Emoji Game - Telemetry Example

actor.ex

# lib/emoji_game/actor.ex

# Non-player character client

defmodule EmojiGame.Actor do
  use GenServer
  
  # ... code ...

  @impl true
  def handle_info(:move, {x, y}) do
    new_x = x + Enum.random(@move_shift_amounts)
    new_y = y + Enum.random(@move_shift_amounts)

    :telemetry.span(
      [:emoji_game, :actor, :move_time],
      %{},
      fn ->
        {EmojiGame.Game.move({new_x, new_y}), %{}}
      end
    )

    Process.send_after(self(), :move, 1_000)

    {:noreply, {new_x, new_y}}
  end
end

game.ex

# lib/emoji_game/game.ex

# Game server

defmodule EmojiGame.Game do
  use GenServer

  # ... code ...

  @impl true
  def handle_call({:move, new_position}, {from_pid, _}, state) do
    # Will this cause problems in responding?
    report_metrics()

    # `move` message handling code
  end
  
  # ... code ...

  # Helpers

  def report_metrics do
    pid = Process.whereis(__MODULE__)
    {:message_queue_len, length} = Process.info(pid, :message_queue_len)

    :telemetry.execute(
      [:emoji_game, :game, :queue],
      %{length: length},
      %{ }
    )

  end
end

telemetry.ex

# lib/emoji_game_web/telemetry.ex

# Phoenix Configuration for Telemetry

defmodule EmojiGameWeb.Telemetry do
  use Supervisor
  import Telemetry.Metrics

  # ... Phoenix scaffold code ...

  def metrics do
    [
      # Game Metrics
      summary("emoji_game.game.queue.length"),
      summary("emoji_game.actor.move_time.stop.duration", unit: {:native, :millisecond}),

      # ... Phoenix scaffold code ...
    ]
  end

  def metrics_statsd_options do
    [
      metrics: [
        summary("emoji_game.game.queue.length"),
        summary("emoji_game.actor.move_time.stop.duration", unit: {:native, :millisecond}),
      ]
    ]
  end

  # ... Phoenix scaffold code ...
end