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 static boolean isExceptionalStatus(int s) { // needed by subclasses
246 return (s & THROWN) != 0;
247 }
248
249 /**
250 * Sets DONE status and wakes up threads waiting to join this task.
251 *
252 * @return status on exit
253 */
254 private int setDone() {
255 int s;
256 if (((s = (int)STATUS.getAndBitwiseOr(this, DONE)) & SIGNAL) != 0)
257 synchronized (this) { notifyAll(); }
258 return s | DONE;
259 }
260
261 /**
262 * Marks cancelled or exceptional completion unless already done.
263 *
264 * @param completion must be DONE | ABNORMAL, ORed with THROWN if exceptional
265 * @return status on exit
266 */
267 private int abnormalCompletion(int completion) {
268 for (int s, ns;;) {
269 if ((s = status) < 0)
270 return s;
271 else if (STATUS.weakCompareAndSet(this, s, ns = s | completion)) {
272 if ((s & SIGNAL) != 0)
273 synchronized (this) { notifyAll(); }
274 return ns;
275 }
276 }
277 }
278
279 /**
280 * Primary execution method for stolen tasks. Unless done, calls
281 * exec and records status if completed, but doesn't wait for
282 * completion otherwise.
283 *
284 * @return status on exit from this method
285 */
286 final int doExec() {
287 int s; boolean completed;
288 if ((s = status) >= 0) {
289 try {
290 completed = exec();
291 } catch (Throwable rex) {
292 completed = false;
293 s = setExceptionalCompletion(rex);
294 }
295 if (completed)
296 s = setDone();
297 }
298 return s;
299 }
300
301 /**
302 * If not done, sets SIGNAL status and performs Object.wait(timeout).
303 * This task may or may not be done on exit. Ignores interrupts.
304 *
305 * @param timeout using Object.wait conventions.
306 */
307 final void internalWait(long timeout) {
308 if ((int)STATUS.getAndBitwiseOr(this, SIGNAL) >= 0) {
309 synchronized (this) {
310 if (status >= 0)
311 try { wait(timeout); } catch (InterruptedException ie) { }
312 else
313 notifyAll();
314 }
315 }
316 }
317
318 /**
319 * Blocks a non-worker-thread until completion.
320 * @return status upon completion
321 */
322 private int externalAwaitDone() {
323 int s = tryExternalHelp();
324 if (s >= 0 && (s = (int)STATUS.getAndBitwiseOr(this, SIGNAL)) >= 0) {
325 boolean interrupted = false;
326 synchronized (this) {
327 for (;;) {
328 if ((s = status) >= 0) {
329 try {
330 wait(0L);
331 } catch (InterruptedException ie) {
332 interrupted = true;
333 }
334 }
335 else {
336 notifyAll();
337 break;
338 }
339 }
340 }
341 if (interrupted)
342 Thread.currentThread().interrupt();
343 }
344 return s;
345 }
346
347 /**
348 * Blocks a non-worker-thread until completion or interruption.
349 */
350 private int externalInterruptibleAwaitDone() throws InterruptedException {
351 int s = tryExternalHelp();
352 if (s >= 0 && (s = (int)STATUS.getAndBitwiseOr(this, SIGNAL)) >= 0) {
353 synchronized (this) {
354 for (;;) {
355 if ((s = status) >= 0)
356 wait(0L);
357 else {
358 notifyAll();
359 break;
360 }
361 }
362 }
363 }
364 else if (Thread.interrupted())
365 throw new InterruptedException();
366 return s;
367 }
368
369 /**
370 * Tries to help with tasks allowed for external callers.
371 *
372 * @return current status
373 */
374 private int tryExternalHelp() {
375 int s;
376 return ((s = status) < 0 ? s:
377 (this instanceof CountedCompleter) ?
378 ForkJoinPool.common.externalHelpComplete(
379 (CountedCompleter<?>)this, 0) :
380 ForkJoinPool.common.tryExternalUnpush(this) ?
381 doExec() : 0);
382 }
383
384 /**
385 * Implementation for join, get, quietlyJoin. Directly handles
386 * only cases of already-completed, external wait, and
387 * unfork+exec. Others are relayed to ForkJoinPool.awaitJoin.
388 *
389 * @return status upon completion
390 */
391 private int doJoin() {
392 int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
393 return (s = status) < 0 ? s :
394 ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
395 (w = (wt = (ForkJoinWorkerThread)t).workQueue).
396 tryUnpush(this) && (s = doExec()) < 0 ? s :
397 wt.pool.awaitJoin(w, this, 0L) :
398 externalAwaitDone();
399 }
400
401 /**
402 * Implementation for invoke, quietlyInvoke.
403 *
404 * @return status upon completion
405 */
406 private int doInvoke() {
407 int s; Thread t; ForkJoinWorkerThread wt;
408 return (s = doExec()) < 0 ? s :
409 ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
410 (wt = (ForkJoinWorkerThread)t).pool.
411 awaitJoin(wt.workQueue, this, 0L) :
412 externalAwaitDone();
413 }
414
415 // Exception table support
416
417 /**
418 * Hash table of exceptions thrown by tasks, to enable reporting
419 * by callers. Because exceptions are rare, we don't directly keep
420 * them with task objects, but instead use a weak ref table. Note
421 * that cancellation exceptions don't appear in the table, but are
422 * instead recorded as status values.
423 *
424 * The exception table has a fixed capacity.
