Re: GHashTable ref counting

[Matthias Clasen <mclasen redhat com>]

On Fri, 2005-11-18 at 14:12 +0100, Tim Janik wrote:
> hi all,
> 
> the GtkRC logical colors bug provides a motivation for reference counted 
> GHashTables:
>    http://bugzilla.gnome.org/show_bug.cgi?id=114355
> several options exist to adress this situation:
> 1) implement an internal ref-counting wrapper for GHashTable, used in the
>     implementation of #114355 solely.
>     access to the hash table is awkward through an extra indirection and
>     this doesn't scale beyond gtk internals, i.e. other apps are likely to
>     have to duplicate this solution.
> 2) introduce a GObject-based GHashTable wrapper (the approach choosen in
>     the attached implementation, called GtkHashTable).
>     access to the hash table is awkward through a GtkHashTable->hash
>     indirection, and Gtk isn't really the right place for a GLib hash
>     table wrapper.
> 3) implement hash table reference counting in GLib natively, also allowing
>     the use of hash tables as boxed types.
> 
> i consider (3) to be the best solution, so i intend to implement the following:
> 
> @@ ghash.h
> +/* keeping hash tables alive */
> +GHashTable* g_hash_table_ref   (GHashTable *hash_table);
> +void        g_hash_table_unref (GHashTable *hash_table);
> @@ gboxed.h
>   /* --- GLib boxed types --- */
>   #define G_TYPE_GSTRING          (g_gstring_get_type ())
> +#define G_TYPE_HASH_TABLE       (g_gstring_get_type ())
> 
> lifetime maintenance of hash tables will look like this:
> 
>    /* create a new hash table with a reference count of 1 */
>    GHashTable* g_hash_table_new               (GHashFunc       hash_func,
>                                                GEqualFunc      key_equal_func);
> 
>    /* remove all nodes from hash table, do a single unref() */
>    void        g_hash_table_destroy           (GHashTable     *hash_table);
> 
>    /* increment reference count by 1 */
>    GHashTable* g_hash_table_ref   (GHashTable *hash_table);
> 
>    /* decrement reference count by 1.
>     * if it drops to 0, remove all nodes, free the hash table structure
>     */
>    void        g_hash_table_unref (GHashTable *hash_table);
> 
> this would mean the semantics of the existing API is preserved while adding
> reference counting.
> 
> the G_TYPE_HASH_TABLE boxed type will use hash table reference counting to
> implement boxed_copy and boxed_free, since copying of entire hash tables can
> not be supported generically anyway (that is, without recursive type
> information, which GType doesn't support).

Looks like a relatively unintrusive way to add the needed functionality.
It will look a bit funny to have some refcounted data structure in glib,
and some non-refcounted ones, but io channels and main loops already set
a precedent for that.

Matthias