Network programming

Hi NG,

I'm trying to develop some application that communicate via the network.
One application (say A) basically sends a command to another (say B),
which will reply with OK or NOT-OK. This is easy enough.
The problem is that application B can also send messages on it's on
initiative to application A. These are events based on actual hardware
events.
The requirements I have are that a command-reply sequence is blocking.
So application A will wait until it gets a reply from application B. If
an event is received a function should be called on a seperate thread.

However application A will not continuously monitor the socket to see if
events are received. So I think (pretty sure) that application A should
have another thread that does monitor the socket continuously and
notifies the main thread when a reply occurs.

This seems a bit messy to me so I was wondering if there's a standard
way of dealing with synchronous and asynchronous communication available?

Can anyone give me some tips on how to continue?
Thank
Mark