Asynchronous Programming With Kotlin Coroutines

Transcript

1. Loveleen Kaur Android Educator Software Engineer, Astrotalk Asynchronous Programming With Kotlin Coroutines
2. • Loveleen Kaur • Software Engineer - Android @ Astrotalk • Core Team Member @ GDG Chandigarh • Android Educator @ Android Educators Community India • Phd Research Scholar • Develop Mobile Applications • Technical Speaker • Happy Android Developer :) Who am I? 󰠁
3. Asynchronous programming
4. How do we write code that waits for something most of the time?
5. A toy problem Kotlin fun requestToken(): Token { // makes request for a token & waits return token // returns result when received } 1
6. fun requestToken(): Token { … } fun createPost(token: Token, item: Item): Post { // sends item to the server & waits return post // returns resulting post } A toy problem 2 Kotlin
7. A toy problem Kotlin fun requestToken(): Token { … } fun createPost(token: Token, item: Item): Post { … } 3 fun processPost(post: Post) { // does some local processing of result }
8. fun requestToken(): Token { … } fun createPost(token: Token, item: Item): Post { … } fun processPost(post: Post) { … } A toy problem fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } 1 2 3 Can be done with threads! Kotlin
9. fun requestToken(): Token { // makes request for a token // blocks the thread waiting for result return token // returns result when received } fun createPost(token: Token, item: Item): Post { … } fun processPost(post: Post) { … } fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } Threads Is anything wrong with it?
10. How many threads we can have? 100
11. How many threads we can have? 1000
12. How many threads we can have? 10 000
13. How many threads we can have? 100 000
14. Callbacks to the rescue Sort of …
15. Callbacks: before fun requestToken(): Token { // makes request for a token & waits return token // returns result when received } 1 Callbacks: after 1 callback fun requestTokenAsync(cb: (Token) -> Unit) { // makes request for a token, invokes callback when done // returns immediately }
16. Callbacks: before fun requestTokenAsync(cb: (Token) -> Unit) { … } fun createPost(token: Token, item: Item): Post { // sends item to the server & waits return post // returns resulting post } 2 Callbacks: after fun requestTokenAsync(cb: (Token) -> Unit) { … } fun createPostAsync(token: Token, item: Item, cb: (Post) -> Unit) { // sends item to the server, invokes callback when done // returns immediately } 2 callback
17. Callbacks: before fun fun requestTokenAsync(cb: (Token) createPostAsync(token: Token, -> Unit) { … } item: Item, cb: (Post) -> Unit) { … } fun processPost(post: Post) { … } fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) }
18. Callbacks: after fun fun requestTokenAsync(cb: (Token) createPostAsync(token: Token, -> Unit) { … } item: Item, cb: (Post) -> Unit) { … } fun processPost(post: Post) { … } fun postItem(item: Item) { requestTokenAsync { token -> createPostAsync(token, item) { post -> processPost(post) } } } aka “callback hell” This is simplified. Handling exceptions makes it a real mess
19. Kotlin Coroutines
20. • The Kotlin team defines coroutines as “lightweight threads”. • They are sort of tasks that the actual threads can execute. • Coroutines were added to Kotlin in version 1.3 and are based on established concepts from other languages. • Kotlin coroutines introduce a new style of concurrency that can be used on Android to simplify async code. Coroutines
21. Kotlin coroutines to the rescue Let’s get real
22. Coroutines: before fun requestTokenAsync(): Promise<Token> { // makes request for a token // returns promise for a future result immediately } 1 Coroutines: after suspend fun requestToken(): Token { // makes request for a token & suspends return token // returns result when received } 1
23. Coroutines: before suspend fun requestToken(): Token { … } fun createPostAsync(token: Token, item: Item): Promise<Post> { // sends item to the server // returns promise for a future result immediately } 2 Coroutines: after suspend fun requestToken(): Token { … } suspend fun createPost(token: Token, item: Item): Post { // sends item to the server & suspends return post // returns result when received } 2
24. Coroutines: before fun postItem(item: Item) { requestTokenAsync() .thenCompose { token -> createPostAsync(token, item) } .thenAccept { post -> processPost(post) } } Coroutines: after suspend fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } suspension points
25. • Regular loops for ((token, item) in list) { createPost(token, item) } Bonus features
26. • Regular exception handing try { createPost(token, item) } catch (e: BadTokenException) { … } Bonus features
