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 (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:

    import scala.concurrent._

    When using things like Futures, it is often required to have an implicit ExecutionContext in scope. The general advice for these implicits are as follows.

    If the code in question is a class or method definition, and no ExecutionContext is available, request one from the caller by adding an implicit parameter list:

    def myMethod(myParam: MyType)(implicit ec: ExecutionContext) = …
    //Or
    class MyClass(myParam: MyType)(implicit ec: ExecutionContext) { … }

    This allows the caller of the method, or creator of the instance of the class, to decide which ExecutionContext should be used.

    For typical REPL usage and experimentation, importing the global ExecutionContext is often desired.

    import scala.concurrent.ExcutionContext.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

class SyncVar[A] extends AnyRef

A class to provide safe concurrent access to a mutable cell. All methods are synchronized.

A

type of the contained value

Source
SyncVar.scala
Version

1.0, 10/03/2003

Linear Supertypes
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Inherited
  1. SyncVar
  2. AnyRef
  3. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
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Visibility
  1. Public
  2. All

Instance Constructors

  1. new SyncVar()

Value Members

  1. def get(timeout: Long): Option[A]

    Wait at least timeout milliseconds (possibly more) for this SyncVar to become defined and then get its value.

    Wait at least timeout milliseconds (possibly more) for this SyncVar to become defined and then get its value.

    timeout

    time in milliseconds to wait

    returns

    None if variable is undefined after timeout, Some(value) otherwise

  2. def get: A

    Wait for this SyncVar to become defined and then get the stored value without modifying it.

    Wait for this SyncVar to become defined and then get the stored value without modifying it.

    returns

    value that is held in this container

  3. def isSet: Boolean

    Check whether a value is stored in the synchronized variable.

  4. def put(x: A): Unit

    Place a value in the SyncVar.

    Place a value in the SyncVar. If the SyncVar already has a stored value, wait until another thread takes it.

  5. def take(timeout: Long): A

    Wait at least timeout milliseconds (possibly more) for this SyncVar to become defined and then get the stored value, unsetting it as a side effect.

    Wait at least timeout milliseconds (possibly more) for this SyncVar to become defined and then get the stored value, unsetting it as a side effect.

    timeout

    the amount of milliseconds to wait

    returns

    the value or a throws an exception if the timeout occurs

    Exceptions thrown

    NoSuchElementException on timeout

  6. def take(): A

    Wait for this SyncVar to become defined and then get the stored value, unsetting it as a side effect.

    Wait for this SyncVar to become defined and then get the stored value, unsetting it as a side effect.

    returns

    value that was held in this container

Deprecated Value Members

  1. def set(x: A): Unit
    Annotations
    @deprecated
    Deprecated

    (Since version 2.10.0) use put to ensure a value cannot be overwritten without a corresponding take

  2. def unset(): Unit
    Annotations
    @deprecated
    Deprecated

    (Since version 2.10.0) use take to ensure a value is never discarded