Prepare for Python "Limited API" in PL/Python

Using the Python Limited API would allow building PL/Python against
any Python 3.x version and using another Python 3.x version at run
time.  This commit does not activate that, but it prepares the code to
only use APIs supported by the Limited API.

Implementation details:

- Convert static types to heap types
  (https://docs.python.org/3/howto/isolating-extensions.html#heap-types).

- Replace PyRun_String() with component functions.

- Replace PyList_SET_ITEM() with PyList_SetItem().

Reviewed-by: Jakob Egger <jakob@eggerapps.at>
Discussion: https://www.postgresql.org/message-id/flat/ee410de1-1e0b-4770-b125-eeefd4726a24@eisentraut.org

1 files changed, 46 insertions, 25 deletions

diff --git a/src/pl/plpython/plpy_cursorobject.c b/src/pl/plpython/plpy_cursorobject.c
index bb3fa8a3909..2a370157f90 100644
--- a/src/pl/plpython/plpy_cursorobject.c
+++ b/src/pl/plpython/plpy_cursorobject.c
@@ -20,7 +20,7 @@
 #include "utils/memutils.h"
 
 static PyObject *PLy_cursor_query(const char *query);
-static void PLy_cursor_dealloc(PyObject *arg);
+static void PLy_cursor_dealloc(PLyCursorObject *self);
 static PyObject *PLy_cursor_iternext(PyObject *self);
 static PyObject *PLy_cursor_fetch(PyObject *self, PyObject *args);
 static PyObject *PLy_cursor_close(PyObject *self, PyObject *unused);
@@ -33,22 +33,43 @@ static PyMethodDef PLy_cursor_methods[] = {
 	{NULL, NULL, 0, NULL}
 };
 
-static PyTypeObject PLy_CursorType = {
-	PyVarObject_HEAD_INIT(NULL, 0)
-	.tp_name = "PLyCursor",
-	.tp_basicsize = sizeof(PLyCursorObject),
-	.tp_dealloc = PLy_cursor_dealloc,
-	.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
-	.tp_doc = PLy_cursor_doc,
-	.tp_iter = PyObject_SelfIter,
-	.tp_iternext = PLy_cursor_iternext,
-	.tp_methods = PLy_cursor_methods,
+static PyType_Slot PLyCursor_slots[] =
+{
+	{
+		Py_tp_dealloc, PLy_cursor_dealloc
+	},
+	{
+		Py_tp_doc, (char *) PLy_cursor_doc
+	},
+	{
+		Py_tp_iter, PyObject_SelfIter
+	},
+	{
+		Py_tp_iternext, PLy_cursor_iternext
+	},
+	{
+		Py_tp_methods, PLy_cursor_methods
+	},
+	{
+		0, NULL
+	}
 };
 
+static PyType_Spec PLyCursor_spec =
+{
+	.name = "PLyCursor",
+		.basicsize = sizeof(PLyCursorObject),
+		.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
+		.slots = PLyCursor_slots,
+};
+
+static PyTypeObject *PLy_CursorType;
+
 void
 PLy_cursor_init_type(void)
 {
-	if (PyType_Ready(&PLy_CursorType) < 0)
+	PLy_CursorType = (PyTypeObject *) PyType_FromSpec(&PLyCursor_spec);
+	if (!PLy_CursorType)
 		elog(ERROR, "could not initialize PLy_CursorType");
 }
 
@@ -80,7 +101,7 @@ PLy_cursor_query(const char *query)
 	volatile MemoryContext oldcontext;
 	volatile ResourceOwner oldowner;
 
-	if ((cursor = PyObject_New(PLyCursorObject, &PLy_CursorType)) == NULL)
+	if ((cursor = PyObject_New(PLyCursorObject, PLy_CursorType)) == NULL)
 		return NULL;
 	cursor->portalname = NULL;
 	cursor->closed = false;
@@ -177,7 +198,7 @@ PLy_cursor_plan(PyObject *ob, PyObject *args)
 		return NULL;
 	}
 
-	if ((cursor = PyObject_New(PLyCursorObject, &PLy_CursorType)) == NULL)
+	if ((cursor = PyObject_New(PLyCursorObject, PLy_CursorType)) == NULL)
 		return NULL;
 	cursor->portalname = NULL;
 	cursor->closed = false;
@@ -272,30 +293,30 @@ PLy_cursor_plan(PyObject *ob, PyObject *args)
 }
 
 static void
-PLy_cursor_dealloc(PyObject *arg)
+PLy_cursor_dealloc(PLyCursorObject *self)
 {
-	PLyCursorObject *cursor;
+	PyTypeObject *tp = Py_TYPE(self);
 	Portal		portal;
 
-	cursor = (PLyCursorObject *) arg;
-
-	if (!cursor->closed)
+	if (!self->closed)
 	{
-		portal = GetPortalByName(cursor->portalname);
+		portal = GetPortalByName(self->portalname);
 
 		if (PortalIsValid(portal))
 		{
 			UnpinPortal(portal);
 			SPI_cursor_close(portal);
 		}
-		cursor->closed = true;
+		self->closed = true;
 	}
-	if (cursor->mcxt)
+	if (self->mcxt)
 	{
-		MemoryContextDelete(cursor->mcxt);
-		cursor->mcxt = NULL;
+		MemoryContextDelete(self->mcxt);
+		self->mcxt = NULL;
 	}
-	arg->ob_type->tp_free(arg);
+
+	PyObject_Free(self);
+	Py_DECREF(tp);
 }
 
 static PyObject *