our @lockstat;
sub readlock
{
  my($fh)=@_;
  my $fileno = fileno($fh);
  defined($fileno) or die "Bad filehandle";
  if ($lockstat[$fileno] && $lockstat[$fileno]{count})
  {
    $lockstat[$fileno]{count}++;
  }
  else
  {
    fcntl_lock($fh,F_RDLCK);
    $lockstat[$fileno]{count}=1;
  }
}

sub readunlock
{
  my($fh)=@_;
  my $fileno = fileno($fh);
  defined($fileno) or die "Bad filehandle";

  return unless
    $lockstat[$fileno] and $lockstat[$fileno]{count};

  if (--$lockstat[$fileno]{count} == 0)
  {
    fcntl_lock($fh,F_UNLCK);
  }
}