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 ExecutionContext

Contains factory methods for creating execution contexts.

Source
ExecutionContext.scala
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Value Members

  1. def defaultReporter: (Throwable) ⇒ Unit

    The default reporter simply prints the stack trace of the Throwable to System.err.

    The default reporter simply prints the stack trace of the Throwable to System.err.

    returns

    the function for error reporting

  2. def fromExecutor(e: Executor): ExecutionContextExecutor

    Creates an ExecutionContext from the given Executor with the default reporter.

    Creates an ExecutionContext from the given Executor with the default reporter.

    e

    the Executor to use. If null, a new Executor is created with default configuration.

    returns

    the ExecutionContext using the given Executor

  3. def fromExecutor(e: Executor, reporter: (Throwable) ⇒ Unit): ExecutionContextExecutor

    Creates an ExecutionContext from the given Executor.

    Creates an ExecutionContext from the given Executor.

    e

    the Executor to use. If null, a new Executor is created with default configuration.

    reporter

    a function for error reporting

    returns

    the ExecutionContext using the given Executor

  4. def fromExecutorService(e: ExecutorService): ExecutionContextExecutorService

    Creates an ExecutionContext from the given ExecutorService with the default reporter.

    Creates an ExecutionContext from the given ExecutorService with the default reporter.

    If it is guaranteed that none of the executed tasks are blocking, a single-threaded ExecutorService can be used to create an ExecutionContext as follows:

    import java.util.concurrent.Executors
    val ec = ExecutionContext.fromExecutorService(Executors.newSingleThreadExecutor())
    e

    the ExecutorService to use. If null, a new ExecutorService is created with default configuration.

    returns

    the ExecutionContext using the given ExecutorService

  5. def fromExecutorService(e: ExecutorService, reporter: (Throwable) ⇒ Unit): ExecutionContextExecutorService

    Creates an ExecutionContext from the given ExecutorService.

    Creates an ExecutionContext from the given ExecutorService.

    e

    the ExecutorService to use. If null, a new ExecutorService is created with default configuration.

    reporter

    a function for error reporting

    returns

    the ExecutionContext using the given ExecutorService

  6. def global: ExecutionContextExecutor

    The explicit global ExecutionContext.

    The explicit global ExecutionContext. Invoke global when you want to provide the global ExecutionContext explicitly.

    The default ExecutionContext implementation is backed by a work-stealing thread pool. By default, the thread pool uses a target number of worker threads equal to the number of available processors.

    returns

    the global ExecutionContext

  7. object Implicits