A thread-safe, concurrent mutable reference.
Provides safe concurrent access and modification of its content, but no functionality for
synchronisation, which is instead handled by Deferred. For this reason, a Ref
is always
initialised to a value.
The default implementation is nonblocking and lightweight, consisting essentially of a purely
functional wrapper over an AtomicReference
. Consequently it ''must not'' be used to store
mutable data as AtomicReference#compareAndSet
and friends are dependent upon object
reference equality.
See also cats.effect.std.AtomicCell
class from cats-effect-std
for an alternative.
Attributes
Members list
Value members
Abstract methods
Obtains a snapshot of the current value, and a setter for updating it.
Obtains a snapshot of the current value, and a setter for updating it.
The setter attempts to modify the contents from the snapshot to the new value (and return
true
). If it cannot do this (because the contents changed since taking the snapshot), the
setter is a noop and returns false
.
Satisfies: r.access.map(_._1) == r.get
and r.access.flatMap { case (v, setter) => setter(f(v)) } == r.tryUpdate(f).map(_.isDefined)
.
Attributes
- Source:
- Ref.scala
Like tryModify
but retries until the update has been successfully made.
Like tryModifyState but retries the modification until successful.
Like tryUpdate
but allows the update function to return an output value of type B
. The
returned action completes with None
if the value is not updated successfully and
Some(b)
otherwise.
Like tryUpdate
but allows the update function to return an output value of type B
. The
returned action completes with None
if the value is not updated successfully and
Some(b)
otherwise.
Attributes
- Source:
- Ref.scala
Update the value of this Ref
with a state computation.
Update the value of this Ref
with a state computation.
The current value of this Ref
is used as the initial state and the computed output state
is stored in this Ref
after computation completes. If a concurrent modification occurs,
None
is returned.
Attributes
- Source:
- Ref.scala
Attempts to modify the current value once, returning false
if another concurrent
modification completes between the time the variable is read and the time it is set.
Attempts to modify the current value once, returning false
if another concurrent
modification completes between the time the variable is read and the time it is set.
Attributes
- Source:
- Ref.scala
Modifies the current value using the supplied update function. If another modification
occurs between the time the current value is read and subsequently updated, the
modification is retried using the new value. Hence, f
may be invoked multiple times.
Modifies the current value using the supplied update function. If another modification
occurs between the time the current value is read and subsequently updated, the
modification is retried using the new value. Hence, f
may be invoked multiple times.
Satisfies: r.update(_ => a) == r.set(a)
Attributes
- Source:
- Ref.scala
Concrete methods
Like modify but schedules resulting effect right after modification.
Like modify but schedules resulting effect right after modification.
Useful for implementing effectful transition of a state machine, in which an effect is performed based on current state and the state must be updated to reflect that this effect will be performed.
Both modification and finalizer are within a single uncancelable region, to prevent canceled finalizers from leaving the Ref's value permanently out of sync with effects actually performed. if you need cancellation mechanic in finalizer please see flatModifyFull.
Attributes
- See also:
- Source:
- Ref.scala
Like modify but schedules resulting effect right after modification.
Like modify but schedules resulting effect right after modification.
Unlike flatModify finalizer cancellation could be unmasked via supplied Poll
.
Modification itself is still uncancelable.
When used as part of a state machine, cancelable regions should usually have an onCancel
finalizer to update the state to reflect that the effect will not be performed.
Attributes
- See also:
- Source:
- Ref.scala
Like modifyState but schedules resulting effect right after state computation & update.
Like modifyState but schedules resulting effect right after state computation & update.
Both modification and finalizer are uncancelable, if you need cancellation mechanic in finalizer please see flatModifyStateFull.
Attributes
- See also:
- Source:
- Ref.scala
Like modifyState but schedules resulting effect right after modification.
Like modifyState but schedules resulting effect right after modification.
Unlike flatModifyState finalizer cancellation could be masked via supplied Poll[F]
.
Modification itself is still uncancelable.
Attributes
- See also:
- Source:
- Ref.scala
Replaces the current value with a
, returning the previous value.
Updates the current value using f
and returns the previous value.
Updates the current value using f
and returns the previous value.
In case of retries caused by concurrent modifications, the returned value will be the last one before a successful update.
Attributes
- Source:
- Ref.scala
Modify the context F
using transformation f
.
Updates the current value using f
, and returns the updated value.