Was writing a multithreaded program in Java with an infinite while loop (for waiting). The thread was never preempted. Added a print statement inside the while loop and everything started working :/

Now I need to print a stupid message just so the program works :P

when working with threads and you have to wait for other processes use wait(); & notify(); ;)

The print probably contains code that releases controll and that lets other code run. Never ever use a loop to wait in multi threaded code.

Only time a loop is valid is in really old platforms with single thread where you use it to actually slow things down.

But there is better ways for that to.

Wait/notify/sleep or something depending on language is always a better idea.

Or callbacks but then you might need some other code to handle timeouts.

Dude go check Jakob Jenkov's tutorials on multothreading and thread 'scheduling'. There you will find the proper way to do it ;)