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dl |
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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/licenses/publicdomain |
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*/ |
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package jsr166y; |
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/** |
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* Recursive result-bearing ForkJoinTasks. |
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* <p> For a classic example, here is a task computing Fibonacci numbers: |
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* |
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* <pre> |
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* class Fibonacci extends RecursiveTask<Integer> { |
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* final int n; |
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* Fibonnaci(int n) { this.n = n; } |
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* Integer compute() { |
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* if (n <= 1) |
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* return n; |
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* Fibonacci f1 = new Fibonacci(n - 1); |
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* f1.fork(); |
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* Fibonacci f2 = new Fibonacci(n - 2); |
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* return f2.compute() + f1.join(); |
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* } |
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* } |
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* </pre> |
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* |
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* However, besides being a dumb way to compute Fibonacci functions |
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* (there is a simple fast linear algorithm that you'd use in |
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* practice), this is likely to perform poorly because the smallest |
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* subtasks are too small to be worthwhile splitting up. Instead, as |
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* is the case for nearly all fork/join applications, you'd pick some |
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* minimum granularity size (for example 10 here) for which you always |
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* sequentially solve rather than subdividing. |
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* |
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*/ |
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public abstract class RecursiveTask<V> extends ForkJoinTask<V> { |
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/** |
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* Empty contructor for use by subclasses. |
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*/ |
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protected RecursiveTask() { |
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} |
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/** |
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* The result returned by compute method. |
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*/ |
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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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*/ |
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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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} |