#include <stdio.h>
#include <mpi.h>
int main( int argc, char ** argv ) {
    int rank, size;
    MPI_Init( 0, 0 );
    MPI_Comm_size( MPI_COMM_WORLD, &size );
    MPI_Comm_rank( MPI_COMM_WORLD, &rank );
    
    
    int sendbuf = rank, recvbuf, probeflag;
    int excessProbesNeeded = 0;
    for ( int i = 0; i < 10; ++i ) {
        for ( int otherrank = 0; otherrank < size; ++otherrank ) {
            if ( otherrank != rank ) {
                MPI_Send( &sendbuf, 1, MPI_INT, otherrank, 0, MPI_COMM_WORLD );
            }
        }
        
        MPI_Barrier( MPI_COMM_WORLD );
        
        for ( int otherrank = 0; otherrank < size; ++otherrank ) {
            if ( otherrank == rank ) {
                continue;
            }
            probeflag = 0;
            int failedBeforeThisTime = 0;
            while( probeflag == 0 ) {
                MPI_Iprobe( otherrank, MPI_ANY_TAG, MPI_COMM_WORLD, &probeflag, 
                            MPI_STATUS_IGNORE );
                if ( !probeflag ) {
                    ++excessProbesNeeded;
                    if ( !failedBeforeThisTime ) {
                        printf( "Probe failed on %d from %d (iteration %d)\n", 
                                rank, otherrank, i );
                        ++failedBeforeThisTime;
                    }
                }
            }
            
            if ( otherrank != rank ) {
                MPI_Recv( &recvbuf, 1, MPI_INT, otherrank, 0, MPI_COMM_WORLD,
                          MPI_STATUS_IGNORE );
            }
        }
    }
    
    int totalExcess = 0;
    MPI_Reduce( &excessProbesNeeded, &totalExcess, 1, MPI_INT,
                MPI_SUM, 0, MPI_COMM_WORLD );

    if ( rank == 0 ) {
        printf( "Excess probes needed: %d\n", totalExcess );
    }

    
    
    MPI_Finalize();
}