sub poll {       # execute code with timeout
   eval {
      local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required
      alarm 30;   # alarm in 30 seconds
      # your code here (could timeout)
      alarm 0;    # cancel alarm 
   };
   if ($@) {
      die $@ unless $@ eq "alarm\n";   # propagate unexpected errors
      # take action for timeout
   }
}