update

Atomically updates the value of this AtomicInt with the value obtained by calling the transform function on the current value.

@ExperimentalAtomicApiexpect inline fun AtomicInt.update(transform: (Int) -> Int)(source)

import kotlin.concurrent.atomic

fun main() {
    val counter = atomic(0)

    // Atomically add 1 to the current value
    val newValue = counter.update { it + 1 }

    println("Initial value: 0")
    println("Updated value: $newValue")   // prints 1
    println("Current value via counter.value: ${counter.value}") // prints 1
}

Source