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Wireshark-dev: Re: [Wireshark-dev] Slot on main thread not called when signal is emitted from a

From: Paul Offord <Paul.Offord@xxxxxxxxxxxx>
Date: Wed, 16 Dec 2015 14:45:42 +0000
Well that was frustrating.  The answer to my problem is that I had mixed release and debug objects.  I have been adding Qt Libraries to the Linker Input list like this:

\Qt\Qt5.5.1\5.5\msvc2013_64\lib\Qt5Core.lib
\Qt\Qt5.5.1\5.5\msvc2013_64\lib\Qt5Widgets.lib
\Qt\Qt5.5.1\5.5\msvc2013_64\lib\Qt5Gui.lib
\Qt\Qt5.5.1\5.5\msvc2013_64\lib\Qt5Network.lib

I have now changed the include list to:

\Qt\Qt5.5.1\5.5\msvc2013_64\lib\Qt5Cored.lib
\Qt\Qt5.5.1\5.5\msvc2013_64\lib\Qt5Widgetsd.lib
\Qt\Qt5.5.1\5.5\msvc2013_64\lib\Qt5Guid.lib
\Qt\Qt5.5.1\5.5\msvc2013_64\lib\Qt5Networkd.lib

Now QApplication::instance() returns the pointer and my slot is now working.

Thanks Gerald for your advice, which in a roundabout way led me to the solution.

Best regards...Paul

-----Original Message-----
From: Paul Offord 
Sent: 16 December 2015 11:45
To: Developer support list for Wireshark <wireshark-dev@xxxxxxxxxxxxx>
Subject: RE: [Wireshark-dev] Slot on main thread not called when signal is emitted from another thread

Sorry - ignore that stupid last question about class name vs. instance.  I should have researched the function a  little so I understood what you are driving at.

I did a bit of research and it seems that although QApplication::instance() doesn't exist but QCoreApplication::instance() does.  I've tried it as a direct replacement and that doesn't work but I've seen a lot of chit chat on the Qt forum about recasting the returned pointer so I'll look further.

Best regards...Paul

-----Original Message-----
From: wireshark-dev-bounces@xxxxxxxxxxxxx [mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of Paul Offord
Sent: 16 December 2015 11:30
To: Developer support list for Wireshark <wireshark-dev@xxxxxxxxxxxxx>
Subject: Re: [Wireshark-dev] Slot on main thread not called when signal is emitted from another thread

Do you mean like this?

syncro.h

#ifndef SYNCRO_H
#define SYNCRO_H
#include <QtCore>

#include "mythread.h"

class Syncro : public QObject
{
	Q_OBJECT

public:
	Syncro();
	void Initialise(MyThread *);

public slots:
	void jumpToFrame(int);
};

#endif // SYNCRO_H


Syncro.cpp

.
.
Syncro::Syncro()
{
	setParent(QApplication::instance());
}
.
.

The setParent(QApplication::instance()) shows as an error in VS - incomplete type is not allowed.  Don't I have to specify the QApplication instance rather than the class name?

Cheers...Paul

-----Original Message-----
From: wireshark-dev-bounces@xxxxxxxxxxxxx [mailto:wireshark-dev-bounces@xxxxxxxxxxxxx] On Behalf Of Gerald Combs
Sent: 15 December 2015 21:19
To: Developer support list for Wireshark <wireshark-dev@xxxxxxxxxxxxx>
Subject: Re: [Wireshark-dev] Slot on main thread not called when signal is emitted from another thread

On 12/15/15 8:15 AM, Paul Offord wrote:

> When I run the code the extra thread starts OK and it starts to cycle 
> around the loop with the 3 second sleep. However, the connected slot 
> function Syncro::jumpToFrame(int new_frame) does not get called. If I 
> change the connect from QueuedConnection to DirectConnection the slot 
> function gets called but, as expected, in the context of my serviceThread.
> I need the slot function to run on the main thread.
> 
> I guess it is because my jumpToFrame slot function is not on the main 
> thread event loop, but I don’t understand how to get it on the loop.

Can you try adding a constructor to Syncro, and add either

  moveToThread(QApplication::instance()->thread());

or

  setParent(QApplication::instance());

to it? I'm not sure if QObjects have a valid thread affinity by default.
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