=============================== Celery 1.0 has been released! ===============================
We're happy to announce the release of Celery 1.0.
What is it? ===========
Celery is a task queue/job queue based on distributed message passing. It is focused on real-time operation, but supports scheduling as well.
The execution units, called tasks, are executed concurrently on one or more worker servers. Tasks can execute asynchronously (in the background) or synchronously (wait until ready).
Celery is already used in production to process millions of tasks a day.
Celery was originally created for use with Django, but is now usable from any Python project. It can also operate with other languages via webhooks.
The recommended message broker is RabbitMQ (http://rabbitmq.org), but support for Redis and databases is also available.
For more information please visit http://celeryproject.org
Stable API ==========
From this version on the public API is considered stable. This means there won't be any backwards incompatible changes in new minor versions. Changes to the API will be deprecated; so, for example, if we decided to remove a function that existed in Celery 1.0:
* Celery 1.2 will contain a backwards-compatible replica of the function which will raise a PendingDeprecationWarning. This warning is silent by default; you need to explicitly turn on display of these warnings. * Celery 1.4 will contain the backwards-compatible replica, but the warning will be promoted to a full-fledged DeprecationWarning. This warning is loud by default, and will likely be quite annoying. * Celery 1.6 will remove the feature outright.
See the Celery Deprecation Timeline for a list of pending removals: http://ask.github.com/celery/internals/deprecation.html
What's new? ===========
* Task decorators
Write tasks as regular functions and decorate them. There are both task(), and periodic_task() decorators.
* Tasks are automatically registered
Registering the tasks manually was getting tedious, so now you don't have to anymore. You can still do it manually if you need to, just disable Task.autoregister. The concept of abstract task classes has also been introduced, this is like django models, where only the subclasses of an abstract task is registered.
If enabled, the worker will send events, telling you what tasks it executes, their results, and how long it took to execute them. It also sends out heartbeats, so listeners are able to detect nonfunctional workers. This is the basis for the new real-time web monitor we're working on (celerymon: http://github.com/ask/celerymon/).
* Rate limiting
Global and per task rate limits. 10 tasks a second? or one an hour? You decide. It's using the token bucket algorithm, which is commonly used for network traffic shaping. It accounts for bursts of activity, so your workers won't be bored by having nothing to do.
* New periodic task service.
Periodic tasks are no longer dispatched by celeryd, but instead by a separate service called *celerybeat*. This is an optimized, centralized service dedicated to your periodic tasks, which means you don't have to worry about deadlocks or race conditions any more. But that does mean you have to make sure only one instance of this service is running at any one time.
**TIP:** If you're only running a single celeryd server, you can embed celerybeat inside it. Just add the --beat argument.
* Broadcast commands
If you change your mind and don't want to run a task after all, you now have the option to revoke it.
Also, you can rate limit tasks or even shut down the worker remotely.
It doesn't have many commands yet, but we're waiting for broadcast commands to reach its full potential, so please share your ideas if you have any.
* Multiple queues
The worker is able to receive tasks on multiple queues at once. This opens up a lot of new possibilities when combined with the impressive routing support in AMQP.
* Platform agnostic message format.
The message format has been standardized and is now using the ISO-8601 format for dates instead of Python datetime objects. This means you can write task consumers in other languages than Python (eceleryd anyone?)
Periodic tasks are now scheduled on the clock, i.e. timedelta(hours=1) means every hour at :00 minutes, not every hour from the server starts. To revert to the previous behavior you have the option to enable PeriodicTask.relative.
* ... and a lot more!
To read about these and other changes in detail, please refer to the change log: http://celeryproject.org/docs/changelog.html This document contains crucial information for those upgrading from a previous version of Celery, so be sure to read the entire change set before you continue.
**TIP:** If you install the setproctitle module you can see which task each worker process is currently executing in ps listings. Just install it using pip: pip install setproctitle.
* Homepage: http://celeryproject.org
* Download: http://pypi.python.org/pypi/celery
* Documentation: http://celeryproject.org/docs/
* Changelog: http://celeryproject.org/docs/changelog.html
* Code: http://github.com/ask/celery/
* Mailing-list: http://groups.google.com/group/celery-users
* IRC: #celery on irc.freenode.net.