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> task1 = ...
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 public StructuredTaskScope(String name, ThreadFactory factory) {
417 this.factory = Objects.requireNonNull(factory, "'factory' is null");
418 if (name == null)
419 name = Objects.toIdentityString(this);
420 this.flock = ThreadFlock.open(name);
421 }
422
423 /**
424 * Creates an unnamed structured task scope that creates virtual threads. The task
425 * scope is owned by the current thread.
426 *
427 * @implSpec This constructor is equivalent to invoking the 2-arg constructor with a
428 * name of {@code null} and a thread factory that creates virtual threads.
429 */
430 public StructuredTaskScope() {
431 this(null, Thread.ofVirtual().factory());
432 }
433
434 private IllegalStateException newIllegalStateExceptionScopeClosed() {
435 return new IllegalStateException("Task scope is closed");
436 }
437
438 private IllegalStateException newIllegalStateExceptionNoJoin() {
439 return new IllegalStateException("Owner did not join after forking subtasks");
440 }
441
442 /**
443 * Throws IllegalStateException if the scope is closed, returning the state if not
444 * closed.
445 */
446 private int ensureOpen() {
447 int s = state;
448 if (s == CLOSED)
449 throw newIllegalStateExceptionScopeClosed();
450 return s;
451 }
452
453 /**
454 * Throws WrongThreadException if the current thread is not the owner.
455 */
456 private void ensureOwner() {
457 if (Thread.currentThread() != flock.owner())
458 throw new WrongThreadException("Current thread not owner");
459 }
460
461 /**
462 * Throws WrongThreadException if the current thread is not the owner
463 * or a thread contained in the tree.
464 */
465 private void ensureOwnerOrContainsThread() {
466 Thread currentThread = Thread.currentThread();
467 if (currentThread != flock.owner() && !flock.containsThread(currentThread))
468 throw new WrongThreadException("Current thread not owner or thread in the tree");
469 }
470
471 /**
472 * Throws IllegalStateException if the current thread is the owner, and the owner did
473 * not join after forking a subtask in the given fork round.
474 */
475 private void ensureJoinedIfOwner(int round) {
476 if (Thread.currentThread() == flock.owner() && (round > lastJoinCompleted)) {
477 throw newIllegalStateExceptionNoJoin();
478 }
479 }
480
481 /**
482 * Ensures that the current thread is the owner of this task scope and that it joined
483 * (with {@link #join()} or {@link #joinUntil(Instant)}) after {@linkplain #fork(Callable)
484 * forking} subtasks.
485 *
486 * @apiNote This method can be used by subclasses that define methods to make available
487 * results, state, or other outcome to code intended to execute after the join method.
488 *
489 * @throws WrongThreadException if the current thread is not the task scope owner
490 * @throws IllegalStateException if the task scope is open and task scope owner did
491 * not join after forking
492 */
493 protected final void ensureOwnerAndJoined() {
494 ensureOwner();
495 if (forkRound > lastJoinCompleted) {
496 throw newIllegalStateExceptionNoJoin();
497 }
498 }
499
500 /**
501 * Invoked by a subtask when it completes successfully or fails in this task scope.
502 * This method is not invoked if a subtask completes after the task scope is
503 * {@linkplain #shutdown() shut down}.
504 *
505 * @implSpec The default implementation throws {@code NullPointerException} if the
506 * subtask is {@code null}. It throws {@link IllegalArgumentException} if the subtask
507 * has not completed.
508 *
509 * @apiNote The {@code handleComplete} method should be thread safe. It may be
510 * invoked by several threads concurrently.
511 *
512 * @param subtask the subtask
513 *
514 * @throws IllegalArgumentException if called with a subtask that has not completed
515 */
516 protected void handleComplete(Subtask<? extends T> subtask) {
517 if (subtask.state() == Subtask.State.UNAVAILABLE)
518 throw new IllegalArgumentException();
519 }
520
521 /**
522 * Starts a new thread in this task scope to execute a value-returning task, thus
523 * creating a <em>subtask</em> of this task scope.
