MPI:Printf语句未在合适的时间执行

Question

我有一个小程序.

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

int main(int argc, char *argv[])
{
int rank, size;
int buf;
int err;
MPI_Status status;

err = MPI_Init(&argc, &argv);
if(err == MPI_SUCCESS) {
MPI_Comm_size(MPI_COMM_WORLD, &size);
MPI_Comm_rank(MPI_COMM_WORLD, &rank);

if(rank == 0) {
printf("Buffer size is less than 10\n");
printf("Enter the buffer size: ");
scanf("%d", &buf);
MPI_Send(&buf, 1, MPI_INT, 1, 10,
MPI_COMM_WORLD);
}
else {
MPI_Recv(&buf, 1, MPI_INT, 0, 10,
MPI_COMM_WORLD, &status);
}
printf("process[%d]: buffer size : %d\n", rank,buf);

}
err = MPI_Finalize();
return 0;
}

输出是:

[veda@home-pc hpc]$ mpicc test.c
[veda@home-pc hpc]$ mpiexec -np 2 a.out
Buffer size is less than 10
3
Enter the buffer size: process[0]: buffer size : 3
process[1]: buffer size : 3

在此输出中,您可以注意到这一点

输入缓冲区大小:

在输入缓冲区大小后打印/提示.

谁能告诉我如何解决这个问题.

Answer 1

我怀疑你的标准输出是行缓冲的.在"Enter the buffer size: "打印"process[%d]: buffer size : %d\n"(包含换行符)之前不会打印.解决方案是显式刷新printf和之间的标准输出scanf:

printf("Enter the buffer size: ");
fflush(stdout);
scanf("%d", &buf);