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, 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

trait Promise[T] extends AnyRef

Promise is an object which can be completed with a value or failed with an exception.

Source
Promise.scala
Linear Supertypes
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Inherited
  1. Promise
  2. AnyRef
  3. Any
Implicitly
  1. by any2stringadd
  2. by StringFormat
  3. by Ensuring
  4. by ArrowAssoc
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Abstract Value Members

  1. abstract def future: Future[T]

    Future containing the value of this promise.

  2. abstract def isCompleted: Boolean

    Returns whether the promise has already been completed with a value or an exception.

    Returns whether the promise has already been completed with a value or an exception.

    Note: Using this method may result in non-deterministic concurrent programs.

    returns

    true if the promise is already completed, false otherwise

  3. abstract def tryComplete(result: Try[T]): Boolean

    Tries to complete the promise with either a value or the exception.

    Tries to complete the promise with either a value or the exception.

    Note: Using this method may result in non-deterministic concurrent programs.

    returns

    If the promise has already been completed returns false, or true otherwise.

Concrete Value Members

  1. final def !=(arg0: Any): Boolean

    Test two objects for inequality.

    Test two objects for inequality.

    returns

    true if !(this == that), false otherwise.

    Definition Classes
    AnyRef → Any
  2. final def ##(): Int

    Equivalent to x.hashCode except for boxed numeric types and null.

    Equivalent to x.hashCode except for boxed numeric types and null. For numerics, it returns a hash value which is consistent with value equality: if two value type instances compare as true, then ## will produce the same hash value for each of them. For null returns a hashcode where null.hashCode throws a NullPointerException.

    returns

    a hash value consistent with ==

    Definition Classes
    AnyRef → Any
  3. def +(other: String): String
    Implicit
    This member is added by an implicit conversion from Promise[T] to any2stringadd[Promise[T]] performed by method any2stringadd in scala.Predef.
    Definition Classes
    any2stringadd
  4. def ->[B](y: B): (Promise[T], B)
    Implicit
    This member is added by an implicit conversion from Promise[T] to ArrowAssoc[Promise[T]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc
    Annotations
    @inline()
  5. final def ==(arg0: Any): Boolean

    The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

    The expression x == that is equivalent to if (x eq null) that eq null else x.equals(that).

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    Definition Classes
    AnyRef → Any
  6. final def asInstanceOf[T0]: T0

    Cast the receiver object to be of type T0.

    Cast the receiver object to be of type T0.

    Note that the success of a cast at runtime is modulo Scala's erasure semantics. Therefore the expression 1.asInstanceOf[String] will throw a ClassCastException at runtime, while the expression List(1).asInstanceOf[List[String]] will not. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the requested type.

    returns

    the receiver object.

    Definition Classes
    Any
    Exceptions thrown

    ClassCastException if the receiver object is not an instance of the erasure of type T0.

  7. def clone(): AnyRef

    Create a copy of the receiver object.

    Create a copy of the receiver object.

    The default implementation of the clone method is platform dependent.

    returns

    a copy of the receiver object.

    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
    Note

    not specified by SLS as a member of AnyRef

  8. def complete(result: Try[T]): Promise.this.type

    Completes the promise with either an exception or a value.

    Completes the promise with either an exception or a value.

    result

    Either the value or the exception to complete the promise with. If the promise has already been fulfilled, failed or has timed out, calling this method will throw an IllegalStateException.

  9. final def completeWith(other: Future[T]): Promise.this.type

    Completes this promise with the specified future, once that future is completed.

    Completes this promise with the specified future, once that future is completed.

    returns

    This promise

  10. def ensuring(cond: (Promise[T]) ⇒ Boolean, msg: ⇒ Any): Promise[T]
    Implicit
    This member is added by an implicit conversion from Promise[T] to Ensuring[Promise[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  11. def ensuring(cond: (Promise[T]) ⇒ Boolean): Promise[T]
    Implicit
    This member is added by an implicit conversion from Promise[T] to Ensuring[Promise[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  12. def ensuring(cond: Boolean, msg: ⇒ Any): Promise[T]
    Implicit
    This member is added by an implicit conversion from Promise[T] to Ensuring[Promise[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  13. def ensuring(cond: Boolean): Promise[T]
    Implicit
    This member is added by an implicit conversion from Promise[T] to Ensuring[Promise[T]] performed by method Ensuring in scala.Predef.
    Definition Classes
    Ensuring
  14. final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (that) is a reference to the receiver object (this).

    Tests whether the argument (that) is a reference to the receiver object (this).

    The eq method implements an equivalence relation on non-null instances of AnyRef, and has three additional properties:

    • It is consistent: for any non-null instances x and y of type AnyRef, multiple invocations of x.eq(y) consistently returns true or consistently returns false.
    • For any non-null instance x of type AnyRef, x.eq(null) and null.eq(x) returns false.
    • null.eq(null) returns true.

    When overriding the equals or hashCode methods, it is important to ensure that their behavior is consistent with reference equality. Therefore, if two objects are references to each other (o1 eq o2), they should be equal to each other (o1 == o2) and they should hash to the same value (o1.hashCode == o2.hashCode).

    returns

    true if the argument is a reference to the receiver object; false otherwise.

    Definition Classes
    AnyRef
  15. def equals(arg0: Any): Boolean

    The equality method for reference types.

