add GHC.HetMet.{hetmet_kappa,hetmet_kappa_app}

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

diff --git a/Data/Unique.hs b/Data/Unique.hs
index a1cbf6f..c4c8827 100644 (file)
--- a/Data/Unique.hs
+++ b/Data/Unique.hs
@@ -1,53 +1,77 @@
+{-# LANGUAGE CPP #-}
+
+#ifdef __GLASGOW_HASKELL__
+{-# LANGUAGE MagicHash, DeriveDataTypeable #-}
+#endif
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Data.Unique
 -- 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: Unique.hs,v 1.2 2002/04/24 16:31:43 simonmar Exp $
---
--- 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