RecursiveTask.java revision 91770798d8b9280d48d30df2ed7f63b3ed9b036f 
1/*
2 * Written by Doug Lea with assistance from members of JCP JSR-166
3 * Expert Group and released to the public domain, as explained at
4 * http://creativecommons.org/publicdomain/zero/1.0/
5 */
6
7package java.util.concurrent;
8
9/**
10 * A recursive result-bearing {@link ForkJoinTask}.
11 *
12 * <p>For a classic example, here is a task computing Fibonacci numbers:
13 *
14 *  <pre> {@code
15 * class Fibonacci extends RecursiveTask<Integer> {
16 *   final int n;
17 *   Fibonacci(int n) { this.n = n; }
18 *   Integer compute() {
19 *     if (n <= 1)
20 *       return n;
21 *     Fibonacci f1 = new Fibonacci(n - 1);
22 *     f1.fork();
23 *     Fibonacci f2 = new Fibonacci(n - 2);
24 *     return f2.compute() + f1.join();
25 *   }
26 * }}</pre>
27 *
28 * However, besides being a dumb way to compute Fibonacci functions
29 * (there is a simple fast linear algorithm that you'd use in
30 * practice), this is likely to perform poorly because the smallest
31 * subtasks are too small to be worthwhile splitting up. Instead, as
32 * is the case for nearly all fork/join applications, you'd pick some
33 * minimum granularity size (for example 10 here) for which you always
34 * sequentially solve rather than subdividing.
35 *
36 * @since 1.7
37 * @hide
38 * @author Doug Lea
39 */
40public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
41    private static final long serialVersionUID = 5232453952276485270L;
42
43    /**
44     * The result of the computation.
45     */
46    V result;
47
48    /**
49     * The main computation performed by this task.
50     */
51    protected abstract V compute();
52
53    public final V getRawResult() {
54        return result;
55    }
56
57    protected final void setRawResult(V value) {
58        result = value;
59    }
60
61    /**
62     * Implements execution conventions for RecursiveTask.
63     */
64    protected final boolean exec() {
65        result = compute();
66        return true;
67    }
68
69}
70