7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25 package java.lang;
26
27 import java.util.Locale;
28 import java.util.Objects;
29 import java.util.concurrent.CountDownLatch;
30 import java.util.concurrent.Executor;
31 import java.util.concurrent.Executors;
32 import java.util.concurrent.ForkJoinPool;
33 import java.util.concurrent.ForkJoinPool.ForkJoinWorkerThreadFactory;
34 import java.util.concurrent.ForkJoinTask;
35 import java.util.concurrent.Future;
36 import java.util.concurrent.RejectedExecutionException;
37 import java.util.concurrent.ScheduledExecutorService;
38 import java.util.concurrent.ScheduledThreadPoolExecutor;
39 import java.util.concurrent.TimeUnit;
40 import jdk.internal.event.VirtualThreadEndEvent;
41 import jdk.internal.event.VirtualThreadStartEvent;
42 import jdk.internal.event.VirtualThreadSubmitFailedEvent;
43 import jdk.internal.misc.CarrierThread;
44 import jdk.internal.misc.InnocuousThread;
45 import jdk.internal.misc.Unsafe;
46 import jdk.internal.vm.Continuation;
47 import jdk.internal.vm.ContinuationScope;
48 import jdk.internal.vm.StackableScope;
49 import jdk.internal.vm.ThreadContainer;
50 import jdk.internal.vm.ThreadContainers;
51 import jdk.internal.vm.annotation.ChangesCurrentThread;
52 import jdk.internal.vm.annotation.Hidden;
53 import jdk.internal.vm.annotation.IntrinsicCandidate;
54 import jdk.internal.vm.annotation.JvmtiHideEvents;
55 import jdk.internal.vm.annotation.JvmtiMountTransition;
56 import jdk.internal.vm.annotation.ReservedStackAccess;
57 import sun.nio.ch.Interruptible;
58 import static java.util.concurrent.TimeUnit.*;
59
60 /**
61 * A thread that is scheduled by the Java virtual machine rather than the operating system.
62 */
63 final class VirtualThread extends BaseVirtualThread {
64 private static final Unsafe U = Unsafe.getUnsafe();
65 private static final ContinuationScope VTHREAD_SCOPE = new ContinuationScope("VirtualThreads");
66 private static final ForkJoinPool DEFAULT_SCHEDULER = createDefaultScheduler();
67
68 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
69 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
70 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
71 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
72 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
73
74 // scheduler and continuation
75 private final Executor scheduler;
76 private final Continuation cont;
77 private final Runnable runContinuation;
78
79 // virtual thread state, accessed by VM
80 private volatile int state;
81
82 /*
83 * Virtual thread state transitions:
84 *
85 * NEW -> STARTED // Thread.start, schedule to run
86 * STARTED -> TERMINATED // failed to start
87 * STARTED -> RUNNING // first run
88 * RUNNING -> TERMINATED // done
89 *
90 * RUNNING -> PARKING // Thread parking with LockSupport.park
91 * PARKING -> PARKED // cont.yield successful, parked indefinitely
92 * PARKING -> PINNED // cont.yield failed, parked indefinitely on carrier
93 * PARKED -> UNPARKED // unparked, may be scheduled to continue
94 * PINNED -> RUNNING // unparked, continue execution on same carrier
95 * UNPARKED -> RUNNING // continue execution after park
151 private static final int TERMINATED = 99; // final state
152
153 // can be suspended from scheduling when unmounted
154 private static final int SUSPENDED = 1 << 8;
155
156 // parking permit made available by LockSupport.unpark
157 private volatile boolean parkPermit;
158
159 // blocking permit made available by unblocker thread when another thread exits monitor
160 private volatile boolean blockPermit;
161
162 // true when on the list of virtual threads waiting to be unblocked
163 private volatile boolean onWaitingList;
164
165 // next virtual thread on the list of virtual threads waiting to be unblocked
166 private volatile VirtualThread next;
167
168 // notified by Object.notify/notifyAll while waiting in Object.wait
169 private volatile boolean notified;
170
171 // timed-wait support
172 private byte timedWaitSeqNo;
173
174 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
175 private long timeout;
176
177 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
178 private Future<?> timeoutTask;
179
180 // carrier thread when mounted, accessed by VM
181 private volatile Thread carrierThread;
182
183 // termination object when joining, created lazily if needed
184 private volatile CountDownLatch termination;
185
186 /**
187 * Returns the default scheduler.
