Bidirectional Networking

[Emanuele D'Arrigo]

Hi everybody! A networking question!

I've been looking at and tinkering a little with the various
networking modules in python. The examples are pretty clear and a
module such as the SimpleXMLRPCServer is actually simple!

All the examples though are based on a client interrogating a server,
with the client initiating the connection, obtaining something and
then closing the connection. Basically the server is a reactive party:
only if the client get in touch the server respond. What if the server
wanted to notify the client of something of interest, i.e. new data
that the client should take into consideration and potentially
process?

One option would be for the client to periodically poll the server for
changes. Fair enough, that would work. But it'd be a bit of a waste if
the changes aren't particularly frequent.

Is it possible then to establish both a server and a client in the
same application? I guess it must be possible but the examples all
rely on some kind of server loop (i.e. SocketServer.serve_forever)
that if started on both client and server sides would create two
listening parties but no talking at all! Furthermore, other libraries
might have their own loop, i.e. a graphical client has a loop to
redraw the screen and the two loops would somehow have to be
interleaved.

I'm not quite seeing how this can be done other than we threads. Is
that the way to do it? Place the listening loop in a thread while the
rest of the application does its own thing?

Or is it SocketServer.handle_request() the key? I could call this
function periodically, but what happens if a request is made while the
application is doing something else? Are the requests queued and dealt
with one per loop?

Thanks for your help!

Manu