Question

I am working on linux and I realized that my application was leaving behind daemon processes when I close it with the “Stop” button on Qt creator IDE. I want to handle these cases so the application close the same way as when I close the main window. To write the handlers, I need to know which signals it corresponds to.

Answer 1

Digging into QtCreator’s code, I can see that QtCreator uses a QProcess internally to launch your app. The red “stop” button is connected to ApplicationLauncher::stop(), which terminates your process in one of two ways depending if it’s a GUI app or a console app, but in both cases, the result end up to be the same on Linux.

For a GUI app, ApplicationLauncher calls QProcess::terminate(), which in turn sends a SIGTERM (on Linux) signal to your daemon. It then waits (with waitForFinished()) for 1 second, and if the daemon hasn’t quit by then, it calls QProcess::kill(), sending SIGKILL.

For a console app, ApplicationLauncher delegates the termination to the ConsoleProcess utility class. On Linux, ConsoleProcess::stop() will act similar to ApplicationLauncher for a GUI app, which is first sending SIGTERM, then waiting for 1 second, and sending SIGKILL if it hasn’t terminated yet.

You will find the relevant code from QtCreator here:

• GUI app termination
• Console app termination (on Linux)
• Console app termination (on Windows)