subsystem services

The Services Subsystem

DroneD is largely a reactive application, meaning that it doesn't do anything on it's own in general. It usually is responding to some outside stimulus or directive. The exception to this however is for certain activities such as maintaining its jabber connectivity or regularly persisting its environment model to disk. This is what services are generally used for.

The Service API

While Twisted comes with a mechanism for writing services, it is kind of clunky and mostly suited to network services. So I decided to write my own service system, and ultimately it is very very simple.

A service is not a class or an object in any direct way, it is simply a module in the droned.services sub-package that exposes the following functions:

• install(rootService) - Where rootService is the root Twisted service. This is useful when you want to write a service that actually is a Twisted service. This includes the Nexus webapp and Manhole SSH server. You have to also write a line in droned-daemon.py that calls this. While not all services actually need an install function to do anything useful, some do and I figured it is best to keep the API consistent.
• start() - When this is called you should start your service. What that means exactly depends on your service. You have to write some code to actually call this. I like to use the AUTOSTART_SERVICES list from the config and put something like this in my install function: if 'myservice' in config.AUTOSTART_SERVICES: start()
• stop() - When this is called you should stop your service. So far I have not actually used this but I figure its a good idea to at least support it.
• running() - Should return True if your service is running, False otherwise.

To see some example services... just read their code. They are generally very simple. The most complicated would be the Jabber service, and still it's "service code" is very minimal.