| 16 |
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* <p><b>Sample Usages.</b> Here is a sketch of a ForkJoin sort that |
| 17 |
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* sorts a given {@code long[]} array: |
| 18 |
|
* |
| 19 |
< |
* <pre> |
| 19 |
> |
* <pre> {@code |
| 20 |
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* class SortTask extends RecursiveAction { |
| 21 |
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* final long[] array; final int lo; final int hi; |
| 22 |
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* SortTask(long[] array, int lo, int hi) { |
| 23 |
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* this.array = array; this.lo = lo; this.hi = hi; |
| 24 |
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* } |
| 25 |
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* protected void compute() { |
| 26 |
< |
* if (hi - lo < THRESHOLD) |
| 26 |
> |
* if (hi - lo < THRESHOLD) |
| 27 |
|
* sequentiallySort(array, lo, hi); |
| 28 |
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* else { |
| 29 |
< |
* int mid = (lo + hi) >>> 1; |
| 29 |
> |
* int mid = (lo + hi) >>> 1; |
| 30 |
|
* invokeAll(new SortTask(array, lo, mid), |
| 31 |
|
* new SortTask(array, mid, hi)); |
| 32 |
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* merge(array, lo, hi); |
| 33 |
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* } |
| 34 |
|
* } |
| 35 |
< |
* } |
| 36 |
< |
* </pre> |
| 35 |
> |
* }}</pre> |
| 36 |
|
* |
| 37 |
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* You could then sort anArray by creating {@code new SortTask(anArray, 0, |
| 38 |
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* anArray.length-1) } and invoking it in a ForkJoinPool. |
| 39 |
|
* As a more concrete simple example, the following task increments |
| 40 |
|
* each element of an array: |
| 41 |
< |
* <pre> |
| 41 |
> |
* <pre> {@code |
| 42 |
|
* class IncrementTask extends RecursiveAction { |
| 43 |
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* final long[] array; final int lo; final int hi; |
| 44 |
|
* IncrementTask(long[] array, int lo, int hi) { |
| 45 |
|
* this.array = array; this.lo = lo; this.hi = hi; |
| 46 |
|
* } |
| 47 |
|
* protected void compute() { |
| 48 |
< |
* if (hi - lo < THRESHOLD) { |
| 49 |
< |
* for (int i = lo; i < hi; ++i) |
| 48 |
> |
* if (hi - lo < THRESHOLD) { |
| 49 |
> |
* for (int i = lo; i < hi; ++i) |
| 50 |
|
* array[i]++; |
| 51 |
|
* } |
| 52 |
|
* else { |
| 53 |
< |
* int mid = (lo + hi) >>> 1; |
| 53 |
> |
* int mid = (lo + hi) >>> 1; |
| 54 |
|
* invokeAll(new IncrementTask(array, lo, mid), |
| 55 |
|
* new IncrementTask(array, mid, hi)); |
| 56 |
|
* } |
| 57 |
|
* } |
| 58 |
< |
* } |
| 60 |
< |
* </pre> |
| 61 |
< |
* |
| 58 |
> |
* }}</pre> |
| 59 |
|
* |
| 60 |
|
* <p>The following example illustrates some refinements and idioms |
| 61 |
|
* that may lead to better performance: RecursiveActions need not be |
| 68 |
|
* potential excess partitioning by directly performing leaf actions |
| 69 |
|
* on unstolen tasks rather than further subdividing. |
| 70 |
|
* |
| 71 |
< |
* <pre> |
| 71 |
> |
* <pre> {@code |
| 72 |
|
* double sumOfSquares(ForkJoinPool pool, double[] array) { |
| 73 |
|
* int n = array.length; |
| 74 |
|
* int seqSize = 1 + n / (8 * pool.getParallelism()); |
| 89 |
|
* |
| 90 |
|
* double atLeaf(int l, int r) { |
| 91 |
|
* double sum = 0; |
| 92 |
< |
* for (int i = l; i < h; ++i) // perform leftmost base step |
| 92 |
> |
* for (int i = l; i < h; ++i) // perform leftmost base step |
| 93 |
|
* sum += array[i] * array[i]; |
| 94 |
|
* return sum; |
| 95 |
|
* } |
| 98 |
|
* int l = lo; |
| 99 |
|
* int h = hi; |
| 100 |
|
* Applyer right = null; |
| 101 |
< |
* while (h - l > 1 && |
| 102 |
< |
* ForkJoinWorkerThread.getEstimatedSurplusTaskCount() <= 3) { |
| 103 |
< |
* int mid = (l + h) >>> 1; |
| 101 |
> |
* while (h - l > 1 && |
| 102 |
> |
* ForkJoinWorkerThread.getEstimatedSurplusTaskCount() <= 3) { |
| 103 |
> |
* int mid = (l + h) >>> 1; |
| 104 |
|
* right = new Applyer(array, mid, h, seqSize, right); |
| 105 |
|
* right.fork(); |
| 106 |
|
* h = mid; |
| 117 |
|
* } |
| 118 |
|
* result = sum; |
| 119 |
|
* } |
| 120 |
< |
* } |
| 124 |
< |
* </pre> |
| 120 |
> |
* }}</pre> |
| 121 |
|
*/ |
| 122 |
|
public abstract class RecursiveAction extends ForkJoinTask<Void> { |
| 123 |
|
|
