Single threaded servers with asynchronous I/O

Node.js is just one example of a class of single threaded servers with asynchronous I/O that are seeing increased popularity. A traditional web or application server associates each incoming request with a thread until all the processing tasks associated with that request are complete and the response has been sent back. If any of those tasks involve I/O, the thread blocks while that I/O takes place. This approach can waste finite resources such as file descriptors and memory since each connection occupies a thread whether or not that thread is actually consuming CPU cycles. An alternative architecture is starting to emerge in implementations like Node.js (a JavaScript server running on Google V8), Nginx (an open source web server and proxy), and Webbit (a Java application server), that uses a single thread to serve many connections, processing all I/O asynchronously. These servers support orders of magnitude more simultaneous connections because each one consumes far fewer resources.