Make safe double remove?

[Jason Ekstrand]

Jonathan,
I have thought on multiple occations about doing this exact thing.  If we
do, we should probably also make wl_list_insert_list safe.

The counter-argument for all this is that you have to keep track of whether
or not your elements are in a list anyway to avoid corruption.  For
instance, you still have to watch for double wl_list_insert which will also
break things badly.  You could say, "We'll modify wl_list_insert so it's
safe too" but then you inserting an element that is already in a list
becomes "safe" from a segfault perspective and you make it easy to have
program logic errors that don't result in a crash, just things being subtly
wrong and impossible to track down.

All said, I think I'd be in favor of making double-remove safe.  However,
it's not a silver bullet.
--Jason Ekstrand
On Jan 28, 2014 11:22 AM, "Jonathan Howard" <jonathan at unbiased.name> wrote:

> Code is already using wl_list_init to have the construction of unlinked
> items in a stable state so that they can be destroyed with wl_list_remove.
>
> A problem is it is easy to write code that calls wl_list_remove during the
> structures life and miss that you need to reset with wl_list_init for when
> it is later destroyed.
>
> Having wl_list_remove place items in this unlinked state makes the
> destruction safe (and makes quite a few lines of code redundant.)
>
> --- wayland-util.c      2014-01-28 16:09:13.179052955 +0000
> +++ wayland-util.c.init 2014-01-28 16:13:32.225704904 +0000
> @@ -52,8 +52,8 @@
>  {
>         elm->prev->next = elm->next;
>         elm->next->prev = elm->prev;
> -       elm->next = NULL;
> -       elm->prev = NULL;
> +       elm->next = elm;
> +       elm->prev = elm;
>  }
>
>  WL_EXPORT int
>
> _______________________________________________
> wayland-devel mailing list
> wayland-devel at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/wayland-devel
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freedesktop.org/archives/wayland-devel/attachments/20140128/1d457f7a/attachment.html>