COORDINATION 2018

1. Forward to a Promising Future Kiko Fernandez-Reyes, Dave Clarke, Elias Castegren and Huu Phuc-Vo Uppsala University, Sweden
2. Active object B Active object A Concurrent & Parallel Programming • Active Objects have existed since mid-80 s = future Abbreviation: active object = actor
3. Active object B Active object A Concurrent & Parallel Programming • Active Objects have existed since mid-80 s = future Abbreviation: active object = actor
4. Active object B Active object A Concurrent & Parallel Programming • Active Objects have existed since mid-80 s Value = future Abbreviation: active object = actor
5. Active object B Active object A Concurrent & Parallel Programming • Active Objects have existed since mid-80 s = future Abbreviation: active object = actor
6. Motivation Many computations block on a future to get its result only to return that result immediately
7. Motivation Many computations block on a future to get its result only to return that result immediately
8. Motivation Many computations block on a future to get its result only to return that result immediately
9. Motivation Many computations block on a future to get its result only to return that result immediately
10. 1. get 2. await Motivation Many computations block on a future to get its result only to return that result immediately
11. 1. get 2. await Motivation Many computations block on a future to get its result only to return that result immediately
12. 1. get 2. await Motivation Many computations block on a future to get its result only to return that result immediately
13. 1. get 2. await Motivation Many computations block on a future to get its result only to return that result immediately Interesting for behavioural design patterns:
14. 1. get 2. await Motivation Many computations block on a future to get its result only to return that result immediately Interesting for behavioural design patterns: Broker Mediator Chain of responsibility PubSub
15. Deep dive into the problem
16. Broker Requesters broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) return get(future) end end 2 1 Problem GET Responders
17. Broker Requesters broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) return get(future) end end 2 1 Problem GET Responders
18. Broker Requesters broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) return get(future) end end 2 1 Problem GET 1 Responders
19. Broker Requesters broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) return get(future) end end 2 1 Problem GET 1 Responders
20. Broker Requesters broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) return get(future) end end 2 1 Problem GET 1 2 Responders
21. Broker Requesters broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) return get(future) end end 2 1 Problem GET Value 1 2 Responders
22. Broker Requesters broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) return get(future) end end 2 1 Problem GET 1 2 Responders
23. Broker Requesters broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) return get(future) end end 2 1 Problem GET 1 2 Responders
24. Broker Requesters broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) return get(future) end end 2 1 Problem GET 1 2 Responders
25. Broker Requesters broker!run( ) new Job(1) Problem Nothing active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): Fut int val worker = this.workers[++this.current % workers.size()] return worker!start(job) end end 1 Responders
26. Broker Requesters broker!run( ) new Job(1) Problem Nothing active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): Fut int val worker = this.workers[++this.current % workers.size()] return worker!start(job) end end 1 Responders
27. Broker Requesters broker!run( ) new Job(1) Problem Nothing active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): Fut int val worker = this.workers[++this.current % workers.size()] return worker!start(job) end end 1 Responders
28. Broker Requesters broker!run( ) new Job(1) Problem Nothing active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): Fut int val worker = this.workers[++this.current % workers.size()] return worker!start(job) end end 1 Responders
29. Broker Requesters broker!run( ) new Job(1) Problem Nothing active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): Fut int val worker = this.workers[++this.current % workers.size()] return worker!start(job) end end 1 Responders 1
30. Broker Requesters broker!run( ) new Job(1) Problem Nothing active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): Fut int val worker = this.workers[++this.current % workers.size()] return worker!start(job) end end 1 Responders 1
31. Broker Requesters broker!run( ) new Job(1) Problem AWAIT active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) await(future) return get(future) end end 2 1 Responders
32. Alternatives?
33. Broker Requesters broker!run(new Job(1),p) Problem Promise active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job, prom: Promise[int]): unit val worker = this.workers[++this.current % workers.size()] worker!start(job, prom) end end 3 Responders let p = new Prom() 1 2
34. Broker Requesters broker!run(new Job(1),p) Problem Promise active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job, prom: Promise[int]): unit val worker = this.workers[++this.current % workers.size()] worker!start(job, prom) end end 3 Responders let p = new Prom() 1 1 2
35. Broker Requesters broker!run(new Job(1),p) Problem Promise active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job, prom: Promise[int]): unit val worker = this.workers[++this.current % workers.size()] worker!start(job, prom) end end 3 Responders let p = new Prom() 1 1 2 2
36. Broker Requesters broker!run(new Job(1),p) Problem Promise active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job, prom: Promise[int]): unit val worker = this.workers[++this.current % workers.size()] worker!start(job, prom) end end 3 Responders let p = new Prom() 1 1 2 2
37. Broker Requesters broker!run(new Job(1),p) Problem Promise active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job, prom: Promise[int]): unit val worker = this.workers[++this.current % workers.size()] worker!start(job, prom) end end 3 Responders let p = new Prom() 1 1 2 2 3
38. Broker Requesters broker!run(new Job(1),p) Problem Promise active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job, prom: Promise[int]): unit val worker = this.workers[++this.current % workers.size()] worker!start(job, prom) end end 3 Responders let p = new Prom() 1 1 2 2 3
39. Broker Requesters broker!run(new Job(1),p) Problem Promise active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job, prom: Promise[int]): unit val worker = this.workers[++this.current % workers.size()] worker!start(job, prom) end end 3 Responders let p = new Prom() 1 1 2 2 3
40. Broker Requesters broker!run(new Job(1),p) Problem Promise active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job, prom: Promise[int]): unit val worker = this.workers[++this.current % workers.size()] worker!start(job, prom) end end 3 Responders let p = new Prom() 1 1 2 2 Value Value 3
41. Alternatives Comparison Futures Promises Pros Static fulfilment guarantees Flexibility Cons Rigid No fulfilment guarantees Fulfilled multiple times?
