声明数组

Question

我有以下代码：

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

void pgmsize (char *filename, int *nx, int *ny);
void pgmread (char *filename, void *vx, int nx, int ny);
void pgmwrite(char *filename, void *vx, int nx, int ny);

#define FILENAME "edge768x768.pgm"
#define M 768
#define N 768

#define P 2
#define DEL 1
#define CHECKFREQ 500

#define MAXITER   5000

int main(int argc, char **argv){

    MPI_Init(&argc, &argv);
    int rank,size;
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);

    FILE *fp;
    char outname[64];
    sprintf(outname,"out_%d.dat",P);
    fp = fopen( outname, "w" );
    fprintf(fp,"del,iter,avg\n");

    MPI_Status status;
    MPI_Request req;
    MPI_Comm cart_comm;

    int dims[2] = {0,0};
    int periods[2] = {0,0};
    int coords[2];
    MPI_Dims_create(P, 2, dims);
    MPI_Cart_create(MPI_COMM_WORLD,2,dims,periods,1, &cart_comm);
    MPI_Cart_coords(cart_comm, rank, 2, coords);
    int Px = dims[0];
    int Py = dims[1];

    int i,j,locali,localj,iter;
    printf("%d,%d,%d\n",rank,M/Px,N/Py);
    double masterarray[M][N];
    double outarray[M][N];
    double local_array[M/Px][N/Py];
    double local_padded_array[M/Px+2][N/Py+2];
    double old[M/Px+2][N/Py+2];

    printf("%d,%d,%d\n",rank,Px,Py);



    fclose(fp);
    MPI_Finalize();
}

编译并运行时会出现以下错误：

  

mpiexec注意到节点My-MacBook-Air上的PID 28696的进程等级0在信号11上退出（分段错误：11）。

但是，如果我将主数组的声明更改为：

float masterarray[M][N]

它编译并运行良好。有人可以帮忙吗？如果所有数组都声明为floats，也可以正常运行。也许更好地理解这两种类型之间的差异可能有助于我了解正在发生的事情。

继续使用所有浮点数组编写代码后，我现在提出了另一个与数组相关的问题。我的代码现在是：

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

void pgmsize (char *filename, int *nx, int *ny);
void pgmread (char *filename, void *vx, int nx, int ny);
void pgmwrite(char *filename, void *vx, int nx, int ny);

#define FILENAME "edge768x768.pgm"
#define M 768
#define N 768

#define P 2
#define DEL 1
#define CHECKFREQ 500

#define MAXITER   5000

int main(int argc, char **argv){

    MPI_Init(&argc, &argv);
    int rank,size;
    MPI_Comm_size(MPI_COMM_WORLD, &size);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);

    FILE *fp;
    char outname[64];
    sprintf(outname,"out_%d.dat",P);
    fp = fopen( outname, "w" );
    fprintf(fp,"del,iter,avg\n");

    MPI_Status status;
    MPI_Request req;
    MPI_Comm cart_comm;

    int dims[2] = {0,0};
    int periods[2] = {0,0};
    int coords[2];
    MPI_Dims_create(P, 2, dims);
    MPI_Cart_create(MPI_COMM_WORLD,2,dims,periods,1, &cart_comm);
    MPI_Cart_coords(cart_comm, rank, 2, coords);
    int Px = dims[0];
    int Py = dims[1];

    int i,j,locali,localj,iter;
    float masterarray[M][N];
    float outarray[M][N];
    float local_array[M/Px][N/Py];
    float local_padded_array[M/Px+2][N/Py+2];
    float old[M/Px+2][N/Py+2];
    float new[M/Px+2][N/Py+2];



    if (rank == 0){
        pgmread(FILENAME, masterarray, M, N);
    }

    MPI_Bcast(masterarray,M*N,MPI_FLOAT,0,MPI_COMM_WORLD);

    for(i=0;i<M/Px;i++){
        for(j=0;j<N/Py;j++){

          locali = i + coords[0] * M/Px;
          localj = j + coords[1] * N/Py;


          local_array[i][j] = masterarray[locali][localj];

        }
    }

    for (i = 0;i<M/Px +2;i++){
        for (j = 0;j<N/Py +2;j++){
            local_padded_array[i][j] = 255.0;
        }
    }

    for (i = 1;i<M/Px +1;i++){
        for (j = 1;j<N/Py +1;j++){
            local_padded_array[i][j] = local_array[i-1][j-1];
        }
    }

    for (i = 0;i<M/Px +2;i++){
        for (j = 0;j<N/Py +2;j++){
            old[i][j] = 255.0;
        }
    }

    int down_rank,up_rank,right_rank,left_rank;
    MPI_Cart_shift(cart_comm,0,1,&right_rank,&left_rank);
    MPI_Cart_shift(cart_comm,1,1,&down_rank,&up_rank);

