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.Executor;
30 import java.util.concurrent.Executors;
31 import java.util.concurrent.ForkJoinPool;
32 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
33 import java.util.concurrent.ForkJoinTask;
34 import java.util.concurrent.Future;
35 import java.util.concurrent.RejectedExecutionException;
36 import java.util.concurrent.ScheduledExecutorService;
37 import java.util.concurrent.ScheduledThreadPoolExecutor;
38 import java.util.concurrent.TimeUnit;
39 import jdk.internal.event.VirtualThreadEndEvent;
40 import jdk.internal.event.VirtualThreadStartEvent;
41 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
42 import jdk.internal.misc.CarrierThread;
43 import jdk.internal.misc.InnocuousThread;
44 import jdk.internal.misc.Unsafe;
45 import jdk.internal.vm.Continuation;
46 import jdk.internal.vm.ContinuationScope;
47 import jdk.internal.vm.StackableScope;
48 import jdk.internal.vm.ThreadContainer;
49 import jdk.internal.vm.ThreadContainers;
50 import jdk.internal.vm.annotation.ChangesCurrentThread;
51 import jdk.internal.vm.annotation.Hidden;
52 import jdk.internal.vm.annotation.IntrinsicCandidate;
53 import jdk.internal.vm.annotation.JvmtiHideEvents;
54 import jdk.internal.vm.annotation.JvmtiMountTransition;
55 import jdk.internal.vm.annotation.ReservedStackAccess;
56 import sun.nio.ch.Interruptible;
57 import static java.util.concurrent.TimeUnit.*;
58
59 /**
60 * A thread that is scheduled by the Java virtual machine rather than the operating system.
61 */
62 final class VirtualThread extends BaseVirtualThread {
63 private static final Unsafe U = Unsafe.getUnsafe();
64 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
65 private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();
66
67 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
68 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
69 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
70 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
71
72 // scheduler and continuation
73 private final Executor scheduler;
74 private final Continuation cont;
75 private final Runnable runContinuation;
76
77 // virtual thread state, accessed by VM
78 private volatile int state;
79
80 /*
81 * Virtual thread state transitions:
82 *
83 * NEW -> STARTED // Thread.start, schedule to run
84 * STARTED -> TERMINATED // failed to start
85 * STARTED -> RUNNING // first run
86 * RUNNING -> TERMINATED // done
87 *
88 * RUNNING -> PARKING // Thread parking with LockSupport.park
89 * PARKING -> PARKED // cont.yield successful, parked indefinitely
90 * PARKED -> UNPARKED // unparked, may be scheduled to continue
91 * UNPARKED -> RUNNING // continue execution after park
92 *
93 * PARKING -> RUNNING // cont.yield failed, need to park on carrier
94 * RUNNING -> PINNED // park on carrier
95 * PINNED -> RUNNING // unparked, continue execution on same carrier
169
170 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
171 private volatile boolean interruptibleWait;
172
173 // timed-wait support
174 private byte timedWaitSeqNo;
175
176 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
177 private long timeout;
178
179 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
180 private Future<?> timeoutTask;
181
182 // carrier thread when mounted, accessed by VM
183 private volatile Thread carrierThread;
184
185 // true to notifyAll after this virtual thread terminates
186 private volatile boolean notifyAllAfterTerminate;
187
188 /**
189 * Returns the default scheduler.
190 */
191 static Executor defaultScheduler() {
192 return DEFAULT_SCHEDULER;
193 }
194
195 /**
196 * Returns the continuation scope used for virtual threads.
197 */
198 static ContinuationScope continuationScope() {
199 return VTHREAD_SCOPE;
200 }
201
202 /**
203 * Creates a new {@code VirtualThread} to run the given task with the given
204 * scheduler. If the given scheduler is {@code null} and the current thread
205 * is a platform thread then the newly created virtual thread will use the
206 * default scheduler. If given scheduler is {@code null} and the current
207 * thread is a virtual thread then the current thread's scheduler is used.
208 *
209 * @param scheduler the scheduler or null
210 * @param name thread name
211 * @param characteristics characteristics
212 * @param task the task to execute
213 */
214 VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
215 super(name, characteristics, /*bound*/ false);
216 Objects.requireNonNull(task);
217
218 // choose scheduler if not specified
219 if (scheduler == null) {
220 Thread parent = Thread.currentThread();
221 if (parent instanceof VirtualThread vparent) {
222 scheduler = vparent.scheduler;
223 } else {
224 scheduler = DEFAULT_SCHEDULER;
225 }
226 }
227
228 this.scheduler = scheduler;
229 this.cont = new VThreadContinuation(this, task);
230 this.runContinuation = this::runContinuation;
231 }
232
233 /**
234 * The continuation that a virtual thread executes.
235 */
236 private static class VThreadContinuation extends Continuation {
237 VThreadContinuation(VirtualThread vthread, Runnable task) {
238 super(VTHREAD_SCOPE, wrap(vthread, task));
239 }
240 @Override
241 protected void onPinned(Continuation.Pinned reason) {
242 }
243 private static Runnable wrap(VirtualThread vthread, Runnable task) {
244 return new Runnable() {
245 @Hidden
246 @JvmtiHideEvents
247 public void run() {
248 vthread.endFirstTransition();
249 try {
250 vthread.run(task);
298 if (cont.isDone()) {
299 afterDone();
300 } else {
301 afterYield();
302 }
303 }
304 }
305
306 /**
307 * Cancel timeout task when continuing after timed-park or timed-wait.
