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.ref.ReferenceQueue;
40 import java.lang.ref.WeakReference;
41 import java.lang.reflect.Constructor;
42 import java.util.Collection;
43 import java.util.List;
44 import java.util.RandomAccess;
45 import java.util.concurrent.locks.ReentrantLock;
46
47 /**
48 * Abstract base class for tasks that run within a {@link ForkJoinPool}.
49 * A {@code ForkJoinTask} is a thread-like entity that is much
50 * lighter weight than a normal thread. Huge numbers of tasks and
51 * subtasks may be hosted by a small number of actual threads in a
52 * ForkJoinPool, at the price of some usage limitations.
53 *
54 * <p>A "main" {@code ForkJoinTask} begins execution when it is
55 * explicitly submitted to a {@link ForkJoinPool}, or, if not already
56 * engaged in a ForkJoin computation, commenced in the {@link
57 * ForkJoinPool#commonPool()} via {@link #fork}, {@link #invoke}, or
58 * related methods. Once started, it will usually in turn start other
59 * subtasks. As indicated by the name of this class, many programs
60 * using {@code ForkJoinTask} employ only methods {@link #fork} and
61 * {@link #join}, or derivatives such as {@link
62 * #invokeAll(ForkJoinTask...) invokeAll}. However, this class also
63 * provides a number of other methods that can come into play in
64 * advanced usages, as well as extension mechanics that allow support
65 * of new forms of fork/join processing.
66 *
67 * <p>A {@code ForkJoinTask} is a lightweight form of {@link Future}.
68 * The efficiency of {@code ForkJoinTask}s stems from a set of
69 * restrictions (that are only partially statically enforceable)
70 * reflecting their main use as computational tasks calculating pure
71 * functions or operating on purely isolated objects. The primary
72 * coordination mechanisms are {@link #fork}, that arranges
73 * asynchronous execution, and {@link #join}, that doesn't proceed
74 * until the task's result has been computed. Computations should
75 * ideally avoid {@code synchronized} methods or blocks, and should
76 * minimize other blocking synchronization apart from joining other
77 * tasks or using synchronizers such as Phasers that are advertised to
78 * cooperate with fork/join scheduling. Subdividable tasks should also
79 * not perform blocking I/O, and should ideally access variables that
80 * are completely independent of those accessed by other running
81 * tasks. These guidelines are loosely enforced by not permitting
82 * checked exceptions such as {@code IOExceptions} to be
83 * thrown. However, computations may still encounter unchecked
84 * exceptions, that are rethrown to callers attempting to join
85 * them. These exceptions may additionally include {@link
86 * RejectedExecutionException} stemming from internal resource
87 * exhaustion, such as failure to allocate internal task
88 * queues. Rethrown exceptions behave in the same way as regular
89 * exceptions, but, when possible, contain stack traces (as displayed
90 * for example using {@code ex.printStackTrace()}) of both the thread
91 * that initiated the computation as well as the thread actually
92 * encountering the exception; minimally only the latter.
93 *
94 * <p>It is possible to define and use ForkJoinTasks that may block,
95 * but doing do requires three further considerations: (1) Completion
96 * of few if any <em>other</em> tasks should be dependent on a task
97 * that blocks on external synchronization or I/O. Event-style async
98 * tasks that are never joined (for example, those subclassing {@link
99 * CountedCompleter}) often fall into this category. (2) To minimize
100 * resource impact, tasks should be small; ideally performing only the
101 * (possibly) blocking action. (3) Unless the {@link
102 * ForkJoinPool.ManagedBlocker} API is used, or the number of possibly
103 * blocked tasks is known to be less than the pool's {@link
104 * ForkJoinPool#getParallelism} level, the pool cannot guarantee that
105 * enough threads will be available to ensure progress or good
106 * performance.
107 *
108 * <p>The primary method for awaiting completion and extracting
109 * results of a task is {@link #join}, but there are several variants:
110 * The {@link Future#get} methods support interruptible and/or timed
111 * waits for completion and report results using {@code Future}
112 * conventions. Method {@link #invoke} is semantically
113 * equivalent to {@code fork(); join()} but always attempts to begin
114 * execution in the current thread. The "<em>quiet</em>" forms of
115 * these methods do not extract results or report exceptions. These
116 * may be useful when a set of tasks are being executed, and you need
117 * to delay processing of results or exceptions until all complete.
118 * Method {@code invokeAll} (available in multiple versions)
119 * performs the most common form of parallel invocation: forking a set
120 * of tasks and joining them all.
121 *
122 * <p>In the most typical usages, a fork-join pair act like a call
123 * (fork) and return (join) from a parallel recursive function. As is
124 * the case with other forms of recursive calls, returns (joins)
125 * should be performed innermost-first. For example, {@code a.fork();
126 * b.fork(); b.join(); a.join();} is likely to be substantially more
127 * efficient than joining {@code a} before {@code b}.
128 *
129 * <p>The execution status of tasks may be queried at several levels
130 * of detail: {@link #isDone} is true if a task completed in any way
131 * (including the case where a task was cancelled without executing);
132 * {@link #isCompletedNormally} is true if a task completed without
133 * cancellation or encountering an exception; {@link #isCancelled} is
134 * true if the task was cancelled (in which case {@link #getException}
135 * returns a {@link java.util.concurrent.CancellationException}); and
136 * {@link #isCompletedAbnormally} is true if a task was either
137 * cancelled or encountered an exception, in which case {@link
138 * #getException} will return either the encountered exception or
139 * {@link java.util.concurrent.CancellationException}.
140 *
141 * <p>The ForkJoinTask class is not usually directly subclassed.
142 * Instead, you subclass one of the abstract classes that support a
143 * particular style of fork/join processing, typically {@link
144 * RecursiveAction} for most computations that do not return results,
145 * {@link RecursiveTask} for those that do, and {@link
146 * CountedCompleter} for those in which completed actions trigger
147 * other actions. Normally, a concrete ForkJoinTask subclass declares
148 * fields comprising its parameters, established in a constructor, and
149 * then defines a {@code compute} method that somehow uses the control
150 * methods supplied by this base class.
151 *
152 * <p>Method {@link #join} and its variants are appropriate for use
153 * only when completion dependencies are acyclic; that is, the
154 * parallel computation can be described as a directed acyclic graph
155 * (DAG). Otherwise, executions may encounter a form of deadlock as
156 * tasks cyclically wait for each other. However, this framework
157 * supports other methods and techniques (for example the use of
158 * {@link Phaser}, {@link #helpQuiesce}, and {@link #complete}) that
159 * may be of use in constructing custom subclasses for problems that
160 * are not statically structured as DAGs. To support such usages, a
161 * ForkJoinTask may be atomically <em>tagged</em> with a {@code short}
162 * value using {@link #setForkJoinTaskTag} or {@link
163 * #compareAndSetForkJoinTaskTag} and checked using {@link
164 * #getForkJoinTaskTag}. The ForkJoinTask implementation does not use
165 * these {@code protected} methods or tags for any purpose, but they
166 * may be of use in the construction of specialized subclasses. For
167 * example, parallel graph traversals can use the supplied methods to
168 * avoid revisiting nodes/tasks that have already been processed.
