Review Request 112277: Fix deadlock by avoid calling Qfont::QFont() in KFontSettingsData

[Àlex Fiestas]

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http://git.reviewboard.kde.org/r/112277/
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(Updated Aug. 25, 2013, 8:38 p.m.)


Review request for KDE Frameworks and Kevin Ottens.


Description
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While writing tests for KFontSettingsData I found this deadlock:
http://paste.kde.org/p1fada663/

Shorter version of the deadlock by calling QFont::QFont in KFontSettingsData::font()
http://paste.kde.org/pda7fc276/

Basically:
QApplicationPrivate::initializeWidgetFontHash
KFontSettingsData::font
QVariant magic, which calls QFont::QFont (http://qt.gitorious.org/qt/qtbase/blobs/stable/src/gui/text/qfont.cpp#line677)
QFont::QFont
QGuiApplication::font
KFontSettingsData::font
QFont::QFont
QGuiApplication::font
And lock takes place

So the patch simply avoids calling QFont::QFont by reusing the QFont we already have (initialized with the default values) and using QFont::fromString in case we have data to set to it.

To reproduce simply set fonts in kdeglobals:
[General]
desktopFont=Ubuntu,9,-1,5,50,0,0,0,0,0
fixed=Ubuntu Mono,10,-1,5,50,0,0,0,0,0
font=Ubuntu,9,-1,5,50,0,0,0,0,0
menuFont=Ubuntu,9,-1,5,50,0,0,0,0,0
smallestReadableFont=Ubuntu,8,-1,5,50,0,0,0,0,0
taskbarFont=Ubuntu,9,-1,5,50,0,0,0,0,0
toolBarFont=Ubuntu,8,-1,5,50,0,0,0,0,0

and then execute QApplication.


Diffs
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  staging/frameworkintegration/src/platformtheme/kfontsettingsdata.cpp 70c1d26 

Diff: http://git.reviewboard.kde.org/r/112277/diff/


Testing
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Tested in different app's using qpa plus the kfontsettingsdata test I'm writing.


Thanks,

Àlex Fiestas

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