Diving into Coroutines

Diving into Coroutines

Bangkok Mobile Days

1. Diving into coroutines for JVM Enrique López Mañas
3. Why do we want coroutines? val user = fetchUserData() textView.text = user.name NetworkOnMainThreadException
4. Why do we want coroutines? thread { val user = fetchUserData() textView.text = user.name } CalledFromAnotherThreadException
5. Why do we want coroutines? fetchUserData { user -> //callback textView.text = user.name } Leaking callbacks all the time
6. Why do we want coroutines?
7. Why do we want coroutines? val subscription = fetchUserData { user -> textView.text = user.name } override fun onStop() { subscription.cancel() }
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() }
9. Why do we want coroutines? object MyTask: AsyncTask() { override fun doInBackground { code } override fun onPostExecute { code } }
10. RxJava fun fetchUser() : Observable<User> = ... fetchUser() .as(autoDisposable(AndroidLifecycleScopeProvider.from(this))) .subscribe{ user -> textView.text = user.name }
11. LiveData fun fetchUser() : LiveData<User> = ... fetchUser().observe(viewLifecycleOwner) { textView.text = user.name }
12. LiveData RxJava Observable Data Holder Observable + Schedulers + Observers Coroutines Suspendable computations
13. LiveData Not fully complete (only supports MainThread)
14. RxJava Complete, but: - Easy to misuse - Feels like an overkill - Learning curve
15. Coroutines - Simplified - Comprehensive - Robust First class support from Google in Jetpack
16. Coroutines In a nutshell: Coroutines simplify async code by replacing callbacks
17. Coroutines blocking.kt fun loadUser() { val user = api.fetchUser() show(user) } fetchUser onDraw onDraw onDraw onDraw Show
18. Coroutines async.kt fun loadUser() { api.fetchUser { user -> show(user) } } fetchUser onDraw onDraw onDraw onDraw Show Ready!
19. Coroutines coroutines.kt suspend fun loadUser() { val user = api.fetchUser() show(user) } fetchUser onDraw onDraw onDraw onDraw Show Ready! suspend resume
20. Coroutines Suspend and resume replace callbacks
21. Coroutines suspend fun loadData(): Data fun loadData(listener: Continuation<Data>)
22. Coroutines
23. Coroutines coroutines.kt suspend fun loadUser() { val user = api.fetchUser() show(user) } async.kt fun loadUser() { api.fetchUser { user -> show(user) } }
24. Coroutines coroutines.kt suspend fun loadUser() { val user = api.fetchUser() show(user) } suspend fun fetchUser() = withContext(Dispatchers.IO) { }
25. Dispatchers .Default .IO .Main CPU Network, Disk Main Thread on Android
26. Coroutines suspend fun fetchUser() = withContext(Dispatchers.IO) { /*put your blocking calls here*/ }
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()
28. Under the hood suspend fun loadUser() { val user = api.fetchUser() show(user) } Main Thread Stack suspend resume api.fetchUser() loadUser()
29. Under the hood suspend fun loadUser() { val user = api.fetchUser() show(user) } Main Thread Stack suspend resume api.fetchUser() loadUser()
30. Summarizing… -They replace callbacks - They provide Main Thread safety
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
32. Building blocks CoroutineContext UI CommonPool Unconfined Dispatch execution into Android MainThread Dispatch execution into Android Background Dispatch execution into Current thread
33. Launch
34. Launch val uiContext: CoroutineContext = UI val bgContext: CoroutineContext = CommonPool
35. Launch private fun loadData() { view.showLoading() val result = dataProvider.provideData() view.showData(result) view.hideLoading() }
36. Launch private fun loadData() = launch(uiContext) { view.showLoading() val result = dataProvider.provideData() view.showData(result) view.hideLoading() }
37. Launch private fun loadData() = launch(uiContext) { view.showLoading() val result = withContext(bgContext) { dataProvider.provideData() } view.showData(result) view.hideLoading() }
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 $result2" // ui thread view.showData(result) view.hideLoading() }
39. Launch two tasks sequentially private fun loadData() = launch(uiContext) { view.showLoading() // ui thread // non ui thread, suspend until task is finished val result1 = withContext(bgContext) { dataProvider.provideData() } // non ui thread, suspend until task is finished val result2 = withContext(bgContext) { dataProvider.provideData() } val result = "$result1 $result2" // ui thread view.showData(result) view.hideLoading() }
