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I’ve got a `kotlin.native.concurrent.InvalidMutabi...
# kotlin-native
r
I’ve got a 
kotlin.native.concurrent.InvalidMutabilityException
that I can’t explain.
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companion object {

        internal var xs: Set<X> by atomic(HashSet())
            private set

        fun registerX(x: X) {
            xs = xs + x
        }

    }
atomic
being:
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inline fun <reified T> atomic(initial: T) = AtomicDelegate(initial)
AtomicDelegate
being:
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class AtomicDelegate<T>(initial: T) : ReadWriteProperty<Any?, T> {

    private val atomic = AtomicReference(initial)

    override fun getValue(thisRef: Any?, property: KProperty<*>): T =
        atomic.get()

    override fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
        atomic.set(value)
    }

}
And 
AtomicReference
here is:
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internal actual class AtomicReference<T> actual constructor(initial: T) {

    private val atomic =
        kotlin.native.concurrent.FreezableAtomicReference(initial)

    actual fun get(): T =
        atomic.value

    actual fun set(newValue: T) {
        atomic.compareAndSet(get(), newValue)
    }

}
The app crashes when 
registerX
is called:
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Uncaught Kotlin exception: kotlin.native.concurrent.InvalidMutabilityException: mutation attempt of frozen kotlin.collections.HashSet@221c288
Where in my code am I attempting to modify a frozen 
HashSet
? I’m pretty sure I’m just creating a new local one, modifying it, then assigning it which makes it frozen (that’s what the 
+
does)
m
Where do you actually freeze the set, though?
I'd assume that delegate's 
setValue
should look like this:
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atomic.set(value.freeze())
r
Well I supposed it got frozen automatically when assigned. The error states it’s frozen. So I suppose that means it’s been frozen before? Is my assumption that local variables aren’t frozen false?
I’m clearly not understanding something because I’m sure I’m not trying to mutate anything frozen. I’m actually not mutating anything in this code
m
AtomicReference expects frozen values, you need to freeze them before assigning them to atomicReference
Not sure if that's the exact cause of your problem, but it could be
r
I forgot to mention that 
AtomicReference
is actually a custom thing, it’s a multiplatform expect, I’m adding it to my main message
So I should use 
atomic.compareAndSet(get(), newValue.freeze())
instead of 
atomic.compareAndSet(get(), newValue)
m
I think so
I see you're trying to make common KMP code K/N-friendly, how's that going?
Btw, Stately has KMP implementations of AtomicReference, freeze(), etc. Might be helpful https://github.com/touchlab/Stately/
d
The only place I see a mutation is 
xs + x
. Is that the entire stacktrace?
r
There’s no stacktrace in native
@Marko Mitic pretty good overall, just a bunch of 
object
`var`s who need to use my 
atomic
delegate, but other than that it’s kinda straightforward. We already have a production Android/iOS app with common backends
@Dominaezzz this mutation occurs on a local instance, so it’s not frozen, right? The source of 
+
(from kotlin):
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public operator fun <T> Set<T>.plus(element: T): Set<T> {
    val result = LinkedHashSet<T>(mapCapacity(size + 1))
    result.addAll(this)
    result.add(element)
    return result
}
add
and 
addAll
are the only mutations I see, and they should work because 
result
should not be frozen, unless I don’t understand something
d
They shouldn't be frozen but it says a 
HashSet
is being mutated.
m
Yeah, Stately doesn't freeze the reference because native AtomicReference doesn't either, they both expect object passed to be frozen already
r
I replaced 
xs = xs + x
with 
xs = setOf(x, *xs.toTypedArray())
and it seems to work. So the local hash map created by 
+
is frozen?
l
r
Yeah that’s basically what I have now
The only problem I have left is that I can’t implement an 
unregisterX
function, I don’t see how I can do that without modifying collections
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