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
296 if (cont.isDone()) {
297 afterDone();
298 } else {
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 ForkJoinPool BUILTIN_DEFAULT_SCHEDULER;
67 private static final VirtualThreadScheduler DEFAULT_SCHEDULER;
68 static {
69 // experimental
70 String propValue = System.getProperty("jdk.virtualThreadScheduler.implClass");
71 if (propValue != null) {
72 var builtinScheduler = createBuiltinDefaultScheduler(true);
73 VirtualThreadScheduler defaultScheduler = builtinScheduler.externalView();
74 for (String cn: propValue.split(",")) {
75 defaultScheduler = loadCustomScheduler(defaultScheduler, cn);
76 }
77 BUILTIN_DEFAULT_SCHEDULER = builtinScheduler;
78 DEFAULT_SCHEDULER = defaultScheduler;
79 } else {
80 var builtinScheduler = createBuiltinDefaultScheduler(false);
81 BUILTIN_DEFAULT_SCHEDULER = builtinScheduler;
82 DEFAULT_SCHEDULER = builtinScheduler;
83 }
84 }
85
86 private static final long STATE = U.objectFieldOffset(VirtualThread.class, "state");
87 private static final long PARK_PERMIT = U.objectFieldOffset(VirtualThread.class, "parkPermit");
88 private static final long CARRIER_THREAD = U.objectFieldOffset(VirtualThread.class, "carrierThread");
89 private static final long TERMINATION = U.objectFieldOffset(VirtualThread.class, "termination");
90 private static final long ON_WAITING_LIST = U.objectFieldOffset(VirtualThread.class, "onWaitingList");
91
92 // scheduler and continuation
93 private final VirtualThreadScheduler scheduler;
94 private final Continuation cont;
95 private final Runnable runContinuation;
96
97 // virtual thread state, accessed by VM
98 private volatile int state;
99
100 /*
101 * Virtual thread state transitions:
102 *
103 * NEW -> STARTED // Thread.start, schedule to run
104 * STARTED -> TERMINATED // failed to start
105 * STARTED -> RUNNING // first run
106 * RUNNING -> TERMINATED // done
107 *
108 * RUNNING -> PARKING // Thread parking with LockSupport.park
109 * PARKING -> PARKED // cont.yield successful, parked indefinitely
110 * PARKING -> PINNED // cont.yield failed, parked indefinitely on carrier
111 * PARKED -> UNPARKED // unparked, may be scheduled to continue
112 * PINNED -> RUNNING // unparked, continue execution on same carrier
113 * UNPARKED -> RUNNING // continue execution after park
169 private static final int TERMINATED = 99; // final state
170
171 // can be suspended from scheduling when unmounted
172 private static final int SUSPENDED = 1 << 8;
173
174 // parking permit made available by LockSupport.unpark
175 private volatile boolean parkPermit;
176
177 // blocking permit made available by unblocker thread when another thread exits monitor
178 private volatile boolean blockPermit;
179
180 // true when on the list of virtual threads waiting to be unblocked
181 private volatile boolean onWaitingList;
182
183 // next virtual thread on the list of virtual threads waiting to be unblocked
184 private volatile VirtualThread next;
185
186 // notified by Object.notify/notifyAll while waiting in Object.wait
187 private volatile boolean notified;
188
189 // true when waiting in Object.wait, false for VM internal uninterruptible Object.wait
190 private volatile boolean interruptibleWait;
191
192 // timed-wait support
193 private byte timedWaitSeqNo;
194
195 // timeout for timed-park and timed-wait, only accessed on current/carrier thread
196 private long timeout;
197
198 // timer task for timed-park and timed-wait, only accessed on current/carrier thread
199 private Future<?> timeoutTask;
200
201 // carrier thread when mounted, accessed by VM
202 private volatile Thread carrierThread;
203
204 // termination object when joining, created lazily if needed
205 private volatile CountDownLatch termination;
206
207 /**
208 * Returns the default scheduler.
209 */
210 static VirtualThreadScheduler defaultScheduler() {
211 return DEFAULT_SCHEDULER;
212 }
213
214 /**
215 * Returns true if using a custom default scheduler.
216 */
217 static boolean isCustomDefaultScheduler() {
218 return DEFAULT_SCHEDULER != BUILTIN_DEFAULT_SCHEDULER;
219 }
220
221 /**
222 * Returns the continuation scope used for virtual threads.
