Remove use of mutex around done chan

cmux.go

@@ -113,7 +113,6 @@ type cMux struct {
 	donec       chan struct{}
 	sls         []matchersListener
 	readTimeout time.Duration
-	mu          sync.Mutex
 }
 
 func matchersToMatchWriters(matchers []Matcher) []MatchWriter {
@@ -149,7 +148,7 @@ func (m *cMux) Serve() error {
 	var wg sync.WaitGroup
 
 	defer func() {
-		m.closeDoneChanLocked()
+		m.closeDoneChan()
 		wg.Wait()
 
 		for _, sl := range m.sls {
@@ -162,13 +161,16 @@ func (m *cMux) Serve() error {
 	}()
 
 	for {
-		c, err := m.root.Accept()
-		if err != nil {
 		select {
-			case <-m.getDoneChan():
+		case <-m.donec:
 			// cmux was closed with cmux.Close()
 			return nil
+		default:
+			// do nothing
 		}
+
+		c, err := m.root.Accept()
+		if err != nil {
 			if !m.handleErr(err) {
 				return err
 			}
@@ -197,7 +199,7 @@ func (m *cMux) serve(c net.Conn, donec <-chan struct{}, wg *sync.WaitGroup) {
 				}
 				select {
 				case sl.l.connc <- muc:
-				case <-m.getDoneChan():
+				case <-m.donec:
 					_ = c.Close()
 				}
 				return
@@ -213,31 +215,15 @@ func (m *cMux) serve(c net.Conn, donec <-chan struct{}, wg *sync.WaitGroup) {
 }
 
 func (m *cMux) Close() {
-	m.mu.Lock()
-	defer m.mu.Unlock()
-	m.closeDoneChanLocked()
+	m.closeDoneChan()
 }
 
-func (m *cMux) getDoneChan() chan struct{} {
-	m.mu.Lock()
-	defer m.mu.Unlock()
-	return m.getDoneChanLocked()
-}
-
-func (m *cMux) getDoneChanLocked() chan struct{} {
-	if m.donec == nil {
-		m.donec = make(chan struct{})
-	}
-	return m.donec
-}
-
-func (m *cMux) closeDoneChanLocked() {
-	ch := m.getDoneChanLocked()
+func (m *cMux) closeDoneChan() {
 	select {
-	case <-ch:
+	case <-m.donec:
 		// Already closed. Don't close again
 	default:
-		close(ch)
+		close(m.donec)
 	}
 }