From 4fb961cf3edac893267d3ad74410dd5cc1859a11 Mon Sep 17 00:00:00 2001
From: Antoine Pitrou <solipsis@pitrou.net>
Date: Thu, 5 Nov 2009 13:44:28 +0000
Subject: [PATCH] Merged revisions 76117 via svnmerge from
 svn+ssh://pythondev@svn.python.org/python/trunk

........
  r76117 | antoine.pitrou | 2009-11-05 14:42:29 +0100 (jeu., 05 nov. 2009) | 5 lines

  Issue #7264: Fix a possible deadlock when deallocating thread-local objects
  which are part of a reference cycle.
........
---
 Lib/_threading_local.py | 8 +++++---
 Lib/threading.py        | 4 ++++
 Misc/NEWS               | 3 +++
 3 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/Lib/_threading_local.py b/Lib/_threading_local.py
index 4eda630bbdc..243d84ef7ca 100644
--- a/Lib/_threading_local.py
+++ b/Lib/_threading_local.py
@@ -218,10 +218,12 @@ class local(_localbase):
         key = object.__getattribute__(self, '_local__key')
 
         try:
-            threads = list(threading.enumerate())
+            # We use the non-locking API since we might already hold the lock
+            # (__del__ can be called at any point by the cyclic GC).
+            threads = threading._enumerate()
         except:
-            # If enumerate fails, as it seems to do during
-            # shutdown, we'll skip cleanup under the assumption
+            # If enumerating the current threads fails, as it seems to do
+            # during shutdown, we'll skip cleanup under the assumption
             # that there is nothing to clean up.
             return
 
diff --git a/Lib/threading.py b/Lib/threading.py
index 1182f192269..18c28b7ffa4 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -815,6 +815,10 @@ def activeCount():
 
 active_count = activeCount
 
+def _enumerate():
+    # Same as enumerate(), but without the lock. Internal use only.
+    return _active.values() + _limbo.values()
+
 def enumerate():
     _active_limbo_lock.acquire()
     active = _active.values() + _limbo.values()
diff --git a/Misc/NEWS b/Misc/NEWS
index 7bcad726295..71d613bf6f9 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -24,6 +24,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #7264: Fix a possible deadlock when deallocating thread-local objects
+  which are part of a reference cycle.
+
 - Issue #7249: Methods of io.BytesIO now allow `long` as well as `int`
   arguments.