425 */
426 private static final ExceptionNode[] exceptionTable
427 = new ExceptionNode[32];
428
429 /** Lock protecting access to exceptionTable. */
430 private static final ReentrantLock exceptionTableLock
431 = new ReentrantLock();
432
433 /** Reference queue of stale exceptionally completed tasks. */
434 private static final ReferenceQueue<ForkJoinTask<?>> exceptionTableRefQueue
435 = new ReferenceQueue<>();
436
437 /**
438 * Key-value nodes for exception table. The chained hash table
439 * uses identity comparisons, full locking, and weak references
440 * for keys. The table has a fixed capacity because it only
441 * maintains task exceptions long enough for joiners to access
442 * them, so should never become very large for sustained
443 * periods. However, since we do not know when the last joiner
444 * completes, we must use weak references and expunge them. We do
445 * so on each operation (hence full locking). Also, some thread in
446 * any ForkJoinPool will call helpExpungeStaleExceptions when its
447 * pool becomes isQuiescent.
448 */
449 static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
450 final Throwable ex;
451 ExceptionNode next;
452 final long thrower; // use id not ref to avoid weak cycles
453 final int hashCode; // store task hashCode before weak ref disappears
454 ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next,
455 ReferenceQueue<ForkJoinTask<?>> exceptionTableRefQueue) {
456 super(task, exceptionTableRefQueue);
457 this.ex = ex;
458 this.next = next;
459 this.thrower = Thread.currentThread().getId();
460 this.hashCode = System.identityHashCode(task);
461 }
462 }
463
464 /**
465 * Records exception and sets status.
466 *
467 * @return status on exit
468 */
469 final int recordExceptionalCompletion(Throwable ex) {
470 int s;
471 if ((s = status) >= 0) {
472 int h = System.identityHashCode(this);
473 final ReentrantLock lock = exceptionTableLock;
474 lock.lock();
475 try {
476 expungeStaleExceptions();
477 ExceptionNode[] t = exceptionTable;
478 int i = h & (t.length - 1);
479 for (ExceptionNode e = t[i]; ; e = e.next) {
480 if (e == null) {
481 t[i] = new ExceptionNode(this, ex, t[i],
482 exceptionTableRefQueue);
483 break;
484 }
485 if (e.get() == this) // already present
486 break;
487 }
488 } finally {
489 lock.unlock();
490 }
491 s = abnormalCompletion(DONE | ABNORMAL | THROWN);
492 }
493 return s;
494 }
495
496 /**
497 * Records exception and possibly propagates.
498 *
499 * @return status on exit
500 */
501 private int setExceptionalCompletion(Throwable ex) {
502 int s = recordExceptionalCompletion(ex);
503 if ((s & THROWN) != 0)
504 internalPropagateException(ex);
505 return s;
506 }
507
508 /**
509 * Hook for exception propagation support for tasks with completers.
510 */
511 void internalPropagateException(Throwable ex) {
512 }
513
514 /**
515 * Cancels, ignoring any exceptions thrown by cancel. Used during
516 * worker and pool shutdown. Cancel is spec'ed not to throw any
517 * exceptions, but if it does anyway, we have no recourse during
518 * shutdown, so guard against this case.
519 */
520 static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
521 if (t != null && t.status >= 0) {
522 try {
523 t.cancel(false);
524 } catch (Throwable ignore) {
525 }
526 }
527 }
528
529 /**
530 * Removes exception node and clears status.
531 */
532 private void clearExceptionalCompletion() {
533 int h = System.identityHashCode(this);
534 final ReentrantLock lock = exceptionTableLock;
535 lock.lock();
536 try {
537 ExceptionNode[] t = exceptionTable;
538 int i = h & (t.length - 1);
539 ExceptionNode e = t[i];
540 ExceptionNode pred = null;
541 while (e != null) {
542 ExceptionNode next = e.next;
543 if (e.get() == this) {
544 if (pred == null)
545 t[i] = next;
546 else
547 pred.next = next;
548 break;
549 }
550 pred = e;
551 e = next;
552 }
553 expungeStaleExceptions();
554 status = 0;
555 } finally {
556 lock.unlock();
557 }
558 }
559
560 /**
561 * Returns a rethrowable exception for this task, if available.
562 * To provide accurate stack traces, if the exception was not
563 * thrown by the current thread, we try to create a new exception
564 * of the same type as the one thrown, but with the recorded
565 * exception as its cause. If there is no such constructor, we
566 * instead try to use a no-arg constructor, followed by initCause,
567 * to the same effect. If none of these apply, or any fail due to
568 * other exceptions, we return the recorded exception, which is
569 * still correct, although it may contain a misleading stack
570 * trace.
571 *
572 * @return the exception, or null if none
573 */
574 private Throwable getThrowableException() {
575 int h = System.identityHashCode(this);
576 ExceptionNode e;
577 final ReentrantLock lock = exceptionTableLock;
578 lock.lock();
579 try {
580 expungeStaleExceptions();
581 ExceptionNode[] t = exceptionTable;
582 e = t[h & (t.length - 1)];
583 while (e != null && e.get() != this)
584 e = e.next;
585 } finally {
586 lock.unlock();
587 }
588 Throwable ex;
589 if (e == null || (ex = e.ex) == null)
590 return null;
591 if (e.thrower != Thread.currentThread().getId()) {
592 try {
593 Constructor<?> noArgCtor = null;
594 // public ctors only
595 for (Constructor<?> c : ex.getClass().getConstructors()) {
596 Class<?>[] ps = c.getParameterTypes();
597 if (ps.length == 0)
598 noArgCtor = c;
599 else if (ps.length == 1 && ps[0] == Throwable.class)
600 return (Throwable)c.newInstance(ex);
601 }
602 if (noArgCtor != null) {
603 Throwable wx = (Throwable)noArgCtor.newInstance();
604 wx.initCause(ex);
605 return wx;
606 }
607 } catch (Exception ignore) {
608 }
609 }
610 return ex;
611 }
612
613 /**
614 * Polls stale refs and removes them. Call only while holding lock.
