util/concurrent/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 java.util.concurrent;

/**
 * A recursive result-bearing {@link ForkJoinTask}.
 *
 * <p>For example, here is a task-based program for computing Factorials:
 *
 * <pre> {@code
 * import java.util.concurrent.RecursiveTask;
 * import java.math.BigInteger;
 * public class Factorial {
 *   static class FactorialTask extends RecursiveTask<BigInteger> {
 *     private final int from, to;
 *     FactorialTask(int from, int to) { this.from = from; this.to = to; }
 *     protected BigInteger compute() {
 *       int range = to - from;
 *       if (range == 0) {                       // base case
 *         return BigInteger.valueOf(from);
 *       } else if (range == 1) {                // too small to parallelize
 *         return BigInteger.valueOf(from).multiply(BigInteger.valueOf(to));
 *       } else {                                // split in half
 *         int mid = from + range / 2;
 *         FactorialTask leftTask = new FactorialTask(from, mid);
 *         leftTask.fork();         // perform about half the work locally
 *         return new FactorialTask(mid + 1, to).compute()
 *                .multiply(leftTask.join());
 *       }
 *     }
 *   }
 *   static BigInteger factorial(int n) { // uses ForkJoinPool.commonPool()
 *     return (n <= 1) ? BigInteger.ONE : new FactorialTask(1, n).invoke();
 *   }
 *   public static void main(String[] args) {
 *     System.out.println(factorial(Integer.parseInt(args[0])));
 *   }
 * }}</pre>
 *
 * @since 1.7
 * @author Doug Lea
 */
public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
    private static final long serialVersionUID = 5232453952276485270L;

    /**
     * Constructor for subclasses to call.
     */
    public RecursiveTask() {}

    /**
     * The result of the computation.
     */
    @SuppressWarnings("serial") // Conditionally serializable
    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:	1.12
Committed:	Fri Mar 18 16:01:42 2022 UTC (2 years, 2 months ago) by dl
Branch:	MAIN
CVS Tags:	HEAD
Changes since 1.11:	+27 -19 lines
Log Message:	jdk17+ suppressWarnings, FJ updates
#	User	Rev	Content
1	jsr166	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	1.5	* http://creativecommons.org/publicdomain/zero/1.0/
5	jsr166	1.1	*/
6
7			package java.util.concurrent;
8
9			/**
10	jsr166	1.4	* A recursive result-bearing {@link ForkJoinTask}.
11			*
12	dl	1.12	* <p>For example, here is a task-based program for computing Factorials:
13	jsr166	1.1	*
14	jsr166	1.9	* <pre> {@code
15	dl	1.12	* import java.util.concurrent.RecursiveTask;
16			* import java.math.BigInteger;
17			* public class Factorial {
18			* static class FactorialTask extends RecursiveTask<BigInteger> {
19			* private final int from, to;
20			* FactorialTask(int from, int to) { this.from = from; this.to = to; }
21			* protected BigInteger compute() {
22			* int range = to - from;
23			* if (range == 0) { // base case
24			* return BigInteger.valueOf(from);
25			* } else if (range == 1) { // too small to parallelize
26			* return BigInteger.valueOf(from).multiply(BigInteger.valueOf(to));
27			* } else { // split in half
28			* int mid = from + range / 2;
29			* FactorialTask leftTask = new FactorialTask(from, mid);
30			* leftTask.fork(); // perform about half the work locally
31			* return new FactorialTask(mid + 1, to).compute()
32			* .multiply(leftTask.join());
33			* }
34			* }
35			* }
36			* static BigInteger factorial(int n) { // uses ForkJoinPool.commonPool()
37			* return (n <= 1) ? BigInteger.ONE : new FactorialTask(1, n).invoke();
38			* }
39			* public static void main(String[] args) {
40			* System.out.println(factorial(Integer.parseInt(args[0])));
41	jsr166	1.1	* }
42			* }}</pre>
43			*
44			* @since 1.7
45			* @author Doug Lea
46			*/
47			public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
48	jsr166	1.3	private static final long serialVersionUID = 5232453952276485270L;
49	jsr166	1.1
50			/**
51	jsr166	1.11	* Constructor for subclasses to call.
52			*/
53			public RecursiveTask() {}
54
55			/**
56	jsr166	1.2	* The result of the computation.
57	jsr166	1.1	*/
58	jsr166	1.10	@SuppressWarnings("serial") // Conditionally serializable
59	jsr166	1.1	V result;
60
61			/**
62			* The main computation performed by this task.
63	jsr166	1.7	* @return the result of the computation
64	jsr166	1.1	*/
65			protected abstract V compute();
66
67			public final V getRawResult() {
68			return result;
69			}
70
71			protected final void setRawResult(V value) {
72			result = value;
73			}
74
75			/**
76			* Implements execution conventions for RecursiveTask.
77			*/
78			protected final boolean exec() {
79			result = compute();
80			return true;
81			}
82
83			}