plpython: Clean up PyModule_AddObject() uses

The comments "PyModule_AddObject does not add a refcount to the
object, for some odd reason" seem distracting.  Arguably, this
behavior is expected, not odd.  Also, the additional references
created by the existing code are apparently not necessary.  But we
should clean up the reference in the error case, as suggested by the
Python documentation.

Reviewed-by: Chao Li <li.evan.chao@gmail.com>
Reviewed-by: Matheus Alcantara <matheusssilv97@gmail.com>
Reviewed-by: li carol <carol.li2025@outlook.com>
Reviewed-by: Kirill Reshke <reshkekirill@gmail.com>
Discussion: https://www.postgresql.org/message-id/f31333f1-fbb7-4098-b209-bf2d71fbd4f3%40eisentraut.org

diff --git a/src/pl/plpython/plpy_plpymodule.c b/src/pl/plpython/plpy_plpymodule.c
index 667812915195c005be40966e50c1d9f6cc999101..0d663ac5110644ec422e065af04ea66d2f0d31c0 100644 (file)
--- a/src/pl/plpython/plpy_plpymodule.c
+++ b/src/pl/plpython/plpy_plpymodule.c
@@ -172,18 +172,6 @@ PLy_add_exceptions(PyObject *plpy)
        PyObject   *excmod;
        HASHCTL         hash_ctl;
 
-       excmod = PyModule_Create(&PLy_exc_module);
-       if (excmod == NULL)
-               PLy_elog(ERROR, "could not create the spiexceptions module");
-
-       /*
-        * PyModule_AddObject does not add a refcount to the object, for some odd
-        * reason; we must do that.
-        */
-       Py_INCREF(excmod);
-       if (PyModule_AddObject(plpy, "spiexceptions", excmod) < 0)
-               PLy_elog(ERROR, "could not add the spiexceptions module");
-
        PLy_exc_error = PLy_create_exception("plpy.Error", NULL, NULL,
                                                                                 "Error", plpy);
        PLy_exc_fatal = PLy_create_exception("plpy.Fatal", NULL, NULL,
@@ -191,16 +179,28 @@ PLy_add_exceptions(PyObject *plpy)
        PLy_exc_spi_error = PLy_create_exception("plpy.SPIError", NULL, NULL,
                                                                                         "SPIError", plpy);
 
+       excmod = PyModule_Create(&PLy_exc_module);
+       if (excmod == NULL)
+               PLy_elog(ERROR, "could not create the spiexceptions module");
+
        hash_ctl.keysize = sizeof(int);
        hash_ctl.entrysize = sizeof(PLyExceptionEntry);
        PLy_spi_exceptions = hash_create("PL/Python SPI exceptions", 256,
                                                                         &hash_ctl, HASH_ELEM | HASH_BLOBS);
 
        PLy_generate_spi_exceptions(excmod, PLy_exc_spi_error);
+
+       if (PyModule_AddObject(plpy, "spiexceptions", excmod) < 0)
+       {
+               Py_XDECREF(excmod);
+               PLy_elog(ERROR, "could not add the spiexceptions module");
+       }
 }
 
 /*
  * Create an exception object and add it to the module
+ *
+ * The created exception object is also returned.
  */
 static PyObject *
 PLy_create_exception(char *name, PyObject *base, PyObject *dict,
@@ -213,18 +213,19 @@ PLy_create_exception(char *name, PyObject *base, PyObject *dict,
                PLy_elog(ERROR, NULL);
 
        /*
-        * PyModule_AddObject does not add a refcount to the object, for some odd
-        * reason; we must do that.
+        * PyModule_AddObject() (below) steals the reference to exc, but we also
+        * want to return the value from this function, so add another ref to
+        * account for that.  (The caller will store a pointer to the exception
+        * object in some permanent variable.)
         */
        Py_INCREF(exc);
-       PyModule_AddObject(mod, modname, exc);
 
-       /*
-        * The caller will also store a pointer to the exception object in some
-        * permanent variable, so add another ref to account for that.  This is
-        * probably excessively paranoid, but let's be sure.
-        */
-       Py_INCREF(exc);
+       if (PyModule_AddObject(mod, modname, exc) < 0)
+       {
+               Py_XDECREF(exc);
+               PLy_elog(ERROR, "could not add exception %s", name);
+       }
+
        return exc;
 }