redis watch命令实现秒杀demo

1.思路

在redis提供了incr命令进行递增操作，可以保证原子性。利用watch实现也可以实现递增递减的操作。
WATCH命令可以监控一个或多个键，一旦其中有一个键被修改（或删除），之后的事务就不会执行。监控一直持续到EXEC命令（事务中的命令是在EXEC之后才执行的，所以在MULTI命令后可以修改WATCH监控的键值）

2.代码实现

public class SecKillDemo implements Runnable {

    private Jedis jedis = new Jedis("192.168.99.100", 6379);

    private String customerName;

    private String key;

    public SecKillDemo(String customerName, String key) {
        this.customerName = customerName;
        this.key = key;
    }

    @Override
    public void run() {
        boolean success = false;
        String data;
        int currentNum;
        while (!success) {//可重复抢购直到成功
           //通过watch实现redis的incr(原子递增操作)
            jedis.watch(key);
            data = jedis.get(key);
            currentNum = Integer.parseInt(data);
            if (currentNum > 0) {
                //开启事务
                Transaction transaction = jedis.multi();
                //设置新值,如果key的值被其它连接的客户端修改，那么当前连接的exec命令将执行失败
                currentNum--;
                transaction.set(key, String.valueOf(currentNum));
                List res = transaction.exec();
                if (res.size() == 0) {
                    System.out.println(customerName + " 抢购失败");
                    success = false;
                } else {
                    success = true;
                    System.out.println(customerName + " 抢购成功,[" + key + "]剩余：" + currentNum);
                }
            } else {
                System.out.println("商品售空,活动结束!");
                System.exit(0);
            }
        }
    }
}

3.测试

public class SecKillTest {

    private static String key = "macbook";

    private static String num = "100";

    private static ExecutorService executorService = Executors.newFixedThreadPool(8);
    

    @Before
    public void before() {
        Jedis jedis = new Jedis("192.168.99.100");
        String script = "redis.call('del',KEYS[1]);return redis.call('set',KEYS[1],ARGV[1])";
        jedis.eval(script, Collections.singletonList(key), Collections.singletonList(num));
        jedis.close();
    }

    @Test
    public void test() {

    }

    public static void main(String[] args) {
        try{
            for (int i = 1; i <= 600; i++) {
                executorService.submit(new SecKillDemo("顾客"+i,key));
            }
        }finally {
            executorService.shutdown();
        }
    }
}

代码：https://github.com/ackFinding/2019/tree/master/distributed/redis-lock/src/main/java/com/watch/seckill

参考：

[1]Redis的事务和watch