Added supervisor(s) for a gen_server, shutdown immediately?

Question

EDIT: Below.

Why is my supervised gen_server shutting down so quickly?

I'll give these organizational names to make it more clear the chain of command that I want in my application: First I'm starting with the "assembly_line_worker" then later I'll add the "marketing_specialist" to my supervision tree...

ceo_supervisor.erl

-module(ceo_supervisor).
-behaviour(supervisor).

-export([start_link/1]).
-export([init/1]).

start_link(State) ->
     supervisor:start_link({local,?MODULE}, ?MODULE, [State]).

init([Args]) ->
     RestartStrategy = {one_for_one, 10, 60},
     ChildSpec= {assembly_line_worker_supervisor,
          {assembly_line_worker_supervisor, start_link, [Args]},
          permanent, infinity, supervisor, [assembly_line_worker_supervisor]},
     {ok, {RestartStrategy, [ChildSpec]}}.

assembly_line_worker_supervisor.erl

-module(assembly_line_worker_supervisor).
-behaviour(supervisor).

-export([start_link/1]).
-export([init/1]). %% Internal

start_link(State) ->
    supervisor:start_link({local, ?MODULE}, ?MODULE, [State]).

init([Args]) ->
    RestartStrategy = {one_for_one, 10, 60},
    ChildSpec = {assembly_line_worker, {assembly_line_worker, start_link, [Args]}, permanent,     
        infinity, worker, [assembly_line_worker]},
    {ok, {RestartStrategy, [ChildSpec]}}.

assembly_line_worker.erl

-module(assembly_line_worker).
...

init([State]) ->
   process_flag(trap_exit, true),
   {ok, State}.

start_link(State) ->
    gen_server:start_link({global, ?MODULE}, ?MODULE, [State], []).

handle_cast(...,State} ->
    io:format("We're getting this message.~n",[]),
    {noreply, State};
...

What's happening is that the assembly line worker does a few bits of work, like receiving a couple of messages that are sent just after the ceo_supervisor:start_link(#innovative_ideas{}) command is called, then it shuts down. Have any idea why? I know that the gen_server is receiving a few messages because it io:format's them to the console.

Thanks!

EDIT: I'm hosting this on Windows via erlsrv.exe and I found that when I start up my program via a function like so:

start() ->
    ceo_supervisor:start_link(#innovative_ideas{}),
    assembly_line_worker:ask_for_more_pay(), %% Prints out "I want more $$$" as expected,
    ok.

...this function exiting immediately causes my supervisors / gen_servers to shut down. I would expect this because all of this is linked via supervision to the original calling process, so when that exits so should the children.

So I guess a better question would be, how can I allow my supervisors to keep running after going through all of the start up configuration? Is there an option other than wrapping all of this in an application? (Which doesn't sound too bad...)

Thanks for the probing questions! I learned more about supervisors that way.

batman

Can you provide more of your asembly_line_worker.erl? If this module crashes more than 10 times in 60 seconds, it won't be restarted again. I'm guessing something is causing it to exceed that max restart limit, but I need to see more code. — Jr0
It's a couple hundred lines long, but I know that I can start it up without the supervisors just fine and it doesn't crash / throw exceptions for that matter. What would it help to see? — batman
Could please give an example of how you call the functions when you start the supervisors? I am wondering if all the lists in your childspecs and init functions match. Unfortunately the documentation uses "Args" to mean both a real necessary list of arguments and just one chunk of argument data. — rvirding
Added more information. Yeah, I've never appreciated that in the docs, I think it should be changed to ArgsList — batman

Andreas Hasselberg Andreas Hasselberg · Accepted Answer · 2012-10-11T09:13:32

To get more information about what is happening start sasl before you start your supervisor: application:start(sasl).

Another way to debug this would be to start the worker from your erlang shell send the sequence of message that crashed the server. Btw: are you sure that you need 2 levels of supervisors?

Added supervisor(s) for a gen_server, shutdown immediately?

2 Answers