615 */
616 private static void expungeStaleExceptions() {
617 for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
618 if (x instanceof ExceptionNode) {
619 ExceptionNode[] t = exceptionTable;
620 int i = ((ExceptionNode)x).hashCode & (t.length - 1);
621 ExceptionNode e = t[i];
622 ExceptionNode pred = null;
623 while (e != null) {
624 ExceptionNode next = e.next;
625 if (e == x) {
626 if (pred == null)
627 t[i] = next;
628 else
629 pred.next = next;
630 break;
631 }
632 pred = e;
633 e = next;
634 }
635 }
636 }
637 }
638
639 /**
640 * If lock is available, polls stale refs and removes them.
641 * Called from ForkJoinPool when pools become quiescent.
642 */
643 static final void helpExpungeStaleExceptions() {
644 final ReentrantLock lock = exceptionTableLock;
645 if (lock.tryLock()) {
646 try {
647 expungeStaleExceptions();
648 } finally {
649 lock.unlock();
650 }
651 }
652 }
653
654 /**
655 * A version of "sneaky throw" to relay exceptions.
656 */
657 static void rethrow(Throwable ex) {
658 ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
659 }
660
661 /**
662 * The sneaky part of sneaky throw, relying on generics
663 * limitations to evade compiler complaints about rethrowing
664 * unchecked exceptions.
665 */
666 @SuppressWarnings("unchecked") static <T extends Throwable>
667 void uncheckedThrow(Throwable t) throws T {
668 if (t != null)
669 throw (T)t; // rely on vacuous cast
670 else
671 throw new Error("Unknown Exception");
672 }
673
674 /**
675 * Throws exception, if any, associated with the given status.
676 */
677 private void reportException(int s) {
678 rethrow((s & THROWN) != 0 ? getThrowableException() :
679 new CancellationException());
680 }
681
682 // public methods
683
684 /**
685 * Arranges to asynchronously execute this task in the pool the
686 * current task is running in, if applicable, or using the {@link
687 * ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. While
688 * it is not necessarily enforced, it is a usage error to fork a
689 * task more than once unless it has completed and been
690 * reinitialized. Subsequent modifications to the state of this
691 * task or any data it operates on are not necessarily
692 * consistently observable by any thread other than the one
693 * executing it unless preceded by a call to {@link #join} or
694 * related methods, or a call to {@link #isDone} returning {@code
695 * true}.
696 *
697 * @return {@code this}, to simplify usage
698 */
699 public final ForkJoinTask<V> fork() {
700 Thread t;
701 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
702 ((ForkJoinWorkerThread)t).workQueue.push(this);
703 else
704 ForkJoinPool.common.externalPush(this);
705 return this;
706 }
707
708 /**
709 * Returns the result of the computation when it
710 * {@linkplain #isDone is done}.
711 * This method differs from {@link #get()} in that abnormal
712 * completion results in {@code RuntimeException} or {@code Error},
713 * not {@code ExecutionException}, and that interrupts of the
714 * calling thread do <em>not</em> cause the method to abruptly
715 * return by throwing {@code InterruptedException}.
716 *
717 * @return the computed result
718 */
719 public final V join() {
720 int s;
721 if (((s = doJoin()) & ABNORMAL) != 0)
722 reportException(s);
723 return getRawResult();
724 }
725
726 /**
727 * Commences performing this task, awaits its completion if
728 * necessary, and returns its result, or throws an (unchecked)
729 * {@code RuntimeException} or {@code Error} if the underlying
730 * computation did so.
731 *
732 * @return the computed result
733 */
734 public final V invoke() {
735 int s;
736 if (((s = doInvoke()) & ABNORMAL) != 0)
737 reportException(s);
738 return getRawResult();
739 }
740
741 /**
742 * Forks the given tasks, returning when {@code isDone} holds for
743 * each task or an (unchecked) exception is encountered, in which
744 * case the exception is rethrown. If more than one task
745 * encounters an exception, then this method throws any one of
746 * these exceptions. If any task encounters an exception, the
747 * other may be cancelled. However, the execution status of
748 * individual tasks is not guaranteed upon exceptional return. The
749 * status of each task may be obtained using {@link
750 * #getException()} and related methods to check if they have been
751 * cancelled, completed normally or exceptionally, or left
752 * unprocessed.
753 *
754 * @param t1 the first task
755 * @param t2 the second task
756 * @throws NullPointerException if any task is null
757 */
758 public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
759 int s1, s2;
760 t2.fork();
761 if (((s1 = t1.doInvoke()) & ABNORMAL) != 0)
762 t1.reportException(s1);
763 if (((s2 = t2.doJoin()) & ABNORMAL) != 0)
764 t2.reportException(s2);
765 }
766
767 /**
768 * Forks the given tasks, returning when {@code isDone} holds for
769 * each task or an (unchecked) exception is encountered, in which
770 * case the exception is rethrown. If more than one task
771 * encounters an exception, then this method throws any one of
772 * these exceptions. If any task encounters an exception, others
773 * may be cancelled. However, the execution status of individual
774 * tasks is not guaranteed upon exceptional return. The status of
775 * each task may be obtained using {@link #getException()} and
776 * related methods to check if they have been cancelled, completed
777 * normally or exceptionally, or left unprocessed.
