Clean up before closing the QCoreApplication

Question

I have a console-based QCoreApplication which has timers and does socket communication and also uses locked mutex.

When I close the application manually

Answer 1

Turns out that closing command line application (checked on Win7 & VS2010) by pressing 'close' (red x button on title bar) passes the STATUS_CONTROL_C_EXIT signal to the application. All threads are aborted with this code.

The thread 'Main Thread' (0x980) has exited with code -1073741510 (0xc000013a).

The thread 'QThread' (0x2388) has exited with code -1073741510 (0xc000013a).

That means that there is no way to intercept this with the QCoreApplication::aboutToQuit() signal.

Take a look at winnt.h or ntstatus.h. That is the value assigned to the manifest constant STATUS_CONTROL_C_EXIT. The runtime is just choosing to end your program with the code to note the user's cancel operation.

Answer 2

Cleanup should be handled by destructors and child-parent relationship.

Make your master object (the one in the main) a child of QApplication so it is destructed with all its childs before QApplication is.

Are you sure you killed all your threads? If it is a thread with an eventloop be sure to call QThread::quit() to exit the eventloop before you call QThread::wait()

You can also use the void QApplication::qAddPostRoutine ( QtCleanUpFunction ptr ) to do some special cleanup.

For debugging those messages you can use QtMsgHandler qInstallMsgHandler ( QtMsgHandler h ) and write your own message handler to capture those warnings. If you can simulate the problem you can set a breakpoint on the message and see on the stack where the message is coming from.

void debugMessageHandler( QtMsgType type, const char *msg ){
    if(QString(msg).contains( "The message you can see in the console" )){
        int breakPointOnThisLine(0);    
    }

    switch ( type ) {
        case QtDebugMsg:
            fprintf( stderr, "Debug: %s\n", msg );
            break;
        case QtWarningMsg:
            fprintf( stderr, "Warning: %s\n", msg );
            break;
        case QtFatalMsg:
            fprintf( stderr, "Fatal: %s\n", msg );
            abort();
    }
}

---

In order to clean up with destructor and child-parent relation ship you can catch the console close signal and call QCoreApplication::exit() to the application instance.

#include <csignal>
#include <QtCore/QCoreApplication>
using namespace std;

struct CleanExit{
    CleanExit() {
        signal(SIGINT, &CleanExit::exitQt);
        signal(SIGTERM, &CleanExit::exitQt);
        signal(SIGBREAK, &CleanExit::exitQt) ;
    }

    static void exitQt(int sig) {
        QCoreApplication::exit(0);
    }
};


int main(int argc, char *argv[])
{
    CleanExit cleanExit;
    QCoreApplication a(argc, argv);
    return a.exec();
}

Answer 3

you can connect to QCoreApplication::aboutToQuit signal and do the necessary clean up there.