Possible bug in signal handling

[Dima Kogan <dima@secretsauce.net>]

Hi. I'm seeing a suspicious behavior in zsh that isn't present in bash
or dash. I'm not 100% sure the way this is supposed to work, so maybe
zsh is still correct here, but filing this report just in case.

The behavior is concerned with the user invoking a pipeline in zsh, then
hitting Ctrl-C to kill it. One of the processes in the pipeline
overrides SIGINT to ignore the first Ctrl-C; I would expect all the
processes in the pipeline to die at the first Ctrl-C, except the
overriding process. I would expect zsh to recognize the one still-alive
process, and to not put up another prompt. When the user hits Ctrl-C a
second time, the overriding process dies in response, and zsh should
detect this, and prompt for a new command. This does happen most of the
time in zsh, but I'm hitting a case where it doesn't:

I have a /tmp/tst.sh script:

   awk '{print; fflush()}' | \
       perl -e 'BEGIN { $SIG{INT} = sub { $SIG{INT} = undef; }; } while(<>) {sleep 1;} sleep 10000;'

This script has a pass-through awk feeding a perl command that overrides
SIGINT, and ignores the first SIGINT that comes in.

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. This
effectively disowns the inner perl, so it cannot be killed
interactively.

If I replace the inner zsh with bash or dash, things work the way I
expect. Things also work the way I expect if I get rid of the awk or if
I get rid of the inner zsh, putting the whole pipeline on the
commandline.

Is this a zsh bug? If not a bug, can this be made to work the way I
expect it to?

Thanks! This is a bit convoluted, but hopefully it was clear enough.

dima