223 */
224 static ContinuationScope continuationScope() {
225 return VTHREAD_SCOPE;
226 }
227
228 /**
229 * Return the scheduler for this thread.
230 * @param revealBuiltin true to reveal the built-in default scheduler, false to hide
231 */
232 VirtualThreadScheduler scheduler(boolean revealBuiltin) {
233 if (scheduler instanceof BuiltinDefaultScheduler builtin && !revealBuiltin) {
234 return builtin.externalView();
235 } else {
236 return scheduler;
237 }
238 }
239
240 /**
241 * Creates a new {@code VirtualThread} to run the given task with the given scheduler.
242 *
243 * @param scheduler the scheduler or null for default scheduler
244 * @param name thread name
245 * @param characteristics characteristics
246 * @param task the task to execute
247 */
248 VirtualThread(VirtualThreadScheduler scheduler,
249 String name,
250 int characteristics,
251 Runnable task) {
252 super(name, characteristics, /*bound*/ false);
253 Objects.requireNonNull(task);
254
255 // use default scheduler if not provided
256 if (scheduler == null) {
257 scheduler = DEFAULT_SCHEDULER;
258 }
259
260 this.scheduler = scheduler;
261 this.cont = new VThreadContinuation(this, task);
262 this.runContinuation = this::runContinuation;
263 }
264
265 /**
266 * The continuation that a virtual thread executes.
267 */
268 private static class VThreadContinuation extends Continuation {
269 VThreadContinuation(VirtualThread vthread, Runnable task) {
270 super(VTHREAD_SCOPE, wrap(vthread, task));
271 }
272 @Override
273 protected void onPinned(Continuation.Pinned reason) {
274 }
275 private static Runnable wrap(VirtualThread vthread, Runnable task) {
276 return new Runnable() {
277 @Hidden
330 if (cont.isDone()) {
331 afterDone();
332 } else {
333 afterYield();
334 }
335 }
336 }
337
338 /**
339 * Cancel timeout task when continuing after timed-park or timed-wait.
340 * The timeout task may be executing, or may have already completed.
341 */
342 private void cancelTimeoutTask() {
343 if (timeoutTask != null) {
344 timeoutTask.cancel(false);
345 timeoutTask = null;
346 }
347 }
348
349 /**
350 * Submits the runContinuation task to the scheduler. For the built-in default
351 * scheduler, the task will be pushed to the local queue if possible, otherwise it
352 * will be pushed to an external submission queue.
353 * @param retryOnOOME true to retry indefinitely if OutOfMemoryError is thrown
354 * @throws RejectedExecutionException
355 */
356 private void submitRunContinuation(boolean retryOnOOME) {
357 boolean done = false;
358 while (!done) {
359 try {
360 // Pin the continuation to prevent the virtual thread from unmounting
361 // when submitting a task. For the default scheduler this ensures that
362 // the carrier doesn't change when pushing a task. For other schedulers
363 // it avoids deadlock that could arise due to carriers and virtual
364 // threads contending for a lock.
365 if (currentThread().isVirtual()) {
366 Continuation.pin();
367 try {
368 scheduler.onContinue(this, runContinuation);
369 } finally {
370 Continuation.unpin();
371 }
372 } else {
373 scheduler.onContinue(this, runContinuation);
374 }
375 done = true;
376 } catch (RejectedExecutionException ree) {
377 submitFailed(ree);
378 throw ree;
379 } catch (OutOfMemoryError e) {
380 if (retryOnOOME) {
381 U.park(false, 100_000_000); // 100ms
382 } else {
383 throw e;
384 }
385 }
386 }
387 }
388
389 /**
390 * Submits the runContinuation task to the scheduler. For the default scheduler,
391 * and calling it on a worker thread, the task will be pushed to the local queue,
392 * otherwise it will be pushed to an external submission queue.
393 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
394 * @throws RejectedExecutionException
395 */
396 private void submitRunContinuation() {
397 submitRunContinuation(true);
398 }
399
400 /**
401 * Invoked from a carrier thread to lazy submit the runContinuation task to the
402 * carrier's local queue if the queue is empty. If not empty, or invoked by a thread
403 * for a custom scheduler, then it just submits the task to the scheduler.
