[Python-checkins] bpo-44422: Fix threading.enumerate() reentrant call (GH-26727)

[vstinner]

https://github.com/python/cpython/commit/243fd01047ddce1a7eb0f99a49732d123e942c63
commit: 243fd01047ddce1a7eb0f99a49732d123e942c63
branch: main
author: Victor Stinner <vstinner at python.org>
committer: vstinner <vstinner at python.org>
date: 2021-06-15T16:14:24+02:00
summary:

bpo-44422: Fix threading.enumerate() reentrant call (GH-26727)

The threading.enumerate() function now uses a reentrant lock to
prevent a hang on reentrant call.

files:
A Misc/NEWS.d/next/Library/2021-06-14-23-28-17.bpo-44422.BlWOgv.rst
M Lib/threading.py

diff --git a/Lib/threading.py b/Lib/threading.py
index 6c3d49c2d5267..766011fa0312b 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -775,8 +775,11 @@ class BrokenBarrierError(RuntimeError):
 def _newname(name_template):
     return name_template % _counter()
 
-# Active thread administration
-_active_limbo_lock = _allocate_lock()
+# Active thread administration.
+#
+# bpo-44422: Use a reentrant lock to allow reentrant calls to functions like
+# threading.enumerate().
+_active_limbo_lock = RLock()
 _active = {}    # maps thread id to Thread object
 _limbo = {}
 _dangling = WeakSet()
@@ -1564,7 +1567,7 @@ def _after_fork():
     # by another (non-forked) thread.  http://bugs.python.org/issue874900
     global _active_limbo_lock, _main_thread
     global _shutdown_locks_lock, _shutdown_locks
-    _active_limbo_lock = _allocate_lock()
+    _active_limbo_lock = RLock()
 
     # fork() only copied the current thread; clear references to others.
     new_active = {}
diff --git a/Misc/NEWS.d/next/Library/2021-06-14-23-28-17.bpo-44422.BlWOgv.rst b/Misc/NEWS.d/next/Library/2021-06-14-23-28-17.bpo-44422.BlWOgv.rst
new file mode 100644
index 0000000000000..09bace01fc779
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2021-06-14-23-28-17.bpo-44422.BlWOgv.rst
@@ -0,0 +1,3 @@
+The :func:`threading.enumerate` function now uses a reentrant lock to
+prevent a hang on reentrant call.
+Patch by Victor Stinner.