pylock 0.3

Python Distributed Lock

Usage

from pylock import Lock

with Lock('a_key', expires=60, timeout=10):
    # do something that should only be done one at a time

Configuration

Backends

There are three available backends:

Open (non-locking) backend

DEFAULT_BACKEND = {
    'class': 'pylock.backends.open_lock.OpenLock',
    'connection': 'open://'
}

Warning This backend is not a real lock since it can always be acquired even if another instance has acquired it already. It is meant to be used for testing when you don’t want to depend on a running redis or memcache instance and don’t care about the lock working.

Redis backend

DEFAULT_BACKEND = {
    'class': 'pylock.backends.redis_lock.RedisLock',
    'connection': 'redis://'
}

Note: all fields after the scheme are optional, and will default to localhost on port 6379, using database 0.

Memcache backend (coming soon)

DEFAULT_TIMEOUT (default: 60)

If another client has already obtained the lock, sleep for a maximum of this many seconds before giving up. A value of 0 means no wait (give up right away).

The default timeout can be overridden when instantiating the lock.

DEFAULT_EXPIRES (default: 10)

We consider any existing lock older than this many seconds to be invalid in order to detect crashed clients. This value must be higher than it takes the critical section to execute.

The default expires can be overridden when instantiating the lock.

KEY_PREFIX (default 'pylock:')

This is used to prefix the key for the generated lock.

For Lock('somekey'), the generated key will be 'pylock:somekey'

Inspired by

Redis backend

The redis backend is almost an exact copy of Ben Bangert’s `retools.lock <https://github.com/bbangert/retools/blob/master/retools/lock.py>`_ which is based on Chris Lamb’s example

Memcache backend (coming soon)

The memcache backend is inspired by the following: - https://github.com/snbuback/DistributedLock - http://jbq.caraldi.com/2010/08/simple-distributed-lock-with-memcached.html - http://www.regexprn.com/2010/05/using-memcached-as-distributed-locking.html

TODO: - better handle redis/memcache connection issues