@ Roman Elizarov relizarov 1
developed high-perf trading software @ Devexperts • Teach concurrent & distributed programming @ St. Petersburg ITMO University • Chief judge @ Northern Eurasia Contest / ICPC • Now team lead in Kotlin Libraries @ JetBrains elizarov @ relizarov 2
= await RequestToken(); var post = await CreatePost(token, item); ProcessPost(post); } C# async modifier Returns a future 1. awaits a future other async functions return future 4 2. awaits a future
= await RequestToken(); var post = await CreatePost(token, item); ProcessPost(post); } C# 5
= await RequestToken(); var post = await CreatePost(token, item); ProcessPost(post); } C# Suspension points! But what about generators with yield return? 6
val token = await(requestToken()) val post = await(createPost(token, item)) processPost(post) } Kotlin Coroutine builder Coroutine scope 7 Regular function
val token = await(requestToken()) val post = await(createPost(token, item)) processPost(post) } Kotlin Coroutine builder await function Coroutine scope Suspending functions 8 Regular function
val token = await(requestToken()) val post = await(createPost(token, item)) processPost(post) } Kotlin 9
val token = await(requestToken()) val post = await(createPost(token, item)) processPost(post) } Kotlin async / await à future 10
val token = yield(requestToken()) val post = yield(createPost(token, item)) processPost(post) } Kotlin async / await à future generate / yield à sequence 11
= await(requestToken()) val post = await(createPost(token, item)) processPost(post) } Kotlin 12
token = requestToken() val post = createPost(token, item) processPost(post) } Kotlin Returns a future 13
= requestToken() val post = createPost(token, item) processPost(post) } Kotlin Suspending function modifier 14
= requestToken() val post = createPost(token, item) processPost(post) } Kotlin 15
post := createPost(token, item) processPost(post) } Go 16
for i := 0; i < 5; i++ { time.Sleep(100 * time.Millisecond) fmt.Println(s) } } func main() { go say("world") say("hello") } Go https://tour.golang.org/concurrency/1 19
for i := 0; i < 5; i++ { time.Sleep(100 * time.Millisecond) fmt.Println(s) } } func main() { go say("world") say("hello") } Go 20 https://tour.golang.org/concurrency/1
for i := 0; i < 5; i++ { time.Sleep(100 * time.Millisecond) fmt.Println(s) } } func main() { go say("world") say("hello") } Go 21 https://tour.golang.org/concurrency/1
for (i in 0..4) { delay(100) println(s) } } fun main() = mainBlocking { go { say("world") } say("hello") } Kotlin 22 Suspending function modifier Suspending function
for (i in 0..4) { delay(100) println(s) } } fun main() = mainBlocking { go { say("world") } say("hello") } Kotlin 23 Suspending function modifier Suspending function Coroutine builder Another builder
for (i in 0..4) { delay(100) println(s) } } fun main() = runBlocking { launch { say("world") } say("hello") } Kotlin 24
int) { x, y := 0, 1 for { select { case c <- x: x, y = y, x+y case <-quit: fmt.Println("quit") return } } } Go https://tour.golang.org/concurrency/5 25
int) { x, y := 0, 1 for { select { case c <- x: x, y = y, x+y case <-quit: fmt.Println("quit") return } } } Go https://tour.golang.org/concurrency/5 26
int) { x, y := 0, 1 for { select { case c <- x: x, y = y, x+y case <-quit: fmt.Println("quit") return } } } Go https://tour.golang.org/concurrency/5 27
int) { x, y := 0, 1 for { select { case c <- x: x, y = y, x+y case <-quit: fmt.Println("quit") return } } } Go https://tour.golang.org/concurrency/5 28
int) { x, y := 0, 1 for { select { case c <- x: x, y = y, x+y case <-quit: fmt.Println("quit") return } } } Go https://tour.golang.org/concurrency/5 29
ReceiveChannel<Int>) { var x = 0 var y = 1 whileSelect { c.onSend(x) { val next = x + y x = y y = next true // continue while loop } quit.onReceive { println("quit") false // break while loop } } } Kotlin 30
ReceiveChannel<Int>) { var x = 0 var y = 1 whileSelect { c.onSend(x) { val next = x + y x = y y = next true // continue while loop } quit.onReceive { println("quit") false // break while loop } } } Kotlin 31 Library types
ReceiveChannel<Int>) { var x = 0 var y = 1 whileSelect { c.onSend(x) { val next = x + y x = y y = next true // continue while loop } quit.onReceive { println("quit") false // break while loop } } } Kotlin 32 Library types Select DSL
