From e0c8512012f87b7a2149a4c0a0c65b1cbd0b9a33 Mon Sep 17 00:00:00 2001
From: Victor Stinner <victor.stinner@gmail.com>
Date: Mon, 21 Aug 2017 23:24:40 +0200
Subject: [PATCH] bpo-31238: pydoc ServerThread.stop() clears ref cycle

ServerThread.stop() now explicitly sets its docserver attribute to
None to break a reference cycle.
---
 Lib/pydoc.py | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/Lib/pydoc.py b/Lib/pydoc.py
index 39db3915dc2cac9..892cdb49f6ffa39 100644
--- a/Lib/pydoc.py
+++ b/Lib/pydoc.py
@@ -2266,6 +2266,9 @@ def ready(self, server):
         def stop(self):
             """Stop the server and this thread nicely"""
             self.docserver.quit = True
+            # explicitly break a reference cycle: DocServer.callback
+            # has indirectly a reference to ServerThread.
+            self.docserver = None
             self.serving = False
             self.url = None