Remove Control.Parallel*, now in package parallel

[haskell-directory.git] / Data / IORef.hs

diff --git a/Data/IORef.hs b/Data/IORef.hs
index d165380..7a6ec7d 100644 (file)
--- a/Data/IORef.hs
+++ b/Data/IORef.hs
@@ -2,34 +2,39 @@
 -- |
 -- Module      :  Data.IORef
 -- Copyright   :  (c) The University of Glasgow 2001
--- License     :  BSD-style (see the file libraries/core/LICENSE)
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
 -- 
 -- Maintainer  :  libraries@haskell.org
 -- Stability   :  experimental
 -- Portability :  portable
 --
--- $Id: IORef.hs,v 1.5 2002/04/24 16:31:39 simonmar Exp $
---
 -- Mutable references in the IO monad.
 --
 -----------------------------------------------------------------------------
 
 module Data.IORef
-       ( 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
+import Prelude -- Explicit dependency helps 'make depend' do the right thing
+
+#ifdef __HUGS__
+import Hugs.IORef
+#endif
 
 #ifdef __GLASGOW_HASKELL__
-import GHC.Base                ( mkWeak# )
+import GHC.Base                ( mkWeak#, atomicModifyMutVar# )
 import GHC.STRef
 import GHC.IOBase
 #if !defined(__PARALLEL_HASKELL__)
@@ -37,28 +42,52 @@ 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'
 mkWeakIORef :: IORef a -> IO () -> IO (Weak (IORef a))
 mkWeakIORef r@(IORef (STRef r#)) f = IO $ \s ->
   case mkWeak# r# r f s of (# s1, w #) -> (# s1, Weak w #)
 #endif
 
-#if defined __HUGS__
-data IORef a        -- mutable variables containing values of type a
-
-primitive newIORef   "newRef" :: a -> IO (IORef a)
-primitive readIORef  "getRef" :: IORef a -> IO a
-primitive writeIORef "setRef" :: IORef a -> a -> IO ()
-primitive eqIORef    "eqRef"  :: IORef a -> IORef a -> Bool
-
-instance Eq (IORef a) where
-    (==) = eqIORef
-#endif /* __HUGS__ */
-
+-- |Mutate the contents of an 'IORef'
 modifyIORef :: IORef a -> (a -> a) -> IO ()
 modifyIORef ref f = writeIORef ref . f =<< readIORef ref
 
-#include "Dynamic.h"
-INSTANCE_TYPEABLE1(IORef,ioRefTc,"IORef")
+
+-- |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 (IORef (STRef r#)) f = IO $ \s -> atomicModifyMutVar# r# f s
+
+#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