2019-07-10_ForkJoinpPool大任务拆解操作记

ForkJoinpPool大任务拆解操作记录
1概述
forkjoin执行任务的核心在于compute()方法,先判断任务是否足够小，如果足够小就直接计算。否则，把自身的任务一拆位二，分别计算。
1.1编写任务处理逻辑
package com.tech.ability.myjacob;

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.concurrent.RecursiveTask;

/**

• @author kikop

• @version 1.0

• @project Name: TechnicalAbilityToolBox

• @file Name: MySumTask

• @desc 功能描述

• @date 2019/7/8

• @time 22:39

• @by IDE: IntelliJ IDEA
  */
  public class MySumTaskLong extends RecursiveTask<Long> {

  static final int THRESHOLD = 100;
  long[] array;
  int start;
  int end;
  String strFileNamePrefix = "D:/myjacobtest/mysumtask_";

  MySumTaskLong(long[] array, int start, int end) {
  this.array = array;
  this.start = start;
  this.end = end;
  }

  @Override
  protected Long compute() {
  if (end - start <= THRESHOLD) {
  // 如果任务足够小,直接计算:
  long sum = 0;
  File file = new File(String.format("%s%03d.doc", strFileNamePrefix, start));
  if (!file.exists()) {
  try {
  file.createNewFile();
  } catch (IOException e) {
  e.printStackTrace();
  }
  }
  try {
  FileWriter fileWriter = new FileWriter(file);
  for (int i = start; i < end; i++) {
  fileWriter.write(i + " ");
  sum += array[i];
  }
  fileWriter.write("\r\n任务执行结果:"+sum + "!");
  fileWriter.flush();

// try {
// Thread.sleep(1000);
// } catch (InterruptedException e) {
// }
System.out.println(String.format("compute %d~%d = %d", start, end, sum));
} catch (IOException e) {
e.printStackTrace();
}

        return sum;
    }
    // 任务太大,一分为二:
    int middle = (end + start) / 2;
    System.out.println(String.format("split %d~%d ==> %d~%d, %d~%d", start, end, start, middle, middle, end));
    MySumTaskLong subtask1 = new MySumTaskLong(this.array, start, middle);
    MySumTaskLong subtask2 = new MySumTaskLong(this.array, middle, end);
    invokeAll(subtask1, subtask2);
    Long subresult1 = subtask1.join();
    Long subresult2 = subtask2.join();
    Long result = subresult1 + subresult2;
    System.out.println("result = " + subresult1 + " + " + subresult2 + " ==> " + result);
    return result;
}

}

1.2测试
package com.tech.ability.myjacob;

import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;

/**

• @author kikop

• @version 1.0

• @project Name: TechnicalAbilityToolBox

• @file Name: MySumTaskTest

• @desc 功能描述

• @date 2019/7/8

• @time 22:39

• @by IDE: IntelliJ IDEA

• 参考:https://www.liaoxuefeng.com/article/1146802219354112
  */
  public class MySumTaskLongTest {

  private static void fillRandom(long[] array) {
  for (int i = 0; i < array.length; i++) {
  array[i] = i;
  }
  }

  public static void main(String[] args) {

   // 创建随机数组成的数组:
   long[] array = new long[400];
   fillRandom(array);
   // fork/join task:
   ForkJoinPool fjp = new ForkJoinPool(4); // 最大并发数4
   ForkJoinTask<Long> task = new MySumTaskLong(array, 0, array.length);
   long startTime = System.currentTimeMillis();
   Long result = fjp.invoke(task);
   long endTime = System.currentTimeMillis();
   System.out.println("Fork/join sum: " + result + " in " + (endTime - startTime) + " ms.");
  

  }
  }
  1.3 结果
  split 0~400 ==> 0~200, 200~400
  split 0~200 ==> 0~100, 100~200
  split 200~400 ==> 200~300, 300~400
  compute 0~100 = 4950
  compute 200~300 = 24950
  compute 100~200 = 14950
  result = 4950 + 14950 ==> 19900
  compute 300~400 = 34950
  result = 24950 + 34950 ==> 59900
  result = 19900 + 59900 ==> 79800
  Fork/join sum: 79800 in 268 ms.
  2 使用注意点
  New Task1
  New Task2
  InvokeAll(task1,task2)
  Task1.join()
  Task2.join()