188 */
189 static Executor defaultScheduler() {
190 return DEFAULT_SCHEDULER;
191 }
192
193 /**
194 * Returns the continuation scope used for virtual threads.
195 */
196 static ContinuationScope continuationScope() {
197 return VTHREAD_SCOPE;
198 }
199
200 /**
201 * Creates a new {@code VirtualThread} to run the given task with the given
202 * scheduler. If the given scheduler is {@code null} and the current thread
203 * is a platform thread then the newly created virtual thread will use the
204 * default scheduler. If given scheduler is {@code null} and the current
205 * thread is a virtual thread then the current thread's scheduler is used.
206 *
207 * @param scheduler the scheduler or null
208 * @param name thread name
209 * @param characteristics characteristics
210 * @param task the task to execute
211 */
212 VirtualThread(Executor scheduler, String name, int characteristics, Runnable task) {
213 super(name, characteristics, /*bound*/ false);
214 Objects.requireNonNull(task);
215
216 // choose scheduler if not specified
217 if (scheduler == null) {
218 Thread parent = Thread.currentThread();
219 if (parent instanceof VirtualThread vparent) {
220 scheduler = vparent.scheduler;
221 } else {
222 scheduler = DEFAULT_SCHEDULER;
223 }
224 }
225
226 this.scheduler = scheduler;
227 this.cont = new VThreadContinuation(this, task);
228 this.runContinuation = this::runContinuation;
229 }
230
231 /**
232 * The continuation that a virtual thread executes.
233 */
234 private static class VThreadContinuation extends Continuation {
235 VThreadContinuation(VirtualThread vthread, Runnable task) {
236 super(VTHREAD_SCOPE, wrap(vthread, task));
237 }
238 @Override
239 protected void onPinned(Continuation.Pinned reason) {
240 }
241 private static Runnable wrap(VirtualThread vthread, Runnable task) {
242 return new Runnable() {
243 @Hidden
299 afterYield();
300 }
301 }
302 }
303
304 /**
305 * Cancel timeout task when continuing after timed-park or timed-wait.
306 * The timeout task may be executing, or may have already completed.
307 */
308 private void cancelTimeoutTask() {
309 if (timeoutTask != null) {
310 timeoutTask.cancel(false);
311 timeoutTask = null;
312 }
313 }
314
315 /**
316 * Submits the runContinuation task to the scheduler. For the default scheduler,
317 * and calling it on a worker thread, the task will be pushed to the local queue,
318 * otherwise it will be pushed to an external submission queue.
319 * @param scheduler the scheduler
320 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
321 * @throws RejectedExecutionException
322 */
323 private void submitRunContinuation(Executor scheduler, boolean retryOnOOME) {
324 boolean done = false;
325 while (!done) {
326 try {
327 // Pin the continuation to prevent the virtual thread from unmounting
328 // when submitting a task. For the default scheduler this ensures that
329 // the carrier doesn't change when pushing a task. For other schedulers
330 // it avoids deadlock that could arise due to carriers and virtual
331 // threads contending for a lock.
332 if (currentThread().isVirtual()) {
333 Continuation.pin();
334 try {
335 scheduler.execute(runContinuation);
336 } finally {
337 Continuation.unpin();
338 }
339 } else {
340 scheduler.execute(runContinuation);
341 }
342 done = true;
343 } catch (RejectedExecutionException ree) {
344 submitFailed(ree);
345 throw ree;
346 } catch (OutOfMemoryError e) {
347 if (retryOnOOME) {
348 U.park(false, 100_000_000); // 100ms
349 } else {
350 throw e;
351 }
352 }
353 }
354 }
355
356 /**
357 * Submits the runContinuation task to the given scheduler as an external submit.
358 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
359 * @throws RejectedExecutionException
360 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
361 */
362 private void externalSubmitRunContinuation(ForkJoinPool pool) {
363 assert Thread.currentThread() instanceof CarrierThread;
364 try {
365 pool.externalSubmit(ForkJoinTask.adapt(runContinuation));
366 } catch (RejectedExecutionException ree) {
367 submitFailed(ree);
368 throw ree;
369 } catch (OutOfMemoryError e) {
370 submitRunContinuation(pool, true);
371 }
372 }
373
374 /**
375 * Submits the runContinuation task to the scheduler. For the default scheduler,
376 * and calling it on a worker thread, the task will be pushed to the local queue,
377 * otherwise it will be pushed to an external submission queue.
