abstract class MVar[F[_], A] extends AnyRef
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
- 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
.
- Source
- MVar.scala
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- MVar
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Instance Constructors
- new MVar()
Abstract Value Members
-
abstract
def
isEmpty: F[Boolean]
Returns
true
if theMVar
is empty and can receive aput
, orfalse
otherwise.Returns
true
if theMVar
is empty and can receive aput
, orfalse
otherwise.Note that due to concurrent tasks, logic built in terms of
isEmpty
is problematic. -
abstract
def
put(a: A): F[Unit]
Fills the
MVar
if it is empty, or blocks (asynchronously) if theMVar
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 theMVar
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 theMVar
, with the given value being next in line to be consumed
-
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
-
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
-
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
-
abstract
def
tryTake: F[Option[A]]
empty the
MVar
if fullempty the
MVar
if full- returns
an Option holding the current value, None means it was empty
Concrete Value Members
-
final
def
!=(arg0: Any): Boolean
- Definition Classes
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-
final
def
##(): Int
- Definition Classes
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-
final
def
==(arg0: Any): Boolean
- Definition Classes
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-
final
def
asInstanceOf[T0]: T0
- Definition Classes
- Any
-
def
clone(): AnyRef
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- protected[java.lang]
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- @native() @throws( ... )
-
final
def
eq(arg0: AnyRef): Boolean
- Definition Classes
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-
def
equals(arg0: Any): Boolean
- Definition Classes
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-
def
finalize(): Unit
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- protected[java.lang]
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- @throws( classOf[java.lang.Throwable] )
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final
def
getClass(): Class[_]
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def
hashCode(): Int
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final
def
isInstanceOf[T0]: Boolean
- Definition Classes
- Any
-
def
mapK[G[_]](f: ~>[F, G]): MVar[G, A]
Modify the context
F
using transformationf
. -
final
def
ne(arg0: AnyRef): Boolean
- Definition Classes
- AnyRef
-
final
def
notify(): Unit
- Definition Classes
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- @native()
-
final
def
notifyAll(): Unit
- Definition Classes
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- @native()
-
final
def
synchronized[T0](arg0: ⇒ T0): T0
- Definition Classes
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-
def
toString(): String
- Definition Classes
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-
final
def
wait(): Unit
- Definition Classes
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- @throws( ... )
-
final
def
wait(arg0: Long, arg1: Int): Unit
- Definition Classes
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- @throws( ... )
-
final
def
wait(arg0: Long): Unit
- Definition Classes
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- @native() @throws( ... )
This is the API documentation for the cats-effect library.
See the cats.effect package for a quick overview.
Links
Canonical documentation links:
Related Cats links (the core):