Merge pull request #863 from nullaus/fix-data-race-schema

Fix data race between event processing and session when concurrent go…

events.go

@@ -106,6 +106,9 @@ func (s *Session) handleEvent(framer *framer) {
 }
 
 func (s *Session) handleSchemaEvent(frames []frame) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
 	if s.schemaDescriber == nil {
 		return
 	}