Merge pull request #1333 from grafana/issue_1332

Prevent blocked go routines to hang forever (issue #1332)

Author: replay

api/cluster.go

@@ -415,35 +415,30 @@ func (s *Server) peerQuerySpeculativeChan(ctx context.Context, data cluster.Trac
 		reqCtx, cancel := context.WithCancel(ctx)
 		defer cancel()
 
-		originalPeers := make(map[string]struct{}, len(peerGroups))
-		receivedResponses := make(map[int32]struct{}, len(peerGroups))
-
-		responses := make(chan struct {
+		type response struct {
 			shardGroup int32
 			data       PeerResponse
 			err        error
-		}, 1)
+		}
+
+		responses := make(chan response)
+		originalPeers := make(map[string]struct{}, len(peerGroups))
+		receivedResponses := make(map[int32]struct{}, len(peerGroups))
 
 		askPeer := func(shardGroup int32, peer cluster.Node) {
 			log.Debugf("HTTP Render querying %s%s", peer.GetName(), path)
 			buf, err := peer.Post(reqCtx, name, path, data)
+			if err != nil {
+				cancel()
+				log.Errorf("HTTP Render error querying %s%s: %q", peer.GetName(), path, err)
+			}
 
 			select {
 			case <-ctx.Done():
 				return
-			default:
-				// Not canceled, continue
-			}
-
-			if err != nil {
-				cancel()
-				log.Errorf("HTTP Render error querying %s%s: %q", peer.GetName(), path, err)
+			case responses <- response{shardGroup, PeerResponse{peer, buf}, err}:
+				return
 			}
-			responses <- struct {
-				shardGroup int32
-				data       PeerResponse
-				err        error
-			}{shardGroup, PeerResponse{peer, buf}, err}
 		}
 
 		for group, peers := range peerGroups {