RE: garbage in zero length arrays

["Hill, Jeff" <johill@lanl.gov>]

Hi Anton,

 

Thanks for taking some time to report this issue.

 

I will emulate the typical computer support personal and respond to a question with an escalating number of questions :-).

 

Ø  The Array has  zero length (NORD=0) after boot. Then I get garbage as first

Ø  character while the number of elements is 128 in my case and this number

Ø  was requested. When specifying 0 at request I get args.count=0 as it should

Ø  with 3.14.12.

 

o Is this issue repeatable when testing with a different client side code other than caget? If so, which ca client code is in use?

 

o Is this issue repeatable when testing with multiple record types and or multiple device support modules?

 

o You mention that the issue is related to NORD being zero just after booting the IOC. Does the problem persist or does it happen only once; if it doesn’t persist then what is the action that causes an improvement? For example, I could imagine some different scenarios where the behavior might improve the second time that a CA client attaches, in a particular client’s second subscription update, the first time that the record processes, or the second time that the record processes.

 

o In what versions of EPICS does it fail, and in  what versions does it work correctly; is it working correctly in 3.14.12?

 

Thanks for your help.

 

best regards,

 

Jeff

 

From: Mezger Anton Christian [mailto:anton.mezger@psi.ch]
Sent: Thursday, January 16, 2014 9:24 AM
To: Hill, Jeff
Cc: tech-talk@aps.anl.gov
Subject: RE: garbage in zero length arrays

 

Hi Jeff,

 

The Array has  zero length (NORD=0) after boot. Then I get garbage as first character while the number of elements is 128 in my case and this number was requested. When specifying 0 at request I get args.count=0 as it should with 3.14.12.

 

Regards

 

Anton

 

__________________________________________
Paul Scherrer Institut
Dr. Anton Christian Mezger
WBGB/103
CH-5232 Villigen PSI

Telefon: +41 56 310 34 06
E-Mail: anton.mezger@psi.ch

From: Hill, Jeff [mailto:johill@lanl.gov]
Sent: Donnerstag, 16. Januar 2014 17:20
To: Mezger Anton Christian
Subject: RE: garbage in zero length arrays

 

Anton,

 

As memory serves, a request for a zero length subscription will probably be rejected by an old version of the CA server.

 

Jeff

 

From: Mezger Anton Christian [mailto:anton.mezger@psi.ch]
Sent: Thursday, January 16, 2014 9:12 AM
To: Hill, Jeff; tech-talk@aps.anl.gov
Subject: RE: garbage in zero length arrays

 

 

Thank you Jeff,

 

this confirms that I can set 0 in the ca_add_event_array. In any case of epics combinations (ioc, client) that would work properly at monitor receive.

 

Thanks and best regards

 

Anton

__________________________________________
Paul Scherrer Institut
Dr. Anton Christian Mezger
WBGB/103
CH-5232 Villigen PSI

Telefon: +41 56 310 34 06
E-Mail: anton.mezger@psi.ch

From: Hill, Jeff [mailto:johill@lanl.gov]
Sent: Donnerstag, 16. Januar 2014 17:07
To: Mezger Anton Christian; tech-talk@aps.anl.gov
Subject: RE: garbage in zero length arrays

 

 

Ø  My question is: when specifying 0, how does that behave in older epics versions and channel

Ø  access gateways. Does it use then the maximum amount of elements ?

 

When a channel connects the maximum number of elements is supplied by the server as a channel attribute. In newer versions of EPICS the current number of elements is returned with each subscription update. In older versions the maximum number of elements was always returned; when the current number of elements was less than the maximum number then any additional elements at the end were zero padded.

 

Jeff

 

 

From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Mezger Anton Christian
Sent: Thursday, January 16, 2014 4:46 AM
To: tech-talk@aps.anl.gov
Subject: garbage in zero length arrays

 

Hi all,

 

When monitoring a non initialized char array with ca_add_event_array, one gets most of the time in the first element of the array.

 

This only when the request uses ca_element_count(chid) which is non zero. When using the dynamic behavior by specifiying 0 elements, the received args.count correspond to the actual size of the array, including zero when not initialized.

 

My question is: when specifying 0, how does that behave in older epics versions and channel access gateways. Does it use then the maximum amount of elements ?

 

Anton

 

__________________________________________
Paul Scherrer Institut
Dr. Anton Christian Mezger
WBGB/103
CH-5232 Villigen PSI

Telefon: +41 56 310 34 06
E-Mail: anton.mezger@psi.ch