    The equality method for reference types. Default implementation delegates to eq.

    See also equals in scala.Any.

    returns

    true if the receiver object is equivalent to the argument; false otherwise.

    Definition Classes
    AnyRef → Any
  16. def failure(cause: Throwable): Promise.this.type

    Completes the promise with an exception.

    Completes the promise with an exception.

    cause

    The throwable to complete the promise with. If the throwable used to fail this promise is an error, a control exception or an interrupted exception, it will be wrapped as a cause within an ExecutionException which will fail the promise. If the promise has already been fulfilled, failed or has timed out, calling this method will throw an IllegalStateException.

  17. def finalize(): Unit

    Called by the garbage collector on the receiver object when there are no more references to the object.

    Called by the garbage collector on the receiver object when there are no more references to the object.

    The details of when and if the finalize method is invoked, as well as the interaction between finalize and non-local returns and exceptions, are all platform dependent.

    Attributes
    protected[java.lang]
    Definition Classes
    AnyRef
    Annotations
    @throws( classOf[java.lang.Throwable] )
    Note

    not specified by SLS as a member of AnyRef

  18. def formatted(fmtstr: String): String

    Returns string formatted according to given format string.

    Returns string formatted according to given format string. Format strings are as for String.format (@see java.lang.String.format).

    Implicit
    This member is added by an implicit conversion from Promise[T] to StringFormat[Promise[T]] performed by method StringFormat in scala.Predef.
    Definition Classes
    StringFormat
    Annotations
    @inline()
  19. final def getClass(): Class[_]

    Returns the runtime class representation of the object.

    Returns the runtime class representation of the object.

    returns

    a class object corresponding to the runtime type of the receiver.

    Definition Classes
    AnyRef → Any
  20. def hashCode(): Int

    The hashCode method for reference types.

    The hashCode method for reference types. See hashCode in scala.Any.

    returns

    the hash code value for this object.

    Definition Classes
    AnyRef → Any
  21. final def isInstanceOf[T0]: Boolean

    Test whether the dynamic type of the receiver object is T0.

    Test whether the dynamic type of the receiver object is T0.

    Note that the result of the test is modulo Scala's erasure semantics. Therefore the expression 1.isInstanceOf[String] will return false, while the expression List(1).isInstanceOf[List[String]] will return true. In the latter example, because the type argument is erased as part of compilation it is not possible to check whether the contents of the list are of the specified type.

    returns

    true if the receiver object is an instance of erasure of type T0; false otherwise.

    Definition Classes
    Any
  22. final def ne(arg0: AnyRef): Boolean

    Equivalent to !(this eq that).

    Equivalent to !(this eq that).

    returns

    true if the argument is not a reference to the receiver object; false otherwise.

    Definition Classes
    AnyRef
  23. final def notify(): Unit

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Wakes up a single thread that is waiting on the receiver object's monitor.

    Definition Classes
    AnyRef
    Note

    not specified by SLS as a member of AnyRef

  24. final def notifyAll(): Unit

    Wakes up all threads that are waiting on the receiver object's monitor.

    Wakes up all threads that are waiting on the receiver object's monitor.

    Definition Classes
    AnyRef
    Note

    not specified by SLS as a member of AnyRef

  25. def success(value: T): Promise.this.type

    Completes the promise with a value.

    Completes the promise with a value.

    value

    The value to complete the promise with. If the promise has already been fulfilled, failed or has timed out, calling this method will throw an IllegalStateException.

  26. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  27. def toString(): String

    Creates a String representation of this object.

    Creates a String representation of this object. The default representation is platform dependent. On the java platform it is the concatenation of the class name, "@", and the object's hashcode in hexadecimal.

    returns

    a String representation of the object.

    Definition Classes
    AnyRef → Any
  28. final def tryCompleteWith(other: Future[T]): Promise.this.type

    Attempts to complete this promise with the specified future, once that future is completed.

    Attempts to complete this promise with the specified future, once that future is completed.

    returns

    This promise

  29. def tryFailure(cause: Throwable): Boolean

    Tries to complete the promise with an exception.

    Tries to complete the promise with an exception.

    Note: Using this method may result in non-deterministic concurrent programs.

    returns

    If the promise has already been completed returns false, or true otherwise.

  30. def trySuccess(value: T): Boolean

    Tries to complete the promise with a value.

    Tries to complete the promise with a value.

    Note: Using this method may result in non-deterministic concurrent programs.

    returns

    If the promise has already been completed returns false, or true otherwise.

  31. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  32. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  33. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  34. def [B](y: B): (Promise[T], B)
    Implicit
    This member is added by an implicit conversion from Promise[T] to ArrowAssoc[Promise[T]] performed by method ArrowAssoc in scala.Predef.
    Definition Classes
    ArrowAssoc

Inherited from AnyRef

Inherited from Any

Inherited by implicit conversion any2stringadd from Promise[T] to any2stringadd[Promise[T]]

Inherited by implicit conversion StringFormat from Promise[T] to StringFormat[Promise[T]]

Inherited by implicit conversion Ensuring from Promise[T] to Ensuring[Promise[T]]

Inherited by implicit conversion ArrowAssoc from Promise[T] to ArrowAssoc[Promise[T]]

Ungrouped