Control.Concurrent.Classy.STM.TVar

Transactional variables, for use with MonadSTM.

Deviations: There is no Eq instance for MonadSTM the TVar type. Furthermore, the newTVarIO and mkWeakTVar functions are not provided.

TVars

newTVar :: MonadSTM stm => a -> stm (TVar stm a)

Create a new TVar containing the given value.

newTVar = newTVarN ""

newTVarN :: MonadSTM stm => String -> a -> stm (TVar stm a)

Create a new TVar containing the given value, but it is given a name which may be used to present more useful debugging information.

If an empty name is given, a counter starting from 0 is used. If names conflict, successive TVars with the same name are given a numeric suffix, counting up from 1.

newTVarN _ = newTVar

readTVar :: MonadSTM stm => TVar stm a -> stm a

Return the current value stored in a TVar.

readTVarConc :: MonadConc m => TVar (STM m) a -> m a

Read the current value stored in a TVar. This may be implemented differently for speed.

readTVarConc = atomically . readTVar

writeTVar :: MonadSTM stm => TVar stm a -> a -> stm ()

Write the supplied value into the TVar.

modifyTVar :: MonadSTM stm => TVar stm a -> (a -> a) -> stm ()

Mutate the contents of a TVar. This is non-strict.

modifyTVar' :: MonadSTM stm => TVar stm a -> (a -> a) -> stm ()

Mutate the contents of a TVar strictly.

swapTVar :: MonadSTM stm => TVar stm a -> a -> stm a

Swap the contents of a TVar, returning the old value.

registerDelay :: MonadConc m => Int -> m (TVar (STM m) Bool)

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