python · ericsnowcurrently · May 6, 2023 · Nov 3, 2022 · Nov 4, 2022 · May 5, 2023
@@ -1861,6 +1861,26 @@ def test_multi_init_extension_non_isolated_compat(self):
         with self.subTest(f'{modname}: not strict'):
             self.check_compatible_here(modname, filename, strict=False)
 
    @unittest.skipIf(_testmultiphase is None, "test requires _testmultiphase module")
+    def test_multi_init_extension_per_interpreter_gil_compat(self):
+        modname = '_test_shared_gil_only'
+        filename = _testmultiphase.__file__
+        loader = ExtensionFileLoader(modname, filename)
+        spec = importlib.util.spec_from_loader(modname, loader)
+        module = importlib.util.module_from_spec(spec)
+        loader.exec_module(module)
+        sys.modules[modname] = module
+
+        require_extension(module)
+        with self.subTest(f'{modname}: isolated, strict'):
+            self.check_incompatible_here(modname, filename, isolated=True)
+        with self.subTest(f'{modname}: not isolated, strict'):
+            self.check_compatible_here(modname, filename,
+                                       strict=True, isolated=False)
+        with self.subTest(f'{modname}: not isolated, not strict'):
+            self.check_compatible_here(modname, filename,
+                                       strict=False, isolated=False)
+
     def test_python_compat(self):
         module = 'threading'
         require_pure_python(module)

diff --git a/Misc/NEWS.d/next/Core and Builtins/2023-05-05-13-18-56.gh-issue-99113.hT1ajK.rst b/Misc/NEWS.d/next/Core and Builtins/2023-05-05-13-18-56.gh-issue-99113.hT1ajK.rst
@@ -0,0 +1,11 @@
+Multi-phase init extension modules may now indicate that they support
+running in subinterpreters that have their own GIL.  This is done by using
+``Py_MOD_PER_INTERPRETER_GIL_SUPPORTED`` as the value for the
+``Py_mod_multiple_interpreters`` module def slot.  Otherwise the module, by
+default, cannot be imported in such subinterpreters.  (This does not affect
+the main interpreter or subinterpreters that do not have their own GIL.)  In
+addition to the isolation that multi-phase init already normally requires,
+support for per-interpreter GIL involves one additional constraint:
+thread-safety.  If the module has external (linked) dependencies and those
+libraries have any state that isn't thread-safe then the module must do the
+additional work to add thread-safety.  This should be an uncommon case.
@@ -892,7 +892,7 @@ PyInit__test_module_state_shared(void)
 }
 
 
-/* multiple interpreters supports */
+/* multiple interpreters support */
 
 static PyModuleDef_Slot non_isolated_slots[] = {
     {Py_mod_exec, execfunc},
@@ -909,3 +909,20 @@ PyInit__test_non_isolated(void)
 {
        return PyModuleDef_Init(&non_isolated_def);
 }
+
+
+static PyModuleDef_Slot shared_gil_only_slots[] = {
+    {Py_mod_exec, execfunc},
+    {Py_mod_multiple_interpreters, Py_MOD_MULTIPLE_INTERPRETERS_SUPPORTED},
+    {0, NULL},
+};
+
+static PyModuleDef shared_gil_only_def = TEST_MODULE_DEF("_test_shared_gil_only",
+                                                         shared_gil_only_slots,
+                                                         testexport_methods);
+
+PyMODINIT_FUNC
+PyInit__test_shared_gil_only(void)
+{
+    return PyModuleDef_Init(&shared_gil_only_def);
+}
@@ -323,7 +323,13 @@ PyModule_FromDefAndSpec2(PyModuleDef* def, PyObject *spec, int module_api_versio
             goto error;
         }
     }
-    // XXX Do a similar check once we have PyInterpreterState.ceval.own_gil.
+    else if (multiple_interpreters != Py_MOD_PER_INTERPRETER_GIL_SUPPORTED
+             && interp->ceval.own_gil
+             && !_Py_IsMainInterpreter(interp)
+             && _PyImport_CheckSubinterpIncompatibleExtensionAllowed(name) < 0)
+    {
+        goto error;
+    }
 
     if (create) {
         m = create(spec, def);