Load library question

[eluser]Sonolin[/eluser]
If multiple have a load->library calls (or load->database calls), would the library actually be loaded multiple times or only once? The reason I ask, is that for custom libraries, I usually load the database and libraries I need inside the custom library while these are sometimes already loaded - and I do not want any unneeded process time/odd things happening from loading things multiple times.

If the libraries are actually loaded multiple times, is there an easy way to check if the library is loaded or not? I'm assuming I can do something like this:

Code:

if (!isset($this->db)) {
$this->load->database();
}

(Not sure exactly if isset works on objects)