Re: [Haskell-cafe] runInteractiveCommand: program ends before writing or reading all the output

15 May 2008

      2008/5/15 Olivier Boudry :
...
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
  where
    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
   waitForProcess pid

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
with Strings....

Hope this helps.
...
Thanks,
Olivier.
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Re: [Haskell-cafe] runInteractiveCommand: program ends before writing or reading all the output

Philip Weaver