## What’s takeaway of this session - The basic use of Promise and Fiber - The combination of Promise and Fiber performs like Async/Await syntax - The naive Async/Await syntax sadly does NOT work efficiently in Graphql-ruby

1. Async/Await functions in Ruby
Sat, Dec. 14th, 2019 @平成Ruby会議01

2. @sat0yu
- Software engineer at
- Building microservices with
gRPC and GraphQL
- Three years of

3. What’s takeaway of this session
1. The basic use of Promise and Fiber
2. ★ The combination of Promise and Fiber performs like Async/Await syntax
3. ★★ The naive Async/Await syntax sadly does NOT work efficiently in
★: hard for @sat0yu to explain

4. GraphQL as an integrator
*Note: just a part of the whole Quipper services

5. N+1 problems with GraphQL

7. ref. https://github.com/rmosolgo/graphql-ruby/blob/master/guides/schema/lazy_execution.md

8. How to use Graphql-batch
- Build a loader so as inherit GraphQL::Batch::Loader
- which need implementing perform(...)fetching data in bulk
- Generate field values through the loader
X.rb Y.rb
ref. https://github.com/Shopify/graphql-batch

9. Nested loaders 🤔
ref. https://github.com/Shopify/graphql-batch

10. “Promise” in Graphql-batch💡
ref. https://github.com/Shopify/graphql-batch

11. - A representation of an eventual value
- The value won’t be calculated until evaluating it (lazy-evaluation)
- Chain-able with other promises through .then(...)
What is “Promise”?
fulfill
rejectpending
fulfilled
rejected
※ .load(...) returns a promise

12. Async/Await syntax with Promise and Genarator
JavaScript

13. Async/Await in JavaScript
- Declared in ES2017(ES8); Almost all browsers have compatibility
- Convenient to write async processing with a synchronized-ish syntax
JavaScript

14. Pause and Resume for promises
- Declared in ES2017(ES8); Almost all browsers have compatibility
- Convenient to write async processing with a synchronized-ish syntax
sleeping...
Pause
Resume
JavaScript

15. Promise + Generator ≈ Async/Await
≈
JavaScript

16. Generator pretends Pause and Resume
JavaScript

17. Generator pretends Pause and Resume
JavaScript
How can we use Pause & Resume in Ruby?

18. Generator pretends Pause and Resume
JavaScript
Fiber (1.9~)

19. What is “Fiber”?
⏸

20. ⏩
What is “Fiber”?

21. ⏩
What is “Fiber”?

22. ⏩
What is “Fiber”?

23. ⏸
What is “Fiber”?

24. ⏩
What is “Fiber”?

25. ⏩
What is “Fiber”?

26. ⏩
What is “Fiber”?

27. ⏸
What is “Fiber”?

28. Async/Await syntax with Promise and Genarator
Fiber

29. 2. Rewrite nested loaders with Fiber
1. Nested loaders implementation 3. Rewrite nested “resume”s

30. 1. Nested loaders implementation
2. Rewrite nested loaders with Fiber
3. Rewrite nested “resume”s

31. 1. Nested loaders implementation

32. 1. Nested loaders implementation

33. 1. Nested loaders implementation

34. 1. Nested loaders implementation

35. 1. Nested loaders implementation
2. Rewrite nested loaders with Fiber
3. Rewrite nested “resume”s

36. 2. Rewrite nested loaders with Fiber

37. ⏸
2. Rewrite nested loaders with Fiber

38. ⏩
2. Rewrite nested loaders with Fiber

39. ⏩
p1
2. Rewrite nested loaders with Fiber

40. ⏸
p1
next
p1
2. Rewrite nested loaders with Fiber

41. ⏸
p1
next
p1
2. Rewrite nested loaders with Fiber

42. ⏩
p1
next
p1
2. Rewrite nested loaders with Fiber

43. ⏩
p1
next
p1
p2
2. Rewrite nested loaders with Fiber

44. ⏸
p1
next
p1
p2
next
p2
2. Rewrite nested loaders with Fiber

45. ⏸
p1
next
p1
p2
next
p2
2. Rewrite nested loaders with Fiber

46. ⏩
p1
next
p1
p2
next
p2
2. Rewrite nested loaders with Fiber

47. p1
next
p1
p2
next
p2
X
2. Rewrite nested loaders with Fiber

48. p1
next
p1
p2
next
p2
X
2. Rewrite nested loaders with Fiber

49. Looks
working
🎉👏
2. Rewrite nested loaders with Fiber

50. 1. Nested loaders implementation
2. Rewrite nested loaders with Fiber
3. Rewrite nested “resume”s

51. 3. Rewrite nested “resume”s

52. 3. Rewrite nested “resume”s

53. 3. Rewrite nested “resume”s

54. 3. Rewrite nested “resume”s

55. 3. Rewrite nested “resume”s

56. 3. Rewrite nested “resume”s

57. 3. Rewrite nested “resume”s

58. Looks
working
🎉👏
3. Rewrite nested “resume”s

59. Let’s apply the naive Async/Await syntax to xx

60. Async/Await in

61. When fetching A and B fields

62. When fetching C and D fields
N+1…🤔

63. What’s wrong with the naive Async/Await?
The naive Async/Await impl. returns
a value, not a promise as a result
Graphql-batch allows fields to
return a promise in place of a value

64. Is it possible to fix it?
- It makes me feel it’s do-able…
but it does not work even if modifying it as returning a promise
- The main difficulty comes from the difference in the promise life-cycle
between Graphql-batch and the handcrafted Async/Await implementation

65. Summary
- Explained the basic usage of Promise and Fiber
- Confirmed the combination of Promise and Fiber works as Async/Await syntax
- Observed that the naive impl. is not enough to work along with Graphql-batch
- Code available: https://github.com/sat0yu/heisei-ruby-kaigi01
Thank you for your time and attention 🙇