IO concurrency

[Simon Marlow]

> Playing with GHC, I met some oddity.
> Consider the example:
>=20
> > import IO
> > import Concurrent
> > import Posix
> > import PosixIO
> >=20
> > main =3D do
> >     (fdIn, fdIn_send) <- createPipe
> >     hIn_send <- fdToHandle fdIn_send
> >     hIn <- fdToHandle fdIn
> >	    -- The "waiter" is a simple tk/tcl script which
> >	    -- prints "click" anytime I click a button.
> >     runProcess "./waiter" [] Nothing Nothing
> > 		Nothing (Just hIn_send) Nothing
> >     -- hSetBuffering hIn LineBuffering {-2-}
> >     -- hSetBuffering stdin LineBuffering
> >     forkIO(interact stdin)
> >     -- forkIO(interact hIn) {-1-}
> >     main_cycle
> >     where
> > 	interact hIn =3D do
> > 	    line <- hGetLine hIn
> >	    numIn <- handleToInt {-made from handleToFd & fdToInt-}
> >	    -- threadWaitRead numIn {-3-}
> > 	    putStrLn line
> > 	    interact hIn
> > 	main_cycle =3D do
> > 	    putStrLn "tick"
> > 	    threadDelay 1000000
> > 	    main_cycle
>=20
>=20
> The example works OK. It prints "tick" once a second and dups my input
> as I type it. But, when I uncomment the line {-1-} to handle=20
> input from
> child as well, everything is hanged on this read operation.=20
> Uncommenting
> the {-3-} line helps, but, first, I'm not sure it is a right way and,
> second, the matter is still unclear - what is the reason of such
> difference?
>=20
> Uncommenting the {-2-} lines doesn't help. I thing the reason is in
> some inner properties of the handlers, but have no idea in which one.

I tried this here on Linux/x86 with 5.02 and it seems to work fine.
Instead of the tcl/tk script you mentioned I used a FIFO in /tmp/fifo
and made the runProcess just call "cat /tmp/fifo".

Which GHC version and platform is this on?

Cheers,
	Simon