[erlang-questions] UDP concurrent server

[Fred Hebert]

On 12/09, Bogdan Andu wrote:
>init([Port, Ip]) ->
>        process_flag(trap_exit, true),
>
>        {ok, Sock} = gen_udp:open(Port, [binary,
>                            {active, false},
>                             {reuseaddr, true},
>                            {ip, Ip}
>        ]),
>
>        {ok, #udp_conn_state{sock = Sock}, 0}.
>handle_info({udp, Socket, Host, Port, Bin}, State) ->
>     {noreply, State, 1};
>
>handle_info(timeout, #udp_conn_state{sock = Sock} = State) ->
>    inet:setopts(Sock, [{active, once}]),
>    {noreply, State};
>
>handle_info(Info, State) ->
>    {noreply, State}.
>

Uh, interesting. So one thing I'd change early would be to go:

    handle_info({udp, Socket, Host, Port, Bin}, State=#udp_conn_state{sock = Sock}) ->
        inet:setopts(Sock, [{active,once}]),
        {noreply, State};

(and do the same in `init/1')

This at least would let yo consume information much faster by avoiding 
manual 1 ms sleeps everywhere. Even a `0' value may help. It doesn't 
explain the leaking at all though.

What would explain it is that if you're not matching the message (as in 
your original email), then you never set the socket to 'active' again, 
and you never receive traffic.

If that's the problem, then you have been measuring a process that 
receives traffic to a process that does not. It certainly would explain 
the bad behaviour you've seen.

If you want to try to see if a garbage collection would help, you can 
try the 'recon' library and call 'recon:bin_leak(10)' and it will take a 
snapshot, run a GC on all processes, then return you those that lost the 
most memory. If yours is in there, then adding 'hibernate' calls from 
time to time (say, every 10,000 packets) could help keep things clean.

It sucks, but that might be what is needed if the shape of your data is 
not amenable to clean GCs. If that doesn't solve it, then we get far 
funner problems with memory allocation.