524 *
525 * <p> The value-returning task is provided to this method as a {@link Callable}, the
526 * thread executes the task's {@link Callable#call() call} method. The thread is
527 * created with the task scope's {@link ThreadFactory}. It inherits the current thread's
528 * {@linkplain ScopedValue scoped value} bindings. The bindings must match the bindings
529 * captured when the task scope was created.
530 *
531 * <p> This method returns a {@link Subtask Subtask} to represent the <em>forked
532 * subtask</em>. The {@code Subtask} object can be used to obtain the result when
533 * the subtask completes successfully, or the exception when the subtask fails. To
534 * ensure correct usage, the {@link Subtask#get() get()} and {@link Subtask#exception()
535 * exception()} methods may only be called by the task scope owner after it has waited
536 * for all threads to finish with the {@link #join() join} or {@link #joinUntil(Instant)}
537 * methods. When the subtask completes, the thread invokes the {@link
538 * #handleComplete(Subtask) handleComplete} method to consume the completed subtask.
539 * If the task scope is {@linkplain #shutdown() shut down} before the subtask completes
540 * then the {@code handleComplete} method will not be invoked.
541 *
542 * <p> If this task scope is {@linkplain #shutdown() shutdown} (or in the process of
543 * shutting down) then the subtask will not run and the {@code handleComplete} method
544 * will not be invoked.
545 *
546 * <p> This method may only be invoked by the task scope owner or threads contained
547 * in the task scope.
548 *
549 * @implSpec This method may be overridden for customization purposes, wrapping tasks
550 * for example. If overridden, the subclass must invoke {@code super.fork} to start a
551 * new thread in this task scope.
552 *
553 * @param task the value-returning task for the thread to execute
554 * @param <U> the result type
555 * @return the subtask
556 * @throws IllegalStateException if this task scope is closed
557 * @throws WrongThreadException if the current thread is not the task scope owner or a
558 * thread contained in the task scope
559 * @throws StructureViolationException if the current scoped value bindings are not
560 * the same as when the task scope was created
561 * @throws RejectedExecutionException if the thread factory rejected creating a
562 * thread to run the subtask
563 */
564 public <U extends T> Subtask<U> fork(Callable<? extends U> task) {
565 Objects.requireNonNull(task, "'task' is null");
566 int s = ensureOpen(); // throws ISE if closed
567
568 // when forked by the owner, the subtask is forked in the current or next round
569 int round = -1;
570 if (Thread.currentThread() == flock.owner()) {
571 round = forkRound;
572 if (forkRound == lastJoinCompleted) {
573 // new round if first fork after join
574 round++;
575 }
576 }
577
578 SubtaskImpl<U> subtask = new SubtaskImpl<>(this, task, round);
579 boolean started = false;
580
581 if (s < SHUTDOWN) {
582 // create thread to run task
583 Thread thread = factory.newThread(subtask);
584 if (thread == null) {
585 throw new RejectedExecutionException("Rejected by thread factory");
586 }
587
588 // attempt to start the thread
589 try {
590 flock.start(thread);
591 started = true;
592 } catch (IllegalStateException e) {
593 // shutdown by another thread, or underlying flock is shutdown due
594 // to unstructured use
595 }
596 }
597
598 // force owner to join if thread started
599 if (started && Thread.currentThread() == flock.owner() && round > forkRound) {
600 forkRound = round;
601 }
602
603 // return forked subtask or a subtask that did not run
604 return subtask;
605 }
606
607 /**
608 * Wait for all threads to finish or the task scope to shut down.
609 */
610 private void implJoin(Duration timeout)
611 throws InterruptedException, TimeoutException
612 {
613 ensureOwner();
614 lastJoinAttempted = forkRound;
615 int s = ensureOpen(); // throws ISE if closed
616 if (s == OPEN) {
617 // wait for all threads, wakeup, interrupt, or timeout
618 if (timeout != null) {
619 flock.awaitAll(timeout);
620 } else {
621 flock.awaitAll();
622 }
623 }
624 lastJoinCompleted = forkRound;
625 }
626
627 /**
628 * Wait for all threads in this task scope to finish or the task scope to shut down.
