Q:

Will UI block when waiting for QThread / How to use QThread properly

If I have a progressbar in the ui thread (window), which shall run endless until a method finishes it's work, will the ui thread block and so the progress bar if I'm waiting for a second QThread to finish? If the ui thread blocks waiting, then i would not to wait for the second thread. I thought to implement a callback method which will be called when the second thread finished, but then: How can i connect to the callback method? 
What do I want to do? 
I have a window, this window has a progressbar which is first not visible. When the user presses a certain button to request data, a method will be called which returns a RequestPointer which contains a method which returns the request status. 
When the user presses the button, i want to make the progress bar visible, running infinitely till the request is finished and i can print the data to the window.
To the Worker i want to pass this pointer and the worker checks in a while (flag) loop, if the status is still running and sleep if so. When the worker finishes, i want to stop the progressbar and make it unvisible again. Do i have to pass the progress bar to the thread, or can i wait for the thread without blocking the ui?
I'm not quite a Qt pro. Really new to it. I tried to get some info from the https://doc.qt.io/Qt-5/qthread.html website, but it's a bit hard for me to understand the code example.
Method in my worker class: 
void Worker::watchRequest(RequestPtr r_ptr)
{
    bool exit = true;

    while (!exit)
    {
        ErrorCode errorCode = r_ptr->Test();

        switch (errorCode)
        {
        case Request_RUNNING:   
            QThread::msleep(10);
            break;
        case Request_ABORTED:
            exit = true;
            break;
        case Request_SUCCESS:
            exit = true;
            break;
        }

    }

A:

If you don't want to block the user interface, all you have to do is to call QApplication::processEvents(); in your while-loop.
I have some code which uses std::future instead of QThread and my code looks like this:
while (!progressIndicator->UserBreak()
    && (future.wait_for(std::chrono::seconds(0)) != std::future_status::ready))
{
    QApplication::processEvents();
}

This works well.

