fixed_typical.scala

class Account(val accountNo: String, beginningBalance: Int){
  private var _balance = beginningBalance
  def balance = this.synchronized{ _balance }
  def credit(amount: Int) = this.synchronized{ _balance = _balance + amount }
  def debit(amount: Int) = this.synchronized { _balance = _balance - amount }
}

object Bank{
        
  val accounts = Map("from" -> new Account("from", 500), "to" -> new Account("to", 500) )

  def transfer(fromNo: String, toNo: String, amount: Int): Unit = {
    val (from, to) = (accounts(fromNo), accounts(toNo))
    val (lockOne, lockTwo) = if(from.accountNo < to.accountNo) (from, to) else (to, from)
    lockOne.synchronized{
      lockTwo.synchronized{
        if(from.balance > amount){
          to.credit(amount)
          from.debit(amount)
        }
      }
    }
  }
  
  def main(args: Array[String]): Unit = {
    import java.util.concurrent._
    import scala.util.Random._
    val executor = Executors.newFixedThreadPool(2)
    for(_ <- 1 to 10000) yield {
      executor.submit(new Runnable(){
        def run = {
          if(nextInt(2) % 2 == 0) Bank.transfer("from", "to", nextInt(50))
          else Bank.transfer("to", "from", nextInt(50))
        }
      })
    }
  }
}