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/* Copyright (c) 2017 Stanislaw Halik <sthalik@misaki.pl>
*
* Permission to use, copy, modify, and/or distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*/
#include "timer-resolution.hpp"
#if defined _WIN32
# include <windows.h>
# include <QLibrary>
# include <QDebug>
typedef LONG (__stdcall *funptr_NtSetTimerResolution) (ULONG, BOOLEAN, PULONG);
static funptr_NtSetTimerResolution init_timer_resolution_funptr();
static funptr_NtSetTimerResolution get_funptr();
static funptr_NtSetTimerResolution init_timer_resolution_funptr()
{
static QLibrary ntdll;
ntdll.setLoadHints(QLibrary::PreventUnloadHint);
ntdll.setFileName("ntdll.dll");
const bool load = ntdll.load();
if (!load)
{
qDebug() << "can't load ntdll:" << ntdll.errorString();
return nullptr;
}
auto ret = reinterpret_cast<funptr_NtSetTimerResolution>(ntdll.resolve("NtSetTimerResolution"));
if (ret == nullptr)
{
qDebug() << "can't find NtSetTimerResolution in ntdll:" << ntdll.errorString();
return nullptr;
}
return ret;
}
static funptr_NtSetTimerResolution get_funptr()
{
static auto ret = init_timer_resolution_funptr();
return ret;
}
timer_resolution::timer_resolution(int msecs) : old_value(-1)
{
if (msecs <= 0 || msecs > 30)
{
qDebug() << "can't set timer resolution to" << msecs << "ms";
return;
}
funptr_NtSetTimerResolution f = get_funptr();
if (f == nullptr)
return;
// hundredth of a nanosecond
const ULONG value = msecs * ULONG(10000);
NTSTATUS error = f(value, TRUE, &old_value);
ULONG old_value_ = -1;
if (error != 0)
{
old_value = -1;
qDebug() << "NtSetTimerResolution erred with" << error;
return;
}
// see if it stuck
error = f(value, TRUE, &old_value_);
if (error != 0)
{
old_value = -1;
qDebug() << "NtSetTimerResolution check erred with" << error;
return;
}
if (old_value_ != old_value)
{
qDebug() << "NtSetTimerResolution:"
<< "old value didn't stick"
<< "current resolution" << old_value_
<< "* 100 ns";
old_value = -1;
return;
}
}
timer_resolution::~timer_resolution()
{
if (old_value != ULONG(-1))
{
funptr_NtSetTimerResolution f = get_funptr();
ULONG fuzz = -1;
(void) f(old_value, TRUE, &fuzz);
}
}
#endif
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