Bug#1012073: perl: restoring default signal handler may warn with 'SIGTERM handler "DEFAULT" not defined'

[Damyan Ivanov]

-=| Niko Tyni, 30.05.2022 09:27:40 +0100 |=-
> On Sun, May 29, 2022 at 05:38:40PM +0000, Damyan Ivanov wrote:
> > Package: perl
> > Version: 5.34.0-4
> > Severity: normal
> 
> > While infestigating a random FTBFS in starlet (#923829), it appeared to me that 
> > the problem is actually in perl.
> 
> > #   Failed test 'No warnings'
> > #   at t/12bad_request_line.t line 24.
> > # SIGTERM handler "DEFAULT" not defined.
> > #  at /usr/share/perl5/Parallel/Prefork.pm line 71.
> > # 	Parallel::Prefork::start(Parallel::Prefork=HASH(0x55cd856355b8)) called at .../lib/Plack/Handler/Starlet.pm line 78
> > # 	Plack::Handler::Starlet::run(Plack::Handler::Starlet=HASH(0x55cd849b0ad8), CODE(0x55cd8562ac98)) called at t/12bad_request_line.t line 28
> 
> Just a quick reply that a smaller reproducer would obviously help.

Yeah. Sorry about that. When I posted this I was already a bit tired 
chasing where the warning comes from.

Here's a cleaner reproducer:

$ cat <<'EOF' > default-signal.pl
use strict;
use warnings;
use Carp::Always;   # to get a line number for the warning

$SIG{TERM} = sub{};
while() {
    my $pid = fork();
    defined($pid) or die 0;

    if ($pid) {
        sleep(0.1);
        kill TERM => $pid;
        wait;
    }
    else {
        $SIG{TERM} = "DEFAULT";
        exit(0);
    }
}
EOF

$ perl default-signal.pl
SIGTERM handler "DEFAULT" not defined.
 at default-signal.pl line 16.
…

On my laptop the warnings start to pour in a second or two.

If I comment out that sleep(), no warnings are shown.

> FWIW this looks somewhat similar to
> 
> https://github.com/perl/perl5/issues/10913
> 
> but I assume the 'prefork' references mean threads are not involved
> here. So perhaps unrelated after all.

This is what I looked at too and came to the same conclusion (threads 
≠ forks).


-- Damyan