JUC---08ForkJion(分支合并)

package com.jenne.juc.forkjion;

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

/**
 * 1、forkjoinPool 通过它来执行
 * 2、计算任务 forkjoinPool.execute(ForkJoinTask task)
 * 3、计算类要继承 ForkJoinTask及其子类
 */


//运行类
public class Demo {

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

    // 一般操作
    public static void test1() {
        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 + " 时间：" + (end - start));
    }

    // 使用ForkJoin
    public static void test2() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> task = new ForkJoinTaskDemo(0L, 10_0000_0000L);
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);// 提交任务
        Long sum = submit.get();
        long end = System.currentTimeMillis();
        System.out.println("sum=" + sum + " 时间：" + (end - start));
    }

    //Stream并行流 
    public static void test3() {
        long start = System.currentTimeMillis();
        // Stream并行流() (]
        long sum = LongStream.rangeClosed(0L, 10_0000_0000L).parallel().reduce(0, Long::sum);
        long end = System.currentTimeMillis();
        System.out.println("sum=" + "时间：" + (end - start));
    }

}


//计算类
class ForkJoinTaskDemo extends RecursiveTask<Long> {
    private Long start; // 1
    private Long end; // 1990900000
    // 临界值
    private Long temp = 10000L;

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

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