778 *
779 * @param tasks the tasks
780 * @throws NullPointerException if any task is null
781 */
782 public static void invokeAll(ForkJoinTask<?>... tasks) {
783 Throwable ex = null;
784 int last = tasks.length - 1;
785 for (int i = last; i >= 0; --i) {
786 ForkJoinTask<?> t = tasks[i];
787 if (t == null) {
788 if (ex == null)
789 ex = new NullPointerException();
790 }
791 else if (i != 0)
792 t.fork();
793 else if ((t.doInvoke() & ABNORMAL) != 0 && ex == null)
794 ex = t.getException();
795 }
796 for (int i = 1; i <= last; ++i) {
797 ForkJoinTask<?> t = tasks[i];
798 if (t != null) {
799 if (ex != null)
800 t.cancel(false);
801 else if ((t.doJoin() & ABNORMAL) != 0)
802 ex = t.getException();
803 }
804 }
805 if (ex != null)
806 rethrow(ex);
807 }
808
809 /**
810 * Forks all tasks in the specified collection, returning when
811 * {@code isDone} holds for each task or an (unchecked) exception
812 * is encountered, in which case the exception is rethrown. If
813 * more than one task encounters an exception, then this method
814 * throws any one of these exceptions. If any task encounters an
815 * exception, others may be cancelled. However, the execution
816 * status of individual tasks is not guaranteed upon exceptional
817 * return. The status of each task may be obtained using {@link
818 * #getException()} and related methods to check if they have been
819 * cancelled, completed normally or exceptionally, or left
820 * unprocessed.
821 *
822 * @param tasks the collection of tasks
823 * @param <T> the type of the values returned from the tasks
824 * @return the tasks argument, to simplify usage
825 * @throws NullPointerException if tasks or any element are null
826 */
827 public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
828 if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
829 invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
830 return tasks;
831 }
832 @SuppressWarnings("unchecked")
833 List<? extends ForkJoinTask<?>> ts =
834 (List<? extends ForkJoinTask<?>>) tasks;
835 Throwable ex = null;
836 int last = ts.size() - 1;
837 for (int i = last; i >= 0; --i) {
838 ForkJoinTask<?> t = ts.get(i);
839 if (t == null) {
840 if (ex == null)
841 ex = new NullPointerException();
842 }
843 else if (i != 0)
844 t.fork();
845 else if ((t.doInvoke() & ABNORMAL) != 0 && ex == null)
846 ex = t.getException();
847 }
848 for (int i = 1; i <= last; ++i) {
849 ForkJoinTask<?> t = ts.get(i);
850 if (t != null) {
851 if (ex != null)
852 t.cancel(false);
853 else if ((t.doJoin() & ABNORMAL) != 0)
854 ex = t.getException();
855 }
856 }
857 if (ex != null)
858 rethrow(ex);
859 return tasks;
860 }
861
862 /**
863 * Attempts to cancel execution of this task. This attempt will
864 * fail if the task has already completed or could not be
865 * cancelled for some other reason. If successful, and this task
866 * has not started when {@code cancel} is called, execution of
867 * this task is suppressed. After this method returns
868 * successfully, unless there is an intervening call to {@link
869 * #reinitialize}, subsequent calls to {@link #isCancelled},
870 * {@link #isDone}, and {@code cancel} will return {@code true}
871 * and calls to {@link #join} and related methods will result in
872 * {@code CancellationException}.
873 *
874 * <p>This method may be overridden in subclasses, but if so, must
875 * still ensure that these properties hold. In particular, the
876 * {@code cancel} method itself must not throw exceptions.
877 *
878 * <p>This method is designed to be invoked by <em>other</em>
879 * tasks. To terminate the current task, you can just return or
880 * throw an unchecked exception from its computation method, or
881 * invoke {@link #completeExceptionally(Throwable)}.
882 *
883 * @param mayInterruptIfRunning this value has no effect in the
884 * default implementation because interrupts are not used to
885 * control cancellation.
886 *
887 * @return {@code true} if this task is now cancelled
888 */
889 public boolean cancel(boolean mayInterruptIfRunning) {
890 int s = abnormalCompletion(DONE | ABNORMAL);
891 return (s & (ABNORMAL | THROWN)) == ABNORMAL;
892 }
893
894 public final boolean isDone() {
895 return status < 0;
896 }
897
898 public final boolean isCancelled() {
899 return (status & (ABNORMAL | THROWN)) == ABNORMAL;
900 }
901
902 /**
903 * Returns {@code true} if this task threw an exception or was cancelled.
904 *
905 * @return {@code true} if this task threw an exception or was cancelled
906 */
907 public final boolean isCompletedAbnormally() {
908 return (status & ABNORMAL) != 0;
909 }
910
911 /**
912 * Returns {@code true} if this task completed without throwing an
913 * exception and was not cancelled.
914 *
915 * @return {@code true} if this task completed without throwing an
916 * exception and was not cancelled
917 */
918 public final boolean isCompletedNormally() {
919 return (status & (DONE | ABNORMAL)) == DONE;
920 }
921
922 /**
923 * Returns the exception thrown by the base computation, or a
924 * {@code CancellationException} if cancelled, or {@code null} if
925 * none or if the method has not yet completed.
