1 /*
2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation. Oracle designates this
7 * particular file as subject to the "Classpath" exception as provided
8 * by Oracle in the LICENSE file that accompanied this code.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 */
24
25 /*
26 * This file is available under and governed by the GNU General Public
27 * License version 2 only, as published by the Free Software Foundation.
28 * However, the following notice accompanied the original version of this
29 * file:
30 *
31 * Written by Doug Lea with assistance from members of JCP JSR-166
32 * Expert Group and released to the public domain, as explained at
33 * http://creativecommons.org/publicdomain/zero/1.0/
34 */
35
36 package java.util.concurrent;
37
38 import java.io.Serializable;
39 import java.lang.invoke.MethodHandles;
40 import java.lang.invoke.VarHandle;
41 import java.lang.reflect.Constructor;
42 import java.util.Collection;
43 import java.util.List;
44 import java.util.RandomAccess;
45 import java.util.concurrent.locks.LockSupport;
46
47 /**
48 * Abstract base class for tasks that run within a {@link ForkJoinPool}.
49 * A {@code ForkJoinTask} is a thread-like entity that is much
50 * lighter weight than a normal thread. Huge numbers of tasks and
51 * subtasks may be hosted by a small number of actual threads in a
52 * ForkJoinPool, at the price of some usage limitations.
53 *
54 * <p>A "main" {@code ForkJoinTask} begins execution when it is
55 * explicitly submitted to a {@link ForkJoinPool}, or, if not already
56 * engaged in a ForkJoin computation, commenced in the {@link
57 * ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or
58 * related methods. Once started, it will usually in turn start other
59 * subtasks. As indicated by the name of this class, many programs
60 * using {@code ForkJoinTask} employ only methods {@link #fork} and
61 * {@link #join}, or derivatives such as {@link
62 * #invokeAll(ForkJoinTask...) invokeAll}. However, this class also
63 * provides a number of other methods that can come into play in
64 * advanced usages, as well as extension mechanics that allow support
65 * of new forms of fork/join processing.
66 *
67 * <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
68 * The efficiency of {@code ForkJoinTask}s stems from a set of
69 * restrictions (that are only partially statically enforceable)
70 * reflecting their main use as computational tasks calculating pure
71 * functions or operating on purely isolated objects. The primary
72 * coordination mechanisms are {@link #fork}, that arranges
73 * asynchronous execution, and {@link #join}, that doesn't proceed
74 * until the task's result has been computed. Computations should
75 * ideally avoid {@code synchronized} methods or blocks, and should
76 * minimize other blocking synchronization apart from joining other
77 * tasks or using synchronizers such as Phasers that are advertised to
78 * cooperate with fork/join scheduling. Subdividable tasks should also
79 * not perform blocking I/O, and should ideally access variables that
80 * are completely independent of those accessed by other running
81 * tasks. These guidelines are loosely enforced by not permitting
82 * checked exceptions such as {@code IOExceptions} to be
83 * thrown. However, computations may still encounter unchecked
84 * exceptions, that are rethrown to callers attempting to join
85 * them. These exceptions may additionally include {@link
86 * RejectedExecutionException} stemming from internal resource
87 * exhaustion, such as failure to allocate internal task
88 * queues. Rethrown exceptions behave in the same way as regular
89 * exceptions, but, when possible, contain stack traces (as displayed
90 * for example using {@code ex.printStackTrace()}) of both the thread
91 * that initiated the computation as well as the thread actually
92 * encountering the exception; minimally only the latter.
93 *
94 * <p>It is possible to define and use ForkJoinTasks that may block,
95 * but doing so requires three further considerations: (1) Completion
96 * of few if any <em>other</em> tasks should be dependent on a task
97 * that blocks on external synchronization or I/O. Event-style async
98 * tasks that are never joined (for example, those subclassing {@link
99 * CountedCompleter}) often fall into this category. (2) To minimize
100 * resource impact, tasks should be small; ideally performing only the
101 * (possibly) blocking action. (3) Unless the {@link
102 * ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
103 * blocked tasks is known to be less than the pool's {@link
104 * ForkJoinPool#getParallelism} level, the pool cannot guarantee that
105 * enough threads will be available to ensure progress or good
106 * performance.
107 *
108 * <p>The primary method for awaiting completion and extracting
109 * results of a task is {@link #join}, but there are several variants:
110 * The {@link Future#get} methods support interruptible and/or timed
111 * waits for completion and report results using {@code Future}
112 * conventions. Method {@link #invoke} is semantically
113 * equivalent to {@code fork(); join()} but always attempts to begin
114 * execution in the current thread. The "<em>quiet</em>" forms of
115 * these methods do not extract results or report exceptions. These
116 * may be useful when a set of tasks are being executed, and you need
117 * to delay processing of results or exceptions until all complete.
118 * Method {@code invokeAll} (available in multiple versions)
119 * performs the most common form of parallel invocation: forking a set
120 * of tasks and joining them all.
121 *
122 * <p>In the most typical usages, a fork-join pair act like a call
123 * (fork) and return (join) from a parallel recursive function. As is
124 * the case with other forms of recursive calls, returns (joins)
125 * should be performed innermost-first. For example, {@code a.fork();
126 * b.fork(); b.join(); a.join();} is likely to be substantially more
127 * efficient than joining {@code a} before {@code b}.
128 *
129 * <p>The execution status of tasks may be queried at several levels
130 * of detail: {@link #isDone} is true if a task completed in any way
131 * (including the case where a task was cancelled without executing);
132 * {@link #isCompletedNormally} is true if a task completed without
133 * cancellation or encountering an exception; {@link #isCancelled} is
134 * true if the task was cancelled (in which case {@link #getException}
135 * returns a {@link CancellationException}); and
136 * {@link #isCompletedAbnormally} is true if a task was either
137 * cancelled or encountered an exception, in which case {@link
138 * #getException} will return either the encountered exception or
139 * {@link CancellationException}.
140 *
141 * <p>The ForkJoinTask class is not usually directly subclassed.
142 * Instead, you subclass one of the abstract classes that support a
143 * particular style of fork/join processing, typically {@link
144 * RecursiveAction} for most computations that do not return results,
145 * {@link RecursiveTask} for those that do, and {@link
146 * CountedCompleter} for those in which completed actions trigger
147 * other actions. Normally, a concrete ForkJoinTask subclass declares
148 * fields comprising its parameters, established in a constructor, and
149 * then defines a {@code compute} method that somehow uses the control
150 * methods supplied by this base class.
151 *
152 * <p>Method {@link #join} and its variants are appropriate for use
153 * only when completion dependencies are acyclic; that is, the
154 * parallel computation can be described as a directed acyclic graph
155 * (DAG). Otherwise, executions may encounter a form of deadlock as
156 * tasks cyclically wait for each other. However, this framework
157 * supports other methods and techniques (for example the use of
158 * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
159 * may be of use in constructing custom subclasses for problems that
160 * are not statically structured as DAGs. To support such usages, a
161 * ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
162 * value using {@link #setForkJoinTaskTag} or {@link
163 * #compareAndSetForkJoinTaskTag} and checked using {@link
164 * #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
165 * these {@code protected} methods or tags for any purpose, but they
166 * may be of use in the construction of specialized subclasses. For
167 * example, parallel graph traversals can use the supplied methods to
168 * avoid revisiting nodes/tasks that have already been processed.
