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) {
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.
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 }
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 propValue = System.getProperty("jdk.virtualThreadScheduler.useSTPE");
93 if (propValue != null) {
94 USE_STPE = Boolean.parseBoolean(propValue);
95 } else {
96 USE_STPE = Runtime.getRuntime().availableProcessors() < 4;
97 }
98 }
99
100 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
101 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
102 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
103 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
104
105 // scheduler and continuation
106 private final VirtualThreadScheduler scheduler;
107 private final Continuation cont;
108 private final VThreadTask runContinuation;
109
110 // virtual thread state, accessed by VM
111 private volatile int state;
112
113 /*
114 * Virtual thread state transitions:
115 *
116 * NEW -> STARTED // Thread.start, schedule to run
117 * STARTED -> TERMINATED // failed to start
118 * STARTED -> RUNNING // first run
119 * RUNNING -> TERMINATED // done
120 *
121 * RUNNING -> PARKING // Thread parking with LockSupport.park
122 * PARKING -> PARKED // cont.yield successful, parked indefinitely
123 * PARKED -> UNPARKED // unparked, may be scheduled to continue
124 * UNPARKED -> RUNNING // continue execution after park
125 *
126 * PARKING -> RUNNING // cont.yield failed, need to park on carrier
127 * RUNNING -> PINNED // park on carrier
128 * PINNED -> RUNNING // unparked, continue execution on same carrier
202
203 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
204 private volatile boolean interruptibleWait;
205
206 // timed-wait support
207 private byte timedWaitSeqNo;
208
209 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
210 private long timeout;
211
212 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
213 private Future<?> timeoutTask;
214
215 // carrier thread when mounted, accessed by VM
216 private volatile Thread carrierThread;
217
218 // true to notifyAll after this virtual thread terminates
219 private volatile boolean notifyAllAfterTerminate;
220
221 /**
222 * Return the built-in scheduler.
223 * @param trusted true if caller is trusted, false if not trusted
224 */
225 static VirtualThreadScheduler builtinScheduler(boolean trusted) {
226 return trusted ? BUILTIN_SCHEDULER : EXTERNAL_VIEW;
227 }
228
229 /**
230 * Returns the default scheduler, usually the same as the built-in scheduler.
231 */
232 static VirtualThreadScheduler defaultScheduler() {
233 return DEFAULT_SCHEDULER;
234 }
235
236 /**
237 * Returns the continuation scope used for virtual threads.
238 */
239 static ContinuationScope continuationScope() {
240 return VTHREAD_SCOPE;
241 }
242
243 /**
244 * Returns the task to start/continue this virtual thread.
245 */
246 VirtualThreadTask virtualThreadTask() {
247 return runContinuation;
248 }
249
250 /**
251 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
252 *
253 * @param scheduler the scheduler or null for default scheduler
254 * @param preferredCarrier the preferred carrier or null
255 * @param name thread name
256 * @param characteristics characteristics
257 * @param task the task to execute
258 */
259 VirtualThread(VirtualThreadScheduler scheduler,
260 Thread preferredCarrier,
261 String name,
262 int characteristics,
263 Runnable task) {
264 super(name, characteristics, /*bound*/ false);
265 Objects.requireNonNull(task);
266
267 // use default scheduler if not provided
268 if (scheduler == null) {
269 scheduler = DEFAULT_SCHEDULER;
270 } else if (scheduler == EXTERNAL_VIEW) {
271 throw new UnsupportedOperationException();
272 }
273 this.scheduler = scheduler;
274 this.cont = new VThreadContinuation(this, task);
275
276 if (scheduler == BUILTIN_SCHEDULER) {
277 this.runContinuation = new VThreadTask(this);
278 } else {
279 this.runContinuation = new CustomVThreadTask(this, preferredCarrier);
280 }
281 }
282
283 /**
284 * The task to start/continue a virtual thread.
285 */
286 static non-sealed class VThreadTask implements VirtualThreadTask {
287 private final VirtualThread vthread;
288 VThreadTask(VirtualThread vthread) {
289 this.vthread = vthread;
290 }
291 @Override
292 public final Thread thread() {
293 return vthread;
294 }
295 @Override
296 public final void run() {
297 vthread.runContinuation();;
298 }
299 @Override
300 public Thread preferredCarrier() {
301 throw new UnsupportedOperationException();
302 }
303 @Override
304 public Object attach(Object att) {
305 throw new UnsupportedOperationException();
306 }
307 @Override
308 public Object attachment() {
309 throw new UnsupportedOperationException();
310 }
311 }
312
313 /**
314 * The task to start/continue a virtual thread when using a custom scheduler.
