Move server shutdown into group.go.

group/group.go

@@ -701,8 +701,12 @@ func kickall(g *Group, message string) {
 	})
 }
 
-func (g *Group) Shutdown(message string) {
-	kickall(g, message)
+func Shutdown(message string) {
+	Range(func(g *Group) bool {
+		g.SetLocked(true, message)
+		kickall(g, message)
+		return true
+	})
 }
 
 type warner interface {

webserver/webserver.go

@@ -70,10 +70,7 @@ func Serve(address string, dataDir string) error {
 		}
 	}
 	s.RegisterOnShutdown(func() {
-		group.Range(func(g *group.Group) bool {
-			go g.Shutdown("server is shutting down")
-			return true
-		})
+		group.Shutdown("server is shutting down")
 	})
 
 	server.Store(s)