Value classes don't work on native

[DRSchlaubi]

Currently this update call never finishes

public value class Value(public val value: Int)

public fun main() {
    val atomic = atomic(Value(1))
    println(atomic)
    atomic.update { Value(2) }
    println(atomic)
}

Might be fixed by #261

[mvicsokolova]

AtomicRef<T>.update function has the following implementation under the hood:

inline fun <T> AtomicRef<T>.update(function: (T) -> T) {
    while (true) {
        val cur = value
        val upd = function(cur)
        if (compareAndSet(cur, upd)) return // compareAndSet never succeeds
    }
}

However, for value classes this invocation of compareAndSet never succeeds due to the design of value classes: Value(1) === Value(1) is false.

It's better to avoid using AtomicReference to value classes and this will be prohibited in the next versions of the plugin. Instead, in this case you may use AtomicInt.

[mvicsokolova]

Furthermore, please note that the atomicfu plugin can only perform transformations of atomic values declared as properties. It won't be able to perform transformations on atomic values declared as local variables. For example, the code below is correct:

private val atomic = atomic(1)

public fun main() {
    println(atomic)
    atomic.update { 2 }
    println(atomic)
}

[DRSchlaubi]

How is this not a bug?

[DRSchlaubi]

If the plugin does not support this behavior it should at least fail at compile time instead of causing a deadlock at runtime

[mvicsokolova]

This behaviour will be prohibited in the compiler plugin: KT-61584