Download large with QNetworkreply :: readAll freezes for a few seconds

When using QNetworkreply::readAll to write data to a QFile , at the time the download arrives at the end, there is a fast freeze of 2 to 4 seconds and it also varies depending on the network or site I am downloading, to normal and the download ends.

It seems that the buffer read increases more than normal at the end

Here is an example code:

int main(int argc, char** argv)
{
    QCoreApplication a(argc, argv);

    QFile file("C:/exemplo/bigfile.7z");

    if(!file.open(QIODevice::WriteOnly)) {
        return 1;
    }

    QNetworkAccessManager manager;

    QNetworkRequest request(QUrl("http://localhost/bigfile.7z"));

    QNetworkReply *reply = manager.get(request);

    QObject::connect(reply, &QNetworkReply::readyRead, [&](){
        QTime time;
        time.start();

        QByteArray ba = reply->readAll();
        file.write(ba);

        int duration= time.elapsed();

        qDebug() << "read" << ba.size() << " bytes of data. (" << duration << " msecs)";
    });

    QObject::connect(reply, &QNetworkReply::finished, [&](){
        qDebug() << "finished!";
        a.quit();
    });

    return a.exec();
}

This problem occurs when I try to download large files like 300mb for example, see the result:

Note that at the end of the download (practically 99%), reply->readAll and write , takes 1617msecs and then 2741msecs, or almost 4 seconds, see that readAll on the last two calls returned much more data .

This causes a small crash in GUI applications (which use QWidget ).