bpo-32604: Expose the subinterpreters C-API in a "private" stdlib module.

Include/internal/pystate.h

@@ -65,6 +65,79 @@ PyAPI_FUNC(_PyInitError) _PyPathConfig_Calculate(
 PyAPI_FUNC(void) _PyPathConfig_Clear(_PyPathConfig *config);
 
 
+/* interpreter state */
+
+PyAPI_FUNC(PyInterpreterState *) _PyInterpreterState_LookUpID(PY_INT64_T);
+
+
+/* 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 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 it is automatically
+ // incref'ed (to match the automatic decref when releaed).
+ 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{
+ PyTypeObject *cls;
+ crossinterpdatafunc getdata;
+ struct _xidregitem *next;
+};
+
+
 /* Full Python runtime state */
 
 typedef struct pyruntimestate{
@@ -86,6 +159,11 @@ typedef struct pyruntimestate{
  using a Python int. */
  int64_t next_id;
  } interpreters;
+ // XXX Remove this field once we have a tp_* slot.
+ struct _xidregistry{
+ PyThread_type_lock mutex;
+ struct _xidregitem *head;
+ } xidregistry;
 
 #define NEXITFUNCS 32
  void (*exitfuncs[NEXITFUNCS])(void);