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Coroutines in Kotlin
This document discusses coroutines in Kotlin, which provide a way to write asynchronous non-blocking code using suspending functions and coroutines. Coroutines are lightweight threads that are cheaper than traditional threads. The document covers the basics of coroutines including terminology, suspending functions, the coroutine builder API, patterns like generators/yield, and libraries like kotlinx.coroutines that provide additional coroutine functionality. It provides examples of common coroutine operations like launch, async, and channels.
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Coroutines in Kotlin
- 1. Coroutines in Kotlin DmytroZaitsev Team Leader @ Lóhika
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- 4. v1: Sequential fun postItem(item:Item) { val token = prepareToken() // 1 val post = submitPost(token, item) // 2 processPost(post) // 3 }
- 5. v2: Async callbacks funpostItem(item: Item) { prepareTokenAsync { token -> // 1 submitPostAsync(token, item) { post -> // 2 processPost(post) // 3 } } }
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- 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 } }
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- 10. Terminology coroutine suspending functionsuspending lambda suspendingfunction type coroutine builder suspension point continuation
- 11. A coroutine is… aninstance of suspendable computation similar to a daemon thread, but very light-weight similar to a future or promise
- 12. Why coroutines? threads areexpensive to keep and switch your code is single threaded you’ve got lots of mutable states
- 13. suspend fun computation thatcan be suspended
- 14. Standard API • Languagesupport (`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
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- 26. produce produces a streamof values by sending them to a channel (ProducerJob)
- 27. actor deals with it’smailbox (ActorJob)
- 28. select waits for theresult of multiple suspending functions
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- 30. Job states State isActiveisCompleted 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” suspendoperator fun <T> WeakReference<T>.invoke(): T = suspendCoroutineOrReturn { get() ?: throw CancellationException() } val activityRef = WeakReference(this) launch(CommonPool) { activityRef().expensiveComputation() }
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- 34. A lot moreleft… 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 Designdocument (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
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