Moduleprimitive-unlifted-2.1.0.0Haskell2010

Data.Primitive.Unlifted.MutVar.Primops

1 type
6 values

Packageprimitive-unlifted-2.1.0.0
Exports7
LanguageHaskell2010
LicenceBSD-3-Clause
SourcePrimops.hs

newtypenewtype UnliftedMutVar# s (a :: UnliftedType)

An UnliftedMutVar# behaves like a single-element mutable array.

valuenewUnliftedMutVar# :: a -> State# s -> (# State# s, UnliftedMutVar# s a #)

valuereadUnliftedMutVar# :: UnliftedMutVar# s a -> State# s -> (# State# s, a #)

valuewriteUnliftedMutVar# :: UnliftedMutVar# s a -> a -> State# s -> State# s

valuesameUnliftedMutVar# :: UnliftedMutVar# s a -> UnliftedMutVar# s a -> Int#

Check whether two UnliftedMutVar#es refer to the same mutable variable. This is a check on object identity, and not on contents.

valuecasUnliftedMutVar#

:: UnliftedMutVar# s a
The UnliftedMutVar# on which to operate
-> a
The expected value
-> a
The new value to install if the 'UnliftedMutVar# contains the expected value
-> State# s
-> (# State# s, Int#, a #)

Performs a machine-level compare and swap (CAS) operation on an UnliftedMutVar#. Returns a tuple containing an Int# which is '1#' when a swap is performed, along with the most "current" value from the UnliftedMutVar#. This return value can be used as the expected value if a CAS loop is required, though it may be better to get a fresh read. Note that this behavior differs from the more common CAS behavior, which is to return the old value before the CAS occured.

valueatomicSwapUnliftedMutVar#

:: UnliftedMutVar# s a
-> a
-> State# s
-> (# State# s, a #)

Atomically replace the value in an UnliftedMutVar# with the given one, returning the old value.

Implementation note: this really should be a GHC primop, because it is supported very efficiently in hardware, but unfortunately it's not (yet), so we implement it as a CAS loop.