Control.Concurrent.BoundedChan

Implements bounded channels. These channels differ from normal Chans in that they are guaranteed to contain no more than a certain number of elements. This is ideal when you may be writing to a channel faster than you are able to read from it.

This module supports all the functions of Control.Concurrent.Chan except unGetChan and dupChan, which are not supported for bounded channels.

Extra consitency: This version enforces that if thread Alice writes e1 followed by e2 then e1 will be returned by readChan before e2. Conversely, if thead Bob reads e1 followed by e2 then it was true that writeChan e1 preceded writeChan e2.

Previous versions did not enforce this consistency: if writeChan were preempted between putMVars or killThread arrived between putMVars then it can fail. Similarly it might fail if readChan were stopped after putMVar and before the second takeMVar. An unlucky pattern of several such deaths might actually break the invariants of the array in an unrecoverable way causing all future reads and writes to block.

Documentation

data BoundedChan a

BoundedChan is an abstract data type representing a bounded channel.

newBoundedChan :: Int -> IO (BoundedChan a)

newBoundedChan n returns a channel than can contain no more than n elements.

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

Write an element to the channel. If the channel is full, this routine will block until it is able to write. Blockers wait in a fair FIFO queue.

tryWriteChan :: BoundedChan a -> a -> IO Bool

A variant of writeChan which, instead of blocking when the channel is full, simply aborts and does not write the element. Note that this routine can still block while waiting for write access to the channel.

readChan :: BoundedChan a -> IO a

Read an element from the channel. If the channel is empty, this routine will block until it is able to read. Blockers wait in a fair FIFO queue.

tryReadChan :: BoundedChan a -> IO (Maybe a)

A variant of readChan which, instead of blocking when the channel is empty, immediately returns Nothing. Otherwise, tryReadChan returns Just a where a is the element read from the channel. Note that this routine can still block while waiting for read access to the channel.

isEmptyChan :: BoundedChan a -> IO Bool

Deprecated: This isEmptyChan can block, no non-blocking substitute yet

DANGER: This may block on an empty channel if there is already a blocked reader. Returns True if the supplied channel is empty.

DEPRECATED

getChanContents :: BoundedChan a -> IO [a]

Return a lazy list representing the contents of the supplied channel. Competing readers might steal from this list.

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

Write a list of elements to the channel. If the channel becomes full, this routine will block until it is able to write. Competing writers may interleave with this one.