Coroutine-first Android Architecture

Coroutines allow us to write asynchronous code in an easy-to-read, declarative style. The structured concurrency pattern allows us to write this code without fear of leaks. But there’s much more to the coroutines API than suspend modifiers and CoroutineScopes, and with these new abilities should come new patterns.

In this talk, we’ll discuss the power behind structured concurrency and how we can use it to make our entire stack lifecycle-aware. We’ll see how we can use the tools coroutines give us to inform our application architecture, so that we can quickly write maintainable and testable features at a large scale.

Transcript

1. rbusarow COROUTINE-FIRST ANDROID ARCHITECTURE Rick Busarow Photo by Flipboard on Unsplash
2. ARCHITECTURE
3. ARCHITECTURE COMPONENTS
4. LiveData
5. class SomeViewModel(private val repository: SomeRepository) { private val _liveData = MutableLiveData<String>() val liveData: LiveData<String> = _liveData }
6. class SomeViewModel(private val repository: SomeRepository) { private val _liveData = MutableLiveData<String>().apply { value = repository.getTheWindsOfWinter() } val liveData: LiveData<String> = _liveData }
7. class SomeScreen : LifecycleOwner { val viewModel: SomeViewModel by lazy { … } fun onCreate() { viewModel.liveData.observe(this, Observer { str !-> tvSomeTextView.text = str }) } }
8. class SomeRepository(val api: Api) { fun getTheWindsOfWinter(): String { Thread.sleep(LONG_TIME) return api.getTwow() } }
9. class SomeRepository(val api: Api) { fun getTheWindsOfWinter(): LiveData<String> { return MutableLiveData<String>().apply { Thread.sleep(LONG_TIME) value = api.getTwow() } } }
10. class SomeViewModel(private val repository: SomeRepository) { private val _liveData = MutableLiveData<String>().apply { value = repository.getTheWindsOfWinter() } val liveData: LiveData<String> = _liveData }
11. class SomeViewModel(private val repository: SomeRepository) { val liveData: LiveData<String> = repository.getTheWindsOfWinter() }
12. class SomeRepository(val api: Api) { fun getTheWindsOfWinter(): LiveData<String> { return MutableLiveData<String>().apply { Thread.sleep(LONG_TIME) value = api.getTwow() } } }
13. class SomeRepository(val api: Api) { fun getTheWindsOfWinter(): LiveData<String> { return MutableLiveData<String>().apply { api.getTwow { value = it } } } }
14. class SomeRepository(val api: Api) { fun getTheWindsOfWinter(): LiveData<String> { return MutableLiveData<String>().apply { api.getTwow { value = it } } } }
15. class SomeRepository(val api: Api) { fun getTheWindsOfWinter(): LiveData<String> { return MutableLiveData<String>().apply { api.getTwow { postValue(it) } } } }
16. class SomeViewModel(private val repository: SomeRepository) { val liveData: LiveData<String> = repository.getTheWindsOfWinter() }
17. class SomeViewModel(private val repository: SomeRepository) { val liveData: LiveData<List<String!>> = Transformations.map(repository.getTheWindsOfWinter()) { novel !-> novel!!!.split("half a hundred") } }
18. class SomeViewModel(private val repository: SomeRepository) { val liveData: LiveData<List<String!>> = Transformations.map(repository.getTheWindsOfWinter()) { novel !-> novel!!!.split("half a hundred") } }
19. class SomeViewModel( private val repository: SomeRepository, private val coroutineScope: CoroutineScope ) { private val _liveData = MutableLiveData<List<String!>>() val liveData: LiveData<List<String!>> = _liveData val transform: LiveData<Unit> = Transformations.map(repository.getTheWindsOfWinter()) { novel !-> coroutineScope.launch { _liveData.postValue(novel!!!.split("half a hundred”)) } } }
20. class SomeViewModel( private val repository: SomeRepository, private val coroutineScope: CoroutineScope ) { private val _liveData = MutableLiveData<List<String!>>() val liveData: LiveData<List<String!>> = _liveData val transform: LiveData<Unit> = Transformations.map(repository.getTheWindsOfWinter()) { novel !-> coroutineScope.launch { _liveData.postValue(novel!!!.split("half a hundred”)) } } }
