Experimental Physics and
Industrial Control System

Ralph Lange <[email protected]> · Tue, 21 Jul 2009 16:48:40 -0400

At some point during 3.14, the name resolution was moved into a separate

thread and handled asynchronously. (Before, there were situations, where

a DNS malfunction or misconfiguration could hang up an otherwise

perfectly working CA system.)

As a side effect, there's now a race condition when you ask for the CA

properties after connecting to a channel. If name resolution finishes

first, you get the name. If it's a bit too slow, you get nothing.

Installing a local caching name server increases the chance for the name

resolution to finish first. It is not needed for CA to work properly,

just for seeing the user/host info immediately.

BTW: a caching name server is not a bad idea, in general. Usually it

improves system stability in cases of DNS trouble.

Best regards,
Ralph

Dirk Zimoch wrote:

Hi Carl,

I think the problem started with 3.14.8. When you try again, you will

see that sometimes the host name is there and sometimes not. I think

the CA library is a bit impatient with the name server. Maybe Jeff can

have a look at some timeout.

Dirk

Carl Schumann wrote:

Hi,

I ran cainfo for a PV but did not get a result for host:

[schumann@smartcon1 ~]$ caget PD_MOD1:tstable
PD_MOD1:tstable                /tmp/table_data.15901.dat
[schumann@smartcon1 ~]$ cainfo PD_MOD1:tstable
PD_MOD1:tstable
    State:         connected
    Host:              Access:        read, write
    Data type:     DBR_STRING (native: DBF_STRING)
    Element count: 1
[schumann@smartcon1 ~]$

Since the caget is working there would it appears have to be a host

of some sort. Is there an explanation for the blank host field?

Attempts to find an explanation at the ANL web site were unsuccessful.

Thanks,
Carl

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System