Asynchronous Programming with KotlinCoroutines · 2018. 4. 28. · Speaker: Roman Elizarov • 17+ years experience • Previously developed high -perf trading software @ Devexperts

AsynchronousProgrammingwithKotlin Coroutines

PresentedatQCon Beijing,2018/RomanElizarov@JetBrains

Speaker:RomanElizarov

• 17+yearsexperience• Previouslydevelopedhigh-perftradingsoftware@Devexperts• Teachconcurrent&[email protected]• Chiefjudge@NorthernEurasiaContest/ACMICPC• NowteamleadinKotlinLibraries@JetBrains

Pragmatic.Concise.Modern.InteroperablewithJava.

AsynchronousProgramming

Howdowewritecodethatwaitsforsomethingmostofthetime?

AtoyproblemKotlin fun requestToken(): Token {

// makes request for a token & waitsreturn token // returns result when received

}

1

fun requestToken(): Token { … }fun createPost(token: Token, item: Item): Post {

// sends item to the server & waits return post // returns resulting post

}

AtoyproblemKotlin

2

fun requestToken(): Token { … }fun createPost(token: Token, item: Item): Post { … }fun processPost(post: Post) {

// does some local processing of result}

AtoyproblemKotlin

3

fun requestToken(): Token { … }fun createPost(token: Token, item: Item): Post { … }fun processPost(post: Post) { … }

AtoyproblemKotlin

fun postItem(item: Item) {val token = requestToken()val post = createPost(token, item)processPost(post)

}

123

Canbedonewiththreads!

fun requestToken(): Token {// makes request for a token // blocks the thread waiting for resultreturn token // returns result when received

}fun createPost(token: Token, item: Item): Post { … }fun processPost(post: Post) { … }

Threads


}

Isanythingwrongwithit?

Howmanythreadswecanhave?

100�


1000�


10000�


100000�

CallbackstotherescueSortof…

Callbacks:beforefun requestToken(): Token {

// makes request for a token & waitsreturn token // returns result when received

}

1

Callbacks:afterfun requestTokenAsync(cb: (Token) -> Unit) {

// makes request for a token, invokes callback when done// returns immediately

}

1callback

Callbacks:beforefun requestTokenAsync(cb: (Token) -> Unit) { … }fun createPost(token: Token, item: Item): Post {

// sends item to the server & waits return post // returns resulting post

}

2

Callbacks:afterfun requestTokenAsync(cb: (Token) -> Unit) { … }fun createPostAsync(token: Token, item: Item,

cb: (Post) -> Unit) {// sends item to the server, invokes callback when done// returns immediately

}

2callback

Callbacks:beforefun requestTokenAsync(cb: (Token) -> Unit) { … }fun createPostAsync(token: Token, item: Item,

cb: (Post) -> Unit) { … }fun processPost(post: Post) { … }


}

Callbacks:afterfun requestTokenAsync(cb: (Token) -> Unit) { … }fun createPostAsync(token: Token, item: Item,

cb: (Post) -> Unit) { … }fun processPost(post: Post) { … }

fun postItem(item: Item) {requestTokenAsync { token ->

createPostAsync(token, item) { post ->processPost(post)

}}

} aka“callbackhell”

Thisissimplified. Handlingexceptionsmakesitarealmess

Futures/Promises/RxtotherescueSortof…

Futures:beforefun requestTokenAsync(cb: (Token) -> Unit) {

// makes request for a token, invokes callback when done// returns immediately

}

1

Futures:afterfun requestTokenAsync(): Promise<Token> {

// makes request for a token// returns promise for a future result immediately

}

1future

Futures:beforefun requestTokenAsync(): Promise<Token> { … }fun createPostAsync(token: Token, item: Item,

cb: (Post) -> Unit) {// sends item to the server, invokes callback when done// returns immediately

}

2

Futures:afterfun requestTokenAsync(): Promise<Token> { … }fun createPostAsync(token: Token, item: Item): Promise<Post> {

// sends item to the server // returns promise for a future result immediately

}

future2

Futures:beforefun requestTokenAsync(): Promise<Token> { … }fun createPostAsync(token: Token, item: Item): Promise<Post> …fun processPost(post: Post) { … }

fun postItem(item: Item) {requestTokenAsync { token ->

createPostAsync(token, item) { post ->processPost(post)

}}

}

Futures:afterfun requestTokenAsync(): Promise<Token> { … }fun createPostAsync(token: Token, item: Item): Promise<Post> …fun processPost(post: Post) { … }

fun postItem(item: Item) { requestTokenAsync() .thenCompose { token -> createPostAsync(token, item) } .thenAccept { post -> processPost(post) }}

