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erlangnntp

Erlang supervisor:start_child parameters

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?

Solution

  • 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.