Hello, can anyone have some practical solutions to...

# kotlin-native

[Qinghua]

Hello, can anyone have some practical solutions to access & modify shared singleton between threads like iOS native sharedInstance behaviour ?
I have read [CONCURRENCY.md](https://github.com/JetBrains/kotlin-native/blob/master/CONCURRENCY.md) and [IMMUTABILITY.md](https://github.com/JetBrains/kotlin-native/blob/master/IMMUTABILITY.md).
However @threadLocal annotation can not share states between threads, but shared instance in iOS domain means it shared states in all threads.

[kpgalligan]

State visible by multiple threads will be frozen. If you need to change it you need to use atomics

[kpgalligan]

https://medium.com/@kpgalligan/kotlin-native-stranger-threads-ep-2-208523d63c8f

[kpgalligan]

Well, will a copy-on-write with frozen state perform worse than NSMutableArray? I would assume yes. NSMutableArray is, as far as I know, not thread safe, so I’m not sure how that would avoid data issues if multiple threads are accessing it. https://stackoverflow.com/a/12098115/227313

[kpgalligan]

However, regardless of what happens on iOS, the Kotlin Native state rules will enforce certain things. I can tell you for sure Stately’s collections were not designed with performance in mind, and will have a review and possibly a new implementation at some point in the next few months. However, they’ll work. There’s also a linked list if COW list isn’t what you’re looking for.

[kpgalligan]

For performance, I’d probably have a list local to a thread and push/pull with a worker, but I have no idea what you’re trying to build.

[Qinghua]

For this solution “For performance, I’d probably have a list local to a thread and push/pull with a worker”, does worker support sync pull mechanism like dispatch_sync ?

[Qinghua]

Thanks for your detailed explanation. Actually, the performance is just my consideration in advance and we have not encountered concrete performance issue in our product now.

[olonho]

also note, that https://github.com/JetBrains/kotlin-native/blob/master/runtime/src/main/kotlin/kotlin/native/concurrent/MutableData.kt can be used for mutable shared binary data.