[erlang-questions] Message Loop in Gen_Server

Lee Sylvester <>
Wed Apr 17 19:57:35 CEST 2013


It's checking for messages from RabbitMQ.

Cheers,
Lee


On 17 Apr 2013, at 18:47, JD Bothma <> wrote:

> Can I ask what your never-exiting loop is doing?
> 
> what is the purpose of the gen_server if the process will forever loop in loop and not deal with gen_server messages?
> 
> 
> On 17 April 2013 19:33, Lee Sylvester <> wrote:
> Hey guys,
> 
> So, I've hit a "best practice" conundrum in OTP; I have a server utilising gen_server for a RabbitMQ consumer.  In the init of that gen_server, I'm setting up a RabbitMQ connection, but I also need to start a loop.  My guess was that I shouldn't call this before init exits, as I was passing the Connection and Channel objects to state for handling elsewhere.  If I handle the loop in init, surely it will never return?
> 
> To simplify what I'm saying (as I'm confusing myself here), here's my code:
> 
> init([]) ->
>     {ok, Connection} = amqp_connection:start(#amqp_params_network{ host="localhost" }),
>     {ok, Channel} = amqp_connection:open_channel(Connection),
>     amqp_channel:call(Channel, #'exchange.declare'{exchange = <<"user_msgs">>,
>                                                    type = <<"direct">>}),
>     #'queue.declare_ok'{queue = Queue} =
>         amqp_channel:call(Channel, #'queue.declare'{exclusive = true}),
>     State = {Channel, Connection},
>     amqp_channel:call(Channel, #'queue.bind'{exchange = <<"user_msgs">>,
>                                               routing_key = term_to_binary(node(self())),
>                                               queue = Queue}),
>     amqp_channel:subscribe(Channel, #'basic.consume'{queue = Queue,
>         no_ack = true}, self()),
>     receive
>         #'basic.consume_ok'{} -> ok
>     end,
>     loop(Channel),
>     {ok, State}.
> 
> Now, if I don't put the loop in my init, then how can I be sure that the loop is called every time the gen_server restarts?  Can someone please suggest the "right" way to call the loop in my gen_server?
> 
> Thanks loads,
> Lee
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