API explosion (Re: [RFC/RFT] calloutng)

[Poul-Henning Kamp]

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In message <CACYV=-Eg542iHm9KfujPvCzZrA4TqepEBVA8RzT1YOHnCgfJnA at mail.gmail.com>
, Davide Italiano writes:

>Right now -- the precision is specified in 'bintime', which is a binary number.
>It's not 32.32, it's 32.64 or 64.64 depending on the size of time_t in
>the specific platform.

And that is way overkill for specifying a callout, at best your clock
has short term stabilities approaching 1e-8, but likely as bad as 1e-6.

(The reason why bintime is important for timekeeping is that we
accumulate timeintervals approx 1e3 times a second, so the rounding
error has to be much smaller than the short term stability in order
to not dominate)

>I do not really think it worth to create another structure for
>handling time (e.g. struct bintime32), as it will lead to code

No, that was exactly my point:  It should be an integer so that
comparisons and arithmetic is trivial.   A 32.32 format fits
nicely into a int64_t which is readily available in the language.

As I said in my previous email:


        typedef dur_t   int64_t;        /* signed for bug catching */
        #define DURSEC  ((dur_t)1 << 32)
        #define DURMIN  (DURSEC * 60)
        #define DURMSEC (DURSEC / 1000)
        #define DURUSEC (DURSEC / 10000000)
        #define DURNSEC (DURSEC / 10000000000)

(Bikeshed the names at your convenience)

Then you can say

	callout_foo(34 * DURSEC)
	callout_foo(2400 * DURMSEC)
or 
	callout_foo(500 * DURNSEC)

With this format you can specify callouts 68 years into the future
with quarter nanosecond resolution, and you can trivially and
efficiently compare dur_t's with
	if (d1 < d2)

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
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