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CommitConf 2018 - Going Async With Kotlin
This document discusses asynchronous programming in Kotlin using various abstractions like callbacks, futures, observables, and coroutines. It presents an example of making multiple asynchronous requests sequentially and shows how different abstractions can execute them in parallel to improve performance. Coroutines are highlighted as providing a synchronous style of programming while allowing asynchronous execution through suspending functions. The conclusions recommend choosing the best abstraction based on the specific use case and considering both simplicity and efficiency.
CommitConf 2018 - Going Async With Kotlin
- 1. MAD · NOV23-24 · 2018 Going Async with Kotlin José María Muñoz Rey Software Engineer at Tuenti MAD · NOV 23-24 · 2018
- 2. MAD · NOV23-24 · 2018 Where should we start? Simplified problem: multiple IO request Index ■ Understand why asynchrony abstractions matters. ■ Asynchrony abstractions. ∘ Callbacks. ∘ Futures (CompletableFutures). ∘ Observables (Reactive Streams/RxJava). ∘ Coroutines.
- 3. MAD · NOV23-24 · 2018 Writing synchronous code Why asynchrony abstraction matters
- 4. MAD · NOV23-24 · 2018 Problem description Simple IO problem: multiple requests to a service. Client: ■ Standard Kotlin, sequential code. ■ Without async abstractions. Server: ■ Ktor. ■ Just responds with a text and waits a custom delay.
- 5. MAD · NOV23-24 · 2018 Our example
- 6. MAD · NOV23-24 · 2018 Simple Synchronous code Request: Session, 500 miliseconds ... Request: Photos, 500 miliseconds Request: News, 500 miliseconds Time required to process this block: 2626 Requests Response
- 7. MAD · NOV23-24 · 2018 Simple Synchronous code What happened? Requests still made sequentially: ■ Main thread blocked: in each request. ■ No parallelism: this code can be benefit from it.
- 8. MAD · NOV23-24 · 2018 What do we need? ■ Last 3 request should run in parallel ■ Abstractions to: ∘ Create them. ∘ Get status, cancel… ∘ Get computed value. We need to call these methods asynchronously.
- 9. MAD · NOV23-24 · 2018 Managing Asynchrony
- 10. MAD · NOV23-24 · 2018 Let’s create Threads for IO !! They help us by letting other code run in parallel, but: ■ They have an high costs (Context switching). ■ They are highly limited. ■ They are hard to manage. ∘ Create/reuse/idle/close. ∘ Cancel work. ∘ Thread pool (computation, IO). ∘ Share info. We need some abstractions.
- 11. MAD · NOV23-24 · 2018 Promises CompletableFuture Futures Deferred Task Asynctask Observable Callbacks Async abstractions!!!! Coroutines/Suspending function
- 12. MAD · NOV23-24 · 2018 What we are going to see today: Main abstractions used in the JVM ■ Callbacks. ■ Futures: CompletableFutures. ■ Observables: Reactive streams (Publisher/subscriber/Observable...). ■ Coroutines.
- 13. MAD · NOV23-24 · 2018 Callbacks
- 14. MAD · NOV23-24 · 2018 Callbacks
- 15. MAD · NOV23-24 · 2018 Callbacks
- 16. MAD · NOV23-24 · 2018 Callbacks ■ Just if necessary. ■ Not enough for Kotlin to handle asynchrony ■ Problems to chain calls (Callbacks hell). ■ Problems to share computed values. ■ Problems to handle errors. Javascript experience: people is moving away. DON’T USE THEM
- 17. MAD · NOV23-24 · 2018 CompetableFutures And well, the others ‘Futures’
- 18. MAD · NOV23-24 · 2018 Promises vs Futures vs CompletableFuture vs Deferred vs Task vs ... “They describe an object that acts as a proxy for a result that is initially unknown, usually because the computation of its value is yet incomplete.” en.wikipedia.org/wiki/Futures_and_promises
- 19. MAD · NOV23-24 · 2018 Promises vs Futures vs CompletableFuture vs Deferred vs Task vs ... They are (practically) the same thing, but named differently in different languages: ■ Futures: practically everywhere. ■ CompletableFutures: JVM (Java, Kotlin...). ■ Promises: Javascript. ■ Task: C# / Android APIs. ■ Deferred: Koltin. ■ ...
