Fault-tolerant event managers in Elixir

fault_tolerant_event_manager.ex

# By default, GenEvent event handlers fail silently and are not automatically restarted. Not good. 
# There's an easy enough way to correct this.
# You'll need to 
# 1. define a supervised event manager as a GenServer, 
# 2. register its GenEvent handlers with monitoring enabled
# 3. catch handler exits as "out of band" messages (handle_info)
# 4. stop the event manager when any handler crashes, relying on the supervisor to restart the event
#  manager who will then restart all of its GenEvent handlers.
# This approach assumes that event handling is either stateless or can reset its state without issues.

defmodule EventManager do
  @moduledoc "An event manager assumed to be started as a permanent worker by its supervisor"
  
  use GenServer
  require Logger
  @name __MODULE__
  @dispatcher :event_dispatcher
  
  # API
  
  def start_link() do
    GenServer.start_link(@name, [], [:name @name])
  end
  
  # Called by whoever generated the event
  def notify_of_something(something) do
    GenServer.cast(@name, {:notify_of_something, something})
  end
  
  # Add other event notification functions here
  
  # CALLBACKS
  
  def init(_) do
    GenEvent.start_link(name: @dispatcher)
    register_handlers()
    {:ok, []}
  end
  
  def handle_cast({:notify_of_something, something}, state) do
    GenEvent.notify(@dispatcher, {:something, something})
    {:noreply, state}
  end
  
  # Add other cast handling callbacks here
  
  @doc "Handles the exit message from crashed, monitored GenEvent handlers"
  def handle_info({:gen_event_EXIT, crashed_handler, error}, state) do
    Logger.error("#{crashed_handler} crashed. Restarting #{@name}.")		
		{:stop, {:handler_died, error}, state}
  end

  # Private
  
  defp register_handlers() do
    # Notice that we call the add_mon_handler function, not add_handler
    GenEvent.add_mon_handler(@dispatcher, SomethingHandler, [])
    # Add other monitored handlers here
  end
  
end

# And that's it. The implementations of the supervisor and the GenEvent handlers are as usual.