scala.concurrent

Future

trait Future[+T] extends Awaitable[T]

The trait that represents futures.

Asynchronous computations that yield futures are created with the future call:

 val s = "Hello"
 val f: Future[String] = future {
   s + " future!"
 }
 f onSuccess {
   case msg => println(msg)
 }
Source
Future.scala
Linear Supertypes
Awaitable[T], AnyRef, Any
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Abstract Value Members

  1. abstract def isCompleted: Boolean

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

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

    Note: using this method yields nondeterministic dataflow programs.

    returns

    true if the future is already completed, false otherwise

  2. abstract def onComplete[U](func: (Try[T]) ⇒ U)(implicit executor: ExecutionContext): Unit

    When this future is completed, either through an exception, or a value, apply the provided function.

    When this future is completed, either through an exception, or a value, apply the provided function.

    If the future has already been completed, this will either be applied immediately or be scheduled asynchronously.

    Multiple callbacks may be registered; there is no guarantee that they will be executed in a particular order.

    The provided callback always runs in the provided implicit ExecutionContext, though there is no guarantee that the execute() method on the ExecutionContext will be called once per callback or that execute() will be called in the current thread. That is, the implementation may run multiple callbacks in a batch within a single execute() and it may run execute() either immediately or asynchronously.

  3. abstract def ready(atMost: Duration)(implicit permit: CanAwait): Future.this.type

    Await the "completed" state of this Awaitable.

    Await the "completed" state of this Awaitable.

    This method should not be called directly; use Await.ready instead.

    atMost

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

    returns

    this Awaitable

    Definition Classes
    Awaitable
    Annotations
    @throws( clazz = classOf[TimeoutException] ) @throws( clazz = classOf[InterruptedException] )
    Exceptions thrown
    IllegalArgumentException

    if atMost is scala.concurrent.duration.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

  4. abstract def result(atMost: Duration)(implicit permit: CanAwait): T

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

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

    This method should not be called directly; use Await.result instead.

    atMost

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

    returns

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

    Definition Classes
    Awaitable
    Annotations
    @throws( clazz = classOf[Exception] )
    Exceptions thrown
    IllegalArgumentException

    if atMost is scala.concurrent.duration.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

  5. abstract def value: Option[Try[T]]

    The value of this Future.

    The value of this Future.

    If the future is not completed the returned value will be None. If the future is completed the value will be Some(Success(t)) if it contains a valid result, or Some(Failure(error)) if it contains an exception.

Concrete Value Members

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

    Definition Classes
    AnyRef
  2. final def !=(arg0: Any): Boolean

    Test two objects for inequality.

    Test two objects for inequality.

    returns

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

    Definition Classes
    Any
  3. final def ##(): Int

    Equivalent to x.hashCode except for boxed numeric types.

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

    returns

    a hash value consistent with ==

    Definition Classes
    AnyRef → Any
  4. final def ==(arg0: AnyRef): Boolean

    Definition Classes
    AnyRef
  5. final def ==(arg0: Any): Boolean

    Test two objects for equality.

    Test two objects for equality.

    returns

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

    Definition Classes
    Any
  6. def andThen[U](pf: PartialFunction[Try[T], U])(implicit executor: ExecutionContext): Future[T]

    Applies the side-effecting function to the result of this future, and returns a new future with the result of this future.

    Applies the side-effecting function to the result of this future, and returns a new future with the result of this future.

    This method allows one to enforce that the callbacks are executed in a specified order.

    Note that if one of the chained andThen callbacks throws an exception, that exception is not propagated to the subsequent andThen callbacks. Instead, the subsequent andThen callbacks are given the original value of this future.

    The following example prints out 5:

     val f = future { 5 }
     f andThen {
       case r => sys.error("runtime exception")
     } andThen {
       case Failure(t) => println(t)
       case Success(v) => println(v)
     }
    
  7. 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.

  8. 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[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
    Note

    not specified by SLS as a member of AnyRef

  9. def collect[S](pf: PartialFunction[T, S])(implicit executor: ExecutionContext): Future[S]

    Creates a new future by mapping the value of the current future, if the given partial function is defined at that value.

    Creates a new future by mapping the value of the current future, if the given partial function is defined at that value.

    If the current future contains a value for which the partial function is defined, the new future will also hold that value. Otherwise, the resulting future will fail with a NoSuchElementException.

    If the current future fails, then the resulting future also fails.

