Sample run of chapter's interpreter examples
// In file futures-and-concurrency/Synchronized.scala var counter = 0 synchronized { // One thread in here at a time counter = counter + 1 }
scala> import scala.concurrent.Future import scala.concurrent.Future scala> val fut = Future { Thread.sleep(10000); 21 + 21 } <console>:11: error: Cannot find an implicit ExecutionContext. You might pass an (implicit ec: ExecutionContext) parameter to your method or import scala.concurrent.ExecutionContext.Implicits.global. val fut = Future { Thread.sleep(10000); 21 + 21 } ^
scala> import scala.concurrent.ExecutionContext.Implicits.global import scala.concurrent.ExecutionContext.Implicits.global scala> val fut = Future { Thread.sleep(10000); 21 + 21 } fut: scala.concurrent.Future[Int] = ...
scala> fut.isCompleted res0: Boolean = false scala> fut.value res1: Option[scala.util.Try[Int]] = None
scala> fut.isCompleted res2: Boolean = true scala> fut.value res3: Option[scala.util.Try[Int]] = Some(Success(42))
scala> val fut = Future { Thread.sleep(10000); 21 / 0 } fut: scala.concurrent.Future[Int] = ... scala> fut.value res4: Option[scala.util.Try[Int]] = None
scala> fut.value res5: Option[scala.util.Try[Int]] = Some(Failure(java.lang.ArithmeticException: / by zero))
scala> val fut = Future { Thread.sleep(10000); 21 + 21 } fut: scala.concurrent.Future[Int] = ...
scala> val result = fut.map(x => x + 1) result: scala.concurrent.Future[Int] = ... scala> result.value res5: Option[scala.util.Try[Int]] = None
scala> result.value res6: Option[scala.util.Try[Int]] = Some(Success(43))
scala> val fut1 = Future { Thread.sleep(10000); 21 + 21 } fut1: scala.concurrent.Future[Int] = ... scala> val fut2 = Future { Thread.sleep(10000); 23 + 23 } fut2: scala.concurrent.Future[Int] = ...
scala> for { x <- fut1 y <- fut2 } yield x + y res7: scala.concurrent.Future[Int] = ...
scala> res7.value res8: Option[scala.util.Try[Int]] = Some(Success(88))
scala> for { x <- Future { Thread.sleep(10000); 21 + 21 } y <- Future { Thread.sleep(10000); 23 + 23 } } yield x + y res9: scala.concurrent.Future[Int] = ... scala> res9.value res27: Option[scala.util.Try[Int]] = None scala> // Will need at least 20 seconds to complete scala> res9.value res28: Option[scala.util.Try[Int]] = Some(Success(88))
scala> Future.successful { 21 + 21 } res2: scala.concurrent.Future[Int] = ...
scala> Future.failed(new Exception("bummer!")) res3: scala.concurrent.Future[Nothing] = ...
scala> import scala.util.{Success,Failure} import scala.util.{Success, Failure} scala> Future.fromTry(Success { 21 + 21 }) res4: scala.concurrent.Future[Int] = ... scala> Future.fromTry(Failure(new Exception("bummer!"))) res5: scala.concurrent.Future[Nothing] = ...
scala> val pro = Promise[Int] pro: scala.concurrent.Promise[Int] = ... scala> val fut = pro.future fut: scala.concurrent.Future[Int] = ... scala> fut.value res8: Option[scala.util.Try[Int]] = None
scala> pro.success(42) res9: pro.type = ... scala> fut.value res10: Option[scala.util.Try[Int]] = Some(Success(42))
scala> val fut = Future { 42 } fut: scala.concurrent.Future[Int] = ... scala> val valid = fut.filter(res => res > 0) valid: scala.concurrent.Future[Int] = ... scala> valid.value res0: Option[scala.util.Try[Int]] = Some(Success(42))
scala> val invalid = fut.filter(res => res < 0) invalid: scala.concurrent.Future[Int] = ... scala> invalid.value res1: Option[scala.util.Try[Int]] = Some(Failure(java.util.NoSuchElementException: Future.filter predicate is not satisfied))
scala> val valid = for (res <- fut if res > 0) yield res valid: scala.concurrent.Future[Int] = ... scala> valid.value res2: Option[scala.util.Try[Int]] = Some(Success(42)) scala> val invalid = for (res <- fut if res < 0) yield res invalid: scala.concurrent.Future[Int] = ... scala> invalid.value res3: Option[scala.util.Try[Int]] = Some(Failure(java.util.NoSuchElementException: Future.filter predicate is not satisfied))
scala> val valid = fut collect { case res if res > 0 => res + 46 } valid: scala.concurrent.Future[Int] = ... scala> valid.value res17: Option[scala.util.Try[Int]] = Some(Success(88))
scala> val invalid = fut collect { case res if res < 0 => res + 46 } invalid: scala.concurrent.Future[Int] = ... scala> invalid.value res18: Option[scala.util.Try[Int]] = Some(Failure(java.util.NoSuchElementException: Future.collect partial function is not defined at: 42))
scala> val failure = Future { 42 / 0 } failure: scala.concurrent.Future[Int] = ... scala> failure.value res23: Option[scala.util.Try[Int]] = Some(Failure(java.lang.ArithmeticException: / by zero)) scala> val expectedFailure = failure.failed expectedFailure: scala.concurrent.Future[Throwable] = ... scala> expectedFailure.value res25: Option[scala.util.Try[Throwable]] = Some(Success(java.lang.ArithmeticException: / by zero))
scala> val success = Future { 42 / 1 } success: scala.concurrent.Future[Int] = ... scala> success.value res21: Option[scala.util.Try[Int]] = Some(Success(42)) scala> val unexpectedSuccess = success.failed unexpectedSuccess: scala.concurrent.Future[Throwable] = ... scala> unexpectedSuccess.value res26: Option[scala.util.Try[Throwable]] = Some(Failure(java.util.NoSuchElementException: Future.failed not completed with a throwable.))
