c - MPI_Gather 段错误

Question

我有这个并行高斯消除代码。调用 MPI_Gather 函数调用时会发生段错误。我知道如果没有为两个缓冲区正确分配内存，这样的错误可能会增加。但是我看不出内存管理代码有什么问题。

有人可以帮忙吗？

谢谢。

注意事项:该程序从名为 input.txt 的同一目录中的 .txt 文件中读取。

代码:

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

/*void print2dAddresses(double** array2d, int rows, int cols)
{
    int i;

    for(i = 0; i < rows; i++)
    {
        int j;

        for(j = 0; j < cols; j++)
        {
            printf("%d ", &(array2d[i][j]));
        }

        printf("\n");
    }

    printf("------------------------------------");
}*/

double** newMatrix(int rows, int cols)
{
    double *data = (double*) malloc(rows * cols * sizeof(double));
    double **array= (double **)malloc(rows * sizeof(double*));
    int i;

    for (i=0; i<rows; i++)
        array[i] = &(data[cols*i]);

    return array;
}

void freeMatrix(double** mat)
{
    free(mat[0]);

    free(mat);
}

double** new2dArray(int nrows, int ncols)
{
    int i;
    double** array2d;

    array2d = (double**) malloc(nrows * sizeof(double*));

    for(i = 0; i < nrows; i++)
    {
        array2d[i] = (double*) malloc(ncols * sizeof(double));
    }

    return array2d;
}

double* new1dArray(int size)
{
    return (double*) malloc(size * sizeof(double));
}

void free2dArray(double** array2d, int nrows)
{
    int i;

    for(i = 0; i < nrows; i++)
    {
        free(array2d[i]);
    }

    free(array2d);
}

void print2dArray(double** array2d, int nrows, int ncols)
{
    int i, j;

    for(i = 0; i < nrows; i++)
    {
        for(j = 0; j < ncols; j++)
        {
            printf("%lf ", array2d[i][j]);
        }

        printf("\n");
    }

    printf("----------------------\n");
}

void print1dArray(double* array, int size)
{
    int i;

    for(i = 0; i < size; i++)
    {
        printf("%lf\n", array[i]);
    }

    printf("----------------------\n");
}

void read2dArray(FILE* fp, double** array2d, int nrows, int ncols)
{
    int i, j;

    for(i = 0; i < nrows; i++)
    {
        for(j = 0; j < ncols; j++)
        {
            fscanf(fp, "%lf", &(array2d[i][j]));
        }
    }
}

void read1dArray(FILE* fp, double* array, int size)
{
    int i;

    for(i = 0; i < size; i++)
    {
        fscanf(fp, "%lf", &(array[i]));
    }
}

void readSymbols(char* symbols, int size, FILE* fp)
{
    int i;

    for(i = 0; i < size; i++)
    {
        char c = '\n';

        while(c == '\n' | c == ' ' | c == '\t' | c == '\r')
            fscanf(fp, "%c", &c);

        symbols[i] = c;
    }
}

void printSolution(char* symbols, double* x, int size)
{
    int i;

    for(i = 0; i < size; i++)
    {
        printf("%c = %lf\n", symbols[i], x[i]);
    }
}

double* copy_1d_array(double* original, int size)
{
    double* copy_version;
    int i;

    copy_version = (double*) malloc(size * sizeof(double));

    for(i = 0; i < size; i++)
    {
        copy_version[i] = original[i];
    }

    return copy_version;
}

int main(int argc, char** argv)
{
    int p, rank, i, j, k, l, msize, rowsPerProcess, remainder, startingRow, dest, rowCounter, remainingRows, neededProcesses;
    double **A, *b, *x, **smallA, *currentRow, *smallB, currentB, **receivedA, *receivedB;
    char *symbols;
    MPI_Status status;

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

    if(rank == 0)
    {
        FILE* fp;

        fp = fopen("input.txt", "r");

        fscanf(fp, "%d", &msize);

        A = newMatrix(msize, msize);
        b = new1dArray(msize);
        x = new1dArray(msize);

        symbols = (char*) malloc(msize * sizeof(char));

        read2dArray(fp, A, msize, msize);
        read1dArray(fp, b, msize);

        readSymbols(symbols, msize, fp);
        fclose(fp);

        /*print2dArray(A, msize, msize);
        print1dArray(b, msize);*/

    }

    MPI_Bcast(&msize, 1, MPI_INT, 0, MPI_COMM_WORLD);


    for(i = 0; i < (msize - 1); i++)
    {
        int maxIndex;
        double maxCoef, tmp, r;
        /*finding max row*/

        if(rank == 0)
        {
            maxIndex = i;
            maxCoef = fabs(A[i][i]);
            for(j = i + 1; j < msize; j++)
            {
                if(fabs(A[j][i]) > maxCoef)
                {
                    maxCoef = A[j][i];
                    maxIndex = j;
                }
            }

