[Nepomuk] Review Request: Fix crash due to dangling pointers by zeroing them.

[Simeon Bird]

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http://git.reviewboard.kde.org/r/107339/
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Review request for Nepomuk.


Description
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    Fix convoluted crash on deletion of Query::Folder.
    
    Sequence of events could be:
    
    1. Folder::~Folder called.
    2. SearchRunnable->cancel called => SearchRunnable->m_folder = 0.
    3. Deletes all connections.
    4. deleteLater called again, during destructor (is this ever safe?)
    5. SearchRunnable::run called => since m_folder is zero, returns and
    deletes SearchRunnable without setting m_folder -> SearchRunnable to
    zero.
    6. mutex unlocked at end of destructor
    7. Folder::~Folder called again by queued deleteLater (?)
    8. SearchRunnable already deleted after step 5. Crash.
    
    Fixed by setting m_currentSearchRunnable = 0 after cancelling the folder
    listing.
    
This is slightly guess-work, but it's the best I can come up with. I'd appreciate if someone who knows more Qt could tell me if my story above is possible or not.


This addresses bug 308773.
    http://bugs.kde.org/show_bug.cgi?id=308773


Diffs
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  services/storage/query/folder.cpp 18e8ff7140eb03e12fcab7bead2b0d4bd6fa7474 

Diff: http://git.reviewboard.kde.org/r/107339/diff/


Testing
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Compiled, ran. Can't reproduce crash, so not certain that it fixes it.


Thanks,

Simeon Bird

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