21. class SomeScreen : LifecycleOwner { val viewModel: SomeViewModel by lazy { … } fun onCreate() { viewModel.liveData.observe(this, Observer { str !-> tvSomeTextView.text = str }) } }
22. class SomeScreen : LifecycleOwner { val viewModel: SomeViewModel by lazy { … } fun onCreate() { viewModel.transform.observe(this, Observer { }) viewModel.liveData.observe(this, Observer { str !-> tvSomeTextView.text = str }) } }
23. class SomeViewModel( private val repository: SomeRepository, private val coroutineScope: CoroutineScope ) { val liveData: LiveData<List<String!>> = Transformations.switchMap( repository.getTheWindsOfWinter() ) { full !-> liveData(Default) { val split = full.split("half a hundred") emit(split) } } } lifecycle-livedata-ktx:2.2.0-alpha02
24. class SomeViewModel( private val repository: SomeRepository, private val coroutineScope: CoroutineScope ) { val liveData: LiveData<List<String!>> = Transformations.switchMap( repository.getTheWindsOfWinter() ) { full !-> liveData(Default) { val split = full.split("half a hundred") emit(split) } } } lifecycle-livedata-ktx:2.2.0-alpha02
25. class SomeViewModel( private val repository: SomeRepository, private val coroutineScope: CoroutineScope ) { val liveData: LiveData<List<String!>> = Transformations.switchMap( repository.getTheWindsOfWinter() ) { full !-> liveData(Default) { val split = full.split("half a hundred") emit(split) } } } lifecycle-livedata-ktx:2.2.0-alpha02
26. class SomeViewModel( private val repository: SomeRepository, private val coroutineScope: CoroutineScope ) { val liveData: LiveData<List<String!>> = repository.getTheWindsOfWinter().switchMap { full !-> liveData(Default) { val split = full.split("half a hundred") emit(split) } } } lifecycle-livedata-ktx:2.2.0-alpha02
27. LiveData
28. LiveData ‣ Always tied to the main thread ‣ Requires LifecycleOwner ‣ Observer-heavy ‣ Written by George R. R. Martin
29. Coroutines
30. CoroutineScope
31. interface CoroutineScope { val coroutineContext: CoroutineContext }
32. CoroutineScope 
 provides
 CoroutineContext
33. fun CoroutineScope.launch( context: CoroutineContext = EmptyCoroutineContext, start: CoroutineStart = CoroutineStart.DEFAULT, block: suspend CoroutineScope.() !-> Unit ): Job { val newContext = newCoroutineContext(context) val coroutine = if (start.isLazy) LazyStandaloneCoroutine(newContext, block) else StandaloneCoroutine(newContext, active = true) coroutine.start(start, coroutine, block) return coroutine }
34. fun CoroutineScope.launch( context: CoroutineContext = EmptyCoroutineContext, start: CoroutineStart = CoroutineStart.DEFAULT, block: suspend CoroutineScope.() !-> Unit ): Job { val newContext = newCoroutineContext(context) val coroutine = if (start.isLazy) LazyStandaloneCoroutine(newContext, block) else StandaloneCoroutine(newContext, active = true) coroutine.start(start, coroutine, block) return coroutine }
35. fun CoroutineScope.newCoroutineContext( context: CoroutineContext ): CoroutineContext { val combined = coroutineContext + context val debug = if (DEBUG) combined + CoroutineId(COROUTINE_ID.incrementAndGet()) else combined return if ( combined !!!== Dispatchers.Default !&& combined[ContinuationInterceptor] !== null ) debug + Dispatchers.Default else debug }
36. fun CoroutineScope.newCoroutineContext( context: CoroutineContext ): CoroutineContext { val combined = coroutineContext + context val debug = if (DEBUG) combined + CoroutineId(COROUTINE_ID.incrementAndGet()) else combined return if ( combined !!!== Dispatchers.Default !&& combined[ContinuationInterceptor] !== null ) debug + Dispatchers.Default else debug }
37. suspend builders derive CoroutineContext
38. suspend fun <T> withContext( context: CoroutineContext, block: suspend CoroutineScope.() !-> T ): T = suspendCoroutineUninterceptedOrReturn sc@ { continuation !-> val oldContext = continuation.context … }
39. suspend fun <T> withContext( context: CoroutineContext, block: suspend CoroutineScope.() !-> T ): T = suspendCoroutineUninterceptedOrReturn sc@ { continuation !-> val oldContext = continuation.context … }
