Return []error from Stop() channel, allow recursive stop groups

pkg/prometheus/server.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 
 	"github.com/chihaya/chihaya/pkg/log"
+	"github.com/chihaya/chihaya/pkg/stop"
 	"github.com/prometheus/client_golang/prometheus"
 )
 
@@ -17,17 +18,13 @@ type Server struct {
 }
 
 // Stop shuts down the server.
-func (s *Server) Stop() <-chan error {
-	c := make(chan error)
+func (s *Server) Stop() stop.Result {
+	c := make(stop.Channel)
 	go func() {
-		if err := s.srv.Shutdown(context.Background()); err != nil {
-			c <- err
-		} else {
-			close(c)
-		}
+		c.Done(s.srv.Shutdown(context.Background()))
 	}()
 
-	return c
+	return c.Result()
 }
 
 // NewServer creates a new instance of a Prometheus server that asynchronously