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/publicdomain/zero/1.0/
 */

package jsr166y;

/**
 * A recursive result-bearing {@link ForkJoinTask}.
 *
 * <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; }
 *   protected 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> {
    private static final long serialVersionUID = 5232453952276485270L;

    /**
     * The result of the computation.
     */
    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:	1.13
Committed:	Fri Jul 26 16:36:21 2013 UTC (10 years, 9 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.12:	+1 -1 lines
Log Message:	make compute() protected
#	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	jsr166	1.11	* http://creativecommons.org/publicdomain/zero/1.0/
5	dl	1.1	*/
6
7			package jsr166y;
8
9			/**
10	jsr166	1.10	* A recursive result-bearing {@link ForkJoinTask}.
11			*
12			* <p>For a classic example, here is a task computing Fibonacci numbers:
13	dl	1.1	*
14	jsr166	1.4	* <pre> {@code
15			* class Fibonacci extends RecursiveTask<Integer> {
16	dl	1.1	* final int n;
17	jsr166	1.3	* Fibonacci(int n) { this.n = n; }
18	jsr166	1.13	* protected Integer compute() {
19	jsr166	1.4	* if (n <= 1)
20	jsr166	1.12	* return n;
21	dl	1.1	* Fibonacci f1 = new Fibonacci(n - 1);
22			* f1.fork();
23			* Fibonacci f2 = new Fibonacci(n - 2);
24			* return f2.compute() + f1.join();
25			* }
26	jsr166	1.4	* }}</pre>
27	dl	1.1	*
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	jsr166	1.2	* sequentially solve rather than subdividing.
35	dl	1.1	*
36	jsr166	1.5	* @since 1.7
37			* @author Doug Lea
38	dl	1.1	*/
39			public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
40	dl	1.9	private static final long serialVersionUID = 5232453952276485270L;
41	dl	1.1
42			/**
43	jsr166	1.8	* The result of the computation.
44	dl	1.1	*/
45			V result;
46
47			/**
48	jsr166	1.2	* The main computation performed by this task.
49	dl	1.1	*/
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	jsr166	1.7	* Implements execution conventions for RecursiveTask.
62	dl	1.1	*/
63			protected final boolean exec() {
64			result = compute();
65			return true;
66			}
67
68			}