From 9b51d5254d9e7e6a4749ab6e1dfc8aad14c1448d Mon Sep 17 00:00:00 2001
From: Akinori Hattori <hattya@gmail.com>
Date: Sat, 15 Oct 2022 10:18:20 +0900
Subject: [PATCH] gh-71936: Fix race condition in multiprocessing.Pool

Proxes of shared objects register a Finalizer in BaseProxy._incref(), and it
will call BaseProxy._decref() when it is GCed. This may cause a race condition
with Pool(maxtasksperchild=None) on Windows.

A connection will be closed and raised TypeError when a GC occurs between
_ConnectionBase._check_writable() and _ConnectionBase._send_bytes() in
_ConnectionBase.send() in the second or later task.

BaseProxy does not count references well.
---
 Lib/multiprocessing/managers.py                          | 9 +++++----
 Misc/ACKS                                                | 1 +
 .../2022-10-15-10-18-20.gh-issue-71936.MzJjc_.rst        | 1 +
 3 files changed, 7 insertions(+), 4 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2022-10-15-10-18-20.gh-issue-71936.MzJjc_.rst

diff --git a/Lib/multiprocessing/managers.py b/Lib/multiprocessing/managers.py
index b6534939b4d98b..85b26517593f87 100644
--- a/Lib/multiprocessing/managers.py
+++ b/Lib/multiprocessing/managers.py
@@ -850,20 +850,21 @@ def _incref(self):
         dispatch(conn, None, 'incref', (self._id,))
         util.debug('INCREF %r', self._token.id)
 
-        self._idset.add(self._id)
+        refid = f'{self._id}.{id(self)}'
+        self._idset.add(refid)
 
         state = self._manager and self._manager._state
 
         self._close = util.Finalize(
             self, BaseProxy._decref,
-            args=(self._token, self._authkey, state,
+            args=(self._token, refid, self._authkey, state,
                   self._tls, self._idset, self._Client),
             exitpriority=10
             )
 
     @staticmethod
-    def _decref(token, authkey, state, tls, idset, _Client):
-        idset.discard(token.id)
+    def _decref(token, refid, authkey, state, tls, idset, _Client):
+        idset.discard(refid)
 
         # check whether manager is still alive
         if state is None or state.value == State.STARTED:
diff --git a/Misc/ACKS b/Misc/ACKS
index ec5e326847b8ca..4c7f880354b2c0 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -706,6 +706,7 @@ Larry Hastings
 Tim Hatch
 Zac Hatfield-Dodds
 Shane Hathaway
+Akinori Hattori
 Michael Haubenwallner
 Janko Hauser
 Flavian Hautbois
diff --git a/Misc/NEWS.d/next/Library/2022-10-15-10-18-20.gh-issue-71936.MzJjc_.rst b/Misc/NEWS.d/next/Library/2022-10-15-10-18-20.gh-issue-71936.MzJjc_.rst
new file mode 100644
index 00000000000000..ac1081e060ba2d
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2022-10-15-10-18-20.gh-issue-71936.MzJjc_.rst
@@ -0,0 +1 @@
+Fix a race condition in :class:`multiprocessing.Pool`.