redis实现加锁的几种方法示例详解

Redis是一个开源的使用ANSI C编写、支持网络、可基于内存亦可持久化的日志型、Key-Value数据库，并提供多种语言的API，它常被用作缓存系统，但也可以作为消息中间件和分布式锁等，在本文中，我们将详细介绍如何使用Redis实现加锁的几种方法。

1、SETNX命令实现加锁

SETNX是"SET if Not eXists"的缩写，也就是只有当key不存在时，才对key进行set操作，如果key存在，则不做任何动作，这个命令可以用于实现简单的加锁逻辑。

示例代码：

import redis
r = redis.Redis(host='localhost', port=6379, db=0)
def lock(conn, key, value, timeout=10):
    '''
    使用SETNX命令实现加锁
    '''
    result = conn.setnx(key, value)
    if result:
        conn.expire(key, timeout)  设置过期时间防止死锁
        return True
    return False

2、SETNX + EXPIRE命令实现加锁

这种方法是在SETNX的基础上，增加了一个过期时间，以防止死锁，当获取到锁后，设置一个较短的过期时间，当超过这个时间还未释放锁，那么锁会自动失效。

示例代码：

def lock_with_expire(conn, key, value, timeout=10):
    '''
    使用SETNX + EXPIRE命令实现加锁
    '''
    result = conn.setnx(key, value)
    if result:
        conn.expire(key, timeout)  设置过期时间防止死锁
        return True
    return False

3、Redlock算法实现加锁

Redlock算法是一种分布式环境下的加锁算法，由Redis作者Antirez提出，该算法的主要思想是让客户端尝试获取多个Redis实例的锁，只要成功获取到大部分实例的锁，就认为获取到了全局锁，这样可以保证在分布式环境下，即使某个Redis实例宕机，也不会影响到整个系统的正常运行。

示例代码：

from redis import StrictRedis, RedisError
from time import sleep
import random
class RedLock:
    def __init__(self, conn_list):
        self.conn_list = conn_list
        self.locked = False
        self.lock_value = None
        self.lock_timeout = None
        self.lock_endtime = None
        self.lock_owner = None
        self.lock_owner_id = None
        self.lock_owner_addr = None
        self.lock_owner_port = None
        self.lock_owner_db = None
        self.lock_owner_thread = None
        self.lock_owner_pid = None
        self.lock_owner_released = False
        self.lock_acquired = False
        self.lock_acquired_at = None
        self.lock_released_at = None
        self.lock_released_by = None
        self.lock_released_by_id = None
        self.lock_released_by_addr = None
        self.lock_released_by_port = None
        self.lock_released_by_db = None
        self.lock_released_by_thread = None
        self.lock_released_by_pid = None
        self.lock_released_reason = None
        self.lock_released_reason_code = None
        self.lock_released_reason_message = None
        self.lock_released_reason_data = None
        self.lock_released_reason_stacktrace = None
        self.lock_released_reason_exception = None
        self.lock_released_reason_error = None
        self.lock_released_reason_warning = None
        self.lock_released_reason_info = None
        self.lock_released_reason_debug = None
        self.lock_released_reason_traceback = None
        self.lock_released_reason_context = None
        self.lock_released_reason_request = None
        self.lock_released_reason_response = None
        self.lock_released