Question

I’m trying to create a “responsive gui”, which basically means that I have an app, and on the main window there is a button. After I press this button I want the “progress bar window” to get displayed which will show the progress of the work being done, and of course this work is being done in separate thread.

Unfortunately my approach with starting a new thread in ctor of this progress_bar window doesn’t seems to work and I got frozen gui.
Here is the link to this project so you can download it and run without the need for copying and pasting anything: http://www.mediafire.com/?w9b2eilc7t4yux0

Could anyone please tell me what I’m doing wrong and how to fix it?

EDIT

progress_dialog::progress_dialog(QWidget *parent) :
    QDialog(parent)
{/*this is this progress dialog which is displayed from main window*/
    setupUi(this);
    working_thread_ = new Threaded;
    connect(working_thread_,SIGNAL(counter_value(int)),progressBar,SLOT(setValue(int)),Qt::QueuedConnection);
    working_thread_->start();//HERE I'M STARTING THIS THREAD
}  

/*this is run fnc from the threaded class*/
void Threaded::run()
{
    unsigned counter = 0;
    while(true)
    {
        emit counter_value(counter);
        counter = counter + 1 % 1000000;
    }
}

Answer 1

Independently from the fact that tight looping is bad, you should limit the rate at which you make changes to the main GUI thread: the signals from your thread are queued as soon they are emitted on the main thread event loop, and as the GUI can’t update that fast, repaint events are queued rather than executed in real time, which freezes the GUI.

And anyways updating the GUI faster than the screen refresh rate is useless.

You could try something like this:

void Threaded::run()
{
    QTime time;
    time.start();   
    unsigned counter = 0;
    // initial update
    emit counter_value(counter);

    while(true)
    {
        counter = (counter + 1) % 1000000;

        // 17 ms => ~ 60 fps
        if(time.elapsed() > 17) {            
            emit counter_value(counter);            
            time.restart();            
        }
    }
}