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.

https://github.com/python/cpython/commit/243fd01047ddce1a7eb0f99a49732d123e942c63

Resolves: rhbz#1959459

diff --git a/Lib/threading.py b/Lib/threading.py

index 0ab1e46..7ab9ad8 100644

--- a/Lib/threading.py

+++ b/Lib/threading.py

@@ -727,8 +727,11 @@ _counter() # Consume 0 so first non-main thread has id 1.

 def _newname(template="Thread-%d"):

     return 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()

@@ -1325,7 +1328,7 @@ def _after_fork():

     # Reset _active_limbo_lock, in case we forked while the lock was held

     # by another (non-forked) thread.  http://bugs.python.org/issue874900

     global _active_limbo_lock, _main_thread

-    _active_limbo_lock = _allocate_lock()

+    _active_limbo_lock = RLock()

     # fork() only copied the current thread; clear references to others.

     new_active = {}