Going with the Flow: Coroutines 1.3.x

Let’s talk reactive coroutines. The coroutines 1.3.0 release graduated Flow to stable, and introduced breaking changes to the Channel api.

When do we use Channels, and when do we use Flows? How do we maintain structured concurrency in our code, and how do we test it? Do we need to re-write our apps into MVFlow?

In this talk, we’ll evaluate the options for reactive programming with coroutines. We’ll go over Android-specific problems and how to fit their solutions into any existing architecture.

Transcript

1. GOING WITH THE FLOW Droidcon San Francisco Nov 26, 2019 rbusarow Rick Busarow COROUTINES 1.3.X
2. @rbusarow Slides bit.ly/GoingWithTheFlow13x
3. @rbusarow suspend
4. @rbusarow fun doSomethingSlow() { api.getAllData() .enqueue { ... } } interface Api { @GET(“/all") fun getAllData(): Call<List<Data>> } Suspend
5. @rbusarow fun doSomethingSlow() { api.getAllData() .enqueue { ... } } interface Api { @GET(“/all") fun getAllData(): Call<List<Data>> } Suspend asynchronous
6. @rbusarow Suspend
7. @rbusarow Suspend domain logic IO library resource
8. @rbusarow Suspend domain logic IO library request + callback resource
9. @rbusarow Suspend domain logic IO library request + callback callbacks callback resource
10. @rbusarow Suspend domain logic IO library request + callback callbacks callback resource request
11. @rbusarow Suspend domain logic IO library request + callback callbacks callback resource request response
12. @rbusarow Suspend domain logic IO library request + callback callbacks callback callback resource request response
13. @rbusarow Suspend domain logic IO library request + callback callbacks callback callback callback(response) resource request response
14. @rbusarow fun doSomethingSlow() { api.getAllData() .enqueue { ... } } interface Api { @GET(“/all") fun getAllData(): Call<List<Data>> } Suspend
15. @rbusarow fun doSomethingSlow() { api.getAllData() .enqueue { ... } } interface Api { @GET(“/all") suspend fun getAllData(): List<Data> } Suspend
16. @rbusarow fun doSomethingSlow() { api.getAllData() } interface Api { @GET(“/all”) suspend fun getAllData(): List<Data> } Suspend
17. @rbusarow fun doSomethingSlow() { api.getAllData() } interface Api { @GET(“/all”) suspend fun getAllData(): List<Data> } Suspend suspend function ‘getAllData’ should be called only from a coroutine or another suspend function
18. @rbusarow suspend fun doSomethingSlow() { api.getAllData() } interface Api { @GET(“/all") suspend fun getAllData(): List<Data> } Suspend
19. @rbusarow Suspend By end of day, sure!
20. @rbusarow suspend fun doSomethingSlow() { api.getAllData() } interface Api { @GET(“/all") suspend fun getAllData(): List<Data> } Suspend
21. @rbusarow suspend fun doSomethingSlow() { api.getAllData() } interface Api { @GET(“/all") suspend fun getAllData(): List<Data> } Suspend Hey compiler! Turn this into a callback!
