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.
 *
 * @since 1.7
 * @author Doug Lea
 */
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:	1.5
Committed:	Wed Jul 22 01:36:51 2009 UTC (14 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.4:	+2 -0 lines
Log Message:	Add @since, @author tags
#	User	Rev	Content
1	dl	1.1	/*
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	jsr166	1.4	* <pre> {@code
14			* class Fibonacci extends RecursiveTask<Integer> {
15	dl	1.1	* final int n;
16	jsr166	1.3	* Fibonacci(int n) { this.n = n; }
17	dl	1.1	* Integer compute() {
18	jsr166	1.4	* if (n <= 1)
19	dl	1.1	* 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	jsr166	1.4	* }}</pre>
26	dl	1.1	*
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	jsr166	1.2	* sequentially solve rather than subdividing.
34	dl	1.1	*
35	jsr166	1.5	* @since 1.7
36			* @author Doug Lea
37	dl	1.1	*/
38			public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
39
40			/**
41	jsr166	1.3	* Empty constructor for use by subclasses.
42	dl	1.1	*/
43			protected RecursiveTask() {
44			}
45
46			/**
47			* The result returned by compute method.
48			*/
49			V result;
50
51			/**
52	jsr166	1.2	* The main computation performed by this task.
53	dl	1.1	*/
54			protected abstract V compute();
55
56			public final V getRawResult() {
57			return result;
58			}
59
60			protected final void setRawResult(V value) {
61			result = value;
62			}
63
64			/**
65			* Implements execution conventions for RecursiveTask
66			*/
67			protected final boolean exec() {
68			result = compute();
69			return true;
70			}
71
72			}