erlang supervisor

file: g.erl

-module(g).
-compile(export_all).

-behaviour(gen_server).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).

%%-------------------------------------------------------------------
%% Public API
%%-------------------------------------------------------------------

start(Name) ->
	gen_server:start({local, Name}, ?MODULE, [], []).

stop(Name) ->
	gen_server:call(Name, stop).

state(Name) ->
	gen_server:call(Name, state).

crash(Name) ->
	gen_server:call(Name, crash).

%%-------------------------------------------------------------------
%% gen_server call backs
%%-------------------------------------------------------------------

init([]) ->
	say("init", []),
	{ok, []}.
 
 
handle_call(stop, _From, State) ->
	say("stopping by ~p, state was ~p.", [_From, State]),
	{stop, normal, stopped, State};

handle_call(state, _From, State) ->
	say("~p is asking for the state.", [_From]),
	{reply, State, State};

handle_call(crash, _From, State) ->
	say("~p is asking for the state.", [_From]),
	{xxxreply, State, State};

handle_call(_Request, _From, State) ->
	say("call ~p, ~p, ~p.", [_Request, _From, State]),
	{reply, ok, State}.


handle_cast(_Msg, State) ->
	say("cast ~p, ~p.", [_Msg, State]),
	{noreply, State}.


handle_info(_Info, State) ->
	say("info ~p, ~p.", [_Info, State]),
	{noreply, State}.


terminate(_Reason, _State) ->
	say("terminate ~p, ~p", [_Reason, _State]),
	ok.

code_change(_OldVsn, State, _Extra) ->
	say("code_change ~p, ~p, ~p", [_OldVsn, State, _Extra]),
	{ok, State}.
 
%%-------------------------------------------------------------------
%% Private functions
%%-------------------------------------------------------------------


say(Format) ->
	say(Format, []).
say(Format, Data) ->
	io:format("~p:~p: ~s~n", [?MODULE, self(), io_lib:format(Format, Data)]).


file: sup.erl

-module(sup).

-behaviour(supervisor).

%% External exports
-export([start_link/0, add_child/1]).

%% supervisor callbacks
-export([init/1]).

%% @spec start_link() -> ServerRet
%% @doc API for starting the supervisor.
start_link() ->
    supervisor:start_link({local, ?MODULE}, ?MODULE, []).

add_child(Name) ->
	Spec = {Name,
		{g, start, [Name]},
		permanent, 1000, worker, dynamic},
	supervisor:start_child(?MODULE, Spec).


%% @spec init([]) -> SupervisorTree
%% @doc supervisor callback.
init([]) ->
	Names = [a, b, c],
	Processes = [{N,
		{g, start, [N]},
		permanent, 1000, worker, dynamic} || N <- Names],

	io:format("Processes: ~p~n", [Processes]),
    {ok, {{one_for_one, 10, 10}, Processes}}.


file: a.erl

-module(a).
-behaviour(application).
-export([ start/2, stop/1 ]).

start(_Type, _StartArgs) ->
	case sup:start_link() of
		{ok, Pid} -> {ok, Pid};
		Other -> {error, Other}
	end.

stop(_State) -> ok.

file: a.app

{application, a,
	[{description, "test"},
	{vsn, "0.1.0"},
	{modules, [a, sup, g]},
	{registered, [sup]},
	{applications, [kernel, stdlib]},
	{mod, {a, []}} ]}.


console output:


Erlang R13B02 (erts-5.7.3) [source] [64-bit] [smp:4:4] [rq:4] [async-threads:0] [kernel-poll:false]

Eshell V5.7.3  (abort with ^G)
1> c(a).
{ok,a}
2> c(sup).
{ok,sup}
3> c(g).
{ok,g}
4> application:start(a).
Processes: [{a,{g,start,[a]},permanent,1000,worker,dynamic},
            {b,{g,start,[b]},permanent,1000,worker,dynamic},
            {c,{g,start,[c]},permanent,1000,worker,dynamic}]
g:<0.54.0>: init
g:<0.55.0>: init
g:<0.56.0>: init
ok
5> g:state(a).
g:<0.54.0>: {<0.33.0>,#Ref<0.0.0.186>} is asking for the state.
[]
6> supervisor:which_children(sup).
[{c,<0.56.0>,worker,dynamic},
 {b,<0.55.0>,worker,dynamic},
 {a,<0.54.0>,worker,dynamic}]
7> g:crash(a).
g:<0.54.0>: {<0.33.0>,#Ref<0.0.0.195>} is asking for the state.
g:<0.54.0>: terminate {bad_return_value,{xxxreply,[],[]}}, []

=ERROR REPORT==== 27-Dec-2010::23:32:11 ===
** Generic server a terminating 
** Last message in was crash
** When Server state == []
** Reason for termination == 
** {bad_return_value,{xxxreply,[],[]}}
** exception exit: {{bad_return_value,{xxxreply,[],[]}},
                    {gen_server,call,[a,crash]}}
     in function  gen_server:call/2
8> supervisor:which_children(sup).
[{c,<0.56.0>,worker,dynamic},
 {b,<0.55.0>,worker,dynamic},
 {a,<0.54.0>,worker,dynamic}]
9> sup:add_child(d).
g:<0.63.0>: init
{ok,<0.63.0>}
10> supervisor:which_children(sup).
[{d,<0.63.0>,worker,dynamic},
 {c,<0.56.0>,worker,dynamic},
 {b,<0.55.0>,worker,dynamic},
 {a,<0.54.0>,worker,dynamic}]
11> g:state(d).
g:<0.63.0>: {<0.60.0>,#Ref<0.0.0.215>} is asking for the state.
[]