Re: Forking EPICS processes

[Michael Davidsaver via Tech-talk <tech-talk at aps.anl.gov>]

On 2/5/25 07:00, Grzegorz Kowalski wrote:
> Hello,
>
> I'm loading libCom, libdbCore and pvxs dynamically.
>  From the backtrace it seems epicsThreadInit is called by dynamic loader when loading libCom:
...
> Looking at the issue you linked it should be safe to fork since my main process is single-threaded and doesn't use any EPICS APIs.
> Is that the case, or is there more to it?
What you suspect is probably the case, at least as long as
nothing goes wrong and triggers the errlog thread to start.

Also, this specific global contructor is one which I have a PR
to remove.  I would appreciate testing/feedback.

https://urldefense.us/v3/__https://github.com/epics-base/epics-base/pull/451__;!!G_uCfscf7eWS!ZWAEaCssmkBQsQ1-YFeKNlJ5UAw3irqFqZM3af3rTB7IYsMs4AriogLuMnMcGiJ1xXblCia600KlCFerrUd-QBjNAQ$ 

I should make clear though.  There are still a few other global
constructors, so this PR by itself will likely not make this
warning go away for you.  However, it is a step in that direction.


> --
> Pozdrawiam / Kind regards,
> Grzegorz Kowalski
>
> Den 2025-02-04 kl. 20:00, skrev Michael Davidsaver:
> > On 2/4/25 05:24, Grzegorz Kowalski via Tech-talk wrote:
> > > Hello,
> > >
> > > I'm working on a multiprocess application using EPICS.
> > > My main process only reads the configuration and spins up child processes where EPICS is actually used.
> > > However, when forking I get this warning:
> > >
> > > Warning: Undefined Behavior!
> > >           Detected use of epicsThread from child process after fork()
> > >
> > > Is there a way to avoid starting any epicsThreads in the main process and only do so in a child process that needs them?
> > To answer this, we would have to know more about your application.
> > Which of the Base libraries you are loading, and how.  What calls
> > are made...
> >
> > If your code is linked as a single executable, I would suggest loading
> > that executable in GDB add setting a break point for epicsThreadInit()
> > to see how it is called.
> >
> > for reference:
> >
> > https://urldefense.us/v3/__https://github.com/epics-base/epics-base/issues/211__;!!G_uCfscf7eWS!ZWAEaCssmkBQsQ1-YFeKNlJ5UAw3irqFqZM3af3rTB7IYsMs4AriogLuMnMcGiJ1xXblCia600KlCFerrUeStKhnFg$