Re: Middleware and post-request processing

[ghazel@gmail.com]

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On Tue, Jun 7, 2011 at 10:20 AM, James Tucker <jftucker@gmail.com> wrote:

>
> On Jun 3, 2011, at 4:23 PM, ghazel wrote:
>
> > It seems to me that Rack is in need of a new post-response stage of
> > processing. This stage would occur after the response is fully written
> > and the client is unblocked, and before the next request is processed.
> >
> > Similar to what OobGC (
> http://bogomips.org/unicorn.git/tree/lib/unicorn/oob_gc.rb#n59
> > ) accomplishes, it is sometimes useful to perform additional
> > operations after the response is written without blocking the client.
> > For example, the Oink middleware logs statistics about the request,
> > but blocks the response since it has no ability not to: (
> >
> https://github.com/noahd1/oink/blob/4158d71bc9150f011072b2c6eefe73c720a78d46/lib/oink/middleware.rb#L16
> > ). This processing takes time, and needlessly delays the response.
> >
> > This proposal would entail something like a single function which is
> > called on each middleware after the response is written to the client
> > and the socket is closed (depending on the server implementation). For
> > servers which have no ability to not block the client or delay further
> > requests the function should still be called, and the impact would be
> > similar to the behavior today.
> >
> > Thoughts?
>
>
> The problem is, this isn't simple. Different servers have different
> scheduling mechanisms, and deferred operations specifications reach into
> scheduling in a horrible way.
>
> Should these run linearly? Should they be able to be pooled if
> env['rack.multithreaded']. In that case should they receive the same number
> of workers as the main request/response pool? Should they work out of the
> same pool?
>
> And that's just some basics with threads...
>
>
Ideally, the callback would be issued from the same process / thread /
fiber / context as the request itself. So all the questions of
parallelization are answered exactly like you would for requests. I'd be
interested to know of a server where this is not possible.


> You can quite easily handle this on your own in middleware or servers a
> number of ways today, without introducing either far reaching / extensive
> specs or incomplete restrictions that parallel some we already have (like
> stack based control).


How can this be quite easily handled today? Many plugins and frameworks do
not manage to do it when they should.

-Greg

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