Persistent server with GUI interactive functions ?

[Frank]

I need to write a GUI app that will serve as a peer to peer
client/server.  At the highest level it would be similar to a chat
client, which has a server component (waiting for any incoming
connections) as well as the client part (initiating a connection,
executing user commands).

Each of those function appears to involve entering an "endless loop"
as the last logical step to initiate processing (i.e. "mainloop()" for
the user interface and "serve_forever()" for the server).  I haven't
yet grasped the logical structure that will allow me to have two
non-returning calls and maintain control of the program.

Is there an example of this around somewhere, or does anyone know of
documentation that will explain this?
(Note:  I will need to have the app run under Win, Linux, and
Solaris.)

Thanks,
Frank