Enumerable.MapSet.reduce function not found about phoenix_pubsub HOT 7 CLOSED

@michelson when in doubt, always add a catch all and see what it looks like:

receive do
  whatever -> IO.inspect whatever
end

:)

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Can you add {:ok, _} = Code.ensure_loaded(Enumerable.MapSet) to def start/2 in your application callback (usually in "lib/my_app.ex") and let us know if the error disappears?

Also please double check you are running in production environment.

This is not a Phoenix bug per se. We have had reports of something similar happening but we could not yet reproduce it.

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Hello @josevalim ,

thanks for your quick reply, I've tunned some sysctl settings on my machine and this error disappeared among other errors.
Also note that I'm using this plugin with a mix application, not a phoenix application. it seems This kinds of errors are raised when process reaches system limits on file descriptors

I'm trying to implement a long polling application which each request is tracked with Tracker and each req starts a PubSub subscriber, if subscriber got message the response is released to the client. (i'm using task async/yield which blocks requests until got response)
I would like to know if this is the correct way to do it, it will scale well ?

  get "/api/process/:key" do
    key2 = key |> String.replace(".json", "")
    Phoenix.Tracker.track(Notify.Tracker, self(), "devices", key2, %{stat: "CONNECTED"})
    proc = self()
    Phoenix.PubSub.subscribe Notify.PubSub, key2

    task = Task.Supervisor.async_nolink(NotifyWeb.TaskSupervisor, fn ->
      try do
        check_process(proc)
      catch
        :exit, _ -> {:error}
      end
    end)


    conn = put_resp_header(conn, "content-type", "application/json")

    # await for task to return, will also return exit process
    case Task.yield(task, 60000) do
      [] -> send_resp(conn, 200, "[]")
      {:ok, res3}   -> 
        case res3 do
          {:ok, [actions: str]} -> deliver_actions(key2, conn, 200, str)
          {:ok, _} -> send_resp(conn, 200, "[]")
        end
          
      {:exit, _}    -> send_resp(conn, 200, "[]")
      {:error, _}   -> send_resp(conn, 200, "[]")
      nil           -> send_resp(conn, 200, "[]")
      _             -> send_resp(conn, 200, "[]")

    end

  end

  def deliver_actions(key, conn, status, str) do
    send_resp(conn, status, str)
  end

  # recursive function to respond when got data
  def check_process(proc) do
    :timer.sleep(1000)
    case Process.info(proc)[:messages] do
      [] -> check_process(proc) 
      {:ok, [actions: res]} -> {:ok, [actions: res]}
      val -> check_process(proc)
    end
  end

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thanks for your quick reply, I've tunned some sysctl settings on my machine and this error disappeared among other errors.

Good call.

I would like to know if this is the correct way to do it, it will scale well ?

Using Process.info(prod)[:messages] and :timer.sleep(1000) are usually a no-no. You want the task process to instead send you a message instead of looking into its inbox at every time interval.

In fact, it seems like you don't need the task at all. You can subscribe directly from the request process and use receive to await for the message and use after for timeout.

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Thanks José , I will investigate how can I implement that

best regards

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You can subscribe directly from the request process and use receive to await for the message and use after for timeout.

having this Process.info(self)[:messages] to read messages, how can I use receive to listen for new messages ?

I'm trying this:

Phoenix.PubSub.subscribe Notify.PubSub, key

receive do
  {:ok, [actions: res]} -> deliver_actions(key, conn, res)
  {msg} -> IO.inspect msg
  after
  60_000 -> send_resp(conn, 200, "[d]")
end

but I only get the after response

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forget it , It was my mistake on the match handling

thanks

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