FokJoin

jdk1.7开始增加FokJoin， 并行执行任务，提高执行效率，大数据量。

image.png
image.png

package com.test.forkjoin;

import java.util.concurrent.RecursiveTask;

// 继承自RecursiveTask
public class ForkJoinDemo extends RecursiveTask<Long>{
    private long start; // 1
    private long end;  // 100000
    private long tmp = 10000;

    public ForkJoinDemo(long start, long end) {
        this.start = start;
        this.end = end;
    }
    
    // 实现compute方法
    @Override
    protected Long compute() {
        if (end - start < tmp) { //比1万小求和，普通计算
            long sum = 0;
            for (long i = start; i < end; i++) {
                sum += i;
            }
            return sum;
        } else { // 使用forkjoin
            long middle = (start + end) /2; // 中间值
            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, end);
            task2.fork(); // 拆分任务，把任务压入线程队列
            return task1.join() + task2.join(); // 合并任务
        }
    }
}

package com.test.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 InterruptedException, ExecutionException {
//      test1();
//      test2();
        test3();
    }
    
    public static void test1() {
        long start = System.currentTimeMillis();
        long sum = 0;
        for (long i = 1; i <= 10_0000_0000; i++) {
            sum += i;
        }
        long end = System.currentTimeMillis();
//      sum = 500000000500000000执行了：283
        System.out.println("sum = "+sum+"执行了："+(end - start));
    }
    
    public static void test2() throws InterruptedException, ExecutionException {
        long start = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> task = new ForkJoinDemo(1 , 10_0000_0000);
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);
        Long sum = submit.get(); // 阻塞等待
        long end = System.currentTimeMillis();
        //sum = 499999999500000000执行了：242
        System.out.println("sum = "+sum+"执行了："+(end - start));
    }
    
    public static void test3() {
        long start = System.currentTimeMillis();
        // 使用stream流计算
        long sum = LongStream.rangeClosed(0, 10_0000_0000).parallel().reduce(0, Long::sum);
        long end = System.currentTimeMillis();
        // sum = 500000000500000000执行了：180
        System.out.println("sum = "+sum+"执行了："+(end - start));
    }


}