如何用redis實(shí)現(xiàn)分布式鎖

引子 redis作為一個(gè)強(qiáng)大的key/value數(shù)據(jù)庫(kù)，其實(shí)還可以用來實(shí)現(xiàn)輕量級(jí)的分布式鎖。 1.實(shí)現(xiàn)方案1 最早官方在SETNX命令頁給了一個(gè)實(shí)現(xiàn)： acquire lock: SETNX lock.foo current Unix time + lock timeout + 1 release lock: DEL lock.foo acquire lock when ti

引子

redis作為一個(gè)強(qiáng)大的key/value數(shù)據(jù)庫(kù)，其實(shí)還可以用來實(shí)現(xiàn)輕量級(jí)的分布式鎖。

1.實(shí)現(xiàn)方案1

最早官方在SETNX命令頁給了一個(gè)實(shí)現(xiàn)：

acquire lock: SETNX lock.foo 

release lock: DEL lock.foo

acquire lock when time expired: GETSET lock.foo 

不過這個(gè)方案有漏洞，就是release lock用的DEL命令不支持cas刪除（delete if current value equals old value），這樣忽略race condition將會(huì)出現(xiàn)問題：

A client will try to release the lock after the expire time deleting the key created by another client that acquired the lock later.

2.實(shí)現(xiàn)方案2

官方在SETNX命令頁介紹了新的方案：SET command + Lua script：

Starting with Redis 2.6.12 it is possible to create a much simpler locking primitive using the SET command to acquire the lock, and a simple Lua script to release the lock. The pattern is documented in the SET command page.

The old SETNX based pattern is documented below for historical reasons.

該方案有2個(gè)優(yōu)化：

（1）SET 命令可以設(shè)置key過期時(shí)間：SET key value [EX seconds] [PX milliseconds] [NX|XX]

The lock will be auto-released after the expire time is reached.

（2）使用Lua腳本實(shí)現(xiàn)cas刪除（詳見SET命令頁）

It is possible to make this system more robust modifying the unlock schema as follows:

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