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!

Dmitriy Kachko · Accepted Answer · 2012-06-06T18:52:55.973

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

edited Jun 06 '12 at 18:52

answered Feb 14 '12 at 22:02

Dmitriy Kachko

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score 0 · Answer 2 · answered Feb 14 '12 at 22:03

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...

Threading a function in Qt

2 Answers2