Diving into Coroutines

Diving into Coroutines

Bangkok Mobile Days

Transcript

1. Diving into
   coroutines for JVM
   Enrique López Mañas
   

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3. Why do we want
   coroutines?
   val user = fetchUserData()
   textView.text = user.name NetworkOnMainThreadException
   

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4. Why do we want
   coroutines?
   thread {
   val user = fetchUserData()
   textView.text = user.name
   }
   CalledFromAnotherThreadException
   

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5. Why do we want
   coroutines?
   fetchUserData { user -> //callback
   textView.text = user.name
   }
   Leaking callbacks all the time
   

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6. Why do we want
   coroutines?
   

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7. Why do we want
   coroutines?
   val subscription = fetchUserData { user ->
   textView.text = user.name
   }
   override fun onStop() {
   subscription.cancel()
   }
   

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8. Why do we want
   coroutines?
   override fun onStop() {
   subscription.cancel()
   subscription1.cancel()
   subscription2.cancel()
   subscription3.cancel()
   subscription4.cancel()
   subscription5.cancel()
   subscription6.cancel()
   subscription7.cancel()
   subscription8.cancel()
   subscription9.cancel()
   }
   

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9. Why do we want
   coroutines?
   object MyTask: AsyncTask() {
   override fun doInBackground { code }
   override fun onPostExecute { code }
   }
   

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10. RxJava
    fun fetchUser() : Observable = ...
    fetchUser()
    .as(autoDisposable(AndroidLifecycleScopeProvider.from(this)))
    .subscribe{ user ->
    textView.text = user.name
    }
    

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11. LiveData
    fun fetchUser() : LiveData = ...
    fetchUser().observe(viewLifecycleOwner) {
    textView.text = user.name
    }
    

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12. LiveData RxJava
    Observable Data Holder
    Observable +
    Schedulers +
    Observers
    Coroutines
    Suspendable computations
    

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13. LiveData
    Not fully complete (only supports MainThread)
    

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14. RxJava
    Complete, but:
    
    - Easy to misuse
    
    - Feels like an overkill
    
    - Learning curve
    

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15. Coroutines
    - Simplified
    
    - Comprehensive
    
    - Robust
    
    First class support from Google in Jetpack
    

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16. Coroutines
    In a nutshell:
    
    Coroutines simplify async code by replacing callbacks
    
    

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17. Coroutines
    blocking.kt
    fun loadUser() {
    val user = api.fetchUser()
    show(user)
    }
    fetchUser
    onDraw
    onDraw
    onDraw
    onDraw
    Show
    

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18. Coroutines
    async.kt
    fun loadUser() {
    api.fetchUser { user ->
    show(user)
    }
    }
    fetchUser
    onDraw
    onDraw
    onDraw
    onDraw
    Show
    Ready!
    

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19. Coroutines
    coroutines.kt
    suspend fun loadUser() {
    val user = api.fetchUser()
    show(user)
    }
    fetchUser
    onDraw
    onDraw
    onDraw
    onDraw
    Show
    Ready!
    suspend
    resume
    

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20. Coroutines
    Suspend and resume replace callbacks
    

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21. Coroutines
    suspend fun loadData(): Data
    fun loadData(listener: Continuation)
    

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22. Coroutines
    

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23. Coroutines
    coroutines.kt
    suspend fun loadUser() {
    val user = api.fetchUser()
    show(user)
    }
    async.kt
    fun loadUser() {
    api.fetchUser { user ->
    show(user)
    }
    }
    

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24. Coroutines
    coroutines.kt
    suspend fun loadUser() {
    val user = api.fetchUser()
    show(user)
    }
    suspend fun fetchUser() =
    withContext(Dispatchers.IO) {
    }
    

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25. Dispatchers
    .Default
    
    .IO
    
    .Main
    
    CPU
    Network, Disk
    Main Thread on Android
    

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26. Coroutines
    suspend fun fetchUser() =
    withContext(Dispatchers.IO) {
    /*put your blocking calls here*/
    }
    

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27. Under the hood
    suspend fun loadUser() {
    val user = api.fetchUser()
    show(user)
    }
    Main Thread Stack
    >
    Suspend marker
    Everything above a coroutine
    Everything underneath a regular function
    loadUser()
    api.fetchUser()
    

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28. Under the hood
    suspend fun loadUser() {
    val user = api.fetchUser()
    show(user)
    }
    Main Thread Stack
    suspend
    resume
    api.fetchUser()
    loadUser()
    

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29. Under the hood
    suspend fun loadUser() {
    val user = api.fetchUser()
    show(user)
    }
    Main Thread Stack
    suspend
    resume
    api.fetchUser()
    loadUser()
    

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30. Summarizing…
    -They replace callbacks
    
    - They provide Main Thread safety
    

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31. Building blocks
    withContext() launch() async()
    T Job Deferred
    Returns result Fire and forget Returns non-blocking
    
    future
    Uncaught exception
    
    Crashes app
    
    Uncaught exception
    
    Crashes app
    
    Uncaught exception is
    
    returned in deferred
    
    

