[Interest] QImage, multithreaded app.

[Thiago Macieira]

On sexta-feira, 27 de setembro de 2013 23:13:44, Alexander Syvak wrote:
>  This is the code of the function saving screenshots. This code is used in
> threads analizing screenshots.
> Debugging the app. when one thread has been paused inside QImage save
> method and other thread wake up invoking the lines below

On the *same* QImage?

Like I said, I need to know what each thread is doing. Saving a QImage from 
any thread should be acceptable, provided no other thread is using the same 
QImage.

> 
> QFile screenshot_iodev(mk_screenshot_path(screenshot_idx++));
> 
> return screenshot.save( &screenshot_iodev, format_raw_ptr );
> 
> where QImage::save returns false failing here
> 
> bool QImageWriter::canWrite() const
> 
> {
> 
>     if (d->device && !d->handler && (d->handler =
> createWriteHandlerHelper(d->device, d->format)) == 0) {
> 
>         d->imageWriterError = QImageWriter::UnsupportedFormatError;
> 
>         d->errorString = QT_TRANSLATE_NOOP(QImageWriter,
> 
>                                            QLatin1String("Unsupported
> image format"));
> 
>         return false;
> 
>     }
> 
> 
> 
> 
> 
> 
> 2013/9/27 Thiago Macieira <thiago.macieira at intel.com>
> 
> > On sexta-feira, 27 de setembro de 2013 16:12:37, Alexander Syvak wrote:
> > > Hello,
> > > 
> > > the method save_screenshot() is used to save a QImage object using
> > > bool QImage::save ( const
> > > QString<http://doc.crossplatform.ru/qt/4.6.x/qstring.html>&
> > > *fileName*, const char * *format* = 0, int *quality* = -1 ) const
> > > 
> > > Howver, it appears that QImage is working with one I/O device and
> > > returns
> > > false if it's busy, i.e. a thread paused at a moment of executing the
> > 
> > save
> > 
> > > method.
> > 
> > Any thread? What is this other thread doing? Also, threads don't pause
> > except
> > if you're using the debugger.
> > 
> > It's far more likely that your mistake can be found in what this other
> > thread
> > is doing.
> > 
> > > Is it better to use
> > > bool QImage::save (
> > > QIODevice<http://doc.crossplatform.ru/qt/4.6.x/qiodevice.html>*
> > > *device*, const char * *format* = 0, int *quality* = -1 ) const
> > > 
> > > method instead with its own I/O device for each thread or
> > > 
> > > to create QMutexLocker in the save_screenshot() method?
> > 
> > --
> > Thiago Macieira - thiago.macieira (AT) intel.com
> > 
> >   Software Architect - Intel Open Source Technology Center
> > 
> > _______________________________________________
> > Interest mailing list
> > Interest at qt-project.org
> > http://lists.qt-project.org/mailman/listinfo/interest

-- 
Thiago Macieira - thiago.macieira (AT) intel.com
  Software Architect - Intel Open Source Technology Center
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