问题
I`m trying to write a code in C++ and using MPI.
In my code, I want to read from a file. I just want the master processor reads the data and later on, I will scatter it to the others. The goal is reading a graph from a file and then scatter its adjacency matrix row-wise.
The issue is when I want to open the file. If I generate a matrix it would scatter it nicely ( I used the code from here and changed it based on my need), so I don`t have any issues with scattering as I tested it several times. The issue is when I want to open and read from a file, and the weird thing is that even opening the file gives me errors, I am not very familiar with MPI and versions and its compatibility with C++. I assume it is something related to C++ or how I compile it.
Here is my code:
#include <iostream>
#include <climits>
#include <fstream>
#include <vector>
#include <set>
#include <stdio.h>
#include <stdlib.h>
#include <algorithm>
#include <list>
#include <queue>
#include <sstream>
#include <mpi.h>
#include <string>
#define BLOCK_LOW(id,p,n) ((id)*(n)/(p))
#define BLOCK_HIGH(id,p,n) ((id+1)*(n)/(p) - 1)
#define BLOCK_SIZE(id,p,n) ((id+1)*(n)/(p) - (id)*(n)/(p))
#define BLOCK_OWNER(index,p,n) (((p)*((index)+1)-1)/(n))
using namespace std;
void matrix_print(double **M, size_t m, size_t n,int my_rank);
int main(int argc, char* argv[])
{
int comm_size, my_rank, root = 0, nVertex = 6, rows, i, j, *sendcounts, *displs,nEdges;
double **adjArray, **adjPart, *stripdata;
double *Adata;
MPI_Status status;
MPI_Init(&argc, &argv);
MPI_Comm_size(MPI_COMM_WORLD,&comm_size);
MPI_Comm_rank(MPI_COMM_WORLD,&my_rank);
if (my_rank == 0){
ifstream myfile;
myfile.open("path/intsance.gr");
if(!myfile)
{
cout << "Error: file could not be opened" << endl;
exit (EXIT_FAILURE);
}
/*
static const int max_line = 65536;
string s;
myfile.ignore(max_line, '\n');
myfile>>s; // Nodes;
myfile>>nVertex;
myfile>>s; // Edges;
myfile>>nEdges;
cout<<"-----File is read..."<<endl;
cout<<"------------------------------------------------------------------------------------------"<<endl;
*/
}
// MPI_Barrier(MPI_COMM_WORLD);
nVertex=6;
if (my_rank == 0){
Adata = (double *)malloc(sizeof(double)*nVertex*nVertex);
adjArray = (double **)malloc(sizeof(double*)*nVertex);
for(int i = 0; i < nVertex; i++)
adjArray[i] = &(Adata[i*nVertex]);
int k=0;
for (int i=0; i<nVertex; i++) {
for (int j=0; j<nVertex; j++) {
adjArray[i][j]=k;
k++;
}
}
cout<<"---Adjacancy Matrix:"<<endl;
for (int i=0; i<nVertex; i++) {
for (int j=0; j<nVertex; j++) {
if(adjArray[i][j]==INT_MAX)
{
cout<< " - ";
}else
{
cout<< adjArray[i][j]<<" ";
}
}
cout<<endl;
}
cout<<"----------------------------------------------------"<<endl;
}
// Array containing the numbers of rows for each process
sendcounts = (int *)malloc(nVertex * sizeof(int));
// Array containing the displacement for each data chunk
displs = (int *)malloc(nVertex * sizeof(int));
// For each process ...
