Kotlin Coroutines: Let it async in • Bapusaheb Patil • BlrKotlin's 9th Meetup

This is the presentation to my talk, titled 'Kotlin Coroutines: Let it async in' in BlrKotlin's 9th Meetup.
October 27th, 2018.

Transcript

1. Kotlin Coroutines: Let it async in Bapusaheb Patil Google Certified Android Developer, IDF Certified UX Designer www.bapspatil.com
2. bapspatil.com Where I work...
3. bapspatil.com boolean isCodelab = false;
4. bapspatil.com boolean isCodelab = false; val isCodelab = false
5. bapspatil.com Who this talk is for… • Kotlin basics • Asynchronous programming basics • Anyone who can handle lame jokes & memes
6. bapspatil.com
7. bapspatil.com What are Coroutines? • Light-weight threads • Asynchronous • Non-blocking code
8. bapspatil.com Why Coroutines?
9. bapspatil.com Let’s talk about refresh rates...
10. bapspatil.com Most phones 60Hz 16ms ASUS ROG 90Hz 12ms Razer, Razer 2 120Hz 8ms
11. bapspatil.com • XML parsing • View inflation • View measurement • View positioning Your app on the Main Thread
12. bapspatil.com
13. bapspatil.com How do we do that?
14. bapspatil.com AsyncTask class MyTask: AsyncTask<URL, Void, String>() { override fun doInBackground(vararg params: URL?): String? { ...... } override fun onPostExecute(result: String?) { super.onPostExecute(result) ...... } }
15. bapspatil.com Loader class MyLoader(context: Context, private val url: URL) : AsyncTaskLoader<String>(context) { override fun onStartLoading() { forceLoad() } override fun loadInBackground(): String? { ......... } }
16. bapspatil.com Thread Thread(Runnable() { override fun run() { ...... } }).start()
17. bapspatil.com CompletableFuture var completableFuture = CompletableFuture.supplyAsync(object:Supplier<String>() { fun get():String { try { doLongTask() } catch (e:InterruptedException) { throw IllegalStateException(e) } return "Result of the asynchronous computation" } }) val result = completableFuture.get() minSdk >= 24
18. bapspatil.com IntentService class MyService : IntentService() { override fun onHandleIntent(Intent intent) { ...... } } <service android:name=”.MyService” android:exported=false />
19. bapspatil.com • JobScheduler • Firebase JobDispatcher • android-job by Evernote
20. bapspatil.com RxJava2 myDisposable.add(myApiService .getMyObservable() .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribe( { result -> updateUIWithResult(result) },{ throwable -> showError() }))
21. bapspatil.com Enter, Coroutines.
22. bapspatil.com Why Coroutines? • Light-weight • No context-switching • Faster than a Thread • Use your cores
23. bapspatil.com How do we use Coroutines?
24. bapspatil.com Experimental Coroutines Stable Coroutines
25. bapspatil.com If you’ve been using Coroutines so far...
26. bapspatil.com Experimental Coroutines
27. bapspatil.com
28. bapspatil.com How to use stable Coroutines...
29. bapspatil.com
30. bapspatil.com
31. bapspatil.com
32. bapspatil.com
33. bapspatil.com
34. Launching your first Coroutine... bapspatil.com
35. Blocking Functions vs. Suspending Functions bapspatil.com
36. Blocking Function bapspatil.com fun A() fun B()
37. Suspending Function bapspatil.com fun A() fun B() suspended
38. Suspending Function bapspatil.com
39. suspend fun doLongTask(): Unit? { ...... } fun doLongTask(): Unit? { ...... } Suspending function bapspatil.com
40. Coroutine Builders • launch Returns Job • async Returns Deferred bapspatil.com
41. launch { doLongTask() } Job // Fire and forget! bapspatil.com
42. val job = launch { doLongTask() } job.join() If you need to suspend the coroutine job.cancel() Job bapspatil.com
43. bapspatil.com
44. async { doLongTask() } suspend fun doLongTask(): String? { ...... return resultString } // Return something in the future Deferred<String> bapspatil.com
45. val deferred = async { doLongTask() } val result = deferred.await() deferred.cancel() Deferred<String> bapspatil.com
46. launch { val result = async { doLongTask() }.await() } bapspatil.com
47. launch { val result = withContext(IO) { doLongTask() } } bapspatil.com
48. Let’s convert sync to async... bapspatil.com