Composable &propagatesexceptions

Nonestingindentation

Futures:afterfun requestTokenAsync(): Promise<Token> { … }fun createPostAsync(token: Token, item: Item): Promise<Post> …fun processPost(post: Post) { … }


Butallthosecombinators…

KotlincoroutinestotherescueLet’sgetreal

Coroutines:beforefun requestTokenAsync(): Promise<Token> {

// makes request for a token// returns promise for a future result immediately

}

1

Coroutines:aftersuspend fun requestToken(): Token {

// makes request for a token & suspendsreturn token // returns result when received

}

1naturalsignature

Coroutines:beforesuspend 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:aftersuspend fun requestToken(): Token { … }suspend fun createPost(token: Token, item: Item): Post {

// sends item to the server & suspendsreturn post // returns result when received

}

2naturalsignature

Coroutines:beforesuspend fun requestToken(): Token { … }suspend fun createPost(token: Token, item: Item): Post { … }fun processPost(post: Post) { … }


Coroutines:aftersuspend 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)

}



}

Likeregular code



}

suspensionpoints

• Regularloops

Bonusfeatures

for ((token, item) in list) {createPost(token, item)

}

• Regularexceptionhanding

Bonusfeatures

try { createPost(token, item)

} catch (e: BadTokenException) { …

}

• Regularhigher-orderfunctions

• forEach,let,apply,repeat,filter,map,use,etc

Bonusfeatures

file.readLines().forEach { line ->createPost(token, line.toItem())

}

• Customhigher-orderfunctions

Bonusfeatures

val post = retryIO {createPost(token, item)

}

Everythinglikeinblockingcode

Howdoesitwork?Aquickpeekbehindthescenes

Kotlinsuspendingfunctions

callback

Kotlin

Java/JVM

suspend fun createPost(token: Token, item: Item): Post { … }

Object createPost(Token token, Item item, Continuation<Post> cont) { … }


callback

Kotlin

Java/JVM

Continuationisagenericcallbackinterface



interface Continuation<in T> {val context: CoroutineContextfun resume(value: T)fun resumeWithException(exception: Throwable)

}


callback

Kotlin

Java/JVM




}


callback

Kotlin

Java/JVM




}


callback

Kotlin

Java/JVM




}

CodewithsuspensionpointsKotlin

Java/JVMCompilestostatemachine(simplifiedcodeshown)

val token = requestToken()val post = createPost(token, item)processPost(post)

switch (cont.label) { case 0: cont.label = 1; requestToken(cont); break; case 1: Token token = (Token) prevResult; cont.label = 2; createPost(token, item, cont); break; case 2: Post post = (Post) prevResult; processPost(post); break;}

CodewithsuspensionpointsKotlin

Java/JVM


switch (cont.label) { case 0: cont.label = 1; requestToken(cont); break; case 1: Token token = (Token) prevResult; cont.label = 2; createPost(token, item, cont); break; case 2: Post post = (Post) prevResult; processPost(post); break;}

IntegrationZoooffuturesonJVM

interface Service {fun createPost(token: Token, item: Item): Call<Post>

}

Retrofitasync


}

suspend fun createPost(token: Token, item: Item): Post =serviceInstance.createPost(token, item).await()

naturalsignature


}

suspend fun createPost(token: Token, item: Item): Post =serviceInstance.createPost(token, item).await()

Suspendingextensionfunctionfromintegrationlibrary

suspend fun <T> Call<T>.await(): T {…

}

Callbackseverywhere

suspend fun <T> Call<T>.await(): T { enqueue(object : Callback<T> { override fun onResponse(call: Call<T>, response: Response<T>) { // todo }

override fun onFailure(call: Call<T>, t: Throwable) { // todo } })}

suspend fun <T> Call<T>.await(): T = suspendCoroutine { cont ->enqueue(object : Callback<T> {

override fun onResponse(call: Call<T>, response: Response<T>) {if (response.isSuccessful)

cont.resume(response.body()!!)else

cont.resumeWithException(ErrorResponse(response))}

override fun onFailure(call: Call<T>, t: Throwable) {cont.resumeWithException(t)

}})

}

suspend fun <T> suspendCoroutine(block: (Continuation<T>) -> Unit): T



Regularfunction

Inspiredbycall/cc fromScheme






}})

}

Installcallback






}})

}

Installcallback






}})

}

Analyzeresponse






}})

}

Analyzeresponse






}})

}That’sall

Out-of-theboxintegrations

kotlinx-coroutines-core

jdk8

guava

nio

reactor

rx1

rx2

CoroutinebuildersHowcanwestartacoroutine?

