How to create a distributed lock with Redis?

Question

On the redis documentation, I found a primitive lock can be implemented via SETNX:

http://redis.io/commands/setnx

• C4 sends SETNX lo

Answer 1

Using redis >= 2.6 the LUA script solution would be great. Lua script always executed atomically so:

--lockscript, parameters: lock_key, lock_timeout
local lock = redis.call('get', KEYS[1])
if not lock then    
    return redis.call('setex', KEYS[1], ARGV[1], "locked");
end
return false

The another solution based on new options of SET command

SET lock_key "locked" EX lock_timeout NX 

Using redis < 2.6 the pattern with multi can be used:

MULTI
SETNX tmp_unique_lock some_value
EXPIRE tmp_unique_lock
RENAMENX tmp_unique_lock real_lock
EXEC

Answer 2

follow the link
nice project explaining locking
http://redis.io/topics/distlock
https://github.com/mrniko/redisson

Answer 3

Use SET instead of SETNX. SET accepts arguments for expiration time in seconds and milliseconds instead of UNIX timestamp value.

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

From SETNX description:

NOTE: 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.

Answer 4

The new arguments for SET are enough for setting the lock, but these only work on Redis >= v2.6.12 you also need to think about how the lock will be unset and expire etc.

I've written a post on our Engineering blog about distributed locks using Redis. It covers scripting on how to set and release the lock reliably, with validation and deadlock prevention. I also include a module written in Node.js you can use for locking straight out of the box.

Answer 5

I gem'ed out the SET EX NX solution that misterion mentioned to a cool gem - simple_redis_lock

The code is simple and looks like this:

def lock(key, timeout)
  if @redis.set(key, Time.now, nx: true, px: timeout)
    begin
      yield
    ensure
      release key
    end
  end
end