并发工具类

CountDownLatch

让主线程等待一组事件发生后继续执行

CountDownLatch是通过一个计数器来实现的，计数器的初始值为线程的数量。每当一个线程完成了自己的任务后，计数器的值就会减1。当计数器值到达0时，它表示所有的线程已经完成了任务，然后在闭锁上等待的线程就可以恢复执行任务。

countDownLatch.countDown() //计数器减一
countDownLatch.await();  //线程等待，直到计数器为0

example

import java.util.concurrent.CountDownLatch;
import java.util.stream.IntStream;

public class Main {
    public static void main(String[] args) throws InterruptedException {
        CountDownLatch countDownLatch = new CountDownLatch(7);
        IntStream.rangeClosed(1, 7).forEach(i -> {
            new Thread(() -> {
                System.out.println(Thread.currentThread().getName() + "\t" + i);
                countDownLatch.countDown();
            }, String.valueOf(i)).start();
        });
        countDownLatch.await();
        System.out.println("finish");

    }
}

CyclicBarrier

CyclicBarrier的功能和CountDownLatch相反，是做加法。（集齐7颗龙珠才能召唤神龙）

一般采用的构造函数

public CyclicBarrier(int parties, Runnable barrierAction) {
        if (parties <= 0) throw new IllegalArgumentException();
        this.parties = parties;
        this.count = parties;
        this.barrierCommand = barrierAction;
    }

即使当累计达到parties数目时，则执行runable。

example

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
import java.util.stream.IntStream;

public class Main {
    public static void main(String[] args) throws InterruptedException {
        CyclicBarrier cyclicBarrier = new CyclicBarrier(7, () -> System.out.println("召唤神龙"));
        IntStream.rangeClosed(1, 14).forEach(i -> new Thread(() -> {
            System.out.println(i);
            try {
                cyclicBarrier.await();
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (BrokenBarrierException e) {
                e.printStackTrace();
            }
        }).start());
    }
}

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召唤神龙
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召唤神龙

并发工具类

原文：https://www.cnblogs.com/lexiaoyao1995/p/13385091.html