22. @rbusarow suspend fun doSomethingSlow() { api.getAllData() } interface Api { @GET(“/all") suspend fun getAllData(): List<Data> } interface Continuation<in T> { val context: CoroutineContext fun resumeWith(result: Result<T>) } Suspend
23. @rbusarow suspend fun doSomethingSlow() { api.getAllData() } interface Api { @GET(“/all") fun getAllData(continuation: Continuation<List<Data>>) } interface Continuation<in T> { val context: CoroutineContext fun resumeWith(result: Result<T>) } Suspend
24. @rbusarow fun doSomethingSlow(continuation: Continuation<Unit>) { api.getAllData(object : Continuation<List<Data>> { override val context = continuation.context override fun resumeWith(result: Result<List<Data>>) { continuation.resumeWith(Result.success(Unit)) } }) } interface Api { @GET(“/all") fun getAllData(continuation: Continuation<List<Data>>) } Suspend
25. @rbusarow fun doSomethingSlow(continuation: Continuation<Unit>) { api.getAllData(object : Continuation<List<Data>> { override val context = continuation.context override fun resumeWith(result: Result<List<Data>>) { continuation.resumeWith(Result.success(Unit)) } }) } interface Api { @GET(“/all") fun getAllData(continuation: Continuation<List<Data>>) } Suspend
26. @rbusarow fun doSomethingSlow(continuation: Continuation<Unit>) { api.getAllData(object : Continuation<List<Data>> { override val context = continuation.context override fun resumeWith(result: Result<List<Data>>) { continuation.resumeWith(Result.success(Unit)) } }) } interface Api { @GET(“/all") fun getAllData(continuation: Continuation<List<Data>>) } Suspend
27. @rbusarow fun doSomethingSlow(continuation: Continuation<Unit>) { api.getAllData(object : Continuation<List<Data>> { override val context = continuation.context override fun resumeWith(result: Result<List<Data>>) { continuation.resumeWith(Result.success(Unit)) } }) } interface Api { @GET(“/all") fun getAllData(continuation: Continuation<List<Data>>) } Suspend
28. @rbusarow fun doSomethingSlow(continuation: Continuation<Unit>) { api.getAllData(object : Continuation<List<Data>> { override val context = continuation.context override fun resumeWith(result: Result<List<Data>>) { continuation.resumeWith(Result.success(Unit)) } }) } interface Api { @GET(“/all") fun getAllData(continuation: Continuation<List<Data>>) } Suspend
29. @rbusarow Hot Channels
30. Coroutine A sender Coroutine B receiver Channels Solution for shared mutable state Suspending queue Bridges the gap between different coroutines @rbusarow
31. Coroutine A sender Coroutine B receiver Channels Solution for shared mutable state Suspending queue Bridges the gap between different coroutines @rbusarow
32. @rbusarow interface Channel<E> : SendChannel<E>, ReceiveChannel<E> interface SendChannel<in E> { suspend fun send(element: E) fun offer(element: E): Boolean } interface ReceiveChannel<out E> { suspend fun receive(): E fun poll(): E? operator fun iterator(): ChannelIterator<E> } Channels
33. @rbusarow interface Channel<E> : SendChannel<E>, ReceiveChannel<E> interface SendChannel<in E> { suspend fun send(element: E) fun offer(element: E): Boolean } interface ReceiveChannel<out E> { suspend fun receive(): E fun poll(): E? operator fun iterator(): ChannelIterator<E> } Channels
34. @rbusarow interface Channel<E> : SendChannel<E>, ReceiveChannel<E> interface SendChannel<in E> { suspend fun send(element: E) fun offer(element: E): Boolean } interface ReceiveChannel<out E> { suspend fun receive(): E fun poll(): E? operator fun iterator(): ChannelIterator<E> } Channels
35. @rbusarow suspend fun main() { val channel = Channel<Int>() } Channels
36. @rbusarow suspend fun main() { val channel = Channel<Int>() repeat(3) { channel.send(it) println("sent $it") } } Channels
37. @rbusarow suspend fun main() = coroutineScope { val channel = Channel<Int>() launch { for (i in channel) { println("received $i") } } repeat(3) { println("sent $it”) channel.send(it) } channel.cancel() } Channels
38. @rbusarow suspend fun main() = coroutineScope { val channel = Channel<Int>() launch { for (i in channel) { println("received $i") } } repeat(3) { println("sent $it”) channel.send(it) } channel.cancel() } Channels
39. @rbusarow suspend fun main() = coroutineScope { val channel = Channel<Int>() launch { for (i in channel) { println("received $i") } } repeat(3) { println("sent $it”) channel.send(it) } channel.cancel() } Channels
40. @rbusarow suspend fun main() = coroutineScope { val channel = Channel<Int>() launch { for (i in channel) { println("received $i") } } repeat(3) { println("sent $it”) channel.send(it) } channel.cancel() } Channels
41. @rbusarow suspend fun main() = coroutineScope { val channel = Channel<Int>() launch { for (i in channel) { println("received $i") } } repeat(3) { println("sent $it”) channel.send(it) } channel.cancel() } Channels output:
