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| Control.Concurrent.STM.TMVar | | Portability | non-portable (requires STM) | | Stability | experimental | | Maintainer | libraries@haskell.org |
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| Description |
| TMVar: Transactional MVars, for use in the STM monad
(GHC only)
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| Synopsis |
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| TMVars
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| data TMVar a |
| 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.
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| newTMVar :: a -> STM (TMVar a) |
| Create a TMVar which contains the supplied value.
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| newEmptyTMVar :: STM (TMVar a) |
| Create a TMVar which is initially empty.
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| newTMVarIO :: a -> IO (TMVar a) |
| IO version of newTMVar. This is useful for creating top-level
TMVars using System.IO.Unsafe.unsafePerformIO, because using
atomically inside System.IO.Unsafe.unsafePerformIO isn't
possible.
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| newEmptyTMVarIO :: IO (TMVar a) |
| IO version of newEmptyTMVar. This is useful for creating top-level
TMVars using System.IO.Unsafe.unsafePerformIO, because using
atomically inside System.IO.Unsafe.unsafePerformIO isn't
possible.
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| takeTMVar :: TMVar a -> STM a |
| Return the contents of the TMVar. If the TMVar is currently
empty, the transaction will retry. After a takeTMVar,
the TMVar is left empty.
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| putTMVar :: TMVar a -> a -> STM () |
| Put a value into a TMVar. If the TMVar is currently full,
putTMVar will retry.
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| readTMVar :: TMVar a -> STM a |
| This is a combination of takeTMVar and putTMVar; ie. it takes the value
from the TMVar, puts it back, and also returns it.
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| swapTMVar :: TMVar a -> a -> STM a |
| Swap the contents of a TMVar for a new value.
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| tryTakeTMVar :: TMVar a -> STM (Maybe a) |
| A version of takeTMVar that does not retry. The tryTakeTMVar
function returns Nothing if the TMVar was empty, or Just a if
the TMVar was full with contents a. After tryTakeTMVar, the
TMVar is left empty.
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| tryPutTMVar :: TMVar a -> a -> STM Bool |
| A version of putTMVar that does not retry. The tryPutTMVar
function attempts to put the value a into the TMVar, returning
True if it was successful, or False otherwise.
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| isEmptyTMVar :: TMVar a -> STM Bool |
Check whether a given TMVar is empty.
Notice that the boolean value returned is just a snapshot of
the state of the TMVar. By the time you get to react on its result,
the TMVar may have been filled (or emptied) - so be extremely
careful when using this operation. Use tryTakeTMVar instead if possible.
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| Produced by Haddock version 2.3.0 |