169 * (Method names for tagging are bulky in part to encourage definition
170 * of methods that reflect their usage patterns.)
171 *
172 * <p>Most base support methods are {@code final}, to prevent
173 * overriding of implementations that are intrinsically tied to the
174 * underlying lightweight task scheduling framework. Developers
175 * creating new basic styles of fork/join processing should minimally
176 * implement {@code protected} methods {@link #exec}, {@link
177 * #setRawResult}, and {@link #getRawResult}, while also introducing
178 * an abstract computational method that can be implemented in its
179 * subclasses, possibly relying on other {@code protected} methods
180 * provided by this class.
181 *
182 * <p>ForkJoinTasks should perform relatively small amounts of
183 * computation. Large tasks should be split into smaller subtasks,
184 * usually via recursive decomposition. As a very rough rule of thumb,
185 * a task should perform more than 100 and less than 10000 basic
186 * computational steps, and should avoid indefinite looping. If tasks
187 * are too big, then parallelism cannot improve throughput. If too
188 * small, then memory and internal task maintenance overhead may
189 * overwhelm processing.
190 *
191 * <p>This class provides {@code adapt} methods for {@link Runnable}
192 * and {@link Callable}, that may be of use when mixing execution of
193 * {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
194 * of this form, consider using a pool constructed in <em>asyncMode</em>.
195 *
196 * <p>ForkJoinTasks are {@code Serializable}, which enables them to be
197 * used in extensions such as remote execution frameworks. It is
198 * sensible to serialize tasks only before or after, but not during,
199 * execution. Serialization is not relied on during execution itself.
200 *
201 * @since 1.7
202 * @author Doug Lea
203 */
204 public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
205
206 /*
207 * See the internal documentation of class ForkJoinPool for a
208 * general implementation overview. ForkJoinTasks are mainly
209 * responsible for maintaining their "status" field amidst relays
210 * to methods in ForkJoinWorkerThread and ForkJoinPool.
211 *
212 * The methods of this class are more-or-less layered into
213 * (1) basic status maintenance
214 * (2) execution and awaiting completion
215 * (3) user-level methods that additionally report results.
216 * This is sometimes hard to see because this file orders exported
217 * methods in a way that flows well in javadocs.
218 *
219 * Revision notes: The use of "Aux" field replaces previous
220 * reliance on a table to hold exceptions and synchronized blocks
221 * and monitors to wait for completion.
222 */
223
224 /**
225 * Nodes for threads waiting for completion, or holding a thrown
226 * exception (never both). Waiting threads prepend nodes
227 * Treiber-stack-style. Signallers detach and unpark
228 * waiters. Cancelled waiters try to unsplice.
229 */
230 static final class Aux {
231 final Thread thread;
232 final Throwable ex; // null if a waiter
233 Aux next; // accessed only via memory-acquire chains
234 Aux(Thread thread, Throwable ex) {
235 this.thread = thread;
236 this.ex = ex;
237 }
238 final boolean casNext(Aux c, Aux v) { // used only in cancellation
239 return NEXT.compareAndSet(this, c, v);
240 }
241 private static final VarHandle NEXT;
242 static {
243 try {
244 NEXT = MethodHandles.lookup()
245 .findVarHandle(Aux.class, "next", Aux.class);
246 } catch (ReflectiveOperationException e) {
247 throw new ExceptionInInitializerError(e);
248 }
249 }
250 }
251
252 /*
253 * The status field holds bits packed into a single int to ensure
254 * atomicity. Status is initially zero, and takes on nonnegative
255 * values until completed, upon which it holds (sign bit) DONE,
256 * possibly with ABNORMAL (cancelled or exceptional) and THROWN
257 * (in which case an exception has been stored). A value of
258 * ABNORMAL without DONE signifies an interrupted wait. These
259 * control bits occupy only (some of) the upper half (16 bits) of
260 * status field. The lower bits are used for user-defined tags.
261 */
262 private static final int DONE = 1 << 31; // must be negative
263 private static final int ABNORMAL = 1 << 16;
264 private static final int THROWN = 1 << 17;
265 private static final int SMASK = 0xffff; // short bits for tags
266 private static final int UNCOMPENSATE = 1 << 16; // helpJoin return sentinel
267
268 // Fields
269 volatile int status; // accessed directly by pool and workers
270 private transient volatile Aux aux; // either waiters or thrown Exception
271
272 // Support for atomic operations
273 private static final VarHandle STATUS;
274 private static final VarHandle AUX;
275 private int getAndBitwiseOrStatus(int v) {
276 return (int)STATUS.getAndBitwiseOr(this, v);
277 }
278 private boolean casStatus(int c, int v) {
279 return STATUS.weakCompareAndSet(this, c, v);
280 }
281 private boolean casAux(Aux c, Aux v) {
282 return AUX.compareAndSet(this, c, v);
283 }
284
285 /** Removes and unparks waiters */
286 private void signalWaiters() {
287 for (Aux a; (a = aux) != null && a.ex == null; ) {
288 if (casAux(a, null)) { // detach entire list
289 for (Thread t; a != null; a = a.next) {
290 if ((t = a.thread) != Thread.currentThread() && t != null)
291 LockSupport.unpark(t); // don't self-signal
292 }
293 break;
294 }
295 }
296 }
297
298 /**
299 * Possibly blocks until task is done or interrupted or timed out.
300 *
301 * @param interruptible true if wait can be cancelled by interrupt
302 * @param deadline if non-zero use timed waits and possibly timeout
303 * @param pool if nonnull pool to uncompensate after unblocking
304 * @return status on exit, or ABNORMAL if interrupted while waiting
305 */
306 private int awaitDone(boolean interruptible, long deadline,
307 ForkJoinPool pool) {
308 int s;
309 boolean interrupted = false, queued = false, parked = false;
310 Aux node = null;
311 while ((s = status) >= 0) {
312 Aux a; long ns;
313 if (parked && Thread.interrupted()) {
314 if (interruptible) {
315 s = ABNORMAL;
316 break;
317 }
318 interrupted = true;
319 }
320 else if (queued) {
321 if (deadline != 0L) {
322 if ((ns = deadline - System.nanoTime()) <= 0L)
323 break;
324 LockSupport.parkNanos(ns);
325 }
326 else
327 LockSupport.park();
328 parked = true;
329 }
330 else if (node != null) {
331 if ((a = aux) != null && a.ex != null)
332 Thread.onSpinWait(); // exception in progress
333 else if (queued = casAux(node.next = a, node))
334 LockSupport.setCurrentBlocker(this);
335 }
336 else {
337 try {
338 node = new Aux(Thread.currentThread(), null);
339 } catch (Throwable ex) { // try to cancel if cannot create
340 casStatus(s, s | (DONE | ABNORMAL));
341 }
342 }
343 }
344 if (pool != null)
345 pool.uncompensate();
346
347 if (queued) {
348 LockSupport.setCurrentBlocker(null);
349 if (s >= 0) { // cancellation similar to AbstractQueuedSynchronizer
350 outer: for (Aux a; (a = aux) != null && a.ex == null; ) {
351 for (Aux trail = null;;) {
352 Aux next = a.next;
353 if (a == node) {
354 if (trail != null)
355 trail.casNext(trail, next);
356 else if (casAux(a, next))
357 break outer; // cannot be re-encountered
358 break; // restart
359 } else {
360 trail = a;
361 if ((a = next) == null)
362 break outer;
363 }
364 }
365 }
366 }
367 else {
368 signalWaiters(); // help clean or signal
369 if (interrupted)
370 Thread.currentThread().interrupt();
371 }
372 }
373 return s;
374 }
375
376 /**
377 * Sets DONE status and wakes up threads waiting to join this task.