42. @rbusarow suspend fun main() = coroutineScope { val channel = Channel<Int>() launch { for (i in channel) { println("received $i") } } repeat(3) { println("sent $it”) channel.send(it) } channel.cancel() } Channels sent 0 received 0 sent 1 received 1 sent 2 received 2 output:
43. @rbusarow Backpresure
44. Backpressure Rendezvous Unlimited Array(size) Conflated @rbusarow
45. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
46. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
47. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
48. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
49. Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure Coroutine A sender
50. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
51. Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure Coroutine A sender
52. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
53. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
54. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
55. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
56. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
57. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
58. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
59. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
60. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
61. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
62. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
63. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
64. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
65. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
66. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
67. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow buffer = 2 Backpressure
68. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
69. Coroutine A sender Coroutine B receiver Rendezvous Unlimited Array(size) Conflated @rbusarow Backpressure
70. @rbusarow https://youtu.be/P7ov_r1JZ1g
71. @rbusarow fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> { val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult) { channel.sendBlocking(locationResult.lastLocation) } } locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() ) channel.invokeOnClose { locationClient.removeLocationUpdates(callback) } return channel } https://youtu.be/P7ov_r1JZ1g?t=2188
72. @rbusarow fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> { val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult) { channel.sendBlocking(locationResult.lastLocation) } } locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() ) channel.invokeOnClose { locationClient.removeLocationUpdates(callback) } return channel } https://youtu.be/P7ov_r1JZ1g?t=2188
73. @rbusarow fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> { val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult) { channel.sendBlocking(locationResult.lastLocation) } } locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() ) channel.invokeOnClose { locationClient.removeLocationUpdates(callback) } return channel } https://youtu.be/P7ov_r1JZ1g?t=2188
74. @rbusarow fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> { val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult) { channel.sendBlocking(locationResult.lastLocation) } } locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() ) channel.invokeOnClose { locationClient.removeLocationUpdates(callback) } return channel } https://youtu.be/P7ov_r1JZ1g?t=2188
75. @rbusarow fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> { val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult) { channel.sendBlocking(locationResult.lastLocation) } } locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() ) channel.invokeOnClose { locationClient.removeLocationUpdates(callback) } return channel } https://youtu.be/P7ov_r1JZ1g?t=2188
76. @rbusarow fun observeLocation( locationRequest: LocationRequest ): ReceiveChannel<Location> { val channel = Channel<Location>() val callback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult) { channel.sendBlocking(locationResult.lastLocation) } } locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() ) channel.invokeOnClose { locationClient.removeLocationUpdates(callback) } return channel } https://youtu.be/P7ov_r1JZ1g?t=2188
77. @rbusarow BroadcastChannels
78. BroadcastChannels Send data to multiple coroutines via .openSubscription() The buffer is on the BroadcastChannel side Shared between all consumers @rbusarow
79. @rbusarow suspend fun main() = coroutineScope { val channel = Channel<Int>() launch { for (i in channel) { println("received $i") } } repeat(3) { println("sent $it”) channel.send(it) } channel.cancel() } BroadcastChannels
