Control.Concurrent.Chan

Unbounded channels.

The channels are implemented with MVars and therefore inherit all the caveats that apply to MVars (possibility of races, deadlocks etc). The stm (software transactional memory) library has a more robust implementation of channels called TChans.

The Chan type

data Chan a

Chan is an abstract type representing an unbounded FIFO channel.

Instances

Eq (Chan a)

Since: base-4.4.0.0

Defined in Control.Concurrent.Chan

Methods

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

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

Operations

newChan :: IO (Chan a)

Build and returns a new instance of Chan.

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

Write a value to a Chan.

readChan :: Chan a -> IO a

Read the next value from the Chan. Blocks when the channel is empty. Since the read end of a channel is an MVar, this operation inherits fairness guarantees of MVars (e.g. threads blocked in this operation are woken up in FIFO order).

Throws BlockedIndefinitelyOnMVar when the channel is empty and no other thread holds a reference to the channel.

dupChan :: Chan a -> IO (Chan a)

Duplicate a Chan: 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.

(Note that a duplicated channel is not equal to its original. So: fmap (c /=) $ dupChan c returns True for all c.)

Stream interface

getChanContents :: Chan a -> IO [a]

Return a lazy list representing the contents of the supplied Chan, much like hGetContents.

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

Write an entire list of items to a Chan.