378 * @return status on exit
379 */
380 private int setDone() {
381 int s = getAndBitwiseOrStatus(DONE) | DONE;
382 signalWaiters();
383 return s;
384 }
385
386 /**
387 * Sets ABNORMAL DONE status unless already done, and wakes up threads
388 * waiting to join this task.
389 * @return status on exit
390 */
391 private int trySetCancelled() {
392 int s;
393 do {} while ((s = status) >= 0 && !casStatus(s, s |= (DONE | ABNORMAL)));
394 signalWaiters();
395 return s;
396 }
397
398 /**
399 * Records exception and sets ABNORMAL THROWN DONE status unless
400 * already done, and wakes up threads waiting to join this task.
401 * If losing a race with setDone or trySetCancelled, the exception
402 * may be recorded but not reported.
403 *
404 * @return status on exit
405 */
406 final int trySetThrown(Throwable ex) {
407 Aux h = new Aux(Thread.currentThread(), ex), p = null;
408 boolean installed = false;
409 int s;
410 while ((s = status) >= 0) {
411 Aux a;
412 if (!installed && ((a = aux) == null || a.ex == null) &&
413 (installed = casAux(a, h)))
414 p = a; // list of waiters replaced by h
415 if (installed && casStatus(s, s |= (DONE | ABNORMAL | THROWN)))
416 break;
417 }
418 for (; p != null; p = p.next)
419 LockSupport.unpark(p.thread);
420 return s;
421 }
422
423 /**
424 * Records exception unless already done. Overridable in subclasses.
425 *
426 * @return status on exit
427 */
428 int trySetException(Throwable ex) {
429 return trySetThrown(ex);
430 }
431
432 /**
433 * Constructor for subclasses to call.
434 */
435 public ForkJoinTask() {}
436
437 static boolean isExceptionalStatus(int s) { // needed by subclasses
438 return (s & THROWN) != 0;
439 }
440
441 /**
442 * Unless done, calls exec and records status if completed, but
443 * doesn't wait for completion otherwise.
444 *
445 * @return status on exit from this method
446 */
447 final int doExec() {
448 int s; boolean completed;
449 if ((s = status) >= 0) {
450 try {
451 completed = exec();
452 } catch (Throwable rex) {
453 s = trySetException(rex);
454 completed = false;
455 }
456 if (completed)
457 s = setDone();
458 }
459 return s;
460 }
461
462 /**
463 * Helps and/or waits for completion from join, get, or invoke;
464 * called from either internal or external threads.
465 *
466 * @param ran true if task known to have been exec'd
467 * @param interruptible true if park interruptibly when external
468 * @param timed true if use timed wait
469 * @param nanos if timed, timeout value
470 * @return ABNORMAL if interrupted, else status on exit
471 */
472 private int awaitJoin(boolean ran, boolean interruptible, boolean timed,
473 long nanos) {
474 boolean internal; ForkJoinPool p; ForkJoinPool.WorkQueue q; int s;
475 Thread t; ForkJoinWorkerThread wt;
476 if (internal = ((t = Thread.currentThread())
477 instanceof ForkJoinWorkerThread)) {
478 p = (wt = (ForkJoinWorkerThread)t).pool;
479 q = wt.workQueue;
480 }
481 else {
482 p = ForkJoinPool.common;
483 q = ForkJoinPool.commonQueue();
484 if (interruptible && Thread.interrupted())
485 return ABNORMAL;
486 }
487 if ((s = status) < 0)
488 return s;
489 long deadline = 0L;
490 if (timed) {
491 if (nanos <= 0L)
492 return 0;
493 else if ((deadline = nanos + System.nanoTime()) == 0L)
494 deadline = 1L;
495 }
496 ForkJoinPool uncompensate = null;
497 if (q != null && p != null) { // try helping
498 if ((!timed || p.isSaturated()) &&
499 ((this instanceof CountedCompleter) ?
500 (s = p.helpComplete(this, q, internal)) < 0 :
501 (q.tryRemove(this, internal) && (s = doExec()) < 0)))
502 return s;
503 if (internal) {
504 if ((s = p.helpJoin(this, q)) < 0)
505 return s;
506 if (s == UNCOMPENSATE)
507 uncompensate = p;
508 interruptible = false;
509 }
510 }
511 return awaitDone(interruptible, deadline, uncompensate);
512 }
513
514 /**
515 * Cancels, ignoring any exceptions thrown by cancel. Cancel is
516 * spec'ed not to throw any exceptions, but if it does anyway, we
517 * have no recourse, so guard against this case.
518 */
519 static final void cancelIgnoringExceptions(Future<?> t) {
520 if (t != null) {
521 try {
522 t.cancel(true);
523 } catch (Throwable ignore) {
524 }
525 }
526 }
527
528 /**
529 * Returns a rethrowable exception for this task, if available.
530 * To provide accurate stack traces, if the exception was not
531 * thrown by the current thread, we try to create a new exception
532 * of the same type as the one thrown, but with the recorded
533 * exception as its cause. If there is no such constructor, we
534 * instead try to use a no-arg constructor, followed by initCause,
535 * to the same effect. If none of these apply, or any fail due to
536 * other exceptions, we return the recorded exception, which is
537 * still correct, although it may contain a misleading stack
538 * trace.
539 *
540 * @return the exception, or null if none
541 */
542 private Throwable getThrowableException() {
543 Throwable ex; Aux a;
544 if ((a = aux) == null)
545 ex = null;
546 else if ((ex = a.ex) != null && a.thread != Thread.currentThread()) {
547 try {
548 Constructor<?> noArgCtor = null, oneArgCtor = null;
549 for (Constructor<?> c : ex.getClass().getConstructors()) {
550 Class<?>[] ps = c.getParameterTypes();
551 if (ps.length == 0)
552 noArgCtor = c;
553 else if (ps.length == 1 && ps[0] == Throwable.class) {
554 oneArgCtor = c;
555 break;
556 }
557 }
558 if (oneArgCtor != null)
559 ex = (Throwable)oneArgCtor.newInstance(ex);
560 else if (noArgCtor != null) {
561 Throwable rx = (Throwable)noArgCtor.newInstance();
562 rx.initCause(ex);
563 ex = rx;
564 }
565 } catch (Exception ignore) {
566 }
567 }
568 return ex;
569 }
570
571 /**
572 * Returns exception associated with the given status, or null if none.
