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Distributed Task Queue for Django

Project description

celery - Distributed Task Queue for Django.

Authors:Ask Solem (askh@opera.com)
Version:0.1.13

Introduction

celery is a distributed task queue framework for Django. More information will follow.

Installation

You can install celery either via the Python Package Index (PyPI) or from source.

To install using pip,:

$ pip install celery

To install using easy_install,:

$ easy_install celery

If you have downloaded a source tarball you can install it by doing the following,:

$ python setup.py build
# python setup.py install # as root

Usage

Have to write a cool tutorial, but here is some simple usage info.

Note You need to have a AMQP message broker running, like RabbitMQ, and you need to have the amqp server setup in your settings file, as described in the carrot distribution README.

Note If you’re running SQLite as the database backend, celeryd will only be able to process one message at a time, this because SQLite doesn’t allow concurrent writes.

Defining tasks

>>> from celery.task import tasks
>>> from celery.log import setup_logger
>>> def do_something(some_arg, **kwargs):
...     logger = setup_logger(**kwargs)
...     logger.info("Did something: %s" % some_arg)
>>> task.register(do_something, "do_something")

Tell the celery daemon to run a task

>>> from celery.task import delay_task
>>> delay_task("do_something", some_arg="foo bar baz")

Running the celery daemon

$ cd mydjangoproject
$ env DJANGO_SETTINGS_MODULE=settings celeryd
[....]
[2009-04-23 17:44:05,115: INFO/Process-1] Did something: foo bar baz
[2009-04-23 17:44:05,118: INFO/MainProcess] Waiting for queue.

Autodiscovery of tasks

celery has an autodiscovery feature like the Django Admin, that automatically loads any tasks.py module in the applications listed in settings.INSTALLED_APPS.

A good place to add this command could be in your urls.py,

from celery.task import tasks
tasks.autodiscover()

Then you can add new tasks in your applications tasks.py module,

from celery.task import tasks
from celery.log import setup_logger
from clickcounter.models import ClickCount

def increment_click(for_url, **kwargs):
    logger = setup_logger(**kwargs)
    clicks_for_url, cr = ClickCount.objects.get_or_create(url=for_url)
    clicks_for_url.clicks = clicks_for_url.clicks + 1
    clicks_for_url.save()
    logger.info("Incremented click count for %s (not at %d)" % (
                    for_url, clicks_for_url.clicks)
tasks.register(increment_click, "increment_click")

Periodic Tasks

Periodic tasks are tasks that are run every n seconds. They don’t support extra arguments. Here’s an example of a periodic task:

>>> from celery.task import tasks, PeriodicTask
>>> from datetime import timedelta
>>> class MyPeriodicTask(PeriodicTask):
...     name = "foo.my-periodic-task"
...     run_every = timedelta(seconds=30)
...
...     def run(self, **kwargs):
...         logger = self.get_logger(**kwargs)
...         logger.info("Running periodic task!")
...
>>> tasks.register(MyPeriodicTask)

For periodic tasks to work you need to add celery to INSTALLED_APPS, and issue a syncdb.

License

This software is licensed under the New BSD License. See the LICENSE file in the top distribution directory for the full license text.

Change history

0.1.13 [2009-05-19 12:36 P.M CET] askh@opera.com

  • Forgot to add yadayada to install requirements.

  • Now deletes all expired task results, not just those marked as done.

  • Able to load the Tokyo Tyrant backend class without django configuration, can specify tyrant settings directly in the class constructor.

  • Improved API documentation

  • Now using the Sphinx documentation system, you can build the html documentation by doing

    $ cd docs
    $ make html
    

and the result will be in docs/.build/html.

0.1.12 [2009-05-18 04:38 P.M CET] askh@opera.com

  • delay_task() etc. now returns celery.task.AsyncResult object, which lets you check the result and any failure that might have happened. It kind of works like the multiprocessing.AsyncResult class returned by multiprocessing.Pool.map_async.

  • Added dmap() and dmap_async(). This works like the * multiprocessing.Pool versions except they are tasks distributed to the celery server. Example:

    >>> from celery.task import dmap
    >>> import operator
    >>> dmap(operator.add, [[2, 2], [4, 4], [8, 8]])
    >>> [4, 8, 16]
    
    >>> from celery.task import dmap_async
    >>> import operator
    >>> result = dmap_async(operator.add, [[2, 2], [4, 4], [8, 8]])
    >>> result.ready()
    False
    >>> time.sleep(1)
    >>> result.ready()
    True
    >>> result.result
    [4, 8, 16]
    
  • Refactored the task metadata cache and database backends, and added a new backend for Tokyo Tyrant. You can set the backend in your django settings file. e.g

    CELERY_BACKEND = “database”; # Uses the database

    CELERY_BACKEND = “cache”; # Uses the django cache framework

    CELERY_BACKEND = “tyrant”; # Uses Tokyo Tyrant TT_HOST = “localhost”; # Hostname for the Tokyo Tyrant server. TT_PORT = 6657; # Port of the Tokyo Tyrant server.

0.1.11 [2009-05-12 02:08 P.M CET] askh@opera.com

  • The logging system was leaking file descriptors, resulting in servers stopping with the EMFILES (too many open files) error. (fixed)

0.1.10 [2009-05-11 12:46 P.M CET] askh@opera.com

  • Tasks now supports both positional arguments and keyword arguments.
  • Requires carrot 0.3.8.
  • The daemon now tries to reconnect if the connection is lost.

0.1.8 [2009-05-07 12:27 P.M CET] askh@opera.com

  • Better test coverage
  • More documentation
  • celeryd doesn’t emit Queue is empty message if settings.CELERYD_EMPTY_MSG_EMIT_EVERY is 0.

0.1.7 [2009-04-30 1:50 P.M CET] askh@opera.com

  • Added some unittests
  • Can now use the database for task metadata (like if the task has been executed or not). Set settings.CELERY_TASK_META
  • Can now run python setup.py test to run the unittests from within the testproj project.
  • Can set the AMQP exchange/routing key/queue using settings.CELERY_AMQP_EXCHANGE, settings.CELERY_AMQP_ROUTING_KEY, and settings.CELERY_AMQP_CONSUMER_QUEUE.

0.1.6 [2009-04-28 2:13 P.M CET] askh@opera.com

  • Introducing TaskSet. A set of subtasks is executed and you can find out how many, or if all them, are done (excellent for progress bars and such)
  • Now catches all exceptions when running Task.__call__, so the daemon doesn’t die. This does’t happen for pure functions yet, only Task classes.
  • autodiscover() now works with zipped eggs.
  • celeryd: Now adds curernt working directory to sys.path for convenience.
  • The run_every attribute of PeriodicTask classes can now be a datetime.timedelta() object.
  • celeryd: You can now set the DJANGO_PROJECT_DIR variable for celeryd and it will add that to sys.path for easy launching.
  • Can now check if a task has been executed or not via HTTP.

You can do this by including the celery urls.py into your project,

>>> url(r'^celery/$', include("celery.urls"))

then visiting the following url,:

http://mysite/celery/$task_id/done/

this will return a JSON dictionary like e.g:

>>> {"task": {"id": $task_id, "executed": true}}
  • delay_task now returns string id, not uuid.UUID instance.
  • Now has PeriodicTasks, to have cron like functionality.
  • Project changed name from crunchy to celery. The details of the name change request is in docs/name_change_request.txt.

0.1.0 [2009-04-24 11:28 A.M CET] askh@opera.com

  • Initial release

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