I got an ```@SharedImmutable private val backgroundDispatcher: CoroutineDispatcher = Dispatchers.Def...

# multiplatform

[Stefan Oltmann]

I got an

@SharedImmutable
private val backgroundDispatcher: CoroutineDispatcher = Dispatchers.Default

and it looks like that every Job started by backgroundDispatcher.launch() runs on the same NSThread. I use 1.6.1-native-mt . The same code on JVM runs every job on another thread.

Do I have to do something extra to get this parallel?

[mkrussel]

on the mt branch Dispatchers.Default is single threaded on native, it's just a different thread than the main thread.

[Stefan Oltmann]

Oh wow, that's shocking. What can I do to have multiple threads?

[Stefan Oltmann]

I was thinking mt stands for *m*ulti*t*hreading 🙈

[Mitchell Syer]

Use regular coroutines 1.6.1 and use the new memory model https://github.com/JetBrains/kotlin/blob/master/kotlin-native/NEW_MM.md

[Stefan Oltmann]

So no chance to solve this with the old model? I fear that the new model might not be stable enough. 🤔

[Stefan Oltmann]

only for evaluation purposes ... I want to ship my app in a few weeks and right now I try to tune performance.

[xiaobailong24]

https://kotlinlang.org/docs/kmm-concurrency-overview.html
https://kotlinlang.org/docs/multiplatform-mobile-concurrent-mutability.html#thread-isolated-state
https://kotlinlang.org/docs/multiplatform-mobile-concurrency-and-coroutines.html

These docs maybe help you. But you must be faced with InvalidMutabilityException with old MM.
Try new MM along with coroutines.

[Stefan Oltmann]

Yes, I use the old MM already with Dispatchers.Default and I have a lot of freeze(), ensureNeverFrozen() and so on of course. I just wasn't aware that Dispatchters.Default is single-threaded, but the more I think of it the better I understand... maybe that's a default so most frameworks just work that don't care about "capture" a value.

But I was thinking there must be a Multi-threaded Dispatcher I could use if I know what I do and only pass frozen state around. But looks like there is none.

[xiaobailong24]

Maybe CourotineWorker is what you want?

[xiaobailong24]

https://github.com/Autodesk/coroutineworker

[Stefan Oltmann]

Could be. Looks like it. I will try that. Thank you. 🙂

[Stefan Oltmann]

@xiaobailong24 Almost works, except for Ktor.

[xiaobailong24]

@Stefan Oltmann Yes. U can see the below mentioned issues:
https://github.com/Autodesk/coroutineworker/issues/83
https://github.com/Autodesk/coroutineworker/issues/72

[Stefan Oltmann]

Ok, thank you. So it's not just me, KTor really can't be used with CoroutineWorker. I can also confirm that for sure.

But CoroutineWorker helps me anyway, because it seems to work nicely together with SQLDelight and so I can use it together with native-mt to load some work like metadata extraction and thumbnail creation to multiple NSThreads. I tried the normal variant (without experimental support), but that one does not work at all.

So I'm now in the situation where I can't multithread anything that is related to REST API communication (since KTor doesn't work), but I can speed up some of the other things.

I guess for my first release this will have to be good enough and as soon as the new memory model becomes production ready I can solve the rest of my performance issues.

Again, thank you for your help.