Tornado is an open source version of the scalable, non-blocking web server and tools that power FriendFeed.
The FriendFeed application is written using a web framework that looks a bit like web.py or Google's webapp,
but with additional tools and optimizations to take advantage of the underlying non-blocking infrastructure.

The framework is distinct from most mainstream web server frameworks (and certainly most Python frameworks)
because it is non-blocking and reasonably fast. Because it is non-blocking and uses epoll, it can handle
thousands of simultaneous standing connections, which means it is ideal for real-time web services. We built
the web server specifically to handle FriendFeed's real-time features — every active user of FriendFeed
maintains an open connection to the FriendFeed servers. (For more information on scaling servers to support
thousands of clients, see The C10K problem.)

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Facebook