What are some patterns to avoid performing heavy lifting tasks in a Genserver's init callback?

Hi everyone, I have been playing with Elixir for a bit and I was told in passing that performing heavy lifting in a Genserver’s init call is an anti-pattern. If so, what are some patterns to do it the right way ?

For example, in the code below, I attempt at sending a message to the process itself and performing the task async. However, it seems like due to some sort of race condition(?), the last line of the handle_info where the process prints out the character count never works.

I am curious about what might be happening here?

defmodule Nine.PartOne do
  use GenServer
  require Logger

  # API
  def start_link(state) do
    GenServer.start_link(__MODULE__, state, name: __MODULE__)
  end

  @impl true
  def init(state) do
    Logger.info("I got started")
    file_path = Application.get_env(:adventofcode, :filepath)
    Process.send(self(), {:solve, file_path}, [])
    {:ok, state}
  end

  @impl true
  def handle_info({:solve, file_path}, _state) do
    IO.puts("I got the message") #this is printed
    res =
      File.read!(file_path)
      |> String.graphemes()
      |> Enum.reduce(
        0,
        fn _x, acc ->
          acc+1
        end
      )
    #this is never printed
    Logger.debug("The result is #{inspect(res)}")
  end
end