uwsgi-tasks 0.3

Asynchronous tasks management with UWSGI server

This package makes it to use UWSGI signal framework for asynchronous tasks management. It’s more functional and flexible than cron scheduler, and can be used as replacement for celery in many cases.

Requirements

The module works only in UWSGI web server environment, you also may have to setup some mules or(http://uwsgi-docs.readthedocs.org/en/latest/Spooler.html) as described in UWSGI documentation.

Installation

Simple execute pip install uwsgi_tasks

Usage

Mules, farms and spoolers

Use case: you have Django project and want to send all emails asynchronously.

Setup some mules with --mule or --mules=<N> parameters, or some spooler processes with --spooler==<path_to_spooler_folder>.

Then write:

# myapp/__init__.py
from django.core.mail import send_mail
from uwsgi_tasks import task, TaskExecutor, set_uwsgi_callbacks

# set default callbacks for mules and spoolers
set_uwsgi_callbacks()

@task(executor=TaskExecutor.MULE)
def send_email_async(subject, body, email_to):
    return send_mail(subject, body, '[e-mail]', [email_to])

...

def my_view():
    # Execute tasks asynchronously on first available mule
    send_email_async('Welcome!', 'Thank you!', '[e-mail]')

Execution of send_email_async will not block execution of my_view, since function will be called by first available mule.

The following tasks execution backends are supported: * AUTO - default mode, mule will be used if it is available and pickled task’s arguments less than 64 KB in size, otherwise spooler will be used. If spooler is not available, than task is executed at runtime. * MULE - execute decorated task on first available mule * SPOOLER - execute decorated task on spooler * RUNTIME - execute task at runtime

When SPOOLER backend is used, the following additional parameters are supported: * priority - string related to priority of this task, larger = less important, so you can simply use digits. spooler-ordered parameter must be set for this feature to work. * at - UNIX timestamp or Python datetime or Python timedelta object. * spooler_return - boolean value, False by default. If True is passed, you can return spooler codes from function, e.g. SPOOL_OK, SPOOL_RETRY and SPOOL_IGNORE. * retry_count - how many times spooler should repeat the task if it returns SPOOL_RETRY code, implies spooler_return=True. * retry_timeout - how many seconds between attempts spooler shoud wait to execute the task. Actual timeout depends on spooler-frequency parameter. Python timedelta object is also supported.

Use case: run task asynchronously and repeat execution 3 times at maximum if it fails, with 5 seconds timeout between attempts.

from functools import wraps
from uwsgi_tasks import task, TaskExecutor


def task_wrapper(func):
    @wraps(func)  # required!
    def _inner(*args, **kwargs):
        print 'Task started with parameters:', args, kwargs
        try:
            func(*args, **kwargs)
        except Exception as ex:  # example
            print 'Exception is occurred', ex, 'repeat the task'
            return uwsgi.SPOOL_RETRY

        print 'Task ended', func
        return uwsgi.SPOOL_OK

    return _inner

@task(executor=TaskExecutor.SPOOLER, retry_count=3, retry_timeout=5)
@task_wrapper
def spooler_task(text):
    print 'Hello, spooler! text =', text
    raise Exception('Sorry, task failed!')

There are some important notes:

Tasks should be imported on project initialization, thus if you use Django, you may place your tasks in app/tasks.py file and import them in app/__init__.py:

# app/__init__.py
from .tasks import *

If Django’s version is >= 1.7, you are encouraged to use AppConfig.ready method as described in official documentation:

from importlib import import_module
from django.apps import AppConfig

class IndexConfig(AppConfig):
    name = 'project.apps.index'
    verbose_name = 'Just index page'

    def ready(self):
        import_module('.tasks', self.name)

It’s necessary to setup required uwsgi callbacks at project’s initialization, you should call set_uwsgi_callbacks in your project/__init__.py file. Don’t do from uwsgidecorators import *, otherwise you will override callbacks.

Make sure task’s arguments must be pickable, since they are serialized and send via socket (mule) or file (spooler).

Timers, red-black timers and cron

This API is similar to uwsgi bundled Python decorators module. One thing to note: you are not able to provide any arguments to timer-like or cron-like tasks. See examples below:

from uwsgi_tasks import *

@timer(seconds=5)
def print_every_5_seconds(signal_number):
    """Prints string every 5 seconds

    Keep in mind: task is created on initialization.
    """
    print 'Task for signal', signal_number

@timer(seconds=5, iterations=3, target='workers')
def print_every_5_seconds(signal_number):
    """Prints string every 5 seconds 3 times"""
    print 'Task with iterations for signal', signal_number

@timer_lazy(seconds=5)
def print_every_5_seconds_after_call(signal_number):
    """Prints string every 5 seconds"""
    print 'Lazy task for signal', signal_number

@cron(minute=-2)
def print_every_2_minutes(signal_number):
    print 'Cron task:', signal_number

@cron_lazy(minute=-2, target='mule')
def print_every_2_minutes_after_call(signal_number):
    print 'Cron task:', signal_number

...

def my_view():
   print_every_5_seconds_after_call()
   print_every_2_minutes_after_call()

Timer and cron decorators supports target parameter, supported values are described here.

Keep in mind the maximum number of timer-like and cron-like tasks is 256 for each available worker.