[ruby-talk:04188] RE: How-to time short intervals?

On Mon, 24 Jul 2000, Aleksi Niemel wrote:

> > I'd like to time some funcs implemented in an extension but they are
> > really fast so:
> > 
> > start = Time.now
> > my_ext_function(args)
> > elapsed_time = Time.now - start
> > 
> > will not do (resolution is microsecs?). 
> 
> Some help might be at the
> http://dev.rubycentral.com/ref/ref_c_time.html#usec
> 
> And my ruby-cygwin run this (shamelessly ripped from excellent reference):
> 
>   ruby -e "t=Time.now; puts ('%10.6f' % t.to_f); puts t.usec;"
> 
> and outputs this:
> 964445231.186000
> 186000
> 
So you're implying that it's only millisecs on your machine then?

If so, then I propose an addition to the FAQ and/or Lib reference 
that answers why / mentions that Time.now.usec is not garantueed to
give you the correct number of usecs.

> > (Platform-specific syscalls not allowed!)
> 
> This has to be quite platform specific, AFAIK C standards do not impose
> requirements for better resolution than second. So my guess, without look to
> sources, is that microseconds are not supported on all platforms (and
> relying on them is not good idea anyway).
>
Ok, so we can't hope for anything better than secs/millisecs without going
platform-specific then. Point taken on relying on anything less than secs.
However I'm not relying on them for any critical func; I'm writing some
performance tests.

Thanks for your reply,

Robert