MySpawn.ex

defmodule MySpawn do
  def spawn_monitor(mod, func, args) do
    root_pid = self()
    spawn(fn ->
      {pid, ref} = :erlang.spawn_monitor(mod, func, args)
      send(root_pid, pid)
      start_time = :calendar.local_time
      receive do
        {:DOWN, ^ref, :process, ^pid, why} -> print_on_exit(start_time, why)
      end
    end)
    receive do
      pid -> pid
    end
  end
  def spawn_link(mod, func, args) do
    root_pid = self()
    spawn(fn ->
      Process.flag(:trap_exit, true)
      pid = :erlang.spawn_link(mod, func, args)
      send(root_pid, pid)
      start_time = :calendar.local_time
      receive do
        {:EXIT, ^pid, why} -> print_on_exit(start_time, why)
      end
    end)
    receive do
      pid -> pid
    end
  end
  def spawn(mod, func, args, time) do
    pid = :erlang.spawn(mod, func, args)
    spawn(fn ->
     receive do
     after time ->
         :io.format("About to kill process, but is it alive? ~p~n", [Process.alive?(pid)])
         Process.exit(pid, :kill)
     end
    end)
    pid
  end

  defp running_loop() do
    receive do
    after 5_000 -> IO.puts "I'm still running"
    end
    running_loop
  end
  def i_am_still_running(name) do
    :erlang.spawn(&running_loop/0) |> Process.register(name)
  end
  defp running_loop_monitor(name) do
    ref = Process.monitor(name)
    receive do
      {:DOWN, ^ref, :process, _, why} -> i_am_still_running(name)
    end
    running_loop_monitor(name)
  end
  def monitor_runner(name) do
    :erlang.spawn(fn -> running_loop_monitor(name) end)
  end
  defp print_on_exit(start_time, why) do
    end_time = :calendar.local_time
    :io.format("Why ~p, worked ~p~n", [why, :calendar.time_difference(start_time, end_time) ])
  end
  def normal() do
    receive do
      after 3_000 -> IO.puts "exiting"
    end
  end
end