    Example:

     val f = future { -5 }
     val g = f collect {
       case x if x < 0 => -x
     }
     val h = f collect {
       case x if x > 0 => x * 2
     }
     await(g, 0) // evaluates to 5
     await(h, 0) // throw a NoSuchElementException
    
  10. final def eq(arg0: AnyRef): Boolean

    Tests whether the argument (arg0) is a reference to the receiver object (this).

    Tests whether the argument (arg0) 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
  11. def equals(arg0: Any): Boolean

    The equality method for reference types.

    The equality method for reference types. See equals in Any.

    returns

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

    Definition Classes
    AnyRef → Any
  12. def failed: Future[Throwable]

    Returns a failed projection of this future.

    Returns a failed projection of this future.

    The failed projection is a future holding a value of type Throwable.

    It is completed with a value which is the throwable of the original future in case the original future is failed.

    It is failed with a NoSuchElementException if the original future is completed successfully.

    Blocking on this future returns a value if the original future is completed with an exception and throws a corresponding exception if the original future fails.

  13. def fallbackTo[U >: T](that: Future[U]): Future[U]

    Creates a new future which holds the result of this future if it was completed successfully, or, if not, the result of the that future if that is completed successfully.

    Creates a new future which holds the result of this future if it was completed successfully, or, if not, the result of the that future if that is completed successfully. If both futures are failed, the resulting future holds the throwable object of the first future.

    Using this method will not cause concurrent programs to become nondeterministic.

    Example:

     val f = future { sys.error("failed") }
     val g = future { 5 }
     val h = f fallbackTo g
     await(h, 0) // evaluates to 5
    
  14. def filter(pred: (T) ⇒ Boolean)(implicit executor: ExecutionContext): Future[T]

    Creates a new future by filtering the value of the current future with a predicate.

    Creates a new future by filtering the value of the current future with a predicate.

    If the current future contains a value which satisfies the predicate, the new future will also hold that value. Otherwise, the resulting future will fail with a NoSuchElementException.

    If the current future fails, then the resulting future also fails.

    Example:

     val f = future { 5 }
     val g = f filter { _ % 2 == 1 }
     val h = f filter { _ % 2 == 0 }
     await(g, 0) // evaluates to 5
     await(h, 0) // throw a NoSuchElementException
    
  15. 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[lang]
    Definition Classes
    AnyRef
    Annotations
    @throws()
    Note

    not specified by SLS as a member of AnyRef

  16. def flatMap[S](f: (T) ⇒ Future[S])(implicit executor: ExecutionContext): Future[S]

    Creates a new future by applying a function to the successful result of this future, and returns the result of the function as the new future.

    Creates a new future by applying a function to the successful result of this future, and returns the result of the function as the new future. If this future is completed with an exception then the new future will also contain this exception.

    Example:

     val f = future { 5 }
     val g = future { 3 }
     val h = for {
       x: Int <- f // returns Future(5)
       y: Int <- g // returns Future(5)
     } yield x + y
    

    is translated to:

     f flatMap { (x: Int) => g map { (y: Int) => x + y } }
    
  17. def foreach[U](f: (T) ⇒ U)(implicit executor: ExecutionContext): Unit

    Asynchronously processes the value in the future once the value becomes available.

    Asynchronously processes the value in the future once the value becomes available.

    Will not be called if the future fails.

  18. final def getClass(): java.lang.Class[_]

    A representation that corresponds to the dynamic class of the receiver object.

    A representation that corresponds to the dynamic class of the receiver object.

    The nature of the representation is platform dependent.

    returns

    a representation that corresponds to the dynamic class of the receiver object.

    Definition Classes
    AnyRef → Any
    Note

    not specified by SLS as a member of AnyRef

  19. def hashCode(): Int

    The hashCode method for reference types.

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

    returns

    the hash code value for this object.

    Definition Classes
    AnyRef → Any
  20. 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
  21. def map[S](f: (T) ⇒ S)(implicit executor: ExecutionContext): Future[S]

    Creates a new future by applying a function to the successful result of this future.

    Creates a new future by applying a function to the successful result of this future. If this future is completed with an exception then the new future will also contain this exception.

    Example:

     val f = future { 5 }
     val g = future { 3 }
     val h = for {
       x: Int <- f // returns Future(5)
       y: Int <- g // returns Future(5)
     } yield x + y
    

    is translated to:

     f flatMap { (x: Int) => g map { (y: Int) => x + y } }
    
  22. def mapTo[S](implicit tag: ClassManifest[S]): Future[S]

    Creates a new Future[S] which is completed with this Future's result if that conforms to S's erased type or a ClassCastException otherwise.

  23. 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
  24. 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

  25. 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

  26. def onFailure[U](callback: PartialFunction[Throwable, U])(implicit executor: ExecutionContext): Unit

    When this future is completed with a failure (i.

