[Interest] When does Qt load its plugins?

[Elvis Stansvik]

2016-07-13 14:00 GMT+02:00 alexander golks <alex at golks.de>:
> Am Wed, 13 Jul 2016 12:37:22 +0200
> schrieb Elvis Stansvik <elvstone at gmail.com>:
>
>> 2016-07-13 12:34 GMT+02:00 Elvis Stansvik <elvstone at gmail.com>:
>> > I'm working on packaging an application using QtWidgets as an AppImage
>> > and I'm looking at which of the Qt plugins I must bundle.
>> >
>> > I'll run an strace while using the application, but I thought I'd also
>> > ask here: When in general does Qt load its plugins? For some plugins
>> > (such as the platform plugin), I expect it to be quite early. But what
>> > about imageformat plugins, is there a policy that they be loaded as
>> > late as possible?
>>
>> To clarify, I wasn't only talking about imageformat plugins, but
>> plugins in general. The imageformat plugins was just an example where
>> I suspect they may be loaded as late as possible?
>>
>> Elvis
>>
>> >
>> > In short I'm wondering if I must use every nook and cranny of the
>> > application during my strace run, to catch all plugins, or if it's
>> > enough to say wait until the QApplication and QMainWindow is up.
>> >
>> > Thanks in advance,
>> > Elvis
>
> i would not use strace to get a packaging list for the plugins to deploy.
> simply use the plugins you want/need.
>
> plugins are loaded when requested first time. so its not safe to wait
> until QApplication and QMainWindow are up.

Alright, yes I realized this after I sent my first mail (see my other
mail just now).

It's easy to know that if I say want to load JPEGs, I need the
imageformats/libqjpeg.so plugin. But there are so many plugins in a Qt
installation it's hard as an application developer to know for sure
which you need.

In the Qt I'm using to build this AppImage, there's currently:

tmp/usr/lib/qt5/plugins/bearer/libqconnmanbearer.so
tmp/usr/lib/qt5/plugins/bearer/libqgenericbearer.so
tmp/usr/lib/qt5/plugins/bearer/libqnmbearer.so
tmp/usr/lib/qt5/plugins/designer/libcontainerextension.so
tmp/usr/lib/qt5/plugins/designer/libcustomwidgetplugin.so
tmp/usr/lib/qt5/plugins/designer/libqquickwidget.so
tmp/usr/lib/qt5/plugins/designer/libtaskmenuextension.so
tmp/usr/lib/qt5/plugins/designer/libworldtimeclockplugin.so
tmp/usr/lib/qt5/plugins/generic/libqevdevkeyboardplugin.so
tmp/usr/lib/qt5/plugins/generic/libqevdevmouseplugin.so
tmp/usr/lib/qt5/plugins/generic/libqevdevtabletplugin.so
tmp/usr/lib/qt5/plugins/generic/libqevdevtouchplugin.so
tmp/usr/lib/qt5/plugins/generic/libqtuiotouchplugin.so
tmp/usr/lib/qt5/plugins/iconengines/libqsvgicon.so
tmp/usr/lib/qt5/plugins/imageformats/libqgif.so
tmp/usr/lib/qt5/plugins/imageformats/libqico.so
tmp/usr/lib/qt5/plugins/imageformats/libqjpeg.so
tmp/usr/lib/qt5/plugins/imageformats/libqsvg.so
tmp/usr/lib/qt5/plugins/platforminputcontexts/libcomposeplatforminputcontextplugin.so
tmp/usr/lib/qt5/plugins/platforminputcontexts/libibusplatforminputcontextplugin.so
tmp/usr/lib/qt5/plugins/platforms/libqlinuxfb.so
tmp/usr/lib/qt5/plugins/platforms/libqminimal.so
tmp/usr/lib/qt5/plugins/platforms/libqoffscreen.so
tmp/usr/lib/qt5/plugins/platforms/libqxcb.so
tmp/usr/lib/qt5/plugins/platformthemes/libqgtk2.so
tmp/usr/lib/qt5/plugins/printsupport/libcupsprintersupport.so
tmp/usr/lib/qt5/plugins/qmltooling/libqmldbg_debugger.so
tmp/usr/lib/qt5/plugins/qmltooling/libqmldbg_inspector.so
tmp/usr/lib/qt5/plugins/qmltooling/libqmldbg_local.so
tmp/usr/lib/qt5/plugins/qmltooling/libqmldbg_native.so
tmp/usr/lib/qt5/plugins/qmltooling/libqmldbg_profiler.so
tmp/usr/lib/qt5/plugins/qmltooling/libqmldbg_server.so
tmp/usr/lib/qt5/plugins/qmltooling/libqmldbg_tcp.so
tmp/usr/lib/qt5/plugins/sqldrivers/libqsqlite.so
tmp/usr/lib/qt5/plugins/xcbglintegrations/libqxcb-glx-integration.so

For some of these it's obvious from their name what they're for, but
others I have no idea. And I also don't know if they're integral to
the working of Qt, or if they're expendable (for example the generic/*
plugins) :/

Elvis

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