80. suspend fun main() = coroutineScope { val broadcastChannel = BroadcastChannel<Int>(capacity = 1) val b: ReceiveChannel<Int> = broadcastChannel.openSubscription() val c: ReceiveChannel<Int> = broadcastChannel.openSubscription() launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } @rbusarow BroadcastChannels
81. suspend fun main() = coroutineScope { val broadcastChannel = BroadcastChannel<Int>(capacity = 1) val b: ReceiveChannel<Int> = broadcastChannel.openSubscription() val c: ReceiveChannel<Int> = broadcastChannel.openSubscription() launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } @rbusarow BroadcastChannels
82. suspend fun main() = coroutineScope { val broadcastChannel = BroadcastChannel<Int>(capacity = 1) val b: ReceiveChannel<Int> = broadcastChannel.openSubscription() val c: ReceiveChannel<Int> = broadcastChannel.openSubscription() launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } @rbusarow BroadcastChannels
83. suspend fun main() = coroutineScope { val broadcastChannel = BroadcastChannel<Int>(capacity = 1) val b: ReceiveChannel<Int> = broadcastChannel.openSubscription() val c: ReceiveChannel<Int> = broadcastChannel.openSubscription() launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } @rbusarow BroadcastChannels
84. suspend fun main() = coroutineScope { val broadcastChannel = BroadcastChannel<Int>(capacity = 1) val b: ReceiveChannel<Int> = broadcastChannel.openSubscription() val c: ReceiveChannel<Int> = broadcastChannel.openSubscription() launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } @rbusarow BroadcastChannels
85. Coroutine C Coroutine B receiver Coroutine A sender 0 @rbusarow BroadcastChannels receiver suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } broadcast b C
86. broadcast b C Coroutine C Coroutine B receiver Coroutine A sender 0 @rbusarow BroadcastChannels receiver suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } }
87. broadcast b C Coroutine C Coroutine B receiver Coroutine A sender 0 @rbusarow BroadcastChannels receiver suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } 0
88. broadcast b C Coroutine C Coroutine B receiver Coroutine A sender @rbusarow BroadcastChannels receiver suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } 0 0
89. broadcast b C Coroutine C Coroutine B receiver Coroutine A sender 0 0 @rbusarow BroadcastChannels receiver suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } }
90. Coroutine C Coroutine B receiver Coroutine A sender 0 @rbusarow BroadcastChannels receiver 0 suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } broadcast b C
91. Coroutine C Coroutine B receiver Coroutine A sender @rbusarow BroadcastChannels receiver suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } broadcast b C
92. Coroutine C Coroutine B receiver Coroutine A sender @rbusarow BroadcastChannels receiver suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } broadcast b C
93. Coroutine C Coroutine A sender @rbusarow BroadcastChannels receiver suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } broadcast b C
94. Coroutine C Coroutine A sender @rbusarow BroadcastChannels receiver 1 suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } broadcast b C
95. broadcast b C Coroutine C Coroutine A sender @rbusarow BroadcastChannels receiver 1 suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } }
96. broadcast b C Coroutine C Coroutine A sender @rbusarow BroadcastChannels receiver 1 suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } 1
97. broadcast b C Coroutine C Coroutine A sender @rbusarow BroadcastChannels receiver 1 suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } 1
98. broadcast b C Coroutine C Coroutine A sender @rbusarow BroadcastChannels receiver suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } 1 1
99. broadcast b C Coroutine C Coroutine A sender @rbusarow BroadcastChannels receiver 1 suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } 1
100. broadcast b C Coroutine A sender @rbusarow BroadcastChannels Coroutine C receiver suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } } 1
101. broadcast b C Coroutine A sender @rbusarow BroadcastChannels 1 Coroutine C receiver 2 suspend fun main() = coroutineScope { ... launch { b.receive() } launch { for (i in c) { ... } } repeat(3) { broadcastChannel.send(it) } }
102. @rbusarow ConflatedBroadcastChannel ≈ MutableLiveData
103. @rbusarow ConflatedBroadcastChannel MutableLiveData Current property .value .value Emit lossless .send(value) .sendBlocking(value) .offer(value) .setValue(value)
 (main thread only) Emit lossy - - - .postValue(value) Multiple observers? yes Yes Backpressure? None None
104. @rbusarow But Structured Concurrency?
