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GOING WITH THE FLOW
Droidcon San Francisco
Nov 26, 2019
rbusarow
Rick Busarow
COROUTINES 1.3.X
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@rbusarow
Slides
bit.ly/GoingWithTheFlow13x
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@rbusarow
suspend
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@rbusarow
fun doSomethingSlow() {
api.getAllData()
.enqueue { ... }
}
interface Api {
@GET(“/all")
fun getAllData(): Call>
}
Suspend
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@rbusarow
fun doSomethingSlow() {
api.getAllData()
.enqueue { ... }
}
interface Api {
@GET(“/all")
fun getAllData(): Call>
}
Suspend
asynchronous
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@rbusarow
Suspend
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@rbusarow
Suspend
domain
logic
IO library
resource
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@rbusarow
Suspend
domain
logic
IO library
request
+
callback
resource
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@rbusarow
Suspend
domain
logic
IO library
request
+
callback
callbacks
callback
resource
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@rbusarow
Suspend
domain
logic
IO library
request
+
callback
callbacks
callback
resource
request
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@rbusarow
Suspend
domain
logic
IO library
request
+
callback
callbacks
callback
resource
request
response
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@rbusarow
Suspend
domain
logic
IO library
request
+
callback
callbacks
callback callback
resource
request
response
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@rbusarow
Suspend
domain
logic
IO library
request
+
callback
callbacks
callback callback
callback(response)
resource
request
response
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@rbusarow
fun doSomethingSlow() {
api.getAllData()
.enqueue { ... }
}
interface Api {
@GET(“/all")
fun getAllData(): Call>
}
Suspend
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@rbusarow
fun doSomethingSlow() {
api.getAllData()
.enqueue { ... }
}
interface Api {
@GET(“/all")
suspend fun getAllData(): List
}
Suspend
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@rbusarow
fun doSomethingSlow() {
api.getAllData()
}
interface Api {
@GET(“/all”)
suspend fun getAllData(): List
}
Suspend
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@rbusarow
fun doSomethingSlow() {
api.getAllData()
}
interface Api {
@GET(“/all”)
suspend fun getAllData(): List
}
Suspend
suspend function ‘getAllData’
should be called only from a coroutine
or another suspend function
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@rbusarow
suspend fun doSomethingSlow() {
api.getAllData()
}
interface Api {
@GET(“/all")
suspend fun getAllData(): List
}
Suspend
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@rbusarow
Suspend
By end of day,
sure!
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@rbusarow
suspend fun doSomethingSlow() {
api.getAllData()
}
interface Api {
@GET(“/all")
suspend fun getAllData(): List
}
Suspend
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@rbusarow
suspend fun doSomethingSlow() {
api.getAllData()
}
interface Api {
@GET(“/all")
suspend fun getAllData(): List
}
Suspend
Hey compiler! Turn this into a callback!
