Re: Forking EPICS processes

[Grzegorz Kowalski via Tech-talk <tech-talk at aps.anl.gov>]

Hello,

I'm loading libCom, libdbCore and pvxs dynamically.
From the backtrace it seems epicsThreadInit is called by dynamic loader 
when loading libCom:
Breakpoint 1, epicsThreadInit () at ../osi/os/posix/osdThread.c:453
warning: Source file is more recent than executable.
453         int status = pthread_once(&once_control,once);
(gdb) bt
#0  epicsThreadInit () at ../osi/os/posix/osdThread.c:453
#1  0x00007ffff7c6066e in epicsThreadGetIdSelf () at 
../osi/os/posix/osdThread.c:867
#2  0x00007ffff7c58688 in initMainThread () at ../osi/epicsThread.cpp:381
#3  0x00007ffff7c586c2 in __static_initialization_and_destruction_0 
(__initialize_p=1, __priority=65535) at ../osi/epicsThread.cpp:387
#4  0x00007ffff7c586e6 in _GLOBAL__sub_I_epicsThread.cpp(void) () at 
../osi/epicsThread.cpp:387
#5  0x00007ffff7fc947e in call_init (l=<optimized out>, 
argc=argc@entry=3, argv=argv@entry=0x7fffffffe108, 
env=env@entry=0x7fffffffe128) at ./elf/dl-init.c:70
#6  0x00007ffff7fc9568 in call_init (env=0x7fffffffe128, 
argv=0x7fffffffe108, argc=3, l=<optimized out>) at ./elf/dl-init.c:33
#7  _dl_init (main_map=0x7ffff7ffe2e0, argc=3, argv=0x7fffffffe108, 
env=0x7fffffffe128) at ./elf/dl-init.c:117
#8  0x00007ffff7fe32ca in _dl_start_user () from /lib64/ld-linux-x86-64.so.2
#9  0x0000000000000003 in ?? ()
#10 0x00007fffffffe4d6 in ?? ()
#11 0x00007fffffffe506 in ?? ()
#12 0x00007fffffffe509 in ?? ()
#13 0x0000000000000000 in ?? ()

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?

--
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!chq3WQM4Zuci8wzS44XZTdz3EXDPmHEiOlkOfS9G0bAX1H0US7aTmMUxqGyjBneXAPW4635_1_ltyBdBwFCfoDu3ubQYrRE$