QML Loader leaks memory

[sierdzio]

This is all rather scary. Happens for me, too - due to big JPGs/PNGs loaded, it adds +40MB per unload.

[aabc]

Does it happen only on Qt 4.7.4 or also on Qt 4.7.3 Qt 4.8 and Qt 5 ?

[altera_2011]

4.7.4 + 4.8.2 I have not tested 5 since we require Windows CE support.

[sierdzio]

In my case:

4.7.4, 4.8.1 - QtQuick 1.
Qt5.0.0 - QtQuick 2.

[aabc]

I also saw it on embedded linux.
Its a very serious leak.
It happens all the time there is a loading of new qml pages

[aabc]

We found that the reason for the memory leak is Qt's function:

QDeclarativeEngine::clearComponentCache()

[andre]

Please report a bug in the bug tracker then. Not many Qt Developers (those building Qt itself, not so much those using it) read these forums.

[aabc]

Can you please send me a link ?

[andre]

The "bugtracker":https://bugreports.qt-project.org we usually call "Jira" (after the name of the system it is using). If you report a bug, please:

Put a link to this forum topic in the bugreport, and

Put a link to the bugreport in this forum topic.

[antonio]

somebody has resolved this issue?

[chrisadams]

Firstly, why is anyone calling clearComponentCache() in QtQuick 1? You have to be extremely careful about the circumstances in which you do so, or all sorts of craziness can occur.

In QtQuick2, I seem to recall that we added / changed the functionality significantly (and updated the documentation) to clearly reflect what those functions should be used for and how.

It's been a while, though, and my memory isn't too great. If someone can link the JIRA task I can take a brief look, but I can't promise to spend too much time on it, unfortunately.

Cheers,
Chris.

[antonio]

I'm not sure if there are leaks.

I added to my qml pages:
@
Component.onDestruction:{
componentX.destroy()
componentY.destroy()
componentZ.destroy()
}
@
for every nested component

and I'm using http://www.sikuli.org/ to test the complete flow (6 pages with many images). I had used my app 2000 times and there is not delay or crash.

Hope this helps

[extronus]

Instead of calling app.exec() exec your event loop like this and see if it still leaks.

{
app.processEvents(..);
view->engine()->collectGarbage();
view->engine()->clearComponentCache();
}

[sbindzau]

We have had a lot of problems with unexplained memory loss running 4.8.2 on Wince 6.0. Using 4.8.5 reduced the problem significantly.

As we have lots of Loaders in qml we also started to call gc() explicity for every onSourceChanged: call. The gc() was hardly ever called, it seemed. I've heard that this has improved in Qt5, but we're not in a position to test this now.