926 *
927 * @return the exception, or {@code null} if none
928 */
929 public final Throwable getException() {
930 int s = status;
931 return ((s & ABNORMAL) == 0 ? null :
932 (s & THROWN) == 0 ? new CancellationException() :
933 getThrowableException());
934 }
935
936 /**
937 * Completes this task abnormally, and if not already aborted or
938 * cancelled, causes it to throw the given exception upon
939 * {@code join} and related operations. This method may be used
940 * to induce exceptions in asynchronous tasks, or to force
941 * completion of tasks that would not otherwise complete. Its use
942 * in other situations is discouraged. This method is
943 * overridable, but overridden versions must invoke {@code super}
944 * implementation to maintain guarantees.
945 *
946 * @param ex the exception to throw. If this exception is not a
947 * {@code RuntimeException} or {@code Error}, the actual exception
948 * thrown will be a {@code RuntimeException} with cause {@code ex}.
949 */
950 public void completeExceptionally(Throwable ex) {
951 setExceptionalCompletion((ex instanceof RuntimeException) ||
952 (ex instanceof Error) ? ex :
953 new RuntimeException(ex));
954 }
955
956 /**
957 * Completes this task, and if not already aborted or cancelled,
958 * returning the given value as the result of subsequent
959 * invocations of {@code join} and related operations. This method
960 * may be used to provide results for asynchronous tasks, or to
961 * provide alternative handling for tasks that would not otherwise
962 * complete normally. Its use in other situations is
963 * discouraged. This method is overridable, but overridden
964 * versions must invoke {@code super} implementation to maintain
965 * guarantees.
966 *
967 * @param value the result value for this task
968 */
969 public void complete(V value) {
970 try {
971 setRawResult(value);
972 } catch (Throwable rex) {
973 setExceptionalCompletion(rex);
974 return;
975 }
976 setDone();
977 }
978
979 /**
980 * Completes this task normally without setting a value. The most
981 * recent value established by {@link #setRawResult} (or {@code
982 * null} by default) will be returned as the result of subsequent
983 * invocations of {@code join} and related operations.
984 *
985 * @since 1.8
986 */
987 public final void quietlyComplete() {
988 setDone();
989 }
990
991 /**
992 * Waits if necessary for the computation to complete, and then
993 * retrieves its result.
994 *
995 * @return the computed result
996 * @throws CancellationException if the computation was cancelled
997 * @throws ExecutionException if the computation threw an
998 * exception
999 * @throws InterruptedException if the current thread is not a
1000 * member of a ForkJoinPool and was interrupted while waiting
1001 */
1002 public final V get() throws InterruptedException, ExecutionException {
1003 int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
1004 doJoin() : externalInterruptibleAwaitDone();
1005 if ((s & THROWN) != 0)
1006 throw new ExecutionException(getThrowableException());
1007 else if ((s & ABNORMAL) != 0)
1008 throw new CancellationException();
1009 else
1010 return getRawResult();
1011 }
1012
1013 /**
1014 * Waits if necessary for at most the given time for the computation
1015 * to complete, and then retrieves its result, if available.
1016 *
1017 * @param timeout the maximum time to wait
1018 * @param unit the time unit of the timeout argument
1019 * @return the computed result
1020 * @throws CancellationException if the computation was cancelled
1021 * @throws ExecutionException if the computation threw an
1022 * exception
1023 * @throws InterruptedException if the current thread is not a
1024 * member of a ForkJoinPool and was interrupted while waiting
1025 * @throws TimeoutException if the wait timed out
1026 */
1027 public final V get(long timeout, TimeUnit unit)
1028 throws InterruptedException, ExecutionException, TimeoutException {
1029 int s;
1030 long nanos = unit.toNanos(timeout);
1031 if (Thread.interrupted())
1032 throw new InterruptedException();
1033 if ((s = status) >= 0 && nanos > 0L) {
1034 long d = System.nanoTime() + nanos;
1035 long deadline = (d == 0L) ? 1L : d; // avoid 0
1036 Thread t = Thread.currentThread();
1037 if (t instanceof ForkJoinWorkerThread) {
1038 ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1039 s = wt.pool.awaitJoin(wt.workQueue, this, deadline);
1040 }
1041 else if ((s = ((this instanceof CountedCompleter) ?
1042 ForkJoinPool.common.externalHelpComplete(
1043 (CountedCompleter<?>)this, 0) :
1044 ForkJoinPool.common.tryExternalUnpush(this) ?
1045 doExec() : 0)) >= 0) {
1046 long ns, ms; // measure in nanosecs, but wait in millisecs
1047 while ((s = status) >= 0 &&
1048 (ns = deadline - System.nanoTime()) > 0L) {
1049 if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
1050 (s = (int)STATUS.getAndBitwiseOr(this, SIGNAL)) >= 0) {
1051 synchronized (this) {
1052 if (status >= 0)
1053 wait(ms); // OK to throw InterruptedException
1054 else
1055 notifyAll();
1056 }
1057 }
1058 }
1059 }
1060 }
1061 if (s >= 0)
1062 throw new TimeoutException();
1063 else if ((s & THROWN) != 0)
1064 throw new ExecutionException(getThrowableException());
1065 else if ((s & ABNORMAL) != 0)
1066 throw new CancellationException();
1067 else
1068 return getRawResult();
1069 }
1070
1071 /**
1072 * Joins this task, without returning its result or throwing its
1073 * exception. This method may be useful when processing
1074 * collections of tasks when some have been cancelled or otherwise
1075 * known to have aborted.
1076 */
1077 public final void quietlyJoin() {
1078 doJoin();
1079 }
1080
1081 /**
1082 * Commences performing this task and awaits its completion if
1083 * necessary, without returning its result or throwing its
1084 * exception.
