Review Request 121134: make KGlobal reference counting threadsafe

[David Faure]

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Ship it!



kdecore/kernel/kglobal.cpp
<https://git.reviewboard.kde.org/r/121134/#comment49283>

    this comment isn't useful, it's obvious that the use of an atomic int is for thread safety.



kdecore/kernel/kglobal.cpp
<https://git.reviewboard.kde.org/r/121134/#comment49284>

    use false instead of 0, and add a "// bool" comment, for the reader to know this is a bool, conceptually, not an int.



kdecore/kernel/kglobal.cpp
<https://git.reviewboard.kde.org/r/121134/#comment49286>

    const int prevRefCount = ...



kdecore/kernel/kglobal.cpp
<https://git.reviewboard.kde.org/r/121134/#comment49285>

    Would s_allowQuit.load() compile? I forgot the Qt4 API since it changed in Qt5.
    
    It would be slightly better imho, for readability.


- David Faure


On Nov. 16, 2014, 8:22 p.m., René J.V. Bertin wrote:
> 
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> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/121134/
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> 
> (Updated Nov. 16, 2014, 8:22 p.m.)
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> 
> Review request for KDE Software on Mac OS X, kdelibs and David Faure.
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> Repository: kdelibs
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> Description
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> 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.
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> 
> Diffs
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>   kdecore/kernel/kglobal.cpp cf003a4 
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> Diff: https://git.reviewboard.kde.org/r/121134/diff/
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> Testing
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> On OS X 10.6.8 only for now.
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> 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.
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> 
> Thanks,
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> René J.V. Bertin
> 
>

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