A Practical Introduction to Coroutines

Kotlin coroutines are stable now, and they're starting to gain adoption. If you're new to coroutines, or if you've never used them, this talk is for you. We'll cover:

* What coroutines are
* What they can do, and where you'll want to use them
* Current limitations
* A practical example of using coroutines

You can find the companion code here:
https://gitlab.com/fuentespatrick/a-practical-introduction-to-coroutines-talk-companion/

Transcript

1. Getting Started with Kotlin Coroutines Patrick Fuentes @pfue
2. What we’ll cover • Basic building blocks and vocabulary • Practical examples • Resources
3. “Coroutines are a way of doing asynchronous, non-blocking code easily” – Andrey Beslav, KotlinConf 2018
4. Avoiding Callback Hell fun loadFriendOrder() { repository.getUser( { user -> repository.getUserContactIds(user, { contactIdList -> val userToDisplay = findUserToDisplay(contactIdList) repository.getOrderHistory(userToDisplay, { orderIdList -> findOrderToDisplay(orderIdList) }, { throwable -> Log.e(TAG, "${throwable.message} - ${throwable.cause}") }) }, { throwable -> Log.e(TAG, "${throwable.message} - ${throwable.cause}") }) }, { throwable -> Log.e(TAG, "${throwable.message} - ${throwable.cause}") }) } suspend fun loadFriendOrder() { try { val user = repository.getUser() val contactIdList = repository.getUserContactIds(user) val userToDisplay = findUserToDisplay(contactIdList) val orderIdList = repository.getOrderHistory(userToDisplay) findOrderToDisplay(orderIdList) } catch (error: Throwable) { Log.e(TAG, "${error.message} - ${error.cause}") } }
5. What are coroutines made of?
6. Suspend
7. Launch { … }
8. Job
9. Join
10. Dispatchers – Where your code runs Default – The default if you don’t specify. Backed by a shared thread pool IO – Best for IO-intensive blocking operations (like file I/O and blocking socket I/O) Main – A special CoroutineDispatcher: confined to the application “Main” or “UI” thread & used for any UI-based activities – usually single threaded Unconfined – Use with extreme caution, not for general code.
11. Thread A Thread B Coroutine 1 Coroutine 8 Coroutine 4 Coroutine 3 Coroutine 2 Coroutine 7 Coroutine 5
12. Dispatchers – etc… Private thread pools can be created with newSingleThreadContext() and newFixedThreadPoolContext()
13. Context = Job + Dispatcher + other info Job Dispatcher Context Other info
14. Async
15. Async
16. Scope Scope Context (Information about your coroutines)
17. Scope async {…} Scope Context Job launch {…} Scope Context Job
18. Time to get practical Let’s see what we can do with coroutines
19. But first… implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-android:1.1.0' implementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.1.0' or
20. Base Coroutine Scope
21. Parent Jobs & Scope
22. Parent Jobs & Scope
23. Parent Jobs & Scope launch {…} Launch Context Parent Job async {…} Launch Scope Async Context Child Job Async Scope
24. Waiting for a few coroutines
25. Waiting for a few coroutines – Parallel
26. Network Activity
27. Network Activity
28. Heavy Processing
29. Resources • Read great resources: ◦ Understanding blocking vs suspending: https://medium.com/@elizarov/blocking-threads-suspending-coroutines-d33e11bf4761 ◦ Networking with coroutines: https://medium.com/exploring-android/android-networking-with-coroutines-and-retrofit-a2f2 0dd40a83 ◦ Demystifying CoroutineContext: https://proandroiddev.com/demystifying-coroutinecontext-1ce5b68407ad ◦ The official documentation is great: https://github.com/Kotlin/kotlinx.coroutines/blob/master/docs/coroutine-context-and-dispatc hers.md ◦ Coroutines Cheatsheet: https://blog.kotlin-academy.com/kotlin-coroutines-cheat-sheet-8cf1e284dc35 ◦ Any KotlinConf talks on Coroutines - especially ‘Coroutines in Practice’ by Roman Elizarov (*AFTER* you understand what we covered in this talk) ◦ Any talks or articles by Roman Elizarov – @relizarov
30. What’s next? • Use coroutines this week – getting started is easy • Read the recommended resources from the last slide • Check out the project with my samples from this talk: https://gitlab.com/fuentespatrick/a-practical-introduction-to-coroutines-talk- companion/ • After you’ve tried the basics of coroutines, learn more ◦ Channels ◦ Select • Feel free to ask me questions on Twitter – @pfue
31. Thank you! • All of you for being here! • St. Louis DevFest organizers for having me • Helping with the talk: ◦ Renee Vandervelde – @RenVandervelde ◦ Dan Lew – @danlew42 ◦ Aaron Weaver ◦ Brendon Justin – @brendonjustin_ ◦ Nate Brunette – @natebrunette