Volker Wysk <[EMAIL PROTECTED]> writes:
> (zu, von) <- createPipe
> vonh <- fdToHandle von
> hSetBuffering vonh NoBuffering
> mpid <- forkProcess
> case mpid of
> Nothing -> do -- child
> -- connect pipe's read end to stdin
> -- and close its write end
> dupTo zu (intToFd 0)
> fdClose zu
> hClose vonh
> executeFile prog True par Nothing
> ... -- (print error message)
> Just pid -> do -- parent
> fdClose zu -- close pipe's read end
> -- ** here **
> hPutStr vonh txt -- write text to forked process
> hClose vonh -- close pipe's write end
> -- wait for child process to finish
> (Just ps) <- getProcessStatus True True pid
> if ps == Exited ExitSuccess
> then return ()
> else ...) -- (error message)
>
> The problem is that the child process doesn't receive all the data which
> the parent sends. It's as if "hPutStr vonh txt" sends the data lazily
> somehow, and "hClose vonh" closes the pipe prematurely.
>
> It varies from run to run exactly which data gets through. If I cause the
> child process to read all its input immediately, the problem doesn't
> seem to occur. Normally, it does so gradually, which takes a few seconds.
>
> I'm using GHC 5.02.2
Quite possibly could be a bug. Lazy IO is rather subtle I
think, specially when done across pipes. I faced some
similar problem with in POpen recently. You can see how I
solved it (worked round it?) by comparing the latest release
1.00 with the previous one 0.00.1:
http://www.01.246.ne.jp/~juhp/haskell/popenhs/
In comparison Posix.runProcess allows attaching file handles
to the in, out and error pipes, which can be written to and
read from eagerly I suppose.
Jens
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