eval {
  local $SIG{ALRM} = sub {die "alarm here"};
  alarm(5);
  long_code();
  alarm(0);
}

##</code><code>##

eval {
  local $SIG{ALRM} = sub {die "alarm here"};
  alarm(5);
  eval {
    long_code();
  };
  alarm(0);
  # see QUESTION 2 below
}
alarm(0); # see QUESTION 1 below
die if $@ && $@ !~ /alarm here/;