clientv3: non-recursive watch

Signed-off-by: Ted Yu <yuzhihong@gmail.com>

clientv3/watch.go

@@ -311,55 +311,63 @@ func (w *watcher) Watch(ctx context.Context, key string, opts ...OpOption) Watch
 	ok := false
 	ctxKey := streamKeyFromCtx(ctx)
 
-	// find or allocate appropriate grpc watch stream
-	w.mu.Lock()
-	if w.streams == nil {
-		// closed
-		w.mu.Unlock()
-		ch := make(chan WatchResponse)
-		close(ch)
-		return ch
-	}
-	wgs := w.streams[ctxKey]
-	if wgs == nil {
-		wgs = w.newWatcherGrpcStream(ctx)
-		w.streams[ctxKey] = wgs
-	}
-	donec := wgs.donec
-	reqc := wgs.reqc
-	w.mu.Unlock()
-
-	// couldn't create channel; return closed channel
-	closeCh := make(chan WatchResponse, 1)
-
-	// submit request
-	select {
-	case reqc <- wr:
-		ok = true
-	case <-wr.ctx.Done():
-	case <-donec:
-		if wgs.closeErr != nil {
-			closeCh <- WatchResponse{Canceled: true, closeErr: wgs.closeErr}
-			break
+	var closeCh chan WatchResponse
+	for {
+		// find or allocate appropriate grpc watch stream
+		w.mu.Lock()
+		if w.streams == nil {
+			// closed
+			w.mu.Unlock()
+			ch := make(chan WatchResponse)
+			close(ch)
+			return ch
 		}
-		// retry; may have dropped stream from no ctxs
-		return w.Watch(ctx, key, opts...)
-	}
+		wgs := w.streams[ctxKey]
+		if wgs == nil {
+			wgs = w.newWatcherGrpcStream(ctx)
+			w.streams[ctxKey] = wgs
+		}
+		donec := wgs.donec
+		reqc := wgs.reqc
+		w.mu.Unlock()
 
-	// receive channel
-	if ok {
+		// couldn't create channel; return closed channel
+		if closeCh == nil {
+			closeCh = make(chan WatchResponse, 1)
+		}
+
+		// submit request
 		select {
-		case ret := <-wr.retc:
-			return ret
-		case <-ctx.Done():
+		case reqc <- wr:
+			ok = true
+		case <-wr.ctx.Done():
+			ok = false
 		case <-donec:
+			ok = false
 			if wgs.closeErr != nil {
 				closeCh <- WatchResponse{Canceled: true, closeErr: wgs.closeErr}
 				break
 			}
 			// retry; may have dropped stream from no ctxs
-			return w.Watch(ctx, key, opts...)
+			continue
 		}
+
+		// receive channel
+		if ok {
+			select {
+			case ret := <-wr.retc:
+				return ret
+			case <-ctx.Done():
+			case <-donec:
+				if wgs.closeErr != nil {
+					closeCh <- WatchResponse{Canceled: true, closeErr: wgs.closeErr}
+					break
+				}
+				// retry; may have dropped stream from no ctxs
+				continue
+			}
+		}
+		break
 	}
 
 	close(closeCh)