Coroutines in Kotlin

Slides from my talk at Kotlin TechTalks@Lohika Kyiv, 2017-09-20

Transcript

1. Coroutines in Kotlin Dmytro Zaitsev Team Leader @ Lóhika
2. Blocking VS Non-blocking
4. v1: Sequential fun postItem(item: Item) {
 val token = prepareToken() / / 1
 val post = submitPost(token, item) / / 2
 processPost(post) / / 3
 }
5. v2: Async callbacks fun postItem(item: Item) {
 prepareTokenAsync { token -> / / 1
 submitPostAsync(token, item) { post -> / / 2
 processPost(post) / / 3
 }
 }
 }
6. Callback hell
7. v3: Reactive fun postItem(item: Item) {
 observeToken()
 .concatMap { token -> observePost(token, item) }
 .subscribe { post -> processPost(post) }
 }
8. v4: Coroutines fun postItem(item: Item) {
 launch(CommonPool) {
 val token = prepareToken() / / 1
 val post = submitPost(token, item) / / 2
 processPost(post) / / 3
 }
 }
9. Experimental status Kotlin 1.1 -Xcoroutines=enable kotlin.coroutines.experimental -> kotlin.coroutines
10. Terminology coroutine suspending function suspending lambda suspending function type coroutine builder suspension point continuation
11. A coroutine is… an instance of suspendable computation similar to a daemon thread, but very light-weight similar to a future or promise
12. Why coroutines? threads are expensive to keep and switch your code is single threaded you’ve got lots of mutable states
13. suspend fun computation that can be suspended
14. Standard API • Language support (`suspend` keyword) • low-level basic API (stdlib: kotlin.coroutines) • high-level APIs that can be used in user code
15. Low-level API (kotlin.coroutines) • kotlin.coroutines.experimental • create/start/suspendCoroutine() • Continuation interface • @RestrictSuspension annotation • kotlin.coroutines.experimental.intrinsics • suspendCoroutineOrReturn()
16. Continuation interface Continuation<in T> {
 val context: CoroutineContext
 fun resume(value: T)
 fun resumeWithException(exception: Throwable)
 }
17. Patterns • generators/yield: C#, Python, Scala • async/await: C#, ECMAScript, Dart • channels, select: Go • actors: Scala
18. Generators API in kotlin.coroutines kotlin.coroutines.experimental: • buildSequence() • buildIterator()
19. buildSequence {
 print("Start")
 yield(1) / / suspension point
 
 var prev = 0
 var cur = 1
 while (true) {
 print(“Next") val next = prev + cur
 yield(next) / / suspension point
 
 prev = cur
 cur = next
 }
 print("End") / / unreachable code
 }.take(8).forEach { print(" $it ") }
 / / Output: Start 1 Next 1 Next 2 Next 3 Next 5 Next 8 Next 13 Next 21
20. kotlinx.coroutines • kotlinx-coroutines-core • integration • guava, jdk8, nio, quasar • reactive • reactive, reactor, rx1, rx2 • ui • android, javafx, swing
21. runBlocking for main functions and tests
22. delay like Thread.sleep(), but non-blocking
23. launch fire and forget (Job)
24. async promise returned (Deferred + await)
25. Channel transfers values between coroutines
26. produce produces a stream of values by sending them to a channel (ProducerJob)
27. actor deals with it’s mailbox (ActorJob)
28. select waits for the result of multiple suspending functions
29. Job lifecycle New Active Cancelling Completed Cancelled
30. Job states State isActive isCompleted isCancelled New - - - Active + - - Completed - + - Cancelling - - + Cancelled - + +
31. val deferred = async(CommonPool) {
 throw SomeException("I'm thrown inside a coroutine")
 }
 try {
 deferred.await() / / re-throws
 } catch (e: SomeException) {
 log(e.message)
 } Exception handling
32. WeakReference “life hack” suspend operator fun <T> WeakReference<T>.invoke(): T = suspendCoroutineOrReturn { get() ?: throw CancellationException() } val activityRef = WeakReference(this)
 launch(CommonPool) {
 activityRef().expensiveComputation()
 }
33. Demo
34. A lot more left… Coroutine dispatchers Mutable state and concurrency UI programming Reactive streams
35. Links Andrey Breslav FAQ:
 https:/ /discuss.kotlinlang.org/t/experimental-status-of-coroutines-in-1-1-and- related-compatibility-concerns/2236 Design document (KEEP):
 https:/ /github.com/Kotlin/kotlin-coroutines/blob/master/kotlin-coroutines- informal.md Full kotlinx.coroutines API:
 http:/ /kotlin.github.io/kotlinx.coroutines Coroutines guide by Roman ELizarov:
 https:/ /github.com/Kotlin/kotlinx.coroutines/blob/master/coroutines-guide.md
36. Thank you! @DmitriyZaitsev