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32. Building blocks
    CoroutineContext
    UI CommonPool Unconfined
    Dispatch execution into
    
    Android MainThread
    Dispatch execution into
    
    Android Background
    Dispatch execution into
    
    Current thread
    

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33. Launch
    

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34. Launch
    val uiContext: CoroutineContext = UI
    val bgContext: CoroutineContext = CommonPool
    

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35. Launch
    private fun loadData() {
    view.showLoading()
    val result = dataProvider.provideData()
    view.showData(result)
    view.hideLoading()
    }
    

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36. Launch
    private fun loadData() = launch(uiContext) {
    view.showLoading()
    val result = dataProvider.provideData()
    view.showData(result)
    view.hideLoading()
    }
    

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37. Launch
    private fun loadData() = launch(uiContext) {
    view.showLoading()
    val result = withContext(bgContext) { dataProvider.provideData() }
    view.showData(result)
    view.hideLoading()
    }
    

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38. Launch two tasks
    sequentially
    private fun loadData() = launch(uiContext) {
    view.showLoading() // ui thread
    // non ui thread, suspend until task is finished
    val result1 = withContext(bgContext) { dataProvider.provideData() }
    // non ui thread, suspend until task is finished
    val result2 = withContext(bgContext) { dataProvider.provideData() }
    val result = "$result1 $result2" // ui thread
    view.showData(result)
    view.hideLoading()
    }
    

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39. Launch two tasks
    sequentially
    private fun loadData() = launch(uiContext) {
    view.showLoading() // ui thread
    // non ui thread, suspend until task is finished
    val result1 = withContext(bgContext) { dataProvider.provideData() }
    // non ui thread, suspend until task is finished
    val result2 = withContext(bgContext) { dataProvider.provideData() }
    val result = "$result1 $result2" // ui thread
    view.showData(result)
    view.hideLoading()
    }
    

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40. Launch two tasks in parallel
    private fun loadData() = launch(uiContext) {
    view.showLoading() // ui thread
    val task1 = async(bgContext) { dataProvider.provideData() }
    val task2 = async(bgContext) { dataProvider.provideData() }
    // non ui thread, suspend until finished
    val result = "${task1.await()} ${task2.await()}"
    view.showData(result) // ui thread
    view.hideLoading()
    }
    

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41. Launch two tasks in parallel
    private fun loadData() = launch(uiContext) {
    view.showLoading() // ui thread
    val task1 = async(bgContext) { dataProvider.provideData() }
    val task2 = async(bgContext) { dataProvider.provideData() }
    // non ui thread, suspend until finished
    val result = "${task1.await()} ${task2.await()}"
    view.showData(result) // ui thread
    view.hideLoading()
    }
    

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42. Launch two tasks in parallel
    private fun loadData() = launch(uiContext) {
    view.showLoading() // ui thread
    val deferred = listOf(
    async(bgContext) { dataProvider.provideData() }
    async(bgContext) { dataProvider.provideData() }
    )
    deferred.awaitAll()
    }
    

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43. Launch coroutine with
    timeout
    private fun loadData() = launch(uiContext) {
    view.showLoading() // ui thread
    // non ui thread, suspend until the task is finished
    // or return null in 2 sec
    val result = withTimeoutOrNull(2, TimeUnit.SECONDS) {
    withContext(bgContext) { dataProvider.provideData() }
    }
    view.showData(result) // ui thread
    view.hideLoading()
    }
    

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44. Launch coroutine with
    timeout
    private fun loadData() = launch(uiContext) {
    view.showLoading() // ui thread
    // non ui thread, suspend until the task is finished
    // or return null in 2 sec
    val result = withTimeoutOrNull(2, TimeUnit.SECONDS) {
    withContext(bgContext) { dataProvider.provideData() }
    }
    view.showData(result) // ui thread
    view.hideLoading()
    }
    

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45. Cancelation
    

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46. Cancel a coroutine
    private var job: Job? = null
    fun onNextClicked() {
    job = loadData()
    }
    fun onBackClicked() {
    job?.cancel()
    }
    private fun loadData() = launch(uiContext) {
    // code
    }
    

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47. Cancel a coroutine
    private var job: Job? = null
    fun onNextClicked() {
    job = loadData()
    }
    fun onBackClicked() {
    job?.cancel()
    }
    private fun loadData() = launch(uiContext) {
    // code
    }
    

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48. Cancel a coroutine
    private var job: Job? = null
    fun onNextClicked() {
    job = loadData()
    }
    fun onBackClicked() {
    job?.cancel()
    }
    private fun loadData() = launch(uiContext) {
    // code
    }
    

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49. More with jobs
    job?.isActive
    job?.isCancelled
    job?.isComplete
    job?.getCancellationException()
    job?.children
    job?.cancelChildren
    job?.invokeOnCompletion {}
    

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50. Error Handling
    

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51. Try-catch
    private fun loadData() = launch(uiContext) {
    view.showLoading() // ui thread
    try {
    val result = withContext(bgContext) { dataProvider.provideData() }
    view.showData(result) // ui thread
    } catch (e: IllegalArgumentException) {
    e.printStackTrace()
    }
    view.hideLoading()
    }
    