33
val result = makeRequest() // display result in UI display(result) } catch (exception: Throwable) { // process exception in UI } } Thread-bound UI programming 34
val result = makeRequest() // display result in UI display(result) } catch (exception: Throwable) { // process exception in UI } } Thread-bound UI programming 35
val result = makeRequest() // display result in UI display(result) } catch (exception: Throwable) { // process exception in UI } } Thread-bound UI programming 36
val result = makeRequest() // display result in UI display(result) } catch (exception: Throwable) { // process exception in UI } } Thread-bound UI programming 37
val result = makeRequest() // display result in UI display(result) } catch (exception: Throwable) { // process exception in UI } } Thread-bound UI programming 38 Coroutine context
val result = makeRequest() // display result in UI run { display(result) } } catch (exception: Throwable) { // process exception in UI } } Thread-bound UI programming 39 Higher-order function Coroutine context
C# Lambda
Display(result); }); await task; C# 1. Function called first 2. Then await
Display(result); }); await task; C# 1. Function called first 2. Then await A call to regular function
is passed along the suspend callstack A call to suspending function
{ x, y := 0, 1 for { select { case c <- x: x, y = y, x+y case <-quit: fmt.Println("quit") return } } } Go https://tour.golang.org/concurrency/5 46 A CancellationToken
{ x, y := 0, 1 for { select { case c <- x: x, y = y, x+y case <-quit: fmt.Println("quit") return } } } Go https://tour.golang.org/concurrency/5 47 A CancellationToken A boilerplate
} Go https://golang.org/pkg/context/
// Done returns a channel that's closed when work done on // behalf of this context should be canceled. … Done() <-chan struct{} } Go https://golang.org/pkg/context/ At Google, we require that Go programmers pass a Context parameter as the first argument to every function on the call path between incoming and outgoing requests.
} Kotlin
Throwable? = null): Boolean } Kotlin
Throwable? = null): Boolean fun onCompletion(handler: CompletionHandler): Registration } Kotlin
Throwable? = null): Boolean fun onCompletion(handler: CompletionHandler): Registration } Kotlin
say("world") } Kotlin
say("world") } job.cancel() Kotlin
say("world") } job.cancel() Kotlin delay(…) throw CancellationException()
job1 job2 Prototype worked like a charm
val job2 = launch { say("world") } Kotlin These jobs are resources
val job2 = launch { say("world") } val jobs = CompositeJob() Kotlin
val job2 = launch { say("world") } val jobs = CompositeJob() jobs.add(job1) jobs.add(job2) Kotlin
val job2 = launch { say("world") } val jobs = CompositeJob() jobs.add(job1) jobs.add(job2) jobs.cancel() Kotlin
fun cancel(reason: Throwable? = null): Boolean fun onCompletion(handler: CompletionHandler): Registration } Kotlin
} launch(job) { say("world") } Kotlin Job is a coroutine context!
} launch(job) { say("world") } job.cancel() Kotlin
} launch(job) { say("world") } job.cancel() Kotlin !
} launch(job) { say("world") } job.cancel() Kotlin Job becomes a CancellationToken !
} launch(coroutineContext) { say("world") } } Kotlin !
say("hello") } launch(coroutineContext) { say("world") } } Kotlin ! !
say("hello") } launch(coroutineContext) { say("world") } } Kotlin ! ! !
say("hello") } launch(coroutineContext) { say("world") } } Kotlin !
} Kotlin It can fail
} Kotlin It can fail
say("hello") } launch(coroutineContext) { say("world") } } Kotlin It can fail It can fail They can fail concurrently Success or failure of this composite job can be known only when all children complete cancel(ex) cancel(ex)
} launch(coroutineContext) { say("world") } } Kotlin
{ say("hello") } launch(coroutineContext) { say("world") } } Kotlin
} suspend fun sayHelloWorld() { launch(coroutineContext) { say("hello") } launch(coroutineContext) { say("world") } } Kotlin
} suspend fun sayHelloWorld() { launch(coroutineContext) { say("hello") } launch(coroutineContext) { say("world") } } Kotlin It can fail
} suspend fun sayHelloWorld() { launch(coroutineContext) { say("hello") } launch(coroutineContext) { say("world") } } Kotlin It can fail But call returns normally! !
