Redis Demo系列之(五)分布式锁

Love The Way You Lie 2022-05-18 00:10 153阅读 0赞

### 前言 ###

线程之间锁问题多解决主要有数据库锁机制、Redis分布式锁、ZooKeeper分布式锁。其中Redis内单节点的分布式锁可以使用`setnx`进行处理。集群环境需要使用`redisson`。

本文相关代码，可在我的Github项目[https://github.com/SeanYanxml/bigdata/tree/master/redis][https_github.com_SeanYanxml_bigdata_tree_master_redis] 目录下可以找到。  
PS: (如果觉得项目不错，可以给我一个Star。)

--------------------

### Demo ###

/** * Jedis lock. * * */
    public class RedisLockDemo { 
    
        public static Jedis jedis = new JedisPoolManager().getJedis();
    
    
        // demo1 Jedis lock can do but not perfect.
        public static boolean notperfectLock(String key){
             Long result = jedis.setnx(key, "This is a Lock.");
             if(result == 1l){
                 return true;
             }else{
                 return false;
             }
        }
    
        // demo1 Jedis unlock can do but not perfect.
        public static boolean notperfectUnlock(String key){
            jedis.del(key);
            return true;
        }
    
        // demo1 Jedis unlock can do but also not perfect.
        public static boolean notperfectUnlock2(String lockKey, String lockValue){
            if(lockKey.equals(jedis.get(lockKey))){
                jedis.del(lockKey);
            }
            return true;
        }
    
        // demo2 perfect lock demo.
        private static final String LOCK_SUCCESS = "OK";
        private static final String SET_IF_NOT_EXISTS = "NX";
        private static final String SET_WITH_EXPIRE_TIME = "PX";
    
        /** * 设置分布式锁 * @param jedis Redis客户端 * @param lockKey 锁 * @param requestId 请求标识 * @param expireTime 生效时间 * @return 是否释放成功 */
        public static boolean tryGetDistributedLock(String lockKey,String requestId,int expireTime){
            String result = jedis.set(lockKey, requestId, SET_IF_NOT_EXISTS,SET_WITH_EXPIRE_TIME,expireTime);
            if(LOCK_SUCCESS.equals(result)){
                return true;
            }
            return false;
        }
    
    
         private static final Long RELEASE_SUCCESS = 1L;
    
            /** * 释放分布式锁 * @param jedis Redis客户端 * @param lockKey 锁 * @param requestId 请求标识 * @return 是否释放成功 */
            public static boolean releaseDistributedLock(Jedis jedis, String lockKey, String requestId) {
    
                String script = "if redis.call('get', KEYS[1]) == ARGV[1] then return redis.call('del', KEYS[1]) else return 0 end";
                Object result = jedis.eval(script, Collections.singletonList(lockKey), Collections.singletonList(requestId));
    
                if (RELEASE_SUCCESS.equals(result)) {
                    return true;
                }
                return false;
    
            }
    
            public static void main(String[] args) {
                releaseDistributedLock(jedis,"hello","hello");
            }
    }

--------------------

### Reference ###

\[1\]. [Redis分布式锁的正确实现方式（Java版）][Redis_Java]  
\[2\]. [分布式锁的几种使用方式（redis、zookeeper、数据库）][redis_zookeeper]  
\[3\]. [Redis学习笔记（六）redis实现分布式锁][Redis_redis]

[https_github.com_SeanYanxml_bigdata_tree_master_redis]: https://github.com/SeanYanxml/bigdata/tree/master/redis
[Redis_Java]: https://wudashan.cn/2017/10/23/Redis-Distributed-Lock-Implement/#%E5%8F%82%E8%80%83%E9%98%85%E8%AF%BB
[redis_zookeeper]: https://blog.csdn.net/u010963948/article/details/79006572
[Redis_redis]: https://blog.csdn.net/liubenlong007/article/details/53782934