42. Main idea • Write future-based code with static fulfilment guarantees with the flexibility of promises Main idea
43. Broker Requesters broker.run( ) new Job(1) Explore Forward Broker broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) forward(future) end end 1 Responders
44. Broker Requesters broker.run( ) new Job(1) Explore Forward Broker broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) forward(future) end end 1 Responders
45. Broker Requesters broker.run( ) new Job(1) Explore Forward Broker broker!run( ) new Job(1) active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) forward(future) end end 1 Responders
46. Broker Requesters broker.run( ) new Job(1) Explore Forward Broker broker!run( ) new Job(1) 1 active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) forward(future) end end 1 Responders
47. Broker Requesters broker.run( ) new Job(1) Explore Forward Broker broker!run( ) new Job(1) 1 active class Broker val workers: Buffered[Worker] var current: uint def run(job: Job): int val worker = this.workers[++this.current % workers.size()] val future : Fut[int] = worker!start(job) forward(future) end end 1 Responders
48. Requesters broker.run( ) new Job(1) Explore Forward Broker broker!run( ) new Job(1) Value Responders forward(x!run(..)) forward(y!run(..)) forward(z!run(..))
49. Requesters broker.run( ) new Job(1) Explore Forward Broker broker!run( ) new Job(1) Value Responders forward(x!run(..)) forward(y!run(..)) forward(z!run(..))
50. Contributions • High-level (future) task-based language • Low-level promise-based language • Compilation strategy from high- to low-level language (proof that translation is semantics preserving) • Implementation and microbenchmarks The formalisation captures the essence of the implementation
51. High-Level Language
52. High-level Language g
53. Typing rules
54. Typing rules return type of a task • forbids the use of forward in contexts where the expected task type is not clear closure can be passed between tasks and run in a context different from their defining contexts
55. Broker Runtime semantics f h
56. Broker Runtime semantics f h
57. Low-Level Language
58. Low-level Language
59. Low-level Language Forward expressed using low-level expressions
60. Static & Dynamic rules Reduction intuition: *
61. Static & Dynamic rules Reduction intuition: *
62. Static & Dynamic rules Reduction intuition: *
63. Static & Dynamic rules Reduction intuition: *
64. Static & Dynamic rules Reduction intuition: *
65. Static & Dynamic rules Reduction intuition: *
66. Compilation Strategy
67. Compilation Strategy • Inductive compilation of: 1. configurations 2. expressions and values 3. types
68. Compilation Strategy Compilation of: • configurations • expressions and values • types
69. Compilation Strategy Compilation of: • configurations • expressions and values • types
70. Compilation Strategy Compilation of: • configurations • expressions and values • types e =future
71. Compilation Strategy Compilation of: • configurations • expressions and values • types e =future
72. Compilation Strategy Compilation of: • configurations • expressions and values • types e =future Bisimulation up-to expansion to proof that it is semantics preserving
73. Implementation
74. Implementation • Encore actor-based language • Compiled from Encore to C • Microbenchmarks Broker pattern: • get • await + get • forward
75. Benchmark Performance (lower is better)
76. Benchmark Performance (lower is better)
77. Benchmark Performance (lower is better) Why?
78. Benchmark Performance (lower is better) Why? Blocking
79. Benchmark Performance (lower is better) Why? Blocking Context switch & creates more futures
80. (lower is better) Benchmark Memory Saves the whole stack on each context switch Creates more futures than the forwarding version Why?
81. More goodies in the paper
82. More goodies in paper Standard reduction rules Optimised reduction rules In-depth explanation of bisimulation using a LTS More examples of: • Reduction rules • Compilation strategy • etc
83. Conclusion
84. Conclusion Main idea • Forward fixes: • get-and-return and • await-get-return Write high-level future-based code & Output low-level promise-based code with static fulfilment guarantees