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
   

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2. Evolution of Async Programming
   

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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
   

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4. (•_•)
   <) )╯
   / \
   \(•_•)
   ( (>
   / \
   (•_•)
   <) )>
   / \
   Decisions
   are made
   in a context
   

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5. What’s a context?
   

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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?
   

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7. Decisions aren’t made in a vacuum
   

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8. Unique, in space…
   and time
   

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9. Adopting a codebase
   

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10. Context includes experience
    

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11. But you don’t have to
    You can never understand
    the context a decision was made in
    

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12. It is enough to appreciate that a
    context existed
    

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13. Be empathetic
    

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14. iOS developers conflate things
    ⽌ •́ ﹏ •̀ ⽎
    

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15. conflate
    verb [ with obj. ]
    combine (two or more ideas,
    texts, etc.) into one.
    

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16. Humans look for patterns
    

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19. What does this have to do with
    iOS development?
    

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20. Some popular development practice
    When learning iOS, we’re bad at that practice
    Popular development practice is bad
    +
    =
    

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21. We get better at iOS development
    New thing comes out, and we’re good at it
    New thing is good
    +
    =
    

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22. This is why new things are
    always so appealing
    

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23. Why do iOS devs do this?
    There are several explanations
    

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24. iOS is young
    … really young
    
    

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25. Always older APIs for us to blame
    iOS is constantly changing
    

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26. I’ve done this a lot
    You probably have, too
    

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27. Only human
    

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28. Remember…
    Don’t be hard on yourself!
    

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29. And don’t be hard on others!
    We’re all just winging it!
    

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30. ⊂_ヽ
    
    　 ＼＼ Λ＿Λ
    
    　　 ＼(　ˇωˇ)
    
    　　 /　⌒
    
    　　/ へ＼
    
    　 / 　/　＼＼
    
    ƀɹϊɹɹ ヽ_つ
    
    　 /　/
    
    　(　(ヽ
    
    　|　|、 \
    
    　| ⼃丿 ＼
    
    　| |　　) /
    
    ノ )　　Lů
    Older solutions have merit
    

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31. –Lots of people, for hundreds of years
    “Those who don’t study history are
    doomed to repeat it.”
    

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32. Wrong
    

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33. –Me, just now
    “Those who don’t study the past can’t make
    informed decisions about the present.”
    

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34. History of Async Programming
    

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35. performSelector: Family
    • iOS 2+
    • Easy(ish)
    • Supports delays
    • Cancellable(ish)
    • Threadsafe(ish)
    

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36. NSThread
    • iOS 2+
    • Difficult, mostly
    • Sometimes, kind of cancellable
    • Complicated
    

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37. NSOperation
    • iOS 2+
    • Supports concurrency
    • Supports dependency graphs
    • Cancellable
    • More boilerplate
    

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38. Blocks / GCD
    • iOS 4+
    • Super-easy
    • Super-dangerous (reference cycles)
    • Better in Swift
    • Not cancellable
    

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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?
    

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40. NSProgress
    • iOS 7+
    • Confusing
    • No one knows what it’s for
    • I don’t know
    • Do you know?
    

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41. NSURLSessionTask
    • iOS 7+
    • Network-specific async abstraction
    • Very nice
    • Seriously, very nice
    • (Will discuss more later)
    

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42. Let’s build something
    Those are only tools
    

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43. Abstraction
    Blocks
    Function pointers
    NSOperation
    ???
    

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44. Example Abstractions
    • Adding block callbacks to UIGestureRecognizer, UIAlertView, etc
    • Futures, promises
    • Sequences, signals (FRP)
    

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45. Those are great abstractions, but…
    I feel we ignore NSOperation
    

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46. NSOperation
    • Cancellable
    • Chainable, dependency graphs
    • Concurrency support
    • Completion handlers
    • Prioritization
    • Interoperate with GCD
    

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47. Why so GCDerious?
    

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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
    

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50. Different solutions work for
    different problems
    

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51. Get familiar with your options
    

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52. Don’t be mean to developers
    who disagree with you
    

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53. There are benefits to older solutions
    (╯°□°）╯︵ ┻━┻
    

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54. Developers (like me ) tend to say
    Objective-C is “old and busted”
    

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55. Old, yes, but not busted
    

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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
    

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57. AFNetworking uses
    NSOperation
    

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58. Let’s look at another example
    

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59. NSURLSession
    • Very protocol-oriented
    • NSURLSessionDelegate
    • NSURLSessionTaskDelegate
    • NSURLSessionDataDelegate
    • NSURLSessionDownloadDelegate
    

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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!
    

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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
    

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62. Try to be more like
    NSURLSession
    

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63. Go read NSOperation.h
    

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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
    

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65. So what’s the best way to do
    asynchronous programming on iOS?
    

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66. It depends.
    ¯\_(ツ)_/¯
    

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