compact1, compact2, compact3

java.util.concurrent

Class RecursiveAction

java.lang.Object

java.util.concurrent.ForkJoinTask<Void>

java.util.concurrent.RecursiveAction

All Implemented Interfaces:

Serializable Future Void >，<

public abstract class RecursiveAction
extends ForkJoinTask<Void>

一个递归的结果 ForkJoinTask。这类结果的行动建立公约 Void ForkJoinTasks参数。因为 null类型是 Void唯一有效的价值，方法如 join总是返回 null完成后。

示例用法。这里是一个简单但完整的forkjoin排序分类给定long[]阵列：

 static class SortTask extends RecursiveAction {
   final long[] array; final int lo, hi;
   SortTask(long[] array, int lo, int hi) {
     this.array = array; this.lo = lo; this.hi = hi;
   }
   SortTask(long[] array) { this(array, 0, array.length); }
   protected void compute() {
     if (hi - lo < THRESHOLD)
       sortSequentially(lo, hi);
     else {
       int mid = (lo + hi) >>> 1;
       invokeAll(new SortTask(array, lo, mid),
                 new SortTask(array, mid, hi));
       merge(lo, mid, hi);
     }
   }
   // implementation details follow:
   static final int THRESHOLD = 1000;
   void sortSequentially(int lo, int hi) {
     Arrays.sort(array, lo, hi);
   }
   void merge(int lo, int mid, int hi) {
     long[] buf = Arrays.copyOfRange(array, lo, mid);
     for (int i = 0, j = lo, k = mid; i < buf.length; j++)
       array[j] = (k == hi || buf[i] < array[k]) ?
         buf[i++] : array[k++];
   }
 }

然后你就可以通过创建 new SortTask(anArray)并调用ForkJoinPool anArray排序。作为更具体的简单的例子，下面的任务增量数组中的每个元素：

 class IncrementTask extends RecursiveAction {
   final long[] array; final int lo, hi;
   IncrementTask(long[] array, int lo, int hi) {
     this.array = array; this.lo = lo; this.hi = hi;
   }
   protected void compute() {
     if (hi - lo < THRESHOLD) {
       for (int i = lo; i < hi; ++i)
         array[i]++;
     }
     else {
       int mid = (lo + hi) >>> 1;
       invokeAll(new IncrementTask(array, lo, mid),
                 new IncrementTask(array, mid, hi));
     }
   }
 }

下面的例子说明了一些改进的习惯，可能会导致更好的性能：recursiveactions不需要完全递归，只要他们保持基本的分而治之的方法。这里是一个类，和一双数组的每个元素的平方，细分出只有右手边的重复区，并跟踪他们的连锁next参考。它采用了一种基于动态阈值的方法getSurplusQueuedTaskCount，但抵消潜在过剩的直接执行叶行动unstolen任务而不是进一步细分的分区。

 double sumOfSquares(ForkJoinPool pool, double[] array) {
   int n = array.length;
   Applyer a = new Applyer(array, 0, n, null);
   pool.invoke(a);
   return a.result;
 }

 class Applyer extends RecursiveAction {
   final double[] array;
   final int lo, hi;
   double result;
   Applyer next; // keeps track of right-hand-side tasks
   Applyer(double[] array, int lo, int hi, Applyer next) {
     this.array = array; this.lo = lo; this.hi = hi;
     this.next = next;
   }

   double atLeaf(int l, int h) {
     double sum = 0;
     for (int i = l; i < h; ++i) // perform leftmost base step
       sum += array[i] * array[i];
     return sum;
   }

   protected void compute() {
     int l = lo;
     int h = hi;
     Applyer right = null;
     while (h - l > 1 && getSurplusQueuedTaskCount() <= 3) {
       int mid = (l + h) >>> 1;
       right = new Applyer(array, mid, h, right);
       right.fork();
       h = mid;
     }
     double sum = atLeaf(l, h);
     while (right != null) {
       if (right.tryUnfork()) // directly calculate if not stolen
         sum += right.atLeaf(right.lo, right.hi);
       else {
         right.join();
         sum += right.result;
       }
       right = right.next;
     }
     result = sum;
   }
 }

从以下版本开始：

一点七

另请参见：

Serialized Form

构造方法摘要

构造方法

Constructor and Description
RecursiveAction()

方法摘要

Modifier and Type	Method and Description
protected abstract void	compute() 此任务执行的主要计算。
protected boolean	exec() 贯彻执行公约recursiveactions。
Void	getRawResult() 总是返回 null。
protected void	setRawResult(Void mustBeNull) 需要空完成值。

Methods inherited from class java.util.concurrent.ForkJoinTask

adapt, adapt, adapt, cancel, compareAndSetForkJoinTaskTag, complete, completeExceptionally, fork, get, get, getException, getForkJoinTaskTag, getPool, getQueuedTaskCount, getSurplusQueuedTaskCount, helpQuiesce, inForkJoinPool, invoke, invokeAll, invokeAll, invokeAll, isCancelled, isCompletedAbnormally, isCompletedNormally, isDone, join, peekNextLocalTask, pollNextLocalTask, pollTask, quietlyComplete, quietlyInvoke, quietlyJoin, reinitialize, setForkJoinTaskTag, tryUnfork

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

RecursiveAction

public RecursiveAction()

方法详细信息

compute

protected abstract void compute()

此任务执行的主要计算。

getRawResult

public final Void getRawResult()

总是返回 null。

Specified by:

getRawResult 方法重写，继承类 ForkJoinTask<Void>

结果

null总是

setRawResult

protected final void setRawResult(Void mustBeNull)

需要空完成值。

Specified by:

setRawResult 方法重写，继承类 ForkJoinTask<Void>

参数

mustBeNull -价值

exec

protected final boolean exec()

贯彻执行公约recursiveactions。

Specified by:

exec 方法重写，继承类 ForkJoinTask<Void>

结果

true如果这个任务已经完成正常