Elixir Elevated: the Ups and Downs of OTP

Given July, 25, 2014 at ElixirConf #1
Using an elevator bank simulator as an overview of the concepts behind OTP. Example code available: https://github.com/gvaughn/elixir_elevated/tree/elixirconf2014

1. Elixir Elevated! The Ups and Downs of OTP Greg V aughn! gvaughn@gmail.com! twitter: @gregvaughn, github/irc: gvaughn
2. Student of Elixir and OTP! Hobbying with Elixir almost 13 months! Texan! Professional Programmer of 20 years! Across 6 languages! Employed by LivingSocial
3. Student of Elixir and OTP! Hobbying with Elixir almost 13 months! Texan! Professional Programmer of 20 years! Across 6 languages! Employed by LivingSocial LivingSocial is Hiring!
4. OTP is …
5. OTP is … Mature / Battle Tested for 16 (18?) years
6. OTP is … Mature / Battle Tested for 16 (18?) years Microservices
7. OTP is … Mature / Battle Tested for 16 (18?) years Microservices Object Oriented (NOT class oriented)
8. OTP is … Mature / Battle Tested for 16 (18?) years Microservices Object Oriented (NOT class oriented) Actor
9. OTP is … Mature / Battle Tested for 16 (18?) years Microservices Object Oriented (NOT class oriented) Actor Framework (Hollywood Principle)
10. OTP is … Mature / Battle Tested for 16 (18?) years Microservices Object Oriented (NOT class oriented) Actor Framework (Hollywood Principle) Design Patterns
11. OTP is … Mature / Battle Tested for 16 (18?) years Microservices Object Oriented (NOT class oriented) Actor Framework (Hollywood Principle) Design Patterns Robust
12. object oriented OOP to me means only messaging, local retention and protection and ! hiding of state-process, and extreme late-binding of all things. — Alan Kay
13. object oriented OOP to me means only messaging, local retention and protection and ! hiding of state-process, and extreme late-binding of all things. — Alan Kay functional a style of building the structure and elements of computer programs that treats computation as the evaluation of mathematical functions and avoids state and mutable data. — Wikipedia
14. object oriented OOP to me means only messaging, local retention and protection and ! hiding of state-process, and extreme late-binding of all things. — Alan Kay functional a style of building the structure and elements of computer programs that treats computation as the evaluation of mathematical functions and avoids state and mutable data. — Wikipedia concurrent The conceptually simultaneous execution of more than one sequential program on a computer or network of computers. — McGraw-Hill Sci & Tech Dictionary
15. object oriented functional concurrent actors
16. Behaviours: Don’t call us, we’ll call you defmodule MyCallback do use GenServer end iex> {:ok, pid} = GenServer.start(MyCallback, [])
17. Behaviours: Don’t call us, we’ll call you defmodule MyCallback do use GenServer end iex> {:ok, pid} = GenServer.start(MyCallback, []) defmodule GenServer do defmacro __using__(_) do quote do @behaviour :gen_server ! def init(args), do: {:ok, args} ! def handle_cast(msg, state), do: {:stop, {:bad_cast, msg}, state} ! def handle_call(msg, _from, state), do: {:stop, {:bad_call, msg}, state} ! def handle_info(_msg, state), do: {:noreply, state} ! def terminate(_reason, _state), do: :ok ! def code_change(_old, state, _extra), do: {:ok, state} ! defoverridable [init: 1, handle_call: 3, handle_info: 2, handle_cast: 2, terminate: 2, code_change: 3] end end … end
18. defmodule MyCallback do use GenServer @initial_state %{} ! def start_link do GenServer.start_link(__MODULE__, @initial_state) end ! def init(arg) do state = arg {:ok, state} end ! def do_it(pid, param) do GenServer.call(pid, {:do_it, param}) end ! def handle_call({:do_it, param}, _from, state) do payload = get_payload(param, state) new_state = update_state(param, state) {:reply, payload, new_state} end ! defp get_payload(param, state), do: “I DONE DID IT!” ! defp update_state(param, state), do: state end
19. defmodule MyCallback do use GenServer @initial_state %{} ! def start_link do GenServer.start_link(__MODULE__, @initial_state) end ! def init(arg) do state = arg {:ok, state} end ! def do_it(pid, param) do GenServer.call(pid, {:do_it, param}) end ! def handle_call({:do_it, param}, _from, state) do payload = get_payload(param, state) new_state = update_state(param, state) {:reply, payload, new_state} end ! defp get_payload(param, state), do: “I DONE DID IT!” ! defp update_state(param, state), do: state end
