redis同时设置key和过期时间实现分布式锁

分手后的思念是犯贱 2022-11-29 13:22 188阅读 0赞

我们想通过同时设置redis的一个key值，用来表示占用到锁。可以用setnx命令实现。但如果此时redis服务发生异常，锁永远无法释放则会产生异常。为了避免这个现象，可以给key设置过期时间，但是两个命令分开执行时，两次命令中间的这段时间也可能产生异常。所以需要设置key-value和expire作为一个原子操作。redis的set命令本身支持这种操作。

> SET key value \[EX seconds|PX milliseconds|EXAT timestamp|PXAT  
> milliseconds-timestamp|KEEPTTL\] \[NX|XX\] \[GET\]
> 
>  *  EX seconds – Set the specified expire time, in seconds.
>  *  PX milliseconds – Set the specified expire time, in milliseconds.
>  *  EXAT timestamp-seconds – Set the specified Unix time at which the key will expire, in seconds.
>  *  PXAT timestamp-milliseconds – Set the specified Unix time at which the key will expire, in milliseconds.
>  *  NX – Only set the key if it does not already exist.
>  *  XX – Only set the key if it already exist.
>  *  KEEPTTL – Retain the time to live associated with the key.
>  *  GET – Return the old value stored at key, or nil when key did not exist.

[参考链接redis官方文档][redis]

于是将这个操作通过如下方式封装，留出key的值用来表示锁，过期时间表示锁过期时间即可。这中方式实现的分布式锁相比于redisson实现的分布式锁，可以更细粒度的控制每个具体锁的过期时间，缺点是没有自动续锁。

package com.dahua.psi.cache.redis.helper;
    
    import org.springframework.beans.factory.InitializingBean;
    import org.springframework.beans.factory.annotation.Autowired;
    import org.springframework.data.redis.core.RedisCallback;
    import org.springframework.data.redis.core.RedisTemplate;
    import org.springframework.data.redis.serializer.RedisSerializer;
    import org.springframework.stereotype.Component;
    
    import java.nio.charset.Charset;
    
    /** * redis锁帮助类，与redisson的分布式锁相比，可任意修改锁超时时间 * * @author susq * @date 2020年11月11日 */
    @Component
    public class RedisClusterHelper implements InitializingBean { 
    
       public boolean setExNx(String key, long expire) { 
            return redisTemplate.execute((RedisCallback<Boolean>) connection -> { 
                byte[] exp = String.valueOf(expire).getBytes(Charset.forName("UTF-8"));
                Object obj = connection.execute("set", keySerializer.serialize(key), valueSerializer.serialize("1"), nx, ex, exp);
                return obj != null;
            });
        }
    
        @Override
        public void afterPropertiesSet() throws Exception { 
            keySerializer = redisTemplate.getKeySerializer();
            valueSerializer = redisTemplate.getValueSerializer();
        }
    
    	@Autowired
        private RedisTemplate<String, String> redisTemplate;
    
        RedisSerializer keySerializer;
    
        RedisSerializer valueSerializer;
    
        private byte[] nx = "NX".getBytes(Charset.forName("UTF-8"));
        private byte[] ex = "EX".getBytes(Charset.forName("UTF-8"));
        
        /** * 获取一个redis锁 * @param key 锁的key * @param expire 过期时间，单位秒 * @return 是否获取成功 */
        public boolean setExNx(String key, long expire) { 
            return redisTemplate.execute((RedisCallback<Boolean>) connection -> { 
                byte[] exp = String.valueOf(expire).getBytes(Charset.forName("UTF-8"));
                Object obj = connection.execute("set", keySerializer.serialize(key), valueSerializer.serialize("1"), nx, ex, exp);
                return obj != null;
            });
        }
    
        @Override
        public void afterPropertiesSet() throws Exception { 
            keySerializer = redisTemplate.getKeySerializer();
            valueSerializer = redisTemplate.getValueSerializer();
        }
    }

[redis]: https://redis.io/commands/set