Issue #12467: warnings: fix a race condition if a warning is emitted at

shutdown, if globals()['__file__'] is None.

Lib/test/test_warnings.py

@@ -530,6 +530,18 @@ class _WarningsTests(BaseTest):
         assert expected_line
         self.assertEqual(second_line, expected_line)
 
+    def test_filename_none(self):
+        # issue #12467: race condition if a warning is emitted at shutdown
+        globals_dict = globals()
+        oldfile = globals_dict['__file__']
+        try:
+            with original_warnings.catch_warnings(module=self.module) as w:
+                self.module.filterwarnings("always", category=UserWarning)
+                globals_dict['__file__'] = None
+                self.module.warn('test', UserWarning)
+        finally:
+            globals_dict['__file__'] = oldfile
+
 
 class WarningsDisplayTests(unittest.TestCase):
 

Misc/NEWS

@@ -18,6 +18,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #12467: warnings: fix a race condition if a warning is emitted at
+  shutdown, if globals()['__file__'] is None.
+
 - Issue #12352: Fix a deadlock in multiprocessing.Heap when a block is freed by
   the garbage collector while the Heap lock is held.
 

Python/_warnings.c

@@ -491,7 +491,7 @@ setup_context(Py_ssize_t stack_level, PyObject **filename, int *lineno,
 
     /* Setup filename. */
     *filename = PyDict_GetItemString(globals, "__file__");
-    if (*filename != NULL) {
+    if (*filename != NULL && PyString_Check(*filename)) {
             Py_ssize_t len = PyString_Size(*filename);
         const char *file_str = PyString_AsString(*filename);
             if (file_str == NULL || (len < 0 && PyErr_Occurred()))