Theory of good signal/event API design?

[Sander Marechal <s marechal jejik com>]

Hello,

I am building an application in which pretty much all functionality is
abstracted away in various modules. All these modules can be loaded and
configured at will and everything communicates by passing
messages/events around. Modules can listen for specific messages and
respond to it, or send out messages of their own, etcetera. Pretty
similar to how GTK works (in fact, it uses the GObject/GstObject system.
All messages are passed over a GStreamer bus).

My question: How do I determine what signals/events I should send out so
that together they make for a nice module API? For now, I am simply
building modules and adding signals to the application as I need them,
but I bet there is a better way to figure out which signals I should add
and where I should add them.

Is there some theory, guidelines, tutorials, whatever about designing an
event/message system, especially about what events/messages/signals to
add at which locations?

My application doesn't use GTK, just GObject and GStreamer, but I am
asking here since GTK works in a similar way.

Kind regards,

-- 
Sander Marechal
http://www.jejik.com