Is Sleep() inaccurate? | 易学教程

问题

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 >>

回答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.

回答2:

Your problem is that the "clock" only ticks 64 times per second (I've seen systems that can go up to 2000, but no higher). If you are creating a timer class, you probably want to have much higher resolution than even 2000. Use QueryPerformanceCounter to get higher resolution. See QueryPerformanceCounter and overflows for an example.

Note that if you want to sleep for very short intervals, you will have to call QueryPerformanceCounter in a tight loop.

回答3:

Sleep() is not accurate in the way you want it to be.

It will cause the thread to sleep for AT LEAST the length of time you specify, but there's no guarantee that the OS will return control to your thread at exactly that specified time.

来源：https://stackoverflow.com/questions/19427034/is-sleep-inaccurate

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