- 20. MAD · NOV23-24 · 2018 CompletableFutures ■ Introduced in Java 8. ■ Improves the actual interface of existing Futures. ■ Compositional programming with chained calls. (Sequential and parallel). ■ Default: Threads from the CommonPool. API: ■ Create: .supplyAsync() ■ Chain: .thenCompose(), .thenApply() or .thenAccept(). ■ Compose: .anyOf(...), .allOf(...). ■ Get value: .get() or .join(). ■ More functionality: .exceptionally(...), .orTimeout().
- 21. MAD · NOV23-24 · 2018 CompletableFutures - Our use case ■ getUserInfo(): CompletableFuture<...>. ■ getPhotos(): CompletableFuture<...>. ■ getFriends(): CompletableFuture<...>. ■ getNews(): CompletableFuture<...>.
- 22. MAD · NOV23-24 · 2018 CompletableFutures - Our use case: Version 1 Request: Session, ... Request: UserInfo, ... Request: Friends, ... Request: Photos, ... Request: News,... Page for ... Time required ...2626 Final line reached
- 23. MAD · NOV23-24 · 2018 CompletableFutures - Our use case: Version 2 Request: Session, ... Request: UserInfo, ... Request: Friends, ... Request: Photos, ... Request: News, ... Page for ... Time required: 1632 Final line reached
- 24. MAD · NOV23-24 · 2018 CompletableFutures - Our use case: Version 3 Final line reached Request: Session ... Request: UserInfo ... Request: Friends ... Request: Photos ... Request: News, ... Page for ... Time required: 1640
- 25. MAD · NOV23-24 · 2018 CompletableFutures - Our use case: Version 4 Final line reached Time required: 17 Request: Session … Request: UserInfo … Request: Photos … Request: Friends … Request: News … Page for …
- 26. MAD · NOV23-24 · 2018 CompletableFutures - Exceptions & Timeouts Final line reached Time required: 26 Request: Session ... Empty page
- 27. MAD · NOV23-24 · 2018 CompletableFutures - Conclusions Good things: ■ A lot of facilidades to manage async operations. ■ Code looks ‘synchronous’. ■ Easy to compose complex async operations. But: ■ Still some sense of callbacks. ■ Still blocks the caller thread in some point. ■ Remember to manage your Thread Pools.
- 28. MAD · NOV23-24 · 2018 Reactive Streams
- 29. MAD · NOV23-24 · 2018 Observable “Everything is a stream, and it's observable.” kotlinlang.org/docs/tutorials/coroutines/async-programming.html
- 30. MAD · NOV23-24 · 2018 Observables ■ Publishers notifies subscriptions about new data. RxJava ■ Implements the Observable pattern and extends it. ■ Creation of flows looks like a Builder. ■ Operators. ■ Backpresure. ■ Schedulers (Default, IO, Compute). ■ RxJava & RxKotlin (and other ~16 languages). Read lines Split by spaces Remove some words Print
- 31. MAD · NOV23-24 · 2018 Observables 1º Publisher ■ Observable<...> / Flowable<...> ∘ Others: Single<...>, Maybe<...>, Completable<...>... 2º Operators ■ Optionals, between 72 and ~500. ■ Transformations: flatMap(), map() ... ■ Mathematical: count(), max(), min()... ■ Filtering: first(), find(), filter()... 3º Subscription ■ Run the flow. ■ Will run the steps in different schedulers: subscribeOn(...) observeOn(...)... Default: Local Thread. ■ Obtain the final value: subscription(...), blockingFirst(...)... Read lines Split by spaces Remove some words Print
- 32. MAD · NOV23-24 · 2018 Observable - Create
- 33. MAD · NOV23-24 · 2018 Observable - Just a try Request: Session ... println ... Request: Session ... println ... Request: Session ... println ... Time required: 1743
- 34. MAD · NOV23-24 · 2018 Observable - Scheduler IO Time required: 190 Request: Session ... Request: Session ... Request: Session ... println … println … println …
- 35. MAD · NOV23-24 · 2018 Observable - Blocking Request: Session … println ... Time required: 771
- 36. MAD · NOV23-24 · 2018 Observable - Our use case 233 ms 1654 ms
- 37. MAD · NOV23-24 · 2018 Reactive Streams A lot of useful diagrams to understand operators: ■ Marbles diagrams - rxmarbles.com
- 38. MAD · NOV23-24 · 2018 Reactive Streams / RxJava - Conclusions Good things: ■ A lot of facilidades to manage async flows. ■ Managed schedulers. ■ A lot of operators. But: ■ Too complex for individual tasks. ■ Has a very big API. ■ Easy to make mistakes (sync, operators…).
