Review Request 121134: make KGlobal reference counting threadsafe

[René J.V. Bertin]

> On Nov. 16, 2014, 8:22 p.m., Thomas Lübking wrote:
> > kdecore/kernel/kglobal.cpp, line 343
> > <https://git.reviewboard.kde.org/r/121134/diff/5/?file=328836#file328836line343>
> >
> >     Does this actually make sense?
> >     The result is "undefined" when used from multiple threads anyway.
> >     
> >     Should one enforce this to be called from the main thread only instead?

How do you mean, undefined? The result will be the value set by whoever called the function last.

You have a point that this doesn't make a lot of sense, there's something to say that the main (master...) thread ought to be the one deciding whether or not it can be quit by the reference counter.


- René J.V.


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On Nov. 16, 2014, 8:19 p.m., René J.V. Bertin wrote:
> 
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/121134/
> -----------------------------------------------------------
> 
> (Updated Nov. 16, 2014, 8:19 p.m.)
> 
> 
> Review request for KDE Software on Mac OS X and kdelibs.
> 
> 
> Repository: kdelibs
> 
> 
> Description
> -------
> 
> I have been experiencing unexpected exits from KDevelop that were not due to any kind of error in the KDevelop code; it was as if someone told the application to exit normally. This happens mostly on OS X, but also sometimes on Linux.
> I finally traced this to `KGlobal::deref` reaching a zero reference count and invoking `QCoreApplication::quit` when called from one of KDevelop's KJob dtors. There does not appear to be a reference counting mismatch in the code, so the issue might be due to a race condition in KGlobal::ref/deref.
> 
> This patch introduces thread-safety to KGlobal's reference counting by turning the simple global `static int s_refCount` into a `static QAtomicInt s_refCount`. I consider this an important bug fix regardless of whether it corrects the issue I have with KDevelop.
> 
> 
> Diffs
> -----
> 
>   kdecore/kernel/kglobal.cpp cf003a4 
> 
> Diff: https://git.reviewboard.kde.org/r/121134/diff/
> 
> 
> Testing
> -------
> 
> On OS X 10.6.8 only for now.
> 
> NB: Qt itself uses the QAtomicInt's parent class (QBasicAtomicInt) for its own reference counter used for implicit sharing. This is thus well-tested code that is unlikely to introduce regressions to a core KDE feature.
> 
> 
> Thanks,
> 
> René J.V. Bertin
> 
>

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