On Samstag, 9. Oktober 2010, Patrick Thomas wrote:
> The channel access reference manual states that:
>
> There is unfortunately no field in the protocol allowing the server
> to indicate that an intervening subscription update was discarded.
>
> Is there a way to ensure that an intervening subscription update will
> not be discarded? Would you have to ensure that each callback
> executes in a certain amount of time, ie, faster that the channel
> update interval?
Relying on timing constraints for correctness of code is strongly
discouraged. There are just too many factors which you cannot reliably
control that can influence the timing, most importantly network
latencies, but also delays in the kernel. For instance, the version of
vxWorks we are (still) using (5.4.3) has the nice property of delaying
all incoming traffic very 5 seconds for a noticeable period (I cannot
remember how long exactly) for whatever reason, probably checking if
the cable is still connected or something similar stupid.
The only reliable way to ensure that events don't get lost is to use a
handshake protocol (or something more optimized, like TCP). One cheap
trick to at least detect (reliably) if and when events get lost is to
make sure (on the IOC) that your events alternate with another event
from a counter.
Cheers
Ben
--
"Never confuse what is natural with what is habitual."
-- Mahatma Gandhi
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