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52. Store inside deferred
    private fun loadData() = async(uiContext) {
    view.showLoading() // ui thread
    val task = async(bgContext) { dataProvider.provideData() }
    val result = task.await() // non ui thread
    view.showData(result) // ui thread
    view.hideLoading()
    }
    

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53. Store inside deferred
    var job: Deferred = loadData()
    job.invokeOnCompletion { it: Throwable? ->
    it?.printStackTrace()
    }
    

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54. Exception Handler
    val exceptionHandler= CoroutineExceptionHandler { _, throwable ->
    throwable.printStackTrace()
    }
    private fun loadData() = launch(uiContext + exceptionHandler) {
    // code
    }
    

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55. Return null if exception
    suspend fun Deferred.awaitSafe(): T? = try {
    await()
    } catch (e: Exception) {
    e.printStackTrace()
    null
    }
    

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56. Return null if exception
    private fun loadData() = launch(uiContext) {
    val task = async(bgContext) { dataProvider.provideData() }
    val result = task.awaitSafe()
    if(result != null) {
    // success
    } else {
    // failure
    }
    }
    

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57. Return
    suspend fun Deferred.awaitResult(): Result = try {
    Result(success = await(), failure = null)
    } catch (e: Exception) {
    Result(success = null, failure = e)
    }
    data class Result(val success: T?, val failure: Exception?)
    

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58. Return
    private fun loadData() = launch(uiContext) {
    val task = async(bgContext) { dataProvider.provideData() }
    val (success, failure) = task.awaitResult()
    if(success != null) {
    // success T
    } else {
    // failure Exception
    }
    }
    

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59. Testing
    

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60. Testing
    class MainPresenter(val uiContext: CoroutineContext = UI,
    val bgContext: CoroutineContext = CommonPool) {
    fun loadData() = launch(uiContext) { ... }
    }
    

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61. Testing
    @Test
    fun test() {
    val presenter = MainPresenter(Unconfined, Unconfined)
    // test
    presenter.loadData()
    // verify
    verify(mockView).showLoading()
    verify(mockDataProvider).provideData()
    }
    

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62. Does this replace RxJava?
    

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63. RxJava analogies
    SubscribeOn = Initial Context
    ObserveOn = withContext
    Disposable <> Jobs
    

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64. More
    // retrofit 2
    interface MyService {
    @GET("/user")
    fun getUser(): Deferred
    // or
    @GET("/user")
    fun getUser(): Deferred>
    }
    

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65. More
    @GET("users/{id}")
    suspend fun user(@Path("id") id: Long): User
    

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66. Room
    @Dao
    interface UsersDao {
    @Query("SELECT * FROM users")
    suspend fun getUsers(): List
    @Query("UPDATE users SET age = age + 1 WHERE userId = :userId")
    suspend fun incrementUserAge(userId: String)
    @Insert
    suspend fun insertUser(user: User)
    @Update
    suspend fun updateUser(user: User)
    @Delete
    suspend fun deleteUser(user: User)
    }
    

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67. Room
    @Dao
    abstract class UsersDao {
    @Transaction
    open suspend fun setLoggedInUser(loggedInUser: User) {
    deleteUser(loggedInUser)
    insertUser(loggedInUser)
    }
    @Query("DELETE FROM users")
    abstract fun deleteUser(user: User)
    @Insert
    abstract suspend fun insertUser(user: User)
    }
    

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68. Room
    class Repository(val database: MyDatabase) {
    suspend fun clearData(){
    database.withTransaction {
    database.userDao().deleteLoggedInUser() // suspend function
    database.commentsDao().deleteComments() // suspend function
    }
    }
    }
    

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69. Room - Testing
    @Test fun insertAndGetUser() = runBlocking {
    // Given a User that has been inserted into the DB
    userDao.insertUser(user)
    // When getting the Users via the DAO
    val usersFromDb = userDao.getUsers()
    // Then the retrieved Users matches the original user object
    assertEquals(listOf(user), userFromDb)
    }
    

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70. Room - Testing
    

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71. Kotlin/Native
    Common
    JVM Native
    iOS
    framework
    Your iOS dev
    Your
    Android Dev
    JS
    

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72. Considerations in state
    An object belongs to one thread
    

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73. Considerations in state
    Frozen objects can be shared by threads
    

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74. Concurrency - frozen objects
    Everything you have written until now is not
    frozen
    

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75. Considerations in state
    

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76. Survey
    

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77. What to do?
    • Greenfield project? Probably try
    
    

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78. What to do?
    • Existing project?

    - Do they suit you?
    
    - Refactoring?

    - Time?
    
    - Small sections?
    
    

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79. Further resources
    Kotlin Slack (kotlinlang.slack.com)
    Kotlin Weekly (http://kotlinweekly.net)
    Coroutines (https://github.com/Kotlin/kotlinx.coroutines)
    Coroutines Guide (https://kotlinlang.org/docs/reference/coroutines/coroutines-guide.html)
    Codelabs (https://codelabs.developers.google.com/codelabs/kotlin-coroutines/#0)
    

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80. Further resources
    

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81. Further resources
    

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