404 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
405 * @throws RejectedExecutionException
406 * @see ForkJoinPool#lazySubmit(ForkJoinTask)
407 */
408 private void lazySubmitRunContinuation() {
409 assert !currentThread().isVirtual();
410 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
411 try {
412 ct.getPool().lazySubmit(ForkJoinTask.adapt(runContinuation));
413 } catch (RejectedExecutionException ree) {
414 submitFailed(ree);
415 throw ree;
416 } catch (OutOfMemoryError e) {
417 submitRunContinuation();
418 }
419 } else {
420 submitRunContinuation();
421 }
422 }
423
424 /**
425 * Invoked from a carrier thread to externally submit the runContinuation task to the
426 * scheduler. If invoked by a thread for a custom scheduler, then it just submits the
427 * task to the scheduler.
428 * If OutOfMemoryError is thrown then the submit will be retried until it succeeds.
429 * @throws RejectedExecutionException
430 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
431 */
432 private void externalSubmitRunContinuation() {
433 assert !currentThread().isVirtual();
434 if (currentThread() instanceof CarrierThread ct) {
435 try {
436 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
437 } catch (RejectedExecutionException ree) {
438 submitFailed(ree);
439 throw ree;
440 } catch (OutOfMemoryError e) {
441 submitRunContinuation();
442 }
443 } else {
444 submitRunContinuation();
445 }
446 }
447
448 /**
449 * Invoked from Thread.start to externally submit the runContinuation task to the
450 * scheduler. If this virtual thread is scheduled by the built-in default scheduler,
451 * and this method is called from a virtual thread scheduled by the built-in default
452 * scheduler, then it uses externalSubmit to ensure that the task is pushed to an
453 * external submission queue rather than the local queue.
454 * @throws RejectedExecutionException
455 * @throws OutOfMemoryError
456 * @see ForkJoinPool#externalSubmit(ForkJoinTask)
457 */
458 private void externalSubmitRunContinuationOrThrow() {
459 try {
460 if (currentThread().isVirtual()) {
461 // Pin the continuation to prevent the virtual thread from unmounting
462 // when submitting a task. This avoids deadlock that could arise due to
463 // carriers and virtual threads contending for a lock.
464 Continuation.pin();
465 try {
466 if (scheduler == BUILTIN_DEFAULT_SCHEDULER
467 && currentCarrierThread() instanceof CarrierThread ct) {
468 ct.getPool().externalSubmit(ForkJoinTask.adapt(runContinuation));
469 } else {
470 scheduler.onStart(this, runContinuation);
471 }
472 } finally {
473 Continuation.unpin();
474 }
475 } else {
476 scheduler.onStart(this, runContinuation);
477 }
478 } catch (RejectedExecutionException ree) {
479 submitFailed(ree);
480 throw ree;
481 }
482 }
483
484 /**
485 * If enabled, emits a JFR VirtualThreadSubmitFailedEvent.
486 */
487 private void submitFailed(RejectedExecutionException ree) {
488 var event = new VirtualThreadSubmitFailedEvent();
489 if (event.isEnabled()) {
490 event.javaThreadId = threadId();
491 event.exceptionMessage = ree.getMessage();
492 event.commit();
493 }
494 }
495
496 /**
497 * Runs a task in the context of this virtual thread.
498 */
499 private void run(Runnable task) {
500 assert Thread.currentThread() == this && state == RUNNING;
615 long timeout = this.timeout;
616 assert timeout > 0;
617 timeoutTask = schedule(this::parkTimeoutExpired, timeout, NANOSECONDS);
618 setState(newState = TIMED_PARKED);
619 }
620
621 // may have been unparked while parking
622 if (parkPermit && compareAndSetState(newState, UNPARKED)) {
623 // lazy submit if local queue is empty
624 lazySubmitRunContinuation();
625 }
626 return;
627 }
628
629 // Thread.yield
630 if (s == YIELDING) {
631 setState(YIELDED);
632
633 // external submit if there are no tasks in the local task queue
634 if (currentThread() instanceof CarrierThread ct && ct.getQueuedTaskCount() == 0) {
635 externalSubmitRunContinuation();
636 } else {
637 submitRunContinuation();
638 }
639 return;
640 }
641
642 // blocking on monitorenter
643 if (s == BLOCKING) {
644 setState(BLOCKED);
645
646 // may have been unblocked while blocking
647 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
648 // lazy submit if local queue is empty
649 lazySubmitRunContinuation();
650 }
651 return;
652 }
653
654 // Object.wait
655 if (s == WAITING || s == TIMED_WAITING) {
656 int newState;
657 boolean interruptible = interruptibleWait;
658 if (s == WAITING) {
659 setState(newState = WAIT);
660 } else {
661 // For timed-wait, a timeout task is scheduled to execute. The timeout
662 // task will change the thread state to UNBLOCKED and submit the thread
663 // to the scheduler. A sequence number is used to ensure that the timeout
664 // task only unblocks the thread for this timed-wait. We synchronize with
665 // the timeout task to coordinate access to the sequence number and to
666 // ensure the timeout task doesn't execute until the thread has got to
667 // the TIMED_WAIT state.
