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package jsr166y; |
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/** |
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* Recursive resultless ForkJoinTasks. This class establishes |
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* conventions to parameterize resultless actions as {@code Void} |
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* ForkJoinTasks. Because {@code null} is the only valid value of |
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* type {@code Void}, methods such as join always return {@code null} |
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* upon completion. |
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* A recursive resultless {@link ForkJoinTask}. This class |
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* establishes conventions to parameterize resultless actions as |
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* {@code Void} {@code ForkJoinTask}s. Because {@code null} is the |
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* only valid value of type {@code Void}, methods such as join always |
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* return {@code null} upon completion. |
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* |
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* <p><b>Sample Usages.</b> Here is a sketch of a ForkJoin sort that |
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* sorts a given {@code long[]} array: |
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* of each element of a double array, by subdividing out only the |
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* right-hand-sides of repeated divisions by two, and keeping track of |
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* them with a chain of {@code next} references. It uses a dynamic |
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* threshold based on method {@code surplus}, but counterbalances |
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* potential excess partitioning by directly performing leaf actions |
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* on unstolen tasks rather than further subdividing. |
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* threshold based on method {@code getSurplusQueuedTaskCount}, but |
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* counterbalances potential excess partitioning by directly |
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* performing leaf actions on unstolen tasks rather than further |
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* subdividing. |
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* |
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* <pre> {@code |
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* double sumOfSquares(ForkJoinPool pool, double[] array) { |
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* int n = array.length; |
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* int seqSize = 1 + n / (8 * pool.getParallelism()); |
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* Applyer a = new Applyer(array, 0, n, seqSize, null); |
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* Applyer a = new Applyer(array, 0, n, null); |
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* pool.invoke(a); |
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* return a.result; |
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* } |
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* |
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* class Applyer extends RecursiveAction { |
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* final double[] array; |
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* final int lo, hi, seqSize; |
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* final int lo, hi; |
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* double result; |
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* Applyer next; // keeps track of right-hand-side tasks |
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* Applyer(double[] array, int lo, int hi, int seqSize, Applyer next) { |
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* Applyer(double[] array, int lo, int hi, Applyer next) { |
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* this.array = array; this.lo = lo; this.hi = hi; |
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* this.seqSize = seqSize; this.next = next; |
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* this.next = next; |
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* } |
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* |
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* double atLeaf(int l, int r) { |
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* double atLeaf(int l, int h) { |
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* double sum = 0; |
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* for (int i = l; i < h; ++i) // perform leftmost base step |
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* sum += array[i] * array[i]; |
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* int l = lo; |
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* int h = hi; |
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* Applyer right = null; |
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* while (h - l > 1 && |
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* ForkJoinWorkerThread.getEstimatedSurplusTaskCount() <= 3) { |
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* while (h - l > 1 && getSurplusQueuedTaskCount() <= 3) { |
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* int mid = (l + h) >>> 1; |
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* right = new Applyer(array, mid, h, seqSize, right); |
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* right = new Applyer(array, mid, h, right); |
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* right.fork(); |
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* h = mid; |
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* } |
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* @author Doug Lea |
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*/ |
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public abstract class RecursiveAction extends ForkJoinTask<Void> { |
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private static final long serialVersionUID = 5232453952276485070L; |
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/** |
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* The main computation performed by this task. |