27. Bonus features • Regular higher-order functions file.readLines().forEach { line -> createPost(token, line.toItem()) } • forEach, let, apply, repeat, filter, map, use, etc Everything like in blocking code
28. Suspending functions
29. Retrofit async interface Service { fun createPost(token: Token, item: Item): Call<Post> }
30. Retrofit async interface Service { fun createPost(token: Token, item: Item): } Call<Post> future
31. Retrofit async interface Service { fun createPost(token: Token, item: Item): Call<Post> } suspend fun createPost(token: Token, item: Item): Post = serviceInstance.createPost(token, item).await()
32. Retrofit async suspend fun createPost(token: Token, item: Item): Post = serviceInstance.createPost(token, item).await() interface Service { fun createPost(token: Token, item: Item): Call<Post> } natural signature
33. Retrofit async interface Service { fun createPost(token: Token, item: Item): Call<Post> } suspend fun createPost(token: Token, item: Item): Post = serviceInstance.createPost(token, item).await() Suspending extension function from integration library
34. Coroutine builders
35. Coroutines revisited suspend fun requestToken(): Token { … } suspend fun createPost(token: Token, item: Item): Post { … } fun processPost(post: Post) { … } suspend fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) }
36. Coroutines revisited suspend fun requestToken(): Token { … } suspend fun createPost(token: Token, item: Item): Post { … } fun processPost(post: Post) { … } fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) }
37. Coroutines revisited suspend fun requestToken(): Token { … } suspend fun createPost(token: Token, item: Item): Post { … } fun processPost(post: Post) { … } fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } Error: Suspend function 'requestToken' should be called only from a coroutine or another suspend function
38. Coroutines revisited suspend fun requestToken(): Token { … } suspend fun createPost(token: Token, item: Item): Post { … } fun processPost(post: Post) { … } fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } Can suspend execution
39. Coroutines revisited suspend fun requestToken(): Token { … } suspend fun createPost(token: Token, item: Item): Post { … } fun processPost(post: Post) { … } fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } Can suspend execution A regular function cannot
40. Coroutines revisited suspend fun requestToken(): Token { … } suspend fun createPost(token: Token, item: Item): Post { … } fun processPost(post: Post) { … } Can suspend execution A regular function cannot fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } One cannot simply invoke a suspending function
41. } Launch coroutine builder fun postItem(item: Item) { launch { val token = requestToken() val post = createPost(token, item) processPost(post) }
42. fun postItem(item: Item) { launch { val token = requestToken() val post = createPost(token, item) processPost(post) } Fire and forget! Returns immediately, coroutine works in background thread pool }
43. fun postItem(item: Item) { launch { val token = requestToken() val post = createPost(token, item) processPost(post) } }
44. fun postItem(item: Item) { launch(UI) { val token = requestToken() val post = createPost(token, item) processPost(post) } } UI Context Just specify the context
45. fun postItem(item: Item) { launch(UI) { val token = requestToken() val post = createPost(token, item) processPost(post) } } UI Context And it gets executed on UI thread
46. Where’s the magic of launch?
47. fun launch( context: CoroutineContext = DefaultDispatcher, block: suspend () -> Unit ): Job { … } A regular function
48. fun launch( context: CoroutineContext = DefaultDispatcher, block: suspend () -> Unit ): Job { … } suspending lambda
49. async / await
50. Kotlin-way Kotlin suspend fun postItem(item: Item) { val token = requestToken() val post = createPost(token, item) processPost(post) } suspend fun requestToken(): Token { … } suspend fun createPost(token: Token, item: Item): Post { … } fun processPost(post: Post) { … }
51. Classic-way C# approach to the same problem (also Python, TS, Dart, coming to JS) C# async Task postItem(Item item) { var token = await requestToken(); var post = await createPost(token, item); processPost(post); } async Task<Token> requestToken() { … } async Task<Post> createPost(Token token, Item item) { … } void processPost(Post post) { … }
52. Why no await keyword in Kotlin? The problem with async requestToken() VALID –> produces Task<Token> await requestToken() VALID –> produces Token concurrent behavior sequential behavior C# C# default
53. Kotlin suspending functions are designed to imitate sequential behavior by default Concurrency is hard Concurrency has to be explicit
54. Kotlin approach to async Concurrency where you need it
55. Kotlin async function fun loadImageAsync(name: String): Deferred<Image> = async { … } Kotlin
