parallelism on the jvm ii

parprog0

class Account(private var amount: Int = 0) {
def transfer(target:Account, n: Int) =
  this.synchronized {
    target.synchronized {
      this.amount -= n
      target.amount += n
      }
     }
 }
 
 def startThread(a: Account, b: Account, n: Int) = {
  val t = new Thread {
    override def run() {
      for (i <- 0 until n) {
        a.transfer(b,1)
        }
       }
      }
      t.start()
      t
     }
     
  val a1 = new Account(500000)
  val a2 = new Account(700000)
  
  val t = startThread(a1, a2, 150000)
  vat s = startThread(a2, a1, 150000)
  t.join()
  s.join()