Add some more explanation to the skip channel example in the MVar docs

[ghc-base.git] / Control / Concurrent.hs

diff --git a/Control/Concurrent.hs b/Control/Concurrent.hs
index 79b8352..514e2e9 100644 (file)
--- a/Control/Concurrent.hs
+++ b/Control/Concurrent.hs
@@ -1,4 +1,11 @@
+{-# LANGUAGE CPP
+           , ForeignFunctionInterface
+           , MagicHash
+           , UnboxedTuples
+           , ScopedTypeVariables
+  #-}
 {-# OPTIONS_GHC -fno-warn-unused-imports #-}
+
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Control.Concurrent
@@ -451,6 +458,11 @@ unsafeResult = either Exception.throwIO return
 
 -- | Block the current thread until data is available to read on the
 -- given file descriptor (GHC only).
+--
+-- This will throw an 'IOError' if the file descriptor was closed
+-- while this thread was blocked.  To safely close a file descriptor
+-- that has been used with 'threadWaitRead', use
+-- 'GHC.Conc.closeFdWith'.
 threadWaitRead :: Fd -> IO ()
 threadWaitRead fd
 #ifdef mingw32_HOST_OS
@@ -471,6 +483,11 @@ threadWaitRead fd
 
 -- | Block the current thread until data can be written to the
 -- given file descriptor (GHC only).
+--
+-- This will throw an 'IOError' if the file descriptor was closed
+-- while this thread was blocked.  To safely close a file descriptor
+-- that has been used with 'threadWaitWrite', use
+-- 'GHC.Conc.closeFdWith'.
 threadWaitWrite :: Fd -> IO ()
 threadWaitWrite fd
 #ifdef mingw32_HOST_OS
@@ -495,7 +512,7 @@ withThread io = do
 waitFd :: Fd -> CInt -> IO ()
 waitFd fd write = do
    throwErrnoIfMinus1_ "fdReady" $
-        fdReady (fromIntegral fd) write (fromIntegral iNFINITE) 0
+        fdReady (fromIntegral fd) write iNFINITE 0
 
 iNFINITE :: CInt
 iNFINITE = 0xFFFFFFFF -- urgh