How would I use a Ktor `HttpClient` in a background thread on iOS? The client needs to always be own...

# kotlin-native

[Marc Knaup]

How would I use a Ktor HttpClient in a background thread on iOS?
The client needs to always be owned by the `Worker`'s thread and be accessible to all executions inside that worker 🤔
I basically need state in a Worker.

[Marc Knaup]

I thought about using an @ThreadLocal variable for that.
But the documentation isn't very assuring on that:

PLEASE NOTE THAT THIS ANNOTATION MAY GO AWAY IN UPCOMING RELEASES.

[olonho]

Yes, if you indeed want to attach state to given worker - @ThreadLocal is OK. In many other cases - maybe KTor on the main thread or frozen one could be OK.

[Marc Knaup]

Thank you. I'll go with @ThreadLocal for now.
HttpClient cannot be frozen as it has mutable state internally.
Using the main thread negatively affects my performance already in the iOS app and I want to get away from that.

[Marc Knaup]

I can't pass a newly created Ktor HttpClient instance to a worker.

Illegal transfer state 🤯

[Marc Knaup]

Debugging illegal state transfers is hardcore…

https://github.com/JetBrains/kotlin-native/issues/3061

[olonho]

as I suggested in the bug, in case above may make sense to transfer factory, not the created object. However, it could be bug/feature in K/N, to check - force GC run after HttpClient is created with https://github.com/JetBrains/kotlin-native/blob/b49b0be2a12f46e771c7f9e20cb543f6845e170c/runtime/src/main/kotlin/kotlin/native/internal/GC.kt#L29

[Marc Knaup]

Also illegal state transfer:
{ HttpClient(Ios).also { GC.collect() } }