How can I schedule code to run every few hours in Elixir or Phoenix framework?

Question

So let\'s say I want to send a bunch of emails or recreate sitemap or whatever every 4 hours, how would I do that in Phoenix or just with Elixir?

Answer 1

I find :timer.send_interval/2 slightly more ergonomic to use with a GenServer than Process.send_after/4 (used in the accepted answer).

Instead of having to reschedule your notification each time you handle it, :timer.send_interval/2 sets up an interval on which you receive a message endlessly—no need to keep calling schedule_work() like the accepted answer uses.

defmodule CountingServer do
  use GenServer

  def init(_) do
    :timer.send_interval(1000, :update)
    {:ok, 1}
  end

  def handle_info(:update, count) do
    IO.puts(count)
    {:noreply, count + 1}
  end
end

Every 1000 ms (i.e., once a second), IntervalServer.handle_info/2 will be called, print the current count, and update the GenServer's state (count + 1), giving you output like:

1
2
3
4
[etc.]