105. @rbusarow Job hierarchy Job
106. @rbusarow Job hierarchy Job Job Job Job Job Job Job Job Job Job Job
107. Job @rbusarow Job hierarchy Job Job Job Job Job Job Job Job Job Job .cancel() Job Job Job
108. Job @rbusarow Job hierarchy Job Job Job Job Job Job Job Job Job Job Job .cancel()
109. @rbusarow https://youtu.be/EOjq4OIWKqM Chris Banes + Adam Powell, ADS 2018
110. @rbusarow suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) = coroutineScope { val done = CompletableDeferred<Unit>() val callback = object : LocationCallback() { val mutex = Mutex(false) var observeJob: Job? = null override fun onLocationResult(result: LocationResult) { observeJob?.cancel() observeJob = launch { mutex.withLock { observer(result) } } } } try { locationClient.requestLocationUpdates(request, callback, Looper.myLooper()) done.await() } finally { locationClient.removeLocationUpdates(callback) } } https://youtu.be/EOjq4OIWKqM?t=1994
111. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) = coroutineScope { val done = CompletableDeferred<Unit>() val callback = object : LocationCallback() { val mutex = Mutex(false) var observeJob: Job? = null override fun onLocationResult(result: LocationResult) { observeJob?.cancel() observeJob = launch { mutex.withLock { observer(result) } } } } try { locationClient.requestLocationUpdates(request, callback, Looper.myLooper()) done.await() } finally { locationClient.removeLocationUpdates(callback) } } @rbusarow https://youtu.be/EOjq4OIWKqM?t=1994
112. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) = coroutineScope { val done = CompletableDeferred<Unit>() val callback = object : LocationCallback() { val mutex = Mutex(false) var observeJob: Job? = null override fun onLocationResult(result: LocationResult) { observeJob?.cancel() observeJob = launch { mutex.withLock { observer(result) } } } } try { locationClient.requestLocationUpdates(request, callback, Looper.myLooper()) done.await() } finally { locationClient.removeLocationUpdates(callback) } } @rbusarow https://youtu.be/EOjq4OIWKqM?t=1994
113. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) = coroutineScope { val done = CompletableDeferred<Unit>() val callback = object : LocationCallback() { val mutex = Mutex(false) var observeJob: Job? = null override fun onLocationResult(result: LocationResult) { observeJob?.cancel() observeJob = launch { mutex.withLock { observer(result) } } } } try { locationClient.requestLocationUpdates(request, callback, Looper.myLooper()) done.await() } finally { locationClient.removeLocationUpdates(callback) } } @rbusarow https://youtu.be/EOjq4OIWKqM?t=1994
114. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) = coroutineScope { val done = CompletableDeferred<Unit>() val callback = object : LocationCallback() { val mutex = Mutex(false) var observeJob: Job? = null override fun onLocationResult(result: LocationResult) { observeJob?.cancel() observeJob = launch { mutex.withLock { observer(result) } } } } try { locationClient.requestLocationUpdates(request, callback, Looper.myLooper()) done.await() } finally { locationClient.removeLocationUpdates(callback) } } @rbusarow https://youtu.be/EOjq4OIWKqM?t=1994
115. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) = coroutineScope { val done = CompletableDeferred<Unit>() val callback = object : LocationCallback() { val mutex = Mutex(false) var observeJob: Job? = null override fun onLocationResult(result: LocationResult) { observeJob?.cancel() observeJob = launch { mutex.withLock { observer(result) } } } } try { locationClient.requestLocationUpdates(request, callback, Looper.myLooper()) done.await() } finally { locationClient.removeLocationUpdates(callback) } } @rbusarow https://youtu.be/EOjq4OIWKqM?t=1994
116. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) @rbusarow Iterating toward Flow
117. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) @rbusarow Iterating toward Flow way too specific
118. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) suspend fun <T> listen(listener: (T) -> Unit) @rbusarow Listenable<T>
119. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) suspend fun <T> listen(listener: (T) -> Unit) @rbusarow Listenable<T> member function?
120. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) suspend fun <T> listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: (T) -> Unit) @rbusarow Listenable<T>
121. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) suspend fun <T> listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: (T) -> Unit) @rbusarow Listenable<T> no coroutine support?
122. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) suspend fun <T> listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: (T) -> Unit) @rbusarow Listenable<T> no coroutine support?
123. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) suspend fun <T> listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: suspend (T) -> Unit) @rbusarow Listenable<T>
124. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) suspend fun <T> listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: suspend (T) -> Unit) @rbusarow Listenable<T> Guaranteed to be in a coroutine
125. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) suspend fun <T> listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: suspend (T) -> Unit) suspend inline fun <T> Listenable<T>.listen(listener: (T) -> Unit) @rbusarow Listenable<T>
126. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) suspend fun <T> listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: suspend (T) -> Unit) suspend inline fun <T> Listenable<T>.listen(listener: (T) -> Unit) suspend fun onNewListenable(listenable: Listenable<Int>) { listenable.listen { delay(1000) println("I'm listening to $it in a coroutine”) } } @rbusarow Listenable<T>
127. suspend fun observeLocation( request: LocationRequest, observer: (LocationResult) -> Unit ) suspend fun <T> listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: (T) -> Unit) suspend fun <T> Listenable<T>.listen(listener: suspend (T) -> Unit) suspend inline fun <T> Listenable<T>.listen(listener: (T) -> Unit) suspend fun onNewListenable(listenable: Listenable<Int>) { listenable.listen { delay(1000) println("I'm listening to $it in a coroutine”) } } @rbusarow Listenable<T>
128. @rbusarow Cold Flows
129. Flow somewhat stable as of coroutines 1.3.0 some operators and builders are still in preview Channel-based functionality is still experimental @rbusarow
130. @rbusarow class SomeClass { val lastName = findLastName() private fun findLastName() = "Rida" } Flow
131. @rbusarow class SomeClass { val lastName = findLastName() val legalName by lazy { "Tramar Lacel Dillard" } private fun findLastName() = "Rida" } Flow
132. @rbusarow class SomeClass { val firstName = { "Flo" } val lastName = findLastName() val legalName by lazy { "Tramar Lacel Dillard" } private fun findLastName() = "Rida" } Flow
133. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { repeat(3) { emit(it) } } } Flow
134. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { repeat(3) { emit(it) } } } Flow
135. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { repeat(3) { emit(it) } } } Flow
136. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.collect { number: Int -> println("collecting $number") } } Flow
137. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.collect { number: Int -> println("collecting $number") } } Flow Flow builder Flow collector
138. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.collect { number: Int -> println("collecting $number") } } Flow output:
139. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.collect { number: Int -> println("collecting $number") } } Flow starting collecting 0 collecting 1 collecting 2 all done output:
140. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.collect { number: Int -> println("collecting $number") } numbers.collect { number: Int -> println("collecting $number again") } } Flow
141. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.collect { number: Int -> println("collecting $number") } numbers.collect { number: Int -> println("collecting $number again") } } Flow output:
142. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.collect { number: Int -> println("collecting $number") } numbers.collect { number: Int -> println("collecting $number again") } } Flow starting collecting 0 collecting 1 collecting 2 all done starting collecting 0 again collecting 1 again collecting 2 again all done output:
143. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.filter { it % 2 == 0 } .collect { number: Int -> println("collecting $number") } } Flow
144. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.filter { it % 2 == 0 } .collect { number: Int -> println("collecting $number") } } Flow output:
145. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.filter { it % 2 == 0 } .collect { number: Int -> println("collecting $number") } } Flow starting collecting 0 collecting 2 all done output:
146. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers .collect { numberString: String -> println("collecting $numberString") } } Flow
147. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.take(2) .collect { numberString: String -> println("collecting $numberString”) } } Flow
148. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.take(2) .collect { number: Int -> println("collecting $number”) } } Flow output: never printed
149. @rbusarow suspend fun main() { val letters = flowOf("a", "b", "c") val numbers = flow<Int> { println("starting") repeat(3) { emit(it) } println("all done") } numbers.take(2) .collect { number: Int -> println("collecting $number”) } } Flow starting collecting 0 collecting 1 output: never printed