629 * This method waits until all threads started in this task scope finish execution,
630 * the {@link #shutdown() shutdown} method is invoked to shut down the task scope,
631 * or the current thread is {@linkplain Thread#interrupt() interrupted}.
632 *
633 * <p> This method may only be invoked by the task scope owner.
634 *
635 * @implSpec This method may be overridden for customization purposes or to return a
636 * more specific return type. If overridden, the subclass must invoke {@code
637 * super.join} to ensure that the method waits for threads in this task scope to
638 * finish.
639 *
640 * @return this task scope
641 * @throws IllegalStateException if this task scope is closed
642 * @throws WrongThreadException if the current thread is not the task scope owner
643 * @throws InterruptedException if interrupted while waiting
644 */
645 public StructuredTaskScope<T> join() throws InterruptedException {
646 try {
647 implJoin(null);
648 } catch (TimeoutException e) {
649 throw new InternalError();
650 }
651 return this;
652 }
653
654 /**
655 * Wait for all threads in this task scope to finish or the task scope to shut down,
656 * up to the given deadline. This method waits until all threads started in the task
657 * scope finish execution, the {@link #shutdown() shutdown} method is invoked to
658 * shut down the task scope, the current thread is {@linkplain Thread#interrupt()
659 * interrupted}, or the deadline is reached.
660 *
661 * <p> This method may only be invoked by the task scope owner.
662 *
663 * @implSpec This method may be overridden for customization purposes or to return a
664 * more specific return type. If overridden, the subclass must invoke {@code
665 * super.joinUntil} to ensure that the method waits for threads in this task scope to
666 * finish.
667 *
668 * @param deadline the deadline
669 * @return this task scope
670 * @throws IllegalStateException if this task scope is closed
671 * @throws WrongThreadException if the current thread is not the task scope owner
672 * @throws InterruptedException if interrupted while waiting
673 * @throws TimeoutException if the deadline is reached while waiting
674 */
675 public StructuredTaskScope<T> joinUntil(Instant deadline)
676 throws InterruptedException, TimeoutException
677 {
678 Duration timeout = Duration.between(Instant.now(), deadline);
679 implJoin(timeout);
680 return this;
681 }
682
683 /**
684 * Interrupt all unfinished threads.
685 */
686 private void implInterruptAll() {
687 flock.threads()
688 .filter(t -> t != Thread.currentThread())
689 .forEach(t -> {
690 try {
691 t.interrupt();
692 } catch (Throwable ignore) { }
693 });
694 }
695
696 @SuppressWarnings("removal")
697 private void interruptAll() {
698 if (System.getSecurityManager() == null) {
699 implInterruptAll();
700 } else {
701 PrivilegedAction<Void> pa = () -> {
702 implInterruptAll();
703 return null;
704 };
705 AccessController.doPrivileged(pa);
706 }
707 }
708
709 /**
710 * Shutdown the task scope if not already shutdown. Return true if this method
711 * shutdowns the task scope, false if already shutdown.
712 */
713 private boolean implShutdown() {
714 shutdownLock.lock();
715 try {
716 if (state < SHUTDOWN) {
717 // prevent new threads from starting
718 flock.shutdown();
719
720 // set status before interrupting tasks
721 state = SHUTDOWN;
722
723 // interrupt all unfinished threads
724 interruptAll();
725
726 return true;
727 } else {
728 // already shutdown
729 return false;
730 }
731 } finally {
732 shutdownLock.unlock();
733 }
734 }
735
736 /**
737 * Shut down this task scope without closing it. Shutting down a task scope prevents
738 * new threads from starting, interrupts all unfinished threads, and causes the
739 * {@link #join() join} method to wakeup. Shutdown is useful for cases where the
740 * results of unfinished subtasks are no longer needed. It will typically be called
741 * by the {@link #handleComplete(Subtask)} implementation of a subclass that
742 * implements a policy to discard unfinished tasks once some outcome is reached.
743 *
744 * <p> More specifically, this method:
745 * <ul>
746 * <li> {@linkplain Thread#interrupt() Interrupts} all unfinished threads in the
747 * task scope (except the current thread).
