Packages

  • package root

    This is the documentation for the Scala standard library.

    This is the documentation for the Scala standard library.

    Package structure

    The scala package contains core types like Int, Float, Array or Option which are accessible in all Scala compilation units without explicit qualification or imports.

    Notable packages include:

    Other packages exist. See the complete list on the right.

    Additional parts of the standard library are shipped as separate libraries. These include:

    • scala.reflect - Scala's reflection API (scala-reflect.jar)
    • scala.xml - XML parsing, manipulation, and serialization (scala-xml.jar)
    • scala.swing - A convenient wrapper around Java's GUI framework called Swing (scala-swing.jar)
    • scala.util.parsing - Parser combinators, including an example implementation of a JSON parser (scala-parser-combinators.jar)

    Automatic imports

    Identifiers in the scala package and the scala.Predef object are always in scope by default.

    Some of these identifiers are type aliases provided as shortcuts to commonly used classes. For example, List is an alias for scala.collection.immutable.List.

    Other aliases refer to classes provided by the underlying platform. For example, on the JVM, String is an alias for java.lang.String.

    Definition Classes
    root
  • package scala

    Core Scala types.

    Core Scala types. They are always available without an explicit import.

    Definition Classes
    root
  • package concurrent

    This package object contains primitives for concurrent and parallel programming.

    This package object contains primitives for concurrent and parallel programming.

    Guide

    A more detailed guide to Futures and Promises, including discussion and examples can be found at http://docs.scala-lang.org/overviews/core/futures.html.

    Common Imports

    When working with Futures, you will often find that importing the whole concurrent package is convenient, furthermore you are likely to need an implicit ExecutionContext in scope for many operations involving Futures and Promises:

    import scala.concurrent._
import ExecutionContext.Implicits.global

    Specifying Durations

    Operations often require a duration to be specified. A duration DSL is available to make defining these easier:

    import scala.concurrent.duration._
val d: Duration = 10.seconds

    Using Futures For Non-blocking Computation

    Basic use of futures is easy with the factory method on Future, which executes a provided function asynchronously, handing you back a future result of that function without blocking the current thread. In order to create the Future you will need either an implicit or explicit ExecutionContext to be provided:

    import scala.concurrent._
import ExecutionContext.Implicits.global  // implicit execution context

val firstZebra: Future[Int] = Future {
  val source = scala.io.Source.fromFile("/etc/dictionaries-common/words")
  source.toSeq.indexOfSlice("zebra")
}

    Avoid Blocking

    Although blocking is possible in order to await results (with a mandatory timeout duration):

    import scala.concurrent.duration._
Await.result(firstZebra, 10.seconds)

    and although this is sometimes necessary to do, in particular for testing purposes, blocking in general is discouraged when working with Futures and concurrency in order to avoid potential deadlocks and improve performance. Instead, use callbacks or combinators to remain in the future domain:

    val animalRange: Future[Int] = for {
  aardvark <- firstAardvark
  zebra <- firstZebra
} yield zebra - aardvark

animalRange.onSuccess {
  case x if x > 500000 => println("It's a long way from Aardvark to Zebra")
}
    Definition Classes
    scala
  • package duration
    Definition Classes
    concurrent
  • package forkjoin
    Definition Classes
    concurrent
  • Await
  • Awaitable
  • BlockContext
  • CanAwait
  • Channel
  • DelayedLazyVal
  • ExecutionContext
  • ExecutionContextExecutor
  • ExecutionContextExecutorService
  • Future
  • JavaConversions
  • Lock
  • OnCompleteRunnable
  • Promise
  • SyncChannel
  • SyncVar

object Await

Await is what is used to ensure proper handling of blocking for Awaitable instances.

While occasionally useful, e.g. for testing, it is recommended that you avoid Await when possible in favor of callbacks and combinators like onComplete and use in for comprehensions. Await will block the thread on which it runs, and could cause performance and deadlock issues.

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Value Members

  1. def ready[T](awaitable: Awaitable[T], atMost: Duration): awaitable.type

    Await the "completed" state of an Awaitable.

    Await the "completed" state of an Awaitable.

    Although this method is blocking, the internal use of blocking ensures that the underlying ExecutionContext is prepared to properly manage the blocking.

    awaitable

    the Awaitable to be awaited

    atMost

    maximum wait time, which may be negative (no waiting is done), Duration.Inf for unbounded waiting, or a finite positive duration

    returns

    the awaitable

    Annotations
    @throws( clazz = classOf[TimeoutException] ) @throws( clazz = classOf[InterruptedException] )
    Exceptions thrown

    IllegalArgumentException if atMost is Duration.Undefined

    InterruptedException if the current thread is interrupted while waiting

    TimeoutException if after waiting for the specified time this Awaitable is still not ready

  2. def result[T](awaitable: Awaitable[T], atMost: Duration): T

    Await and return the result (of type T) of an Awaitable.

    Await and return the result (of type T) of an Awaitable.

    Although this method is blocking, the internal use of blocking ensures that the underlying ExecutionContext to properly detect blocking and ensure that there are no deadlocks.

    awaitable

    the Awaitable to be awaited

    atMost

    maximum wait time, which may be negative (no waiting is done), Duration.Inf for unbounded waiting, or a finite positive duration

    returns

    the result value if awaitable is completed within the specific maximum wait time

    Annotations
    @throws( clazz = classOf[Exception] )
    Exceptions thrown

    IllegalArgumentException if atMost is Duration.Undefined

    InterruptedException if the current thread is interrupted while waiting

    TimeoutException if after waiting for the specified time awaitable is still not ready