|Do you know where your variables are?|
You took that code from this thread (which has exactly the same name): asynchronous socket comunication with perl tk
In that thread, the request was for: "... an example of asynchronous socket communication happening through a perl tk application. A very simple and primitive one."
When I wrote that code last month, I included links to related documentation. If you follow those links, particularly the ones to sections of perlipc, you'll find examples of more complex socket I/O (including multiple clients).
In reply to Re: asynchronous socket communication with perl tk