QThread trying to limit threads

[spawn9997]

I have a function in my code that takes a list of points () from a QMap with key 'linekey'. Linekey is a QString describing which 'Line' I want to get from the map. My code is as follows:

foreach (const QString linekey, linekeys) {
 
            if (groupValues.contains(linekey))
                continue;
            QList<ReceiverGraphicsItem *> receiverlist =  lineGroup.values(linekey);
            if (lod <= .03) {
                points2[0] = mapToPix(receiverlist.at(0)->pos());
                points2[1] = mapToPix(receiverlist.at(receiverlist.size()/4)->pos());
                points2[2] =  mapToPix(receiverlist.at((receiverlist.size()*2)/4)->pos());
                points2[3] =  mapToPix(receiverlist.at((receiverlist.size()*3)/4)->pos());
                points2[4] =  mapToPix(receiverlist.at((receiverlist.size()-1))->pos());
                ptrr.drawPolyline(points2,small);
            } else {
                points[0] = mapToPix(receiverlist.at(0)->pos());
                points[1] = mapToPix(receiverlist.at(receiverlist.size()/14)->pos());
                points[2] =  mapToPix(receiverlist.at((receiverlist.size()*2)/14)->pos());
                points[3] =  mapToPix(receiverlist.at((receiverlist.size()*3)/14)->pos());
                points[4] =  mapToPix(receiverlist.at((receiverlist.size()*4)/14)->pos());
                points[5] =  mapToPix(receiverlist.at((receiverlist.size()*5)/14)->pos());
                points[6] =  mapToPix(receiverlist.at((receiverlist.size()*6)/14)->pos());
                points[7] =  mapToPix(receiverlist.at((receiverlist.size()*7)/14)->pos());
                points[8] =  mapToPix(receiverlist.at((receiverlist.size()*8)/14)->pos());
                points[9] =  mapToPix(receiverlist.at((receiverlist.size()*9)/14)->pos());
                points[10] =  mapToPix(receiverlist.at((receiverlist.size()*10)/14)->pos());
                points[11] =  mapToPix(receiverlist.at((receiverlist.size()*11)/14)->pos());
                points[12] =  mapToPix(receiverlist.at((receiverlist.size()*12)/14)->pos());
                points[13] =  mapToPix(receiverlist.at((receiverlist.size()*13)/14)->pos());
                points[14] =  mapToPix(receiverlist.at((receiverlist.size()-1))->pos());
                ptrr.drawPolyline(points,big);
            }
        }

foreach (const QString linekey, linekeys) {

            if (groupValues.contains(linekey))
                continue;
            QList<ReceiverGraphicsItem *> receiverlist =  lineGroup.values(linekey);
            if (lod <= .03) {
                points2[0] = mapToPix(receiverlist.at(0)->pos());
                points2[1] = mapToPix(receiverlist.at(receiverlist.size()/4)->pos());
                points2[2] =  mapToPix(receiverlist.at((receiverlist.size()*2)/4)->pos());
                points2[3] =  mapToPix(receiverlist.at((receiverlist.size()*3)/4)->pos());
                points2[4] =  mapToPix(receiverlist.at((receiverlist.size()-1))->pos());
                ptrr.drawPolyline(points2,small);
            } else {
                points[0] = mapToPix(receiverlist.at(0)->pos());
                points[1] = mapToPix(receiverlist.at(receiverlist.size()/14)->pos());
                points[2] =  mapToPix(receiverlist.at((receiverlist.size()*2)/14)->pos());
                points[3] =  mapToPix(receiverlist.at((receiverlist.size()*3)/14)->pos());
                points[4] =  mapToPix(receiverlist.at((receiverlist.size()*4)/14)->pos());
                points[5] =  mapToPix(receiverlist.at((receiverlist.size()*5)/14)->pos());
                points[6] =  mapToPix(receiverlist.at((receiverlist.size()*6)/14)->pos());
                points[7] =  mapToPix(receiverlist.at((receiverlist.size()*7)/14)->pos());
                points[8] =  mapToPix(receiverlist.at((receiverlist.size()*8)/14)->pos());
                points[9] =  mapToPix(receiverlist.at((receiverlist.size()*9)/14)->pos());
                points[10] =  mapToPix(receiverlist.at((receiverlist.size()*10)/14)->pos());
                points[11] =  mapToPix(receiverlist.at((receiverlist.size()*11)/14)->pos());
                points[12] =  mapToPix(receiverlist.at((receiverlist.size()*12)/14)->pos());
                points[13] =  mapToPix(receiverlist.at((receiverlist.size()*13)/14)->pos());
                points[14] =  mapToPix(receiverlist.at((receiverlist.size()-1))->pos());
                ptrr.drawPolyline(points,big);
            }
        }

To copy to clipboard, switch view to plain text mode 

The ptrr is a QPainter that is connected to a QPixmap (QImage in threaded version!).

This works fine but is slow with hundreds of lines to draw; thus the idea is to use Threads. if I use the loop method directly as it was but in a thread class then I get hundreds of threads; My question is, how do I make it so that only x number of threads run at one time? I have heard of a queue but have not seen one example of it. Maybe there is a better way to split up this job to use threading?


thank you,

JW
sw developer

"Some days you just can't get rid of a bomb." Batman movie - 1966

[wysota]

Read about QtConcurrent.

[spawn9997]

Thanks, but after reading about QtConcurrent and other articles you have posted on threading. I decided another approach would be better serving. I now have 2 threads for the two items of concern and they do all of the work in the background after I put up a temp pixmap.


JW
sw developer