On 2004-10-26, Peter Simons
John Goerzen writes:
(progname): forkProcess: uncaught exception
Quoting from the documentation:
forkProcess :: IO () -> IO ProcessID
[...] On success, forkProcess returns the child's ProcessID to the parent process; in case of an error, an exception is thrown.
What I assume is happening is this: The child terminates _right away_, with a non-success error code, no less. And my guess is that forkProcess interprets this as the /fork/ having failed and throws an exception.
If you follow this a little bit, you'll find that forkProcess is *NOT* throwing the exception that is being reported here. The message is being printed by the RTS of the child process. No exception is thrown in the parent. (Believe me, I've tried to catch it!) I thought about that a bit, and realized that is the only way it could be; there's no way an exception could propogate from a child forked process to the parent. In my particular case, in my child process, the problem was occuring when I detected an exec failure and wnated to terminate with an error code for the parent to catch. I called dupTo a few times in the child before that, so while it failed fast, it was doing things.
The following program, for example, works fine:
import System.Exit import System.Posix.Process import Control.Concurrent main = forkProcess (threadDelay (10*1000000) >> exitFailure)
I have no idea why that would be. Sigh.
Peter
-- John Goerzen Author, Foundations of Python Network Programming http://www.amazon.com/exec/obidos/tg/detail/-/1590593715