Coroutine-First Android Architecture -- droidcon Lisbon

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. @rbusarow Coroutines First
3. 12 SEPTEMBER 2018 @rbusarow
4. 12 SEPTEMBER 2018 @rbusarow
5. http://bit.ly/Structured-Concurrency-Article 12 SEPTEMBER 2018 @rbusarow
6. 12 SEPTEMBER 2018 @rbusarow http://bit.ly/Structured-Concurrency-GitHub
7. @rbusarow Structured Concurrency
8. @rbusarow Job hierarchy
9. @rbusarow class SomeViewModel : ViewModel() { fun doSomething() { val job = launch { … } } } Pre- Structured Concurrency
10. @rbusarow class SomeViewModel : ViewModel() { fun doSomething() { val job = launch { … } } } Pre- Structured Concurrency
11. @rbusarow class SomeViewModel : ViewModel() { fun doSomething() { val job = launch { … } } } Pre- Structured Concurrency
12. @rbusarow class SomeViewModel : ViewModel() { fun doSomething() { val job = launch { … } } } Pre- Structured Concurrency
13. @rbusarow Job hierarchy Job
14. @rbusarow Job hierarchy Job Job Job Job Job Job Job Job Job Job Job
15. Job @rbusarow Job hierarchy Explicit cancellation Job Job Job Job Job Job Job Job Job Job Job Job Job
16. Job @rbusarow Job hierarchy Explicit cancellation Job Job Job Job Job Job Job Job Job Job .cancel() Job Job Job
17. Job @rbusarow Job hierarchy Explicit cancellation Job Job Job Job Job Job Job Job Job Job Job .cancel()
18. @rbusarow class SomeViewModel : ViewModel() { fun doSomething() { val job = launch { … } } } Pre- Structured Concurrency
19. @rbusarow class SomeViewModel : ViewModel() { fun doSomething() { val job = launch { … } } } Pre- Structured Concurrency Completely
 Autonomous
20. @rbusarow 0.26 to 1.0
21. @rbusarow class SomeViewModel : ViewModel() { fun doSomething() { val job = launch { … } } } 0.26 to 1.0
22. @rbusarow class SomeViewModel : ViewModel() { fun doSomething() { val job = launch { … } } } fun CoroutineScope.launch( context: CoroutineContext = EmptyCoroutineContext, start: CoroutineStart = CoroutineStart.DEFAULT, block: suspend CoroutineScope.() !-> Unit ): Job { … } 0.26 to 1.0
23. @rbusarow class SomeViewModel : ViewModel(), CoroutineScope { override val coroutineContext = Job() + Dispatchers.Main fun doSomething() { val job = launch { … } } } Structured Concurrency
24. @rbusarow class SomeViewModel : ViewModel(), CoroutineScope { override val coroutineContext = Job() + Dispatchers.Main fun doSomething() { val job = launch { … } } override fun onCleared() { super.onCleared() coroutineContext.cancel() } } Structured Concurrency
25. @rbusarow Lifecycle
26. @rbusarow Androidx Lifecycle
27. @rbusarow Androidx Lifecycle
28. @rbusarow Androidx Lifecycle INITIALIZED STARTED RESUMED CREATED
29. @rbusarow Androidx Lifecycle INITIALIZED STARTED RESUMED CREATED STARTED CREATED DESTROYED
30. @rbusarow Androidx Lifecycle INITIALIZED STARTED RESUMED CREATED STARTED CREATED DESTROYED viewModel init viewModel.onCleared()
31. @rbusarow Androidx Lifecycle STARTED RESUMED CREATED
32. @rbusarow Androidx Lifecycle STARTED RESUMED CREATED onCreate()
33. @rbusarow Androidx Lifecycle STARTED RESUMED CREATED onStart()
34. @rbusarow Androidx Lifecycle STARTED RESUMED CREATED onResume()
35. @rbusarow Androidx Lifecycle STARTED RESUMED CREATED Lifecycle B STARTED RESUMED CREATED Lifecycle A
36. @rbusarow Androidx Lifecycle STARTED RESUMED CREATED Lifecycle C STARTED RESUMED CREATED Lifecycle B STARTED RESUMED CREATED Lifecycle A
37. @rbusarow Androidx Lifecycle STARTED RESUMED CREATED Lifecycle C STARTED RESUMED CREATED Lifecycle B STARTED RESUMED CREATED Lifecycle A …DESTROYED? ¯\_(ツ)_/¯
38. @rbusarow class MainViewModel : ViewModel(), CoroutineScope { override val coroutineContext: CoroutineContext = SupervisorJob() + Dispatchers.Main val reminder = launch { while (true) { delay(1_000) Log.v("MainViewModel", "still alive! --> ${UUID.randomUUID()}") } } override fun onCleared() { super.onCleared() cancel() } } ViewModel lifecycle
