Following code shows how pthreads can be used for matrix multiplication. Pthread is a POSIX standard for threads. The standard defines an API for creating and manipulating threads.You can download the code here.
/******************************************************************************
* Matrix Multiplication Program
* Heshan Suriyaarachchi
* ABOUT:
* Matrix multiplication is done via pthreads
*
******************************************************************************/
#include <stdio.h>
#include <sys/types.h>
#include <pthread.h>
#define MAX_THREAD 20 /* number of threads */
#define NDIM 200 /* number of NDIMs */
double a[NDIM][NDIM];
double b[NDIM][NDIM];
double c[NDIM][NDIM];
typedef struct
{
int id; /* identification */
int noproc; /* process */
int dim; /* number of threads */
double (*a)[NDIM][NDIM],(*b)[NDIM][NDIM],(*c)[NDIM][NDIM];
} parm;
void mm(int me_no, int noproc, int n, double a[NDIM][NDIM], double b[NDIM][NDIM], double c[NDIM][NDIM])
{
int i,j,k;
double sum;
i=me_no;
while (i<n) {
for (j = 0; j < n; j++) {
sum = 0.0;
for (k = 0; k < n; k++) {
sum = sum + a[i][k] * b[k][j];
}
c[i][j] = sum;
}
i+=noproc;
}
}
void * worker(void *arg)
{
parm *p = (parm *) arg;
mm(p->id, p->noproc, p->dim, *(p->a), *(p->b), *(p->c));
}
void main(int argc, char *argv[])
{
int j, k, noproc, me_no;
double sum;
double t1, t2;
pthread_t *threads;
parm *arg;
int n, i;
for (i = 0; i < NDIM; i++)
for (j = 0; j < NDIM; j++)
{
a[i][j] = i + j;
b[i][j] = i + j;
}
if (argc != 2)
{
printf("Usage: %s n\n where n is no. of thread\n", argv[0]);
exit(1);
}
n = atoi(argv[1]);
if ((n < 1) || (n > MAX_THREAD))
{
printf("The no of thread should between 1 and %d.\n", MAX_THREAD);
exit(1);
}
threads = (pthread_t *) malloc(n * sizeof(pthread_t));
arg=(parm *)malloc(sizeof(parm)*n);
/* setup barrier */
/* Start up thread */
/* Spawn thread */
for (i = 0; i < n; i++)
{
arg[i].id = i;
arg[i].noproc = n;
arg[i].dim = NDIM;
arg[i].a = &a;
arg[i].b = &b;
arg[i].c = &c;
pthread_create(&threads[i], NULL, worker, (void *)(arg+i));
}
for (i = 0; i < n; i++)
{
pthread_join(threads[i], NULL);
}
/* print_matrix(NDIM); */
check_matrix(NDIM);
free(arg);
}
print_matrix(dim)
int dim;
{
int i,j;
printf("The %d * %d matrix is\n", dim,dim);
for(i=0;i<dim;i++){
for(j=0;j<dim;j++)
printf("%lf ", c[i][j]);
printf("\n");
}
}
check_matrix(dim)
int dim;
{
int i,j,k;
int error=0;
printf("Now checking the results\n");
for(i=0;i<dim;i++)
for(j=0;j<dim;j++) {
double e=0.0;
for (k=0;k<dim;k++)
e+=a[i][k]*b[k][j];
if (e!=c[i][j]) {
printf("(%d,%d) error\n",i,j);
error++;
}
}
if (error)
printf("%d elements error\n",error);
else
printf("success\n");
}
