Re: GNAT.Sockets: Timeval_Duration is in milliseconds?

[Simon Wright <simon.j.wright@mac.com>]

gpriv@axonx.com writes:

> On Dec 8, 5:11 pm, Simon Wright <simon.j.wri...@mac.com> wrote:
>> gp...@axonx.com writes:
>> > I find it somewhat misleading that Timeout values use different scale
>> > than Ada duration while share that type (not Ada way).  Is there a
>> > purpose in that (other than direct translation in socket library).  It
>> > does cost some headache to figure that out and it would be more
>> > appropriate in Ada style to make a new type for timeouts or scale it
>> > back to seconds.  Anyone would agree?
>>
>> GNAT GPL 2006[1] agrees with you! from GNAT.Sockets,
>>
>>    --  Timeval_Duration is a subtype of Standard.Duration because the full
>>    --  range of Standard.Duration cannot be represented in the equivalent C
>>    --  structure. Moreover, negative values are not allowed to avoid system
>>    --  incompatibilities.
>>
>>    Immediate : constant := 0.0;
>>    Forever   : constant := Duration (Integer'Last) * 1.0;
>>
>>    subtype Timeval_Duration is Duration range Immediate .. Forever;
>>
>> [1] No GNAT GPL 2007 for Mac OS X :-(
>
> But that was precisely my point to rather make a new type instead of
> subtyping, since scales are totally different.  But that is subjective
> I guess.

Oh. I don't understand why you think that milliseconds are involved at
all?

*If* a Timeval_Duration was in units of milliseconds you would be
 completely right. But it is in seconds, just as it should be.

If you look at GNAT.Sockets'Body you'll find

   function To_Timeval (Val : Timeval_Duration) return Timeval is
      S  : time_t;
      uS : suseconds_t;

   begin
      --  If zero, set result as zero (otherwise it gets rounded down to -1)

      if Val = 0.0 then
         S  := 0;
         uS := 0;

      --  Normal case where we do round down

      else
         S  := time_t (Val - 0.5);
         uS := suseconds_t (1_000_000 * (Val - Selector_Duration (S)));
      end if;

      return (S, uS);
   end To_Timeval;

which is pretty clearly based on *seconds*.

(If you wanted to ask what Selector_Duration is doing there -- it's an
unconstrained subtype of Timeval_Duration -- you'd have a point!)