    MPI_Datatype col;
    MPI_Type_vector(M/Px,1,N/Py+2,MPI_FLOAT,&col);
    MPI_Type_commit(&col);

    float globaldel = 1000.0;
    float globalsum = 0.0;
    double time1 = MPI_Wtime();
    for(iter = 0;iter < MAXITER;iter++){

        MPI_Issend(&old[1][N/Py], 1,col,up_rank, 0,cart_comm, &req);
        MPI_Recv(&old[1][0], 1,col, down_rank, 0,cart_comm, &status);

        MPI_Issend(&old[1][1], 1,col ,down_rank, 0,cart_comm, &req);
        MPI_Recv(&old[1][N/Py+1], 1,col ,up_rank, 0,cart_comm, &status);

        MPI_Issend(&old[M/Px][1], N/Py,MPI_FLOAT,left_rank, 0,cart_comm, &req);
        MPI_Recv(&old[0][1], N/Py,MPI_FLOAT, right_rank, 0,cart_comm, &status);

        MPI_Issend(&old[1][1], N/Py,MPI_FLOAT,right_rank, 0,cart_comm, &req);
        MPI_Recv(&old[M/Px+1][1], N/Py,MPI_FLOAT, left_rank, 0,cart_comm, &status);

        for (i = 1;i<M/Px +1;i++){
        for (j = 1;j<N/Py +1;j++){
                new[i][j] = 0.25*(old[i][j-1]+old[i][j+1]+old[i-1][j]+old[i+1][j] - local_padded_array[i][j]);
            }
         }
    }

    printf("%d,%d,%d\n",rank,M/Px,N/Py);
    fclose(fp);
    MPI_Finalize();
}

当运行时会产生另一个分段错误，如果在最后一个循环中我似乎没有在新数组中设置元素。所以似乎在创建我的数组时存在一些主要问题！如果使用#define P 3而不是#define P 2

，代码似乎也可以正常运行

Answer 1

你可能在堆栈上内存不足。如果您不熟悉堆栈和堆之间的区别，请查看：What and where are the stack and heap?。如果我改为使用堆，那很好。

要从堆中为数组分配内存，请使用：

    double *masterarray = malloc(sizeof(double) * M * N);
    double *outarray = malloc(sizeof(double) * M * N);
    double *local_array = malloc(sizeof(double) * M/Px * N/Py);
    double *local_padded_array = malloc(sizeof(double) * (M/Px+2) * (N/Py+2));
    double *old = malloc(sizeof(double) * (M/Px+2) * (N/Py+2));

这是我的原始代码版本运行正常（删除了一些额外的垃圾以避免创建文件等）：

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

#define M 768
#define N 768

#define P 2
#define DEL 1
#define CHECKFREQ 500

#define MAXITER   5000

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

    MPI_Status status;
    MPI_Request req;
    MPI_Comm cart_comm;

    int dims[2] = {0,0};
    int periods[2] = {0,0};
    int coords[2];
    MPI_Dims_create(P, 2, dims);
    MPI_Cart_create(MPI_COMM_WORLD,2,dims,periods,1, &cart_comm);
    MPI_Cart_coords(cart_comm, rank, 2, coords);
    int Px = dims[0];
    int Py = dims[1];

    int i,j,locali,localj,iter;
    printf("%d,%d,%d\n",rank,M/Px,N/Py);

    double *masterarray = malloc(sizeof(double) * M * N);
    double *outarray = malloc(sizeof(double) * M * N);
    double *local_array = malloc(sizeof(double) * M/Px * N/Py);
    double *local_padded_array = malloc(sizeof(double) * (M/Px+2) * (N/Py+2));
    double *old = malloc(sizeof(double) * (M/Px+2) * (N/Py+2));

    if (masterarray == NULL) fprintf(stderr, "MASTERARRAY == NULL");
    if (outarray == NULL) fprintf(stderr, "OUTARRAY == NULL");
    if (local_array == NULL) fprintf(stderr, "LOCAL_ARRAY == NULL");
    if (local_padded_array == NULL) fprintf(stderr, "LOCAL_PADDED_ARRAY == NULL");
    if (old == NULL) fprintf(stderr, "OLD == NULL");

    printf("%d,%d,%d\n",rank,Px,Py);

    MPI_Finalize();

    return 0;
}