A single UDP port in a multithreaded server

Question

I'm trying to write a server application that creates a thread for every client. The server/client communication is a combination of TCP and UDP, and I want to use a fixed TCP/UDP port on the server side to make it easier to use behind NAT routers. Here's a summary of what I have done and what I want to achieve:
- The server creates a TCP and UDP channel (I'm using the NIO interface) on the specified ports
- The server waits for incoming clients by calling accept() on the TCP channel
- The server creates a new thread for the new client, and gives the TCP and UDP channels as arguments
- The client informs the server about its UDP port over the TCP connection
- The new server thread connect()s the UDP channel to the IP:port pair received over the TCP connection
I believed that connecting the UDP socket to the IP:port of the client in each thread would make it possible to use a single UDP port for the multithreaded application, but it seems that the connect() call affects the parent thread as well. The next client that tries to connect() gets a "Connect already invoked" error. I tried calling clone() on the UDP channel argument I passed to the new thread, but was not allowed to call clone() because it's protected.
Can someone tell me if what I'm trying to do is possible, and if so, how to achieve it?

Answer 1

Peter__Lawrey wrote:It sounds like you want to bind a UDP socket to a listening port and the sender as well. So you can have a thread per sending IP:port. (Not sure why you would want to...)
To my knowledge you can only bind a socket based on the listening port. You could have a dispatcher thread which passes these packets to the thread for that sender.
To me, client/server means a request/response based interaction with a request from the client and the response from the server back to the client. This interaction is typically point to point and lossless.-I wanted one thread per client because it's the simplest thing to implement. For example, I don't have to create data structures for storing state information for each individual client (e.g., bitrate, block size, duration, etc), since each thread has only one single client. Still, I don't want to use hacks like having a dispatcher thread, so if it is correct that UDP ports can't be used in the same way as TCP ports, I guess I'll just have to implement the server as a single-threaded process. :(
As for client/server, a better description would be master/slave (and that's what I'm using in my program), but I thought I'd make it simple and use the more common client/server terms in this thread since it doesn't matter for the question I'm asking.