stm

Software Transactional Memory

https://wiki.haskell.org/Software_transactional_memory

Version on this page:2.5.0.0
LTS Haskell 24.16:2.5.3.1
Stackage Nightly 2025-10-24:2.5.3.1
Latest on Hackage:2.5.3.1@rev:1

See all snapshots stm appears in

BSD-3-Clause licensed
Maintained by [email protected]
This version can be pinned in stack with:stm-2.5.0.0@sha256:1fb8bd117550d560d1b33a6404e27fdb090e70921e0f6434722cdbbce20d8256,2086

Module documentation for 2.5.0.0

Depends on 2 packages(full list with versions):
array, base

Software Transactional Memory, or STM, is an abstraction for concurrent communication. The main benefits of STM are composability and modularity. That is, using STM you can write concurrent abstractions that can be easily composed with any other abstraction built using STM, without exposing the details of how your abstraction ensures safety. This is typically not the case with other forms of concurrent communication, such as locks or MVars.

Changes

Changelog for stm package

2.5.0.0 Sep 2018

  • Removed alwaysSucceeds and always, GHC’s invariant checking primitives. (GHC #14324)

  • Add lengthTBQueue to Control.Concurrent.STM.TBQueue (gh-9)

  • Add stateTVar :: TVar s -> (s -> (a, s)) -> STM a combinator (gh-14)

  • Switched newTBQueue and newTBQueueIO to accept Natural as size (gh-17)

  • Switched signalTSemN and newTSem to accept Natural and Integer respectively (gh-17)

2.4.5.1 Sep 2018

  • Fix incorrect bookkeeping of write capacity in flushTBQueue (gh-9)

  • Avoid redundant writeTVars in flushTQueue to avoid unncessarily invalidating other transactions (gh-6)

2.4.5.0 Feb 2018

  • Fix space leak in TBQueue (gh-2, GHC#14494)

  • Make signalTSem resilient against Int overflows (gh-4)

  • Make definition of readTQueue consistent with readTBQueue (gh-3, GHC#9539)

  • Add flushTQueue to Control.Concurrent.STM.TQueue (gh-1)

  • Add flushTBQueue to Control.Concurrent.STM.TBQueue (gh-1)

  • Add signalTSemN operation (gh-5)

2.4.4.1 Dec 2015

  • Add support for base-4.9.0.0

  • Drop support for GHC 6.12 / base-4.2

2.4.4 Dec 2014

  • Add support for base-4.8.0.0

  • Tighten Safe Haskell bounds

  • Add mkWeakTMVar to Control.Concurrent.STM.TMVar

  • Add @since-annotations

2.4.3 Mar 2014

  • Update behaviour of newBroadcastTChanIO to match newBroadcastTChan in causing an error on a read from the broadcast channel

  • Add mkWeakTVar

  • Add isFullTBQueue

  • Fix TChan created via newBroadcastTChanIO to throw same exception on a readTChan as when created via newBroadcastTChan

  • Update to Cabal 1.10 format

2.4.2 Nov 2012

  • Add Control.Concurrent.STM.TSem (transactional semaphore)

  • Add Applicative/Alternative instances of STM for GHC <7.0

  • Throw proper exception when readTChan called on a broadcast TChan

2.4 Jul 2012

  • Add Control.Concurrent.STM.TQueue (a faster TChan)

  • Add Control.Concurrent.STM.TBQueue (a bounded channel based on TQueue)

  • Add Eq instance for TChan

  • Add newBroadcastTChan and newBroadcastTChanIO

  • Some performance improvements for TChan

  • Add cloneTChan