From: Vinay Sajip <vinay_sajip@yahoo.co.uk>
Date: Fri, 4 Apr 2014 09:51:49 +0000 (+0100)
Subject: Issue #21149: Improved thread-safety in logging cleanup during interpreter shutdown.
X-Git-Tag: v3.4.1rc1~129
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=156307bfd67aacbdeb393c6bf831b6a63df92eb2;p=python

Issue #21149: Improved thread-safety in logging cleanup during interpreter shutdown.
---

diff --git a/Lib/logging/__init__.py b/Lib/logging/__init__.py
index 478c5afdae..181bc150d0 100644
--- a/Lib/logging/__init__.py
+++ b/Lib/logging/__init__.py
@@ -711,16 +711,17 @@ def _removeHandlerRef(wr):
     Remove a handler reference from the internal cleanup list.
     """
     # This function can be called during module teardown, when globals are
-    # set to None. If _acquireLock is None, assume this is the case and do
-    # nothing.
-    if (_acquireLock is not None and _handlerList is not None and
-        _releaseLock is not None):
-        _acquireLock()
+    # set to None. It can also be called from another thread. So we need to
+    # pre-emptively grab the necessary globals and check if they're None,
+    # to prevent race conditions and failures during interpreter shutdown.
+    acquire, release, handlers = _acquireLock, _releaseLock, _handlerList
+    if acquire and release and handlers:
+        acquire()
         try:
-            if wr in _handlerList:
-                _handlerList.remove(wr)
+            if wr in handlers:
+                handlers.remove(wr)
         finally:
-            _releaseLock()
+            release()
 
 def _addHandlerRef(handler):
     """
diff --git a/Misc/NEWS b/Misc/NEWS
index 9e59154011..4f27a991e9 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -27,6 +27,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #21149: Improved thread-safety in logging cleanup during interpreter
+  shutdown. Thanks to Devin Jeanpierre for the patch.
+
 - Issue #20145: `assertRaisesRegex` and `assertWarnsRegex` now raise a
   TypeError if the second argument is not a string or compiled regex.