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<p>Well, i suggest that you let the Socket stuff be handled by separate processes that communicate asynchronously with the gen_server and are <code>linked</code> with it. I have a sample code snippet that would show you how this could be done. The gen_server starts and spawns a TCP listener which after successfully obtaining a listening socket informs our gen_server as to change its internal state. I have arranged the code from top down. All relevant functions have been showed. Focus on the socket handling processes and how they interact with the gen_server</p> <pre> -define(PEER_CLIENT_TIMEOUT,timer:seconds(20)). -define(PORT_RANGE,{10245,10265}). -define(DEBUG(X,Y),error_logger:info_msg(X,Y)). -define(ERROR(L),error_logger:error_report(L)). -define(SOCKET_OPTS(IP),[inet,binary,{backlog,100},{packet,0}, {reuseaddr,true},{active,true}, {ip,IP}]). %%---------------------------------------------------- %% gen_server starts here.... start(PeerName)-> gen_server:start_link({local,?MODULE},?MODULE,PeerName,[]). %%%------------------------------------------- %% Gen_server init/1 function init(PeerName)-> process_flag(trap_exit,true), %% starting the whole Socket chain below.. start_link_listener(), %% Socket stuff started, gen_server can now wait for async %% messages {ok,[]}. %%% ---- Socket handling functions --------- %% Function: start_link_listener/0 %% Purpose: Starts the whole chain of listening %% and waiting for connections. Executed %% directly by the gen_server process, But %% spawns a separate process to do the rest start_link_listener()-> Ip_address = get_myaddr(), spawn_link(fun() -> listener(?SOCKET_OPTS(Ip_address)) end). %%%---------------------------------------------- %% Function: get_myaddr/0 %% Purpose: To pick the active IP address on my machine to %% listen on get_myaddr()-> ?DEBUG("Server> Trying to extract My Local Ip Address....",[]), {ok,Name} = inet:gethostname(), {ok,IP} = inet:getaddr(Name,inet), ?DEBUG("Server> Found Alive Local IP address: ~p.....~n",[IP]), IP. %%%-------------------------------------------------- %% Function: listener/1, executed in a separate process %% Purpose: Tries a given ?PORT_RANGE, with the given Socket Options %% Once it acquires a ListenSocket, it will cast the gen_server! listener(SocketOpts)-> process_flag(trap_exit,true), Ports = lists:seq(element(1,?PORT_RANGE),element(2,?PORT_RANGE)), case try_listening(SocketOpts,Ports) of {ok,Port,LSocket}-> PP = proplists:get_value(ip,SocketOpts), ?MODULE:started_listener(Port,PP,LSocket), accept_connection(LSocket); {error,failed} -> {error,failed,SocketOpts} end. try_listening(_Opts,[])-> {error,failed}; try_listening(Opts,[Port|Rest])-> case gen_tcp:listen(Port,Opts) of {ok,Listen_Socket} -> {ok,Port,Listen_Socket}; {error,_} -> try_listening(Opts,Rest) end. %%%--------------------------------------------------------- %% Helper Functions for Converting IP Address from tuple %% to string and vice versa str(X) when is_integer(X)-> integer_to_list(X). formalise_ipaddress({A,B,C,D})-> str(A) ++ "." ++ str(B) ++ "." ++ str(C) ++ "." ++ str(D). unformalise_address(String)-> [A,B,C,D] = string:tokens(String,"."), {list_to_integer(A),list_to_integer(B),list_to_integer(C),list_to_integer(D)}. %%%-------------------------------------------------- %% Function: get_source_connection/1 %% Purpose: Retrieving the IP and Port at the other %% end of the connection get_source_connection(Socket)-> try inet:peername(Socket) of {ok,{IP_Address, Port}} -> [{ipAddress,formalise_ipaddress(IP_Address)},{port,Port}]; _ -> failed_to_retrieve_address catch _:_ -> failed_to_retrieve_address end. %%%----------------------------------------------------- %% Function: accept_connection/1 %% Purpose: waits for a connection and re-uses the %% ListenSocket by spawning another thread %% to take it and listen too. It casts the gen_server %% at each connection and provides details about it. accept_connection(ListenSocket)-> case gen_tcp:accept(ListenSocket,infinity) of {ok, Socket}-> %% re-use the ListenSocket below..... spawn_link(fun() -> accept_connection(ListenSocket) end), OtherEnd = get_source_connection(Socket), ?MODULE:accepted_connection(OtherEnd), loop(Socket,OtherEnd); {error,_} = Reason -> ?ERROR(["Listener has failed to accept a connection", {listener,self()},{reason,Reason}]) end. %%%------------------------------------------------------------------------- %% Function: loop/2 %% Purpose: TCP reception loop, it casts the gen_server %% as soon as it receives something. gen_server %% is responsible for generating reponse %% OtherEnd ::= [{ipAddress,StringIPAddress},{Port,Port}] or 'failed_to_retrieve_address' loop(Socket,OtherEnd)-> receive {tcp, Socket, Data}-> ?DEBUG("Acceptor: ~p has received a binary message from: ~p~n",[self(),OtherEnd]), Reply = ?MODULE:incoming_binary_message(Data,OtherEnd), gen_tcp:send(Socket,Reply), gen_tcp:close(Socket), exit(normal); {tcp_closed, Socket} -> ?DEBUG("Acceptor: ~p. Socket closed by other end: ~p~n",[self(),OtherEnd]), ?MODULE:socket_closed(OtherEnd), exit(normal); Any -> ?DEBUG("Acceptor: ~p has received a message: ~p~n",[self(),Any]) end. %%%---------------------------------------------- %% Gen_server Asynchronous APIs accepted_connection(failed_to_retrieve_address)-> ok; accepted_connection([{ipAddress,StringIPAddress},{Port,Port}])-> gen_server:cast(?MODULE,{connected,StringIPAddress,Port}). socket_closed(failed_to_retrieve_address)-> ok; socket_closed([{ipAddress,StringIPAddress},{Port,Port}])-> gen_server:cast(?MODULE,{socket_closed,StringIPAddress,Port}). incoming_binary_message(Data,_OtherEnd)-> %% expecting a binary reply case analyse_protocol(Data) of wrong -> term_to_binary("protocol violation!"); Val -> gen_server:call(?MODULE,{request,Val},infinity) end. %%% -------------------- handle cast ------------------------------------------ handle_cast({listener_starts,_Port,_MyTupleIP,_LSocket} = Object,State)-> NewState = do_something_with_the_listen_report(Object), {noreply,NewState}; handle_cast({connected,_StringIPAddress,_Port} = Object,State)-> NewState = do_something_with_the_connection_report(Object), {noreply,NewState}; handle_cast({socket_closed,_StringIPAddress,_Port} = Object,State)-> NewState = do_something_with_the_closed_connection_report(Object), {noreply,NewState}; handle_cast(Any,State)-> ?DEBUG("Server> I have been casted some unknown message: ~p~n",[Any]), {noreply,State}. %%%% ---------------------- handle call -------------- handle_call({request,Val},_,State)-> {NewState,Reply} = req(Val,State), {reply,Reply,NewState}; handle_call(_,_,State)-> {reply,[],State}. req(Val,State)-> %% modify gen_server state and %% build reply {NewState,Reply} = modify_state_and_get_reply(State,Val), {NewState,Reply}. %%------------------- terminate/2 -------------------- terminate(_Reason,_State)-> ok. %%----------------- code_change/3 ------------------ code_change(_,State,_)-> {ok,State}. </pre> <p>With the asynchronous capability of the gen_server, we can handle the socket details from separate linked processes. These processes then would communicate with the gen_server via <code>cast</code> and without blocking the gen_server from its concurrent nature.</p>
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