subchannel.go
func (subChMap *subChannelMap) getOrAdd(serviceName string, ch *Channel) (_ *SubChannel, added bool) {
	if sc, ok := subChMap.get(serviceName); ok {
		return sc, false
	}

	return subChMap.registerNewSubChannel(serviceName, ch)
}
func (subChMap *subChannelMap) getOrAdd(serviceName string, ch *Channel) (_ *SubChannel, added bool) {
	if sc, ok := subChMap.get(serviceName); ok {
		return sc, false
	}

	return subChMap.registerNewSubChannel(serviceName, ch)
}
// GetOrAdd a subchannel for the given serviceName on the map