Question

{ok,Socket} = gen_udp:open(9000, [binary,{active,false}, {reuseaddr,true}]),

Pid0 = spawn_link( fun() -> loop_passive( Socket ) end ),

Pid1 = spawn_link( fun() -> loop_passive( Socket ) end ) --> error
.. (many overlapped receiving per a binded socket)
N

loop_passive(Socket) ->
   case gen_udp:recv(Socket, 0) of
     {ok, {Addr,Port,Packet}} ->
        process(Socket,Addr,Port,Packet),
        loop_passive(Socket);
     Error ->
          io:format("udp_passive error: ~p~n", [Error])
    end.

I’ll make scalabe UDP server.
Erlang UDP mechanism was simple once at a time.
Ever, there is not another way?

Answer 1

Let us look at that code where it is readable:

 {ok,Socket} = gen_udp:open(9000, [binary,{active,false}, {reuseaddr,true}]),
 Pid0 = spawn_link( fun() ->
           loop_passive( Socket ) end ),
 Pid1 = spawn_link( fun() ->
           loop_passive( Socket ) end ).

This means that self() opens the UDP socket, and Pid0 and Pid1 gets passed the resulting socket. Note that self() (the process running the above code) is the controlling process of the socket.

 loop_passive(Socket) ->
   case gen_udp:recv(Socket, 0) of
      {ok, {Addr,Port,Packet}} ->
           process(Socket,Addr,Port,Packet),
           loop_passive(Socket);
      Error -> io:format("udp_passive error: ~p~n", [Error])
   end.

This is just a simple loop on incoming packets. It means that Pid0 and Pid1 are the ones that are reading off data from the socket, whenever goes first.

The usual problems in this case are:

• The controlling process dies and thus the socket is closed