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Comparing jsr166/src/jsr166y/RecursiveAction.java (file contents):
Revision 1.7 by jsr166, Mon Jul 27 03:33:28 2009 UTC vs.
Revision 1.18 by jsr166, Sat Jun 25 03:25:00 2011 UTC

# Line 1 | Line 1
1   /*
2   * Written by Doug Lea with assistance from members of JCP JSR-166
3   * Expert Group and released to the public domain, as explained at
4 < * http://creativecommons.org/licenses/publicdomain
4 > * http://creativecommons.org/publicdomain/zero/1.0/
5   */
6  
7   package jsr166y;
8  
9   /**
10 < * Recursive resultless ForkJoinTasks. This class establishes
11 < * conventions to parameterize resultless actions as {@code Void}
12 < * ForkJoinTasks. Because {@code null} is the only valid value of
13 < * type {@code Void}, methods such as join always return {@code null}
14 < * upon completion.
10 > * A recursive resultless {@link ForkJoinTask}.  This class
11 > * establishes conventions to parameterize resultless actions as
12 > * {@code Void} {@code ForkJoinTask}s. Because {@code null} is the
13 > * only valid value of type {@code Void}, methods such as {@code join}
14 > * always return {@code null} upon completion.
15   *
16   * <p><b>Sample Usages.</b> Here is a sketch of a ForkJoin sort that
17   * sorts a given {@code long[]} array:
18   *
19   *  <pre> {@code
20   * class SortTask extends RecursiveAction {
21 < *   final long[] array; final int lo; final int hi;
21 > *   final long[] array; final int lo, hi;
22   *   SortTask(long[] array, int lo, int hi) {
23   *     this.array = array; this.lo = lo; this.hi = hi;
24   *   }
# Line 29 | Line 29 | package jsr166y;
29   *       int mid = (lo + hi) >>> 1;
30   *       invokeAll(new SortTask(array, lo, mid),
31   *                 new SortTask(array, mid, hi));
32 < *       merge(array, lo, hi);
32 > *       merge(array, lo, mid, hi);
33   *     }
34   *   }
35   * }}</pre>
36   *
37   * You could then sort {@code anArray} by creating {@code new
38 < * SortTask(anArray, 0, anArray.length-1) } and invoking it in a
38 > * SortTask(anArray, 0, anArray.length) } and invoking it in a
39   * ForkJoinPool.  As a more concrete simple example, the following
40   * task increments each element of an array:
41   *  <pre> {@code
42   * class IncrementTask extends RecursiveAction {
43 < *   final long[] array; final int lo; final int hi;
43 > *   final long[] array; final int lo, hi;
44   *   IncrementTask(long[] array, int lo, int hi) {
45   *     this.array = array; this.lo = lo; this.hi = hi;
46   *   }
# Line 64 | Line 64 | package jsr166y;
64   * of each element of a double array, by subdividing out only the
65   * right-hand-sides of repeated divisions by two, and keeping track of
66   * them with a chain of {@code next} references. It uses a dynamic
67 < * threshold based on method {@code surplus}, but counterbalances
68 < * potential excess partitioning by directly performing leaf actions
69 < * on unstolen tasks rather than further subdividing.
67 > * threshold based on method {@code getSurplusQueuedTaskCount}, but
68 > * counterbalances potential excess partitioning by directly
69 > * performing leaf actions on unstolen tasks rather than further
70 > * subdividing.
71   *
72   *  <pre> {@code
73   * double sumOfSquares(ForkJoinPool pool, double[] array) {
74   *   int n = array.length;
75 < *   int seqSize = 1 + n / (8 * pool.getParallelism());
75 < *   Applyer a = new Applyer(array, 0, n, seqSize, null);
75 > *   Applyer a = new Applyer(array, 0, n, null);
76   *   pool.invoke(a);
77   *   return a.result;
78   * }
79   *
80   * class Applyer extends RecursiveAction {
81   *   final double[] array;
82 < *   final int lo, hi, seqSize;
82 > *   final int lo, hi;
83   *   double result;
84   *   Applyer next; // keeps track of right-hand-side tasks
85 < *   Applyer(double[] array, int lo, int hi, int seqSize, Applyer next) {
85 > *   Applyer(double[] array, int lo, int hi, Applyer next) {
86   *     this.array = array; this.lo = lo; this.hi = hi;
87 < *     this.seqSize = seqSize; this.next = next;
87 > *     this.next = next;
88   *   }
89   *
90 < *   double atLeaf(int l, int r) {
90 > *   double atLeaf(int l, int h) {
91   *     double sum = 0;
92   *     for (int i = l; i < h; ++i) // perform leftmost base step
93   *       sum += array[i] * array[i];
# Line 98 | Line 98 | package jsr166y;
98   *     int l = lo;
99   *     int h = hi;
100   *     Applyer right = null;
101 < *     while (h - l > 1 &&
102 < *        ForkJoinWorkerThread.getEstimatedSurplusTaskCount() <= 3) {
101 > *     while (h - l > 1 && getSurplusQueuedTaskCount() <= 3) {
102   *        int mid = (l + h) >>> 1;
103 < *        right = new Applyer(array, mid, h, seqSize, right);
103 > *        right = new Applyer(array, mid, h, right);
104   *        right.fork();
105   *        h = mid;
106   *     }
# Line 110 | Line 109 | package jsr166y;
109   *        if (right.tryUnfork()) // directly calculate if not stolen
110   *          sum += right.atLeaf(right.lo, right.hi);
111   *       else {
112 < *          right.helpJoin();
112 > *          right.join();
113   *          sum += right.result;
114   *        }
115   *        right = right.next;
# Line 123 | Line 122 | package jsr166y;
122   * @author Doug Lea
123   */
124   public abstract class RecursiveAction extends ForkJoinTask<Void> {
125 +    private static final long serialVersionUID = 5232453952276485070L;
126  
127      /**
128       * The main computation performed by this task.
# Line 130 | Line 130 | public abstract class RecursiveAction ex
130      protected abstract void compute();
131  
132      /**
133 <     * Always returns null.
133 >     * Always returns {@code null}.
134 >     *
135 >     * @return {@code null} always
136       */
137      public final Void getRawResult() { return null; }
138  

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