Evolution of Asynchronous Programming on iOS

Presented at Mobiconf 2015: http://2015.mobiconf.org

Transcript

1. Ash Furrow, Artsy (on iOS) Evolution of Asynchronous Programming
2. Evolution of Async Programming
3. Agenda • All decisions are made in a context • iOS developers are human; we tend to conflate things • Older solutions have value, too • There are benefits to using older technology
4. (•_•) <) )╯ / \ \(•_•) ( (> / \ (•_•) <) )> / \ Decisions are made in a context
5. What’s a context?
6. Contextual Questions • What technology is available? • How much do I understand the options? What about my team? • How popular is the technology? • How stable are the tools I would need to use? • How easy is it to learn? • How quickly do I need to complete the task?
7. Decisions aren’t made in a vacuum
8. Unique, in space… and time
9. Adopting a codebase
10. Context includes experience
11. But you don’t have to You can never understand the context a decision was made in
12. It is enough to appreciate that a context existed
13. Be empathetic
14. iOS developers conflate things ⽌ •́ ﹏ •̀ ⽎
15. conflate verb [ with obj. ] combine (two or more ideas, texts, etc.) into one.
16. Humans look for patterns
19. What does this have to do with iOS development?
20. Some popular development practice When learning iOS, we’re bad at that practice Popular development practice is bad + =
21. We get better at iOS development New thing comes out, and we’re good at it New thing is good + =
22. This is why new things are always so appealing
23. Why do iOS devs do this? There are several explanations
24. iOS is young … really young
25. Always older APIs for us to blame iOS is constantly changing
26. I’ve done this a lot You probably have, too
27. Only human
28. Remember… Don’t be hard on yourself!
29. And don’t be hard on others! We’re all just winging it!
30. ⊂_ヽ 　 ＼＼ Λ＿Λ 　　 ＼(　ˇωˇ) 　　 /　⌒ 　　/ へ＼ 　 / 　/　＼＼ ƀɹϊɹɹ ヽ_つ 　 /　/ 　(　(ヽ 　|　|、 \ 　| ⼃丿 ＼ 　| |　　) / ノ )　　Lů Older solutions have merit
31. –Lots of people, for hundreds of years “Those who don’t study history are doomed to repeat it.”
32. Wrong
33. –Me, just now “Those who don’t study the past can’t make informed decisions about the present.”
34. History of Async Programming
35. performSelector: Family • iOS 2+ • Easy(ish) • Supports delays • Cancellable(ish) • Threadsafe(ish)
36. NSThread • iOS 2+ • Difficult, mostly • Sometimes, kind of cancellable • Complicated
37. NSOperation • iOS 2+ • Supports concurrency • Supports dependency graphs • Cancellable • More boilerplate
38. Blocks / GCD • iOS 4+ • Super-easy • Super-dangerous (reference cycles) • Better in Swift • Not cancellable
39. NSOperation + Blocks • iOS 4+ • Everything from NSOperation, but also with blocks • Less boilerplate • Slightly more verbose than blocks (this is Objective-C, remember) • Not popular – why?
40. NSProgress • iOS 7+ • Confusing • No one knows what it’s for • I don’t know • Do you know?
41. NSURLSessionTask • iOS 7+ • Network-specific async abstraction • Very nice • Seriously, very nice • (Will discuss more later)
42. Let’s build something Those are only tools
43. Abstraction Blocks Function pointers NSOperation ???
44. Example Abstractions • Adding block callbacks to UIGestureRecognizer, UIAlertView, etc • Futures, promises • Sequences, signals (FRP)
45. Those are great abstractions, but… I feel we ignore NSOperation
46. NSOperation • Cancellable • Chainable, dependency graphs • Concurrency support • Completion handlers • Prioritization • Interoperate with GCD
47. Why so GCDerious?
48. Why GCD? • iOS devs favour GCD over other suitable abstractions • Why? • NSOperation is unfamiliar, feels unnecessary • Not-invented-here-syndrome • Apple is good at marketing
50. Different solutions work for different problems
51. Get familiar with your options
52. Don’t be mean to developers who disagree with you
53. There are benefits to older solutions (╯°□°）╯︵ ┻━┻
54. Developers (like me ) tend to say Objective-C is “old and busted”
55. Old, yes, but not busted
56. Older Technology • “Old” is stable • “Old” is usually well-documented • “Old” is easy to hire for • “Old” has a lot of helpful resources, libraries, tutorials, etc
57. AFNetworking uses NSOperation
58. Let’s look at another example
59. NSURLSession • Very protocol-oriented • NSURLSessionDelegate • NSURLSessionTaskDelegate • NSURLSessionDataDelegate • NSURLSessionDownloadDelegate
60. NSURLSession • Separate delegates isolate different areas of concern • One object may conform to all protocols • Many, small protocols are better than one massive one • Swift protocols don’t even support optional functions!
61. NSURLSession • Could have been completely blocks-based… • Instead, based on ideas behind NSOperation • NSURLSession probably wraps an NSOperation, anyway • This is good! No leaky abstractions
62. Try to be more like NSURLSession
63. Go read NSOperation.h
64. Wrap Up • Decisions are made in an unknowable context • Developers are bad at evaluating things • New and shiny things aren’t always better • Old solutions carry extrinsic benefits
65. So what’s the best way to do asynchronous programming on iOS?
66. It depends. ¯\_(ツ)_/¯