20. defmodule MyCallback do use GenServer @initial_state %{} ! def start_link do GenServer.start_link(__MODULE__, @initial_state) end ! def init(arg) do state = arg {:ok, state} end ! def do_it(pid, param) do GenServer.call(pid, {:do_it, param}) end ! def handle_call({:do_it, param}, _from, state) do payload = get_payload(param, state) new_state = update_state(param, state) {:reply, payload, new_state} end ! defp get_payload(param, state), do: “I DONE DID IT!” ! defp update_state(param, state), do: state end
21. defmodule MyCallback do use GenServer @initial_state %{} ! def start_link do GenServer.start_link(__MODULE__, @initial_state) end ! def init(arg) do state = arg {:ok, state} end ! def do_it(pid, param) do GenServer.call(pid, {:do_it, param}) end ! def handle_call({:do_it, param}, _from, state) do payload = get_payload(param, state) new_state = update_state(param, state) {:reply, payload, new_state} end ! defp get_payload(param, state), do: “I DONE DID IT!” ! defp update_state(param, state), do: state end
22. defmodule MyCallback do use GenServer @initial_state %{} ! def start_link do GenServer.start_link(__MODULE__, @initial_state) end ! def init(arg) do state = arg {:ok, state} end ! def do_it(pid, param) do GenServer.call(pid, {:do_it, param}) end ! def handle_call({:do_it, param}, _from, state) do payload = get_payload(param, state) new_state = update_state(param, state) {:reply, payload, new_state} end ! defp get_payload(param, state), do: “I DONE DID IT!” ! defp update_state(param, state), do: state end Client Process Server Process
23. Elevators 101
24. A rider on any floor presses the up or down button! An elevator car arrives! Rider enters and presses a destination floor button rider hall! signal hall! signal car car rider floor hail retrieve arrival arrival go to
25. A rider on any floor presses the up or down button! An elevator car arrives! Rider enters and presses a destination floor button rider hall! signal hall! signal car car rider floor hail retrieve arrival arrival go to Hail struct
26. Show Me The Code
27. Let It Fail … and Respond Separation of Concerns! Think Long and Hard about Failure Response! BEAM (not OS) Processes! Finer Grained Control
28. Prepare to Fail Car! Supervisor Car 1 Car n … one_for_one
29. Prepare to Fail Car! Supervisor Car 1 Car n … one_for_one Hall! Signal
30. Prepare to Fail Car! Supervisor Car 1 Car n … one_for_one Gen! Event Hall! Signal
31. Prepare to Fail Car! Supervisor Car 1 Car n … one_for_one Gen! Event Hall! Signal Bank! Supervisor rest_for_one
32. Prepare to Fail Gen! Event HS Bank A! Supervisor CS Gen! Event HS Bank B! Supervisor CS Elevator! Supervisor one_for_one
33. Prepare to Fail Gen! Event HS Bank A! Supervisor CS Gen! Event HS Bank B! Supervisor CS Elevator! Supervisor one_for_one Gen Event Gen Event
34. Don’t Trip defmodule MySupervisor do use Supervisor ! def init(…) do workers = worker(MyCallback, [p1, p2, [name: :myc]], [id: :mine]) supervise(workers, strategy: one_for_one) end end ! defmodule MyCallback do use GenServer ! def start_link(p1, p2, opts \\ []) GenServer.start_link(__MODULE__, [p1, p2], opts) end ! def init([p1, p2]) do {:ok, %{p1: p1, p2: p2}} end end
35. Don’t Trip defmodule MySupervisor do use Supervisor ! def init(…) do workers = worker(MyCallback, [p1, p2, [name: :myc]], [id: :mine]) supervise(workers, strategy: one_for_one) end end ! defmodule MyCallback do use GenServer ! def start_link(p1, p2, opts \\ []) GenServer.start_link(__MODULE__, [p1, p2], opts) end ! def init([p1, p2]) do {:ok, %{p1: p1, p2: p2}} end end apply: list of params
36. Don’t Trip defmodule MySupervisor do use Supervisor ! def init(…) do workers = worker(MyCallback, [p1, p2, [name: :myc]], [id: :mine]) supervise(workers, strategy: one_for_one) end end ! defmodule MyCallback do use GenServer ! def start_link(p1, p2, opts \\ []) GenServer.start_link(__MODULE__, [p1, p2], opts) end ! def init([p1, p2]) do {:ok, %{p1: p1, p2: p2}} end end apply: list of params single term for init/1
37. Trip-less Convention? defmodule MySupervisor do use Supervisor ! def init(…) do workers = worker(MyCallback, [{p1, p2}, name: :myc], [id: :mine]) supervise(workers, strategy: one_for_one) end end ! defmodule MyCallback do use GenServer ! def start_link(init_params, opts \\ []) GenServer.start_link(__MODULE__, init_params, opts) end ! def init({p1, p2}) do {:ok, %{p1: p1, p2: p2}} end end
38. Show Me The Code
39. Takeaways Behaviours vs. Callback Modules! Watch your initialization steps! Watch parameter and return value contracts! Supervisors and Strategies! Config
40. Thank you Elixir Elevated! The Ups and Downs of OTP! ! Greg Vaughn! ! gvaughn@gmail.com! twitter: @gregvaughn! github/irc: gvaughn http://github.com/gvaughn/elixir_elevated/tree/elixirconf2014