concurrency.world em Elixir

Um breve sumário sobre actors e promises como ferramentas de concorrência, e como esses conceitos aparecem dentro de Elixir.

Links:
- History of Actors: https://eighty-twenty.org/2016/10/18/actors-hopl
- How do Promises Work: https://robotlolita.me/articles/2015/how-do-promises-work/
- Elixir Language Guides: https://elixir-lang.org/getting-started/introduction.html

Transcript

1. concurrency.world (in elixir)
2. AHHH… MY FULL COMBO... http://robotlolita.me @robotlolita mostly everywhere Quil (in idol hell)
3. YES, there will be kittens.
4. Agenda WHY? (motivation) WHAT? (definitions) HOW? (concurrency models) I. II. III.
5. A long, long time ago... (or not so long)
6. Only one program could execute at a time.
7. And programs were simple, sequential instructions.
8. They’re complaining they need to wait “too long”... *pushes* Shall we give ‘em chairs? Slap a progress bar on it Inspired by @HEJIBITS
9. But not everything was lost...
10. Concurrency Parallelism is not Concurrency, R. Harper
11. PROBLEM: who gets to decide this? \ up you go~ /
12. Concurrency Models
13. Actors (1973) Lisp Smalltalk Packet Switching (originally made for AI)
14. Actors “What if every tiny piece of a program ran in its own tiny computer?”
15. Each actor is an isolated, complete processing unit. Actors
16. They have an address and a mailbox
17. To interact, actors send messages to these mailboxes.
18. And messages are asynchronous Can you print this for me? ALL OF IT!?
19. They also don’t have a defined arrival order
20. Finally, actors reply sending messages back \ mailboxes are magic /
21. Irene Greif Contributed significantly to this concept by formalising Actors in her doctoral thesis! (she was also the first woman to get a MIT PhD)
22. Elixir LET’S TALK ABOUT
23. In Elixir, Actors are called Processes these cuties
24. They have their own spaces to store things, too! a.k.a. the heap
25. SPAWN is used to create processes. \ c-cute... / But another SPAWN. Spawn is (c) Todd McFarlane
26. SPAWN is used to create processes. a wild process appears!
27. SPAWN is used to create processes. It returns an address. a wild process appears!
28. SEND puts messages in the mailbox.
29. AND... nothing happens.
30. When an actor receives a message, it just gets stored in the MAILBOX
31. We’ve defined a process, but not how to process the incoming messages. WHICH MEANS: Accumulated messages
32. RECEIVE lets us process our mailbox We define reactions based on patterns the messages exhibit.
33. ALL TOGETHER NOW.
35. What happens if we send another message?
36. DISAPPOINTINGLY, nothing. \ alice is dead /
37. RECEIVE processes exactly 1 (one) message
38. MODULES Are logical groupings of functions.
39. OUR PROCESS Is now captured in a named function.
40. NOW, every time we process a message, we’ll go back to process more. (which is why this is generally called a loop)
41. From the top... LET’S TRY AGAIN
42. WE CREATE OUR PROCESS (SPAWN) a wild process appears!
43. and SEND messages to them.
44. WE PROCESS THEM (one at a time)
45. AND REPEAT (endlessly, perhaps)
46. So we do everything using Actors?
47. NOPE. (but actors form a good basis for concurrency)
48. Promises (1976~77) Multi-processing Distributed Programming Since we had problems with:
49. Promises “Instead of just waiting for things that may take a long time, why not just give out a numbered ticket and pick it up later?”
50. Some operations may take a really long time to finish.
51. Stopping everything and waiting for them is a waste of time.
52. Promises, however, are returned immediately.
53. And this lets us do other things while we wait.
54. And any time we need, we can just go pick up our Promised thing.
55. Barbara Liskov Invented one of the most interesting concepts in distributed computing with promises: PROMISE PIPELINES
56. Elixir? HOW DO WE DO THIS IN
57. TASK. (well, they’re not exactly promises, but...)
58. TASK.ASYNC Create processes with a single purpose -- a task. \ ぺ・ル・ソ・ナ /
59. \ nani the fudge / And we get back an identifier for the task, not an actor!
60. TASK.AWAIT Stops the process until a value is available, and then returns it.
61. TASK.AWAIT Stops the process until a value is available, and then returns it.
62. A short review...
63. Actors ISOLATED PROCESSES MESSAGES CONCURRENCY ARE SEND FOR
64. Promises EVENTUAL VALUES LONG OPERATIONS LATENCY ARE FOR REDUCE
65. OTHER MODELS? There are several other interesting concurrency models for the BEAM!
66. RECOMMENDED LITERATURE History of Actors (Tony Garnock-Jones, 2016) How Do Promises Work? (Quil, 2015) The Elixir Documentation N/A
67. The end. Get these slides from: concurrency.world