40. CoroutineScope is just a CoroutineContext Provider
41. CoroutineScope CoroutineContext
42. CoroutineScope CoroutineContext
43. CoroutineScope CoroutineContext interface CoroutineContext { val job: Job val continuationInterceptor: ContinuationInterceptor val coroutineExceptionHandler: CoroutineExceptionHandler val coroutineName: CoroutineName }
44. CoroutineScope CoroutineContext interface CoroutineContext { val job: Job val continuationInterceptor: ContinuationInterceptor val coroutineExceptionHandler: CoroutineExceptionHandler val coroutineName: CoroutineName }
45. CoroutineScope CoroutineContext Job
46. Job Structured Concurrency
47. class SomeClass : CoroutineScope { val A = Job() override val coroutineContext = A fun someFunction() { val B = launch { val D = launch {} val E = launch {} } val C = launch { val F = launch {} } } }
48. class SomeClass : CoroutineScope { val A = Job() override val coroutineContext = A fun someFunction() { val B = launch { val D = launch {} val E = launch {} } val C = launch { val F = launch {} } } }
49. class SomeClass : CoroutineScope { val A = Job() override val coroutineContext = A fun someFunction() { val B = launch { val D = launch {} val E = launch {} } val C = launch { val F = launch {} } } }
50. A
51. A B
52. A B C D
53. A B C F E D
54. class SomeClass : CoroutineScope { val A = Job() override val coroutineContext = A fun someFunction() { val B = launch { val D = launch {} val E = launch {} } val C = launch { val F = launch {} } } }
55. A B C F E D
56. Cancellations
57. A B C F E D .cancel()
58. JOB JOB JOB JOB JOB JOB JOB .cancel()
59. A B C F E D .cancel()
60. A B C F E D .cancel()
61. Exceptions
62. A B C F E D .throw(Exception(“oops”))
63. A B C F E D .throw(Exception(“oops”))
64. SupervisorJob
65. class SomeClass : CoroutineScope { val A = Job() override val coroutineContext = A fun someFunction() { val B = launch { val D = launch {} val E = launch {} } val C = launch { val F = launch {} } } }
66. class SomeClass : CoroutineScope { val A = SupervisorJob() override val coroutineContext = A fun someFunction() { val B = launch { val D = launch {} val E = launch {} } val C = launch { val F = launch {} } } }
67. class SomeClass : CoroutineScope { val A = SupervisorJob() override val coroutineContext = A fun someFunction() { val B = launch { val D = launch {} val E = launch {} } val C = launch { val F = launch {} } } }
68. A B C F E D SupervisorJob
69. A B C F E D SupervisorJob .throw(Exception(“oops”))
70. A B C F E D SupervisorJob .throw(Exception(“oops”))
71. Don’t implement CoroutineScope
72. class FileParser(file: File) : CoroutineScope { override val coroutineContext = Job() + Dispatchers.IO suspend fun parse(): String = TODO() }
73. class FileParser(file: File) : CoroutineScope { override val coroutineContext = Job() + Dispatchers.IO suspend fun parse(): String = TODO() } class SomeOtherClass { var novel: String? = null suspend fun onUpdatedFile(file: File) { novel = FileParser(file).parse() } }
74. class FileParser(file: File) : CoroutineScope { override val coroutineContext = Job() + Dispatchers.IO suspend fun parse(): String = TODO() } class SomeOtherClass { var novel: String? = null suspend fun onUpdatedFile(file: File) { FileParser(file).launch { … } } }
75. class FileParser(file: File) { private val scope = CoroutineScope(Job() + Dispatchers.IO) suspend fun parse(): String = TODO() } class SomeOtherClass { var novel: String? = null suspend fun onUpdatedFile(file: File) { FileParser(file).launch { … } } }
76. https://bit.ly/2y2NDuJ
77. Factories
78. fun SupervisorScope( continuationInterceptor: ContinuationInterceptor = Dispatchers.Default ): CoroutineScope = CoroutineScope(SupervisorJob() + continuationInterceptor)
79. fun SupervisorScope( continuationInterceptor: ContinuationInterceptor = Dispatchers.Default ): CoroutineScope = CoroutineScope(SupervisorJob() + continuationInterceptor) fun DefaultCoroutineScope() = SupervisorScope(Dispatchers.Default) fun IOCoroutineScope() = SupervisorScope(Dispatchers.IO)
