https://github.com/python/cpython/commit/1822f59dc783bc11ed478b78d822537a0425cf74
commit: 1822f59dc783bc11ed478b78d822537a0425cf74
branch: 3.13
author: Serhiy Storchaka <[email protected]>
committer: serhiy-storchaka <[email protected]>
date: 2026-01-12T10:05:09Z
summary:
[3.13] gh-142881: Fix concurrent and reentrant call of atexit.unregister()
(GH-142901) (GH-143722)
(cherry picked from commit dbd10a6c29ba1cfc9348924a090b5dc514470002)
files:
A Misc/NEWS.d/next/Library/2025-12-17-20-18-17.gh-issue-142881.5IizIQ.rst
M Lib/test/_test_atexit.py
M Modules/atexitmodule.c
diff --git a/Lib/test/_test_atexit.py b/Lib/test/_test_atexit.py
index 490b0686a0c179..2e961d6a4854a0 100644
--- a/Lib/test/_test_atexit.py
+++ b/Lib/test/_test_atexit.py
@@ -148,6 +148,40 @@ def __eq__(self, other):
atexit.unregister(Evil())
atexit._clear()
+ def test_eq_unregister(self):
+ # Issue #112127: callback's __eq__ may call unregister
+ def f1():
+ log.append(1)
+ def f2():
+ log.append(2)
+ def f3():
+ log.append(3)
+
+ class Pred:
+ def __eq__(self, other):
+ nonlocal cnt
+ cnt += 1
+ if cnt == when:
+ atexit.unregister(what)
+ if other is f2:
+ return True
+ return False
+
+ for what, expected in (
+ (f1, [3]),
+ (f2, [3, 1]),
+ (f3, [1]),
+ ):
+ for when in range(1, 4):
+ with self.subTest(what=what.__name__, when=when):
+ cnt = 0
+ log = []
+ for f in (f1, f2, f3):
+ atexit.register(f)
+ atexit.unregister(Pred())
+ atexit._run_exitfuncs()
+ self.assertEqual(log, expected)
+
if __name__ == "__main__":
unittest.main()
diff --git
a/Misc/NEWS.d/next/Library/2025-12-17-20-18-17.gh-issue-142881.5IizIQ.rst
b/Misc/NEWS.d/next/Library/2025-12-17-20-18-17.gh-issue-142881.5IizIQ.rst
new file mode 100644
index 00000000000000..02f22d367bd831
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2025-12-17-20-18-17.gh-issue-142881.5IizIQ.rst
@@ -0,0 +1 @@
+Fix concurrent and reentrant call of :func:`atexit.unregister`.
diff --git a/Modules/atexitmodule.c b/Modules/atexitmodule.c
index 93d4c4ede32513..23fcc1b9d35dc0 100644
--- a/Modules/atexitmodule.c
+++ b/Modules/atexitmodule.c
@@ -57,6 +57,9 @@ static void
atexit_delete_cb(struct atexit_state *state, int i)
{
atexit_py_callback *cb = state->callbacks[i];
+ if (cb == NULL) {
+ return;
+ }
state->callbacks[i] = NULL;
Py_DECREF(cb->func);
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