Set the handler class for a subsystem in server mode.  If a request
        for this subsystem is made on an open ssh channel later, this handler
        will be constructed and called -- see `.SubsystemHandler` for more
        detailed documentation.

        Any extra parameters (including keyword arguments) are saved and
        passed to the `.SubsystemHandler` constructor later.

        :param str name: name of the subsystem.
        :param handler:
            subclass of `.SubsystemHandler` that handles this subsystem.

def set_subsystem_handler(self, name, handler, *larg, **kwarg):
        """
        Set the handler class for a subsystem in server mode.  If a request
        for this subsystem is made on an open ssh channel later, this handler
        will be constructed and called -- see `.SubsystemHandler` for more
        detailed documentation.

        Any extra parameters (including keyword arguments) are saved and
        passed to the `.SubsystemHandler` constructor later.

        :param str name: name of the subsystem.
        :param handler:
            subclass of `.SubsystemHandler` that handles this subsystem.
        """
        try:
            self.lock.acquire()
            self.subsystem_table[name] = (handler, larg, kwarg)
        finally:
            self.lock.release()