Re: Patch: FYI: System.nanoTime

[David Daney <ddaney at avtrex dot com>]

Cédric Berger wrote:
> Hi Tom,
>
> +jlong
> +_Jv_platform_nanotime ()
> +{
> +#ifdef HAVE_CLOCK_GETTIME
> +  struct timespec now;
> +  if (clock_gettime (CLOCK_REALTIME, &now) == 0)
> +    {
> +      jlong result = (jlong) now.tv_sec;
> +      result = result * 1000 * 1000 + now.tv_nsec;
> +      return result;
> +    }
> +  // clock_gettime failed, but we can fall through.
> +#endif // HAVE_CLOCK_GETTIME
> +  return _Jv_platform_gettimeofday () * 1000LL;
> +}
>
> Why do you use CLOCK_REALTIME? it represents the time
> from the epoch, but nanoTime() javadoc atate that
> nanoTime() value should be used for measuring elapsed
> time and is unrelated to wall-clock time.
>
> The problem is when you use CLOCK_REALTIME to measure
> elapsed time and the user changes the time...
> I had to write the same code for another project, and
> I used the following snipped for Linux/BSD/Solaris:
>
>   int        id;
>   #ifdef CLOCK_MONOTONIC
>     id = CLOCK_MONOTONIC;
>   #else
>   #ifdef CLOCK_HIGHRES
>     id = CLOCK_HIGHRES;
>   #else
>   #error bad platform
>   #endif
>   #endif
>     if (clock_gettime(id, &tv) - 0)

I think this is an excellent idea.

I cannot begin to tell you how much a pain in the a** it is to manage 
multiple time outs on a single thread while at the same time trying to 
maintain a 'wall clock' the can be changed.

David Daney