MutableSharedFlow

As explained in Kotlin in Action, 2E

MutableSharedFlow is a kotlinx.coroutines type that represents a shared flow whose emissions and configuration can be changed by its producer.

MutableSharedFlow broadcasts emitted values to all subscribers that are currently collecting. Producers emit independently of collectors, unlike cold flows, and can configure replay for new subscribers. section 16.3.1

Broadcasting messages

private val _messageFlow = MutableSharedFlow<Int>() val messageFlow = _messageFlow.asSharedFlow() fun beginBroadcasting(scope: CoroutineScope) { scope.launch { while (true) { delay(500.milliseconds) _messageFlow.emit(Random.nextInt(0..10)) } } } Keep the mutable flow private and expose the read-only SharedFlow view. Multiple collectors of messageFlow receive the same emissions while subscribed. section 16.3.1

Configure delivery behavior according to subscriber timing:

• Without replay, subscribers receive only emissions occurring after collect starts. section 16.3.1
• Set replay = 5 to cache the latest five values for newly subscribed collectors. section 16.3.1
• Use shareIn when an existing cold Flow should be converted into one shared stream for multiple collectors. section 16.3.1

Figure 16.5 Shared flows operate in a broadcast fashion. When an element is emitted into the shared flow, all subscribers currently collecting the flow will receive this emission.

Shows the broadcast relationship between one shared-flow emission and all currently collecting subscribers. section 16.3.1

How Kotlin in Action, 2E covers it

How deep it goes

Explains construction, encapsulation, emission, subscription timing, replay, and the related shareIn conversion, without deeper implementation internals.

Examples

Uses a RadioStation broadcasting random integers, delayed collectors, replayed messages, and shared sensor temperatures.

What it assumes

Assumes familiarity with Kotlin coroutines, CoroutineScope, launch, Flow, emit, delay, and collect.

What you can do after

Apply it via kotlinx.coroutines to broadcast emissions, expose a read-only flow, and replay recent values for new subscribers.

How it connects

Connects SharedFlow with cold flow, Flow, coroutines, collect, and shareIn.

liveBookmanning.com

Read Kotlin in Action, 2E on liveBook Get the book at manning.com

Related concepts

• MutableStateFlowincludes · MutableStateFlow is a kotlinx.coroutines type that represents a state flow whose current value can be updated.

This explainer was generated by Manning's knowledge graph from the text of Kotlin in Action, 2E. The section links point to the parts of the book it draws on.