Hi there! I trying to dig into Kotlin MPP and cor...

# kotlin-native

[Anthony Pages]

Hi there!

I trying to dig into Kotlin MPP and coroutines, especially on iOS, but I don’t understand something.
I have the following class in my Kotlin Library :

@ThreadLocal
var counter = MutableStateFlow(0)

class FlowAndCoroutines {
    fun observeOnMain(callback: () -> Unit){
        MainScope().async(Dispatchers.Main) {
            counter.collect {value ->
                callback()
            }
        }
    }

    fun triggerCollect() {
        MainScope().async(Dispatchers.Main) {
            counter.emit(counter.value + 1)
        }
    }
}

Now on iOS,

let flowTest = FlowAndCoroutines()

flowTest.observeOnMain {
    print("Callback called")
}

// In MAIN thread
flowTest.triggerCollect() // output "Callback called"

// In another thread 
flowTest.triggerCollect() // Throw exception IncorrectDereferenceException

[Kris Wong]

you can't instantiate an object on one thread and reference it on another, unless it's frozen

[Anthony Pages]

Yes, I have seen this but was thinking that the @ThreadLocal will help me

[Anthony Pages]

And the other thing I do not understand is
this kotlin code :

MainScope().async(Dispatchers.Main) { }

is different from this Swift code :

DispatchQueue.main.async { }

? why ?

[Kris Wong]

you have @ThreadLocal on counter, not on flowTest

[Kris Wong]

as for your second question, 1 is using coroutines (Kotlin), and the other is using GCD (platform)

[Anthony Pages]

Q1: Ok, then how could I have a frozen instance ? I have seen that I could use freeze() method but not on the Swift side.

Q2: yes ok, was thinking it was the same behavior behind

[Kris Wong]

either have the object freeze itself in the init method, or add an API to freeze it.

[Anthony Pages]

Didn’t have the freeze method neither on the kotlin side. Am I missing something ? Did you have any documentation or link to share ?

[Anthony Pages]

(nvm I found it in the specific platform code)

[Anthony Pages]

Thank you very much, I will try that way.

[Anthony Pages]

Edit: The freeze() method in the init works perfectly, Thx !