IMPORTANT: READ ME
In version 0.1.4, we are introducing two major changes:
- Tasks now have a
createddatetime field. This was added to make sure
--replayfailedreplayed tasks in the appropriate order
- Introduced South migrations.
IF YOU HAVE ALREADY INSTALLED
django-ztask - you can "fake" the first migration, and then run the second migration:
./manage.py migrate django_ztask --fake 0001 ./manage.py migrate django_ztask
If you are not using South in your Django project, it is strongly recommended you do. If you are not, you will have to add the "created" field to your database manually.
Download and install 0MQ version 2.1.3 or better from http://www.zeromq.org
Install pyzmq and django-ztask using PIP:
pip install pyzmq pip install -e firstname.lastname@example.org:dmgctrl/django-ztask.git#egg=django_ztask
django_ztask to your
INSTALLED_APPS setting in
INSTALLED_APPS = ( ..., 'django_ztask', )
python manage.py syncdb
Running the server
Run django-ztask using the manage.py command:
python manage.py ztaskd
ztaskd command takes a series of command-line arguments:
ztaskd will use the built-in Django reloader
to reload the server whenever a change is made to a python file. Passing
--noreload will prevent it from listening for changed files.
(Good to use in production.)
If a command has failed more times than allowed in the
ZTASKD_RETRY_COUNT (see below for more), the task is
logged as failed. Passing in
--replayfailed will cause all
failed tasks to be re-run.
There are several settings that you can put in your
settings.py file in
your Django project. These are the settings and their defaults
ZTASKD_URL = 'tcp://127.0.0.1:5555'
ztaskd will run over TCP, listening on 127.0.0.1 port 5555.
ZTASKD_ALWAYS_EAGER = False
If set to
.after tasks will be run in-process and
not sent to the
ztaskd process. Good for task debugging.
ZTASKD_DISABLED = False
If set, all tasks will be logged, but not executed. This setting is often
used during testing runs. If you set
ZTASKD_DISABLED before running
python manage.py test, tasks will be logged, but not executed.
ZTASKD_RETRY_COUNT = 5
The number of times a task should be reattempted before it is considered failed.
ZTASKD_RETRY_AFTER = 5
The number, in seconds, to wait in-between task retries.
ZTASKD_ON_LOAD = ()
This is a list of callables - either classes or functions - that are called when the server first
starts. This is implemented to support several possible Django setup scenarios when launching
ztask - for an example, see the section below called Implementing with Johnny Cache.
Running in production
A recommended way to run in production would be to put something similar to
the following in to your
rc.local file. This example has been tested on
Ubuntu 10.04 and Ubuntu 10.10:
#!/bin/bash -e pushd /var/www/path/to/site sudo -u www-data python manage.py ztaskd --noreload -f /var/log/ztaskd.log & popd
Making functions in to tasks
Decorators and function extensions make tasks able to run.
Unlike some solutions, tasks can be in any file anywhere.
When the file is imported,
ztaskd will register the task for running.
Important note: all functions and their arguments must be able to be pickled.
It is a recommended best practice that instead of passing a Django model object to a task, you intead pass along the model's ID or primary key, and re-get the object in the task function.
The Task Decorator
from django_ztask.decorators import task
@task() decorator will turn any normal function in to a
django_ztask task if called using one of the function extensions.
Any function can be called in one of three ways:
Calling a function normally will bypass the decorator and call the function directly
Calling a function with
.async will cause the function task to be called asyncronously
on the ztaskd server. For backwards compatability,
.delay will do the same thing as
.async, but is deprecated.
func.after(seconds, *args, **kwargs)
This will cause the task to be sent to the
ztaskd server, which will wait
seconds to execute.
from django_ztask.decorators import task @task() def print_this(what_to_print): print what_to_print if __name__ == '__main__': # Call the function directly print_this('Hello world!') # Call the function asynchronously print_this.async('This will print to the ztaskd log') # Call the function asynchronously # after a 5 second delay print_this.after(5, 'This will print to the ztaskd log')
Implementing with Johnny Cache
Because Johnny Cache monkey-patches all the Django query compilers,
any changes to models in django-ztask that aren't properly patched won't reflect on your site until the cache
is cleared. Since django-ztask doesn't concern itself with Middleware, you must put Johnny Cache's query cache
middleware in as a callable in the
ZTASKD_ON_LOAD = ( 'johnny.middleware.QueryCacheMiddleware', ... )
If you wanted to do this and other things, you could write your own function, and pass that in to
ZTASKD_ON_LOAD, as in this example:
def ztaskd_startup_stuff(): ''' Stuff to run every time the ztaskd server is started or reloaded ''' from johnny import middleware middleware.QueryCacheMiddleware() ... # Other setup stuff
ZTASKD_ON_LOAD = ( 'myutilities.ztaskd_startup_stuff', ... )