Audio latency measuring sample for Windows

This code sample demonstrates how to measure minimum, maximum and average execution times of a routine or a portion of code with high resolution time stamps in Visual C++. The values obtained are calculated in microseconds.

// Code to measure minimum, maximum and average execution times of a routine in microseconds
// NOTE: build a RELEASE version of this code to get useful results

// The data that we are interested in:
float minExecutionTime,maxExecutionTime,averageExecutionTime;


// Other vars
float currentExecutionTime,totalExecutionTime,freqFactor;
ULONG executionCount;
BOOL doMeasure;


void Initialization(void) ;
void UpdateStats(LONGLONG elapsed);



// Run this code only once at initialization
void Initialization(void)
{
    LARGE_INTEGER perfFrequency;

    currentExecutionTime=0;
    executionCount=0;
    minExecutionTime=0;
    maxExecutionTime=0;
    averageExecutionTime=0;
    totalExecutionTime=0;
    doMeasure=FALSE;

    // Get performance frequency in counts per second
    if (QueryPerformanceFrequency(&perfFrequency)!=TRUE)
    {
        // Something went wrong, measuring will not work
        freqFactor=0;
    }
    else
    {
        // The freqFactor is the amount of microseconds of a single performance count
        freqFactor=(float)1000000/perfFrequency.QuadPart;

        doMeasure=TRUE;
    }
}



void UpdateStats(LONGLONG elapsed)
{
    // Calculated elapsed execution time in microseconds
    currentExecutionTime=elapsed*freqFactor;

    // Update minimum execution time
    if (currentExecutionTime < minExecutionTime || minExecutionTime==0)
        minExecutionTime=currentExecutionTime;

    // Update maximum execution time
    if (currentExecutionTime > maxExecutionTime)
        maxExecutionTime=currentExecutionTime;

    // increase number of successful measurings
    executionCount++;

    // Update total and average
    totalExecutionTime+=currentExecutionTime;
    averageExecutionTime=totalExecutionTime/executionCount;

}




// Your code to be measured, this could be your audio process function
// Make sure that Initialization() has been called once before
void MyCodeToBeMeasured(void)
{
    LARGE_INTEGER start={0,0},end={0,0};


    if (doMeasure==TRUE)
    {
        // Set this code to run only at first CPU
        // If we are running on another CPU then we get rescheduled immediately
        SetThreadAffinityMask (GetCurrentThread(),1);

        // Get the performance time stamp at the beginning of your code
        QueryPerformanceCounter(&start);
    }


    // ...
    // now run the code you wish to be measured
    // ...

    // Get the performance time stamp at the end of your code
    // and update our data
    if (doMeasure==TRUE)
    {
        QueryPerformanceCounter(&end);

        if (start.QuadPart > 0 && end.QuadPart > 0)
        {
            UpdateStats(end.QuadPart-start.QuadPart);
        }

        // minExecutionTime, maxExecutionTime and averageExecutionTime are now filled
        // with useful data representing execution times in microseconds

    }

}