[erlang-questions] Supervising UDP listener

[Kamrul Khan]

Hello Steve,
Thanks for your response. I want to check if the supervisor is doing its job. Whats the best way for me to simulate an abnormal termination.
CheersKamrul
Date: Fri, 20 Nov 2015 18:53:11 +0000
From: steve@REDACTED
To: ulf@REDACTED; dodul@REDACTED
CC: erlang-questions@REDACTED
Subject: Re: [erlang-questions] Supervising UDP listener






You create udp_listener with spawn_link, which would kill the parent *if* udp_listener terminates abnormally. In your case, udp_listener is exiting cleanly, so it won't cause the parent to die.


Cheers.



Steve



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On 20 Nov 2015, 17:38 +0000, Kamrul Khan <dodul@REDACTED>, wrote:


I didnt get any response for my question. I am posting it again ( with the typo fix)


I am trying to make a UDP listener that will be supervised by a supervisor module (Just for learning purpose).  below id my Supervisor code:


-module(pdmanager_sup).
-behaviour(supervisor).
 
-export([start_link/1]).
-export([init/1]).
 
start_link(Port) ->
supervisor:start_link({local,?MODULE}, ?MODULE, Port).
 
init(Port) ->
    {ok, {{one_for_one, 5, 60},
        [{listener,
            {pdmanager, start_link, Port},
            permanent, 1000, worker, [pdmanager]}
        ]}}.



And my udp listener (pdmanager) looks like the below:


-module(pdmanager).
-behaviour(gen_server).

-export([start_link/1]).
-export([init/1]).
-export([
    udplistener/1,
    handleudp/1
]).

-record(state, {socket}).

start_link(Port) ->
    gen_server:start_link({local, pdmanager}, pdmanager, Port, []).

init(Port) ->
    io:format("UDP Server starting ~n",[]),
    {ok, Socket} = gen_udp:open(Port, [binary, {active, false}]),
    spawn_link(pdmanager,udplistener,[Socket]),
    {ok, #state{socket=Socket}}.

udplistener(Socket) ->
    {ok,Packet} = gen_udp:recv(Socket,0),
    {_,_,Msg} = Packet,
    if
        Msg /= "stop" ->
            io:format("Stoping UDP listener ~n", []);
        true ->
            spawn(pdmanager,handleudp,[Packet]),
            udplistener(Socket)
    end.
    
handleudp(Packet) ->
    {_,_, Msg} = Packet,
    io:format("I have got message : ~s ~n",[Msg]),
    {handeling, Packet}.



Now: after compiling I start my program with :

pdmanager_sup:start_link(5678).

It gets started and I can see the "UDP server starting" message in my screen. Next, when I send a message to UDP 5678 port I see the message "stoping UDP listener" as expected.  However, it doesnt restart my server.  I called udplistener/1 function from init/1 using spawn_link. I expected spawn_link will link the new process (udp listener) with the calling process (the worker process in this case) and if udplistener goes down the worker will go down aswell and that will cause the supervisor to restart the worker. However, I didnt work that way. 

How should I do it ? 




From: dodul@REDACTED

To: ulf@REDACTED

Date: Fri, 20 Nov 2015 13:33:13 +0600

CC: erlang-questions@REDACTED

Subject: Re: [erlang-questions] Supervising UDP listener




Typo. Sorry about that. should be 
pdmanager_sup:start_link(5678).





Subject: Re: [erlang-questions] Supervising UDP listener

From: ulf@REDACTED

Date: Thu, 19 Nov 2015 21:56:09 -0800

CC: erlang-questions@REDACTED

To: dodul@REDACTED







On 19 Nov 2015, at 15:45, Kamrul Khan <dodul@REDACTED> wrote:


Now: after compiling I start my program with :


pdmanager:start_link(5678).





Not pdmanager_sup:start_link(5678)?


BR,
Ulf W





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