Writing cronjobs

Writing cronjobs works similar to plugins. The invokation and arguments passed are different though. A minimal cronjob looks like this:

import datetime
from debexpo.cronjobs import BaseCronjob

class ImportUpload(BaseCronjob):
    def setup(self):
        pass

    def teardown(self):
        pass

    def invoke(self):
        self.log.debug("Hello World")

cronjob = ImportUpload
schedule = datetime.timedelta(seconds = 10)

The architecture

A cronjob should be subclassed from BaseCronjob. That ensure API compliant invokation. A worker thread runs your jobs cyclically, persistence is guaranteed for the object runtime. Technically, you must define two objects in your module.

Invokation::

cronjob = ImportUpload schedule = datetime.timedelta(seconds = 10)

The ‘cronjob’ attribute is an object reference which should be instantiated upon cronjob invokation. The ‘schedule’ attribute defines how often your cronjob should invoke your worker method. This must be a datetime.timedelta object. This is a soft guarantee. The Worker thread will gurantee you not to run the job more often than you specified, but it will not invoke it precisely for every delta. Your cronjob will not be invoked if another cronjob is still pending or running once your delta expires. Additionally the Worker thread does not execute the worker queue more often than every debexpo.cronjob_delay milliseconds.

The constructor

Please don’t override the base class constructor, it will call your setup method if you need any setup. The following attributes will be instantiated for your cronjob:

self.parent

This is a reference to the worker object, which instantiated your cronjob. You can call any method in from there, if necessary.

self.config

This is an instantiated configuration object. You can access every Debexpo configuration setting from it.

self.log

An instantiated log object, use it to display messages within the worker thread

The destructor

Similarly to the constructor, don’t override the destructor. Use the teardown method instead

The worker method invokation

Implement the invoke method as your working horse. It will be called regularly and run your stuff. The Worker is designed as single threaded application, which means your method will block the entire cron job architecture. Don’t do anything which shall not be run synchronously.