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.ForkJoinPool.ForkJoinWorkerThreadFactory;
35 import java.util.concurrent.ForkJoinTask;
36 import java.util.concurrent.Future;
37 import java.util.concurrent.RejectedExecutionException;
38 import java.util.concurrent.ScheduledExecutorService;
39 import java.util.concurrent.ScheduledFuture;
40 import java.util.concurrent.ScheduledThreadPoolExecutor;
41 import java.util.concurrent.TimeUnit;
42 import jdk.internal.event.VirtualThreadEndEvent;
43 import jdk.internal.event.VirtualThreadStartEvent;
44 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
45 import jdk.internal.invoke.MhUtil;
46 import jdk.internal.misc.CarrierThread;
47 import jdk.internal.misc.InnocuousThread;
48 import jdk.internal.misc.Unsafe;
49 import jdk.internal.vm.Continuation;
50 import jdk.internal.vm.ContinuationScope;
51 import jdk.internal.vm.StackableScope;
52 import jdk.internal.vm.ThreadContainer;
53 import jdk.internal.vm.ThreadContainers;
54 import jdk.internal.vm.annotation.ChangesCurrentThread;
55 import jdk.internal.vm.annotation.Hidden;
56 import jdk.internal.vm.annotation.IntrinsicCandidate;
57 import jdk.internal.vm.annotation.JvmtiHideEvents;
58 import jdk.internal.vm.annotation.JvmtiMountTransition;
59 import jdk.internal.vm.annotation.ReservedStackAccess;
60 import sun.nio.ch.Interruptible;
61 import static java.util.concurrent.TimeUnit.*;
62
63 /**
64 * A thread that is scheduled by the Java virtual machine rather than the operating system.
65 */
66 final class VirtualThread extends BaseVirtualThread {
67 private static final Unsafe U = Unsafe.getUnsafe();
68 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
69
70 private static final VirtualThreadScheduler BUILTIN_SCHEDULER;
71 private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
72 private static final VirtualThreadScheduler EXTERNAL_VIEW;
73 private static final boolean USE_STPE;
74 static {
75 // experimental
76 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
77 if (propValue != null) {
78 VirtualThreadScheduler builtinScheduler = createBuiltinScheduler(true);
79 VirtualThreadScheduler externalView = createExternalView(builtinScheduler);
80 VirtualThreadScheduler defaultScheduler = loadCustomScheduler(externalView, propValue);
81 BUILTIN_SCHEDULER = builtinScheduler;
82 DEFAULT_SCHEDULER = defaultScheduler;
83 EXTERNAL_VIEW = externalView;
84 } else {
85 var builtinScheduler = createBuiltinScheduler(false);
86 BUILTIN_SCHEDULER = builtinScheduler;
87 DEFAULT_SCHEDULER = builtinScheduler;
88 EXTERNAL_VIEW = createExternalView(builtinScheduler);
89 }
90 USE_STPE = Boolean.getBoolean("jdk.virtualThreadScheduler.useSTPE");
91 }
92
93 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
94 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
95 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
96 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
97
98 // scheduler and continuation
99 private final VirtualThreadScheduler scheduler;
100 private final Continuation cont;
101 private final VThreadTask runContinuation;
102
103 // virtual thread state, accessed by VM
104 private volatile int state;
105
106 /*
107 * Virtual thread state transitions:
108 *
109 * NEW -> STARTED // Thread.start, schedule to run
110 * STARTED -> TERMINATED // failed to start
111 * STARTED -> RUNNING // first run
112 * RUNNING -> TERMINATED // done
113 *
114 * RUNNING -> PARKING // Thread parking with LockSupport.park
115 * PARKING -> PARKED // cont.yield successful, parked indefinitely
116 * PARKED -> UNPARKED // unparked, may be scheduled to continue
117 * UNPARKED -> RUNNING // continue execution after park
118 *
119 * PARKING -> RUNNING // cont.yield failed, need to park on carrier
120 * RUNNING -> PINNED // park on carrier
121 * PINNED -> RUNNING // unparked, continue execution on same carrier
195
196 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
197 private volatile boolean interruptibleWait;
198
199 // timed-wait support
200 private byte timedWaitSeqNo;
201
202 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
203 private long timeout;
204
205 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
206 private Future<?> timeoutTask;
207
208 // carrier thread when mounted, accessed by VM
209 private volatile Thread carrierThread;
210
211 // true to notifyAll after this virtual thread terminates
212 private volatile boolean notifyAllAfterTerminate;
213
214 /**
215 * Return the built-in scheduler.
