On the Ibuildings blog today there's a new post from Martin Roest looking at parallel processing in PHP scripts and how it can help you with performance and simplifying your applications.

The idea of parallel processing is when you take an atomic transaction or operation called a 'process' and run a couple of those at the same time. [...] In this example I had a PHP CLI script. The purpose of this script was to process remote documents and save it local. It fetched the document from a remote location, processed it and saved the result local - let's call this the transaction. Transactions were done sequentially. It took about 1 second for a transaction to complete and the script had to do roughly 3500 transactions.

Obviously, this script/testing method was not very effective, so he went searching for an alternative. The best option came in the shape of forking processes - spawning off a separate script (via PHP's forking functionality) to do the work on one or multiple entries. It uses the pcntl_fork and pcntl_waitpid functions to spawn and manage these children. Once they're all finished - working in parallel - they return back to the main script to wait for the slower ones to catch up.