1 /*
2 * Copyright (c) 2021, 2023, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
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).
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24 */
25 package java.util.concurrent;
26
27 import java.lang.invoke.MethodHandles;
28 import java.lang.invoke.VarHandle;
29 import java.security.AccessController;
30 import java.security.PrivilegedAction;
31 import java.time.Duration;
32 import java.time.Instant;
33 import java.util.Objects;
34 import java.util.Optional;
35 import java.util.concurrent.locks.ReentrantLock;
36 import java.util.function.Function;
37 import java.util.function.Supplier;
38 import jdk.internal.javac.PreviewFeature;
39 import jdk.internal.misc.ThreadFlock;
40
41 /**
42 * A basic API for <em>structured concurrency</em>. {@code StructuredTaskScope} supports
43 * cases where a task splits into several concurrent subtasks, and where the subtasks must
44 * complete before the main task continues. A {@code StructuredTaskScope} can be used to
45 * ensure that the lifetime of a concurrent operation is confined by a <em>syntax block</em>,
46 * just like that of a sequential operation in structured programming.
47 *
48 * <h2>Basic operation</h2>
49 *
50 * A {@code StructuredTaskScope} is created with one of its public constructors. It defines
51 * the {@link #fork(Callable) fork} method to start a thread to execute a subtask, the {@link
52 * #join() join} method to wait for all subtasks to finish, and the {@link #close() close}
53 * method to close the task scope. The API is intended to be used with the {@code
54 * try-with-resources} statement. The intention is that code in the try <em>block</em>
55 * uses the {@code fork} method to fork threads to execute the subtasks, wait for the
56 * subtasks to finish with the {@code join} method, and then <em>process the results</em>.
57 * A call to the {@code fork} method returns a {@link Subtask Subtask} to representing
58 * the <em>forked subtask</em>. Once {@code join} is called, the {@code Subtask} can be
59 * used to get the result completed successfully, or the exception if the subtask failed.
60 * {@snippet lang=java :
61 * Callable<String> task1 = ...
62 * Callable<Integer> task2 = ...
63 *
64 * try (var scope = new StructuredTaskScope<Object>()) {
65 *
66 * Subtask<String> subtask1 = scope.fork(task1); // @highlight substring="fork"
67 * Subtask<Integer> subtask2 = scope.fork(task2); // @highlight substring="fork"
68 *
69 * scope.join(); // @highlight substring="join"
70 *
71 * ... process results/exceptions ...
72 *
73 * } // close // @highlight substring="close"
74 * }
75 * <p> The following example forks a collection of homogeneous subtasks, waits for all of
76 * them to complete with the {@code join} method, and uses the {@link Subtask.State
77 * Subtask.State} to partition the subtasks into a set of the subtasks that completed
78 * successfully and another for the subtasks that failed.
79 * {@snippet lang=java :
80 * List<Callable<String>> callables = ...
81 *
82 * try (var scope = new StructuredTaskScope<String>()) {
83 *
84 * List<Subtask<String>> subtasks = callables.stream().map(scope::fork).toList();
85 *
86 * scope.join();
87 *
88 * Map<Boolean, Set<Subtask<String>>> map = subtasks.stream()
89 * .collect(Collectors.partitioningBy(h -> h.state() == Subtask.State.SUCCESS,
90 * Collectors.toSet()));
91 *
92 * } // close
93 * }
94 *
95 * <p> To ensure correct usage, the {@code join} and {@code close} methods may only be
96 * invoked by the <em>owner</em> (the thread that opened/created the task scope), and the
97 * {@code close} method throws an exception after closing if the owner did not invoke the
98 * {@code join} method after forking.
99 *
100 * <p> {@code StructuredTaskScope} defines the {@link #shutdown() shutdown} method to shut
101 * down a task scope without closing it. The {@code shutdown()} method <em>cancels</em> all
102 * unfinished subtasks by {@linkplain Thread#interrupt() interrupting} the threads. It
103 * prevents new threads from starting in the task scope. If the owner is waiting in the
104 * {@code join} method then it will wakeup.
105 *
106 * <p> Shutdown is used for <em>short-circuiting</em> and allow subclasses to implement
107 * <em>policy</em> that does not require all subtasks to finish.
108 *
109 * <h2>Subclasses with policies for common cases</h2>
110 *
111 * Two subclasses of {@code StructuredTaskScope} are defined to implement policy for
112 * common cases:
113 * <ol>
114 * <li> {@link ShutdownOnSuccess ShutdownOnSuccess} captures the result of the first
115 * subtask to complete successfully. Once captured, it shuts down the task scope to
116 * interrupt unfinished threads and wakeup the owner. This class is intended for cases
117 * where the result of any subtask will do ("invoke any") and where there is no need to
118 * wait for results of other unfinished subtasks. It defines methods to get the first
119 * result or throw an exception if all subtasks fail.
120 * <li> {@link ShutdownOnFailure ShutdownOnFailure} captures the exception of the first
121 * subtask to fail. Once captured, it shuts down the task scope to interrupt unfinished
122 * threads and wakeup the owner. This class is intended for cases where the results of all
123 * subtasks are required ("invoke all"); if any subtask fails then the results of other
124 * unfinished subtasks are no longer needed. If defines methods to throw an exception if
125 * any of the subtasks fail.
126 * </ol>
127 *
128 * <p> The following are two examples that use the two classes. In both cases, a pair of
129 * subtasks are forked to fetch resources from two URL locations "left" and "right". The
130 * first example creates a ShutdownOnSuccess object to capture the result of the first
131 * subtask to complete successfully, cancelling the other by way of shutting down the task
132 * scope. The main task waits in {@code join} until either subtask completes with a result
133 * or both subtasks fail. It invokes {@link ShutdownOnSuccess#result(Function)
134 * result(Function)} method to get the captured result. If both subtasks fail then this
135 * method throws a {@code WebApplicationException} with the exception from one of the
136 * subtasks as the cause.
137 * {@snippet lang=java :
138 * try (var scope = new StructuredTaskScope.ShutdownOnSuccess<String>()) {
139 *
140 * scope.fork(() -> fetch(left));
141 * scope.fork(() -> fetch(right));
142 *
143 * scope.join();
144 *
145 * // @link regex="result(?=\()" target="ShutdownOnSuccess#result" :
146 * String result = scope.result(e -> new WebApplicationException(e));
147 *
148 * ...
149 * }
150 * }
151 * The second example creates a ShutdownOnFailure object to capture the exception of the
152 * first subtask to fail, cancelling the other by way of shutting down the task scope. The
153 * main task waits in {@link #joinUntil(Instant)} until both subtasks complete with a
154 * result, either fails, or a deadline is reached. It invokes {@link
155 * ShutdownOnFailure#throwIfFailed(Function) throwIfFailed(Function)} to throw an exception
156 * if either subtask fails. This method is a no-op if both subtasks complete successfully.
