QtConcurrent::run() is failing sometimes

Praveen.Illa

Hello All,

I have a requirement of executing a method in thread where the time consuming activity is happens in a thread and emits a signal to QML when the data is available.
After lots of googling, I have found QtConcurrent::run() feature provided by the QML.

I have used QtConcurrent::run() feature, but it is failing some times.
modelThread.isRunning() is returning "false" on qDebug().

I dont know why, Can anyone please help me on this ?

Below is the pseudo code

Please note, QFuture<void> modelThread is a member variable.

**sampleClass.cpp**
sampleClass::sampleClass()
{
	QObject::connect(this, SIGNAL(fillRequest()), this, SLOT(updateRequest()));
}

~sampleClass::sampleClass()
{
	modelThread.waitForFinished();
}

void sampleClass::sendRequest(QString arg1, int arg2)
{
	//assigning arguments to member variables
	
	emit fillRequest();
}

void sampleClass::updateRequest()
{
	modelThread = QtConcurrent::run(this, &sampleClass::processRequest);
	```
        qDebug() << "modelThread =  " << modelThread.isRunning();
        ```
}

void sampleClass::processRequest()
{
	//Time consuming processing happens in this method
	
	// emit signal to inform QML that model is ready
    emit processRequestIsReady();
}


In sample.qml,
sampleClassObject {
	id: local_ObjectModel
	}
	
	Component.onCompleted: {
	local_ObjectModel.sendRequest(arg1, agr2)
        local_ObjectModel.processRequestIsReady.connect(gridView.sigHandler)
		}
		
	function sigHandler() {
        gridView.model = local_ObjectModel;
    }

SGaist

Hi,

As they documentation of the function states:

Runs function in a separate thread.
The thread is taken from the global QThreadPool.
Note that function may not run immediately; function will only be run once a thread becomes available.

Praveen.Illa

@SGaist - Thanks for the information. The issue is resolved now. Below is the sample code

QFutureWatcher<void> *modelThread = setFuture(QtConcurrent::run(this, &classname::method));