GUI application as DLL. Repaint is blocked.

[Grinchman]

Hello!
I have Qt4 GUI project. It`s implemented as DLL. The main application which uses my DLL calling interface functions from MainThread. Here is the message loop of main application:

while(buckets_rendered<numRects && events!=0)
 {
  while(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) 
  {
   TranslateMessage(&msg);
   DispatchMessage(&msg); 
  }
 
  stat = MsgWaitForMultipleObjects(numHandles, handles, FALSE, INFINITE, QS_ALLINPUT);
  if(stat == (WAIT_OBJECT_0 + numHandles))
  {
   continue;
  }
  else // message comes from the events
  {
   id = stat - WAIT_OBJECT_0;
   --events;
 
   // ...
  }
 }

while(buckets_rendered<numRects && events!=0)
 {
  while(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE)) 
  {
   TranslateMessage(&msg);
   DispatchMessage(&msg); 
  }
  
  stat = MsgWaitForMultipleObjects(numHandles, handles, FALSE, INFINITE, QS_ALLINPUT);
  if(stat == (WAIT_OBJECT_0 + numHandles))
  {
   continue;
  }
  else // message comes from the events
  {
   id = stat - WAIT_OBJECT_0;
   --events;
 
   // ...
  }
 }

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All works fine with Qt 4.7.3, but when we use Qt 4.5.3 my DLL is ‘blocked’! When I click some button in my GUI app, nothing happens. But when next I click right mouse button some events occure and I see an effect from the first left mouse button click and an effect from right button click…Why only right mouse button click force repaint? I`m confused…

[wysota]

Where do you process Qt's events?

[Grinchman]

Where do you process Qt's events?

I really don`t do any special managment for events. I just have this code for MyApplication class (inherited from QApplication):

bool MyApplication::notify(QObject * obj, QEvent * event) {
    try {
        return QApplication::notify(obj, event);
    }
    catch(std::exception & ex) {
        handleError(ex.what());
    }
    catch(...) {
        handleError(tr("Critical error: unhandled exception"));
    }
    return false;
}

bool MyApplication::notify(QObject * obj, QEvent * event) {
    try {
        return QApplication::notify(obj, event);
    }
    catch(std::exception & ex) {
        handleError(ex.what());
    }
    catch(...) {
        handleError(tr("Critical error: unhandled exception"));
    }
    return false;
}

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---

Added after 13 minutes:

Maybe it`ll be useful if I show you a code of creating and using MyApplication object.
Main dll function is:

BOOL APIENTRY DllMain(HANDLE hinstDLL, DWORD ul_reason_for_call, LPVOID lpReserved)
{
	BOOL ret = TRUE;	
 
	switch(ul_reason_for_call) 
	{
	case DLL_PROCESS_ATTACH:
		{
			qInstallMsgHandler(myMessageHandler);
		}
		break;
 
	case DLL_THREAD_ATTACH:
		break;
 
	case DLL_THREAD_DETACH:
		break;
 
	case DLL_PROCESS_DETACH:
		{
			fBitmapManager *bmmManager = fr_get_bitmap_mgr();
			if(bmmManager)
				bmmManager->DeleteAllVFBs("defaultvfb");
		}
		break;
	}
 
	return ret;
}

BOOL APIENTRY DllMain(HANDLE hinstDLL, DWORD ul_reason_for_call, LPVOID lpReserved)
{
	BOOL ret = TRUE;	

	switch(ul_reason_for_call) 
	{
	case DLL_PROCESS_ATTACH:
		{
			qInstallMsgHandler(myMessageHandler);
		}
		break;

	case DLL_THREAD_ATTACH:
		break;

	case DLL_THREAD_DETACH:
		break;

	case DLL_PROCESS_DETACH:
		{
			fBitmapManager *bmmManager = fr_get_bitmap_mgr();
			if(bmmManager)
				bmmManager->DeleteAllVFBs("defaultvfb");
		}
		break;
	}

	return ret;
}

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As you see, nothing special...