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@rbusarow
suspend fun doSomethingSlow() {
api.getAllData()
}
interface Api {
@GET(“/all")
suspend fun getAllData(): List
}
interface Continuation {
val context: CoroutineContext
fun resumeWith(result: Result)
}
Suspend
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@rbusarow
suspend fun doSomethingSlow() {
api.getAllData()
}
interface Api {
@GET(“/all")
fun getAllData(continuation: Continuation>)
}
interface Continuation {
val context: CoroutineContext
fun resumeWith(result: Result)
}
Suspend
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@rbusarow
fun doSomethingSlow(continuation: Continuation) {
api.getAllData(object : Continuation> {
override val context = continuation.context
override fun resumeWith(result: Result>) {
continuation.resumeWith(Result.success(Unit))
}
})
}
interface Api {
@GET(“/all")
fun getAllData(continuation: Continuation>)
}
Suspend
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@rbusarow
fun doSomethingSlow(continuation: Continuation) {
api.getAllData(object : Continuation> {
override val context = continuation.context
override fun resumeWith(result: Result>) {
continuation.resumeWith(Result.success(Unit))
}
})
}
interface Api {
@GET(“/all")
fun getAllData(continuation: Continuation>)
}
Suspend
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@rbusarow
fun doSomethingSlow(continuation: Continuation) {
api.getAllData(object : Continuation> {
override val context = continuation.context
override fun resumeWith(result: Result>) {
continuation.resumeWith(Result.success(Unit))
}
})
}
interface Api {
@GET(“/all")
fun getAllData(continuation: Continuation>)
}
Suspend
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@rbusarow
fun doSomethingSlow(continuation: Continuation) {
api.getAllData(object : Continuation> {
override val context = continuation.context
override fun resumeWith(result: Result>) {
continuation.resumeWith(Result.success(Unit))
}
})
}
interface Api {
@GET(“/all")
fun getAllData(continuation: Continuation>)
}
Suspend
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@rbusarow
fun doSomethingSlow(continuation: Continuation) {
api.getAllData(object : Continuation> {
override val context = continuation.context
override fun resumeWith(result: Result>) {
continuation.resumeWith(Result.success(Unit))
}
})
}
interface Api {
@GET(“/all")
fun getAllData(continuation: Continuation>)
}
Suspend
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@rbusarow
Hot Channels
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Coroutine A
sender
Coroutine B
receiver
Channels
Solution for shared mutable state
Suspending queue
Bridges the gap between different
coroutines
@rbusarow
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Coroutine A
sender
Coroutine B
receiver
Channels
Solution for shared mutable state
Suspending queue
Bridges the gap between different
coroutines
@rbusarow
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@rbusarow
interface Channel : SendChannel, ReceiveChannel
interface SendChannel {
suspend fun send(element: E)
fun offer(element: E): Boolean
}
interface ReceiveChannel {
suspend fun receive(): E
fun poll(): E?
operator fun iterator(): ChannelIterator
}
Channels
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@rbusarow
interface Channel : SendChannel, ReceiveChannel
interface SendChannel {
suspend fun send(element: E)
fun offer(element: E): Boolean
}
interface ReceiveChannel {
suspend fun receive(): E
fun poll(): E?
operator fun iterator(): ChannelIterator
}
Channels
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@rbusarow
interface Channel : SendChannel, ReceiveChannel
interface SendChannel {
suspend fun send(element: E)
fun offer(element: E): Boolean
}
interface ReceiveChannel {
suspend fun receive(): E
fun poll(): E?
operator fun iterator(): ChannelIterator
}
Channels
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@rbusarow
suspend fun main() {
val channel = Channel()
}
Channels
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@rbusarow
suspend fun main() {
val channel = Channel()
repeat(3) {
channel.send(it)
println("sent $it")
}
}
Channels
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@rbusarow
suspend fun main() = coroutineScope {
val channel = Channel()
launch {
for (i in channel) {
println("received $i")
}
}
repeat(3) {
println("sent $it”)
channel.send(it)
}
channel.cancel()
}
Channels
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@rbusarow
suspend fun main() = coroutineScope {
val channel = Channel()
launch {
for (i in channel) {
println("received $i")
}
}
repeat(3) {
println("sent $it”)
channel.send(it)
}
channel.cancel()
}
Channels
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@rbusarow
suspend fun main() = coroutineScope {
val channel = Channel()
launch {
for (i in channel) {
println("received $i")
}
}
repeat(3) {
println("sent $it”)
channel.send(it)
}
channel.cancel()
}
Channels
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@rbusarow
suspend fun main() = coroutineScope {
val channel = Channel()
launch {
for (i in channel) {
println("received $i")
}
}
repeat(3) {
println("sent $it”)
channel.send(it)
}
channel.cancel()
}
Channels
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@rbusarow
suspend fun main() = coroutineScope {
val channel = Channel()
launch {
for (i in channel) {
println("received $i")
}
}
repeat(3) {
println("sent $it”)
channel.send(it)
}
channel.cancel()
}
Channels
output:
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@rbusarow
suspend fun main() = coroutineScope {
val channel = Channel()
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:
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@rbusarow
Backpresure
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Backpressure
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
Coroutine A
sender
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
Coroutine A
sender
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
buffer = 2
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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Coroutine A
