Should a client handling process be added to the supervisor tree?

erlang, erlang-supervisor

Solution

Yes, you should add these processes to the supervision heirarchy as you want them to be correctly/gracefully shutdown when your application is stopped. (Otherwise you end up leaking connections that will fail as the application infrastructure they depend on been shutdown).

You could create a `simple_one_for_one` strategy supervisor say `yourapp_client_sup` that has a child spec of `{Id, {yourapp_client_connection, start_link_with_socket, []}, Restart, Shutdown, worker, temporary}`. The `temporary` type here is important because there's normally no useful restart strategy for a connection handler - you can't connect out to the client to restart the connection. `temporary` here will cause the supervisor to report the connection handler exit but otherwise ignore it.

The process that does `gen_tcp:accept` will then create the connection handler process by doing `supervisor:start_child(yourapp_client_sup, [Socket,Options,...])` rather than `yourapp_client_sup:start_link(Socket, Options, ...)`. Ensure that the `youreapp_client_connection:start_link_with_socket` function starts the child via `gen_server` or `proc_lib` functions (a requirement of the `supervisor` module) and that the function transfers control of the socket to the child with `gen_tcp:controlling_process` otherwise the child won't be able to use the socket.

An alternate approach is to create a dummy `yourapp_client_sup` process that `yourclient_connection_handler` processes can link to at startup. The `yourapp_client_sup` process will just exist to propagate `EXIT` messages from its parent to the connection handler processes. It will need to trap exists and ignore all `EXIT` messages other than those from its parent. On the whole, I prefer to use the `simple_one_for_one` supervisor approach.

Problem

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