- 39. MAD · NOV23-24 · 2018 Coroutines
- 40. MAD · NOV23-24 · 2018 Coroutines “The idea that a function can suspend its execution at some point and resume later on.” kotlinlang.org/docs/tutorials/coroutines/async-programming.html
- 41. MAD · NOV23-24 · 2018 Suspending functions - Coroutines Suspending Functions (our code): ■ Async code written Synchronous, that can run asynchronously. Sync by default. ■ Async/await in Javacript, C#, Python. Coroutines (runners): ■ ‘Light-weight’ Threads BUT Coroutines != Threads. ∘ Coroutines run in threads (1.000.000s). ∘ A SUSPENDED coroutine: · Does not consume a thread. · Is not bound to a thread.
- 42. MAD · NOV23-24 · 2018 Default context (Thread Pool) in Kotlin Scope Coroutine Coroutine Coroutine IO context Scope Coroutine Main Thread Scope Coroutine
- 43. MAD · NOV23-24 · 2018 Coroutines - Creation in IO IO context Scope Coroutine Scope Coroutine
- 44. MAD · NOV23-24 · 2018 Coroutines in Kotlin Request: Session ... Request: UserInfo ... Request: Friends … Request: Photos … Request: News ... Page for … Time required: 2676
- 45. MAD · NOV23-24 · 2018 Coroutines in Kotlin Request: Session ... Request: UserInfo ... Request: Friends … Request: Photos … Request: News ... Page for … Time required: 1653
- 46. MAD · NOV23-24 · 2018 Coroutines in Kotlin Kotlin release: ■ API stable in Kotlin 1.3 ■ Implementation version (kotlinx-coroutines-core): 1.0.1 More functionality: ■ Parent-child & Jobs -> cancellables. ■ Try/Catch & Stacktraces. ■ Channels (fan-in, fan-out, pipelines…). ■ Actors. ■ Multi-platform: JS, Native, Reactive, Android.
- 47. MAD · NOV23-24 · 2018 Coroutines - Conclusions Good things: ■ Strong primitives to build async software. ■ Sometimes it feels just synchronous (Try catch). ■ For our use case ~efficiency than CompletableFuture. But: ■ Scopes and contexts are a little bit messy. ■ Partial ‘non-blocking’. You still need to take care of Threads. ■ Could be too low level.
- 48. MAD · NOV23-24 · 2018 General - Conclusions ■ Concurrency/parallelism is hard. ■ UnitTest and measure (!) your implementations. ■ Coroutines improved readability and efficiency, but: ∘ Final version just released. ∘ Community support just started. ∘ Take care of threads. ∘ Use the conversions with other abstractions. ■ Look for the better abstraction for your use case. ∘ CompletableFuture: Simple and efficient over single jobs. ∘ Coroutines: Abstractions over single jobs and other primitives. ∘ Reactive Streams: Abstractions over an stream of jobs.
- 49. MAD · NOV23-24 · 2018 Resources ■ Slides & Code: @Koletzilla ■ Kotlin proposal (KEEP) ∘ https://github.com/Kotlin/KEEP/blob/master/proposals/coroutines.md ■ Kotlin/kotlinx.coroutines ∘ https://github.com/Kotlin/kotlinx.coroutines ■ Introduction to Coroutines @ KotlinConf 2017 - by Roman Elizarov ∘ https://www.youtube.com/watch?v=_hfBv0a09Jc ∘ https://www.slideshare.net/elizarov/introduction-to-coroutines-kotlinconf-2017 ■ Kotlin Coroutines in Practice @ KotlinConf 2018 - by Roman Elizarov ∘ https://www.youtube.com/watch?v=a3agLJQ6vt8 ∘ https://www.slideshare.net/elizarov/kotlin-coroutines-in-practice-kotlinconf-2018
- 50. MAD · NOV23-24 · 2018 Thank you!! Questions? @Koletzilla