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Subject: Re: [boost] Cycle between Graph and GraphParallel
From: Edward Diener (eldiener_at_[hidden])
Date: 2018-10-06 02:43:23

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:
> #  include <boost/graph/distributed/breadth_first_search.hpp>
> #endif
> at its end, and boost/graph/distributed/breadth_first_search.hpp does:
> #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.

> Comments?

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