How to abort subrequest properly?

[Yichun Zhang (agentzh)]

Hello!

On Wed, Jul 3, 2013 at 6:17 AM, Marat Dakota wrote:
> Are there any adequately hardcore methods to close subrequest's connection?
> I mean, what steps should be done internally?
>

I was also thinking hard about this problem when I was implementing
the "light thread" model in our ngx_lua module.

The subrequest mechanism does not know the details of the target
location's handlers. The target location's handler may introduce
multiple upstream connections. It's not safe at all to assume any
thing here.

A possible work-around here is to actively call the cleanup handlers
registered by the subrequest. But unfortunately, the cleanup handlers
are registered into the main request, it's not easy to distinguish a
specific subrequest's cleanup handlers from others. Another challenge
here is that the subrequest is sharing the same memory pool with its
ancestors, so freeing up all the memory associated with the subrequest
is not possible.

To conclude, it's not easy to abort a pending subrequest without
aborting the main request. And I also decide to throw out an error in
my ngx_lua module when the user Lua code is trying to abort a "light
thread" with a pending subrequest.

> For now, I'm just setting a flag in subrequest's context and just ignoring
> the data in subrequest's body filter depending on this flag. It is ok, but
> if there is a relatively simple way to close the connection to avoid
> meaningless data transfers and meaningless waits for subrequest to be
> finished — it would be nice.
>

See above :)

Best regards,
-agentzh