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Subject: Re: [OMPI devel] OpenMPI and R
From: Jeffrey Squyres (jsquyres_at_[hidden])
Date: 2012-04-06 08:45:38

On Apr 5, 2012, at 9:07 PM, Benedict Holland wrote:

> Oh how interesting and I hope this helps someone. Following another link, I had to use:
> ./configure --prefix /usr --enable-shared --enable-static

This makes sense. You were falling victim to the fact that R dlopens libmpi as a dynamic library in a private namespace. Hence, when Open MPI then dlopens its own plugins, it can't find libmpi's symbols. This is a generic problem with any system that opens plugins that, themselves, open plugns. I wish there was a better solution to this -- the OS guys need to give us a better mechanism here. :-(

OMPI's --enable-static option does two things:

- it builds libmpi.a (vs.
- it slurps all of OMPI's plugins into libmpi.a (so it doesn't need to dlopen anything at run-time)

It's the latter point that is saving you.

Note that you could also just --disable-dlopen (vs. --disable-shared --enable-static), which just does the latter of the above things (meaning: OMPI still builds, and it should also work for you.

> when compiling this for Rmpi. Just curious, why isn't --enable-static a default option?

Among other reasons, shared libraries generally help save memory at run time. This is somewhat important as core counts go up. If you "mpirun -np 32" on a single, 32-core machine, would you rather have 32 independent copies of libmpi.a loaded into RAM, or just one copy that all processes share?

Using enables the latter option.

Make sense?

Jeff Squyres
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