usleep() for Windows (C/C++) + set timer resolution to lowest possible supported by system

test_usleep.cpp

#define WIN32_LEAN_AND_MEAN
#include <Windows.h>
#include <stdio.h>
#include "usleep.h"

int main()
{
	// not actually needed when calling usleep
	setHighestTimerResolution(1);

	LARGE_INTEGER qpc_begin, qpc_end, qpc_freq;

	QueryPerformanceCounter(&qpc_begin);
	QueryPerformanceFrequency(&qpc_freq);

	// usleep(1) sleeps at lowest possible amount of time
	int times = 1000;
	for (int i=0; i<times; i++)
		usleep(1);

	QueryPerformanceCounter(&qpc_end);
	
	double delay = (qpc_end.QuadPart - qpc_begin.QuadPart) / (double)qpc_freq.QuadPart;
	delay *= 1000.0 / times;

	printf_s("Average sleep time of usleep(1): %lfms\n", delay);

	return 0;
}

usleep.cpp

#define WIN32_LEAN_AND_MEAN
#include <Windows.h>
#include <limits.h>
#include <winnt.h>
#include "usleep.h"

unsigned long currentResolution = 0;

unsigned long setHighestTimerResolution(unsigned long timer_res_us)
{
	unsigned long timer_current_res = ULONG_MAX;
	const HINSTANCE ntdll = LoadLibrary("NTDLL.dll");
	if (ntdll != NULL)
	{
		typedef long(NTAPI* pNtSetTimerResolution)(unsigned long RequestedResolution, BOOLEAN Set, unsigned long* ActualResolution);

		pNtSetTimerResolution NtSetTimerResolution = (pNtSetTimerResolution) GetProcAddress(ntdll, "NtSetTimerResolution");
		if (NtSetTimerResolution != NULL)
		{
			// bounds are validated and set to the highest allowed resolution
			NtSetTimerResolution(timer_res_us, TRUE, &timer_current_res);
		}
		// we can decrement the internal reference count by one
		// and NTDLL.DLL still remains loaded in the process
		FreeLibrary(ntdll);
	}

	return timer_current_res;
}

void usleep(__int64 usec)
{
	HANDLE timer;
	LARGE_INTEGER period;

	if (currentResolution == 0)
		currentResolution = setHighestTimerResolution(1);

	// negative values are for relative time
	period.QuadPart = -(10*usec);

	timer = CreateWaitableTimer(NULL, TRUE, NULL);
	SetWaitableTimer(timer, &period, 0, NULL, NULL, 0);
	WaitForSingleObject(timer, INFINITE);
	CloseHandle(timer);
}

usleep.h

#pragma once

// Sets resolution of timers used by Sleep() and SetWaitableTimer() to most accurate and lowest values possible supported by system.
// Same as timeBeginPeriod() but accepts microsecond precision for requested resolution.
unsigned long setHighestTimerResolution(unsigned long timer_res_us);

// Suspends the current thread in sleep for time period, in microseconds.
void usleep(__int64 usec);