Loading image concurrently

[Jonathan Levanon]

Hi,

I'm trying to load images from a directory. The amount of images can be a couple thousands, so I thought about doing it concurrently and save some IO blocking time. The trick it that I need to wait until all of the images are loaded. The code I've written gets into a deadlock sometime, and almost always when debugging, and I don't really understand why.

Here's what I have -

     for (int i=0; i <filesToDisp.size(); ++i) {
        QString extenstion = filesToDisp[i].split('.').last();
        if (isImage(extenstion)) {
            QString name = filesToDisp[i];
            if (name.contains("/")) {
                name = path + "/" + name.split("/")[1];
            } else {
                name = path + "/" + filesToDisp[i];
            }
            QFuture<QPair<QImage, QString>> f =
                    QtConcurrent::run(this, &imageManager::getImageByName, name, filesToDisp[i]);
            fs.append(f);
        }
    }

    // Waiting for all run to finish
    bool flag = true;
    while (flag) {
        flag = false;
        for (auto& f : fs) {
            if (!f.isFinished()) {
                flag = true;
            } else {
                QPair<QImage, QString> p = f.result();
                _imageQueue.enqueue(new IEimage(new QImage(p.first), p.second, getFreeId()));
                fs.removeOne(f);
            }
        }
    }

getImageByName returns a pair of image and string.

Any ideas?

[Christian Ehrlicher]

@Jonathan-Levanon said in Loading image concurrently:

fs.removeOne(f);

You're modifying the container while looping over it. Better use iterators + erase(iterator) and simply check if the container is empty as abort condition instead the flag stuff.

[Jonathan Levanon]

Such a rookie mistake :) Thanks, it works!

[fcarney]

@Jonathan-Levanon said in Loading image concurrently:

Such a rookie mistake :) Thanks, it works!

But you found it NOW and not have it create errors that are hard to detect later. It would have been much worse if you somehow "made it work".