RE: cac_select_io Segmentation fault

["Al Honey" <ahoney@keck.hawaii.edu>]

No negativity noticed J

 

We have deployed r3.14 caRepeaters. And we have some random issues: sometimes we have ‘get’ failure responses, indicating channels are disconnected or non-existant, in one client, whilst other clients are happy; responses from multiple IOCs for a given channel when only one of those IOCs has that channel. I have not had time to delve into those. The errors seem to be realtime IOC/board and/or possibly vxWorks related, as there is one newer processor (not PPC as are most of the others) running a newer version of vxWorks, from which I never see those types of errors.

 

I think our big issue, with respect to forging forward with multi-thread clients, (i.e. using r3.14 for all clients) is that major modifications would need to be made to the layer we have between CA and our clients (said layer hides CA, as it is not the only inter-process/processor communications mechanism in place, for instance we have numerous RPC systems; and other socket based systems). Most of our operational clients do not interface directly to CA. Hence, that ‘layer’ is critical. It was the application interface provided to all our sister institutions (which create non-EPICS/CA instruments/systems) back in the early 90’s. I have been studying that ‘layer’ in great detail, in my attempt to solve the multi-threaded issue (r3.13.10), and it may be that I am now sufficiently less ignorant that I can make those modifications. If that is the case then I will no doubt have more questions.  So, thanks for pointing me to pertinent documents that will make the transition form r3.13.10 to r.3.14 possible.

 

Does someone have a simple multi-threaded example, utilizing r3.14 (so I can compare the CA library calls with what we are currently using in r3.13.10)?

 

Cheers,

Al

 

 

 

 

 

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From: Jeff Hill [mailto:johill@lanl.gov]
Sent: Wednesday, April 07, 2010 6:45 AM
To: Al Honey
Cc: tech-talk@aps.anl.gov
Subject: RE: cac_select_io Segmentation fault

 

Aloha again Allan,

 

Sorry, after rereading my message,  the tone sounds a bit negative which wasn’t my intent. I should have said, “please read also the section in the reference manual entitled - Thread Safety and Preemptive Callback to User Code”. When designing this type of application, one must decide if CA callbacks should occur only when periodically executing in a CA client library function such as ca_poll, or if the CA callbacks should occur asynchronously, as soon as the network messages are processed by the auxiliary threads in the library. Either approach can be used in a multi-threaded program.

 

Jeff
______________________________________________________
Jeffrey O. Hill           Email        johill@lanl.gov
LANL MS H820              Voice        505 665 1831
Los Alamos NM 87545 USA   FAX          505 665 5107

 

Message content: TSPA

 

From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Jeff Hill
Sent: Wednesday, April 07, 2010 8:38 AM
To: 'Al Honey'; tech-talk@aps.anl.gov
Subject: RE: cac_select_io Segmentation fault

 

Aloha Allan,

 

Ø    Does the seg fault occur because r3.13.10 is NOT thread safe?

 

The R3.13 CA Client library is definitely __not__ thread safe, and I can easily imagine that this might be the cause of your seg fault.

 

Ø   Does anyone have an example of a multi-threaded app using r3.13.10 on UNIX?

 

The R3.14 CA client library _is_ thread safe, and it should also interoperate fine with R3.13 IOCs. We routinely operate LANSCE with that configuration in our production system. Our control room runs R3.14, but many of our IOCs still run R3.13. You should read the section in the reference manual entitled “Thread Safety and Preemptive Callback to User Code“.

Jeff
______________________________________________________
Jeffrey O. Hill           Email        johill@lanl.gov
LANL MS H820              Voice        505 665 1831
Los Alamos NM 87545 USA   FAX          505 665 5107

 

Message content: TSPA

 

From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Al Honey
Sent: Tuesday, April 06, 2010 5:57 PM
To: tech-talk@aps.anl.gov
Subject: cac_select_io Segmentation fault

 

Aloha

 

I am trying to get a multi-threaded application working on SunOs 5.10 with connection to two UNIX IOC’s.

I get a seg fault for ellDelete, two statements from the end of cac_select_io() (epics/r3.13.10/base/src/ca/bsd_depen.c).

 

The seg fault does not occur immediately but within a couple of minutes (connections are to two IOC’s running on UNIX, with events from two long records on each IOC, where one record on each system is updated at 1 hz and the other at 10 hz).

 

Does the seg fault occur because r3.13.10 is NOT thread safe?

 

Does anyone have an example of a multi-threaded app using r3.13.10 on UNIX?

 

Thanks,

Allan