315 */
316 static final class CustomVThreadTask extends VThreadTask {
317 private static final VarHandle ATT =
318 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class);
319 private final Thread preferredCarrier;
320 private volatile Object att;
321 CustomVThreadTask(VirtualThread vthread, Thread preferredCarrier) {
322 super(vthread);
323 this.preferredCarrier = preferredCarrier;
324 }
325 @Override
326 public Thread preferredCarrier() {
327 return preferredCarrier;
328 }
329 @Override
330 public Object attach(Object att) {
331 return ATT.getAndSet(this, att);
332 }
333 @Override
334 public Object attachment() {
335 return att;
336 }
337 }
338
339 /**
340 * The continuation that a virtual thread executes.
341 */
342 private static class VThreadContinuation extends Continuation {
343 VThreadContinuation(VirtualThread vthread, Runnable task) {
344 super(VTHREAD_SCOPE, wrap(vthread, task));
345 }
346 @Override
347 protected void onPinned(Continuation.Pinned reason) {
348 }
349 private static Runnable wrap(VirtualThread vthread, Runnable task) {
350 return new Runnable() {
351 @Hidden
352 @JvmtiHideEvents
353 public void run() {
354 vthread.endFirstTransition();
355 try {
356 vthread.run(task);
404 if (cont.isDone()) {
405 afterDone();
406 } else {
407 afterYield();
408 }
409 }
410 }
411
412 /**
413 * Cancel timeout task when continuing after timed-park or timed-wait.
414 * The timeout task may be executing, or may have already completed.
415 */
416 private void cancelTimeoutTask() {
417 if (timeoutTask != null) {
418 timeoutTask.cancel(false);
419 timeoutTask = null;
420 }
421 }
422
423 /**
424 * Submits the runContinuation task to the scheduler. For the built-in scheduler,
425 * the task will be pushed to the local queue if possible, otherwise it will be
426 * pushed to an external submission queue.
427 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
428 * @throws RejectedExecutionException
429 */
430 private void submitRunContinuation(boolean retryOnOOME) {
431 boolean done = false;
432 while (!done) {
433 try {
434 // Pin the continuation to prevent the virtual thread from unmounting
435 // when submitting a task. For the default scheduler this ensures that
436 // the carrier doesn't change when pushing a task. For other schedulers
437 // it avoids deadlock that could arise due to carriers and virtual
438 // threads contending for a lock.
439 if (currentThread().isVirtual()) {
440 Continuation.pin();
441 try {
442 scheduler.onContinue(runContinuation);
443 } finally {
444 Continuation.unpin();
445 }
446 } else {
447 scheduler.onContinue(runContinuation);
448 }
449 done = true;
450 } catch (RejectedExecutionException ree) {
451 submitFailed(ree);
452 throw ree;
453 } catch (OutOfMemoryError e) {
454 if (retryOnOOME) {
455 U.park(false, 100_000_000); // 100ms
456 } else {
457 throw e;
458 }
459 }
460 }
461 }
462
463 /**
464 * Submits the runContinuation task to the scheduler. For the default scheduler,
465 * and calling it on a worker thread, the task will be pushed to the local queue,
466 * otherwise it will be pushed to an external submission queue.
467 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
468 * @throws RejectedExecutionException
469 */
470 private void submitRunContinuation() {
471 submitRunContinuation(true);
472 }
473
474 /**
475 * Invoked from a carrier thread to lazy submit the runContinuation task to the
476 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
477 * for a custom scheduler, then it just submits the task to the scheduler.
478 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
479 * @throws RejectedExecutionException
480 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
481 */
482 private void lazySubmitRunContinuation() {
483 assert !currentThread().isVirtual();
484 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
485 try {
486 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
487 } catch (RejectedExecutionException ree) {
488 submitFailed(ree);
489 throw ree;
490 } catch (OutOfMemoryError e) {
491 submitRunContinuation();
492 }
493 } else {
494 submitRunContinuation();
495 }
496 }
497
498 /**
499 * Invoked from a carrier thread to externally submit the runContinuation task to the
500 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
501 * task to the scheduler.
