> -----Original Message-----
> From: ext Olivier MATZ [mailto:olivier.matz at 6wind.com]
> Sent: Tuesday, August 04, 2015 8:57 PM
> To: Yan, Liming (Nokia - CN/Hangzhou); dev at dpdk.org
> Subject: Re: [dpdk-dev] Could DPDK ring provide peek interface or any
> comments for this function?
>
> 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.
>
[limiyan wrote]
Seems it's good for sc-ring. Could this be promoted into formal DPDK?
For mc-ring peek, at least I think it's quite complicated even if we use
something like ref_count and delayed free.
>
> 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
> >
> >
