Hey Philip,
Thanks for your patience...
It is certainly possible that ARPQuerier should do the queueing instead of
ARPTable.
The "logic" for for the current behavior is as follows: ARP responses are
sensitive to a given NIC, so if multiple ARPQueriers share an ARPTable, it's
OK that all queued packets are emitted from *WHICHEVER* ARPQuerier happens to
receive the response.
I don't completely buy this "logic". But could you explain more about your
application, to help me understand the ideal final behavior? Why do you want
to share ARPTables? Is this a sort of a RouterBricks thing, where you have
multiple ARPQueriers on different threads, writing to multiple output queues
on THE SAME output NIC?
Eddie
On 02/12/2011 11:22 AM, Philip Prindeville wrote:
> I wanted to make a change to ARPTable which would give it the ability to
> invoke a hook back to ARPQuerier when it deletes queued up packages, but
> wasn't sure if there's a clean way to do this.
>
> In C, I'd just set a pointer to a callback function, but this isn't C.
>
> So what's the best way to do it? Keep in mind that the ARPTable might have
> been
>
> Also, it's the case that the same ARPTable instance might be shared amongst
> several ARPQuerier instances (because we're in a multi-core environment with
> several threads running on the same NIC).
>
> Oh, one other question about ARPTable vs. ARPQuerier interactions... if I
> have that same situation where I'm running multithreaded, and a response
> packet gets delivered to one ARPQuerier, thereby updating the ARPTable...
> will the queued up packets in each instance of the ARPQueriers get updated
> and unblock the packets?
>
> Or are the queued packets actually held by the ARPTable (and therefore in a
> single place)?
>
> Looking at how ARPQuerier::handle_ip() and ARPQuerier::handle_response()
> interact, it looks like the packets are all held by the ARPTable, and when
> the queue gets drained, all drained by the same instance... so any affinity
> of individual packets to threads is lost.
>
> Packet *cached_packet;
> arpt->insert(ipa, ena,&cached_packet);
>
> while (cached_packet) {
> Packet *next = cached_packet->next();
> handle_ip(cached_packet, true);
> cached_packet = next;
> }
>
>
> Correct?
>
> Thanks.
>
> -Philip
>
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