502 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
503 * @throws RejectedExecutionException
504 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
505 */
506 private void externalSubmitRunContinuation() {
507 assert !currentThread().isVirtual();
508 if (currentThread() instanceof CarrierThread ct) {
509 try {
510 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
511 } catch (RejectedExecutionException ree) {
512 submitFailed(ree);
513 throw ree;
514 } catch (OutOfMemoryError e) {
515 submitRunContinuation();
516 }
517 } else {
518 submitRunContinuation();
519 }
520 }
521
522 /**
523 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
524 */
525 private void submitFailed(RejectedExecutionException ree) {
526 var event = new VirtualThreadSubmitFailedEvent();
527 if (event.isEnabled()) {
528 event.javaThreadId = threadId();
529 event.exceptionMessage = ree.getMessage();
530 event.commit();
531 }
532 }
533
534 /**
535 * Runs a task in the context of this virtual thread.
536 */
537 private void run(Runnable task) {
538 assert Thread.currentThread() == this && state == RUNNING;
655 long timeout = this.timeout;
656 assert timeout > 0;
657 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
658 setState(newState = TIMED_PARKED);
659 }
660
661 // may have been unparked while parking
662 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
663 // lazy submit if local queue is empty
664 lazySubmitRunContinuation();
665 }
666 return;
667 }
668
669 // Thread.yield
670 if (s == YIELDING) {
671 setState(YIELDED);
672
673 // external submit if there are no tasks in the local task queue
674 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
675 externalSubmitRunContinuation();
676 } else {
677 submitRunContinuation();
678 }
679 return;
680 }
681
682 // blocking on monitorenter
683 if (s == BLOCKING) {
684 setState(BLOCKED);
685
686 // may have been unblocked while blocking
687 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
688 // lazy submit if local queue is empty
689 lazySubmitRunContinuation();
690 }
691 return;
692 }
693
694 // Object.wait
695 if (s == WAITING || s == TIMED_WAITING) {
780 @Override
781 void start(ThreadContainer container) {
782 if (!compareAndSetState(NEW, STARTED)) {
783 throw new IllegalThreadStateException("Already started");
784 }
785
786 // bind thread to container
787 assert threadContainer() == null;
788 setThreadContainer(container);
789
790 // start thread
791 boolean addedToContainer = false;
792 boolean started = false;
793 try {
794 container.add(this); // may throw
795 addedToContainer = true;
796
797 // scoped values may be inherited
798 inheritScopedValueBindings(container);
799
800 // submit task to schedule
801 try {
802 if (currentThread().isVirtual()) {
803 Continuation.pin();
804 try {
805 if (scheduler == BUILTIN_SCHEDULER
806 && currentCarrierThread() instanceof CarrierThread ct) {
807 ForkJoinPool pool = ct.getPool();
808 ForkJoinTask<?> task = ForkJoinTask.adapt(runContinuation);
809 pool.externalSubmit(task);
810 } else {
811 scheduler.onStart(runContinuation);
812 }
813 } finally {
814 Continuation.unpin();
815 }
816 } else {
817 scheduler.onStart(runContinuation);
818 }
819 } catch (RejectedExecutionException ree) {
820 submitFailed(ree);
821 throw ree;
822 }
823
824 started = true;
825 } finally {
826 if (!started) {
827 afterDone(addedToContainer);
828 }
829 }
830 }
831
832 @Override
833 public void start() {
834 start(ThreadContainers.root());
835 }
836
837 @Override
838 public void run() {
839 // do nothing
840 }
841
842 /**
843 * Invoked by Thread.join before a thread waits for this virtual thread to terminate.
958 * Call into VM when pinned to record a JFR jdk.VirtualThreadPinned event.
959 * Recording the event in the VM avoids having JFR event recorded in Java
960 * with the same name, but different ID, to events recorded by the VM.
