[Xcb] GTK-XCB is in progress
Barton C Massey
bart at cs.pdx.edu
Wed Nov 8 09:36:10 PST 2006
Yeah, I meant to do that last night when I wrote it---thanks
for the reminder! http://xcb.freedesktop.org/wiki/XcbNotes
In message <4551D65C.10608 at brandeis.edu> you wrote:
> Hi Bart,
> Can you put that on the wiki? It would clear up some confusion...
> especially when porting xlib programs to xcb.
> Barton C Massey wrote:
> > In message <934b4cdf0611072334j6c42d5b9i15f988e0834e3281 at mail.gmail.com> you wrote:
> >> Oh, maybe I haven't made use of the round-trip delays sufficiently. I
> >> understand that it is obvious to use round-trip when many requests are sent
> >> in a loop, so we can get the cookies together, then ask for all the replies.
> >> But in many situations that a single request is sent, we cannot suppress the
> >> round-trips. Is that?
> > The general ruleset I always intended for using a cookie to
> > hide latency is this:
> > 1. Always send a request as soon as you legally can.
> > 2. Never force the returned cookie until you actually need
> > to examine the result.
> > In the presence of multiple requests, it gets a bit more
> > complicated.
> > 1. Always send each request as soon as you legally can.
> > 1a. If you can send multiple requests at the same time,
> > send the one whose value you expect to need first,
> > first.
> > 1b. If rule 1a doesn't help, a secondary tiebreaker
> > is that it's better to send requests the server
> > can process quickly first, followed by those
> > the server might run slowly.
> > 2. Never force a returned cookie until you actually need
> > to examine the result.
> > The idea of rule 1b is that if you're lucky, you can be
> > working on the quick results while the server is processing
> > the slow request. In general, don't worry about ordering of
> > simultaneous requests too much. It's hard to construct a
> > realistic example where these kinds of corner cases matter.
> > Note that rule 2 is stronger than necessary in the presence
> > of multiple requests. If you need to force a cookie returned
> > for a request r, it is harmless to also force cookies
> > returned from requests earlier than r: these values will be
> > available anyway, since the server always returns results in
> > order. However, it is also harmless to wait to force a
> > cookie until you need the value, and it makes it clearer
> > that you've done the right thing.
> > If you follow these rules, you will be getting about all the
> > latency hiding you can expect from what is a fundamentally
> > serialized protocol without using threading or some
> > equivalent mechanism.
> > Hope this helps. Comment welcome.
> > Bart
> > _______________________________________________
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> > Xcb at lists.freedesktop.org
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