[erlang-questions] Message Loop in Gen_Server

Lee Sylvester <>
Wed Apr 17 19:33:04 CEST 2013


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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