ffi.dlopen is unable to load shared library - OSError: cannot load library

[Alex Chekunkov]

Hey,

I ran into the problem with a python package that uses cffi - the comprehensive description is in https://github.com/nanomsg/nnpy/issues/40. Short summary - when ffi.dlopen loads library ctypes.util.find_library is able to find correct library name, but after that backend.load_library fails with OSError: cannot load library libnanomsg.so.5.0.0

Does anyone have an idea what's going wrong there and how to fix that?

[Armin Rigo]

Hi Alex,

Not really. I don't understand how ctypes.util.find_library() manages
to find the library name (it shouldn't look in LD_LIBRARY_PATH); and
then I don't understand why dlopen() *fails* to do the same (it
*should* look in LD_LIBRARY_PATH). Indeed, the line
backend.load_library() in cffi/api.py just calls the C function
dlopen() without any further tweaking of the path.

I guess it's time to read very carefully "man dlopen" and see if there
are extra distribution-specific hacks in there. If all else fails,
you can try to (1) make very sure about what the C-level dlopen() is
called with, possibly with strace; (2) try to reproduce the problem by
writing a custom C program that calls dlopen() with the same
arguments.


A bientôt,

Armin.

[Alex Chekunkov]

Hi Armin,

thanks for the proposed options, I'll try them and will get back here if I find something.

Best,

Alex

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