Use portal pinning in PL/Perl and PL/Python

PL/pgSQL "pins" internally generated portals so that user code cannot
close them by guessing their names.  Add this functionality to PL/Perl
and PL/Python as well, preventing users from manually closing cursors
created by spi_query and plpy.cursor, respectively.  (PL/Tcl does not
currently offer any cursor functionality.)

src/pl/plperl/plperl.c

@@ -3406,6 +3406,8 @@ plperl_spi_query(char *query)
 				 SPI_result_code_string(SPI_result));
 		cursor = cstr2sv(portal->name);
 
+		PinPortal(portal);
+
 		/* Commit the inner transaction, return to outer xact context */
 		ReleaseCurrentSubTransaction();
 		MemoryContextSwitchTo(oldcontext);
@@ -3469,6 +3471,7 @@ plperl_spi_fetchrow(char *cursor)
 			SPI_cursor_fetch(p, true, 1);
 			if (SPI_processed == 0)
 			{
+				UnpinPortal(p);
 				SPI_cursor_close(p);
 				row = &PL_sv_undef;
 			}
@@ -3520,7 +3523,10 @@ plperl_spi_cursor_close(char *cursor)
 	p = SPI_cursor_find(cursor);
 
 	if (p)
+	{
+		UnpinPortal(p);
 		SPI_cursor_close(p);
+	}
 }
 
 SV *
@@ -3884,6 +3890,8 @@ plperl_spi_query_prepared(char *query, int argc, SV **argv)
 
 		cursor = cstr2sv(portal->name);
 
+		PinPortal(portal);
+
 		/* Commit the inner transaction, return to outer xact context */
 		ReleaseCurrentSubTransaction();
 		MemoryContextSwitchTo(oldcontext);

src/pl/plpython/plpy_cursorobject.c

@@ -151,6 +151,8 @@ PLy_cursor_query(const char *query)
 
 		cursor->portalname = MemoryContextStrdup(cursor->mcxt, portal->name);
 
+		PinPortal(portal);
+
 		PLy_spi_subtransaction_commit(oldcontext, oldowner);
 	}
 	PG_CATCH();
@@ -266,6 +268,8 @@ PLy_cursor_plan(PyObject *ob, PyObject *args)
 
 		cursor->portalname = MemoryContextStrdup(cursor->mcxt, portal->name);
 
+		PinPortal(portal);
+
 		PLy_spi_subtransaction_commit(oldcontext, oldowner);
 	}
 	PG_CATCH();
@@ -317,7 +321,10 @@ PLy_cursor_dealloc(PyObject *arg)
 		portal = GetPortalByName(cursor->portalname);
 
 		if (PortalIsValid(portal))
+		{
+			UnpinPortal(portal);
 			SPI_cursor_close(portal);
+		}
 		cursor->closed = true;
 	}
 	if (cursor->mcxt)
@@ -508,6 +515,7 @@ PLy_cursor_close(PyObject *self, PyObject *unused)
 			return NULL;
 		}
 
+		UnpinPortal(portal);
 		SPI_cursor_close(portal);
 		cursor->closed = true;
 	}