sender
Coroutine B
receiver
Rendezvous
Unlimited
Array(size)
Conflated
@rbusarow
Backpressure
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@rbusarow
https://youtu.be/P7ov_r1JZ1g
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@rbusarow
fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {
val channel = Channel()
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
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@rbusarow
fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {
val channel = Channel()
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
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@rbusarow
fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {
val channel = Channel()
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
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@rbusarow
fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {
val channel = Channel()
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
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@rbusarow
fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {
val channel = Channel()
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
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@rbusarow
fun observeLocation(
locationRequest: LocationRequest
): ReceiveChannel {
val channel = Channel()
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
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@rbusarow
BroadcastChannels
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BroadcastChannels
Send data to multiple coroutines via .openSubscription()
The buffer is on the BroadcastChannel side
Shared between all consumers
@rbusarow
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@rbusarow
suspend fun main() = coroutineScope {
val channel = Channel()
launch {
for (i in channel) {
println("received $i")
}
}
repeat(3) {
println("sent $it”)
channel.send(it)
}
channel.cancel()
}
BroadcastChannels
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suspend fun main() = coroutineScope {
val broadcastChannel = BroadcastChannel(capacity = 1)
val b: ReceiveChannel = broadcastChannel.openSubscription()
val c: ReceiveChannel = broadcastChannel.openSubscription()
launch {
b.receive()
}
launch {
for (i in c) { ... }
}
repeat(3) {
broadcastChannel.send(it)
}
}
@rbusarow
BroadcastChannels
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suspend fun main() = coroutineScope {
val broadcastChannel = BroadcastChannel(capacity = 1)
val b: ReceiveChannel = broadcastChannel.openSubscription()
val c: ReceiveChannel = broadcastChannel.openSubscription()
launch {
b.receive()
}
launch {
for (i in c) { ... }
}
repeat(3) {
broadcastChannel.send(it)
}
}
@rbusarow
BroadcastChannels
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suspend fun main() = coroutineScope {
val broadcastChannel = BroadcastChannel(capacity = 1)
val b: ReceiveChannel = broadcastChannel.openSubscription()
val c: ReceiveChannel = broadcastChannel.openSubscription()
launch {
b.receive()
}
launch {
for (i in c) { ... }
}
repeat(3) {
broadcastChannel.send(it)
}
}
@rbusarow
BroadcastChannels
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suspend fun main() = coroutineScope {
val broadcastChannel = BroadcastChannel(capacity = 1)
val b: ReceiveChannel = broadcastChannel.openSubscription()
val c: ReceiveChannel = broadcastChannel.openSubscription()
launch {
b.receive()
}
launch {
for (i in c) { ... }
}
repeat(3) {
broadcastChannel.send(it)
}
}
@rbusarow
BroadcastChannels
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suspend fun main() = coroutineScope {
val broadcastChannel = BroadcastChannel(capacity = 1)
val b: ReceiveChannel = broadcastChannel.openSubscription()
val c: ReceiveChannel = broadcastChannel.openSubscription()
launch {
b.receive()
}
launch {
for (i in c) { ... }
}
repeat(3) {
broadcastChannel.send(it)
}
}
@rbusarow
BroadcastChannels
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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
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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)
}
}
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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
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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
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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)
}
}
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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
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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
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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
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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
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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
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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)
}
}
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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
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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
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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
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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
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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
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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)
}
}
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@rbusarow
ConflatedBroadcastChannel ≈ MutableLiveData
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@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
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@rbusarow
But Structured Concurrency?
