Review Request 128944: Reduce temporary allocations in the DesktopFileParser

[Mark Gaiser]

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I think you might be better off (and faster) if you use http://doc.qt.io/qt-5/qbytearray.html#fromRawData which smells like a "QByteArrayRef". That saves you the conversion from QByteArray to QString (you only need to do that where you actually need it). Try it, you might save more reallocations this way :)


src/lib/plugin/desktopfileparser.cpp (line 280)
<https://git.reviewboard.kde.org/r/128944/#comment66863>

    You can optimize this one further.
    http://doc.qt.io/qt-5/qbytearray.html#fromRawData
    
    You'd just have to figure out the first position from where you want to have the string. QByteArray::lastIndexOf(...) probably helps you there.


- Mark Gaiser


On sep 19, 2016, 3:20 p.m., Aleix Pol Gonzalez wrote:
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> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/128944/
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> 
> (Updated sep 19, 2016, 3:20 p.m.)
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> 
> Review request for KDE Frameworks.
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> Repository: kcoreaddons
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> Description
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> While analising plasmashell under heaptrack, one of the sore spots is temporary allocations within DesktopFileParser. This improves the situation by:
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> * Only converting to QString/utf8 once.
> * Using QStringRef instead of fully splitting QString to parse them.
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> Diffs
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>   src/lib/plugin/desktopfileparser.cpp 2eb198d 
>   src/lib/plugin/desktopfileparser_p.h c61b297 
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> Diff: https://git.reviewboard.kde.org/r/128944/diff/
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> 
> Testing
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> tests still pass, plasma still works normally.
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> heaptrack plasmashell:
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> after:
>         allocations:            4169312
>         leaked allocations:     83225
>         temporary allocations:  606902
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> before:
>         allocations:            4680691
>         leaked allocations:     84825
>         temporary allocations:  819292
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> 
> Thanks,
> 
> Aleix Pol Gonzalez
> 
>

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