stm-2.4.4: 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) 

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.

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

Strict version of modifyTVar.

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

Swap the contents of a TVar for a new value.

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