I'm trying to understand this bit of supervisor code from ErlNNTP and I can't make sense of it even after reading the erlang documentation (Erlang n00b) on start-child (http://www.erlang.org/doc/man/supervisor.html#start_child-2)
start_connection_handler (Socket) -> supervisor:start_child (?MODULE, {Socket, {connection_handler, start_link, [Socket]}, permanent, 10000, worker, [connection_handler]}).
I do't quite get the 'Socket' parameter which I expect to be a SupRef. I'm obviously not parsing the parameter list correctly or understanding the call. Can anyone explain it to me?
The second arg to supervisor:start_child/2 is a child specification with the format:
{Id,StartFunction,RestartType,Shutdowntime,ProcessType,Modules}
where
Id is an identifier of the child which is unique in the supervisor, it can be any datatype.
StartFunction is a tuple {Module,Function,Args} which is the call to start the child process.
RestartType tells the supervisor how this child is to be restart, it can have the values permanent, transient or temporary.
ShutdownTime is how much the child process is allowed to spend in termination before it is killed.
ProcessType whether the child is a worker or supervisor.
Modules list of modules implementing the child
The last two are used when code upgrading.
So in your case Socket is being use as a identifier. Doing it this way means when you start a handler for a new socket you will get a unique identifier.