ceph/src/boost/libs/mpi/example/string_cat.cpp

   1 // Copyright (C) 2006 Douglas Gregor <doug.gregor@gmail.com>
   2
   3 // Use, modification and distribution is subject to the Boost Software
   4 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   5 // http://www.boost.org/LICENSE_1_0.txt)
   6
   7 // An example using Boost.MPI's reduce() to concatenate strings.
   8 #include <boost/mpi.hpp>
   9 #include <iostream>
  10 #include <string>
  11 #include <boost/serialization/string.hpp> // Important for sending strings!
  12 namespace mpi = boost::mpi;
  13
  14 /* Defining STRING_CONCAT_COMMUTATIVE lies to Boost.MPI by forcing it
  15  * to assume that string concatenation is commutative, which it is
  16  * not. However, doing so illustrates how the results of a reduction
  17  * can change when a non-commutative operator is assumed to be
  18  * commutative.
  19  */
  20 #ifdef STRING_CONCAT_COMMUTATIVE
  21 namespace boost { namespace mpi {
  22
  23 template<>
  24 struct is_commutative<std::plus<std::string>, std::string> : mpl::true_ { };
  25
  26 } } // end namespace boost::mpi
  27 #endif
  28
  29 int main(int argc, char* argv[])
  30 {
  31   mpi::environment env(argc, argv);
  32   mpi::communicator world;
  33
  34   std::string names[10] = { "zero ", "one ", "two ", "three ", "four ",
  35                             "five ", "six ", "seven ", "eight ", "nine " };
  36
  37   std::string result;
  38   reduce(world,
  39          world.rank() < 10? names[world.rank()] : std::string("many "),
  40          result, std::plus<std::string>(), 0);
  41
  42   if (world.rank() == 0)
  43     std::cout << "The result is " << result << std::endl;
  44
  45   return 0;
  46 }