src/jsr166y/RecursiveTask.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/licenses/publicdomain
 */

package jsr166y;

/**
 * Recursive result-bearing ForkJoinTasks.
 * <p> For a classic example, here is a task computing Fibonacci numbers:
 *
 *  <pre> {@code
 * class Fibonacci extends RecursiveTask<Integer> {
 *   final int n;
 *   Fibonacci(int n) { this.n = n; }
 *   Integer compute() {
 *     if (n <= 1)
 *        return n;
 *     Fibonacci f1 = new Fibonacci(n - 1);
 *     f1.fork();
 *     Fibonacci f2 = new Fibonacci(n - 2);
 *     return f2.compute() + f1.join();
 *   }
 * }}</pre>
 *
 * However, besides being a dumb way to compute Fibonacci functions
 * (there is a simple fast linear algorithm that you'd use in
 * practice), this is likely to perform poorly because the smallest
 * subtasks are too small to be worthwhile splitting up. Instead, as
 * is the case for nearly all fork/join applications, you'd pick some
 * minimum granularity size (for example 10 here) for which you always
 * sequentially solve rather than subdividing.
 *
 */
public abstract class RecursiveTask<V> extends ForkJoinTask<V> {

    /**
     * Empty constructor for use by subclasses.
     */
    protected RecursiveTask() {
    }

    /**
     * The result returned by compute method.
     */
    V result;

    /**
     * The main computation performed by this task.
     */
    protected abstract V compute();

    public final V getRawResult() {
        return result;
    }

    protected final void setRawResult(V value) {
        result = value;
    }

    /**
     * Implements execution conventions for RecursiveTask
     */
    protected final boolean exec() {
        result = compute();
        return true;
    }

}
Revision:	1.4
Committed:	Mon Jul 20 22:40:09 2009 UTC (14 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.3:	+4 -5 lines
Log Message:	<pre> => <pre> @code
#	Content
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/licenses/publicdomain
5	*/
6
7	package jsr166y;
8
9	/**
10	* Recursive result-bearing ForkJoinTasks.
11	* <p> For a classic example, here is a task computing Fibonacci numbers:
12	*
13	* <pre> {@code
14	* class Fibonacci extends RecursiveTask<Integer> {
15	* final int n;
16	* Fibonacci(int n) { this.n = n; }
17	* Integer compute() {
18	* if (n <= 1)
19	* return n;
20	* Fibonacci f1 = new Fibonacci(n - 1);
21	* f1.fork();
22	* Fibonacci f2 = new Fibonacci(n - 2);
23	* return f2.compute() + f1.join();
24	* }
25	* }}</pre>
26	*
27	* However, besides being a dumb way to compute Fibonacci functions
28	* (there is a simple fast linear algorithm that you'd use in
29	* practice), this is likely to perform poorly because the smallest
30	* subtasks are too small to be worthwhile splitting up. Instead, as
31	* is the case for nearly all fork/join applications, you'd pick some
32	* minimum granularity size (for example 10 here) for which you always
33	* sequentially solve rather than subdividing.
34	*
35	*/
36	public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
37
38	/**
39	* Empty constructor for use by subclasses.
40	*/
41	protected RecursiveTask() {
42	}
43
44	/**
45	* The result returned by compute method.
46	*/
47	V result;
48
49	/**
50	* The main computation performed by this task.
51	*/
52	protected abstract V compute();
53
54	public final V getRawResult() {
55	return result;
56	}
57
58	protected final void setRawResult(V value) {
59	result = value;
60	}
61
62	/**
63	* Implements execution conventions for RecursiveTask
64	*/
65	protected final boolean exec() {
66	result = compute();
67	return true;
68	}
69
70	}