668 long timeout = this.timeout;
669 assert timeout > 0;
670 synchronized (timedWaitLock()) {
671 byte seqNo = ++timedWaitSeqNo;
672 timeoutTask = schedule(() -> waitTimeoutExpired(seqNo), timeout, MILLISECONDS);
673 setState(newState = TIMED_WAIT);
674 }
675 }
676
677 // may have been notified while in transition to wait state
678 if (notified && compareAndSetState(newState, BLOCKED)) {
679 // may have even been unblocked already
680 if (blockPermit && compareAndSetState(BLOCKED, UNBLOCKED)) {
681 submitRunContinuation();
682 }
683 return;
684 }
685
686 // may have been interrupted while in transition to wait state
687 if (interruptible && interrupted && compareAndSetState(newState, UNBLOCKED)) {
688 submitRunContinuation();
689 return;
690 }
691 return;
692 }
693
694 assert false;
695 }
696
697 /**
698 * Invoked after the continuation completes.
699 */
700 private void afterDone() {
701 afterDone(true);
702 }
703
704 /**
705 * Invoked after the continuation completes (or start failed). Sets the thread
706 * state to TERMINATED and notifies anyone waiting for the thread to terminate.
707 *
1454 @IntrinsicCandidate
1455 @JvmtiMountTransition
1456 private native void notifyJvmtiMount(boolean hide);
1457
1458 @IntrinsicCandidate
1459 @JvmtiMountTransition
1460 private native void notifyJvmtiUnmount(boolean hide);
1461
1462 @IntrinsicCandidate
1463 private static native void notifyJvmtiDisableSuspend(boolean enter);
1464
1465 private static native void registerNatives();
1466 static {
1467 registerNatives();
1468
1469 // ensure VTHREAD_GROUP is created, may be accessed by JVMTI
1470 var group = Thread.virtualThreadGroup();
1471 }
1472
1473 /**
1474 * Loads a VirtualThreadScheduler with the given class name. The class must be public
1475 * in an exported package, with public one-arg or no-arg constructor, and be visible
1476 * to the system class loader.
1477 * @param delegate the scheduler that the custom scheduler may delegate to
1478 * @param cn the class name of the custom scheduler
1479 */
1480 private static VirtualThreadScheduler loadCustomScheduler(VirtualThreadScheduler delegate, String cn) {
1481 try {
1482 Class<?> clazz = Class.forName(cn, true, ClassLoader.getSystemClassLoader());
1483 VirtualThreadScheduler scheduler;
1484 try {
1485 // 1-arg constructor
1486 Constructor<?> ctor = clazz.getConstructor(VirtualThreadScheduler.class);
1487 scheduler = (VirtualThreadScheduler) ctor.newInstance(delegate);
1488 } catch (NoSuchMethodException e) {
1489 // 0-arg constructor
1490 Constructor<?> ctor = clazz.getConstructor();
1491 scheduler = (VirtualThreadScheduler) ctor.newInstance();
1492 }
1493 System.err.println("""
1494 WARNING: Using custom default scheduler, this is an experimental feature!""");
1495 return scheduler;
1496 } catch (Exception ex) {
1497 throw new Error(ex);
1498 }
1499 }
1500
1501 /**
1502 * Creates the built-in default ForkJoinPool scheduler.
1503 * @param wrapped true if wrapped by a custom default scheduler
1504 */
1505 private static BuiltinDefaultScheduler createBuiltinDefaultScheduler(boolean wrapped) {
1506 int parallelism, maxPoolSize, minRunnable;
1507 String parallelismValue = System.getProperty("jdk.virtualThreadScheduler.parallelism");
1508 String maxPoolSizeValue = System.getProperty("jdk.virtualThreadScheduler.maxPoolSize");
1509 String minRunnableValue = System.getProperty("jdk.virtualThreadScheduler.minRunnable");
1510 if (parallelismValue != null) {
1511 parallelism = Integer.parseInt(parallelismValue);
1512 } else {
1513 parallelism = Runtime.getRuntime().availableProcessors();
1514 }
1515 if (maxPoolSizeValue != null) {
1516 maxPoolSize = Integer.parseInt(maxPoolSizeValue);
1517 parallelism = Integer.min(parallelism, maxPoolSize);
1518 } else {
1519 maxPoolSize = Integer.max(parallelism, 256);
1520 }
1521 if (minRunnableValue != null) {
1522 minRunnable = Integer.parseInt(minRunnableValue);
1523 } else {
1524 minRunnable = Integer.max(parallelism / 2, 1);
1525 }
1526 return new BuiltinDefaultScheduler(parallelism, maxPoolSize, minRunnable, wrapped);
1527 }
1528
1529 /**
1530 * The built-in default ForkJoinPool scheduler.