for (j = 0; j < comm_size; j++) {
// Sets each number of rows
sendcounts[j] = BLOCK_SIZE(j, comm_size, nVertex)*nVertex;
// Sets each displacement
displs[j] = BLOCK_LOW(j, comm_size, nVertex)*nVertex;
}
// Each process gets the number of rows that he is going to get
rows = sendcounts[my_rank]/nVertex;
// Creates the empty matrixes for the parts of M
// adjPart = (double**)matrix_create(rows, nVertex, sizeof(double));
stripdata = (double *)malloc(sizeof(double)*rows*nVertex);
adjPart = (double **)malloc(sizeof(double*)*rows);
for(int i= 0; i< rows; i++) {
adjPart[i] = &(stripdata[i*nVertex]);
}
// Scatters the matrix parts through all the processes
MPI_Scatterv(&adjArray[0][0], sendcounts, displs, MPI_DOUBLE, &adjPart[0][0], sendcounts[my_rank], MPI_DOUBLE, root, MPI_COMM_WORLD);
// This is where I get the Segmentation Fault
matrix_print(adjPart, rows, nVertex,my_rank);
MPI_Finalize();
return 0;
}
void matrix_print(double **M, size_t m, size_t n,int my_rank) {
size_t i,j;
cout<<"Rank: "<<my_rank<<endl;
for(i=0; i<m; ++i) {
printf("\n ");
for(j=0; j<n; ++j)
printf("%f ",M[i][j]);
}
cout<<endl;
}
Here is how I compile and run it:
mpic++ file.cpp -o outPut
mpirun -np 4 ./outPut
And I get the following result, which I don`t understand where is the issue:
---Adjacancy Matrix:
0 1 2 3 4 5
6 7 8 9 10 11
12 13 14 15 16 17
18 19 20 21 22 23
24 25 26 27 28 29
30 31 32 33 34 35
----------------------------------------------------
[S-MacBook-Pro:25734] *** Process received signal ***
[S-MacBook-Pro:25734] Signal: Segmentation fault: 11 (11)
[S-MacBook-Pro:25734] Signal code: Address not mapped (1)
[S-MacBook-Pro:25734] Failing at address: 0x0
[S-MacBook-Pro:25734] [ 0] 0 libsystem_platform.dylib 0x00007fff7221ff5a _sigtramp + 26
[S-MacBook-Pro:25734] [ 1] 0 ??? 0x000000010a630b5a 0x0 + 4469230426
[S-MacBook-Pro:25734] [ 2] 0 libdyld.dylib 0x00007fff71f9e115 start + 1
[S-MacBook-Pro:25734] *** End of error message ***
Rank: 0
0.000000 1.000000 2.000000 3.000000 4.000000 5.000000
[S-MacBook-Pro:25732] *** Process received signal ***
[S-MacBook-Pro:25732] Signal: Segmentation fault: 11 (11)
[S-MacBook-Pro:25732] Signal code: Address not mapped (1)
[S-MacBook-Pro:25732] Failing at address: 0x0
[S-MacBook-Pro:25732] [ 0] 0 libsystem_platform.dylib 0x00007fff7221ff5a _sigtramp + 26
[S-MacBook-Pro:25732] [ 1] 0 ??? 0x000000010e9cfb5a 0x0 + 4540136282
[S-MacBook-Pro:25732] [ 2] 0 libdyld.dylib 0x00007fff71f9e115 start + 1
[S-MacBook-Pro:25732] *** End of error message ***
[S-MacBook-Pro:25733] *** Process received signal ***
[S-MacBook-Pro:25733] Signal: Segmentation fault: 11 (11)
[S-MacBook-Pro:25733] Signal code: Address not mapped (1)
[S-MacBook-Pro:25733] Failing at address: 0x0
[S-MacBook-Pro:25733] [ 0] 0 libsystem_platform.dylib 0x00007fff7221ff5a _sigtramp + 26
[S-MacBook-Pro:25733] [ 1] 0 ??? 0x00000001100acb5a 0x0 + 4564110170
[S-MacBook-Pro:25733] [ 2] 0 libdyld.dylib 0x00007fff71f9e115 start + 1
[S-MacBook-Pro:25733] *** End of error message ***
--------------------------------------------------------------------------
mpirun noticed that process rank 3 with PID 25734 on node S-MacBook-Pro exited on signal 11 (Segmentation fault: 11).
Note that since I didn`t know where the issue comes from, I kept the matrix as I generate it in my code, for now I just want to know why it gives me errors by opening the file. Any help would be appreciated!
来源：https://stackoverflow.com/questions/49579791/error-while-reading-from-a-file-in-mpi-c-programming