Parallel subrequests for multi-source long polling?

agentzh agentzh at
Thu Nov 19 07:26:32 MSK 2009

On Wed, Nov 18, 2009 at 4:24 PM, agentzh <agentzh at> wrote:
> 4. In your output filter, first check if there's a ctx object
> associated with the current request. If yes, then you're filtering one
> of the subrequests that your content handler starts. So now simply
> buffer the response chain link in this ctx object (in meomory or on
> disk, it's up to you).

We should also abort the current (sub)request if the ctx shows
"success", which means another brother subrequest has succeeded
already ;)

> If the "failures" counter reaches the total number of the subrequests
> (which means all tests are failed), then returns the final failure
> (and set the main request's status code if appropriate and send
> headers for the main request.)
> Your main request, i.e., the content handler should not send headers
> or any contents by itself and should return NGX_DONE.

I was a bit hand-waving here. To be more accurate:

In the "post_subrequest" handler, sends headers and contents directly
on "r->parent" rather than "r" because the latter references the
current subrequest while the former is our "main request". Also never
forget to call ngx_http_finalize_request on "r->parent", or you'll
observe that "mysterious hang" for nginx 0.8.21+ mentioned in one of
my earlier replies ;)

> I think this model should work after my various experiments in the
> "echo" module, but I could be wrong ;) Feel free to tell us your
> findings on your way :)

Now I believe it should work ;)

Thanks for making me thinking about this issue very hard again :)


More information about the nginx mailing list