Merge pull request #4242 from xigang/release-1.5

cherry pick of #4212: Fix lock race affects watch RestChan not close, causing client watch api to hang.

pkg/search/proxy/store/util.go

@@ -193,9 +193,21 @@ func (w *watchMux) AddSource(watcher watch.Interface, decorator func(watch.Event
 
 // Start run the watcher
 func (w *watchMux) Start() {
-	for _, source := range w.sources {
-		go w.startWatchSource(source.watcher, source.decorator)
+	wg := sync.WaitGroup{}
+	for i := range w.sources {
+		source := w.sources[i]
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			w.startWatchSource(source.watcher, source.decorator)
+		}()
 	}
+
+	go func() {
+		// close result chan after all goroutines exit, avoiding data race.
+		defer close(w.result)
+		wg.Wait()
+	}()
 }
 
 // ResultChan implements watch.Interface
@@ -218,7 +230,6 @@ func (w *watchMux) Stop() {
 	case <-w.done:
 	default:
 		close(w.done)
-		close(w.result)
 	}
 }
 
@@ -244,19 +255,8 @@ func (w *watchMux) startWatchSource(source watch.Interface, decorator func(watch
 		select {
 		case <-w.done:
 			return
-		default:
+		case w.result <- copyEvent:
 		}
-
-		func() {
-			w.lock.RLock()
-			defer w.lock.RUnlock()
-			select {
-			case <-w.done:
-				return
-			default:
-				w.result <- copyEvent
-			}
-		}()
 	}
 }