The document discusses Kotlin coroutines and how they allow writing asynchronous code in a sequential way. Coroutines create lightweight threads to handle asynchronous code, allowing developers to write code sequentially without callbacks. This is done by converting coroutine code internally to continuation-passing style. Libraries can also be adapted to work with coroutines by converting callback-based APIs to return suspensions.

1. Programação assíncrona
utilizando Coroutines

2. Diego Gonçalves Santos
Desenvolvedor @

3. Coroutines

4. Código Assíncrono

5. Cenário
Imagine que você está usando a API do TDC e que para usar
os serviços é necessário enviar sua chave e receber os
tokens de autenticação.

6. Single Thread
fun listEvents() {
val token = getToken()
val events = getEvents(token)
displayEvents(events)
}

7. Callbacks
fun listEvents() {
getTokenAsync { token ->
getEventsAsync(token) { events ->
displayEvents(events)
}
}
}

8. Callbacks
fun listEvents() {
getTokenAsync { token ->
getEventsAsync(token) { events ->
displayEvents(events)
}
}
}
Callback
Hell!!

9. RX
R
Exemplo de código usando Rx
fun listEvents() {
requestTokenAsync()
.flatMap { token -> requestEventsAsync(token) }
.subscribe({ events -> displayEvents(events)})
}

10. RX
Curva de aprendizado íngreme

11. Coroutines
suspend fun getTokenAsync() {...}
suspend fun getEventsAsync() {...}
suspend fun listEvents() {
val token = getTokenAsync()
val events = getEventsAsync(token)
displayEvents(events)
}

12. Coroutines
Coroutines permitem que você escreva seu código de forma
sequencial e cria light-weight threads para lidar com o código
assíncrono.

13. Coroutines
Coroutines precisam de um contexto especial para rodar,
portanto elas só rodam dentro de Coroutine Builders ou
dentro de outras Coroutines

14. Launch (sequencial)

15. Coroutines Builders
Launch
launch {
delay(1000L)
println("World!")
}
println("Hello,")
Thread.sleep(2000L)

16. Coroutines Builders
Launch
launch {
delay(1000L)
println("World!")
}
println("Hello,")
Thread.sleep(2000L)
Hello,
World!

17. Coroutines Builders
Launch - Job Join
val job = launch {
delay(1000L)
println("World!")
}
println("Hello,")
job.join()

18. Coroutines Builders
Launch - Job Join
val job = launch {
delay(1000L)
println("World!")
}
println("Hello,")
job.join()
Fork Coroutine
Main Thread
Join

19. Coroutines Builders
Launch - Job Join
val job = launch {
delay(1000L)
println("World!")
}
println("Hello,")
job.join()
Hello,
World!

20. Coroutines Builders
Launch - Job Cancel
val job = launch {
repeat(1000) { i ->
println("I'm sleeping $i ...")
delay(500L)
}
}
delay(1300L) // delay a bit
println("main: I'm tired of waiting!")
job.cancel() // cancels the job
job.join() // waits for job's completion
println("main: Now I can quit.")

21. Coroutines Builders
Launch - Job Cancel
val job = launch {
repeat(1000) { i ->
println("I'm sleeping $i ...")
delay(500L)
}
}
delay(1300L) // delay a bit
println("main: I'm tired of waiting!")
job.cancel() // cancels the job
job.join() // waits for job's completion
println("main: Now I can quit.")
I'm sleeping 0 ...
I'm sleeping 1 ...
I'm sleeping 2 ...
main: I'm tired of waiting!
main: Now I can quit.

22. Coroutines Builders
Launch - Job Cancel And Join
val job = launch {
repeat(1000) { i ->
println("I'm sleeping $i ...")
delay(500L)
}
}
delay(1300L) // delay a bit
println("main: I'm tired of waiting!")
job.cancelAndJoin()
println("main: Now I can quit.")
I'm sleeping 0 ...
I'm sleeping 1 ...
I'm sleeping 2 ...
main: I'm tired of waiting!
main: Now I can quit.

