CPS-chained subrequests with I/O interceptions no longer work in nginx 0.8.21 (Was Re: Custom event + timer regressions caused by the new release)

[agentzh]

On Tue, Oct 27, 2009 at 5:41 PM, agentzh <agentzh at gmail.com> wrote:
>
> Sorry, the failures should be rephrased a bit:
>
> "All the regression tests for my "echo" module's echo_sleep directive
> that is used in subrequests chained by "post_subrequest" callback
> accepted by ngx_http_subrequest."
>

Okay, more investigation shows that the real problem has nothing to do
with "sleep", custom events, nor timers. It's the chained subrequest
model with "I/O interceptions" that no longer works in nginx 0.8.21.

The problem is much easier to phrase in terms of the "echo" module's directives:

    location /main {
        echo_location /foo;
        echo_location /sub1;
    }
    location /sub1 {
        proxy_pass 'http://127.0.0.1:$server_port/foo';
    }
    location /foo {
        echo $echo_request_uri;
    }

This is the minimal test case that I can produce. Basically, the
"post_subrequest" handler for the /foo subrequest issued directly by
/main issues a subrequest to /sub1. Then /sub1 in turn calls the
standard proxy module's handler to do some I/O operation. Then the
whole connection never terminates properly and hangs forever.

If no I/O operation is involved, then the whole request completes
normally in 0.8.21, no matter it's "echo_sleep" or "proxy_pass" that
do the actual I/O interception.

The "echo_location" directive and its async friend are defined in the
following .c file (for total 130+ lines of code only):

    http://github.com/agentzh/echo-nginx-module/blob/master/src/location.c

Could anyone give me a handle? :)

Thanks!
-agentzh