Celey Mutex

Celery Mutex is a mutex for Celery Tasks, optionally refined based on provided keys. This mutex prevents execution of concurrent tasks, as opposed to delaying execution.

Installation

Simply run pip install celery_mutex

Requirements

Celery Mutex relies on ZooKeeper.

Usage

Celery Mutex takes advantage of Abstract Tasks for Celery. To utilize this abstract task, add it as a base for the task:

import celery_mutex

@app.task(base=celery_mutex.MutexTask)
def my_task(a, b):
    return a + b

A new configuration variable is required in order to let Celery Mutex know about your ZooKeeper servers:

ZOOKEEPER_HOSTS = 'localhost:2181'

This is a comma-separated list of hosts to connect to.

By default a mutex times out after one hour. This can be changed globally by setting MUTEX_TIMEOUT or per-task by setting mutex_timeout on the task. For both the value is an integer for the number of seconds to set the time out.

A second configuration option allows you to refine the mutex for a given task. By default, Celery Mutex only allows one instance of a task at a time. However, there may be a need to further refine what is controlled by the mutex. This can be done by setting mutex_keys on the task. The value is a list of keys that are to be used for determining exclusivity.

Using our above example, adding the two optional parameters would yield:

import celery_mutex

@app.task(base=celery_mutex.MutexTask, mutex_timeout=30, mutex_keys=('a',))
def my_task(a, b):
    return a + b

This would cause the mutex to only prevent execution for tasks that share the same value for "a".