Packages

abstract class MVar[F[_], A] extends MVarDocumentation

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

It has the following fundamental atomic operations:

  • put which fills the var if empty, or blocks (asynchronously) until the var is empty again
  • tryPut which fills the var if empty. returns true if successful
  • take which empties the var if full, returning the contained value, or blocks (asynchronously) otherwise until there is a value to pull
  • tryTake empties if full, returns None if empty.
  • read which reads the current value without touching it, assuming there is one, or otherwise it waits until a value is made available via put
  • tryRead returns a variable if it exists. Implemented in the successor MVar2
  • swap takes a value, replaces it and returns the taken value. Implemented in the successor MVar2
  • isEmpty returns true if currently empty

The MVar 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 done asynchronously (via Async or Concurrent data types, such as IO).

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

Inspired by Control.Concurrent.MVar from Haskell and by scalaz.concurrent.MVar.

Annotations
@deprecated
Deprecated

(Since version 2.2.0) MVar is now deprecated in favour of a new generation MVar2 with tryRead and swap support

Source
MVar.scala
Linear Supertypes
MVarDocumentation, AnyRef, Any
Known Subclasses
MVar2
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Instance Constructors

  1. new MVar()

Abstract Value Members

  1. abstract def isEmpty: F[Boolean]

    Returns true if the MVar is empty and can receive a put, or false otherwise.

    Returns true if the MVar is empty and can receive a put, or false otherwise.

    Note that due to concurrent tasks, logic built in terms of isEmpty is problematic.

  2. abstract def put(a: A): F[Unit]

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

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

    This operation is atomic.

    returns

    a task that on evaluation will complete when the put operation succeeds in filling the MVar, with the given value being next in line to be consumed

  3. abstract def read: F[A]

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

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

    This operation is atomic.

    returns

    a task that on evaluation will be completed after a value has been read

  4. abstract def take: F[A]

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

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

    This operation is atomic.

    returns

    a task that on evaluation will be completed after a value was retrieved

  5. abstract def tryPut(a: A): F[Boolean]

    Fill the MVar if we can do it without blocking,

    Fill the MVar if we can do it without blocking,

    returns

    whether or not the put succeeded

  6. abstract def tryTake: F[Option[A]]

    empty the MVar if full

    empty the MVar if full

    returns

    an Option holding the current value, None means it was empty

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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  6. final def eq(arg0: AnyRef): Boolean
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  7. def equals(arg0: Any): Boolean
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  8. def finalize(): Unit
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  9. final def getClass(): Class[_]
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  10. def hashCode(): Int
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  11. final def isInstanceOf[T0]: Boolean
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  12. final def ne(arg0: AnyRef): Boolean
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  13. final def notify(): Unit
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  14. final def notifyAll(): Unit
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  15. final def synchronized[T0](arg0: ⇒ T0): T0
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  16. def toString(): String
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  17. final def wait(): Unit
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  18. final def wait(arg0: Long, arg1: Int): Unit
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  19. final def wait(arg0: Long): Unit
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Deprecated Value Members

  1. def mapK[G[_]](f: ~>[F, G]): MVar[G, A]

    Modify the context F using transformation f.

    Modify the context F using transformation f.

    Annotations
    @deprecated
    Deprecated

    (Since version 2.2.0) mapK is deprecated in favor of imapK which supports the new invariant MVar2 interface

Inherited from MVarDocumentation

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