Examin signal delivery behavior in perl

sigtest.pl

use warnings;
use strict;

use POSIX qw(:signal_h);

my $sigset = POSIX::SigSet->new(SIGCHLD);

my $oldset = POSIX::SigSet->new;

my $counter = 0;

$SIG{CHLD} = sub {
  print "SIGCHLD received: $counter \n";
  $counter++;
};

print "$$\n";

sub ublk {
  print "unblocking... ";
  unless (defined sigprocmask(SIG_UNBLOCK, $oldset)) {
        die "Could not unblock SIGINT\n";
  }
  print "unblocked\n";
}

sub blk {
  print "blocking...";
  unless (defined sigprocmask(SIG_BLOCK, $sigset, $oldset)) {
        die "Could not block SIGINT\n";
  }
  print "blocked\n";
}

sub check_pending {
  print "looking for pending signals...";
  my $es = POSIX::SigSet->new;
  unless (defined  sigpending($es)) {
    die "Could not investigate pending signals\n";
  }
  if( $es->ismember(SIGCHLD)) {
      print " SIGCHLD pending\n";
  }
  else {
    print " no signal pending\n";
  }
}

my $var = "sven";
while (1) {
  check_pending;
  blk;
  sleep(5);
  check_pending;
  ublk;
  $var .= "sven";
}