check_status.c

#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int main(int argc, char** argv) {
  MPI_Init(NULL, NULL);

  int world_size;
  MPI_Comm_size(MPI_COMM_WORLD, &world_size);
  if (world_size != 2) {
    fprintf(stderr, "Must use two processes for this example\n");
    MPI_Abort(MPI_COMM_WORLD, 1);
  }
  int world_rank;
  MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);

  const int MAX_NUMBERS = 100;
  int numbers[MAX_NUMBERS];
  int number_amount;
  if (world_rank == 0) {
    // Pick a random amount of integers to send to process one
    srand(time(NULL));
    number_amount = (rand() / (float)RAND_MAX) * MAX_NUMBERS;
    // Send the amount of integers to process one
    MPI_Send(numbers, number_amount, MPI_INT, 1, 0, MPI_COMM_WORLD);
    printf("0 sent %d numbers to 1\n", number_amount);
  } else if (world_rank == 1) {
    MPI_Status status;
    // Receive at most MAX_NUMBERS from process zero
    MPI_Recv(numbers, MAX_NUMBERS, MPI_INT, 0, 0, MPI_COMM_WORLD, &status);
    // After receiving the message, check the status to determine how many
    // numbers were actually received
    MPI_Get_count(&status, MPI_INT, &number_amount);
    // Print off the amount of numbers, and also print additional information
    // in the status object
    printf("1 received %d numbers from 0. Message source = %d, tag = %d\n",
           number_amount, status.MPI_SOURCE, status.MPI_TAG);
  }
  MPI_Barrier(MPI_COMM_WORLD);
  MPI_Finalize();
}