[Xcb] GTK-XCB is in progress

[Jeremy Kolb]

Hi Bart,

Can you put that on the wiki?  It would clear up some confusion...
especially when porting xlib programs to xcb.

Jeremy

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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