HelloParMOAB.cpp

Read mesh into MOAB and resolve/exchange/report shared and ghosted entities
To run: mpiexec -np 4 HelloParMOAB [filename]

It shows how to load the mesh independently, on multiple communicators (with second argument, the number of comms)

mpiexec -np 8 HelloParMOAB [filename] [nbComms]

/** @example HelloParMOAB.cpp \n
 * \brief Read mesh into MOAB and resolve/exchange/report shared and ghosted entities \n
 * <b>To run</b>: mpiexec -np 4 HelloParMOAB [filename]\n
 *
 * It shows how to load the mesh independently, on multiple
 * communicators (with second argument, the number of comms)
 *
 * mpiexec -np 8 HelloParMOAB [filename] [nbComms]
 */
 
#include "moab/Core.hpp"
#ifdef MOAB_HAVE_MPI
#include "moab/ParallelComm.hpp"
#endif
#include "MBParallelConventions.h"
#include <iostream>
 
using namespace moab;
using namespace std;
 
string test_file_name = string( MESH_DIR ) + string( "/64bricks_512hex_256part.h5m" );
 
int main( int argc, char** argv )
{
#ifdef MOAB_HAVE_MPI
 MPI_Init( &argc, &argv );
 
 string options;
 
 // Need option handling here for input filename
 if( argc > 1 )
 {
 // User has input a mesh file
 test_file_name = argv[1];
 }
 
 int nbComms = 1;
 if( argc > 2 ) nbComms = atoi( argv[2] );
 
 options = "PARALLEL=READ_PART;PARTITION=PARALLEL_PARTITION;PARALLEL_RESOLVE_SHARED_ENTS";
 
 // Get MOAB instance
 Interface* mb = new( std::nothrow ) Core;
 if( NULL == mb ) return 1;
 
 MPI_Comm comm;
 int global_rank, global_size;
 MPI_Comm_rank( MPI_COMM_WORLD, &global_rank );
 MPI_Comm_rank( MPI_COMM_WORLD, &global_size );
 
 int color = global_rank % nbComms; // For each angle group a different color
 if( nbComms > 1 )
 {
 // Split the communicator, into ngroups = nbComms
 MPI_Comm_split( MPI_COMM_WORLD, color, global_rank, &comm );
 }
 else
 comm = MPI_COMM_WORLD;
 
 // Get the ParallelComm instance
 ParallelComm* pcomm = new ParallelComm( mb, comm );
 int nprocs = pcomm->proc_config().proc_size();
 int rank = pcomm->proc_config().proc_rank();
#ifndef NDEBUG
 MPI_Comm rcomm = pcomm->proc_config().proc_comm();
 assert( rcomm == comm );
#endif
 if( 0 == global_rank )
 cout << " global rank:" << global_rank << " color:" << color << " rank:" << rank << " of " << nprocs
 << " processors\n";
 
 if( 1 == global_rank )
 cout << " global rank:" << global_rank << " color:" << color << " rank:" << rank << " of " << nprocs
 << " processors\n";
 
 MPI_Barrier( MPI_COMM_WORLD );
 
 if( 0 == global_rank )
 cout << "Reading file " << test_file_name << "\n with options: " << options << "\n on " << nprocs
 << " processors on " << nbComms << " communicator(s)\n";
 
 // Read the file with the specified options
 ErrorCode rval = mb->load_file( test_file_name.c_str(), 0, options.c_str() );MB_CHK_ERR( rval );
 
 Range shared_ents;
 // Get entities shared with all other processors
 rval = pcomm->get_shared_entities( -1, shared_ents );MB_CHK_ERR( rval );
 
 // Filter shared entities with not not_owned, which means owned
 Range owned_entities;
 rval = pcomm->filter_pstatus( shared_ents, PSTATUS_NOT_OWNED, PSTATUS_NOT, -1, &owned_entities );MB_CHK_ERR( rval );
 
 unsigned int nums[4] = { 0 }; // to store the owned entities per dimension
 for( int i = 0; i < 4; i++ )
 nums[i] = (int)owned_entities.num_of_dimension( i );
 vector< int > rbuf( nprocs * 4, 0 );
 MPI_Gather( nums, 4, MPI_INT, &rbuf[0], 4, MPI_INT, 0, comm );
 // Print the stats gathered:
 if( 0 == global_rank )
 {
 for( int i = 0; i < nprocs; i++ )
 cout << " Shared, owned entities on proc " << i << ": " << rbuf[4 * i] << " verts, " << rbuf[4 * i + 1]
 << " edges, " << rbuf[4 * i + 2] << " faces, " << rbuf[4 * i + 3] << " elements" << endl;
 }
 
 // Now exchange 1 layer of ghost elements, using vertices as bridge
 // (we could have done this as part of reading process, using the PARALLEL_GHOSTS read option)
 rval = pcomm->exchange_ghost_cells( 3, // int ghost_dim
 0, // int bridge_dim
 1, // int num_layers
 0, // int addl_ents
 true );MB_CHK_ERR( rval ); // bool store_remote_handles
 
 // Repeat the reports, after ghost exchange
 shared_ents.clear();
 owned_entities.clear();
 rval = pcomm->get_shared_entities( -1, shared_ents );MB_CHK_ERR( rval );
 rval = pcomm->filter_pstatus( shared_ents, PSTATUS_NOT_OWNED, PSTATUS_NOT, -1, &owned_entities );MB_CHK_ERR( rval );
 
 // Find out how many shared entities of each dimension are owned on this processor
 for( int i = 0; i < 4; i++ )
 nums[i] = (int)owned_entities.num_of_dimension( i );
 
 // Gather the statistics on processor 0
 MPI_Gather( nums, 4, MPI_INT, &rbuf[0], 4, MPI_INT, 0, comm );
 if( 0 == global_rank )
 {
 cout << " \n\n After exchanging one ghost layer: \n";
 for( int i = 0; i < nprocs; i++ )
 {
 cout << " Shared, owned entities on proc " << i << ": " << rbuf[4 * i] << " verts, " << rbuf[4 * i + 1]
 << " edges, " << rbuf[4 * i + 2] << " faces, " << rbuf[4 * i + 3] << " elements" << endl;
 }
 }
 
 delete mb;
 
 MPI_Finalize();
#else
 std::cout << " compile with MPI and hdf5 for this example to work\n";
 
#endif
 return 0;
}