169 * (Method names for tagging are bulky in part to encourage definition
170 * of methods that reflect their usage patterns.)
171 *
172 * <p>Most base support methods are {@code final}, to prevent
173 * overriding of implementations that are intrinsically tied to the
174 * underlying lightweight task scheduling framework. Developers
175 * creating new basic styles of fork/join processing should minimally
176 * implement {@code protected} methods {@link #exec}, {@link
177 * #setRawResult}, and {@link #getRawResult}, while also introducing
178 * an abstract computational method that can be implemented in its
179 * subclasses, possibly relying on other {@code protected} methods
180 * provided by this class.
181 *
182 * <p>ForkJoinTasks should perform relatively small amounts of
183 * computation. Large tasks should be split into smaller subtasks,
184 * usually via recursive decomposition. As a very rough rule of thumb,
185 * a task should perform more than 100 and less than 10000 basic
186 * computational steps, and should avoid indefinite looping. If tasks
187 * are too big, then parallelism cannot improve throughput. If too
188 * small, then memory and internal task maintenance overhead may
189 * overwhelm processing.
190 *
191 * <p>This class provides {@code adapt} methods for {@link Runnable}
192 * and {@link Callable}, that may be of use when mixing execution of
193 * {@code ForkJoinTasks} with other kinds of tasks. When all tasks are
194 * of this form, consider using a pool constructed in <em>asyncMode</em>.
195 *
196 * <p>ForkJoinTasks are {@code Serializable}, which enables them to be
197 * used in extensions such as remote execution frameworks. It is
198 * sensible to serialize tasks only before or after, but not during,
199 * execution. Serialization is not relied on during execution itself.
200 *
201 * @since 1.7
202 * @author Doug Lea
203 */
204 public abstract class ForkJoinTask<V> implements Future<V>, Serializable {
205
206 /*
207 * See the internal documentation of class ForkJoinPool for a
208 * general implementation overview. ForkJoinTasks are mainly
209 * responsible for maintaining their "status" field amidst relays
210 * to methods in ForkJoinWorkerThread and ForkJoinPool.
211 *
212 * The methods of this class are more-or-less layered into
213 * (1) basic status maintenance
214 * (2) execution and awaiting completion
215 * (3) user-level methods that additionally report results.
216 * This is sometimes hard to see because this file orders exported
217 * methods in a way that flows well in javadocs.
218 */
219
220 /*
221 * The status field holds run control status bits packed into a
222 * single int to minimize footprint and to ensure atomicity (via
223 * CAS). Status is initially zero, and takes on nonnegative
224 * values until completed, upon which status (anded with
225 * DONE_MASK) holds value NORMAL, CANCELLED, or EXCEPTIONAL. Tasks
226 * undergoing blocking waits by other threads have the SIGNAL bit
227 * set. Completion of a stolen task with SIGNAL set awakens any
228 * waiters via notifyAll. Even though suboptimal for some
229 * purposes, we use basic builtin wait/notify to take advantage of
230 * "monitor inflation" in JVMs that we would otherwise need to
231 * emulate to avoid adding further per-task bookkeeping overhead.
232 * We want these monitors to be "fat", i.e., not use biasing or
233 * thin-lock techniques, so use some odd coding idioms that tend
234 * to avoid them, mainly by arranging that every synchronized
235 * block performs a wait, notifyAll or both.
236 *
237 * These control bits occupy only (some of) the upper half (16
238 * bits) of status field. The lower bits are used for user-defined
239 * tags.
240 */
241
242 /** The run status of this task */
243 volatile int status; // accessed directly by pool and workers
244 static final int DONE_MASK = 0xf0000000; // mask out non-completion bits
245 static final int NORMAL = 0xf0000000; // must be negative
246 static final int CANCELLED = 0xc0000000; // must be < NORMAL
247 static final int EXCEPTIONAL = 0x80000000; // must be < CANCELLED
248 static final int SIGNAL = 0x00010000; // must be >= 1 << 16
249 static final int SMASK = 0x0000ffff; // short bits for tags
250
251 /**
252 * Marks completion and wakes up threads waiting to join this
253 * task.
254 *
255 * @param completion one of NORMAL, CANCELLED, EXCEPTIONAL
256 * @return completion status on exit
257 */
258 private int setCompletion(int completion) {
259 for (int s;;) {
260 if ((s = status) < 0)
261 return s;
262 if (U.compareAndSwapInt(this, STATUS, s, s | completion)) {
263 if ((s >>> 16) != 0)
264 synchronized (this) { notifyAll(); }
265 return completion;
266 }
267 }
268 }
269
270 /**
271 * Primary execution method for stolen tasks. Unless done, calls
272 * exec and records status if completed, but doesn't wait for
273 * completion otherwise.
274 *
275 * @return status on exit from this method
276 */
277 final int doExec() {
278 int s; boolean completed;
279 if ((s = status) >= 0) {
280 try {
281 completed = exec();
282 } catch (Throwable rex) {
283 return setExceptionalCompletion(rex);
284 }
285 if (completed)
286 s = setCompletion(NORMAL);
287 }
288 return s;
289 }
290
291 /**
292 * If not done, sets SIGNAL status and performs Object.wait(timeout).
293 * This task may or may not be done on exit. Ignores interrupts.
294 *
295 * @param timeout using Object.wait conventions.
296 */
297 final void internalWait(long timeout) {
298 int s;
299 if ((s = status) >= 0 && // force completer to issue notify
300 U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
301 synchronized (this) {
302 if (status >= 0)
303 try { wait(timeout); } catch (InterruptedException ie) { }
304 else
305 notifyAll();
306 }
307 }
308 }
309
310 /**
311 * Blocks a non-worker-thread until completion.
312 * @return status upon completion
313 */
314 private int externalAwaitDone() {
315 int s = ((this instanceof CountedCompleter) ? // try helping
316 ForkJoinPool.common.externalHelpComplete(
317 (CountedCompleter<?>)this, 0) :
318 ForkJoinPool.common.tryExternalUnpush(this) ? doExec() : 0);
319 if (s >= 0 && (s = status) >= 0) {
320 boolean interrupted = false;
321 do {
322 if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
323 synchronized (this) {
324 if (status >= 0) {
325 try {
326 wait(0L);
327 } catch (InterruptedException ie) {
328 interrupted = true;
329 }
330 }
331 else
332 notifyAll();
333 }
334 }
335 } while ((s = status) >= 0);
336 if (interrupted)
337 Thread.currentThread().interrupt();
338 }
339 return s;
340 }
341
342 /**
343 * Blocks a non-worker-thread until completion or interruption.
344 */
345 private int externalInterruptibleAwaitDone() throws InterruptedException {
346 int s;
347 if (Thread.interrupted())
348 throw new InterruptedException();
349 if ((s = status) >= 0 &&
350 (s = ((this instanceof CountedCompleter) ?
