Packages

final class MVar[A] extends AnyRef

An MVar[A] is a mutable location that is either empty or contains a value of type A. It has two fundamental operations: put which fills an MVar if it is empty and blocks otherwise, and take which empties an MVar if it is full and blocks otherwise. They can be used in multiple different ways:

  • As synchronized mutable variables,
  • As channels, with take and put as receive and send, and
  • As a binary semaphore MVar[Unit], with take and put as wait and signal.

They were introduced in the paper "Concurrent Haskell" by Simon Peyton Jones, Andrew Gordon and Sigbjorn Finne.

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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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  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. def isEmpty: UIO[Boolean]

    Check whether the MVar is empty.

    Check whether the MVar is empty.

    Notice that the boolean value returned is just a snapshot of the state of the MVar. By the time you get to react on its result, the MVar may have been filled (or emptied) - so be extremely careful when using this operation. Use tryTake instead if possible.

  12. final def isInstanceOf[T0]: Boolean
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  13. def modify[B](f: (A) ⇒ (B, A)): UIO[B]

    A slight variation on update that allows a value to be returned (b) in addition to the modified value of the MVar.

  14. final def ne(arg0: AnyRef): Boolean
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  15. final def notify(): Unit
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  16. final def notifyAll(): Unit
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  17. def put(x: A): UIO[Unit]

    Put a value into an MVar.

    Put a value into an MVar. If the MVar is currently full, put will wait until it becomes empty.

  18. def read: UIO[A]

    Atomically read the contents of an MVar.

    Atomically read the contents of an MVar. If the MVar is currently empty, read will wait until it is full. read is guaranteed to receive the next put.

  19. def swap(x: A): UIO[A]

    Take a value from an MVar, put a new value into the MVar and return the value taken.

  20. final def synchronized[T0](arg0: ⇒ T0): T0
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  21. def take: UIO[A]

    Return the contents of the MVar.

    Return the contents of the MVar. If the MVar is currently empty, take will wait until it is full. After a take, the MVar is left empty.

  22. def toString(): String
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  23. def tryPut(x: A): UIO[Boolean]

    A non-blocking version of put.

    A non-blocking version of put. The tryPut function attempts to put the value x into the MVar, returning true if it was successful, or false otherwise.

  24. def tryRead: UIO[Option[A]]

    A non-blocking version of read.

    A non-blocking version of read. The tryRead function returns immediately, with None if the MVar was empty, or Some(x) if the MVar was full with contents x.

  25. def tryTake: UIO[Option[A]]

    A non-blocking version of take.

    A non-blocking version of take. The tryTake action returns immediately, with None if the MVar was empty, or Some(x) if the MVar was full with contents x. After tryTake, the MVar is left empty.

  26. def update(f: (A) ⇒ A): UIO[Unit]

    Replaces the contents of an MVar with the result of f(a).

  27. final def wait(): Unit
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    @throws( ... )
  28. final def wait(arg0: Long, arg1: Int): Unit
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    @throws( ... )
  29. final def wait(arg0: Long): Unit
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