stm-chans-3.0.0.2: Additional types of channels for STM.

CopyrightCopyright (c) 2011--2013 wren gayle romano
LicenseBSD
Maintainerwren@community.haskell.org
Stabilityprovisional
Portabilitynon-portable (GHC STM, DeriveDataTypeable)
Safe HaskellTrustworthy
LanguageHaskell98

Control.Concurrent.STM.TMChan

Contents

Description

A version of Control.Concurrent.STM.TChan where the queue is closeable. This is similar to a TChan (Maybe a) with a monotonicity guarantee that once there's a Nothing there will always be Nothing.

Synopsis

The TMChan type

data TMChan a Source

TMChan is an abstract type representing a closeable FIFO channel.

Instances

Typeable (* -> *) TMChan 

Creating TMChans

newTMChan :: STM (TMChan a) Source

Build and returns a new instance of TMChan.

newTMChanIO :: IO (TMChan a) Source

IO version of newTMChan. This is useful for creating top-level TMChans using unsafePerformIO, because using atomically inside unsafePerformIO isn't possible.

dupTMChan :: TMChan a -> STM (TMChan a) Source

Duplicate a TMChan: the duplicate channel begins empty, but data written to either channel from then on will be available from both, and closing one copy will close them all. Hence this creates a kind of broadcast channel, where data written by anyone is seen by everyone else.

newBroadcastTMChanIO :: IO (TMChan a) Source

IO version of newBroadcastTMChan.

Since: 2.1.0

Reading from TMChans

readTMChan :: TMChan a -> STM (Maybe a) Source

Read the next value from the TMChan, retrying if the channel is empty (and not closed). We return Nothing immediately if the channel is closed and empty.

tryReadTMChan :: TMChan a -> STM (Maybe (Maybe a)) Source

A version of readTMChan which does not retry. Instead it returns Just Nothing if the channel is open but no value is available; it still returns Nothing if the channel is closed and empty.

peekTMChan :: TMChan a -> STM (Maybe a) Source

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

tryPeekTMChan :: TMChan a -> STM (Maybe (Maybe a)) Source

A version of peekTMChan which does not retry. Instead it returns Just Nothing if the channel is open but no value is available; it still returns Nothing if the channel is closed and empty.

Writing to TMChans

writeTMChan :: TMChan a -> a -> STM () Source

Write a value to a TMChan. If the channel is closed then the value is silently discarded. Use isClosedTMChan to determine if the channel is closed before writing, as needed.

unGetTMChan :: TMChan a -> a -> STM () Source

Put a data item back onto a channel, where it will be the next item read. If the channel is closed then the value is silently discarded; you can use peekTMChan to circumvent this in certain circumstances.

Closing TMChans

closeTMChan :: TMChan a -> STM () Source

Closes the TMChan, preventing any further writes.

Predicates

isClosedTMChan :: TMChan a -> STM Bool Source

Returns True if the supplied TMChan has been closed.

isEmptyTMChan :: TMChan a -> STM Bool Source

Returns True if the supplied TMChan is empty.