gh-140080: Clear atexit callbacks when memory allocation fails during finalization (GH-140103)

This fixes a regression introduced by GH-136004, in which finalization would hang while executing atexit handlers if the system was out of memory.
---------
Signed-off-by: yihong0618 <zouzou0208@gmail.com>
Co-authored-by: Peter Bierma <zintensitydev@gmail.com>
Co-authored-by: Victor Stinner <vstinner@python.org>

Author: 3 people

Lib/test/test_atexit.py

@@ -1,9 +1,11 @@
 importatexit
 importos
+importsubprocess
 importtextwrap
 importunittest
 fromtestimportsupport
-fromtest.supportimportscript_helper
+fromtest.supportimportSuppressCrashReport, script_helper
+fromtest.supportimportos_helper
 fromtest.supportimportthreading_helper
 
 classGeneralTest(unittest.TestCase):
@@ -189,6 +191,37 @@ def callback():
 self.assertEqual(os.read(r, len(expected)), expected)
 os.close(r)
 
+# Python built with Py_TRACE_REFS fail with a fatal error in
+# _PyRefchain_Trace() on memory allocation error.
+@unittest.skipIf(support.Py_TRACE_REFS, 'cannot test Py_TRACE_REFS build')
+deftest_atexit_with_low_memory(self):
+# gh-140080: Test that setting low memory after registering an atexit
+# callback doesn't cause an infinite loop during finalization.
+code=textwrap.dedent("""
+ import atexit
+ import _testcapi
+
+ def callback():
+ print("hello")
+
+ atexit.register(callback)
+ # Simulate low memory condition
+ _testcapi.set_nomemory(0)
+ """)
+
+withos_helper.temp_dir() astemp_dir:
+script=script_helper.make_script(temp_dir, 'test_atexit_script', code)
+withSuppressCrashReport():
+withscript_helper.spawn_python(script,
+stderr=subprocess.PIPE) asproc:
+proc.wait()
+stdout=proc.stdout.read()
+stderr=proc.stderr.read()
+
+self.assertIn(proc.returncode, (0, 1))
+self.assertNotIn(b"hello", stdout)
+self.assertIn(b"MemoryError", stderr)
+
 
 if__name__=="__main__":
 unittest.main()

Misc/NEWS.d/next/Core_and_Builtins/2025-10-14-20-18-31.gh-issue-140080.8ROjxW.rst

@@ -0,0 +1 @@
+Fix hang during finalization when attempting to call :mod:`atexit` handlers under no memory.

Modules/atexitmodule.c

@@ -112,6 +112,7 @@ atexit_callfuncs(struct atexit_state *state)
  {
 PyErr_FormatUnraisable("Exception ignored while "
 "copying atexit callbacks");
+atexit_cleanup(state);
 return;
  }