#!/usr/bin/perl
use strict;
use warnings;
$|++;
my $s = 0;

use POSIX qw(SIGALRM);
POSIX::sigaction(SIGALRM, POSIX::SigAction->new( sub { warn "skipping $s (took too long)\n"; die } )) || die "Error setting SIGALRM handler: $!\n";

my $str = 'ffvadsvefwdvewrfvt4vketwrhjkbveqwkjhfkghjlfghjkufghjkfhjkfjkgfghfkhjfkhjgfhjgfhgfhkgfhkgfhkgfhkgfkhjgfkjgfkghjfkhjgfhjgfkhjgfhjkfk' x 40960;
$str .= 'hjkbklklhbjklercvqewrqereqrfqeerv;;;jnrveervnlknrvlerlvnerlnvelrvnervlkenvlervojubnertvffff;kn;kff;kn;fk;k;;kmnff;knmf;nff;mnkf;;k;;' x 40960;
my $str2 = $str x 8;
my $str3 = 'furrfu';

my $re = qr/(f((\w?)(\w*?))?)+/;

print time . "\n\n";

for ( $str, $str2, $str3 ) {
    $s++;
    my $res;
    alarm 2;
    eval {
        $res = $_ =~ s/$re/ ^_^ /g;
    };
    print "$s made $res\n" unless $@;
}

print  "\n" . time . "\n";
exit;

##</code><code>##

1401392795

1 made 1310721
skipping 2 (took too long)
3 made 2

1401392798

##</code><code>##

This is perl 5, version 16, subversion 2 (v5.16.2) built for darwin-thread-multi-2level
(with 3 registered patches, see perl -V for more detail)