Re: [Merge] ~freddie-akeroyd/epics-base:fix_win32_monotonic_time into epics-base:7.0

[Freddie Akeroyd via Core-talk <core-talk at aps.anl.gov>]

Diff comments:

> diff --git a/modules/libcom/src/osi/os/WIN32/osdMonotonic.c b/modules/libcom/src/osi/os/WIN32/osdMonotonic.c
> index cb84643..208c1aa 100644
> --- a/modules/libcom/src/osi/os/WIN32/osdMonotonic.c
> +++ b/modules/libcom/src/osi/os/WIN32/osdMonotonic.c
> @@ -39,15 +42,10 @@ epicsUInt64 epicsMonotonicResolution(void)
>  epicsUInt64 epicsMonotonicGet(void)
>  {
>      LARGE_INTEGER val;
> -    if(osdUsePrefCounter) {
> -        if(!QueryPerformanceCounter(&val)) {
> -            errMessage(errlogMinor, "Warning: failed to fetch performance counter\n");
> -            return 0;
> -        } else
> -            return val.QuadPart;
> +    if(!QueryPerformanceCounter(&val)) {
> +        cantProceed("epicsMonotonicGet: Failed to read Windows Performance Counter\n");
> +        return 0;
>      } else {
> -        epicsUInt64 ret = GetTickCount();
> -        ret *= 1000000;
> -        return ret;
> +        return (epicsUInt64)(val.QuadPart * perfCounterScale + 0.5); /* return value in nanoseconds */

Thinking more about the precision, the issue is that we could end up subtracting two large numbers returned from epicsMonotonicGet() as we are forcing the return value into nanoseconds. Could we change the monotonic interface to be more like the current epics time one so refer to an epicsMonotonic system dependent type (which on windows would contain the val.QuadPart LARGE_INTEGER as is) and then use an epicsMonotonicDiffInSeconds() type command to compute required deltas

>      }
>  }


-- 
https://code.launchpad.net/~freddie-akeroyd/epics-base/+git/epics-base/+merge/391018
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