748 * <li> Wakes up the task scope owner if it is waiting in {@link #join()} or {@link
749 * #joinUntil(Instant)}. If the task scope owner is not waiting then its next call to
750 * {@code join} or {@code joinUntil} will return immediately.
751 * </ul>
752 *
753 * <p> This method may only be invoked by the task scope owner or threads contained
754 * in the task scope.
755 *
756 * @implSpec This method may be overridden for customization purposes. If overridden,
757 * the subclass must invoke {@code super.shutdown} to ensure that the method shuts
758 * down the task scope.
759 *
760 * @apiNote
761 * There may be threads that have not finished because they are executing code that
762 * did not respond (or respond promptly) to thread interrupt. This method does not wait
763 * for these threads. When the owner invokes the {@link #close() close} method
764 * to close the task scope then it will wait for the remaining threads to finish.
765 *
766 * @throws IllegalStateException if this task scope is closed
767 * @throws WrongThreadException if the current thread is not the task scope owner or
768 * a thread contained in the task scope
769 * @see #isShutdown()
770 */
771 public void shutdown() {
772 ensureOwnerOrContainsThread();
773 int s = ensureOpen(); // throws ISE if closed
774 if (s < SHUTDOWN && implShutdown())
775 flock.wakeup();
776 }
777
778 /**
779 * {@return true if this task scope is shutdown, otherwise false}
780 * @see #shutdown()
781 */
782 public final boolean isShutdown() {
783 return state >= SHUTDOWN;
784 }
785
786 /**
787 * Closes this task scope.
788 *
789 * <p> This method first shuts down the task scope (as if by invoking the {@link
790 * #shutdown() shutdown} method). It then waits for the threads executing any
791 * unfinished tasks to finish. If interrupted, this method will continue to wait for
792 * the threads to finish before completing with the interrupt status set.
793 *
794 * <p> This method may only be invoked by the task scope owner. If the task scope
795 * is already closed then the task scope owner invoking this method has no effect.
796 *
797 * <p> A {@code StructuredTaskScope} is intended to be used in a <em>structured
798 * manner</em>. If this method is called to close a task scope before nested task
799 * scopes are closed then it closes the underlying construct of each nested task scope
800 * (in the reverse order that they were created in), closes this task scope, and then
801 * throws {@link StructureViolationException}.
802 * Similarly, if this method is called to close a task scope while executing with
803 * {@linkplain ScopedValue scoped value} bindings, and the task scope was created
804 * before the scoped values were bound, then {@code StructureViolationException} is
805 * thrown after closing the task scope.
806 * If a thread terminates without first closing task scopes that it owns then
807 * termination will cause the underlying construct of each of its open tasks scopes to
808 * be closed. Closing is performed in the reverse order that the task scopes were
809 * created in. Thread termination may therefore be delayed when the task scope owner
810 * has to wait for threads forked in these task scopes to finish.
811 *
812 * @implSpec This method may be overridden for customization purposes. If overridden,
813 * the subclass must invoke {@code super.close} to close the task scope.
814 *
815 * @throws IllegalStateException thrown after closing the task scope if the task scope
816 * owner did not attempt to join after forking
817 * @throws WrongThreadException if the current thread is not the task scope owner
818 * @throws StructureViolationException if a structure violation was detected
819 */
820 @Override
821 public void close() {
822 ensureOwner();
823 int s = state;
824 if (s == CLOSED)
825 return;
826
827 try {
828 if (s < SHUTDOWN)
829 implShutdown();
830 flock.close();
831 } finally {
832 state = CLOSED;
833 }
834
835 // throw ISE if the owner didn't attempt to join after forking
836 if (forkRound > lastJoinAttempted) {
837 lastJoinCompleted = forkRound;
838 throw newIllegalStateExceptionNoJoin();
839 }
840 }
841
842 @Override
843 public String toString() {
844 String name = flock.name();
845 return switch (state) {
846 case OPEN -> name;
847 case SHUTDOWN -> name + "/shutdown";
848 case CLOSED -> name + "/closed";
849 default -> throw new InternalError();
850 };
851 }
852
853 /**
854 * Subtask implementation, runs the task specified to the fork method.