39. @rbusarow class MainViewModel : ViewModel(), CoroutineScope { override val coroutineContext: CoroutineContext = SupervisorJob() + Dispatchers.Main val reminder = launch { while (true) { delay(1_000) Log.v("MainViewModel", "still alive! --> ${UUID.randomUUID()}") } } override fun onCleared() { super.onCleared() cancel() } } ViewModel lifecycle
40. @rbusarow class MainViewModel : ViewModel(), CoroutineScope { override val coroutineContext: CoroutineContext = SupervisorJob() + Dispatchers.Main val reminder = launch { while (true) { delay(1_000) Log.v("MainViewModel", "still alive! --> ${UUID.randomUUID()}") } } override fun onCleared() { super.onCleared() cancel() } } ViewModel lifecycle
43. @rbusarow class MainViewModel : ViewModel(), CoroutineScope { override val coroutineContext: CoroutineContext = SupervisorJob() + Dispatchers.Main val reminder = launch { while (true) { delay(1_000) Log.v("MainViewModel", "still alive! --> ${UUID.randomUUID()}") } } override fun onCleared() { super.onCleared() cancel() } } ViewModel lifecycle
44. @rbusarow class MainViewModel : ViewModel() { val reminder = viewModelScope.launch { while (true) { delay(1_000) Log.v("MainViewModel", "still alive! --> ${UUID.randomUUID()}") } } } ViewModel lifecycle
45. @rbusarow CoroutineContext
46. @rbusarow class MainViewModel : ViewModel(), CoroutineScope { override val coroutineContext: CoroutineContext = SupervisorJob() + Dispatchers.Main } CoroutineContext
47. @rbusarow class MainViewModel : ViewModel(), CoroutineScope { override val coroutineContext: CoroutineContext = SupervisorJob() + Dispatchers.Main } CoroutineContext parent Job
48. @rbusarow class MainViewModel : ViewModel(), CoroutineScope { override val coroutineContext: CoroutineContext = SupervisorJob() + Dispatchers.Main } CoroutineContext parent Job default Dispatcher
49. @rbusarow class MainViewModel : ViewModel(), CoroutineScope { override val coroutineContext: CoroutineContext = SupervisorJob() + Dispatchers.Main } CoroutineContext interface CoroutineContext { val job: Job val continuationInterceptor: ContinuationInterceptor val coroutineExceptionHandler: CoroutineExceptionHandler val coroutineName: CoroutineName }
50. @rbusarow 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 } CoroutineContext
51. @rbusarow 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 } CoroutineContext
52. @rbusarow 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 } CoroutineContext
53. @rbusarow 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 } CoroutineContext
54. @rbusarow public operator fun plus(context: CoroutineContext): CoroutineContext = if (context === EmptyCoroutineContext) this else // fast path -- avoid lambda creation context.fold(this) { acc, element -> val removed = acc.minusKey(element.key) if (removed === EmptyCoroutineContext) element else { // make sure interceptor is always last in the context (and thus is fast to get when present) val interceptor = removed[ContinuationInterceptor] if (interceptor == null) CombinedContext(removed, element) else { val left = removed.minusKey(ContinuationInterceptor) if (left === EmptyCoroutineContext) CombinedContext(element, interceptor) else CombinedContext(CombinedContext(left, element), interceptor) } } } CoroutineContext
55. @rbusarow public operator fun plus(context: CoroutineContext): CoroutineContext = if (context === EmptyCoroutineContext) this else // fast path -- avoid lambda creation context.fold(this) { acc, element -> val removed = acc.minusKey(element.key) if (removed === EmptyCoroutineContext) element else { // make sure interceptor is always last in the context (and thus is fast to get when present) val interceptor = removed[ContinuationInterceptor] if (interceptor == null) CombinedContext(removed, element) else { val left = removed.minusKey(ContinuationInterceptor) if (left === EmptyCoroutineContext) CombinedContext(element, interceptor) else CombinedContext(CombinedContext(left, element), interceptor) } } } CoroutineContext
