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

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 *

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);
 }
 
 

src/pl/plpython/plpy_procedure.c

@@ -350,6 +350,7 @@ PLy_procedure_compile(PLyProcedure *proc, const char *src)
 {
 	PyObject   *crv = NULL;
 	char	   *msrc;
+	PyObject   *code0;
 
 	proc->globals = PyDict_Copy(PLy_interp_globals);
 
@@ -368,7 +369,9 @@ PLy_procedure_compile(PLyProcedure *proc, const char *src)
 	msrc = PLy_procedure_munge_source(proc->pyname, src);
 	/* Save the mangled source for later inclusion in tracebacks */
 	proc->src = MemoryContextStrdup(proc->mcxt, msrc);
-	crv = PyRun_String(msrc, Py_file_input, proc->globals, NULL);
+	code0 = Py_CompileString(msrc, "<string>", Py_file_input);
+	if (code0)
+		crv = PyEval_EvalCode(code0, proc->globals, NULL);
 	pfree(msrc);
 
 	if (crv != NULL)

src/pl/plpython/plpy_resultobject.c

@@ -10,7 +10,7 @@
 #include "plpy_resultobject.h"
 #include "plpython.h"
 
-static void PLy_result_dealloc(PyObject *arg);
+static void PLy_result_dealloc(PLyResultObject *self);
 static PyObject *PLy_result_colnames(PyObject *self, PyObject *unused);
 static PyObject *PLy_result_coltypes(PyObject *self, PyObject *unused);
 static PyObject *PLy_result_coltypmods(PyObject *self, PyObject *unused);
@@ -24,17 +24,6 @@ static int	PLy_result_ass_subscript(PyObject *arg, PyObject *item, PyObject *val
 
 static char PLy_result_doc[] = "Results of a PostgreSQL query";
 
-static PySequenceMethods PLy_result_as_sequence = {
-	.sq_length = PLy_result_length,
-	.sq_item = PLy_result_item,
-};
-
-static PyMappingMethods PLy_result_as_mapping = {
-	.mp_length = PLy_result_length,
-	.mp_subscript = PLy_result_subscript,
-	.mp_ass_subscript = PLy_result_ass_subscript,
-};
-
 static PyMethodDef PLy_result_methods[] = {
 	{"colnames", PLy_result_colnames, METH_NOARGS, NULL},
 	{"coltypes", PLy_result_coltypes, METH_NOARGS, NULL},
@@ -44,23 +33,55 @@ static PyMethodDef PLy_result_methods[] = {
 	{NULL, NULL, 0, NULL}
 };
 
-static PyTypeObject PLy_ResultType = {
-	PyVarObject_HEAD_INIT(NULL, 0)
-	.tp_name = "PLyResult",
-	.tp_basicsize = sizeof(PLyResultObject),
-	.tp_dealloc = PLy_result_dealloc,
-	.tp_as_sequence = &PLy_result_as_sequence,
-	.tp_as_mapping = &PLy_result_as_mapping,
-	.tp_str = &PLy_result_str,
-	.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
-	.tp_doc = PLy_result_doc,
-	.tp_methods = PLy_result_methods,
+static PyType_Slot PLyResult_slots[] =
+{
+	{
+		Py_tp_dealloc, PLy_result_dealloc
+	},
+	{
+		Py_sq_length, PLy_result_length
+	},
+	{
+		Py_sq_item, PLy_result_item
+	},
+	{
+		Py_mp_length, PLy_result_length
+	},
+	{
+		Py_mp_subscript, PLy_result_subscript
+	},
+	{
+		Py_mp_ass_subscript, PLy_result_ass_subscript
+	},
+	{
+		Py_tp_str, PLy_result_str
+	},
+	{
+		Py_tp_doc, (char *) PLy_result_doc
+	},
+	{
+		Py_tp_methods, PLy_result_methods
+	},
+	{
+		0, NULL
+	}
 };
 
