--- a/mercurial/commandserver.py	Sat Jul 15 15:01:29 2017 +0900
+++ b/mercurial/commandserver.py	Sun Jul 16 04:39:32 2017 -0700
@@ -519,6 +519,7 @@
                         self.ui.traceback(force=True)
                     finally:
                         os._exit(255)
+        selector.close()
 
     def _sigchldhandler(self, signal, frame):
         self._reapworkers(os.WNOHANG)