'Called when a barrier has been received'

def notify(self, event):

    self.xids.discard((event.dpid, event.xid))
    if (len(self.xids) == 0):
        if self.packet:
            log.debug(('Sending    delayed    packet    out    %s' % (dpid_to_str(self.first_switch),)))
            msg = of.ofp_packet_out(data=self.packet, action=of.ofp_action_output(port=of.OFPP_TABLE))
            core.openflow.sendToDPID(self.first_switch, msg)
        core.l2_multi.raiseEvent(PathInstalled(self.path))
