/******************************************************************************
* FILE: unsafe.c
* DESCRIPTION:
*  This simple program is unsafe when run under IBM's MPI because its 
*  successful execution depends upon system buffer space. It uses a message 
*  size which by default, is sent in eager mode and requires buffering on the 
*  receive side. The receive process has more work to do than the send process,
*  and eventually, the incoming messages exhaust its buffer space.
*  To run this program, use the default settings for MP_EAGER_LIMIT and 
*  MP_BUFFER_MEM.   When IP communications (MP_EUILIB=ip) are used, it will 
*  fail within a few seconds.  If US communications (MP_EUILIB=us) are used, 
*  it will fail when MP_CSS_INTERRUPT is set to "yes".
* LAST REVISED: 2/15/99 Blaise Barney
******************************************************************************/

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

#define EAGERSIZE 4096   /* Default eager size for 2 tasks */

int main(argc,argv)
int argc;
char *argv[];
{

int        numtasks, rank, i, tag=111, dest=1, source=0, count=0;
char       data[EAGERSIZE];
double     start, end, result;
MPI_Status status;

MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD, &numtasks);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);

if (numtasks != 2) {
  printf("Please run this test with 2 tasks. Terminating\n");
  MPI_Finalize();
  }
printf ("MPI task %d started...\n", rank);


/******************************* Send task **********************************/
if (rank == 0) {

  /* Initialize send data */
  for(i=0; i<EAGERSIZE; i++)
     data[i] =  'x';

  start = MPI_Wtime();
  while (1) {
    MPI_Send(data, EAGERSIZE, MPI_BYTE, dest, tag, MPI_COMM_WORLD);
    count++;
    if (count % 100 == 0) {
      end = MPI_Wtime();
      printf("Count = %d  Time= %f sec.\n", count, end-start);
      start = MPI_Wtime();
      }
    }
  }

/****************************** Receive task ********************************/
/* 
*  This task has more work to do than send task, creating a race condition. 
*  Sending in eager mode requires system buffer space, which is exhausted by
*  this load imbalance.
*/

if (rank == 1) {
  result = 0.0;
  while (1) {
    MPI_Recv(data, EAGERSIZE, MPI_BYTE, source, tag, MPI_COMM_WORLD, &status);

    /* Do some work  - at least more than the send task */
    for (i=0; i < 1000000; i++) 
      result = result + (double)random();
    }
  }

MPI_Finalize();
}