Eirik Hoem on his blog provides an overview of PHP’s register_shutdown_function, and suggests using it for the cases when for whatever reason your Web page ran out of memory, fatal’ed, and you don’t want to display a blank page to the users.
register_shutdown_function is also useful for command-line scripts with PHP. Pretty frequently your script has to do some task like parse a large XML file, and the test examples when it was originally written did not account for the XML file possible being huge. Therefore your script dies with like 23% completion, and you’re left with 23% of the XML file parsed. Not ideal, but a quick duct-tape-style fix, would be to introduce a register_shutdown_function call to system(), to which you pass the script itself.
If you happen to keep track of which line you’re on while parsing, you can pass the line number as the first parameter to your own script, and make it start off after that 23% mark, or wherever it died. The script then needs to be launched with 0 passed as the first parameter. It will run out of memory, die, launch register_shutdown_function, which will launch another copy of the script (while successfully shutting down the original process) with a new line number, which will repeat the process.
Again, this is a duct tape approach to PHP memory consumption issues while working with large data sets.
It’s better to use reverse proxies in front of PHP-bloated Apache for default page that is always there even if everything is bad.
This is also good since this proxy can output static files and maybe even cache results (depending on software).
Some good choices include Squid and Nginx.