Following Dave Thomas’s course, I have an Application that starts a supervised Agent that is hardcoded to crash 1/3 times.

After crashing multiple times by running Dictionary.random_word, for some reason the Application itself exits.

Why does the Application crash as well?

mix.exs
lib/
  dictionary/
    application.ex
    word_list.ex
  dictionary.ex

application.ex

defmodule Dictionary.Application do

  use Application

  def start(_type, _args) do

    children = [
      Dictionary.WordList
    ]

    options = [
      name: Dictionary.Supervisor,
      strategy: :one_for_one
    ]

    Supervisor.start_link(children, options)
  end
end

word_list.ex

defmodule Dictionary.WordList do

  use Agent

  @me __MODULE__

  def start_link(_opts) do
    Agent.start_link(&word_list/0, name: @me)
  end

  def random_word() do
    if :rand.uniform < 0.33 do
      Agent.get(@me, fn _ -> exit(:boom) end)
    end

    Agent.get(@me, &Enum.random/1)
  end

  def word_list do
    "../../assets/words.txt"
    |> Path.expand(__DIR__)
    |> File.read!()
    |> String.split(~r/\n/)
  end
end

dictionary.ex

defmodule Dictionary do
  alias Dictionary.WordList

  defdelegate random_word(), to: WordList

end

mix.exs

defmodule Dictionary.MixProject do
  use Mix.Project

  def project do
    [
      app: :dictionary,
      version: "0.1.0",
      elixir: "~> 1.11",
      start_permanent: Mix.env() == :prod,
      deps: deps()
    ]
  end

  def application do
    [
      mod: { Dictionary.Application, [] },
      extra_applications: [:logger]
    ]
  end

  defp deps do
    []
  end
end

log

iex(15)> Dictionary.random_word
** (exit) exited in: GenServer.call(Dictionary.WordList, {:get, #Function<0.122627474/1 in Dictionary.WordList.random_word/0>}, 5000)
    ** (EXIT) :boom
    (elixir 1.11.3) lib/gen_server.ex:1027: GenServer.call/3
    (dictionary 0.1.0) lib/dictionary/word_list.ex:13: Dictionary.WordList.random_word/0

20:34:02.920 [error] GenServer Dictionary.WordList terminating
** (stop) :boom
    (dictionary 0.1.0) lib/dictionary/word_list.ex:13: anonymous fn/1 in Dictionary.WordList.random_word/0
    (elixir 1.11.3) lib/agent/server.ex:12: Agent.Server.handle_call/3
    (stdlib 3.14) gen_server.erl:715: :gen_server.try_handle_call/4
    (stdlib 3.14) gen_server.erl:744: :gen_server.handle_msg/6
    (stdlib 3.14) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message (from #PID<0.142.0>): {:get, #Function<0.122627474/1 in Dictionary.WordList.random_word/0>}
State: ["that", "this", "with", "from", "your", "have", "more", "will", "home", "about", "page", "search", "free", "other", "information", "time", "they", "site", "what", "which", "their", "news", "there", "only", "when", "contact", "here", "business", "also", "help", "view", "online", "first", "been", "would", "were", "services", "some", "these", "click", "like", "service", "than", "find", "price", "date", "back", "people", "list", "name", ...]
Client #PID<0.142.0> is alive

    (stdlib 3.14) gen.erl:208: :gen.do_call/4
    (elixir 1.11.3) lib/gen_server.ex:1024: GenServer.call/3
    (dictionary 0.1.0) lib/dictionary/word_list.ex:13: Dictionary.WordList.random_word/0
    (stdlib 3.14) erl_eval.erl:680: :erl_eval.do_apply/6
    (elixir 1.11.3) src/elixir.erl:280: :elixir.recur_eval/3
    (elixir 1.11.3) src/elixir.erl:265: :elixir.eval_forms/3
    (iex 1.11.3) lib/iex/evaluator.ex:261: IEx.Evaluator.handle_eval/5
    (iex 1.11.3) lib/iex/evaluator.ex:242: IEx.Evaluator.do_eval/3
iex(15)>
20:34:02.922 [info]  Application dictionary exited: shutdown