+static PyType_Spec PLyResult_spec =
+{
+	.name = "PLyResult",
+		.basicsize = sizeof(PLyResultObject),
+		.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
+		.slots = PLyResult_slots,
+};
+
+static PyTypeObject *PLy_ResultType;
+
 void
 PLy_result_init_type(void)
 {
-	if (PyType_Ready(&PLy_ResultType) < 0)
+	PLy_ResultType = (PyTypeObject *) PyType_FromSpec(&PLyResult_spec);
+	if (!PLy_ResultType)
 		elog(ERROR, "could not initialize PLy_ResultType");
 }
 
@@ -69,7 +90,7 @@ PLy_result_new(void)
 {
 	PLyResultObject *ob;
 
-	if ((ob = PyObject_New(PLyResultObject, &PLy_ResultType)) == NULL)
+	if ((ob = PyObject_New(PLyResultObject, PLy_ResultType)) == NULL)
 		return NULL;
 
 	/* ob->tuples = NULL; */
@@ -89,20 +110,21 @@ PLy_result_new(void)
 }
 
 static void
-PLy_result_dealloc(PyObject *arg)
+PLy_result_dealloc(PLyResultObject *self)
 {
-	PLyResultObject *ob = (PLyResultObject *) arg;
+	PyTypeObject *tp = Py_TYPE(self);
 
-	Py_XDECREF(ob->nrows);
-	Py_XDECREF(ob->rows);
-	Py_XDECREF(ob->status);
-	if (ob->tupdesc)
+	Py_XDECREF(self->nrows);
+	Py_XDECREF(self->rows);
+	Py_XDECREF(self->status);
+	if (self->tupdesc)
 	{
-		FreeTupleDesc(ob->tupdesc);
-		ob->tupdesc = NULL;
+		FreeTupleDesc(self->tupdesc);
+		self->tupdesc = NULL;
 	}
 
-	arg->ob_type->tp_free(arg);
+	PyObject_Free(self);
+	Py_DECREF(tp);
 }
 
 static PyObject *
@@ -125,7 +147,7 @@ PLy_result_colnames(PyObject *self, PyObject *unused)
 	{
 		Form_pg_attribute attr = TupleDescAttr(ob->tupdesc, i);
 
-		PyList_SET_ITEM(list, i, PLyUnicode_FromString(NameStr(attr->attname)));
+		PyList_SetItem(list, i, PLyUnicode_FromString(NameStr(attr->attname)));
 	}
 
 	return list;
@@ -151,7 +173,7 @@ PLy_result_coltypes(PyObject *self, PyObject *unused)
 	{
 		Form_pg_attribute attr = TupleDescAttr(ob->tupdesc, i);
 
-		PyList_SET_ITEM(list, i, PyLong_FromLong(attr->atttypid));
+		PyList_SetItem(list, i, PyLong_FromLong(attr->atttypid));
 	}
 
 	return list;
@@ -177,7 +199,7 @@ PLy_result_coltypmods(PyObject *self, PyObject *unused)
 	{
 		Form_pg_attribute attr = TupleDescAttr(ob->tupdesc, i);
 
-		PyList_SET_ITEM(list, i, PyLong_FromLong(attr->atttypmod));
+		PyList_SetItem(list, i, PyLong_FromLong(attr->atttypmod));
 	}
 
 	return list;
@@ -227,7 +249,7 @@ PLy_result_str(PyObject *arg)
 	PLyResultObject *ob = (PLyResultObject *) arg;
 
 	return PyUnicode_FromFormat("<%s status=%S nrows=%S rows=%S>",
-								Py_TYPE(ob)->tp_name,
+								"PLyResult",
 								ob->status,
 								ob->nrows,
 								ob->rows);

src/pl/plpython/plpy_subxactobject.c

@@ -15,7 +15,6 @@
 List	   *explicit_subtransactions = NIL;
 
