Multiple programs using the same UDP port? Possible?

Question

I currently have a small Python script that I'm using to spawn multiple executables, (voice chat servers), and in the next version of the software, the servers have the ability to receive heartbeat signals on the UDP port. (There will be possibly thousands of servers on one machine, ranging from ports 7878 and up)

My problem is that these servers might (read: will) be running on the same machine as my Python script and I had planned on opening a UDP port, and just sending the heartbeat, waiting for the reply, and voila...I could restart servers when/if they weren't responding by killing the task and re-loading the server.

Problem is that I cannot open a UDP port that the server is already using. Is there a way around this? The project lead is implementing the heartbeat still, so I'm sure any suggestions in how the heartbeat system could be implemented would be welcome also. -- This is a pretty generic script though that might apply to other programs so my main focus is still communicating on that UDP port.

Answer 1

I don't think this is possible. What you'll have to do is have one UDP master program that handles all UDP communication over the one port, and communicates with your servers in another way (UDP on different ports, named pipes, ...)

Answer 2

I'm pretty sure this is possible on Linux; I don't know about other UNIXes.

There are two ways to propagate a file descriptor from one process to another:

• When a process fork()s, the child inherits all the file descriptors of the parent.
• A process can send a file descriptor to another process over a "UNIX Domain Socket". See sendmsg() and recvmsg(). In Python, the _multiprocessing extension module will do this for you; see _multiprocessing.sendfd() and _multiprocessing.recvfd().

I haven't experimented with multiple processes listening on UDP sockets. But for TCP, on Linux, if multiple processes all listen on a single TCP socket, one of them will be randomly chosen when a connection comes in. So I suspect Linux does something sensible when multiple processes are all listening on the same UDP socket.

Try it and let us know!