Copyright	(c) Justin Bonnar 2011 Roman Leshchinskiy 2011-2012
License	BSD-style
Maintainer	Roman Leshchinskiy <rl@cse.unsw.edu.au>
Portability	non-portable
Safe Haskell	None
Language	Haskell2010

Data.Primitive.MutVar

Description

Primitive boxed mutable variables. This is a generalization of Data.IORef , Data.STRef and Data.STRef.Lazy to work in any PrimMonad .

Synopsis

data MutVar s a = MutVar ( MutVar# s a)
newMutVar :: PrimMonad m => a -> m ( MutVar ( PrimState m) a)
readMutVar :: PrimMonad m => MutVar ( PrimState m) a -> m a
writeMutVar :: PrimMonad m => MutVar ( PrimState m) a -> a -> m ()
atomicModifyMutVar :: PrimMonad m => MutVar ( PrimState m) a -> (a -> (a, b)) -> m b
atomicModifyMutVar' :: PrimMonad m => MutVar ( PrimState m) a -> (a -> (a, b)) -> m b
modifyMutVar :: PrimMonad m => MutVar ( PrimState m) a -> (a -> a) -> m ()
modifyMutVar' :: PrimMonad m => MutVar ( PrimState m) a -> (a -> a) -> m ()

Documentation

data MutVar s a Source #

A MutVar behaves like a single-element mutable array associated with a primitive state token.

Constructors

MutVar ( MutVar# s a)

Instances

Instances details

Eq ( MutVar s a) Source #
Instance details Defined in Data.Primitive.MutVar Methods (==) :: MutVar s a -> MutVar s a -> Bool Source # (/=) :: MutVar s a -> MutVar s a -> Bool Source #

newMutVar :: PrimMonad m => a -> m ( MutVar ( PrimState m) a) Source #

Create a new MutVar with the specified initial value.

readMutVar :: PrimMonad m => MutVar ( PrimState m) a -> m a Source #

Read the value of a MutVar .

writeMutVar :: PrimMonad m => MutVar ( PrimState m) a -> a -> m () Source #

Write a new value into a MutVar .

atomicModifyMutVar :: PrimMonad m => MutVar ( PrimState m) a -> (a -> (a, b)) -> m b Source #

Atomically mutate the contents of a MutVar .

This function is useful for using MutVar in a safe way in a multithreaded program. If you only have one MutVar , then using atomicModifyMutVar to access and modify it will prevent race conditions.

Extending the atomicity to multiple MutVar s is problematic, so if you need to do anything more complicated, using MVar instead is a good idea.

atomicModifyMutVar does not apply the function strictly. This means if a program calls atomicModifyMutVar many times, but seldom uses the value, thunks will pile up in memory resulting in a space leak. To avoid this problem, use atomicModifyMutVar' instead.

atomicModifyMutVar' :: PrimMonad m => MutVar ( PrimState m) a -> (a -> (a, b)) -> m b Source #

Strict version of atomicModifyMutVar . This forces both the value stored in the MutVar as well as the value returned.

modifyMutVar :: PrimMonad m => MutVar ( PrimState m) a -> (a -> a) -> m () Source #

Mutate the contents of a MutVar .

modifyMutVar does not apply the function strictly. This means if a program calls modifyMutVar many times, but seldom uses the value, thunks will pile up in memory resulting in a space leak. To avoid this problem, use modifyMutVar' instead.

modifyMutVar' :: PrimMonad m => MutVar ( PrimState m) a -> (a -> a) -> m () Source #

Strict version of modifyMutVar .