Thread Scheduling - please help

Hi,
i am working on scheduling of threds...i am having a thread library different from pthreads.

I wanted to switch b/w the threads. Its possible for me to switch, if thread
finishes its execution, using signals...but when a thread doing its execution
(for example if thred contains an infinite loop), i am not able to switch...

Is there any event handling techniques available in C to do that....


Thanks in advance