Investigation of optimal sleep time calculation in game loop

Question

When programming animations and little games I\'ve come to know the incredible importance of Thread.sleep(n); I rely on this method to tell the operating system

Answer 1

You could use a cyclic timer associated with a mutex. This is IHMO the most efficient way of doing what you want. But then you should think about skipping frames in case the computer lags (You can do it with another nonblocking mutex in the timer code.)

Edit: Some pseudo-code to clarify

Timer code:

While(true):
  if acquireIfPossible(mutexSkipRender):
    release(mutexSkipRender)
    release(mutexRender)

Sleep code:

acquire(mutexSkipRender)
acquire(mutexRender)
release(mutexSkipRender)

Starting values:

mutexSkipRender = 1
mutexRender = 0

Edit: corrected initialization values.

The following code work pretty well on windows (loops at exactly 50fps with a precision to the millisecond)

import java.util.Date;
import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.Semaphore;


public class Main {
    public static void main(String[] args) throws InterruptedException {
        final Semaphore mutexRefresh = new Semaphore(0);
        final Semaphore mutexRefreshing = new Semaphore(1);
        int refresh = 0;

        Timer timRefresh = new Timer();
        timRefresh.scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                if(mutexRefreshing.tryAcquire()) {
                    mutexRefreshing.release();
                    mutexRefresh.release();
                }
            }
        }, 0, 1000/50);

        // The timer is started and configured for 50fps
        Date startDate = new Date();
        while(true) { // Refreshing loop
            mutexRefresh.acquire();
            mutexRefreshing.acquire();

            // Refresh 
            refresh += 1;

            if(refresh % 50 == 0) {
                Date endDate = new Date();
                System.out.println(String.valueOf(50.0*1000/(endDate.getTime() - startDate.getTime())) + " fps.");
                startDate = new Date();
            }

            mutexRefreshing.release();
        }
    }
}