Close previous conn when switching to new conn.

This is a different attempt at
#350. Feels a bit cleaner,
i. e. if the internal `conn atomic.Value` is replaced, the previous
`conn` is closed before doing that.

signalclient.go

@@ -38,9 +38,9 @@ const PROTOCOL = 8
 type SignalClient struct {
 	conn            atomic.Value // *websocket.Conn
 	lock            sync.Mutex
-	isClosed        atomic.Bool
 	isStarted       atomic.Bool
 	pendingResponse *livekit.SignalResponse
+	readerClosedCh  chan struct{}
 
 	OnClose                 func()
 	OnAnswer                func(sd webrtc.SessionDescription)
@@ -66,6 +66,7 @@ func (c *SignalClient) Start() {
 	if c.isStarted.Swap(true) {
 		return
 	}
+	c.readerClosedCh = make(chan struct{})
 	go c.readWorker()
 }
 
@@ -139,7 +140,7 @@ func (c *SignalClient) Join(urlPrefix string, token string, params *ConnectParam
 			return nil, errors.New(errString)
 		}
 	}
-	c.isClosed.Store(false)
+	c.Close() // close previous conn, if any
 	c.conn.Store(conn)
 
 	// server should send join as soon as connected
@@ -172,12 +173,13 @@ func (c *SignalClient) Join(urlPrefix string, token string, params *ConnectParam
 }
 
 func (c *SignalClient) Close() {
-	if c.isClosed.Swap(true) {
-		return
-	}
+	isStarted := c.IsStarted()
 	if conn := c.websocketConn(); conn != nil {
 		_ = conn.Close()
 	}
+	if isStarted {
+		<-c.readerClosedCh
+	}
 }
 
 func (c *SignalClient) SendICECandidate(candidate webrtc.ICECandidateInit, target livekit.SignalTarget) error {
@@ -263,10 +265,6 @@ func (c *SignalClient) SendUpdateParticipantMetadata(metadata *livekit.UpdatePar
 }
 
 func (c *SignalClient) readResponse() (*livekit.SignalResponse, error) {
-	if c.isClosed.Load() {
-		return nil, io.EOF
-	}
-
 	conn := c.websocketConn()
 	if conn == nil {
 		return nil, errors.New("cannot read response before join")
@@ -351,15 +349,17 @@ func (c *SignalClient) readWorker() {
 		if c.OnClose != nil {
 			c.OnClose()
 		}
+		c.conn.Store((*websocket.Conn)(nil))
+		close(c.readerClosedCh)
 	}()
 	if pending := c.pendingResponse; pending != nil {
 		c.handleResponse(pending)
 		c.pendingResponse = nil
 	}
-	for !c.isClosed.Load() {
+	for {
 		res, err := c.readResponse()
 		if err != nil {
-			if !isIgnoredWebsocketError(err) && !c.isClosed.Load() {
+			if !isIgnoredWebsocketError(err) {
 				logger.Infow("error while reading from signal client", "err", err)
 			}
 			return