Re: Design: Adding ASSOCIATED_ONLY

[Patrick McManus <[e-mail]>]

I think its worth noting that in spdy RST_STREAM was, as Martin says,
specified to terminate all associated streams in addition to the parent
stream. But afaict (willchan, correct me if I'm wrong) *nobody implementing
it did that*. which is a pretty strong signal that the mechanism should
just be removed from the spec rather than extended into priority semantics
too.



On Wed, Jun 19, 2013 at 2:07 PM, Martin Thomson <[e-mail]>wrote:

> On 19 June 2013 10:56, James M Snell <[e-mail]> wrote:
> > https://github.com/http2/http2-spec/pull/144
> >
> > This was a technical change brought up and discussed as part of the
> > "layering taskforce" breakout but was never discussed in the larger
> > interim discussions.
> >
> > Essentially, this PR would add an "ASSOCIATED_ONLY" flag to PRIORITY
> > and RST_STREAM frames that would allow terminating and reprioritizing
> > promised streams as a group.
> >
> > Sending PRIORITY(ASSOCIATED_ONLY) would ONLY set the priority for
> > associated streams, not the referenced stream.
> >
> > Sending RST_STREAM(ASSOCIATED_ONLY) would terminate ONLY the
> > associated streams, not the referenced stream.
> >
> > Without this, we would have to send PRIORITY and RST_STREAM for each
> > individual associated stream, which is obviously quite inefficient.
>
> What James omits is:
>
> RST_STREAM is currently specified to terminate all associated streams
> in addition to the parent stream.  This would remove this coupling,
> which is considered by some to be problematic.
>
> It's not possible to reprioritise associated streams as a group.  We
> did agree that associated streams would inherit a priority that is
> lower (by one) than the parent stream.  As it stands, changing all of
> them requires first discovering the stream ID that will be used, then
> sending individual PRIORITY frames for each.
>
> There's not a lot of experience with this area of the specification.
>
>