157 * The example uses {@link Supplier#get()} to get the result of each subtask. Using
158 * {@code Supplier} instead of {@code Subtask} is preferred for common cases where the
159 * object returned by fork is only used to get the result of a subtask that completed
160 * successfully.
161 * {@snippet lang=java :
162 * Instant deadline = ...
163 *
164 * try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
165 *
166 * Supplier<String> supplier1 = scope.fork(() -> query(left));
167 * Supplier<String> supplier2 = scope.fork(() -> query(right));
168 *
169 * scope.joinUntil(deadline);
170 *
171 * // @link substring="throwIfFailed" target="ShutdownOnFailure#throwIfFailed" :
172 * scope.throwIfFailed(e -> new WebApplicationException(e));
173 *
174 * // both subtasks completed successfully
175 * String result = Stream.of(supplier1, supplier2)
176 * .map(Supplier::get)
177 * .collect(Collectors.joining(", ", "{ ", " }"));
178 *
179 * ...
180 * }
181 * }
182 *
183 * <h2>Extending StructuredTaskScope</h2>
184 *
185 * {@code StructuredTaskScope} can be extended, and the {@link #handleComplete(Subtask)
186 * handleComplete} method overridden, to implement policies other than those implemented
187 * by {@code ShutdownOnSuccess} and {@code ShutdownOnFailure}. A subclass may, for example,
188 * collect the results of subtasks that complete successfully and ignore subtasks that
189 * fail. It may collect exceptions when subtasks fail. It may invoke the {@link #shutdown()
190 * shutdown} method to shut down and cause {@link #join() join} to wakeup when some
191 * condition arises.
192 *
193 * <p> A subclass will typically define methods to make available results, state, or other
194 * outcome to code that executes after the {@code join} method. A subclass that collects
195 * results and ignores subtasks that fail may define a method that returns the results.
196 * A subclass that implements a policy to shut down when a subtask fails may define a
197 * method to get the exception of the first subtask to fail.
198 *
199 * <p> The following is an example of a simple {@code StructuredTaskScope} implementation
200 * that collects homogenous subtasks that complete successfully. It defines the method
201 * "{@code completedSuccessfully()}" that the main task can invoke after it joins.
202 * {@snippet lang=java :
203 * class CollectingScope<T> extends StructuredTaskScope<T> {
204 * private final Queue<Subtask<? extends T>> subtasks = new LinkedTransferQueue<>();
205 *
206 * @Override
207 * protected void handleComplete(Subtask<? extends T> subtask) {
208 * if (subtask.state() == Subtask.State.SUCCESS) {
209 * subtasks.add(subtask);
210 * }
211 * }
212 *
213 * @Override
214 * public CollectingScope<T> join() throws InterruptedException {
215 * super.join();
216 * return this;
217 * }
218 *
219 * public Stream<Subtask<? extends T>> completedSuccessfully() {
220 * // @link substring="ensureOwnerAndJoined" target="ensureOwnerAndJoined" :
221 * super.ensureOwnerAndJoined();
222 * return subtasks.stream();
223 * }
224 * }
225 * }
226 * <p> The implementations of the {@code completedSuccessfully()} method in the example
227 * invokes {@link #ensureOwnerAndJoined()} to ensure that the method can only be invoked
228 * by the owner thread and only after it has joined.
229 *
230 * <h2><a id="TreeStructure">Tree structure</a></h2>
231 *
232 * Task scopes form a tree where parent-child relations are established implicitly when
233 * opening a new task scope:
234 * <ul>
235 * <li> A parent-child relation is established when a thread started in a task scope
236 * opens its own task scope. A thread started in task scope "A" that opens task scope
237 * "B" establishes a parent-child relation where task scope "A" is the parent of task
238 * scope "B".
239 * <li> A parent-child relation is established with nesting. If a thread opens task
240 * scope "B", then opens task scope "C" (before it closes "B"), then the enclosing task
241 * scope "B" is the parent of the nested task scope "C".
242 * </ul>
243 *
244 * The <i>descendants</i> of a task scope are the child task scopes that it is a parent
245 * of, plus the descendants of the child task scopes, recursively.
246 *
247 * <p> The tree structure supports:
248 * <ul>
249 * <li> Inheritance of {@linkplain ScopedValue scoped values} across threads.
250 * <li> Confinement checks. The phrase "threads contained in the task scope" in method
251 * descriptions means threads started in the task scope or descendant scopes.
252 * </ul>
253 *
254 * <p> The following example demonstrates the inheritance of a scoped value. A scoped
255 * value {@code USERNAME} is bound to the value "{@code duke}". A {@code StructuredTaskScope}
256 * is created and its {@code fork} method invoked to start a thread to execute {@code
257 * childTask}. The thread inherits the scoped value <em>bindings</em> captured when
258 * creating the task scope. The code in {@code childTask} uses the value of the scoped
259 * value and so reads the value "{@code duke}".
260 * {@snippet lang=java :
261 * private static final ScopedValue<String> USERNAME = ScopedValue.newInstance();
262 *
263 * // @link substring="runWhere" target="ScopedValue#runWhere(ScopedValue, Object, Runnable)" :
264 * ScopedValue.runWhere(USERNAME, "duke", () -> {
265 * try (var scope = new StructuredTaskScope<String>()) {
266 *
267 * scope.fork(() -> childTask()); // @highlight substring="fork"
268 * ...
269 * }
270 * });
271 *
272 * ...
273 *
274 * String childTask() {
275 * // @link substring="get" target="ScopedValue#get()" :
276 * String name = USERNAME.get(); // "duke"
277 * ...
278 * }
279 * }
280 *
281 * <p> {@code StructuredTaskScope} does not define APIs that exposes the tree structure
282 * at this time.
283 *
284 * <p> Unless otherwise specified, passing a {@code null} argument to a constructor
285 * or method in this class will cause a {@link NullPointerException} to be thrown.
286 *
287 * <h2>Memory consistency effects</h2>
288 *
289 * <p> Actions in the owner thread of, or a thread contained in, the task scope prior to
290 * {@linkplain #fork forking} of a subtask
291 * <a href="{@docRoot}/java.base/java/util/concurrent/package-summary.html#MemoryVisibility">
292 * <i>happen-before</i></a> any actions taken by that subtask, which in turn <i>happen-before</i>
293 * the subtask result is {@linkplain Subtask#get() retrieved} or <i>happen-before</i> any
294 * actions taken in a thread after {@linkplain #join() joining} of the task scope.
