preventing double remove of Avl_node_base

[Norman Feske]

Hi Jaeyong,

> Avl_node_base::remove function removes itself from the Avl_tree and leaves
> the _parent and _child[] variables as they are.
> Since someone could try to remove the same Avl_node_base twice by mistake,
> it results in the crash of Avl_tree datastructure.
> So, how about setting _parent and _child[] to NULL at Avl_node_base::remove
> and, at the entry of the remove function, if someone tries to remove twice,
> we could warn him.

thank you for this sensible suggestion. I have just added it to the
issue tracker:

  https://github.com/genodelabs/genode/issues/597

Best regards
Norman

-- 
Dr.-Ing. Norman Feske
Genode Labs

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