855 */
856 private static final class SubtaskImpl<T> implements Subtask<T>, Runnable {
857 private static final AltResult RESULT_NULL = new AltResult(Subtask.State.SUCCESS);
858
859 private record AltResult(Subtask.State state, Throwable exception) {
860 AltResult(Subtask.State state) {
861 this(state, null);
862 }
863 }
864
865 private final StructuredTaskScope<? super T> scope;
866 private final Callable<? extends T> task;
867 private final int round;
868 private volatile Object result;
869
870 SubtaskImpl(StructuredTaskScope<? super T> scope,
871 Callable<? extends T> task,
872 int round) {
873 this.scope = scope;
874 this.task = task;
875 this.round = round;
876 }
877
878 @Override
879 public void run() {
880 T result = null;
881 Throwable ex = null;
882 try {
883 result = task.call();
884 } catch (Throwable e) {
885 ex = e;
886 }
887
888 // nothing to do if task scope is shutdown
889 if (scope.isShutdown())
890 return;
891
892 // capture result or exception, invoke handleComplete
893 if (ex == null) {
894 this.result = (result != null) ? result : RESULT_NULL;
895 } else {
896 this.result = new AltResult(State.FAILED, ex);
897 }
898 scope.handleComplete(this);
899 }
900
901 @Override
902 public Callable<? extends T> task() {
903 return task;
904 }
905
906 @Override
907 public Subtask.State state() {
908 Object result = this.result;
909 if (result == null) {
910 return State.UNAVAILABLE;
911 } else if (result instanceof AltResult alt) {
912 // null or failed
913 return alt.state();
914 } else {
915 return State.SUCCESS;
916 }
917 }
918
919 @Override
920 public T get() {
921 scope.ensureJoinedIfOwner(round);
922 Object result = this.result;
923 if (result instanceof AltResult) {
924 if (result == RESULT_NULL) return null;
925 } else if (result != null) {
926 @SuppressWarnings("unchecked")
927 T r = (T) result;
928 return r;
929 }
930 throw new IllegalStateException("Subtask not completed or did not complete successfully");
931 }
932
933 @Override
934 public Throwable exception() {
935 scope.ensureJoinedIfOwner(round);
936 Object result = this.result;
937 if (result instanceof AltResult alt && alt.state() == State.FAILED) {
938 return alt.exception();
939 }
940 throw new IllegalStateException("Subtask not completed or did not complete with exception");
941 }
942
943 @Override
944 public String toString() {
945 String stateAsString = switch (state()) {
946 case UNAVAILABLE -> "[Unavailable]";
947 case SUCCESS -> "[Completed successfully]";
948 case FAILED -> {
949 Throwable ex = ((AltResult) result).exception();
950 yield "[Failed: " + ex + "]";
951 }
952 };
953 return Objects.toIdentityString(this ) + stateAsString;
954 }
955 }
956
957 /**
958 * A {@code StructuredTaskScope} that captures the result of the first subtask to
959 * complete {@linkplain Subtask.State#SUCCESS successfully}. Once captured, it
960 * invokes the {@linkplain #shutdown() shutdown} method to interrupt unfinished threads
961 * and wakeup the task scope owner. The policy implemented by this class is intended
962 * for cases where the result of any subtask will do ("invoke any") and where the
963 * results of other unfinished subtasks are no longer needed.
964 *
965 * <p> Unless otherwise specified, passing a {@code null} argument to a method
966 * in this class will cause a {@link NullPointerException} to be thrown.
