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abstract class Deferred[F[_], A] extends AnyRef

A purely functional synchronization primitive which represents a single value which may not yet be available.

When created, a Deferred is empty. It can then be completed exactly once, and never be made empty again.

get on an empty Deferred will block until the Deferred is completed. get on a completed Deferred will always immediately return its content.

complete(a) on an empty Deferred will set it to a, and notify any and all readers currently blocked on a call to get. complete(a) on a Deferred that has already been completed will not modify its content, and result in a failed F.

Albeit simple, Deferred can be used in conjunction with Ref to build complex concurrent behaviour and data structures like queues and semaphores.

Finally, the blocking mentioned above is semantic only, no actual threads are blocked by the implementation.

Source
Deferred.scala
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Instance Constructors

  1. new Deferred()

Abstract Value Members

  1. abstract def complete(a: A): F[Unit]

    If this Deferred is empty, sets the current value to a, and notifies any and all readers currently blocked on a get.

    If this Deferred is empty, sets the current value to a, and notifies any and all readers currently blocked on a get.

    Note that the returned action may complete after the reference has been successfully set: use F.start(r.complete) if you want asynchronous behaviour.

    If this Deferred has already been completed, the returned action immediately fails with an IllegalStateException. In the uncommon scenario where this behavior is problematic, you can handle failure explicitly using attempt or any other ApplicativeError/MonadError combinator on the returned action.

    Satisfies: Deferred[F, A].flatMap(r => r.complete(a) *> r.get) == a.pure[F]

  2. abstract def get: F[A]

    Obtains the value of the Deferred, or waits until it has been completed.

    Obtains the value of the Deferred, or waits until it has been completed. The returned value may be canceled.

Concrete Value Members

  1. final def !=(arg0: Any): Boolean
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  2. final def ##: Int
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  3. final def ==(arg0: Any): Boolean
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  4. final def asInstanceOf[T0]: T0
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  5. def clone(): AnyRef
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    protected[lang]
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    @throws(classOf[java.lang.CloneNotSupportedException]) @native()
  6. final def eq(arg0: AnyRef): Boolean
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  7. def equals(arg0: AnyRef): Boolean
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  8. def finalize(): Unit
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    @throws(classOf[java.lang.Throwable])
  9. final def getClass(): Class[_ <: AnyRef]
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  10. def hashCode(): Int
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  11. final def isInstanceOf[T0]: Boolean
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  12. def mapK[G[_]](f: ~>[F, G]): Deferred[G, A]

    Modify the context F using transformation f.

  13. final def ne(arg0: AnyRef): Boolean
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  14. final def notify(): Unit
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    @native()
  15. final def notifyAll(): Unit
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  16. final def synchronized[T0](arg0: => T0): T0
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  17. def toString(): String
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  18. final def wait(): Unit
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    @throws(classOf[java.lang.InterruptedException])
  19. final def wait(arg0: Long, arg1: Int): Unit
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    @throws(classOf[java.lang.InterruptedException])
  20. final def wait(arg0: Long): Unit
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    @throws(classOf[java.lang.InterruptedException]) @native()

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