Droidcon Lisbon: RxJava & Coroutines: A Practical Analysis

Kotlin has taken the Android world by storm, and is quickly becoming the most popular language of choice. With Coroutines now stable, does it make sense to replace your RxJava implementations for Coroutines?

Despite the hype, it may not make sense to jump on the bandwagon just yet. RxJava has already proven its stability and usefulness, and a comparison between the two frameworks shows that they are simply better suited for different purposes.

In this talk you’ll learn:
- how to utilise the strengths of each framework
- how to correctly choose the best solution for the requirements of your project
- whether it may be beneficial to migrate or run them concurrently
- and how you can start doing so for your project

Transcript

1. RxJava & Coroutines
   A Practical Analysis
   Droidcon Lisbon
   !
   @askashdavies
   

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2. @askashdavies
   

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3. @askashdavies
   

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4. pusher.com/state-of-kotlin
   

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5. blog.jetbrains.com/kotlin/2016/02/kotlin-1-0-released-pragmatic-language-for-jvm-and-android/
   

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6. Coroutines
   @askashdavies
   

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7. fun main() {
   GlobalScope.launch {
   delay(1000L)
   println("World!")
   }
   println("Hello,")
   Thread.sleep(2000L)
   }
   // Hello,
   // World!
   @askashdavies
   

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8. fun main() {
   GlobalScope.launch {
   delay(1000L)
   println("World!")
   }
   println("Hello,")
   Thread.sleep(2000L)
   }
   // Hello,
   // World!
   @askashdavies
   

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9. fun main() {
   GlobalScope.launch {
   delay(1000L)
   println("World!")
   }
   println("Hello,")
   Thread.sleep(2000L)
   }
   // Hello,
   // World!
   @askashdavies
   

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10. Coroutine Builders
    @askashdavies
    

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11. Coroutine Builders
    val deferred: Deferred = async { "Hello World!" }
    @askashdavies
    

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12. Coroutine Builders
    val deferred: Deferred = async { "Hello World!" }
    val result: String = deferred.await()
    @askashdavies
    

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13. Coroutine Builders
    val deferred: Deferred = async { "Hello World!" }
    val result: String = deferred.await()
    val job: Job = launch { "Hello World!" }
    @askashdavies
    

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14. Coroutine Builders
    val deferred: Deferred = async { "Hello World!" }
    val result: String = deferred.await()
    val job: Job = launch { "Hello World!" }
    job.join()
    @askashdavies
    

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15. ⚖
    Stability
    @askashdavies
    

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16. @askashdavies
    

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17. @Annotations
    (
    !
    Here be dragons)
    @askashdavies
    

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18. Annotations
    @ExperimentalCoroutinesApi //
    @askashdavies
    

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19. Annotations
    @ExperimentalCoroutinesApi //
    @FlowPreview //
    ⚠
    @askashdavies
    

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20. Annotations
    @ExperimentalCoroutinesApi //
    @FlowPreview //
    ⚠
    @ObsoleteCoroutinesApi //
    ⚠
    @askashdavies
    

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21. Annotations
    @ExperimentalCoroutinesApi //
    @FlowPreview //
    ⚠
    @ObsoleteCoroutinesApi //
    ⚠
    @InternalCoroutinesApi //
    ☠
    @askashdavies
    

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22. Annotations
    @Experimental
    @askashdavies
    

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23. !
    Coroutines
    @askashdavies
    

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24. !
    Native first-party
    library
    @askashdavies
    

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25. !
    Easy-to-use
    @askashdavies
    

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26. !
    suspend fun
    @askashdavies
    

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27. Dispatchers
    » Default
    » IO
    » Main
    » Android (Main Thread Dispatcher)
    » JavaFx (Application Thread Dispatcher)
    » Swing (Event Dispatcher Thread)
    » Unconfined
    @askashdavies
    

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28. !
    History of Android
    @askashdavies
    

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29. Background Processes
    @askashdavies
    

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30. Background Processes
    !
    Runnable / Handler
    @askashdavies
    

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31. Background Processes
    !
    AsyncTask
    @askashdavies
    

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32. Background Processes
    !
    IntentService
    @askashdavies
    

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33. Background Processes
    !
    Loader
    @askashdavies
    

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34. Background Processes
    WorkManager
    @askashdavies
    

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35. !
    @askashdavies
    

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36. xkcd.com/927/
    

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37. RxJava to the
    rescue
    @askashdavies
    

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38. ⛓
    Chained operations
    @askashdavies
    

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39. ⬆ ⬇
    Abstract threading
    @askashdavies
    

