ForkIn VS Stream

forkin分支合并

将一个大任务分割成若干小任务，最终汇总每个小任务的结果得到这个大任务的结果

并行执行任务，提高效率，大数据量。
类似MapReduce大任务拆分为小任务

 

forkjoin:工作窃取，维护的双端队列

测试1

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;

//大数据量的时候使用
public class ForkInVSStreamTest {
    public static void main(String[] args) throws ExecutionException, InterruptedException {
        test01();
        test02();
        test03();
    }

    //普通的
    public static void test01() {
        long sum = 0L;
        long start = System.currentTimeMillis();
        for (long i = 1; i < 10_0000_0000L; i++) {
            sum += i;
        }

        long end = System.currentTimeMillis();
        System.out.println("sum=" + sum + "时间： " + (end - start));
    }

    //使用forkjion的人员
    public static void test02() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> tast = new Sum(0L, 10_0000_0000L);
        ForkJoinTask<Long> submit = forkJoinPool.submit(tast);//提交任务
        Long sum = submit.get();

        long end = System.currentTimeMillis();
        System.out.println("forkin=》sum=" + sum + "时间： " + (end - start));
    }

    //使用Stream计算的人员
    public static void test03() {
        long start = System.currentTimeMillis();
        //Stream 并行流
        //求和
        long sum = LongStream.rangeClosed(0L, 10_0000_0000)
                .parallel()
                .reduce(0, Long::sum);

        long end = System.currentTimeMillis();
        System.out.println("stream=》sum=" + sum + "时间： " + (end - start));
    }
}

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

    public Sum(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 {
            //分支合并计算 forkjoin
            long middle = (start + end) / 2; //中间值
            Sum sum1 = new Sum(start, middle);
            sum1.fork(); //拆分任务，把任务压入线程队列
            Sum sum2 = new Sum(middle + 1, end);
            sum2.fork();//拆分任务，把任务压入线程队列
            return sum1.join() + sum2.join();
        }
    }
}