X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FUnique.hs;h=c4c882743301bd1cd43acd74db055010fdafe978;hb=HEAD;hp=6f8c24f0e3dc3da0f641904d3307f68c7903e1ad;hpb=72e4fe7801d2d8ab5b243cbb430272b45010f59d;p=ghc-base.git

diff --git a/Data/Unique.hs b/Data/Unique.hs
index 6f8c24f..c4c8827 100644
--- a/Data/Unique.hs
+++ b/Data/Unique.hs
@@ -1,3 +1,9 @@
+{-# LANGUAGE CPP #-}
+
+#ifdef __GLASGOW_HASKELL__
+{-# LANGUAGE MagicHash, DeriveDataTypeable #-}
+#endif
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.Unique
@@ -21,20 +27,25 @@ module Data.Unique (
 
 import Prelude
 
-import Control.Concurrent.MVar
 import System.IO.Unsafe (unsafePerformIO)
 
 #ifdef __GLASGOW_HASKELL__
 import GHC.Base
 import GHC.Num
+import GHC.Conc
+import Data.Typeable
 #endif
 
 -- | An abstract unique object.  Objects of type 'Unique' may be
 -- compared for equality and ordering and hashed into 'Int'.
-newtype Unique = Unique Integer deriving (Eq,Ord)
+newtype Unique = Unique Integer deriving (Eq,Ord
+#ifdef __GLASGOW_HASKELL__
+   ,Typeable
+#endif
+   )
 
-uniqSource :: MVar Integer
-uniqSource = unsafePerformIO (newMVar 0)
+uniqSource :: TVar Integer
+uniqSource = unsafePerformIO (newTVarIO 0)
 {-# NOINLINE uniqSource #-}
 
 -- | Creates a new object of type 'Unique'.  The value returned will
@@ -42,11 +53,18 @@ uniqSource = unsafePerformIO (newMVar 0)
 -- previous calls to 'newUnique'.  There is no limit on the number of
 -- times 'newUnique' may be called.
 newUnique :: IO Unique
-newUnique = do
-   val <- takeMVar uniqSource
-   let next = val+1
-   putMVar uniqSource next
-   return (Unique next)
+newUnique = atomically $ do
+  val <- readTVar uniqSource
+  let next = val+1
+  writeTVar uniqSource $! next
+  return (Unique next)
+
+-- SDM (18/3/2010): changed from MVar to STM.  This fixes
+--  1. there was no async exception protection
+--  2. there was a space leak (now new value is strict)
+--  3. using atomicModifyIORef would be slightly quicker, but can
+--     suffer from adverse scheduling issues (see #3838)
+--  4. also, the STM version is faster.
 
 -- | Hashes a 'Unique' into an 'Int'.  Two 'Unique's may hash to the
 -- same value, although in practice this is unlikely.  The 'Int'