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40. !
    Reactive
    @askashdavies
    

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41. @askashdavies
    

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42. @askashdavies
    

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43. @askashdavies
    

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44. @askashdavies
    

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45. @askashdavies
    

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46. !
    Asynchronous APIs
    Synchronous APIs
    @askashdavies
    

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47. @askashdavies
    

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48. !
    Observable
    .fromIterable(resourceDraft.getResources())
    .flatMap(resourceServiceApiClient::createUploadContainer)
    .zipWith(Observable.fromIterable(resourceDraft.getResources()), Pair::create)
    .flatMap(uploadResources())
    .toList()
    .toObservable()
    .flatMapMaybe(resourceCache.getResourceCachedItem())
    .defaultIfEmpty(Resource.getDefaultItem())
    .flatMap(postResource(resourceId, resourceDraft.getText(), currentUser, resourceDraft.getIntent()))
    .observeOn(AndroidSchedulers.mainThread())
    .subscribeOn(Schedulers.io())
    .subscribe(
    resource -> repository.setResource(resourceId, resource, provisionalResourceId),
    resourceUploadError(resourceId, resourceDraft, provisionalResourceId)
    );
    @askashdavies
    

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49. Anchorman: The Legend of Ron Burgundy (DreamWorks Pictures)
    

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50. ⚙
    Hidden complexity
    @askashdavies
    

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51. !
    Hidden gotchas
    @askashdavies
    

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52. !
    Memory footprint
    @askashdavies
    

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53. ⤴
    Steep learning curve
    @askashdavies
    

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54. @askashdavies
    

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55. #RxMustDie
    pca.st/7IJG
    @askashdavies
    

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56. "If all you have is a hammer,
    everything looks like a nail"
    — Abraham Maslow, The Psychology of Science, 1966
    @askashdavies
    

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57. Coroutine Use Cases
    @askashdavies
    

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58. Network Call Handling
    // RxJava2: Single
    fun getUser(): Single = Single.fromCallable {
    /* ... */
    }
    // Coroutines: T
    suspend fun getUser(): User = /* ... */
    @askashdavies
    

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59. Cache Retrieval
    // RxJava2: Maybe
    fun getUser(): Maybe = Maybe.fromCallable {
    /* ... */
    }
    // Coroutines: T?
    suspend fun getUser(): User? = /* ... */
    @askashdavies
    

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60. Background Task Handling
    // RxJava2: Completable
    fun storeUser(user: User): Completable.fromCallable {
    /* ... */
    }
    // Coroutines: Unit
    suspend fun storeUser(user: User) { /* ... */ }
    @askashdavies
    

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61. Thread Handling
    // RxJava2
    getUser()
    .subscribeOn(Schedulers.io())
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe { /* Do something */ }
    // Coroutines
    launch(Dispatchers.Main) {
    withContext(Dispatchers.IO) {
    val user = getUser()
    /* Do something */
    }
    }
    @askashdavies
    

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62. !
    FlatMap
    // RxJava2
    getUser()
    .flatMap { doSomethingWithUser(it) }
    .subscribeOn(Schedulers.computation())
    .observeOn(AndroidSchedulers.mainThread())
    .subscribe { /* Do something else */ }
    // Coroutines
    launch(Dispatchers.Main) {
    val user = getUser()
    val smth = doSomethingWithUser(user)
    /* Do something else */
    }
    @askashdavies
    

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63. Callback Consumption
    // RxJava2
    fun getSingle(): Single = Single.create { emitter ->
    doSomethingAsync(object: Callback {
    override fun onComplete(result: T) = emitter.onSuccess(result)
    override fun onException(exception: Exception) = emitter.onError(exception)
    })
    }
    // Coroutines
    suspend fun getCoroutine() : T = suspendCoroutine { continuation ->
    doSomethingAsync(object : Callback {
    override fun onComplete(result: T) = continuation.resume(result)
    override fun onException(exception: Exception) = continuation.resumeWithException(exception)
    })
    }
    @askashdavies
    

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64. Task Cancellation
    // RxJava2
    val disposable: Disposable = Single
    .create { /* Do something */ }
    .subscribe { /* Do something else */ }
    disposable.dispose()
    // Coroutine
    val parent: Job = Job()
    launch(Dispatchers.Main + parent) { /* Do something */ }
    parent.cancelChildren()
    @askashdavies
    

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65. !
    Backpressure
    @askashdavies
    

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66. !
    Backpressure
    launch {
    channel.send("Hello")
    }
    @askashdavies
    

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67. ViewModel.viewModelScope
    androidx.lifecycle:2.1.0
    @askashdavies
    

