Why does an empty loop use so much processor time?

Question

If I have an empty while loop in my code such as:

while(true);

It will drive the processor usage up to about 25%. However if I do the followin

Answer 1

I am going to guess that you have four cores on your multicore processor, which would explain the 25%, as you are completely tying up one processor doing your busy loop, as the only break in it is when the application is delayed so another application can run (but that may not happen depending on the load).

When you put a thread to sleep then it allows the OS to do other operations, and it knows when, as a minimum, to come back and wake up the thread, so it can continue it's work.