295 *
296 * @jls 17.4.5 Happens-before Order
297 *
298 * @param <T> the result type of tasks executed in the task scope
299 * @since 21
300 */
301 @PreviewFeature(feature = PreviewFeature.Feature.STRUCTURED_CONCURRENCY)
302 public class StructuredTaskScope<T> implements AutoCloseable {
303 private final ThreadFactory factory;
304 private final ThreadFlock flock;
305 private final ReentrantLock shutdownLock = new ReentrantLock();
306
307 // states: OPEN -> SHUTDOWN -> CLOSED
308 private static final int OPEN = 0; // initial state
309 private static final int SHUTDOWN = 1;
310 private static final int CLOSED = 2;
311
312 // state: set to SHUTDOWN by any thread, set to CLOSED by owner, read by any thread
313 private volatile int state;
314
315 // Counters to support checking that the task scope owner joins before processing
316 // results and attempts join before closing the task scope. These counters are
317 // accessed only by the owner thread.
318 private int forkRound; // incremented when the first subtask is forked after join
319 private int lastJoinAttempted; // set to the current fork round when join is attempted
320 private int lastJoinCompleted; // set to the current fork round when join completes
321
322 /**
323 * Represents a subtask forked with {@link #fork(Callable)}.
324 * @param <T> the result type
325 * @since 21
326 */
327 @PreviewFeature(feature = PreviewFeature.Feature.STRUCTURED_CONCURRENCY)
328 public sealed interface Subtask<T> extends Supplier<T> permits SubtaskImpl {
329 /**
330 * {@return the value returning task provided to the {@code fork} method}
331 *
332 * @apiNote Task objects with unique identity may be used for correlation by
333 * implementations of {@link #handleComplete(Subtask) handleComplete}.
334 */
335 Callable<? extends T> task();
336
337 /**
338 * Represents the state of a subtask.
339 * @see Subtask#state()
340 * @since 21
341 */
342 @PreviewFeature(feature = PreviewFeature.Feature.STRUCTURED_CONCURRENCY)
343 enum State {
344 /**
345 * The subtask result or exception is not available. This state indicates that
346 * the subtask was forked but has not completed, it completed after the task
347 * scope was {@linkplain #shutdown() shut down}, or it was forked after the
348 * task scope was shut down.
349 */
350 UNAVAILABLE,
351 /**
352 * The subtask completed successfully with a result. The {@link Subtask#get()
353 * Subtask.get()} method can be used to obtain the result. This is a terminal
354 * state.
355 */
356 SUCCESS,
357 /**
358 * The subtask failed with an exception. The {@link Subtask#exception()
359 * Subtask.exception()} method can be used to obtain the exception. This is a
360 * terminal state.
361 */
362 FAILED,
363 }
364
365 /**
366 * {@return the state of the subtask}
367 */
368 State state();
369
370 /**
371 * Returns the result of the subtask.
372 *
373 * <p> To ensure correct usage, if the scope owner {@linkplain #fork(Callable) forks}
374 * a subtask, then it must join (with {@link #join() join} or {@link #joinUntil(Instant)
375 * joinUntil}) before it can obtain the result of the subtask.
376 *
377 * @return the possibly-null result
378 * @throws IllegalStateException if the subtask has not completed, did not complete
379 * successfully, or the current thread is the task scope owner and did not join
380 * after forking
381 * @see State#SUCCESS
382 */
383 T get();
384
385 /**
386 * {@return the exception thrown by the subtask}
387 *
388 * <p> To ensure correct usage, if the scope owner {@linkplain #fork(Callable) forks}
389 * a subtask, then it must join (with {@link #join() join} or {@link #joinUntil(Instant)
390 * joinUntil}) before it can obtain the exception thrown by the subtask.
391 *
392 * @throws IllegalStateException if the subtask has not completed, completed with
393 * a result, or the current thread is the task scope owner and did not join after
394 * forking
395 * @see State#FAILED
396 */
397 Throwable exception();
398 }
399
400 /**
401 * Creates a structured task scope with the given name and thread factory. The task
402 * scope is optionally named for the purposes of monitoring and management. The thread
403 * factory is used to {@link ThreadFactory#newThread(Runnable) create} threads when
404 * subtasks are {@linkplain #fork(Callable) forked}. The task scope is owned by the
405 * current thread.
406 *
407 * <p> Construction captures the current thread's {@linkplain ScopedValue scoped value}
408 * bindings for inheritance by threads started in the task scope. The
409 * <a href="#TreeStructure">Tree Structure</a> section in the class description details
410 * how parent-child relations are established implicitly for the purpose of inheritance
411 * of scoped value bindings.
412 *
413 * @param name the name of the task scope, can be null
414 * @param factory the thread factory
415 */
416 @SuppressWarnings("this-escape")
417 public StructuredTaskScope(String name, ThreadFactory factory) {
418 this.factory = Objects.requireNonNull(factory, "'factory' is null");
419 if (name == null)
420 name = Objects.toIdentityString(this);
421 this.flock = ThreadFlock.open(name);
422 }
423
424 /**
425 * Creates an unnamed structured task scope that creates virtual threads. The task
426 * scope is owned by the current thread.
427 *
428 * @implSpec This constructor is equivalent to invoking the 2-arg constructor with a
429 * name of {@code null} and a thread factory that creates virtual threads.
430 */
431 public StructuredTaskScope() {
432 this(null, Thread.ofVirtual().factory());
433 }
434
435 private IllegalStateException newIllegalStateExceptionScopeClosed() {
436 return new IllegalStateException("Task scope is closed");
437 }
438
439 private IllegalStateException newIllegalStateExceptionNoJoin() {
440 return new IllegalStateException("Owner did not join after forking subtasks");
441 }
442
443 /**
444 * Throws IllegalStateException if the scope is closed, returning the state if not
445 * closed.
446 */
447 private int ensureOpen() {
448 int s = state;
449 if (s == CLOSED)
450 throw newIllegalStateExceptionScopeClosed();
451 return s;
452 }
453
454 /**
455 * Throws WrongThreadException if the current thread is not the owner.
456 */
457 private void ensureOwner() {
458 if (Thread.currentThread() != flock.owner())
459 throw new WrongThreadException("Current thread not owner");
460 }
461
462 /**
463 * Throws WrongThreadException if the current thread is not the owner
464 * or a thread contained in the tree.
465 */
466 private void ensureOwnerOrContainsThread() {
467 Thread currentThread = Thread.currentThread();
468 if (currentThread != flock.owner() && !flock.containsThread(currentThread))
469 throw new WrongThreadException("Current thread not owner or thread in the tree");
470 }
471
472 /**
473 * Throws IllegalStateException if the current thread is the owner, and the owner did
474 * not join after forking a subtask in the given fork round.
