Re: [boost] Cycle between Graph and GraphParallel

Subject: Re: [boost] Cycle between Graph and GraphParallel
From: Karen Shaeffer (shaeffer_at_[hidden])
Date: 2018-10-06 03:14:56

On Fri, Oct 05, 2018 at 10:43:23PM -0400, Edward Diener via Boost wrote:
> On 10/5/2018 8:18 PM, Peter Dimov via Boost wrote:
> > Currently we have a dependency cycle between `graph` and
> > `graph_parallel`. It's not the only one, but it's notable with the fact
> > that both libraries are buildable and we therefore can't ignore it as we
> > can ignore cycles between header-only libraries that at release time
> > become a single directory.
> > 
> > In the particular, this impedes efforts to generate CMake config files.
> > Under one scheme I'm currently working on, for instance, Boost.Python
> > can't be installed because it tries to install Graph, which tries to
> > install GraphParallel, which tries to install Graph.
> > 
> > The cycle between these two is an interesting one.
> > boost/graph/breadth_first_search.hpp does:
> > 
> > #ifdef BOOST_GRAPH_USE_MPI
> > #  include <boost/graph/distributed/breadth_first_search.hpp>
> > #endif
> > 
> > at its end, and boost/graph/distributed/breadth_first_search.hpp does:
> > 
> > #ifndef BOOST_GRAPH_USE_MPI
> > #error "Parallel BGL files should not be included unless
> > <boost/graph/use_mpi.hpp> has been included"
> > #endif
> > 
> > #include <boost/graph/breadth_first_search.hpp>
> > 
> > at its very start. So these headers include each other.
> > 
> > One would naively think that only the parallel header should include the
> > normal one, but one is not well versed in graph library architectures,
> > so one might quite possibly be missing something, or a lot.
> 
> I believe you are correct here. Boost Graph should not depend on Boost Graph
> Parallel in any situation. Boost Graph Parallel is a library end-users
> should be able to use as they choose and Boost Graph itself should be usable
> without ever bringing in the Parallel code.

I concur.

I worked with these two libraries a few years ago, and my recollection
is Boost Graph was implemented first and has no dependency on Boost
Graph Parallel. At least for my use cases, this was true.

Karen.
-- 
Karen Shaeffer                 The subconscious mind is driven by your deeply
Neuralscape Services           held beliefs -- not your deeply held desires.