Re: [Boost-bugs] [Boost C++ Libraries] #6704: Boost version of mpi_in_place

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #6704: Boost version of mpi_in_place
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2012-12-31 11:39:10

#6704: Boost version of mpi_in_place
-----------------------------------------------------+----------------------
  Reporter:  Alain Miniussi <alain.miniussi@…>       |       Owner:  dgregor
      Type:  Bugs                                    |      Status:  new    
 Milestone:  To Be Determined                        |   Component:  mpi    
   Version:  Boost 1.48.0                            |    Severity:  Problem
Resolution:                                          |    Keywords:         
-----------------------------------------------------+----------------------

Comment (by anonymous):

 Replying to [comment:9 anonymous]:
 > One more question:
 >
 > Right now, in the attached patch, we have
 > {{{
 > template<typename T, typename Op>
 >   void all_reduce(const communicator & comm, const T & in_value,
 >                   T & out_value, Op op);
 > template<typename T, typename Op>
 >   T all_reduce(const communicator & comm, const T & in_value, Op op);
 > template<typename T, typename Op>
 >   void all_reduce(const communicator & comm, const T * in_values, int n,
 >                   T * out_values, Op op);
 > }}}
 > plus
 > {{{
 > template<typename T, typename Op>
 >   void all_reduce(const communicator & comm, T * inout_values, int n,
 >                   Op op);
 > }}}
 > but we do not have:
 > {{{
 > template<typename T, typename Op>
 >   void all_reduce(const communicator & comm, T & in_value, Op op);
 > }}}
 > that's based on the assumption that there isn't much usage for it and
 that it would cause confusing overload issues.


 After discussing this I find that actually an in-place version that does
 not return a copy makes more sense for in-place semantics, and the call
 might be as
 {{{
 template<typename T, typename Op>
 void all_reduce(const communicator & comm, mpi::inplace_t<T> in_value, Op
 op);
 }}}
 where mpi::inplace_t<T> wrapper might be created by an mpi::inplace
 function. Thus by using mpi::inplace around the one argument we don't
 return anything. I would not use a two-parameter version where one
 parameter is replaced by an mpi::inplace placeholder like the C API does.
 We should go for a nicer C++ API and not try to just copy the C API as the
 deprecated official MPI C++ API did.

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/6704#comment:13>
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