+{-# OPTIONS_GHC -XNoImplicitPrelude #-}
-----------------------------------------------------------------------------
-- |
-- Module : Data.IORef
module Data.IORef
(
- -- * IORefs
- IORef, -- abstract, instance of: Eq, Typeable
- newIORef, -- :: a -> IO (IORef a)
- readIORef, -- :: IORef a -> IO a
- writeIORef, -- :: IORef a -> a -> IO ()
- modifyIORef, -- :: IORef a -> (a -> a) -> IO ()
+ -- * IORefs
+ IORef, -- abstract, instance of: Eq, Typeable
+ newIORef, -- :: a -> IO (IORef a)
+ readIORef, -- :: IORef a -> IO a
+ writeIORef, -- :: IORef a -> a -> IO ()
+ modifyIORef, -- :: IORef a -> (a -> a) -> IO ()
+ atomicModifyIORef, -- :: IORef a -> (a -> (a,b)) -> IO b
#if !defined(__PARALLEL_HASKELL__) && defined(__GLASGOW_HASKELL__)
- mkWeakIORef, -- :: IORef a -> IO () -> IO (Weak (IORef a))
+ mkWeakIORef, -- :: IORef a -> IO () -> IO (Weak (IORef a))
#endif
- ) where
-
-import Prelude
+ ) where
#ifdef __HUGS__
import Hugs.IORef
#endif
#ifdef __GLASGOW_HASKELL__
-import GHC.Base ( mkWeak# )
+import GHC.Base
import GHC.STRef
-import GHC.IOBase
+-- import GHC.IO
+import GHC.IORef hiding (atomicModifyIORef)
+import qualified GHC.IORef
#if !defined(__PARALLEL_HASKELL__)
import GHC.Weak
#endif
#endif /* __GLASGOW_HASKELL__ */
-import Data.Dynamic
+#ifdef __NHC__
+import NHC.IOExtras
+ ( IORef
+ , newIORef
+ , readIORef
+ , writeIORef
+ , excludeFinalisers
+ )
+#endif
#if defined(__GLASGOW_HASKELL__) && !defined(__PARALLEL_HASKELL__)
-- |Make a 'Weak' pointer to an 'IORef'
-- |Mutate the contents of an 'IORef'
modifyIORef :: IORef a -> (a -> a) -> IO ()
-modifyIORef ref f = writeIORef ref . f =<< readIORef ref
+modifyIORef ref f = readIORef ref >>= writeIORef ref . f
+
+
+-- |Atomically modifies the contents of an 'IORef'.
+--
+-- This function is useful for using 'IORef' in a safe way in a multithreaded
+-- program. If you only have one 'IORef', then using 'atomicModifyIORef' to
+-- access and modify it will prevent race conditions.
+--
+-- Extending the atomicity to multiple 'IORef's is problematic, so it
+-- is recommended that if you need to do anything more complicated
+-- then using 'Control.Concurrent.MVar.MVar' instead is a good idea.
+--
+atomicModifyIORef :: IORef a -> (a -> (a,b)) -> IO b
+#if defined(__GLASGOW_HASKELL__)
+atomicModifyIORef = GHC.IORef.atomicModifyIORef
-#include "Dynamic.h"
-INSTANCE_TYPEABLE1(IORef,ioRefTc,"IORef")
+#elif defined(__HUGS__)
+atomicModifyIORef = plainModifyIORef -- Hugs has no preemption
+ where plainModifyIORef r f = do
+ a <- readIORef r
+ case f a of (a',b) -> writeIORef r a' >> return b
+#elif defined(__NHC__)
+atomicModifyIORef r f =
+ excludeFinalisers $ do
+ a <- readIORef r
+ let (a',b) = f a
+ writeIORef r a'
+ return b
+#endif