Debugging programs with multiple threads

How does /prog/ do it?

I set up a separate thread that can be sent messages,and puts them into a FIFO to ensure its printed in the correct order, but is there a better way? I want to just drop in print statements ;_;

It's not really difficult. You think about the execution of threads and where they may possibly overlap. Ask yourself what happens if the threads execute in a certain order - and if you have no answer or your answer is "I don't know," you probably have a threading bug.