308 * The timeout task may be executing, or may have already completed.
309 */
310 private void cancelTimeoutTask() {
311 if (timeoutTask != null) {
312 timeoutTask.cancel(false);
313 timeoutTask = null;
314 }
315 }
316
317 /**
318 * Submits the given task to the given executor. If the scheduler is a
319 * ForkJoinPool then the task is first adapted to a ForkJoinTask.
320 */
321 private void submit(Executor executor, Runnable task) {
322 if (executor instanceof ForkJoinPool pool) {
323 pool.submit(ForkJoinTask.adapt(task));
324 } else {
325 executor.execute(task);
326 }
327 }
328
329 /**
330 * Submits the runContinuation task to the scheduler. For the default scheduler,
331 * and calling it on a worker thread, the task will be pushed to the local queue,
332 * otherwise it will be pushed to an external submission queue.
333 * @param scheduler the scheduler
334 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
335 * @throws RejectedExecutionException
336 */
337 private void submitRunContinuation(Executor scheduler, boolean retryOnOOME) {
338 boolean done = false;
339 while (!done) {
340 try {
341 // Pin the continuation to prevent the virtual thread from unmounting
342 // when submitting a task. For the default scheduler this ensures that
343 // the carrier doesn't change when pushing a task. For other schedulers
344 // it avoids deadlock that could arise due to carriers and virtual
345 // threads contending for a lock.
346 if (currentThread().isVirtual()) {
347 Continuation.pin();
348 try {
349 submit(scheduler, runContinuation);
350 } finally {
351 Continuation.unpin();
352 }
353 } else {
354 submit(scheduler, runContinuation);
355 }
356 done = true;
357 } catch (RejectedExecutionException ree) {
358 submitFailed(ree);
359 throw ree;
360 } catch (OutOfMemoryError e) {
361 if (retryOnOOME) {
362 U.park(false, 100_000_000); // 100ms
363 } else {
364 throw e;
365 }
366 }
367 }
368 }
369
370 /**
371 * Submits the runContinuation task to the given scheduler as an external submit.
372 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
373 * @throws RejectedExecutionException
374 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
375 */
376 private void externalSubmitRunContinuation(ForkJoinPool pool) {
377 assert Thread.currentThread() instanceof CarrierThread;
378 try {
379 pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
380 } catch (RejectedExecutionException ree) {
381 submitFailed(ree);
382 throw ree;
383 } catch (OutOfMemoryError e) {
384 submitRunContinuation(pool, true);
385 }
386 }
387
388 /**
389 * Submits the runContinuation task to the scheduler. For the default scheduler,
390 * and calling it on a worker thread, the task will be pushed to the local queue,
391 * otherwise it will be pushed to an external submission queue.
392 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
393 * @throws RejectedExecutionException
394 */
395 private void submitRunContinuation() {
396 submitRunContinuation(scheduler, true);
397 }
398
399 /**
400 * Lazy submit the runContinuation task if invoked on a carrier thread and its local
401 * queue is empty. If not empty, or invoked by another thread, then this method works
402 * like submitRunContinuation and just submits the task to the scheduler.
403 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
404 * @throws RejectedExecutionException
405 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
406 */
407 private void lazySubmitRunContinuation() {
408 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
409 ForkJoinPool pool = ct.getPool();
410 try {
411 pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
412 } catch (RejectedExecutionException ree) {
413 submitFailed(ree);
414 throw ree;
415 } catch (OutOfMemoryError e) {
416 submitRunContinuation();
417 }
418 } else {
419 submitRunContinuation();
420 }
421 }
422
423 /**
424 * Submits the runContinuation task to the scheduler. For the default scheduler, and
425 * calling it a virtual thread that uses the default scheduler, the task will be
426 * pushed to an external submission queue. This method may throw OutOfMemoryError.
427 * @throws RejectedExecutionException
428 * @throws OutOfMemoryError
429 */
430 private void externalSubmitRunContinuationOrThrow() {
431 if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
432 try {
433 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
434 } catch (RejectedExecutionException ree) {
435 submitFailed(ree);
436 throw ree;
437 }
438 } else {
439 submitRunContinuation(scheduler, false);
440 }
441 }
442
443 /**
444 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
445 */
446 private void submitFailed(RejectedExecutionException ree) {
447 var event = new VirtualThreadSubmitFailedEvent();
448 if (event.isEnabled()) {
449 event.javaThreadId = threadId();
450 event.exceptionMessage = ree.getMessage();
451 event.commit();
452 }
453 }
454
455 /**
456 * Runs a task in the context of this virtual thread.
457 */
458 private void run(Runnable task) {
459 assert Thread.currentThread() == this && state == RUNNING;
576 long timeout = this.timeout;
577 assert timeout > 0;
578 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
579 setState(newState = TIMED_PARKED);
580 }
581
582 // may have been unparked while parking
583 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
584 // lazy submit if local queue is empty
585 lazySubmitRunContinuation();
586 }
587 return;
588 }
589
590 // Thread.yield
591 if (s == YIELDING) {
592 setState(YIELDED);
593
594 // external submit if there are no tasks in the local task queue
595 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
596 externalSubmitRunContinuation(ct.getPool());
597 } else {
598 submitRunContinuation();
599 }
600 return;
601 }
602
603 // blocking on monitorenter
604 if (s == BLOCKING) {
605 setState(BLOCKED);
606
607 // may have been unblocked while blocking
608 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
609 // lazy submit if local queue is empty
610 lazySubmitRunContinuation();
611 }
612 return;
613 }
614
615 // Object.wait
616 if (s == WAITING || s == TIMED_WAITING) {
681 notifyAll();
682 }
683 }
684
685 // notify container
686 if (notifyContainer) {
687 threadContainer().remove(this);
688 }
689
690 // clear references to thread locals
691 clearReferences();
692 }
693
694 /**
695 * Schedules this {@code VirtualThread} to execute.
