src/jsr166e/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 jsr166e;

/**
 * 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.
     * @return the result of the computation
     */
    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:	Fri Jul 26 16:36:21 2013 UTC (10 years, 8 months ago) by jsr166
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.3:	+1 -1 lines
Log Message:	make compute() protected
#	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/publicdomain/zero/1.0/
5	*/
6
7	package jsr166e;
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	* protected 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	*/
39	public 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	* @return the result of the computation
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	}