573 */
574 private Throwable getException(int s) {
575 Throwable ex = null;
576 if ((s & ABNORMAL) != 0 &&
577 ((s & THROWN) == 0 || (ex = getThrowableException()) == null))
578 ex = new CancellationException();
579 return ex;
580 }
581
582 /**
583 * Throws exception associated with the given status, or
584 * CancellationException if none recorded.
585 */
586 private void reportException(int s) {
587 ForkJoinTask.<RuntimeException>uncheckedThrow(
588 (s & THROWN) != 0 ? getThrowableException() : null);
589 }
590
591 /**
592 * Throws exception for (timed or untimed) get, wrapping if
593 * necessary in an ExecutionException.
594 */
595 private void reportExecutionException(int s) {
596 Throwable ex = null;
597 if (s == ABNORMAL)
598 ex = new InterruptedException();
599 else if (s >= 0)
600 ex = new TimeoutException();
601 else if ((s & THROWN) != 0 && (ex = getThrowableException()) != null)
602 ex = new ExecutionException(ex);
603 ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
604 }
605
606 /**
607 * A version of "sneaky throw" to relay exceptions in other
608 * contexts.
609 */
610 static void rethrow(Throwable ex) {
611 ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
612 }
613
614 /**
615 * The sneaky part of sneaky throw, relying on generics
616 * limitations to evade compiler complaints about rethrowing
617 * unchecked exceptions. If argument null, throws
618 * CancellationException.
619 */
620 @SuppressWarnings("unchecked") static <T extends Throwable>
621 void uncheckedThrow(Throwable t) throws T {
622 if (t == null)
623 t = new CancellationException();
624 throw (T)t; // rely on vacuous cast
625 }
626
627 // public methods
628
629 /**
630 * Arranges to asynchronously execute this task in the pool the
631 * current task is running in, if applicable, or using the {@link
632 * ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. While
633 * it is not necessarily enforced, it is a usage error to fork a
634 * task more than once unless it has completed and been
635 * reinitialized. Subsequent modifications to the state of this
636 * task or any data it operates on are not necessarily
637 * consistently observable by any thread other than the one
638 * executing it unless preceded by a call to {@link #join} or
639 * related methods, or a call to {@link #isDone} returning {@code
640 * true}.
641 *
642 * @return {@code this}, to simplify usage
643 */
644 public final ForkJoinTask<V> fork() {
645 Thread t; ForkJoinWorkerThread w;
646 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
647 (w = (ForkJoinWorkerThread)t).workQueue.push(this, w.pool);
648 else
649 ForkJoinPool.common.externalPush(this);
650 return this;
651 }
652
653 /**
654 * Returns the result of the computation when it
655 * {@linkplain #isDone is done}.
656 * This method differs from {@link #get()} in that abnormal
657 * completion results in {@code RuntimeException} or {@code Error},
658 * not {@code ExecutionException}, and that interrupts of the
659 * calling thread do <em>not</em> cause the method to abruptly
660 * return by throwing {@code InterruptedException}.
661 *
662 * @return the computed result
663 */
664 public final V join() {
665 int s;
666 if ((s = status) >= 0)
667 s = awaitJoin(false, false, false, 0L);
668 if ((s & ABNORMAL) != 0)
669 reportException(s);
670 return getRawResult();
671 }
672
673 /**
674 * Commences performing this task, awaits its completion if
675 * necessary, and returns its result, or throws an (unchecked)
676 * {@code RuntimeException} or {@code Error} if the underlying
677 * computation did so.
678 *
679 * @return the computed result
680 */
681 public final V invoke() {
682 int s;
683 if ((s = doExec()) >= 0)
684 s = awaitJoin(true, false, false, 0L);
685 if ((s & ABNORMAL) != 0)
686 reportException(s);
687 return getRawResult();
688 }
689
690 /**
691 * Forks the given tasks, returning when {@code isDone} holds for
692 * each task or an (unchecked) exception is encountered, in which
693 * case the exception is rethrown. If more than one task
694 * encounters an exception, then this method throws any one of
695 * these exceptions. If any task encounters an exception, the
696 * other may be cancelled. However, the execution status of
697 * individual tasks is not guaranteed upon exceptional return. The
698 * status of each task may be obtained using {@link
699 * #getException()} and related methods to check if they have been
700 * cancelled, completed normally or exceptionally, or left
701 * unprocessed.
702 *
703 * @param t1 the first task
704 * @param t2 the second task
705 * @throws NullPointerException if any task is null
706 */
707 public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
708 int s1, s2;
709 if (t1 == null || t2 == null)
710 throw new NullPointerException();
711 t2.fork();
712 if ((s1 = t1.doExec()) >= 0)
713 s1 = t1.awaitJoin(true, false, false, 0L);
714 if ((s1 & ABNORMAL) != 0) {
715 cancelIgnoringExceptions(t2);
716 t1.reportException(s1);
717 }
718 else if (((s2 = t2.awaitJoin(false, false, false, 0L)) & ABNORMAL) != 0)
719 t2.reportException(s2);
720 }
721
722 /**
723 * Forks the given tasks, returning when {@code isDone} holds for
724 * each task or an (unchecked) exception is encountered, in which
725 * case the exception is rethrown. If more than one task
726 * encounters an exception, then this method throws any one of
727 * these exceptions. If any task encounters an exception, others
728 * may be cancelled. However, the execution status of individual
729 * tasks is not guaranteed upon exceptional return. The status of
730 * each task may be obtained using {@link #getException()} and
731 * related methods to check if they have been cancelled, completed
732 * normally or exceptionally, or left unprocessed.
733 *
734 * @param tasks the tasks
735 * @throws NullPointerException if any task is null
736 */
737 public static void invokeAll(ForkJoinTask<?>... tasks) {
738 Throwable ex = null;
739 int last = tasks.length - 1;
740 for (int i = last; i >= 0; --i) {
741 ForkJoinTask<?> t;
742 if ((t = tasks[i]) == null) {
743 ex = new NullPointerException();
744 break;
745 }
746 if (i == 0) {
747 int s;
748 if ((s = t.doExec()) >= 0)
749 s = t.awaitJoin(true, false, false, 0L);
750 if ((s & ABNORMAL) != 0)
751 ex = t.getException(s);
752 break;
753 }
754 t.fork();
755 }
756 if (ex == null) {
757 for (int i = 1; i <= last; ++i) {
758 ForkJoinTask<?> t;
759 if ((t = tasks[i]) != null) {
760 int s;
761 if ((s = t.status) >= 0)
762 s = t.awaitJoin(false, false, false, 0L);
763 if ((s & ABNORMAL) != 0 && (ex = t.getException(s)) != null)
764 break;
765 }
766 }
767 }
768 if (ex != null) {
769 for (int i = 1; i <= last; ++i)
770 cancelIgnoringExceptions(tasks[i]);
771 rethrow(ex);
772 }
773 }
774
775 /**
776 * Forks all tasks in the specified collection, returning when
777 * {@code isDone} holds for each task or an (unchecked) exception
778 * is encountered, in which case the exception is rethrown. If
779 * more than one task encounters an exception, then this method
780 * throws any one of these exceptions. If any task encounters an
781 * exception, others may be cancelled. However, the execution
782 * status of individual tasks is not guaranteed upon exceptional
783 * return. The status of each task may be obtained using {@link
784 * #getException()} and related methods to check if they have been
785 * cancelled, completed normally or exceptionally, or left
786 * unprocessed.