56. @rbusarow ViewModel lifecycle http://bit.ly/Demystifying-CoroutineContext
57. @rbusarow Dispatchers
58. @rbusarow object Dispatchers { val Default: CoroutineDispatcher val IO: CoroutineDispatcher val Main: CoroutineDispatcher val Unconfined: CoroutineDispatcher } Dispatchers
59. @rbusarow object Dispatchers { val Default: CoroutineDispatcher val IO: CoroutineDispatcher val Main: CoroutineDispatcher val Unconfined: CoroutineDispatcher } Dispatchers CPU-bound
60. @rbusarow object Dispatchers { val Default: CoroutineDispatcher val IO: CoroutineDispatcher val Main: CoroutineDispatcher val Unconfined: CoroutineDispatcher } Dispatchers CPU-bound IO-bound
61. @rbusarow object Dispatchers { val Default: CoroutineDispatcher val IO: CoroutineDispatcher val Main: CoroutineDispatcher val Unconfined: CoroutineDispatcher } Dispatchers CPU-bound IO-bound UI
62. @rbusarow object Dispatchers { val Default: CoroutineDispatcher val IO: CoroutineDispatcher val Main: CoroutineDispatcher val Unconfined: CoroutineDispatcher } Dispatchers CPU-bound IO-bound UI Debugging
63. @rbusarow object Dispatchers { val Default: CoroutineDispatcher val IO: CoroutineDispatcher val Main: CoroutineDispatcher val Unconfined: CoroutineDispatcher } fun doSomething() = launch(Dispatchers.IO) { … } suspend fun doSomethingElse() = withContext(Dispatchers.Main) { … } Dispatchers
64. @rbusarow object Dispatchers { val Default: CoroutineDispatcher val IO: CoroutineDispatcher val Main: CoroutineDispatcher val Unconfined: CoroutineDispatcher } fun doSomething() = launch(Dispatchers.IO) { … } suspend fun doSomethingElse() = withContext(Dispatchers.Main) { … } Dispatchers Test CoroutineDispatcher?
65. @rbusarow TestCoroutineDispatcher
66. @rbusarow advanceTimeBy() advanceUntilIdle() pauseDispatcher() resumeDispatcher() cleanupTestCoroutines() TestCoroutineDispatcher
67. @rbusarow class SomeViewModel : ViewModel(), CoroutineScope { override val coroutineContext = Job() + Dispatchers.Main fun doSomething() { val job = launch { … } } override fun onCleared() { super.onCleared() coroutineContext.cancel() } } CoroutineScope Injection
68. @rbusarow class SomeViewModel(val coroutineScope: CoroutineScope) : ViewModel() { fun doSomething() { coroutineScope.launch { … } } override fun onCleared() { super.onCleared() coroutineScope.cancel() } } CoroutineScope Injection
69. @rbusarow val myScope = object: CoroutineScope { override val coroutineContext = Job() + Dispatchers.Main } val myOtherScope = object: CoroutineScope { override val coroutineContext = Job() + Dispatchers.Default } CoroutineScope Injection
70. @rbusarow class MainCoroutineScope: CoroutineScope { override val coroutineContext = Job() + Dispatchers.Main } class DefaultCoroutineScope: CoroutineScope { override val coroutineContext = Job() + Dispatchers.Default } CoroutineScope Injection
71. @rbusarow class MainCoroutineScopeImpl: MainCoroutineScope { override val coroutineContext = Job() + Dispatchers.Main } class DefaultCoroutineScopeImpl: DefaultCoroutineScope { override val coroutineContext = Job() + Dispatchers.Default } interface MainCoroutineScope: CoroutineScope interface DefaultCoroutineScope: CoroutineScope CoroutineScope Injection
72. @rbusarow class SomeViewModel(val coroutineScope: CoroutineScope) : ViewModel() { fun doSomething() { coroutineScope.launch { … } } override fun onCleared() { super.onCleared() coroutineScope.cancel() } } CoroutineScope Injection
73. @rbusarow class SomeViewModel(val coroutineScope: MainCoroutineScope) : ViewModel() { fun doSomething() { coroutineScope.launch { … } } override fun onCleared() { super.onCleared() coroutineScope.cancel() } } CoroutineScope Injection