216 * @param trusted true if caller is trusted, false if not trusted
217 */
218 static VirtualThreadScheduler builtinScheduler(boolean trusted) {
219 return trusted ? BUILTIN_SCHEDULER : EXTERNAL_VIEW;
220 }
221
222 /**
223 * Returns the default scheduler, usually the same as the built-in scheduler.
224 */
225 static VirtualThreadScheduler defaultScheduler() {
226 return DEFAULT_SCHEDULER;
227 }
228
229 /**
230 * Returns the continuation scope used for virtual threads.
231 */
232 static ContinuationScope continuationScope() {
233 return VTHREAD_SCOPE;
234 }
235
236 /**
237 * Returns the task to start/continue this virtual thread.
238 */
239 VirtualThreadTask virtualThreadTask() {
240 return runContinuation;
241 }
242
243 /**
244 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
245 *
246 * @param scheduler the scheduler or null for default scheduler
247 * @param preferredCarrier the preferred carrier or null
248 * @param name thread name
249 * @param characteristics characteristics
250 * @param task the task to execute
251 */
252 VirtualThread(VirtualThreadScheduler scheduler,
253 Thread preferredCarrier,
254 String name,
255 int characteristics,
256 Runnable task) {
257 super(name, characteristics, /*bound*/ false);
258 Objects.requireNonNull(task);
259
260 // use default scheduler if not provided
261 if (scheduler == null) {
262 scheduler = DEFAULT_SCHEDULER;
263 } else if (scheduler == EXTERNAL_VIEW) {
264 throw new UnsupportedOperationException();
265 }
266 this.scheduler = scheduler;
267 this.cont = new VThreadContinuation(this, task);
268
269 if (scheduler == BUILTIN_SCHEDULER) {
270 this.runContinuation = new VThreadTask(this);
271 } else {
272 this.runContinuation = new CustomVThreadTask(this, preferredCarrier);
273 }
274 }
275
276 /**
277 * The task to start/continue a virtual thread.
278 */
279 static non-sealed class VThreadTask implements VirtualThreadTask {
280 private final VirtualThread vthread;
281 VThreadTask(VirtualThread vthread) {
282 this.vthread = vthread;
283 }
284 @Override
285 public final Thread thread() {
286 return vthread;
287 }
288 @Override
289 public final void run() {
290 vthread.runContinuation();;
291 }
292 @Override
293 public Thread preferredCarrier() {
294 throw new UnsupportedOperationException();
295 }
296 @Override
297 public Object attach(Object att) {
298 throw new UnsupportedOperationException();
299 }
300 @Override
301 public Object attachment() {
302 throw new UnsupportedOperationException();
303 }
304 }
305
306 /**
307 * The task to start/continue a virtual thread when using a custom scheduler.
308 */
309 static final class CustomVThreadTask extends VThreadTask {
310 private static final VarHandle ATT =
311 MhUtil.findVarHandle(MethodHandles.lookup(), "att", Object.class);
312 private final Thread preferredCarrier;
313 private volatile Object att;
314 CustomVThreadTask(VirtualThread vthread, Thread preferredCarrier) {
315 super(vthread);
316 this.preferredCarrier = preferredCarrier;
317 }
318 @Override
319 public Thread preferredCarrier() {
320 return preferredCarrier;
321 }
322 @Override
323 public Object attach(Object att) {
324 return ATT.getAndSet(this, att);
325 }
326 @Override
327 public Object attachment() {
328 return att;
329 }
330 }
331
332 /**
333 * The continuation that a virtual thread executes.
