diff --git a/relay/schema.go b/relay/schema.go
index 354d322..664d18b 100644
--- a/relay/schema.go
+++ b/relay/schema.go
@@ -3,6 +3,7 @@ package relay
 import (
 	"encoding/json"
 	"strings"
+	"sync"
 
 	"go.uber.org/zap/zapcore"
 )
@@ -81,30 +82,43 @@ func cachedMessageKey(topic string) string {
 }
 
 // TopicClientSet stores topic -> clients relationship
-type TopicClientSet map[string]map[*client]struct{}
+type TopicClientSet struct {
+	*sync.RWMutex
+	Data map[string]map[*client]struct{}
+}
 
-func NewTopicClientSet() TopicClientSet {
-	return make(map[string]map[*client]struct{})
+func NewTopicClientSet() *TopicClientSet {
+	return &TopicClientSet{
+		RWMutex: &sync.RWMutex{},
+		Data:    map[string]map[*client]struct{}{},
+	}
 }
 
-func (ts TopicClientSet) Get(topic string) map[*client]struct{} {
-	return ts[topic]
+func (ts *TopicClientSet) Get(topic string) map[*client]struct{} {
+	ts.RLock()
+	defer ts.RUnlock()
+	return ts.Data[topic]
 }
 
-func (ts TopicClientSet) Set(topic string, c *client) {
-	if _, ok := ts[topic]; !ok {
-		ts[topic] = make(map[*client]struct{})
+func (ts *TopicClientSet) Set(topic string, c *client) {
+	ts.Lock()
+	defer ts.Unlock()
+	if _, ok := ts.Data[topic]; !ok {
+		ts.Data[topic] = make(map[*client]struct{})
 	}
 
-	ts[topic][c] = struct{}{}
+	ts.Data[topic][c] = struct{}{}
 }
 
 // GetTopicsByClient returns the topics associated with the specified client,
 // meanwhile, remove the client from these topics if `clear` is true
 // returns the topics the client has associated with
-func (ts TopicClientSet) GetTopicsByClient(c *client, clear bool) []string {
+func (ts *TopicClientSet) GetTopicsByClient(c *client, clear bool) []string {
+	// Write lock in a read func because we may remove the client from the topics
+	ts.Lock()
+	defer ts.Unlock()
 	topics := []string{}
-	for topic, set := range ts {
+	for topic, set := range ts.Data {
 		if _, ok := set[c]; ok {
 			topics = append(topics, topic)
 		}
@@ -115,26 +129,46 @@ func (ts TopicClientSet) GetTopicsByClient(c *client, clear bool) []string {
 	return topics
 }
 
-func (ts TopicClientSet) Unset(topic string, c *client) {
-	delete(ts[topic], c)
+func (ts *TopicClientSet) Unset(topic string, c *client) {
+	ts.Lock()
+	defer ts.Unlock()
+	delete(ts.Data[topic], c)
+}
+
+func (ts *TopicClientSet) Len(topic string) int {
+	ts.RLock()
+	defer ts.RUnlock()
+	return len(ts.Data[topic])
 }
 
-func (ts TopicClientSet) Len(topic string) int {
-	return len(ts[topic])
+func (ts *TopicClientSet) Clear(topic string) {
+	ts.Lock()
+	defer ts.Unlock()
+	delete(ts.Data, topic)
 }
 
-func (ts TopicClientSet) Clear(topic string) {
-	delete(ts, topic)
+type TopicSet struct {
+	*sync.RWMutex
+	Data map[string]struct{}
 }
 
-type TopicSet map[string]struct{}
+func NewTopicSet() *TopicSet {
+	return &TopicSet{
+		RWMutex: &sync.RWMutex{},
+		Data:    map[string]struct{}{},
+	}
+}
 
-func NewTopicSet() TopicSet {
-	return make(map[string]struct{})
+func (tm TopicSet) Set(topic string) {
+	tm.Lock()
+	defer tm.Unlock()
+	tm.Data[topic] = struct{}{}
 }
 
 func (tm TopicSet) MarshalLogArray(encoder zapcore.ArrayEncoder) error {
-	for topic := range tm {
+	tm.Lock()
+	defer tm.Unlock()
+	for topic := range tm.Data {
 		encoder.AppendString(topic)
 	}
 	return nil
diff --git a/relay/wsconn.go b/relay/wsconn.go
index 57a78ae..a056e02 100644
--- a/relay/wsconn.go
+++ b/relay/wsconn.go
@@ -22,8 +22,8 @@ type client struct {
 	active    bool     // heartbeat related
 	role      RoleType // dapp or wallet
 	session   string   // session id
-	pubTopics TopicSet
-	subTopics TopicSet
+	pubTopics *TopicSet
+	subTopics *TopicSet
 
 	sendbuf chan SocketMessage // send buffer
 	ping    chan struct{}
diff --git a/relay/wsserver.go b/relay/wsserver.go
index ace6226..1df8d54 100644
--- a/relay/wsserver.go
+++ b/relay/wsserver.go
@@ -29,8 +29,8 @@ type WsServer struct {
 	redisConn    *redis.Client
 	redisSubConn *redis.PubSub
 
-	publishers  TopicClientSet
-	subscribers TopicClientSet
+	publishers  *TopicClientSet
+	subscribers *TopicClientSet
 
 	localCh chan SocketMessage // for handling message of local clients
 }
@@ -109,12 +109,12 @@ func (ws *WsServer) Run() {
 			switch message.Type {
 			case Pub:
 				// do not modify wsserver's local variable in seperate goroutine
-				message.client.pubTopics[message.Topic] = struct{}{}
+				message.client.pubTopics.Set(message.Topic)
 				ws.publishers.Set(message.Topic, message.client)
 				go ws.pubMessage(message)
 				log.Info("local message", zap.Any("client", message.client), zap.Any("message", message))
 			case Sub:
-				message.client.subTopics[message.Topic] = struct{}{}
+				message.client.subTopics.Set(message.Topic)
 				ws.subscribers.Set(message.Topic, message.client)
 				go ws.subMessage(message)
 				log.Info("local message", zap.Any("client", message.client), zap.Any("message", message))