Issues with pyepics finding libca

[tacaswell]

With a 2021-1.2 environment

[tcaswell@xf28id2-srv1 ~]$ conda activate /opt/bluesky/qserver/conda_envs/qserver-collection-2021-1.2/(/opt/bluesky/qserver/conda_envs/qserver-collection-2021-1.2) [tcaswell@xf28id2-srv1 ~]$ conda list | grep -i epic
epics-base                7.0.4                h68659b9_0    nsls2forge
pyepics                   3.4.3                    py37_0    nsls2forge

Trying to import pyepics will eventually fail with:

(/opt/bluesky/qserver/conda_envs/qserver-collection-2021-1.2) [tcaswell@xf28id2-srv1 ~]$ ipython
impPython 3.7.7 (default, Mar 26 2020, 15:48:22) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.21.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import epics.ca

In [2]: epics.ca.find_libca()
---------------------------------------------------------------------------
ChannelAccessException                    Traceback (most recent call last)
<ipython-input-2-476db334b910> in <module>
----> 1 epics.ca.find_libca()

/opt/bluesky/qserver/conda_envs/qserver-collection-2021-1.2/lib/python3.7/site-packages/epics/ca.py in find_libca()
    331 
    332 def find_libca():
--> 333     return _find_lib('ca')
    334 
    335 def find_libCom():

/opt/bluesky/qserver/conda_envs/qserver-collection-2021-1.2/lib/python3.7/site-packages/epics/ca.py in _find_lib(inp_lib_name)
    327         return dllpath
    328 
--> 329     raise ChannelAccessException('cannot find Epics CA DLL')
    330 
    331 

ChannelAccessException: cannot find Epics CA DLL

Debugging this, the search path for pyepics ad-hoc library search path does not include where the epics libraries actually are (the underlying bug here is that pyepics re-implements library discovery but unfortunately that is not actually fixable upstream). A work-around is to do

export PYEPICS_LIBCA=/opt/bluesky/qserver/conda_envs/qserver-collection-2021-1.2/epics/lib/linux-x86_64/libca.so

before starting IPython, but this is obviously not a generalizable solution.

It is possible that this will need to be addressed in the CF builds of either pyepics or epics-base.

[mrakitin]

Thanks for the report, @tacaswell! Is it reproducible on newer conda envs, such as 2021-3.0?

I also wonder if the "DLL" is Windows slang, but I assume it was meant to be "shared object" libraries.

[tacaswell]

Yeah, the error message is from pyepic's home-grown search logic and has a windows-specific accent.

[mrakitin]

@tacaswell, do you have a solution for that? I don't think I observed any issues on the floor with the new conda env...