Is it possible to mutate a singleton instance from...

# kotlin-native

[Sam Schilling]

Is it possible to mutate a singleton instance from a background thread via Worker.execute with TransferMode.SAFE?

Basically I want to keep a global cache as a singleton instance and have the background workers able to add things to the cache. But I think that may violate mutable XOR global.

[Jeremy]

You should be able to use AtomicReference or DetachedObjectGraph

[Jeremy]

Or perform mutation on callback

[Sam Schilling]

hmm good point on mutating on callback. My use case is a bit more complicated so that alone won’t work but you gave me an idea of what I could do as a work around

[basher]

you can update a reference that looks like this:

@SharedImmutable
val someRef = AtomicReference<SomObject?>(null)

[basher]

then someRef.value = newValue.freeze() (has to be frozen)

[Sam Schilling]

wouldn’t that mean i can no longer mutate someRef.value?

[Jeremy]

Yes you'd need to copy and replace with a different object

[Jeremy]

I think DetachedObjectGraph should allow you to transfer ownership and mutate

[Sam Schilling]

The thing is I will have many threads running concurrently at any given time and all will need to update the cache. Transferring seems tricky in that scenario

[basher]

you won't be able to mutate the thing you stored in someRef.value anymore, correct

[Jeremy]

KN is designed explicitly to prevent multiple threads from updating shared mutate state

[Sam Schilling]

I know, but in some cases it is useful or even necessary

[Jeremy]

You may need to abstract that logic and implement on each platform