TODO: this needs a lot more examples
Each status plugin is an object which provides the
twisted.application.service.IService interface, which creates a
tree of Services with the buildmaster at the top [not strictly true].
The status plugins are all children of an object which implements
buildbot.interfaces.IStatus, the main status object. From this
object, the plugin can retrieve anything it wants about current and
past builds. It can also subscribe to hear about new and upcoming
builds.
Status plugins which only react to human queries (like the Waterfall display) never need to subscribe to anything: they are idle until someone asks a question, then wake up and extract the information they need to answer it, then they go back to sleep. Plugins which need to act spontaneously when builds complete (like the MailNotifier plugin) need to subscribe to hear about new builds.
If the status plugin needs to run network services (like the HTTP
server used by the Waterfall plugin), they can be attached as Service
children of the plugin itself, using the IServiceCollection
interface.