#5797: readRawBufferPtr cannot be interrupted by exception on Windows with
-threaded
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Reporter: joeyadams | Owner:
Type: bug | Status: new
Priority: normal | Milestone:
Component: libraries/base | Version: 7.2.2
Keywords: | Os: Windows
Architecture: x86 | Failure: Incorrect result at runtime
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by simonmar):
Ah, so I forgot that we did try to make `threadWaitRead` do something on
Windows. Here's its implementation:
{{{
threadWaitRead :: Fd -> IO ()
threadWaitRead fd
#ifdef mingw32_HOST_OS
-- we have no IO manager implementing threadWaitRead on Windows.
-- fdReady does the right thing, but we have to call it in a
-- separate thread, otherwise threadWaitRead won't be interruptible,
-- and this only works with -threaded.
| threaded = withThread (waitFd fd 0)
| otherwise = case fd of
0 -> do _ <- hWaitForInput stdin (-1)
return ()
-- hWaitForInput does work properly, but we can
only
-- do this for stdin since we know its FD.
_ -> error "threadWaitRead requires -threaded on
Windows, or use System.IO.hWaitForInput"
#else
= GHC.Conc.threadWaitRead fd
#endif
withThread :: IO a -> IO a
withThread io = do
m <- newEmptyMVar
_ <- mask_ $ forkIO $ try io >>= putMVar m
x <- takeMVar m
case x of
Right a -> return a
Left e -> throwIO (e :: IOException)
waitFd :: Fd -> CInt -> IO ()
waitFd fd write = do
throwErrnoIfMinus1_ "fdReady" $
fdReady (fromIntegral fd) write iNFINITE 0
iNFINITE :: CInt
iNFINITE = 0xFFFFFFFF -- urgh
foreign import ccall safe "fdReady"
fdReady :: CInt -> CInt -> CInt -> CInt -> IO CInt
}}}
And we can see why it doesn't work with a socket: the 4th argument to
`fdReady` should be non-zero for a socket, but we're always passing zero
here, because we have no information about whether the `Fd` passed to
`threadWaitRead` is a socket or not.
You could build your own version of `threadWaitRead` that works for
sockets quite easy by modifying the above code.
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/5797#comment:5>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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