696 *
697 * @throws IllegalStateException if the container is shutdown or closed
698 * @throws IllegalThreadStateException if the thread has already been started
699 * @throws RejectedExecutionException if the scheduler cannot accept a task
700 */
701 @Override
702 void start(ThreadContainer container) {
703 if (!compareAndSetState(NEW, STARTED)) {
704 throw new IllegalThreadStateException("Already started");
705 }
706
707 // bind thread to container
708 assert threadContainer() == null;
709 setThreadContainer(container);
710
711 // start thread
712 boolean addedToContainer = false;
713 boolean started = false;
714 try {
715 container.add(this); // may throw
716 addedToContainer = true;
717
718 // scoped values may be inherited
719 inheritScopedValueBindings(container);
720
721 // submit task to run thread, using externalSubmit if possible
722 externalSubmitRunContinuationOrThrow();
723 started = true;
724 } finally {
725 if (!started) {
726 afterDone(addedToContainer);
727 }
728 }
729 }
730
731 @Override
732 public void start() {
733 start(ThreadContainers.root());
734 }
735
736 @Override
737 public void run() {
738 // do nothing
739 }
740
741 /**
742 * Invoked by Thread.join before a thread waits for this virtual thread to terminate.
743 */
744 void beforeJoin() {
745 notifyAllAfterTerminate = true;
746 }
747
748 /**
749 * Parks until unparked or interrupted. If already unparked then the parking
750 * permit is consumed and this method completes immediately (meaning it doesn't
751 * yield). It also completes immediately if the interrupted status is set.
752 */
753 @Override
857 * Call into VM when pinned to record a JFR jdk.VirtualThreadPinned event.
858 * Recording the event in the VM avoids having JFR event recorded in Java
859 * with the same name, but different ID, to events recorded by the VM.
860 */
861 @Hidden
862 private static native void postPinnedEvent(String op);
863
864 /**
865 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
866 * then its task is scheduled to continue, otherwise its next call to {@code park} or
867 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
868 * @param lazySubmit to use lazySubmit if possible
869 * @throws RejectedExecutionException if the scheduler cannot accept a task
870 */
871 private void unpark(boolean lazySubmit) {
872 if (!getAndSetParkPermit(true) && currentThread() != this) {
873 int s = state();
874
875 // unparked while parked
876 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
877 if (lazySubmit) {
878 lazySubmitRunContinuation();
879 } else {
880 submitRunContinuation();
881 }
882 return;
883 }
884
885 // unparked while parked when pinned
886 if (s == PINNED || s == TIMED_PINNED) {
887 // unpark carrier thread when pinned
888 disableSuspendAndPreempt();
889 try {
890 synchronized (carrierThreadAccessLock()) {
891 Thread carrier = carrierThread;
892 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
893 U.unpark(carrier);
894 }
895 }
896 } finally {
897 enableSuspendAndPreempt();
898 }
899 return;
900 }
901 }
902 }
903
904 @Override
905 void unpark() {
906 unpark(false);
907 }
908
909 /**
910 * Invoked by unblocker thread to unblock this virtual thread.
911 */
912 private void unblock() {
913 assert !Thread.currentThread().isVirtual();
914 blockPermit = true;
915 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) {
916 submitRunContinuation();
917 }
918 }
919
920 /**
921 * Invoked by FJP worker thread or STPE thread when park timeout expires.
922 */
923 private void parkTimeoutExpired() {
924 assert !VirtualThread.currentThread().isVirtual();
925 unpark(true);
926 }
927
928 /**
1308 @IntrinsicCandidate
1309 @JvmtiMountTransition
1310 private native void startTransition(boolean mount);
1311
1312 @IntrinsicCandidate
1313 @JvmtiMountTransition
1314 private native void endTransition(boolean mount);
1315
1316 @IntrinsicCandidate
1317 private static native void notifyJvmtiDisableSuspend(boolean enter);
1318
1319 private static native void registerNatives();
1320 static {
1321 registerNatives();
1322
1323 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1324 var group = Thread.virtualThreadGroup();
1325 }
1326
1327 /**
1328 * Creates the default ForkJoinPool scheduler.
1329 */
1330 private static ForkJoinPool createDefaultScheduler() {
1331 ForkJoinWorkerThreadFactory factory = pool -> new CarrierThread(pool);
1332 int parallelism, maxPoolSize, minRunnable;
1333 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1334 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1335 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1336 if (parallelismValue != null) {
1337 parallelism = Integer.parseInt(parallelismValue);
1338 } else {
1339 parallelism = Runtime.getRuntime().availableProcessors();
1340 }
1341 if (maxPoolSizeValue != null) {
1342 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1343 parallelism = Integer.min(parallelism, maxPoolSize);
1344 } else {
1345 maxPoolSize = Integer.max(parallelism, 256);
1346 }
1347 if (minRunnableValue != null) {
1348 minRunnable = Integer.parseInt(minRunnableValue);
1349 } else {
1350 minRunnable = Integer.max(parallelism / 2, 1);
1351 }
1352 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1353 boolean asyncMode = true; // FIFO
1354 return new ForkJoinPool(parallelism, factory, handler, asyncMode,
1355 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1356 }
1357
1358 /**
1359 * Schedule a runnable task to run after a delay.
