Issue with AnyEvent::AIO

[Dominik Csapak]

Hi all,

We have an issue with AnyEvent::AIO, basically we don't use it directly, but as
soon as it's installed on a machine, our AnyEvent based daemon (a http-sever basically)
uses 100% cpu time on one core (per forked subprocess).

I have created a small reproducer:
(sorry for the ugly code)

---8<---
#!/usr/bin/env perl

use strict;
use warnings;

use AnyEvent::IO;
use IO::Socket::IP;
use Socket qw(SOMAXCONN);
use POSIX ":sys_wait_h";

my $condvar = AnyEvent->condvar;

my $socket = IO::Socket::IP->new( LocalHost => "::", (
     LocalPort => 8888,
     Listen => SOMAXCONN,
     Proto => 'tcp',
     GetAddrInfoFlags => 0,
     ReuseAddr => 1,
));


my $child_list = [];

sub fork_child {
     print "forking\n";
     if (my $child = fork()) {
         push @$child_list, $child;
         return 0;
     } else {
         return 1;
     }
}

while (scalar(@$child_list) < 2) {
     if (fork_child()) {
         last;
     }
}

if (scalar(@$child_list)) {
     while (1) {
         print "waiting\n";
         my $ret = waitpid(-1, WNOHANG);
         if ($ret < 0) {
             exit;
         }
         sleep 1;
     }
}

my $sw = AnyEvent->io(fh => $socket, poll => 'r', cb => sub {
     warn "conn";
     $socket->accept();
});

$condvar->recv();
--->8---

We use Debian (currently 12/Bookworm) as our base and installing the package
'libanyevent-aio-perl' and restarting the daemons is enough to trigger it.

Without the package installed it behaves normally.

When using the part from perldoc:

---8<---
undef $AnyEvent::AIO::WATCHER;
--->8---

it also prevents this behavior (and the page says to report if it's necessary).

Any Idea what we might do wrong here?
The real code handles the accepted connections/saves/replies/etc. ofc,
but for the reproducer this was enough.

(also bear with me, I'm not super deep into AnyEvent ;) )

Thanks
Kind Regards
Dominik