poll_shenanigans.pl

use Mojo::Base 'Mojolicious';

use Mojo::Server;
use File::Basename qw(basename);

use Scalar::Util qw(openhandle);
use IO::Poll qw(POLLERR POLLHUP POLLPRI POLLNVAL);
use POSIX qw(setsid);

our $_parent;
our $_child;

my $app = __PACKAGE__->new(moniker => lc(basename($0, (".pl"))));
$app->log->path("log/development.log");
$app->log->level("debug");

# File handle for child communication
pipe($_parent, $_child) or die "Can't create pipe: $!";
$_parent->autoflush(1);
$_child->autoflush(1);

die "Can't fork: $!" unless defined(my $pid = fork);
if ($pid) {
    close($_parent);

    while (1) { 
      $app->log->debug("Parent: $$: 0.25");
      select(undef, undef, undef, 0.25);
    }

    exit;
}

POSIX::setsid or die "Can't start a new session: $!";
close($_child);

my $poll = IO::Poll->new;

$poll->mask($_parent => POLLPRI|POLLNVAL|POLLERR|POLLHUP);

while (1) { 
  $poll->poll(0.25);

  my @stuff = $poll->handles(POLLNVAL|POLLHUP|POLLERR);

  $app->log->debug("Child: $$: 0.25: " . scalar(@stuff));
  $app->log->debug("Child: $$: " . (openhandle($_parent) // "-1"));

  foreach my $handle ($poll->handles) {
    foreach my $events ($poll->events($handle)) {
      $app->log->debug("Child: $$: events: $events");

      if ($events & (POLLHUP|POLLERR) ) {
        $app->log->debug("Child: exit");
        exit(0);
      }
    }
  }
}
exit(0);