Hello, I'm trying to write a program that calculates up to a 1024 x 1024 matrix using multi-threading. For example, I need to run a 1024 x 1024 using 256, 64, 16 or 4 threads. Or I need to run a 64 x 64 matrix using 16 or 4 threads. All the Matrices are square. I thought I coded my program correctly, however I get a segmentation fault when I use a 720 x 720 matrix or higher, heres the code. -
#include <iostream>
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#include <stdio.h>
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#include <pthread.h>
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using namespace std;
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const int DIM = 720; //works up to 719, crashes at 720
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const int num_of_thr = 4;
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int matrix_A[DIM][DIM];
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int matrix_B[DIM][DIM];
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int c[DIM][DIM];
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struct v
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{
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int i;
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int j;
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};
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//worker thread
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void* matrix_multi(void* data)
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{
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for(int i = 0; i < DIM; i++)
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{
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for(int j = 0; j < DIM; j++)
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{
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c[i][j] = 0;
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for(int k = 0; k < DIM; k++)
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{
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c[i][j] += matrix_A[i][k] * matrix_B[k][j];
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}
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}
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}
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pthread_exit(0);
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}
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int main()
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{
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pthread_t thr_id[DIM][DIM];
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pthread_attr_t thr_attr;
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pthread_attr_init(&thr_attr);
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-
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//Filling the Matrices
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for(int i = 0; i < DIM; i++)
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{
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for(int j = 0; j < DIM; j++)
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{
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matrix_A[i][j]= i + j;
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matrix_B[i][j] = i + 3;
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}
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}
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//create the threads
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for(int i = 0; i < num_of_thr/2; i++)
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{
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for(int j = 0; j < num_of_thr/2; j++)
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{
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struct v *data = (struct v *) malloc(sizeof(struct v));
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data->i = i;
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data->j = j;
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pthread_create(&thr_id[i][j],NULL,matrix_multi, &data);
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}
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}
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//joining the threads
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for(int i = 0; i < num_of_thr/2; i++)
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{
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for(int j = 0; j < num_of_thr/2; j++)
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{
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pthread_join(thr_id[i][j],NULL);
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}
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}
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return 0;
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}
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Any help would be appreciated, thanks in advance.
4  6648  ashitpro 542
Recognized Expert Contributor
I just ran this code on my CentOS machine (g++ 4.1.2).
It worked pretty well, no seg fault. Even if I increase the number of threads and dimensions.
Seems that your compiler doesn't like huge variables in data segment (matrix_a) and/or stack (thr_id). Allocate them on the heap. (btw - why do you need thr_id be of size [DIM][DIM] when you only fill it to num_of_thr/2 in each dimension?
Thanks for the quick help. I changed my code quite a bit since yesterday. However I now get a "invalid conversion from `void*' to `__pthread_t**" on line 63 of my code. Here is the updated code: -
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#include <pthread.h>
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#include <stdlib.h>
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#include <stdio.h>
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#define SIZE 10 /* Size of matrices */
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int N; /* number of threads */
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int A[SIZE][SIZE], B[SIZE][SIZE], C[SIZE][SIZE];
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void fill_matrix(int m[SIZE][SIZE])
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{
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int i, j, n = 0;
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for (i=0; i<SIZE; i++)
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for (j=0; j<SIZE; j++)
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m[i][j] = n++;
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}
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void print_matrix(int m[SIZE][SIZE])
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{
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int i, j = 0;
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for (i=0; i<SIZE; i++) {
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printf("\n\t| ");
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for (j=0; j<SIZE; j++)
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printf("%2d ", m[i][j]);
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printf("|");
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}
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}
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void* mmult (void* slice)
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{
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int s = (int)slice;
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int from = (s * SIZE)/N; /* note that this 'slicing' works fine */
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int to = ((s+1) * SIZE)/N; /* even if SIZE is not divisible by N */
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int i,j,k;
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printf("computing slice %d (from row %d to %d)\n", s, from, to-1);
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for (i=from; i<to; i++)
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for (j=0; j<SIZE; j++) {
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C[i][j]=0;
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for (k=0; k<SIZE; k++)
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C[i][j] += A[i][k]*B[k][j];
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}
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printf("finished slice %d\n", s);
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return 0;
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}
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int main(int argc, char *argv[])
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{
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pthread_t *thread;
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int i;
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if (argc!=2) {
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printf("Usage: %s number_of_threads\n",argv[0]);
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exit(-1);
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}
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N=atoi(argv[1]);
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fill_matrix(A);
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fill_matrix(B);
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thread = malloc(N*sizeof(pthread_t));
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for (i=1; i<N; i++) {
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if (pthread_create (&thread[i], NULL, mmult, (void*)i) != 0 ) {
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perror("Can't create thread");
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exit(-1);
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}
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}
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/* master thread is thread 0 so: */
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mmult(0);
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for (i=1; i<N; i++) pthread_join (thread[i], NULL);
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printf("\n\n");
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print_matrix(A);
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printf("\n\n\t * \n");
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print_matrix(B);
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printf("\n\n\t = \n");
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print_matrix(C);
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printf("\n\n");
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return 0;
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}
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Any help would be appreciated, thanks in advance
ashitpro 542
Recognized Expert Contributor
Explicit type casting should work.. -
thread = (pthread_t *)malloc(N*sizeof(pthread_t));
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