Refs #44 -- Added optional celery background queue for mails

doc/admin/config.rst

@@ -210,4 +210,21 @@ to speed up various operations::
 If no redis is configured, pretix will store sessions and locks in the database. If memcached
 is configured, memcached will be used for caching instead of redis.
 
-.. _Python documentation: https://docs.python.org/3/library/configparser.html?highlight=configparser#supported-ini-file-structure
+Celery task queue
+-----------------
+
+For processing long-running tasks asynchronously, pretix needs help of the celery task queue.
+For communicating between the web server and the task workers in both direction, a messaging
+queue and a result backend is needed. You can use a redis database for both directions, or
+an AMQP server (e.h. RabbitMQ) as a broker and redis or your database as a result backend::
+
+    [celery]
+    broker=amqp://guest:guest@localhost:5672//
+    backend=redis://localhost/0
+
+RabbitMQ might be the better choice if you have a complex, multi-server, high-performance setup,
+but as you already should have a redis instance ready for session and lock storage, we recommend
+redis for convenience. See the `Celery documentation`_ for more details.
+
+.. _Python documentation: https://docs.python.org/3/library/configparser.html?highlight=configparser#supported-ini-file-structure
+.. _Celery documentation: http://docs.celeryproject.org/en/latest/configuration.html

src/pretix/__init__.py

@@ -1 +1,6 @@
 __version__ = "0.0.0"
+
+try:
+    from .celery import app as celery_app
+except ImportError:
+    pass

src/pretix/base/services/mail.py

@@ -2,7 +2,6 @@ import logging
 
 from django.conf import settings
 from django.core.mail import EmailMessage
-from django.core.urlresolvers import reverse
 from django.template.loader import get_template
 from django.utils import translation
 from django.utils.translation import ugettext as _
@@ -66,10 +65,16 @@ def mail(user: User, subject: str, template: str, context: dict=None, event: Eve
         }
     )
     body += "\r\n"
+    try:
+        return mail_send([user.email], subject, body, sender)
+    finally:
+        translation.activate(_lng)
 
+
+def mail_send(to, subject, body, sender):
     email = EmailMessage(
         subject, body, sender,
-        to=[user.email]
+        to=to
     )
 
     try:
@@ -78,5 +83,10 @@ def mail(user: User, subject: str, template: str, context: dict=None, event: Eve
     except Exception:
         logger.exception('Error sending e-mail')
         return False
-    finally:
-        translation.activate(_lng)
+
+
+if settings.HAS_CELERY:
+    from pretix.celery import app
+
+    mail_send_task = app.task(mail_send)
+    mail_send = lambda *args, **kwargs: mail_send_task.apply_async(args=args, kwargs=kwargs)

src/pretix/celery.py

@@ -0,0 +1,12 @@
+import os
+
+os.environ.setdefault("DJANGO_SETTINGS_MODULE", "pretix.settings")
+
+from django.conf import settings
+
+if settings.HAS_CELERY:
+    from celery import Celery
+    app = Celery('pretix')
+
+    app.config_from_object('django.conf:settings')
+    app.autodiscover_tasks(lambda: settings.INSTALLED_APPS)

src/pretix/settings.py

@@ -114,6 +114,12 @@ if HAS_REDIS:
         SESSION_ENGINE = "django.contrib.sessions.backends.cache"
         SESSION_CACHE_ALIAS = "redis"
 
+HAS_CELERY = config.has_option('celery', 'broker')
+if HAS_CELERY:
+    BROKER_URL = config.get('celery', 'broker')
+    CELERY_RESULT_BACKEND = config.get('celery', 'backend')
+    CELERY_SEND_TASK_ERROR_EMAILS = bool(ADMINS)
+
 # Internal settings
 
 STATIC_ROOT = '_static'
@@ -330,3 +336,6 @@ LOGGING = {
         }
     },
 }
+
+CELERY_TASK_SERIALIZER = 'json'
+CELERY_RESULT_SERIALIZER = 'json'

src/requirements/celery.txt

@@ -0,0 +1,2 @@
+celery>=3.1,<3.2
+

src/setup.cfg

@@ -12,4 +12,4 @@ known_first_party = pretix
 known_third_party = versions
 multi_line_output = 5
 not_skip = __init__.py
-skip = make_testdata.py,wsgi.py,bootstrap
+skip = make_testdata.py,wsgi.py,bootstrap,celery.py