ForkJoin

ForkJoin

ForkJoin

图片来源：狂神说Java

ForkJoin 任务窃取

这个任务中维护的都是双端队列

B的任务执行完了，去帮助A执行

图片来源：狂神说Java

package com.sw.forkjoin;

import java.util.concurrent.RecursiveTask;

/**
 * @Author suaxi
 * @Date 2021/2/16 17:24
 * 1、通过forkjoinPool来执行
 * 2、计算任务forkjoinPool.execute(ForkJoinTask task)
 * 3、计算类要继承 ForkJoinTask
 */
public class ForkJoinTest extends RecursiveTask<Long> {

    private Long start;
    private Long end;
    //临界值
    private Long temp = 1000L;

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

    //计算任务
    @Override
    protected Long compute() {
        if ((end-start)<temp){
            Long sum = 0L;
            for (Long i = start; i <= end; i++) {
                sum += i;
            }
            return sum;
        }else { //forkjoin递归
            long middle = (start + end)/2;
            ForkJoinTest task1 = new ForkJoinTest(start, middle);
            task1.fork(); //拆分任务，把任务压入线程队列
            ForkJoinTest task2 = new ForkJoinTest(middle+1, end);
            task2.fork(); //同理
            return task1.join() + task2.join();
        }
    }
}

测试类：

package com.sw.forkjoin;

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

/**
 * @Author suaxi
 * @Date 2021/2/16 17:37
 */
public class Test {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        //test01(); //计算时间=7166
        //test02(); //计算时间=5244
        test03(); //计算时间=312
    }

    //常规计算方法
    public static void test01(){
        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+" 计算时间="+ (end - start));
    }

    //ForkJoin
    public static void test02() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();
        //1、通过ForkJoinPool执行
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> task = new ForkJoinTest(0L, 10_0000_0000L);
        //2、计算任务forkjoinPool.execute(ForkJoinTask task)
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);
        Long sum = submit.get();
        long end = System.currentTimeMillis();
        System.out.println("sum="+sum+" 计算时间="+ (end - start));
    }

    //Stream并行流
    public static void test03(){
        long start = System.currentTimeMillis();
        //parallel并行
        Long sum = LongStream.rangeClosed(0L,10_0000_0000L).parallel().reduce(0,Long::sum);
        long end = System.currentTimeMillis();
        System.out.println("sum="+sum+" 计算时间="+ (end - start));
    }
}