Question about shared state in Android/iOS MPP. I ...

# multiplatform

[Henrik]

Question about shared state in Android/iOS MPP.
I have a working setup with compilation to Android and iOS, but now I have run into the whole frozen state world (new to me) and is stuck after some hours of trawling the web for info and examples. Simplified, I have a static global variable CurrentConfig which points to the current version of a parsed JSON config. This is used in many places of the app, so they should not load and parse it all the time on their own, but share it. Once in a while, the config is replaced with a freshly downloaded one on the fly.
I guess this is an often seen pattern, but I have no idea how to solve it using Kotlin Native. Anyone have a best practice example to accomplish something like this?

[Olenyov Kirill]

The same situation, looking for some common caching solutions..

[Piasy]

In Android, you don't need to freeze it, so no special care is needed. In iOS, you must freeze it, then you can use AtomicReference, and call compareAndSet when you want to update it.

[Olenyov Kirill]

Is there any kind of ConcurrentHashMap for K/N?

[Piasy]

I think there isn't.

[Henrik]

Thanks Piasy. Do I need to add some kind of reference or library to Gradle to use AtomicReference? I can't resolve it. And can I use it on all platforms? The code is a shared library, so it would be nice if it worked in Android too?

[Piasy]

You don't need. AtomicReference can only be accessed in Kotlin Native.

[Henrik]

OK, thanks. Will look into it and give it a go

[Henrik]

I keep getting Unresolved reference: AtomicReference, even if I only use it in iOS-specific code and build for IosX64:
val testRef = AtomicReference(someData)

[Piasy]

Do you add import kotlin.native.concurrent.AtomicReference ?

[Henrik]

Argh, sorry. I have been spending too much time with C# lately, so I only had import kotlin.native.concurrent
That seems to do the trick, thank you again!

[kpgalligan]

There are multiple options for caches. Check out https://github.com/touchlab/Stately

[kpgalligan]

There’s a common definition of AtomicReference, as well as a concurrent hash map, although I’m rewriting that because the implementation isn’t really performant (rewriting right now, actually)

[kpgalligan]

For a simple parsed json cache, either AtomicReference, or if you know all reads will happen on, say, the main thread, you could mark the object @ThreadLocal

[kpgalligan]

See https://dev.to/touchlab/practical-kotlin-native-concurrency-ac7 and

https://www.youtube.com/watch?v=oxQ6e1VeH4M▾

for more info

[Henrik]

Thanks Kevin. And thanks for some of your well explained online articles as well. Very useful information all of it 🙂
I considered ThreadLocal but I don't think it is the right fit in this context

[kpgalligan]

Yeah, you need to be careful with it, and if you’re not quite sure of thread context, it’ll be bad.

[Henrik]

Quick question to help my understanding. If an AtomicReference is used as a private variable inside a frozen class, will it then be frozen too, so that I cannot update it using compareAndSet?