openmp flag in OSX

[alainjwst]

We had trouble with batman-package-2.4.6 with OpenMP flag on OSX 10.12 with clang
(on such OSX, gcc is a link to clang, without OpenMP operational ... we do have to deactivate openmp flag. Furthermore, on OSX & clang, the OpenMP flag is -fgomp)

I just add a line after the line 65

parallel_args = ['-fopenmp', '-std=c99'] if has_openmp else ['-std=c99']

diff -i setup.py_ref setup.py
65a66
> parallel_args = ['-std=c99']

and then succeed to go to the end

[bhilbert4]

@lkreidberg I've had a couple of people now who have not been able to install batman (as a dependency of Mirage on their machines running Mac OSX 10.14. Removing -fopenmp from setup.py seems to have solved the problem in at least one case (See the Mirage issue above). I'm not really familiar with OpenMP at all. Does this make sense as a general solution?

[alainjwst]

for me, it would be much better to activate OpenMP since most modern CPUs are multi-core :)

the problem is options is C compilers on OSX are a mess, options are changing, and you need to have a full LLVM to have OpenMP in Clang in recent OSX (eg 10.14). Documentation is unclear or missleading. One of my students, making regression on OSX and C compilers (gcc & clang) on a large code, spend weeks to realize the horrible details & differences between options and effective (or not) activations of OpenMP on OSX 10.12, 10.13 then 10.14. A mess. Often, solutions on Web site are just for a given version of a give compiler & OSX version. Take care.

My solution above should be more general. (need a recent Cmake). But not garantee on last OSX.

[lkreidberg]

Thanks for raising this issue Bryan, and for your comment Alain. Yeah, Alain is right - OpenMP is a huge hassle on OSX! If you don't need parallel processing capability it's fine to just remove the -fopenmp flag. If you do want to run the code in parallel, here are some instructions for installing LLVM: https://stackoverflow.com/questions/43555410/enable-openmp-support-in-clang-in-mac-os-x-sierra-mojave. Good luck, hope that helps!