is it possible to use QtConcurrent::mapped inside a QThread ?

RahibeMeryem

Hi,

I want to process my my opencv captured frames in 4 threads.

one producer (opencv capture ) is very fast

four worker (detection cpu based) slower than producer (4 times almost)

I created producer thread and moved a thread.

1 - Can I create a QtConcurred::mapped in this producer Thread ?

what is the best practices for this multithreaded video processing in Qt ?

SGaist

Hi,

AFAIK, yes you can.

You have to benchmark the processings you need before designing a pipeline for your video application.

RahibeMeryem

@SGaist

I have below error:

struct frames_facePhotos
    {
        cv::Mat frames;
        cv::Mat face_photo;
    };
QVector<frames_facePhotos> framesVector;

           frames_facePhotos process_request;

            process_request.face_photo = face_photo;
            process_request.frames = image;
            framesVector.push_back (process_request);
            cap>>image;
            process_request.frames = image;
            framesVector.push_back (process_request);

            auto res  = QtConcurrent::mapped(framesVector , &detecFaceModifyFrames );

void FaceDetector::detecFaceModifyFrames(frames_facePhotos frames_faces)
{
    int frame_count = 111;


        QString find_face = bc_face->findFace(frames_faces.frames, frames_faces.face_photo,frame_count);



//    return frames_faces;

}

Error
../BC_DETECTOR/face_detector.cpp:165:60: error: must explicitly qualify name of member function when taking its address
auto res = QtConcurrent::mapped(framesVector , &detecFaceModifyFrames );
^~~~~~~~~~~~~~~~~~~~~~
FaceDetector::

2nd Error
/Users/xx/Qt5.12.1/5.12.1/clang_64/lib/QtConcurrent.framework/Headers/qtconcurrentmapkernel.h:175:19: error: no matching function for call to object of type 'QtConcurrent::MemberFunctionWrapper1<void, FaceDetector, FaceDetector::frames_facePhotos>'
*result = map(*it);
^~~

when I change to :

            auto res  = QtConcurrent::mapped(framesVector , &FaceDetector::detecFaceModifyFrames );

first error gone but second is there.

jsulm

@RahibeMeryem Try to use lambda instead of detecFaceModifyFrames. detecFaceModifyFrames is a non static method and cannot be used without class instance.

RahibeMeryem

@jsulm

when I think that I started to capture C++ something like this happening. as a being decent java girl its make me crazy :)

how can I write its as a lamba ?

jsulm

@RahibeMeryem

auto res  = QtConcurrent::mapped(framesVector , [this](frames_facePhotos frames_faces) {
        detecFaceModifyFrames(frame_faces);
    });