final class MVar[F[_], A] extends cats.effect.concurrent.MVar[F, A]

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 Some(a) if full, without modifying the var, or else returns None
  • 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 is pure and that doesn't block any threads, all waiting being done asynchronously.

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

N.B. this is a reimplementation of the interface exposed in Cats-Effect, see: cats.effect.concurrent.MVar

Inspired by Control.Concurrent.MVar from Haskell.

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cats.effect.concurrent.MVar[F, A], AnyRef, Any
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  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[java.lang]
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    @native() @throws( ... )
  6. final def eq(arg0: AnyRef): Boolean
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  7. def equals(arg0: Any): Boolean
    Definition Classes
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  8. def finalize(): Unit
    Attributes
    protected[java.lang]
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    @throws( classOf[java.lang.Throwable] )
  9. final def getClass(): Class[_]
    Definition Classes
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    @native()
  10. def hashCode(): Int
    Definition Classes
    AnyRef → Any
    Annotations
    @native()
  11. def isEmpty: F[Boolean]

    Returns true if the var is empty, false if full.

    Returns true if the var is empty, false if full.

    Definition Classes
    MVar → MVar
  12. final def isInstanceOf[T0]: Boolean
    Definition Classes
    Any
  13. def mapK[G[_]](f: ~>[F, G]): cats.effect.concurrent.MVar[G, A]
    Definition Classes
    MVar
  14. final def ne(arg0: AnyRef): Boolean
    Definition Classes
    AnyRef
  15. final def notify(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  16. final def notifyAll(): Unit
    Definition Classes
    AnyRef
    Annotations
    @native()
  17. 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

    Definition Classes
    MVar → MVar
  18. 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

    Definition Classes
    MVar → MVar
  19. final def synchronized[T0](arg0: ⇒ T0): T0
    Definition Classes
    AnyRef
  20. 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

    Definition Classes
    MVar → MVar
  21. def toString(): String
    Definition Classes
    AnyRef → Any
  22. 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

    Definition Classes
    MVar → MVar
  23. def tryRead: F[Option[A]]

    Tries reading the current value, returning Some(a) if the var is full, but without modifying the var in any way.

    Tries reading the current value, returning Some(a) if the var is full, but without modifying the var in any way. Or None if the var is empty.

  24. 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

    Definition Classes
    MVar → MVar
  25. final def wait(): Unit
    Definition Classes
    AnyRef
    Annotations
    @throws( ... )
  26. final def wait(arg0: Long, arg1: Int): Unit
    Definition Classes
    AnyRef
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    @throws( ... )
  27. final def wait(arg0: Long): Unit
    Definition Classes
    AnyRef
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    @native() @throws( ... )

Inherited from cats.effect.concurrent.MVar[F, A]

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