我遇到了一些MPI代码问题（我写这篇文章是为了测试另一个程序，其中不同的工作负载与不同的处理器相关联）。问题是，当我使用的处理器数量不同于1或 arraySize 时，（本例中为4），程序在 MPI_Send 期间被阻塞，特别是当我运行mpirun -np 2 MPItest时，程序在调用过程中被阻塞。我现在没有使用任何调试器，我只是想了解为什么它适用于1和4个处理器，但它不具有2个处理器（每个处理器阵列中有2个点），代码如下：

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

int main(int argc, char** argv) {
    int rank, size;
    const int arraySize = 4;
    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);

    // every processor have a different workload (1 or more spots on the array to send to the other processors)
    // every processor sends to every other processor its designated spots

    int* sendbuf = new int[arraySize];
    int* recvbuf = new int[arraySize];

    int istart = arraySize/size * rank;
    int istop = (rank == size) ? arraySize : istart + arraySize/size;

    for (int i = istart; i < istop; i++) {
        sendbuf[i] = i;
    }

    std::cout << "Rank " << rank << " sendbuf :" << std::endl;
    //print the sendbuf before receiving its other values
    for (int i = 0; i < arraySize; i++) {
        std::cout << sendbuf[i] << ", ";
    }
    std::cout << std::endl;

    // sending designated spots of sendbuf to other processors
    for(int i = istart; i < istop; i++){
        for(int j = 0; j < size; j++){
            MPI_Send(&sendbuf[i], 1, MPI_INT, j, i, MPI_COMM_WORLD);
        }
    }

    // receiving the full array
    for(int i = 0; i < arraySize ; i++){
        int recvRank = i/(arraySize/size);
        MPI_Recv(&recvbuf[i], 1, MPI_INT, recvRank, i, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    }

    // print the recvbuf after receiving its other values
    std::cout << "Rank " << rank << " recvbuf :" << std::endl;
    for (int i = 0; i < arraySize; i++) {
        std::cout << recvbuf[i] << ", ";
    }
    std::cout << std::endl;

    delete[] sendbuf;
    delete[] recvbuf;

    MPI_Finalize();
    return 0;
}

字符串
我正在使用标签来区分阵列中的不同点（也许这就是问题所在？）
我尝试使用不同数量的处理器，使用1个处理器程序可以工作，使用4个处理器程序也可以工作，使用3个处理器程序崩溃，使用2个处理器程序被阻塞。我还尝试使用MPI_Isend，但它也不工作（标志为0），MPI_Isend修改后的代码如下：

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

int main(int argc, char** argv) {
    int rank, size;
    const int arraySize = 4;
    MPI_Init(&argc, &argv);
    MPI_Comm_rank(MPI_COMM_WORLD, &rank);
    MPI_Comm_size(MPI_COMM_WORLD, &size);

    // every processor have a different workload (1 or more spots on the array to send to the other processors)
    // every processor sends to every other processor its designated spots

    int* sendbuf = new int[arraySize];
    int* recvbuf = new int[arraySize];

    int istart = arraySize/size * rank;
    int istop = (rank == size) ? arraySize : istart + arraySize/size;

    for (int i = istart; i < istop; i++) {
        sendbuf[i] = i;
    }

    std::cout << "Rank " << rank << " sendbuf :" << std::endl;
    //print the sendbuf before receiving its other values
    for (int i = 0; i < arraySize; i++) {
        std::cout << sendbuf[i] << ", ";
    }
    std::cout << std::endl;

    // sending designated spots of sendbuf to other processors
    for(int i = istart; i < istop; i++){
        for(int j = 0; j < size; j++){
            MPI_Request request;
            //MPI_Send(&sendbuf[i], 1, MPI_INT, j, i, MPI_COMM_WORLD);
            MPI_Isend(&sendbuf[i], 1, MPI_INT, j, i, MPI_COMM_WORLD, &request);
            // control if the send is completed
            int flag = 0;
            MPI_Test(&request, &flag, MPI_STATUS_IGNORE);
            const int numberOfRetries = 10;
            if(flag == 0){ // operation not completed
                std::cerr << "Error in sending, waiting" << std::endl;
                for(int k = 0; k < numberOfRetries; k++){
                    MPI_Test(&request, &flag, MPI_STATUS_IGNORE);
                    if(flag == 1){
                        break;
                    }
                }
                if(flag == 0){
                    std::cerr << "Error in sending, aborting" << std::endl;
                    MPI_Abort(MPI_COMM_WORLD, 1);
                }
                
            }
        }
    }

    // receiving the full array
    for(int i = 0; i < arraySize ; i++){
        int recvRank = i/(arraySize/size);
        MPI_Recv(&recvbuf[i], 1, MPI_INT, recvRank, i, MPI_COMM_WORLD, MPI_STATUS_IGNORE);
    }

    // print the recvbuf after receiving its other values
    std::cout << "Rank " << rank << " recvbuf :" << std::endl;
    for (int i = 0; i < arraySize; i++) {
        std::cout << recvbuf[i] << ", ";
    }
    std::cout << std::endl;

  
    //MPI_Alltoall(sendbuf, 1, MPI_INT, recvbuf, 1, MPI_INT, MPI_COMM_WORLD);

    delete[] sendbuf;
    delete[] recvbuf;

    MPI_Finalize();
    return 0;
}

型
对于这段代码，-np 4 也不起作用。