[erlang-questions] Help! with gen_server and a chat_server

Bengt Kleberg <>
Thu Apr 12 08:18:24 CEST 2012


Greetings,

Your first crash is the function call
servidor:call(login,irene,6666).

I do not see such a function in the servidor module. Perhaps you have
forgotten to add it?

After that crash your process is dead (you are linked to it) and nothing
will work.


bengt

On Thu, 2012-04-12 at 01:03 +0200, megalomania wrote:
> *Hi all,
> Im newbie on Erlang and trying lear to use gen_server but i begin to
> understan that maybe im wrong.
> 
> Im just trying to making a chat_server with gen_serve, so the idea is a
> client on an another node could try to login in the chat_server who will be
> in another node.
> 
> here is my code:
> *
> 
> -module(servidor) .
> -behavior(gen_server) . 
> 
> % API functions
> -export([start_link/0, hi/0, login/2, logout/1, times/2, stop/0]).
> 
> % Callback functions
> -export([init/1, handle_call/3, handle_info/2, terminate/2, handle_cast/2,
> code_change/3]).
> 
> -define(NAME_SERVER, ?MODULE).
> -define(LOGUEADOS, logeados).
> 
> 
> start_link() ->
> 	gen_server:start_link({local, ?NAME_SERVER}, ?MODULE, [], []).%Se registra
> el proceso con el nombre del modulo(servidor)
> 
> hi() ->
> 	gen_server:cast(?MODULE, hi) .
> 
> stop() -> 
> 	gen_server:cast(?MODULE, stop).
> 
> login(Nick,Pid) ->
> 	gen_server:call(?MODULE, {login, Nick, Pid}).
> 
> logout(Nick) ->
> 	gen_server:call(?MODULE, {logout, Nick}).
> 
> times(N, M) ->
> 	?MODULE ! {times_request, self(), {N, M}}.
> 
> 
> 
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> %% Callback functions implementation %%
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
> 
> init([]) ->
> 	{ok, ets:new(?LOGUEADOS, [set])}.
> 
> terminate(_Reason, _State) ->
> 	{_, Tab} = _State,
> 	ets:delete(Tab),
> 	ok.
> 
> 
> handle_call({login, Nick, Pid}, _From, _State) ->
> 	%% En el login habra que crear una nodo del que haga el login // Para
> probarlo, miro simplemente si existe en la BD.
> 	io:format("Loggin.. y state=~w: ~n", [_State]),
> 	BOOL = ets:member(_State, Nick),
> 	io:format("The user is online? = ~w ~n", [BOOL]),
> 	if
> 		BOOL == true -> io:format("~w its already login", [Nick]);
> 		true -> ets:insert(_State, {Nick,Pid}), io:format("Login succesful ~n")
> 	end,
> 	{reply, {login, Nick}, _State};
> 
> 
> handle_call({logout, Nick}, _From, _State) ->
> 	io:format("Logout...~n", []),
> 	ets:delete(_State, Nick).
> 
> 
> handle_cast(hi, State) -> 
> 	io:fwrite("\t\tHi!\~n"),
> 	{noreply, State} ;
> 
> handle_cast(stop, _State) ->
> 	io:format("Stopped~n", []),
> 	{_, Tab} = _State,
> 	ets:delete(Tab),
> 	{stop, normal, _State} .
> 
> 	
> handle_info({times_request, Pid, {N, M}}, State) ->
> 	io:fwrite("\t~w server handling info, request number ~w~n", [?MODULE,
> State]),
> 	Pid ! {times_response, N*M},
> 	{noreply, State} .
> 
> code_change(_OldVsn, _State, _Extra) ->
> 	{ok, _State}.
> 
> 
> *and then i typed this in one console:*
> 
> >erl -sname server
> ()1> c(servidor).
> {ok,servidor}
> ()2> servidor:start_link().
> {ok,<0.45.0>}
> ()3>       
> 
> 
> *and then i typed this in another console:*
> )25> {} ! {servidor,login,irene,777}.         
> {servidor,login,irene,777}
> ()26> {} ! {servidor,login,irene,777}.
> {servidor,login,irene,777}
> ()27> {} !
> servidor:call(login,irene,6666).
> ** exception error: undefined function servidor:call/3
> ()28> {} ! servidor:login(irene,6666).        
> ** exception exit: {noproc,{gen_server,call,[servidor,{login,irene,6666}]}}
>      in function  gen_server:call/2
> ()29> {} !
> process_request(login,{irene,2321}).
> ** exception error: undefined shell command process_request/2
> ()30> {} ! {hi}.                               
> {hi}
> ()31> {} ! {async,hi}.
> 
> 
> *almost or the most of instructions makes server_node crash :(*
> 
> My question is, what im doing wrong? It is the correct way?
> 
> 
> --
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