[Qt-interest] QtConcurrent::run results in random crashes

[Anders Bakken]

On Wed, Jul 28, 2010 at 05:44:07AM +0100, Mandeep Sandhu wrote:
> > Thanks for that, I really didn't know that using QPixmap outside the
> > Main/GUI thread is a problem. I will do the scaling of my thumbnails
>
> I had a similar problem (of app crashing when trying to create a
> QPixmap in a console app).
>
> You will  need an instance of "QApplication" for using QPixmaps since
> it initializes the underlying OS's graphics subsystem, which will be
> there in your main GUI thread. Once that is done, I "think" it should
> be safe to use QPixmaps in another thread as well.

This is from qpixmap.cpp:

static bool qt_pixmap_thread_test()
{
    if (!qApp) {
        qFatal("QPixmap: Must construct a QApplication before a QPaintDevice");
        return false;
    }
#ifndef Q_WS_WIN
    if (qApp->thread() != QThread::currentThread()) {
        qWarning("QPixmap: It is not safe to use pixmaps outside the GUI thread");
        return false;
    }
#endif
    return true;
}

>
> If you're NOT going to do any pixel manipulation of your images and
> instead only want to paint them (after scaling) then I guess it's
> better to use QPixmaps than QImage.
>
> HTH,
> -mandeep

regards

--
Anders Bakken

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