1531 */
1532 private static class BuiltinDefaultScheduler
1533 extends ForkJoinPool implements VirtualThreadScheduler {
1534
1535 private static final StableValue<VirtualThreadScheduler> VIEW = StableValue.of();
1536
1537 BuiltinDefaultScheduler(int parallelism, int maxPoolSize, int minRunnable, boolean wrapped) {
1538 ForkJoinWorkerThreadFactory factory = wrapped
1539 ? ForkJoinPool.defaultForkJoinWorkerThreadFactory
1540 : CarrierThread::new;
1541 Thread.UncaughtExceptionHandler handler = (t, e) -> { };
1542 boolean asyncMode = true; // FIFO
1543 super(parallelism, factory, handler, asyncMode,
1544 0, maxPoolSize, minRunnable, pool -> true, 30, SECONDS);
1545 }
1546
1547 private void adaptAndExecute(Runnable task) {
1548 execute(ForkJoinTask.adapt(task));
1549 }
1550
1551 @Override
1552 public void onStart(Thread vthread, Runnable task) {
1553 adaptAndExecute(task);
1554 }
1555
1556 @Override
1557 public void onContinue(Thread vthread, Runnable task) {
1558 adaptAndExecute(task);
1559 }
1560
1561 /**
1562 * Wraps the scheduler to avoid leaking a direct reference.
1563 */
1564 VirtualThreadScheduler externalView() {
1565 BuiltinDefaultScheduler builtin = this;
1566 return VIEW.orElseSet(() -> {
1567 return new VirtualThreadScheduler() {
1568 private void execute(Thread thread, Runnable task) {
1569 Objects.requireNonNull(thread);
1570 if (thread instanceof VirtualThread vthread) {
1571 VirtualThreadScheduler scheduler = vthread.scheduler;
1572 if (scheduler == this || scheduler == DEFAULT_SCHEDULER) {
1573 builtin.adaptAndExecute(task);
1574 } else {
1575 throw new IllegalArgumentException();
1576 }
1577 } else {
1578 throw new UnsupportedOperationException();
1579 }
1580 }
1581 @Override
1582 public void onStart(Thread thread, Runnable task) {
1583 execute(thread, task);
1584 }
1585 @Override
1586 public void onContinue(Thread thread, Runnable task) {
1587 execute(thread, task);
1588 }
1589 };
1590 });
1591 }
1592 }
1593
1594 /**
1595 * Schedule a runnable task to run after a delay.
1596 */
1597 private Future<?> schedule(Runnable command, long delay, TimeUnit unit) {
1598 if (scheduler instanceof ForkJoinPool pool) {
1599 return pool.schedule(command, delay, unit);
1600 } else {
1601 return DelayedTaskSchedulers.schedule(command, delay, unit);
1602 }
1603 }
1604
1605 /**
1606 * Supports scheduling a runnable task to run after a delay. It uses a number
1607 * of ScheduledThreadPoolExecutor instances to reduce contention on the delayed
1608 * work queue used. This class is used when using a custom scheduler.
1609 */
1610 private static class DelayedTaskSchedulers {
1611 private static final ScheduledExecutorService[] INSTANCE = createDelayedTaskSchedulers();
1661 assert changed;
1662 vthread.unblock();
1663
1664 vthread = nextThread;
1665 }
1666 }
1667 }
1668
1669 /**
1670 * Retrieves the list of virtual threads that are waiting to be unblocked, waiting
1671 * if necessary until a list of one or more threads becomes available.
1672 */
1673 private static native VirtualThread takeVirtualThreadListToUnblock();
1674
1675 static {
1676 var unblocker = InnocuousThread.newThread("VirtualThread-unblocker",
1677 VirtualThread::unblockVirtualThreads);
1678 unblocker.setDaemon(true);
1679 unblocker.start();
1680 }
1681 }
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