lazy.scala

class Lazy[T](computeValue: => T) {
  @volatile private var computed = false
  @volatile private var computing = false // ignore me
  private var value: T = _

  def get: T = {
    if (!computed)
      //synchronized
      {
        if (!computed) {
          //assert(!computing)
          computing = true
          value = computeValue
          computed = true
          computing = false
        }
      }
    value
  }

object Lazy {
  def apply[T](computeValue: => T) = new Lazy(computeValue)
}

object A {
  def compute: Int = {
    var res = 0
    val t = new Thread() {
      override def run(): Unit = { res = B.lazyB.get }
    }
    t.start()
    t.join()
    res
  }
  val lazyA = Lazy(compute)
}

object B {
  def compute: Int = {
    var res = 0
    val t = new Thread() {
      override def run(): Unit = { res = A.lazyA.get }
    }
    t.start()
    t.join()
    res
  }
  val lazyB = Lazy(compute)
}

object ReinteringLock extends App {
  println(A.lazyA.get)
}