[dpdk-dev] preallocation of void ** obj_p of rte_ring_dequeue

[Cyril Cressent]

On Wed, Nov 06, 2013 at 12:47:13AM +0800, Jose Gavine Cueto wrote:

> Your'e welcome, and by the way the multiprocess example of simple_mp seems
> confusing here:
> 
> static int
> lcore_recv(__attribute__((unused)) void *arg)
> {
> unsigned lcore_id = rte_lcore_id();
> 
> printf("Starting core %u\n", lcore_id);
> while (!quit){
> void *msg;
> if (rte_ring_dequeue(recv_ring, &msg) < 0){
> usleep(5);
> continue;
> }
> printf("core %u: Received '%s'\n", lcore_id, (char *)msg);
> rte_mempool_put(message_pool, msg);
> }
> 
> return 0;
> }
> 
> It seems that it isn't allocating msg here, or maybe I'm just missing something

I understand your question better now, and in that light I think my
previous answer was confusing. Let me try to clarify:

A ring only holds *pointers* to objects.  You enqueue pointers, and
dequeue those pointers later, somewhere else, usually in another thread.
The allocation/deallocation of the actual objects is none the concern of
the ring and its enqueue/dequeue operations.

If we take the simple_mp example, the msg dequeued by the lcore_recv()
thread is created in mp_command.c and a pointer to that message is
enqueued on "send_ring". If you read carefully how the rings are created
you'll understand how "send_ring" and "recv_ring" relate to each other.

I hope this is a bit clearer,

Cyril