stm 2.4 → 2.4.2

raw patch · 4 files changed

+83/−5 lines, 4 files

Files

• Control/Concurrent/STM/TChan.hs +1/−2
• Control/Concurrent/STM/TSem.hs +54/−0
• Control/Monad/STM.hs +18/−2
• stm.cabal +10/−1

@@ -97,9 +97,8 @@ -- garbage collected after clients have seen them. newBroadcastTChan :: STM (TChan a) newBroadcastTChan = do-    dummy_hole <- newTVar TNil     write_hole <- newTVar TNil-    read <- newTVar dummy_hole+    read <- newTVar (error "reading from a TChan created by newBroadcastTChan; use dupTChan first")     write <- newTVar write_hole     return (TChan read write) 

@@ -0,0 +1,54 @@+-----------------------------------------------------------------------------+-- |+-- Module      :  Control.Concurrent.STM.TSem+-- Copyright   :  (c) The University of Glasgow 2012+-- License     :  BSD-style (see the file libraries/base/LICENSE)+-- +-- Maintainer  :  libraries@haskell.org+-- Stability   :  experimental+-- Portability :  non-portable (requires STM)+--+-- 'TSem': transactional semaphores.+--+-----------------------------------------------------------------------------++{-# LANGUAGE DeriveDataTypeable #-}+module Control.Concurrent.STM.TSem (+      TSem, newTSem, waitTSem, signalTSem+  ) where++import Control.Concurrent.STM+import Control.Monad+import Data.Typeable+import Control.Exception++-- | 'TSem' is a transactional semaphore.  It holds a certain number+-- of units, and units may be acquired or released by 'waitTSem' and+-- 'signalTSem' respectively.  When the 'TSem' is empty, 'waitTSem'+-- blocks.+--+-- Note that 'TSem' has no concept of fairness, and there is no+-- guarantee that threads blocked in `waitTSem` will be unblocked in+-- the same order; in fact they will all be unblocked at the same time+-- and will fight over the 'TSem'.  Hence 'TSem' is not suitable if+-- you expect there to be a high number of threads contending for the+-- resource.  However, like other STM abstractions, 'TSem' is+-- composable.+--+newtype TSem = TSem (TVar Int)+  deriving (Eq, Typeable)++newTSem :: Int -> STM TSem+newTSem i = fmap TSem (newTVar i)++waitTSem :: TSem -> STM ()+waitTSem (TSem t) = do+  i <- readTVar t+  when (i <= 0) retry+  writeTVar t $! (i-1)++signalTSem :: TSem -> STM ()+signalTSem (TSem t) = do+  i <- readTVar t+  writeTVar t $! i+1+

@@ -57,13 +57,29 @@  #ifdef __GLASGOW_HASKELL__ #if ! (MIN_VERSION_base(4,3,0))+import Control.Applicative+import Control.Monad (ap)+#endif+#endif+++#ifdef __GLASGOW_HASKELL__+#if ! (MIN_VERSION_base(4,3,0)) instance MonadPlus STM where   mzero = retry   mplus = orElse++instance Applicative STM where+  pure = return+  (<*>) = ap++instance Alternative STM where+  empty = retry+  (<|>) = orElse #endif -check :: Bool -> STM a-check b = if b then return undefined else retry+check :: Bool -> STM ()+check b = if b then return () else retry #endif  #if ! (MIN_VERSION_base(4,3,0))

@@ -1,5 +1,5 @@ name:		stm-version:        2.4+version:        2.4.2 license:	BSD3 license-file:	LICENSE maintainer:	libraries@haskell.org@@ -8,6 +8,14 @@ description:  A modular composable concurrency abstraction.  .+ Changes in version 2.4.2+ .+ * Added "Control.Concurrent.STM.TSem" (transactional semaphore)+ .+ Changes in version 2.4.1+ .+ * Added Applicative/Alternative instances of STM for GHC <7.0+ .  Changes in version 2.4  .  * Added "Control.Concurrent.STM.TQueue" (a faster @TChan@)@@ -40,6 +48,7 @@     Control.Concurrent.STM.TMVar     Control.Concurrent.STM.TQueue     Control.Concurrent.STM.TBQueue+    Control.Concurrent.STM.TSem     Control.Monad.STM   other-modules:     Control.Sequential.STM