[Kde-games-devel] Data migration issue

[Matthew Dawson]

On March 3, 2015 10:59:21 PM Mathias Kraus wrote:
> Hi,
> 
> I noticed a problem with the data migration in the kdegames transition from
> kdelibs4 to kf5 and Albert Astals Cid suggested to ask frameworks devel for
> advice.
> 
> In short, when the migration is run after the QCoreApplication is created,
> the migrated config is not used but the default values. This results in a
> lost migration if the users changes some settings during the first run of
> the kf5 version of the game. Also, if the user plays a game and wins, all
> the previous high scores will be lost. Ian Wadham assumes there will be
> also other issues.
> 
> If the migration is run before the creation of the QCoreApplication, it
> seems to work correct.
Taking a look into what is happening, it appears that other libraries are 
accessing the kminesrc file once QCoreApplication is created by using 
KSharedConfig::openConfig.  This function caches that instance of 
KSharedConfig, which is working ontop of an empty file and thus does nothing.

One backtrace I got looks like:
#5  0x00007ffff5adc3c0 in KSharedConfig::openConfig (_fileName=..., flags=..., 
resType=QStandardPaths::GenericConfigLocation) at 
/home/matthew/kde/kconfig/src/core/ksharedconfig.cpp:87
#6  0x00007fffe21ed296 in KHintsSettings::KHintsSettings (this=0x683380) at 
/usr/src/debug/kde-
frameworks/frameworkintegration-9999/frameworkintegration-9999/src/platformtheme/khintssettings.cpp:65
#7  0x00007fffe21e94f7 in KdePlatformTheme::loadSettings (this=0x67f930) at 
/usr/src/debug/kde-
frameworks/frameworkintegration-9999/frameworkintegration-9999/src/platformtheme/kdeplatformtheme.cpp:121
#8  0x00007fffe21fc6bb in KdePlatformThemePlugin::create (this=<optimized 
out>, key=..., paramList=...) at /usr/src/debug/kde-
frameworks/frameworkintegration-9999/frameworkintegration-9999/src/platformtheme/main.cpp:52
#9  0x00007ffff4aaa44e in qLoadPlugin1<QPlatformTheme, QPlatformThemePlugin, 
QStringList> (parameter1=..., key=..., loader=0x7ffff4f63ab0 
<_ZZN12_GLOBAL__N_112Q_QGS_loader13innerFunctionEvE6holder>) at 
/usr/include/qt5/QtCore/5.4.0/QtCore/private/qfactoryloader_p.h:107
#10 QPlatformThemeFactory::create (key=..., platformPluginPath=...) at 
kernel/qplatformthemefactory.cpp:64
#11 0x00007ffff4ab4012 in init_platform (argv=0x7fffffffce58, 
argc=@0x7fffffffcc7c: 1, platformThemeName=..., platformPluginPath=..., 
pluginArgument=...) at kernel/qguiapplication.cpp:1045
#12 QGuiApplicationPrivate::createPlatformIntegration (this=0x63dec0) at 
kernel/qguiapplication.cpp:1166
#13 0x00007ffff4ab4ced in QGuiApplicationPrivate::createEventDispatcher 
(this=<optimized out>) at kernel/qguiapplication.cpp:1183
#14 0x00007ffff4704126 in QCoreApplication::init 
(this=this at entry=0x7fffffffcd30) at kernel/qcoreapplication.cpp:727
#15 0x00007ffff4704186 in QCoreApplication::QCoreApplication 
(this=0x7fffffffcd30, p=...) at kernel/qcoreapplication.cpp:650
#16 0x00007ffff4ab6ea9 in QGuiApplication::QGuiApplication 
(this=0x7fffffffcd30, p=...) at kernel/qguiapplication.cpp:560
#17 0x00007ffff50c0c05 in QApplication::QApplication (this=0x7fffffffcd30, 
argc=@0x7fffffffcc7c: 1, argv=0x7fffffffce58, _internal=328704) at 
kernel/qapplication.cpp:562
#18 0x000000000042d68c in main (argc=1, argv=0x7fffffffce58) at 
/home/matthew/kde/kmines/main.cpp:35

Which I think might be avoidable anyways, as the hints should only read from 
the globals?  Migrating first would of course avoid this issue (but see 
below), and I think calling reparseConfiguration after migrating may also 
work.  Alternately, tracking down why kminesrc is opened early might be 
another solution.

> 
> Laurent Montel, the creator of kdelibs4configmigrator, suggests the former
> procedure (first QCoreApplication, then migration), though.
If kdelibs4configmigrator uses KConfig itself for anything, then it really 
should only be used after QCoreApplication is created.  Doing otherwise is 
very fragile and may break in the future.

Hope that helps,
-- 
Matthew
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