Experimental Physics and
Industrial Control System

Ralph Lange <[email protected]> · Wed, 08 Jul 2009 11:08:43 +0200

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: [email protected] on behalf of Bruno Coudoin
Sent: Tue 7/7/2009 1:00 PM
To: [email protected]
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.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System