Review Request 128944: Reduce temporary allocations in the DesktopFileParser

[Alex Richardson]

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https://git.reviewboard.kde.org/r/128944/#review99278
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Thanks for looking into this!

When I wrote the code I thought it would be mostly transitional so I didn't pay much attention to efficiency.


src/lib/plugin/desktopfileparser.cpp (line 215)
<https://git.reviewboard.kde.org/r/128944/#comment66850>

    I guess the same optimization could be applied here.



src/lib/plugin/desktopfileparser.cpp (line 477)
<https://git.reviewboard.kde.org/r/128944/#comment66849>

    Using readLineInto() is really useful to reduce unnecessary allocations. However the function is quite new: `This function was introduced in Qt 5.5`
    
    Do we depend on Qt 5.5 already?



src/lib/plugin/desktopfileparser.cpp (line 478)
<https://git.reviewboard.kde.org/r/128944/#comment66851>

    If I read this correctly we no longer handle leading/trailing spaces properly. Does the test still pass? Or maybe I forgot to add tests for this case.
    trimmed() will add another allocation, maybe we can change the string in place?
    
    There is `QStringRef::trimmed()` so `line.midRef(0).trimmed()` should work without any extra allocations, right?



src/lib/plugin/desktopfileparser.cpp (line 506)
<https://git.reviewboard.kde.org/r/128944/#comment66848>

    We can remove valueEscaped now that both are of type QString


- Alex Richardson


On Sept. 19, 2016, 4:20 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 Sept. 19, 2016, 4:20 p.m.)
> 
> 
> Review request for KDE Frameworks.
> 
> 
> 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 
> 
> 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.
> 
> 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
> 
> 
> Thanks,
> 
> Aleix Pol Gonzalez
> 
>

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