Fix adding to chanotify on blocking select

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

chanotify/chanotify.go

@@ -19,7 +19,7 @@ type dataPair struct {
 type Notifier struct {
 	c     chan string
 	chMap map[<-chan struct{}]*dataPair
-	exit  chan struct{}
+	ctrl  chan struct{}
 	m     sync.Mutex
 }
 
@@ -28,7 +28,7 @@ func New() *Notifier {
 	s := &Notifier{
 		c:     make(chan string),
 		chMap: make(map[<-chan struct{}]*dataPair),
-		exit:  make(chan struct{}),
+		ctrl:  make(chan struct{}),
 	}
 	go s.start()
 	return s
@@ -51,12 +51,13 @@ func (s *Notifier) Add(ch <-chan struct{}, id string) {
 		},
 	}
 	s.m.Unlock()
+	s.ctrl <- struct{}{}
 }
 
 // Close stops Notifier to listen for any notifications and closes its
 // "client-side" channel.
 func (s *Notifier) Close() {
-	close(s.exit)
+	close(s.ctrl)
 }
 
 func (s *Notifier) start() {
@@ -64,7 +65,10 @@ func (s *Notifier) start() {
 		c := s.createCase()
 		i, _, ok := reflect.Select(c)
 		if i == 0 {
-			// exit was closed, we can safely close output
+			if ok {
+				continue
+			}
+			// ctrl was closed, we can safely close output
 			close(s.c)
 			return
 		}
@@ -81,11 +85,11 @@ func (s *Notifier) start() {
 }
 
 func (s *Notifier) createCase() []reflect.SelectCase {
-	// put exit channel as 0 element of select
+	// put ctrl channel as 0 element of select
 	out := []reflect.SelectCase{
 		reflect.SelectCase{
 			Dir:  reflect.SelectRecv,
-			Chan: reflect.ValueOf(s.exit),
+			Chan: reflect.ValueOf(s.ctrl),
 		},
 	}
 	s.m.Lock()

chanotify/chanotify_test.go

@@ -78,3 +78,18 @@ func TestConcurrentNotifier(t *testing.T) {
 		}
 	}
 }
+
+func TestAddToBlocked(t *testing.T) {
+	s := New()
+	ch := make(chan struct{}, 1)
+	go func() {
+		// give some time to start first select
+		time.Sleep(1 * time.Second)
+		s.Add(ch, "1")
+		ch <- struct{}{}
+	}()
+	val := <-s.Chan()
+	if val != "1" {
+		t.Fatalf("Expected 1, got %s", val)
+	}
+}