On AlternateInterior.com, there's the start of something that could be used to speed up the execution of your app - multi-threading in PHP.
PHP does not have threading anywhere in its massive core. We can, however, fake it by relying on the underlying operating system's multitasking abilities instead of PHP. This article will show you how.
PHP has no built in support for threading. But there can still be times when you've got lengthy code to run and idle CPU cycles you'd like to capitalize on. We can treat child processes as threads.
He (Brian Bosh) uses the example of executing five other PHP scripts inside of another through the use of a multi-threading class he's developed. Included is the code for both the class and the example code to use it.