787 *
788 * @param tasks the collection of tasks
789 * @param <T> the type of the values returned from the tasks
790 * @return the tasks argument, to simplify usage
791 * @throws NullPointerException if tasks or any element are null
792 */
793 public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
794 if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
795 invokeAll(tasks.toArray(new ForkJoinTask<?>[0]));
796 return tasks;
797 }
798 @SuppressWarnings("unchecked")
799 List<? extends ForkJoinTask<?>> ts =
800 (List<? extends ForkJoinTask<?>>) tasks;
801 Throwable ex = null;
802 int last = ts.size() - 1; // nearly same as array version
803 for (int i = last; i >= 0; --i) {
804 ForkJoinTask<?> t;
805 if ((t = ts.get(i)) == null) {
806 ex = new NullPointerException();
807 break;
808 }
809 if (i == 0) {
810 int s;
811 if ((s = t.doExec()) >= 0)
812 s = t.awaitJoin(true, false, false, 0L);
813 if ((s & ABNORMAL) != 0)
814 ex = t.getException(s);
815 break;
816 }
817 t.fork();
818 }
819 if (ex == null) {
820 for (int i = 1; i <= last; ++i) {
821 ForkJoinTask<?> t;
822 if ((t = ts.get(i)) != null) {
823 int s;
824 if ((s = t.status) >= 0)
825 s = t.awaitJoin(false, false, false, 0L);
826 if ((s & ABNORMAL) != 0 && (ex = t.getException(s)) != null)
827 break;
828 }
829 }
830 }
831 if (ex != null) {
832 for (int i = 1; i <= last; ++i)
833 cancelIgnoringExceptions(ts.get(i));
834 rethrow(ex);
835 }
836 return tasks;
837 }
838
839 /**
840 * Attempts to cancel execution of this task. This attempt will
841 * fail if the task has already completed or could not be
842 * cancelled for some other reason. If successful, and this task
843 * has not started when {@code cancel} is called, execution of
844 * this task is suppressed. After this method returns
845 * successfully, unless there is an intervening call to {@link
846 * #reinitialize}, subsequent calls to {@link #isCancelled},
847 * {@link #isDone}, and {@code cancel} will return {@code true}
848 * and calls to {@link #join} and related methods will result in
849 * {@code CancellationException}.
850 *
851 * <p>This method may be overridden in subclasses, but if so, must
852 * still ensure that these properties hold. In particular, the
853 * {@code cancel} method itself must not throw exceptions.
854 *
855 * <p>This method is designed to be invoked by <em>other</em>
856 * tasks. To terminate the current task, you can just return or
857 * throw an unchecked exception from its computation method, or
858 * invoke {@link #completeExceptionally(Throwable)}.
859 *
860 * @param mayInterruptIfRunning this value has no effect in the
861 * default implementation because interrupts are not used to
862 * control cancellation.
863 *
864 * @return {@code true} if this task is now cancelled
865 */
866 public boolean cancel(boolean mayInterruptIfRunning) {
867 return (trySetCancelled() & (ABNORMAL | THROWN)) == ABNORMAL;
868 }
869
870 public final boolean isDone() {
871 return status < 0;
872 }
873
874 public final boolean isCancelled() {
875 return (status & (ABNORMAL | THROWN)) == ABNORMAL;
876 }
877
878 /**
879 * Returns {@code true} if this task threw an exception or was cancelled.
880 *
881 * @return {@code true} if this task threw an exception or was cancelled
882 */
883 public final boolean isCompletedAbnormally() {
884 return (status & ABNORMAL) != 0;
885 }
886
887 /**
888 * Returns {@code true} if this task completed without throwing an
889 * exception and was not cancelled.
890 *
891 * @return {@code true} if this task completed without throwing an
892 * exception and was not cancelled
893 */
894 public final boolean isCompletedNormally() {
895 return (status & (DONE | ABNORMAL)) == DONE;
896 }
897
898 /**
899 * Returns the exception thrown by the base computation, or a
900 * {@code CancellationException} if cancelled, or {@code null} if
901 * none or if the method has not yet completed.
902 *
903 * @return the exception, or {@code null} if none
904 */
905 public final Throwable getException() {
906 return getException(status);
907 }
908
909 /**
910 * Completes this task abnormally, and if not already aborted or
911 * cancelled, causes it to throw the given exception upon
912 * {@code join} and related operations. This method may be used
913 * to induce exceptions in asynchronous tasks, or to force
914 * completion of tasks that would not otherwise complete. Its use
915 * in other situations is discouraged. This method is
916 * overridable, but overridden versions must invoke {@code super}
917 * implementation to maintain guarantees.
918 *
919 * @param ex the exception to throw. If this exception is not a
920 * {@code RuntimeException} or {@code Error}, the actual exception
921 * thrown will be a {@code RuntimeException} with cause {@code ex}.
922 */
923 public void completeExceptionally(Throwable ex) {
924 trySetException((ex instanceof RuntimeException) ||
925 (ex instanceof Error) ? ex :
926 new RuntimeException(ex));
927 }
928
929 /**
930 * Completes this task, and if not already aborted or cancelled,
931 * returning the given value as the result of subsequent
932 * invocations of {@code join} and related operations. This method
933 * may be used to provide results for asynchronous tasks, or to
934 * provide alternative handling for tasks that would not otherwise
935 * complete normally. Its use in other situations is
936 * discouraged. This method is overridable, but overridden
937 * versions must invoke {@code super} implementation to maintain
938 * guarantees.
939 *
940 * @param value the result value for this task
941 */
942 public void complete(V value) {
943 try {
944 setRawResult(value);
945 } catch (Throwable rex) {
946 trySetException(rex);
947 return;
948 }
949 setDone();
950 }
951
952 /**
953 * Completes this task normally without setting a value. The most
954 * recent value established by {@link #setRawResult} (or {@code
955 * null} by default) will be returned as the result of subsequent
956 * invocations of {@code join} and related operations.
957 *
958 * @since 1.8
959 */
960 public final void quietlyComplete() {
961 setDone();
962 }
963
964 /**
965 * Waits if necessary for the computation to complete, and then
966 * retrieves its result.
967 *
968 * @return the computed result
969 * @throws CancellationException if the computation was cancelled
970 * @throws ExecutionException if the computation threw an
971 * exception
972 * @throws InterruptedException if the current thread is not a
973 * member of a ForkJoinPool and was interrupted while waiting
974 */
975 public final V get() throws InterruptedException, ExecutionException {
976 int s;
977 if (((s = awaitJoin(false, true, false, 0L)) & ABNORMAL) != 0)
978 reportExecutionException(s);
979 return getRawResult();
980 }
981
982 /**
983 * Waits if necessary for at most the given time for the computation
984 * to complete, and then retrieves its result, if available.
