Change event code to use gdbpy_ref

This changes the event code in the Python layer to use
gdbpy_ref, simplifying the logic in many places.

It also changes evpy_emit_event not to steal a reference to its
argument.  This is simpler to do now that gdbpy_ref is in use;
it's also a reasonable cleanup in its own right.  While doing this I
realized that evpy_emit_event should not be calling gdbpy_print_stack
(all the outermost callers do this if needed), so I removed this as
well.

2017-01-10  Tom Tromey  <tom@tromey.com>

	* python/py-threadevent.c (create_thread_event_object): Use
	gdbpy_ref.
	* python/py-stopevent.c (create_stop_event_object): Simplify.
	(emit_stop_event): Use gdbpy_ref.
	* python/py-signalevent.c (create_signal_event_object): Use
	gdbpy_ref.
	* python/py-newobjfileevent.c (create_new_objfile_event_object)
	(emit_new_objfile_event, create_clear_objfiles_event_object)
	(emit_clear_objfiles_event): Use gdbpy_ref.
	* python/py-infevents.c (create_inferior_call_event_object)
	(create_register_changed_event_object)
	(create_memory_changed_event_object, emit_inferior_call_event)
	(emit_memory_changed_event, emit_register_changed_event): Use
	gdbpy_ref.
	* python/py-exitedevent.c (create_exited_event_object)
	(emit_exited_event): Use gdbpy_ref.
	* python/py-event.h (evpy_emit_event): Remove
	CPYCHECKER_STEALS_REFERENCE_TO_ARG annotation.
	* python/py-event.c (evpy_emit_event): Use gdbpy_ref.
	* python/py-continueevent.c (emit_continue_event): Use
	gdbpy_ref.
	* python/py-breakpoint.c (gdbpy_breakpoint_created)
	(gdbpy_breakpoint_deleted, gdbpy_breakpoint_modified): Use
	gdbpy_ref.
	* python/py-bpevent.c (create_breakpoint_event_object): Use
	gdbpy_ref.

gdb/python/py-event.c

@@ -89,26 +89,24 @@ int
 evpy_emit_event (PyObject *event,
                  eventregistry_object *registry)
 {
-  PyObject *callback_list_copy = NULL;
   Py_ssize_t i;
 
   /* Create a copy of call back list and use that for
      notifying listeners to avoid skipping callbacks
      in the case of a callback being disconnected during
      a notification.  */
-  callback_list_copy = PySequence_List (registry->callbacks);
-  if (!callback_list_copy)
-    goto fail;
+  gdbpy_ref callback_list_copy (PySequence_List (registry->callbacks));
+  if (callback_list_copy == NULL)
+    return -1;
 
-  for (i = 0; i < PyList_Size (callback_list_copy); i++)
+  for (i = 0; i < PyList_Size (callback_list_copy.get ()); i++)
     {
-      PyObject *func = PyList_GetItem (callback_list_copy, i);
-      PyObject *func_result;
+      PyObject *func = PyList_GetItem (callback_list_copy.get (), i);
 
       if (func == NULL)
-	goto fail;
+	return -1;
 
-      func_result = PyObject_CallFunctionObjArgs (func, event, NULL);
+      gdbpy_ref func_result (PyObject_CallFunctionObjArgs (func, event, NULL));
 
       if (func_result == NULL)
 	{
@@ -116,21 +114,9 @@ evpy_emit_event (PyObject *event,
 	     call all of the callbacks even if one is broken.  */
 	  gdbpy_print_stack ();
 	}
-      else
-	{
-	  Py_DECREF (func_result);
-	}
     }
 
-  Py_XDECREF (callback_list_copy);
-  Py_XDECREF (event);
   return 0;
-
- fail:
-  gdbpy_print_stack ();
-  Py_XDECREF (callback_list_copy);
-  Py_XDECREF (event);
-  return -1;
 }
 
 static PyGetSetDef event_object_getset[] =