ForkJoin

ForkJoin(工作窃取)

在大数据量的时候使用，提高效率。

大数据：Map Reduce（把大任务拆分成小任务）

例子：
//定义一个forkjoin操作类，继承于RecursiveTask（递归任务）

import java.util.concurrent.RecursiveTask;

//求和计算的任务
public class ForkJoinDemo extends RecursiveTask<Long> {
    public static void main(String[] args) {

    }
    private long start;
    private long end;
    private long temp = 10000000;

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

    @Override
    protected Long compute() {
        if((end - start) < temp){
            long sum = 0;
            for (long i = start; i <= end; i++) {
                sum += i;
            }
            return sum;
        }else{
            long middle = (start + end) / 2;
            ForkJoinDemo forkJoinDemo = new ForkJoinDemo(start, middle);
            forkJoinDemo.fork();
            ForkJoinDemo forkJoinDemo1 = new ForkJoinDemo(middle + 1, end);
            forkJoinDemo1.fork();
            return forkJoinDemo.join() + forkJoinDemo1.join();
        }
    }
}


//调用程序，三种方式

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

public class ForkJoinTest {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        test03();
    }

    public static final long maxEnd = 10_0000_0000;
    //普通方法，最差
    public static void test01(){
        long start = System.currentTimeMillis();
        long sum = 0;
        for (int i = 1; i <= maxEnd; i++) {
            sum += i;
        }
        long end = System.currentTimeMillis();
        System.out.println("结果：" + sum + ",耗时：" + (end - start));
    }

    //forkjoin方法，次优
    public static void test02() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();
        long sum = 0;
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> task = new ForkJoinDemo(0, maxEnd);
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);
        sum = submit.get();
        long end = System.currentTimeMillis();
        System.out.println("结果：" + sum + ",耗时：" + (end - start));
        forkJoinPool.shutdown();
    }

    //stream方法，并行流,最优
    public static void test03(){
        long start = System.currentTimeMillis();
        long sum = 0;

        long reduce = LongStream.rangeClosed(0, maxEnd).parallel().reduce(0, Long::sum);

        long end = System.currentTimeMillis();
        System.out.println("结果：" + reduce + ",耗时：" + (end - start));
    }
}

标签：end,sum,System,long,start,ForkJoin,public
来源： https://www.cnblogs.com/gdstcymc/p/15103554.html