[rekonq] Re: Review Request: Don't crash on exit

[José Manuel Santamaría Lema]

> On April 5, 2011, 3:20 p.m., Andrea Diamantini wrote:
> > Josè, 
> > many thanks for your patch and for the interesting Qt-BUG pointed out! I'll ask my Qt-devs around and try to merge your patch in a while. Anyway, I'd like to understand why this bug occurs just in a few systems. Any ideas about?
> 
> José Manuel  Santamaría Lema wrote:
>     > I'd like to understand why this bug occurs just in a few systems. Any ideas about?
>     
>     Yes. C&P from http://doc.trolltech.com/4.7/objecttrees.html#construction-destruction-order-of-qobjects
>     
>     > When QObjects are created on the heap (i.e., created with new), a tree can be constructed from them in any order, and later, the objects in the tree can be destroyed in any order.
>     
>     My conjecture is: 
>     
>     The problem is that in my system some QWidget is deleted after the QApplication, triggering the Qt bug/feature #16974. However, since the objects in the tree can be destroyed in any order, I think it's reasonable to guess that in different systems the the deletion order may be different, thus you may or may not get the crash. Hence why I am deleting various objects in Application::~Application and not just the BookmarkProvider instance; I hope this would save you from headaches now and/or in the future, because (with a bit of bad luck) this may happen:
>     
>     1. You add a QWidget to the object tree of ... let's say m_sessionManager (if you aren't doing it already).
>     2. The program works perfectly for you.
>     3. Some of your users get the crash and you can't reproduce it.
>     
>     Just in case you want a system where you could reproduce the crash: I reproduced the bug in Debian sid with this semi-official repo http://qt-kde.debian.net/
>     I could reproduce under the circumstances explained here https://bugs.kde.org/show_bug.cgi?id=269490#c3 both in a virtualbox machine used to test our debian packages and in my main desktop.

P.S. Sorry for the late reply, I've just realized that I didn't pushed the "Publish" button for the above comment. Also, thanks for commiting and just for the record I've been using the browser with the patch and I never got the crash again.


- José Manuel


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On April 5, 2011, 1:26 a.m., José Manuel  Santamaría Lema wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> http://git.reviewboard.kde.org/r/101027/
> -----------------------------------------------------------
> 
> (Updated April 5, 2011, 1:26 a.m.)
> 
> 
> Review request for rekonq.
> 
> 
> Summary
> -------
> 
> Hi,
> 
> I'm not 100% sure but I tend to think you must not set a QApplication as the parent of a BookmarkProvider.
> 
> I think the problem is that any BookmarkProvider has QWidgets in its tree of QObjects. Therefore, you will get problems when deleting the children because of this:
> http://bugreports.qt.nokia.com/browse/QTBUG-16974
> 
> So I just deleted some objects in Application::~Application in order to make sure these objects are deleted before the QApplication. Just deleting the BookmarkProvider in Application::~Application would be enough to fix the crash here, but I'm deleting the other objects ...
> 1 ... because if now or in the future these objects had a QWidget in its object tree I think you might get a crash.
> 2 ... just in case.
> 
> By the way, I think the bug mentioned in this request was introduced in this commit 2b4efa406780920631af1166e79d54e54092322a
> 
> I have push permissions, if you give me the ok I will push this patch to 0.7-branch.
> 
> 
> This addresses bug 269490.
>     /show_bug.cgi?id=269490
> 
> 
> Diffs
> -----
> 
>   src/application.cpp 7fcbfe8 
> 
> Diff: http://git.reviewboard.kde.org/r/101027/diff
> 
> 
> Testing
> -------
> 
> I have built rekonq with the patch; problem solved for me.
> 
> 
> Thanks,
> 
> José Manuel
> 
>

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