Background tasks to be run either by uwsgi, or directly if on dev server.

tasks.py

"""Background tasks to be run either by uwsgi, or directly if on dev server.
"""

import cPickle as pickle
import logging

from django.core.mail import send_mail

LOG = logging.getLogger(__name__)
HAS_UWSGI = False
TASKS = {}

# Filled in after successful uwsgi import. Needed for unit testing.
SPOOL_OK = 1
SPOOL = lambda x: x

#
# Plumbing
#


def backstage_spooler(env):
    """uwsgi spooler function, called by uwsgi, runs background tasks.
    http://projects.unbit.it/uwsgi/wiki/Spooler
    """
    unpacked = pickle.loads(env["__task_kwargs"])
    target = TASKS[env["__task_name"]]
    try:
        target(**unpacked)
    except:
        LOG.exception("Exception calling task %s", env["__task_name"])
        raise
    return SPOOL_OK

try:
    import uwsgi                                        # pylint: disable=F0401

    HAS_UWSGI = True
    uwsgi.spooler = backstage_spooler
    SPOOL_OK = uwsgi.SPOOL_OK
    SPOOL = uwsgi.spool

except ImportError:
    HAS_UWSGI = False


def task(func):
    """Decorator to run the wrapped func
     - as a uwsgi spool if in uwsgi
     - directly if not
    """
    return utask(func) if HAS_UWSGI else func


def utask(func):
    """Decorator. Wraps a function to run as a uwsgi spool task.
    Don't use this directly, use @task instead.
    """
    def enqueue(**kwargs):
        """Ask the uwsgi spooler to run our task.
        Wraps up the arguments in a pickle, to allow non-string kwargs.
        """
        packed = pickle.dumps(kwargs)
        params = {"__task_kwargs": packed, "__task_name": func.__name__}
        SPOOL(params)

    TASKS[func.__name__] = func
    return enqueue

#
# Write your tasks here
#
# - Tasks can only use kwargs (not positional args)
# - All kwargs must be pickleable
#


@task
def task_email(subject=None, body=None,
               from_email=None, recipient_user=None):
    """Start background task to send an email.

    Putting email in a background task only makes sense if we use
    a remote mail server. If the mail server is on our local machine,
    socket connection will be as fast as memcached, no background needed.
    """

    send_mail(subject, body, from_email,
              recipient_list=[recipient_user],
              fail_silently=False)