Threading a function in Qt

Question

I have a for-loop that will run a fixed number of times, usually in the 100-300 range depending on the input. Every iteration of this loop calls a function that I want to be threaded. The function to thread grabs data from an input file, does some stuff with it, then writes it out in a new format to an output file...

Here is some high-level code:

void myClass::processFile()
{
    ...

    for (int index = 0; index < 200; index++)
    {
        //Function or loop to thread
        generateData(someMapOfMaps1[index], someMapOfMaps2[index]);
    }
}

Then inside generateData within the same class:

void myClass::generateData(QMap<float, foo*> mapA, QMap<float, foo*> mapB)
{
    //read in data from a file
    //process data
    //write data to a different file
}

I played around with QtConcurrent::run() and QtConcurrent::mapped() but didn't have much luck. I believe mapped() would have been a great choice, but my function takes 2 maps instead of just one.

I was using this as a resource, around slide 25: http://www.develer.com/promo/workshop/enhancing_with_multi_threading.pdf

Thanks!

Answer 1

• read this http://developer.qt.nokia.com/doc/qt-4.8/qwaitcondition.html
• inherit your class from QThread
• put in run() call of your function in endless loop
• stop loop by QWaitCondition before call generateData
• wake up condition in your for cycle

Answer 2

Put the loop, files read/write, 'some stuff', the lot in the thread. Trying to thread off one function call per loop is, well, just too much avoidable inter-thread comms. Pack the filespecs etc. into a myClass object, signal it to the thread and just let it go...