Hi,
On 08/04/2015 04:20 AM, Yan, Liming (Nokia - CN/Hangzhou) wrote:
> Hi,
> As we see, DPDK ring has mainly the enqueue/dequeue APIs for SINGLE/MULTI
> producer/consumer. I have a requirement in work to take a peek on the top
> object in the ring. I don't want to consume it, just check the reference of
> the object. How could this be supported? Or any alternative solution for
> my requirement? Thanks.
> I wrote my own simple peek interface but it's not MC-safe. I think it's
> better if DPDK can support it officially.
I think it's a good idea. I think we could avoid a test by using
the same naming convention than other functions applying to single
consumer rings.
I'm not sure the function is safe on mc rings: the pointer returned
via peek() should not be accessed while another core dequeues the
object and modify/free it.
A simplified version would be something like that:
/**
* Peek one object from a single-consumer ring
*
* The returned object is not dequeued. This function does not work
* on a multi-consumers ring.
*
* @param r
* A pointer to the ring structure.
* @param obj_p
* A pointer to a void * pointer (object) that will be filled.
* @return
* - 0: Success; objects dequeued.
* - -ENOENT: Not enough entries in the ring to peek
*/
static inline int
rte_ring_sc_peek(struct rte_ring *r, void **obj_p)
{
if (unlikely(rte_ring_empty(r)))
return -ENOENT;
*obj_p = r->ring[r->cons.head & r->prod.mask];
return 0;
}
Regards,
Olivier
>
>
> /**
> + * Just take a peek on the top object from a ring but not consume it.
> + * Note: This interface is MC and multi-thread not safe.
> + * It can only be used for ring with RING_F_SC_DEQ attribute.
> + *
> + * @param r
> + * A pointer to the ring structure.
> + * @param obj_p
> + * A pointer to a void * pointer (object) that will be filled.
> + * @return
> + * - 0: Success, object is peeked.
> + * - -ENOENT: Not entries in the ring.
> + * - - EPERM: Operation not permitted/supported
> + */
> +static inline int __attribute__((always_inline))
> +rte_ring_peek(const struct rte_ring *r, void **obj_p)
> +{
> + uint32_t cons_head, prod_tail;
> +
> + if (r->cons.sc_dequeue) {
> + cons_head = r->cons.head;
> + prod_tail = r->prod.tail;
> +
> + if (prod_tail - cons_head == 0) {
> + return -ENOENT;
> + }
> + *obj_p = r->ring[cons_head & r->prod.mask];
> + } else {
> + return -EPERM;
> + }
> + return 0;
> +}
> +
> +/**
>
>
> --------^_^--------
> Best Regards
> Yan Limin
>
>
