On Tue, Feb 12, 2019 at 06:29:58PM +1100, Tobin C. Harding wrote:
> The XArray is, in a way, a replacement data structure for linked lists,
> as such, on first use developers may wonder if it is safe to remove
> items while iterating over the array.
>
> For example, this is fine:
>
> DEFINE_XARRAY(things);
>
> void cleanup()
> {
> struct thing *thing;
> unsigned long index;
>
> xa_for_each(&things, index, thing)
> xa_erase(&things, index);
> }
>
> Document this feature explicitly in the docs and also for the macro
> definition.
>
> Signed-off-by: Tobin C. Harding <tobin@xxxxxxxxxx>
> ---
>
> Hi Willy,
>
> I had my first go using the XArray today and during that I wondered if
> it was safe to remove items during iteration. Conceptually it seems
> fine and it seemed to work just fine in code - is this something people
> should not be doing for any reason? Is this the best way to traverse
> the tree and get every thing just to erase it? Are we even supposed to
> be thinking this is a tree or should we just be thinking it is an array?
>
> (As you might have guessed I _still_ don't know exactly how a radix tree
> works :)
>
> Oh, and FTR the XArray is hot - good effort man.
>
> thanks,
> Tobin.
>
>
> Documentation/core-api/xarray.rst | 3 ++-
> include/linux/xarray.h | 2 ++
> 2 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/core-api/xarray.rst b/Documentation/core-api/xarray.rst
> index 5d54b27c6eba..2578e0bdaa17 100644
> --- a/Documentation/core-api/xarray.rst
> +++ b/Documentation/core-api/xarray.rst
> @@ -97,7 +97,8 @@ You can copy entries out of the XArray into a plain array by calling
> :c:func:`xa_extract`. Or you can iterate over the present entries in
> the XArray by calling :c:func:`xa_for_each`. You may prefer to use
> :c:func:`xa_find` or :c:func:`xa_find_after` to move to the next present
> -entry in the XArray.
> +entry in the XArray. It is safe to call :c:func:`xa_release` on entries
> +as you iterate over the array using :c:func:`xa_for_each`.
Re-reading documentation this line may be in the wrong place .
Perhaps it would be better added at the end of the 'Normal API' section?
Finally, you can remove all entries from an XArray by calling
:c:func:`xa_destroy`. If the XArray entries are pointers, you may wish
to free the entries first. You can do this by iterating over all present
entries in the XArray using the :c:func:`xa_for_each` iterator. It is safe
to call :c:func:`xa_erase` while iterating the array.
I'm a bit lazy when I read docs and soon as I find an answer I stop
reading (bad Tobin) so it might be nice to tie the first mention of
xa_for_each with the comment on xa_erase _and_ the section on
xa_destroy. Man, writing docs is never as easy as it first appears.
Oh and I sent v2 already but it hasn't shown up in my inbox so replying
here on v1.
thanks,
Tobin.
