Cleaning up after QApplication

[Gints]

I'm porting a Qt desktop application to Linux (Ubuntu 19.10, 64bit desktop, Qt 5.12.5, gcc version 9.2.1), and am seeing some unexpected threads remaining alive after QApplication is finished.

Here's the minimum repro:

#include <QApplication>
#include <unistd.h>
int main(int argc, char * argv[]) {
    {
        QApplication app(argc, argv);
        sleep(1);
    }
    sleep(10);
    return 0;
}

If I debug the application at various points in time, here's what I see:

• Before the constructor of QApplication is run, just one thread, the main thread, exists, as expected.
• After the constructor of QApplication is run, 4 additional threads get created:
  • QXcbEventQueue
  • gmain
  • gdbus
  • QDBusConnection
• After the destructor of QApplication is run, the QXcbEventQueue thread goes away.
• Even after the second sleep of 10 seconds is done, the 3 other threads, besides the main thead, remain alive:
  • gmain
  • gdbus
  • QDBusConnection

I'm looking for a way to properly end these threads (and do other clean up that I might not be aware of at the moment) after QApplication has finished (of course, in the real app I call app.exec() and do other things) and has been destroyed.

This is not an issue in the application itself, which does not seem to have a problem with reaching the end of main with those 3 threads still alive.

The application is part of a larger suite of libraries / other applications that are thoroughly tested using Google Test, and the tests include some Death Tests, which, if executed after having run some tests that involve running a QApplication, complain about forking an application that has multiple threads, and get stuck and never finish, presumably, for this reason.

Any hints on how I might be able to get rid of those threads & perform a full cleanup of other stuff (if any) after QApplication?