Experimental Physics and
Industrial Control System

"J. Lewis Muir" <[email protected]> · Wed, 16 Dec 2015 10:10:21 -0600

On 12/15/15 6:39 PM, Andrew Johnson wrote:
> On 12/15/2015 05:19 PM, Michael Davidsaver wrote:
>> I would point out that allowing jumps backwards will allow timers to
>> expire early as the timer queue uses general time.
>
> The epicsEventWaitWithTimeout() and epicsThreadSleep() APIs are both
> safe since they're implemented using tick counts on the two RTOS's,
> but you're talking about Jeff's epicsTimer implementations, which I
> now see do absolute time comparisons to determine when a timer should
> go off.

Hi, Andrew!

So those two APIs are safe on the two RTOSes (vxWorks and RTEMS, I
assume), but not on others, right?  Obviously, there are *lots* of soft
IOCs out there, so this issue would apply to all of those.

> I'm not sure how big a problem this is in practice.

To me, a timer or similar API that expires early is a bug (unless
documented to allow for early expiration, but that might make the API
difficult to use or worthless) and can lead to all kinds of problematic
behavior.  I would love for all timers to work correctly on all
platforms.  I'm not closely following the core development, but perhaps
you could implement a monotonic time source and use it for soft IOC
timer implementations.

Regards,

Lewis

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System