985 *
986 * @param timeout the maximum time to wait
987 * @param unit the time unit of the timeout argument
988 * @return the computed result
989 * @throws CancellationException if the computation was cancelled
990 * @throws ExecutionException if the computation threw an
991 * exception
992 * @throws InterruptedException if the current thread is not a
993 * member of a ForkJoinPool and was interrupted while waiting
994 * @throws TimeoutException if the wait timed out
995 */
996 public final V get(long timeout, TimeUnit unit)
997 throws InterruptedException, ExecutionException, TimeoutException {
998 int s;
999 if ((s = awaitJoin(false, true, true, unit.toNanos(timeout))) >= 0 ||
1000 (s & ABNORMAL) != 0)
1001 reportExecutionException(s);
1002 return getRawResult();
1003 }
1004
1005 /**
1006 * Joins this task, without returning its result or throwing its
1007 * exception. This method may be useful when processing
1008 * collections of tasks when some have been cancelled or otherwise
1009 * known to have aborted.
1010 */
1011 public final void quietlyJoin() {
1012 if (status >= 0)
1013 awaitJoin(false, false, false, 0L);
1014 }
1015
1016 /**
1017 * Commences performing this task and awaits its completion if
1018 * necessary, without returning its result or throwing its
1019 * exception.
1020 */
1021 public final void quietlyInvoke() {
1022 if (doExec() >= 0)
1023 awaitJoin(true, false, false, 0L);
1024 }
1025
1026 /**
1027 * Possibly executes tasks until the pool hosting the current task
1028 * {@linkplain ForkJoinPool#isQuiescent is quiescent}. This
1029 * method may be of use in designs in which many tasks are forked,
1030 * but none are explicitly joined, instead executing them until
1031 * all are processed.
1032 */
1033 public static void helpQuiesce() {
1034 Thread t; ForkJoinWorkerThread w; ForkJoinPool p;
1035 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread &&
1036 (p = (w = (ForkJoinWorkerThread)t).pool) != null)
1037 p.helpQuiescePool(w.workQueue, Long.MAX_VALUE, false);
1038 else
1039 ForkJoinPool.common.externalHelpQuiescePool(Long.MAX_VALUE, false);
1040 }
1041
1042 /**
1043 * Resets the internal bookkeeping state of this task, allowing a
1044 * subsequent {@code fork}. This method allows repeated reuse of
1045 * this task, but only if reuse occurs when this task has either
1046 * never been forked, or has been forked, then completed and all
1047 * outstanding joins of this task have also completed. Effects
1048 * under any other usage conditions are not guaranteed.
1049 * This method may be useful when executing
1050 * pre-constructed trees of subtasks in loops.
1051 *
1052 * <p>Upon completion of this method, {@code isDone()} reports
1053 * {@code false}, and {@code getException()} reports {@code
1054 * null}. However, the value returned by {@code getRawResult} is
1055 * unaffected. To clear this value, you can invoke {@code
1056 * setRawResult(null)}.
1057 */
1058 public void reinitialize() {
1059 aux = null;
1060 status = 0;
1061 }
1062
1063 /**
1064 * Returns the pool hosting the current thread, or {@code null}
1065 * if the current thread is executing outside of any ForkJoinPool.
1066 *
1067 * <p>This method returns {@code null} if and only if {@link
1068 * #inForkJoinPool} returns {@code false}.
1069 *
1070 * @return the pool, or {@code null} if none
1071 */
1072 public static ForkJoinPool getPool() {
1073 Thread t;
1074 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1075 ((ForkJoinWorkerThread) t).pool : null);
1076 }
1077
1078 /**
1079 * Returns {@code true} if the current thread is a {@link
1080 * ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1081 *
1082 * @return {@code true} if the current thread is a {@link
1083 * ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1084 * or {@code false} otherwise
1085 */
1086 public static boolean inForkJoinPool() {
1087 return Thread.currentThread() instanceof ForkJoinWorkerThread;
1088 }
1089
1090 /**
1091 * Tries to unschedule this task for execution. This method will
1092 * typically (but is not guaranteed to) succeed if this task is
1093 * the most recently forked task by the current thread, and has
1094 * not commenced executing in another thread. This method may be
1095 * useful when arranging alternative local processing of tasks
1096 * that could have been, but were not, stolen.
1097 *
1098 * @return {@code true} if unforked
1099 */
1100 public boolean tryUnfork() {
1101 Thread t; ForkJoinPool.WorkQueue q;
1102 return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1103 ? (q = ((ForkJoinWorkerThread)t).workQueue) != null
1104 && q.tryUnpush(this)
1105 : (q = ForkJoinPool.commonQueue()) != null
1106 && q.externalTryUnpush(this);
1107 }
1108
1109 /**
1110 * Returns an estimate of the number of tasks that have been
1111 * forked by the current worker thread but not yet executed. This
1112 * value may be useful for heuristic decisions about whether to
1113 * fork other tasks.
1114 *
1115 * @return the number of tasks
1116 */
1117 public static int getQueuedTaskCount() {
1118 Thread t; ForkJoinPool.WorkQueue q;
1119 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1120 q = ((ForkJoinWorkerThread)t).workQueue;
1121 else
1122 q = ForkJoinPool.commonQueue();
1123 return (q == null) ? 0 : q.queueSize();
1124 }
1125
1126 /**
1127 * Returns an estimate of how many more locally queued tasks are
1128 * held by the current worker thread than there are other worker
1129 * threads that might steal them, or zero if this thread is not
1130 * operating in a ForkJoinPool. This value may be useful for
1131 * heuristic decisions about whether to fork other tasks. In many
1132 * usages of ForkJoinTasks, at steady state, each worker should
1133 * aim to maintain a small constant surplus (for example, 3) of
1134 * tasks, and to process computations locally if this threshold is
1135 * exceeded.
1136 *
1137 * @return the surplus number of tasks, which may be negative
1138 */
1139 public static int getSurplusQueuedTaskCount() {
1140 return ForkJoinPool.getSurplusQueuedTaskCount();
1141 }
1142
1143 // Extension methods
1144
1145 /**
1146 * Returns the result that would be returned by {@link #join}, even
1147 * if this task completed abnormally, or {@code null} if this task
1148 * is not known to have been completed. This method is designed
1149 * to aid debugging, as well as to support extensions. Its use in
1150 * any other context is discouraged.
1151 *
1152 * @return the result, or {@code null} if not completed
1153 */
1154 public abstract V getRawResult();
1155
1156 /**
1157 * Forces the given value to be returned as a result. This method
1158 * is designed to support extensions, and should not in general be
1159 * called otherwise.
1160 *
1161 * @param value the value
1162 */
1163 protected abstract void setRawResult(V value);
1164
1165 /**
1166 * Immediately performs the base action of this task and returns
1167 * true if, upon return from this method, this task is guaranteed
1168 * to have completed. This method may return false otherwise, to
1169 * indicate that this task is not necessarily complete (or is not
1170 * known to be complete), for example in asynchronous actions that
1171 * require explicit invocations of completion methods. This method
1172 * may also throw an (unchecked) exception to indicate abnormal
1173 * exit. This method is designed to support extensions, and should
1174 * not in general be called otherwise.
