[erlang-questions] UDP client/server performance

Michael Santos <>
Wed Aug 15 16:03:07 CEST 2012

On Wed, Aug 15, 2012 at 09:59:22AM +0200, Ronny Meeus wrote:
> On Wed, Aug 15, 2012 at 2:53 AM, Michael Santos
> <> wrote:
> > On Tue, Aug 14, 2012 at 10:10:57PM +0200, Ronny Meeus wrote:
> >> Hello
> >>
> >> thanks for the info.
> >> I'm currently playing with the procket and it is working well.
> >>
> >> I have 2 questions:
> >>
> >> - I need to run the erl as root (or use sudo to start it) or I get:
> >>
> >> 2> {ok, FD} = procket:open(53, [{protocol, udp},{type, dgram},{family, inet}]).
> >> ** exception error: no match of right hand side value {error,eperm}
> >
> > Make priv/procket setuid or allow your user to call priv/procket using
> > sudo.
> I tried all options mentioned in your readme already before but non of
> them seem to work on Ubuntu. I think there is an issue with the sudo
> stuff on this distribution since no matter what I do, it always ask
> for a password when the procket command is executed.
> Now I succeeded by explicitly specifying the name of the program to use:
> procket:open(53, [{progname,"/usr/local/bin/procket"},{protocol,
> udp},{type,dgram}]).

procket uses priv/procket as the default path. Sorry, README should be

> >> - How do I use recvfrom/4 in the server? If I call recvfrom/4 when
> >> there is no message present in the socket, it returns an error since
> >> the socket is put in async mode.
> >
> > Yes, the socket has to be non-blocking or it will block the scheduler.
> >
> >> Does this mean that the socket needs
> >> to be polled by the Erlang process or is it possible to get a
> >> notification (msg) when there is data present in the socket so that
> >> the recvfrom/4 can be called at that moment?
> >
> > You could plug the fd back into gen_udp:open(Port, [{fd, FD}]) ;)
> >
> > For a UDP socket, I can't think of any options other than the ones
> > you've mentioned: either spin on EAGAIN or use another NIF to notify you
> > when the socket is ready. There are a few ports to libev and libuv around.
> OK I will look around.
> Thanks.
> Yesterday I did a quick test and created an application that once it
> receives a message, it starts to send this back in a loop.
> It looks like it is able to send almost 200Kpkts/sec on a low end PC
> while the gen_udp solution only was able to send something like
> 10Kpks/sec on a much more powerful PC. So it looks promising ...

That's cool! But remember, the C and the Erlang examples you posted are
doing different things. The C code is single tasking. It doesn't do any
error handling either. The Erlang code is multitasking, switching
between processes, monitoring processes for failure, ....

If you run C NIF code in a tight loop, you'll get something closer to
the single tasking C code at the expense of concurrency. Maybe that is
fine for your needs though. Anyway, good luck in hitting your numbers!

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