    When this future is completed with a failure (i.e. with a throwable), apply the provided callback to the throwable.

    The future may contain a throwable object and this means that the future failed. Futures obtained through combinators have the same exception as the future they were obtained from. The following throwable objects are not contained in the future:

    • Error - errors are not contained within futures
    • InterruptedException - not contained within futures
    • all scala.util.control.ControlThrowable except NonLocalReturnControl - not contained within futures

    Instead, the future is completed with a ExecutionException with one of the exceptions above as the cause. If a future is failed with a scala.runtime.NonLocalReturnControl, it is completed with a value from that throwable instead.

    If the future has already been completed with a failure, this will either be applied immediately or be scheduled asynchronously.

    Will not be called in case that the future is completed with a value.

    Multiple callbacks may be registered; there is no guarantee that they will be executed in a particular order.

    The provided callback always runs in the provided implicit ExecutionContext, though there is no guarantee that the execute() method on the ExecutionContext will be called once per callback or that execute() will be called in the current thread. That is, the implementation may run multiple callbacks in a batch within a single execute() and it may run execute() either immediately or asynchronously.

  27. def onSuccess[U](pf: PartialFunction[T, U])(implicit executor: ExecutionContext): Unit

    When this future is completed successfully (i.

    When this future is completed successfully (i.e. with a value), apply the provided partial function to the value if the partial function is defined at that value.

    If the future has already been completed with a value, this will either be applied immediately or be scheduled asynchronously.

    Multiple callbacks may be registered; there is no guarantee that they will be executed in a particular order.

    The provided callback always runs in the provided implicit ExecutionContext, though there is no guarantee that the execute() method on the ExecutionContext will be called once per callback or that execute() will be called in the current thread. That is, the implementation may run multiple callbacks in a batch within a single execute() and it may run execute() either immediately or asynchronously.

  28. def recover[U >: T](pf: PartialFunction[Throwable, U])(implicit executor: ExecutionContext): Future[U]

    Creates a new future that will handle any matching throwable that this future might contain.

    Creates a new future that will handle any matching throwable that this future might contain. If there is no match, or if this future contains a valid result then the new future will contain the same.

    Example:

     future (6 / 0) recover { case e: ArithmeticException => 0 } // result: 0
     future (6 / 0) recover { case e: NotFoundException   => 0 } // result: exception
     future (6 / 2) recover { case e: ArithmeticException => 0 } // result: 3
    
  29. def recoverWith[U >: T](pf: PartialFunction[Throwable, Future[U]])(implicit executor: ExecutionContext): Future[U]

    Creates a new future that will handle any matching throwable that this future might contain by assigning it a value of another future.

    Creates a new future that will handle any matching throwable that this future might contain by assigning it a value of another future.

    If there is no match, or if this future contains a valid result then the new future will contain the same result.

    Example:

     val f = future { Int.MaxValue }
     future (6 / 0) recoverWith { case e: ArithmeticException => f } // result: Int.MaxValue
    
  30. final def synchronized[T0](arg0: ⇒ T0): T0

    Definition Classes
    AnyRef
  31. 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
  32. def transform[S](s: (T) ⇒ S, f: (Throwable) ⇒ Throwable)(implicit executor: ExecutionContext): Future[S]

    Creates a new future by applying the 's' function to the successful result of this future, or the 'f' function to the failed result.

    Creates a new future by applying the 's' function to the successful result of this future, or the 'f' function to the failed result. If there is any non-fatal exception thrown when 's' or 'f' is applied, that exception will be propagated to the resulting future.

    s

    function that transforms a successful result of the receiver into a successful result of the returned future

    f

    function that transforms a failure of the receiver into a failure of the returned future

    returns

    a future that will be completed with the transformed value

  33. final def wait(): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()
  34. final def wait(arg0: Long, arg1: Int): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()
  35. final def wait(arg0: Long): Unit

    Definition Classes
    AnyRef
    Annotations
    @throws()
  36. final def withFilter(p: (T) ⇒ Boolean)(implicit executor: ExecutionContext): Future[T]

    Used by for-comprehensions.

  37. def zip[U](that: Future[U]): Future[(T, U)]

    Zips the values of this and that future, and creates a new future holding the tuple of their results.

    Zips the values of this and that future, and creates a new future holding the tuple of their results.

    If this future fails, the resulting future is failed with the throwable stored in this. Otherwise, if that future fails, the resulting future is failed with the throwable stored in that.

Inherited from Awaitable[T]

Inherited from AnyRef

Inherited from Any