ForkJoin、普通方法、stream并行流计算对比

1.什么是ForkJoin?

orkJoin 在 JDK 1.7 ，并行执行任务！提高效率。大数据量！
大数据：Map Reduce （把大任务拆分为小任务）
在这里插入图片描述
2.ForkJoin特点
工作窃取，这个里面维护的都是双端队列

3.ForkJoin结构

4.简单代码实现：
首先贴出forkjoinTask中的RecursiveTask的实现类

java">import java.util.concurrent.RecursiveTask;

/**
 * @program: juc
 * @description
 * @author: 不会编程的派大星
 * @create: 2021-04-27 10:20
 **/
public class ForkJoinDemo  extends RecursiveTask<Long> {
    
    private Long start;
    
    private Long end;
    
    private Long temp = 100000L;

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

    @Override
    protected Long compute() {
        if((end - start) < temp){
            Long sum = 0L;
            for ( long i = start; i <= end; i++) {
                sum = sum+i;
            }
            return sum;
        }else{
            Long middle = (start + end) / 2;
            ForkJoinDemo task1 = new ForkJoinDemo(start, middle);
            task1.fork();//拆分任务，把任务压进线程队列
            ForkJoinDemo task2 = new ForkJoinDemo(middle+1,end);
            task2.fork();
            return task1.join()+task2.join();
        }

    }
}

再来看看test类：

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

/**
 * @program: juc
 * @description
 * @author: 不会编程的派大星
 * @create: 2021-04-27 10:19
 **/
public class ForkJoinTest {

    public static void main(String[] args) throws ExecutionException, InterruptedException {
        test1();
        test2();
        test3();

    }

    // 普通程序员
    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));
    }
    // 会使用ForkJoin
    public static void test2() throws ExecutionException, InterruptedException {
        long start = System.currentTimeMillis();
        ForkJoinPool forkJoinPool = new ForkJoinPool();
        ForkJoinTask<Long> task = new ForkJoinDemo(
                0L, 10_0000_0000L);
        // 提交任务
        ForkJoinTask<Long> submit = forkJoinPool.submit(task);
        Long sum = submit.get();// 获得结果
        long end = System.currentTimeMillis();
        System.out.println("sum="+sum+" 时间："+(end-start));
    }
    public static void test3(){
        long start = System.currentTimeMillis();
        // Stream并行流 ()  (]
        long sum = LongStream
                .rangeClosed(0L, 10_0000_0000L) // 计算范围(,]
                .parallel() // 并行计算
                .reduce(0, Long::sum); // 输出结果
        long end = System.currentTimeMillis();
        System.out.println("sum="+"时间："+(end-start));
    }
}