How to deal with Leaks Pixmap in Qt?

leonardoMB

Here is the heob top part of the stack:

1: malloc in 
  2: QArrayData::allocate(unsigned long long, unsigned long long, unsigned long long, QFlags<QArrayData::AllocationOption>) in C:/Qt/Qt5.15.2/5.15.2/mingw81_64/bin/Qt5Core.dll
  3: QString::QString(int, Qt::Initialization) in C:/Qt/Qt5.15.2/5.15.2/mingw81_64/bin/Qt5Core.dll
  4: QPixmap::load(QString const&, char const*, QFlags<Qt::ImageConversionFlag>) in C:/Qt/Qt5.15.2/5.15.2/mingw81_64/bin/Qt5Gui.dll
  5: C:/mylibrary.dll

I basically pass a QPixmap("image.png") to some classes and functions, all by reference, and I use a QIcon::setPixmap in the end. I don't see any reason to existence of leakage here, any Idea?

Christian Ehrlicher

The 'leak' in QPixmapCache is a false positive - it's a cache and (mYBE9 not cleared on exit so the leak checker will complain but it's not a memleak in the classic way. Add it to the ignore list of your leak checker.
The leak in your first post is imo also a false positive. You can check it when you allocate and deallocate a pixmap several thousand times in a loop.

JonB

@leonardoMB
The "leak" code you show has nothing to do with QPixmap, it's just to do with the QString handling of "image.png".

I doubt there is any leakage going on, but I don't know enough about what heob reports to argue.

leonardoMB

@JonB
And in things like this?:

1: malloc in 
  2: operator new(unsigned long long) in C:/Qt/Qt5.15.2/5.15.2/mingw81_64/bin/libstdc++-6.dll
  3: QPixmapCache::Key::operator=(QPixmapCache::Key const&) in C:/Qt/Qt5.15.2/5.15.2/mingw81_64/bin/Qt5Gui.dll
  4: QPixmapCache::remove(QString const&) in C:/Qt/Qt5.15.2/5.15.2/mingw81_64/bin/Qt5Gui.dll
  5: QPixmap::load(QString const&, char const*, QFlags<Qt::ImageConversionFlag>) in C:/Qt/Qt5.15.2/5.15.2/mingw81_64/bin/Qt5Gui.dll

JonB

@leonardoMB
Not sure that's on a QString! :)
It seems so fundamental I would have thought any leaks like this would have been spotted.
But I leave other experts to comment further.

Christian Ehrlicher

The 'leak' in QPixmapCache is a false positive - it's a cache and (mYBE9 not cleared on exit so the leak checker will complain but it's not a memleak in the classic way. Add it to the ignore list of your leak checker.
The leak in your first post is imo also a false positive. You can check it when you allocate and deallocate a pixmap several thousand times in a loop.

leonardoMB

@Christian-Ehrlicher Thanks for the answer, This is the first time I use a memory profile and i'm recent to Qt too. Would you recommend something to analyze if something is a false positive? I ask this because I got "leaks" in a lot of metacalls and I couldn't judge properly anything

Christian Ehrlicher

From my pov you can ignore everything your tool finds inside Qt - it's very unlikely.