Existing codebases: I'm starting my first job soon and expect this'll be a challenge for me as well, since it's not covered in curriculi. My plan is to spend some time during the (short) summer break poking at http://aosabook.org/en/index.html .
Yeah, for some odd reason it doesn't load when I click it either. If I refresh the new tab, it loads though. Weird. Anyway, you should be able to find it easily by doing a web search for 'supermemo sleep'.