351 ForkJoinPool.common.externalHelpComplete(
352 (CountedCompleter<?>)this, 0) :
353 ForkJoinPool.common.tryExternalUnpush(this) ? doExec() :
354 0)) >= 0) {
355 while ((s = status) >= 0) {
356 if (U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
357 synchronized (this) {
358 if (status >= 0)
359 wait(0L);
360 else
361 notifyAll();
362 }
363 }
364 }
365 }
366 return s;
367 }
368
369 /**
370 * Implementation for join, get, quietlyJoin. Directly handles
371 * only cases of already-completed, external wait, and
372 * unfork+exec. Others are relayed to ForkJoinPool.awaitJoin.
373 *
374 * @return status upon completion
375 */
376 private int doJoin() {
377 int s; Thread t; ForkJoinWorkerThread wt; ForkJoinPool.WorkQueue w;
378 return (s = status) < 0 ? s :
379 ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
380 (w = (wt = (ForkJoinWorkerThread)t).workQueue).
381 tryUnpush(this) && (s = doExec()) < 0 ? s :
382 wt.pool.awaitJoin(w, this, 0L) :
383 externalAwaitDone();
384 }
385
386 /**
387 * Implementation for invoke, quietlyInvoke.
388 *
389 * @return status upon completion
390 */
391 private int doInvoke() {
392 int s; Thread t; ForkJoinWorkerThread wt;
393 return (s = doExec()) < 0 ? s :
394 ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
395 (wt = (ForkJoinWorkerThread)t).pool.
396 awaitJoin(wt.workQueue, this, 0L) :
397 externalAwaitDone();
398 }
399
400 // Exception table support
401
402 /**
403 * Table of exceptions thrown by tasks, to enable reporting by
404 * callers. Because exceptions are rare, we don't directly keep
405 * them with task objects, but instead use a weak ref table. Note
406 * that cancellation exceptions don't appear in the table, but are
407 * instead recorded as status values.
408 *
409 * Note: These statics are initialized below in static block.
410 */
411 private static final ExceptionNode[] exceptionTable;
412 private static final ReentrantLock exceptionTableLock;
413 private static final ReferenceQueue<Object> exceptionTableRefQueue;
414
415 /**
416 * Fixed capacity for exceptionTable.
417 */
418 private static final int EXCEPTION_MAP_CAPACITY = 32;
419
420 /**
421 * Key-value nodes for exception table. The chained hash table
422 * uses identity comparisons, full locking, and weak references
423 * for keys. The table has a fixed capacity because it only
424 * maintains task exceptions long enough for joiners to access
425 * them, so should never become very large for sustained
426 * periods. However, since we do not know when the last joiner
427 * completes, we must use weak references and expunge them. We do
428 * so on each operation (hence full locking). Also, some thread in
429 * any ForkJoinPool will call helpExpungeStaleExceptions when its
430 * pool becomes isQuiescent.
431 */
432 static final class ExceptionNode extends WeakReference<ForkJoinTask<?>> {
433 final Throwable ex;
434 ExceptionNode next;
435 final long thrower; // use id not ref to avoid weak cycles
436 final int hashCode; // store task hashCode before weak ref disappears
437 ExceptionNode(ForkJoinTask<?> task, Throwable ex, ExceptionNode next,
438 ReferenceQueue<Object> exceptionTableRefQueue) {
439 super(task, exceptionTableRefQueue);
440 this.ex = ex;
441 this.next = next;
442 this.thrower = Thread.currentThread().getId();
443 this.hashCode = System.identityHashCode(task);
444 }
445 }
446
447 /**
448 * Records exception and sets status.
449 *
450 * @return status on exit
451 */
452 final int recordExceptionalCompletion(Throwable ex) {
453 int s;
454 if ((s = status) >= 0) {
455 int h = System.identityHashCode(this);
456 final ReentrantLock lock = exceptionTableLock;
457 lock.lock();
458 try {
459 expungeStaleExceptions();
460 ExceptionNode[] t = exceptionTable;
461 int i = h & (t.length - 1);
462 for (ExceptionNode e = t[i]; ; e = e.next) {
463 if (e == null) {
464 t[i] = new ExceptionNode(this, ex, t[i],
465 exceptionTableRefQueue);
466 break;
467 }
468 if (e.get() == this) // already present
469 break;
470 }
471 } finally {
472 lock.unlock();
473 }
474 s = setCompletion(EXCEPTIONAL);
475 }
476 return s;
477 }
478
479 /**
480 * Records exception and possibly propagates.
481 *
482 * @return status on exit
483 */
484 private int setExceptionalCompletion(Throwable ex) {
485 int s = recordExceptionalCompletion(ex);
486 if ((s & DONE_MASK) == EXCEPTIONAL)
487 internalPropagateException(ex);
488 return s;
489 }
490
491 /**
492 * Hook for exception propagation support for tasks with completers.
493 */
494 void internalPropagateException(Throwable ex) {
495 }
496
497 /**
498 * Cancels, ignoring any exceptions thrown by cancel. Used during
499 * worker and pool shutdown. Cancel is spec'ed not to throw any
500 * exceptions, but if it does anyway, we have no recourse during
501 * shutdown, so guard against this case.
502 */
503 static final void cancelIgnoringExceptions(ForkJoinTask<?> t) {
504 if (t != null && t.status >= 0) {
505 try {
506 t.cancel(false);
507 } catch (Throwable ignore) {
508 }
509 }
510 }
511
512 /**
513 * Removes exception node and clears status.
514 */
515 private void clearExceptionalCompletion() {
516 int h = System.identityHashCode(this);
517 final ReentrantLock lock = exceptionTableLock;
518 lock.lock();
519 try {
520 ExceptionNode[] t = exceptionTable;
521 int i = h & (t.length - 1);
522 ExceptionNode e = t[i];
523 ExceptionNode pred = null;
524 while (e != null) {
525 ExceptionNode next = e.next;
526 if (e.get() == this) {
527 if (pred == null)
528 t[i] = next;
529 else
530 pred.next = next;
531 break;
532 }
533 pred = e;
534 e = next;
535 }
536 expungeStaleExceptions();
537 status = 0;
538 } finally {
539 lock.unlock();
540 }
541 }
542
543 /**
544 * Returns a rethrowable exception for the given task, if
545 * available. To provide accurate stack traces, if the exception
546 * was not thrown by the current thread, we try to create a new
547 * exception of the same type as the one thrown, but with the
548 * recorded exception as its cause. If there is no such
549 * constructor, we instead try to use a no-arg constructor,
550 * followed by initCause, to the same effect. If none of these
551 * apply, or any fail due to other exceptions, we return the
552 * recorded exception, which is still correct, although it may
553 * contain a misleading stack trace.
