what does @tornado.web.asynchronous decorator mean?

Question

1. If code didn't use this decorator, is it non-blocking?
2. Why this name is asynchronous, it means add decorator let code asynchronous?
3. Why @tornado.gen always use with @tornado.web.asynchronous together?

Answer 1

@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() .

1. Code not using this decorator can block, or not. Using the decorator doesn't change that in any way.

2. As @Steve Peak said, you use the decorator for asynchronous requests, eg database retrieval.

3. 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.

Answer 2

1. Answered here: asynchronous vs non-blocking

2. 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).

3. They are simular. You most likely will use @tornado.web.asynchronous .

   • Read more here: http://www.tornadoweb.org/documentation/gen.html
   • Example: chaining asynchronous operations before writing to client (python - tornado)

Answer 3

@tornado.web.asynchronous本质上只是一个标记，你放在一个像get()或post()这样的处理程序方法上，告诉框架它不应该在方法返回时自动调用finish() ，因为它包含的代码是将要设置finish()以便稍后调用。