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List: kde-core-devel
Subject: Re: Review Request 127866: Oxygen: Fix QCache usage
From: Frank Reininghaus <frank78ac () googlemail ! com>
Date: 2016-05-23 21:10:32
Message-ID: 20160523211032.12263.47385 () mimi ! kde ! org
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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:
>
> -----------------------------------------------------------
> This is an automatically generated e-mail. To reply, visit:
> https://git.reviewboard.kde.org/r/127866/
> -----------------------------------------------------------
>
> (Updated May 22, 2016, 4:20 a.m.)
>
>
> Review request for kde-workspace and Hugo Pereira Da Costa.
>
>
> Repository: oxygen
>
>
> Description
> -------
>
> 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).
> *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.
> 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.
> 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...).
>
> Diffs
> -----
>
> 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
>
> Diff: https://git.reviewboard.kde.org/r/127866/diff/
>
>
> Testing
> -------
>
> 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.
>
> Thanks,
>
> Michael Pyne
>
>
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This is an automatically generated e-mail. To reply, visit:
<a href="https://git.reviewboard.kde.org/r/127866/">https://git.reviewboard.kde.org/r/127866/</a>
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<br />
<pre style="white-space: pre-wrap; white-space: -moz-pre-wrap; \
white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">+1 from me - looks much \
better without the while loops indeed :-)</p> <p style="padding: \
0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: \
inherit;">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.</p> <p style="padding: 0;text-rendering: \
inherit;margin: 0;line-height: inherit;white-space: inherit;">FIFOCache \
looks like a simple solution to the problems that Coverity found with \
QCache (at least if the max cost is bounded) - nice!</p></pre> <br />
<p>- Frank Reininghaus</p>
<br />
<p>On May 22nd, 2016, 4:20 a.m. UTC, Michael Pyne wrote:</p>
<table bgcolor="#fefadf" width="100%" cellspacing="0" cellpadding="12" \
style="border: 1px #888a85 solid; border-radius: 6px; -moz-border-radius: \
6px; -webkit-border-radius: 6px;"> <tr>
<td>
<div>Review request for kde-workspace and Hugo Pereira Da Costa.</div>
<div>By Michael Pyne.</div>
<p style="color: grey;"><i>Updated May 22, 2016, 4:20 a.m.</i></p>
<div style="margin-top: 1.5em;">
<b style="color: #575012; font-size: 10pt;">Repository: </b>
oxygen
</div>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Description \
</h1> <table width="100%" bgcolor="#ffffff" cellspacing="0" \
cellpadding="10" style="border: 1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">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).</p> <p style="padding: 0;text-rendering: \
inherit;margin: 0;line-height: inherit;white-space: inherit;"><em \
style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: normal;">NOTE</em> 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.</p> <p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">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 <em \
style="padding: 0;text-rendering: inherit;margin: 0;line-height: \
inherit;white-space: normal;">must</em> 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.</p> <p style="padding: \
0;text-rendering: inherit;margin: 0;line-height: inherit;white-space: \
inherit;">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...).</p></pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Testing \
</h1> <table width="100%" bgcolor="#ffffff" cellspacing="0" \
cellpadding="10" style="border: 1px solid #b8b5a0"> <tr>
<td>
<pre style="margin: 0; padding: 0; white-space: pre-wrap; white-space: \
-moz-pre-wrap; white-space: -pre-wrap; white-space: -o-pre-wrap; word-wrap: \
break-word;"><p style="padding: 0;text-rendering: inherit;margin: \
0;line-height: inherit;white-space: inherit;">Compiled without warnings, \
installed and ran <code style="text-rendering: inherit;color: \
#4444cc;padding: 0;white-space: normal;margin: 0;line-height: \
inherit;">oxygen-demo5 -style oxygen</code>. Used the GUI Benchmark feature \
to automatically cycle through all the listed features -- no crashes or \
obvious rendering errors.</p></pre> </td>
</tr>
</table>
<h1 style="color: #575012; font-size: 10pt; margin-top: 1.5em;">Diffs</b> \
</h1> <ul style="margin-left: 3em; padding-left: 0;">
<li>kdecoration/oxygendecohelper.cpp <span style="color: \
grey">(aa75eca)</span></li>
<li>kstyle/oxygenstyle.cpp <span style="color: grey">(e428606)</span></li>
<li>kstyle/oxygenstylehelper.h <span style="color: \
grey">(9510a60)</span></li>
<li>kstyle/oxygenstylehelper.cpp <span style="color: \
grey">(612ba37)</span></li>
<li>liboxygen/oxygenhelper.h <span style="color: \
grey">(a6453a0)</span></li>
<li>liboxygen/oxygenhelper.cpp <span style="color: \
grey">(4843604)</span></li>
<li>liboxygen/oxygenshadowcache.cpp <span style="color: \
grey">(907e586)</span></li>
</ul>
<p><a href="https://git.reviewboard.kde.org/r/127866/diff/" \
style="margin-left: 3em;">View Diff</a></p>
</td>
</tr>
</table>
</div>
</body>
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