Reference Death Listener

gistfile1.txt

object Sentries {

    private val callbacks = ConcurrentHashMap<Reference<*>, () -> Unit>()
    private val refs = HashSet<WeakReference<*>>()
    private val refQueue = ReferenceQueue<Sentry<*>>()
    private val poller =
        Observable.interval(10000, TimeUnit.MILLISECONDS)
            .subscribe {
                refQueue.poll()?.let { ref ->
                    callbacks.remove(ref)?.invoke()
                }
            }

    fun addSentry(sentry: Sentry<*>, onFinalize: () -> Unit) {
        val ref = WeakReference(sentry, refQueue)
        callbacks[ref] = onFinalize
        refs.add(ref)
    }
    
    fun finalize() {
        poller.dispose()
    }

}

class Sentry<T>(entity: T) {

    private var entityRef: T = entity

    operator fun getValue(thisRef: Any?, property: KProperty<*>): T = entityRef

    operator fun setValue(thisRef: Any?, property: KProperty<*>, value: T) {
        entityRef = value
    }

}

fun <T> sentry(initValue: T, onFinalize: () -> Unit): Sentry<T> {
    val sentry = Sentry(initValue)
    Sentries.addSentry(sentry, onFinalize)
    return sentry
}