1360 */
1361 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1362 if (scheduler instanceof ForkJoinPool pool) {
1363 return pool.schedule(command, delay, unit);
1364 } else {
1365 return DelayedTaskSchedulers.schedule(command, delay, unit);
1366 }
1367 }
1368
1369 /**
1370 * Supports scheduling a runnable task to run after a delay. It uses a number
1371 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1372 * work queue used. This class is used when using a custom scheduler.
1373 */
1374 private static class DelayedTaskSchedulers {
1375 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1376
1377 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1378 long tid = Thread.currentThread().threadId();
1379 int index = (int) tid & (INSTANCE.length - 1);
1380 return INSTANCE[index].schedule(command, delay, unit);
1381 }
1382
1383 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1384 String propName = "jdk.virtualThreadScheduler.timerQueues";
1385 String propValue = System.getProperty(propName);
1386 int queueCount;
1387 if (propValue != null) {
1388 queueCount = Integer.parseInt(propValue);
1389 if (queueCount != Integer.highestOneBit(queueCount)) {
1390 throw new RuntimeException("Value of " + propName + " must be power of 2");
1391 }
1392 } else {
1393 int ncpus = Runtime.getRuntime().availableProcessors();
1394 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.Executors;
33 import java.util.concurrent.ForkJoinPool;
34 import java.util.concurrent.ForkJoinTask;
35 import java.util.concurrent.Future;
36 import java.util.concurrent.LinkedTransferQueue;
37 import java.util.concurrent.RejectedExecutionException;
38 import java.util.concurrent.ScheduledExecutorService;
39 import java.util.concurrent.ScheduledFuture;
40 import java.util.concurrent.ScheduledThreadPoolExecutor;
41 import java.util.concurrent.ThreadFactory;
42 import java.util.concurrent.ThreadPoolExecutor;
43 import java.util.concurrent.TimeUnit;
44 import jdk.internal.event.VirtualThreadEndEvent;
45 import jdk.internal.event.VirtualThreadStartEvent;
46 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
47 import jdk.internal.invoke.MhUtil;
48 import jdk.internal.misc.CarrierThread;
49 import jdk.internal.misc.InnocuousThread;
50 import jdk.internal.misc.Unsafe;
51 import jdk.internal.vm.Continuation;
52 import jdk.internal.vm.ContinuationScope;
53 import jdk.internal.vm.StackableScope;
54 import jdk.internal.vm.ThreadContainer;
55 import jdk.internal.vm.ThreadContainers;
56 import jdk.internal.vm.annotation.ChangesCurrentThread;
57 import jdk.internal.vm.annotation.Hidden;
58 import jdk.internal.vm.annotation.IntrinsicCandidate;
59 import jdk.internal.vm.annotation.JvmtiHideEvents;
60 import jdk.internal.vm.annotation.JvmtiMountTransition;
61 import jdk.internal.vm.annotation.ReservedStackAccess;
62 import sun.nio.ch.Interruptible;
63 import static java.util.concurrent.TimeUnit.*;
64
65 /**
66 * A thread that is scheduled by the Java virtual machine rather than the operating system.
67 */
68 final class VirtualThread extends BaseVirtualThread {
69 private static final Unsafe U = Unsafe.getUnsafe();
70 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
71
72 private static final VirtualThreadScheduler BUILTIN_SCHEDULER;
73 private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
74 private static final VirtualThreadScheduler EXTERNAL_VIEW;
75 private static final boolean USE_STPE;
76 static {
77 // experimental
78 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
79 if (propValue != null) {
80 VirtualThreadScheduler builtinScheduler = createBuiltinScheduler(true);
81 VirtualThreadScheduler externalView = createExternalView(builtinScheduler);
82 VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue);
83 BUILTIN_SCHEDULER = builtinScheduler;
84 DEFAULT_SCHEDULER = defaultScheduler;
85 EXTERNAL_VIEW = externalView;
86 } else {
87 var builtinScheduler = createBuiltinScheduler(false);
88 BUILTIN_SCHEDULER = builtinScheduler;
89 DEFAULT_SCHEDULER = builtinScheduler;
90 EXTERNAL_VIEW = createExternalView(builtinScheduler);
91 }
92 USE_STPE = Boolean.getBoolean("jdk.virtualThreadScheduler.useSTPE");
93 }
94
95 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
96 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
97 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
98 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
99
100 // scheduler and continuation
101 private final VirtualThreadScheduler scheduler;
102 private final Continuation cont;
103 private final VThreadTask runContinuation;
104
105 // virtual thread state, accessed by VM
106 private volatile int state;
107
108 /*
109 * Virtual thread state transitions:
110 *
111 * NEW -> STARTED // Thread.start, schedule to run
112 * STARTED -> TERMINATED // failed to start
113 * STARTED -> RUNNING // first run
114 * RUNNING -> TERMINATED // done
115 *
116 * RUNNING -> PARKING // Thread parking with LockSupport.park
117 * PARKING -> PARKED // cont.yield successful, parked indefinitely
118 * PARKED -> UNPARKED // unparked, may be scheduled to continue
119 * UNPARKED -> RUNNING // continue execution after park
120 *
121 * PARKING -> RUNNING // cont.yield failed, need to park on carrier
122 * RUNNING -> PINNED // park on carrier
123 * PINNED -> RUNNING // unparked, continue execution on same carrier
197
198 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
199 private volatile boolean interruptibleWait;
200
201 // timed-wait support
202 private byte timedWaitSeqNo;
203
204 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
205 private long timeout;
206
207 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
208 private Future<?> timeoutTask;
209
210 // carrier thread when mounted, accessed by VM
211 private volatile Thread carrierThread;
212
213 // true to notifyAll after this virtual thread terminates
214 private volatile boolean notifyAllAfterTerminate;
215
216 /**
217 * Return the built-in scheduler.