            /*swapping the current row with the max row*/
            for(j = 0; j < msize; j++)
            {
                tmp = A[i][j];
                A[i][j] = A[maxIndex][j];
                A[maxIndex][j] = tmp;
            }

            tmp = b[i];
            b[i] = b[maxIndex];
            b[maxIndex] = tmp;


            /*elimination*/
            /*for(j = i + 1; j < msize; j++)
            {
                double r = A[j][i] / A[i][i];

                subtracting r * row i from row j
                for(k = i; k < msize; k++)
                {
                    A[j][k] -= r * A[i][k];
                }

                b[j] -= r * b[i];
            }*/

            /*parallel elimination*/
            startingRow = i + 1;
            neededProcesses = p;

            remainingRows = msize - startingRow;

            if(remainingRows < neededProcesses)
            {
                neededProcesses = remainingRows;
            }

            rowsPerProcess = remainingRows / neededProcesses;
            remainder = remainingRows % neededProcesses;
        }

        MPI_Bcast(&startingRow, 1, MPI_INT, 0, MPI_COMM_WORLD);
        MPI_Bcast(&rowsPerProcess, 1, MPI_INT, 0, MPI_COMM_WORLD);

        if(rank == 0)
        {
            currentRow = copy_1d_array(A[startingRow-1], msize);
            currentB = b[startingRow-1];
        }
        else
        {
            currentRow = new1dArray(msize);
        }

        MPI_Bcast(currentRow, msize, MPI_DOUBLE, 0, MPI_COMM_WORLD);
        MPI_Bcast(&currentB, 1, MPI_DOUBLE, 0, MPI_COMM_WORLD);

        if(rank == 0)
        {
            receivedA = newMatrix(remainingRows, msize);
            receivedB = new1dArray(remainingRows);
        }
        smallA = newMatrix(rowsPerProcess, msize);
        smallB = new1dArray(rowsPerProcess);

        MPI_Scatter(&(A[startingRow][0]), rowsPerProcess*msize, MPI_DOUBLE, &(smallA[0][0]), rowsPerProcess*msize, MPI_DOUBLE, 0, MPI_COMM_WORLD);

        MPI_Scatter(&(b[startingRow]), rowsPerProcess, MPI_DOUBLE, &(smallB[0]), rowsPerProcess, MPI_DOUBLE, 0, MPI_COMM_WORLD);

        for(j = 0; j < rowsPerProcess; j++)
        {
            r = smallA[j][startingRow-1] / currentRow[startingRow-1];

            for(k = 0; k < msize; k++)
            {
                smallA[j][k] -= r * currentRow[k];
            }

            smallB[j] -= r * currentB;
        }

        MPI_Gather(&(smallA[0][0]), rowsPerProcess*msize, MPI_DOUBLE, &(receivedA[0][0]), rowsPerProcess*msize, MPI_DOUBLE, 0, MPI_COMM_WORLD);

        MPI_Gather(&(smallB[0]), rowsPerProcess, MPI_DOUBLE, &(receivedB[0]), rowsPerProcess, MPI_DOUBLE, 0, MPI_COMM_WORLD);

        freeMatrix(smallA);
        free(smallB);

        if(rank == 0)
        {
            for(j = 0; j < remainingRows; j++)
            {
                for(k = 0; k < msize; k++)
                {
                    A[j+startingRow][k] = receivedA[j][k];
                }

                b[j+startingRow] = receivedB[j];
            }
            free(currentRow);
            freeMatrix(receivedA);
            free(receivedB);
        }

        if(rank == 0)
        {
            if(remainder > 0)
            {
                for(j = (msize - remainder); j < msize; j++)
                {
                    r = A[j][i] / A[i][i];

                    for(k = 0; k < msize; k++)
                    {
                        A[j][k] -= r * A[i][k];
                    }

                    b[j] -= r * b[i];
                }
            }
        }

    }

    if(rank == 0)
    {
        /*backward substitution*/

        for(i = msize - 1; i >= 0; i--)
        {
            x[i] = b[i];

            for(j = msize - 1; j > i; j--)
            {
                x[i] -= A[i][j] * x[j];
            }

            x[i] /= A[i][i];
        }

        printf("solution = \n");
        //print1dArray(x, msize);

        printSolution(symbols, x, msize);

        freeMatrix(A);
        free(b);
        free(x);
        free(symbols);
    }


    MPI_Finalize();
    return 0;
}

输入文件:

3
1 1 1
1 1 3
2 1 4
4
9
12
x
y
z

Answer 1

可能是这样的:&(receivedA[0][0]) 在 rank != 0 的进程上。您正在索引一个尚未分配的数组。您可能需要创建另一个指针，如下所示:

    if(rank == 0)
    {
        receivedA = newMatrix(remainingRows, msize);
        recievedAHead = &(receivedA[0][0]);
        receivedB = new1dArray(remainingRows);
    }
    else {
        recievedAHead = NULL;
    }

并在 MPI_Gather 调用中使用 recievedAHead。