Re: Detecting data lost from a subscriber

[Ralph Lange <Ralph.Lange@bessy.de>]

Hello Bruno,

you should take Bob's statement as a "no".

Channel Access itself silently overwrites entries in the send queue, and 
does not provide the client with information that or how many updates 
were lost.
If you want that functionality, you have to add the needed information 
to the data. E.g. use a sub record and add C code that acts as a simple 
counter and mangles a sequence number into your data. Plus client code 
to separate things again.
Careful: Array data is not put into the server side queue (only 
references to the array), so using an array to add the sequence number 
would at the same time enable you to detect missing updates and create a 
lot of missing updates. (Probably not what you want.)
Another option is to reverse client and server sides: If your data 
source acts as a CA client, it can use CA put-complete calls that would 
implement a handshake. That technique doesn't allow multiple 
subscriptions to the same value, of course.
Good luck!
Ralph


On 07.07.2009 19:22 Dalesio, Leo wrote:
> The last value in the queue is overwritten with the latest value.
> Bob
>
> -----Original Message-----
> From: tech-talk-bounces@aps.anl.gov on behalf of Bruno Coudoin
> Sent: Tue 7/7/2009 1:00 PM
> To: tech-talk@aps.anl.gov
> Subject: Detecting data lost from a subscriber
>  
>
> Hi,
>
> As I understand it, the CAS server just discards data if the queue is
> full for a subscriber.  
>
> In this case, is there a way for the subscriber to know that a sample
> has been lost ?
>
> Thanks,
> Bruno.
>
>
>
>