如何使用C语言在MPI中调用相同等级？

我正在尝试学习MPI编程，并编写了以下程序。它添加了整行数组并输出总和。在等级0（或进程0）处，它将调用其所有从属等级进行计算。我只想使用其他两个从属等级/进程来执行此操作。每当我尝试两次调用相同的等级（如下面的代码所示）时，我的代码就会挂在中间而无法执行。如果我不两次调用相同的等级，代码将正常工作

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

int main (int argc, char *argv[])
{
        MPI_Init(&argc, &argv);
        int world_rank;
        MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
        int world_size;
        MPI_Comm_size(MPI_COMM_WORLD, &world_size);
        int tag2 = 1;       
        int arr[30] = {0};

        MPI_Request request;
        MPI_Status status;

        printf ("\n--Current Rank: %d\n", world_rank);
        int index;
        int source = 0;
        int dest;
        if (world_rank == 0)
        {
            int i;

            printf("* Rank 0 excecuting\n");
            index = 0;
            dest = 1;
            for ( i = 0; i < 30; i++ )
            {
                arr[ i ] = i + 1; 
            }           
            MPI_Send(&arr[0], 30, MPI_INT, dest, tag2, MPI_COMM_WORLD); 

            index = 0;
            dest = 2;
            for ( i = 0; i < 30; i++ )
            {
                arr[ i ] = 0; 
            }
            MPI_Send(&arr[0], 30, MPI_INT, dest, tag2, MPI_COMM_WORLD);         

            index = 0;
            dest = 2; //Problem happens here when I try to call the same destination(or rank 2) twice
            //If I change this dest value to 3 and run using: mpirun -np 4 test, this code will work correctly
            for ( i = 0; i < 30; i++ )
            {
                arr[ i ] = 1; 
            }
            MPI_Send(&arr[0], 30, MPI_INT, dest, tag2, MPI_COMM_WORLD);
        }
        else 
        {
            int sum = 0;
            int i;
            MPI_Irecv(&arr[0], 30, MPI_INT, source, tag2, MPI_COMM_WORLD, &request);
            MPI_Wait (&request, &status);
            for(i = 0; i<30; i++)
            {   
                sum = arr[i]+sum;
            }
            printf("\nSum is: %d at rank: %d\n", sum, world_rank);
        }       

        MPI_Finalize();
}

使用时的结果：mpirun -np 3测试

--Current Rank: 2

Sum is: 0 at rank: 2

--Current Rank: 0
* Rank 0 excecuting

--Current Rank: 1

Sum is: 524800 at rank: 1
                  //Program hangs here and wouldn't show sum of 30 

请让我知道我怎么能两次叫相同的等级。例如，如果我只有两个可以调用的从属进程。如果可能，请举例说明