Re: Understanding PRIntervalTime

Joachim Ziegler wrote, On 2008-07-30 04:40:
> Hello,
> 
> I do not understand the meaning of the following sentences from
> 
> http://www.mozilla.org/projects/nspr/reference/html/prinrvl.html#20947
> 
> "Interval times are accurate regardless of host processing requirements
> and are very cheap to acquire.
> 
> The constants PR_INTERVAL_MIN and PR_INTERVAL_MAX define a range in
> ticks per second. These constants bound both the period and the
> resolution of a PRIntervalTime object."

These statements are descriptions of boundary conditions, requirements,
placed on the platform-dependent implementations of PRIntervalTime.

The underlying implementation may be VERY different from platform to
platform, The actual time resolution of PRIntervalTime varies from
box to box, but on all platforms:

- They are low overhead, quick, appropriate for use in loops.
  Less overhead than, say, gettimeofday

- the minimum amount of time, and the maximum amount of time, between
successive PRIntervalTime values is a value between the _MIN and _MAX
values (whose definitions are NOT platform dependent)

- They are believed to be accurate (if imprecise).  That is, they are
implemented in such a way that sample error (due to imprecision) is not
cumulative.   Of course, how such values are USED may be inaccurate,
but ...