554 *
555 * @return the exception, or null if none
556 */
557 private Throwable getThrowableException() {
558 int h = System.identityHashCode(this);
559 ExceptionNode e;
560 final ReentrantLock lock = exceptionTableLock;
561 lock.lock();
562 try {
563 expungeStaleExceptions();
564 ExceptionNode[] t = exceptionTable;
565 e = t[h & (t.length - 1)];
566 while (e != null && e.get() != this)
567 e = e.next;
568 } finally {
569 lock.unlock();
570 }
571 Throwable ex;
572 if (e == null || (ex = e.ex) == null)
573 return null;
574 if (e.thrower != Thread.currentThread().getId()) {
575 Class<? extends Throwable> ec = ex.getClass();
576 try {
577 Constructor<?> noArgCtor = null;
578 Constructor<?>[] cs = ec.getConstructors();// public ctors only
579 for (int i = 0; i < cs.length; ++i) {
580 Constructor<?> c = cs[i];
581 Class<?>[] ps = c.getParameterTypes();
582 if (ps.length == 0)
583 noArgCtor = c;
584 else if (ps.length == 1 && ps[0] == Throwable.class) {
585 Throwable wx = (Throwable)c.newInstance(ex);
586 return (wx == null) ? ex : wx;
587 }
588 }
589 if (noArgCtor != null) {
590 Throwable wx = (Throwable)(noArgCtor.newInstance());
591 if (wx != null) {
592 wx.initCause(ex);
593 return wx;
594 }
595 }
596 } catch (Exception ignore) {
597 }
598 }
599 return ex;
600 }
601
602 /**
603 * Polls stale refs and removes them. Call only while holding lock.
604 */
605 private static void expungeStaleExceptions() {
606 for (Object x; (x = exceptionTableRefQueue.poll()) != null;) {
607 if (x instanceof ExceptionNode) {
608 int hashCode = ((ExceptionNode)x).hashCode;
609 ExceptionNode[] t = exceptionTable;
610 int i = hashCode & (t.length - 1);
611 ExceptionNode e = t[i];
612 ExceptionNode pred = null;
613 while (e != null) {
614 ExceptionNode next = e.next;
615 if (e == x) {
616 if (pred == null)
617 t[i] = next;
618 else
619 pred.next = next;
620 break;
621 }
622 pred = e;
623 e = next;
624 }
625 }
626 }
627 }
628
629 /**
630 * If lock is available, polls stale refs and removes them.
631 * Called from ForkJoinPool when pools become quiescent.
632 */
633 static final void helpExpungeStaleExceptions() {
634 final ReentrantLock lock = exceptionTableLock;
635 if (lock.tryLock()) {
636 try {
637 expungeStaleExceptions();
638 } finally {
639 lock.unlock();
640 }
641 }
642 }
643
644 /**
645 * A version of "sneaky throw" to relay exceptions.
646 */
647 static void rethrow(Throwable ex) {
648 ForkJoinTask.<RuntimeException>uncheckedThrow(ex);
649 }
650
651 /**
652 * The sneaky part of sneaky throw, relying on generics
653 * limitations to evade compiler complaints about rethrowing
654 * unchecked exceptions.
655 */
656 @SuppressWarnings("unchecked") static <T extends Throwable>
657 void uncheckedThrow(Throwable t) throws T {
658 if (t != null)
659 throw (T)t; // rely on vacuous cast
660 else
661 throw new Error("Unknown Exception");
662 }
663
664 /**
665 * Throws exception, if any, associated with the given status.
666 */
667 private void reportException(int s) {
668 if (s == CANCELLED)
669 throw new CancellationException();
670 if (s == EXCEPTIONAL)
671 rethrow(getThrowableException());
672 }
673
674 // public methods
675
676 /**
677 * Arranges to asynchronously execute this task in the pool the
678 * current task is running in, if applicable, or using the {@link
679 * ForkJoinPool#commonPool()} if not {@link #inForkJoinPool}. While
680 * it is not necessarily enforced, it is a usage error to fork a
681 * task more than once unless it has completed and been
682 * reinitialized. Subsequent modifications to the state of this
683 * task or any data it operates on are not necessarily
684 * consistently observable by any thread other than the one
685 * executing it unless preceded by a call to {@link #join} or
686 * related methods, or a call to {@link #isDone} returning {@code
687 * true}.
688 *
689 * @return {@code this}, to simplify usage
690 */
691 public final ForkJoinTask<V> fork() {
692 Thread t;
693 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
694 ((ForkJoinWorkerThread)t).workQueue.push(this);
695 else
696 ForkJoinPool.common.externalPush(this);
697 return this;
698 }
699
700 /**
701 * Returns the result of the computation when it {@link #isDone is
702 * done}. This method differs from {@link #get()} in that
703 * abnormal completion results in {@code RuntimeException} or
704 * {@code Error}, not {@code ExecutionException}, and that
705 * interrupts of the calling thread do <em>not</em> cause the
706 * method to abruptly return by throwing {@code
707 * InterruptedException}.
708 *
709 * @return the computed result
710 */
711 public final V join() {
712 int s;
713 if ((s = doJoin() & DONE_MASK) != NORMAL)
714 reportException(s);
715 return getRawResult();
716 }
717
718 /**
719 * Commences performing this task, awaits its completion if
720 * necessary, and returns its result, or throws an (unchecked)
721 * {@code RuntimeException} or {@code Error} if the underlying
722 * computation did so.
723 *
724 * @return the computed result
725 */
726 public final V invoke() {
727 int s;
728 if ((s = doInvoke() & DONE_MASK) != NORMAL)
729 reportException(s);
730 return getRawResult();
731 }
732
733 /**
734 * Forks the given tasks, returning when {@code isDone} holds for
735 * each task or an (unchecked) exception is encountered, in which
736 * case the exception is rethrown. If more than one task
737 * encounters an exception, then this method throws any one of
738 * these exceptions. If any task encounters an exception, the
739 * other may be cancelled. However, the execution status of
740 * individual tasks is not guaranteed upon exceptional return. The
741 * status of each task may be obtained using {@link
742 * #getException()} and related methods to check if they have been
743 * cancelled, completed normally or exceptionally, or left
744 * unprocessed.
745 *
746 * @param t1 the first task
747 * @param t2 the second task
748 * @throws NullPointerException if any task is null
749 */
750 public static void invokeAll(ForkJoinTask<?> t1, ForkJoinTask<?> t2) {
751 int s1, s2;
752 t2.fork();
753 if ((s1 = t1.doInvoke() & DONE_MASK) != NORMAL)
754 t1.reportException(s1);
755 if ((s2 = t2.doJoin() & DONE_MASK) != NORMAL)
756 t2.reportException(s2);
757 }
758
759 /**
760 * Forks the given tasks, returning when {@code isDone} holds for
761 * each task or an (unchecked) exception is encountered, in which
762 * case the exception is rethrown. If more than one task
763 * encounters an exception, then this method throws any one of
764 * these exceptions. If any task encounters an exception, others
765 * may be cancelled. However, the execution status of individual
766 * tasks is not guaranteed upon exceptional return. The status of
767 * each task may be obtained using {@link #getException()} and
768 * related methods to check if they have been cancelled, completed
769 * normally or exceptionally, or left unprocessed.
