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Subject: Re: [OMPI devel] Shared library versioning
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2009-07-25 13:59:25

On Jul 25, 2009, at 12:59 PM, Iain Bason wrote:

> > We have talked many times about doing proper versioning for
> > OMPI's .so libraries (e.g., -- *not* our component DSOs).
> Forgive me if this has been hashed out, but won't you run into trouble
> by not versioning the components?

This is a good question; it has been discussed a few times, but it's
good to get it here on the web archives. More below.

> What happens when there are
> multiple versions of libmpi installed? The user program will pick up
> the correct one because of versioning, but how will libmpi pick up the
> correct versions of the components?

Even with this shared library versioning, you will still only really
install one OMPI per directory tree anyway. The library versioning
won't allow you to install N different versions of OMPI in a single
tree because of multiple things:

- support files are not versioned (e.g., show_help text files)
- include files are not versioned (e.g., mpi.h)
- OMPI's DSOs actually are versioned, but more work would be needed in
this area to make that versioning scheme work in real world scenarios
- ...and probably some other things that I'm not thinking of...

We probably could solve all of these problems if we wanted to (and
therefore make it safe to install multiple OMPI's in a single
directory tree), but there hasn't been much demand for it. The
rationale for library versioning is:

- We're weird (and lying) for always using 0:0:0 in different releases
- The rest of the world does shared library versioning
- I've gotten pushback from Red Hat, Suse, and Debian
- It'll prevent at least some cases of MPI apps accidentally using an
incompatible libmpi

Jeff Squyres