safe access to shared collections

Author: Ivan Kh

server/src/main/main.go

@@ -39,11 +39,9 @@ func (cr *ChatRoom) Init(db *bolt.DB) {
         return
       }
 
-      chat.clientsMtx.Lock()
-      client, ok := cr.namedClients[to]
-      chat.clientsMtx.Unlock()
+      client := getNamedClient(to)
 
-      if ok == false {
+      if client == nil {
         fmt.Println("Can't find " + to)
       } else {
         which := message.Which
@@ -63,6 +61,45 @@ func (cr *ChatRoom) Init(db *bolt.DB) {
   }()
 }
 
+func getClient(sessionId string) (*Client) {
+  var result *Client
+
+  //fmt.Println("getClient will lock")
+  chat.clientsMtx.Lock()
+  result = chat.clients[sessionId]
+  chat.clientsMtx.Unlock()
+  //fmt.Println("getClient did lock")
+
+  return result
+}
+
+func setClient(sessionId string, client *Client) {
+  //fmt.Println("setClient lock")
+  chat.clientsMtx.Lock()
+  chat.clients[sessionId] = client
+  chat.clientsMtx.Unlock()
+  //fmt.Println("setClient unlock")
+}
+
+func getNamedClient(name string) (*Client) {
+  var result *Client
+
+  //fmt.Println("getNamedClient lock")
+  chat.clientsMtx.Lock()
+  result = chat.namedClients[name]
+  chat.clientsMtx.Unlock()
+  //fmt.Println("getNamedClient unlock")
+
+  return result
+}
+
+func setNamedClient(name string, client *Client) {
+  //fmt.Println("setNamedClient lock")
+  chat.clientsMtx.Lock()
+  chat.namedClients[name] = client
+  chat.clientsMtx.Unlock()
+  //fmt.Println("setNamedClient unlock")
+}
 // Client
 
 type Client struct {
@@ -156,6 +193,7 @@ func wsHandler(w http.ResponseWriter, r *http.Request) {
     for {
       _, data, err := conn.ReadMessage()
       if err != nil {
+        fmt.Println("Error ", err)
         fmt.Println("\nConnection closed for session " + sessionId)
         updatePresence(sessionId, false)
         return
@@ -202,7 +240,7 @@ func wsHandler(w http.ResponseWriter, r *http.Request) {
       case Haber_CALL_STOP:
         fallthrough
       case Haber_FILE:
-        if _,ok := chat.clients[sessionId]; ok {
+        if getClient(sessionId) != nil {
           forward(sessionId, haber)
         }
       }
@@ -211,14 +249,16 @@ func wsHandler(w http.ResponseWriter, r *http.Request) {
 }
 
 func updatePresence(sessionId string, online bool) {
-  if client, ok := chat.clients[sessionId]; ok {
+  client := getClient(sessionId)
+
+  if client != nil {
     if online == client.online {
       fmt.Printf("updatePresence: %s is already %t\n", client.name, client.online)
       return
     }
     fmt.Println("updatePresence sessionId=" + sessionId)
     client.online = online
-    chat.clients[sessionId] = client
+    setClient(sessionId, client)
     // inform subscribers
     from := client.name
     fmt.Println("\t from=" + from)
@@ -274,26 +314,23 @@ func remove(s []string, r string) []string {
 
 func receivedUsername(conn *websocket.Conn, username string) string {
   fmt.Println("\nreceivedUsername: " + username)
-  defer chat.clientsMtx.Unlock()
-  chat.clientsMtx.Lock()
 
   sessionId := createSessionId()
 
-  var client *Client
-  if c, ok := chat.namedClients[username]; ok {
-    client = c
-  } else {
+  client := getNamedClient(username)
+  if client == nil {
     client = &Client{
       name:     username,
       sessions: make(map[string]*websocket.Conn),
       online: false,
     }
+    setNamedClient(username, client)
+    fmt.Println("new client for ", username)
   }
   client.sessions[sessionId] = conn
-  chat.namedClients[username] = client
   fmt.Println("new client name=" + client.name + " session=" + sessionId)
   client.Load(chat.db)
-  chat.clients[sessionId] = client
+  setClient(sessionId, client)
   sendContacts(client, sessionId)
   updatePresence(sessionId, true)
 
@@ -302,8 +339,7 @@ func receivedUsername(conn *websocket.Conn, username string) string {
 
 func sendContacts(client *Client, sessionId string) {
   for _,contact := range client.contacts {
-    _,ok := chat.namedClients[contact.Name]
-    contact.Online = ok
+    contact.Online = getNamedClient(contact.Name) != nil
   }
 
   buds := &Haber {
@@ -316,14 +352,14 @@ func sendContacts(client *Client, sessionId string) {
 }
 
 func forward(sessionId string, haber *Haber) {
-  sourceClient := chat.clients[sessionId]
+  sourceClient := getClient(sessionId)
   haber.From = sourceClient.name
   chat.queue <- *haber  // forward to all devices with source's and destination's names
 }
 
 func receivedContacts(sessionId string, haber *Haber) {
   fmt.Println("receivedContacts for session " + sessionId)
-  client := chat.clients[sessionId]
+  client := getClient(sessionId)
   client.contacts = haber.GetContacts()
   client.subscribeToContacts()
   client.Save(chat.db, haber)