MPI派生的数据类型问题是由结构填充和无阻塞通信缓冲区的问题引起的

嗨，我正在编写一个c++程序，我希望MPI通过派生数据类型进行通信。但是接收者没有收到发送者发出的完整信息。

这是我构建派生数据类型的方法：

// dg_derived_datatype.cpp

#include <mpi.h>
#include "dg_derived_datatype.h"

namespace Hash{

    MPI_Datatype Face_type;
};

void Construct_data_type(){

    MPI_Face_type();

}

void MPI_Face_type(){

    int num = 3;

    // Number of elements in each block (array of integers)
    int elem_blocklength[num]{2, 1, 5};

    // Byte displacement of each block (array of integers).
    MPI_Aint array_of_offsets[num];
    MPI_Aint intex, charex;
    MPI_Aint lb;
    MPI_Type_get_extent(MPI_INT, &lb, &intex);
    MPI_Type_get_extent(MPI_CHAR, &lb, &charex);

    array_of_offsets[0] = (MPI_Aint) 0;
    array_of_offsets[1] = array_of_offsets[0] + intex * 2;
    array_of_offsets[2] = array_of_offsets[1] + charex;

    MPI_Datatype array_of_types[num]{MPI_INT, MPI_CHAR, MPI_INT};

    // create and MPI datatype
    MPI_Type_create_struct(num, elem_blocklength, array_of_offsets, array_of_types, &Hash::Face_type);  
    MPI_Type_commit(&Hash::Face_type);

}

void Free_type(){

    MPI_Type_free(&Hash::Face_type);    

}

在这里，我导出我的数据类型Hash::Face_type并提交它。该Hash::Face_type用于传送我的结构（face_pack2 INT + 1吨焦炭+ 5 INT）载体。

// dg_derived_datatype.h

#ifndef DG_DERIVED_DATA_TYPE_H
#define DG_DERIVED_DATA_TYPE_H

#include <mpi.h>

struct face_pack{

    int owners_key; 

    int facei; 

    char face_type;

    int hlevel;

    int porderx;

    int pordery; 

    int key;

    int rank;

};

namespace Hash{

    extern MPI_Datatype Face_type;
};

void Construct_data_type();

void Free_type();

#endif

然后在我的主程序中

// dg_main.cpp

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

void Recv_face(int source, int tag, std::vector<face_pack>& recv_face);

int main(){
// Initialize MPI. 
// some code here.
// I create a vector of struct: std::vector<face_pack> face_info,
// to store the info I want to let proccesors communicate. 

Construct_data_type(); // construct my derived data type

MPI_Request request_pre1, request_pre2, request_next1, request_next2;

// send
if(num_next > 0){ // If fullfilled the current processor send info to the next processor (myrank + 1)

std::vector<face_pack> face_info;
// some code to construct face_info

// source my_rank, destination my_rank + 1
MPI_Isend(&face_info[0], num_n, Hash::Face_type, mpi::rank + 1, mpi::rank + 1, MPI_COMM_WORLD, &request_next2);

}

// recv
if(some critira){ // recv from the former processor (my_rank - 1)

std::vector<face_pack> recv_face;

Recv_face(mpi::rank - 1, mpi::rank, recv_face); // recv info from former processor

}
if(num_next > 0){

        MPI_Status status;
        MPI_Wait(&request_next2, &status);

}

Free_type();

// finialize MPI
}

void Recv_face(int source, int tag, std::vector<face_pack>& recv_face){

    MPI_Status status1, status2;

    MPI_Probe(source, tag, MPI_COMM_WORLD, &status1);

    int count;
    MPI_Get_count(&status1, Hash::Face_type, &count);

    recv_face = std::vector<face_pack>(count);

    MPI_Recv(&recv_face[0], count, Hash::Face_type, source, tag, MPI_COMM_WORLD, &status2);
}

问题在于接收者有时会收到不完整的信息。

例如，我face_info在发出之前先打印出：

// rank 2
owners_key3658 facei 0 face_type M neighbour 192 n_rank 0
owners_key3658 facei 1 face_type L neighbour 66070 n_rank 1
owners_key3658 facei 1 face_type L neighbour 76640 n_rank 1
owners_key3658 facei 2 face_type M neighbour 2631 n_rank 0
owners_key3658 facei 3 face_type L neighbour 4953 n_rank 1
...
owners_key49144 facei 1 face_type M neighbour 844354 n_rank 2
owners_key49144 facei 1 face_type M neighbour 913280 n_rank 2
owners_key49144 facei 2 face_type L neighbour 41619 n_rank 1
owners_key49144 facei 3 face_type M neighbour 57633 n_rank 2

哪个是正确的。

但是在接收方，我打印出接收到的消息：

owners_key3658 facei 0 face_type M neighbour 192 n_rank 0
owners_key3658 facei 1 face_type L neighbour 66070 n_rank 1
owners_key3658 facei 1 face_type L neighbour 76640 n_rank 1
owners_key3658 facei 2 face_type M neighbour 2631 n_rank 0
owners_key3658 facei 3 face_type L neighbour 4953 n_rank 1

... // at the beginning it's fine, however, at the end it messed up

owners_key242560 facei 2 face_type ! neighbour 2 n_rank 2
owners_key217474 facei 2 face_type ! neighbour 2 n_rank 2
owners_key17394 facei 2 face_type ! neighbour 2 n_rank 2
owners_key216815 facei 2 face_type ! neighbour 2 n_rank 2

当然，它丢失了face_type信息，这是一个字符。据我所知，std::vector权证在这里是连续的。所以我不确定派生的mpi数据类型的哪一部分是错误的。消息传递有时有效，有时无效。