Remove unused imports from base

[ghc-base.git] / Data / IORef.hs

diff --git a/Data/IORef.hs b/Data/IORef.hs
index f073827..f885751 100644 (file)
--- a/Data/IORef.hs
+++ b/Data/IORef.hs
@@ -1,57 +1,94 @@
+{-# OPTIONS_GHC -XNoImplicitPrelude #-}
 -----------------------------------------------------------------------------
--- 
+-- |
 -- 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 :  non-portable
---
--- $Id: IORef.hs,v 1.1 2001/06/28 14:15:02 simonmar Exp $
+-- Portability :  portable
 --
 -- 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
+        ) where
 
-import Prelude
+#ifdef __HUGS__
+import Hugs.IORef
+#endif
 
 #ifdef __GLASGOW_HASKELL__
-import GHC.Prim                ( 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__ */
 
-#ifdef __HUGS__
-import IOExts          ( IORef, newIORef, writeIORef, readIORef )
-import ST              ( stToIO, newSTRef, readSTRef, writeSTRef )
+#ifdef __NHC__
+import NHC.IOExtras
+    ( IORef
+    , newIORef
+    , readIORef
+    , writeIORef
+    , excludeFinalisers
+    )
 #endif
 
-import Data.Dynamic
-
-#ifndef __PARALLEL_HASKELL__
+#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
 
+-- |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
 
-#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 = GHC.IORef.atomicModifyIORef
+
+#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