Scala example source code file (FutureTest.scala)

This example Scala source code file (FutureTest.scala) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Scala by Example" ^TM.

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Java - Scala tags/keywords

equal, future, futureequal, futuretest, int, nondeterminism, set, speclite, threading, threads, timed, unit

The FutureTest.scala Scala example source code

package scalaz
package concurrent

import scalaz.scalacheck.ScalazProperties._
import scalaz.scalacheck.ScalazArbitrary._
import std.AllInstances._
import java.util.concurrent._
import ConcurrentTest._

object FutureTest extends SpecLite {
  implicit def FutureEqual[A: Equal] =
    Equal[A].contramap((_: Future[A]).unsafePerformSync)

  checkAll(monad.laws[Future])

  val non = Nondeterminism[Future]

  "Future" should {
    "not deadlock when using Nondeterminism#chooseAny" in {
      withTimeout(2000) {
        deadlocks(3).unsafePerformSync.length must_== 4
      }
    }
    "have a run method that returns" in {
      "when constructed from Future.now" in prop{(n: Int) =>
        Future.now(n).unsafePerformSync must_== n
      }
      "when constructed from Future.delay" in prop{(n: Int) =>
        Future.delay(n).unsafePerformSync must_== n
      }
      "when constructed from Future.fork" in prop{(n: Int) =>
        Future.fork(Future.now(n)).unsafePerformSync must_== n
      }
      "when constructed from Future.suspend" ! prop{(n: Int) =>
        Future.suspend(Future.now(n)).unsafePerformSync must_== n
      }
      "when constructed from Future.async" ! prop{(n: Int) =>
        def callback(call: Int => Unit): Unit = call(n)
        Future.async(callback).unsafePerformSync must_== n
      }
      "when constructed from Future.apply" ! prop{(n: Int) =>
        Future.apply(n).unsafePerformSync must_== n
      }
    }
  }

  "Nondeterminism[Future]" should {
    import scalaz.concurrent.Future._
    implicit val es = Executors.newFixedThreadPool(1)
    val intSetReducer = Reducer.unitReducer[Int, Set[Int]](Set(_))

    "correctly process reduceUnordered for >1 futures in non-blocking way" in {
      val f1 = fork(now(1))(es)
      val f2 = delay(7).flatMap(_=>fork(now(2))(es))
      val f3 = fork(now(3))(es)

      val f = fork(Future.reduceUnordered(Seq(f1,f2,f3))(intSetReducer))(es)

      f.unsafePerformSync must_== Set(1,2,3)
    }


    "correctly process reduceUnordered for 1 future in non-blocking way" in {
      val f1 = fork(now(1))(es)

      val f = fork(Future.reduceUnordered(Seq(f1))(intSetReducer))(es)

      f.unsafePerformSync must_== Set(1)
    }

    "correctly process reduceUnordered for empty seq of futures in non-blocking way" in {
      val f = fork(Future.reduceUnordered(Seq())(intSetReducer))(es)

      f.unsafePerformSync must_== Set()
    }
  }

  "Timed Future" should {
    "not run futures sequentially" in {
      val times = Stream.iterate(100)(_ + 100).take(10)

      val start  = System.currentTimeMillis()
      val result = Future.fork(Future.gatherUnordered(times.map { time =>
        Future.fork {
          Thread.sleep(time)
          Future.now(time)
        }
      })).unsafePerformSync
      val duration = System.currentTimeMillis() - start

      result.length must_== times.size and duration.toInt mustBe_< times.fold(0)(_ + _)
    }
  }

  /*
   * This is a little deadlock factory based on the code in #308.
   *
   * Basically it builds a tree of futures that run in a
   * non-determistic order. The sleep(x) provides an increase
   * in the number of collisions, and chance for deadlock.
   *
   * Before #312 patch, this triggered deadlock approx 1 in every
   * 3 runs.
   */
  def deadlocks(depth: Int): Future[List[Long]] =
    if (depth == 1)
      Future.fork(
        Future.delay({
          Thread.sleep(20)
          List(System.currentTimeMillis)
        })
      )
    else
      Future.fork(
        non.both(deadlocks(depth - 1), deadlocks(depth - 1)) map ({
          case (l, r) => l ++ r
        })
      )
}