Future example 1

future_example1.scala

import scala.util.{Failure, Success}
import scala.concurrent.Future
import scala.concurrent.ExecutionContext.Implicits.global

/**
  * Computation 1 depends on nothing
  * Computation 1b depends on result of 1
  * Computation 2 depends on nothing
  *
  * Computation 1b may thrown an exception
  */
object TestApp extends App{
  val r = scala.util.Random

  type computation1Result = Int

  case class ComputationException(e: String) extends Exception

  val computation1: Future[computation1Result] = Future {
    Thread.sleep(r.nextInt(2000))
    val result = r.nextInt(100)
    println(s"Computation1 complete with result $result")
    result
  }

  def computation1b(c1: computation1Result): Future[Int] = Future {
    Thread.sleep(r.nextInt(2000))
    if(r.nextInt(2) == 0 ) throw ComputationException(s"computation1b Runtime exception")
    val result = c1 * r.nextInt(100)
    println(s"Computation1b complete with result $result")
    result
  }

  val computation2: Future[Int] = Future {
    Thread.sleep(r.nextInt(200))
    val result = r.nextInt(100)
    println(s"Computation2 complete with result $result")
    result
  }

  val result = for {
    c1 <- computation1
    c1b <- computation1b(c1)
    c2 <- computation2
  } yield(c1 * c1b * c2)

  result.onComplete(r => r match {
    case Success(s) => println(s"Success: $s")
    case Failure(f) => println(s"Failure: $f")
  })

  Thread.sleep(5000)
}