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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 | } | ||