115 lines
3.8 KiB
Java
115 lines
3.8 KiB
Java
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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/*
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* This file is available under and governed by the GNU General Public
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* License version 2 only, as published by the Free Software Foundation.
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* However, the following notice accompanied the original version of this
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* file:
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*
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* Written by Doug Lea with assistance from members of JCP JSR-166
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* Expert Group and released to the public domain, as explained at
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* http://creativecommons.org/publicdomain/zero/1.0/
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*/
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package java.util.concurrent;
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/**
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* A recursive result-bearing {@link ForkJoinTask}.
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*
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* <p>For example, here is a task-based program for computing Factorials:
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*
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* <pre> {@code
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* import java.util.concurrent.RecursiveTask;
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* import java.math.BigInteger;
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* public class Factorial {
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* static class FactorialTask extends RecursiveTask<BigInteger> {
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* private final int from, to;
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* FactorialTask(int from, int to) { this.from = from; this.to = to; }
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* protected BigInteger compute() {
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* int range = to - from;
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* if (range == 0) { // base case
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* return BigInteger.valueOf(from);
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* } else if (range == 1) { // too small to parallelize
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* return BigInteger.valueOf(from).multiply(BigInteger.valueOf(to));
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* } else { // split in half
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* int mid = from + range / 2;
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* FactorialTask leftTask = new FactorialTask(from, mid);
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* leftTask.fork(); // perform about half the work locally
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* return new FactorialTask(mid + 1, to).compute()
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* .multiply(leftTask.join());
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* }
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* }
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* }
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* static BigInteger factorial(int n) { // uses ForkJoinPool.commonPool()
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* return (n <= 1) ? BigInteger.ONE : new FactorialTask(1, n).invoke();
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* }
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* public static void main(String[] args) {
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* System.out.println(factorial(Integer.parseInt(args[0])));
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* }
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* }}</pre>
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*
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* @param <V> the type of the result of the task
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*
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* @since 1.7
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* @author Doug Lea
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*/
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public abstract class RecursiveTask<V> extends ForkJoinTask<V> {
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private static final long serialVersionUID = 5232453952276485270L;
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/**
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* Constructor for subclasses to call.
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*/
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public RecursiveTask() {}
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/**
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* The result of the computation.
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*/
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@SuppressWarnings("serial") // Conditionally serializable
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V result;
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/**
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* The main computation performed by this task.
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* @return the result of the computation
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*/
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protected abstract V compute();
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public final V getRawResult() {
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return result;
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}
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protected final void setRawResult(V value) {
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result = value;
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}
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/**
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* Implements execution conventions for RecursiveTask.
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*/
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protected final boolean exec() {
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result = compute();
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return true;
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}
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}
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