Parallel Tasks

[Jonathan Hutchins]

" If n is not given, all currently active child  processes
are  waited for, and the return status is zero."

So it's not necessary to add a "wait" for each process, one wait covers all
of them.  I'm not clear on how you would specify a process to wait for, as
you'd have to determine it's PID, but I don't care right now, and I know
I've seen code to check for a PID.

<Original dialog quoted complete for context.>

> -----Original Message-----
> From: david nicol [mailto:whatever at davidnicol.com]
> Sent: Monday, July 22, 2002 7:40 PM
> To: Jonathan Hutchins
> Cc: kclug at kclug.org
> Subject: Re: Parallel Tasks
> 
> 
> Jonathan Hutchins wrote:
> > 
> > To take it to the next level, how do I:
> > 
> > Start three tasks in parallel, then
> > 
> > Wait until all three have completed before taking the next step?
> > 
> majordomo at kclug.org
> 
> 
> from bash(1):
> 
>        wait [n]
>               Wait for the specified process and return its  ter­
>               mination  status.   n  may be a process ID or a job
>               specification; if a job spec  is  given,  all  pro­
>               cesses in that job's pipeline are waited for.  If n
>               is not given, all currently active child  processes
>               are  waited for, and the return status is zero.  If
>               n specifies a  non-existent  process  or  job,  the
>               return status is 127.  Otherwise, the return status
>               is the exit status  of  the  last  process  or  job
>               waited for.
> 
> 
> so you could do
> 
> 	checklinks site1 &
> 	checklinks site2 &
> 	checklinks site3 &
> 	checklinks site4 &
> 
> 	# one wait for each backgrounded checklinks
> 	wait
> 	wait
> 	wait
> 	wait
> 
> 
> I believe it is slightly superior to have each backgrounded process
> clean up after itself than to depend on wait, because it is 
> easy to add
> a new site and forget to add a new "wait" for instance.  So you could
> launch
> all the checkers at 3 pm and launch the check-log-analyzer at 9 pm and
> still
> have daily log analysis.
>