[project @ 2005-01-07 11:37:02 by simonmar]

[ghc-base.git] / GHC / Conc.lhs

diff --git a/GHC/Conc.lhs b/GHC/Conc.lhs
index eb4c88a..ee94777 100644 (file)
--- a/GHC/Conc.lhs
+++ b/GHC/Conc.lhs
@@ -53,6 +53,7 @@ module GHC.Conc
        , newTVar       -- :: a -> STM (TVar a)
        , readTVar      -- :: TVar a -> STM a
        , writeTVar     -- :: a -> TVar a -> STM ()
+       , unsafeIOToSTM -- :: IO a -> STM a
 
 #ifdef mingw32_TARGET_OS
        , asyncRead     -- :: Int -> Int -> Int -> Ptr a -> IO (Int, Int)
@@ -79,7 +80,6 @@ import GHC.Base               ( Int(..) )
 import GHC.Exception    ( Exception(..), AsyncException(..) )
 import GHC.Pack                ( packCString# )
 import GHC.Ptr          ( Ptr(..), plusPtr, FunPtr(..) )
-import GHC.STRef
 
 infixr 0 `par`, `pseq`
 \end{code}
@@ -213,7 +213,7 @@ instance  Monad STM  where
     {-# INLINE return #-}
     {-# INLINE (>>)   #-}
     {-# INLINE (>>=)  #-}
-    m >> k      =  m >>= \_ -> k
+    m >> k      = thenSTM m k
     return x   = returnSTM x
     m >>= k     = bindSTM m k
 
@@ -232,6 +232,10 @@ thenSTM (STM m) k = STM ( \s ->
 returnSTM :: a -> STM a
 returnSTM x = STM (\s -> (# s, x #))
 
+-- | Unsafely performs IO in the STM monad.
+unsafeIOToSTM :: IO a -> STM a
+unsafeIOToSTM (IO m) = STM m
+
 -- |Perform a series of STM actions atomically.
 atomically :: STM a -> IO a
 atomically (STM m) = IO (\s -> (atomically# m) s )
@@ -587,10 +591,10 @@ service_loop wakeup readfds writefds ptimeval old_reqs old_delays = do
   res <- do_select
   -- ToDo: check result
 
-  old <- atomicModifyIORef prodding (\old -> (False,old))
-  if old 
-       then alloca $ \p -> do c_read (fromIntegral wakeup) p 1; return ()
-       else return ()
+  b <- takeMVar prodding
+  if b then alloca $ \p -> do c_read (fromIntegral wakeup) p 1; return ()
+       else return ()
+  putMVar prodding False
 
   reqs' <- completeRequests reqs readfds writefds []
   service_loop wakeup readfds writefds ptimeval reqs' delays'
@@ -599,19 +603,18 @@ stick :: IORef Fd
 {-# NOINLINE stick #-}
 stick = unsafePerformIO (newIORef 0)
 
-prodding :: IORef Bool
+prodding :: MVar Bool
 {-# NOINLINE prodding #-}
-prodding = unsafePerformIO (newIORef False)
+prodding = unsafePerformIO (newMVar False)
 
 prodServiceThread :: IO ()
 prodServiceThread = do
-  b <- atomicModifyIORef prodding (\old -> (True,old)) -- compare & swap!
-  if (not b)
-       then do
-         fd <- readIORef stick
-         with 42 $ \pbuf -> do c_write (fromIntegral fd) pbuf 1; return ()
-       else
-         return ()
+  b <- takeMVar prodding
+  if (not b) 
+    then do fd <- readIORef stick
+           with 42 $ \pbuf -> do c_write (fromIntegral fd) pbuf 1; return ()
+    else return ()
+  putMVar prodding True
 
 -- -----------------------------------------------------------------------------
 -- IO requests