Packages

final class AsyncVar[A] extends GenericVar[A, Cancelable]

Asynchronous mutable location, that is either empty or contains a value of type A.

It has these fundamental atomic operations:

  • put which fills the var if empty, or waits (asynchronously) otherwise until the var is empty again (with the putByCallback overload)
  • tryPut which fills the var if empty, returning true if it succeeded, or returning immediately false in case the var was full and thus the operation failed
  • take which empties the var if full, returning the contained value, or waits (asynchronously) otherwise until there is a value to pull (with the takeByCallback overload)
  • tryTake which empties the var if full, returning the contained value immediately as Some(a), or otherwise returning None in case the var was empty and thus the operation failed
  • read which reads the var if full, but without taking it from the interval var, or waits (asynchronously) until there is a value to read
  • tryRead tries reading the var without modifying it in any way; if full then returns Some(a), or None if empty

The AsyncVar is appropriate for building synchronization primitives and performing simple inter-thread communications. If it helps, it's similar with a BlockingQueue(capacity = 1), except that it doesn't block any threads, all waiting being callback-based.

Given its asynchronous, non-blocking nature, it can be used on top of Javascript as well.

This is inspired by Control.Concurrent.MVar from Haskell, except that the implementation is made to work with plain Scala futures (and is thus impure).

Source
AsyncVar.scala
Linear Supertypes
GenericVar[A, Cancelable], AnyRef, Any
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Value Members

  1. def iEmpty(): Boolean

    Returns true if the var is empty, false otherwise.

    Returns true if the var is empty, false otherwise.

    Annotations
    @UnsafeProtocol() @UnsafeBecauseImpure()
  2. def put(a: A): CancelableFuture[Unit]

    Fills the AsyncVar if it is empty, or blocks (asynchronously) if the AsyncVar is full, until the given value is next in line to be consumed on take.

    Fills the AsyncVar if it is empty, or blocks (asynchronously) if the AsyncVar is full, until the given value is next in line to be consumed on take.

    This operation is atomic.

    returns

    a future that will complete when the put operation succeeds in filling the AsyncVar, with the given value being next in line to be consumed; note that this is a cancelable future that can be canceled to avoid memory leaks in race conditions

    Annotations
    @UnsafeBecauseImpure()
    See also

    putByCallback for the raw, unsafe version that can work with plain callbacks.

  3. def putByCallback(a: A, await: Callback[Nothing, Unit]): Cancelable

    Fills the AsyncVar if it is empty, or blocks (asynchronously) if the AsyncVar is full, until the given value is next in line to be consumed on take.

    Fills the AsyncVar if it is empty, or blocks (asynchronously) if the AsyncVar is full, until the given value is next in line to be consumed on take.

    This operation is atomic.

    a

    is the value to store

    await

    is a callback that will be called when the operation succeeded with a result

    returns

    a cancelable token that can be used to cancel the computation to avoid memory leaks in race conditions

    Annotations
    @UnsafeProtocol() @UnsafeBecauseImpure()
    See also

    put for the safe future-enabled version.

  4. def read(): CancelableFuture[A]

    Tries reading the current value, or waits (asynchronously) until there is a value available.

    Tries reading the current value, or waits (asynchronously) until there is a value available.

    This operation is atomic.

    returns

    a future that might already be completed in case the result is available immediately

    Annotations
    @UnsafeBecauseImpure()
    See also

    readByCallback for the raw, unsafe version that can work with plain callbacks.

  5. def readByCallback(await: Callback[Nothing, A]): Cancelable

    Tries reading the current value, or waits (asynchronously) until there is a value available.

    Tries reading the current value, or waits (asynchronously) until there is a value available.

    This operation is atomic.

    await

    is a callback that will be called when the operation succeeded with a result

    returns

    a cancelable token that can be used to cancel the computation to avoid memory leaks in race conditions

    Annotations
    @UnsafeProtocol() @UnsafeBecauseImpure()
    See also

    read for the safe future-enabled version.

  6. def take(): CancelableFuture[A]

    Empties the var if full, returning the contained value, or blocks (asynchronously) until a value is available.

    Empties the var if full, returning the contained value, or blocks (asynchronously) until a value is available.

    This operation is atomic.

    Annotations
    @UnsafeBecauseImpure()
    See also

    takeByCallback for the raw, unsafe version that can work with plain callbacks.

  7. def takeByCallback(await: Callback[Nothing, A]): Cancelable

    Empties the var if full, returning the contained value, or blocks (asynchronously) until a value is available.

    Empties the var if full, returning the contained value, or blocks (asynchronously) until a value is available.

    This operation is atomic.

    await

    is a callback that will be called when the operation succeeded with a result

    returns

    a cancelable token that can be used to cancel the computation to avoid memory leaks in race conditions

    Annotations
    @UnsafeProtocol() @UnsafeBecauseImpure()
    See also

    take for the safe future-enabled version.

  8. def tryPut(a: A): Boolean

    Tries to put a value in the underlying var, returning true if the operation succeeded and thus the var was empty, or false if the var was full and thus the operation failed.

    Tries to put a value in the underlying var, returning true if the operation succeeded and thus the var was empty, or false if the var was full and thus the operation failed.

    Annotations
    @UnsafeProtocol() @UnsafeBecauseImpure()
    See also

    put for the version that can asynchronously wait for the var to become empty

  9. def tryRead(): Option[A]

    Tries reading the current value, without modifying the var in any way:

    Tries reading the current value, without modifying the var in any way:

    • if full, returns Some(a)
    • if empty, returns None
    Annotations
    @UnsafeProtocol() @UnsafeBecauseImpure()
  10. def tryTake(): Option[A]

    Tries to take a value from the underlying var, returning Some(a) if the operation succeeded and thus the var was full, or None if the var was empty and thus the operation failed.

    Tries to take a value from the underlying var, returning Some(a) if the operation succeeded and thus the var was full, or None if the var was empty and thus the operation failed.

    Annotations
    @UnsafeProtocol() @UnsafeBecauseImpure()
    See also

    take for the version that can asynchronously wait for the var to become full