770 *
771 * @param tasks the tasks
772 * @throws NullPointerException if any task is null
773 */
774 public static void invokeAll(ForkJoinTask<?>... tasks) {
775 Throwable ex = null;
776 int last = tasks.length - 1;
777 for (int i = last; i >= 0; --i) {
778 ForkJoinTask<?> t = tasks[i];
779 if (t == null) {
780 if (ex == null)
781 ex = new NullPointerException();
782 }
783 else if (i != 0)
784 t.fork();
785 else if (t.doInvoke() < NORMAL && ex == null)
786 ex = t.getException();
787 }
788 for (int i = 1; i <= last; ++i) {
789 ForkJoinTask<?> t = tasks[i];
790 if (t != null) {
791 if (ex != null)
792 t.cancel(false);
793 else if (t.doJoin() < NORMAL)
794 ex = t.getException();
795 }
796 }
797 if (ex != null)
798 rethrow(ex);
799 }
800
801 /**
802 * Forks all tasks in the specified collection, returning when
803 * {@code isDone} holds for each task or an (unchecked) exception
804 * is encountered, in which case the exception is rethrown. If
805 * more than one task encounters an exception, then this method
806 * throws any one of these exceptions. If any task encounters an
807 * exception, others may be cancelled. However, the execution
808 * status of individual tasks is not guaranteed upon exceptional
809 * return. The status of each task may be obtained using {@link
810 * #getException()} and related methods to check if they have been
811 * cancelled, completed normally or exceptionally, or left
812 * unprocessed.
813 *
814 * @param tasks the collection of tasks
815 * @param <T> the type of the values returned from the tasks
816 * @return the tasks argument, to simplify usage
817 * @throws NullPointerException if tasks or any element are null
818 */
819 public static <T extends ForkJoinTask<?>> Collection<T> invokeAll(Collection<T> tasks) {
820 if (!(tasks instanceof RandomAccess) || !(tasks instanceof List<?>)) {
821 invokeAll(tasks.toArray(new ForkJoinTask<?>[tasks.size()]));
822 return tasks;
823 }
824 @SuppressWarnings("unchecked")
825 List<? extends ForkJoinTask<?>> ts =
826 (List<? extends ForkJoinTask<?>>) tasks;
827 Throwable ex = null;
828 int last = ts.size() - 1;
829 for (int i = last; i >= 0; --i) {
830 ForkJoinTask<?> t = ts.get(i);
831 if (t == null) {
832 if (ex == null)
833 ex = new NullPointerException();
834 }
835 else if (i != 0)
836 t.fork();
837 else if (t.doInvoke() < NORMAL && ex == null)
838 ex = t.getException();
839 }
840 for (int i = 1; i <= last; ++i) {
841 ForkJoinTask<?> t = ts.get(i);
842 if (t != null) {
843 if (ex != null)
844 t.cancel(false);
845 else if (t.doJoin() < NORMAL)
846 ex = t.getException();
847 }
848 }
849 if (ex != null)
850 rethrow(ex);
851 return tasks;
852 }
853
854 /**
855 * Attempts to cancel execution of this task. This attempt will
856 * fail if the task has already completed or could not be
857 * cancelled for some other reason. If successful, and this task
858 * has not started when {@code cancel} is called, execution of
859 * this task is suppressed. After this method returns
860 * successfully, unless there is an intervening call to {@link
861 * #reinitialize}, subsequent calls to {@link #isCancelled},
862 * {@link #isDone}, and {@code cancel} will return {@code true}
863 * and calls to {@link #join} and related methods will result in
864 * {@code CancellationException}.
865 *
866 * <p>This method may be overridden in subclasses, but if so, must
867 * still ensure that these properties hold. In particular, the
868 * {@code cancel} method itself must not throw exceptions.
869 *
870 * <p>This method is designed to be invoked by <em>other</em>
871 * tasks. To terminate the current task, you can just return or
872 * throw an unchecked exception from its computation method, or
873 * invoke {@link #completeExceptionally(Throwable)}.
874 *
875 * @param mayInterruptIfRunning this value has no effect in the
876 * default implementation because interrupts are not used to
877 * control cancellation.
878 *
879 * @return {@code true} if this task is now cancelled
880 */
881 public boolean cancel(boolean mayInterruptIfRunning) {
882 return (setCompletion(CANCELLED) & DONE_MASK) == CANCELLED;
883 }
884
885 public final boolean isDone() {
886 return status < 0;
887 }
888
889 public final boolean isCancelled() {
890 return (status & DONE_MASK) == CANCELLED;
891 }
892
893 /**
894 * Returns {@code true} if this task threw an exception or was cancelled.
895 *
896 * @return {@code true} if this task threw an exception or was cancelled
897 */
898 public final boolean isCompletedAbnormally() {
899 return status < NORMAL;
900 }
901
902 /**
903 * Returns {@code true} if this task completed without throwing an
904 * exception and was not cancelled.
905 *
906 * @return {@code true} if this task completed without throwing an
907 * exception and was not cancelled
908 */
909 public final boolean isCompletedNormally() {
910 return (status & DONE_MASK) == NORMAL;
911 }
912
913 /**
914 * Returns the exception thrown by the base computation, or a
915 * {@code CancellationException} if cancelled, or {@code null} if
916 * none or if the method has not yet completed.
917 *
918 * @return the exception, or {@code null} if none
919 */
920 public final Throwable getException() {
921 int s = status & DONE_MASK;
922 return ((s >= NORMAL) ? null :
923 (s == CANCELLED) ? new CancellationException() :
924 getThrowableException());
925 }
926
927 /**
928 * Completes this task abnormally, and if not already aborted or
929 * cancelled, causes it to throw the given exception upon
930 * {@code join} and related operations. This method may be used
931 * to induce exceptions in asynchronous tasks, or to force
932 * completion of tasks that would not otherwise complete. Its use
933 * in other situations is discouraged. This method is
934 * overridable, but overridden versions must invoke {@code super}
935 * implementation to maintain guarantees.
936 *
937 * @param ex the exception to throw. If this exception is not a
938 * {@code RuntimeException} or {@code Error}, the actual exception
939 * thrown will be a {@code RuntimeException} with cause {@code ex}.
940 */
941 public void completeExceptionally(Throwable ex) {
942 setExceptionalCompletion((ex instanceof RuntimeException) ||
943 (ex instanceof Error) ? ex :
944 new RuntimeException(ex));
945 }
946
947 /**
948 * Completes this task, and if not already aborted or cancelled,
949 * returning the given value as the result of subsequent
950 * invocations of {@code join} and related operations. This method
951 * may be used to provide results for asynchronous tasks, or to
952 * provide alternative handling for tasks that would not otherwise
953 * complete normally. Its use in other situations is
954 * discouraged. This method is overridable, but overridden
955 * versions must invoke {@code super} implementation to maintain
956 * guarantees.
957 *
958 * @param value the result value for this task
959 */
960 public void complete(V value) {
961 try {
962 setRawResult(value);
963 } catch (Throwable rex) {
964 setExceptionalCompletion(rex);
965 return;
966 }
967 setCompletion(NORMAL);
968 }
969
970 /**
971 * Completes this task normally without setting a value. The most
972 * recent value established by {@link #setRawResult} (or {@code
973 * null} by default) will be returned as the result of subsequent
974 * invocations of {@code join} and related operations.
