X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Control%2FConcurrent%2FMVar.hs;h=9a95b8ff0817236d34d952bd8e0673da8c6b2f97;hb=41e8fba828acbae1751628af50849f5352b27873;hp=aef89698b4a1b0950d963b3c3799af2720e0f0ef;hpb=9812e0a321ec0ed8f9e53eb2febfb14c79564200;p=ghc-base.git

diff --git a/Control/Concurrent/MVar.hs b/Control/Concurrent/MVar.hs
index aef8969..9a95b8f 100644
--- a/Control/Concurrent/MVar.hs
+++ b/Control/Concurrent/MVar.hs
@@ -1,3 +1,5 @@
+{-# LANGUAGE CPP, NoImplicitPrelude #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Control.Concurrent.MVar
@@ -13,64 +15,69 @@
 -----------------------------------------------------------------------------
 
 module Control.Concurrent.MVar
-	( 
-	  -- * @MVar@s
-	  MVar		-- abstract
-	, newEmptyMVar  -- :: IO (MVar a)
-	, newMVar 	-- :: a -> IO (MVar a)
-	, takeMVar 	-- :: MVar a -> IO a
-	, putMVar  	-- :: MVar a -> a -> IO ()
-	, readMVar 	-- :: MVar a -> IO a
-	, swapMVar 	-- :: MVar a -> a -> IO a
-	, tryTakeMVar   -- :: MVar a -> IO (Maybe a)
-	, tryPutMVar    -- :: MVar a -> a -> IO Bool
-	, isEmptyMVar	-- :: MVar a -> IO Bool
-	, withMVar	-- :: MVar a -> (a -> IO b) -> IO b
-	, modifyMVar_ 	-- :: MVar a -> (a -> IO a) -> IO ()
-	, modifyMVar 	-- :: MVar a -> (a -> IO (a,b)) -> IO b
+        (
+          -- * @MVar@s
+          MVar          -- abstract
+        , newEmptyMVar  -- :: IO (MVar a)
+        , newMVar       -- :: a -> IO (MVar a)
+        , takeMVar      -- :: MVar a -> IO a
+        , putMVar       -- :: MVar a -> a -> IO ()
+        , readMVar      -- :: MVar a -> IO a
+        , swapMVar      -- :: MVar a -> a -> IO a
+        , tryTakeMVar   -- :: MVar a -> IO (Maybe a)
+        , tryPutMVar    -- :: MVar a -> a -> IO Bool
+        , isEmptyMVar   -- :: MVar a -> IO Bool
+        , withMVar      -- :: MVar a -> (a -> IO b) -> IO b
+        , modifyMVar_   -- :: MVar a -> (a -> IO a) -> IO ()
+        , modifyMVar    -- :: MVar a -> (a -> IO (a,b)) -> IO b
 #ifndef __HUGS__
-	, addMVarFinalizer -- :: MVar a -> IO () -> IO ()
+        , addMVarFinalizer -- :: MVar a -> IO () -> IO ()
 #endif
     ) where
 
 #ifdef __HUGS__
 import Hugs.ConcBase ( MVar, newEmptyMVar, newMVar, takeMVar, putMVar,
-		  tryTakeMVar, tryPutMVar, isEmptyMVar,
-                  readMVar, swapMVar,
-		)
+                  tryTakeMVar, tryPutMVar, isEmptyMVar,
+                )
 #endif
 
 #ifdef __GLASGOW_HASKELL__
-import GHC.Conc	( MVar, newEmptyMVar, newMVar, takeMVar, putMVar,
-		  tryTakeMVar, tryPutMVar, isEmptyMVar, addMVarFinalizer
-		)
+import GHC.MVar ( MVar, newEmptyMVar, newMVar, takeMVar, putMVar,
+                  tryTakeMVar, tryPutMVar, isEmptyMVar, addMVarFinalizer
+                )
 #endif
 
+#ifdef __GLASGOW_HASKELL__
+import GHC.Base
+#else
 import Prelude
-import Control.Exception as Exception
-
-#ifdef __HUGS__
--- This is as close as Hugs gets to providing throw
-throw :: Exception -> IO a
-throw = throwIO
 #endif
 
-#ifdef __GLASGOW_HASKELL__
+import Control.Exception.Base
+
 {-|
   This is a combination of 'takeMVar' and 'putMVar'; ie. it takes the value
   from the 'MVar', puts it back, and also returns it.
 -}
 readMVar :: MVar a -> IO a
 readMVar m =
-  block $ do
+  mask_ $ do
     a <- takeMVar m
     putMVar m a
     return a
 
--- |Swap the contents of an 'MVar' for a new value.
+{-|
+  Take a value from an 'MVar', put a new value into the 'MVar' and
+  return the value taken. Note that there is a race condition whereby
+  another process can put something in the 'MVar' after the take
+  happens but before the put does.
+-}
 swapMVar :: MVar a -> a -> IO a
-swapMVar mvar new = modifyMVar mvar (\old -> return (new,old))
-#endif
+swapMVar mvar new =
+  mask_ $ do
+    old <- takeMVar mvar
+    putMVar mvar new
+    return old
 
 {-|
   'withMVar' is a safe wrapper for operating on the contents of an
@@ -78,12 +85,14 @@ swapMVar mvar new = modifyMVar mvar (\old -> return (new,old))
   original contents of the 'MVar' if an exception is raised (see
   "Control.Exception").
 -}
+{-# INLINE withMVar #-}
+-- inlining has been reported to have dramatic effects; see
+-- http://www.haskell.org//pipermail/haskell/2006-May/017907.html
 withMVar :: MVar a -> (a -> IO b) -> IO b
-withMVar m io = 
-  block $ do
+withMVar m io =
+  mask $ \restore -> do
     a <- takeMVar m
-    b <- Exception.catch (unblock (io a))
-      	    (\e -> do putMVar m a; throw e)
+    b <- restore (io a) `onException` putMVar m a
     putMVar m a
     return b
 
@@ -92,23 +101,23 @@ withMVar m io =
   'modifyMVar' will replace the original contents of the 'MVar' if an
   exception is raised during the operation.
 -}
+{-# INLINE modifyMVar_ #-}
 modifyMVar_ :: MVar a -> (a -> IO a) -> IO ()
-modifyMVar_ m io = 
-  block $ do
+modifyMVar_ m io =
+  mask $ \restore -> do
     a  <- takeMVar m
-    a' <- Exception.catch (unblock (io a))
-      	    (\e -> do putMVar m a; throw e)
+    a' <- restore (io a) `onException` putMVar m a
     putMVar m a'
 
 {-|
   A slight variation on 'modifyMVar_' that allows a value to be
   returned (@b@) in addition to the modified value of the 'MVar'.
 -}
+{-# INLINE modifyMVar #-}
 modifyMVar :: MVar a -> (a -> IO (a,b)) -> IO b
-modifyMVar m io = 
-  block $ do
+modifyMVar m io =
+  mask $ \restore -> do
     a      <- takeMVar m
-    (a',b) <- Exception.catch (unblock (io a))
-      	        (\e -> do putMVar m a; throw e)
+    (a',b) <- restore (io a) `onException` putMVar m a
     putMVar m a'
     return b