378 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
379 * @throws RejectedExecutionException
380 */
381 private void submitRunContinuation() {
382 submitRunContinuation(scheduler, true);
383 }
384
385 /**
386 * Lazy submit the runContinuation task if invoked on a carrier thread and its local
387 * queue is empty. If not empty, or invoked by another thread, then this method works
388 * like submitRunContinuation and just submits the task to the scheduler.
389 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
390 * @throws RejectedExecutionException
391 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
392 */
393 private void lazySubmitRunContinuation() {
394 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
395 ForkJoinPool pool = ct.getPool();
396 try {
397 pool.lazySubmit(ForkJoinTask.adapt(runContinuation));
398 } catch (RejectedExecutionException ree) {
399 submitFailed(ree);
400 throw ree;
401 } catch (OutOfMemoryError e) {
402 submitRunContinuation();
403 }
404 } else {
405 submitRunContinuation();
406 }
407 }
408
409 /**
410 * Submits the runContinuation task to the scheduler. For the default scheduler, and
411 * calling it a virtual thread that uses the default scheduler, the task will be
412 * pushed to an external submission queue. This method may throw OutOfMemoryError.
413 * @throws RejectedExecutionException
414 * @throws OutOfMemoryError
415 */
416 private void externalSubmitRunContinuationOrThrow() {
417 if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
418 try {
419 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
420 } catch (RejectedExecutionException ree) {
421 submitFailed(ree);
422 throw ree;
423 }
424 } else {
425 submitRunContinuation(scheduler, false);
426 }
427 }
428
429 /**
430 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
431 */
432 private void submitFailed(RejectedExecutionException ree) {
433 var event = new VirtualThreadSubmitFailedEvent();
434 if (event.isEnabled()) {
435 event.javaThreadId = threadId();
436 event.exceptionMessage = ree.getMessage();
437 event.commit();
438 }
439 }
440
441 /**
442 * Runs a task in the context of this virtual thread.
443 */
444 private void run(Runnable task) {
445 assert Thread.currentThread() == this && state == RUNNING;
560 long timeout = this.timeout;
561 assert timeout > 0;
562 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
563 setState(newState = TIMED_PARKED);
564 }
565
566 // may have been unparked while parking
567 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
568 // lazy submit if local queue is empty
569 lazySubmitRunContinuation();
570 }
571 return;
572 }
573
574 // Thread.yield
575 if (s == YIELDING) {
576 setState(YIELDED);
577
578 // external submit if there are no tasks in the local task queue
579 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
580 externalSubmitRunContinuation(ct.getPool());
581 } else {
582 submitRunContinuation();
583 }
584 return;
585 }
586
587 // blocking on monitorenter
588 if (s == BLOCKING) {
589 setState(BLOCKED);
590
591 // may have been unblocked while blocking
592 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
593 // lazy submit if local queue is empty
594 lazySubmitRunContinuation();
595 }
596 return;
597 }
598
599 // Object.wait
600 if (s == WAITING || s == TIMED_WAITING) {
601 int newState;
602 if (s == WAITING) {
603 setState(newState = WAIT);
604 } else {
605 // For timed-wait, a timeout task is scheduled to execute. The timeout
606 // task will change the thread state to UNBLOCKED and submit the thread
607 // to the scheduler. A sequence number is used to ensure that the timeout
608 // task only unblocks the thread for this timed-wait. We synchronize with
609 // the timeout task to coordinate access to the sequence number and to
610 // ensure the timeout task doesn't execute until the thread has got to
611 // the TIMED_WAIT state.