218 * @param trusted true if caller is trusted, false if not trusted
219 */
220 static VirtualThreadScheduler builtinScheduler(boolean trusted) {
221 return trusted ? BUILTIN_SCHEDULER : EXTERNAL_VIEW;
222 }
223
224 /**
225 * Returns the default scheduler, usually the same as the built-in scheduler.
226 */
227 static VirtualThreadScheduler defaultScheduler() {
228 return DEFAULT_SCHEDULER;
229 }
230
231 /**
232 * Returns the continuation scope used for virtual threads.
233 */
234 static ContinuationScope continuationScope() {
235 return VTHREAD_SCOPE;
236 }
237
238 /**
239 * Returns the task to start/continue this virtual thread.
240 */
241 VirtualThreadTask virtualThreadTask() {
242 return runContinuation;
243 }
244
245 /**
246 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
247 *
248 * @param scheduler the scheduler or null for default scheduler
249 * @param preferredCarrier the preferred carrier or null
250 * @param name thread name
251 * @param characteristics characteristics
252 * @param task the task to execute
253 */
254 VirtualThread(VirtualThreadScheduler scheduler,
255 Thread preferredCarrier,
256 String name,
257 int characteristics,
258 Runnable task) {
259 super(name, characteristics, /*bound*/ false);
260 Objects.requireNonNull(task);
261
262 // use default scheduler if not provided
263 if (scheduler == null) {
264 scheduler = DEFAULT_SCHEDULER;
265 } else if (scheduler == EXTERNAL_VIEW) {
266 throw new UnsupportedOperationException();
267 }
268 this.scheduler = scheduler;
269 this.cont = new VThreadContinuation(this, task);
270
271 if (scheduler == BUILTIN_SCHEDULER) {
272 this.runContinuation = new VThreadTask(this);
273 } else {
274 this.runContinuation = new CustomVThreadTask(this, preferredCarrier);
275 }
276 }
277
278 /**
279 * The task to start/continue a virtual thread.
280 */
281 static non-sealed class VThreadTask implements VirtualThreadTask {
282 private final VirtualThread vthread;
283 VThreadTask(VirtualThread vthread) {
284 this.vthread = vthread;
285 }
286 @Override
287 public final Thread thread() {
288 return vthread;
289 }
290 @Override
291 public final void run() {
292 vthread.runContinuation();;
293 }
294 @Override
295 public Thread preferredCarrier() {
296 throw new UnsupportedOperationException();
297 }
298 @Override
299 public Object attach(Object att) {
300 throw new UnsupportedOperationException();
301 }
302 @Override
303 public Object attachment() {
304 throw new UnsupportedOperationException();
305 }
306 }
307
308 /**
309 * The task to start/continue a virtual thread when using a custom scheduler.
310 */
311 static final class CustomVThreadTask extends VThreadTask {
312 private static final VarHandle ATT =
313 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class);
314 private final Thread preferredCarrier;
315 private volatile Object att;
316 CustomVThreadTask(VirtualThread vthread, Thread preferredCarrier) {
317 super(vthread);
318 this.preferredCarrier = preferredCarrier;
319 }
320 @Override
321 public Thread preferredCarrier() {
322 return preferredCarrier;
323 }
324 @Override
325 public Object attach(Object att) {
326 return ATT.getAndSet(this, att);
327 }
328 @Override
329 public Object attachment() {
330 return att;
331 }
332 }
333
334 /**
335 * The continuation that a virtual thread executes.
336 */
337 private static class VThreadContinuation extends Continuation {
338 VThreadContinuation(VirtualThread vthread, Runnable task) {
339 super(VTHREAD_SCOPE, wrap(vthread, task));
340 }
341 @Override
342 protected void onPinned(Continuation.Pinned reason) {
343 }
344 private static Runnable wrap(VirtualThread vthread, Runnable task) {
345 return new Runnable() {
346 @Hidden
347 @JvmtiHideEvents
348 public void run() {
349 vthread.endFirstTransition();
350 try {
351 vthread.run(task);
399 if (cont.isDone()) {
400 afterDone();
401 } else {
402 afterYield();
403 }
404 }
405 }
406
407 /**
408 * Cancel timeout task when continuing after timed-park or timed-wait.
409 * The timeout task may be executing, or may have already completed.
410 */
411 private void cancelTimeoutTask() {
412 if (timeoutTask != null) {
413 timeoutTask.cancel(false);
414 timeoutTask = null;
415 }
416 }
417
418 /**
419 * Submits the runContinuation task to the scheduler. For the built-in scheduler,
420 * the task will be pushed to the local queue if possible, otherwise it will be
421 * pushed to an external submission queue.
422 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
423 * @throws RejectedExecutionException
424 */
425 private void submitRunContinuation(boolean retryOnOOME) {
426 boolean done = false;
427 while (!done) {
428 try {
429 // Pin the continuation to prevent the virtual thread from unmounting
430 // when submitting a task. For the default scheduler this ensures that
431 // the carrier doesn't change when pushing a task. For other schedulers
432 // it avoids deadlock that could arise due to carriers and virtual
433 // threads contending for a lock.
