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