967 *
968 * @param <T> the result type
969 * @since 21
970 */
971 @PreviewFeature(feature = PreviewFeature.Feature.STRUCTURED_CONCURRENCY)
972 public static final class ShutdownOnSuccess<T> extends StructuredTaskScope<T> {
973 private static final Object RESULT_NULL = new Object();
974 private static final VarHandle FIRST_RESULT;
975 private static final VarHandle FIRST_EXCEPTION;
976 static {
977 try {
978 MethodHandles.Lookup l = MethodHandles.lookup();
979 FIRST_RESULT = l.findVarHandle(ShutdownOnSuccess.class, "firstResult", Object.class);
980 FIRST_EXCEPTION = l.findVarHandle(ShutdownOnSuccess.class, "firstException", Throwable.class);
981 } catch (Exception e) {
982 throw new ExceptionInInitializerError(e);
983 }
984 }
985 private volatile Object firstResult;
986 private volatile Throwable firstException;
987
988 /**
989 * Constructs a new {@code ShutdownOnSuccess} with the given name and thread factory.
990 * The task scope is optionally named for the purposes of monitoring and management.
991 * The thread factory is used to {@link ThreadFactory#newThread(Runnable) create}
992 * threads when subtasks are {@linkplain #fork(Callable) forked}. The task scope
993 * is owned by the current thread.
994 *
995 * <p> Construction captures the current thread's {@linkplain ScopedValue scoped
996 * value} bindings for inheritance by threads started in the task scope. The
997 * <a href="#TreeStructure">Tree Structure</a> section in the class description
998 * details how parent-child relations are established implicitly for the purpose
999 * of inheritance of scoped value bindings.
1000 *
1001 * @param name the name of the task scope, can be null
1002 * @param factory the thread factory
1003 */
1004 public ShutdownOnSuccess(String name, ThreadFactory factory) {
1005 super(name, factory);
1006 }
1007
1008 /**
1009 * Constructs a new unnamed {@code ShutdownOnSuccess} that creates virtual threads.
1010 *
1011 * @implSpec This constructor is equivalent to invoking the 2-arg constructor with
1012 * a name of {@code null} and a thread factory that creates virtual threads.
1013 */
1014 public ShutdownOnSuccess() {
1015 this(null, Thread.ofVirtual().factory());
1016 }
1017
1018 @Override
1019 protected void handleComplete(Subtask<? extends T> subtask) {
1020 super.handleComplete(subtask);
1021
1022 if (firstResult != null) {
1023 // already captured a result
1024 return;
1025 }
1026
1027 if (subtask.state() == Subtask.State.SUCCESS) {
1028 // task succeeded
1029 T result = subtask.get();
1030 Object r = (result != null) ? result : RESULT_NULL;
1031 if (FIRST_RESULT.compareAndSet(this, null, r)) {
1032 super.shutdown();
1033 }
1034 } else if (firstException == null) {
1035 // capture the exception thrown by the first subtask that failed
1036 FIRST_EXCEPTION.compareAndSet(this, null, subtask.exception());
1037 }
1038 }
1039
1040 /**
1041 * {@inheritDoc}
1042 * @return this task scope
1043 * @throws IllegalStateException {@inheritDoc}
1044 * @throws WrongThreadException {@inheritDoc}
1045 */
1046 @Override
1047 public ShutdownOnSuccess<T> join() throws InterruptedException {
1048 super.join();
1049 return this;
1050 }
1051
1052 /**
1053 * {@inheritDoc}
1054 * @return this task scope
1055 * @throws IllegalStateException {@inheritDoc}
1056 * @throws WrongThreadException {@inheritDoc}
1057 */
1058 @Override
1059 public ShutdownOnSuccess<T> joinUntil(Instant deadline)
1060 throws InterruptedException, TimeoutException
1061 {
1062 super.joinUntil(deadline);
1063 return this;
1064 }
1065
1066 /**
1067 * {@return the result of the first subtask that completed {@linkplain
1068 * Subtask.State#SUCCESS successfully}}
1069 *
1070 * <p> When no subtask completed successfully, but a subtask {@linkplain
1071 * Subtask.State#FAILED failed} then {@code ExecutionException} is thrown with
1072 * the subtask's exception as the {@linkplain Throwable#getCause() cause}.