40. Launch two tasks in parallel private fun loadData() = launch(uiContext) { view.showLoading() // ui thread val task1 = async(bgContext) { dataProvider.provideData() } val task2 = async(bgContext) { dataProvider.provideData() } // non ui thread, suspend until finished val result = "${task1.await()} ${task2.await()}" view.showData(result) // ui thread view.hideLoading() }
41. Launch two tasks in parallel private fun loadData() = launch(uiContext) { view.showLoading() // ui thread val task1 = async(bgContext) { dataProvider.provideData() } val task2 = async(bgContext) { dataProvider.provideData() } // non ui thread, suspend until finished val result = "${task1.await()} ${task2.await()}" view.showData(result) // ui thread view.hideLoading() }
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() }
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() }
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() }
45. Cancelation
46. Cancel a coroutine private var job: Job? = null fun onNextClicked() { job = loadData() } fun onBackClicked() { job?.cancel() } private fun loadData() = launch(uiContext) { // code }
47. Cancel a coroutine private var job: Job? = null fun onNextClicked() { job = loadData() } fun onBackClicked() { job?.cancel() } private fun loadData() = launch(uiContext) { // code }
48. Cancel a coroutine private var job: Job? = null fun onNextClicked() { job = loadData() } fun onBackClicked() { job?.cancel() } private fun loadData() = launch(uiContext) { // code }
49. More with jobs job?.isActive job?.isCancelled job?.isComplete job?.getCancellationException() job?.children job?.cancelChildren job?.invokeOnCompletion {}
50. Error Handling
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() }
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() }
53. Store inside deferred var job: Deferred = loadData() job.invokeOnCompletion { it: Throwable? -> it?.printStackTrace() }
54. Exception Handler val exceptionHandler= CoroutineExceptionHandler { _, throwable -> throwable.printStackTrace() } private fun loadData() = launch(uiContext + exceptionHandler) { // code }
55. Return null if exception suspend fun <T> Deferred<T>.awaitSafe(): T? = try { await() } catch (e: Exception) { e.printStackTrace() null }
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 } }
57. Return <T> suspend fun <T> Deferred<T>.awaitResult(): Result<T> = try { Result(success = await(), failure = null) } catch (e: Exception) { Result(success = null, failure = e) } data class Result<out T>(val success: T?, val failure: Exception?)
58. Return <T> private fun loadData() = launch(uiContext) { val task = async(bgContext) { dataProvider.provideData() } val (success, failure) = task.awaitResult() if(success != null) { // success T } else { // failure Exception } }
59. Testing
60. Testing class MainPresenter(val uiContext: CoroutineContext = UI, val bgContext: CoroutineContext = CommonPool) { fun loadData() = launch(uiContext) { ... } }
61. Testing @Test fun test() { val presenter = MainPresenter(Unconfined, Unconfined) // test presenter.loadData() // verify verify(mockView).showLoading() verify(mockDataProvider).provideData() }
62. Does this replace RxJava?
63. RxJava analogies SubscribeOn = Initial Context ObserveOn = withContext Disposable <> Jobs
64. More // retrofit 2 interface MyService { @GET("/user") fun getUser(): Deferred<User> // or @GET("/user") fun getUser(): Deferred<Response<User>> }
65. More @GET("users/{id}") suspend fun user(@Path("id") id: Long): User
66. Room @Dao interface UsersDao { @Query("SELECT * FROM users") suspend fun getUsers(): List<User> @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) }
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) }
68. Room class Repository(val database: MyDatabase) { suspend fun clearData(){ database.withTransaction { database.userDao().deleteLoggedInUser() // suspend function database.commentsDao().deleteComments() // suspend function } } }
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) }
70. Room - Testing
71. Kotlin/Native Common JVM Native iOS framework Your iOS dev Your Android Dev JS
72. Considerations in state An object belongs to one thread
73. Considerations in state Frozen objects can be shared by threads
74. Concurrency - frozen objects Everything you have written until now is not frozen
75. Considerations in state
76. Survey
77. What to do? • Greenfield project? Probably try
78. What to do? • Existing project?
 - Do they suit you? - Refactoring?
 - Time? - Small sections?
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)
80. Further resources
81. Further resources