void externalSubmitRunContinuation() {
505 assert !currentThread().isVirtual();
506 if (currentThread() instanceof CarrierThread ct) {
507 try {
508 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
509 } catch (RejectedExecutionException ree) {
510 submitFailed(ree);
511 throw ree;
512 } catch (OutOfMemoryError e) {
513 submitRunContinuation();
514 }
515 } else {
516 submitRunContinuation();
517 }
518 }
519
520 /**
521 * Invoked from Thread.start to externally submit the runContinuation task to the
522 * scheduler. If this virtual thread is scheduled by the built-in scheduler,
523 * and this method is called from a virtual thread scheduled by the built-in
524 * scheduler, then it uses externalSubmit to ensure that the task is pushed to an
525 * external submission queue rather than the local queue.
526 * @throws RejectedExecutionException
527 * @throws OutOfMemoryError
528 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
529 */
530 private void externalSubmitRunContinuationOrThrow() {
531 try {
532 if (currentThread().isVirtual()) {
533 // Pin the continuation to prevent the virtual thread from unmounting
534 // when submitting a task. This avoids deadlock that could arise due to
535 // carriers and virtual threads contending for a lock.
536 Continuation.pin();
537 try {
538 if (scheduler == BUILTIN_SCHEDULER
539 && currentCarrierThread() instanceof CarrierThread ct) {
540 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
541 } else {
542 scheduler.onStart(runContinuation);
543 }
544 } finally {
545 Continuation.unpin();
546 }
547 } else {
548 scheduler.onStart(runContinuation);
549 }
550 } catch (RejectedExecutionException ree) {
551 submitFailed(ree);
552 throw ree;
553 }
554 }
555
556 /**
557 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
558 */
559 private void submitFailed(RejectedExecutionException ree) {
560 var event = new VirtualThreadSubmitFailedEvent();
561 if (event.isEnabled()) {
562 event.javaThreadId = threadId();
563 event.exceptionMessage = ree.getMessage();
564 event.commit();
565 }
566 }
567
568 /**
569 * Runs a task in the context of this virtual thread.
570 */
571 private void run(Runnable task) {
572 assert Thread.currentThread() == this && state == RUNNING;
689 long timeout = this.timeout;
690 assert timeout > 0;
691 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
692 setState(newState = TIMED_PARKED);
693 }
694
695 // may have been unparked while parking
696 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
697 // lazy submit if local queue is empty
698 lazySubmitRunContinuation();
699 }
700 return;
701 }
702
703 // Thread.yield
704 if (s == YIELDING) {
705 setState(YIELDED);
706
707 // external submit if there are no tasks in the local task queue
708 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
709 externalSubmitRunContinuation();
710 } else {
711 submitRunContinuation();
712 }
713 return;
714 }
715
716 // blocking on monitorenter
717 if (s == BLOCKING) {
718 setState(BLOCKED);
719
720 // may have been unblocked while blocking
721 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
722 // lazy submit if local queue is empty
723 lazySubmitRunContinuation();
724 }
725 return;
726 }
727
728 // Object.wait
729 if (s == WAITING || s == TIMED_WAITING) {
849 @Override
850 public void run() {
851 // do nothing
852 }
853
854 /**
855 * Parks until unparked or interrupted. If already unparked then the parking
856 * permit is consumed and this method completes immediately (meaning it doesn't
857 * yield). It also completes immediately if the interrupted status is set.
858 */
859 @Override
860 void park() {
861 assert Thread.currentThread() == this;
862
863 // complete immediately if parking permit available or interrupted
864 if (getAndSetParkPermit(false) || interrupted)
865 return;
866
867 // park the thread
868 boolean yielded = false;
869 long eventStartTime = VirtualThreadParkEvent.eventStartTime();
870 setState(PARKING);
871 try {
872 yielded = yieldContinuation();
873 } catch (OutOfMemoryError e) {
874 // park on carrier
875 } finally {
876 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
877 if (yielded) {
878 VirtualThreadParkEvent.offer(eventStartTime, Long.MIN_VALUE);
879 } else {
880 assert state() == PARKING;
881 setState(RUNNING);
882 }
883 }
884
885 // park on the carrier thread when pinned
886 if (!yielded) {
887 parkOnCarrierThread(false, 0);
888 }
889 }
890
891 /**
892 * Parks up to the given waiting time or until unparked or interrupted.
893 * If already unparked then the parking permit is consumed and this method
894 * completes immediately (meaning it doesn't yield). It also completes immediately
895 * if the interrupted status is set or the waiting time is {@code <= 0}.
