为什么我在 MPI 下实现的 Ping Pong 代码会进入空闲状态？

问：

这是我从 MPITotor 下载的乒乓球代码

// Author: Wes Kendall
// Copyright 2011 www.mpitutorial.com
// This code is provided freely with the tutorials on mpitutorial.com. Feel
// free to modify it for your own use. Any distribution of the code must
// either provide a link to www.mpitutorial.com or keep this header intact.
//
// Ping pong example with MPI_Send and MPI_Recv. Two processes ping pong a
// number back and forth, incrementing it until it reaches a given value.
//
#include <mpi.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char** argv) {
  const int PING_PONG_LIMIT = 10;

  // Initialize the MPI environment
  MPI_Init(NULL, NULL);
  // Find out rank, size
  int world_rank;
  MPI_Comm_rank(MPI_COMM_WORLD, &world_rank);
  int world_size;
  MPI_Comm_size(MPI_COMM_WORLD, &world_size);

  // We are assuming 2 processes for this task
  if (world_size != 2) {
    fprintf(stderr, "World size must be two for %s\n", argv[0]);
    MPI_Abort(MPI_COMM_WORLD, 1);
  }

  int ping_pong_count = 0;
  int partner_rank = (world_rank + 1) % 2;
  while (ping_pong_count < PING_PONG_LIMIT) {
    if (world_rank == ping_pong_count % 2) {
      // Increment the ping pong count before you send it
      ping_pong_count++;
      MPI_Send(&ping_pong_count, 1, MPI_INT, partner_rank, 0, MPI_COMM_WORLD);
      printf("%d sent and incremented ping_pong_count %d to %d\n",
             world_rank, ping_pong_count, partner_rank);
    } else {
      MPI_Recv(&ping_pong_count, 1, MPI_INT, partner_rank, 0, MPI_COMM_WORLD,
               MPI_STATUS_IGNORE);
      printf("%d received ping_pong_count %d from %d\n",
             world_rank, ping_pong_count, partner_rank);
    }
  }
  MPI_Finalize();
}

这是我的执行日志：

$ mpicc ./ping_pong.c -o ping_pong
$ mpirun -np 2 ./ping_pong        
0 sent and incremented ping_pong_count 1 to 1
0 received ping_pong_count 2 from 1
0 sent and incremented ping_pong_count 3 to 1
0 received ping_pong_count 4 from 1
1 received ping_pong_count 1 from 0
1 sent and incremented ping_pong_count 2 to 0
1 received ping_pong_count 3 from 0
1 sent and incremented ping_pong_count 4 to 0
^C

如上所述，当程序增加到 4 并发送时，程序将不再输出。但是代码中设置的限制是 10，我不知道为什么会这样。ping_pong_count

我预计变量最终会增加到 10。ping_pong_count

我的平台是 archlinux，我正在使用 openmpi 4.1.5 版本。