fix: client blocking when connecting (#131)

ccore/nebula/gateway/pool/pool.go

@@ -213,8 +213,6 @@ func ListParams(args string, tmpParameter types.ParameterMap, sessionMap types.P
 
 func NewClient(address string, port int, username string, password string, opts ...nebula.Option) (*ClientInfo, error) {
 	var err error
-	clientMux.Lock()
-	defer clientMux.Unlock()
 
 	// TODO: it's better to add a schedule to make it instead
 	if currentClientNum > clientRecycleNum {
@@ -253,8 +251,11 @@ func NewClient(address string, port int, username string, password string, opts
 		},
 		timezone: c.GetTimezoneInfo(),
 	}
+
+	clientMux.Lock()
 	clientPool[nsid] = client
 	currentClientNum++
+	clientMux.Unlock()
 
 	// Make a goroutine to deal with concurrent requests from each connection
 	go handleRequest(nsid)