612 long timeout = this.timeout;
613 assert timeout > 0;
614 synchronized (timedWaitLock()) {
615 byte seqNo = ++timedWaitSeqNo;
616 timeoutTask = schedule(() -> waitTimeoutExpired(seqNo), timeout, MILLISECONDS);
617 setState(newState = TIMED_WAIT);
618 }
619 }
620
621 // may have been notified while in transition to wait state
622 if (notified && compareAndSetState(newState, BLOCKED)) {
623 // may have even been unblocked already
624 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
625 submitRunContinuation();
626 }
627 return;
628 }
629
630 // may have been interrupted while in transition to wait state
631 if (interrupted && compareAndSetState(newState, UNBLOCKED)) {
632 submitRunContinuation();
633 return;
634 }
635 return;
636 }
637
638 assert false;
639 }
640
641 /**
642 * Invoked after the continuation completes.
643 */
644 private void afterDone() {
645 afterDone(true);
646 }
647
648 /**
649 * Invoked after the continuation completes (or start failed). Sets the thread
650 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
651 *
1398 @IntrinsicCandidate
1399 @JvmtiMountTransition
1400 private native void notifyJvmtiMount(boolean hide);
1401
1402 @IntrinsicCandidate
1403 @JvmtiMountTransition
1404 private native void notifyJvmtiUnmount(boolean hide);
1405
1406 @IntrinsicCandidate
1407 private static native void notifyJvmtiDisableSuspend(boolean enter);
1408
1409 private static native void registerNatives();
1410 static {
1411 registerNatives();
1412
1413 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1414 var group = Thread.virtualThreadGroup();
1415 }
1416
1417 /**
1418 * Creates the default ForkJoinPool scheduler.
1419 */
1420 private static ForkJoinPool createDefaultScheduler() {
1421 ForkJoinWorkerThreadFactory factory = pool -> new CarrierThread(pool);
1422 int parallelism, maxPoolSize, minRunnable;
1423 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1424 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1425 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1426 if (parallelismValue != null) {
1427 parallelism = Integer.parseInt(parallelismValue);
1428 } else {
1429 parallelism = Runtime.getRuntime().availableProcessors();
1430 }
1431 if (maxPoolSizeValue != null) {
1432 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1433 parallelism = Integer.min(parallelism, maxPoolSize);
1434 } else {
1435 maxPoolSize = Integer.max(parallelism, 256);
1436 }
1437 if (minRunnableValue != null) {
1438 minRunnable = Integer.parseInt(minRunnableValue);
1439 } else {
1440 minRunnable = Integer.max(parallelism / 2, 1);
1441 }
1442 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1443 boolean asyncMode = true; // FIFO
1444 return new ForkJoinPool(parallelism, factory, handler, asyncMode,
1445 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1446 }
1447
1448 /**
1449 * Schedule a runnable task to run after a delay.
1450 */
1451 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1452 if (scheduler instanceof ForkJoinPool pool) {
1453 return pool.schedule(command, delay, unit);
1454 } else {
1455 return DelayedTaskSchedulers.schedule(command, delay, unit);
1456 }
1457 }
1458
1459 /**
1460 * Supports scheduling a runnable task to run after a delay. It uses a number
1461 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1462 * work queue used. This class is used when using a custom scheduler.
1463 */
1464 private static class DelayedTaskSchedulers {
1465 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1515 assert changed;
1516 vthread.unblock();
1517
1518 vthread = nextThread;
1519 }
1520 }
1521 }
1522
1523 /**
1524 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting
1525 * if necessary until a list of one or more threads becomes available.
