PartitionDispatcher Consumers not receiving events?

Questions & Help Questions
1

Playing around with getting a basic GenStage with PartitionDispatcher working.

Unfortunately my Consumers are never receiving any events.

GitHub repo with my code: GitHub - hauntedhost/gen_stage_partition_dispatcher: Experimenting with GenStage PartitionDispatcher. · GitHub

And here is a trimmed view of the relevant code:

  # PRODUCER

  def init(initial_state) do
    dispatcher_options = [
      partitions: partitions_list,
      hash: &partition_by_first_letter/1
    ]
    {:producer, initial_state, dispatcher: {PartitionDispatcher, dispatcher_options}}
  end

  def handle_demand(demand, state) when demand > 0 do
    words = Enum.map(1..demand, fn(_) -> Faker.Lorem.word end)
    {:noreply, words, state}
  end

  def partitions_list do
    ~w(one two three four)
  end

  def partition_by_first_letter(event) do
    partition = case first_char_downcase(event) do
      c when c in ~w(a b c d e f g h i) -> "one"
      c when c in ~w(j k l m n o p q r) -> "two"
      c when c in ~w(s t u v w x y z)   -> "three"
      _                                 -> "four"
    end
    {event, partition}
  end

  # CONSUMER

  def init(initial_state) do
    {:consumer, initial_state}
  end

  def handle_events(words, _from_producer, state) do
    IO.puts("=== received words ===")
    IO.inspect(words)

    {:noreply, [], state}
  end

  # START

  {:ok, producer} = Producer.start_link
  Producer.partitions_list
  |> Enum.each(fn(partition) ->
    {:ok, consumer} = Consumer.start_link
    GenStage.sync_subscribe(consumer,
      to: producer,
      partition: partition,
      min_demand: 5,
      max_demand: 10
    )
  end)

Any tips appreciated. :slight_smile:

Thanks,
Sean