[Haskell-cafe] getChar + System.Cmd.system + threads causes hangups

20 Feb 2006

      Hello

Using system or any variant of it from System.Process
seems broken in multithreaded environments. This
example will fail with and without -threaded.

When run the program will print "hello: start" and
then freeze. After pressing enter (the first getChar)
System.Cmd.system will complete, but without that
it will freeze for all eternity.

What is the best way to fix this? I could use System.Posix,
but that would lose windows portablity which is needed.

import Control.Concurrent
import System.Cmd

main = do forkIO (threadDelay 100000 >> hello)
          getChar
          getChar

hello = do putStrLn "hello: start"
           system "echo hello world!"
           putStrLn "hello: done"

- Einar Karttunen