961 */
962 @Hidden
963 private static native void postPinnedEvent(String op);
964
965 /**
966 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
967 * then its task is scheduled to continue, otherwise its next call to {@code park} or
968 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
969 * @param lazySubmit to use lazySubmit if possible
970 * @throws RejectedExecutionException if the scheduler cannot accept a task
971 */
972 private void unpark(boolean lazySubmit) {
973 if (!getAndSetParkPermit(true) && currentThread() != this) {
974 int s = state();
975
976 // unparked while parked
977 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
978
979 if (lazySubmit && currentThread().isVirtual()) {
980 Continuation.pin();
981 try {
982 if (scheduler == BUILTIN_SCHEDULER
983 && currentCarrierThread() instanceof CarrierThread ct) {
984 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
985 return;
986 }
987 } catch (RejectedExecutionException ree) {
988 submitFailed(ree);
989 throw ree;
990 } catch (OutOfMemoryError e) {
991 // fall-though
992 } finally {
993 Continuation.unpin();
994 }
995 }
996
997 submitRunContinuation();
998 return;
999 }
1000
1001 // unparked while parked when pinned
1002 if (s == PINNED || s == TIMED_PINNED) {
1003 // unpark carrier thread when pinned
1004 disableSuspendAndPreempt();
1005 try {
1006 synchronized (carrierThreadAccessLock()) {
1007 Thread carrier = carrierThread;
1008 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
1009 U.unpark(carrier);
1010 }
1011 }
1012 } finally {
1013 enableSuspendAndPreempt();
1014 }
1015 return;
1016 }
1017 }
1424 @IntrinsicCandidate
1425 @JvmtiMountTransition
1426 private native void startTransition(boolean mount);
1427
1428 @IntrinsicCandidate
1429 @JvmtiMountTransition
1430 private native void endTransition(boolean mount);
1431
1432 @IntrinsicCandidate
1433 private static native void notifyJvmtiDisableSuspend(boolean enter);
1434
1435 private static native void registerNatives();
1436 static {
1437 registerNatives();
1438
1439 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1440 var group = Thread.virtualThreadGroup();
1441 }
1442
1443 /**
1444 * Loads a VirtualThreadScheduler with the given class name. The class must be public
1445 * in an exported package, with public one-arg or no-arg constructor, and be visible
1446 * to the system class loader.
1447 * @param delegate the scheduler that the custom scheduler may delegate to
1448 * @param cn the class name of the custom scheduler
1449 */
1450 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
1451 VirtualThreadScheduler scheduler;
1452 try {
1453 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1454 // 1-arg constructor
1455 try {
1456 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1457 return (VirtualThreadScheduler) ctor.newInstance(delegate);
1458 } catch (NoSuchMethodException e) {
1459 // 0-arg constructor
1460 Constructor<?> ctor = clazz.getConstructor();
1461 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1462 }
1463 } catch (Exception ex) {
1464 throw new Error(ex);
1465 }
1466 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!");
1467 return scheduler;
1468 }
1469
1470 /**
1471 * Creates the built-in ForkJoinPool scheduler.
1472 * @param wrapped true if wrapped by a custom default scheduler
1473 */
1474 private static VirtualThreadScheduler createBuiltinScheduler(boolean wrapped) {
1475 int parallelism, maxPoolSize, minRunnable;
1476 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1477 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1478 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1479 if (parallelismValue != null) {
1480 parallelism = Integer.parseInt(parallelismValue);
1481 } else {
1482 parallelism = Runtime.getRuntime().availableProcessors();
1483 }
1484 if (maxPoolSizeValue != null) {
1485 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1486 parallelism = Integer.min(parallelism, maxPoolSize);
1487 } else {
1488 maxPoolSize = Integer.max(parallelism, 256);
1489 }
1490 if (minRunnableValue != null) {
1491 minRunnable = Integer.parseInt(minRunnableValue);
1492 } else {
1493 minRunnable = Integer.max(parallelism / 2, 1);
1494 }
1495 if (Boolean.getBoolean("jdk.virtualThreadScheduler.useTPE")) {
1496 return new BuiltinThreadPoolExecutorScheduler(parallelism);
1497 } else {
1498 return new BuiltinForkJoinPoolScheduler(parallelism, maxPoolSize, minRunnable, wrapped);
1499 }
1500 }
1501
1502 /**
1503 * The built-in ForkJoinPool scheduler.
