c++ - 使用 MPI_Scatter 时出现段错误

Question

我对 MPI_Scatter 有疑问。不知道如何使用它，我当前的程序在启动时因段错误而崩溃。

我猜 MPI_Scatter 的参数存在问题，尤其是在使用正确的运算符(& 或 * 或 void)调用它时，但我几乎尝试了所有组合，但没有任何实际帮助。

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

// k = 3, N = 12,  1,2,3, 4,5,6, 7,8,9, 10,11,12

int main(int argc, char **argv) {
    int N, size, myrank;
    int k;
    std::cin >> N;
    std::cin >> k;
    int *mass = new int[N];
    int *recv = new int[k];

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

    if (myrank == 0) {
        std::cout << "get k and n \n";

        for (int i = 0; i < N; ++i) {
            mass[i] = i;
            std::cout << i << " written\n";
        }
    }

    MPI_Scatter(mass, k, MPI_INT, recv, k, MPI_INT, 0, MPI_COMM_WORLD);

    int sum = 0;
    std::cout << "myrank" << myrank << '\n';
    for (int i = 0; i < k; ++i) {
        std::cout << recv[i] << '\n';
    }

    MPI_Finalize();

    return 0;
}

当我启动这段代码时，它会打印:

N = 12
k = 3
get k and n 
0 written
1 written
2 written
3 written
4 written
5 written
6 written
7 written
8 written
9 written
10 written
11 written
myrank0
0
1
2
myrank1
myrank3
myrank2
[1570583203.522390] [calc:32739:0]          mpool.c:38   UCX  WARN  object 0x7fe1f08b2f60 was not returned to mpool mm_recv_desc
[1570583203.523214] [calc:32740:0]          mpool.c:38   UCX  WARN  object 0x7f4643986f60 was not returned to mpool mm_recv_desc
[1570583203.524205] [calc:32741:0]          mpool.c:38   UCX  WARN  object 0x7f22535d4f60 was not returned to mpool mm_recv_desc

Answer 1

MPI 通常会将 stdout 重定向到等级 0，因此 N 和 k 没有正确设置在其他等级上。

这是你的程序的工作版本

#include <iostream>
#include <cassert>
#include <stdio.h>
#include <mpi.h>

// k = 3, N = 12,  1,2,3, 4,5,6, 7,8,9, 10,11,12

int main(int argc, char **argv) {
    int k, N, size, myrank;
    int *mass;

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


    if (myrank == 0) {
        std::cout << "get k and n \n";
        std::cin >> N;
        std::cin >> k;
        assert (N >= k*size);
        mass = new int[N];
        for (int i = 0; i < N; ++i) {
            mass[i] = i;
            std::cout << i << " written\n";
        }
    }
    MPI_Bcast(&k, 1, MPI_INT, 0, MPI_COMM_WORLD);

    int *recv = new int[k];

    MPI_Scatter(mass, k, MPI_INT, recv, k, MPI_INT, 0, MPI_COMM_WORLD);

    int sum = 0;
    std::cout << "myrank" << myrank << '\n';
    for (int i = 0; i < k; ++i) {
        std::cout << recv[i] << '\n';
    }

    MPI_Finalize();

    return 0;
}