Portability | non-portable (requires STM) |
---|---|
Stability | experimental |
Maintainer | libraries@haskell.org |
Safe Haskell | Trustworthy |
TMVar: Transactional MVars, for use in the STM monad (GHC only)
- data TMVar a
- newTMVar :: a -> STM (TMVar a)
- newEmptyTMVar :: STM (TMVar a)
- newTMVarIO :: a -> IO (TMVar a)
- newEmptyTMVarIO :: IO (TMVar a)
- takeTMVar :: TMVar a -> STM a
- putTMVar :: TMVar a -> a -> STM ()
- readTMVar :: TMVar a -> STM a
- tryReadTMVar :: TMVar a -> STM (Maybe a)
- swapTMVar :: TMVar a -> a -> STM a
- tryTakeTMVar :: TMVar a -> STM (Maybe a)
- tryPutTMVar :: TMVar a -> a -> STM Bool
- isEmptyTMVar :: TMVar a -> STM Bool
TMVars
A TMVar
is a synchronising variable, used
for communication between concurrent threads. It can be thought of
as a box, which may be empty or full.
newEmptyTMVar :: STM (TMVar a)Source
Create a TMVar
which is initially empty.
newTMVarIO :: a -> IO (TMVar a)Source
IO
version of newTMVar
. This is useful for creating top-level
TMVar
s using unsafePerformIO
, because using
atomically
inside unsafePerformIO
isn't
possible.
newEmptyTMVarIO :: IO (TMVar a)Source
IO
version of newEmptyTMVar
. This is useful for creating top-level
TMVar
s using unsafePerformIO
, because using
atomically
inside unsafePerformIO
isn't
possible.
tryReadTMVar :: TMVar a -> STM (Maybe a)Source
A version of readTMVar
which does not retry. Instead it
returns Nothing
if no value is available.
tryTakeTMVar :: TMVar a -> STM (Maybe a)Source
A version of takeTMVar
that does not retry
. The tryTakeTMVar
function returns Nothing
if the TMVar
was empty, or
if
the Just
aTMVar
was full with contents a
. After tryTakeTMVar
, the
TMVar
is left empty.
tryPutTMVar :: TMVar a -> a -> STM BoolSource