From:	kagel AT quasar DOT bloomberg DOT com
Date:	Mon, 15 Jan 1996 08:54:14 -0500
To:	oandico AT gollum DOT eee DOT upd DOT edu DOT ph
Cc:	djgpp AT delorie DOT com
Reply-To:	kagel AT quasar DOT bloomberg DOT com

   Date: Sat, 13 Jan 1996 13:28:06 -0800 (GMT)
   From: Orlando Andico <oandico AT gollum DOT eee DOT upd DOT edu DOT ph>

   Does anyone know why gcc on multitasking systems doesn't have spawn...()? 
   (sorry if this isn't related directly to DJGPP...) I use spawn with DJGPP 
   all the time... now I want to do the same thing under Linux. But there's 
   no spawn. Apparently, the solution is to fork(), do nothing in the child 
   (return value == 0) and execve() the _thing_to_be_spawned_ in the parent 
   (overwriting momma).

   This seems to work, but the problem is, my program is inherently 
   single-threaded and needs something from the _thing_that_is_spawned_. But 
   due to the fork(), I can't know if the _thing_to_be_spawned_ has done its 
   thing yet... (unlike spawn which returns when the _thing..._ has done its 
   potty). Any ideas?

   Thanks,

I think the UNIX/LINUX function you are looking for is 'system()' which forks,
execs a shell and hands the shell its argument string as a command.  System()
blocks until the command completes unless the command backgrounds itself
(either internally or because you have included and ampersand (&) at the end of
the command).

To simulate this by hand, fork then, in the child, exec the program you need
while in the parent call wait() which will wait for all child processes to exit
before returning.  If you want to get some work done while the program churns
you can call wait afterwards or set a signal handler to trap SIGCHLD (or SIGCLD
I don't know which define LINUX supports, maybe both), then call wait() in the
signal handler to avoid zombying (or DEFUNCTing) your child and set a flag you
can test later in your main-line code.

-- 
Art S. Kagel, kagel AT quasar DOT bloomberg DOT com

A proverb is no proverb to you 'till life has illustrated it.  -- John Keats

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