[erlang-questions] supervisor woes

Brian Williams <>
Wed Sep 8 22:21:22 CEST 2010


This may help you get more detailed error reports, but I'm not sure it
works if you're running outside of an application.
application:load(sasl).
application:start(sasl).

* generate your error *

I usually get better error messages when this is running.



On Wed, Sep 8, 2010 at 3:16 PM, Jared Nance <> wrote:
> Hi Adam-
> Here's the definition of ios_faux_card:start_link/1
>
> start_link(CardSlot) when is_atom(CardSlot) ->
>        gen_server:start_link({local,CardSlot}, ?MODULE, [CardSlot,2], []).
>
> Is this the problem?
>
> JN
>
> On Sep 8, 2010, at 11:59 AM, Adam Kocoloski wrote:
>
>> On Sep 8, 2010, at 11:36 AM, Jared Nance wrote:
>>
>>> Hello List-
>>> Thanks in advance for whatever help you can offer.  I'm putting together a supervision tree which is rather simple - at the moment, there is a supervisor that manages several other supervisors, and those supervisors each manage only worker nodes.  The problem I am having is with one of my supervisors which manages 4 worker nodes.  Each node is a gen_server that uses the same callback module, but with different arguments to start_link.  The childspec for the worker nodes looks like
>>>
>>> {cardA, {ios_faux_card, start_link, [cardA]}, permanent, brutal_kill, worker, [ios_faux_card]}
>>>
>>> and so the supervisor for these workers is started with a child spec that looks like
>>>
>>> {{one_for_one, 5, 10}, [{ios_card_super, {ios_card_super, start_link, [{cardA, {ios_faux_card, start_link, [cardA]}, permanent, brutal_kill, worker, [ios_faux_card]}], permanent, infinity, supervisor, [ios_card_super]}
>>>
>>> and that works just fine.  the problem arises when i try to add a second (or third, or fourth) gen_server to the list of processes that the ios_card_super is supervising.  if i try starting it with this child spec instead:
>>>
>>> {{one_for_one, 5, 10}, [{ios_card_super, {ios_card_super, start_link, [{cardA, {ios_faux_card, start_link, [cardA]}, permanent, brutal_kill, worker, [ios_faux_card]},{cardB,{ios_faux_card, start_link, [cardB]}, permanent, brutal_kill, worker, [ios_faux_card]}], permanent, infinity, supervisor, [ios_card_super]}
>>>
>>> it refuses to start.  what's more, the only response I get out of it is {error, shutdown}.  I have put io:format debug statements in the ios_faux_card module and it's clear that start_link/1is never being called when there are 2+ workers to supervise.
>>>
>>> Thanks for whatever help you can offer on this very frustrating issue.
>>>
>>> Jared N
>>
>> Hi Jared, you wouldn't happen to be trying to register the process in ios_faux_card, would you?
>>
>> Adam
>>
>>
>>
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-- 
Brian E. Williams

http://www.techhouse.us/wordpress-mu/brianw

"Never attribute to malice that which can be adequately
explained by stupidity." - Hanlon's Razor


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