Concurrency.TMVar

TMVar

data TMVar a

A TMVar is a synchronising variable, used for communication between concurrent threads. It can be thought of as a box, which may be empty or full.

Instances

Eq (TMVar a)

Defined in Control.Concurrent.STM.TMVar

Methods

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

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

newTMVar :: a -> STM (TMVar a)

Create a TMVar which contains the supplied value.

newTMVarIO :: MonadIO m => a -> m (TMVar a)

Lifted version of newTMVarIO

Since: unliftio-0.2.1.0

newEmptyTMVar :: STM (TMVar a)

Create a TMVar which is initially empty.

newEmptyTMVarIO :: MonadIO m => m (TMVar a)

Lifted version of newEmptyTMVarIO

Since: unliftio-0.2.1.0

takeTMVar :: TMVar a -> STM a

Return the contents of the TMVar. If the TMVar is currently empty, the transaction will retry. After a takeTMVar, the TMVar is left empty.

tryTakeTMVar :: TMVar a -> STM (Maybe a)

A version of takeTMVar that does not retry. The tryTakeTMVar function returns Nothing if the TMVar was empty, or Just a if the TMVar was full with contents a. After tryTakeTMVar, the TMVar is left empty.

putTMVar :: TMVar a -> a -> STM ()

Put a value into a TMVar. If the TMVar is currently full, putTMVar will retry.

tryPutTMVar :: TMVar a -> a -> STM Bool

A version of putTMVar that does not retry. The tryPutTMVar function attempts to put the value a into the TMVar, returning True if it was successful, or False otherwise.

readTMVar :: TMVar a -> STM a

This is a combination of takeTMVar and putTMVar; ie. it takes the value from the TMVar, puts it back, and also returns it.

tryReadTMVar :: TMVar a -> STM (Maybe a)

A version of readTMVar which does not retry. Instead it returns Nothing if no value is available.

Since: stm-2.3

swapTMVar :: TMVar a -> a -> STM a

Swap the contents of a TMVar for a new value.

isEmptyTMVar :: TMVar a -> STM Bool

Check whether a given TMVar is empty.

mkWeakTMVar :: MonadUnliftIO m => TMVar a -> m () -> m (Weak (TMVar a))

Lifted version of mkWeakTMVar

Since: unliftio-0.2.1.0