[Development] QPA triggers nested event processing

[David Faure]

This was quite unexpected: in Qt5, creating a QApplication instance triggers event processing already,
much before calling QApplication::exec().

This comes from QWindowSystemInterface::sendWindowSystemEvents calling sendPostedEvent(), see bt below.
Shouldn't it be more specific about which posted events, for which targets, should be flushed
at that point?

I'm pretty sure that nobody expects other events (timers, sockets, dbus, etc.) to be handled yet.
Even processing GUI-related events doesn't sound like a good idea to me, so early in the game.

#7  0x00007ffff3ba16fd in q_dbus_connection_dispatch (connection=0x61c6b0) at qdbus_symbols_p.h:115
#8  0x00007ffff3ba6e6e in QDBusConnectionPrivate::doDispatch (this=0x612600) at qdbusintegrator.cpp:1125
#9  0x00007ffff3bee5fe in QDBusConnectionPrivate::qt_static_metacall (_o=0x612600, _c=QMetaObject::InvokeMetaMethod, _id=3, _a=0x61c220) at .moc/debug-shared/moc_qdbusco
nnection_p.cpp:130
#10 0x00007ffff70ab991 in QMetaCallEvent::placeMetaCall (this=0x61f770, object=0x612600) at kernel/qobject.cpp:467
#11 0x00007ffff70ac8f8 in QObject::event (this=0x612600, e=0x61f770) at kernel/qobject.cpp:1048
#12 0x00007ffff70728e8 in QCoreApplicationPrivate::notify_helper (this=0x626750, receiver=0x612600, event=0x61f770) at kernel/qcoreapplication.cpp:837
#13 0x00007ffff70725dc in QCoreApplication::notify (this=0x7fffffffd330, receiver=0x612600, event=0x61f770) at kernel/qcoreapplication.cpp:783
#14 0x00007ffff3f0a80e in QGuiApplication::notify (this=0x7fffffffd330, object=0x612600, event=0x61f770) at kernel/qguiapplication.cpp:1052
#15 0x00007ffff70724e8 in QCoreApplication::notifyInternal (this=0x7fffffffd330, receiver=0x612600, event=0x61f770) at kernel/qcoreapplication.cpp:721
#16 0x00007ffff707622d in QCoreApplication::sendEvent (receiver=0x612600, event=0x61f770) at kernel/qcoreapplication.h:207
#17 0x00007ffff70735ac in QCoreApplicationPrivate::sendPostedEvents (receiver=0x0, event_type=0, data=0x607df0) at kernel/qcoreapplication.cpp:1321
#18 0x00007ffff707316d in QCoreApplication::sendPostedEvents (receiver=0x0, event_type=0) at kernel/qcoreapplication.cpp:1181
#19 0x00007ffff3efd466 in QWindowSystemInterface::sendWindowSystemEvents (flags=...) at kernel/qwindowsysteminterface.cpp:509
#20 0x00007ffff3f0a449 in QGuiApplicationPrivate::init (this=0x626750) at kernel/qguiapplication.cpp:880
#21 0x00007ffff3f0860d in QGuiApplication::QGuiApplication (this=0x7fffffffd330, p=...) at kernel/qguiapplication.cpp:348
#22 0x00007ffff46b4d15 in QApplication::QApplication (this=0x7fffffffd330, argc=@0x7ffff6bf5568, argv=0x624270, GUIenabled=true, _internal=327680) at kernel/qapplication
.cpp:577
[...]
#26 0x0000000000402cf8 in main (argc=1, argv=0x7fffffffd598) at /d/kde/src/kf5-qt5/kdelibs-frameworks/staging/kde4support/autotests/kuniqueapptest.cpp:93

What's the reason for the sendWindowSystemEvents in QGuiApplicationPrivate::init ?
It comes from ef2efafcc6b28791df6258fa1c5d565090a9577a (hi Simon), but the above looks like a rather
unexpected large side effect for a small issue...

-- 
David Faure, faure at kde.org, http://www.davidfaure.fr
Sponsored by Nokia to work on KDE, incl. KDE Frameworks 5