Re: [PATCH v25 0/9] MR3103: server: Create and use a desktop shared mapping for GetCursorPos.

[Rémi Bernon (＠rbernon)]

On Sat Mar 16 09:44:22 2024 +0000, Jinoh Kang wrote:
> This will scan the entire objects array once the last index has been
> occupied (object_count full).
> Instead, how about replacing `object_count` with `last_object_index`?
> This field doesn't actually count valid objects anyway, since some
> objects in the middle could be freed later. Instead, I would keep track
> of the *last* object index and start from there.
>     unsigned int index = session.last_object_index;
>     for (;;)
>     {
>         index = (index + 1) % session.shared->object_capacity;
>         if (!session.shared->objects[index].obj.id)
>         {
>             /* found a free index */
>             break;
>         }
>         /* check if we're back to the starting point */
>         if (index == session.last_object_index)
>         {
>             /* all slots exhausted; skip to first index to be allocated */
>             index = session.shared->object_capacity;
>             break;
>         }
>     }
>     while (index >= session.shared->object_capacity)
>     {
>         if (grow_session_mapping()) return -1;
>     }
>     session.last_object_index = index;
>     SHARED_WRITE_BEGIN( &session.shared->objects[index], session_obj_t )
>     {
>         assert(!shared->obj.id);
>         shared->obj.id = ++session.last_object_id;
>     }
>     SHARED_WRITE_END;
>
> Note that the following initialization is also required:
>     session.last_object_index = -1;

I've changed it to something similar, though mostly because it makes the code slightly simpler. I don't see what difference it makes as looking from a free index starting from the previous one doesn't seem obviously more efficient than from the beginning.