1 /*
   2  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   3  *
   4  * This code is free software; you can redistribute it and/or modify it
   5  * under the terms of the GNU General Public License version 2 only, as
   6  * published by the Free Software Foundation.  Oracle designates this
   7  * particular file as subject to the "Classpath" exception as provided
   8  * by Oracle in the LICENSE file that accompanied this code.
   9  *
  10  * This code is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  13  * version 2 for more details (a copy is included in the LICENSE file that
  14  * accompanied this code).
  15  *
  16  * You should have received a copy of the GNU General Public License version
  17  * 2 along with this work; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  19  *
  20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  21  * or visit www.oracle.com if you need additional information or have any
  22  * questions.
  23  */
  24 
  25 /*
  26  * This file is available under and governed by the GNU General Public
  27  * License version 2 only, as published by the Free Software Foundation.
  28  * However, the following notice accompanied the original version of this
  29  * file:
  30  *
  31  * Written by Doug Lea with assistance from members of JCP JSR-166
  32  * Expert Group and released to the public domain, as explained at
  33  * http://creativecommons.org/publicdomain/zero/1.0/
  34  */
  35 
  36 package java.util.concurrent;
  37 
  38 /**
  39  * A recursive result-bearing {@link ForkJoinTask}.
  40  *
  41  * <p>For a classic example, here is a task computing Fibonacci numbers:
  42  *
  43  * <pre> {@code
  44  * class Fibonacci extends RecursiveTask<Integer> {
  45  *   final int n;
  46  *   Fibonacci(int n) { this.n = n; }
  47  *   protected Integer compute() {
  48  *     if (n <= 1)
  49  *       return n;
  50  *     Fibonacci f1 = new Fibonacci(n - 1);
  51  *     f1.fork();
  52  *     Fibonacci f2 = new Fibonacci(n - 2);
  53  *     return f2.compute() + f1.join();
  54  *   }
  55  * }}</pre>
  56  *
  57  * However, besides being a dumb way to compute Fibonacci functions
  58  * (there is a simple fast linear algorithm that you'd use in
  59  * practice), this is likely to perform poorly because the smallest
  60  * subtasks are too small to be worthwhile splitting up. Instead, as
  61  * is the case for nearly all fork/join applications, you'd pick some
  62  * minimum granularity size (for example 10 here) for which you always
  63  * sequentially solve rather than subdividing.
  64  *
  65  * @since 1.7
  66  * @author Doug Lea
  67  */
  68 public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
  69     private static final long serialVersionUID = 5232453952276485270L;
  70 
  71     /**
  72      * Constructor for subclasses to call.
  73      */
  74     public RecursiveTask() {}
  75 
  76     /**
  77      * The result of the computation.
  78      */
  79     @SuppressWarnings("serial") // Conditionally serializable
  80     V result;
  81 
  82     /**
  83      * The main computation performed by this task.
  84      * @return the result of the computation
  85      */
  86     protected abstract V compute();
  87 
  88     public final V getRawResult() {
  89         return result;
  90     }
  91 
  92     protected final void setRawResult(V value) {
  93         result = value;
  94     }
  95 
  96     /**
  97      * Implements execution conventions for RecursiveTask.
  98      */
  99     protected final boolean exec() {
 100         result = compute();
 101         return true;
 102     }
 103 
 104 }