Re: [Haskell-cafe] Re: Running a "sub-process" which dies with the main program

19 Jun 2009

      Cum, 2009-06-19 tarihinde 13:09 +0200 saatinde, Deniz Dogan yazdı:
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2009/6/19 Aycan iRiCAN :
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Cum, 2009-06-19 tarihinde 12:42 +0200 saatinde, Deniz Dogan yazdı:
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2009/6/19 Aycan iRiCAN :
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Cum, 2009-06-19 tarihinde 11:58 +0200 saatinde, Deniz Dogan yazdı:
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2009/6/18 Deniz Dogan :
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Hi
I couldn't come up with a better subject than this one, so anyways...
I have a small program which spawns a subprocess. However, when I hit
C-c, the subprocess won't die, instead it will just keep running until
it's done or until I kill it. I've looked around in System.Process for
something suitable for my needs, but I can't seem to find it. Any
ideas?
With a tip from a person outside of the mailing list I found
System.Process.system, which essentially does exactly what I was
asking for.
Hey I'm already subscribed :) You can read from "sout" and "serr" with
below example. Hope that it helps.
module Main where
import System.Process  -- using process-1.0.1.1
main = do
 (_, sout, serr, p) <- createProcess (proc "sleep" ["10"])
                       { std_out = CreatePipe
                       , std_err = CreatePipe }
 r <- waitForProcess p
 return ()
Thanks!
But this was the approach I used before I went to
System.Process.system and it did not work on my Linux machine.
Give it a try. Try to send CTRL-C and look if "sleep 10" (which is a
subprocess) process terminates.
aycan@aycan:~/haskell$ time ./deniz2 && ps -ef | grep sleep
^C
real    0m0.707s
user    0m0.001s
sys     0m0.004s
  aycan 13098  4430   0 13:50:23 pts/7       0:00 grep sleep
It terminates with ghc 6.10.3 on OpenSolaris.
This is copied verbatim from my terminal. I used the exact some code
that you gave me.
% time ./test && ps -ef | grep sleep
^C
real	0m10.005s
user	0m0.003s
sys	0m0.003s
deniz    14095 14047  0 13:05 pts/1    00:00:00 grep sleep
What's strange though is that when I hit C-c *twice*, I get this behavior:
Hmm, I think GHC RTS handles SIGINT. I recompiled with thread support and got the same behavour. 

See: http://hackage.haskell.org/trac/ghc/wiki/Commentary/Rts/Signals

        When the interrupt signal is received, the default behaviour of
        the runtime is to attempt to shut down the Haskell program
        gracefully. It does this by calling interruptStgRts() in
        rts/Schedule.c (see Commentary/Rts/Scheduler#ShuttingDown). If a
        second interrupt signal is received, then we terminate the
        process immediately; this is just in case the normal shutdown
        procedure failed or hung for some reason, the user is always
        able to stop the process with two control-C keystrokes.

You better install signal handlers using installHandler.

Best Regards,
--
aycan