[RFA] fix ref counting of inferior_to_inferior_object

[Doug Evans <dje@google.com>]

Hi.
While adding an inferior attribute to the newobjfile event,
I noticed inferior_to_inferior_object sometimes returns (AFAICT)
a new reference and sometimes returns a borrowed reference.

This patch makes it consistently return a borrowed reference
(for consistency with obfile_to_objfile_object), and then
updates the rest of the code.

Regression tested on amd64-linux.
Ok to check in?

2013-09-12  Doug Evans  <dje@google.com>

	* python/py-exitedevent.c (create_exited_event_object): Add comment.
	* python/py-inferior.c (inferior_to_inferior_object): Always return
	a borrowed reference.
	(find_inferior_object): Return a new reference to the inferior object.
	(build_inferior_list): Update, inferior_to_inferior_object returns
	a borrowed reference.
	(gdbpy_selected_inferior): Ditto.

Index: python/py-exitedevent.c
===================================================================
RCS file: /cvs/src/src/gdb/python/py-exitedevent.c,v
retrieving revision 1.8
diff -u -p -r1.8 py-exitedevent.c
--- python/py-exitedevent.c	20 May 2013 20:09:01 -0000	1.8
+++ python/py-exitedevent.c	12 Sep 2013 22:19:49 -0000
@@ -49,6 +49,8 @@ create_exited_event_object (const LONGES
 	goto fail;
     }
 
+  /* Note that inferior_to_inferior_object returns a borrowed reference,
+     so we don't need a decref here.  */
   inf_obj = inferior_to_inferior_object (inf);
   if (!inf_obj || evpy_add_attribute (exited_event,
                                       "inferior",
Index: python/py-inferior.c
===================================================================
RCS file: /cvs/src/src/gdb/python/py-inferior.c,v
retrieving revision 1.36
diff -u -p -r1.36 py-inferior.c
--- python/py-inferior.c	18 Jun 2013 18:43:27 -0000	1.36
+++ python/py-inferior.c	12 Sep 2013 22:19:50 -0000
@@ -161,8 +161,9 @@ python_new_objfile (struct objfile *objf
 
 /* Return a reference to the Python object of type Inferior
    representing INFERIOR.  If the object has already been created,
-   return it and increment the reference count,  otherwise, create it.
+   return it,  otherwise create it.  The result is a borrowed reference.
    Return NULL on failure.  */
+
 PyObject *
 inferior_to_inferior_object (struct inferior *inferior)
 {
@@ -180,15 +181,12 @@ inferior_to_inferior_object (struct infe
       inf_obj->nthreads = 0;
 
       set_inferior_data (inferior, infpy_inf_data_key, inf_obj);
-
     }
-  else
-    Py_INCREF ((PyObject *)inf_obj);
 
   return (PyObject *) inf_obj;
 }
 
-/* Finds the Python Inferior object for the given PID.  Returns a
+/* Finds the Python Inferior object for the given PID.  Returns a new
    reference, or NULL if PID does not match any inferior object. */
 
 PyObject *
@@ -197,7 +195,12 @@ find_inferior_object (int pid)
   struct inferior *inf = find_inferior_pid (pid);
 
   if (inf)
-    return inferior_to_inferior_object (inf);
+    {
+      PyObject *inf_obj = inferior_to_inferior_object (inf);
+
+      Py_XINCREF (inf_obj);
+      return inf_obj;
+    }
 
   return NULL;
 }
@@ -384,7 +387,6 @@ build_inferior_list (struct inferior *in
     return 0;
 
   success = PyList_Append (list, inferior);
-  Py_DECREF (inferior);
 
   if (success)
     return 1;
@@ -768,12 +770,16 @@ py_free_inferior (struct inferior *inf, 
 }
 
 /* Implementation of gdb.selected_inferior() -> gdb.Inferior.
-   Returns the current inferior object.  */
+   Returns a new reference to the current inferior object.  */
 
 PyObject *
 gdbpy_selected_inferior (PyObject *self, PyObject *args)
 {
-  return inferior_to_inferior_object (current_inferior ());
+  PyObject *inf_obj;
+
+  inf_obj = inferior_to_inferior_object (current_inferior ());
+  Py_XINCREF (inf_obj);
+  return inf_obj;
 }
 
 int