Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Thu, 2 Jun 2016 18:17:49 -0500

Hi Mark,

On 06/02/2016 05:25 PM, Mark Rivers wrote:
> My Windows IOCs just started printing the following messages at a high rate:
>  
> currentTime::getCurrentTime(): 0.000003 sec time discontinuity detected
> currentTime::getCurrentTime(): 0.000003 sec time discontinuity detected
> currentTime::getCurrentTime(): 0.000004 sec time discontinuity detected
> currentTime::getCurrentTime(): 0.000004 sec time discontinuity detected
> currentTime::getCurrentTime(): 0.000002 sec time discontinuity detected
> currentTime::getCurrentTime(): 0.000004 sec time discontinuity detected

> This is base 3.14.12.5.
>  
> What can cause this?  The time on the Windows machine appears to agree
> within 1 second to that on a Linux server.

This message gets printed when the WIN32 time provider sees the current
time as being *earlier* than when it last looked, in your case by around
2-4 microseconds.

On Windows the current time is retrieved by fetching the value of a
high-frequency Performance Counter whose frequency is measured against
the OS wall-clock time (which is only provided at a lower resolution and
may take some time to be read) using a PLL. It's actually the value of
that counter which appears to be stepping backwards, so it may be that
on an SMP system the values read from the Counter can differ slightly
between CPUs, although I'm only guessing there. Microsoft's
documentation implies that the difference between threads should be no
more than ±1 tick, but I don't know how big a tick is in seconds.

I can't explain why this might have only just started though, did these
systems get a Windows update recently?

- Andrew

-- 
Arguing for surveillance because you have nothing to hide is no
different than making the claim, "I don't care about freedom of
speech because I have nothing to say." -- Edward Snowdon

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System