49. suspend fun fetchMovieData() { val popularMovies = apiService.getMoviesByType(“POPULAR”) val topRatedMovies = apiService.getMoviesByType(“TOP_RATED”) val upcomingMovies = apiService.getMoviesByType(“UPCOMING”) val nowPlayingMovies = apiService.getMoviesByType(“NOW_PLAYING”) val allMovies = mergeAllMovies(popularMovies, topRatedMovies, upcomingMovies, nowPlayingMovies) database.saveToDb(allMovies) } Takes 4.8 seconds bapspatil.com
50. suspend fun fetchMovieData() { val popularDeferred = async { apiService.getMoviesByType(“POPULAR”) } val topRatedDeferred = async { apiService.getMoviesByType(“TOP_RATED”) } val upcomingDeferred = async { apiService.getMoviesByType(“UPCOMING”) } val nowPlayingDeferred = async { apiService.getMoviesByType(“NOW_PLAYING”) } val popularMovies = popularDeferred.await() val topRatedMovies = topRatedDeferred.await() val upcomingMovies = upcomingDeferred.await() val nowPlayingMovies = nowPlayingDeferred.await() val allMovies = mergeAllMovies(popularMovies, topRatedMovies, upcomingMovies, nowPlayingMovies) database.saveToDb(allMovies) } bapspatil.com
51. suspend fun fetchMovieData() { val popularDeferred = async { apiService.getMoviesByType(“POPULAR”) } val topRatedDeferred = async { apiService.getMoviesByType(“TOP_RATED”) } val upcomingDeferred = async { apiService.getMoviesByType(“UPCOMING”) } val nowPlayingDeferred = async { apiService.getMoviesByType(“NOW_PLAYING”) } val allMovies = mergeAllMovies(popularDeferred.await(), topRatedDeferred.await(), upcomingDeferred.await(), nowPlayingDeferred.await()) database.saveToDb(allMovies) } Takes 2.6 seconds bapspatil.com
52. suspend fun fetchMovieData() { val popularDeferred = async { apiService.getMoviesByType(“POPULAR”) } val topRatedDeferred = async { apiService.getMoviesByType(“TOP_RATED”) } val upcomingDeferred = async { apiService.getMoviesByType(“UPCOMING”) } val nowPlayingDeferred = async { apiService.getMoviesByType(“NOW_PLAYING”) } val allMovies = mergeAllMovies(popularDeferred.await(), topRatedDeferred.await(), upcomingDeferred.await(), nowPlayingDeferred.await()) database.saveToDb(allMovies) // Update the UI from the suspending function runOnUiThread { updateUI(allMovies) } } Updating the UI... bapspatil.com
53. Launching a Coroutine from another Coroutine... bapspatil.com
54. launch { doSomeWork() launch { val result = async { getSomeResult() } doMoreWork(result.await()) } launch { doEvenMoreWork() } } bapspatil.com
55. Coroutines in an Activity... bapspatil.com
56. class MyActivity : AppCompatActivity() { private val compositeDisposable = CompositeDisposable() override fun onCreate() { // ... compositeDisposable.add(getFirstObservable()) compositeDisposable.add(getSecondObservable()) } override fun onDestroy() { super.onDestroy() compositeDisposable.clear() } } bapspatil.com
57. class MyActivity : AppCompatActivity() { private var firstJob: Job? = null private var secondJob: Job? = null override fun onCreate() { // ... firstJob = launch { doSomeWork() } secondJob = launch { doSomeMoreWork() } } override fun onDestroy() { super.onDestroy() firstJob.cancel() secondJob.cancel() } } bapspatil.com
58. bapspatil.com
59. RxJava2 → CompositeDisposable Coroutines → Job bapspatil.com
60. class MyActivity : AppCompatActivity() { lateinit var activityJob: Job override fun onCreate() { activityJob = Job() val outerJob = launch(parent = activityJob) { val firstJob = launch { doSomeWork() } val secondJob = launch { doSomeMoreWork() } } } override fun onDestroy() { super.onDestroy() activityJob.cancel() } } bapspatil.com
61. val outerJob = launch(parent = activityJob) { val firstJob = launch { doSomeWork() } val secondJob = launch { doSomeMoreWork() } } • outerJob gets canceled. • firstJob & secondJob do not! bapspatil.com
62. val outerJob = launch(parent = activityJob) { val firstJob = launch { doSomeWork() } val secondJob = launch { doSomeMoreWork() } } bapspatil.com
63. val outerJob = launch(parent = activityJob) { val firstJob = launch(parent = activityJob) { doSomeWork() } val secondJob = launch(parent = activityJob) { doSomeMoreWork() } } bapspatil.com
