GenStage in the Kitchen

Slides for Elixir.LDN 2016 talk.

Abstract:

GenStage is the Elixir core team’s effort to provide a set of flexible, composable primitives for concurrent, demand-driven event processing.

Our use case is a restaurant simulation, with tables placing orders, a waiter, a chef and line cooks ready to prepare amazing dishes.
We’ll map GenStage’s core concepts to constraints in our restaurant simulation and see how our system copes by stressing its different components, isolating some useful principles along the way.

Transcript

1. www.erlang-solutions.com GEN STAGE IN THE KITCHEN
2. www.erlang-solutions.com HELLO! Claudio Ortolina claudio.ortolina@erlang-solutions.com www.erlang-solutions.com @cloud8421
3. www.erlang-solutions.com “ What would you like to be if you weren't a software developer?
4. www.erlang-solutions.com A CHEF Trying to, at least
5. www.erlang-solutions.com MEET MASSIMO BOTTURA. HE RUNS OSTERIA FRANCESCANA, THE BEST RESTAURANT IN THE WORLD
6. www.erlang-solutions.com NEXT BEST THING GEN STAGE TO MODEL A RESTAURANT* * Simplified version
7. www.erlang-solutions.com 1. GEN STAGE PRIMER
8. www.erlang-solutions.com TRADITIONAL EVENT DRIVEN FLOW PRODUCER PRODUCER/CONSUMER CONSUMER PUSH 10 PUSH 10 QUEUE ALL GOOD HERE
9. www.erlang-solutions.com DEMAND DRIVEN FLOW PRODUCER PRODUCER/CONSUMER CONSUMER ASK 10 ASK 10 ALL GOOD HERE QUEUE/FAILS
10. www.erlang-solutions.com MIN_DEMAND AND MAX_DEMAND PRODUCER CONSUMER (MIN 3, MAX 5) ASK 2 ASK 5 PROCESS 3 ASK 2 PROCESS 3
11. www.erlang-solutions.com PROCESS WHILE REQUESTING No one stays idle
12. www.erlang-solutions.com TABLE 1 TABLE 2 TABLE 3 TABLE 4 WAITER CHEF LINE COOK (GRILL) LINE COOK (OVEN) ... ...
13. www.erlang-solutions.com TABLES ▸ People take some time to choose a dish from the menu ▸ When everyone has decided, they call the waiter; they get upset and leave if the waiter doesn't reply in 5 seconds ▸ After ordering, they wait until 30 seconds for the first dish to be delivered. When they receive it, they can wait another 30 seconds. ▸ If dishes aren't delivered on time, they will leave.
14. www.erlang-solutions.com WAITER ▸ Collects orders from tables ▸ Delivers orders to the chef ▸ When dishes are ready, delivers them to the appropriate table
15. www.erlang-solutions.com CHEF ▸ Receives orders ▸ Distributes dishes to each line cook
16. www.erlang-solutions.com LINE COOK ▸ Receives a dish request ▸ Prepares dish and informs the waiter so that it can be picked up
17. www.erlang-solutions.com TABLE 1 TABLE 2 TABLE 3 TABLE 4 WAITER CHEF LINE COOK (MEAT) LINE COOK (OVEN) ... ... PLACE ORDERS DEMANDS ORDERS DEMAND DISHES
18. www.erlang-solutions.com TABLE WAITER CHEF LINE COOK LINE COOK TABLE Icons Designed by Freepik and distributed by Flaticon GenStage
19. www.erlang-solutions.com TABLE WAITER CHEF LINE COOK LINE COOK TABLE Icons Designed by Freepik and distributed by Flaticon PRODUCER BROADCAST DISPATCHER GenStage
20. www.erlang-solutions.com TABLE WAITER CHEF LINE COOK LINE COOK TABLE Icons Designed by Freepik and distributed by Flaticon PRODUCER/CONSUMER PARTITION DISPATCHER GenStage
21. www.erlang-solutions.com TABLE WAITER CHEF LINE COOK LINE COOK TABLE Icons Designed by Freepik and distributed by Flaticon CONSUMER PARTITION CONSUMER PARTITION GenStage
22. www.erlang-solutions.com TABLES - LOOK AT THE MENU defmodule Osteria.Table do use GenServer def init([number, size]) do … send(self(), :look_at_menu) … end def handle_info(:look_at_menu, state) do schedule_decide() {:noreply, state} end end
23. www.erlang-solutions.com TABLES - DECIDING DISHES defp schedule_decide do time = Enum.random(50..500) Process.send_after(self(), :decide, time) end def handle_info(:decide, state = %__MODULE__{number: number, size: size, dishes: dishes}) do case length(dishes) do ^size -> inform_waiter(number, dishes) {:noreply, %{state | phase: :waiting}, waiting_time()} _ -> schedule_decide() {:noreply, %{state | dishes: [random_dish() | dishes]}} end end
24. www.erlang-solutions.com TABLE WAITER GenStage.reply ORDER GenStage.call ...
25. www.erlang-solutions.com INFORMING A WAITER REQUIRES A REPLY You do wanna know if they got your order
26. www.erlang-solutions.com ORDER ORDER ORDER :queue.in :queue.out TABLE 1 CHEF WAITER (DISPATCHER)
27. www.erlang-solutions.com WAITER handle_demand/2 GenStage.async_subscribe CHEF handle_events/3 ORDER
28. www.erlang-solutions.com CHEF LINE COOK handle_demand/2 GenStage.async_subscribe handle_events/3 DISH
29. www.erlang-solutions.com LINE COOK handle_cast/2 GenStage.cast handle_cast/2 WAITER TABLE 1 GenServer.cast DISH DISH ...
30. www.erlang-solutions.com DEMAND IS DRIVEN BY LINE COOKS The faster they cook, the faster food can be served at the table
31. www.erlang-solutions.com DEMO TIME
32. www.erlang-solutions.com THANK YOU! Any questions? claudio.ortolina@erlang-solutions.com www.erlang-solutions.com @cloud8421