475 */
476 private void ensureJoinedIfOwner(int round) {
477 if (Thread.currentThread() == flock.owner() && (round > lastJoinCompleted)) {
478 throw newIllegalStateExceptionNoJoin();
479 }
480 }
481
482 /**
483 * Ensures that the current thread is the owner of this task scope and that it joined
484 * (with {@link #join()} or {@link #joinUntil(Instant)}) after {@linkplain #fork(Callable)
485 * forking} subtasks.
486 *
487 * @apiNote This method can be used by subclasses that define methods to make available
488 * results, state, or other outcome to code intended to execute after the join method.
489 *
490 * @throws WrongThreadException if the current thread is not the task scope owner
491 * @throws IllegalStateException if the task scope is open and task scope owner did
492 * not join after forking
493 */
494 protected final void ensureOwnerAndJoined() {
495 ensureOwner();
496 if (forkRound > lastJoinCompleted) {
497 throw newIllegalStateExceptionNoJoin();
498 }
499 }
500
501 /**
502 * Invoked by a subtask when it completes successfully or fails in this task scope.
503 * This method is not invoked if a subtask completes after the task scope is
504 * {@linkplain #shutdown() shut down}.
505 *
506 * @implSpec The default implementation throws {@code NullPointerException} if the
507 * subtask is {@code null}. It throws {@link IllegalArgumentException} if the subtask
508 * has not completed.
509 *
510 * @apiNote The {@code handleComplete} method should be thread safe. It may be
511 * invoked by several threads concurrently.
512 *
513 * @param subtask the subtask
514 *
515 * @throws IllegalArgumentException if called with a subtask that has not completed
516 */
517 protected void handleComplete(Subtask<? extends T> subtask) {
518 if (subtask.state() == Subtask.State.UNAVAILABLE)
519 throw new IllegalArgumentException();
520 }
521
522 /**
523 * Starts a new thread in this task scope to execute a value-returning task, thus
524 * creating a <em>subtask</em> of this task scope.
525 *
526 * <p> The value-returning task is provided to this method as a {@link Callable}, the
527 * thread executes the task's {@link Callable#call() call} method. The thread is
528 * created with the task scope's {@link ThreadFactory}. It inherits the current thread's
529 * {@linkplain ScopedValue scoped value} bindings. The bindings must match the bindings
530 * captured when the task scope was created.
531 *
532 * <p> This method returns a {@link Subtask Subtask} to represent the <em>forked
533 * subtask</em>. The {@code Subtask} object can be used to obtain the result when
534 * the subtask completes successfully, or the exception when the subtask fails. To
535 * ensure correct usage, the {@link Subtask#get() get()} and {@link Subtask#exception()
536 * exception()} methods may only be called by the task scope owner after it has waited
537 * for all threads to finish with the {@link #join() join} or {@link #joinUntil(Instant)}
538 * methods. When the subtask completes, the thread invokes the {@link
539 * #handleComplete(Subtask) handleComplete} method to consume the completed subtask.
540 * If the task scope is {@linkplain #shutdown() shut down} before the subtask completes
541 * then the {@code handleComplete} method will not be invoked.
542 *
543 * <p> If this task scope is {@linkplain #shutdown() shutdown} (or in the process of
544 * shutting down) then the subtask will not run and the {@code handleComplete} method
545 * will not be invoked.
546 *
547 * <p> This method may only be invoked by the task scope owner or threads contained
548 * in the task scope.
549 *
550 * @implSpec This method may be overridden for customization purposes, wrapping tasks
551 * for example. If overridden, the subclass must invoke {@code super.fork} to start a
552 * new thread in this task scope.
553 *
554 * @param task the value-returning task for the thread to execute
555 * @param <U> the result type
556 * @return the subtask
557 * @throws IllegalStateException if this task scope is closed
558 * @throws WrongThreadException if the current thread is not the task scope owner or a
559 * thread contained in the task scope
560 * @throws StructureViolationException if the current scoped value bindings are not
561 * the same as when the task scope was created
562 * @throws RejectedExecutionException if the thread factory rejected creating a
563 * thread to run the subtask
564 */
565 public <U extends T> Subtask<U> fork(Callable<? extends U> task) {
566 Objects.requireNonNull(task, "'task' is null");
567 int s = ensureOpen(); // throws ISE if closed
568
569 // when forked by the owner, the subtask is forked in the current or next round
570 int round = -1;
571 if (Thread.currentThread() == flock.owner()) {
572 round = forkRound;
573 if (forkRound == lastJoinCompleted) {
574 // new round if first fork after join
575 round++;
576 }
577 }
578
579 SubtaskImpl<U> subtask = new SubtaskImpl<>(this, task, round);
580 if (s < SHUTDOWN) {
581 // create thread to run task
582 Thread thread = factory.newThread(subtask);
583 if (thread == null) {
584 throw new RejectedExecutionException("Rejected by thread factory");
585 }
586
587 // attempt to start the thread
588 try {
589 flock.start(thread);
590 } catch (IllegalStateException e) {
591 // shutdown by another thread, or underlying flock is shutdown due
592 // to unstructured use
593 }
594 }
595
596 // force owner to join if this is the first fork in the round
597 if (Thread.currentThread() == flock.owner() && round > forkRound) {
598 forkRound = round;
599 }
600
601 // return forked subtask or a subtask that did not run
602 return subtask;
603 }
604
605 /**
606 * Wait for all threads to finish or the task scope to shut down.
607 */
608 private void implJoin(Duration timeout)
609 throws InterruptedException, TimeoutException
610 {
611 ensureOwner();
612 lastJoinAttempted = forkRound;
613 int s = ensureOpen(); // throws ISE if closed
614 if (s == OPEN) {
615 // wait for all threads, wakeup, interrupt, or timeout
616 if (timeout != null) {
617 flock.awaitAll(timeout);
618 } else {
619 flock.awaitAll();
620 }
621 }
622 lastJoinCompleted = forkRound;
623 }
624
625 /**
626 * Wait for all subtasks started in this task scope to finish or the task scope to
627 * shut down.
628 *
629 * <p> This method waits for all subtasks by waiting for all threads {@linkplain
630 * #fork(Callable) started} in this task scope to finish execution. It stops waiting
631 * when all threads finish, the task scope is {@linkplain #shutdown() shut down}, or
632 * the current thread is {@linkplain Thread#interrupt() interrupted}.
633 *
634 * <p> This method may only be invoked by the task scope owner.
635 *
636 * @implSpec This method may be overridden for customization purposes or to return a
637 * more specific return type. If overridden, the subclass must invoke {@code
638 * super.join} to ensure that the method waits for threads in this task scope to
639 * finish.
