Control.Concurrent.Chan.Unagi

Documentation

General-purpose concurrent FIFO queue. If you are trying to send messages of a primitive unboxed type, you may wish to use Control.Concurrent.Chan.Unagi.Unboxed which should be slightly faster and perform better when a queue grows very large. If you need a bounded queue, see Control.Concurrent.Chan.Unagi.Bounded. And if your application doesn't require blocking reads, or is single-producer or single-consumer, then Control.Concurrent.Chan.Unagi.NoBlocking will offer lowest latency.

Creating channels

newChan :: IO (InChan a, OutChan a)

Create a new channel, returning its write and read ends.

data InChan a

The write end of a channel created with newChan.

Instances

Eq (InChan a)

Typeable (* -> *) InChan

data OutChan a

The read end of a channel created with newChan.

Instances

Eq (OutChan a)

Typeable (* -> *) OutChan

Channel operations

Reading

readChan :: OutChan a -> IO a

Read an element from the chan, blocking if the chan is empty.

Note re. exceptions: When an async exception is raised during a readChan the message that the read would have returned is likely to be lost, even when the read is known to be blocked on an empty queue. If you need to handle this scenario, you can use readChanOnException.

readChanOnException :: OutChan a -> (IO a -> IO ()) -> IO a

Like readChan but allows recovery of the queue element which would have been read, in the case that an async exception is raised during the read. To be precise exceptions are raised, and the handler run, only when readChanOnException is blocking.

The second argument is a handler that takes a blocking IO action returning the element, and performs some recovery action. When the handler is called, the passed IO a is the only way to access the element.

tryReadChan :: OutChan a -> IO (Element a)

Returns immediately with an Element a future, which returns one unique element when it becomes available via tryRead. If you're using this function exclusively you might find the implementation in Control.Concurrent.Chan.Unagi.NoBlocking is faster.

Note re. exceptions: When an async exception is raised during a tryReadChan the message that the read would have returned is likely to be lost, just as it would be when raised directly after this function returns.

newtype Element a

An IO action that returns a particular enqueued element when and if it becomes available.

Each Element corresponds to a particular enqueued element, i.e. a returned Element always offers the only means to access one particular enqueued item. The value returned by tryRead moves monotonically from Nothing to Just a when and if an element becomes available, and is idempotent at that point.

Constructors

Element

Fields

tryRead :: IO (Maybe a)

Instances

Alternative Element

Monad Element

Functor Element

MonadFix Element

MonadPlus Element

Applicative Element

getChanContents :: OutChan a -> IO [a]

Return a lazy list representing the contents of the supplied OutChan, much like System.IO.hGetContents.

Writing

writeChan :: InChan a -> a -> IO ()

Write a value to the channel.

writeList2Chan :: InChan a -> [a] -> IO ()

Write an entire list of items to a chan type. Writes here from multiple threads may be interleaved, and infinite lists are supported.

Broadcasting

dupChan :: InChan a -> IO (OutChan a)

Duplicate a chan: the returned OutChan begins empty, but data written to the argument InChan from then on will be available from both the original OutChan and the one returned here, creating a kind of broadcast channel.