scala> val fallback = failure.fallbackTo(success) fallback: scala.concurrent.Future[Int] = ... scala> fallback.value res27: Option[scala.util.Try[Int]] = Some(Success(42))
scala> val failedFallback = failure.fallbackTo( Future { val res = 42; require(res < 0); res } ) failedFallback: scala.concurrent.Future[Int] = ... scala> failedFallback.value res28: Option[scala.util.Try[Int]] = Some(Failure(java.lang.ArithmeticException: / by zero))
scala> val recovered = failedFallback recover { case ex: ArithmeticException => -1 } recovered: scala.concurrent.Future[Int] = ... scala> recovered.value res32: Option[scala.util.Try[Int]] = Some(Success(-1))
scala> val unrecovered = fallback recover { case ex: ArithmeticException => -1 } unrecovered: scala.concurrent.Future[Int] = ... scala> unrecovered.value res33: Option[scala.util.Try[Int]] = Some(Success(42))
scala> val alsoUnrecovered = failedFallback recover { case ex: IllegalArgumentException => -2 } alsoUnrecovered: scala.concurrent.Future[Int] = ... scala> alsoUnrecovered.value res34: Option[scala.util.Try[Int]] = Some(Failure(java.lang.ArithmeticException: / by zero))
scala> val alsoRecovered = failedFallback recoverWith { case ex: ArithmeticException => Future { 42 + 46 } } alsoRecovered: scala.concurrent.Future[Int] = ... scala> alsoRecovered.value res35: Option[scala.util.Try[Int]] = Some(Success(88))
scala> val first = success.transform( res => res * -1, ex => new Exception("see cause", ex) ) first: scala.concurrent.Future[Int] = ...
scala> first.value res42: Option[scala.util.Try[Int]] = Some(Success(-42))
scala> val second = failure.transform( res => res * -1, ex => new Exception("see cause", ex) ) second: scala.concurrent.Future[Int] = ... scala> second.value res43: Option[scala.util.Try[Int]] = Some(Failure(java.lang.Exception: see cause))
scala> val firstCase = success.transform { // Scala 2.12 case Success(res) => Success(res * -1) case Failure(ex) => Failure(new Exception("see cause", ex)) } first: scala.concurrent.Future[Int] = ... scala> firstCase.value res6: Option[scala.util.Try[Int]] = Some(Success(-42)) scala> val secondCase = failure.transform { case Success(res) => Success(res * -1) case Failure(ex) => Failure(new Exception("see cause", ex)) } secondCase: scala.concurrent.Future[Int] = ... scala> secondCase.value res8: Option[scala.util.Try[Int]] = Some(Failure(java.lang.Exception: see cause))
scala> val nonNegative = failure.transform { // Scala 2.12 case Success(res) => Success(res.abs + 1) case Failure(_) => Success(0) } nonNegative: scala.concurrent.Future[Int] = ... scala> nonNegative.value res11: Option[scala.util.Try[Int]] = Some(Success(0))
scala> val zippedSuccess = success zip recovered zippedSuccess: scala.concurrent.Future[(Int, Int)] = ... scala> zippedSuccess.value res46: Option[scala.util.Try[(Int, Int)]] = Some(Success((42,-1)))
scala> val zippedFailure = success zip failure zippedFailure: scala.concurrent.Future[(Int, Int)] = ... scala> zippedFailure.value res48: Option[scala.util.Try[(Int, Int)]] = Some(Failure(java.lang.ArithmeticException: / by zero))
scala> val fortyTwo = Future { 21 + 21 } fortyTwo: scala.concurrent.Future[Int] = ... scala> val fortySix = Future { 23 + 23 } fortySix: scala.concurrent.Future[Int] = ... scala> val futureNums = List(fortyTwo, fortySix) futureNums: List[scala.concurrent.Future[Int]] = ... scala> val folded = Future.fold(futureNums)(0) { (acc, num) => acc + num } folded: scala.concurrent.Future[Int] = ... scala> folded.value res53: Option[scala.util.Try[Int]] = Some(Success(88))
scala> val reduced = Future.reduce(futureNums) { (acc, num) => acc + num } reduced: scala.concurrent.Future[Int] = ... scala> reduced.value res54: Option[scala.util.Try[Int]] = Some(Success(88))