1085 */
1086 public final void quietlyInvoke() {
1087 doInvoke();
1088 }
1089
1090 /**
1091 * Possibly executes tasks until the pool hosting the current task
1092 * {@linkplain ForkJoinPool#isQuiescent is quiescent}. This
1093 * method may be of use in designs in which many tasks are forked,
1094 * but none are explicitly joined, instead executing them until
1095 * all are processed.
1096 */
1097 public static void helpQuiesce() {
1098 Thread t;
1099 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
1100 ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1101 wt.pool.helpQuiescePool(wt.workQueue);
1102 }
1103 else
1104 ForkJoinPool.quiesceCommonPool();
1105 }
1106
1107 /**
1108 * Resets the internal bookkeeping state of this task, allowing a
1109 * subsequent {@code fork}. This method allows repeated reuse of
1110 * this task, but only if reuse occurs when this task has either
1111 * never been forked, or has been forked, then completed and all
1112 * outstanding joins of this task have also completed. Effects
1113 * under any other usage conditions are not guaranteed.
1114 * This method may be useful when executing
1115 * pre-constructed trees of subtasks in loops.
1116 *
1117 * <p>Upon completion of this method, {@code isDone()} reports
1118 * {@code false}, and {@code getException()} reports {@code
1119 * null}. However, the value returned by {@code getRawResult} is
1120 * unaffected. To clear this value, you can invoke {@code
1121 * setRawResult(null)}.
1122 */
1123 public void reinitialize() {
1124 if ((status & THROWN) != 0)
1125 clearExceptionalCompletion();
1126 else
1127 status = 0;
1128 }
1129
1130 /**
1131 * Returns the pool hosting the current thread, or {@code null}
1132 * if the current thread is executing outside of any ForkJoinPool.
1133 *
1134 * <p>This method returns {@code null} if and only if {@link
1135 * #inForkJoinPool} returns {@code false}.
1136 *
1137 * @return the pool, or {@code null} if none
1138 */
1139 public static ForkJoinPool getPool() {
1140 Thread t = Thread.currentThread();
1141 return (t instanceof ForkJoinWorkerThread) ?
1142 ((ForkJoinWorkerThread) t).pool : null;
1143 }
1144
1145 /**
1146 * Returns {@code true} if the current thread is a {@link
1147 * ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1148 *
1149 * @return {@code true} if the current thread is a {@link
1150 * ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1151 * or {@code false} otherwise
1152 */
1153 public static boolean inForkJoinPool() {
1154 return Thread.currentThread() instanceof ForkJoinWorkerThread;
1155 }
1156
1157 /**
1158 * Tries to unschedule this task for execution. This method will
1159 * typically (but is not guaranteed to) succeed if this task is
1160 * the most recently forked task by the current thread, and has
1161 * not commenced executing in another thread. This method may be
1162 * useful when arranging alternative local processing of tasks
1163 * that could have been, but were not, stolen.
1164 *
1165 * @return {@code true} if unforked
1166 */
1167 public boolean tryUnfork() {
1168 Thread t;
1169 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1170 ((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
1171 ForkJoinPool.common.tryExternalUnpush(this));
1172 }
1173
1174 /**
1175 * Returns an estimate of the number of tasks that have been
1176 * forked by the current worker thread but not yet executed. This
1177 * value may be useful for heuristic decisions about whether to
1178 * fork other tasks.
1179 *
1180 * @return the number of tasks
1181 */
1182 public static int getQueuedTaskCount() {
1183 Thread t; ForkJoinPool.WorkQueue q;
1184 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1185 q = ((ForkJoinWorkerThread)t).workQueue;
1186 else
1187 q = ForkJoinPool.commonSubmitterQueue();
1188 return (q == null) ? 0 : q.queueSize();
1189 }
1190
1191 /**
1192 * Returns an estimate of how many more locally queued tasks are
1193 * held by the current worker thread than there are other worker
1194 * threads that might steal them, or zero if this thread is not
1195 * operating in a ForkJoinPool. This value may be useful for
1196 * heuristic decisions about whether to fork other tasks. In many
1197 * usages of ForkJoinTasks, at steady state, each worker should
1198 * aim to maintain a small constant surplus (for example, 3) of
1199 * tasks, and to process computations locally if this threshold is
1200 * exceeded.
1201 *
1202 * @return the surplus number of tasks, which may be negative
1203 */
1204 public static int getSurplusQueuedTaskCount() {
1205 return ForkJoinPool.getSurplusQueuedTaskCount();
1206 }
1207
1208 // Extension methods
1209
1210 /**
1211 * Returns the result that would be returned by {@link #join}, even
1212 * if this task completed abnormally, or {@code null} if this task
1213 * is not known to have been completed. This method is designed
1214 * to aid debugging, as well as to support extensions. Its use in
1215 * any other context is discouraged.
1216 *
1217 * @return the result, or {@code null} if not completed
1218 */
1219 public abstract V getRawResult();
1220
1221 /**
1222 * Forces the given value to be returned as a result. This method
1223 * is designed to support extensions, and should not in general be
1224 * called otherwise.
1225 *
1226 * @param value the value
1227 */
1228 protected abstract void setRawResult(V value);
1229
1230 /**
1231 * Immediately performs the base action of this task and returns
1232 * true if, upon return from this method, this task is guaranteed
1233 * to have completed normally. This method may return false
1234 * otherwise, to indicate that this task is not necessarily
1235 * complete (or is not known to be complete), for example in
1236 * asynchronous actions that require explicit invocations of
1237 * completion methods. This method may also throw an (unchecked)
1238 * exception to indicate abnormal exit. This method is designed to
1239 * support extensions, and should not in general be called
1240 * otherwise.
