Events after Object destruction

[JKSH]

@anli From your logs, I suspect that it's just as you say: The deleted button doesn't get properly removed from the event queue.

I'm not sure what's the best way forward though. The first thing I'd recommend is to upgrade to Qt 4.8.7 and see if the issue exists there.

[anli]

Hello JKSH,

in the meantime we already tried this. We also changed the hardware platform to a faster one to get an idea, if this is maybe the reason, but also with QT 4.8.7 we get there the effect.

It seems to me as if the QWS window list does not get updated in time...

[JonB]

@anli
You're still trying to sort out object deletion and signal/slot delivery etc., right?

At this point if it were me, I would set up a new, standalone, minimal project, without worrying about "slow" or "embedded" etc., and just test what's going on in the simplest case, so that you understand. Having your full, complex, existing application code is just going to obscure whatever issue there is.

[J.Hilk]

Might be a stupid workaround, but what happens when you, in your slot, set the PushButton to disabled, this should happe as the very first thing of course ?

[anli]

@JonB :
We tried it and currently do not get the problems there. We are currently trying to understand why.

@J-Hilk :
We also tried this, but the second event got fired, before the button is disabled...

[anli]

For further information, I now attach a backtrace for the moment, when toolbutton is destroyed:

0	layout_n::manager_c::slotButtonDeleted	layoutmanager.cpp	526	0x27eb70	
1	layout_n::manager_c::qt_static_metacall	moc_layoutmanager.cpp	243	0x28a4b4	
2	QMetaObject::activate	qobject.cpp	3540	0xd6c2f0	
3	QObject::destroyed	moc_qobject.cpp	149	0xd6dce8	
4	QObject::~QObject	qobject.cpp	843	0xd66c3c	
5	QWidget::~QWidget	qwidget.cpp	1705	0x38be4c	
6	QAbstractButton::~QAbstractButton	qabstractbutton.cpp	608	0x77284c	
7	QToolButton::~QToolButton	qtoolbutton.cpp	409	0x803c48	
8	layout_n::toolButton_c::~toolButton_c	layoutmanager.h	185	0x28b934	
9	layout_n::toolButton_c::~toolButton_c	layoutmanager.h	185	0x28b994	
10	QObjectPrivate::deleteChildren	qobject.cpp	1908	0xd68368	
11	QWidget::~QWidget	qwidget.cpp	1681	0x38bd90	
12	QWidget::~QWidget	qwidget.cpp	1705	0x38bec8	
13	qDeleteInEventHandler	qobject.cpp	4270	0xd6d858	
14	QObject::event	qobject.cpp	1175	0xd67384	
15	QWidget::event	qwidget.cpp	8846	0x39e564	
16	QApplicationPrivate::notify_helper	qapplication.cpp	4566	0x348428	
17	QApplication::notify	qapplication.cpp	4530	0x348260	
18	QCoreApplication::notifyInternal	qcoreapplication.cpp	947	0xd4e6b4	
19	QCoreApplication::sendEvent	qcoreapplication.h	231	0x34aee4	
20	QCoreApplicationPrivate::sendPostedEvents	qcoreapplication.cpp	1572	0xd4f950	
21	QCoreApplication::sendPostedEvents	qcoreapplication.cpp	1468	0xd4f548	
22	QCoreApplication::sendPostedEvents	qcoreapplication.h	236	0x3d2e68	
23	QEventDispatcherQWS::flush	qeventdispatcher_qws.cpp	164	0x3d2dbc	
24	QCoreApplication::flush	qcoreapplication.cpp	683	0xd4e0d0	
25	QAbstractButton::mousePressEvent	qabstractbutton.cpp	1101	0x773910	
26	QToolButton::mousePressEvent	qtoolbutton.cpp	710	0x804a90	
27	QWidget::event	qwidget.cpp	8371	0x39d230	
28	QAbstractButton::event	qabstractbutton.cpp	1085	0x77384c	
29	QToolButton::event	qtoolbutton.cpp	1162	0x8060cc	
30	QApplicationPrivate::notify_helper	qapplication.cpp	4566	0x348428	
31	QApplication::notify	qapplication.cpp	4108	0x3466e4	
32	QCoreApplication::notifyInternal	qcoreapplication.cpp	947	0xd4e6b4	
33	QCoreApplication::sendSpontaneousEvent	qcoreapplication.h	234	0x34af58	
34	QETWidget::translateMouseEvent	qapplication_qws.cpp	3539	0x3cbe08	
35	QApplication::qwsProcessEvent	qapplication_qws.cpp	2984	0x3c9d48	
36	QEventDispatcherQWS::processEvents	qeventdispatcher_qws.cpp	121	0x3d2b5c	
37	QEventLoop::processEvents	qeventloop.cpp	149	0xd4bc7c	
38	QEventLoop::exec	qeventloop.cpp	200	0xd4be10	
39	QCoreApplication::exec	qcoreapplication.cpp	1221	0xd4eec8	
40	QApplication::exec	qapplication.cpp	3823	0x34551c	
41	main	main.cpp	650	0x2192b4	

There you can see, that the mouse button press is captured by the QWS system around line 34, beeing then forwarded to the respective button, which should paint the button as pressed (line 25) and performs a flush of the event queue to get the paint event processed, which in this case also finds the 'delete later' (line 13), that has been posted to the event queue by the previous mouse button press event and performs this deletion. After leaving the flush function, it will continue to operate on illegal pointer variables, because its own object has already been destroyed

[JKSH]

@anli said in Events after Object destruction:

@JonB :
We tried it and currently do not get the problems there. We are currently trying to understand why.

Alternatively, make a copy of your project and gradually simplify your code until the issue disappears.

[J.Hilk]

@anli said in Events after Object destruction:

We also tried this, but the second event got fired, before the button is disabled...

mmh, I'll like to throw in a new idea.
You should check, if your connection between button and slot is unique. If you called connect somewhere twice, than this could lead to the race condition.

[anli]

@JKSH :
Good idea! I will try this next.

@J-Hilk :
I have checked the code for hat, but did not find any issues.
The problem is not always there, it just occurs, if I make several clicks on the same button while the software is busy doing some work.

[jmhd12]

Hello, Have you figured it out what was the problem? I'm having a similar issue.