add comments.

Author: ExplodingDragon

services/packages/arch/repository.go

@@ -104,6 +104,7 @@ func NewFileSign(ctx context.Context, ownerID int64, input io.Reader) (*packages
 
 // BuildPacmanDB Create db signature cache
 func BuildPacmanDB(ctx context.Context, ownerID int64, group, arch string) error {
+	// Prevent `update/delete` and `cron clean task` from running concurrently.
 	lock, err := globallock.Lock(ctx, fmt.Sprintf("pkg_arch_db_%s", group))
 	if err != nil {
 		return err