1073 *
1074 * @throws ExecutionException if no subtasks completed successfully but at least
1075 * one subtask failed
1076 * @throws IllegalStateException if the handleComplete method was not invoked with
1077 * a completed subtask, or the task scope owner did not join after forking
1078 * @throws WrongThreadException if the current thread is not the task scope owner
1079 */
1080 public T result() throws ExecutionException {
1081 return result(ExecutionException::new);
1082 }
1083
1084 /**
1085 * Returns the result of the first subtask that completed {@linkplain
1086 * Subtask.State#SUCCESS successfully}, otherwise throws an exception produced
1087 * by the given exception supplying function.
1088 *
1089 * <p> When no subtask completed successfully, but a subtask {@linkplain
1090 * Subtask.State#FAILED failed}, then the exception supplying function is invoked
1091 * with subtask's exception.
1092 *
1093 * @param esf the exception supplying function
1094 * @param <X> type of the exception to be thrown
1095 * @return the result of the first subtask that completed with a result
1096 *
1097 * @throws X if no subtasks completed successfully but at least one subtask failed
1098 * @throws IllegalStateException if the handleComplete method was not invoked with
1099 * a completed subtask, or the task scope owner did not join after forking
1100 * @throws WrongThreadException if the current thread is not the task scope owner
1101 */
1102 public <X extends Throwable> T result(Function<Throwable, ? extends X> esf) throws X {
1103 Objects.requireNonNull(esf);
1104 ensureOwnerAndJoined();
1105
1106 Object result = firstResult;
1107 if (result == RESULT_NULL) {
1108 return null;
1109 } else if (result != null) {
1110 @SuppressWarnings("unchecked")
1111 T r = (T) result;
1112 return r;
1113 }
1114
1115 Throwable exception = firstException;
1116 if (exception != null) {
1117 X ex = esf.apply(exception);
1118 Objects.requireNonNull(ex, "esf returned null");
1119 throw ex;
1120 }
1121
1122 throw new IllegalStateException("No completed subtasks");
1123 }
1124 }
1125
1126 /**
1127 * A {@code StructuredTaskScope} that captures the exception of the first subtask to
1128 * {@linkplain Subtask.State#FAILED fail}. Once captured, it invokes the {@linkplain
1129 * #shutdown() shutdown} method to interrupt unfinished threads and wakeup the task
1130 * scope owner. The policy implemented by this class is intended for cases where the
1131 * results for all subtasks are required ("invoke all"); if any subtask fails then the
1132 * results of other unfinished subtasks are no longer needed.
1133 *
1134 * <p> Unless otherwise specified, passing a {@code null} argument to a method
1135 * in this class will cause a {@link NullPointerException} to be thrown.
1136 *
1137 * @since 21
1138 */
1139 @PreviewFeature(feature = PreviewFeature.Feature.STRUCTURED_CONCURRENCY)
1140 public static final class ShutdownOnFailure extends StructuredTaskScope<Object> {
1141 private static final VarHandle FIRST_EXCEPTION;
1142 static {
1143 try {
1144 MethodHandles.Lookup l = MethodHandles.lookup();
1145 FIRST_EXCEPTION = l.findVarHandle(ShutdownOnFailure.class, "firstException", Throwable.class);
1146 } catch (Exception e) {
1147 throw new ExceptionInInitializerError(e);
1148 }
1149 }
1150 private volatile Throwable firstException;
1151
1152 /**
1153 * Constructs a new {@code ShutdownOnFailure} with the given name and thread factory.
1154 * The task scope is optionally named for the purposes of monitoring and management.
1155 * The thread factory is used to {@link ThreadFactory#newThread(Runnable) create}
1156 * threads when subtasks are {@linkplain #fork(Callable) forked}. The task scope
1157 * is owned by the current thread.
1158 *
1159 * <p> Construction captures the current thread's {@linkplain ScopedValue scoped
1160 * value} bindings for inheritance by threads started in the task scope. The
1161 * <a href="#TreeStructure">Tree Structure</a> section in the class description
1162 * details how parent-child relations are established implicitly for the purpose
1163 * of inheritance of scoped value bindings.