334 */
335 private static class VThreadContinuation extends Continuation {
336 VThreadContinuation(VirtualThread vthread, Runnable task) {
337 super(VTHREAD_SCOPE, wrap(vthread, task));
338 }
339 @Override
340 protected void onPinned(Continuation.Pinned reason) {
341 }
342 private static Runnable wrap(VirtualThread vthread, Runnable task) {
343 return new Runnable() {
344 @Hidden
345 @JvmtiHideEvents
346 public void run() {
347 vthread.endFirstTransition();
348 try {
349 vthread.run(task);
397 if (cont.isDone()) {
398 afterDone();
399 } else {
400 afterYield();
401 }
402 }
403 }
404
405 /**
406 * Cancel timeout task when continuing after timed-park or timed-wait.
407 * The timeout task may be executing, or may have already completed.
408 */
409 private void cancelTimeoutTask() {
410 if (timeoutTask != null) {
411 timeoutTask.cancel(false);
412 timeoutTask = null;
413 }
414 }
415
416 /**
417 * Submits the runContinuation task to the scheduler. For the built-in scheduler,
418 * the task will be pushed to the local queue if possible, otherwise it will be
419 * pushed to an external submission queue.
420 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
421 * @throws RejectedExecutionException
422 */
423 private void submitRunContinuation(boolean retryOnOOME) {
424 boolean done = false;
425 while (!done) {
426 try {
427 // Pin the continuation to prevent the virtual thread from unmounting
428 // when submitting a task. For the default scheduler this ensures that
429 // the carrier doesn't change when pushing a task. For other schedulers
430 // it avoids deadlock that could arise due to carriers and virtual
431 // threads contending for a lock.
432 if (currentThread().isVirtual()) {
433 Continuation.pin();
434 try {
435 scheduler.onContinue(runContinuation);
436 } finally {
437 Continuation.unpin();
438 }
439 } else {
440 scheduler.onContinue(runContinuation);
441 }
442 done = true;
443 } catch (RejectedExecutionException ree) {
444 submitFailed(ree);
445 throw ree;
446 } catch (OutOfMemoryError e) {
447 if (retryOnOOME) {
448 U.park(false, 100_000_000); // 100ms
449 } else {
450 throw e;
451 }
452 }
453 }
454 }
455
456 /**
457 * Submits the runContinuation task to the scheduler. For the default scheduler,
458 * and calling it on a worker thread, the task will be pushed to the local queue,
459 * otherwise it will be pushed to an external submission queue.
460 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
461 * @throws RejectedExecutionException
462 */
463 private void submitRunContinuation() {
464 submitRunContinuation(true);
465 }
466
467 /**
468 * Invoked from a carrier thread to lazy submit the runContinuation task to the
469 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
470 * for a custom scheduler, then it just submits the task to the scheduler.
471 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
472 * @throws RejectedExecutionException
473 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
474 */
475 private void lazySubmitRunContinuation() {
476 assert !currentThread().isVirtual();
477 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
478 try {
479 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
480 } catch (RejectedExecutionException ree) {
481 submitFailed(ree);
482 throw ree;
483 } catch (OutOfMemoryError e) {
484 submitRunContinuation();
485 }
486 } else {
487 submitRunContinuation();
488 }
489 }
490
491 /**
492 * Invoked from a carrier thread to externally submit the runContinuation task to the
493 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
494 * task to the scheduler.
495 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
496 * @throws RejectedExecutionException
497 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
498 */
499 private void externalSubmitRunContinuation() {
500 assert !currentThread().isVirtual();
501 if (currentThread() instanceof CarrierThread ct) {
502 try {
503 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
504 } catch (RejectedExecutionException ree) {
505 submitFailed(ree);
506 throw ree;
507 } catch (OutOfMemoryError e) {
508 submitRunContinuation();
509 }
510 } else {
511 submitRunContinuation();
512 }
513 }
514
515 /**
516 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
517 */
518 private void submitFailed(RejectedExecutionException ree) {
519 var event = new VirtualThreadSubmitFailedEvent();
520 if (event.isEnabled()) {
521 event.javaThreadId = threadId();
522 event.exceptionMessage = ree.getMessage();
523 event.commit();
524 }
525 }
526
527 /**
528 * Runs a task in the context of this virtual thread.
