stm-chans-3.0.0.6: Additional types of channels for STM.
CopyrightCopyright (c) 2011--2021 wren gayle romano
LicenseBSD
Maintainerwren@cpan.org
Stabilityprovisional
Portabilitynon-portable (GHC STM, DeriveDataTypeable)
Safe HaskellSafe
LanguageHaskell2010

Control.Concurrent.STM.TMChan

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.

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.