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@rbusarow
Job hierarchy
Job
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@rbusarow
Job hierarchy
Job
Job Job
Job
Job
Job
Job
Job
Job
Job Job
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Job
@rbusarow
Job hierarchy
Job
Job
Job
Job
Job
Job
Job
Job
Job Job
.cancel()
Job
Job
Job
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Job
@rbusarow
Job hierarchy
Job
Job
Job
Job
Job
Job
Job
Job
Job
Job
Job
.cancel()
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@rbusarow
https://youtu.be/EOjq4OIWKqM
Chris Banes + Adam Powell, ADS 2018
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@rbusarow
suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
) = coroutineScope {
val done = CompletableDeferred()
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
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
) = coroutineScope {
val done = CompletableDeferred()
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
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
) = coroutineScope {
val done = CompletableDeferred()
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
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
) = coroutineScope {
val done = CompletableDeferred()
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
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
) = coroutineScope {
val done = CompletableDeferred()
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
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
) = coroutineScope {
val done = CompletableDeferred()
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
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
@rbusarow
Iterating toward Flow
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
@rbusarow
Iterating toward Flow
way too specific
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
suspend fun listen(listener: (T) -> Unit)
@rbusarow
Listenable
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
suspend fun listen(listener: (T) -> Unit)
@rbusarow
Listenable
member function?
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
suspend fun listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: (T) -> Unit)
@rbusarow
Listenable
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
suspend fun listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: (T) -> Unit)
@rbusarow
Listenable
no coroutine support?
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
suspend fun listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: (T) -> Unit)
@rbusarow
Listenable
no coroutine support?
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
suspend fun listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: suspend (T) -> Unit)
@rbusarow
Listenable
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
suspend fun listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: suspend (T) -> Unit)
@rbusarow
Listenable
Guaranteed to be in a coroutine
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
suspend fun listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: suspend (T) -> Unit)
suspend inline fun Listenable.listen(listener: (T) -> Unit)
@rbusarow
Listenable
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
suspend fun listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: suspend (T) -> Unit)
suspend inline fun Listenable.listen(listener: (T) -> Unit)
suspend fun onNewListenable(listenable: Listenable) {
listenable.listen {
delay(1000)
println("I'm listening to $it in a coroutine”)
}
}
@rbusarow
Listenable
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suspend fun observeLocation(
request: LocationRequest, observer: (LocationResult) -> Unit
)
suspend fun listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: (T) -> Unit)
suspend fun Listenable.listen(listener: suspend (T) -> Unit)
suspend inline fun Listenable.listen(listener: (T) -> Unit)
suspend fun onNewListenable(listenable: Listenable) {
listenable.listen {
delay(1000)
println("I'm listening to $it in a coroutine”)
}
}
@rbusarow
Listenable
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@rbusarow
Cold Flows
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Flow
somewhat stable as of coroutines 1.3.0
some operators and builders are still in preview
Channel-based functionality is still experimental
@rbusarow
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@rbusarow
class SomeClass {
val lastName = findLastName()
private fun findLastName() = "Rida"
}
Flow
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@rbusarow
class SomeClass {
val lastName = findLastName()
val legalName by lazy { "Tramar Lacel Dillard" }
private fun findLastName() = "Rida"
}
Flow
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@rbusarow
class SomeClass {
val firstName = { "Flo" }
val lastName = findLastName()
val legalName by lazy { "Tramar Lacel Dillard" }
private fun findLastName() = "Rida"
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
repeat(3) {
emit(it)
}
}
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
repeat(3) {
emit(it)
}
}
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
repeat(3) {
emit(it)
}
}
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
println("starting")
repeat(3) {
emit(it)
}
println("all done")
}
numbers.collect { number: Int ->
println("collecting $number")
}
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
