The right approach to "ask" data to the running thread..

[sylvaticus]

I think I got it.. I'll clean the code (I made a mess while tempting) and then I will post here if someone is interested ;-)))

Many thanks,
Sylvaticus

[sylvaticus]

ok.. this is what I done so far.. it took me longer as the first approach (query executed directly by the GUI trough a signal) was working without problems in Linux but randomly crash in Windows..
Does the following looks as a good approach or it is advisable to be done in an other way??

I have three classes involved, a MainWindow (QMainWindow derived), ThreadManager (QThread derived) and MainProgram (independent class with the model code).

MainWindow starts the thread calling QThread::start().

The QThread::start() call really executes the code in the ThreadManager::run() function that contain MainProgram::run() with all the model code.

The pause and stop system is implemented with the bool ThreadManager::running and bool ThreadManager::stopped variables.
Often (every few seconds) the model code goes to check the status of that variables that can be changed also from the GUI. The code is:

void
ThreadManager::refreshGUI(){
		checkQuery(0,0,false);
		while (!running){
			if(stopped){
				break;
			}
		}
		if (stopped){
			emit upgradeLogArea("Model has been stopped.");
			running= false;
			throw(2);
		}
}

void
ThreadManager::refreshGUI(){
		checkQuery(0,0,false);
		while (!running){
			if(stopped){
				break;
			}
		}
		if (stopped){
			emit upgradeLogArea("Model has been stopped.");
			running= false;
			throw(2);
		}
}

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checkQuery(int, int, bool) is a function that can be called both from the GUI trough a signal or from the running thread trough refreshGUI(), and it is so protected with a QMutex.
It's role is to change/control the status of the query parameters that are members of ThreadManager. The third function parameter is a bool that tell the function if the query parameters should be set (if the query come from the GUI) or if the query should be executed and its results sent back to the GUI with a signal (if the call come from the running thread).
The code is :

void
ThreadManager::checkQuery(int px_ID, int currentLayerIndex, bool newRequest){
	QMutexLocker locker(&mutex);
	if(newRequest){
		pxQueryID = px_ID;
		layerQueryPos = currentLayerIndex;
		if(stopped){computeQuery(pxQueryID, layerQueryPos);layerQueryPos = -1;} // model is stopped, no way the model thread will do the query work
		else{emit publishQueryResults("<i>..wait.. processing query..</i>");} // model is running.. it will be the model thread to execute the query		
		return;
	} else {
		if(layerQueryPos<0){
			return;
		} else {
			computeQuery(pxQueryID, layerQueryPos);
			layerQueryPos = -1;
			return;
		}
	}
}

void
ThreadManager::checkQuery(int px_ID, int currentLayerIndex, bool newRequest){
	QMutexLocker locker(&mutex);
	if(newRequest){
		pxQueryID = px_ID;
		layerQueryPos = currentLayerIndex;
		if(stopped){computeQuery(pxQueryID, layerQueryPos);layerQueryPos = -1;} // model is stopped, no way the model thread will do the query work
		else{emit publishQueryResults("<i>..wait.. processing query..</i>");} // model is running.. it will be the model thread to execute the query		
		return;
	} else {
		if(layerQueryPos<0){
			return;
		} else {
			computeQuery(pxQueryID, layerQueryPos);
			layerQueryPos = -1;
			return;
		}
	}
}

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The whole code is located at:
http://www.regmas.org/doc/referenceM...ainWindow.html
http://www.regmas.org/doc/referenceM...adManager.html
http://www.regmas.org/doc/referenceM...inProgram.html

Thank you.. I think I finally found a pleace to discuss the Qt programming.. the mailing list looks too technical for a beginner like me...

Cheers...
Sylvaticus

[jacek]

The problem might be in automatic connections. QThread object lives in the GUI thread, so automatic connections between widgets and the thread object will behave like if they were direct, which might cause troubles.

This problem was discussed several times, so please search the forum. A few examples:
http://www.qtcentre.org/forum/f-qt-p...eads-6060.html
http://www.qtcentre.org/forum/f-qt-p...read-3943.html

[sylvaticus]

Thanks for the explanation & the links.....