Re: [Boost-users] [mpi/serialization] Potential bug or just library misunderstanding?

30 Sep 2011


      Thanks for the reply Julio. I thought that the purpose of using the
skeleton/content approach was precisely to deal with situations such as
this. The object (a map in this case) I am trying to send is fully populated
when the skeleton is sent and thus it's "shape" does not change and the
buffer should be of the appropriate size. If this is not the case then how
does one go about sending a std::map at all? Also, I'm failing to see how
this situation differs from sending a std::vector, which works fine.

Thanks again,
Tim

2011/9/30 Júlio Hoffimann 
...
Hi Tim,
This is not a bug, the MPI_ERR_TRUNCATE is related to the underlying MPI
implementation and occurs when the receive buffer is lesser than the message
size. For to use the Boost.MPI skeleton and content approach you must
guarantee a fixed "shape" object. So, for example, you should not use this
approach with boost::optional<> unless you know it's state beforehand
because it's "shape" depends on it. (as a discriminated union, it could be
seen as a one element or a empty container)
In other words, Boost.MPI can deal with all Boost.Serialization types, but
not all of them are adequate to do "skeleton and content" in common tasks.
Regards,
Júlio.
2011/9/30 Tim Jacobs 
...
I'm not sure why the following test-class produces this error: "MPI_Recv:
MPI_ERR_TRUNCATE: message truncated"
If the std::map has only a single element (ie I remove one of the
test[].push_back() lines) the error does not occur. Can someone verify that
this is indeed a bug and not just novice misuse of the library?
Thanks,
Tim
#include 
#include 
#include 
#include 
int
main( int argc, char * argv [] )
{
  boost::mpi::environment env(argc, argv);
  boost::mpi::communicator world;
if(world.rank()==0){
      std::mapstd::string > test;
      test[1].push_back("FOO");
      test[50].push_back("BAR");
      world.send(1, 1, boost::mpi::skeleton(test));
      world.send(1, 1, boost::mpi::get_content(test));
      std::cout << "sent" << std::endl;
  }
  else{
      std::mapstd::string > test;
      world.recv(0,1,boost::mpi::skeleton(test));
      world.recv(0,1,boost::mpi::get_content(test));
  }
}
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