Elixir - Kernel.spawn/1 & Async

async_test.ex

defmodule AsyncTest do
  @contents ["foo", "bar", "foobar"]
  @output "async_test"

  def run do
    File.rm_rf!(@output)
    File.mkdir_p!(@output)
    @contents
    |> Enum.with_index
    |> Enum.map(&write_content_async(&1))
    |> Enum.map(fn _ ->
      receive do
        :ok -> :ok
        {:error, reason} -> IO.puts :stderr, "Error: #{reason}"
      after 3000 ->
        IO.puts :stderr, "Timeout"
      end
    end)
  end

  def write_content_async(params) do
    caller = self()
    spawn(fn ->
      seconds = :rand.uniform(10) * 1000
      :timer.sleep(seconds)
      send(caller, write_content(params))
    end)
  end

  def write_content({content, index})do
    IO.puts "Write \"#{content}\" into a file"
    File.write("#{@output}/test_#{index + 1}.txt", content)
  end
end

async_test_2.ex

defmodule AsyncTest2 do
  @contents ["foo", "bar", "foobar"]
  @output "async_test"

  def run do
    File.rm_rf!(@output)
    File.mkdir_p!(@output)
    @contents
    |> Enum.with_index
    |> Enum.map(&Task.async(fn ->
         write_content(&1)
       end))
    |> Enum.map(&Task.await/1)
  end

  def write_content({content, index}) do
    seconds = :rand.uniform(5) * 1000
    :timer.sleep(seconds)
    IO.puts "Write \"#{content}\" into a file"
    File.write("#{@output}/test_#{index + 1}.txt", content)
  end
e