Measure CPU time on Windows using GetProcessTimes

Question

I would like to measure CPU time of some function. I know how to use GetProcessTimes, but I have a problem implementing it with some kind of 'restarting':

Normally, I would do it like this:

#include "stdafx.h"
#include <math.h>
#include <windows.h>

double cputimer()
{
    FILETIME createTime;
    FILETIME exitTime;
    FILETIME kernelTime;
    FILETIME userTime;

    if ( GetProcessTimes( GetCurrentProcess( ),
        &createTime, &exitTime, &kernelTime, &userTime ) != -1 )
    {
        SYSTEMTIME userSystemTime;
        if ( FileTimeToSystemTime( &userTime, &userSystemTime ) != -1 )
            return (double)userSystemTime.wHour * 3600.0 +
            (double)userSystemTime.wMinute * 60.0 +
            (double)userSystemTime.wSecond +
            (double)userSystemTime.wMilliseconds / 1000.0;
    }
}

int _tmain(int argc, _TCHAR* argv[])
{
    double start, stop;
    long sum = 0L;

    start = cputimer();
    for (long long i = 1; i < 10000000; i++){
        sum += log((double)i);
    }
    stop = cputimer();

    printf("Time taken: %f [seconds]\n", stop - start);

    return 0;
}

But with 'reset' I'm not sure if I have right results:

#include "stdafx.h"
#include <math.h>
#include <windows.h>

#define START    1
#define STOP    0

double cputimer(int reset)
{
    FILETIME createTime;
    FILETIME exitTime;
    FILETIME kernelTime;
    FILETIME userTime;

    double now = 0, then = 0;

    if ( GetProcessTimes( GetCurrentProcess( ),
        &createTime, &exitTime, &kernelTime, &userTime ) != -1 )
    {
        SYSTEMTIME userSystemTime;
        if ( FileTimeToSystemTime( &userTime, &userSystemTime ) != -1 )
            now = (double)userSystemTime.wHour * 3600.0 +
            (double)userSystemTime.wMinute * 60.0 +
            (double)userSystemTime.wSecond +
            (double)userSystemTime.wMilliseconds / 1000.0;
    }

    if(reset)
    {
        then = now;
    }
    else
    {
        then = now - then;
    }

    return then;
}

int _tmain(int argc, _TCHAR* argv[])
{
    double s;
    long sum = 0L;

    cputimer(START);
    for (long long i = 1; i < 10000000; i++){
        sum += log((double)i);
    }
    s = cputimer(STOP);


    printf("Time taken: %f [seconds]\n", s);

    return 0;
}

Am I doing it correctly?

Answer 1

I suggest you go with a simpler solution on Windows like this if your process does not run for too long:

#define WIN32_LEAN_AND_MEAN
#include <windows.h>

double getTime() {
  LARGE_INTEGER freq, val;
  QueryPerformanceFrequency(&freq);
  QueryPerformanceCounter(&val);
  return (double)val.QuadPart / (double)freq.QuadPart;
}

Then you could just use it like this:

double d0 = getTime();
// function to measure
double timeInMilliseconds = 1000* (getTime() - d0);

You could wrap this into a function to achieve similar behavior as your code.

double cputimer(int reset)
{
  static double startTime = 0;
  if(reset)
  {
    startTime = getTime();
    return 0.0;
  } else
  {
    return 1000* (getTime() - startTime);
  }
}

UPDATE: If the real intention was to query for the usertime one should replace the getTime() function (with the one used by the OP) but the logic in cputimer() remains the same.

Answer 2

The failure return value for both functions is 0, not -1.