If you want to keep waiting on data from the client, you need to keep reading from the client. See for example "TCP Servers with IO::Socket" in perlipc.

However, I would strongly recommend against writing a server at such a low level. Nowadays, I think that event loops are the way to go. I've used POE, but that has a fairly high learning curve, and so I can recommend Mojo::IOLoop. Yes Mojolicious is a web framework, but the aforementioned module can be used independently of the framework to write TCP servers IMHO very easily. Example code here.