Question

我正在尝试实现一个非常简单的GenStage，目的是确保我理解它并在开始介绍我的特定应用程序逻辑之前使其工作。我从Producer返回数据时收到错误。数据看起来对我而言。我已经读过返回的元组中的第二个值必须是一个列表，它似乎是一个。

这是我的GenStage实现：

defmodule CoachActivity.Event.Producer do
  use GenStage

  def start_link(page) do
    GenStage.start_link(CoachActivity.Event.Producer, page)
  end

  def init(page) do
    {:producer, page}
  end

  def handle_demand(demand, page) when demand > 0 do
    # in here we need to run the ecto query for the next X items?
    events = get_fake(page)

    IO.puts "PRODUCER: preparing to return events"
    IO.puts "PRODUCER: page will be: #{page + 1}"

    {:no_reply, events, page + 1}
  end

  defp get_fake(page) do
    IO.puts "PRODUCER: generating events for page #{page}"
    [
      "Event One",
      "Event Two",
      "Event Three",
      "Event Four",
      "Event Five"
    ]
  end
end

defmodule CoachActivity.Event.ProducerConsumer do
  use GenStage

  def start_link(page) do
    GenStage.start_link(CoachActivity.Event.ProducerConsumer, page)
  end

  def init(number) do
    {:producer_consumer, number}
  end

  def handle_events(events, _from, number) do
    # in here we will do the transformation of events
    IO.puts "PRODUCER_CONSUMER: importing a bunch of events"

    events = Enum.map(events, fn(event) ->
      CoachActivity.Event.ImportEvent.import(event)
    end)

    {:noreply, events, number}
  end
end

defmodule CoachActivity.Event.Consumer do
  use GenStage

  def start_link() do
    GenStage.start_link(CoachActivity.Event.Consumer, :ok)
  end

  def init(:ok) do
    {:consumer, :the_state_does_not_matter}
  end

  def handle_events(events, _from, state) do
    # Wait for a second.
    Process.sleep(1000)

    # Inspect the events.
    IO.inspect(events)

    # We are a consumer, so we would never emit items.
    {:noreply, [], state}
  end
end

defmodule CoachActivity.Event.ImportEvent do
  def import(event) do
    IO.puts "Converting an event: #{event}"
  end
end

defmodule KickStart do
  def start do
    {:ok, producer} = CoachActivity.Event.Producer.start_link(0)
    {:ok, producer_consumer} = CoachActivity.Event.ProducerConsumer.start_link(2)
    {:ok, consumer} = CoachActivity.Event.Consumer.start_link()

    GenStage.sync_subscribe(consumer, to: producer_consumer)
    GenStage.sync_subscribe(producer_consumer, to: producer)
  end
end

当我这样做时

KickStart.start

我收到此错误消息输出：

iex(4)> KickStart.start
PRODUCER: generating events for page 0
{:ok, #Reference<0.2077982655.942931969.179180>}
PRODUCER: preparing to return events
PRODUCER: page will be: 1
iex(5)> [error] GenServer #PID<0.1066.0> terminating
** (stop) bad return value: {:no_reply, ["Event One", "Event Two", "Event Three", "Event Four", "Event Five"], 1}
Last message: {:"$gen_producer", {#PID<0.1067.0>, #Reference<0.2077982655.942931969.179180>}, {:ask, 1000}}
State: 0
** (EXIT from #PID<0.1002.0>) evaluator process exited with reason: bad return value: {:no_reply, ["Event One", "Event Two", "Event Three", "Event Four", "Event Five"], 1}

我正在努力的是a）了解错误信息的含义，当然还有为什么会出现错误信息。

GenStage：错误的返回值

0 个答案: