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|
{-# LANGUAGE MagicHash, UnboxedTuples, DeriveDataTypeable #-}
-- |
-- Module : Data.Primitive.MutVar
-- Copyright : (c) Justin Bonnar 2011, Roman Leshchinskiy 2011-2012
-- License : BSD-style
--
-- Maintainer : Roman Leshchinskiy <rl@cse.unsw.edu.au>
-- Portability : non-portable
--
-- Primitive boxed mutable variables
--
module Data.Primitive.MutVar (
MutVar(..),
newMutVar,
readMutVar,
writeMutVar,
atomicModifyMutVar,
atomicModifyMutVar',
modifyMutVar,
modifyMutVar'
) where
import Control.Monad.Primitive ( PrimMonad(..), primitive_ )
import GHC.Prim ( MutVar#, sameMutVar#, newMutVar#,
readMutVar#, writeMutVar#, atomicModifyMutVar# )
import Data.Primitive.Internal.Compat ( isTrue# )
import Data.Typeable ( Typeable )
-- | A 'MutVar' behaves like a single-element mutable array associated
-- with a primitive state token.
data MutVar s a = MutVar (MutVar# s a)
deriving ( Typeable )
instance Eq (MutVar s a) where
MutVar mva# == MutVar mvb# = isTrue# (sameMutVar# mva# mvb#)
-- | Create a new 'MutVar' with the specified initial value
newMutVar :: PrimMonad m => a -> m (MutVar (PrimState m) a)
{-# INLINE newMutVar #-}
newMutVar initialValue = primitive $ \s# ->
case newMutVar# initialValue s# of
(# s'#, mv# #) -> (# s'#, MutVar mv# #)
-- | Read the value of a 'MutVar'
readMutVar :: PrimMonad m => MutVar (PrimState m) a -> m a
{-# INLINE readMutVar #-}
readMutVar (MutVar mv#) = primitive (readMutVar# mv#)
-- | Write a new value into a 'MutVar'
writeMutVar :: PrimMonad m => MutVar (PrimState m) a -> a -> m ()
{-# INLINE writeMutVar #-}
writeMutVar (MutVar mv#) newValue = primitive_ (writeMutVar# mv# newValue)
-- | Atomically mutate the contents of a 'MutVar'
atomicModifyMutVar :: PrimMonad m => MutVar (PrimState m) a -> (a -> (a,b)) -> m b
{-# INLINE atomicModifyMutVar #-}
atomicModifyMutVar (MutVar mv#) f = primitive $ atomicModifyMutVar# mv# f
-- | Strict version of 'atomicModifyMutVar'. This forces both the value stored
-- in the 'MutVar' as well as the value returned.
atomicModifyMutVar' :: PrimMonad m => MutVar (PrimState m) a -> (a -> (a, b)) -> m b
{-# INLINE atomicModifyMutVar' #-}
atomicModifyMutVar' mv f = do
b <- atomicModifyMutVar mv force
b `seq` return b
where
force x = let (a, b) = f x in (a, a `seq` b)
-- | Mutate the contents of a 'MutVar'
modifyMutVar :: PrimMonad m => MutVar (PrimState m) a -> (a -> a) -> m ()
{-# INLINE modifyMutVar #-}
modifyMutVar (MutVar mv#) g = primitive_ $ \s# ->
case readMutVar# mv# s# of
(# s'#, a #) -> writeMutVar# mv# (g a) s'#
-- | Strict version of 'modifyMutVar'
modifyMutVar' :: PrimMonad m => MutVar (PrimState m) a -> (a -> a) -> m ()
{-# INLINE modifyMutVar' #-}
modifyMutVar' (MutVar mv#) g = primitive_ $ \s# ->
case readMutVar# mv# s# of
(# s'#, a #) -> let a' = g a in a' `seq` writeMutVar# mv# a' s'#
|
