Which OTP behavior should I use for an "endless" repetition of tasks?

Question

I want to repeatedly run the same sequence of operations over and over again next to a Phoenix application (without crashing the whole web-app if something brakes in the worker of course) and don't really know wether I should use a GenServer, Elixir's Tasks, an Agent or something completely different I haven't thought about so far.

When I start my Phoenix app a worker should start as well, that periodically pulls some values of a serial-connection, broadcasts them through a Phoenix channel, collects them until @save_interval is reached and then calculates the median, broadcasts that median via a different channel and writes it to an InfluxDB. Right now I have something (kind of working) like this:

def do_your_thing(serial_pid) do
  Stream.interval(@interval_live)
    |> get_new_values_from_serial(serial_pid)
    |> broadcast!("live-channel:#{@name}")
    |> Enum.take(div(@interval_save, @interval_live))
    |> calculate_medians()
    |> broadcast!("update-channel:#{@name}")
    |> write_to_database()

  do_your_thing(serial_pid) # repeat
end

I'm only starting to figure all that OTP stuff out and hope someone of you could help me stumble into the right direction here.

Answer 1

You should use a GenServer that sends itself messages after x seconds (60 seconds in the example below):

defmodule MyApp.Worker do
  use GenServer

  def start_link() do
    GenServer.start_link(__MODULE__, [])
  end

  def init([]) do
    schedule_work()
    {:ok, []}
  end

  def handle_info(:work, state) do
    state = do_work(state)
    schedule_work()
    {:noreply, state}
  end

  defp do_work(state) do
    # Do your work here and return state
  end

  defp schedule_work do
    Process.send_after(self(), :work, 60_000)
  end
end