Coroutinesrevisitedsuspend fun requestToken(): Token { … }suspend fun createPost(token: Token, item: Item): Post { … }fun processPost(post: Post) { … }


}



}



}

Error: Suspendfunction'requestToken'shouldbecalledonlyfromacoroutineoranothersuspendfunction



}

Cansuspend execution



}

Cansuspend executionAregularfunctioncannot



}

Cansuspend executionAregularfunctioncannot

Onecannotsimplyinvokeasuspendingfunction

Launch

fun postItem(item: Item) {launch {


}}

coroutinebuilder



}}

Fireandforget!

Returnsimmediately,coroutineworksinbackgroundthreadpool



}}

fun postItem(item: Item) {launch(UI) {


}}

UIContext

Justspecifythecontext

fun postItem(item: Item) {launch(UI) {


}}

UIContext

AnditgetsexecutedonUIthread

Where’sthemagicoflaunch?

fun launch(context: CoroutineContext = DefaultDispatcher,block: suspend () -> Unit

): Job { … }

Aregularfunction


): Job { … } suspending lambda


): Job { … }

async /awaitTheclassicapproach

Kotlin-way


}

suspend fun requestToken(): Token { … }suspend fun createPost(token: Token, item: Item): Post { … }fun processPost(post: Post) { … }

Kotlin

async Task postItem(Item item) { var token = await requestToken(); var post = await createPost(token, item); processPost(post);

}

Classic-way

C#approachtothesameproblem(alsoPython,TS,Dart,comingtoJS)

async Task<Token> requestToken() { … }async Task<Post> createPost(Token token, Item item) { … }void processPost(Post post) { … }

C#


}

Classic-way

markwithasync


C#


}

Classic-way

useawaittosuspend


C#


}

Classic-way

returnsafuture


C#

Whynoawait keywordinKotlin?

Theproblemwithasync

requestToken() VALID –>producesTask<Token>

await requestToken() VALID –>producesToken

concurrentbehavior

sequentialbehavior

C#

C#

default

ConcurrencyishardConcurrencyhastobeexplicit

Kotlinsuspendingfunctionsaredesignedtoimitatesequential behavior

bydefault

ConcurrencyishardConcurrencyhastobeexplicit

KotlinapproachtoasyncConcurrencywhereyouneed it

Use-caseforasync

async Task<Image> loadImageAsync(String name) { … } C#

Use-caseforasync

var promise1 = loadImageAsync(name1);var promise2 = loadImageAsync(name2);

async Task<Image> loadImageAsync(String name) { … }

Startmultipleoperationsconcurrently

C#

Use-caseforasync


var image1 = await promise1;var image2 = await promise2;

async Task<Image> loadImageAsync(String name) { … }

andthenwaitforthem

C#

Use-caseforasync

var result = combineImages(image1, image2);


var image1 = await promise1;var image2 = await promise2;

async Task<Image> loadImageAsync(String name) { … } C#

Kotlinasync function

fun loadImageAsync(name: String): Deferred<Image> = async { … }

Kotlin



Aregularfunction

Kotlin



Kotlin’s futuretype

Kotlin



async coroutinebuilder

Kotlin



val deferred1 = loadImageAsync(name1)val deferred2 = loadImageAsync(name2)

Startmultipleoperationsconcurrently

Kotlin




val image1 = deferred1.await()val image2 = deferred2.await() andthenwaitforthem

awaitfunction

Suspendsuntildeferrediscomplete

Kotlin




val image1 = deferred1.await()val image2 = deferred2.await()

val result = combineImages(image1, image2)

Kotlin

Usingasync functionwhenneeded

suspend fun loadImage(name: String): Image { … }

Isdefinedassuspendingfunction,notasync



suspend fun loadAndCombine(name1: String, name2: String): Image { val deferred1 = async { loadImage(name1) }val deferred2 = async { loadImage(name2) }return combineImages(deferred1.await(), deferred2.await())

}




}




}




}

Kotlinapproachtoasync

requestToken() VALID –>producesToken

async { requestToken() } VALID –>producesDeferred<Token>

sequentialbehavior

concurrentbehavior

Kotlin

Kotlin

default

Whatarecoroutinesconceptually?

Whatarecoroutinesconceptually?Coroutinesarelikevery light-weightthreads

fun main(args: Array<String>) = runBlocking<Unit> {val jobs = List(100_000) {

launch {delay(1000L)print(".")