529 */
530 private void run(Runnable task) {
531 assert Thread.currentThread() == this && state == RUNNING;
648 long timeout = this.timeout;
649 assert timeout > 0;
650 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
651 setState(newState = TIMED_PARKED);
652 }
653
654 // may have been unparked while parking
655 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
656 // lazy submit if local queue is empty
657 lazySubmitRunContinuation();
658 }
659 return;
660 }
661
662 // Thread.yield
663 if (s == YIELDING) {
664 setState(YIELDED);
665
666 // external submit if there are no tasks in the local task queue
667 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
668 externalSubmitRunContinuation();
669 } else {
670 submitRunContinuation();
671 }
672 return;
673 }
674
675 // blocking on monitorenter
676 if (s == BLOCKING) {
677 setState(BLOCKED);
678
679 // may have been unblocked while blocking
680 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
681 // lazy submit if local queue is empty
682 lazySubmitRunContinuation();
683 }
684 return;
685 }
686
687 // Object.wait
688 if (s == WAITING || s == TIMED_WAITING) {
773 @Override
774 void start(ThreadContainer container) {
775 if (!compareAndSetState(NEW, STARTED)) {
776 throw new IllegalThreadStateException("Already started");
777 }
778
779 // bind thread to container
780 assert threadContainer() == null;
781 setThreadContainer(container);
782
783 // start thread
784 boolean addedToContainer = false;
785 boolean started = false;
786 try {
787 container.add(this); // may throw
788 addedToContainer = true;
789
790 // scoped values may be inherited
791 inheritScopedValueBindings(container);
792
793 // submit task to schedule
794 try {
795 if (currentThread().isVirtual()) {
796 Continuation.pin();
797 try {
798 if (scheduler == BUILTIN_SCHEDULER
799 && currentCarrierThread() instanceof CarrierThread ct) {
800 ForkJoinPool pool = ct.getPool();
801 ForkJoinTask<?> task = ForkJoinTask.adapt(runContinuation);
802 pool.externalSubmit(task);
803 } else {
804 scheduler.onStart(runContinuation);
805 }
806 } finally {
807 Continuation.unpin();
808 }
809 } else {
810 scheduler.onStart(runContinuation);
811 }
812 } catch (RejectedExecutionException ree) {
813 submitFailed(ree);
814 throw ree;
815 }
816
817 started = true;
818 } finally {
819 if (!started) {
820 afterDone(addedToContainer);
821 }
822 }
823 }
824
825 @Override
826 public void start() {
827 start(ThreadContainers.root());
828 }
829
830 @Override
831 public void run() {
832 // do nothing
833 }
834
835 /**
836 * Invoked by Thread.join before a thread waits for this virtual thread to terminate.
951 * Call into VM when pinned to record a JFR jdk.VirtualThreadPinned event.
952 * Recording the event in the VM avoids having JFR event recorded in Java
953 * with the same name, but different ID, to events recorded by the VM.
954 */
955 @Hidden
956 private static native void postPinnedEvent(String op);
957
958 /**
959 * Re-enables this virtual thread for scheduling. If this virtual thread is parked
960 * then its task is scheduled to continue, otherwise its next call to {@code park} or
961 * {@linkplain #parkNanos(long) parkNanos} is guaranteed not to block.
