gh-136421: Fix crash in _datetime when initialized/finalized concurrently

Lib/test/datetimetester.py

@@ -7295,6 +7295,28 @@ def test_update_type_cache(self):
             """)
         script_helper.assert_python_ok('-c', script)
 
+    @unittest.skipIf(_interpreters is None, "missing _interpreters module")
+    def test_static_type_concurrent_init_fini(self):
+        # gh-136421
+        script = textwrap.dedent("""
+            import threading
+            import _interpreters
+
+            def run(id):
+                _interpreters.exec(id, "import _datetime; print('a', end='')")
+                _interpreters.destroy(id)
+
+            ids = [_interpreters.create() for i in range(10)]
+            ts = [threading.Thread(target=run, args=(id,)) for id in ids]
+            for t in ts:
+                t.start()
+            for t in ts:
+                t.join()
+            """)
+        _, out, err = script_helper.assert_python_ok('-c', script)
+        self.assertEqual(out, b'a' * 10)
+        self.assertEqual(err, b'')
+
 
 def load_tests(loader, standard_tests, pattern):
     standard_tests.addTest(ZoneInfoCompleteTest())

Misc/NEWS.d/next/Library/2025-07-13-01-02-31.gh-issue-136421.5HKeoS.rst

@@ -0,0 +1,2 @@
+Fix crash in :mod:`datetime` when its static types are initialized or
+finalized by multiple interpreters concurrently.

Modules/_datetimemodule.c

@@ -7335,6 +7335,11 @@ init_static_types(PyInterpreterState *interp, int reloading)
     if (reloading) {
         return 0;
     }
+    if (_Py_IsMainInterpreter(interp)
+        && PyType_HasFeature(&PyDateTime_DateType, Py_TPFLAGS_READY)) {
+        // This function was already called from PyInit__datetime()
+        return 0;
+    }
 
     // `&...` is not a constant expression according to a strict reading
     // of C standards. Fill tp_base at run-time rather than statically.
@@ -7564,6 +7569,11 @@ static PyModuleDef datetimemodule = {
 PyMODINIT_FUNC
 PyInit__datetime(void)
 {
+    PyInterpreterState *interp = PyInterpreterState_Get();
+    // gh-136421: Ensure static types are fully finalized at the shutdown of
+    // the main interpreter rather than subinterpreters for concurrency.
+    assert(_Py_IsMainInterpreter(interp));
+    init_static_types(interp, 0);
     return PyModuleDef_Init(&datetimemodule);
 }