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, 40 insertions, 21 deletions

diff --git a/src/pl/plpython/plpy_planobject.c b/src/pl/plpython/plpy_planobject.c
index 9427674d2f4..1b97b5cbd2a 100644
--- a/src/pl/plpython/plpy_planobject.c
+++ b/src/pl/plpython/plpy_planobject.c
@@ -12,7 +12,7 @@
 #include "plpython.h"
 #include "utils/memutils.h"
 
-static void PLy_plan_dealloc(PyObject *arg);
+static void PLy_plan_dealloc(PLyPlanObject *self);
 static PyObject *PLy_plan_cursor(PyObject *self, PyObject *args);
 static PyObject *PLy_plan_execute(PyObject *self, PyObject *args);
 static PyObject *PLy_plan_status(PyObject *self, PyObject *args);
@@ -26,20 +26,37 @@ static PyMethodDef PLy_plan_methods[] = {
 	{NULL, NULL, 0, NULL}
 };
 
-static PyTypeObject PLy_PlanType = {
-	PyVarObject_HEAD_INIT(NULL, 0)
-	.tp_name = "PLyPlan",
-	.tp_basicsize = sizeof(PLyPlanObject),
-	.tp_dealloc = PLy_plan_dealloc,
-	.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
-	.tp_doc = PLy_plan_doc,
-	.tp_methods = PLy_plan_methods,
+static PyType_Slot PLyPlan_slots[] =
+{
+	{
+		Py_tp_dealloc, PLy_plan_dealloc
+	},
+	{
+		Py_tp_doc, (char *) PLy_plan_doc
+	},
+	{
+		Py_tp_methods, PLy_plan_methods
+	},
+	{
+		0, NULL
+	}
 };
 
+static PyType_Spec PLyPlan_spec =
+{
+	.name = "PLyPlan",
+		.basicsize = sizeof(PLyPlanObject),
+		.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
+		.slots = PLyPlan_slots,
+};
+
+static PyTypeObject *PLy_PlanType;
+
 void
 PLy_plan_init_type(void)
 {
-	if (PyType_Ready(&PLy_PlanType) < 0)
+	PLy_PlanType = (PyTypeObject *) PyType_FromSpec(&PLyPlan_spec);
+	if (!PLy_PlanType)
 		elog(ERROR, "could not initialize PLy_PlanType");
 }
 
@@ -48,7 +65,7 @@ PLy_plan_new(void)
 {
 	PLyPlanObject *ob;
 
-	if ((ob = PyObject_New(PLyPlanObject, &PLy_PlanType)) == NULL)
+	if ((ob = PyObject_New(PLyPlanObject, PLy_PlanType)) == NULL)
 		return NULL;
 
 	ob->plan = NULL;
@@ -63,25 +80,27 @@ PLy_plan_new(void)
 bool
 is_PLyPlanObject(PyObject *ob)
 {
-	return ob->ob_type == &PLy_PlanType;
+	return ob->ob_type == PLy_PlanType;
 }
 
 static void
-PLy_plan_dealloc(PyObject *arg)
+PLy_plan_dealloc(PLyPlanObject *self)
 {
-	PLyPlanObject *ob = (PLyPlanObject *) arg;
+	PyTypeObject *tp = Py_TYPE(self);
 
-	if (ob->plan)
+	if (self->plan)
 	{
-		SPI_freeplan(ob->plan);
-		ob->plan = NULL;
+		SPI_freeplan(self->plan);
+		self->plan = NULL;
 	}
-	if (ob->mcxt)
+	if (self->mcxt)
 	{
-		MemoryContextDelete(ob->mcxt);
-		ob->mcxt = NULL;
+		MemoryContextDelete(self->mcxt);
+		self->mcxt = NULL;
 	}
-	arg->ob_type->tp_free(arg);
+
+	PyObject_Free(self);
+	Py_DECREF(tp);
 }