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References: <87wpu0g19r.fsf@secretsauce.net> <151103201631.ZM19473@torch.brasslantern.com>
From: Dima Kogan <dima@secretsauce.net>
To: Bart Schaefer <schaefer@brasslantern.com>
Cc: zsh-workers <zsh-workers@zsh.org>
Subject: Re: Possible bug in signal handling
In-reply-to: <151103201631.ZM19473@torch.brasslantern.com>
Date: Tue, 03 Nov 2015 20:27:00 -0800
Message-ID: <87vb9ifkyz.fsf@secretsauce.net>
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Bart Schaefer <schaefer@brasslantern.com> writes:

> On Nov 2,  2:10am, Dima Kogan wrote:
> }
> } I have a /tmp/tst.sh script:
> } 
> }    awk '{print; fflush()}' | \
> }        perl -e 'BEGIN { $SIG{INT} = sub { $SIG{INT} = undef; }; } while(<>) {sleep 1;} sleep 10000;'
> } 
> } I invoke this script thusly:
> } 
> } $ seq 5000 | perl -nE 'say "xxx"; sleep(1)' | zsh /tmp/tst.sh
> } 
> } So it's a mostly do-nothing pipeline. When the user hits Ctrl-C the
> } first time, I expect everything but the inner zsh and the inner perl
> } processes to die, and the outer zsh to NOT display another prompt until
> } a second Ctrl-C. Instead I see everything except the inner perl die
> } (inner zsh dies too), and the prompt is returned immediately.
>
> I'm able to get bash to orphan that perl process sometimes, too, just
> not reliably.
>
> The difference seems to be that bash calls waitpid() whereas zsh uses
> sigpause() and doesn't do the wait*() until the SIGCHLD arrives.  The
> order of arrival of the CHLD and INT signals may therefore determine
> whether the shell continues waiting or not.
>
> Changing the script to this --
>
>    trap '' INT
>    { trap - INT; awk '{print; fflush()}'; } | \
>           perl -e 'BEGIN { $g = getpgrp($$); print "$g\n"; $SIG{INT} = sub {
> $SIG{INT} = undef; }; } while(<>)
>           {sleep 1;} sleep 10000;'
>
> -- gets both shells to wait for perl to exit before the script exits.

Thanks for looking at this, Bart. I don't really understand this area in
detail, but should those changes be necessary? Is it not a bug in zsh
(and bash, I guess) that the perl process is orphaned?