1241 *
1242 * @return {@code true} if this task is known to have completed normally
1243 */
1244 protected abstract boolean exec();
1245
1246 /**
1247 * Returns, but does not unschedule or execute, a task queued by
1248 * the current thread but not yet executed, if one is immediately
1249 * available. There is no guarantee that this task will actually
1250 * be polled or executed next. Conversely, this method may return
1251 * null even if a task exists but cannot be accessed without
1252 * contention with other threads. This method is designed
1253 * primarily to support extensions, and is unlikely to be useful
1254 * otherwise.
1255 *
1256 * @return the next task, or {@code null} if none are available
1257 */
1258 protected static ForkJoinTask<?> peekNextLocalTask() {
1259 Thread t; ForkJoinPool.WorkQueue q;
1260 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1261 q = ((ForkJoinWorkerThread)t).workQueue;
1262 else
1263 q = ForkJoinPool.commonSubmitterQueue();
1264 return (q == null) ? null : q.peek();
1265 }
1266
1267 /**
1268 * Unschedules and returns, without executing, the next task
1269 * queued by the current thread but not yet executed, if the
1270 * current thread is operating in a ForkJoinPool. This method is
1271 * designed primarily to support extensions, and is unlikely to be
1272 * useful otherwise.
1273 *
1274 * @return the next task, or {@code null} if none are available
1275 */
1276 protected static ForkJoinTask<?> pollNextLocalTask() {
1277 Thread t;
1278 return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1279 ((ForkJoinWorkerThread)t).workQueue.nextLocalTask() :
1280 null;
1281 }
1282
1283 /**
1284 * If the current thread is operating in a ForkJoinPool,
1285 * unschedules and returns, without executing, the next task
1286 * queued by the current thread but not yet executed, if one is
1287 * available, or if not available, a task that was forked by some
1288 * other thread, if available. Availability may be transient, so a
1289 * {@code null} result does not necessarily imply quiescence of
1290 * the pool this task is operating in. This method is designed
1291 * primarily to support extensions, and is unlikely to be useful
1292 * otherwise.
1293 *
1294 * @return a task, or {@code null} if none are available
1295 */
1296 protected static ForkJoinTask<?> pollTask() {
1297 Thread t; ForkJoinWorkerThread wt;
1298 return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1299 (wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) :
1300 null;
1301 }
1302
1303 /**
1304 * If the current thread is operating in a ForkJoinPool,
1305 * unschedules and returns, without executing, a task externally
1306 * submitted to the pool, if one is available. Availability may be
1307 * transient, so a {@code null} result does not necessarily imply
1308 * quiescence of the pool. This method is designed primarily to
1309 * support extensions, and is unlikely to be useful otherwise.
1310 *
1311 * @return a task, or {@code null} if none are available
1312 * @since 9
1313 */
1314 protected static ForkJoinTask<?> pollSubmission() {
1315 Thread t;
1316 return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1317 ((ForkJoinWorkerThread)t).pool.pollSubmission() : null;
1318 }
1319
1320 // tag operations
1321
1322 /**
1323 * Returns the tag for this task.
1324 *
1325 * @return the tag for this task
1326 * @since 1.8
1327 */
1328 public final short getForkJoinTaskTag() {
1329 return (short)status;
1330 }
1331
1332 /**
1333 * Atomically sets the tag value for this task and returns the old value.
1334 *
1335 * @param newValue the new tag value
1336 * @return the previous value of the tag
1337 * @since 1.8
1338 */
1339 public final short setForkJoinTaskTag(short newValue) {
1340 for (int s;;) {
1341 if (STATUS.weakCompareAndSet(this, s = status,
1342 (s & ~SMASK) | (newValue & SMASK)))
1343 return (short)s;
1344 }
1345 }
1346
1347 /**
1348 * Atomically conditionally sets the tag value for this task.
1349 * Among other applications, tags can be used as visit markers
1350 * in tasks operating on graphs, as in methods that check: {@code
1351 * if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1352 * before processing, otherwise exiting because the node has
1353 * already been visited.
1354 *
1355 * @param expect the expected tag value
1356 * @param update the new tag value
1357 * @return {@code true} if successful; i.e., the current value was
1358 * equal to {@code expect} and was changed to {@code update}.
1359 * @since 1.8
1360 */
1361 public final boolean compareAndSetForkJoinTaskTag(short expect, short update) {
1362 for (int s;;) {
1363 if ((short)(s = status) != expect)
1364 return false;
1365 if (STATUS.weakCompareAndSet(this, s,
1366 (s & ~SMASK) | (update & SMASK)))
1367 return true;
1368 }
1369 }
1370
1371 /**
1372 * Adapter for Runnables. This implements RunnableFuture
1373 * to be compliant with AbstractExecutorService constraints
1374 * when used in ForkJoinPool.
1375 */
1376 static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1377 implements RunnableFuture<T> {
1378 final Runnable runnable;
1379 T result;
1380 AdaptedRunnable(Runnable runnable, T result) {
1381 if (runnable == null) throw new NullPointerException();
1382 this.runnable = runnable;
1383 this.result = result; // OK to set this even before completion
1384 }
1385 public final T getRawResult() { return result; }
1386 public final void setRawResult(T v) { result = v; }
1387 public final boolean exec() { runnable.run(); return true; }
1388 public final void run() { invoke(); }
1389 public String toString() {
1390 return super.toString() + "[Wrapped task = " + runnable + "]";
1391 }
1392 private static final long serialVersionUID = 5232453952276885070L;
1393 }
1394
1395 /**
1396 * Adapter for Runnables without results.
