ForkJion

ForkJoin

什么是ForkJoin

ForkJion 在JDK1.7,并行執行任務！提高效率，大資料量！
大資料：Map Reduce(將大任務拆分為小任務)

ForkJion 特點：作業竊取
這個里面維護的都是雙端佇列，A 執行緒沒有執行完，B執行緒執行完了，B 執行緒則去 執行A 中的（紅框）未執行完任務

ForkJion

代碼案例：

package com.forkjoin;


import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.stream.LongStream;

/**
 * 3000 6000(ForkJoin) 9000(Stream并行流)
 */
public class Test {


    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //test1();//8039
        //test2(); //4369
        test3(); //152
    }

      public  static  void  test1(){
        Long sum =0L;
          long start = System.currentTimeMillis();
          for (Long i = 1L; i < 10_0000_0000; i++) {
              sum+=i;
          }
          long end = System.currentTimeMillis();
          System.out.println("sum="+sum+"時間:"+(end -start));
      }

    public  static  void  test2() throws ExecutionException, InterruptedException {
        Long sum =0L;
        long start = System.currentTimeMillis();
        //forkJoin 池子
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        //實體化業務方法
        ForkJoinTask<Long> task = new ForkJoinDemo(0L,10_0000_0000L);

        //在池子中執行業務
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);

        sum = submit.get();

        long end = System.currentTimeMillis();
        System.out.println("sum="+sum+"時間:"+(end -start));
    }

    public  static  void  test3() throws ExecutionException, InterruptedException {
        Long sum =0L;
        long start = System.currentTimeMillis();
        //Stream  并行流 range 不包含后面的,rangeClosed 包含后面的
        sum = LongStream.rangeClosed(0L, 10_0000_0000L).parallel().reduce(0, Long::sum);

        long end = System.currentTimeMillis();
        System.out.println("sum="+sum+"時間:"+(end -start));
    }

}

package com.forkjoin;


import java.util.concurrent.RecursiveTask;

/**
 * 
 * 求和計算的任務！
 *
 * 3000, 6000(ForkJoin) 9000(Stream 并行流)
 * 如何使用forkJoin
 * 1.forkJoinPool 通過它來執行
 * 2.計算任務forkjoinPoolexecute
 * 3.計算類要繼承ForkJoinTask
 *
 * Recursive : 發音 rekusive
 *
 */
public class ForkJoinDemo extends RecursiveTask<Long> {


    private Long  start;

    private Long  end;

    //臨界值
    private Long temp = 10000L;


    public ForkJoinDemo(Long start, Long end) {
        this.start = start;
        this.end = end;
    }

    public static void main(String[] args) {
//        int sum =0;
//        for (int i = 0; i < 10_0000_0000; i++) {
//            sum+=i;
//        }
//        System.out.println(sum);
//
//

       }

       public void test(){
        //100 -50 >50
        if((end -start) >temp){
            int sum =0;
            for (int i = 0; i < 10_0000_0000; i++) {
                sum+=i;
            }
            System.out.println(sum);
        }
       }

       //計算的回傳值就是 RecursiveTask 的泛型
    @Override
    protected Long compute() {
        //如果范圍比 1 萬還小我們就不用分支合并
        if((end -start) <temp){
            Long sum =0L;
            for (long i =start; i <=end; i++) {
                sum+=i;
            }
           return sum;
        }else{ //forkjoin: 一個任務拆分為多個任務 ,像遞回
            long middle = (start + end) / 2; //中間值
            ForkJoinDemo task1 = new ForkJoinDemo(start, middle);
            task1.fork(); //拆分任務,把任務壓入到執行緒佇列


            ForkJoinDemo task2 = new ForkJoinDemo(middle+1, end);
            task2.fork();
            return task1.join() + task2 .join();
        }
    }
}