diff options
Diffstat (limited to 'libraries/base/Control/Concurrent')
| -rw-r--r-- | libraries/base/Control/Concurrent/Chan.hs | 42 | ||||
| -rw-r--r-- | libraries/base/Control/Concurrent/MVar.hs | 12 | ||||
| -rw-r--r-- | libraries/base/Control/Concurrent/QSem.hs | 2 | ||||
| -rw-r--r-- | libraries/base/Control/Concurrent/QSemN.hs | 2 |
4 files changed, 14 insertions, 44 deletions
diff --git a/libraries/base/Control/Concurrent/Chan.hs b/libraries/base/Control/Concurrent/Chan.hs index ebbec7ea99..874e48a1a1 100644 --- a/libraries/base/Control/Concurrent/Chan.hs +++ b/libraries/base/Control/Concurrent/Chan.hs @@ -1,13 +1,12 @@ {-# LANGUAGE Trustworthy #-} {-# LANGUAGE CPP #-} -{-# LANGUAGE StandaloneDeriving #-} ----------------------------------------------------------------------------- -- | -- Module : Control.Concurrent.Chan -- Copyright : (c) The University of Glasgow 2001 -- License : BSD-style (see the file libraries/base/LICENSE) --- +-- -- Maintainer : libraries@haskell.org -- Stability : experimental -- Portability : non-portable (concurrency) @@ -22,7 +21,7 @@ ----------------------------------------------------------------------------- module Control.Concurrent.Chan - ( + ( -- * The 'Chan' type Chan, -- abstract @@ -31,8 +30,6 @@ module Control.Concurrent.Chan writeChan, readChan, dupChan, - unGetChan, - isEmptyChan, -- * Stream interface getChanContents, @@ -53,7 +50,7 @@ import Control.Exception (mask_) data Chan a = Chan _UPK_(MVar (Stream a)) _UPK_(MVar (Stream a)) -- Invariant: the Stream a is always an empty MVar - deriving (Eq) + deriving Eq -- ^ @since 4.4.0.0 type Stream a = MVar (ChItem a) @@ -105,25 +102,16 @@ writeChan (Chan _ writeVar) val = do -- guarantees of 'MVar's (e.g. threads blocked in this operation are woken up in -- FIFO order). -- --- Throws 'BlockedIndefinitelyOnMVar' when the channel is empty and no other --- thread holds a reference to the channel. +-- Throws 'Control.Exception.BlockedIndefinitelyOnMVar' when the channel is +-- empty and no other thread holds a reference to the channel. readChan :: Chan a -> IO a readChan (Chan readVar _) = do - modifyMVarMasked readVar $ \read_end -> do -- Note [modifyMVarMasked] + modifyMVar readVar $ \read_end -> do (ChItem val new_read_end) <- readMVar read_end -- Use readMVar here, not takeMVar, -- else dupChan doesn't work return (new_read_end, val) --- Note [modifyMVarMasked] --- This prevents a theoretical deadlock if an asynchronous exception --- happens during the readMVar while the MVar is empty. In that case --- the read_end MVar will be left empty, and subsequent readers will --- deadlock. Using modifyMVarMasked prevents this. The deadlock can --- be reproduced, but only by expanding readMVar and inserting an --- artificial yield between its takeMVar and putMVar operations. - - -- |Duplicate a 'Chan': the duplicate channel begins empty, but data written to -- either channel from then on will be available from both. Hence this creates -- a kind of broadcast channel, where data written by anyone is seen by @@ -137,24 +125,6 @@ dupChan (Chan _ writeVar) = do newReadVar <- newMVar hole return (Chan newReadVar writeVar) --- |Put a data item back onto a channel, where it will be the next item read. -unGetChan :: Chan a -> a -> IO () -unGetChan (Chan readVar _) val = do - new_read_end <- newEmptyMVar - modifyMVar_ readVar $ \read_end -> do - putMVar new_read_end (ChItem val read_end) - return new_read_end -{-# DEPRECATED unGetChan "if you need this operation, use Control.Concurrent.STM.TChan instead. See <http://ghc.haskell.org/trac/ghc/ticket/4154> for