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I understand that both tornado and gevent are asynchronous python frameworks.

While reading the bottle documentation I found that gevent actually is NOT asynchronous, and you can create thousands to pseudo-threads that work synchronously.

Seondly, in gevent, you can not terminate the request handler early and you need to return the full response, while in tornado you can. (correct me if I'm wrong here)

Can some one describe in detail how these systems work internally, and in what ways they are different. Also, how does WSGI play with the asynchronous nature of these systems? Do these frameworks conform to WSGI, if yes, how?

treecoder
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2 Answers2

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gevent and Tornado are a bit different. gevent is much more like Twisted - an asynchronous network framework, whereas Tornado is a web only framework.

The main highlight of gevent is that it utilizes coroutines and makes code look like it's running synchronously, but in fact most IO blocking functions are non-blocking and return control to the gevent main loop. This is very important for IO bound programming since it allows you to write highly efficient single thread code the same way you would write multithreaded code, which is much more resource hungry.

gevent also includes a WSGI request handler so it can be used to handle HTTP requests in a standalone manner, like Tornado.

Tornado is an asynchronous web framework which relies on the programmer to write asynchronous code in Python, which is often a pain in the Backend because there are no multiline anonymous closures or classes, like in JavaScript or Java. Therefore, writing good code using Tornado is really hard. For example, using blocking libraries becomes a pain.

Indeed both frameworks are asynchronous at their core, but the resulting code looks a bit different (easier to program with gevent).

You can actually use Torando and gevent together, but I haven't tried it out (yet).

Phyo Arkar Lwin
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Ron Reiter
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  • +1 but you forgot to say that tornado has a wsgi container and that become it a web server. – BlaShadow Sep 06 '13 at 20:10
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    I don't know if it's harder to write async code with Tornado. If anything, the `yield` keyword - which JavaScript lacks for now - makes the code very clean and easy to follow. There is no callback passing. In addition, centralized exception handling with Tornado is way cleaner than with, say, NodeJS, where you have to know what you are doing, or else you get a memory leak. – Andrei Taranchenko Dec 16 '14 at 20:43
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    "pain in the backend" - love it! – FullStack Jul 01 '16 at 19:06
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Have a read of:

http://en.wikipedia.org/wiki/Coroutines

and:

http://en.wikipedia.org/wiki/Event-driven_architecture

http://en.wikipedia.org/wiki/Event-driven_programming

The gevent package uses coroutines and Tornado is event driven.

Even driven systems don't readily map to WSGI, but a coroutine system, because it looks like threads, can be made to support WSGI if blocking points can be patched to switch coroutines when things would block.

Graham Dumpleton
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