bpo-36097: Use only public C-API in the_xxsubinterpreters module (adding as necessary).

Include/cpython/interpreteridobject.h

@@ -0,0 +1,21 @@
+#ifndef Py_CPYTHON_INTERPRETERIDOBJECT_H
+#  error "this header file must not be included directly"
+#endif
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/* Interpreter ID Object */
+
+PyAPI_DATA(PyTypeObject) _PyInterpreterID_Type;
+
+PyAPI_FUNC(PyObject *) _PyInterpreterID_New(int64_t);
+PyAPI_FUNC(PyObject *) _PyInterpreterState_GetIDObject(PyInterpreterState *);
+PyAPI_FUNC(PyInterpreterState *) _PyInterpreterID_LookUp(PyObject *);
+
+PyAPI_FUNC(int64_t) _Py_CoerceID(PyObject *);
+
+#ifdef __cplusplus
+}
+#endif

Include/cpython/pystate.h

@@ -30,9 +30,13 @@ typedef struct {
     (_PyMainInterpreterConfig){.install_signal_handlers = -1}
 /* Note: _PyMainInterpreterConfig_INIT sets other fields to 0/NULL */
 
+PyAPI_FUNC(int) _PyInterpreterState_RequiresIDRef(PyInterpreterState *);
+PyAPI_FUNC(void) _PyInterpreterState_RequireIDRef(PyInterpreterState *, int);
+
 PyAPI_FUNC(_PyCoreConfig *) _PyInterpreterState_GetCoreConfig(PyInterpreterState *);
 PyAPI_FUNC(_PyMainInterpreterConfig *) _PyInterpreterState_GetMainConfig(PyInterpreterState *);
 
+PyAPI_FUNC(PyObject *) _PyInterpreterState_GetMainModule(PyInterpreterState *);
 
 /* State unique per thread */
 
@@ -214,6 +218,65 @@ PyAPI_FUNC(PyThreadState *) PyThreadState_Next(PyThreadState *);
 
 typedef struct _frame *(*PyThreadFrameGetter)(PyThreadState *self_);
 
+/* cross-interpreter data */
+
+struct _xid;
+
+// _PyCrossInterpreterData is similar to Py_buffer as an effectively
+// opaque struct that holds data outside the object machinery.  This
+// is necessary to pass safely between interpreters in the same process.
+typedef struct _xid {
+    // data is the cross-interpreter-safe derivation of a Python object
+    // (see _PyObject_GetCrossInterpreterData).  It will be NULL if the
+    // new_object func (below) encodes the data.
+    void *data;
+    // obj is the Python object from which the data was derived.  This
+    // is non-NULL only if the data remains bound to the object in some
+    // way, such that the object must be "released" (via a decref) when
+    // the data is released.  In that case the code that sets the field,
+    // likely a registered "crossinterpdatafunc", is responsible for
+    // ensuring it owns the reference (i.e. incref).
+    PyObject *obj;
+    // interp is the ID of the owning interpreter of the original
+    // object.  It corresponds to the active interpreter when
+    // _PyObject_GetCrossInterpreterData() was called.  This should only
+    // be set by the cross-interpreter machinery.
+    //
+    // We use the ID rather than the PyInterpreterState to avoid issues
+    // with deleted interpreters.  Note that IDs are never re-used, so
+    // each one will always correspond to a specific interpreter
+    // (whether still alive or not).
+    int64_t interp;
+    // new_object is a function that returns a new object in the current
+    // interpreter given the data.  The resulting object (a new
+    // reference) will be equivalent to the original object.  This field
+    // is required.
+    PyObject *(*new_object)(struct _xid *);
+    // 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
+    // to NULL.  However, for most the data was allocated just for
+    // cross-interpreter use, so it must be freed when
+    // _PyCrossInterpreterData_Release is called or the memory will
+    // 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 *);
+} _PyCrossInterpreterData;
+
+PyAPI_FUNC(int) _PyObject_GetCrossInterpreterData(PyObject *, _PyCrossInterpreterData *);
+PyAPI_FUNC(PyObject *) _PyCrossInterpreterData_NewObject(_PyCrossInterpreterData *);
+PyAPI_FUNC(void) _PyCrossInterpreterData_Release(_PyCrossInterpreterData *);
+
+PyAPI_FUNC(int) _PyObject_CheckCrossInterpreterData(PyObject *);
+
+/* cross-interpreter data registry */
+
+typedef int (*crossinterpdatafunc)(PyObject *, struct _xid *);
+
+PyAPI_FUNC(int) _PyCrossInterpreterData_RegisterClass(PyTypeObject *, crossinterpdatafunc);
+PyAPI_FUNC(crossinterpdatafunc) _PyCrossInterpreterData_Lookup(PyObject *);
+
 #ifdef __cplusplus
 }
 #endif

