Hello.
The following program demonstrates the bug:
import GHC.Handle
import GHC.IOBase
import GHC.Conc
import IO
main = do
h <- openFile "/tmp/out" WriteMode
hDuplicateTo h stdout
fdh <- getfd h
fdstdout <- getfd stdout
hPutStrLn stderr ("h: " ++ show fdh ++ "\nstdout: " ++ show fdstdout)
hClose h
putStrLn "bla"
getfd h@(FileHandle _ mvar) = do
h__ <- takeMVar mvar
let fd = fromIntegral (haFD h__)
putMVar mvar h__
return fd
The output:
h: 1
stdout: 1
dup: <stdout>: hPutChar: invalid argument (Bad file descriptor)
After hDuplicateTo, both handles use the same file descriptor. Closing one of
them invalidates the file descriptor underneath the other.
The documentation isn't completely clear about what hDuplicateTo is supposed
to do. But from the name and the comment in base/GHC/Handle.hs I conclude
that it should make two handles which use two different fds which refer to
the same file, like dup2 does.
Bye,
V.W.
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