what is event driven web server

Question

I want to understand basics of Event Driven web server, I know one of them is Tornado, but any other information is much appreciated.

Thanks

Answer 1

There's a nice analogy of this described here:

http://daverecycles.tumblr.com/post/3104767110/explain-event-driven-web-servers-to-your-grandma

Answer 2

Event-driven manner aims at resolving the C10K Problem. It turns the traditional 'push model' into a 'pull model' to create a non-blocking evented I/O. Simply put, the event-driven architecture avoid spawning additional threads and thread context switching overheads, and usually ends up with better performance and less resource consumption.

Some overview from a rails developer, also includes analogy: http://odysseyonrails.com/articles/8

Answer 3

A web server needs to handle concurrent connections. There are many ways to do this, some of them are:

• A process per connection.
• A process per connection, and have a pool of processes ready to use.
• A thread per connection.
• A thread per connection, and have a pool of threads ready to use.
• A single process, handle every event (accepted connection, data available to read, can write to client, ...) on a callback.
• Some combination of the above.
• ...

At the end, the distinction ends up being in how you store each connection state (explicitly in a context structure, implicitly in the stack, implicitly in a continuation, ...) and how you schedule between connections (let the OS scheduler do it, let the OS polling primitives do it, ...).