Tornado is a Python web framework and asynchronous networking library, originally developed at FriendFeed.
Coroutines use the Python await keyword to suspend and resume execution instead of a chain of callbacks (cooperative lightweight threads as seen in frameworks like gevent are sometimes called coroutines as well, but in Tornado all coroutines use explicit context switches and are called as asynchronous functions).
The reason is that Tornado is an asynchronous server with only one thread.
@tornado.web.asynchronous
prevents the the RequestHandler
from automatically calling self.finish()
. That's it; it just means Tornado will keep the connection open until you manually call self.finish()
.
Code not using this decorator can block, or not. Using the decorator doesn't change that in any way.
As @Steve Peak said, you use the decorator for asynchronous requests, e.g. database retrieval.
Updated for Tornado 3.1+: If you use @gen.coroutine
, you don't need to use @asynchronous
as well. The older @gen.engine
interface still requires @asynchronous
, I believe.
Answered here: asynchronous vs non-blocking
Think of it like this. When you need to make a request to say a database or another url to retrieve data you do not want to block your tornado IO. So the @tornado.web.asynchronous
will allow the IO to handle other requests while it waits for the content to load (ex. database or url).
They are simular. You most likely will use @tornado.web.asynchronous
.
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