I think I have clearly mentioned what the client and server program mean. The server starts and wait for the client to connect to it and send data. I will process that sent data from client and display that in gui. But the gui is not starting.
Can you please point me what mistake I am making.

I think I have clearly mentioned ...

Well, neither the server nor the client you posted in that other thread have have a package declaration or a constructor called new ... so this code isn't code that compiles/runs/demonstrates the problem -- a mention is great, but its not like a Short, Self Contained, Compilable, Example

Can you please point me what mistake I am making.

You're trying to share the mainwindow between both server and client -- and probably between threads -- that simply isn't going to work well

On top of that, one or both of server/client are blocking

Just like MainLoop is also blocking

I linked one way to do this with threads and a que, and if you follow the other links (esp their parents), you'll find other solutions by other monks, and/or some Tk tips

on gui loops , on gui loops2 , on gui loops4 , on gui loops3 , on gui loops3 , on gui loops3

POE::Wheel::Run & Tk Problems - Solved / http://poe.perl.org/?POE_Cookbook/Tk_Interfaces, POE Tk - An RSS Newsreader, Graphical interaction with POE and Tk (Apr 04)