1526 */
1527 private static native VirtualThread takeVirtualThreadListToUnblock();
1528
1529 static {
1530 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker",
1531 VirtualThread::unblockVirtualThreads);
1532 unblocker.setDaemon(true);
1533 unblocker.start();
1534 }
1535 }
|
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25 package java.lang;
26
27 import java.lang.reflect.Constructor;
28 import java.util.Locale;
29 import java.util.Objects;
30 import java.util.concurrent.CountDownLatch;
31 import java.util.concurrent.Executors;
32 import java.util.concurrent.ForkJoinPool;
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
66 private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
67 private static final boolean IS_CUSTOM_DEFAULT_SCHEDULER;
68 static {
69 // experimental
70 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
71 if (propValue != null) {
72 DEFAULT_SCHEDULER = createCustomDefaultScheduler(propValue);
73 IS_CUSTOM_DEFAULT_SCHEDULER = true;
74 } else {
75 DEFAULT_SCHEDULER = createDefaultForkJoinPoolScheduler();
76 IS_CUSTOM_DEFAULT_SCHEDULER = false;
77 }
78 }
79
80 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
81 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
82 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
83 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
84 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
85
86 // scheduler and continuation
87 private final VirtualThreadScheduler scheduler;
88 private final Continuation cont;
89 private final Runnable runContinuation;
90
91 // virtual thread state, accessed by VM
92 private volatile int state;
93
94 /*
95 * Virtual thread state transitions:
96 *
97 * NEW -> STARTED // Thread.start, schedule to run
98 * STARTED -> TERMINATED // failed to start
99 * STARTED -> RUNNING // first run
100 * RUNNING -> TERMINATED // done
101 *
102 * RUNNING -> PARKING // Thread parking with LockSupport.park
103 * PARKING -> PARKED // cont.yield successful, parked indefinitely
104 * PARKING -> PINNED // cont.yield failed, parked indefinitely on carrier
105 * PARKED -> UNPARKED // unparked, may be scheduled to continue
106 * PINNED -> RUNNING // unparked, continue execution on same carrier
107 * UNPARKED -> RUNNING // continue execution after park
163 private static final int TERMINATED = 99; // final state
164
165 // can be suspended from scheduling when unmounted
166 private static final int SUSPENDED = 1 << 8;
167
168 // parking permit made available by LockSupport.unpark
169 private volatile boolean parkPermit;
170
171 // blocking permit made available by unblocker thread when another thread exits monitor
172 private volatile boolean blockPermit;
173
174 // true when on the list of virtual threads waiting to be unblocked
175 private volatile boolean onWaitingList;
176
177 // next virtual thread on the list of virtual threads waiting to be unblocked
178 private volatile VirtualThread next;
179
180 // notified by Object.notify/notifyAll while waiting in Object.wait
181 private volatile boolean notified;
182
183 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
184 private volatile boolean interruptableWait;
185
186 // timed-wait support
187 private byte timedWaitSeqNo;
188
189 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
190 private long timeout;
191
192 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
193 private Future<?> timeoutTask;
194
195 // carrier thread when mounted, accessed by VM
196 private volatile Thread carrierThread;
197
198 // termination object when joining, created lazily if needed
199 private volatile CountDownLatch termination;
200
201 /**
202 * Returns the default scheduler.
203 */
204 static VirtualThreadScheduler defaultScheduler() {
205 return DEFAULT_SCHEDULER;
206 }
207
208 /**
209 * Returns true if using a custom default scheduler.
210 */
211 static boolean isCustomDefaultScheduler() {
212 return IS_CUSTOM_DEFAULT_SCHEDULER;
213 }
214
215 /**
216 * Returns the continuation scope used for virtual threads.
217 */
218 static ContinuationScope continuationScope() {
219 return VTHREAD_SCOPE;
220 }
221
222 /**
223 * Return the scheduler for this thread.
224 * @param revealBuiltin true to reveal the built-in default scheduler, false to hide
225 */
226 VirtualThreadScheduler scheduler(boolean revealBuiltin) {
227 if (scheduler instanceof BuiltinDefaultScheduler builtin && !revealBuiltin) {
228 return builtin.externalView();
229 } else {
230 return scheduler;
231 }
232 }
233
234 /**
235 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
236 *
237 * @param scheduler the scheduler or null for default scheduler
238 * @param name thread name
239 * @param characteristics characteristics
240 * @param task the task to execute
241 */
242 VirtualThread(VirtualThreadScheduler scheduler,
243 String name,
244 int characteristics,
245 Runnable task) {
246 super(name, characteristics, /*bound*/ false);
247 Objects.requireNonNull(task);
248
249 // use default scheduler if not provided
250 if (scheduler == null) {
251 scheduler = DEFAULT_SCHEDULER;
252 }
253
254 this.scheduler = scheduler;
255 this.cont = new VThreadContinuation(this, task);
256 this.runContinuation = this::runContinuation;
257 }
258
259 /**
260 * The continuation that a virtual thread executes.
261 */
262 private static class VThreadContinuation extends Continuation {
263 VThreadContinuation(VirtualThread vthread, Runnable task) {
264 super(VTHREAD_SCOPE, wrap(vthread, task));
265 }
266 @Override
267 protected void onPinned(Continuation.Pinned reason) {
268 }
269 private static Runnable wrap(VirtualThread vthread, Runnable task) {
270 return new Runnable() {
271 @Hidden
327 afterYield();
328 }
329 }
330 }
331
332 /**
333 * Cancel timeout task when continuing after timed-park or timed-wait.
