On 10/9/15 2:42 PM, Ian Jackson wrote:
> Hi.
>
> I've been wrestling recently[1] with a bash script which invokes a
> number of subprocesses in parallel and collects the output. The
> problem is that if you ^C the script, the subprocesses carry on
> running. This is because of the standards-mandated resetting of
> SIGINT (and QUIT) to SIG_IGN in children.
>
> Working around this in a race-free way with additional code in the
> script is very hard indeed. I can't see how to do it without having
> the parent install an INT trap handler which synchronises with all the
> children, or something equally baroque.
>
>
> The reason for SIGINT being ignored is purely historical: back in the
> dawn of time, there was no job control. If you interactively spawned
> a background process with &, you wouldn't want your attempts to ^C
> your foreground process to kill it. This SIGINT-ignoring also applied
> to noninteractive shells and of course came to be relied on. So it is
> too late to change the default :-/.
>
>
> However, it would be very easy for bash to provide an option (via `set
> -o' perhaps) to disable this behaviour. That is, to allow SIGINT to
> be delivered normally to child processes.
I'm restricting non-standard options to `shopt' to avoid any possible
conflict with future posix changes.
>
> With such an option, scripts which run on modern systems and which
> attempt to parallelise their work, would be able to arrange that ^C
> properly cleans up the whole process group, rather than leaving the
> background tasks running (doing needless work and perhaps causing
> lossage).
I'd be willing to look at a patch that implemented a new option to
enable this. You only need one option; you only have two behavior
modes and you're introducing one new behavior.
> 2. In the child, reset SIGINT and SIGQUIT to the values found at
> shell startup. That is, uninstall trap handlers. This is what
> most ordinary scripts will want, because they don't want the trap
> handler running in both parent and child. It's the same as is
> done for all other signals, and for all signals in non-background
> subshells and subprocesses.
This is the behavior that any new option would toggle. Some name like
`async_sig_ignore' or `async_sig_restore' would work.
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU c...@case.edu http://cnswww.cns.cwru.edu/~chet/
