Trilha Programação Funcional How we figured out we had a SRE team at - Creating a stealing points game server with elixir

1. CREATING A
STEALING POINTS
GAME SERVER
WITH ELIXIR

2. Kleber N. Gueriero
Web Developer
Ruby Developer

4. There is this alchemists
language ...

6. Created by José Valim
(Rails Core Team)

7. Influenced by nice
Languages(such as
Ruby and Erlang)

8. Functional

9. Runs on Erlang VM
and has a lot of
Erlang inheritance

10. Which kind of
inheritances?

11. Ready to Fault-tolerance

12. Handles High
Concurrency

15. The Game

20. Structs

21. defmodule ExStealerGame.Player do
defstruct [:id, :name, :score, :client_pid]
end
The Structs
defmodule ExStealerGame.Match do
defstruct [:last_id, {:players, []}]
end

22. defmodule ExStealerGame do
use Application
def start(_type, _args) do
IO.puts "STARTING THE APPLICATION"
ExStealerGame.Supervisor.start_link
end
end
Starting Point

23. Supervisors

27. New server
process was
started by
Supervisor

28. defmodule ExStealerGame.Supervisor do
use Supervisor
def start_link() do
Supervisor.start_link(__MODULE__, [])
End
...
end
The Supervisor

29. defmodule ExStealerGame.Supervisor do
use Supervisor
…
def init(_) do
children = [
worker(Task, [Server, :start_server, []]),
worker(Match, [])]
supervise children, strategy: :one_for_one
end
end
The Supervisor

30. Keeping State
- Elixir is Immutable
- Processes are used to keep state
- Processes sends and receives messages to
each other to request to receive/set this state

31. Agents

32. defmodule ExStealerGame.Match do
...
def start_link do
Agent.start_link(fn -> %Match{last_id: 0} end, name: __MODULE__)
end
end
The Match’s State

33. defmodule ExStealerGame.Match do
...
def register_player(player_name, client_pid) do
new_player = %Player{id: next_id(), name: player_name,
score: @starting_score, client_pid: client_pid}
Agent.update(__MODULE__, fn(current) ->
%{current | players: [new_player | current.players]}
end)
new_player
end
end
The Match’s State

34. defmodule ExStealerGame.Match do
...
def get_players do
Agent.get(__MODULE__, fn(current_match) -> current_match.players end)
end
end
The Match’s State

35. defmodule ExStealerGame.Server do
def start_server() do
{:ok, socket} = :gen_tcp.listen(@port, [some_options])
accept_connection(socket)
end
end
Starting the Server

36. Tasks

37. defmodule ExStealerGame.Server do
…
defp accept_connection(socket) do
{:ok, client} = :gen_tcp.accept(socket)
handle_player_join(client) # keep player with Agent and send msg to client
{:ok, pid} = Task.start(fn -> match_loop(client) end)
:gen_tcp.controlling_process(client, pid)
accept_connection(socket) # recursively keeps open to new connections
end
end
Connecting to Clients

38. defmodule ExStealerGame.Server do
…
defp match_loop(client) do
client
|> read_client() #wait for client’s message and receive it
|> handle_match_message(client)
match_loop(client) #again, recursively, keeps the game’s match running
end
end
The Game Loop

39. Pattern Matching

40. defmodule ExStealerGame.Server do
defp handle_match_message("quit", client) do
quit_player(client)
end
defp handle_match_message(message, client) do
...
end
end
Quitting the Game

41. defmodule ExStealerGame.Server do
defp quit_player(client) do
IO.puts "PLAYER QUITTING"
Match.get_player(client)
|> Match.remove_player
send_score_to_clients() # send message to clients with players list and score
Process.exit(self(), :kill) # kills current process, along with the conection
end
end
Quitting the Game

42. defmodule ExStealerGame.Server do
defp handle_match_message(message, client) do
case Integer.parse(message) do
{target_id, _} ->
Match.get_player(client).id
|> Match.execute_steal(target_id)
Match.get_winners
|> handle_match_state
:error -> send_score_to_clients()
end
end
end
Stealing Points

43. defmodule ExStealerGame.Server do
defp handle_match_state([]) do
send_score_to_clients()
end
defp handle_match_state(winners) do
...
end
end
Checking if there is a winner

44. defmodule ExStealerGame.Server do
defp handle_match_state(winners) do
Match.get_players
|> Enum.each(fn(player) ->
"<End of Match Message>"
|> send_to_client(player.client_pid)
end)
:timer.sleep 2000
Match.restart_match
send_score_to_clients
end
end
Checking if there is a winner

45. - Structs
- Supervisors
- Agents
- Tasks
- Pattern Matching

46. Thank’s!