django與celery實現異步隊列任務

Django使用初步

Using Celery with Django

Note

Previous versions of Celery required a separate library to work with Django, but since 3.1 this is no longer the case. Django is supported out of the box now so this document only contains a basic way to integrate Celery and Django. You’ll use the same API as non-Django users so you’re recommended to read the First Steps with Celery tutorial first and come back to this tutorial. When you have a working example you can continue to the Next Steps guide.

Note

Celery 4.0 supports Django 1.8 and newer versions. Please use Celery 3.1 for versions older than Django 1.8.

To use Celery with your Django project you must first define an instance of the Celery library (called an 「app」)

If you have a modern Django project layout like:

- proj/
  - proj/__init__.py
  - proj/settings.py
  - proj/urls.py
- manage.py

then the recommended way is to create a new proj/proj/celery.py module that defines the Celery instance:

file:	proj/proj/celery.py

from __future__ import absolute_import, unicode_literals
import os
from celery import Celery

# set the default Django settings module for the 'celery' program.
os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'proj.settings')

app = Celery('proj')

# Using a string here means the worker don't have to serialize
# the configuration object to child processes.
# - namespace='CELERY' means all celery-related configuration keys
#   should have a `CELERY_` prefix.
app.config_from_object('django.conf:settings', namespace='CELERY')

# Load task modules from all registered Django app configs.
app.autodiscover_tasks()


@app.task(bind=True)
def debug_task(self):
    print('Request: {0!r}'.format(self.request))

Then you need to import this app in your proj/proj/__init__.py module. This ensures that the app is loaded when Django starts so that the @shared_task decorator (mentioned later) will use it:

proj/proj/__init__.py:

from __future__ import absolute_import, unicode_literals

# This will make sure the app is always imported when
# Django starts so that shared_task will use this app.
from .celery import app as celery_app

__all__ = ['celery_app']

Note that this example project layout is suitable for larger projects, for simple projects you may use a single contained module that defines both the app and tasks, like in the First Steps with Celery tutorial.

Let’s break down what happens in the first module, first we import absolute imports from the future, so that our celery.py module won’t clash with the library:

from __future__ import absolute_import

Then we set the default DJANGO_SETTINGS_MODULE environment variable for the celery command-line program:

os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'proj.settings')

You don’t need this line, but it saves you from always passing in the settings module to the celery program. It must always come before creating the app instances, as is what we do next:

app = Celery('proj')

This is our instance of the library, you can have many instances but there’s probably no reason for that when using Django.

We also add the Django settings module as a configuration source for Celery. This means that you don’t have to use multiple configuration files, and instead configure Celery directly from the Django settings; but you can also separate them if wanted.

The uppercase name-space means that all Celery configuration options must be specified in uppercase instead of lowercase, and start with CELERY_, so for example the task_always_eager` setting becomes CELERY_TASK_ALWAYS_EAGER, and the broker_urlsetting becomes CELERY_BROKER_URL.

You can pass the object directly here, but using a string is better since then the worker doesn’t have to serialize the object.

app.config_from_object('django.conf:settings', namespace='CELERY')

Next, a common practice for reusable apps is to define all tasks in a separate tasks.pymodule, and Celery does have a way to  auto-discover these modules:

app.autodiscover_tasks()

With the line above Celery will automatically discover tasks from all of your installed apps, following the tasks.py convention:

- app1/
    - tasks.py
    - models.py
- app2/
    - tasks.py
    - models.py

This way you don’t have to manually add the individual modules to the CELERY_IMPORTSsetting.

Finally, the debug_task example is a task that dumps its own request information. This is using the new bind=True task option introduced in Celery 3.1 to easily refer to the current task instance.

Using the @shared_task decorator

The tasks you write will probably live in reusable apps, and reusable apps cannot depend on the project itself, so you also cannot import your app instance directly.

The @shared_task decorator lets you create tasks without having any concrete app instance:

demoapp/tasks.py:

# Create your tasks here
from __future__ import absolute_import, unicode_literals
from celery import shared_task


@shared_task
def add(x, y):
    return x + y


@shared_task
def mul(x, y):
    return x * y


@shared_task
def xsum(numbers):
    return sum(numbers)

See also

You can find the full source code for the Django example project at:https://github.com/celery/celery/tree/master/examples/django/

Relative Imports

You have to be consistent in how you import the task module. For example, if you have project.app in INSTALLED_APPS, then you must also import the tasks from project.appor else the names  of the tasks will end up being different.

See Automatic naming and relative imports

Extensions

django-celery-results - Using the Django ORM/Cache as a result backend

The django-celery-results extension provides result backends using either the Django ORM, or the Django Cache framework.

To use this with your project you need to follow these steps:

1. Install the django-celery-results library:

   $ pip install django-celery-results

1. Add django_celery_results to INSTALLED_APPS.

   Note that there’s no dashes in this name, only underscores.

2. Create the Celery database tables by performing a database migrations:

   $ python manage.py migrate django_celery_results

3. Configure Celery to use the django-celery-results backend.

   Assuming you are using Django’s settings.py to also configure Celery, add the following settings:

   CELERY_RESULT_BACKEND = 'django-db'

   For the cache backend you can use:

   CELERY_RESULT_BACKEND = 'django-cache'

django-celery-beat - Database-backed Periodic Tasks with Admin interface.

See Using custom scheduler classes for more information.

Starting the worker process

In a production environment you’ll want to run the worker in the background as a daemon - see Daemonization - but for testing and development it is useful to be able to start a worker instance by using the celery worker manage command, much as you’d use Django’s manage.py runserver:

$ celery -A proj worker -l info

For a complete listing of the command-line options available, use the help command:

$ celery help

Where to go from here

If you want to learn more you should continue to the Next Steps tutorial, and after that you can study the User Guide.