Proper way to initialize and terminate a Qt Application? - c++

Question

I am currently coding a program in C++/ Qt 5.9 to control a 3D Printer.
I have divided the project into several libraries :
The GUI Lib: The view
The Device Lib: Control each device (movement, printing tool, sensors)
The Controller Lib: Links the View with the Device lib
etc...
My problem is that I do not know how to initialize and terminate properly the execution of the program. More specifically, the Device library has a class named DeviceManager with two functions :
initialize() : which connect to each device and initialize them. This actions can take several seconds (10s for example)
finalize() : which closes all the connexions, can also take several seconds
What I would like to do is initialize the Device Lib in the right place without blocking the GUI and then finalize it in the right and not block the GUI
This is my main code :
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
MainWindow w;
w.show();
return a.exec();
}
My solution now is to call DeviceManager::initialize() in the MainWindow constructor and DeviceManager::finalize() in the MainWindow::closeEvent().
The problem: even if I use concurrency to initialize and finalize in a different thread, the application displays its window several seconds after it was launched and the display freezes when the application is closed because it has to wait for the finalize function to be done.
How should I properly handle this initialization and finalization problem, please ? Do I need to reimplement the QApplication class? Do I try and do it in the main? Do you know any great example of an open source application doing that kind of initialize and finalize work?

Answer 1

The problem: even if I use concurrency to initialize and finalize in a different thread, the application displays its window several seconds after it was launched and the display freezes when the application is closed because it has to wait for the finalize function to be done.
You could start the initialize() function as own detached thread before starting the MainWindow. This could cause problems if the initializing thread doesn't terminate before the first initialized "thing" is needed. Something like:
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
std::thread{initialize}.detach();
MainWindow w;
w.show();
finialize();
return a.exec();
}
To prevent the problem, and maybe lock some function in the GUI, then you probably need to have a state variable that it sets under a mutex on its way out, and which you examine under a mutex to see if it has been set.