There is interface functions for my dll:

bool RegisterPlugins(fPluginManager *plugMgr)
{
        plugMgr->RegisterPlugin("vfb", "defaultvfb", VFBPluginModel::getInstance,0,0);		
        return TRUE;
}
 
bool UnRegisterPlugins(fPluginManager *plugMgr)
{
        plugMgr->UnRegisterPlugin("vfb", "defaultvfb");
        return TRUE;
}
 
extern "C" fplug_export fBool initializePlugins(fPluginManager *plugMgr)
{
	return RegisterPlugins(plugMgr);
}
 
extern "C" fplug_export fBool uninitializePlugins(fPluginManager *plugMgr)
{
	return UnRegisterPlugins(plugMgr);
}

bool RegisterPlugins(fPluginManager *plugMgr)
{
        plugMgr->RegisterPlugin("vfb", "defaultvfb", VFBPluginModel::getInstance,0,0);		
        return TRUE;
}

bool UnRegisterPlugins(fPluginManager *plugMgr)
{
        plugMgr->UnRegisterPlugin("vfb", "defaultvfb");
        return TRUE;
}

extern "C" fplug_export fBool initializePlugins(fPluginManager *plugMgr)
{
	return RegisterPlugins(plugMgr);
}

extern "C" fplug_export fBool uninitializePlugins(fPluginManager *plugMgr)
{
	return UnRegisterPlugins(plugMgr);
}

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We interested in VFBPluginModel::getInstance code. This is a singletone wich creates an QApplication object.
Class definition:

class VFBPluginModel :   public QObject                      
{
    Q_OBJECT
 
public:
 
    VFBPluginModel();
    virtual ~VFBPluginModel();
 
    static void *getInstance();
 
...
 
 
private:
	VFBApplication a;
};

class VFBPluginModel :   public QObject                      
{
    Q_OBJECT

public:

    VFBPluginModel();
    virtual ~VFBPluginModel();

    static void *getInstance();

...


private:
	VFBApplication a;
};

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And creating:

VFBPluginModel::VFBPluginModel() : a(i, &name, this)
{
 
}

VFBPluginModel::VFBPluginModel() : a(i, &name, this)
{

}

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Code for VFBApplication class:

class VFBApplication: public QApplication {
    Q_OBJECT
 
public:
    VFBApplication(int & argc, char ** argv, VFBPluginModel* plugin);
    virtual ~VFBApplication();
 
    virtual bool notify(QObject * obj, QEvent * event);
 
...
};
 
 
VFBApplication::VFBApplication(int & argc, char ** argv, VFBPluginModel* plugin):   QApplication(argc, argv)																	mainWnd_(NULL)
{
   mainWnd_ = new MainWindow(appModel_);
   mainWnd_->show();
}

class VFBApplication: public QApplication {
    Q_OBJECT

public:
    VFBApplication(int & argc, char ** argv, VFBPluginModel* plugin);
    virtual ~VFBApplication();

    virtual bool notify(QObject * obj, QEvent * event);

...
};


VFBApplication::VFBApplication(int & argc, char ** argv, VFBPluginModel* plugin):   QApplication(argc, argv)																	mainWnd_(NULL)
{
   mainWnd_ = new MainWindow(appModel_);
   mainWnd_->show();
}

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[wysota]

So if you don't process Qt events from within your non-Qt app, then how do you expect them to be handled? Do you have a call to QCoreApplication::exec() or QCoreApplication::processEvents() anywhere?

[Grinchman]

No, I don`t use it. I little bit confused about using exec() in dll.
But, anyway....my application works fine in Qt 4.7.3...what fundamental difference between 4.7.3 and 4.5.3? (

[wysota]

Make sure it indeed works fine in Qt 4.7.3 because there is no way for it to work fine if you don't process Qt's events.

[Grinchman]

Just tested. It works fine in Qt 4.7.3...
My dll originally was a standalone GUI app, and it had main function with app.exec() call. When it migrated into dll I just replaced main function by showed above DLLMain function (without app.exec() call) with several dll_export functions....

[wysota]

Does your notify() implementation ever get called? Place a debug statement there and find out. Print the object name and event type from the arguments the method receives.

[Grinchman]

Yeah, it`s always called. And sequences of events are quite common: ApplicationActivate....MouseButtonClicked and so on...And objects are ordinary: QApplication object, MainWindow object, internal widgets, buttons and etc...

[wysota]

Yeah, it`s always called.

In both 4.5 and 4.7?

And sequences of events are quite common: ApplicationActivate....MouseButtonClicked and so on...And objects are ordinary: QApplication object, MainWindow object, internal widgets, buttons and etc...

Please grep your code for calls to QApplication and QCoreApplication classes and paste them here.

[Grinchman]

wysota, your tip about processEvent was really helpful. Now non-Qt application is forcing my object QApplication to process events when it gets some windows message and it works! ) So, we may conclude that Qt 4.7 is somehow forcing processEvent without exec() and manualy call of processEvent()...

So, thank you so much for your time and help!

[wysota]

No, it is not forcing processEvents().