334 * The timeout task may be executing, or may have already completed.
335 */
336 private void cancelTimeoutTask() {
337 if (timeoutTask != null) {
338 timeoutTask.cancel(false);
339 timeoutTask = null;
340 }
341 }
342
343 /**
344 * Submits the runContinuation task to the scheduler. For the default scheduler,
345 * and calling it on a worker thread, the task will be pushed to the local queue,
346 * otherwise it will be pushed to an external submission queue.
347 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
348 * @throws RejectedExecutionException
349 */
350 private void submitRunContinuation(boolean retryOnOOME) {
351 boolean done = false;
352 while (!done) {
353 try {
354 // Pin the continuation to prevent the virtual thread from unmounting
355 // when submitting a task. For the default scheduler this ensures that
356 // the carrier doesn't change when pushing a task. For other schedulers
357 // it avoids deadlock that could arise due to carriers and virtual
358 // threads contending for a lock.
359 if (currentThread().isVirtual()) {
360 Continuation.pin();
361 try {
362 scheduler.execute(this, runContinuation);
363 } finally {
364 Continuation.unpin();
365 }
366 } else {
367 scheduler.execute(this, runContinuation);
368 }
369 done = true;
370 } catch (RejectedExecutionException ree) {
371 submitFailed(ree);
372 throw ree;
373 } catch (OutOfMemoryError e) {
374 if (retryOnOOME) {
375 U.park(false, 100_000_000); // 100ms
376 } else {
377 throw e;
378 }
379 }
380 }
381 }
382
383 /**
384 * Submits the runContinuation task to the scheduler. For the default scheduler,
385 * and calling it on a worker thread, the task will be pushed to the local queue,
386 * otherwise it will be pushed to an external submission queue.
387 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
388 * @throws RejectedExecutionException
389 */
390 private void submitRunContinuation() {
391 submitRunContinuation(true);
392 }
393
394 /**
395 * Lazy submit the runContinuation task if invoked on a carrier thread and its local
396 * queue is empty. If not empty, or invoked by another thread, then this method works
397 * like submitRunContinuation and just submits the task to the scheduler.
398 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
399 * @throws RejectedExecutionException
400 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
401 */
402 private void lazySubmitRunContinuation() {
403 if (scheduler == DEFAULT_SCHEDULER
404 && currentCarrierThread() instanceof CarrierThread ct
405 && ct.getQueuedTaskCount() == 0) {
406 try {
407 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
408 } catch (RejectedExecutionException ree) {
409 submitFailed(ree);
410 throw ree;
411 } catch (OutOfMemoryError e) {
412 submitRunContinuation();
413 }
414 } else {
415 submitRunContinuation();
416 }
417 }
418
419 /**
420 * Submits the runContinuation task to the scheduler. For the default scheduler, and
421 * calling it a virtual thread that uses the default scheduler, the task will be
422 * pushed to an external submission queue.
423 * @throws RejectedExecutionException
424 */
425 private void externalSubmitRunContinuation() {
426 if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
427 try {
428 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
429 } catch (RejectedExecutionException ree) {
430 submitFailed(ree);
431 throw ree;
432 } catch (OutOfMemoryError e) {
433 submitRunContinuation();
434 }
435 } else {
436 submitRunContinuation();
437 }
438 }
439
440 /**
441 * Submits the runContinuation task to the scheduler. For the default scheduler, and
442 * calling it a virtual thread that uses the default scheduler, the task will be
443 * pushed to an external submission queue. This method may throw OutOfMemoryError.
444 * @throws RejectedExecutionException
445 * @throws OutOfMemoryError
446 */
447 private void externalSubmitRunContinuationOrThrow() {
448 if (scheduler == DEFAULT_SCHEDULER && currentCarrierThread() instanceof CarrierThread ct) {
449 try {
450 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
451 } catch (RejectedExecutionException ree) {
452 submitFailed(ree);
453 throw ree;
454 }
455 } else {
456 submitRunContinuation(false);
457 }
458 }
459
460 /**
461 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
462 */
463 private void submitFailed(RejectedExecutionException ree) {
464 var event = new VirtualThreadSubmitFailedEvent();
465 if (event.isEnabled()) {
466 event.javaThreadId = threadId();
467 event.exceptionMessage = ree.getMessage();
468 event.commit();
469 }
470 }
471
472 /**
473 * Runs a task in the context of this virtual thread.
