Review Request 127866: Oxygen: Fix QCache usage

[Frank Reininghaus]

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+1 from me - looks much better without the while loops indeed :-)

Do you know what the maximum cache limit that will be set with FIFOCache::setMaxCost is? I'm asking because FIFOCache::find is linear in the cache size. It might be a problem if this is potentially unlimited, but if it's never much more than the default value of 256, then it probabaly doesn't matter much, because the runtime cost of re-generating the cached values is probably much larger.

FIFOCache looks like a simple solution to the problems that Coverity found with QCache (at least if the max cost is bounded) - nice!

- Frank Reininghaus


On May 22, 2016, 4:20 a.m., Michael Pyne wrote:
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> https://git.reviewboard.kde.org/r/127866/
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> (Updated May 22, 2016, 4:20 a.m.)
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> 
> Review request for kde-workspace and Hugo Pereira Da Costa.
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> Repository: oxygen
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> Description
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> This should mostly complete the QCache fixes I kicked off in a previous RR, 127837. Hugo noted there were many other similar usages, and boy he wasn't kidding! ;) The long story short is that these usages can theoretically cause use-after-free behavior (which can lead to crashes and even undefined behavior if the compiler ever gets smart).
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> *NOTE* It is -much- easier to review if you download the diff to your git repository for oxygen and then run "git diff -b" to ignore whitespace changes, particularly for the QPixmap changes.
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> For QPixmaps we return values instead of pointers, so we simply make a separate copy to be cached when we do insert. For QColor we return references to values so we *must* return pointers, and those have to be owned by a QCache to avoid memleaks. So I added a helper function to loop until the cache accepts the new entry. TileSets are a similar concern, except those have manual loops since I was uncertain about whether TileSet's copy constructor was the best idea or not.
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> This fixes a ton of Coverity issues (59717 - 259733, 259739, 259742 - 259752, 1336154, 1336155) and might be associated with Qt bug 38142 and KDE bug 219055 (which doesn't actually appear to be a dupe of a different bug to me...).
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> Diffs
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>   kdecoration/oxygendecohelper.cpp aa75eca 
>   kstyle/oxygenstyle.cpp e428606 
>   kstyle/oxygenstylehelper.h 9510a60 
>   kstyle/oxygenstylehelper.cpp 612ba37 
>   liboxygen/oxygenhelper.h a6453a0 
>   liboxygen/oxygenhelper.cpp 4843604 
>   liboxygen/oxygenshadowcache.cpp 907e586 
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> Diff: https://git.reviewboard.kde.org/r/127866/diff/
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> Testing
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> Compiled without warnings, installed and ran `oxygen-demo5 -style oxygen`. Used the GUI Benchmark feature to automatically cycle through all the listed features -- no crashes or obvious rendering errors.
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> Thanks,
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> Michael Pyne
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