Experimental Physics and
Industrial Control System

Dear Michael Davidsaver.

 

Thank you for your quick reply.

 > By adding the function (ca_context_create(ca_enable_preemptive_callback)) you mentioned, the execution result and the following error message occur.

CA.Client.Exception...............................................

    Error: "Preemptive callback not enabled - additional threads may not join context"
    Context: "ca_context_create"
    Source File: ../IVCCaInfo.c line 69
    Current Time: Thu Aug 17 2023 16:20:30.309541425

> Related issues could be found on the site below.
     https://epics.anl.gov/tech-talk/2017/msg00042.php

--- Original Message ---
From : "Michael Davidsaver"<mdavidsaver at gmail.com>
To : "김대영"<dykim1114 at dawonsys.com>
Cc : "박상욱/수석/SnE팀"<screenbe at dawonsys.com>, "박진용/책임/CnS팀"<pjy0429 at dawonsys.com>, tech-talk at aps.anl.gov
Date : 2023/08/17 목요일 오후 3:25:38
Subject : Re: Questions about ca_search and ca_create_channel

On 8/16/23 19:18, 김대영 via Tech-talk wrote:
> Dear All
> 
> First of all, thank you for your help.

Please copy in text and not screenshots, which complicate quoting in replies.


> I have the following question.
> 
> Before calling the iocsh (argv[1]) function that runs the st.cmd file, the ca_search or ca_create_channel function works normal.
> 
> 
> 
> However, if a ca_search or ca_create_channel function is called after the iocsh (argv[1]) function is called,
> 
> a Segmentation fault or dbContext preemptive callback problem occurs.
> 
> In other words, I made a driver called pv in st.cmd and made a thread on this driver to call ca_search

The error "preemptive callback required ..." means that a call to
`ca_context_create(ca_enable_preemptive_callback)` is needed.

"dbContext" is the code behind "local CA" links.  This is a shortcut
which allows the CA server and client of an IOC to talk to each other
without actually going over the network.

This code only supports libca in the newer preemptive mode.


>> I don't know the cause.
> 
> Our st.cmd file is as follows.
> 
> 
> I would appreciate it if you could solve my curiosity.
> 
> Have a good day.
> 
> Thank you.
>