1164 *
1165 * @param name the name of the task scope, can be null
1166 * @param factory the thread factory
1167 */
1168 public ShutdownOnFailure(String name, ThreadFactory factory) {
1169 super(name, factory);
1170 }
1171
1172 /**
1173 * Constructs a new unnamed {@code ShutdownOnFailure} that creates virtual threads.
1174 *
1175 * @implSpec This constructor is equivalent to invoking the 2-arg constructor with
1176 * a name of {@code null} and a thread factory that creates virtual threads.
1177 */
1178 public ShutdownOnFailure() {
1179 this(null, Thread.ofVirtual().factory());
1180 }
1181
1182 @Override
1183 protected void handleComplete(Subtask<?> subtask) {
1184 super.handleComplete(subtask);
1185 if (subtask.state() == Subtask.State.FAILED
1186 && firstException == null
1187 && FIRST_EXCEPTION.compareAndSet(this, null, subtask.exception())) {
1188 super.shutdown();
1189 }
1190 }
1191
1192 /**
1193 * {@inheritDoc}
1194 * @return this task scope
1195 * @throws IllegalStateException {@inheritDoc}
1196 * @throws WrongThreadException {@inheritDoc}
1197 */
1198 @Override
1199 public ShutdownOnFailure join() throws InterruptedException {
1200 super.join();
1201 return this;
1202 }
1203
1204 /**
1205 * {@inheritDoc}
1206 * @return this task scope
1207 * @throws IllegalStateException {@inheritDoc}
1208 * @throws WrongThreadException {@inheritDoc}
1209 */
1210 @Override
1211 public ShutdownOnFailure joinUntil(Instant deadline)
1212 throws InterruptedException, TimeoutException
1213 {
1214 super.joinUntil(deadline);
1215 return this;
1216 }
1217
1218 /**
1219 * Returns the exception of the first subtask that {@linkplain Subtask.State#FAILED
1220 * failed}. If no subtasks failed then an empty {@code Optional} is returned.
1221 *
1222 * @return the exception for the first subtask to fail or an empty optional if no
1223 * subtasks failed
1224 *
1225 * @throws WrongThreadException if the current thread is not the task scope owner
1226 * @throws IllegalStateException if the task scope owner did not join after forking
1227 */
1228 public Optional<Throwable> exception() {
1229 ensureOwnerAndJoined();
1230 return Optional.ofNullable(firstException);
1231 }
1232
1233 /**
1234 * Throws if a subtask {@linkplain Subtask.State#FAILED failed}.
1235 * If any subtask failed with an exception then {@code ExecutionException} is
1236 * thrown with the exception of the first subtask to fail as the {@linkplain
1237 * Throwable#getCause() cause}. This method does nothing if no subtasks failed.
1238 *
1239 * @throws ExecutionException if a subtask failed
1240 * @throws WrongThreadException if the current thread is not the task scope owner
1241 * @throws IllegalStateException if the task scope owner did not join after forking
1242 */
1243 public void throwIfFailed() throws ExecutionException {
1244 throwIfFailed(ExecutionException::new);
1245 }
1246
1247 /**
1248 * Throws the exception produced by the given exception supplying function if a
1249 * subtask {@linkplain Subtask.State#FAILED failed}. If any subtask failed with
1250 * an exception then the function is invoked with the exception of the first
1251 * subtask to fail. The exception returned by the function is thrown. This method
1252 * does nothing if no subtasks failed.
1253 *
1254 * @param esf the exception supplying function
1255 * @param <X> type of the exception to be thrown
1256 *
1257 * @throws X produced by the exception supplying function
1258 * @throws WrongThreadException if the current thread is not the task scope owner
1259 * @throws IllegalStateException if the task scope owner did not join after forking
1260 */
1261 public <X extends Throwable>
1262 void throwIfFailed(Function<Throwable, ? extends X> esf) throws X {
1263 ensureOwnerAndJoined();
1264 Objects.requireNonNull(esf);
1265 Throwable exception = firstException;
1266 if (exception != null) {
1267 X ex = esf.apply(exception);
1268 Objects.requireNonNull(ex, "esf returned null");
1269 throw ex;
1270 }
1271 }
1272 }
1273 }