gh-116322: Add Py_mod_gil module slot (#116882)

This PR adds the ability to enable the GIL if it was disabled at
interpreter startup, and modifies the multi-phase module initialization
path to enable the GIL when loading a module, unless that module's spec
includes a slot indicating it can run safely without the GIL.

PEP 703 called the constant for the slot `Py_mod_gil_not_used`; I went
with `Py_MOD_GIL_NOT_USED` for consistency with gh-104148.

A warning will be issued up to once per interpreter for the first
GIL-using module that is loaded. If `-v` is given, a shorter message
will be printed to stderr every time a GIL-using module is loaded
(including the first one that issues a warning).

1 files changed, 7 insertions, 2 deletions

diff --git a/Modules/_xxtestfuzz/_xxtestfuzz.c b/Modules/_xxtestfuzz/_xxtestfuzz.c
index a2dbabc..2952d70 100644
--- a/Modules/_xxtestfuzz/_xxtestfuzz.c
+++ b/Modules/_xxtestfuzz/_xxtestfuzz.c
@@ -28,13 +28,18 @@ static PyMethodDef module_methods[] = {
     {NULL},
 };
 
+static PyModuleDef_Slot module_slots[] = {
+    {Py_mod_gil, Py_MOD_GIL_NOT_USED},
+    {0, NULL},
+};
+
 static struct PyModuleDef _fuzzmodule = {
         PyModuleDef_HEAD_INIT,
         "_fuzz",
         NULL,
         0,
         module_methods,
-        NULL,
+        module_slots,
         NULL,
         NULL,
         NULL
@@ -43,5 +48,5 @@ static struct PyModuleDef _fuzzmodule = {
 PyMODINIT_FUNC
 PyInit__xxtestfuzz(void)
 {
-    return PyModule_Create(&_fuzzmodule);
+    return PyModuleDef_Init(&_fuzzmodule);
 }