896 *
897 * @param nanos the maximum number of nanoseconds to wait.
898 */
899 @Override
900 void parkNanos(long nanos) {
901 assert Thread.currentThread() == this;
902
903 // complete immediately if parking permit available or interrupted
904 if (getAndSetParkPermit(false) || interrupted)
905 return;
906
907 // park the thread for the waiting time
908 if (nanos > 0) {
909 long startTime = System.nanoTime();
910
911 // park the thread, afterYield will schedule the thread to unpark
912 boolean yielded = false;
913 long eventStartTime = VirtualThreadParkEvent.eventStartTime();
914 timeout = nanos;
915 setState(TIMED_PARKING);
916 try {
917 yielded = yieldContinuation();
918 } catch (OutOfMemoryError e) {
919 // park on carrier
920 } finally {
921 assert (Thread.currentThread() == this) && (yielded == (state() == RUNNING));
922 if (yielded) {
923 VirtualThreadParkEvent.offer(eventStartTime, nanos);
924 } else {
925 assert state() == TIMED_PARKING;
926 setState(RUNNING);
927 }
928 }
929
930 // park on carrier thread for remaining time when pinned (or OOME)
931 if (!yielded) {
932 long remainingNanos = nanos - (System.nanoTime() - startTime);
933 parkOnCarrierThread(true, remainingNanos);
934 }
935 }
936 }
937
938 /**
939 * Parks the current carrier thread up to the given waiting time or until
940 * unparked or interrupted. If the virtual thread is interrupted then the
941 * interrupted status will be propagated to the carrier thread.
942 * @param timed true for a timed park, false for untimed
943 * @param nanos the waiting time in nanoseconds
944 */
1461 @JvmtiMountTransition
1462 private native void startFinalTransition();
1463
1464 @IntrinsicCandidate
1465 @JvmtiMountTransition
1466 private native void startTransition(boolean mount);
1467
1468 @IntrinsicCandidate
1469 @JvmtiMountTransition
1470 private native void endTransition(boolean mount);
1471
1472 @IntrinsicCandidate
1473 private static native void notifyJvmtiDisableSuspend(boolean enter);
1474
1475 private static native void registerNatives();
1476 static {
1477 registerNatives();
1478
1479 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1480 var group = Thread.virtualThreadGroup();
1481
1482 // ensure event class is initialized
1483 try {
1484 MethodHandles.lookup().ensureInitialized(VirtualThreadParkEvent.class);
1485 } catch (IllegalAccessException e) {
1486 throw new ExceptionInInitializerError(e);
1487 }
1488 }
1489
1490 /**
1491 * Loads a VirtualThreadScheduler with the given class name. The class must be public
1492 * in an exported package, with public one-arg or no-arg constructor, and be visible
1493 * to the system class loader.
1494 * @param delegate the scheduler that the custom scheduler may delegate to
1495 * @param cn the class name of the custom scheduler
1496 */
1497 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
1498 VirtualThreadScheduler scheduler;
1499 try {
1500 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1501 // 1-arg constructor
1502 try {
1503 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1504 return (VirtualThreadScheduler) ctor.newInstance(delegate);
1505 } catch (NoSuchMethodException e) {
1506 // 0-arg constructor
1507 Constructor<?> ctor = clazz.getConstructor();
1508 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1509 }
1510 } catch (Exception ex) {
1511 throw new Error(ex);
1512 }
1513 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!");
1514 return scheduler;
1515 }
1516
1517 /**
1518 * Creates the built-in ForkJoinPool scheduler.
1519 * @param wrapped true if wrapped by a custom default scheduler
1520 */
1521 private static VirtualThreadScheduler createBuiltinScheduler(boolean wrapped) {
1522 int parallelism, maxPoolSize, minRunnable;
1523 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1524 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1525 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1526 if (parallelismValue != null) {
1527 parallelism = Integer.parseInt(parallelismValue);
1528 } else {
1529 parallelism = Runtime.getRuntime().availableProcessors();
1530 }
1531 if (maxPoolSizeValue != null) {
1532 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1533 parallelism = Integer.min(parallelism, maxPoolSize);
1534 } else {
1535 maxPoolSize = Integer.max(parallelism, 256);
1536 }
1537 if (minRunnableValue != null) {
1538 minRunnable = Integer.parseInt(minRunnableValue);
1539 } else {
1540 minRunnable = Integer.max(parallelism / 2, 1);
1541 }
1542 if (Boolean.getBoolean("jdk.virtualThreadScheduler.useTPE")) {
1543 return new BuiltinThreadPoolExecutorScheduler(parallelism);
1544 } else {
1545 return new BuiltinForkJoinPoolScheduler(parallelism, maxPoolSize, minRunnable, wrapped);
1546 }
1547 }
1548
1549 /**
1550 * The built-in ForkJoinPool scheduler.
