/* test program to find out how much buffering a system supplies */

#include "mpi.h"
#include <stdio.h>

int main(argc,argv)
int argc;
char *argv[];
{
    int  myid, numprocs;
    int  namelen;
    char processor_name[MPI_MAX_PROCESSOR_NAME];
    char *buf;
    int  bufsize, other, done, i;
    double t1, t2, tbase;
    MPI_Status status;

    MPI_Init(&argc,&argv);
    MPI_Comm_size(MPI_COMM_WORLD,&numprocs);
    MPI_Comm_rank(MPI_COMM_WORLD,&myid);
    
    /* Output processor names in rank order */
    MPI_Get_processor_name(processor_name,&namelen);
    if (myid > 0) 
        MPI_Recv( MPI_BOTTOM, 0, MPI_INT, myid - 1, 5, MPI_COMM_WORLD, 
                  &status );
    fprintf(stderr,"Process %d on %s\n", myid, processor_name);
    fflush( stderr );
    if (myid + 1 < numprocs)
        MPI_Send( MPI_BOTTOM, 0, MPI_INT, myid + 1, 5, MPI_COMM_WORLD );


    bufsize = 1024;
    other   = (myid + 1) % 2;
    done    = 0;

    while (!done && bufsize < 1024*1024*16) {
        if ((buf = (char *) malloc (bufsize)) == NULL) {
            fprintf(stderr, "%d could not malloc %d bytes\n", myid, bufsize );
            MPI_Abort( MPI_COMM_WORLD, 1 );
            exit(-1);
        }
        /* fprintf(stderr,"%d sending %d to %d\n", myid, bufsize, other ); */
        if ((myid % 2) == 0) {
            MPI_Send( MPI_BOTTOM, 0, MPI_INT, other, 1, MPI_COMM_WORLD );
            MPI_Recv( MPI_BOTTOM, 0, MPI_INT, other, 2, MPI_COMM_WORLD, 
                      &status );
            /* Compute a time to send when the receive is waiting */
            t1 = MPI_Wtime();
            MPI_Send( buf, bufsize, MPI_CHAR, other, 100, MPI_COMM_WORLD );
            t2 = MPI_Wtime();
            tbase = t2 - t1;
            MPI_Recv( MPI_BOTTOM, 0, MPI_INT, other, 2, MPI_COMM_WORLD, 
                      &status );
            /* Compute a time when the receive is NOT waiting */
            t1 = MPI_Wtime();
            MPI_Send( buf, bufsize, MPI_CHAR, other, 100, MPI_COMM_WORLD );
            t2 = MPI_Wtime();
            if (t2 - t1 > 1.5 && t2 - t1 > 2.0 * tbase) {
                printf( "MPI_Send blocks with buffers of size %d\n", 
                        bufsize );
                done = 1;
            }
        }
        else {
            MPI_Recv( MPI_BOTTOM, 0, MPI_INT, other, 1, MPI_COMM_WORLD, 
                      &status );
            t1 = MPI_Wtime();
            MPI_Send( MPI_BOTTOM, 0, MPI_INT, other, 2, MPI_COMM_WORLD );
            MPI_Recv( buf, bufsize, MPI_CHAR, other, 100, MPI_COMM_WORLD, 
                      &status );
            MPI_Send( MPI_BOTTOM, 0, MPI_INT, other, 2, MPI_COMM_WORLD );
            while (MPI_Wtime() - t1 < 2.0) ;
            MPI_Recv( buf, bufsize, MPI_CHAR, other, 100, MPI_COMM_WORLD, 
                      &status );
        }
        fprintf(stderr,"%d received %d from %d\n", myid, bufsize, other );
        free( buf );
        i = done;
        MPI_Allreduce( &i, &done, 1, MPI_INT, MPI_SUM, MPI_COMM_WORLD );
        bufsize *= 2;
    }
    MPI_Finalize();
    return 0;
}