dummy_scala_thread_deadlock_avoid_example.scala

dummy_scala_thread_deadlock_avoid_example.scala

package parallelProg.week1


object Example0501 extends App {
  // Resolving deadlocks: acquire resources in the same order

  class Account(var amount:Int = 0, val name:String) {
    private val x = new AnyRef {}
    private var uidCount = 0L
    val uid = getUniqueId()


    private def lockAndTransfer(target: Account, n: Int) = {
      this.synchronized {
        target.synchronized {
          this.amount -= n
          target.amount += n
          println(this.name +".amount " +this.amount)
          println(n)
          println(target.name +".amount " +target.amount)
          println(this.amount)

          Thread.sleep(2000)
        }
      }
    }


    def getUniqueId():Long = x.synchronized {
      uidCount +=1
      uidCount
    }

    def transfer(target:Account, n:Int) = {
      if(this.uid < target.uid) this.lockAndTransfer(target, n)
      else target.lockAndTransfer(this, -n)
    }
  }

  def startThread(a: Account, b:Account, n:Int):Thread = {
    val t = new Thread {
      override def run: Unit = {
        for(i <- 0 until n) {
          val amount = i+1
          println("Transfering: " +amount + "€ from "+ a.name +" (with uid: "
            + a.uid +") to " + b.name + " (with uid: " + b.uid+")")
          a.transfer(b, 1)
        }
      }
    }
    t.start()
    t
  }

  val a3 = new Account(50, "C")
  a3.amount +=5
  println("A3 " + a3.amount)

  val a1 = new Account(50, "A")
  val a2 = new Account(50, "B")
  val t = startThread(a1, a2, 1)
  val s = startThread(a2, a1, 5)

  t.join()
  s.join()

}