1397 */
1398 static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1399 implements RunnableFuture<Void> {
1400 final Runnable runnable;
1401 AdaptedRunnableAction(Runnable runnable) {
1402 if (runnable == null) throw new NullPointerException();
1403 this.runnable = runnable;
1404 }
1405 public final Void getRawResult() { return null; }
1406 public final void setRawResult(Void v) { }
1407 public final boolean exec() { runnable.run(); return true; }
1408 public final void run() { invoke(); }
1409 public String toString() {
1410 return super.toString() + "[Wrapped task = " + runnable + "]";
1411 }
1412 private static final long serialVersionUID = 5232453952276885070L;
1413 }
1414
1415 /**
1416 * Adapter for Runnables in which failure forces worker exception.
1417 */
1418 static final class RunnableExecuteAction extends ForkJoinTask<Void> {
1419 final Runnable runnable;
1420 RunnableExecuteAction(Runnable runnable) {
1421 if (runnable == null) throw new NullPointerException();
1422 this.runnable = runnable;
1423 }
1424 public final Void getRawResult() { return null; }
1425 public final void setRawResult(Void v) { }
1426 public final boolean exec() { runnable.run(); return true; }
1427 void internalPropagateException(Throwable ex) {
1428 rethrow(ex); // rethrow outside exec() catches.
1429 }
1430 private static final long serialVersionUID = 5232453952276885070L;
1431 }
1432
1433 /**
1434 * Adapter for Callables.
1435 */
1436 static final class AdaptedCallable<T> extends ForkJoinTask<T>
1437 implements RunnableFuture<T> {
1438 final Callable<? extends T> callable;
1439 T result;
1440 AdaptedCallable(Callable<? extends T> callable) {
1441 if (callable == null) throw new NullPointerException();
1442 this.callable = callable;
1443 }
1444 public final T getRawResult() { return result; }
1445 public final void setRawResult(T v) { result = v; }
1446 public final boolean exec() {
1447 try {
1448 result = callable.call();
1449 return true;
1450 } catch (RuntimeException rex) {
1451 throw rex;
1452 } catch (Exception ex) {
1453 throw new RuntimeException(ex);
1454 }
1455 }
1456 public final void run() { invoke(); }
1457 public String toString() {
1458 return super.toString() + "[Wrapped task = " + callable + "]";
1459 }
1460 private static final long serialVersionUID = 2838392045355241008L;
1461 }
1462
1463 /**
1464 * Returns a new {@code ForkJoinTask} that performs the {@code run}
1465 * method of the given {@code Runnable} as its action, and returns
1466 * a null result upon {@link #join}.
1467 *
1468 * @param runnable the runnable action
1469 * @return the task
1470 */
1471 public static ForkJoinTask<?> adapt(Runnable runnable) {
1472 return new AdaptedRunnableAction(runnable);
1473 }
1474
1475 /**
1476 * Returns a new {@code ForkJoinTask} that performs the {@code run}
1477 * method of the given {@code Runnable} as its action, and returns
1478 * the given result upon {@link #join}.
1479 *
1480 * @param runnable the runnable action
1481 * @param result the result upon completion
1482 * @param <T> the type of the result
1483 * @return the task
1484 */
1485 public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1486 return new AdaptedRunnable<T>(runnable, result);
1487 }
1488
1489 /**
1490 * Returns a new {@code ForkJoinTask} that performs the {@code call}
1491 * method of the given {@code Callable} as its action, and returns
1492 * its result upon {@link #join}, translating any checked exceptions
1493 * encountered into {@code RuntimeException}.
1494 *
1495 * @param callable the callable action
1496 * @param <T> the type of the callable's result
1497 * @return the task
1498 */
1499 public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1500 return new AdaptedCallable<T>(callable);
1501 }
1502
1503 // Serialization support
1504
1505 private static final long serialVersionUID = -7721805057305804111L;
1506
1507 /**
1508 * Saves this task to a stream (that is, serializes it).
1509 *
1510 * @param s the stream
1511 * @throws java.io.IOException if an I/O error occurs
1512 * @serialData the current run status and the exception thrown
1513 * during execution, or {@code null} if none
1514 */
1515 private void writeObject(java.io.ObjectOutputStream s)
1516 throws java.io.IOException {
1517 s.defaultWriteObject();
1518 s.writeObject(getException());
1519 }
1520
1521 /**
1522 * Reconstitutes this task from a stream (that is, deserializes it).
1523 * @param s the stream
1524 * @throws ClassNotFoundException if the class of a serialized object
1525 * could not be found
1526 * @throws java.io.IOException if an I/O error occurs
1527 */
1528 private void readObject(java.io.ObjectInputStream s)
1529 throws java.io.IOException, ClassNotFoundException {
1530 s.defaultReadObject();
1531 Object ex = s.readObject();
1532 if (ex != null)
1533 setExceptionalCompletion((Throwable)ex);
1534 }
1535
1536 // VarHandle mechanics
1537 private static final VarHandle STATUS;
1538 static {
1539 try {
1540 MethodHandles.Lookup l = MethodHandles.lookup();
1541 STATUS = l.findVarHandle(ForkJoinTask.class, "status", int.class);
1542 } catch (ReflectiveOperationException e) {
1543 throw new Error(e);
1544 }
1545 }
1546
1547 }