[erlang-questions] EPmail-0.1 released

Johan Wärlander <>
Fri Jan 28 21:02:15 CET 2011

Hi Alexander,

I'm also fairly new to Erlang, and I've tried a couple of different models
for accepting TCP connections. The model I eventually arrived at was this:

1) Setting up an "acceptor supervisor", which starts a listener process and
an acceptor pool supervisor in one_for_all mode.
2) When I call listen(Port, Acceptors) on the listener gen_server process it
will gen_tcp:listen() and then start a number of child processes in the
acceptor pool, which all wait in gen_tcp:accept() for incoming connections.
3) The acceptor pool is a simple_one_for_one supervisor, which will restart
any of its acceptor processes if they die.
4) The acceptor child processes themselves have only this job: to wait for
an incoming connection, then start an actual worker process (in your case
the gen_fsm), and hand off the socket to that process. They will then go
back to listening for the next incoming connection.

Not sure if this is too complex a model (certainly others here will have
opinions about that - do share!), but the reason I did it this way is that
to me, it seems to provide better fault tolerance. If my acceptor child
processes die for some reason, after a while the acceptor pool will restart
itself. Since the top acceptor supervisor uses one_for_all strategy, it will
then also restart the listener, which in turn reopens the listening socket
and starts new acceptor child processes in the pool, getting us back to a
known state.

Feel free to have a look here:

The files in question are em_acceptor_sup.erl (the top one_for_all acceptor
supervisor), em_acceptor_pool.erl (the simple_one_for_one acceptor pool),
em_acceptor.erl (acceptor child processes) and em_listener.erl (opening the
listening socket and tells em_acceptor_pool to start acceptor child


On Fri, Jan 28, 2011 at 6:30 PM, Alexander Kuleshov

> Hi to all,
> I startin to implement gen_fsm.
> When client connect to server by listen socket i started want to start
> new gen_fsm for client request handling.
> I think i must create supervisor and started gen_fsm child every time
> that i accept new connection.
> Is it true way?
> Thank you.
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