php - Sleep function uses server resources?

Question

I've got two reasons to use a sleep function: first, to automatically send a confirmation email to a client 20 minutes after they contact us. I don't want to use cron jobs because I want it to be exactly 20 minutes (and I'm sick of my web server sending me emails telling me they initiated a cron job.....a new email every 20 minutes!)

Second reason: I've heard of people sending out mass emails using the sleep function. Since my server will only allow 100 emails an hour, I want to use the sleep function to have the script sleep for an hour then continue where it picked up.

My question is this: does it use server resources? Will it slow things down? Are there any other problems with using the sleep function? Thanks in advance!

Answer 1

While a process is sleeping it will not consume CPU time, but the process' working set still requires physical memory and/or pagefile to support that process. In other words, the PHP interpreter process needs to keep running. So long as your server has enough RAM this shouldn't be a problem though.