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| 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 | +/** | |
| 39 | + * A recursive result-bearing {@link ForkJoinTask}. | |
| 40 | + * | |
| 41 | + * <p>For a classic example, here is a task computing Fibonacci numbers: | |
| 42 | + * | |
| 43 | + * <pre> {@code | |
| 44 | + * class Fibonacci extends RecursiveTask<Integer> { | |
| 45 | + * final int n; | |
| 46 | + * Fibonacci(int n) { this.n = n; } | |
| 47 | + * Integer compute() { | |
| 48 | + * if (n <= 1) | |
| 49 | + * return n; | |
| 50 | + * Fibonacci f1 = new Fibonacci(n - 1); | |
| 51 | + * f1.fork(); | |
| 52 | + * Fibonacci f2 = new Fibonacci(n - 2); | |
| 53 | + * return f2.compute() + f1.join(); | |
| 54 | + * } | |
| 55 | + * }}</pre> | |
| 56 | + * | |
| 57 | + * However, besides being a dumb way to compute Fibonacci functions | |
| 58 | + * (there is a simple fast linear algorithm that you'd use in | |
| 59 | + * practice), this is likely to perform poorly because the smallest | |
| 60 | + * subtasks are too small to be worthwhile splitting up. Instead, as | |
| 61 | + * is the case for nearly all fork/join applications, you'd pick some | |
| 62 | + * minimum granularity size (for example 10 here) for which you always | |
| 63 | + * sequentially solve rather than subdividing. | |
| 64 | + * | |
| 65 | + * @since 1.7 | |
| 66 | + * @author Doug Lea | |
| 67 | + */ | |
| 68 | +public abstract class RecursiveTask<V> extends ForkJoinTask<V> { | |
| 69 | + private static final long serialVersionUID = 5232453952276485270L; | |
| 70 | + | |
| 71 | + /** | |
| 72 | + * The result of the computation. | |
| 73 | + */ | |
| 74 | + V result; | |
| 75 | + | |
| 76 | + /** | |
| 77 | + * The main computation performed by this task. | |
| 78 | + */ | |
| 79 | + protected abstract V compute(); | |
| 80 | + | |
| 81 | + public final V getRawResult() { | |
| 82 | + return result; | |
| 83 | + } | |
| 84 | + | |
| 85 | + protected final void setRawResult(V value) { | |
| 86 | + result = value; | |
| 87 | + } | |
| 88 | + | |
| 89 | + /** | |
| 90 | + * Implements execution conventions for RecursiveTask. | |
| 91 | + */ | |
| 92 | + protected final boolean exec() { | |
| 93 | + result = compute(); | |
| 94 | + return true; | |
| 95 | + } | |
| 96 | + | |
| 97 | +} | |