}}jobs.forEach { it.join() }

}

Example




}

Example Thiscoroutinebuilderrunscoroutineinthecontextofinvokerthread




}

Example




}

Example




}

Example

Suspendsfor1second




}

Example

Wecanjoinajobjustlikeathread




}

Example

Trythatwith100kthreads!

Prints100kdotsafteroneseconddelay




}

Example

fun main(args: Array<String>) {val jobs = List(100_000) {

thread {Thread.sleep(1000L)print(".")


}

Example

fun main(args: Array<String>) {val jobs = List(100_000) {

thread {Thread.sleep(1000L)print(".")


}

Example

Exceptioninthread"main"java.lang.OutOfMemoryError:unabletocreatenewnativethread

JavainteropCanweuseKotlincoroutineswithJavacode?

Javainterop

CompletableFuture<Image> loadImageAsync(String name) { … }Java

CompletableFuture<Image> loadImageAsync(String name) { … }

CompletableFuture<Image> loadAndCombineAsync(String name1, String name2)

Java

Imagineimplementing itinJava…

CompletableFuture<Image> loadImageAsync(String name) { … }

CompletableFuture<Image> loadAndCombineAsync(String name1,String name2)

{CompletableFuture<Image> future1 = loadImageAsync(name1);CompletableFuture<Image> future2 = loadImageAsync(name2);return future1.thenCompose(image1 ->

future2.thenCompose(image2 ->CompletableFuture.supplyAsync(() ->

combineImages(image1, image2))));}

Java


fun loadAndCombineAsync(name1: String, name2: String

): CompletableFuture<Image> =…

Kotlin



): CompletableFuture<Image> =future {

val future1 = loadImageAsync(name1)val future2 = loadImageAsync(name2)combineImages(future1.await(), future2.await())

}

Kotlin





}

Kotlinfuturecoroutinebuilder





}

Kotlin





}

Kotlin

BeyondasynchronouscodeKotlin’s approachtogenerate/yield– synchronouscoroutines

Fibonaccisequence

val fibonacci: Sequence<Int> = …

Fibonaccisequence

val fibonacci = buildSequence {var cur = 1var next = 1while (true) {

yield(cur) val tmp = cur + nextcur = nextnext = tmp

}}

Fibonaccisequence



}}

println(fibonacci.take(10).toList())

Fibonaccisequence



}}


>> [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

Fibonaccisequence



}}

Acoroutinebuilderwithrestrictedsuspension

Fibonaccisequence



}}

AsuspendingfunctioninthescopeofbuildSequence

Fibonaccisequence



}}


Synchronous

Fibonaccisequence



}}

val iter = fibonacci.iterator()

Fibonaccisequence



}}

val iter = fibonacci.iterator()println(iter.next())

Fibonaccisequence



}}


Fibonaccisequence



}}


Fibonaccisequence



}}


Fibonaccisequence



}}

val iter = fibonacci.iterator()println(iter.next()) // 1

Fibonaccisequence



}}

val iter = fibonacci.iterator()println(iter.next()) // 1println(iter.next())

Fibonaccisequence



}}


Fibonaccisequence



}}


Fibonaccisequence



}}


Fibonaccisequence



}}


Fibonaccisequence



}}

val iter = fibonacci.iterator()println(iter.next()) // 1println(iter.next()) // 1

Fibonaccisequence



}}

val iter = fibonacci.iterator()println(iter.next()) // 1println(iter.next()) // 1 etc adinfinum

LibraryvsLanguageKeepingthecorelanguagesmall

Classicasync

async/awaitgenerate/yield Keywords

Kotlincoroutines

suspend Modifier

Kotlincoroutines

Standardlibrary

Kotlincoroutines

Standardlibrary

kotlinx-coroutines

launch,async,runBlocking,future,delay,

Job,Deferred,etc

http://github.com/kotlin/kotlinx.coroutines

Thereismore

• CommunicatingSequentialProcesses(CSP)Style• ChannelsandActors• Selectionandsynchronization• Jobhierarchiesandcancellation

• LearnmoreinGuidetokotlinx.coroutinesbyexample

• KotlinConf 2018 (3-5Oct)inAmsterdam

Thankyou

Anyquestions?

Slidesareavailableatwww.slideshare.net/elizarovemailmetoelizarov atgmail

relizarov

Documents

Asynchronous Programming with KotlinCoroutines · 2018. 4. 28. · Speaker: Roman Elizarov • 17+ years experience • Previously developed high -perf trading software @ Devexperts