use strict;
use warnings;


my $start;
my $diff;
my $timeout;


sub tst {
    $timeout=shift;
    my $str = "a"x10000;
    $str   .= "b";
    $start = time;
    $str =~ /^ (( a*
		   (?{
		       $diff= time-$start;
		       die "stopped after $diff sec"
		          if $diff >=$timeout;
		   })
	       )*)*
	   $/x;
}

tst(10);