[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?

> 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.


- 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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