Question

您能解释一下为什么这段代码可以很好地工作吗？

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

typedef struct Point
{
    double x;
    double y;
} point;

int main(int argc, char *argv[]) {
  int rank, size;
  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &size);

  MPI_Datatype mpi_point;
  MPI_Type_contiguous(2, MPI_DOUBLE, &mpi_point);
  MPI_Type_commit(&mpi_point);


  point local[2];

  if(rank==0)
  {
    point *buf;
    buf = malloc(10*sizeof(point));
    for(int i = 0; i<10; i++)
    {
        buf[i].x= (double)i;
        buf[i].y= (double)i+i;
    }
    MPI_Scatter(buf, 2, mpi_point, &local, 2, mpi_point, 0, MPI_COMM_WORLD);
    free(buf);
  }
  else
  {
    point *buf = NULL;
    MPI_Scatter(buf, 2, mpi_point, &local, 2, mpi_point, 0, MPI_COMM_WORLD);
  }

  printf("Hello, process %d has points: 1-> %f %f 2-> %f %f\n", rank, local[0].x, local[0].y, local[1].x, local[1].y);
  MPI_Finalize();
  return 0;
}

下面的这个不起作用？许多错误输出以segmentation fault结尾。

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

typedef struct Point
{
    double x;
    double y;
} point;

int main(int argc, char *argv[]) {
  int rank, size;
  MPI_Init(&argc, &argv);
  MPI_Comm_rank(MPI_COMM_WORLD, &rank);
  MPI_Comm_size(MPI_COMM_WORLD, &size);

  MPI_Datatype mpi_point;
  MPI_Type_contiguous(2, MPI_DOUBLE, &mpi_point);
  MPI_Type_commit(&mpi_point);


  point *local;

  if(rank==0)
  {
    point *buf;
    buf = malloc(10*sizeof(point));
    for(int i = 0; i<10; i++)
    {
        buf[i].x= (double)i;
        buf[i].y= (double)i+i;
    }
    MPI_Scatter(buf, 2, mpi_point, &local, 2, mpi_point, 0, MPI_COMM_WORLD);
    free(buf);
  }
  else
  {
    point *buf = NULL;
    local = malloc(2*sizeof(point));
    MPI_Scatter(buf, 2, mpi_point, &local, 2, mpi_point, 0, MPI_COMM_WORLD);
  }

  printf("Hello, process %d has points: 1-> %f %f 2-> %f %f\n", rank, local[0].x, local[0].y, local[1].x, local[1].y);
  MPI_Finalize();
  return 0;
}

唯一的区别是，local在一种情况下被定义为向量“直接”，而在另一种情况下被定义为指针，然后我进行了malloc处理。难道不是同一回事吗？两者都以相同的维度分配在堆栈中，那么带有malloc的那个怎么可能不起作用？

使用malloc的MPI_Scatter分段错误

0 个答案: