testing async_nolink task messages and shutdown

gistfile1.txt

defmodule Cryptod.Executor.TestTask do
  use GenServer
  require Logger

  def start_link(state \\ %{}) do
    GenServer.start_link(__MODULE__, state, name: :test_task)
  end

  def run_task(id, timeout) do
    GenServer.call(:test_task, {:fire, id, timeout})
  end

  def kill_task(id, timeout) do
    GenServer.call(:test_task, {:kill, id, timeout})
  end

  def init(_args) do
    {:ok, %{}}
  end

  def handle_call({:fire, id, timeout}, _from, state) do
    task =
      Task.Supervisor.async_nolink(
        Cryptod.Executor.APITaskSupervisor,
        fn ->
          Logger.debug("run_async_task start")
          :timer.sleep(timeout)
          Logger.debug("run_async_task end")
          :ok
        end
      )

    {:reply, :ok, Map.put(state, id, task)}
  end

  def handle_call({:kill, id, timeout}, _from, state) do
    task = Map.get(state, id)

    if task do
      with {:ok, result} <- Task.shutdown(task, timeout) do
        Logger.debug("task #{id} returned #{result} after shutdown")
        {:reply, {:ok, result}, Map.delete(state, id)}
      else
        {:exit, reason} ->
          Logger.debug("task #{id} exited with reason #{reason} after shutdown")
          {:reply, {:exit, reason}, Map.delete(state, id)}

        nil ->
          Logger.debug("task #{id} still running after shutdown")
          {:reply, nil, state}
      end
    else
      {:reply, {:error, "NOT_FOUND"}, state}
    end
  end

  def handle_info({ref, task_result}, state) do
    # the effect of the following line is that we do not get a :DOWN message unless the task crashes
    Process.demonitor(ref, [:flush])
    {task_id, task} = Enum.find(state, fn {id, task} -> ref == task.ref end)
    Logger.debug("Got task results #{inspect(task_result)} from task #{task_id}")
    {:noreply, Map.delete(state, task_id)}
  end

  def handle_info({:DOWN, ref, _process, _pid, reason}, state) do
    task_id = Enum.find(state, fn {id, task} -> ref == task.ref end)
    Logger.debug("Got :DOWN message for task #{task_id}")
    {:noreply, Map.delete(state, task_id)}
  end
end

# now do sth like:
# iex(27)> Cryptod.Executor.TestTask.run_task(1, 10000) 
# [debug] run_async_task start
# :ok
# iex(28)> Cryptod.Executor.TestTask.kill_task(1, 100)  
# [debug] task 1 still running after shutdown
# nil
# iex(29)> Cryptod.Executor.TestTask.kill_task(1, 100)
# [debug] task 1 exited with reason noproc after shutdown
# {:exit, :noproc}
# iex(30)> Cryptod.Executor.TestTask.kill_task(1, 100)
# {:error, "NOT_FOUND"}