975 *
976 * @since 1.8
977 */
978 public final void quietlyComplete() {
979 setCompletion(NORMAL);
980 }
981
982 /**
983 * Waits if necessary for the computation to complete, and then
984 * retrieves its result.
985 *
986 * @return the computed result
987 * @throws CancellationException if the computation was cancelled
988 * @throws ExecutionException if the computation threw an
989 * exception
990 * @throws InterruptedException if the current thread is not a
991 * member of a ForkJoinPool and was interrupted while waiting
992 */
993 public final V get() throws InterruptedException, ExecutionException {
994 int s = (Thread.currentThread() instanceof ForkJoinWorkerThread) ?
995 doJoin() : externalInterruptibleAwaitDone();
996 if ((s &= DONE_MASK) == CANCELLED)
997 throw new CancellationException();
998 if (s == EXCEPTIONAL)
999 throw new ExecutionException(getThrowableException());
1000 return getRawResult();
1001 }
1002
1003 /**
1004 * Waits if necessary for at most the given time for the computation
1005 * to complete, and then retrieves its result, if available.
1006 *
1007 * @param timeout the maximum time to wait
1008 * @param unit the time unit of the timeout argument
1009 * @return the computed result
1010 * @throws CancellationException if the computation was cancelled
1011 * @throws ExecutionException if the computation threw an
1012 * exception
1013 * @throws InterruptedException if the current thread is not a
1014 * member of a ForkJoinPool and was interrupted while waiting
1015 * @throws TimeoutException if the wait timed out
1016 */
1017 public final V get(long timeout, TimeUnit unit)
1018 throws InterruptedException, ExecutionException, TimeoutException {
1019 int s;
1020 long nanos = unit.toNanos(timeout);
1021 if (Thread.interrupted())
1022 throw new InterruptedException();
1023 if ((s = status) >= 0 && nanos > 0L) {
1024 long d = System.nanoTime() + nanos;
1025 long deadline = (d == 0L) ? 1L : d; // avoid 0
1026 Thread t = Thread.currentThread();
1027 if (t instanceof ForkJoinWorkerThread) {
1028 ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1029 s = wt.pool.awaitJoin(wt.workQueue, this, deadline);
1030 }
1031 else if ((s = ((this instanceof CountedCompleter) ?
1032 ForkJoinPool.common.externalHelpComplete(
1033 (CountedCompleter<?>)this, 0) :
1034 ForkJoinPool.common.tryExternalUnpush(this) ?
1035 doExec() : 0)) >= 0) {
1036 long ns, ms; // measure in nanosecs, but wait in millisecs
1037 while ((s = status) >= 0 &&
1038 (ns = deadline - System.nanoTime()) > 0L) {
1039 if ((ms = TimeUnit.NANOSECONDS.toMillis(ns)) > 0L &&
1040 U.compareAndSwapInt(this, STATUS, s, s | SIGNAL)) {
1041 synchronized (this) {
1042 if (status >= 0)
1043 wait(ms); // OK to throw InterruptedException
1044 else
1045 notifyAll();
1046 }
1047 }
1048 }
1049 }
1050 }
1051 if (s >= 0)
1052 s = status;
1053 if ((s &= DONE_MASK) != NORMAL) {
1054 if (s == CANCELLED)
1055 throw new CancellationException();
1056 if (s != EXCEPTIONAL)
1057 throw new TimeoutException();
1058 throw new ExecutionException(getThrowableException());
1059 }
1060 return getRawResult();
1061 }
1062
1063 /**
1064 * Joins this task, without returning its result or throwing its
1065 * exception. This method may be useful when processing
1066 * collections of tasks when some have been cancelled or otherwise
1067 * known to have aborted.
1068 */
1069 public final void quietlyJoin() {
1070 doJoin();
1071 }
1072
1073 /**
1074 * Commences performing this task and awaits its completion if
1075 * necessary, without returning its result or throwing its
1076 * exception.
1077 */
1078 public final void quietlyInvoke() {
1079 doInvoke();
1080 }
1081
1082 /**
1083 * Possibly executes tasks until the pool hosting the current task
1084 * {@linkplain ForkJoinPool#isQuiescent is quiescent}. This
1085 * method may be of use in designs in which many tasks are forked,
1086 * but none are explicitly joined, instead executing them until
1087 * all are processed.
1088 */
1089 public static void helpQuiesce() {
1090 Thread t;
1091 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) {
1092 ForkJoinWorkerThread wt = (ForkJoinWorkerThread)t;
1093 wt.pool.helpQuiescePool(wt.workQueue);
1094 }
1095 else
1096 ForkJoinPool.quiesceCommonPool();
1097 }
1098
1099 /**
1100 * Resets the internal bookkeeping state of this task, allowing a
1101 * subsequent {@code fork}. This method allows repeated reuse of
1102 * this task, but only if reuse occurs when this task has either
1103 * never been forked, or has been forked, then completed and all
1104 * outstanding joins of this task have also completed. Effects
1105 * under any other usage conditions are not guaranteed.
1106 * This method may be useful when executing
1107 * pre-constructed trees of subtasks in loops.
1108 *
1109 * <p>Upon completion of this method, {@code isDone()} reports
1110 * {@code false}, and {@code getException()} reports {@code
1111 * null}. However, the value returned by {@code getRawResult} is
1112 * unaffected. To clear this value, you can invoke {@code
1113 * setRawResult(null)}.
1114 */
1115 public void reinitialize() {
1116 if ((status & DONE_MASK) == EXCEPTIONAL)
1117 clearExceptionalCompletion();
1118 else
1119 status = 0;
1120 }
1121
1122 /**
1123 * Returns the pool hosting the current thread, or {@code null}
1124 * if the current thread is executing outside of any ForkJoinPool.
1125 *
1126 * <p>This method returns {@code null} if and only if {@link
1127 * #inForkJoinPool} returns {@code false}.
1128 *
1129 * @return the pool, or {@code null} if none
1130 */
1131 public static ForkJoinPool getPool() {
1132 Thread t = Thread.currentThread();
1133 return (t instanceof ForkJoinWorkerThread) ?
1134 ((ForkJoinWorkerThread) t).pool : null;
1135 }
1136
1137 /**
1138 * Returns {@code true} if the current thread is a {@link
1139 * ForkJoinWorkerThread} executing as a ForkJoinPool computation.
1140 *
1141 * @return {@code true} if the current thread is a {@link
1142 * ForkJoinWorkerThread} executing as a ForkJoinPool computation,
1143 * or {@code false} otherwise
1144 */
1145 public static boolean inForkJoinPool() {
1146 return Thread.currentThread() instanceof ForkJoinWorkerThread;
1147 }
1148
1149 /**
1150 * Tries to unschedule this task for execution. This method will
1151 * typically (but is not guaranteed to) succeed if this task is
1152 * the most recently forked task by the current thread, and has
1153 * not commenced executing in another thread. This method may be
1154 * useful when arranging alternative local processing of tasks
1155 * that could have been, but were not, stolen.
