MPI

Question

这是我的一段代码：

int world_size;
MPI_Comm_size(MPI_COMM_WORLD , &world_size);

int world_rank;
MPI_Comm_rank(MPI_COMM_WORLD , &world_rank);

int *rbuf , arr[world_size];
if (world_rank == 0)
{
    rbuf = (int *) malloc(world_size * 1 * sizeof(int));
}
else
{
    rbuf[0] = rand() % 100;
    MPI_Send(rbuf , 1 , MPI_INT , 0 , 0 , MPI_COMM_WORLD);
}
if (world_rank == 0)
{
    MPI_Gather(arr , world_size , MPI_INT , rbuf , 1 , MPI_INT , 0 , MPI_COMM_WORLD);
    for (int i = 0; i < world_size; ++i)
    {
        printf("%d " , arr[i]);
    }
    printf("\n");
}

我想在非根进程的每个进程中生成一个随机数。然后我希望每个这样的进程将生成的数字发送到根进程，即。根进程应该收集每个进程生成的所有数字。

当我尝试运行此代码时，出现错误：

Fatal error in PMPI_Gather: Message truncated, error stack:
PMPI_Gather(896)......: MPI_Gather(sbuf=0x7ffc3b23c180, scount=10, MPI_INT, rbuf=0x564a753dc790, rcount=1, MPI_INT, root=0, MPI_COMM_WORLD) failed
MPIR_Gather_impl(718).: 
MPIR_Gather(678)......: 
MPIR_Gather_intra(184): 
MPIR_Localcopy(74)....: Message truncated; 40 bytes received but buffer size is 4

(PS。我运行这个程序使用mpirun -n 10 ./helloworld)

Answer 1

MPI_Gather 从所有级别发送消息到 root 并自己接收它不需要 MPI_Send.

我改变了你的例子：

#include<stdio.h>
#include<mpi.h>
#include<stdlib.h>
#include<time.h>
int main(int argc, char **argv){

  MPI_Init(&argc, &argv);
  int world_size;
  MPI_Comm_size(MPI_COMM_WORLD , &world_size);
  int world_rank;
  MPI_Comm_rank(MPI_COMM_WORLD , &world_rank);

  srand(time(NULL)+world_rank);
  int *rbuf,*sender;
  if (world_rank == 0)
  {
    rbuf = (int *) malloc(world_size * 1 * sizeof(int));
  }
  sender = (int *) malloc( 1 * sizeof(int));
  sender[0] = rand() % 100;

  MPI_Gather(sender , 1 , MPI_INT , rbuf , 1 , MPI_INT , 0 , MPI_COMM_WORLD);
  if (world_rank == 0)
  {
    for (int i = 0; i < world_size; ++i)
    {
        printf("%d " , rbuf[i]);
    }
    printf("\n");
  }
  MPI_Finalize();
}

MPI - 将随机整数发送到根进程时出错

MPI - Error sending random int to root process

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