80. Coroutine LiveData?
81. LiveData !~= BroadcastChannel
82. What’s a Channel?
83. Channel ‣ Observable type ‣ Linked blocking queue ‣ Thread Concurrency-safe ‣ Synchronization primitive ‣ Sender and receiver have their own CoroutineScope
84. suspend fun talkToYourself() { val channel = Channel<Int>() scope.launch { repeat(5) { channel.send(it) } } val output = mutableListOf<Int>() for (i in channel) { output.add(i) } output shouldBe listOf(0, 1, 2, 3, 5) }
85. suspend fun talkToYourself() { val channel = Channel<Int>() scope.launch { repeat(5) { channel.send(it) } } val output = mutableListOf<Int>() for (i in channel) { output.add(i) } output shouldBe listOf(0, 1, 2, 3, 5) }
86. suspend fun talkToYourself() { val channel = Channel<Int>() scope.launch { repeat(5) { channel.send(it) } } val output = mutableListOf<Int>() for (i in channel) { output.add(i) } output shouldBe listOf(0, 1, 2, 3, 5) }
87. suspend fun talkToYourself() { val channel = Channel<Int>() scope.launch { repeat(5) { channel.send(it) } } val output = mutableListOf<Int>() for (i in channel) { output.add(i) } output shouldBe listOf(0, 1, 2, 3, 5) }
88. suspend fun talkToYourself() { val channel = Channel<Int>() scope.launch { repeat(5) { channel.send(it) } } val output = mutableListOf<Int>() for (i in channel) { output.add(i) } output shouldBe listOf(0, 1, 2, 3, 5) } ORDER OF OPERATIONS Send 0 Receive 0 Send 1 Receive 1 …
89. Buffers
90. Buffers ‣ Rendezvous ‣ LinkedList ‣ Array(size) ‣ Conflated
91. Emitters
92. Emmitters suspend fun <T> send(t: T) fun <T> offer(t: T): Boolean
93. BroadcastChannels
94. val channel: ReceiveChannel<String> = BroadcastChannel<String>(CONFLATED).openSubscription()
95. Broadcast buffers ‣ Array(size) ‣ Conflated ‣ No Rendezvous ‣ No LinkedList
96. ReceiveChannel Vs SendChannel
97. class SomeClass { private val _channel = Channel<Int>() val channel: ReceiveChannel<Int> = _channel }
98. Observing!
99. fun <T> ReceiveChannel<T>.observe( coroutineScope: CoroutineScope, observer: CoroutineScope.(t: T) !-> Unit ): Job = coroutineScope.launch { for (t in this@observe) { observer(t) } }
100. fun <T> ReceiveChannel<T>.observe( coroutineScope: CoroutineScope, observer: CoroutineScope.(t: T) !-> Unit ): Job = coroutineScope.launch { for (t in this@observe) { observer(t) } }
101. fun <T> ReceiveChannel<T>.observe( coroutineScope: CoroutineScope, observer: CoroutineScope.(t: T) !-> Unit ): Job = coroutineScope.launch { for (t in this@observe) { observer(t) } }
102. fun <T> ReceiveChannel<T>.observe( coroutineScope: CoroutineScope, observer: CoroutineScope.(t: T) !-> Unit ): Job = coroutineScope.launch { for (t in this@observe) { observer(t) } }
103. class SomeClass( val someRepository: SomeRepository, val scope: CoroutineScope ) { init { someRepository.channel.observe(scope) { emitted !-> println(emitted) } } }
104. class SomeClass( val someRepository: SomeRepository, val scope: CoroutineScope ) { init { someRepository.channel.observe(scope) { emitted !-> println(emitted) } } }
105. CoroutineScope and the Android lifecycle
106. interface Screen : LifecycleOwner, CoroutineScope
107. fun Screen.whileResumed(block: CoroutineScope.() !-> Job) { var job: Job? = null val observer = object : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_RESUME) fun onResume() { job = block() } @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE) fun onPause() { job!?.cancel() } } lifecycle.addObserver(observer) }
108. fun Screen.whileResumed(block: CoroutineScope.() !-> Job) { var job: Job? = null val observer = object : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_RESUME) fun onResume() { job = block() } @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE) fun onPause() { job!?.cancel() } } lifecycle.addObserver(observer) }
