Windows Sleep Function Extremely Slow

Question

I am making a program using the Sleep command via Windows.h, and am experiencing a frustrating difference between running my program on Windows 10 instead of Windows 7. I simplified my program to the program below which exhibits the same behavior as my more complicated program.

On Windows 7 this 5000 count loop runs with the Sleep function at 1ms. This takes 5 seconds to complete.

On Windows 10 when I run the exact same program (exact same binary executable file), this program takes almost a minute to complete.

For my application this is completely unacceptable as I need to have the 1ms timing delay in order to interact with hardware I am using.

I also tried a suggestion from another post to use the select() command (via winsock2), but that command did not work to delay 1ms either. I have tried this program on multiple Windows 7 and Windows 10 PC's and the root cause of the issue always points to using Windows 10 instead of Windows 7. The program always runs within ~5 seconds on numerous Windows 7 PC's, and on the multiple Windows 10 PC's that I have tested the duration has been much longer ~60 seconds.

I have been using Microsoft Visual Studio Express 2010 (C/C++) as well as Microsoft Visual Studio Express 2017 (C/C++) to compile the programs. The version of visual studio does not influence the results.

I have also changed the compile options from 'Debug' to 'Release' and tried to optimize the compiler but this will not help either.

Any suggestions would be greatly appreciated.

#include <stdio.h>
#include <Windows.h>

#define LOOP_COUNT      5000

int main()
{
    int i = 0;

    for (i; i < LOOP_COUNT; i++){
        Sleep(1);
    }

    return 0;
}

Answer 1

I need to have the 1ms timing delay in order to interact with hardware I am using

Windows is the wrong tool for this job.

If you insist on using this wrong tool, you are going to have to make compromises (such as using a busy-wait and accepting the corresponding poor battery life).

You can make Sleep() more accurate using timeBeginPeriod(1) but depending on your hardware peripheral's limits on the "one millisecond" delay -- is that a minimum, maximum, or the middle of some range? -- it still will fail to meet your timing requirement with some non-zero probability.

The timeBeginPeriod function requests a minimum resolution for periodic timers.

The right solution for talking to hardware with tight timing tolerances is an embedded microcontroller which talks to the Windows PC through some very flexible interface such as UART or Ethernet, buffers data, and uses hardware timers to generate signals with very well-defined timing.

In some cases, you might be able to use embedded circuitry already existing within your Windows PC, such as "sound card" functionality.

Answer 2

@BenVoigt & @mzimmers thank you for your responses and suggestions. I did find a unique solution to this question and the solution was inspired by the post I have linked directly below.

Units of QueryPerformanceFrequency

In this post BrianP007 writes a function to see how fast the Sleep(1000) command takes. However, while I was playing around I realized that Sleep() accepts 0. Therefore I used a similar structure to the linked post to find the time that it takes to loop until reaching a delta t of 1ms.

For my purposes I increased i by 100, however it can be increased by 10 or by 1 in order to get a more accurate estimate as to what i should be.

Once you get a value for i, you can use that value to get an approximate delay for 1ms on your machine. If you run this function in a loop (I ran it 100 times) I was able to get anywhere from i = 3000 to i = 6000. However, my machine averages out around 5500. This spread is probably due to jitter/clock frequency changes through time in the processor.

The processor_check() function below only finds out what value should be returned for the for loop argument; the actual 'timer' needs to just have the for loop with Sleep(0) inside of it to run a timer with ~1ms resolution on the machine.

While this method is not perfect, it is much closer and works a ton better than using Sleep(1). I have to test this more thoroughly, but please let me know if this works for you as well. Please feel free to use the code below if you need it for your own applications. This code should be able to be copy and pasted into an empty command prompt C program in Visual Studio directly without modification.

/*ZKR Sleep_ZR()*/

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

/*Gets for loop value*/
int processor_check()
{
    double delta_time = 0;
    int i = 0;
    int n = 0;

    while(delta_time < 0.001){
        LARGE_INTEGER sklick, eklick, cpu_khz;

        QueryPerformanceFrequency(&cpu_khz);
        QueryPerformanceCounter(&sklick);
        for(n = 0; n < i; n++){
            Sleep(0);
        }
        QueryPerformanceCounter(&eklick);
        delta_time = (eklick.QuadPart-sklick.QuadPart) / (double)cpu_khz.QuadPart;

        i = i + 100;
    }
    return i;
}

/*Timer*/    
void Sleep_ZR(int cnt)
{
    int i = 0;
    for(i; i < cnt; i++){
        Sleep(0);
    }
}


/*Main*/
int main(int argc, char** argv)
{
    double average = 0;
    int i = 0;
    
    /*Single use*/
    int loop_count = processor_check();
    Sleep_ZR(loop_count);
    
    /*Average based on processor to get more accurate Sleep_ZR*/
    for(i = 0; i < 100; i++){
        loop_count = processor_check();
        average = average + loop_count;
    }
    average = average / 100;
    printf("Average: %f\n", average);

    /*10 second test*/
    for (i = 0; i < 10000; i++){
        Sleep_ZR((int)average);
    }

    return 0;
}