php blocking functions

Hello everyone, I am searching for an alternate way to accomplish user synchronization. I would like two or more users to block on the read of some stream, so that when one person writes to it, the other person(s) will read it. The only way I currently know to do this is with the socket functions. However, this poses a small problem. If I use the socket functions, I have to keep a script running on the server at all times. I would really like to have users block at the end of a file until new information is appended. I certainly don't want to have all my clients sit in infinite while loops, and I'm sure my isp doesn't either. I may be shit out of luck anyway, if they are killing processes that run for too long. I appreciate any and all suggestions. If someone knows exactly which functions block, aside from the socket functions, could you please tell me? Thank you. Respectfully, Chad