Koroutinify ; Lessons learned from applying Coroutines in Kotlin Backend ; Deep dive into Coroutines

1. Koroutinify Lessons learned from applying Coroutines in Kotlin Backend Deep dive into Coroutines Ohad Shai - Software Engineer & Kotlin Advocate @Outbrain https://medium.com/@OhadShai
2. What we will talk about •A quick recap on coroutines •We’ll take a look under the hood •Tips and tricks
3. What can go wrong?
4. Disclaimer • I don’t know all coroutines bits and bytes • We will look on coroutines from a *specific* angle - coroutines has more to offer • Some of the things reflects my opinion
5. Motivation • We want to serve many users by few servers • Imagine that we have only one core and one thread for our service • When we suspend, our thread is free to go to serve other users
6. Thread per core vs Thread per request https://thepracticaldeveloper.com/2018/01/02/full-reactive-stack-conclusions/
7. What is coroutines • Write async code sequentially • Lightweight threads • aka callback-hell without the hell
8. Where does coroutines shines?
9. Where does coroutines shines? suspend fun <A> Connection.inTransaction( f: suspend (Connection) -> A): A { try { this.sendQuery("BEGIN") val result = f(this) this.sendQuery("COMMIT") return result } catch (e: Throwable) { this.sendQuery("ROLLBACK") throw e } }
10. Where does coroutines shines? fun <A> Connection.inTransaction( f: (Connection) -> CompletableFuture<A>) : CompletableFuture<A> { return this.sendQuery("BEGIN").flatMap { val p = CompletableFuture<A>() f(this).onComplete { ty1 -> sendQuery( if (ty1.isFailure) "ROLLBACK" else "COMMIT") .onComplete { ty2 -> if (ty2.isFailure && ty1.isSuccess) p.failed((ty2 as Failure).exception) else p.complete(ty1) } } p } }
11. How to? What is the syntax?
12. Basic syntax
13. Basic syntax
14. How does it work?
15. How does it work?
16. How does it work?
17. How does it work?
18. How does it work?
19. How does it work?
20. How does it work?
21. How does it work? Suspend
22. How does it work? Resume
23. How does it work?
24. How does it work?
25. How does it work?
26. How does it work?
27. How does it work?
28. How does it work?
29. How does it work?
30. How does it work?
31. How does it work? Suspend
32. How does it work? Resume
33. How does it work?
34. How does it work?
35. How does it work?
36. How does it *really* work?
37. How does it *really* work?
38. How does it *really* work?
39. How does it *really* work?
40. How does it *really* work? Parent Continuation
41. Parent Continuation X Continuation How does it *really* work?
42. Parent Continuation X Continuation How does it *really* work?
43. Parent Continuation X Continuation Y Continuation How does it *really* work?
44. Parent Continuation X Continuation Y Continuation Query Future How does it *really* work?
45. Parent Continuation X Continuation Y Continuation Query Future How does it *really* work?
46. Parent Continuation X Continuation Y Continuation Query Future Suspend CoroutineSingletons. COROUTINE_SUSPENDED How does it *really* work?
47. Resume CompletableFuture.whenComplete() BaseContinuationImpl.resumeWith(value)
48. Resume val outcome = current.invokeSuspend(param) if (outcome === COROUTINE_SUSPENDED) return current = completion param = outcome Continuation Completion - The parent Continuation invokeSuspend() - The installed callback; the method to return to label - where to return in the method
49. Resume val outcome = current.invokeSuspend(param) if (outcome === COROUTINE_SUSPENDED) return current = completion param = outcome Continuation Completion - The parent Continuation invokeSuspend() - The installed callback; the method to return to label - where to return in the method Repeat until root continuation
50. Parent Continuation X Continuation Y Continuation Query Future Resume How does it *really* work?
51. Parent Continuation X Continuation Y Continuation Query Future How does it *really* work?
52. Parent Continuation X Continuation Y Continuation How does it *really* work?
53. Parent Continuation X Continuation Y Continuation How does it *really* work?
54. Parent Continuation X Continuation Y Continuation How does it *really* work?
55. Parent Continuation X Continuation How does it *really* work?
56. Parent Continuation X Continuation How does it *really* work?
57. Parent Continuation X Continuation Z Continuation How does it *really* work?
58. Parent Continuation X Continuation Z Continuation Query Future How does it *really* work?
59. Parent Continuation X Continuation Z Continuation Query Future How does it *really* work?
60. Parent Continuation X Continuation Z Continuation Query Future Suspend CoroutineSingletons. COROUTINE_SUSPENDED How does it *really* work?
61. Parent Continuation X Continuation Z Continuation Query Future Resume How does it *really* work?
62. Parent Continuation X Continuation Z Continuation Query Future How does it *really* work?
63. Parent Continuation X Continuation Z Continuation How does it *really* work?
64. Parent Continuation X Continuation Z Continuation How does it *really* work?
65. Parent Continuation X Continuation Z Continuation How does it *really* work?
66. Parent Continuation X Continuation How does it *really* work?
67. Parent Continuation X Continuation How does it *really* work?
68. Parent Continuation How does it *really* work?
69. Questions?
70. Tips & Pitfalls
71. What coroutines made of • std-lib support for suspend functions • kotlinx.coroutines - a rich library for coroutines developed by JetBrains
72. Reduce latency | Concurrency | async/await
73. Reduce latency | Concurrency | async/await
74. What can go wrong?
75. What can go wrong? Why call await after async?
76. What can go wrong?
77. What can go wrong? Don’t catch exceptions of await()! https:// github.com/Kotlin/ kotlinx.coroutines/ issues/763
78. How to catch
79. Scope / Exception and Cancellation
80. Scope / Exception and Cancellation • Hierarchy coroutineScope { … }
81. Scope / Exception and Cancellation • Hierarchy coroutineScope { … } • GlobalScope • Live in the application lifetime
82. Scope / Exception and Cancellation • Hierarchy coroutineScope { … } • GlobalScope • Live in the application lifetime • SupervisorJob / Job
83. What can go wrong?
84. What can go wrong? Blocking code horrors
85. Blocking code • Replace with async libs
86. Blocking code • Replace with async libs • Use IO Dispatcher / dedicated thread pool async(Dispatcher.IO) {…}
87. Dispatchers • Default • Unconfined • IO • FixedThreadPoolContext
88. @Experimental Status • As of 1.3 coroutines was GA https://www.kiwico.com/blog/2016/09/26/10-easy-science-experiments-for-kids/
89. @Experimental Status • As of 1.3 coroutines was GA • But… https://www.kiwico.com/blog/2016/09/26/10-easy-science-experiments-for-kids/
90. @Experimental Status • As of 1.3 coroutines was GA • But… Many API’s are still experimental https://www.kiwico.com/blog/2016/09/26/10-easy-science-experiments-for-kids/
91. Conclusion Use with care https://www.etsy.com/il-en/listing/263170291/care-bears-pop-up-birthday-invitation?ref=landingpage_similar_listing_top-4
92. What’s in it for me? • Use it in your micro-service • Find a side use case • Actor / Channels
93. Questions?
94. Thanks!