[Web-SIG] Proposal for asynchronous WSGI variant
cstawarz at csail.mit.edu
Wed May 7 00:01:19 CEST 2008
On May 6, 2008, at 6:17 AM, Manlio Perillo wrote:
> I'm glad to know that there are some other people interested in
> asynchronous application, do you have seen my extensions to WSGI in
> my module for Nginx?
Yes, I have, and I had your module in mind as a potential provider of
the AWSGI interface.
> Note that in Nginx the request body is pre-read before the
> application is called (in fact wsgi.input is either a cStringIO or
> File object).
Although I didn't state it explicitly in my spec, my intention is for
the server to be able to implement awsgi.input in any way it likes, as
long as it provides a recv() method. It's totally acceptable for the
request body to be pre-read.
> Unfortunately there is a *big* usability problem: the extension is
> based on a well specified feature of WSGI: the gateway can suspend
> the execution of the WSGI application when it yields.
> However if the asynchronous code is present in a "child" function,
> we have something like this:
> That is, all the functions in the "chain" have to yield, and is not
> very good.
Yes, you're right. However, if you're willing/able to use Python 2.5,
you can use the new features of generators to implement a call stack
that lets you call child functions and receive return values and
exceptions from them. I've implemented this in awsgiref.callstack.
Have a look at
for an example of how it works.
> The solution is to use coroutines, and I'm planning to integrate
> greenlets (from the pylib project) into the WSGI module for Nginx.
Interesting, but it's not clear to me how/if this would work. Can you
explain more or point me to some code?
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