add client id for all metadata listening clients

weed/server/filer_server.go

@@ -81,6 +81,10 @@ type FilerServer struct {
 	listenersLock sync.Mutex
 	listenersCond *sync.Cond
 
+	// track known metadata listeners
+	knownListenersLock sync.Mutex
+	knownListeners     map[int32]struct{}
+
 	brokers     map[string]map[string]bool
 	brokersLock sync.Mutex
 
@@ -93,6 +97,7 @@ func NewFilerServer(defaultMux, readonlyMux *http.ServeMux, option *FilerOption)
 	fs = &FilerServer{
 		option:                option,
 		grpcDialOption:        security.LoadClientTLS(util.GetViper(), "grpc.filer"),
+		knownListeners:        make(map[int32]struct{}),
 		brokers:               make(map[string]map[string]bool),
 		inFlightDataLimitCond: sync.NewCond(new(sync.Mutex)),
 	}