[Xcb] GTK-XCB is in progress
vtorri at univ-evry.fr
Wed Nov 8 07:30:45 PST 2006
Maybe that could go into the tutorial too (in the part # 18)
On Wed, 8 Nov 2006, Jeremy Kolb 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
>> 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,
>> 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.
>> Xcb mailing list
>> Xcb at lists.freedesktop.org
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