474 */
475 private void run(Runnable task) {
476 assert Thread.currentThread() == this && state == RUNNING;
591 long timeout = this.timeout;
592 assert timeout > 0;
593 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
594 setState(newState = TIMED_PARKED);
595 }
596
597 // may have been unparked while parking
598 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
599 // lazy submit if local queue is empty
600 lazySubmitRunContinuation();
601 }
602 return;
603 }
604
605 // Thread.yield
606 if (s == YIELDING) {
607 setState(YIELDED);
608
609 // external submit if there are no tasks in the local task queue
610 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
611 externalSubmitRunContinuation();
612 } else {
613 submitRunContinuation();
614 }
615 return;
616 }
617
618 // blocking on monitorenter
619 if (s == BLOCKING) {
620 setState(BLOCKED);
621
622 // may have been unblocked while blocking
623 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
624 // lazy submit if local queue is empty
625 lazySubmitRunContinuation();
626 }
627 return;
628 }
629
630 // Object.wait
631 if (s == WAITING || s == TIMED_WAITING) {
632 int newState;
633 boolean interruptable = interruptableWait;
634 if (s == WAITING) {
635 setState(newState = WAIT);
636 } else {
637 // For timed-wait, a timeout task is scheduled to execute. The timeout
638 // task will change the thread state to UNBLOCKED and submit the thread
639 // to the scheduler. A sequence number is used to ensure that the timeout
640 // task only unblocks the thread for this timed-wait. We synchronize with
641 // the timeout task to coordinate access to the sequence number and to
642 // ensure the timeout task doesn't execute until the thread has got to
643 // the TIMED_WAIT state.
644 long timeout = this.timeout;
645 assert timeout > 0;
646 synchronized (timedWaitLock()) {
647 byte seqNo = ++timedWaitSeqNo;
648 timeoutTask = schedule(() -> waitTimeoutExpired(seqNo), timeout, MILLISECONDS);
649 setState(newState = TIMED_WAIT);
650 }
651 }
652
653 // may have been notified while in transition to wait state
654 if (notified && compareAndSetState(newState, BLOCKED)) {
655 // may have even been unblocked already
656 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
657 submitRunContinuation();
658 }
659 return;
660 }
661
662 // may have been interrupted while in transition to wait state
663 if (interruptable && interrupted && compareAndSetState(newState, UNBLOCKED)) {
664 submitRunContinuation();
665 return;
666 }
667 return;
668 }
669
670 assert false;
671 }
672
673 /**
674 * Invoked after the continuation completes.
675 */
676 private void afterDone() {
677 afterDone(true);
678 }
679
680 /**
681 * Invoked after the continuation completes (or start failed). Sets the thread
682 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
683 *
1430 @IntrinsicCandidate
1431 @JvmtiMountTransition
1432 private native void notifyJvmtiMount(boolean hide);
1433
1434 @IntrinsicCandidate
1435 @JvmtiMountTransition
1436 private native void notifyJvmtiUnmount(boolean hide);
1437
1438 @IntrinsicCandidate
1439 private static native void notifyJvmtiDisableSuspend(boolean enter);
1440
1441 private static native void registerNatives();
1442 static {
1443 registerNatives();
1444
1445 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1446 var group = Thread.virtualThreadGroup();
1447 }
1448
1449 /**
1450 * Loads a VirtualThreadScheduler with the given class name to use at the
1451 * default scheduler. The class is public in an exported package, has a public
1452 * one-arg or no-arg constructor, and is visible to the system class loader.
