diff options
Diffstat (limited to 'libraries/base/Data/IORef.hs')
| -rw-r--r-- | libraries/base/Data/IORef.hs | 53 |
1 files changed, 24 insertions, 29 deletions
diff --git a/libraries/base/Data/IORef.hs b/libraries/base/Data/IORef.hs index c6275f5433..44769268cf 100644 --- a/libraries/base/Data/IORef.hs +++ b/libraries/base/Data/IORef.hs @@ -1,5 +1,6 @@ {-# LANGUAGE Trustworthy #-} {-# LANGUAGE NoImplicitPrelude, MagicHash, UnboxedTuples #-} +{-# LANGUAGE BangPatterns #-} ----------------------------------------------------------------------------- -- | @@ -36,8 +37,7 @@ module Data.IORef import GHC.Base import GHC.STRef -import GHC.IORef hiding (atomicModifyIORef) -import qualified GHC.IORef +import GHC.IORef import GHC.Weak -- |Make a 'Weak' pointer to an 'IORef', using the second argument as a finalizer @@ -91,18 +91,9 @@ modifyIORef' ref f = do -- Use 'atomicModifyIORef'' or 'atomicWriteIORef' to avoid this problem. -- atomicModifyIORef :: IORef a -> (a -> (a,b)) -> IO b -atomicModifyIORef = GHC.IORef.atomicModifyIORef - --- | Strict version of 'atomicModifyIORef'. This forces both the value stored --- in the 'IORef' as well as the value returned. --- --- @since 4.6.0.0 -atomicModifyIORef' :: IORef a -> (a -> (a,b)) -> IO b -atomicModifyIORef' ref f = do - b <- atomicModifyIORef ref $ \a -> - case f a of - v@(a',_) -> a' `seq` v - b `seq` return b +atomicModifyIORef ref f = do + (_old, ~(_new, res)) <- atomicModifyIORef2 ref f + pure res -- | Variant of 'writeIORef' with the \"barrier to reordering\" property that -- 'atomicModifyIORef' has. @@ -110,8 +101,8 @@ atomicModifyIORef' ref f = do -- @since 4.6.0.0 atomicWriteIORef :: IORef a -> a -> IO () atomicWriteIORef ref a = do - x <- atomicModifyIORef ref (\_ -> (a, ())) - x `seq` return () + _ <- atomicSwapIORef ref a + pure () {- $memmodel @@ -120,19 +111,23 @@ atomicWriteIORef ref a = do processor architecture. For example, on x86, loads can move ahead of stores, so in the following example: -> maybePrint :: IORef Bool -> IORef Bool -> IO () -> maybePrint myRef yourRef = do -> writeIORef myRef True -> yourVal <- readIORef yourRef -> unless yourVal $ putStrLn "critical section" -> -> main :: IO () -> main = do -> r1 <- newIORef False -> r2 <- newIORef False -> forkIO $ maybePrint r1 r2 -> forkIO $ maybePrint r2 r1 -> threadDelay 1000000 + > import Data.IORef + > import Control.Monad (unless) + > import Control.Concurrent (forkIO, threadDelay) + > + > maybePrint :: IORef Bool -> IORef Bool -> IO () + > maybePrint myRef yourRef = do + > writeIORef myRef True + > yourVal <- readIORef yourRef + > unless yourVal $ putStrLn "critical section" + > + > main :: IO () + > main = do + > r1 <- newIORef False + > r2 <- newIORef False + > forkIO $ maybePrint r1 r2 + > forkIO $ maybePrint r2 r1 + > threadDelay 1000000 it is possible that the string @"critical section"@ is printed twice, even though there is no interleaving of the operations of the |