Safe Haskell | None |
---|---|
Language | Haskell2010 |
An
is mutable location that is either empty or contains a
value of type MVar
tt
. It has two fundamental operations: putMVar
which fills an MVar
if it is empty and blocks otherwise, and
takeMVar
which empties an MVar
if it is full and blocks
otherwise. They can be used in multiple different ways:
- As synchronized mutable variables,
- As channels, with
takeMVar
andputMVar
as receive and send, and - As a binary semaphore
, withMVar
()takeMVar
andputMVar
as wait and signal.
Deviations: There is no Eq
instance for MonadConc
the
MVar
type. Furthermore, the mkWeakMVar
and addMVarFinalizer
functions are not provided. Finally, normal MVar
s have a fairness
guarantee, which dejafu does not currently make use of when
generating schedules to test, so your program may be tested with
unfair schedules.
- newEmptyMVar :: MonadConc m => m (MVar m a)
- newEmptyMVarN :: MonadConc m => String -> m (MVar m a)
- newMVar :: MonadConc m => a -> m (MVar m a)
- newMVarN :: MonadConc m => String -> a -> m (MVar m a)
- takeMVar :: MonadConc m => MVar m a -> m a
- putMVar :: MonadConc m => MVar m a -> a -> m ()
- readMVar :: MonadConc m => MVar m a -> m a
- swapMVar :: MonadConc m => MVar m a -> a -> m a
- tryTakeMVar :: MonadConc m => MVar m a -> m (Maybe a)
- tryPutMVar :: MonadConc m => MVar m a -> a -> m Bool
- isEmptyMVar :: MonadConc m => MVar m a -> m Bool
- withMVar :: MonadConc m => MVar m a -> (a -> m b) -> m b
- withMVarMasked :: MonadConc m => MVar m a -> (a -> m b) -> m b
- modifyMVar_ :: MonadConc m => MVar m a -> (a -> m a) -> m ()
- modifyMVar :: MonadConc m => MVar m a -> (a -> m (a, b)) -> m b
- modifyMVarMasked_ :: MonadConc m => MVar m a -> (a -> m a) -> m ()
- modifyMVarMasked :: MonadConc m => MVar m a -> (a -> m (a, b)) -> m b
MVar
s
newEmptyMVar :: MonadConc m => m (MVar m a) Source
Create a new empty MVar
.
newEmptyMVar = newEmptyMVarN ""
newEmptyMVarN :: MonadConc m => String -> m (MVar m a) Source
Create a new empty MVar
, but it is given a name which may be
used to present more useful debugging information.
If an empty name is given, a counter starting from 0 is used. If
names conflict, successive MVar
s with the same name are given a
numeric suffix, counting up from 1.
newEmptyMVarN _ = newEmptyMVar
newMVarN :: MonadConc m => String -> a -> m (MVar m a) Source
Create a new MVar
containing a value, but it is given a name
which may be used to present more useful debugging information.
If no name is given, a counter starting from 0 is used. If names
conflict, successive MVar
s with the same name are given a numeric
suffix, counting up from 1.
takeMVar :: MonadConc m => MVar m a -> m a Source
Take a value from a MVar
. This "empties" the MVar
,
allowing a new value to be put in. This will block if there is no
value in the MVar
already, until one has been put.
putMVar :: MonadConc m => MVar m a -> a -> m () Source
Put a value into a MVar
. If there is already a value there,
this will block until that value has been taken, at which point
the value will be stored.
readMVar :: MonadConc m => MVar m a -> m a Source
Block until a value is present in the MVar
, and then return
it. As with readMVar
, this does not "remove" the value,
multiple reads are possible.
swapMVar :: MonadConc m => MVar m a -> a -> m a Source
Swap the contents of a MVar
, and return the value taken. This
function is atomic only if there are no other producers fro this
MVar
.
tryTakeMVar :: MonadConc m => MVar m a -> m (Maybe a) Source
tryPutMVar :: MonadConc m => MVar m a -> a -> m Bool Source
isEmptyMVar :: MonadConc m => MVar m a -> m Bool Source
Check if a MVar
is empty.
withMVar :: MonadConc m => MVar m a -> (a -> m b) -> m b Source
Operate on the contents of a MVar
, replacing the contents after
finishing. This operation is exception-safe: it will replace the
original contents of the MVar
if an exception is raised. However,
it is only atomic if there are no other producers for this MVar
.
withMVarMasked :: MonadConc m => MVar m a -> (a -> m b) -> m b Source
Like withMVar
, but the IO
action in the second argument is
executed with asynchronous exceptions masked.
modifyMVar_ :: MonadConc m => MVar m a -> (a -> m a) -> m () Source
An exception-safe wrapper for modifying the contents of a MVar
.
Like withMVar
, modifyMVar
will replace the original contents of
the MVar
if an exception is raised during the operation. This
function is only atomic if there are no other producers for this
MVar
.
modifyMVar :: MonadConc m => MVar m a -> (a -> m (a, b)) -> m b Source
A slight variation on modifyMVar_
that allows a value to be
returned (b
) in addition to the modified value of the MVar
.
modifyMVarMasked_ :: MonadConc m => MVar m a -> (a -> m a) -> m () Source
Like modifyMVar_
, but the IO
action in the second argument is
executed with asynchronous exceptions masked.
modifyMVarMasked :: MonadConc m => MVar m a -> (a -> m (a, b)) -> m b Source
Like modifyMVar
, but the IO
action in the second argument is
executed with asynchronous exceptions masked.