How to restart a crashed supervised process after a certain amount of time?

Question

I have a simple GenServer based app that parses a webpage and plays with the data that it got from it. The code looks roughly like this:

def start_link do
  GenServer.start_link(__MODULE__, %{})
end

def init(state) do
  schedule_work(1)
  {:ok, state}
end

def handle_info(:work, state) do
  // Request webpage using HTTPoisson
  // Parse data using Floki
  // Use it

  schedule_work(10 * 60) # Reschedule after 10 minutes
  {:noreply, state}
end

defp schedule_work(timeout) do
  Process.send_after(self(), :work, timeout * 1000)
end

Today the 3rd party site stopped delivering the correct markup for some time and the parsing failed and crashed the GenServer. Supervisor restarted it and it crashed immediatley. After :max_restarts the Supervisor eventually stopped the application.

I don't want simply increase the :max_restarts. Is there a way to tell Supervisor to attempt restarts after certain amount of time? Or should I do more error handling in my parsing code to prevent the process from crashing in the first place (I assume this would be against the "Let it crash" philosophy)?

Answer 1

I'd say the best thing to do is to both handle errors better and crash better.

You mentioned you didn't want to simply increase the max_restarts option. You could alternatively lower the max_seconds option which defaults to 5.

Also, you could trap exits with Process.flag(:trap_exit, true) and, in case of parsing errors, exit with a specific message (e.g., Process.exit(pid, :bad_parsing) and use that to reschedule. This might need little changes here and there in the way you supervise things, though.