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>
 * class Fibonacci extends RecursiveTask&lt;Integer&gt; {
 *   final int n;
 *   Fibonnaci(int n) { this.n = n; }
 *   Integer compute() {
 *     if (n &lt;= 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 contructor 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:	1.2
Committed:	Mon Jul 20 21:45:06 2009 UTC (14 years, 9 months ago) by jsr166
Branch:	MAIN
Changes since 1.1:	+2 -2 lines
Log Message:	whitespace
#	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			* <pre>
14			* class Fibonacci extends RecursiveTask<Integer> {
15			* final int n;
16			* Fibonnaci(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			* }
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	jsr166	1.2	* sequentially solve rather than subdividing.
35	dl	1.1	*
36			*/
37			public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
38
39			/**
40			* Empty contructor for use by subclasses.
41			*/
42			protected RecursiveTask() {
43			}
44
45			/**
46			* The result returned by compute method.
47			*/
48			V result;
49
50			/**
51	jsr166	1.2	* The main computation performed by this task.
52	dl	1.1	*/
53			protected abstract V compute();
54
55			public final V getRawResult() {
56			return result;
57			}
58
59			protected final void setRawResult(V value) {
60			result = value;
61			}
62
63			/**
64			* Implements execution conventions for RecursiveTask
65			*/
66			protected final boolean exec() {
67			result = compute();
68			return true;
69			}
70
71			}