gen_tcp and active mode

Previously...

• I was able to send and receive messages.
• I changed the pass-through from single to multi-threaded.
• IT ACTUALLY WORKED!

One of the things I came across while developing megaphone and working with erlang has been the notion of "active mode" when dealing with TCP sockets.  When using gen_tcp, you can open a socket in active mode or passive mode.  

In active mode, when a packet of data arrives at the socket, the process associated with the socket gets an erlang message.  In passive mode, the process must ask for data via gen_tcp:recv.  

In a language like C or Java one would always use what is more or less passive mode: you perform a read to get the next block of data.  Coming from that background I had trouble understanding what the rationale behind active mode was.  I think now I understand a little better.

Languages like C and Java do not have the notion of message passing that erlang does, hence active mode does not make as much sense.  With erlang, I can use active mode and create one process (thread) that handles both sending and receiving data:

loop(Socket) ->

    receive

        { tcp, ReceiveSocket, Data } -> do something...

        { write, Data } ->

            gen_tcp:send(Socket, Data)

    end,

    loop(Socket).

Note that the "write" message would have to be sent from another process.

I find this a more natural way of handling socket I/O than the C/Java approaches that I've used.  

Next time: some results from testing with ejabberd.