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, 16 insertions, 10 deletions

diff --git a/Modules/_testimportmultiple.c b/Modules/_testimportmultiple.c
index a65ca51..c147596 100644
--- a/Modules/_testimportmultiple.c
+++ b/Modules/_testimportmultiple.c
@@ -6,18 +6,24 @@
 
 #include "pyconfig.h"   // Py_GIL_DISABLED
 #ifndef Py_GIL_DISABLED
-#  define Py_LIMITED_API 0x03020000
+#  define Py_LIMITED_API 0x030d0000
 #endif
 
 #include <Python.h>
 
+static PyModuleDef_Slot shared_slots[] = {
+    {Py_mod_multiple_interpreters, Py_MOD_MULTIPLE_INTERPRETERS_NOT_SUPPORTED},
+    {Py_mod_gil, Py_MOD_GIL_NOT_USED},
+    {0, NULL},
+};
+
 static struct PyModuleDef _testimportmultiple = {
     PyModuleDef_HEAD_INIT,
     "_testimportmultiple",
     "_testimportmultiple doc",
-    -1,
-    NULL,
+    0,
     NULL,
+    shared_slots,
     NULL,
     NULL,
     NULL
@@ -25,16 +31,16 @@ static struct PyModuleDef _testimportmultiple = {
 
 PyMODINIT_FUNC PyInit__testimportmultiple(void)
 {
-    return PyModule_Create(&_testimportmultiple);
+    return PyModuleDef_Init(&_testimportmultiple);
 }
 
 static struct PyModuleDef _foomodule = {
     PyModuleDef_HEAD_INIT,
     "_testimportmultiple_foo",
     "_testimportmultiple_foo doc",
-    -1,
-    NULL,
+    0,
     NULL,
+    shared_slots,
     NULL,
     NULL,
     NULL
@@ -42,21 +48,21 @@ static struct PyModuleDef _foomodule = {
 
 PyMODINIT_FUNC PyInit__testimportmultiple_foo(void)
 {
-    return PyModule_Create(&_foomodule);
+    return PyModuleDef_Init(&_foomodule);
 }
 
 static struct PyModuleDef _barmodule = {
     PyModuleDef_HEAD_INIT,
     "_testimportmultiple_bar",
     "_testimportmultiple_bar doc",
-    -1,
-    NULL,
+    0,
     NULL,
+    shared_slots,
     NULL,
     NULL,
     NULL
 };
 
 PyMODINIT_FUNC PyInit__testimportmultiple_bar(void){
-    return PyModule_Create(&_barmodule);
+    return PyModuleDef_Init(&_barmodule);
 }