GenServer Callbacks

GenServer

GenServer is an OTP protocol. OTP works by assuming that our module defines a number of callback functions. There are six in the case of a GenServer. If we were writing a GenServer in Erlang, our code would have to contain implementations of all six functions.

When we add the statement use GenServer to a module, Elixir creates default implementations of these six callback functions. All we have to do is override the ones where we add our own application-specific behavior. Our examples so far have used the three callbacks init, handle_call, and handle_cast. Here, we’ll look at the full list.

init(start_arguments)

GenServer calls init(start_arguments) when starting a new server. The parameter is the second argument passed to start_link. It should return {:ok, state} on success, or {:stop, reason} if the server couldn’t be started.

We can specify an ...