962 * @param lazySubmit to use lazySubmit if possible
963 * @throws RejectedExecutionException if the scheduler cannot accept a task
964 */
965 private void unpark(boolean lazySubmit) {
966 if (!getAndSetParkPermit(true) && currentThread() != this) {
967 int s = state();
968
969 // unparked while parked
970 if ((s == PARKED || s == TIMED_PARKED) && compareAndSetState(s, UNPARKED)) {
971
972 if (lazySubmit && currentThread().isVirtual()) {
973 Continuation.pin();
974 try {
975 if (scheduler == BUILTIN_SCHEDULER
976 && currentCarrierThread() instanceof CarrierThread ct) {
977 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
978 return;
979 }
980 } catch (RejectedExecutionException ree) {
981 submitFailed(ree);
982 throw ree;
983 } catch (OutOfMemoryError e) {
984 // fall-though
985 } finally {
986 Continuation.unpin();
987 }
988 }
989
990 submitRunContinuation();
991 return;
992 }
993
994 // unparked while parked when pinned
995 if (s == PINNED || s == TIMED_PINNED) {
996 // unpark carrier thread when pinned
997 disableSuspendAndPreempt();
998 try {
999 synchronized (carrierThreadAccessLock()) {
1000 Thread carrier = carrierThread;
1001 if (carrier != null && ((s = state()) == PINNED || s == TIMED_PINNED)) {
1002 U.unpark(carrier);
1003 }
1004 }
1005 } finally {
1006 enableSuspendAndPreempt();
1007 }
1008 return;
1009 }
1010 }
1417 @IntrinsicCandidate
1418 @JvmtiMountTransition
1419 private native void startTransition(boolean mount);
1420
1421 @IntrinsicCandidate
1422 @JvmtiMountTransition
1423 private native void endTransition(boolean mount);
1424
1425 @IntrinsicCandidate
1426 private static native void notifyJvmtiDisableSuspend(boolean enter);
1427
1428 private static native void registerNatives();
1429 static {
1430 registerNatives();
1431
1432 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1433 var group = Thread.virtualThreadGroup();
1434 }
1435
1436 /**
1437 * Loads a VirtualThreadScheduler with the given class name. The class must be public
1438 * in an exported package, with public one-arg or no-arg constructor, and be visible
1439 * to the system class loader.
1440 * @param delegate the scheduler that the custom scheduler may delegate to
1441 * @param cn the class name of the custom scheduler
1442 */
1443 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
1444 VirtualThreadScheduler scheduler;
1445 try {
1446 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1447 // 1-arg constructor
1448 try {
1449 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1450 return (VirtualThreadScheduler) ctor.newInstance(delegate);
1451 } catch (NoSuchMethodException e) {
1452 // 0-arg constructor
1453 Constructor<?> ctor = clazz.getConstructor();
1454 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1455 }
1456 } catch (Exception ex) {
1457 throw new Error(ex);
1458 }
1459 System.err.println("WARNING: Using custom default scheduler, this is an experimental feature!");
1460 return scheduler;
1461 }
1462
1463 /**
1464 * Creates the built-in ForkJoinPool scheduler.
1465 * @param wrapped true if wrapped by a custom default scheduler
1466 */
1467 private static VirtualThreadScheduler createBuiltinScheduler(boolean wrapped) {
1468 int parallelism, maxPoolSize, minRunnable;
1469 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1470 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1471 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1472 if (parallelismValue != null) {
1473 parallelism = Integer.parseInt(parallelismValue);
1474 } else {
1475 parallelism = Runtime.getRuntime().availableProcessors();
1476 }
1477 if (maxPoolSizeValue != null) {
1478 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1479 parallelism = Integer.min(parallelism, maxPoolSize);
1480 } else {
1481 maxPoolSize = Integer.max(parallelism, 256);
1482 }
1483 if (minRunnableValue != null) {
1484 minRunnable = Integer.parseInt(minRunnableValue);
1485 } else {
1486 minRunnable = Integer.max(parallelism / 2, 1);
1487 }
1488 ForkJoinWorkerThreadFactory factory;
1489 if (wrapped) {
1490 factory = ForkJoinPool.defaultForkJoinWorkerThreadFactory;
1491 } else {
1492 String cn = System.getProperty("jdk.virtualThreadScheduler.threadFactory");
1493 if (cn != null) {
1494 try {
1495 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1496 Constructor<?> ctor = clazz.getConstructor();
1497 factory = (ForkJoinWorkerThreadFactory) ctor.newInstance();
1498 } catch (Exception ex) {
1499 throw new Error(ex);
1500 }
1501 } else {
1502 factory = CarrierThread::new;
1503 }
1504 }
1505 return new BuiltinForkJoinPoolScheduler(parallelism, maxPoolSize, minRunnable, factory);
1506 }
1507
1508 /**
1509 * The built-in ForkJoinPool scheduler.
