// c++ -fPIC -lQt6Core -lQt6DBus -L/usr/local/lib/qt6 -I/usr/local/include/qt6 -I/usr/local/include/qt6/QtCore -I/usr/local/include/qt6/QtGui -I/usr/local/include/qt6/QtWidgets -I/usr/local/include/qt6/QtDBus -g

#include <unistd.h>
#include <sys/wait.h>

#include <iostream>

#include <QCoreApplication>
#include <QDBusConnection>

using namespace std;

int usage();
void do_fork();
void do_stuff();

int main(int argc, char* argv[])
{
    if (argc != 3)
        return usage();

    QCoreApplication app(argc, argv);

    if (string(argv[1]) == "fork") {
        do_fork();
        do_stuff();
    } else {
        do_stuff();
        do_fork();
    }
}

void do_stuff()
{
    // this triggers creation of the global static QDBusConnectionManager within Qt
    // the hang then occurs in QDBusConnectionManager destructor after the child calls exit()
    QDBusConnection conn("blah");
}

void do_fork()
{
    pid_t pid = ::fork();
    if (pid < 0) {
        cout << "fork failed";
        return;
    }

    // child
    if (pid == 0) {
        ::sleep(1);
        ::exit(0);
        return;
    }

    // parent
    int status;
    int r = waitpid(pid, &status, 0);
    if (r < 0) {
        cout << "waitpid failed";
        return;
    }
}

int usage()
{
    cout << "works: ./a.out fork stuff" << endl
         << "hangs: ./a.out stuff fork" << endl;

    return 1;
}