clientv3/watch.go
func (w *watchGrpcStream) broadcastResponse(wr *WatchResponse) bool {
	for _, ws := range w.substreams {
		select {
		case ws.recvc <- wr:
		case <-ws.donec:
		}
	}
	return true
}
func (w *watchGrpcStream) broadcastResponse(wr *WatchResponse) bool {
	for _, ws := range w.substreams {
		select {
		case ws.recvc <- wr:
		case <-ws.donec:
		}
	}
	return true
}
// broadcastResponse send a watch response to all watch substreams.