RecursiveTask.java revision 29957558cf0db700bfaae360a80c42dc3871d0e5 
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
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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
36package 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 *   protected 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 */
68public 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     * @return the result of the computation
79     */
80    protected abstract V compute();
81
82    public final V getRawResult() {
83        return result;
84    }
85
86    protected final void setRawResult(V value) {
87        result = value;
88    }
89
90    /**
91     * Implements execution conventions for RecursiveTask.
92     */
93    protected final boolean exec() {
94        result = compute();
95        return true;
96    }
97
98}
99