1175 *
1176 * @return {@code true} if this task is known to have completed normally
1177 */
1178 protected abstract boolean exec();
1179
1180 /**
1181 * Returns, but does not unschedule or execute, a task queued by
1182 * the current thread but not yet executed, if one is immediately
1183 * available. There is no guarantee that this task will actually
1184 * be polled or executed next. Conversely, this method may return
1185 * null even if a task exists but cannot be accessed without
1186 * contention with other threads. This method is designed
1187 * primarily to support extensions, and is unlikely to be useful
1188 * otherwise.
1189 *
1190 * @return the next task, or {@code null} if none are available
1191 */
1192 protected static ForkJoinTask<?> peekNextLocalTask() {
1193 Thread t; ForkJoinPool.WorkQueue q;
1194 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1195 q = ((ForkJoinWorkerThread)t).workQueue;
1196 else
1197 q = ForkJoinPool.commonQueue();
1198 return (q == null) ? null : q.peek();
1199 }
1200
1201 /**
1202 * Unschedules and returns, without executing, the next task
1203 * queued by the current thread but not yet executed, if the
1204 * current thread is operating in a ForkJoinPool. This method is
1205 * designed primarily to support extensions, and is unlikely to be
1206 * useful otherwise.
1207 *
1208 * @return the next task, or {@code null} if none are available
1209 */
1210 protected static ForkJoinTask<?> pollNextLocalTask() {
1211 Thread t;
1212 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1213 ((ForkJoinWorkerThread)t).workQueue.nextLocalTask() : null);
1214 }
1215
1216 /**
1217 * If the current thread is operating in a ForkJoinPool,
1218 * unschedules and returns, without executing, the next task
1219 * queued by the current thread but not yet executed, if one is
1220 * available, or if not available, a task that was forked by some
1221 * other thread, if available. Availability may be transient, so a
1222 * {@code null} result does not necessarily imply quiescence of
1223 * the pool this task is operating in. This method is designed
1224 * primarily to support extensions, and is unlikely to be useful
1225 * otherwise.
1226 *
1227 * @return a task, or {@code null} if none are available
1228 */
1229 protected static ForkJoinTask<?> pollTask() {
1230 Thread t; ForkJoinWorkerThread w;
1231 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1232 (w = (ForkJoinWorkerThread)t).pool.nextTaskFor(w.workQueue) :
1233 null);
1234 }
1235
1236 /**
1237 * If the current thread is operating in a ForkJoinPool,
1238 * unschedules and returns, without executing, a task externally
1239 * submitted to the pool, if one is available. Availability may be
1240 * transient, so a {@code null} result does not necessarily imply
1241 * quiescence of the pool. This method is designed primarily to
1242 * support extensions, and is unlikely to be useful otherwise.
1243 *
1244 * @return a task, or {@code null} if none are available
1245 * @since 9
1246 */
1247 protected static ForkJoinTask<?> pollSubmission() {
1248 Thread t;
1249 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1250 ((ForkJoinWorkerThread)t).pool.pollSubmission() : null);
1251 }
1252
1253 // tag operations
1254
1255 /**
1256 * Returns the tag for this task.
1257 *
1258 * @return the tag for this task
1259 * @since 1.8
1260 */
1261 public final short getForkJoinTaskTag() {
1262 return (short)status;
1263 }
1264
1265 /**
1266 * Atomically sets the tag value for this task and returns the old value.
1267 *
1268 * @param newValue the new tag value
1269 * @return the previous value of the tag
1270 * @since 1.8
1271 */
1272 public final short setForkJoinTaskTag(short newValue) {
1273 for (int s;;) {
1274 if (casStatus(s = status, (s & ~SMASK) | (newValue & SMASK)))
1275 return (short)s;
1276 }
1277 }
1278
1279 /**
1280 * Atomically conditionally sets the tag value for this task.
1281 * Among other applications, tags can be used as visit markers
1282 * in tasks operating on graphs, as in methods that check: {@code
1283 * if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1284 * before processing, otherwise exiting because the node has
1285 * already been visited.
1286 *
1287 * @param expect the expected tag value
1288 * @param update the new tag value
1289 * @return {@code true} if successful; i.e., the current value was
1290 * equal to {@code expect} and was changed to {@code update}.
1291 * @since 1.8
1292 */
1293 public final boolean compareAndSetForkJoinTaskTag(short expect, short update) {
1294 for (int s;;) {
1295 if ((short)(s = status) != expect)
1296 return false;
1297 if (casStatus(s, (s & ~SMASK) | (update & SMASK)))
1298 return true;
1299 }
1300 }
1301
1302 /**
1303 * Adapter for Runnables. This implements RunnableFuture
1304 * to be compliant with AbstractExecutorService constraints
1305 * when used in ForkJoinPool.
1306 */
1307 static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1308 implements RunnableFuture<T> {
1309 @SuppressWarnings("serial") // Conditionally serializable
1310 final Runnable runnable;
1311 @SuppressWarnings("serial") // Conditionally serializable
1312 T result;
1313 AdaptedRunnable(Runnable runnable, T result) {
1314 if (runnable == null) throw new NullPointerException();
1315 this.runnable = runnable;
1316 this.result = result; // OK to set this even before completion
1317 }
1318 public final T getRawResult() { return result; }
1319 public final void setRawResult(T v) { result = v; }
1320 public final boolean exec() { runnable.run(); return true; }
1321 public final void run() { invoke(); }
1322 public String toString() {
1323 return super.toString() + "[Wrapped task = " + runnable + "]";
1324 }
1325 private static final long serialVersionUID = 5232453952276885070L;
1326 }
1327
1328 /**
1329 * Adapter for Runnables without results.
1330 */
1331 static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1332 implements RunnableFuture<Void> {
1333 @SuppressWarnings("serial") // Conditionally serializable
1334 final Runnable runnable;
1335 AdaptedRunnableAction(Runnable runnable) {
1336 if (runnable == null) throw new NullPointerException();
1337 this.runnable = runnable;
1338 }
1339 public final Void getRawResult() { return null; }
1340 public final void setRawResult(Void v) { }
1341 public final boolean exec() { runnable.run(); return true; }
1342 public final void run() { invoke(); }
1343 public String toString() {
1344 return super.toString() + "[Wrapped task = " + runnable + "]";
1345 }
1346 private static final long serialVersionUID = 5232453952276885070L;
1347 }
1348
1349 /**
1350 * Adapter for Runnables in which failure forces worker exception.
1351 */
1352 static final class RunnableExecuteAction extends ForkJoinTask<Void> {
1353 @SuppressWarnings("serial") // Conditionally serializable
1354 final Runnable runnable;
1355 RunnableExecuteAction(Runnable runnable) {
1356 if (runnable == null) throw new NullPointerException();
1357 this.runnable = runnable;
1358 }
1359 public final Void getRawResult() { return null; }
1360 public final void setRawResult(Void v) { }
1361 public final boolean exec() { runnable.run(); return true; }
1362 int trySetException(Throwable ex) { // if a handler, invoke it
1363 int s; Thread t; java.lang.Thread.UncaughtExceptionHandler h;
1364 if (isExceptionalStatus(s = trySetThrown(ex)) &&
1365 (h = ((t = Thread.currentThread()).
