使用 MPI_Scather 后打印每个等级数组的好方法

Question

我想以适当的方式打印每个等级的数组。首先，这段代码的问题是输出没有顺序，其次，我只是想取消使用 if 条件来打印每个等级的数据。可能吗？

#include <fstream>
#include <iostream>
#include <vector>
#include "mpi.h"
using namespace std;
const int N = 3;

    int main()
    {
        MPI_Init(NULL, NULL);
        int rank;
        int size;
        int root = 0; 
        vector<int> x(N);
        vector<int> receive_data(N); 
        MPI_Comm_rank(MPI_COMM_WORLD, &rank);
        MPI_Comm_size(MPI_COMM_WORLD, &size);
        
        
        const int leng = size * N; 
        vector<int> single_arr(leng);
        
    
        for (int i = 0; i < N;i++) {
            x[i] = 1000*rank + i; 
        }
    
        MPI_Gather(x.data(), N, MPI_INT, single_arr.data(), N, MPI_INT, root, MPI_COMM_WORLD);
    
        if (rank == root) {
            cout << " After the gathering data inside single array at root is : " << endl; 
            for (int i = 0; i < single_arr.size();i++) {
                cout << i << "\t" << single_arr[i] << endl; 
            }
        }
        MPI_Scatter(single_arr.data(),N, MPI_INT, receive_data.data(), N, 
        MPI_INT, root, MPI_COMM_WORLD);
        MPI_Barrier(MPI_COMM_WORLD); 
        // now checks for data of each rank: 
    
        if (rank == root) {
            //cout << " After scattering the data: " << endl;
            cout << " My rank is : " << rank << endl;
            for (int i = 0; i < receive_data.size(); i++) {
                cout << i << "\t" << receive_data[i] << endl;
                cout << endl;
            }
        }
    
        if (rank == 1) {
            //cout << " After scattering the data: " << endl;
            cout << " My rank is : " << rank<<"\t"<< endl;
            for (int i = 0; i < receive_data.size(); i++) {
                cout << i << "\t" << receive_data[i] << endl;
                cout << endl;
            }
        }
       MPI_Finalize();
    }

结果是：

0       0
1       1
2       2
3       1000
4       1001
5       1002
6       2000
7       2001
8       2002
9       3000
10      3001
11      3002
 My rank is : 0
0       0

 My rank is : 1
1       1
0       1000


2       2
1       1001


2       1002

但是，我想在不对每个等级使用 if 条件的情况下看到这个：

My rank is : 0
0     0
1     1
2     2
My rank is: 1
0          1000
1          1001
2          1002

Answer 1

First, the problem with this code is that output is not ordered, and second, I just want to eliminate the use of if the condition for printing the data of each rank. Is it possible?

这不是 MPI 的用途，实际上是一般 IMO 中的并行性。在进程之间将输出打印到控制台的协调将大大降低并行版本的性能，这违背了并行的目的之一，即减少整体执行时间。

大多数时候最好让一个进程负责将输出打印到控制台（通常是 master 进程即处理 rank = 0).

引用@Gilles Gouaillardet：

Your best bet is to have all the data sent to one rank and have this rank print everything.

您可以尝试使用 MPI_Barrier 以打印您想要的输出的方式协调流程，但是（引用 Hristo Iliev）：

Using barriers like that only works for local launches when (and if) the processes share the same controlling terminal. Otherwise, it is entirely to the discretion of the I/O redirection mechanism of the MPI implementation.

使用 MPI_Scather 后打印每个等级数组的好方法

A good way to print array of each rank after using MPI_Scather

c++

parallel-processing

output

mpi

hpc