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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 <QLibrary>
# include <QDebug>
using namespace timer_impl;
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()
{
// starting with C++11 static initializers are fully
// thread-safe and run the first time function is called
// cf. http://stackoverflow.com/questions/8102125/is-local-static-variable-initialization-thread-safe-in-c11
static auto ret = init_timer_resolution_funptr();
return ret;
}
timer_resolution::timer_resolution(int msecs) : old_value(fail_())
{
if (msecs <= 0 || msecs > 100)
{
qDebug() << "can't set timer resolution to" << msecs << "ms";
return;
}
funptr_NtSetTimerResolution set_timer_res = get_funptr();
if (set_timer_res == nullptr)
return;
// hundredth of a nanosecond
const ulong_ value = msecs * ulong_(10000);
ntstatus_ res;
res = set_timer_res(value, true_(), &old_value);
if (res < 0)
{
old_value = fail_();
qDebug() << "NtSetTimerResolution erred with" << res;
return;
}
// see if it stuck
ulong_ old_value_ = fail_();
res = set_timer_res(value, true_(), &old_value_);
if (res < 0)
{
old_value = fail_();
qDebug() << "NtSetTimerResolution check erred with" << res;
return;
}
if (old_value_ != old_value)
{
using t = long long;
qDebug() << "NtSetTimerResolution:"
<< "old value didn't stick"
<< "current resolution" << (t(old_value_) * t(100))
<< "ns";
old_value = fail_();
return;
}
}
timer_resolution::~timer_resolution()
{
if (old_value != fail_())
{
funptr_NtSetTimerResolution f = get_funptr();
ulong_ fuzz = fail_();
(void) f(old_value, true_(), &fuzz);
}
}
#endif
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