println("starting")
repeat(3) {
emit(it)
}
println("all done")
}
numbers.collect { number: Int ->
println("collecting $number")
}
}
Flow
Flow builder
Flow collector
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
println("starting")
repeat(3) {
emit(it)
}
println("all done")
}
numbers.collect { number: Int ->
println("collecting $number")
}
}
Flow
output:
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
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:
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
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
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
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:
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
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:
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
println("starting")
repeat(3) {
emit(it)
}
println("all done")
}
numbers.filter { it % 2 == 0 }
.collect { number: Int ->
println("collecting $number")
}
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
println("starting")
repeat(3) {
emit(it)
}
println("all done")
}
numbers.filter { it % 2 == 0 }
.collect { number: Int ->
println("collecting $number")
}
}
Flow
output:
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
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:
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
println("starting")
repeat(3) {
emit(it)
}
println("all done")
}
numbers
.collect { numberString: String ->
println("collecting $numberString")
}
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
println("starting")
repeat(3) {
emit(it)
}
println("all done")
}
numbers.take(2)
.collect { numberString: String ->
println("collecting $numberString”)
}
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
println("starting")
repeat(3) {
emit(it)
}
println("all done")
}
numbers.take(2)
.collect { number: Int ->
println("collecting $number”)
}
}
Flow
output:
never printed
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", "c")
val numbers = flow {
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
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", “c”)
val numbers = flowOf(1, 2, 3)
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", “c”)
val numbers = flowOf(1, 2, 3)
val pairs: Flow> = listOf(letters, numbers).asFlow()
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", “c”)
val numbers = flowOf(1, 2, 3)
val pairs: Flow> = listOf(letters, numbers).asFlow()
val events: Flow = all.flattenMerge(2)
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", “c”)
val numbers = flowOf(1, 2, 3)
val pairs: Flow> = listOf(letters, numbers).asFlow()
val events: Flow = all.flattenMerge(2)
events.collect {
when(it) {
is String -> println("collecting String : $it")
is Int -> println("collecting Int : $it")
}
}
}
Flow
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", “c”)
val numbers = flowOf(1, 2, 3)
val pairs: Flow> = listOf(letters, numbers).asFlow()
val events: Flow = all.flattenMerge(2)
events.collect {
when(it) {
is String -> println("collecting String : $it")
is Int -> println("collecting Int : $it")
}
}
}
Flow
buffer size
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", “c”)
val numbers = flowOf(1, 2, 3)
val pairs: Flow> = listOf(letters, numbers).asFlow()
val events: Flow = all.flattenMerge(2)
events.collect {
when(it) {
is String -> println("collecting String : $it")
is Int -> println("collecting Int : $it")
}
}
}
Flow
output:
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@rbusarow
suspend fun main() {
val letters = flowOf("a", "b", “c”)
val numbers = flowOf(1, 2, 3)
val pairs: Flow> = listOf(letters, numbers).asFlow()
val events: Flow = 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:
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@rbusarow
Practical coroutines
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@rbusarow
…but how do I emit new values?
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@rbusarow
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@rbusarow
class SomeViewModel {
private val _channel = ConflatedBroadcastChannel(1)
val flow: Flow
get() = _channel.asFlow()
init {
_channel.sendBlocking(2)
}
}
ConflatedBroadcastChannel usage
Send from anywhere
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@rbusarow
Location Tracking v3
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@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
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@rbusarow
priority = LocationRequest.PRIORITY_HIGH_ACCURACY
}
val locations: Flow = 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
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@rbusarow
priority = LocationRequest.PRIORITY_HIGH_ACCURACY
}
val locations: Flow = 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
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@rbusarow
priority = LocationRequest.PRIORITY_HIGH_ACCURACY
}
val locations: Flow = 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
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@rbusarow
priority = LocationRequest.PRIORITY_HIGH_ACCURACY
}
val locations: Flow = 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
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@rbusarow
https://youtu.be/B8ppnjGPAGE?t=1091
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@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