gh-99741: Implement Multi-Phase Init for the _xxsubinterpreters Module (gh-99742)

_xxsubinterpreters is an internal module used for testing.

#99741

Author: ericsnowcurrently

Include/cpython/pystate.h

@@ -353,6 +353,9 @@ PyAPI_FUNC(const PyConfig*) _Py_GetConfig(void);
 // is necessary to pass safely between interpreters in the same process.
 typedef struct _xid _PyCrossInterpreterData;
 
+typedef PyObject *(*xid_newobjectfunc)(_PyCrossInterpreterData *);
+typedef void (*xid_freefunc)(void *);
+
 struct _xid {
     // data is the cross-interpreter-safe derivation of a Python object
     // (see _PyObject_GetCrossInterpreterData).  It will be NULL if the
@@ -379,7 +382,7 @@ struct _xid {
     // interpreter given the data.  The resulting object (a new
     // reference) will be equivalent to the original object.  This field
     // is required.
-    PyObject *(*new_object)(_PyCrossInterpreterData *);
+    xid_newobjectfunc new_object;
     // free is called when the data is released.  If it is NULL then
     // nothing will be done to free the data.  For some types this is
     // okay (e.g. bytes) and for those types this field should be set
@@ -389,9 +392,20 @@ struct _xid {
     // leak.  In that case, at the very least this field should be set
     // to PyMem_RawFree (the default if not explicitly set to NULL).
     // The call will happen with the original interpreter activated.
-    void (*free)(void *);
+    xid_freefunc free;
 };
 
+PyAPI_FUNC(void) _PyCrossInterpreterData_Init(
+        _PyCrossInterpreterData *data,
+        PyInterpreterState *interp, void *shared, PyObject *obj,
+        xid_newobjectfunc new_object);
+PyAPI_FUNC(int) _PyCrossInterpreterData_InitWithSize(
+        _PyCrossInterpreterData *,
+        PyInterpreterState *interp, const size_t, PyObject *,
+        xid_newobjectfunc);
+PyAPI_FUNC(void) _PyCrossInterpreterData_Clear(
+        PyInterpreterState *, _PyCrossInterpreterData *);
+
 PyAPI_FUNC(int) _PyObject_GetCrossInterpreterData(PyObject *, _PyCrossInterpreterData *);
 PyAPI_FUNC(PyObject *) _PyCrossInterpreterData_NewObject(_PyCrossInterpreterData *);
 PyAPI_FUNC(int) _PyCrossInterpreterData_Release(_PyCrossInterpreterData *);
@@ -400,7 +414,8 @@ PyAPI_FUNC(int) _PyObject_CheckCrossInterpreterData(PyObject *);
 
 /* cross-interpreter data registry */
 
-typedef int (*crossinterpdatafunc)(PyObject *, _PyCrossInterpreterData *);
+typedef int (*crossinterpdatafunc)(PyThreadState *tstate, PyObject *,
+                                   _PyCrossInterpreterData *);
 
 PyAPI_FUNC(int) _PyCrossInterpreterData_RegisterClass(PyTypeObject *, crossinterpdatafunc);
 PyAPI_FUNC(int) _PyCrossInterpreterData_UnregisterClass(PyTypeObject *);

Lib/test/test__xxsubinterpreters.py

@@ -295,8 +295,8 @@ def clean_up_channels():
 class TestBase(unittest.TestCase):
 
     def tearDown(self):
-        clean_up_interpreters()
         clean_up_channels()
+        clean_up_interpreters()
 
 
 ##################################
@@ -411,6 +411,15 @@ def test_non_shareable_int(self):
                     interpreters.channel_send(self.cid, i)
 
 
+class ModuleTests(TestBase):
+
+    def test_import_in_interpreter(self):
+        _run_output(
+            interpreters.create(),
+            'import _xxsubinterpreters as _interpreters',
+        )
+
+
 ##################################
 # interpreter tests
 

Misc/NEWS.d/next/Tests/2022-11-23-18-32-16.gh-issue-99741.q4R7NH.rst

@@ -0,0 +1,2 @@
+We've implemented multi-phase init (PEP 489/630/687)
+for the internal (for testing) _xxsubinterpreters module.