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/Haskell 8

Control.Concurrent.STM.TVar

Copyright (c) The University of Glasgow 2004
License BSD-style (see the file libraries/base/LICENSE)
Maintainer [email protected]
Stability experimental
Portability non-portable (requires STM)
Safe Haskell Trustworthy
Language Haskell2010

Contents

Description

TVar: Transactional variables

TVars

data TVar a Source

Shared memory locations that support atomic memory transactions.

Instances
Eq (TVar a)

Since: base-4.8.0.0

Instance details

Defined in GHC.Conc.Sync

Methods

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

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

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

Create a new TVar holding a value supplied

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

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 Source

Return the current value stored in a TVar.

readTVarIO :: TVar a -> IO a Source

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 () Source

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: stm-2.3

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

Strict version of modifyTVar.

Since: stm-2.3

stateTVar :: TVar s -> (s -> (a, s)) -> STM a Source

Like modifyTVar' but the function is a simple state transition that can return a side value which is passed on as the result of the STM.

Since: stm-2.5.0

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

Swap the contents of a TVar for a new value.

Since: stm-2.3

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

Switch the value of returned TVar from initial value False 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: stm-2.4.3

© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.6.1/docs/html/libraries/stm-2.5.0.0/Control-Concurrent-STM-TVar.html