More of a for argument as I see it. With unlinked state you can have if
desired a wl_list_unlinked function (identical to empty as used on the
head.)
Changing wl_list_insert is a code breaker as it is used to initialise at
the moment so can't inspect the element. There remains other unsafe
calls you should not do.
wl_list_remove changed isn't 100% guaranteed to not break anything, on
the other hand there is no guarantee the code does not have the fatal
double remove already. I would rather not have to debug to figure out
remove was double called as the extremely likely fix is correcting that
I wanted the call to be safe.
On 28/01/14 19:36, Jason Ekstrand wrote:
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" <[email protected]
<mailto:[email protected]>> 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
<tel: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
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