10.Redisson源码-CountDownLatch源码剖析

一、CountDownLatch基本原理

1. countDownLatch最基本的原理其实就是，现在有4个客户端，分别是A、B、C、D,客户端A进行加锁后，设置三个线程来获取锁，那么，必须让接下来的三个客户端BCD都获取锁成功后，客户端A的逻辑才会继续向下走
2. 如果说，指定3个客户端获取锁，获取锁的客户端数量没有到达3的话，客户端A是不会逻辑是不会向下走的，会被阻塞住

源码

代码片段一、demo

public static void main(String[] args) throws Exception {
        Config config = new Config();
        config.useClusterServers()
                .addNodeAddress("redis://192.168.0.107:7001")
                .addNodeAddress("redis://192.168.0.107:7002")
                .addNodeAddress("redis://192.168.0.110:7003")
                .addNodeAddress("redis://192.168.0.110:7004")
                .addNodeAddress("redis://192.168.0.111:7005")
                .addNodeAddress("redis://192.168.0.111:7006");

        final RedissonClient redisson = Redisson.create(config);

        RCountDownLatch latch = redisson.getCountDownLatch("anyCountDownLatch");
        // 这里会设置几个客户端来获取锁成功的数量,代码片段二、
        latch.trySetCount(3);
        System.out.println(new Date() + "：线程[" + Thread.currentThread().getName() + "]设置了必须有3个线程执行countDown，进入等待中。。。");

        for (int i = 0; i < 3; i++) {
            new Thread(new Runnable() {
                public void run() {
                    try {
                        System.out.println(new Date() + "：线程[" + Thread.currentThread().getName() + "]在做一些操作，请耐心等待。。。。。。");
                        Thread.sleep(3000);
                        RCountDownLatch localLatch = redisson.getCountDownLatch("anyCountDownLatch”);
                        // 代码片段三、
                        localLatch.countDown();
                        System.out.println(new Date() + "：线程[" + Thread.currentThread().getName() + "]执行countDown操作");
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            }).start();
        }

        // 代码片段四、
        latch.await();
        System.out.println(new Date() + "：线程[" + Thread.currentThread().getName() + "]收到通知，有3个线程都执行了countDown操作，可以继续往下走");

    }

代码片段二、RedissonCountDownLatch

1. 参数：
   KEYS[1]= “anyCountDownLatch”
   ARGV[2] = 3,其实就是count参数的值

@Override
public boolean trySetCount(long count) {
    // 这里设置的客户端获取锁的个数为3
    return get(trySetCountAsync(count));
}

// count = 3
@Override
public RFuture trySetCountAsync(long count) {
    return commandExecutor.evalWriteAsync(getName(), 
    LongCodec.INSTANCE, RedisCommands.EVAL_BOOLEAN,
            //1.exists anyCountDownLatch 客户端A进来不存在，
            // 进入if逻辑
            "if redis.call('exists', KEYS[1]) == 0 then “
                //1.set anyCountDownLatch 3
                + "redis.call('set', KEYS[1], ARGV[2]); "
                + "redis.call('publish', KEYS[2], ARGV[1]); “   
                //1.返回1代表成功
                + "return 1 "
            + "else "
                + "return 0 "
            + "end",
            Arrays.