readIORef, -- :: IORef a -> IO a
writeIORef, -- :: IORef a -> a -> IO ()
modifyIORef, -- :: IORef a -> (a -> a) -> IO ()
- atomicModifyIORef, -- :: IORef a -> (a -> (a,b)) -> IO ()
+ atomicModifyIORef, -- :: IORef a -> (a -> (a,b)) -> IO b
#if !defined(__PARALLEL_HASKELL__) && defined(__GLASGOW_HASKELL__)
mkWeakIORef, -- :: IORef a -> IO () -> IO (Weak (IORef a))
modifyIORef :: IORef a -> (a -> a) -> IO ()
modifyIORef ref f = writeIORef ref . f =<< readIORef ref
+
-- |Atomically modifies the contents of an 'IORef'.
--
-- This function is useful for using 'IORef' in a safe way in a multithreaded
-- then using '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
-#ifndef __NHC__
-#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
#endif