Hi all
I have following module that implement GenServer, the code is from book elixir in action.
defmodule Todo.DatabaseWorker do
use GenServer
def start_link(db_folder, worker_id) do
IO.puts "Starting database worker #{worker_id}"
GenServer.start_link(
__MODULE__, db_folder,
name: via_tuple(worker_id)
)
end
defp via_tuple(worker_id) do
{:via, Todo.ProcessRegistry, {:database_worker, worker_id}}
end
end
What I do not understand is the name parameter in the start_link function. What does it mean, why the function via_tuple function return a tuple?
Read this, I blogged about namig processes earlier today:
In your example, it’s slightly more complicted scenario, where you are using third party registry Todo.ProcessRegistry. Read this (after you read above):
When normally (without using the name: option) creating a GenServer, the only way to refer to it, is by its Process ID (PID).
In most simple cases, this is good enough. However, in some cases it is annoying that there isn’t a different alias you can refer to, which means you’ll end up passing a list of PIDs around all over your application.
So instead, it is possible to register a process under a name, which is then stored globally (for the current node!) in Erlang. This means that one can refer to the process by using that name (as well as by its PID). This is often used when you only ever need a single process doing a certain kind. It is very common to have constructs like name: __MODULE__, which means that you only want a single GenServer to run using the code in the current module.
