if 任务足够小：
 直接执行任务
else：
 将任务切成两个小任务
 执行两个小任务并等待结果

package com.zhyea.robin;
 
import java.util.concurrent.RecursiveAction;
 
public class ForkBlur extends RecursiveAction {
 
  private int[] mSource;
  private int mStart;
  private int mLength;
  private int[] mDestination;
 
  // 处理窗口大小; 需要是一个奇数.
  private int mBlurWidth = 15;
 
  public ForkBlur(int[] src, int start, int length, int[] dst) {
    mSource = src;
    mStart = start;
    mLength = length;
    mDestination = dst;
  }
 
  protected void computeDirectly() {
    int sidePixels = (mBlurWidth - 1) / 2;
    for (int index = mStart; index < mStart + mLength; index++) {
      // 计算平均值.
      float rt = 0, gt = 0, bt = 0;
      for (int mi = -sidePixels; mi <= sidePixels; mi++) {
 
        int mindex = Math.min(Math.max(mi + index, 0), mSource.length - 1);
 
        int pixel = mSource[mindex];
        rt += (float) ((pixel & 0x00ff0000) >> 16) / mBlurWidth;
        gt += (float) ((pixel & 0x0000ff00) >> 8) / mBlurWidth;
        bt += (float) ((pixel & 0x000000ff) >> 0) / mBlurWidth;
      }
 
      // 重组目标像素.
      int dpixel = (0xff000000) |
          (((int) rt) << 16) |
          (((int) gt) << 8) |
          (((int) bt) << 0);
      mDestination[index] = dpixel;
    }
  }
  
  ....
}

  protected static int sThreshold = 100000;
 
  protected void compute() {
    if (mLength < sThreshold) {
      computeDirectly();
      return;
    }
 
    int split = mLength / 2;
 
    invokeAll(new ForkBlur(mSource, mStart, split, mDestination),
        new ForkBlur(mSource, mStart + split, mLength - split,
            mDestination));
  }

// src 表示源图片像素的数组
// dst 表示生成的图片的像素
ForkBlur fb = new ForkBlur(src, 0, src.length, dst);