redlock-py

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SPSCommerce / redlock-py

Redis distributed locks in Python

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redlock-py - Redis distributed locks in Python

This python lib implements the Redis-based distributed lock manager algorithm described in this blog post.

To create a lock manager:

dlm = Redlock([{"host": "localhost", "port": 6379, "db": 0}, ])

To acquire a lock:

my_lock = dlm.lock("my_resource_name",1000)

Where the resource name is an unique identifier of what you are trying to lock and 1000 is the number of milliseconds for the validity time.

The returned value is

False
if the lock was not acquired (you may try again), otherwise an namedtuple representing the lock is returned, having three fields:
  • validity, an integer representing the number of milliseconds the lock will be valid.
  • resource, the name of the locked resource as specified by the user.
  • key, a random value which is used to safe reclaim the lock.

To release a lock:

dlm.unlock(my_lock)

It is possible to setup the number of retries (by default 3) and the retry delay (by default 200 milliseconds) used to acquire the lock.

Both

dlm.lock
and
dlm.unlock
raise a exception
MultipleRedlockException
if there are errors when communicating with one or more redis masters. The caller of
dlm
should use a try-catch-finally block to handle this exception. A
MultipleRedlockException
object encapsulates multiple
redis-py.exceptions.RedisError
objects.

Disclaimer: This code implements an algorithm which is currently a proposal, it was not formally analyzed. Make sure to understand how it works before using it in your production environments.

Further Reading: http://redis.io/topics/distlock http://martin.kleppmann.com/2016/02/08/how-to-do-distributed-locking.html http://antirez.com/news/101 https://medium.com/@talentdeficit/redlock-unsafe-at-any-time-40ceac109dbb#.uj9ffh96x

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