ForkJoin分支合并

什么是ForkJoin？

并行执行任务！提高工作效率，大数据量的时候使用！
Map Reduce（把大任务拆分为小任务）
ForkJoin：

ForkJoin的特点：工作窃取！
双端队列

**ForkJoinTask：的两个子类
RecursiveAction 递归事件，没有返回值 RecursiveTask 递归任务，有返回值**

package com.liao.forkjoin;

import java.util.concurrent.RecursiveTask;


public class ForkJoinDemo extends RecursiveTask {

    private Long start;
    private Long end;
    //临界值
    private Long temp = 10000L;

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

    //计算的方法
    @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;
            ForkJoinDemo task1 = new ForkJoinDemo(start, middle);
            task1.fork();//拆分任务，把任务压入线程队列
            ForkJoinDemo task2 = new ForkJoinDemo(middle+1, end);
            task2.fork();//
            return task1.join() + task2.join();
        }
    }
}

测试类：

package com.liao.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();//6135
        //test2();//5668
        test3();//192 效率最高
    }
    public static void test1(){
        Long sum = 0L;
        long start = System.currentTimeMillis();
        for (Long i = 1L; i <= 1000000000; i++) {
            sum += i;
        }
        long end = System.currentTimeMillis();
        System.out.println("sum： "+sum+"时间： "+(end-start));

    }
    //forkjoin
    public static void test2() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();//执行forkjoin必须通过new ForkJoinPool
        ForkJoinDemo forkJoinDemo = new ForkJoinDemo(0L, 1000000000L);
        //forkJoinPool.execute(forkJoinDemo);//同步执行提交，需要丢入一个计算任务,但是没有结果
        ForkJoinTask submit = forkJoinPool.submit(forkJoinDemo);//异步提交
        Long aLong = submit.get();
        //Long aLong = forkJoinDemo.get();
        long end = System.currentTimeMillis();
        System.out.println("sum: "+aLong+"时间: "+(end-start));

    }
    //Sream并行流
    public static void test3(){
        long start = System.currentTimeMillis();
        long reduce = LongStream.rangeClosed(0L, 1000000000L).parallel().reduce(0, Long::sum);//parallel平行的计算
        long end = System.currentTimeMillis();
        System.out.println("sum: "+reduce+"时间: "+(end-start));
    }
}

Stream效率最高