multithreaded programming is rare in PHP, but sometimes useful.
One of the areas where it can be succesfully used to increase performance in PHP is caching.
Practically every PHP cache system Im familiar with has no process synchronisation and therefore brings possibility of slamming. This can be problematic on busy websites, where caching is most useful.
That's why I've created "No Slam Cache" library. It is cache system with process synchronisation:
In the readme im explaining the problem of Slamming, the Solution to it, and usage of the Library.