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68. Channels
    @askashdavies
    

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69. Roman Elizarov
    Cold flows, hot
    channels
    flow {
    emit("Hello")
    emit("World")
    }
    medium.com/@elizarov/cold-flows-hot-channels-d74769805f9
    

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70. Flow
    !
    Observable.create { emitter: ObservableEmitter ->
    emitter.onNext("Hello")
    emitter.onNext("World")
    }
    @askashdavies
    

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71. Flow
    !
    flow { collector: FlowCollector ->
    collector.emit("Hello")
    collector.emit("World")
    }
    @askashdavies
    

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72. Flow
    !
    flow { emit("Hello world") }
    .onEach { delay(500) }
    .map { it.length }
    .collect { println("Length: $it") }
    @askashdavies
    

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73. Testing
    @Test
    fun testFoo() = runBlockingTest {
    val actual = foo()
    // ...
    }
    suspend fun foo() {
    delay(1_000)
    // ...
    }
    github.com/Kotlin/kotlinx.coroutines/tree/master/kotlinx-coroutines-test
    

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74. runBlockingTest
    » Auto-advancing of time
    ⏱⏩
    » Explicit time control
    #
    » Eager execution of launch or async
    » Pause, manually advance, and restart execution
    » Report uncaught exceptions as test failures
    @askashdavies
    

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75. ⚙
    RxJava: Complex Business Logic
    @askashdavies
    

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76. Asynchronicity Comparison
    Manuel Vivo (@manuelvicnt)
    medium.com/capital-one-tech/coroutines-and-rxjava-an-asynchronicity-comparison-part-1-asynchronous-programming-e726a925342a
    

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77. Is Coroutines a replacement for RxJava?
    @askashdavies
    

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78. Maybe...
    @askashdavies
    

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79. Should I migrate to Coroutines?
    @askashdavies
    

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80. Probably not...
    @askashdavies
    

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81. "If it ain't broke, don't fix it"
    — Bert Lance, Nation's Business, 1977
    @askashdavies
    

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82. © 2019 Viacom International Inc.
    

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83. Did "you" migrate to Coroutines?
    @askashdavies
    

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84. @askashdavies
    

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85. How could I migrate to Coroutines?
    @askashdavies
    

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86. !
    Migration Policy
    @askashdavies
    

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87. Retrofit Services
    @askashdavies
    

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88. Retrofit 2.6.0
    Built-in suspend support
    github.com/square/retrofit/blob/master/CHANGELOG.md#version-260-2019-06-05
    

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89. interface UserService {
    @GET("/user")
    suspend fun getUser(): User
    }
    GlobalScope.launch {
    val user = retrofit
    .create() // >= 2.5.0
    .getUser()
    }
    @askashdavies
    

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90. Coroutines RxJava2
    org.jetbrains.kotlinx:kotlinx-coroutines-rx2:+
    @askashdavies
    

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91. Name Scope Description
    rxCompletable CoroutineScope Cold completable that starts
    coroutine on subscribe
    rxMaybe CoroutineScope Cold maybe that starts coroutine
    on subscribe
    rxSingle CoroutineScope Cold single that starts coroutine
    on subscribe
    rxObservable ProducerScope Cold observable that starts
    coroutine on subscribe
    rxFlowable ProducerScope Cold observable that starts
    coroutine on subscribe with
    backpressure support
    @askashdavies
    

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92. val service: UserService = retrofit.create() // >= 2.5.0
    GlobalScope
    .rxSingle { service.getUser() }
    .observeOn(AndroidSchedulers.mainThread())
    .subscribeOn(Schedulers.io())
    .subscribe(
    { /* Do something with user */ },
    { /* Handle error ... probably */ }
    )
    @askashdavies
    

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93. Completable.await()
    GlobalScope.launch {
    Completable
    .complete()
    .await()
    }
    @askashdavies
    

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94. Maybe.await()
    GlobalScope.launch {
    val result: String? = Maybe
    .fromCallable { null as String? }
    .await()
    // result == null
    }
    @askashdavies
    

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95. Observable.await...
    val observable = Observable.just(1, 2, 3, 4)
    // Await first item
    val item = observable.awaitFirst()
    // Print each item
    observable.consumeEach(::println)
    // Consume all items
    observable
    .openSubscription()
    .consume {
    println(it.size)
    }
    kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-rx2/kotlinx.coroutines.rx2/io.reactivex.-observable-source/index.html
    

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96. Exceptions
    @askashdavies
    

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97. !
    Conclusion
    @askashdavies
    

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98. Cheers!
    !
    @askashdavies
    

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