MPI_Rsend not raising error when it should

问题

The man page for Open MPI's implementation of MPI_Rsend states that

A ready send may only be called if the user can guarantee that a receive is already posted. It is an error if the receive is not posted before the ready send is called.

I'm trying to write a small program to see how this error would manifest itself (I thought it would be a runtime error followed by abort), but this program works perfectly:

#include <assert.h>
#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>  /* malloc */
#include <unistd.h>  /* sleep */

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

  int my_rank;
  MPI_Comm_rank(MPI_COMM_WORLD, &my_rank);

  const int ARRAY_SIZE = 100000;

  int* array = (int*)malloc(sizeof(int) * ARRAY_SIZE);
  assert(array != NULL);

  if (my_rank == 0) {
    // Populate array with something.
    for (int i = 0; i < ARRAY_SIZE; ++i) { array[i] = i; }

    int error_val;
    printf("[%d] Called Rsend\n", my_rank);
    error_val = MPI_Rsend(array, ARRAY_SIZE, MPI_INT, 1, 0, MPI_COMM_WORLD);
    printf("[%d] Done with success? %d\n", my_rank, error_val == MPI_SUCCESS);
  }
  else {
    sleep(5);
    MPI_Recv(array, ARRAY_SIZE, MPI_INT, 0, 0, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    printf("[%d] Last element of array is: %d\n", my_rank,
           array[ARRAY_SIZE -1 ]);
  }

  MPI_Finalize();
  return 0;
}

Output is:

$ mpicc -o mpi_rsend_example mpi_rsend_example.c
$ mpiexec -n 2 ./mpi_rsend_example
[0] Called Rsend
[0] Done with success? 1
[1] Last element of array is: 99999

Shouldn't there be an error, since the MPI_Recv call certainly happens after the MPI_Rsend call? (I'm running the program locally, so both ranks run on my computer).

来源：https://stackoverflow.com/questions/34223226/mpi-rsend-not-raising-error-when-it-should

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mpi

openmpi