[erlang-questions] Need help with simple_one_for_one

Mazen Harake <>
Wed Aug 20 19:00:51 CEST 2008


Hi Matt,

Sorry this might be a stupid question but did you send it an event?

/Mazen

Matt Williamson wrote:
> I hate to keep bugging with simple problems, but I'm stuck again. My 
> FSM dosn't seem to be executing its first state. Here is my init function:
>
> /init(StartArgs) ->
>     InitialState = case StartArgs of
>     {store_chunk, Chunk} ->
>         io:format("FSM Storing chunk...~n"),
>         {ok, storing_chunk, [Chunk]};
>     {get_chunk, Args} ->
>         {ok, getting_chunk, Args};
>     Else ->
>         %% @todo Add error logging here.
>         io:format("Bad arg for FSM: ~p~n", [StartArgs])
>     end,
>     io:format("FSM Initial State: ~p~n", [InitialState]),
>     InitialState./
>
> storing_chunk/2 is exported and I'm not getting any errors. Here is 
> that function:
>
> /storing_chunk(_Event, [Chunk]) ->
>     io:format("STATE: storing_chunk~n"),
>     case erlfs_store_lib:store_chunk() of
>     ok ->
>         {next_state, notifying_tracker, Chunk};
>     {error, Reason} ->
>         %% @todo Add error logging here.
>         io:format("FSM Stopped: ~p~n", [Reason]),
>         {stop, {file, Reason}, Chunk#chunk.chunk_meta}
>     end./
>
> On Wed, Aug 20, 2008 at 11:04 AM, Serge Aleynikov < 
> <mailto:>> wrote:
>
>     The error you reported earlier:
>
>     {'EXIT', {badarg, [{erlang, apply,
>        [erlfs_store_worker_fsm, start_link, {store_chunk, ...}]}]}}
>
>     was a clear indication that erlang:apply(M,F,A) was called with A
>     being a tuple rather than a list.  If this still doesn't work
>     after replacing tuple with a list in the second argument of the
>     supervisor:start_child/2 call, this means that you probably have
>     other issues in the erlfs_store_worker_fsm:start_link/1 itself.
>
>     I can't say anything more without seeing a more detailed error report.
>
>     Serge
>
>
>     Matt Williamson wrote:
>
>         Yes, I saw that in the docs. What I was saying is that calling
>         apply(M, F,
>         A++List) =:= apply(M, F, List) when A =:= [].
>
>         I did try your suggestion anyway with the same results.
>
>         On Wed, Aug 20, 2008 at 9:54 AM, Serge Aleynikov
>         < <mailto:>> wrote:
>
>             What is the arity of erlfs_store_worker_fsm:start_link
>             function?
>
>             Not quite sure what you mean by [] ++ 1 below.
>
>             The supervisor:start_child/2 takes a list [term()] as the
>             second parameter.
>              Here's its docs:
>
>             "If the case of a simple_one_for_one supervisor, the child
>             specification
>             defined in Module:init/1 will be used and ChildSpec should
>             instead be an
>             arbitrary list of terms List. The child process will then
>             be started by
>             appending List to the existing start function arguments,
>             i.e. by calling
>             apply(M, F, A++List) where {M,F,A} is the start function
>             defined in the
>             child specification."
>
>             Note the A++List part.
>
>
>             Matt Williamson wrote:
>
>                 I'm afraid that did not work. I am passing an empty
>                 list, and if I execute
>                 [] ++ 1 in the shell I get 1.
>
>                 On Wed, Aug 20, 2008 at 9:31 AM, Serge Aleynikov
>                 < <mailto:>>
>                 wrote:
>
>                  Try starting it as:
>
>                     supervisor:start_child(erlfs_store_worker_sup,
>                     [{store_chunk, Chunk}])
>
>                     The simple_one_for_one strategy appends the
>                     arguments passed to
>                     supervisor:start_child/2 to the list of args
>                     specified in the
>                     supervisor's
>                     spec.
>
>                     Serge
>
>                     Matt Williamson wrote:
>
>                      Hello,
>
>                         I am starting a gen_fsm with
>                         supervisor:start_child(erlfs_store_worker_sup,
>                         {store_chunk, Chunk}) but I get the following
>                         error:
>
>                         {error,
>                                                         {'EXIT',
>                                                          {badarg,
>                                                           [{erlang,
>                                                             apply,
>                                                            
>                         [erlfs_store_worker_fsm,
>                                                              start_link,
>                                                              {store_chunk,
>                                                               {chunk,
>                                                              
>                          {chunk_meta,
>                                                                
>                         {file_meta,
>                                                                
>                          "test123",
>                                                                
>                          "test.txt",
>                                                                  0,
>                                                                
>                          "text/plain",
>                                                                
>                          {{0,1,1},{0,0,0}}},
>                                                                 0,
>                                                                 0,
>                                                                 []},
>                                                              
>                          <<"Hello world!">>}}]},
>                                                          
>                          {supervisor,do_start_child_i,3},
>                                                          
>                          {supervisor,handle_call,3},
>                                                          
>                          {gen_server,handle_msg,6},
>                                                          
>                          {proc_lib,init_p,5}]}}}
>
>                         I've been trying to figure it out for a while,
>                         but I am having a hard
>                         time.
>                         Here is the Child Spec in the supervisor
>                         (erlfs_store_worker_sup):
>
>                         init(Args) ->
>                          WorkerSpec = {erlfs_store_worker_fsm,
>                         {erlfs_store_worker_fsm,
>                                             start_link, []},
>                                temporary, 2000, worker,
>                         [erlfs_store_worker_fsm]},
>                          {ok,{{simple_one_for_one, 0, 1}, [WorkerSpec]}}.
>
>
>
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-- 
Mazen Harake <>
Erlang Software Developer and Consultant,
Erlang Training & Consulting, Ltd

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