Review Request 121134: make KGlobal reference counting threadsafe

[Pino Toscano]

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kdecore/kernel/kglobal.cpp
<https://git.reviewboard.kde.org/r/121134/#comment49274>

    QAtomicInt is not a POD, so it is not safe to be used this way. You rather need to use the semi-private QBasicAtomicInt, which is not a POD, like:
    
        static QBasicAtomicInt s_allowQuit = Q_BASIC_ATOMIC_INITIALIZER(0);
    
    The API should be the same.


- Pino Toscano


On Nov. 16, 2014, 7:01 p.m., René J.V. Bertin wrote:
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> https://git.reviewboard.kde.org/r/121134/
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> (Updated Nov. 16, 2014, 7:01 p.m.)
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> Review request for KDE Software on Mac OS X and kdelibs.
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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.
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> 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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