23. Coroutines Builders
Launch - Quando a Coroutine para de ser processada ?
val job = launch {
var i = 0
while (i <= 5000) {
println("I'm sleeping ${i++} ...")
}
}
delay(1300L)
println("main: I'm tired of waiting!")
job.cancelAndJoin()
println("main: Now I can quit.")
I'm sleeping 0 ...
I'm sleeping 1 ...
I'm sleeping 2 …
…
I'm sleeping 5000 …
main: I'm tired of waiting!
main: Now I can quit.

24. Coroutines Builders
Launch - Garantindo que a Coroutine vai parar quando solicitado
val job = launch {
var i = 0
while (isActive) {
if(i <= 5000) { println("I'm sleeping ${i++} ...")}
}
delay(1000)
println("main: I'm tired of waiting!")
job.cancelAndJoin()
println("main: Now I can quit.")
I'm sleeping 0 ...
I'm sleeping 1 ...
I'm sleeping 2 ...
main: I'm tired of waiting!
main: Now I can quit.

25. RunBlocking (Bloqueia
Thread)

26. Coroutines Builders
Run Blocking
val job = runBlocking {
delay(1000L)
println("World!")
}
println("Hello,")
job.join()

27. Coroutines Builders
Run Blocking
val job = runBlocking {
delay(1000L)
println("World!")
}
println("Hello,")
job.join()
World!
Hello,

28. Coroutines Builders
Launch - UI Context
suspend fun listEvents() {
launch(UI) {
val token = getTokenAsync()
val events = getEventsAsync(token)
displayEvents(events)
}
}

29. Async (concorrente)

30. Coroutines Builders
Launch - Sequencial
launch{
val image1 = loadImage1()
val image2 = loadImage2()
setBackgrounds(image1, image2)
}

31. Coroutines Builders
Async - Concorrente
val image1 = async { loadImage1() }
val image2 = async { loadImage2() }
setBackgrounds(image1.await(), image2.await())

32. Codifique sequencialmente sem
receio!
Use loops, high-order functions, etc
for (i in 1..100_000) {
launch {
doSomethingHeavy()
}
}

33. Coroutines vs Threads

34. Cenário
Sistema que recebe uma requisição, lê o arquivo local, faz o
upload desse arquivo e retorna a url para acessar esse
arquivo

35. Single Thread

36. Multiple Threads

37. Coroutines - Sub-rotinas

38. Coroutines - non-preemptive multi-tasking
Usar os recursos de forma
eficiente e multi-tarefas
colaborativa onde as
próprias funções controlam o
fluxo, disponibilizam a
thread e continuam depois de
onde pararam, sem a
intervenção de um SO.

39. Coroutines - SÃO light-weight threads
val jobs = List(100_000) {
launch {
delay(1000L)
print(".")
}
}
jobs.forEach { it.join() }

40. Não existe mágica: De
Callbacks para código
sequencial

41. Direct Style vs
Continuation-Passing
Style

42. Direct Style
fun listEvents() {
val token = getToken()
val events = getEvents(token)
displayEvents(events)
}
Continuation

43. Continuation-Passing Style
fun listEvents() {
getTokenAsync { token ->
getEventsAsync(token) { events ->
displayEvents(events)
}
}
}
Continuation

44. Coroutines Direct Style
suspend fun listEvents() {
val token = getToken()
val events = getEvents(token)
displayEvents(events)
}
Continuation

45. Como é possível código
assíncrono sem
callbacks?

46. Convertendo para CPS
suspend fun listEvents() {...}

47. Convertendo para CPS
suspend fun listEvents() {...}
Java/JVM callback
Object listEvents(Continuation<Void> cont) {...}

48. Convertendo para CPS
suspend fun listEvents() {...}
Java/JVM callback
Object listEvents(Continuation<Void> cont) {...}
interface Continuation<in T> {
val context: CoroutineContext
fun resume(value: T)
fun resumeWithException(exception: Throwable)
}

49. Convertendo para CPS
suspend fun listEvents() {
val token = getToken()
val events = getEvents(token)
displayEvents(events)
}
Continuation
Inicial

50. Convertendo para CPS
suspend fun listEvents() {
val token = getToken()
val events = getEvents(token)
displayEvents(events)
}
Continuation

51. Convertendo para CPS
suspend fun listEvents() {
val token = getToken()
val events = getEvents(token)
displayEvents(events)
}
Continuation