1156 *
1157 * @return {@code true} if unforked
1158 */
1159 public boolean tryUnfork() {
1160 Thread t;
1161 return (((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1162 ((ForkJoinWorkerThread)t).workQueue.tryUnpush(this) :
1163 ForkJoinPool.common.tryExternalUnpush(this));
1164 }
1165
1166 /**
1167 * Returns an estimate of the number of tasks that have been
1168 * forked by the current worker thread but not yet executed. This
1169 * value may be useful for heuristic decisions about whether to
1170 * fork other tasks.
1171 *
1172 * @return the number of tasks
1173 */
1174 public static int getQueuedTaskCount() {
1175 Thread t; ForkJoinPool.WorkQueue q;
1176 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1177 q = ((ForkJoinWorkerThread)t).workQueue;
1178 else
1179 q = ForkJoinPool.commonSubmitterQueue();
1180 return (q == null) ? 0 : q.queueSize();
1181 }
1182
1183 /**
1184 * Returns an estimate of how many more locally queued tasks are
1185 * held by the current worker thread than there are other worker
1186 * threads that might steal them, or zero if this thread is not
1187 * operating in a ForkJoinPool. This value may be useful for
1188 * heuristic decisions about whether to fork other tasks. In many
1189 * usages of ForkJoinTasks, at steady state, each worker should
1190 * aim to maintain a small constant surplus (for example, 3) of
1191 * tasks, and to process computations locally if this threshold is
1192 * exceeded.
1193 *
1194 * @return the surplus number of tasks, which may be negative
1195 */
1196 public static int getSurplusQueuedTaskCount() {
1197 return ForkJoinPool.getSurplusQueuedTaskCount();
1198 }
1199
1200 // Extension methods
1201
1202 /**
1203 * Returns the result that would be returned by {@link #join}, even
1204 * if this task completed abnormally, or {@code null} if this task
1205 * is not known to have been completed. This method is designed
1206 * to aid debugging, as well as to support extensions. Its use in
1207 * any other context is discouraged.
1208 *
1209 * @return the result, or {@code null} if not completed
1210 */
1211 public abstract V getRawResult();
1212
1213 /**
1214 * Forces the given value to be returned as a result. This method
1215 * is designed to support extensions, and should not in general be
1216 * called otherwise.
1217 *
1218 * @param value the value
1219 */
1220 protected abstract void setRawResult(V value);
1221
1222 /**
1223 * Immediately performs the base action of this task and returns
1224 * true if, upon return from this method, this task is guaranteed
1225 * to have completed normally. This method may return false
1226 * otherwise, to indicate that this task is not necessarily
1227 * complete (or is not known to be complete), for example in
1228 * asynchronous actions that require explicit invocations of
1229 * completion methods. This method may also throw an (unchecked)
1230 * exception to indicate abnormal exit. This method is designed to
1231 * support extensions, and should not in general be called
1232 * otherwise.
1233 *
1234 * @return {@code true} if this task is known to have completed normally
1235 */
1236 protected abstract boolean exec();
1237
1238 /**
1239 * Returns, but does not unschedule or execute, a task queued by
1240 * the current thread but not yet executed, if one is immediately
1241 * available. There is no guarantee that this task will actually
1242 * be polled or executed next. Conversely, this method may return
1243 * null even if a task exists but cannot be accessed without
1244 * contention with other threads. This method is designed
1245 * primarily to support extensions, and is unlikely to be useful
1246 * otherwise.
1247 *
1248 * @return the next task, or {@code null} if none are available
1249 */
1250 protected static ForkJoinTask<?> peekNextLocalTask() {
1251 Thread t; ForkJoinPool.WorkQueue q;
1252 if ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread)
1253 q = ((ForkJoinWorkerThread)t).workQueue;
1254 else
1255 q = ForkJoinPool.commonSubmitterQueue();
1256 return (q == null) ? null : q.peek();
1257 }
1258
1259 /**
1260 * Unschedules and returns, without executing, the next task
1261 * queued by the current thread but not yet executed, if the
1262 * current thread is operating in a ForkJoinPool. This method is
1263 * designed primarily to support extensions, and is unlikely to be
1264 * useful otherwise.
1265 *
1266 * @return the next task, or {@code null} if none are available
1267 */
1268 protected static ForkJoinTask<?> pollNextLocalTask() {
1269 Thread t;
1270 return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1271 ((ForkJoinWorkerThread)t).workQueue.nextLocalTask() :
1272 null;
1273 }
1274
1275 /**
1276 * If the current thread is operating in a ForkJoinPool,
1277 * unschedules and returns, without executing, the next task
1278 * queued by the current thread but not yet executed, if one is
1279 * available, or if not available, a task that was forked by some
1280 * other thread, if available. Availability may be transient, so a
1281 * {@code null} result does not necessarily imply quiescence of
1282 * the pool this task is operating in. This method is designed
1283 * primarily to support extensions, and is unlikely to be useful
1284 * otherwise.
1285 *
1286 * @return a task, or {@code null} if none are available
1287 */
1288 protected static ForkJoinTask<?> pollTask() {
1289 Thread t; ForkJoinWorkerThread wt;
1290 return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1291 (wt = (ForkJoinWorkerThread)t).pool.nextTaskFor(wt.workQueue) :
1292 null;
1293 }
1294
1295 /**
1296 * If the current thread is operating in a ForkJoinPool,
1297 * unschedules and returns, without executing, a task externally
1298 * submitted to the pool, if one is available. Availability may be
1299 * transient, so a {@code null} result does not necessarily imply
1300 * quiescence of the pool. This method is designed primarily to
1301 * support extensions, and is unlikely to be useful otherwise.
1302 *
1303 * @return a task, or {@code null} if none are available
1304 * @since 1.9
1305 */
1306 protected static ForkJoinTask<?> pollSubmission() {
1307 Thread t;
1308 return ((t = Thread.currentThread()) instanceof ForkJoinWorkerThread) ?
1309 ((ForkJoinWorkerThread)t).pool.pollSubmission() : null;
1310 }
1311
1312 // tag operations
1313
1314 /**
1315 * Returns the tag for this task.
1316 *
1317 * @return the tag for this task
1318 * @since 1.8
1319 */
1320 public final short getForkJoinTaskTag() {
1321 return (short)status;
1322 }
1323
1324 /**
1325 * Atomically sets the tag value for this task and returns the old value.
1326 *
1327 * @param newValue the new tag value
1328 * @return the previous value of the tag
1329 * @since 1.8
1330 */
1331 public final short setForkJoinTaskTag(short newValue) {
1332 for (int s;;) {
1333 if (U.compareAndSwapInt(this, STATUS, s = status,
1334 (s & ~SMASK) | (newValue & SMASK)))
1335 return (short)s;
1336 }
1337 }
1338
1339 /**
1340 * Atomically conditionally sets the tag value for this task.
1341 * Among other applications, tags can be used as visit markers
1342 * in tasks operating on graphs, as in methods that check: {@code
1343 * if (task.compareAndSetForkJoinTaskTag((short)0, (short)1))}
1344 * before processing, otherwise exiting because the node has
1345 * already been visited.
