def destroySingleton(cls):
        """
        Destroys the singleton instance of this class, if one exists.
        """
        singleton_key = '_{0}__singleton'.format(cls.__name__)
        singleton = getattr(cls, singleton_key, None)
        
        if singleton is not None:
            setattr(cls, singleton_key, None)

            singleton.close()
            singleton.deleteLater()