74. @rbusarow class MainCoroutineScopeImpl: MainCoroutineScope { override val coroutineContext = Job() + Dispatchers.Main } interface MainCoroutineScope: CoroutineScope class TestMainCoroutineScope: MainCoroutineScope { override val coroutineContext = Job() + TestCoroutineDispatcher() } CoroutineScope Injection
75. @rbusarow fun doSomething() = launch(Dispatchers.IO) { … } suspend fun doSomethingElse() = withContext(Dispatchers.Main) { … } CoroutineScope Injection
76. @rbusarow No hard-coded Dispatchers
77. @rbusarow interface DispatcherProvider { val default: CoroutineDispatcher val io: CoroutineDispatcher val main: CoroutineDispatcher val mainImmediate: CoroutineDispatcher val unconfined: CoroutineDispatcher } DispatcherProvider
78. @rbusarow interface DispatcherProvider : CoroutineContext.Element { override val key: CoroutineContext.Key<*> get() = Key val default: CoroutineDispatcher val io: CoroutineDispatcher val main: CoroutineDispatcher val mainImmediate: CoroutineDispatcher val unconfined: CoroutineDispatcher companion object Key : CoroutineContext.Key<DispatcherProvider> } DispatcherProvider
79. @rbusarow class MainCoroutineScope: CoroutineScope { override val coroutineContext = Job() + Dispatchers.Main } DispatcherProvider
80. @rbusarow class MainCoroutineScopeImpl( dispatcherProvider: DispatcherProvider = DefaultDispatcherProvider() ): MainCoroutineScope = MainCoroutineScope { override val coroutineContext = Job() + dispatcherProvider.main + dispatcherProvider } DispatcherProvider
81. @rbusarow class MainCoroutineScopeImpl( dispatcherProvider: DispatcherProvider = DefaultDispatcherProvider() ): MainCoroutineScope = MainCoroutineScope { override val coroutineContext = Job() + dispatcherProvider.main + dispatcherProvider } DispatcherProvider
82. @rbusarow val CoroutineContext.dispatcherProvider: DispatcherProvider get() = get(DispatcherProvider) ?: DefaultDispatcherProvider() DispatcherProvider
83. @rbusarow val CoroutineContext.dispatcherProvider: DispatcherProvider get() = get(DispatcherProvider) ?: DefaultDispatcherProvider() val CoroutineScope.mainDispatcher: CoroutineDispatcher get() = dispatcherProvider.main DispatcherProvider
84. @rbusarow val CoroutineContext.dispatcherProvider: DispatcherProvider get() = get(DispatcherProvider) ?: DefaultDispatcherProvider() val CoroutineScope.mainDispatcher: CoroutineDispatcher get() = dispatcherProvider.main DispatcherProvider
85. @rbusarow class SomeViewModel(val coroutineScope: MainCoroutineScope) : ViewModel() { fun doSomething() { coroutineScope.launch(Dispatchers.Main) { … } } override fun onCleared() { super.onCleared() coroutineScope.cancel() } } CoroutineScope Injection
86. @rbusarow class SomeViewModel(val coroutineScope: MainCoroutineScope) : ViewModel() { fun doSomething() { coroutineScope.launch(coroutineScope.mainDispatcher) { … } } override fun onCleared() { super.onCleared() coroutineScope.cancel() } } CoroutineScope Injection
87. @rbusarow class TestDispatcherProvider( override val default: TestCoroutineDispatcher = TestCoroutineDispatcher(), override val io: TestCoroutineDispatcher = TestCoroutineDispatcher(), override val main: TestCoroutineDispatcher = TestCoroutineDispatcher(), override val mainImmediate: TestCoroutineDispatcher = TestCoroutineDispatcher(), override val unconfined: TestCoroutineDispatcher = TestCoroutineDispatcher() ) : DispatcherProvider TestDispatcherProvider
88. @rbusarow class TestDispatcherProvider( override val default: TestCoroutineDispatcher = TestCoroutineDispatcher(), override val io: TestCoroutineDispatcher = TestCoroutineDispatcher(), override val main: TestCoroutineDispatcher = TestCoroutineDispatcher(), override val mainImmediate: TestCoroutineDispatcher = TestCoroutineDispatcher(), override val unconfined: TestCoroutineDispatcher = TestCoroutineDispatcher() ) : DispatcherProvider fun TestDispatcherProvider(dispatcher: TestCoroutineDispatcher): TestDispatcherProvider = TestDispatcherProvider( default = dispatcher, io = dispatcher, main = dispatcher, mainImmediate = dispatcher, unconfined = dispatcher ) TestDispatcherProvider
