Something broke when reading from FIFOs in the transition from
5.00 to 5.02. The following program behaves as it should in
5.00, but with 5.02 it fails after printing the last line
(strangely for varying numbers of "last"!) with
Fail: end of file
Action: hGetChar
Handle: {loc=foo,type=readable,binary=False,buffering=none}
File: foo
Another issue is that it won't work at all with LineBuffering:
It will just print one line and then sit around doing nothing.
The program will create a FIFO named "foo" and simply echo
everything back to you, so you'd probably want to try
> ./t &
> ls -1 >foo
Sometimes, if you just pipe the 'head' of something, it will
work without terminating, so you can try repeated invocations
of 'ls'. Looks like somethings wrong in the IO/buffering code.
ghc -package posix -package concurrent -o t t.lhs
\begin{code}
module Main where
import IO
import Posix
import Monad
import Maybe
import Concurrent
import System
main :: IO ()
main = do
let fifoname = "foo"
h <- openFIFO fifoname
hSetBuffering h NoBuffering
dummy <- openFile fifoname WriteMode
fifoReadLoop h
where
fifoReadLoop h = do
fd <- handleToFd h
threadWaitRead (fdToInt fd)
msg <- hGetLine h
print msg
fifoReadLoop h
openFIFO :: String -> IO Handle
openFIFO fifoname = do
catch (openFile fifoname ReadMode)
(\e -> if (isDoesNotExistError e)
then do
putStrLn $ "Creating FIFO " ++ fifoname
system $ "/usr/bin/mkfifo " ++ fifoname
openFile fifoname ReadMode
else error $ "Canīt create FIFO " ++ fifoname
)
\end{code}
--
Volker Stolz * [EMAIL PROTECTED] * PGP + S/MIME
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