/* * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ /* * This file is available under and governed by the GNU General Public * License version 2 only, as published by the Free Software Foundation. * However, the following notice accompanied the original version of this * file: * * 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}. * *

For example, here is a task-based program for computing Factorials: * *

 {@code
 * import java.util.concurrent.RecursiveTask;
 * import java.math.BigInteger;
 * public class Factorial {
 *   static class FactorialTask extends RecursiveTask {
 *     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])));
 *   }
 * }}
* * @param the type of the result of the task * * @since 1.7 * @author Doug Lea */ public abstract class RecursiveTask extends ForkJoinTask { 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; } }