Release ONLY Debug Error: ASSERT "Cannot send events to objects owned by a different thread."

[rezger]

Debug Error!

Program: ...
Module: 4.5.2
File: global\qglobal.cpp
Line: 2030

ASSERT failure in QCoreApplication::sendEvent: "Cannot send events to objects owned by a different thread. Current thread 2be7670.
Receiver '' (of type 'QWidget') was created in thread 2306c00", file kernel\qcoreapplication.cpp, line 305

Using coin3d / SoQt as follow the error above is catched:

@
QWidget *HauptFenster = new QWidget(this);
setCentralWidget(HauptFenster);
SoQt::init(HauptFenster);
Vp = new Robo_Viewer(HauptFenster);

or (with exactly same error):

QWidget *HauptFenster = new QWidget(this);
SoQt::init(HauptFenster);
Vp = new Robo_Viewer(HauptFenster); // error will not happen, if i comment this line out (but the application cannot use this widget then)
setCentralWidget(HauptFenster); // neither happens, if this line is commented out

Robo_Viewer::Robo_Viewer(QWidget * parent)
:QWidget( parent), SoQtExaminerViewer(parent, NULL, true,
SoQtFullViewer::BUILD_ALL, SoQtFullViewer::BROWSER, true)
{
SoDB::init();
SoNodeKit::init();
SoInteraction::init();
root = new SoSeparator;
root->ref();
}
@
EDIT (Gerolf) added the @ tags

[vcsala]

Can you please use '@' tags around your code to make it more readable.

[dangelog]

http://developer.qt.nokia.com/wiki/ThreadsEventsQObjects .

I feel that writing that article was the right thing to do :-)

[rezger]

Sorry, it was my first posting here, second try:

msgbox:
"Debug Error!

Program: D:\FTP\Robo\release\Robo.exe
Module: 4.5.2
File: global\qglobal.cpp
Line: 2030

ASSERT failure in QCoreApplication::sendEvent: "Cannot send events to objects owned by a different thread. Current thread 2be7670.
Receiver '' (of type 'QWidget') was created in thread 2306c00", file kernel\qcoreapplication.cpp, line 305"

Using coin3d / SoQt as follow the error above is catched:

@QWidget *HauptFenster = new QWidget(this);
setCentralWidget(HauptFenster);
SoQt::init(HauptFenster);
Vp = new Robo_Viewer(HauptFenster);
@

or (with exactly same error):

@QWidget *HauptFenster = new QWidget(this);
SoQt::init(HauptFenster);
Vp = new Robo_Viewer(HauptFenster); // error will not happen, if i comment this line out (but the application cannot use this widget then)
setCentralWidget(HauptFenster); // neither happens, if this line is commented out
@

Class SoQtViewer:
@Robo_Viewer::Robo_Viewer(QWidget * parent)
:QWidget( parent), SoQtExaminerViewer(parent, NULL, true,
SoQtFullViewer::BUILD_ALL, SoQtFullViewer::BROWSER, true)
{
SoDB::init();
SoNodeKit::init();
SoInteraction::init();
root = new SoSeparator;
root->ref();
}
@

[rezger]

at peppe:
thank you very much for your fast answer and the link, but i still do not really understand what the problem is in reality, because the debug build is working fine :-)
should i not use "this" @new QWidget(this)@ ?
but why it works in debug?
how i can use a workaround?
thank you very much!

[giesbert]

Hi rezger,
you can edit your posts for adding such tags. Just click on edit under your avatar.

The interesting thing is, where is the event send and which event.
QApplication::sendEvent is a synchronous eventing mechanism. It is not allowed to "send" events cross threads.

You can set a breakpoint to the location where the assert happens and look at the stack trace to find the sender. Or have a look at the coin3d / SoQt whether you should not use QWidgets for the connection, or if they use threads.

[rezger]

at Gerolf:
i understood nearly everything what you told.
there is a check in release if the receiver is valid, but this is not checked in debug.
and the debug works quite fine, even using a not allowed synchronous event across threads, so ...
but as i am actually debugging third-party-code, it is not that easy, and i am not used in this. i believe it would be helpful to have a class- and thread-diagramm at hand, and i just wish visual c++ would give me such a thing at click. any suggestions to get such a diagram at ease? maybe another tool examinating my project?

[giesbert]

Sorry, I know currently no tool giving this. If the assert only happens in release mode, debug release mode (yes, it's possible :-) ) and set the breakpoint there and look at the call stack. That's the way, I normally go.

[rezger]

gregor, i tried it the last 25 minutes, how to debug release?
it does not stop at breakpoint ... ;-(

[giesbert]

You have to add debug info to the build. How to do that depends on the compilers you use.
With MS compilers, it's adding /Zi for the compiler and /DEBUG for the linker. For gcc you can use -ggdb (see "here":http://gcc.gnu.org/onlinedocs/gcc/Debugging-Options.html ). But perhaps you also have to add this to Qt (means rebuild Qt) to set breakpoints there. If you compile SoQt by your own, I would build that one with debug info and yours and look for sendEvent in SoQt and set breakpoints.