RecursiveTask.java revision fe4f216fd6ef2518bfefd6b7970f60befacf5cdd 
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 * @author Doug Lea
38 */
39public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
40    private static final long serialVersionUID = 5232453952276485270L;
41
42    /**
43     * The result of the computation.
44     */
45    V result;
46
47    /**
48     * The main computation performed by this task.
49     */
50    protected abstract V compute();
51
52    public final V getRawResult() {
53        return result;
54    }
55
56    protected final void setRawResult(V value) {
57        result = value;
58    }
59
60    /**
61     * Implements execution conventions for RecursiveTask.
62     */
63    protected final boolean exec() {
64        result = compute();
65        return true;
66    }
67
68}
69