Coroutines Flow & Channels Workshop Slides
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The document provides an extensive overview of Kotlin coroutines, focusing specifically on the concept of 'flow' as an asynchronous data stream. It covers various aspects such as flow types, builders, design, operators, and comparisons between cold and hot flows, as well as channels and shared flows. Additionally, it includes references for further reading and practice questions to test understanding of the material.
Coroutines Flow & Channels Workshop Slides
- 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
- 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:
- 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