X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FUnique.hs;h=c4c882743301bd1cd43acd74db055010fdafe978;hb=HEAD;hp=81fe6d87a02f58b1fe2d294b2703f2fefd0fb283;hpb=f7a485978f04e84b086f1974b88887cc72d832d0;p=ghc-base.git

diff --git a/Data/Unique.hs b/Data/Unique.hs
index 81fe6d8..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
@@ -8,44 +14,64 @@
 -- Stability   :  experimental
 -- Portability :  non-portable
 --
--- An infinite supply of unique objects, supporting ordering and equality.
+-- An abstract interface to a unique symbol generator.
 --
 -----------------------------------------------------------------------------
 
 module Data.Unique (
-   Unique,		-- instance (Eq, Ord)
-   newUnique, 		-- :: IO Unique
-   hashUnique 		-- :: Unique -> Int
+   -- * Unique objects
+   Unique,              -- instance (Eq, Ord)
+   newUnique,           -- :: IO Unique
+   hashUnique           -- :: Unique -> Int
  ) where
 
 import Prelude
 
-import Control.Concurrent
 import System.IO.Unsafe (unsafePerformIO)
 
 #ifdef __GLASGOW_HASKELL__
 import GHC.Base
-import GHC.Num 	( Integer(..) )
+import GHC.Num
+import GHC.Conc
+import Data.Typeable
 #endif
 
-newtype Unique = Unique Integer deriving (Eq,Ord)
+-- | 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
+#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
+-- not compare equal to any other value of type 'Unique' returned by
+-- 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'
+-- returned makes a good hash key.
 hashUnique :: Unique -> Int
-#ifdef __GLASGOW_HASKELL__ 
-hashUnique (Unique (S# i))   = I# i
-hashUnique (Unique (J# s d)) | s ==# 0#  = 0
-			     | otherwise = I# (indexIntArray# d 0#)
+#if defined(__GLASGOW_HASKELL__)
+hashUnique (Unique i) = I# (hashInteger i)
 #else
-hashUnique (Unique u) = u `mod` (fromIntegral (maxBound :: Int) + 1)
+hashUnique (Unique u) = fromInteger (u `mod` (toInteger (maxBound :: Int) + 1))
 #endif