89. @rbusarow interface TestProvidedCoroutineScope : TestCoroutineScope, DefaultCoroutineScope, IOCoroutineScope, MainCoroutineScope, MainImmediateCoroutineScope, UnconfinedCoroutineScope { val dispatcherProvider: DispatcherProvider } TestDispatcherProvider
90. @rbusarow class TestProvidedCoroutineScopeImpl( override val dispatcherProvider: DispatcherProvider, context: CoroutineContext = EmptyCoroutineContext ) : TestProvidedCoroutineScope, TestCoroutineScope by TestCoroutineScope(context + dispatcherProvider) TestDispatcherProvider
91. @rbusarow class TestProvidedCoroutineScopeImpl( override val dispatcherProvider: DispatcherProvider, context: CoroutineContext = EmptyCoroutineContext ) : TestProvidedCoroutineScope, TestCoroutineScope by TestCoroutineScope(context + dispatcherProvider) fun TestProvidedCoroutineScope( dispatcher: TestCoroutineDispatcher = TestCoroutineDispatcher(), dispatcherProvider: TestDispatcherProvider = TestDispatcherProvider(dispatcher), context: CoroutineContext = EmptyCoroutineContext ): TestProvidedCoroutineScope = TestProvidedCoroutineScopeImpl( dispatcherProvider = dispatcherProvider, context = context + dispatcher ) TestDispatcherProvider
92. @rbusarow class TestProvidedCoroutineScopeImpl( override val dispatcherProvider: DispatcherProvider, context: CoroutineContext = EmptyCoroutineContext ) : TestProvidedCoroutineScope, TestCoroutineScope by TestCoroutineScope(context + dispatcherProvider) fun TestProvidedCoroutineScope( dispatcher: TestCoroutineDispatcher = TestCoroutineDispatcher(), dispatcherProvider: TestDispatcherProvider = TestDispatcherProvider(dispatcher), context: CoroutineContext = EmptyCoroutineContext ): TestProvidedCoroutineScope = TestProvidedCoroutineScopeImpl( dispatcherProvider = dispatcherProvider, context = context + dispatcher ) val myScope = TestProvidedCoroutineScope() TestDispatcherProvider
93. @rbusarow class SomeViewModel(val coroutineScope: MainCoroutineScope) : ViewModel() { fun doSomething() { coroutineScope.launch(coroutineScope.mainDispatcher) { … } } override fun onCleared() { super.onCleared() coroutineScope.cancel() } } CoroutineScope Injection
94. @rbusarow class SomeViewModel(val coroutineScope: MainCoroutineScope) : ViewModel() { fun doSomething() { coroutineScope.launch(coroutineScope.mainDispatcher) { … } } override fun onCleared() { super.onCleared() coroutineScope.cancel() } } CoroutineScope Injection
95. @rbusarow class SomeRepository { suspend fun doSomething() = withContext(Dispatchers.IO) { ... } } CoroutineScope Injection
96. @rbusarow class SomeRepository { suspend fun doSomething() = withContext(Dispatchers.IO) { ... } } val CoroutineContext.dispatcherProvider: DispatcherProvider get() = get(DispatcherProvider) ?: DefaultDispatcherProvider() CoroutineScope Injection
97. @rbusarow class SomeRepository { suspend fun doSomething() = withContext(Dispatchers.IO) { ... } } val CoroutineContext.dispatcherProvider: DispatcherProvider get() = get(DispatcherProvider) ?: DefaultDispatcherProvider() suspend fun <T> withIO( context: CoroutineContext = EmptyCoroutineContext, block: suspend CoroutineScope.() -> T ): T { val newContext = coroutineContext.dispatcherProvider.io + context return withContext(newContext, block) } CoroutineScope Injection
98. @rbusarow class SomeRepository { suspend fun doSomething() = withIO { ... } } val CoroutineContext.dispatcherProvider: DispatcherProvider get() = get(DispatcherProvider) ?: DefaultDispatcherProvider() suspend fun <T> withIO( context: CoroutineContext = EmptyCoroutineContext, block: suspend CoroutineScope.() -> T ): T { val newContext = coroutineContext.dispatcherProvider.io + context return withContext(newContext, block) } CoroutineScope Injection
99. @rbusarow github.com/RBusarow/DispatcherProvider
100. rbusarow rbusarow rbusarow THANKS! Rick Busarow rickbusarow@gmail.com