[Digikam-devel] I'm back with questions - AutoCorrections tool memory usage and resource leaks

[Gilles Caulier]

Hi Mathias,

Yes, you have right. All recent changes in svn trunk come from me.


2010/3/4 Matthias Welwarsky <matze at welwarsky.de>:
> Hello all,
>
> I've not been able to do much work on Digikam for quite some time but I still use it regularely and follow the development. Recently I have
> noticed that the AutoCorrections tool seems to drive up memory consumption of digikam a lot and also seems to leak memory since I've
> been getting strange crashes of Digikam recently that came from failed memory allocations during DImg construction.
>
> I've looked into it and found two reasons. First is in the constructor of each of the correction filters:
>
> NormalizeFilter::NormalizeFilter(DImg* orgImage, DImg* refImage, QObject* parent)
>               : DImgThreadedFilter(orgImage, parent, "NormalizeFilter")
> {
>    m_refImage = refImage->copy();
>    initFilter();
> }
>
> Each filter does a deep copy of the reference image. For 12MP 16bit images this amounts to 100MB for each filter. The PreviewList has
> one filter instance for each effect, so that's 5 times the memory of the image. Yet the filters don't change the reference image at all, so
> detaching from the original data is not necessary. My current quick hack is to change DImg m_refImage to const DImg* m_pRefImage
> and correct all the const'ness down the chain but it violates the ImageIface paradigm to never store the DImg* acquired through
> ImageIface::getOriginalImage(). Since DImg copies are refcounted it should be possible by other means especially since all uses of the
> refImage are const.
>
> The first problem itself does not create a mem leak, it just largely exaggerates the memory usage.

The deep copy refimage is not necessary here of course. it can be removed.

> The second problem, which leads to
> the mem leak is the undefined lifetime of the effect filters, especially those in the PreviewList.
>
> The filter instances are never explicitely destroyed. They are either tied to the lifetime of the AutoCorrectionTool instance or the lifetime of
> the PreviewList. But the PreviewList is created and tied to the _parent_ object of the AutoCorrectionTool, which is unfortunately the
> ImagePlugin_Core instance, which has near infinite lifetime. I think you get the picture ;)
>

What the real solution here ? To pass a widget object as parent
instead image_plugin core instance ?

> I hope I didn't annoy you with this long storytelling, but it teaches to be careful with the lifetime of objects, especially since memory
> leaks like this don't show up in valgrind, due to the parent/child relationship the parent QObject will always hold a pointer to all its
> children and valgrind will not notice the leak.
>
> So, the patch for the PreviewList is trivial, but I would like your advice for fixing the image copying in the >effect filters.

Well, i'm waiting your patch...

Gilles