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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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|
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package java.util.concurrent; |
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|
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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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* @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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/** |
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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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/** |
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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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/** |
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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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|
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public final V getRawResult() { |
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return result; |
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} |
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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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/** |
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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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} |