56. Kotlin async function fun loadImageAsync(name: String): Deferred<Image> = async { … } Kotlin A regular function
57. Kotlin async function fun loadImageAsync(name: String): Deferred<Image> = async { … } Kotlin’s future type Kotlin
58. Kotlin async function fun loadImageAsync(name: String): Deferred<Image> = async { … } async coroutine builder Kotlin
59. Kotlin async function fun loadImageAsync(name: String): Deferred<Image> = async { … } val deferred1 = loadImageAsync(name1) val deferred2 = loadImageAsync(name2) Start multiple operations concurrently Kotlin
60. Kotlin async function fun loadImageAsync(name: String): Deferred<Image> = async { … } val deferred1 = loadImageAsync(name1) val deferred2 = loadImageAsync(name2) and then wait for them val image1 = deferred1.await() val image2 = deferred2.await() await function Suspends until deferred is complete Kotlin
61. Kotlin async function fun loadImageAsync(name: String): Deferred<Image> = async { … } val deferred1 = loadImageAsync(name1) val deferred2 = loadImageAsync(name2) val image1 = deferred1.await() val image2 = deferred2.await() val result = combineImages(image1, image2) Kotlin
62. Using async function when needed suspend fun loadImage(name: String): Image { … } Is defined as suspending function, not async
63. Using async function when needed suspend fun loadImage(name: String): Image { … } suspend fun loadAndCombine(name1: String, name2: String): Image { val deferred1 = async { loadImage(name1) } val deferred2 = async { loadImage(name2) } return combineImages(deferred1.await(), deferred2.await()) }
64. Using async function when needed suspend fun loadImage(name: String): Image { … } suspend fun loadAndCombine(name1: String, name2: String): Image { async val deferred1 = { loadImage(name1) } val deferred2 = async { loadImage(name2) } return combineImages(deferred1.await(), deferred2.await()) }
65. Using async function when needed suspend fun loadImage(name: String): Image { … } suspend fun loadAndCombine(name1: String, name2: String): Image { val deferred1 = async { loadImage(name1) } async val deferred2 = { loadImage(name2) } return combineImages(deferred1.await(), deferred2.await()) }
66. Using async function when needed suspend fun loadImage(name: String): Image { … } suspend fun loadAndCombine(name1: String, name2: String): Image { val deferred1 = async { loadImage(name1) } val deferred2 = async { loadImage(name2) } return combineImages(deferred1.await(), deferred2.await()) }
67. Kotlin approach to async requestToken() VALID –> produces Token async { requestToken() } VALID –> produces Deferred<Token> sequential behavior concurrent behavior Kotlin Kotlin default
68. Coroutines
69. What are coroutines conceptually?
70. What are coroutines conceptually? Coroutines are like very light-weight threads
71. fun main(args: Array<String>) = runBlocking<Unit> { val jobs = List(100_000) { launch { delay(1000L) print(".") } } jobs.forEach { it.join() } } Example
72. fun main(args: Array<String>) = runBlocking<Unit> { val jobs = List(100_000) { launch { delay(1000L) print(".") } } jobs.forEach { it.join() } } Example This coroutine builder runs coroutine in the context of invoker thread
73. fun main(args: Array<String>) = runBlocking<Unit> { val jobs = List(100_000) { launch { delay(1000L) print(".") } } jobs.forEach { it.join() } } Example
74. fun main(args: Array<String>) = runBlocking<Unit> { val jobs = List(100_000) { launch { delay(1000L) print(".") } } jobs.forEach { it.join() } } Example
75. fun main(args: Array<String>) = runBlocking<Unit> { val jobs = List(100_000) { launch { delay(1000L) print(".") } } jobs.forEach { it.join() } } Example Suspends for 1 second
76. fun main(args: Array<String>) = runBlocking<Unit> { val jobs = List(100_000) { launch { delay(1000L) print(".") } } jobs.forEach { it.join() } } Example We can join a job just like a thread
77. Example Try that with 100k threads! fun main(args: Array<String>) = runBlocking<Unit> { val jobs = List(100_000) { launch { delay(1000L) print(".") } } jobs.forEach { it.join() } } Prints 100k dots after one second delay
78. fun main(args: Array<String>) = val jobs = List(100_000) { runBlocking<Unit> { launch { delay(1000L) print(".") } } jobs.forEach { it.join() } } Example
79. fun main(args: Array<String>) { val jobs = List(100_000) { thread { Thread.sleep(1000L) print(".") } } jobs.forEach { it.join() } } Example
80. Library vs Language
81. Classic async async/await generate/yield Keywords
82. Kotlin coroutines suspend Modifier
83. Kotlin coroutines Standard library
84. Kotlin coroutines Standard library kotlinx-coroutines launch, async, runBlocking, future, delay, Job, Deferred, etc http://github.com/kotlin/kotlinx.coroutines
85. Thank you Loveleen Kaur https://www.linkedin.com/in/loveleen-kaur/ https://twitter.com/loveleen_nancy