BEGIN {
    # decide at compile time how to check for a process' memory size.
    if (($Config{'osname'} eq 'solaris') &&
	 ($Config{'osvers'} >= 2.6)) {
	$HOW_BIG_IS_IT = \&solaris_2_6_size_check;
    } elsif ($Config{'osname'} eq 'linux') {
	$HOW_BIG_IS_IT = \&linux_size_check;
    } elsif ($Config{'osname'} =~ /(bsd|aix)/i) {
	# will getrusage work on all BSDs?  I should hope so.
	if (eval("require BSD::Resource;")) {
	    $HOW_BIG_IS_IT = \&bsd_size_check;
	} else {
	    die "you must install BSD::Resource for Apache::SizeLimit to work on your platform.";
	}
    } else {
	die "Apache::SizeLimit not implemented on your platform.";
    }
}