stm- Software Transactional Memory

Copyright(c) The University of Glasgow 2004
LicenseBSD-style (see the file libraries/base/LICENSE)
Portabilitynon-portable (requires STM)
Safe HaskellTrustworthy




TVar: Transactional variables



data TVar a #

Shared memory locations that support atomic memory transactions.

Eq (TVar a)


Instance details


(==) :: TVar a -> TVar a -> Bool #

(/=) :: TVar a -> TVar a -> Bool #

newTVar :: a -> STM (TVar a) #

Create a new TVar holding a value supplied

newTVarIO :: a -> IO (TVar a) #

IO version of newTVar. This is useful for creating top-level TVars using unsafePerformIO, because using atomically inside unsafePerformIO isn't possible.

readTVar :: TVar a -> STM a #

Return the current value stored in a TVar.

readTVarIO :: TVar a -> IO a #

Return the current value stored in a TVar. This is equivalent to

 readTVarIO = atomically . readTVar

but works much faster, because it doesn't perform a complete transaction, it just reads the current value of the TVar.

writeTVar :: TVar a -> a -> STM () #

Write the supplied value into a TVar.

modifyTVar :: TVar a -> (a -> a) -> STM () Source #

Mutate the contents of a TVar. N.B., this version is non-strict.

Since: 2.3

modifyTVar' :: TVar a -> (a -> a) -> STM () Source #

Strict version of modifyTVar.

Since: 2.3

swapTVar :: TVar a -> a -> STM a Source #

Swap the contents of a TVar for a new value.

Since: 2.3

registerDelay :: Int -> IO (TVar Bool) #

Set the value of returned TVar to True after a given number of microseconds. The caveats associated with threadDelay also apply.

mkWeakTVar :: TVar a -> IO () -> IO (Weak (TVar a)) Source #

Make a Weak pointer to a TVar, using the second argument as a finalizer to run when TVar is garbage-collected

Since: 2.4.3