1366 getUncaughtExceptionHandler())) != null) {
1367 try {
1368 h.uncaughtException(t, ex);
1369 } catch (Throwable ignore) {
1370 }
1371 }
1372 return s;
1373 }
1374 private static final long serialVersionUID = 5232453952276885070L;
1375 }
1376
1377 /**
1378 * Adapter for Callables.
1379 */
1380 static final class AdaptedCallable<T> extends ForkJoinTask<T>
1381 implements RunnableFuture<T> {
1382 @SuppressWarnings("serial") // Conditionally serializable
1383 final Callable<? extends T> callable;
1384 @SuppressWarnings("serial") // Conditionally serializable
1385 T result;
1386 AdaptedCallable(Callable<? extends T> callable) {
1387 if (callable == null) throw new NullPointerException();
1388 this.callable = callable;
1389 }
1390 public final T getRawResult() { return result; }
1391 public final void setRawResult(T v) { result = v; }
1392 public final boolean exec() {
1393 try {
1394 result = callable.call();
1395 return true;
1396 } catch (RuntimeException rex) {
1397 throw rex;
1398 } catch (Exception ex) {
1399 throw new RuntimeException(ex);
1400 }
1401 }
1402 public final void run() { invoke(); }
1403 public String toString() {
1404 return super.toString() + "[Wrapped task = " + callable + "]";
1405 }
1406 private static final long serialVersionUID = 2838392045355241008L;
1407 }
1408
1409 static final class AdaptedInterruptibleCallable<T> extends ForkJoinTask<T>
1410 implements RunnableFuture<T> {
1411 @SuppressWarnings("serial") // Conditionally serializable
1412 final Callable<? extends T> callable;
1413 @SuppressWarnings("serial") // Conditionally serializable
1414 transient volatile Thread runner;
1415 T result;
1416 AdaptedInterruptibleCallable(Callable<? extends T> callable) {
1417 if (callable == null) throw new NullPointerException();
1418 this.callable = callable;
1419 }
1420 public final T getRawResult() { return result; }
1421 public final void setRawResult(T v) { result = v; }
1422 public final boolean exec() {
1423 Thread.interrupted();
1424 runner = Thread.currentThread();
1425 try {
1426 if (!isDone()) // recheck
1427 result = callable.call();
1428 return true;
1429 } catch (RuntimeException rex) {
1430 throw rex;
1431 } catch (Exception ex) {
1432 throw new RuntimeException(ex);
1433 } finally {
1434 runner = null;
1435 Thread.interrupted();
1436 }
1437 }
1438 public final void run() { invoke(); }
1439 public final boolean cancel(boolean mayInterruptIfRunning) {
1440 Thread t;
1441 boolean stat = super.cancel(false);
1442 if (mayInterruptIfRunning && (t = runner) != null) {
1443 try {
1444 t.interrupt();
1445 } catch (Throwable ignore) {
1446 }
1447 }
1448 return stat;
1449 }
1450 public String toString() {
1451 return super.toString() + "[Wrapped task = " + callable + "]";
1452 }
1453 private static final long serialVersionUID = 2838392045355241008L;
1454 }
1455
1456 /**
1457 * Returns a new {@code ForkJoinTask} that performs the {@code run}
1458 * method of the given {@code Runnable} as its action, and returns
1459 * a null result upon {@link #join}.
1460 *
1461 * @param runnable the runnable action
1462 * @return the task
1463 */
1464 public static ForkJoinTask<?> adapt(Runnable runnable) {
1465 return new AdaptedRunnableAction(runnable);
1466 }
1467
1468 /**
1469 * Returns a new {@code ForkJoinTask} that performs the {@code run}
1470 * method of the given {@code Runnable} as its action, and returns
1471 * the given result upon {@link #join}.
1472 *
1473 * @param runnable the runnable action
1474 * @param result the result upon completion
1475 * @param <T> the type of the result
1476 * @return the task
1477 */
1478 public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1479 return new AdaptedRunnable<T>(runnable, result);
1480 }
1481
1482 /**
1483 * Returns a new {@code ForkJoinTask} that performs the {@code call}
1484 * method of the given {@code Callable} as its action, and returns
1485 * its result upon {@link #join}, translating any checked exceptions
1486 * encountered into {@code RuntimeException}.
1487 *
1488 * @param callable the callable action
1489 * @param <T> the type of the callable's result
1490 * @return the task
1491 */
1492 public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1493 return new AdaptedCallable<T>(callable);
1494 }
1495
1496 /**
1497 * Returns a new {@code ForkJoinTask} that performs the {@code call}
1498 * method of the given {@code Callable} as its action, and returns
1499 * its result upon {@link #join}, translating any checked exceptions
1500 * encountered into {@code RuntimeException}. Additionally,
1501 * invocations of {@code cancel} with {@code mayInterruptIfRunning
1502 * true} will attempt to interrupt the thread performing the task.
1503 *
1504 * @param callable the callable action
1505 * @param <T> the type of the callable's result
1506 * @return the task
1507 *
1508 * @since 17
1509 */
1510 // adaptInterruptible deferred to its own independent change
1511 // https://bugs.openjdk.java.net/browse/JDK-8246587
1512 /* TODO: public */ private static <T> ForkJoinTask<T> adaptInterruptible(Callable<? extends T> callable) {
1513 return new AdaptedInterruptibleCallable<T>(callable);
1514 }
1515
1516 // Serialization support
1517
1518 private static final long serialVersionUID = -7721805057305804111L;
1519
1520 /**
1521 * Saves this task to a stream (that is, serializes it).
1522 *
1523 * @param s the stream
1524 * @throws java.io.IOException if an I/O error occurs
1525 * @serialData the current run status and the exception thrown
1526 * during execution, or {@code null} if none
1527 */
1528 private void writeObject(java.io.ObjectOutputStream s)
1529 throws java.io.IOException {
1530 Aux a;
1531 s.defaultWriteObject();
1532 s.writeObject((a = aux) == null ? null : a.ex);
1533 }
1534
1535 /**
1536 * Reconstitutes this task from a stream (that is, deserializes it).
1537 * @param s the stream
1538 * @throws ClassNotFoundException if the class of a serialized object
1539 * could not be found
1540 * @throws java.io.IOException if an I/O error occurs
1541 */
1542 private void readObject(java.io.ObjectInputStream s)
1543 throws java.io.IOException, ClassNotFoundException {
1544 s.defaultReadObject();
1545 Object ex = s.readObject();
1546 if (ex != null)
1547 trySetThrown((Throwable)ex);
1548 }
1549
1550 static {
1551 try {
1552 MethodHandles.Lookup l = MethodHandles.lookup();
1553 STATUS = l.findVarHandle(ForkJoinTask.class, "status", int.class);
1554 AUX = l.findVarHandle(ForkJoinTask.class, "aux", Aux.class);
1555 } catch (ReflectiveOperationException e) {
1556 throw new ExceptionInInitializerError(e);
1557 }
1558 }
1559
1560 }