1504 */
1505 private static class BuiltinForkJoinPoolScheduler
1506 extends ForkJoinPool implements VirtualThreadScheduler {
1507
1508 BuiltinForkJoinPoolScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) {
1509 ForkJoinWorkerThreadFactory factory = wrapped
1510 ? ForkJoinPool.defaultForkJoinWorkerThreadFactory
1511 : CarrierThread::new;
1512 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1513 boolean asyncMode = true; // FIFO
1514 super(parallelism, factory, handler, asyncMode,
1515 0, maxPoolSize, minRunnable, pool -> true, 30L, SECONDS);
1516 }
1517
1518 @Override
1519 public void onStart(VirtualThreadTask task) {
1520 execute(ForkJoinTask.adapt(task));
1521 }
1522
1523 @Override
1524 public void onContinue(VirtualThreadTask task) {
1525 execute(ForkJoinTask.adapt(task));
1526 }
1527
1528 @Override
1529 public ScheduledFuture<?> schedule(Runnable task, long delay, TimeUnit unit) {
1530 return super.schedule(task, delay, unit);
1531 }
1532 }
1533
1534 /**
1535 * Built-in ThreadPoolExecutor scheduler.
1536 */
1537 private static class BuiltinThreadPoolExecutorScheduler
1538 extends ThreadPoolExecutor implements VirtualThreadScheduler {
1539
1540 BuiltinThreadPoolExecutorScheduler(int maxPoolSize) {
1541 ThreadFactory factory = task -> {
1542 Thread t = InnocuousThread.newThread(task);
1543 t.setDaemon(true);
1544 return t;
1545 };
1546 super(maxPoolSize, maxPoolSize,
1547 0L, SECONDS,
1548 new LinkedTransferQueue<>(),
1549 factory);
1550 }
1551
1552 @Override
1553 public void onStart(VirtualThreadTask task) {
1554 execute(task);
1555 }
1556
1557 @Override
1558 public void onContinue(VirtualThreadTask task) {
1559 execute(task);
1560 }
1561 }
1562
1563 /**
1564 * Wraps the scheduler to avoid leaking a direct reference to built-in scheduler.
1565 */
1566 static VirtualThreadScheduler createExternalView(VirtualThreadScheduler delegate) {
1567 return new VirtualThreadScheduler() {
1568 private void check(VirtualThreadTask task) {
1569 var vthread = (VirtualThread) task.thread();
1570 VirtualThreadScheduler scheduler = vthread.scheduler;
1571 if (scheduler != this && scheduler != DEFAULT_SCHEDULER) {
1572 throw new IllegalArgumentException();
1573 }
1574 }
1575 @Override
1576 public void onStart(VirtualThreadTask task) {
1577 check(task);
1578 delegate.onStart(task);
1579 }
1580 @Override
1581 public void onContinue(VirtualThreadTask task) {
1582 check(task);
1583 delegate.onContinue(task);
1584 }
1585 @Override
1586 public String toString() {
1587 return delegate.toString();
1588 }
1589 };
1590 }
1591
1592 /**
1593 * Schedule a runnable task to run after a delay.
1594 */
1595 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1596 if (USE_STPE) {
1597 return DelayedTaskSchedulers.schedule(command, delay, unit);
1598 } else {
1599 return scheduler.schedule(command, delay, unit);
1600 }
1601 }
1602
1603 /**
1604 * Supports scheduling a runnable task to run after a delay. It uses a number
1605 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1606 * work queue used. This class is used when using a custom scheduler.
1607 */
1608 static class DelayedTaskSchedulers {
1609 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1610
1611 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1612 long tid = Thread.currentThread().threadId();
1613 int index = (int) tid & (INSTANCE.length - 1);
1614 return INSTANCE[index].schedule(command, delay, unit);
1615 }
1616
1617 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1618 String propName = "jdk.virtualThreadScheduler.timerQueues";
1619 String propValue = System.getProperty(propName);
1620 int queueCount;
1621 if (propValue != null) {
1622 queueCount = Integer.parseInt(propValue);
1623 if (queueCount != Integer.highestOneBit(queueCount)) {
1624 throw new RuntimeException("Value of " + propName + " must be power of 2");
1625 }
1626 } else {
1627 int ncpus = Runtime.getRuntime().availableProcessors();
1628 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
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