Stephan Tobies wrote:
> [...] So what I want to do is, to start a subprocess which receives
> some input from its stdin which is piped into by the main process.
>
> The problem: There is no fdToHandle, is there???
It's in the Posix library. But when you are forking another process,
you should be carefule closing the right file descriptors. Otherwise
EOF ist not seen on the other end of a pipe, because both processes
write on the *same* pipe. To make this a little clearer, here's my
helper function for connecting a Haskell program to another program
via a pipe (we use this for interfacing Haskell to the graph layout
program daVinci):
import IO(stderr,Handle,BufferMode(..),hSetBuffering,hGetLine,hPutStrLn)
import Posix(forkProcess,executeFile,Fd,createPipe,dupTo,fdClose,
intToFd,fdToHandle,handleToFd)
import PosixUtil(ProcessID)
import Directory(setCurrentDirectory)
runPiped :: FilePath -- Command
-> [String] -- Arguments
-> Maybe [(String, String)] -- Environment
-> Maybe FilePath -- Working directory
-> IO (ProcessID,Handle,Handle) -- (pid, fromChild, toChild)
runPiped path args env dir =
do (rd1,wd1) <- createPipe
(rd2,wd2) <- createPipe
maybePid <- forkProcess
case maybePid of
-- child
Nothing -> do case dir of
Nothing -> return ()
Just x -> setCurrentDirectory x
dupTo rd1 (intToFd 0)
dupTo wd2 (intToFd 1)
fdClose rd1
fdClose wd1
fdClose rd2
fdClose wd2
executeFile path True args env
fail (userError "runPiped")
-- parent
Just pid -> do fdClose rd1
fdClose wd2
fromChild <- fdToHandle rd2
toChild <- fdToHandle wd1
hSetBuffering fromChild LineBuffering
hSetBuffering toChild LineBuffering
return (pid, fromChild, toChild)
-- Strange: hClose does *not* really close a file from fdToHandle!!
-- No idea why. So we have to use this function...
reallyClose :: Handle -> IO ()
reallyClose handle = do fd <- handleToFd handle
fdClose fd
--
Sven Panne Tel.: +49/89/2178-2235
LMU, Institut fuer Informatik FAX : +49/89/2178-2211
LFE Programmier- und Modellierungssprachen Oettingenstr. 67
mailto:[EMAIL PROTECTED] D-80538 Muenchen
http://www.pms.informatik.uni-muenchen.de/mitarbeiter/panne
