parallel.scala

// $ SBT_OPTS="-Xmx12G" sbt run

object MainApp extends App {

  def async[R](f: => R): Thread = new Thread {
    override def run(): Unit = f
  }

  def parallel[A, B](f: => A, g: => B): (A, B) = {
    var x: Option[A] = None
    var y: Option[B] = None
    val t1 = async { x = Some(f) }
    val t2 = async { y = Some(g) }
    t1.start()
    t2.start()
    t1.join()
    t2.join()
    (x.get, y.get)
  }

  def sumArr(a: Array[Int], s: Int, e: Int): Int = {
    var result = 0

    for (i <- s until e) {
      result += a(i)
    }

    result
  }

  var arr = Array.fill(2 * 1000 * 1000 * 1000) { 1 }

  val m1 = arr.length / 4;
  val m2 = arr.length / 2;
  val m3 = m1 + m2;
  val m4 = arr.length;

  println("ok")

  var (s1, s2) = parallel(
    { 
      val (s1, s2) = parallel(
        sumArr(arr, 0, m1),
        sumArr(arr, m1, m2)
      ) 
      s1 + s2
    },
    {
      val (s3, s4) = parallel(
        sumArr(arr, m2, m3),
        sumArr(arr, m3, m4)
      )
      s3 + s4
    }
  );

  println(s1 + s2)

  //println( sumArr(arr, 0, arr.length) )
}