52. Callbacks?
fun listEvents() {
getTokenAsync { token ->
getEventsAsync(token) { events ->
displayEvents(events)
}
}
}

53. Convertendo para CPS
suspend fun listEvents() {
// Label 0
val token = getToken()
// Label 1
val events = getEvents(token)
// Label 2
displayEvents(events)
}

54. Convertendo para CPS
suspend fun listEvents(Continuation<Void> cont) {
val sm = object: CoroutineImpl {...}
switch(sm.label) {
case 0:
getToken(sm)
case 1:
getEvents(sm.token, sm)
case 2:
displayEvents(sm.events)
}
}

55. Convertendo para CPS
suspend fun listEvents(Continuation<Void> cont) {
val sm = object: CoroutineImpl {...}
switch(sm.label) {
case 0:
sm.label = 1
getToken(sm)
case 1:
...
}
}

56. Convertendo para CPS
suspend fun listEvents(Continuation<Void> cont) {
val sm = object: CoroutineImpl {
fun resume(...) {
listEvents(this)
}
}
switch(sm.label) {
case 0:
...
}
}

57. Convertendo para CPS
suspend fun listEvents(Continuation<Void> cont) {
val sm = object: CoroutineImpl {...}
switch(sm.label) {
case 0:
...
case 1:
sm.label = 2
getEvents(sm.token, sm)
}
}

58. Extensions

59. Extension em Strings
fun String.toNumber(): String {
return NumberFormat.getInstance()
.format(this.toDouble())
}

60. Extension em Strings
fun String.toNumber(): String {
return NumberFormat.getInstance()
.format(this.toDouble())
}
val numberString = “1”
val number = numberString.toNumber()

61. Adaptando callbacks
para Coroutines

62. Chamada convencional Retrofit
requestToken().
enqueue(object : Callback<T> {
override fun onResponse(call: Call<T>?, response: Response<T>) {
// Handle response
}
override fun onFailure(call: Call<T>, t: Throwable) {
// Handle error
}
})

63. Chamada convertida para Coroutine
suspend fun <T : Any?> Call<T>.awaitResponse(): Response<T> {
return suspendCancellableCoroutine { continuation ->
enqueue(object : Callback<T> {
override fun onResponse(call: Call<T>?, response: Response<T>) {
if (response.isSuccessful) continuation.resume(response)
else continuation.resumeWithException(Throwable())
}
override fun onFailure(call: Call<T>, t: Throwable) {
if (continuation.isCancelled) return
continuation.resumeWithException(t)
}
})
}
}

64. Chamada convertida para Coroutine
suspend fun <T : Any?> Call<T>.awaitResponse(): Response<T>
{
...
}
val token = requestToken().awaitResponse()

65. Libs interessantes usando Coroutines
● Kotlin Coroutines for Retrofit
https://github.com/gildor/kotlin-coroutines-retrofit
● Kotlin Coroutine (Experimental) Adapter
https://github.com/JakeWharton/retrofit2-kotlin-coroutines-adapter
● Peko
https://github.com/deva666/Peko
● Anko Coroutines
https://github.com/Kotlin/anko/wiki/Anko-Coroutines
● Prefekt
https://github.com/StylingAndroid/Prefekt

66. Projeto de Exemplo
https://github.com/DiegoGSantos/Coroutines-Example

67. Referências
KotlinConf 2017 - Introduction to Coroutines by Roman Elizarov
https://www.youtube.com/watch?v=_hfBv0a09Jc&t=34s
KotlinConf 2017 Deep Dive into Coroutines on JVM by Roman Elizarov
https://www.youtube.com/watch?v=YrrUCSi72E8
Github official: https://github.com/Kotlin/kotlinx.coroutines
Android + kotlin coroutines: Async de um jeito "diferente", por Walmyr Carvalho (Android Meetup #55)
https://www.youtube.com/watch?v=Yr2p4gLUwBA

68. Referências
Artigos
http://blog.alexnesterov.com/post/coroutines/
https://superkotlin.com/coroutines/
https://en.wikipedia.org/wiki/Cooperative_multitasking
https://android.jlelse.eu/a-first-walk-into-kotlin-coroutines-on-android-fe4a6e25f46a

69. Obrigado!
Diego Gonçalves Santos
DiegoGSantosDiegoGSantos @DiegoGSantos