434 if (currentThread().isVirtual()) {
435 Continuation.pin();
436 try {
437 scheduler.onContinue(runContinuation);
438 } finally {
439 Continuation.unpin();
440 }
441 } else {
442 scheduler.onContinue(runContinuation);
443 }
444 done = true;
445 } catch (RejectedExecutionException ree) {
446 submitFailed(ree);
447 throw ree;
448 } catch (OutOfMemoryError e) {
449 if (retryOnOOME) {
450 U.park(false, 100_000_000); // 100ms
451 } else {
452 throw e;
453 }
454 }
455 }
456 }
457
458 /**
459 * Submits the runContinuation task to the scheduler. For the default scheduler,
460 * and calling it on a worker thread, the task will be pushed to the local queue,
461 * otherwise it will be pushed to an external submission queue.
462 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
463 * @throws RejectedExecutionException
464 */
465 private void submitRunContinuation() {
466 submitRunContinuation(true);
467 }
468
469 /**
470 * Invoked from a carrier thread to lazy submit the runContinuation task to the
471 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
472 * for a custom scheduler, then it just submits the task to the scheduler.
473 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
474 * @throws RejectedExecutionException
475 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
476 */
477 private void lazySubmitRunContinuation() {
478 assert !currentThread().isVirtual();
479 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
480 try {
481 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
482 } catch (RejectedExecutionException ree) {
483 submitFailed(ree);
484 throw ree;
485 } catch (OutOfMemoryError e) {
486 submitRunContinuation();
487 }
488 } else {
489 submitRunContinuation();
490 }
491 }
492
493 /**
494 * Invoked from a carrier thread to externally submit the runContinuation task to the
495 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
496 * task to the scheduler.
497 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
498 * @throws RejectedExecutionException
499 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
500 */
501 private void externalSubmitRunContinuation() {
502 assert !currentThread().isVirtual();
503 if (currentThread() instanceof CarrierThread ct) {
504 try {
505 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
506 } catch (RejectedExecutionException ree) {
507 submitFailed(ree);
508 throw ree;
509 } catch (OutOfMemoryError e) {
510 submitRunContinuation();
511 }
512 } else {
513 submitRunContinuation();
514 }
515 }
516
517 /**
518 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
519 */
520 private void submitFailed(RejectedExecutionException ree) {
521 var event = new VirtualThreadSubmitFailedEvent();
522 if (event.isEnabled()) {
523 event.javaThreadId = threadId();
524 event.exceptionMessage = ree.getMessage();
525 event.commit();
526 }
527 }
528
529 /**
530 * Runs a task in the context of this virtual thread.
531 */
532 private void run(Runnable task) {
533 assert Thread.currentThread() == this && state == RUNNING;
650 long timeout = this.timeout;
651 assert timeout > 0;
652 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
653 setState(newState = TIMED_PARKED);
654 }
655
656 // may have been unparked while parking
657 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
658 // lazy submit if local queue is empty
659 lazySubmitRunContinuation();
660 }
661 return;
662 }
663
664 // Thread.yield
665 if (s == YIELDING) {
666 setState(YIELDED);
667
668 // external submit if there are no tasks in the local task queue
669 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
670 externalSubmitRunContinuation();
671 } else {
672 submitRunContinuation();
673 }
674 return;
675 }
676
677 // blocking on monitorenter
678 if (s == BLOCKING) {
679 setState(BLOCKED);
680
681 // may have been unblocked while blocking
682 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
683 // lazy submit if local queue is empty
684 lazySubmitRunContinuation();
685 }
686 return;
687 }
688
689 // Object.wait
690 if (s == WAITING || s == TIMED_WAITING) {
755 notifyAll();
756 }
757 }
758
759 // notify container
760 if (notifyContainer) {
761 threadContainer().remove(this);
762 }
763
764 // clear references to thread locals
765 clearReferences();
766 }
767
768 /**
769 * Schedules this {@code VirtualThread} to execute.
770 *
771 * @throws IllegalStateException if the container is shutdown or closed
772 * @throws IllegalThreadStateException if the thread has already been started
773 * @throws RejectedExecutionException if the scheduler cannot accept a task
774 */
775 private void start(ThreadContainer container, boolean lazy) {
776 if (!compareAndSetState(NEW, STARTED)) {
777 throw new IllegalThreadStateException("Already started");
778 }
779
780 // bind thread to container
781 assert threadContainer() == null;
782 setThreadContainer(container);
783
784 // start thread
785 boolean addedToContainer = false;
786 boolean started = false;
787 try {
788 container.add(this); // may throw
789 addedToContainer = true;
790
791 // scoped values may be inherited
792 inheritScopedValueBindings(container);
793
794 // submit task to schedule
795 try {
796 if (currentThread().isVirtual()) {
797 Continuation.pin();
798 try {
799 if (scheduler == BUILTIN_SCHEDULER
800 && currentCarrierThread() instanceof CarrierThread ct) {
801 ForkJoinPool pool = ct.getPool();
802 ForkJoinTask<?> task = ForkJoinTask.adapt(runContinuation);
803 if (lazy) {
804 pool.lazySubmit(task);
805 } else {
806 pool.externalSubmit(task);
807 }
808 } else {
809 scheduler.onStart(runContinuation);
810 }
811 } finally {
812 Continuation.unpin();
813 }
814 } else {
815 scheduler.onStart(runContinuation);
816 }
817 } catch (RejectedExecutionException ree) {
818 submitFailed(ree);
819 throw ree;
820 }
821
822 started = true;
823 } finally {
824 if (!started) {
825 afterDone(addedToContainer);
826 }
827 }
828 }
829
830 @Override
831 void start(ThreadContainer container) {
832 start(container, false);
833 }
834
835 @Override
836 public void start() {
837 start(ThreadContainers.root(), false);
838 }
839
840 /**
841 * Schedules this thread to begin execution without guarantee that it will execute.