640 *
641 * @return this task scope
642 * @throws IllegalStateException if this task scope is closed
643 * @throws WrongThreadException if the current thread is not the task scope owner
644 * @throws InterruptedException if interrupted while waiting
645 */
646 public StructuredTaskScope<T> join() throws InterruptedException {
647 try {
648 implJoin(null);
649 } catch (TimeoutException e) {
650 throw new InternalError();
651 }
652 return this;
653 }
654
655 /**
656 * Wait for all subtasks started in this task scope to finish or the task scope to
657 * shut down, up to the given deadline.
658 *
659 * <p> This method waits for all subtasks by waiting for all threads {@linkplain
660 * #fork(Callable) started} in this task scope to finish execution. It stops waiting
661 * when all threads finish, the task scope is {@linkplain #shutdown() shut down}, the
662 * deadline is reached, or the current thread is {@linkplain Thread#interrupt()
663 * interrupted}.
664 *
665 * <p> This method may only be invoked by the task scope owner.
666 *
667 * @implSpec This method may be overridden for customization purposes or to return a
668 * more specific return type. If overridden, the subclass must invoke {@code
669 * super.joinUntil} to ensure that the method waits for threads in this task scope to
670 * finish.
671 *
672 * @param deadline the deadline
673 * @return this task scope
674 * @throws IllegalStateException if this task scope is closed
675 * @throws WrongThreadException if the current thread is not the task scope owner
676 * @throws InterruptedException if interrupted while waiting
677 * @throws TimeoutException if the deadline is reached while waiting
678 */
679 public StructuredTaskScope<T> joinUntil(Instant deadline)
680 throws InterruptedException, TimeoutException
681 {
682 Duration timeout = Duration.between(Instant.now(), deadline);
683 implJoin(timeout);
684 return this;
685 }
686
687 /**
688 * Interrupt all unfinished threads.
689 */
690 private void implInterruptAll() {
691 flock.threads()
692 .filter(t -> t != Thread.currentThread())
693 .forEach(t -> {
694 try {
695 t.interrupt();
696 } catch (Throwable ignore) { }
697 });
698 }
699
700 @SuppressWarnings("removal")
701 private void interruptAll() {
702 if (System.getSecurityManager() == null) {
703 implInterruptAll();
704 } else {
705 PrivilegedAction<Void> pa = () -> {
706 implInterruptAll();
707 return null;
708 };
709 AccessController.doPrivileged(pa);
710 }
711 }
712
713 /**
714 * Shutdown the task scope if not already shutdown. Return true if this method
715 * shutdowns the task scope, false if already shutdown.
716 */
717 private boolean implShutdown() {
718 shutdownLock.lock();
719 try {
720 if (state < SHUTDOWN) {
721 // prevent new threads from starting
722 flock.shutdown();
723
724 // set status before interrupting tasks
725 state = SHUTDOWN;
726
727 // interrupt all unfinished threads
728 interruptAll();
729
730 return true;
731 } else {
732 // already shutdown
733 return false;
734 }
735 } finally {
736 shutdownLock.unlock();
737 }
738 }
739
740 /**
741 * Shut down this task scope without closing it. Shutting down a task scope prevents
742 * new threads from starting, interrupts all unfinished threads, and causes the
743 * {@link #join() join} method to wakeup. Shutdown is useful for cases where the
744 * results of unfinished subtasks are no longer needed. It will typically be called
745 * by the {@link #handleComplete(Subtask)} implementation of a subclass that
746 * implements a policy to discard unfinished tasks once some outcome is reached.
747 *
748 * <p> More specifically, this method:
749 * <ul>
750 * <li> {@linkplain Thread#interrupt() Interrupts} all unfinished threads in the
751 * task scope (except the current thread).
752 * <li> Wakes up the task scope owner if it is waiting in {@link #join()} or {@link
753 * #joinUntil(Instant)}. If the task scope owner is not waiting then its next call to
754 * {@code join} or {@code joinUntil} will return immediately.
755 * </ul>
756 *
757 * <p> The {@linkplain Subtask.State state} of unfinished subtasks that complete at
758 * around the time that the task scope is shutdown is not defined. A subtask that
759 * completes successfully with a result, or fails with an exception, at around
760 * the time that the task scope is shutdown may or may not <i>transition</i> to a
761 * terminal state.
762 *
763 * <p> This method may only be invoked by the task scope owner or threads contained
764 * in the task scope.
765 *
766 * @implSpec This method may be overridden for customization purposes. If overridden,
767 * the subclass must invoke {@code super.shutdown} to ensure that the method shuts
768 * down the task scope.
769 *
770 * @apiNote
771 * There may be threads that have not finished because they are executing code that
772 * did not respond (or respond promptly) to thread interrupt. This method does not wait
773 * for these threads. When the owner invokes the {@link #close() close} method
774 * to close the task scope then it will wait for the remaining threads to finish.
775 *
776 * @throws IllegalStateException if this task scope is closed
777 * @throws WrongThreadException if the current thread is not the task scope owner or
778 * a thread contained in the task scope
779 * @see #isShutdown()
780 */
781 public void shutdown() {
782 ensureOwnerOrContainsThread();
783 int s = ensureOpen(); // throws ISE if closed
784 if (s < SHUTDOWN && implShutdown())
785 flock.wakeup();
786 }
787
788 /**
789 * {@return true if this task scope is shutdown, otherwise false}
790 * @see #shutdown()
791 */
792 public final boolean isShutdown() {
793 return state >= SHUTDOWN;
794 }
795
796 /**
797 * Closes this task scope.
798 *
799 * <p> This method first shuts down the task scope (as if by invoking the {@link
800 * #shutdown() shutdown} method). It then waits for the threads executing any
801 * unfinished tasks to finish. If interrupted, this method will continue to wait for
802 * the threads to finish before completing with the interrupt status set.
803 *
804 * <p> This method may only be invoked by the task scope owner. If the task scope
805 * is already closed then the task scope owner invoking this method has no effect.
806 *
807 * <p> A {@code StructuredTaskScope} is intended to be used in a <em>structured
808 * manner</em>. If this method is called to close a task scope before nested task
809 * scopes are closed then it closes the underlying construct of each nested task scope
810 * (in the reverse order that they were created in), closes this task scope, and then
811 * throws {@link StructureViolationException}.
812 * Similarly, if this method is called to close a task scope while executing with
813 * {@linkplain ScopedValue scoped value} bindings, and the task scope was created
814 * before the scoped values were bound, then {@code StructureViolationException} is
815 * thrown after closing the task scope.
816 * If a thread terminates without first closing task scopes that it owns then
817 * termination will cause the underlying construct of each of its open tasks scopes to
818 * be closed. Closing is performed in the reverse order that the task scopes were
819 * created in. Thread termination may therefore be delayed when the task scope owner
820 * has to wait for threads forked in these task scopes to finish.
