In early 2014 there was an interesting article on how to build high performance with PHP applications with ReactPHP. The original article discusses using the Full Stack Symfony Framework. Drupal 8 is built upon the Symfony HttpKernel component and other bits and pieces from that very same team.
Drupal 8 is set to be released on November 19th 2015. It brings improvements to many aspects of the popular CMS, but the most significant ones remain hidden from user.
One of the core components that Drupal 8 adopted from the Symfony Project is the HttpKernel. This handled all incoming and outgoing HTTP traffic. In addition to the convenience and clarity, it also handles requests independently from each other.