How to make thread sleep less than a millisecond on Windows

By : smink
Source: Stackoverflow.com
Question!

On Windows I have a problem I never encountered on Unix. That is how to get a thread to sleep for less than one millisecond. On Unix you typically have a number of choices (sleep, usleep and nanosleep) to fit your needs. On Windows, however, there is only Sleep with millisecond granularity.

On Unix, I can use the use the select system call to create a microsecond sleep which is pretty straightforward:

int usleep(long usec)
{
    struct timeval tv;
    tv.tv_sec = usec/1000000L;
    tv.tv_usec = usec%1000000L;
    return select(0, 0, 0, 0, &tv);
}

How can I achieve the same on Windows?

By : smink


Answers

Sleep function that is way less than a millisecond-maybe

I found that sleep(0) worked for me. On a system with a near 0% load on the cpu in task manager, I wrote a simple console program and the sleep(0) function slept for a consistent 1-3 microseconds, which is way less than a millisecond.

But from the above answers in this thread, I know that the amount sleep(0) sleeps can vary much more wildly than this on systems with a large cpu load.

But as I understand it, the sleep function should not be used as a timer. It should be used to make the program use the least percentage of the cpu as possible and execute as frequently as possible. For my purposes, such as moving a projectile across the screen in a videogame much faster than one pixel a millisecond, sleep(0) works, I think.

You would just make sure the sleep interval is way smaller than the largest amount of time it would sleep. You don't use the sleep as a timer but just to make the game use the minimum amount of cpu percentage possible. You would use a separate function that has nothing to do is sleep to get to know when a particular amount of time has passed and then move the projectile one pixel across the screen-at a time of say 1/10th of a millisecond or 100 microseconds.

The pseudo-code would go something like this.

while (timer1 < 100 microseconds) {
sleep(0);
}

if (timer2 >=100 microseconds) {
move projectile one pixel
}

//Rest of code in iteration here

I know the answer may not work for advanced issues or programs but may work for some or many programs.

By : rauprog


#include <Windows.h>

static NTSTATUS(__stdcall *NtDelayExecution)(BOOL Alertable, PLARGE_INTEGER DelayInterval) = (NTSTATUS(__stdcall*)(BOOL, PLARGE_INTEGER)) GetProcAddress(GetModuleHandle("ntdll.dll"), "NtDelayExecution");

static NTSTATUS(__stdcall *ZwSetTimerResolution)(IN ULONG RequestedResolution, IN BOOLEAN Set, OUT PULONG ActualResolution) = (NTSTATUS(__stdcall*)(ULONG, BOOLEAN, PULONG)) GetProcAddress(GetModuleHandle("ntdll.dll"), "ZwSetTimerResolution");




static void SleepShort(float milliseconds) {
    static bool once = true;
    if (once) {
        ULONG actualResolution;
        ZwSetTimerResolution(1, true, &actualResolution);
        once = false;
    }

    LARGE_INTEGER interval;
    interval.QuadPart = -1 * (int)(milliseconds * 10000.0f);
    NtDelayExecution(false, &interval);
}

yes it uses some undocumented kernel functions, but it works very well, I use SleepShort(0.5); in some of my threds



Try using SetWaitableTimer...

By : andrewrk


This video can help you solving your question :)
By: admin