1346 *
1347 * @param expect the expected tag value
1348 * @param update the new tag value
1349 * @return {@code true} if successful; i.e., the current value was
1350 * equal to {@code expect} and was changed to {@code update}.
1351 * @since 1.8
1352 */
1353 public final boolean compareAndSetForkJoinTaskTag(short expect, short update) {
1354 for (int s;;) {
1355 if ((short)(s = status) != expect)
1356 return false;
1357 if (U.compareAndSwapInt(this, STATUS, s,
1358 (s & ~SMASK) | (update & SMASK)))
1359 return true;
1360 }
1361 }
1362
1363 /**
1364 * Adapter for Runnables. This implements RunnableFuture
1365 * to be compliant with AbstractExecutorService constraints
1366 * when used in ForkJoinPool.
1367 */
1368 static final class AdaptedRunnable<T> extends ForkJoinTask<T>
1369 implements RunnableFuture<T> {
1370 final Runnable runnable;
1371 T result;
1372 AdaptedRunnable(Runnable runnable, T result) {
1373 if (runnable == null) throw new NullPointerException();
1374 this.runnable = runnable;
1375 this.result = result; // OK to set this even before completion
1376 }
1377 public final T getRawResult() { return result; }
1378 public final void setRawResult(T v) { result = v; }
1379 public final boolean exec() { runnable.run(); return true; }
1380 public final void run() { invoke(); }
1381 private static final long serialVersionUID = 5232453952276885070L;
1382 }
1383
1384 /**
1385 * Adapter for Runnables without results.
1386 */
1387 static final class AdaptedRunnableAction extends ForkJoinTask<Void>
1388 implements RunnableFuture<Void> {
1389 final Runnable runnable;
1390 AdaptedRunnableAction(Runnable runnable) {
1391 if (runnable == null) throw new NullPointerException();
1392 this.runnable = runnable;
1393 }
1394 public final Void getRawResult() { return null; }
1395 public final void setRawResult(Void v) { }
1396 public final boolean exec() { runnable.run(); return true; }
1397 public final void run() { invoke(); }
1398 private static final long serialVersionUID = 5232453952276885070L;
1399 }
1400
1401 /**
1402 * Adapter for Runnables in which failure forces worker exception.
1403 */
1404 static final class RunnableExecuteAction extends ForkJoinTask<Void> {
1405 final Runnable runnable;
1406 RunnableExecuteAction(Runnable runnable) {
1407 if (runnable == null) throw new NullPointerException();
1408 this.runnable = runnable;
1409 }
1410 public final Void getRawResult() { return null; }
1411 public final void setRawResult(Void v) { }
1412 public final boolean exec() { runnable.run(); return true; }
1413 void internalPropagateException(Throwable ex) {
1414 rethrow(ex); // rethrow outside exec() catches.
1415 }
1416 private static final long serialVersionUID = 5232453952276885070L;
1417 }
1418
1419 /**
1420 * Adapter for Callables.
1421 */
1422 static final class AdaptedCallable<T> extends ForkJoinTask<T>
1423 implements RunnableFuture<T> {
1424 final Callable<? extends T> callable;
1425 T result;
1426 AdaptedCallable(Callable<? extends T> callable) {
1427 if (callable == null) throw new NullPointerException();
1428 this.callable = callable;
1429 }
1430 public final T getRawResult() { return result; }
1431 public final void setRawResult(T v) { result = v; }
1432 public final boolean exec() {
1433 try {
1434 result = callable.call();
1435 return true;
1436 } catch (RuntimeException rex) {
1437 throw rex;
1438 } catch (Exception ex) {
1439 throw new RuntimeException(ex);
1440 }
1441 }
1442 public final void run() { invoke(); }
1443 private static final long serialVersionUID = 2838392045355241008L;
1444 }
1445
1446 /**
1447 * Returns a new {@code ForkJoinTask} that performs the {@code run}
1448 * method of the given {@code Runnable} as its action, and returns
1449 * a null result upon {@link #join}.
1450 *
1451 * @param runnable the runnable action
1452 * @return the task
1453 */
1454 public static ForkJoinTask<?> adapt(Runnable runnable) {
1455 return new AdaptedRunnableAction(runnable);
1456 }
1457
1458 /**
1459 * Returns a new {@code ForkJoinTask} that performs the {@code run}
1460 * method of the given {@code Runnable} as its action, and returns
1461 * the given result upon {@link #join}.
1462 *
1463 * @param runnable the runnable action
1464 * @param result the result upon completion
1465 * @param <T> the type of the result
1466 * @return the task
1467 */
1468 public static <T> ForkJoinTask<T> adapt(Runnable runnable, T result) {
1469 return new AdaptedRunnable<T>(runnable, result);
1470 }
1471
1472 /**
1473 * Returns a new {@code ForkJoinTask} that performs the {@code call}
1474 * method of the given {@code Callable} as its action, and returns
1475 * its result upon {@link #join}, translating any checked exceptions
1476 * encountered into {@code RuntimeException}.
1477 *
1478 * @param callable the callable action
1479 * @param <T> the type of the callable's result
1480 * @return the task
1481 */
1482 public static <T> ForkJoinTask<T> adapt(Callable<? extends T> callable) {
1483 return new AdaptedCallable<T>(callable);
1484 }
1485
1486 // Serialization support
1487
1488 private static final long serialVersionUID = -7721805057305804111L;
1489
1490 /**
1491 * Saves this task to a stream (that is, serializes it).
1492 *
1493 * @param s the stream
1494 * @throws java.io.IOException if an I/O error occurs
1495 * @serialData the current run status and the exception thrown
1496 * during execution, or {@code null} if none
1497 */
1498 private void writeObject(java.io.ObjectOutputStream s)
1499 throws java.io.IOException {
1500 s.defaultWriteObject();
1501 s.writeObject(getException());
1502 }
1503
1504 /**
1505 * Reconstitutes this task from a stream (that is, deserializes it).
1506 * @param s the stream
1507 * @throws ClassNotFoundException if the class of a serialized object
1508 * could not be found
1509 * @throws java.io.IOException if an I/O error occurs
1510 */
1511 private void readObject(java.io.ObjectInputStream s)
1512 throws java.io.IOException, ClassNotFoundException {
1513 s.defaultReadObject();
1514 Object ex = s.readObject();
1515 if (ex != null)
1516 setExceptionalCompletion((Throwable)ex);
1517 }
1518
1519 // Unsafe mechanics
1520 private static final sun.misc.Unsafe U = sun.misc.Unsafe.getUnsafe();
1521 private static final long STATUS;
1522
1523 static {
1524 exceptionTableLock = new ReentrantLock();
1525 exceptionTableRefQueue = new ReferenceQueue<Object>();
1526 exceptionTable = new ExceptionNode[EXCEPTION_MAP_CAPACITY];
1527 try {
1528 STATUS = U.objectFieldOffset
1529 (ForkJoinTask.class.getDeclaredField("status"));
1530 } catch (ReflectiveOperationException e) {
1531 throw new Error(e);
1532 }
1533 }
1534
1535 }