Re: [clutter] About clutter_actor_set_parent and reference counting

[Michael Boccara]

Thanks Emmanuele, I understand the rationale. It just goes against my belief in a rule of thumb that the reference count of a pointer should always be incremented as soon as this pointer is assigned. Although the clutter scene graph should be seen as a descending graph only, every actor *does* hold a persistent pointer to the parent, and somehow supposes that this pointer is valid in many places, while there is no ref mechanism to guarantee such thing. Also, relying on clutter_actor_set_parent to increment the ref count of self is just not very intuitive. The chain of references up to the stage could have been consistently maintained by reversing the reference counting process of parenting, and  no parent would be referenced in the stage. In the end the stage would have a reference count greater than the total number of actors in its scene graph, which is healthy in the same way in my mind. Michael Emmanuele Bassi wrote: On Sun, 2009-03-08 at 02:17 +0200, Michael Boccara wrote: Hi, Sorry if this is a dumb question, or if it was asked 1000 times before. In clutter_actor_set_parent, self ref is incremented. g_object_ref_sink (self); priv->parent_actor = parent; But shouldn't it be the parent actor whose reference should be incremented ? no, that would be wrong. Otherwise, how do you guarantee the validity of the parent_actor pointer ? at some point, an actor must be parented to a Stage -- which does not have a parent actor (and that's also why you don't incremenent the reference count of the parent). hence, every actor is now owned by the stage at the root of the scenegraph. the parenting process should not be viewed as "reference counting management": that is an implementation detail. when you set the parent of an actor you are effectively saying that the parent now owns the child; in GObject-land this means that the parent takes a reference on the child, and releases is when unparent() is called on the child itself. ciao, Emmanuele. -- To unsubscribe send a mail to clutter+unsubscr...@o-hand.com