} suspend fun sayHelloWorld() { withScope { // new job in the context launch(coroutineContext) { say("hello") } launch(coroutineContext) { say("world") } } } Kotlin Throws exception on failure Encapsulated concurrent decomposition
} suspend fun sayHelloWorld() { withScope { launch(coroutineContext) { say("hello") } launch(coroutineContext) { say("world") } } } Kotlin
sayHelloWorld() } suspend fun sayHelloWorld() { withScope { launch(coroutineContext) { say("hello") } launch(coroutineContext) { say("world") } } } Kotlin Error-pone
sayHelloWorld() } suspend fun sayHelloWorld() { withScope { launch(coroutineContext) { say("hello") } launch(coroutineContext) { say("world") } } } Kotlin Error-pone Verbose
sayHelloWorld() } suspend fun sayHelloWorld() { withScope { launch { say("hello") } launch { say("world") } } } Kotlin Extension function
sayHelloWorld() } suspend fun sayHelloWorld() { withScope { // this: CoroutineScope launch { say("hello") } launch { say("world") } } } Kotlin Extension function
} suspend fun sayHelloWorld() { coroutineScope { // this: CoroutineScope launch { say("hello") } launch { say("world") } } } Kotlin Extension function
} suspend fun sayHelloWorld() { coroutineScope { // this: CoroutineScope launch { say("hello") } launch { say("world") } } } Kotlin !
// this: CoroutineScope for (w in listOf("hello", "world")) { launch { say(w) } } } }
// this: CoroutineScope for (w in listOf("hello", "world")) { launch { say(w) } } } }
// this: CoroutineScope for (w in listOf("hello", "world")) { launchSay(w) } } } fun CoroutineScope.launchSay(w: String) = launch { say(w) }
// this: CoroutineScope for (w in listOf("hello", "world")) { launchSay(w) } } } fun CoroutineScope.launchSay(w: String) = launch { say(w) }
// this: CoroutineScope for (w in listOf("hello", "world")) { launchSay(w) } } } fun CoroutineScope.launchSay(w: String) = launch { say(w) } But name for all of it?
https://vorpus.org/blog/notes-on-structured-concurrency-or-go-statement-considered-harmful/
cleanup • Never loose a working coroutine • Error propagation • Never loose an exception 106
… Python https://vorpus.org/blog/notes-on-structured-concurrency-or-go-statement-considered-harmful/ CoroutineScope / Job
True: incoming_connection = await server_socket.accept() nursery.start_soon(connection_handler, incoming_connection) Python https://vorpus.org/blog/notes-on-structured-concurrency-or-go-statement-considered-harmful/ launch
scope = FiberScope.cancellable()) { while (...) { Socket s = listener.accept(); scope.schedule(() -> handle(s)); } } Java https://trio.discourse.group/t/project-loom-lightweight-concurrency-for-the-jvm/97 CoroutineScope / Job launch
/ Job
:= range urls { // Launch a goroutine to fetch the URL. url := url // https://golang.org/doc/faq#closures_and_goroutines g.Go(func() error { resp, err := http.Get(url) if err == nil { resp.Body.Close() } return err }) } Go https://godoc.org/golang.org/x/sync/errgroup launch
:= range urls { // Launch a goroutine to fetch the URL. url := url // https://golang.org/doc/faq#closures_and_goroutines g.Go(func() error { resp, err := http.Get(url) if err == nil { resp.Body.Close() } return err }) } // Wait for all HTTP fetches to complete. if err := g.Wait(); err == nil { fmt.Println("Successfully fetched all URLs.") } Go https://godoc.org/golang.org/x/sync/errgroup scope completion
… }
… }
https://kotlinlang.org/docs/reference/coroutines/coroutines-guide.html • Library source and issues https://github.com/Kotlin/kotlinx.coroutines • Ongoing improvement work! 120
Elizarov relizarov 121
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