1510 */
1511 private static class BuiltinForkJoinPoolScheduler
1512 extends ForkJoinPool implements VirtualThreadScheduler {
1513
1514 BuiltinForkJoinPoolScheduler(int parallelism,
1515 int maxPoolSize,
1516 int minRunnable,
1517 ForkJoinWorkerThreadFactory factory) {
1518 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1519 boolean asyncMode = true; // FIFO
1520 super(parallelism, factory, handler, asyncMode,
1521 0, maxPoolSize, minRunnable, pool -> true, 30L, SECONDS);
1522 }
1523
1524 @Override
1525 public void onStart(VirtualThreadTask task) {
1526 execute(ForkJoinTask.adapt(task));
1527 }
1528
1529 @Override
1530 public void onContinue(VirtualThreadTask task) {
1531 execute(ForkJoinTask.adapt(task));
1532 }
1533
1534 @Override
1535 public ScheduledFuture<?> schedule(Runnable task, long delay, TimeUnit unit) {
1536 return super.schedule(task, delay, unit);
1537 }
1538 }
1539
1540 /**
1541 * Wraps the scheduler to avoid leaking a direct reference to built-in scheduler.
1542 */
1543 static VirtualThreadScheduler createExternalView(VirtualThreadScheduler delegate) {
1544 return new VirtualThreadScheduler() {
1545 private void check(VirtualThreadTask task) {
1546 var vthread = (VirtualThread) task.thread();
1547 VirtualThreadScheduler scheduler = vthread.scheduler;
1548 if (scheduler != this && scheduler != DEFAULT_SCHEDULER) {
1549 throw new IllegalArgumentException();
1550 }
1551 }
1552 @Override
1553 public void onStart(VirtualThreadTask task) {
1554 check(task);
1555 delegate.onStart(task);
1556 }
1557 @Override
1558 public void onContinue(VirtualThreadTask task) {
1559 check(task);
1560 delegate.onContinue(task);
1561 }
1562 @Override
1563 public String toString() {
1564 return delegate.toString();
1565 }
1566 };
1567 }
1568
1569 /**
1570 * Schedule a runnable task to run after a delay.
1571 */
1572 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1573 if (USE_STPE) {
1574 return DelayedTaskSchedulers.schedule(command, delay, unit);
1575 } else {
1576 return scheduler.schedule(command, delay, unit);
1577 }
1578 }
1579
1580 /**
1581 * Supports scheduling a runnable task to run after a delay. It uses a number
1582 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1583 * work queue used. This class is used when using a custom scheduler.
1584 */
1585 static class DelayedTaskSchedulers {
1586 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1587
1588 static Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1589 long tid = Thread.currentThread().threadId();
1590 int index = (int) tid & (INSTANCE.length - 1);
1591 return INSTANCE[index].schedule(command, delay, unit);
1592 }
1593
1594 private static ScheduledExecutorService[] createDelayedTaskSchedulers() {
1595 String propName = "jdk.virtualThreadScheduler.timerQueues";
1596 String propValue = System.getProperty(propName);
1597 int queueCount;
1598 if (propValue != null) {
1599 queueCount = Integer.parseInt(propValue);
1600 if (queueCount != Integer.highestOneBit(queueCount)) {
1601 throw new RuntimeException("Value of " + propName + " must be power of 2");
1602 }
1603 } else {
1604 int ncpus = Runtime.getRuntime().availableProcessors();
1605 queueCount = Math.max(Integer.highestOneBit(ncpus / 4), 1);
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