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-newobjfileevent.c

@@ -28,26 +28,22 @@ extern PyTypeObject clear_objfiles_event_object_type
 static PyObject *
 create_new_objfile_event_object (struct objfile *objfile)
 {
-  PyObject *objfile_event;
   PyObject *py_objfile;
 
-  objfile_event = create_event_object (&new_objfile_event_object_type);
-  if (!objfile_event)
-    goto fail;
+  gdbpy_ref objfile_event
+    (create_event_object (&new_objfile_event_object_type));
+  if (objfile_event == NULL)
+    return NULL;
 
   /* Note that objfile_to_objfile_object returns a borrowed reference,
      so we don't need a decref here.  */
   py_objfile = objfile_to_objfile_object (objfile);
-  if (!py_objfile || evpy_add_attribute (objfile_event,
+  if (!py_objfile || evpy_add_attribute (objfile_event.get (),
                                          "new_objfile",
                                          py_objfile) < 0)
-    goto fail;
+    return NULL;
 
-  return objfile_event;
-
- fail:
-  Py_XDECREF (objfile_event);
-  return NULL;
+  return objfile_event.release ();
 }
 
 /* Callback function which notifies observers when a new objfile event occurs.
@@ -57,14 +53,12 @@ create_new_objfile_event_object (struct objfile *objfile)
 int
 emit_new_objfile_event (struct objfile *objfile)
 {
-  PyObject *event;
-
   if (evregpy_no_listeners_p (gdb_py_events.new_objfile))
     return 0;
 
-  event = create_new_objfile_event_object (objfile);
-  if (event)
-    return evpy_emit_event (event, gdb_py_events.new_objfile);
+  gdbpy_ref event (create_new_objfile_event_object (objfile));
+  if (event != NULL)
+    return evpy_emit_event (event.get (), gdb_py_events.new_objfile);
   return -1;
 }
 
@@ -79,26 +73,22 @@ GDBPY_NEW_EVENT_TYPE (new_objfile,
 static PyObject *
 create_clear_objfiles_event_object (void)
 {
-  PyObject *objfile_event;
   PyObject *py_progspace;
 
-  objfile_event = create_event_object (&clear_objfiles_event_object_type);
-  if (!objfile_event)
-    goto fail;
+  gdbpy_ref objfile_event
+    (create_event_object (&clear_objfiles_event_object_type));
+  if (objfile_event == NULL)
+    return NULL;
 
   /* Note that pspace_to_pspace_object returns a borrowed reference,
      so we don't need a decref here.  */
   py_progspace = pspace_to_pspace_object (current_program_space);
-  if (!py_progspace || evpy_add_attribute (objfile_event,
+  if (!py_progspace || evpy_add_attribute (objfile_event.get (),
 					   "progspace",
 					   py_progspace) < 0)
-    goto fail;
+    return NULL;
 
-  return objfile_event;
-
- fail:
-  Py_XDECREF (objfile_event);
-  return NULL;
+  return objfile_event.release ();
 }
 
 /* Callback function which notifies observers when the "clear objfiles"
@@ -109,14 +99,12 @@ create_clear_objfiles_event_object (void)
 int
 emit_clear_objfiles_event (void)
 {
-  PyObject *event;
-
   if (evregpy_no_listeners_p (gdb_py_events.clear_objfiles))
     return 0;
 
-  event = create_clear_objfiles_event_object ();
-  if (event)
-    return evpy_emit_event (event, gdb_py_events.clear_objfiles);
+  gdbpy_ref event (create_clear_objfiles_event_object ());
+  if (event != NULL)
+    return evpy_emit_event (event.get (), gdb_py_events.clear_objfiles);
   return -1;
 }