sending user-defined messages to widgets?

["Lars Ruoff" <lars ruoff sxb bsf alcatel fr>]

Hi,
i would like to send messages between widgets. (for example to inform a
widget that some information in a global variable has been updated etc.).
The goal is to not adress the widget directly, but rather send the message
to the top-level window, which dispatches it to every widget that is
interested in receiving the message.
(As you see, i'm experienced with GUI development, but i'm totally new to
GTK).
At a first glance to the docs, i think gtk_emit_signal could be the function
to go for, but i didn't get it work so far.
What do i have to do to define a user_defined message that can be sent to a
widget hirarchie, and for which widgets can register?

Lars Ruoff.