1551 */
1552 private static class BuiltinForkJoinPoolScheduler
1553 extends ForkJoinPool implements VirtualThreadScheduler {
1554
1555 BuiltinForkJoinPoolScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) {
1556 ForkJoinWorkerThreadFactory factory = wrapped
1557 ? ForkJoinPool.defaultForkJoinWorkerThreadFactory
1558 : CarrierThread::new;
1559 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1560 boolean asyncMode = true; // FIFO
1561 super(parallelism, factory, handler, asyncMode,
1562 0, maxPoolSize, minRunnable, pool -> true, 30L, SECONDS);
1563 }
1564
1565 @Override
1566 public void onStart(VirtualThreadTask task) {
1567 execute(ForkJoinTask.adapt(task));
1568 }
1569
1570 @Override
1571 public void onContinue(VirtualThreadTask task) {
1572 execute(ForkJoinTask.adapt(task));
1573 }
1574
1575 @Override
1576 public ScheduledFuture<?> schedule(Runnable task, long delay, TimeUnit unit) {
1577 return super.schedule(task, delay, unit);
1578 }
1579 }
1580
1581 /**
1582 * Built-in ThreadPoolExecutor scheduler.
1583 */
1584 private static class BuiltinThreadPoolExecutorScheduler
1585 extends ThreadPoolExecutor implements VirtualThreadScheduler {
1586
1587 BuiltinThreadPoolExecutorScheduler(int maxPoolSize) {
1588 ThreadFactory factory = task -> {
1589 Thread t = InnocuousThread.newThread(task);
1590 t.setDaemon(true);
1591 return t;
1592 };
1593 super(maxPoolSize, maxPoolSize,
1594 0L, SECONDS,
1595 new LinkedTransferQueue<>(),
1596 factory);
1597 }
1598
1599 @Override
1600 public void onStart(VirtualThreadTask task) {
1601 execute(task);
1602 }
1603
1604 @Override
1605 public void onContinue(VirtualThreadTask task) {
1606 execute(task);
1607 }
1608 }
1609
1610 /**
1611 * Wraps the scheduler to avoid leaking a direct reference with
1612 * {@link VirtualThreadScheduler#current()}.
1613 */
1614 static VirtualThreadScheduler createExternalView(VirtualThreadScheduler delegate) {
1615 return new VirtualThreadScheduler() {
1616 private void check(VirtualThreadTask task) {
1617 var vthread = (VirtualThread) task.thread();
1618 VirtualThreadScheduler scheduler = vthread.scheduler;
1619 if (scheduler != this && scheduler != DEFAULT_SCHEDULER) {
1620 throw new IllegalArgumentException();
1621 }
1622 }
1623 @Override
1624 public void onStart(VirtualThreadTask task) {
1625 check(task);
1626 delegate.onStart(task);
1627 }
1628 @Override
1629 public void onContinue(VirtualThreadTask task) {
1630 check(task);
1631 delegate.onContinue(task);
1632 }
1633 @Override
1634 public String toString() {
1635 return delegate.toString();
1636 }
1637 };
1638 }
1639
1640 /**
1641 * Schedule a runnable task to run after a delay.
1642 */
1643 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1644 if (USE_STPE) {
1645 return DelayedTaskSchedulers.schedule(command, delay, unit);
1646 } else {
1647 return scheduler.schedule(command, delay, unit);
1648 }
1649 }
1650
1651 /**
1652 * Supports scheduling a runnable task to run after a delay. It uses a number
1653 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1654 * work queue used. This class is used when using a custom scheduler.
1655 */
1656 static class DelayedTaskSchedulers {
1657 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1658
1659 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1660 long tid = Thread.currentThread().threadId();
1661 int index = (int) tid & (INSTANCE.length - 1);
1662 return INSTANCE[index].schedule(command, delay, unit);
1663 }
1664
1665 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1666 String propName = "jdk.virtualThreadScheduler.timerQueues";
1667 String propValue = System.getProperty(propName);
1668 int queueCount;
1669 if (propValue != null) {
1670 queueCount = Integer.parseInt(propValue);
1671 if (queueCount != Integer.highestOneBit(queueCount)) {
1672 throw new RuntimeException("Value of " + propName + " must be power of 2");
1673 }
1674 } else {
1675 int ncpus = Runtime.getRuntime().availableProcessors();
1676 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
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