File Writing / Reading Question

Hi Everyone, First Thankxs reading. I'm starting to learn PHP (it's great by the way) and have a little newbie question which i search the online docs but failed to find... I want to write a error log file for any site errors, and read it latter on a web page. The thing is does PHP use any file locking ? for example if at the same time there is a attempt to write on the log file what appends ? on Perl i had to lock the file, do i have to do this on PHP ? or is it a automatic lock ? Plus, do you have any advice on how to read the file from back to start, to generate a html file starting with the most recent messages, also generating the html has fast has possible all feedbacks are welcome. Stay well and happy Miguel Angelo