Handle_info callback not called

idragnev · October 13, 2019, 11:36am

Hi all,

My handle_info callback for GenServer is not called.
Here is the code:

IDragnev/IncludeUpdator/blob/master/lib/include_updator/gatherer.ex

defmodule IncludeUpdator.Gatherer do

  use GenServer

  @gatherer __MODULE__

  #API
  def start_link(workers_count) do
    GenServer.start_link __MODULE__, workers_count, name: @gatherer
  end
  def worker_done do
    GenServer.cast @gatherer, :worker_done
  end
  def add_filename(filename) do
    GenServer.cast @gatherer, {:add_filename, filename}
  end
  #server implementation
  def init(workers_count) do
    Process.send_after(self(), :kickoff, 0)
    {:ok, workers_count}

This file has been truncated. show original

On line 18 in init I send myself a :kickoff message but the callback is not invoked.
The same code was working when my top-level module used the Application behaviour.
But I needed command-line arguments and restructured the code - I parse my arguments in the CLI module and pass them to the Application module which just calls Supervisor.start_link. And it stopped working and I can’t figure out why.

kokolegorille · October 13, 2019, 11:43am

Hello and welcome…

handle_info/2, not 3! but You pass 3 parameters… it’s not going to work

I use tuple in such case, like {:kickoff, params}

Process.send_after(self(), {:kickoff, 0})
...
def handle_info({:kickoff, workers_count}, state) do
...
end

BTW, there is also handle_continue You can benefit from… in init.

idragnev · October 13, 2019, 11:58am

The 0 in send_after is not intended as a message - its the timeout.
I want to just finish initialization and handle the :kickoff message immediately after that, using the workers_count (which is my state) to launch this number of workers.

hubertlepicki · October 13, 2019, 11:58am

On a side note, recent Elixir and Erlang versions ship with “handle_continue” which you may want to use instead of custom kickoff message sent from init. Not much of functional change but a nice syntax designed to do initialization specifically after process is started.

kokolegorille · October 13, 2019, 12:01pm

So handle_continue is for You…

BTW I think You are mistaken about timeout meaning, it’s the time You allow for response to comeback… before returning a timeout.

idragnev · October 13, 2019, 12:16pm

Yes, I picked the wrong word. But handle_continue solved the problem, thanks.