def handle_new_heart(self, heart):
        """handler to attach to heartbeater.
        Called when a new heart starts to beat.
        Triggers completion of registration."""
        self.log.debug("heartbeat::handle_new_heart(%r)", heart)
        if heart not in self.incoming_registrations:
            self.log.info("heartbeat::ignoring new heart: %r", heart)
        else:
            self.finish_registration(heart)
handler to attach to heartbeater.
        Called when a new heart starts to beat.
        Triggers completion of registration.