UnliftIO.STM

A monad supporting atomic memory transactions.

Lifted version of atomically

Renamed retry for unqualified export

Renamed check for unqualified export

Compose two alternative STM actions (GHC only).

If the first action completes without retrying then it forms the result of the orElse. Otherwise, if the first action retries, then the second action is tried in its place. If both actions retry then the orElse as a whole retries.

Shared memory locations that support atomic memory transactions.

Lifted version of newTVarIO

Lifted version of readTVarIO

Create a new TVar holding a value supplied

Return the current value stored in a TVar.

Write the supplied value into a TVar.

Mutate the contents of a TVar. N.B., this version is non-strict.

Strict version of modifyTVar.

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.

Swap the contents of a TVar for a new value.

Lifted version of registerDelay

Lifted version of mkWeakTVar

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.

Create a TMVar which contains the supplied value.

Create a TMVar which is initially empty.

Lifted version of newTMVarIO

Lifted version of newEmptyTMVarIO

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

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

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

Non-blocking write of a new value to a TMVar Puts if empty. Replaces if populated.

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

Swap the contents of a TMVar for a new value.

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.

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.

Check whether a given TMVar is empty.

Lifted version of mkWeakTMVar

TChan is an abstract type representing an unbounded FIFO channel.

Build and return a new instance of TChan

Lifted version of newTChanIO

Create a write-only TChan. More precisely, readTChan will retry even after items have been written to the channel. The only way to read a broadcast channel is to duplicate it with dupTChan.

Consider a server that broadcasts messages to clients:

serve :: TChan Message -> Client -> IO loop
serve broadcastChan client = do
    myChan <- dupTChan broadcastChan
    forever $ do
        message <- readTChan myChan
        send client message

The problem with using newTChan to create the broadcast channel is that if it is only written to and never read, items will pile up in memory. By using newBroadcastTChan to create the broadcast channel, items can be garbage collected after clients have seen them.

Lifted version of newBroadcastTChanIO

Duplicate a TChan: the duplicate channel begins empty, but data written to either channel from then on will be available from both. Hence this creates a kind of broadcast channel, where data written by anyone is seen by everyone else.

Clone a TChan: similar to dupTChan, but the cloned channel starts with the same content available as the original channel.

Read the next value from the TChan.

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

Get the next value from the TChan without removing it, retrying if the channel is empty.

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

Write a value to a TChan.

Put a data item back onto a channel, where it will be the next item read.

Returns True if the supplied TChan is empty.

TQueue is an abstract type representing an unbounded FIFO channel.

Build and returns a new instance of TQueue

Lifted version of newTQueueIO

Read the next value from the TQueue.

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

Get the next value from the TQueue without removing it, retrying if the channel is empty.

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

Write a value to a TQueue.

Put a data item back onto a channel, where it will be the next item read.

Returns True if the supplied TQueue is empty.

TBQueue is an abstract type representing a bounded FIFO channel.

Builds and returns a new instance of TBQueue.

Lifted version of newTBQueueIO

Read the next value from the TBQueue.

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

Efficiently read the entire contents of a TBQueue into a list. This function never retries.

Get the next value from the TBQueue without removing it, retrying if the channel is empty.

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

Write a value to a TBQueue; blocks if the queue is full.

Put a data item back onto a channel, where it will be the next item read. Blocks if the queue is full.

Return the length of a TBQueue.

Returns True if the supplied TBQueue is empty.

Returns True if the supplied TBQueue is full.