| License | BSD2 |
|---|---|
| Portability | non-portable |
| Safe Haskell | None |
| Language | Haskell2010 |
Data.Primitive.MVar
Description
Primitive operations on MVar. This module provides a similar interface
to Control.Concurrent.MVar. However, the functions are generalized to
work in any PrimMonad instead of only working in IO. Note that all
of the functions here are completely deterministic. Users of MVar are
responsible for designing abstractions that guarantee determinism in
the presence of multi-threading.
Since: 0.6.4.0
Synopsis
- data MVar s a = MVar (MVar# s a)
- newMVar :: PrimMonad m => a -> m (MVar (PrimState m) a)
- isEmptyMVar :: PrimMonad m => MVar (PrimState m) a -> m Bool
- newEmptyMVar :: PrimMonad m => m (MVar (PrimState m) a)
- putMVar :: PrimMonad m => MVar (PrimState m) a -> a -> m ()
- readMVar :: PrimMonad m => MVar (PrimState m) a -> m a
- takeMVar :: PrimMonad m => MVar (PrimState m) a -> m a
- tryPutMVar :: PrimMonad m => MVar (PrimState m) a -> a -> m Bool
- tryReadMVar :: PrimMonad m => MVar (PrimState m) a -> m (Maybe a)
- tryTakeMVar :: PrimMonad m => MVar (PrimState m) a -> m (Maybe a)
Documentation
newMVar :: PrimMonad m => a -> m (MVar (PrimState m) a) #
Create a new MVar that holds the supplied argument.
isEmptyMVar :: PrimMonad m => MVar (PrimState m) a -> m Bool #
Check whether a given MVar is empty.
Notice that the boolean value returned is just a snapshot of
the state of the MVar. By the time you get to react on its result,
the MVar may have been filled (or emptied) - so be extremely
careful when using this operation. Use tryTakeMVar instead if possible.
readMVar :: PrimMonad m => MVar (PrimState m) a -> m a #
Atomically read the contents of an MVar. If the MVar is
currently empty, readMVar will wait until it is full.
readMVar is guaranteed to receive the next putMVar.
Multiple Wakeup: readMVar is multiple-wakeup, so when multiple readers
are blocked on an MVar, all of them are woken up at the same time.
Compatibility note: On GHCs prior to 7.8, readMVar is a combination
of takeMVar and putMVar. Consequently, its behavior differs in the
following ways:
tryPutMVar :: PrimMonad m => MVar (PrimState m) a -> a -> m Bool #
A non-blocking version of putMVar. The tryPutMVar function
attempts to put the value a into the MVar, returning True if
it was successful, or False otherwise.
tryReadMVar :: PrimMonad m => MVar (PrimState m) a -> m (Maybe a) #
A non-blocking version of readMVar. The tryReadMVar function
returns immediately, with Nothing if the MVar was empty, or
if the Just aMVar was full with contents a.
Compatibility note: On GHCs prior to 7.8, tryReadMVar is a combination
of tryTakeMVar and putMVar. Consequently, its behavior differs in the
following ways:
- It is single-wakeup instead of multiple-wakeup.
- In the presence of other threads calling
putMVar,tryReadMVarmay block. - If another thread puts a value in the
MVarin between the calls totryTakeMVarandputMVar, that value may be overridden.
tryTakeMVar :: PrimMonad m => MVar (PrimState m) a -> m (Maybe a) #
A non-blocking version of takeMVar. The tryTakeMVar function
returns immediately, with Nothing if the MVar was empty, or
if the Just aMVar was full with contents a. After tryTakeMVar,
the MVar is left empty.