109. fun Screen.whileResumed(block: CoroutineScope.() !-> Job) { var job: Job? = null val observer = object : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_RESUME) fun onResume() { job = block() } @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE) fun onPause() { job!?.cancel() } } lifecycle.addObserver(observer) }
110. fun Screen.whileResumed(block: CoroutineScope.() !-> Job) { var job: Job? = null val observer = object : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_RESUME) fun onResume() { job = block() } @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE) fun onPause() { job!?.cancel() } } lifecycle.addObserver(observer) }
111. fun Screen.whileResumed(block: CoroutineScope.() !-> Job) { var job: Job? = null val observer = object : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_RESUME) fun onResume() { job = block() } @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE) fun onPause() { job!?.cancel() } } lifecycle.addObserver(observer) }
112. fun Screen.whileResumed(block: CoroutineScope.() !-> Job) { var job: Job? = null val observer = object : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_RESUME) fun onResume() { job = block() } @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE) fun onPause() { job!?.cancel() } } lifecycle.addObserver(observer) }
113. fun Screen.whileResumed(block: CoroutineScope.() !-> Job) { var job: Job? = null val observer = object : LifecycleObserver { @OnLifecycleEvent(Lifecycle.Event.ON_RESUME) fun onResume() { job = block() } @OnLifecycleEvent(Lifecycle.Event.ON_PAUSE) fun onPause() { job!?.cancel() } } lifecycle.addObserver(observer) }
114. Coroutining the Uncoroutine
115. fun getUserProfile(): Deferred<UserProfile?> { val deferred = CompletableDeferred<UserProfile?>() api.getUserProfile() .enqueue(object : Callback<UserProfile> { override fun onResponse(call: Call<UserProfile>, response: Response<UserProfile>) { deferred.complete(response.body()) } override fun onFailure(call: Call<UserProfile>, t: Throwable) { deferred.complete(null) } }) return deferred }
116. fun getUserProfile(): Deferred<UserProfile?> { val deferred = CompletableDeferred<UserProfile?>() api.getUserProfile() .enqueue(object : Callback<UserProfile> { override fun onResponse(call: Call<UserProfile>, response: Response<UserProfile>) { deferred.complete(response.body()) } override fun onFailure(call: Call<UserProfile>, t: Throwable) { deferred.complete(null) } }) return deferred }
117. fun getUserProfile(): Deferred<UserProfile?> { val deferred = CompletableDeferred<UserProfile?>() api.getUserProfile() .enqueue(object : Callback<UserProfile> { override fun onResponse(call: Call<UserProfile>, response: Response<UserProfile>) { deferred.complete(response.body()) } override fun onFailure(call: Call<UserProfile>, t: Throwable) { deferred.complete(null) } }) return deferred }
118. fun getUserProfile(): Deferred<UserProfile?> { val deferred = CompletableDeferred<UserProfile?>() api.getUserProfile() .enqueue(object : Callback<UserProfile> { override fun onResponse(call: Call<UserProfile>, response: Response<UserProfile>) { deferred.complete(response.body()) } override fun onFailure(call: Call<UserProfile>, t: Throwable) { deferred.complete(null) } }) return deferred }
119. fun getUserProfile(): Deferred<UserProfile?> { val deferred = CompletableDeferred<UserProfile?>() api.getUserProfile() .enqueue(object : Callback<UserProfile> { override fun onResponse(call: Call<UserProfile>, response: Response<UserProfile>) { deferred.complete(response.body()) } override fun onFailure(call: Call<UserProfile>, t: Throwable) { deferred.complete(null) } }) return deferred }
120. class SomeClass(val repository: ProfileRepository) { var profile: UserProfile? = null suspend fun updateProfile() { profile = repository.getUserProfile().await() } }
121. class SomeClass(val repository: ProfileRepository) { var profile: UserProfile? = null suspend fun updateProfile() { profile = repository.getUserProfile().await() } }
122. rbusarow rbusarow rbusarow Thanks! Rick Busarow