842 */
843 void lazyStart() {
844 start(ThreadContainers.root(), true);
845 }
846
847 @Override
848 public void run() {
849 // do nothing
850 }
851
852 /**
853 * Invoked by Thread.join before a thread waits for this virtual thread to terminate.
854 */
855 void beforeJoin() {
856 notifyAllAfterTerminate = true;
857 }
858
859 /**
860 * Parks until unparked or interrupted. If already unparked then the parking
861 * permit is consumed and this method completes immediately (meaning it doesn't
862 * yield). It also completes immediately if the interrupted status is set.
863 */
864 @Override
968 * Call into VM when pinned to record a JFR jdk.VirtualThreadPinned event.
969 * Recording the event in the VM avoids having JFR event recorded in Java
970 * with the same name, but different ID, to events recorded by the VM.
971 */
972 @Hidden
973 private static native void postPinnedEvent(String op);
974
975 /**
976 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
977 * then its task is scheduled to continue, otherwise its next call to {@code park} or
978 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
979 * @param lazySubmit to use lazySubmit if possible
980 * @throws RejectedExecutionException if the scheduler cannot accept a task
981 */
982 private void unpark(boolean lazySubmit) {
983 if (!getAndSetParkPermit(true) && currentThread() != this) {
984 int s = state();
985
986 // unparked while parked
987 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
988
989 if (lazySubmit && currentThread().isVirtual()) {
990 Continuation.pin();
991 try {
992 if (scheduler == BUILTIN_SCHEDULER
993 && currentCarrierThread() instanceof CarrierThread ct) {
994 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
995 return;
996 }
997 } catch (RejectedExecutionException ree) {
998 submitFailed(ree);
999 throw ree;
1000 } catch (OutOfMemoryError e) {
1001 // fall-though
1002 } finally {
1003 Continuation.unpin();
1004 }
1005 }
1006
1007 submitRunContinuation();
1008 return;
1009 }
1010
1011 // unparked while parked when pinned
1012 if (s == PINNED || s == TIMED_PINNED) {
1013 // unpark carrier thread when pinned
1014 disableSuspendAndPreempt();
1015 try {
1016 synchronized (carrierThreadAccessLock()) {
1017 Thread carrier = carrierThread;
1018 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
1019 U.unpark(carrier);
1020 }
1021 }
1022 } finally {
1023 enableSuspendAndPreempt();
1024 }
1025 return;
1026 }
1027 }
1028 }
1029
1030 @Override
1031 void unpark() {
1032 unpark(false);
1033 }
1034
1035 @Override
1036 void lazyUnpark() {
1037 unpark(true);
1038 }
1039
1040 /**
1041 * Invoked by unblocker thread to unblock this virtual thread.
1042 */
1043 private void unblock() {
1044 assert !Thread.currentThread().isVirtual();
1045 blockPermit = true;
1046 if (state() == BLOCKED && compareAndSetState(BLOCKED, UNBLOCKED)) {
1047 submitRunContinuation();
1048 }
1049 }
1050
1051 /**
1052 * Invoked by FJP worker thread or STPE thread when park timeout expires.
1053 */
1054 private void parkTimeoutExpired() {
1055 assert !VirtualThread.currentThread().isVirtual();
1056 unpark(true);
1057 }
1058
1059 /**
1439 @IntrinsicCandidate
1440 @JvmtiMountTransition
1441 private native void startTransition(boolean mount);
1442
1443 @IntrinsicCandidate
1444 @JvmtiMountTransition
1445 private native void endTransition(boolean mount);
1446
1447 @IntrinsicCandidate
1448 private static native void notifyJvmtiDisableSuspend(boolean enter);
1449
1450 private static native void registerNatives();
1451 static {
1452 registerNatives();
1453
1454 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1455 var group = Thread.virtualThreadGroup();
1456 }
1457
1458 /**
1459 * Loads a VirtualThreadScheduler with the given class name. The class must be public
1460 * in an exported package, with public one-arg or no-arg constructor, and be visible
1461 * to the system class loader.
1462 * @param delegate the scheduler that the custom scheduler may delegate to
1463 * @param cn the class name of the custom scheduler
1464 */
1465 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
1466 VirtualThreadScheduler scheduler;
1467 try {
1468 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1469 // 1-arg constructor
1470 try {
1471 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1472 return (VirtualThreadScheduler) ctor.newInstance(delegate);
1473 } catch (NoSuchMethodException e) {
1474 // 0-arg constructor
1475 Constructor<?> ctor = clazz.getConstructor();
1476 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1477 }
1478 } catch (Exception ex) {
1479 throw new Error(ex);
1480 }
1481 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!");
1482 return scheduler;
1483 }
1484
1485 /**
1486 * Creates the built-in ForkJoinPool scheduler.