821 *
822 * @implSpec This method may be overridden for customization purposes. If overridden,
823 * the subclass must invoke {@code super.close} to close the task scope.
824 *
825 * @throws IllegalStateException thrown after closing the task scope if the task scope
826 * owner did not attempt to join after forking
827 * @throws WrongThreadException if the current thread is not the task scope owner
828 * @throws StructureViolationException if a structure violation was detected
829 */
830 @Override
831 public void close() {
832 ensureOwner();
833 int s = state;
834 if (s == CLOSED)
835 return;
836
837 try {
838 if (s < SHUTDOWN)
839 implShutdown();
840 flock.close();
841 } finally {
842 state = CLOSED;
843 }
844
845 // throw ISE if the owner didn't attempt to join after forking
846 if (forkRound > lastJoinAttempted) {
847 lastJoinCompleted = forkRound;
848 throw newIllegalStateExceptionNoJoin();
849 }
850 }
851
852 @Override
853 public String toString() {
854 String name = flock.name();
855 return switch (state) {
856 case OPEN -> name;
857 case SHUTDOWN -> name + "/shutdown";
858 case CLOSED -> name + "/closed";
859 default -> throw new InternalError();
860 };
861 }
862
863 /**
864 * Subtask implementation, runs the task specified to the fork method.
865 */
866 private static final class SubtaskImpl<T> implements Subtask<T>, Runnable {
867 private static final AltResult RESULT_NULL = new AltResult(Subtask.State.SUCCESS);
868
869 private record AltResult(Subtask.State state, Throwable exception) {
870 AltResult(Subtask.State state) {
871 this(state, null);
872 }
873 }
874
875 private final StructuredTaskScope<? super T> scope;
876 private final Callable<? extends T> task;
877 private final int round;
878 private volatile Object result;
879
880 SubtaskImpl(StructuredTaskScope<? super T> scope,
881 Callable<? extends T> task,
882 int round) {
883 this.scope = scope;
884 this.task = task;
885 this.round = round;
886 }
887
888 @Override
889 public void run() {
890 T result = null;
891 Throwable ex = null;
892 try {
893 result = task.call();
894 } catch (Throwable e) {
895 ex = e;
896 }
897
898 // nothing to do if task scope is shutdown
899 if (scope.isShutdown())
900 return;
901
902 // capture result or exception, invoke handleComplete
903 if (ex == null) {
904 this.result = (result != null) ? result : RESULT_NULL;
905 } else {
906 this.result = new AltResult(State.FAILED, ex);
907 }
908 scope.handleComplete(this);
909 }
910
911 @Override
912 public Callable<? extends T> task() {
913 return task;
914 }
915
916 @Override
917 public Subtask.State state() {
918 Object result = this.result;
919 if (result == null) {
920 return State.UNAVAILABLE;
921 } else if (result instanceof AltResult alt) {
922 // null or failed
923 return alt.state();
924 } else {
925 return State.SUCCESS;
926 }
927 }
928
929 @Override
930 public T get() {
931 scope.ensureJoinedIfOwner(round);
932 Object result = this.result;
933 if (result instanceof AltResult) {
934 if (result == RESULT_NULL) return null;
935 } else if (result != null) {
936 @SuppressWarnings("unchecked")
937 T r = (T) result;
938 return r;
939 }
940 throw new IllegalStateException(
941 "Result is unavailable or subtask did not complete successfully");
942 }
943
944 @Override
945 public Throwable exception() {
946 scope.ensureJoinedIfOwner(round);
947 Object result = this.result;
948 if (result instanceof AltResult alt && alt.state() == State.FAILED) {
949 return alt.exception();
950 }
951 throw new IllegalStateException(
952 "Exception is unavailable or subtask did not complete with exception");
953 }
954
955 @Override
956 public String toString() {
957 String stateAsString = switch (state()) {
958 case UNAVAILABLE -> "[Unavailable]";
959 case SUCCESS -> "[Completed successfully]";
960 case FAILED -> {
961 Throwable ex = ((AltResult) result).exception();
962 yield "[Failed: " + ex + "]";
963 }
964 };
965 return Objects.toIdentityString(this) + stateAsString;
966 }
967 }
968
969 /**
970 * A {@code StructuredTaskScope} that captures the result of the first subtask to
971 * complete {@linkplain Subtask.State#SUCCESS successfully}. Once captured, it
972 * {@linkplain #shutdown() shuts down} the task scope to interrupt unfinished threads
973 * and wakeup the task scope owner. The policy implemented by this class is intended
974 * for cases where the result of any subtask will do ("invoke any") and where the
975 * results of other unfinished subtasks are no longer needed.
976 *
977 * <p> Unless otherwise specified, passing a {@code null} argument to a method
978 * in this class will cause a {@link NullPointerException} to be thrown.
979 *
980 * @apiNote This class implements a policy to shut down the task scope when a subtask
981 * completes successfully. There shouldn't be any need to directly shut down the task
982 * scope with the {@link #shutdown() shutdown} method.
983 *
984 * @param <T> the result type
985 * @since 21
986 */
987 @PreviewFeature(feature = PreviewFeature.Feature.STRUCTURED_CONCURRENCY)
988 public static final class ShutdownOnSuccess<T> extends StructuredTaskScope<T> {
989 private static final Object RESULT_NULL = new Object();
990 private static final VarHandle FIRST_RESULT;
991 private static final VarHandle FIRST_EXCEPTION;
992 static {
993 try {
994 MethodHandles.Lookup l = MethodHandles.lookup();
995 FIRST_RESULT = l.findVarHandle(ShutdownOnSuccess.class, "firstResult", Object.class);
996 FIRST_EXCEPTION = l.findVarHandle(ShutdownOnSuccess.class, "firstException", Throwable.class);
997 } catch (Exception e) {
998 throw new ExceptionInInitializerError(e);
999 }
1000 }
1001 private volatile Object firstResult;
1002 private volatile Throwable firstException;
1003
1004 /**
1005 * Constructs a new {@code ShutdownOnSuccess} with the given name and thread factory.
1006 * The task scope is optionally named for the purposes of monitoring and management.
1007 * The thread factory is used to {@link ThreadFactory#newThread(Runnable) create}
1008 * threads when subtasks are {@linkplain #fork(Callable) forked}. The task scope
1009 * is owned by the current thread.
1010 *
1011 * <p> Construction captures the current thread's {@linkplain ScopedValue scoped
1012 * value} bindings for inheritance by threads started in the task scope. The
1013 * <a href="#TreeStructure">Tree Structure</a> section in the class description
1014 * details how parent-child relations are established implicitly for the purpose
1015 * of inheritance of scoped value bindings.
