anyone who REALY knows about file locking?

hi, i'm after some sample code of correct file locking procedures. I'm working on a high traffic site, and do not want to loose information due to overwriting or anything like that, especially if two people try and do the same thing at the same time. what happens when person A accesses the file, has it locked, and person B tries to open it? does the PHP script wait until it's unlocked, or does it return an error? is there a timeout? has any one realy pushed this stuff, or do we just bang it together & hope flock() does a good job? What am i after? - sample code for correct locking procedure which covers all my queries above, and any i've missed - any information / testing results as to what happens when people try to access a locked file - any tutorials or anything that realy pushes the file locking stuff, making sure i won't get errors or "file cannot be accessed" stuff when there is simultaneous attempts to work with a file. I know that in most cases --and in this case-- that the chances of two people writing to a file at the same instant is highly unlikely, and that the writing process could only take half a second or less (probably appending under 1K to a flat text file), but i think this is an area where perfection is probably worth a little effort :) Thanks in advance, Justin French