details" #-} -- deprecated in 7.0 - --- |Returns 'True' if the supplied 'Chan' is empty. -isEmptyChan :: Chan a -> IO Bool -isEmptyChan (Chan readVar writeVar) = do - withMVar readVar $ \r -> do - w <- readMVar writeVar - let eq = r == w - eq `seq` return eq -{-# DEPRECATED isEmptyChan "if you need this operation, use Control.Concurrent.STM.TChan instead. See <http://ghc.haskell.org/trac/ghc/ticket/4154> for details" #-} -- deprecated in 7.0 - -- Operators for interfacing with functional streams. -- |Return a lazy list representing the contents of the supplied diff --git a/libraries/base/Control/Concurrent/MVar.hs b/libraries/base/Control/Concurrent/MVar.hs index 393fca89e2..df28fe8406 100644 --- a/libraries/base/Control/Concurrent/MVar.hs +++ b/libraries/base/Control/Concurrent/MVar.hs @@ -33,16 +33,16 @@ -- -- === Applicability -- --- 'MVar's offer more flexibility than 'IORef's, but less flexibility --- than 'STM'. They are appropriate for building synchronization +-- 'MVar's offer more flexibility than 'Data.IORef.IORef's, but less flexibility +-- than 'GHC.Conc.STM'. They are appropriate for building synchronization -- primitives and performing simple interthread communication; however -- they are very simple and susceptible to race conditions, deadlocks or -- uncaught exceptions. Do not use them if you need perform larger --- atomic operations such as reading from multiple variables: use 'STM' +-- atomic operations such as reading from multiple variables: use 'GHC.Conc.STM' -- instead. -- --- In particular, the "bigger" functions in this module ('readMVar', --- 'swapMVar', 'withMVar', 'modifyMVar_' and 'modifyMVar') are simply +-- In particular, the "bigger" functions in this module ('swapMVar', +-- 'withMVar', 'modifyMVar_' and 'modifyMVar') are simply -- the composition of a 'takeMVar' followed by a 'putMVar' with -- exception safety. -- These only have atomicity guarantees if all other threads @@ -70,7 +70,7 @@ -- -- 'MVar' operations are always observed to take place in the order -- they are written in the program, regardless of the memory model of --- the underlying machine. This is in contrast to 'IORef' operations +-- the underlying machine. This is in contrast to 'Data.IORef.IORef' operations -- which may appear out-of-order to another thread in some cases. -- -- === Example diff --git a/libraries/base/Control/Concurrent/QSem.hs b/libraries/base/Control/Concurrent/QSem.hs index 51624e4777..ea396255a4 100644 --- a/libraries/base/Control/Concurrent/QSem.hs +++ b/libraries/base/Control/Concurrent/QSem.hs @@ -29,7 +29,7 @@ import Control.Concurrent.MVar ( MVar, newEmptyMVar, takeMVar, tryTakeMVar import Control.Exception import Data.Maybe --- | 'QSem' is a quantity semaphore in which the resource is aqcuired +-- | 'QSem' is a quantity semaphore in which the resource is acquired -- and released in units of one. It provides guaranteed FIFO ordering -- for satisfying blocked `waitQSem` calls. -- diff --git a/libraries/base/Control/Concurrent/QSemN.hs b/libraries/base/Control/Concurrent/QSemN.hs index 7686d3f327..b8c9274057 100644 --- a/libraries/base/Control/Concurrent/QSemN.hs +++ b/libraries/base/Control/Concurrent/QSemN.hs @@ -31,7 +31,7 @@ import Control.Concurrent.MVar ( MVar, newEmptyMVar, takeMVar, tryTakeMVar import Control.Exception import Data.Maybe --- | 'QSemN' is a quantity semaphore in which the resource is aqcuired +-- | 'QSemN' is a quantity semaphore in which the resource is acquired -- and released in units of one. It provides guaranteed FIFO ordering -- for satisfying blocked `waitQSemN` calls. -- |