1016 *
1017 * @param name the name of the task scope, can be null
1018 * @param factory the thread factory
1019 */
1020 public ShutdownOnSuccess(String name, ThreadFactory factory) {
1021 super(name, factory);
1022 }
1023
1024 /**
1025 * Constructs a new unnamed {@code ShutdownOnSuccess} that creates virtual threads.
1026 *
1027 * @implSpec This constructor is equivalent to invoking the 2-arg constructor with
1028 * a name of {@code null} and a thread factory that creates virtual threads.
1029 */
1030 public ShutdownOnSuccess() {
1031 this(null, Thread.ofVirtual().factory());
1032 }
1033
1034 @Override
1035 protected void handleComplete(Subtask<? extends T> subtask) {
1036 if (firstResult != null) {
1037 // already captured a result
1038 return;
1039 }
1040
1041 if (subtask.state() == Subtask.State.SUCCESS) {
1042 // task succeeded
1043 T result = subtask.get();
1044 Object r = (result != null) ? result : RESULT_NULL;
1045 if (FIRST_RESULT.compareAndSet(this, null, r)) {
1046 super.shutdown();
1047 }
1048 } else if (firstException == null) {
1049 // capture the exception thrown by the first subtask that failed
1050 FIRST_EXCEPTION.compareAndSet(this, null, subtask.exception());
1051 }
1052 }
1053
1054 /**
1055 * Wait for a subtask started in this task scope to complete {@linkplain
1056 * Subtask.State#SUCCESS successfully} or all subtasks to complete.
1057 *
1058 * <p> This method waits for all subtasks by waiting for all threads {@linkplain
1059 * #fork(Callable) started} in this task scope to finish execution. It stops waiting
1060 * when all threads finish, a subtask completes successfully, or the current
1061 * thread is {@linkplain Thread#interrupt() interrupted}. It also stops waiting
1062 * if the {@link #shutdown() shutdown} method is invoked directly to shut down
1063 * this task scope.
1064 *
1065 * <p> This method may only be invoked by the task scope owner.
1066 *
1067 * @throws IllegalStateException {@inheritDoc}
1068 * @throws WrongThreadException {@inheritDoc}
1069 */
1070 @Override
1071 public ShutdownOnSuccess<T> join() throws InterruptedException {
1072 super.join();
1073 return this;
1074 }
1075
1076 /**
1077 * Wait for a subtask started in this task scope to complete {@linkplain
1078 * Subtask.State#SUCCESS successfully} or all subtasks to complete, up to the
1079 * given deadline.
1080 *
1081 * <p> This method waits for all subtasks by waiting for all threads {@linkplain
1082 * #fork(Callable) started} in this task scope to finish execution. It stops waiting
1083 * when all threads finish, a subtask completes successfully, the deadline is
1084 * reached, or the current thread is {@linkplain Thread#interrupt() interrupted}.
1085 * It also stops waiting if the {@link #shutdown() shutdown} method is invoked
1086 * directly to shut down this task scope.
1087 *
1088 * <p> This method may only be invoked by the task scope owner.
1089 *
1090 * @throws IllegalStateException {@inheritDoc}
1091 * @throws WrongThreadException {@inheritDoc}
1092 */
1093 @Override
1094 public ShutdownOnSuccess<T> joinUntil(Instant deadline)
1095 throws InterruptedException, TimeoutException
1096 {
1097 super.joinUntil(deadline);
1098 return this;
1099 }
1100
1101 /**
1102 * {@return the result of the first subtask that completed {@linkplain
1103 * Subtask.State#SUCCESS successfully}}
1104 *
1105 * <p> When no subtask completed successfully, but a subtask {@linkplain
1106 * Subtask.State#FAILED failed} then {@code ExecutionException} is thrown with
1107 * the subtask's exception as the {@linkplain Throwable#getCause() cause}.
1108 *
1109 * @throws ExecutionException if no subtasks completed successfully but at least
1110 * one subtask failed
1111 * @throws IllegalStateException if no subtasks completed or the task scope owner
1112 * did not join after forking
1113 * @throws WrongThreadException if the current thread is not the task scope owner
1114 */
1115 public T result() throws ExecutionException {
1116 return result(ExecutionException::new);
1117 }
1118
1119 /**
1120 * Returns the result of the first subtask that completed {@linkplain
1121 * Subtask.State#SUCCESS successfully}, otherwise throws an exception produced
1122 * by the given exception supplying function.
1123 *
1124 * <p> When no subtask completed successfully, but a subtask {@linkplain
1125 * Subtask.State#FAILED failed}, then the exception supplying function is invoked
1126 * with subtask's exception.
1127 *
1128 * @param esf the exception supplying function
1129 * @param <X> type of the exception to be thrown
1130 * @return the result of the first subtask that completed with a result
1131 *
1132 * @throws X if no subtasks completed successfully but at least one subtask failed
1133 * @throws IllegalStateException if no subtasks completed or the task scope owner
1134 * did not join after forking
1135 * @throws WrongThreadException if the current thread is not the task scope owner
1136 */
1137 public <X extends Throwable> T result(Function<Throwable, ? extends X> esf) throws X {
1138 Objects.requireNonNull(esf);
1139 ensureOwnerAndJoined();
1140
1141 Object result = firstResult;
1142 if (result == RESULT_NULL) {
1143 return null;
1144 } else if (result != null) {
1145 @SuppressWarnings("unchecked")
1146 T r = (T) result;
1147 return r;
1148 }
1149
1150 Throwable exception = firstException;
1151 if (exception != null) {
1152 X ex = esf.apply(exception);
1153 Objects.requireNonNull(ex, "esf returned null");
1154 throw ex;
1155 }
1156
1157 throw new IllegalStateException("No completed subtasks");
1158 }
1159 }
1160
1161 /**
1162 * A {@code StructuredTaskScope} that captures the exception of the first subtask to
1163 * {@linkplain Subtask.State#FAILED fail}. Once captured, it {@linkplain #shutdown()
1164 * shuts down} the task scope to interrupt unfinished threads and wakeup the task
1165 * scope owner. The policy implemented by this class is intended for cases where the
1166 * results for all subtasks are required ("invoke all"); if any subtask fails then the
1167 * results of other unfinished subtasks are no longer needed.
1168 *
1169 * <p> Unless otherwise specified, passing a {@code null} argument to a method
1170 * in this class will cause a {@link NullPointerException} to be thrown.
1171 *
1172 * @apiNote This class implements a policy to shut down the task scope when a subtask
1173 * fails. There shouldn't be any need to directly shut down the task scope with the
1174 * {@link #shutdown() shutdown} method.