150. @rbusarow suspend fun main() { val letters = flowOf("a", "b", “c”) val numbers = flowOf(1, 2, 3) } Flow
151. @rbusarow suspend fun main() { val letters = flowOf("a", "b", “c”) val numbers = flowOf(1, 2, 3) val pairs: Flow<Flow<Any>> = listOf(letters, numbers).asFlow() } Flow
152. @rbusarow suspend fun main() { val letters = flowOf("a", "b", “c”) val numbers = flowOf(1, 2, 3) val pairs: Flow<Flow<Any>> = listOf(letters, numbers).asFlow() val events: Flow<Any> = all.flattenMerge(2) } Flow
153. @rbusarow suspend fun main() { val letters = flowOf("a", "b", “c”) val numbers = flowOf(1, 2, 3) val pairs: Flow<Flow<Any>> = listOf(letters, numbers).asFlow() val events: Flow<Any> = all.flattenMerge(2) events.collect { when(it) { is String -> println("collecting String : $it") is Int -> println("collecting Int : $it") } } } Flow
154. @rbusarow suspend fun main() { val letters = flowOf("a", "b", “c”) val numbers = flowOf(1, 2, 3) val pairs: Flow<Flow<Any>> = listOf(letters, numbers).asFlow() val events: Flow<Any> = all.flattenMerge(2) events.collect { when(it) { is String -> println("collecting String : $it") is Int -> println("collecting Int : $it") } } } Flow buffer size
155. @rbusarow suspend fun main() { val letters = flowOf("a", "b", “c”) val numbers = flowOf(1, 2, 3) val pairs: Flow<Flow<Any>> = listOf(letters, numbers).asFlow() val events: Flow<Any> = all.flattenMerge(2) events.collect { when(it) { is String -> println("collecting String : $it") is Int -> println("collecting Int : $it") } } } Flow output:
156. @rbusarow suspend fun main() { val letters = flowOf("a", "b", “c”) val numbers = flowOf(1, 2, 3) val pairs: Flow<Flow<Any>> = listOf(letters, numbers).asFlow() val events: Flow<Any> = all.flattenMerge(2) events.collect { when(it) { is String -> println("collecting String : $it") is Int -> println("collecting Int : $it") } } } Flow collecting String : a collecting Int : 1 collecting Int : 2 collecting Int : 3 collecting String : b collecting String : c output:
157. @rbusarow Practical coroutines
158. @rbusarow …but how do I emit new values?
159. @rbusarow
160. @rbusarow class SomeViewModel { private val _channel = ConflatedBroadcastChannel(1) val flow: Flow<Int> get() = _channel.asFlow() init { _channel.sendBlocking(2) } } ConflatedBroadcastChannel usage Send from anywhere
161. @rbusarow Location Tracking v3
162. @rbusarow class SomeLocationService @Inject constructor( private val locationClient: FusedLocationProviderClient, coroutineScope: CoroutineScope ) { private val locationRequest = LocationRequest().apply { fastestInterval = 1000 interval = 1000 priority = LocationRequest.PRIORITY_HIGH_ACCURACY } ... } http://bit.ly/BroadcastFlow
163. @rbusarow priority = LocationRequest.PRIORITY_HIGH_ACCURACY } val locations: Flow<Location> = broadcastFlow(coroutineScope) { val callback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult) { sendBlockingOrNull(locationResult.lastLocation) } } locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() ) awaitClose { locationClient.removeLocationUpdates(callback) } } } http://bit.ly/BroadcastFlow
164. @rbusarow priority = LocationRequest.PRIORITY_HIGH_ACCURACY } val locations: Flow<Location> = broadcastFlow(coroutineScope) { val callback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult) { sendBlockingOrNull(locationResult.lastLocation) } } locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() ) awaitClose { locationClient.removeLocationUpdates(callback) } } } http://bit.ly/BroadcastFlow
165. @rbusarow priority = LocationRequest.PRIORITY_HIGH_ACCURACY } val locations: Flow<Location> = broadcastFlow(coroutineScope) { val callback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult) { sendBlocking(locationResult.lastLocation) } } locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() ) awaitClose { locationClient.removeLocationUpdates(callback) } } } http://bit.ly/BroadcastFlow
166. @rbusarow priority = LocationRequest.PRIORITY_HIGH_ACCURACY } val locations: Flow<Location> = broadcastFlow(coroutineScope) { val callback = object : LocationCallback() { override fun onLocationResult(locationResult: LocationResult) { sendBlocking(locationResult.lastLocation) } } locationClient.requestLocationUpdates( locationRequest, callback, Looper.myLooper() ) awaitClose { locationClient.removeLocationUpdates(callback) } } } http://bit.ly/BroadcastFlow
167. @rbusarow https://youtu.be/B8ppnjGPAGE?t=1091
168. @rbusarow Slides: bit.ly/GoingWithTheFlow13x Jetbrains docs: https://kotlinlang.org/docs/reference/coroutines/flow.html Android Suspenders at KotlinConf: https://youtu.be/P7ov_r1JZ1g Android Suspenders at ADS ’18: https://youtu.be/EOjq4OIWKqM LiveData with Coroutines and Flow at ADS ’19: https://youtu.be/B8ppnjGPAGE rbusarow Rick Busarow