64. launch(parent = activityJob) Restricts the scope of the coroutine to Activity’s lifecycle, but not its child coroutines. bapspatil.com
65. Deprecated launch(parent = activityJob) Restricts the scope of the coroutine to Activity’s lifecycle, but not its child coroutines. Coroutines 0.26+ → Forget it. bapspatil.com
66. Job CoroutineScope bapspatil.com
67. CoroutineScope & CoroutineContext bapspatil.com • Activities • Fragments • ViewModels
68. bapspatil.com
69. class MyActivity : AppCompatActivity(), CoroutineScope { lateinit var activityJob: Job override val coroutineContext: CoroutineContext get() = activityJob + Dispatchers.Main override fun onCreate() { // ... activityJob = Job() val outerJob = this.launch(context = coroutineContext) { val firstJob = launch { doSomeWork() } val secondJob = launch { doSomeMoreWork() } } } override fun onDestroy() { super.onDestroy() activityJob.cancel() } } bapspatil.com
70. launch(context = coroutineContext) • Restricts the scope of the coroutine to Activity’s lifecycle. • Cancels all nested coroutines if parent coroutine is canceled. bapspatil.com
71. fun CoroutineScope.launch( context: CoroutineContext = EmptyCoroutineContext, start: CoroutineStart = CoroutineStart.DEFAULT, block: suspend CoroutineScope.() -> Unit ): Job (source) bapspatil.com
72. CoroutineStart bapspatil.com • DEFAULT • LAZY • ATOMIC • UNDISPATCHED
73. What’s a Coroutine Dispatcher? bapspatil.com
74. CoroutineDispatcher 2+ 64+ Android Main Thread bapspatil.com • Dispatchers.Default • Dispatchers.IO • Dispatchers.Main • Dispatchers.Unconfined
75. val result = withContext(IO) { doLongTask() } bapspatil.com
76. override val coroutineContext: CoroutineContext get() = activityJob + Dispatchers.Main bapspatil.com
77. bapspatil.com Coroutines over RxJava2...
78. bapspatil.com suspend fun getFullMovieData(id: Int): Single<FullMovieData> { val movieData = moviesRepo.getMovieData(id).subscribeOn(Schedulers.io) val castData = moviesRepo.getCastData(id).subscribeOn(Schedulers.io) return Single.zip(movieData, castData, BiFunction { movieData, castData -> FullMovieData(movieData, castData) }) }
79. bapspatil.com suspend fun getFullMovieData(id: Int): FullMovieData { id.let { val movieData = async { moviesRepo.getMovieData(it) } val castData = async { moviesRepo.getCastData(it) } return FullMovieData(movieData.await(), castData.await()) } return FullMovieData() }
80. bapspatil.com suspend fun getMovieTitle(query: String?): Single<String> { return moviesRepo.searchForMovies(query).map { movieResults -> if(movieResults.isNotEmpty() && movieResults[0].title != null) { movieResults[0].title } else { errorString } } }
81. bapspatil.com suspend fun getMovieTitle(query: String?): String? { query?.let { val movieResults = withContext(IO) { moviesRepo.searchForMovies(it) } val movieTitle = movieResults?.getOrNull(0)?.title return movieTitle ?: errorString } return “” }
82. bapspatil.com
83. bapspatil.com Easy threading
84. bapspatil.com subscribeOn observeOn
85. bapspatil.com subscribeOn observeOn CoroutineDispatchers Coroutine Builders
86. bapspatil.com kotlinx-coroutines-rx2
87. bapspatil.com rxSingle Single rxCompletable Completable rxMaybe Maybe rxObservable Observable rxFlowable Flowable
88. bapspatil.com Retrofit
89. bapspatil.com fun getPopularMovies(): Single<List<Movie>>
90. bapspatil.com fun getPopularMovies(): Single<List<Movie>> suspend fun getPopularMovies(): List<Movie> Coming soon!
91. bapspatil.com Coroutines + Retrofit
92. bapspatil.com Where do I learn Coroutines?
93. bapspatil.com codelabs.developers.google.com/codelabs/kotlin-coroutines
94. bapspatil.com kotlinexpertise.com
95. bapspatil.com kotlinlang.org/docs/reference/coroutines-overview.html
96. bapspatil.com kotlin.github.io/kotlinx.coroutines
97. bapspatil.com android.jlelse.eu proandroiddev.com
98. bapspatil.com
99. bapspatil.com
100. Thank you. linkedin.com/in/bapspatil medium.com/@bapspatil instagram.com/bapspatil twitter.com/baps_patil (couldn’t get @bapspatil for this one! ☹) Bapusaheb Patil Google Certified Android Developer • IDF Certified UX Designer www.bapspatil.com