Kotlin Coroutines Flow & Channels Workshop Slides

Kotlin Coroutines Flow & Channels Workshop at Tapsell

YouTube:
https://www.youtube.com/watch?v=SAVRGpgIgXE

Source Code:
https://github.com/MortezaNedaei/Kotlin-Coroutines-Workshop

Transcript

1. Kotlin Coroutines Flow Morteza Nedaei github.com/MortezaNedaei/Kotlin-Coroutines-Workshop linkedin.com/in/nedaei
2. Agenda • History • What is Flow? • Stream Types • Flow Builders • Flow Design • Flow Operators • Flow Constrains • Channels • SharedFlow & StateFlow • SharedFlow Design • Combine Flows • Flows CRUD • Flows Lifecycle • Convert Flows • Practice J
3. History Channel Async Await Shared Flow State Flow Flow Channel https://arxiv.org/pdf/2211.04986 https://github.com/Kotlin/kotlinx.coroutines/issues/3621
4. What is Flow? “An asynchronous data stream that sequentially emits values and completes normally or with an exception.”
5. Stream Types COLD 🥶 🥵 § flow § callbackFlow § channelFlow § SharedFlow § StateFlow § Channel LAZY MULTICAST HOT
6. Flow Builders • emptyFlow() • flowOf() • flow { emit() or emitAll() } • asFlow() • callbackFlow {} • channelFlow {} • MutableSharedFlow<*>() • MutableStateFlow<*>(null)
7. Flow Design Extension Function Type Functional Interface This block is executed each time by calling emit Higher Order Function
8. Flow Design
9. Flow Terminal Operators • collect() • collectLatest() – Conflated • launchIn(scope) = scope.launch { flow.collect() } • toList() • toSet() • first() • single() • fold() – both terminal and transform operator • reduce() both terminal and transform operator
10. Flow Transform Operators • transform() • transformLatest • onEach() • map(), mapNotNull {} • filter(), filterNotNull {} • fold(), runningFold() • scan = runningFold() • reduce(), runningReduce()
11. Flow Constraints 1. Context Preservation Flow encapsulates its own execution context and never propagates or leaks it downstream 2. Exception Transparency Flow implementations never catch or handle exceptions that occur in downstream flows
12. Channels Channel is a non-blocking primitive for communication between two or more coroutines using a sender (via SendChannel) and a receiver (via ReceiveChannel). Provide a way to transfer a stream of values while Deferred Values are used to transfer a single value between coroutines. similar to Java's BlockingQueue, but has suspending operations instead of blocking ones and can be closed.
13. Channels
14. Channel Buffer Strategies Capacity § RENDEZVOUS (Default behavior) § UNLIMITED (Int.MAX) § CONFLATED (DROP_OLDEST ) § BUFFERED (Default = 64) § SUSPEND § DROP_OLDEST (Conflated) § DROP_LATEST Overflow Strategies Channel example: Gopark Goready
15. SharedFlow 1. SharedFlow 2. StateFlow: Customized SharedFlow to hold latest value Uses Lock to manage thread safety NEVER COMPLETES
16. StateFlow 1. Conflation – Drop Oldest: onBufferOverflow = BufferOverflow.DROP_OLDEST 2. distinctUntilChanged() 3. Replay Cache = 1: replay = 1 4. Value property: Holds the current state It’s a SharedFlow with the following properties:
17. SharedFlow Design
18. Combine Flows • combine() • zip() • merge()
19. Flows CRUD Show me the code !
20. Flows Lifecycle • onStart() • onEach() • onCompletion()
21. Convert Flows • produceIn() • shareIn() • stateIn()
22. Practice :) 1. What’s the differences between Cold Flows and Hot Flows? 2. What’s the differences between Channels and SharedFlows? 3. What is the time complexity of emit function in SharedFlow ? 4. Are Coroutine Channels hot or cold? 5. What is the Logical structure of the buffer in SharedFlow?
23. References • https://elizarov.medium.com/cold-flows-hot-channels-d74769805f9 • https://elizarov.medium.com/shared-flows-broadcast-channels-899b675e805c • https://elizarov.medium.com/kotlin-flows-and-coroutines-256260fb3bdb • https://elizarov.medium.com/execution-context-of-kotlin-flows-b8c151c9309b • https://elizarov.medium.com/exceptions-in-kotlin-flows-b59643c940fb • https://elizarov.medium.com/callbacks-and-kotlin-flows-2b53aa2525cf • https://github.com/Kotlin/kotlinx.coroutines/issues/254 • https://github.com/Kotlin/kotlinx.coroutines/issues/285 • https://github.com/Kotlin/kotlinx.coroutines/issues/2680 • https://arxiv.org/pdf/2211.04986 • https://kotlinlang.org/docs/flow.html • https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow Elizarov papers Papers Kotlin docs GitHub
24. Thanks for your attention J Morteza Nedaei github.com/MortezaNedaei/Kotlin-Coroutines-Workshop linkedin.com/in/nedaei