[project @ 2000-07-07 11:03:57 by simonmar]

[ghc-hetmet.git] / ghc / lib / std / PrelConc.lhs

diff --git a/ghc/lib/std/PrelConc.lhs b/ghc/lib/std/PrelConc.lhs
index f2b7b01..4594a6b 100644 (file)
--- a/ghc/lib/std/PrelConc.lhs
+++ b/ghc/lib/std/PrelConc.lhs
@@ -1,5 +1,7 @@
+% -----------------------------------------------------------------------------
+% $Id: PrelConc.lhs,v 1.20 2000/07/07 11:03:58 simonmar Exp $
 %
-% (c) The AQUA Project, Glasgow University, 1994-1996
+% (c) The University of Glasgow, 1994-2000
 %
 
 \section[PrelConc]{Module @PrelConc@}
@@ -15,7 +17,7 @@ module PrelConc
        -- Forking and suchlike
        , myThreadId    -- :: IO ThreadId
        , killThread    -- :: ThreadId -> IO ()
-       , raiseInThread -- :: ThreadId -> Exception -> IO ()
+       , throwTo       -- :: ThreadId -> Exception -> IO ()
        , par           -- :: a -> b -> b
        , seq           -- :: a -> b -> b
        , yield         -- :: IO ()
@@ -33,14 +35,15 @@ module PrelConc
        , putMVar       -- :: MVar a -> a -> IO ()
        , readMVar      -- :: MVar a -> IO a
        , swapMVar      -- :: MVar a -> a -> IO a
+       , tryTakeMVar   -- :: MVar a -> IO (Maybe a)
        , isEmptyMVar   -- :: MVar a -> IO Bool
 
     ) where
 
 import PrelBase
+import PrelMaybe
 import PrelErr ( parError, seqError )
-import PrelST          ( liftST )
-import PrelIOBase      ( IO(..), MVar(..), unsafePerformIO )
+import PrelIOBase      ( IO(..), MVar(..) )
 import PrelBase                ( Int(..) )
 import PrelException    ( Exception(..), AsyncException(..) )
 
@@ -65,8 +68,8 @@ killThread :: ThreadId -> IO ()
 killThread (ThreadId id) = IO $ \ s ->
    case (killThread# id (AsyncException ThreadKilled) s) of s1 -> (# s1, () #)
 
-raiseInThread :: ThreadId -> Exception -> IO ()
-raiseInThread (ThreadId id) ex = IO $ \ s ->
+throwTo :: ThreadId -> Exception -> IO ()
+throwTo (ThreadId id) ex = IO $ \ s ->
    case (killThread# id ex s) of s1 -> (# s1, () #)
 
 myThreadId :: IO ThreadId
@@ -92,14 +95,9 @@ yield = IO $ \s ->
 seq :: a -> b -> b
 seq  x y = case (seq#  x) of { 0# -> seqError; _ -> y }
 
-par :: a -> b -> b
-
 {-# INLINE par  #-}
-#if defined(__PARALLEL_HASKELL__) || defined (__GRANSIM__)
+par :: a -> b -> b
 par  x y = case (par# x) of { 0# -> parError; _ -> y }
-#else
-par  _ y = y
-#endif
 \end{code}
 
 %************************************************************************
@@ -120,48 +118,51 @@ writes.
 --Defined in IOBase to avoid cycle: data MVar a = MVar (SynchVar# RealWorld a)
 
 newEmptyMVar  :: IO (MVar a)
-
 newEmptyMVar = IO $ \ s# ->
     case newMVar# s# of
          (# s2#, svar# #) -> (# s2#, MVar svar# #)
 
 takeMVar :: MVar a -> IO a
-
 takeMVar (MVar mvar#) = IO $ \ s# -> takeMVar# mvar# s#
 
 putMVar  :: MVar a -> a -> IO ()
-
 putMVar (MVar mvar#) x = IO $ \ s# ->
     case putMVar# mvar# x s# of
         s2# -> (# s2#, () #)
 
 newMVar :: a -> IO (MVar a)
-
 newMVar value =
     newEmptyMVar       >>= \ mvar ->
     putMVar mvar value >>
     return mvar
 
 readMVar :: MVar a -> IO a
-
 readMVar mvar =
     takeMVar mvar      >>= \ value ->
     putMVar mvar value >>
     return value
 
 swapMVar :: MVar a -> a -> IO a
-
 swapMVar mvar new =
     takeMVar mvar      >>= \ old ->
     putMVar mvar new   >>
     return old
 
+-- tryTakeMVar is a non-blocking takeMVar
+tryTakeMVar :: MVar a -> IO (Maybe a)
+tryTakeMVar (MVar m) = IO $ \ s ->
+    case tryTakeMVar# m s of
+       (# s, 0#, _ #) -> (# s, Nothing #)      -- MVar is empty
+       (# s, _,  a #) -> (# s, Just a  #)      -- MVar is full
+
 {- 
  Low-level op. for checking whether an MVar is filled-in or not.
  Notice that the boolean value returned  is just a snapshot of
  the state of the MVar. By the time you get to react on its result,
  the MVar may have been filled (or emptied) - so be extremely
- careful when using this operation.
+ careful when using this operation.  
+
+ Use tryTakeMVar instead if possible.
 
  If you can re-work your abstractions to avoid having to
  depend on isEmptyMVar, then you're encouraged to do so,