1487 * @param wrapped true if wrapped by a custom default scheduler
1488 */
1489 private static VirtualThreadScheduler createBuiltinScheduler(boolean wrapped) {
1490 int parallelism, maxPoolSize, minRunnable;
1491 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1492 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1493 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1494 if (parallelismValue != null) {
1495 parallelism = Integer.parseInt(parallelismValue);
1496 } else {
1497 parallelism = Runtime.getRuntime().availableProcessors();
1498 }
1499 if (maxPoolSizeValue != null) {
1500 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1501 parallelism = Integer.min(parallelism, maxPoolSize);
1502 } else {
1503 maxPoolSize = Integer.max(parallelism, 256);
1504 }
1505 if (minRunnableValue != null) {
1506 minRunnable = Integer.parseInt(minRunnableValue);
1507 } else {
1508 minRunnable = Integer.max(parallelism / 2, 1);
1509 }
1510 if (Boolean.getBoolean("jdk.virtualThreadScheduler.useTPE")) {
1511 return new BuiltinThreadPoolExecutorScheduler(parallelism);
1512 } else {
1513 return new BuiltinForkJoinPoolScheduler(parallelism, maxPoolSize, minRunnable, wrapped);
1514 }
1515 }
1516
1517 /**
1518 * The built-in ForkJoinPool scheduler.
1519 */
1520 private static class BuiltinForkJoinPoolScheduler
1521 extends ForkJoinPool implements VirtualThreadScheduler {
1522
1523 BuiltinForkJoinPoolScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) {
1524 ForkJoinWorkerThreadFactory factory = wrapped
1525 ? ForkJoinPool.defaultForkJoinWorkerThreadFactory
1526 : CarrierThread::new;
1527 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1528 boolean asyncMode = true; // FIFO
1529 super(parallelism, factory, handler, asyncMode,
1530 0, maxPoolSize, minRunnable, pool -> true, 30L, SECONDS);
1531 }
1532
1533 @Override
1534 public void onStart(VirtualThreadTask task) {
1535 execute(ForkJoinTask.adapt(task));
1536 }
1537
1538 @Override
1539 public void onContinue(VirtualThreadTask task) {
1540 execute(ForkJoinTask.adapt(task));
1541 }
1542
1543 @Override
1544 public ScheduledFuture<?> schedule(Runnable task, long delay, TimeUnit unit) {
1545 return super.schedule(task, delay, unit);
1546 }
1547 }
1548
1549 /**
1550 * Built-in ThreadPoolExecutor scheduler.
1551 */
1552 private static class BuiltinThreadPoolExecutorScheduler
1553 extends ThreadPoolExecutor implements VirtualThreadScheduler {
1554
1555 BuiltinThreadPoolExecutorScheduler(int maxPoolSize) {
1556 ThreadFactory factory = task -> {
1557 Thread t = InnocuousThread.newThread(task);
1558 t.setDaemon(true);
1559 return t;
1560 };
1561 super(maxPoolSize, maxPoolSize,
1562 0L, SECONDS,
1563 new LinkedTransferQueue<>(),
1564 factory);
1565 }
1566
1567 @Override
1568 public void onStart(VirtualThreadTask task) {
1569 execute(task);
1570 }
1571
1572 @Override
1573 public void onContinue(VirtualThreadTask task) {
1574 execute(task);
1575 }
1576 }
1577
1578 /**
1579 * Wraps the scheduler to avoid leaking a direct reference to built-in scheduler.
1580 */
1581 static VirtualThreadScheduler createExternalView(VirtualThreadScheduler delegate) {
1582 return new VirtualThreadScheduler() {
1583 private void check(VirtualThreadTask task) {
1584 var vthread = (VirtualThread) task.thread();
1585 VirtualThreadScheduler scheduler = vthread.scheduler;
1586 if (scheduler != this && scheduler != DEFAULT_SCHEDULER) {
1587 throw new IllegalArgumentException();
1588 }
1589 }
1590 @Override
1591 public void onStart(VirtualThreadTask task) {
1592 check(task);
1593 delegate.onStart(task);
1594 }
1595 @Override
1596 public void onContinue(VirtualThreadTask task) {
1597 check(task);
1598 delegate.onContinue(task);
1599 }
1600 @Override
1601 public String toString() {
1602 return delegate.toString();
1603 }
1604 };
1605 }
1606
1607 /**
1608 * Schedule a runnable task to run after a delay.
1609 */
1610 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1611 if (USE_STPE) {
1612 return DelayedTaskSchedulers.schedule(command, delay, unit);
1613 } else {
1614 return scheduler.schedule(command, delay, unit);
1615 }
1616 }
1617
1618 /**
1619 * Supports scheduling a runnable task to run after a delay. It uses a number
1620 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1621 * work queue used. This class is used when using a custom scheduler.
1622 */
1623 static class DelayedTaskSchedulers {
1624 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1625
1626 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1627 long tid = Thread.currentThread().threadId();
1628 int index = (int) tid & (INSTANCE.length - 1);
1629 return INSTANCE[index].schedule(command, delay, unit);
1630 }
1631
1632 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1633 String propName = "jdk.virtualThreadScheduler.timerQueues";
1634 String propValue = System.getProperty(propName);
1635 int queueCount;
1636 if (propValue != null) {
1637 queueCount = Integer.parseInt(propValue);
1638 if (queueCount != Integer.highestOneBit(queueCount)) {
1639 throw new RuntimeException("Value of " + propName + " must be power of 2");
1640 }
1641 } else {
1642 int ncpus = Runtime.getRuntime().availableProcessors();
1643 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
|