MPI_Neighbor_alltoall段错误

Question

我正在研究一个需要使用（分布式）图形通信器在节点之间进行通信的MPI应用程序。在某些情况下，最简单的事情是节点与自己进行通信。在测试代​​码时我遇到了段错误的问题，我无法解释。这是一个重现问题的最小例子（在OpenMPI 1.8.1中）：

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

int main(void) {
    MPI_Init(NULL, NULL);

    MPI_Comm mpi_neighbor_comm;
    int v[2] = {0, 0}, w[2] = {0, 0};
    MPI_Dist_graph_create_adjacent(MPI_COMM_WORLD,
        2, v, (int *)MPI_UNWEIGHTED,
        2, w, (int *)MPI_UNWEIGHTED,
        MPI_INFO_NULL, 0, &mpi_neighbor_comm);

    int major, minor;
    MPI_Get_version(&major, &minor);
    std::cerr << "Version " << major << '.' << minor << std::endl;

    int indegree, outdegree, weighted;
    MPI_Dist_graph_neighbors_count(mpi_neighbor_comm, &indegree, &outdegree, &weighted);
    std::cerr << "Degrees: " << indegree << ", " << outdegree << std::endl;

    std::vector<int> in(indegree, 0), out(outdegree, 1);

    MPI_Neighbor_alltoall(&out[0], 1, MPI_INT,
        &in[0], 1, MPI_INT, mpi_neighbor_comm);

    std::cerr << in[0] << std::endl;

    MPI_Comm_free(&mpi_neighbor_comm);
    MPI_Finalize();

    return 0;
}

当使用1个进程运行时，这会给出以下输出：

$ mpiexec -n 1 ./mpi_test
Version 3.0
Degrees: 2, 2
1
[LMC-038262:51444] *** Process received signal ***
[LMC-038262:51444] Signal: Segmentation fault: 11 (11)
[LMC-038262:51444] Signal code: Address not mapped (1)
[LMC-038262:51444] Failing at address: 0x0
[LMC-038262:51444] *** End of error message ***

因为价值＆＃34; 1＆＃34;传送到in，似乎通信工作 - 但程序然后段错误。怎么了？如果我注释掉MPI_Neighbor_alltoall的号码，则段错误就会消失。