IsolateState can not work with coroutines MutableStateFlow: kotlin.native.concurrent.FreezingException: freezing of Ok(result=kotlinx.coroutines.flow.StateFlowImpl@80804878) has failed, first blocker is kotlinx.coroutines.flow.StateFlowImpl@80804878

[xiaobailong24]

org.jetbrains.kotlinx:kotlinx-coroutines-core:1.5.1-native-mt

iosTest sorceset:

import kotlinx.coroutines.*
import kotlinx.coroutines.flow.MutableStateFlow
import kotlinx.coroutines.flow.asStateFlow
import kotlinx.coroutines.flow.collect
import kotlin.coroutines.CoroutineContext
import kotlin.test.Test

// https://github.com/Kotlin/kotlinx.coroutines/issues/1996
//iOS code:
val testCoroutineContext: CoroutineContext =
    newSingleThreadContext("testRunner")

fun runBlockingTest(block: suspend CoroutineScope.() -> Unit) =
    runBlocking(testCoroutineContext) { this.block() }

class IsoStateTest {

    private val flowState =
        IsolateState {
            MutableStateFlow("")
        }

    @OptIn(ExperimentalCoroutinesApi::class)
    @Test
    fun test() = runBlockingTest {
        println("runBlockingTest start")
        val job = launch {
            flowState
                .access { it }
                .asStateFlow().collect {
                    run()
                }
        }

        flowState.access { it.value = "123" }

//        job.cancel()
        println("runBlockingTest end")
    }

    private suspend fun run() {
        println("collect:${flowState.access { it.value }}")
    }
}

got error:

runBlockingTest start
runBlockingTest end

kotlin.native.concurrent.FreezingException: freezing of Ok(result=kotlinx.coroutines.flow.StateFlowImpl@80804878) has failed, first blocker is kotlinx.coroutines.flow.StateFlowImpl@80804878
kotlin.native.concurrent.FreezingException: freezing of Ok(result=kotlinx.coroutines.flow.StateFlowImpl@80804878) has failed, first blocker is kotlinx.coroutines.flow.StateFlowImpl@80804878
	at kotlin.Throwable#<init>(/Users/teamcity1/teamcity_work/7c4fade2802b7783/kotlin/kotlin-native/runtime/src/main/kotlin/kotlin/Throwable.kt:23)
	at kotlin.Exception#<init>(/Users/teamcity1/teamcity_work/7c4fade2802b7783/kotlin/kotlin-native/runtime/src/main/kotlin/kotlin/Exceptions.kt:23)
	at kotlin.RuntimeException#<init>(/Users/teamcity1/teamcity_work/7c4fade2802b7783/kotlin/kotlin-native/runtime/src/main/kotlin/kotlin/Exceptions.kt:34)
	at kotlin.native.concurrent.FreezingException#<init>(/Users/teamcity1/teamcity_work/7c4fade2802b7783/kotlin/kotlin-native/runtime/src/main/kotlin/kotlin/native/concurrent/Freezing.kt:15)
	at <global>.ThrowFreezingException(/Users/teamcity1/teamcity_work/7c4fade2802b7783/kotlin/kotlin-native/runtime/src/main/kotlin/kotlin/native/concurrent/Internal.kt:88)
	at <global>.FreezeSubgraph(Unknown Source)
	at <global>.Kotlin_Worker_freezeInternal(Unknown Source)
	at kotlin.native.concurrent#freeze__at__0:0(/Users/teamcity1/teamcity_work/7c4fade2802b7783/kotlin/kotlin-native/runtime/src/main/kotlin/kotlin/native/concurrent/Freezing.kt:33)
	at co.touchlab.stately.isolate.BackgroundStateRunner.stateRun$lambda-1#internal(co.touchlab.stately.isolate/BackgroundStateRunner.kt:15)
	at <global>._ZN6Worker19processQueueElementEb(Unknown Source)
	at <global>._ZN12_GLOBAL__N_113workerRoutineEPv(Unknown Source)
	at <global>._pthread_start(Unknown Source)
	at <global>.thread_start(Unknown Source)

[xiaobailong24]

Kotlin/kotlinx.coroutines#2584

[kpgalligan]

This code directly violates the basic concept of IsolateState.

flowState
      .access { it }

The thing that's kept isolated, MutableStateFlow(""), has ensureNeverFrozen() called on it when you init the IsolateState instance (https://github.com/touchlab/Stately/blob/main/stately-isolate/src/nativeCommonMain/kotlin/co/touchlab/stately/isolate/Platform.kt#L15).

The exception is happening because when you try to return the MutableStateFlow instance in the above code, it needs to be frozen as per K/N memory model rules, but you can't (because ensureNeverFrozen() ).

As for what you should do instead, I'm not sure. Flows are freezable, generally speaking. The bug you linked is old and fixed.

[xiaobailong24]

@kpgalligan Thanks for your replay. But how to use MutableStateFlow with IsolateState please?

[xiaobailong24]

Use Result wrapper the flow to solve the poblem:

 private val flowState =
        IsolateState {
            Result.success(MutableStateFlow("1"))
        }


    @OptIn(ExperimentalCoroutinesApi::class)
    @Test
    fun test() = runBlockingTest {
        println("runBlockingTest start")
        val job = launch {
            flowState
                .access {
                    it.getOrNull()!!
                }
                .asStateFlow()
                .collect {
                    run()
                }
        }

        flowState.access { it.getOrNull()?.value = "123" }

//        job.cancel()
        println("runBlockingTest end")
    }

    private suspend fun run() {
        println("collect:${flowState.access { it.getOrNull()?.value }}")
    }

[kpgalligan]

Why are you using IsolateState at all in that case? The MutableStateFlow instance will be frozen. Try this:

private val flowState = MutableStateFlow("1")

    @OptIn(ExperimentalCoroutinesApi::class)
    @Test
    fun test() = runBlockingTest {
        println("runBlockingTest start")
        val job = launch {
            flowState
                .asStateFlow()
                .collect {
                    run()
                }
        }

        flowState.value = "123"

//        job.cancel()
        println("runBlockingTest end")
    }

    private suspend fun run() {
        println("collect:${flowState.value}")
    }

[xiaobailong24]

Because the MutableStateFlow instance may be accessed to get or set new value in multi-thread.

[xiaobailong24]

@kpgalligan
access() block param will block main thread in iOS platform?

fun test() {
        val map = IsolateState{ mutableMapOf<Int,String>()}
        map.access { _map->
            // will block main thread?
            repeat(100_1000){
                _map[it] = "$it"
            }
        }
    }

[kpgalligan]

Yes, until your loop is done. IsolateState isn't async and access isn't a suspend.

[xiaobailong24]

Is there a workaround to handle time-consuming task and don't block main thread?