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

Subject: RE: CA client within Asyn
From: "Mooney, Tim M." <mooney@aps.anl.gov>
To: Eric Norum <eric@norum.ca>, Benoit RAT <benoit@sevensols.com>
Cc: EPICS mailing list <tech-talk@aps.anl.gov>
Date: Tue, 11 Apr 2017 15:51:24 +0000
Hi Benoit,

I second Eric's suggestion to look into using the sequencer.  If you decide, nevertheless, to stay in C code...

makeBaseApp.pl will make several kinds of example applications, including two Channel Access examples.
See the Application Developer's Guide.

I don't know of other /good/ examples (that is, examples that were intended primarily to teach or demonstrate) of doing CA in a thread, but there are several examples:

motorUtil* in the motor module.
recDynLink.c in the sscan module
save_restore.c in the autosave module

All of these modules are on github: https://github.com/epics-modules/

 

Tim Mooney (mooney@aps.anl.gov) (630)252-5417
Beamline Controls Group (www.aps.anl.gov)
Advanced Photon Source, Argonne National Lab


From: tech-talk-bounces@aps.anl.gov [tech-talk-bounces@aps.anl.gov] on behalf of Eric Norum [eric@norum.ca]
Sent: Tuesday, April 11, 2017 10:00 AM
To: Benoit RAT
Cc: EPICS mailing list
Subject: Re: CA client within Asyn

Have you investigated the EPICS sequencer?  
I don’t think I’ve heard of anyone attempting to issue channel access calls from an ASYN thread.

On Apr 11, 2017, at 4:00 AM, Benoit RAT <benoit@sevensols.com> wrote:

Hi everybody,

Within my Asyn IOC I need sometime to modify some PV from other IOC. 
I did try to do this using the .db but the task was too complex and I am now trying to setup my own CA client inside Asyn.
As I am using Asyn I have also linked all the callback from CA to the one from Asyn... 
This seems to work more or less but I have some problems with the ca_put.


quick resume of what I am doing
===========================

--------------- # Part 1 (OK)

At the setup of the IOC I call:

ca_context_create (ca_enable_preemptive_callback);
...
ca_search_and_connect(pvext_write1->name,&(pvext_write1->chan_id),callback_coHaAr,NULL);
ca_search_and_connect(pvext_write2->name,&(pvext_write2->chan_id),callback_coHaAr,NULL);
...
ca_search_and_connect(pvext_writeN->name,&(pvext_writeN->chan_id),callback_coHaAr,NULL);

and at the end of the setup I call

ca_flush_io()

This work fine and after some seconds I enter callback_coHaAr() for each of the CA created.

--------------- # Part 2

Then at some point in my code, changes of value my internal PV, I modify external PV.

status=ca_put_callback (DBR_DOUBLE, pvext_write1->chan_id, &(pvext_write1->val.float64),callback_put,pvext_write1);
status=ca_put_callback (DBR_DOUBLE, pvext_write2->chan_id, &(pvext_write2->val.float64),callback_put,pvext_write2);
....
status=ca_put_callback (DBR_DOUBLE, pvext_writeN->chan_id, &(pvext_writeN->val.float64),callback_put,pvext_writeN);

And after all my writes has been put, I call

ca_flush_io()


And this is when sometime my hook callback_put() is correctly called back (Almost 90% the first time)

 callback_put() > chid:0x949a3a0 usr:0x94c86a8 (status:x1)

But then if I make succesive call, the hook callback_put() might be called back some more time.. and then never


However If I shutdown the remote IOC, all my callback appears


If only one was missing, I get on my epicConsole:

callback_put() > chid:0x95074c8 usr:0x9535860 (status:xc0) 
callback_coHaAr() > chid:0x95074c8 op:7 (down) 


If 4 were missing:

callback_put() > chid:0x98623f8 usr:0x9890790 (status:xc0)
callback_put() > chid:0x98623f8 usr:0x9890790 (status:xc0)
callback_put() > chid:0x98623f8 usr:0x9890790 (status:xc0)
callback_put() > chid:0x98623f8 usr:0x9890790 (status:xc0)
callback_coHaAr() > chid:0x98623f8 op:7 (down)
 


Conclusion
===========================

I think I am missing something while mixing the epicsThread of asyn and ca, but I really don't know what to try more and I don't find any good examples of ChannelAccess client with thread.

  • Where could I find a good documentation of ca client?
  • Do you think I am missing something?
  • Should I use ca_enable_preemptive_callback...? I am not sure that it is what I need within asyn...
  • Shouid I use something more than flush_io()...? 
  • Should I create a thread for this operation and call ca_pend_event() ... I did try to call ca_pend_event(2) for testing but it doesn't seem to correct my problems.

Best,





--
 

Benoit RAT LAMY
fix. (+34) 958 285 024


-- 
Eric Norum
eric@norum.ca





References:
CA client within Asyn Benoit RAT
Re: CA client within Asyn Eric Norum

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