How to implement redis distributed lock

redis distributed lock:
1. Implementation principle
Use the set command in redis to implement distributed lock.

Starting from Redis version 2.6.12, set can use the following parameters:

SET KEY VALUE [EX seconds] [PX milliseconds] [NX|XX]

EX second: Set the expiration time of the key to seconds. The effect of SET key value EX second is equivalent to SETEX key second value.
PX millisecond: Set the expiration time of the key to millisecond milliseconds. SET key value PX millisecond effect is equivalent to PSETEX key millisecond value.
NX: The key is set only when the key does not exist. The effect of SET key value NX is equivalent to SETNX key value.
XX: The key is set only when the key already exists.
Return value:
SET returns OK only when the setting operation is successfully completed.
If NX or XX is set, but the setting operation is not executed because the conditions are not met, the command returns a NULL Bulk Reply.
Command:
> SET key value EX ttl NX

The general idea is:
(a) SET lock currentTime expireTime EX 600 NX, use set to set the lock value and set the expiration time is 600 seconds. If successful, the lock is acquired;

(b) After acquiring the lock, if the node goes offline, the ock value will automatically expire at the expiration time;
(c) When releasing the lock, use del deletes the lock key value;
Using a redis stand-alone machine to provide distributed lock services may cause single point problems, resulting in poor service availability. Therefore, in situations where service stability requirements are high, the official recommendation is to use a redis cluster (for example, 5 units) , if more than 3 successful lock requests are made, it is considered as acquiring the lock) to implement redis distributed lock. See RedLock for details.
2. Advantages
High performance, redis can be persisted and data is not easily lost;
redis cluster method improves stability.
3. Disadvantages
Some data may be lost when using redis master-slave switching.
4. Open source implementation
Open source implementation of the python version: python-redis-lock.

The specific implementation method of redis distributed lock:

The method of locking and unlocking:

private static final String LOCK_SUCCESS = "OK";
    private static final String SET_IF_NOT_EXIST = "NX";
    private static final String SET_WITH_EXPIRE_TIME = "PX";
    private static final Long RELEASE_SUCCESS = 1L; 

    /**
     * 尝试获取分布式锁
     * @param lockKey 锁
     * @param requestId 请求标识
     * @param expireTime 超期时间
     * @return 是否获取成功
     */
    public Boolean tryGetDistributedLock(String lockKey, String requestId, int expireTime) {
        Jedis jedis = this.jedisPool.getResource();
        String result = jedis.set(lockKey, requestId, SET_IF_NOT_EXIST, SET_WITH_EXPIRE_TIME, expireTime);
        if (LOCK_SUCCESS.equals(result)) {
            return true;
        }
        return false;

    }

     /**
     * 释放分布式锁
     * @param lockKey 锁
     * @param requestId 请求标识
     * @return 是否释放成功
     */
    public Boolean releaseDistributedLock(String lockKey, String requestId) {
        Jedis jedis = this.jedisPool.getResource();
        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;

    }

2. Specific application

try{
String requestId = UUID.randomUUID().toString();
Boolean flag = tryGetDistributedLock(lock,requestId,1000);
int n = 0;
while(!flag){
      //如果没有获取锁，可以尝试下一个lock，如果都没有，则尝试 n 次，退出
     ...
     if(n++>5){ throw new Exception("尝试获取锁失败");}  
     ...  
}
if(!flag){
throw new Exception("尝试获取锁失败");
}
}catch(){
}finally{
    releaseDistributedLock(lock,requestId);
}

For more Redis related knowledge, please visit the Redis usage tutorial column!

The above is the detailed content of How to implement redis distributed lock. For more information, please follow other related articles on the PHP Chinese website!