1175 *
1176 * @since 21
1177 */
1178 @PreviewFeature(feature = PreviewFeature.Feature.STRUCTURED_CONCURRENCY)
1179 public static final class ShutdownOnFailure extends StructuredTaskScope<Object> {
1180 private static final VarHandle FIRST_EXCEPTION;
1181 static {
1182 try {
1183 MethodHandles.Lookup l = MethodHandles.lookup();
1184 FIRST_EXCEPTION = l.findVarHandle(ShutdownOnFailure.class, "firstException", Throwable.class);
1185 } catch (Exception e) {
1186 throw new ExceptionInInitializerError(e);
1187 }
1188 }
1189 private volatile Throwable firstException;
1190
1191 /**
1192 * Constructs a new {@code ShutdownOnFailure} with the given name and thread factory.
1193 * The task scope is optionally named for the purposes of monitoring and management.
1194 * The thread factory is used to {@link ThreadFactory#newThread(Runnable) create}
1195 * threads when subtasks are {@linkplain #fork(Callable) forked}. The task scope
1196 * is owned by the current thread.
1197 *
1198 * <p> Construction captures the current thread's {@linkplain ScopedValue scoped
1199 * value} bindings for inheritance by threads started in the task scope. The
1200 * <a href="#TreeStructure">Tree Structure</a> section in the class description
1201 * details how parent-child relations are established implicitly for the purpose
1202 * of inheritance of scoped value bindings.
1203 *
1204 * @param name the name of the task scope, can be null
1205 * @param factory the thread factory
1206 */
1207 public ShutdownOnFailure(String name, ThreadFactory factory) {
1208 super(name, factory);
1209 }
1210
1211 /**
1212 * Constructs a new unnamed {@code ShutdownOnFailure} that creates virtual threads.
1213 *
1214 * @implSpec This constructor is equivalent to invoking the 2-arg constructor with
1215 * a name of {@code null} and a thread factory that creates virtual threads.
1216 */
1217 public ShutdownOnFailure() {
1218 this(null, Thread.ofVirtual().factory());
1219 }
1220
1221 @Override
1222 protected void handleComplete(Subtask<?> subtask) {
1223 if (subtask.state() == Subtask.State.FAILED
1224 && firstException == null
1225 && FIRST_EXCEPTION.compareAndSet(this, null, subtask.exception())) {
1226 super.shutdown();
1227 }
1228 }
1229
1230 /**
1231 * Wait for all subtasks started in this task scope to complete or for a subtask
1232 * to {@linkplain Subtask.State#FAILED fail}.
1233 *
1234 * <p> This method waits for all subtasks by waiting for all threads {@linkplain
1235 * #fork(Callable) started} in this task scope to finish execution. It stops waiting
1236 * when all threads finish, a subtask fails, or the current thread is {@linkplain
1237 * Thread#interrupt() interrupted}. It also stops waiting if the {@link #shutdown()
1238 * shutdown} method is invoked directly to shut down this task scope.
1239 *
1240 * <p> This method may only be invoked by the task scope owner.
1241 *
1242 * @throws IllegalStateException {@inheritDoc}
1243 * @throws WrongThreadException {@inheritDoc}
1244 */
1245 @Override
1246 public ShutdownOnFailure join() throws InterruptedException {
1247 super.join();
1248 return this;
1249 }
1250
1251 /**
1252 * Wait for all subtasks started in this task scope to complete or for a subtask
1253 * to {@linkplain Subtask.State#FAILED fail}, up to the given deadline.
1254 *
1255 * <p> This method waits for all subtasks by waiting for all threads {@linkplain
1256 * #fork(Callable) started} in this task scope to finish execution. It stops waiting
1257 * when all threads finish, a subtask fails, the deadline is reached, or the current
1258 * thread is {@linkplain Thread#interrupt() interrupted}. It also stops waiting
1259 * if the {@link #shutdown() shutdown} method is invoked directly to shut down
1260 * this task scope.
1261 *
1262 * <p> This method may only be invoked by the task scope owner.
1263 *
1264 * @throws IllegalStateException {@inheritDoc}
1265 * @throws WrongThreadException {@inheritDoc}
1266 */
1267 @Override
1268 public ShutdownOnFailure joinUntil(Instant deadline)
1269 throws InterruptedException, TimeoutException
1270 {
1271 super.joinUntil(deadline);
1272 return this;
1273 }
1274
1275 /**
1276 * Returns the exception of the first subtask that {@linkplain Subtask.State#FAILED
1277 * failed}. If no subtasks failed then an empty {@code Optional} is returned.
1278 *
1279 * @return the exception for the first subtask to fail or an empty optional if no
1280 * subtasks failed
1281 *
1282 * @throws WrongThreadException if the current thread is not the task scope owner
1283 * @throws IllegalStateException if the task scope owner did not join after forking
1284 */
1285 public Optional<Throwable> exception() {
1286 ensureOwnerAndJoined();
1287 return Optional.ofNullable(firstException);
1288 }
1289
1290 /**
1291 * Throws if a subtask {@linkplain Subtask.State#FAILED failed}.
1292 * If any subtask failed with an exception then {@code ExecutionException} is
1293 * thrown with the exception of the first subtask to fail as the {@linkplain
1294 * Throwable#getCause() cause}. This method does nothing if no subtasks failed.
1295 *
1296 * @throws ExecutionException if a subtask failed
1297 * @throws WrongThreadException if the current thread is not the task scope owner
1298 * @throws IllegalStateException if the task scope owner did not join after forking
1299 */
1300 public void throwIfFailed() throws ExecutionException {
1301 throwIfFailed(ExecutionException::new);
1302 }
1303
1304 /**
1305 * Throws the exception produced by the given exception supplying function if a
1306 * subtask {@linkplain Subtask.State#FAILED failed}. If any subtask failed with
1307 * an exception then the function is invoked with the exception of the first
1308 * subtask to fail. The exception returned by the function is thrown. This method
1309 * does nothing if no subtasks failed.
1310 *
1311 * @param esf the exception supplying function
1312 * @param <X> type of the exception to be thrown
1313 *
1314 * @throws X produced by the exception supplying function
1315 * @throws WrongThreadException if the current thread is not the task scope owner
1316 * @throws IllegalStateException if the task scope owner did not join after forking
1317 */
1318 public <X extends Throwable>
1319 void throwIfFailed(Function<Throwable, ? extends X> esf) throws X {
1320 ensureOwnerAndJoined();
1321 Objects.requireNonNull(esf);
1322 Throwable exception = firstException;
1323 if (exception != null) {
1324 X ex = esf.apply(exception);
1325 Objects.requireNonNull(ex, "esf returned null");
1326 throw ex;
1327 }
1328 }
1329 }
1330 }