#!/usr/bin/perl

use strict;
use warnings;

use POSIX qw(SIGALRM);
POSIX::sigaction(SIGALRM,
                 POSIX::SigAction->new(sub { die "alarm" }))
    or die "Error setting SIGALRM handler: $!\n";

#use Perl::Unsafe::Signals;

my $regexp = '(a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?a?)(\1)b';

my $str = 'aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaab';

my @results = ();
eval {
    alarm(1);

    local $SIG{ALRM} = sub { die "alarm\n" };

    @results = $str =~ /$regexp/;

    alarm(0);
};
warn $@ if $@;