Test the maximum timeout value for a genserver, using a binary search.

timeout_tester.ex

defmodule TimeoutChecker do
  @moduledoc """
  test the maximum timeout value for a genserver, using a binary search.

  TimeoutChecker.run():

      16:31:16.907 [warn]  Testing the maximum genserver timeout value…
      16:31:17.064 [warn]  The maximum timeout value is: 4294967295

  """

  require Logger

  defmodule Tester do
    use GenServer
    require Logger

    def start(t) do
      GenServer.start(__MODULE__, t)
    end

    def init(t) do
      Process.send_after(self(), :stop, 10)
      {:ok, t, t}
    end

    def handle_info(:stop, _) do
      {:stop, :normal, nil}
    end
  end

  def test_one(t) do
    {:ok, pid} = Tester.start(t)
    Process.monitor(pid)

    receive do
      {:DOWN, _, _, _, r} -> r
    end == :normal
  end

  def run() do
    Logger.warn("Testing the maximum genserver timeout value…")
    t = test(5_000_000_000_000)
    Logger.warn("The maximum timeout value is: #{t}")
  end

  def test(t, t_prev \\ 0)

  def test(t, t) do
    t
  end

  def test(t, t_prev) do
    half = trunc((t - t_prev) / 2)

    case test_one(t) do
      true ->
        test(t + trunc((t - t_prev) / 2), t)

      false ->
        test(t_prev + trunc((t - t_prev) / 2), t_prev)
    end
  end
end