Two approaches to schedule work with GenServer

schedule_work_approaches.exs

defmodule Worker do
  use GenServer

  @delay 5

  defp work(source) do
    IO.puts("work from #{source}")
  end

  # Client

  def start_link(state) do
    GenServer.start_link(__MODULE__, state)
  end

  def schedule_work_1(server) do
    Process.send_after(server, :work, @delay)
  end

  def schedule_work_2(server) do
    spawn(fn ->
      Process.sleep(@delay)
      GenServer.cast(server, :work)
    end)
  end

  # Server (callbacks)

  @impl true
  def handle_info(:work, state) do
    work("handle_info")
    {:noreply, state}
  end

  @impl true
  def init(init_arg) do
    {:ok, init_arg}
  end

  @impl true
  def handle_cast(:work, state) do
    work("handle_cast")
    {:noreply, state}
  end
end

{:ok, pid} = GenServer.start_link(Worker, nil)
timer_ref = Worker.schedule_work_1(pid)
pid = Worker.schedule_work_2(pid)
if false do
  Process.cancel_timer(timer_ref)
  Process.exit(pid, :kill)
end
Process.sleep(10)