I am running a simulation and transmitting data through XML-RPC to a remote client. I'm using a thread to run the XML-RPC part.
But for some reason, the program runs really slow until I a make a request from any of clients that connect. And after I run the very first request, the program then runs fine.
I have a class that inherits from Threading, and that I use in order to start the XML-RPC stuff
I cannot really show you the code, but do you have any suggestions as to why this is happening? 
Thanks, and I hope my question is clear enough
In Python, due to the GIL, threads doesn't really execute in parallel. If the RPC part is waiting in an active way (loop poling for connection instead of waiting), you most probably will have the behavior you are describing. However, without seeing any code, this is just wild guess.
XML-RPC Python Slow before first request