Re: VOTE: --timeout with suspendable children or killing children?

[Jay Hacker]

So currently parallel runs all jobs in the same process group, and
CTRL-Z suspends everything in the current terminal process group,
which is a nice feature.

If you wanted to kill all descendants of a job, you'd have to put them
in a separate process group, but this breaks CTRL-Z.  So currently
parallel only kills its immediate children.  The timeout command (I'm
guessing) puts things in a different process group (so it can kill its
children), which prevents CTRL-Z from working.

Do I have that right?

Two ideas I can see exploring:

1. Walk the process tree and kill all descendents of all jobs.  I
don't know if there is a portable way to do this (surely CPAN has
something? ;)

2. Have parallel kill its own process group, effectively committing
mass family suicide.  Hey, it's about to exit anyway.  :)  This may be
unpalatable because parallel needs to do some cleanup; perhaps
parallel could install a SIGTERM handler, do its cleanup in there
(which seems reasonable anyway), and then send the final SIGKILL to
the process group.

If neither of those works, I'd prefer --timeout kills a jobs children;
usually when using CTRL-Z I just want to get back to my terminal, and
the first thing I type is 'bg' anyway, so suspending the children is
not that big a deal.  Also FWIW, RedHat 5 doesn't have a timeout
command that I can find.





On Wed, Nov 30, 2011 at 6:27 PM, Ole Tange <tange@gnu.org> wrote:
> In the following note the big difference between the option --timeout
> and the command timeout.
>
> --timeout right now kills the job running. It does not kill off any
> children started by the job:
>
> echo 'sleep 60; true' | parallel --timeout=3
> ps f -t $(tty) -o pid,pgid,args
> [ ... the $SHELL started is killed, but the sleep 60 is still running ... ]
>
> A solution to that is using the command 'timeout':
>
> echo 'sleep 60; true' | parallel timeout 3 bash -c {}
> ps f -t $(tty) -o pid,pgid,args
>
> A problem by that is that you have to install 'timeout' (on Debian it
> is part of coreutils, so it might not be a big issue).
>
> Another problem is that suspend (CTRL-Z) will not suspend the children:
>
> parallel -q timeout 10 perl -e '$a=1;while($a<{}){$a++}' :::
> 1000000000 1000000001
> <CTRL-Z>
> top
> [ ... 2 perl processes take up 100% CPU ... ]
>
> Right now suspending works:
>
> parallel -q --timeout 10 perl -e '$a=1;while($a<{}){$a++}' :::
> 1000000000 1000000001
> <CTRL-Z>
> top
> [ ... 2 perl processes take up 0% CPU ... ]
>
> I do not see a way to implement both, so you should now vote:
>
> [ ] I prefer the current behaviour (CTRL-Z suspends children when
> using --timeout)
> [ ] I prefer --timeout kills off a job's children (CTRL-Z suspends
> parallel, but not children when using --timeout)
>
>
> /Ole
>