I recently decided that I needed to change from using milliseconds to microseconds for my Timer class, and after some research I've decided that QueryPerformanceCounter is probably my safest bet. (The warning on Boost::Posix
that it may not works on Win32 API put me off a bit). However, I'm not really sure how to implement it.
What I'm doing is calling whatever GetTicks()
esque function I'm using and assigning it to Timer's startingTicks
variable. Then to find the amount of time passed I just subtract the function's return value from the startingTicks
, and when I reset the timer I just call the function again and assign startingTicks to it. Unfortunately, from the code I've seen it isn't as simple as just calling QueryPerformanceCounter()
, and I'm not sure what I'm supposed to pass as its argument.
I would extend this question with a NDIS driver example on getting time. As one knows, KeQuerySystemTime (mimicked under NdisGetCurrentSystemTime) has a low resolution above milliseconds, and there are some processes like network packets or other IRPs which may need a better timestamp;
The example is just as simple:
LONG_INTEGER data, frequency;
LONGLONG diff;
data = KeQueryPerformanceCounter((LARGE_INTEGER *)&frequency)
diff = data.QuadPart / (Frequency.QuadPart/$divisor)
where divisor is 10^3, or 10^6 depending on required resolution.
I use these defines:
/** Use to init the clock */
#define TIMER_INIT \
LARGE_INTEGER frequency; \
LARGE_INTEGER t1,t2; \
double elapsedTime; \
QueryPerformanceFrequency(&frequency);
/** Use to start the performance timer */
#define TIMER_START QueryPerformanceCounter(&t1);
/** Use to stop the performance timer and output the result to the standard stream. Less verbose than \c TIMER_STOP_VERBOSE */
#define TIMER_STOP \
QueryPerformanceCounter(&t2); \
elapsedTime=(float)(t2.QuadPart-t1.QuadPart)/frequency.QuadPart; \
std::wcout<<elapsedTime<<L" sec"<<endl;
Usage (brackets to prevent redefines):
TIMER_INIT
{
TIMER_START
Sleep(1000);
TIMER_STOP
}
{
TIMER_START
Sleep(1234);
TIMER_STOP
}
Output from usage example:
1.00003 sec
1.23407 sec
Assuming you're on Windows (if so you should tag your question as such!), on this MSDN page you can find the source for a simple, useful HRTimer
C++ class that wraps the needed system calls to do something very close to what you require (it would be easy to add a GetTicks()
method to it, in particular, to do exactly what you require).
On non-Windows platforms, there's no QueryPerformanceCounter function, so the solution won't be directly portable. However, if you do wrap it in a class such as the above-mentioned HRTimer
, it will be easier to change the class's implementation to use what the current platform is indeed able to offer (maybe via Boost or whatever!).
Source: Stackoverflow.com