Stop Thread started by QtConcurrent::run?

Question

Is it possible to stop a Thread by its associated QFuture Object ? Currently i've been starting a video capturing process like this.

this->cameraThreadRepresentation = QtConcurrent::run(this,&MainWindow::startLiveCapturing);

Inside the startLiveCapturing-Method an infinite loop is running that captures images and displays them. So if the user wants to stop that process he should simply press a button and that operation stops. But it seems that i can not stop this thread by calling the cancel method like this ?

this->cameraThreadRepresentation.cancel();

What i am doing wrong and how can i stop that thread or operation.

Answer 1

From the documentation of QtConcurrent::run:

Note that the QFuture returned by QtConcurrent::run() does not support canceling, pausing, or progress reporting. The QFuture returned can only be used to query for the running/finished status and the return value of the function.

What you could do is have a button press set a boolean flag in your main window and build your infinite loop like this:

_aborted = false;

forever    // Qt syntax for "while( 1 )"
{
    if( _aborted ) return;

    // do your actual work here
}

Answer 2

Why don't you create a boolean flag that you can test inside your capturing loop and when it is set, it jumps out and the thread exits?

Something like:

MainWindow::onCancelClick() // a slot
{
    QMutexLocker locker(&cancelMutex);
    stopCapturing = true;
}

And then for your threaded function:

MainWindow::startLiveCapturing()
{
   forever
   {

       ...
       QMutexLocker locker(&cancelMutex);
       if (stopCapturing) break;
   }

}

Answer 3

as Qt Document said, you can not use cancel() function fir QConcurrent::run() but you can cancel tasks by this answer :

https://stackoverflow.com/a/16729619/14906306