Experimental Physics and
Industrial Control System

Michael Davidsaver via Tech-talk <[email protected]> · Sat, 4 May 2019 11:34:26 -0700

On 5/4/19 8:29 AM, Matt Newville wrote:> 
...
> OK, thanks -- that might be useful. To be clear, this returns False for me in the "normal" case of actually loading `libca` for the first time from a Python session:

This depends on how LoadLibrary() is calling dlopen().  cf. RTLD_LOCAL vs. RTLD_GLOBAL.
The default is RTLD_LOCAL.  fyi. this is actually controllable with
sys.setdlopenflags(), though I've not tried changing this myself.

Libraries loaded during normal process start behave as RTLD_GLOBAL.

> $ softIocPy2.7
> epics> py "from ctypes import cdll"
> epics> py "print hasattr(cdll.LoadLibrary(None), 'ca_context_create')"
> True

> So that might be a reliable way to answer the question "am I running as an embedded Python within an IOC-like process that has loaded libca?".  That would be good to know.  Registering epicsAtExit() might be useful in all cases, but it seems like we might really need to do that when embedded in an IOC.

Since libca is registering its own exit handler pyepics would want to
do the same (after ca context creation) to avoid racing against this
cleanup when epicsExit() is called.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System