Is Sleep() inaccurate?

Question

I'm working on a timing system and I'll implement a timer class.

#include <windows.h>
#include <stdio.h>
#include <time.h>

int main()
{
    clock_t t1, t2;
    t1 = clock();
    Sleep(10);
    t2 = clock();
    printf("%i\n", (int)(t2 - t1));
    return 0;
}

This program should print "10" but it prints "15" or "16". I need more accurate which is less than 1 ms! Suggestions? (maybe with select()'s timeout?)

NOTE: I've run this program on Windows 7 Ultimate x86. Program compiled with MinGW (C/C++) x86.

NOW I THINK >>

Answer 1

Sleep() is accurate to the operating system's clock interrupt rate. Which by default on Windows ticks 64 times per second. Or once every 15.625 msec, as you found out.

You can increase that rate, call timeBeginPeriod(10). Use timeEndPeriod(10) when you're done. You are still subject to normal thread scheduling latencies so you still don't have a guarantee that your thread will resume running after 10 msec. And won't when the machine is heavily loaded. Using SetThreadPriority() to boost the priority, increasing the odds that it will.