A memoizer that memoizes partial thunks, and caches values only if found (unsafe)

Memoize.scala

import kadai.concurrent.Atomic

class Memoize[A](thunk: => Option[A]) {
  val atom: Atomic[Ref] = Atomic(Empty)

  def get: A = 
    atom.get match {
      case Value(a) => a
      case exec @ Executing() => exec.await match {
        case Some(a) => if (atom.get == exec && atom.compareAndSet(exec, Value(a))) a else get
        case None => get
      }
      case Empty => atom.compareAndSet(Empty, Executing()); get
    }
  
  sealed trait Ref
  case object Empty extends Ref
  case class Executing() extends Ref {
    lazy val await: Option[A] = thunk
  }
  case class Value(a: A) extends Ref
}