1453 */
1454 private static VirtualThreadScheduler createCustomDefaultScheduler(String cn) {
1455 try {
1456 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1457 VirtualThreadScheduler scheduler;
1458 try {
1459 // 1-arg constructor
1460 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1461 var builtin = createDefaultForkJoinPoolScheduler();
1462 scheduler = (VirtualThreadScheduler) ctor.newInstance(builtin.externalView());
1463 } catch (NoSuchMethodException e) {
1464 // 0-arg constructor
1465 Constructor<?> ctor = clazz.getConstructor();
1466 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1467 }
1468 System.err.println("""
1469 WARNING: Using custom default scheduler, this is an experimental feature!""");
1470 return scheduler;
1471 } catch (Exception ex) {
1472 throw new Error(ex);
1473 }
1474 }
1475
1476 /**
1477 * Creates the built-in default ForkJoinPool scheduler.
1478 */
1479 private static BuiltinDefaultScheduler createDefaultForkJoinPoolScheduler() {
1480 int parallelism, maxPoolSize, minRunnable;
1481 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1482 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1483 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1484 if (parallelismValue != null) {
1485 parallelism = Integer.parseInt(parallelismValue);
1486 } else {
1487 parallelism = Runtime.getRuntime().availableProcessors();
1488 }
1489 if (maxPoolSizeValue != null) {
1490 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1491 parallelism = Integer.min(parallelism, maxPoolSize);
1492 } else {
1493 maxPoolSize = Integer.max(parallelism, 256);
1494 }
1495 if (minRunnableValue != null) {
1496 minRunnable = Integer.parseInt(minRunnableValue);
1497 } else {
1498 minRunnable = Integer.max(parallelism / 2, 1);
1499 }
1500 return new BuiltinDefaultScheduler(parallelism, maxPoolSize, minRunnable);
1501 }
1502
1503 /**
1504 * The built-in default ForkJoinPool scheduler.
1505 */
1506 private static class BuiltinDefaultScheduler
1507 extends ForkJoinPool implements VirtualThreadScheduler {
1508
1509 private static final StableValue<VirtualThreadScheduler> VIEW = StableValue.of();
1510
1511 BuiltinDefaultScheduler(int parallelism, int maxPoolSize, int minRunnable) {
1512 ForkJoinWorkerThreadFactory factory = pool -> new CarrierThread(pool);
1513 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1514 boolean asyncMode = true; // FIFO
1515 super(parallelism, factory, handler, asyncMode,
1516 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1517 }
1518
1519 @Override
1520 public void execute(Thread vthread, Runnable task) {
1521 execute(ForkJoinTask.adapt(task));
1522 }
1523
1524 /**
1525 * Wraps the scheduler to avoid leaking a direct reference.
1526 */
1527 VirtualThreadScheduler externalView() {
1528 VirtualThreadScheduler builtin = this;
1529 return VIEW.orElseSet(() -> {
1530 return new VirtualThreadScheduler() {
1531 @Override
1532 public void execute(Thread thread, Runnable task) {
1533 Objects.requireNonNull(thread);
1534 if (thread instanceof VirtualThread vthread) {
1535 VirtualThreadScheduler scheduler = vthread.scheduler;
1536 if (scheduler == this || scheduler == DEFAULT_SCHEDULER) {
1537 builtin.execute(thread, task);
1538 } else {
1539 throw new IllegalArgumentException();
1540 }
1541 } else {
1542 throw new UnsupportedOperationException();
1543 }
1544 }
1545 };
1546 });
1547 }
1548 }
1549
1550 /**
1551 * Schedule a runnable task to run after a delay.
1552 */
1553 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1554 if (scheduler instanceof ForkJoinPool pool) {
1555 return pool.schedule(command, delay, unit);
1556 } else {
1557 return DelayedTaskSchedulers.schedule(command, delay, unit);
1558 }
1559 }
1560
1561 /**
1562 * Supports scheduling a runnable task to run after a delay. It uses a number
1563 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1564 * work queue used. This class is used when using a custom scheduler.
1565 */
1566 private static class DelayedTaskSchedulers {
1567 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1617 assert changed;
1618 vthread.unblock();
1619
1620 vthread = nextThread;
1621 }
1622 }
1623 }
1624
1625 /**
1626 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting
1627 * if necessary until a list of one or more threads becomes available.
1628 */
1629 private static native VirtualThread takeVirtualThreadListToUnblock();
1630
1631 static {
1632 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker",
1633 VirtualThread::unblockVirtualThreads);
1634 unblocker.setDaemon(true);
1635 unblocker.start();
1636 }
1637 }
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