I think you have already known that require/include is faster than require_once/include_one. But sometime, we also need the functionality of require_once but do not suffer from the performance tradeoff. So here is a better way to re-invent PHP implement.
function requireOnce($file)
{
static $dict=array();
if (!isset($dict[$file]))
{
require $file;
$dict[$file] = true;
}
}
