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<== Date ==> <== Thread ==>

Subject: Re: caget() from C++
From: "Church, Eric D" <eric.church@pnnl.gov>
To: Mark Rivers <rivers@cars.uchicago.edu>, Andrew Johnson <anj@aps.anl.gov>, "tech-talk@aps.anl.gov" <tech-talk@aps.anl.gov>
Cc: "Mendez, Jennifer M" <Jennifer.Mendez@pnnl.gov>
Date: Mon, 4 Dec 2017 18:47:39 +0000
Hi, Mark:

Yes, this is our configuration, and everything is on one computer. My only client process for now is cainfo.

Disabling iptables has no effect.

I just tried your advice to unset both those EPICS envt variables EPICS_CA_SERVER_PORT and EPICS_CA_ADDR_LIST and restart the IOCs. For me EPICS_CA_AUTO_ADDR_LIST=NO always.

After I do this, in another terminal with those envt variables also as above I can try cainfo. This fails, with cainfo complaining about not knowing what machine to look on; I seem to need to  set EPICS_CA_ADDR_LIST=localhost at least. If I do this I see my IOC is connected on port 5064 and can happily interrogate PVs. As soon as I fire up my next IOC, after a couple seconds, a cainfo shows my first IOC no longer has a port number after some delay. It can retrieve no PVs. My newest IOC is happily running on a port like 36444 (some 5-digit number, usually), and cainfo now happily retrieves its PVs. If I restart IOCs in the other order, I get the symmetric result. The second one started works on some new high-numbered port and the first one which had been on 5064 is disconnected as far as cainfo can see. It may be interesting to note that if I kill my IOCs and restart one of ‘em, after trying to set EPICS_CA_SERVER_PORT=36444 (say) cainfo fails to find the connected PVs even for just this one running IOC.

- Eric

On 12/2/17, 6:07 AM, "Mark Rivers" <rivers@cars.uchicago.edu> wrote:

    Do I understand that you have the following configuration:
    
    
    - 2 IOCs running on the same host
    
    - No PV Gateway running
    
    - You want to access the PVs on the 2 IOCS from IOC computer itself or from other computers on the same subnet
    
    If so, that is a very common configuration.  It should work fine with no special setting of EPICS_CA_ADDR_LIST or EPICS_CA_AUTO_ADDR_LIST.  Unset both of those environment variables, both for client processes and for the IOC server processes.
    
    If you suspect the problem is due to iptables then have you tried temporarily disabling iptables and seeing if that fixes it?
    
    Mark
    
    
    ________________________________
    From: tech-talk-bounces@aps.anl.gov <tech-talk-bounces@aps.anl.gov> on behalf of Church, Eric D <eric.church@pnnl.gov>
    Sent: Friday, December 1, 2017 7:51 PM
    To: Andrew Johnson; tech-talk@aps.anl.gov
    Cc: Mendez, Jennifer M
    Subject: Re: caget() from C++
    
    Hi, Andrew:
    
    Eric here again. We (my colleague Jen, actually) indeed solved our last problem with ca_put and ca_get in threaded C++. We’re happily connecting and reading/writing from/to our IOC now. Many thanks for the help.
    
    Our next problem is that we now have two identical power supplies on same localhost we need to do this with. We see we’re not the only ones to have come across this issue where starting up the second IOC makes cainfo calls to the first one not work. The channels are uniquely named and the IOCs successfully connect to the HVCAEN and appear to be running. However, cainfo to PVs on the second IOC work and report a 5-digit port number that it’s using, while the first IOC, which had been working fine on 5064 is suddenly disconnected. We tried following the instructions from your link below to change the iptables routing. /var/log/messages doesn’t complain, but nothing from subsequent iptables commands confirms to us that the instruction actually took hold. And the cainfo behavior does not change after IOC restarts. We also tried, per Kay’s instructions somewhere, changing EPICS_CA_ADDR_LIST=”192.168.1.255 5064, 192.168.1.255 5064” from it’s former value of NO, which didn’t help
    
    Do you have a nudge that can get us past this problem?
    
    Thx -- Eric
    
    
    
    From: "Mendez, Jennifer M" <Jennifer.Mendez@pnnl.gov>
    Date: Friday, December 1, 2017 at 5:25 PM
    To: "Church, Eric D" <eric.church@pnnl.gov>
    Subject: iptables line
    
    https://wiki-ext.aps.anl.gov/epics/index.php/How_to_Make_Channel_Access_Reach_Multiple_Soft_IOCs_on_a_Linux_Host#On_RedHat_and_Derivatives
    
    
    arxe:/etc/NetworkManager/dispatcher.d$ sudo  /sbin/iptables -t nat -A PREROUTING -d $addr -p udp --dport 5064 -j DNAT --to-destination $bcast
    arxe:/etc/NetworkManager/dispatcher.d$ echo $addr
    192.168.1.11
    arxe:/etc/NetworkManager/dispatcher.d$ echo $bcast
    192.168.1.255
    
    
    On 11/9/17, 11:59 AM, "Andrew Johnson" <anj@aps.anl.gov> wrote:
    
        Hi Eric,
    
        On 11/08/2017 10:05 AM, Church, Eric D wrote:
        > We are trying to use caput() and caget() from a C++ program. The IOC is
        > up and I can issue caputs and cagets from the command line and put and
        > retrieve reasonable values into our EPICS records. We’re having some
        > difficulty in compiled C++, however.
        >
        > I include below the apparently necessary gymnastics to successfully
        > ca_get() anything in C++. We want to do this with a total of about 48
        > PVs once every 15 seconds. The first thing we note is we need to do a
        > context_create and create_channel each of those 48 times each 15
        > seconds. Which necessitates the channel clear and context destroy at the
        > end. We can not use our class member chid over and over with each run
        > through this function, it seems.
    
        I want to make sure I understand your requirements first: Is the problem
        you describe (that you continually have to create and destroy channels)
        because your application is structured such that you don't have a single
        long-running process, or because you're having problems coding it to
        keep all those channels connected?
    
        For efficiency reasons it is much better to connect everything once and
        keep the connection to the IOC(s) open all the time, re-useing the same
        chids every time you want to do some more I/O. You do have to make sure
        that your client code can cope with the IOC shutting down, rebooting or
        not being turned on until some time after the client has been started,
        but that is generally just a matter of getting the code right.
    
        Unfortunately our standard CA client code examples only really show the
        quick-and-dirty approach of connecting channels, doing some I/O and then
        shutting down again almost immediately. When you're writing a long-lived
        client though you should generally only use the CA APIs that use
        callbacks to notify you when the client library gets messages from the
        IOC servers it's connected to. The ca_pend_io() routine is not suitable
        for this style of programming, where your code generally consists of
        routines that react to events from outside and work out what to do next.
        It is legal to call most CA routines from within a callback (the CA
        reference manual describes the 2 or 3 routines where that is not
        allowed, ca_pend_io() being one of them).
    
        I think I'm going to stop here and wait for your reply to the above
        question before I write any more or review the code you posted.
    
        - Andrew
    
        --
        Arguing for surveillance because you have nothing to hide is no
        different than making the claim, "I don't care about freedom of
        speech because I have nothing to say." -- Edward Snowdon
    
    
    
    


Replies:
RE: caget() from C++ Mark Rivers
References:
caget() from C++ Church, Eric D
Re: caget() from C++ Andrew Johnson
Re: caget() from C++ Church, Eric D
Re: caget() from C++ Mark Rivers

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