[ltt-dev] [PATCH 2/9] keep the last position for failed lookup

[Mathieu Desnoyers]

* Lai Jiangshan (laijs at cn.fujitsu.com) wrote:
> Signed-off-by: Lai Jiangshan <laijs at cn.fujitsu.com>
> ---
>  rculfhash.c            |   19 +++++++++++--------
>  tests/test_urcu_hash.c |    5 +++--
>  urcu/rculfhash.h       |   17 +++++++++++------
>  3 files changed, 25 insertions(+), 16 deletions(-)
> 
> diff --git a/rculfhash.c b/rculfhash.c
> index bda3bd6..cbfc79e 100644
> --- a/rculfhash.c
> +++ b/rculfhash.c
> @@ -1381,27 +1381,28 @@ struct cds_lfht *_cds_lfht_new(unsigned long init_size,
>  	return ht;
>  }
>  
> -void cds_lfht_lookup(struct cds_lfht *ht, unsigned long hash,
> +bool cds_lfht_lookup(struct cds_lfht *ht, unsigned long hash,
>  		cds_lfht_match_fct match, void *key,
>  		struct cds_lfht_iter *iter)
>  {

[...]

>  #define cds_lfht_for_each_duplicate(ht, hash, match, key, iter, node)	\
> -	for (cds_lfht_lookup(ht, hash, match, key, iter),		\
> -			node = cds_lfht_iter_get_node(iter);		\
> +	for (node = cds_lfht_lookup(ht, hash, match, key, iter) ?	\
> +			cds_lfht_iter_get_node(iter) : NULL;		\

Hrm, is it me or this just complexifies use of this API ? Now, instead
of a 

  cds_lfht_lookup -> cds_lfht_iter_get_node -> check for null

chain, we need to do:

  cds_lfht_lookup -> check for nonzero return ? cds_lfht_iter_get_node :
                                                    NULL -> check for NULL

actually adding one test into the caller code.

What use-case is it allowing to justify this added API complexity ?

Thanks,

Mathieu

>  		node != NULL;						\
>  		cds_lfht_next_duplicate(ht, match, key, iter),		\
>  			node = cds_lfht_iter_get_node(iter))
> @@ -391,8 +395,9 @@ void cds_lfht_resize(struct cds_lfht *ht, unsigned long new_size);
>  
>  #define cds_lfht_for_each_entry_duplicate(ht, hash, match, key,		\
>  				iter, pos, member)			\
> -	for (cds_lfht_lookup(ht, hash, match, key, iter),		\
> -			pos = caa_container_of(cds_lfht_iter_get_node(iter), \
> +	for (pos = caa_container_of(					\
> +			cds_lfht_lookup(ht, hash, match, key, iter) ?	\
> +			cds_lfht_iter_get_node(iter) : NULL,		\
>  					typeof(*(pos)), member);	\
>  		&(pos)->member != NULL;					\
>  		cds_lfht_next_duplicate(ht, match, key, iter),		\
> -- 
> 1.7.4.4
> 

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com