kotlinx.coroutines 1.4.0: Introducing StateFlow and SharedFlow

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Today we are happy to announce the release of version  1.4.0 of  the Kotlin Coroutines library. The major innovations in this release are StateFlow  and  SharedFlow , which are now stable APIs. StateFlow and SharedFlow are intended for use when state management is required in the context of asynchronous execution using Kotlin Coroutines.

API- Flow Kotlin , . , Flow — . Kotlin  Flow  ,  Sequences: , , . .  Sequences  Flow  Kotlin ,  Flow  .

 Flow : , API- Flow.  Flow  backpressure,  — .

val flow: Flow<Int> = flow {
	delay(100)
	for(i in 1..10) {
		emit(i)
	}
}.map {
	delay(100)
	it * it
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

Flow , Sequences. Flow , backpressure.

Flow API-, , . , . : , «» «», «» «». : .

API- Flow , .  ConflatedBroadcastChannel. ConflatedBroadcastChannel . , , . , . , - !

ConflatedBroadcastChannel API- — StateFlow  SharedFlow!

StateFlow

StateFlow : StateFlow  MutableStateFlow:

public interface StateFlow<out T> : SharedFlow<T> {
   public val value: T
}

public interface MutableStateFlow<out T>: StateFlow<T>, MutableSharedFlow<T> {
   public override var value: T
   public fun compareAndSet(expect: T, update: T): Boolean
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

. .

, API-.

class DownloadingModel {

   private val _state.value = MutableStateFlow<DownloadStatus>(DownloadStatus.NOT_REQUESTED)
   val state: StateFlow<DownloadStatus> get() = _state

   suspend fun download() {
       _state.value = DownloadStatus.INITIALIZED
       initializeConnection()
       processAvailableContent {
               partialData: ByteArray,
               downloadedBytes: Long,
               totalBytes: Long
           ->
           storePartialData(partialData)
           _state = DownloadProgress(downloadedBytes.toDouble() / totalBytes)
       }
       _state.value = DownloadStatus.SUCCESS
   }
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

 state,  (state) . : state.value = DownloadStatus.INITIALIZED



. , , . , state



  , .

, API . , - . , , state



Flow.

SharedFlow

, , ? API-  SharedFlow. API- , .

public interface SharedFlow<out T> : Flow<T> {
   public val replayCache: List<T>
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

 — , , . , .

SharedFlow  MutableSharedFlow.

interface MutableSharedFlow<T> : SharedFlow<T>, FlowCollector<T> {
   suspend fun emit(value: T)
   fun tryEmit(value: T): Boolean
   val subscriptionCount: StateFlow<Int>
   fun resetReplayCache()
}
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

MutableSharedFlow . , MutableSharedFlow . , .

MutableSharedFlow . SharedFlow.

public fun <T> MutableSharedFlow(
   replay: Int,
   extraBufferCapacity: Int = 0,
   onBufferOverflow: BufferOverflow = BufferOverflow.SUSPEND
): MutableSharedFlow<T>
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

MutableSharedFlow , , , , , . , , .

,  Flow.shareIn



.

public fun <T> Flow<T>.shareIn(
   scope: CoroutineScope,
   replay: Int,
   started: SharingStarted = SharingStarted.Eagerly
)
      
      

        
        
        
      

    
        
        
        
      
      

        
        
        
      

    
    

API- StateFlow SharedFlow Kotlin . , .

API, !

Kotlin Coroutines , Kotlin 1.4 Online Event.

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