什么是ForkJoin？

ForkJoin 在JDK1.7，并行执行任务！提高效率~。在大数据量速率会更快！

大数据中：MapReduce 核心思想->把大任务拆分为小任务！

 

ForkJoin 特点： 工作窃取！ 

实现原理是：双端队列！从上面和下面都可以去拿到任务进行执行！

 

如何使用ForkJoin? 

• 1、通过ForkJoinPool来执行

• 2、计算任务 execute(ForkJoinTask<?> task)

 

• 3、计算类要去继承ForkJoinTask；

ForkJoin的计算类！

package com.ogj.forkjoin;

import java.util.concurrent.RecursiveTask;

public class ForkJoinDemo extends RecursiveTask<Long> {

    private long star;
    private long end;

    //临界值
    private long temp=1000000L;

    public ForkJoinDemo(long star, long end) {
        this.star = star;
        this.end = end;
    }

    /**
     * 计算方法
     * @return Long
     */
    @Override
    protected Long compute() {
        if((end-star)<temp){
            Long sum = 0L;
            for (Long i = star; i < end; i++) {
                sum+=i;
            }
//            System.out.println(sum);
            return sum;
        }else {
            //使用forkJoin 分而治之 计算
            //计算平均值
            long middle = (star+ end)/2;
            ForkJoinDemo forkJoinDemoTask1 = new ForkJoinDemo(star, middle);
            forkJoinDemoTask1.fork();  //拆分任务，把线程任务压入线程队列
            ForkJoinDemo forkJoinDemoTask2 = new ForkJoinDemo(middle, end);
            forkJoinDemoTask2.fork();  //拆分任务，把线程任务压入线程队列
            long taskSum = forkJoinDemoTask1.join() + forkJoinDemoTask2.join();
            return taskSum;
        }
    }
}

测试类！

package com.ogj.forkjoin;

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

public class Test {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        test1();
        test2();
        test3();
    }

    /**
     * 普通计算
     */
    public static void test1(){
        long star = System.currentTimeMillis();
        long sum = 0L;
        for (long i = 1; i < 20_0000_0000; i++) {
            sum+=i;
        }
        long end = System.currentTimeMillis();
        System.out.println("sum="+"时间："+(end-star));
        System.out.println(sum);
    }

    /**
     * 使用ForkJoin
     */
    public static void test2() throws ExecutionException, InterruptedException {
        long star = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> task = new ForkJoinDemo(0L, 20_0000_0000L);
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);
        Long aLong = submit.get();
        System.out.println(aLong);
        long end = System.currentTimeMillis();
        System.out.println("sum="+"时间："+(end-star));
    }


    /**
     * 使用Stream 并行流
     */
    public static void test3(){
        long star = System.currentTimeMillis();
        //Stream并行流()
        long sum = LongStream.range(0L, 20_0000_0000L).parallel().reduce(0, Long::sum);
        System.out.println(sum);
        long end = System.currentTimeMillis();
        System.out.println("sum="+"时间："+(end-star));
    }
}

.parallel().reduce(0, Long::sum使用一个并行流去计算整个计算，提高效率。

 

reduce方法的优点：