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Limitting program CPU usage

Started by Striken Feb 27, 2008 at 6:34 PM 6 replies 1k views

Original Post

Striken

Feb 27, 2008 at 6:34 PM

Hi all, I need a bit of advice; really simple question - for a program (*NOT* a game) that runs constantly:


int main() {
  bool done = false;
  while(!done) {
    //do stuff
  }
  return 0;
}

What is the best way to manage it's CPU usage? If I wanted to run a roughly *frame* a second, would Sleep(1000-x) (where x is the time in ms taken to process that frame) would that be sufficient for a high performace app? Thanks in advance.

Hodgman

Mod

5,991

Hodgman

Feb 27, 2008 at 6:39 PM

Quote:
Original post by Striken
If I wanted to run a roughly *frame* a second, would Sleep(1000-x) (where x is the time in ms taken to process that frame) would that be sufficient for a high performace app?

I'm maintaining a rendering tool that does exactly what you just described.
But make sure to check that 1000-x isn't negative, in which case you don't have to sleep ;)

swiftcoder

Mod

2,296

swiftcoder

Feb 27, 2008 at 6:40 PM

Sleep functions have very lousy accuracy in general (and especially on Windows), so you will want to sleep for a bit less than the full (1000 - x) you have calculated, say for instance (900 - x). Other than that, yes this approach works and is usually the simplest way to yield the CPU.

Striken

Author

Striken

Feb 27, 2008 at 7:16 PM

Thanks guys, I guess I should have put this in the beginners forum in hindsight :)

MJP

Mod

2,105

MJP

Feb 27, 2008 at 10:20 PM

If you're using Win32 and you have a UI app, be careful not to Sleep for long periods of time. While your thread is sleeping the day away, nobody is processing your thread's messages so they could be building up. Either keep your Sleeps to a minimum (15ms or so), or use a function like MsgWaitForMultipleObjects that will wake you up if a message arrives.

iMalc

182

iMalc

Feb 27, 2008 at 11:56 PM

Assuming this is a Windows program, use a standard Windows message loop with GetMessage etc, start a timer, and do the work upon receiving the WM_TIMER messages.