[Haskell-cafe] runInteractiveCommand: program ends before writing
or reading all the output
philip.weaver at gmail.com
Thu May 15 13:54:17 EDT 2008
2008/5/15 Olivier Boudry <olivier.boudry at gmail.com>:
> Hi all,
> It's the first time I use the runInteractiveCommand and I was probably
> bitten by laziness.
> When I run the following program and send its output to a file using '>'
> redirection I get the full output of the called process. But if I run it in
> the console I get only half of the output. As console is slower than disk I
> assume the called process terminates before all data has been read from it
> or the main process terminates before data has been written to stdout. I
> thought using waitForProcess, closing called process output and flushing
> stdout would solve the problem but it doesn't.
>> -- Compile with -threaded option
>> module Main where
>> import Control.Concurrent (forkIO)
>> import System.Environment (getArgs)
>> import System.FilePath (dropExtension, takeFileName)
>> import System.IO (Handle, hClose, hFlush, hGetContents, stdout)
>> import System.Process (runInteractiveCommand, waitForProcess)
>> main :: IO ()
>> main = do
>> (file:_) <- getArgs
>> (_, out, _, pid) <- runInteractiveCommand $ "dumpbin /EXPORTS " ++ file
>> forkIO (createDefFile file out)
>> waitForProcess pid
>> hClose out
>> hFlush stdout
>> createDefFile :: String -> Handle -> IO ()
>> createDefFile file inp = do
>> putStrLn $ "LIBRARY " ++ (dropExtension . takeFileName) file ++ ".dll"
>> putStrLn "EXPORTS"
>> text <- hGetContents inp
>> mapM_ writeExport $ keepExports $ map words $ lines text
>> keepExports :: [[String]] -> [String]
>> keepExports = map head
>> . filter (not . null)
>> . takeWhile (["Summary"]/=)
>> . drop 1
>> . dropWhile (["ordinal","name"]/=)
>> writeExport ('_':xs) = putStrLn xs
>> writeExport xs = putStrLn xs
> Any idea regarding the cause of this problem?
I think I've encountered the same problem several times, and it was
because I was reading from the handle lazily, like this:
(_, out, _, pid) <- runInteractiveProcess ...
str <- hGetContents out
But I didn't use 'str' until after the process finishes. My solution
was to use strict IO, usually by replacing String with a strict
ByteString. I hear there is now a library that lets you do strict IO
Hope this helps.
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
More information about the Haskell-Cafe