Visit Our UNIX and Linux User Community


(MPI) Segmentation fault with dynamic allocated 2D array


 
Thread Tools Search this Thread
Top Forums Programming (MPI) Segmentation fault with dynamic allocated 2D array
# 1  
Old 12-12-2007
(MPI) Segmentation fault with dynamic allocated 2D array

Hi all,
I'm getting segmentation fault errors when I try to send/receive 2 rows of a matrix as a block, and I can't figure out why.

Basically, I have a 4x5 matrix with an extra top row and an extra leftmost column, making it a (4+1)x(5+1) matrix stored in P0. I'm trying to send the 2nd and 3rd row as a block to P1, print out the contents, send the 4th and 5th row as a block to P1, then print out the contents again. I have dynamically allocated a (4+1)x(5+1) memory block to cellblock, then used the pointers cell[i] to point to each "row" of cellblock, so I can access the 2D array by cell[i][j].

I get the correct output, but with segmentation fault at the end.

Here is my code:

Code:
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>

int main(int argc, char** argv)
{
   int rank, i, j, k = 1;
   int **cell, *row1, *cellblock;
   MPI_Status status;
   MPI_Init(&argc, &argv);
   MPI_Comm_rank(MPI_COMM_WORLD, &rank);
   row1 = (int*)calloc((5+1) * 2, sizeof(int));
   cellblock = (int*)calloc((4+1)*(5+1), sizeof(int));
   cell = &cellblock;
   for (i = 0 ; i < (4+1) ; i++)
        cell[i] = &cellblock[i*(5+1)];
   if (rank == 0)
   {
        for (i = 0 ; i < (4+1) ; i++)
              for (j = 0 ; j < (5+1) ; j++)
                   cell[i][j] = k++;
        for (i = 1 ; i < 5 ; i+=2)
              MPI_Send(&(cell[i][0]), (5+1)*2, MPI_INT, 1, 1, MPI_COMM_WORLD);
   }
   if (rank == 1)
   {
        for (i = 0 ; i < 2 ; i++)
        {
            MPI_Recv(row1, (5+1)*2, MPI_INT, 0, 1, MPI_COMM_WORLD, &status);
            for (j = 0 ; j < (5+1)*2 ; j++)
                printf("%d ", row1[j]);
            printf("\n");
       }
   }
   free(row1);
   free(cellblock);
   MPI_Finalize();
   return 0;

}

Please advise. Thank you.

Regards,
Rayne
# 2  
Old 12-12-2007
Quote:
Originally Posted by lancer6238
Please advise. Thank you.
Firstly, make a backup.

Then remove all the code that refers to arrays of ints and just prove that you can pass a buffer of characters around, effectively an MPI Hello World. Confirm that this cleanly exits.

Then be careful with your type casting whereever there is a void *, for instance the first argument to MPI_Send.

If you want to send 'ints' then change that to a

Code:
int *mySendData=&(cell[i][0]);
MPI_Send(mySendData,.....

and similarly on the read, this lets the compiler do type checking for you.

Also, run the thing under a debugger or use the core dump to find out where the thing is failing. Have you not closed the library down correctly? Is this a build issue? Is it compiler options or selection of libraries?

Previous Thread | Next Thread
Test Your Knowledge in Computers #265
Difficulty: Easy
Alan Turing was prosecuted by the UK in 1952 for homosexual acts.
True or False?

10 More Discussions You Might Find Interesting

1. Programming

C. To segmentation fault or not to segmentation fault, that is the question.

Oddities with gcc, 2.95.3 for the AMIGA and 4.2.1 for MY current OSX 10.14.1... I am creating a basic calculator for the AMIGA ADE *NIX emulator in C as it does not have one. Below are two very condensed snippets of which I have added the results inside the each code section. IMPORTANT!... (11 Replies)
Discussion started by: wisecracker
11 Replies

2. Programming

Segmentation fault

I keep getting this fault on a lot of the codes I write, I'm not exactly sure why so I'd really appreciate it if someone could explain the idea to me. For example this code #include <stdio.h> main() { unsigned long a=0; unsigned long b=0; int z; { printf("Enter two... (2 Replies)
Discussion started by: sizzler786
2 Replies

3. Programming

Using gdb, ignore beginning segmentation fault until reproduce environment segmentation fault

I use a binary name (ie polo) it gets some parameter , so for debugging normally i do this : i wrote script for watchdog my app (polo) and check every second if it's not running then start it , the problem is , if my app , remain in state of segmentation fault for a while (ie 15 ... (6 Replies)
Discussion started by: pooyair
6 Replies

4. Programming

segmentation fault.

This code is causing a segmentation fault and I can't figure out why. I'm new to UNIX and I need to learn how to avoid this segmentation fault thing. Thank you so much. Thanks also for the great answers to my last post.:):b: int main() { mysqlpp::Connection conn(false); if... (3 Replies)
Discussion started by: sepoto
3 Replies

5. Programming

Segmentation fault.

I'm getting a segmentation fault. I'm new to Linux programming. Thanks so much for all of your input.:eek: #include </usr/include/mysql++/mysql++.h> #include <stdio.h> #include <iostream> #include <sstream> #include <string.h> using namespace std; int outputToImport(const char*... (1 Reply)
Discussion started by: sepoto
1 Replies

6. Programming

segmentation fault

What is segmentation fault(core dumped) (1 Reply)
Discussion started by: gokult
1 Replies

7. Programming

segmentation fault

If I do this. Assume struct life { char *nolife; } struct life **life; // malloc initialization & everything if(life->nolife == 0) Would I get error at life->nolife if it is equal to 0. wrong accession? (3 Replies)
Discussion started by: joey
3 Replies

8. Programming

Hi! segmentation fault

I have written a program which takes a directory as command line arguments and displays all the dir and files in it. I don't know why I have a problem with the /etc directory.It displays all the directories and files untill it reaches a sub directory called peers which is in /etc/ppp/peers.the... (4 Replies)
Discussion started by: vijlak
4 Replies

9. UNIX for Dummies Questions & Answers

Segmentation Fault

hello all, I tried a program on an array to intialise array elements from the standard input device.it is an integer array of 5 elements.but after entering the 4th element it throws a message called "Segmentation Fault" and returns to the command prompt without asking for the 5th element. ... (3 Replies)
Discussion started by: compbug
3 Replies

10. Programming

segmentation fault

hi all i'm trying to execute a c program under linux RH and it gives me segmentation fault, this program was running under unix at&t anybody kow what the problem could be? thanx in advance regards (2 Replies)
Discussion started by: omran
2 Replies

Featured Tech Videos