Scala, waiting to execute foreach on parallel collection

Question

I have code like below

    val g = new Graph(vertices)

        //Firts part

        (1 to vertices).par.foreach( i => g + new Vertex(i))

       //Second part

          for (i <- 1 to edges) {
            val data = scala.io.StdIn.readLine()
            val d = data.split(" ")
            val v1 = d(0).toInt
            val v2 = d(1).toInt
            val length = d(2).toInt
            g+(v1, v2, length)
        }

I want to execute first and second part of code sequentially. At present for loop run before the all Vertex have added to g. In code + (plus) define add new instance of Vertex to MutableList.

I'am new in scala, please help

Answer 1

I find out the solution. I read more about add new elements to collection parallel and it isn't thread save. I replaced MutableList to fixedsize array, and I add new element by index.

Some code below:

class Graph(val end: Int) {

  private val vertices : Array[Vertex] = new Array[Vertex](end)

  def +(index: Int, v: Vertex): Unit = {
    vertices(index) = v
  }  

  (...)
}

     //Firts part
      (1 to vertices).par.foreach( i => g + (i-1,new Vertex(i))) //add new vertex to array by index