Include/internal/pycore_pystate.h

@@ -29,6 +29,7 @@ struct _is {
 
     int64_t id;
     int64_t id_refcount;
+    int requires_idref;
     PyThread_type_lock id_mutex;
 
     int finalizing;
@@ -89,66 +90,12 @@ PyAPI_FUNC(void) _PyInterpreterState_IDIncref(struct _is *);
 PyAPI_FUNC(void) _PyInterpreterState_IDDecref(struct _is *);
 
 
-/* cross-interpreter data */
-
-struct _xid;
-
-// _PyCrossInterpreterData is similar to Py_buffer as an effectively
-// opaque struct that holds data outside the object machinery.  This
-// is necessary to pass safely between interpreters in the same process.
-typedef struct _xid {
-    // data is the cross-interpreter-safe derivation of a Python object
-    // (see _PyObject_GetCrossInterpreterData).  It will be NULL if the
-    // new_object func (below) encodes the data.
-    void *data;
-    // obj is the Python object from which the data was derived.  This
-    // is non-NULL only if the data remains bound to the object in some
-    // way, such that the object must be "released" (via a decref) when
-    // the data is released.  In that case the code that sets the field,
-    // likely a registered "crossinterpdatafunc", is responsible for
-    // ensuring it owns the reference (i.e. incref).
-    PyObject *obj;
-    // interp is the ID of the owning interpreter of the original
-    // object.  It corresponds to the active interpreter when
-    // _PyObject_GetCrossInterpreterData() was called.  This should only
-    // be set by the cross-interpreter machinery.
-    //
-    // We use the ID rather than the PyInterpreterState to avoid issues
-    // with deleted interpreters.
-    int64_t interp;
-    // new_object is a function that returns a new object in the current
-    // interpreter given the data.  The resulting object (a new
-    // reference) will be equivalent to the original object.  This field
-    // is required.
-    PyObject *(*new_object)(struct _xid *);
-    // 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
-    // to NULL.  However, for most the data was allocated just for
-    // cross-interpreter use, so it must be freed when
-    // _PyCrossInterpreterData_Release is called or the memory will
-    // 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 *);
-} _PyCrossInterpreterData;
-
-typedef int (*crossinterpdatafunc)(PyObject *, _PyCrossInterpreterData *);
-PyAPI_FUNC(int) _PyObject_CheckCrossInterpreterData(PyObject *);
-
-PyAPI_FUNC(int) _PyObject_GetCrossInterpreterData(PyObject *, _PyCrossInterpreterData *);
-PyAPI_FUNC(PyObject *) _PyCrossInterpreterData_NewObject(_PyCrossInterpreterData *);
-PyAPI_FUNC(void) _PyCrossInterpreterData_Release(_PyCrossInterpreterData *);
-
 /* cross-interpreter data registry */
 
 /* For now we use a global registry of shareable classes.  An
    alternative would be to add a tp_* slot for a class's
    crossinterpdatafunc. It would be simpler and more efficient. */
 
-PyAPI_FUNC(int) _PyCrossInterpreterData_Register_Class(PyTypeObject *, crossinterpdatafunc);
-PyAPI_FUNC(crossinterpdatafunc) _PyCrossInterpreterData_Lookup(PyObject *);
-
 struct _xidregitem;
 
 struct _xidregitem {

Include/interpreteridobject.h

@@ -0,0 +1,17 @@
+#ifndef Py_INTERPRETERIDOBJECT_H
+#define Py_INTERPRETERIDOBJECT_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#ifndef Py_LIMITED_API
+#  define Py_CPYTHON_INTERPRETERIDOBJECT_H
+#  include  "cpython/interpreteridobject.h"
+#  undef Py_CPYTHON_INTERPRETERIDOBJECT_H
+#endif
+
+#ifdef __cplusplus
+}
+#endif
+#endif /* !Py_INTERPRETERIDOBJECT_H */

Makefile.pre.in

@@ -391,6 +391,7 @@ OBJECT_OBJS=	\
 		Objects/floatobject.o \
 		Objects/frameobject.o \
 		Objects/funcobject.o \
+		Objects/interpreteridobject.o \
 		Objects/iterobject.o \
 		Objects/listobject.o \
 		Objects/longobject.o \
@@ -977,6 +978,7 @@ PYTHON_HEADERS= \
 		$(srcdir)/Include/funcobject.h \
 		$(srcdir)/Include/genobject.h \
 		$(srcdir)/Include/import.h \
+		$(srcdir)/Include/interpreteridobject.h \
 		$(srcdir)/Include/intrcheck.h \
 		$(srcdir)/Include/iterobject.h \
 		$(srcdir)/Include/listobject.h \
@@ -1039,6 +1041,7 @@ PYTHON_HEADERS= \
 		$(srcdir)/Include/cpython/abstract.h \
 		$(srcdir)/Include/cpython/coreconfig.h \
 		$(srcdir)/Include/cpython/dictobject.h \
+		$(srcdir)/Include/cpython/interpreteridobject.h \
 		$(srcdir)/Include/cpython/object.h \
 		$(srcdir)/Include/cpython/objimpl.h \
 		$(srcdir)/Include/cpython/pyerrors.h \