 
-static void PLy_subtransaction_dealloc(PyObject *subxact);
 static PyObject *PLy_subtransaction_enter(PyObject *self, PyObject *unused);
 static PyObject *PLy_subtransaction_exit(PyObject *self, PyObject *args);
 
@@ -31,21 +30,35 @@ static PyMethodDef PLy_subtransaction_methods[] = {
 	{NULL, NULL, 0, NULL}
 };
 
-static PyTypeObject PLy_SubtransactionType = {
-	PyVarObject_HEAD_INIT(NULL, 0)
-	.tp_name = "PLySubtransaction",
-	.tp_basicsize = sizeof(PLySubtransactionObject),
-	.tp_dealloc = PLy_subtransaction_dealloc,
-	.tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
-	.tp_doc = PLy_subtransaction_doc,
-	.tp_methods = PLy_subtransaction_methods,
+static PyType_Slot PLySubtransaction_slots[] =
+{
+	{
+		Py_tp_doc, (char *) PLy_subtransaction_doc
+	},
+	{
+		Py_tp_methods, PLy_subtransaction_methods
+	},
+	{
+		0, NULL
+	}
+};
+
+static PyType_Spec PLySubtransaction_spec =
+{
+	.name = "PLySubtransaction",
+		.basicsize = sizeof(PLySubtransactionObject),
+		.flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
+		.slots = PLySubtransaction_slots,
 };
 
+static PyTypeObject *PLy_SubtransactionType;
+
 
 void
 PLy_subtransaction_init_type(void)
 {
-	if (PyType_Ready(&PLy_SubtransactionType) < 0)
+	PLy_SubtransactionType = (PyTypeObject *) PyType_FromSpec(&PLySubtransaction_spec);
+	if (!PLy_SubtransactionType)
 		elog(ERROR, "could not initialize PLy_SubtransactionType");
 }
 
@@ -55,7 +68,7 @@ PLy_subtransaction_new(PyObject *self, PyObject *unused)
 {
 	PLySubtransactionObject *ob;
 
-	ob = PyObject_New(PLySubtransactionObject, &PLy_SubtransactionType);
+	ob = PyObject_New(PLySubtransactionObject, PLy_SubtransactionType);
 
 	if (ob == NULL)
 		return NULL;
@@ -66,12 +79,6 @@ PLy_subtransaction_new(PyObject *self, PyObject *unused)
 	return (PyObject *) ob;
 }
 
-/* Python requires a dealloc function to be defined */
-static void
-PLy_subtransaction_dealloc(PyObject *subxact)
-{
-}
-
 /*
  * subxact.__enter__() or subxact.enter()
  *

src/pl/plpython/plpy_typeio.c

@@ -723,7 +723,7 @@ PLyList_FromArray_recurse(PLyDatumToOb *elm, int *dims, int ndim, int dim,
 
 			sublist = PLyList_FromArray_recurse(elm, dims, ndim, dim + 1,
 												dataptr_p, bitmap_p, bitmask_p);
-			PyList_SET_ITEM(list, i, sublist);
+			PyList_SetItem(list, i, sublist);
 		}
 	}
 	else
@@ -742,14 +742,14 @@ PLyList_FromArray_recurse(PLyDatumToOb *elm, int *dims, int ndim, int dim,
 			if (bitmap && (*bitmap & bitmask) == 0)
 			{
 				Py_INCREF(Py_None);
-				PyList_SET_ITEM(list, i, Py_None);
+				PyList_SetItem(list, i, Py_None);
 			}
 			else
 			{
 				Datum		itemvalue;
 
 				itemvalue = fetch_att(dataptr, elm->typbyval, elm->typlen);
-				PyList_SET_ITEM(list, i, elm->func(elm, itemvalue));
+				PyList_SetItem(list, i, elm->func(elm, itemvalue));
 				dataptr = att_addlength_pointer(dataptr, elm->typlen, dataptr);
 				dataptr = (char *) att_align_nominal(dataptr, elm->typalign);
 			}