scala> val futureList = Future.sequence(futureNums) futureList: scala.concurrent.Future[List[Int]] = ... scala> futureList.value res55: Option[scala.util.Try[List[Int]]] = Some(Success(List(42, 46)))
scala> val traversed = Future.traverse(List(1, 2, 3)) { i => Future(i) } traversed: scala.concurrent.Future[List[Int]] = ... scala> traversed.value res58: Option[scala.util.Try[List[Int]]] = Some(Success(List(1, 2, 3)))
scala> failure.foreach(ex => println(ex)) scala> success.foreach(res => println(res)) 42
scala> for (res <- failure) println(res) scala> for (res <- success) println(res) 42
scala> import scala.util.{Success, Failure} import scala.util.{Success, Failure} scala> success onComplete { case Success(res) => println(res) case Failure(ex) => println(ex) } 42 scala> failure onComplete { case Success(res) => println(res) case Failure(ex) => println(ex) } java.lang.ArithmeticException: / by zero
scala> val newFuture = success andThen { case Success(res) => println(res) case Failure(ex) => println(ex) } 42 newFuture: scala.concurrent.Future[Int] = ... scala> newFuture.value res76: Option[scala.util.Try[Int]] = Some(Success(42))
scala> val nestedFuture = Future { Future { 42 } } nestedFuture: Future[Future[Int]] = ... scala> val flattened = nestedFuture.flatten // Scala 2.12 flattened: scala.concurrent.Future[Int] = Future(Success(42))
scala> val futNum = Future { 21 + 21 } futNum: scala.concurrent.Future[Int] = ... scala> val futStr = Future { "ans" + "wer" } futStr: scala.concurrent.Future[String] = ... scala> val zipped = futNum zip futStr zipped: scala.concurrent.Future[(Int, String)] = ... scala> val mapped = zipped map { case (num, str) => s"$num is the $str" } mapped: scala.concurrent.Future[String] = ... scala> mapped.value res2: Option[scala.util.Try[String]] = Some(Success(42 is the answer))
scala> val fut = futNum.zipWith(futStr) { // Scala 2.12 case (num, str) => s"num is the str" } zipWithed: scala.concurrent.Future[String] = ... scala> fut.value res3: Option[scala.util.Try[String]] = Some(Success(42 is the answer))
scala> val flipped = success.transformWith { // Scala 2.12 | case Success(res) => | Future { throw new Exception(res.toString) } | case Failure(ex) => Future { 21 + 21 } | } flipped: scala.concurrent.Future[Int] = ... scala> flipped.value res5: Option[scala.util.Try[Int]] = Some(Failure(java.lang.Exception: 42))
scala> import scala.concurrent.Await import scala.concurrent.Await scala> import scala.concurrent.duration._ import scala.concurrent.duration._ scala> val fut = Future { Thread.sleep(10000); 21 + 21 } fut: scala.concurrent.Future[Int] = ... scala> val x = Await.result(fut, 15.seconds) // blocks x: Int = 42
scala> import org.scalatest.Matchers._ import org.scalatest.Matchers._ scala> x should be (42) res0: org.scalatest.Assertion = Succeeded
scala> import org.scalatest.concurrent.ScalaFutures._ import org.scalatest.concurrent.ScalaFutures._ scala> val fut = Future { Thread.sleep(10000); 21 + 21 } fut: scala.concurrent.Future[Int] = ... scala> fut.futureValue should be (42) // futureValue blocks res1: org.scalatest.Assertion = Succeeded
import org.scalatest.AsyncFunSpec import scala.concurrent.Future class AddSpec extends AsyncFunSpec { def addSoon(addends: Int*): Future[Int] = Future { addends.sum } describe("addSoon") { it("will eventually compute a sum of passed Ints") { val futureSum: Future[Int] = addSoon(1, 2) // You can map assertions onto a Future, then return // the resulting Future[Assertion] to ScalaTest: futureSum map { sum => assert(sum == 3) } } } }
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