stm- Software Transactional Memory

Portabilitynon-portable (requires STM)




TVar: Transactional variables



data TVar a

Shared memory locations that support atomic memory transactions.


newTVar :: a -> STM (TVar a)

Create a new TVar holding a value supplied

readTVar :: TVar a -> STM a

Return the current value stored in a TVar

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

Write the supplied value into a TVar

newTVarIO :: a -> IO (TVar a)

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

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.

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.