MOAB: Mesh Oriented datABase  (version 5.4.1)
CrystalRouterExample.cpp

generalized gather scatter using tuples
To run: mpiexec -np <n> CrystalRouterExample -r [reportrank] -t [num_tuples] -n [num_comms]

/*
* This example will show one of the building blocks of parallel infrastructure in MOAB
* More exactly, if we have some homogeneous data to communicate from each processor to a list of
* other processors, how do we do it?
*
* introduce the TupleList and crystal router to MOAB users.
*
* This technology is used in resolving shared vertices / sets between partitions
* It is used in the mbcoupler for sending data (target points) to the proper processor, and
* communicate back the results. Also, it is used to communicate departure mesh for intersection in
* parallel
*
*  It is a way of doing  MPI_gatheralltoallv(), when the communication matrix is sparse
*
*  It is assumed that every proc needs to communicate only with a few of the other processors.
*  If every processor needs to communicate with all other, then we will have to use paired isend
* and irecv, the communication matrix is full
*
*  the example needs to be launched in parallel.
*  Every proc will build a list of tuples, that will be send to a few procs;
*  We vary num_comms and num_tuples for processor
*
*  we will send long ints of the form
*    100000 * send + 1000* rank +j, where j is the index of tuple
*
*  after routing, we verify we received
*    100000 * rank + 1000 * from
*
*    For some reportrank we also print the tuples.
*
*  after routing, we will see if we received, as expected. Should run on at least 2 processors.
*
* Note: We do not need a moab instance for this example
*
*/

/** @example CrystalRouterExample.cpp \n
* \brief generalized gather scatter using tuples \n
* <b>To run</b>: mpiexec -np <n> CrystalRouterExample -r [reportrank] -t [num_tuples] -n
* [num_comms] \n
*
*/
//
#include "moab/MOABConfig.h"
#ifdef MOAB_HAVE_MPI
#include "moab/ProcConfig.hpp"
#endif
#include "moab/TupleList.hpp"
#include "moab/ProgOptions.hpp"
#include "moab/ErrorHandler.hpp"
#include <ctime>
#include <iostream>
#include <sstream>

const char BRIEF_DESC[] = "Example of gather scatter with tuple lists \n";
std::ostringstream LONG_DESC;

using namespace moab;
using namespace std;

int main( int argc, char** argv )
{
#ifdef MOAB_HAVE_MPI
MPI_Init( &argc, &argv );

// Initialize error handler, required for this example (not using a moab instance)
MBErrorHandler_Init();

ProcConfig pc( MPI_COMM_WORLD );
int size = pc.proc_size();
int rank = pc.proc_rank();

// Start copy
LONG_DESC << "This program does a gather scatter with a list of tuples. \n"
" It tries to see how much communication costs in terms of time and memory. \n"
<< "It starts with creating a list of tuples to be sent from each processor, \n to a "
"list of other processors.\n"
<< "The number of tuples and how many tasks to communicate to are controlled by "
"input parameters.\n"
<< "After communication, we verify locally if we received what we expected. \n";
ProgOptions opts( LONG_DESC.str(), BRIEF_DESC );

// How many procs communicate to current proc, on average (we will vary that too)
int num_comms = 2;
&num_comms );

int num_tuples = 4;
&num_tuples );

int reportrank = size + 1;
"this rank will report the tuples sent and the tuples received; it could "
"be higher than num_procs, then no reporting",
&reportrank );

opts.parseCommandLine( argc, argv );

if( rank == reportrank || ( reportrank >= size && 0 == rank ) )
{
cout << " There are " << size << " tasks in example.\n";
cout << " We will send groups of " << num_tuples << " from each task towards " << num_comms
}

// Send some data from proc i to i + n/2, also to i + n/2 + 1 modulo n, where n is num procs

gs_data::crystal_data* cd = pc.crystal_router();

long total_n_tuples = num_comms * num_tuples;

// Vary the number of tasks to send to, and the number of tuples to send
if( rank < size / 2 )
num_comms--;
else
num_comms++;

if( rank < size / 3 )
num_tuples *= 2;
else if( rank > size - size / 3 )
num_tuples /= 2;

TupleList tl;
// At most num_tuples* num_comms to send
// We do a preallocate with this; some tuples on some processors might need more memory, to be
// able to grow locally; Some tasks might receive more tuples though, and in the process, some
// might grow more than others. By doing these logP sends/receives, we do not grow local memory
// too much.
tl.initialize( 1, 1, 0, 1, num_tuples * num_comms );
tl.enableWriteAccess();
// Form num_tuples*num_comms tuples, send to various ranks
unsigned int n = tl.get_n();
for( int i = 0; i < num_comms; i++ )
{
int sendTo     = rank + i * size / 2 + 1;  // Spread out the send to, for a stress-like test
sendTo         = sendTo % size;            //
long intToSend = 1000 * rank + 100000 * sendTo;
for( int j = 0; j < num_tuples; j++ )
{
n           = tl.get_n();
tl.vi_wr[n] = sendTo;
tl.vl_wr[n] = intToSend + j;
tl.vr_wr[n] = 10000. * rank + j;
tl.inc_n();
}
}

if( rank == reportrank )
{
cout << "rank " << rank << "\n";
tl.print( " before sending" );
}

clock_t tt = clock();
// All communication happens here; no mpi calls for the user
ErrorCode rval = cd->gs_transfer( 1, tl, 0 );MB_CHK_SET_ERR( rval, "Error in tuple transfer" );

double secs = 0;
if( rank == reportrank || ( reportrank >= size && 0 == rank ) )
{
secs = ( clock() - tt ) / (double)CLOCKS_PER_SEC;
}
if( rank == reportrank )
{
cout << "rank " << rank << "\n";
tl.print( " after transfer" );
}

// Check that all tuples received have the form 10000*rank + 100*from
for( int i = 0; i < (int)received; i++ )
{
int from      = tl.vi_rd[i];
long valrec   = tl.vl_rd[i];
int remainder = valrec - 100000 * rank - 1000 * from;
if( remainder < 0 || remainder >= num_tuples * 4 )
cout << " error: tuple " << i << " received at proc rank " << rank << " from proc " << from << " has value "
<< valrec << " remainder " << remainder << "\n";
}

if( rank == reportrank || ( reportrank >= size && 0 == rank ) )
{
cout << "communication of about " << total_n_tuples << " tuples/per proc took " << secs << " seconds"
<< "\n";
tt = clock();
}

// Finalize error handler, required for this example (not using a moab instance)
MBErrorHandler_Finalize();

MPI_Finalize();
#else
std::cout << " Build with MPI for this example to work\n";
#endif

return 0;
}